1// SPDX-License-Identifier: GPL-2.0
   2/*
   3 * INET		An implementation of the TCP/IP protocol suite for the LINUX
   4 *		operating system.  INET is implemented using the  BSD Socket
   5 *		interface as the means of communication with the user level.
   6 *
   7 *		Implementation of the Transmission Control Protocol(TCP).
   8 *
   9 * Authors:	Ross Biro
  10 *		Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
  11 *		Mark Evans, <evansmp@uhura.aston.ac.uk>
  12 *		Corey Minyard <wf-rch!minyard@relay.EU.net>
  13 *		Florian La Roche, <flla@stud.uni-sb.de>
  14 *		Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
  15 *		Linus Torvalds, <torvalds@cs.helsinki.fi>
  16 *		Alan Cox, <gw4pts@gw4pts.ampr.org>
  17 *		Matthew Dillon, <dillon@apollo.west.oic.com>
  18 *		Arnt Gulbrandsen, <agulbra@nvg.unit.no>
  19 *		Jorge Cwik, <jorge@laser.satlink.net>
  20 */
  21
  22/*
  23 * Changes:
  24 *		Pedro Roque	:	Fast Retransmit/Recovery.
  25 *					Two receive queues.
  26 *					Retransmit queue handled by TCP.
  27 *					Better retransmit timer handling.
  28 *					New congestion avoidance.
  29 *					Header prediction.
  30 *					Variable renaming.
  31 *
  32 *		Eric		:	Fast Retransmit.
  33 *		Randy Scott	:	MSS option defines.
  34 *		Eric Schenk	:	Fixes to slow start algorithm.
  35 *		Eric Schenk	:	Yet another double ACK bug.
  36 *		Eric Schenk	:	Delayed ACK bug fixes.
  37 *		Eric Schenk	:	Floyd style fast retrans war avoidance.
  38 *		David S. Miller	:	Don't allow zero congestion window.
  39 *		Eric Schenk	:	Fix retransmitter so that it sends
  40 *					next packet on ack of previous packet.
  41 *		Andi Kleen	:	Moved open_request checking here
  42 *					and process RSTs for open_requests.
  43 *		Andi Kleen	:	Better prune_queue, and other fixes.
  44 *		Andrey Savochkin:	Fix RTT measurements in the presence of
  45 *					timestamps.
  46 *		Andrey Savochkin:	Check sequence numbers correctly when
  47 *					removing SACKs due to in sequence incoming
  48 *					data segments.
  49 *		Andi Kleen:		Make sure we never ack data there is not
  50 *					enough room for. Also make this condition
  51 *					a fatal error if it might still happen.
  52 *		Andi Kleen:		Add tcp_measure_rcv_mss to make
  53 *					connections with MSS<min(MTU,ann. MSS)
  54 *					work without delayed acks.
  55 *		Andi Kleen:		Process packets with PSH set in the
  56 *					fast path.
  57 *		J Hadi Salim:		ECN support
  58 *	 	Andrei Gurtov,
  59 *		Pasi Sarolahti,
  60 *		Panu Kuhlberg:		Experimental audit of TCP (re)transmission
  61 *					engine. Lots of bugs are found.
  62 *		Pasi Sarolahti:		F-RTO for dealing with spurious RTOs
  63 */
  64
  65#define pr_fmt(fmt) "TCP: " fmt
  66
  67#include <linux/mm.h>
  68#include <linux/slab.h>
  69#include <linux/module.h>
  70#include <linux/sysctl.h>
  71#include <linux/kernel.h>
  72#include <linux/prefetch.h>
  73#include <net/dst.h>
  74#include <net/tcp.h>
  75#include <net/inet_common.h>
  76#include <linux/ipsec.h>
  77#include <asm/unaligned.h>
  78#include <linux/errqueue.h>
  79#include <trace/events/tcp.h>
  80#include <linux/jump_label_ratelimit.h>
  81#include <net/busy_poll.h>
  82#include <net/mptcp.h>
  83
  84int sysctl_tcp_max_orphans __read_mostly = NR_FILE;
  85
  86#define FLAG_DATA		0x01 /* Incoming frame contained data.		*/
  87#define FLAG_WIN_UPDATE		0x02 /* Incoming ACK was a window update.	*/
  88#define FLAG_DATA_ACKED		0x04 /* This ACK acknowledged new data.		*/
  89#define FLAG_RETRANS_DATA_ACKED	0x08 /* "" "" some of which was retransmitted.	*/
  90#define FLAG_SYN_ACKED		0x10 /* This ACK acknowledged SYN.		*/
  91#define FLAG_DATA_SACKED	0x20 /* New SACK.				*/
  92#define FLAG_ECE		0x40 /* ECE in this ACK				*/
  93#define FLAG_LOST_RETRANS	0x80 /* This ACK marks some retransmission lost */
  94#define FLAG_SLOWPATH		0x100 /* Do not skip RFC checks for window update.*/
  95#define FLAG_ORIG_SACK_ACKED	0x200 /* Never retransmitted data are (s)acked	*/
  96#define FLAG_SND_UNA_ADVANCED	0x400 /* Snd_una was changed (!= FLAG_DATA_ACKED) */
  97#define FLAG_DSACKING_ACK	0x800 /* SACK blocks contained D-SACK info */
  98#define FLAG_SET_XMIT_TIMER	0x1000 /* Set TLP or RTO timer */
  99#define FLAG_SACK_RENEGING	0x2000 /* snd_una advanced to a sacked seq */
 100#define FLAG_UPDATE_TS_RECENT	0x4000 /* tcp_replace_ts_recent() */
 101#define FLAG_NO_CHALLENGE_ACK	0x8000 /* do not call tcp_send_challenge_ack()	*/
 102#define FLAG_ACK_MAYBE_DELAYED	0x10000 /* Likely a delayed ACK */
 103#define FLAG_DSACK_TLP		0x20000 /* DSACK for tail loss probe */
 104
 105#define FLAG_ACKED		(FLAG_DATA_ACKED|FLAG_SYN_ACKED)
 106#define FLAG_NOT_DUP		(FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED)
 107#define FLAG_CA_ALERT		(FLAG_DATA_SACKED|FLAG_ECE|FLAG_DSACKING_ACK)
 108#define FLAG_FORWARD_PROGRESS	(FLAG_ACKED|FLAG_DATA_SACKED)
 109
 110#define TCP_REMNANT (TCP_FLAG_FIN|TCP_FLAG_URG|TCP_FLAG_SYN|TCP_FLAG_PSH)
 111#define TCP_HP_BITS (~(TCP_RESERVED_BITS|TCP_FLAG_PSH))
 112
 113#define REXMIT_NONE	0 /* no loss recovery to do */
 114#define REXMIT_LOST	1 /* retransmit packets marked lost */
 115#define REXMIT_NEW	2 /* FRTO-style transmit of unsent/new packets */
 116
 117#if IS_ENABLED(CONFIG_TLS_DEVICE)
 118static DEFINE_STATIC_KEY_DEFERRED_FALSE(clean_acked_data_enabled, HZ);
 119
 120void clean_acked_data_enable(struct inet_connection_sock *icsk,
 121			     void (*cad)(struct sock *sk, u32 ack_seq))
 122{
 123	icsk->icsk_clean_acked = cad;
 124	static_branch_deferred_inc(&clean_acked_data_enabled);
 125}
 126EXPORT_SYMBOL_GPL(clean_acked_data_enable);
 127
 128void clean_acked_data_disable(struct inet_connection_sock *icsk)
 129{
 130	static_branch_slow_dec_deferred(&clean_acked_data_enabled);
 131	icsk->icsk_clean_acked = NULL;
 132}
 133EXPORT_SYMBOL_GPL(clean_acked_data_disable);
 134
 135void clean_acked_data_flush(void)
 136{
 137	static_key_deferred_flush(&clean_acked_data_enabled);
 138}
 139EXPORT_SYMBOL_GPL(clean_acked_data_flush);
 140#endif
 141
 142#ifdef CONFIG_CGROUP_BPF
 143static void bpf_skops_parse_hdr(struct sock *sk, struct sk_buff *skb)
 144{
 145	bool unknown_opt = tcp_sk(sk)->rx_opt.saw_unknown &&
 146		BPF_SOCK_OPS_TEST_FLAG(tcp_sk(sk),
 147				       BPF_SOCK_OPS_PARSE_UNKNOWN_HDR_OPT_CB_FLAG);
 148	bool parse_all_opt = BPF_SOCK_OPS_TEST_FLAG(tcp_sk(sk),
 149						    BPF_SOCK_OPS_PARSE_ALL_HDR_OPT_CB_FLAG);
 150	struct bpf_sock_ops_kern sock_ops;
 151
 152	if (likely(!unknown_opt && !parse_all_opt))
 153		return;
 154
 155	/* The skb will be handled in the
 156	 * bpf_skops_established() or
 157	 * bpf_skops_write_hdr_opt().
 158	 */
 159	switch (sk->sk_state) {
 160	case TCP_SYN_RECV:
 161	case TCP_SYN_SENT:
 162	case TCP_LISTEN:
 163		return;
 164	}
 165
 166	sock_owned_by_me(sk);
 167
 168	memset(&sock_ops, 0, offsetof(struct bpf_sock_ops_kern, temp));
 169	sock_ops.op = BPF_SOCK_OPS_PARSE_HDR_OPT_CB;
 170	sock_ops.is_fullsock = 1;
 171	sock_ops.sk = sk;
 172	bpf_skops_init_skb(&sock_ops, skb, tcp_hdrlen(skb));
 173
 174	BPF_CGROUP_RUN_PROG_SOCK_OPS(&sock_ops);
 175}
 176
 177static void bpf_skops_established(struct sock *sk, int bpf_op,
 178				  struct sk_buff *skb)
 179{
 180	struct bpf_sock_ops_kern sock_ops;
 181
 182	sock_owned_by_me(sk);
 183
 184	memset(&sock_ops, 0, offsetof(struct bpf_sock_ops_kern, temp));
 185	sock_ops.op = bpf_op;
 186	sock_ops.is_fullsock = 1;
 187	sock_ops.sk = sk;
 188	/* sk with TCP_REPAIR_ON does not have skb in tcp_finish_connect */
 189	if (skb)
 190		bpf_skops_init_skb(&sock_ops, skb, tcp_hdrlen(skb));
 191
 192	BPF_CGROUP_RUN_PROG_SOCK_OPS(&sock_ops);
 193}
 194#else
 195static void bpf_skops_parse_hdr(struct sock *sk, struct sk_buff *skb)
 196{
 197}
 198
 199static void bpf_skops_established(struct sock *sk, int bpf_op,
 200				  struct sk_buff *skb)
 201{
 202}
 203#endif
 204
 205static void tcp_gro_dev_warn(struct sock *sk, const struct sk_buff *skb,
 206			     unsigned int len)
 207{
 208	static bool __once __read_mostly;
 209
 210	if (!__once) {
 211		struct net_device *dev;
 212
 213		__once = true;
 214
 215		rcu_read_lock();
 216		dev = dev_get_by_index_rcu(sock_net(sk), skb->skb_iif);
 217		if (!dev || len >= dev->mtu)
 218			pr_warn("%s: Driver has suspect GRO implementation, TCP performance may be compromised.\n",
 219				dev ? dev->name : "Unknown driver");
 220		rcu_read_unlock();
 221	}
 222}
 223
 224/* Adapt the MSS value used to make delayed ack decision to the
 225 * real world.
 226 */
 227static void tcp_measure_rcv_mss(struct sock *sk, const struct sk_buff *skb)
 228{
 229	struct inet_connection_sock *icsk = inet_csk(sk);
 230	const unsigned int lss = icsk->icsk_ack.last_seg_size;
 231	unsigned int len;
 232
 233	icsk->icsk_ack.last_seg_size = 0;
 234
 235	/* skb->len may jitter because of SACKs, even if peer
 236	 * sends good full-sized frames.
 237	 */
 238	len = skb_shinfo(skb)->gso_size ? : skb->len;
 239	if (len >= icsk->icsk_ack.rcv_mss) {
 240		icsk->icsk_ack.rcv_mss = min_t(unsigned int, len,
 241					       tcp_sk(sk)->advmss);
 242		/* Account for possibly-removed options */
 243		if (unlikely(len > icsk->icsk_ack.rcv_mss +
 244				   MAX_TCP_OPTION_SPACE))
 245			tcp_gro_dev_warn(sk, skb, len);
 246	} else {
 247		/* Otherwise, we make more careful check taking into account,
 248		 * that SACKs block is variable.
 249		 *
 250		 * "len" is invariant segment length, including TCP header.
 251		 */
 252		len += skb->data - skb_transport_header(skb);
 253		if (len >= TCP_MSS_DEFAULT + sizeof(struct tcphdr) ||
 254		    /* If PSH is not set, packet should be
 255		     * full sized, provided peer TCP is not badly broken.
 256		     * This observation (if it is correct 8)) allows
 257		     * to handle super-low mtu links fairly.
 258		     */
 259		    (len >= TCP_MIN_MSS + sizeof(struct tcphdr) &&
 260		     !(tcp_flag_word(tcp_hdr(skb)) & TCP_REMNANT))) {
 261			/* Subtract also invariant (if peer is RFC compliant),
 262			 * tcp header plus fixed timestamp option length.
 263			 * Resulting "len" is MSS free of SACK jitter.
 264			 */
 265			len -= tcp_sk(sk)->tcp_header_len;
 266			icsk->icsk_ack.last_seg_size = len;
 267			if (len == lss) {
 268				icsk->icsk_ack.rcv_mss = len;
 269				return;
 270			}
 271		}
 272		if (icsk->icsk_ack.pending & ICSK_ACK_PUSHED)
 273			icsk->icsk_ack.pending |= ICSK_ACK_PUSHED2;
 274		icsk->icsk_ack.pending |= ICSK_ACK_PUSHED;
 275	}
 276}
 277
 278static void tcp_incr_quickack(struct sock *sk, unsigned int max_quickacks)
 279{
 280	struct inet_connection_sock *icsk = inet_csk(sk);
 281	unsigned int quickacks = tcp_sk(sk)->rcv_wnd / (2 * icsk->icsk_ack.rcv_mss);
 282
 283	if (quickacks == 0)
 284		quickacks = 2;
 285	quickacks = min(quickacks, max_quickacks);
 286	if (quickacks > icsk->icsk_ack.quick)
 287		icsk->icsk_ack.quick = quickacks;
 288}
 289
 290void tcp_enter_quickack_mode(struct sock *sk, unsigned int max_quickacks)
 291{
 292	struct inet_connection_sock *icsk = inet_csk(sk);
 293
 294	tcp_incr_quickack(sk, max_quickacks);
 295	inet_csk_exit_pingpong_mode(sk);
 296	icsk->icsk_ack.ato = TCP_ATO_MIN;
 297}
 298EXPORT_SYMBOL(tcp_enter_quickack_mode);
 299
 300/* Send ACKs quickly, if "quick" count is not exhausted
 301 * and the session is not interactive.
 302 */
 303
 304static bool tcp_in_quickack_mode(struct sock *sk)
 305{
 306	const struct inet_connection_sock *icsk = inet_csk(sk);
 307	const struct dst_entry *dst = __sk_dst_get(sk);
 308
 309	return (dst && dst_metric(dst, RTAX_QUICKACK)) ||
 310		(icsk->icsk_ack.quick && !inet_csk_in_pingpong_mode(sk));
 311}
 312
 313static void tcp_ecn_queue_cwr(struct tcp_sock *tp)
 314{
 315	if (tp->ecn_flags & TCP_ECN_OK)
 316		tp->ecn_flags |= TCP_ECN_QUEUE_CWR;
 317}
 318
 319static void tcp_ecn_accept_cwr(struct sock *sk, const struct sk_buff *skb)
 320{
 321	if (tcp_hdr(skb)->cwr) {
 322		tcp_sk(sk)->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
 323
 324		/* If the sender is telling us it has entered CWR, then its
 325		 * cwnd may be very low (even just 1 packet), so we should ACK
 326		 * immediately.
 327		 */
 328		if (TCP_SKB_CB(skb)->seq != TCP_SKB_CB(skb)->end_seq)
 329			inet_csk(sk)->icsk_ack.pending |= ICSK_ACK_NOW;
 330	}
 331}
 332
 333static void tcp_ecn_withdraw_cwr(struct tcp_sock *tp)
 334{
 335	tp->ecn_flags &= ~TCP_ECN_QUEUE_CWR;
 336}
 337
 338static void __tcp_ecn_check_ce(struct sock *sk, const struct sk_buff *skb)
 339{
 340	struct tcp_sock *tp = tcp_sk(sk);
 341
 342	switch (TCP_SKB_CB(skb)->ip_dsfield & INET_ECN_MASK) {
 343	case INET_ECN_NOT_ECT:
 344		/* Funny extension: if ECT is not set on a segment,
 345		 * and we already seen ECT on a previous segment,
 346		 * it is probably a retransmit.
 347		 */
 348		if (tp->ecn_flags & TCP_ECN_SEEN)
 349			tcp_enter_quickack_mode(sk, 2);
 350		break;
 351	case INET_ECN_CE:
 352		if (tcp_ca_needs_ecn(sk))
 353			tcp_ca_event(sk, CA_EVENT_ECN_IS_CE);
 354
 355		if (!(tp->ecn_flags & TCP_ECN_DEMAND_CWR)) {
 356			/* Better not delay acks, sender can have a very low cwnd */
 357			tcp_enter_quickack_mode(sk, 2);
 358			tp->ecn_flags |= TCP_ECN_DEMAND_CWR;
 359		}
 360		tp->ecn_flags |= TCP_ECN_SEEN;
 361		break;
 362	default:
 363		if (tcp_ca_needs_ecn(sk))
 364			tcp_ca_event(sk, CA_EVENT_ECN_NO_CE);
 365		tp->ecn_flags |= TCP_ECN_SEEN;
 366		break;
 367	}
 368}
 369
 370static void tcp_ecn_check_ce(struct sock *sk, const struct sk_buff *skb)
 371{
 372	if (tcp_sk(sk)->ecn_flags & TCP_ECN_OK)
 373		__tcp_ecn_check_ce(sk, skb);
 374}
 375
 376static void tcp_ecn_rcv_synack(struct tcp_sock *tp, const struct tcphdr *th)
 377{
 378	if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || th->cwr))
 379		tp->ecn_flags &= ~TCP_ECN_OK;
 380}
 381
 382static void tcp_ecn_rcv_syn(struct tcp_sock *tp, const struct tcphdr *th)
 383{
 384	if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || !th->cwr))
 385		tp->ecn_flags &= ~TCP_ECN_OK;
 386}
 387
 388static bool tcp_ecn_rcv_ecn_echo(const struct tcp_sock *tp, const struct tcphdr *th)
 389{
 390	if (th->ece && !th->syn && (tp->ecn_flags & TCP_ECN_OK))
 391		return true;
 392	return false;
 393}
 394
 395/* Buffer size and advertised window tuning.
 396 *
 397 * 1. Tuning sk->sk_sndbuf, when connection enters established state.
 398 */
 399
 400static void tcp_sndbuf_expand(struct sock *sk)
 401{
 402	const struct tcp_sock *tp = tcp_sk(sk);
 403	const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;
 404	int sndmem, per_mss;
 405	u32 nr_segs;
 406
 407	/* Worst case is non GSO/TSO : each frame consumes one skb
 408	 * and skb->head is kmalloced using power of two area of memory
 409	 */
 410	per_mss = max_t(u32, tp->rx_opt.mss_clamp, tp->mss_cache) +
 411		  MAX_TCP_HEADER +
 412		  SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
 413
 414	per_mss = roundup_pow_of_two(per_mss) +
 415		  SKB_DATA_ALIGN(sizeof(struct sk_buff));
 416
 417	nr_segs = max_t(u32, TCP_INIT_CWND, tcp_snd_cwnd(tp));
 418	nr_segs = max_t(u32, nr_segs, tp->reordering + 1);
 419
 420	/* Fast Recovery (RFC 5681 3.2) :
 421	 * Cubic needs 1.7 factor, rounded to 2 to include
 422	 * extra cushion (application might react slowly to EPOLLOUT)
 423	 */
 424	sndmem = ca_ops->sndbuf_expand ? ca_ops->sndbuf_expand(sk) : 2;
 425	sndmem *= nr_segs * per_mss;
 426
 427	if (sk->sk_sndbuf < sndmem)
 428		WRITE_ONCE(sk->sk_sndbuf,
 429			   min(sndmem, READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_wmem[2])));
 430}
 431
 432/* 2. Tuning advertised window (window_clamp, rcv_ssthresh)
 433 *
 434 * All tcp_full_space() is split to two parts: "network" buffer, allocated
 435 * forward and advertised in receiver window (tp->rcv_wnd) and
 436 * "application buffer", required to isolate scheduling/application
 437 * latencies from network.
 438 * window_clamp is maximal advertised window. It can be less than
 439 * tcp_full_space(), in this case tcp_full_space() - window_clamp
 440 * is reserved for "application" buffer. The less window_clamp is
 441 * the smoother our behaviour from viewpoint of network, but the lower
 442 * throughput and the higher sensitivity of the connection to losses. 8)
 443 *
 444 * rcv_ssthresh is more strict window_clamp used at "slow start"
 445 * phase to predict further behaviour of this connection.
 446 * It is used for two goals:
 447 * - to enforce header prediction at sender, even when application
 448 *   requires some significant "application buffer". It is check #1.
 449 * - to prevent pruning of receive queue because of misprediction
 450 *   of receiver window. Check #2.
 451 *
 452 * The scheme does not work when sender sends good segments opening
 453 * window and then starts to feed us spaghetti. But it should work
 454 * in common situations. Otherwise, we have to rely on queue collapsing.
 455 */
 456
 457/* Slow part of check#2. */
 458static int __tcp_grow_window(const struct sock *sk, const struct sk_buff *skb,
 459			     unsigned int skbtruesize)
 460{
 461	struct tcp_sock *tp = tcp_sk(sk);
 462	/* Optimize this! */
 463	int truesize = tcp_win_from_space(sk, skbtruesize) >> 1;
 464	int window = tcp_win_from_space(sk, READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_rmem[2])) >> 1;
 465
 466	while (tp->rcv_ssthresh <= window) {
 467		if (truesize <= skb->len)
 468			return 2 * inet_csk(sk)->icsk_ack.rcv_mss;
 469
 470		truesize >>= 1;
 471		window >>= 1;
 472	}
 473	return 0;
 474}
 475
 476/* Even if skb appears to have a bad len/truesize ratio, TCP coalescing
 477 * can play nice with us, as sk_buff and skb->head might be either
 478 * freed or shared with up to MAX_SKB_FRAGS segments.
 479 * Only give a boost to drivers using page frag(s) to hold the frame(s),
 480 * and if no payload was pulled in skb->head before reaching us.
 481 */
 482static u32 truesize_adjust(bool adjust, const struct sk_buff *skb)
 483{
 484	u32 truesize = skb->truesize;
 485
 486	if (adjust && !skb_headlen(skb)) {
 487		truesize -= SKB_TRUESIZE(skb_end_offset(skb));
 488		/* paranoid check, some drivers might be buggy */
 489		if (unlikely((int)truesize < (int)skb->len))
 490			truesize = skb->truesize;
 491	}
 492	return truesize;
 493}
 494
 495static void tcp_grow_window(struct sock *sk, const struct sk_buff *skb,
 496			    bool adjust)
 497{
 498	struct tcp_sock *tp = tcp_sk(sk);
 499	int room;
 500
 501	room = min_t(int, tp->window_clamp, tcp_space(sk)) - tp->rcv_ssthresh;
 502
 503	if (room <= 0)
 504		return;
 505
 506	/* Check #1 */
 507	if (!tcp_under_memory_pressure(sk)) {
 508		unsigned int truesize = truesize_adjust(adjust, skb);
 509		int incr;
 510
 511		/* Check #2. Increase window, if skb with such overhead
 512		 * will fit to rcvbuf in future.
 513		 */
 514		if (tcp_win_from_space(sk, truesize) <= skb->len)
 515			incr = 2 * tp->advmss;
 516		else
 517			incr = __tcp_grow_window(sk, skb, truesize);
 518
 519		if (incr) {
 520			incr = max_t(int, incr, 2 * skb->len);
 521			tp->rcv_ssthresh += min(room, incr);
 522			inet_csk(sk)->icsk_ack.quick |= 1;
 523		}
 524	} else {
 525		/* Under pressure:
 526		 * Adjust rcv_ssthresh according to reserved mem
 527		 */
 528		tcp_adjust_rcv_ssthresh(sk);
 529	}
 530}
 531
 532/* 3. Try to fixup all. It is made immediately after connection enters
 533 *    established state.
 534 */
 535static void tcp_init_buffer_space(struct sock *sk)
 536{
 537	int tcp_app_win = READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_app_win);
 538	struct tcp_sock *tp = tcp_sk(sk);
 539	int maxwin;
 540
 541	if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK))
 542		tcp_sndbuf_expand(sk);
 543
 
 544	tcp_mstamp_refresh(tp);
 545	tp->rcvq_space.time = tp->tcp_mstamp;
 546	tp->rcvq_space.seq = tp->copied_seq;
 547
 548	maxwin = tcp_full_space(sk);
 549
 550	if (tp->window_clamp >= maxwin) {
 551		tp->window_clamp = maxwin;
 552
 553		if (tcp_app_win && maxwin > 4 * tp->advmss)
 554			tp->window_clamp = max(maxwin -
 555					       (maxwin >> tcp_app_win),
 556					       4 * tp->advmss);
 557	}
 558
 559	/* Force reservation of one segment. */
 560	if (tcp_app_win &&
 561	    tp->window_clamp > 2 * tp->advmss &&
 562	    tp->window_clamp + tp->advmss > maxwin)
 563		tp->window_clamp = max(2 * tp->advmss, maxwin - tp->advmss);
 564
 565	tp->rcv_ssthresh = min(tp->rcv_ssthresh, tp->window_clamp);
 566	tp->snd_cwnd_stamp = tcp_jiffies32;
 567	tp->rcvq_space.space = min3(tp->rcv_ssthresh, tp->rcv_wnd,
 568				    (u32)TCP_INIT_CWND * tp->advmss);
 569}
 570
 571/* 4. Recalculate window clamp after socket hit its memory bounds. */
 572static void tcp_clamp_window(struct sock *sk)
 573{
 574	struct tcp_sock *tp = tcp_sk(sk);
 575	struct inet_connection_sock *icsk = inet_csk(sk);
 576	struct net *net = sock_net(sk);
 577	int rmem2;
 578
 579	icsk->icsk_ack.quick = 0;
 580	rmem2 = READ_ONCE(net->ipv4.sysctl_tcp_rmem[2]);
 581
 582	if (sk->sk_rcvbuf < rmem2 &&
 583	    !(sk->sk_userlocks & SOCK_RCVBUF_LOCK) &&
 584	    !tcp_under_memory_pressure(sk) &&
 585	    sk_memory_allocated(sk) < sk_prot_mem_limits(sk, 0)) {
 586		WRITE_ONCE(sk->sk_rcvbuf,
 587			   min(atomic_read(&sk->sk_rmem_alloc), rmem2));
 
 588	}
 589	if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf)
 590		tp->rcv_ssthresh = min(tp->window_clamp, 2U * tp->advmss);
 591}
 592
 593/* Initialize RCV_MSS value.
 594 * RCV_MSS is an our guess about MSS used by the peer.
 595 * We haven't any direct information about the MSS.
 596 * It's better to underestimate the RCV_MSS rather than overestimate.
 597 * Overestimations make us ACKing less frequently than needed.
 598 * Underestimations are more easy to detect and fix by tcp_measure_rcv_mss().
 599 */
 600void tcp_initialize_rcv_mss(struct sock *sk)
 601{
 602	const struct tcp_sock *tp = tcp_sk(sk);
 603	unsigned int hint = min_t(unsigned int, tp->advmss, tp->mss_cache);
 604
 605	hint = min(hint, tp->rcv_wnd / 2);
 606	hint = min(hint, TCP_MSS_DEFAULT);
 607	hint = max(hint, TCP_MIN_MSS);
 608
 609	inet_csk(sk)->icsk_ack.rcv_mss = hint;
 610}
 611EXPORT_SYMBOL(tcp_initialize_rcv_mss);
 612
 613/* Receiver "autotuning" code.
 614 *
 615 * The algorithm for RTT estimation w/o timestamps is based on
 616 * Dynamic Right-Sizing (DRS) by Wu Feng and Mike Fisk of LANL.
 617 * <https://public.lanl.gov/radiant/pubs.html#DRS>
 618 *
 619 * More detail on this code can be found at
 620 * <http://staff.psc.edu/jheffner/>,
 621 * though this reference is out of date.  A new paper
 622 * is pending.
 623 */
 624static void tcp_rcv_rtt_update(struct tcp_sock *tp, u32 sample, int win_dep)
 625{
 626	u32 new_sample = tp->rcv_rtt_est.rtt_us;
 627	long m = sample;
 628
 629	if (new_sample != 0) {
 630		/* If we sample in larger samples in the non-timestamp
 631		 * case, we could grossly overestimate the RTT especially
 632		 * with chatty applications or bulk transfer apps which
 633		 * are stalled on filesystem I/O.
 634		 *
 635		 * Also, since we are only going for a minimum in the
 636		 * non-timestamp case, we do not smooth things out
 637		 * else with timestamps disabled convergence takes too
 638		 * long.
 639		 */
 640		if (!win_dep) {
 641			m -= (new_sample >> 3);
 642			new_sample += m;
 643		} else {
 644			m <<= 3;
 645			if (m < new_sample)
 646				new_sample = m;
 647		}
 648	} else {
 649		/* No previous measure. */
 650		new_sample = m << 3;
 651	}
 652
 653	tp->rcv_rtt_est.rtt_us = new_sample;
 654}
 655
 656static inline void tcp_rcv_rtt_measure(struct tcp_sock *tp)
 657{
 658	u32 delta_us;
 659
 660	if (tp->rcv_rtt_est.time == 0)
 661		goto new_measure;
 662	if (before(tp->rcv_nxt, tp->rcv_rtt_est.seq))
 663		return;
 664	delta_us = tcp_stamp_us_delta(tp->tcp_mstamp, tp->rcv_rtt_est.time);
 665	if (!delta_us)
 666		delta_us = 1;
 667	tcp_rcv_rtt_update(tp, delta_us, 1);
 668
 669new_measure:
 670	tp->rcv_rtt_est.seq = tp->rcv_nxt + tp->rcv_wnd;
 671	tp->rcv_rtt_est.time = tp->tcp_mstamp;
 672}
 673
 674static inline void tcp_rcv_rtt_measure_ts(struct sock *sk,
 675					  const struct sk_buff *skb)
 676{
 677	struct tcp_sock *tp = tcp_sk(sk);
 678
 679	if (tp->rx_opt.rcv_tsecr == tp->rcv_rtt_last_tsecr)
 680		return;
 681	tp->rcv_rtt_last_tsecr = tp->rx_opt.rcv_tsecr;
 682
 683	if (TCP_SKB_CB(skb)->end_seq -
 684	    TCP_SKB_CB(skb)->seq >= inet_csk(sk)->icsk_ack.rcv_mss) {
 685		u32 delta = tcp_time_stamp(tp) - tp->rx_opt.rcv_tsecr;
 686		u32 delta_us;
 687
 688		if (likely(delta < INT_MAX / (USEC_PER_SEC / TCP_TS_HZ))) {
 689			if (!delta)
 690				delta = 1;
 691			delta_us = delta * (USEC_PER_SEC / TCP_TS_HZ);
 692			tcp_rcv_rtt_update(tp, delta_us, 0);
 693		}
 694	}
 695}
 696
 697/*
 698 * This function should be called every time data is copied to user space.
 699 * It calculates the appropriate TCP receive buffer space.
 700 */
 701void tcp_rcv_space_adjust(struct sock *sk)
 702{
 703	struct tcp_sock *tp = tcp_sk(sk);
 704	u32 copied;
 705	int time;
 706
 707	trace_tcp_rcv_space_adjust(sk);
 708
 709	tcp_mstamp_refresh(tp);
 710	time = tcp_stamp_us_delta(tp->tcp_mstamp, tp->rcvq_space.time);
 711	if (time < (tp->rcv_rtt_est.rtt_us >> 3) || tp->rcv_rtt_est.rtt_us == 0)
 712		return;
 713
 714	/* Number of bytes copied to user in last RTT */
 715	copied = tp->copied_seq - tp->rcvq_space.seq;
 716	if (copied <= tp->rcvq_space.space)
 717		goto new_measure;
 718
 719	/* A bit of theory :
 720	 * copied = bytes received in previous RTT, our base window
 721	 * To cope with packet losses, we need a 2x factor
 722	 * To cope with slow start, and sender growing its cwin by 100 %
 723	 * every RTT, we need a 4x factor, because the ACK we are sending
 724	 * now is for the next RTT, not the current one :
 725	 * <prev RTT . ><current RTT .. ><next RTT .... >
 726	 */
 727
 728	if (READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_moderate_rcvbuf) &&
 729	    !(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) {
 730		int rcvmem, rcvbuf;
 731		u64 rcvwin, grow;
 732
 733		/* minimal window to cope with packet losses, assuming
 734		 * steady state. Add some cushion because of small variations.
 735		 */
 736		rcvwin = ((u64)copied << 1) + 16 * tp->advmss;
 737
 738		/* Accommodate for sender rate increase (eg. slow start) */
 739		grow = rcvwin * (copied - tp->rcvq_space.space);
 740		do_div(grow, tp->rcvq_space.space);
 741		rcvwin += (grow << 1);
 742
 743		rcvmem = SKB_TRUESIZE(tp->advmss + MAX_TCP_HEADER);
 744		while (tcp_win_from_space(sk, rcvmem) < tp->advmss)
 745			rcvmem += 128;
 746
 747		do_div(rcvwin, tp->advmss);
 748		rcvbuf = min_t(u64, rcvwin * rcvmem,
 749			       READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_rmem[2]));
 750		if (rcvbuf > sk->sk_rcvbuf) {
 751			WRITE_ONCE(sk->sk_rcvbuf, rcvbuf);
 752
 753			/* Make the window clamp follow along.  */
 754			tp->window_clamp = tcp_win_from_space(sk, rcvbuf);
 755		}
 756	}
 757	tp->rcvq_space.space = copied;
 758
 759new_measure:
 760	tp->rcvq_space.seq = tp->copied_seq;
 761	tp->rcvq_space.time = tp->tcp_mstamp;
 762}
 763
 764/* There is something which you must keep in mind when you analyze the
 765 * behavior of the tp->ato delayed ack timeout interval.  When a
 766 * connection starts up, we want to ack as quickly as possible.  The
 767 * problem is that "good" TCP's do slow start at the beginning of data
 768 * transmission.  The means that until we send the first few ACK's the
 769 * sender will sit on his end and only queue most of his data, because
 770 * he can only send snd_cwnd unacked packets at any given time.  For
 771 * each ACK we send, he increments snd_cwnd and transmits more of his
 772 * queue.  -DaveM
 773 */
 774static void tcp_event_data_recv(struct sock *sk, struct sk_buff *skb)
 775{
 776	struct tcp_sock *tp = tcp_sk(sk);
 777	struct inet_connection_sock *icsk = inet_csk(sk);
 778	u32 now;
 779
 780	inet_csk_schedule_ack(sk);
 781
 782	tcp_measure_rcv_mss(sk, skb);
 783
 784	tcp_rcv_rtt_measure(tp);
 785
 786	now = tcp_jiffies32;
 787
 788	if (!icsk->icsk_ack.ato) {
 789		/* The _first_ data packet received, initialize
 790		 * delayed ACK engine.
 791		 */
 792		tcp_incr_quickack(sk, TCP_MAX_QUICKACKS);
 793		icsk->icsk_ack.ato = TCP_ATO_MIN;
 794	} else {
 795		int m = now - icsk->icsk_ack.lrcvtime;
 796
 797		if (m <= TCP_ATO_MIN / 2) {
 798			/* The fastest case is the first. */
 799			icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + TCP_ATO_MIN / 2;
 800		} else if (m < icsk->icsk_ack.ato) {
 801			icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + m;
 802			if (icsk->icsk_ack.ato > icsk->icsk_rto)
 803				icsk->icsk_ack.ato = icsk->icsk_rto;
 804		} else if (m > icsk->icsk_rto) {
 805			/* Too long gap. Apparently sender failed to
 806			 * restart window, so that we send ACKs quickly.
 807			 */
 808			tcp_incr_quickack(sk, TCP_MAX_QUICKACKS);
 
 809		}
 810	}
 811	icsk->icsk_ack.lrcvtime = now;
 812
 813	tcp_ecn_check_ce(sk, skb);
 814
 815	if (skb->len >= 128)
 816		tcp_grow_window(sk, skb, true);
 817}
 818
 819/* Called to compute a smoothed rtt estimate. The data fed to this
 820 * routine either comes from timestamps, or from segments that were
 821 * known _not_ to have been retransmitted [see Karn/Partridge
 822 * Proceedings SIGCOMM 87]. The algorithm is from the SIGCOMM 88
 823 * piece by Van Jacobson.
 824 * NOTE: the next three routines used to be one big routine.
 825 * To save cycles in the RFC 1323 implementation it was better to break
 826 * it up into three procedures. -- erics
 827 */
 828static void tcp_rtt_estimator(struct sock *sk, long mrtt_us)
 829{
 830	struct tcp_sock *tp = tcp_sk(sk);
 831	long m = mrtt_us; /* RTT */
 832	u32 srtt = tp->srtt_us;
 833
 834	/*	The following amusing code comes from Jacobson's
 835	 *	article in SIGCOMM '88.  Note that rtt and mdev
 836	 *	are scaled versions of rtt and mean deviation.
 837	 *	This is designed to be as fast as possible
 838	 *	m stands for "measurement".
 839	 *
 840	 *	On a 1990 paper the rto value is changed to:
 841	 *	RTO = rtt + 4 * mdev
 842	 *
 843	 * Funny. This algorithm seems to be very broken.
 844	 * These formulae increase RTO, when it should be decreased, increase
 845	 * too slowly, when it should be increased quickly, decrease too quickly
 846	 * etc. I guess in BSD RTO takes ONE value, so that it is absolutely
 847	 * does not matter how to _calculate_ it. Seems, it was trap
 848	 * that VJ failed to avoid. 8)
 849	 */
 850	if (srtt != 0) {
 851		m -= (srtt >> 3);	/* m is now error in rtt est */
 852		srtt += m;		/* rtt = 7/8 rtt + 1/8 new */
 853		if (m < 0) {
 854			m = -m;		/* m is now abs(error) */
 855			m -= (tp->mdev_us >> 2);   /* similar update on mdev */
 856			/* This is similar to one of Eifel findings.
 857			 * Eifel blocks mdev updates when rtt decreases.
 858			 * This solution is a bit different: we use finer gain
 859			 * for mdev in this case (alpha*beta).
 860			 * Like Eifel it also prevents growth of rto,
 861			 * but also it limits too fast rto decreases,
 862			 * happening in pure Eifel.
 863			 */
 864			if (m > 0)
 865				m >>= 3;
 866		} else {
 867			m -= (tp->mdev_us >> 2);   /* similar update on mdev */
 868		}
 869		tp->mdev_us += m;		/* mdev = 3/4 mdev + 1/4 new */
 870		if (tp->mdev_us > tp->mdev_max_us) {
 871			tp->mdev_max_us = tp->mdev_us;
 872			if (tp->mdev_max_us > tp->rttvar_us)
 873				tp->rttvar_us = tp->mdev_max_us;
 874		}
 875		if (after(tp->snd_una, tp->rtt_seq)) {
 876			if (tp->mdev_max_us < tp->rttvar_us)
 877				tp->rttvar_us -= (tp->rttvar_us - tp->mdev_max_us) >> 2;
 878			tp->rtt_seq = tp->snd_nxt;
 879			tp->mdev_max_us = tcp_rto_min_us(sk);
 880
 881			tcp_bpf_rtt(sk);
 882		}
 883	} else {
 884		/* no previous measure. */
 885		srtt = m << 3;		/* take the measured time to be rtt */
 886		tp->mdev_us = m << 1;	/* make sure rto = 3*rtt */
 887		tp->rttvar_us = max(tp->mdev_us, tcp_rto_min_us(sk));
 888		tp->mdev_max_us = tp->rttvar_us;
 889		tp->rtt_seq = tp->snd_nxt;
 890
 891		tcp_bpf_rtt(sk);
 892	}
 893	tp->srtt_us = max(1U, srtt);
 894}
 895
 896static void tcp_update_pacing_rate(struct sock *sk)
 897{
 898	const struct tcp_sock *tp = tcp_sk(sk);
 899	u64 rate;
 900
 901	/* set sk_pacing_rate to 200 % of current rate (mss * cwnd / srtt) */
 902	rate = (u64)tp->mss_cache * ((USEC_PER_SEC / 100) << 3);
 903
 904	/* current rate is (cwnd * mss) / srtt
 905	 * In Slow Start [1], set sk_pacing_rate to 200 % the current rate.
 906	 * In Congestion Avoidance phase, set it to 120 % the current rate.
 907	 *
 908	 * [1] : Normal Slow Start condition is (tp->snd_cwnd < tp->snd_ssthresh)
 909	 *	 If snd_cwnd >= (tp->snd_ssthresh / 2), we are approaching
 910	 *	 end of slow start and should slow down.
 911	 */
 912	if (tcp_snd_cwnd(tp) < tp->snd_ssthresh / 2)
 913		rate *= READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_pacing_ss_ratio);
 914	else
 915		rate *= READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_pacing_ca_ratio);
 916
 917	rate *= max(tcp_snd_cwnd(tp), tp->packets_out);
 918
 919	if (likely(tp->srtt_us))
 920		do_div(rate, tp->srtt_us);
 921
 922	/* WRITE_ONCE() is needed because sch_fq fetches sk_pacing_rate
 923	 * without any lock. We want to make sure compiler wont store
 924	 * intermediate values in this location.
 925	 */
 926	WRITE_ONCE(sk->sk_pacing_rate, min_t(u64, rate,
 927					     sk->sk_max_pacing_rate));
 928}
 929
 930/* Calculate rto without backoff.  This is the second half of Van Jacobson's
 931 * routine referred to above.
 932 */
 933static void tcp_set_rto(struct sock *sk)
 934{
 935	const struct tcp_sock *tp = tcp_sk(sk);
 936	/* Old crap is replaced with new one. 8)
 937	 *
 938	 * More seriously:
 939	 * 1. If rtt variance happened to be less 50msec, it is hallucination.
 940	 *    It cannot be less due to utterly erratic ACK generation made
 941	 *    at least by solaris and freebsd. "Erratic ACKs" has _nothing_
 942	 *    to do with delayed acks, because at cwnd>2 true delack timeout
 943	 *    is invisible. Actually, Linux-2.4 also generates erratic
 944	 *    ACKs in some circumstances.
 945	 */
 946	inet_csk(sk)->icsk_rto = __tcp_set_rto(tp);
 947
 948	/* 2. Fixups made earlier cannot be right.
 949	 *    If we do not estimate RTO correctly without them,
 950	 *    all the algo is pure shit and should be replaced
 951	 *    with correct one. It is exactly, which we pretend to do.
 952	 */
 953
 954	/* NOTE: clamping at TCP_RTO_MIN is not required, current algo
 955	 * guarantees that rto is higher.
 956	 */
 957	tcp_bound_rto(sk);
 958}
 959
 960__u32 tcp_init_cwnd(const struct tcp_sock *tp, const struct dst_entry *dst)
 961{
 962	__u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0);
 963
 964	if (!cwnd)
 965		cwnd = TCP_INIT_CWND;
 966	return min_t(__u32, cwnd, tp->snd_cwnd_clamp);
 967}
 968
 969struct tcp_sacktag_state {
 970	/* Timestamps for earliest and latest never-retransmitted segment
 971	 * that was SACKed. RTO needs the earliest RTT to stay conservative,
 972	 * but congestion control should still get an accurate delay signal.
 973	 */
 974	u64	first_sackt;
 975	u64	last_sackt;
 976	u32	reord;
 977	u32	sack_delivered;
 978	int	flag;
 979	unsigned int mss_now;
 980	struct rate_sample *rate;
 981};
 982
 983/* Take a notice that peer is sending D-SACKs. Skip update of data delivery
 984 * and spurious retransmission information if this DSACK is unlikely caused by
 985 * sender's action:
 986 * - DSACKed sequence range is larger than maximum receiver's window.
 987 * - Total no. of DSACKed segments exceed the total no. of retransmitted segs.
 988 */
 989static u32 tcp_dsack_seen(struct tcp_sock *tp, u32 start_seq,
 990			  u32 end_seq, struct tcp_sacktag_state *state)
 991{
 992	u32 seq_len, dup_segs = 1;
 993
 994	if (!before(start_seq, end_seq))
 995		return 0;
 996
 997	seq_len = end_seq - start_seq;
 998	/* Dubious DSACK: DSACKed range greater than maximum advertised rwnd */
 999	if (seq_len > tp->max_window)
1000		return 0;
1001	if (seq_len > tp->mss_cache)
1002		dup_segs = DIV_ROUND_UP(seq_len, tp->mss_cache);
1003	else if (tp->tlp_high_seq && tp->tlp_high_seq == end_seq)
1004		state->flag |= FLAG_DSACK_TLP;
1005
1006	tp->dsack_dups += dup_segs;
1007	/* Skip the DSACK if dup segs weren't retransmitted by sender */
1008	if (tp->dsack_dups > tp->total_retrans)
1009		return 0;
1010
1011	tp->rx_opt.sack_ok |= TCP_DSACK_SEEN;
1012	/* We increase the RACK ordering window in rounds where we receive
1013	 * DSACKs that may have been due to reordering causing RACK to trigger
1014	 * a spurious fast recovery. Thus RACK ignores DSACKs that happen
1015	 * without having seen reordering, or that match TLP probes (TLP
1016	 * is timer-driven, not triggered by RACK).
1017	 */
1018	if (tp->reord_seen && !(state->flag & FLAG_DSACK_TLP))
1019		tp->rack.dsack_seen = 1;
1020
1021	state->flag |= FLAG_DSACKING_ACK;
1022	/* A spurious retransmission is delivered */
1023	state->sack_delivered += dup_segs;
1024
1025	return dup_segs;
1026}
1027
1028/* It's reordering when higher sequence was delivered (i.e. sacked) before
1029 * some lower never-retransmitted sequence ("low_seq"). The maximum reordering
1030 * distance is approximated in full-mss packet distance ("reordering").
1031 */
1032static void tcp_check_sack_reordering(struct sock *sk, const u32 low_seq,
1033				      const int ts)
1034{
1035	struct tcp_sock *tp = tcp_sk(sk);
1036	const u32 mss = tp->mss_cache;
1037	u32 fack, metric;
1038
1039	fack = tcp_highest_sack_seq(tp);
1040	if (!before(low_seq, fack))
1041		return;
1042
1043	metric = fack - low_seq;
1044	if ((metric > tp->reordering * mss) && mss) {
1045#if FASTRETRANS_DEBUG > 1
1046		pr_debug("Disorder%d %d %u f%u s%u rr%d\n",
1047			 tp->rx_opt.sack_ok, inet_csk(sk)->icsk_ca_state,
1048			 tp->reordering,
1049			 0,
1050			 tp->sacked_out,
1051			 tp->undo_marker ? tp->undo_retrans : 0);
1052#endif
1053		tp->reordering = min_t(u32, (metric + mss - 1) / mss,
1054				       READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_max_reordering));
1055	}
1056
1057	/* This exciting event is worth to be remembered. 8) */
1058	tp->reord_seen++;
1059	NET_INC_STATS(sock_net(sk),
1060		      ts ? LINUX_MIB_TCPTSREORDER : LINUX_MIB_TCPSACKREORDER);
1061}
1062
1063 /* This must be called before lost_out or retrans_out are updated
1064  * on a new loss, because we want to know if all skbs previously
1065  * known to be lost have already been retransmitted, indicating
1066  * that this newly lost skb is our next skb to retransmit.
1067  */
1068static void tcp_verify_retransmit_hint(struct tcp_sock *tp, struct sk_buff *skb)
1069{
1070	if ((!tp->retransmit_skb_hint && tp->retrans_out >= tp->lost_out) ||
1071	    (tp->retransmit_skb_hint &&
1072	     before(TCP_SKB_CB(skb)->seq,
1073		    TCP_SKB_CB(tp->retransmit_skb_hint)->seq)))
1074		tp->retransmit_skb_hint = skb;
1075}
1076
1077/* Sum the number of packets on the wire we have marked as lost, and
1078 * notify the congestion control module that the given skb was marked lost.
 
 
 
 
1079 */
1080static void tcp_notify_skb_loss_event(struct tcp_sock *tp, const struct sk_buff *skb)
1081{
1082	tp->lost += tcp_skb_pcount(skb);
 
 
 
 
1083}
1084
1085void tcp_mark_skb_lost(struct sock *sk, struct sk_buff *skb)
1086{
1087	__u8 sacked = TCP_SKB_CB(skb)->sacked;
1088	struct tcp_sock *tp = tcp_sk(sk);
1089
1090	if (sacked & TCPCB_SACKED_ACKED)
1091		return;
 
 
 
1092
 
 
1093	tcp_verify_retransmit_hint(tp, skb);
1094	if (sacked & TCPCB_LOST) {
1095		if (sacked & TCPCB_SACKED_RETRANS) {
1096			/* Account for retransmits that are lost again */
1097			TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
1098			tp->retrans_out -= tcp_skb_pcount(skb);
1099			NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPLOSTRETRANSMIT,
1100				      tcp_skb_pcount(skb));
1101			tcp_notify_skb_loss_event(tp, skb);
1102		}
1103	} else {
1104		tp->lost_out += tcp_skb_pcount(skb);
1105		TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1106		tcp_notify_skb_loss_event(tp, skb);
1107	}
1108}
1109
1110/* Updates the delivered and delivered_ce counts */
1111static void tcp_count_delivered(struct tcp_sock *tp, u32 delivered,
1112				bool ece_ack)
1113{
1114	tp->delivered += delivered;
1115	if (ece_ack)
1116		tp->delivered_ce += delivered;
1117}
1118
1119/* This procedure tags the retransmission queue when SACKs arrive.
1120 *
1121 * We have three tag bits: SACKED(S), RETRANS(R) and LOST(L).
1122 * Packets in queue with these bits set are counted in variables
1123 * sacked_out, retrans_out and lost_out, correspondingly.
1124 *
1125 * Valid combinations are:
1126 * Tag  InFlight	Description
1127 * 0	1		- orig segment is in flight.
1128 * S	0		- nothing flies, orig reached receiver.
1129 * L	0		- nothing flies, orig lost by net.
1130 * R	2		- both orig and retransmit are in flight.
1131 * L|R	1		- orig is lost, retransmit is in flight.
1132 * S|R  1		- orig reached receiver, retrans is still in flight.
1133 * (L|S|R is logically valid, it could occur when L|R is sacked,
1134 *  but it is equivalent to plain S and code short-curcuits it to S.
1135 *  L|S is logically invalid, it would mean -1 packet in flight 8))
1136 *
1137 * These 6 states form finite state machine, controlled by the following events:
1138 * 1. New ACK (+SACK) arrives. (tcp_sacktag_write_queue())
1139 * 2. Retransmission. (tcp_retransmit_skb(), tcp_xmit_retransmit_queue())
1140 * 3. Loss detection event of two flavors:
1141 *	A. Scoreboard estimator decided the packet is lost.
1142 *	   A'. Reno "three dupacks" marks head of queue lost.
1143 *	B. SACK arrives sacking SND.NXT at the moment, when the
1144 *	   segment was retransmitted.
1145 * 4. D-SACK added new rule: D-SACK changes any tag to S.
1146 *
1147 * It is pleasant to note, that state diagram turns out to be commutative,
1148 * so that we are allowed not to be bothered by order of our actions,
1149 * when multiple events arrive simultaneously. (see the function below).
1150 *
1151 * Reordering detection.
1152 * --------------------
1153 * Reordering metric is maximal distance, which a packet can be displaced
1154 * in packet stream. With SACKs we can estimate it:
1155 *
1156 * 1. SACK fills old hole and the corresponding segment was not
1157 *    ever retransmitted -> reordering. Alas, we cannot use it
1158 *    when segment was retransmitted.
1159 * 2. The last flaw is solved with D-SACK. D-SACK arrives
1160 *    for retransmitted and already SACKed segment -> reordering..
1161 * Both of these heuristics are not used in Loss state, when we cannot
1162 * account for retransmits accurately.
1163 *
1164 * SACK block validation.
1165 * ----------------------
1166 *
1167 * SACK block range validation checks that the received SACK block fits to
1168 * the expected sequence limits, i.e., it is between SND.UNA and SND.NXT.
1169 * Note that SND.UNA is not included to the range though being valid because
1170 * it means that the receiver is rather inconsistent with itself reporting
1171 * SACK reneging when it should advance SND.UNA. Such SACK block this is
1172 * perfectly valid, however, in light of RFC2018 which explicitly states
1173 * that "SACK block MUST reflect the newest segment.  Even if the newest
1174 * segment is going to be discarded ...", not that it looks very clever
1175 * in case of head skb. Due to potentional receiver driven attacks, we
1176 * choose to avoid immediate execution of a walk in write queue due to
1177 * reneging and defer head skb's loss recovery to standard loss recovery
1178 * procedure that will eventually trigger (nothing forbids us doing this).
1179 *
1180 * Implements also blockage to start_seq wrap-around. Problem lies in the
1181 * fact that though start_seq (s) is before end_seq (i.e., not reversed),
1182 * there's no guarantee that it will be before snd_nxt (n). The problem
1183 * happens when start_seq resides between end_seq wrap (e_w) and snd_nxt
1184 * wrap (s_w):
1185 *
1186 *         <- outs wnd ->                          <- wrapzone ->
1187 *         u     e      n                         u_w   e_w  s n_w
1188 *         |     |      |                          |     |   |  |
1189 * |<------------+------+----- TCP seqno space --------------+---------->|
1190 * ...-- <2^31 ->|                                           |<--------...
1191 * ...---- >2^31 ------>|                                    |<--------...
1192 *
1193 * Current code wouldn't be vulnerable but it's better still to discard such
1194 * crazy SACK blocks. Doing this check for start_seq alone closes somewhat
1195 * similar case (end_seq after snd_nxt wrap) as earlier reversed check in
1196 * snd_nxt wrap -> snd_una region will then become "well defined", i.e.,
1197 * equal to the ideal case (infinite seqno space without wrap caused issues).
1198 *
1199 * With D-SACK the lower bound is extended to cover sequence space below
1200 * SND.UNA down to undo_marker, which is the last point of interest. Yet
1201 * again, D-SACK block must not to go across snd_una (for the same reason as
1202 * for the normal SACK blocks, explained above). But there all simplicity
1203 * ends, TCP might receive valid D-SACKs below that. As long as they reside
1204 * fully below undo_marker they do not affect behavior in anyway and can
1205 * therefore be safely ignored. In rare cases (which are more or less
1206 * theoretical ones), the D-SACK will nicely cross that boundary due to skb
1207 * fragmentation and packet reordering past skb's retransmission. To consider
1208 * them correctly, the acceptable range must be extended even more though
1209 * the exact amount is rather hard to quantify. However, tp->max_window can
1210 * be used as an exaggerated estimate.
1211 */
1212static bool tcp_is_sackblock_valid(struct tcp_sock *tp, bool is_dsack,
1213				   u32 start_seq, u32 end_seq)
1214{
1215	/* Too far in future, or reversed (interpretation is ambiguous) */
1216	if (after(end_seq, tp->snd_nxt) || !before(start_seq, end_seq))
1217		return false;
1218
1219	/* Nasty start_seq wrap-around check (see comments above) */
1220	if (!before(start_seq, tp->snd_nxt))
1221		return false;
1222
1223	/* In outstanding window? ...This is valid exit for D-SACKs too.
1224	 * start_seq == snd_una is non-sensical (see comments above)
1225	 */
1226	if (after(start_seq, tp->snd_una))
1227		return true;
1228
1229	if (!is_dsack || !tp->undo_marker)
1230		return false;
1231
1232	/* ...Then it's D-SACK, and must reside below snd_una completely */
1233	if (after(end_seq, tp->snd_una))
1234		return false;
1235
1236	if (!before(start_seq, tp->undo_marker))
1237		return true;
1238
1239	/* Too old */
1240	if (!after(end_seq, tp->undo_marker))
1241		return false;
1242
1243	/* Undo_marker boundary crossing (overestimates a lot). Known already:
1244	 *   start_seq < undo_marker and end_seq >= undo_marker.
1245	 */
1246	return !before(start_seq, end_seq - tp->max_window);
1247}
1248
1249static bool tcp_check_dsack(struct sock *sk, const struct sk_buff *ack_skb,
1250			    struct tcp_sack_block_wire *sp, int num_sacks,
1251			    u32 prior_snd_una, struct tcp_sacktag_state *state)
1252{
1253	struct tcp_sock *tp = tcp_sk(sk);
1254	u32 start_seq_0 = get_unaligned_be32(&sp[0].start_seq);
1255	u32 end_seq_0 = get_unaligned_be32(&sp[0].end_seq);
1256	u32 dup_segs;
1257
1258	if (before(start_seq_0, TCP_SKB_CB(ack_skb)->ack_seq)) {
1259		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKRECV);
1260	} else if (num_sacks > 1) {
1261		u32 end_seq_1 = get_unaligned_be32(&sp[1].end_seq);
1262		u32 start_seq_1 = get_unaligned_be32(&sp[1].start_seq);
1263
1264		if (after(end_seq_0, end_seq_1) || before(start_seq_0, start_seq_1))
1265			return false;
1266		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKOFORECV);
1267	} else {
1268		return false;
1269	}
1270
1271	dup_segs = tcp_dsack_seen(tp, start_seq_0, end_seq_0, state);
1272	if (!dup_segs) {	/* Skip dubious DSACK */
1273		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKIGNOREDDUBIOUS);
1274		return false;
1275	}
1276
1277	NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPDSACKRECVSEGS, dup_segs);
1278
1279	/* D-SACK for already forgotten data... Do dumb counting. */
1280	if (tp->undo_marker && tp->undo_retrans > 0 &&
1281	    !after(end_seq_0, prior_snd_una) &&
1282	    after(end_seq_0, tp->undo_marker))
1283		tp->undo_retrans = max_t(int, 0, tp->undo_retrans - dup_segs);
1284
1285	return true;
1286}
1287
1288/* Check if skb is fully within the SACK block. In presence of GSO skbs,
1289 * the incoming SACK may not exactly match but we can find smaller MSS
1290 * aligned portion of it that matches. Therefore we might need to fragment
1291 * which may fail and creates some hassle (caller must handle error case
1292 * returns).
1293 *
1294 * FIXME: this could be merged to shift decision code
1295 */
1296static int tcp_match_skb_to_sack(struct sock *sk, struct sk_buff *skb,
1297				  u32 start_seq, u32 end_seq)
1298{
1299	int err;
1300	bool in_sack;
1301	unsigned int pkt_len;
1302	unsigned int mss;
1303
1304	in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1305		  !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1306
1307	if (tcp_skb_pcount(skb) > 1 && !in_sack &&
1308	    after(TCP_SKB_CB(skb)->end_seq, start_seq)) {
1309		mss = tcp_skb_mss(skb);
1310		in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
1311
1312		if (!in_sack) {
1313			pkt_len = start_seq - TCP_SKB_CB(skb)->seq;
1314			if (pkt_len < mss)
1315				pkt_len = mss;
1316		} else {
1317			pkt_len = end_seq - TCP_SKB_CB(skb)->seq;
1318			if (pkt_len < mss)
1319				return -EINVAL;
1320		}
1321
1322		/* Round if necessary so that SACKs cover only full MSSes
1323		 * and/or the remaining small portion (if present)
1324		 */
1325		if (pkt_len > mss) {
1326			unsigned int new_len = (pkt_len / mss) * mss;
1327			if (!in_sack && new_len < pkt_len)
1328				new_len += mss;
1329			pkt_len = new_len;
1330		}
1331
1332		if (pkt_len >= skb->len && !in_sack)
1333			return 0;
1334
1335		err = tcp_fragment(sk, TCP_FRAG_IN_RTX_QUEUE, skb,
1336				   pkt_len, mss, GFP_ATOMIC);
1337		if (err < 0)
1338			return err;
1339	}
1340
1341	return in_sack;
1342}
1343
1344/* Mark the given newly-SACKed range as such, adjusting counters and hints. */
1345static u8 tcp_sacktag_one(struct sock *sk,
1346			  struct tcp_sacktag_state *state, u8 sacked,
1347			  u32 start_seq, u32 end_seq,
1348			  int dup_sack, int pcount,
1349			  u64 xmit_time)
1350{
1351	struct tcp_sock *tp = tcp_sk(sk);
1352
1353	/* Account D-SACK for retransmitted packet. */
1354	if (dup_sack && (sacked & TCPCB_RETRANS)) {
1355		if (tp->undo_marker && tp->undo_retrans > 0 &&
1356		    after(end_seq, tp->undo_marker))
1357			tp->undo_retrans = max_t(int, 0, tp->undo_retrans - pcount);
1358		if ((sacked & TCPCB_SACKED_ACKED) &&
1359		    before(start_seq, state->reord))
1360				state->reord = start_seq;
1361	}
1362
1363	/* Nothing to do; acked frame is about to be dropped (was ACKed). */
1364	if (!after(end_seq, tp->snd_una))
1365		return sacked;
1366
1367	if (!(sacked & TCPCB_SACKED_ACKED)) {
1368		tcp_rack_advance(tp, sacked, end_seq, xmit_time);
1369
1370		if (sacked & TCPCB_SACKED_RETRANS) {
1371			/* If the segment is not tagged as lost,
1372			 * we do not clear RETRANS, believing
1373			 * that retransmission is still in flight.
1374			 */
1375			if (sacked & TCPCB_LOST) {
1376				sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS);
1377				tp->lost_out -= pcount;
1378				tp->retrans_out -= pcount;
1379			}
1380		} else {
1381			if (!(sacked & TCPCB_RETRANS)) {
1382				/* New sack for not retransmitted frame,
1383				 * which was in hole. It is reordering.
1384				 */
1385				if (before(start_seq,
1386					   tcp_highest_sack_seq(tp)) &&
1387				    before(start_seq, state->reord))
1388					state->reord = start_seq;
1389
1390				if (!after(end_seq, tp->high_seq))
1391					state->flag |= FLAG_ORIG_SACK_ACKED;
1392				if (state->first_sackt == 0)
1393					state->first_sackt = xmit_time;
1394				state->last_sackt = xmit_time;
1395			}
1396
1397			if (sacked & TCPCB_LOST) {
1398				sacked &= ~TCPCB_LOST;
1399				tp->lost_out -= pcount;
1400			}
1401		}
1402
1403		sacked |= TCPCB_SACKED_ACKED;
1404		state->flag |= FLAG_DATA_SACKED;
1405		tp->sacked_out += pcount;
1406		/* Out-of-order packets delivered */
1407		state->sack_delivered += pcount;
1408
1409		/* Lost marker hint past SACKed? Tweak RFC3517 cnt */
1410		if (tp->lost_skb_hint &&
1411		    before(start_seq, TCP_SKB_CB(tp->lost_skb_hint)->seq))
1412			tp->lost_cnt_hint += pcount;
1413	}
1414
1415	/* D-SACK. We can detect redundant retransmission in S|R and plain R
1416	 * frames and clear it. undo_retrans is decreased above, L|R frames
1417	 * are accounted above as well.
1418	 */
1419	if (dup_sack && (sacked & TCPCB_SACKED_RETRANS)) {
1420		sacked &= ~TCPCB_SACKED_RETRANS;
1421		tp->retrans_out -= pcount;
1422	}
1423
1424	return sacked;
1425}
1426
1427/* Shift newly-SACKed bytes from this skb to the immediately previous
1428 * already-SACKed sk_buff. Mark the newly-SACKed bytes as such.
1429 */
1430static bool tcp_shifted_skb(struct sock *sk, struct sk_buff *prev,
1431			    struct sk_buff *skb,
1432			    struct tcp_sacktag_state *state,
1433			    unsigned int pcount, int shifted, int mss,
1434			    bool dup_sack)
1435{
1436	struct tcp_sock *tp = tcp_sk(sk);
1437	u32 start_seq = TCP_SKB_CB(skb)->seq;	/* start of newly-SACKed */
1438	u32 end_seq = start_seq + shifted;	/* end of newly-SACKed */
1439
1440	BUG_ON(!pcount);
1441
1442	/* Adjust counters and hints for the newly sacked sequence
1443	 * range but discard the return value since prev is already
1444	 * marked. We must tag the range first because the seq
1445	 * advancement below implicitly advances
1446	 * tcp_highest_sack_seq() when skb is highest_sack.
1447	 */
1448	tcp_sacktag_one(sk, state, TCP_SKB_CB(skb)->sacked,
1449			start_seq, end_seq, dup_sack, pcount,
1450			tcp_skb_timestamp_us(skb));
1451	tcp_rate_skb_delivered(sk, skb, state->rate);
1452
1453	if (skb == tp->lost_skb_hint)
1454		tp->lost_cnt_hint += pcount;
1455
1456	TCP_SKB_CB(prev)->end_seq += shifted;
1457	TCP_SKB_CB(skb)->seq += shifted;
1458
1459	tcp_skb_pcount_add(prev, pcount);
1460	WARN_ON_ONCE(tcp_skb_pcount(skb) < pcount);
1461	tcp_skb_pcount_add(skb, -pcount);
1462
1463	/* When we're adding to gso_segs == 1, gso_size will be zero,
1464	 * in theory this shouldn't be necessary but as long as DSACK
1465	 * code can come after this skb later on it's better to keep
1466	 * setting gso_size to something.
1467	 */
1468	if (!TCP_SKB_CB(prev)->tcp_gso_size)
1469		TCP_SKB_CB(prev)->tcp_gso_size = mss;
1470
1471	/* CHECKME: To clear or not to clear? Mimics normal skb currently */
1472	if (tcp_skb_pcount(skb) <= 1)
1473		TCP_SKB_CB(skb)->tcp_gso_size = 0;
1474
1475	/* Difference in this won't matter, both ACKed by the same cumul. ACK */
1476	TCP_SKB_CB(prev)->sacked |= (TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS);
1477
1478	if (skb->len > 0) {
1479		BUG_ON(!tcp_skb_pcount(skb));
1480		NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKSHIFTED);
1481		return false;
1482	}
1483
1484	/* Whole SKB was eaten :-) */
1485
1486	if (skb == tp->retransmit_skb_hint)
1487		tp->retransmit_skb_hint = prev;
1488	if (skb == tp->lost_skb_hint) {
1489		tp->lost_skb_hint = prev;
1490		tp->lost_cnt_hint -= tcp_skb_pcount(prev);
1491	}
1492
1493	TCP_SKB_CB(prev)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags;
1494	TCP_SKB_CB(prev)->eor = TCP_SKB_CB(skb)->eor;
1495	if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
1496		TCP_SKB_CB(prev)->end_seq++;
1497
1498	if (skb == tcp_highest_sack(sk))
1499		tcp_advance_highest_sack(sk, skb);
1500
1501	tcp_skb_collapse_tstamp(prev, skb);
1502	if (unlikely(TCP_SKB_CB(prev)->tx.delivered_mstamp))
1503		TCP_SKB_CB(prev)->tx.delivered_mstamp = 0;
1504
1505	tcp_rtx_queue_unlink_and_free(skb, sk);
1506
1507	NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKMERGED);
1508
1509	return true;
1510}
1511
1512/* I wish gso_size would have a bit more sane initialization than
1513 * something-or-zero which complicates things
1514 */
1515static int tcp_skb_seglen(const struct sk_buff *skb)
1516{
1517	return tcp_skb_pcount(skb) == 1 ? skb->len : tcp_skb_mss(skb);
1518}
1519
1520/* Shifting pages past head area doesn't work */
1521static int skb_can_shift(const struct sk_buff *skb)
1522{
1523	return !skb_headlen(skb) && skb_is_nonlinear(skb);
1524}
1525
1526int tcp_skb_shift(struct sk_buff *to, struct sk_buff *from,
1527		  int pcount, int shiftlen)
1528{
1529	/* TCP min gso_size is 8 bytes (TCP_MIN_GSO_SIZE)
1530	 * Since TCP_SKB_CB(skb)->tcp_gso_segs is 16 bits, we need
1531	 * to make sure not storing more than 65535 * 8 bytes per skb,
1532	 * even if current MSS is bigger.
1533	 */
1534	if (unlikely(to->len + shiftlen >= 65535 * TCP_MIN_GSO_SIZE))
1535		return 0;
1536	if (unlikely(tcp_skb_pcount(to) + pcount > 65535))
1537		return 0;
1538	return skb_shift(to, from, shiftlen);
1539}
1540
1541/* Try collapsing SACK blocks spanning across multiple skbs to a single
1542 * skb.
1543 */
1544static struct sk_buff *tcp_shift_skb_data(struct sock *sk, struct sk_buff *skb,
1545					  struct tcp_sacktag_state *state,
1546					  u32 start_seq, u32 end_seq,
1547					  bool dup_sack)
1548{
1549	struct tcp_sock *tp = tcp_sk(sk);
1550	struct sk_buff *prev;
1551	int mss;
1552	int pcount = 0;
1553	int len;
1554	int in_sack;
1555
1556	/* Normally R but no L won't result in plain S */
1557	if (!dup_sack &&
1558	    (TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_RETRANS)) == TCPCB_SACKED_RETRANS)
1559		goto fallback;
1560	if (!skb_can_shift(skb))
1561		goto fallback;
1562	/* This frame is about to be dropped (was ACKed). */
1563	if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1564		goto fallback;
1565
1566	/* Can only happen with delayed DSACK + discard craziness */
1567	prev = skb_rb_prev(skb);
1568	if (!prev)
1569		goto fallback;
1570
1571	if ((TCP_SKB_CB(prev)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED)
1572		goto fallback;
1573
1574	if (!tcp_skb_can_collapse(prev, skb))
1575		goto fallback;
1576
1577	in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1578		  !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1579
1580	if (in_sack) {
1581		len = skb->len;
1582		pcount = tcp_skb_pcount(skb);
1583		mss = tcp_skb_seglen(skb);
1584
1585		/* TODO: Fix DSACKs to not fragment already SACKed and we can
1586		 * drop this restriction as unnecessary
1587		 */
1588		if (mss != tcp_skb_seglen(prev))
1589			goto fallback;
1590	} else {
1591		if (!after(TCP_SKB_CB(skb)->end_seq, start_seq))
1592			goto noop;
1593		/* CHECKME: This is non-MSS split case only?, this will
1594		 * cause skipped skbs due to advancing loop btw, original
1595		 * has that feature too
1596		 */
1597		if (tcp_skb_pcount(skb) <= 1)
1598			goto noop;
1599
1600		in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
1601		if (!in_sack) {
1602			/* TODO: head merge to next could be attempted here
1603			 * if (!after(TCP_SKB_CB(skb)->end_seq, end_seq)),
1604			 * though it might not be worth of the additional hassle
1605			 *
1606			 * ...we can probably just fallback to what was done
1607			 * previously. We could try merging non-SACKed ones
1608			 * as well but it probably isn't going to buy off
1609			 * because later SACKs might again split them, and
1610			 * it would make skb timestamp tracking considerably
1611			 * harder problem.
1612			 */
1613			goto fallback;
1614		}
1615
1616		len = end_seq - TCP_SKB_CB(skb)->seq;
1617		BUG_ON(len < 0);
1618		BUG_ON(len > skb->len);
1619
1620		/* MSS boundaries should be honoured or else pcount will
1621		 * severely break even though it makes things bit trickier.
1622		 * Optimize common case to avoid most of the divides
1623		 */
1624		mss = tcp_skb_mss(skb);
1625
1626		/* TODO: Fix DSACKs to not fragment already SACKed and we can
1627		 * drop this restriction as unnecessary
1628		 */
1629		if (mss != tcp_skb_seglen(prev))
1630			goto fallback;
1631
1632		if (len == mss) {
1633			pcount = 1;
1634		} else if (len < mss) {
1635			goto noop;
1636		} else {
1637			pcount = len / mss;
1638			len = pcount * mss;
1639		}
1640	}
1641
1642	/* tcp_sacktag_one() won't SACK-tag ranges below snd_una */
1643	if (!after(TCP_SKB_CB(skb)->seq + len, tp->snd_una))
1644		goto fallback;
1645
1646	if (!tcp_skb_shift(prev, skb, pcount, len))
1647		goto fallback;
1648	if (!tcp_shifted_skb(sk, prev, skb, state, pcount, len, mss, dup_sack))
1649		goto out;
1650
1651	/* Hole filled allows collapsing with the next as well, this is very
1652	 * useful when hole on every nth skb pattern happens
1653	 */
1654	skb = skb_rb_next(prev);
1655	if (!skb)
1656		goto out;
1657
1658	if (!skb_can_shift(skb) ||
1659	    ((TCP_SKB_CB(skb)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED) ||
1660	    (mss != tcp_skb_seglen(skb)))
1661		goto out;
1662
1663	if (!tcp_skb_can_collapse(prev, skb))
1664		goto out;
1665	len = skb->len;
1666	pcount = tcp_skb_pcount(skb);
1667	if (tcp_skb_shift(prev, skb, pcount, len))
1668		tcp_shifted_skb(sk, prev, skb, state, pcount,
1669				len, mss, 0);
1670
1671out:
1672	return prev;
1673
1674noop:
1675	return skb;
1676
1677fallback:
1678	NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKSHIFTFALLBACK);
1679	return NULL;
1680}
1681
1682static struct sk_buff *tcp_sacktag_walk(struct sk_buff *skb, struct sock *sk,
1683					struct tcp_sack_block *next_dup,
1684					struct tcp_sacktag_state *state,
1685					u32 start_seq, u32 end_seq,
1686					bool dup_sack_in)
1687{
1688	struct tcp_sock *tp = tcp_sk(sk);
1689	struct sk_buff *tmp;
1690
1691	skb_rbtree_walk_from(skb) {
1692		int in_sack = 0;
1693		bool dup_sack = dup_sack_in;
1694
1695		/* queue is in-order => we can short-circuit the walk early */
1696		if (!before(TCP_SKB_CB(skb)->seq, end_seq))
1697			break;
1698
1699		if (next_dup  &&
1700		    before(TCP_SKB_CB(skb)->seq, next_dup->end_seq)) {
1701			in_sack = tcp_match_skb_to_sack(sk, skb,
1702							next_dup->start_seq,
1703							next_dup->end_seq);
1704			if (in_sack > 0)
1705				dup_sack = true;
1706		}
1707
1708		/* skb reference here is a bit tricky to get right, since
1709		 * shifting can eat and free both this skb and the next,
1710		 * so not even _safe variant of the loop is enough.
1711		 */
1712		if (in_sack <= 0) {
1713			tmp = tcp_shift_skb_data(sk, skb, state,
1714						 start_seq, end_seq, dup_sack);
1715			if (tmp) {
1716				if (tmp != skb) {
1717					skb = tmp;
1718					continue;
1719				}
1720
1721				in_sack = 0;
1722			} else {
1723				in_sack = tcp_match_skb_to_sack(sk, skb,
1724								start_seq,
1725								end_seq);
1726			}
1727		}
1728
1729		if (unlikely(in_sack < 0))
1730			break;
1731
1732		if (in_sack) {
1733			TCP_SKB_CB(skb)->sacked =
1734				tcp_sacktag_one(sk,
1735						state,
1736						TCP_SKB_CB(skb)->sacked,
1737						TCP_SKB_CB(skb)->seq,
1738						TCP_SKB_CB(skb)->end_seq,
1739						dup_sack,
1740						tcp_skb_pcount(skb),
1741						tcp_skb_timestamp_us(skb));
1742			tcp_rate_skb_delivered(sk, skb, state->rate);
1743			if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
1744				list_del_init(&skb->tcp_tsorted_anchor);
1745
1746			if (!before(TCP_SKB_CB(skb)->seq,
1747				    tcp_highest_sack_seq(tp)))
1748				tcp_advance_highest_sack(sk, skb);
1749		}
1750	}
1751	return skb;
1752}
1753
1754static struct sk_buff *tcp_sacktag_bsearch(struct sock *sk, u32 seq)
1755{
1756	struct rb_node *parent, **p = &sk->tcp_rtx_queue.rb_node;
1757	struct sk_buff *skb;
1758
1759	while (*p) {
1760		parent = *p;
1761		skb = rb_to_skb(parent);
1762		if (before(seq, TCP_SKB_CB(skb)->seq)) {
1763			p = &parent->rb_left;
1764			continue;
1765		}
1766		if (!before(seq, TCP_SKB_CB(skb)->end_seq)) {
1767			p = &parent->rb_right;
1768			continue;
1769		}
1770		return skb;
1771	}
1772	return NULL;
1773}
1774
1775static struct sk_buff *tcp_sacktag_skip(struct sk_buff *skb, struct sock *sk,
1776					u32 skip_to_seq)
1777{
1778	if (skb && after(TCP_SKB_CB(skb)->seq, skip_to_seq))
1779		return skb;
1780
1781	return tcp_sacktag_bsearch(sk, skip_to_seq);
1782}
1783
1784static struct sk_buff *tcp_maybe_skipping_dsack(struct sk_buff *skb,
1785						struct sock *sk,
1786						struct tcp_sack_block *next_dup,
1787						struct tcp_sacktag_state *state,
1788						u32 skip_to_seq)
1789{
1790	if (!next_dup)
1791		return skb;
1792
1793	if (before(next_dup->start_seq, skip_to_seq)) {
1794		skb = tcp_sacktag_skip(skb, sk, next_dup->start_seq);
1795		skb = tcp_sacktag_walk(skb, sk, NULL, state,
1796				       next_dup->start_seq, next_dup->end_seq,
1797				       1);
1798	}
1799
1800	return skb;
1801}
1802
1803static int tcp_sack_cache_ok(const struct tcp_sock *tp, const struct tcp_sack_block *cache)
1804{
1805	return cache < tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
1806}
1807
1808static int
1809tcp_sacktag_write_queue(struct sock *sk, const struct sk_buff *ack_skb,
1810			u32 prior_snd_una, struct tcp_sacktag_state *state)
1811{
1812	struct tcp_sock *tp = tcp_sk(sk);
1813	const unsigned char *ptr = (skb_transport_header(ack_skb) +
1814				    TCP_SKB_CB(ack_skb)->sacked);
1815	struct tcp_sack_block_wire *sp_wire = (struct tcp_sack_block_wire *)(ptr+2);
1816	struct tcp_sack_block sp[TCP_NUM_SACKS];
1817	struct tcp_sack_block *cache;
1818	struct sk_buff *skb;
1819	int num_sacks = min(TCP_NUM_SACKS, (ptr[1] - TCPOLEN_SACK_BASE) >> 3);
1820	int used_sacks;
1821	bool found_dup_sack = false;
1822	int i, j;
1823	int first_sack_index;
1824
1825	state->flag = 0;
1826	state->reord = tp->snd_nxt;
1827
1828	if (!tp->sacked_out)
1829		tcp_highest_sack_reset(sk);
1830
1831	found_dup_sack = tcp_check_dsack(sk, ack_skb, sp_wire,
1832					 num_sacks, prior_snd_una, state);
1833
1834	/* Eliminate too old ACKs, but take into
1835	 * account more or less fresh ones, they can
1836	 * contain valid SACK info.
1837	 */
1838	if (before(TCP_SKB_CB(ack_skb)->ack_seq, prior_snd_una - tp->max_window))
1839		return 0;
1840
1841	if (!tp->packets_out)
1842		goto out;
1843
1844	used_sacks = 0;
1845	first_sack_index = 0;
1846	for (i = 0; i < num_sacks; i++) {
1847		bool dup_sack = !i && found_dup_sack;
1848
1849		sp[used_sacks].start_seq = get_unaligned_be32(&sp_wire[i].start_seq);
1850		sp[used_sacks].end_seq = get_unaligned_be32(&sp_wire[i].end_seq);
1851
1852		if (!tcp_is_sackblock_valid(tp, dup_sack,
1853					    sp[used_sacks].start_seq,
1854					    sp[used_sacks].end_seq)) {
1855			int mib_idx;
1856
1857			if (dup_sack) {
1858				if (!tp->undo_marker)
1859					mib_idx = LINUX_MIB_TCPDSACKIGNOREDNOUNDO;
1860				else
1861					mib_idx = LINUX_MIB_TCPDSACKIGNOREDOLD;
1862			} else {
1863				/* Don't count olds caused by ACK reordering */
1864				if ((TCP_SKB_CB(ack_skb)->ack_seq != tp->snd_una) &&
1865				    !after(sp[used_sacks].end_seq, tp->snd_una))
1866					continue;
1867				mib_idx = LINUX_MIB_TCPSACKDISCARD;
1868			}
1869
1870			NET_INC_STATS(sock_net(sk), mib_idx);
1871			if (i == 0)
1872				first_sack_index = -1;
1873			continue;
1874		}
1875
1876		/* Ignore very old stuff early */
1877		if (!after(sp[used_sacks].end_seq, prior_snd_una)) {
1878			if (i == 0)
1879				first_sack_index = -1;
1880			continue;
1881		}
1882
1883		used_sacks++;
1884	}
1885
1886	/* order SACK blocks to allow in order walk of the retrans queue */
1887	for (i = used_sacks - 1; i > 0; i--) {
1888		for (j = 0; j < i; j++) {
1889			if (after(sp[j].start_seq, sp[j + 1].start_seq)) {
1890				swap(sp[j], sp[j + 1]);
1891
1892				/* Track where the first SACK block goes to */
1893				if (j == first_sack_index)
1894					first_sack_index = j + 1;
1895			}
1896		}
1897	}
1898
1899	state->mss_now = tcp_current_mss(sk);
1900	skb = NULL;
1901	i = 0;
1902
1903	if (!tp->sacked_out) {
1904		/* It's already past, so skip checking against it */
1905		cache = tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
1906	} else {
1907		cache = tp->recv_sack_cache;
1908		/* Skip empty blocks in at head of the cache */
1909		while (tcp_sack_cache_ok(tp, cache) && !cache->start_seq &&
1910		       !cache->end_seq)
1911			cache++;
1912	}
1913
1914	while (i < used_sacks) {
1915		u32 start_seq = sp[i].start_seq;
1916		u32 end_seq = sp[i].end_seq;
1917		bool dup_sack = (found_dup_sack && (i == first_sack_index));
1918		struct tcp_sack_block *next_dup = NULL;
1919
1920		if (found_dup_sack && ((i + 1) == first_sack_index))
1921			next_dup = &sp[i + 1];
1922
1923		/* Skip too early cached blocks */
1924		while (tcp_sack_cache_ok(tp, cache) &&
1925		       !before(start_seq, cache->end_seq))
1926			cache++;
1927
1928		/* Can skip some work by looking recv_sack_cache? */
1929		if (tcp_sack_cache_ok(tp, cache) && !dup_sack &&
1930		    after(end_seq, cache->start_seq)) {
1931
1932			/* Head todo? */
1933			if (before(start_seq, cache->start_seq)) {
1934				skb = tcp_sacktag_skip(skb, sk, start_seq);
1935				skb = tcp_sacktag_walk(skb, sk, next_dup,
1936						       state,
1937						       start_seq,
1938						       cache->start_seq,
1939						       dup_sack);
1940			}
1941
1942			/* Rest of the block already fully processed? */
1943			if (!after(end_seq, cache->end_seq))
1944				goto advance_sp;
1945
1946			skb = tcp_maybe_skipping_dsack(skb, sk, next_dup,
1947						       state,
1948						       cache->end_seq);
1949
1950			/* ...tail remains todo... */
1951			if (tcp_highest_sack_seq(tp) == cache->end_seq) {
1952				/* ...but better entrypoint exists! */
1953				skb = tcp_highest_sack(sk);
1954				if (!skb)
1955					break;
1956				cache++;
1957				goto walk;
1958			}
1959
1960			skb = tcp_sacktag_skip(skb, sk, cache->end_seq);
1961			/* Check overlap against next cached too (past this one already) */
1962			cache++;
1963			continue;
1964		}
1965
1966		if (!before(start_seq, tcp_highest_sack_seq(tp))) {
1967			skb = tcp_highest_sack(sk);
1968			if (!skb)
1969				break;
1970		}
1971		skb = tcp_sacktag_skip(skb, sk, start_seq);
1972
1973walk:
1974		skb = tcp_sacktag_walk(skb, sk, next_dup, state,
1975				       start_seq, end_seq, dup_sack);
1976
1977advance_sp:
1978		i++;
1979	}
1980
1981	/* Clear the head of the cache sack blocks so we can skip it next time */
1982	for (i = 0; i < ARRAY_SIZE(tp->recv_sack_cache) - used_sacks; i++) {
1983		tp->recv_sack_cache[i].start_seq = 0;
1984		tp->recv_sack_cache[i].end_seq = 0;
1985	}
1986	for (j = 0; j < used_sacks; j++)
1987		tp->recv_sack_cache[i++] = sp[j];
1988
1989	if (inet_csk(sk)->icsk_ca_state != TCP_CA_Loss || tp->undo_marker)
1990		tcp_check_sack_reordering(sk, state->reord, 0);
1991
1992	tcp_verify_left_out(tp);
1993out:
1994
1995#if FASTRETRANS_DEBUG > 0
1996	WARN_ON((int)tp->sacked_out < 0);
1997	WARN_ON((int)tp->lost_out < 0);
1998	WARN_ON((int)tp->retrans_out < 0);
1999	WARN_ON((int)tcp_packets_in_flight(tp) < 0);
2000#endif
2001	return state->flag;
2002}
2003
2004/* Limits sacked_out so that sum with lost_out isn't ever larger than
2005 * packets_out. Returns false if sacked_out adjustement wasn't necessary.
2006 */
2007static bool tcp_limit_reno_sacked(struct tcp_sock *tp)
2008{
2009	u32 holes;
2010
2011	holes = max(tp->lost_out, 1U);
2012	holes = min(holes, tp->packets_out);
2013
2014	if ((tp->sacked_out + holes) > tp->packets_out) {
2015		tp->sacked_out = tp->packets_out - holes;
2016		return true;
2017	}
2018	return false;
2019}
2020
2021/* If we receive more dupacks than we expected counting segments
2022 * in assumption of absent reordering, interpret this as reordering.
2023 * The only another reason could be bug in receiver TCP.
2024 */
2025static void tcp_check_reno_reordering(struct sock *sk, const int addend)
2026{
2027	struct tcp_sock *tp = tcp_sk(sk);
2028
2029	if (!tcp_limit_reno_sacked(tp))
2030		return;
2031
2032	tp->reordering = min_t(u32, tp->packets_out + addend,
2033			       READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_max_reordering));
2034	tp->reord_seen++;
2035	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRENOREORDER);
2036}
2037
2038/* Emulate SACKs for SACKless connection: account for a new dupack. */
2039
2040static void tcp_add_reno_sack(struct sock *sk, int num_dupack, bool ece_ack)
2041{
2042	if (num_dupack) {
2043		struct tcp_sock *tp = tcp_sk(sk);
2044		u32 prior_sacked = tp->sacked_out;
2045		s32 delivered;
2046
2047		tp->sacked_out += num_dupack;
2048		tcp_check_reno_reordering(sk, 0);
2049		delivered = tp->sacked_out - prior_sacked;
2050		if (delivered > 0)
2051			tcp_count_delivered(tp, delivered, ece_ack);
2052		tcp_verify_left_out(tp);
2053	}
2054}
2055
2056/* Account for ACK, ACKing some data in Reno Recovery phase. */
2057
2058static void tcp_remove_reno_sacks(struct sock *sk, int acked, bool ece_ack)
2059{
2060	struct tcp_sock *tp = tcp_sk(sk);
2061
2062	if (acked > 0) {
2063		/* One ACK acked hole. The rest eat duplicate ACKs. */
2064		tcp_count_delivered(tp, max_t(int, acked - tp->sacked_out, 1),
2065				    ece_ack);
2066		if (acked - 1 >= tp->sacked_out)
2067			tp->sacked_out = 0;
2068		else
2069			tp->sacked_out -= acked - 1;
2070	}
2071	tcp_check_reno_reordering(sk, acked);
2072	tcp_verify_left_out(tp);
2073}
2074
2075static inline void tcp_reset_reno_sack(struct tcp_sock *tp)
2076{
2077	tp->sacked_out = 0;
2078}
2079
2080void tcp_clear_retrans(struct tcp_sock *tp)
2081{
2082	tp->retrans_out = 0;
2083	tp->lost_out = 0;
2084	tp->undo_marker = 0;
2085	tp->undo_retrans = -1;
2086	tp->sacked_out = 0;
2087}
2088
2089static inline void tcp_init_undo(struct tcp_sock *tp)
2090{
2091	tp->undo_marker = tp->snd_una;
2092	/* Retransmission still in flight may cause DSACKs later. */
2093	tp->undo_retrans = tp->retrans_out ? : -1;
2094}
2095
2096static bool tcp_is_rack(const struct sock *sk)
2097{
2098	return READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_recovery) &
2099		TCP_RACK_LOSS_DETECTION;
2100}
2101
2102/* If we detect SACK reneging, forget all SACK information
2103 * and reset tags completely, otherwise preserve SACKs. If receiver
2104 * dropped its ofo queue, we will know this due to reneging detection.
2105 */
2106static void tcp_timeout_mark_lost(struct sock *sk)
2107{
2108	struct tcp_sock *tp = tcp_sk(sk);
2109	struct sk_buff *skb, *head;
2110	bool is_reneg;			/* is receiver reneging on SACKs? */
2111
2112	head = tcp_rtx_queue_head(sk);
2113	is_reneg = head && (TCP_SKB_CB(head)->sacked & TCPCB_SACKED_ACKED);
2114	if (is_reneg) {
2115		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSACKRENEGING);
2116		tp->sacked_out = 0;
2117		/* Mark SACK reneging until we recover from this loss event. */
2118		tp->is_sack_reneg = 1;
2119	} else if (tcp_is_reno(tp)) {
2120		tcp_reset_reno_sack(tp);
2121	}
2122
2123	skb = head;
2124	skb_rbtree_walk_from(skb) {
2125		if (is_reneg)
2126			TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED;
2127		else if (tcp_is_rack(sk) && skb != head &&
2128			 tcp_rack_skb_timeout(tp, skb, 0) > 0)
2129			continue; /* Don't mark recently sent ones lost yet */
2130		tcp_mark_skb_lost(sk, skb);
2131	}
2132	tcp_verify_left_out(tp);
2133	tcp_clear_all_retrans_hints(tp);
2134}
2135
2136/* Enter Loss state. */
2137void tcp_enter_loss(struct sock *sk)
2138{
2139	const struct inet_connection_sock *icsk = inet_csk(sk);
2140	struct tcp_sock *tp = tcp_sk(sk);
2141	struct net *net = sock_net(sk);
2142	bool new_recovery = icsk->icsk_ca_state < TCP_CA_Recovery;
2143	u8 reordering;
2144
2145	tcp_timeout_mark_lost(sk);
2146
2147	/* Reduce ssthresh if it has not yet been made inside this window. */
2148	if (icsk->icsk_ca_state <= TCP_CA_Disorder ||
2149	    !after(tp->high_seq, tp->snd_una) ||
2150	    (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) {
2151		tp->prior_ssthresh = tcp_current_ssthresh(sk);
2152		tp->prior_cwnd = tcp_snd_cwnd(tp);
2153		tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
2154		tcp_ca_event(sk, CA_EVENT_LOSS);
2155		tcp_init_undo(tp);
2156	}
2157	tcp_snd_cwnd_set(tp, tcp_packets_in_flight(tp) + 1);
2158	tp->snd_cwnd_cnt   = 0;
2159	tp->snd_cwnd_stamp = tcp_jiffies32;
2160
2161	/* Timeout in disordered state after receiving substantial DUPACKs
2162	 * suggests that the degree of reordering is over-estimated.
2163	 */
2164	reordering = READ_ONCE(net->ipv4.sysctl_tcp_reordering);
2165	if (icsk->icsk_ca_state <= TCP_CA_Disorder &&
2166	    tp->sacked_out >= reordering)
2167		tp->reordering = min_t(unsigned int, tp->reordering,
2168				       reordering);
2169
2170	tcp_set_ca_state(sk, TCP_CA_Loss);
2171	tp->high_seq = tp->snd_nxt;
2172	tcp_ecn_queue_cwr(tp);
2173
2174	/* F-RTO RFC5682 sec 3.1 step 1: retransmit SND.UNA if no previous
2175	 * loss recovery is underway except recurring timeout(s) on
2176	 * the same SND.UNA (sec 3.2). Disable F-RTO on path MTU probing
2177	 */
2178	tp->frto = READ_ONCE(net->ipv4.sysctl_tcp_frto) &&
2179		   (new_recovery || icsk->icsk_retransmits) &&
2180		   !inet_csk(sk)->icsk_mtup.probe_size;
2181}
2182
2183/* If ACK arrived pointing to a remembered SACK, it means that our
2184 * remembered SACKs do not reflect real state of receiver i.e.
2185 * receiver _host_ is heavily congested (or buggy).
2186 *
2187 * To avoid big spurious retransmission bursts due to transient SACK
2188 * scoreboard oddities that look like reneging, we give the receiver a
2189 * little time (max(RTT/2, 10ms)) to send us some more ACKs that will
2190 * restore sanity to the SACK scoreboard. If the apparent reneging
2191 * persists until this RTO then we'll clear the SACK scoreboard.
2192 */
2193static bool tcp_check_sack_reneging(struct sock *sk, int flag)
2194{
2195	if (flag & FLAG_SACK_RENEGING &&
2196	    flag & FLAG_SND_UNA_ADVANCED) {
2197		struct tcp_sock *tp = tcp_sk(sk);
2198		unsigned long delay = max(usecs_to_jiffies(tp->srtt_us >> 4),
2199					  msecs_to_jiffies(10));
2200
2201		inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
2202					  delay, TCP_RTO_MAX);
2203		return true;
2204	}
2205	return false;
2206}
2207
2208/* Heurestics to calculate number of duplicate ACKs. There's no dupACKs
2209 * counter when SACK is enabled (without SACK, sacked_out is used for
2210 * that purpose).
2211 *
2212 * With reordering, holes may still be in flight, so RFC3517 recovery
2213 * uses pure sacked_out (total number of SACKed segments) even though
2214 * it violates the RFC that uses duplicate ACKs, often these are equal
2215 * but when e.g. out-of-window ACKs or packet duplication occurs,
2216 * they differ. Since neither occurs due to loss, TCP should really
2217 * ignore them.
2218 */
2219static inline int tcp_dupack_heuristics(const struct tcp_sock *tp)
2220{
2221	return tp->sacked_out + 1;
2222}
2223
2224/* Linux NewReno/SACK/ECN state machine.
2225 * --------------------------------------
2226 *
2227 * "Open"	Normal state, no dubious events, fast path.
2228 * "Disorder"   In all the respects it is "Open",
2229 *		but requires a bit more attention. It is entered when
2230 *		we see some SACKs or dupacks. It is split of "Open"
2231 *		mainly to move some processing from fast path to slow one.
2232 * "CWR"	CWND was reduced due to some Congestion Notification event.
2233 *		It can be ECN, ICMP source quench, local device congestion.
2234 * "Recovery"	CWND was reduced, we are fast-retransmitting.
2235 * "Loss"	CWND was reduced due to RTO timeout or SACK reneging.
2236 *
2237 * tcp_fastretrans_alert() is entered:
2238 * - each incoming ACK, if state is not "Open"
2239 * - when arrived ACK is unusual, namely:
2240 *	* SACK
2241 *	* Duplicate ACK.
2242 *	* ECN ECE.
2243 *
2244 * Counting packets in flight is pretty simple.
2245 *
2246 *	in_flight = packets_out - left_out + retrans_out
2247 *
2248 *	packets_out is SND.NXT-SND.UNA counted in packets.
2249 *
2250 *	retrans_out is number of retransmitted segments.
2251 *
2252 *	left_out is number of segments left network, but not ACKed yet.
2253 *
2254 *		left_out = sacked_out + lost_out
2255 *
2256 *     sacked_out: Packets, which arrived to receiver out of order
2257 *		   and hence not ACKed. With SACKs this number is simply
2258 *		   amount of SACKed data. Even without SACKs
2259 *		   it is easy to give pretty reliable estimate of this number,
2260 *		   counting duplicate ACKs.
2261 *
2262 *       lost_out: Packets lost by network. TCP has no explicit
2263 *		   "loss notification" feedback from network (for now).
2264 *		   It means that this number can be only _guessed_.
2265 *		   Actually, it is the heuristics to predict lossage that
2266 *		   distinguishes different algorithms.
2267 *
2268 *	F.e. after RTO, when all the queue is considered as lost,
2269 *	lost_out = packets_out and in_flight = retrans_out.
2270 *
2271 *		Essentially, we have now a few algorithms detecting
2272 *		lost packets.
2273 *
2274 *		If the receiver supports SACK:
2275 *
2276 *		RFC6675/3517: It is the conventional algorithm. A packet is
2277 *		considered lost if the number of higher sequence packets
2278 *		SACKed is greater than or equal the DUPACK thoreshold
2279 *		(reordering). This is implemented in tcp_mark_head_lost and
2280 *		tcp_update_scoreboard.
2281 *
2282 *		RACK (draft-ietf-tcpm-rack-01): it is a newer algorithm
2283 *		(2017-) that checks timing instead of counting DUPACKs.
2284 *		Essentially a packet is considered lost if it's not S/ACKed
2285 *		after RTT + reordering_window, where both metrics are
2286 *		dynamically measured and adjusted. This is implemented in
2287 *		tcp_rack_mark_lost.
2288 *
2289 *		If the receiver does not support SACK:
2290 *
2291 *		NewReno (RFC6582): in Recovery we assume that one segment
2292 *		is lost (classic Reno). While we are in Recovery and
2293 *		a partial ACK arrives, we assume that one more packet
2294 *		is lost (NewReno). This heuristics are the same in NewReno
2295 *		and SACK.
2296 *
2297 * Really tricky (and requiring careful tuning) part of algorithm
2298 * is hidden in functions tcp_time_to_recover() and tcp_xmit_retransmit_queue().
2299 * The first determines the moment _when_ we should reduce CWND and,
2300 * hence, slow down forward transmission. In fact, it determines the moment
2301 * when we decide that hole is caused by loss, rather than by a reorder.
2302 *
2303 * tcp_xmit_retransmit_queue() decides, _what_ we should retransmit to fill
2304 * holes, caused by lost packets.
2305 *
2306 * And the most logically complicated part of algorithm is undo
2307 * heuristics. We detect false retransmits due to both too early
2308 * fast retransmit (reordering) and underestimated RTO, analyzing
2309 * timestamps and D-SACKs. When we detect that some segments were
2310 * retransmitted by mistake and CWND reduction was wrong, we undo
2311 * window reduction and abort recovery phase. This logic is hidden
2312 * inside several functions named tcp_try_undo_<something>.
2313 */
2314
2315/* This function decides, when we should leave Disordered state
2316 * and enter Recovery phase, reducing congestion window.
2317 *
2318 * Main question: may we further continue forward transmission
2319 * with the same cwnd?
2320 */
2321static bool tcp_time_to_recover(struct sock *sk, int flag)
2322{
2323	struct tcp_sock *tp = tcp_sk(sk);
2324
2325	/* Trick#1: The loss is proven. */
2326	if (tp->lost_out)
2327		return true;
2328
2329	/* Not-A-Trick#2 : Classic rule... */
2330	if (!tcp_is_rack(sk) && tcp_dupack_heuristics(tp) > tp->reordering)
2331		return true;
2332
2333	return false;
2334}
2335
2336/* Detect loss in event "A" above by marking head of queue up as lost.
2337 * For RFC3517 SACK, a segment is considered lost if it
2338 * has at least tp->reordering SACKed seqments above it; "packets" refers to
2339 * the maximum SACKed segments to pass before reaching this limit.
2340 */
2341static void tcp_mark_head_lost(struct sock *sk, int packets, int mark_head)
2342{
2343	struct tcp_sock *tp = tcp_sk(sk);
2344	struct sk_buff *skb;
2345	int cnt;
2346	/* Use SACK to deduce losses of new sequences sent during recovery */
2347	const u32 loss_high = tp->snd_nxt;
2348
2349	WARN_ON(packets > tp->packets_out);
2350	skb = tp->lost_skb_hint;
2351	if (skb) {
2352		/* Head already handled? */
2353		if (mark_head && after(TCP_SKB_CB(skb)->seq, tp->snd_una))
2354			return;
2355		cnt = tp->lost_cnt_hint;
2356	} else {
2357		skb = tcp_rtx_queue_head(sk);
2358		cnt = 0;
2359	}
2360
2361	skb_rbtree_walk_from(skb) {
2362		/* TODO: do this better */
2363		/* this is not the most efficient way to do this... */
2364		tp->lost_skb_hint = skb;
2365		tp->lost_cnt_hint = cnt;
2366
2367		if (after(TCP_SKB_CB(skb)->end_seq, loss_high))
2368			break;
2369
2370		if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
2371			cnt += tcp_skb_pcount(skb);
2372
2373		if (cnt > packets)
2374			break;
2375
2376		if (!(TCP_SKB_CB(skb)->sacked & TCPCB_LOST))
2377			tcp_mark_skb_lost(sk, skb);
2378
2379		if (mark_head)
2380			break;
2381	}
2382	tcp_verify_left_out(tp);
2383}
2384
2385/* Account newly detected lost packet(s) */
2386
2387static void tcp_update_scoreboard(struct sock *sk, int fast_rexmit)
2388{
2389	struct tcp_sock *tp = tcp_sk(sk);
2390
2391	if (tcp_is_sack(tp)) {
2392		int sacked_upto = tp->sacked_out - tp->reordering;
2393		if (sacked_upto >= 0)
2394			tcp_mark_head_lost(sk, sacked_upto, 0);
2395		else if (fast_rexmit)
2396			tcp_mark_head_lost(sk, 1, 1);
2397	}
2398}
2399
2400static bool tcp_tsopt_ecr_before(const struct tcp_sock *tp, u32 when)
2401{
2402	return tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
2403	       before(tp->rx_opt.rcv_tsecr, when);
2404}
2405
2406/* skb is spurious retransmitted if the returned timestamp echo
2407 * reply is prior to the skb transmission time
2408 */
2409static bool tcp_skb_spurious_retrans(const struct tcp_sock *tp,
2410				     const struct sk_buff *skb)
2411{
2412	return (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS) &&
2413	       tcp_tsopt_ecr_before(tp, tcp_skb_timestamp(skb));
2414}
2415
2416/* Nothing was retransmitted or returned timestamp is less
2417 * than timestamp of the first retransmission.
2418 */
2419static inline bool tcp_packet_delayed(const struct tcp_sock *tp)
2420{
2421	return tp->retrans_stamp &&
2422	       tcp_tsopt_ecr_before(tp, tp->retrans_stamp);
2423}
2424
2425/* Undo procedures. */
2426
2427/* We can clear retrans_stamp when there are no retransmissions in the
2428 * window. It would seem that it is trivially available for us in
2429 * tp->retrans_out, however, that kind of assumptions doesn't consider
2430 * what will happen if errors occur when sending retransmission for the
2431 * second time. ...It could the that such segment has only
2432 * TCPCB_EVER_RETRANS set at the present time. It seems that checking
2433 * the head skb is enough except for some reneging corner cases that
2434 * are not worth the effort.
2435 *
2436 * Main reason for all this complexity is the fact that connection dying
2437 * time now depends on the validity of the retrans_stamp, in particular,
2438 * that successive retransmissions of a segment must not advance
2439 * retrans_stamp under any conditions.
2440 */
2441static bool tcp_any_retrans_done(const struct sock *sk)
2442{
2443	const struct tcp_sock *tp = tcp_sk(sk);
2444	struct sk_buff *skb;
2445
2446	if (tp->retrans_out)
2447		return true;
2448
2449	skb = tcp_rtx_queue_head(sk);
2450	if (unlikely(skb && TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS))
2451		return true;
2452
2453	return false;
2454}
2455
2456static void DBGUNDO(struct sock *sk, const char *msg)
2457{
2458#if FASTRETRANS_DEBUG > 1
2459	struct tcp_sock *tp = tcp_sk(sk);
2460	struct inet_sock *inet = inet_sk(sk);
2461
2462	if (sk->sk_family == AF_INET) {
2463		pr_debug("Undo %s %pI4/%u c%u l%u ss%u/%u p%u\n",
2464			 msg,
2465			 &inet->inet_daddr, ntohs(inet->inet_dport),
2466			 tcp_snd_cwnd(tp), tcp_left_out(tp),
2467			 tp->snd_ssthresh, tp->prior_ssthresh,
2468			 tp->packets_out);
2469	}
2470#if IS_ENABLED(CONFIG_IPV6)
2471	else if (sk->sk_family == AF_INET6) {
2472		pr_debug("Undo %s %pI6/%u c%u l%u ss%u/%u p%u\n",
2473			 msg,
2474			 &sk->sk_v6_daddr, ntohs(inet->inet_dport),
2475			 tcp_snd_cwnd(tp), tcp_left_out(tp),
2476			 tp->snd_ssthresh, tp->prior_ssthresh,
2477			 tp->packets_out);
2478	}
2479#endif
2480#endif
2481}
2482
2483static void tcp_undo_cwnd_reduction(struct sock *sk, bool unmark_loss)
2484{
2485	struct tcp_sock *tp = tcp_sk(sk);
2486
2487	if (unmark_loss) {
2488		struct sk_buff *skb;
2489
2490		skb_rbtree_walk(skb, &sk->tcp_rtx_queue) {
2491			TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
2492		}
2493		tp->lost_out = 0;
2494		tcp_clear_all_retrans_hints(tp);
2495	}
2496
2497	if (tp->prior_ssthresh) {
2498		const struct inet_connection_sock *icsk = inet_csk(sk);
2499
2500		tcp_snd_cwnd_set(tp, icsk->icsk_ca_ops->undo_cwnd(sk));
2501
2502		if (tp->prior_ssthresh > tp->snd_ssthresh) {
2503			tp->snd_ssthresh = tp->prior_ssthresh;
2504			tcp_ecn_withdraw_cwr(tp);
2505		}
2506	}
2507	tp->snd_cwnd_stamp = tcp_jiffies32;
2508	tp->undo_marker = 0;
2509	tp->rack.advanced = 1; /* Force RACK to re-exam losses */
2510}
2511
2512static inline bool tcp_may_undo(const struct tcp_sock *tp)
2513{
2514	return tp->undo_marker && (!tp->undo_retrans || tcp_packet_delayed(tp));
2515}
2516
2517static bool tcp_is_non_sack_preventing_reopen(struct sock *sk)
2518{
2519	struct tcp_sock *tp = tcp_sk(sk);
2520
2521	if (tp->snd_una == tp->high_seq && tcp_is_reno(tp)) {
2522		/* Hold old state until something *above* high_seq
2523		 * is ACKed. For Reno it is MUST to prevent false
2524		 * fast retransmits (RFC2582). SACK TCP is safe. */
2525		if (!tcp_any_retrans_done(sk))
2526			tp->retrans_stamp = 0;
2527		return true;
2528	}
2529	return false;
2530}
2531
2532/* People celebrate: "We love our President!" */
2533static bool tcp_try_undo_recovery(struct sock *sk)
2534{
2535	struct tcp_sock *tp = tcp_sk(sk);
2536
2537	if (tcp_may_undo(tp)) {
2538		int mib_idx;
2539
2540		/* Happy end! We did not retransmit anything
2541		 * or our original transmission succeeded.
2542		 */
2543		DBGUNDO(sk, inet_csk(sk)->icsk_ca_state == TCP_CA_Loss ? "loss" : "retrans");
2544		tcp_undo_cwnd_reduction(sk, false);
2545		if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss)
2546			mib_idx = LINUX_MIB_TCPLOSSUNDO;
2547		else
2548			mib_idx = LINUX_MIB_TCPFULLUNDO;
2549
2550		NET_INC_STATS(sock_net(sk), mib_idx);
2551	} else if (tp->rack.reo_wnd_persist) {
2552		tp->rack.reo_wnd_persist--;
2553	}
2554	if (tcp_is_non_sack_preventing_reopen(sk))
 
 
 
 
 
2555		return true;
 
2556	tcp_set_ca_state(sk, TCP_CA_Open);
2557	tp->is_sack_reneg = 0;
2558	return false;
2559}
2560
2561/* Try to undo cwnd reduction, because D-SACKs acked all retransmitted data */
2562static bool tcp_try_undo_dsack(struct sock *sk)
2563{
2564	struct tcp_sock *tp = tcp_sk(sk);
2565
2566	if (tp->undo_marker && !tp->undo_retrans) {
2567		tp->rack.reo_wnd_persist = min(TCP_RACK_RECOVERY_THRESH,
2568					       tp->rack.reo_wnd_persist + 1);
2569		DBGUNDO(sk, "D-SACK");
2570		tcp_undo_cwnd_reduction(sk, false);
2571		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKUNDO);
2572		return true;
2573	}
2574	return false;
2575}
2576
2577/* Undo during loss recovery after partial ACK or using F-RTO. */
2578static bool tcp_try_undo_loss(struct sock *sk, bool frto_undo)
2579{
2580	struct tcp_sock *tp = tcp_sk(sk);
2581
2582	if (frto_undo || tcp_may_undo(tp)) {
2583		tcp_undo_cwnd_reduction(sk, true);
2584
2585		DBGUNDO(sk, "partial loss");
2586		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPLOSSUNDO);
2587		if (frto_undo)
2588			NET_INC_STATS(sock_net(sk),
2589					LINUX_MIB_TCPSPURIOUSRTOS);
2590		inet_csk(sk)->icsk_retransmits = 0;
2591		if (tcp_is_non_sack_preventing_reopen(sk))
2592			return true;
2593		if (frto_undo || tcp_is_sack(tp)) {
2594			tcp_set_ca_state(sk, TCP_CA_Open);
2595			tp->is_sack_reneg = 0;
2596		}
2597		return true;
2598	}
2599	return false;
2600}
2601
2602/* The cwnd reduction in CWR and Recovery uses the PRR algorithm in RFC 6937.
2603 * It computes the number of packets to send (sndcnt) based on packets newly
2604 * delivered:
2605 *   1) If the packets in flight is larger than ssthresh, PRR spreads the
2606 *	cwnd reductions across a full RTT.
2607 *   2) Otherwise PRR uses packet conservation to send as much as delivered.
2608 *      But when SND_UNA is acked without further losses,
2609 *      slow starts cwnd up to ssthresh to speed up the recovery.
2610 */
2611static void tcp_init_cwnd_reduction(struct sock *sk)
2612{
2613	struct tcp_sock *tp = tcp_sk(sk);
2614
2615	tp->high_seq = tp->snd_nxt;
2616	tp->tlp_high_seq = 0;
2617	tp->snd_cwnd_cnt = 0;
2618	tp->prior_cwnd = tcp_snd_cwnd(tp);
2619	tp->prr_delivered = 0;
2620	tp->prr_out = 0;
2621	tp->snd_ssthresh = inet_csk(sk)->icsk_ca_ops->ssthresh(sk);
2622	tcp_ecn_queue_cwr(tp);
2623}
2624
2625void tcp_cwnd_reduction(struct sock *sk, int newly_acked_sacked, int newly_lost, int flag)
2626{
2627	struct tcp_sock *tp = tcp_sk(sk);
2628	int sndcnt = 0;
2629	int delta = tp->snd_ssthresh - tcp_packets_in_flight(tp);
2630
2631	if (newly_acked_sacked <= 0 || WARN_ON_ONCE(!tp->prior_cwnd))
2632		return;
2633
2634	tp->prr_delivered += newly_acked_sacked;
2635	if (delta < 0) {
2636		u64 dividend = (u64)tp->snd_ssthresh * tp->prr_delivered +
2637			       tp->prior_cwnd - 1;
2638		sndcnt = div_u64(dividend, tp->prior_cwnd) - tp->prr_out;
 
 
 
 
 
2639	} else {
2640		sndcnt = max_t(int, tp->prr_delivered - tp->prr_out,
2641			       newly_acked_sacked);
2642		if (flag & FLAG_SND_UNA_ADVANCED && !newly_lost)
2643			sndcnt++;
2644		sndcnt = min(delta, sndcnt);
2645	}
2646	/* Force a fast retransmit upon entering fast recovery */
2647	sndcnt = max(sndcnt, (tp->prr_out ? 0 : 1));
2648	tcp_snd_cwnd_set(tp, tcp_packets_in_flight(tp) + sndcnt);
2649}
2650
2651static inline void tcp_end_cwnd_reduction(struct sock *sk)
2652{
2653	struct tcp_sock *tp = tcp_sk(sk);
2654
2655	if (inet_csk(sk)->icsk_ca_ops->cong_control)
2656		return;
2657
2658	/* Reset cwnd to ssthresh in CWR or Recovery (unless it's undone) */
2659	if (tp->snd_ssthresh < TCP_INFINITE_SSTHRESH &&
2660	    (inet_csk(sk)->icsk_ca_state == TCP_CA_CWR || tp->undo_marker)) {
2661		tcp_snd_cwnd_set(tp, tp->snd_ssthresh);
2662		tp->snd_cwnd_stamp = tcp_jiffies32;
2663	}
2664	tcp_ca_event(sk, CA_EVENT_COMPLETE_CWR);
2665}
2666
2667/* Enter CWR state. Disable cwnd undo since congestion is proven with ECN */
2668void tcp_enter_cwr(struct sock *sk)
2669{
2670	struct tcp_sock *tp = tcp_sk(sk);
2671
2672	tp->prior_ssthresh = 0;
2673	if (inet_csk(sk)->icsk_ca_state < TCP_CA_CWR) {
2674		tp->undo_marker = 0;
2675		tcp_init_cwnd_reduction(sk);
2676		tcp_set_ca_state(sk, TCP_CA_CWR);
2677	}
2678}
2679EXPORT_SYMBOL(tcp_enter_cwr);
2680
2681static void tcp_try_keep_open(struct sock *sk)
2682{
2683	struct tcp_sock *tp = tcp_sk(sk);
2684	int state = TCP_CA_Open;
2685
2686	if (tcp_left_out(tp) || tcp_any_retrans_done(sk))
2687		state = TCP_CA_Disorder;
2688
2689	if (inet_csk(sk)->icsk_ca_state != state) {
2690		tcp_set_ca_state(sk, state);
2691		tp->high_seq = tp->snd_nxt;
2692	}
2693}
2694
2695static void tcp_try_to_open(struct sock *sk, int flag)
2696{
2697	struct tcp_sock *tp = tcp_sk(sk);
2698
2699	tcp_verify_left_out(tp);
2700
2701	if (!tcp_any_retrans_done(sk))
2702		tp->retrans_stamp = 0;
2703
2704	if (flag & FLAG_ECE)
2705		tcp_enter_cwr(sk);
2706
2707	if (inet_csk(sk)->icsk_ca_state != TCP_CA_CWR) {
2708		tcp_try_keep_open(sk);
2709	}
2710}
2711
2712static void tcp_mtup_probe_failed(struct sock *sk)
2713{
2714	struct inet_connection_sock *icsk = inet_csk(sk);
2715
2716	icsk->icsk_mtup.search_high = icsk->icsk_mtup.probe_size - 1;
2717	icsk->icsk_mtup.probe_size = 0;
2718	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMTUPFAIL);
2719}
2720
2721static void tcp_mtup_probe_success(struct sock *sk)
2722{
2723	struct tcp_sock *tp = tcp_sk(sk);
2724	struct inet_connection_sock *icsk = inet_csk(sk);
2725	u64 val;
2726
 
2727	tp->prior_ssthresh = tcp_current_ssthresh(sk);
2728
2729	val = (u64)tcp_snd_cwnd(tp) * tcp_mss_to_mtu(sk, tp->mss_cache);
2730	do_div(val, icsk->icsk_mtup.probe_size);
2731	DEBUG_NET_WARN_ON_ONCE((u32)val != val);
2732	tcp_snd_cwnd_set(tp, max_t(u32, 1U, val));
2733
2734	tp->snd_cwnd_cnt = 0;
2735	tp->snd_cwnd_stamp = tcp_jiffies32;
2736	tp->snd_ssthresh = tcp_current_ssthresh(sk);
2737
2738	icsk->icsk_mtup.search_low = icsk->icsk_mtup.probe_size;
2739	icsk->icsk_mtup.probe_size = 0;
2740	tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
2741	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMTUPSUCCESS);
2742}
2743
2744/* Do a simple retransmit without using the backoff mechanisms in
2745 * tcp_timer. This is used for path mtu discovery.
2746 * The socket is already locked here.
2747 */
2748void tcp_simple_retransmit(struct sock *sk)
2749{
2750	const struct inet_connection_sock *icsk = inet_csk(sk);
2751	struct tcp_sock *tp = tcp_sk(sk);
2752	struct sk_buff *skb;
2753	int mss;
2754
2755	/* A fastopen SYN request is stored as two separate packets within
2756	 * the retransmit queue, this is done by tcp_send_syn_data().
2757	 * As a result simply checking the MSS of the frames in the queue
2758	 * will not work for the SYN packet.
2759	 *
2760	 * Us being here is an indication of a path MTU issue so we can
2761	 * assume that the fastopen SYN was lost and just mark all the
2762	 * frames in the retransmit queue as lost. We will use an MSS of
2763	 * -1 to mark all frames as lost, otherwise compute the current MSS.
2764	 */
2765	if (tp->syn_data && sk->sk_state == TCP_SYN_SENT)
2766		mss = -1;
2767	else
2768		mss = tcp_current_mss(sk);
2769
2770	skb_rbtree_walk(skb, &sk->tcp_rtx_queue) {
2771		if (tcp_skb_seglen(skb) > mss)
2772			tcp_mark_skb_lost(sk, skb);
 
 
 
 
 
 
2773	}
2774
2775	tcp_clear_retrans_hints_partial(tp);
2776
2777	if (!tp->lost_out)
2778		return;
2779
2780	if (tcp_is_reno(tp))
2781		tcp_limit_reno_sacked(tp);
2782
2783	tcp_verify_left_out(tp);
2784
2785	/* Don't muck with the congestion window here.
2786	 * Reason is that we do not increase amount of _data_
2787	 * in network, but units changed and effective
2788	 * cwnd/ssthresh really reduced now.
2789	 */
2790	if (icsk->icsk_ca_state != TCP_CA_Loss) {
2791		tp->high_seq = tp->snd_nxt;
2792		tp->snd_ssthresh = tcp_current_ssthresh(sk);
2793		tp->prior_ssthresh = 0;
2794		tp->undo_marker = 0;
2795		tcp_set_ca_state(sk, TCP_CA_Loss);
2796	}
2797	tcp_xmit_retransmit_queue(sk);
2798}
2799EXPORT_SYMBOL(tcp_simple_retransmit);
2800
2801void tcp_enter_recovery(struct sock *sk, bool ece_ack)
2802{
2803	struct tcp_sock *tp = tcp_sk(sk);
2804	int mib_idx;
2805
2806	if (tcp_is_reno(tp))
2807		mib_idx = LINUX_MIB_TCPRENORECOVERY;
2808	else
2809		mib_idx = LINUX_MIB_TCPSACKRECOVERY;
2810
2811	NET_INC_STATS(sock_net(sk), mib_idx);
2812
2813	tp->prior_ssthresh = 0;
2814	tcp_init_undo(tp);
2815
2816	if (!tcp_in_cwnd_reduction(sk)) {
2817		if (!ece_ack)
2818			tp->prior_ssthresh = tcp_current_ssthresh(sk);
2819		tcp_init_cwnd_reduction(sk);
2820	}
2821	tcp_set_ca_state(sk, TCP_CA_Recovery);
2822}
2823
2824/* Process an ACK in CA_Loss state. Move to CA_Open if lost data are
2825 * recovered or spurious. Otherwise retransmits more on partial ACKs.
2826 */
2827static void tcp_process_loss(struct sock *sk, int flag, int num_dupack,
2828			     int *rexmit)
2829{
2830	struct tcp_sock *tp = tcp_sk(sk);
2831	bool recovered = !before(tp->snd_una, tp->high_seq);
2832
2833	if ((flag & FLAG_SND_UNA_ADVANCED || rcu_access_pointer(tp->fastopen_rsk)) &&
2834	    tcp_try_undo_loss(sk, false))
2835		return;
2836
2837	if (tp->frto) { /* F-RTO RFC5682 sec 3.1 (sack enhanced version). */
2838		/* Step 3.b. A timeout is spurious if not all data are
2839		 * lost, i.e., never-retransmitted data are (s)acked.
2840		 */
2841		if ((flag & FLAG_ORIG_SACK_ACKED) &&
2842		    tcp_try_undo_loss(sk, true))
2843			return;
2844
2845		if (after(tp->snd_nxt, tp->high_seq)) {
2846			if (flag & FLAG_DATA_SACKED || num_dupack)
2847				tp->frto = 0; /* Step 3.a. loss was real */
2848		} else if (flag & FLAG_SND_UNA_ADVANCED && !recovered) {
2849			tp->high_seq = tp->snd_nxt;
2850			/* Step 2.b. Try send new data (but deferred until cwnd
2851			 * is updated in tcp_ack()). Otherwise fall back to
2852			 * the conventional recovery.
2853			 */
2854			if (!tcp_write_queue_empty(sk) &&
2855			    after(tcp_wnd_end(tp), tp->snd_nxt)) {
2856				*rexmit = REXMIT_NEW;
2857				return;
2858			}
2859			tp->frto = 0;
2860		}
2861	}
2862
2863	if (recovered) {
2864		/* F-RTO RFC5682 sec 3.1 step 2.a and 1st part of step 3.a */
2865		tcp_try_undo_recovery(sk);
2866		return;
2867	}
2868	if (tcp_is_reno(tp)) {
2869		/* A Reno DUPACK means new data in F-RTO step 2.b above are
2870		 * delivered. Lower inflight to clock out (re)tranmissions.
2871		 */
2872		if (after(tp->snd_nxt, tp->high_seq) && num_dupack)
2873			tcp_add_reno_sack(sk, num_dupack, flag & FLAG_ECE);
2874		else if (flag & FLAG_SND_UNA_ADVANCED)
2875			tcp_reset_reno_sack(tp);
2876	}
2877	*rexmit = REXMIT_LOST;
2878}
2879
2880static bool tcp_force_fast_retransmit(struct sock *sk)
2881{
2882	struct tcp_sock *tp = tcp_sk(sk);
2883
2884	return after(tcp_highest_sack_seq(tp),
2885		     tp->snd_una + tp->reordering * tp->mss_cache);
2886}
2887
2888/* Undo during fast recovery after partial ACK. */
2889static bool tcp_try_undo_partial(struct sock *sk, u32 prior_snd_una,
2890				 bool *do_lost)
2891{
2892	struct tcp_sock *tp = tcp_sk(sk);
2893
2894	if (tp->undo_marker && tcp_packet_delayed(tp)) {
2895		/* Plain luck! Hole if filled with delayed
2896		 * packet, rather than with a retransmit. Check reordering.
2897		 */
2898		tcp_check_sack_reordering(sk, prior_snd_una, 1);
2899
2900		/* We are getting evidence that the reordering degree is higher
2901		 * than we realized. If there are no retransmits out then we
2902		 * can undo. Otherwise we clock out new packets but do not
2903		 * mark more packets lost or retransmit more.
2904		 */
2905		if (tp->retrans_out)
2906			return true;
2907
2908		if (!tcp_any_retrans_done(sk))
2909			tp->retrans_stamp = 0;
2910
2911		DBGUNDO(sk, "partial recovery");
2912		tcp_undo_cwnd_reduction(sk, true);
2913		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPPARTIALUNDO);
2914		tcp_try_keep_open(sk);
2915	} else {
2916		/* Partial ACK arrived. Force fast retransmit. */
2917		*do_lost = tcp_force_fast_retransmit(sk);
2918	}
2919	return false;
2920}
2921
2922static void tcp_identify_packet_loss(struct sock *sk, int *ack_flag)
2923{
2924	struct tcp_sock *tp = tcp_sk(sk);
2925
2926	if (tcp_rtx_queue_empty(sk))
2927		return;
2928
2929	if (unlikely(tcp_is_reno(tp))) {
2930		tcp_newreno_mark_lost(sk, *ack_flag & FLAG_SND_UNA_ADVANCED);
2931	} else if (tcp_is_rack(sk)) {
2932		u32 prior_retrans = tp->retrans_out;
2933
2934		if (tcp_rack_mark_lost(sk))
2935			*ack_flag &= ~FLAG_SET_XMIT_TIMER;
2936		if (prior_retrans > tp->retrans_out)
2937			*ack_flag |= FLAG_LOST_RETRANS;
2938	}
2939}
2940
 
 
 
 
 
 
 
 
2941/* Process an event, which can update packets-in-flight not trivially.
2942 * Main goal of this function is to calculate new estimate for left_out,
2943 * taking into account both packets sitting in receiver's buffer and
2944 * packets lost by network.
2945 *
2946 * Besides that it updates the congestion state when packet loss or ECN
2947 * is detected. But it does not reduce the cwnd, it is done by the
2948 * congestion control later.
2949 *
2950 * It does _not_ decide what to send, it is made in function
2951 * tcp_xmit_retransmit_queue().
2952 */
2953static void tcp_fastretrans_alert(struct sock *sk, const u32 prior_snd_una,
2954				  int num_dupack, int *ack_flag, int *rexmit)
2955{
2956	struct inet_connection_sock *icsk = inet_csk(sk);
2957	struct tcp_sock *tp = tcp_sk(sk);
2958	int fast_rexmit = 0, flag = *ack_flag;
2959	bool ece_ack = flag & FLAG_ECE;
2960	bool do_lost = num_dupack || ((flag & FLAG_DATA_SACKED) &&
2961				      tcp_force_fast_retransmit(sk));
2962
2963	if (!tp->packets_out && tp->sacked_out)
2964		tp->sacked_out = 0;
2965
2966	/* Now state machine starts.
2967	 * A. ECE, hence prohibit cwnd undoing, the reduction is required. */
2968	if (ece_ack)
2969		tp->prior_ssthresh = 0;
2970
2971	/* B. In all the states check for reneging SACKs. */
2972	if (tcp_check_sack_reneging(sk, flag))
2973		return;
2974
2975	/* C. Check consistency of the current state. */
2976	tcp_verify_left_out(tp);
2977
2978	/* D. Check state exit conditions. State can be terminated
2979	 *    when high_seq is ACKed. */
2980	if (icsk->icsk_ca_state == TCP_CA_Open) {
2981		WARN_ON(tp->retrans_out != 0 && !tp->syn_data);
2982		tp->retrans_stamp = 0;
2983	} else if (!before(tp->snd_una, tp->high_seq)) {
2984		switch (icsk->icsk_ca_state) {
2985		case TCP_CA_CWR:
2986			/* CWR is to be held something *above* high_seq
2987			 * is ACKed for CWR bit to reach receiver. */
2988			if (tp->snd_una != tp->high_seq) {
2989				tcp_end_cwnd_reduction(sk);
2990				tcp_set_ca_state(sk, TCP_CA_Open);
2991			}
2992			break;
2993
2994		case TCP_CA_Recovery:
2995			if (tcp_is_reno(tp))
2996				tcp_reset_reno_sack(tp);
2997			if (tcp_try_undo_recovery(sk))
2998				return;
2999			tcp_end_cwnd_reduction(sk);
3000			break;
3001		}
3002	}
3003
3004	/* E. Process state. */
3005	switch (icsk->icsk_ca_state) {
3006	case TCP_CA_Recovery:
3007		if (!(flag & FLAG_SND_UNA_ADVANCED)) {
3008			if (tcp_is_reno(tp))
3009				tcp_add_reno_sack(sk, num_dupack, ece_ack);
3010		} else if (tcp_try_undo_partial(sk, prior_snd_una, &do_lost))
3011			return;
3012
3013		if (tcp_try_undo_dsack(sk))
3014			tcp_try_keep_open(sk);
3015
3016		tcp_identify_packet_loss(sk, ack_flag);
3017		if (icsk->icsk_ca_state != TCP_CA_Recovery) {
3018			if (!tcp_time_to_recover(sk, flag))
3019				return;
3020			/* Undo reverts the recovery state. If loss is evident,
3021			 * starts a new recovery (e.g. reordering then loss);
3022			 */
3023			tcp_enter_recovery(sk, ece_ack);
 
 
3024		}
 
3025		break;
3026	case TCP_CA_Loss:
3027		tcp_process_loss(sk, flag, num_dupack, rexmit);
3028		tcp_identify_packet_loss(sk, ack_flag);
3029		if (!(icsk->icsk_ca_state == TCP_CA_Open ||
3030		      (*ack_flag & FLAG_LOST_RETRANS)))
3031			return;
3032		/* Change state if cwnd is undone or retransmits are lost */
3033		fallthrough;
3034	default:
3035		if (tcp_is_reno(tp)) {
3036			if (flag & FLAG_SND_UNA_ADVANCED)
3037				tcp_reset_reno_sack(tp);
3038			tcp_add_reno_sack(sk, num_dupack, ece_ack);
3039		}
3040
3041		if (icsk->icsk_ca_state <= TCP_CA_Disorder)
3042			tcp_try_undo_dsack(sk);
3043
3044		tcp_identify_packet_loss(sk, ack_flag);
3045		if (!tcp_time_to_recover(sk, flag)) {
3046			tcp_try_to_open(sk, flag);
3047			return;
3048		}
3049
3050		/* MTU probe failure: don't reduce cwnd */
3051		if (icsk->icsk_ca_state < TCP_CA_CWR &&
3052		    icsk->icsk_mtup.probe_size &&
3053		    tp->snd_una == tp->mtu_probe.probe_seq_start) {
3054			tcp_mtup_probe_failed(sk);
3055			/* Restores the reduction we did in tcp_mtup_probe() */
3056			tcp_snd_cwnd_set(tp, tcp_snd_cwnd(tp) + 1);
3057			tcp_simple_retransmit(sk);
3058			return;
3059		}
3060
3061		/* Otherwise enter Recovery state */
3062		tcp_enter_recovery(sk, ece_ack);
3063		fast_rexmit = 1;
3064	}
3065
3066	if (!tcp_is_rack(sk) && do_lost)
3067		tcp_update_scoreboard(sk, fast_rexmit);
3068	*rexmit = REXMIT_LOST;
3069}
3070
3071static void tcp_update_rtt_min(struct sock *sk, u32 rtt_us, const int flag)
3072{
3073	u32 wlen = READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_min_rtt_wlen) * HZ;
3074	struct tcp_sock *tp = tcp_sk(sk);
3075
3076	if ((flag & FLAG_ACK_MAYBE_DELAYED) && rtt_us > tcp_min_rtt(tp)) {
3077		/* If the remote keeps returning delayed ACKs, eventually
3078		 * the min filter would pick it up and overestimate the
3079		 * prop. delay when it expires. Skip suspected delayed ACKs.
3080		 */
3081		return;
3082	}
3083	minmax_running_min(&tp->rtt_min, wlen, tcp_jiffies32,
3084			   rtt_us ? : jiffies_to_usecs(1));
3085}
3086
3087static bool tcp_ack_update_rtt(struct sock *sk, const int flag,
3088			       long seq_rtt_us, long sack_rtt_us,
3089			       long ca_rtt_us, struct rate_sample *rs)
3090{
3091	const struct tcp_sock *tp = tcp_sk(sk);
3092
3093	/* Prefer RTT measured from ACK's timing to TS-ECR. This is because
3094	 * broken middle-boxes or peers may corrupt TS-ECR fields. But
3095	 * Karn's algorithm forbids taking RTT if some retransmitted data
3096	 * is acked (RFC6298).
3097	 */
3098	if (seq_rtt_us < 0)
3099		seq_rtt_us = sack_rtt_us;
3100
3101	/* RTTM Rule: A TSecr value received in a segment is used to
3102	 * update the averaged RTT measurement only if the segment
3103	 * acknowledges some new data, i.e., only if it advances the
3104	 * left edge of the send window.
3105	 * See draft-ietf-tcplw-high-performance-00, section 3.3.
3106	 */
3107	if (seq_rtt_us < 0 && tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
3108	    flag & FLAG_ACKED) {
3109		u32 delta = tcp_time_stamp(tp) - tp->rx_opt.rcv_tsecr;
3110
3111		if (likely(delta < INT_MAX / (USEC_PER_SEC / TCP_TS_HZ))) {
3112			if (!delta)
3113				delta = 1;
3114			seq_rtt_us = delta * (USEC_PER_SEC / TCP_TS_HZ);
3115			ca_rtt_us = seq_rtt_us;
3116		}
3117	}
3118	rs->rtt_us = ca_rtt_us; /* RTT of last (S)ACKed packet (or -1) */
3119	if (seq_rtt_us < 0)
3120		return false;
3121
3122	/* ca_rtt_us >= 0 is counting on the invariant that ca_rtt_us is
3123	 * always taken together with ACK, SACK, or TS-opts. Any negative
3124	 * values will be skipped with the seq_rtt_us < 0 check above.
3125	 */
3126	tcp_update_rtt_min(sk, ca_rtt_us, flag);
3127	tcp_rtt_estimator(sk, seq_rtt_us);
3128	tcp_set_rto(sk);
3129
3130	/* RFC6298: only reset backoff on valid RTT measurement. */
3131	inet_csk(sk)->icsk_backoff = 0;
3132	return true;
3133}
3134
3135/* Compute time elapsed between (last) SYNACK and the ACK completing 3WHS. */
3136void tcp_synack_rtt_meas(struct sock *sk, struct request_sock *req)
3137{
3138	struct rate_sample rs;
3139	long rtt_us = -1L;
3140
3141	if (req && !req->num_retrans && tcp_rsk(req)->snt_synack)
3142		rtt_us = tcp_stamp_us_delta(tcp_clock_us(), tcp_rsk(req)->snt_synack);
3143
3144	tcp_ack_update_rtt(sk, FLAG_SYN_ACKED, rtt_us, -1L, rtt_us, &rs);
3145}
3146
3147
3148static void tcp_cong_avoid(struct sock *sk, u32 ack, u32 acked)
3149{
3150	const struct inet_connection_sock *icsk = inet_csk(sk);
3151
3152	icsk->icsk_ca_ops->cong_avoid(sk, ack, acked);
3153	tcp_sk(sk)->snd_cwnd_stamp = tcp_jiffies32;
3154}
3155
3156/* Restart timer after forward progress on connection.
3157 * RFC2988 recommends to restart timer to now+rto.
3158 */
3159void tcp_rearm_rto(struct sock *sk)
3160{
3161	const struct inet_connection_sock *icsk = inet_csk(sk);
3162	struct tcp_sock *tp = tcp_sk(sk);
3163
3164	/* If the retrans timer is currently being used by Fast Open
3165	 * for SYN-ACK retrans purpose, stay put.
3166	 */
3167	if (rcu_access_pointer(tp->fastopen_rsk))
3168		return;
3169
3170	if (!tp->packets_out) {
3171		inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS);
3172	} else {
3173		u32 rto = inet_csk(sk)->icsk_rto;
3174		/* Offset the time elapsed after installing regular RTO */
3175		if (icsk->icsk_pending == ICSK_TIME_REO_TIMEOUT ||
3176		    icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) {
3177			s64 delta_us = tcp_rto_delta_us(sk);
3178			/* delta_us may not be positive if the socket is locked
3179			 * when the retrans timer fires and is rescheduled.
3180			 */
3181			rto = usecs_to_jiffies(max_t(int, delta_us, 1));
3182		}
3183		tcp_reset_xmit_timer(sk, ICSK_TIME_RETRANS, rto,
3184				     TCP_RTO_MAX);
3185	}
3186}
3187
3188/* Try to schedule a loss probe; if that doesn't work, then schedule an RTO. */
3189static void tcp_set_xmit_timer(struct sock *sk)
3190{
3191	if (!tcp_schedule_loss_probe(sk, true))
3192		tcp_rearm_rto(sk);
3193}
3194
3195/* If we get here, the whole TSO packet has not been acked. */
3196static u32 tcp_tso_acked(struct sock *sk, struct sk_buff *skb)
3197{
3198	struct tcp_sock *tp = tcp_sk(sk);
3199	u32 packets_acked;
3200
3201	BUG_ON(!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una));
3202
3203	packets_acked = tcp_skb_pcount(skb);
3204	if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
3205		return 0;
3206	packets_acked -= tcp_skb_pcount(skb);
3207
3208	if (packets_acked) {
3209		BUG_ON(tcp_skb_pcount(skb) == 0);
3210		BUG_ON(!before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq));
3211	}
3212
3213	return packets_acked;
3214}
3215
3216static void tcp_ack_tstamp(struct sock *sk, struct sk_buff *skb,
3217			   const struct sk_buff *ack_skb, u32 prior_snd_una)
3218{
3219	const struct skb_shared_info *shinfo;
3220
3221	/* Avoid cache line misses to get skb_shinfo() and shinfo->tx_flags */
3222	if (likely(!TCP_SKB_CB(skb)->txstamp_ack))
3223		return;
3224
3225	shinfo = skb_shinfo(skb);
3226	if (!before(shinfo->tskey, prior_snd_una) &&
3227	    before(shinfo->tskey, tcp_sk(sk)->snd_una)) {
3228		tcp_skb_tsorted_save(skb) {
3229			__skb_tstamp_tx(skb, ack_skb, NULL, sk, SCM_TSTAMP_ACK);
3230		} tcp_skb_tsorted_restore(skb);
3231	}
3232}
3233
3234/* Remove acknowledged frames from the retransmission queue. If our packet
3235 * is before the ack sequence we can discard it as it's confirmed to have
3236 * arrived at the other end.
3237 */
3238static int tcp_clean_rtx_queue(struct sock *sk, const struct sk_buff *ack_skb,
3239			       u32 prior_fack, u32 prior_snd_una,
3240			       struct tcp_sacktag_state *sack, bool ece_ack)
3241{
3242	const struct inet_connection_sock *icsk = inet_csk(sk);
3243	u64 first_ackt, last_ackt;
3244	struct tcp_sock *tp = tcp_sk(sk);
3245	u32 prior_sacked = tp->sacked_out;
3246	u32 reord = tp->snd_nxt; /* lowest acked un-retx un-sacked seq */
3247	struct sk_buff *skb, *next;
3248	bool fully_acked = true;
3249	long sack_rtt_us = -1L;
3250	long seq_rtt_us = -1L;
3251	long ca_rtt_us = -1L;
3252	u32 pkts_acked = 0;
 
3253	bool rtt_update;
3254	int flag = 0;
3255
3256	first_ackt = 0;
3257
3258	for (skb = skb_rb_first(&sk->tcp_rtx_queue); skb; skb = next) {
3259		struct tcp_skb_cb *scb = TCP_SKB_CB(skb);
3260		const u32 start_seq = scb->seq;
3261		u8 sacked = scb->sacked;
3262		u32 acked_pcount;
3263
3264		/* Determine how many packets and what bytes were acked, tso and else */
3265		if (after(scb->end_seq, tp->snd_una)) {
3266			if (tcp_skb_pcount(skb) == 1 ||
3267			    !after(tp->snd_una, scb->seq))
3268				break;
3269
3270			acked_pcount = tcp_tso_acked(sk, skb);
3271			if (!acked_pcount)
3272				break;
3273			fully_acked = false;
3274		} else {
3275			acked_pcount = tcp_skb_pcount(skb);
3276		}
3277
3278		if (unlikely(sacked & TCPCB_RETRANS)) {
3279			if (sacked & TCPCB_SACKED_RETRANS)
3280				tp->retrans_out -= acked_pcount;
3281			flag |= FLAG_RETRANS_DATA_ACKED;
3282		} else if (!(sacked & TCPCB_SACKED_ACKED)) {
3283			last_ackt = tcp_skb_timestamp_us(skb);
3284			WARN_ON_ONCE(last_ackt == 0);
3285			if (!first_ackt)
3286				first_ackt = last_ackt;
3287
 
3288			if (before(start_seq, reord))
3289				reord = start_seq;
3290			if (!after(scb->end_seq, tp->high_seq))
3291				flag |= FLAG_ORIG_SACK_ACKED;
3292		}
3293
3294		if (sacked & TCPCB_SACKED_ACKED) {
3295			tp->sacked_out -= acked_pcount;
3296		} else if (tcp_is_sack(tp)) {
3297			tcp_count_delivered(tp, acked_pcount, ece_ack);
3298			if (!tcp_skb_spurious_retrans(tp, skb))
3299				tcp_rack_advance(tp, sacked, scb->end_seq,
3300						 tcp_skb_timestamp_us(skb));
3301		}
3302		if (sacked & TCPCB_LOST)
3303			tp->lost_out -= acked_pcount;
3304
3305		tp->packets_out -= acked_pcount;
3306		pkts_acked += acked_pcount;
3307		tcp_rate_skb_delivered(sk, skb, sack->rate);
3308
3309		/* Initial outgoing SYN's get put onto the write_queue
3310		 * just like anything else we transmit.  It is not
3311		 * true data, and if we misinform our callers that
3312		 * this ACK acks real data, we will erroneously exit
3313		 * connection startup slow start one packet too
3314		 * quickly.  This is severely frowned upon behavior.
3315		 */
3316		if (likely(!(scb->tcp_flags & TCPHDR_SYN))) {
3317			flag |= FLAG_DATA_ACKED;
3318		} else {
3319			flag |= FLAG_SYN_ACKED;
3320			tp->retrans_stamp = 0;
3321		}
3322
3323		if (!fully_acked)
3324			break;
3325
3326		tcp_ack_tstamp(sk, skb, ack_skb, prior_snd_una);
3327
3328		next = skb_rb_next(skb);
3329		if (unlikely(skb == tp->retransmit_skb_hint))
3330			tp->retransmit_skb_hint = NULL;
3331		if (unlikely(skb == tp->lost_skb_hint))
3332			tp->lost_skb_hint = NULL;
3333		tcp_highest_sack_replace(sk, skb, next);
3334		tcp_rtx_queue_unlink_and_free(skb, sk);
3335	}
3336
3337	if (!skb)
3338		tcp_chrono_stop(sk, TCP_CHRONO_BUSY);
3339
3340	if (likely(between(tp->snd_up, prior_snd_una, tp->snd_una)))
3341		tp->snd_up = tp->snd_una;
3342
3343	if (skb) {
3344		tcp_ack_tstamp(sk, skb, ack_skb, prior_snd_una);
3345		if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
3346			flag |= FLAG_SACK_RENEGING;
3347	}
3348
3349	if (likely(first_ackt) && !(flag & FLAG_RETRANS_DATA_ACKED)) {
3350		seq_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, first_ackt);
3351		ca_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, last_ackt);
3352
3353		if (pkts_acked == 1 && fully_acked && !prior_sacked &&
3354		    (tp->snd_una - prior_snd_una) < tp->mss_cache &&
3355		    sack->rate->prior_delivered + 1 == tp->delivered &&
3356		    !(flag & (FLAG_CA_ALERT | FLAG_SYN_ACKED))) {
3357			/* Conservatively mark a delayed ACK. It's typically
3358			 * from a lone runt packet over the round trip to
3359			 * a receiver w/o out-of-order or CE events.
3360			 */
3361			flag |= FLAG_ACK_MAYBE_DELAYED;
3362		}
3363	}
3364	if (sack->first_sackt) {
3365		sack_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, sack->first_sackt);
3366		ca_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, sack->last_sackt);
3367	}
3368	rtt_update = tcp_ack_update_rtt(sk, flag, seq_rtt_us, sack_rtt_us,
3369					ca_rtt_us, sack->rate);
3370
3371	if (flag & FLAG_ACKED) {
3372		flag |= FLAG_SET_XMIT_TIMER;  /* set TLP or RTO timer */
3373		if (unlikely(icsk->icsk_mtup.probe_size &&
3374			     !after(tp->mtu_probe.probe_seq_end, tp->snd_una))) {
3375			tcp_mtup_probe_success(sk);
3376		}
3377
3378		if (tcp_is_reno(tp)) {
3379			tcp_remove_reno_sacks(sk, pkts_acked, ece_ack);
3380
3381			/* If any of the cumulatively ACKed segments was
3382			 * retransmitted, non-SACK case cannot confirm that
3383			 * progress was due to original transmission due to
3384			 * lack of TCPCB_SACKED_ACKED bits even if some of
3385			 * the packets may have been never retransmitted.
3386			 */
3387			if (flag & FLAG_RETRANS_DATA_ACKED)
3388				flag &= ~FLAG_ORIG_SACK_ACKED;
3389		} else {
3390			int delta;
3391
3392			/* Non-retransmitted hole got filled? That's reordering */
3393			if (before(reord, prior_fack))
3394				tcp_check_sack_reordering(sk, reord, 0);
3395
3396			delta = prior_sacked - tp->sacked_out;
3397			tp->lost_cnt_hint -= min(tp->lost_cnt_hint, delta);
3398		}
3399	} else if (skb && rtt_update && sack_rtt_us >= 0 &&
3400		   sack_rtt_us > tcp_stamp_us_delta(tp->tcp_mstamp,
3401						    tcp_skb_timestamp_us(skb))) {
3402		/* Do not re-arm RTO if the sack RTT is measured from data sent
3403		 * after when the head was last (re)transmitted. Otherwise the
3404		 * timeout may continue to extend in loss recovery.
3405		 */
3406		flag |= FLAG_SET_XMIT_TIMER;  /* set TLP or RTO timer */
3407	}
3408
3409	if (icsk->icsk_ca_ops->pkts_acked) {
3410		struct ack_sample sample = { .pkts_acked = pkts_acked,
3411					     .rtt_us = sack->rate->rtt_us };
 
3412
3413		sample.in_flight = tp->mss_cache *
3414			(tp->delivered - sack->rate->prior_delivered);
3415		icsk->icsk_ca_ops->pkts_acked(sk, &sample);
3416	}
3417
3418#if FASTRETRANS_DEBUG > 0
3419	WARN_ON((int)tp->sacked_out < 0);
3420	WARN_ON((int)tp->lost_out < 0);
3421	WARN_ON((int)tp->retrans_out < 0);
3422	if (!tp->packets_out && tcp_is_sack(tp)) {
3423		icsk = inet_csk(sk);
3424		if (tp->lost_out) {
3425			pr_debug("Leak l=%u %d\n",
3426				 tp->lost_out, icsk->icsk_ca_state);
3427			tp->lost_out = 0;
3428		}
3429		if (tp->sacked_out) {
3430			pr_debug("Leak s=%u %d\n",
3431				 tp->sacked_out, icsk->icsk_ca_state);
3432			tp->sacked_out = 0;
3433		}
3434		if (tp->retrans_out) {
3435			pr_debug("Leak r=%u %d\n",
3436				 tp->retrans_out, icsk->icsk_ca_state);
3437			tp->retrans_out = 0;
3438		}
3439	}
3440#endif
3441	return flag;
3442}
3443
3444static void tcp_ack_probe(struct sock *sk)
3445{
3446	struct inet_connection_sock *icsk = inet_csk(sk);
3447	struct sk_buff *head = tcp_send_head(sk);
3448	const struct tcp_sock *tp = tcp_sk(sk);
3449
3450	/* Was it a usable window open? */
3451	if (!head)
3452		return;
3453	if (!after(TCP_SKB_CB(head)->end_seq, tcp_wnd_end(tp))) {
3454		icsk->icsk_backoff = 0;
3455		icsk->icsk_probes_tstamp = 0;
3456		inet_csk_clear_xmit_timer(sk, ICSK_TIME_PROBE0);
3457		/* Socket must be waked up by subsequent tcp_data_snd_check().
3458		 * This function is not for random using!
3459		 */
3460	} else {
3461		unsigned long when = tcp_probe0_when(sk, TCP_RTO_MAX);
3462
3463		when = tcp_clamp_probe0_to_user_timeout(sk, when);
3464		tcp_reset_xmit_timer(sk, ICSK_TIME_PROBE0, when, TCP_RTO_MAX);
3465	}
3466}
3467
3468static inline bool tcp_ack_is_dubious(const struct sock *sk, const int flag)
3469{
3470	return !(flag & FLAG_NOT_DUP) || (flag & FLAG_CA_ALERT) ||
3471		inet_csk(sk)->icsk_ca_state != TCP_CA_Open;
3472}
3473
3474/* Decide wheather to run the increase function of congestion control. */
3475static inline bool tcp_may_raise_cwnd(const struct sock *sk, const int flag)
3476{
3477	/* If reordering is high then always grow cwnd whenever data is
3478	 * delivered regardless of its ordering. Otherwise stay conservative
3479	 * and only grow cwnd on in-order delivery (RFC5681). A stretched ACK w/
3480	 * new SACK or ECE mark may first advance cwnd here and later reduce
3481	 * cwnd in tcp_fastretrans_alert() based on more states.
3482	 */
3483	if (tcp_sk(sk)->reordering >
3484	    READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_reordering))
3485		return flag & FLAG_FORWARD_PROGRESS;
3486
3487	return flag & FLAG_DATA_ACKED;
3488}
3489
3490/* The "ultimate" congestion control function that aims to replace the rigid
3491 * cwnd increase and decrease control (tcp_cong_avoid,tcp_*cwnd_reduction).
3492 * It's called toward the end of processing an ACK with precise rate
3493 * information. All transmission or retransmission are delayed afterwards.
3494 */
3495static void tcp_cong_control(struct sock *sk, u32 ack, u32 acked_sacked,
3496			     int flag, const struct rate_sample *rs)
3497{
3498	const struct inet_connection_sock *icsk = inet_csk(sk);
3499
3500	if (icsk->icsk_ca_ops->cong_control) {
3501		icsk->icsk_ca_ops->cong_control(sk, rs);
3502		return;
3503	}
3504
3505	if (tcp_in_cwnd_reduction(sk)) {
3506		/* Reduce cwnd if state mandates */
3507		tcp_cwnd_reduction(sk, acked_sacked, rs->losses, flag);
3508	} else if (tcp_may_raise_cwnd(sk, flag)) {
3509		/* Advance cwnd if state allows */
3510		tcp_cong_avoid(sk, ack, acked_sacked);
3511	}
3512	tcp_update_pacing_rate(sk);
3513}
3514
3515/* Check that window update is acceptable.
3516 * The function assumes that snd_una<=ack<=snd_next.
3517 */
3518static inline bool tcp_may_update_window(const struct tcp_sock *tp,
3519					const u32 ack, const u32 ack_seq,
3520					const u32 nwin)
3521{
3522	return	after(ack, tp->snd_una) ||
3523		after(ack_seq, tp->snd_wl1) ||
3524		(ack_seq == tp->snd_wl1 && nwin > tp->snd_wnd);
3525}
3526
3527/* If we update tp->snd_una, also update tp->bytes_acked */
3528static void tcp_snd_una_update(struct tcp_sock *tp, u32 ack)
3529{
3530	u32 delta = ack - tp->snd_una;
3531
3532	sock_owned_by_me((struct sock *)tp);
3533	tp->bytes_acked += delta;
3534	tp->snd_una = ack;
3535}
3536
3537/* If we update tp->rcv_nxt, also update tp->bytes_received */
3538static void tcp_rcv_nxt_update(struct tcp_sock *tp, u32 seq)
3539{
3540	u32 delta = seq - tp->rcv_nxt;
3541
3542	sock_owned_by_me((struct sock *)tp);
3543	tp->bytes_received += delta;
3544	WRITE_ONCE(tp->rcv_nxt, seq);
3545}
3546
3547/* Update our send window.
3548 *
3549 * Window update algorithm, described in RFC793/RFC1122 (used in linux-2.2
3550 * and in FreeBSD. NetBSD's one is even worse.) is wrong.
3551 */
3552static int tcp_ack_update_window(struct sock *sk, const struct sk_buff *skb, u32 ack,
3553				 u32 ack_seq)
3554{
3555	struct tcp_sock *tp = tcp_sk(sk);
3556	int flag = 0;
3557	u32 nwin = ntohs(tcp_hdr(skb)->window);
3558
3559	if (likely(!tcp_hdr(skb)->syn))
3560		nwin <<= tp->rx_opt.snd_wscale;
3561
3562	if (tcp_may_update_window(tp, ack, ack_seq, nwin)) {
3563		flag |= FLAG_WIN_UPDATE;
3564		tcp_update_wl(tp, ack_seq);
3565
3566		if (tp->snd_wnd != nwin) {
3567			tp->snd_wnd = nwin;
3568
3569			/* Note, it is the only place, where
3570			 * fast path is recovered for sending TCP.
3571			 */
3572			tp->pred_flags = 0;
3573			tcp_fast_path_check(sk);
3574
3575			if (!tcp_write_queue_empty(sk))
3576				tcp_slow_start_after_idle_check(sk);
3577
3578			if (nwin > tp->max_window) {
3579				tp->max_window = nwin;
3580				tcp_sync_mss(sk, inet_csk(sk)->icsk_pmtu_cookie);
3581			}
3582		}
3583	}
3584
3585	tcp_snd_una_update(tp, ack);
3586
3587	return flag;
3588}
3589
3590static bool __tcp_oow_rate_limited(struct net *net, int mib_idx,
3591				   u32 *last_oow_ack_time)
3592{
3593	if (*last_oow_ack_time) {
3594		s32 elapsed = (s32)(tcp_jiffies32 - *last_oow_ack_time);
3595
3596		if (0 <= elapsed &&
3597		    elapsed < READ_ONCE(net->ipv4.sysctl_tcp_invalid_ratelimit)) {
3598			NET_INC_STATS(net, mib_idx);
3599			return true;	/* rate-limited: don't send yet! */
3600		}
3601	}
3602
3603	*last_oow_ack_time = tcp_jiffies32;
3604
3605	return false;	/* not rate-limited: go ahead, send dupack now! */
3606}
3607
3608/* Return true if we're currently rate-limiting out-of-window ACKs and
3609 * thus shouldn't send a dupack right now. We rate-limit dupacks in
3610 * response to out-of-window SYNs or ACKs to mitigate ACK loops or DoS
3611 * attacks that send repeated SYNs or ACKs for the same connection. To
3612 * do this, we do not send a duplicate SYNACK or ACK if the remote
3613 * endpoint is sending out-of-window SYNs or pure ACKs at a high rate.
3614 */
3615bool tcp_oow_rate_limited(struct net *net, const struct sk_buff *skb,
3616			  int mib_idx, u32 *last_oow_ack_time)
3617{
3618	/* Data packets without SYNs are not likely part of an ACK loop. */
3619	if ((TCP_SKB_CB(skb)->seq != TCP_SKB_CB(skb)->end_seq) &&
3620	    !tcp_hdr(skb)->syn)
3621		return false;
3622
3623	return __tcp_oow_rate_limited(net, mib_idx, last_oow_ack_time);
3624}
3625
3626/* RFC 5961 7 [ACK Throttling] */
3627static void tcp_send_challenge_ack(struct sock *sk)
3628{
 
 
 
3629	struct tcp_sock *tp = tcp_sk(sk);
3630	struct net *net = sock_net(sk);
3631	u32 count, now, ack_limit;
3632
3633	/* First check our per-socket dupack rate limit. */
3634	if (__tcp_oow_rate_limited(net,
3635				   LINUX_MIB_TCPACKSKIPPEDCHALLENGE,
3636				   &tp->last_oow_ack_time))
3637		return;
3638
3639	ack_limit = READ_ONCE(net->ipv4.sysctl_tcp_challenge_ack_limit);
3640	if (ack_limit == INT_MAX)
3641		goto send_ack;
3642
3643	/* Then check host-wide RFC 5961 rate limit. */
3644	now = jiffies / HZ;
3645	if (now != READ_ONCE(net->ipv4.tcp_challenge_timestamp)) {
 
3646		u32 half = (ack_limit + 1) >> 1;
3647
3648		WRITE_ONCE(net->ipv4.tcp_challenge_timestamp, now);
3649		WRITE_ONCE(net->ipv4.tcp_challenge_count,
3650			   get_random_u32_inclusive(half, ack_limit + half - 1));
3651	}
3652	count = READ_ONCE(net->ipv4.tcp_challenge_count);
3653	if (count > 0) {
3654		WRITE_ONCE(net->ipv4.tcp_challenge_count, count - 1);
3655send_ack:
3656		NET_INC_STATS(net, LINUX_MIB_TCPCHALLENGEACK);
3657		tcp_send_ack(sk);
3658	}
3659}
3660
3661static void tcp_store_ts_recent(struct tcp_sock *tp)
3662{
3663	tp->rx_opt.ts_recent = tp->rx_opt.rcv_tsval;
3664	tp->rx_opt.ts_recent_stamp = ktime_get_seconds();
3665}
3666
3667static void tcp_replace_ts_recent(struct tcp_sock *tp, u32 seq)
3668{
3669	if (tp->rx_opt.saw_tstamp && !after(seq, tp->rcv_wup)) {
3670		/* PAWS bug workaround wrt. ACK frames, the PAWS discard
3671		 * extra check below makes sure this can only happen
3672		 * for pure ACK frames.  -DaveM
3673		 *
3674		 * Not only, also it occurs for expired timestamps.
3675		 */
3676
3677		if (tcp_paws_check(&tp->rx_opt, 0))
3678			tcp_store_ts_recent(tp);
3679	}
3680}
3681
3682/* This routine deals with acks during a TLP episode and ends an episode by
3683 * resetting tlp_high_seq. Ref: TLP algorithm in draft-ietf-tcpm-rack
3684 */
3685static void tcp_process_tlp_ack(struct sock *sk, u32 ack, int flag)
3686{
3687	struct tcp_sock *tp = tcp_sk(sk);
3688
3689	if (before(ack, tp->tlp_high_seq))
3690		return;
3691
3692	if (!tp->tlp_retrans) {
3693		/* TLP of new data has been acknowledged */
3694		tp->tlp_high_seq = 0;
3695	} else if (flag & FLAG_DSACK_TLP) {
3696		/* This DSACK means original and TLP probe arrived; no loss */
3697		tp->tlp_high_seq = 0;
3698	} else if (after(ack, tp->tlp_high_seq)) {
3699		/* ACK advances: there was a loss, so reduce cwnd. Reset
3700		 * tlp_high_seq in tcp_init_cwnd_reduction()
3701		 */
3702		tcp_init_cwnd_reduction(sk);
3703		tcp_set_ca_state(sk, TCP_CA_CWR);
3704		tcp_end_cwnd_reduction(sk);
3705		tcp_try_keep_open(sk);
3706		NET_INC_STATS(sock_net(sk),
3707				LINUX_MIB_TCPLOSSPROBERECOVERY);
3708	} else if (!(flag & (FLAG_SND_UNA_ADVANCED |
3709			     FLAG_NOT_DUP | FLAG_DATA_SACKED))) {
3710		/* Pure dupack: original and TLP probe arrived; no loss */
3711		tp->tlp_high_seq = 0;
3712	}
3713}
3714
3715static inline void tcp_in_ack_event(struct sock *sk, u32 flags)
3716{
3717	const struct inet_connection_sock *icsk = inet_csk(sk);
3718
3719	if (icsk->icsk_ca_ops->in_ack_event)
3720		icsk->icsk_ca_ops->in_ack_event(sk, flags);
3721}
3722
3723/* Congestion control has updated the cwnd already. So if we're in
3724 * loss recovery then now we do any new sends (for FRTO) or
3725 * retransmits (for CA_Loss or CA_recovery) that make sense.
3726 */
3727static void tcp_xmit_recovery(struct sock *sk, int rexmit)
3728{
3729	struct tcp_sock *tp = tcp_sk(sk);
3730
3731	if (rexmit == REXMIT_NONE || sk->sk_state == TCP_SYN_SENT)
3732		return;
3733
3734	if (unlikely(rexmit == REXMIT_NEW)) {
3735		__tcp_push_pending_frames(sk, tcp_current_mss(sk),
3736					  TCP_NAGLE_OFF);
3737		if (after(tp->snd_nxt, tp->high_seq))
3738			return;
3739		tp->frto = 0;
3740	}
3741	tcp_xmit_retransmit_queue(sk);
3742}
3743
3744/* Returns the number of packets newly acked or sacked by the current ACK */
3745static u32 tcp_newly_delivered(struct sock *sk, u32 prior_delivered, int flag)
3746{
3747	const struct net *net = sock_net(sk);
3748	struct tcp_sock *tp = tcp_sk(sk);
3749	u32 delivered;
3750
3751	delivered = tp->delivered - prior_delivered;
3752	NET_ADD_STATS(net, LINUX_MIB_TCPDELIVERED, delivered);
3753	if (flag & FLAG_ECE)
3754		NET_ADD_STATS(net, LINUX_MIB_TCPDELIVEREDCE, delivered);
3755
3756	return delivered;
3757}
3758
3759/* This routine deals with incoming acks, but not outgoing ones. */
3760static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
3761{
3762	struct inet_connection_sock *icsk = inet_csk(sk);
3763	struct tcp_sock *tp = tcp_sk(sk);
3764	struct tcp_sacktag_state sack_state;
3765	struct rate_sample rs = { .prior_delivered = 0 };
3766	u32 prior_snd_una = tp->snd_una;
3767	bool is_sack_reneg = tp->is_sack_reneg;
3768	u32 ack_seq = TCP_SKB_CB(skb)->seq;
3769	u32 ack = TCP_SKB_CB(skb)->ack_seq;
3770	int num_dupack = 0;
3771	int prior_packets = tp->packets_out;
3772	u32 delivered = tp->delivered;
3773	u32 lost = tp->lost;
3774	int rexmit = REXMIT_NONE; /* Flag to (re)transmit to recover losses */
3775	u32 prior_fack;
3776
3777	sack_state.first_sackt = 0;
3778	sack_state.rate = &rs;
3779	sack_state.sack_delivered = 0;
3780
3781	/* We very likely will need to access rtx queue. */
3782	prefetch(sk->tcp_rtx_queue.rb_node);
3783
3784	/* If the ack is older than previous acks
3785	 * then we can probably ignore it.
3786	 */
3787	if (before(ack, prior_snd_una)) {
3788		/* RFC 5961 5.2 [Blind Data Injection Attack].[Mitigation] */
3789		if (before(ack, prior_snd_una - tp->max_window)) {
3790			if (!(flag & FLAG_NO_CHALLENGE_ACK))
3791				tcp_send_challenge_ack(sk);
3792			return -SKB_DROP_REASON_TCP_TOO_OLD_ACK;
3793		}
3794		goto old_ack;
3795	}
3796
3797	/* If the ack includes data we haven't sent yet, discard
3798	 * this segment (RFC793 Section 3.9).
3799	 */
3800	if (after(ack, tp->snd_nxt))
3801		return -SKB_DROP_REASON_TCP_ACK_UNSENT_DATA;
3802
3803	if (after(ack, prior_snd_una)) {
3804		flag |= FLAG_SND_UNA_ADVANCED;
3805		icsk->icsk_retransmits = 0;
3806
3807#if IS_ENABLED(CONFIG_TLS_DEVICE)
3808		if (static_branch_unlikely(&clean_acked_data_enabled.key))
3809			if (icsk->icsk_clean_acked)
3810				icsk->icsk_clean_acked(sk, ack);
3811#endif
3812	}
3813
3814	prior_fack = tcp_is_sack(tp) ? tcp_highest_sack_seq(tp) : tp->snd_una;
3815	rs.prior_in_flight = tcp_packets_in_flight(tp);
3816
3817	/* ts_recent update must be made after we are sure that the packet
3818	 * is in window.
3819	 */
3820	if (flag & FLAG_UPDATE_TS_RECENT)
3821		tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
3822
3823	if ((flag & (FLAG_SLOWPATH | FLAG_SND_UNA_ADVANCED)) ==
3824	    FLAG_SND_UNA_ADVANCED) {
3825		/* Window is constant, pure forward advance.
3826		 * No more checks are required.
3827		 * Note, we use the fact that SND.UNA>=SND.WL2.
3828		 */
3829		tcp_update_wl(tp, ack_seq);
3830		tcp_snd_una_update(tp, ack);
3831		flag |= FLAG_WIN_UPDATE;
3832
3833		tcp_in_ack_event(sk, CA_ACK_WIN_UPDATE);
3834
3835		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPHPACKS);
3836	} else {
3837		u32 ack_ev_flags = CA_ACK_SLOWPATH;
3838
3839		if (ack_seq != TCP_SKB_CB(skb)->end_seq)
3840			flag |= FLAG_DATA;
3841		else
3842			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPPUREACKS);
3843
3844		flag |= tcp_ack_update_window(sk, skb, ack, ack_seq);
3845
3846		if (TCP_SKB_CB(skb)->sacked)
3847			flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una,
3848							&sack_state);
3849
3850		if (tcp_ecn_rcv_ecn_echo(tp, tcp_hdr(skb))) {
3851			flag |= FLAG_ECE;
3852			ack_ev_flags |= CA_ACK_ECE;
3853		}
3854
3855		if (sack_state.sack_delivered)
3856			tcp_count_delivered(tp, sack_state.sack_delivered,
3857					    flag & FLAG_ECE);
3858
3859		if (flag & FLAG_WIN_UPDATE)
3860			ack_ev_flags |= CA_ACK_WIN_UPDATE;
3861
3862		tcp_in_ack_event(sk, ack_ev_flags);
3863	}
3864
3865	/* This is a deviation from RFC3168 since it states that:
3866	 * "When the TCP data sender is ready to set the CWR bit after reducing
3867	 * the congestion window, it SHOULD set the CWR bit only on the first
3868	 * new data packet that it transmits."
3869	 * We accept CWR on pure ACKs to be more robust
3870	 * with widely-deployed TCP implementations that do this.
3871	 */
3872	tcp_ecn_accept_cwr(sk, skb);
3873
3874	/* We passed data and got it acked, remove any soft error
3875	 * log. Something worked...
3876	 */
3877	sk->sk_err_soft = 0;
3878	icsk->icsk_probes_out = 0;
3879	tp->rcv_tstamp = tcp_jiffies32;
3880	if (!prior_packets)
3881		goto no_queue;
3882
3883	/* See if we can take anything off of the retransmit queue. */
3884	flag |= tcp_clean_rtx_queue(sk, skb, prior_fack, prior_snd_una,
3885				    &sack_state, flag & FLAG_ECE);
3886
3887	tcp_rack_update_reo_wnd(sk, &rs);
3888
3889	if (tp->tlp_high_seq)
3890		tcp_process_tlp_ack(sk, ack, flag);
 
 
 
3891
3892	if (tcp_ack_is_dubious(sk, flag)) {
3893		if (!(flag & (FLAG_SND_UNA_ADVANCED |
3894			      FLAG_NOT_DUP | FLAG_DSACKING_ACK))) {
3895			num_dupack = 1;
3896			/* Consider if pure acks were aggregated in tcp_add_backlog() */
3897			if (!(flag & FLAG_DATA))
3898				num_dupack = max_t(u16, 1, skb_shinfo(skb)->gso_segs);
3899		}
3900		tcp_fastretrans_alert(sk, prior_snd_una, num_dupack, &flag,
3901				      &rexmit);
3902	}
3903
3904	/* If needed, reset TLP/RTO timer when RACK doesn't set. */
3905	if (flag & FLAG_SET_XMIT_TIMER)
3906		tcp_set_xmit_timer(sk);
3907
3908	if ((flag & FLAG_FORWARD_PROGRESS) || !(flag & FLAG_NOT_DUP))
3909		sk_dst_confirm(sk);
3910
3911	delivered = tcp_newly_delivered(sk, delivered, flag);
3912	lost = tp->lost - lost;			/* freshly marked lost */
3913	rs.is_ack_delayed = !!(flag & FLAG_ACK_MAYBE_DELAYED);
3914	tcp_rate_gen(sk, delivered, lost, is_sack_reneg, sack_state.rate);
3915	tcp_cong_control(sk, ack, delivered, flag, sack_state.rate);
3916	tcp_xmit_recovery(sk, rexmit);
3917	return 1;
3918
3919no_queue:
3920	/* If data was DSACKed, see if we can undo a cwnd reduction. */
3921	if (flag & FLAG_DSACKING_ACK) {
3922		tcp_fastretrans_alert(sk, prior_snd_una, num_dupack, &flag,
3923				      &rexmit);
3924		tcp_newly_delivered(sk, delivered, flag);
3925	}
3926	/* If this ack opens up a zero window, clear backoff.  It was
3927	 * being used to time the probes, and is probably far higher than
3928	 * it needs to be for normal retransmission.
3929	 */
3930	tcp_ack_probe(sk);
3931
3932	if (tp->tlp_high_seq)
3933		tcp_process_tlp_ack(sk, ack, flag);
3934	return 1;
3935
3936old_ack:
3937	/* If data was SACKed, tag it and see if we should send more data.
3938	 * If data was DSACKed, see if we can undo a cwnd reduction.
3939	 */
3940	if (TCP_SKB_CB(skb)->sacked) {
3941		flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una,
3942						&sack_state);
3943		tcp_fastretrans_alert(sk, prior_snd_una, num_dupack, &flag,
3944				      &rexmit);
3945		tcp_newly_delivered(sk, delivered, flag);
3946		tcp_xmit_recovery(sk, rexmit);
3947	}
3948
3949	return 0;
3950}
3951
3952static void tcp_parse_fastopen_option(int len, const unsigned char *cookie,
3953				      bool syn, struct tcp_fastopen_cookie *foc,
3954				      bool exp_opt)
3955{
3956	/* Valid only in SYN or SYN-ACK with an even length.  */
3957	if (!foc || !syn || len < 0 || (len & 1))
3958		return;
3959
3960	if (len >= TCP_FASTOPEN_COOKIE_MIN &&
3961	    len <= TCP_FASTOPEN_COOKIE_MAX)
3962		memcpy(foc->val, cookie, len);
3963	else if (len != 0)
3964		len = -1;
3965	foc->len = len;
3966	foc->exp = exp_opt;
3967}
3968
3969static bool smc_parse_options(const struct tcphdr *th,
3970			      struct tcp_options_received *opt_rx,
3971			      const unsigned char *ptr,
3972			      int opsize)
3973{
3974#if IS_ENABLED(CONFIG_SMC)
3975	if (static_branch_unlikely(&tcp_have_smc)) {
3976		if (th->syn && !(opsize & 1) &&
3977		    opsize >= TCPOLEN_EXP_SMC_BASE &&
3978		    get_unaligned_be32(ptr) == TCPOPT_SMC_MAGIC) {
3979			opt_rx->smc_ok = 1;
3980			return true;
3981		}
3982	}
3983#endif
3984	return false;
3985}
3986
3987/* Try to parse the MSS option from the TCP header. Return 0 on failure, clamped
3988 * value on success.
3989 */
3990u16 tcp_parse_mss_option(const struct tcphdr *th, u16 user_mss)
3991{
3992	const unsigned char *ptr = (const unsigned char *)(th + 1);
3993	int length = (th->doff * 4) - sizeof(struct tcphdr);
3994	u16 mss = 0;
3995
3996	while (length > 0) {
3997		int opcode = *ptr++;
3998		int opsize;
3999
4000		switch (opcode) {
4001		case TCPOPT_EOL:
4002			return mss;
4003		case TCPOPT_NOP:	/* Ref: RFC 793 section 3.1 */
4004			length--;
4005			continue;
4006		default:
4007			if (length < 2)
4008				return mss;
4009			opsize = *ptr++;
4010			if (opsize < 2) /* "silly options" */
4011				return mss;
4012			if (opsize > length)
4013				return mss;	/* fail on partial options */
4014			if (opcode == TCPOPT_MSS && opsize == TCPOLEN_MSS) {
4015				u16 in_mss = get_unaligned_be16(ptr);
4016
4017				if (in_mss) {
4018					if (user_mss && user_mss < in_mss)
4019						in_mss = user_mss;
4020					mss = in_mss;
4021				}
4022			}
4023			ptr += opsize - 2;
4024			length -= opsize;
4025		}
4026	}
4027	return mss;
4028}
4029EXPORT_SYMBOL_GPL(tcp_parse_mss_option);
4030
4031/* Look for tcp options. Normally only called on SYN and SYNACK packets.
4032 * But, this can also be called on packets in the established flow when
4033 * the fast version below fails.
4034 */
4035void tcp_parse_options(const struct net *net,
4036		       const struct sk_buff *skb,
4037		       struct tcp_options_received *opt_rx, int estab,
4038		       struct tcp_fastopen_cookie *foc)
4039{
4040	const unsigned char *ptr;
4041	const struct tcphdr *th = tcp_hdr(skb);
4042	int length = (th->doff * 4) - sizeof(struct tcphdr);
4043
4044	ptr = (const unsigned char *)(th + 1);
4045	opt_rx->saw_tstamp = 0;
4046	opt_rx->saw_unknown = 0;
4047
4048	while (length > 0) {
4049		int opcode = *ptr++;
4050		int opsize;
4051
4052		switch (opcode) {
4053		case TCPOPT_EOL:
4054			return;
4055		case TCPOPT_NOP:	/* Ref: RFC 793 section 3.1 */
4056			length--;
4057			continue;
4058		default:
4059			if (length < 2)
4060				return;
4061			opsize = *ptr++;
4062			if (opsize < 2) /* "silly options" */
4063				return;
4064			if (opsize > length)
4065				return;	/* don't parse partial options */
4066			switch (opcode) {
4067			case TCPOPT_MSS:
4068				if (opsize == TCPOLEN_MSS && th->syn && !estab) {
4069					u16 in_mss = get_unaligned_be16(ptr);
4070					if (in_mss) {
4071						if (opt_rx->user_mss &&
4072						    opt_rx->user_mss < in_mss)
4073							in_mss = opt_rx->user_mss;
4074						opt_rx->mss_clamp = in_mss;
4075					}
4076				}
4077				break;
4078			case TCPOPT_WINDOW:
4079				if (opsize == TCPOLEN_WINDOW && th->syn &&
4080				    !estab && READ_ONCE(net->ipv4.sysctl_tcp_window_scaling)) {
4081					__u8 snd_wscale = *(__u8 *)ptr;
4082					opt_rx->wscale_ok = 1;
4083					if (snd_wscale > TCP_MAX_WSCALE) {
4084						net_info_ratelimited("%s: Illegal window scaling value %d > %u received\n",
4085								     __func__,
4086								     snd_wscale,
4087								     TCP_MAX_WSCALE);
4088						snd_wscale = TCP_MAX_WSCALE;
4089					}
4090					opt_rx->snd_wscale = snd_wscale;
4091				}
4092				break;
4093			case TCPOPT_TIMESTAMP:
4094				if ((opsize == TCPOLEN_TIMESTAMP) &&
4095				    ((estab && opt_rx->tstamp_ok) ||
4096				     (!estab && READ_ONCE(net->ipv4.sysctl_tcp_timestamps)))) {
4097					opt_rx->saw_tstamp = 1;
4098					opt_rx->rcv_tsval = get_unaligned_be32(ptr);
4099					opt_rx->rcv_tsecr = get_unaligned_be32(ptr + 4);
4100				}
4101				break;
4102			case TCPOPT_SACK_PERM:
4103				if (opsize == TCPOLEN_SACK_PERM && th->syn &&
4104				    !estab && READ_ONCE(net->ipv4.sysctl_tcp_sack)) {
4105					opt_rx->sack_ok = TCP_SACK_SEEN;
4106					tcp_sack_reset(opt_rx);
4107				}
4108				break;
4109
4110			case TCPOPT_SACK:
4111				if ((opsize >= (TCPOLEN_SACK_BASE + TCPOLEN_SACK_PERBLOCK)) &&
4112				   !((opsize - TCPOLEN_SACK_BASE) % TCPOLEN_SACK_PERBLOCK) &&
4113				   opt_rx->sack_ok) {
4114					TCP_SKB_CB(skb)->sacked = (ptr - 2) - (unsigned char *)th;
4115				}
4116				break;
4117#ifdef CONFIG_TCP_MD5SIG
4118			case TCPOPT_MD5SIG:
4119				/*
4120				 * The MD5 Hash has already been
4121				 * checked (see tcp_v{4,6}_do_rcv()).
4122				 */
4123				break;
4124#endif
4125			case TCPOPT_FASTOPEN:
4126				tcp_parse_fastopen_option(
4127					opsize - TCPOLEN_FASTOPEN_BASE,
4128					ptr, th->syn, foc, false);
4129				break;
4130
4131			case TCPOPT_EXP:
4132				/* Fast Open option shares code 254 using a
4133				 * 16 bits magic number.
4134				 */
4135				if (opsize >= TCPOLEN_EXP_FASTOPEN_BASE &&
4136				    get_unaligned_be16(ptr) ==
4137				    TCPOPT_FASTOPEN_MAGIC) {
4138					tcp_parse_fastopen_option(opsize -
4139						TCPOLEN_EXP_FASTOPEN_BASE,
4140						ptr + 2, th->syn, foc, true);
4141					break;
4142				}
4143
4144				if (smc_parse_options(th, opt_rx, ptr, opsize))
4145					break;
4146
4147				opt_rx->saw_unknown = 1;
4148				break;
4149
4150			default:
4151				opt_rx->saw_unknown = 1;
4152			}
4153			ptr += opsize-2;
4154			length -= opsize;
4155		}
4156	}
4157}
4158EXPORT_SYMBOL(tcp_parse_options);
4159
4160static bool tcp_parse_aligned_timestamp(struct tcp_sock *tp, const struct tcphdr *th)
4161{
4162	const __be32 *ptr = (const __be32 *)(th + 1);
4163
4164	if (*ptr == htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16)
4165			  | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP)) {
4166		tp->rx_opt.saw_tstamp = 1;
4167		++ptr;
4168		tp->rx_opt.rcv_tsval = ntohl(*ptr);
4169		++ptr;
4170		if (*ptr)
4171			tp->rx_opt.rcv_tsecr = ntohl(*ptr) - tp->tsoffset;
4172		else
4173			tp->rx_opt.rcv_tsecr = 0;
4174		return true;
4175	}
4176	return false;
4177}
4178
4179/* Fast parse options. This hopes to only see timestamps.
4180 * If it is wrong it falls back on tcp_parse_options().
4181 */
4182static bool tcp_fast_parse_options(const struct net *net,
4183				   const struct sk_buff *skb,
4184				   const struct tcphdr *th, struct tcp_sock *tp)
4185{
4186	/* In the spirit of fast parsing, compare doff directly to constant
4187	 * values.  Because equality is used, short doff can be ignored here.
4188	 */
4189	if (th->doff == (sizeof(*th) / 4)) {
4190		tp->rx_opt.saw_tstamp = 0;
4191		return false;
4192	} else if (tp->rx_opt.tstamp_ok &&
4193		   th->doff == ((sizeof(*th) + TCPOLEN_TSTAMP_ALIGNED) / 4)) {
4194		if (tcp_parse_aligned_timestamp(tp, th))
4195			return true;
4196	}
4197
4198	tcp_parse_options(net, skb, &tp->rx_opt, 1, NULL);
4199	if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
4200		tp->rx_opt.rcv_tsecr -= tp->tsoffset;
4201
4202	return true;
4203}
4204
4205#ifdef CONFIG_TCP_MD5SIG
4206/*
4207 * Parse MD5 Signature option
4208 */
4209const u8 *tcp_parse_md5sig_option(const struct tcphdr *th)
4210{
4211	int length = (th->doff << 2) - sizeof(*th);
4212	const u8 *ptr = (const u8 *)(th + 1);
4213
4214	/* If not enough data remaining, we can short cut */
4215	while (length >= TCPOLEN_MD5SIG) {
4216		int opcode = *ptr++;
4217		int opsize;
4218
4219		switch (opcode) {
4220		case TCPOPT_EOL:
4221			return NULL;
4222		case TCPOPT_NOP:
4223			length--;
4224			continue;
4225		default:
4226			opsize = *ptr++;
4227			if (opsize < 2 || opsize > length)
4228				return NULL;
4229			if (opcode == TCPOPT_MD5SIG)
4230				return opsize == TCPOLEN_MD5SIG ? ptr : NULL;
4231		}
4232		ptr += opsize - 2;
4233		length -= opsize;
4234	}
4235	return NULL;
4236}
4237EXPORT_SYMBOL(tcp_parse_md5sig_option);
4238#endif
4239
4240/* Sorry, PAWS as specified is broken wrt. pure-ACKs -DaveM
4241 *
4242 * It is not fatal. If this ACK does _not_ change critical state (seqs, window)
4243 * it can pass through stack. So, the following predicate verifies that
4244 * this segment is not used for anything but congestion avoidance or
4245 * fast retransmit. Moreover, we even are able to eliminate most of such
4246 * second order effects, if we apply some small "replay" window (~RTO)
4247 * to timestamp space.
4248 *
4249 * All these measures still do not guarantee that we reject wrapped ACKs
4250 * on networks with high bandwidth, when sequence space is recycled fastly,
4251 * but it guarantees that such events will be very rare and do not affect
4252 * connection seriously. This doesn't look nice, but alas, PAWS is really
4253 * buggy extension.
4254 *
4255 * [ Later note. Even worse! It is buggy for segments _with_ data. RFC
4256 * states that events when retransmit arrives after original data are rare.
4257 * It is a blatant lie. VJ forgot about fast retransmit! 8)8) It is
4258 * the biggest problem on large power networks even with minor reordering.
4259 * OK, let's give it small replay window. If peer clock is even 1hz, it is safe
4260 * up to bandwidth of 18Gigabit/sec. 8) ]
4261 */
4262
4263static int tcp_disordered_ack(const struct sock *sk, const struct sk_buff *skb)
4264{
4265	const struct tcp_sock *tp = tcp_sk(sk);
4266	const struct tcphdr *th = tcp_hdr(skb);
4267	u32 seq = TCP_SKB_CB(skb)->seq;
4268	u32 ack = TCP_SKB_CB(skb)->ack_seq;
4269
4270	return (/* 1. Pure ACK with correct sequence number. */
4271		(th->ack && seq == TCP_SKB_CB(skb)->end_seq && seq == tp->rcv_nxt) &&
4272
4273		/* 2. ... and duplicate ACK. */
4274		ack == tp->snd_una &&
4275
4276		/* 3. ... and does not update window. */
4277		!tcp_may_update_window(tp, ack, seq, ntohs(th->window) << tp->rx_opt.snd_wscale) &&
4278
4279		/* 4. ... and sits in replay window. */
4280		(s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) <= (inet_csk(sk)->icsk_rto * 1024) / HZ);
4281}
4282
4283static inline bool tcp_paws_discard(const struct sock *sk,
4284				   const struct sk_buff *skb)
4285{
4286	const struct tcp_sock *tp = tcp_sk(sk);
4287
4288	return !tcp_paws_check(&tp->rx_opt, TCP_PAWS_WINDOW) &&
4289	       !tcp_disordered_ack(sk, skb);
4290}
4291
4292/* Check segment sequence number for validity.
4293 *
4294 * Segment controls are considered valid, if the segment
4295 * fits to the window after truncation to the window. Acceptability
4296 * of data (and SYN, FIN, of course) is checked separately.
4297 * See tcp_data_queue(), for example.
4298 *
4299 * Also, controls (RST is main one) are accepted using RCV.WUP instead
4300 * of RCV.NXT. Peer still did not advance his SND.UNA when we
4301 * delayed ACK, so that hisSND.UNA<=ourRCV.WUP.
4302 * (borrowed from freebsd)
4303 */
4304
4305static inline bool tcp_sequence(const struct tcp_sock *tp, u32 seq, u32 end_seq)
4306{
4307	return	!before(end_seq, tp->rcv_wup) &&
4308		!after(seq, tp->rcv_nxt + tcp_receive_window(tp));
4309}
4310
4311/* When we get a reset we do this. */
4312void tcp_reset(struct sock *sk, struct sk_buff *skb)
4313{
4314	trace_tcp_receive_reset(sk);
4315
4316	/* mptcp can't tell us to ignore reset pkts,
4317	 * so just ignore the return value of mptcp_incoming_options().
4318	 */
4319	if (sk_is_mptcp(sk))
4320		mptcp_incoming_options(sk, skb);
4321
4322	/* We want the right error as BSD sees it (and indeed as we do). */
4323	switch (sk->sk_state) {
4324	case TCP_SYN_SENT:
4325		sk->sk_err = ECONNREFUSED;
4326		break;
4327	case TCP_CLOSE_WAIT:
4328		sk->sk_err = EPIPE;
4329		break;
4330	case TCP_CLOSE:
4331		return;
4332	default:
4333		sk->sk_err = ECONNRESET;
4334	}
4335	/* This barrier is coupled with smp_rmb() in tcp_poll() */
4336	smp_wmb();
4337
4338	tcp_write_queue_purge(sk);
4339	tcp_done(sk);
4340
4341	if (!sock_flag(sk, SOCK_DEAD))
4342		sk_error_report(sk);
4343}
4344
4345/*
4346 * 	Process the FIN bit. This now behaves as it is supposed to work
4347 *	and the FIN takes effect when it is validly part of sequence
4348 *	space. Not before when we get holes.
4349 *
4350 *	If we are ESTABLISHED, a received fin moves us to CLOSE-WAIT
4351 *	(and thence onto LAST-ACK and finally, CLOSE, we never enter
4352 *	TIME-WAIT)
4353 *
4354 *	If we are in FINWAIT-1, a received FIN indicates simultaneous
4355 *	close and we go into CLOSING (and later onto TIME-WAIT)
4356 *
4357 *	If we are in FINWAIT-2, a received FIN moves us to TIME-WAIT.
4358 */
4359void tcp_fin(struct sock *sk)
4360{
4361	struct tcp_sock *tp = tcp_sk(sk);
4362
4363	inet_csk_schedule_ack(sk);
4364
4365	sk->sk_shutdown |= RCV_SHUTDOWN;
4366	sock_set_flag(sk, SOCK_DONE);
4367
4368	switch (sk->sk_state) {
4369	case TCP_SYN_RECV:
4370	case TCP_ESTABLISHED:
4371		/* Move to CLOSE_WAIT */
4372		tcp_set_state(sk, TCP_CLOSE_WAIT);
4373		inet_csk_enter_pingpong_mode(sk);
4374		break;
4375
4376	case TCP_CLOSE_WAIT:
4377	case TCP_CLOSING:
4378		/* Received a retransmission of the FIN, do
4379		 * nothing.
4380		 */
4381		break;
4382	case TCP_LAST_ACK:
4383		/* RFC793: Remain in the LAST-ACK state. */
4384		break;
4385
4386	case TCP_FIN_WAIT1:
4387		/* This case occurs when a simultaneous close
4388		 * happens, we must ack the received FIN and
4389		 * enter the CLOSING state.
4390		 */
4391		tcp_send_ack(sk);
4392		tcp_set_state(sk, TCP_CLOSING);
4393		break;
4394	case TCP_FIN_WAIT2:
4395		/* Received a FIN -- send ACK and enter TIME_WAIT. */
4396		tcp_send_ack(sk);
4397		tcp_time_wait(sk, TCP_TIME_WAIT, 0);
4398		break;
4399	default:
4400		/* Only TCP_LISTEN and TCP_CLOSE are left, in these
4401		 * cases we should never reach this piece of code.
4402		 */
4403		pr_err("%s: Impossible, sk->sk_state=%d\n",
4404		       __func__, sk->sk_state);
4405		break;
4406	}
4407
4408	/* It _is_ possible, that we have something out-of-order _after_ FIN.
4409	 * Probably, we should reset in this case. For now drop them.
4410	 */
4411	skb_rbtree_purge(&tp->out_of_order_queue);
4412	if (tcp_is_sack(tp))
4413		tcp_sack_reset(&tp->rx_opt);
 
4414
4415	if (!sock_flag(sk, SOCK_DEAD)) {
4416		sk->sk_state_change(sk);
4417
4418		/* Do not send POLL_HUP for half duplex close. */
4419		if (sk->sk_shutdown == SHUTDOWN_MASK ||
4420		    sk->sk_state == TCP_CLOSE)
4421			sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_HUP);
4422		else
4423			sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_IN);
4424	}
4425}
4426
4427static inline bool tcp_sack_extend(struct tcp_sack_block *sp, u32 seq,
4428				  u32 end_seq)
4429{
4430	if (!after(seq, sp->end_seq) && !after(sp->start_seq, end_seq)) {
4431		if (before(seq, sp->start_seq))
4432			sp->start_seq = seq;
4433		if (after(end_seq, sp->end_seq))
4434			sp->end_seq = end_seq;
4435		return true;
4436	}
4437	return false;
4438}
4439
4440static void tcp_dsack_set(struct sock *sk, u32 seq, u32 end_seq)
4441{
4442	struct tcp_sock *tp = tcp_sk(sk);
4443
4444	if (tcp_is_sack(tp) && READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_dsack)) {
4445		int mib_idx;
4446
4447		if (before(seq, tp->rcv_nxt))
4448			mib_idx = LINUX_MIB_TCPDSACKOLDSENT;
4449		else
4450			mib_idx = LINUX_MIB_TCPDSACKOFOSENT;
4451
4452		NET_INC_STATS(sock_net(sk), mib_idx);
4453
4454		tp->rx_opt.dsack = 1;
4455		tp->duplicate_sack[0].start_seq = seq;
4456		tp->duplicate_sack[0].end_seq = end_seq;
4457	}
4458}
4459
4460static void tcp_dsack_extend(struct sock *sk, u32 seq, u32 end_seq)
4461{
4462	struct tcp_sock *tp = tcp_sk(sk);
4463
4464	if (!tp->rx_opt.dsack)
4465		tcp_dsack_set(sk, seq, end_seq);
4466	else
4467		tcp_sack_extend(tp->duplicate_sack, seq, end_seq);
4468}
4469
4470static void tcp_rcv_spurious_retrans(struct sock *sk, const struct sk_buff *skb)
4471{
4472	/* When the ACK path fails or drops most ACKs, the sender would
4473	 * timeout and spuriously retransmit the same segment repeatedly.
4474	 * The receiver remembers and reflects via DSACKs. Leverage the
4475	 * DSACK state and change the txhash to re-route speculatively.
4476	 */
4477	if (TCP_SKB_CB(skb)->seq == tcp_sk(sk)->duplicate_sack[0].start_seq &&
4478	    sk_rethink_txhash(sk))
4479		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDUPLICATEDATAREHASH);
 
4480}
4481
4482static void tcp_send_dupack(struct sock *sk, const struct sk_buff *skb)
4483{
4484	struct tcp_sock *tp = tcp_sk(sk);
4485
4486	if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
4487	    before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
4488		NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
4489		tcp_enter_quickack_mode(sk, TCP_MAX_QUICKACKS);
4490
4491		if (tcp_is_sack(tp) && READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_dsack)) {
4492			u32 end_seq = TCP_SKB_CB(skb)->end_seq;
4493
4494			tcp_rcv_spurious_retrans(sk, skb);
4495			if (after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))
4496				end_seq = tp->rcv_nxt;
4497			tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, end_seq);
4498		}
4499	}
4500
4501	tcp_send_ack(sk);
4502}
4503
4504/* These routines update the SACK block as out-of-order packets arrive or
4505 * in-order packets close up the sequence space.
4506 */
4507static void tcp_sack_maybe_coalesce(struct tcp_sock *tp)
4508{
4509	int this_sack;
4510	struct tcp_sack_block *sp = &tp->selective_acks[0];
4511	struct tcp_sack_block *swalk = sp + 1;
4512
4513	/* See if the recent change to the first SACK eats into
4514	 * or hits the sequence space of other SACK blocks, if so coalesce.
4515	 */
4516	for (this_sack = 1; this_sack < tp->rx_opt.num_sacks;) {
4517		if (tcp_sack_extend(sp, swalk->start_seq, swalk->end_seq)) {
4518			int i;
4519
4520			/* Zap SWALK, by moving every further SACK up by one slot.
4521			 * Decrease num_sacks.
4522			 */
4523			tp->rx_opt.num_sacks--;
4524			for (i = this_sack; i < tp->rx_opt.num_sacks; i++)
4525				sp[i] = sp[i + 1];
4526			continue;
4527		}
4528		this_sack++;
4529		swalk++;
4530	}
4531}
4532
4533static void tcp_sack_compress_send_ack(struct sock *sk)
4534{
4535	struct tcp_sock *tp = tcp_sk(sk);
4536
4537	if (!tp->compressed_ack)
4538		return;
4539
4540	if (hrtimer_try_to_cancel(&tp->compressed_ack_timer) == 1)
4541		__sock_put(sk);
4542
4543	/* Since we have to send one ack finally,
4544	 * substract one from tp->compressed_ack to keep
4545	 * LINUX_MIB_TCPACKCOMPRESSED accurate.
4546	 */
4547	NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPACKCOMPRESSED,
4548		      tp->compressed_ack - 1);
4549
4550	tp->compressed_ack = 0;
4551	tcp_send_ack(sk);
4552}
4553
4554/* Reasonable amount of sack blocks included in TCP SACK option
4555 * The max is 4, but this becomes 3 if TCP timestamps are there.
4556 * Given that SACK packets might be lost, be conservative and use 2.
4557 */
4558#define TCP_SACK_BLOCKS_EXPECTED 2
4559
4560static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq)
4561{
4562	struct tcp_sock *tp = tcp_sk(sk);
4563	struct tcp_sack_block *sp = &tp->selective_acks[0];
4564	int cur_sacks = tp->rx_opt.num_sacks;
4565	int this_sack;
4566
4567	if (!cur_sacks)
4568		goto new_sack;
4569
4570	for (this_sack = 0; this_sack < cur_sacks; this_sack++, sp++) {
4571		if (tcp_sack_extend(sp, seq, end_seq)) {
4572			if (this_sack >= TCP_SACK_BLOCKS_EXPECTED)
4573				tcp_sack_compress_send_ack(sk);
4574			/* Rotate this_sack to the first one. */
4575			for (; this_sack > 0; this_sack--, sp--)
4576				swap(*sp, *(sp - 1));
4577			if (cur_sacks > 1)
4578				tcp_sack_maybe_coalesce(tp);
4579			return;
4580		}
4581	}
4582
4583	if (this_sack >= TCP_SACK_BLOCKS_EXPECTED)
4584		tcp_sack_compress_send_ack(sk);
4585
4586	/* Could not find an adjacent existing SACK, build a new one,
4587	 * put it at the front, and shift everyone else down.  We
4588	 * always know there is at least one SACK present already here.
4589	 *
4590	 * If the sack array is full, forget about the last one.
4591	 */
4592	if (this_sack >= TCP_NUM_SACKS) {
4593		this_sack--;
4594		tp->rx_opt.num_sacks--;
4595		sp--;
4596	}
4597	for (; this_sack > 0; this_sack--, sp--)
4598		*sp = *(sp - 1);
4599
4600new_sack:
4601	/* Build the new head SACK, and we're done. */
4602	sp->start_seq = seq;
4603	sp->end_seq = end_seq;
4604	tp->rx_opt.num_sacks++;
4605}
4606
4607/* RCV.NXT advances, some SACKs should be eaten. */
4608
4609static void tcp_sack_remove(struct tcp_sock *tp)
4610{
4611	struct tcp_sack_block *sp = &tp->selective_acks[0];
4612	int num_sacks = tp->rx_opt.num_sacks;
4613	int this_sack;
4614
4615	/* Empty ofo queue, hence, all the SACKs are eaten. Clear. */
4616	if (RB_EMPTY_ROOT(&tp->out_of_order_queue)) {
4617		tp->rx_opt.num_sacks = 0;
4618		return;
4619	}
4620
4621	for (this_sack = 0; this_sack < num_sacks;) {
4622		/* Check if the start of the sack is covered by RCV.NXT. */
4623		if (!before(tp->rcv_nxt, sp->start_seq)) {
4624			int i;
4625
4626			/* RCV.NXT must cover all the block! */
4627			WARN_ON(before(tp->rcv_nxt, sp->end_seq));
4628
4629			/* Zap this SACK, by moving forward any other SACKS. */
4630			for (i = this_sack+1; i < num_sacks; i++)
4631				tp->selective_acks[i-1] = tp->selective_acks[i];
4632			num_sacks--;
4633			continue;
4634		}
4635		this_sack++;
4636		sp++;
4637	}
4638	tp->rx_opt.num_sacks = num_sacks;
4639}
4640
4641/**
4642 * tcp_try_coalesce - try to merge skb to prior one
4643 * @sk: socket
4644 * @to: prior buffer
4645 * @from: buffer to add in queue
4646 * @fragstolen: pointer to boolean
4647 *
4648 * Before queueing skb @from after @to, try to merge them
4649 * to reduce overall memory use and queue lengths, if cost is small.
4650 * Packets in ofo or receive queues can stay a long time.
4651 * Better try to coalesce them right now to avoid future collapses.
4652 * Returns true if caller should free @from instead of queueing it
4653 */
4654static bool tcp_try_coalesce(struct sock *sk,
4655			     struct sk_buff *to,
4656			     struct sk_buff *from,
4657			     bool *fragstolen)
4658{
4659	int delta;
4660
4661	*fragstolen = false;
4662
4663	/* Its possible this segment overlaps with prior segment in queue */
4664	if (TCP_SKB_CB(from)->seq != TCP_SKB_CB(to)->end_seq)
4665		return false;
4666
4667	if (!mptcp_skb_can_collapse(to, from))
4668		return false;
4669
4670#ifdef CONFIG_TLS_DEVICE
4671	if (from->decrypted != to->decrypted)
4672		return false;
4673#endif
4674
4675	if (!skb_try_coalesce(to, from, fragstolen, &delta))
4676		return false;
4677
4678	atomic_add(delta, &sk->sk_rmem_alloc);
4679	sk_mem_charge(sk, delta);
4680	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVCOALESCE);
4681	TCP_SKB_CB(to)->end_seq = TCP_SKB_CB(from)->end_seq;
4682	TCP_SKB_CB(to)->ack_seq = TCP_SKB_CB(from)->ack_seq;
4683	TCP_SKB_CB(to)->tcp_flags |= TCP_SKB_CB(from)->tcp_flags;
4684
4685	if (TCP_SKB_CB(from)->has_rxtstamp) {
4686		TCP_SKB_CB(to)->has_rxtstamp = true;
4687		to->tstamp = from->tstamp;
4688		skb_hwtstamps(to)->hwtstamp = skb_hwtstamps(from)->hwtstamp;
4689	}
4690
4691	return true;
4692}
4693
4694static bool tcp_ooo_try_coalesce(struct sock *sk,
4695			     struct sk_buff *to,
4696			     struct sk_buff *from,
4697			     bool *fragstolen)
4698{
4699	bool res = tcp_try_coalesce(sk, to, from, fragstolen);
4700
4701	/* In case tcp_drop_reason() is called later, update to->gso_segs */
4702	if (res) {
4703		u32 gso_segs = max_t(u16, 1, skb_shinfo(to)->gso_segs) +
4704			       max_t(u16, 1, skb_shinfo(from)->gso_segs);
4705
4706		skb_shinfo(to)->gso_segs = min_t(u32, gso_segs, 0xFFFF);
4707	}
4708	return res;
4709}
4710
4711static void tcp_drop_reason(struct sock *sk, struct sk_buff *skb,
4712			    enum skb_drop_reason reason)
4713{
4714	sk_drops_add(sk, skb);
4715	kfree_skb_reason(skb, reason);
4716}
4717
4718/* This one checks to see if we can put data from the
4719 * out_of_order queue into the receive_queue.
4720 */
4721static void tcp_ofo_queue(struct sock *sk)
4722{
4723	struct tcp_sock *tp = tcp_sk(sk);
4724	__u32 dsack_high = tp->rcv_nxt;
4725	bool fin, fragstolen, eaten;
4726	struct sk_buff *skb, *tail;
4727	struct rb_node *p;
4728
4729	p = rb_first(&tp->out_of_order_queue);
4730	while (p) {
4731		skb = rb_to_skb(p);
4732		if (after(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
4733			break;
4734
4735		if (before(TCP_SKB_CB(skb)->seq, dsack_high)) {
4736			__u32 dsack = dsack_high;
4737			if (before(TCP_SKB_CB(skb)->end_seq, dsack_high))
4738				dsack_high = TCP_SKB_CB(skb)->end_seq;
4739			tcp_dsack_extend(sk, TCP_SKB_CB(skb)->seq, dsack);
4740		}
4741		p = rb_next(p);
4742		rb_erase(&skb->rbnode, &tp->out_of_order_queue);
4743
4744		if (unlikely(!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))) {
4745			tcp_drop_reason(sk, skb, SKB_DROP_REASON_TCP_OFO_DROP);
4746			continue;
4747		}
4748
4749		tail = skb_peek_tail(&sk->sk_receive_queue);
4750		eaten = tail && tcp_try_coalesce(sk, tail, skb, &fragstolen);
4751		tcp_rcv_nxt_update(tp, TCP_SKB_CB(skb)->end_seq);
4752		fin = TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN;
4753		if (!eaten)
4754			__skb_queue_tail(&sk->sk_receive_queue, skb);
4755		else
4756			kfree_skb_partial(skb, fragstolen);
4757
4758		if (unlikely(fin)) {
4759			tcp_fin(sk);
4760			/* tcp_fin() purges tp->out_of_order_queue,
4761			 * so we must end this loop right now.
4762			 */
4763			break;
4764		}
4765	}
4766}
4767
4768static bool tcp_prune_ofo_queue(struct sock *sk, const struct sk_buff *in_skb);
4769static int tcp_prune_queue(struct sock *sk, const struct sk_buff *in_skb);
4770
4771static int tcp_try_rmem_schedule(struct sock *sk, struct sk_buff *skb,
4772				 unsigned int size)
4773{
4774	if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
4775	    !sk_rmem_schedule(sk, skb, size)) {
4776
4777		if (tcp_prune_queue(sk, skb) < 0)
4778			return -1;
4779
4780		while (!sk_rmem_schedule(sk, skb, size)) {
4781			if (!tcp_prune_ofo_queue(sk, skb))
4782				return -1;
4783		}
4784	}
4785	return 0;
4786}
4787
4788static void tcp_data_queue_ofo(struct sock *sk, struct sk_buff *skb)
4789{
4790	struct tcp_sock *tp = tcp_sk(sk);
4791	struct rb_node **p, *parent;
4792	struct sk_buff *skb1;
4793	u32 seq, end_seq;
4794	bool fragstolen;
4795
4796	tcp_ecn_check_ce(sk, skb);
4797
4798	if (unlikely(tcp_try_rmem_schedule(sk, skb, skb->truesize))) {
4799		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFODROP);
4800		sk->sk_data_ready(sk);
4801		tcp_drop_reason(sk, skb, SKB_DROP_REASON_PROTO_MEM);
4802		return;
4803	}
4804
4805	/* Disable header prediction. */
4806	tp->pred_flags = 0;
4807	inet_csk_schedule_ack(sk);
4808
4809	tp->rcv_ooopack += max_t(u16, 1, skb_shinfo(skb)->gso_segs);
4810	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFOQUEUE);
4811	seq = TCP_SKB_CB(skb)->seq;
4812	end_seq = TCP_SKB_CB(skb)->end_seq;
4813
4814	p = &tp->out_of_order_queue.rb_node;
4815	if (RB_EMPTY_ROOT(&tp->out_of_order_queue)) {
4816		/* Initial out of order segment, build 1 SACK. */
4817		if (tcp_is_sack(tp)) {
4818			tp->rx_opt.num_sacks = 1;
4819			tp->selective_acks[0].start_seq = seq;
4820			tp->selective_acks[0].end_seq = end_seq;
4821		}
4822		rb_link_node(&skb->rbnode, NULL, p);
4823		rb_insert_color(&skb->rbnode, &tp->out_of_order_queue);
4824		tp->ooo_last_skb = skb;
4825		goto end;
4826	}
4827
4828	/* In the typical case, we are adding an skb to the end of the list.
4829	 * Use of ooo_last_skb avoids the O(Log(N)) rbtree lookup.
4830	 */
4831	if (tcp_ooo_try_coalesce(sk, tp->ooo_last_skb,
4832				 skb, &fragstolen)) {
4833coalesce_done:
4834		/* For non sack flows, do not grow window to force DUPACK
4835		 * and trigger fast retransmit.
4836		 */
4837		if (tcp_is_sack(tp))
4838			tcp_grow_window(sk, skb, true);
4839		kfree_skb_partial(skb, fragstolen);
4840		skb = NULL;
4841		goto add_sack;
4842	}
4843	/* Can avoid an rbtree lookup if we are adding skb after ooo_last_skb */
4844	if (!before(seq, TCP_SKB_CB(tp->ooo_last_skb)->end_seq)) {
4845		parent = &tp->ooo_last_skb->rbnode;
4846		p = &parent->rb_right;
4847		goto insert;
4848	}
4849
4850	/* Find place to insert this segment. Handle overlaps on the way. */
4851	parent = NULL;
4852	while (*p) {
4853		parent = *p;
4854		skb1 = rb_to_skb(parent);
4855		if (before(seq, TCP_SKB_CB(skb1)->seq)) {
4856			p = &parent->rb_left;
4857			continue;
4858		}
4859		if (before(seq, TCP_SKB_CB(skb1)->end_seq)) {
4860			if (!after(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
4861				/* All the bits are present. Drop. */
4862				NET_INC_STATS(sock_net(sk),
4863					      LINUX_MIB_TCPOFOMERGE);
4864				tcp_drop_reason(sk, skb,
4865						SKB_DROP_REASON_TCP_OFOMERGE);
4866				skb = NULL;
4867				tcp_dsack_set(sk, seq, end_seq);
4868				goto add_sack;
4869			}
4870			if (after(seq, TCP_SKB_CB(skb1)->seq)) {
4871				/* Partial overlap. */
4872				tcp_dsack_set(sk, seq, TCP_SKB_CB(skb1)->end_seq);
4873			} else {
4874				/* skb's seq == skb1's seq and skb covers skb1.
4875				 * Replace skb1 with skb.
4876				 */
4877				rb_replace_node(&skb1->rbnode, &skb->rbnode,
4878						&tp->out_of_order_queue);
4879				tcp_dsack_extend(sk,
4880						 TCP_SKB_CB(skb1)->seq,
4881						 TCP_SKB_CB(skb1)->end_seq);
4882				NET_INC_STATS(sock_net(sk),
4883					      LINUX_MIB_TCPOFOMERGE);
4884				tcp_drop_reason(sk, skb1,
4885						SKB_DROP_REASON_TCP_OFOMERGE);
4886				goto merge_right;
4887			}
4888		} else if (tcp_ooo_try_coalesce(sk, skb1,
4889						skb, &fragstolen)) {
4890			goto coalesce_done;
4891		}
4892		p = &parent->rb_right;
4893	}
4894insert:
4895	/* Insert segment into RB tree. */
4896	rb_link_node(&skb->rbnode, parent, p);
4897	rb_insert_color(&skb->rbnode, &tp->out_of_order_queue);
4898
4899merge_right:
4900	/* Remove other segments covered by skb. */
4901	while ((skb1 = skb_rb_next(skb)) != NULL) {
4902		if (!after(end_seq, TCP_SKB_CB(skb1)->seq))
4903			break;
4904		if (before(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
4905			tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
4906					 end_seq);
4907			break;
4908		}
4909		rb_erase(&skb1->rbnode, &tp->out_of_order_queue);
4910		tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
4911				 TCP_SKB_CB(skb1)->end_seq);
4912		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFOMERGE);
4913		tcp_drop_reason(sk, skb1, SKB_DROP_REASON_TCP_OFOMERGE);
4914	}
4915	/* If there is no skb after us, we are the last_skb ! */
4916	if (!skb1)
4917		tp->ooo_last_skb = skb;
4918
4919add_sack:
4920	if (tcp_is_sack(tp))
4921		tcp_sack_new_ofo_skb(sk, seq, end_seq);
4922end:
4923	if (skb) {
4924		/* For non sack flows, do not grow window to force DUPACK
4925		 * and trigger fast retransmit.
4926		 */
4927		if (tcp_is_sack(tp))
4928			tcp_grow_window(sk, skb, false);
4929		skb_condense(skb);
4930		skb_set_owner_r(skb, sk);
4931	}
4932}
4933
4934static int __must_check tcp_queue_rcv(struct sock *sk, struct sk_buff *skb,
4935				      bool *fragstolen)
4936{
4937	int eaten;
4938	struct sk_buff *tail = skb_peek_tail(&sk->sk_receive_queue);
4939
4940	eaten = (tail &&
4941		 tcp_try_coalesce(sk, tail,
4942				  skb, fragstolen)) ? 1 : 0;
4943	tcp_rcv_nxt_update(tcp_sk(sk), TCP_SKB_CB(skb)->end_seq);
4944	if (!eaten) {
4945		__skb_queue_tail(&sk->sk_receive_queue, skb);
4946		skb_set_owner_r(skb, sk);
4947	}
4948	return eaten;
4949}
4950
4951int tcp_send_rcvq(struct sock *sk, struct msghdr *msg, size_t size)
4952{
4953	struct sk_buff *skb;
4954	int err = -ENOMEM;
4955	int data_len = 0;
4956	bool fragstolen;
4957
4958	if (size == 0)
4959		return 0;
4960
4961	if (size > PAGE_SIZE) {
4962		int npages = min_t(size_t, size >> PAGE_SHIFT, MAX_SKB_FRAGS);
4963
4964		data_len = npages << PAGE_SHIFT;
4965		size = data_len + (size & ~PAGE_MASK);
4966	}
4967	skb = alloc_skb_with_frags(size - data_len, data_len,
4968				   PAGE_ALLOC_COSTLY_ORDER,
4969				   &err, sk->sk_allocation);
4970	if (!skb)
4971		goto err;
4972
4973	skb_put(skb, size - data_len);
4974	skb->data_len = data_len;
4975	skb->len = size;
4976
4977	if (tcp_try_rmem_schedule(sk, skb, skb->truesize)) {
4978		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVQDROP);
4979		goto err_free;
4980	}
4981
4982	err = skb_copy_datagram_from_iter(skb, 0, &msg->msg_iter, size);
4983	if (err)
4984		goto err_free;
4985
4986	TCP_SKB_CB(skb)->seq = tcp_sk(sk)->rcv_nxt;
4987	TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq + size;
4988	TCP_SKB_CB(skb)->ack_seq = tcp_sk(sk)->snd_una - 1;
4989
4990	if (tcp_queue_rcv(sk, skb, &fragstolen)) {
4991		WARN_ON_ONCE(fragstolen); /* should not happen */
4992		__kfree_skb(skb);
4993	}
4994	return size;
4995
4996err_free:
4997	kfree_skb(skb);
4998err:
4999	return err;
5000
5001}
5002
5003void tcp_data_ready(struct sock *sk)
5004{
5005	if (tcp_epollin_ready(sk, sk->sk_rcvlowat) || sock_flag(sk, SOCK_DONE))
5006		sk->sk_data_ready(sk);
 
 
 
 
 
 
5007}
5008
5009static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
5010{
5011	struct tcp_sock *tp = tcp_sk(sk);
5012	enum skb_drop_reason reason;
5013	bool fragstolen;
5014	int eaten;
5015
5016	/* If a subflow has been reset, the packet should not continue
5017	 * to be processed, drop the packet.
5018	 */
5019	if (sk_is_mptcp(sk) && !mptcp_incoming_options(sk, skb)) {
5020		__kfree_skb(skb);
5021		return;
5022	}
5023
5024	if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq) {
5025		__kfree_skb(skb);
5026		return;
5027	}
5028	skb_dst_drop(skb);
5029	__skb_pull(skb, tcp_hdr(skb)->doff * 4);
5030
5031	reason = SKB_DROP_REASON_NOT_SPECIFIED;
5032	tp->rx_opt.dsack = 0;
5033
5034	/*  Queue data for delivery to the user.
5035	 *  Packets in sequence go to the receive queue.
5036	 *  Out of sequence packets to the out_of_order_queue.
5037	 */
5038	if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
5039		if (tcp_receive_window(tp) == 0) {
5040			reason = SKB_DROP_REASON_TCP_ZEROWINDOW;
5041			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPZEROWINDOWDROP);
5042			goto out_of_window;
5043		}
5044
5045		/* Ok. In sequence. In window. */
5046queue_and_out:
5047		if (skb_queue_len(&sk->sk_receive_queue) == 0)
5048			sk_forced_mem_schedule(sk, skb->truesize);
5049		else if (tcp_try_rmem_schedule(sk, skb, skb->truesize)) {
5050			reason = SKB_DROP_REASON_PROTO_MEM;
5051			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVQDROP);
5052			sk->sk_data_ready(sk);
5053			goto drop;
5054		}
5055
5056		eaten = tcp_queue_rcv(sk, skb, &fragstolen);
5057		if (skb->len)
5058			tcp_event_data_recv(sk, skb);
5059		if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
5060			tcp_fin(sk);
5061
5062		if (!RB_EMPTY_ROOT(&tp->out_of_order_queue)) {
5063			tcp_ofo_queue(sk);
5064
5065			/* RFC5681. 4.2. SHOULD send immediate ACK, when
5066			 * gap in queue is filled.
5067			 */
5068			if (RB_EMPTY_ROOT(&tp->out_of_order_queue))
5069				inet_csk(sk)->icsk_ack.pending |= ICSK_ACK_NOW;
5070		}
5071
5072		if (tp->rx_opt.num_sacks)
5073			tcp_sack_remove(tp);
5074
5075		tcp_fast_path_check(sk);
5076
5077		if (eaten > 0)
5078			kfree_skb_partial(skb, fragstolen);
5079		if (!sock_flag(sk, SOCK_DEAD))
5080			tcp_data_ready(sk);
5081		return;
5082	}
5083
5084	if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
5085		tcp_rcv_spurious_retrans(sk, skb);
5086		/* A retransmit, 2nd most common case.  Force an immediate ack. */
5087		reason = SKB_DROP_REASON_TCP_OLD_DATA;
5088		NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
5089		tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
5090
5091out_of_window:
5092		tcp_enter_quickack_mode(sk, TCP_MAX_QUICKACKS);
5093		inet_csk_schedule_ack(sk);
5094drop:
5095		tcp_drop_reason(sk, skb, reason);
5096		return;
5097	}
5098
5099	/* Out of window. F.e. zero window probe. */
5100	if (!before(TCP_SKB_CB(skb)->seq,
5101		    tp->rcv_nxt + tcp_receive_window(tp))) {
5102		reason = SKB_DROP_REASON_TCP_OVERWINDOW;
5103		goto out_of_window;
5104	}
5105
5106	if (before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
5107		/* Partial packet, seq < rcv_next < end_seq */
5108		tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, tp->rcv_nxt);
5109
5110		/* If window is closed, drop tail of packet. But after
5111		 * remembering D-SACK for its head made in previous line.
5112		 */
5113		if (!tcp_receive_window(tp)) {
5114			reason = SKB_DROP_REASON_TCP_ZEROWINDOW;
5115			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPZEROWINDOWDROP);
5116			goto out_of_window;
5117		}
5118		goto queue_and_out;
5119	}
5120
5121	tcp_data_queue_ofo(sk, skb);
5122}
5123
5124static struct sk_buff *tcp_skb_next(struct sk_buff *skb, struct sk_buff_head *list)
5125{
5126	if (list)
5127		return !skb_queue_is_last(list, skb) ? skb->next : NULL;
5128
5129	return skb_rb_next(skb);
5130}
5131
5132static struct sk_buff *tcp_collapse_one(struct sock *sk, struct sk_buff *skb,
5133					struct sk_buff_head *list,
5134					struct rb_root *root)
5135{
5136	struct sk_buff *next = tcp_skb_next(skb, list);
5137
5138	if (list)
5139		__skb_unlink(skb, list);
5140	else
5141		rb_erase(&skb->rbnode, root);
5142
5143	__kfree_skb(skb);
5144	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVCOLLAPSED);
5145
5146	return next;
5147}
5148
5149/* Insert skb into rb tree, ordered by TCP_SKB_CB(skb)->seq */
5150void tcp_rbtree_insert(struct rb_root *root, struct sk_buff *skb)
5151{
5152	struct rb_node **p = &root->rb_node;
5153	struct rb_node *parent = NULL;
5154	struct sk_buff *skb1;
5155
5156	while (*p) {
5157		parent = *p;
5158		skb1 = rb_to_skb(parent);
5159		if (before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb1)->seq))
5160			p = &parent->rb_left;
5161		else
5162			p = &parent->rb_right;
5163	}
5164	rb_link_node(&skb->rbnode, parent, p);
5165	rb_insert_color(&skb->rbnode, root);
5166}
5167
5168/* Collapse contiguous sequence of skbs head..tail with
5169 * sequence numbers start..end.
5170 *
5171 * If tail is NULL, this means until the end of the queue.
5172 *
5173 * Segments with FIN/SYN are not collapsed (only because this
5174 * simplifies code)
5175 */
5176static void
5177tcp_collapse(struct sock *sk, struct sk_buff_head *list, struct rb_root *root,
5178	     struct sk_buff *head, struct sk_buff *tail, u32 start, u32 end)
5179{
5180	struct sk_buff *skb = head, *n;
5181	struct sk_buff_head tmp;
5182	bool end_of_skbs;
5183
5184	/* First, check that queue is collapsible and find
5185	 * the point where collapsing can be useful.
5186	 */
5187restart:
5188	for (end_of_skbs = true; skb != NULL && skb != tail; skb = n) {
5189		n = tcp_skb_next(skb, list);
5190
5191		/* No new bits? It is possible on ofo queue. */
5192		if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
5193			skb = tcp_collapse_one(sk, skb, list, root);
5194			if (!skb)
5195				break;
5196			goto restart;
5197		}
5198
5199		/* The first skb to collapse is:
5200		 * - not SYN/FIN and
5201		 * - bloated or contains data before "start" or
5202		 *   overlaps to the next one and mptcp allow collapsing.
5203		 */
5204		if (!(TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)) &&
5205		    (tcp_win_from_space(sk, skb->truesize) > skb->len ||
5206		     before(TCP_SKB_CB(skb)->seq, start))) {
5207			end_of_skbs = false;
5208			break;
5209		}
5210
5211		if (n && n != tail && mptcp_skb_can_collapse(skb, n) &&
5212		    TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(n)->seq) {
5213			end_of_skbs = false;
5214			break;
5215		}
5216
5217		/* Decided to skip this, advance start seq. */
5218		start = TCP_SKB_CB(skb)->end_seq;
5219	}
5220	if (end_of_skbs ||
5221	    (TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)))
5222		return;
5223
5224	__skb_queue_head_init(&tmp);
5225
5226	while (before(start, end)) {
5227		int copy = min_t(int, SKB_MAX_ORDER(0, 0), end - start);
5228		struct sk_buff *nskb;
5229
5230		nskb = alloc_skb(copy, GFP_ATOMIC);
5231		if (!nskb)
5232			break;
5233
5234		memcpy(nskb->cb, skb->cb, sizeof(skb->cb));
5235#ifdef CONFIG_TLS_DEVICE
5236		nskb->decrypted = skb->decrypted;
5237#endif
5238		TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(nskb)->end_seq = start;
5239		if (list)
5240			__skb_queue_before(list, skb, nskb);
5241		else
5242			__skb_queue_tail(&tmp, nskb); /* defer rbtree insertion */
5243		skb_set_owner_r(nskb, sk);
5244		mptcp_skb_ext_move(nskb, skb);
5245
5246		/* Copy data, releasing collapsed skbs. */
5247		while (copy > 0) {
5248			int offset = start - TCP_SKB_CB(skb)->seq;
5249			int size = TCP_SKB_CB(skb)->end_seq - start;
5250
5251			BUG_ON(offset < 0);
5252			if (size > 0) {
5253				size = min(copy, size);
5254				if (skb_copy_bits(skb, offset, skb_put(nskb, size), size))
5255					BUG();
5256				TCP_SKB_CB(nskb)->end_seq += size;
5257				copy -= size;
5258				start += size;
5259			}
5260			if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
5261				skb = tcp_collapse_one(sk, skb, list, root);
5262				if (!skb ||
5263				    skb == tail ||
5264				    !mptcp_skb_can_collapse(nskb, skb) ||
5265				    (TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)))
5266					goto end;
5267#ifdef CONFIG_TLS_DEVICE
5268				if (skb->decrypted != nskb->decrypted)
5269					goto end;
5270#endif
5271			}
5272		}
5273	}
5274end:
5275	skb_queue_walk_safe(&tmp, skb, n)
5276		tcp_rbtree_insert(root, skb);
5277}
5278
5279/* Collapse ofo queue. Algorithm: select contiguous sequence of skbs
5280 * and tcp_collapse() them until all the queue is collapsed.
5281 */
5282static void tcp_collapse_ofo_queue(struct sock *sk)
5283{
5284	struct tcp_sock *tp = tcp_sk(sk);
5285	u32 range_truesize, sum_tiny = 0;
5286	struct sk_buff *skb, *head;
5287	u32 start, end;
5288
5289	skb = skb_rb_first(&tp->out_of_order_queue);
5290new_range:
5291	if (!skb) {
5292		tp->ooo_last_skb = skb_rb_last(&tp->out_of_order_queue);
5293		return;
5294	}
5295	start = TCP_SKB_CB(skb)->seq;
5296	end = TCP_SKB_CB(skb)->end_seq;
5297	range_truesize = skb->truesize;
5298
5299	for (head = skb;;) {
5300		skb = skb_rb_next(skb);
5301
5302		/* Range is terminated when we see a gap or when
5303		 * we are at the queue end.
5304		 */
5305		if (!skb ||
5306		    after(TCP_SKB_CB(skb)->seq, end) ||
5307		    before(TCP_SKB_CB(skb)->end_seq, start)) {
5308			/* Do not attempt collapsing tiny skbs */
5309			if (range_truesize != head->truesize ||
5310			    end - start >= SKB_WITH_OVERHEAD(PAGE_SIZE)) {
5311				tcp_collapse(sk, NULL, &tp->out_of_order_queue,
5312					     head, skb, start, end);
5313			} else {
5314				sum_tiny += range_truesize;
5315				if (sum_tiny > sk->sk_rcvbuf >> 3)
5316					return;
5317			}
5318			goto new_range;
5319		}
5320
5321		range_truesize += skb->truesize;
5322		if (unlikely(before(TCP_SKB_CB(skb)->seq, start)))
5323			start = TCP_SKB_CB(skb)->seq;
5324		if (after(TCP_SKB_CB(skb)->end_seq, end))
5325			end = TCP_SKB_CB(skb)->end_seq;
5326	}
5327}
5328
5329/*
5330 * Clean the out-of-order queue to make room.
5331 * We drop high sequences packets to :
5332 * 1) Let a chance for holes to be filled.
5333 *    This means we do not drop packets from ooo queue if their sequence
5334 *    is before incoming packet sequence.
5335 * 2) not add too big latencies if thousands of packets sit there.
5336 *    (But if application shrinks SO_RCVBUF, we could still end up
5337 *     freeing whole queue here)
5338 * 3) Drop at least 12.5 % of sk_rcvbuf to avoid malicious attacks.
5339 *
5340 * Return true if queue has shrunk.
5341 */
5342static bool tcp_prune_ofo_queue(struct sock *sk, const struct sk_buff *in_skb)
5343{
5344	struct tcp_sock *tp = tcp_sk(sk);
5345	struct rb_node *node, *prev;
5346	bool pruned = false;
5347	int goal;
5348
5349	if (RB_EMPTY_ROOT(&tp->out_of_order_queue))
5350		return false;
5351
 
5352	goal = sk->sk_rcvbuf >> 3;
5353	node = &tp->ooo_last_skb->rbnode;
5354
5355	do {
5356		struct sk_buff *skb = rb_to_skb(node);
5357
5358		/* If incoming skb would land last in ofo queue, stop pruning. */
5359		if (after(TCP_SKB_CB(in_skb)->seq, TCP_SKB_CB(skb)->seq))
5360			break;
5361		pruned = true;
5362		prev = rb_prev(node);
5363		rb_erase(node, &tp->out_of_order_queue);
5364		goal -= skb->truesize;
5365		tcp_drop_reason(sk, skb, SKB_DROP_REASON_TCP_OFO_QUEUE_PRUNE);
5366		tp->ooo_last_skb = rb_to_skb(prev);
5367		if (!prev || goal <= 0) {
 
5368			if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf &&
5369			    !tcp_under_memory_pressure(sk))
5370				break;
5371			goal = sk->sk_rcvbuf >> 3;
5372		}
5373		node = prev;
5374	} while (node);
 
5375
5376	if (pruned) {
5377		NET_INC_STATS(sock_net(sk), LINUX_MIB_OFOPRUNED);
5378		/* Reset SACK state.  A conforming SACK implementation will
5379		 * do the same at a timeout based retransmit.  When a connection
5380		 * is in a sad state like this, we care only about integrity
5381		 * of the connection not performance.
5382		 */
5383		if (tp->rx_opt.sack_ok)
5384			tcp_sack_reset(&tp->rx_opt);
5385	}
5386	return pruned;
5387}
5388
5389/* Reduce allocated memory if we can, trying to get
5390 * the socket within its memory limits again.
5391 *
5392 * Return less than zero if we should start dropping frames
5393 * until the socket owning process reads some of the data
5394 * to stabilize the situation.
5395 */
5396static int tcp_prune_queue(struct sock *sk, const struct sk_buff *in_skb)
5397{
5398	struct tcp_sock *tp = tcp_sk(sk);
5399
5400	NET_INC_STATS(sock_net(sk), LINUX_MIB_PRUNECALLED);
5401
5402	if (atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf)
5403		tcp_clamp_window(sk);
5404	else if (tcp_under_memory_pressure(sk))
5405		tcp_adjust_rcv_ssthresh(sk);
5406
5407	if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
5408		return 0;
5409
5410	tcp_collapse_ofo_queue(sk);
5411	if (!skb_queue_empty(&sk->sk_receive_queue))
5412		tcp_collapse(sk, &sk->sk_receive_queue, NULL,
5413			     skb_peek(&sk->sk_receive_queue),
5414			     NULL,
5415			     tp->copied_seq, tp->rcv_nxt);
 
5416
5417	if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
5418		return 0;
5419
5420	/* Collapsing did not help, destructive actions follow.
5421	 * This must not ever occur. */
5422
5423	tcp_prune_ofo_queue(sk, in_skb);
5424
5425	if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
5426		return 0;
5427
5428	/* If we are really being abused, tell the caller to silently
5429	 * drop receive data on the floor.  It will get retransmitted
5430	 * and hopefully then we'll have sufficient space.
5431	 */
5432	NET_INC_STATS(sock_net(sk), LINUX_MIB_RCVPRUNED);
5433
5434	/* Massive buffer overcommit. */
5435	tp->pred_flags = 0;
5436	return -1;
5437}
5438
5439static bool tcp_should_expand_sndbuf(struct sock *sk)
5440{
5441	const struct tcp_sock *tp = tcp_sk(sk);
5442
5443	/* If the user specified a specific send buffer setting, do
5444	 * not modify it.
5445	 */
5446	if (sk->sk_userlocks & SOCK_SNDBUF_LOCK)
5447		return false;
5448
5449	/* If we are under global TCP memory pressure, do not expand.  */
5450	if (tcp_under_memory_pressure(sk)) {
5451		int unused_mem = sk_unused_reserved_mem(sk);
5452
5453		/* Adjust sndbuf according to reserved mem. But make sure
5454		 * it never goes below SOCK_MIN_SNDBUF.
5455		 * See sk_stream_moderate_sndbuf() for more details.
5456		 */
5457		if (unused_mem > SOCK_MIN_SNDBUF)
5458			WRITE_ONCE(sk->sk_sndbuf, unused_mem);
5459
5460		return false;
5461	}
5462
5463	/* If we are under soft global TCP memory pressure, do not expand.  */
5464	if (sk_memory_allocated(sk) >= sk_prot_mem_limits(sk, 0))
5465		return false;
5466
5467	/* If we filled the congestion window, do not expand.  */
5468	if (tcp_packets_in_flight(tp) >= tcp_snd_cwnd(tp))
5469		return false;
5470
5471	return true;
5472}
5473
 
 
 
 
 
 
5474static void tcp_new_space(struct sock *sk)
5475{
5476	struct tcp_sock *tp = tcp_sk(sk);
5477
5478	if (tcp_should_expand_sndbuf(sk)) {
5479		tcp_sndbuf_expand(sk);
5480		tp->snd_cwnd_stamp = tcp_jiffies32;
5481	}
5482
5483	INDIRECT_CALL_1(sk->sk_write_space, sk_stream_write_space, sk);
5484}
5485
5486/* Caller made space either from:
5487 * 1) Freeing skbs in rtx queues (after tp->snd_una has advanced)
5488 * 2) Sent skbs from output queue (and thus advancing tp->snd_nxt)
5489 *
5490 * We might be able to generate EPOLLOUT to the application if:
5491 * 1) Space consumed in output/rtx queues is below sk->sk_sndbuf/2
5492 * 2) notsent amount (tp->write_seq - tp->snd_nxt) became
5493 *    small enough that tcp_stream_memory_free() decides it
5494 *    is time to generate EPOLLOUT.
5495 */
5496void tcp_check_space(struct sock *sk)
5497{
5498	/* pairs with tcp_poll() */
5499	smp_mb();
5500	if (sk->sk_socket &&
5501	    test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
5502		tcp_new_space(sk);
5503		if (!test_bit(SOCK_NOSPACE, &sk->sk_socket->flags))
5504			tcp_chrono_stop(sk, TCP_CHRONO_SNDBUF_LIMITED);
5505	}
5506}
5507
5508static inline void tcp_data_snd_check(struct sock *sk)
5509{
5510	tcp_push_pending_frames(sk);
5511	tcp_check_space(sk);
5512}
5513
5514/*
5515 * Check if sending an ack is needed.
5516 */
5517static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible)
5518{
5519	struct tcp_sock *tp = tcp_sk(sk);
5520	unsigned long rtt, delay;
5521
5522	    /* More than one full frame received... */
5523	if (((tp->rcv_nxt - tp->rcv_wup) > inet_csk(sk)->icsk_ack.rcv_mss &&
5524	     /* ... and right edge of window advances far enough.
5525	      * (tcp_recvmsg() will send ACK otherwise).
5526	      * If application uses SO_RCVLOWAT, we want send ack now if
5527	      * we have not received enough bytes to satisfy the condition.
5528	      */
5529	    (tp->rcv_nxt - tp->copied_seq < sk->sk_rcvlowat ||
5530	     __tcp_select_window(sk) >= tp->rcv_wnd)) ||
5531	    /* We ACK each frame or... */
5532	    tcp_in_quickack_mode(sk) ||
5533	    /* Protocol state mandates a one-time immediate ACK */
5534	    inet_csk(sk)->icsk_ack.pending & ICSK_ACK_NOW) {
5535send_now:
5536		tcp_send_ack(sk);
5537		return;
5538	}
5539
5540	if (!ofo_possible || RB_EMPTY_ROOT(&tp->out_of_order_queue)) {
5541		tcp_send_delayed_ack(sk);
5542		return;
5543	}
5544
5545	if (!tcp_is_sack(tp) ||
5546	    tp->compressed_ack >= READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_comp_sack_nr))
5547		goto send_now;
5548
5549	if (tp->compressed_ack_rcv_nxt != tp->rcv_nxt) {
5550		tp->compressed_ack_rcv_nxt = tp->rcv_nxt;
5551		tp->dup_ack_counter = 0;
5552	}
5553	if (tp->dup_ack_counter < TCP_FASTRETRANS_THRESH) {
5554		tp->dup_ack_counter++;
5555		goto send_now;
5556	}
5557	tp->compressed_ack++;
5558	if (hrtimer_is_queued(&tp->compressed_ack_timer))
5559		return;
5560
5561	/* compress ack timer : 5 % of rtt, but no more than tcp_comp_sack_delay_ns */
5562
5563	rtt = tp->rcv_rtt_est.rtt_us;
5564	if (tp->srtt_us && tp->srtt_us < rtt)
5565		rtt = tp->srtt_us;
5566
5567	delay = min_t(unsigned long,
5568		      READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_comp_sack_delay_ns),
5569		      rtt * (NSEC_PER_USEC >> 3)/20);
5570	sock_hold(sk);
5571	hrtimer_start_range_ns(&tp->compressed_ack_timer, ns_to_ktime(delay),
5572			       READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_comp_sack_slack_ns),
5573			       HRTIMER_MODE_REL_PINNED_SOFT);
5574}
5575
5576static inline void tcp_ack_snd_check(struct sock *sk)
5577{
5578	if (!inet_csk_ack_scheduled(sk)) {
5579		/* We sent a data segment already. */
5580		return;
5581	}
5582	__tcp_ack_snd_check(sk, 1);
5583}
5584
5585/*
5586 *	This routine is only called when we have urgent data
5587 *	signaled. Its the 'slow' part of tcp_urg. It could be
5588 *	moved inline now as tcp_urg is only called from one
5589 *	place. We handle URGent data wrong. We have to - as
5590 *	BSD still doesn't use the correction from RFC961.
5591 *	For 1003.1g we should support a new option TCP_STDURG to permit
5592 *	either form (or just set the sysctl tcp_stdurg).
5593 */
5594
5595static void tcp_check_urg(struct sock *sk, const struct tcphdr *th)
5596{
5597	struct tcp_sock *tp = tcp_sk(sk);
5598	u32 ptr = ntohs(th->urg_ptr);
5599
5600	if (ptr && !READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_stdurg))
5601		ptr--;
5602	ptr += ntohl(th->seq);
5603
5604	/* Ignore urgent data that we've already seen and read. */
5605	if (after(tp->copied_seq, ptr))
5606		return;
5607
5608	/* Do not replay urg ptr.
5609	 *
5610	 * NOTE: interesting situation not covered by specs.
5611	 * Misbehaving sender may send urg ptr, pointing to segment,
5612	 * which we already have in ofo queue. We are not able to fetch
5613	 * such data and will stay in TCP_URG_NOTYET until will be eaten
5614	 * by recvmsg(). Seems, we are not obliged to handle such wicked
5615	 * situations. But it is worth to think about possibility of some
5616	 * DoSes using some hypothetical application level deadlock.
5617	 */
5618	if (before(ptr, tp->rcv_nxt))
5619		return;
5620
5621	/* Do we already have a newer (or duplicate) urgent pointer? */
5622	if (tp->urg_data && !after(ptr, tp->urg_seq))
5623		return;
5624
5625	/* Tell the world about our new urgent pointer. */
5626	sk_send_sigurg(sk);
5627
5628	/* We may be adding urgent data when the last byte read was
5629	 * urgent. To do this requires some care. We cannot just ignore
5630	 * tp->copied_seq since we would read the last urgent byte again
5631	 * as data, nor can we alter copied_seq until this data arrives
5632	 * or we break the semantics of SIOCATMARK (and thus sockatmark())
5633	 *
5634	 * NOTE. Double Dutch. Rendering to plain English: author of comment
5635	 * above did something sort of 	send("A", MSG_OOB); send("B", MSG_OOB);
5636	 * and expect that both A and B disappear from stream. This is _wrong_.
5637	 * Though this happens in BSD with high probability, this is occasional.
5638	 * Any application relying on this is buggy. Note also, that fix "works"
5639	 * only in this artificial test. Insert some normal data between A and B and we will
5640	 * decline of BSD again. Verdict: it is better to remove to trap
5641	 * buggy users.
5642	 */
5643	if (tp->urg_seq == tp->copied_seq && tp->urg_data &&
5644	    !sock_flag(sk, SOCK_URGINLINE) && tp->copied_seq != tp->rcv_nxt) {
5645		struct sk_buff *skb = skb_peek(&sk->sk_receive_queue);
5646		tp->copied_seq++;
5647		if (skb && !before(tp->copied_seq, TCP_SKB_CB(skb)->end_seq)) {
5648			__skb_unlink(skb, &sk->sk_receive_queue);
5649			__kfree_skb(skb);
5650		}
5651	}
5652
5653	WRITE_ONCE(tp->urg_data, TCP_URG_NOTYET);
5654	WRITE_ONCE(tp->urg_seq, ptr);
5655
5656	/* Disable header prediction. */
5657	tp->pred_flags = 0;
5658}
5659
5660/* This is the 'fast' part of urgent handling. */
5661static void tcp_urg(struct sock *sk, struct sk_buff *skb, const struct tcphdr *th)
5662{
5663	struct tcp_sock *tp = tcp_sk(sk);
5664
5665	/* Check if we get a new urgent pointer - normally not. */
5666	if (unlikely(th->urg))
5667		tcp_check_urg(sk, th);
5668
5669	/* Do we wait for any urgent data? - normally not... */
5670	if (unlikely(tp->urg_data == TCP_URG_NOTYET)) {
5671		u32 ptr = tp->urg_seq - ntohl(th->seq) + (th->doff * 4) -
5672			  th->syn;
5673
5674		/* Is the urgent pointer pointing into this packet? */
5675		if (ptr < skb->len) {
5676			u8 tmp;
5677			if (skb_copy_bits(skb, ptr, &tmp, 1))
5678				BUG();
5679			WRITE_ONCE(tp->urg_data, TCP_URG_VALID | tmp);
5680			if (!sock_flag(sk, SOCK_DEAD))
5681				sk->sk_data_ready(sk);
5682		}
5683	}
5684}
5685
5686/* Accept RST for rcv_nxt - 1 after a FIN.
5687 * When tcp connections are abruptly terminated from Mac OSX (via ^C), a
5688 * FIN is sent followed by a RST packet. The RST is sent with the same
5689 * sequence number as the FIN, and thus according to RFC 5961 a challenge
5690 * ACK should be sent. However, Mac OSX rate limits replies to challenge
5691 * ACKs on the closed socket. In addition middleboxes can drop either the
5692 * challenge ACK or a subsequent RST.
5693 */
5694static bool tcp_reset_check(const struct sock *sk, const struct sk_buff *skb)
5695{
5696	struct tcp_sock *tp = tcp_sk(sk);
5697
5698	return unlikely(TCP_SKB_CB(skb)->seq == (tp->rcv_nxt - 1) &&
5699			(1 << sk->sk_state) & (TCPF_CLOSE_WAIT | TCPF_LAST_ACK |
5700					       TCPF_CLOSING));
5701}
5702
5703/* Does PAWS and seqno based validation of an incoming segment, flags will
5704 * play significant role here.
5705 */
5706static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
5707				  const struct tcphdr *th, int syn_inerr)
5708{
5709	struct tcp_sock *tp = tcp_sk(sk);
5710	SKB_DR(reason);
5711
5712	/* RFC1323: H1. Apply PAWS check first. */
5713	if (tcp_fast_parse_options(sock_net(sk), skb, th, tp) &&
5714	    tp->rx_opt.saw_tstamp &&
5715	    tcp_paws_discard(sk, skb)) {
5716		if (!th->rst) {
5717			NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);
5718			if (!tcp_oow_rate_limited(sock_net(sk), skb,
5719						  LINUX_MIB_TCPACKSKIPPEDPAWS,
5720						  &tp->last_oow_ack_time))
5721				tcp_send_dupack(sk, skb);
5722			SKB_DR_SET(reason, TCP_RFC7323_PAWS);
5723			goto discard;
5724		}
5725		/* Reset is accepted even if it did not pass PAWS. */
5726	}
5727
5728	/* Step 1: check sequence number */
5729	if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) {
5730		/* RFC793, page 37: "In all states except SYN-SENT, all reset
5731		 * (RST) segments are validated by checking their SEQ-fields."
5732		 * And page 69: "If an incoming segment is not acceptable,
5733		 * an acknowledgment should be sent in reply (unless the RST
5734		 * bit is set, if so drop the segment and return)".
5735		 */
5736		if (!th->rst) {
5737			if (th->syn)
5738				goto syn_challenge;
5739			if (!tcp_oow_rate_limited(sock_net(sk), skb,
5740						  LINUX_MIB_TCPACKSKIPPEDSEQ,
5741						  &tp->last_oow_ack_time))
5742				tcp_send_dupack(sk, skb);
5743		} else if (tcp_reset_check(sk, skb)) {
5744			goto reset;
5745		}
5746		SKB_DR_SET(reason, TCP_INVALID_SEQUENCE);
5747		goto discard;
5748	}
5749
5750	/* Step 2: check RST bit */
5751	if (th->rst) {
5752		/* RFC 5961 3.2 (extend to match against (RCV.NXT - 1) after a
5753		 * FIN and SACK too if available):
5754		 * If seq num matches RCV.NXT or (RCV.NXT - 1) after a FIN, or
5755		 * the right-most SACK block,
5756		 * then
5757		 *     RESET the connection
5758		 * else
5759		 *     Send a challenge ACK
5760		 */
5761		if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt ||
5762		    tcp_reset_check(sk, skb))
5763			goto reset;
5764
5765		if (tcp_is_sack(tp) && tp->rx_opt.num_sacks > 0) {
5766			struct tcp_sack_block *sp = &tp->selective_acks[0];
5767			int max_sack = sp[0].end_seq;
5768			int this_sack;
5769
5770			for (this_sack = 1; this_sack < tp->rx_opt.num_sacks;
5771			     ++this_sack) {
5772				max_sack = after(sp[this_sack].end_seq,
5773						 max_sack) ?
5774					sp[this_sack].end_seq : max_sack;
5775			}
5776
5777			if (TCP_SKB_CB(skb)->seq == max_sack)
5778				goto reset;
5779		}
5780
5781		/* Disable TFO if RST is out-of-order
5782		 * and no data has been received
5783		 * for current active TFO socket
5784		 */
5785		if (tp->syn_fastopen && !tp->data_segs_in &&
5786		    sk->sk_state == TCP_ESTABLISHED)
5787			tcp_fastopen_active_disable(sk);
5788		tcp_send_challenge_ack(sk);
5789		SKB_DR_SET(reason, TCP_RESET);
 
 
 
5790		goto discard;
5791	}
5792
5793	/* step 3: check security and precedence [ignored] */
5794
5795	/* step 4: Check for a SYN
5796	 * RFC 5961 4.2 : Send a challenge ack
5797	 */
5798	if (th->syn) {
5799syn_challenge:
5800		if (syn_inerr)
5801			TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);
5802		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSYNCHALLENGE);
5803		tcp_send_challenge_ack(sk);
5804		SKB_DR_SET(reason, TCP_INVALID_SYN);
5805		goto discard;
5806	}
5807
5808	bpf_skops_parse_hdr(sk, skb);
5809
5810	return true;
5811
5812discard:
5813	tcp_drop_reason(sk, skb, reason);
5814	return false;
5815
5816reset:
5817	tcp_reset(sk, skb);
5818	__kfree_skb(skb);
5819	return false;
5820}
5821
5822/*
5823 *	TCP receive function for the ESTABLISHED state.
5824 *
5825 *	It is split into a fast path and a slow path. The fast path is
5826 * 	disabled when:
5827 *	- A zero window was announced from us - zero window probing
5828 *        is only handled properly in the slow path.
5829 *	- Out of order segments arrived.
5830 *	- Urgent data is expected.
5831 *	- There is no buffer space left
5832 *	- Unexpected TCP flags/window values/header lengths are received
5833 *	  (detected by checking the TCP header against pred_flags)
5834 *	- Data is sent in both directions. Fast path only supports pure senders
5835 *	  or pure receivers (this means either the sequence number or the ack
5836 *	  value must stay constant)
5837 *	- Unexpected TCP option.
5838 *
5839 *	When these conditions are not satisfied it drops into a standard
5840 *	receive procedure patterned after RFC793 to handle all cases.
5841 *	The first three cases are guaranteed by proper pred_flags setting,
5842 *	the rest is checked inline. Fast processing is turned on in
5843 *	tcp_data_queue when everything is OK.
5844 */
5845void tcp_rcv_established(struct sock *sk, struct sk_buff *skb)
5846{
5847	enum skb_drop_reason reason = SKB_DROP_REASON_NOT_SPECIFIED;
5848	const struct tcphdr *th = (const struct tcphdr *)skb->data;
5849	struct tcp_sock *tp = tcp_sk(sk);
5850	unsigned int len = skb->len;
5851
5852	/* TCP congestion window tracking */
5853	trace_tcp_probe(sk, skb);
5854
5855	tcp_mstamp_refresh(tp);
5856	if (unlikely(!rcu_access_pointer(sk->sk_rx_dst)))
5857		inet_csk(sk)->icsk_af_ops->sk_rx_dst_set(sk, skb);
5858	/*
5859	 *	Header prediction.
5860	 *	The code loosely follows the one in the famous
5861	 *	"30 instruction TCP receive" Van Jacobson mail.
5862	 *
5863	 *	Van's trick is to deposit buffers into socket queue
5864	 *	on a device interrupt, to call tcp_recv function
5865	 *	on the receive process context and checksum and copy
5866	 *	the buffer to user space. smart...
5867	 *
5868	 *	Our current scheme is not silly either but we take the
5869	 *	extra cost of the net_bh soft interrupt processing...
5870	 *	We do checksum and copy also but from device to kernel.
5871	 */
5872
5873	tp->rx_opt.saw_tstamp = 0;
5874
5875	/*	pred_flags is 0xS?10 << 16 + snd_wnd
5876	 *	if header_prediction is to be made
5877	 *	'S' will always be tp->tcp_header_len >> 2
5878	 *	'?' will be 0 for the fast path, otherwise pred_flags is 0 to
5879	 *  turn it off	(when there are holes in the receive
5880	 *	 space for instance)
5881	 *	PSH flag is ignored.
5882	 */
5883
5884	if ((tcp_flag_word(th) & TCP_HP_BITS) == tp->pred_flags &&
5885	    TCP_SKB_CB(skb)->seq == tp->rcv_nxt &&
5886	    !after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt)) {
5887		int tcp_header_len = tp->tcp_header_len;
5888
5889		/* Timestamp header prediction: tcp_header_len
5890		 * is automatically equal to th->doff*4 due to pred_flags
5891		 * match.
5892		 */
5893
5894		/* Check timestamp */
5895		if (tcp_header_len == sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) {
5896			/* No? Slow path! */
5897			if (!tcp_parse_aligned_timestamp(tp, th))
5898				goto slow_path;
5899
5900			/* If PAWS failed, check it more carefully in slow path */
5901			if ((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) < 0)
5902				goto slow_path;
5903
5904			/* DO NOT update ts_recent here, if checksum fails
5905			 * and timestamp was corrupted part, it will result
5906			 * in a hung connection since we will drop all
5907			 * future packets due to the PAWS test.
5908			 */
5909		}
5910
5911		if (len <= tcp_header_len) {
5912			/* Bulk data transfer: sender */
5913			if (len == tcp_header_len) {
5914				/* Predicted packet is in window by definition.
5915				 * seq == rcv_nxt and rcv_wup <= rcv_nxt.
5916				 * Hence, check seq<=rcv_wup reduces to:
5917				 */
5918				if (tcp_header_len ==
5919				    (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
5920				    tp->rcv_nxt == tp->rcv_wup)
5921					tcp_store_ts_recent(tp);
5922
5923				/* We know that such packets are checksummed
5924				 * on entry.
5925				 */
5926				tcp_ack(sk, skb, 0);
5927				__kfree_skb(skb);
5928				tcp_data_snd_check(sk);
5929				/* When receiving pure ack in fast path, update
5930				 * last ts ecr directly instead of calling
5931				 * tcp_rcv_rtt_measure_ts()
5932				 */
5933				tp->rcv_rtt_last_tsecr = tp->rx_opt.rcv_tsecr;
5934				return;
5935			} else { /* Header too small */
5936				reason = SKB_DROP_REASON_PKT_TOO_SMALL;
5937				TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);
5938				goto discard;
5939			}
5940		} else {
5941			int eaten = 0;
5942			bool fragstolen = false;
5943
5944			if (tcp_checksum_complete(skb))
5945				goto csum_error;
5946
5947			if ((int)skb->truesize > sk->sk_forward_alloc)
5948				goto step5;
5949
5950			/* Predicted packet is in window by definition.
5951			 * seq == rcv_nxt and rcv_wup <= rcv_nxt.
5952			 * Hence, check seq<=rcv_wup reduces to:
5953			 */
5954			if (tcp_header_len ==
5955			    (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
5956			    tp->rcv_nxt == tp->rcv_wup)
5957				tcp_store_ts_recent(tp);
5958
5959			tcp_rcv_rtt_measure_ts(sk, skb);
5960
5961			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPHPHITS);
5962
5963			/* Bulk data transfer: receiver */
5964			skb_dst_drop(skb);
5965			__skb_pull(skb, tcp_header_len);
5966			eaten = tcp_queue_rcv(sk, skb, &fragstolen);
5967
5968			tcp_event_data_recv(sk, skb);
5969
5970			if (TCP_SKB_CB(skb)->ack_seq != tp->snd_una) {
5971				/* Well, only one small jumplet in fast path... */
5972				tcp_ack(sk, skb, FLAG_DATA);
5973				tcp_data_snd_check(sk);
5974				if (!inet_csk_ack_scheduled(sk))
5975					goto no_ack;
5976			} else {
5977				tcp_update_wl(tp, TCP_SKB_CB(skb)->seq);
5978			}
5979
5980			__tcp_ack_snd_check(sk, 0);
5981no_ack:
5982			if (eaten)
5983				kfree_skb_partial(skb, fragstolen);
5984			tcp_data_ready(sk);
5985			return;
5986		}
5987	}
5988
5989slow_path:
5990	if (len < (th->doff << 2) || tcp_checksum_complete(skb))
5991		goto csum_error;
5992
5993	if (!th->ack && !th->rst && !th->syn) {
5994		reason = SKB_DROP_REASON_TCP_FLAGS;
5995		goto discard;
5996	}
5997
5998	/*
5999	 *	Standard slow path.
6000	 */
6001
6002	if (!tcp_validate_incoming(sk, skb, th, 1))
6003		return;
6004
6005step5:
6006	reason = tcp_ack(sk, skb, FLAG_SLOWPATH | FLAG_UPDATE_TS_RECENT);
6007	if ((int)reason < 0) {
6008		reason = -reason;
6009		goto discard;
6010	}
6011	tcp_rcv_rtt_measure_ts(sk, skb);
6012
6013	/* Process urgent data. */
6014	tcp_urg(sk, skb, th);
6015
6016	/* step 7: process the segment text */
6017	tcp_data_queue(sk, skb);
6018
6019	tcp_data_snd_check(sk);
6020	tcp_ack_snd_check(sk);
6021	return;
6022
6023csum_error:
6024	reason = SKB_DROP_REASON_TCP_CSUM;
6025	trace_tcp_bad_csum(skb);
6026	TCP_INC_STATS(sock_net(sk), TCP_MIB_CSUMERRORS);
6027	TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);
6028
6029discard:
6030	tcp_drop_reason(sk, skb, reason);
6031}
6032EXPORT_SYMBOL(tcp_rcv_established);
6033
6034void tcp_init_transfer(struct sock *sk, int bpf_op, struct sk_buff *skb)
6035{
6036	struct inet_connection_sock *icsk = inet_csk(sk);
6037	struct tcp_sock *tp = tcp_sk(sk);
6038
6039	tcp_mtup_init(sk);
6040	icsk->icsk_af_ops->rebuild_header(sk);
6041	tcp_init_metrics(sk);
6042
6043	/* Initialize the congestion window to start the transfer.
6044	 * Cut cwnd down to 1 per RFC5681 if SYN or SYN-ACK has been
6045	 * retransmitted. In light of RFC6298 more aggressive 1sec
6046	 * initRTO, we only reset cwnd when more than 1 SYN/SYN-ACK
6047	 * retransmission has occurred.
6048	 */
6049	if (tp->total_retrans > 1 && tp->undo_marker)
6050		tcp_snd_cwnd_set(tp, 1);
6051	else
6052		tcp_snd_cwnd_set(tp, tcp_init_cwnd(tp, __sk_dst_get(sk)));
6053	tp->snd_cwnd_stamp = tcp_jiffies32;
6054
6055	bpf_skops_established(sk, bpf_op, skb);
6056	/* Initialize congestion control unless BPF initialized it already: */
6057	if (!icsk->icsk_ca_initialized)
6058		tcp_init_congestion_control(sk);
6059	tcp_init_buffer_space(sk);
6060}
6061
6062void tcp_finish_connect(struct sock *sk, struct sk_buff *skb)
6063{
6064	struct tcp_sock *tp = tcp_sk(sk);
6065	struct inet_connection_sock *icsk = inet_csk(sk);
6066
6067	tcp_set_state(sk, TCP_ESTABLISHED);
6068	icsk->icsk_ack.lrcvtime = tcp_jiffies32;
6069
6070	if (skb) {
6071		icsk->icsk_af_ops->sk_rx_dst_set(sk, skb);
6072		security_inet_conn_established(sk, skb);
6073		sk_mark_napi_id(sk, skb);
6074	}
6075
6076	tcp_init_transfer(sk, BPF_SOCK_OPS_ACTIVE_ESTABLISHED_CB, skb);
6077
6078	/* Prevent spurious tcp_cwnd_restart() on first data
6079	 * packet.
6080	 */
6081	tp->lsndtime = tcp_jiffies32;
6082
6083	if (sock_flag(sk, SOCK_KEEPOPEN))
6084		inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tp));
6085
6086	if (!tp->rx_opt.snd_wscale)
6087		__tcp_fast_path_on(tp, tp->snd_wnd);
6088	else
6089		tp->pred_flags = 0;
6090}
6091
6092static bool tcp_rcv_fastopen_synack(struct sock *sk, struct sk_buff *synack,
6093				    struct tcp_fastopen_cookie *cookie)
6094{
6095	struct tcp_sock *tp = tcp_sk(sk);
6096	struct sk_buff *data = tp->syn_data ? tcp_rtx_queue_head(sk) : NULL;
6097	u16 mss = tp->rx_opt.mss_clamp, try_exp = 0;
6098	bool syn_drop = false;
6099
6100	if (mss == tp->rx_opt.user_mss) {
6101		struct tcp_options_received opt;
6102
6103		/* Get original SYNACK MSS value if user MSS sets mss_clamp */
6104		tcp_clear_options(&opt);
6105		opt.user_mss = opt.mss_clamp = 0;
6106		tcp_parse_options(sock_net(sk), synack, &opt, 0, NULL);
6107		mss = opt.mss_clamp;
6108	}
6109
6110	if (!tp->syn_fastopen) {
6111		/* Ignore an unsolicited cookie */
6112		cookie->len = -1;
6113	} else if (tp->total_retrans) {
6114		/* SYN timed out and the SYN-ACK neither has a cookie nor
6115		 * acknowledges data. Presumably the remote received only
6116		 * the retransmitted (regular) SYNs: either the original
6117		 * SYN-data or the corresponding SYN-ACK was dropped.
6118		 */
6119		syn_drop = (cookie->len < 0 && data);
6120	} else if (cookie->len < 0 && !tp->syn_data) {
6121		/* We requested a cookie but didn't get it. If we did not use
6122		 * the (old) exp opt format then try so next time (try_exp=1).
6123		 * Otherwise we go back to use the RFC7413 opt (try_exp=2).
6124		 */
6125		try_exp = tp->syn_fastopen_exp ? 2 : 1;
6126	}
6127
6128	tcp_fastopen_cache_set(sk, mss, cookie, syn_drop, try_exp);
6129
6130	if (data) { /* Retransmit unacked data in SYN */
6131		if (tp->total_retrans)
6132			tp->fastopen_client_fail = TFO_SYN_RETRANSMITTED;
6133		else
6134			tp->fastopen_client_fail = TFO_DATA_NOT_ACKED;
6135		skb_rbtree_walk_from(data)
6136			 tcp_mark_skb_lost(sk, data);
6137		tcp_xmit_retransmit_queue(sk);
 
 
6138		NET_INC_STATS(sock_net(sk),
6139				LINUX_MIB_TCPFASTOPENACTIVEFAIL);
6140		return true;
6141	}
6142	tp->syn_data_acked = tp->syn_data;
6143	if (tp->syn_data_acked) {
6144		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFASTOPENACTIVE);
6145		/* SYN-data is counted as two separate packets in tcp_ack() */
6146		if (tp->delivered > 1)
6147			--tp->delivered;
6148	}
6149
6150	tcp_fastopen_add_skb(sk, synack);
6151
6152	return false;
6153}
6154
6155static void smc_check_reset_syn(struct tcp_sock *tp)
6156{
6157#if IS_ENABLED(CONFIG_SMC)
6158	if (static_branch_unlikely(&tcp_have_smc)) {
6159		if (tp->syn_smc && !tp->rx_opt.smc_ok)
6160			tp->syn_smc = 0;
6161	}
6162#endif
6163}
6164
6165static void tcp_try_undo_spurious_syn(struct sock *sk)
6166{
6167	struct tcp_sock *tp = tcp_sk(sk);
6168	u32 syn_stamp;
6169
6170	/* undo_marker is set when SYN or SYNACK times out. The timeout is
6171	 * spurious if the ACK's timestamp option echo value matches the
6172	 * original SYN timestamp.
6173	 */
6174	syn_stamp = tp->retrans_stamp;
6175	if (tp->undo_marker && syn_stamp && tp->rx_opt.saw_tstamp &&
6176	    syn_stamp == tp->rx_opt.rcv_tsecr)
6177		tp->undo_marker = 0;
6178}
6179
6180static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
6181					 const struct tcphdr *th)
6182{
6183	struct inet_connection_sock *icsk = inet_csk(sk);
6184	struct tcp_sock *tp = tcp_sk(sk);
6185	struct tcp_fastopen_cookie foc = { .len = -1 };
6186	int saved_clamp = tp->rx_opt.mss_clamp;
6187	bool fastopen_fail;
6188	SKB_DR(reason);
6189
6190	tcp_parse_options(sock_net(sk), skb, &tp->rx_opt, 0, &foc);
6191	if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
6192		tp->rx_opt.rcv_tsecr -= tp->tsoffset;
6193
6194	if (th->ack) {
6195		/* rfc793:
6196		 * "If the state is SYN-SENT then
6197		 *    first check the ACK bit
6198		 *      If the ACK bit is set
6199		 *	  If SEG.ACK =< ISS, or SEG.ACK > SND.NXT, send
6200		 *        a reset (unless the RST bit is set, if so drop
6201		 *        the segment and return)"
6202		 */
6203		if (!after(TCP_SKB_CB(skb)->ack_seq, tp->snd_una) ||
6204		    after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt)) {
6205			/* Previous FIN/ACK or RST/ACK might be ignored. */
6206			if (icsk->icsk_retransmits == 0)
6207				inet_csk_reset_xmit_timer(sk,
6208						ICSK_TIME_RETRANS,
6209						TCP_TIMEOUT_MIN, TCP_RTO_MAX);
6210			goto reset_and_undo;
6211		}
6212
6213		if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
6214		    !between(tp->rx_opt.rcv_tsecr, tp->retrans_stamp,
6215			     tcp_time_stamp(tp))) {
6216			NET_INC_STATS(sock_net(sk),
6217					LINUX_MIB_PAWSACTIVEREJECTED);
6218			goto reset_and_undo;
6219		}
6220
6221		/* Now ACK is acceptable.
6222		 *
6223		 * "If the RST bit is set
6224		 *    If the ACK was acceptable then signal the user "error:
6225		 *    connection reset", drop the segment, enter CLOSED state,
6226		 *    delete TCB, and return."
6227		 */
6228
6229		if (th->rst) {
6230			tcp_reset(sk, skb);
6231consume:
6232			__kfree_skb(skb);
6233			return 0;
6234		}
6235
6236		/* rfc793:
6237		 *   "fifth, if neither of the SYN or RST bits is set then
6238		 *    drop the segment and return."
6239		 *
6240		 *    See note below!
6241		 *                                        --ANK(990513)
6242		 */
6243		if (!th->syn) {
6244			SKB_DR_SET(reason, TCP_FLAGS);
6245			goto discard_and_undo;
6246		}
6247		/* rfc793:
6248		 *   "If the SYN bit is on ...
6249		 *    are acceptable then ...
6250		 *    (our SYN has been ACKed), change the connection
6251		 *    state to ESTABLISHED..."
6252		 */
6253
6254		tcp_ecn_rcv_synack(tp, th);
6255
6256		tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);
6257		tcp_try_undo_spurious_syn(sk);
6258		tcp_ack(sk, skb, FLAG_SLOWPATH);
6259
6260		/* Ok.. it's good. Set up sequence numbers and
6261		 * move to established.
6262		 */
6263		WRITE_ONCE(tp->rcv_nxt, TCP_SKB_CB(skb)->seq + 1);
6264		tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
6265
6266		/* RFC1323: The window in SYN & SYN/ACK segments is
6267		 * never scaled.
6268		 */
6269		tp->snd_wnd = ntohs(th->window);
6270
6271		if (!tp->rx_opt.wscale_ok) {
6272			tp->rx_opt.snd_wscale = tp->rx_opt.rcv_wscale = 0;
6273			tp->window_clamp = min(tp->window_clamp, 65535U);
6274		}
6275
6276		if (tp->rx_opt.saw_tstamp) {
6277			tp->rx_opt.tstamp_ok	   = 1;
6278			tp->tcp_header_len =
6279				sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
6280			tp->advmss	    -= TCPOLEN_TSTAMP_ALIGNED;
6281			tcp_store_ts_recent(tp);
6282		} else {
6283			tp->tcp_header_len = sizeof(struct tcphdr);
6284		}
6285
6286		tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
6287		tcp_initialize_rcv_mss(sk);
6288
6289		/* Remember, tcp_poll() does not lock socket!
6290		 * Change state from SYN-SENT only after copied_seq
6291		 * is initialized. */
6292		WRITE_ONCE(tp->copied_seq, tp->rcv_nxt);
6293
6294		smc_check_reset_syn(tp);
6295
6296		smp_mb();
6297
6298		tcp_finish_connect(sk, skb);
6299
6300		fastopen_fail = (tp->syn_fastopen || tp->syn_data) &&
6301				tcp_rcv_fastopen_synack(sk, skb, &foc);
6302
6303		if (!sock_flag(sk, SOCK_DEAD)) {
6304			sk->sk_state_change(sk);
6305			sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT);
6306		}
6307		if (fastopen_fail)
6308			return -1;
6309		if (sk->sk_write_pending ||
6310		    icsk->icsk_accept_queue.rskq_defer_accept ||
6311		    inet_csk_in_pingpong_mode(sk)) {
6312			/* Save one ACK. Data will be ready after
6313			 * several ticks, if write_pending is set.
6314			 *
6315			 * It may be deleted, but with this feature tcpdumps
6316			 * look so _wonderfully_ clever, that I was not able
6317			 * to stand against the temptation 8)     --ANK
6318			 */
6319			inet_csk_schedule_ack(sk);
6320			tcp_enter_quickack_mode(sk, TCP_MAX_QUICKACKS);
6321			inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
6322						  TCP_DELACK_MAX, TCP_RTO_MAX);
6323			goto consume;
 
 
 
 
 
6324		}
6325		tcp_send_ack(sk);
6326		return -1;
6327	}
6328
6329	/* No ACK in the segment */
6330
6331	if (th->rst) {
6332		/* rfc793:
6333		 * "If the RST bit is set
6334		 *
6335		 *      Otherwise (no ACK) drop the segment and return."
6336		 */
6337		SKB_DR_SET(reason, TCP_RESET);
6338		goto discard_and_undo;
6339	}
6340
6341	/* PAWS check. */
6342	if (tp->rx_opt.ts_recent_stamp && tp->rx_opt.saw_tstamp &&
6343	    tcp_paws_reject(&tp->rx_opt, 0)) {
6344		SKB_DR_SET(reason, TCP_RFC7323_PAWS);
6345		goto discard_and_undo;
6346	}
6347	if (th->syn) {
6348		/* We see SYN without ACK. It is attempt of
6349		 * simultaneous connect with crossed SYNs.
6350		 * Particularly, it can be connect to self.
6351		 */
6352		tcp_set_state(sk, TCP_SYN_RECV);
6353
6354		if (tp->rx_opt.saw_tstamp) {
6355			tp->rx_opt.tstamp_ok = 1;
6356			tcp_store_ts_recent(tp);
6357			tp->tcp_header_len =
6358				sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
6359		} else {
6360			tp->tcp_header_len = sizeof(struct tcphdr);
6361		}
6362
6363		WRITE_ONCE(tp->rcv_nxt, TCP_SKB_CB(skb)->seq + 1);
6364		WRITE_ONCE(tp->copied_seq, tp->rcv_nxt);
6365		tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
6366
6367		/* RFC1323: The window in SYN & SYN/ACK segments is
6368		 * never scaled.
6369		 */
6370		tp->snd_wnd    = ntohs(th->window);
6371		tp->snd_wl1    = TCP_SKB_CB(skb)->seq;
6372		tp->max_window = tp->snd_wnd;
6373
6374		tcp_ecn_rcv_syn(tp, th);
6375
6376		tcp_mtup_init(sk);
6377		tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
6378		tcp_initialize_rcv_mss(sk);
6379
6380		tcp_send_synack(sk);
6381#if 0
6382		/* Note, we could accept data and URG from this segment.
6383		 * There are no obstacles to make this (except that we must
6384		 * either change tcp_recvmsg() to prevent it from returning data
6385		 * before 3WHS completes per RFC793, or employ TCP Fast Open).
6386		 *
6387		 * However, if we ignore data in ACKless segments sometimes,
6388		 * we have no reasons to accept it sometimes.
6389		 * Also, seems the code doing it in step6 of tcp_rcv_state_process
6390		 * is not flawless. So, discard packet for sanity.
6391		 * Uncomment this return to process the data.
6392		 */
6393		return -1;
6394#else
6395		goto consume;
6396#endif
6397	}
6398	/* "fifth, if neither of the SYN or RST bits is set then
6399	 * drop the segment and return."
6400	 */
6401
6402discard_and_undo:
6403	tcp_clear_options(&tp->rx_opt);
6404	tp->rx_opt.mss_clamp = saved_clamp;
6405	tcp_drop_reason(sk, skb, reason);
6406	return 0;
6407
6408reset_and_undo:
6409	tcp_clear_options(&tp->rx_opt);
6410	tp->rx_opt.mss_clamp = saved_clamp;
6411	return 1;
6412}
6413
6414static void tcp_rcv_synrecv_state_fastopen(struct sock *sk)
6415{
6416	struct request_sock *req;
6417
6418	/* If we are still handling the SYNACK RTO, see if timestamp ECR allows
6419	 * undo. If peer SACKs triggered fast recovery, we can't undo here.
6420	 */
6421	if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss)
6422		tcp_try_undo_loss(sk, false);
6423
6424	/* Reset rtx states to prevent spurious retransmits_timed_out() */
6425	tcp_sk(sk)->retrans_stamp = 0;
6426	inet_csk(sk)->icsk_retransmits = 0;
6427
6428	/* Once we leave TCP_SYN_RECV or TCP_FIN_WAIT_1,
6429	 * we no longer need req so release it.
6430	 */
6431	req = rcu_dereference_protected(tcp_sk(sk)->fastopen_rsk,
6432					lockdep_sock_is_held(sk));
6433	reqsk_fastopen_remove(sk, req, false);
6434
6435	/* Re-arm the timer because data may have been sent out.
6436	 * This is similar to the regular data transmission case
6437	 * when new data has just been ack'ed.
6438	 *
6439	 * (TFO) - we could try to be more aggressive and
6440	 * retransmitting any data sooner based on when they
6441	 * are sent out.
6442	 */
6443	tcp_rearm_rto(sk);
6444}
6445
6446/*
6447 *	This function implements the receiving procedure of RFC 793 for
6448 *	all states except ESTABLISHED and TIME_WAIT.
6449 *	It's called from both tcp_v4_rcv and tcp_v6_rcv and should be
6450 *	address independent.
6451 */
6452
6453int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
6454{
6455	struct tcp_sock *tp = tcp_sk(sk);
6456	struct inet_connection_sock *icsk = inet_csk(sk);
6457	const struct tcphdr *th = tcp_hdr(skb);
6458	struct request_sock *req;
6459	int queued = 0;
6460	bool acceptable;
6461	SKB_DR(reason);
6462
6463	switch (sk->sk_state) {
6464	case TCP_CLOSE:
6465		SKB_DR_SET(reason, TCP_CLOSE);
6466		goto discard;
6467
6468	case TCP_LISTEN:
6469		if (th->ack)
6470			return 1;
6471
6472		if (th->rst) {
6473			SKB_DR_SET(reason, TCP_RESET);
6474			goto discard;
6475		}
6476		if (th->syn) {
6477			if (th->fin) {
6478				SKB_DR_SET(reason, TCP_FLAGS);
6479				goto discard;
6480			}
6481			/* It is possible that we process SYN packets from backlog,
6482			 * so we need to make sure to disable BH and RCU right there.
6483			 */
6484			rcu_read_lock();
6485			local_bh_disable();
6486			acceptable = icsk->icsk_af_ops->conn_request(sk, skb) >= 0;
6487			local_bh_enable();
6488			rcu_read_unlock();
6489
6490			if (!acceptable)
6491				return 1;
6492			consume_skb(skb);
6493			return 0;
6494		}
6495		SKB_DR_SET(reason, TCP_FLAGS);
6496		goto discard;
6497
6498	case TCP_SYN_SENT:
6499		tp->rx_opt.saw_tstamp = 0;
6500		tcp_mstamp_refresh(tp);
6501		queued = tcp_rcv_synsent_state_process(sk, skb, th);
6502		if (queued >= 0)
6503			return queued;
6504
6505		/* Do step6 onward by hand. */
6506		tcp_urg(sk, skb, th);
6507		__kfree_skb(skb);
6508		tcp_data_snd_check(sk);
6509		return 0;
6510	}
6511
6512	tcp_mstamp_refresh(tp);
6513	tp->rx_opt.saw_tstamp = 0;
6514	req = rcu_dereference_protected(tp->fastopen_rsk,
6515					lockdep_sock_is_held(sk));
6516	if (req) {
6517		bool req_stolen;
6518
6519		WARN_ON_ONCE(sk->sk_state != TCP_SYN_RECV &&
6520		    sk->sk_state != TCP_FIN_WAIT1);
6521
6522		if (!tcp_check_req(sk, skb, req, true, &req_stolen)) {
6523			SKB_DR_SET(reason, TCP_FASTOPEN);
6524			goto discard;
6525		}
6526	}
6527
6528	if (!th->ack && !th->rst && !th->syn) {
6529		SKB_DR_SET(reason, TCP_FLAGS);
6530		goto discard;
6531	}
6532	if (!tcp_validate_incoming(sk, skb, th, 0))
6533		return 0;
6534
6535	/* step 5: check the ACK field */
6536	acceptable = tcp_ack(sk, skb, FLAG_SLOWPATH |
6537				      FLAG_UPDATE_TS_RECENT |
6538				      FLAG_NO_CHALLENGE_ACK) > 0;
6539
6540	if (!acceptable) {
6541		if (sk->sk_state == TCP_SYN_RECV)
6542			return 1;	/* send one RST */
6543		tcp_send_challenge_ack(sk);
6544		SKB_DR_SET(reason, TCP_OLD_ACK);
6545		goto discard;
6546	}
6547	switch (sk->sk_state) {
6548	case TCP_SYN_RECV:
6549		tp->delivered++; /* SYN-ACK delivery isn't tracked in tcp_ack */
6550		if (!tp->srtt_us)
6551			tcp_synack_rtt_meas(sk, req);
6552
6553		if (req) {
6554			tcp_rcv_synrecv_state_fastopen(sk);
6555		} else {
6556			tcp_try_undo_spurious_syn(sk);
6557			tp->retrans_stamp = 0;
6558			tcp_init_transfer(sk, BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB,
6559					  skb);
6560			WRITE_ONCE(tp->copied_seq, tp->rcv_nxt);
6561		}
6562		smp_mb();
6563		tcp_set_state(sk, TCP_ESTABLISHED);
6564		sk->sk_state_change(sk);
6565
6566		/* Note, that this wakeup is only for marginal crossed SYN case.
6567		 * Passively open sockets are not waked up, because
6568		 * sk->sk_sleep == NULL and sk->sk_socket == NULL.
6569		 */
6570		if (sk->sk_socket)
6571			sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT);
6572
6573		tp->snd_una = TCP_SKB_CB(skb)->ack_seq;
6574		tp->snd_wnd = ntohs(th->window) << tp->rx_opt.snd_wscale;
6575		tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);
6576
6577		if (tp->rx_opt.tstamp_ok)
6578			tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;
6579
6580		if (!inet_csk(sk)->icsk_ca_ops->cong_control)
6581			tcp_update_pacing_rate(sk);
6582
6583		/* Prevent spurious tcp_cwnd_restart() on first data packet */
6584		tp->lsndtime = tcp_jiffies32;
6585
6586		tcp_initialize_rcv_mss(sk);
6587		tcp_fast_path_on(tp);
6588		break;
6589
6590	case TCP_FIN_WAIT1: {
6591		int tmo;
6592
6593		if (req)
6594			tcp_rcv_synrecv_state_fastopen(sk);
6595
6596		if (tp->snd_una != tp->write_seq)
6597			break;
6598
6599		tcp_set_state(sk, TCP_FIN_WAIT2);
6600		sk->sk_shutdown |= SEND_SHUTDOWN;
6601
6602		sk_dst_confirm(sk);
6603
6604		if (!sock_flag(sk, SOCK_DEAD)) {
6605			/* Wake up lingering close() */
6606			sk->sk_state_change(sk);
6607			break;
6608		}
6609
6610		if (tp->linger2 < 0) {
6611			tcp_done(sk);
6612			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
6613			return 1;
6614		}
6615		if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
6616		    after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) {
6617			/* Receive out of order FIN after close() */
6618			if (tp->syn_fastopen && th->fin)
6619				tcp_fastopen_active_disable(sk);
6620			tcp_done(sk);
6621			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
6622			return 1;
6623		}
6624
6625		tmo = tcp_fin_time(sk);
6626		if (tmo > TCP_TIMEWAIT_LEN) {
6627			inet_csk_reset_keepalive_timer(sk, tmo - TCP_TIMEWAIT_LEN);
6628		} else if (th->fin || sock_owned_by_user(sk)) {
6629			/* Bad case. We could lose such FIN otherwise.
6630			 * It is not a big problem, but it looks confusing
6631			 * and not so rare event. We still can lose it now,
6632			 * if it spins in bh_lock_sock(), but it is really
6633			 * marginal case.
6634			 */
6635			inet_csk_reset_keepalive_timer(sk, tmo);
6636		} else {
6637			tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
6638			goto consume;
6639		}
6640		break;
6641	}
6642
6643	case TCP_CLOSING:
6644		if (tp->snd_una == tp->write_seq) {
6645			tcp_time_wait(sk, TCP_TIME_WAIT, 0);
6646			goto consume;
6647		}
6648		break;
6649
6650	case TCP_LAST_ACK:
6651		if (tp->snd_una == tp->write_seq) {
6652			tcp_update_metrics(sk);
6653			tcp_done(sk);
6654			goto consume;
6655		}
6656		break;
6657	}
6658
6659	/* step 6: check the URG bit */
6660	tcp_urg(sk, skb, th);
6661
6662	/* step 7: process the segment text */
6663	switch (sk->sk_state) {
6664	case TCP_CLOSE_WAIT:
6665	case TCP_CLOSING:
6666	case TCP_LAST_ACK:
6667		if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
6668			/* If a subflow has been reset, the packet should not
6669			 * continue to be processed, drop the packet.
6670			 */
6671			if (sk_is_mptcp(sk) && !mptcp_incoming_options(sk, skb))
6672				goto discard;
6673			break;
6674		}
6675		fallthrough;
6676	case TCP_FIN_WAIT1:
6677	case TCP_FIN_WAIT2:
6678		/* RFC 793 says to queue data in these states,
6679		 * RFC 1122 says we MUST send a reset.
6680		 * BSD 4.4 also does reset.
6681		 */
6682		if (sk->sk_shutdown & RCV_SHUTDOWN) {
6683			if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
6684			    after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) {
6685				NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
6686				tcp_reset(sk, skb);
6687				return 1;
6688			}
6689		}
6690		fallthrough;
6691	case TCP_ESTABLISHED:
6692		tcp_data_queue(sk, skb);
6693		queued = 1;
6694		break;
6695	}
6696
6697	/* tcp_data could move socket to TIME-WAIT */
6698	if (sk->sk_state != TCP_CLOSE) {
6699		tcp_data_snd_check(sk);
6700		tcp_ack_snd_check(sk);
6701	}
6702
6703	if (!queued) {
6704discard:
6705		tcp_drop_reason(sk, skb, reason);
6706	}
6707	return 0;
6708
6709consume:
6710	__kfree_skb(skb);
6711	return 0;
6712}
6713EXPORT_SYMBOL(tcp_rcv_state_process);
6714
6715static inline void pr_drop_req(struct request_sock *req, __u16 port, int family)
6716{
6717	struct inet_request_sock *ireq = inet_rsk(req);
6718
6719	if (family == AF_INET)
6720		net_dbg_ratelimited("drop open request from %pI4/%u\n",
6721				    &ireq->ir_rmt_addr, port);
6722#if IS_ENABLED(CONFIG_IPV6)
6723	else if (family == AF_INET6)
6724		net_dbg_ratelimited("drop open request from %pI6/%u\n",
6725				    &ireq->ir_v6_rmt_addr, port);
6726#endif
6727}
6728
6729/* RFC3168 : 6.1.1 SYN packets must not have ECT/ECN bits set
6730 *
6731 * If we receive a SYN packet with these bits set, it means a
6732 * network is playing bad games with TOS bits. In order to
6733 * avoid possible false congestion notifications, we disable
6734 * TCP ECN negotiation.
6735 *
6736 * Exception: tcp_ca wants ECN. This is required for DCTCP
6737 * congestion control: Linux DCTCP asserts ECT on all packets,
6738 * including SYN, which is most optimal solution; however,
6739 * others, such as FreeBSD do not.
6740 *
6741 * Exception: At least one of the reserved bits of the TCP header (th->res1) is
6742 * set, indicating the use of a future TCP extension (such as AccECN). See
6743 * RFC8311 §4.3 which updates RFC3168 to allow the development of such
6744 * extensions.
6745 */
6746static void tcp_ecn_create_request(struct request_sock *req,
6747				   const struct sk_buff *skb,
6748				   const struct sock *listen_sk,
6749				   const struct dst_entry *dst)
6750{
6751	const struct tcphdr *th = tcp_hdr(skb);
6752	const struct net *net = sock_net(listen_sk);
6753	bool th_ecn = th->ece && th->cwr;
6754	bool ect, ecn_ok;
6755	u32 ecn_ok_dst;
6756
6757	if (!th_ecn)
6758		return;
6759
6760	ect = !INET_ECN_is_not_ect(TCP_SKB_CB(skb)->ip_dsfield);
6761	ecn_ok_dst = dst_feature(dst, DST_FEATURE_ECN_MASK);
6762	ecn_ok = READ_ONCE(net->ipv4.sysctl_tcp_ecn) || ecn_ok_dst;
6763
6764	if (((!ect || th->res1) && ecn_ok) || tcp_ca_needs_ecn(listen_sk) ||
6765	    (ecn_ok_dst & DST_FEATURE_ECN_CA) ||
6766	    tcp_bpf_ca_needs_ecn((struct sock *)req))
6767		inet_rsk(req)->ecn_ok = 1;
6768}
6769
6770static void tcp_openreq_init(struct request_sock *req,
6771			     const struct tcp_options_received *rx_opt,
6772			     struct sk_buff *skb, const struct sock *sk)
6773{
6774	struct inet_request_sock *ireq = inet_rsk(req);
6775
6776	req->rsk_rcv_wnd = 0;		/* So that tcp_send_synack() knows! */
6777	tcp_rsk(req)->rcv_isn = TCP_SKB_CB(skb)->seq;
6778	tcp_rsk(req)->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
6779	tcp_rsk(req)->snt_synack = 0;
6780	tcp_rsk(req)->last_oow_ack_time = 0;
6781	req->mss = rx_opt->mss_clamp;
6782	req->ts_recent = rx_opt->saw_tstamp ? rx_opt->rcv_tsval : 0;
6783	ireq->tstamp_ok = rx_opt->tstamp_ok;
6784	ireq->sack_ok = rx_opt->sack_ok;
6785	ireq->snd_wscale = rx_opt->snd_wscale;
6786	ireq->wscale_ok = rx_opt->wscale_ok;
6787	ireq->acked = 0;
6788	ireq->ecn_ok = 0;
6789	ireq->ir_rmt_port = tcp_hdr(skb)->source;
6790	ireq->ir_num = ntohs(tcp_hdr(skb)->dest);
6791	ireq->ir_mark = inet_request_mark(sk, skb);
6792#if IS_ENABLED(CONFIG_SMC)
6793	ireq->smc_ok = rx_opt->smc_ok && !(tcp_sk(sk)->smc_hs_congested &&
6794			tcp_sk(sk)->smc_hs_congested(sk));
6795#endif
6796}
6797
6798struct request_sock *inet_reqsk_alloc(const struct request_sock_ops *ops,
6799				      struct sock *sk_listener,
6800				      bool attach_listener)
6801{
6802	struct request_sock *req = reqsk_alloc(ops, sk_listener,
6803					       attach_listener);
6804
6805	if (req) {
6806		struct inet_request_sock *ireq = inet_rsk(req);
6807
6808		ireq->ireq_opt = NULL;
6809#if IS_ENABLED(CONFIG_IPV6)
6810		ireq->pktopts = NULL;
6811#endif
6812		atomic64_set(&ireq->ir_cookie, 0);
6813		ireq->ireq_state = TCP_NEW_SYN_RECV;
6814		write_pnet(&ireq->ireq_net, sock_net(sk_listener));
6815		ireq->ireq_family = sk_listener->sk_family;
6816		req->timeout = TCP_TIMEOUT_INIT;
6817	}
6818
6819	return req;
6820}
6821EXPORT_SYMBOL(inet_reqsk_alloc);
6822
6823/*
6824 * Return true if a syncookie should be sent
6825 */
6826static bool tcp_syn_flood_action(const struct sock *sk, const char *proto)
6827{
6828	struct request_sock_queue *queue = &inet_csk(sk)->icsk_accept_queue;
6829	const char *msg = "Dropping request";
6830	struct net *net = sock_net(sk);
6831	bool want_cookie = false;
6832	u8 syncookies;
6833
6834	syncookies = READ_ONCE(net->ipv4.sysctl_tcp_syncookies);
6835
6836#ifdef CONFIG_SYN_COOKIES
6837	if (syncookies) {
6838		msg = "Sending cookies";
6839		want_cookie = true;
6840		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPREQQFULLDOCOOKIES);
6841	} else
6842#endif
6843		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPREQQFULLDROP);
6844
6845	if (!READ_ONCE(queue->synflood_warned) && syncookies != 2 &&
6846	    xchg(&queue->synflood_warned, 1) == 0) {
6847		if (IS_ENABLED(CONFIG_IPV6) && sk->sk_family == AF_INET6) {
6848			net_info_ratelimited("%s: Possible SYN flooding on port [%pI6c]:%u. %s.\n",
6849					proto, inet6_rcv_saddr(sk),
6850					sk->sk_num, msg);
6851		} else {
6852			net_info_ratelimited("%s: Possible SYN flooding on port %pI4:%u. %s.\n",
6853					proto, &sk->sk_rcv_saddr,
6854					sk->sk_num, msg);
6855		}
6856	}
6857
6858	return want_cookie;
6859}
6860
6861static void tcp_reqsk_record_syn(const struct sock *sk,
6862				 struct request_sock *req,
6863				 const struct sk_buff *skb)
6864{
6865	if (tcp_sk(sk)->save_syn) {
6866		u32 len = skb_network_header_len(skb) + tcp_hdrlen(skb);
6867		struct saved_syn *saved_syn;
6868		u32 mac_hdrlen;
6869		void *base;
6870
6871		if (tcp_sk(sk)->save_syn == 2) {  /* Save full header. */
6872			base = skb_mac_header(skb);
6873			mac_hdrlen = skb_mac_header_len(skb);
6874			len += mac_hdrlen;
6875		} else {
6876			base = skb_network_header(skb);
6877			mac_hdrlen = 0;
6878		}
6879
6880		saved_syn = kmalloc(struct_size(saved_syn, data, len),
6881				    GFP_ATOMIC);
6882		if (saved_syn) {
6883			saved_syn->mac_hdrlen = mac_hdrlen;
6884			saved_syn->network_hdrlen = skb_network_header_len(skb);
6885			saved_syn->tcp_hdrlen = tcp_hdrlen(skb);
6886			memcpy(saved_syn->data, base, len);
6887			req->saved_syn = saved_syn;
6888		}
6889	}
6890}
6891
6892/* If a SYN cookie is required and supported, returns a clamped MSS value to be
6893 * used for SYN cookie generation.
6894 */
6895u16 tcp_get_syncookie_mss(struct request_sock_ops *rsk_ops,
6896			  const struct tcp_request_sock_ops *af_ops,
6897			  struct sock *sk, struct tcphdr *th)
6898{
6899	struct tcp_sock *tp = tcp_sk(sk);
6900	u16 mss;
6901
6902	if (READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_syncookies) != 2 &&
6903	    !inet_csk_reqsk_queue_is_full(sk))
6904		return 0;
6905
6906	if (!tcp_syn_flood_action(sk, rsk_ops->slab_name))
6907		return 0;
6908
6909	if (sk_acceptq_is_full(sk)) {
6910		NET_INC_STATS(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS);
6911		return 0;
6912	}
6913
6914	mss = tcp_parse_mss_option(th, tp->rx_opt.user_mss);
6915	if (!mss)
6916		mss = af_ops->mss_clamp;
6917
6918	return mss;
6919}
6920EXPORT_SYMBOL_GPL(tcp_get_syncookie_mss);
6921
6922int tcp_conn_request(struct request_sock_ops *rsk_ops,
6923		     const struct tcp_request_sock_ops *af_ops,
6924		     struct sock *sk, struct sk_buff *skb)
6925{
6926	struct tcp_fastopen_cookie foc = { .len = -1 };
6927	__u32 isn = TCP_SKB_CB(skb)->tcp_tw_isn;
6928	struct tcp_options_received tmp_opt;
6929	struct tcp_sock *tp = tcp_sk(sk);
6930	struct net *net = sock_net(sk);
6931	struct sock *fastopen_sk = NULL;
6932	struct request_sock *req;
6933	bool want_cookie = false;
6934	struct dst_entry *dst;
6935	struct flowi fl;
6936	u8 syncookies;
6937
6938	syncookies = READ_ONCE(net->ipv4.sysctl_tcp_syncookies);
6939
6940	/* TW buckets are converted to open requests without
6941	 * limitations, they conserve resources and peer is
6942	 * evidently real one.
6943	 */
6944	if ((syncookies == 2 || inet_csk_reqsk_queue_is_full(sk)) && !isn) {
 
6945		want_cookie = tcp_syn_flood_action(sk, rsk_ops->slab_name);
6946		if (!want_cookie)
6947			goto drop;
6948	}
6949
6950	if (sk_acceptq_is_full(sk)) {
6951		NET_INC_STATS(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS);
6952		goto drop;
6953	}
6954
6955	req = inet_reqsk_alloc(rsk_ops, sk, !want_cookie);
6956	if (!req)
6957		goto drop;
6958
6959	req->syncookie = want_cookie;
6960	tcp_rsk(req)->af_specific = af_ops;
6961	tcp_rsk(req)->ts_off = 0;
6962#if IS_ENABLED(CONFIG_MPTCP)
6963	tcp_rsk(req)->is_mptcp = 0;
6964#endif
6965
6966	tcp_clear_options(&tmp_opt);
6967	tmp_opt.mss_clamp = af_ops->mss_clamp;
6968	tmp_opt.user_mss  = tp->rx_opt.user_mss;
6969	tcp_parse_options(sock_net(sk), skb, &tmp_opt, 0,
6970			  want_cookie ? NULL : &foc);
6971
6972	if (want_cookie && !tmp_opt.saw_tstamp)
6973		tcp_clear_options(&tmp_opt);
6974
6975	if (IS_ENABLED(CONFIG_SMC) && want_cookie)
6976		tmp_opt.smc_ok = 0;
6977
6978	tmp_opt.tstamp_ok = tmp_opt.saw_tstamp;
6979	tcp_openreq_init(req, &tmp_opt, skb, sk);
6980	inet_rsk(req)->no_srccheck = inet_sk(sk)->transparent;
6981
6982	/* Note: tcp_v6_init_req() might override ir_iif for link locals */
6983	inet_rsk(req)->ir_iif = inet_request_bound_dev_if(sk, skb);
6984
6985	dst = af_ops->route_req(sk, skb, &fl, req);
6986	if (!dst)
 
6987		goto drop_and_free;
6988
6989	if (tmp_opt.tstamp_ok)
6990		tcp_rsk(req)->ts_off = af_ops->init_ts_off(net, skb);
6991
6992	if (!want_cookie && !isn) {
6993		int max_syn_backlog = READ_ONCE(net->ipv4.sysctl_max_syn_backlog);
 
6994
 
6995		/* Kill the following clause, if you dislike this way. */
6996		if (!syncookies &&
6997		    (max_syn_backlog - inet_csk_reqsk_queue_len(sk) <
6998		     (max_syn_backlog >> 2)) &&
6999		    !tcp_peer_is_proven(req, dst)) {
7000			/* Without syncookies last quarter of
7001			 * backlog is filled with destinations,
7002			 * proven to be alive.
7003			 * It means that we continue to communicate
7004			 * to destinations, already remembered
7005			 * to the moment of synflood.
7006			 */
7007			pr_drop_req(req, ntohs(tcp_hdr(skb)->source),
7008				    rsk_ops->family);
7009			goto drop_and_release;
7010		}
7011
7012		isn = af_ops->init_seq(skb);
7013	}
7014
7015	tcp_ecn_create_request(req, skb, sk, dst);
7016
7017	if (want_cookie) {
7018		isn = cookie_init_sequence(af_ops, sk, skb, &req->mss);
7019		if (!tmp_opt.tstamp_ok)
7020			inet_rsk(req)->ecn_ok = 0;
7021	}
7022
7023	tcp_rsk(req)->snt_isn = isn;
7024	tcp_rsk(req)->txhash = net_tx_rndhash();
7025	tcp_rsk(req)->syn_tos = TCP_SKB_CB(skb)->ip_dsfield;
7026	tcp_openreq_init_rwin(req, sk, dst);
7027	sk_rx_queue_set(req_to_sk(req), skb);
7028	if (!want_cookie) {
7029		tcp_reqsk_record_syn(sk, req, skb);
7030		fastopen_sk = tcp_try_fastopen(sk, skb, req, &foc, dst);
7031	}
7032	if (fastopen_sk) {
7033		af_ops->send_synack(fastopen_sk, dst, &fl, req,
7034				    &foc, TCP_SYNACK_FASTOPEN, skb);
7035		/* Add the child socket directly into the accept queue */
7036		if (!inet_csk_reqsk_queue_add(sk, req, fastopen_sk)) {
7037			reqsk_fastopen_remove(fastopen_sk, req, false);
7038			bh_unlock_sock(fastopen_sk);
7039			sock_put(fastopen_sk);
7040			goto drop_and_free;
7041		}
7042		sk->sk_data_ready(sk);
7043		bh_unlock_sock(fastopen_sk);
7044		sock_put(fastopen_sk);
7045	} else {
7046		tcp_rsk(req)->tfo_listener = false;
7047		if (!want_cookie) {
7048			req->timeout = tcp_timeout_init((struct sock *)req);
7049			inet_csk_reqsk_queue_hash_add(sk, req, req->timeout);
7050		}
7051		af_ops->send_synack(sk, dst, &fl, req, &foc,
7052				    !want_cookie ? TCP_SYNACK_NORMAL :
7053						   TCP_SYNACK_COOKIE,
7054				    skb);
7055		if (want_cookie) {
7056			reqsk_free(req);
7057			return 0;
7058		}
7059	}
7060	reqsk_put(req);
7061	return 0;
7062
7063drop_and_release:
7064	dst_release(dst);
7065drop_and_free:
7066	__reqsk_free(req);
7067drop:
7068	tcp_listendrop(sk);
7069	return 0;
7070}
7071EXPORT_SYMBOL(tcp_conn_request);