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#include <linux/mm.h>
  65#include <linux/slab.h>
  66#include <linux/module.h>
  67#include <linux/sysctl.h>
  68#include <linux/kernel.h>
  69#include <net/dst.h>
  70#include <net/tcp.h>
  71#include <net/inet_common.h>
  72#include <linux/ipsec.h>
  73#include <asm/unaligned.h>
  74#include <net/netdma.h>
  75
  76int sysctl_tcp_timestamps __read_mostly = 1;
  77int sysctl_tcp_window_scaling __read_mostly = 1;
  78int sysctl_tcp_sack __read_mostly = 1;
  79int sysctl_tcp_fack __read_mostly = 1;
  80int sysctl_tcp_reordering __read_mostly = TCP_FASTRETRANS_THRESH;
  81EXPORT_SYMBOL(sysctl_tcp_reordering);
  82int sysctl_tcp_ecn __read_mostly = 2;
  83EXPORT_SYMBOL(sysctl_tcp_ecn);
  84int sysctl_tcp_dsack __read_mostly = 1;
  85int sysctl_tcp_app_win __read_mostly = 31;
  86int sysctl_tcp_adv_win_scale __read_mostly = 2;
  87EXPORT_SYMBOL(sysctl_tcp_adv_win_scale);
  88
  89int sysctl_tcp_stdurg __read_mostly;
  90int sysctl_tcp_rfc1337 __read_mostly;
  91int sysctl_tcp_max_orphans __read_mostly = NR_FILE;
  92int sysctl_tcp_frto __read_mostly = 2;
  93int sysctl_tcp_frto_response __read_mostly;
  94int sysctl_tcp_nometrics_save __read_mostly;
  95
  96int sysctl_tcp_thin_dupack __read_mostly;
  97
  98int sysctl_tcp_moderate_rcvbuf __read_mostly = 1;
  99int sysctl_tcp_abc __read_mostly;
 
 100
 101#define FLAG_DATA		0x01 /* Incoming frame contained data.		*/
 102#define FLAG_WIN_UPDATE		0x02 /* Incoming ACK was a window update.	*/
 103#define FLAG_DATA_ACKED		0x04 /* This ACK acknowledged new data.		*/
 104#define FLAG_RETRANS_DATA_ACKED	0x08 /* "" "" some of which was retransmitted.	*/
 105#define FLAG_SYN_ACKED		0x10 /* This ACK acknowledged SYN.		*/
 106#define FLAG_DATA_SACKED	0x20 /* New SACK.				*/
 107#define FLAG_ECE		0x40 /* ECE in this ACK				*/
 108#define FLAG_DATA_LOST		0x80 /* SACK detected data lossage.		*/
 109#define FLAG_SLOWPATH		0x100 /* Do not skip RFC checks for window update.*/
 110#define FLAG_ONLY_ORIG_SACKED	0x200 /* SACKs only non-rexmit sent before RTO */
 111#define FLAG_SND_UNA_ADVANCED	0x400 /* Snd_una was changed (!= FLAG_DATA_ACKED) */
 112#define FLAG_DSACKING_ACK	0x800 /* SACK blocks contained D-SACK info */
 113#define FLAG_NONHEAD_RETRANS_ACKED	0x1000 /* Non-head rexmitted data was ACKed */
 114#define FLAG_SACK_RENEGING	0x2000 /* snd_una advanced to a sacked seq */
 115
 116#define FLAG_ACKED		(FLAG_DATA_ACKED|FLAG_SYN_ACKED)
 117#define FLAG_NOT_DUP		(FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED)
 118#define FLAG_CA_ALERT		(FLAG_DATA_SACKED|FLAG_ECE)
 119#define FLAG_FORWARD_PROGRESS	(FLAG_ACKED|FLAG_DATA_SACKED)
 120#define FLAG_ANY_PROGRESS	(FLAG_FORWARD_PROGRESS|FLAG_SND_UNA_ADVANCED)
 121
 122#define TCP_REMNANT (TCP_FLAG_FIN|TCP_FLAG_URG|TCP_FLAG_SYN|TCP_FLAG_PSH)
 123#define TCP_HP_BITS (~(TCP_RESERVED_BITS|TCP_FLAG_PSH))
 124
 125/* Adapt the MSS value used to make delayed ack decision to the
 126 * real world.
 127 */
 128static void tcp_measure_rcv_mss(struct sock *sk, const struct sk_buff *skb)
 129{
 130	struct inet_connection_sock *icsk = inet_csk(sk);
 131	const unsigned int lss = icsk->icsk_ack.last_seg_size;
 132	unsigned int len;
 133
 134	icsk->icsk_ack.last_seg_size = 0;
 135
 136	/* skb->len may jitter because of SACKs, even if peer
 137	 * sends good full-sized frames.
 138	 */
 139	len = skb_shinfo(skb)->gso_size ? : skb->len;
 140	if (len >= icsk->icsk_ack.rcv_mss) {
 141		icsk->icsk_ack.rcv_mss = len;
 142	} else {
 143		/* Otherwise, we make more careful check taking into account,
 144		 * that SACKs block is variable.
 145		 *
 146		 * "len" is invariant segment length, including TCP header.
 147		 */
 148		len += skb->data - skb_transport_header(skb);
 149		if (len >= TCP_MSS_DEFAULT + sizeof(struct tcphdr) ||
 150		    /* If PSH is not set, packet should be
 151		     * full sized, provided peer TCP is not badly broken.
 152		     * This observation (if it is correct 8)) allows
 153		     * to handle super-low mtu links fairly.
 154		     */
 155		    (len >= TCP_MIN_MSS + sizeof(struct tcphdr) &&
 156		     !(tcp_flag_word(tcp_hdr(skb)) & TCP_REMNANT))) {
 157			/* Subtract also invariant (if peer is RFC compliant),
 158			 * tcp header plus fixed timestamp option length.
 159			 * Resulting "len" is MSS free of SACK jitter.
 160			 */
 161			len -= tcp_sk(sk)->tcp_header_len;
 162			icsk->icsk_ack.last_seg_size = len;
 163			if (len == lss) {
 164				icsk->icsk_ack.rcv_mss = len;
 165				return;
 166			}
 167		}
 168		if (icsk->icsk_ack.pending & ICSK_ACK_PUSHED)
 169			icsk->icsk_ack.pending |= ICSK_ACK_PUSHED2;
 170		icsk->icsk_ack.pending |= ICSK_ACK_PUSHED;
 171	}
 172}
 173
 174static void tcp_incr_quickack(struct sock *sk)
 175{
 176	struct inet_connection_sock *icsk = inet_csk(sk);
 177	unsigned quickacks = tcp_sk(sk)->rcv_wnd / (2 * icsk->icsk_ack.rcv_mss);
 178
 179	if (quickacks == 0)
 180		quickacks = 2;
 181	if (quickacks > icsk->icsk_ack.quick)
 182		icsk->icsk_ack.quick = min(quickacks, TCP_MAX_QUICKACKS);
 183}
 184
 185static void tcp_enter_quickack_mode(struct sock *sk)
 186{
 187	struct inet_connection_sock *icsk = inet_csk(sk);
 188	tcp_incr_quickack(sk);
 189	icsk->icsk_ack.pingpong = 0;
 190	icsk->icsk_ack.ato = TCP_ATO_MIN;
 191}
 192
 193/* Send ACKs quickly, if "quick" count is not exhausted
 194 * and the session is not interactive.
 195 */
 196
 197static inline int tcp_in_quickack_mode(const struct sock *sk)
 198{
 199	const struct inet_connection_sock *icsk = inet_csk(sk);
 
 200	return icsk->icsk_ack.quick && !icsk->icsk_ack.pingpong;
 201}
 202
 203static inline void TCP_ECN_queue_cwr(struct tcp_sock *tp)
 204{
 205	if (tp->ecn_flags & TCP_ECN_OK)
 206		tp->ecn_flags |= TCP_ECN_QUEUE_CWR;
 207}
 208
 209static inline void TCP_ECN_accept_cwr(struct tcp_sock *tp, struct sk_buff *skb)
 210{
 211	if (tcp_hdr(skb)->cwr)
 212		tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
 213}
 214
 215static inline void TCP_ECN_withdraw_cwr(struct tcp_sock *tp)
 216{
 217	tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
 218}
 219
 220static inline void TCP_ECN_check_ce(struct tcp_sock *tp, struct sk_buff *skb)
 221{
 222	if (tp->ecn_flags & TCP_ECN_OK) {
 223		if (INET_ECN_is_ce(TCP_SKB_CB(skb)->flags))
 224			tp->ecn_flags |= TCP_ECN_DEMAND_CWR;
 
 
 225		/* Funny extension: if ECT is not set on a segment,
 226		 * it is surely retransmit. It is not in ECN RFC,
 227		 * but Linux follows this rule. */
 228		else if (INET_ECN_is_not_ect((TCP_SKB_CB(skb)->flags)))
 
 229			tcp_enter_quickack_mode((struct sock *)tp);
 
 
 
 
 
 
 230	}
 231}
 232
 233static inline void TCP_ECN_rcv_synack(struct tcp_sock *tp, struct tcphdr *th)
 234{
 235	if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || th->cwr))
 236		tp->ecn_flags &= ~TCP_ECN_OK;
 237}
 238
 239static inline void TCP_ECN_rcv_syn(struct tcp_sock *tp, struct tcphdr *th)
 240{
 241	if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || !th->cwr))
 242		tp->ecn_flags &= ~TCP_ECN_OK;
 243}
 244
 245static inline int TCP_ECN_rcv_ecn_echo(struct tcp_sock *tp, struct tcphdr *th)
 246{
 247	if (th->ece && !th->syn && (tp->ecn_flags & TCP_ECN_OK))
 248		return 1;
 249	return 0;
 250}
 251
 252/* Buffer size and advertised window tuning.
 253 *
 254 * 1. Tuning sk->sk_sndbuf, when connection enters established state.
 255 */
 256
 257static void tcp_fixup_sndbuf(struct sock *sk)
 258{
 259	int sndmem = tcp_sk(sk)->rx_opt.mss_clamp + MAX_TCP_HEADER + 16 +
 260		     sizeof(struct sk_buff);
 261
 262	if (sk->sk_sndbuf < 3 * sndmem) {
 263		sk->sk_sndbuf = 3 * sndmem;
 264		if (sk->sk_sndbuf > sysctl_tcp_wmem[2])
 265			sk->sk_sndbuf = sysctl_tcp_wmem[2];
 266	}
 267}
 268
 269/* 2. Tuning advertised window (window_clamp, rcv_ssthresh)
 270 *
 271 * All tcp_full_space() is split to two parts: "network" buffer, allocated
 272 * forward and advertised in receiver window (tp->rcv_wnd) and
 273 * "application buffer", required to isolate scheduling/application
 274 * latencies from network.
 275 * window_clamp is maximal advertised window. It can be less than
 276 * tcp_full_space(), in this case tcp_full_space() - window_clamp
 277 * is reserved for "application" buffer. The less window_clamp is
 278 * the smoother our behaviour from viewpoint of network, but the lower
 279 * throughput and the higher sensitivity of the connection to losses. 8)
 280 *
 281 * rcv_ssthresh is more strict window_clamp used at "slow start"
 282 * phase to predict further behaviour of this connection.
 283 * It is used for two goals:
 284 * - to enforce header prediction at sender, even when application
 285 *   requires some significant "application buffer". It is check #1.
 286 * - to prevent pruning of receive queue because of misprediction
 287 *   of receiver window. Check #2.
 288 *
 289 * The scheme does not work when sender sends good segments opening
 290 * window and then starts to feed us spaghetti. But it should work
 291 * in common situations. Otherwise, we have to rely on queue collapsing.
 292 */
 293
 294/* Slow part of check#2. */
 295static int __tcp_grow_window(const struct sock *sk, const struct sk_buff *skb)
 296{
 297	struct tcp_sock *tp = tcp_sk(sk);
 298	/* Optimize this! */
 299	int truesize = tcp_win_from_space(skb->truesize) >> 1;
 300	int window = tcp_win_from_space(sysctl_tcp_rmem[2]) >> 1;
 301
 302	while (tp->rcv_ssthresh <= window) {
 303		if (truesize <= skb->len)
 304			return 2 * inet_csk(sk)->icsk_ack.rcv_mss;
 305
 306		truesize >>= 1;
 307		window >>= 1;
 308	}
 309	return 0;
 310}
 311
 312static void tcp_grow_window(struct sock *sk, struct sk_buff *skb)
 313{
 314	struct tcp_sock *tp = tcp_sk(sk);
 315
 316	/* Check #1 */
 317	if (tp->rcv_ssthresh < tp->window_clamp &&
 318	    (int)tp->rcv_ssthresh < tcp_space(sk) &&
 319	    !tcp_memory_pressure) {
 320		int incr;
 321
 322		/* Check #2. Increase window, if skb with such overhead
 323		 * will fit to rcvbuf in future.
 324		 */
 325		if (tcp_win_from_space(skb->truesize) <= skb->len)
 326			incr = 2 * tp->advmss;
 327		else
 328			incr = __tcp_grow_window(sk, skb);
 329
 330		if (incr) {
 
 331			tp->rcv_ssthresh = min(tp->rcv_ssthresh + incr,
 332					       tp->window_clamp);
 333			inet_csk(sk)->icsk_ack.quick |= 1;
 334		}
 335	}
 336}
 337
 338/* 3. Tuning rcvbuf, when connection enters established state. */
 339
 340static void tcp_fixup_rcvbuf(struct sock *sk)
 341{
 342	struct tcp_sock *tp = tcp_sk(sk);
 343	int rcvmem = tp->advmss + MAX_TCP_HEADER + 16 + sizeof(struct sk_buff);
 
 344
 345	/* Try to select rcvbuf so that 4 mss-sized segments
 346	 * will fit to window and corresponding skbs will fit to our rcvbuf.
 347	 * (was 3; 4 is minimum to allow fast retransmit to work.)
 348	 */
 349	while (tcp_win_from_space(rcvmem) < tp->advmss)
 
 
 
 
 350		rcvmem += 128;
 351	if (sk->sk_rcvbuf < 4 * rcvmem)
 352		sk->sk_rcvbuf = min(4 * rcvmem, sysctl_tcp_rmem[2]);
 
 
 
 353}
 354
 355/* 4. Try to fixup all. It is made immediately after connection enters
 356 *    established state.
 357 */
 358static void tcp_init_buffer_space(struct sock *sk)
 359{
 360	struct tcp_sock *tp = tcp_sk(sk);
 361	int maxwin;
 362
 363	if (!(sk->sk_userlocks & SOCK_RCVBUF_LOCK))
 364		tcp_fixup_rcvbuf(sk);
 365	if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK))
 366		tcp_fixup_sndbuf(sk);
 367
 368	tp->rcvq_space.space = tp->rcv_wnd;
 369
 370	maxwin = tcp_full_space(sk);
 371
 372	if (tp->window_clamp >= maxwin) {
 373		tp->window_clamp = maxwin;
 374
 375		if (sysctl_tcp_app_win && maxwin > 4 * tp->advmss)
 376			tp->window_clamp = max(maxwin -
 377					       (maxwin >> sysctl_tcp_app_win),
 378					       4 * tp->advmss);
 379	}
 380
 381	/* Force reservation of one segment. */
 382	if (sysctl_tcp_app_win &&
 383	    tp->window_clamp > 2 * tp->advmss &&
 384	    tp->window_clamp + tp->advmss > maxwin)
 385		tp->window_clamp = max(2 * tp->advmss, maxwin - tp->advmss);
 386
 387	tp->rcv_ssthresh = min(tp->rcv_ssthresh, tp->window_clamp);
 388	tp->snd_cwnd_stamp = tcp_time_stamp;
 389}
 390
 391/* 5. Recalculate window clamp after socket hit its memory bounds. */
 392static void tcp_clamp_window(struct sock *sk)
 393{
 394	struct tcp_sock *tp = tcp_sk(sk);
 395	struct inet_connection_sock *icsk = inet_csk(sk);
 396
 397	icsk->icsk_ack.quick = 0;
 398
 399	if (sk->sk_rcvbuf < sysctl_tcp_rmem[2] &&
 400	    !(sk->sk_userlocks & SOCK_RCVBUF_LOCK) &&
 401	    !tcp_memory_pressure &&
 402	    atomic_long_read(&tcp_memory_allocated) < sysctl_tcp_mem[0]) {
 403		sk->sk_rcvbuf = min(atomic_read(&sk->sk_rmem_alloc),
 404				    sysctl_tcp_rmem[2]);
 405	}
 406	if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf)
 407		tp->rcv_ssthresh = min(tp->window_clamp, 2U * tp->advmss);
 408}
 409
 410/* Initialize RCV_MSS value.
 411 * RCV_MSS is an our guess about MSS used by the peer.
 412 * We haven't any direct information about the MSS.
 413 * It's better to underestimate the RCV_MSS rather than overestimate.
 414 * Overestimations make us ACKing less frequently than needed.
 415 * Underestimations are more easy to detect and fix by tcp_measure_rcv_mss().
 416 */
 417void tcp_initialize_rcv_mss(struct sock *sk)
 418{
 419	struct tcp_sock *tp = tcp_sk(sk);
 420	unsigned int hint = min_t(unsigned int, tp->advmss, tp->mss_cache);
 421
 422	hint = min(hint, tp->rcv_wnd / 2);
 423	hint = min(hint, TCP_MSS_DEFAULT);
 424	hint = max(hint, TCP_MIN_MSS);
 425
 426	inet_csk(sk)->icsk_ack.rcv_mss = hint;
 427}
 428EXPORT_SYMBOL(tcp_initialize_rcv_mss);
 429
 430/* Receiver "autotuning" code.
 431 *
 432 * The algorithm for RTT estimation w/o timestamps is based on
 433 * Dynamic Right-Sizing (DRS) by Wu Feng and Mike Fisk of LANL.
 434 * <http://public.lanl.gov/radiant/pubs.html#DRS>
 435 *
 436 * More detail on this code can be found at
 437 * <http://staff.psc.edu/jheffner/>,
 438 * though this reference is out of date.  A new paper
 439 * is pending.
 440 */
 441static void tcp_rcv_rtt_update(struct tcp_sock *tp, u32 sample, int win_dep)
 442{
 443	u32 new_sample = tp->rcv_rtt_est.rtt;
 444	long m = sample;
 445
 446	if (m == 0)
 447		m = 1;
 448
 449	if (new_sample != 0) {
 450		/* If we sample in larger samples in the non-timestamp
 451		 * case, we could grossly overestimate the RTT especially
 452		 * with chatty applications or bulk transfer apps which
 453		 * are stalled on filesystem I/O.
 454		 *
 455		 * Also, since we are only going for a minimum in the
 456		 * non-timestamp case, we do not smooth things out
 457		 * else with timestamps disabled convergence takes too
 458		 * long.
 459		 */
 460		if (!win_dep) {
 461			m -= (new_sample >> 3);
 462			new_sample += m;
 463		} else if (m < new_sample)
 464			new_sample = m << 3;
 
 
 
 465	} else {
 466		/* No previous measure. */
 467		new_sample = m << 3;
 468	}
 469
 470	if (tp->rcv_rtt_est.rtt != new_sample)
 471		tp->rcv_rtt_est.rtt = new_sample;
 472}
 473
 474static inline void tcp_rcv_rtt_measure(struct tcp_sock *tp)
 475{
 476	if (tp->rcv_rtt_est.time == 0)
 477		goto new_measure;
 478	if (before(tp->rcv_nxt, tp->rcv_rtt_est.seq))
 479		return;
 480	tcp_rcv_rtt_update(tp, jiffies - tp->rcv_rtt_est.time, 1);
 481
 482new_measure:
 483	tp->rcv_rtt_est.seq = tp->rcv_nxt + tp->rcv_wnd;
 484	tp->rcv_rtt_est.time = tcp_time_stamp;
 485}
 486
 487static inline void tcp_rcv_rtt_measure_ts(struct sock *sk,
 488					  const struct sk_buff *skb)
 489{
 490	struct tcp_sock *tp = tcp_sk(sk);
 491	if (tp->rx_opt.rcv_tsecr &&
 492	    (TCP_SKB_CB(skb)->end_seq -
 493	     TCP_SKB_CB(skb)->seq >= inet_csk(sk)->icsk_ack.rcv_mss))
 494		tcp_rcv_rtt_update(tp, tcp_time_stamp - tp->rx_opt.rcv_tsecr, 0);
 495}
 496
 497/*
 498 * This function should be called every time data is copied to user space.
 499 * It calculates the appropriate TCP receive buffer space.
 500 */
 501void tcp_rcv_space_adjust(struct sock *sk)
 502{
 503	struct tcp_sock *tp = tcp_sk(sk);
 504	int time;
 505	int space;
 506
 507	if (tp->rcvq_space.time == 0)
 508		goto new_measure;
 509
 510	time = tcp_time_stamp - tp->rcvq_space.time;
 511	if (time < (tp->rcv_rtt_est.rtt >> 3) || tp->rcv_rtt_est.rtt == 0)
 512		return;
 513
 514	space = 2 * (tp->copied_seq - tp->rcvq_space.seq);
 515
 516	space = max(tp->rcvq_space.space, space);
 517
 518	if (tp->rcvq_space.space != space) {
 519		int rcvmem;
 520
 521		tp->rcvq_space.space = space;
 522
 523		if (sysctl_tcp_moderate_rcvbuf &&
 524		    !(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) {
 525			int new_clamp = space;
 526
 527			/* Receive space grows, normalize in order to
 528			 * take into account packet headers and sk_buff
 529			 * structure overhead.
 530			 */
 531			space /= tp->advmss;
 532			if (!space)
 533				space = 1;
 534			rcvmem = (tp->advmss + MAX_TCP_HEADER +
 535				  16 + sizeof(struct sk_buff));
 536			while (tcp_win_from_space(rcvmem) < tp->advmss)
 537				rcvmem += 128;
 538			space *= rcvmem;
 539			space = min(space, sysctl_tcp_rmem[2]);
 540			if (space > sk->sk_rcvbuf) {
 541				sk->sk_rcvbuf = space;
 542
 543				/* Make the window clamp follow along.  */
 544				tp->window_clamp = new_clamp;
 545			}
 546		}
 547	}
 548
 549new_measure:
 550	tp->rcvq_space.seq = tp->copied_seq;
 551	tp->rcvq_space.time = tcp_time_stamp;
 552}
 553
 554/* There is something which you must keep in mind when you analyze the
 555 * behavior of the tp->ato delayed ack timeout interval.  When a
 556 * connection starts up, we want to ack as quickly as possible.  The
 557 * problem is that "good" TCP's do slow start at the beginning of data
 558 * transmission.  The means that until we send the first few ACK's the
 559 * sender will sit on his end and only queue most of his data, because
 560 * he can only send snd_cwnd unacked packets at any given time.  For
 561 * each ACK we send, he increments snd_cwnd and transmits more of his
 562 * queue.  -DaveM
 563 */
 564static void tcp_event_data_recv(struct sock *sk, struct sk_buff *skb)
 565{
 566	struct tcp_sock *tp = tcp_sk(sk);
 567	struct inet_connection_sock *icsk = inet_csk(sk);
 568	u32 now;
 569
 570	inet_csk_schedule_ack(sk);
 571
 572	tcp_measure_rcv_mss(sk, skb);
 573
 574	tcp_rcv_rtt_measure(tp);
 575
 576	now = tcp_time_stamp;
 577
 578	if (!icsk->icsk_ack.ato) {
 579		/* The _first_ data packet received, initialize
 580		 * delayed ACK engine.
 581		 */
 582		tcp_incr_quickack(sk);
 583		icsk->icsk_ack.ato = TCP_ATO_MIN;
 584	} else {
 585		int m = now - icsk->icsk_ack.lrcvtime;
 586
 587		if (m <= TCP_ATO_MIN / 2) {
 588			/* The fastest case is the first. */
 589			icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + TCP_ATO_MIN / 2;
 590		} else if (m < icsk->icsk_ack.ato) {
 591			icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + m;
 592			if (icsk->icsk_ack.ato > icsk->icsk_rto)
 593				icsk->icsk_ack.ato = icsk->icsk_rto;
 594		} else if (m > icsk->icsk_rto) {
 595			/* Too long gap. Apparently sender failed to
 596			 * restart window, so that we send ACKs quickly.
 597			 */
 598			tcp_incr_quickack(sk);
 599			sk_mem_reclaim(sk);
 600		}
 601	}
 602	icsk->icsk_ack.lrcvtime = now;
 603
 604	TCP_ECN_check_ce(tp, skb);
 605
 606	if (skb->len >= 128)
 607		tcp_grow_window(sk, skb);
 608}
 609
 610/* Called to compute a smoothed rtt estimate. The data fed to this
 611 * routine either comes from timestamps, or from segments that were
 612 * known _not_ to have been retransmitted [see Karn/Partridge
 613 * Proceedings SIGCOMM 87]. The algorithm is from the SIGCOMM 88
 614 * piece by Van Jacobson.
 615 * NOTE: the next three routines used to be one big routine.
 616 * To save cycles in the RFC 1323 implementation it was better to break
 617 * it up into three procedures. -- erics
 618 */
 619static void tcp_rtt_estimator(struct sock *sk, const __u32 mrtt)
 620{
 621	struct tcp_sock *tp = tcp_sk(sk);
 622	long m = mrtt; /* RTT */
 623
 624	/*	The following amusing code comes from Jacobson's
 625	 *	article in SIGCOMM '88.  Note that rtt and mdev
 626	 *	are scaled versions of rtt and mean deviation.
 627	 *	This is designed to be as fast as possible
 628	 *	m stands for "measurement".
 629	 *
 630	 *	On a 1990 paper the rto value is changed to:
 631	 *	RTO = rtt + 4 * mdev
 632	 *
 633	 * Funny. This algorithm seems to be very broken.
 634	 * These formulae increase RTO, when it should be decreased, increase
 635	 * too slowly, when it should be increased quickly, decrease too quickly
 636	 * etc. I guess in BSD RTO takes ONE value, so that it is absolutely
 637	 * does not matter how to _calculate_ it. Seems, it was trap
 638	 * that VJ failed to avoid. 8)
 639	 */
 640	if (m == 0)
 641		m = 1;
 642	if (tp->srtt != 0) {
 643		m -= (tp->srtt >> 3);	/* m is now error in rtt est */
 644		tp->srtt += m;		/* rtt = 7/8 rtt + 1/8 new */
 645		if (m < 0) {
 646			m = -m;		/* m is now abs(error) */
 647			m -= (tp->mdev >> 2);   /* similar update on mdev */
 648			/* This is similar to one of Eifel findings.
 649			 * Eifel blocks mdev updates when rtt decreases.
 650			 * This solution is a bit different: we use finer gain
 651			 * for mdev in this case (alpha*beta).
 652			 * Like Eifel it also prevents growth of rto,
 653			 * but also it limits too fast rto decreases,
 654			 * happening in pure Eifel.
 655			 */
 656			if (m > 0)
 657				m >>= 3;
 658		} else {
 659			m -= (tp->mdev >> 2);   /* similar update on mdev */
 660		}
 661		tp->mdev += m;	    	/* mdev = 3/4 mdev + 1/4 new */
 662		if (tp->mdev > tp->mdev_max) {
 663			tp->mdev_max = tp->mdev;
 664			if (tp->mdev_max > tp->rttvar)
 665				tp->rttvar = tp->mdev_max;
 666		}
 667		if (after(tp->snd_una, tp->rtt_seq)) {
 668			if (tp->mdev_max < tp->rttvar)
 669				tp->rttvar -= (tp->rttvar - tp->mdev_max) >> 2;
 670			tp->rtt_seq = tp->snd_nxt;
 671			tp->mdev_max = tcp_rto_min(sk);
 672		}
 673	} else {
 674		/* no previous measure. */
 675		tp->srtt = m << 3;	/* take the measured time to be rtt */
 676		tp->mdev = m << 1;	/* make sure rto = 3*rtt */
 677		tp->mdev_max = tp->rttvar = max(tp->mdev, tcp_rto_min(sk));
 678		tp->rtt_seq = tp->snd_nxt;
 679	}
 680}
 681
 682/* Calculate rto without backoff.  This is the second half of Van Jacobson's
 683 * routine referred to above.
 684 */
 685static inline void tcp_set_rto(struct sock *sk)
 686{
 687	const struct tcp_sock *tp = tcp_sk(sk);
 688	/* Old crap is replaced with new one. 8)
 689	 *
 690	 * More seriously:
 691	 * 1. If rtt variance happened to be less 50msec, it is hallucination.
 692	 *    It cannot be less due to utterly erratic ACK generation made
 693	 *    at least by solaris and freebsd. "Erratic ACKs" has _nothing_
 694	 *    to do with delayed acks, because at cwnd>2 true delack timeout
 695	 *    is invisible. Actually, Linux-2.4 also generates erratic
 696	 *    ACKs in some circumstances.
 697	 */
 698	inet_csk(sk)->icsk_rto = __tcp_set_rto(tp);
 699
 700	/* 2. Fixups made earlier cannot be right.
 701	 *    If we do not estimate RTO correctly without them,
 702	 *    all the algo is pure shit and should be replaced
 703	 *    with correct one. It is exactly, which we pretend to do.
 704	 */
 705
 706	/* NOTE: clamping at TCP_RTO_MIN is not required, current algo
 707	 * guarantees that rto is higher.
 708	 */
 709	tcp_bound_rto(sk);
 710}
 711
 712/* Save metrics learned by this TCP session.
 713   This function is called only, when TCP finishes successfully
 714   i.e. when it enters TIME-WAIT or goes from LAST-ACK to CLOSE.
 715 */
 716void tcp_update_metrics(struct sock *sk)
 717{
 718	struct tcp_sock *tp = tcp_sk(sk);
 719	struct dst_entry *dst = __sk_dst_get(sk);
 720
 721	if (sysctl_tcp_nometrics_save)
 722		return;
 723
 724	dst_confirm(dst);
 725
 726	if (dst && (dst->flags & DST_HOST)) {
 727		const struct inet_connection_sock *icsk = inet_csk(sk);
 728		int m;
 729		unsigned long rtt;
 730
 731		if (icsk->icsk_backoff || !tp->srtt) {
 732			/* This session failed to estimate rtt. Why?
 733			 * Probably, no packets returned in time.
 734			 * Reset our results.
 735			 */
 736			if (!(dst_metric_locked(dst, RTAX_RTT)))
 737				dst_metric_set(dst, RTAX_RTT, 0);
 738			return;
 739		}
 740
 741		rtt = dst_metric_rtt(dst, RTAX_RTT);
 742		m = rtt - tp->srtt;
 743
 744		/* If newly calculated rtt larger than stored one,
 745		 * store new one. Otherwise, use EWMA. Remember,
 746		 * rtt overestimation is always better than underestimation.
 747		 */
 748		if (!(dst_metric_locked(dst, RTAX_RTT))) {
 749			if (m <= 0)
 750				set_dst_metric_rtt(dst, RTAX_RTT, tp->srtt);
 751			else
 752				set_dst_metric_rtt(dst, RTAX_RTT, rtt - (m >> 3));
 753		}
 754
 755		if (!(dst_metric_locked(dst, RTAX_RTTVAR))) {
 756			unsigned long var;
 757			if (m < 0)
 758				m = -m;
 759
 760			/* Scale deviation to rttvar fixed point */
 761			m >>= 1;
 762			if (m < tp->mdev)
 763				m = tp->mdev;
 764
 765			var = dst_metric_rtt(dst, RTAX_RTTVAR);
 766			if (m >= var)
 767				var = m;
 768			else
 769				var -= (var - m) >> 2;
 770
 771			set_dst_metric_rtt(dst, RTAX_RTTVAR, var);
 772		}
 773
 774		if (tcp_in_initial_slowstart(tp)) {
 775			/* Slow start still did not finish. */
 776			if (dst_metric(dst, RTAX_SSTHRESH) &&
 777			    !dst_metric_locked(dst, RTAX_SSTHRESH) &&
 778			    (tp->snd_cwnd >> 1) > dst_metric(dst, RTAX_SSTHRESH))
 779				dst_metric_set(dst, RTAX_SSTHRESH, tp->snd_cwnd >> 1);
 780			if (!dst_metric_locked(dst, RTAX_CWND) &&
 781			    tp->snd_cwnd > dst_metric(dst, RTAX_CWND))
 782				dst_metric_set(dst, RTAX_CWND, tp->snd_cwnd);
 783		} else if (tp->snd_cwnd > tp->snd_ssthresh &&
 784			   icsk->icsk_ca_state == TCP_CA_Open) {
 785			/* Cong. avoidance phase, cwnd is reliable. */
 786			if (!dst_metric_locked(dst, RTAX_SSTHRESH))
 787				dst_metric_set(dst, RTAX_SSTHRESH,
 788					       max(tp->snd_cwnd >> 1, tp->snd_ssthresh));
 789			if (!dst_metric_locked(dst, RTAX_CWND))
 790				dst_metric_set(dst, RTAX_CWND,
 791					       (dst_metric(dst, RTAX_CWND) +
 792						tp->snd_cwnd) >> 1);
 793		} else {
 794			/* Else slow start did not finish, cwnd is non-sense,
 795			   ssthresh may be also invalid.
 796			 */
 797			if (!dst_metric_locked(dst, RTAX_CWND))
 798				dst_metric_set(dst, RTAX_CWND,
 799					       (dst_metric(dst, RTAX_CWND) +
 800						tp->snd_ssthresh) >> 1);
 801			if (dst_metric(dst, RTAX_SSTHRESH) &&
 802			    !dst_metric_locked(dst, RTAX_SSTHRESH) &&
 803			    tp->snd_ssthresh > dst_metric(dst, RTAX_SSTHRESH))
 804				dst_metric_set(dst, RTAX_SSTHRESH, tp->snd_ssthresh);
 805		}
 806
 807		if (!dst_metric_locked(dst, RTAX_REORDERING)) {
 808			if (dst_metric(dst, RTAX_REORDERING) < tp->reordering &&
 809			    tp->reordering != sysctl_tcp_reordering)
 810				dst_metric_set(dst, RTAX_REORDERING, tp->reordering);
 811		}
 812	}
 813}
 814
 815__u32 tcp_init_cwnd(struct tcp_sock *tp, struct dst_entry *dst)
 816{
 817	__u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0);
 818
 819	if (!cwnd)
 820		cwnd = TCP_INIT_CWND;
 821	return min_t(__u32, cwnd, tp->snd_cwnd_clamp);
 822}
 823
 824/* Set slow start threshold and cwnd not falling to slow start */
 825void tcp_enter_cwr(struct sock *sk, const int set_ssthresh)
 826{
 827	struct tcp_sock *tp = tcp_sk(sk);
 828	const struct inet_connection_sock *icsk = inet_csk(sk);
 829
 830	tp->prior_ssthresh = 0;
 831	tp->bytes_acked = 0;
 832	if (icsk->icsk_ca_state < TCP_CA_CWR) {
 833		tp->undo_marker = 0;
 834		if (set_ssthresh)
 835			tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
 836		tp->snd_cwnd = min(tp->snd_cwnd,
 837				   tcp_packets_in_flight(tp) + 1U);
 838		tp->snd_cwnd_cnt = 0;
 839		tp->high_seq = tp->snd_nxt;
 840		tp->snd_cwnd_stamp = tcp_time_stamp;
 841		TCP_ECN_queue_cwr(tp);
 842
 843		tcp_set_ca_state(sk, TCP_CA_CWR);
 844	}
 845}
 846
 847/*
 848 * Packet counting of FACK is based on in-order assumptions, therefore TCP
 849 * disables it when reordering is detected
 850 */
 851static void tcp_disable_fack(struct tcp_sock *tp)
 852{
 853	/* RFC3517 uses different metric in lost marker => reset on change */
 854	if (tcp_is_fack(tp))
 855		tp->lost_skb_hint = NULL;
 856	tp->rx_opt.sack_ok &= ~2;
 857}
 858
 859/* Take a notice that peer is sending D-SACKs */
 860static void tcp_dsack_seen(struct tcp_sock *tp)
 861{
 862	tp->rx_opt.sack_ok |= 4;
 863}
 864
 865/* Initialize metrics on socket. */
 866
 867static void tcp_init_metrics(struct sock *sk)
 868{
 869	struct tcp_sock *tp = tcp_sk(sk);
 870	struct dst_entry *dst = __sk_dst_get(sk);
 871
 872	if (dst == NULL)
 873		goto reset;
 874
 875	dst_confirm(dst);
 876
 877	if (dst_metric_locked(dst, RTAX_CWND))
 878		tp->snd_cwnd_clamp = dst_metric(dst, RTAX_CWND);
 879	if (dst_metric(dst, RTAX_SSTHRESH)) {
 880		tp->snd_ssthresh = dst_metric(dst, RTAX_SSTHRESH);
 881		if (tp->snd_ssthresh > tp->snd_cwnd_clamp)
 882			tp->snd_ssthresh = tp->snd_cwnd_clamp;
 883	} else {
 884		/* ssthresh may have been reduced unnecessarily during.
 885		 * 3WHS. Restore it back to its initial default.
 886		 */
 887		tp->snd_ssthresh = TCP_INFINITE_SSTHRESH;
 888	}
 889	if (dst_metric(dst, RTAX_REORDERING) &&
 890	    tp->reordering != dst_metric(dst, RTAX_REORDERING)) {
 891		tcp_disable_fack(tp);
 
 892		tp->reordering = dst_metric(dst, RTAX_REORDERING);
 893	}
 894
 895	if (dst_metric(dst, RTAX_RTT) == 0 || tp->srtt == 0)
 896		goto reset;
 897
 898	/* Initial rtt is determined from SYN,SYN-ACK.
 899	 * The segment is small and rtt may appear much
 900	 * less than real one. Use per-dst memory
 901	 * to make it more realistic.
 902	 *
 903	 * A bit of theory. RTT is time passed after "normal" sized packet
 904	 * is sent until it is ACKed. In normal circumstances sending small
 905	 * packets force peer to delay ACKs and calculation is correct too.
 906	 * The algorithm is adaptive and, provided we follow specs, it
 907	 * NEVER underestimate RTT. BUT! If peer tries to make some clever
 908	 * tricks sort of "quick acks" for time long enough to decrease RTT
 909	 * to low value, and then abruptly stops to do it and starts to delay
 910	 * ACKs, wait for troubles.
 911	 */
 912	if (dst_metric_rtt(dst, RTAX_RTT) > tp->srtt) {
 913		tp->srtt = dst_metric_rtt(dst, RTAX_RTT);
 914		tp->rtt_seq = tp->snd_nxt;
 915	}
 916	if (dst_metric_rtt(dst, RTAX_RTTVAR) > tp->mdev) {
 917		tp->mdev = dst_metric_rtt(dst, RTAX_RTTVAR);
 918		tp->mdev_max = tp->rttvar = max(tp->mdev, tcp_rto_min(sk));
 919	}
 920	tcp_set_rto(sk);
 921reset:
 922	if (tp->srtt == 0) {
 923		/* RFC2988bis: We've failed to get a valid RTT sample from
 924		 * 3WHS. This is most likely due to retransmission,
 925		 * including spurious one. Reset the RTO back to 3secs
 926		 * from the more aggressive 1sec to avoid more spurious
 927		 * retransmission.
 928		 */
 929		tp->mdev = tp->mdev_max = tp->rttvar = TCP_TIMEOUT_FALLBACK;
 930		inet_csk(sk)->icsk_rto = TCP_TIMEOUT_FALLBACK;
 931	}
 932	/* Cut cwnd down to 1 per RFC5681 if SYN or SYN-ACK has been
 933	 * retransmitted. In light of RFC2988bis' more aggressive 1sec
 934	 * initRTO, we only reset cwnd when more than 1 SYN/SYN-ACK
 935	 * retransmission has occurred.
 936	 */
 937	if (tp->total_retrans > 1)
 938		tp->snd_cwnd = 1;
 939	else
 940		tp->snd_cwnd = tcp_init_cwnd(tp, dst);
 941	tp->snd_cwnd_stamp = tcp_time_stamp;
 942}
 943
 944static void tcp_update_reordering(struct sock *sk, const int metric,
 945				  const int ts)
 946{
 947	struct tcp_sock *tp = tcp_sk(sk);
 948	if (metric > tp->reordering) {
 949		int mib_idx;
 950
 951		tp->reordering = min(TCP_MAX_REORDERING, metric);
 952
 953		/* This exciting event is worth to be remembered. 8) */
 954		if (ts)
 955			mib_idx = LINUX_MIB_TCPTSREORDER;
 956		else if (tcp_is_reno(tp))
 957			mib_idx = LINUX_MIB_TCPRENOREORDER;
 958		else if (tcp_is_fack(tp))
 959			mib_idx = LINUX_MIB_TCPFACKREORDER;
 960		else
 961			mib_idx = LINUX_MIB_TCPSACKREORDER;
 962
 963		NET_INC_STATS_BH(sock_net(sk), mib_idx);
 964#if FASTRETRANS_DEBUG > 1
 965		printk(KERN_DEBUG "Disorder%d %d %u f%u s%u rr%d\n",
 966		       tp->rx_opt.sack_ok, inet_csk(sk)->icsk_ca_state,
 967		       tp->reordering,
 968		       tp->fackets_out,
 969		       tp->sacked_out,
 970		       tp->undo_marker ? tp->undo_retrans : 0);
 971#endif
 972		tcp_disable_fack(tp);
 973	}
 
 
 
 974}
 975
 976/* This must be called before lost_out is incremented */
 977static void tcp_verify_retransmit_hint(struct tcp_sock *tp, struct sk_buff *skb)
 978{
 979	if ((tp->retransmit_skb_hint == NULL) ||
 980	    before(TCP_SKB_CB(skb)->seq,
 981		   TCP_SKB_CB(tp->retransmit_skb_hint)->seq))
 982		tp->retransmit_skb_hint = skb;
 983
 984	if (!tp->lost_out ||
 985	    after(TCP_SKB_CB(skb)->end_seq, tp->retransmit_high))
 986		tp->retransmit_high = TCP_SKB_CB(skb)->end_seq;
 987}
 988
 989static void tcp_skb_mark_lost(struct tcp_sock *tp, struct sk_buff *skb)
 990{
 991	if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) {
 992		tcp_verify_retransmit_hint(tp, skb);
 993
 994		tp->lost_out += tcp_skb_pcount(skb);
 995		TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
 996	}
 997}
 998
 999static void tcp_skb_mark_lost_uncond_verify(struct tcp_sock *tp,
1000					    struct sk_buff *skb)
1001{
1002	tcp_verify_retransmit_hint(tp, skb);
1003
1004	if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) {
1005		tp->lost_out += tcp_skb_pcount(skb);
1006		TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1007	}
1008}
1009
1010/* This procedure tags the retransmission queue when SACKs arrive.
1011 *
1012 * We have three tag bits: SACKED(S), RETRANS(R) and LOST(L).
1013 * Packets in queue with these bits set are counted in variables
1014 * sacked_out, retrans_out and lost_out, correspondingly.
1015 *
1016 * Valid combinations are:
1017 * Tag  InFlight	Description
1018 * 0	1		- orig segment is in flight.
1019 * S	0		- nothing flies, orig reached receiver.
1020 * L	0		- nothing flies, orig lost by net.
1021 * R	2		- both orig and retransmit are in flight.
1022 * L|R	1		- orig is lost, retransmit is in flight.
1023 * S|R  1		- orig reached receiver, retrans is still in flight.
1024 * (L|S|R is logically valid, it could occur when L|R is sacked,
1025 *  but it is equivalent to plain S and code short-curcuits it to S.
1026 *  L|S is logically invalid, it would mean -1 packet in flight 8))
1027 *
1028 * These 6 states form finite state machine, controlled by the following events:
1029 * 1. New ACK (+SACK) arrives. (tcp_sacktag_write_queue())
1030 * 2. Retransmission. (tcp_retransmit_skb(), tcp_xmit_retransmit_queue())
1031 * 3. Loss detection event of one of three flavors:
1032 *	A. Scoreboard estimator decided the packet is lost.
1033 *	   A'. Reno "three dupacks" marks head of queue lost.
1034 *	   A''. Its FACK modfication, head until snd.fack is lost.
1035 *	B. SACK arrives sacking data transmitted after never retransmitted
1036 *	   hole was sent out.
1037 *	C. SACK arrives sacking SND.NXT at the moment, when the
1038 *	   segment was retransmitted.
1039 * 4. D-SACK added new rule: D-SACK changes any tag to S.
1040 *
1041 * It is pleasant to note, that state diagram turns out to be commutative,
1042 * so that we are allowed not to be bothered by order of our actions,
1043 * when multiple events arrive simultaneously. (see the function below).
1044 *
1045 * Reordering detection.
1046 * --------------------
1047 * Reordering metric is maximal distance, which a packet can be displaced
1048 * in packet stream. With SACKs we can estimate it:
1049 *
1050 * 1. SACK fills old hole and the corresponding segment was not
1051 *    ever retransmitted -> reordering. Alas, we cannot use it
1052 *    when segment was retransmitted.
1053 * 2. The last flaw is solved with D-SACK. D-SACK arrives
1054 *    for retransmitted and already SACKed segment -> reordering..
1055 * Both of these heuristics are not used in Loss state, when we cannot
1056 * account for retransmits accurately.
1057 *
1058 * SACK block validation.
1059 * ----------------------
1060 *
1061 * SACK block range validation checks that the received SACK block fits to
1062 * the expected sequence limits, i.e., it is between SND.UNA and SND.NXT.
1063 * Note that SND.UNA is not included to the range though being valid because
1064 * it means that the receiver is rather inconsistent with itself reporting
1065 * SACK reneging when it should advance SND.UNA. Such SACK block this is
1066 * perfectly valid, however, in light of RFC2018 which explicitly states
1067 * that "SACK block MUST reflect the newest segment.  Even if the newest
1068 * segment is going to be discarded ...", not that it looks very clever
1069 * in case of head skb. Due to potentional receiver driven attacks, we
1070 * choose to avoid immediate execution of a walk in write queue due to
1071 * reneging and defer head skb's loss recovery to standard loss recovery
1072 * procedure that will eventually trigger (nothing forbids us doing this).
1073 *
1074 * Implements also blockage to start_seq wrap-around. Problem lies in the
1075 * fact that though start_seq (s) is before end_seq (i.e., not reversed),
1076 * there's no guarantee that it will be before snd_nxt (n). The problem
1077 * happens when start_seq resides between end_seq wrap (e_w) and snd_nxt
1078 * wrap (s_w):
1079 *
1080 *         <- outs wnd ->                          <- wrapzone ->
1081 *         u     e      n                         u_w   e_w  s n_w
1082 *         |     |      |                          |     |   |  |
1083 * |<------------+------+----- TCP seqno space --------------+---------->|
1084 * ...-- <2^31 ->|                                           |<--------...
1085 * ...---- >2^31 ------>|                                    |<--------...
1086 *
1087 * Current code wouldn't be vulnerable but it's better still to discard such
1088 * crazy SACK blocks. Doing this check for start_seq alone closes somewhat
1089 * similar case (end_seq after snd_nxt wrap) as earlier reversed check in
1090 * snd_nxt wrap -> snd_una region will then become "well defined", i.e.,
1091 * equal to the ideal case (infinite seqno space without wrap caused issues).
1092 *
1093 * With D-SACK the lower bound is extended to cover sequence space below
1094 * SND.UNA down to undo_marker, which is the last point of interest. Yet
1095 * again, D-SACK block must not to go across snd_una (for the same reason as
1096 * for the normal SACK blocks, explained above). But there all simplicity
1097 * ends, TCP might receive valid D-SACKs below that. As long as they reside
1098 * fully below undo_marker they do not affect behavior in anyway and can
1099 * therefore be safely ignored. In rare cases (which are more or less
1100 * theoretical ones), the D-SACK will nicely cross that boundary due to skb
1101 * fragmentation and packet reordering past skb's retransmission. To consider
1102 * them correctly, the acceptable range must be extended even more though
1103 * the exact amount is rather hard to quantify. However, tp->max_window can
1104 * be used as an exaggerated estimate.
1105 */
1106static int tcp_is_sackblock_valid(struct tcp_sock *tp, int is_dsack,
1107				  u32 start_seq, u32 end_seq)
1108{
1109	/* Too far in future, or reversed (interpretation is ambiguous) */
1110	if (after(end_seq, tp->snd_nxt) || !before(start_seq, end_seq))
1111		return 0;
1112
1113	/* Nasty start_seq wrap-around check (see comments above) */
1114	if (!before(start_seq, tp->snd_nxt))
1115		return 0;
1116
1117	/* In outstanding window? ...This is valid exit for D-SACKs too.
1118	 * start_seq == snd_una is non-sensical (see comments above)
1119	 */
1120	if (after(start_seq, tp->snd_una))
1121		return 1;
1122
1123	if (!is_dsack || !tp->undo_marker)
1124		return 0;
1125
1126	/* ...Then it's D-SACK, and must reside below snd_una completely */
1127	if (after(end_seq, tp->snd_una))
1128		return 0;
1129
1130	if (!before(start_seq, tp->undo_marker))
1131		return 1;
1132
1133	/* Too old */
1134	if (!after(end_seq, tp->undo_marker))
1135		return 0;
1136
1137	/* Undo_marker boundary crossing (overestimates a lot). Known already:
1138	 *   start_seq < undo_marker and end_seq >= undo_marker.
1139	 */
1140	return !before(start_seq, end_seq - tp->max_window);
1141}
1142
1143/* Check for lost retransmit. This superb idea is borrowed from "ratehalving".
1144 * Event "C". Later note: FACK people cheated me again 8), we have to account
1145 * for reordering! Ugly, but should help.
1146 *
1147 * Search retransmitted skbs from write_queue that were sent when snd_nxt was
1148 * less than what is now known to be received by the other end (derived from
1149 * highest SACK block). Also calculate the lowest snd_nxt among the remaining
1150 * retransmitted skbs to avoid some costly processing per ACKs.
1151 */
1152static void tcp_mark_lost_retrans(struct sock *sk)
1153{
1154	const struct inet_connection_sock *icsk = inet_csk(sk);
1155	struct tcp_sock *tp = tcp_sk(sk);
1156	struct sk_buff *skb;
1157	int cnt = 0;
1158	u32 new_low_seq = tp->snd_nxt;
1159	u32 received_upto = tcp_highest_sack_seq(tp);
1160
1161	if (!tcp_is_fack(tp) || !tp->retrans_out ||
1162	    !after(received_upto, tp->lost_retrans_low) ||
1163	    icsk->icsk_ca_state != TCP_CA_Recovery)
1164		return;
1165
1166	tcp_for_write_queue(skb, sk) {
1167		u32 ack_seq = TCP_SKB_CB(skb)->ack_seq;
1168
1169		if (skb == tcp_send_head(sk))
1170			break;
1171		if (cnt == tp->retrans_out)
1172			break;
1173		if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1174			continue;
1175
1176		if (!(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS))
1177			continue;
1178
1179		/* TODO: We would like to get rid of tcp_is_fack(tp) only
1180		 * constraint here (see above) but figuring out that at
1181		 * least tp->reordering SACK blocks reside between ack_seq
1182		 * and received_upto is not easy task to do cheaply with
1183		 * the available datastructures.
1184		 *
1185		 * Whether FACK should check here for tp->reordering segs
1186		 * in-between one could argue for either way (it would be
1187		 * rather simple to implement as we could count fack_count
1188		 * during the walk and do tp->fackets_out - fack_count).
1189		 */
1190		if (after(received_upto, ack_seq)) {
1191			TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
1192			tp->retrans_out -= tcp_skb_pcount(skb);
1193
1194			tcp_skb_mark_lost_uncond_verify(tp, skb);
1195			NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPLOSTRETRANSMIT);
1196		} else {
1197			if (before(ack_seq, new_low_seq))
1198				new_low_seq = ack_seq;
1199			cnt += tcp_skb_pcount(skb);
1200		}
1201	}
1202
1203	if (tp->retrans_out)
1204		tp->lost_retrans_low = new_low_seq;
1205}
1206
1207static int tcp_check_dsack(struct sock *sk, struct sk_buff *ack_skb,
1208			   struct tcp_sack_block_wire *sp, int num_sacks,
1209			   u32 prior_snd_una)
1210{
1211	struct tcp_sock *tp = tcp_sk(sk);
1212	u32 start_seq_0 = get_unaligned_be32(&sp[0].start_seq);
1213	u32 end_seq_0 = get_unaligned_be32(&sp[0].end_seq);
1214	int dup_sack = 0;
1215
1216	if (before(start_seq_0, TCP_SKB_CB(ack_skb)->ack_seq)) {
1217		dup_sack = 1;
1218		tcp_dsack_seen(tp);
1219		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPDSACKRECV);
1220	} else if (num_sacks > 1) {
1221		u32 end_seq_1 = get_unaligned_be32(&sp[1].end_seq);
1222		u32 start_seq_1 = get_unaligned_be32(&sp[1].start_seq);
1223
1224		if (!after(end_seq_0, end_seq_1) &&
1225		    !before(start_seq_0, start_seq_1)) {
1226			dup_sack = 1;
1227			tcp_dsack_seen(tp);
1228			NET_INC_STATS_BH(sock_net(sk),
1229					LINUX_MIB_TCPDSACKOFORECV);
1230		}
1231	}
1232
1233	/* D-SACK for already forgotten data... Do dumb counting. */
1234	if (dup_sack && tp->undo_marker && tp->undo_retrans &&
1235	    !after(end_seq_0, prior_snd_una) &&
1236	    after(end_seq_0, tp->undo_marker))
1237		tp->undo_retrans--;
1238
1239	return dup_sack;
1240}
1241
1242struct tcp_sacktag_state {
1243	int reord;
1244	int fack_count;
1245	int flag;
1246};
1247
1248/* Check if skb is fully within the SACK block. In presence of GSO skbs,
1249 * the incoming SACK may not exactly match but we can find smaller MSS
1250 * aligned portion of it that matches. Therefore we might need to fragment
1251 * which may fail and creates some hassle (caller must handle error case
1252 * returns).
1253 *
1254 * FIXME: this could be merged to shift decision code
1255 */
1256static int tcp_match_skb_to_sack(struct sock *sk, struct sk_buff *skb,
1257				 u32 start_seq, u32 end_seq)
1258{
1259	int in_sack, err;
 
1260	unsigned int pkt_len;
1261	unsigned int mss;
1262
1263	in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1264		  !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1265
1266	if (tcp_skb_pcount(skb) > 1 && !in_sack &&
1267	    after(TCP_SKB_CB(skb)->end_seq, start_seq)) {
1268		mss = tcp_skb_mss(skb);
1269		in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
1270
1271		if (!in_sack) {
1272			pkt_len = start_seq - TCP_SKB_CB(skb)->seq;
1273			if (pkt_len < mss)
1274				pkt_len = mss;
1275		} else {
1276			pkt_len = end_seq - TCP_SKB_CB(skb)->seq;
1277			if (pkt_len < mss)
1278				return -EINVAL;
1279		}
1280
1281		/* Round if necessary so that SACKs cover only full MSSes
1282		 * and/or the remaining small portion (if present)
1283		 */
1284		if (pkt_len > mss) {
1285			unsigned int new_len = (pkt_len / mss) * mss;
1286			if (!in_sack && new_len < pkt_len) {
1287				new_len += mss;
1288				if (new_len > skb->len)
1289					return 0;
1290			}
1291			pkt_len = new_len;
1292		}
1293		err = tcp_fragment(sk, skb, pkt_len, mss);
1294		if (err < 0)
1295			return err;
1296	}
1297
1298	return in_sack;
1299}
1300
1301static u8 tcp_sacktag_one(struct sk_buff *skb, struct sock *sk,
1302			  struct tcp_sacktag_state *state,
1303			  int dup_sack, int pcount)
 
 
1304{
1305	struct tcp_sock *tp = tcp_sk(sk);
1306	u8 sacked = TCP_SKB_CB(skb)->sacked;
1307	int fack_count = state->fack_count;
1308
1309	/* Account D-SACK for retransmitted packet. */
1310	if (dup_sack && (sacked & TCPCB_RETRANS)) {
1311		if (tp->undo_marker && tp->undo_retrans &&
1312		    after(TCP_SKB_CB(skb)->end_seq, tp->undo_marker))
1313			tp->undo_retrans--;
1314		if (sacked & TCPCB_SACKED_ACKED)
1315			state->reord = min(fack_count, state->reord);
1316	}
1317
1318	/* Nothing to do; acked frame is about to be dropped (was ACKed). */
1319	if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1320		return sacked;
1321
1322	if (!(sacked & TCPCB_SACKED_ACKED)) {
1323		if (sacked & TCPCB_SACKED_RETRANS) {
1324			/* If the segment is not tagged as lost,
1325			 * we do not clear RETRANS, believing
1326			 * that retransmission is still in flight.
1327			 */
1328			if (sacked & TCPCB_LOST) {
1329				sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS);
1330				tp->lost_out -= pcount;
1331				tp->retrans_out -= pcount;
1332			}
1333		} else {
1334			if (!(sacked & TCPCB_RETRANS)) {
1335				/* New sack for not retransmitted frame,
1336				 * which was in hole. It is reordering.
1337				 */
1338				if (before(TCP_SKB_CB(skb)->seq,
1339					   tcp_highest_sack_seq(tp)))
1340					state->reord = min(fack_count,
1341							   state->reord);
1342
1343				/* SACK enhanced F-RTO (RFC4138; Appendix B) */
1344				if (!after(TCP_SKB_CB(skb)->end_seq, tp->frto_highmark))
1345					state->flag |= FLAG_ONLY_ORIG_SACKED;
1346			}
1347
1348			if (sacked & TCPCB_LOST) {
1349				sacked &= ~TCPCB_LOST;
1350				tp->lost_out -= pcount;
1351			}
1352		}
1353
1354		sacked |= TCPCB_SACKED_ACKED;
1355		state->flag |= FLAG_DATA_SACKED;
1356		tp->sacked_out += pcount;
1357
1358		fack_count += pcount;
1359
1360		/* Lost marker hint past SACKed? Tweak RFC3517 cnt */
1361		if (!tcp_is_fack(tp) && (tp->lost_skb_hint != NULL) &&
1362		    before(TCP_SKB_CB(skb)->seq,
1363			   TCP_SKB_CB(tp->lost_skb_hint)->seq))
1364			tp->lost_cnt_hint += pcount;
1365
1366		if (fack_count > tp->fackets_out)
1367			tp->fackets_out = fack_count;
1368	}
1369
1370	/* D-SACK. We can detect redundant retransmission in S|R and plain R
1371	 * frames and clear it. undo_retrans is decreased above, L|R frames
1372	 * are accounted above as well.
1373	 */
1374	if (dup_sack && (sacked & TCPCB_SACKED_RETRANS)) {
1375		sacked &= ~TCPCB_SACKED_RETRANS;
1376		tp->retrans_out -= pcount;
1377	}
1378
1379	return sacked;
1380}
1381
1382static int tcp_shifted_skb(struct sock *sk, struct sk_buff *skb,
1383			   struct tcp_sacktag_state *state,
1384			   unsigned int pcount, int shifted, int mss,
1385			   int dup_sack)
 
 
 
1386{
1387	struct tcp_sock *tp = tcp_sk(sk);
1388	struct sk_buff *prev = tcp_write_queue_prev(sk, skb);
 
 
1389
1390	BUG_ON(!pcount);
1391
 
 
 
 
 
 
 
 
 
1392	if (skb == tp->lost_skb_hint)
1393		tp->lost_cnt_hint += pcount;
1394
1395	TCP_SKB_CB(prev)->end_seq += shifted;
1396	TCP_SKB_CB(skb)->seq += shifted;
1397
1398	skb_shinfo(prev)->gso_segs += pcount;
1399	BUG_ON(skb_shinfo(skb)->gso_segs < pcount);
1400	skb_shinfo(skb)->gso_segs -= pcount;
1401
1402	/* When we're adding to gso_segs == 1, gso_size will be zero,
1403	 * in theory this shouldn't be necessary but as long as DSACK
1404	 * code can come after this skb later on it's better to keep
1405	 * setting gso_size to something.
1406	 */
1407	if (!skb_shinfo(prev)->gso_size) {
1408		skb_shinfo(prev)->gso_size = mss;
1409		skb_shinfo(prev)->gso_type = sk->sk_gso_type;
1410	}
1411
1412	/* CHECKME: To clear or not to clear? Mimics normal skb currently */
1413	if (skb_shinfo(skb)->gso_segs <= 1) {
1414		skb_shinfo(skb)->gso_size = 0;
1415		skb_shinfo(skb)->gso_type = 0;
1416	}
1417
1418	/* We discard results */
1419	tcp_sacktag_one(skb, sk, state, dup_sack, pcount);
1420
1421	/* Difference in this won't matter, both ACKed by the same cumul. ACK */
1422	TCP_SKB_CB(prev)->sacked |= (TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS);
1423
1424	if (skb->len > 0) {
1425		BUG_ON(!tcp_skb_pcount(skb));
1426		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SACKSHIFTED);
1427		return 0;
1428	}
1429
1430	/* Whole SKB was eaten :-) */
1431
1432	if (skb == tp->retransmit_skb_hint)
1433		tp->retransmit_skb_hint = prev;
1434	if (skb == tp->scoreboard_skb_hint)
1435		tp->scoreboard_skb_hint = prev;
1436	if (skb == tp->lost_skb_hint) {
1437		tp->lost_skb_hint = prev;
1438		tp->lost_cnt_hint -= tcp_skb_pcount(prev);
1439	}
1440
1441	TCP_SKB_CB(skb)->flags |= TCP_SKB_CB(prev)->flags;
1442	if (skb == tcp_highest_sack(sk))
1443		tcp_advance_highest_sack(sk, skb);
1444
1445	tcp_unlink_write_queue(skb, sk);
1446	sk_wmem_free_skb(sk, skb);
1447
1448	NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SACKMERGED);
1449
1450	return 1;
1451}
1452
1453/* I wish gso_size would have a bit more sane initialization than
1454 * something-or-zero which complicates things
1455 */
1456static int tcp_skb_seglen(struct sk_buff *skb)
1457{
1458	return tcp_skb_pcount(skb) == 1 ? skb->len : tcp_skb_mss(skb);
1459}
1460
1461/* Shifting pages past head area doesn't work */
1462static int skb_can_shift(struct sk_buff *skb)
1463{
1464	return !skb_headlen(skb) && skb_is_nonlinear(skb);
1465}
1466
1467/* Try collapsing SACK blocks spanning across multiple skbs to a single
1468 * skb.
1469 */
1470static struct sk_buff *tcp_shift_skb_data(struct sock *sk, struct sk_buff *skb,
1471					  struct tcp_sacktag_state *state,
1472					  u32 start_seq, u32 end_seq,
1473					  int dup_sack)
1474{
1475	struct tcp_sock *tp = tcp_sk(sk);
1476	struct sk_buff *prev;
1477	int mss;
1478	int pcount = 0;
1479	int len;
1480	int in_sack;
1481
1482	if (!sk_can_gso(sk))
1483		goto fallback;
1484
1485	/* Normally R but no L won't result in plain S */
1486	if (!dup_sack &&
1487	    (TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_RETRANS)) == TCPCB_SACKED_RETRANS)
1488		goto fallback;
1489	if (!skb_can_shift(skb))
1490		goto fallback;
1491	/* This frame is about to be dropped (was ACKed). */
1492	if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1493		goto fallback;
1494
1495	/* Can only happen with delayed DSACK + discard craziness */
1496	if (unlikely(skb == tcp_write_queue_head(sk)))
1497		goto fallback;
1498	prev = tcp_write_queue_prev(sk, skb);
1499
1500	if ((TCP_SKB_CB(prev)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED)
1501		goto fallback;
1502
1503	in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1504		  !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1505
1506	if (in_sack) {
1507		len = skb->len;
1508		pcount = tcp_skb_pcount(skb);
1509		mss = tcp_skb_seglen(skb);
1510
1511		/* TODO: Fix DSACKs to not fragment already SACKed and we can
1512		 * drop this restriction as unnecessary
1513		 */
1514		if (mss != tcp_skb_seglen(prev))
1515			goto fallback;
1516	} else {
1517		if (!after(TCP_SKB_CB(skb)->end_seq, start_seq))
1518			goto noop;
1519		/* CHECKME: This is non-MSS split case only?, this will
1520		 * cause skipped skbs due to advancing loop btw, original
1521		 * has that feature too
1522		 */
1523		if (tcp_skb_pcount(skb) <= 1)
1524			goto noop;
1525
1526		in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
1527		if (!in_sack) {
1528			/* TODO: head merge to next could be attempted here
1529			 * if (!after(TCP_SKB_CB(skb)->end_seq, end_seq)),
1530			 * though it might not be worth of the additional hassle
1531			 *
1532			 * ...we can probably just fallback to what was done
1533			 * previously. We could try merging non-SACKed ones
1534			 * as well but it probably isn't going to buy off
1535			 * because later SACKs might again split them, and
1536			 * it would make skb timestamp tracking considerably
1537			 * harder problem.
1538			 */
1539			goto fallback;
1540		}
1541
1542		len = end_seq - TCP_SKB_CB(skb)->seq;
1543		BUG_ON(len < 0);
1544		BUG_ON(len > skb->len);
1545
1546		/* MSS boundaries should be honoured or else pcount will
1547		 * severely break even though it makes things bit trickier.
1548		 * Optimize common case to avoid most of the divides
1549		 */
1550		mss = tcp_skb_mss(skb);
1551
1552		/* TODO: Fix DSACKs to not fragment already SACKed and we can
1553		 * drop this restriction as unnecessary
1554		 */
1555		if (mss != tcp_skb_seglen(prev))
1556			goto fallback;
1557
1558		if (len == mss) {
1559			pcount = 1;
1560		} else if (len < mss) {
1561			goto noop;
1562		} else {
1563			pcount = len / mss;
1564			len = pcount * mss;
1565		}
1566	}
1567
 
 
 
 
1568	if (!skb_shift(prev, skb, len))
1569		goto fallback;
1570	if (!tcp_shifted_skb(sk, skb, state, pcount, len, mss, dup_sack))
1571		goto out;
1572
1573	/* Hole filled allows collapsing with the next as well, this is very
1574	 * useful when hole on every nth skb pattern happens
1575	 */
1576	if (prev == tcp_write_queue_tail(sk))
1577		goto out;
1578	skb = tcp_write_queue_next(sk, prev);
1579
1580	if (!skb_can_shift(skb) ||
1581	    (skb == tcp_send_head(sk)) ||
1582	    ((TCP_SKB_CB(skb)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED) ||
1583	    (mss != tcp_skb_seglen(skb)))
1584		goto out;
1585
1586	len = skb->len;
1587	if (skb_shift(prev, skb, len)) {
1588		pcount += tcp_skb_pcount(skb);
1589		tcp_shifted_skb(sk, skb, state, tcp_skb_pcount(skb), len, mss, 0);
1590	}
1591
1592out:
1593	state->fack_count += pcount;
1594	return prev;
1595
1596noop:
1597	return skb;
1598
1599fallback:
1600	NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SACKSHIFTFALLBACK);
1601	return NULL;
1602}
1603
1604static struct sk_buff *tcp_sacktag_walk(struct sk_buff *skb, struct sock *sk,
1605					struct tcp_sack_block *next_dup,
1606					struct tcp_sacktag_state *state,
1607					u32 start_seq, u32 end_seq,
1608					int dup_sack_in)
1609{
1610	struct tcp_sock *tp = tcp_sk(sk);
1611	struct sk_buff *tmp;
1612
1613	tcp_for_write_queue_from(skb, sk) {
1614		int in_sack = 0;
1615		int dup_sack = dup_sack_in;
1616
1617		if (skb == tcp_send_head(sk))
1618			break;
1619
1620		/* queue is in-order => we can short-circuit the walk early */
1621		if (!before(TCP_SKB_CB(skb)->seq, end_seq))
1622			break;
1623
1624		if ((next_dup != NULL) &&
1625		    before(TCP_SKB_CB(skb)->seq, next_dup->end_seq)) {
1626			in_sack = tcp_match_skb_to_sack(sk, skb,
1627							next_dup->start_seq,
1628							next_dup->end_seq);
1629			if (in_sack > 0)
1630				dup_sack = 1;
1631		}
1632
1633		/* skb reference here is a bit tricky to get right, since
1634		 * shifting can eat and free both this skb and the next,
1635		 * so not even _safe variant of the loop is enough.
1636		 */
1637		if (in_sack <= 0) {
1638			tmp = tcp_shift_skb_data(sk, skb, state,
1639						 start_seq, end_seq, dup_sack);
1640			if (tmp != NULL) {
1641				if (tmp != skb) {
1642					skb = tmp;
1643					continue;
1644				}
1645
1646				in_sack = 0;
1647			} else {
1648				in_sack = tcp_match_skb_to_sack(sk, skb,
1649								start_seq,
1650								end_seq);
1651			}
1652		}
1653
1654		if (unlikely(in_sack < 0))
1655			break;
1656
1657		if (in_sack) {
1658			TCP_SKB_CB(skb)->sacked = tcp_sacktag_one(skb, sk,
1659								  state,
1660								  dup_sack,
1661								  tcp_skb_pcount(skb));
 
 
 
 
1662
1663			if (!before(TCP_SKB_CB(skb)->seq,
1664				    tcp_highest_sack_seq(tp)))
1665				tcp_advance_highest_sack(sk, skb);
1666		}
1667
1668		state->fack_count += tcp_skb_pcount(skb);
1669	}
1670	return skb;
1671}
1672
1673/* Avoid all extra work that is being done by sacktag while walking in
1674 * a normal way
1675 */
1676static struct sk_buff *tcp_sacktag_skip(struct sk_buff *skb, struct sock *sk,
1677					struct tcp_sacktag_state *state,
1678					u32 skip_to_seq)
1679{
1680	tcp_for_write_queue_from(skb, sk) {
1681		if (skb == tcp_send_head(sk))
1682			break;
1683
1684		if (after(TCP_SKB_CB(skb)->end_seq, skip_to_seq))
1685			break;
1686
1687		state->fack_count += tcp_skb_pcount(skb);
1688	}
1689	return skb;
1690}
1691
1692static struct sk_buff *tcp_maybe_skipping_dsack(struct sk_buff *skb,
1693						struct sock *sk,
1694						struct tcp_sack_block *next_dup,
1695						struct tcp_sacktag_state *state,
1696						u32 skip_to_seq)
1697{
1698	if (next_dup == NULL)
1699		return skb;
1700
1701	if (before(next_dup->start_seq, skip_to_seq)) {
1702		skb = tcp_sacktag_skip(skb, sk, state, next_dup->start_seq);
1703		skb = tcp_sacktag_walk(skb, sk, NULL, state,
1704				       next_dup->start_seq, next_dup->end_seq,
1705				       1);
1706	}
1707
1708	return skb;
1709}
1710
1711static int tcp_sack_cache_ok(struct tcp_sock *tp, struct tcp_sack_block *cache)
1712{
1713	return cache < tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
1714}
1715
1716static int
1717tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb,
1718			u32 prior_snd_una)
1719{
1720	const struct inet_connection_sock *icsk = inet_csk(sk);
1721	struct tcp_sock *tp = tcp_sk(sk);
1722	unsigned char *ptr = (skb_transport_header(ack_skb) +
1723			      TCP_SKB_CB(ack_skb)->sacked);
1724	struct tcp_sack_block_wire *sp_wire = (struct tcp_sack_block_wire *)(ptr+2);
1725	struct tcp_sack_block sp[TCP_NUM_SACKS];
1726	struct tcp_sack_block *cache;
1727	struct tcp_sacktag_state state;
1728	struct sk_buff *skb;
1729	int num_sacks = min(TCP_NUM_SACKS, (ptr[1] - TCPOLEN_SACK_BASE) >> 3);
1730	int used_sacks;
1731	int found_dup_sack = 0;
1732	int i, j;
1733	int first_sack_index;
1734
1735	state.flag = 0;
1736	state.reord = tp->packets_out;
1737
1738	if (!tp->sacked_out) {
1739		if (WARN_ON(tp->fackets_out))
1740			tp->fackets_out = 0;
1741		tcp_highest_sack_reset(sk);
1742	}
1743
1744	found_dup_sack = tcp_check_dsack(sk, ack_skb, sp_wire,
1745					 num_sacks, prior_snd_una);
1746	if (found_dup_sack)
1747		state.flag |= FLAG_DSACKING_ACK;
1748
1749	/* Eliminate too old ACKs, but take into
1750	 * account more or less fresh ones, they can
1751	 * contain valid SACK info.
1752	 */
1753	if (before(TCP_SKB_CB(ack_skb)->ack_seq, prior_snd_una - tp->max_window))
1754		return 0;
1755
1756	if (!tp->packets_out)
1757		goto out;
1758
1759	used_sacks = 0;
1760	first_sack_index = 0;
1761	for (i = 0; i < num_sacks; i++) {
1762		int dup_sack = !i && found_dup_sack;
1763
1764		sp[used_sacks].start_seq = get_unaligned_be32(&sp_wire[i].start_seq);
1765		sp[used_sacks].end_seq = get_unaligned_be32(&sp_wire[i].end_seq);
1766
1767		if (!tcp_is_sackblock_valid(tp, dup_sack,
1768					    sp[used_sacks].start_seq,
1769					    sp[used_sacks].end_seq)) {
1770			int mib_idx;
1771
1772			if (dup_sack) {
1773				if (!tp->undo_marker)
1774					mib_idx = LINUX_MIB_TCPDSACKIGNOREDNOUNDO;
1775				else
1776					mib_idx = LINUX_MIB_TCPDSACKIGNOREDOLD;
1777			} else {
1778				/* Don't count olds caused by ACK reordering */
1779				if ((TCP_SKB_CB(ack_skb)->ack_seq != tp->snd_una) &&
1780				    !after(sp[used_sacks].end_seq, tp->snd_una))
1781					continue;
1782				mib_idx = LINUX_MIB_TCPSACKDISCARD;
1783			}
1784
1785			NET_INC_STATS_BH(sock_net(sk), mib_idx);
1786			if (i == 0)
1787				first_sack_index = -1;
1788			continue;
1789		}
1790
1791		/* Ignore very old stuff early */
1792		if (!after(sp[used_sacks].end_seq, prior_snd_una))
1793			continue;
1794
1795		used_sacks++;
1796	}
1797
1798	/* order SACK blocks to allow in order walk of the retrans queue */
1799	for (i = used_sacks - 1; i > 0; i--) {
1800		for (j = 0; j < i; j++) {
1801			if (after(sp[j].start_seq, sp[j + 1].start_seq)) {
1802				swap(sp[j], sp[j + 1]);
1803
1804				/* Track where the first SACK block goes to */
1805				if (j == first_sack_index)
1806					first_sack_index = j + 1;
1807			}
1808		}
1809	}
1810
1811	skb = tcp_write_queue_head(sk);
1812	state.fack_count = 0;
1813	i = 0;
1814
1815	if (!tp->sacked_out) {
1816		/* It's already past, so skip checking against it */
1817		cache = tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
1818	} else {
1819		cache = tp->recv_sack_cache;
1820		/* Skip empty blocks in at head of the cache */
1821		while (tcp_sack_cache_ok(tp, cache) && !cache->start_seq &&
1822		       !cache->end_seq)
1823			cache++;
1824	}
1825
1826	while (i < used_sacks) {
1827		u32 start_seq = sp[i].start_seq;
1828		u32 end_seq = sp[i].end_seq;
1829		int dup_sack = (found_dup_sack && (i == first_sack_index));
1830		struct tcp_sack_block *next_dup = NULL;
1831
1832		if (found_dup_sack && ((i + 1) == first_sack_index))
1833			next_dup = &sp[i + 1];
1834
1835		/* Event "B" in the comment above. */
1836		if (after(end_seq, tp->high_seq))
1837			state.flag |= FLAG_DATA_LOST;
1838
1839		/* Skip too early cached blocks */
1840		while (tcp_sack_cache_ok(tp, cache) &&
1841		       !before(start_seq, cache->end_seq))
1842			cache++;
1843
1844		/* Can skip some work by looking recv_sack_cache? */
1845		if (tcp_sack_cache_ok(tp, cache) && !dup_sack &&
1846		    after(end_seq, cache->start_seq)) {
1847
1848			/* Head todo? */
1849			if (before(start_seq, cache->start_seq)) {
1850				skb = tcp_sacktag_skip(skb, sk, &state,
1851						       start_seq);
1852				skb = tcp_sacktag_walk(skb, sk, next_dup,
1853						       &state,
1854						       start_seq,
1855						       cache->start_seq,
1856						       dup_sack);
1857			}
1858
1859			/* Rest of the block already fully processed? */
1860			if (!after(end_seq, cache->end_seq))
1861				goto advance_sp;
1862
1863			skb = tcp_maybe_skipping_dsack(skb, sk, next_dup,
1864						       &state,
1865						       cache->end_seq);
1866
1867			/* ...tail remains todo... */
1868			if (tcp_highest_sack_seq(tp) == cache->end_seq) {
1869				/* ...but better entrypoint exists! */
1870				skb = tcp_highest_sack(sk);
1871				if (skb == NULL)
1872					break;
1873				state.fack_count = tp->fackets_out;
1874				cache++;
1875				goto walk;
1876			}
1877
1878			skb = tcp_sacktag_skip(skb, sk, &state, cache->end_seq);
1879			/* Check overlap against next cached too (past this one already) */
1880			cache++;
1881			continue;
1882		}
1883
1884		if (!before(start_seq, tcp_highest_sack_seq(tp))) {
1885			skb = tcp_highest_sack(sk);
1886			if (skb == NULL)
1887				break;
1888			state.fack_count = tp->fackets_out;
1889		}
1890		skb = tcp_sacktag_skip(skb, sk, &state, start_seq);
1891
1892walk:
1893		skb = tcp_sacktag_walk(skb, sk, next_dup, &state,
1894				       start_seq, end_seq, dup_sack);
1895
1896advance_sp:
1897		/* SACK enhanced FRTO (RFC4138, Appendix B): Clearing correct
1898		 * due to in-order walk
1899		 */
1900		if (after(end_seq, tp->frto_highmark))
1901			state.flag &= ~FLAG_ONLY_ORIG_SACKED;
1902
1903		i++;
1904	}
1905
1906	/* Clear the head of the cache sack blocks so we can skip it next time */
1907	for (i = 0; i < ARRAY_SIZE(tp->recv_sack_cache) - used_sacks; i++) {
1908		tp->recv_sack_cache[i].start_seq = 0;
1909		tp->recv_sack_cache[i].end_seq = 0;
1910	}
1911	for (j = 0; j < used_sacks; j++)
1912		tp->recv_sack_cache[i++] = sp[j];
1913
1914	tcp_mark_lost_retrans(sk);
1915
1916	tcp_verify_left_out(tp);
1917
1918	if ((state.reord < tp->fackets_out) &&
1919	    ((icsk->icsk_ca_state != TCP_CA_Loss) || tp->undo_marker) &&
1920	    (!tp->frto_highmark || after(tp->snd_una, tp->frto_highmark)))
1921		tcp_update_reordering(sk, tp->fackets_out - state.reord, 0);
1922
1923out:
1924
1925#if FASTRETRANS_DEBUG > 0
1926	WARN_ON((int)tp->sacked_out < 0);
1927	WARN_ON((int)tp->lost_out < 0);
1928	WARN_ON((int)tp->retrans_out < 0);
1929	WARN_ON((int)tcp_packets_in_flight(tp) < 0);
1930#endif
1931	return state.flag;
1932}
1933
1934/* Limits sacked_out so that sum with lost_out isn't ever larger than
1935 * packets_out. Returns zero if sacked_out adjustement wasn't necessary.
1936 */
1937static int tcp_limit_reno_sacked(struct tcp_sock *tp)
1938{
1939	u32 holes;
1940
1941	holes = max(tp->lost_out, 1U);
1942	holes = min(holes, tp->packets_out);
1943
1944	if ((tp->sacked_out + holes) > tp->packets_out) {
1945		tp->sacked_out = tp->packets_out - holes;
1946		return 1;
1947	}
1948	return 0;
1949}
1950
1951/* If we receive more dupacks than we expected counting segments
1952 * in assumption of absent reordering, interpret this as reordering.
1953 * The only another reason could be bug in receiver TCP.
1954 */
1955static void tcp_check_reno_reordering(struct sock *sk, const int addend)
1956{
1957	struct tcp_sock *tp = tcp_sk(sk);
1958	if (tcp_limit_reno_sacked(tp))
1959		tcp_update_reordering(sk, tp->packets_out + addend, 0);
1960}
1961
1962/* Emulate SACKs for SACKless connection: account for a new dupack. */
1963
1964static void tcp_add_reno_sack(struct sock *sk)
1965{
1966	struct tcp_sock *tp = tcp_sk(sk);
1967	tp->sacked_out++;
1968	tcp_check_reno_reordering(sk, 0);
1969	tcp_verify_left_out(tp);
1970}
1971
1972/* Account for ACK, ACKing some data in Reno Recovery phase. */
1973
1974static void tcp_remove_reno_sacks(struct sock *sk, int acked)
1975{
1976	struct tcp_sock *tp = tcp_sk(sk);
1977
1978	if (acked > 0) {
1979		/* One ACK acked hole. The rest eat duplicate ACKs. */
1980		if (acked - 1 >= tp->sacked_out)
1981			tp->sacked_out = 0;
1982		else
1983			tp->sacked_out -= acked - 1;
1984	}
1985	tcp_check_reno_reordering(sk, acked);
1986	tcp_verify_left_out(tp);
1987}
1988
1989static inline void tcp_reset_reno_sack(struct tcp_sock *tp)
1990{
1991	tp->sacked_out = 0;
1992}
1993
1994static int tcp_is_sackfrto(const struct tcp_sock *tp)
1995{
1996	return (sysctl_tcp_frto == 0x2) && !tcp_is_reno(tp);
1997}
1998
1999/* F-RTO can only be used if TCP has never retransmitted anything other than
2000 * head (SACK enhanced variant from Appendix B of RFC4138 is more robust here)
2001 */
2002int tcp_use_frto(struct sock *sk)
2003{
2004	const struct tcp_sock *tp = tcp_sk(sk);
2005	const struct inet_connection_sock *icsk = inet_csk(sk);
2006	struct sk_buff *skb;
2007
2008	if (!sysctl_tcp_frto)
2009		return 0;
2010
2011	/* MTU probe and F-RTO won't really play nicely along currently */
2012	if (icsk->icsk_mtup.probe_size)
2013		return 0;
2014
2015	if (tcp_is_sackfrto(tp))
2016		return 1;
2017
2018	/* Avoid expensive walking of rexmit queue if possible */
2019	if (tp->retrans_out > 1)
2020		return 0;
2021
2022	skb = tcp_write_queue_head(sk);
2023	if (tcp_skb_is_last(sk, skb))
2024		return 1;
2025	skb = tcp_write_queue_next(sk, skb);	/* Skips head */
2026	tcp_for_write_queue_from(skb, sk) {
2027		if (skb == tcp_send_head(sk))
2028			break;
2029		if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS)
2030			return 0;
2031		/* Short-circuit when first non-SACKed skb has been checked */
2032		if (!(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
2033			break;
2034	}
2035	return 1;
2036}
2037
2038/* RTO occurred, but do not yet enter Loss state. Instead, defer RTO
2039 * recovery a bit and use heuristics in tcp_process_frto() to detect if
2040 * the RTO was spurious. Only clear SACKED_RETRANS of the head here to
2041 * keep retrans_out counting accurate (with SACK F-RTO, other than head
2042 * may still have that bit set); TCPCB_LOST and remaining SACKED_RETRANS
2043 * bits are handled if the Loss state is really to be entered (in
2044 * tcp_enter_frto_loss).
2045 *
2046 * Do like tcp_enter_loss() would; when RTO expires the second time it
2047 * does:
2048 *  "Reduce ssthresh if it has not yet been made inside this window."
2049 */
2050void tcp_enter_frto(struct sock *sk)
2051{
2052	const struct inet_connection_sock *icsk = inet_csk(sk);
2053	struct tcp_sock *tp = tcp_sk(sk);
2054	struct sk_buff *skb;
2055
2056	if ((!tp->frto_counter && icsk->icsk_ca_state <= TCP_CA_Disorder) ||
2057	    tp->snd_una == tp->high_seq ||
2058	    ((icsk->icsk_ca_state == TCP_CA_Loss || tp->frto_counter) &&
2059	     !icsk->icsk_retransmits)) {
2060		tp->prior_ssthresh = tcp_current_ssthresh(sk);
2061		/* Our state is too optimistic in ssthresh() call because cwnd
2062		 * is not reduced until tcp_enter_frto_loss() when previous F-RTO
2063		 * recovery has not yet completed. Pattern would be this: RTO,
2064		 * Cumulative ACK, RTO (2xRTO for the same segment does not end
2065		 * up here twice).
2066		 * RFC4138 should be more specific on what to do, even though
2067		 * RTO is quite unlikely to occur after the first Cumulative ACK
2068		 * due to back-off and complexity of triggering events ...
2069		 */
2070		if (tp->frto_counter) {
2071			u32 stored_cwnd;
2072			stored_cwnd = tp->snd_cwnd;
2073			tp->snd_cwnd = 2;
2074			tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
2075			tp->snd_cwnd = stored_cwnd;
2076		} else {
2077			tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
2078		}
2079		/* ... in theory, cong.control module could do "any tricks" in
2080		 * ssthresh(), which means that ca_state, lost bits and lost_out
2081		 * counter would have to be faked before the call occurs. We
2082		 * consider that too expensive, unlikely and hacky, so modules
2083		 * using these in ssthresh() must deal these incompatibility
2084		 * issues if they receives CA_EVENT_FRTO and frto_counter != 0
2085		 */
2086		tcp_ca_event(sk, CA_EVENT_FRTO);
2087	}
2088
2089	tp->undo_marker = tp->snd_una;
2090	tp->undo_retrans = 0;
2091
2092	skb = tcp_write_queue_head(sk);
2093	if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS)
2094		tp->undo_marker = 0;
2095	if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
2096		TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
2097		tp->retrans_out -= tcp_skb_pcount(skb);
2098	}
2099	tcp_verify_left_out(tp);
2100
2101	/* Too bad if TCP was application limited */
2102	tp->snd_cwnd = min(tp->snd_cwnd, tcp_packets_in_flight(tp) + 1);
2103
2104	/* Earlier loss recovery underway (see RFC4138; Appendix B).
2105	 * The last condition is necessary at least in tp->frto_counter case.
2106	 */
2107	if (tcp_is_sackfrto(tp) && (tp->frto_counter ||
2108	    ((1 << icsk->icsk_ca_state) & (TCPF_CA_Recovery|TCPF_CA_Loss))) &&
2109	    after(tp->high_seq, tp->snd_una)) {
2110		tp->frto_highmark = tp->high_seq;
2111	} else {
2112		tp->frto_highmark = tp->snd_nxt;
2113	}
2114	tcp_set_ca_state(sk, TCP_CA_Disorder);
2115	tp->high_seq = tp->snd_nxt;
2116	tp->frto_counter = 1;
2117}
2118
2119/* Enter Loss state after F-RTO was applied. Dupack arrived after RTO,
2120 * which indicates that we should follow the traditional RTO recovery,
2121 * i.e. mark everything lost and do go-back-N retransmission.
2122 */
2123static void tcp_enter_frto_loss(struct sock *sk, int allowed_segments, int flag)
2124{
2125	struct tcp_sock *tp = tcp_sk(sk);
2126	struct sk_buff *skb;
2127
2128	tp->lost_out = 0;
2129	tp->retrans_out = 0;
2130	if (tcp_is_reno(tp))
2131		tcp_reset_reno_sack(tp);
2132
2133	tcp_for_write_queue(skb, sk) {
2134		if (skb == tcp_send_head(sk))
2135			break;
2136
2137		TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
2138		/*
2139		 * Count the retransmission made on RTO correctly (only when
2140		 * waiting for the first ACK and did not get it)...
2141		 */
2142		if ((tp->frto_counter == 1) && !(flag & FLAG_DATA_ACKED)) {
2143			/* For some reason this R-bit might get cleared? */
2144			if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS)
2145				tp->retrans_out += tcp_skb_pcount(skb);
2146			/* ...enter this if branch just for the first segment */
2147			flag |= FLAG_DATA_ACKED;
2148		} else {
2149			if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS)
2150				tp->undo_marker = 0;
2151			TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
2152		}
2153
2154		/* Marking forward transmissions that were made after RTO lost
2155		 * can cause unnecessary retransmissions in some scenarios,
2156		 * SACK blocks will mitigate that in some but not in all cases.
2157		 * We used to not mark them but it was causing break-ups with
2158		 * receivers that do only in-order receival.
2159		 *
2160		 * TODO: we could detect presence of such receiver and select
2161		 * different behavior per flow.
2162		 */
2163		if (!(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) {
2164			TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
2165			tp->lost_out += tcp_skb_pcount(skb);
2166			tp->retransmit_high = TCP_SKB_CB(skb)->end_seq;
2167		}
2168	}
2169	tcp_verify_left_out(tp);
2170
2171	tp->snd_cwnd = tcp_packets_in_flight(tp) + allowed_segments;
2172	tp->snd_cwnd_cnt = 0;
2173	tp->snd_cwnd_stamp = tcp_time_stamp;
2174	tp->frto_counter = 0;
2175	tp->bytes_acked = 0;
2176
2177	tp->reordering = min_t(unsigned int, tp->reordering,
2178			       sysctl_tcp_reordering);
2179	tcp_set_ca_state(sk, TCP_CA_Loss);
2180	tp->high_seq = tp->snd_nxt;
2181	TCP_ECN_queue_cwr(tp);
2182
2183	tcp_clear_all_retrans_hints(tp);
2184}
2185
2186static void tcp_clear_retrans_partial(struct tcp_sock *tp)
2187{
2188	tp->retrans_out = 0;
2189	tp->lost_out = 0;
2190
2191	tp->undo_marker = 0;
2192	tp->undo_retrans = 0;
2193}
2194
2195void tcp_clear_retrans(struct tcp_sock *tp)
2196{
2197	tcp_clear_retrans_partial(tp);
2198
2199	tp->fackets_out = 0;
2200	tp->sacked_out = 0;
2201}
2202
2203/* Enter Loss state. If "how" is not zero, forget all SACK information
2204 * and reset tags completely, otherwise preserve SACKs. If receiver
2205 * dropped its ofo queue, we will know this due to reneging detection.
2206 */
2207void tcp_enter_loss(struct sock *sk, int how)
2208{
2209	const struct inet_connection_sock *icsk = inet_csk(sk);
2210	struct tcp_sock *tp = tcp_sk(sk);
2211	struct sk_buff *skb;
2212
2213	/* Reduce ssthresh if it has not yet been made inside this window. */
2214	if (icsk->icsk_ca_state <= TCP_CA_Disorder || tp->snd_una == tp->high_seq ||
2215	    (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) {
2216		tp->prior_ssthresh = tcp_current_ssthresh(sk);
2217		tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
2218		tcp_ca_event(sk, CA_EVENT_LOSS);
2219	}
2220	tp->snd_cwnd	   = 1;
2221	tp->snd_cwnd_cnt   = 0;
2222	tp->snd_cwnd_stamp = tcp_time_stamp;
2223
2224	tp->bytes_acked = 0;
2225	tcp_clear_retrans_partial(tp);
2226
2227	if (tcp_is_reno(tp))
2228		tcp_reset_reno_sack(tp);
2229
2230	if (!how) {
2231		/* Push undo marker, if it was plain RTO and nothing
2232		 * was retransmitted. */
2233		tp->undo_marker = tp->snd_una;
2234	} else {
2235		tp->sacked_out = 0;
2236		tp->fackets_out = 0;
2237	}
2238	tcp_clear_all_retrans_hints(tp);
2239
2240	tcp_for_write_queue(skb, sk) {
2241		if (skb == tcp_send_head(sk))
2242			break;
2243
2244		if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS)
2245			tp->undo_marker = 0;
2246		TCP_SKB_CB(skb)->sacked &= (~TCPCB_TAGBITS)|TCPCB_SACKED_ACKED;
2247		if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED) || how) {
2248			TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED;
2249			TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
2250			tp->lost_out += tcp_skb_pcount(skb);
2251			tp->retransmit_high = TCP_SKB_CB(skb)->end_seq;
2252		}
2253	}
2254	tcp_verify_left_out(tp);
2255
2256	tp->reordering = min_t(unsigned int, tp->reordering,
2257			       sysctl_tcp_reordering);
2258	tcp_set_ca_state(sk, TCP_CA_Loss);
2259	tp->high_seq = tp->snd_nxt;
2260	TCP_ECN_queue_cwr(tp);
2261	/* Abort F-RTO algorithm if one is in progress */
2262	tp->frto_counter = 0;
2263}
2264
2265/* If ACK arrived pointing to a remembered SACK, it means that our
2266 * remembered SACKs do not reflect real state of receiver i.e.
2267 * receiver _host_ is heavily congested (or buggy).
2268 *
2269 * Do processing similar to RTO timeout.
2270 */
2271static int tcp_check_sack_reneging(struct sock *sk, int flag)
2272{
2273	if (flag & FLAG_SACK_RENEGING) {
2274		struct inet_connection_sock *icsk = inet_csk(sk);
2275		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSACKRENEGING);
2276
2277		tcp_enter_loss(sk, 1);
2278		icsk->icsk_retransmits++;
2279		tcp_retransmit_skb(sk, tcp_write_queue_head(sk));
2280		inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
2281					  icsk->icsk_rto, TCP_RTO_MAX);
2282		return 1;
2283	}
2284	return 0;
2285}
2286
2287static inline int tcp_fackets_out(struct tcp_sock *tp)
2288{
2289	return tcp_is_reno(tp) ? tp->sacked_out + 1 : tp->fackets_out;
2290}
2291
2292/* Heurestics to calculate number of duplicate ACKs. There's no dupACKs
2293 * counter when SACK is enabled (without SACK, sacked_out is used for
2294 * that purpose).
2295 *
2296 * Instead, with FACK TCP uses fackets_out that includes both SACKed
2297 * segments up to the highest received SACK block so far and holes in
2298 * between them.
2299 *
2300 * With reordering, holes may still be in flight, so RFC3517 recovery
2301 * uses pure sacked_out (total number of SACKed segments) even though
2302 * it violates the RFC that uses duplicate ACKs, often these are equal
2303 * but when e.g. out-of-window ACKs or packet duplication occurs,
2304 * they differ. Since neither occurs due to loss, TCP should really
2305 * ignore them.
2306 */
2307static inline int tcp_dupack_heuristics(struct tcp_sock *tp)
2308{
2309	return tcp_is_fack(tp) ? tp->fackets_out : tp->sacked_out + 1;
2310}
2311
2312static inline int tcp_skb_timedout(struct sock *sk, struct sk_buff *skb)
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
2313{
2314	return tcp_time_stamp - TCP_SKB_CB(skb)->when > inet_csk(sk)->icsk_rto;
2315}
2316
2317static inline int tcp_head_timedout(struct sock *sk)
2318{
2319	struct tcp_sock *tp = tcp_sk(sk);
2320
2321	return tp->packets_out &&
2322	       tcp_skb_timedout(sk, tcp_write_queue_head(sk));
2323}
2324
2325/* Linux NewReno/SACK/FACK/ECN state machine.
2326 * --------------------------------------
2327 *
2328 * "Open"	Normal state, no dubious events, fast path.
2329 * "Disorder"   In all the respects it is "Open",
2330 *		but requires a bit more attention. It is entered when
2331 *		we see some SACKs or dupacks. It is split of "Open"
2332 *		mainly to move some processing from fast path to slow one.
2333 * "CWR"	CWND was reduced due to some Congestion Notification event.
2334 *		It can be ECN, ICMP source quench, local device congestion.
2335 * "Recovery"	CWND was reduced, we are fast-retransmitting.
2336 * "Loss"	CWND was reduced due to RTO timeout or SACK reneging.
2337 *
2338 * tcp_fastretrans_alert() is entered:
2339 * - each incoming ACK, if state is not "Open"
2340 * - when arrived ACK is unusual, namely:
2341 *	* SACK
2342 *	* Duplicate ACK.
2343 *	* ECN ECE.
2344 *
2345 * Counting packets in flight is pretty simple.
2346 *
2347 *	in_flight = packets_out - left_out + retrans_out
2348 *
2349 *	packets_out is SND.NXT-SND.UNA counted in packets.
2350 *
2351 *	retrans_out is number of retransmitted segments.
2352 *
2353 *	left_out is number of segments left network, but not ACKed yet.
2354 *
2355 *		left_out = sacked_out + lost_out
2356 *
2357 *     sacked_out: Packets, which arrived to receiver out of order
2358 *		   and hence not ACKed. With SACKs this number is simply
2359 *		   amount of SACKed data. Even without SACKs
2360 *		   it is easy to give pretty reliable estimate of this number,
2361 *		   counting duplicate ACKs.
2362 *
2363 *       lost_out: Packets lost by network. TCP has no explicit
2364 *		   "loss notification" feedback from network (for now).
2365 *		   It means that this number can be only _guessed_.
2366 *		   Actually, it is the heuristics to predict lossage that
2367 *		   distinguishes different algorithms.
2368 *
2369 *	F.e. after RTO, when all the queue is considered as lost,
2370 *	lost_out = packets_out and in_flight = retrans_out.
2371 *
2372 *		Essentially, we have now two algorithms counting
2373 *		lost packets.
2374 *
2375 *		FACK: It is the simplest heuristics. As soon as we decided
2376 *		that something is lost, we decide that _all_ not SACKed
2377 *		packets until the most forward SACK are lost. I.e.
2378 *		lost_out = fackets_out - sacked_out and left_out = fackets_out.
2379 *		It is absolutely correct estimate, if network does not reorder
2380 *		packets. And it loses any connection to reality when reordering
2381 *		takes place. We use FACK by default until reordering
2382 *		is suspected on the path to this destination.
2383 *
2384 *		NewReno: when Recovery is entered, we assume that one segment
2385 *		is lost (classic Reno). While we are in Recovery and
2386 *		a partial ACK arrives, we assume that one more packet
2387 *		is lost (NewReno). This heuristics are the same in NewReno
2388 *		and SACK.
2389 *
2390 *  Imagine, that's all! Forget about all this shamanism about CWND inflation
2391 *  deflation etc. CWND is real congestion window, never inflated, changes
2392 *  only according to classic VJ rules.
2393 *
2394 * Really tricky (and requiring careful tuning) part of algorithm
2395 * is hidden in functions tcp_time_to_recover() and tcp_xmit_retransmit_queue().
2396 * The first determines the moment _when_ we should reduce CWND and,
2397 * hence, slow down forward transmission. In fact, it determines the moment
2398 * when we decide that hole is caused by loss, rather than by a reorder.
2399 *
2400 * tcp_xmit_retransmit_queue() decides, _what_ we should retransmit to fill
2401 * holes, caused by lost packets.
2402 *
2403 * And the most logically complicated part of algorithm is undo
2404 * heuristics. We detect false retransmits due to both too early
2405 * fast retransmit (reordering) and underestimated RTO, analyzing
2406 * timestamps and D-SACKs. When we detect that some segments were
2407 * retransmitted by mistake and CWND reduction was wrong, we undo
2408 * window reduction and abort recovery phase. This logic is hidden
2409 * inside several functions named tcp_try_undo_<something>.
2410 */
2411
2412/* This function decides, when we should leave Disordered state
2413 * and enter Recovery phase, reducing congestion window.
2414 *
2415 * Main question: may we further continue forward transmission
2416 * with the same cwnd?
2417 */
2418static int tcp_time_to_recover(struct sock *sk)
2419{
2420	struct tcp_sock *tp = tcp_sk(sk);
2421	__u32 packets_out;
2422
2423	/* Do not perform any recovery during F-RTO algorithm */
2424	if (tp->frto_counter)
2425		return 0;
2426
2427	/* Trick#1: The loss is proven. */
2428	if (tp->lost_out)
2429		return 1;
2430
2431	/* Not-A-Trick#2 : Classic rule... */
2432	if (tcp_dupack_heuristics(tp) > tp->reordering)
2433		return 1;
2434
2435	/* Trick#3 : when we use RFC2988 timer restart, fast
2436	 * retransmit can be triggered by timeout of queue head.
2437	 */
2438	if (tcp_is_fack(tp) && tcp_head_timedout(sk))
2439		return 1;
2440
2441	/* Trick#4: It is still not OK... But will it be useful to delay
2442	 * recovery more?
2443	 */
2444	packets_out = tp->packets_out;
2445	if (packets_out <= tp->reordering &&
2446	    tp->sacked_out >= max_t(__u32, packets_out/2, sysctl_tcp_reordering) &&
2447	    !tcp_may_send_now(sk)) {
2448		/* We have nothing to send. This connection is limited
2449		 * either by receiver window or by application.
2450		 */
2451		return 1;
2452	}
2453
2454	/* If a thin stream is detected, retransmit after first
2455	 * received dupack. Employ only if SACK is supported in order
2456	 * to avoid possible corner-case series of spurious retransmissions
2457	 * Use only if there are no unsent data.
2458	 */
2459	if ((tp->thin_dupack || sysctl_tcp_thin_dupack) &&
2460	    tcp_stream_is_thin(tp) && tcp_dupack_heuristics(tp) > 1 &&
2461	    tcp_is_sack(tp) && !tcp_send_head(sk))
2462		return 1;
2463
2464	return 0;
 
 
 
 
 
 
 
 
 
 
2465}
2466
2467/* New heuristics: it is possible only after we switched to restart timer
2468 * each time when something is ACKed. Hence, we can detect timed out packets
2469 * during fast retransmit without falling to slow start.
2470 *
2471 * Usefulness of this as is very questionable, since we should know which of
2472 * the segments is the next to timeout which is relatively expensive to find
2473 * in general case unless we add some data structure just for that. The
2474 * current approach certainly won't find the right one too often and when it
2475 * finally does find _something_ it usually marks large part of the window
2476 * right away (because a retransmission with a larger timestamp blocks the
2477 * loop from advancing). -ij
2478 */
2479static void tcp_timeout_skbs(struct sock *sk)
2480{
2481	struct tcp_sock *tp = tcp_sk(sk);
2482	struct sk_buff *skb;
2483
2484	if (!tcp_is_fack(tp) || !tcp_head_timedout(sk))
2485		return;
2486
2487	skb = tp->scoreboard_skb_hint;
2488	if (tp->scoreboard_skb_hint == NULL)
2489		skb = tcp_write_queue_head(sk);
2490
2491	tcp_for_write_queue_from(skb, sk) {
2492		if (skb == tcp_send_head(sk))
2493			break;
2494		if (!tcp_skb_timedout(sk, skb))
2495			break;
2496
2497		tcp_skb_mark_lost(tp, skb);
2498	}
2499
2500	tp->scoreboard_skb_hint = skb;
2501
2502	tcp_verify_left_out(tp);
2503}
2504
2505/* Mark head of queue up as lost. With RFC3517 SACK, the packets is
2506 * is against sacked "cnt", otherwise it's against facked "cnt"
 
 
 
2507 */
2508static void tcp_mark_head_lost(struct sock *sk, int packets, int mark_head)
2509{
2510	struct tcp_sock *tp = tcp_sk(sk);
2511	struct sk_buff *skb;
2512	int cnt, oldcnt;
2513	int err;
2514	unsigned int mss;
 
 
2515
2516	WARN_ON(packets > tp->packets_out);
2517	if (tp->lost_skb_hint) {
2518		skb = tp->lost_skb_hint;
2519		cnt = tp->lost_cnt_hint;
2520		/* Head already handled? */
2521		if (mark_head && skb != tcp_write_queue_head(sk))
2522			return;
2523	} else {
2524		skb = tcp_write_queue_head(sk);
2525		cnt = 0;
2526	}
2527
2528	tcp_for_write_queue_from(skb, sk) {
2529		if (skb == tcp_send_head(sk))
2530			break;
2531		/* TODO: do this better */
2532		/* this is not the most efficient way to do this... */
2533		tp->lost_skb_hint = skb;
2534		tp->lost_cnt_hint = cnt;
2535
2536		if (after(TCP_SKB_CB(skb)->end_seq, tp->high_seq))
2537			break;
2538
2539		oldcnt = cnt;
2540		if (tcp_is_fack(tp) || tcp_is_reno(tp) ||
2541		    (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
2542			cnt += tcp_skb_pcount(skb);
2543
2544		if (cnt > packets) {
2545			if ((tcp_is_sack(tp) && !tcp_is_fack(tp)) ||
 
2546			    (oldcnt >= packets))
2547				break;
2548
2549			mss = skb_shinfo(skb)->gso_size;
2550			err = tcp_fragment(sk, skb, (packets - oldcnt) * mss, mss);
2551			if (err < 0)
2552				break;
2553			cnt = packets;
2554		}
2555
2556		tcp_skb_mark_lost(tp, skb);
2557
2558		if (mark_head)
2559			break;
2560	}
2561	tcp_verify_left_out(tp);
2562}
2563
2564/* Account newly detected lost packet(s) */
2565
2566static void tcp_update_scoreboard(struct sock *sk, int fast_rexmit)
2567{
2568	struct tcp_sock *tp = tcp_sk(sk);
2569
2570	if (tcp_is_reno(tp)) {
2571		tcp_mark_head_lost(sk, 1, 1);
2572	} else if (tcp_is_fack(tp)) {
2573		int lost = tp->fackets_out - tp->reordering;
2574		if (lost <= 0)
2575			lost = 1;
2576		tcp_mark_head_lost(sk, lost, 0);
2577	} else {
2578		int sacked_upto = tp->sacked_out - tp->reordering;
2579		if (sacked_upto >= 0)
2580			tcp_mark_head_lost(sk, sacked_upto, 0);
2581		else if (fast_rexmit)
2582			tcp_mark_head_lost(sk, 1, 1);
2583	}
2584
2585	tcp_timeout_skbs(sk);
2586}
2587
2588/* CWND moderation, preventing bursts due to too big ACKs
2589 * in dubious situations.
2590 */
2591static inline void tcp_moderate_cwnd(struct tcp_sock *tp)
2592{
2593	tp->snd_cwnd = min(tp->snd_cwnd,
2594			   tcp_packets_in_flight(tp) + tcp_max_burst(tp));
2595	tp->snd_cwnd_stamp = tcp_time_stamp;
2596}
2597
2598/* Lower bound on congestion window is slow start threshold
2599 * unless congestion avoidance choice decides to overide it.
2600 */
2601static inline u32 tcp_cwnd_min(const struct sock *sk)
2602{
2603	const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;
2604
2605	return ca_ops->min_cwnd ? ca_ops->min_cwnd(sk) : tcp_sk(sk)->snd_ssthresh;
2606}
2607
2608/* Decrease cwnd each second ack. */
2609static void tcp_cwnd_down(struct sock *sk, int flag)
2610{
2611	struct tcp_sock *tp = tcp_sk(sk);
2612	int decr = tp->snd_cwnd_cnt + 1;
2613
2614	if ((flag & (FLAG_ANY_PROGRESS | FLAG_DSACKING_ACK)) ||
2615	    (tcp_is_reno(tp) && !(flag & FLAG_NOT_DUP))) {
2616		tp->snd_cwnd_cnt = decr & 1;
2617		decr >>= 1;
2618
2619		if (decr && tp->snd_cwnd > tcp_cwnd_min(sk))
2620			tp->snd_cwnd -= decr;
2621
2622		tp->snd_cwnd = min(tp->snd_cwnd, tcp_packets_in_flight(tp) + 1);
2623		tp->snd_cwnd_stamp = tcp_time_stamp;
2624	}
2625}
2626
2627/* Nothing was retransmitted or returned timestamp is less
2628 * than timestamp of the first retransmission.
2629 */
2630static inline int tcp_packet_delayed(struct tcp_sock *tp)
2631{
2632	return !tp->retrans_stamp ||
2633		(tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
2634		 before(tp->rx_opt.rcv_tsecr, tp->retrans_stamp));
2635}
2636
2637/* Undo procedures. */
2638
2639#if FASTRETRANS_DEBUG > 1
2640static void DBGUNDO(struct sock *sk, const char *msg)
2641{
2642	struct tcp_sock *tp = tcp_sk(sk);
2643	struct inet_sock *inet = inet_sk(sk);
2644
2645	if (sk->sk_family == AF_INET) {
2646		printk(KERN_DEBUG "Undo %s %pI4/%u c%u l%u ss%u/%u p%u\n",
2647		       msg,
2648		       &inet->inet_daddr, ntohs(inet->inet_dport),
2649		       tp->snd_cwnd, tcp_left_out(tp),
2650		       tp->snd_ssthresh, tp->prior_ssthresh,
2651		       tp->packets_out);
2652	}
2653#if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
2654	else if (sk->sk_family == AF_INET6) {
2655		struct ipv6_pinfo *np = inet6_sk(sk);
2656		printk(KERN_DEBUG "Undo %s %pI6/%u c%u l%u ss%u/%u p%u\n",
2657		       msg,
2658		       &np->daddr, ntohs(inet->inet_dport),
2659		       tp->snd_cwnd, tcp_left_out(tp),
2660		       tp->snd_ssthresh, tp->prior_ssthresh,
2661		       tp->packets_out);
2662	}
2663#endif
2664}
2665#else
2666#define DBGUNDO(x...) do { } while (0)
2667#endif
2668
2669static void tcp_undo_cwr(struct sock *sk, const bool undo_ssthresh)
2670{
2671	struct tcp_sock *tp = tcp_sk(sk);
2672
2673	if (tp->prior_ssthresh) {
2674		const struct inet_connection_sock *icsk = inet_csk(sk);
2675
2676		if (icsk->icsk_ca_ops->undo_cwnd)
2677			tp->snd_cwnd = icsk->icsk_ca_ops->undo_cwnd(sk);
2678		else
2679			tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh << 1);
2680
2681		if (undo_ssthresh && tp->prior_ssthresh > tp->snd_ssthresh) {
2682			tp->snd_ssthresh = tp->prior_ssthresh;
2683			TCP_ECN_withdraw_cwr(tp);
2684		}
2685	} else {
2686		tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh);
2687	}
2688	tp->snd_cwnd_stamp = tcp_time_stamp;
2689}
2690
2691static inline int tcp_may_undo(struct tcp_sock *tp)
2692{
2693	return tp->undo_marker && (!tp->undo_retrans || tcp_packet_delayed(tp));
2694}
2695
2696/* People celebrate: "We love our President!" */
2697static int tcp_try_undo_recovery(struct sock *sk)
2698{
2699	struct tcp_sock *tp = tcp_sk(sk);
2700
2701	if (tcp_may_undo(tp)) {
2702		int mib_idx;
2703
2704		/* Happy end! We did not retransmit anything
2705		 * or our original transmission succeeded.
2706		 */
2707		DBGUNDO(sk, inet_csk(sk)->icsk_ca_state == TCP_CA_Loss ? "loss" : "retrans");
2708		tcp_undo_cwr(sk, true);
2709		if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss)
2710			mib_idx = LINUX_MIB_TCPLOSSUNDO;
2711		else
2712			mib_idx = LINUX_MIB_TCPFULLUNDO;
2713
2714		NET_INC_STATS_BH(sock_net(sk), mib_idx);
2715		tp->undo_marker = 0;
2716	}
2717	if (tp->snd_una == tp->high_seq && tcp_is_reno(tp)) {
2718		/* Hold old state until something *above* high_seq
2719		 * is ACKed. For Reno it is MUST to prevent false
2720		 * fast retransmits (RFC2582). SACK TCP is safe. */
2721		tcp_moderate_cwnd(tp);
2722		return 1;
2723	}
2724	tcp_set_ca_state(sk, TCP_CA_Open);
2725	return 0;
2726}
2727
2728/* Try to undo cwnd reduction, because D-SACKs acked all retransmitted data */
2729static void tcp_try_undo_dsack(struct sock *sk)
2730{
2731	struct tcp_sock *tp = tcp_sk(sk);
2732
2733	if (tp->undo_marker && !tp->undo_retrans) {
2734		DBGUNDO(sk, "D-SACK");
2735		tcp_undo_cwr(sk, true);
2736		tp->undo_marker = 0;
2737		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPDSACKUNDO);
2738	}
2739}
2740
2741/* We can clear retrans_stamp when there are no retransmissions in the
2742 * window. It would seem that it is trivially available for us in
2743 * tp->retrans_out, however, that kind of assumptions doesn't consider
2744 * what will happen if errors occur when sending retransmission for the
2745 * second time. ...It could the that such segment has only
2746 * TCPCB_EVER_RETRANS set at the present time. It seems that checking
2747 * the head skb is enough except for some reneging corner cases that
2748 * are not worth the effort.
2749 *
2750 * Main reason for all this complexity is the fact that connection dying
2751 * time now depends on the validity of the retrans_stamp, in particular,
2752 * that successive retransmissions of a segment must not advance
2753 * retrans_stamp under any conditions.
2754 */
2755static int tcp_any_retrans_done(struct sock *sk)
2756{
2757	struct tcp_sock *tp = tcp_sk(sk);
2758	struct sk_buff *skb;
2759
2760	if (tp->retrans_out)
2761		return 1;
2762
2763	skb = tcp_write_queue_head(sk);
2764	if (unlikely(skb && TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS))
2765		return 1;
2766
2767	return 0;
2768}
2769
2770/* Undo during fast recovery after partial ACK. */
2771
2772static int tcp_try_undo_partial(struct sock *sk, int acked)
2773{
2774	struct tcp_sock *tp = tcp_sk(sk);
2775	/* Partial ACK arrived. Force Hoe's retransmit. */
2776	int failed = tcp_is_reno(tp) || (tcp_fackets_out(tp) > tp->reordering);
2777
2778	if (tcp_may_undo(tp)) {
2779		/* Plain luck! Hole if filled with delayed
2780		 * packet, rather than with a retransmit.
2781		 */
2782		if (!tcp_any_retrans_done(sk))
2783			tp->retrans_stamp = 0;
2784
2785		tcp_update_reordering(sk, tcp_fackets_out(tp) + acked, 1);
2786
2787		DBGUNDO(sk, "Hoe");
2788		tcp_undo_cwr(sk, false);
2789		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPPARTIALUNDO);
2790
2791		/* So... Do not make Hoe's retransmit yet.
2792		 * If the first packet was delayed, the rest
2793		 * ones are most probably delayed as well.
2794		 */
2795		failed = 0;
2796	}
2797	return failed;
2798}
2799
2800/* Undo during loss recovery after partial ACK. */
2801static int tcp_try_undo_loss(struct sock *sk)
2802{
2803	struct tcp_sock *tp = tcp_sk(sk);
2804
2805	if (tcp_may_undo(tp)) {
2806		struct sk_buff *skb;
2807		tcp_for_write_queue(skb, sk) {
2808			if (skb == tcp_send_head(sk))
2809				break;
2810			TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
2811		}
2812
2813		tcp_clear_all_retrans_hints(tp);
2814
2815		DBGUNDO(sk, "partial loss");
2816		tp->lost_out = 0;
2817		tcp_undo_cwr(sk, true);
2818		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPLOSSUNDO);
2819		inet_csk(sk)->icsk_retransmits = 0;
2820		tp->undo_marker = 0;
2821		if (tcp_is_sack(tp))
2822			tcp_set_ca_state(sk, TCP_CA_Open);
2823		return 1;
2824	}
2825	return 0;
2826}
2827
2828static inline void tcp_complete_cwr(struct sock *sk)
2829{
2830	struct tcp_sock *tp = tcp_sk(sk);
2831	/* Do not moderate cwnd if it's already undone in cwr or recovery */
2832	if (tp->undo_marker && tp->snd_cwnd > tp->snd_ssthresh) {
2833		tp->snd_cwnd = tp->snd_ssthresh;
2834		tp->snd_cwnd_stamp = tcp_time_stamp;
 
 
 
 
 
 
 
2835	}
2836	tcp_ca_event(sk, CA_EVENT_COMPLETE_CWR);
2837}
2838
2839static void tcp_try_keep_open(struct sock *sk)
2840{
2841	struct tcp_sock *tp = tcp_sk(sk);
2842	int state = TCP_CA_Open;
2843
2844	if (tcp_left_out(tp) || tcp_any_retrans_done(sk) || tp->undo_marker)
2845		state = TCP_CA_Disorder;
2846
2847	if (inet_csk(sk)->icsk_ca_state != state) {
2848		tcp_set_ca_state(sk, state);
2849		tp->high_seq = tp->snd_nxt;
2850	}
2851}
2852
2853static void tcp_try_to_open(struct sock *sk, int flag)
2854{
2855	struct tcp_sock *tp = tcp_sk(sk);
2856
2857	tcp_verify_left_out(tp);
2858
2859	if (!tp->frto_counter && !tcp_any_retrans_done(sk))
2860		tp->retrans_stamp = 0;
2861
2862	if (flag & FLAG_ECE)
2863		tcp_enter_cwr(sk, 1);
2864
2865	if (inet_csk(sk)->icsk_ca_state != TCP_CA_CWR) {
2866		tcp_try_keep_open(sk);
2867		tcp_moderate_cwnd(tp);
 
2868	} else {
2869		tcp_cwnd_down(sk, flag);
2870	}
2871}
2872
2873static void tcp_mtup_probe_failed(struct sock *sk)
2874{
2875	struct inet_connection_sock *icsk = inet_csk(sk);
2876
2877	icsk->icsk_mtup.search_high = icsk->icsk_mtup.probe_size - 1;
2878	icsk->icsk_mtup.probe_size = 0;
2879}
2880
2881static void tcp_mtup_probe_success(struct sock *sk)
2882{
2883	struct tcp_sock *tp = tcp_sk(sk);
2884	struct inet_connection_sock *icsk = inet_csk(sk);
2885
2886	/* FIXME: breaks with very large cwnd */
2887	tp->prior_ssthresh = tcp_current_ssthresh(sk);
2888	tp->snd_cwnd = tp->snd_cwnd *
2889		       tcp_mss_to_mtu(sk, tp->mss_cache) /
2890		       icsk->icsk_mtup.probe_size;
2891	tp->snd_cwnd_cnt = 0;
2892	tp->snd_cwnd_stamp = tcp_time_stamp;
2893	tp->snd_ssthresh = tcp_current_ssthresh(sk);
2894
2895	icsk->icsk_mtup.search_low = icsk->icsk_mtup.probe_size;
2896	icsk->icsk_mtup.probe_size = 0;
2897	tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
2898}
2899
2900/* Do a simple retransmit without using the backoff mechanisms in
2901 * tcp_timer. This is used for path mtu discovery.
2902 * The socket is already locked here.
2903 */
2904void tcp_simple_retransmit(struct sock *sk)
2905{
2906	const struct inet_connection_sock *icsk = inet_csk(sk);
2907	struct tcp_sock *tp = tcp_sk(sk);
2908	struct sk_buff *skb;
2909	unsigned int mss = tcp_current_mss(sk);
2910	u32 prior_lost = tp->lost_out;
2911
2912	tcp_for_write_queue(skb, sk) {
2913		if (skb == tcp_send_head(sk))
2914			break;
2915		if (tcp_skb_seglen(skb) > mss &&
2916		    !(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) {
2917			if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
2918				TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
2919				tp->retrans_out -= tcp_skb_pcount(skb);
2920			}
2921			tcp_skb_mark_lost_uncond_verify(tp, skb);
2922		}
2923	}
2924
2925	tcp_clear_retrans_hints_partial(tp);
2926
2927	if (prior_lost == tp->lost_out)
2928		return;
2929
2930	if (tcp_is_reno(tp))
2931		tcp_limit_reno_sacked(tp);
2932
2933	tcp_verify_left_out(tp);
2934
2935	/* Don't muck with the congestion window here.
2936	 * Reason is that we do not increase amount of _data_
2937	 * in network, but units changed and effective
2938	 * cwnd/ssthresh really reduced now.
2939	 */
2940	if (icsk->icsk_ca_state != TCP_CA_Loss) {
2941		tp->high_seq = tp->snd_nxt;
2942		tp->snd_ssthresh = tcp_current_ssthresh(sk);
2943		tp->prior_ssthresh = 0;
2944		tp->undo_marker = 0;
2945		tcp_set_ca_state(sk, TCP_CA_Loss);
2946	}
2947	tcp_xmit_retransmit_queue(sk);
2948}
2949EXPORT_SYMBOL(tcp_simple_retransmit);
2950
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
2951/* Process an event, which can update packets-in-flight not trivially.
2952 * Main goal of this function is to calculate new estimate for left_out,
2953 * taking into account both packets sitting in receiver's buffer and
2954 * packets lost by network.
2955 *
2956 * Besides that it does CWND reduction, when packet loss is detected
2957 * and changes state of machine.
2958 *
2959 * It does _not_ decide what to send, it is made in function
2960 * tcp_xmit_retransmit_queue().
2961 */
2962static void tcp_fastretrans_alert(struct sock *sk, int pkts_acked, int flag)
 
 
2963{
2964	struct inet_connection_sock *icsk = inet_csk(sk);
2965	struct tcp_sock *tp = tcp_sk(sk);
2966	int is_dupack = !(flag & (FLAG_SND_UNA_ADVANCED | FLAG_NOT_DUP));
2967	int do_lost = is_dupack || ((flag & FLAG_DATA_SACKED) &&
2968				    (tcp_fackets_out(tp) > tp->reordering));
2969	int fast_rexmit = 0, mib_idx;
 
2970
2971	if (WARN_ON(!tp->packets_out && tp->sacked_out))
2972		tp->sacked_out = 0;
2973	if (WARN_ON(!tp->sacked_out && tp->fackets_out))
2974		tp->fackets_out = 0;
2975
2976	/* Now state machine starts.
2977	 * A. ECE, hence prohibit cwnd undoing, the reduction is required. */
2978	if (flag & FLAG_ECE)
2979		tp->prior_ssthresh = 0;
2980
2981	/* B. In all the states check for reneging SACKs. */
2982	if (tcp_check_sack_reneging(sk, flag))
2983		return;
2984
2985	/* C. Process data loss notification, provided it is valid. */
2986	if (tcp_is_fack(tp) && (flag & FLAG_DATA_LOST) &&
2987	    before(tp->snd_una, tp->high_seq) &&
2988	    icsk->icsk_ca_state != TCP_CA_Open &&
2989	    tp->fackets_out > tp->reordering) {
2990		tcp_mark_head_lost(sk, tp->fackets_out - tp->reordering, 0);
2991		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPLOSS);
2992	}
2993
2994	/* D. Check consistency of the current state. */
2995	tcp_verify_left_out(tp);
2996
2997	/* E. Check state exit conditions. State can be terminated
2998	 *    when high_seq is ACKed. */
2999	if (icsk->icsk_ca_state == TCP_CA_Open) {
3000		WARN_ON(tp->retrans_out != 0);
3001		tp->retrans_stamp = 0;
3002	} else if (!before(tp->snd_una, tp->high_seq)) {
3003		switch (icsk->icsk_ca_state) {
3004		case TCP_CA_Loss:
3005			icsk->icsk_retransmits = 0;
3006			if (tcp_try_undo_recovery(sk))
3007				return;
3008			break;
3009
3010		case TCP_CA_CWR:
3011			/* CWR is to be held something *above* high_seq
3012			 * is ACKed for CWR bit to reach receiver. */
3013			if (tp->snd_una != tp->high_seq) {
3014				tcp_complete_cwr(sk);
3015				tcp_set_ca_state(sk, TCP_CA_Open);
3016			}
3017			break;
3018
3019		case TCP_CA_Disorder:
3020			tcp_try_undo_dsack(sk);
3021			if (!tp->undo_marker ||
3022			    /* For SACK case do not Open to allow to undo
3023			     * catching for all duplicate ACKs. */
3024			    tcp_is_reno(tp) || tp->snd_una != tp->high_seq) {
3025				tp->undo_marker = 0;
3026				tcp_set_ca_state(sk, TCP_CA_Open);
3027			}
3028			break;
3029
3030		case TCP_CA_Recovery:
3031			if (tcp_is_reno(tp))
3032				tcp_reset_reno_sack(tp);
3033			if (tcp_try_undo_recovery(sk))
3034				return;
3035			tcp_complete_cwr(sk);
3036			break;
3037		}
3038	}
3039
3040	/* F. Process state. */
3041	switch (icsk->icsk_ca_state) {
3042	case TCP_CA_Recovery:
3043		if (!(flag & FLAG_SND_UNA_ADVANCED)) {
3044			if (tcp_is_reno(tp) && is_dupack)
3045				tcp_add_reno_sack(sk);
3046		} else
3047			do_lost = tcp_try_undo_partial(sk, pkts_acked);
 
3048		break;
3049	case TCP_CA_Loss:
3050		if (flag & FLAG_DATA_ACKED)
3051			icsk->icsk_retransmits = 0;
3052		if (tcp_is_reno(tp) && flag & FLAG_SND_UNA_ADVANCED)
3053			tcp_reset_reno_sack(tp);
3054		if (!tcp_try_undo_loss(sk)) {
3055			tcp_moderate_cwnd(tp);
3056			tcp_xmit_retransmit_queue(sk);
3057			return;
3058		}
3059		if (icsk->icsk_ca_state != TCP_CA_Open)
3060			return;
3061		/* Loss is undone; fall through to processing in Open state. */
3062	default:
3063		if (tcp_is_reno(tp)) {
3064			if (flag & FLAG_SND_UNA_ADVANCED)
3065				tcp_reset_reno_sack(tp);
3066			if (is_dupack)
3067				tcp_add_reno_sack(sk);
3068		}
 
3069
3070		if (icsk->icsk_ca_state == TCP_CA_Disorder)
3071			tcp_try_undo_dsack(sk);
3072
3073		if (!tcp_time_to_recover(sk)) {
3074			tcp_try_to_open(sk, flag);
3075			return;
3076		}
3077
3078		/* MTU probe failure: don't reduce cwnd */
3079		if (icsk->icsk_ca_state < TCP_CA_CWR &&
3080		    icsk->icsk_mtup.probe_size &&
3081		    tp->snd_una == tp->mtu_probe.probe_seq_start) {
3082			tcp_mtup_probe_failed(sk);
3083			/* Restores the reduction we did in tcp_mtup_probe() */
3084			tp->snd_cwnd++;
3085			tcp_simple_retransmit(sk);
3086			return;
3087		}
3088
3089		/* Otherwise enter Recovery state */
3090
3091		if (tcp_is_reno(tp))
3092			mib_idx = LINUX_MIB_TCPRENORECOVERY;
3093		else
3094			mib_idx = LINUX_MIB_TCPSACKRECOVERY;
3095
3096		NET_INC_STATS_BH(sock_net(sk), mib_idx);
3097
3098		tp->high_seq = tp->snd_nxt;
3099		tp->prior_ssthresh = 0;
3100		tp->undo_marker = tp->snd_una;
3101		tp->undo_retrans = tp->retrans_out;
3102
3103		if (icsk->icsk_ca_state < TCP_CA_CWR) {
3104			if (!(flag & FLAG_ECE))
3105				tp->prior_ssthresh = tcp_current_ssthresh(sk);
3106			tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
3107			TCP_ECN_queue_cwr(tp);
3108		}
3109
3110		tp->bytes_acked = 0;
3111		tp->snd_cwnd_cnt = 0;
3112		tcp_set_ca_state(sk, TCP_CA_Recovery);
3113		fast_rexmit = 1;
3114	}
3115
3116	if (do_lost || (tcp_is_fack(tp) && tcp_head_timedout(sk)))
3117		tcp_update_scoreboard(sk, fast_rexmit);
3118	tcp_cwnd_down(sk, flag);
 
3119	tcp_xmit_retransmit_queue(sk);
3120}
3121
3122void tcp_valid_rtt_meas(struct sock *sk, u32 seq_rtt)
3123{
3124	tcp_rtt_estimator(sk, seq_rtt);
3125	tcp_set_rto(sk);
3126	inet_csk(sk)->icsk_backoff = 0;
3127}
3128EXPORT_SYMBOL(tcp_valid_rtt_meas);
3129
3130/* Read draft-ietf-tcplw-high-performance before mucking
3131 * with this code. (Supersedes RFC1323)
3132 */
3133static void tcp_ack_saw_tstamp(struct sock *sk, int flag)
3134{
3135	/* RTTM Rule: A TSecr value received in a segment is used to
3136	 * update the averaged RTT measurement only if the segment
3137	 * acknowledges some new data, i.e., only if it advances the
3138	 * left edge of the send window.
3139	 *
3140	 * See draft-ietf-tcplw-high-performance-00, section 3.3.
3141	 * 1998/04/10 Andrey V. Savochkin <saw@msu.ru>
3142	 *
3143	 * Changed: reset backoff as soon as we see the first valid sample.
3144	 * If we do not, we get strongly overestimated rto. With timestamps
3145	 * samples are accepted even from very old segments: f.e., when rtt=1
3146	 * increases to 8, we retransmit 5 times and after 8 seconds delayed
3147	 * answer arrives rto becomes 120 seconds! If at least one of segments
3148	 * in window is lost... Voila.	 			--ANK (010210)
3149	 */
3150	struct tcp_sock *tp = tcp_sk(sk);
3151
3152	tcp_valid_rtt_meas(sk, tcp_time_stamp - tp->rx_opt.rcv_tsecr);
3153}
3154
3155static void tcp_ack_no_tstamp(struct sock *sk, u32 seq_rtt, int flag)
3156{
3157	/* We don't have a timestamp. Can only use
3158	 * packets that are not retransmitted to determine
3159	 * rtt estimates. Also, we must not reset the
3160	 * backoff for rto until we get a non-retransmitted
3161	 * packet. This allows us to deal with a situation
3162	 * where the network delay has increased suddenly.
3163	 * I.e. Karn's algorithm. (SIGCOMM '87, p5.)
3164	 */
3165
3166	if (flag & FLAG_RETRANS_DATA_ACKED)
3167		return;
3168
3169	tcp_valid_rtt_meas(sk, seq_rtt);
3170}
3171
3172static inline void tcp_ack_update_rtt(struct sock *sk, const int flag,
3173				      const s32 seq_rtt)
3174{
3175	const struct tcp_sock *tp = tcp_sk(sk);
3176	/* Note that peer MAY send zero echo. In this case it is ignored. (rfc1323) */
3177	if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
3178		tcp_ack_saw_tstamp(sk, flag);
3179	else if (seq_rtt >= 0)
3180		tcp_ack_no_tstamp(sk, seq_rtt, flag);
3181}
3182
3183static void tcp_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
3184{
3185	const struct inet_connection_sock *icsk = inet_csk(sk);
3186	icsk->icsk_ca_ops->cong_avoid(sk, ack, in_flight);
3187	tcp_sk(sk)->snd_cwnd_stamp = tcp_time_stamp;
3188}
3189
3190/* Restart timer after forward progress on connection.
3191 * RFC2988 recommends to restart timer to now+rto.
3192 */
3193static void tcp_rearm_rto(struct sock *sk)
3194{
3195	struct tcp_sock *tp = tcp_sk(sk);
3196
3197	if (!tp->packets_out) {
3198		inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS);
3199	} else {
3200		inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
3201					  inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
 
 
 
 
 
 
 
 
 
 
 
 
3202	}
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
3203}
3204
3205/* If we get here, the whole TSO packet has not been acked. */
3206static u32 tcp_tso_acked(struct sock *sk, struct sk_buff *skb)
3207{
3208	struct tcp_sock *tp = tcp_sk(sk);
3209	u32 packets_acked;
3210
3211	BUG_ON(!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una));
3212
3213	packets_acked = tcp_skb_pcount(skb);
3214	if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
3215		return 0;
3216	packets_acked -= tcp_skb_pcount(skb);
3217
3218	if (packets_acked) {
3219		BUG_ON(tcp_skb_pcount(skb) == 0);
3220		BUG_ON(!before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq));
3221	}
3222
3223	return packets_acked;
3224}
3225
3226/* Remove acknowledged frames from the retransmission queue. If our packet
3227 * is before the ack sequence we can discard it as it's confirmed to have
3228 * arrived at the other end.
3229 */
3230static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
3231			       u32 prior_snd_una)
3232{
3233	struct tcp_sock *tp = tcp_sk(sk);
3234	const struct inet_connection_sock *icsk = inet_csk(sk);
3235	struct sk_buff *skb;
3236	u32 now = tcp_time_stamp;
3237	int fully_acked = 1;
3238	int flag = 0;
3239	u32 pkts_acked = 0;
3240	u32 reord = tp->packets_out;
3241	u32 prior_sacked = tp->sacked_out;
3242	s32 seq_rtt = -1;
3243	s32 ca_seq_rtt = -1;
3244	ktime_t last_ackt = net_invalid_timestamp();
3245
3246	while ((skb = tcp_write_queue_head(sk)) && skb != tcp_send_head(sk)) {
3247		struct tcp_skb_cb *scb = TCP_SKB_CB(skb);
3248		u32 acked_pcount;
3249		u8 sacked = scb->sacked;
3250
3251		/* Determine how many packets and what bytes were acked, tso and else */
3252		if (after(scb->end_seq, tp->snd_una)) {
3253			if (tcp_skb_pcount(skb) == 1 ||
3254			    !after(tp->snd_una, scb->seq))
3255				break;
3256
3257			acked_pcount = tcp_tso_acked(sk, skb);
3258			if (!acked_pcount)
3259				break;
3260
3261			fully_acked = 0;
3262		} else {
3263			acked_pcount = tcp_skb_pcount(skb);
3264		}
3265
3266		if (sacked & TCPCB_RETRANS) {
3267			if (sacked & TCPCB_SACKED_RETRANS)
3268				tp->retrans_out -= acked_pcount;
3269			flag |= FLAG_RETRANS_DATA_ACKED;
3270			ca_seq_rtt = -1;
3271			seq_rtt = -1;
3272			if ((flag & FLAG_DATA_ACKED) || (acked_pcount > 1))
3273				flag |= FLAG_NONHEAD_RETRANS_ACKED;
3274		} else {
3275			ca_seq_rtt = now - scb->when;
3276			last_ackt = skb->tstamp;
3277			if (seq_rtt < 0) {
3278				seq_rtt = ca_seq_rtt;
3279			}
3280			if (!(sacked & TCPCB_SACKED_ACKED))
3281				reord = min(pkts_acked, reord);
3282		}
3283
3284		if (sacked & TCPCB_SACKED_ACKED)
3285			tp->sacked_out -= acked_pcount;
3286		if (sacked & TCPCB_LOST)
3287			tp->lost_out -= acked_pcount;
3288
3289		tp->packets_out -= acked_pcount;
3290		pkts_acked += acked_pcount;
3291
3292		/* Initial outgoing SYN's get put onto the write_queue
3293		 * just like anything else we transmit.  It is not
3294		 * true data, and if we misinform our callers that
3295		 * this ACK acks real data, we will erroneously exit
3296		 * connection startup slow start one packet too
3297		 * quickly.  This is severely frowned upon behavior.
3298		 */
3299		if (!(scb->flags & TCPHDR_SYN)) {
3300			flag |= FLAG_DATA_ACKED;
3301		} else {
3302			flag |= FLAG_SYN_ACKED;
3303			tp->retrans_stamp = 0;
3304		}
3305
3306		if (!fully_acked)
3307			break;
3308
3309		tcp_unlink_write_queue(skb, sk);
3310		sk_wmem_free_skb(sk, skb);
3311		tp->scoreboard_skb_hint = NULL;
3312		if (skb == tp->retransmit_skb_hint)
3313			tp->retransmit_skb_hint = NULL;
3314		if (skb == tp->lost_skb_hint)
3315			tp->lost_skb_hint = NULL;
3316	}
3317
3318	if (likely(between(tp->snd_up, prior_snd_una, tp->snd_una)))
3319		tp->snd_up = tp->snd_una;
3320
3321	if (skb && (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
3322		flag |= FLAG_SACK_RENEGING;
3323
3324	if (flag & FLAG_ACKED) {
3325		const struct tcp_congestion_ops *ca_ops
3326			= inet_csk(sk)->icsk_ca_ops;
3327
3328		if (unlikely(icsk->icsk_mtup.probe_size &&
3329			     !after(tp->mtu_probe.probe_seq_end, tp->snd_una))) {
3330			tcp_mtup_probe_success(sk);
3331		}
3332
3333		tcp_ack_update_rtt(sk, flag, seq_rtt);
3334		tcp_rearm_rto(sk);
3335
3336		if (tcp_is_reno(tp)) {
3337			tcp_remove_reno_sacks(sk, pkts_acked);
3338		} else {
3339			int delta;
3340
3341			/* Non-retransmitted hole got filled? That's reordering */
3342			if (reord < prior_fackets)
3343				tcp_update_reordering(sk, tp->fackets_out - reord, 0);
3344
3345			delta = tcp_is_fack(tp) ? pkts_acked :
3346						  prior_sacked - tp->sacked_out;
3347			tp->lost_cnt_hint -= min(tp->lost_cnt_hint, delta);
3348		}
3349
3350		tp->fackets_out -= min(pkts_acked, tp->fackets_out);
3351
3352		if (ca_ops->pkts_acked) {
3353			s32 rtt_us = -1;
3354
3355			/* Is the ACK triggering packet unambiguous? */
3356			if (!(flag & FLAG_RETRANS_DATA_ACKED)) {
3357				/* High resolution needed and available? */
3358				if (ca_ops->flags & TCP_CONG_RTT_STAMP &&
3359				    !ktime_equal(last_ackt,
3360						 net_invalid_timestamp()))
3361					rtt_us = ktime_us_delta(ktime_get_real(),
3362								last_ackt);
3363				else if (ca_seq_rtt >= 0)
3364					rtt_us = jiffies_to_usecs(ca_seq_rtt);
3365			}
3366
3367			ca_ops->pkts_acked(sk, pkts_acked, rtt_us);
3368		}
3369	}
3370
3371#if FASTRETRANS_DEBUG > 0
3372	WARN_ON((int)tp->sacked_out < 0);
3373	WARN_ON((int)tp->lost_out < 0);
3374	WARN_ON((int)tp->retrans_out < 0);
3375	if (!tp->packets_out && tcp_is_sack(tp)) {
3376		icsk = inet_csk(sk);
3377		if (tp->lost_out) {
3378			printk(KERN_DEBUG "Leak l=%u %d\n",
3379			       tp->lost_out, icsk->icsk_ca_state);
3380			tp->lost_out = 0;
3381		}
3382		if (tp->sacked_out) {
3383			printk(KERN_DEBUG "Leak s=%u %d\n",
3384			       tp->sacked_out, icsk->icsk_ca_state);
3385			tp->sacked_out = 0;
3386		}
3387		if (tp->retrans_out) {
3388			printk(KERN_DEBUG "Leak r=%u %d\n",
3389			       tp->retrans_out, icsk->icsk_ca_state);
3390			tp->retrans_out = 0;
3391		}
3392	}
3393#endif
3394	return flag;
3395}
3396
3397static void tcp_ack_probe(struct sock *sk)
3398{
3399	const struct tcp_sock *tp = tcp_sk(sk);
3400	struct inet_connection_sock *icsk = inet_csk(sk);
3401
3402	/* Was it a usable window open? */
3403
3404	if (!after(TCP_SKB_CB(tcp_send_head(sk))->end_seq, tcp_wnd_end(tp))) {
3405		icsk->icsk_backoff = 0;
3406		inet_csk_clear_xmit_timer(sk, ICSK_TIME_PROBE0);
3407		/* Socket must be waked up by subsequent tcp_data_snd_check().
3408		 * This function is not for random using!
3409		 */
3410	} else {
3411		inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
3412					  min(icsk->icsk_rto << icsk->icsk_backoff, TCP_RTO_MAX),
3413					  TCP_RTO_MAX);
3414	}
3415}
3416
3417static inline int tcp_ack_is_dubious(const struct sock *sk, const int flag)
3418{
3419	return !(flag & FLAG_NOT_DUP) || (flag & FLAG_CA_ALERT) ||
3420		inet_csk(sk)->icsk_ca_state != TCP_CA_Open;
3421}
3422
3423static inline int tcp_may_raise_cwnd(const struct sock *sk, const int flag)
3424{
3425	const struct tcp_sock *tp = tcp_sk(sk);
3426	return (!(flag & FLAG_ECE) || tp->snd_cwnd < tp->snd_ssthresh) &&
3427		!((1 << inet_csk(sk)->icsk_ca_state) & (TCPF_CA_Recovery | TCPF_CA_CWR));
3428}
3429
3430/* Check that window update is acceptable.
3431 * The function assumes that snd_una<=ack<=snd_next.
3432 */
3433static inline int tcp_may_update_window(const struct tcp_sock *tp,
3434					const u32 ack, const u32 ack_seq,
3435					const u32 nwin)
3436{
3437	return	after(ack, tp->snd_una) ||
3438		after(ack_seq, tp->snd_wl1) ||
3439		(ack_seq == tp->snd_wl1 && nwin > tp->snd_wnd);
3440}
3441
3442/* Update our send window.
3443 *
3444 * Window update algorithm, described in RFC793/RFC1122 (used in linux-2.2
3445 * and in FreeBSD. NetBSD's one is even worse.) is wrong.
3446 */
3447static int tcp_ack_update_window(struct sock *sk, struct sk_buff *skb, u32 ack,
3448				 u32 ack_seq)
3449{
3450	struct tcp_sock *tp = tcp_sk(sk);
3451	int flag = 0;
3452	u32 nwin = ntohs(tcp_hdr(skb)->window);
3453
3454	if (likely(!tcp_hdr(skb)->syn))
3455		nwin <<= tp->rx_opt.snd_wscale;
3456
3457	if (tcp_may_update_window(tp, ack, ack_seq, nwin)) {
3458		flag |= FLAG_WIN_UPDATE;
3459		tcp_update_wl(tp, ack_seq);
3460
3461		if (tp->snd_wnd != nwin) {
3462			tp->snd_wnd = nwin;
3463
3464			/* Note, it is the only place, where
3465			 * fast path is recovered for sending TCP.
3466			 */
3467			tp->pred_flags = 0;
3468			tcp_fast_path_check(sk);
3469
3470			if (nwin > tp->max_window) {
3471				tp->max_window = nwin;
3472				tcp_sync_mss(sk, inet_csk(sk)->icsk_pmtu_cookie);
3473			}
3474		}
3475	}
3476
3477	tp->snd_una = ack;
3478
3479	return flag;
3480}
3481
3482/* A very conservative spurious RTO response algorithm: reduce cwnd and
3483 * continue in congestion avoidance.
3484 */
3485static void tcp_conservative_spur_to_response(struct tcp_sock *tp)
3486{
3487	tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
3488	tp->snd_cwnd_cnt = 0;
3489	tp->bytes_acked = 0;
3490	TCP_ECN_queue_cwr(tp);
3491	tcp_moderate_cwnd(tp);
3492}
3493
3494/* A conservative spurious RTO response algorithm: reduce cwnd using
3495 * rate halving and continue in congestion avoidance.
3496 */
3497static void tcp_ratehalving_spur_to_response(struct sock *sk)
3498{
3499	tcp_enter_cwr(sk, 0);
3500}
3501
3502static void tcp_undo_spur_to_response(struct sock *sk, int flag)
3503{
3504	if (flag & FLAG_ECE)
3505		tcp_ratehalving_spur_to_response(sk);
3506	else
3507		tcp_undo_cwr(sk, true);
3508}
3509
3510/* F-RTO spurious RTO detection algorithm (RFC4138)
3511 *
3512 * F-RTO affects during two new ACKs following RTO (well, almost, see inline
3513 * comments). State (ACK number) is kept in frto_counter. When ACK advances
3514 * window (but not to or beyond highest sequence sent before RTO):
3515 *   On First ACK,  send two new segments out.
3516 *   On Second ACK, RTO was likely spurious. Do spurious response (response
3517 *                  algorithm is not part of the F-RTO detection algorithm
3518 *                  given in RFC4138 but can be selected separately).
3519 * Otherwise (basically on duplicate ACK), RTO was (likely) caused by a loss
3520 * and TCP falls back to conventional RTO recovery. F-RTO allows overriding
3521 * of Nagle, this is done using frto_counter states 2 and 3, when a new data
3522 * segment of any size sent during F-RTO, state 2 is upgraded to 3.
3523 *
3524 * Rationale: if the RTO was spurious, new ACKs should arrive from the
3525 * original window even after we transmit two new data segments.
3526 *
3527 * SACK version:
3528 *   on first step, wait until first cumulative ACK arrives, then move to
3529 *   the second step. In second step, the next ACK decides.
3530 *
3531 * F-RTO is implemented (mainly) in four functions:
3532 *   - tcp_use_frto() is used to determine if TCP is can use F-RTO
3533 *   - tcp_enter_frto() prepares TCP state on RTO if F-RTO is used, it is
3534 *     called when tcp_use_frto() showed green light
3535 *   - tcp_process_frto() handles incoming ACKs during F-RTO algorithm
3536 *   - tcp_enter_frto_loss() is called if there is not enough evidence
3537 *     to prove that the RTO is indeed spurious. It transfers the control
3538 *     from F-RTO to the conventional RTO recovery
3539 */
3540static int tcp_process_frto(struct sock *sk, int flag)
3541{
3542	struct tcp_sock *tp = tcp_sk(sk);
3543
3544	tcp_verify_left_out(tp);
3545
3546	/* Duplicate the behavior from Loss state (fastretrans_alert) */
3547	if (flag & FLAG_DATA_ACKED)
3548		inet_csk(sk)->icsk_retransmits = 0;
3549
3550	if ((flag & FLAG_NONHEAD_RETRANS_ACKED) ||
3551	    ((tp->frto_counter >= 2) && (flag & FLAG_RETRANS_DATA_ACKED)))
3552		tp->undo_marker = 0;
3553
3554	if (!before(tp->snd_una, tp->frto_highmark)) {
3555		tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 2 : 3), flag);
3556		return 1;
3557	}
3558
3559	if (!tcp_is_sackfrto(tp)) {
3560		/* RFC4138 shortcoming in step 2; should also have case c):
3561		 * ACK isn't duplicate nor advances window, e.g., opposite dir
3562		 * data, winupdate
3563		 */
3564		if (!(flag & FLAG_ANY_PROGRESS) && (flag & FLAG_NOT_DUP))
3565			return 1;
3566
3567		if (!(flag & FLAG_DATA_ACKED)) {
3568			tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 0 : 3),
3569					    flag);
3570			return 1;
3571		}
3572	} else {
3573		if (!(flag & FLAG_DATA_ACKED) && (tp->frto_counter == 1)) {
3574			/* Prevent sending of new data. */
3575			tp->snd_cwnd = min(tp->snd_cwnd,
3576					   tcp_packets_in_flight(tp));
3577			return 1;
3578		}
3579
3580		if ((tp->frto_counter >= 2) &&
3581		    (!(flag & FLAG_FORWARD_PROGRESS) ||
3582		     ((flag & FLAG_DATA_SACKED) &&
3583		      !(flag & FLAG_ONLY_ORIG_SACKED)))) {
3584			/* RFC4138 shortcoming (see comment above) */
3585			if (!(flag & FLAG_FORWARD_PROGRESS) &&
3586			    (flag & FLAG_NOT_DUP))
3587				return 1;
3588
3589			tcp_enter_frto_loss(sk, 3, flag);
3590			return 1;
3591		}
3592	}
3593
3594	if (tp->frto_counter == 1) {
3595		/* tcp_may_send_now needs to see updated state */
3596		tp->snd_cwnd = tcp_packets_in_flight(tp) + 2;
3597		tp->frto_counter = 2;
3598
3599		if (!tcp_may_send_now(sk))
3600			tcp_enter_frto_loss(sk, 2, flag);
3601
3602		return 1;
3603	} else {
3604		switch (sysctl_tcp_frto_response) {
3605		case 2:
3606			tcp_undo_spur_to_response(sk, flag);
3607			break;
3608		case 1:
3609			tcp_conservative_spur_to_response(tp);
3610			break;
3611		default:
3612			tcp_ratehalving_spur_to_response(sk);
3613			break;
3614		}
3615		tp->frto_counter = 0;
3616		tp->undo_marker = 0;
3617		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSPURIOUSRTOS);
3618	}
3619	return 0;
3620}
3621
3622/* This routine deals with incoming acks, but not outgoing ones. */
3623static int tcp_ack(struct sock *sk, struct sk_buff *skb, int flag)
3624{
3625	struct inet_connection_sock *icsk = inet_csk(sk);
3626	struct tcp_sock *tp = tcp_sk(sk);
3627	u32 prior_snd_una = tp->snd_una;
3628	u32 ack_seq = TCP_SKB_CB(skb)->seq;
3629	u32 ack = TCP_SKB_CB(skb)->ack_seq;
 
3630	u32 prior_in_flight;
3631	u32 prior_fackets;
3632	int prior_packets;
3633	int frto_cwnd = 0;
 
 
3634
3635	/* If the ack is older than previous acks
3636	 * then we can probably ignore it.
3637	 */
3638	if (before(ack, prior_snd_una))
3639		goto old_ack;
3640
3641	/* If the ack includes data we haven't sent yet, discard
3642	 * this segment (RFC793 Section 3.9).
3643	 */
3644	if (after(ack, tp->snd_nxt))
3645		goto invalid_ack;
3646
 
 
 
3647	if (after(ack, prior_snd_una))
3648		flag |= FLAG_SND_UNA_ADVANCED;
3649
3650	if (sysctl_tcp_abc) {
3651		if (icsk->icsk_ca_state < TCP_CA_CWR)
3652			tp->bytes_acked += ack - prior_snd_una;
3653		else if (icsk->icsk_ca_state == TCP_CA_Loss)
3654			/* we assume just one segment left network */
3655			tp->bytes_acked += min(ack - prior_snd_una,
3656					       tp->mss_cache);
3657	}
3658
3659	prior_fackets = tp->fackets_out;
3660	prior_in_flight = tcp_packets_in_flight(tp);
3661
3662	if (!(flag & FLAG_SLOWPATH) && after(ack, prior_snd_una)) {
3663		/* Window is constant, pure forward advance.
3664		 * No more checks are required.
3665		 * Note, we use the fact that SND.UNA>=SND.WL2.
3666		 */
3667		tcp_update_wl(tp, ack_seq);
3668		tp->snd_una = ack;
3669		flag |= FLAG_WIN_UPDATE;
3670
3671		tcp_ca_event(sk, CA_EVENT_FAST_ACK);
3672
3673		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPACKS);
3674	} else {
3675		if (ack_seq != TCP_SKB_CB(skb)->end_seq)
3676			flag |= FLAG_DATA;
3677		else
3678			NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPPUREACKS);
3679
3680		flag |= tcp_ack_update_window(sk, skb, ack, ack_seq);
3681
3682		if (TCP_SKB_CB(skb)->sacked)
3683			flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una);
3684
3685		if (TCP_ECN_rcv_ecn_echo(tp, tcp_hdr(skb)))
3686			flag |= FLAG_ECE;
3687
3688		tcp_ca_event(sk, CA_EVENT_SLOW_ACK);
3689	}
3690
3691	/* We passed data and got it acked, remove any soft error
3692	 * log. Something worked...
3693	 */
3694	sk->sk_err_soft = 0;
3695	icsk->icsk_probes_out = 0;
3696	tp->rcv_tstamp = tcp_time_stamp;
3697	prior_packets = tp->packets_out;
3698	if (!prior_packets)
3699		goto no_queue;
3700
3701	/* See if we can take anything off of the retransmit queue. */
3702	flag |= tcp_clean_rtx_queue(sk, prior_fackets, prior_snd_una);
3703
 
 
3704	if (tp->frto_counter)
3705		frto_cwnd = tcp_process_frto(sk, flag);
3706	/* Guarantee sacktag reordering detection against wrap-arounds */
3707	if (before(tp->frto_highmark, tp->snd_una))
3708		tp->frto_highmark = 0;
3709
3710	if (tcp_ack_is_dubious(sk, flag)) {
3711		/* Advance CWND, if state allows this. */
3712		if ((flag & FLAG_DATA_ACKED) && !frto_cwnd &&
3713		    tcp_may_raise_cwnd(sk, flag))
3714			tcp_cong_avoid(sk, ack, prior_in_flight);
3715		tcp_fastretrans_alert(sk, prior_packets - tp->packets_out,
3716				      flag);
 
3717	} else {
3718		if ((flag & FLAG_DATA_ACKED) && !frto_cwnd)
3719			tcp_cong_avoid(sk, ack, prior_in_flight);
3720	}
3721
3722	if ((flag & FLAG_FORWARD_PROGRESS) || !(flag & FLAG_NOT_DUP))
3723		dst_confirm(__sk_dst_get(sk));
3724
3725	return 1;
3726
3727no_queue:
 
 
 
 
3728	/* If this ack opens up a zero window, clear backoff.  It was
3729	 * being used to time the probes, and is probably far higher than
3730	 * it needs to be for normal retransmission.
3731	 */
3732	if (tcp_send_head(sk))
3733		tcp_ack_probe(sk);
3734	return 1;
3735
3736invalid_ack:
3737	SOCK_DEBUG(sk, "Ack %u after %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
3738	return -1;
3739
3740old_ack:
 
 
 
3741	if (TCP_SKB_CB(skb)->sacked) {
3742		tcp_sacktag_write_queue(sk, skb, prior_snd_una);
3743		if (icsk->icsk_ca_state == TCP_CA_Open)
3744			tcp_try_keep_open(sk);
3745	}
3746
3747	SOCK_DEBUG(sk, "Ack %u before %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
3748	return 0;
3749}
3750
3751/* Look for tcp options. Normally only called on SYN and SYNACK packets.
3752 * But, this can also be called on packets in the established flow when
3753 * the fast version below fails.
3754 */
3755void tcp_parse_options(struct sk_buff *skb, struct tcp_options_received *opt_rx,
3756		       u8 **hvpp, int estab)
3757{
3758	unsigned char *ptr;
3759	struct tcphdr *th = tcp_hdr(skb);
3760	int length = (th->doff * 4) - sizeof(struct tcphdr);
3761
3762	ptr = (unsigned char *)(th + 1);
3763	opt_rx->saw_tstamp = 0;
3764
3765	while (length > 0) {
3766		int opcode = *ptr++;
3767		int opsize;
3768
3769		switch (opcode) {
3770		case TCPOPT_EOL:
3771			return;
3772		case TCPOPT_NOP:	/* Ref: RFC 793 section 3.1 */
3773			length--;
3774			continue;
3775		default:
3776			opsize = *ptr++;
3777			if (opsize < 2) /* "silly options" */
3778				return;
3779			if (opsize > length)
3780				return;	/* don't parse partial options */
3781			switch (opcode) {
3782			case TCPOPT_MSS:
3783				if (opsize == TCPOLEN_MSS && th->syn && !estab) {
3784					u16 in_mss = get_unaligned_be16(ptr);
3785					if (in_mss) {
3786						if (opt_rx->user_mss &&
3787						    opt_rx->user_mss < in_mss)
3788							in_mss = opt_rx->user_mss;
3789						opt_rx->mss_clamp = in_mss;
3790					}
3791				}
3792				break;
3793			case TCPOPT_WINDOW:
3794				if (opsize == TCPOLEN_WINDOW && th->syn &&
3795				    !estab && sysctl_tcp_window_scaling) {
3796					__u8 snd_wscale = *(__u8 *)ptr;
3797					opt_rx->wscale_ok = 1;
3798					if (snd_wscale > 14) {
3799						if (net_ratelimit())
3800							printk(KERN_INFO "tcp_parse_options: Illegal window "
3801							       "scaling value %d >14 received.\n",
3802							       snd_wscale);
3803						snd_wscale = 14;
3804					}
3805					opt_rx->snd_wscale = snd_wscale;
3806				}
3807				break;
3808			case TCPOPT_TIMESTAMP:
3809				if ((opsize == TCPOLEN_TIMESTAMP) &&
3810				    ((estab && opt_rx->tstamp_ok) ||
3811				     (!estab && sysctl_tcp_timestamps))) {
3812					opt_rx->saw_tstamp = 1;
3813					opt_rx->rcv_tsval = get_unaligned_be32(ptr);
3814					opt_rx->rcv_tsecr = get_unaligned_be32(ptr + 4);
3815				}
3816				break;
3817			case TCPOPT_SACK_PERM:
3818				if (opsize == TCPOLEN_SACK_PERM && th->syn &&
3819				    !estab && sysctl_tcp_sack) {
3820					opt_rx->sack_ok = 1;
3821					tcp_sack_reset(opt_rx);
3822				}
3823				break;
3824
3825			case TCPOPT_SACK:
3826				if ((opsize >= (TCPOLEN_SACK_BASE + TCPOLEN_SACK_PERBLOCK)) &&
3827				   !((opsize - TCPOLEN_SACK_BASE) % TCPOLEN_SACK_PERBLOCK) &&
3828				   opt_rx->sack_ok) {
3829					TCP_SKB_CB(skb)->sacked = (ptr - 2) - (unsigned char *)th;
3830				}
3831				break;
3832#ifdef CONFIG_TCP_MD5SIG
3833			case TCPOPT_MD5SIG:
3834				/*
3835				 * The MD5 Hash has already been
3836				 * checked (see tcp_v{4,6}_do_rcv()).
3837				 */
3838				break;
3839#endif
3840			case TCPOPT_COOKIE:
3841				/* This option is variable length.
3842				 */
3843				switch (opsize) {
3844				case TCPOLEN_COOKIE_BASE:
3845					/* not yet implemented */
3846					break;
3847				case TCPOLEN_COOKIE_PAIR:
3848					/* not yet implemented */
3849					break;
3850				case TCPOLEN_COOKIE_MIN+0:
3851				case TCPOLEN_COOKIE_MIN+2:
3852				case TCPOLEN_COOKIE_MIN+4:
3853				case TCPOLEN_COOKIE_MIN+6:
3854				case TCPOLEN_COOKIE_MAX:
3855					/* 16-bit multiple */
3856					opt_rx->cookie_plus = opsize;
3857					*hvpp = ptr;
3858					break;
3859				default:
3860					/* ignore option */
3861					break;
3862				}
3863				break;
3864			}
3865
3866			ptr += opsize-2;
3867			length -= opsize;
3868		}
3869	}
3870}
3871EXPORT_SYMBOL(tcp_parse_options);
3872
3873static int tcp_parse_aligned_timestamp(struct tcp_sock *tp, struct tcphdr *th)
3874{
3875	__be32 *ptr = (__be32 *)(th + 1);
3876
3877	if (*ptr == htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16)
3878			  | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP)) {
3879		tp->rx_opt.saw_tstamp = 1;
3880		++ptr;
3881		tp->rx_opt.rcv_tsval = ntohl(*ptr);
3882		++ptr;
3883		tp->rx_opt.rcv_tsecr = ntohl(*ptr);
3884		return 1;
3885	}
3886	return 0;
3887}
3888
3889/* Fast parse options. This hopes to only see timestamps.
3890 * If it is wrong it falls back on tcp_parse_options().
3891 */
3892static int tcp_fast_parse_options(struct sk_buff *skb, struct tcphdr *th,
3893				  struct tcp_sock *tp, u8 **hvpp)
 
3894{
3895	/* In the spirit of fast parsing, compare doff directly to constant
3896	 * values.  Because equality is used, short doff can be ignored here.
3897	 */
3898	if (th->doff == (sizeof(*th) / 4)) {
3899		tp->rx_opt.saw_tstamp = 0;
3900		return 0;
3901	} else if (tp->rx_opt.tstamp_ok &&
3902		   th->doff == ((sizeof(*th) + TCPOLEN_TSTAMP_ALIGNED) / 4)) {
3903		if (tcp_parse_aligned_timestamp(tp, th))
3904			return 1;
3905	}
3906	tcp_parse_options(skb, &tp->rx_opt, hvpp, 1);
3907	return 1;
3908}
3909
3910#ifdef CONFIG_TCP_MD5SIG
3911/*
3912 * Parse MD5 Signature option
3913 */
3914u8 *tcp_parse_md5sig_option(struct tcphdr *th)
3915{
3916	int length = (th->doff << 2) - sizeof (*th);
3917	u8 *ptr = (u8*)(th + 1);
3918
3919	/* If the TCP option is too short, we can short cut */
3920	if (length < TCPOLEN_MD5SIG)
3921		return NULL;
3922
3923	while (length > 0) {
3924		int opcode = *ptr++;
3925		int opsize;
3926
3927		switch(opcode) {
3928		case TCPOPT_EOL:
3929			return NULL;
3930		case TCPOPT_NOP:
3931			length--;
3932			continue;
3933		default:
3934			opsize = *ptr++;
3935			if (opsize < 2 || opsize > length)
3936				return NULL;
3937			if (opcode == TCPOPT_MD5SIG)
3938				return opsize == TCPOLEN_MD5SIG ? ptr : NULL;
3939		}
3940		ptr += opsize - 2;
3941		length -= opsize;
3942	}
3943	return NULL;
3944}
3945EXPORT_SYMBOL(tcp_parse_md5sig_option);
3946#endif
3947
3948static inline void tcp_store_ts_recent(struct tcp_sock *tp)
3949{
3950	tp->rx_opt.ts_recent = tp->rx_opt.rcv_tsval;
3951	tp->rx_opt.ts_recent_stamp = get_seconds();
3952}
3953
3954static inline void tcp_replace_ts_recent(struct tcp_sock *tp, u32 seq)
3955{
3956	if (tp->rx_opt.saw_tstamp && !after(seq, tp->rcv_wup)) {
3957		/* PAWS bug workaround wrt. ACK frames, the PAWS discard
3958		 * extra check below makes sure this can only happen
3959		 * for pure ACK frames.  -DaveM
3960		 *
3961		 * Not only, also it occurs for expired timestamps.
3962		 */
3963
3964		if (tcp_paws_check(&tp->rx_opt, 0))
3965			tcp_store_ts_recent(tp);
3966	}
3967}
3968
3969/* Sorry, PAWS as specified is broken wrt. pure-ACKs -DaveM
3970 *
3971 * It is not fatal. If this ACK does _not_ change critical state (seqs, window)
3972 * it can pass through stack. So, the following predicate verifies that
3973 * this segment is not used for anything but congestion avoidance or
3974 * fast retransmit. Moreover, we even are able to eliminate most of such
3975 * second order effects, if we apply some small "replay" window (~RTO)
3976 * to timestamp space.
3977 *
3978 * All these measures still do not guarantee that we reject wrapped ACKs
3979 * on networks with high bandwidth, when sequence space is recycled fastly,
3980 * but it guarantees that such events will be very rare and do not affect
3981 * connection seriously. This doesn't look nice, but alas, PAWS is really
3982 * buggy extension.
3983 *
3984 * [ Later note. Even worse! It is buggy for segments _with_ data. RFC
3985 * states that events when retransmit arrives after original data are rare.
3986 * It is a blatant lie. VJ forgot about fast retransmit! 8)8) It is
3987 * the biggest problem on large power networks even with minor reordering.
3988 * OK, let's give it small replay window. If peer clock is even 1hz, it is safe
3989 * up to bandwidth of 18Gigabit/sec. 8) ]
3990 */
3991
3992static int tcp_disordered_ack(const struct sock *sk, const struct sk_buff *skb)
3993{
3994	struct tcp_sock *tp = tcp_sk(sk);
3995	struct tcphdr *th = tcp_hdr(skb);
3996	u32 seq = TCP_SKB_CB(skb)->seq;
3997	u32 ack = TCP_SKB_CB(skb)->ack_seq;
3998
3999	return (/* 1. Pure ACK with correct sequence number. */
4000		(th->ack && seq == TCP_SKB_CB(skb)->end_seq && seq == tp->rcv_nxt) &&
4001
4002		/* 2. ... and duplicate ACK. */
4003		ack == tp->snd_una &&
4004
4005		/* 3. ... and does not update window. */
4006		!tcp_may_update_window(tp, ack, seq, ntohs(th->window) << tp->rx_opt.snd_wscale) &&
4007
4008		/* 4. ... and sits in replay window. */
4009		(s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) <= (inet_csk(sk)->icsk_rto * 1024) / HZ);
4010}
4011
4012static inline int tcp_paws_discard(const struct sock *sk,
4013				   const struct sk_buff *skb)
4014{
4015	const struct tcp_sock *tp = tcp_sk(sk);
4016
4017	return !tcp_paws_check(&tp->rx_opt, TCP_PAWS_WINDOW) &&
4018	       !tcp_disordered_ack(sk, skb);
4019}
4020
4021/* Check segment sequence number for validity.
4022 *
4023 * Segment controls are considered valid, if the segment
4024 * fits to the window after truncation to the window. Acceptability
4025 * of data (and SYN, FIN, of course) is checked separately.
4026 * See tcp_data_queue(), for example.
4027 *
4028 * Also, controls (RST is main one) are accepted using RCV.WUP instead
4029 * of RCV.NXT. Peer still did not advance his SND.UNA when we
4030 * delayed ACK, so that hisSND.UNA<=ourRCV.WUP.
4031 * (borrowed from freebsd)
4032 */
4033
4034static inline int tcp_sequence(struct tcp_sock *tp, u32 seq, u32 end_seq)
4035{
4036	return	!before(end_seq, tp->rcv_wup) &&
4037		!after(seq, tp->rcv_nxt + tcp_receive_window(tp));
4038}
4039
4040/* When we get a reset we do this. */
4041static void tcp_reset(struct sock *sk)
4042{
4043	/* We want the right error as BSD sees it (and indeed as we do). */
4044	switch (sk->sk_state) {
4045	case TCP_SYN_SENT:
4046		sk->sk_err = ECONNREFUSED;
4047		break;
4048	case TCP_CLOSE_WAIT:
4049		sk->sk_err = EPIPE;
4050		break;
4051	case TCP_CLOSE:
4052		return;
4053	default:
4054		sk->sk_err = ECONNRESET;
4055	}
4056	/* This barrier is coupled with smp_rmb() in tcp_poll() */
4057	smp_wmb();
4058
4059	if (!sock_flag(sk, SOCK_DEAD))
4060		sk->sk_error_report(sk);
4061
4062	tcp_done(sk);
4063}
4064
4065/*
4066 * 	Process the FIN bit. This now behaves as it is supposed to work
4067 *	and the FIN takes effect when it is validly part of sequence
4068 *	space. Not before when we get holes.
4069 *
4070 *	If we are ESTABLISHED, a received fin moves us to CLOSE-WAIT
4071 *	(and thence onto LAST-ACK and finally, CLOSE, we never enter
4072 *	TIME-WAIT)
4073 *
4074 *	If we are in FINWAIT-1, a received FIN indicates simultaneous
4075 *	close and we go into CLOSING (and later onto TIME-WAIT)
4076 *
4077 *	If we are in FINWAIT-2, a received FIN moves us to TIME-WAIT.
4078 */
4079static void tcp_fin(struct sk_buff *skb, struct sock *sk, struct tcphdr *th)
4080{
4081	struct tcp_sock *tp = tcp_sk(sk);
4082
4083	inet_csk_schedule_ack(sk);
4084
4085	sk->sk_shutdown |= RCV_SHUTDOWN;
4086	sock_set_flag(sk, SOCK_DONE);
4087
4088	switch (sk->sk_state) {
4089	case TCP_SYN_RECV:
4090	case TCP_ESTABLISHED:
4091		/* Move to CLOSE_WAIT */
4092		tcp_set_state(sk, TCP_CLOSE_WAIT);
4093		inet_csk(sk)->icsk_ack.pingpong = 1;
4094		break;
4095
4096	case TCP_CLOSE_WAIT:
4097	case TCP_CLOSING:
4098		/* Received a retransmission of the FIN, do
4099		 * nothing.
4100		 */
4101		break;
4102	case TCP_LAST_ACK:
4103		/* RFC793: Remain in the LAST-ACK state. */
4104		break;
4105
4106	case TCP_FIN_WAIT1:
4107		/* This case occurs when a simultaneous close
4108		 * happens, we must ack the received FIN and
4109		 * enter the CLOSING state.
4110		 */
4111		tcp_send_ack(sk);
4112		tcp_set_state(sk, TCP_CLOSING);
4113		break;
4114	case TCP_FIN_WAIT2:
4115		/* Received a FIN -- send ACK and enter TIME_WAIT. */
4116		tcp_send_ack(sk);
4117		tcp_time_wait(sk, TCP_TIME_WAIT, 0);
4118		break;
4119	default:
4120		/* Only TCP_LISTEN and TCP_CLOSE are left, in these
4121		 * cases we should never reach this piece of code.
4122		 */
4123		printk(KERN_ERR "%s: Impossible, sk->sk_state=%d\n",
4124		       __func__, sk->sk_state);
4125		break;
4126	}
4127
4128	/* It _is_ possible, that we have something out-of-order _after_ FIN.
4129	 * Probably, we should reset in this case. For now drop them.
4130	 */
4131	__skb_queue_purge(&tp->out_of_order_queue);
4132	if (tcp_is_sack(tp))
4133		tcp_sack_reset(&tp->rx_opt);
4134	sk_mem_reclaim(sk);
4135
4136	if (!sock_flag(sk, SOCK_DEAD)) {
4137		sk->sk_state_change(sk);
4138
4139		/* Do not send POLL_HUP for half duplex close. */
4140		if (sk->sk_shutdown == SHUTDOWN_MASK ||
4141		    sk->sk_state == TCP_CLOSE)
4142			sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_HUP);
4143		else
4144			sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_IN);
4145	}
4146}
4147
4148static inline int tcp_sack_extend(struct tcp_sack_block *sp, u32 seq,
4149				  u32 end_seq)
4150{
4151	if (!after(seq, sp->end_seq) && !after(sp->start_seq, end_seq)) {
4152		if (before(seq, sp->start_seq))
4153			sp->start_seq = seq;
4154		if (after(end_seq, sp->end_seq))
4155			sp->end_seq = end_seq;
4156		return 1;
4157	}
4158	return 0;
4159}
4160
4161static void tcp_dsack_set(struct sock *sk, u32 seq, u32 end_seq)
4162{
4163	struct tcp_sock *tp = tcp_sk(sk);
4164
4165	if (tcp_is_sack(tp) && sysctl_tcp_dsack) {
4166		int mib_idx;
4167
4168		if (before(seq, tp->rcv_nxt))
4169			mib_idx = LINUX_MIB_TCPDSACKOLDSENT;
4170		else
4171			mib_idx = LINUX_MIB_TCPDSACKOFOSENT;
4172
4173		NET_INC_STATS_BH(sock_net(sk), mib_idx);
4174
4175		tp->rx_opt.dsack = 1;
4176		tp->duplicate_sack[0].start_seq = seq;
4177		tp->duplicate_sack[0].end_seq = end_seq;
4178	}
4179}
4180
4181static void tcp_dsack_extend(struct sock *sk, u32 seq, u32 end_seq)
4182{
4183	struct tcp_sock *tp = tcp_sk(sk);
4184
4185	if (!tp->rx_opt.dsack)
4186		tcp_dsack_set(sk, seq, end_seq);
4187	else
4188		tcp_sack_extend(tp->duplicate_sack, seq, end_seq);
4189}
4190
4191static void tcp_send_dupack(struct sock *sk, struct sk_buff *skb)
4192{
4193	struct tcp_sock *tp = tcp_sk(sk);
4194
4195	if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
4196	    before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
4197		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
4198		tcp_enter_quickack_mode(sk);
4199
4200		if (tcp_is_sack(tp) && sysctl_tcp_dsack) {
4201			u32 end_seq = TCP_SKB_CB(skb)->end_seq;
4202
4203			if (after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))
4204				end_seq = tp->rcv_nxt;
4205			tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, end_seq);
4206		}
4207	}
4208
4209	tcp_send_ack(sk);
4210}
4211
4212/* These routines update the SACK block as out-of-order packets arrive or
4213 * in-order packets close up the sequence space.
4214 */
4215static void tcp_sack_maybe_coalesce(struct tcp_sock *tp)
4216{
4217	int this_sack;
4218	struct tcp_sack_block *sp = &tp->selective_acks[0];
4219	struct tcp_sack_block *swalk = sp + 1;
4220
4221	/* See if the recent change to the first SACK eats into
4222	 * or hits the sequence space of other SACK blocks, if so coalesce.
4223	 */
4224	for (this_sack = 1; this_sack < tp->rx_opt.num_sacks;) {
4225		if (tcp_sack_extend(sp, swalk->start_seq, swalk->end_seq)) {
4226			int i;
4227
4228			/* Zap SWALK, by moving every further SACK up by one slot.
4229			 * Decrease num_sacks.
4230			 */
4231			tp->rx_opt.num_sacks--;
4232			for (i = this_sack; i < tp->rx_opt.num_sacks; i++)
4233				sp[i] = sp[i + 1];
4234			continue;
4235		}
4236		this_sack++, swalk++;
4237	}
4238}
4239
4240static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq)
4241{
4242	struct tcp_sock *tp = tcp_sk(sk);
4243	struct tcp_sack_block *sp = &tp->selective_acks[0];
4244	int cur_sacks = tp->rx_opt.num_sacks;
4245	int this_sack;
4246
4247	if (!cur_sacks)
4248		goto new_sack;
4249
4250	for (this_sack = 0; this_sack < cur_sacks; this_sack++, sp++) {
4251		if (tcp_sack_extend(sp, seq, end_seq)) {
4252			/* Rotate this_sack to the first one. */
4253			for (; this_sack > 0; this_sack--, sp--)
4254				swap(*sp, *(sp - 1));
4255			if (cur_sacks > 1)
4256				tcp_sack_maybe_coalesce(tp);
4257			return;
4258		}
4259	}
4260
4261	/* Could not find an adjacent existing SACK, build a new one,
4262	 * put it at the front, and shift everyone else down.  We
4263	 * always know there is at least one SACK present already here.
4264	 *
4265	 * If the sack array is full, forget about the last one.
4266	 */
4267	if (this_sack >= TCP_NUM_SACKS) {
4268		this_sack--;
4269		tp->rx_opt.num_sacks--;
4270		sp--;
4271	}
4272	for (; this_sack > 0; this_sack--, sp--)
4273		*sp = *(sp - 1);
4274
4275new_sack:
4276	/* Build the new head SACK, and we're done. */
4277	sp->start_seq = seq;
4278	sp->end_seq = end_seq;
4279	tp->rx_opt.num_sacks++;
4280}
4281
4282/* RCV.NXT advances, some SACKs should be eaten. */
4283
4284static void tcp_sack_remove(struct tcp_sock *tp)
4285{
4286	struct tcp_sack_block *sp = &tp->selective_acks[0];
4287	int num_sacks = tp->rx_opt.num_sacks;
4288	int this_sack;
4289
4290	/* Empty ofo queue, hence, all the SACKs are eaten. Clear. */
4291	if (skb_queue_empty(&tp->out_of_order_queue)) {
4292		tp->rx_opt.num_sacks = 0;
4293		return;
4294	}
4295
4296	for (this_sack = 0; this_sack < num_sacks;) {
4297		/* Check if the start of the sack is covered by RCV.NXT. */
4298		if (!before(tp->rcv_nxt, sp->start_seq)) {
4299			int i;
4300
4301			/* RCV.NXT must cover all the block! */
4302			WARN_ON(before(tp->rcv_nxt, sp->end_seq));
4303
4304			/* Zap this SACK, by moving forward any other SACKS. */
4305			for (i=this_sack+1; i < num_sacks; i++)
4306				tp->selective_acks[i-1] = tp->selective_acks[i];
4307			num_sacks--;
4308			continue;
4309		}
4310		this_sack++;
4311		sp++;
4312	}
4313	tp->rx_opt.num_sacks = num_sacks;
4314}
4315
4316/* This one checks to see if we can put data from the
4317 * out_of_order queue into the receive_queue.
4318 */
4319static void tcp_ofo_queue(struct sock *sk)
4320{
4321	struct tcp_sock *tp = tcp_sk(sk);
4322	__u32 dsack_high = tp->rcv_nxt;
4323	struct sk_buff *skb;
4324
4325	while ((skb = skb_peek(&tp->out_of_order_queue)) != NULL) {
4326		if (after(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
4327			break;
4328
4329		if (before(TCP_SKB_CB(skb)->seq, dsack_high)) {
4330			__u32 dsack = dsack_high;
4331			if (before(TCP_SKB_CB(skb)->end_seq, dsack_high))
4332				dsack_high = TCP_SKB_CB(skb)->end_seq;
4333			tcp_dsack_extend(sk, TCP_SKB_CB(skb)->seq, dsack);
4334		}
4335
4336		if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
4337			SOCK_DEBUG(sk, "ofo packet was already received\n");
4338			__skb_unlink(skb, &tp->out_of_order_queue);
4339			__kfree_skb(skb);
4340			continue;
4341		}
4342		SOCK_DEBUG(sk, "ofo requeuing : rcv_next %X seq %X - %X\n",
4343			   tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
4344			   TCP_SKB_CB(skb)->end_seq);
4345
4346		__skb_unlink(skb, &tp->out_of_order_queue);
4347		__skb_queue_tail(&sk->sk_receive_queue, skb);
4348		tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
4349		if (tcp_hdr(skb)->fin)
4350			tcp_fin(skb, sk, tcp_hdr(skb));
4351	}
4352}
4353
4354static int tcp_prune_ofo_queue(struct sock *sk);
4355static int tcp_prune_queue(struct sock *sk);
4356
4357static inline int tcp_try_rmem_schedule(struct sock *sk, unsigned int size)
4358{
4359	if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
4360	    !sk_rmem_schedule(sk, size)) {
4361
4362		if (tcp_prune_queue(sk) < 0)
4363			return -1;
4364
4365		if (!sk_rmem_schedule(sk, size)) {
4366			if (!tcp_prune_ofo_queue(sk))
4367				return -1;
4368
4369			if (!sk_rmem_schedule(sk, size))
4370				return -1;
4371		}
4372	}
4373	return 0;
4374}
4375
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
4376static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
4377{
4378	struct tcphdr *th = tcp_hdr(skb);
4379	struct tcp_sock *tp = tcp_sk(sk);
4380	int eaten = -1;
 
4381
4382	if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq)
4383		goto drop;
4384
4385	skb_dst_drop(skb);
4386	__skb_pull(skb, th->doff * 4);
4387
4388	TCP_ECN_accept_cwr(tp, skb);
4389
4390	tp->rx_opt.dsack = 0;
4391
4392	/*  Queue data for delivery to the user.
4393	 *  Packets in sequence go to the receive queue.
4394	 *  Out of sequence packets to the out_of_order_queue.
4395	 */
4396	if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
4397		if (tcp_receive_window(tp) == 0)
4398			goto out_of_window;
4399
4400		/* Ok. In sequence. In window. */
4401		if (tp->ucopy.task == current &&
4402		    tp->copied_seq == tp->rcv_nxt && tp->ucopy.len &&
4403		    sock_owned_by_user(sk) && !tp->urg_data) {
4404			int chunk = min_t(unsigned int, skb->len,
4405					  tp->ucopy.len);
4406
4407			__set_current_state(TASK_RUNNING);
4408
4409			local_bh_enable();
4410			if (!skb_copy_datagram_iovec(skb, 0, tp->ucopy.iov, chunk)) {
4411				tp->ucopy.len -= chunk;
4412				tp->copied_seq += chunk;
4413				eaten = (chunk == skb->len);
4414				tcp_rcv_space_adjust(sk);
4415			}
4416			local_bh_disable();
4417		}
4418
4419		if (eaten <= 0) {
4420queue_and_out:
4421			if (eaten < 0 &&
4422			    tcp_try_rmem_schedule(sk, skb->truesize))
4423				goto drop;
4424
4425			skb_set_owner_r(skb, sk);
4426			__skb_queue_tail(&sk->sk_receive_queue, skb);
4427		}
4428		tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
4429		if (skb->len)
4430			tcp_event_data_recv(sk, skb);
4431		if (th->fin)
4432			tcp_fin(skb, sk, th);
4433
4434		if (!skb_queue_empty(&tp->out_of_order_queue)) {
4435			tcp_ofo_queue(sk);
4436
4437			/* RFC2581. 4.2. SHOULD send immediate ACK, when
4438			 * gap in queue is filled.
4439			 */
4440			if (skb_queue_empty(&tp->out_of_order_queue))
4441				inet_csk(sk)->icsk_ack.pingpong = 0;
4442		}
4443
4444		if (tp->rx_opt.num_sacks)
4445			tcp_sack_remove(tp);
4446
4447		tcp_fast_path_check(sk);
4448
4449		if (eaten > 0)
4450			__kfree_skb(skb);
4451		else if (!sock_flag(sk, SOCK_DEAD))
4452			sk->sk_data_ready(sk, 0);
4453		return;
4454	}
4455
4456	if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
4457		/* A retransmit, 2nd most common case.  Force an immediate ack. */
4458		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
4459		tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
4460
4461out_of_window:
4462		tcp_enter_quickack_mode(sk);
4463		inet_csk_schedule_ack(sk);
4464drop:
4465		__kfree_skb(skb);
4466		return;
4467	}
4468
4469	/* Out of window. F.e. zero window probe. */
4470	if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt + tcp_receive_window(tp)))
4471		goto out_of_window;
4472
4473	tcp_enter_quickack_mode(sk);
4474
4475	if (before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
4476		/* Partial packet, seq < rcv_next < end_seq */
4477		SOCK_DEBUG(sk, "partial packet: rcv_next %X seq %X - %X\n",
4478			   tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
4479			   TCP_SKB_CB(skb)->end_seq);
4480
4481		tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, tp->rcv_nxt);
4482
4483		/* If window is closed, drop tail of packet. But after
4484		 * remembering D-SACK for its head made in previous line.
4485		 */
4486		if (!tcp_receive_window(tp))
4487			goto out_of_window;
4488		goto queue_and_out;
4489	}
4490
4491	TCP_ECN_check_ce(tp, skb);
4492
4493	if (tcp_try_rmem_schedule(sk, skb->truesize))
4494		goto drop;
4495
4496	/* Disable header prediction. */
4497	tp->pred_flags = 0;
4498	inet_csk_schedule_ack(sk);
4499
4500	SOCK_DEBUG(sk, "out of order segment: rcv_next %X seq %X - %X\n",
4501		   tp->rcv_nxt, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
4502
4503	skb_set_owner_r(skb, sk);
4504
4505	if (!skb_peek(&tp->out_of_order_queue)) {
4506		/* Initial out of order segment, build 1 SACK. */
4507		if (tcp_is_sack(tp)) {
4508			tp->rx_opt.num_sacks = 1;
4509			tp->selective_acks[0].start_seq = TCP_SKB_CB(skb)->seq;
4510			tp->selective_acks[0].end_seq =
4511						TCP_SKB_CB(skb)->end_seq;
4512		}
4513		__skb_queue_head(&tp->out_of_order_queue, skb);
4514	} else {
4515		struct sk_buff *skb1 = skb_peek_tail(&tp->out_of_order_queue);
4516		u32 seq = TCP_SKB_CB(skb)->seq;
4517		u32 end_seq = TCP_SKB_CB(skb)->end_seq;
4518
4519		if (seq == TCP_SKB_CB(skb1)->end_seq) {
4520			__skb_queue_after(&tp->out_of_order_queue, skb1, skb);
4521
4522			if (!tp->rx_opt.num_sacks ||
4523			    tp->selective_acks[0].end_seq != seq)
4524				goto add_sack;
4525
4526			/* Common case: data arrive in order after hole. */
4527			tp->selective_acks[0].end_seq = end_seq;
4528			return;
4529		}
4530
4531		/* Find place to insert this segment. */
4532		while (1) {
4533			if (!after(TCP_SKB_CB(skb1)->seq, seq))
4534				break;
4535			if (skb_queue_is_first(&tp->out_of_order_queue, skb1)) {
4536				skb1 = NULL;
4537				break;
4538			}
4539			skb1 = skb_queue_prev(&tp->out_of_order_queue, skb1);
4540		}
4541
4542		/* Do skb overlap to previous one? */
4543		if (skb1 && before(seq, TCP_SKB_CB(skb1)->end_seq)) {
4544			if (!after(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
4545				/* All the bits are present. Drop. */
4546				__kfree_skb(skb);
4547				tcp_dsack_set(sk, seq, end_seq);
4548				goto add_sack;
4549			}
4550			if (after(seq, TCP_SKB_CB(skb1)->seq)) {
4551				/* Partial overlap. */
4552				tcp_dsack_set(sk, seq,
4553					      TCP_SKB_CB(skb1)->end_seq);
4554			} else {
4555				if (skb_queue_is_first(&tp->out_of_order_queue,
4556						       skb1))
4557					skb1 = NULL;
4558				else
4559					skb1 = skb_queue_prev(
4560						&tp->out_of_order_queue,
4561						skb1);
4562			}
4563		}
4564		if (!skb1)
4565			__skb_queue_head(&tp->out_of_order_queue, skb);
4566		else
4567			__skb_queue_after(&tp->out_of_order_queue, skb1, skb);
4568
4569		/* And clean segments covered by new one as whole. */
4570		while (!skb_queue_is_last(&tp->out_of_order_queue, skb)) {
4571			skb1 = skb_queue_next(&tp->out_of_order_queue, skb);
4572
4573			if (!after(end_seq, TCP_SKB_CB(skb1)->seq))
4574				break;
4575			if (before(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
4576				tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
4577						 end_seq);
4578				break;
4579			}
4580			__skb_unlink(skb1, &tp->out_of_order_queue);
4581			tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
4582					 TCP_SKB_CB(skb1)->end_seq);
4583			__kfree_skb(skb1);
4584		}
4585
4586add_sack:
4587		if (tcp_is_sack(tp))
4588			tcp_sack_new_ofo_skb(sk, seq, end_seq);
4589	}
4590}
4591
4592static struct sk_buff *tcp_collapse_one(struct sock *sk, struct sk_buff *skb,
4593					struct sk_buff_head *list)
4594{
4595	struct sk_buff *next = NULL;
4596
4597	if (!skb_queue_is_last(list, skb))
4598		next = skb_queue_next(list, skb);
4599
4600	__skb_unlink(skb, list);
4601	__kfree_skb(skb);
4602	NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPRCVCOLLAPSED);
4603
4604	return next;
4605}
4606
4607/* Collapse contiguous sequence of skbs head..tail with
4608 * sequence numbers start..end.
4609 *
4610 * If tail is NULL, this means until the end of the list.
4611 *
4612 * Segments with FIN/SYN are not collapsed (only because this
4613 * simplifies code)
4614 */
4615static void
4616tcp_collapse(struct sock *sk, struct sk_buff_head *list,
4617	     struct sk_buff *head, struct sk_buff *tail,
4618	     u32 start, u32 end)
4619{
4620	struct sk_buff *skb, *n;
4621	bool end_of_skbs;
4622
4623	/* First, check that queue is collapsible and find
4624	 * the point where collapsing can be useful. */
4625	skb = head;
4626restart:
4627	end_of_skbs = true;
4628	skb_queue_walk_from_safe(list, skb, n) {
4629		if (skb == tail)
4630			break;
4631		/* No new bits? It is possible on ofo queue. */
4632		if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
4633			skb = tcp_collapse_one(sk, skb, list);
4634			if (!skb)
4635				break;
4636			goto restart;
4637		}
4638
4639		/* The first skb to collapse is:
4640		 * - not SYN/FIN and
4641		 * - bloated or contains data before "start" or
4642		 *   overlaps to the next one.
4643		 */
4644		if (!tcp_hdr(skb)->syn && !tcp_hdr(skb)->fin &&
4645		    (tcp_win_from_space(skb->truesize) > skb->len ||
4646		     before(TCP_SKB_CB(skb)->seq, start))) {
4647			end_of_skbs = false;
4648			break;
4649		}
4650
4651		if (!skb_queue_is_last(list, skb)) {
4652			struct sk_buff *next = skb_queue_next(list, skb);
4653			if (next != tail &&
4654			    TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(next)->seq) {
4655				end_of_skbs = false;
4656				break;
4657			}
4658		}
4659
4660		/* Decided to skip this, advance start seq. */
4661		start = TCP_SKB_CB(skb)->end_seq;
4662	}
4663	if (end_of_skbs || tcp_hdr(skb)->syn || tcp_hdr(skb)->fin)
4664		return;
4665
4666	while (before(start, end)) {
4667		struct sk_buff *nskb;
4668		unsigned int header = skb_headroom(skb);
4669		int copy = SKB_MAX_ORDER(header, 0);
4670
4671		/* Too big header? This can happen with IPv6. */
4672		if (copy < 0)
4673			return;
4674		if (end - start < copy)
4675			copy = end - start;
4676		nskb = alloc_skb(copy + header, GFP_ATOMIC);
4677		if (!nskb)
4678			return;
4679
4680		skb_set_mac_header(nskb, skb_mac_header(skb) - skb->head);
4681		skb_set_network_header(nskb, (skb_network_header(skb) -
4682					      skb->head));
4683		skb_set_transport_header(nskb, (skb_transport_header(skb) -
4684						skb->head));
4685		skb_reserve(nskb, header);
4686		memcpy(nskb->head, skb->head, header);
4687		memcpy(nskb->cb, skb->cb, sizeof(skb->cb));
4688		TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(nskb)->end_seq = start;
4689		__skb_queue_before(list, skb, nskb);
4690		skb_set_owner_r(nskb, sk);
4691
4692		/* Copy data, releasing collapsed skbs. */
4693		while (copy > 0) {
4694			int offset = start - TCP_SKB_CB(skb)->seq;
4695			int size = TCP_SKB_CB(skb)->end_seq - start;
4696
4697			BUG_ON(offset < 0);
4698			if (size > 0) {
4699				size = min(copy, size);
4700				if (skb_copy_bits(skb, offset, skb_put(nskb, size), size))
4701					BUG();
4702				TCP_SKB_CB(nskb)->end_seq += size;
4703				copy -= size;
4704				start += size;
4705			}
4706			if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
4707				skb = tcp_collapse_one(sk, skb, list);
4708				if (!skb ||
4709				    skb == tail ||
4710				    tcp_hdr(skb)->syn ||
4711				    tcp_hdr(skb)->fin)
4712					return;
4713			}
4714		}
4715	}
4716}
4717
4718/* Collapse ofo queue. Algorithm: select contiguous sequence of skbs
4719 * and tcp_collapse() them until all the queue is collapsed.
4720 */
4721static void tcp_collapse_ofo_queue(struct sock *sk)
4722{
4723	struct tcp_sock *tp = tcp_sk(sk);
4724	struct sk_buff *skb = skb_peek(&tp->out_of_order_queue);
4725	struct sk_buff *head;
4726	u32 start, end;
4727
4728	if (skb == NULL)
4729		return;
4730
4731	start = TCP_SKB_CB(skb)->seq;
4732	end = TCP_SKB_CB(skb)->end_seq;
4733	head = skb;
4734
4735	for (;;) {
4736		struct sk_buff *next = NULL;
4737
4738		if (!skb_queue_is_last(&tp->out_of_order_queue, skb))
4739			next = skb_queue_next(&tp->out_of_order_queue, skb);
4740		skb = next;
4741
4742		/* Segment is terminated when we see gap or when
4743		 * we are at the end of all the queue. */
4744		if (!skb ||
4745		    after(TCP_SKB_CB(skb)->seq, end) ||
4746		    before(TCP_SKB_CB(skb)->end_seq, start)) {
4747			tcp_collapse(sk, &tp->out_of_order_queue,
4748				     head, skb, start, end);
4749			head = skb;
4750			if (!skb)
4751				break;
4752			/* Start new segment */
4753			start = TCP_SKB_CB(skb)->seq;
4754			end = TCP_SKB_CB(skb)->end_seq;
4755		} else {
4756			if (before(TCP_SKB_CB(skb)->seq, start))
4757				start = TCP_SKB_CB(skb)->seq;
4758			if (after(TCP_SKB_CB(skb)->end_seq, end))
4759				end = TCP_SKB_CB(skb)->end_seq;
4760		}
4761	}
4762}
4763
4764/*
4765 * Purge the out-of-order queue.
4766 * Return true if queue was pruned.
4767 */
4768static int tcp_prune_ofo_queue(struct sock *sk)
4769{
4770	struct tcp_sock *tp = tcp_sk(sk);
4771	int res = 0;
4772
4773	if (!skb_queue_empty(&tp->out_of_order_queue)) {
4774		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_OFOPRUNED);
4775		__skb_queue_purge(&tp->out_of_order_queue);
4776
4777		/* Reset SACK state.  A conforming SACK implementation will
4778		 * do the same at a timeout based retransmit.  When a connection
4779		 * is in a sad state like this, we care only about integrity
4780		 * of the connection not performance.
4781		 */
4782		if (tp->rx_opt.sack_ok)
4783			tcp_sack_reset(&tp->rx_opt);
4784		sk_mem_reclaim(sk);
4785		res = 1;
4786	}
4787	return res;
4788}
4789
4790/* Reduce allocated memory if we can, trying to get
4791 * the socket within its memory limits again.
4792 *
4793 * Return less than zero if we should start dropping frames
4794 * until the socket owning process reads some of the data
4795 * to stabilize the situation.
4796 */
4797static int tcp_prune_queue(struct sock *sk)
4798{
4799	struct tcp_sock *tp = tcp_sk(sk);
4800
4801	SOCK_DEBUG(sk, "prune_queue: c=%x\n", tp->copied_seq);
4802
4803	NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PRUNECALLED);
4804
4805	if (atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf)
4806		tcp_clamp_window(sk);
4807	else if (tcp_memory_pressure)
4808		tp->rcv_ssthresh = min(tp->rcv_ssthresh, 4U * tp->advmss);
4809
4810	tcp_collapse_ofo_queue(sk);
4811	if (!skb_queue_empty(&sk->sk_receive_queue))
4812		tcp_collapse(sk, &sk->sk_receive_queue,
4813			     skb_peek(&sk->sk_receive_queue),
4814			     NULL,
4815			     tp->copied_seq, tp->rcv_nxt);
4816	sk_mem_reclaim(sk);
4817
4818	if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
4819		return 0;
4820
4821	/* Collapsing did not help, destructive actions follow.
4822	 * This must not ever occur. */
4823
4824	tcp_prune_ofo_queue(sk);
4825
4826	if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
4827		return 0;
4828
4829	/* If we are really being abused, tell the caller to silently
4830	 * drop receive data on the floor.  It will get retransmitted
4831	 * and hopefully then we'll have sufficient space.
4832	 */
4833	NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_RCVPRUNED);
4834
4835	/* Massive buffer overcommit. */
4836	tp->pred_flags = 0;
4837	return -1;
4838}
4839
4840/* RFC2861, slow part. Adjust cwnd, after it was not full during one rto.
4841 * As additional protections, we do not touch cwnd in retransmission phases,
4842 * and if application hit its sndbuf limit recently.
4843 */
4844void tcp_cwnd_application_limited(struct sock *sk)
4845{
4846	struct tcp_sock *tp = tcp_sk(sk);
4847
4848	if (inet_csk(sk)->icsk_ca_state == TCP_CA_Open &&
4849	    sk->sk_socket && !test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
4850		/* Limited by application or receiver window. */
4851		u32 init_win = tcp_init_cwnd(tp, __sk_dst_get(sk));
4852		u32 win_used = max(tp->snd_cwnd_used, init_win);
4853		if (win_used < tp->snd_cwnd) {
4854			tp->snd_ssthresh = tcp_current_ssthresh(sk);
4855			tp->snd_cwnd = (tp->snd_cwnd + win_used) >> 1;
4856		}
4857		tp->snd_cwnd_used = 0;
4858	}
4859	tp->snd_cwnd_stamp = tcp_time_stamp;
4860}
4861
4862static int tcp_should_expand_sndbuf(struct sock *sk)
4863{
4864	struct tcp_sock *tp = tcp_sk(sk);
4865
4866	/* If the user specified a specific send buffer setting, do
4867	 * not modify it.
4868	 */
4869	if (sk->sk_userlocks & SOCK_SNDBUF_LOCK)
4870		return 0;
4871
4872	/* If we are under global TCP memory pressure, do not expand.  */
4873	if (tcp_memory_pressure)
4874		return 0;
4875
4876	/* If we are under soft global TCP memory pressure, do not expand.  */
4877	if (atomic_long_read(&tcp_memory_allocated) >= sysctl_tcp_mem[0])
4878		return 0;
4879
4880	/* If we filled the congestion window, do not expand.  */
4881	if (tp->packets_out >= tp->snd_cwnd)
4882		return 0;
4883
4884	return 1;
4885}
4886
4887/* When incoming ACK allowed to free some skb from write_queue,
4888 * we remember this event in flag SOCK_QUEUE_SHRUNK and wake up socket
4889 * on the exit from tcp input handler.
4890 *
4891 * PROBLEM: sndbuf expansion does not work well with largesend.
4892 */
4893static void tcp_new_space(struct sock *sk)
4894{
4895	struct tcp_sock *tp = tcp_sk(sk);
4896
4897	if (tcp_should_expand_sndbuf(sk)) {
4898		int sndmem = max_t(u32, tp->rx_opt.mss_clamp, tp->mss_cache) +
4899			MAX_TCP_HEADER + 16 + sizeof(struct sk_buff);
 
 
4900		int demanded = max_t(unsigned int, tp->snd_cwnd,
4901				     tp->reordering + 1);
4902		sndmem *= 2 * demanded;
4903		if (sndmem > sk->sk_sndbuf)
4904			sk->sk_sndbuf = min(sndmem, sysctl_tcp_wmem[2]);
4905		tp->snd_cwnd_stamp = tcp_time_stamp;
4906	}
4907
4908	sk->sk_write_space(sk);
4909}
4910
4911static void tcp_check_space(struct sock *sk)
4912{
4913	if (sock_flag(sk, SOCK_QUEUE_SHRUNK)) {
4914		sock_reset_flag(sk, SOCK_QUEUE_SHRUNK);
4915		if (sk->sk_socket &&
4916		    test_bit(SOCK_NOSPACE, &sk->sk_socket->flags))
4917			tcp_new_space(sk);
4918	}
4919}
4920
4921static inline void tcp_data_snd_check(struct sock *sk)
4922{
4923	tcp_push_pending_frames(sk);
4924	tcp_check_space(sk);
4925}
4926
4927/*
4928 * Check if sending an ack is needed.
4929 */
4930static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible)
4931{
4932	struct tcp_sock *tp = tcp_sk(sk);
4933
4934	    /* More than one full frame received... */
4935	if (((tp->rcv_nxt - tp->rcv_wup) > inet_csk(sk)->icsk_ack.rcv_mss &&
4936	     /* ... and right edge of window advances far enough.
4937	      * (tcp_recvmsg() will send ACK otherwise). Or...
4938	      */
4939	     __tcp_select_window(sk) >= tp->rcv_wnd) ||
4940	    /* We ACK each frame or... */
4941	    tcp_in_quickack_mode(sk) ||
4942	    /* We have out of order data. */
4943	    (ofo_possible && skb_peek(&tp->out_of_order_queue))) {
4944		/* Then ack it now */
4945		tcp_send_ack(sk);
4946	} else {
4947		/* Else, send delayed ack. */
4948		tcp_send_delayed_ack(sk);
4949	}
4950}
4951
4952static inline void tcp_ack_snd_check(struct sock *sk)
4953{
4954	if (!inet_csk_ack_scheduled(sk)) {
4955		/* We sent a data segment already. */
4956		return;
4957	}
4958	__tcp_ack_snd_check(sk, 1);
4959}
4960
4961/*
4962 *	This routine is only called when we have urgent data
4963 *	signaled. Its the 'slow' part of tcp_urg. It could be
4964 *	moved inline now as tcp_urg is only called from one
4965 *	place. We handle URGent data wrong. We have to - as
4966 *	BSD still doesn't use the correction from RFC961.
4967 *	For 1003.1g we should support a new option TCP_STDURG to permit
4968 *	either form (or just set the sysctl tcp_stdurg).
4969 */
4970
4971static void tcp_check_urg(struct sock *sk, struct tcphdr *th)
4972{
4973	struct tcp_sock *tp = tcp_sk(sk);
4974	u32 ptr = ntohs(th->urg_ptr);
4975
4976	if (ptr && !sysctl_tcp_stdurg)
4977		ptr--;
4978	ptr += ntohl(th->seq);
4979
4980	/* Ignore urgent data that we've already seen and read. */
4981	if (after(tp->copied_seq, ptr))
4982		return;
4983
4984	/* Do not replay urg ptr.
4985	 *
4986	 * NOTE: interesting situation not covered by specs.
4987	 * Misbehaving sender may send urg ptr, pointing to segment,
4988	 * which we already have in ofo queue. We are not able to fetch
4989	 * such data and will stay in TCP_URG_NOTYET until will be eaten
4990	 * by recvmsg(). Seems, we are not obliged to handle such wicked
4991	 * situations. But it is worth to think about possibility of some
4992	 * DoSes using some hypothetical application level deadlock.
4993	 */
4994	if (before(ptr, tp->rcv_nxt))
4995		return;
4996
4997	/* Do we already have a newer (or duplicate) urgent pointer? */
4998	if (tp->urg_data && !after(ptr, tp->urg_seq))
4999		return;
5000
5001	/* Tell the world about our new urgent pointer. */
5002	sk_send_sigurg(sk);
5003
5004	/* We may be adding urgent data when the last byte read was
5005	 * urgent. To do this requires some care. We cannot just ignore
5006	 * tp->copied_seq since we would read the last urgent byte again
5007	 * as data, nor can we alter copied_seq until this data arrives
5008	 * or we break the semantics of SIOCATMARK (and thus sockatmark())
5009	 *
5010	 * NOTE. Double Dutch. Rendering to plain English: author of comment
5011	 * above did something sort of 	send("A", MSG_OOB); send("B", MSG_OOB);
5012	 * and expect that both A and B disappear from stream. This is _wrong_.
5013	 * Though this happens in BSD with high probability, this is occasional.
5014	 * Any application relying on this is buggy. Note also, that fix "works"
5015	 * only in this artificial test. Insert some normal data between A and B and we will
5016	 * decline of BSD again. Verdict: it is better to remove to trap
5017	 * buggy users.
5018	 */
5019	if (tp->urg_seq == tp->copied_seq && tp->urg_data &&
5020	    !sock_flag(sk, SOCK_URGINLINE) && tp->copied_seq != tp->rcv_nxt) {
5021		struct sk_buff *skb = skb_peek(&sk->sk_receive_queue);
5022		tp->copied_seq++;
5023		if (skb && !before(tp->copied_seq, TCP_SKB_CB(skb)->end_seq)) {
5024			__skb_unlink(skb, &sk->sk_receive_queue);
5025			__kfree_skb(skb);
5026		}
5027	}
5028
5029	tp->urg_data = TCP_URG_NOTYET;
5030	tp->urg_seq = ptr;
5031
5032	/* Disable header prediction. */
5033	tp->pred_flags = 0;
5034}
5035
5036/* This is the 'fast' part of urgent handling. */
5037static void tcp_urg(struct sock *sk, struct sk_buff *skb, struct tcphdr *th)
5038{
5039	struct tcp_sock *tp = tcp_sk(sk);
5040
5041	/* Check if we get a new urgent pointer - normally not. */
5042	if (th->urg)
5043		tcp_check_urg(sk, th);
5044
5045	/* Do we wait for any urgent data? - normally not... */
5046	if (tp->urg_data == TCP_URG_NOTYET) {
5047		u32 ptr = tp->urg_seq - ntohl(th->seq) + (th->doff * 4) -
5048			  th->syn;
5049
5050		/* Is the urgent pointer pointing into this packet? */
5051		if (ptr < skb->len) {
5052			u8 tmp;
5053			if (skb_copy_bits(skb, ptr, &tmp, 1))
5054				BUG();
5055			tp->urg_data = TCP_URG_VALID | tmp;
5056			if (!sock_flag(sk, SOCK_DEAD))
5057				sk->sk_data_ready(sk, 0);
5058		}
5059	}
5060}
5061
5062static int tcp_copy_to_iovec(struct sock *sk, struct sk_buff *skb, int hlen)
5063{
5064	struct tcp_sock *tp = tcp_sk(sk);
5065	int chunk = skb->len - hlen;
5066	int err;
5067
5068	local_bh_enable();
5069	if (skb_csum_unnecessary(skb))
5070		err = skb_copy_datagram_iovec(skb, hlen, tp->ucopy.iov, chunk);
5071	else
5072		err = skb_copy_and_csum_datagram_iovec(skb, hlen,
5073						       tp->ucopy.iov);
5074
5075	if (!err) {
5076		tp->ucopy.len -= chunk;
5077		tp->copied_seq += chunk;
5078		tcp_rcv_space_adjust(sk);
5079	}
5080
5081	local_bh_disable();
5082	return err;
5083}
5084
5085static __sum16 __tcp_checksum_complete_user(struct sock *sk,
5086					    struct sk_buff *skb)
5087{
5088	__sum16 result;
5089
5090	if (sock_owned_by_user(sk)) {
5091		local_bh_enable();
5092		result = __tcp_checksum_complete(skb);
5093		local_bh_disable();
5094	} else {
5095		result = __tcp_checksum_complete(skb);
5096	}
5097	return result;
5098}
5099
5100static inline int tcp_checksum_complete_user(struct sock *sk,
5101					     struct sk_buff *skb)
5102{
5103	return !skb_csum_unnecessary(skb) &&
5104	       __tcp_checksum_complete_user(sk, skb);
5105}
5106
5107#ifdef CONFIG_NET_DMA
5108static int tcp_dma_try_early_copy(struct sock *sk, struct sk_buff *skb,
5109				  int hlen)
5110{
5111	struct tcp_sock *tp = tcp_sk(sk);
5112	int chunk = skb->len - hlen;
5113	int dma_cookie;
5114	int copied_early = 0;
5115
5116	if (tp->ucopy.wakeup)
5117		return 0;
5118
5119	if (!tp->ucopy.dma_chan && tp->ucopy.pinned_list)
5120		tp->ucopy.dma_chan = dma_find_channel(DMA_MEMCPY);
5121
5122	if (tp->ucopy.dma_chan && skb_csum_unnecessary(skb)) {
5123
5124		dma_cookie = dma_skb_copy_datagram_iovec(tp->ucopy.dma_chan,
5125							 skb, hlen,
5126							 tp->ucopy.iov, chunk,
5127							 tp->ucopy.pinned_list);
5128
5129		if (dma_cookie < 0)
5130			goto out;
5131
5132		tp->ucopy.dma_cookie = dma_cookie;
5133		copied_early = 1;
5134
5135		tp->ucopy.len -= chunk;
5136		tp->copied_seq += chunk;
5137		tcp_rcv_space_adjust(sk);
5138
5139		if ((tp->ucopy.len == 0) ||
5140		    (tcp_flag_word(tcp_hdr(skb)) & TCP_FLAG_PSH) ||
5141		    (atomic_read(&sk->sk_rmem_alloc) > (sk->sk_rcvbuf >> 1))) {
5142			tp->ucopy.wakeup = 1;
5143			sk->sk_data_ready(sk, 0);
5144		}
5145	} else if (chunk > 0) {
5146		tp->ucopy.wakeup = 1;
5147		sk->sk_data_ready(sk, 0);
5148	}
5149out:
5150	return copied_early;
5151}
5152#endif /* CONFIG_NET_DMA */
5153
5154/* Does PAWS and seqno based validation of an incoming segment, flags will
5155 * play significant role here.
5156 */
5157static int tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
5158			      struct tcphdr *th, int syn_inerr)
5159{
5160	u8 *hash_location;
5161	struct tcp_sock *tp = tcp_sk(sk);
5162
5163	/* RFC1323: H1. Apply PAWS check first. */
5164	if (tcp_fast_parse_options(skb, th, tp, &hash_location) &&
5165	    tp->rx_opt.saw_tstamp &&
5166	    tcp_paws_discard(sk, skb)) {
5167		if (!th->rst) {
5168			NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);
5169			tcp_send_dupack(sk, skb);
5170			goto discard;
5171		}
5172		/* Reset is accepted even if it did not pass PAWS. */
5173	}
5174
5175	/* Step 1: check sequence number */
5176	if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) {
5177		/* RFC793, page 37: "In all states except SYN-SENT, all reset
5178		 * (RST) segments are validated by checking their SEQ-fields."
5179		 * And page 69: "If an incoming segment is not acceptable,
5180		 * an acknowledgment should be sent in reply (unless the RST
5181		 * bit is set, if so drop the segment and return)".
5182		 */
5183		if (!th->rst)
5184			tcp_send_dupack(sk, skb);
5185		goto discard;
5186	}
5187
5188	/* Step 2: check RST bit */
5189	if (th->rst) {
5190		tcp_reset(sk);
5191		goto discard;
5192	}
5193
5194	/* ts_recent update must be made after we are sure that the packet
5195	 * is in window.
5196	 */
5197	tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
5198
5199	/* step 3: check security and precedence [ignored] */
5200
5201	/* step 4: Check for a SYN in window. */
5202	if (th->syn && !before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
5203		if (syn_inerr)
5204			TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS);
5205		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONSYN);
5206		tcp_reset(sk);
5207		return -1;
5208	}
5209
5210	return 1;
5211
5212discard:
5213	__kfree_skb(skb);
5214	return 0;
5215}
5216
5217/*
5218 *	TCP receive function for the ESTABLISHED state.
5219 *
5220 *	It is split into a fast path and a slow path. The fast path is
5221 * 	disabled when:
5222 *	- A zero window was announced from us - zero window probing
5223 *        is only handled properly in the slow path.
5224 *	- Out of order segments arrived.
5225 *	- Urgent data is expected.
5226 *	- There is no buffer space left
5227 *	- Unexpected TCP flags/window values/header lengths are received
5228 *	  (detected by checking the TCP header against pred_flags)
5229 *	- Data is sent in both directions. Fast path only supports pure senders
5230 *	  or pure receivers (this means either the sequence number or the ack
5231 *	  value must stay constant)
5232 *	- Unexpected TCP option.
5233 *
5234 *	When these conditions are not satisfied it drops into a standard
5235 *	receive procedure patterned after RFC793 to handle all cases.
5236 *	The first three cases are guaranteed by proper pred_flags setting,
5237 *	the rest is checked inline. Fast processing is turned on in
5238 *	tcp_data_queue when everything is OK.
5239 */
5240int tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
5241			struct tcphdr *th, unsigned len)
5242{
5243	struct tcp_sock *tp = tcp_sk(sk);
5244	int res;
5245
5246	/*
5247	 *	Header prediction.
5248	 *	The code loosely follows the one in the famous
5249	 *	"30 instruction TCP receive" Van Jacobson mail.
5250	 *
5251	 *	Van's trick is to deposit buffers into socket queue
5252	 *	on a device interrupt, to call tcp_recv function
5253	 *	on the receive process context and checksum and copy
5254	 *	the buffer to user space. smart...
5255	 *
5256	 *	Our current scheme is not silly either but we take the
5257	 *	extra cost of the net_bh soft interrupt processing...
5258	 *	We do checksum and copy also but from device to kernel.
5259	 */
5260
5261	tp->rx_opt.saw_tstamp = 0;
5262
5263	/*	pred_flags is 0xS?10 << 16 + snd_wnd
5264	 *	if header_prediction is to be made
5265	 *	'S' will always be tp->tcp_header_len >> 2
5266	 *	'?' will be 0 for the fast path, otherwise pred_flags is 0 to
5267	 *  turn it off	(when there are holes in the receive
5268	 *	 space for instance)
5269	 *	PSH flag is ignored.
5270	 */
5271
5272	if ((tcp_flag_word(th) & TCP_HP_BITS) == tp->pred_flags &&
5273	    TCP_SKB_CB(skb)->seq == tp->rcv_nxt &&
5274	    !after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt)) {
5275		int tcp_header_len = tp->tcp_header_len;
5276
5277		/* Timestamp header prediction: tcp_header_len
5278		 * is automatically equal to th->doff*4 due to pred_flags
5279		 * match.
5280		 */
5281
5282		/* Check timestamp */
5283		if (tcp_header_len == sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) {
5284			/* No? Slow path! */
5285			if (!tcp_parse_aligned_timestamp(tp, th))
5286				goto slow_path;
5287
5288			/* If PAWS failed, check it more carefully in slow path */
5289			if ((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) < 0)
5290				goto slow_path;
5291
5292			/* DO NOT update ts_recent here, if checksum fails
5293			 * and timestamp was corrupted part, it will result
5294			 * in a hung connection since we will drop all
5295			 * future packets due to the PAWS test.
5296			 */
5297		}
5298
5299		if (len <= tcp_header_len) {
5300			/* Bulk data transfer: sender */
5301			if (len == tcp_header_len) {
5302				/* Predicted packet is in window by definition.
5303				 * seq == rcv_nxt and rcv_wup <= rcv_nxt.
5304				 * Hence, check seq<=rcv_wup reduces to:
5305				 */
5306				if (tcp_header_len ==
5307				    (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
5308				    tp->rcv_nxt == tp->rcv_wup)
5309					tcp_store_ts_recent(tp);
5310
5311				/* We know that such packets are checksummed
5312				 * on entry.
5313				 */
5314				tcp_ack(sk, skb, 0);
5315				__kfree_skb(skb);
5316				tcp_data_snd_check(sk);
5317				return 0;
5318			} else { /* Header too small */
5319				TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS);
5320				goto discard;
5321			}
5322		} else {
5323			int eaten = 0;
5324			int copied_early = 0;
 
5325
5326			if (tp->copied_seq == tp->rcv_nxt &&
5327			    len - tcp_header_len <= tp->ucopy.len) {
5328#ifdef CONFIG_NET_DMA
5329				if (tcp_dma_try_early_copy(sk, skb, tcp_header_len)) {
 
 
5330					copied_early = 1;
5331					eaten = 1;
5332				}
5333#endif
5334				if (tp->ucopy.task == current &&
5335				    sock_owned_by_user(sk) && !copied_early) {
5336					__set_current_state(TASK_RUNNING);
5337
5338					if (!tcp_copy_to_iovec(sk, skb, tcp_header_len))
5339						eaten = 1;
5340				}
5341				if (eaten) {
5342					/* Predicted packet is in window by definition.
5343					 * seq == rcv_nxt and rcv_wup <= rcv_nxt.
5344					 * Hence, check seq<=rcv_wup reduces to:
5345					 */
5346					if (tcp_header_len ==
5347					    (sizeof(struct tcphdr) +
5348					     TCPOLEN_TSTAMP_ALIGNED) &&
5349					    tp->rcv_nxt == tp->rcv_wup)
5350						tcp_store_ts_recent(tp);
5351
5352					tcp_rcv_rtt_measure_ts(sk, skb);
5353
5354					__skb_pull(skb, tcp_header_len);
5355					tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
5356					NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPHITSTOUSER);
5357				}
5358				if (copied_early)
5359					tcp_cleanup_rbuf(sk, skb->len);
5360			}
5361			if (!eaten) {
5362				if (tcp_checksum_complete_user(sk, skb))
5363					goto csum_error;
5364
5365				/* Predicted packet is in window by definition.
5366				 * seq == rcv_nxt and rcv_wup <= rcv_nxt.
5367				 * Hence, check seq<=rcv_wup reduces to:
5368				 */
5369				if (tcp_header_len ==
5370				    (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
5371				    tp->rcv_nxt == tp->rcv_wup)
5372					tcp_store_ts_recent(tp);
5373
5374				tcp_rcv_rtt_measure_ts(sk, skb);
5375
5376				if ((int)skb->truesize > sk->sk_forward_alloc)
5377					goto step5;
5378
5379				NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPHITS);
5380
5381				/* Bulk data transfer: receiver */
5382				__skb_pull(skb, tcp_header_len);
5383				__skb_queue_tail(&sk->sk_receive_queue, skb);
5384				skb_set_owner_r(skb, sk);
5385				tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
5386			}
5387
5388			tcp_event_data_recv(sk, skb);
5389
5390			if (TCP_SKB_CB(skb)->ack_seq != tp->snd_una) {
5391				/* Well, only one small jumplet in fast path... */
5392				tcp_ack(sk, skb, FLAG_DATA);
5393				tcp_data_snd_check(sk);
5394				if (!inet_csk_ack_scheduled(sk))
5395					goto no_ack;
5396			}
5397
5398			if (!copied_early || tp->rcv_nxt != tp->rcv_wup)
5399				__tcp_ack_snd_check(sk, 0);
5400no_ack:
5401#ifdef CONFIG_NET_DMA
5402			if (copied_early)
5403				__skb_queue_tail(&sk->sk_async_wait_queue, skb);
5404			else
5405#endif
5406			if (eaten)
5407				__kfree_skb(skb);
5408			else
5409				sk->sk_data_ready(sk, 0);
5410			return 0;
5411		}
5412	}
5413
5414slow_path:
5415	if (len < (th->doff << 2) || tcp_checksum_complete_user(sk, skb))
5416		goto csum_error;
5417
5418	/*
5419	 *	Standard slow path.
5420	 */
5421
5422	res = tcp_validate_incoming(sk, skb, th, 1);
5423	if (res <= 0)
5424		return -res;
5425
5426step5:
5427	if (th->ack && tcp_ack(sk, skb, FLAG_SLOWPATH) < 0)
5428		goto discard;
5429
5430	tcp_rcv_rtt_measure_ts(sk, skb);
5431
5432	/* Process urgent data. */
5433	tcp_urg(sk, skb, th);
5434
5435	/* step 7: process the segment text */
5436	tcp_data_queue(sk, skb);
5437
5438	tcp_data_snd_check(sk);
5439	tcp_ack_snd_check(sk);
5440	return 0;
5441
5442csum_error:
5443	TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS);
5444
5445discard:
5446	__kfree_skb(skb);
5447	return 0;
5448}
5449EXPORT_SYMBOL(tcp_rcv_established);
5450
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
5451static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
5452					 struct tcphdr *th, unsigned len)
5453{
5454	u8 *hash_location;
5455	struct inet_connection_sock *icsk = inet_csk(sk);
5456	struct tcp_sock *tp = tcp_sk(sk);
5457	struct tcp_cookie_values *cvp = tp->cookie_values;
5458	int saved_clamp = tp->rx_opt.mss_clamp;
5459
5460	tcp_parse_options(skb, &tp->rx_opt, &hash_location, 0);
5461
5462	if (th->ack) {
5463		/* rfc793:
5464		 * "If the state is SYN-SENT then
5465		 *    first check the ACK bit
5466		 *      If the ACK bit is set
5467		 *	  If SEG.ACK =< ISS, or SEG.ACK > SND.NXT, send
5468		 *        a reset (unless the RST bit is set, if so drop
5469		 *        the segment and return)"
5470		 *
5471		 *  We do not send data with SYN, so that RFC-correct
5472		 *  test reduces to:
5473		 */
5474		if (TCP_SKB_CB(skb)->ack_seq != tp->snd_nxt)
5475			goto reset_and_undo;
5476
5477		if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
5478		    !between(tp->rx_opt.rcv_tsecr, tp->retrans_stamp,
5479			     tcp_time_stamp)) {
5480			NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSACTIVEREJECTED);
5481			goto reset_and_undo;
5482		}
5483
5484		/* Now ACK is acceptable.
5485		 *
5486		 * "If the RST bit is set
5487		 *    If the ACK was acceptable then signal the user "error:
5488		 *    connection reset", drop the segment, enter CLOSED state,
5489		 *    delete TCB, and return."
5490		 */
5491
5492		if (th->rst) {
5493			tcp_reset(sk);
5494			goto discard;
5495		}
5496
5497		/* rfc793:
5498		 *   "fifth, if neither of the SYN or RST bits is set then
5499		 *    drop the segment and return."
5500		 *
5501		 *    See note below!
5502		 *                                        --ANK(990513)
5503		 */
5504		if (!th->syn)
5505			goto discard_and_undo;
5506
5507		/* rfc793:
5508		 *   "If the SYN bit is on ...
5509		 *    are acceptable then ...
5510		 *    (our SYN has been ACKed), change the connection
5511		 *    state to ESTABLISHED..."
5512		 */
5513
5514		TCP_ECN_rcv_synack(tp, th);
5515
5516		tp->snd_wl1 = TCP_SKB_CB(skb)->seq;
5517		tcp_ack(sk, skb, FLAG_SLOWPATH);
5518
5519		/* Ok.. it's good. Set up sequence numbers and
5520		 * move to established.
5521		 */
5522		tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
5523		tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
5524
5525		/* RFC1323: The window in SYN & SYN/ACK segments is
5526		 * never scaled.
5527		 */
5528		tp->snd_wnd = ntohs(th->window);
5529		tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);
5530
5531		if (!tp->rx_opt.wscale_ok) {
5532			tp->rx_opt.snd_wscale = tp->rx_opt.rcv_wscale = 0;
5533			tp->window_clamp = min(tp->window_clamp, 65535U);
5534		}
5535
5536		if (tp->rx_opt.saw_tstamp) {
5537			tp->rx_opt.tstamp_ok	   = 1;
5538			tp->tcp_header_len =
5539				sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
5540			tp->advmss	    -= TCPOLEN_TSTAMP_ALIGNED;
5541			tcp_store_ts_recent(tp);
5542		} else {
5543			tp->tcp_header_len = sizeof(struct tcphdr);
5544		}
5545
5546		if (tcp_is_sack(tp) && sysctl_tcp_fack)
5547			tcp_enable_fack(tp);
5548
5549		tcp_mtup_init(sk);
5550		tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
5551		tcp_initialize_rcv_mss(sk);
5552
5553		/* Remember, tcp_poll() does not lock socket!
5554		 * Change state from SYN-SENT only after copied_seq
5555		 * is initialized. */
5556		tp->copied_seq = tp->rcv_nxt;
5557
5558		if (cvp != NULL &&
5559		    cvp->cookie_pair_size > 0 &&
5560		    tp->rx_opt.cookie_plus > 0) {
5561			int cookie_size = tp->rx_opt.cookie_plus
5562					- TCPOLEN_COOKIE_BASE;
5563			int cookie_pair_size = cookie_size
5564					     + cvp->cookie_desired;
5565
5566			/* A cookie extension option was sent and returned.
5567			 * Note that each incoming SYNACK replaces the
5568			 * Responder cookie.  The initial exchange is most
5569			 * fragile, as protection against spoofing relies
5570			 * entirely upon the sequence and timestamp (above).
5571			 * This replacement strategy allows the correct pair to
5572			 * pass through, while any others will be filtered via
5573			 * Responder verification later.
5574			 */
5575			if (sizeof(cvp->cookie_pair) >= cookie_pair_size) {
5576				memcpy(&cvp->cookie_pair[cvp->cookie_desired],
5577				       hash_location, cookie_size);
5578				cvp->cookie_pair_size = cookie_pair_size;
5579			}
5580		}
5581
5582		smp_mb();
5583		tcp_set_state(sk, TCP_ESTABLISHED);
5584
5585		security_inet_conn_established(sk, skb);
5586
5587		/* Make sure socket is routed, for correct metrics.  */
5588		icsk->icsk_af_ops->rebuild_header(sk);
5589
5590		tcp_init_metrics(sk);
5591
5592		tcp_init_congestion_control(sk);
5593
5594		/* Prevent spurious tcp_cwnd_restart() on first data
5595		 * packet.
5596		 */
5597		tp->lsndtime = tcp_time_stamp;
5598
5599		tcp_init_buffer_space(sk);
5600
5601		if (sock_flag(sk, SOCK_KEEPOPEN))
5602			inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tp));
5603
5604		if (!tp->rx_opt.snd_wscale)
5605			__tcp_fast_path_on(tp, tp->snd_wnd);
5606		else
5607			tp->pred_flags = 0;
5608
5609		if (!sock_flag(sk, SOCK_DEAD)) {
5610			sk->sk_state_change(sk);
5611			sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT);
5612		}
5613
5614		if (sk->sk_write_pending ||
5615		    icsk->icsk_accept_queue.rskq_defer_accept ||
5616		    icsk->icsk_ack.pingpong) {
5617			/* Save one ACK. Data will be ready after
5618			 * several ticks, if write_pending is set.
5619			 *
5620			 * It may be deleted, but with this feature tcpdumps
5621			 * look so _wonderfully_ clever, that I was not able
5622			 * to stand against the temptation 8)     --ANK
5623			 */
5624			inet_csk_schedule_ack(sk);
5625			icsk->icsk_ack.lrcvtime = tcp_time_stamp;
5626			icsk->icsk_ack.ato	 = TCP_ATO_MIN;
5627			tcp_incr_quickack(sk);
5628			tcp_enter_quickack_mode(sk);
5629			inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
5630						  TCP_DELACK_MAX, TCP_RTO_MAX);
5631
5632discard:
5633			__kfree_skb(skb);
5634			return 0;
5635		} else {
5636			tcp_send_ack(sk);
5637		}
5638		return -1;
5639	}
5640
5641	/* No ACK in the segment */
5642
5643	if (th->rst) {
5644		/* rfc793:
5645		 * "If the RST bit is set
5646		 *
5647		 *      Otherwise (no ACK) drop the segment and return."
5648		 */
5649
5650		goto discard_and_undo;
5651	}
5652
5653	/* PAWS check. */
5654	if (tp->rx_opt.ts_recent_stamp && tp->rx_opt.saw_tstamp &&
5655	    tcp_paws_reject(&tp->rx_opt, 0))
5656		goto discard_and_undo;
5657
5658	if (th->syn) {
5659		/* We see SYN without ACK. It is attempt of
5660		 * simultaneous connect with crossed SYNs.
5661		 * Particularly, it can be connect to self.
5662		 */
5663		tcp_set_state(sk, TCP_SYN_RECV);
5664
5665		if (tp->rx_opt.saw_tstamp) {
5666			tp->rx_opt.tstamp_ok = 1;
5667			tcp_store_ts_recent(tp);
5668			tp->tcp_header_len =
5669				sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
5670		} else {
5671			tp->tcp_header_len = sizeof(struct tcphdr);
5672		}
5673
5674		tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
5675		tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
5676
5677		/* RFC1323: The window in SYN & SYN/ACK segments is
5678		 * never scaled.
5679		 */
5680		tp->snd_wnd    = ntohs(th->window);
5681		tp->snd_wl1    = TCP_SKB_CB(skb)->seq;
5682		tp->max_window = tp->snd_wnd;
5683
5684		TCP_ECN_rcv_syn(tp, th);
5685
5686		tcp_mtup_init(sk);
5687		tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
5688		tcp_initialize_rcv_mss(sk);
5689
5690		tcp_send_synack(sk);
5691#if 0
5692		/* Note, we could accept data and URG from this segment.
5693		 * There are no obstacles to make this.
5694		 *
5695		 * However, if we ignore data in ACKless segments sometimes,
5696		 * we have no reasons to accept it sometimes.
5697		 * Also, seems the code doing it in step6 of tcp_rcv_state_process
5698		 * is not flawless. So, discard packet for sanity.
5699		 * Uncomment this return to process the data.
5700		 */
5701		return -1;
5702#else
5703		goto discard;
5704#endif
5705	}
5706	/* "fifth, if neither of the SYN or RST bits is set then
5707	 * drop the segment and return."
5708	 */
5709
5710discard_and_undo:
5711	tcp_clear_options(&tp->rx_opt);
5712	tp->rx_opt.mss_clamp = saved_clamp;
5713	goto discard;
5714
5715reset_and_undo:
5716	tcp_clear_options(&tp->rx_opt);
5717	tp->rx_opt.mss_clamp = saved_clamp;
5718	return 1;
5719}
5720
5721/*
5722 *	This function implements the receiving procedure of RFC 793 for
5723 *	all states except ESTABLISHED and TIME_WAIT.
5724 *	It's called from both tcp_v4_rcv and tcp_v6_rcv and should be
5725 *	address independent.
5726 */
5727
5728int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
5729			  struct tcphdr *th, unsigned len)
5730{
5731	struct tcp_sock *tp = tcp_sk(sk);
5732	struct inet_connection_sock *icsk = inet_csk(sk);
5733	int queued = 0;
5734	int res;
5735
5736	tp->rx_opt.saw_tstamp = 0;
5737
5738	switch (sk->sk_state) {
5739	case TCP_CLOSE:
5740		goto discard;
5741
5742	case TCP_LISTEN:
5743		if (th->ack)
5744			return 1;
5745
5746		if (th->rst)
5747			goto discard;
5748
5749		if (th->syn) {
 
 
5750			if (icsk->icsk_af_ops->conn_request(sk, skb) < 0)
5751				return 1;
5752
5753			/* Now we have several options: In theory there is
5754			 * nothing else in the frame. KA9Q has an option to
5755			 * send data with the syn, BSD accepts data with the
5756			 * syn up to the [to be] advertised window and
5757			 * Solaris 2.1 gives you a protocol error. For now
5758			 * we just ignore it, that fits the spec precisely
5759			 * and avoids incompatibilities. It would be nice in
5760			 * future to drop through and process the data.
5761			 *
5762			 * Now that TTCP is starting to be used we ought to
5763			 * queue this data.
5764			 * But, this leaves one open to an easy denial of
5765			 * service attack, and SYN cookies can't defend
5766			 * against this problem. So, we drop the data
5767			 * in the interest of security over speed unless
5768			 * it's still in use.
5769			 */
5770			kfree_skb(skb);
5771			return 0;
5772		}
5773		goto discard;
5774
5775	case TCP_SYN_SENT:
5776		queued = tcp_rcv_synsent_state_process(sk, skb, th, len);
5777		if (queued >= 0)
5778			return queued;
5779
5780		/* Do step6 onward by hand. */
5781		tcp_urg(sk, skb, th);
5782		__kfree_skb(skb);
5783		tcp_data_snd_check(sk);
5784		return 0;
5785	}
5786
5787	res = tcp_validate_incoming(sk, skb, th, 0);
5788	if (res <= 0)
5789		return -res;
5790
5791	/* step 5: check the ACK field */
5792	if (th->ack) {
5793		int acceptable = tcp_ack(sk, skb, FLAG_SLOWPATH) > 0;
5794
5795		switch (sk->sk_state) {
5796		case TCP_SYN_RECV:
5797			if (acceptable) {
5798				tp->copied_seq = tp->rcv_nxt;
5799				smp_mb();
5800				tcp_set_state(sk, TCP_ESTABLISHED);
5801				sk->sk_state_change(sk);
5802
5803				/* Note, that this wakeup is only for marginal
5804				 * crossed SYN case. Passively open sockets
5805				 * are not waked up, because sk->sk_sleep ==
5806				 * NULL and sk->sk_socket == NULL.
5807				 */
5808				if (sk->sk_socket)
5809					sk_wake_async(sk,
5810						      SOCK_WAKE_IO, POLL_OUT);
5811
5812				tp->snd_una = TCP_SKB_CB(skb)->ack_seq;
5813				tp->snd_wnd = ntohs(th->window) <<
5814					      tp->rx_opt.snd_wscale;
5815				tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);
5816
5817				if (tp->rx_opt.tstamp_ok)
5818					tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;
5819
5820				/* Make sure socket is routed, for
5821				 * correct metrics.
5822				 */
5823				icsk->icsk_af_ops->rebuild_header(sk);
5824
5825				tcp_init_metrics(sk);
5826
5827				tcp_init_congestion_control(sk);
5828
5829				/* Prevent spurious tcp_cwnd_restart() on
5830				 * first data packet.
5831				 */
5832				tp->lsndtime = tcp_time_stamp;
5833
5834				tcp_mtup_init(sk);
5835				tcp_initialize_rcv_mss(sk);
5836				tcp_init_buffer_space(sk);
5837				tcp_fast_path_on(tp);
5838			} else {
5839				return 1;
5840			}
5841			break;
5842
5843		case TCP_FIN_WAIT1:
5844			if (tp->snd_una == tp->write_seq) {
5845				tcp_set_state(sk, TCP_FIN_WAIT2);
5846				sk->sk_shutdown |= SEND_SHUTDOWN;
5847				dst_confirm(__sk_dst_get(sk));
5848
5849				if (!sock_flag(sk, SOCK_DEAD))
5850					/* Wake up lingering close() */
5851					sk->sk_state_change(sk);
5852				else {
5853					int tmo;
5854
5855					if (tp->linger2 < 0 ||
5856					    (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
5857					     after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt))) {
5858						tcp_done(sk);
5859						NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
5860						return 1;
5861					}
5862
5863					tmo = tcp_fin_time(sk);
5864					if (tmo > TCP_TIMEWAIT_LEN) {
5865						inet_csk_reset_keepalive_timer(sk, tmo - TCP_TIMEWAIT_LEN);
5866					} else if (th->fin || sock_owned_by_user(sk)) {
5867						/* Bad case. We could lose such FIN otherwise.
5868						 * It is not a big problem, but it looks confusing
5869						 * and not so rare event. We still can lose it now,
5870						 * if it spins in bh_lock_sock(), but it is really
5871						 * marginal case.
5872						 */
5873						inet_csk_reset_keepalive_timer(sk, tmo);
5874					} else {
5875						tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
5876						goto discard;
5877					}
5878				}
5879			}
5880			break;
5881
5882		case TCP_CLOSING:
5883			if (tp->snd_una == tp->write_seq) {
5884				tcp_time_wait(sk, TCP_TIME_WAIT, 0);
5885				goto discard;
5886			}
5887			break;
5888
5889		case TCP_LAST_ACK:
5890			if (tp->snd_una == tp->write_seq) {
5891				tcp_update_metrics(sk);
5892				tcp_done(sk);
5893				goto discard;
5894			}
5895			break;
5896		}
5897	} else
5898		goto discard;
5899
5900	/* step 6: check the URG bit */
5901	tcp_urg(sk, skb, th);
5902
5903	/* step 7: process the segment text */
5904	switch (sk->sk_state) {
5905	case TCP_CLOSE_WAIT:
5906	case TCP_CLOSING:
5907	case TCP_LAST_ACK:
5908		if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
5909			break;
5910	case TCP_FIN_WAIT1:
5911	case TCP_FIN_WAIT2:
5912		/* RFC 793 says to queue data in these states,
5913		 * RFC 1122 says we MUST send a reset.
5914		 * BSD 4.4 also does reset.
5915		 */
5916		if (sk->sk_shutdown & RCV_SHUTDOWN) {
5917			if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
5918			    after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) {
5919				NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
5920				tcp_reset(sk);
5921				return 1;
5922			}
5923		}
5924		/* Fall through */
5925	case TCP_ESTABLISHED:
5926		tcp_data_queue(sk, skb);
5927		queued = 1;
5928		break;
5929	}
5930
5931	/* tcp_data could move socket to TIME-WAIT */
5932	if (sk->sk_state != TCP_CLOSE) {
5933		tcp_data_snd_check(sk);
5934		tcp_ack_snd_check(sk);
5935	}
5936
5937	if (!queued) {
5938discard:
5939		__kfree_skb(skb);
5940	}
5941	return 0;
5942}
5943EXPORT_SYMBOL(tcp_rcv_state_process);