1/*
   2 * INET		An implementation of the TCP/IP protocol suite for the LINUX
   3 *		operating system.  INET is implemented using the  BSD Socket
   4 *		interface as the means of communication with the user level.
   5 *
   6 *		Implementation of the Transmission Control Protocol(TCP).
   7 *
   8 * Authors:	Ross Biro
   9 *		Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
  10 *		Mark Evans, <evansmp@uhura.aston.ac.uk>
  11 *		Corey Minyard <wf-rch!minyard@relay.EU.net>
  12 *		Florian La Roche, <flla@stud.uni-sb.de>
  13 *		Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
  14 *		Linus Torvalds, <torvalds@cs.helsinki.fi>
  15 *		Alan Cox, <gw4pts@gw4pts.ampr.org>
  16 *		Matthew Dillon, <dillon@apollo.west.oic.com>
  17 *		Arnt Gulbrandsen, <agulbra@nvg.unit.no>
  18 *		Jorge Cwik, <jorge@laser.satlink.net>
  19 */
  20
  21/*
  22 * Changes:
  23 *		Pedro Roque	:	Fast Retransmit/Recovery.
  24 *					Two receive queues.
  25 *					Retransmit queue handled by TCP.
  26 *					Better retransmit timer handling.
  27 *					New congestion avoidance.
  28 *					Header prediction.
  29 *					Variable renaming.
  30 *
  31 *		Eric		:	Fast Retransmit.
  32 *		Randy Scott	:	MSS option defines.
  33 *		Eric Schenk	:	Fixes to slow start algorithm.
  34 *		Eric Schenk	:	Yet another double ACK bug.
  35 *		Eric Schenk	:	Delayed ACK bug fixes.
  36 *		Eric Schenk	:	Floyd style fast retrans war avoidance.
  37 *		David S. Miller	:	Don't allow zero congestion window.
  38 *		Eric Schenk	:	Fix retransmitter so that it sends
  39 *					next packet on ack of previous packet.
  40 *		Andi Kleen	:	Moved open_request checking here
  41 *					and process RSTs for open_requests.
  42 *		Andi Kleen	:	Better prune_queue, and other fixes.
  43 *		Andrey Savochkin:	Fix RTT measurements in the presence of
  44 *					timestamps.
  45 *		Andrey Savochkin:	Check sequence numbers correctly when
  46 *					removing SACKs due to in sequence incoming
  47 *					data segments.
  48 *		Andi Kleen:		Make sure we never ack data there is not
  49 *					enough room for. Also make this condition
  50 *					a fatal error if it might still happen.
  51 *		Andi Kleen:		Add tcp_measure_rcv_mss to make
  52 *					connections with MSS<min(MTU,ann. MSS)
  53 *					work without delayed acks.
  54 *		Andi Kleen:		Process packets with PSH set in the
  55 *					fast path.
  56 *		J Hadi Salim:		ECN support
  57 *	 	Andrei Gurtov,
  58 *		Pasi Sarolahti,
  59 *		Panu Kuhlberg:		Experimental audit of TCP (re)transmission
  60 *					engine. Lots of bugs are found.
  61 *		Pasi Sarolahti:		F-RTO for dealing with spurious RTOs
  62 */
  63
  64#define pr_fmt(fmt) "TCP: " fmt
  65
  66#include <linux/mm.h>
  67#include <linux/slab.h>
  68#include <linux/module.h>
  69#include <linux/sysctl.h>
  70#include <linux/kernel.h>
 
  71#include <net/dst.h>
  72#include <net/tcp.h>
  73#include <net/inet_common.h>
  74#include <linux/ipsec.h>
  75#include <asm/unaligned.h>
  76#include <net/netdma.h>
 
 
 
 
  77
  78int sysctl_tcp_timestamps __read_mostly = 1;
  79int sysctl_tcp_window_scaling __read_mostly = 1;
  80int sysctl_tcp_sack __read_mostly = 1;
  81int sysctl_tcp_fack __read_mostly = 1;
  82int sysctl_tcp_reordering __read_mostly = TCP_FASTRETRANS_THRESH;
  83EXPORT_SYMBOL(sysctl_tcp_reordering);
  84int sysctl_tcp_ecn __read_mostly = 2;
  85EXPORT_SYMBOL(sysctl_tcp_ecn);
  86int sysctl_tcp_dsack __read_mostly = 1;
  87int sysctl_tcp_app_win __read_mostly = 31;
  88int sysctl_tcp_adv_win_scale __read_mostly = 1;
  89EXPORT_SYMBOL(sysctl_tcp_adv_win_scale);
  90
  91int sysctl_tcp_stdurg __read_mostly;
  92int sysctl_tcp_rfc1337 __read_mostly;
  93int sysctl_tcp_max_orphans __read_mostly = NR_FILE;
  94int sysctl_tcp_frto __read_mostly = 2;
  95int sysctl_tcp_frto_response __read_mostly;
  96int sysctl_tcp_nometrics_save __read_mostly;
  97
  98int sysctl_tcp_thin_dupack __read_mostly;
  99
 100int sysctl_tcp_moderate_rcvbuf __read_mostly = 1;
 101int sysctl_tcp_abc __read_mostly;
 102int sysctl_tcp_early_retrans __read_mostly = 2;
 103
 104#define FLAG_DATA		0x01 /* Incoming frame contained data.		*/
 105#define FLAG_WIN_UPDATE		0x02 /* Incoming ACK was a window update.	*/
 106#define FLAG_DATA_ACKED		0x04 /* This ACK acknowledged new data.		*/
 107#define FLAG_RETRANS_DATA_ACKED	0x08 /* "" "" some of which was retransmitted.	*/
 108#define FLAG_SYN_ACKED		0x10 /* This ACK acknowledged SYN.		*/
 109#define FLAG_DATA_SACKED	0x20 /* New SACK.				*/
 110#define FLAG_ECE		0x40 /* ECE in this ACK				*/
 
 111#define FLAG_SLOWPATH		0x100 /* Do not skip RFC checks for window update.*/
 112#define FLAG_ONLY_ORIG_SACKED	0x200 /* SACKs only non-rexmit sent before RTO */
 113#define FLAG_SND_UNA_ADVANCED	0x400 /* Snd_una was changed (!= FLAG_DATA_ACKED) */
 114#define FLAG_DSACKING_ACK	0x800 /* SACK blocks contained D-SACK info */
 115#define FLAG_NONHEAD_RETRANS_ACKED	0x1000 /* Non-head rexmitted data was ACKed */
 116#define FLAG_SACK_RENEGING	0x2000 /* snd_una advanced to a sacked seq */
 
 
 
 
 117
 118#define FLAG_ACKED		(FLAG_DATA_ACKED|FLAG_SYN_ACKED)
 119#define FLAG_NOT_DUP		(FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED)
 120#define FLAG_CA_ALERT		(FLAG_DATA_SACKED|FLAG_ECE)
 121#define FLAG_FORWARD_PROGRESS	(FLAG_ACKED|FLAG_DATA_SACKED)
 122#define FLAG_ANY_PROGRESS	(FLAG_FORWARD_PROGRESS|FLAG_SND_UNA_ADVANCED)
 123
 124#define TCP_REMNANT (TCP_FLAG_FIN|TCP_FLAG_URG|TCP_FLAG_SYN|TCP_FLAG_PSH)
 125#define TCP_HP_BITS (~(TCP_RESERVED_BITS|TCP_FLAG_PSH))
 126
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 127/* Adapt the MSS value used to make delayed ack decision to the
 128 * real world.
 129 */
 130static void tcp_measure_rcv_mss(struct sock *sk, const struct sk_buff *skb)
 131{
 132	struct inet_connection_sock *icsk = inet_csk(sk);
 133	const unsigned int lss = icsk->icsk_ack.last_seg_size;
 134	unsigned int len;
 135
 136	icsk->icsk_ack.last_seg_size = 0;
 137
 138	/* skb->len may jitter because of SACKs, even if peer
 139	 * sends good full-sized frames.
 140	 */
 141	len = skb_shinfo(skb)->gso_size ? : skb->len;
 142	if (len >= icsk->icsk_ack.rcv_mss) {
 143		icsk->icsk_ack.rcv_mss = len;
 
 
 
 
 
 144	} else {
 145		/* Otherwise, we make more careful check taking into account,
 146		 * that SACKs block is variable.
 147		 *
 148		 * "len" is invariant segment length, including TCP header.
 149		 */
 150		len += skb->data - skb_transport_header(skb);
 151		if (len >= TCP_MSS_DEFAULT + sizeof(struct tcphdr) ||
 152		    /* If PSH is not set, packet should be
 153		     * full sized, provided peer TCP is not badly broken.
 154		     * This observation (if it is correct 8)) allows
 155		     * to handle super-low mtu links fairly.
 156		     */
 157		    (len >= TCP_MIN_MSS + sizeof(struct tcphdr) &&
 158		     !(tcp_flag_word(tcp_hdr(skb)) & TCP_REMNANT))) {
 159			/* Subtract also invariant (if peer is RFC compliant),
 160			 * tcp header plus fixed timestamp option length.
 161			 * Resulting "len" is MSS free of SACK jitter.
 162			 */
 163			len -= tcp_sk(sk)->tcp_header_len;
 164			icsk->icsk_ack.last_seg_size = len;
 165			if (len == lss) {
 166				icsk->icsk_ack.rcv_mss = len;
 167				return;
 168			}
 169		}
 170		if (icsk->icsk_ack.pending & ICSK_ACK_PUSHED)
 171			icsk->icsk_ack.pending |= ICSK_ACK_PUSHED2;
 172		icsk->icsk_ack.pending |= ICSK_ACK_PUSHED;
 173	}
 174}
 175
 176static void tcp_incr_quickack(struct sock *sk)
 177{
 178	struct inet_connection_sock *icsk = inet_csk(sk);
 179	unsigned int quickacks = tcp_sk(sk)->rcv_wnd / (2 * icsk->icsk_ack.rcv_mss);
 180
 181	if (quickacks == 0)
 182		quickacks = 2;
 
 183	if (quickacks > icsk->icsk_ack.quick)
 184		icsk->icsk_ack.quick = min(quickacks, TCP_MAX_QUICKACKS);
 185}
 186
 187static void tcp_enter_quickack_mode(struct sock *sk)
 188{
 189	struct inet_connection_sock *icsk = inet_csk(sk);
 190	tcp_incr_quickack(sk);
 191	icsk->icsk_ack.pingpong = 0;
 
 192	icsk->icsk_ack.ato = TCP_ATO_MIN;
 193}
 
 194
 195/* Send ACKs quickly, if "quick" count is not exhausted
 196 * and the session is not interactive.
 197 */
 198
 199static inline bool tcp_in_quickack_mode(const struct sock *sk)
 200{
 201	const struct inet_connection_sock *icsk = inet_csk(sk);
 
 202
 203	return icsk->icsk_ack.quick && !icsk->icsk_ack.pingpong;
 
 204}
 205
 206static inline void TCP_ECN_queue_cwr(struct tcp_sock *tp)
 207{
 208	if (tp->ecn_flags & TCP_ECN_OK)
 209		tp->ecn_flags |= TCP_ECN_QUEUE_CWR;
 210}
 211
 212static inline void TCP_ECN_accept_cwr(struct tcp_sock *tp, const struct sk_buff *skb)
 213{
 214	if (tcp_hdr(skb)->cwr)
 215		tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
 
 
 
 
 
 
 
 
 216}
 217
 218static inline void TCP_ECN_withdraw_cwr(struct tcp_sock *tp)
 219{
 220	tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
 221}
 222
 223static inline void TCP_ECN_check_ce(struct tcp_sock *tp, const struct sk_buff *skb)
 224{
 225	if (!(tp->ecn_flags & TCP_ECN_OK))
 226		return;
 227
 228	switch (TCP_SKB_CB(skb)->ip_dsfield & INET_ECN_MASK) {
 229	case INET_ECN_NOT_ECT:
 230		/* Funny extension: if ECT is not set on a segment,
 231		 * and we already seen ECT on a previous segment,
 232		 * it is probably a retransmit.
 233		 */
 234		if (tp->ecn_flags & TCP_ECN_SEEN)
 235			tcp_enter_quickack_mode((struct sock *)tp);
 236		break;
 237	case INET_ECN_CE:
 238		tp->ecn_flags |= TCP_ECN_DEMAND_CWR;
 239		/* fallinto */
 
 
 
 
 
 
 
 
 240	default:
 
 
 241		tp->ecn_flags |= TCP_ECN_SEEN;
 
 242	}
 243}
 244
 245static inline void TCP_ECN_rcv_synack(struct tcp_sock *tp, const struct tcphdr *th)
 
 
 
 
 
 
 246{
 247	if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || th->cwr))
 248		tp->ecn_flags &= ~TCP_ECN_OK;
 249}
 250
 251static inline void TCP_ECN_rcv_syn(struct tcp_sock *tp, const struct tcphdr *th)
 252{
 253	if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || !th->cwr))
 254		tp->ecn_flags &= ~TCP_ECN_OK;
 255}
 256
 257static bool TCP_ECN_rcv_ecn_echo(const struct tcp_sock *tp, const struct tcphdr *th)
 258{
 259	if (th->ece && !th->syn && (tp->ecn_flags & TCP_ECN_OK))
 260		return true;
 261	return false;
 262}
 263
 264/* Buffer size and advertised window tuning.
 265 *
 266 * 1. Tuning sk->sk_sndbuf, when connection enters established state.
 267 */
 268
 269static void tcp_fixup_sndbuf(struct sock *sk)
 270{
 271	int sndmem = SKB_TRUESIZE(tcp_sk(sk)->rx_opt.mss_clamp + MAX_TCP_HEADER);
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 272
 273	sndmem *= TCP_INIT_CWND;
 274	if (sk->sk_sndbuf < sndmem)
 275		sk->sk_sndbuf = min(sndmem, sysctl_tcp_wmem[2]);
 
 276}
 277
 278/* 2. Tuning advertised window (window_clamp, rcv_ssthresh)
 279 *
 280 * All tcp_full_space() is split to two parts: "network" buffer, allocated
 281 * forward and advertised in receiver window (tp->rcv_wnd) and
 282 * "application buffer", required to isolate scheduling/application
 283 * latencies from network.
 284 * window_clamp is maximal advertised window. It can be less than
 285 * tcp_full_space(), in this case tcp_full_space() - window_clamp
 286 * is reserved for "application" buffer. The less window_clamp is
 287 * the smoother our behaviour from viewpoint of network, but the lower
 288 * throughput and the higher sensitivity of the connection to losses. 8)
 289 *
 290 * rcv_ssthresh is more strict window_clamp used at "slow start"
 291 * phase to predict further behaviour of this connection.
 292 * It is used for two goals:
 293 * - to enforce header prediction at sender, even when application
 294 *   requires some significant "application buffer". It is check #1.
 295 * - to prevent pruning of receive queue because of misprediction
 296 *   of receiver window. Check #2.
 297 *
 298 * The scheme does not work when sender sends good segments opening
 299 * window and then starts to feed us spaghetti. But it should work
 300 * in common situations. Otherwise, we have to rely on queue collapsing.
 301 */
 302
 303/* Slow part of check#2. */
 304static int __tcp_grow_window(const struct sock *sk, const struct sk_buff *skb)
 
 305{
 306	struct tcp_sock *tp = tcp_sk(sk);
 307	/* Optimize this! */
 308	int truesize = tcp_win_from_space(skb->truesize) >> 1;
 309	int window = tcp_win_from_space(sysctl_tcp_rmem[2]) >> 1;
 310
 311	while (tp->rcv_ssthresh <= window) {
 312		if (truesize <= skb->len)
 313			return 2 * inet_csk(sk)->icsk_ack.rcv_mss;
 314
 315		truesize >>= 1;
 316		window >>= 1;
 317	}
 318	return 0;
 319}
 320
 321static void tcp_grow_window(struct sock *sk, const struct sk_buff *skb)
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 322{
 323	struct tcp_sock *tp = tcp_sk(sk);
 
 
 
 
 
 
 324
 325	/* Check #1 */
 326	if (tp->rcv_ssthresh < tp->window_clamp &&
 327	    (int)tp->rcv_ssthresh < tcp_space(sk) &&
 328	    !sk_under_memory_pressure(sk)) {
 329		int incr;
 330
 331		/* Check #2. Increase window, if skb with such overhead
 332		 * will fit to rcvbuf in future.
 333		 */
 334		if (tcp_win_from_space(skb->truesize) <= skb->len)
 335			incr = 2 * tp->advmss;
 336		else
 337			incr = __tcp_grow_window(sk, skb);
 338
 339		if (incr) {
 340			incr = max_t(int, incr, 2 * skb->len);
 341			tp->rcv_ssthresh = min(tp->rcv_ssthresh + incr,
 342					       tp->window_clamp);
 343			inet_csk(sk)->icsk_ack.quick |= 1;
 344		}
 
 
 
 
 
 345	}
 346}
 347
 348/* 3. Tuning rcvbuf, when connection enters established state. */
 349
 350static void tcp_fixup_rcvbuf(struct sock *sk)
 351{
 352	u32 mss = tcp_sk(sk)->advmss;
 353	u32 icwnd = TCP_DEFAULT_INIT_RCVWND;
 354	int rcvmem;
 355
 356	/* Limit to 10 segments if mss <= 1460,
 357	 * or 14600/mss segments, with a minimum of two segments.
 358	 */
 359	if (mss > 1460)
 360		icwnd = max_t(u32, (1460 * TCP_DEFAULT_INIT_RCVWND) / mss, 2);
 361
 362	rcvmem = SKB_TRUESIZE(mss + MAX_TCP_HEADER);
 363	while (tcp_win_from_space(rcvmem) < mss)
 364		rcvmem += 128;
 365
 366	rcvmem *= icwnd;
 367
 368	if (sk->sk_rcvbuf < rcvmem)
 369		sk->sk_rcvbuf = min(rcvmem, sysctl_tcp_rmem[2]);
 370}
 371
 372/* 4. Try to fixup all. It is made immediately after connection enters
 373 *    established state.
 374 */
 375static void tcp_init_buffer_space(struct sock *sk)
 376{
 
 377	struct tcp_sock *tp = tcp_sk(sk);
 378	int maxwin;
 379
 380	if (!(sk->sk_userlocks & SOCK_RCVBUF_LOCK))
 381		tcp_fixup_rcvbuf(sk);
 382	if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK))
 383		tcp_fixup_sndbuf(sk);
 384
 385	tp->rcvq_space.space = tp->rcv_wnd;
 
 
 386
 387	maxwin = tcp_full_space(sk);
 388
 389	if (tp->window_clamp >= maxwin) {
 390		tp->window_clamp = maxwin;
 391
 392		if (sysctl_tcp_app_win && maxwin > 4 * tp->advmss)
 393			tp->window_clamp = max(maxwin -
 394					       (maxwin >> sysctl_tcp_app_win),
 395					       4 * tp->advmss);
 396	}
 397
 398	/* Force reservation of one segment. */
 399	if (sysctl_tcp_app_win &&
 400	    tp->window_clamp > 2 * tp->advmss &&
 401	    tp->window_clamp + tp->advmss > maxwin)
 402		tp->window_clamp = max(2 * tp->advmss, maxwin - tp->advmss);
 403
 404	tp->rcv_ssthresh = min(tp->rcv_ssthresh, tp->window_clamp);
 405	tp->snd_cwnd_stamp = tcp_time_stamp;
 
 
 406}
 407
 408/* 5. Recalculate window clamp after socket hit its memory bounds. */
 409static void tcp_clamp_window(struct sock *sk)
 410{
 411	struct tcp_sock *tp = tcp_sk(sk);
 412	struct inet_connection_sock *icsk = inet_csk(sk);
 
 
 413
 414	icsk->icsk_ack.quick = 0;
 
 415
 416	if (sk->sk_rcvbuf < sysctl_tcp_rmem[2] &&
 417	    !(sk->sk_userlocks & SOCK_RCVBUF_LOCK) &&
 418	    !sk_under_memory_pressure(sk) &&
 419	    sk_memory_allocated(sk) < sk_prot_mem_limits(sk, 0)) {
 420		sk->sk_rcvbuf = min(atomic_read(&sk->sk_rmem_alloc),
 421				    sysctl_tcp_rmem[2]);
 422	}
 423	if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf)
 424		tp->rcv_ssthresh = min(tp->window_clamp, 2U * tp->advmss);
 425}
 426
 427/* Initialize RCV_MSS value.
 428 * RCV_MSS is an our guess about MSS used by the peer.
 429 * We haven't any direct information about the MSS.
 430 * It's better to underestimate the RCV_MSS rather than overestimate.
 431 * Overestimations make us ACKing less frequently than needed.
 432 * Underestimations are more easy to detect and fix by tcp_measure_rcv_mss().
 433 */
 434void tcp_initialize_rcv_mss(struct sock *sk)
 435{
 436	const struct tcp_sock *tp = tcp_sk(sk);
 437	unsigned int hint = min_t(unsigned int, tp->advmss, tp->mss_cache);
 438
 439	hint = min(hint, tp->rcv_wnd / 2);
 440	hint = min(hint, TCP_MSS_DEFAULT);
 441	hint = max(hint, TCP_MIN_MSS);
 442
 443	inet_csk(sk)->icsk_ack.rcv_mss = hint;
 444}
 445EXPORT_SYMBOL(tcp_initialize_rcv_mss);
 446
 447/* Receiver "autotuning" code.
 448 *
 449 * The algorithm for RTT estimation w/o timestamps is based on
 450 * Dynamic Right-Sizing (DRS) by Wu Feng and Mike Fisk of LANL.
 451 * <http://public.lanl.gov/radiant/pubs.html#DRS>
 452 *
 453 * More detail on this code can be found at
 454 * <http://staff.psc.edu/jheffner/>,
 455 * though this reference is out of date.  A new paper
 456 * is pending.
 457 */
 458static void tcp_rcv_rtt_update(struct tcp_sock *tp, u32 sample, int win_dep)
 459{
 460	u32 new_sample = tp->rcv_rtt_est.rtt;
 461	long m = sample;
 462
 463	if (m == 0)
 464		m = 1;
 465
 466	if (new_sample != 0) {
 467		/* If we sample in larger samples in the non-timestamp
 468		 * case, we could grossly overestimate the RTT especially
 469		 * with chatty applications or bulk transfer apps which
 470		 * are stalled on filesystem I/O.
 471		 *
 472		 * Also, since we are only going for a minimum in the
 473		 * non-timestamp case, we do not smooth things out
 474		 * else with timestamps disabled convergence takes too
 475		 * long.
 476		 */
 477		if (!win_dep) {
 478			m -= (new_sample >> 3);
 479			new_sample += m;
 480		} else {
 481			m <<= 3;
 482			if (m < new_sample)
 483				new_sample = m;
 484		}
 485	} else {
 486		/* No previous measure. */
 487		new_sample = m << 3;
 488	}
 489
 490	if (tp->rcv_rtt_est.rtt != new_sample)
 491		tp->rcv_rtt_est.rtt = new_sample;
 492}
 493
 494static inline void tcp_rcv_rtt_measure(struct tcp_sock *tp)
 495{
 
 
 496	if (tp->rcv_rtt_est.time == 0)
 497		goto new_measure;
 498	if (before(tp->rcv_nxt, tp->rcv_rtt_est.seq))
 499		return;
 500	tcp_rcv_rtt_update(tp, tcp_time_stamp - tp->rcv_rtt_est.time, 1);
 
 
 
 501
 502new_measure:
 503	tp->rcv_rtt_est.seq = tp->rcv_nxt + tp->rcv_wnd;
 504	tp->rcv_rtt_est.time = tcp_time_stamp;
 505}
 506
 507static inline void tcp_rcv_rtt_measure_ts(struct sock *sk,
 508					  const struct sk_buff *skb)
 509{
 510	struct tcp_sock *tp = tcp_sk(sk);
 511	if (tp->rx_opt.rcv_tsecr &&
 512	    (TCP_SKB_CB(skb)->end_seq -
 513	     TCP_SKB_CB(skb)->seq >= inet_csk(sk)->icsk_ack.rcv_mss))
 514		tcp_rcv_rtt_update(tp, tcp_time_stamp - tp->rx_opt.rcv_tsecr, 0);
 
 
 
 
 
 
 
 
 
 
 
 
 
 515}
 516
 517/*
 518 * This function should be called every time data is copied to user space.
 519 * It calculates the appropriate TCP receive buffer space.
 520 */
 521void tcp_rcv_space_adjust(struct sock *sk)
 522{
 523	struct tcp_sock *tp = tcp_sk(sk);
 
 524	int time;
 525	int space;
 526
 527	if (tp->rcvq_space.time == 0)
 528		goto new_measure;
 529
 530	time = tcp_time_stamp - tp->rcvq_space.time;
 531	if (time < (tp->rcv_rtt_est.rtt >> 3) || tp->rcv_rtt_est.rtt == 0)
 
 532		return;
 533
 534	space = 2 * (tp->copied_seq - tp->rcvq_space.seq);
 
 
 
 
 
 
 
 
 
 
 
 
 535
 536	space = max(tp->rcvq_space.space, space);
 
 
 
 537
 538	if (tp->rcvq_space.space != space) {
 539		int rcvmem;
 
 
 540
 541		tp->rcvq_space.space = space;
 
 
 
 542
 543		if (sysctl_tcp_moderate_rcvbuf &&
 544		    !(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) {
 545			int new_clamp = space;
 546
 547			/* Receive space grows, normalize in order to
 548			 * take into account packet headers and sk_buff
 549			 * structure overhead.
 550			 */
 551			space /= tp->advmss;
 552			if (!space)
 553				space = 1;
 554			rcvmem = SKB_TRUESIZE(tp->advmss + MAX_TCP_HEADER);
 555			while (tcp_win_from_space(rcvmem) < tp->advmss)
 556				rcvmem += 128;
 557			space *= rcvmem;
 558			space = min(space, sysctl_tcp_rmem[2]);
 559			if (space > sk->sk_rcvbuf) {
 560				sk->sk_rcvbuf = space;
 561
 562				/* Make the window clamp follow along.  */
 563				tp->window_clamp = new_clamp;
 564			}
 565		}
 566	}
 
 567
 568new_measure:
 569	tp->rcvq_space.seq = tp->copied_seq;
 570	tp->rcvq_space.time = tcp_time_stamp;
 571}
 572
 573/* There is something which you must keep in mind when you analyze the
 574 * behavior of the tp->ato delayed ack timeout interval.  When a
 575 * connection starts up, we want to ack as quickly as possible.  The
 576 * problem is that "good" TCP's do slow start at the beginning of data
 577 * transmission.  The means that until we send the first few ACK's the
 578 * sender will sit on his end and only queue most of his data, because
 579 * he can only send snd_cwnd unacked packets at any given time.  For
 580 * each ACK we send, he increments snd_cwnd and transmits more of his
 581 * queue.  -DaveM
 582 */
 583static void tcp_event_data_recv(struct sock *sk, struct sk_buff *skb)
 584{
 585	struct tcp_sock *tp = tcp_sk(sk);
 586	struct inet_connection_sock *icsk = inet_csk(sk);
 587	u32 now;
 588
 589	inet_csk_schedule_ack(sk);
 590
 591	tcp_measure_rcv_mss(sk, skb);
 592
 593	tcp_rcv_rtt_measure(tp);
 594
 595	now = tcp_time_stamp;
 596
 597	if (!icsk->icsk_ack.ato) {
 598		/* The _first_ data packet received, initialize
 599		 * delayed ACK engine.
 600		 */
 601		tcp_incr_quickack(sk);
 602		icsk->icsk_ack.ato = TCP_ATO_MIN;
 603	} else {
 604		int m = now - icsk->icsk_ack.lrcvtime;
 605
 606		if (m <= TCP_ATO_MIN / 2) {
 607			/* The fastest case is the first. */
 608			icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + TCP_ATO_MIN / 2;
 609		} else if (m < icsk->icsk_ack.ato) {
 610			icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + m;
 611			if (icsk->icsk_ack.ato > icsk->icsk_rto)
 612				icsk->icsk_ack.ato = icsk->icsk_rto;
 613		} else if (m > icsk->icsk_rto) {
 614			/* Too long gap. Apparently sender failed to
 615			 * restart window, so that we send ACKs quickly.
 616			 */
 617			tcp_incr_quickack(sk);
 618			sk_mem_reclaim(sk);
 619		}
 620	}
 621	icsk->icsk_ack.lrcvtime = now;
 622
 623	TCP_ECN_check_ce(tp, skb);
 624
 625	if (skb->len >= 128)
 626		tcp_grow_window(sk, skb);
 627}
 628
 629/* Called to compute a smoothed rtt estimate. The data fed to this
 630 * routine either comes from timestamps, or from segments that were
 631 * known _not_ to have been retransmitted [see Karn/Partridge
 632 * Proceedings SIGCOMM 87]. The algorithm is from the SIGCOMM 88
 633 * piece by Van Jacobson.
 634 * NOTE: the next three routines used to be one big routine.
 635 * To save cycles in the RFC 1323 implementation it was better to break
 636 * it up into three procedures. -- erics
 637 */
 638static void tcp_rtt_estimator(struct sock *sk, const __u32 mrtt)
 639{
 640	struct tcp_sock *tp = tcp_sk(sk);
 641	long m = mrtt; /* RTT */
 
 642
 643	/*	The following amusing code comes from Jacobson's
 644	 *	article in SIGCOMM '88.  Note that rtt and mdev
 645	 *	are scaled versions of rtt and mean deviation.
 646	 *	This is designed to be as fast as possible
 647	 *	m stands for "measurement".
 648	 *
 649	 *	On a 1990 paper the rto value is changed to:
 650	 *	RTO = rtt + 4 * mdev
 651	 *
 652	 * Funny. This algorithm seems to be very broken.
 653	 * These formulae increase RTO, when it should be decreased, increase
 654	 * too slowly, when it should be increased quickly, decrease too quickly
 655	 * etc. I guess in BSD RTO takes ONE value, so that it is absolutely
 656	 * does not matter how to _calculate_ it. Seems, it was trap
 657	 * that VJ failed to avoid. 8)
 658	 */
 659	if (m == 0)
 660		m = 1;
 661	if (tp->srtt != 0) {
 662		m -= (tp->srtt >> 3);	/* m is now error in rtt est */
 663		tp->srtt += m;		/* rtt = 7/8 rtt + 1/8 new */
 664		if (m < 0) {
 665			m = -m;		/* m is now abs(error) */
 666			m -= (tp->mdev >> 2);   /* similar update on mdev */
 667			/* This is similar to one of Eifel findings.
 668			 * Eifel blocks mdev updates when rtt decreases.
 669			 * This solution is a bit different: we use finer gain
 670			 * for mdev in this case (alpha*beta).
 671			 * Like Eifel it also prevents growth of rto,
 672			 * but also it limits too fast rto decreases,
 673			 * happening in pure Eifel.
 674			 */
 675			if (m > 0)
 676				m >>= 3;
 677		} else {
 678			m -= (tp->mdev >> 2);   /* similar update on mdev */
 679		}
 680		tp->mdev += m;	    	/* mdev = 3/4 mdev + 1/4 new */
 681		if (tp->mdev > tp->mdev_max) {
 682			tp->mdev_max = tp->mdev;
 683			if (tp->mdev_max > tp->rttvar)
 684				tp->rttvar = tp->mdev_max;
 685		}
 686		if (after(tp->snd_una, tp->rtt_seq)) {
 687			if (tp->mdev_max < tp->rttvar)
 688				tp->rttvar -= (tp->rttvar - tp->mdev_max) >> 2;
 689			tp->rtt_seq = tp->snd_nxt;
 690			tp->mdev_max = tcp_rto_min(sk);
 
 
 691		}
 692	} else {
 693		/* no previous measure. */
 694		tp->srtt = m << 3;	/* take the measured time to be rtt */
 695		tp->mdev = m << 1;	/* make sure rto = 3*rtt */
 696		tp->mdev_max = tp->rttvar = max(tp->mdev, tcp_rto_min(sk));
 
 697		tp->rtt_seq = tp->snd_nxt;
 
 
 698	}
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 699}
 700
 701/* Calculate rto without backoff.  This is the second half of Van Jacobson's
 702 * routine referred to above.
 703 */
 704static inline void tcp_set_rto(struct sock *sk)
 705{
 706	const struct tcp_sock *tp = tcp_sk(sk);
 707	/* Old crap is replaced with new one. 8)
 708	 *
 709	 * More seriously:
 710	 * 1. If rtt variance happened to be less 50msec, it is hallucination.
 711	 *    It cannot be less due to utterly erratic ACK generation made
 712	 *    at least by solaris and freebsd. "Erratic ACKs" has _nothing_
 713	 *    to do with delayed acks, because at cwnd>2 true delack timeout
 714	 *    is invisible. Actually, Linux-2.4 also generates erratic
 715	 *    ACKs in some circumstances.
 716	 */
 717	inet_csk(sk)->icsk_rto = __tcp_set_rto(tp);
 718
 719	/* 2. Fixups made earlier cannot be right.
 720	 *    If we do not estimate RTO correctly without them,
 721	 *    all the algo is pure shit and should be replaced
 722	 *    with correct one. It is exactly, which we pretend to do.
 723	 */
 724
 725	/* NOTE: clamping at TCP_RTO_MIN is not required, current algo
 726	 * guarantees that rto is higher.
 727	 */
 728	tcp_bound_rto(sk);
 729}
 730
 731/* Save metrics learned by this TCP session.
 732   This function is called only, when TCP finishes successfully
 733   i.e. when it enters TIME-WAIT or goes from LAST-ACK to CLOSE.
 734 */
 735void tcp_update_metrics(struct sock *sk)
 736{
 737	struct tcp_sock *tp = tcp_sk(sk);
 738	struct dst_entry *dst = __sk_dst_get(sk);
 739
 740	if (sysctl_tcp_nometrics_save)
 741		return;
 742
 743	dst_confirm(dst);
 744
 745	if (dst && (dst->flags & DST_HOST)) {
 746		const struct inet_connection_sock *icsk = inet_csk(sk);
 747		int m;
 748		unsigned long rtt;
 749
 750		if (icsk->icsk_backoff || !tp->srtt) {
 751			/* This session failed to estimate rtt. Why?
 752			 * Probably, no packets returned in time.
 753			 * Reset our results.
 754			 */
 755			if (!(dst_metric_locked(dst, RTAX_RTT)))
 756				dst_metric_set(dst, RTAX_RTT, 0);
 757			return;
 758		}
 759
 760		rtt = dst_metric_rtt(dst, RTAX_RTT);
 761		m = rtt - tp->srtt;
 762
 763		/* If newly calculated rtt larger than stored one,
 764		 * store new one. Otherwise, use EWMA. Remember,
 765		 * rtt overestimation is always better than underestimation.
 766		 */
 767		if (!(dst_metric_locked(dst, RTAX_RTT))) {
 768			if (m <= 0)
 769				set_dst_metric_rtt(dst, RTAX_RTT, tp->srtt);
 770			else
 771				set_dst_metric_rtt(dst, RTAX_RTT, rtt - (m >> 3));
 772		}
 773
 774		if (!(dst_metric_locked(dst, RTAX_RTTVAR))) {
 775			unsigned long var;
 776			if (m < 0)
 777				m = -m;
 778
 779			/* Scale deviation to rttvar fixed point */
 780			m >>= 1;
 781			if (m < tp->mdev)
 782				m = tp->mdev;
 783
 784			var = dst_metric_rtt(dst, RTAX_RTTVAR);
 785			if (m >= var)
 786				var = m;
 787			else
 788				var -= (var - m) >> 2;
 789
 790			set_dst_metric_rtt(dst, RTAX_RTTVAR, var);
 791		}
 792
 793		if (tcp_in_initial_slowstart(tp)) {
 794			/* Slow start still did not finish. */
 795			if (dst_metric(dst, RTAX_SSTHRESH) &&
 796			    !dst_metric_locked(dst, RTAX_SSTHRESH) &&
 797			    (tp->snd_cwnd >> 1) > dst_metric(dst, RTAX_SSTHRESH))
 798				dst_metric_set(dst, RTAX_SSTHRESH, tp->snd_cwnd >> 1);
 799			if (!dst_metric_locked(dst, RTAX_CWND) &&
 800			    tp->snd_cwnd > dst_metric(dst, RTAX_CWND))
 801				dst_metric_set(dst, RTAX_CWND, tp->snd_cwnd);
 802		} else if (tp->snd_cwnd > tp->snd_ssthresh &&
 803			   icsk->icsk_ca_state == TCP_CA_Open) {
 804			/* Cong. avoidance phase, cwnd is reliable. */
 805			if (!dst_metric_locked(dst, RTAX_SSTHRESH))
 806				dst_metric_set(dst, RTAX_SSTHRESH,
 807					       max(tp->snd_cwnd >> 1, tp->snd_ssthresh));
 808			if (!dst_metric_locked(dst, RTAX_CWND))
 809				dst_metric_set(dst, RTAX_CWND,
 810					       (dst_metric(dst, RTAX_CWND) +
 811						tp->snd_cwnd) >> 1);
 812		} else {
 813			/* Else slow start did not finish, cwnd is non-sense,
 814			   ssthresh may be also invalid.
 815			 */
 816			if (!dst_metric_locked(dst, RTAX_CWND))
 817				dst_metric_set(dst, RTAX_CWND,
 818					       (dst_metric(dst, RTAX_CWND) +
 819						tp->snd_ssthresh) >> 1);
 820			if (dst_metric(dst, RTAX_SSTHRESH) &&
 821			    !dst_metric_locked(dst, RTAX_SSTHRESH) &&
 822			    tp->snd_ssthresh > dst_metric(dst, RTAX_SSTHRESH))
 823				dst_metric_set(dst, RTAX_SSTHRESH, tp->snd_ssthresh);
 824		}
 825
 826		if (!dst_metric_locked(dst, RTAX_REORDERING)) {
 827			if (dst_metric(dst, RTAX_REORDERING) < tp->reordering &&
 828			    tp->reordering != sysctl_tcp_reordering)
 829				dst_metric_set(dst, RTAX_REORDERING, tp->reordering);
 830		}
 831	}
 832}
 833
 834__u32 tcp_init_cwnd(const struct tcp_sock *tp, const struct dst_entry *dst)
 835{
 836	__u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0);
 837
 838	if (!cwnd)
 839		cwnd = TCP_INIT_CWND;
 840	return min_t(__u32, cwnd, tp->snd_cwnd_clamp);
 841}
 842
 843/* Set slow start threshold and cwnd not falling to slow start */
 844void tcp_enter_cwr(struct sock *sk, const int set_ssthresh)
 845{
 846	struct tcp_sock *tp = tcp_sk(sk);
 847	const struct inet_connection_sock *icsk = inet_csk(sk);
 848
 849	tp->prior_ssthresh = 0;
 850	tp->bytes_acked = 0;
 851	if (icsk->icsk_ca_state < TCP_CA_CWR) {
 852		tp->undo_marker = 0;
 853		if (set_ssthresh)
 854			tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
 855		tp->snd_cwnd = min(tp->snd_cwnd,
 856				   tcp_packets_in_flight(tp) + 1U);
 857		tp->snd_cwnd_cnt = 0;
 858		tp->high_seq = tp->snd_nxt;
 859		tp->snd_cwnd_stamp = tcp_time_stamp;
 860		TCP_ECN_queue_cwr(tp);
 861
 862		tcp_set_ca_state(sk, TCP_CA_CWR);
 863	}
 864}
 865
 866/*
 867 * Packet counting of FACK is based on in-order assumptions, therefore TCP
 868 * disables it when reordering is detected
 
 
 869 */
 870static void tcp_disable_fack(struct tcp_sock *tp)
 871{
 872	/* RFC3517 uses different metric in lost marker => reset on change */
 873	if (tcp_is_fack(tp))
 874		tp->lost_skb_hint = NULL;
 875	tp->rx_opt.sack_ok &= ~TCP_FACK_ENABLED;
 876}
 877
 878/* Take a notice that peer is sending D-SACKs */
 879static void tcp_dsack_seen(struct tcp_sock *tp)
 880{
 881	tp->rx_opt.sack_ok |= TCP_DSACK_SEEN;
 882}
 883
 884/* Initialize metrics on socket. */
 885
 886static void tcp_init_metrics(struct sock *sk)
 887{
 888	struct tcp_sock *tp = tcp_sk(sk);
 889	struct dst_entry *dst = __sk_dst_get(sk);
 890
 891	if (dst == NULL)
 892		goto reset;
 893
 894	dst_confirm(dst);
 
 
 
 
 
 
 
 
 
 
 
 
 895
 896	if (dst_metric_locked(dst, RTAX_CWND))
 897		tp->snd_cwnd_clamp = dst_metric(dst, RTAX_CWND);
 898	if (dst_metric(dst, RTAX_SSTHRESH)) {
 899		tp->snd_ssthresh = dst_metric(dst, RTAX_SSTHRESH);
 900		if (tp->snd_ssthresh > tp->snd_cwnd_clamp)
 901			tp->snd_ssthresh = tp->snd_cwnd_clamp;
 902	} else {
 903		/* ssthresh may have been reduced unnecessarily during.
 904		 * 3WHS. Restore it back to its initial default.
 905		 */
 906		tp->snd_ssthresh = TCP_INFINITE_SSTHRESH;
 907	}
 908	if (dst_metric(dst, RTAX_REORDERING) &&
 909	    tp->reordering != dst_metric(dst, RTAX_REORDERING)) {
 910		tcp_disable_fack(tp);
 911		tcp_disable_early_retrans(tp);
 912		tp->reordering = dst_metric(dst, RTAX_REORDERING);
 913	}
 914
 915	if (dst_metric(dst, RTAX_RTT) == 0 || tp->srtt == 0)
 916		goto reset;
 
 917
 918	/* Initial rtt is determined from SYN,SYN-ACK.
 919	 * The segment is small and rtt may appear much
 920	 * less than real one. Use per-dst memory
 921	 * to make it more realistic.
 922	 *
 923	 * A bit of theory. RTT is time passed after "normal" sized packet
 924	 * is sent until it is ACKed. In normal circumstances sending small
 925	 * packets force peer to delay ACKs and calculation is correct too.
 926	 * The algorithm is adaptive and, provided we follow specs, it
 927	 * NEVER underestimate RTT. BUT! If peer tries to make some clever
 928	 * tricks sort of "quick acks" for time long enough to decrease RTT
 929	 * to low value, and then abruptly stops to do it and starts to delay
 930	 * ACKs, wait for troubles.
 931	 */
 932	if (dst_metric_rtt(dst, RTAX_RTT) > tp->srtt) {
 933		tp->srtt = dst_metric_rtt(dst, RTAX_RTT);
 934		tp->rtt_seq = tp->snd_nxt;
 935	}
 936	if (dst_metric_rtt(dst, RTAX_RTTVAR) > tp->mdev) {
 937		tp->mdev = dst_metric_rtt(dst, RTAX_RTTVAR);
 938		tp->mdev_max = tp->rttvar = max(tp->mdev, tcp_rto_min(sk));
 939	}
 940	tcp_set_rto(sk);
 941reset:
 942	if (tp->srtt == 0) {
 943		/* RFC6298: 5.7 We've failed to get a valid RTT sample from
 944		 * 3WHS. This is most likely due to retransmission,
 945		 * including spurious one. Reset the RTO back to 3secs
 946		 * from the more aggressive 1sec to avoid more spurious
 947		 * retransmission.
 948		 */
 949		tp->mdev = tp->mdev_max = tp->rttvar = TCP_TIMEOUT_FALLBACK;
 950		inet_csk(sk)->icsk_rto = TCP_TIMEOUT_FALLBACK;
 951	}
 952	/* Cut cwnd down to 1 per RFC5681 if SYN or SYN-ACK has been
 953	 * retransmitted. In light of RFC6298 more aggressive 1sec
 954	 * initRTO, we only reset cwnd when more than 1 SYN/SYN-ACK
 955	 * retransmission has occurred.
 956	 */
 957	if (tp->total_retrans > 1)
 958		tp->snd_cwnd = 1;
 959	else
 960		tp->snd_cwnd = tcp_init_cwnd(tp, dst);
 961	tp->snd_cwnd_stamp = tcp_time_stamp;
 962}
 963
 964static void tcp_update_reordering(struct sock *sk, const int metric,
 965				  const int ts)
 
 
 
 
 966{
 967	struct tcp_sock *tp = tcp_sk(sk);
 968	if (metric > tp->reordering) {
 969		int mib_idx;
 970
 971		tp->reordering = min(TCP_MAX_REORDERING, metric);
 972
 973		/* This exciting event is worth to be remembered. 8) */
 974		if (ts)
 975			mib_idx = LINUX_MIB_TCPTSREORDER;
 976		else if (tcp_is_reno(tp))
 977			mib_idx = LINUX_MIB_TCPRENOREORDER;
 978		else if (tcp_is_fack(tp))
 979			mib_idx = LINUX_MIB_TCPFACKREORDER;
 980		else
 981			mib_idx = LINUX_MIB_TCPSACKREORDER;
 982
 983		NET_INC_STATS_BH(sock_net(sk), mib_idx);
 
 984#if FASTRETRANS_DEBUG > 1
 985		pr_debug("Disorder%d %d %u f%u s%u rr%d\n",
 986			 tp->rx_opt.sack_ok, inet_csk(sk)->icsk_ca_state,
 987			 tp->reordering,
 988			 tp->fackets_out,
 989			 tp->sacked_out,
 990			 tp->undo_marker ? tp->undo_retrans : 0);
 991#endif
 992		tcp_disable_fack(tp);
 
 993	}
 994
 995	if (metric > 0)
 996		tcp_disable_early_retrans(tp);
 
 
 997}
 998
 999/* This must be called before lost_out is incremented */
 
 
 
 
1000static void tcp_verify_retransmit_hint(struct tcp_sock *tp, struct sk_buff *skb)
1001{
1002	if ((tp->retransmit_skb_hint == NULL) ||
1003	    before(TCP_SKB_CB(skb)->seq,
1004		   TCP_SKB_CB(tp->retransmit_skb_hint)->seq))
 
1005		tp->retransmit_skb_hint = skb;
 
1006
1007	if (!tp->lost_out ||
1008	    after(TCP_SKB_CB(skb)->end_seq, tp->retransmit_high))
1009		tp->retransmit_high = TCP_SKB_CB(skb)->end_seq;
 
 
 
1010}
1011
1012static void tcp_skb_mark_lost(struct tcp_sock *tp, struct sk_buff *skb)
1013{
1014	if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) {
1015		tcp_verify_retransmit_hint(tp, skb);
 
 
 
1016
 
 
 
 
 
 
 
 
 
 
 
1017		tp->lost_out += tcp_skb_pcount(skb);
1018		TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
 
1019	}
1020}
1021
1022static void tcp_skb_mark_lost_uncond_verify(struct tcp_sock *tp,
1023					    struct sk_buff *skb)
 
1024{
1025	tcp_verify_retransmit_hint(tp, skb);
1026
1027	if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) {
1028		tp->lost_out += tcp_skb_pcount(skb);
1029		TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1030	}
1031}
1032
1033/* This procedure tags the retransmission queue when SACKs arrive.
1034 *
1035 * We have three tag bits: SACKED(S), RETRANS(R) and LOST(L).
1036 * Packets in queue with these bits set are counted in variables
1037 * sacked_out, retrans_out and lost_out, correspondingly.
1038 *
1039 * Valid combinations are:
1040 * Tag  InFlight	Description
1041 * 0	1		- orig segment is in flight.
1042 * S	0		- nothing flies, orig reached receiver.
1043 * L	0		- nothing flies, orig lost by net.
1044 * R	2		- both orig and retransmit are in flight.
1045 * L|R	1		- orig is lost, retransmit is in flight.
1046 * S|R  1		- orig reached receiver, retrans is still in flight.
1047 * (L|S|R is logically valid, it could occur when L|R is sacked,
1048 *  but it is equivalent to plain S and code short-curcuits it to S.
1049 *  L|S is logically invalid, it would mean -1 packet in flight 8))
1050 *
1051 * These 6 states form finite state machine, controlled by the following events:
1052 * 1. New ACK (+SACK) arrives. (tcp_sacktag_write_queue())
1053 * 2. Retransmission. (tcp_retransmit_skb(), tcp_xmit_retransmit_queue())
1054 * 3. Loss detection event of two flavors:
1055 *	A. Scoreboard estimator decided the packet is lost.
1056 *	   A'. Reno "three dupacks" marks head of queue lost.
1057 *	   A''. Its FACK modification, head until snd.fack is lost.
1058 *	B. SACK arrives sacking SND.NXT at the moment, when the
1059 *	   segment was retransmitted.
1060 * 4. D-SACK added new rule: D-SACK changes any tag to S.
1061 *
1062 * It is pleasant to note, that state diagram turns out to be commutative,
1063 * so that we are allowed not to be bothered by order of our actions,
1064 * when multiple events arrive simultaneously. (see the function below).
1065 *
1066 * Reordering detection.
1067 * --------------------
1068 * Reordering metric is maximal distance, which a packet can be displaced
1069 * in packet stream. With SACKs we can estimate it:
1070 *
1071 * 1. SACK fills old hole and the corresponding segment was not
1072 *    ever retransmitted -> reordering. Alas, we cannot use it
1073 *    when segment was retransmitted.
1074 * 2. The last flaw is solved with D-SACK. D-SACK arrives
1075 *    for retransmitted and already SACKed segment -> reordering..
1076 * Both of these heuristics are not used in Loss state, when we cannot
1077 * account for retransmits accurately.
1078 *
1079 * SACK block validation.
1080 * ----------------------
1081 *
1082 * SACK block range validation checks that the received SACK block fits to
1083 * the expected sequence limits, i.e., it is between SND.UNA and SND.NXT.
1084 * Note that SND.UNA is not included to the range though being valid because
1085 * it means that the receiver is rather inconsistent with itself reporting
1086 * SACK reneging when it should advance SND.UNA. Such SACK block this is
1087 * perfectly valid, however, in light of RFC2018 which explicitly states
1088 * that "SACK block MUST reflect the newest segment.  Even if the newest
1089 * segment is going to be discarded ...", not that it looks very clever
1090 * in case of head skb. Due to potentional receiver driven attacks, we
1091 * choose to avoid immediate execution of a walk in write queue due to
1092 * reneging and defer head skb's loss recovery to standard loss recovery
1093 * procedure that will eventually trigger (nothing forbids us doing this).
1094 *
1095 * Implements also blockage to start_seq wrap-around. Problem lies in the
1096 * fact that though start_seq (s) is before end_seq (i.e., not reversed),
1097 * there's no guarantee that it will be before snd_nxt (n). The problem
1098 * happens when start_seq resides between end_seq wrap (e_w) and snd_nxt
1099 * wrap (s_w):
1100 *
1101 *         <- outs wnd ->                          <- wrapzone ->
1102 *         u     e      n                         u_w   e_w  s n_w
1103 *         |     |      |                          |     |   |  |
1104 * |<------------+------+----- TCP seqno space --------------+---------->|
1105 * ...-- <2^31 ->|                                           |<--------...
1106 * ...---- >2^31 ------>|                                    |<--------...
1107 *
1108 * Current code wouldn't be vulnerable but it's better still to discard such
1109 * crazy SACK blocks. Doing this check for start_seq alone closes somewhat
1110 * similar case (end_seq after snd_nxt wrap) as earlier reversed check in
1111 * snd_nxt wrap -> snd_una region will then become "well defined", i.e.,
1112 * equal to the ideal case (infinite seqno space without wrap caused issues).
1113 *
1114 * With D-SACK the lower bound is extended to cover sequence space below
1115 * SND.UNA down to undo_marker, which is the last point of interest. Yet
1116 * again, D-SACK block must not to go across snd_una (for the same reason as
1117 * for the normal SACK blocks, explained above). But there all simplicity
1118 * ends, TCP might receive valid D-SACKs below that. As long as they reside
1119 * fully below undo_marker they do not affect behavior in anyway and can
1120 * therefore be safely ignored. In rare cases (which are more or less
1121 * theoretical ones), the D-SACK will nicely cross that boundary due to skb
1122 * fragmentation and packet reordering past skb's retransmission. To consider
1123 * them correctly, the acceptable range must be extended even more though
1124 * the exact amount is rather hard to quantify. However, tp->max_window can
1125 * be used as an exaggerated estimate.
1126 */
1127static bool tcp_is_sackblock_valid(struct tcp_sock *tp, bool is_dsack,
1128				   u32 start_seq, u32 end_seq)
1129{
1130	/* Too far in future, or reversed (interpretation is ambiguous) */
1131	if (after(end_seq, tp->snd_nxt) || !before(start_seq, end_seq))
1132		return false;
1133
1134	/* Nasty start_seq wrap-around check (see comments above) */
1135	if (!before(start_seq, tp->snd_nxt))
1136		return false;
1137
1138	/* In outstanding window? ...This is valid exit for D-SACKs too.
1139	 * start_seq == snd_una is non-sensical (see comments above)
1140	 */
1141	if (after(start_seq, tp->snd_una))
1142		return true;
1143
1144	if (!is_dsack || !tp->undo_marker)
1145		return false;
1146
1147	/* ...Then it's D-SACK, and must reside below snd_una completely */
1148	if (after(end_seq, tp->snd_una))
1149		return false;
1150
1151	if (!before(start_seq, tp->undo_marker))
1152		return true;
1153
1154	/* Too old */
1155	if (!after(end_seq, tp->undo_marker))
1156		return false;
1157
1158	/* Undo_marker boundary crossing (overestimates a lot). Known already:
1159	 *   start_seq < undo_marker and end_seq >= undo_marker.
1160	 */
1161	return !before(start_seq, end_seq - tp->max_window);
1162}
1163
1164/* Check for lost retransmit. This superb idea is borrowed from "ratehalving".
1165 * Event "B". Later note: FACK people cheated me again 8), we have to account
1166 * for reordering! Ugly, but should help.
1167 *
1168 * Search retransmitted skbs from write_queue that were sent when snd_nxt was
1169 * less than what is now known to be received by the other end (derived from
1170 * highest SACK block). Also calculate the lowest snd_nxt among the remaining
1171 * retransmitted skbs to avoid some costly processing per ACKs.
1172 */
1173static void tcp_mark_lost_retrans(struct sock *sk)
1174{
1175	const struct inet_connection_sock *icsk = inet_csk(sk);
1176	struct tcp_sock *tp = tcp_sk(sk);
1177	struct sk_buff *skb;
1178	int cnt = 0;
1179	u32 new_low_seq = tp->snd_nxt;
1180	u32 received_upto = tcp_highest_sack_seq(tp);
1181
1182	if (!tcp_is_fack(tp) || !tp->retrans_out ||
1183	    !after(received_upto, tp->lost_retrans_low) ||
1184	    icsk->icsk_ca_state != TCP_CA_Recovery)
1185		return;
1186
1187	tcp_for_write_queue(skb, sk) {
1188		u32 ack_seq = TCP_SKB_CB(skb)->ack_seq;
1189
1190		if (skb == tcp_send_head(sk))
1191			break;
1192		if (cnt == tp->retrans_out)
1193			break;
1194		if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1195			continue;
1196
1197		if (!(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS))
1198			continue;
1199
1200		/* TODO: We would like to get rid of tcp_is_fack(tp) only
1201		 * constraint here (see above) but figuring out that at
1202		 * least tp->reordering SACK blocks reside between ack_seq
1203		 * and received_upto is not easy task to do cheaply with
1204		 * the available datastructures.
1205		 *
1206		 * Whether FACK should check here for tp->reordering segs
1207		 * in-between one could argue for either way (it would be
1208		 * rather simple to implement as we could count fack_count
1209		 * during the walk and do tp->fackets_out - fack_count).
1210		 */
1211		if (after(received_upto, ack_seq)) {
1212			TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
1213			tp->retrans_out -= tcp_skb_pcount(skb);
1214
1215			tcp_skb_mark_lost_uncond_verify(tp, skb);
1216			NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPLOSTRETRANSMIT);
1217		} else {
1218			if (before(ack_seq, new_low_seq))
1219				new_low_seq = ack_seq;
1220			cnt += tcp_skb_pcount(skb);
1221		}
1222	}
1223
1224	if (tp->retrans_out)
1225		tp->lost_retrans_low = new_low_seq;
1226}
1227
1228static bool tcp_check_dsack(struct sock *sk, const struct sk_buff *ack_skb,
1229			    struct tcp_sack_block_wire *sp, int num_sacks,
1230			    u32 prior_snd_una)
1231{
1232	struct tcp_sock *tp = tcp_sk(sk);
1233	u32 start_seq_0 = get_unaligned_be32(&sp[0].start_seq);
1234	u32 end_seq_0 = get_unaligned_be32(&sp[0].end_seq);
1235	bool dup_sack = false;
1236
1237	if (before(start_seq_0, TCP_SKB_CB(ack_skb)->ack_seq)) {
1238		dup_sack = true;
1239		tcp_dsack_seen(tp);
1240		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPDSACKRECV);
1241	} else if (num_sacks > 1) {
1242		u32 end_seq_1 = get_unaligned_be32(&sp[1].end_seq);
1243		u32 start_seq_1 = get_unaligned_be32(&sp[1].start_seq);
1244
1245		if (!after(end_seq_0, end_seq_1) &&
1246		    !before(start_seq_0, start_seq_1)) {
1247			dup_sack = true;
1248			tcp_dsack_seen(tp);
1249			NET_INC_STATS_BH(sock_net(sk),
1250					LINUX_MIB_TCPDSACKOFORECV);
1251		}
 
 
 
 
1252	}
1253
 
 
1254	/* D-SACK for already forgotten data... Do dumb counting. */
1255	if (dup_sack && tp->undo_marker && tp->undo_retrans &&
1256	    !after(end_seq_0, prior_snd_una) &&
1257	    after(end_seq_0, tp->undo_marker))
1258		tp->undo_retrans--;
1259
1260	return dup_sack;
1261}
1262
1263struct tcp_sacktag_state {
1264	int reord;
1265	int fack_count;
1266	int flag;
1267};
1268
1269/* Check if skb is fully within the SACK block. In presence of GSO skbs,
1270 * the incoming SACK may not exactly match but we can find smaller MSS
1271 * aligned portion of it that matches. Therefore we might need to fragment
1272 * which may fail and creates some hassle (caller must handle error case
1273 * returns).
1274 *
1275 * FIXME: this could be merged to shift decision code
1276 */
1277static int tcp_match_skb_to_sack(struct sock *sk, struct sk_buff *skb,
1278				  u32 start_seq, u32 end_seq)
1279{
1280	int err;
1281	bool in_sack;
1282	unsigned int pkt_len;
1283	unsigned int mss;
1284
1285	in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1286		  !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1287
1288	if (tcp_skb_pcount(skb) > 1 && !in_sack &&
1289	    after(TCP_SKB_CB(skb)->end_seq, start_seq)) {
1290		mss = tcp_skb_mss(skb);
1291		in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
1292
1293		if (!in_sack) {
1294			pkt_len = start_seq - TCP_SKB_CB(skb)->seq;
1295			if (pkt_len < mss)
1296				pkt_len = mss;
1297		} else {
1298			pkt_len = end_seq - TCP_SKB_CB(skb)->seq;
1299			if (pkt_len < mss)
1300				return -EINVAL;
1301		}
1302
1303		/* Round if necessary so that SACKs cover only full MSSes
1304		 * and/or the remaining small portion (if present)
1305		 */
1306		if (pkt_len > mss) {
1307			unsigned int new_len = (pkt_len / mss) * mss;
1308			if (!in_sack && new_len < pkt_len) {
1309				new_len += mss;
1310				if (new_len > skb->len)
1311					return 0;
1312			}
1313			pkt_len = new_len;
1314		}
1315		err = tcp_fragment(sk, skb, pkt_len, mss);
 
 
 
 
 
1316		if (err < 0)
1317			return err;
1318	}
1319
1320	return in_sack;
1321}
1322
1323/* Mark the given newly-SACKed range as such, adjusting counters and hints. */
1324static u8 tcp_sacktag_one(struct sock *sk,
1325			  struct tcp_sacktag_state *state, u8 sacked,
1326			  u32 start_seq, u32 end_seq,
1327			  bool dup_sack, int pcount)
 
1328{
1329	struct tcp_sock *tp = tcp_sk(sk);
1330	int fack_count = state->fack_count;
1331
1332	/* Account D-SACK for retransmitted packet. */
1333	if (dup_sack && (sacked & TCPCB_RETRANS)) {
1334		if (tp->undo_marker && tp->undo_retrans &&
1335		    after(end_seq, tp->undo_marker))
1336			tp->undo_retrans--;
1337		if (sacked & TCPCB_SACKED_ACKED)
1338			state->reord = min(fack_count, state->reord);
 
1339	}
1340
1341	/* Nothing to do; acked frame is about to be dropped (was ACKed). */
1342	if (!after(end_seq, tp->snd_una))
1343		return sacked;
1344
1345	if (!(sacked & TCPCB_SACKED_ACKED)) {
 
 
1346		if (sacked & TCPCB_SACKED_RETRANS) {
1347			/* If the segment is not tagged as lost,
1348			 * we do not clear RETRANS, believing
1349			 * that retransmission is still in flight.
1350			 */
1351			if (sacked & TCPCB_LOST) {
1352				sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS);
1353				tp->lost_out -= pcount;
1354				tp->retrans_out -= pcount;
1355			}
1356		} else {
1357			if (!(sacked & TCPCB_RETRANS)) {
1358				/* New sack for not retransmitted frame,
1359				 * which was in hole. It is reordering.
1360				 */
1361				if (before(start_seq,
1362					   tcp_highest_sack_seq(tp)))
1363					state->reord = min(fack_count,
1364							   state->reord);
1365
1366				/* SACK enhanced F-RTO (RFC4138; Appendix B) */
1367				if (!after(end_seq, tp->frto_highmark))
1368					state->flag |= FLAG_ONLY_ORIG_SACKED;
 
 
1369			}
1370
1371			if (sacked & TCPCB_LOST) {
1372				sacked &= ~TCPCB_LOST;
1373				tp->lost_out -= pcount;
1374			}
1375		}
1376
1377		sacked |= TCPCB_SACKED_ACKED;
1378		state->flag |= FLAG_DATA_SACKED;
1379		tp->sacked_out += pcount;
1380
1381		fack_count += pcount;
1382
1383		/* Lost marker hint past SACKed? Tweak RFC3517 cnt */
1384		if (!tcp_is_fack(tp) && (tp->lost_skb_hint != NULL) &&
1385		    before(start_seq, TCP_SKB_CB(tp->lost_skb_hint)->seq))
1386			tp->lost_cnt_hint += pcount;
1387
1388		if (fack_count > tp->fackets_out)
1389			tp->fackets_out = fack_count;
1390	}
1391
1392	/* D-SACK. We can detect redundant retransmission in S|R and plain R
1393	 * frames and clear it. undo_retrans is decreased above, L|R frames
1394	 * are accounted above as well.
1395	 */
1396	if (dup_sack && (sacked & TCPCB_SACKED_RETRANS)) {
1397		sacked &= ~TCPCB_SACKED_RETRANS;
1398		tp->retrans_out -= pcount;
1399	}
1400
1401	return sacked;
1402}
1403
1404/* Shift newly-SACKed bytes from this skb to the immediately previous
1405 * already-SACKed sk_buff. Mark the newly-SACKed bytes as such.
1406 */
1407static bool tcp_shifted_skb(struct sock *sk, struct sk_buff *skb,
 
1408			    struct tcp_sacktag_state *state,
1409			    unsigned int pcount, int shifted, int mss,
1410			    bool dup_sack)
1411{
1412	struct tcp_sock *tp = tcp_sk(sk);
1413	struct sk_buff *prev = tcp_write_queue_prev(sk, skb);
1414	u32 start_seq = TCP_SKB_CB(skb)->seq;	/* start of newly-SACKed */
1415	u32 end_seq = start_seq + shifted;	/* end of newly-SACKed */
1416
1417	BUG_ON(!pcount);
1418
1419	/* Adjust counters and hints for the newly sacked sequence
1420	 * range but discard the return value since prev is already
1421	 * marked. We must tag the range first because the seq
1422	 * advancement below implicitly advances
1423	 * tcp_highest_sack_seq() when skb is highest_sack.
1424	 */
1425	tcp_sacktag_one(sk, state, TCP_SKB_CB(skb)->sacked,
1426			start_seq, end_seq, dup_sack, pcount);
 
 
1427
1428	if (skb == tp->lost_skb_hint)
1429		tp->lost_cnt_hint += pcount;
1430
1431	TCP_SKB_CB(prev)->end_seq += shifted;
1432	TCP_SKB_CB(skb)->seq += shifted;
1433
1434	skb_shinfo(prev)->gso_segs += pcount;
1435	BUG_ON(skb_shinfo(skb)->gso_segs < pcount);
1436	skb_shinfo(skb)->gso_segs -= pcount;
1437
1438	/* When we're adding to gso_segs == 1, gso_size will be zero,
1439	 * in theory this shouldn't be necessary but as long as DSACK
1440	 * code can come after this skb later on it's better to keep
1441	 * setting gso_size to something.
1442	 */
1443	if (!skb_shinfo(prev)->gso_size) {
1444		skb_shinfo(prev)->gso_size = mss;
1445		skb_shinfo(prev)->gso_type = sk->sk_gso_type;
1446	}
1447
1448	/* CHECKME: To clear or not to clear? Mimics normal skb currently */
1449	if (skb_shinfo(skb)->gso_segs <= 1) {
1450		skb_shinfo(skb)->gso_size = 0;
1451		skb_shinfo(skb)->gso_type = 0;
1452	}
1453
1454	/* Difference in this won't matter, both ACKed by the same cumul. ACK */
1455	TCP_SKB_CB(prev)->sacked |= (TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS);
1456
1457	if (skb->len > 0) {
1458		BUG_ON(!tcp_skb_pcount(skb));
1459		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SACKSHIFTED);
1460		return false;
1461	}
1462
1463	/* Whole SKB was eaten :-) */
1464
1465	if (skb == tp->retransmit_skb_hint)
1466		tp->retransmit_skb_hint = prev;
1467	if (skb == tp->scoreboard_skb_hint)
1468		tp->scoreboard_skb_hint = prev;
1469	if (skb == tp->lost_skb_hint) {
1470		tp->lost_skb_hint = prev;
1471		tp->lost_cnt_hint -= tcp_skb_pcount(prev);
1472	}
1473
1474	TCP_SKB_CB(skb)->tcp_flags |= TCP_SKB_CB(prev)->tcp_flags;
 
 
 
 
1475	if (skb == tcp_highest_sack(sk))
1476		tcp_advance_highest_sack(sk, skb);
1477
1478	tcp_unlink_write_queue(skb, sk);
1479	sk_wmem_free_skb(sk, skb);
 
 
 
1480
1481	NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SACKMERGED);
1482
1483	return true;
1484}
1485
1486/* I wish gso_size would have a bit more sane initialization than
1487 * something-or-zero which complicates things
1488 */
1489static int tcp_skb_seglen(const struct sk_buff *skb)
1490{
1491	return tcp_skb_pcount(skb) == 1 ? skb->len : tcp_skb_mss(skb);
1492}
1493
1494/* Shifting pages past head area doesn't work */
1495static int skb_can_shift(const struct sk_buff *skb)
1496{
1497	return !skb_headlen(skb) && skb_is_nonlinear(skb);
1498}
1499
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1500/* Try collapsing SACK blocks spanning across multiple skbs to a single
1501 * skb.
1502 */
1503static struct sk_buff *tcp_shift_skb_data(struct sock *sk, struct sk_buff *skb,
1504					  struct tcp_sacktag_state *state,
1505					  u32 start_seq, u32 end_seq,
1506					  bool dup_sack)
1507{
1508	struct tcp_sock *tp = tcp_sk(sk);
1509	struct sk_buff *prev;
1510	int mss;
1511	int pcount = 0;
1512	int len;
1513	int in_sack;
1514
1515	if (!sk_can_gso(sk))
1516		goto fallback;
1517
1518	/* Normally R but no L won't result in plain S */
1519	if (!dup_sack &&
1520	    (TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_RETRANS)) == TCPCB_SACKED_RETRANS)
1521		goto fallback;
1522	if (!skb_can_shift(skb))
1523		goto fallback;
1524	/* This frame is about to be dropped (was ACKed). */
1525	if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1526		goto fallback;
1527
1528	/* Can only happen with delayed DSACK + discard craziness */
1529	if (unlikely(skb == tcp_write_queue_head(sk)))
 
1530		goto fallback;
1531	prev = tcp_write_queue_prev(sk, skb);
1532
1533	if ((TCP_SKB_CB(prev)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED)
1534		goto fallback;
1535
 
 
 
1536	in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1537		  !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1538
1539	if (in_sack) {
1540		len = skb->len;
1541		pcount = tcp_skb_pcount(skb);
1542		mss = tcp_skb_seglen(skb);
1543
1544		/* TODO: Fix DSACKs to not fragment already SACKed and we can
1545		 * drop this restriction as unnecessary
1546		 */
1547		if (mss != tcp_skb_seglen(prev))
1548			goto fallback;
1549	} else {
1550		if (!after(TCP_SKB_CB(skb)->end_seq, start_seq))
1551			goto noop;
1552		/* CHECKME: This is non-MSS split case only?, this will
1553		 * cause skipped skbs due to advancing loop btw, original
1554		 * has that feature too
1555		 */
1556		if (tcp_skb_pcount(skb) <= 1)
1557			goto noop;
1558
1559		in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
1560		if (!in_sack) {
1561			/* TODO: head merge to next could be attempted here
1562			 * if (!after(TCP_SKB_CB(skb)->end_seq, end_seq)),
1563			 * though it might not be worth of the additional hassle
1564			 *
1565			 * ...we can probably just fallback to what was done
1566			 * previously. We could try merging non-SACKed ones
1567			 * as well but it probably isn't going to buy off
1568			 * because later SACKs might again split them, and
1569			 * it would make skb timestamp tracking considerably
1570			 * harder problem.
1571			 */
1572			goto fallback;
1573		}
1574
1575		len = end_seq - TCP_SKB_CB(skb)->seq;
1576		BUG_ON(len < 0);
1577		BUG_ON(len > skb->len);
1578
1579		/* MSS boundaries should be honoured or else pcount will
1580		 * severely break even though it makes things bit trickier.
1581		 * Optimize common case to avoid most of the divides
1582		 */
1583		mss = tcp_skb_mss(skb);
1584
1585		/* TODO: Fix DSACKs to not fragment already SACKed and we can
1586		 * drop this restriction as unnecessary
1587		 */
1588		if (mss != tcp_skb_seglen(prev))
1589			goto fallback;
1590
1591		if (len == mss) {
1592			pcount = 1;
1593		} else if (len < mss) {
1594			goto noop;
1595		} else {
1596			pcount = len / mss;
1597			len = pcount * mss;
1598		}
1599	}
1600
1601	/* tcp_sacktag_one() won't SACK-tag ranges below snd_una */
1602	if (!after(TCP_SKB_CB(skb)->seq + len, tp->snd_una))
1603		goto fallback;
1604
1605	if (!skb_shift(prev, skb, len))
1606		goto fallback;
1607	if (!tcp_shifted_skb(sk, skb, state, pcount, len, mss, dup_sack))
1608		goto out;
1609
1610	/* Hole filled allows collapsing with the next as well, this is very
1611	 * useful when hole on every nth skb pattern happens
1612	 */
1613	if (prev == tcp_write_queue_tail(sk))
 
1614		goto out;
1615	skb = tcp_write_queue_next(sk, prev);
1616
1617	if (!skb_can_shift(skb) ||
1618	    (skb == tcp_send_head(sk)) ||
1619	    ((TCP_SKB_CB(skb)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED) ||
1620	    (mss != tcp_skb_seglen(skb)))
1621		goto out;
1622
 
 
1623	len = skb->len;
1624	if (skb_shift(prev, skb, len)) {
1625		pcount += tcp_skb_pcount(skb);
1626		tcp_shifted_skb(sk, skb, state, tcp_skb_pcount(skb), len, mss, 0);
1627	}
1628
1629out:
1630	state->fack_count += pcount;
1631	return prev;
1632
1633noop:
1634	return skb;
1635
1636fallback:
1637	NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SACKSHIFTFALLBACK);
1638	return NULL;
1639}
1640
1641static struct sk_buff *tcp_sacktag_walk(struct sk_buff *skb, struct sock *sk,
1642					struct tcp_sack_block *next_dup,
1643					struct tcp_sacktag_state *state,
1644					u32 start_seq, u32 end_seq,
1645					bool dup_sack_in)
1646{
1647	struct tcp_sock *tp = tcp_sk(sk);
1648	struct sk_buff *tmp;
1649
1650	tcp_for_write_queue_from(skb, sk) {
1651		int in_sack = 0;
1652		bool dup_sack = dup_sack_in;
1653
1654		if (skb == tcp_send_head(sk))
1655			break;
1656
1657		/* queue is in-order => we can short-circuit the walk early */
1658		if (!before(TCP_SKB_CB(skb)->seq, end_seq))
1659			break;
1660
1661		if ((next_dup != NULL) &&
1662		    before(TCP_SKB_CB(skb)->seq, next_dup->end_seq)) {
1663			in_sack = tcp_match_skb_to_sack(sk, skb,
1664							next_dup->start_seq,
1665							next_dup->end_seq);
1666			if (in_sack > 0)
1667				dup_sack = true;
1668		}
1669
1670		/* skb reference here is a bit tricky to get right, since
1671		 * shifting can eat and free both this skb and the next,
1672		 * so not even _safe variant of the loop is enough.
1673		 */
1674		if (in_sack <= 0) {
1675			tmp = tcp_shift_skb_data(sk, skb, state,
1676						 start_seq, end_seq, dup_sack);
1677			if (tmp != NULL) {
1678				if (tmp != skb) {
1679					skb = tmp;
1680					continue;
1681				}
1682
1683				in_sack = 0;
1684			} else {
1685				in_sack = tcp_match_skb_to_sack(sk, skb,
1686								start_seq,
1687								end_seq);
1688			}
1689		}
1690
1691		if (unlikely(in_sack < 0))
1692			break;
1693
1694		if (in_sack) {
1695			TCP_SKB_CB(skb)->sacked =
1696				tcp_sacktag_one(sk,
1697						state,
1698						TCP_SKB_CB(skb)->sacked,
1699						TCP_SKB_CB(skb)->seq,
1700						TCP_SKB_CB(skb)->end_seq,
1701						dup_sack,
1702						tcp_skb_pcount(skb));
 
 
 
 
1703
1704			if (!before(TCP_SKB_CB(skb)->seq,
1705				    tcp_highest_sack_seq(tp)))
1706				tcp_advance_highest_sack(sk, skb);
1707		}
1708
1709		state->fack_count += tcp_skb_pcount(skb);
1710	}
1711	return skb;
1712}
1713
1714/* Avoid all extra work that is being done by sacktag while walking in
1715 * a normal way
1716 */
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1717static struct sk_buff *tcp_sacktag_skip(struct sk_buff *skb, struct sock *sk,
1718					struct tcp_sacktag_state *state,
1719					u32 skip_to_seq)
1720{
1721	tcp_for_write_queue_from(skb, sk) {
1722		if (skb == tcp_send_head(sk))
1723			break;
1724
1725		if (after(TCP_SKB_CB(skb)->end_seq, skip_to_seq))
1726			break;
1727
1728		state->fack_count += tcp_skb_pcount(skb);
1729	}
1730	return skb;
1731}
1732
1733static struct sk_buff *tcp_maybe_skipping_dsack(struct sk_buff *skb,
1734						struct sock *sk,
1735						struct tcp_sack_block *next_dup,
1736						struct tcp_sacktag_state *state,
1737						u32 skip_to_seq)
1738{
1739	if (next_dup == NULL)
1740		return skb;
1741
1742	if (before(next_dup->start_seq, skip_to_seq)) {
1743		skb = tcp_sacktag_skip(skb, sk, state, next_dup->start_seq);
1744		skb = tcp_sacktag_walk(skb, sk, NULL, state,
1745				       next_dup->start_seq, next_dup->end_seq,
1746				       1);
1747	}
1748
1749	return skb;
1750}
1751
1752static int tcp_sack_cache_ok(const struct tcp_sock *tp, const struct tcp_sack_block *cache)
1753{
1754	return cache < tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
1755}
1756
1757static int
1758tcp_sacktag_write_queue(struct sock *sk, const struct sk_buff *ack_skb,
1759			u32 prior_snd_una)
1760{
1761	const struct inet_connection_sock *icsk = inet_csk(sk);
1762	struct tcp_sock *tp = tcp_sk(sk);
1763	const unsigned char *ptr = (skb_transport_header(ack_skb) +
1764				    TCP_SKB_CB(ack_skb)->sacked);
1765	struct tcp_sack_block_wire *sp_wire = (struct tcp_sack_block_wire *)(ptr+2);
1766	struct tcp_sack_block sp[TCP_NUM_SACKS];
1767	struct tcp_sack_block *cache;
1768	struct tcp_sacktag_state state;
1769	struct sk_buff *skb;
1770	int num_sacks = min(TCP_NUM_SACKS, (ptr[1] - TCPOLEN_SACK_BASE) >> 3);
1771	int used_sacks;
1772	bool found_dup_sack = false;
1773	int i, j;
1774	int first_sack_index;
1775
1776	state.flag = 0;
1777	state.reord = tp->packets_out;
1778
1779	if (!tp->sacked_out) {
1780		if (WARN_ON(tp->fackets_out))
1781			tp->fackets_out = 0;
1782		tcp_highest_sack_reset(sk);
1783	}
1784
1785	found_dup_sack = tcp_check_dsack(sk, ack_skb, sp_wire,
1786					 num_sacks, prior_snd_una);
1787	if (found_dup_sack)
1788		state.flag |= FLAG_DSACKING_ACK;
1789
1790	/* Eliminate too old ACKs, but take into
1791	 * account more or less fresh ones, they can
1792	 * contain valid SACK info.
1793	 */
1794	if (before(TCP_SKB_CB(ack_skb)->ack_seq, prior_snd_una - tp->max_window))
1795		return 0;
1796
1797	if (!tp->packets_out)
1798		goto out;
1799
1800	used_sacks = 0;
1801	first_sack_index = 0;
1802	for (i = 0; i < num_sacks; i++) {
1803		bool dup_sack = !i && found_dup_sack;
1804
1805		sp[used_sacks].start_seq = get_unaligned_be32(&sp_wire[i].start_seq);
1806		sp[used_sacks].end_seq = get_unaligned_be32(&sp_wire[i].end_seq);
1807
1808		if (!tcp_is_sackblock_valid(tp, dup_sack,
1809					    sp[used_sacks].start_seq,
1810					    sp[used_sacks].end_seq)) {
1811			int mib_idx;
1812
1813			if (dup_sack) {
1814				if (!tp->undo_marker)
1815					mib_idx = LINUX_MIB_TCPDSACKIGNOREDNOUNDO;
1816				else
1817					mib_idx = LINUX_MIB_TCPDSACKIGNOREDOLD;
1818			} else {
1819				/* Don't count olds caused by ACK reordering */
1820				if ((TCP_SKB_CB(ack_skb)->ack_seq != tp->snd_una) &&
1821				    !after(sp[used_sacks].end_seq, tp->snd_una))
1822					continue;
1823				mib_idx = LINUX_MIB_TCPSACKDISCARD;
1824			}
1825
1826			NET_INC_STATS_BH(sock_net(sk), mib_idx);
1827			if (i == 0)
1828				first_sack_index = -1;
1829			continue;
1830		}
1831
1832		/* Ignore very old stuff early */
1833		if (!after(sp[used_sacks].end_seq, prior_snd_una))
 
 
1834			continue;
 
1835
1836		used_sacks++;
1837	}
1838
1839	/* order SACK blocks to allow in order walk of the retrans queue */
1840	for (i = used_sacks - 1; i > 0; i--) {
1841		for (j = 0; j < i; j++) {
1842			if (after(sp[j].start_seq, sp[j + 1].start_seq)) {
1843				swap(sp[j], sp[j + 1]);
1844
1845				/* Track where the first SACK block goes to */
1846				if (j == first_sack_index)
1847					first_sack_index = j + 1;
1848			}
1849		}
1850	}
1851
1852	skb = tcp_write_queue_head(sk);
1853	state.fack_count = 0;
1854	i = 0;
1855
1856	if (!tp->sacked_out) {
1857		/* It's already past, so skip checking against it */
1858		cache = tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
1859	} else {
1860		cache = tp->recv_sack_cache;
1861		/* Skip empty blocks in at head of the cache */
1862		while (tcp_sack_cache_ok(tp, cache) && !cache->start_seq &&
1863		       !cache->end_seq)
1864			cache++;
1865	}
1866
1867	while (i < used_sacks) {
1868		u32 start_seq = sp[i].start_seq;
1869		u32 end_seq = sp[i].end_seq;
1870		bool dup_sack = (found_dup_sack && (i == first_sack_index));
1871		struct tcp_sack_block *next_dup = NULL;
1872
1873		if (found_dup_sack && ((i + 1) == first_sack_index))
1874			next_dup = &sp[i + 1];
1875
1876		/* Skip too early cached blocks */
1877		while (tcp_sack_cache_ok(tp, cache) &&
1878		       !before(start_seq, cache->end_seq))
1879			cache++;
1880
1881		/* Can skip some work by looking recv_sack_cache? */
1882		if (tcp_sack_cache_ok(tp, cache) && !dup_sack &&
1883		    after(end_seq, cache->start_seq)) {
1884
1885			/* Head todo? */
1886			if (before(start_seq, cache->start_seq)) {
1887				skb = tcp_sacktag_skip(skb, sk, &state,
1888						       start_seq);
1889				skb = tcp_sacktag_walk(skb, sk, next_dup,
1890						       &state,
1891						       start_seq,
1892						       cache->start_seq,
1893						       dup_sack);
1894			}
1895
1896			/* Rest of the block already fully processed? */
1897			if (!after(end_seq, cache->end_seq))
1898				goto advance_sp;
1899
1900			skb = tcp_maybe_skipping_dsack(skb, sk, next_dup,
1901						       &state,
1902						       cache->end_seq);
1903
1904			/* ...tail remains todo... */
1905			if (tcp_highest_sack_seq(tp) == cache->end_seq) {
1906				/* ...but better entrypoint exists! */
1907				skb = tcp_highest_sack(sk);
1908				if (skb == NULL)
1909					break;
1910				state.fack_count = tp->fackets_out;
1911				cache++;
1912				goto walk;
1913			}
1914
1915			skb = tcp_sacktag_skip(skb, sk, &state, cache->end_seq);
1916			/* Check overlap against next cached too (past this one already) */
1917			cache++;
1918			continue;
1919		}
1920
1921		if (!before(start_seq, tcp_highest_sack_seq(tp))) {
1922			skb = tcp_highest_sack(sk);
1923			if (skb == NULL)
1924				break;
1925			state.fack_count = tp->fackets_out;
1926		}
1927		skb = tcp_sacktag_skip(skb, sk, &state, start_seq);
1928
1929walk:
1930		skb = tcp_sacktag_walk(skb, sk, next_dup, &state,
1931				       start_seq, end_seq, dup_sack);
1932
1933advance_sp:
1934		/* SACK enhanced FRTO (RFC4138, Appendix B): Clearing correct
1935		 * due to in-order walk
1936		 */
1937		if (after(end_seq, tp->frto_highmark))
1938			state.flag &= ~FLAG_ONLY_ORIG_SACKED;
1939
1940		i++;
1941	}
1942
1943	/* Clear the head of the cache sack blocks so we can skip it next time */
1944	for (i = 0; i < ARRAY_SIZE(tp->recv_sack_cache) - used_sacks; i++) {
1945		tp->recv_sack_cache[i].start_seq = 0;
1946		tp->recv_sack_cache[i].end_seq = 0;
1947	}
1948	for (j = 0; j < used_sacks; j++)
1949		tp->recv_sack_cache[i++] = sp[j];
1950
1951	tcp_mark_lost_retrans(sk);
 
1952
1953	tcp_verify_left_out(tp);
1954
1955	if ((state.reord < tp->fackets_out) &&
1956	    ((icsk->icsk_ca_state != TCP_CA_Loss) || tp->undo_marker) &&
1957	    (!tp->frto_highmark || after(tp->snd_una, tp->frto_highmark)))
1958		tcp_update_reordering(sk, tp->fackets_out - state.reord, 0);
1959
1960out:
1961
1962#if FASTRETRANS_DEBUG > 0
1963	WARN_ON((int)tp->sacked_out < 0);
1964	WARN_ON((int)tp->lost_out < 0);
1965	WARN_ON((int)tp->retrans_out < 0);
1966	WARN_ON((int)tcp_packets_in_flight(tp) < 0);
1967#endif
1968	return state.flag;
1969}
1970
1971/* Limits sacked_out so that sum with lost_out isn't ever larger than
1972 * packets_out. Returns false if sacked_out adjustement wasn't necessary.
1973 */
1974static bool tcp_limit_reno_sacked(struct tcp_sock *tp)
1975{
1976	u32 holes;
1977
1978	holes = max(tp->lost_out, 1U);
1979	holes = min(holes, tp->packets_out);
1980
1981	if ((tp->sacked_out + holes) > tp->packets_out) {
1982		tp->sacked_out = tp->packets_out - holes;
1983		return true;
1984	}
1985	return false;
1986}
1987
1988/* If we receive more dupacks than we expected counting segments
1989 * in assumption of absent reordering, interpret this as reordering.
1990 * The only another reason could be bug in receiver TCP.
1991 */
1992static void tcp_check_reno_reordering(struct sock *sk, const int addend)
1993{
1994	struct tcp_sock *tp = tcp_sk(sk);
1995	if (tcp_limit_reno_sacked(tp))
1996		tcp_update_reordering(sk, tp->packets_out + addend, 0);
 
 
 
 
 
 
1997}
1998
1999/* Emulate SACKs for SACKless connection: account for a new dupack. */
2000
2001static void tcp_add_reno_sack(struct sock *sk)
2002{
2003	struct tcp_sock *tp = tcp_sk(sk);
2004	tp->sacked_out++;
2005	tcp_check_reno_reordering(sk, 0);
2006	tcp_verify_left_out(tp);
 
 
 
 
 
 
 
 
2007}
2008
2009/* Account for ACK, ACKing some data in Reno Recovery phase. */
2010
2011static void tcp_remove_reno_sacks(struct sock *sk, int acked)
2012{
2013	struct tcp_sock *tp = tcp_sk(sk);
2014
2015	if (acked > 0) {
2016		/* One ACK acked hole. The rest eat duplicate ACKs. */
 
 
2017		if (acked - 1 >= tp->sacked_out)
2018			tp->sacked_out = 0;
2019		else
2020			tp->sacked_out -= acked - 1;
2021	}
2022	tcp_check_reno_reordering(sk, acked);
2023	tcp_verify_left_out(tp);
2024}
2025
2026static inline void tcp_reset_reno_sack(struct tcp_sock *tp)
2027{
2028	tp->sacked_out = 0;
2029}
2030
2031static int tcp_is_sackfrto(const struct tcp_sock *tp)
2032{
2033	return (sysctl_tcp_frto == 0x2) && !tcp_is_reno(tp);
 
 
 
 
2034}
2035
2036/* F-RTO can only be used if TCP has never retransmitted anything other than
2037 * head (SACK enhanced variant from Appendix B of RFC4138 is more robust here)
2038 */
2039bool tcp_use_frto(struct sock *sk)
2040{
2041	const struct tcp_sock *tp = tcp_sk(sk);
2042	const struct inet_connection_sock *icsk = inet_csk(sk);
2043	struct sk_buff *skb;
2044
2045	if (!sysctl_tcp_frto)
2046		return false;
2047
2048	/* MTU probe and F-RTO won't really play nicely along currently */
2049	if (icsk->icsk_mtup.probe_size)
2050		return false;
2051
2052	if (tcp_is_sackfrto(tp))
2053		return true;
2054
2055	/* Avoid expensive walking of rexmit queue if possible */
2056	if (tp->retrans_out > 1)
2057		return false;
2058
2059	skb = tcp_write_queue_head(sk);
2060	if (tcp_skb_is_last(sk, skb))
2061		return true;
2062	skb = tcp_write_queue_next(sk, skb);	/* Skips head */
2063	tcp_for_write_queue_from(skb, sk) {
2064		if (skb == tcp_send_head(sk))
2065			break;
2066		if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS)
2067			return false;
2068		/* Short-circuit when first non-SACKed skb has been checked */
2069		if (!(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
2070			break;
2071	}
2072	return true;
2073}
2074
2075/* RTO occurred, but do not yet enter Loss state. Instead, defer RTO
2076 * recovery a bit and use heuristics in tcp_process_frto() to detect if
2077 * the RTO was spurious. Only clear SACKED_RETRANS of the head here to
2078 * keep retrans_out counting accurate (with SACK F-RTO, other than head
2079 * may still have that bit set); TCPCB_LOST and remaining SACKED_RETRANS
2080 * bits are handled if the Loss state is really to be entered (in
2081 * tcp_enter_frto_loss).
2082 *
2083 * Do like tcp_enter_loss() would; when RTO expires the second time it
2084 * does:
2085 *  "Reduce ssthresh if it has not yet been made inside this window."
2086 */
2087void tcp_enter_frto(struct sock *sk)
2088{
2089	const struct inet_connection_sock *icsk = inet_csk(sk);
2090	struct tcp_sock *tp = tcp_sk(sk);
2091	struct sk_buff *skb;
2092
2093	if ((!tp->frto_counter && icsk->icsk_ca_state <= TCP_CA_Disorder) ||
2094	    tp->snd_una == tp->high_seq ||
2095	    ((icsk->icsk_ca_state == TCP_CA_Loss || tp->frto_counter) &&
2096	     !icsk->icsk_retransmits)) {
2097		tp->prior_ssthresh = tcp_current_ssthresh(sk);
2098		/* Our state is too optimistic in ssthresh() call because cwnd
2099		 * is not reduced until tcp_enter_frto_loss() when previous F-RTO
2100		 * recovery has not yet completed. Pattern would be this: RTO,
2101		 * Cumulative ACK, RTO (2xRTO for the same segment does not end
2102		 * up here twice).
2103		 * RFC4138 should be more specific on what to do, even though
2104		 * RTO is quite unlikely to occur after the first Cumulative ACK
2105		 * due to back-off and complexity of triggering events ...
2106		 */
2107		if (tp->frto_counter) {
2108			u32 stored_cwnd;
2109			stored_cwnd = tp->snd_cwnd;
2110			tp->snd_cwnd = 2;
2111			tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
2112			tp->snd_cwnd = stored_cwnd;
2113		} else {
2114			tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
2115		}
2116		/* ... in theory, cong.control module could do "any tricks" in
2117		 * ssthresh(), which means that ca_state, lost bits and lost_out
2118		 * counter would have to be faked before the call occurs. We
2119		 * consider that too expensive, unlikely and hacky, so modules
2120		 * using these in ssthresh() must deal these incompatibility
2121		 * issues if they receives CA_EVENT_FRTO and frto_counter != 0
2122		 */
2123		tcp_ca_event(sk, CA_EVENT_FRTO);
2124	}
2125
2126	tp->undo_marker = tp->snd_una;
2127	tp->undo_retrans = 0;
2128
2129	skb = tcp_write_queue_head(sk);
2130	if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS)
2131		tp->undo_marker = 0;
2132	if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
2133		TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
2134		tp->retrans_out -= tcp_skb_pcount(skb);
2135	}
2136	tcp_verify_left_out(tp);
2137
2138	/* Too bad if TCP was application limited */
2139	tp->snd_cwnd = min(tp->snd_cwnd, tcp_packets_in_flight(tp) + 1);
2140
2141	/* Earlier loss recovery underway (see RFC4138; Appendix B).
2142	 * The last condition is necessary at least in tp->frto_counter case.
2143	 */
2144	if (tcp_is_sackfrto(tp) && (tp->frto_counter ||
2145	    ((1 << icsk->icsk_ca_state) & (TCPF_CA_Recovery|TCPF_CA_Loss))) &&
2146	    after(tp->high_seq, tp->snd_una)) {
2147		tp->frto_highmark = tp->high_seq;
2148	} else {
2149		tp->frto_highmark = tp->snd_nxt;
2150	}
2151	tcp_set_ca_state(sk, TCP_CA_Disorder);
2152	tp->high_seq = tp->snd_nxt;
2153	tp->frto_counter = 1;
2154}
2155
2156/* Enter Loss state after F-RTO was applied. Dupack arrived after RTO,
2157 * which indicates that we should follow the traditional RTO recovery,
2158 * i.e. mark everything lost and do go-back-N retransmission.
2159 */
2160static void tcp_enter_frto_loss(struct sock *sk, int allowed_segments, int flag)
2161{
2162	struct tcp_sock *tp = tcp_sk(sk);
2163	struct sk_buff *skb;
 
2164
2165	tp->lost_out = 0;
2166	tp->retrans_out = 0;
2167	if (tcp_is_reno(tp))
 
 
 
 
 
2168		tcp_reset_reno_sack(tp);
 
2169
2170	tcp_for_write_queue(skb, sk) {
2171		if (skb == tcp_send_head(sk))
2172			break;
2173
2174		TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
2175		/*
2176		 * Count the retransmission made on RTO correctly (only when
2177		 * waiting for the first ACK and did not get it)...
2178		 */
2179		if ((tp->frto_counter == 1) && !(flag & FLAG_DATA_ACKED)) {
2180			/* For some reason this R-bit might get cleared? */
2181			if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS)
2182				tp->retrans_out += tcp_skb_pcount(skb);
2183			/* ...enter this if branch just for the first segment */
2184			flag |= FLAG_DATA_ACKED;
2185		} else {
2186			if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS)
2187				tp->undo_marker = 0;
2188			TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
2189		}
2190
2191		/* Marking forward transmissions that were made after RTO lost
2192		 * can cause unnecessary retransmissions in some scenarios,
2193		 * SACK blocks will mitigate that in some but not in all cases.
2194		 * We used to not mark them but it was causing break-ups with
2195		 * receivers that do only in-order receival.
2196		 *
2197		 * TODO: we could detect presence of such receiver and select
2198		 * different behavior per flow.
2199		 */
2200		if (!(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) {
2201			TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
2202			tp->lost_out += tcp_skb_pcount(skb);
2203			tp->retransmit_high = TCP_SKB_CB(skb)->end_seq;
2204		}
2205	}
2206	tcp_verify_left_out(tp);
2207
2208	tp->snd_cwnd = tcp_packets_in_flight(tp) + allowed_segments;
2209	tp->snd_cwnd_cnt = 0;
2210	tp->snd_cwnd_stamp = tcp_time_stamp;
2211	tp->frto_counter = 0;
2212	tp->bytes_acked = 0;
2213
2214	tp->reordering = min_t(unsigned int, tp->reordering,
2215			       sysctl_tcp_reordering);
2216	tcp_set_ca_state(sk, TCP_CA_Loss);
2217	tp->high_seq = tp->snd_nxt;
2218	TCP_ECN_queue_cwr(tp);
2219
2220	tcp_clear_all_retrans_hints(tp);
2221}
2222
2223static void tcp_clear_retrans_partial(struct tcp_sock *tp)
2224{
2225	tp->retrans_out = 0;
2226	tp->lost_out = 0;
2227
2228	tp->undo_marker = 0;
2229	tp->undo_retrans = 0;
2230}
2231
2232void tcp_clear_retrans(struct tcp_sock *tp)
2233{
2234	tcp_clear_retrans_partial(tp);
2235
2236	tp->fackets_out = 0;
2237	tp->sacked_out = 0;
2238}
2239
2240/* Enter Loss state. If "how" is not zero, forget all SACK information
2241 * and reset tags completely, otherwise preserve SACKs. If receiver
2242 * dropped its ofo queue, we will know this due to reneging detection.
2243 */
2244void tcp_enter_loss(struct sock *sk, int how)
2245{
2246	const struct inet_connection_sock *icsk = inet_csk(sk);
2247	struct tcp_sock *tp = tcp_sk(sk);
2248	struct sk_buff *skb;
 
 
 
 
2249
2250	/* Reduce ssthresh if it has not yet been made inside this window. */
2251	if (icsk->icsk_ca_state <= TCP_CA_Disorder || tp->snd_una == tp->high_seq ||
 
2252	    (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) {
2253		tp->prior_ssthresh = tcp_current_ssthresh(sk);
 
2254		tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
2255		tcp_ca_event(sk, CA_EVENT_LOSS);
 
2256	}
2257	tp->snd_cwnd	   = 1;
2258	tp->snd_cwnd_cnt   = 0;
2259	tp->snd_cwnd_stamp = tcp_time_stamp;
2260
2261	tp->bytes_acked = 0;
2262	tcp_clear_retrans_partial(tp);
2263
2264	if (tcp_is_reno(tp))
2265		tcp_reset_reno_sack(tp);
2266
2267	if (!how) {
2268		/* Push undo marker, if it was plain RTO and nothing
2269		 * was retransmitted. */
2270		tp->undo_marker = tp->snd_una;
2271	} else {
2272		tp->sacked_out = 0;
2273		tp->fackets_out = 0;
2274	}
2275	tcp_clear_all_retrans_hints(tp);
2276
2277	tcp_for_write_queue(skb, sk) {
2278		if (skb == tcp_send_head(sk))
2279			break;
2280
2281		if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS)
2282			tp->undo_marker = 0;
2283		TCP_SKB_CB(skb)->sacked &= (~TCPCB_TAGBITS)|TCPCB_SACKED_ACKED;
2284		if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED) || how) {
2285			TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED;
2286			TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
2287			tp->lost_out += tcp_skb_pcount(skb);
2288			tp->retransmit_high = TCP_SKB_CB(skb)->end_seq;
2289		}
2290	}
2291	tcp_verify_left_out(tp);
2292
2293	tp->reordering = min_t(unsigned int, tp->reordering,
2294			       sysctl_tcp_reordering);
2295	tcp_set_ca_state(sk, TCP_CA_Loss);
2296	tp->high_seq = tp->snd_nxt;
2297	TCP_ECN_queue_cwr(tp);
2298	/* Abort F-RTO algorithm if one is in progress */
2299	tp->frto_counter = 0;
 
 
 
 
 
 
2300}
2301
2302/* If ACK arrived pointing to a remembered SACK, it means that our
2303 * remembered SACKs do not reflect real state of receiver i.e.
2304 * receiver _host_ is heavily congested (or buggy).
2305 *
2306 * Do processing similar to RTO timeout.
 
 
 
 
2307 */
2308static bool tcp_check_sack_reneging(struct sock *sk, int flag)
2309{
2310	if (flag & FLAG_SACK_RENEGING) {
2311		struct inet_connection_sock *icsk = inet_csk(sk);
2312		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSACKRENEGING);
2313
2314		tcp_enter_loss(sk, 1);
2315		icsk->icsk_retransmits++;
2316		tcp_retransmit_skb(sk, tcp_write_queue_head(sk));
2317		inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
2318					  icsk->icsk_rto, TCP_RTO_MAX);
2319		return true;
2320	}
2321	return false;
2322}
2323
2324static inline int tcp_fackets_out(const struct tcp_sock *tp)
2325{
2326	return tcp_is_reno(tp) ? tp->sacked_out + 1 : tp->fackets_out;
2327}
2328
2329/* Heurestics to calculate number of duplicate ACKs. There's no dupACKs
2330 * counter when SACK is enabled (without SACK, sacked_out is used for
2331 * that purpose).
2332 *
2333 * Instead, with FACK TCP uses fackets_out that includes both SACKed
2334 * segments up to the highest received SACK block so far and holes in
2335 * between them.
2336 *
2337 * With reordering, holes may still be in flight, so RFC3517 recovery
2338 * uses pure sacked_out (total number of SACKed segments) even though
2339 * it violates the RFC that uses duplicate ACKs, often these are equal
2340 * but when e.g. out-of-window ACKs or packet duplication occurs,
2341 * they differ. Since neither occurs due to loss, TCP should really
2342 * ignore them.
2343 */
2344static inline int tcp_dupack_heuristics(const struct tcp_sock *tp)
2345{
2346	return tcp_is_fack(tp) ? tp->fackets_out : tp->sacked_out + 1;
2347}
2348
2349static bool tcp_pause_early_retransmit(struct sock *sk, int flag)
2350{
2351	struct tcp_sock *tp = tcp_sk(sk);
2352	unsigned long delay;
2353
2354	/* Delay early retransmit and entering fast recovery for
2355	 * max(RTT/4, 2msec) unless ack has ECE mark, no RTT samples
2356	 * available, or RTO is scheduled to fire first.
2357	 */
2358	if (sysctl_tcp_early_retrans < 2 || (flag & FLAG_ECE) || !tp->srtt)
2359		return false;
2360
2361	delay = max_t(unsigned long, (tp->srtt >> 5), msecs_to_jiffies(2));
2362	if (!time_after(inet_csk(sk)->icsk_timeout, (jiffies + delay)))
2363		return false;
2364
2365	inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, delay, TCP_RTO_MAX);
2366	tp->early_retrans_delayed = 1;
2367	return true;
2368}
2369
2370static inline int tcp_skb_timedout(const struct sock *sk,
2371				   const struct sk_buff *skb)
2372{
2373	return tcp_time_stamp - TCP_SKB_CB(skb)->when > inet_csk(sk)->icsk_rto;
2374}
2375
2376static inline int tcp_head_timedout(const struct sock *sk)
2377{
2378	const struct tcp_sock *tp = tcp_sk(sk);
2379
2380	return tp->packets_out &&
2381	       tcp_skb_timedout(sk, tcp_write_queue_head(sk));
2382}
2383
2384/* Linux NewReno/SACK/FACK/ECN state machine.
2385 * --------------------------------------
2386 *
2387 * "Open"	Normal state, no dubious events, fast path.
2388 * "Disorder"   In all the respects it is "Open",
2389 *		but requires a bit more attention. It is entered when
2390 *		we see some SACKs or dupacks. It is split of "Open"
2391 *		mainly to move some processing from fast path to slow one.
2392 * "CWR"	CWND was reduced due to some Congestion Notification event.
2393 *		It can be ECN, ICMP source quench, local device congestion.
2394 * "Recovery"	CWND was reduced, we are fast-retransmitting.
2395 * "Loss"	CWND was reduced due to RTO timeout or SACK reneging.
2396 *
2397 * tcp_fastretrans_alert() is entered:
2398 * - each incoming ACK, if state is not "Open"
2399 * - when arrived ACK is unusual, namely:
2400 *	* SACK
2401 *	* Duplicate ACK.
2402 *	* ECN ECE.
2403 *
2404 * Counting packets in flight is pretty simple.
2405 *
2406 *	in_flight = packets_out - left_out + retrans_out
2407 *
2408 *	packets_out is SND.NXT-SND.UNA counted in packets.
2409 *
2410 *	retrans_out is number of retransmitted segments.
2411 *
2412 *	left_out is number of segments left network, but not ACKed yet.
2413 *
2414 *		left_out = sacked_out + lost_out
2415 *
2416 *     sacked_out: Packets, which arrived to receiver out of order
2417 *		   and hence not ACKed. With SACKs this number is simply
2418 *		   amount of SACKed data. Even without SACKs
2419 *		   it is easy to give pretty reliable estimate of this number,
2420 *		   counting duplicate ACKs.
2421 *
2422 *       lost_out: Packets lost by network. TCP has no explicit
2423 *		   "loss notification" feedback from network (for now).
2424 *		   It means that this number can be only _guessed_.
2425 *		   Actually, it is the heuristics to predict lossage that
2426 *		   distinguishes different algorithms.
2427 *
2428 *	F.e. after RTO, when all the queue is considered as lost,
2429 *	lost_out = packets_out and in_flight = retrans_out.
2430 *
2431 *		Essentially, we have now two algorithms counting
2432 *		lost packets.
2433 *
2434 *		FACK: It is the simplest heuristics. As soon as we decided
2435 *		that something is lost, we decide that _all_ not SACKed
2436 *		packets until the most forward SACK are lost. I.e.
2437 *		lost_out = fackets_out - sacked_out and left_out = fackets_out.
2438 *		It is absolutely correct estimate, if network does not reorder
2439 *		packets. And it loses any connection to reality when reordering
2440 *		takes place. We use FACK by default until reordering
2441 *		is suspected on the path to this destination.
 
 
 
 
 
 
 
 
2442 *
2443 *		NewReno: when Recovery is entered, we assume that one segment
2444 *		is lost (classic Reno). While we are in Recovery and
2445 *		a partial ACK arrives, we assume that one more packet
2446 *		is lost (NewReno). This heuristics are the same in NewReno
2447 *		and SACK.
2448 *
2449 *  Imagine, that's all! Forget about all this shamanism about CWND inflation
2450 *  deflation etc. CWND is real congestion window, never inflated, changes
2451 *  only according to classic VJ rules.
2452 *
2453 * Really tricky (and requiring careful tuning) part of algorithm
2454 * is hidden in functions tcp_time_to_recover() and tcp_xmit_retransmit_queue().
2455 * The first determines the moment _when_ we should reduce CWND and,
2456 * hence, slow down forward transmission. In fact, it determines the moment
2457 * when we decide that hole is caused by loss, rather than by a reorder.
2458 *
2459 * tcp_xmit_retransmit_queue() decides, _what_ we should retransmit to fill
2460 * holes, caused by lost packets.
2461 *
2462 * And the most logically complicated part of algorithm is undo
2463 * heuristics. We detect false retransmits due to both too early
2464 * fast retransmit (reordering) and underestimated RTO, analyzing
2465 * timestamps and D-SACKs. When we detect that some segments were
2466 * retransmitted by mistake and CWND reduction was wrong, we undo
2467 * window reduction and abort recovery phase. This logic is hidden
2468 * inside several functions named tcp_try_undo_<something>.
2469 */
2470
2471/* This function decides, when we should leave Disordered state
2472 * and enter Recovery phase, reducing congestion window.
2473 *
2474 * Main question: may we further continue forward transmission
2475 * with the same cwnd?
2476 */
2477static bool tcp_time_to_recover(struct sock *sk, int flag)
2478{
2479	struct tcp_sock *tp = tcp_sk(sk);
2480	__u32 packets_out;
2481
2482	/* Do not perform any recovery during F-RTO algorithm */
2483	if (tp->frto_counter)
2484		return false;
2485
2486	/* Trick#1: The loss is proven. */
2487	if (tp->lost_out)
2488		return true;
2489
2490	/* Not-A-Trick#2 : Classic rule... */
2491	if (tcp_dupack_heuristics(tp) > tp->reordering)
2492		return true;
2493
2494	/* Trick#3 : when we use RFC2988 timer restart, fast
2495	 * retransmit can be triggered by timeout of queue head.
2496	 */
2497	if (tcp_is_fack(tp) && tcp_head_timedout(sk))
2498		return true;
2499
2500	/* Trick#4: It is still not OK... But will it be useful to delay
2501	 * recovery more?
2502	 */
2503	packets_out = tp->packets_out;
2504	if (packets_out <= tp->reordering &&
2505	    tp->sacked_out >= max_t(__u32, packets_out/2, sysctl_tcp_reordering) &&
2506	    !tcp_may_send_now(sk)) {
2507		/* We have nothing to send. This connection is limited
2508		 * either by receiver window or by application.
2509		 */
2510		return true;
2511	}
2512
2513	/* If a thin stream is detected, retransmit after first
2514	 * received dupack. Employ only if SACK is supported in order
2515	 * to avoid possible corner-case series of spurious retransmissions
2516	 * Use only if there are no unsent data.
2517	 */
2518	if ((tp->thin_dupack || sysctl_tcp_thin_dupack) &&
2519	    tcp_stream_is_thin(tp) && tcp_dupack_heuristics(tp) > 1 &&
2520	    tcp_is_sack(tp) && !tcp_send_head(sk))
2521		return true;
2522
2523	/* Trick#6: TCP early retransmit, per RFC5827.  To avoid spurious
2524	 * retransmissions due to small network reorderings, we implement
2525	 * Mitigation A.3 in the RFC and delay the retransmission for a short
2526	 * interval if appropriate.
2527	 */
2528	if (tp->do_early_retrans && !tp->retrans_out && tp->sacked_out &&
2529	    (tp->packets_out == (tp->sacked_out + 1) && tp->packets_out < 4) &&
2530	    !tcp_may_send_now(sk))
2531		return !tcp_pause_early_retransmit(sk, flag);
2532
2533	return false;
2534}
2535
2536/* New heuristics: it is possible only after we switched to restart timer
2537 * each time when something is ACKed. Hence, we can detect timed out packets
2538 * during fast retransmit without falling to slow start.
2539 *
2540 * Usefulness of this as is very questionable, since we should know which of
2541 * the segments is the next to timeout which is relatively expensive to find
2542 * in general case unless we add some data structure just for that. The
2543 * current approach certainly won't find the right one too often and when it
2544 * finally does find _something_ it usually marks large part of the window
2545 * right away (because a retransmission with a larger timestamp blocks the
2546 * loop from advancing). -ij
2547 */
2548static void tcp_timeout_skbs(struct sock *sk)
2549{
2550	struct tcp_sock *tp = tcp_sk(sk);
2551	struct sk_buff *skb;
2552
2553	if (!tcp_is_fack(tp) || !tcp_head_timedout(sk))
2554		return;
2555
2556	skb = tp->scoreboard_skb_hint;
2557	if (tp->scoreboard_skb_hint == NULL)
2558		skb = tcp_write_queue_head(sk);
2559
2560	tcp_for_write_queue_from(skb, sk) {
2561		if (skb == tcp_send_head(sk))
2562			break;
2563		if (!tcp_skb_timedout(sk, skb))
2564			break;
2565
2566		tcp_skb_mark_lost(tp, skb);
2567	}
2568
2569	tp->scoreboard_skb_hint = skb;
2570
2571	tcp_verify_left_out(tp);
2572}
2573
2574/* Detect loss in event "A" above by marking head of queue up as lost.
2575 * For FACK or non-SACK(Reno) senders, the first "packets" number of segments
2576 * are considered lost. For RFC3517 SACK, a segment is considered lost if it
2577 * has at least tp->reordering SACKed seqments above it; "packets" refers to
2578 * the maximum SACKed segments to pass before reaching this limit.
2579 */
2580static void tcp_mark_head_lost(struct sock *sk, int packets, int mark_head)
2581{
2582	struct tcp_sock *tp = tcp_sk(sk);
2583	struct sk_buff *skb;
2584	int cnt, oldcnt;
2585	int err;
2586	unsigned int mss;
2587	/* Use SACK to deduce losses of new sequences sent during recovery */
2588	const u32 loss_high = tcp_is_sack(tp) ?  tp->snd_nxt : tp->high_seq;
2589
2590	WARN_ON(packets > tp->packets_out);
2591	if (tp->lost_skb_hint) {
2592		skb = tp->lost_skb_hint;
2593		cnt = tp->lost_cnt_hint;
2594		/* Head already handled? */
2595		if (mark_head && skb != tcp_write_queue_head(sk))
2596			return;
 
2597	} else {
2598		skb = tcp_write_queue_head(sk);
2599		cnt = 0;
2600	}
2601
2602	tcp_for_write_queue_from(skb, sk) {
2603		if (skb == tcp_send_head(sk))
2604			break;
2605		/* TODO: do this better */
2606		/* this is not the most efficient way to do this... */
2607		tp->lost_skb_hint = skb;
2608		tp->lost_cnt_hint = cnt;
2609
2610		if (after(TCP_SKB_CB(skb)->end_seq, loss_high))
2611			break;
2612
2613		oldcnt = cnt;
2614		if (tcp_is_fack(tp) || tcp_is_reno(tp) ||
2615		    (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
2616			cnt += tcp_skb_pcount(skb);
2617
2618		if (cnt > packets) {
2619			if ((tcp_is_sack(tp) && !tcp_is_fack(tp)) ||
2620			    (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED) ||
2621			    (oldcnt >= packets))
2622				break;
2623
2624			mss = skb_shinfo(skb)->gso_size;
2625			err = tcp_fragment(sk, skb, (packets - oldcnt) * mss, mss);
2626			if (err < 0)
2627				break;
2628			cnt = packets;
2629		}
2630
2631		tcp_skb_mark_lost(tp, skb);
 
2632
2633		if (mark_head)
2634			break;
2635	}
2636	tcp_verify_left_out(tp);
2637}
2638
2639/* Account newly detected lost packet(s) */
2640
2641static void tcp_update_scoreboard(struct sock *sk, int fast_rexmit)
2642{
2643	struct tcp_sock *tp = tcp_sk(sk);
2644
2645	if (tcp_is_reno(tp)) {
2646		tcp_mark_head_lost(sk, 1, 1);
2647	} else if (tcp_is_fack(tp)) {
2648		int lost = tp->fackets_out - tp->reordering;
2649		if (lost <= 0)
2650			lost = 1;
2651		tcp_mark_head_lost(sk, lost, 0);
2652	} else {
2653		int sacked_upto = tp->sacked_out - tp->reordering;
2654		if (sacked_upto >= 0)
2655			tcp_mark_head_lost(sk, sacked_upto, 0);
2656		else if (fast_rexmit)
2657			tcp_mark_head_lost(sk, 1, 1);
2658	}
2659
2660	tcp_timeout_skbs(sk);
2661}
2662
2663/* CWND moderation, preventing bursts due to too big ACKs
2664 * in dubious situations.
2665 */
2666static inline void tcp_moderate_cwnd(struct tcp_sock *tp)
2667{
2668	tp->snd_cwnd = min(tp->snd_cwnd,
2669			   tcp_packets_in_flight(tp) + tcp_max_burst(tp));
2670	tp->snd_cwnd_stamp = tcp_time_stamp;
2671}
2672
2673/* Lower bound on congestion window is slow start threshold
2674 * unless congestion avoidance choice decides to overide it.
2675 */
2676static inline u32 tcp_cwnd_min(const struct sock *sk)
 
2677{
2678	const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;
2679
2680	return ca_ops->min_cwnd ? ca_ops->min_cwnd(sk) : tcp_sk(sk)->snd_ssthresh;
2681}
2682
2683/* Decrease cwnd each second ack. */
2684static void tcp_cwnd_down(struct sock *sk, int flag)
2685{
2686	struct tcp_sock *tp = tcp_sk(sk);
2687	int decr = tp->snd_cwnd_cnt + 1;
2688
2689	if ((flag & (FLAG_ANY_PROGRESS | FLAG_DSACKING_ACK)) ||
2690	    (tcp_is_reno(tp) && !(flag & FLAG_NOT_DUP))) {
2691		tp->snd_cwnd_cnt = decr & 1;
2692		decr >>= 1;
2693
2694		if (decr && tp->snd_cwnd > tcp_cwnd_min(sk))
2695			tp->snd_cwnd -= decr;
2696
2697		tp->snd_cwnd = min(tp->snd_cwnd, tcp_packets_in_flight(tp) + 1);
2698		tp->snd_cwnd_stamp = tcp_time_stamp;
2699	}
2700}
2701
2702/* Nothing was retransmitted or returned timestamp is less
2703 * than timestamp of the first retransmission.
2704 */
2705static inline int tcp_packet_delayed(const struct tcp_sock *tp)
2706{
2707	return !tp->retrans_stamp ||
2708		(tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
2709		 before(tp->rx_opt.rcv_tsecr, tp->retrans_stamp));
2710}
2711
2712/* Undo procedures. */
2713
2714#if FASTRETRANS_DEBUG > 1
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
2715static void DBGUNDO(struct sock *sk, const char *msg)
2716{
 
2717	struct tcp_sock *tp = tcp_sk(sk);
2718	struct inet_sock *inet = inet_sk(sk);
2719
2720	if (sk->sk_family == AF_INET) {
2721		pr_debug("Undo %s %pI4/%u c%u l%u ss%u/%u p%u\n",
2722			 msg,
2723			 &inet->inet_daddr, ntohs(inet->inet_dport),
2724			 tp->snd_cwnd, tcp_left_out(tp),
2725			 tp->snd_ssthresh, tp->prior_ssthresh,
2726			 tp->packets_out);
2727	}
2728#if IS_ENABLED(CONFIG_IPV6)
2729	else if (sk->sk_family == AF_INET6) {
2730		struct ipv6_pinfo *np = inet6_sk(sk);
2731		pr_debug("Undo %s %pI6/%u c%u l%u ss%u/%u p%u\n",
2732			 msg,
2733			 &np->daddr, ntohs(inet->inet_dport),
2734			 tp->snd_cwnd, tcp_left_out(tp),
2735			 tp->snd_ssthresh, tp->prior_ssthresh,
2736			 tp->packets_out);
2737	}
2738#endif
2739}
2740#else
2741#define DBGUNDO(x...) do { } while (0)
2742#endif
 
2743
2744static void tcp_undo_cwr(struct sock *sk, const bool undo_ssthresh)
2745{
2746	struct tcp_sock *tp = tcp_sk(sk);
2747
 
 
 
 
 
 
 
 
 
 
2748	if (tp->prior_ssthresh) {
2749		const struct inet_connection_sock *icsk = inet_csk(sk);
2750
2751		if (icsk->icsk_ca_ops->undo_cwnd)
2752			tp->snd_cwnd = icsk->icsk_ca_ops->undo_cwnd(sk);
2753		else
2754			tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh << 1);
2755
2756		if (undo_ssthresh && tp->prior_ssthresh > tp->snd_ssthresh) {
2757			tp->snd_ssthresh = tp->prior_ssthresh;
2758			TCP_ECN_withdraw_cwr(tp);
2759		}
2760	} else {
2761		tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh);
2762	}
2763	tp->snd_cwnd_stamp = tcp_time_stamp;
 
 
2764}
2765
2766static inline int tcp_may_undo(const struct tcp_sock *tp)
2767{
2768	return tp->undo_marker && (!tp->undo_retrans || tcp_packet_delayed(tp));
2769}
2770
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
2771/* People celebrate: "We love our President!" */
2772static bool tcp_try_undo_recovery(struct sock *sk)
2773{
2774	struct tcp_sock *tp = tcp_sk(sk);
2775
2776	if (tcp_may_undo(tp)) {
2777		int mib_idx;
2778
2779		/* Happy end! We did not retransmit anything
2780		 * or our original transmission succeeded.
2781		 */
2782		DBGUNDO(sk, inet_csk(sk)->icsk_ca_state == TCP_CA_Loss ? "loss" : "retrans");
2783		tcp_undo_cwr(sk, true);
2784		if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss)
2785			mib_idx = LINUX_MIB_TCPLOSSUNDO;
2786		else
2787			mib_idx = LINUX_MIB_TCPFULLUNDO;
2788
2789		NET_INC_STATS_BH(sock_net(sk), mib_idx);
2790		tp->undo_marker = 0;
 
2791	}
2792	if (tp->snd_una == tp->high_seq && tcp_is_reno(tp)) {
2793		/* Hold old state until something *above* high_seq
2794		 * is ACKed. For Reno it is MUST to prevent false
2795		 * fast retransmits (RFC2582). SACK TCP is safe. */
2796		tcp_moderate_cwnd(tp);
2797		return true;
2798	}
2799	tcp_set_ca_state(sk, TCP_CA_Open);
 
2800	return false;
2801}
2802
2803/* Try to undo cwnd reduction, because D-SACKs acked all retransmitted data */
2804static void tcp_try_undo_dsack(struct sock *sk)
2805{
2806	struct tcp_sock *tp = tcp_sk(sk);
2807
2808	if (tp->undo_marker && !tp->undo_retrans) {
 
 
2809		DBGUNDO(sk, "D-SACK");
2810		tcp_undo_cwr(sk, true);
2811		tp->undo_marker = 0;
2812		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPDSACKUNDO);
2813	}
 
2814}
2815
2816/* We can clear retrans_stamp when there are no retransmissions in the
2817 * window. It would seem that it is trivially available for us in
2818 * tp->retrans_out, however, that kind of assumptions doesn't consider
2819 * what will happen if errors occur when sending retransmission for the
2820 * second time. ...It could the that such segment has only
2821 * TCPCB_EVER_RETRANS set at the present time. It seems that checking
2822 * the head skb is enough except for some reneging corner cases that
2823 * are not worth the effort.
2824 *
2825 * Main reason for all this complexity is the fact that connection dying
2826 * time now depends on the validity of the retrans_stamp, in particular,
2827 * that successive retransmissions of a segment must not advance
2828 * retrans_stamp under any conditions.
2829 */
2830static bool tcp_any_retrans_done(const struct sock *sk)
2831{
2832	const struct tcp_sock *tp = tcp_sk(sk);
2833	struct sk_buff *skb;
2834
2835	if (tp->retrans_out)
2836		return true;
2837
2838	skb = tcp_write_queue_head(sk);
2839	if (unlikely(skb && TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS))
 
 
 
 
 
 
 
 
 
 
2840		return true;
2841
2842	return false;
2843}
2844
2845/* Undo during fast recovery after partial ACK. */
2846
2847static int tcp_try_undo_partial(struct sock *sk, int acked)
 
 
 
 
 
 
 
2848{
2849	struct tcp_sock *tp = tcp_sk(sk);
2850	/* Partial ACK arrived. Force Hoe's retransmit. */
2851	int failed = tcp_is_reno(tp) || (tcp_fackets_out(tp) > tp->reordering);
2852
2853	if (tcp_may_undo(tp)) {
2854		/* Plain luck! Hole if filled with delayed
2855		 * packet, rather than with a retransmit.
2856		 */
2857		if (!tcp_any_retrans_done(sk))
2858			tp->retrans_stamp = 0;
 
 
 
2859
2860		tcp_update_reordering(sk, tcp_fackets_out(tp) + acked, 1);
 
 
 
 
2861
2862		DBGUNDO(sk, "Hoe");
2863		tcp_undo_cwr(sk, false);
2864		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPPARTIALUNDO);
2865
2866		/* So... Do not make Hoe's retransmit yet.
2867		 * If the first packet was delayed, the rest
2868		 * ones are most probably delayed as well.
2869		 */
2870		failed = 0;
 
 
 
 
 
 
2871	}
2872	return failed;
 
 
2873}
2874
2875/* Undo during loss recovery after partial ACK. */
2876static bool tcp_try_undo_loss(struct sock *sk)
2877{
2878	struct tcp_sock *tp = tcp_sk(sk);
2879
2880	if (tcp_may_undo(tp)) {
2881		struct sk_buff *skb;
2882		tcp_for_write_queue(skb, sk) {
2883			if (skb == tcp_send_head(sk))
2884				break;
2885			TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
2886		}
2887
2888		tcp_clear_all_retrans_hints(tp);
2889
2890		DBGUNDO(sk, "partial loss");
2891		tp->lost_out = 0;
2892		tcp_undo_cwr(sk, true);
2893		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPLOSSUNDO);
2894		inet_csk(sk)->icsk_retransmits = 0;
2895		tp->undo_marker = 0;
2896		if (tcp_is_sack(tp))
2897			tcp_set_ca_state(sk, TCP_CA_Open);
2898		return true;
2899	}
2900	return false;
2901}
2902
2903static inline void tcp_complete_cwr(struct sock *sk)
 
2904{
2905	struct tcp_sock *tp = tcp_sk(sk);
2906
2907	/* Do not moderate cwnd if it's already undone in cwr or recovery. */
2908	if (tp->undo_marker) {
2909		if (inet_csk(sk)->icsk_ca_state == TCP_CA_CWR) {
2910			tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
2911			tp->snd_cwnd_stamp = tcp_time_stamp;
2912		} else if (tp->snd_ssthresh < TCP_INFINITE_SSTHRESH) {
2913			/* PRR algorithm. */
2914			tp->snd_cwnd = tp->snd_ssthresh;
2915			tp->snd_cwnd_stamp = tcp_time_stamp;
2916		}
2917	}
2918	tcp_ca_event(sk, CA_EVENT_COMPLETE_CWR);
2919}
 
2920
2921static void tcp_try_keep_open(struct sock *sk)
2922{
2923	struct tcp_sock *tp = tcp_sk(sk);
2924	int state = TCP_CA_Open;
2925
2926	if (tcp_left_out(tp) || tcp_any_retrans_done(sk))
2927		state = TCP_CA_Disorder;
2928
2929	if (inet_csk(sk)->icsk_ca_state != state) {
2930		tcp_set_ca_state(sk, state);
2931		tp->high_seq = tp->snd_nxt;
2932	}
2933}
2934
2935static void tcp_try_to_open(struct sock *sk, int flag)
2936{
2937	struct tcp_sock *tp = tcp_sk(sk);
2938
2939	tcp_verify_left_out(tp);
2940
2941	if (!tp->frto_counter && !tcp_any_retrans_done(sk))
2942		tp->retrans_stamp = 0;
2943
2944	if (flag & FLAG_ECE)
2945		tcp_enter_cwr(sk, 1);
2946
2947	if (inet_csk(sk)->icsk_ca_state != TCP_CA_CWR) {
2948		tcp_try_keep_open(sk);
2949		if (inet_csk(sk)->icsk_ca_state != TCP_CA_Open)
2950			tcp_moderate_cwnd(tp);
2951	} else {
2952		tcp_cwnd_down(sk, flag);
2953	}
2954}
2955
2956static void tcp_mtup_probe_failed(struct sock *sk)
2957{
2958	struct inet_connection_sock *icsk = inet_csk(sk);
2959
2960	icsk->icsk_mtup.search_high = icsk->icsk_mtup.probe_size - 1;
2961	icsk->icsk_mtup.probe_size = 0;
 
2962}
2963
2964static void tcp_mtup_probe_success(struct sock *sk)
2965{
2966	struct tcp_sock *tp = tcp_sk(sk);
2967	struct inet_connection_sock *icsk = inet_csk(sk);
 
2968
2969	/* FIXME: breaks with very large cwnd */
2970	tp->prior_ssthresh = tcp_current_ssthresh(sk);
2971	tp->snd_cwnd = tp->snd_cwnd *
2972		       tcp_mss_to_mtu(sk, tp->mss_cache) /
2973		       icsk->icsk_mtup.probe_size;
 
 
 
2974	tp->snd_cwnd_cnt = 0;
2975	tp->snd_cwnd_stamp = tcp_time_stamp;
2976	tp->snd_ssthresh = tcp_current_ssthresh(sk);
2977
2978	icsk->icsk_mtup.search_low = icsk->icsk_mtup.probe_size;
2979	icsk->icsk_mtup.probe_size = 0;
2980	tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
 
2981}
2982
2983/* Do a simple retransmit without using the backoff mechanisms in
2984 * tcp_timer. This is used for path mtu discovery.
2985 * The socket is already locked here.
2986 */
2987void tcp_simple_retransmit(struct sock *sk)
2988{
2989	const struct inet_connection_sock *icsk = inet_csk(sk);
2990	struct tcp_sock *tp = tcp_sk(sk);
2991	struct sk_buff *skb;
2992	unsigned int mss = tcp_current_mss(sk);
2993	u32 prior_lost = tp->lost_out;
2994
2995	tcp_for_write_queue(skb, sk) {
2996		if (skb == tcp_send_head(sk))
2997			break;
2998		if (tcp_skb_seglen(skb) > mss &&
2999		    !(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) {
3000			if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
3001				TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
3002				tp->retrans_out -= tcp_skb_pcount(skb);
3003			}
3004			tcp_skb_mark_lost_uncond_verify(tp, skb);
3005		}
 
 
 
 
 
 
 
3006	}
3007
3008	tcp_clear_retrans_hints_partial(tp);
3009
3010	if (prior_lost == tp->lost_out)
3011		return;
3012
3013	if (tcp_is_reno(tp))
3014		tcp_limit_reno_sacked(tp);
3015
3016	tcp_verify_left_out(tp);
3017
3018	/* Don't muck with the congestion window here.
3019	 * Reason is that we do not increase amount of _data_
3020	 * in network, but units changed and effective
3021	 * cwnd/ssthresh really reduced now.
3022	 */
3023	if (icsk->icsk_ca_state != TCP_CA_Loss) {
3024		tp->high_seq = tp->snd_nxt;
3025		tp->snd_ssthresh = tcp_current_ssthresh(sk);
3026		tp->prior_ssthresh = 0;
3027		tp->undo_marker = 0;
3028		tcp_set_ca_state(sk, TCP_CA_Loss);
3029	}
3030	tcp_xmit_retransmit_queue(sk);
3031}
3032EXPORT_SYMBOL(tcp_simple_retransmit);
3033
3034/* This function implements the PRR algorithm, specifcally the PRR-SSRB
3035 * (proportional rate reduction with slow start reduction bound) as described in
3036 * http://www.ietf.org/id/draft-mathis-tcpm-proportional-rate-reduction-01.txt.
3037 * It computes the number of packets to send (sndcnt) based on packets newly
3038 * delivered:
3039 *   1) If the packets in flight is larger than ssthresh, PRR spreads the
3040 *	cwnd reductions across a full RTT.
3041 *   2) If packets in flight is lower than ssthresh (such as due to excess
3042 *	losses and/or application stalls), do not perform any further cwnd
3043 *	reductions, but instead slow start up to ssthresh.
3044 */
3045static void tcp_update_cwnd_in_recovery(struct sock *sk, int newly_acked_sacked,
3046					int fast_rexmit, int flag)
3047{
3048	struct tcp_sock *tp = tcp_sk(sk);
3049	int sndcnt = 0;
3050	int delta = tp->snd_ssthresh - tcp_packets_in_flight(tp);
3051
3052	if (tcp_packets_in_flight(tp) > tp->snd_ssthresh) {
3053		u64 dividend = (u64)tp->snd_ssthresh * tp->prr_delivered +
3054			       tp->prior_cwnd - 1;
3055		sndcnt = div_u64(dividend, tp->prior_cwnd) - tp->prr_out;
3056	} else {
3057		sndcnt = min_t(int, delta,
3058			       max_t(int, tp->prr_delivered - tp->prr_out,
3059				     newly_acked_sacked) + 1);
3060	}
3061
3062	sndcnt = max(sndcnt, (fast_rexmit ? 1 : 0));
3063	tp->snd_cwnd = tcp_packets_in_flight(tp) + sndcnt;
3064}
3065
3066static void tcp_enter_recovery(struct sock *sk, bool ece_ack)
3067{
3068	struct tcp_sock *tp = tcp_sk(sk);
3069	int mib_idx;
3070
3071	if (tcp_is_reno(tp))
3072		mib_idx = LINUX_MIB_TCPRENORECOVERY;
3073	else
3074		mib_idx = LINUX_MIB_TCPSACKRECOVERY;
3075
3076	NET_INC_STATS_BH(sock_net(sk), mib_idx);
3077
3078	tp->high_seq = tp->snd_nxt;
3079	tp->prior_ssthresh = 0;
3080	tp->undo_marker = tp->snd_una;
3081	tp->undo_retrans = tp->retrans_out;
3082
3083	if (inet_csk(sk)->icsk_ca_state < TCP_CA_CWR) {
3084		if (!ece_ack)
3085			tp->prior_ssthresh = tcp_current_ssthresh(sk);
3086		tp->snd_ssthresh = inet_csk(sk)->icsk_ca_ops->ssthresh(sk);
3087		TCP_ECN_queue_cwr(tp);
3088	}
3089
3090	tp->bytes_acked = 0;
3091	tp->snd_cwnd_cnt = 0;
3092	tp->prior_cwnd = tp->snd_cwnd;
3093	tp->prr_delivered = 0;
3094	tp->prr_out = 0;
3095	tcp_set_ca_state(sk, TCP_CA_Recovery);
3096}
3097
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
3098/* Process an event, which can update packets-in-flight not trivially.
3099 * Main goal of this function is to calculate new estimate for left_out,
3100 * taking into account both packets sitting in receiver's buffer and
3101 * packets lost by network.
3102 *
3103 * Besides that it does CWND reduction, when packet loss is detected
3104 * and changes state of machine.
 
3105 *
3106 * It does _not_ decide what to send, it is made in function
3107 * tcp_xmit_retransmit_queue().
3108 */
3109static void tcp_fastretrans_alert(struct sock *sk, int pkts_acked,
3110				  int prior_sacked, bool is_dupack,
3111				  int flag)
3112{
3113	struct inet_connection_sock *icsk = inet_csk(sk);
3114	struct tcp_sock *tp = tcp_sk(sk);
3115	int do_lost = is_dupack || ((flag & FLAG_DATA_SACKED) &&
3116				    (tcp_fackets_out(tp) > tp->reordering));
3117	int newly_acked_sacked = 0;
3118	int fast_rexmit = 0;
3119
3120	if (WARN_ON(!tp->packets_out && tp->sacked_out))
3121		tp->sacked_out = 0;
3122	if (WARN_ON(!tp->sacked_out && tp->fackets_out))
3123		tp->fackets_out = 0;
3124
3125	/* Now state machine starts.
3126	 * A. ECE, hence prohibit cwnd undoing, the reduction is required. */
3127	if (flag & FLAG_ECE)
3128		tp->prior_ssthresh = 0;
3129
3130	/* B. In all the states check for reneging SACKs. */
3131	if (tcp_check_sack_reneging(sk, flag))
3132		return;
3133
3134	/* C. Check consistency of the current state. */
3135	tcp_verify_left_out(tp);
3136
3137	/* D. Check state exit conditions. State can be terminated
3138	 *    when high_seq is ACKed. */
3139	if (icsk->icsk_ca_state == TCP_CA_Open) {
3140		WARN_ON(tp->retrans_out != 0);
3141		tp->retrans_stamp = 0;
3142	} else if (!before(tp->snd_una, tp->high_seq)) {
3143		switch (icsk->icsk_ca_state) {
3144		case TCP_CA_Loss:
3145			icsk->icsk_retransmits = 0;
3146			if (tcp_try_undo_recovery(sk))
3147				return;
3148			break;
3149
3150		case TCP_CA_CWR:
3151			/* CWR is to be held something *above* high_seq
3152			 * is ACKed for CWR bit to reach receiver. */
3153			if (tp->snd_una != tp->high_seq) {
3154				tcp_complete_cwr(sk);
3155				tcp_set_ca_state(sk, TCP_CA_Open);
3156			}
3157			break;
3158
3159		case TCP_CA_Recovery:
3160			if (tcp_is_reno(tp))
3161				tcp_reset_reno_sack(tp);
3162			if (tcp_try_undo_recovery(sk))
3163				return;
3164			tcp_complete_cwr(sk);
3165			break;
3166		}
3167	}
3168
3169	/* E. Process state. */
3170	switch (icsk->icsk_ca_state) {
3171	case TCP_CA_Recovery:
3172		if (!(flag & FLAG_SND_UNA_ADVANCED)) {
3173			if (tcp_is_reno(tp) && is_dupack)
3174				tcp_add_reno_sack(sk);
3175		} else
3176			do_lost = tcp_try_undo_partial(sk, pkts_acked);
3177		newly_acked_sacked = pkts_acked + tp->sacked_out - prior_sacked;
3178		break;
3179	case TCP_CA_Loss:
3180		if (flag & FLAG_DATA_ACKED)
3181			icsk->icsk_retransmits = 0;
3182		if (tcp_is_reno(tp) && flag & FLAG_SND_UNA_ADVANCED)
3183			tcp_reset_reno_sack(tp);
3184		if (!tcp_try_undo_loss(sk)) {
3185			tcp_moderate_cwnd(tp);
3186			tcp_xmit_retransmit_queue(sk);
3187			return;
 
 
 
 
 
 
 
 
 
 
 
 
3188		}
3189		if (icsk->icsk_ca_state != TCP_CA_Open)
 
 
 
 
 
3190			return;
3191		/* Loss is undone; fall through to processing in Open state. */
 
3192	default:
3193		if (tcp_is_reno(tp)) {
3194			if (flag & FLAG_SND_UNA_ADVANCED)
3195				tcp_reset_reno_sack(tp);
3196			if (is_dupack)
3197				tcp_add_reno_sack(sk);
3198		}
3199		newly_acked_sacked = pkts_acked + tp->sacked_out - prior_sacked;
3200
3201		if (icsk->icsk_ca_state <= TCP_CA_Disorder)
3202			tcp_try_undo_dsack(sk);
3203
 
3204		if (!tcp_time_to_recover(sk, flag)) {
3205			tcp_try_to_open(sk, flag);
3206			return;
3207		}
3208
3209		/* MTU probe failure: don't reduce cwnd */
3210		if (icsk->icsk_ca_state < TCP_CA_CWR &&
3211		    icsk->icsk_mtup.probe_size &&
3212		    tp->snd_una == tp->mtu_probe.probe_seq_start) {
3213			tcp_mtup_probe_failed(sk);
3214			/* Restores the reduction we did in tcp_mtup_probe() */
3215			tp->snd_cwnd++;
3216			tcp_simple_retransmit(sk);
3217			return;
3218		}
3219
3220		/* Otherwise enter Recovery state */
3221		tcp_enter_recovery(sk, (flag & FLAG_ECE));
3222		fast_rexmit = 1;
3223	}
3224
3225	if (do_lost || (tcp_is_fack(tp) && tcp_head_timedout(sk)))
3226		tcp_update_scoreboard(sk, fast_rexmit);
3227	tp->prr_delivered += newly_acked_sacked;
3228	tcp_update_cwnd_in_recovery(sk, newly_acked_sacked, fast_rexmit, flag);
3229	tcp_xmit_retransmit_queue(sk);
3230}
3231
3232void tcp_valid_rtt_meas(struct sock *sk, u32 seq_rtt)
3233{
3234	tcp_rtt_estimator(sk, seq_rtt);
3235	tcp_set_rto(sk);
3236	inet_csk(sk)->icsk_backoff = 0;
 
 
 
 
 
 
 
 
 
3237}
3238EXPORT_SYMBOL(tcp_valid_rtt_meas);
3239
3240/* Read draft-ietf-tcplw-high-performance before mucking
3241 * with this code. (Supersedes RFC1323)
3242 */
3243static void tcp_ack_saw_tstamp(struct sock *sk, int flag)
3244{
 
 
 
 
 
 
 
 
 
 
3245	/* RTTM Rule: A TSecr value received in a segment is used to
3246	 * update the averaged RTT measurement only if the segment
3247	 * acknowledges some new data, i.e., only if it advances the
3248	 * left edge of the send window.
3249	 *
3250	 * See draft-ietf-tcplw-high-performance-00, section 3.3.
3251	 * 1998/04/10 Andrey V. Savochkin <saw@msu.ru>
3252	 *
3253	 * Changed: reset backoff as soon as we see the first valid sample.
3254	 * If we do not, we get strongly overestimated rto. With timestamps
3255	 * samples are accepted even from very old segments: f.e., when rtt=1
3256	 * increases to 8, we retransmit 5 times and after 8 seconds delayed
3257	 * answer arrives rto becomes 120 seconds! If at least one of segments
3258	 * in window is lost... Voila.	 			--ANK (010210)
3259	 */
3260	struct tcp_sock *tp = tcp_sk(sk);
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
3261
3262	tcp_valid_rtt_meas(sk, tcp_time_stamp - tp->rx_opt.rcv_tsecr);
 
 
3263}
3264
3265static void tcp_ack_no_tstamp(struct sock *sk, u32 seq_rtt, int flag)
 
3266{
3267	/* We don't have a timestamp. Can only use
3268	 * packets that are not retransmitted to determine
3269	 * rtt estimates. Also, we must not reset the
3270	 * backoff for rto until we get a non-retransmitted
3271	 * packet. This allows us to deal with a situation
3272	 * where the network delay has increased suddenly.
3273	 * I.e. Karn's algorithm. (SIGCOMM '87, p5.)
3274	 */
3275
3276	if (flag & FLAG_RETRANS_DATA_ACKED)
3277		return;
3278
3279	tcp_valid_rtt_meas(sk, seq_rtt);
3280}
3281
3282static inline void tcp_ack_update_rtt(struct sock *sk, const int flag,
3283				      const s32 seq_rtt)
3284{
3285	const struct tcp_sock *tp = tcp_sk(sk);
3286	/* Note that peer MAY send zero echo. In this case it is ignored. (rfc1323) */
3287	if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
3288		tcp_ack_saw_tstamp(sk, flag);
3289	else if (seq_rtt >= 0)
3290		tcp_ack_no_tstamp(sk, seq_rtt, flag);
3291}
3292
3293static void tcp_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
3294{
3295	const struct inet_connection_sock *icsk = inet_csk(sk);
3296	icsk->icsk_ca_ops->cong_avoid(sk, ack, in_flight);
3297	tcp_sk(sk)->snd_cwnd_stamp = tcp_time_stamp;
 
3298}
3299
3300/* Restart timer after forward progress on connection.
3301 * RFC2988 recommends to restart timer to now+rto.
3302 */
3303void tcp_rearm_rto(struct sock *sk)
3304{
 
3305	struct tcp_sock *tp = tcp_sk(sk);
3306
 
 
 
 
 
 
3307	if (!tp->packets_out) {
3308		inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS);
3309	} else {
3310		u32 rto = inet_csk(sk)->icsk_rto;
3311		/* Offset the time elapsed after installing regular RTO */
3312		if (tp->early_retrans_delayed) {
3313			struct sk_buff *skb = tcp_write_queue_head(sk);
3314			const u32 rto_time_stamp = TCP_SKB_CB(skb)->when + rto;
3315			s32 delta = (s32)(rto_time_stamp - tcp_time_stamp);
3316			/* delta may not be positive if the socket is locked
3317			 * when the delayed ER timer fires and is rescheduled.
3318			 */
3319			if (delta > 0)
3320				rto = delta;
3321		}
3322		inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, rto,
3323					  TCP_RTO_MAX);
3324	}
3325	tp->early_retrans_delayed = 0;
3326}
3327
3328/* This function is called when the delayed ER timer fires. TCP enters
3329 * fast recovery and performs fast-retransmit.
3330 */
3331void tcp_resume_early_retransmit(struct sock *sk)
3332{
3333	struct tcp_sock *tp = tcp_sk(sk);
3334
3335	tcp_rearm_rto(sk);
3336
3337	/* Stop if ER is disabled after the delayed ER timer is scheduled */
3338	if (!tp->do_early_retrans)
3339		return;
3340
3341	tcp_enter_recovery(sk, false);
3342	tcp_update_scoreboard(sk, 1);
3343	tcp_xmit_retransmit_queue(sk);
3344}
3345
3346/* If we get here, the whole TSO packet has not been acked. */
3347static u32 tcp_tso_acked(struct sock *sk, struct sk_buff *skb)
3348{
3349	struct tcp_sock *tp = tcp_sk(sk);
3350	u32 packets_acked;
3351
3352	BUG_ON(!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una));
3353
3354	packets_acked = tcp_skb_pcount(skb);
3355	if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
3356		return 0;
3357	packets_acked -= tcp_skb_pcount(skb);
3358
3359	if (packets_acked) {
3360		BUG_ON(tcp_skb_pcount(skb) == 0);
3361		BUG_ON(!before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq));
3362	}
3363
3364	return packets_acked;
3365}
3366
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
3367/* Remove acknowledged frames from the retransmission queue. If our packet
3368 * is before the ack sequence we can discard it as it's confirmed to have
3369 * arrived at the other end.
3370 */
3371static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
3372			       u32 prior_snd_una)
 
3373{
3374	struct tcp_sock *tp = tcp_sk(sk);
3375	const struct inet_connection_sock *icsk = inet_csk(sk);
3376	struct sk_buff *skb;
3377	u32 now = tcp_time_stamp;
3378	int fully_acked = true;
3379	int flag = 0;
3380	u32 pkts_acked = 0;
3381	u32 reord = tp->packets_out;
3382	u32 prior_sacked = tp->sacked_out;
3383	s32 seq_rtt = -1;
3384	s32 ca_seq_rtt = -1;
3385	ktime_t last_ackt = net_invalid_timestamp();
 
 
 
 
 
 
 
 
3386
3387	while ((skb = tcp_write_queue_head(sk)) && skb != tcp_send_head(sk)) {
3388		struct tcp_skb_cb *scb = TCP_SKB_CB(skb);
3389		u32 acked_pcount;
3390		u8 sacked = scb->sacked;
 
3391
3392		/* Determine how many packets and what bytes were acked, tso and else */
3393		if (after(scb->end_seq, tp->snd_una)) {
3394			if (tcp_skb_pcount(skb) == 1 ||
3395			    !after(tp->snd_una, scb->seq))
3396				break;
3397
3398			acked_pcount = tcp_tso_acked(sk, skb);
3399			if (!acked_pcount)
3400				break;
3401
3402			fully_acked = false;
3403		} else {
3404			acked_pcount = tcp_skb_pcount(skb);
3405		}
3406
3407		if (sacked & TCPCB_RETRANS) {
3408			if (sacked & TCPCB_SACKED_RETRANS)
3409				tp->retrans_out -= acked_pcount;
3410			flag |= FLAG_RETRANS_DATA_ACKED;
3411			ca_seq_rtt = -1;
3412			seq_rtt = -1;
3413			if ((flag & FLAG_DATA_ACKED) || (acked_pcount > 1))
3414				flag |= FLAG_NONHEAD_RETRANS_ACKED;
3415		} else {
3416			ca_seq_rtt = now - scb->when;
3417			last_ackt = skb->tstamp;
3418			if (seq_rtt < 0) {
3419				seq_rtt = ca_seq_rtt;
3420			}
3421			if (!(sacked & TCPCB_SACKED_ACKED))
3422				reord = min(pkts_acked, reord);
3423		}
3424
3425		if (sacked & TCPCB_SACKED_ACKED)
3426			tp->sacked_out -= acked_pcount;
 
 
 
 
 
 
3427		if (sacked & TCPCB_LOST)
3428			tp->lost_out -= acked_pcount;
3429
3430		tp->packets_out -= acked_pcount;
3431		pkts_acked += acked_pcount;
 
3432
3433		/* Initial outgoing SYN's get put onto the write_queue
3434		 * just like anything else we transmit.  It is not
3435		 * true data, and if we misinform our callers that
3436		 * this ACK acks real data, we will erroneously exit
3437		 * connection startup slow start one packet too
3438		 * quickly.  This is severely frowned upon behavior.
3439		 */
3440		if (!(scb->tcp_flags & TCPHDR_SYN)) {
3441			flag |= FLAG_DATA_ACKED;
3442		} else {
3443			flag |= FLAG_SYN_ACKED;
3444			tp->retrans_stamp = 0;
3445		}
3446
3447		if (!fully_acked)
3448			break;
3449
3450		tcp_unlink_write_queue(skb, sk);
3451		sk_wmem_free_skb(sk, skb);
3452		tp->scoreboard_skb_hint = NULL;
3453		if (skb == tp->retransmit_skb_hint)
3454			tp->retransmit_skb_hint = NULL;
3455		if (skb == tp->lost_skb_hint)
3456			tp->lost_skb_hint = NULL;
 
 
3457	}
3458
 
 
 
3459	if (likely(between(tp->snd_up, prior_snd_una, tp->snd_una)))
3460		tp->snd_up = tp->snd_una;
3461
3462	if (skb && (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
3463		flag |= FLAG_SACK_RENEGING;
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
3464
3465	if (flag & FLAG_ACKED) {
3466		const struct tcp_congestion_ops *ca_ops
3467			= inet_csk(sk)->icsk_ca_ops;
3468
3469		if (unlikely(icsk->icsk_mtup.probe_size &&
3470			     !after(tp->mtu_probe.probe_seq_end, tp->snd_una))) {
3471			tcp_mtup_probe_success(sk);
3472		}
3473
3474		tcp_ack_update_rtt(sk, flag, seq_rtt);
3475		tcp_rearm_rto(sk);
3476
3477		if (tcp_is_reno(tp)) {
3478			tcp_remove_reno_sacks(sk, pkts_acked);
 
 
 
 
 
 
 
 
 
3479		} else {
3480			int delta;
3481
3482			/* Non-retransmitted hole got filled? That's reordering */
3483			if (reord < prior_fackets)
3484				tcp_update_reordering(sk, tp->fackets_out - reord, 0);
3485
3486			delta = tcp_is_fack(tp) ? pkts_acked :
3487						  prior_sacked - tp->sacked_out;
3488			tp->lost_cnt_hint -= min(tp->lost_cnt_hint, delta);
3489		}
3490
3491		tp->fackets_out -= min(pkts_acked, tp->fackets_out);
3492
3493		if (ca_ops->pkts_acked) {
3494			s32 rtt_us = -1;
3495
3496			/* Is the ACK triggering packet unambiguous? */
3497			if (!(flag & FLAG_RETRANS_DATA_ACKED)) {
3498				/* High resolution needed and available? */
3499				if (ca_ops->flags & TCP_CONG_RTT_STAMP &&
3500				    !ktime_equal(last_ackt,
3501						 net_invalid_timestamp()))
3502					rtt_us = ktime_us_delta(ktime_get_real(),
3503								last_ackt);
3504				else if (ca_seq_rtt >= 0)
3505					rtt_us = jiffies_to_usecs(ca_seq_rtt);
3506			}
3507
3508			ca_ops->pkts_acked(sk, pkts_acked, rtt_us);
3509		}
3510	}
3511
3512#if FASTRETRANS_DEBUG > 0
3513	WARN_ON((int)tp->sacked_out < 0);
3514	WARN_ON((int)tp->lost_out < 0);
3515	WARN_ON((int)tp->retrans_out < 0);
3516	if (!tp->packets_out && tcp_is_sack(tp)) {
3517		icsk = inet_csk(sk);
3518		if (tp->lost_out) {
3519			pr_debug("Leak l=%u %d\n",
3520				 tp->lost_out, icsk->icsk_ca_state);
3521			tp->lost_out = 0;
3522		}
3523		if (tp->sacked_out) {
3524			pr_debug("Leak s=%u %d\n",
3525				 tp->sacked_out, icsk->icsk_ca_state);
3526			tp->sacked_out = 0;
3527		}
3528		if (tp->retrans_out) {
3529			pr_debug("Leak r=%u %d\n",
3530				 tp->retrans_out, icsk->icsk_ca_state);
3531			tp->retrans_out = 0;
3532		}
3533	}
3534#endif
3535	return flag;
3536}
3537
3538static void tcp_ack_probe(struct sock *sk)
3539{
3540	const struct tcp_sock *tp = tcp_sk(sk);
3541	struct inet_connection_sock *icsk = inet_csk(sk);
 
 
3542
3543	/* Was it a usable window open? */
3544
3545	if (!after(TCP_SKB_CB(tcp_send_head(sk))->end_seq, tcp_wnd_end(tp))) {
 
3546		icsk->icsk_backoff = 0;
 
3547		inet_csk_clear_xmit_timer(sk, ICSK_TIME_PROBE0);
3548		/* Socket must be waked up by subsequent tcp_data_snd_check().
3549		 * This function is not for random using!
3550		 */
3551	} else {
3552		inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
3553					  min(icsk->icsk_rto << icsk->icsk_backoff, TCP_RTO_MAX),
3554					  TCP_RTO_MAX);
 
3555	}
3556}
3557
3558static inline int tcp_ack_is_dubious(const struct sock *sk, const int flag)
3559{
3560	return !(flag & FLAG_NOT_DUP) || (flag & FLAG_CA_ALERT) ||
3561		inet_csk(sk)->icsk_ca_state != TCP_CA_Open;
3562}
3563
3564static inline int tcp_may_raise_cwnd(const struct sock *sk, const int flag)
 
3565{
3566	const struct tcp_sock *tp = tcp_sk(sk);
3567	return (!(flag & FLAG_ECE) || tp->snd_cwnd < tp->snd_ssthresh) &&
3568		!((1 << inet_csk(sk)->icsk_ca_state) & (TCPF_CA_Recovery | TCPF_CA_CWR));
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
3569}
3570
3571/* Check that window update is acceptable.
3572 * The function assumes that snd_una<=ack<=snd_next.
3573 */
3574static inline int tcp_may_update_window(const struct tcp_sock *tp,
3575					const u32 ack, const u32 ack_seq,
3576					const u32 nwin)
3577{
3578	return	after(ack, tp->snd_una) ||
3579		after(ack_seq, tp->snd_wl1) ||
3580		(ack_seq == tp->snd_wl1 && nwin > tp->snd_wnd);
3581}
3582
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
3583/* Update our send window.
3584 *
3585 * Window update algorithm, described in RFC793/RFC1122 (used in linux-2.2
3586 * and in FreeBSD. NetBSD's one is even worse.) is wrong.
3587 */
3588static int tcp_ack_update_window(struct sock *sk, const struct sk_buff *skb, u32 ack,
3589				 u32 ack_seq)
3590{
3591	struct tcp_sock *tp = tcp_sk(sk);
3592	int flag = 0;
3593	u32 nwin = ntohs(tcp_hdr(skb)->window);
3594
3595	if (likely(!tcp_hdr(skb)->syn))
3596		nwin <<= tp->rx_opt.snd_wscale;
3597
3598	if (tcp_may_update_window(tp, ack, ack_seq, nwin)) {
3599		flag |= FLAG_WIN_UPDATE;
3600		tcp_update_wl(tp, ack_seq);
3601
3602		if (tp->snd_wnd != nwin) {
3603			tp->snd_wnd = nwin;
3604
3605			/* Note, it is the only place, where
3606			 * fast path is recovered for sending TCP.
3607			 */
3608			tp->pred_flags = 0;
3609			tcp_fast_path_check(sk);
3610
 
 
 
3611			if (nwin > tp->max_window) {
3612				tp->max_window = nwin;
3613				tcp_sync_mss(sk, inet_csk(sk)->icsk_pmtu_cookie);
3614			}
3615		}
3616	}
3617
3618	tp->snd_una = ack;
3619
3620	return flag;
3621}
3622
3623/* A very conservative spurious RTO response algorithm: reduce cwnd and
3624 * continue in congestion avoidance.
3625 */
3626static void tcp_conservative_spur_to_response(struct tcp_sock *tp)
3627{
3628	tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
3629	tp->snd_cwnd_cnt = 0;
3630	tp->bytes_acked = 0;
3631	TCP_ECN_queue_cwr(tp);
3632	tcp_moderate_cwnd(tp);
 
 
 
 
 
 
 
 
3633}
3634
3635/* A conservative spurious RTO response algorithm: reduce cwnd using
3636 * rate halving and continue in congestion avoidance.
 
 
 
 
3637 */
3638static void tcp_ratehalving_spur_to_response(struct sock *sk)
 
3639{
3640	tcp_enter_cwr(sk, 0);
3641}
 
 
3642
3643static void tcp_undo_spur_to_response(struct sock *sk, int flag)
3644{
3645	if (flag & FLAG_ECE)
3646		tcp_ratehalving_spur_to_response(sk);
3647	else
3648		tcp_undo_cwr(sk, true);
3649}
3650
3651/* F-RTO spurious RTO detection algorithm (RFC4138)
3652 *
3653 * F-RTO affects during two new ACKs following RTO (well, almost, see inline
3654 * comments). State (ACK number) is kept in frto_counter. When ACK advances
3655 * window (but not to or beyond highest sequence sent before RTO):
3656 *   On First ACK,  send two new segments out.
3657 *   On Second ACK, RTO was likely spurious. Do spurious response (response
3658 *                  algorithm is not part of the F-RTO detection algorithm
3659 *                  given in RFC4138 but can be selected separately).
3660 * Otherwise (basically on duplicate ACK), RTO was (likely) caused by a loss
3661 * and TCP falls back to conventional RTO recovery. F-RTO allows overriding
3662 * of Nagle, this is done using frto_counter states 2 and 3, when a new data
3663 * segment of any size sent during F-RTO, state 2 is upgraded to 3.
3664 *
3665 * Rationale: if the RTO was spurious, new ACKs should arrive from the
3666 * original window even after we transmit two new data segments.
3667 *
3668 * SACK version:
3669 *   on first step, wait until first cumulative ACK arrives, then move to
3670 *   the second step. In second step, the next ACK decides.
3671 *
3672 * F-RTO is implemented (mainly) in four functions:
3673 *   - tcp_use_frto() is used to determine if TCP is can use F-RTO
3674 *   - tcp_enter_frto() prepares TCP state on RTO if F-RTO is used, it is
3675 *     called when tcp_use_frto() showed green light
3676 *   - tcp_process_frto() handles incoming ACKs during F-RTO algorithm
3677 *   - tcp_enter_frto_loss() is called if there is not enough evidence
3678 *     to prove that the RTO is indeed spurious. It transfers the control
3679 *     from F-RTO to the conventional RTO recovery
3680 */
3681static bool tcp_process_frto(struct sock *sk, int flag)
3682{
3683	struct tcp_sock *tp = tcp_sk(sk);
 
 
3684
3685	tcp_verify_left_out(tp);
 
 
 
 
3686
3687	/* Duplicate the behavior from Loss state (fastretrans_alert) */
3688	if (flag & FLAG_DATA_ACKED)
3689		inet_csk(sk)->icsk_retransmits = 0;
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
3690
3691	if ((flag & FLAG_NONHEAD_RETRANS_ACKED) ||
3692	    ((tp->frto_counter >= 2) && (flag & FLAG_RETRANS_DATA_ACKED)))
3693		tp->undo_marker = 0;
 
 
3694
3695	if (!before(tp->snd_una, tp->frto_highmark)) {
3696		tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 2 : 3), flag);
3697		return true;
 
 
 
 
 
 
 
 
 
3698	}
 
 
 
 
 
 
 
 
 
 
 
3699
3700	if (!tcp_is_sackfrto(tp)) {
3701		/* RFC4138 shortcoming in step 2; should also have case c):
3702		 * ACK isn't duplicate nor advances window, e.g., opposite dir
3703		 * data, winupdate
 
 
 
 
 
3704		 */
3705		if (!(flag & FLAG_ANY_PROGRESS) && (flag & FLAG_NOT_DUP))
3706			return true;
 
 
 
 
 
 
 
 
 
 
3707
3708		if (!(flag & FLAG_DATA_ACKED)) {
3709			tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 0 : 3),
3710					    flag);
3711			return true;
3712		}
3713	} else {
3714		if (!(flag & FLAG_DATA_ACKED) && (tp->frto_counter == 1)) {
3715			/* Prevent sending of new data. */
3716			tp->snd_cwnd = min(tp->snd_cwnd,
3717					   tcp_packets_in_flight(tp));
3718			return true;
3719		}
3720
3721		if ((tp->frto_counter >= 2) &&
3722		    (!(flag & FLAG_FORWARD_PROGRESS) ||
3723		     ((flag & FLAG_DATA_SACKED) &&
3724		      !(flag & FLAG_ONLY_ORIG_SACKED)))) {
3725			/* RFC4138 shortcoming (see comment above) */
3726			if (!(flag & FLAG_FORWARD_PROGRESS) &&
3727			    (flag & FLAG_NOT_DUP))
3728				return true;
3729
3730			tcp_enter_frto_loss(sk, 3, flag);
3731			return true;
3732		}
 
 
 
 
 
 
 
 
 
 
 
 
 
 
3733	}
 
 
3734
3735	if (tp->frto_counter == 1) {
3736		/* tcp_may_send_now needs to see updated state */
3737		tp->snd_cwnd = tcp_packets_in_flight(tp) + 2;
3738		tp->frto_counter = 2;
 
 
3739
3740		if (!tcp_may_send_now(sk))
3741			tcp_enter_frto_loss(sk, 2, flag);
 
 
3742
3743		return true;
3744	} else {
3745		switch (sysctl_tcp_frto_response) {
3746		case 2:
3747			tcp_undo_spur_to_response(sk, flag);
3748			break;
3749		case 1:
3750			tcp_conservative_spur_to_response(tp);
3751			break;
3752		default:
3753			tcp_ratehalving_spur_to_response(sk);
3754			break;
3755		}
3756		tp->frto_counter = 0;
3757		tp->undo_marker = 0;
3758		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSPURIOUSRTOS);
3759	}
3760	return false;
3761}
3762
3763/* This routine deals with incoming acks, but not outgoing ones. */
3764static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
3765{
3766	struct inet_connection_sock *icsk = inet_csk(sk);
3767	struct tcp_sock *tp = tcp_sk(sk);
 
 
3768	u32 prior_snd_una = tp->snd_una;
 
3769	u32 ack_seq = TCP_SKB_CB(skb)->seq;
3770	u32 ack = TCP_SKB_CB(skb)->ack_seq;
3771	bool is_dupack = false;
3772	u32 prior_in_flight;
3773	u32 prior_fackets;
3774	int prior_packets;
3775	int prior_sacked = tp->sacked_out;
3776	int pkts_acked = 0;
3777	bool frto_cwnd = false;
 
 
 
 
 
 
3778
3779	/* If the ack is older than previous acks
3780	 * then we can probably ignore it.
3781	 */
3782	if (before(ack, prior_snd_una))
 
 
 
 
 
 
3783		goto old_ack;
 
3784
3785	/* If the ack includes data we haven't sent yet, discard
3786	 * this segment (RFC793 Section 3.9).
3787	 */
3788	if (after(ack, tp->snd_nxt))
3789		goto invalid_ack;
3790
3791	if (tp->early_retrans_delayed)
3792		tcp_rearm_rto(sk);
3793
3794	if (after(ack, prior_snd_una))
3795		flag |= FLAG_SND_UNA_ADVANCED;
 
3796
3797	if (sysctl_tcp_abc) {
3798		if (icsk->icsk_ca_state < TCP_CA_CWR)
3799			tp->bytes_acked += ack - prior_snd_una;
3800		else if (icsk->icsk_ca_state == TCP_CA_Loss)
3801			/* we assume just one segment left network */
3802			tp->bytes_acked += min(ack - prior_snd_una,
3803					       tp->mss_cache);
3804	}
3805
3806	prior_fackets = tp->fackets_out;
3807	prior_in_flight = tcp_packets_in_flight(tp);
 
 
 
 
 
 
3808
3809	if (!(flag & FLAG_SLOWPATH) && after(ack, prior_snd_una)) {
 
3810		/* Window is constant, pure forward advance.
3811		 * No more checks are required.
3812		 * Note, we use the fact that SND.UNA>=SND.WL2.
3813		 */
3814		tcp_update_wl(tp, ack_seq);
3815		tp->snd_una = ack;
3816		flag |= FLAG_WIN_UPDATE;
3817
3818		tcp_ca_event(sk, CA_EVENT_FAST_ACK);
3819
3820		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPACKS);
3821	} else {
 
 
3822		if (ack_seq != TCP_SKB_CB(skb)->end_seq)
3823			flag |= FLAG_DATA;
3824		else
3825			NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPPUREACKS);
3826
3827		flag |= tcp_ack_update_window(sk, skb, ack, ack_seq);
3828
3829		if (TCP_SKB_CB(skb)->sacked)
3830			flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una);
 
3831
3832		if (TCP_ECN_rcv_ecn_echo(tp, tcp_hdr(skb)))
3833			flag |= FLAG_ECE;
 
 
 
 
 
 
3834
3835		tcp_ca_event(sk, CA_EVENT_SLOW_ACK);
 
 
 
3836	}
3837
 
 
 
 
 
 
 
 
 
3838	/* We passed data and got it acked, remove any soft error
3839	 * log. Something worked...
3840	 */
3841	sk->sk_err_soft = 0;
3842	icsk->icsk_probes_out = 0;
3843	tp->rcv_tstamp = tcp_time_stamp;
3844	prior_packets = tp->packets_out;
3845	if (!prior_packets)
3846		goto no_queue;
3847
3848	/* See if we can take anything off of the retransmit queue. */
3849	flag |= tcp_clean_rtx_queue(sk, prior_fackets, prior_snd_una);
 
3850
3851	pkts_acked = prior_packets - tp->packets_out;
3852
3853	if (tp->frto_counter)
3854		frto_cwnd = tcp_process_frto(sk, flag);
3855	/* Guarantee sacktag reordering detection against wrap-arounds */
3856	if (before(tp->frto_highmark, tp->snd_una))
3857		tp->frto_highmark = 0;
3858
3859	if (tcp_ack_is_dubious(sk, flag)) {
3860		/* Advance CWND, if state allows this. */
3861		if ((flag & FLAG_DATA_ACKED) && !frto_cwnd &&
3862		    tcp_may_raise_cwnd(sk, flag))
3863			tcp_cong_avoid(sk, ack, prior_in_flight);
3864		is_dupack = !(flag & (FLAG_SND_UNA_ADVANCED | FLAG_NOT_DUP));
3865		tcp_fastretrans_alert(sk, pkts_acked, prior_sacked,
3866				      is_dupack, flag);
3867	} else {
3868		if ((flag & FLAG_DATA_ACKED) && !frto_cwnd)
3869			tcp_cong_avoid(sk, ack, prior_in_flight);
3870	}
3871
 
 
 
 
3872	if ((flag & FLAG_FORWARD_PROGRESS) || !(flag & FLAG_NOT_DUP))
3873		dst_confirm(__sk_dst_get(sk));
3874
 
 
 
 
 
 
3875	return 1;
3876
3877no_queue:
3878	/* If data was DSACKed, see if we can undo a cwnd reduction. */
3879	if (flag & FLAG_DSACKING_ACK)
3880		tcp_fastretrans_alert(sk, pkts_acked, prior_sacked,
3881				      is_dupack, flag);
 
 
3882	/* If this ack opens up a zero window, clear backoff.  It was
3883	 * being used to time the probes, and is probably far higher than
3884	 * it needs to be for normal retransmission.
3885	 */
3886	if (tcp_send_head(sk))
3887		tcp_ack_probe(sk);
3888	return 1;
3889
3890invalid_ack:
3891	SOCK_DEBUG(sk, "Ack %u after %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
3892	return -1;
3893
3894old_ack:
3895	/* If data was SACKed, tag it and see if we should send more data.
3896	 * If data was DSACKed, see if we can undo a cwnd reduction.
3897	 */
3898	if (TCP_SKB_CB(skb)->sacked) {
3899		flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una);
3900		tcp_fastretrans_alert(sk, pkts_acked, prior_sacked,
3901				      is_dupack, flag);
 
 
 
3902	}
3903
3904	SOCK_DEBUG(sk, "Ack %u before %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
3905	return 0;
3906}
3907
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
3908/* Look for tcp options. Normally only called on SYN and SYNACK packets.
3909 * But, this can also be called on packets in the established flow when
3910 * the fast version below fails.
3911 */
3912void tcp_parse_options(const struct sk_buff *skb, struct tcp_options_received *opt_rx,
3913		       const u8 **hvpp, int estab)
 
 
3914{
3915	const unsigned char *ptr;
3916	const struct tcphdr *th = tcp_hdr(skb);
3917	int length = (th->doff * 4) - sizeof(struct tcphdr);
3918
3919	ptr = (const unsigned char *)(th + 1);
3920	opt_rx->saw_tstamp = 0;
 
3921
3922	while (length > 0) {
3923		int opcode = *ptr++;
3924		int opsize;
3925
3926		switch (opcode) {
3927		case TCPOPT_EOL:
3928			return;
3929		case TCPOPT_NOP:	/* Ref: RFC 793 section 3.1 */
3930			length--;
3931			continue;
3932		default:
 
 
3933			opsize = *ptr++;
3934			if (opsize < 2) /* "silly options" */
3935				return;
3936			if (opsize > length)
3937				return;	/* don't parse partial options */
3938			switch (opcode) {
3939			case TCPOPT_MSS:
3940				if (opsize == TCPOLEN_MSS && th->syn && !estab) {
3941					u16 in_mss = get_unaligned_be16(ptr);
3942					if (in_mss) {
3943						if (opt_rx->user_mss &&
3944						    opt_rx->user_mss < in_mss)
3945							in_mss = opt_rx->user_mss;
3946						opt_rx->mss_clamp = in_mss;
3947					}
3948				}
3949				break;
3950			case TCPOPT_WINDOW:
3951				if (opsize == TCPOLEN_WINDOW && th->syn &&
3952				    !estab && sysctl_tcp_window_scaling) {
3953					__u8 snd_wscale = *(__u8 *)ptr;
3954					opt_rx->wscale_ok = 1;
3955					if (snd_wscale > 14) {
3956						net_info_ratelimited("%s: Illegal window scaling value %d >14 received\n",
3957								     __func__,
3958								     snd_wscale);
3959						snd_wscale = 14;
 
3960					}
3961					opt_rx->snd_wscale = snd_wscale;
3962				}
3963				break;
3964			case TCPOPT_TIMESTAMP:
3965				if ((opsize == TCPOLEN_TIMESTAMP) &&
3966				    ((estab && opt_rx->tstamp_ok) ||
3967				     (!estab && sysctl_tcp_timestamps))) {
3968					opt_rx->saw_tstamp = 1;
3969					opt_rx->rcv_tsval = get_unaligned_be32(ptr);
3970					opt_rx->rcv_tsecr = get_unaligned_be32(ptr + 4);
3971				}
3972				break;
3973			case TCPOPT_SACK_PERM:
3974				if (opsize == TCPOLEN_SACK_PERM && th->syn &&
3975				    !estab && sysctl_tcp_sack) {
3976					opt_rx->sack_ok = TCP_SACK_SEEN;
3977					tcp_sack_reset(opt_rx);
3978				}
3979				break;
3980
3981			case TCPOPT_SACK:
3982				if ((opsize >= (TCPOLEN_SACK_BASE + TCPOLEN_SACK_PERBLOCK)) &&
3983				   !((opsize - TCPOLEN_SACK_BASE) % TCPOLEN_SACK_PERBLOCK) &&
3984				   opt_rx->sack_ok) {
3985					TCP_SKB_CB(skb)->sacked = (ptr - 2) - (unsigned char *)th;
3986				}
3987				break;
3988#ifdef CONFIG_TCP_MD5SIG
3989			case TCPOPT_MD5SIG:
3990				/*
3991				 * The MD5 Hash has already been
3992				 * checked (see tcp_v{4,6}_do_rcv()).
3993				 */
3994				break;
3995#endif
3996			case TCPOPT_COOKIE:
3997				/* This option is variable length.
 
 
 
 
 
 
 
3998				 */
3999				switch (opsize) {
4000				case TCPOLEN_COOKIE_BASE:
4001					/* not yet implemented */
4002					break;
4003				case TCPOLEN_COOKIE_PAIR:
4004					/* not yet implemented */
4005					break;
4006				case TCPOLEN_COOKIE_MIN+0:
4007				case TCPOLEN_COOKIE_MIN+2:
4008				case TCPOLEN_COOKIE_MIN+4:
4009				case TCPOLEN_COOKIE_MIN+6:
4010				case TCPOLEN_COOKIE_MAX:
4011					/* 16-bit multiple */
4012					opt_rx->cookie_plus = opsize;
4013					*hvpp = ptr;
4014					break;
4015				default:
4016					/* ignore option */
4017					break;
4018				}
 
 
 
 
 
4019				break;
4020			}
4021
 
 
 
4022			ptr += opsize-2;
4023			length -= opsize;
4024		}
4025	}
4026}
4027EXPORT_SYMBOL(tcp_parse_options);
4028
4029static bool tcp_parse_aligned_timestamp(struct tcp_sock *tp, const struct tcphdr *th)
4030{
4031	const __be32 *ptr = (const __be32 *)(th + 1);
4032
4033	if (*ptr == htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16)
4034			  | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP)) {
4035		tp->rx_opt.saw_tstamp = 1;
4036		++ptr;
4037		tp->rx_opt.rcv_tsval = ntohl(*ptr);
4038		++ptr;
4039		tp->rx_opt.rcv_tsecr = ntohl(*ptr);
 
 
 
4040		return true;
4041	}
4042	return false;
4043}
4044
4045/* Fast parse options. This hopes to only see timestamps.
4046 * If it is wrong it falls back on tcp_parse_options().
4047 */
4048static bool tcp_fast_parse_options(const struct sk_buff *skb,
4049				   const struct tcphdr *th,
4050				   struct tcp_sock *tp, const u8 **hvpp)
4051{
4052	/* In the spirit of fast parsing, compare doff directly to constant
4053	 * values.  Because equality is used, short doff can be ignored here.
4054	 */
4055	if (th->doff == (sizeof(*th) / 4)) {
4056		tp->rx_opt.saw_tstamp = 0;
4057		return false;
4058	} else if (tp->rx_opt.tstamp_ok &&
4059		   th->doff == ((sizeof(*th) + TCPOLEN_TSTAMP_ALIGNED) / 4)) {
4060		if (tcp_parse_aligned_timestamp(tp, th))
4061			return true;
4062	}
4063	tcp_parse_options(skb, &tp->rx_opt, hvpp, 1);
 
 
 
 
4064	return true;
4065}
4066
4067#ifdef CONFIG_TCP_MD5SIG
4068/*
4069 * Parse MD5 Signature option
4070 */
4071const u8 *tcp_parse_md5sig_option(const struct tcphdr *th)
4072{
4073	int length = (th->doff << 2) - sizeof(*th);
4074	const u8 *ptr = (const u8 *)(th + 1);
4075
4076	/* If the TCP option is too short, we can short cut */
4077	if (length < TCPOLEN_MD5SIG)
4078		return NULL;
4079
4080	while (length > 0) {
4081		int opcode = *ptr++;
4082		int opsize;
4083
4084		switch(opcode) {
4085		case TCPOPT_EOL:
4086			return NULL;
4087		case TCPOPT_NOP:
4088			length--;
4089			continue;
4090		default:
4091			opsize = *ptr++;
4092			if (opsize < 2 || opsize > length)
4093				return NULL;
4094			if (opcode == TCPOPT_MD5SIG)
4095				return opsize == TCPOLEN_MD5SIG ? ptr : NULL;
4096		}
4097		ptr += opsize - 2;
4098		length -= opsize;
4099	}
4100	return NULL;
4101}
4102EXPORT_SYMBOL(tcp_parse_md5sig_option);
4103#endif
4104
4105static inline void tcp_store_ts_recent(struct tcp_sock *tp)
4106{
4107	tp->rx_opt.ts_recent = tp->rx_opt.rcv_tsval;
4108	tp->rx_opt.ts_recent_stamp = get_seconds();
4109}
4110
4111static inline void tcp_replace_ts_recent(struct tcp_sock *tp, u32 seq)
4112{
4113	if (tp->rx_opt.saw_tstamp && !after(seq, tp->rcv_wup)) {
4114		/* PAWS bug workaround wrt. ACK frames, the PAWS discard
4115		 * extra check below makes sure this can only happen
4116		 * for pure ACK frames.  -DaveM
4117		 *
4118		 * Not only, also it occurs for expired timestamps.
4119		 */
4120
4121		if (tcp_paws_check(&tp->rx_opt, 0))
4122			tcp_store_ts_recent(tp);
4123	}
4124}
4125
4126/* Sorry, PAWS as specified is broken wrt. pure-ACKs -DaveM
4127 *
4128 * It is not fatal. If this ACK does _not_ change critical state (seqs, window)
4129 * it can pass through stack. So, the following predicate verifies that
4130 * this segment is not used for anything but congestion avoidance or
4131 * fast retransmit. Moreover, we even are able to eliminate most of such
4132 * second order effects, if we apply some small "replay" window (~RTO)
4133 * to timestamp space.
4134 *
4135 * All these measures still do not guarantee that we reject wrapped ACKs
4136 * on networks with high bandwidth, when sequence space is recycled fastly,
4137 * but it guarantees that such events will be very rare and do not affect
4138 * connection seriously. This doesn't look nice, but alas, PAWS is really
4139 * buggy extension.
4140 *
4141 * [ Later note. Even worse! It is buggy for segments _with_ data. RFC
4142 * states that events when retransmit arrives after original data are rare.
4143 * It is a blatant lie. VJ forgot about fast retransmit! 8)8) It is
4144 * the biggest problem on large power networks even with minor reordering.
4145 * OK, let's give it small replay window. If peer clock is even 1hz, it is safe
4146 * up to bandwidth of 18Gigabit/sec. 8) ]
4147 */
4148
4149static int tcp_disordered_ack(const struct sock *sk, const struct sk_buff *skb)
4150{
4151	const struct tcp_sock *tp = tcp_sk(sk);
4152	const struct tcphdr *th = tcp_hdr(skb);
4153	u32 seq = TCP_SKB_CB(skb)->seq;
4154	u32 ack = TCP_SKB_CB(skb)->ack_seq;
4155
4156	return (/* 1. Pure ACK with correct sequence number. */
4157		(th->ack && seq == TCP_SKB_CB(skb)->end_seq && seq == tp->rcv_nxt) &&
4158
4159		/* 2. ... and duplicate ACK. */
4160		ack == tp->snd_una &&
4161
4162		/* 3. ... and does not update window. */
4163		!tcp_may_update_window(tp, ack, seq, ntohs(th->window) << tp->rx_opt.snd_wscale) &&
4164
4165		/* 4. ... and sits in replay window. */
4166		(s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) <= (inet_csk(sk)->icsk_rto * 1024) / HZ);
4167}
4168
4169static inline int tcp_paws_discard(const struct sock *sk,
4170				   const struct sk_buff *skb)
4171{
4172	const struct tcp_sock *tp = tcp_sk(sk);
4173
4174	return !tcp_paws_check(&tp->rx_opt, TCP_PAWS_WINDOW) &&
4175	       !tcp_disordered_ack(sk, skb);
4176}
4177
4178/* Check segment sequence number for validity.
4179 *
4180 * Segment controls are considered valid, if the segment
4181 * fits to the window after truncation to the window. Acceptability
4182 * of data (and SYN, FIN, of course) is checked separately.
4183 * See tcp_data_queue(), for example.
4184 *
4185 * Also, controls (RST is main one) are accepted using RCV.WUP instead
4186 * of RCV.NXT. Peer still did not advance his SND.UNA when we
4187 * delayed ACK, so that hisSND.UNA<=ourRCV.WUP.
4188 * (borrowed from freebsd)
4189 */
4190
4191static inline int tcp_sequence(const struct tcp_sock *tp, u32 seq, u32 end_seq)
4192{
4193	return	!before(end_seq, tp->rcv_wup) &&
4194		!after(seq, tp->rcv_nxt + tcp_receive_window(tp));
4195}
4196
4197/* When we get a reset we do this. */
4198static void tcp_reset(struct sock *sk)
4199{
 
 
 
 
 
 
 
 
4200	/* We want the right error as BSD sees it (and indeed as we do). */
4201	switch (sk->sk_state) {
4202	case TCP_SYN_SENT:
4203		sk->sk_err = ECONNREFUSED;
4204		break;
4205	case TCP_CLOSE_WAIT:
4206		sk->sk_err = EPIPE;
4207		break;
4208	case TCP_CLOSE:
4209		return;
4210	default:
4211		sk->sk_err = ECONNRESET;
4212	}
4213	/* This barrier is coupled with smp_rmb() in tcp_poll() */
4214	smp_wmb();
4215
4216	if (!sock_flag(sk, SOCK_DEAD))
4217		sk->sk_error_report(sk);
4218
4219	tcp_done(sk);
 
 
 
4220}
4221
4222/*
4223 * 	Process the FIN bit. This now behaves as it is supposed to work
4224 *	and the FIN takes effect when it is validly part of sequence
4225 *	space. Not before when we get holes.
4226 *
4227 *	If we are ESTABLISHED, a received fin moves us to CLOSE-WAIT
4228 *	(and thence onto LAST-ACK and finally, CLOSE, we never enter
4229 *	TIME-WAIT)
4230 *
4231 *	If we are in FINWAIT-1, a received FIN indicates simultaneous
4232 *	close and we go into CLOSING (and later onto TIME-WAIT)
4233 *
4234 *	If we are in FINWAIT-2, a received FIN moves us to TIME-WAIT.
4235 */
4236static void tcp_fin(struct sock *sk)
4237{
4238	struct tcp_sock *tp = tcp_sk(sk);
4239
4240	inet_csk_schedule_ack(sk);
4241
4242	sk->sk_shutdown |= RCV_SHUTDOWN;
4243	sock_set_flag(sk, SOCK_DONE);
4244
4245	switch (sk->sk_state) {
4246	case TCP_SYN_RECV:
4247	case TCP_ESTABLISHED:
4248		/* Move to CLOSE_WAIT */
4249		tcp_set_state(sk, TCP_CLOSE_WAIT);
4250		inet_csk(sk)->icsk_ack.pingpong = 1;
4251		break;
4252
4253	case TCP_CLOSE_WAIT:
4254	case TCP_CLOSING:
4255		/* Received a retransmission of the FIN, do
4256		 * nothing.
4257		 */
4258		break;
4259	case TCP_LAST_ACK:
4260		/* RFC793: Remain in the LAST-ACK state. */
4261		break;
4262
4263	case TCP_FIN_WAIT1:
4264		/* This case occurs when a simultaneous close
4265		 * happens, we must ack the received FIN and
4266		 * enter the CLOSING state.
4267		 */
4268		tcp_send_ack(sk);
4269		tcp_set_state(sk, TCP_CLOSING);
4270		break;
4271	case TCP_FIN_WAIT2:
4272		/* Received a FIN -- send ACK and enter TIME_WAIT. */
4273		tcp_send_ack(sk);
4274		tcp_time_wait(sk, TCP_TIME_WAIT, 0);
4275		break;
4276	default:
4277		/* Only TCP_LISTEN and TCP_CLOSE are left, in these
4278		 * cases we should never reach this piece of code.
4279		 */
4280		pr_err("%s: Impossible, sk->sk_state=%d\n",
4281		       __func__, sk->sk_state);
4282		break;
4283	}
4284
4285	/* It _is_ possible, that we have something out-of-order _after_ FIN.
4286	 * Probably, we should reset in this case. For now drop them.
4287	 */
4288	__skb_queue_purge(&tp->out_of_order_queue);
4289	if (tcp_is_sack(tp))
4290		tcp_sack_reset(&tp->rx_opt);
4291	sk_mem_reclaim(sk);
4292
4293	if (!sock_flag(sk, SOCK_DEAD)) {
4294		sk->sk_state_change(sk);
4295
4296		/* Do not send POLL_HUP for half duplex close. */
4297		if (sk->sk_shutdown == SHUTDOWN_MASK ||
4298		    sk->sk_state == TCP_CLOSE)
4299			sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_HUP);
4300		else
4301			sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_IN);
4302	}
4303}
4304
4305static inline bool tcp_sack_extend(struct tcp_sack_block *sp, u32 seq,
4306				  u32 end_seq)
4307{
4308	if (!after(seq, sp->end_seq) && !after(sp->start_seq, end_seq)) {
4309		if (before(seq, sp->start_seq))
4310			sp->start_seq = seq;
4311		if (after(end_seq, sp->end_seq))
4312			sp->end_seq = end_seq;
4313		return true;
4314	}
4315	return false;
4316}
4317
4318static void tcp_dsack_set(struct sock *sk, u32 seq, u32 end_seq)
4319{
4320	struct tcp_sock *tp = tcp_sk(sk);
4321
4322	if (tcp_is_sack(tp) && sysctl_tcp_dsack) {
4323		int mib_idx;
4324
4325		if (before(seq, tp->rcv_nxt))
4326			mib_idx = LINUX_MIB_TCPDSACKOLDSENT;
4327		else
4328			mib_idx = LINUX_MIB_TCPDSACKOFOSENT;
4329
4330		NET_INC_STATS_BH(sock_net(sk), mib_idx);
4331
4332		tp->rx_opt.dsack = 1;
4333		tp->duplicate_sack[0].start_seq = seq;
4334		tp->duplicate_sack[0].end_seq = end_seq;
4335	}
4336}
4337
4338static void tcp_dsack_extend(struct sock *sk, u32 seq, u32 end_seq)
4339{
4340	struct tcp_sock *tp = tcp_sk(sk);
4341
4342	if (!tp->rx_opt.dsack)
4343		tcp_dsack_set(sk, seq, end_seq);
4344	else
4345		tcp_sack_extend(tp->duplicate_sack, seq, end_seq);
4346}
4347
 
 
 
 
 
 
 
 
 
 
 
 
4348static void tcp_send_dupack(struct sock *sk, const struct sk_buff *skb)
4349{
4350	struct tcp_sock *tp = tcp_sk(sk);
4351
4352	if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
4353	    before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
4354		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
4355		tcp_enter_quickack_mode(sk);
4356
4357		if (tcp_is_sack(tp) && sysctl_tcp_dsack) {
4358			u32 end_seq = TCP_SKB_CB(skb)->end_seq;
4359
 
4360			if (after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))
4361				end_seq = tp->rcv_nxt;
4362			tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, end_seq);
4363		}
4364	}
4365
4366	tcp_send_ack(sk);
4367}
4368
4369/* These routines update the SACK block as out-of-order packets arrive or
4370 * in-order packets close up the sequence space.
4371 */
4372static void tcp_sack_maybe_coalesce(struct tcp_sock *tp)
4373{
4374	int this_sack;
4375	struct tcp_sack_block *sp = &tp->selective_acks[0];
4376	struct tcp_sack_block *swalk = sp + 1;
4377
4378	/* See if the recent change to the first SACK eats into
4379	 * or hits the sequence space of other SACK blocks, if so coalesce.
4380	 */
4381	for (this_sack = 1; this_sack < tp->rx_opt.num_sacks;) {
4382		if (tcp_sack_extend(sp, swalk->start_seq, swalk->end_seq)) {
4383			int i;
4384
4385			/* Zap SWALK, by moving every further SACK up by one slot.
4386			 * Decrease num_sacks.
4387			 */
4388			tp->rx_opt.num_sacks--;
4389			for (i = this_sack; i < tp->rx_opt.num_sacks; i++)
4390				sp[i] = sp[i + 1];
4391			continue;
4392		}
4393		this_sack++, swalk++;
 
4394	}
4395}
4396
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
4397static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq)
4398{
4399	struct tcp_sock *tp = tcp_sk(sk);
4400	struct tcp_sack_block *sp = &tp->selective_acks[0];
4401	int cur_sacks = tp->rx_opt.num_sacks;
4402	int this_sack;
4403
4404	if (!cur_sacks)
4405		goto new_sack;
4406
4407	for (this_sack = 0; this_sack < cur_sacks; this_sack++, sp++) {
4408		if (tcp_sack_extend(sp, seq, end_seq)) {
 
 
4409			/* Rotate this_sack to the first one. */
4410			for (; this_sack > 0; this_sack--, sp--)
4411				swap(*sp, *(sp - 1));
4412			if (cur_sacks > 1)
4413				tcp_sack_maybe_coalesce(tp);
4414			return;
4415		}
4416	}
4417
 
 
 
4418	/* Could not find an adjacent existing SACK, build a new one,
4419	 * put it at the front, and shift everyone else down.  We
4420	 * always know there is at least one SACK present already here.
4421	 *
4422	 * If the sack array is full, forget about the last one.
4423	 */
4424	if (this_sack >= TCP_NUM_SACKS) {
4425		this_sack--;
4426		tp->rx_opt.num_sacks--;
4427		sp--;
4428	}
4429	for (; this_sack > 0; this_sack--, sp--)
4430		*sp = *(sp - 1);
4431
4432new_sack:
4433	/* Build the new head SACK, and we're done. */
4434	sp->start_seq = seq;
4435	sp->end_seq = end_seq;
4436	tp->rx_opt.num_sacks++;
4437}
4438
4439/* RCV.NXT advances, some SACKs should be eaten. */
4440
4441static void tcp_sack_remove(struct tcp_sock *tp)
4442{
4443	struct tcp_sack_block *sp = &tp->selective_acks[0];
4444	int num_sacks = tp->rx_opt.num_sacks;
4445	int this_sack;
4446
4447	/* Empty ofo queue, hence, all the SACKs are eaten. Clear. */
4448	if (skb_queue_empty(&tp->out_of_order_queue)) {
4449		tp->rx_opt.num_sacks = 0;
4450		return;
4451	}
4452
4453	for (this_sack = 0; this_sack < num_sacks;) {
4454		/* Check if the start of the sack is covered by RCV.NXT. */
4455		if (!before(tp->rcv_nxt, sp->start_seq)) {
4456			int i;
4457
4458			/* RCV.NXT must cover all the block! */
4459			WARN_ON(before(tp->rcv_nxt, sp->end_seq));
4460
4461			/* Zap this SACK, by moving forward any other SACKS. */
4462			for (i=this_sack+1; i < num_sacks; i++)
4463				tp->selective_acks[i-1] = tp->selective_acks[i];
4464			num_sacks--;
4465			continue;
4466		}
4467		this_sack++;
4468		sp++;
4469	}
4470	tp->rx_opt.num_sacks = num_sacks;
4471}
4472
4473/* This one checks to see if we can put data from the
4474 * out_of_order queue into the receive_queue.
4475 */
4476static void tcp_ofo_queue(struct sock *sk)
4477{
4478	struct tcp_sock *tp = tcp_sk(sk);
4479	__u32 dsack_high = tp->rcv_nxt;
4480	struct sk_buff *skb;
4481
4482	while ((skb = skb_peek(&tp->out_of_order_queue)) != NULL) {
4483		if (after(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
4484			break;
4485
4486		if (before(TCP_SKB_CB(skb)->seq, dsack_high)) {
4487			__u32 dsack = dsack_high;
4488			if (before(TCP_SKB_CB(skb)->end_seq, dsack_high))
4489				dsack_high = TCP_SKB_CB(skb)->end_seq;
4490			tcp_dsack_extend(sk, TCP_SKB_CB(skb)->seq, dsack);
4491		}
4492
4493		if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
4494			SOCK_DEBUG(sk, "ofo packet was already received\n");
4495			__skb_unlink(skb, &tp->out_of_order_queue);
4496			__kfree_skb(skb);
4497			continue;
4498		}
4499		SOCK_DEBUG(sk, "ofo requeuing : rcv_next %X seq %X - %X\n",
4500			   tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
4501			   TCP_SKB_CB(skb)->end_seq);
4502
4503		__skb_unlink(skb, &tp->out_of_order_queue);
4504		__skb_queue_tail(&sk->sk_receive_queue, skb);
4505		tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
4506		if (tcp_hdr(skb)->fin)
4507			tcp_fin(sk);
4508	}
4509}
4510
4511static bool tcp_prune_ofo_queue(struct sock *sk);
4512static int tcp_prune_queue(struct sock *sk);
4513
4514static int tcp_try_rmem_schedule(struct sock *sk, unsigned int size)
4515{
4516	if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
4517	    !sk_rmem_schedule(sk, size)) {
4518
4519		if (tcp_prune_queue(sk) < 0)
4520			return -1;
4521
4522		if (!sk_rmem_schedule(sk, size)) {
4523			if (!tcp_prune_ofo_queue(sk))
4524				return -1;
4525
4526			if (!sk_rmem_schedule(sk, size))
4527				return -1;
4528		}
4529	}
4530	return 0;
4531}
4532
4533/**
4534 * tcp_try_coalesce - try to merge skb to prior one
4535 * @sk: socket
4536 * @to: prior buffer
4537 * @from: buffer to add in queue
4538 * @fragstolen: pointer to boolean
4539 *
4540 * Before queueing skb @from after @to, try to merge them
4541 * to reduce overall memory use and queue lengths, if cost is small.
4542 * Packets in ofo or receive queues can stay a long time.
4543 * Better try to coalesce them right now to avoid future collapses.
4544 * Returns true if caller should free @from instead of queueing it
4545 */
4546static bool tcp_try_coalesce(struct sock *sk,
4547			     struct sk_buff *to,
4548			     struct sk_buff *from,
4549			     bool *fragstolen)
4550{
4551	int delta;
4552
4553	*fragstolen = false;
4554
4555	if (tcp_hdr(from)->fin)
4556		return false;
4557
4558	/* Its possible this segment overlaps with prior segment in queue */
4559	if (TCP_SKB_CB(from)->seq != TCP_SKB_CB(to)->end_seq)
4560		return false;
4561
 
 
 
 
 
 
 
 
4562	if (!skb_try_coalesce(to, from, fragstolen, &delta))
4563		return false;
4564
4565	atomic_add(delta, &sk->sk_rmem_alloc);
4566	sk_mem_charge(sk, delta);
4567	NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPRCVCOALESCE);
4568	TCP_SKB_CB(to)->end_seq = TCP_SKB_CB(from)->end_seq;
4569	TCP_SKB_CB(to)->ack_seq = TCP_SKB_CB(from)->ack_seq;
 
 
 
 
 
 
 
 
4570	return true;
4571}
4572
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
4573static void tcp_data_queue_ofo(struct sock *sk, struct sk_buff *skb)
4574{
4575	struct tcp_sock *tp = tcp_sk(sk);
 
4576	struct sk_buff *skb1;
4577	u32 seq, end_seq;
 
4578
4579	TCP_ECN_check_ce(tp, skb);
4580
4581	if (tcp_try_rmem_schedule(sk, skb->truesize)) {
4582		/* TODO: should increment a counter */
4583		__kfree_skb(skb);
 
4584		return;
4585	}
4586
4587	/* Disable header prediction. */
4588	tp->pred_flags = 0;
4589	inet_csk_schedule_ack(sk);
4590
4591	SOCK_DEBUG(sk, "out of order segment: rcv_next %X seq %X - %X\n",
4592		   tp->rcv_nxt, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
 
 
4593
4594	skb1 = skb_peek_tail(&tp->out_of_order_queue);
4595	if (!skb1) {
4596		/* Initial out of order segment, build 1 SACK. */
4597		if (tcp_is_sack(tp)) {
4598			tp->rx_opt.num_sacks = 1;
4599			tp->selective_acks[0].start_seq = TCP_SKB_CB(skb)->seq;
4600			tp->selective_acks[0].end_seq =
4601						TCP_SKB_CB(skb)->end_seq;
4602		}
4603		__skb_queue_head(&tp->out_of_order_queue, skb);
 
 
4604		goto end;
4605	}
4606
4607	seq = TCP_SKB_CB(skb)->seq;
4608	end_seq = TCP_SKB_CB(skb)->end_seq;
4609
4610	if (seq == TCP_SKB_CB(skb1)->end_seq) {
4611		bool fragstolen;
4612
4613		if (!tcp_try_coalesce(sk, skb1, skb, &fragstolen)) {
4614			__skb_queue_after(&tp->out_of_order_queue, skb1, skb);
4615		} else {
4616			kfree_skb_partial(skb, fragstolen);
4617			skb = NULL;
4618		}
4619
4620		if (!tp->rx_opt.num_sacks ||
4621		    tp->selective_acks[0].end_seq != seq)
4622			goto add_sack;
4623
4624		/* Common case: data arrive in order after hole. */
4625		tp->selective_acks[0].end_seq = end_seq;
4626		goto end;
4627	}
4628
4629	/* Find place to insert this segment. */
4630	while (1) {
4631		if (!after(TCP_SKB_CB(skb1)->seq, seq))
4632			break;
4633		if (skb_queue_is_first(&tp->out_of_order_queue, skb1)) {
4634			skb1 = NULL;
4635			break;
4636		}
4637		skb1 = skb_queue_prev(&tp->out_of_order_queue, skb1);
4638	}
4639
4640	/* Do skb overlap to previous one? */
4641	if (skb1 && before(seq, TCP_SKB_CB(skb1)->end_seq)) {
4642		if (!after(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
4643			/* All the bits are present. Drop. */
4644			__kfree_skb(skb);
4645			skb = NULL;
4646			tcp_dsack_set(sk, seq, end_seq);
4647			goto add_sack;
4648		}
4649		if (after(seq, TCP_SKB_CB(skb1)->seq)) {
4650			/* Partial overlap. */
4651			tcp_dsack_set(sk, seq,
4652				      TCP_SKB_CB(skb1)->end_seq);
4653		} else {
4654			if (skb_queue_is_first(&tp->out_of_order_queue,
4655					       skb1))
4656				skb1 = NULL;
4657			else
4658				skb1 = skb_queue_prev(
4659					&tp->out_of_order_queue,
4660					skb1);
4661		}
4662	}
4663	if (!skb1)
4664		__skb_queue_head(&tp->out_of_order_queue, skb);
4665	else
4666		__skb_queue_after(&tp->out_of_order_queue, skb1, skb);
4667
4668	/* And clean segments covered by new one as whole. */
4669	while (!skb_queue_is_last(&tp->out_of_order_queue, skb)) {
4670		skb1 = skb_queue_next(&tp->out_of_order_queue, skb);
4671
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
4672		if (!after(end_seq, TCP_SKB_CB(skb1)->seq))
4673			break;
4674		if (before(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
4675			tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
4676					 end_seq);
4677			break;
4678		}
4679		__skb_unlink(skb1, &tp->out_of_order_queue);
4680		tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
4681				 TCP_SKB_CB(skb1)->end_seq);
4682		__kfree_skb(skb1);
 
4683	}
 
 
 
4684
4685add_sack:
4686	if (tcp_is_sack(tp))
4687		tcp_sack_new_ofo_skb(sk, seq, end_seq);
4688end:
4689	if (skb)
 
 
 
 
 
 
4690		skb_set_owner_r(skb, sk);
 
4691}
4692
4693static int __must_check tcp_queue_rcv(struct sock *sk, struct sk_buff *skb, int hdrlen,
4694		  bool *fragstolen)
4695{
4696	int eaten;
4697	struct sk_buff *tail = skb_peek_tail(&sk->sk_receive_queue);
4698
4699	__skb_pull(skb, hdrlen);
4700	eaten = (tail &&
4701		 tcp_try_coalesce(sk, tail, skb, fragstolen)) ? 1 : 0;
4702	tcp_sk(sk)->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
 
4703	if (!eaten) {
4704		__skb_queue_tail(&sk->sk_receive_queue, skb);
4705		skb_set_owner_r(skb, sk);
4706	}
4707	return eaten;
4708}
4709
4710int tcp_send_rcvq(struct sock *sk, struct msghdr *msg, size_t size)
4711{
4712	struct sk_buff *skb;
4713	struct tcphdr *th;
 
4714	bool fragstolen;
4715
4716	if (tcp_try_rmem_schedule(sk, size + sizeof(*th)))
4717		goto err;
4718
4719	skb = alloc_skb(size + sizeof(*th), sk->sk_allocation);
 
 
 
 
 
 
 
 
4720	if (!skb)
4721		goto err;
4722
4723	th = (struct tcphdr *)skb_put(skb, sizeof(*th));
4724	skb_reset_transport_header(skb);
4725	memset(th, 0, sizeof(*th));
4726
4727	if (memcpy_fromiovec(skb_put(skb, size), msg->msg_iov, size))
 
 
 
 
 
 
4728		goto err_free;
4729
4730	TCP_SKB_CB(skb)->seq = tcp_sk(sk)->rcv_nxt;
4731	TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq + size;
4732	TCP_SKB_CB(skb)->ack_seq = tcp_sk(sk)->snd_una - 1;
4733
4734	if (tcp_queue_rcv(sk, skb, sizeof(*th), &fragstolen)) {
4735		WARN_ON_ONCE(fragstolen); /* should not happen */
4736		__kfree_skb(skb);
4737	}
4738	return size;
4739
4740err_free:
4741	kfree_skb(skb);
4742err:
4743	return -ENOMEM;
 
 
 
 
 
 
 
4744}
4745
4746static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
4747{
4748	const struct tcphdr *th = tcp_hdr(skb);
4749	struct tcp_sock *tp = tcp_sk(sk);
4750	int eaten = -1;
4751	bool fragstolen = false;
 
4752
4753	if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq)
4754		goto drop;
 
 
 
 
 
4755
 
 
 
 
4756	skb_dst_drop(skb);
4757	__skb_pull(skb, th->doff * 4);
4758
4759	TCP_ECN_accept_cwr(tp, skb);
4760
 
4761	tp->rx_opt.dsack = 0;
4762
4763	/*  Queue data for delivery to the user.
4764	 *  Packets in sequence go to the receive queue.
4765	 *  Out of sequence packets to the out_of_order_queue.
4766	 */
4767	if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
4768		if (tcp_receive_window(tp) == 0)
 
 
4769			goto out_of_window;
4770
4771		/* Ok. In sequence. In window. */
4772		if (tp->ucopy.task == current &&
4773		    tp->copied_seq == tp->rcv_nxt && tp->ucopy.len &&
4774		    sock_owned_by_user(sk) && !tp->urg_data) {
4775			int chunk = min_t(unsigned int, skb->len,
4776					  tp->ucopy.len);
4777
4778			__set_current_state(TASK_RUNNING);
4779
4780			local_bh_enable();
4781			if (!skb_copy_datagram_iovec(skb, 0, tp->ucopy.iov, chunk)) {
4782				tp->ucopy.len -= chunk;
4783				tp->copied_seq += chunk;
4784				eaten = (chunk == skb->len);
4785				tcp_rcv_space_adjust(sk);
4786			}
4787			local_bh_disable();
4788		}
4789
4790		if (eaten <= 0) {
4791queue_and_out:
4792			if (eaten < 0 &&
4793			    tcp_try_rmem_schedule(sk, skb->truesize))
4794				goto drop;
4795
4796			eaten = tcp_queue_rcv(sk, skb, 0, &fragstolen);
 
 
4797		}
4798		tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
 
4799		if (skb->len)
4800			tcp_event_data_recv(sk, skb);
4801		if (th->fin)
4802			tcp_fin(sk);
4803
4804		if (!skb_queue_empty(&tp->out_of_order_queue)) {
4805			tcp_ofo_queue(sk);
4806
4807			/* RFC2581. 4.2. SHOULD send immediate ACK, when
4808			 * gap in queue is filled.
4809			 */
4810			if (skb_queue_empty(&tp->out_of_order_queue))
4811				inet_csk(sk)->icsk_ack.pingpong = 0;
4812		}
4813
4814		if (tp->rx_opt.num_sacks)
4815			tcp_sack_remove(tp);
4816
4817		tcp_fast_path_check(sk);
4818
4819		if (eaten > 0)
4820			kfree_skb_partial(skb, fragstolen);
4821		else if (!sock_flag(sk, SOCK_DEAD))
4822			sk->sk_data_ready(sk, 0);
4823		return;
4824	}
4825
4826	if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
 
4827		/* A retransmit, 2nd most common case.  Force an immediate ack. */
4828		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
 
4829		tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
4830
4831out_of_window:
4832		tcp_enter_quickack_mode(sk);
4833		inet_csk_schedule_ack(sk);
4834drop:
4835		__kfree_skb(skb);
4836		return;
4837	}
4838
4839	/* Out of window. F.e. zero window probe. */
4840	if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt + tcp_receive_window(tp)))
 
 
4841		goto out_of_window;
4842
4843	tcp_enter_quickack_mode(sk);
4844
4845	if (before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
4846		/* Partial packet, seq < rcv_next < end_seq */
4847		SOCK_DEBUG(sk, "partial packet: rcv_next %X seq %X - %X\n",
4848			   tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
4849			   TCP_SKB_CB(skb)->end_seq);
4850
4851		tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, tp->rcv_nxt);
4852
4853		/* If window is closed, drop tail of packet. But after
4854		 * remembering D-SACK for its head made in previous line.
4855		 */
4856		if (!tcp_receive_window(tp))
 
 
4857			goto out_of_window;
 
4858		goto queue_and_out;
4859	}
4860
4861	tcp_data_queue_ofo(sk, skb);
4862}
4863
 
 
 
 
 
 
 
 
4864static struct sk_buff *tcp_collapse_one(struct sock *sk, struct sk_buff *skb,
4865					struct sk_buff_head *list)
 
4866{
4867	struct sk_buff *next = NULL;
4868
4869	if (!skb_queue_is_last(list, skb))
4870		next = skb_queue_next(list, skb);
 
 
4871
4872	__skb_unlink(skb, list);
4873	__kfree_skb(skb);
4874	NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPRCVCOLLAPSED);
4875
4876	return next;
4877}
4878
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
4879/* Collapse contiguous sequence of skbs head..tail with
4880 * sequence numbers start..end.
4881 *
4882 * If tail is NULL, this means until the end of the list.
4883 *
4884 * Segments with FIN/SYN are not collapsed (only because this
4885 * simplifies code)
4886 */
4887static void
4888tcp_collapse(struct sock *sk, struct sk_buff_head *list,
4889	     struct sk_buff *head, struct sk_buff *tail,
4890	     u32 start, u32 end)
4891{
4892	struct sk_buff *skb, *n;
 
4893	bool end_of_skbs;
4894
4895	/* First, check that queue is collapsible and find
4896	 * the point where collapsing can be useful. */
4897	skb = head;
4898restart:
4899	end_of_skbs = true;
4900	skb_queue_walk_from_safe(list, skb, n) {
4901		if (skb == tail)
4902			break;
4903		/* No new bits? It is possible on ofo queue. */
4904		if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
4905			skb = tcp_collapse_one(sk, skb, list);
4906			if (!skb)
4907				break;
4908			goto restart;
4909		}
4910
4911		/* The first skb to collapse is:
4912		 * - not SYN/FIN and
4913		 * - bloated or contains data before "start" or
4914		 *   overlaps to the next one.
4915		 */
4916		if (!tcp_hdr(skb)->syn && !tcp_hdr(skb)->fin &&
4917		    (tcp_win_from_space(skb->truesize) > skb->len ||
4918		     before(TCP_SKB_CB(skb)->seq, start))) {
4919			end_of_skbs = false;
4920			break;
4921		}
4922
4923		if (!skb_queue_is_last(list, skb)) {
4924			struct sk_buff *next = skb_queue_next(list, skb);
4925			if (next != tail &&
4926			    TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(next)->seq) {
4927				end_of_skbs = false;
4928				break;
4929			}
4930		}
4931
4932		/* Decided to skip this, advance start seq. */
4933		start = TCP_SKB_CB(skb)->end_seq;
4934	}
4935	if (end_of_skbs || tcp_hdr(skb)->syn || tcp_hdr(skb)->fin)
 
4936		return;
4937
 
 
4938	while (before(start, end)) {
 
4939		struct sk_buff *nskb;
4940		unsigned int header = skb_headroom(skb);
4941		int copy = SKB_MAX_ORDER(header, 0);
4942
4943		/* Too big header? This can happen with IPv6. */
4944		if (copy < 0)
4945			return;
4946		if (end - start < copy)
4947			copy = end - start;
4948		nskb = alloc_skb(copy + header, GFP_ATOMIC);
4949		if (!nskb)
4950			return;
4951
4952		skb_set_mac_header(nskb, skb_mac_header(skb) - skb->head);
4953		skb_set_network_header(nskb, (skb_network_header(skb) -
4954					      skb->head));
4955		skb_set_transport_header(nskb, (skb_transport_header(skb) -
4956						skb->head));
4957		skb_reserve(nskb, header);
4958		memcpy(nskb->head, skb->head, header);
4959		memcpy(nskb->cb, skb->cb, sizeof(skb->cb));
 
 
 
4960		TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(nskb)->end_seq = start;
4961		__skb_queue_before(list, skb, nskb);
 
 
 
4962		skb_set_owner_r(nskb, sk);
 
4963
4964		/* Copy data, releasing collapsed skbs. */
4965		while (copy > 0) {
4966			int offset = start - TCP_SKB_CB(skb)->seq;
4967			int size = TCP_SKB_CB(skb)->end_seq - start;
4968
4969			BUG_ON(offset < 0);
4970			if (size > 0) {
4971				size = min(copy, size);
4972				if (skb_copy_bits(skb, offset, skb_put(nskb, size), size))
4973					BUG();
4974				TCP_SKB_CB(nskb)->end_seq += size;
4975				copy -= size;
4976				start += size;
4977			}
4978			if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
4979				skb = tcp_collapse_one(sk, skb, list);
4980				if (!skb ||
4981				    skb == tail ||
4982				    tcp_hdr(skb)->syn ||
4983				    tcp_hdr(skb)->fin)
4984					return;
 
 
 
 
4985			}
4986		}
4987	}
 
 
 
4988}
4989
4990/* Collapse ofo queue. Algorithm: select contiguous sequence of skbs
4991 * and tcp_collapse() them until all the queue is collapsed.
4992 */
4993static void tcp_collapse_ofo_queue(struct sock *sk)
4994{
4995	struct tcp_sock *tp = tcp_sk(sk);
4996	struct sk_buff *skb = skb_peek(&tp->out_of_order_queue);
4997	struct sk_buff *head;
4998	u32 start, end;
4999
5000	if (skb == NULL)
 
 
 
5001		return;
5002
5003	start = TCP_SKB_CB(skb)->seq;
5004	end = TCP_SKB_CB(skb)->end_seq;
5005	head = skb;
5006
5007	for (;;) {
5008		struct sk_buff *next = NULL;
5009
5010		if (!skb_queue_is_last(&tp->out_of_order_queue, skb))
5011			next = skb_queue_next(&tp->out_of_order_queue, skb);
5012		skb = next;
5013
5014		/* Segment is terminated when we see gap or when
5015		 * we are at the end of all the queue. */
5016		if (!skb ||
5017		    after(TCP_SKB_CB(skb)->seq, end) ||
5018		    before(TCP_SKB_CB(skb)->end_seq, start)) {
5019			tcp_collapse(sk, &tp->out_of_order_queue,
5020				     head, skb, start, end);
5021			head = skb;
5022			if (!skb)
5023				break;
5024			/* Start new segment */
 
 
 
 
 
 
 
 
 
5025			start = TCP_SKB_CB(skb)->seq;
 
5026			end = TCP_SKB_CB(skb)->end_seq;
5027		} else {
5028			if (before(TCP_SKB_CB(skb)->seq, start))
5029				start = TCP_SKB_CB(skb)->seq;
5030			if (after(TCP_SKB_CB(skb)->end_seq, end))
5031				end = TCP_SKB_CB(skb)->end_seq;
5032		}
5033	}
5034}
5035
5036/*
5037 * Purge the out-of-order queue.
5038 * Return true if queue was pruned.
5039 */
5040static bool tcp_prune_ofo_queue(struct sock *sk)
5041{
5042	struct tcp_sock *tp = tcp_sk(sk);
5043	bool res = false;
 
 
 
 
 
 
 
 
 
 
 
5044
5045	if (!skb_queue_empty(&tp->out_of_order_queue)) {
5046		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_OFOPRUNED);
5047		__skb_queue_purge(&tp->out_of_order_queue);
5048
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
5049		/* Reset SACK state.  A conforming SACK implementation will
5050		 * do the same at a timeout based retransmit.  When a connection
5051		 * is in a sad state like this, we care only about integrity
5052		 * of the connection not performance.
5053		 */
5054		if (tp->rx_opt.sack_ok)
5055			tcp_sack_reset(&tp->rx_opt);
5056		sk_mem_reclaim(sk);
5057		res = true;
5058	}
5059	return res;
5060}
5061
5062/* Reduce allocated memory if we can, trying to get
5063 * the socket within its memory limits again.
5064 *
5065 * Return less than zero if we should start dropping frames
5066 * until the socket owning process reads some of the data
5067 * to stabilize the situation.
5068 */
5069static int tcp_prune_queue(struct sock *sk)
5070{
5071	struct tcp_sock *tp = tcp_sk(sk);
5072
5073	SOCK_DEBUG(sk, "prune_queue: c=%x\n", tp->copied_seq);
5074
5075	NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PRUNECALLED);
5076
5077	if (atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf)
5078		tcp_clamp_window(sk);
5079	else if (sk_under_memory_pressure(sk))
5080		tp->rcv_ssthresh = min(tp->rcv_ssthresh, 4U * tp->advmss);
 
 
 
5081
5082	tcp_collapse_ofo_queue(sk);
5083	if (!skb_queue_empty(&sk->sk_receive_queue))
5084		tcp_collapse(sk, &sk->sk_receive_queue,
5085			     skb_peek(&sk->sk_receive_queue),
5086			     NULL,
5087			     tp->copied_seq, tp->rcv_nxt);
5088	sk_mem_reclaim(sk);
5089
5090	if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
5091		return 0;
5092
5093	/* Collapsing did not help, destructive actions follow.
5094	 * This must not ever occur. */
5095
5096	tcp_prune_ofo_queue(sk);
5097
5098	if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
5099		return 0;
5100
5101	/* If we are really being abused, tell the caller to silently
5102	 * drop receive data on the floor.  It will get retransmitted
5103	 * and hopefully then we'll have sufficient space.
5104	 */
5105	NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_RCVPRUNED);
5106
5107	/* Massive buffer overcommit. */
5108	tp->pred_flags = 0;
5109	return -1;
5110}
5111
5112/* RFC2861, slow part. Adjust cwnd, after it was not full during one rto.
5113 * As additional protections, we do not touch cwnd in retransmission phases,
5114 * and if application hit its sndbuf limit recently.
5115 */
5116void tcp_cwnd_application_limited(struct sock *sk)
5117{
5118	struct tcp_sock *tp = tcp_sk(sk);
5119
5120	if (inet_csk(sk)->icsk_ca_state == TCP_CA_Open &&
5121	    sk->sk_socket && !test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
5122		/* Limited by application or receiver window. */
5123		u32 init_win = tcp_init_cwnd(tp, __sk_dst_get(sk));
5124		u32 win_used = max(tp->snd_cwnd_used, init_win);
5125		if (win_used < tp->snd_cwnd) {
5126			tp->snd_ssthresh = tcp_current_ssthresh(sk);
5127			tp->snd_cwnd = (tp->snd_cwnd + win_used) >> 1;
5128		}
5129		tp->snd_cwnd_used = 0;
5130	}
5131	tp->snd_cwnd_stamp = tcp_time_stamp;
5132}
5133
5134static bool tcp_should_expand_sndbuf(const struct sock *sk)
5135{
5136	const struct tcp_sock *tp = tcp_sk(sk);
5137
5138	/* If the user specified a specific send buffer setting, do
5139	 * not modify it.
5140	 */
5141	if (sk->sk_userlocks & SOCK_SNDBUF_LOCK)
5142		return false;
5143
5144	/* If we are under global TCP memory pressure, do not expand.  */
5145	if (sk_under_memory_pressure(sk))
 
 
 
 
 
 
 
 
 
5146		return false;
 
5147
5148	/* If we are under soft global TCP memory pressure, do not expand.  */
5149	if (sk_memory_allocated(sk) >= sk_prot_mem_limits(sk, 0))
5150		return false;
5151
5152	/* If we filled the congestion window, do not expand.  */
5153	if (tp->packets_out >= tp->snd_cwnd)
5154		return false;
5155
5156	return true;
5157}
5158
5159/* When incoming ACK allowed to free some skb from write_queue,
5160 * we remember this event in flag SOCK_QUEUE_SHRUNK and wake up socket
5161 * on the exit from tcp input handler.
5162 *
5163 * PROBLEM: sndbuf expansion does not work well with largesend.
5164 */
5165static void tcp_new_space(struct sock *sk)
5166{
5167	struct tcp_sock *tp = tcp_sk(sk);
5168
5169	if (tcp_should_expand_sndbuf(sk)) {
5170		int sndmem = SKB_TRUESIZE(max_t(u32,
5171						tp->rx_opt.mss_clamp,
5172						tp->mss_cache) +
5173					  MAX_TCP_HEADER);
5174		int demanded = max_t(unsigned int, tp->snd_cwnd,
5175				     tp->reordering + 1);
5176		sndmem *= 2 * demanded;
5177		if (sndmem > sk->sk_sndbuf)
5178			sk->sk_sndbuf = min(sndmem, sysctl_tcp_wmem[2]);
5179		tp->snd_cwnd_stamp = tcp_time_stamp;
5180	}
5181
5182	sk->sk_write_space(sk);
5183}
5184
5185static void tcp_check_space(struct sock *sk)
5186{
5187	if (sock_flag(sk, SOCK_QUEUE_SHRUNK)) {
5188		sock_reset_flag(sk, SOCK_QUEUE_SHRUNK);
5189		if (sk->sk_socket &&
5190		    test_bit(SOCK_NOSPACE, &sk->sk_socket->flags))
5191			tcp_new_space(sk);
 
 
 
 
5192	}
5193}
5194
5195static inline void tcp_data_snd_check(struct sock *sk)
5196{
5197	tcp_push_pending_frames(sk);
5198	tcp_check_space(sk);
5199}
5200
5201/*
5202 * Check if sending an ack is needed.
5203 */
5204static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible)
5205{
5206	struct tcp_sock *tp = tcp_sk(sk);
 
5207
5208	    /* More than one full frame received... */
5209	if (((tp->rcv_nxt - tp->rcv_wup) > inet_csk(sk)->icsk_ack.rcv_mss &&
5210	     /* ... and right edge of window advances far enough.
5211	      * (tcp_recvmsg() will send ACK otherwise). Or...
 
 
5212	      */
5213	     __tcp_select_window(sk) >= tp->rcv_wnd) ||
 
5214	    /* We ACK each frame or... */
5215	    tcp_in_quickack_mode(sk) ||
5216	    /* We have out of order data. */
5217	    (ofo_possible && skb_peek(&tp->out_of_order_queue))) {
5218		/* Then ack it now */
5219		tcp_send_ack(sk);
5220	} else {
5221		/* Else, send delayed ack. */
 
 
5222		tcp_send_delayed_ack(sk);
 
 
 
 
 
 
 
 
 
 
 
 
 
 
5223	}
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
5224}
5225
5226static inline void tcp_ack_snd_check(struct sock *sk)
5227{
5228	if (!inet_csk_ack_scheduled(sk)) {
5229		/* We sent a data segment already. */
5230		return;
5231	}
5232	__tcp_ack_snd_check(sk, 1);
5233}
5234
5235/*
5236 *	This routine is only called when we have urgent data
5237 *	signaled. Its the 'slow' part of tcp_urg. It could be
5238 *	moved inline now as tcp_urg is only called from one
5239 *	place. We handle URGent data wrong. We have to - as
5240 *	BSD still doesn't use the correction from RFC961.
5241 *	For 1003.1g we should support a new option TCP_STDURG to permit
5242 *	either form (or just set the sysctl tcp_stdurg).
5243 */
5244
5245static void tcp_check_urg(struct sock *sk, const struct tcphdr *th)
5246{
5247	struct tcp_sock *tp = tcp_sk(sk);
5248	u32 ptr = ntohs(th->urg_ptr);
5249
5250	if (ptr && !sysctl_tcp_stdurg)
5251		ptr--;
5252	ptr += ntohl(th->seq);
5253
5254	/* Ignore urgent data that we've already seen and read. */
5255	if (after(tp->copied_seq, ptr))
5256		return;
5257
5258	/* Do not replay urg ptr.
5259	 *
5260	 * NOTE: interesting situation not covered by specs.
5261	 * Misbehaving sender may send urg ptr, pointing to segment,
5262	 * which we already have in ofo queue. We are not able to fetch
5263	 * such data and will stay in TCP_URG_NOTYET until will be eaten
5264	 * by recvmsg(). Seems, we are not obliged to handle such wicked
5265	 * situations. But it is worth to think about possibility of some
5266	 * DoSes using some hypothetical application level deadlock.
5267	 */
5268	if (before(ptr, tp->rcv_nxt))
5269		return;
5270
5271	/* Do we already have a newer (or duplicate) urgent pointer? */
5272	if (tp->urg_data && !after(ptr, tp->urg_seq))
5273		return;
5274
5275	/* Tell the world about our new urgent pointer. */
5276	sk_send_sigurg(sk);
5277
5278	/* We may be adding urgent data when the last byte read was
5279	 * urgent. To do this requires some care. We cannot just ignore
5280	 * tp->copied_seq since we would read the last urgent byte again
5281	 * as data, nor can we alter copied_seq until this data arrives
5282	 * or we break the semantics of SIOCATMARK (and thus sockatmark())
5283	 *
5284	 * NOTE. Double Dutch. Rendering to plain English: author of comment
5285	 * above did something sort of 	send("A", MSG_OOB); send("B", MSG_OOB);
5286	 * and expect that both A and B disappear from stream. This is _wrong_.
5287	 * Though this happens in BSD with high probability, this is occasional.
5288	 * Any application relying on this is buggy. Note also, that fix "works"
5289	 * only in this artificial test. Insert some normal data between A and B and we will
5290	 * decline of BSD again. Verdict: it is better to remove to trap
5291	 * buggy users.
5292	 */
5293	if (tp->urg_seq == tp->copied_seq && tp->urg_data &&
5294	    !sock_flag(sk, SOCK_URGINLINE) && tp->copied_seq != tp->rcv_nxt) {
5295		struct sk_buff *skb = skb_peek(&sk->sk_receive_queue);
5296		tp->copied_seq++;
5297		if (skb && !before(tp->copied_seq, TCP_SKB_CB(skb)->end_seq)) {
5298			__skb_unlink(skb, &sk->sk_receive_queue);
5299			__kfree_skb(skb);
5300		}
5301	}
5302
5303	tp->urg_data = TCP_URG_NOTYET;
5304	tp->urg_seq = ptr;
5305
5306	/* Disable header prediction. */
5307	tp->pred_flags = 0;
5308}
5309
5310/* This is the 'fast' part of urgent handling. */
5311static void tcp_urg(struct sock *sk, struct sk_buff *skb, const struct tcphdr *th)
5312{
5313	struct tcp_sock *tp = tcp_sk(sk);
5314
5315	/* Check if we get a new urgent pointer - normally not. */
5316	if (th->urg)
5317		tcp_check_urg(sk, th);
5318
5319	/* Do we wait for any urgent data? - normally not... */
5320	if (tp->urg_data == TCP_URG_NOTYET) {
5321		u32 ptr = tp->urg_seq - ntohl(th->seq) + (th->doff * 4) -
5322			  th->syn;
5323
5324		/* Is the urgent pointer pointing into this packet? */
5325		if (ptr < skb->len) {
5326			u8 tmp;
5327			if (skb_copy_bits(skb, ptr, &tmp, 1))
5328				BUG();
5329			tp->urg_data = TCP_URG_VALID | tmp;
5330			if (!sock_flag(sk, SOCK_DEAD))
5331				sk->sk_data_ready(sk, 0);
5332		}
5333	}
5334}
5335
5336static int tcp_copy_to_iovec(struct sock *sk, struct sk_buff *skb, int hlen)
5337{
5338	struct tcp_sock *tp = tcp_sk(sk);
5339	int chunk = skb->len - hlen;
5340	int err;
5341
5342	local_bh_enable();
5343	if (skb_csum_unnecessary(skb))
5344		err = skb_copy_datagram_iovec(skb, hlen, tp->ucopy.iov, chunk);
5345	else
5346		err = skb_copy_and_csum_datagram_iovec(skb, hlen,
5347						       tp->ucopy.iov);
5348
5349	if (!err) {
5350		tp->ucopy.len -= chunk;
5351		tp->copied_seq += chunk;
5352		tcp_rcv_space_adjust(sk);
5353	}
5354
5355	local_bh_disable();
5356	return err;
5357}
5358
5359static __sum16 __tcp_checksum_complete_user(struct sock *sk,
5360					    struct sk_buff *skb)
5361{
5362	__sum16 result;
5363
5364	if (sock_owned_by_user(sk)) {
5365		local_bh_enable();
5366		result = __tcp_checksum_complete(skb);
5367		local_bh_disable();
5368	} else {
5369		result = __tcp_checksum_complete(skb);
5370	}
5371	return result;
5372}
5373
5374static inline int tcp_checksum_complete_user(struct sock *sk,
5375					     struct sk_buff *skb)
5376{
5377	return !skb_csum_unnecessary(skb) &&
5378	       __tcp_checksum_complete_user(sk, skb);
5379}
5380
5381#ifdef CONFIG_NET_DMA
5382static bool tcp_dma_try_early_copy(struct sock *sk, struct sk_buff *skb,
5383				  int hlen)
5384{
5385	struct tcp_sock *tp = tcp_sk(sk);
5386	int chunk = skb->len - hlen;
5387	int dma_cookie;
5388	bool copied_early = false;
5389
5390	if (tp->ucopy.wakeup)
5391		return false;
5392
5393	if (!tp->ucopy.dma_chan && tp->ucopy.pinned_list)
5394		tp->ucopy.dma_chan = net_dma_find_channel();
5395
5396	if (tp->ucopy.dma_chan && skb_csum_unnecessary(skb)) {
5397
5398		dma_cookie = dma_skb_copy_datagram_iovec(tp->ucopy.dma_chan,
5399							 skb, hlen,
5400							 tp->ucopy.iov, chunk,
5401							 tp->ucopy.pinned_list);
5402
5403		if (dma_cookie < 0)
5404			goto out;
5405
5406		tp->ucopy.dma_cookie = dma_cookie;
5407		copied_early = true;
5408
5409		tp->ucopy.len -= chunk;
5410		tp->copied_seq += chunk;
5411		tcp_rcv_space_adjust(sk);
5412
5413		if ((tp->ucopy.len == 0) ||
5414		    (tcp_flag_word(tcp_hdr(skb)) & TCP_FLAG_PSH) ||
5415		    (atomic_read(&sk->sk_rmem_alloc) > (sk->sk_rcvbuf >> 1))) {
5416			tp->ucopy.wakeup = 1;
5417			sk->sk_data_ready(sk, 0);
5418		}
5419	} else if (chunk > 0) {
5420		tp->ucopy.wakeup = 1;
5421		sk->sk_data_ready(sk, 0);
5422	}
5423out:
5424	return copied_early;
5425}
5426#endif /* CONFIG_NET_DMA */
5427
5428/* Does PAWS and seqno based validation of an incoming segment, flags will
5429 * play significant role here.
5430 */
5431static int tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
5432			      const struct tcphdr *th, int syn_inerr)
5433{
5434	const u8 *hash_location;
5435	struct tcp_sock *tp = tcp_sk(sk);
 
5436
5437	/* RFC1323: H1. Apply PAWS check first. */
5438	if (tcp_fast_parse_options(skb, th, tp, &hash_location) &&
5439	    tp->rx_opt.saw_tstamp &&
5440	    tcp_paws_discard(sk, skb)) {
5441		if (!th->rst) {
5442			NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);
5443			tcp_send_dupack(sk, skb);
 
 
 
 
5444			goto discard;
5445		}
5446		/* Reset is accepted even if it did not pass PAWS. */
5447	}
5448
5449	/* Step 1: check sequence number */
5450	if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) {
5451		/* RFC793, page 37: "In all states except SYN-SENT, all reset
5452		 * (RST) segments are validated by checking their SEQ-fields."
5453		 * And page 69: "If an incoming segment is not acceptable,
5454		 * an acknowledgment should be sent in reply (unless the RST
5455		 * bit is set, if so drop the segment and return)".
5456		 */
5457		if (!th->rst)
5458			tcp_send_dupack(sk, skb);
 
 
 
 
 
 
 
 
 
5459		goto discard;
5460	}
5461
5462	/* Step 2: check RST bit */
5463	if (th->rst) {
5464		tcp_reset(sk);
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
5465		goto discard;
5466	}
5467
5468	/* ts_recent update must be made after we are sure that the packet
5469	 * is in window.
5470	 */
5471	tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
5472
5473	/* step 3: check security and precedence [ignored] */
5474
5475	/* step 4: Check for a SYN in window. */
5476	if (th->syn && !before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
 
 
 
5477		if (syn_inerr)
5478			TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS);
5479		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONSYN);
5480		tcp_reset(sk);
5481		return -1;
 
5482	}
5483
5484	return 1;
 
 
5485
5486discard:
 
 
 
 
 
5487	__kfree_skb(skb);
5488	return 0;
5489}
5490
5491/*
5492 *	TCP receive function for the ESTABLISHED state.
5493 *
5494 *	It is split into a fast path and a slow path. The fast path is
5495 * 	disabled when:
5496 *	- A zero window was announced from us - zero window probing
5497 *        is only handled properly in the slow path.
5498 *	- Out of order segments arrived.
5499 *	- Urgent data is expected.
5500 *	- There is no buffer space left
5501 *	- Unexpected TCP flags/window values/header lengths are received
5502 *	  (detected by checking the TCP header against pred_flags)
5503 *	- Data is sent in both directions. Fast path only supports pure senders
5504 *	  or pure receivers (this means either the sequence number or the ack
5505 *	  value must stay constant)
5506 *	- Unexpected TCP option.
5507 *
5508 *	When these conditions are not satisfied it drops into a standard
5509 *	receive procedure patterned after RFC793 to handle all cases.
5510 *	The first three cases are guaranteed by proper pred_flags setting,
5511 *	the rest is checked inline. Fast processing is turned on in
5512 *	tcp_data_queue when everything is OK.
5513 */
5514int tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
5515			const struct tcphdr *th, unsigned int len)
5516{
 
 
5517	struct tcp_sock *tp = tcp_sk(sk);
5518	int res;
5519
 
 
 
 
 
 
5520	/*
5521	 *	Header prediction.
5522	 *	The code loosely follows the one in the famous
5523	 *	"30 instruction TCP receive" Van Jacobson mail.
5524	 *
5525	 *	Van's trick is to deposit buffers into socket queue
5526	 *	on a device interrupt, to call tcp_recv function
5527	 *	on the receive process context and checksum and copy
5528	 *	the buffer to user space. smart...
5529	 *
5530	 *	Our current scheme is not silly either but we take the
5531	 *	extra cost of the net_bh soft interrupt processing...
5532	 *	We do checksum and copy also but from device to kernel.
5533	 */
5534
5535	tp->rx_opt.saw_tstamp = 0;
5536
5537	/*	pred_flags is 0xS?10 << 16 + snd_wnd
5538	 *	if header_prediction is to be made
5539	 *	'S' will always be tp->tcp_header_len >> 2
5540	 *	'?' will be 0 for the fast path, otherwise pred_flags is 0 to
5541	 *  turn it off	(when there are holes in the receive
5542	 *	 space for instance)
5543	 *	PSH flag is ignored.
5544	 */
5545
5546	if ((tcp_flag_word(th) & TCP_HP_BITS) == tp->pred_flags &&
5547	    TCP_SKB_CB(skb)->seq == tp->rcv_nxt &&
5548	    !after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt)) {
5549		int tcp_header_len = tp->tcp_header_len;
5550
5551		/* Timestamp header prediction: tcp_header_len
5552		 * is automatically equal to th->doff*4 due to pred_flags
5553		 * match.
5554		 */
5555
5556		/* Check timestamp */
5557		if (tcp_header_len == sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) {
5558			/* No? Slow path! */
5559			if (!tcp_parse_aligned_timestamp(tp, th))
5560				goto slow_path;
5561
5562			/* If PAWS failed, check it more carefully in slow path */
5563			if ((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) < 0)
5564				goto slow_path;
5565
5566			/* DO NOT update ts_recent here, if checksum fails
5567			 * and timestamp was corrupted part, it will result
5568			 * in a hung connection since we will drop all
5569			 * future packets due to the PAWS test.
5570			 */
5571		}
5572
5573		if (len <= tcp_header_len) {
5574			/* Bulk data transfer: sender */
5575			if (len == tcp_header_len) {
5576				/* Predicted packet is in window by definition.
5577				 * seq == rcv_nxt and rcv_wup <= rcv_nxt.
5578				 * Hence, check seq<=rcv_wup reduces to:
5579				 */
5580				if (tcp_header_len ==
5581				    (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
5582				    tp->rcv_nxt == tp->rcv_wup)
5583					tcp_store_ts_recent(tp);
5584
5585				/* We know that such packets are checksummed
5586				 * on entry.
5587				 */
5588				tcp_ack(sk, skb, 0);
5589				__kfree_skb(skb);
5590				tcp_data_snd_check(sk);
5591				return 0;
 
 
 
 
 
5592			} else { /* Header too small */
5593				TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS);
 
5594				goto discard;
5595			}
5596		} else {
5597			int eaten = 0;
5598			int copied_early = 0;
5599			bool fragstolen = false;
5600
5601			if (tp->copied_seq == tp->rcv_nxt &&
5602			    len - tcp_header_len <= tp->ucopy.len) {
5603#ifdef CONFIG_NET_DMA
5604				if (tp->ucopy.task == current &&
5605				    sock_owned_by_user(sk) &&
5606				    tcp_dma_try_early_copy(sk, skb, tcp_header_len)) {
5607					copied_early = 1;
5608					eaten = 1;
5609				}
5610#endif
5611				if (tp->ucopy.task == current &&
5612				    sock_owned_by_user(sk) && !copied_early) {
5613					__set_current_state(TASK_RUNNING);
5614
5615					if (!tcp_copy_to_iovec(sk, skb, tcp_header_len))
5616						eaten = 1;
5617				}
5618				if (eaten) {
5619					/* Predicted packet is in window by definition.
5620					 * seq == rcv_nxt and rcv_wup <= rcv_nxt.
5621					 * Hence, check seq<=rcv_wup reduces to:
5622					 */
5623					if (tcp_header_len ==
5624					    (sizeof(struct tcphdr) +
5625					     TCPOLEN_TSTAMP_ALIGNED) &&
5626					    tp->rcv_nxt == tp->rcv_wup)
5627						tcp_store_ts_recent(tp);
5628
5629					tcp_rcv_rtt_measure_ts(sk, skb);
5630
5631					__skb_pull(skb, tcp_header_len);
5632					tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
5633					NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPHITSTOUSER);
5634				}
5635				if (copied_early)
5636					tcp_cleanup_rbuf(sk, skb->len);
5637			}
5638			if (!eaten) {
5639				if (tcp_checksum_complete_user(sk, skb))
5640					goto csum_error;
5641
5642				/* Predicted packet is in window by definition.
5643				 * seq == rcv_nxt and rcv_wup <= rcv_nxt.
5644				 * Hence, check seq<=rcv_wup reduces to:
5645				 */
5646				if (tcp_header_len ==
5647				    (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
5648				    tp->rcv_nxt == tp->rcv_wup)
5649					tcp_store_ts_recent(tp);
5650
5651				tcp_rcv_rtt_measure_ts(sk, skb);
5652
5653				if ((int)skb->truesize > sk->sk_forward_alloc)
5654					goto step5;
5655
5656				NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPHITS);
5657
5658				/* Bulk data transfer: receiver */
5659				eaten = tcp_queue_rcv(sk, skb, tcp_header_len,
5660						      &fragstolen);
5661			}
5662
5663			tcp_event_data_recv(sk, skb);
5664
5665			if (TCP_SKB_CB(skb)->ack_seq != tp->snd_una) {
5666				/* Well, only one small jumplet in fast path... */
5667				tcp_ack(sk, skb, FLAG_DATA);
5668				tcp_data_snd_check(sk);
5669				if (!inet_csk_ack_scheduled(sk))
5670					goto no_ack;
 
 
5671			}
5672
5673			if (!copied_early || tp->rcv_nxt != tp->rcv_wup)
5674				__tcp_ack_snd_check(sk, 0);
5675no_ack:
5676#ifdef CONFIG_NET_DMA
5677			if (copied_early)
5678				__skb_queue_tail(&sk->sk_async_wait_queue, skb);
5679			else
5680#endif
5681			if (eaten)
5682				kfree_skb_partial(skb, fragstolen);
5683			else
5684				sk->sk_data_ready(sk, 0);
5685			return 0;
5686		}
5687	}
5688
5689slow_path:
5690	if (len < (th->doff << 2) || tcp_checksum_complete_user(sk, skb))
5691		goto csum_error;
5692
 
 
 
 
 
5693	/*
5694	 *	Standard slow path.
5695	 */
5696
5697	res = tcp_validate_incoming(sk, skb, th, 1);
5698	if (res <= 0)
5699		return -res;
5700
5701step5:
5702	if (th->ack && tcp_ack(sk, skb, FLAG_SLOWPATH) < 0)
 
 
5703		goto discard;
5704
5705	tcp_rcv_rtt_measure_ts(sk, skb);
5706
5707	/* Process urgent data. */
5708	tcp_urg(sk, skb, th);
5709
5710	/* step 7: process the segment text */
5711	tcp_data_queue(sk, skb);
5712
5713	tcp_data_snd_check(sk);
5714	tcp_ack_snd_check(sk);
5715	return 0;
5716
5717csum_error:
5718	TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS);
 
 
 
5719
5720discard:
5721	__kfree_skb(skb);
5722	return 0;
5723}
5724EXPORT_SYMBOL(tcp_rcv_established);
5725
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
5726void tcp_finish_connect(struct sock *sk, struct sk_buff *skb)
5727{
5728	struct tcp_sock *tp = tcp_sk(sk);
5729	struct inet_connection_sock *icsk = inet_csk(sk);
5730
5731	tcp_set_state(sk, TCP_ESTABLISHED);
 
5732
5733	if (skb != NULL)
 
5734		security_inet_conn_established(sk, skb);
 
 
5735
5736	/* Make sure socket is routed, for correct metrics.  */
5737	icsk->icsk_af_ops->rebuild_header(sk);
5738
5739	tcp_init_metrics(sk);
5740
5741	tcp_init_congestion_control(sk);
5742
5743	/* Prevent spurious tcp_cwnd_restart() on first data
5744	 * packet.
5745	 */
5746	tp->lsndtime = tcp_time_stamp;
5747
5748	tcp_init_buffer_space(sk);
5749
5750	if (sock_flag(sk, SOCK_KEEPOPEN))
5751		inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tp));
5752
5753	if (!tp->rx_opt.snd_wscale)
5754		__tcp_fast_path_on(tp, tp->snd_wnd);
5755	else
5756		tp->pred_flags = 0;
 
5757
5758	if (!sock_flag(sk, SOCK_DEAD)) {
5759		sk->sk_state_change(sk);
5760		sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT);
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
5761	}
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
5762}
5763
5764static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
5765					 const struct tcphdr *th, unsigned int len)
5766{
5767	const u8 *hash_location;
5768	struct inet_connection_sock *icsk = inet_csk(sk);
5769	struct tcp_sock *tp = tcp_sk(sk);
5770	struct tcp_cookie_values *cvp = tp->cookie_values;
5771	int saved_clamp = tp->rx_opt.mss_clamp;
 
 
5772
5773	tcp_parse_options(skb, &tp->rx_opt, &hash_location, 0);
 
 
5774
5775	if (th->ack) {
5776		/* rfc793:
5777		 * "If the state is SYN-SENT then
5778		 *    first check the ACK bit
5779		 *      If the ACK bit is set
5780		 *	  If SEG.ACK =< ISS, or SEG.ACK > SND.NXT, send
5781		 *        a reset (unless the RST bit is set, if so drop
5782		 *        the segment and return)"
5783		 *
5784		 *  We do not send data with SYN, so that RFC-correct
5785		 *  test reduces to:
5786		 */
5787		if (TCP_SKB_CB(skb)->ack_seq != tp->snd_nxt)
 
 
 
 
 
 
5788			goto reset_and_undo;
 
5789
5790		if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
5791		    !between(tp->rx_opt.rcv_tsecr, tp->retrans_stamp,
5792			     tcp_time_stamp)) {
5793			NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSACTIVEREJECTED);
 
5794			goto reset_and_undo;
5795		}
5796
5797		/* Now ACK is acceptable.
5798		 *
5799		 * "If the RST bit is set
5800		 *    If the ACK was acceptable then signal the user "error:
5801		 *    connection reset", drop the segment, enter CLOSED state,
5802		 *    delete TCB, and return."
5803		 */
5804
5805		if (th->rst) {
5806			tcp_reset(sk);
5807			goto discard;
 
 
5808		}
5809
5810		/* rfc793:
5811		 *   "fifth, if neither of the SYN or RST bits is set then
5812		 *    drop the segment and return."
5813		 *
5814		 *    See note below!
5815		 *                                        --ANK(990513)
5816		 */
5817		if (!th->syn)
 
5818			goto discard_and_undo;
5819
5820		/* rfc793:
5821		 *   "If the SYN bit is on ...
5822		 *    are acceptable then ...
5823		 *    (our SYN has been ACKed), change the connection
5824		 *    state to ESTABLISHED..."
5825		 */
5826
5827		TCP_ECN_rcv_synack(tp, th);
5828
5829		tp->snd_wl1 = TCP_SKB_CB(skb)->seq;
 
5830		tcp_ack(sk, skb, FLAG_SLOWPATH);
5831
5832		/* Ok.. it's good. Set up sequence numbers and
5833		 * move to established.
5834		 */
5835		tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
5836		tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
5837
5838		/* RFC1323: The window in SYN & SYN/ACK segments is
5839		 * never scaled.
5840		 */
5841		tp->snd_wnd = ntohs(th->window);
5842		tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);
5843
5844		if (!tp->rx_opt.wscale_ok) {
5845			tp->rx_opt.snd_wscale = tp->rx_opt.rcv_wscale = 0;
5846			tp->window_clamp = min(tp->window_clamp, 65535U);
5847		}
5848
5849		if (tp->rx_opt.saw_tstamp) {
5850			tp->rx_opt.tstamp_ok	   = 1;
5851			tp->tcp_header_len =
5852				sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
5853			tp->advmss	    -= TCPOLEN_TSTAMP_ALIGNED;
5854			tcp_store_ts_recent(tp);
5855		} else {
5856			tp->tcp_header_len = sizeof(struct tcphdr);
5857		}
5858
5859		if (tcp_is_sack(tp) && sysctl_tcp_fack)
5860			tcp_enable_fack(tp);
5861
5862		tcp_mtup_init(sk);
5863		tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
5864		tcp_initialize_rcv_mss(sk);
5865
5866		/* Remember, tcp_poll() does not lock socket!
5867		 * Change state from SYN-SENT only after copied_seq
5868		 * is initialized. */
5869		tp->copied_seq = tp->rcv_nxt;
5870
5871		if (cvp != NULL &&
5872		    cvp->cookie_pair_size > 0 &&
5873		    tp->rx_opt.cookie_plus > 0) {
5874			int cookie_size = tp->rx_opt.cookie_plus
5875					- TCPOLEN_COOKIE_BASE;
5876			int cookie_pair_size = cookie_size
5877					     + cvp->cookie_desired;
5878
5879			/* A cookie extension option was sent and returned.
5880			 * Note that each incoming SYNACK replaces the
5881			 * Responder cookie.  The initial exchange is most
5882			 * fragile, as protection against spoofing relies
5883			 * entirely upon the sequence and timestamp (above).
5884			 * This replacement strategy allows the correct pair to
5885			 * pass through, while any others will be filtered via
5886			 * Responder verification later.
5887			 */
5888			if (sizeof(cvp->cookie_pair) >= cookie_pair_size) {
5889				memcpy(&cvp->cookie_pair[cvp->cookie_desired],
5890				       hash_location, cookie_size);
5891				cvp->cookie_pair_size = cookie_pair_size;
5892			}
5893		}
5894
5895		smp_mb();
5896
5897		tcp_finish_connect(sk, skb);
5898
 
 
 
 
 
 
 
 
 
5899		if (sk->sk_write_pending ||
5900		    icsk->icsk_accept_queue.rskq_defer_accept ||
5901		    icsk->icsk_ack.pingpong) {
5902			/* Save one ACK. Data will be ready after
5903			 * several ticks, if write_pending is set.
5904			 *
5905			 * It may be deleted, but with this feature tcpdumps
5906			 * look so _wonderfully_ clever, that I was not able
5907			 * to stand against the temptation 8)     --ANK
5908			 */
5909			inet_csk_schedule_ack(sk);
5910			icsk->icsk_ack.lrcvtime = tcp_time_stamp;
5911			tcp_enter_quickack_mode(sk);
5912			inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
5913						  TCP_DELACK_MAX, TCP_RTO_MAX);
5914
5915discard:
5916			__kfree_skb(skb);
5917			return 0;
5918		} else {
5919			tcp_send_ack(sk);
5920		}
 
5921		return -1;
5922	}
5923
5924	/* No ACK in the segment */
5925
5926	if (th->rst) {
5927		/* rfc793:
5928		 * "If the RST bit is set
5929		 *
5930		 *      Otherwise (no ACK) drop the segment and return."
5931		 */
5932
5933		goto discard_and_undo;
5934	}
5935
5936	/* PAWS check. */
5937	if (tp->rx_opt.ts_recent_stamp && tp->rx_opt.saw_tstamp &&
5938	    tcp_paws_reject(&tp->rx_opt, 0))
 
5939		goto discard_and_undo;
5940
5941	if (th->syn) {
5942		/* We see SYN without ACK. It is attempt of
5943		 * simultaneous connect with crossed SYNs.
5944		 * Particularly, it can be connect to self.
5945		 */
5946		tcp_set_state(sk, TCP_SYN_RECV);
5947
5948		if (tp->rx_opt.saw_tstamp) {
5949			tp->rx_opt.tstamp_ok = 1;
5950			tcp_store_ts_recent(tp);
5951			tp->tcp_header_len =
5952				sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
5953		} else {
5954			tp->tcp_header_len = sizeof(struct tcphdr);
5955		}
5956
5957		tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
 
5958		tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
5959
5960		/* RFC1323: The window in SYN & SYN/ACK segments is
5961		 * never scaled.
5962		 */
5963		tp->snd_wnd    = ntohs(th->window);
5964		tp->snd_wl1    = TCP_SKB_CB(skb)->seq;
5965		tp->max_window = tp->snd_wnd;
5966
5967		TCP_ECN_rcv_syn(tp, th);
5968
5969		tcp_mtup_init(sk);
5970		tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
5971		tcp_initialize_rcv_mss(sk);
5972
5973		tcp_send_synack(sk);
5974#if 0
5975		/* Note, we could accept data and URG from this segment.
5976		 * There are no obstacles to make this.
 
 
5977		 *
5978		 * However, if we ignore data in ACKless segments sometimes,
5979		 * we have no reasons to accept it sometimes.
5980		 * Also, seems the code doing it in step6 of tcp_rcv_state_process
5981		 * is not flawless. So, discard packet for sanity.
5982		 * Uncomment this return to process the data.
5983		 */
5984		return -1;
5985#else
5986		goto discard;
5987#endif
5988	}
5989	/* "fifth, if neither of the SYN or RST bits is set then
5990	 * drop the segment and return."
5991	 */
5992
5993discard_and_undo:
5994	tcp_clear_options(&tp->rx_opt);
5995	tp->rx_opt.mss_clamp = saved_clamp;
5996	goto discard;
 
5997
5998reset_and_undo:
5999	tcp_clear_options(&tp->rx_opt);
6000	tp->rx_opt.mss_clamp = saved_clamp;
6001	return 1;
6002}
6003
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
6004/*
6005 *	This function implements the receiving procedure of RFC 793 for
6006 *	all states except ESTABLISHED and TIME_WAIT.
6007 *	It's called from both tcp_v4_rcv and tcp_v6_rcv and should be
6008 *	address independent.
6009 */
6010
6011int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
6012			  const struct tcphdr *th, unsigned int len)
6013{
6014	struct tcp_sock *tp = tcp_sk(sk);
6015	struct inet_connection_sock *icsk = inet_csk(sk);
 
 
6016	int queued = 0;
6017	int res;
6018
6019	tp->rx_opt.saw_tstamp = 0;
6020
6021	switch (sk->sk_state) {
6022	case TCP_CLOSE:
 
6023		goto discard;
6024
6025	case TCP_LISTEN:
6026		if (th->ack)
6027			return 1;
6028
6029		if (th->rst)
 
6030			goto discard;
6031
6032		if (th->syn) {
6033			if (th->fin)
 
6034				goto discard;
6035			if (icsk->icsk_af_ops->conn_request(sk, skb) < 0)
6036				return 1;
6037
6038			/* Now we have several options: In theory there is
6039			 * nothing else in the frame. KA9Q has an option to
6040			 * send data with the syn, BSD accepts data with the
6041			 * syn up to the [to be] advertised window and
6042			 * Solaris 2.1 gives you a protocol error. For now
6043			 * we just ignore it, that fits the spec precisely
6044			 * and avoids incompatibilities. It would be nice in
6045			 * future to drop through and process the data.
6046			 *
6047			 * Now that TTCP is starting to be used we ought to
6048			 * queue this data.
6049			 * But, this leaves one open to an easy denial of
6050			 * service attack, and SYN cookies can't defend
6051			 * against this problem. So, we drop the data
6052			 * in the interest of security over speed unless
6053			 * it's still in use.
6054			 */
6055			kfree_skb(skb);
 
 
 
 
 
 
 
 
6056			return 0;
6057		}
 
6058		goto discard;
6059
6060	case TCP_SYN_SENT:
6061		queued = tcp_rcv_synsent_state_process(sk, skb, th, len);
 
 
6062		if (queued >= 0)
6063			return queued;
6064
6065		/* Do step6 onward by hand. */
6066		tcp_urg(sk, skb, th);
6067		__kfree_skb(skb);
6068		tcp_data_snd_check(sk);
6069		return 0;
6070	}
6071
6072	res = tcp_validate_incoming(sk, skb, th, 0);
6073	if (res <= 0)
6074		return -res;
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
6075
6076	/* step 5: check the ACK field */
6077	if (th->ack) {
6078		int acceptable = tcp_ack(sk, skb, FLAG_SLOWPATH) > 0;
 
 
 
 
 
 
 
 
 
 
 
 
 
 
6079
6080		switch (sk->sk_state) {
6081		case TCP_SYN_RECV:
6082			if (acceptable) {
6083				tp->copied_seq = tp->rcv_nxt;
6084				smp_mb();
6085				tcp_set_state(sk, TCP_ESTABLISHED);
6086				sk->sk_state_change(sk);
6087
6088				/* Note, that this wakeup is only for marginal
6089				 * crossed SYN case. Passively open sockets
6090				 * are not waked up, because sk->sk_sleep ==
6091				 * NULL and sk->sk_socket == NULL.
6092				 */
6093				if (sk->sk_socket)
6094					sk_wake_async(sk,
6095						      SOCK_WAKE_IO, POLL_OUT);
6096
6097				tp->snd_una = TCP_SKB_CB(skb)->ack_seq;
6098				tp->snd_wnd = ntohs(th->window) <<
6099					      tp->rx_opt.snd_wscale;
6100				tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);
6101
6102				if (tp->rx_opt.tstamp_ok)
6103					tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;
 
 
 
 
6104
6105				/* Make sure socket is routed, for
6106				 * correct metrics.
6107				 */
6108				icsk->icsk_af_ops->rebuild_header(sk);
6109
6110				tcp_init_metrics(sk);
 
6111
6112				tcp_init_congestion_control(sk);
 
6113
6114				/* Prevent spurious tcp_cwnd_restart() on
6115				 * first data packet.
6116				 */
6117				tp->lsndtime = tcp_time_stamp;
6118
6119				tcp_mtup_init(sk);
6120				tcp_initialize_rcv_mss(sk);
6121				tcp_init_buffer_space(sk);
6122				tcp_fast_path_on(tp);
6123			} else {
6124				return 1;
6125			}
6126			break;
6127
6128		case TCP_FIN_WAIT1:
6129			if (tp->snd_una == tp->write_seq) {
6130				tcp_set_state(sk, TCP_FIN_WAIT2);
6131				sk->sk_shutdown |= SEND_SHUTDOWN;
6132				dst_confirm(__sk_dst_get(sk));
6133
6134				if (!sock_flag(sk, SOCK_DEAD))
6135					/* Wake up lingering close() */
6136					sk->sk_state_change(sk);
6137				else {
6138					int tmo;
6139
6140					if (tp->linger2 < 0 ||
6141					    (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
6142					     after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt))) {
6143						tcp_done(sk);
6144						NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
6145						return 1;
6146					}
6147
6148					tmo = tcp_fin_time(sk);
6149					if (tmo > TCP_TIMEWAIT_LEN) {
6150						inet_csk_reset_keepalive_timer(sk, tmo - TCP_TIMEWAIT_LEN);
6151					} else if (th->fin || sock_owned_by_user(sk)) {
6152						/* Bad case. We could lose such FIN otherwise.
6153						 * It is not a big problem, but it looks confusing
6154						 * and not so rare event. We still can lose it now,
6155						 * if it spins in bh_lock_sock(), but it is really
6156						 * marginal case.
6157						 */
6158						inet_csk_reset_keepalive_timer(sk, tmo);
6159					} else {
6160						tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
6161						goto discard;
6162					}
6163				}
6164			}
6165			break;
6166
6167		case TCP_CLOSING:
6168			if (tp->snd_una == tp->write_seq) {
6169				tcp_time_wait(sk, TCP_TIME_WAIT, 0);
6170				goto discard;
6171			}
6172			break;
6173
6174		case TCP_LAST_ACK:
6175			if (tp->snd_una == tp->write_seq) {
6176				tcp_update_metrics(sk);
6177				tcp_done(sk);
6178				goto discard;
6179			}
 
 
6180			break;
6181		}
6182	} else
6183		goto discard;
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
6184
6185	/* step 6: check the URG bit */
6186	tcp_urg(sk, skb, th);
6187
6188	/* step 7: process the segment text */
6189	switch (sk->sk_state) {
6190	case TCP_CLOSE_WAIT:
6191	case TCP_CLOSING:
6192	case TCP_LAST_ACK:
6193		if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
 
 
 
 
 
6194			break;
 
 
6195	case TCP_FIN_WAIT1:
6196	case TCP_FIN_WAIT2:
6197		/* RFC 793 says to queue data in these states,
6198		 * RFC 1122 says we MUST send a reset.
6199		 * BSD 4.4 also does reset.
6200		 */
6201		if (sk->sk_shutdown & RCV_SHUTDOWN) {
6202			if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
6203			    after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) {
6204				NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
6205				tcp_reset(sk);
6206				return 1;
6207			}
6208		}
6209		/* Fall through */
6210	case TCP_ESTABLISHED:
6211		tcp_data_queue(sk, skb);
6212		queued = 1;
6213		break;
6214	}
6215
6216	/* tcp_data could move socket to TIME-WAIT */
6217	if (sk->sk_state != TCP_CLOSE) {
6218		tcp_data_snd_check(sk);
6219		tcp_ack_snd_check(sk);
6220	}
6221
6222	if (!queued) {
6223discard:
6224		__kfree_skb(skb);
6225	}
6226	return 0;
 
 
 
 
6227}
6228EXPORT_SYMBOL(tcp_rcv_state_process);