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
  83int sysctl_tcp_max_orphans __read_mostly = NR_FILE;
  84
  85#define FLAG_DATA		0x01 /* Incoming frame contained data.		*/
  86#define FLAG_WIN_UPDATE		0x02 /* Incoming ACK was a window update.	*/
  87#define FLAG_DATA_ACKED		0x04 /* This ACK acknowledged new data.		*/
  88#define FLAG_RETRANS_DATA_ACKED	0x08 /* "" "" some of which was retransmitted.	*/
  89#define FLAG_SYN_ACKED		0x10 /* This ACK acknowledged SYN.		*/
  90#define FLAG_DATA_SACKED	0x20 /* New SACK.				*/
  91#define FLAG_ECE		0x40 /* ECE in this ACK				*/
  92#define FLAG_LOST_RETRANS	0x80 /* This ACK marks some retransmission lost */
  93#define FLAG_SLOWPATH		0x100 /* Do not skip RFC checks for window update.*/
  94#define FLAG_ORIG_SACK_ACKED	0x200 /* Never retransmitted data are (s)acked	*/
  95#define FLAG_SND_UNA_ADVANCED	0x400 /* Snd_una was changed (!= FLAG_DATA_ACKED) */
  96#define FLAG_DSACKING_ACK	0x800 /* SACK blocks contained D-SACK info */
  97#define FLAG_SET_XMIT_TIMER	0x1000 /* Set TLP or RTO timer */
  98#define FLAG_SACK_RENEGING	0x2000 /* snd_una advanced to a sacked seq */
  99#define FLAG_UPDATE_TS_RECENT	0x4000 /* tcp_replace_ts_recent() */
 100#define FLAG_NO_CHALLENGE_ACK	0x8000 /* do not call tcp_send_challenge_ack()	*/
 101#define FLAG_ACK_MAYBE_DELAYED	0x10000 /* Likely a delayed ACK */
 102
 103#define FLAG_ACKED		(FLAG_DATA_ACKED|FLAG_SYN_ACKED)
 104#define FLAG_NOT_DUP		(FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED)
 105#define FLAG_CA_ALERT		(FLAG_DATA_SACKED|FLAG_ECE|FLAG_DSACKING_ACK)
 106#define FLAG_FORWARD_PROGRESS	(FLAG_ACKED|FLAG_DATA_SACKED)
 107
 108#define TCP_REMNANT (TCP_FLAG_FIN|TCP_FLAG_URG|TCP_FLAG_SYN|TCP_FLAG_PSH)
 109#define TCP_HP_BITS (~(TCP_RESERVED_BITS|TCP_FLAG_PSH))
 110
 111#define REXMIT_NONE	0 /* no loss recovery to do */
 112#define REXMIT_LOST	1 /* retransmit packets marked lost */
 113#define REXMIT_NEW	2 /* FRTO-style transmit of unsent/new packets */
 114
 115#if IS_ENABLED(CONFIG_TLS_DEVICE)
 116static DEFINE_STATIC_KEY_DEFERRED_FALSE(clean_acked_data_enabled, HZ);
 117
 118void clean_acked_data_enable(struct inet_connection_sock *icsk,
 119			     void (*cad)(struct sock *sk, u32 ack_seq))
 120{
 121	icsk->icsk_clean_acked = cad;
 122	static_branch_deferred_inc(&clean_acked_data_enabled);
 123}
 124EXPORT_SYMBOL_GPL(clean_acked_data_enable);
 125
 126void clean_acked_data_disable(struct inet_connection_sock *icsk)
 127{
 128	static_branch_slow_dec_deferred(&clean_acked_data_enabled);
 129	icsk->icsk_clean_acked = NULL;
 130}
 131EXPORT_SYMBOL_GPL(clean_acked_data_disable);
 132
 133void clean_acked_data_flush(void)
 134{
 135	static_key_deferred_flush(&clean_acked_data_enabled);
 136}
 137EXPORT_SYMBOL_GPL(clean_acked_data_flush);
 138#endif
 139
 140static void tcp_gro_dev_warn(struct sock *sk, const struct sk_buff *skb,
 141			     unsigned int len)
 142{
 143	static bool __once __read_mostly;
 144
 145	if (!__once) {
 146		struct net_device *dev;
 147
 148		__once = true;
 149
 150		rcu_read_lock();
 151		dev = dev_get_by_index_rcu(sock_net(sk), skb->skb_iif);
 152		if (!dev || len >= dev->mtu)
 153			pr_warn("%s: Driver has suspect GRO implementation, TCP performance may be compromised.\n",
 154				dev ? dev->name : "Unknown driver");
 155		rcu_read_unlock();
 156	}
 157}
 158
 159/* Adapt the MSS value used to make delayed ack decision to the
 160 * real world.
 161 */
 162static void tcp_measure_rcv_mss(struct sock *sk, const struct sk_buff *skb)
 163{
 164	struct inet_connection_sock *icsk = inet_csk(sk);
 165	const unsigned int lss = icsk->icsk_ack.last_seg_size;
 166	unsigned int len;
 167
 168	icsk->icsk_ack.last_seg_size = 0;
 169
 170	/* skb->len may jitter because of SACKs, even if peer
 171	 * sends good full-sized frames.
 172	 */
 173	len = skb_shinfo(skb)->gso_size ? : skb->len;
 174	if (len >= icsk->icsk_ack.rcv_mss) {
 175		icsk->icsk_ack.rcv_mss = min_t(unsigned int, len,
 176					       tcp_sk(sk)->advmss);
 177		/* Account for possibly-removed options */
 178		if (unlikely(len > icsk->icsk_ack.rcv_mss +
 179				   MAX_TCP_OPTION_SPACE))
 180			tcp_gro_dev_warn(sk, skb, len);
 181	} else {
 182		/* Otherwise, we make more careful check taking into account,
 183		 * that SACKs block is variable.
 184		 *
 185		 * "len" is invariant segment length, including TCP header.
 186		 */
 187		len += skb->data - skb_transport_header(skb);
 188		if (len >= TCP_MSS_DEFAULT + sizeof(struct tcphdr) ||
 189		    /* If PSH is not set, packet should be
 190		     * full sized, provided peer TCP is not badly broken.
 191		     * This observation (if it is correct 8)) allows
 192		     * to handle super-low mtu links fairly.
 193		     */
 194		    (len >= TCP_MIN_MSS + sizeof(struct tcphdr) &&
 195		     !(tcp_flag_word(tcp_hdr(skb)) & TCP_REMNANT))) {
 196			/* Subtract also invariant (if peer is RFC compliant),
 197			 * tcp header plus fixed timestamp option length.
 198			 * Resulting "len" is MSS free of SACK jitter.
 199			 */
 200			len -= tcp_sk(sk)->tcp_header_len;
 201			icsk->icsk_ack.last_seg_size = len;
 202			if (len == lss) {
 203				icsk->icsk_ack.rcv_mss = len;
 204				return;
 205			}
 206		}
 207		if (icsk->icsk_ack.pending & ICSK_ACK_PUSHED)
 208			icsk->icsk_ack.pending |= ICSK_ACK_PUSHED2;
 209		icsk->icsk_ack.pending |= ICSK_ACK_PUSHED;
 210	}
 211}
 212
 213static void tcp_incr_quickack(struct sock *sk, unsigned int max_quickacks)
 214{
 215	struct inet_connection_sock *icsk = inet_csk(sk);
 216	unsigned int quickacks = tcp_sk(sk)->rcv_wnd / (2 * icsk->icsk_ack.rcv_mss);
 217
 218	if (quickacks == 0)
 219		quickacks = 2;
 220	quickacks = min(quickacks, max_quickacks);
 221	if (quickacks > icsk->icsk_ack.quick)
 222		icsk->icsk_ack.quick = quickacks;
 223}
 224
 225void tcp_enter_quickack_mode(struct sock *sk, unsigned int max_quickacks)
 226{
 227	struct inet_connection_sock *icsk = inet_csk(sk);
 228
 229	tcp_incr_quickack(sk, max_quickacks);
 230	inet_csk_exit_pingpong_mode(sk);
 231	icsk->icsk_ack.ato = TCP_ATO_MIN;
 232}
 233EXPORT_SYMBOL(tcp_enter_quickack_mode);
 234
 235/* Send ACKs quickly, if "quick" count is not exhausted
 236 * and the session is not interactive.
 237 */
 238
 239static bool tcp_in_quickack_mode(struct sock *sk)
 240{
 241	const struct inet_connection_sock *icsk = inet_csk(sk);
 242	const struct dst_entry *dst = __sk_dst_get(sk);
 243
 244	return (dst && dst_metric(dst, RTAX_QUICKACK)) ||
 245		(icsk->icsk_ack.quick && !inet_csk_in_pingpong_mode(sk));
 246}
 247
 248static void tcp_ecn_queue_cwr(struct tcp_sock *tp)
 249{
 250	if (tp->ecn_flags & TCP_ECN_OK)
 251		tp->ecn_flags |= TCP_ECN_QUEUE_CWR;
 252}
 253
 254static void tcp_ecn_accept_cwr(struct sock *sk, const struct sk_buff *skb)
 255{
 256	if (tcp_hdr(skb)->cwr) {
 257		tcp_sk(sk)->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
 258
 259		/* If the sender is telling us it has entered CWR, then its
 260		 * cwnd may be very low (even just 1 packet), so we should ACK
 261		 * immediately.
 262		 */
 263		inet_csk(sk)->icsk_ack.pending |= ICSK_ACK_NOW;
 264	}
 265}
 266
 267static void tcp_ecn_withdraw_cwr(struct tcp_sock *tp)
 268{
 269	tp->ecn_flags &= ~TCP_ECN_QUEUE_CWR;
 270}
 271
 272static void __tcp_ecn_check_ce(struct sock *sk, const struct sk_buff *skb)
 273{
 274	struct tcp_sock *tp = tcp_sk(sk);
 275
 276	switch (TCP_SKB_CB(skb)->ip_dsfield & INET_ECN_MASK) {
 277	case INET_ECN_NOT_ECT:
 278		/* Funny extension: if ECT is not set on a segment,
 279		 * and we already seen ECT on a previous segment,
 280		 * it is probably a retransmit.
 281		 */
 282		if (tp->ecn_flags & TCP_ECN_SEEN)
 283			tcp_enter_quickack_mode(sk, 2);
 284		break;
 285	case INET_ECN_CE:
 286		if (tcp_ca_needs_ecn(sk))
 287			tcp_ca_event(sk, CA_EVENT_ECN_IS_CE);
 288
 289		if (!(tp->ecn_flags & TCP_ECN_DEMAND_CWR)) {
 290			/* Better not delay acks, sender can have a very low cwnd */
 291			tcp_enter_quickack_mode(sk, 2);
 292			tp->ecn_flags |= TCP_ECN_DEMAND_CWR;
 293		}
 294		tp->ecn_flags |= TCP_ECN_SEEN;
 295		break;
 296	default:
 297		if (tcp_ca_needs_ecn(sk))
 298			tcp_ca_event(sk, CA_EVENT_ECN_NO_CE);
 299		tp->ecn_flags |= TCP_ECN_SEEN;
 300		break;
 301	}
 302}
 303
 304static void tcp_ecn_check_ce(struct sock *sk, const struct sk_buff *skb)
 305{
 306	if (tcp_sk(sk)->ecn_flags & TCP_ECN_OK)
 307		__tcp_ecn_check_ce(sk, skb);
 308}
 309
 310static void tcp_ecn_rcv_synack(struct tcp_sock *tp, const struct tcphdr *th)
 311{
 312	if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || th->cwr))
 313		tp->ecn_flags &= ~TCP_ECN_OK;
 314}
 315
 316static void tcp_ecn_rcv_syn(struct tcp_sock *tp, const struct tcphdr *th)
 317{
 318	if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || !th->cwr))
 319		tp->ecn_flags &= ~TCP_ECN_OK;
 320}
 321
 322static bool tcp_ecn_rcv_ecn_echo(const struct tcp_sock *tp, const struct tcphdr *th)
 323{
 324	if (th->ece && !th->syn && (tp->ecn_flags & TCP_ECN_OK))
 325		return true;
 326	return false;
 327}
 328
 329/* Buffer size and advertised window tuning.
 330 *
 331 * 1. Tuning sk->sk_sndbuf, when connection enters established state.
 332 */
 333
 334static void tcp_sndbuf_expand(struct sock *sk)
 335{
 336	const struct tcp_sock *tp = tcp_sk(sk);
 337	const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;
 338	int sndmem, per_mss;
 339	u32 nr_segs;
 340
 341	/* Worst case is non GSO/TSO : each frame consumes one skb
 342	 * and skb->head is kmalloced using power of two area of memory
 343	 */
 344	per_mss = max_t(u32, tp->rx_opt.mss_clamp, tp->mss_cache) +
 345		  MAX_TCP_HEADER +
 346		  SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
 347
 348	per_mss = roundup_pow_of_two(per_mss) +
 349		  SKB_DATA_ALIGN(sizeof(struct sk_buff));
 350
 351	nr_segs = max_t(u32, TCP_INIT_CWND, tp->snd_cwnd);
 352	nr_segs = max_t(u32, nr_segs, tp->reordering + 1);
 353
 354	/* Fast Recovery (RFC 5681 3.2) :
 355	 * Cubic needs 1.7 factor, rounded to 2 to include
 356	 * extra cushion (application might react slowly to EPOLLOUT)
 357	 */
 358	sndmem = ca_ops->sndbuf_expand ? ca_ops->sndbuf_expand(sk) : 2;
 359	sndmem *= nr_segs * per_mss;
 360
 361	if (sk->sk_sndbuf < sndmem)
 362		WRITE_ONCE(sk->sk_sndbuf,
 363			   min(sndmem, sock_net(sk)->ipv4.sysctl_tcp_wmem[2]));
 364}
 365
 366/* 2. Tuning advertised window (window_clamp, rcv_ssthresh)
 367 *
 368 * All tcp_full_space() is split to two parts: "network" buffer, allocated
 369 * forward and advertised in receiver window (tp->rcv_wnd) and
 370 * "application buffer", required to isolate scheduling/application
 371 * latencies from network.
 372 * window_clamp is maximal advertised window. It can be less than
 373 * tcp_full_space(), in this case tcp_full_space() - window_clamp
 374 * is reserved for "application" buffer. The less window_clamp is
 375 * the smoother our behaviour from viewpoint of network, but the lower
 376 * throughput and the higher sensitivity of the connection to losses. 8)
 377 *
 378 * rcv_ssthresh is more strict window_clamp used at "slow start"
 379 * phase to predict further behaviour of this connection.
 380 * It is used for two goals:
 381 * - to enforce header prediction at sender, even when application
 382 *   requires some significant "application buffer". It is check #1.
 383 * - to prevent pruning of receive queue because of misprediction
 384 *   of receiver window. Check #2.
 385 *
 386 * The scheme does not work when sender sends good segments opening
 387 * window and then starts to feed us spaghetti. But it should work
 388 * in common situations. Otherwise, we have to rely on queue collapsing.
 389 */
 390
 391/* Slow part of check#2. */
 392static int __tcp_grow_window(const struct sock *sk, const struct sk_buff *skb)
 393{
 394	struct tcp_sock *tp = tcp_sk(sk);
 395	/* Optimize this! */
 396	int truesize = tcp_win_from_space(sk, skb->truesize) >> 1;
 397	int window = tcp_win_from_space(sk, sock_net(sk)->ipv4.sysctl_tcp_rmem[2]) >> 1;
 398
 399	while (tp->rcv_ssthresh <= window) {
 400		if (truesize <= skb->len)
 401			return 2 * inet_csk(sk)->icsk_ack.rcv_mss;
 402
 403		truesize >>= 1;
 404		window >>= 1;
 405	}
 406	return 0;
 407}
 408
 409static void tcp_grow_window(struct sock *sk, const struct sk_buff *skb)
 410{
 411	struct tcp_sock *tp = tcp_sk(sk);
 412	int room;
 413
 414	room = min_t(int, tp->window_clamp, tcp_space(sk)) - tp->rcv_ssthresh;
 415
 416	/* Check #1 */
 417	if (room > 0 && !tcp_under_memory_pressure(sk)) {
 
 
 418		int incr;
 419
 420		/* Check #2. Increase window, if skb with such overhead
 421		 * will fit to rcvbuf in future.
 422		 */
 423		if (tcp_win_from_space(sk, skb->truesize) <= skb->len)
 424			incr = 2 * tp->advmss;
 425		else
 426			incr = __tcp_grow_window(sk, skb);
 427
 428		if (incr) {
 429			incr = max_t(int, incr, 2 * skb->len);
 430			tp->rcv_ssthresh += min(room, incr);
 
 431			inet_csk(sk)->icsk_ack.quick |= 1;
 432		}
 433	}
 434}
 435
 436/* 3. Try to fixup all. It is made immediately after connection enters
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 437 *    established state.
 438 */
 439void tcp_init_buffer_space(struct sock *sk)
 440{
 441	int tcp_app_win = sock_net(sk)->ipv4.sysctl_tcp_app_win;
 442	struct tcp_sock *tp = tcp_sk(sk);
 443	int maxwin;
 444
 
 
 445	if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK))
 446		tcp_sndbuf_expand(sk);
 447
 448	tp->rcvq_space.space = min_t(u32, tp->rcv_wnd, TCP_INIT_CWND * tp->advmss);
 449	tcp_mstamp_refresh(tp);
 450	tp->rcvq_space.time = tp->tcp_mstamp;
 451	tp->rcvq_space.seq = tp->copied_seq;
 452
 453	maxwin = tcp_full_space(sk);
 454
 455	if (tp->window_clamp >= maxwin) {
 456		tp->window_clamp = maxwin;
 457
 458		if (tcp_app_win && maxwin > 4 * tp->advmss)
 459			tp->window_clamp = max(maxwin -
 460					       (maxwin >> tcp_app_win),
 461					       4 * tp->advmss);
 462	}
 463
 464	/* Force reservation of one segment. */
 465	if (tcp_app_win &&
 466	    tp->window_clamp > 2 * tp->advmss &&
 467	    tp->window_clamp + tp->advmss > maxwin)
 468		tp->window_clamp = max(2 * tp->advmss, maxwin - tp->advmss);
 469
 470	tp->rcv_ssthresh = min(tp->rcv_ssthresh, tp->window_clamp);
 471	tp->snd_cwnd_stamp = tcp_jiffies32;
 472}
 473
 474/* 4. Recalculate window clamp after socket hit its memory bounds. */
 475static void tcp_clamp_window(struct sock *sk)
 476{
 477	struct tcp_sock *tp = tcp_sk(sk);
 478	struct inet_connection_sock *icsk = inet_csk(sk);
 479	struct net *net = sock_net(sk);
 480
 481	icsk->icsk_ack.quick = 0;
 482
 483	if (sk->sk_rcvbuf < net->ipv4.sysctl_tcp_rmem[2] &&
 484	    !(sk->sk_userlocks & SOCK_RCVBUF_LOCK) &&
 485	    !tcp_under_memory_pressure(sk) &&
 486	    sk_memory_allocated(sk) < sk_prot_mem_limits(sk, 0)) {
 487		WRITE_ONCE(sk->sk_rcvbuf,
 488			   min(atomic_read(&sk->sk_rmem_alloc),
 489			       net->ipv4.sysctl_tcp_rmem[2]));
 490	}
 491	if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf)
 492		tp->rcv_ssthresh = min(tp->window_clamp, 2U * tp->advmss);
 493}
 494
 495/* Initialize RCV_MSS value.
 496 * RCV_MSS is an our guess about MSS used by the peer.
 497 * We haven't any direct information about the MSS.
 498 * It's better to underestimate the RCV_MSS rather than overestimate.
 499 * Overestimations make us ACKing less frequently than needed.
 500 * Underestimations are more easy to detect and fix by tcp_measure_rcv_mss().
 501 */
 502void tcp_initialize_rcv_mss(struct sock *sk)
 503{
 504	const struct tcp_sock *tp = tcp_sk(sk);
 505	unsigned int hint = min_t(unsigned int, tp->advmss, tp->mss_cache);
 506
 507	hint = min(hint, tp->rcv_wnd / 2);
 508	hint = min(hint, TCP_MSS_DEFAULT);
 509	hint = max(hint, TCP_MIN_MSS);
 510
 511	inet_csk(sk)->icsk_ack.rcv_mss = hint;
 512}
 513EXPORT_SYMBOL(tcp_initialize_rcv_mss);
 514
 515/* Receiver "autotuning" code.
 516 *
 517 * The algorithm for RTT estimation w/o timestamps is based on
 518 * Dynamic Right-Sizing (DRS) by Wu Feng and Mike Fisk of LANL.
 519 * <http://public.lanl.gov/radiant/pubs.html#DRS>
 520 *
 521 * More detail on this code can be found at
 522 * <http://staff.psc.edu/jheffner/>,
 523 * though this reference is out of date.  A new paper
 524 * is pending.
 525 */
 526static void tcp_rcv_rtt_update(struct tcp_sock *tp, u32 sample, int win_dep)
 527{
 528	u32 new_sample = tp->rcv_rtt_est.rtt_us;
 529	long m = sample;
 530
 531	if (new_sample != 0) {
 532		/* If we sample in larger samples in the non-timestamp
 533		 * case, we could grossly overestimate the RTT especially
 534		 * with chatty applications or bulk transfer apps which
 535		 * are stalled on filesystem I/O.
 536		 *
 537		 * Also, since we are only going for a minimum in the
 538		 * non-timestamp case, we do not smooth things out
 539		 * else with timestamps disabled convergence takes too
 540		 * long.
 541		 */
 542		if (!win_dep) {
 543			m -= (new_sample >> 3);
 544			new_sample += m;
 545		} else {
 546			m <<= 3;
 547			if (m < new_sample)
 548				new_sample = m;
 549		}
 550	} else {
 551		/* No previous measure. */
 552		new_sample = m << 3;
 553	}
 554
 555	tp->rcv_rtt_est.rtt_us = new_sample;
 556}
 557
 558static inline void tcp_rcv_rtt_measure(struct tcp_sock *tp)
 559{
 560	u32 delta_us;
 561
 562	if (tp->rcv_rtt_est.time == 0)
 563		goto new_measure;
 564	if (before(tp->rcv_nxt, tp->rcv_rtt_est.seq))
 565		return;
 566	delta_us = tcp_stamp_us_delta(tp->tcp_mstamp, tp->rcv_rtt_est.time);
 567	if (!delta_us)
 568		delta_us = 1;
 569	tcp_rcv_rtt_update(tp, delta_us, 1);
 570
 571new_measure:
 572	tp->rcv_rtt_est.seq = tp->rcv_nxt + tp->rcv_wnd;
 573	tp->rcv_rtt_est.time = tp->tcp_mstamp;
 574}
 575
 576static inline void tcp_rcv_rtt_measure_ts(struct sock *sk,
 577					  const struct sk_buff *skb)
 578{
 579	struct tcp_sock *tp = tcp_sk(sk);
 580
 581	if (tp->rx_opt.rcv_tsecr == tp->rcv_rtt_last_tsecr)
 582		return;
 583	tp->rcv_rtt_last_tsecr = tp->rx_opt.rcv_tsecr;
 584
 585	if (TCP_SKB_CB(skb)->end_seq -
 586	    TCP_SKB_CB(skb)->seq >= inet_csk(sk)->icsk_ack.rcv_mss) {
 587		u32 delta = tcp_time_stamp(tp) - tp->rx_opt.rcv_tsecr;
 588		u32 delta_us;
 589
 590		if (likely(delta < INT_MAX / (USEC_PER_SEC / TCP_TS_HZ))) {
 591			if (!delta)
 592				delta = 1;
 593			delta_us = delta * (USEC_PER_SEC / TCP_TS_HZ);
 594			tcp_rcv_rtt_update(tp, delta_us, 0);
 595		}
 596	}
 597}
 598
 599/*
 600 * This function should be called every time data is copied to user space.
 601 * It calculates the appropriate TCP receive buffer space.
 602 */
 603void tcp_rcv_space_adjust(struct sock *sk)
 604{
 605	struct tcp_sock *tp = tcp_sk(sk);
 606	u32 copied;
 607	int time;
 608
 609	trace_tcp_rcv_space_adjust(sk);
 610
 611	tcp_mstamp_refresh(tp);
 612	time = tcp_stamp_us_delta(tp->tcp_mstamp, tp->rcvq_space.time);
 613	if (time < (tp->rcv_rtt_est.rtt_us >> 3) || tp->rcv_rtt_est.rtt_us == 0)
 614		return;
 615
 616	/* Number of bytes copied to user in last RTT */
 617	copied = tp->copied_seq - tp->rcvq_space.seq;
 618	if (copied <= tp->rcvq_space.space)
 619		goto new_measure;
 620
 621	/* A bit of theory :
 622	 * copied = bytes received in previous RTT, our base window
 623	 * To cope with packet losses, we need a 2x factor
 624	 * To cope with slow start, and sender growing its cwin by 100 %
 625	 * every RTT, we need a 4x factor, because the ACK we are sending
 626	 * now is for the next RTT, not the current one :
 627	 * <prev RTT . ><current RTT .. ><next RTT .... >
 628	 */
 629
 630	if (sock_net(sk)->ipv4.sysctl_tcp_moderate_rcvbuf &&
 631	    !(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) {
 632		int rcvmem, rcvbuf;
 633		u64 rcvwin, grow;
 634
 635		/* minimal window to cope with packet losses, assuming
 636		 * steady state. Add some cushion because of small variations.
 637		 */
 638		rcvwin = ((u64)copied << 1) + 16 * tp->advmss;
 639
 640		/* Accommodate for sender rate increase (eg. slow start) */
 641		grow = rcvwin * (copied - tp->rcvq_space.space);
 642		do_div(grow, tp->rcvq_space.space);
 643		rcvwin += (grow << 1);
 644
 645		rcvmem = SKB_TRUESIZE(tp->advmss + MAX_TCP_HEADER);
 646		while (tcp_win_from_space(sk, rcvmem) < tp->advmss)
 647			rcvmem += 128;
 648
 649		do_div(rcvwin, tp->advmss);
 650		rcvbuf = min_t(u64, rcvwin * rcvmem,
 651			       sock_net(sk)->ipv4.sysctl_tcp_rmem[2]);
 652		if (rcvbuf > sk->sk_rcvbuf) {
 653			WRITE_ONCE(sk->sk_rcvbuf, rcvbuf);
 654
 655			/* Make the window clamp follow along.  */
 656			tp->window_clamp = tcp_win_from_space(sk, rcvbuf);
 657		}
 658	}
 659	tp->rcvq_space.space = copied;
 660
 661new_measure:
 662	tp->rcvq_space.seq = tp->copied_seq;
 663	tp->rcvq_space.time = tp->tcp_mstamp;
 664}
 665
 666/* There is something which you must keep in mind when you analyze the
 667 * behavior of the tp->ato delayed ack timeout interval.  When a
 668 * connection starts up, we want to ack as quickly as possible.  The
 669 * problem is that "good" TCP's do slow start at the beginning of data
 670 * transmission.  The means that until we send the first few ACK's the
 671 * sender will sit on his end and only queue most of his data, because
 672 * he can only send snd_cwnd unacked packets at any given time.  For
 673 * each ACK we send, he increments snd_cwnd and transmits more of his
 674 * queue.  -DaveM
 675 */
 676static void tcp_event_data_recv(struct sock *sk, struct sk_buff *skb)
 677{
 678	struct tcp_sock *tp = tcp_sk(sk);
 679	struct inet_connection_sock *icsk = inet_csk(sk);
 680	u32 now;
 681
 682	inet_csk_schedule_ack(sk);
 683
 684	tcp_measure_rcv_mss(sk, skb);
 685
 686	tcp_rcv_rtt_measure(tp);
 687
 688	now = tcp_jiffies32;
 689
 690	if (!icsk->icsk_ack.ato) {
 691		/* The _first_ data packet received, initialize
 692		 * delayed ACK engine.
 693		 */
 694		tcp_incr_quickack(sk, TCP_MAX_QUICKACKS);
 695		icsk->icsk_ack.ato = TCP_ATO_MIN;
 696	} else {
 697		int m = now - icsk->icsk_ack.lrcvtime;
 698
 699		if (m <= TCP_ATO_MIN / 2) {
 700			/* The fastest case is the first. */
 701			icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + TCP_ATO_MIN / 2;
 702		} else if (m < icsk->icsk_ack.ato) {
 703			icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + m;
 704			if (icsk->icsk_ack.ato > icsk->icsk_rto)
 705				icsk->icsk_ack.ato = icsk->icsk_rto;
 706		} else if (m > icsk->icsk_rto) {
 707			/* Too long gap. Apparently sender failed to
 708			 * restart window, so that we send ACKs quickly.
 709			 */
 710			tcp_incr_quickack(sk, TCP_MAX_QUICKACKS);
 711			sk_mem_reclaim(sk);
 712		}
 713	}
 714	icsk->icsk_ack.lrcvtime = now;
 715
 716	tcp_ecn_check_ce(sk, skb);
 717
 718	if (skb->len >= 128)
 719		tcp_grow_window(sk, skb);
 720}
 721
 722/* Called to compute a smoothed rtt estimate. The data fed to this
 723 * routine either comes from timestamps, or from segments that were
 724 * known _not_ to have been retransmitted [see Karn/Partridge
 725 * Proceedings SIGCOMM 87]. The algorithm is from the SIGCOMM 88
 726 * piece by Van Jacobson.
 727 * NOTE: the next three routines used to be one big routine.
 728 * To save cycles in the RFC 1323 implementation it was better to break
 729 * it up into three procedures. -- erics
 730 */
 731static void tcp_rtt_estimator(struct sock *sk, long mrtt_us)
 732{
 733	struct tcp_sock *tp = tcp_sk(sk);
 734	long m = mrtt_us; /* RTT */
 735	u32 srtt = tp->srtt_us;
 736
 737	/*	The following amusing code comes from Jacobson's
 738	 *	article in SIGCOMM '88.  Note that rtt and mdev
 739	 *	are scaled versions of rtt and mean deviation.
 740	 *	This is designed to be as fast as possible
 741	 *	m stands for "measurement".
 742	 *
 743	 *	On a 1990 paper the rto value is changed to:
 744	 *	RTO = rtt + 4 * mdev
 745	 *
 746	 * Funny. This algorithm seems to be very broken.
 747	 * These formulae increase RTO, when it should be decreased, increase
 748	 * too slowly, when it should be increased quickly, decrease too quickly
 749	 * etc. I guess in BSD RTO takes ONE value, so that it is absolutely
 750	 * does not matter how to _calculate_ it. Seems, it was trap
 751	 * that VJ failed to avoid. 8)
 752	 */
 753	if (srtt != 0) {
 754		m -= (srtt >> 3);	/* m is now error in rtt est */
 755		srtt += m;		/* rtt = 7/8 rtt + 1/8 new */
 756		if (m < 0) {
 757			m = -m;		/* m is now abs(error) */
 758			m -= (tp->mdev_us >> 2);   /* similar update on mdev */
 759			/* This is similar to one of Eifel findings.
 760			 * Eifel blocks mdev updates when rtt decreases.
 761			 * This solution is a bit different: we use finer gain
 762			 * for mdev in this case (alpha*beta).
 763			 * Like Eifel it also prevents growth of rto,
 764			 * but also it limits too fast rto decreases,
 765			 * happening in pure Eifel.
 766			 */
 767			if (m > 0)
 768				m >>= 3;
 769		} else {
 770			m -= (tp->mdev_us >> 2);   /* similar update on mdev */
 771		}
 772		tp->mdev_us += m;		/* mdev = 3/4 mdev + 1/4 new */
 773		if (tp->mdev_us > tp->mdev_max_us) {
 774			tp->mdev_max_us = tp->mdev_us;
 775			if (tp->mdev_max_us > tp->rttvar_us)
 776				tp->rttvar_us = tp->mdev_max_us;
 777		}
 778		if (after(tp->snd_una, tp->rtt_seq)) {
 779			if (tp->mdev_max_us < tp->rttvar_us)
 780				tp->rttvar_us -= (tp->rttvar_us - tp->mdev_max_us) >> 2;
 781			tp->rtt_seq = tp->snd_nxt;
 782			tp->mdev_max_us = tcp_rto_min_us(sk);
 783
 784			tcp_bpf_rtt(sk);
 785		}
 786	} else {
 787		/* no previous measure. */
 788		srtt = m << 3;		/* take the measured time to be rtt */
 789		tp->mdev_us = m << 1;	/* make sure rto = 3*rtt */
 790		tp->rttvar_us = max(tp->mdev_us, tcp_rto_min_us(sk));
 791		tp->mdev_max_us = tp->rttvar_us;
 792		tp->rtt_seq = tp->snd_nxt;
 793
 794		tcp_bpf_rtt(sk);
 795	}
 796	tp->srtt_us = max(1U, srtt);
 797}
 798
 799static void tcp_update_pacing_rate(struct sock *sk)
 800{
 801	const struct tcp_sock *tp = tcp_sk(sk);
 802	u64 rate;
 803
 804	/* set sk_pacing_rate to 200 % of current rate (mss * cwnd / srtt) */
 805	rate = (u64)tp->mss_cache * ((USEC_PER_SEC / 100) << 3);
 806
 807	/* current rate is (cwnd * mss) / srtt
 808	 * In Slow Start [1], set sk_pacing_rate to 200 % the current rate.
 809	 * In Congestion Avoidance phase, set it to 120 % the current rate.
 810	 *
 811	 * [1] : Normal Slow Start condition is (tp->snd_cwnd < tp->snd_ssthresh)
 812	 *	 If snd_cwnd >= (tp->snd_ssthresh / 2), we are approaching
 813	 *	 end of slow start and should slow down.
 814	 */
 815	if (tp->snd_cwnd < tp->snd_ssthresh / 2)
 816		rate *= sock_net(sk)->ipv4.sysctl_tcp_pacing_ss_ratio;
 817	else
 818		rate *= sock_net(sk)->ipv4.sysctl_tcp_pacing_ca_ratio;
 819
 820	rate *= max(tp->snd_cwnd, tp->packets_out);
 821
 822	if (likely(tp->srtt_us))
 823		do_div(rate, tp->srtt_us);
 824
 825	/* WRITE_ONCE() is needed because sch_fq fetches sk_pacing_rate
 826	 * without any lock. We want to make sure compiler wont store
 827	 * intermediate values in this location.
 828	 */
 829	WRITE_ONCE(sk->sk_pacing_rate, min_t(u64, rate,
 830					     sk->sk_max_pacing_rate));
 831}
 832
 833/* Calculate rto without backoff.  This is the second half of Van Jacobson's
 834 * routine referred to above.
 835 */
 836static void tcp_set_rto(struct sock *sk)
 837{
 838	const struct tcp_sock *tp = tcp_sk(sk);
 839	/* Old crap is replaced with new one. 8)
 840	 *
 841	 * More seriously:
 842	 * 1. If rtt variance happened to be less 50msec, it is hallucination.
 843	 *    It cannot be less due to utterly erratic ACK generation made
 844	 *    at least by solaris and freebsd. "Erratic ACKs" has _nothing_
 845	 *    to do with delayed acks, because at cwnd>2 true delack timeout
 846	 *    is invisible. Actually, Linux-2.4 also generates erratic
 847	 *    ACKs in some circumstances.
 848	 */
 849	inet_csk(sk)->icsk_rto = __tcp_set_rto(tp);
 850
 851	/* 2. Fixups made earlier cannot be right.
 852	 *    If we do not estimate RTO correctly without them,
 853	 *    all the algo is pure shit and should be replaced
 854	 *    with correct one. It is exactly, which we pretend to do.
 855	 */
 856
 857	/* NOTE: clamping at TCP_RTO_MIN is not required, current algo
 858	 * guarantees that rto is higher.
 859	 */
 860	tcp_bound_rto(sk);
 861}
 862
 863__u32 tcp_init_cwnd(const struct tcp_sock *tp, const struct dst_entry *dst)
 864{
 865	__u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0);
 866
 867	if (!cwnd)
 868		cwnd = TCP_INIT_CWND;
 869	return min_t(__u32, cwnd, tp->snd_cwnd_clamp);
 870}
 871
 872/* Take a notice that peer is sending D-SACKs */
 873static void tcp_dsack_seen(struct tcp_sock *tp)
 874{
 875	tp->rx_opt.sack_ok |= TCP_DSACK_SEEN;
 876	tp->rack.dsack_seen = 1;
 877	tp->dsack_dups++;
 878}
 879
 880/* It's reordering when higher sequence was delivered (i.e. sacked) before
 881 * some lower never-retransmitted sequence ("low_seq"). The maximum reordering
 882 * distance is approximated in full-mss packet distance ("reordering").
 883 */
 884static void tcp_check_sack_reordering(struct sock *sk, const u32 low_seq,
 885				      const int ts)
 886{
 887	struct tcp_sock *tp = tcp_sk(sk);
 888	const u32 mss = tp->mss_cache;
 889	u32 fack, metric;
 890
 891	fack = tcp_highest_sack_seq(tp);
 892	if (!before(low_seq, fack))
 893		return;
 894
 895	metric = fack - low_seq;
 896	if ((metric > tp->reordering * mss) && mss) {
 897#if FASTRETRANS_DEBUG > 1
 898		pr_debug("Disorder%d %d %u f%u s%u rr%d\n",
 899			 tp->rx_opt.sack_ok, inet_csk(sk)->icsk_ca_state,
 900			 tp->reordering,
 901			 0,
 902			 tp->sacked_out,
 903			 tp->undo_marker ? tp->undo_retrans : 0);
 904#endif
 905		tp->reordering = min_t(u32, (metric + mss - 1) / mss,
 906				       sock_net(sk)->ipv4.sysctl_tcp_max_reordering);
 907	}
 908
 
 909	/* This exciting event is worth to be remembered. 8) */
 910	tp->reord_seen++;
 911	NET_INC_STATS(sock_net(sk),
 912		      ts ? LINUX_MIB_TCPTSREORDER : LINUX_MIB_TCPSACKREORDER);
 913}
 914
 915/* This must be called before lost_out is incremented */
 916static void tcp_verify_retransmit_hint(struct tcp_sock *tp, struct sk_buff *skb)
 917{
 918	if (!tp->retransmit_skb_hint ||
 919	    before(TCP_SKB_CB(skb)->seq,
 920		   TCP_SKB_CB(tp->retransmit_skb_hint)->seq))
 921		tp->retransmit_skb_hint = skb;
 922}
 923
 924/* Sum the number of packets on the wire we have marked as lost.
 925 * There are two cases we care about here:
 926 * a) Packet hasn't been marked lost (nor retransmitted),
 927 *    and this is the first loss.
 928 * b) Packet has been marked both lost and retransmitted,
 929 *    and this means we think it was lost again.
 930 */
 931static void tcp_sum_lost(struct tcp_sock *tp, struct sk_buff *skb)
 932{
 933	__u8 sacked = TCP_SKB_CB(skb)->sacked;
 934
 935	if (!(sacked & TCPCB_LOST) ||
 936	    ((sacked & TCPCB_LOST) && (sacked & TCPCB_SACKED_RETRANS)))
 937		tp->lost += tcp_skb_pcount(skb);
 938}
 939
 940static void tcp_skb_mark_lost(struct tcp_sock *tp, struct sk_buff *skb)
 941{
 942	if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) {
 943		tcp_verify_retransmit_hint(tp, skb);
 944
 945		tp->lost_out += tcp_skb_pcount(skb);
 946		tcp_sum_lost(tp, skb);
 947		TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
 948	}
 949}
 950
 951void tcp_skb_mark_lost_uncond_verify(struct tcp_sock *tp, struct sk_buff *skb)
 952{
 953	tcp_verify_retransmit_hint(tp, skb);
 954
 955	tcp_sum_lost(tp, skb);
 956	if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) {
 957		tp->lost_out += tcp_skb_pcount(skb);
 958		TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
 959	}
 960}
 961
 962/* This procedure tags the retransmission queue when SACKs arrive.
 963 *
 964 * We have three tag bits: SACKED(S), RETRANS(R) and LOST(L).
 965 * Packets in queue with these bits set are counted in variables
 966 * sacked_out, retrans_out and lost_out, correspondingly.
 967 *
 968 * Valid combinations are:
 969 * Tag  InFlight	Description
 970 * 0	1		- orig segment is in flight.
 971 * S	0		- nothing flies, orig reached receiver.
 972 * L	0		- nothing flies, orig lost by net.
 973 * R	2		- both orig and retransmit are in flight.
 974 * L|R	1		- orig is lost, retransmit is in flight.
 975 * S|R  1		- orig reached receiver, retrans is still in flight.
 976 * (L|S|R is logically valid, it could occur when L|R is sacked,
 977 *  but it is equivalent to plain S and code short-curcuits it to S.
 978 *  L|S is logically invalid, it would mean -1 packet in flight 8))
 979 *
 980 * These 6 states form finite state machine, controlled by the following events:
 981 * 1. New ACK (+SACK) arrives. (tcp_sacktag_write_queue())
 982 * 2. Retransmission. (tcp_retransmit_skb(), tcp_xmit_retransmit_queue())
 983 * 3. Loss detection event of two flavors:
 984 *	A. Scoreboard estimator decided the packet is lost.
 985 *	   A'. Reno "three dupacks" marks head of queue lost.
 986 *	B. SACK arrives sacking SND.NXT at the moment, when the
 987 *	   segment was retransmitted.
 988 * 4. D-SACK added new rule: D-SACK changes any tag to S.
 989 *
 990 * It is pleasant to note, that state diagram turns out to be commutative,
 991 * so that we are allowed not to be bothered by order of our actions,
 992 * when multiple events arrive simultaneously. (see the function below).
 993 *
 994 * Reordering detection.
 995 * --------------------
 996 * Reordering metric is maximal distance, which a packet can be displaced
 997 * in packet stream. With SACKs we can estimate it:
 998 *
 999 * 1. SACK fills old hole and the corresponding segment was not
1000 *    ever retransmitted -> reordering. Alas, we cannot use it
1001 *    when segment was retransmitted.
1002 * 2. The last flaw is solved with D-SACK. D-SACK arrives
1003 *    for retransmitted and already SACKed segment -> reordering..
1004 * Both of these heuristics are not used in Loss state, when we cannot
1005 * account for retransmits accurately.
1006 *
1007 * SACK block validation.
1008 * ----------------------
1009 *
1010 * SACK block range validation checks that the received SACK block fits to
1011 * the expected sequence limits, i.e., it is between SND.UNA and SND.NXT.
1012 * Note that SND.UNA is not included to the range though being valid because
1013 * it means that the receiver is rather inconsistent with itself reporting
1014 * SACK reneging when it should advance SND.UNA. Such SACK block this is
1015 * perfectly valid, however, in light of RFC2018 which explicitly states
1016 * that "SACK block MUST reflect the newest segment.  Even if the newest
1017 * segment is going to be discarded ...", not that it looks very clever
1018 * in case of head skb. Due to potentional receiver driven attacks, we
1019 * choose to avoid immediate execution of a walk in write queue due to
1020 * reneging and defer head skb's loss recovery to standard loss recovery
1021 * procedure that will eventually trigger (nothing forbids us doing this).
1022 *
1023 * Implements also blockage to start_seq wrap-around. Problem lies in the
1024 * fact that though start_seq (s) is before end_seq (i.e., not reversed),
1025 * there's no guarantee that it will be before snd_nxt (n). The problem
1026 * happens when start_seq resides between end_seq wrap (e_w) and snd_nxt
1027 * wrap (s_w):
1028 *
1029 *         <- outs wnd ->                          <- wrapzone ->
1030 *         u     e      n                         u_w   e_w  s n_w
1031 *         |     |      |                          |     |   |  |
1032 * |<------------+------+----- TCP seqno space --------------+---------->|
1033 * ...-- <2^31 ->|                                           |<--------...
1034 * ...---- >2^31 ------>|                                    |<--------...
1035 *
1036 * Current code wouldn't be vulnerable but it's better still to discard such
1037 * crazy SACK blocks. Doing this check for start_seq alone closes somewhat
1038 * similar case (end_seq after snd_nxt wrap) as earlier reversed check in
1039 * snd_nxt wrap -> snd_una region will then become "well defined", i.e.,
1040 * equal to the ideal case (infinite seqno space without wrap caused issues).
1041 *
1042 * With D-SACK the lower bound is extended to cover sequence space below
1043 * SND.UNA down to undo_marker, which is the last point of interest. Yet
1044 * again, D-SACK block must not to go across snd_una (for the same reason as
1045 * for the normal SACK blocks, explained above). But there all simplicity
1046 * ends, TCP might receive valid D-SACKs below that. As long as they reside
1047 * fully below undo_marker they do not affect behavior in anyway and can
1048 * therefore be safely ignored. In rare cases (which are more or less
1049 * theoretical ones), the D-SACK will nicely cross that boundary due to skb
1050 * fragmentation and packet reordering past skb's retransmission. To consider
1051 * them correctly, the acceptable range must be extended even more though
1052 * the exact amount is rather hard to quantify. However, tp->max_window can
1053 * be used as an exaggerated estimate.
1054 */
1055static bool tcp_is_sackblock_valid(struct tcp_sock *tp, bool is_dsack,
1056				   u32 start_seq, u32 end_seq)
1057{
1058	/* Too far in future, or reversed (interpretation is ambiguous) */
1059	if (after(end_seq, tp->snd_nxt) || !before(start_seq, end_seq))
1060		return false;
1061
1062	/* Nasty start_seq wrap-around check (see comments above) */
1063	if (!before(start_seq, tp->snd_nxt))
1064		return false;
1065
1066	/* In outstanding window? ...This is valid exit for D-SACKs too.
1067	 * start_seq == snd_una is non-sensical (see comments above)
1068	 */
1069	if (after(start_seq, tp->snd_una))
1070		return true;
1071
1072	if (!is_dsack || !tp->undo_marker)
1073		return false;
1074
1075	/* ...Then it's D-SACK, and must reside below snd_una completely */
1076	if (after(end_seq, tp->snd_una))
1077		return false;
1078
1079	if (!before(start_seq, tp->undo_marker))
1080		return true;
1081
1082	/* Too old */
1083	if (!after(end_seq, tp->undo_marker))
1084		return false;
1085
1086	/* Undo_marker boundary crossing (overestimates a lot). Known already:
1087	 *   start_seq < undo_marker and end_seq >= undo_marker.
1088	 */
1089	return !before(start_seq, end_seq - tp->max_window);
1090}
1091
1092static bool tcp_check_dsack(struct sock *sk, const struct sk_buff *ack_skb,
1093			    struct tcp_sack_block_wire *sp, int num_sacks,
1094			    u32 prior_snd_una)
1095{
1096	struct tcp_sock *tp = tcp_sk(sk);
1097	u32 start_seq_0 = get_unaligned_be32(&sp[0].start_seq);
1098	u32 end_seq_0 = get_unaligned_be32(&sp[0].end_seq);
1099	bool dup_sack = false;
1100
1101	if (before(start_seq_0, TCP_SKB_CB(ack_skb)->ack_seq)) {
1102		dup_sack = true;
1103		tcp_dsack_seen(tp);
1104		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKRECV);
1105	} else if (num_sacks > 1) {
1106		u32 end_seq_1 = get_unaligned_be32(&sp[1].end_seq);
1107		u32 start_seq_1 = get_unaligned_be32(&sp[1].start_seq);
1108
1109		if (!after(end_seq_0, end_seq_1) &&
1110		    !before(start_seq_0, start_seq_1)) {
1111			dup_sack = true;
1112			tcp_dsack_seen(tp);
1113			NET_INC_STATS(sock_net(sk),
1114					LINUX_MIB_TCPDSACKOFORECV);
1115		}
1116	}
1117
1118	/* D-SACK for already forgotten data... Do dumb counting. */
1119	if (dup_sack && tp->undo_marker && tp->undo_retrans > 0 &&
1120	    !after(end_seq_0, prior_snd_una) &&
1121	    after(end_seq_0, tp->undo_marker))
1122		tp->undo_retrans--;
1123
1124	return dup_sack;
1125}
1126
1127struct tcp_sacktag_state {
1128	u32	reord;
1129	/* Timestamps for earliest and latest never-retransmitted segment
1130	 * that was SACKed. RTO needs the earliest RTT to stay conservative,
1131	 * but congestion control should still get an accurate delay signal.
1132	 */
1133	u64	first_sackt;
1134	u64	last_sackt;
1135	struct rate_sample *rate;
1136	int	flag;
1137	unsigned int mss_now;
1138};
1139
1140/* Check if skb is fully within the SACK block. In presence of GSO skbs,
1141 * the incoming SACK may not exactly match but we can find smaller MSS
1142 * aligned portion of it that matches. Therefore we might need to fragment
1143 * which may fail and creates some hassle (caller must handle error case
1144 * returns).
1145 *
1146 * FIXME: this could be merged to shift decision code
1147 */
1148static int tcp_match_skb_to_sack(struct sock *sk, struct sk_buff *skb,
1149				  u32 start_seq, u32 end_seq)
1150{
1151	int err;
1152	bool in_sack;
1153	unsigned int pkt_len;
1154	unsigned int mss;
1155
1156	in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1157		  !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1158
1159	if (tcp_skb_pcount(skb) > 1 && !in_sack &&
1160	    after(TCP_SKB_CB(skb)->end_seq, start_seq)) {
1161		mss = tcp_skb_mss(skb);
1162		in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
1163
1164		if (!in_sack) {
1165			pkt_len = start_seq - TCP_SKB_CB(skb)->seq;
1166			if (pkt_len < mss)
1167				pkt_len = mss;
1168		} else {
1169			pkt_len = end_seq - TCP_SKB_CB(skb)->seq;
1170			if (pkt_len < mss)
1171				return -EINVAL;
1172		}
1173
1174		/* Round if necessary so that SACKs cover only full MSSes
1175		 * and/or the remaining small portion (if present)
1176		 */
1177		if (pkt_len > mss) {
1178			unsigned int new_len = (pkt_len / mss) * mss;
1179			if (!in_sack && new_len < pkt_len)
1180				new_len += mss;
1181			pkt_len = new_len;
1182		}
1183
1184		if (pkt_len >= skb->len && !in_sack)
1185			return 0;
1186
1187		err = tcp_fragment(sk, TCP_FRAG_IN_RTX_QUEUE, skb,
1188				   pkt_len, mss, GFP_ATOMIC);
1189		if (err < 0)
1190			return err;
1191	}
1192
1193	return in_sack;
1194}
1195
1196/* Mark the given newly-SACKed range as such, adjusting counters and hints. */
1197static u8 tcp_sacktag_one(struct sock *sk,
1198			  struct tcp_sacktag_state *state, u8 sacked,
1199			  u32 start_seq, u32 end_seq,
1200			  int dup_sack, int pcount,
1201			  u64 xmit_time)
1202{
1203	struct tcp_sock *tp = tcp_sk(sk);
1204
1205	/* Account D-SACK for retransmitted packet. */
1206	if (dup_sack && (sacked & TCPCB_RETRANS)) {
1207		if (tp->undo_marker && tp->undo_retrans > 0 &&
1208		    after(end_seq, tp->undo_marker))
1209			tp->undo_retrans--;
1210		if ((sacked & TCPCB_SACKED_ACKED) &&
1211		    before(start_seq, state->reord))
1212				state->reord = start_seq;
1213	}
1214
1215	/* Nothing to do; acked frame is about to be dropped (was ACKed). */
1216	if (!after(end_seq, tp->snd_una))
1217		return sacked;
1218
1219	if (!(sacked & TCPCB_SACKED_ACKED)) {
1220		tcp_rack_advance(tp, sacked, end_seq, xmit_time);
1221
1222		if (sacked & TCPCB_SACKED_RETRANS) {
1223			/* If the segment is not tagged as lost,
1224			 * we do not clear RETRANS, believing
1225			 * that retransmission is still in flight.
1226			 */
1227			if (sacked & TCPCB_LOST) {
1228				sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS);
1229				tp->lost_out -= pcount;
1230				tp->retrans_out -= pcount;
1231			}
1232		} else {
1233			if (!(sacked & TCPCB_RETRANS)) {
1234				/* New sack for not retransmitted frame,
1235				 * which was in hole. It is reordering.
1236				 */
1237				if (before(start_seq,
1238					   tcp_highest_sack_seq(tp)) &&
1239				    before(start_seq, state->reord))
1240					state->reord = start_seq;
1241
1242				if (!after(end_seq, tp->high_seq))
1243					state->flag |= FLAG_ORIG_SACK_ACKED;
1244				if (state->first_sackt == 0)
1245					state->first_sackt = xmit_time;
1246				state->last_sackt = xmit_time;
1247			}
1248
1249			if (sacked & TCPCB_LOST) {
1250				sacked &= ~TCPCB_LOST;
1251				tp->lost_out -= pcount;
1252			}
1253		}
1254
1255		sacked |= TCPCB_SACKED_ACKED;
1256		state->flag |= FLAG_DATA_SACKED;
1257		tp->sacked_out += pcount;
1258		tp->delivered += pcount;  /* Out-of-order packets delivered */
1259
1260		/* Lost marker hint past SACKed? Tweak RFC3517 cnt */
1261		if (tp->lost_skb_hint &&
1262		    before(start_seq, TCP_SKB_CB(tp->lost_skb_hint)->seq))
1263			tp->lost_cnt_hint += pcount;
1264	}
1265
1266	/* D-SACK. We can detect redundant retransmission in S|R and plain R
1267	 * frames and clear it. undo_retrans is decreased above, L|R frames
1268	 * are accounted above as well.
1269	 */
1270	if (dup_sack && (sacked & TCPCB_SACKED_RETRANS)) {
1271		sacked &= ~TCPCB_SACKED_RETRANS;
1272		tp->retrans_out -= pcount;
1273	}
1274
1275	return sacked;
1276}
1277
1278/* Shift newly-SACKed bytes from this skb to the immediately previous
1279 * already-SACKed sk_buff. Mark the newly-SACKed bytes as such.
1280 */
1281static bool tcp_shifted_skb(struct sock *sk, struct sk_buff *prev,
1282			    struct sk_buff *skb,
1283			    struct tcp_sacktag_state *state,
1284			    unsigned int pcount, int shifted, int mss,
1285			    bool dup_sack)
1286{
1287	struct tcp_sock *tp = tcp_sk(sk);
1288	u32 start_seq = TCP_SKB_CB(skb)->seq;	/* start of newly-SACKed */
1289	u32 end_seq = start_seq + shifted;	/* end of newly-SACKed */
1290
1291	BUG_ON(!pcount);
1292
1293	/* Adjust counters and hints for the newly sacked sequence
1294	 * range but discard the return value since prev is already
1295	 * marked. We must tag the range first because the seq
1296	 * advancement below implicitly advances
1297	 * tcp_highest_sack_seq() when skb is highest_sack.
1298	 */
1299	tcp_sacktag_one(sk, state, TCP_SKB_CB(skb)->sacked,
1300			start_seq, end_seq, dup_sack, pcount,
1301			tcp_skb_timestamp_us(skb));
1302	tcp_rate_skb_delivered(sk, skb, state->rate);
1303
1304	if (skb == tp->lost_skb_hint)
1305		tp->lost_cnt_hint += pcount;
1306
1307	TCP_SKB_CB(prev)->end_seq += shifted;
1308	TCP_SKB_CB(skb)->seq += shifted;
1309
1310	tcp_skb_pcount_add(prev, pcount);
1311	WARN_ON_ONCE(tcp_skb_pcount(skb) < pcount);
1312	tcp_skb_pcount_add(skb, -pcount);
1313
1314	/* When we're adding to gso_segs == 1, gso_size will be zero,
1315	 * in theory this shouldn't be necessary but as long as DSACK
1316	 * code can come after this skb later on it's better to keep
1317	 * setting gso_size to something.
1318	 */
1319	if (!TCP_SKB_CB(prev)->tcp_gso_size)
1320		TCP_SKB_CB(prev)->tcp_gso_size = mss;
1321
1322	/* CHECKME: To clear or not to clear? Mimics normal skb currently */
1323	if (tcp_skb_pcount(skb) <= 1)
1324		TCP_SKB_CB(skb)->tcp_gso_size = 0;
1325
1326	/* Difference in this won't matter, both ACKed by the same cumul. ACK */
1327	TCP_SKB_CB(prev)->sacked |= (TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS);
1328
1329	if (skb->len > 0) {
1330		BUG_ON(!tcp_skb_pcount(skb));
1331		NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKSHIFTED);
1332		return false;
1333	}
1334
1335	/* Whole SKB was eaten :-) */
1336
1337	if (skb == tp->retransmit_skb_hint)
1338		tp->retransmit_skb_hint = prev;
1339	if (skb == tp->lost_skb_hint) {
1340		tp->lost_skb_hint = prev;
1341		tp->lost_cnt_hint -= tcp_skb_pcount(prev);
1342	}
1343
1344	TCP_SKB_CB(prev)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags;
1345	TCP_SKB_CB(prev)->eor = TCP_SKB_CB(skb)->eor;
1346	if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
1347		TCP_SKB_CB(prev)->end_seq++;
1348
1349	if (skb == tcp_highest_sack(sk))
1350		tcp_advance_highest_sack(sk, skb);
1351
1352	tcp_skb_collapse_tstamp(prev, skb);
1353	if (unlikely(TCP_SKB_CB(prev)->tx.delivered_mstamp))
1354		TCP_SKB_CB(prev)->tx.delivered_mstamp = 0;
1355
1356	tcp_rtx_queue_unlink_and_free(skb, sk);
1357
1358	NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKMERGED);
1359
1360	return true;
1361}
1362
1363/* I wish gso_size would have a bit more sane initialization than
1364 * something-or-zero which complicates things
1365 */
1366static int tcp_skb_seglen(const struct sk_buff *skb)
1367{
1368	return tcp_skb_pcount(skb) == 1 ? skb->len : tcp_skb_mss(skb);
1369}
1370
1371/* Shifting pages past head area doesn't work */
1372static int skb_can_shift(const struct sk_buff *skb)
1373{
1374	return !skb_headlen(skb) && skb_is_nonlinear(skb);
1375}
1376
1377int tcp_skb_shift(struct sk_buff *to, struct sk_buff *from,
1378		  int pcount, int shiftlen)
1379{
1380	/* TCP min gso_size is 8 bytes (TCP_MIN_GSO_SIZE)
1381	 * Since TCP_SKB_CB(skb)->tcp_gso_segs is 16 bits, we need
1382	 * to make sure not storing more than 65535 * 8 bytes per skb,
1383	 * even if current MSS is bigger.
1384	 */
1385	if (unlikely(to->len + shiftlen >= 65535 * TCP_MIN_GSO_SIZE))
1386		return 0;
1387	if (unlikely(tcp_skb_pcount(to) + pcount > 65535))
1388		return 0;
1389	return skb_shift(to, from, shiftlen);
1390}
1391
1392/* Try collapsing SACK blocks spanning across multiple skbs to a single
1393 * skb.
1394 */
1395static struct sk_buff *tcp_shift_skb_data(struct sock *sk, struct sk_buff *skb,
1396					  struct tcp_sacktag_state *state,
1397					  u32 start_seq, u32 end_seq,
1398					  bool dup_sack)
1399{
1400	struct tcp_sock *tp = tcp_sk(sk);
1401	struct sk_buff *prev;
1402	int mss;
1403	int pcount = 0;
1404	int len;
1405	int in_sack;
1406
1407	/* Normally R but no L won't result in plain S */
1408	if (!dup_sack &&
1409	    (TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_RETRANS)) == TCPCB_SACKED_RETRANS)
1410		goto fallback;
1411	if (!skb_can_shift(skb))
1412		goto fallback;
1413	/* This frame is about to be dropped (was ACKed). */
1414	if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1415		goto fallback;
1416
1417	/* Can only happen with delayed DSACK + discard craziness */
1418	prev = skb_rb_prev(skb);
1419	if (!prev)
1420		goto fallback;
1421
1422	if ((TCP_SKB_CB(prev)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED)
1423		goto fallback;
1424
1425	if (!tcp_skb_can_collapse_to(prev))
1426		goto fallback;
1427
1428	in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1429		  !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1430
1431	if (in_sack) {
1432		len = skb->len;
1433		pcount = tcp_skb_pcount(skb);
1434		mss = tcp_skb_seglen(skb);
1435
1436		/* TODO: Fix DSACKs to not fragment already SACKed and we can
1437		 * drop this restriction as unnecessary
1438		 */
1439		if (mss != tcp_skb_seglen(prev))
1440			goto fallback;
1441	} else {
1442		if (!after(TCP_SKB_CB(skb)->end_seq, start_seq))
1443			goto noop;
1444		/* CHECKME: This is non-MSS split case only?, this will
1445		 * cause skipped skbs due to advancing loop btw, original
1446		 * has that feature too
1447		 */
1448		if (tcp_skb_pcount(skb) <= 1)
1449			goto noop;
1450
1451		in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
1452		if (!in_sack) {
1453			/* TODO: head merge to next could be attempted here
1454			 * if (!after(TCP_SKB_CB(skb)->end_seq, end_seq)),
1455			 * though it might not be worth of the additional hassle
1456			 *
1457			 * ...we can probably just fallback to what was done
1458			 * previously. We could try merging non-SACKed ones
1459			 * as well but it probably isn't going to buy off
1460			 * because later SACKs might again split them, and
1461			 * it would make skb timestamp tracking considerably
1462			 * harder problem.
1463			 */
1464			goto fallback;
1465		}
1466
1467		len = end_seq - TCP_SKB_CB(skb)->seq;
1468		BUG_ON(len < 0);
1469		BUG_ON(len > skb->len);
1470
1471		/* MSS boundaries should be honoured or else pcount will
1472		 * severely break even though it makes things bit trickier.
1473		 * Optimize common case to avoid most of the divides
1474		 */
1475		mss = tcp_skb_mss(skb);
1476
1477		/* TODO: Fix DSACKs to not fragment already SACKed and we can
1478		 * drop this restriction as unnecessary
1479		 */
1480		if (mss != tcp_skb_seglen(prev))
1481			goto fallback;
1482
1483		if (len == mss) {
1484			pcount = 1;
1485		} else if (len < mss) {
1486			goto noop;
1487		} else {
1488			pcount = len / mss;
1489			len = pcount * mss;
1490		}
1491	}
1492
1493	/* tcp_sacktag_one() won't SACK-tag ranges below snd_una */
1494	if (!after(TCP_SKB_CB(skb)->seq + len, tp->snd_una))
1495		goto fallback;
1496
1497	if (!tcp_skb_shift(prev, skb, pcount, len))
1498		goto fallback;
1499	if (!tcp_shifted_skb(sk, prev, skb, state, pcount, len, mss, dup_sack))
1500		goto out;
1501
1502	/* Hole filled allows collapsing with the next as well, this is very
1503	 * useful when hole on every nth skb pattern happens
1504	 */
1505	skb = skb_rb_next(prev);
1506	if (!skb)
1507		goto out;
1508
1509	if (!skb_can_shift(skb) ||
1510	    ((TCP_SKB_CB(skb)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED) ||
1511	    (mss != tcp_skb_seglen(skb)))
1512		goto out;
1513
1514	len = skb->len;
1515	pcount = tcp_skb_pcount(skb);
1516	if (tcp_skb_shift(prev, skb, pcount, len))
1517		tcp_shifted_skb(sk, prev, skb, state, pcount,
1518				len, mss, 0);
 
1519
1520out:
1521	return prev;
1522
1523noop:
1524	return skb;
1525
1526fallback:
1527	NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKSHIFTFALLBACK);
1528	return NULL;
1529}
1530
1531static struct sk_buff *tcp_sacktag_walk(struct sk_buff *skb, struct sock *sk,
1532					struct tcp_sack_block *next_dup,
1533					struct tcp_sacktag_state *state,
1534					u32 start_seq, u32 end_seq,
1535					bool dup_sack_in)
1536{
1537	struct tcp_sock *tp = tcp_sk(sk);
1538	struct sk_buff *tmp;
1539
1540	skb_rbtree_walk_from(skb) {
1541		int in_sack = 0;
1542		bool dup_sack = dup_sack_in;
1543
1544		/* queue is in-order => we can short-circuit the walk early */
1545		if (!before(TCP_SKB_CB(skb)->seq, end_seq))
1546			break;
1547
1548		if (next_dup  &&
1549		    before(TCP_SKB_CB(skb)->seq, next_dup->end_seq)) {
1550			in_sack = tcp_match_skb_to_sack(sk, skb,
1551							next_dup->start_seq,
1552							next_dup->end_seq);
1553			if (in_sack > 0)
1554				dup_sack = true;
1555		}
1556
1557		/* skb reference here is a bit tricky to get right, since
1558		 * shifting can eat and free both this skb and the next,
1559		 * so not even _safe variant of the loop is enough.
1560		 */
1561		if (in_sack <= 0) {
1562			tmp = tcp_shift_skb_data(sk, skb, state,
1563						 start_seq, end_seq, dup_sack);
1564			if (tmp) {
1565				if (tmp != skb) {
1566					skb = tmp;
1567					continue;
1568				}
1569
1570				in_sack = 0;
1571			} else {
1572				in_sack = tcp_match_skb_to_sack(sk, skb,
1573								start_seq,
1574								end_seq);
1575			}
1576		}
1577
1578		if (unlikely(in_sack < 0))
1579			break;
1580
1581		if (in_sack) {
1582			TCP_SKB_CB(skb)->sacked =
1583				tcp_sacktag_one(sk,
1584						state,
1585						TCP_SKB_CB(skb)->sacked,
1586						TCP_SKB_CB(skb)->seq,
1587						TCP_SKB_CB(skb)->end_seq,
1588						dup_sack,
1589						tcp_skb_pcount(skb),
1590						tcp_skb_timestamp_us(skb));
1591			tcp_rate_skb_delivered(sk, skb, state->rate);
1592			if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
1593				list_del_init(&skb->tcp_tsorted_anchor);
1594
1595			if (!before(TCP_SKB_CB(skb)->seq,
1596				    tcp_highest_sack_seq(tp)))
1597				tcp_advance_highest_sack(sk, skb);
1598		}
1599	}
1600	return skb;
1601}
1602
1603static struct sk_buff *tcp_sacktag_bsearch(struct sock *sk, u32 seq)
 
 
1604{
1605	struct rb_node *parent, **p = &sk->tcp_rtx_queue.rb_node;
1606	struct sk_buff *skb;
1607
1608	while (*p) {
1609		parent = *p;
1610		skb = rb_to_skb(parent);
1611		if (before(seq, TCP_SKB_CB(skb)->seq)) {
1612			p = &parent->rb_left;
1613			continue;
1614		}
1615		if (!before(seq, TCP_SKB_CB(skb)->end_seq)) {
1616			p = &parent->rb_right;
1617			continue;
1618		}
1619		return skb;
1620	}
1621	return NULL;
1622}
1623
1624static struct sk_buff *tcp_sacktag_skip(struct sk_buff *skb, struct sock *sk,
 
1625					u32 skip_to_seq)
1626{
1627	if (skb && after(TCP_SKB_CB(skb)->seq, skip_to_seq))
1628		return skb;
1629
1630	return tcp_sacktag_bsearch(sk, skip_to_seq);
1631}
1632
1633static struct sk_buff *tcp_maybe_skipping_dsack(struct sk_buff *skb,
1634						struct sock *sk,
1635						struct tcp_sack_block *next_dup,
1636						struct tcp_sacktag_state *state,
1637						u32 skip_to_seq)
1638{
1639	if (!next_dup)
1640		return skb;
1641
1642	if (before(next_dup->start_seq, skip_to_seq)) {
1643		skb = tcp_sacktag_skip(skb, sk, next_dup->start_seq);
1644		skb = tcp_sacktag_walk(skb, sk, NULL, state,
1645				       next_dup->start_seq, next_dup->end_seq,
1646				       1);
1647	}
1648
1649	return skb;
1650}
1651
1652static int tcp_sack_cache_ok(const struct tcp_sock *tp, const struct tcp_sack_block *cache)
1653{
1654	return cache < tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
1655}
1656
1657static int
1658tcp_sacktag_write_queue(struct sock *sk, const struct sk_buff *ack_skb,
1659			u32 prior_snd_una, struct tcp_sacktag_state *state)
1660{
1661	struct tcp_sock *tp = tcp_sk(sk);
1662	const unsigned char *ptr = (skb_transport_header(ack_skb) +
1663				    TCP_SKB_CB(ack_skb)->sacked);
1664	struct tcp_sack_block_wire *sp_wire = (struct tcp_sack_block_wire *)(ptr+2);
1665	struct tcp_sack_block sp[TCP_NUM_SACKS];
1666	struct tcp_sack_block *cache;
1667	struct sk_buff *skb;
1668	int num_sacks = min(TCP_NUM_SACKS, (ptr[1] - TCPOLEN_SACK_BASE) >> 3);
1669	int used_sacks;
1670	bool found_dup_sack = false;
1671	int i, j;
1672	int first_sack_index;
1673
1674	state->flag = 0;
1675	state->reord = tp->snd_nxt;
1676
1677	if (!tp->sacked_out)
1678		tcp_highest_sack_reset(sk);
1679
1680	found_dup_sack = tcp_check_dsack(sk, ack_skb, sp_wire,
1681					 num_sacks, prior_snd_una);
1682	if (found_dup_sack) {
1683		state->flag |= FLAG_DSACKING_ACK;
1684		tp->delivered++; /* A spurious retransmission is delivered */
1685	}
1686
1687	/* Eliminate too old ACKs, but take into
1688	 * account more or less fresh ones, they can
1689	 * contain valid SACK info.
1690	 */
1691	if (before(TCP_SKB_CB(ack_skb)->ack_seq, prior_snd_una - tp->max_window))
1692		return 0;
1693
1694	if (!tp->packets_out)
1695		goto out;
1696
1697	used_sacks = 0;
1698	first_sack_index = 0;
1699	for (i = 0; i < num_sacks; i++) {
1700		bool dup_sack = !i && found_dup_sack;
1701
1702		sp[used_sacks].start_seq = get_unaligned_be32(&sp_wire[i].start_seq);
1703		sp[used_sacks].end_seq = get_unaligned_be32(&sp_wire[i].end_seq);
1704
1705		if (!tcp_is_sackblock_valid(tp, dup_sack,
1706					    sp[used_sacks].start_seq,
1707					    sp[used_sacks].end_seq)) {
1708			int mib_idx;
1709
1710			if (dup_sack) {
1711				if (!tp->undo_marker)
1712					mib_idx = LINUX_MIB_TCPDSACKIGNOREDNOUNDO;
1713				else
1714					mib_idx = LINUX_MIB_TCPDSACKIGNOREDOLD;
1715			} else {
1716				/* Don't count olds caused by ACK reordering */
1717				if ((TCP_SKB_CB(ack_skb)->ack_seq != tp->snd_una) &&
1718				    !after(sp[used_sacks].end_seq, tp->snd_una))
1719					continue;
1720				mib_idx = LINUX_MIB_TCPSACKDISCARD;
1721			}
1722
1723			NET_INC_STATS(sock_net(sk), mib_idx);
1724			if (i == 0)
1725				first_sack_index = -1;
1726			continue;
1727		}
1728
1729		/* Ignore very old stuff early */
1730		if (!after(sp[used_sacks].end_seq, prior_snd_una))
1731			continue;
1732
1733		used_sacks++;
1734	}
1735
1736	/* order SACK blocks to allow in order walk of the retrans queue */
1737	for (i = used_sacks - 1; i > 0; i--) {
1738		for (j = 0; j < i; j++) {
1739			if (after(sp[j].start_seq, sp[j + 1].start_seq)) {
1740				swap(sp[j], sp[j + 1]);
1741
1742				/* Track where the first SACK block goes to */
1743				if (j == first_sack_index)
1744					first_sack_index = j + 1;
1745			}
1746		}
1747	}
1748
1749	state->mss_now = tcp_current_mss(sk);
1750	skb = NULL;
1751	i = 0;
1752
1753	if (!tp->sacked_out) {
1754		/* It's already past, so skip checking against it */
1755		cache = tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
1756	} else {
1757		cache = tp->recv_sack_cache;
1758		/* Skip empty blocks in at head of the cache */
1759		while (tcp_sack_cache_ok(tp, cache) && !cache->start_seq &&
1760		       !cache->end_seq)
1761			cache++;
1762	}
1763
1764	while (i < used_sacks) {
1765		u32 start_seq = sp[i].start_seq;
1766		u32 end_seq = sp[i].end_seq;
1767		bool dup_sack = (found_dup_sack && (i == first_sack_index));
1768		struct tcp_sack_block *next_dup = NULL;
1769
1770		if (found_dup_sack && ((i + 1) == first_sack_index))
1771			next_dup = &sp[i + 1];
1772
1773		/* Skip too early cached blocks */
1774		while (tcp_sack_cache_ok(tp, cache) &&
1775		       !before(start_seq, cache->end_seq))
1776			cache++;
1777
1778		/* Can skip some work by looking recv_sack_cache? */
1779		if (tcp_sack_cache_ok(tp, cache) && !dup_sack &&
1780		    after(end_seq, cache->start_seq)) {
1781
1782			/* Head todo? */
1783			if (before(start_seq, cache->start_seq)) {
1784				skb = tcp_sacktag_skip(skb, sk, start_seq);
 
1785				skb = tcp_sacktag_walk(skb, sk, next_dup,
1786						       state,
1787						       start_seq,
1788						       cache->start_seq,
1789						       dup_sack);
1790			}
1791
1792			/* Rest of the block already fully processed? */
1793			if (!after(end_seq, cache->end_seq))
1794				goto advance_sp;
1795
1796			skb = tcp_maybe_skipping_dsack(skb, sk, next_dup,
1797						       state,
1798						       cache->end_seq);
1799
1800			/* ...tail remains todo... */
1801			if (tcp_highest_sack_seq(tp) == cache->end_seq) {
1802				/* ...but better entrypoint exists! */
1803				skb = tcp_highest_sack(sk);
1804				if (!skb)
1805					break;
1806				cache++;
1807				goto walk;
1808			}
1809
1810			skb = tcp_sacktag_skip(skb, sk, cache->end_seq);
1811			/* Check overlap against next cached too (past this one already) */
1812			cache++;
1813			continue;
1814		}
1815
1816		if (!before(start_seq, tcp_highest_sack_seq(tp))) {
1817			skb = tcp_highest_sack(sk);
1818			if (!skb)
1819				break;
1820		}
1821		skb = tcp_sacktag_skip(skb, sk, start_seq);
1822
1823walk:
1824		skb = tcp_sacktag_walk(skb, sk, next_dup, state,
1825				       start_seq, end_seq, dup_sack);
1826
1827advance_sp:
1828		i++;
1829	}
1830
1831	/* Clear the head of the cache sack blocks so we can skip it next time */
1832	for (i = 0; i < ARRAY_SIZE(tp->recv_sack_cache) - used_sacks; i++) {
1833		tp->recv_sack_cache[i].start_seq = 0;
1834		tp->recv_sack_cache[i].end_seq = 0;
1835	}
1836	for (j = 0; j < used_sacks; j++)
1837		tp->recv_sack_cache[i++] = sp[j];
1838
1839	if (inet_csk(sk)->icsk_ca_state != TCP_CA_Loss || tp->undo_marker)
1840		tcp_check_sack_reordering(sk, state->reord, 0);
1841
1842	tcp_verify_left_out(tp);
1843out:
1844
1845#if FASTRETRANS_DEBUG > 0
1846	WARN_ON((int)tp->sacked_out < 0);
1847	WARN_ON((int)tp->lost_out < 0);
1848	WARN_ON((int)tp->retrans_out < 0);
1849	WARN_ON((int)tcp_packets_in_flight(tp) < 0);
1850#endif
1851	return state->flag;
1852}
1853
1854/* Limits sacked_out so that sum with lost_out isn't ever larger than
1855 * packets_out. Returns false if sacked_out adjustement wasn't necessary.
1856 */
1857static bool tcp_limit_reno_sacked(struct tcp_sock *tp)
1858{
1859	u32 holes;
1860
1861	holes = max(tp->lost_out, 1U);
1862	holes = min(holes, tp->packets_out);
1863
1864	if ((tp->sacked_out + holes) > tp->packets_out) {
1865		tp->sacked_out = tp->packets_out - holes;
1866		return true;
1867	}
1868	return false;
1869}
1870
1871/* If we receive more dupacks than we expected counting segments
1872 * in assumption of absent reordering, interpret this as reordering.
1873 * The only another reason could be bug in receiver TCP.
1874 */
1875static void tcp_check_reno_reordering(struct sock *sk, const int addend)
1876{
1877	struct tcp_sock *tp = tcp_sk(sk);
1878
1879	if (!tcp_limit_reno_sacked(tp))
1880		return;
1881
1882	tp->reordering = min_t(u32, tp->packets_out + addend,
1883			       sock_net(sk)->ipv4.sysctl_tcp_max_reordering);
1884	tp->reord_seen++;
1885	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRENOREORDER);
1886}
1887
1888/* Emulate SACKs for SACKless connection: account for a new dupack. */
1889
1890static void tcp_add_reno_sack(struct sock *sk, int num_dupack)
1891{
1892	if (num_dupack) {
1893		struct tcp_sock *tp = tcp_sk(sk);
1894		u32 prior_sacked = tp->sacked_out;
1895		s32 delivered;
1896
1897		tp->sacked_out += num_dupack;
1898		tcp_check_reno_reordering(sk, 0);
1899		delivered = tp->sacked_out - prior_sacked;
1900		if (delivered > 0)
1901			tp->delivered += delivered;
1902		tcp_verify_left_out(tp);
1903	}
1904}
1905
1906/* Account for ACK, ACKing some data in Reno Recovery phase. */
1907
1908static void tcp_remove_reno_sacks(struct sock *sk, int acked)
1909{
1910	struct tcp_sock *tp = tcp_sk(sk);
1911
1912	if (acked > 0) {
1913		/* One ACK acked hole. The rest eat duplicate ACKs. */
1914		tp->delivered += max_t(int, acked - tp->sacked_out, 1);
1915		if (acked - 1 >= tp->sacked_out)
1916			tp->sacked_out = 0;
1917		else
1918			tp->sacked_out -= acked - 1;
1919	}
1920	tcp_check_reno_reordering(sk, acked);
1921	tcp_verify_left_out(tp);
1922}
1923
1924static inline void tcp_reset_reno_sack(struct tcp_sock *tp)
1925{
1926	tp->sacked_out = 0;
1927}
1928
1929void tcp_clear_retrans(struct tcp_sock *tp)
1930{
1931	tp->retrans_out = 0;
1932	tp->lost_out = 0;
1933	tp->undo_marker = 0;
1934	tp->undo_retrans = -1;
1935	tp->sacked_out = 0;
1936}
1937
1938static inline void tcp_init_undo(struct tcp_sock *tp)
1939{
1940	tp->undo_marker = tp->snd_una;
1941	/* Retransmission still in flight may cause DSACKs later. */
1942	tp->undo_retrans = tp->retrans_out ? : -1;
1943}
1944
1945static bool tcp_is_rack(const struct sock *sk)
1946{
1947	return sock_net(sk)->ipv4.sysctl_tcp_recovery & TCP_RACK_LOSS_DETECTION;
1948}
1949
1950/* If we detect SACK reneging, forget all SACK information
1951 * and reset tags completely, otherwise preserve SACKs. If receiver
1952 * dropped its ofo queue, we will know this due to reneging detection.
1953 */
1954static void tcp_timeout_mark_lost(struct sock *sk)
1955{
1956	struct tcp_sock *tp = tcp_sk(sk);
1957	struct sk_buff *skb, *head;
1958	bool is_reneg;			/* is receiver reneging on SACKs? */
1959
1960	head = tcp_rtx_queue_head(sk);
1961	is_reneg = head && (TCP_SKB_CB(head)->sacked & TCPCB_SACKED_ACKED);
1962	if (is_reneg) {
1963		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSACKRENEGING);
1964		tp->sacked_out = 0;
1965		/* Mark SACK reneging until we recover from this loss event. */
1966		tp->is_sack_reneg = 1;
1967	} else if (tcp_is_reno(tp)) {
1968		tcp_reset_reno_sack(tp);
1969	}
1970
1971	skb = head;
1972	skb_rbtree_walk_from(skb) {
1973		if (is_reneg)
1974			TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED;
1975		else if (tcp_is_rack(sk) && skb != head &&
1976			 tcp_rack_skb_timeout(tp, skb, 0) > 0)
1977			continue; /* Don't mark recently sent ones lost yet */
1978		tcp_mark_skb_lost(sk, skb);
1979	}
1980	tcp_verify_left_out(tp);
1981	tcp_clear_all_retrans_hints(tp);
1982}
1983
1984/* Enter Loss state. */
1985void tcp_enter_loss(struct sock *sk)
1986{
1987	const struct inet_connection_sock *icsk = inet_csk(sk);
1988	struct tcp_sock *tp = tcp_sk(sk);
1989	struct net *net = sock_net(sk);
 
1990	bool new_recovery = icsk->icsk_ca_state < TCP_CA_Recovery;
1991
1992	tcp_timeout_mark_lost(sk);
1993
1994	/* Reduce ssthresh if it has not yet been made inside this window. */
1995	if (icsk->icsk_ca_state <= TCP_CA_Disorder ||
1996	    !after(tp->high_seq, tp->snd_una) ||
1997	    (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) {
1998		tp->prior_ssthresh = tcp_current_ssthresh(sk);
1999		tp->prior_cwnd = tp->snd_cwnd;
2000		tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
2001		tcp_ca_event(sk, CA_EVENT_LOSS);
2002		tcp_init_undo(tp);
2003	}
2004	tp->snd_cwnd	   = tcp_packets_in_flight(tp) + 1;
2005	tp->snd_cwnd_cnt   = 0;
2006	tp->snd_cwnd_stamp = tcp_jiffies32;
2007
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
2008	/* Timeout in disordered state after receiving substantial DUPACKs
2009	 * suggests that the degree of reordering is over-estimated.
2010	 */
2011	if (icsk->icsk_ca_state <= TCP_CA_Disorder &&
2012	    tp->sacked_out >= net->ipv4.sysctl_tcp_reordering)
2013		tp->reordering = min_t(unsigned int, tp->reordering,
2014				       net->ipv4.sysctl_tcp_reordering);
2015	tcp_set_ca_state(sk, TCP_CA_Loss);
2016	tp->high_seq = tp->snd_nxt;
2017	tcp_ecn_queue_cwr(tp);
2018
2019	/* F-RTO RFC5682 sec 3.1 step 1: retransmit SND.UNA if no previous
2020	 * loss recovery is underway except recurring timeout(s) on
2021	 * the same SND.UNA (sec 3.2). Disable F-RTO on path MTU probing
2022	 */
2023	tp->frto = net->ipv4.sysctl_tcp_frto &&
2024		   (new_recovery || icsk->icsk_retransmits) &&
2025		   !inet_csk(sk)->icsk_mtup.probe_size;
2026}
2027
2028/* If ACK arrived pointing to a remembered SACK, it means that our
2029 * remembered SACKs do not reflect real state of receiver i.e.
2030 * receiver _host_ is heavily congested (or buggy).
2031 *
2032 * To avoid big spurious retransmission bursts due to transient SACK
2033 * scoreboard oddities that look like reneging, we give the receiver a
2034 * little time (max(RTT/2, 10ms)) to send us some more ACKs that will
2035 * restore sanity to the SACK scoreboard. If the apparent reneging
2036 * persists until this RTO then we'll clear the SACK scoreboard.
2037 */
2038static bool tcp_check_sack_reneging(struct sock *sk, int flag)
2039{
2040	if (flag & FLAG_SACK_RENEGING) {
2041		struct tcp_sock *tp = tcp_sk(sk);
2042		unsigned long delay = max(usecs_to_jiffies(tp->srtt_us >> 4),
2043					  msecs_to_jiffies(10));
2044
2045		inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
2046					  delay, TCP_RTO_MAX);
2047		return true;
2048	}
2049	return false;
2050}
2051
2052/* Heurestics to calculate number of duplicate ACKs. There's no dupACKs
2053 * counter when SACK is enabled (without SACK, sacked_out is used for
2054 * that purpose).
2055 *
2056 * With reordering, holes may still be in flight, so RFC3517 recovery
2057 * uses pure sacked_out (total number of SACKed segments) even though
2058 * it violates the RFC that uses duplicate ACKs, often these are equal
2059 * but when e.g. out-of-window ACKs or packet duplication occurs,
2060 * they differ. Since neither occurs due to loss, TCP should really
2061 * ignore them.
2062 */
2063static inline int tcp_dupack_heuristics(const struct tcp_sock *tp)
2064{
2065	return tp->sacked_out + 1;
2066}
2067
2068/* Linux NewReno/SACK/ECN state machine.
2069 * --------------------------------------
2070 *
2071 * "Open"	Normal state, no dubious events, fast path.
2072 * "Disorder"   In all the respects it is "Open",
2073 *		but requires a bit more attention. It is entered when
2074 *		we see some SACKs or dupacks. It is split of "Open"
2075 *		mainly to move some processing from fast path to slow one.
2076 * "CWR"	CWND was reduced due to some Congestion Notification event.
2077 *		It can be ECN, ICMP source quench, local device congestion.
2078 * "Recovery"	CWND was reduced, we are fast-retransmitting.
2079 * "Loss"	CWND was reduced due to RTO timeout or SACK reneging.
2080 *
2081 * tcp_fastretrans_alert() is entered:
2082 * - each incoming ACK, if state is not "Open"
2083 * - when arrived ACK is unusual, namely:
2084 *	* SACK
2085 *	* Duplicate ACK.
2086 *	* ECN ECE.
2087 *
2088 * Counting packets in flight is pretty simple.
2089 *
2090 *	in_flight = packets_out - left_out + retrans_out
2091 *
2092 *	packets_out is SND.NXT-SND.UNA counted in packets.
2093 *
2094 *	retrans_out is number of retransmitted segments.
2095 *
2096 *	left_out is number of segments left network, but not ACKed yet.
2097 *
2098 *		left_out = sacked_out + lost_out
2099 *
2100 *     sacked_out: Packets, which arrived to receiver out of order
2101 *		   and hence not ACKed. With SACKs this number is simply
2102 *		   amount of SACKed data. Even without SACKs
2103 *		   it is easy to give pretty reliable estimate of this number,
2104 *		   counting duplicate ACKs.
2105 *
2106 *       lost_out: Packets lost by network. TCP has no explicit
2107 *		   "loss notification" feedback from network (for now).
2108 *		   It means that this number can be only _guessed_.
2109 *		   Actually, it is the heuristics to predict lossage that
2110 *		   distinguishes different algorithms.
2111 *
2112 *	F.e. after RTO, when all the queue is considered as lost,
2113 *	lost_out = packets_out and in_flight = retrans_out.
2114 *
2115 *		Essentially, we have now a few algorithms detecting
2116 *		lost packets.
2117 *
2118 *		If the receiver supports SACK:
2119 *
2120 *		RFC6675/3517: It is the conventional algorithm. A packet is
2121 *		considered lost if the number of higher sequence packets
2122 *		SACKed is greater than or equal the DUPACK thoreshold
2123 *		(reordering). This is implemented in tcp_mark_head_lost and
2124 *		tcp_update_scoreboard.
2125 *
2126 *		RACK (draft-ietf-tcpm-rack-01): it is a newer algorithm
2127 *		(2017-) that checks timing instead of counting DUPACKs.
2128 *		Essentially a packet is considered lost if it's not S/ACKed
2129 *		after RTT + reordering_window, where both metrics are
2130 *		dynamically measured and adjusted. This is implemented in
2131 *		tcp_rack_mark_lost.
2132 *
2133 *		If the receiver does not support SACK:
2134 *
2135 *		NewReno (RFC6582): in Recovery we assume that one segment
2136 *		is lost (classic Reno). While we are in Recovery and
2137 *		a partial ACK arrives, we assume that one more packet
2138 *		is lost (NewReno). This heuristics are the same in NewReno
2139 *		and SACK.
2140 *
2141 * Really tricky (and requiring careful tuning) part of algorithm
2142 * is hidden in functions tcp_time_to_recover() and tcp_xmit_retransmit_queue().
2143 * The first determines the moment _when_ we should reduce CWND and,
2144 * hence, slow down forward transmission. In fact, it determines the moment
2145 * when we decide that hole is caused by loss, rather than by a reorder.
2146 *
2147 * tcp_xmit_retransmit_queue() decides, _what_ we should retransmit to fill
2148 * holes, caused by lost packets.
2149 *
2150 * And the most logically complicated part of algorithm is undo
2151 * heuristics. We detect false retransmits due to both too early
2152 * fast retransmit (reordering) and underestimated RTO, analyzing
2153 * timestamps and D-SACKs. When we detect that some segments were
2154 * retransmitted by mistake and CWND reduction was wrong, we undo
2155 * window reduction and abort recovery phase. This logic is hidden
2156 * inside several functions named tcp_try_undo_<something>.
2157 */
2158
2159/* This function decides, when we should leave Disordered state
2160 * and enter Recovery phase, reducing congestion window.
2161 *
2162 * Main question: may we further continue forward transmission
2163 * with the same cwnd?
2164 */
2165static bool tcp_time_to_recover(struct sock *sk, int flag)
2166{
2167	struct tcp_sock *tp = tcp_sk(sk);
2168
2169	/* Trick#1: The loss is proven. */
2170	if (tp->lost_out)
2171		return true;
2172
2173	/* Not-A-Trick#2 : Classic rule... */
2174	if (!tcp_is_rack(sk) && tcp_dupack_heuristics(tp) > tp->reordering)
2175		return true;
2176
2177	return false;
2178}
2179
2180/* Detect loss in event "A" above by marking head of queue up as lost.
2181 * For non-SACK(Reno) senders, the first "packets" number of segments
2182 * are considered lost. For RFC3517 SACK, a segment is considered lost if it
2183 * has at least tp->reordering SACKed seqments above it; "packets" refers to
2184 * the maximum SACKed segments to pass before reaching this limit.
2185 */
2186static void tcp_mark_head_lost(struct sock *sk, int packets, int mark_head)
2187{
2188	struct tcp_sock *tp = tcp_sk(sk);
2189	struct sk_buff *skb;
2190	int cnt, oldcnt, lost;
2191	unsigned int mss;
2192	/* Use SACK to deduce losses of new sequences sent during recovery */
2193	const u32 loss_high = tcp_is_sack(tp) ?  tp->snd_nxt : tp->high_seq;
2194
2195	WARN_ON(packets > tp->packets_out);
2196	skb = tp->lost_skb_hint;
2197	if (skb) {
2198		/* Head already handled? */
2199		if (mark_head && after(TCP_SKB_CB(skb)->seq, tp->snd_una))
2200			return;
2201		cnt = tp->lost_cnt_hint;
2202	} else {
2203		skb = tcp_rtx_queue_head(sk);
2204		cnt = 0;
2205	}
2206
2207	skb_rbtree_walk_from(skb) {
2208		/* TODO: do this better */
2209		/* this is not the most efficient way to do this... */
2210		tp->lost_skb_hint = skb;
2211		tp->lost_cnt_hint = cnt;
2212
2213		if (after(TCP_SKB_CB(skb)->end_seq, loss_high))
2214			break;
2215
2216		oldcnt = cnt;
2217		if (tcp_is_reno(tp) ||
2218		    (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
2219			cnt += tcp_skb_pcount(skb);
2220
2221		if (cnt > packets) {
2222			if (tcp_is_sack(tp) ||
2223			    (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED) ||
2224			    (oldcnt >= packets))
2225				break;
2226
2227			mss = tcp_skb_mss(skb);
2228			/* If needed, chop off the prefix to mark as lost. */
2229			lost = (packets - oldcnt) * mss;
2230			if (lost < skb->len &&
2231			    tcp_fragment(sk, TCP_FRAG_IN_RTX_QUEUE, skb,
2232					 lost, mss, GFP_ATOMIC) < 0)
2233				break;
2234			cnt = packets;
2235		}
2236
2237		tcp_skb_mark_lost(tp, skb);
2238
2239		if (mark_head)
2240			break;
2241	}
2242	tcp_verify_left_out(tp);
2243}
2244
2245/* Account newly detected lost packet(s) */
2246
2247static void tcp_update_scoreboard(struct sock *sk, int fast_rexmit)
2248{
2249	struct tcp_sock *tp = tcp_sk(sk);
2250
2251	if (tcp_is_sack(tp)) {
 
 
2252		int sacked_upto = tp->sacked_out - tp->reordering;
2253		if (sacked_upto >= 0)
2254			tcp_mark_head_lost(sk, sacked_upto, 0);
2255		else if (fast_rexmit)
2256			tcp_mark_head_lost(sk, 1, 1);
2257	}
2258}
2259
2260static bool tcp_tsopt_ecr_before(const struct tcp_sock *tp, u32 when)
2261{
2262	return tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
2263	       before(tp->rx_opt.rcv_tsecr, when);
2264}
2265
2266/* skb is spurious retransmitted if the returned timestamp echo
2267 * reply is prior to the skb transmission time
2268 */
2269static bool tcp_skb_spurious_retrans(const struct tcp_sock *tp,
2270				     const struct sk_buff *skb)
2271{
2272	return (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS) &&
2273	       tcp_tsopt_ecr_before(tp, tcp_skb_timestamp(skb));
2274}
2275
2276/* Nothing was retransmitted or returned timestamp is less
2277 * than timestamp of the first retransmission.
2278 */
2279static inline bool tcp_packet_delayed(const struct tcp_sock *tp)
2280{
2281	return tp->retrans_stamp &&
2282	       tcp_tsopt_ecr_before(tp, tp->retrans_stamp);
2283}
2284
2285/* Undo procedures. */
2286
2287/* We can clear retrans_stamp when there are no retransmissions in the
2288 * window. It would seem that it is trivially available for us in
2289 * tp->retrans_out, however, that kind of assumptions doesn't consider
2290 * what will happen if errors occur when sending retransmission for the
2291 * second time. ...It could the that such segment has only
2292 * TCPCB_EVER_RETRANS set at the present time. It seems that checking
2293 * the head skb is enough except for some reneging corner cases that
2294 * are not worth the effort.
2295 *
2296 * Main reason for all this complexity is the fact that connection dying
2297 * time now depends on the validity of the retrans_stamp, in particular,
2298 * that successive retransmissions of a segment must not advance
2299 * retrans_stamp under any conditions.
2300 */
2301static bool tcp_any_retrans_done(const struct sock *sk)
2302{
2303	const struct tcp_sock *tp = tcp_sk(sk);
2304	struct sk_buff *skb;
2305
2306	if (tp->retrans_out)
2307		return true;
2308
2309	skb = tcp_rtx_queue_head(sk);
2310	if (unlikely(skb && TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS))
2311		return true;
2312
2313	return false;
2314}
2315
2316static void DBGUNDO(struct sock *sk, const char *msg)
2317{
2318#if FASTRETRANS_DEBUG > 1
2319	struct tcp_sock *tp = tcp_sk(sk);
2320	struct inet_sock *inet = inet_sk(sk);
2321
2322	if (sk->sk_family == AF_INET) {
2323		pr_debug("Undo %s %pI4/%u c%u l%u ss%u/%u p%u\n",
2324			 msg,
2325			 &inet->inet_daddr, ntohs(inet->inet_dport),
2326			 tp->snd_cwnd, tcp_left_out(tp),
2327			 tp->snd_ssthresh, tp->prior_ssthresh,
2328			 tp->packets_out);
2329	}
2330#if IS_ENABLED(CONFIG_IPV6)
2331	else if (sk->sk_family == AF_INET6) {
2332		pr_debug("Undo %s %pI6/%u c%u l%u ss%u/%u p%u\n",
2333			 msg,
2334			 &sk->sk_v6_daddr, ntohs(inet->inet_dport),
2335			 tp->snd_cwnd, tcp_left_out(tp),
2336			 tp->snd_ssthresh, tp->prior_ssthresh,
2337			 tp->packets_out);
2338	}
2339#endif
2340#endif
2341}
2342
2343static void tcp_undo_cwnd_reduction(struct sock *sk, bool unmark_loss)
2344{
2345	struct tcp_sock *tp = tcp_sk(sk);
2346
2347	if (unmark_loss) {
2348		struct sk_buff *skb;
2349
2350		skb_rbtree_walk(skb, &sk->tcp_rtx_queue) {
2351			TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
2352		}
2353		tp->lost_out = 0;
2354		tcp_clear_all_retrans_hints(tp);
2355	}
2356
2357	if (tp->prior_ssthresh) {
2358		const struct inet_connection_sock *icsk = inet_csk(sk);
2359
2360		tp->snd_cwnd = icsk->icsk_ca_ops->undo_cwnd(sk);
2361
2362		if (tp->prior_ssthresh > tp->snd_ssthresh) {
2363			tp->snd_ssthresh = tp->prior_ssthresh;
2364			tcp_ecn_withdraw_cwr(tp);
2365		}
2366	}
2367	tp->snd_cwnd_stamp = tcp_jiffies32;
2368	tp->undo_marker = 0;
2369	tp->rack.advanced = 1; /* Force RACK to re-exam losses */
2370}
2371
2372static inline bool tcp_may_undo(const struct tcp_sock *tp)
2373{
2374	return tp->undo_marker && (!tp->undo_retrans || tcp_packet_delayed(tp));
2375}
2376
2377/* People celebrate: "We love our President!" */
2378static bool tcp_try_undo_recovery(struct sock *sk)
2379{
2380	struct tcp_sock *tp = tcp_sk(sk);
2381
2382	if (tcp_may_undo(tp)) {
2383		int mib_idx;
2384
2385		/* Happy end! We did not retransmit anything
2386		 * or our original transmission succeeded.
2387		 */
2388		DBGUNDO(sk, inet_csk(sk)->icsk_ca_state == TCP_CA_Loss ? "loss" : "retrans");
2389		tcp_undo_cwnd_reduction(sk, false);
2390		if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss)
2391			mib_idx = LINUX_MIB_TCPLOSSUNDO;
2392		else
2393			mib_idx = LINUX_MIB_TCPFULLUNDO;
2394
2395		NET_INC_STATS(sock_net(sk), mib_idx);
2396	} else if (tp->rack.reo_wnd_persist) {
2397		tp->rack.reo_wnd_persist--;
2398	}
2399	if (tp->snd_una == tp->high_seq && tcp_is_reno(tp)) {
2400		/* Hold old state until something *above* high_seq
2401		 * is ACKed. For Reno it is MUST to prevent false
2402		 * fast retransmits (RFC2582). SACK TCP is safe. */
2403		if (!tcp_any_retrans_done(sk))
2404			tp->retrans_stamp = 0;
2405		return true;
2406	}
2407	tcp_set_ca_state(sk, TCP_CA_Open);
2408	tp->is_sack_reneg = 0;
2409	return false;
2410}
2411
2412/* Try to undo cwnd reduction, because D-SACKs acked all retransmitted data */
2413static bool tcp_try_undo_dsack(struct sock *sk)
2414{
2415	struct tcp_sock *tp = tcp_sk(sk);
2416
2417	if (tp->undo_marker && !tp->undo_retrans) {
2418		tp->rack.reo_wnd_persist = min(TCP_RACK_RECOVERY_THRESH,
2419					       tp->rack.reo_wnd_persist + 1);
2420		DBGUNDO(sk, "D-SACK");
2421		tcp_undo_cwnd_reduction(sk, false);
2422		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKUNDO);
2423		return true;
2424	}
2425	return false;
2426}
2427
2428/* Undo during loss recovery after partial ACK or using F-RTO. */
2429static bool tcp_try_undo_loss(struct sock *sk, bool frto_undo)
2430{
2431	struct tcp_sock *tp = tcp_sk(sk);
2432
2433	if (frto_undo || tcp_may_undo(tp)) {
2434		tcp_undo_cwnd_reduction(sk, true);
2435
2436		DBGUNDO(sk, "partial loss");
2437		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPLOSSUNDO);
2438		if (frto_undo)
2439			NET_INC_STATS(sock_net(sk),
2440					LINUX_MIB_TCPSPURIOUSRTOS);
2441		inet_csk(sk)->icsk_retransmits = 0;
2442		if (frto_undo || tcp_is_sack(tp)) {
2443			tcp_set_ca_state(sk, TCP_CA_Open);
2444			tp->is_sack_reneg = 0;
2445		}
2446		return true;
2447	}
2448	return false;
2449}
2450
2451/* The cwnd reduction in CWR and Recovery uses the PRR algorithm in RFC 6937.
2452 * It computes the number of packets to send (sndcnt) based on packets newly
2453 * delivered:
2454 *   1) If the packets in flight is larger than ssthresh, PRR spreads the
2455 *	cwnd reductions across a full RTT.
2456 *   2) Otherwise PRR uses packet conservation to send as much as delivered.
2457 *      But when the retransmits are acked without further losses, PRR
2458 *      slow starts cwnd up to ssthresh to speed up the recovery.
2459 */
2460static void tcp_init_cwnd_reduction(struct sock *sk)
2461{
2462	struct tcp_sock *tp = tcp_sk(sk);
2463
2464	tp->high_seq = tp->snd_nxt;
2465	tp->tlp_high_seq = 0;
2466	tp->snd_cwnd_cnt = 0;
2467	tp->prior_cwnd = tp->snd_cwnd;
2468	tp->prr_delivered = 0;
2469	tp->prr_out = 0;
2470	tp->snd_ssthresh = inet_csk(sk)->icsk_ca_ops->ssthresh(sk);
2471	tcp_ecn_queue_cwr(tp);
2472}
2473
2474void tcp_cwnd_reduction(struct sock *sk, int newly_acked_sacked, int flag)
2475{
2476	struct tcp_sock *tp = tcp_sk(sk);
2477	int sndcnt = 0;
2478	int delta = tp->snd_ssthresh - tcp_packets_in_flight(tp);
2479
2480	if (newly_acked_sacked <= 0 || WARN_ON_ONCE(!tp->prior_cwnd))
2481		return;
2482
2483	tp->prr_delivered += newly_acked_sacked;
2484	if (delta < 0) {
2485		u64 dividend = (u64)tp->snd_ssthresh * tp->prr_delivered +
2486			       tp->prior_cwnd - 1;
2487		sndcnt = div_u64(dividend, tp->prior_cwnd) - tp->prr_out;
2488	} else if ((flag & (FLAG_RETRANS_DATA_ACKED | FLAG_LOST_RETRANS)) ==
2489		   FLAG_RETRANS_DATA_ACKED) {
2490		sndcnt = min_t(int, delta,
2491			       max_t(int, tp->prr_delivered - tp->prr_out,
2492				     newly_acked_sacked) + 1);
2493	} else {
2494		sndcnt = min(delta, newly_acked_sacked);
2495	}
2496	/* Force a fast retransmit upon entering fast recovery */
2497	sndcnt = max(sndcnt, (tp->prr_out ? 0 : 1));
2498	tp->snd_cwnd = tcp_packets_in_flight(tp) + sndcnt;
2499}
2500
2501static inline void tcp_end_cwnd_reduction(struct sock *sk)
2502{
2503	struct tcp_sock *tp = tcp_sk(sk);
2504
2505	if (inet_csk(sk)->icsk_ca_ops->cong_control)
2506		return;
2507
2508	/* Reset cwnd to ssthresh in CWR or Recovery (unless it's undone) */
2509	if (tp->snd_ssthresh < TCP_INFINITE_SSTHRESH &&
2510	    (inet_csk(sk)->icsk_ca_state == TCP_CA_CWR || tp->undo_marker)) {
2511		tp->snd_cwnd = tp->snd_ssthresh;
2512		tp->snd_cwnd_stamp = tcp_jiffies32;
2513	}
2514	tcp_ca_event(sk, CA_EVENT_COMPLETE_CWR);
2515}
2516
2517/* Enter CWR state. Disable cwnd undo since congestion is proven with ECN */
2518void tcp_enter_cwr(struct sock *sk)
2519{
2520	struct tcp_sock *tp = tcp_sk(sk);
2521
2522	tp->prior_ssthresh = 0;
2523	if (inet_csk(sk)->icsk_ca_state < TCP_CA_CWR) {
2524		tp->undo_marker = 0;
2525		tcp_init_cwnd_reduction(sk);
2526		tcp_set_ca_state(sk, TCP_CA_CWR);
2527	}
2528}
2529EXPORT_SYMBOL(tcp_enter_cwr);
2530
2531static void tcp_try_keep_open(struct sock *sk)
2532{
2533	struct tcp_sock *tp = tcp_sk(sk);
2534	int state = TCP_CA_Open;
2535
2536	if (tcp_left_out(tp) || tcp_any_retrans_done(sk))
2537		state = TCP_CA_Disorder;
2538
2539	if (inet_csk(sk)->icsk_ca_state != state) {
2540		tcp_set_ca_state(sk, state);
2541		tp->high_seq = tp->snd_nxt;
2542	}
2543}
2544
2545static void tcp_try_to_open(struct sock *sk, int flag)
2546{
2547	struct tcp_sock *tp = tcp_sk(sk);
2548
2549	tcp_verify_left_out(tp);
2550
2551	if (!tcp_any_retrans_done(sk))
2552		tp->retrans_stamp = 0;
2553
2554	if (flag & FLAG_ECE)
2555		tcp_enter_cwr(sk);
2556
2557	if (inet_csk(sk)->icsk_ca_state != TCP_CA_CWR) {
2558		tcp_try_keep_open(sk);
2559	}
2560}
2561
2562static void tcp_mtup_probe_failed(struct sock *sk)
2563{
2564	struct inet_connection_sock *icsk = inet_csk(sk);
2565
2566	icsk->icsk_mtup.search_high = icsk->icsk_mtup.probe_size - 1;
2567	icsk->icsk_mtup.probe_size = 0;
2568	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMTUPFAIL);
2569}
2570
2571static void tcp_mtup_probe_success(struct sock *sk)
2572{
2573	struct tcp_sock *tp = tcp_sk(sk);
2574	struct inet_connection_sock *icsk = inet_csk(sk);
2575
2576	/* FIXME: breaks with very large cwnd */
2577	tp->prior_ssthresh = tcp_current_ssthresh(sk);
2578	tp->snd_cwnd = tp->snd_cwnd *
2579		       tcp_mss_to_mtu(sk, tp->mss_cache) /
2580		       icsk->icsk_mtup.probe_size;
2581	tp->snd_cwnd_cnt = 0;
2582	tp->snd_cwnd_stamp = tcp_jiffies32;
2583	tp->snd_ssthresh = tcp_current_ssthresh(sk);
2584
2585	icsk->icsk_mtup.search_low = icsk->icsk_mtup.probe_size;
2586	icsk->icsk_mtup.probe_size = 0;
2587	tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
2588	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMTUPSUCCESS);
2589}
2590
2591/* Do a simple retransmit without using the backoff mechanisms in
2592 * tcp_timer. This is used for path mtu discovery.
2593 * The socket is already locked here.
2594 */
2595void tcp_simple_retransmit(struct sock *sk)
2596{
2597	const struct inet_connection_sock *icsk = inet_csk(sk);
2598	struct tcp_sock *tp = tcp_sk(sk);
2599	struct sk_buff *skb;
2600	unsigned int mss = tcp_current_mss(sk);
2601
2602	skb_rbtree_walk(skb, &sk->tcp_rtx_queue) {
2603		if (tcp_skb_seglen(skb) > mss &&
2604		    !(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) {
2605			if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
2606				TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
2607				tp->retrans_out -= tcp_skb_pcount(skb);
2608			}
2609			tcp_skb_mark_lost_uncond_verify(tp, skb);
2610		}
2611	}
2612
2613	tcp_clear_retrans_hints_partial(tp);
2614
2615	if (!tp->lost_out)
2616		return;
2617
2618	if (tcp_is_reno(tp))
2619		tcp_limit_reno_sacked(tp);
2620
2621	tcp_verify_left_out(tp);
2622
2623	/* Don't muck with the congestion window here.
2624	 * Reason is that we do not increase amount of _data_
2625	 * in network, but units changed and effective
2626	 * cwnd/ssthresh really reduced now.
2627	 */
2628	if (icsk->icsk_ca_state != TCP_CA_Loss) {
2629		tp->high_seq = tp->snd_nxt;
2630		tp->snd_ssthresh = tcp_current_ssthresh(sk);
2631		tp->prior_ssthresh = 0;
2632		tp->undo_marker = 0;
2633		tcp_set_ca_state(sk, TCP_CA_Loss);
2634	}
2635	tcp_xmit_retransmit_queue(sk);
2636}
2637EXPORT_SYMBOL(tcp_simple_retransmit);
2638
2639void tcp_enter_recovery(struct sock *sk, bool ece_ack)
2640{
2641	struct tcp_sock *tp = tcp_sk(sk);
2642	int mib_idx;
2643
2644	if (tcp_is_reno(tp))
2645		mib_idx = LINUX_MIB_TCPRENORECOVERY;
2646	else
2647		mib_idx = LINUX_MIB_TCPSACKRECOVERY;
2648
2649	NET_INC_STATS(sock_net(sk), mib_idx);
2650
2651	tp->prior_ssthresh = 0;
2652	tcp_init_undo(tp);
2653
2654	if (!tcp_in_cwnd_reduction(sk)) {
2655		if (!ece_ack)
2656			tp->prior_ssthresh = tcp_current_ssthresh(sk);
2657		tcp_init_cwnd_reduction(sk);
2658	}
2659	tcp_set_ca_state(sk, TCP_CA_Recovery);
2660}
2661
2662/* Process an ACK in CA_Loss state. Move to CA_Open if lost data are
2663 * recovered or spurious. Otherwise retransmits more on partial ACKs.
2664 */
2665static void tcp_process_loss(struct sock *sk, int flag, int num_dupack,
2666			     int *rexmit)
2667{
2668	struct tcp_sock *tp = tcp_sk(sk);
2669	bool recovered = !before(tp->snd_una, tp->high_seq);
2670
2671	if ((flag & FLAG_SND_UNA_ADVANCED || rcu_access_pointer(tp->fastopen_rsk)) &&
2672	    tcp_try_undo_loss(sk, false))
2673		return;
2674
2675	if (tp->frto) { /* F-RTO RFC5682 sec 3.1 (sack enhanced version). */
2676		/* Step 3.b. A timeout is spurious if not all data are
2677		 * lost, i.e., never-retransmitted data are (s)acked.
2678		 */
2679		if ((flag & FLAG_ORIG_SACK_ACKED) &&
2680		    tcp_try_undo_loss(sk, true))
2681			return;
2682
2683		if (after(tp->snd_nxt, tp->high_seq)) {
2684			if (flag & FLAG_DATA_SACKED || num_dupack)
2685				tp->frto = 0; /* Step 3.a. loss was real */
2686		} else if (flag & FLAG_SND_UNA_ADVANCED && !recovered) {
2687			tp->high_seq = tp->snd_nxt;
2688			/* Step 2.b. Try send new data (but deferred until cwnd
2689			 * is updated in tcp_ack()). Otherwise fall back to
2690			 * the conventional recovery.
2691			 */
2692			if (!tcp_write_queue_empty(sk) &&
2693			    after(tcp_wnd_end(tp), tp->snd_nxt)) {
2694				*rexmit = REXMIT_NEW;
2695				return;
2696			}
2697			tp->frto = 0;
2698		}
2699	}
2700
2701	if (recovered) {
2702		/* F-RTO RFC5682 sec 3.1 step 2.a and 1st part of step 3.a */
2703		tcp_try_undo_recovery(sk);
2704		return;
2705	}
2706	if (tcp_is_reno(tp)) {
2707		/* A Reno DUPACK means new data in F-RTO step 2.b above are
2708		 * delivered. Lower inflight to clock out (re)tranmissions.
2709		 */
2710		if (after(tp->snd_nxt, tp->high_seq) && num_dupack)
2711			tcp_add_reno_sack(sk, num_dupack);
2712		else if (flag & FLAG_SND_UNA_ADVANCED)
2713			tcp_reset_reno_sack(tp);
2714	}
2715	*rexmit = REXMIT_LOST;
2716}
2717
2718/* Undo during fast recovery after partial ACK. */
2719static bool tcp_try_undo_partial(struct sock *sk, u32 prior_snd_una)
2720{
2721	struct tcp_sock *tp = tcp_sk(sk);
2722
2723	if (tp->undo_marker && tcp_packet_delayed(tp)) {
2724		/* Plain luck! Hole if filled with delayed
2725		 * packet, rather than with a retransmit. Check reordering.
2726		 */
2727		tcp_check_sack_reordering(sk, prior_snd_una, 1);
2728
2729		/* We are getting evidence that the reordering degree is higher
2730		 * than we realized. If there are no retransmits out then we
2731		 * can undo. Otherwise we clock out new packets but do not
2732		 * mark more packets lost or retransmit more.
2733		 */
2734		if (tp->retrans_out)
2735			return true;
2736
2737		if (!tcp_any_retrans_done(sk))
2738			tp->retrans_stamp = 0;
2739
2740		DBGUNDO(sk, "partial recovery");
2741		tcp_undo_cwnd_reduction(sk, true);
2742		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPPARTIALUNDO);
2743		tcp_try_keep_open(sk);
2744		return true;
2745	}
2746	return false;
2747}
2748
2749static void tcp_identify_packet_loss(struct sock *sk, int *ack_flag)
2750{
2751	struct tcp_sock *tp = tcp_sk(sk);
2752
2753	if (tcp_rtx_queue_empty(sk))
2754		return;
2755
2756	if (unlikely(tcp_is_reno(tp))) {
2757		tcp_newreno_mark_lost(sk, *ack_flag & FLAG_SND_UNA_ADVANCED);
2758	} else if (tcp_is_rack(sk)) {
2759		u32 prior_retrans = tp->retrans_out;
2760
2761		tcp_rack_mark_lost(sk);
2762		if (prior_retrans > tp->retrans_out)
2763			*ack_flag |= FLAG_LOST_RETRANS;
2764	}
2765}
2766
2767static bool tcp_force_fast_retransmit(struct sock *sk)
2768{
2769	struct tcp_sock *tp = tcp_sk(sk);
2770
2771	return after(tcp_highest_sack_seq(tp),
2772		     tp->snd_una + tp->reordering * tp->mss_cache);
2773}
2774
2775/* Process an event, which can update packets-in-flight not trivially.
2776 * Main goal of this function is to calculate new estimate for left_out,
2777 * taking into account both packets sitting in receiver's buffer and
2778 * packets lost by network.
2779 *
2780 * Besides that it updates the congestion state when packet loss or ECN
2781 * is detected. But it does not reduce the cwnd, it is done by the
2782 * congestion control later.
2783 *
2784 * It does _not_ decide what to send, it is made in function
2785 * tcp_xmit_retransmit_queue().
2786 */
2787static void tcp_fastretrans_alert(struct sock *sk, const u32 prior_snd_una,
2788				  int num_dupack, int *ack_flag, int *rexmit)
2789{
2790	struct inet_connection_sock *icsk = inet_csk(sk);
2791	struct tcp_sock *tp = tcp_sk(sk);
2792	int fast_rexmit = 0, flag = *ack_flag;
2793	bool do_lost = num_dupack || ((flag & FLAG_DATA_SACKED) &&
2794				      tcp_force_fast_retransmit(sk));
2795
2796	if (!tp->packets_out && tp->sacked_out)
2797		tp->sacked_out = 0;
2798
2799	/* Now state machine starts.
2800	 * A. ECE, hence prohibit cwnd undoing, the reduction is required. */
2801	if (flag & FLAG_ECE)
2802		tp->prior_ssthresh = 0;
2803
2804	/* B. In all the states check for reneging SACKs. */
2805	if (tcp_check_sack_reneging(sk, flag))
2806		return;
2807
2808	/* C. Check consistency of the current state. */
2809	tcp_verify_left_out(tp);
2810
2811	/* D. Check state exit conditions. State can be terminated
2812	 *    when high_seq is ACKed. */
2813	if (icsk->icsk_ca_state == TCP_CA_Open) {
2814		WARN_ON(tp->retrans_out != 0);
2815		tp->retrans_stamp = 0;
2816	} else if (!before(tp->snd_una, tp->high_seq)) {
2817		switch (icsk->icsk_ca_state) {
2818		case TCP_CA_CWR:
2819			/* CWR is to be held something *above* high_seq
2820			 * is ACKed for CWR bit to reach receiver. */
2821			if (tp->snd_una != tp->high_seq) {
2822				tcp_end_cwnd_reduction(sk);
2823				tcp_set_ca_state(sk, TCP_CA_Open);
2824			}
2825			break;
2826
2827		case TCP_CA_Recovery:
2828			if (tcp_is_reno(tp))
2829				tcp_reset_reno_sack(tp);
2830			if (tcp_try_undo_recovery(sk))
2831				return;
2832			tcp_end_cwnd_reduction(sk);
2833			break;
2834		}
2835	}
2836
2837	/* E. Process state. */
2838	switch (icsk->icsk_ca_state) {
2839	case TCP_CA_Recovery:
2840		if (!(flag & FLAG_SND_UNA_ADVANCED)) {
2841			if (tcp_is_reno(tp))
2842				tcp_add_reno_sack(sk, num_dupack);
2843		} else {
2844			if (tcp_try_undo_partial(sk, prior_snd_una))
2845				return;
2846			/* Partial ACK arrived. Force fast retransmit. */
2847			do_lost = tcp_is_reno(tp) ||
2848				  tcp_force_fast_retransmit(sk);
2849		}
2850		if (tcp_try_undo_dsack(sk)) {
2851			tcp_try_keep_open(sk);
2852			return;
2853		}
2854		tcp_identify_packet_loss(sk, ack_flag);
2855		break;
2856	case TCP_CA_Loss:
2857		tcp_process_loss(sk, flag, num_dupack, rexmit);
2858		tcp_identify_packet_loss(sk, ack_flag);
2859		if (!(icsk->icsk_ca_state == TCP_CA_Open ||
2860		      (*ack_flag & FLAG_LOST_RETRANS)))
2861			return;
2862		/* Change state if cwnd is undone or retransmits are lost */
2863		/* fall through */
2864	default:
2865		if (tcp_is_reno(tp)) {
2866			if (flag & FLAG_SND_UNA_ADVANCED)
2867				tcp_reset_reno_sack(tp);
2868			tcp_add_reno_sack(sk, num_dupack);
 
2869		}
2870
2871		if (icsk->icsk_ca_state <= TCP_CA_Disorder)
2872			tcp_try_undo_dsack(sk);
2873
2874		tcp_identify_packet_loss(sk, ack_flag);
2875		if (!tcp_time_to_recover(sk, flag)) {
2876			tcp_try_to_open(sk, flag);
2877			return;
2878		}
2879
2880		/* MTU probe failure: don't reduce cwnd */
2881		if (icsk->icsk_ca_state < TCP_CA_CWR &&
2882		    icsk->icsk_mtup.probe_size &&
2883		    tp->snd_una == tp->mtu_probe.probe_seq_start) {
2884			tcp_mtup_probe_failed(sk);
2885			/* Restores the reduction we did in tcp_mtup_probe() */
2886			tp->snd_cwnd++;
2887			tcp_simple_retransmit(sk);
2888			return;
2889		}
2890
2891		/* Otherwise enter Recovery state */
2892		tcp_enter_recovery(sk, (flag & FLAG_ECE));
2893		fast_rexmit = 1;
2894	}
2895
2896	if (!tcp_is_rack(sk) && do_lost)
2897		tcp_update_scoreboard(sk, fast_rexmit);
2898	*rexmit = REXMIT_LOST;
2899}
2900
2901static void tcp_update_rtt_min(struct sock *sk, u32 rtt_us, const int flag)
2902{
2903	u32 wlen = sock_net(sk)->ipv4.sysctl_tcp_min_rtt_wlen * HZ;
2904	struct tcp_sock *tp = tcp_sk(sk);
2905
2906	if ((flag & FLAG_ACK_MAYBE_DELAYED) && rtt_us > tcp_min_rtt(tp)) {
2907		/* If the remote keeps returning delayed ACKs, eventually
2908		 * the min filter would pick it up and overestimate the
2909		 * prop. delay when it expires. Skip suspected delayed ACKs.
2910		 */
2911		return;
2912	}
2913	minmax_running_min(&tp->rtt_min, wlen, tcp_jiffies32,
2914			   rtt_us ? : jiffies_to_usecs(1));
2915}
2916
2917static bool tcp_ack_update_rtt(struct sock *sk, const int flag,
2918			       long seq_rtt_us, long sack_rtt_us,
2919			       long ca_rtt_us, struct rate_sample *rs)
2920{
2921	const struct tcp_sock *tp = tcp_sk(sk);
2922
2923	/* Prefer RTT measured from ACK's timing to TS-ECR. This is because
2924	 * broken middle-boxes or peers may corrupt TS-ECR fields. But
2925	 * Karn's algorithm forbids taking RTT if some retransmitted data
2926	 * is acked (RFC6298).
2927	 */
2928	if (seq_rtt_us < 0)
2929		seq_rtt_us = sack_rtt_us;
2930
2931	/* RTTM Rule: A TSecr value received in a segment is used to
2932	 * update the averaged RTT measurement only if the segment
2933	 * acknowledges some new data, i.e., only if it advances the
2934	 * left edge of the send window.
2935	 * See draft-ietf-tcplw-high-performance-00, section 3.3.
2936	 */
2937	if (seq_rtt_us < 0 && tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
2938	    flag & FLAG_ACKED) {
2939		u32 delta = tcp_time_stamp(tp) - tp->rx_opt.rcv_tsecr;
 
2940
2941		if (likely(delta < INT_MAX / (USEC_PER_SEC / TCP_TS_HZ))) {
2942			seq_rtt_us = delta * (USEC_PER_SEC / TCP_TS_HZ);
2943			ca_rtt_us = seq_rtt_us;
2944		}
2945	}
2946	rs->rtt_us = ca_rtt_us; /* RTT of last (S)ACKed packet (or -1) */
2947	if (seq_rtt_us < 0)
2948		return false;
2949
2950	/* ca_rtt_us >= 0 is counting on the invariant that ca_rtt_us is
2951	 * always taken together with ACK, SACK, or TS-opts. Any negative
2952	 * values will be skipped with the seq_rtt_us < 0 check above.
2953	 */
2954	tcp_update_rtt_min(sk, ca_rtt_us, flag);
2955	tcp_rtt_estimator(sk, seq_rtt_us);
2956	tcp_set_rto(sk);
2957
2958	/* RFC6298: only reset backoff on valid RTT measurement. */
2959	inet_csk(sk)->icsk_backoff = 0;
2960	return true;
2961}
2962
2963/* Compute time elapsed between (last) SYNACK and the ACK completing 3WHS. */
2964void tcp_synack_rtt_meas(struct sock *sk, struct request_sock *req)
2965{
2966	struct rate_sample rs;
2967	long rtt_us = -1L;
2968
2969	if (req && !req->num_retrans && tcp_rsk(req)->snt_synack)
2970		rtt_us = tcp_stamp_us_delta(tcp_clock_us(), tcp_rsk(req)->snt_synack);
2971
2972	tcp_ack_update_rtt(sk, FLAG_SYN_ACKED, rtt_us, -1L, rtt_us, &rs);
2973}
2974
2975
2976static void tcp_cong_avoid(struct sock *sk, u32 ack, u32 acked)
2977{
2978	const struct inet_connection_sock *icsk = inet_csk(sk);
2979
2980	icsk->icsk_ca_ops->cong_avoid(sk, ack, acked);
2981	tcp_sk(sk)->snd_cwnd_stamp = tcp_jiffies32;
2982}
2983
2984/* Restart timer after forward progress on connection.
2985 * RFC2988 recommends to restart timer to now+rto.
2986 */
2987void tcp_rearm_rto(struct sock *sk)
2988{
2989	const struct inet_connection_sock *icsk = inet_csk(sk);
2990	struct tcp_sock *tp = tcp_sk(sk);
2991
2992	/* If the retrans timer is currently being used by Fast Open
2993	 * for SYN-ACK retrans purpose, stay put.
2994	 */
2995	if (rcu_access_pointer(tp->fastopen_rsk))
2996		return;
2997
2998	if (!tp->packets_out) {
2999		inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS);
3000	} else {
3001		u32 rto = inet_csk(sk)->icsk_rto;
3002		/* Offset the time elapsed after installing regular RTO */
3003		if (icsk->icsk_pending == ICSK_TIME_REO_TIMEOUT ||
3004		    icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) {
3005			s64 delta_us = tcp_rto_delta_us(sk);
3006			/* delta_us may not be positive if the socket is locked
3007			 * when the retrans timer fires and is rescheduled.
3008			 */
3009			rto = usecs_to_jiffies(max_t(int, delta_us, 1));
3010		}
3011		tcp_reset_xmit_timer(sk, ICSK_TIME_RETRANS, rto,
3012				     TCP_RTO_MAX, tcp_rtx_queue_head(sk));
3013	}
3014}
3015
3016/* Try to schedule a loss probe; if that doesn't work, then schedule an RTO. */
3017static void tcp_set_xmit_timer(struct sock *sk)
3018{
3019	if (!tcp_schedule_loss_probe(sk, true))
3020		tcp_rearm_rto(sk);
3021}
3022
3023/* If we get here, the whole TSO packet has not been acked. */
3024static u32 tcp_tso_acked(struct sock *sk, struct sk_buff *skb)
3025{
3026	struct tcp_sock *tp = tcp_sk(sk);
3027	u32 packets_acked;
3028
3029	BUG_ON(!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una));
3030
3031	packets_acked = tcp_skb_pcount(skb);
3032	if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
3033		return 0;
3034	packets_acked -= tcp_skb_pcount(skb);
3035
3036	if (packets_acked) {
3037		BUG_ON(tcp_skb_pcount(skb) == 0);
3038		BUG_ON(!before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq));
3039	}
3040
3041	return packets_acked;
3042}
3043
3044static void tcp_ack_tstamp(struct sock *sk, struct sk_buff *skb,
3045			   u32 prior_snd_una)
3046{
3047	const struct skb_shared_info *shinfo;
3048
3049	/* Avoid cache line misses to get skb_shinfo() and shinfo->tx_flags */
3050	if (likely(!TCP_SKB_CB(skb)->txstamp_ack))
3051		return;
3052
3053	shinfo = skb_shinfo(skb);
3054	if (!before(shinfo->tskey, prior_snd_una) &&
3055	    before(shinfo->tskey, tcp_sk(sk)->snd_una)) {
3056		tcp_skb_tsorted_save(skb) {
3057			__skb_tstamp_tx(skb, NULL, sk, SCM_TSTAMP_ACK);
3058		} tcp_skb_tsorted_restore(skb);
3059	}
3060}
3061
3062/* Remove acknowledged frames from the retransmission queue. If our packet
3063 * is before the ack sequence we can discard it as it's confirmed to have
3064 * arrived at the other end.
3065 */
3066static int tcp_clean_rtx_queue(struct sock *sk, u32 prior_fack,
3067			       u32 prior_snd_una,
3068			       struct tcp_sacktag_state *sack)
3069{
3070	const struct inet_connection_sock *icsk = inet_csk(sk);
3071	u64 first_ackt, last_ackt;
3072	struct tcp_sock *tp = tcp_sk(sk);
3073	u32 prior_sacked = tp->sacked_out;
3074	u32 reord = tp->snd_nxt; /* lowest acked un-retx un-sacked seq */
3075	struct sk_buff *skb, *next;
3076	bool fully_acked = true;
3077	long sack_rtt_us = -1L;
3078	long seq_rtt_us = -1L;
3079	long ca_rtt_us = -1L;
3080	u32 pkts_acked = 0;
3081	u32 last_in_flight = 0;
3082	bool rtt_update;
3083	int flag = 0;
3084
3085	first_ackt = 0;
3086
3087	for (skb = skb_rb_first(&sk->tcp_rtx_queue); skb; skb = next) {
3088		struct tcp_skb_cb *scb = TCP_SKB_CB(skb);
3089		const u32 start_seq = scb->seq;
3090		u8 sacked = scb->sacked;
3091		u32 acked_pcount;
3092
3093		tcp_ack_tstamp(sk, skb, prior_snd_una);
3094
3095		/* Determine how many packets and what bytes were acked, tso and else */
3096		if (after(scb->end_seq, tp->snd_una)) {
3097			if (tcp_skb_pcount(skb) == 1 ||
3098			    !after(tp->snd_una, scb->seq))
3099				break;
3100
3101			acked_pcount = tcp_tso_acked(sk, skb);
3102			if (!acked_pcount)
3103				break;
3104			fully_acked = false;
3105		} else {
3106			acked_pcount = tcp_skb_pcount(skb);
3107		}
3108
3109		if (unlikely(sacked & TCPCB_RETRANS)) {
3110			if (sacked & TCPCB_SACKED_RETRANS)
3111				tp->retrans_out -= acked_pcount;
3112			flag |= FLAG_RETRANS_DATA_ACKED;
3113		} else if (!(sacked & TCPCB_SACKED_ACKED)) {
3114			last_ackt = tcp_skb_timestamp_us(skb);
3115			WARN_ON_ONCE(last_ackt == 0);
3116			if (!first_ackt)
3117				first_ackt = last_ackt;
3118
3119			last_in_flight = TCP_SKB_CB(skb)->tx.in_flight;
3120			if (before(start_seq, reord))
3121				reord = start_seq;
3122			if (!after(scb->end_seq, tp->high_seq))
3123				flag |= FLAG_ORIG_SACK_ACKED;
3124		}
3125
3126		if (sacked & TCPCB_SACKED_ACKED) {
3127			tp->sacked_out -= acked_pcount;
3128		} else if (tcp_is_sack(tp)) {
3129			tp->delivered += acked_pcount;
3130			if (!tcp_skb_spurious_retrans(tp, skb))
3131				tcp_rack_advance(tp, sacked, scb->end_seq,
3132						 tcp_skb_timestamp_us(skb));
3133		}
3134		if (sacked & TCPCB_LOST)
3135			tp->lost_out -= acked_pcount;
3136
3137		tp->packets_out -= acked_pcount;
3138		pkts_acked += acked_pcount;
3139		tcp_rate_skb_delivered(sk, skb, sack->rate);
3140
3141		/* Initial outgoing SYN's get put onto the write_queue
3142		 * just like anything else we transmit.  It is not
3143		 * true data, and if we misinform our callers that
3144		 * this ACK acks real data, we will erroneously exit
3145		 * connection startup slow start one packet too
3146		 * quickly.  This is severely frowned upon behavior.
3147		 */
3148		if (likely(!(scb->tcp_flags & TCPHDR_SYN))) {
3149			flag |= FLAG_DATA_ACKED;
3150		} else {
3151			flag |= FLAG_SYN_ACKED;
3152			tp->retrans_stamp = 0;
3153		}
3154
3155		if (!fully_acked)
3156			break;
3157
3158		next = skb_rb_next(skb);
3159		if (unlikely(skb == tp->retransmit_skb_hint))
3160			tp->retransmit_skb_hint = NULL;
3161		if (unlikely(skb == tp->lost_skb_hint))
3162			tp->lost_skb_hint = NULL;
3163		tcp_rtx_queue_unlink_and_free(skb, sk);
3164	}
3165
3166	if (!skb)
3167		tcp_chrono_stop(sk, TCP_CHRONO_BUSY);
3168
3169	if (likely(between(tp->snd_up, prior_snd_una, tp->snd_una)))
3170		tp->snd_up = tp->snd_una;
3171
3172	if (skb && (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
3173		flag |= FLAG_SACK_RENEGING;
3174
3175	if (likely(first_ackt) && !(flag & FLAG_RETRANS_DATA_ACKED)) {
3176		seq_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, first_ackt);
3177		ca_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, last_ackt);
3178
3179		if (pkts_acked == 1 && last_in_flight < tp->mss_cache &&
3180		    last_in_flight && !prior_sacked && fully_acked &&
3181		    sack->rate->prior_delivered + 1 == tp->delivered &&
3182		    !(flag & (FLAG_CA_ALERT | FLAG_SYN_ACKED))) {
3183			/* Conservatively mark a delayed ACK. It's typically
3184			 * from a lone runt packet over the round trip to
3185			 * a receiver w/o out-of-order or CE events.
3186			 */
3187			flag |= FLAG_ACK_MAYBE_DELAYED;
3188		}
3189	}
3190	if (sack->first_sackt) {
3191		sack_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, sack->first_sackt);
3192		ca_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, sack->last_sackt);
3193	}
3194	rtt_update = tcp_ack_update_rtt(sk, flag, seq_rtt_us, sack_rtt_us,
3195					ca_rtt_us, sack->rate);
3196
3197	if (flag & FLAG_ACKED) {
3198		flag |= FLAG_SET_XMIT_TIMER;  /* set TLP or RTO timer */
3199		if (unlikely(icsk->icsk_mtup.probe_size &&
3200			     !after(tp->mtu_probe.probe_seq_end, tp->snd_una))) {
3201			tcp_mtup_probe_success(sk);
3202		}
3203
3204		if (tcp_is_reno(tp)) {
3205			tcp_remove_reno_sacks(sk, pkts_acked);
3206
3207			/* If any of the cumulatively ACKed segments was
3208			 * retransmitted, non-SACK case cannot confirm that
3209			 * progress was due to original transmission due to
3210			 * lack of TCPCB_SACKED_ACKED bits even if some of
3211			 * the packets may have been never retransmitted.
3212			 */
3213			if (flag & FLAG_RETRANS_DATA_ACKED)
3214				flag &= ~FLAG_ORIG_SACK_ACKED;
3215		} else {
3216			int delta;
3217
3218			/* Non-retransmitted hole got filled? That's reordering */
3219			if (before(reord, prior_fack))
3220				tcp_check_sack_reordering(sk, reord, 0);
3221
3222			delta = prior_sacked - tp->sacked_out;
3223			tp->lost_cnt_hint -= min(tp->lost_cnt_hint, delta);
3224		}
3225	} else if (skb && rtt_update && sack_rtt_us >= 0 &&
3226		   sack_rtt_us > tcp_stamp_us_delta(tp->tcp_mstamp,
3227						    tcp_skb_timestamp_us(skb))) {
3228		/* Do not re-arm RTO if the sack RTT is measured from data sent
3229		 * after when the head was last (re)transmitted. Otherwise the
3230		 * timeout may continue to extend in loss recovery.
3231		 */
3232		flag |= FLAG_SET_XMIT_TIMER;  /* set TLP or RTO timer */
3233	}
3234
3235	if (icsk->icsk_ca_ops->pkts_acked) {
3236		struct ack_sample sample = { .pkts_acked = pkts_acked,
3237					     .rtt_us = sack->rate->rtt_us,
3238					     .in_flight = last_in_flight };
3239
3240		icsk->icsk_ca_ops->pkts_acked(sk, &sample);
3241	}
3242
3243#if FASTRETRANS_DEBUG > 0
3244	WARN_ON((int)tp->sacked_out < 0);
3245	WARN_ON((int)tp->lost_out < 0);
3246	WARN_ON((int)tp->retrans_out < 0);
3247	if (!tp->packets_out && tcp_is_sack(tp)) {
3248		icsk = inet_csk(sk);
3249		if (tp->lost_out) {
3250			pr_debug("Leak l=%u %d\n",
3251				 tp->lost_out, icsk->icsk_ca_state);
3252			tp->lost_out = 0;
3253		}
3254		if (tp->sacked_out) {
3255			pr_debug("Leak s=%u %d\n",
3256				 tp->sacked_out, icsk->icsk_ca_state);
3257			tp->sacked_out = 0;
3258		}
3259		if (tp->retrans_out) {
3260			pr_debug("Leak r=%u %d\n",
3261				 tp->retrans_out, icsk->icsk_ca_state);
3262			tp->retrans_out = 0;
3263		}
3264	}
3265#endif
3266	return flag;
3267}
3268
3269static void tcp_ack_probe(struct sock *sk)
3270{
3271	struct inet_connection_sock *icsk = inet_csk(sk);
3272	struct sk_buff *head = tcp_send_head(sk);
3273	const struct tcp_sock *tp = tcp_sk(sk);
3274
3275	/* Was it a usable window open? */
3276	if (!head)
3277		return;
3278	if (!after(TCP_SKB_CB(head)->end_seq, tcp_wnd_end(tp))) {
3279		icsk->icsk_backoff = 0;
3280		inet_csk_clear_xmit_timer(sk, ICSK_TIME_PROBE0);
3281		/* Socket must be waked up by subsequent tcp_data_snd_check().
3282		 * This function is not for random using!
3283		 */
3284	} else {
3285		unsigned long when = tcp_probe0_when(sk, TCP_RTO_MAX);
3286
3287		tcp_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
3288				     when, TCP_RTO_MAX, NULL);
3289	}
3290}
3291
3292static inline bool tcp_ack_is_dubious(const struct sock *sk, const int flag)
3293{
3294	return !(flag & FLAG_NOT_DUP) || (flag & FLAG_CA_ALERT) ||
3295		inet_csk(sk)->icsk_ca_state != TCP_CA_Open;
3296}
3297
3298/* Decide wheather to run the increase function of congestion control. */
3299static inline bool tcp_may_raise_cwnd(const struct sock *sk, const int flag)
3300{
3301	/* If reordering is high then always grow cwnd whenever data is
3302	 * delivered regardless of its ordering. Otherwise stay conservative
3303	 * and only grow cwnd on in-order delivery (RFC5681). A stretched ACK w/
3304	 * new SACK or ECE mark may first advance cwnd here and later reduce
3305	 * cwnd in tcp_fastretrans_alert() based on more states.
3306	 */
3307	if (tcp_sk(sk)->reordering > sock_net(sk)->ipv4.sysctl_tcp_reordering)
3308		return flag & FLAG_FORWARD_PROGRESS;
3309
3310	return flag & FLAG_DATA_ACKED;
3311}
3312
3313/* The "ultimate" congestion control function that aims to replace the rigid
3314 * cwnd increase and decrease control (tcp_cong_avoid,tcp_*cwnd_reduction).
3315 * It's called toward the end of processing an ACK with precise rate
3316 * information. All transmission or retransmission are delayed afterwards.
3317 */
3318static void tcp_cong_control(struct sock *sk, u32 ack, u32 acked_sacked,
3319			     int flag, const struct rate_sample *rs)
3320{
3321	const struct inet_connection_sock *icsk = inet_csk(sk);
3322
3323	if (icsk->icsk_ca_ops->cong_control) {
3324		icsk->icsk_ca_ops->cong_control(sk, rs);
3325		return;
3326	}
3327
3328	if (tcp_in_cwnd_reduction(sk)) {
3329		/* Reduce cwnd if state mandates */
3330		tcp_cwnd_reduction(sk, acked_sacked, flag);
3331	} else if (tcp_may_raise_cwnd(sk, flag)) {
3332		/* Advance cwnd if state allows */
3333		tcp_cong_avoid(sk, ack, acked_sacked);
3334	}
3335	tcp_update_pacing_rate(sk);
3336}
3337
3338/* Check that window update is acceptable.
3339 * The function assumes that snd_una<=ack<=snd_next.
3340 */
3341static inline bool tcp_may_update_window(const struct tcp_sock *tp,
3342					const u32 ack, const u32 ack_seq,
3343					const u32 nwin)
3344{
3345	return	after(ack, tp->snd_una) ||
3346		after(ack_seq, tp->snd_wl1) ||
3347		(ack_seq == tp->snd_wl1 && nwin > tp->snd_wnd);
3348}
3349
3350/* If we update tp->snd_una, also update tp->bytes_acked */
3351static void tcp_snd_una_update(struct tcp_sock *tp, u32 ack)
3352{
3353	u32 delta = ack - tp->snd_una;
3354
3355	sock_owned_by_me((struct sock *)tp);
3356	tp->bytes_acked += delta;
3357	tp->snd_una = ack;
3358}
3359
3360/* If we update tp->rcv_nxt, also update tp->bytes_received */
3361static void tcp_rcv_nxt_update(struct tcp_sock *tp, u32 seq)
3362{
3363	u32 delta = seq - tp->rcv_nxt;
3364
3365	sock_owned_by_me((struct sock *)tp);
3366	tp->bytes_received += delta;
3367	WRITE_ONCE(tp->rcv_nxt, seq);
3368}
3369
3370/* Update our send window.
3371 *
3372 * Window update algorithm, described in RFC793/RFC1122 (used in linux-2.2
3373 * and in FreeBSD. NetBSD's one is even worse.) is wrong.
3374 */
3375static int tcp_ack_update_window(struct sock *sk, const struct sk_buff *skb, u32 ack,
3376				 u32 ack_seq)
3377{
3378	struct tcp_sock *tp = tcp_sk(sk);
3379	int flag = 0;
3380	u32 nwin = ntohs(tcp_hdr(skb)->window);
3381
3382	if (likely(!tcp_hdr(skb)->syn))
3383		nwin <<= tp->rx_opt.snd_wscale;
3384
3385	if (tcp_may_update_window(tp, ack, ack_seq, nwin)) {
3386		flag |= FLAG_WIN_UPDATE;
3387		tcp_update_wl(tp, ack_seq);
3388
3389		if (tp->snd_wnd != nwin) {
3390			tp->snd_wnd = nwin;
3391
3392			/* Note, it is the only place, where
3393			 * fast path is recovered for sending TCP.
3394			 */
3395			tp->pred_flags = 0;
3396			tcp_fast_path_check(sk);
3397
3398			if (!tcp_write_queue_empty(sk))
3399				tcp_slow_start_after_idle_check(sk);
3400
3401			if (nwin > tp->max_window) {
3402				tp->max_window = nwin;
3403				tcp_sync_mss(sk, inet_csk(sk)->icsk_pmtu_cookie);
3404			}
3405		}
3406	}
3407
3408	tcp_snd_una_update(tp, ack);
3409
3410	return flag;
3411}
3412
3413static bool __tcp_oow_rate_limited(struct net *net, int mib_idx,
3414				   u32 *last_oow_ack_time)
3415{
3416	if (*last_oow_ack_time) {
3417		s32 elapsed = (s32)(tcp_jiffies32 - *last_oow_ack_time);
3418
3419		if (0 <= elapsed && elapsed < net->ipv4.sysctl_tcp_invalid_ratelimit) {
3420			NET_INC_STATS(net, mib_idx);
3421			return true;	/* rate-limited: don't send yet! */
3422		}
3423	}
3424
3425	*last_oow_ack_time = tcp_jiffies32;
3426
3427	return false;	/* not rate-limited: go ahead, send dupack now! */
3428}
3429
3430/* Return true if we're currently rate-limiting out-of-window ACKs and
3431 * thus shouldn't send a dupack right now. We rate-limit dupacks in
3432 * response to out-of-window SYNs or ACKs to mitigate ACK loops or DoS
3433 * attacks that send repeated SYNs or ACKs for the same connection. To
3434 * do this, we do not send a duplicate SYNACK or ACK if the remote
3435 * endpoint is sending out-of-window SYNs or pure ACKs at a high rate.
3436 */
3437bool tcp_oow_rate_limited(struct net *net, const struct sk_buff *skb,
3438			  int mib_idx, u32 *last_oow_ack_time)
3439{
3440	/* Data packets without SYNs are not likely part of an ACK loop. */
3441	if ((TCP_SKB_CB(skb)->seq != TCP_SKB_CB(skb)->end_seq) &&
3442	    !tcp_hdr(skb)->syn)
3443		return false;
3444
3445	return __tcp_oow_rate_limited(net, mib_idx, last_oow_ack_time);
3446}
3447
3448/* RFC 5961 7 [ACK Throttling] */
3449static void tcp_send_challenge_ack(struct sock *sk, const struct sk_buff *skb)
3450{
3451	/* unprotected vars, we dont care of overwrites */
3452	static u32 challenge_timestamp;
3453	static unsigned int challenge_count;
3454	struct tcp_sock *tp = tcp_sk(sk);
3455	struct net *net = sock_net(sk);
3456	u32 count, now;
3457
3458	/* First check our per-socket dupack rate limit. */
3459	if (__tcp_oow_rate_limited(net,
3460				   LINUX_MIB_TCPACKSKIPPEDCHALLENGE,
3461				   &tp->last_oow_ack_time))
3462		return;
3463
3464	/* Then check host-wide RFC 5961 rate limit. */
3465	now = jiffies / HZ;
3466	if (now != challenge_timestamp) {
3467		u32 ack_limit = net->ipv4.sysctl_tcp_challenge_ack_limit;
3468		u32 half = (ack_limit + 1) >> 1;
3469
3470		challenge_timestamp = now;
3471		WRITE_ONCE(challenge_count, half + prandom_u32_max(ack_limit));
3472	}
3473	count = READ_ONCE(challenge_count);
3474	if (count > 0) {
3475		WRITE_ONCE(challenge_count, count - 1);
3476		NET_INC_STATS(net, LINUX_MIB_TCPCHALLENGEACK);
3477		tcp_send_ack(sk);
3478	}
3479}
3480
3481static void tcp_store_ts_recent(struct tcp_sock *tp)
3482{
3483	tp->rx_opt.ts_recent = tp->rx_opt.rcv_tsval;
3484	tp->rx_opt.ts_recent_stamp = ktime_get_seconds();
3485}
3486
3487static void tcp_replace_ts_recent(struct tcp_sock *tp, u32 seq)
3488{
3489	if (tp->rx_opt.saw_tstamp && !after(seq, tp->rcv_wup)) {
3490		/* PAWS bug workaround wrt. ACK frames, the PAWS discard
3491		 * extra check below makes sure this can only happen
3492		 * for pure ACK frames.  -DaveM
3493		 *
3494		 * Not only, also it occurs for expired timestamps.
3495		 */
3496
3497		if (tcp_paws_check(&tp->rx_opt, 0))
3498			tcp_store_ts_recent(tp);
3499	}
3500}
3501
3502/* This routine deals with acks during a TLP episode.
3503 * We mark the end of a TLP episode on receiving TLP dupack or when
3504 * ack is after tlp_high_seq.
3505 * Ref: loss detection algorithm in draft-dukkipati-tcpm-tcp-loss-probe.
3506 */
3507static void tcp_process_tlp_ack(struct sock *sk, u32 ack, int flag)
3508{
3509	struct tcp_sock *tp = tcp_sk(sk);
3510
3511	if (before(ack, tp->tlp_high_seq))
3512		return;
3513
3514	if (flag & FLAG_DSACKING_ACK) {
3515		/* This DSACK means original and TLP probe arrived; no loss */
3516		tp->tlp_high_seq = 0;
3517	} else if (after(ack, tp->tlp_high_seq)) {
3518		/* ACK advances: there was a loss, so reduce cwnd. Reset
3519		 * tlp_high_seq in tcp_init_cwnd_reduction()
3520		 */
3521		tcp_init_cwnd_reduction(sk);
3522		tcp_set_ca_state(sk, TCP_CA_CWR);
3523		tcp_end_cwnd_reduction(sk);
3524		tcp_try_keep_open(sk);
3525		NET_INC_STATS(sock_net(sk),
3526				LINUX_MIB_TCPLOSSPROBERECOVERY);
3527	} else if (!(flag & (FLAG_SND_UNA_ADVANCED |
3528			     FLAG_NOT_DUP | FLAG_DATA_SACKED))) {
3529		/* Pure dupack: original and TLP probe arrived; no loss */
3530		tp->tlp_high_seq = 0;
3531	}
3532}
3533
3534static inline void tcp_in_ack_event(struct sock *sk, u32 flags)
3535{
3536	const struct inet_connection_sock *icsk = inet_csk(sk);
3537
3538	if (icsk->icsk_ca_ops->in_ack_event)
3539		icsk->icsk_ca_ops->in_ack_event(sk, flags);
3540}
3541
3542/* Congestion control has updated the cwnd already. So if we're in
3543 * loss recovery then now we do any new sends (for FRTO) or
3544 * retransmits (for CA_Loss or CA_recovery) that make sense.
3545 */
3546static void tcp_xmit_recovery(struct sock *sk, int rexmit)
3547{
3548	struct tcp_sock *tp = tcp_sk(sk);
3549
3550	if (rexmit == REXMIT_NONE || sk->sk_state == TCP_SYN_SENT)
3551		return;
3552
3553	if (unlikely(rexmit == 2)) {
3554		__tcp_push_pending_frames(sk, tcp_current_mss(sk),
3555					  TCP_NAGLE_OFF);
3556		if (after(tp->snd_nxt, tp->high_seq))
3557			return;
3558		tp->frto = 0;
3559	}
3560	tcp_xmit_retransmit_queue(sk);
3561}
3562
3563/* Returns the number of packets newly acked or sacked by the current ACK */
3564static u32 tcp_newly_delivered(struct sock *sk, u32 prior_delivered, int flag)
3565{
3566	const struct net *net = sock_net(sk);
3567	struct tcp_sock *tp = tcp_sk(sk);
3568	u32 delivered;
3569
3570	delivered = tp->delivered - prior_delivered;
3571	NET_ADD_STATS(net, LINUX_MIB_TCPDELIVERED, delivered);
3572	if (flag & FLAG_ECE) {
3573		tp->delivered_ce += delivered;
3574		NET_ADD_STATS(net, LINUX_MIB_TCPDELIVEREDCE, delivered);
3575	}
3576	return delivered;
3577}
3578
3579/* This routine deals with incoming acks, but not outgoing ones. */
3580static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
3581{
3582	struct inet_connection_sock *icsk = inet_csk(sk);
3583	struct tcp_sock *tp = tcp_sk(sk);
3584	struct tcp_sacktag_state sack_state;
3585	struct rate_sample rs = { .prior_delivered = 0 };
3586	u32 prior_snd_una = tp->snd_una;
3587	bool is_sack_reneg = tp->is_sack_reneg;
3588	u32 ack_seq = TCP_SKB_CB(skb)->seq;
3589	u32 ack = TCP_SKB_CB(skb)->ack_seq;
3590	int num_dupack = 0;
3591	int prior_packets = tp->packets_out;
3592	u32 delivered = tp->delivered;
3593	u32 lost = tp->lost;
3594	int rexmit = REXMIT_NONE; /* Flag to (re)transmit to recover losses */
3595	u32 prior_fack;
3596
3597	sack_state.first_sackt = 0;
3598	sack_state.rate = &rs;
3599
3600	/* We very likely will need to access rtx queue. */
3601	prefetch(sk->tcp_rtx_queue.rb_node);
3602
3603	/* If the ack is older than previous acks
3604	 * then we can probably ignore it.
3605	 */
3606	if (before(ack, prior_snd_una)) {
3607		/* RFC 5961 5.2 [Blind Data Injection Attack].[Mitigation] */
3608		if (before(ack, prior_snd_una - tp->max_window)) {
3609			if (!(flag & FLAG_NO_CHALLENGE_ACK))
3610				tcp_send_challenge_ack(sk, skb);
3611			return -1;
3612		}
3613		goto old_ack;
3614	}
3615
3616	/* If the ack includes data we haven't sent yet, discard
3617	 * this segment (RFC793 Section 3.9).
3618	 */
3619	if (after(ack, tp->snd_nxt))
3620		return -1;
3621
3622	if (after(ack, prior_snd_una)) {
3623		flag |= FLAG_SND_UNA_ADVANCED;
3624		icsk->icsk_retransmits = 0;
3625
3626#if IS_ENABLED(CONFIG_TLS_DEVICE)
3627		if (static_branch_unlikely(&clean_acked_data_enabled.key))
3628			if (icsk->icsk_clean_acked)
3629				icsk->icsk_clean_acked(sk, ack);
3630#endif
3631	}
3632
3633	prior_fack = tcp_is_sack(tp) ? tcp_highest_sack_seq(tp) : tp->snd_una;
3634	rs.prior_in_flight = tcp_packets_in_flight(tp);
3635
3636	/* ts_recent update must be made after we are sure that the packet
3637	 * is in window.
3638	 */
3639	if (flag & FLAG_UPDATE_TS_RECENT)
3640		tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
3641
3642	if ((flag & (FLAG_SLOWPATH | FLAG_SND_UNA_ADVANCED)) ==
3643	    FLAG_SND_UNA_ADVANCED) {
3644		/* Window is constant, pure forward advance.
3645		 * No more checks are required.
3646		 * Note, we use the fact that SND.UNA>=SND.WL2.
3647		 */
3648		tcp_update_wl(tp, ack_seq);
3649		tcp_snd_una_update(tp, ack);
3650		flag |= FLAG_WIN_UPDATE;
3651
3652		tcp_in_ack_event(sk, CA_ACK_WIN_UPDATE);
3653
3654		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPHPACKS);
3655	} else {
3656		u32 ack_ev_flags = CA_ACK_SLOWPATH;
3657
3658		if (ack_seq != TCP_SKB_CB(skb)->end_seq)
3659			flag |= FLAG_DATA;
3660		else
3661			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPPUREACKS);
3662
3663		flag |= tcp_ack_update_window(sk, skb, ack, ack_seq);
3664
3665		if (TCP_SKB_CB(skb)->sacked)
3666			flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una,
3667							&sack_state);
3668
3669		if (tcp_ecn_rcv_ecn_echo(tp, tcp_hdr(skb))) {
3670			flag |= FLAG_ECE;
3671			ack_ev_flags |= CA_ACK_ECE;
3672		}
3673
3674		if (flag & FLAG_WIN_UPDATE)
3675			ack_ev_flags |= CA_ACK_WIN_UPDATE;
3676
3677		tcp_in_ack_event(sk, ack_ev_flags);
3678	}
3679
3680	/* We passed data and got it acked, remove any soft error
3681	 * log. Something worked...
3682	 */
3683	sk->sk_err_soft = 0;
3684	icsk->icsk_probes_out = 0;
3685	tp->rcv_tstamp = tcp_jiffies32;
3686	if (!prior_packets)
3687		goto no_queue;
3688
3689	/* See if we can take anything off of the retransmit queue. */
3690	flag |= tcp_clean_rtx_queue(sk, prior_fack, prior_snd_una, &sack_state);
3691
3692	tcp_rack_update_reo_wnd(sk, &rs);
3693
3694	if (tp->tlp_high_seq)
3695		tcp_process_tlp_ack(sk, ack, flag);
3696	/* If needed, reset TLP/RTO timer; RACK may later override this. */
3697	if (flag & FLAG_SET_XMIT_TIMER)
3698		tcp_set_xmit_timer(sk);
3699
3700	if (tcp_ack_is_dubious(sk, flag)) {
3701		if (!(flag & (FLAG_SND_UNA_ADVANCED | FLAG_NOT_DUP))) {
3702			num_dupack = 1;
3703			/* Consider if pure acks were aggregated in tcp_add_backlog() */
3704			if (!(flag & FLAG_DATA))
3705				num_dupack = max_t(u16, 1, skb_shinfo(skb)->gso_segs);
3706		}
3707		tcp_fastretrans_alert(sk, prior_snd_una, num_dupack, &flag,
3708				      &rexmit);
3709	}
3710
3711	if ((flag & FLAG_FORWARD_PROGRESS) || !(flag & FLAG_NOT_DUP))
3712		sk_dst_confirm(sk);
3713
3714	delivered = tcp_newly_delivered(sk, delivered, flag);
3715	lost = tp->lost - lost;			/* freshly marked lost */
3716	rs.is_ack_delayed = !!(flag & FLAG_ACK_MAYBE_DELAYED);
3717	tcp_rate_gen(sk, delivered, lost, is_sack_reneg, sack_state.rate);
3718	tcp_cong_control(sk, ack, delivered, flag, sack_state.rate);
3719	tcp_xmit_recovery(sk, rexmit);
3720	return 1;
3721
3722no_queue:
3723	/* If data was DSACKed, see if we can undo a cwnd reduction. */
3724	if (flag & FLAG_DSACKING_ACK) {
3725		tcp_fastretrans_alert(sk, prior_snd_una, num_dupack, &flag,
3726				      &rexmit);
3727		tcp_newly_delivered(sk, delivered, flag);
3728	}
3729	/* If this ack opens up a zero window, clear backoff.  It was
3730	 * being used to time the probes, and is probably far higher than
3731	 * it needs to be for normal retransmission.
3732	 */
3733	tcp_ack_probe(sk);
3734
3735	if (tp->tlp_high_seq)
3736		tcp_process_tlp_ack(sk, ack, flag);
3737	return 1;
3738
 
 
 
 
3739old_ack:
3740	/* If data was SACKed, tag it and see if we should send more data.
3741	 * If data was DSACKed, see if we can undo a cwnd reduction.
3742	 */
3743	if (TCP_SKB_CB(skb)->sacked) {
3744		flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una,
3745						&sack_state);
3746		tcp_fastretrans_alert(sk, prior_snd_una, num_dupack, &flag,
3747				      &rexmit);
3748		tcp_newly_delivered(sk, delivered, flag);
3749		tcp_xmit_recovery(sk, rexmit);
3750	}
3751
 
3752	return 0;
3753}
3754
3755static void tcp_parse_fastopen_option(int len, const unsigned char *cookie,
3756				      bool syn, struct tcp_fastopen_cookie *foc,
3757				      bool exp_opt)
3758{
3759	/* Valid only in SYN or SYN-ACK with an even length.  */
3760	if (!foc || !syn || len < 0 || (len & 1))
3761		return;
3762
3763	if (len >= TCP_FASTOPEN_COOKIE_MIN &&
3764	    len <= TCP_FASTOPEN_COOKIE_MAX)
3765		memcpy(foc->val, cookie, len);
3766	else if (len != 0)
3767		len = -1;
3768	foc->len = len;
3769	foc->exp = exp_opt;
3770}
3771
3772static void smc_parse_options(const struct tcphdr *th,
3773			      struct tcp_options_received *opt_rx,
3774			      const unsigned char *ptr,
3775			      int opsize)
3776{
3777#if IS_ENABLED(CONFIG_SMC)
3778	if (static_branch_unlikely(&tcp_have_smc)) {
3779		if (th->syn && !(opsize & 1) &&
3780		    opsize >= TCPOLEN_EXP_SMC_BASE &&
3781		    get_unaligned_be32(ptr) == TCPOPT_SMC_MAGIC)
3782			opt_rx->smc_ok = 1;
3783	}
3784#endif
3785}
3786
3787/* Try to parse the MSS option from the TCP header. Return 0 on failure, clamped
3788 * value on success.
3789 */
3790static u16 tcp_parse_mss_option(const struct tcphdr *th, u16 user_mss)
3791{
3792	const unsigned char *ptr = (const unsigned char *)(th + 1);
3793	int length = (th->doff * 4) - sizeof(struct tcphdr);
3794	u16 mss = 0;
3795
3796	while (length > 0) {
3797		int opcode = *ptr++;
3798		int opsize;
3799
3800		switch (opcode) {
3801		case TCPOPT_EOL:
3802			return mss;
3803		case TCPOPT_NOP:	/* Ref: RFC 793 section 3.1 */
3804			length--;
3805			continue;
3806		default:
3807			if (length < 2)
3808				return mss;
3809			opsize = *ptr++;
3810			if (opsize < 2) /* "silly options" */
3811				return mss;
3812			if (opsize > length)
3813				return mss;	/* fail on partial options */
3814			if (opcode == TCPOPT_MSS && opsize == TCPOLEN_MSS) {
3815				u16 in_mss = get_unaligned_be16(ptr);
3816
3817				if (in_mss) {
3818					if (user_mss && user_mss < in_mss)
3819						in_mss = user_mss;
3820					mss = in_mss;
3821				}
3822			}
3823			ptr += opsize - 2;
3824			length -= opsize;
3825		}
3826	}
3827	return mss;
3828}
3829
3830/* Look for tcp options. Normally only called on SYN and SYNACK packets.
3831 * But, this can also be called on packets in the established flow when
3832 * the fast version below fails.
3833 */
3834void tcp_parse_options(const struct net *net,
3835		       const struct sk_buff *skb,
3836		       struct tcp_options_received *opt_rx, int estab,
3837		       struct tcp_fastopen_cookie *foc)
3838{
3839	const unsigned char *ptr;
3840	const struct tcphdr *th = tcp_hdr(skb);
3841	int length = (th->doff * 4) - sizeof(struct tcphdr);
3842
3843	ptr = (const unsigned char *)(th + 1);
3844	opt_rx->saw_tstamp = 0;
3845
3846	while (length > 0) {
3847		int opcode = *ptr++;
3848		int opsize;
3849
3850		switch (opcode) {
3851		case TCPOPT_EOL:
3852			return;
3853		case TCPOPT_NOP:	/* Ref: RFC 793 section 3.1 */
3854			length--;
3855			continue;
3856		default:
3857			if (length < 2)
3858				return;
3859			opsize = *ptr++;
3860			if (opsize < 2) /* "silly options" */
3861				return;
3862			if (opsize > length)
3863				return;	/* don't parse partial options */
3864			switch (opcode) {
3865			case TCPOPT_MSS:
3866				if (opsize == TCPOLEN_MSS && th->syn && !estab) {
3867					u16 in_mss = get_unaligned_be16(ptr);
3868					if (in_mss) {
3869						if (opt_rx->user_mss &&
3870						    opt_rx->user_mss < in_mss)
3871							in_mss = opt_rx->user_mss;
3872						opt_rx->mss_clamp = in_mss;
3873					}
3874				}
3875				break;
3876			case TCPOPT_WINDOW:
3877				if (opsize == TCPOLEN_WINDOW && th->syn &&
3878				    !estab && net->ipv4.sysctl_tcp_window_scaling) {
3879					__u8 snd_wscale = *(__u8 *)ptr;
3880					opt_rx->wscale_ok = 1;
3881					if (snd_wscale > TCP_MAX_WSCALE) {
3882						net_info_ratelimited("%s: Illegal window scaling value %d > %u received\n",
3883								     __func__,
3884								     snd_wscale,
3885								     TCP_MAX_WSCALE);
3886						snd_wscale = TCP_MAX_WSCALE;
3887					}
3888					opt_rx->snd_wscale = snd_wscale;
3889				}
3890				break;
3891			case TCPOPT_TIMESTAMP:
3892				if ((opsize == TCPOLEN_TIMESTAMP) &&
3893				    ((estab && opt_rx->tstamp_ok) ||
3894				     (!estab && net->ipv4.sysctl_tcp_timestamps))) {
3895					opt_rx->saw_tstamp = 1;
3896					opt_rx->rcv_tsval = get_unaligned_be32(ptr);
3897					opt_rx->rcv_tsecr = get_unaligned_be32(ptr + 4);
3898				}
3899				break;
3900			case TCPOPT_SACK_PERM:
3901				if (opsize == TCPOLEN_SACK_PERM && th->syn &&
3902				    !estab && net->ipv4.sysctl_tcp_sack) {
3903					opt_rx->sack_ok = TCP_SACK_SEEN;
3904					tcp_sack_reset(opt_rx);
3905				}
3906				break;
3907
3908			case TCPOPT_SACK:
3909				if ((opsize >= (TCPOLEN_SACK_BASE + TCPOLEN_SACK_PERBLOCK)) &&
3910				   !((opsize - TCPOLEN_SACK_BASE) % TCPOLEN_SACK_PERBLOCK) &&
3911				   opt_rx->sack_ok) {
3912					TCP_SKB_CB(skb)->sacked = (ptr - 2) - (unsigned char *)th;
3913				}
3914				break;
3915#ifdef CONFIG_TCP_MD5SIG
3916			case TCPOPT_MD5SIG:
3917				/*
3918				 * The MD5 Hash has already been
3919				 * checked (see tcp_v{4,6}_do_rcv()).
3920				 */
3921				break;
3922#endif
3923			case TCPOPT_FASTOPEN:
3924				tcp_parse_fastopen_option(
3925					opsize - TCPOLEN_FASTOPEN_BASE,
3926					ptr, th->syn, foc, false);
3927				break;
3928
3929			case TCPOPT_EXP:
3930				/* Fast Open option shares code 254 using a
3931				 * 16 bits magic number.
3932				 */
3933				if (opsize >= TCPOLEN_EXP_FASTOPEN_BASE &&
3934				    get_unaligned_be16(ptr) ==
3935				    TCPOPT_FASTOPEN_MAGIC)
3936					tcp_parse_fastopen_option(opsize -
3937						TCPOLEN_EXP_FASTOPEN_BASE,
3938						ptr + 2, th->syn, foc, true);
3939				else
3940					smc_parse_options(th, opt_rx, ptr,
3941							  opsize);
3942				break;
3943
3944			}
3945			ptr += opsize-2;
3946			length -= opsize;
3947		}
3948	}
3949}
3950EXPORT_SYMBOL(tcp_parse_options);
3951
3952static bool tcp_parse_aligned_timestamp(struct tcp_sock *tp, const struct tcphdr *th)
3953{
3954	const __be32 *ptr = (const __be32 *)(th + 1);
3955
3956	if (*ptr == htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16)
3957			  | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP)) {
3958		tp->rx_opt.saw_tstamp = 1;
3959		++ptr;
3960		tp->rx_opt.rcv_tsval = ntohl(*ptr);
3961		++ptr;
3962		if (*ptr)
3963			tp->rx_opt.rcv_tsecr = ntohl(*ptr) - tp->tsoffset;
3964		else
3965			tp->rx_opt.rcv_tsecr = 0;
3966		return true;
3967	}
3968	return false;
3969}
3970
3971/* Fast parse options. This hopes to only see timestamps.
3972 * If it is wrong it falls back on tcp_parse_options().
3973 */
3974static bool tcp_fast_parse_options(const struct net *net,
3975				   const struct sk_buff *skb,
3976				   const struct tcphdr *th, struct tcp_sock *tp)
3977{
3978	/* In the spirit of fast parsing, compare doff directly to constant
3979	 * values.  Because equality is used, short doff can be ignored here.
3980	 */
3981	if (th->doff == (sizeof(*th) / 4)) {
3982		tp->rx_opt.saw_tstamp = 0;
3983		return false;
3984	} else if (tp->rx_opt.tstamp_ok &&
3985		   th->doff == ((sizeof(*th) + TCPOLEN_TSTAMP_ALIGNED) / 4)) {
3986		if (tcp_parse_aligned_timestamp(tp, th))
3987			return true;
3988	}
3989
3990	tcp_parse_options(net, skb, &tp->rx_opt, 1, NULL);
3991	if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
3992		tp->rx_opt.rcv_tsecr -= tp->tsoffset;
3993
3994	return true;
3995}
3996
3997#ifdef CONFIG_TCP_MD5SIG
3998/*
3999 * Parse MD5 Signature option
4000 */
4001const u8 *tcp_parse_md5sig_option(const struct tcphdr *th)
4002{
4003	int length = (th->doff << 2) - sizeof(*th);
4004	const u8 *ptr = (const u8 *)(th + 1);
4005
4006	/* If not enough data remaining, we can short cut */
4007	while (length >= TCPOLEN_MD5SIG) {
4008		int opcode = *ptr++;
4009		int opsize;
4010
4011		switch (opcode) {
4012		case TCPOPT_EOL:
4013			return NULL;
4014		case TCPOPT_NOP:
4015			length--;
4016			continue;
4017		default:
4018			opsize = *ptr++;
4019			if (opsize < 2 || opsize > length)
4020				return NULL;
4021			if (opcode == TCPOPT_MD5SIG)
4022				return opsize == TCPOLEN_MD5SIG ? ptr : NULL;
4023		}
4024		ptr += opsize - 2;
4025		length -= opsize;
4026	}
4027	return NULL;
4028}
4029EXPORT_SYMBOL(tcp_parse_md5sig_option);
4030#endif
4031
4032/* Sorry, PAWS as specified is broken wrt. pure-ACKs -DaveM
4033 *
4034 * It is not fatal. If this ACK does _not_ change critical state (seqs, window)
4035 * it can pass through stack. So, the following predicate verifies that
4036 * this segment is not used for anything but congestion avoidance or
4037 * fast retransmit. Moreover, we even are able to eliminate most of such
4038 * second order effects, if we apply some small "replay" window (~RTO)
4039 * to timestamp space.
4040 *
4041 * All these measures still do not guarantee that we reject wrapped ACKs
4042 * on networks with high bandwidth, when sequence space is recycled fastly,
4043 * but it guarantees that such events will be very rare and do not affect
4044 * connection seriously. This doesn't look nice, but alas, PAWS is really
4045 * buggy extension.
4046 *
4047 * [ Later note. Even worse! It is buggy for segments _with_ data. RFC
4048 * states that events when retransmit arrives after original data are rare.
4049 * It is a blatant lie. VJ forgot about fast retransmit! 8)8) It is
4050 * the biggest problem on large power networks even with minor reordering.
4051 * OK, let's give it small replay window. If peer clock is even 1hz, it is safe
4052 * up to bandwidth of 18Gigabit/sec. 8) ]
4053 */
4054
4055static int tcp_disordered_ack(const struct sock *sk, const struct sk_buff *skb)
4056{
4057	const struct tcp_sock *tp = tcp_sk(sk);
4058	const struct tcphdr *th = tcp_hdr(skb);
4059	u32 seq = TCP_SKB_CB(skb)->seq;
4060	u32 ack = TCP_SKB_CB(skb)->ack_seq;
4061
4062	return (/* 1. Pure ACK with correct sequence number. */
4063		(th->ack && seq == TCP_SKB_CB(skb)->end_seq && seq == tp->rcv_nxt) &&
4064
4065		/* 2. ... and duplicate ACK. */
4066		ack == tp->snd_una &&
4067
4068		/* 3. ... and does not update window. */
4069		!tcp_may_update_window(tp, ack, seq, ntohs(th->window) << tp->rx_opt.snd_wscale) &&
4070
4071		/* 4. ... and sits in replay window. */
4072		(s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) <= (inet_csk(sk)->icsk_rto * 1024) / HZ);
4073}
4074
4075static inline bool tcp_paws_discard(const struct sock *sk,
4076				   const struct sk_buff *skb)
4077{
4078	const struct tcp_sock *tp = tcp_sk(sk);
4079
4080	return !tcp_paws_check(&tp->rx_opt, TCP_PAWS_WINDOW) &&
4081	       !tcp_disordered_ack(sk, skb);
4082}
4083
4084/* Check segment sequence number for validity.
4085 *
4086 * Segment controls are considered valid, if the segment
4087 * fits to the window after truncation to the window. Acceptability
4088 * of data (and SYN, FIN, of course) is checked separately.
4089 * See tcp_data_queue(), for example.
4090 *
4091 * Also, controls (RST is main one) are accepted using RCV.WUP instead
4092 * of RCV.NXT. Peer still did not advance his SND.UNA when we
4093 * delayed ACK, so that hisSND.UNA<=ourRCV.WUP.
4094 * (borrowed from freebsd)
4095 */
4096
4097static inline bool tcp_sequence(const struct tcp_sock *tp, u32 seq, u32 end_seq)
4098{
4099	return	!before(end_seq, tp->rcv_wup) &&
4100		!after(seq, tp->rcv_nxt + tcp_receive_window(tp));
4101}
4102
4103/* When we get a reset we do this. */
4104void tcp_reset(struct sock *sk)
4105{
4106	trace_tcp_receive_reset(sk);
4107
4108	/* We want the right error as BSD sees it (and indeed as we do). */
4109	switch (sk->sk_state) {
4110	case TCP_SYN_SENT:
4111		sk->sk_err = ECONNREFUSED;
4112		break;
4113	case TCP_CLOSE_WAIT:
4114		sk->sk_err = EPIPE;
4115		break;
4116	case TCP_CLOSE:
4117		return;
4118	default:
4119		sk->sk_err = ECONNRESET;
4120	}
4121	/* This barrier is coupled with smp_rmb() in tcp_poll() */
4122	smp_wmb();
4123
4124	tcp_write_queue_purge(sk);
4125	tcp_done(sk);
4126
4127	if (!sock_flag(sk, SOCK_DEAD))
4128		sk->sk_error_report(sk);
4129}
4130
4131/*
4132 * 	Process the FIN bit. This now behaves as it is supposed to work
4133 *	and the FIN takes effect when it is validly part of sequence
4134 *	space. Not before when we get holes.
4135 *
4136 *	If we are ESTABLISHED, a received fin moves us to CLOSE-WAIT
4137 *	(and thence onto LAST-ACK and finally, CLOSE, we never enter
4138 *	TIME-WAIT)
4139 *
4140 *	If we are in FINWAIT-1, a received FIN indicates simultaneous
4141 *	close and we go into CLOSING (and later onto TIME-WAIT)
4142 *
4143 *	If we are in FINWAIT-2, a received FIN moves us to TIME-WAIT.
4144 */
4145void tcp_fin(struct sock *sk)
4146{
4147	struct tcp_sock *tp = tcp_sk(sk);
4148
4149	inet_csk_schedule_ack(sk);
4150
4151	sk->sk_shutdown |= RCV_SHUTDOWN;
4152	sock_set_flag(sk, SOCK_DONE);
4153
4154	switch (sk->sk_state) {
4155	case TCP_SYN_RECV:
4156	case TCP_ESTABLISHED:
4157		/* Move to CLOSE_WAIT */
4158		tcp_set_state(sk, TCP_CLOSE_WAIT);
4159		inet_csk_enter_pingpong_mode(sk);
4160		break;
4161
4162	case TCP_CLOSE_WAIT:
4163	case TCP_CLOSING:
4164		/* Received a retransmission of the FIN, do
4165		 * nothing.
4166		 */
4167		break;
4168	case TCP_LAST_ACK:
4169		/* RFC793: Remain in the LAST-ACK state. */
4170		break;
4171
4172	case TCP_FIN_WAIT1:
4173		/* This case occurs when a simultaneous close
4174		 * happens, we must ack the received FIN and
4175		 * enter the CLOSING state.
4176		 */
4177		tcp_send_ack(sk);
4178		tcp_set_state(sk, TCP_CLOSING);
4179		break;
4180	case TCP_FIN_WAIT2:
4181		/* Received a FIN -- send ACK and enter TIME_WAIT. */
4182		tcp_send_ack(sk);
4183		tcp_time_wait(sk, TCP_TIME_WAIT, 0);
4184		break;
4185	default:
4186		/* Only TCP_LISTEN and TCP_CLOSE are left, in these
4187		 * cases we should never reach this piece of code.
4188		 */
4189		pr_err("%s: Impossible, sk->sk_state=%d\n",
4190		       __func__, sk->sk_state);
4191		break;
4192	}
4193
4194	/* It _is_ possible, that we have something out-of-order _after_ FIN.
4195	 * Probably, we should reset in this case. For now drop them.
4196	 */
4197	skb_rbtree_purge(&tp->out_of_order_queue);
4198	if (tcp_is_sack(tp))
4199		tcp_sack_reset(&tp->rx_opt);
4200	sk_mem_reclaim(sk);
4201
4202	if (!sock_flag(sk, SOCK_DEAD)) {
4203		sk->sk_state_change(sk);
4204
4205		/* Do not send POLL_HUP for half duplex close. */
4206		if (sk->sk_shutdown == SHUTDOWN_MASK ||
4207		    sk->sk_state == TCP_CLOSE)
4208			sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_HUP);
4209		else
4210			sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_IN);
4211	}
4212}
4213
4214static inline bool tcp_sack_extend(struct tcp_sack_block *sp, u32 seq,
4215				  u32 end_seq)
4216{
4217	if (!after(seq, sp->end_seq) && !after(sp->start_seq, end_seq)) {
4218		if (before(seq, sp->start_seq))
4219			sp->start_seq = seq;
4220		if (after(end_seq, sp->end_seq))
4221			sp->end_seq = end_seq;
4222		return true;
4223	}
4224	return false;
4225}
4226
4227static void tcp_dsack_set(struct sock *sk, u32 seq, u32 end_seq)
4228{
4229	struct tcp_sock *tp = tcp_sk(sk);
4230
4231	if (tcp_is_sack(tp) && sock_net(sk)->ipv4.sysctl_tcp_dsack) {
4232		int mib_idx;
4233
4234		if (before(seq, tp->rcv_nxt))
4235			mib_idx = LINUX_MIB_TCPDSACKOLDSENT;
4236		else
4237			mib_idx = LINUX_MIB_TCPDSACKOFOSENT;
4238
4239		NET_INC_STATS(sock_net(sk), mib_idx);
4240
4241		tp->rx_opt.dsack = 1;
4242		tp->duplicate_sack[0].start_seq = seq;
4243		tp->duplicate_sack[0].end_seq = end_seq;
4244	}
4245}
4246
4247static void tcp_dsack_extend(struct sock *sk, u32 seq, u32 end_seq)
4248{
4249	struct tcp_sock *tp = tcp_sk(sk);
4250
4251	if (!tp->rx_opt.dsack)
4252		tcp_dsack_set(sk, seq, end_seq);
4253	else
4254		tcp_sack_extend(tp->duplicate_sack, seq, end_seq);
4255}
4256
4257static void tcp_rcv_spurious_retrans(struct sock *sk, const struct sk_buff *skb)
4258{
4259	/* When the ACK path fails or drops most ACKs, the sender would
4260	 * timeout and spuriously retransmit the same segment repeatedly.
4261	 * The receiver remembers and reflects via DSACKs. Leverage the
4262	 * DSACK state and change the txhash to re-route speculatively.
4263	 */
4264	if (TCP_SKB_CB(skb)->seq == tcp_sk(sk)->duplicate_sack[0].start_seq)
4265		sk_rethink_txhash(sk);
4266}
4267
4268static void tcp_send_dupack(struct sock *sk, const struct sk_buff *skb)
4269{
4270	struct tcp_sock *tp = tcp_sk(sk);
4271
4272	if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
4273	    before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
4274		NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
4275		tcp_enter_quickack_mode(sk, TCP_MAX_QUICKACKS);
4276
4277		if (tcp_is_sack(tp) && sock_net(sk)->ipv4.sysctl_tcp_dsack) {
4278			u32 end_seq = TCP_SKB_CB(skb)->end_seq;
4279
4280			tcp_rcv_spurious_retrans(sk, skb);
4281			if (after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))
4282				end_seq = tp->rcv_nxt;
4283			tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, end_seq);
4284		}
4285	}
4286
4287	tcp_send_ack(sk);
4288}
4289
4290/* These routines update the SACK block as out-of-order packets arrive or
4291 * in-order packets close up the sequence space.
4292 */
4293static void tcp_sack_maybe_coalesce(struct tcp_sock *tp)
4294{
4295	int this_sack;
4296	struct tcp_sack_block *sp = &tp->selective_acks[0];
4297	struct tcp_sack_block *swalk = sp + 1;
4298
4299	/* See if the recent change to the first SACK eats into
4300	 * or hits the sequence space of other SACK blocks, if so coalesce.
4301	 */
4302	for (this_sack = 1; this_sack < tp->rx_opt.num_sacks;) {
4303		if (tcp_sack_extend(sp, swalk->start_seq, swalk->end_seq)) {
4304			int i;
4305
4306			/* Zap SWALK, by moving every further SACK up by one slot.
4307			 * Decrease num_sacks.
4308			 */
4309			tp->rx_opt.num_sacks--;
4310			for (i = this_sack; i < tp->rx_opt.num_sacks; i++)
4311				sp[i] = sp[i + 1];
4312			continue;
4313		}
4314		this_sack++, swalk++;
4315	}
4316}
4317
4318static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq)
4319{
4320	struct tcp_sock *tp = tcp_sk(sk);
4321	struct tcp_sack_block *sp = &tp->selective_acks[0];
4322	int cur_sacks = tp->rx_opt.num_sacks;
4323	int this_sack;
4324
4325	if (!cur_sacks)
4326		goto new_sack;
4327
4328	for (this_sack = 0; this_sack < cur_sacks; this_sack++, sp++) {
4329		if (tcp_sack_extend(sp, seq, end_seq)) {
4330			/* Rotate this_sack to the first one. */
4331			for (; this_sack > 0; this_sack--, sp--)
4332				swap(*sp, *(sp - 1));
4333			if (cur_sacks > 1)
4334				tcp_sack_maybe_coalesce(tp);
4335			return;
4336		}
4337	}
4338
4339	/* Could not find an adjacent existing SACK, build a new one,
4340	 * put it at the front, and shift everyone else down.  We
4341	 * always know there is at least one SACK present already here.
4342	 *
4343	 * If the sack array is full, forget about the last one.
4344	 */
4345	if (this_sack >= TCP_NUM_SACKS) {
4346		if (tp->compressed_ack > TCP_FASTRETRANS_THRESH)
4347			tcp_send_ack(sk);
4348		this_sack--;
4349		tp->rx_opt.num_sacks--;
4350		sp--;
4351	}
4352	for (; this_sack > 0; this_sack--, sp--)
4353		*sp = *(sp - 1);
4354
4355new_sack:
4356	/* Build the new head SACK, and we're done. */
4357	sp->start_seq = seq;
4358	sp->end_seq = end_seq;
4359	tp->rx_opt.num_sacks++;
4360}
4361
4362/* RCV.NXT advances, some SACKs should be eaten. */
4363
4364static void tcp_sack_remove(struct tcp_sock *tp)
4365{
4366	struct tcp_sack_block *sp = &tp->selective_acks[0];
4367	int num_sacks = tp->rx_opt.num_sacks;
4368	int this_sack;
4369
4370	/* Empty ofo queue, hence, all the SACKs are eaten. Clear. */
4371	if (RB_EMPTY_ROOT(&tp->out_of_order_queue)) {
4372		tp->rx_opt.num_sacks = 0;
4373		return;
4374	}
4375
4376	for (this_sack = 0; this_sack < num_sacks;) {
4377		/* Check if the start of the sack is covered by RCV.NXT. */
4378		if (!before(tp->rcv_nxt, sp->start_seq)) {
4379			int i;
4380
4381			/* RCV.NXT must cover all the block! */
4382			WARN_ON(before(tp->rcv_nxt, sp->end_seq));
4383
4384			/* Zap this SACK, by moving forward any other SACKS. */
4385			for (i = this_sack+1; i < num_sacks; i++)
4386				tp->selective_acks[i-1] = tp->selective_acks[i];
4387			num_sacks--;
4388			continue;
4389		}
4390		this_sack++;
4391		sp++;
4392	}
4393	tp->rx_opt.num_sacks = num_sacks;
4394}
4395
4396/**
4397 * tcp_try_coalesce - try to merge skb to prior one
4398 * @sk: socket
4399 * @dest: destination queue
4400 * @to: prior buffer
4401 * @from: buffer to add in queue
4402 * @fragstolen: pointer to boolean
4403 *
4404 * Before queueing skb @from after @to, try to merge them
4405 * to reduce overall memory use and queue lengths, if cost is small.
4406 * Packets in ofo or receive queues can stay a long time.
4407 * Better try to coalesce them right now to avoid future collapses.
4408 * Returns true if caller should free @from instead of queueing it
4409 */
4410static bool tcp_try_coalesce(struct sock *sk,
4411			     struct sk_buff *to,
4412			     struct sk_buff *from,
4413			     bool *fragstolen)
4414{
4415	int delta;
4416
4417	*fragstolen = false;
4418
4419	/* Its possible this segment overlaps with prior segment in queue */
4420	if (TCP_SKB_CB(from)->seq != TCP_SKB_CB(to)->end_seq)
4421		return false;
4422
4423#ifdef CONFIG_TLS_DEVICE
4424	if (from->decrypted != to->decrypted)
4425		return false;
4426#endif
4427
4428	if (!skb_try_coalesce(to, from, fragstolen, &delta))
4429		return false;
4430
4431	atomic_add(delta, &sk->sk_rmem_alloc);
4432	sk_mem_charge(sk, delta);
4433	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVCOALESCE);
4434	TCP_SKB_CB(to)->end_seq = TCP_SKB_CB(from)->end_seq;
4435	TCP_SKB_CB(to)->ack_seq = TCP_SKB_CB(from)->ack_seq;
4436	TCP_SKB_CB(to)->tcp_flags |= TCP_SKB_CB(from)->tcp_flags;
4437
4438	if (TCP_SKB_CB(from)->has_rxtstamp) {
4439		TCP_SKB_CB(to)->has_rxtstamp = true;
4440		to->tstamp = from->tstamp;
4441		skb_hwtstamps(to)->hwtstamp = skb_hwtstamps(from)->hwtstamp;
4442	}
4443
4444	return true;
4445}
4446
4447static bool tcp_ooo_try_coalesce(struct sock *sk,
4448			     struct sk_buff *to,
4449			     struct sk_buff *from,
4450			     bool *fragstolen)
4451{
4452	bool res = tcp_try_coalesce(sk, to, from, fragstolen);
4453
4454	/* In case tcp_drop() is called later, update to->gso_segs */
4455	if (res) {
4456		u32 gso_segs = max_t(u16, 1, skb_shinfo(to)->gso_segs) +
4457			       max_t(u16, 1, skb_shinfo(from)->gso_segs);
4458
4459		skb_shinfo(to)->gso_segs = min_t(u32, gso_segs, 0xFFFF);
4460	}
4461	return res;
4462}
4463
4464static void tcp_drop(struct sock *sk, struct sk_buff *skb)
4465{
4466	sk_drops_add(sk, skb);
4467	__kfree_skb(skb);
4468}
4469
4470/* This one checks to see if we can put data from the
4471 * out_of_order queue into the receive_queue.
4472 */
4473static void tcp_ofo_queue(struct sock *sk)
4474{
4475	struct tcp_sock *tp = tcp_sk(sk);
4476	__u32 dsack_high = tp->rcv_nxt;
4477	bool fin, fragstolen, eaten;
4478	struct sk_buff *skb, *tail;
4479	struct rb_node *p;
4480
4481	p = rb_first(&tp->out_of_order_queue);
4482	while (p) {
4483		skb = rb_to_skb(p);
4484		if (after(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
4485			break;
4486
4487		if (before(TCP_SKB_CB(skb)->seq, dsack_high)) {
4488			__u32 dsack = dsack_high;
4489			if (before(TCP_SKB_CB(skb)->end_seq, dsack_high))
4490				dsack_high = TCP_SKB_CB(skb)->end_seq;
4491			tcp_dsack_extend(sk, TCP_SKB_CB(skb)->seq, dsack);
4492		}
4493		p = rb_next(p);
4494		rb_erase(&skb->rbnode, &tp->out_of_order_queue);
4495
4496		if (unlikely(!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))) {
 
4497			tcp_drop(sk, skb);
4498			continue;
4499		}
 
 
 
4500
4501		tail = skb_peek_tail(&sk->sk_receive_queue);
4502		eaten = tail && tcp_try_coalesce(sk, tail, skb, &fragstolen);
4503		tcp_rcv_nxt_update(tp, TCP_SKB_CB(skb)->end_seq);
4504		fin = TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN;
4505		if (!eaten)
4506			__skb_queue_tail(&sk->sk_receive_queue, skb);
4507		else
4508			kfree_skb_partial(skb, fragstolen);
4509
4510		if (unlikely(fin)) {
4511			tcp_fin(sk);
4512			/* tcp_fin() purges tp->out_of_order_queue,
4513			 * so we must end this loop right now.
4514			 */
4515			break;
4516		}
4517	}
4518}
4519
4520static bool tcp_prune_ofo_queue(struct sock *sk);
4521static int tcp_prune_queue(struct sock *sk);
4522
4523static int tcp_try_rmem_schedule(struct sock *sk, struct sk_buff *skb,
4524				 unsigned int size)
4525{
4526	if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
4527	    !sk_rmem_schedule(sk, skb, size)) {
4528
4529		if (tcp_prune_queue(sk) < 0)
4530			return -1;
4531
4532		while (!sk_rmem_schedule(sk, skb, size)) {
4533			if (!tcp_prune_ofo_queue(sk))
4534				return -1;
4535		}
4536	}
4537	return 0;
4538}
4539
4540static void tcp_data_queue_ofo(struct sock *sk, struct sk_buff *skb)
4541{
4542	struct tcp_sock *tp = tcp_sk(sk);
4543	struct rb_node **p, *parent;
4544	struct sk_buff *skb1;
4545	u32 seq, end_seq;
4546	bool fragstolen;
4547
4548	tcp_ecn_check_ce(sk, skb);
4549
4550	if (unlikely(tcp_try_rmem_schedule(sk, skb, skb->truesize))) {
4551		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFODROP);
4552		tcp_drop(sk, skb);
4553		return;
4554	}
4555
4556	/* Disable header prediction. */
4557	tp->pred_flags = 0;
4558	inet_csk_schedule_ack(sk);
4559
4560	tp->rcv_ooopack += max_t(u16, 1, skb_shinfo(skb)->gso_segs);
4561	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFOQUEUE);
4562	seq = TCP_SKB_CB(skb)->seq;
4563	end_seq = TCP_SKB_CB(skb)->end_seq;
 
 
4564
4565	p = &tp->out_of_order_queue.rb_node;
4566	if (RB_EMPTY_ROOT(&tp->out_of_order_queue)) {
4567		/* Initial out of order segment, build 1 SACK. */
4568		if (tcp_is_sack(tp)) {
4569			tp->rx_opt.num_sacks = 1;
4570			tp->selective_acks[0].start_seq = seq;
4571			tp->selective_acks[0].end_seq = end_seq;
4572		}
4573		rb_link_node(&skb->rbnode, NULL, p);
4574		rb_insert_color(&skb->rbnode, &tp->out_of_order_queue);
4575		tp->ooo_last_skb = skb;
4576		goto end;
4577	}
4578
4579	/* In the typical case, we are adding an skb to the end of the list.
4580	 * Use of ooo_last_skb avoids the O(Log(N)) rbtree lookup.
4581	 */
4582	if (tcp_ooo_try_coalesce(sk, tp->ooo_last_skb,
4583				 skb, &fragstolen)) {
4584coalesce_done:
4585		tcp_grow_window(sk, skb);
4586		kfree_skb_partial(skb, fragstolen);
4587		skb = NULL;
4588		goto add_sack;
4589	}
4590	/* Can avoid an rbtree lookup if we are adding skb after ooo_last_skb */
4591	if (!before(seq, TCP_SKB_CB(tp->ooo_last_skb)->end_seq)) {
4592		parent = &tp->ooo_last_skb->rbnode;
4593		p = &parent->rb_right;
4594		goto insert;
4595	}
4596
4597	/* Find place to insert this segment. Handle overlaps on the way. */
4598	parent = NULL;
4599	while (*p) {
4600		parent = *p;
4601		skb1 = rb_to_skb(parent);
4602		if (before(seq, TCP_SKB_CB(skb1)->seq)) {
4603			p = &parent->rb_left;
4604			continue;
4605		}
4606		if (before(seq, TCP_SKB_CB(skb1)->end_seq)) {
4607			if (!after(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
4608				/* All the bits are present. Drop. */
4609				NET_INC_STATS(sock_net(sk),
4610					      LINUX_MIB_TCPOFOMERGE);
4611				tcp_drop(sk, skb);
4612				skb = NULL;
4613				tcp_dsack_set(sk, seq, end_seq);
4614				goto add_sack;
4615			}
4616			if (after(seq, TCP_SKB_CB(skb1)->seq)) {
4617				/* Partial overlap. */
4618				tcp_dsack_set(sk, seq, TCP_SKB_CB(skb1)->end_seq);
4619			} else {
4620				/* skb's seq == skb1's seq and skb covers skb1.
4621				 * Replace skb1 with skb.
4622				 */
4623				rb_replace_node(&skb1->rbnode, &skb->rbnode,
4624						&tp->out_of_order_queue);
4625				tcp_dsack_extend(sk,
4626						 TCP_SKB_CB(skb1)->seq,
4627						 TCP_SKB_CB(skb1)->end_seq);
4628				NET_INC_STATS(sock_net(sk),
4629					      LINUX_MIB_TCPOFOMERGE);
4630				tcp_drop(sk, skb1);
4631				goto merge_right;
4632			}
4633		} else if (tcp_ooo_try_coalesce(sk, skb1,
4634						skb, &fragstolen)) {
4635			goto coalesce_done;
4636		}
4637		p = &parent->rb_right;
4638	}
4639insert:
4640	/* Insert segment into RB tree. */
4641	rb_link_node(&skb->rbnode, parent, p);
4642	rb_insert_color(&skb->rbnode, &tp->out_of_order_queue);
4643
4644merge_right:
4645	/* Remove other segments covered by skb. */
4646	while ((skb1 = skb_rb_next(skb)) != NULL) {
4647		if (!after(end_seq, TCP_SKB_CB(skb1)->seq))
4648			break;
4649		if (before(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
4650			tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
4651					 end_seq);
4652			break;
4653		}
4654		rb_erase(&skb1->rbnode, &tp->out_of_order_queue);
4655		tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
4656				 TCP_SKB_CB(skb1)->end_seq);
4657		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFOMERGE);
4658		tcp_drop(sk, skb1);
4659	}
4660	/* If there is no skb after us, we are the last_skb ! */
4661	if (!skb1)
4662		tp->ooo_last_skb = skb;
4663
4664add_sack:
4665	if (tcp_is_sack(tp))
4666		tcp_sack_new_ofo_skb(sk, seq, end_seq);
4667end:
4668	if (skb) {
4669		tcp_grow_window(sk, skb);
4670		skb_condense(skb);
4671		skb_set_owner_r(skb, sk);
4672	}
4673}
4674
4675static int __must_check tcp_queue_rcv(struct sock *sk, struct sk_buff *skb,
4676				      bool *fragstolen)
4677{
4678	int eaten;
4679	struct sk_buff *tail = skb_peek_tail(&sk->sk_receive_queue);
4680
 
4681	eaten = (tail &&
4682		 tcp_try_coalesce(sk, tail,
4683				  skb, fragstolen)) ? 1 : 0;
4684	tcp_rcv_nxt_update(tcp_sk(sk), TCP_SKB_CB(skb)->end_seq);
4685	if (!eaten) {
4686		__skb_queue_tail(&sk->sk_receive_queue, skb);
4687		skb_set_owner_r(skb, sk);
4688	}
4689	return eaten;
4690}
4691
4692int tcp_send_rcvq(struct sock *sk, struct msghdr *msg, size_t size)
4693{
4694	struct sk_buff *skb;
4695	int err = -ENOMEM;
4696	int data_len = 0;
4697	bool fragstolen;
4698
4699	if (size == 0)
4700		return 0;
4701
4702	if (size > PAGE_SIZE) {
4703		int npages = min_t(size_t, size >> PAGE_SHIFT, MAX_SKB_FRAGS);
4704
4705		data_len = npages << PAGE_SHIFT;
4706		size = data_len + (size & ~PAGE_MASK);
4707	}
4708	skb = alloc_skb_with_frags(size - data_len, data_len,
4709				   PAGE_ALLOC_COSTLY_ORDER,
4710				   &err, sk->sk_allocation);
4711	if (!skb)
4712		goto err;
4713
4714	skb_put(skb, size - data_len);
4715	skb->data_len = data_len;
4716	skb->len = size;
4717
4718	if (tcp_try_rmem_schedule(sk, skb, skb->truesize)) {
4719		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVQDROP);
4720		goto err_free;
4721	}
4722
4723	err = skb_copy_datagram_from_iter(skb, 0, &msg->msg_iter, size);
4724	if (err)
4725		goto err_free;
4726
4727	TCP_SKB_CB(skb)->seq = tcp_sk(sk)->rcv_nxt;
4728	TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq + size;
4729	TCP_SKB_CB(skb)->ack_seq = tcp_sk(sk)->snd_una - 1;
4730
4731	if (tcp_queue_rcv(sk, skb, &fragstolen)) {
4732		WARN_ON_ONCE(fragstolen); /* should not happen */
4733		__kfree_skb(skb);
4734	}
4735	return size;
4736
4737err_free:
4738	kfree_skb(skb);
4739err:
4740	return err;
4741
4742}
4743
4744void tcp_data_ready(struct sock *sk)
4745{
4746	const struct tcp_sock *tp = tcp_sk(sk);
4747	int avail = tp->rcv_nxt - tp->copied_seq;
4748
4749	if (avail < sk->sk_rcvlowat && !sock_flag(sk, SOCK_DONE))
4750		return;
4751
4752	sk->sk_data_ready(sk);
4753}
4754
4755static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
4756{
4757	struct tcp_sock *tp = tcp_sk(sk);
4758	bool fragstolen;
4759	int eaten;
4760
4761	if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq) {
4762		__kfree_skb(skb);
4763		return;
4764	}
4765	skb_dst_drop(skb);
4766	__skb_pull(skb, tcp_hdr(skb)->doff * 4);
4767
4768	tcp_ecn_accept_cwr(sk, skb);
4769
4770	tp->rx_opt.dsack = 0;
4771
4772	/*  Queue data for delivery to the user.
4773	 *  Packets in sequence go to the receive queue.
4774	 *  Out of sequence packets to the out_of_order_queue.
4775	 */
4776	if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
4777		if (tcp_receive_window(tp) == 0) {
4778			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPZEROWINDOWDROP);
4779			goto out_of_window;
4780		}
4781
4782		/* Ok. In sequence. In window. */
4783queue_and_out:
4784		if (skb_queue_len(&sk->sk_receive_queue) == 0)
4785			sk_forced_mem_schedule(sk, skb->truesize);
4786		else if (tcp_try_rmem_schedule(sk, skb, skb->truesize)) {
4787			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVQDROP);
4788			goto drop;
4789		}
4790
4791		eaten = tcp_queue_rcv(sk, skb, &fragstolen);
 
4792		if (skb->len)
4793			tcp_event_data_recv(sk, skb);
4794		if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
4795			tcp_fin(sk);
4796
4797		if (!RB_EMPTY_ROOT(&tp->out_of_order_queue)) {
4798			tcp_ofo_queue(sk);
4799
4800			/* RFC5681. 4.2. SHOULD send immediate ACK, when
4801			 * gap in queue is filled.
4802			 */
4803			if (RB_EMPTY_ROOT(&tp->out_of_order_queue))
4804				inet_csk(sk)->icsk_ack.pending |= ICSK_ACK_NOW;
4805		}
4806
4807		if (tp->rx_opt.num_sacks)
4808			tcp_sack_remove(tp);
4809
4810		tcp_fast_path_check(sk);
4811
4812		if (eaten > 0)
4813			kfree_skb_partial(skb, fragstolen);
4814		if (!sock_flag(sk, SOCK_DEAD))
4815			tcp_data_ready(sk);
4816		return;
4817	}
4818
4819	if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
4820		tcp_rcv_spurious_retrans(sk, skb);
4821		/* A retransmit, 2nd most common case.  Force an immediate ack. */
4822		NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
4823		tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
4824
4825out_of_window:
4826		tcp_enter_quickack_mode(sk, TCP_MAX_QUICKACKS);
4827		inet_csk_schedule_ack(sk);
4828drop:
4829		tcp_drop(sk, skb);
4830		return;
4831	}
4832
4833	/* Out of window. F.e. zero window probe. */
4834	if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt + tcp_receive_window(tp)))
4835		goto out_of_window;
4836
 
 
4837	if (before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
4838		/* Partial packet, seq < rcv_next < end_seq */
 
 
 
 
4839		tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, tp->rcv_nxt);
4840
4841		/* If window is closed, drop tail of packet. But after
4842		 * remembering D-SACK for its head made in previous line.
4843		 */
4844		if (!tcp_receive_window(tp)) {
4845			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPZEROWINDOWDROP);
4846			goto out_of_window;
4847		}
4848		goto queue_and_out;
4849	}
4850
4851	tcp_data_queue_ofo(sk, skb);
4852}
4853
4854static struct sk_buff *tcp_skb_next(struct sk_buff *skb, struct sk_buff_head *list)
4855{
4856	if (list)
4857		return !skb_queue_is_last(list, skb) ? skb->next : NULL;
4858
4859	return skb_rb_next(skb);
4860}
4861
4862static struct sk_buff *tcp_collapse_one(struct sock *sk, struct sk_buff *skb,
4863					struct sk_buff_head *list,
4864					struct rb_root *root)
4865{
4866	struct sk_buff *next = tcp_skb_next(skb, list);
4867
4868	if (list)
4869		__skb_unlink(skb, list);
4870	else
4871		rb_erase(&skb->rbnode, root);
4872
4873	__kfree_skb(skb);
4874	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVCOLLAPSED);
4875
4876	return next;
4877}
4878
4879/* Insert skb into rb tree, ordered by TCP_SKB_CB(skb)->seq */
4880void tcp_rbtree_insert(struct rb_root *root, struct sk_buff *skb)
4881{
4882	struct rb_node **p = &root->rb_node;
4883	struct rb_node *parent = NULL;
4884	struct sk_buff *skb1;
4885
4886	while (*p) {
4887		parent = *p;
4888		skb1 = rb_to_skb(parent);
4889		if (before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb1)->seq))
4890			p = &parent->rb_left;
4891		else
4892			p = &parent->rb_right;
4893	}
4894	rb_link_node(&skb->rbnode, parent, p);
4895	rb_insert_color(&skb->rbnode, root);
4896}
4897
4898/* Collapse contiguous sequence of skbs head..tail with
4899 * sequence numbers start..end.
4900 *
4901 * If tail is NULL, this means until the end of the queue.
4902 *
4903 * Segments with FIN/SYN are not collapsed (only because this
4904 * simplifies code)
4905 */
4906static void
4907tcp_collapse(struct sock *sk, struct sk_buff_head *list, struct rb_root *root,
4908	     struct sk_buff *head, struct sk_buff *tail, u32 start, u32 end)
4909{
4910	struct sk_buff *skb = head, *n;
4911	struct sk_buff_head tmp;
4912	bool end_of_skbs;
4913
4914	/* First, check that queue is collapsible and find
4915	 * the point where collapsing can be useful.
4916	 */
4917restart:
4918	for (end_of_skbs = true; skb != NULL && skb != tail; skb = n) {
4919		n = tcp_skb_next(skb, list);
4920
4921		/* No new bits? It is possible on ofo queue. */
4922		if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
4923			skb = tcp_collapse_one(sk, skb, list, root);
4924			if (!skb)
4925				break;
4926			goto restart;
4927		}
4928
4929		/* The first skb to collapse is:
4930		 * - not SYN/FIN and
4931		 * - bloated or contains data before "start" or
4932		 *   overlaps to the next one.
4933		 */
4934		if (!(TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)) &&
4935		    (tcp_win_from_space(sk, skb->truesize) > skb->len ||
4936		     before(TCP_SKB_CB(skb)->seq, start))) {
4937			end_of_skbs = false;
4938			break;
4939		}
4940
4941		if (n && n != tail &&
4942		    TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(n)->seq) {
4943			end_of_skbs = false;
4944			break;
4945		}
4946
4947		/* Decided to skip this, advance start seq. */
4948		start = TCP_SKB_CB(skb)->end_seq;
4949	}
4950	if (end_of_skbs ||
4951	    (TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)))
4952		return;
4953
4954	__skb_queue_head_init(&tmp);
4955
4956	while (before(start, end)) {
4957		int copy = min_t(int, SKB_MAX_ORDER(0, 0), end - start);
4958		struct sk_buff *nskb;
4959
4960		nskb = alloc_skb(copy, GFP_ATOMIC);
4961		if (!nskb)
4962			break;
4963
4964		memcpy(nskb->cb, skb->cb, sizeof(skb->cb));
4965#ifdef CONFIG_TLS_DEVICE
4966		nskb->decrypted = skb->decrypted;
4967#endif
4968		TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(nskb)->end_seq = start;
4969		if (list)
4970			__skb_queue_before(list, skb, nskb);
4971		else
4972			__skb_queue_tail(&tmp, nskb); /* defer rbtree insertion */
4973		skb_set_owner_r(nskb, sk);
4974
4975		/* Copy data, releasing collapsed skbs. */
4976		while (copy > 0) {
4977			int offset = start - TCP_SKB_CB(skb)->seq;
4978			int size = TCP_SKB_CB(skb)->end_seq - start;
4979
4980			BUG_ON(offset < 0);
4981			if (size > 0) {
4982				size = min(copy, size);
4983				if (skb_copy_bits(skb, offset, skb_put(nskb, size), size))
4984					BUG();
4985				TCP_SKB_CB(nskb)->end_seq += size;
4986				copy -= size;
4987				start += size;
4988			}
4989			if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
4990				skb = tcp_collapse_one(sk, skb, list, root);
4991				if (!skb ||
4992				    skb == tail ||
4993				    (TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)))
4994					goto end;
4995#ifdef CONFIG_TLS_DEVICE
4996				if (skb->decrypted != nskb->decrypted)
4997					goto end;
4998#endif
4999			}
5000		}
5001	}
5002end:
5003	skb_queue_walk_safe(&tmp, skb, n)
5004		tcp_rbtree_insert(root, skb);
5005}
5006
5007/* Collapse ofo queue. Algorithm: select contiguous sequence of skbs
5008 * and tcp_collapse() them until all the queue is collapsed.
5009 */
5010static void tcp_collapse_ofo_queue(struct sock *sk)
5011{
5012	struct tcp_sock *tp = tcp_sk(sk);
5013	u32 range_truesize, sum_tiny = 0;
5014	struct sk_buff *skb, *head;
5015	u32 start, end;
5016
5017	skb = skb_rb_first(&tp->out_of_order_queue);
5018new_range:
5019	if (!skb) {
5020		tp->ooo_last_skb = skb_rb_last(&tp->out_of_order_queue);
5021		return;
5022	}
5023	start = TCP_SKB_CB(skb)->seq;
5024	end = TCP_SKB_CB(skb)->end_seq;
5025	range_truesize = skb->truesize;
5026
5027	for (head = skb;;) {
5028		skb = skb_rb_next(skb);
5029
5030		/* Range is terminated when we see a gap or when
5031		 * we are at the queue end.
5032		 */
5033		if (!skb ||
5034		    after(TCP_SKB_CB(skb)->seq, end) ||
5035		    before(TCP_SKB_CB(skb)->end_seq, start)) {
5036			/* Do not attempt collapsing tiny skbs */
5037			if (range_truesize != head->truesize ||
5038			    end - start >= SKB_WITH_OVERHEAD(SK_MEM_QUANTUM)) {
5039				tcp_collapse(sk, NULL, &tp->out_of_order_queue,
5040					     head, skb, start, end);
5041			} else {
5042				sum_tiny += range_truesize;
5043				if (sum_tiny > sk->sk_rcvbuf >> 3)
5044					return;
5045			}
5046			goto new_range;
5047		}
5048
5049		range_truesize += skb->truesize;
5050		if (unlikely(before(TCP_SKB_CB(skb)->seq, start)))
5051			start = TCP_SKB_CB(skb)->seq;
5052		if (after(TCP_SKB_CB(skb)->end_seq, end))
5053			end = TCP_SKB_CB(skb)->end_seq;
5054	}
5055}
5056
5057/*
5058 * Clean the out-of-order queue to make room.
5059 * We drop high sequences packets to :
5060 * 1) Let a chance for holes to be filled.
5061 * 2) not add too big latencies if thousands of packets sit there.
5062 *    (But if application shrinks SO_RCVBUF, we could still end up
5063 *     freeing whole queue here)
5064 * 3) Drop at least 12.5 % of sk_rcvbuf to avoid malicious attacks.
5065 *
5066 * Return true if queue has shrunk.
5067 */
5068static bool tcp_prune_ofo_queue(struct sock *sk)
5069{
5070	struct tcp_sock *tp = tcp_sk(sk);
5071	struct rb_node *node, *prev;
5072	int goal;
5073
5074	if (RB_EMPTY_ROOT(&tp->out_of_order_queue))
5075		return false;
5076
5077	NET_INC_STATS(sock_net(sk), LINUX_MIB_OFOPRUNED);
5078	goal = sk->sk_rcvbuf >> 3;
5079	node = &tp->ooo_last_skb->rbnode;
5080	do {
5081		prev = rb_prev(node);
5082		rb_erase(node, &tp->out_of_order_queue);
5083		goal -= rb_to_skb(node)->truesize;
5084		tcp_drop(sk, rb_to_skb(node));
5085		if (!prev || goal <= 0) {
5086			sk_mem_reclaim(sk);
5087			if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf &&
5088			    !tcp_under_memory_pressure(sk))
5089				break;
5090			goal = sk->sk_rcvbuf >> 3;
5091		}
5092		node = prev;
5093	} while (node);
5094	tp->ooo_last_skb = rb_to_skb(prev);
5095
5096	/* Reset SACK state.  A conforming SACK implementation will
5097	 * do the same at a timeout based retransmit.  When a connection
5098	 * is in a sad state like this, we care only about integrity
5099	 * of the connection not performance.
5100	 */
5101	if (tp->rx_opt.sack_ok)
5102		tcp_sack_reset(&tp->rx_opt);
5103	return true;
5104}
5105
5106/* Reduce allocated memory if we can, trying to get
5107 * the socket within its memory limits again.
5108 *
5109 * Return less than zero if we should start dropping frames
5110 * until the socket owning process reads some of the data
5111 * to stabilize the situation.
5112 */
5113static int tcp_prune_queue(struct sock *sk)
5114{
5115	struct tcp_sock *tp = tcp_sk(sk);
5116
 
 
5117	NET_INC_STATS(sock_net(sk), LINUX_MIB_PRUNECALLED);
5118
5119	if (atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf)
5120		tcp_clamp_window(sk);
5121	else if (tcp_under_memory_pressure(sk))
5122		tp->rcv_ssthresh = min(tp->rcv_ssthresh, 4U * tp->advmss);
5123
5124	if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
5125		return 0;
5126
5127	tcp_collapse_ofo_queue(sk);
5128	if (!skb_queue_empty(&sk->sk_receive_queue))
5129		tcp_collapse(sk, &sk->sk_receive_queue, NULL,
5130			     skb_peek(&sk->sk_receive_queue),
5131			     NULL,
5132			     tp->copied_seq, tp->rcv_nxt);
5133	sk_mem_reclaim(sk);
5134
5135	if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
5136		return 0;
5137
5138	/* Collapsing did not help, destructive actions follow.
5139	 * This must not ever occur. */
5140
5141	tcp_prune_ofo_queue(sk);
5142
5143	if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
5144		return 0;
5145
5146	/* If we are really being abused, tell the caller to silently
5147	 * drop receive data on the floor.  It will get retransmitted
5148	 * and hopefully then we'll have sufficient space.
5149	 */
5150	NET_INC_STATS(sock_net(sk), LINUX_MIB_RCVPRUNED);
5151
5152	/* Massive buffer overcommit. */
5153	tp->pred_flags = 0;
5154	return -1;
5155}
5156
5157static bool tcp_should_expand_sndbuf(const struct sock *sk)
5158{
5159	const struct tcp_sock *tp = tcp_sk(sk);
5160
5161	/* If the user specified a specific send buffer setting, do
5162	 * not modify it.
5163	 */
5164	if (sk->sk_userlocks & SOCK_SNDBUF_LOCK)
5165		return false;
5166
5167	/* If we are under global TCP memory pressure, do not expand.  */
5168	if (tcp_under_memory_pressure(sk))
5169		return false;
5170
5171	/* If we are under soft global TCP memory pressure, do not expand.  */
5172	if (sk_memory_allocated(sk) >= sk_prot_mem_limits(sk, 0))
5173		return false;
5174
5175	/* If we filled the congestion window, do not expand.  */
5176	if (tcp_packets_in_flight(tp) >= tp->snd_cwnd)
5177		return false;
5178
5179	return true;
5180}
5181
5182/* When incoming ACK allowed to free some skb from write_queue,
5183 * we remember this event in flag SOCK_QUEUE_SHRUNK and wake up socket
5184 * on the exit from tcp input handler.
5185 *
5186 * PROBLEM: sndbuf expansion does not work well with largesend.
5187 */
5188static void tcp_new_space(struct sock *sk)
5189{
5190	struct tcp_sock *tp = tcp_sk(sk);
5191
5192	if (tcp_should_expand_sndbuf(sk)) {
5193		tcp_sndbuf_expand(sk);
5194		tp->snd_cwnd_stamp = tcp_jiffies32;
5195	}
5196
5197	sk->sk_write_space(sk);
5198}
5199
5200static void tcp_check_space(struct sock *sk)
5201{
5202	if (sock_flag(sk, SOCK_QUEUE_SHRUNK)) {
5203		sock_reset_flag(sk, SOCK_QUEUE_SHRUNK);
5204		/* pairs with tcp_poll() */
5205		smp_mb();
5206		if (sk->sk_socket &&
5207		    test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
5208			tcp_new_space(sk);
5209			if (!test_bit(SOCK_NOSPACE, &sk->sk_socket->flags))
5210				tcp_chrono_stop(sk, TCP_CHRONO_SNDBUF_LIMITED);
5211		}
5212	}
5213}
5214
5215static inline void tcp_data_snd_check(struct sock *sk)
5216{
5217	tcp_push_pending_frames(sk);
5218	tcp_check_space(sk);
5219}
5220
5221/*
5222 * Check if sending an ack is needed.
5223 */
5224static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible)
5225{
5226	struct tcp_sock *tp = tcp_sk(sk);
5227	unsigned long rtt, delay;
5228
5229	    /* More than one full frame received... */
5230	if (((tp->rcv_nxt - tp->rcv_wup) > inet_csk(sk)->icsk_ack.rcv_mss &&
5231	     /* ... and right edge of window advances far enough.
5232	      * (tcp_recvmsg() will send ACK otherwise).
5233	      * If application uses SO_RCVLOWAT, we want send ack now if
5234	      * we have not received enough bytes to satisfy the condition.
5235	      */
5236	    (tp->rcv_nxt - tp->copied_seq < sk->sk_rcvlowat ||
5237	     __tcp_select_window(sk) >= tp->rcv_wnd)) ||
5238	    /* We ACK each frame or... */
5239	    tcp_in_quickack_mode(sk) ||
5240	    /* Protocol state mandates a one-time immediate ACK */
5241	    inet_csk(sk)->icsk_ack.pending & ICSK_ACK_NOW) {
5242send_now:
5243		tcp_send_ack(sk);
5244		return;
5245	}
5246
5247	if (!ofo_possible || RB_EMPTY_ROOT(&tp->out_of_order_queue)) {
5248		tcp_send_delayed_ack(sk);
5249		return;
5250	}
5251
5252	if (!tcp_is_sack(tp) ||
5253	    tp->compressed_ack >= sock_net(sk)->ipv4.sysctl_tcp_comp_sack_nr)
5254		goto send_now;
5255
5256	if (tp->compressed_ack_rcv_nxt != tp->rcv_nxt) {
5257		tp->compressed_ack_rcv_nxt = tp->rcv_nxt;
5258		if (tp->compressed_ack > TCP_FASTRETRANS_THRESH)
5259			NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPACKCOMPRESSED,
5260				      tp->compressed_ack - TCP_FASTRETRANS_THRESH);
5261		tp->compressed_ack = 0;
5262	}
5263
5264	if (++tp->compressed_ack <= TCP_FASTRETRANS_THRESH)
5265		goto send_now;
5266
5267	if (hrtimer_is_queued(&tp->compressed_ack_timer))
5268		return;
5269
5270	/* compress ack timer : 5 % of rtt, but no more than tcp_comp_sack_delay_ns */
5271
5272	rtt = tp->rcv_rtt_est.rtt_us;
5273	if (tp->srtt_us && tp->srtt_us < rtt)
5274		rtt = tp->srtt_us;
5275
5276	delay = min_t(unsigned long, sock_net(sk)->ipv4.sysctl_tcp_comp_sack_delay_ns,
5277		      rtt * (NSEC_PER_USEC >> 3)/20);
5278	sock_hold(sk);
5279	hrtimer_start(&tp->compressed_ack_timer, ns_to_ktime(delay),
5280		      HRTIMER_MODE_REL_PINNED_SOFT);
5281}
5282
5283static inline void tcp_ack_snd_check(struct sock *sk)
5284{
5285	if (!inet_csk_ack_scheduled(sk)) {
5286		/* We sent a data segment already. */
5287		return;
5288	}
5289	__tcp_ack_snd_check(sk, 1);
5290}
5291
5292/*
5293 *	This routine is only called when we have urgent data
5294 *	signaled. Its the 'slow' part of tcp_urg. It could be
5295 *	moved inline now as tcp_urg is only called from one
5296 *	place. We handle URGent data wrong. We have to - as
5297 *	BSD still doesn't use the correction from RFC961.
5298 *	For 1003.1g we should support a new option TCP_STDURG to permit
5299 *	either form (or just set the sysctl tcp_stdurg).
5300 */
5301
5302static void tcp_check_urg(struct sock *sk, const struct tcphdr *th)
5303{
5304	struct tcp_sock *tp = tcp_sk(sk);
5305	u32 ptr = ntohs(th->urg_ptr);
5306
5307	if (ptr && !sock_net(sk)->ipv4.sysctl_tcp_stdurg)
5308		ptr--;
5309	ptr += ntohl(th->seq);
5310
5311	/* Ignore urgent data that we've already seen and read. */
5312	if (after(tp->copied_seq, ptr))
5313		return;
5314
5315	/* Do not replay urg ptr.
5316	 *
5317	 * NOTE: interesting situation not covered by specs.
5318	 * Misbehaving sender may send urg ptr, pointing to segment,
5319	 * which we already have in ofo queue. We are not able to fetch
5320	 * such data and will stay in TCP_URG_NOTYET until will be eaten
5321	 * by recvmsg(). Seems, we are not obliged to handle such wicked
5322	 * situations. But it is worth to think about possibility of some
5323	 * DoSes using some hypothetical application level deadlock.
5324	 */
5325	if (before(ptr, tp->rcv_nxt))
5326		return;
5327
5328	/* Do we already have a newer (or duplicate) urgent pointer? */
5329	if (tp->urg_data && !after(ptr, tp->urg_seq))
5330		return;
5331
5332	/* Tell the world about our new urgent pointer. */
5333	sk_send_sigurg(sk);
5334
5335	/* We may be adding urgent data when the last byte read was
5336	 * urgent. To do this requires some care. We cannot just ignore
5337	 * tp->copied_seq since we would read the last urgent byte again
5338	 * as data, nor can we alter copied_seq until this data arrives
5339	 * or we break the semantics of SIOCATMARK (and thus sockatmark())
5340	 *
5341	 * NOTE. Double Dutch. Rendering to plain English: author of comment
5342	 * above did something sort of 	send("A", MSG_OOB); send("B", MSG_OOB);
5343	 * and expect that both A and B disappear from stream. This is _wrong_.
5344	 * Though this happens in BSD with high probability, this is occasional.
5345	 * Any application relying on this is buggy. Note also, that fix "works"
5346	 * only in this artificial test. Insert some normal data between A and B and we will
5347	 * decline of BSD again. Verdict: it is better to remove to trap
5348	 * buggy users.
5349	 */
5350	if (tp->urg_seq == tp->copied_seq && tp->urg_data &&
5351	    !sock_flag(sk, SOCK_URGINLINE) && tp->copied_seq != tp->rcv_nxt) {
5352		struct sk_buff *skb = skb_peek(&sk->sk_receive_queue);
5353		tp->copied_seq++;
5354		if (skb && !before(tp->copied_seq, TCP_SKB_CB(skb)->end_seq)) {
5355			__skb_unlink(skb, &sk->sk_receive_queue);
5356			__kfree_skb(skb);
5357		}
5358	}
5359
5360	tp->urg_data = TCP_URG_NOTYET;
5361	WRITE_ONCE(tp->urg_seq, ptr);
5362
5363	/* Disable header prediction. */
5364	tp->pred_flags = 0;
5365}
5366
5367/* This is the 'fast' part of urgent handling. */
5368static void tcp_urg(struct sock *sk, struct sk_buff *skb, const struct tcphdr *th)
5369{
5370	struct tcp_sock *tp = tcp_sk(sk);
5371
5372	/* Check if we get a new urgent pointer - normally not. */
5373	if (th->urg)
5374		tcp_check_urg(sk, th);
5375
5376	/* Do we wait for any urgent data? - normally not... */
5377	if (tp->urg_data == TCP_URG_NOTYET) {
5378		u32 ptr = tp->urg_seq - ntohl(th->seq) + (th->doff * 4) -
5379			  th->syn;
5380
5381		/* Is the urgent pointer pointing into this packet? */
5382		if (ptr < skb->len) {
5383			u8 tmp;
5384			if (skb_copy_bits(skb, ptr, &tmp, 1))
5385				BUG();
5386			tp->urg_data = TCP_URG_VALID | tmp;
5387			if (!sock_flag(sk, SOCK_DEAD))
5388				sk->sk_data_ready(sk);
5389		}
5390	}
5391}
5392
5393/* Accept RST for rcv_nxt - 1 after a FIN.
5394 * When tcp connections are abruptly terminated from Mac OSX (via ^C), a
5395 * FIN is sent followed by a RST packet. The RST is sent with the same
5396 * sequence number as the FIN, and thus according to RFC 5961 a challenge
5397 * ACK should be sent. However, Mac OSX rate limits replies to challenge
5398 * ACKs on the closed socket. In addition middleboxes can drop either the
5399 * challenge ACK or a subsequent RST.
5400 */
5401static bool tcp_reset_check(const struct sock *sk, const struct sk_buff *skb)
5402{
5403	struct tcp_sock *tp = tcp_sk(sk);
5404
5405	return unlikely(TCP_SKB_CB(skb)->seq == (tp->rcv_nxt - 1) &&
5406			(1 << sk->sk_state) & (TCPF_CLOSE_WAIT | TCPF_LAST_ACK |
5407					       TCPF_CLOSING));
5408}
5409
5410/* Does PAWS and seqno based validation of an incoming segment, flags will
5411 * play significant role here.
5412 */
5413static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
5414				  const struct tcphdr *th, int syn_inerr)
5415{
5416	struct tcp_sock *tp = tcp_sk(sk);
5417	bool rst_seq_match = false;
5418
5419	/* RFC1323: H1. Apply PAWS check first. */
5420	if (tcp_fast_parse_options(sock_net(sk), skb, th, tp) &&
5421	    tp->rx_opt.saw_tstamp &&
5422	    tcp_paws_discard(sk, skb)) {
5423		if (!th->rst) {
5424			NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);
5425			if (!tcp_oow_rate_limited(sock_net(sk), skb,
5426						  LINUX_MIB_TCPACKSKIPPEDPAWS,
5427						  &tp->last_oow_ack_time))
5428				tcp_send_dupack(sk, skb);
5429			goto discard;
5430		}
5431		/* Reset is accepted even if it did not pass PAWS. */
5432	}
5433
5434	/* Step 1: check sequence number */
5435	if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) {
5436		/* RFC793, page 37: "In all states except SYN-SENT, all reset
5437		 * (RST) segments are validated by checking their SEQ-fields."
5438		 * And page 69: "If an incoming segment is not acceptable,
5439		 * an acknowledgment should be sent in reply (unless the RST
5440		 * bit is set, if so drop the segment and return)".
5441		 */
5442		if (!th->rst) {
5443			if (th->syn)
5444				goto syn_challenge;
5445			if (!tcp_oow_rate_limited(sock_net(sk), skb,
5446						  LINUX_MIB_TCPACKSKIPPEDSEQ,
5447						  &tp->last_oow_ack_time))
5448				tcp_send_dupack(sk, skb);
5449		} else if (tcp_reset_check(sk, skb)) {
5450			tcp_reset(sk);
5451		}
5452		goto discard;
5453	}
5454
5455	/* Step 2: check RST bit */
5456	if (th->rst) {
5457		/* RFC 5961 3.2 (extend to match against (RCV.NXT - 1) after a
5458		 * FIN and SACK too if available):
5459		 * If seq num matches RCV.NXT or (RCV.NXT - 1) after a FIN, or
5460		 * the right-most SACK block,
5461		 * then
5462		 *     RESET the connection
5463		 * else
5464		 *     Send a challenge ACK
5465		 */
5466		if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt ||
5467		    tcp_reset_check(sk, skb)) {
5468			rst_seq_match = true;
5469		} else if (tcp_is_sack(tp) && tp->rx_opt.num_sacks > 0) {
5470			struct tcp_sack_block *sp = &tp->selective_acks[0];
5471			int max_sack = sp[0].end_seq;
5472			int this_sack;
5473
5474			for (this_sack = 1; this_sack < tp->rx_opt.num_sacks;
5475			     ++this_sack) {
5476				max_sack = after(sp[this_sack].end_seq,
5477						 max_sack) ?
5478					sp[this_sack].end_seq : max_sack;
5479			}
5480
5481			if (TCP_SKB_CB(skb)->seq == max_sack)
5482				rst_seq_match = true;
5483		}
5484
5485		if (rst_seq_match)
5486			tcp_reset(sk);
5487		else {
5488			/* Disable TFO if RST is out-of-order
5489			 * and no data has been received
5490			 * for current active TFO socket
5491			 */
5492			if (tp->syn_fastopen && !tp->data_segs_in &&
5493			    sk->sk_state == TCP_ESTABLISHED)
5494				tcp_fastopen_active_disable(sk);
5495			tcp_send_challenge_ack(sk, skb);
5496		}
5497		goto discard;
5498	}
5499
5500	/* step 3: check security and precedence [ignored] */
5501
5502	/* step 4: Check for a SYN
5503	 * RFC 5961 4.2 : Send a challenge ack
5504	 */
5505	if (th->syn) {
5506syn_challenge:
5507		if (syn_inerr)
5508			TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);
5509		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSYNCHALLENGE);
5510		tcp_send_challenge_ack(sk, skb);
5511		goto discard;
5512	}
5513
5514	return true;
5515
5516discard:
5517	tcp_drop(sk, skb);
5518	return false;
5519}
5520
5521/*
5522 *	TCP receive function for the ESTABLISHED state.
5523 *
5524 *	It is split into a fast path and a slow path. The fast path is
5525 * 	disabled when:
5526 *	- A zero window was announced from us - zero window probing
5527 *        is only handled properly in the slow path.
5528 *	- Out of order segments arrived.
5529 *	- Urgent data is expected.
5530 *	- There is no buffer space left
5531 *	- Unexpected TCP flags/window values/header lengths are received
5532 *	  (detected by checking the TCP header against pred_flags)
5533 *	- Data is sent in both directions. Fast path only supports pure senders
5534 *	  or pure receivers (this means either the sequence number or the ack
5535 *	  value must stay constant)
5536 *	- Unexpected TCP option.
5537 *
5538 *	When these conditions are not satisfied it drops into a standard
5539 *	receive procedure patterned after RFC793 to handle all cases.
5540 *	The first three cases are guaranteed by proper pred_flags setting,
5541 *	the rest is checked inline. Fast processing is turned on in
5542 *	tcp_data_queue when everything is OK.
5543 */
5544void tcp_rcv_established(struct sock *sk, struct sk_buff *skb)
 
5545{
5546	const struct tcphdr *th = (const struct tcphdr *)skb->data;
5547	struct tcp_sock *tp = tcp_sk(sk);
5548	unsigned int len = skb->len;
 
5549
5550	/* TCP congestion window tracking */
5551	trace_tcp_probe(sk, skb);
5552
5553	tcp_mstamp_refresh(tp);
5554	if (unlikely(!sk->sk_rx_dst))
5555		inet_csk(sk)->icsk_af_ops->sk_rx_dst_set(sk, skb);
5556	/*
5557	 *	Header prediction.
5558	 *	The code loosely follows the one in the famous
5559	 *	"30 instruction TCP receive" Van Jacobson mail.
5560	 *
5561	 *	Van's trick is to deposit buffers into socket queue
5562	 *	on a device interrupt, to call tcp_recv function
5563	 *	on the receive process context and checksum and copy
5564	 *	the buffer to user space. smart...
5565	 *
5566	 *	Our current scheme is not silly either but we take the
5567	 *	extra cost of the net_bh soft interrupt processing...
5568	 *	We do checksum and copy also but from device to kernel.
5569	 */
5570
5571	tp->rx_opt.saw_tstamp = 0;
5572
5573	/*	pred_flags is 0xS?10 << 16 + snd_wnd
5574	 *	if header_prediction is to be made
5575	 *	'S' will always be tp->tcp_header_len >> 2
5576	 *	'?' will be 0 for the fast path, otherwise pred_flags is 0 to
5577	 *  turn it off	(when there are holes in the receive
5578	 *	 space for instance)
5579	 *	PSH flag is ignored.
5580	 */
5581
5582	if ((tcp_flag_word(th) & TCP_HP_BITS) == tp->pred_flags &&
5583	    TCP_SKB_CB(skb)->seq == tp->rcv_nxt &&
5584	    !after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt)) {
5585		int tcp_header_len = tp->tcp_header_len;
5586
5587		/* Timestamp header prediction: tcp_header_len
5588		 * is automatically equal to th->doff*4 due to pred_flags
5589		 * match.
5590		 */
5591
5592		/* Check timestamp */
5593		if (tcp_header_len == sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) {
5594			/* No? Slow path! */
5595			if (!tcp_parse_aligned_timestamp(tp, th))
5596				goto slow_path;
5597
5598			/* If PAWS failed, check it more carefully in slow path */
5599			if ((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) < 0)
5600				goto slow_path;
5601
5602			/* DO NOT update ts_recent here, if checksum fails
5603			 * and timestamp was corrupted part, it will result
5604			 * in a hung connection since we will drop all
5605			 * future packets due to the PAWS test.
5606			 */
5607		}
5608
5609		if (len <= tcp_header_len) {
5610			/* Bulk data transfer: sender */
5611			if (len == tcp_header_len) {
5612				/* Predicted packet is in window by definition.
5613				 * seq == rcv_nxt and rcv_wup <= rcv_nxt.
5614				 * Hence, check seq<=rcv_wup reduces to:
5615				 */
5616				if (tcp_header_len ==
5617				    (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
5618				    tp->rcv_nxt == tp->rcv_wup)
5619					tcp_store_ts_recent(tp);
5620
5621				/* We know that such packets are checksummed
5622				 * on entry.
5623				 */
5624				tcp_ack(sk, skb, 0);
5625				__kfree_skb(skb);
5626				tcp_data_snd_check(sk);
5627				/* When receiving pure ack in fast path, update
5628				 * last ts ecr directly instead of calling
5629				 * tcp_rcv_rtt_measure_ts()
5630				 */
5631				tp->rcv_rtt_last_tsecr = tp->rx_opt.rcv_tsecr;
5632				return;
5633			} else { /* Header too small */
5634				TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);
5635				goto discard;
5636			}
5637		} else {
5638			int eaten = 0;
5639			bool fragstolen = false;
5640
5641			if (tcp_checksum_complete(skb))
5642				goto csum_error;
5643
5644			if ((int)skb->truesize > sk->sk_forward_alloc)
5645				goto step5;
5646
5647			/* Predicted packet is in window by definition.
5648			 * seq == rcv_nxt and rcv_wup <= rcv_nxt.
5649			 * Hence, check seq<=rcv_wup reduces to:
5650			 */
5651			if (tcp_header_len ==
5652			    (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
5653			    tp->rcv_nxt == tp->rcv_wup)
5654				tcp_store_ts_recent(tp);
5655
5656			tcp_rcv_rtt_measure_ts(sk, skb);
5657
5658			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPHPHITS);
5659
5660			/* Bulk data transfer: receiver */
5661			__skb_pull(skb, tcp_header_len);
5662			eaten = tcp_queue_rcv(sk, skb, &fragstolen);
5663
5664			tcp_event_data_recv(sk, skb);
5665
5666			if (TCP_SKB_CB(skb)->ack_seq != tp->snd_una) {
5667				/* Well, only one small jumplet in fast path... */
5668				tcp_ack(sk, skb, FLAG_DATA);
5669				tcp_data_snd_check(sk);
5670				if (!inet_csk_ack_scheduled(sk))
5671					goto no_ack;
5672			}
5673
5674			__tcp_ack_snd_check(sk, 0);
5675no_ack:
5676			if (eaten)
5677				kfree_skb_partial(skb, fragstolen);
5678			tcp_data_ready(sk);
5679			return;
5680		}
5681	}
5682
5683slow_path:
5684	if (len < (th->doff << 2) || tcp_checksum_complete(skb))
5685		goto csum_error;
5686
5687	if (!th->ack && !th->rst && !th->syn)
5688		goto discard;
5689
5690	/*
5691	 *	Standard slow path.
5692	 */
5693
5694	if (!tcp_validate_incoming(sk, skb, th, 1))
5695		return;
5696
5697step5:
5698	if (tcp_ack(sk, skb, FLAG_SLOWPATH | FLAG_UPDATE_TS_RECENT) < 0)
5699		goto discard;
5700
5701	tcp_rcv_rtt_measure_ts(sk, skb);
5702
5703	/* Process urgent data. */
5704	tcp_urg(sk, skb, th);
5705
5706	/* step 7: process the segment text */
5707	tcp_data_queue(sk, skb);
5708
5709	tcp_data_snd_check(sk);
5710	tcp_ack_snd_check(sk);
5711	return;
5712
5713csum_error:
5714	TCP_INC_STATS(sock_net(sk), TCP_MIB_CSUMERRORS);
5715	TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);
5716
5717discard:
5718	tcp_drop(sk, skb);
5719}
5720EXPORT_SYMBOL(tcp_rcv_established);
5721
5722void tcp_init_transfer(struct sock *sk, int bpf_op)
5723{
5724	struct inet_connection_sock *icsk = inet_csk(sk);
5725	struct tcp_sock *tp = tcp_sk(sk);
5726
5727	tcp_mtup_init(sk);
5728	icsk->icsk_af_ops->rebuild_header(sk);
5729	tcp_init_metrics(sk);
5730
5731	/* Initialize the congestion window to start the transfer.
5732	 * Cut cwnd down to 1 per RFC5681 if SYN or SYN-ACK has been
5733	 * retransmitted. In light of RFC6298 more aggressive 1sec
5734	 * initRTO, we only reset cwnd when more than 1 SYN/SYN-ACK
5735	 * retransmission has occurred.
5736	 */
5737	if (tp->total_retrans > 1 && tp->undo_marker)
5738		tp->snd_cwnd = 1;
5739	else
5740		tp->snd_cwnd = tcp_init_cwnd(tp, __sk_dst_get(sk));
5741	tp->snd_cwnd_stamp = tcp_jiffies32;
5742
5743	tcp_call_bpf(sk, bpf_op, 0, NULL);
5744	tcp_init_congestion_control(sk);
5745	tcp_init_buffer_space(sk);
5746}
5747
5748void tcp_finish_connect(struct sock *sk, struct sk_buff *skb)
5749{
5750	struct tcp_sock *tp = tcp_sk(sk);
5751	struct inet_connection_sock *icsk = inet_csk(sk);
5752
5753	tcp_set_state(sk, TCP_ESTABLISHED);
5754	icsk->icsk_ack.lrcvtime = tcp_jiffies32;
5755
5756	if (skb) {
5757		icsk->icsk_af_ops->sk_rx_dst_set(sk, skb);
5758		security_inet_conn_established(sk, skb);
5759		sk_mark_napi_id(sk, skb);
5760	}
5761
5762	tcp_init_transfer(sk, BPF_SOCK_OPS_ACTIVE_ESTABLISHED_CB);
5763
5764	/* Prevent spurious tcp_cwnd_restart() on first data
5765	 * packet.
5766	 */
5767	tp->lsndtime = tcp_jiffies32;
5768
5769	if (sock_flag(sk, SOCK_KEEPOPEN))
5770		inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tp));
5771
5772	if (!tp->rx_opt.snd_wscale)
5773		__tcp_fast_path_on(tp, tp->snd_wnd);
5774	else
5775		tp->pred_flags = 0;
5776}
5777
5778static bool tcp_rcv_fastopen_synack(struct sock *sk, struct sk_buff *synack,
5779				    struct tcp_fastopen_cookie *cookie)
5780{
5781	struct tcp_sock *tp = tcp_sk(sk);
5782	struct sk_buff *data = tp->syn_data ? tcp_rtx_queue_head(sk) : NULL;
5783	u16 mss = tp->rx_opt.mss_clamp, try_exp = 0;
5784	bool syn_drop = false;
5785
5786	if (mss == tp->rx_opt.user_mss) {
5787		struct tcp_options_received opt;
5788
5789		/* Get original SYNACK MSS value if user MSS sets mss_clamp */
5790		tcp_clear_options(&opt);
5791		opt.user_mss = opt.mss_clamp = 0;
5792		tcp_parse_options(sock_net(sk), synack, &opt, 0, NULL);
5793		mss = opt.mss_clamp;
5794	}
5795
5796	if (!tp->syn_fastopen) {
5797		/* Ignore an unsolicited cookie */
5798		cookie->len = -1;
5799	} else if (tp->total_retrans) {
5800		/* SYN timed out and the SYN-ACK neither has a cookie nor
5801		 * acknowledges data. Presumably the remote received only
5802		 * the retransmitted (regular) SYNs: either the original
5803		 * SYN-data or the corresponding SYN-ACK was dropped.
5804		 */
5805		syn_drop = (cookie->len < 0 && data);
5806	} else if (cookie->len < 0 && !tp->syn_data) {
5807		/* We requested a cookie but didn't get it. If we did not use
5808		 * the (old) exp opt format then try so next time (try_exp=1).
5809		 * Otherwise we go back to use the RFC7413 opt (try_exp=2).
5810		 */
5811		try_exp = tp->syn_fastopen_exp ? 2 : 1;
5812	}
5813
5814	tcp_fastopen_cache_set(sk, mss, cookie, syn_drop, try_exp);
5815
5816	if (data) { /* Retransmit unacked data in SYN */
5817		skb_rbtree_walk_from(data) {
5818			if (__tcp_retransmit_skb(sk, data, 1))
5819				break;
5820		}
5821		tcp_rearm_rto(sk);
5822		NET_INC_STATS(sock_net(sk),
5823				LINUX_MIB_TCPFASTOPENACTIVEFAIL);
5824		return true;
5825	}
5826	tp->syn_data_acked = tp->syn_data;
5827	if (tp->syn_data_acked) {
5828		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFASTOPENACTIVE);
5829		/* SYN-data is counted as two separate packets in tcp_ack() */
5830		if (tp->delivered > 1)
5831			--tp->delivered;
5832	}
5833
5834	tcp_fastopen_add_skb(sk, synack);
5835
5836	return false;
5837}
5838
5839static void smc_check_reset_syn(struct tcp_sock *tp)
5840{
5841#if IS_ENABLED(CONFIG_SMC)
5842	if (static_branch_unlikely(&tcp_have_smc)) {
5843		if (tp->syn_smc && !tp->rx_opt.smc_ok)
5844			tp->syn_smc = 0;
5845	}
5846#endif
5847}
5848
5849static void tcp_try_undo_spurious_syn(struct sock *sk)
5850{
5851	struct tcp_sock *tp = tcp_sk(sk);
5852	u32 syn_stamp;
5853
5854	/* undo_marker is set when SYN or SYNACK times out. The timeout is
5855	 * spurious if the ACK's timestamp option echo value matches the
5856	 * original SYN timestamp.
5857	 */
5858	syn_stamp = tp->retrans_stamp;
5859	if (tp->undo_marker && syn_stamp && tp->rx_opt.saw_tstamp &&
5860	    syn_stamp == tp->rx_opt.rcv_tsecr)
5861		tp->undo_marker = 0;
5862}
5863
5864static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
5865					 const struct tcphdr *th)
5866{
5867	struct inet_connection_sock *icsk = inet_csk(sk);
5868	struct tcp_sock *tp = tcp_sk(sk);
5869	struct tcp_fastopen_cookie foc = { .len = -1 };
5870	int saved_clamp = tp->rx_opt.mss_clamp;
5871	bool fastopen_fail;
5872
5873	tcp_parse_options(sock_net(sk), skb, &tp->rx_opt, 0, &foc);
5874	if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
5875		tp->rx_opt.rcv_tsecr -= tp->tsoffset;
5876
5877	if (th->ack) {
5878		/* rfc793:
5879		 * "If the state is SYN-SENT then
5880		 *    first check the ACK bit
5881		 *      If the ACK bit is set
5882		 *	  If SEG.ACK =< ISS, or SEG.ACK > SND.NXT, send
5883		 *        a reset (unless the RST bit is set, if so drop
5884		 *        the segment and return)"
5885		 */
5886		if (!after(TCP_SKB_CB(skb)->ack_seq, tp->snd_una) ||
5887		    after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt))
5888			goto reset_and_undo;
5889
5890		if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
5891		    !between(tp->rx_opt.rcv_tsecr, tp->retrans_stamp,
5892			     tcp_time_stamp(tp))) {
5893			NET_INC_STATS(sock_net(sk),
5894					LINUX_MIB_PAWSACTIVEREJECTED);
5895			goto reset_and_undo;
5896		}
5897
5898		/* Now ACK is acceptable.
5899		 *
5900		 * "If the RST bit is set
5901		 *    If the ACK was acceptable then signal the user "error:
5902		 *    connection reset", drop the segment, enter CLOSED state,
5903		 *    delete TCB, and return."
5904		 */
5905
5906		if (th->rst) {
5907			tcp_reset(sk);
5908			goto discard;
5909		}
5910
5911		/* rfc793:
5912		 *   "fifth, if neither of the SYN or RST bits is set then
5913		 *    drop the segment and return."
5914		 *
5915		 *    See note below!
5916		 *                                        --ANK(990513)
5917		 */
5918		if (!th->syn)
5919			goto discard_and_undo;
5920
5921		/* rfc793:
5922		 *   "If the SYN bit is on ...
5923		 *    are acceptable then ...
5924		 *    (our SYN has been ACKed), change the connection
5925		 *    state to ESTABLISHED..."
5926		 */
5927
5928		tcp_ecn_rcv_synack(tp, th);
5929
5930		tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);
5931		tcp_try_undo_spurious_syn(sk);
5932		tcp_ack(sk, skb, FLAG_SLOWPATH);
5933
5934		/* Ok.. it's good. Set up sequence numbers and
5935		 * move to established.
5936		 */
5937		WRITE_ONCE(tp->rcv_nxt, TCP_SKB_CB(skb)->seq + 1);
5938		tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
5939
5940		/* RFC1323: The window in SYN & SYN/ACK segments is
5941		 * never scaled.
5942		 */
5943		tp->snd_wnd = ntohs(th->window);
5944
5945		if (!tp->rx_opt.wscale_ok) {
5946			tp->rx_opt.snd_wscale = tp->rx_opt.rcv_wscale = 0;
5947			tp->window_clamp = min(tp->window_clamp, 65535U);
5948		}
5949
5950		if (tp->rx_opt.saw_tstamp) {
5951			tp->rx_opt.tstamp_ok	   = 1;
5952			tp->tcp_header_len =
5953				sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
5954			tp->advmss	    -= TCPOLEN_TSTAMP_ALIGNED;
5955			tcp_store_ts_recent(tp);
5956		} else {
5957			tp->tcp_header_len = sizeof(struct tcphdr);
5958		}
5959
5960		tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
5961		tcp_initialize_rcv_mss(sk);
5962
5963		/* Remember, tcp_poll() does not lock socket!
5964		 * Change state from SYN-SENT only after copied_seq
5965		 * is initialized. */
5966		WRITE_ONCE(tp->copied_seq, tp->rcv_nxt);
5967
5968		smc_check_reset_syn(tp);
5969
5970		smp_mb();
5971
5972		tcp_finish_connect(sk, skb);
5973
5974		fastopen_fail = (tp->syn_fastopen || tp->syn_data) &&
5975				tcp_rcv_fastopen_synack(sk, skb, &foc);
5976
5977		if (!sock_flag(sk, SOCK_DEAD)) {
5978			sk->sk_state_change(sk);
5979			sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT);
5980		}
5981		if (fastopen_fail)
5982			return -1;
5983		if (sk->sk_write_pending ||
5984		    icsk->icsk_accept_queue.rskq_defer_accept ||
5985		    inet_csk_in_pingpong_mode(sk)) {
5986			/* Save one ACK. Data will be ready after
5987			 * several ticks, if write_pending is set.
5988			 *
5989			 * It may be deleted, but with this feature tcpdumps
5990			 * look so _wonderfully_ clever, that I was not able
5991			 * to stand against the temptation 8)     --ANK
5992			 */
5993			inet_csk_schedule_ack(sk);
5994			tcp_enter_quickack_mode(sk, TCP_MAX_QUICKACKS);
5995			inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
5996						  TCP_DELACK_MAX, TCP_RTO_MAX);
5997
5998discard:
5999			tcp_drop(sk, skb);
6000			return 0;
6001		} else {
6002			tcp_send_ack(sk);
6003		}
6004		return -1;
6005	}
6006
6007	/* No ACK in the segment */
6008
6009	if (th->rst) {
6010		/* rfc793:
6011		 * "If the RST bit is set
6012		 *
6013		 *      Otherwise (no ACK) drop the segment and return."
6014		 */
6015
6016		goto discard_and_undo;
6017	}
6018
6019	/* PAWS check. */
6020	if (tp->rx_opt.ts_recent_stamp && tp->rx_opt.saw_tstamp &&
6021	    tcp_paws_reject(&tp->rx_opt, 0))
6022		goto discard_and_undo;
6023
6024	if (th->syn) {
6025		/* We see SYN without ACK. It is attempt of
6026		 * simultaneous connect with crossed SYNs.
6027		 * Particularly, it can be connect to self.
6028		 */
6029		tcp_set_state(sk, TCP_SYN_RECV);
6030
6031		if (tp->rx_opt.saw_tstamp) {
6032			tp->rx_opt.tstamp_ok = 1;
6033			tcp_store_ts_recent(tp);
6034			tp->tcp_header_len =
6035				sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
6036		} else {
6037			tp->tcp_header_len = sizeof(struct tcphdr);
6038		}
6039
6040		WRITE_ONCE(tp->rcv_nxt, TCP_SKB_CB(skb)->seq + 1);
6041		WRITE_ONCE(tp->copied_seq, tp->rcv_nxt);
6042		tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
6043
6044		/* RFC1323: The window in SYN & SYN/ACK segments is
6045		 * never scaled.
6046		 */
6047		tp->snd_wnd    = ntohs(th->window);
6048		tp->snd_wl1    = TCP_SKB_CB(skb)->seq;
6049		tp->max_window = tp->snd_wnd;
6050
6051		tcp_ecn_rcv_syn(tp, th);
6052
6053		tcp_mtup_init(sk);
6054		tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
6055		tcp_initialize_rcv_mss(sk);
6056
6057		tcp_send_synack(sk);
6058#if 0
6059		/* Note, we could accept data and URG from this segment.
6060		 * There are no obstacles to make this (except that we must
6061		 * either change tcp_recvmsg() to prevent it from returning data
6062		 * before 3WHS completes per RFC793, or employ TCP Fast Open).
6063		 *
6064		 * However, if we ignore data in ACKless segments sometimes,
6065		 * we have no reasons to accept it sometimes.
6066		 * Also, seems the code doing it in step6 of tcp_rcv_state_process
6067		 * is not flawless. So, discard packet for sanity.
6068		 * Uncomment this return to process the data.
6069		 */
6070		return -1;
6071#else
6072		goto discard;
6073#endif
6074	}
6075	/* "fifth, if neither of the SYN or RST bits is set then
6076	 * drop the segment and return."
6077	 */
6078
6079discard_and_undo:
6080	tcp_clear_options(&tp->rx_opt);
6081	tp->rx_opt.mss_clamp = saved_clamp;
6082	goto discard;
6083
6084reset_and_undo:
6085	tcp_clear_options(&tp->rx_opt);
6086	tp->rx_opt.mss_clamp = saved_clamp;
6087	return 1;
6088}
6089
6090static void tcp_rcv_synrecv_state_fastopen(struct sock *sk)
6091{
6092	struct request_sock *req;
6093
6094	tcp_try_undo_loss(sk, false);
6095
6096	/* Reset rtx states to prevent spurious retransmits_timed_out() */
6097	tcp_sk(sk)->retrans_stamp = 0;
6098	inet_csk(sk)->icsk_retransmits = 0;
6099
6100	/* Once we leave TCP_SYN_RECV or TCP_FIN_WAIT_1,
6101	 * we no longer need req so release it.
6102	 */
6103	req = rcu_dereference_protected(tcp_sk(sk)->fastopen_rsk,
6104					lockdep_sock_is_held(sk));
6105	reqsk_fastopen_remove(sk, req, false);
6106
6107	/* Re-arm the timer because data may have been sent out.
6108	 * This is similar to the regular data transmission case
6109	 * when new data has just been ack'ed.
6110	 *
6111	 * (TFO) - we could try to be more aggressive and
6112	 * retransmitting any data sooner based on when they
6113	 * are sent out.
6114	 */
6115	tcp_rearm_rto(sk);
6116}
6117
6118/*
6119 *	This function implements the receiving procedure of RFC 793 for
6120 *	all states except ESTABLISHED and TIME_WAIT.
6121 *	It's called from both tcp_v4_rcv and tcp_v6_rcv and should be
6122 *	address independent.
6123 */
6124
6125int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
6126{
6127	struct tcp_sock *tp = tcp_sk(sk);
6128	struct inet_connection_sock *icsk = inet_csk(sk);
6129	const struct tcphdr *th = tcp_hdr(skb);
6130	struct request_sock *req;
6131	int queued = 0;
6132	bool acceptable;
6133
6134	switch (sk->sk_state) {
6135	case TCP_CLOSE:
6136		goto discard;
6137
6138	case TCP_LISTEN:
6139		if (th->ack)
6140			return 1;
6141
6142		if (th->rst)
6143			goto discard;
6144
6145		if (th->syn) {
6146			if (th->fin)
6147				goto discard;
6148			/* It is possible that we process SYN packets from backlog,
6149			 * so we need to make sure to disable BH and RCU right there.
6150			 */
6151			rcu_read_lock();
6152			local_bh_disable();
6153			acceptable = icsk->icsk_af_ops->conn_request(sk, skb) >= 0;
6154			local_bh_enable();
6155			rcu_read_unlock();
6156
6157			if (!acceptable)
6158				return 1;
6159			consume_skb(skb);
6160			return 0;
6161		}
6162		goto discard;
6163
6164	case TCP_SYN_SENT:
6165		tp->rx_opt.saw_tstamp = 0;
6166		tcp_mstamp_refresh(tp);
6167		queued = tcp_rcv_synsent_state_process(sk, skb, th);
6168		if (queued >= 0)
6169			return queued;
6170
6171		/* Do step6 onward by hand. */
6172		tcp_urg(sk, skb, th);
6173		__kfree_skb(skb);
6174		tcp_data_snd_check(sk);
6175		return 0;
6176	}
6177
6178	tcp_mstamp_refresh(tp);
6179	tp->rx_opt.saw_tstamp = 0;
6180	req = rcu_dereference_protected(tp->fastopen_rsk,
6181					lockdep_sock_is_held(sk));
6182	if (req) {
6183		bool req_stolen;
6184
6185		WARN_ON_ONCE(sk->sk_state != TCP_SYN_RECV &&
6186		    sk->sk_state != TCP_FIN_WAIT1);
6187
6188		if (!tcp_check_req(sk, skb, req, true, &req_stolen))
6189			goto discard;
6190	}
6191
6192	if (!th->ack && !th->rst && !th->syn)
6193		goto discard;
6194
6195	if (!tcp_validate_incoming(sk, skb, th, 0))
6196		return 0;
6197
6198	/* step 5: check the ACK field */
6199	acceptable = tcp_ack(sk, skb, FLAG_SLOWPATH |
6200				      FLAG_UPDATE_TS_RECENT |
6201				      FLAG_NO_CHALLENGE_ACK) > 0;
6202
6203	if (!acceptable) {
6204		if (sk->sk_state == TCP_SYN_RECV)
6205			return 1;	/* send one RST */
6206		tcp_send_challenge_ack(sk, skb);
6207		goto discard;
6208	}
6209	switch (sk->sk_state) {
6210	case TCP_SYN_RECV:
6211		tp->delivered++; /* SYN-ACK delivery isn't tracked in tcp_ack */
6212		if (!tp->srtt_us)
6213			tcp_synack_rtt_meas(sk, req);
6214
 
 
 
6215		if (req) {
6216			tcp_rcv_synrecv_state_fastopen(sk);
 
 
 
 
 
 
 
 
 
 
6217		} else {
6218			tcp_try_undo_spurious_syn(sk);
6219			tp->retrans_stamp = 0;
6220			tcp_init_transfer(sk, BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB);
6221			WRITE_ONCE(tp->copied_seq, tp->rcv_nxt);
6222		}
6223		smp_mb();
6224		tcp_set_state(sk, TCP_ESTABLISHED);
6225		sk->sk_state_change(sk);
6226
6227		/* Note, that this wakeup is only for marginal crossed SYN case.
6228		 * Passively open sockets are not waked up, because
6229		 * sk->sk_sleep == NULL and sk->sk_socket == NULL.
6230		 */
6231		if (sk->sk_socket)
6232			sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT);
6233
6234		tp->snd_una = TCP_SKB_CB(skb)->ack_seq;
6235		tp->snd_wnd = ntohs(th->window) << tp->rx_opt.snd_wscale;
6236		tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);
6237
6238		if (tp->rx_opt.tstamp_ok)
6239			tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;
6240
6241		if (!inet_csk(sk)->icsk_ca_ops->cong_control)
6242			tcp_update_pacing_rate(sk);
6243
6244		/* Prevent spurious tcp_cwnd_restart() on first data packet */
6245		tp->lsndtime = tcp_jiffies32;
6246
6247		tcp_initialize_rcv_mss(sk);
6248		tcp_fast_path_on(tp);
6249		break;
6250
6251	case TCP_FIN_WAIT1: {
6252		int tmo;
6253
6254		if (req)
6255			tcp_rcv_synrecv_state_fastopen(sk);
6256
 
 
 
 
 
 
 
6257		if (tp->snd_una != tp->write_seq)
6258			break;
6259
6260		tcp_set_state(sk, TCP_FIN_WAIT2);
6261		sk->sk_shutdown |= SEND_SHUTDOWN;
6262
6263		sk_dst_confirm(sk);
6264
6265		if (!sock_flag(sk, SOCK_DEAD)) {
6266			/* Wake up lingering close() */
6267			sk->sk_state_change(sk);
6268			break;
6269		}
6270
6271		if (tp->linger2 < 0) {
6272			tcp_done(sk);
6273			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
6274			return 1;
6275		}
6276		if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
6277		    after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) {
6278			/* Receive out of order FIN after close() */
6279			if (tp->syn_fastopen && th->fin)
6280				tcp_fastopen_active_disable(sk);
6281			tcp_done(sk);
6282			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
6283			return 1;
6284		}
6285
6286		tmo = tcp_fin_time(sk);
6287		if (tmo > TCP_TIMEWAIT_LEN) {
6288			inet_csk_reset_keepalive_timer(sk, tmo - TCP_TIMEWAIT_LEN);
6289		} else if (th->fin || sock_owned_by_user(sk)) {
6290			/* Bad case. We could lose such FIN otherwise.
6291			 * It is not a big problem, but it looks confusing
6292			 * and not so rare event. We still can lose it now,
6293			 * if it spins in bh_lock_sock(), but it is really
6294			 * marginal case.
6295			 */
6296			inet_csk_reset_keepalive_timer(sk, tmo);
6297		} else {
6298			tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
6299			goto discard;
6300		}
6301		break;
6302	}
6303
6304	case TCP_CLOSING:
6305		if (tp->snd_una == tp->write_seq) {
6306			tcp_time_wait(sk, TCP_TIME_WAIT, 0);
6307			goto discard;
6308		}
6309		break;
6310
6311	case TCP_LAST_ACK:
6312		if (tp->snd_una == tp->write_seq) {
6313			tcp_update_metrics(sk);
6314			tcp_done(sk);
6315			goto discard;
6316		}
6317		break;
6318	}
6319
6320	/* step 6: check the URG bit */
6321	tcp_urg(sk, skb, th);
6322
6323	/* step 7: process the segment text */
6324	switch (sk->sk_state) {
6325	case TCP_CLOSE_WAIT:
6326	case TCP_CLOSING:
6327	case TCP_LAST_ACK:
6328		if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
6329			break;
6330		/* fall through */
6331	case TCP_FIN_WAIT1:
6332	case TCP_FIN_WAIT2:
6333		/* RFC 793 says to queue data in these states,
6334		 * RFC 1122 says we MUST send a reset.
6335		 * BSD 4.4 also does reset.
6336		 */
6337		if (sk->sk_shutdown & RCV_SHUTDOWN) {
6338			if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
6339			    after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) {
6340				NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
6341				tcp_reset(sk);
6342				return 1;
6343			}
6344		}
6345		/* Fall through */
6346	case TCP_ESTABLISHED:
6347		tcp_data_queue(sk, skb);
6348		queued = 1;
6349		break;
6350	}
6351
6352	/* tcp_data could move socket to TIME-WAIT */
6353	if (sk->sk_state != TCP_CLOSE) {
6354		tcp_data_snd_check(sk);
6355		tcp_ack_snd_check(sk);
6356	}
6357
6358	if (!queued) {
6359discard:
6360		tcp_drop(sk, skb);
6361	}
6362	return 0;
6363}
6364EXPORT_SYMBOL(tcp_rcv_state_process);
6365
6366static inline void pr_drop_req(struct request_sock *req, __u16 port, int family)
6367{
6368	struct inet_request_sock *ireq = inet_rsk(req);
6369
6370	if (family == AF_INET)
6371		net_dbg_ratelimited("drop open request from %pI4/%u\n",
6372				    &ireq->ir_rmt_addr, port);
6373#if IS_ENABLED(CONFIG_IPV6)
6374	else if (family == AF_INET6)
6375		net_dbg_ratelimited("drop open request from %pI6/%u\n",
6376				    &ireq->ir_v6_rmt_addr, port);
6377#endif
6378}
6379
6380/* RFC3168 : 6.1.1 SYN packets must not have ECT/ECN bits set
6381 *
6382 * If we receive a SYN packet with these bits set, it means a
6383 * network is playing bad games with TOS bits. In order to
6384 * avoid possible false congestion notifications, we disable
6385 * TCP ECN negotiation.
6386 *
6387 * Exception: tcp_ca wants ECN. This is required for DCTCP
6388 * congestion control: Linux DCTCP asserts ECT on all packets,
6389 * including SYN, which is most optimal solution; however,
6390 * others, such as FreeBSD do not.
6391 *
6392 * Exception: At least one of the reserved bits of the TCP header (th->res1) is
6393 * set, indicating the use of a future TCP extension (such as AccECN). See
6394 * RFC8311 §4.3 which updates RFC3168 to allow the development of such
6395 * extensions.
6396 */
6397static void tcp_ecn_create_request(struct request_sock *req,
6398				   const struct sk_buff *skb,
6399				   const struct sock *listen_sk,
6400				   const struct dst_entry *dst)
6401{
6402	const struct tcphdr *th = tcp_hdr(skb);
6403	const struct net *net = sock_net(listen_sk);
6404	bool th_ecn = th->ece && th->cwr;
6405	bool ect, ecn_ok;
6406	u32 ecn_ok_dst;
6407
6408	if (!th_ecn)
6409		return;
6410
6411	ect = !INET_ECN_is_not_ect(TCP_SKB_CB(skb)->ip_dsfield);
6412	ecn_ok_dst = dst_feature(dst, DST_FEATURE_ECN_MASK);
6413	ecn_ok = net->ipv4.sysctl_tcp_ecn || ecn_ok_dst;
6414
6415	if (((!ect || th->res1) && ecn_ok) || tcp_ca_needs_ecn(listen_sk) ||
6416	    (ecn_ok_dst & DST_FEATURE_ECN_CA) ||
6417	    tcp_bpf_ca_needs_ecn((struct sock *)req))
6418		inet_rsk(req)->ecn_ok = 1;
6419}
6420
6421static void tcp_openreq_init(struct request_sock *req,
6422			     const struct tcp_options_received *rx_opt,
6423			     struct sk_buff *skb, const struct sock *sk)
6424{
6425	struct inet_request_sock *ireq = inet_rsk(req);
6426
6427	req->rsk_rcv_wnd = 0;		/* So that tcp_send_synack() knows! */
6428	req->cookie_ts = 0;
6429	tcp_rsk(req)->rcv_isn = TCP_SKB_CB(skb)->seq;
6430	tcp_rsk(req)->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
6431	tcp_rsk(req)->snt_synack = 0;
6432	tcp_rsk(req)->last_oow_ack_time = 0;
6433	req->mss = rx_opt->mss_clamp;
6434	req->ts_recent = rx_opt->saw_tstamp ? rx_opt->rcv_tsval : 0;
6435	ireq->tstamp_ok = rx_opt->tstamp_ok;
6436	ireq->sack_ok = rx_opt->sack_ok;
6437	ireq->snd_wscale = rx_opt->snd_wscale;
6438	ireq->wscale_ok = rx_opt->wscale_ok;
6439	ireq->acked = 0;
6440	ireq->ecn_ok = 0;
6441	ireq->ir_rmt_port = tcp_hdr(skb)->source;
6442	ireq->ir_num = ntohs(tcp_hdr(skb)->dest);
6443	ireq->ir_mark = inet_request_mark(sk, skb);
6444#if IS_ENABLED(CONFIG_SMC)
6445	ireq->smc_ok = rx_opt->smc_ok;
6446#endif
6447}
6448
6449struct request_sock *inet_reqsk_alloc(const struct request_sock_ops *ops,
6450				      struct sock *sk_listener,
6451				      bool attach_listener)
6452{
6453	struct request_sock *req = reqsk_alloc(ops, sk_listener,
6454					       attach_listener);
6455
6456	if (req) {
6457		struct inet_request_sock *ireq = inet_rsk(req);
6458
6459		ireq->ireq_opt = NULL;
6460#if IS_ENABLED(CONFIG_IPV6)
6461		ireq->pktopts = NULL;
6462#endif
6463		atomic64_set(&ireq->ir_cookie, 0);
6464		ireq->ireq_state = TCP_NEW_SYN_RECV;
6465		write_pnet(&ireq->ireq_net, sock_net(sk_listener));
6466		ireq->ireq_family = sk_listener->sk_family;
6467	}
6468
6469	return req;
6470}
6471EXPORT_SYMBOL(inet_reqsk_alloc);
6472
6473/*
6474 * Return true if a syncookie should be sent
6475 */
6476static bool tcp_syn_flood_action(const struct sock *sk, const char *proto)
 
 
6477{
6478	struct request_sock_queue *queue = &inet_csk(sk)->icsk_accept_queue;
6479	const char *msg = "Dropping request";
6480	bool want_cookie = false;
6481	struct net *net = sock_net(sk);
6482
6483#ifdef CONFIG_SYN_COOKIES
6484	if (net->ipv4.sysctl_tcp_syncookies) {
6485		msg = "Sending cookies";
6486		want_cookie = true;
6487		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPREQQFULLDOCOOKIES);
6488	} else
6489#endif
6490		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPREQQFULLDROP);
6491
6492	if (!queue->synflood_warned &&
6493	    net->ipv4.sysctl_tcp_syncookies != 2 &&
6494	    xchg(&queue->synflood_warned, 1) == 0)
6495		net_info_ratelimited("%s: Possible SYN flooding on port %d. %s.  Check SNMP counters.\n",
6496				     proto, sk->sk_num, msg);
6497
6498	return want_cookie;
6499}
6500
6501static void tcp_reqsk_record_syn(const struct sock *sk,
6502				 struct request_sock *req,
6503				 const struct sk_buff *skb)
6504{
6505	if (tcp_sk(sk)->save_syn) {
6506		u32 len = skb_network_header_len(skb) + tcp_hdrlen(skb);
6507		u32 *copy;
6508
6509		copy = kmalloc(len + sizeof(u32), GFP_ATOMIC);
6510		if (copy) {
6511			copy[0] = len;
6512			memcpy(&copy[1], skb_network_header(skb), len);
6513			req->saved_syn = copy;
6514		}
6515	}
6516}
6517
6518/* If a SYN cookie is required and supported, returns a clamped MSS value to be
6519 * used for SYN cookie generation.
6520 */
6521u16 tcp_get_syncookie_mss(struct request_sock_ops *rsk_ops,
6522			  const struct tcp_request_sock_ops *af_ops,
6523			  struct sock *sk, struct tcphdr *th)
6524{
6525	struct tcp_sock *tp = tcp_sk(sk);
6526	u16 mss;
6527
6528	if (sock_net(sk)->ipv4.sysctl_tcp_syncookies != 2 &&
6529	    !inet_csk_reqsk_queue_is_full(sk))
6530		return 0;
6531
6532	if (!tcp_syn_flood_action(sk, rsk_ops->slab_name))
6533		return 0;
6534
6535	if (sk_acceptq_is_full(sk)) {
6536		NET_INC_STATS(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS);
6537		return 0;
6538	}
6539
6540	mss = tcp_parse_mss_option(th, tp->rx_opt.user_mss);
6541	if (!mss)
6542		mss = af_ops->mss_clamp;
6543
6544	return mss;
6545}
6546EXPORT_SYMBOL_GPL(tcp_get_syncookie_mss);
6547
6548int tcp_conn_request(struct request_sock_ops *rsk_ops,
6549		     const struct tcp_request_sock_ops *af_ops,
6550		     struct sock *sk, struct sk_buff *skb)
6551{
6552	struct tcp_fastopen_cookie foc = { .len = -1 };
6553	__u32 isn = TCP_SKB_CB(skb)->tcp_tw_isn;
6554	struct tcp_options_received tmp_opt;
6555	struct tcp_sock *tp = tcp_sk(sk);
6556	struct net *net = sock_net(sk);
6557	struct sock *fastopen_sk = NULL;
6558	struct request_sock *req;
6559	bool want_cookie = false;
6560	struct dst_entry *dst;
6561	struct flowi fl;
6562
6563	/* TW buckets are converted to open requests without
6564	 * limitations, they conserve resources and peer is
6565	 * evidently real one.
6566	 */
6567	if ((net->ipv4.sysctl_tcp_syncookies == 2 ||
6568	     inet_csk_reqsk_queue_is_full(sk)) && !isn) {
6569		want_cookie = tcp_syn_flood_action(sk, rsk_ops->slab_name);
6570		if (!want_cookie)
6571			goto drop;
6572	}
6573
6574	if (sk_acceptq_is_full(sk)) {
6575		NET_INC_STATS(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS);
6576		goto drop;
6577	}
6578
6579	req = inet_reqsk_alloc(rsk_ops, sk, !want_cookie);
6580	if (!req)
6581		goto drop;
6582
6583	tcp_rsk(req)->af_specific = af_ops;
6584	tcp_rsk(req)->ts_off = 0;
6585
6586	tcp_clear_options(&tmp_opt);
6587	tmp_opt.mss_clamp = af_ops->mss_clamp;
6588	tmp_opt.user_mss  = tp->rx_opt.user_mss;
6589	tcp_parse_options(sock_net(sk), skb, &tmp_opt, 0,
6590			  want_cookie ? NULL : &foc);
6591
6592	if (want_cookie && !tmp_opt.saw_tstamp)
6593		tcp_clear_options(&tmp_opt);
6594
6595	if (IS_ENABLED(CONFIG_SMC) && want_cookie)
6596		tmp_opt.smc_ok = 0;
6597
6598	tmp_opt.tstamp_ok = tmp_opt.saw_tstamp;
6599	tcp_openreq_init(req, &tmp_opt, skb, sk);
6600	inet_rsk(req)->no_srccheck = inet_sk(sk)->transparent;
6601
6602	/* Note: tcp_v6_init_req() might override ir_iif for link locals */
6603	inet_rsk(req)->ir_iif = inet_request_bound_dev_if(sk, skb);
6604
6605	af_ops->init_req(req, sk, skb);
6606
6607	if (security_inet_conn_request(sk, skb, req))
6608		goto drop_and_free;
6609
6610	if (tmp_opt.tstamp_ok)
6611		tcp_rsk(req)->ts_off = af_ops->init_ts_off(net, skb);
6612
6613	dst = af_ops->route_req(sk, &fl, req);
6614	if (!dst)
6615		goto drop_and_free;
6616
6617	if (!want_cookie && !isn) {
6618		/* Kill the following clause, if you dislike this way. */
6619		if (!net->ipv4.sysctl_tcp_syncookies &&
6620		    (net->ipv4.sysctl_max_syn_backlog - inet_csk_reqsk_queue_len(sk) <
6621		     (net->ipv4.sysctl_max_syn_backlog >> 2)) &&
6622		    !tcp_peer_is_proven(req, dst)) {
6623			/* Without syncookies last quarter of
6624			 * backlog is filled with destinations,
6625			 * proven to be alive.
6626			 * It means that we continue to communicate
6627			 * to destinations, already remembered
6628			 * to the moment of synflood.
6629			 */
6630			pr_drop_req(req, ntohs(tcp_hdr(skb)->source),
6631				    rsk_ops->family);
6632			goto drop_and_release;
6633		}
6634
6635		isn = af_ops->init_seq(skb);
6636	}
6637
6638	tcp_ecn_create_request(req, skb, sk, dst);
6639
6640	if (want_cookie) {
6641		isn = cookie_init_sequence(af_ops, sk, skb, &req->mss);
6642		req->cookie_ts = tmp_opt.tstamp_ok;
6643		if (!tmp_opt.tstamp_ok)
6644			inet_rsk(req)->ecn_ok = 0;
6645	}
6646
6647	tcp_rsk(req)->snt_isn = isn;
6648	tcp_rsk(req)->txhash = net_tx_rndhash();
6649	tcp_openreq_init_rwin(req, sk, dst);
6650	sk_rx_queue_set(req_to_sk(req), skb);
6651	if (!want_cookie) {
6652		tcp_reqsk_record_syn(sk, req, skb);
6653		fastopen_sk = tcp_try_fastopen(sk, skb, req, &foc, dst);
6654	}
6655	if (fastopen_sk) {
6656		af_ops->send_synack(fastopen_sk, dst, &fl, req,
6657				    &foc, TCP_SYNACK_FASTOPEN);
6658		/* Add the child socket directly into the accept queue */
6659		if (!inet_csk_reqsk_queue_add(sk, req, fastopen_sk)) {
6660			reqsk_fastopen_remove(fastopen_sk, req, false);
6661			bh_unlock_sock(fastopen_sk);
6662			sock_put(fastopen_sk);
6663			goto drop_and_free;
6664		}
6665		sk->sk_data_ready(sk);
6666		bh_unlock_sock(fastopen_sk);
6667		sock_put(fastopen_sk);
6668	} else {
6669		tcp_rsk(req)->tfo_listener = false;
6670		if (!want_cookie)
6671			inet_csk_reqsk_queue_hash_add(sk, req,
6672				tcp_timeout_init((struct sock *)req));
6673		af_ops->send_synack(sk, dst, &fl, req, &foc,
6674				    !want_cookie ? TCP_SYNACK_NORMAL :
6675						   TCP_SYNACK_COOKIE);
6676		if (want_cookie) {
6677			reqsk_free(req);
6678			return 0;
6679		}
6680	}
6681	reqsk_put(req);
6682	return 0;
6683
6684drop_and_release:
6685	dst_release(dst);
6686drop_and_free:
6687	__reqsk_free(req);
6688drop:
6689	tcp_listendrop(sk);
6690	return 0;
6691}
6692EXPORT_SYMBOL(tcp_conn_request);