Linux/net/ipv4/tcp_input.c

  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/module.h>
 66 #include <linux/sysctl.h>
 67 #include <linux/kernel.h>
 68 #include <net/dst.h>
 69 #include <net/tcp.h>
 70 #include <net/inet_common.h>
 71 #include <linux/ipsec.h>
 72 #include <asm/unaligned.h>
 73 #include <net/netdma.h>
 74 
 75 int sysctl_tcp_timestamps __read_mostly = 1;
 76 int sysctl_tcp_window_scaling __read_mostly = 1;
 77 int sysctl_tcp_sack __read_mostly = 1;
 78 int sysctl_tcp_fack __read_mostly = 1;
 79 int sysctl_tcp_reordering __read_mostly = TCP_FASTRETRANS_THRESH;
 80 int sysctl_tcp_ecn __read_mostly = 2;
 81 int sysctl_tcp_dsack __read_mostly = 1;
 82 int sysctl_tcp_app_win __read_mostly = 31;
 83 int sysctl_tcp_adv_win_scale __read_mostly = 2;
 84 
 85 int sysctl_tcp_stdurg __read_mostly;
 86 int sysctl_tcp_rfc1337 __read_mostly;
 87 int sysctl_tcp_max_orphans __read_mostly = NR_FILE;
 88 int sysctl_tcp_frto __read_mostly = 2;
 89 int sysctl_tcp_frto_response __read_mostly;
 90 int sysctl_tcp_nometrics_save __read_mostly;
 91 
 92 int sysctl_tcp_moderate_rcvbuf __read_mostly = 1;
 93 int sysctl_tcp_abc __read_mostly;
 94 
 95 #define FLAG_DATA               0x01 /* Incoming frame contained data.          */
 96 #define FLAG_WIN_UPDATE         0x02 /* Incoming ACK was a window update.       */
 97 #define FLAG_DATA_ACKED         0x04 /* This ACK acknowledged new data.         */
 98 #define FLAG_RETRANS_DATA_ACKED 0x08 /* "" "" some of which was retransmitted.  */
 99 #define FLAG_SYN_ACKED          0x10 /* This ACK acknowledged SYN.              */
100 #define FLAG_DATA_SACKED        0x20 /* New SACK.                               */
101 #define FLAG_ECE                0x40 /* ECE in this ACK                         */
102 #define FLAG_DATA_LOST          0x80 /* SACK detected data lossage.             */
103 #define FLAG_SLOWPATH           0x100 /* Do not skip RFC checks for window update.*/
104 #define FLAG_ONLY_ORIG_SACKED   0x200 /* SACKs only non-rexmit sent before RTO */
105 #define FLAG_SND_UNA_ADVANCED   0x400 /* Snd_una was changed (!= FLAG_DATA_ACKED) */
106 #define FLAG_DSACKING_ACK       0x800 /* SACK blocks contained D-SACK info */
107 #define FLAG_NONHEAD_RETRANS_ACKED      0x1000 /* Non-head rexmitted data was ACKed */
108 #define FLAG_SACK_RENEGING      0x2000 /* snd_una advanced to a sacked seq */
109 
110 #define FLAG_ACKED              (FLAG_DATA_ACKED|FLAG_SYN_ACKED)
111 #define FLAG_NOT_DUP            (FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED)
112 #define FLAG_CA_ALERT           (FLAG_DATA_SACKED|FLAG_ECE)
113 #define FLAG_FORWARD_PROGRESS   (FLAG_ACKED|FLAG_DATA_SACKED)
114 #define FLAG_ANY_PROGRESS       (FLAG_FORWARD_PROGRESS|FLAG_SND_UNA_ADVANCED)
115 
116 #define TCP_REMNANT (TCP_FLAG_FIN|TCP_FLAG_URG|TCP_FLAG_SYN|TCP_FLAG_PSH)
117 #define TCP_HP_BITS (~(TCP_RESERVED_BITS|TCP_FLAG_PSH))
118 
119 /* Adapt the MSS value used to make delayed ack decision to the
120  * real world.
121  */
122 static void tcp_measure_rcv_mss(struct sock *sk, const struct sk_buff *skb)
123 {
124         struct inet_connection_sock *icsk = inet_csk(sk);
125         const unsigned int lss = icsk->icsk_ack.last_seg_size;
126         unsigned int len;
127 
128         icsk->icsk_ack.last_seg_size = 0;
129 
130         /* skb->len may jitter because of SACKs, even if peer
131          * sends good full-sized frames.
132          */
133         len = skb_shinfo(skb)->gso_size ? : skb->len;
134         if (len >= icsk->icsk_ack.rcv_mss) {
135                 icsk->icsk_ack.rcv_mss = len;
136         } else {
137                 /* Otherwise, we make more careful check taking into account,
138                  * that SACKs block is variable.
139                  *
140                  * "len" is invariant segment length, including TCP header.
141                  */
142                 len += skb->data - skb_transport_header(skb);
143                 if (len >= TCP_MIN_RCVMSS + sizeof(struct tcphdr) ||
144                     /* If PSH is not set, packet should be
145                      * full sized, provided peer TCP is not badly broken.
146                      * This observation (if it is correct 8)) allows
147                      * to handle super-low mtu links fairly.
148                      */
149                     (len >= TCP_MIN_MSS + sizeof(struct tcphdr) &&
150                      !(tcp_flag_word(tcp_hdr(skb)) & TCP_REMNANT))) {
151                         /* Subtract also invariant (if peer is RFC compliant),
152                          * tcp header plus fixed timestamp option length.
153                          * Resulting "len" is MSS free of SACK jitter.
154                          */
155                         len -= tcp_sk(sk)->tcp_header_len;
156                         icsk->icsk_ack.last_seg_size = len;
157                         if (len == lss) {
158                                 icsk->icsk_ack.rcv_mss = len;
159                                 return;
160                         }
161                 }
162                 if (icsk->icsk_ack.pending & ICSK_ACK_PUSHED)
163                         icsk->icsk_ack.pending |= ICSK_ACK_PUSHED2;
164                 icsk->icsk_ack.pending |= ICSK_ACK_PUSHED;
165         }
166 }
167 
168 static void tcp_incr_quickack(struct sock *sk)
169 {
170         struct inet_connection_sock *icsk = inet_csk(sk);
171         unsigned quickacks = tcp_sk(sk)->rcv_wnd / (2 * icsk->icsk_ack.rcv_mss);
172 
173         if (quickacks == 0)
174                 quickacks = 2;
175         if (quickacks > icsk->icsk_ack.quick)
176                 icsk->icsk_ack.quick = min(quickacks, TCP_MAX_QUICKACKS);
177 }
178 
179 void tcp_enter_quickack_mode(struct sock *sk)
180 {
181         struct inet_connection_sock *icsk = inet_csk(sk);
182         tcp_incr_quickack(sk);
183         icsk->icsk_ack.pingpong = 0;
184         icsk->icsk_ack.ato = TCP_ATO_MIN;
185 }
186 
187 /* Send ACKs quickly, if "quick" count is not exhausted
188  * and the session is not interactive.
189  */
190 
191 static inline int tcp_in_quickack_mode(const struct sock *sk)
192 {
193         const struct inet_connection_sock *icsk = inet_csk(sk);
194         return icsk->icsk_ack.quick && !icsk->icsk_ack.pingpong;
195 }
196 
197 static inline void TCP_ECN_queue_cwr(struct tcp_sock *tp)
198 {
199         if (tp->ecn_flags & TCP_ECN_OK)
200                 tp->ecn_flags |= TCP_ECN_QUEUE_CWR;
201 }
202 
203 static inline void TCP_ECN_accept_cwr(struct tcp_sock *tp, struct sk_buff *skb)
204 {
205         if (tcp_hdr(skb)->cwr)
206                 tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
207 }
208 
209 static inline void TCP_ECN_withdraw_cwr(struct tcp_sock *tp)
210 {
211         tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
212 }
213 
214 static inline void TCP_ECN_check_ce(struct tcp_sock *tp, struct sk_buff *skb)
215 {
216         if (tp->ecn_flags & TCP_ECN_OK) {
217                 if (INET_ECN_is_ce(TCP_SKB_CB(skb)->flags))
218                         tp->ecn_flags |= TCP_ECN_DEMAND_CWR;
219                 /* Funny extension: if ECT is not set on a segment,
220                  * it is surely retransmit. It is not in ECN RFC,
221                  * but Linux follows this rule. */
222                 else if (INET_ECN_is_not_ect((TCP_SKB_CB(skb)->flags)))
223                         tcp_enter_quickack_mode((struct sock *)tp);
224         }
225 }
226 
227 static inline void TCP_ECN_rcv_synack(struct tcp_sock *tp, struct tcphdr *th)
228 {
229         if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || th->cwr))
230                 tp->ecn_flags &= ~TCP_ECN_OK;
231 }
232 
233 static inline void TCP_ECN_rcv_syn(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 
239 static inline int TCP_ECN_rcv_ecn_echo(struct tcp_sock *tp, struct tcphdr *th)
240 {
241         if (th->ece && !th->syn && (tp->ecn_flags & TCP_ECN_OK))
242                 return 1;
243         return 0;
244 }
245 
246 /* Buffer size and advertised window tuning.
247  *
248  * 1. Tuning sk->sk_sndbuf, when connection enters established state.
249  */
250 
251 static void tcp_fixup_sndbuf(struct sock *sk)
252 {
253         int sndmem = tcp_sk(sk)->rx_opt.mss_clamp + MAX_TCP_HEADER + 16 +
254                      sizeof(struct sk_buff);
255 
256         if (sk->sk_sndbuf < 3 * sndmem)
257                 sk->sk_sndbuf = min(3 * sndmem, sysctl_tcp_wmem[2]);
258 }
259 
260 /* 2. Tuning advertised window (window_clamp, rcv_ssthresh)
261  *
262  * All tcp_full_space() is split to two parts: "network" buffer, allocated
263  * forward and advertised in receiver window (tp->rcv_wnd) and
264  * "application buffer", required to isolate scheduling/application
265  * latencies from network.
266  * window_clamp is maximal advertised window. It can be less than
267  * tcp_full_space(), in this case tcp_full_space() - window_clamp
268  * is reserved for "application" buffer. The less window_clamp is
269  * the smoother our behaviour from viewpoint of network, but the lower
270  * throughput and the higher sensitivity of the connection to losses. 8)
271  *
272  * rcv_ssthresh is more strict window_clamp used at "slow start"
273  * phase to predict further behaviour of this connection.
274  * It is used for two goals:
275  * - to enforce header prediction at sender, even when application
276  *   requires some significant "application buffer". It is check #1.
277  * - to prevent pruning of receive queue because of misprediction
278  *   of receiver window. Check #2.
279  *
280  * The scheme does not work when sender sends good segments opening
281  * window and then starts to feed us spaghetti. But it should work
282  * in common situations. Otherwise, we have to rely on queue collapsing.
283  */
284 
285 /* Slow part of check#2. */
286 static int __tcp_grow_window(const struct sock *sk, const struct sk_buff *skb)
287 {
288         struct tcp_sock *tp = tcp_sk(sk);
289         /* Optimize this! */
290         int truesize = tcp_win_from_space(skb->truesize) >> 1;
291         int window = tcp_win_from_space(sysctl_tcp_rmem[2]) >> 1;
292 
293         while (tp->rcv_ssthresh <= window) {
294                 if (truesize <= skb->len)
295                         return 2 * inet_csk(sk)->icsk_ack.rcv_mss;
296 
297                 truesize >>= 1;
298                 window >>= 1;
299         }
300         return 0;
301 }
302 
303 static void tcp_grow_window(struct sock *sk, struct sk_buff *skb)
304 {
305         struct tcp_sock *tp = tcp_sk(sk);
306 
307         /* Check #1 */
308         if (tp->rcv_ssthresh < tp->window_clamp &&
309             (int)tp->rcv_ssthresh < tcp_space(sk) &&
310             !tcp_memory_pressure) {
311                 int incr;
312 
313                 /* Check #2. Increase window, if skb with such overhead
314                  * will fit to rcvbuf in future.
315                  */
316                 if (tcp_win_from_space(skb->truesize) <= skb->len)
317                         incr = 2 * tp->advmss;
318                 else
319                         incr = __tcp_grow_window(sk, skb);
320 
321                 if (incr) {
322                         tp->rcv_ssthresh = min(tp->rcv_ssthresh + incr,
323                                                tp->window_clamp);
324                         inet_csk(sk)->icsk_ack.quick |= 1;
325                 }
326         }
327 }
328 
329 /* 3. Tuning rcvbuf, when connection enters established state. */
330 
331 static void tcp_fixup_rcvbuf(struct sock *sk)
332 {
333         struct tcp_sock *tp = tcp_sk(sk);
334         int rcvmem = tp->advmss + MAX_TCP_HEADER + 16 + sizeof(struct sk_buff);
335 
336         /* Try to select rcvbuf so that 4 mss-sized segments
337          * will fit to window and corresponding skbs will fit to our rcvbuf.
338          * (was 3; 4 is minimum to allow fast retransmit to work.)
339          */
340         while (tcp_win_from_space(rcvmem) < tp->advmss)
341                 rcvmem += 128;
342         if (sk->sk_rcvbuf < 4 * rcvmem)
343                 sk->sk_rcvbuf = min(4 * rcvmem, sysctl_tcp_rmem[2]);
344 }
345 
346 /* 4. Try to fixup all. It is made immediately after connection enters
347  *    established state.
348  */
349 static void tcp_init_buffer_space(struct sock *sk)
350 {
351         struct tcp_sock *tp = tcp_sk(sk);
352         int maxwin;
353 
354         if (!(sk->sk_userlocks & SOCK_RCVBUF_LOCK))
355                 tcp_fixup_rcvbuf(sk);
356         if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK))
357                 tcp_fixup_sndbuf(sk);
358 
359         tp->rcvq_space.space = tp->rcv_wnd;
360 
361         maxwin = tcp_full_space(sk);
362 
363         if (tp->window_clamp >= maxwin) {
364                 tp->window_clamp = maxwin;
365 
366                 if (sysctl_tcp_app_win && maxwin > 4 * tp->advmss)
367                         tp->window_clamp = max(maxwin -
368                                                (maxwin >> sysctl_tcp_app_win),
369                                                4 * tp->advmss);
370         }
371 
372         /* Force reservation of one segment. */
373         if (sysctl_tcp_app_win &&
374             tp->window_clamp > 2 * tp->advmss &&
375             tp->window_clamp + tp->advmss > maxwin)
376                 tp->window_clamp = max(2 * tp->advmss, maxwin - tp->advmss);
377 
378         tp->rcv_ssthresh = min(tp->rcv_ssthresh, tp->window_clamp);
379         tp->snd_cwnd_stamp = tcp_time_stamp;
380 }
381 
382 /* 5. Recalculate window clamp after socket hit its memory bounds. */
383 static void tcp_clamp_window(struct sock *sk)
384 {
385         struct tcp_sock *tp = tcp_sk(sk);
386         struct inet_connection_sock *icsk = inet_csk(sk);
387 
388         icsk->icsk_ack.quick = 0;
389 
390         if (sk->sk_rcvbuf < sysctl_tcp_rmem[2] &&
391             !(sk->sk_userlocks & SOCK_RCVBUF_LOCK) &&
392             !tcp_memory_pressure &&
393             atomic_read(&tcp_memory_allocated) < sysctl_tcp_mem[0]) {
394                 sk->sk_rcvbuf = min(atomic_read(&sk->sk_rmem_alloc),
395                                     sysctl_tcp_rmem[2]);
396         }
397         if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf)
398                 tp->rcv_ssthresh = min(tp->window_clamp, 2U * tp->advmss);
399 }
400 
401 /* Initialize RCV_MSS value.
402  * RCV_MSS is an our guess about MSS used by the peer.
403  * We haven't any direct information about the MSS.
404  * It's better to underestimate the RCV_MSS rather than overestimate.
405  * Overestimations make us ACKing less frequently than needed.
406  * Underestimations are more easy to detect and fix by tcp_measure_rcv_mss().
407  */
408 void tcp_initialize_rcv_mss(struct sock *sk)
409 {
410         struct tcp_sock *tp = tcp_sk(sk);
411         unsigned int hint = min_t(unsigned int, tp->advmss, tp->mss_cache);
412 
413         hint = min(hint, tp->rcv_wnd / 2);
414         hint = min(hint, TCP_MIN_RCVMSS);
415         hint = max(hint, TCP_MIN_MSS);
416 
417         inet_csk(sk)->icsk_ack.rcv_mss = hint;
418 }
419 
420 /* Receiver "autotuning" code.
421  *
422  * The algorithm for RTT estimation w/o timestamps is based on
423  * Dynamic Right-Sizing (DRS) by Wu Feng and Mike Fisk of LANL.
424  * <http://www.lanl.gov/radiant/website/pubs/drs/lacsi2001.ps>
425  *
426  * More detail on this code can be found at
427  * <http://www.psc.edu/~jheffner/senior_thesis.ps>,
428  * though this reference is out of date.  A new paper
429  * is pending.
430  */
431 static void tcp_rcv_rtt_update(struct tcp_sock *tp, u32 sample, int win_dep)
432 {
433         u32 new_sample = tp->rcv_rtt_est.rtt;
434         long m = sample;
435 
436         if (m == 0)
437                 m = 1;
438 
439         if (new_sample != 0) {
440                 /* If we sample in larger samples in the non-timestamp
441                  * case, we could grossly overestimate the RTT especially
442                  * with chatty applications or bulk transfer apps which
443                  * are stalled on filesystem I/O.
444                  *
445                  * Also, since we are only going for a minimum in the
446                  * non-timestamp case, we do not smooth things out
447                  * else with timestamps disabled convergence takes too
448                  * long.
449                  */
450                 if (!win_dep) {
451                         m -= (new_sample >> 3);
452                         new_sample += m;
453                 } else if (m < new_sample)
454                         new_sample = m << 3;
455         } else {
456                 /* No previous measure. */
457                 new_sample = m << 3;
458         }
459 
460         if (tp->rcv_rtt_est.rtt != new_sample)
461                 tp->rcv_rtt_est.rtt = new_sample;
462 }
463 
464 static inline void tcp_rcv_rtt_measure(struct tcp_sock *tp)
465 {
466         if (tp->rcv_rtt_est.time == 0)
467                 goto new_measure;
468         if (before(tp->rcv_nxt, tp->rcv_rtt_est.seq))
469                 return;
470         tcp_rcv_rtt_update(tp, jiffies - tp->rcv_rtt_est.time, 1);
471 
472 new_measure:
473         tp->rcv_rtt_est.seq = tp->rcv_nxt + tp->rcv_wnd;
474         tp->rcv_rtt_est.time = tcp_time_stamp;
475 }
476 
477 static inline void tcp_rcv_rtt_measure_ts(struct sock *sk,
478                                           const struct sk_buff *skb)
479 {
480         struct tcp_sock *tp = tcp_sk(sk);
481         if (tp->rx_opt.rcv_tsecr &&
482             (TCP_SKB_CB(skb)->end_seq -
483              TCP_SKB_CB(skb)->seq >= inet_csk(sk)->icsk_ack.rcv_mss))
484                 tcp_rcv_rtt_update(tp, tcp_time_stamp - tp->rx_opt.rcv_tsecr, 0);
485 }
486 
487 /*
488  * This function should be called every time data is copied to user space.
489  * It calculates the appropriate TCP receive buffer space.
490  */
491 void tcp_rcv_space_adjust(struct sock *sk)
492 {
493         struct tcp_sock *tp = tcp_sk(sk);
494         int time;
495         int space;
496 
497         if (tp->rcvq_space.time == 0)
498                 goto new_measure;
499 
500         time = tcp_time_stamp - tp->rcvq_space.time;
501         if (time < (tp->rcv_rtt_est.rtt >> 3) || tp->rcv_rtt_est.rtt == 0)
502                 return;
503 
504         space = 2 * (tp->copied_seq - tp->rcvq_space.seq);
505 
506         space = max(tp->rcvq_space.space, space);
507 
508         if (tp->rcvq_space.space != space) {
509                 int rcvmem;
510 
511                 tp->rcvq_space.space = space;
512 
513                 if (sysctl_tcp_moderate_rcvbuf &&
514                     !(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) {
515                         int new_clamp = space;
516 
517                         /* Receive space grows, normalize in order to
518                          * take into account packet headers and sk_buff
519                          * structure overhead.
520                          */
521                         space /= tp->advmss;
522                         if (!space)
523                                 space = 1;
524                         rcvmem = (tp->advmss + MAX_TCP_HEADER +
525                                   16 + sizeof(struct sk_buff));
526                         while (tcp_win_from_space(rcvmem) < tp->advmss)
527                                 rcvmem += 128;
528                         space *= rcvmem;
529                         space = min(space, sysctl_tcp_rmem[2]);
530                         if (space > sk->sk_rcvbuf) {
531                                 sk->sk_rcvbuf = space;
532 
533                                 /* Make the window clamp follow along.  */
534                                 tp->window_clamp = new_clamp;
535                         }
536                 }
537         }
538 
539 new_measure:
540         tp->rcvq_space.seq = tp->copied_seq;
541         tp->rcvq_space.time = tcp_time_stamp;
542 }
543 
544 /* There is something which you must keep in mind when you analyze the
545  * behavior of the tp->ato delayed ack timeout interval.  When a
546  * connection starts up, we want to ack as quickly as possible.  The
547  * problem is that "good" TCP's do slow start at the beginning of data
548  * transmission.  The means that until we send the first few ACK's the
549  * sender will sit on his end and only queue most of his data, because
550  * he can only send snd_cwnd unacked packets at any given time.  For
551  * each ACK we send, he increments snd_cwnd and transmits more of his
552  * queue.  -DaveM
553  */
554 static void tcp_event_data_recv(struct sock *sk, struct sk_buff *skb)
555 {
556         struct tcp_sock *tp = tcp_sk(sk);
557         struct inet_connection_sock *icsk = inet_csk(sk);
558         u32 now;
559 
560         inet_csk_schedule_ack(sk);
561 
562         tcp_measure_rcv_mss(sk, skb);
563 
564         tcp_rcv_rtt_measure(tp);
565 
566         now = tcp_time_stamp;
567 
568         if (!icsk->icsk_ack.ato) {
569                 /* The _first_ data packet received, initialize
570                  * delayed ACK engine.
571                  */
572                 tcp_incr_quickack(sk);
573                 icsk->icsk_ack.ato = TCP_ATO_MIN;
574         } else {
575                 int m = now - icsk->icsk_ack.lrcvtime;
576 
577                 if (m <= TCP_ATO_MIN / 2) {
578                         /* The fastest case is the first. */
579                         icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + TCP_ATO_MIN / 2;
580                 } else if (m < icsk->icsk_ack.ato) {
581                         icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + m;
582                         if (icsk->icsk_ack.ato > icsk->icsk_rto)
583                                 icsk->icsk_ack.ato = icsk->icsk_rto;
584                 } else if (m > icsk->icsk_rto) {
585                         /* Too long gap. Apparently sender failed to
586                          * restart window, so that we send ACKs quickly.
587                          */
588                         tcp_incr_quickack(sk);
589                         sk_mem_reclaim(sk);
590                 }
591         }
592         icsk->icsk_ack.lrcvtime = now;
593 
594         TCP_ECN_check_ce(tp, skb);
595 
596         if (skb->len >= 128)
597                 tcp_grow_window(sk, skb);
598 }
599 
600 /* Called to compute a smoothed rtt estimate. The data fed to this
601  * routine either comes from timestamps, or from segments that were
602  * known _not_ to have been retransmitted [see Karn/Partridge
603  * Proceedings SIGCOMM 87]. The algorithm is from the SIGCOMM 88
604  * piece by Van Jacobson.
605  * NOTE: the next three routines used to be one big routine.
606  * To save cycles in the RFC 1323 implementation it was better to break
607  * it up into three procedures. -- erics
608  */
609 static void tcp_rtt_estimator(struct sock *sk, const __u32 mrtt)
610 {
611         struct tcp_sock *tp = tcp_sk(sk);
612         long m = mrtt; /* RTT */
613 
614         /*      The following amusing code comes from Jacobson's
615          *      article in SIGCOMM '88.  Note that rtt and mdev
616          *      are scaled versions of rtt and mean deviation.
617          *      This is designed to be as fast as possible
618          *      m stands for "measurement".
619          *
620          *      On a 1990 paper the rto value is changed to:
621          *      RTO = rtt + 4 * mdev
622          *
623          * Funny. This algorithm seems to be very broken.
624          * These formulae increase RTO, when it should be decreased, increase
625          * too slowly, when it should be increased quickly, decrease too quickly
626          * etc. I guess in BSD RTO takes ONE value, so that it is absolutely
627          * does not matter how to _calculate_ it. Seems, it was trap
628          * that VJ failed to avoid. 8)
629          */
630         if (m == 0)
631                 m = 1;
632         if (tp->srtt != 0) {
633                 m -= (tp->srtt >> 3);   /* m is now error in rtt est */
634                 tp->srtt += m;          /* rtt = 7/8 rtt + 1/8 new */
635                 if (m < 0) {
636                         m = -m;         /* m is now abs(error) */
637                         m -= (tp->mdev >> 2);   /* similar update on mdev */
638                         /* This is similar to one of Eifel findings.
639                          * Eifel blocks mdev updates when rtt decreases.
640                          * This solution is a bit different: we use finer gain
641                          * for mdev in this case (alpha*beta).
642                          * Like Eifel it also prevents growth of rto,
643                          * but also it limits too fast rto decreases,
644                          * happening in pure Eifel.
645                          */
646                         if (m > 0)
647                                 m >>= 3;
648                 } else {
649                         m -= (tp->mdev >> 2);   /* similar update on mdev */
650                 }
651                 tp->mdev += m;          /* mdev = 3/4 mdev + 1/4 new */
652                 if (tp->mdev > tp->mdev_max) {
653                         tp->mdev_max = tp->mdev;
654                         if (tp->mdev_max > tp->rttvar)
655                                 tp->rttvar = tp->mdev_max;
656                 }
657                 if (after(tp->snd_una, tp->rtt_seq)) {
658                         if (tp->mdev_max < tp->rttvar)
659                                 tp->rttvar -= (tp->rttvar - tp->mdev_max) >> 2;
660                         tp->rtt_seq = tp->snd_nxt;
661                         tp->mdev_max = tcp_rto_min(sk);
662                 }
663         } else {
664                 /* no previous measure. */
665                 tp->srtt = m << 3;      /* take the measured time to be rtt */
666                 tp->mdev = m << 1;      /* make sure rto = 3*rtt */
667                 tp->mdev_max = tp->rttvar = max(tp->mdev, tcp_rto_min(sk));
668                 tp->rtt_seq = tp->snd_nxt;
669         }
670 }
671 
672 /* Calculate rto without backoff.  This is the second half of Van Jacobson's
673  * routine referred to above.
674  */
675 static inline void tcp_set_rto(struct sock *sk)
676 {
677         const struct tcp_sock *tp = tcp_sk(sk);
678         /* Old crap is replaced with new one. 8)
679          *
680          * More seriously:
681          * 1. If rtt variance happened to be less 50msec, it is hallucination.
682          *    It cannot be less due to utterly erratic ACK generation made
683          *    at least by solaris and freebsd. "Erratic ACKs" has _nothing_
684          *    to do with delayed acks, because at cwnd>2 true delack timeout
685          *    is invisible. Actually, Linux-2.4 also generates erratic
686          *    ACKs in some circumstances.
687          */
688         inet_csk(sk)->icsk_rto = __tcp_set_rto(tp);
689 
690         /* 2. Fixups made earlier cannot be right.
691          *    If we do not estimate RTO correctly without them,
692          *    all the algo is pure shit and should be replaced
693          *    with correct one. It is exactly, which we pretend to do.
694          */
695 
696         /* NOTE: clamping at TCP_RTO_MIN is not required, current algo
697          * guarantees that rto is higher.
698          */
699         tcp_bound_rto(sk);
700 }
701 
702 /* Save metrics learned by this TCP session.
703    This function is called only, when TCP finishes successfully
704    i.e. when it enters TIME-WAIT or goes from LAST-ACK to CLOSE.
705  */
706 void tcp_update_metrics(struct sock *sk)
707 {
708         struct tcp_sock *tp = tcp_sk(sk);
709         struct dst_entry *dst = __sk_dst_get(sk);
710 
711         if (sysctl_tcp_nometrics_save)
712                 return;
713 
714         dst_confirm(dst);
715 
716         if (dst && (dst->flags & DST_HOST)) {
717                 const struct inet_connection_sock *icsk = inet_csk(sk);
718                 int m;
719                 unsigned long rtt;
720 
721                 if (icsk->icsk_backoff || !tp->srtt) {
722                         /* This session failed to estimate rtt. Why?
723                          * Probably, no packets returned in time.
724                          * Reset our results.
725                          */
726                         if (!(dst_metric_locked(dst, RTAX_RTT)))
727                                 dst->metrics[RTAX_RTT - 1] = 0;
728                         return;
729                 }
730 
731                 rtt = dst_metric_rtt(dst, RTAX_RTT);
732                 m = rtt - tp->srtt;
733 
734                 /* If newly calculated rtt larger than stored one,
735                  * store new one. Otherwise, use EWMA. Remember,
736                  * rtt overestimation is always better than underestimation.
737                  */
738                 if (!(dst_metric_locked(dst, RTAX_RTT))) {
739                         if (m <= 0)
740                                 set_dst_metric_rtt(dst, RTAX_RTT, tp->srtt);
741                         else
742                                 set_dst_metric_rtt(dst, RTAX_RTT, rtt - (m >> 3));
743                 }
744 
745                 if (!(dst_metric_locked(dst, RTAX_RTTVAR))) {
746                         unsigned long var;
747                         if (m < 0)
748                                 m = -m;
749 
750                         /* Scale deviation to rttvar fixed point */
751                         m >>= 1;
752                         if (m < tp->mdev)
753                                 m = tp->mdev;
754 
755                         var = dst_metric_rtt(dst, RTAX_RTTVAR);
756                         if (m >= var)
757                                 var = m;
758                         else
759                                 var -= (var - m) >> 2;
760 
761                         set_dst_metric_rtt(dst, RTAX_RTTVAR, var);
762                 }
763 
764                 if (tcp_in_initial_slowstart(tp)) {
765                         /* Slow start still did not finish. */
766                         if (dst_metric(dst, RTAX_SSTHRESH) &&
767                             !dst_metric_locked(dst, RTAX_SSTHRESH) &&
768                             (tp->snd_cwnd >> 1) > dst_metric(dst, RTAX_SSTHRESH))
769                                 dst->metrics[RTAX_SSTHRESH-1] = tp->snd_cwnd >> 1;
770                         if (!dst_metric_locked(dst, RTAX_CWND) &&
771                             tp->snd_cwnd > dst_metric(dst, RTAX_CWND))
772                                 dst->metrics[RTAX_CWND - 1] = tp->snd_cwnd;
773                 } else if (tp->snd_cwnd > tp->snd_ssthresh &&
774                            icsk->icsk_ca_state == TCP_CA_Open) {
775                         /* Cong. avoidance phase, cwnd is reliable. */
776                         if (!dst_metric_locked(dst, RTAX_SSTHRESH))
777                                 dst->metrics[RTAX_SSTHRESH-1] =
778                                         max(tp->snd_cwnd >> 1, tp->snd_ssthresh);
779                         if (!dst_metric_locked(dst, RTAX_CWND))
780                                 dst->metrics[RTAX_CWND-1] = (dst_metric(dst, RTAX_CWND) + tp->snd_cwnd) >> 1;
781                 } else {
782                         /* Else slow start did not finish, cwnd is non-sense,
783                            ssthresh may be also invalid.
784                          */
785                         if (!dst_metric_locked(dst, RTAX_CWND))
786                                 dst->metrics[RTAX_CWND-1] = (dst_metric(dst, RTAX_CWND) + tp->snd_ssthresh) >> 1;
787                         if (dst_metric(dst, RTAX_SSTHRESH) &&
788                             !dst_metric_locked(dst, RTAX_SSTHRESH) &&
789                             tp->snd_ssthresh > dst_metric(dst, RTAX_SSTHRESH))
790                                 dst->metrics[RTAX_SSTHRESH-1] = tp->snd_ssthresh;
791                 }
792 
793                 if (!dst_metric_locked(dst, RTAX_REORDERING)) {
794                         if (dst_metric(dst, RTAX_REORDERING) < tp->reordering &&
795                             tp->reordering != sysctl_tcp_reordering)
796                                 dst->metrics[RTAX_REORDERING-1] = tp->reordering;
797                 }
798         }
799 }
800 
801 /* Numbers are taken from RFC3390.
802  *
803  * John Heffner states:
804  *
805  *      The RFC specifies a window of no more than 4380 bytes
806  *      unless 2*MSS > 4380.  Reading the pseudocode in the RFC
807  *      is a bit misleading because they use a clamp at 4380 bytes
808  *      rather than use a multiplier in the relevant range.
809  */
810 __u32 tcp_init_cwnd(struct tcp_sock *tp, struct dst_entry *dst)
811 {
812         __u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0);
813 
814         if (!cwnd) {
815                 if (tp->mss_cache > 1460)
816                         cwnd = 2;
817                 else
818                         cwnd = (tp->mss_cache > 1095) ? 3 : 4;
819         }
820         return min_t(__u32, cwnd, tp->snd_cwnd_clamp);
821 }
822 
823 /* Set slow start threshold and cwnd not falling to slow start */
824 void tcp_enter_cwr(struct sock *sk, const int set_ssthresh)
825 {
826         struct tcp_sock *tp = tcp_sk(sk);
827         const struct inet_connection_sock *icsk = inet_csk(sk);
828 
829         tp->prior_ssthresh = 0;
830         tp->bytes_acked = 0;
831         if (icsk->icsk_ca_state < TCP_CA_CWR) {
832                 tp->undo_marker = 0;
833                 if (set_ssthresh)
834                         tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
835                 tp->snd_cwnd = min(tp->snd_cwnd,
836                                    tcp_packets_in_flight(tp) + 1U);
837                 tp->snd_cwnd_cnt = 0;
838                 tp->high_seq = tp->snd_nxt;
839                 tp->snd_cwnd_stamp = tcp_time_stamp;
840                 TCP_ECN_queue_cwr(tp);
841 
842                 tcp_set_ca_state(sk, TCP_CA_CWR);
843         }
844 }
845 
846 /*
847  * Packet counting of FACK is based on in-order assumptions, therefore TCP
848  * disables it when reordering is detected
849  */
850 static void tcp_disable_fack(struct tcp_sock *tp)
851 {
852         /* RFC3517 uses different metric in lost marker => reset on change */
853         if (tcp_is_fack(tp))
854                 tp->lost_skb_hint = NULL;
855         tp->rx_opt.sack_ok &= ~2;
856 }
857 
858 /* Take a notice that peer is sending D-SACKs */
859 static void tcp_dsack_seen(struct tcp_sock *tp)
860 {
861         tp->rx_opt.sack_ok |= 4;
862 }
863 
864 /* Initialize metrics on socket. */
865 
866 static void tcp_init_metrics(struct sock *sk)
867 {
868         struct tcp_sock *tp = tcp_sk(sk);
869         struct dst_entry *dst = __sk_dst_get(sk);
870 
871         if (dst == NULL)
872                 goto reset;
873 
874         dst_confirm(dst);
875 
876         if (dst_metric_locked(dst, RTAX_CWND))
877                 tp->snd_cwnd_clamp = dst_metric(dst, RTAX_CWND);
878         if (dst_metric(dst, RTAX_SSTHRESH)) {
879                 tp->snd_ssthresh = dst_metric(dst, RTAX_SSTHRESH);
880                 if (tp->snd_ssthresh > tp->snd_cwnd_clamp)
881                         tp->snd_ssthresh = tp->snd_cwnd_clamp;
882         }
883         if (dst_metric(dst, RTAX_REORDERING) &&
884             tp->reordering != dst_metric(dst, RTAX_REORDERING)) {
885                 tcp_disable_fack(tp);
886                 tp->reordering = dst_metric(dst, RTAX_REORDERING);
887         }
888 
889         if (dst_metric(dst, RTAX_RTT) == 0)
890                 goto reset;
891 
892         if (!tp->srtt && dst_metric_rtt(dst, RTAX_RTT) < (TCP_TIMEOUT_INIT << 3))
893                 goto reset;
894 
895         /* Initial rtt is determined from SYN,SYN-ACK.
896          * The segment is small and rtt may appear much
897          * less than real one. Use per-dst memory
898          * to make it more realistic.
899          *
900          * A bit of theory. RTT is time passed after "normal" sized packet
901          * is sent until it is ACKed. In normal circumstances sending small
902          * packets force peer to delay ACKs and calculation is correct too.
903          * The algorithm is adaptive and, provided we follow specs, it
904          * NEVER underestimate RTT. BUT! If peer tries to make some clever
905          * tricks sort of "quick acks" for time long enough to decrease RTT
906          * to low value, and then abruptly stops to do it and starts to delay
907          * ACKs, wait for troubles.
908          */
909         if (dst_metric_rtt(dst, RTAX_RTT) > tp->srtt) {
910                 tp->srtt = dst_metric_rtt(dst, RTAX_RTT);
911                 tp->rtt_seq = tp->snd_nxt;
912         }
913         if (dst_metric_rtt(dst, RTAX_RTTVAR) > tp->mdev) {
914                 tp->mdev = dst_metric_rtt(dst, RTAX_RTTVAR);
915                 tp->mdev_max = tp->rttvar = max(tp->mdev, tcp_rto_min(sk));
916         }
917         tcp_set_rto(sk);
918         if (inet_csk(sk)->icsk_rto < TCP_TIMEOUT_INIT && !tp->rx_opt.saw_tstamp)
919                 goto reset;
920 
921 cwnd:
922         tp->snd_cwnd = tcp_init_cwnd(tp, dst);
923         tp->snd_cwnd_stamp = tcp_time_stamp;
924         return;
925 
926 reset:
927         /* Play conservative. If timestamps are not
928          * supported, TCP will fail to recalculate correct
929          * rtt, if initial rto is too small. FORGET ALL AND RESET!
930          */
931         if (!tp->rx_opt.saw_tstamp && tp->srtt) {
932                 tp->srtt = 0;
933                 tp->mdev = tp->mdev_max = tp->rttvar = TCP_TIMEOUT_INIT;
934                 inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT;
935         }
936         goto cwnd;
937 }
938 
939 static void tcp_update_reordering(struct sock *sk, const int metric,
940                                   const int ts)
941 {
942         struct tcp_sock *tp = tcp_sk(sk);
943         if (metric > tp->reordering) {
944                 int mib_idx;
945 
946                 tp->reordering = min(TCP_MAX_REORDERING, metric);
947 
948                 /* This exciting event is worth to be remembered. 8) */
949                 if (ts)
950                         mib_idx = LINUX_MIB_TCPTSREORDER;
951                 else if (tcp_is_reno(tp))
952                         mib_idx = LINUX_MIB_TCPRENOREORDER;
953                 else if (tcp_is_fack(tp))
954                         mib_idx = LINUX_MIB_TCPFACKREORDER;
955                 else
956                         mib_idx = LINUX_MIB_TCPSACKREORDER;
957 
958                 NET_INC_STATS_BH(sock_net(sk), mib_idx);
959 #if FASTRETRANS_DEBUG > 1
960                 printk(KERN_DEBUG "Disorder%d %d %u f%u s%u rr%d\n",
961                        tp->rx_opt.sack_ok, inet_csk(sk)->icsk_ca_state,
962                        tp->reordering,
963                        tp->fackets_out,
964                        tp->sacked_out,
965                        tp->undo_marker ? tp->undo_retrans : 0);
966 #endif
967                 tcp_disable_fack(tp);
968         }
969 }
970 
971 /* This must be called before lost_out is incremented */
972 static void tcp_verify_retransmit_hint(struct tcp_sock *tp, struct sk_buff *skb)
973 {
974         if ((tp->retransmit_skb_hint == NULL) ||
975             before(TCP_SKB_CB(skb)->seq,
976                    TCP_SKB_CB(tp->retransmit_skb_hint)->seq))
977                 tp->retransmit_skb_hint = skb;
978 
979         if (!tp->lost_out ||
980             after(TCP_SKB_CB(skb)->end_seq, tp->retransmit_high))
981                 tp->retransmit_high = TCP_SKB_CB(skb)->end_seq;
982 }
983 
984 static void tcp_skb_mark_lost(struct tcp_sock *tp, struct sk_buff *skb)
985 {
986         if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) {
987                 tcp_verify_retransmit_hint(tp, skb);
988 
989                 tp->lost_out += tcp_skb_pcount(skb);
990                 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
991         }
992 }
993 
994 static void tcp_skb_mark_lost_uncond_verify(struct tcp_sock *tp,
995                                             struct sk_buff *skb)
996 {
997         tcp_verify_retransmit_hint(tp, skb);
998 
999         if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) {
1000                 tp->lost_out += tcp_skb_pcount(skb);
1001                 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1002         }
1003 }
1004 
1005 /* This procedure tags the retransmission queue when SACKs arrive.
1006  *
1007  * We have three tag bits: SACKED(S), RETRANS(R) and LOST(L).
1008  * Packets in queue with these bits set are counted in variables
1009  * sacked_out, retrans_out and lost_out, correspondingly.
1010  *
1011  * Valid combinations are:
1012  * Tag  InFlight        Description
1013  * 0    1               - orig segment is in flight.
1014  * S    0               - nothing flies, orig reached receiver.
1015  * L    0               - nothing flies, orig lost by net.
1016  * R    2               - both orig and retransmit are in flight.
1017  * L|R  1               - orig is lost, retransmit is in flight.
1018  * S|R  1               - orig reached receiver, retrans is still in flight.
1019  * (L|S|R is logically valid, it could occur when L|R is sacked,
1020  *  but it is equivalent to plain S and code short-curcuits it to S.
1021  *  L|S is logically invalid, it would mean -1 packet in flight 8))
1022  *
1023  * These 6 states form finite state machine, controlled by the following events:
1024  * 1. New ACK (+SACK) arrives. (tcp_sacktag_write_queue())
1025  * 2. Retransmission. (tcp_retransmit_skb(), tcp_xmit_retransmit_queue())
1026  * 3. Loss detection event of one of three flavors:
1027  *      A. Scoreboard estimator decided the packet is lost.
1028  *         A'. Reno "three dupacks" marks head of queue lost.
1029  *         A''. Its FACK modfication, head until snd.fack is lost.
1030  *      B. SACK arrives sacking data transmitted after never retransmitted
1031  *         hole was sent out.
1032  *      C. SACK arrives sacking SND.NXT at the moment, when the
1033  *         segment was retransmitted.
1034  * 4. D-SACK added new rule: D-SACK changes any tag to S.
1035  *
1036  * It is pleasant to note, that state diagram turns out to be commutative,
1037  * so that we are allowed not to be bothered by order of our actions,
1038  * when multiple events arrive simultaneously. (see the function below).
1039  *
1040  * Reordering detection.
1041  * --------------------
1042  * Reordering metric is maximal distance, which a packet can be displaced
1043  * in packet stream. With SACKs we can estimate it:
1044  *
1045  * 1. SACK fills old hole and the corresponding segment was not
1046  *    ever retransmitted -> reordering. Alas, we cannot use it
1047  *    when segment was retransmitted.
1048  * 2. The last flaw is solved with D-SACK. D-SACK arrives
1049  *    for retransmitted and already SACKed segment -> reordering..
1050  * Both of these heuristics are not used in Loss state, when we cannot
1051  * account for retransmits accurately.
1052  *
1053  * SACK block validation.
1054  * ----------------------
1055  *
1056  * SACK block range validation checks that the received SACK block fits to
1057  * the expected sequence limits, i.e., it is between SND.UNA and SND.NXT.
1058  * Note that SND.UNA is not included to the range though being valid because
1059  * it means that the receiver is rather inconsistent with itself reporting
1060  * SACK reneging when it should advance SND.UNA. Such SACK block this is
1061  * perfectly valid, however, in light of RFC2018 which explicitly states
1062  * that "SACK block MUST reflect the newest segment.  Even if the newest
1063  * segment is going to be discarded ...", not that it looks very clever
1064  * in case of head skb. Due to potentional receiver driven attacks, we
1065  * choose to avoid immediate execution of a walk in write queue due to
1066  * reneging and defer head skb's loss recovery to standard loss recovery
1067  * procedure that will eventually trigger (nothing forbids us doing this).
1068  *
1069  * Implements also blockage to start_seq wrap-around. Problem lies in the
1070  * fact that though start_seq (s) is before end_seq (i.e., not reversed),
1071  * there's no guarantee that it will be before snd_nxt (n). The problem
1072  * happens when start_seq resides between end_seq wrap (e_w) and snd_nxt
1073  * wrap (s_w):
1074  *
1075  *         <- outs wnd ->                          <- wrapzone ->
1076  *         u     e      n                         u_w   e_w  s n_w
1077  *         |     |      |                          |     |   |  |
1078  * |<------------+------+----- TCP seqno space --------------+---------->|
1079  * ...-- <2^31 ->|                                           |<--------...
1080  * ...---- >2^31 ------>|                                    |<--------...
1081  *
1082  * Current code wouldn't be vulnerable but it's better still to discard such
1083  * crazy SACK blocks. Doing this check for start_seq alone closes somewhat
1084  * similar case (end_seq after snd_nxt wrap) as earlier reversed check in
1085  * snd_nxt wrap -> snd_una region will then become "well defined", i.e.,
1086  * equal to the ideal case (infinite seqno space without wrap caused issues).
1087  *
1088  * With D-SACK the lower bound is extended to cover sequence space below
1089  * SND.UNA down to undo_marker, which is the last point of interest. Yet
1090  * again, D-SACK block must not to go across snd_una (for the same reason as
1091  * for the normal SACK blocks, explained above). But there all simplicity
1092  * ends, TCP might receive valid D-SACKs below that. As long as they reside
1093  * fully below undo_marker they do not affect behavior in anyway and can
1094  * therefore be safely ignored. In rare cases (which are more or less
1095  * theoretical ones), the D-SACK will nicely cross that boundary due to skb
1096  * fragmentation and packet reordering past skb's retransmission. To consider
1097  * them correctly, the acceptable range must be extended even more though
1098  * the exact amount is rather hard to quantify. However, tp->max_window can
1099  * be used as an exaggerated estimate.
1100  */
1101 static int tcp_is_sackblock_valid(struct tcp_sock *tp, int is_dsack,
1102                                   u32 start_seq, u32 end_seq)
1103 {
1104         /* Too far in future, or reversed (interpretation is ambiguous) */
1105         if (after(end_seq, tp->snd_nxt) || !before(start_seq, end_seq))
1106                 return 0;
1107 
1108         /* Nasty start_seq wrap-around check (see comments above) */
1109         if (!before(start_seq, tp->snd_nxt))
1110                 return 0;
1111 
1112         /* In outstanding window? ...This is valid exit for D-SACKs too.
1113          * start_seq == snd_una is non-sensical (see comments above)
1114          */
1115         if (after(start_seq, tp->snd_una))
1116                 return 1;
1117 
1118         if (!is_dsack || !tp->undo_marker)
1119                 return 0;
1120 
1121         /* ...Then it's D-SACK, and must reside below snd_una completely */
1122         if (!after(end_seq, tp->snd_una))
1123                 return 0;
1124 
1125         if (!before(start_seq, tp->undo_marker))
1126                 return 1;
1127 
1128         /* Too old */
1129         if (!after(end_seq, tp->undo_marker))
1130                 return 0;
1131 
1132         /* Undo_marker boundary crossing (overestimates a lot). Known already:
1133          *   start_seq < undo_marker and end_seq >= undo_marker.
1134          */
1135         return !before(start_seq, end_seq - tp->max_window);
1136 }
1137 
1138 /* Check for lost retransmit. This superb idea is borrowed from "ratehalving".
1139  * Event "C". Later note: FACK people cheated me again 8), we have to account
1140  * for reordering! Ugly, but should help.
1141  *
1142  * Search retransmitted skbs from write_queue that were sent when snd_nxt was
1143  * less than what is now known to be received by the other end (derived from
1144  * highest SACK block). Also calculate the lowest snd_nxt among the remaining
1145  * retransmitted skbs to avoid some costly processing per ACKs.
1146  */
1147 static void tcp_mark_lost_retrans(struct sock *sk)
1148 {
1149         const struct inet_connection_sock *icsk = inet_csk(sk);
1150         struct tcp_sock *tp = tcp_sk(sk);
1151         struct sk_buff *skb;
1152         int cnt = 0;
1153         u32 new_low_seq = tp->snd_nxt;
1154         u32 received_upto = tcp_highest_sack_seq(tp);
1155 
1156         if (!tcp_is_fack(tp) || !tp->retrans_out ||
1157             !after(received_upto, tp->lost_retrans_low) ||
1158             icsk->icsk_ca_state != TCP_CA_Recovery)
1159                 return;
1160 
1161         tcp_for_write_queue(skb, sk) {
1162                 u32 ack_seq = TCP_SKB_CB(skb)->ack_seq;
1163 
1164                 if (skb == tcp_send_head(sk))
1165                         break;
1166                 if (cnt == tp->retrans_out)
1167                         break;
1168                 if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1169                         continue;
1170 
1171                 if (!(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS))
1172                         continue;
1173 
1174                 /* TODO: We would like to get rid of tcp_is_fack(tp) only
1175                  * constraint here (see above) but figuring out that at
1176                  * least tp->reordering SACK blocks reside between ack_seq
1177                  * and received_upto is not easy task to do cheaply with
1178                  * the available datastructures.
1179                  *
1180                  * Whether FACK should check here for tp->reordering segs
1181                  * in-between one could argue for either way (it would be
1182                  * rather simple to implement as we could count fack_count
1183                  * during the walk and do tp->fackets_out - fack_count).
1184                  */
1185                 if (after(received_upto, ack_seq)) {
1186                         TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
1187                         tp->retrans_out -= tcp_skb_pcount(skb);
1188 
1189                         tcp_skb_mark_lost_uncond_verify(tp, skb);
1190                         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPLOSTRETRANSMIT);
1191                 } else {
1192                         if (before(ack_seq, new_low_seq))
1193                                 new_low_seq = ack_seq;
1194                         cnt += tcp_skb_pcount(skb);
1195                 }
1196         }
1197 
1198         if (tp->retrans_out)
1199                 tp->lost_retrans_low = new_low_seq;
1200 }
1201 
1202 static int tcp_check_dsack(struct sock *sk, struct sk_buff *ack_skb,
1203                            struct tcp_sack_block_wire *sp, int num_sacks,
1204                            u32 prior_snd_una)
1205 {
1206         struct tcp_sock *tp = tcp_sk(sk);
1207         u32 start_seq_0 = get_unaligned_be32(&sp[0].start_seq);
1208         u32 end_seq_0 = get_unaligned_be32(&sp[0].end_seq);
1209         int dup_sack = 0;
1210 
1211         if (before(start_seq_0, TCP_SKB_CB(ack_skb)->ack_seq)) {
1212                 dup_sack = 1;
1213                 tcp_dsack_seen(tp);
1214                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPDSACKRECV);
1215         } else if (num_sacks > 1) {
1216                 u32 end_seq_1 = get_unaligned_be32(&sp[1].end_seq);
1217                 u32 start_seq_1 = get_unaligned_be32(&sp[1].start_seq);
1218 
1219                 if (!after(end_seq_0, end_seq_1) &&
1220                     !before(start_seq_0, start_seq_1)) {
1221                         dup_sack = 1;
1222                         tcp_dsack_seen(tp);
1223                         NET_INC_STATS_BH(sock_net(sk),
1224                                         LINUX_MIB_TCPDSACKOFORECV);
1225                 }
1226         }
1227 
1228         /* D-SACK for already forgotten data... Do dumb counting. */
1229         if (dup_sack &&
1230             !after(end_seq_0, prior_snd_una) &&
1231             after(end_seq_0, tp->undo_marker))
1232                 tp->undo_retrans--;
1233 
1234         return dup_sack;
1235 }
1236 
1237 struct tcp_sacktag_state {
1238         int reord;
1239         int fack_count;
1240         int flag;
1241 };
1242 
1243 /* Check if skb is fully within the SACK block. In presence of GSO skbs,
1244  * the incoming SACK may not exactly match but we can find smaller MSS
1245  * aligned portion of it that matches. Therefore we might need to fragment
1246  * which may fail and creates some hassle (caller must handle error case
1247  * returns).
1248  *
1249  * FIXME: this could be merged to shift decision code
1250  */
1251 static int tcp_match_skb_to_sack(struct sock *sk, struct sk_buff *skb,
1252                                  u32 start_seq, u32 end_seq)
1253 {
1254         int in_sack, err;
1255         unsigned int pkt_len;
1256         unsigned int mss;
1257 
1258         in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1259                   !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1260 
1261         if (tcp_skb_pcount(skb) > 1 && !in_sack &&
1262             after(TCP_SKB_CB(skb)->end_seq, start_seq)) {
1263                 mss = tcp_skb_mss(skb);
1264                 in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
1265 
1266                 if (!in_sack) {
1267                         pkt_len = start_seq - TCP_SKB_CB(skb)->seq;
1268                         if (pkt_len < mss)
1269                                 pkt_len = mss;
1270                 } else {
1271                         pkt_len = end_seq - TCP_SKB_CB(skb)->seq;
1272                         if (pkt_len < mss)
1273                                 return -EINVAL;
1274                 }
1275 
1276                 /* Round if necessary so that SACKs cover only full MSSes
1277                  * and/or the remaining small portion (if present)
1278                  */
1279                 if (pkt_len > mss) {
1280                         unsigned int new_len = (pkt_len / mss) * mss;
1281                         if (!in_sack && new_len < pkt_len) {
1282                                 new_len += mss;
1283                                 if (new_len > skb->len)
1284                                         return 0;
1285                         }
1286                         pkt_len = new_len;
1287                 }
1288                 err = tcp_fragment(sk, skb, pkt_len, mss);
1289                 if (err < 0)
1290                         return err;
1291         }
1292 
1293         return in_sack;
1294 }
1295 
1296 static u8 tcp_sacktag_one(struct sk_buff *skb, struct sock *sk,
1297                           struct tcp_sacktag_state *state,
1298                           int dup_sack, int pcount)
1299 {
1300         struct tcp_sock *tp = tcp_sk(sk);
1301         u8 sacked = TCP_SKB_CB(skb)->sacked;
1302         int fack_count = state->fack_count;
1303 
1304         /* Account D-SACK for retransmitted packet. */
1305         if (dup_sack && (sacked & TCPCB_RETRANS)) {
1306                 if (after(TCP_SKB_CB(skb)->end_seq, tp->undo_marker))
1307                         tp->undo_retrans--;
1308                 if (sacked & TCPCB_SACKED_ACKED)
1309                         state->reord = min(fack_count, state->reord);
1310         }
1311 
1312         /* Nothing to do; acked frame is about to be dropped (was ACKed). */
1313         if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1314                 return sacked;
1315 
1316         if (!(sacked & TCPCB_SACKED_ACKED)) {
1317                 if (sacked & TCPCB_SACKED_RETRANS) {
1318                         /* If the segment is not tagged as lost,
1319                          * we do not clear RETRANS, believing
1320                          * that retransmission is still in flight.
1321                          */
1322                         if (sacked & TCPCB_LOST) {
1323                                 sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS);
1324                                 tp->lost_out -= pcount;
1325                                 tp->retrans_out -= pcount;
1326                         }
1327                 } else {
1328                         if (!(sacked & TCPCB_RETRANS)) {
1329                                 /* New sack for not retransmitted frame,
1330                                  * which was in hole. It is reordering.
1331                                  */
1332                                 if (before(TCP_SKB_CB(skb)->seq,
1333                                            tcp_highest_sack_seq(tp)))
1334                                         state->reord = min(fack_count,
1335                                                            state->reord);
1336 
1337                                 /* SACK enhanced F-RTO (RFC4138; Appendix B) */
1338                                 if (!after(TCP_SKB_CB(skb)->end_seq, tp->frto_highmark))
1339                                         state->flag |= FLAG_ONLY_ORIG_SACKED;
1340                         }
1341 
1342                         if (sacked & TCPCB_LOST) {
1343                                 sacked &= ~TCPCB_LOST;
1344                                 tp->lost_out -= pcount;
1345                         }
1346                 }
1347 
1348                 sacked |= TCPCB_SACKED_ACKED;
1349                 state->flag |= FLAG_DATA_SACKED;
1350                 tp->sacked_out += pcount;
1351 
1352                 fack_count += pcount;
1353 
1354                 /* Lost marker hint past SACKed? Tweak RFC3517 cnt */
1355                 if (!tcp_is_fack(tp) && (tp->lost_skb_hint != NULL) &&
1356                     before(TCP_SKB_CB(skb)->seq,
1357                            TCP_SKB_CB(tp->lost_skb_hint)->seq))
1358                         tp->lost_cnt_hint += pcount;
1359 
1360                 if (fack_count > tp->fackets_out)
1361                         tp->fackets_out = fack_count;
1362         }
1363 
1364         /* D-SACK. We can detect redundant retransmission in S|R and plain R
1365          * frames and clear it. undo_retrans is decreased above, L|R frames
1366          * are accounted above as well.
1367          */
1368         if (dup_sack && (sacked & TCPCB_SACKED_RETRANS)) {
1369                 sacked &= ~TCPCB_SACKED_RETRANS;
1370                 tp->retrans_out -= pcount;
1371         }
1372 
1373         return sacked;
1374 }
1375 
1376 static int tcp_shifted_skb(struct sock *sk, struct sk_buff *skb,
1377                            struct tcp_sacktag_state *state,
1378                            unsigned int pcount, int shifted, int mss,
1379                            int dup_sack)
1380 {
1381         struct tcp_sock *tp = tcp_sk(sk);
1382         struct sk_buff *prev = tcp_write_queue_prev(sk, skb);
1383 
1384         BUG_ON(!pcount);
1385 
1386         /* Tweak before seqno plays */
1387         if (!tcp_is_fack(tp) && tcp_is_sack(tp) && tp->lost_skb_hint &&
1388             !before(TCP_SKB_CB(tp->lost_skb_hint)->seq, TCP_SKB_CB(skb)->seq))
1389                 tp->lost_cnt_hint += pcount;
1390 
1391         TCP_SKB_CB(prev)->end_seq += shifted;
1392         TCP_SKB_CB(skb)->seq += shifted;
1393 
1394         skb_shinfo(prev)->gso_segs += pcount;
1395         BUG_ON(skb_shinfo(skb)->gso_segs < pcount);
1396         skb_shinfo(skb)->gso_segs -= pcount;
1397 
1398         /* When we're adding to gso_segs == 1, gso_size will be zero,
1399          * in theory this shouldn't be necessary but as long as DSACK
1400          * code can come after this skb later on it's better to keep
1401          * setting gso_size to something.
1402          */
1403         if (!skb_shinfo(prev)->gso_size) {
1404                 skb_shinfo(prev)->gso_size = mss;
1405                 skb_shinfo(prev)->gso_type = sk->sk_gso_type;
1406         }
1407 
1408         /* CHECKME: To clear or not to clear? Mimics normal skb currently */
1409         if (skb_shinfo(skb)->gso_segs <= 1) {
1410                 skb_shinfo(skb)->gso_size = 0;
1411                 skb_shinfo(skb)->gso_type = 0;
1412         }
1413 
1414         /* We discard results */
1415         tcp_sacktag_one(skb, sk, state, dup_sack, pcount);
1416 
1417         /* Difference in this won't matter, both ACKed by the same cumul. ACK */
1418         TCP_SKB_CB(prev)->sacked |= (TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS);
1419 
1420         if (skb->len > 0) {
1421                 BUG_ON(!tcp_skb_pcount(skb));
1422                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SACKSHIFTED);
1423                 return 0;
1424         }
1425 
1426         /* Whole SKB was eaten :-) */
1427 
1428         if (skb == tp->retransmit_skb_hint)
1429                 tp->retransmit_skb_hint = prev;
1430         if (skb == tp->scoreboard_skb_hint)
1431                 tp->scoreboard_skb_hint = prev;
1432         if (skb == tp->lost_skb_hint) {
1433                 tp->lost_skb_hint = prev;
1434                 tp->lost_cnt_hint -= tcp_skb_pcount(prev);
1435         }
1436 
1437         TCP_SKB_CB(skb)->flags |= TCP_SKB_CB(prev)->flags;
1438         if (skb == tcp_highest_sack(sk))
1439                 tcp_advance_highest_sack(sk, skb);
1440 
1441         tcp_unlink_write_queue(skb, sk);
1442         sk_wmem_free_skb(sk, skb);
1443 
1444         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SACKMERGED);
1445 
1446         return 1;
1447 }
1448 
1449 /* I wish gso_size would have a bit more sane initialization than
1450  * something-or-zero which complicates things
1451  */
1452 static int tcp_skb_seglen(struct sk_buff *skb)
1453 {
1454         return tcp_skb_pcount(skb) == 1 ? skb->len : tcp_skb_mss(skb);
1455 }
1456 
1457 /* Shifting pages past head area doesn't work */
1458 static int skb_can_shift(struct sk_buff *skb)
1459 {
1460         return !skb_headlen(skb) && skb_is_nonlinear(skb);
1461 }
1462 
1463 /* Try collapsing SACK blocks spanning across multiple skbs to a single
1464  * skb.
1465  */
1466 static struct sk_buff *tcp_shift_skb_data(struct sock *sk, struct sk_buff *skb,
1467                                           struct tcp_sacktag_state *state,
1468                                           u32 start_seq, u32 end_seq,
1469                                           int dup_sack)
1470 {
1471         struct tcp_sock *tp = tcp_sk(sk);
1472         struct sk_buff *prev;
1473         int mss;
1474         int pcount = 0;
1475         int len;
1476         int in_sack;
1477 
1478         if (!sk_can_gso(sk))
1479                 goto fallback;
1480 
1481         /* Normally R but no L won't result in plain S */
1482         if (!dup_sack &&
1483             (TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_RETRANS)) == TCPCB_SACKED_RETRANS)
1484                 goto fallback;
1485         if (!skb_can_shift(skb))
1486                 goto fallback;
1487         /* This frame is about to be dropped (was ACKed). */
1488         if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1489                 goto fallback;
1490 
1491         /* Can only happen with delayed DSACK + discard craziness */
1492         if (unlikely(skb == tcp_write_queue_head(sk)))
1493                 goto fallback;
1494         prev = tcp_write_queue_prev(sk, skb);
1495 
1496         if ((TCP_SKB_CB(prev)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED)
1497                 goto fallback;
1498 
1499         in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1500                   !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1501 
1502         if (in_sack) {
1503                 len = skb->len;
1504                 pcount = tcp_skb_pcount(skb);
1505                 mss = tcp_skb_seglen(skb);
1506 
1507                 /* TODO: Fix DSACKs to not fragment already SACKed and we can
1508                  * drop this restriction as unnecessary
1509                  */
1510                 if (mss != tcp_skb_seglen(prev))
1511                         goto fallback;
1512         } else {
1513                 if (!after(TCP_SKB_CB(skb)->end_seq, start_seq))
1514                         goto noop;
1515                 /* CHECKME: This is non-MSS split case only?, this will
1516                  * cause skipped skbs due to advancing loop btw, original
1517                  * has that feature too
1518                  */
1519                 if (tcp_skb_pcount(skb) <= 1)
1520                         goto noop;
1521 
1522                 in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
1523                 if (!in_sack) {
1524                         /* TODO: head merge to next could be attempted here
1525                          * if (!after(TCP_SKB_CB(skb)->end_seq, end_seq)),
1526                          * though it might not be worth of the additional hassle
1527                          *
1528                          * ...we can probably just fallback to what was done
1529                          * previously. We could try merging non-SACKed ones
1530                          * as well but it probably isn't going to buy off
1531                          * because later SACKs might again split them, and
1532                          * it would make skb timestamp tracking considerably
1533                          * harder problem.
1534                          */
1535                         goto fallback;
1536                 }
1537 
1538                 len = end_seq - TCP_SKB_CB(skb)->seq;
1539                 BUG_ON(len < 0);
1540                 BUG_ON(len > skb->len);
1541 
1542                 /* MSS boundaries should be honoured or else pcount will
1543                  * severely break even though it makes things bit trickier.
1544                  * Optimize common case to avoid most of the divides
1545                  */
1546                 mss = tcp_skb_mss(skb);
1547 
1548                 /* TODO: Fix DSACKs to not fragment already SACKed and we can
1549                  * drop this restriction as unnecessary
1550                  */
1551                 if (mss != tcp_skb_seglen(prev))
1552                         goto fallback;
1553 
1554                 if (len == mss) {
1555                         pcount = 1;
1556                 } else if (len < mss) {
1557                         goto noop;
1558                 } else {
1559                         pcount = len / mss;
1560                         len = pcount * mss;
1561                 }
1562         }
1563 
1564         if (!skb_shift(prev, skb, len))
1565                 goto fallback;
1566         if (!tcp_shifted_skb(sk, skb, state, pcount, len, mss, dup_sack))
1567                 goto out;
1568 
1569         /* Hole filled allows collapsing with the next as well, this is very
1570          * useful when hole on every nth skb pattern happens
1571          */
1572         if (prev == tcp_write_queue_tail(sk))
1573                 goto out;
1574         skb = tcp_write_queue_next(sk, prev);
1575 
1576         if (!skb_can_shift(skb) ||
1577             (skb == tcp_send_head(sk)) ||
1578             ((TCP_SKB_CB(skb)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED) ||
1579             (mss != tcp_skb_seglen(skb)))
1580                 goto out;
1581 
1582         len = skb->len;
1583         if (skb_shift(prev, skb, len)) {
1584                 pcount += tcp_skb_pcount(skb);
1585                 tcp_shifted_skb(sk, skb, state, tcp_skb_pcount(skb), len, mss, 0);
1586         }
1587 
1588 out:
1589         state->fack_count += pcount;
1590         return prev;
1591 
1592 noop:
1593         return skb;
1594 
1595 fallback:
1596         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SACKSHIFTFALLBACK);
1597         return NULL;
1598 }
1599 
1600 static struct sk_buff *tcp_sacktag_walk(struct sk_buff *skb, struct sock *sk,
1601                                         struct tcp_sack_block *next_dup,
1602                                         struct tcp_sacktag_state *state,
1603                                         u32 start_seq, u32 end_seq,
1604                                         int dup_sack_in)
1605 {
1606         struct tcp_sock *tp = tcp_sk(sk);
1607         struct sk_buff *tmp;
1608 
1609         tcp_for_write_queue_from(skb, sk) {
1610                 int in_sack = 0;
1611                 int dup_sack = dup_sack_in;
1612 
1613                 if (skb == tcp_send_head(sk))
1614                         break;
1615 
1616                 /* queue is in-order => we can short-circuit the walk early */
1617                 if (!before(TCP_SKB_CB(skb)->seq, end_seq))
1618                         break;
1619 
1620                 if ((next_dup != NULL) &&
1621                     before(TCP_SKB_CB(skb)->seq, next_dup->end_seq)) {
1622                         in_sack = tcp_match_skb_to_sack(sk, skb,
1623                                                         next_dup->start_seq,
1624                                                         next_dup->end_seq);
1625                         if (in_sack > 0)
1626                                 dup_sack = 1;
1627                 }
1628 
1629                 /* skb reference here is a bit tricky to get right, since
1630                  * shifting can eat and free both this skb and the next,
1631                  * so not even _safe variant of the loop is enough.
1632                  */
1633                 if (in_sack <= 0) {
1634                         tmp = tcp_shift_skb_data(sk, skb, state,
1635                                                  start_seq, end_seq, dup_sack);
1636                         if (tmp != NULL) {
1637                                 if (tmp != skb) {
1638                                         skb = tmp;
1639                                         continue;
1640                                 }
1641 
1642                                 in_sack = 0;
1643                         } else {
1644                                 in_sack = tcp_match_skb_to_sack(sk, skb,
1645                                                                 start_seq,
1646                                                                 end_seq);
1647                         }
1648                 }
1649 
1650                 if (unlikely(in_sack < 0))
1651                         break;
1652 
1653                 if (in_sack) {
1654                         TCP_SKB_CB(skb)->sacked = tcp_sacktag_one(skb, sk,
1655                                                                   state,
1656                                                                   dup_sack,
1657                                                                   tcp_skb_pcount(skb));
1658 
1659                         if (!before(TCP_SKB_CB(skb)->seq,
1660                                     tcp_highest_sack_seq(tp)))
1661                                 tcp_advance_highest_sack(sk, skb);
1662                 }
1663 
1664                 state->fack_count += tcp_skb_pcount(skb);
1665         }
1666         return skb;
1667 }
1668 
1669 /* Avoid all extra work that is being done by sacktag while walking in
1670  * a normal way
1671  */
1672 static struct sk_buff *tcp_sacktag_skip(struct sk_buff *skb, struct sock *sk,
1673                                         struct tcp_sacktag_state *state,
1674                                         u32 skip_to_seq)
1675 {
1676         tcp_for_write_queue_from(skb, sk) {
1677                 if (skb == tcp_send_head(sk))
1678                         break;
1679 
1680                 if (after(TCP_SKB_CB(skb)->end_seq, skip_to_seq))
1681                         break;
1682 
1683                 state->fack_count += tcp_skb_pcount(skb);
1684         }
1685         return skb;
1686 }
1687 
1688 static struct sk_buff *tcp_maybe_skipping_dsack(struct sk_buff *skb,
1689                                                 struct sock *sk,
1690                                                 struct tcp_sack_block *next_dup,
1691                                                 struct tcp_sacktag_state *state,
1692                                                 u32 skip_to_seq)
1693 {
1694         if (next_dup == NULL)
1695                 return skb;
1696 
1697         if (before(next_dup->start_seq, skip_to_seq)) {
1698                 skb = tcp_sacktag_skip(skb, sk, state, next_dup->start_seq);
1699                 skb = tcp_sacktag_walk(skb, sk, NULL, state,
1700                                        next_dup->start_seq, next_dup->end_seq,
1701                                        1);
1702         }
1703 
1704         return skb;
1705 }
1706 
1707 static int tcp_sack_cache_ok(struct tcp_sock *tp, struct tcp_sack_block *cache)
1708 {
1709         return cache < tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
1710 }
1711 
1712 static int
1713 tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb,
1714                         u32 prior_snd_una)
1715 {
1716         const struct inet_connection_sock *icsk = inet_csk(sk);
1717         struct tcp_sock *tp = tcp_sk(sk);
1718         unsigned char *ptr = (skb_transport_header(ack_skb) +
1719                               TCP_SKB_CB(ack_skb)->sacked);
1720         struct tcp_sack_block_wire *sp_wire = (struct tcp_sack_block_wire *)(ptr+2);
1721         struct tcp_sack_block sp[TCP_NUM_SACKS];
1722         struct tcp_sack_block *cache;
1723         struct tcp_sacktag_state state;
1724         struct sk_buff *skb;
1725         int num_sacks = min(TCP_NUM_SACKS, (ptr[1] - TCPOLEN_SACK_BASE) >> 3);
1726         int used_sacks;
1727         int found_dup_sack = 0;
1728         int i, j;
1729         int first_sack_index;
1730 
1731         state.flag = 0;
1732         state.reord = tp->packets_out;
1733 
1734         if (!tp->sacked_out) {
1735                 if (WARN_ON(tp->fackets_out))
1736                         tp->fackets_out = 0;
1737                 tcp_highest_sack_reset(sk);
1738         }
1739 
1740         found_dup_sack = tcp_check_dsack(sk, ack_skb, sp_wire,
1741                                          num_sacks, prior_snd_una);
1742         if (found_dup_sack)
1743                 state.flag |= FLAG_DSACKING_ACK;
1744 
1745         /* Eliminate too old ACKs, but take into
1746          * account more or less fresh ones, they can
1747          * contain valid SACK info.
1748          */
1749         if (before(TCP_SKB_CB(ack_skb)->ack_seq, prior_snd_una - tp->max_window))
1750                 return 0;
1751 
1752         if (!tp->packets_out)
1753                 goto out;
1754 
1755         used_sacks = 0;
1756         first_sack_index = 0;
1757         for (i = 0; i < num_sacks; i++) {
1758                 int dup_sack = !i && found_dup_sack;
1759 
1760                 sp[used_sacks].start_seq = get_unaligned_be32(&sp_wire[i].start_seq);
1761                 sp[used_sacks].end_seq = get_unaligned_be32(&sp_wire[i].end_seq);
1762 
1763                 if (!tcp_is_sackblock_valid(tp, dup_sack,
1764                                             sp[used_sacks].start_seq,
1765                                             sp[used_sacks].end_seq)) {
1766                         int mib_idx;
1767 
1768                         if (dup_sack) {
1769                                 if (!tp->undo_marker)
1770                                         mib_idx = LINUX_MIB_TCPDSACKIGNOREDNOUNDO;
1771                                 else
1772                                         mib_idx = LINUX_MIB_TCPDSACKIGNOREDOLD;
1773                         } else {
1774                                 /* Don't count olds caused by ACK reordering */
1775                                 if ((TCP_SKB_CB(ack_skb)->ack_seq != tp->snd_una) &&
1776                                     !after(sp[used_sacks].end_seq, tp->snd_una))
1777                                         continue;
1778                                 mib_idx = LINUX_MIB_TCPSACKDISCARD;
1779                         }
1780 
1781                         NET_INC_STATS_BH(sock_net(sk), mib_idx);
1782                         if (i == 0)
1783                                 first_sack_index = -1;
1784                         continue;
1785                 }
1786 
1787                 /* Ignore very old stuff early */
1788                 if (!after(sp[used_sacks].end_seq, prior_snd_una))
1789                         continue;
1790 
1791                 used_sacks++;
1792         }
1793 
1794         /* order SACK blocks to allow in order walk of the retrans queue */
1795         for (i = used_sacks - 1; i > 0; i--) {
1796                 for (j = 0; j < i; j++) {
1797                         if (after(sp[j].start_seq, sp[j + 1].start_seq)) {
1798                                 swap(sp[j], sp[j + 1]);
1799 
1800                                 /* Track where the first SACK block goes to */
1801                                 if (j == first_sack_index)
1802                                         first_sack_index = j + 1;
1803                         }
1804                 }
1805         }
1806 
1807         skb = tcp_write_queue_head(sk);
1808         state.fack_count = 0;
1809         i = 0;
1810 
1811         if (!tp->sacked_out) {
1812                 /* It's already past, so skip checking against it */
1813                 cache = tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
1814         } else {
1815                 cache = tp->recv_sack_cache;
1816                 /* Skip empty blocks in at head of the cache */
1817                 while (tcp_sack_cache_ok(tp, cache) && !cache->start_seq &&
1818                        !cache->end_seq)
1819                         cache++;
1820         }
1821 
1822         while (i < used_sacks) {
1823                 u32 start_seq = sp[i].start_seq;
1824                 u32 end_seq = sp[i].end_seq;
1825                 int dup_sack = (found_dup_sack && (i == first_sack_index));
1826                 struct tcp_sack_block *next_dup = NULL;
1827 
1828                 if (found_dup_sack && ((i + 1) == first_sack_index))
1829                         next_dup = &sp[i + 1];
1830 
1831                 /* Event "B" in the comment above. */
1832                 if (after(end_seq, tp->high_seq))
1833                         state.flag |= FLAG_DATA_LOST;
1834 
1835                 /* Skip too early cached blocks */
1836                 while (tcp_sack_cache_ok(tp, cache) &&
1837                        !before(start_seq, cache->end_seq))
1838                         cache++;
1839 
1840                 /* Can skip some work by looking recv_sack_cache? */
1841                 if (tcp_sack_cache_ok(tp, cache) && !dup_sack &&
1842                     after(end_seq, cache->start_seq)) {
1843 
1844                         /* Head todo? */
1845                         if (before(start_seq, cache->start_seq)) {
1846                                 skb = tcp_sacktag_skip(skb, sk, &state,
1847                                                        start_seq);
1848                                 skb = tcp_sacktag_walk(skb, sk, next_dup,
1849                                                        &state,
1850                                                        start_seq,
1851                                                        cache->start_seq,
1852                                                        dup_sack);
1853                         }
1854 
1855                         /* Rest of the block already fully processed? */
1856                         if (!after(end_seq, cache->end_seq))
1857                                 goto advance_sp;
1858 
1859                         skb = tcp_maybe_skipping_dsack(skb, sk, next_dup,
1860                                                        &state,
1861                                                        cache->end_seq);
1862 
1863                         /* ...tail remains todo... */
1864                         if (tcp_highest_sack_seq(tp) == cache->end_seq) {
1865                                 /* ...but better entrypoint exists! */
1866                                 skb = tcp_highest_sack(sk);
1867                                 if (skb == NULL)
1868                                         break;
1869                                 state.fack_count = tp->fackets_out;
1870                                 cache++;
1871                                 goto walk;
1872                         }
1873 
1874                         skb = tcp_sacktag_skip(skb, sk, &state, cache->end_seq);
1875                         /* Check overlap against next cached too (past this one already) */
1876                         cache++;
1877                         continue;
1878                 }
1879 
1880                 if (!before(start_seq, tcp_highest_sack_seq(tp))) {
1881                         skb = tcp_highest_sack(sk);
1882                         if (skb == NULL)
1883                                 break;
1884                         state.fack_count = tp->fackets_out;
1885                 }
1886                 skb = tcp_sacktag_skip(skb, sk, &state, start_seq);
1887 
1888 walk:
1889                 skb = tcp_sacktag_walk(skb, sk, next_dup, &state,
1890                                        start_seq, end_seq, dup_sack);
1891 
1892 advance_sp:
1893                 /* SACK enhanced FRTO (RFC4138, Appendix B): Clearing correct
1894                  * due to in-order walk
1895                  */
1896                 if (after(end_seq, tp->frto_highmark))
1897                         state.flag &= ~FLAG_ONLY_ORIG_SACKED;
1898 
1899                 i++;
1900         }
1901 
1902         /* Clear the head of the cache sack blocks so we can skip it next time */
1903         for (i = 0; i < ARRAY_SIZE(tp->recv_sack_cache) - used_sacks; i++) {
1904                 tp->recv_sack_cache[i].start_seq = 0;
1905                 tp->recv_sack_cache[i].end_seq = 0;
1906         }
1907         for (j = 0; j < used_sacks; j++)
1908                 tp->recv_sack_cache[i++] = sp[j];
1909 
1910         tcp_mark_lost_retrans(sk);
1911 
1912         tcp_verify_left_out(tp);
1913 
1914         if ((state.reord < tp->fackets_out) &&
1915             ((icsk->icsk_ca_state != TCP_CA_Loss) || tp->undo_marker) &&
1916             (!tp->frto_highmark || after(tp->snd_una, tp->frto_highmark)))
1917                 tcp_update_reordering(sk, tp->fackets_out - state.reord, 0);
1918 
1919 out:
1920 
1921 #if FASTRETRANS_DEBUG > 0
1922         WARN_ON((int)tp->sacked_out < 0);
1923         WARN_ON((int)tp->lost_out < 0);
1924         WARN_ON((int)tp->retrans_out < 0);
1925         WARN_ON((int)tcp_packets_in_flight(tp) < 0);
1926 #endif
1927         return state.flag;
1928 }
1929 
1930 /* Limits sacked_out so that sum with lost_out isn't ever larger than
1931  * packets_out. Returns zero if sacked_out adjustement wasn't necessary.
1932  */
1933 static int tcp_limit_reno_sacked(struct tcp_sock *tp)
1934 {
1935         u32 holes;
1936 
1937         holes = max(tp->lost_out, 1U);
1938         holes = min(holes, tp->packets_out);
1939 
1940         if ((tp->sacked_out + holes) > tp->packets_out) {
1941                 tp->sacked_out = tp->packets_out - holes;
1942                 return 1;
1943         }
1944         return 0;
1945 }
1946 
1947 /* If we receive more dupacks than we expected counting segments
1948  * in assumption of absent reordering, interpret this as reordering.
1949  * The only another reason could be bug in receiver TCP.
1950  */
1951 static void tcp_check_reno_reordering(struct sock *sk, const int addend)
1952 {
1953         struct tcp_sock *tp = tcp_sk(sk);
1954         if (tcp_limit_reno_sacked(tp))
1955                 tcp_update_reordering(sk, tp->packets_out + addend, 0);
1956 }
1957 
1958 /* Emulate SACKs for SACKless connection: account for a new dupack. */
1959 
1960 static void tcp_add_reno_sack(struct sock *sk)
1961 {
1962         struct tcp_sock *tp = tcp_sk(sk);
1963         tp->sacked_out++;
1964         tcp_check_reno_reordering(sk, 0);
1965         tcp_verify_left_out(tp);
1966 }
1967 
1968 /* Account for ACK, ACKing some data in Reno Recovery phase. */
1969 
1970 static void tcp_remove_reno_sacks(struct sock *sk, int acked)
1971 {
1972         struct tcp_sock *tp = tcp_sk(sk);
1973 
1974         if (acked > 0) {
1975                 /* One ACK acked hole. The rest eat duplicate ACKs. */
1976                 if (acked - 1 >= tp->sacked_out)
1977                         tp->sacked_out = 0;
1978                 else
1979                         tp->sacked_out -= acked - 1;
1980         }
1981         tcp_check_reno_reordering(sk, acked);
1982         tcp_verify_left_out(tp);
1983 }
1984 
1985 static inline void tcp_reset_reno_sack(struct tcp_sock *tp)
1986 {
1987         tp->sacked_out = 0;
1988 }
1989 
1990 static int tcp_is_sackfrto(const struct tcp_sock *tp)
1991 {
1992         return (sysctl_tcp_frto == 0x2) && !tcp_is_reno(tp);
1993 }
1994 
1995 /* F-RTO can only be used if TCP has never retransmitted anything other than
1996  * head (SACK enhanced variant from Appendix B of RFC4138 is more robust here)
1997  */
1998 int tcp_use_frto(struct sock *sk)
1999 {
2000         const struct tcp_sock *tp = tcp_sk(sk);
2001         const struct inet_connection_sock *icsk = inet_csk(sk);
2002         struct sk_buff *skb;
2003 
2004         if (!sysctl_tcp_frto)
2005                 return 0;
2006 
2007         /* MTU probe and F-RTO won't really play nicely along currently */
2008         if (icsk->icsk_mtup.probe_size)
2009                 return 0;
2010 
2011         if (tcp_is_sackfrto(tp))
2012                 return 1;
2013 
2014         /* Avoid expensive walking of rexmit queue if possible */
2015         if (tp->retrans_out > 1)
2016                 return 0;
2017 
2018         skb = tcp_write_queue_head(sk);
2019         if (tcp_skb_is_last(sk, skb))
2020                 return 1;
2021         skb = tcp_write_queue_next(sk, skb);    /* Skips head */
2022         tcp_for_write_queue_from(skb, sk) {
2023                 if (skb == tcp_send_head(sk))
2024                         break;
2025                 if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS)
2026                         return 0;
2027                 /* Short-circuit when first non-SACKed skb has been checked */
2028                 if (!(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
2029                         break;
2030         }
2031         return 1;
2032 }
2033 
2034 /* RTO occurred, but do not yet enter Loss state. Instead, defer RTO
2035  * recovery a bit and use heuristics in tcp_process_frto() to detect if
2036  * the RTO was spurious. Only clear SACKED_RETRANS of the head here to
2037  * keep retrans_out counting accurate (with SACK F-RTO, other than head
2038  * may still have that bit set); TCPCB_LOST and remaining SACKED_RETRANS
2039  * bits are handled if the Loss state is really to be entered (in
2040  * tcp_enter_frto_loss).
2041  *
2042  * Do like tcp_enter_loss() would; when RTO expires the second time it
2043  * does:
2044  *  "Reduce ssthresh if it has not yet been made inside this window."
2045  */
2046 void tcp_enter_frto(struct sock *sk)
2047 {
2048         const struct inet_connection_sock *icsk = inet_csk(sk);
2049         struct tcp_sock *tp = tcp_sk(sk);
2050         struct sk_buff *skb;
2051 
2052         if ((!tp->frto_counter && icsk->icsk_ca_state <= TCP_CA_Disorder) ||
2053             tp->snd_una == tp->high_seq ||
2054             ((icsk->icsk_ca_state == TCP_CA_Loss || tp->frto_counter) &&
2055              !icsk->icsk_retransmits)) {
2056                 tp->prior_ssthresh = tcp_current_ssthresh(sk);
2057                 /* Our state is too optimistic in ssthresh() call because cwnd
2058                  * is not reduced until tcp_enter_frto_loss() when previous F-RTO
2059                  * recovery has not yet completed. Pattern would be this: RTO,
2060                  * Cumulative ACK, RTO (2xRTO for the same segment does not end
2061                  * up here twice).
2062                  * RFC4138 should be more specific on what to do, even though
2063                  * RTO is quite unlikely to occur after the first Cumulative ACK
2064                  * due to back-off and complexity of triggering events ...
2065                  */
2066                 if (tp->frto_counter) {
2067                         u32 stored_cwnd;
2068                         stored_cwnd = tp->snd_cwnd;
2069                         tp->snd_cwnd = 2;
2070                         tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
2071                         tp->snd_cwnd = stored_cwnd;
2072                 } else {
2073                         tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
2074                 }
2075                 /* ... in theory, cong.control module could do "any tricks" in
2076                  * ssthresh(), which means that ca_state, lost bits and lost_out
2077                  * counter would have to be faked before the call occurs. We
2078                  * consider that too expensive, unlikely and hacky, so modules
2079                  * using these in ssthresh() must deal these incompatibility
2080                  * issues if they receives CA_EVENT_FRTO and frto_counter != 0
2081                  */
2082                 tcp_ca_event(sk, CA_EVENT_FRTO);
2083         }
2084 
2085         tp->undo_marker = tp->snd_una;
2086         tp->undo_retrans = 0;
2087 
2088         skb = tcp_write_queue_head(sk);
2089         if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS)
2090                 tp->undo_marker = 0;
2091         if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
2092                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
2093                 tp->retrans_out -= tcp_skb_pcount(skb);
2094         }
2095         tcp_verify_left_out(tp);
2096 
2097         /* Too bad if TCP was application limited */
2098         tp->snd_cwnd = min(tp->snd_cwnd, tcp_packets_in_flight(tp) + 1);
2099 
2100         /* Earlier loss recovery underway (see RFC4138; Appendix B).
2101          * The last condition is necessary at least in tp->frto_counter case.
2102          */
2103         if (tcp_is_sackfrto(tp) && (tp->frto_counter ||
2104             ((1 << icsk->icsk_ca_state) & (TCPF_CA_Recovery|TCPF_CA_Loss))) &&
2105             after(tp->high_seq, tp->snd_una)) {
2106                 tp->frto_highmark = tp->high_seq;
2107         } else {
2108                 tp->frto_highmark = tp->snd_nxt;
2109         }
2110         tcp_set_ca_state(sk, TCP_CA_Disorder);
2111         tp->high_seq = tp->snd_nxt;
2112         tp->frto_counter = 1;
2113 }
2114 
2115 /* Enter Loss state after F-RTO was applied. Dupack arrived after RTO,
2116  * which indicates that we should follow the traditional RTO recovery,
2117  * i.e. mark everything lost and do go-back-N retransmission.
2118  */
2119 static void tcp_enter_frto_loss(struct sock *sk, int allowed_segments, int flag)
2120 {
2121         struct tcp_sock *tp = tcp_sk(sk);
2122         struct sk_buff *skb;
2123 
2124         tp->lost_out = 0;
2125         tp->retrans_out = 0;
2126         if (tcp_is_reno(tp))
2127                 tcp_reset_reno_sack(tp);
2128 
2129         tcp_for_write_queue(skb, sk) {
2130                 if (skb == tcp_send_head(sk))
2131                         break;
2132 
2133                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
2134                 /*
2135                  * Count the retransmission made on RTO correctly (only when
2136                  * waiting for the first ACK and did not get it)...
2137                  */
2138                 if ((tp->frto_counter == 1) && !(flag & FLAG_DATA_ACKED)) {
2139                         /* For some reason this R-bit might get cleared? */
2140                         if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS)
2141                                 tp->retrans_out += tcp_skb_pcount(skb);
2142                         /* ...enter this if branch just for the first segment */
2143                         flag |= FLAG_DATA_ACKED;
2144                 } else {
2145                         if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS)
2146                                 tp->undo_marker = 0;
2147                         TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
2148                 }
2149 
2150                 /* Marking forward transmissions that were made after RTO lost
2151                  * can cause unnecessary retransmissions in some scenarios,
2152                  * SACK blocks will mitigate that in some but not in all cases.
2153                  * We used to not mark them but it was causing break-ups with
2154                  * receivers that do only in-order receival.
2155                  *
2156                  * TODO: we could detect presence of such receiver and select
2157                  * different behavior per flow.
2158                  */
2159                 if (!(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) {
2160                         TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
2161                         tp->lost_out += tcp_skb_pcount(skb);
2162                         tp->retransmit_high = TCP_SKB_CB(skb)->end_seq;
2163                 }
2164         }
2165         tcp_verify_left_out(tp);
2166 
2167         tp->snd_cwnd = tcp_packets_in_flight(tp) + allowed_segments;
2168         tp->snd_cwnd_cnt = 0;
2169         tp->snd_cwnd_stamp = tcp_time_stamp;
2170         tp->frto_counter = 0;
2171         tp->bytes_acked = 0;
2172 
2173         tp->reordering = min_t(unsigned int, tp->reordering,
2174                                sysctl_tcp_reordering);
2175         tcp_set_ca_state(sk, TCP_CA_Loss);
2176         tp->high_seq = tp->snd_nxt;
2177         TCP_ECN_queue_cwr(tp);
2178 
2179         tcp_clear_all_retrans_hints(tp);
2180 }
2181 
2182 static void tcp_clear_retrans_partial(struct tcp_sock *tp)
2183 {
2184         tp->retrans_out = 0;
2185         tp->lost_out = 0;
2186 
2187         tp->undo_marker = 0;
2188         tp->undo_retrans = 0;
2189 }
2190 
2191 void tcp_clear_retrans(struct tcp_sock *tp)
2192 {
2193         tcp_clear_retrans_partial(tp);
2194 
2195         tp->fackets_out = 0;
2196         tp->sacked_out = 0;
2197 }
2198 
2199 /* Enter Loss state. If "how" is not zero, forget all SACK information
2200  * and reset tags completely, otherwise preserve SACKs. If receiver
2201  * dropped its ofo queue, we will know this due to reneging detection.
2202  */
2203 void tcp_enter_loss(struct sock *sk, int how)
2204 {
2205         const struct inet_connection_sock *icsk = inet_csk(sk);
2206         struct tcp_sock *tp = tcp_sk(sk);
2207         struct sk_buff *skb;
2208 
2209         /* Reduce ssthresh if it has not yet been made inside this window. */
2210         if (icsk->icsk_ca_state <= TCP_CA_Disorder || tp->snd_una == tp->high_seq ||
2211             (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) {
2212                 tp->prior_ssthresh = tcp_current_ssthresh(sk);
2213                 tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
2214                 tcp_ca_event(sk, CA_EVENT_LOSS);
2215         }
2216         tp->snd_cwnd       = 1;
2217         tp->snd_cwnd_cnt   = 0;
2218         tp->snd_cwnd_stamp = tcp_time_stamp;
2219 
2220         tp->bytes_acked = 0;
2221         tcp_clear_retrans_partial(tp);
2222 
2223         if (tcp_is_reno(tp))
2224                 tcp_reset_reno_sack(tp);
2225 
2226         if (!how) {
2227                 /* Push undo marker, if it was plain RTO and nothing
2228                  * was retransmitted. */
2229                 tp->undo_marker = tp->snd_una;
2230         } else {
2231                 tp->sacked_out = 0;
2232                 tp->fackets_out = 0;
2233         }
2234         tcp_clear_all_retrans_hints(tp);
2235 
2236         tcp_for_write_queue(skb, sk) {
2237                 if (skb == tcp_send_head(sk))
2238                         break;
2239 
2240                 if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS)
2241                         tp->undo_marker = 0;
2242                 TCP_SKB_CB(skb)->sacked &= (~TCPCB_TAGBITS)|TCPCB_SACKED_ACKED;
2243                 if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED) || how) {
2244                         TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED;
2245                         TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
2246                         tp->lost_out += tcp_skb_pcount(skb);
2247                         tp->retransmit_high = TCP_SKB_CB(skb)->end_seq;
2248                 }
2249         }
2250         tcp_verify_left_out(tp);
2251 
2252         tp->reordering = min_t(unsigned int, tp->reordering,
2253                                sysctl_tcp_reordering);
2254         tcp_set_ca_state(sk, TCP_CA_Loss);
2255         tp->high_seq = tp->snd_nxt;
2256         TCP_ECN_queue_cwr(tp);
2257         /* Abort F-RTO algorithm if one is in progress */
2258         tp->frto_counter = 0;
2259 }
2260 
2261 /* If ACK arrived pointing to a remembered SACK, it means that our
2262  * remembered SACKs do not reflect real state of receiver i.e.
2263  * receiver _host_ is heavily congested (or buggy).
2264  *
2265  * Do processing similar to RTO timeout.
2266  */
2267 static int tcp_check_sack_reneging(struct sock *sk, int flag)
2268 {
2269         if (flag & FLAG_SACK_RENEGING) {
2270                 struct inet_connection_sock *icsk = inet_csk(sk);
2271                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSACKRENEGING);
2272 
2273                 tcp_enter_loss(sk, 1);
2274                 icsk->icsk_retransmits++;
2275                 tcp_retransmit_skb(sk, tcp_write_queue_head(sk));
2276                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
2277                                           icsk->icsk_rto, TCP_RTO_MAX);
2278                 return 1;
2279         }
2280         return 0;
2281 }
2282 
2283 static inline int tcp_fackets_out(struct tcp_sock *tp)
2284 {
2285         return tcp_is_reno(tp) ? tp->sacked_out + 1 : tp->fackets_out;
2286 }
2287 
2288 /* Heurestics to calculate number of duplicate ACKs. There's no dupACKs
2289  * counter when SACK is enabled (without SACK, sacked_out is used for
2290  * that purpose).
2291  *
2292  * Instead, with FACK TCP uses fackets_out that includes both SACKed
2293  * segments up to the highest received SACK block so far and holes in
2294  * between them.
2295  *
2296  * With reordering, holes may still be in flight, so RFC3517 recovery
2297  * uses pure sacked_out (total number of SACKed segments) even though
2298  * it violates the RFC that uses duplicate ACKs, often these are equal
2299  * but when e.g. out-of-window ACKs or packet duplication occurs,
2300  * they differ. Since neither occurs due to loss, TCP should really
2301  * ignore them.
2302  */
2303 static inline int tcp_dupack_heurestics(struct tcp_sock *tp)
2304 {
2305         return tcp_is_fack(tp) ? tp->fackets_out : tp->sacked_out + 1;
2306 }
2307 
2308 static inline int tcp_skb_timedout(struct sock *sk, struct sk_buff *skb)
2309 {
2310         return (tcp_time_stamp - TCP_SKB_CB(skb)->when > inet_csk(sk)->icsk_rto);
2311 }
2312 
2313 static inline int tcp_head_timedout(struct sock *sk)
2314 {
2315         struct tcp_sock *tp = tcp_sk(sk);
2316 
2317         return tp->packets_out &&
2318                tcp_skb_timedout(sk, tcp_write_queue_head(sk));
2319 }
2320 
2321 /* Linux NewReno/SACK/FACK/ECN state machine.
2322  * --------------------------------------
2323  *
2324  * "Open"       Normal state, no dubious events, fast path.
2325  * "Disorder"   In all the respects it is "Open",
2326  *              but requires a bit more attention. It is entered when
2327  *              we see some SACKs or dupacks. It is split of "Open"
2328  *              mainly to move some processing from fast path to slow one.
2329  * "CWR"        CWND was reduced due to some Congestion Notification event.
2330  *              It can be ECN, ICMP source quench, local device congestion.
2331  * "Recovery"   CWND was reduced, we are fast-retransmitting.
2332  * "Loss"       CWND was reduced due to RTO timeout or SACK reneging.
2333  *
2334  * tcp_fastretrans_alert() is entered:
2335  * - each incoming ACK, if state is not "Open"
2336  * - when arrived ACK is unusual, namely:
2337  *      * SACK
2338  *      * Duplicate ACK.
2339  *      * ECN ECE.
2340  *
2341  * Counting packets in flight is pretty simple.
2342  *
2343  *      in_flight = packets_out - left_out + retrans_out
2344  *
2345  *      packets_out is SND.NXT-SND.UNA counted in packets.
2346  *
2347  *      retrans_out is number of retransmitted segments.
2348  *
2349  *      left_out is number of segments left network, but not ACKed yet.
2350  *
2351  *              left_out = sacked_out + lost_out
2352  *
2353  *     sacked_out: Packets, which arrived to receiver out of order
2354  *                 and hence not ACKed. With SACKs this number is simply
2355  *                 amount of SACKed data. Even without SACKs
2356  *                 it is easy to give pretty reliable estimate of this number,
2357  *                 counting duplicate ACKs.
2358  *
2359  *       lost_out: Packets lost by network. TCP has no explicit
2360  *                 "loss notification" feedback from network (for now).
2361  *                 It means that this number can be only _guessed_.
2362  *                 Actually, it is the heuristics to predict lossage that
2363  *                 distinguishes different algorithms.
2364  *
2365  *      F.e. after RTO, when all the queue is considered as lost,
2366  *      lost_out = packets_out and in_flight = retrans_out.
2367  *
2368  *              Essentially, we have now two algorithms counting
2369  *              lost packets.
2370  *
2371  *              FACK: It is the simplest heuristics. As soon as we decided
2372  *              that something is lost, we decide that _all_ not SACKed
2373  *              packets until the most forward SACK are lost. I.e.
2374  *              lost_out = fackets_out - sacked_out and left_out = fackets_out.
2375  *              It is absolutely correct estimate, if network does not reorder
2376  *              packets. And it loses any connection to reality when reordering
2377  *              takes place. We use FACK by default until reordering
2378  *              is suspected on the path to this destination.
2379  *
2380  *              NewReno: when Recovery is entered, we assume that one segment
2381  *              is lost (classic Reno). While we are in Recovery and
2382  *              a partial ACK arrives, we assume that one more packet
2383  *              is lost (NewReno). This heuristics are the same in NewReno
2384  *              and SACK.
2385  *
2386  *  Imagine, that's all! Forget about all this shamanism about CWND inflation
2387  *  deflation etc. CWND is real congestion window, never inflated, changes
2388  *  only according to classic VJ rules.
2389  *
2390  * Really tricky (and requiring careful tuning) part of algorithm
2391  * is hidden in functions tcp_time_to_recover() and tcp_xmit_retransmit_queue().
2392  * The first determines the moment _when_ we should reduce CWND and,
2393  * hence, slow down forward transmission. In fact, it determines the moment
2394  * when we decide that hole is caused by loss, rather than by a reorder.
2395  *
2396  * tcp_xmit_retransmit_queue() decides, _what_ we should retransmit to fill
2397  * holes, caused by lost packets.
2398  *
2399  * And the most logically complicated part of algorithm is undo
2400  * heuristics. We detect false retransmits due to both too early
2401  * fast retransmit (reordering) and underestimated RTO, analyzing
2402  * timestamps and D-SACKs. When we detect that some segments were
2403  * retransmitted by mistake and CWND reduction was wrong, we undo
2404  * window reduction and abort recovery phase. This logic is hidden
2405  * inside several functions named tcp_try_undo_<something>.
2406  */
2407 
2408 /* This function decides, when we should leave Disordered state
2409  * and enter Recovery phase, reducing congestion window.
2410  *
2411  * Main question: may we further continue forward transmission
2412  * with the same cwnd?
2413  */
2414 static int tcp_time_to_recover(struct sock *sk)
2415 {
2416         struct tcp_sock *tp = tcp_sk(sk);
2417         __u32 packets_out;
2418 
2419         /* Do not perform any recovery during F-RTO algorithm */
2420         if (tp->frto_counter)
2421                 return 0;
2422 
2423         /* Trick#1: The loss is proven. */
2424         if (tp->lost_out)
2425                 return 1;
2426 
2427         /* Not-A-Trick#2 : Classic rule... */
2428         if (tcp_dupack_heurestics(tp) > tp->reordering)
2429                 return 1;
2430 
2431         /* Trick#3 : when we use RFC2988 timer restart, fast
2432          * retransmit can be triggered by timeout of queue head.
2433          */
2434         if (tcp_is_fack(tp) && tcp_head_timedout(sk))
2435                 return 1;
2436 
2437         /* Trick#4: It is still not OK... But will it be useful to delay
2438          * recovery more?
2439          */
2440         packets_out = tp->packets_out;
2441         if (packets_out <= tp->reordering &&
2442             tp->sacked_out >= max_t(__u32, packets_out/2, sysctl_tcp_reordering) &&
2443             !tcp_may_send_now(sk)) {
2444                 /* We have nothing to send. This connection is limited
2445                  * either by receiver window or by application.
2446                  */
2447                 return 1;
2448         }
2449 
2450         return 0;
2451 }
2452 
2453 /* New heuristics: it is possible only after we switched to restart timer
2454  * each time when something is ACKed. Hence, we can detect timed out packets
2455  * during fast retransmit without falling to slow start.
2456  *
2457  * Usefulness of this as is very questionable, since we should know which of
2458  * the segments is the next to timeout which is relatively expensive to find
2459  * in general case unless we add some data structure just for that. The
2460  * current approach certainly won't find the right one too often and when it
2461  * finally does find _something_ it usually marks large part of the window
2462  * right away (because a retransmission with a larger timestamp blocks the
2463  * loop from advancing). -ij
2464  */
2465 static void tcp_timeout_skbs(struct sock *sk)
2466 {
2467         struct tcp_sock *tp = tcp_sk(sk);
2468         struct sk_buff *skb;
2469 
2470         if (!tcp_is_fack(tp) || !tcp_head_timedout(sk))
2471                 return;
2472 
2473         skb = tp->scoreboard_skb_hint;
2474         if (tp->scoreboard_skb_hint == NULL)
2475                 skb = tcp_write_queue_head(sk);
2476 
2477         tcp_for_write_queue_from(skb, sk) {
2478                 if (skb == tcp_send_head(sk))
2479                         break;
2480                 if (!tcp_skb_timedout(sk, skb))
2481                         break;
2482 
2483                 tcp_skb_mark_lost(tp, skb);
2484         }
2485 
2486         tp->scoreboard_skb_hint = skb;
2487 
2488         tcp_verify_left_out(tp);
2489 }
2490 
2491 /* Mark head of queue up as lost. With RFC3517 SACK, the packets is
2492  * is against sacked "cnt", otherwise it's against facked "cnt"
2493  */
2494 static void tcp_mark_head_lost(struct sock *sk, int packets)
2495 {
2496         struct tcp_sock *tp = tcp_sk(sk);
2497         struct sk_buff *skb;
2498         int cnt, oldcnt;
2499         int err;
2500         unsigned int mss;
2501 
2502         WARN_ON(packets > tp->packets_out);
2503         if (tp->lost_skb_hint) {
2504                 skb = tp->lost_skb_hint;
2505                 cnt = tp->lost_cnt_hint;
2506         } else {
2507                 skb = tcp_write_queue_head(sk);
2508                 cnt = 0;
2509         }
2510 
2511         tcp_for_write_queue_from(skb, sk) {
2512                 if (skb == tcp_send_head(sk))
2513                         break;
2514                 /* TODO: do this better */
2515                 /* this is not the most efficient way to do this... */
2516                 tp->lost_skb_hint = skb;
2517                 tp->lost_cnt_hint = cnt;
2518 
2519                 if (after(TCP_SKB_CB(skb)->end_seq, tp->high_seq))
2520                         break;
2521 
2522                 oldcnt = cnt;
2523                 if (tcp_is_fack(tp) || tcp_is_reno(tp) ||
2524                     (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
2525                         cnt += tcp_skb_pcount(skb);
2526 
2527                 if (cnt > packets) {
2528                         if (tcp_is_sack(tp) || (oldcnt >= packets))
2529                                 break;
2530 
2531                         mss = skb_shinfo(skb)->gso_size;
2532                         err = tcp_fragment(sk, skb, (packets - oldcnt) * mss, mss);
2533                         if (err < 0)
2534                                 break;
2535                         cnt = packets;
2536                 }
2537 
2538                 tcp_skb_mark_lost(tp, skb);
2539         }
2540         tcp_verify_left_out(tp);
2541 }
2542 
2543 /* Account newly detected lost packet(s) */
2544 
2545 static void tcp_update_scoreboard(struct sock *sk, int fast_rexmit)
2546 {
2547         struct tcp_sock *tp = tcp_sk(sk);
2548 
2549         if (tcp_is_reno(tp)) {
2550                 tcp_mark_head_lost(sk, 1);
2551         } else if (tcp_is_fack(tp)) {
2552                 int lost = tp->fackets_out - tp->reordering;
2553                 if (lost <= 0)
2554                         lost = 1;
2555                 tcp_mark_head_lost(sk, lost);
2556         } else {
2557                 int sacked_upto = tp->sacked_out - tp->reordering;
2558                 if (sacked_upto < fast_rexmit)
2559                         sacked_upto = fast_rexmit;
2560                 tcp_mark_head_lost(sk, sacked_upto);
2561         }
2562 
2563         tcp_timeout_skbs(sk);
2564 }
2565 
2566 /* CWND moderation, preventing bursts due to too big ACKs
2567  * in dubious situations.
2568  */
2569 static inline void tcp_moderate_cwnd(struct tcp_sock *tp)
2570 {
2571         tp->snd_cwnd = min(tp->snd_cwnd,
2572                            tcp_packets_in_flight(tp) + tcp_max_burst(tp));
2573         tp->snd_cwnd_stamp = tcp_time_stamp;
2574 }
2575 
2576 /* Lower bound on congestion window is slow start threshold
2577  * unless congestion avoidance choice decides to overide it.
2578  */
2579 static inline u32 tcp_cwnd_min(const struct sock *sk)
2580 {
2581         const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;
2582 
2583         return ca_ops->min_cwnd ? ca_ops->min_cwnd(sk) : tcp_sk(sk)->snd_ssthresh;
2584 }
2585 
2586 /* Decrease cwnd each second ack. */
2587 static void tcp_cwnd_down(struct sock *sk, int flag)
2588 {
2589         struct tcp_sock *tp = tcp_sk(sk);
2590         int decr = tp->snd_cwnd_cnt + 1;
2591 
2592         if ((flag & (FLAG_ANY_PROGRESS | FLAG_DSACKING_ACK)) ||
2593             (tcp_is_reno(tp) && !(flag & FLAG_NOT_DUP))) {
2594                 tp->snd_cwnd_cnt = decr & 1;
2595                 decr >>= 1;
2596 
2597                 if (decr && tp->snd_cwnd > tcp_cwnd_min(sk))
2598                         tp->snd_cwnd -= decr;
2599 
2600                 tp->snd_cwnd = min(tp->snd_cwnd, tcp_packets_in_flight(tp) + 1);
2601                 tp->snd_cwnd_stamp = tcp_time_stamp;
2602         }
2603 }
2604 
2605 /* Nothing was retransmitted or returned timestamp is less
2606  * than timestamp of the first retransmission.
2607  */
2608 static inline int tcp_packet_delayed(struct tcp_sock *tp)
2609 {
2610         return !tp->retrans_stamp ||
2611                 (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
2612                  before(tp->rx_opt.rcv_tsecr, tp->retrans_stamp));
2613 }
2614 
2615 /* Undo procedures. */
2616 
2617 #if FASTRETRANS_DEBUG > 1
2618 static void DBGUNDO(struct sock *sk, const char *msg)
2619 {
2620         struct tcp_sock *tp = tcp_sk(sk);
2621         struct inet_sock *inet = inet_sk(sk);
2622 
2623         if (sk->sk_family == AF_INET) {
2624                 printk(KERN_DEBUG "Undo %s %pI4/%u c%u l%u ss%u/%u p%u\n",
2625                        msg,
2626                        &inet->daddr, ntohs(inet->dport),
2627                        tp->snd_cwnd, tcp_left_out(tp),
2628                        tp->snd_ssthresh, tp->prior_ssthresh,
2629                        tp->packets_out);
2630         }
2631 #if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
2632         else if (sk->sk_family == AF_INET6) {
2633                 struct ipv6_pinfo *np = inet6_sk(sk);
2634                 printk(KERN_DEBUG "Undo %s %pI6/%u c%u l%u ss%u/%u p%u\n",
2635                        msg,
2636                        &np->daddr, ntohs(inet->dport),
2637                        tp->snd_cwnd, tcp_left_out(tp),
2638                        tp->snd_ssthresh, tp->prior_ssthresh,
2639                        tp->packets_out);
2640         }
2641 #endif
2642 }
2643 #else
2644 #define DBGUNDO(x...) do { } while (0)
2645 #endif
2646 
2647 static void tcp_undo_cwr(struct sock *sk, const int undo)
2648 {
2649         struct tcp_sock *tp = tcp_sk(sk);
2650 
2651         if (tp->prior_ssthresh) {
2652                 const struct inet_connection_sock *icsk = inet_csk(sk);
2653 
2654                 if (icsk->icsk_ca_ops->undo_cwnd)
2655                         tp->snd_cwnd = icsk->icsk_ca_ops->undo_cwnd(sk);
2656                 else
2657                         tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh << 1);
2658 
2659                 if (undo && tp->prior_ssthresh > tp->snd_ssthresh) {
2660                         tp->snd_ssthresh = tp->prior_ssthresh;
2661                         TCP_ECN_withdraw_cwr(tp);
2662                 }
2663         } else {
2664                 tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh);
2665         }
2666         tcp_moderate_cwnd(tp);
2667         tp->snd_cwnd_stamp = tcp_time_stamp;
2668 }
2669 
2670 static inline int tcp_may_undo(struct tcp_sock *tp)
2671 {
2672         return tp->undo_marker && (!tp->undo_retrans || tcp_packet_delayed(tp));
2673 }
2674 
2675 /* People celebrate: "We love our President!" */
2676 static int tcp_try_undo_recovery(struct sock *sk)
2677 {
2678         struct tcp_sock *tp = tcp_sk(sk);
2679 
2680         if (tcp_may_undo(tp)) {
2681                 int mib_idx;
2682 
2683                 /* Happy end! We did not retransmit anything
2684                  * or our original transmission succeeded.
2685                  */
2686                 DBGUNDO(sk, inet_csk(sk)->icsk_ca_state == TCP_CA_Loss ? "loss" : "retrans");
2687                 tcp_undo_cwr(sk, 1);
2688                 if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss)
2689                         mib_idx = LINUX_MIB_TCPLOSSUNDO;
2690                 else
2691                         mib_idx = LINUX_MIB_TCPFULLUNDO;
2692 
2693                 NET_INC_STATS_BH(sock_net(sk), mib_idx);
2694                 tp->undo_marker = 0;
2695         }
2696         if (tp->snd_una == tp->high_seq && tcp_is_reno(tp)) {
2697                 /* Hold old state until something *above* high_seq
2698                  * is ACKed. For Reno it is MUST to prevent false
2699                  * fast retransmits (RFC2582). SACK TCP is safe. */
2700                 tcp_moderate_cwnd(tp);
2701                 return 1;
2702         }
2703         tcp_set_ca_state(sk, TCP_CA_Open);
2704         return 0;
2705 }
2706 
2707 /* Try to undo cwnd reduction, because D-SACKs acked all retransmitted data */
2708 static void tcp_try_undo_dsack(struct sock *sk)
2709 {
2710         struct tcp_sock *tp = tcp_sk(sk);
2711 
2712         if (tp->undo_marker && !tp->undo_retrans) {
2713                 DBGUNDO(sk, "D-SACK");
2714                 tcp_undo_cwr(sk, 1);
2715                 tp->undo_marker = 0;
2716                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPDSACKUNDO);
2717         }
2718 }
2719 
2720 /* Undo during fast recovery after partial ACK. */
2721 
2722 static int tcp_try_undo_partial(struct sock *sk, int acked)
2723 {
2724         struct tcp_sock *tp = tcp_sk(sk);
2725         /* Partial ACK arrived. Force Hoe's retransmit. */
2726         int failed = tcp_is_reno(tp) || (tcp_fackets_out(tp) > tp->reordering);
2727 
2728         if (tcp_may_undo(tp)) {
2729                 /* Plain luck! Hole if filled with delayed
2730                  * packet, rather than with a retransmit.
2731                  */
2732                 if (tp->retrans_out == 0)
2733                         tp->retrans_stamp = 0;
2734 
2735                 tcp_update_reordering(sk, tcp_fackets_out(tp) + acked, 1);
2736 
2737                 DBGUNDO(sk, "Hoe");
2738                 tcp_undo_cwr(sk, 0);
2739                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPPARTIALUNDO);
2740 
2741                 /* So... Do not make Hoe's retransmit yet.
2742                  * If the first packet was delayed, the rest
2743                  * ones are most probably delayed as well.
2744                  */
2745                 failed = 0;
2746         }
2747         return failed;
2748 }
2749 
2750 /* Undo during loss recovery after partial ACK. */
2751 static int tcp_try_undo_loss(struct sock *sk)
2752 {
2753         struct tcp_sock *tp = tcp_sk(sk);
2754 
2755         if (tcp_may_undo(tp)) {
2756                 struct sk_buff *skb;
2757                 tcp_for_write_queue(skb, sk) {
2758                         if (skb == tcp_send_head(sk))
2759                                 break;
2760                         TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
2761                 }
2762 
2763                 tcp_clear_all_retrans_hints(tp);
2764 
2765                 DBGUNDO(sk, "partial loss");
2766                 tp->lost_out = 0;
2767                 tcp_undo_cwr(sk, 1);
2768                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPLOSSUNDO);
2769                 inet_csk(sk)->icsk_retransmits = 0;
2770                 tp->undo_marker = 0;
2771                 if (tcp_is_sack(tp))
2772                         tcp_set_ca_state(sk, TCP_CA_Open);
2773                 return 1;
2774         }
2775         return 0;
2776 }
2777 
2778 static inline void tcp_complete_cwr(struct sock *sk)
2779 {
2780         struct tcp_sock *tp = tcp_sk(sk);
2781         tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
2782         tp->snd_cwnd_stamp = tcp_time_stamp;
2783         tcp_ca_event(sk, CA_EVENT_COMPLETE_CWR);
2784 }
2785 
2786 static void tcp_try_keep_open(struct sock *sk)
2787 {
2788         struct tcp_sock *tp = tcp_sk(sk);
2789         int state = TCP_CA_Open;
2790 
2791         if (tcp_left_out(tp) || tp->retrans_out || tp->undo_marker)
2792                 state = TCP_CA_Disorder;
2793 
2794         if (inet_csk(sk)->icsk_ca_state != state) {
2795                 tcp_set_ca_state(sk, state);
2796                 tp->high_seq = tp->snd_nxt;
2797         }
2798 }
2799 
2800 static void tcp_try_to_open(struct sock *sk, int flag)
2801 {
2802         struct tcp_sock *tp = tcp_sk(sk);
2803 
2804         tcp_verify_left_out(tp);
2805 
2806         if (!tp->frto_counter && tp->retrans_out == 0)
2807                 tp->retrans_stamp = 0;
2808 
2809         if (flag & FLAG_ECE)
2810                 tcp_enter_cwr(sk, 1);
2811 
2812         if (inet_csk(sk)->icsk_ca_state != TCP_CA_CWR) {
2813                 tcp_try_keep_open(sk);
2814                 tcp_moderate_cwnd(tp);
2815         } else {
2816                 tcp_cwnd_down(sk, flag);
2817         }
2818 }
2819 
2820 static void tcp_mtup_probe_failed(struct sock *sk)
2821 {
2822         struct inet_connection_sock *icsk = inet_csk(sk);
2823 
2824         icsk->icsk_mtup.search_high = icsk->icsk_mtup.probe_size - 1;
2825         icsk->icsk_mtup.probe_size = 0;
2826 }
2827 
2828 static void tcp_mtup_probe_success(struct sock *sk)
2829 {
2830         struct tcp_sock *tp = tcp_sk(sk);
2831         struct inet_connection_sock *icsk = inet_csk(sk);
2832 
2833         /* FIXME: breaks with very large cwnd */
2834         tp->prior_ssthresh = tcp_current_ssthresh(sk);
2835         tp->snd_cwnd = tp->snd_cwnd *
2836                        tcp_mss_to_mtu(sk, tp->mss_cache) /
2837                        icsk->icsk_mtup.probe_size;
2838         tp->snd_cwnd_cnt = 0;
2839         tp->snd_cwnd_stamp = tcp_time_stamp;
2840         tp->rcv_ssthresh = tcp_current_ssthresh(sk);
2841 
2842         icsk->icsk_mtup.search_low = icsk->icsk_mtup.probe_size;
2843         icsk->icsk_mtup.probe_size = 0;
2844         tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
2845 }
2846 
2847 /* Do a simple retransmit without using the backoff mechanisms in
2848  * tcp_timer. This is used for path mtu discovery.
2849  * The socket is already locked here.
2850  */
2851 void tcp_simple_retransmit(struct sock *sk)
2852 {
2853         const struct inet_connection_sock *icsk = inet_csk(sk);
2854         struct tcp_sock *tp = tcp_sk(sk);
2855         struct sk_buff *skb;
2856         unsigned int mss = tcp_current_mss(sk);
2857         u32 prior_lost = tp->lost_out;
2858 
2859         tcp_for_write_queue(skb, sk) {
2860                 if (skb == tcp_send_head(sk))
2861                         break;
2862                 if (tcp_skb_seglen(skb) > mss &&
2863                     !(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) {
2864                         if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
2865                                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
2866                                 tp->retrans_out -= tcp_skb_pcount(skb);
2867                         }
2868                         tcp_skb_mark_lost_uncond_verify(tp, skb);
2869                 }
2870         }
2871 
2872         tcp_clear_retrans_hints_partial(tp);
2873 
2874         if (prior_lost == tp->lost_out)
2875                 return;
2876 
2877         if (tcp_is_reno(tp))
2878                 tcp_limit_reno_sacked(tp);
2879 
2880         tcp_verify_left_out(tp);
2881 
2882         /* Don't muck with the congestion window here.
2883          * Reason is that we do not increase amount of _data_
2884          * in network, but units changed and effective
2885          * cwnd/ssthresh really reduced now.
2886          */
2887         if (icsk->icsk_ca_state != TCP_CA_Loss) {
2888                 tp->high_seq = tp->snd_nxt;
2889                 tp->snd_ssthresh = tcp_current_ssthresh(sk);
2890                 tp->prior_ssthresh = 0;
2891                 tp->undo_marker = 0;
2892                 tcp_set_ca_state(sk, TCP_CA_Loss);
2893         }
2894         tcp_xmit_retransmit_queue(sk);
2895 }
2896 
2897 /* Process an event, which can update packets-in-flight not trivially.
2898  * Main goal of this function is to calculate new estimate for left_out,
2899  * taking into account both packets sitting in receiver's buffer and
2900  * packets lost by network.
2901  *
2902  * Besides that it does CWND reduction, when packet loss is detected
2903  * and changes state of machine.
2904  *
2905  * It does _not_ decide what to send, it is made in function
2906  * tcp_xmit_retransmit_queue().
2907  */
2908 static void tcp_fastretrans_alert(struct sock *sk, int pkts_acked, int flag)
2909 {
2910         struct inet_connection_sock *icsk = inet_csk(sk);
2911         struct tcp_sock *tp = tcp_sk(sk);
2912         int is_dupack = !(flag & (FLAG_SND_UNA_ADVANCED | FLAG_NOT_DUP));
2913         int do_lost = is_dupack || ((flag & FLAG_DATA_SACKED) &&
2914                                     (tcp_fackets_out(tp) > tp->reordering));
2915         int fast_rexmit = 0, mib_idx;
2916 
2917         if (WARN_ON(!tp->packets_out && tp->sacked_out))
2918                 tp->sacked_out = 0;
2919         if (WARN_ON(!tp->sacked_out && tp->fackets_out))
2920                 tp->fackets_out = 0;
2921 
2922         /* Now state machine starts.
2923          * A. ECE, hence prohibit cwnd undoing, the reduction is required. */
2924         if (flag & FLAG_ECE)
2925                 tp->prior_ssthresh = 0;
2926 
2927         /* B. In all the states check for reneging SACKs. */
2928         if (tcp_check_sack_reneging(sk, flag))
2929                 return;
2930 
2931         /* C. Process data loss notification, provided it is valid. */
2932         if (tcp_is_fack(tp) && (flag & FLAG_DATA_LOST) &&
2933             before(tp->snd_una, tp->high_seq) &&
2934             icsk->icsk_ca_state != TCP_CA_Open &&
2935             tp->fackets_out > tp->reordering) {
2936                 tcp_mark_head_lost(sk, tp->fackets_out - tp->reordering);
2937                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPLOSS);
2938         }
2939 
2940         /* D. Check consistency of the current state. */
2941         tcp_verify_left_out(tp);
2942 
2943         /* E. Check state exit conditions. State can be terminated
2944          *    when high_seq is ACKed. */
2945         if (icsk->icsk_ca_state == TCP_CA_Open) {
2946                 WARN_ON(tp->retrans_out != 0);
2947                 tp->retrans_stamp = 0;
2948         } else if (!before(tp->snd_una, tp->high_seq)) {
2949                 switch (icsk->icsk_ca_state) {
2950                 case TCP_CA_Loss:
2951                         icsk->icsk_retransmits = 0;
2952                         if (tcp_try_undo_recovery(sk))
2953                                 return;
2954                         break;
2955 
2956                 case TCP_CA_CWR:
2957                         /* CWR is to be held something *above* high_seq
2958                          * is ACKed for CWR bit to reach receiver. */
2959                         if (tp->snd_una != tp->high_seq) {
2960                                 tcp_complete_cwr(sk);
2961                                 tcp_set_ca_state(sk, TCP_CA_Open);
2962                         }
2963                         break;
2964 
2965                 case TCP_CA_Disorder:
2966                         tcp_try_undo_dsack(sk);
2967                         if (!tp->undo_marker ||
2968                             /* For SACK case do not Open to allow to undo
2969                              * catching for all duplicate ACKs. */
2970                             tcp_is_reno(tp) || tp->snd_una != tp->high_seq) {
2971                                 tp->undo_marker = 0;
2972                                 tcp_set_ca_state(sk, TCP_CA_Open);
2973                         }
2974                         break;
2975 
2976                 case TCP_CA_Recovery:
2977                         if (tcp_is_reno(tp))
2978                                 tcp_reset_reno_sack(tp);
2979                         if (tcp_try_undo_recovery(sk))
2980                                 return;
2981                         tcp_complete_cwr(sk);
2982                         break;
2983                 }
2984         }
2985 
2986         /* F. Process state. */
2987         switch (icsk->icsk_ca_state) {
2988         case TCP_CA_Recovery:
2989                 if (!(flag & FLAG_SND_UNA_ADVANCED)) {
2990                         if (tcp_is_reno(tp) && is_dupack)
2991                                 tcp_add_reno_sack(sk);
2992                 } else
2993                         do_lost = tcp_try_undo_partial(sk, pkts_acked);
2994                 break;
2995         case TCP_CA_Loss:
2996                 if (flag & FLAG_DATA_ACKED)
2997                         icsk->icsk_retransmits = 0;
2998                 if (tcp_is_reno(tp) && flag & FLAG_SND_UNA_ADVANCED)
2999                         tcp_reset_reno_sack(tp);
3000                 if (!tcp_try_undo_loss(sk)) {
3001                         tcp_moderate_cwnd(tp);
3002                         tcp_xmit_retransmit_queue(sk);
3003                         return;
3004                 }
3005                 if (icsk->icsk_ca_state != TCP_CA_Open)
3006                         return;
3007                 /* Loss is undone; fall through to processing in Open state. */
3008         default:
3009                 if (tcp_is_reno(tp)) {
3010                         if (flag & FLAG_SND_UNA_ADVANCED)
3011                                 tcp_reset_reno_sack(tp);
3012                         if (is_dupack)
3013                                 tcp_add_reno_sack(sk);
3014                 }
3015 
3016                 if (icsk->icsk_ca_state == TCP_CA_Disorder)
3017                         tcp_try_undo_dsack(sk);
3018 
3019                 if (!tcp_time_to_recover(sk)) {
3020                         tcp_try_to_open(sk, flag);
3021                         return;
3022                 }
3023 
3024                 /* MTU probe failure: don't reduce cwnd */
3025                 if (icsk->icsk_ca_state < TCP_CA_CWR &&
3026                     icsk->icsk_mtup.probe_size &&
3027                     tp->snd_una == tp->mtu_probe.probe_seq_start) {
3028                         tcp_mtup_probe_failed(sk);
3029                         /* Restores the reduction we did in tcp_mtup_probe() */
3030                         tp->snd_cwnd++;
3031                         tcp_simple_retransmit(sk);
3032                         return;
3033                 }
3034 
3035                 /* Otherwise enter Recovery state */
3036 
3037                 if (tcp_is_reno(tp))
3038                         mib_idx = LINUX_MIB_TCPRENORECOVERY;
3039                 else
3040                         mib_idx = LINUX_MIB_TCPSACKRECOVERY;
3041 
3042                 NET_INC_STATS_BH(sock_net(sk), mib_idx);
3043 
3044                 tp->high_seq = tp->snd_nxt;
3045                 tp->prior_ssthresh = 0;
3046                 tp->undo_marker = tp->snd_una;
3047                 tp->undo_retrans = tp->retrans_out;
3048 
3049                 if (icsk->icsk_ca_state < TCP_CA_CWR) {
3050                         if (!(flag & FLAG_ECE))
3051                                 tp->prior_ssthresh = tcp_current_ssthresh(sk);
3052                         tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
3053                         TCP_ECN_queue_cwr(tp);
3054                 }
3055 
3056                 tp->bytes_acked = 0;
3057                 tp->snd_cwnd_cnt = 0;
3058                 tcp_set_ca_state(sk, TCP_CA_Recovery);
3059                 fast_rexmit = 1;
3060         }
3061 
3062         if (do_lost || (tcp_is_fack(tp) && tcp_head_timedout(sk)))
3063                 tcp_update_scoreboard(sk, fast_rexmit);
3064         tcp_cwnd_down(sk, flag);
3065         tcp_xmit_retransmit_queue(sk);
3066 }
3067 
3068 static void tcp_valid_rtt_meas(struct sock *sk, u32 seq_rtt)
3069 {
3070         tcp_rtt_estimator(sk, seq_rtt);
3071         tcp_set_rto(sk);
3072         inet_csk(sk)->icsk_backoff = 0;
3073 }
3074 
3075 /* Read draft-ietf-tcplw-high-performance before mucking
3076  * with this code. (Supersedes RFC1323)
3077  */
3078 static void tcp_ack_saw_tstamp(struct sock *sk, int flag)
3079 {
3080         /* RTTM Rule: A TSecr value received in a segment is used to
3081          * update the averaged RTT measurement only if the segment
3082          * acknowledges some new data, i.e., only if it advances the
3083          * left edge of the send window.
3084          *
3085          * See draft-ietf-tcplw-high-performance-00, section 3.3.
3086          * 1998/04/10 Andrey V. Savochkin <saw@msu.ru>
3087          *
3088          * Changed: reset backoff as soon as we see the first valid sample.
3089          * If we do not, we get strongly overestimated rto. With timestamps
3090          * samples are accepted even from very old segments: f.e., when rtt=1
3091          * increases to 8, we retransmit 5 times and after 8 seconds delayed
3092          * answer arrives rto becomes 120 seconds! If at least one of segments
3093          * in window is lost... Voila.                          --ANK (010210)
3094          */
3095         struct tcp_sock *tp = tcp_sk(sk);
3096 
3097         tcp_valid_rtt_meas(sk, tcp_time_stamp - tp->rx_opt.rcv_tsecr);
3098 }
3099 
3100 static void tcp_ack_no_tstamp(struct sock *sk, u32 seq_rtt, int flag)
3101 {
3102         /* We don't have a timestamp. Can only use
3103          * packets that are not retransmitted to determine
3104          * rtt estimates. Also, we must not reset the
3105          * backoff for rto until we get a non-retransmitted
3106          * packet. This allows us to deal with a situation
3107          * where the network delay has increased suddenly.
3108          * I.e. Karn's algorithm. (SIGCOMM '87, p5.)
3109          */
3110 
3111         if (flag & FLAG_RETRANS_DATA_ACKED)
3112                 return;
3113 
3114         tcp_valid_rtt_meas(sk, seq_rtt);
3115 }
3116 
3117 static inline void tcp_ack_update_rtt(struct sock *sk, const int flag,
3118                                       const s32 seq_rtt)
3119 {
3120         const struct tcp_sock *tp = tcp_sk(sk);
3121         /* Note that peer MAY send zero echo. In this case it is ignored. (rfc1323) */
3122         if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
3123                 tcp_ack_saw_tstamp(sk, flag);
3124         else if (seq_rtt >= 0)
3125                 tcp_ack_no_tstamp(sk, seq_rtt, flag);
3126 }
3127 
3128 static void tcp_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
3129 {
3130         const struct inet_connection_sock *icsk = inet_csk(sk);
3131         icsk->icsk_ca_ops->cong_avoid(sk, ack, in_flight);
3132         tcp_sk(sk)->snd_cwnd_stamp = tcp_time_stamp;
3133 }
3134 
3135 /* Restart timer after forward progress on connection.
3136  * RFC2988 recommends to restart timer to now+rto.
3137  */
3138 static void tcp_rearm_rto(struct sock *sk)
3139 {
3140         struct tcp_sock *tp = tcp_sk(sk);
3141 
3142         if (!tp->packets_out) {
3143                 inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS);
3144         } else {
3145                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
3146                                           inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
3147         }
3148 }
3149 
3150 /* If we get here, the whole TSO packet has not been acked. */
3151 static u32 tcp_tso_acked(struct sock *sk, struct sk_buff *skb)
3152 {
3153         struct tcp_sock *tp = tcp_sk(sk);
3154         u32 packets_acked;
3155 
3156         BUG_ON(!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una));
3157 
3158         packets_acked = tcp_skb_pcount(skb);
3159         if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
3160                 return 0;
3161         packets_acked -= tcp_skb_pcount(skb);
3162 
3163         if (packets_acked) {
3164                 BUG_ON(tcp_skb_pcount(skb) == 0);
3165                 BUG_ON(!before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq));
3166         }
3167 
3168         return packets_acked;
3169 }
3170 
3171 /* Remove acknowledged frames from the retransmission queue. If our packet
3172  * is before the ack sequence we can discard it as it's confirmed to have
3173  * arrived at the other end.
3174  */
3175 static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
3176                                u32 prior_snd_una)
3177 {
3178         struct tcp_sock *tp = tcp_sk(sk);
3179         const struct inet_connection_sock *icsk = inet_csk(sk);
3180         struct sk_buff *skb;
3181         u32 now = tcp_time_stamp;
3182         int fully_acked = 1;
3183         int flag = 0;
3184         u32 pkts_acked = 0;
3185         u32 reord = tp->packets_out;
3186         u32 prior_sacked = tp->sacked_out;
3187         s32 seq_rtt = -1;
3188         s32 ca_seq_rtt = -1;
3189         ktime_t last_ackt = net_invalid_timestamp();
3190 
3191         while ((skb = tcp_write_queue_head(sk)) && skb != tcp_send_head(sk)) {
3192                 struct tcp_skb_cb *scb = TCP_SKB_CB(skb);
3193                 u32 acked_pcount;
3194                 u8 sacked = scb->sacked;
3195 
3196                 /* Determine how many packets and what bytes were acked, tso and else */
3197                 if (after(scb->end_seq, tp->snd_una)) {
3198                         if (tcp_skb_pcount(skb) == 1 ||
3199                             !after(tp->snd_una, scb->seq))
3200                                 break;
3201 
3202                         acked_pcount = tcp_tso_acked(sk, skb);
3203                         if (!acked_pcount)
3204                                 break;
3205 
3206                         fully_acked = 0;
3207                 } else {
3208                         acked_pcount = tcp_skb_pcount(skb);
3209                 }
3210 
3211                 if (sacked & TCPCB_RETRANS) {
3212                         if (sacked & TCPCB_SACKED_RETRANS)
3213                                 tp->retrans_out -= acked_pcount;
3214                         flag |= FLAG_RETRANS_DATA_ACKED;
3215                         ca_seq_rtt = -1;
3216                         seq_rtt = -1;
3217                         if ((flag & FLAG_DATA_ACKED) || (acked_pcount > 1))
3218                                 flag |= FLAG_NONHEAD_RETRANS_ACKED;
3219                 } else {
3220                         ca_seq_rtt = now - scb->when;
3221                         last_ackt = skb->tstamp;
3222                         if (seq_rtt < 0) {
3223                                 seq_rtt = ca_seq_rtt;
3224                         }
3225                         if (!(sacked & TCPCB_SACKED_ACKED))
3226                                 reord = min(pkts_acked, reord);
3227                 }
3228 
3229                 if (sacked & TCPCB_SACKED_ACKED)
3230                         tp->sacked_out -= acked_pcount;
3231                 if (sacked & TCPCB_LOST)
3232                         tp->lost_out -= acked_pcount;
3233 
3234                 tp->packets_out -= acked_pcount;
3235                 pkts_acked += acked_pcount;
3236 
3237                 /* Initial outgoing SYN's get put onto the write_queue
3238                  * just like anything else we transmit.  It is not
3239                  * true data, and if we misinform our callers that
3240                  * this ACK acks real data, we will erroneously exit
3241                  * connection startup slow start one packet too
3242                  * quickly.  This is severely frowned upon behavior.
3243                  */
3244                 if (!(scb->flags & TCPCB_FLAG_SYN)) {
3245                         flag |= FLAG_DATA_ACKED;
3246                 } else {
3247                         flag |= FLAG_SYN_ACKED;
3248                         tp->retrans_stamp = 0;
3249                 }
3250 
3251                 if (!fully_acked)
3252                         break;
3253 
3254                 tcp_unlink_write_queue(skb, sk);
3255                 sk_wmem_free_skb(sk, skb);
3256                 tp->scoreboard_skb_hint = NULL;
3257                 if (skb == tp->retransmit_skb_hint)
3258                         tp->retransmit_skb_hint = NULL;
3259                 if (skb == tp->lost_skb_hint)
3260                         tp->lost_skb_hint = NULL;
3261         }
3262 
3263         if (likely(between(tp->snd_up, prior_snd_una, tp->snd_una)))
3264                 tp->snd_up = tp->snd_una;
3265 
3266         if (skb && (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
3267                 flag |= FLAG_SACK_RENEGING;
3268 
3269         if (flag & FLAG_ACKED) {
3270                 const struct tcp_congestion_ops *ca_ops
3271                         = inet_csk(sk)->icsk_ca_ops;
3272 
3273                 if (unlikely(icsk->icsk_mtup.probe_size &&
3274                              !after(tp->mtu_probe.probe_seq_end, tp->snd_una))) {
3275                         tcp_mtup_probe_success(sk);
3276                 }
3277 
3278                 tcp_ack_update_rtt(sk, flag, seq_rtt);
3279                 tcp_rearm_rto(sk);
3280 
3281                 if (tcp_is_reno(tp)) {
3282                         tcp_remove_reno_sacks(sk, pkts_acked);
3283                 } else {
3284                         int delta;
3285 
3286                         /* Non-retransmitted hole got filled? That's reordering */
3287                         if (reord < prior_fackets)
3288                                 tcp_update_reordering(sk, tp->fackets_out - reord, 0);
3289 
3290                         delta = tcp_is_fack(tp) ? pkts_acked :
3291                                                   prior_sacked - tp->sacked_out;
3292                         tp->lost_cnt_hint -= min(tp->lost_cnt_hint, delta);
3293                 }
3294 
3295                 tp->fackets_out -= min(pkts_acked, tp->fackets_out);
3296 
3297                 if (ca_ops->pkts_acked) {
3298                         s32 rtt_us = -1;
3299 
3300                         /* Is the ACK triggering packet unambiguous? */
3301                         if (!(flag & FLAG_RETRANS_DATA_ACKED)) {
3302                                 /* High resolution needed and available? */
3303                                 if (ca_ops->flags & TCP_CONG_RTT_STAMP &&
3304                                     !ktime_equal(last_ackt,
3305                                                  net_invalid_timestamp()))
3306                                         rtt_us = ktime_us_delta(ktime_get_real(),
3307                                                                 last_ackt);
3308                                 else if (ca_seq_rtt > 0)
3309                                         rtt_us = jiffies_to_usecs(ca_seq_rtt);
3310                         }
3311 
3312                         ca_ops->pkts_acked(sk, pkts_acked, rtt_us);
3313                 }
3314         }
3315 
3316 #if FASTRETRANS_DEBUG > 0
3317         WARN_ON((int)tp->sacked_out < 0);
3318         WARN_ON((int)tp->lost_out < 0);
3319         WARN_ON((int)tp->retrans_out < 0);
3320         if (!tp->packets_out && tcp_is_sack(tp)) {
3321                 icsk = inet_csk(sk);
3322                 if (tp->lost_out) {
3323                         printk(KERN_DEBUG "Leak l=%u %d\n",
3324                                tp->lost_out, icsk->icsk_ca_state);
3325                         tp->lost_out = 0;
3326                 }
3327                 if (tp->sacked_out) {
3328                         printk(KERN_DEBUG "Leak s=%u %d\n",
3329                                tp->sacked_out, icsk->icsk_ca_state);
3330                         tp->sacked_out = 0;
3331                 }
3332                 if (tp->retrans_out) {
3333                         printk(KERN_DEBUG "Leak r=%u %d\n",
3334                                tp->retrans_out, icsk->icsk_ca_state);
3335                         tp->retrans_out = 0;
3336                 }
3337         }
3338 #endif
3339         return flag;
3340 }
3341 
3342 static void tcp_ack_probe(struct sock *sk)
3343 {
3344         const struct tcp_sock *tp = tcp_sk(sk);
3345         struct inet_connection_sock *icsk = inet_csk(sk);
3346 
3347         /* Was it a usable window open? */
3348 
3349         if (!after(TCP_SKB_CB(tcp_send_head(sk))->end_seq, tcp_wnd_end(tp))) {
3350                 icsk->icsk_backoff = 0;
3351                 inet_csk_clear_xmit_timer(sk, ICSK_TIME_PROBE0);
3352                 /* Socket must be waked up by subsequent tcp_data_snd_check().
3353                  * This function is not for random using!
3354                  */
3355         } else {
3356                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
3357                                           min(icsk->icsk_rto << icsk->icsk_backoff, TCP_RTO_MAX),
3358                                           TCP_RTO_MAX);
3359         }
3360 }
3361 
3362 static inline int tcp_ack_is_dubious(const struct sock *sk, const int flag)
3363 {
3364         return (!(flag & FLAG_NOT_DUP) || (flag & FLAG_CA_ALERT) ||
3365                 inet_csk(sk)->icsk_ca_state != TCP_CA_Open);
3366 }
3367 
3368 static inline int tcp_may_raise_cwnd(const struct sock *sk, const int flag)
3369 {
3370         const struct tcp_sock *tp = tcp_sk(sk);
3371         return (!(flag & FLAG_ECE) || tp->snd_cwnd < tp->snd_ssthresh) &&
3372                 !((1 << inet_csk(sk)->icsk_ca_state) & (TCPF_CA_Recovery | TCPF_CA_CWR));
3373 }
3374 
3375 /* Check that window update is acceptable.
3376  * The function assumes that snd_una<=ack<=snd_next.
3377  */
3378 static inline int tcp_may_update_window(const struct tcp_sock *tp,
3379                                         const u32 ack, const u32 ack_seq,
3380                                         const u32 nwin)
3381 {
3382         return (after(ack, tp->snd_una) ||
3383                 after(ack_seq, tp->snd_wl1) ||
3384                 (ack_seq == tp->snd_wl1 && nwin > tp->snd_wnd));
3385 }
3386 
3387 /* Update our send window.
3388  *
3389  * Window update algorithm, described in RFC793/RFC1122 (used in linux-2.2
3390  * and in FreeBSD. NetBSD's one is even worse.) is wrong.
3391  */
3392 static int tcp_ack_update_window(struct sock *sk, struct sk_buff *skb, u32 ack,
3393                                  u32 ack_seq)
3394 {
3395         struct tcp_sock *tp = tcp_sk(sk);
3396         int flag = 0;
3397         u32 nwin = ntohs(tcp_hdr(skb)->window);
3398 
3399         if (likely(!tcp_hdr(skb)->syn))
3400                 nwin <<= tp->rx_opt.snd_wscale;
3401 
3402         if (tcp_may_update_window(tp, ack, ack_seq, nwin)) {
3403                 flag |= FLAG_WIN_UPDATE;
3404                 tcp_update_wl(tp, ack_seq);
3405 
3406                 if (tp->snd_wnd != nwin) {
3407                         tp->snd_wnd = nwin;
3408 
3409                         /* Note, it is the only place, where
3410                          * fast path is recovered for sending TCP.
3411                          */
3412                         tp->pred_flags = 0;
3413                         tcp_fast_path_check(sk);
3414 
3415                         if (nwin > tp->max_window) {
3416                                 tp->max_window = nwin;
3417                                 tcp_sync_mss(sk, inet_csk(sk)->icsk_pmtu_cookie);
3418                         }
3419                 }
3420         }
3421 
3422         tp->snd_una = ack;
3423 
3424         return flag;
3425 }
3426 
3427 /* A very conservative spurious RTO response algorithm: reduce cwnd and
3428  * continue in congestion avoidance.
3429  */
3430 static void tcp_conservative_spur_to_response(struct tcp_sock *tp)
3431 {
3432         tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
3433         tp->snd_cwnd_cnt = 0;
3434         tp->bytes_acked = 0;
3435         TCP_ECN_queue_cwr(tp);
3436         tcp_moderate_cwnd(tp);
3437 }
3438 
3439 /* A conservative spurious RTO response algorithm: reduce cwnd using
3440  * rate halving and continue in congestion avoidance.
3441  */
3442 static void tcp_ratehalving_spur_to_response(struct sock *sk)
3443 {
3444         tcp_enter_cwr(sk, 0);
3445 }
3446 
3447 static void tcp_undo_spur_to_response(struct sock *sk, int flag)
3448 {
3449         if (flag & FLAG_ECE)
3450                 tcp_ratehalving_spur_to_response(sk);
3451         else
3452                 tcp_undo_cwr(sk, 1);
3453 }
3454 
3455 /* F-RTO spurious RTO detection algorithm (RFC4138)
3456  *
3457  * F-RTO affects during two new ACKs following RTO (well, almost, see inline
3458  * comments). State (ACK number) is kept in frto_counter. When ACK advances
3459  * window (but not to or beyond highest sequence sent before RTO):
3460  *   On First ACK,  send two new segments out.
3461  *   On Second ACK, RTO was likely spurious. Do spurious response (response
3462  *                  algorithm is not part of the F-RTO detection algorithm
3463  *                  given in RFC4138 but can be selected separately).
3464  * Otherwise (basically on duplicate ACK), RTO was (likely) caused by a loss
3465  * and TCP falls back to conventional RTO recovery. F-RTO allows overriding
3466  * of Nagle, this is done using frto_counter states 2 and 3, when a new data
3467  * segment of any size sent during F-RTO, state 2 is upgraded to 3.
3468  *
3469  * Rationale: if the RTO was spurious, new ACKs should arrive from the
3470  * original window even after we transmit two new data segments.
3471  *
3472  * SACK version:
3473  *   on first step, wait until first cumulative ACK arrives, then move to
3474  *   the second step. In second step, the next ACK decides.
3475  *
3476  * F-RTO is implemented (mainly) in four functions:
3477  *   - tcp_use_frto() is used to determine if TCP is can use F-RTO
3478  *   - tcp_enter_frto() prepares TCP state on RTO if F-RTO is used, it is
3479  *     called when tcp_use_frto() showed green light
3480  *   - tcp_process_frto() handles incoming ACKs during F-RTO algorithm
3481  *   - tcp_enter_frto_loss() is called if there is not enough evidence
3482  *     to prove that the RTO is indeed spurious. It transfers the control
3483  *     from F-RTO to the conventional RTO recovery
3484  */
3485 static int tcp_process_frto(struct sock *sk, int flag)
3486 {
3487         struct tcp_sock *tp = tcp_sk(sk);
3488 
3489         tcp_verify_left_out(tp);
3490 
3491         /* Duplicate the behavior from Loss state (fastretrans_alert) */
3492         if (flag & FLAG_DATA_ACKED)
3493                 inet_csk(sk)->icsk_retransmits = 0;
3494 
3495         if ((flag & FLAG_NONHEAD_RETRANS_ACKED) ||
3496             ((tp->frto_counter >= 2) && (flag & FLAG_RETRANS_DATA_ACKED)))
3497                 tp->undo_marker = 0;
3498 
3499         if (!before(tp->snd_una, tp->frto_highmark)) {
3500                 tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 2 : 3), flag);
3501                 return 1;
3502         }
3503 
3504         if (!tcp_is_sackfrto(tp)) {
3505                 /* RFC4138 shortcoming in step 2; should also have case c):
3506                  * ACK isn't duplicate nor advances window, e.g., opposite dir
3507                  * data, winupdate
3508                  */
3509                 if (!(flag & FLAG_ANY_PROGRESS) && (flag & FLAG_NOT_DUP))
3510                         return 1;
3511 
3512                 if (!(flag & FLAG_DATA_ACKED)) {
3513                         tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 0 : 3),
3514                                             flag);
3515                         return 1;
3516                 }
3517         } else {
3518                 if (!(flag & FLAG_DATA_ACKED) && (tp->frto_counter == 1)) {
3519                         /* Prevent sending of new data. */
3520                         tp->snd_cwnd = min(tp->snd_cwnd,
3521                                            tcp_packets_in_flight(tp));
3522                         return 1;
3523                 }
3524 
3525                 if ((tp->frto_counter >= 2) &&
3526                     (!(flag & FLAG_FORWARD_PROGRESS) ||
3527                      ((flag & FLAG_DATA_SACKED) &&
3528                       !(flag & FLAG_ONLY_ORIG_SACKED)))) {
3529                         /* RFC4138 shortcoming (see comment above) */
3530                         if (!(flag & FLAG_FORWARD_PROGRESS) &&
3531                             (flag & FLAG_NOT_DUP))
3532                                 return 1;
3533 
3534                         tcp_enter_frto_loss(sk, 3, flag);
3535                         return 1;
3536                 }
3537         }
3538 
3539         if (tp->frto_counter == 1) {
3540                 /* tcp_may_send_now needs to see updated state */
3541                 tp->snd_cwnd = tcp_packets_in_flight(tp) + 2;
3542                 tp->frto_counter = 2;
3543 
3544                 if (!tcp_may_send_now(sk))
3545                         tcp_enter_frto_loss(sk, 2, flag);
3546 
3547                 return 1;
3548         } else {
3549                 switch (sysctl_tcp_frto_response) {
3550                 case 2:
3551                         tcp_undo_spur_to_response(sk, flag);
3552                         break;
3553                 case 1:
3554                         tcp_conservative_spur_to_response(tp);
3555                         break;
3556                 default:
3557                         tcp_ratehalving_spur_to_response(sk);
3558                         break;
3559                 }
3560                 tp->frto_counter = 0;
3561                 tp->undo_marker = 0;
3562                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSPURIOUSRTOS);
3563         }
3564         return 0;
3565 }
3566 
3567 /* This routine deals with incoming acks, but not outgoing ones. */
3568 static int tcp_ack(struct sock *sk, struct sk_buff *skb, int flag)
3569 {
3570         struct inet_connection_sock *icsk = inet_csk(sk);
3571         struct tcp_sock *tp = tcp_sk(sk);
3572         u32 prior_snd_una = tp->snd_una;
3573         u32 ack_seq = TCP_SKB_CB(skb)->seq;
3574         u32 ack = TCP_SKB_CB(skb)->ack_seq;
3575         u32 prior_in_flight;
3576         u32 prior_fackets;
3577         int prior_packets;
3578         int frto_cwnd = 0;
3579 
3580         /* If the ack is older than previous acks
3581          * then we can probably ignore it.
3582          */
3583         if (before(ack, prior_snd_una))
3584                 goto old_ack;
3585 
3586         /* If the ack includes data we haven't sent yet, discard
3587          * this segment (RFC793 Section 3.9).
3588          */
3589         if (after(ack, tp->snd_nxt))
3590                 goto invalid_ack;
3591 
3592         if (after(ack, prior_snd_una))
3593                 flag |= FLAG_SND_UNA_ADVANCED;
3594 
3595         if (sysctl_tcp_abc) {
3596                 if (icsk->icsk_ca_state < TCP_CA_CWR)
3597                         tp->bytes_acked += ack - prior_snd_una;
3598                 else if (icsk->icsk_ca_state == TCP_CA_Loss)
3599                         /* we assume just one segment left network */
3600                         tp->bytes_acked += min(ack - prior_snd_una,
3601                                                tp->mss_cache);
3602         }
3603 
3604         prior_fackets = tp->fackets_out;
3605         prior_in_flight = tcp_packets_in_flight(tp);
3606 
3607         if (!(flag & FLAG_SLOWPATH) && after(ack, prior_snd_una)) {
3608                 /* Window is constant, pure forward advance.
3609                  * No more checks are required.
3610                  * Note, we use the fact that SND.UNA>=SND.WL2.
3611                  */
3612                 tcp_update_wl(tp, ack_seq);
3613                 tp->snd_una = ack;
3614                 flag |= FLAG_WIN_UPDATE;
3615 
3616                 tcp_ca_event(sk, CA_EVENT_FAST_ACK);
3617 
3618                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPACKS);
3619         } else {
3620                 if (ack_seq != TCP_SKB_CB(skb)->end_seq)
3621                         flag |= FLAG_DATA;
3622                 else
3623                         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPPUREACKS);
3624 
3625                 flag |= tcp_ack_update_window(sk, skb, ack, ack_seq);
3626 
3627                 if (TCP_SKB_CB(skb)->sacked)
3628                         flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una);
3629 
3630                 if (TCP_ECN_rcv_ecn_echo(tp, tcp_hdr(skb)))
3631                         flag |= FLAG_ECE;
3632 
3633                 tcp_ca_event(sk, CA_EVENT_SLOW_ACK);
3634         }
3635 
3636         /* We passed data and got it acked, remove any soft error
3637          * log. Something worked...
3638          */
3639         sk->sk_err_soft = 0;
3640         icsk->icsk_probes_out = 0;
3641         tp->rcv_tstamp = tcp_time_stamp;
3642         prior_packets = tp->packets_out;
3643         if (!prior_packets)
3644                 goto no_queue;
3645 
3646         /* See if we can take anything off of the retransmit queue. */
3647         flag |= tcp_clean_rtx_queue(sk, prior_fackets, prior_snd_una);
3648 
3649         if (tp->frto_counter)
3650                 frto_cwnd = tcp_process_frto(sk, flag);
3651         /* Guarantee sacktag reordering detection against wrap-arounds */
3652         if (before(tp->frto_highmark, tp->snd_una))
3653                 tp->frto_highmark = 0;
3654 
3655         if (tcp_ack_is_dubious(sk, flag)) {
3656                 /* Advance CWND, if state allows this. */
3657                 if ((flag & FLAG_DATA_ACKED) && !frto_cwnd &&
3658                     tcp_may_raise_cwnd(sk, flag))
3659                         tcp_cong_avoid(sk, ack, prior_in_flight);
3660                 tcp_fastretrans_alert(sk, prior_packets - tp->packets_out,
3661                                       flag);
3662         } else {
3663                 if ((flag & FLAG_DATA_ACKED) && !frto_cwnd)
3664                         tcp_cong_avoid(sk, ack, prior_in_flight);
3665         }
3666 
3667         if ((flag & FLAG_FORWARD_PROGRESS) || !(flag & FLAG_NOT_DUP))
3668                 dst_confirm(sk->sk_dst_cache);
3669 
3670         return 1;
3671 
3672 no_queue:
3673         /* If this ack opens up a zero window, clear backoff.  It was
3674          * being used to time the probes, and is probably far higher than
3675          * it needs to be for normal retransmission.
3676          */
3677         if (tcp_send_head(sk))
3678                 tcp_ack_probe(sk);
3679         return 1;
3680 
3681 invalid_ack:
3682         SOCK_DEBUG(sk, "Ack %u after %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
3683         return -1;
3684 
3685 old_ack:
3686         if (TCP_SKB_CB(skb)->sacked) {
3687                 tcp_sacktag_write_queue(sk, skb, prior_snd_una);
3688                 if (icsk->icsk_ca_state == TCP_CA_Open)
3689                         tcp_try_keep_open(sk);
3690         }
3691 
3692         SOCK_DEBUG(sk, "Ack %u before %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
3693         return 0;
3694 }
3695 
3696 /* Look for tcp options. Normally only called on SYN and SYNACK packets.
3697  * But, this can also be called on packets in the established flow when
3698  * the fast version below fails.
3699  */
3700 void tcp_parse_options(struct sk_buff *skb, struct tcp_options_received *opt_rx,
3701                        int estab)
3702 {
3703         unsigned char *ptr;
3704         struct tcphdr *th = tcp_hdr(skb);
3705         int length = (th->doff * 4) - sizeof(struct tcphdr);
3706 
3707         ptr = (unsigned char *)(th + 1);
3708         opt_rx->saw_tstamp = 0;
3709 
3710         while (length > 0) {
3711                 int opcode = *ptr++;
3712                 int opsize;
3713 
3714                 switch (opcode) {
3715                 case TCPOPT_EOL:
3716                         return;
3717                 case TCPOPT_NOP:        /* Ref: RFC 793 section 3.1 */
3718                         length--;
3719                         continue;
3720                 default:
3721                         opsize = *ptr++;
3722                         if (opsize < 2) /* "silly options" */
3723                                 return;
3724                         if (opsize > length)
3725                                 return; /* don't parse partial options */
3726                         switch (opcode) {
3727                         case TCPOPT_MSS:
3728                                 if (opsize == TCPOLEN_MSS && th->syn && !estab) {
3729                                         u16 in_mss = get_unaligned_be16(ptr);
3730                                         if (in_mss) {
3731                                                 if (opt_rx->user_mss &&
3732                                                     opt_rx->user_mss < in_mss)
3733                                                         in_mss = opt_rx->user_mss;
3734                                                 opt_rx->mss_clamp = in_mss;
3735                                         }
3736                                 }
3737                                 break;
3738                         case TCPOPT_WINDOW:
3739                                 if (opsize == TCPOLEN_WINDOW && th->syn &&
3740                                     !estab && sysctl_tcp_window_scaling) {
3741                                         __u8 snd_wscale = *(__u8 *)ptr;
3742                                         opt_rx->wscale_ok = 1;
3743                                         if (snd_wscale > 14) {
3744                                                 if (net_ratelimit())
3745                                                         printk(KERN_INFO "tcp_parse_options: Illegal window "
3746                                                                "scaling value %d >14 received.\n",
3747                                                                snd_wscale);
3748                                                 snd_wscale = 14;
3749                                         }
3750                                         opt_rx->snd_wscale = snd_wscale;
3751                                 }
3752                                 break;
3753                         case TCPOPT_TIMESTAMP:
3754                                 if ((opsize == TCPOLEN_TIMESTAMP) &&
3755                                     ((estab && opt_rx->tstamp_ok) ||
3756                                      (!estab && sysctl_tcp_timestamps))) {
3757                                         opt_rx->saw_tstamp = 1;
3758                                         opt_rx->rcv_tsval = get_unaligned_be32(ptr);
3759                                         opt_rx->rcv_tsecr = get_unaligned_be32(ptr + 4);
3760                                 }
3761                                 break;
3762                         case TCPOPT_SACK_PERM:
3763                                 if (opsize == TCPOLEN_SACK_PERM && th->syn &&
3764                                     !estab && sysctl_tcp_sack) {
3765                                         opt_rx->sack_ok = 1;
3766                                         tcp_sack_reset(opt_rx);
3767                                 }
3768                                 break;
3769 
3770                         case TCPOPT_SACK:
3771                                 if ((opsize >= (TCPOLEN_SACK_BASE + TCPOLEN_SACK_PERBLOCK)) &&
3772                                    !((opsize - TCPOLEN_SACK_BASE) % TCPOLEN_SACK_PERBLOCK) &&
3773                                    opt_rx->sack_ok) {
3774                                         TCP_SKB_CB(skb)->sacked = (ptr - 2) - (unsigned char *)th;
3775                                 }
3776                                 break;
3777 #ifdef CONFIG_TCP_MD5SIG
3778                         case TCPOPT_MD5SIG:
3779                                 /*
3780                                  * The MD5 Hash has already been
3781                                  * checked (see tcp_v{4,6}_do_rcv()).
3782                                  */
3783                                 break;
3784 #endif
3785                         }
3786 
3787                         ptr += opsize-2;
3788                         length -= opsize;
3789                 }
3790         }
3791 }
3792 
3793 static int tcp_parse_aligned_timestamp(struct tcp_sock *tp, struct tcphdr *th)
3794 {
3795         __be32 *ptr = (__be32 *)(th + 1);
3796 
3797         if (*ptr == htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16)
3798                           | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP)) {
3799                 tp->rx_opt.saw_tstamp = 1;
3800                 ++ptr;
3801                 tp->rx_opt.rcv_tsval = ntohl(*ptr);
3802                 ++ptr;
3803                 tp->rx_opt.rcv_tsecr = ntohl(*ptr);
3804                 return 1;
3805         }
3806         return 0;
3807 }
3808 
3809 /* Fast parse options. This hopes to only see timestamps.
3810  * If it is wrong it falls back on tcp_parse_options().
3811  */
3812 static int tcp_fast_parse_options(struct sk_buff *skb, struct tcphdr *th,
3813                                   struct tcp_sock *tp)
3814 {
3815         if (th->doff == sizeof(struct tcphdr) >> 2) {
3816                 tp->rx_opt.saw_tstamp = 0;
3817                 return 0;
3818         } else if (tp->rx_opt.tstamp_ok &&
3819                    th->doff == (sizeof(struct tcphdr)>>2)+(TCPOLEN_TSTAMP_ALIGNED>>2)) {
3820                 if (tcp_parse_aligned_timestamp(tp, th))
3821                         return 1;
3822         }
3823         tcp_parse_options(skb, &tp->rx_opt, 1);
3824         return 1;
3825 }
3826 
3827 #ifdef CONFIG_TCP_MD5SIG
3828 /*
3829  * Parse MD5 Signature option
3830  */
3831 u8 *tcp_parse_md5sig_option(struct tcphdr *th)
3832 {
3833         int length = (th->doff << 2) - sizeof (*th);
3834         u8 *ptr = (u8*)(th + 1);
3835 
3836         /* If the TCP option is too short, we can short cut */
3837         if (length < TCPOLEN_MD5SIG)
3838                 return NULL;
3839 
3840         while (length > 0) {
3841                 int opcode = *ptr++;
3842                 int opsize;
3843 
3844                 switch(opcode) {
3845                 case TCPOPT_EOL:
3846                         return NULL;
3847                 case TCPOPT_NOP:
3848                         length--;
3849                         continue;
3850                 default:
3851                         opsize = *ptr++;
3852                         if (opsize < 2 || opsize > length)
3853                                 return NULL;
3854                         if (opcode == TCPOPT_MD5SIG)
3855                                 return ptr;
3856                 }
3857                 ptr += opsize - 2;
3858                 length -= opsize;
3859         }
3860         return NULL;
3861 }
3862 #endif
3863 
3864 static inline void tcp_store_ts_recent(struct tcp_sock *tp)
3865 {
3866         tp->rx_opt.ts_recent = tp->rx_opt.rcv_tsval;
3867         tp->rx_opt.ts_recent_stamp = get_seconds();
3868 }
3869 
3870 static inline void tcp_replace_ts_recent(struct tcp_sock *tp, u32 seq)
3871 {
3872         if (tp->rx_opt.saw_tstamp && !after(seq, tp->rcv_wup)) {
3873                 /* PAWS bug workaround wrt. ACK frames, the PAWS discard
3874                  * extra check below makes sure this can only happen
3875                  * for pure ACK frames.  -DaveM
3876                  *
3877                  * Not only, also it occurs for expired timestamps.
3878                  */
3879 
3880                 if (tcp_paws_check(&tp->rx_opt, 0))
3881                         tcp_store_ts_recent(tp);
3882         }
3883 }
3884 
3885 /* Sorry, PAWS as specified is broken wrt. pure-ACKs -DaveM
3886  *
3887  * It is not fatal. If this ACK does _not_ change critical state (seqs, window)
3888  * it can pass through stack. So, the following predicate verifies that
3889  * this segment is not used for anything but congestion avoidance or
3890  * fast retransmit. Moreover, we even are able to eliminate most of such
3891  * second order effects, if we apply some small "replay" window (~RTO)
3892  * to timestamp space.
3893  *
3894  * All these measures still do not guarantee that we reject wrapped ACKs
3895  * on networks with high bandwidth, when sequence space is recycled fastly,
3896  * but it guarantees that such events will be very rare and do not affect
3897  * connection seriously. This doesn't look nice, but alas, PAWS is really
3898  * buggy extension.
3899  *
3900  * [ Later note. Even worse! It is buggy for segments _with_ data. RFC
3901  * states that events when retransmit arrives after original data are rare.
3902  * It is a blatant lie. VJ forgot about fast retransmit! 8)8) It is
3903  * the biggest problem on large power networks even with minor reordering.
3904  * OK, let's give it small replay window. If peer clock is even 1hz, it is safe
3905  * up to bandwidth of 18Gigabit/sec. 8) ]
3906  */
3907 
3908 static int tcp_disordered_ack(const struct sock *sk, const struct sk_buff *skb)
3909 {
3910         struct tcp_sock *tp = tcp_sk(sk);
3911         struct tcphdr *th = tcp_hdr(skb);
3912         u32 seq = TCP_SKB_CB(skb)->seq;
3913         u32 ack = TCP_SKB_CB(skb)->ack_seq;
3914 
3915         return (/* 1. Pure ACK with correct sequence number. */
3916                 (th->ack && seq == TCP_SKB_CB(skb)->end_seq && seq == tp->rcv_nxt) &&
3917 
3918                 /* 2. ... and duplicate ACK. */
3919                 ack == tp->snd_una &&
3920 
3921                 /* 3. ... and does not update window. */
3922                 !tcp_may_update_window(tp, ack, seq, ntohs(th->window) << tp->rx_opt.snd_wscale) &&
3923 
3924                 /* 4. ... and sits in replay window. */
3925                 (s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) <= (inet_csk(sk)->icsk_rto * 1024) / HZ);
3926 }
3927 
3928 static inline int tcp_paws_discard(const struct sock *sk,
3929                                    const struct sk_buff *skb)
3930 {
3931         const struct tcp_sock *tp = tcp_sk(sk);
3932 
3933         return !tcp_paws_check(&tp->rx_opt, TCP_PAWS_WINDOW) &&
3934                !tcp_disordered_ack(sk, skb);
3935 }
3936 
3937 /* Check segment sequence number for validity.
3938  *
3939  * Segment controls are considered valid, if the segment
3940  * fits to the window after truncation to the window. Acceptability
3941  * of data (and SYN, FIN, of course) is checked separately.
3942  * See tcp_data_queue(), for example.
3943  *
3944  * Also, controls (RST is main one) are accepted using RCV.WUP instead
3945  * of RCV.NXT. Peer still did not advance his SND.UNA when we
3946  * delayed ACK, so that hisSND.UNA<=ourRCV.WUP.
3947  * (borrowed from freebsd)
3948  */
3949 
3950 static inline int tcp_sequence(struct tcp_sock *tp, u32 seq, u32 end_seq)
3951 {
3952         return  !before(end_seq, tp->rcv_wup) &&
3953                 !after(seq, tp->rcv_nxt + tcp_receive_window(tp));
3954 }
3955 
3956 /* When we get a reset we do this. */
3957 static void tcp_reset(struct sock *sk)
3958 {
3959         /* We want the right error as BSD sees it (and indeed as we do). */
3960         switch (sk->sk_state) {
3961         case TCP_SYN_SENT:
3962                 sk->sk_err = ECONNREFUSED;
3963                 break;
3964         case TCP_CLOSE_WAIT:
3965                 sk->sk_err = EPIPE;
3966                 break;
3967         case TCP_CLOSE:
3968                 return;
3969         default:
3970                 sk->sk_err = ECONNRESET;
3971         }
3972         /* This barrier is coupled with smp_rmb() in tcp_poll() */
3973         smp_wmb();
3974 
3975         if (!sock_flag(sk, SOCK_DEAD))
3976                 sk->sk_error_report(sk);
3977 
3978         tcp_done(sk);
3979 }
3980 
3981 /*
3982  *      Process the FIN bit. This now behaves as it is supposed to work
3983  *      and the FIN takes effect when it is validly part of sequence
3984  *      space. Not before when we get holes.
3985  *
3986  *      If we are ESTABLISHED, a received fin moves us to CLOSE-WAIT
3987  *      (and thence onto LAST-ACK and finally, CLOSE, we never enter
3988  *      TIME-WAIT)
3989  *
3990  *      If we are in FINWAIT-1, a received FIN indicates simultaneous
3991  *      close and we go into CLOSING (and later onto TIME-WAIT)
3992  *
3993  *      If we are in FINWAIT-2, a received FIN moves us to TIME-WAIT.
3994  */
3995 static void tcp_fin(struct sk_buff *skb, struct sock *sk, struct tcphdr *th)
3996 {
3997         struct tcp_sock *tp = tcp_sk(sk);
3998 
3999         inet_csk_schedule_ack(sk);
4000 
4001         sk->sk_shutdown |= RCV_SHUTDOWN;
4002         sock_set_flag(sk, SOCK_DONE);
4003 
4004         switch (sk->sk_state) {
4005         case TCP_SYN_RECV:
4006         case TCP_ESTABLISHED:
4007                 /* Move to CLOSE_WAIT */
4008                 tcp_set_state(sk, TCP_CLOSE_WAIT);
4009                 inet_csk(sk)->icsk_ack.pingpong = 1;
4010                 break;
4011 
4012         case TCP_CLOSE_WAIT:
4013         case TCP_CLOSING:
4014                 /* Received a retransmission of the FIN, do
4015                  * nothing.
4016                  */
4017                 break;
4018         case TCP_LAST_ACK:
4019                 /* RFC793: Remain in the LAST-ACK state. */
4020                 break;
4021 
4022         case TCP_FIN_WAIT1:
4023                 /* This case occurs when a simultaneous close
4024                  * happens, we must ack the received FIN and
4025                  * enter the CLOSING state.
4026                  */
4027                 tcp_send_ack(sk);
4028                 tcp_set_state(sk, TCP_CLOSING);
4029                 break;
4030         case TCP_FIN_WAIT2:
4031                 /* Received a FIN -- send ACK and enter TIME_WAIT. */
4032                 tcp_send_ack(sk);
4033                 tcp_time_wait(sk, TCP_TIME_WAIT, 0);
4034                 break;
4035         default:
4036                 /* Only TCP_LISTEN and TCP_CLOSE are left, in these
4037                  * cases we should never reach this piece of code.
4038                  */
4039                 printk(KERN_ERR "%s: Impossible, sk->sk_state=%d\n",
4040                        __func__, sk->sk_state);
4041                 break;
4042         }
4043 
4044         /* It _is_ possible, that we have something out-of-order _after_ FIN.
4045          * Probably, we should reset in this case. For now drop them.
4046          */
4047         __skb_queue_purge(&tp->out_of_order_queue);
4048         if (tcp_is_sack(tp))
4049                 tcp_sack_reset(&tp->rx_opt);
4050         sk_mem_reclaim(sk);
4051 
4052         if (!sock_flag(sk, SOCK_DEAD)) {
4053                 sk->sk_state_change(sk);
4054 
4055                 /* Do not send POLL_HUP for half duplex close. */
4056                 if (sk->sk_shutdown == SHUTDOWN_MASK ||
4057                     sk->sk_state == TCP_CLOSE)
4058                         sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_HUP);
4059                 else
4060                         sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_IN);
4061         }
4062 }
4063 
4064 static inline int tcp_sack_extend(struct tcp_sack_block *sp, u32 seq,
4065                                   u32 end_seq)
4066 {
4067         if (!after(seq, sp->end_seq) && !after(sp->start_seq, end_seq)) {
4068                 if (before(seq, sp->start_seq))
4069                         sp->start_seq = seq;
4070                 if (after(end_seq, sp->end_seq))
4071                         sp->end_seq = end_seq;
4072                 return 1;
4073         }
4074         return 0;
4075 }
4076 
4077 static void tcp_dsack_set(struct sock *sk, u32 seq, u32 end_seq)
4078 {
4079         struct tcp_sock *tp = tcp_sk(sk);
4080 
4081         if (tcp_is_sack(tp) && sysctl_tcp_dsack) {
4082                 int mib_idx;
4083 
4084                 if (before(seq, tp->rcv_nxt))
4085                         mib_idx = LINUX_MIB_TCPDSACKOLDSENT;
4086                 else
4087                         mib_idx = LINUX_MIB_TCPDSACKOFOSENT;
4088 
4089                 NET_INC_STATS_BH(sock_net(sk), mib_idx);
4090 
4091                 tp->rx_opt.dsack = 1;
4092                 tp->duplicate_sack[0].start_seq = seq;
4093                 tp->duplicate_sack[0].end_seq = end_seq;
4094         }
4095 }
4096 
4097 static void tcp_dsack_extend(struct sock *sk, u32 seq, u32 end_seq)
4098 {
4099         struct tcp_sock *tp = tcp_sk(sk);
4100 
4101         if (!tp->rx_opt.dsack)
4102                 tcp_dsack_set(sk, seq, end_seq);
4103         else
4104                 tcp_sack_extend(tp->duplicate_sack, seq, end_seq);
4105 }
4106 
4107 static void tcp_send_dupack(struct sock *sk, struct sk_buff *skb)
4108 {
4109         struct tcp_sock *tp = tcp_sk(sk);
4110 
4111         if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
4112             before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
4113                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
4114                 tcp_enter_quickack_mode(sk);
4115 
4116                 if (tcp_is_sack(tp) && sysctl_tcp_dsack) {
4117                         u32 end_seq = TCP_SKB_CB(skb)->end_seq;
4118 
4119                         if (after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))
4120                                 end_seq = tp->rcv_nxt;
4121                         tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, end_seq);
4122                 }
4123         }
4124 
4125         tcp_send_ack(sk);
4126 }
4127 
4128 /* These routines update the SACK block as out-of-order packets arrive or
4129  * in-order packets close up the sequence space.
4130  */
4131 static void tcp_sack_maybe_coalesce(struct tcp_sock *tp)
4132 {
4133         int this_sack;
4134         struct tcp_sack_block *sp = &tp->selective_acks[0];
4135         struct tcp_sack_block *swalk = sp + 1;
4136 
4137         /* See if the recent change to the first SACK eats into
4138          * or hits the sequence space of other SACK blocks, if so coalesce.
4139          */
4140         for (this_sack = 1; this_sack < tp->rx_opt.num_sacks;) {
4141                 if (tcp_sack_extend(sp, swalk->start_seq, swalk->end_seq)) {
4142                         int i;
4143 
4144                         /* Zap SWALK, by moving every further SACK up by one slot.
4145                          * Decrease num_sacks.
4146                          */
4147                         tp->rx_opt.num_sacks--;
4148                         for (i = this_sack; i < tp->rx_opt.num_sacks; i++)
4149                                 sp[i] = sp[i + 1];
4150                         continue;
4151                 }
4152                 this_sack++, swalk++;
4153         }
4154 }
4155 
4156 static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq)
4157 {
4158         struct tcp_sock *tp = tcp_sk(sk);
4159         struct tcp_sack_block *sp = &tp->selective_acks[0];
4160         int cur_sacks = tp->rx_opt.num_sacks;
4161         int this_sack;
4162 
4163         if (!cur_sacks)
4164                 goto new_sack;
4165 
4166         for (this_sack = 0; this_sack < cur_sacks; this_sack++, sp++) {
4167                 if (tcp_sack_extend(sp, seq, end_seq)) {
4168                         /* Rotate this_sack to the first one. */
4169                         for (; this_sack > 0; this_sack--, sp--)
4170                                 swap(*sp, *(sp - 1));
4171                         if (cur_sacks > 1)
4172                                 tcp_sack_maybe_coalesce(tp);
4173                         return;
4174                 }
4175         }
4176 
4177         /* Could not find an adjacent existing SACK, build a new one,
4178          * put it at the front, and shift everyone else down.  We
4179          * always know there is at least one SACK present already here.
4180          *
4181          * If the sack array is full, forget about the last one.
4182          */
4183         if (this_sack >= TCP_NUM_SACKS) {
4184                 this_sack--;
4185                 tp->rx_opt.num_sacks--;
4186                 sp--;
4187         }
4188         for (; this_sack > 0; this_sack--, sp--)
4189                 *sp = *(sp - 1);
4190 
4191 new_sack:
4192         /* Build the new head SACK, and we're done. */
4193         sp->start_seq = seq;
4194         sp->end_seq = end_seq;
4195         tp->rx_opt.num_sacks++;
4196 }
4197 
4198 /* RCV.NXT advances, some SACKs should be eaten. */
4199 
4200 static void tcp_sack_remove(struct tcp_sock *tp)
4201 {
4202         struct tcp_sack_block *sp = &tp->selective_acks[0];
4203         int num_sacks = tp->rx_opt.num_sacks;
4204         int this_sack;
4205 
4206         /* Empty ofo queue, hence, all the SACKs are eaten. Clear. */
4207         if (skb_queue_empty(&tp->out_of_order_queue)) {
4208                 tp->rx_opt.num_sacks = 0;
4209                 return;
4210         }
4211 
4212         for (this_sack = 0; this_sack < num_sacks;) {
4213                 /* Check if the start of the sack is covered by RCV.NXT. */
4214                 if (!before(tp->rcv_nxt, sp->start_seq)) {
4215                         int i;
4216 
4217                         /* RCV.NXT must cover all the block! */
4218                         WARN_ON(before(tp->rcv_nxt, sp->end_seq));
4219 
4220                         /* Zap this SACK, by moving forward any other SACKS. */
4221                         for (i=this_sack+1; i < num_sacks; i++)
4222                                 tp->selective_acks[i-1] = tp->selective_acks[i];
4223                         num_sacks--;
4224                         continue;
4225                 }
4226                 this_sack++;
4227                 sp++;
4228         }
4229         tp->rx_opt.num_sacks = num_sacks;
4230 }
4231 
4232 /* This one checks to see if we can put data from the
4233  * out_of_order queue into the receive_queue.
4234  */
4235 static void tcp_ofo_queue(struct sock *sk)
4236 {
4237         struct tcp_sock *tp = tcp_sk(sk);
4238         __u32 dsack_high = tp->rcv_nxt;
4239         struct sk_buff *skb;
4240 
4241         while ((skb = skb_peek(&tp->out_of_order_queue)) != NULL) {
4242                 if (after(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
4243                         break;
4244 
4245                 if (before(TCP_SKB_CB(skb)->seq, dsack_high)) {
4246                         __u32 dsack = dsack_high;
4247                         if (before(TCP_SKB_CB(skb)->end_seq, dsack_high))
4248                                 dsack_high = TCP_SKB_CB(skb)->end_seq;
4249                         tcp_dsack_extend(sk, TCP_SKB_CB(skb)->seq, dsack);
4250                 }
4251 
4252                 if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
4253                         SOCK_DEBUG(sk, "ofo packet was already received \n");
4254                         __skb_unlink(skb, &tp->out_of_order_queue);
4255                         __kfree_skb(skb);
4256                         continue;
4257                 }
4258                 SOCK_DEBUG(sk, "ofo requeuing : rcv_next %X seq %X - %X\n",
4259                            tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
4260                            TCP_SKB_CB(skb)->end_seq);
4261 
4262                 __skb_unlink(skb, &tp->out_of_order_queue);
4263                 __skb_queue_tail(&sk->sk_receive_queue, skb);
4264                 tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
4265                 if (tcp_hdr(skb)->fin)
4266                         tcp_fin(skb, sk, tcp_hdr(skb));
4267         }
4268 }
4269 
4270 static int tcp_prune_ofo_queue(struct sock *sk);
4271 static int tcp_prune_queue(struct sock *sk);
4272 
4273 static inline int tcp_try_rmem_schedule(struct sock *sk, unsigned int size)
4274 {
4275         if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
4276             !sk_rmem_schedule(sk, size)) {
4277 
4278                 if (tcp_prune_queue(sk) < 0)
4279                         return -1;
4280 
4281                 if (!sk_rmem_schedule(sk, size)) {
4282                         if (!tcp_prune_ofo_queue(sk))
4283                                 return -1;
4284 
4285                         if (!sk_rmem_schedule(sk, size))
4286                                 return -1;
4287                 }
4288         }
4289         return 0;
4290 }
4291 
4292 static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
4293 {
4294         struct tcphdr *th = tcp_hdr(skb);
4295         struct tcp_sock *tp = tcp_sk(sk);
4296         int eaten = -1;
4297 
4298         if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq)
4299                 goto drop;
4300 
4301         __skb_pull(skb, th->doff * 4);
4302 
4303         TCP_ECN_accept_cwr(tp, skb);
4304 
4305         tp->rx_opt.dsack = 0;
4306 
4307         /*  Queue data for delivery to the user.
4308          *  Packets in sequence go to the receive queue.
4309          *  Out of sequence packets to the out_of_order_queue.
4310          */
4311         if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
4312                 if (tcp_receive_window(tp) == 0)
4313                         goto out_of_window;
4314 
4315                 /* Ok. In sequence. In window. */
4316                 if (tp->ucopy.task == current &&
4317                     tp->copied_seq == tp->rcv_nxt && tp->ucopy.len &&
4318                     sock_owned_by_user(sk) && !tp->urg_data) {
4319                         int chunk = min_t(unsigned int, skb->len,
4320                                           tp->ucopy.len);
4321 
4322                         __set_current_state(TASK_RUNNING);
4323 
4324                         local_bh_enable();
4325                         if (!skb_copy_datagram_iovec(skb, 0, tp->ucopy.iov, chunk)) {
4326                                 tp->ucopy.len -= chunk;
4327                                 tp->copied_seq += chunk;
4328                                 eaten = (chunk == skb->len && !th->fin);
4329                                 tcp_rcv_space_adjust(sk);
4330                         }
4331                         local_bh_disable();
4332                 }
4333 
4334                 if (eaten <= 0) {
4335 queue_and_out:
4336                         if (eaten < 0 &&
4337                             tcp_try_rmem_schedule(sk, skb->truesize))
4338                                 goto drop;
4339 
4340                         skb_set_owner_r(skb, sk);
4341                         __skb_queue_tail(&sk->sk_receive_queue, skb);
4342                 }
4343                 tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
4344                 if (skb->len)
4345                         tcp_event_data_recv(sk, skb);
4346                 if (th->fin)
4347                         tcp_fin(skb, sk, th);
4348 
4349                 if (!skb_queue_empty(&tp->out_of_order_queue)) {
4350                         tcp_ofo_queue(sk);
4351 
4352                         /* RFC2581. 4.2. SHOULD send immediate ACK, when
4353                          * gap in queue is filled.
4354                          */
4355                         if (skb_queue_empty(&tp->out_of_order_queue))
4356                                 inet_csk(sk)->icsk_ack.pingpong = 0;
4357                 }
4358 
4359                 if (tp->rx_opt.num_sacks)
4360                         tcp_sack_remove(tp);
4361 
4362                 tcp_fast_path_check(sk);
4363 
4364                 if (eaten > 0)
4365                         __kfree_skb(skb);
4366                 else if (!sock_flag(sk, SOCK_DEAD))
4367                         sk->sk_data_ready(sk, 0);
4368                 return;
4369         }
4370 
4371         if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
4372                 /* A retransmit, 2nd most common case.  Force an immediate ack. */
4373                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
4374                 tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
4375 
4376 out_of_window:
4377                 tcp_enter_quickack_mode(sk);
4378                 inet_csk_schedule_ack(sk);
4379 drop:
4380                 __kfree_skb(skb);
4381                 return;
4382         }
4383 
4384         /* Out of window. F.e. zero window probe. */
4385         if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt + tcp_receive_window(tp)))
4386                 goto out_of_window;
4387 
4388         tcp_enter_quickack_mode(sk);
4389 
4390         if (before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
4391                 /* Partial packet, seq < rcv_next < end_seq */
4392                 SOCK_DEBUG(sk, "partial packet: rcv_next %X seq %X - %X\n",
4393                            tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
4394                            TCP_SKB_CB(skb)->end_seq);
4395 
4396                 tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, tp->rcv_nxt);
4397 
4398                 /* If window is closed, drop tail of packet. But after
4399                  * remembering D-SACK for its head made in previous line.
4400                  */
4401                 if (!tcp_receive_window(tp))
4402                         goto out_of_window;
4403                 goto queue_and_out;
4404         }
4405 
4406         TCP_ECN_check_ce(tp, skb);
4407 
4408         if (tcp_try_rmem_schedule(sk, skb->truesize))
4409                 goto drop;
4410 
4411         /* Disable header prediction. */
4412         tp->pred_flags = 0;
4413         inet_csk_schedule_ack(sk);
4414 
4415         SOCK_DEBUG(sk, "out of order segment: rcv_next %X seq %X - %X\n",
4416                    tp->rcv_nxt, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
4417 
4418         skb_set_owner_r(skb, sk);
4419 
4420         if (!skb_peek(&tp->out_of_order_queue)) {
4421                 /* Initial out of order segment, build 1 SACK. */
4422                 if (tcp_is_sack(tp)) {
4423                         tp->rx_opt.num_sacks = 1;
4424                         tp->selective_acks[0].start_seq = TCP_SKB_CB(skb)->seq;
4425                         tp->selective_acks[0].end_seq =
4426                                                 TCP_SKB_CB(skb)->end_seq;
4427                 }
4428                 __skb_queue_head(&tp->out_of_order_queue, skb);
4429         } else {
4430                 struct sk_buff *skb1 = skb_peek_tail(&tp->out_of_order_queue);
4431                 u32 seq = TCP_SKB_CB(skb)->seq;
4432                 u32 end_seq = TCP_SKB_CB(skb)->end_seq;
4433 
4434                 if (seq == TCP_SKB_CB(skb1)->end_seq) {
4435                         __skb_queue_after(&tp->out_of_order_queue, skb1, skb);
4436 
4437                         if (!tp->rx_opt.num_sacks ||
4438                             tp->selective_acks[0].end_seq != seq)
4439                                 goto add_sack;
4440 
4441                         /* Common case: data arrive in order after hole. */
4442                         tp->selective_acks[0].end_seq = end_seq;
4443                         return;
4444                 }
4445 
4446                 /* Find place to insert this segment. */
4447                 while (1) {
4448                         if (!after(TCP_SKB_CB(skb1)->seq, seq))
4449                                 break;
4450                         if (skb_queue_is_first(&tp->out_of_order_queue, skb1)) {
4451                                 skb1 = NULL;
4452                                 break;
4453                         }
4454                         skb1 = skb_queue_prev(&tp->out_of_order_queue, skb1);
4455                 }
4456 
4457                 /* Do skb overlap to previous one? */
4458                 if (skb1 && before(seq, TCP_SKB_CB(skb1)->end_seq)) {
4459                         if (!after(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
4460                                 /* All the bits are present. Drop. */
4461                                 __kfree_skb(skb);
4462                                 tcp_dsack_set(sk, seq, end_seq);
4463                                 goto add_sack;
4464                         }
4465                         if (after(seq, TCP_SKB_CB(skb1)->seq)) {
4466                                 /* Partial overlap. */
4467                                 tcp_dsack_set(sk, seq,
4468                                               TCP_SKB_CB(skb1)->end_seq);
4469                         } else {
4470                                 if (skb_queue_is_first(&tp->out_of_order_queue,
4471                                                        skb1))
4472                                         skb1 = NULL;
4473                                 else
4474                                         skb1 = skb_queue_prev(
4475                                                 &tp->out_of_order_queue,
4476                                                 skb1);
4477                         }
4478                 }
4479                 if (!skb1)
4480                         __skb_queue_head(&tp->out_of_order_queue, skb);
4481                 else
4482                         __skb_queue_after(&tp->out_of_order_queue, skb1, skb);
4483 
4484                 /* And clean segments covered by new one as whole. */
4485                 while (!skb_queue_is_last(&tp->out_of_order_queue, skb)) {
4486                         skb1 = skb_queue_next(&tp->out_of_order_queue, skb);
4487 
4488                         if (!after(end_seq, TCP_SKB_CB(skb1)->seq))
4489                                 break;
4490                         if (before(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
4491                                 tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
4492                                                  end_seq);
4493                                 break;
4494                         }
4495                         __skb_unlink(skb1, &tp->out_of_order_queue);
4496                         tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
4497                                          TCP_SKB_CB(skb1)->end_seq);
4498                         __kfree_skb(skb1);
4499                 }
4500 
4501 add_sack:
4502                 if (tcp_is_sack(tp))
4503                         tcp_sack_new_ofo_skb(sk, seq, end_seq);
4504         }
4505 }
4506 
4507 static struct sk_buff *tcp_collapse_one(struct sock *sk, struct sk_buff *skb,
4508                                         struct sk_buff_head *list)
4509 {
4510         struct sk_buff *next = NULL;
4511 
4512         if (!skb_queue_is_last(list, skb))
4513                 next = skb_queue_next(list, skb);
4514 
4515         __skb_unlink(skb, list);
4516         __kfree_skb(skb);
4517         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPRCVCOLLAPSED);
4518 
4519         return next;
4520 }
4521 
4522 /* Collapse contiguous sequence of skbs head..tail with
4523  * sequence numbers start..end.
4524  *
4525  * If tail is NULL, this means until the end of the list.
4526  *
4527  * Segments with FIN/SYN are not collapsed (only because this
4528  * simplifies code)
4529  */
4530 static void
4531 tcp_collapse(struct sock *sk, struct sk_buff_head *list,
4532              struct sk_buff *head, struct sk_buff *tail,
4533              u32 start, u32 end)
4534 {
4535         struct sk_buff *skb, *n;
4536         bool end_of_skbs;
4537 
4538         /* First, check that queue is collapsible and find
4539          * the point where collapsing can be useful. */
4540         skb = head;
4541 restart:
4542         end_of_skbs = true;
4543         skb_queue_walk_from_safe(list, skb, n) {
4544                 if (skb == tail)
4545                         break;
4546                 /* No new bits? It is possible on ofo queue. */
4547                 if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
4548                         skb = tcp_collapse_one(sk, skb, list);
4549                         if (!skb)
4550                                 break;
4551                         goto restart;
4552                 }
4553 
4554                 /* The first skb to collapse is:
4555                  * - not SYN/FIN and
4556                  * - bloated or contains data before "start" or
4557                  *   overlaps to the next one.
4558                  */
4559                 if (!tcp_hdr(skb)->syn && !tcp_hdr(skb)->fin &&
4560                     (tcp_win_from_space(skb->truesize) > skb->len ||
4561                      before(TCP_SKB_CB(skb)->seq, start))) {
4562                         end_of_skbs = false;
4563                         break;
4564                 }
4565 
4566                 if (!skb_queue_is_last(list, skb)) {
4567                         struct sk_buff *next = skb_queue_next(list, skb);
4568                         if (next != tail &&
4569                             TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(next)->seq) {
4570                                 end_of_skbs = false;
4571                                 break;
4572                         }
4573                 }
4574 
4575                 /* Decided to skip this, advance start seq. */
4576                 start = TCP_SKB_CB(skb)->end_seq;
4577         }
4578         if (end_of_skbs || tcp_hdr(skb)->syn || tcp_hdr(skb)->fin)
4579                 return;
4580 
4581         while (before(start, end)) {
4582                 struct sk_buff *nskb;
4583                 unsigned int header = skb_headroom(skb);
4584                 int copy = SKB_MAX_ORDER(header, 0);
4585 
4586                 /* Too big header? This can happen with IPv6. */
4587                 if (copy < 0)
4588                         return;
4589                 if (end - start < copy)
4590                         copy = end - start;
4591                 nskb = alloc_skb(copy + header, GFP_ATOMIC);
4592                 if (!nskb)
4593                         return;
4594 
4595                 skb_set_mac_header(nskb, skb_mac_header(skb) - skb->head);
4596                 skb_set_network_header(nskb, (skb_network_header(skb) -
4597                                               skb->head));
4598                 skb_set_transport_header(nskb, (skb_transport_header(skb) -
4599                                                 skb->head));
4600                 skb_reserve(nskb, header);
4601                 memcpy(nskb->head, skb->head, header);
4602                 memcpy(nskb->cb, skb->cb, sizeof(skb->cb));
4603                 TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(nskb)->end_seq = start;
4604                 __skb_queue_before(list, skb, nskb);
4605                 skb_set_owner_r(nskb, sk);
4606 
4607                 /* Copy data, releasing collapsed skbs. */
4608                 while (copy > 0) {
4609                         int offset = start - TCP_SKB_CB(skb)->seq;
4610                         int size = TCP_SKB_CB(skb)->end_seq - start;
4611 
4612                         BUG_ON(offset < 0);
4613                         if (size > 0) {
4614                                 size = min(copy, size);
4615                                 if (skb_copy_bits(skb, offset, skb_put(nskb, size), size))
4616                                         BUG();
4617                                 TCP_SKB_CB(nskb)->end_seq += size;
4618                                 copy -= size;
4619                                 start += size;
4620                         }
4621                         if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
4622                                 skb = tcp_collapse_one(sk, skb, list);
4623                                 if (!skb ||
4624                                     skb == tail ||
4625                                     tcp_hdr(skb)->syn ||
4626                                     tcp_hdr(skb)->fin)
4627                                         return;
4628                         }
4629                 }
4630         }
4631 }
4632 
4633 /* Collapse ofo queue. Algorithm: select contiguous sequence of skbs
4634  * and tcp_collapse() them until all the queue is collapsed.
4635  */
4636 static void tcp_collapse_ofo_queue(struct sock *sk)
4637 {
4638         struct tcp_sock *tp = tcp_sk(sk);
4639         struct sk_buff *skb = skb_peek(&tp->out_of_order_queue);
4640         struct sk_buff *head;
4641         u32 start, end;
4642 
4643         if (skb == NULL)
4644                 return;
4645 
4646         start = TCP_SKB_CB(skb)->seq;
4647         end = TCP_SKB_CB(skb)->end_seq;
4648         head = skb;
4649 
4650         for (;;) {
4651                 struct sk_buff *next = NULL;
4652 
4653                 if (!skb_queue_is_last(&tp->out_of_order_queue, skb))
4654                         next = skb_queue_next(&tp->out_of_order_queue, skb);
4655                 skb = next;
4656 
4657                 /* Segment is terminated when we see gap or when
4658                  * we are at the end of all the queue. */
4659                 if (!skb ||
4660                     after(TCP_SKB_CB(skb)->seq, end) ||
4661                     before(TCP_SKB_CB(skb)->end_seq, start)) {
4662                         tcp_collapse(sk, &tp->out_of_order_queue,
4663                                      head, skb, start, end);
4664                         head = skb;
4665                         if (!skb)
4666                                 break;
4667                         /* Start new segment */
4668                         start = TCP_SKB_CB(skb)->seq;
4669                         end = TCP_SKB_CB(skb)->end_seq;
4670                 } else {
4671                         if (before(TCP_SKB_CB(skb)->seq, start))
4672                                 start = TCP_SKB_CB(skb)->seq;
4673                         if (after(TCP_SKB_CB(skb)->end_seq, end))
4674                                 end = TCP_SKB_CB(skb)->end_seq;
4675                 }
4676         }
4677 }
4678 
4679 /*
4680  * Purge the out-of-order queue.
4681  * Return true if queue was pruned.
4682  */
4683 static int tcp_prune_ofo_queue(struct sock *sk)
4684 {
4685         struct tcp_sock *tp = tcp_sk(sk);
4686         int res = 0;
4687 
4688         if (!skb_queue_empty(&tp->out_of_order_queue)) {
4689                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_OFOPRUNED);
4690                 __skb_queue_purge(&tp->out_of_order_queue);
4691 
4692                 /* Reset SACK state.  A conforming SACK implementation will
4693                  * do the same at a timeout based retransmit.  When a connection
4694                  * is in a sad state like this, we care only about integrity
4695                  * of the connection not performance.
4696                  */
4697                 if (tp->rx_opt.sack_ok)
4698                         tcp_sack_reset(&tp->rx_opt);
4699                 sk_mem_reclaim(sk);
4700                 res = 1;
4701         }
4702         return res;
4703 }
4704 
4705 /* Reduce allocated memory if we can, trying to get
4706  * the socket within its memory limits again.
4707  *
4708  * Return less than zero if we should start dropping frames
4709  * until the socket owning process reads some of the data
4710  * to stabilize the situation.
4711  */
4712 static int tcp_prune_queue(struct sock *sk)
4713 {
4714         struct tcp_sock *tp = tcp_sk(sk);
4715 
4716         SOCK_DEBUG(sk, "prune_queue: c=%x\n", tp->copied_seq);
4717 
4718         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PRUNECALLED);
4719 
4720         if (atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf)
4721                 tcp_clamp_window(sk);
4722         else if (tcp_memory_pressure)
4723                 tp->rcv_ssthresh = min(tp->rcv_ssthresh, 4U * tp->advmss);
4724 
4725         tcp_collapse_ofo_queue(sk);
4726         if (!skb_queue_empty(&sk->sk_receive_queue))
4727                 tcp_collapse(sk, &sk->sk_receive_queue,
4728                              skb_peek(&sk->sk_receive_queue),
4729                              NULL,
4730                              tp->copied_seq, tp->rcv_nxt);
4731         sk_mem_reclaim(sk);
4732 
4733         if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
4734                 return 0;
4735 
4736         /* Collapsing did not help, destructive actions follow.
4737          * This must not ever occur. */
4738 
4739         tcp_prune_ofo_queue(sk);
4740 
4741         if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
4742                 return 0;
4743 
4744         /* If we are really being abused, tell the caller to silently
4745          * drop receive data on the floor.  It will get retransmitted
4746          * and hopefully then we'll have sufficient space.
4747          */
4748         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_RCVPRUNED);
4749 
4750         /* Massive buffer overcommit. */
4751         tp->pred_flags = 0;
4752         return -1;
4753 }
4754 
4755 /* RFC2861, slow part. Adjust cwnd, after it was not full during one rto.
4756  * As additional protections, we do not touch cwnd in retransmission phases,
4757  * and if application hit its sndbuf limit recently.
4758  */
4759 void tcp_cwnd_application_limited(struct sock *sk)
4760 {
4761         struct tcp_sock *tp = tcp_sk(sk);
4762 
4763         if (inet_csk(sk)->icsk_ca_state == TCP_CA_Open &&
4764             sk->sk_socket && !test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
4765                 /* Limited by application or receiver window. */
4766                 u32 init_win = tcp_init_cwnd(tp, __sk_dst_get(sk));
4767                 u32 win_used = max(tp->snd_cwnd_used, init_win);
4768                 if (win_used < tp->snd_cwnd) {
4769                         tp->snd_ssthresh = tcp_current_ssthresh(sk);
4770                         tp->snd_cwnd = (tp->snd_cwnd + win_used) >> 1;
4771                 }
4772                 tp->snd_cwnd_used = 0;
4773         }
4774         tp->snd_cwnd_stamp = tcp_time_stamp;
4775 }
4776 
4777 static int tcp_should_expand_sndbuf(struct sock *sk)
4778 {
4779         struct tcp_sock *tp = tcp_sk(sk);
4780 
4781         /* If the user specified a specific send buffer setting, do
4782          * not modify it.
4783          */
4784         if (sk->sk_userlocks & SOCK_SNDBUF_LOCK)
4785                 return 0;
4786 
4787         /* If we are under global TCP memory pressure, do not expand.  */
4788         if (tcp_memory_pressure)
4789                 return 0;
4790 
4791         /* If we are under soft global TCP memory pressure, do not expand.  */
4792         if (atomic_read(&tcp_memory_allocated) >= sysctl_tcp_mem[0])
4793                 return 0;
4794 
4795         /* If we filled the congestion window, do not expand.  */
4796         if (tp->packets_out >= tp->snd_cwnd)
4797                 return 0;
4798 
4799         return 1;
4800 }
4801 
4802 /* When incoming ACK allowed to free some skb from write_queue,
4803  * we remember this event in flag SOCK_QUEUE_SHRUNK and wake up socket
4804  * on the exit from tcp input handler.
4805  *
4806  * PROBLEM: sndbuf expansion does not work well with largesend.
4807  */
4808 static void tcp_new_space(struct sock *sk)
4809 {
4810         struct tcp_sock *tp = tcp_sk(sk);
4811 
4812         if (tcp_should_expand_sndbuf(sk)) {
4813                 int sndmem = max_t(u32, tp->rx_opt.mss_clamp, tp->mss_cache) +
4814                         MAX_TCP_HEADER + 16 + sizeof(struct sk_buff);
4815                 int demanded = max_t(unsigned int, tp->snd_cwnd,
4816                                      tp->reordering + 1);
4817                 sndmem *= 2 * demanded;
4818                 if (sndmem > sk->sk_sndbuf)
4819                         sk->sk_sndbuf = min(sndmem, sysctl_tcp_wmem[2]);
4820                 tp->snd_cwnd_stamp = tcp_time_stamp;
4821         }
4822 
4823         sk->sk_write_space(sk);
4824 }
4825 
4826 static void tcp_check_space(struct sock *sk)
4827 {
4828         if (sock_flag(sk, SOCK_QUEUE_SHRUNK)) {
4829                 sock_reset_flag(sk, SOCK_QUEUE_SHRUNK);
4830                 if (sk->sk_socket &&
4831                     test_bit(SOCK_NOSPACE, &sk->sk_socket->flags))
4832                         tcp_new_space(sk);
4833         }
4834 }
4835 
4836 static inline void tcp_data_snd_check(struct sock *sk)
4837 {
4838         tcp_push_pending_frames(sk);
4839         tcp_check_space(sk);
4840 }
4841 
4842 /*
4843  * Check if sending an ack is needed.
4844  */
4845 static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible)
4846 {
4847         struct tcp_sock *tp = tcp_sk(sk);
4848 
4849             /* More than one full frame received... */
4850         if (((tp->rcv_nxt - tp->rcv_wup) > inet_csk(sk)->icsk_ack.rcv_mss
4851              /* ... and right edge of window advances far enough.
4852               * (tcp_recvmsg() will send ACK otherwise). Or...
4853               */
4854              && __tcp_select_window(sk) >= tp->rcv_wnd) ||
4855             /* We ACK each frame or... */
4856             tcp_in_quickack_mode(sk) ||
4857             /* We have out of order data. */
4858             (ofo_possible && skb_peek(&tp->out_of_order_queue))) {
4859                 /* Then ack it now */
4860                 tcp_send_ack(sk);
4861         } else {
4862                 /* Else, send delayed ack. */
4863                 tcp_send_delayed_ack(sk);
4864         }
4865 }
4866 
4867 static inline void tcp_ack_snd_check(struct sock *sk)
4868 {
4869         if (!inet_csk_ack_scheduled(sk)) {
4870                 /* We sent a data segment already. */
4871                 return;
4872         }
4873         __tcp_ack_snd_check(sk, 1);
4874 }
4875 
4876 /*
4877  *      This routine is only called when we have urgent data
4878  *      signaled. Its the 'slow' part of tcp_urg. It could be
4879  *      moved inline now as tcp_urg is only called from one
4880  *      place. We handle URGent data wrong. We have to - as
4881  *      BSD still doesn't use the correction from RFC961.
4882  *      For 1003.1g we should support a new option TCP_STDURG to permit
4883  *      either form (or just set the sysctl tcp_stdurg).
4884  */
4885 
4886 static void tcp_check_urg(struct sock *sk, struct tcphdr *th)
4887 {
4888         struct tcp_sock *tp = tcp_sk(sk);
4889         u32 ptr = ntohs(th->urg_ptr);
4890 
4891         if (ptr && !sysctl_tcp_stdurg)
4892                 ptr--;
4893         ptr += ntohl(th->seq);
4894 
4895         /* Ignore urgent data that we've already seen and read. */
4896         if (after(tp->copied_seq, ptr))
4897                 return;
4898 
4899         /* Do not replay urg ptr.
4900          *
4901          * NOTE: interesting situation not covered by specs.
4902          * Misbehaving sender may send urg ptr, pointing to segment,
4903          * which we already have in ofo queue. We are not able to fetch
4904          * such data and will stay in TCP_URG_NOTYET until will be eaten
4905          * by recvmsg(). Seems, we are not obliged to handle such wicked
4906          * situations. But it is worth to think about possibility of some
4907          * DoSes using some hypothetical application level deadlock.
4908          */
4909         if (before(ptr, tp->rcv_nxt))
4910                 return;
4911 
4912         /* Do we already have a newer (or duplicate) urgent pointer? */
4913         if (tp->urg_data && !after(ptr, tp->urg_seq))
4914                 return;
4915 
4916         /* Tell the world about our new urgent pointer. */
4917         sk_send_sigurg(sk);
4918 
4919         /* We may be adding urgent data when the last byte read was
4920          * urgent. To do this requires some care. We cannot just ignore
4921          * tp->copied_seq since we would read the last urgent byte again
4922          * as data, nor can we alter copied_seq until this data arrives
4923          * or we break the semantics of SIOCATMARK (and thus sockatmark())
4924          *
4925          * NOTE. Double Dutch. Rendering to plain English: author of comment
4926          * above did something sort of  send("A", MSG_OOB); send("B", MSG_OOB);
4927          * and expect that both A and B disappear from stream. This is _wrong_.
4928          * Though this happens in BSD with high probability, this is occasional.
4929          * Any application relying on this is buggy. Note also, that fix "works"
4930          * only in this artificial test. Insert some normal data between A and B and we will
4931          * decline of BSD again. Verdict: it is better to remove to trap
4932          * buggy users.
4933          */
4934         if (tp->urg_seq == tp->copied_seq && tp->urg_data &&
4935             !sock_flag(sk, SOCK_URGINLINE) && tp->copied_seq != tp->rcv_nxt) {
4936                 struct sk_buff *skb = skb_peek(&sk->sk_receive_queue);
4937                 tp->copied_seq++;
4938                 if (skb && !before(tp->copied_seq, TCP_SKB_CB(skb)->end_seq)) {
4939                         __skb_unlink(skb, &sk->sk_receive_queue);
4940                         __kfree_skb(skb);
4941                 }
4942         }
4943 
4944         tp->urg_data = TCP_URG_NOTYET;
4945         tp->urg_seq = ptr;
4946 
4947         /* Disable header prediction. */
4948         tp->pred_flags = 0;
4949 }
4950 
4951 /* This is the 'fast' part of urgent handling. */
4952 static void tcp_urg(struct sock *sk, struct sk_buff *skb, struct tcphdr *th)
4953 {
4954         struct tcp_sock *tp = tcp_sk(sk);
4955 
4956         /* Check if we get a new urgent pointer - normally not. */
4957         if (th->urg)
4958                 tcp_check_urg(sk, th);
4959 
4960         /* Do we wait for any urgent data? - normally not... */
4961         if (tp->urg_data == TCP_URG_NOTYET) {
4962                 u32 ptr = tp->urg_seq - ntohl(th->seq) + (th->doff * 4) -
4963                           th->syn;
4964 
4965                 /* Is the urgent pointer pointing into this packet? */
4966                 if (ptr < skb->len) {
4967                         u8 tmp;
4968                         if (skb_copy_bits(skb, ptr, &tmp, 1))
4969                                 BUG();
4970                         tp->urg_data = TCP_URG_VALID | tmp;
4971                         if (!sock_flag(sk, SOCK_DEAD))
4972                                 sk->sk_data_ready(sk, 0);
4973                 }
4974         }
4975 }
4976 
4977 static int tcp_copy_to_iovec(struct sock *sk, struct sk_buff *skb, int hlen)
4978 {
4979         struct tcp_sock *tp = tcp_sk(sk);
4980         int chunk = skb->len - hlen;
4981         int err;
4982 
4983         local_bh_enable();
4984         if (skb_csum_unnecessary(skb))
4985                 err = skb_copy_datagram_iovec(skb, hlen, tp->ucopy.iov, chunk);
4986         else
4987                 err = skb_copy_and_csum_datagram_iovec(skb, hlen,
4988                                                        tp->ucopy.iov);
4989 
4990         if (!err) {
4991                 tp->ucopy.len -= chunk;
4992                 tp->copied_seq += chunk;
4993                 tcp_rcv_space_adjust(sk);
4994         }
4995 
4996         local_bh_disable();
4997         return err;
4998 }
4999 
5000 static __sum16 __tcp_checksum_complete_user(struct sock *sk,
5001                                             struct sk_buff *skb)
5002 {
5003         __sum16 result;
5004 
5005         if (sock_owned_by_user(sk)) {
5006                 local_bh_enable();
5007                 result = __tcp_checksum_complete(skb);
5008                 local_bh_disable();
5009         } else {
5010                 result = __tcp_checksum_complete(skb);
5011         }
5012         return result;
5013 }
5014 
5015 static inline int tcp_checksum_complete_user(struct sock *sk,
5016                                              struct sk_buff *skb)
5017 {
5018         return !skb_csum_unnecessary(skb) &&
5019                __tcp_checksum_complete_user(sk, skb);
5020 }
5021 
5022 #ifdef CONFIG_NET_DMA
5023 static int tcp_dma_try_early_copy(struct sock *sk, struct sk_buff *skb,
5024                                   int hlen)
5025 {
5026         struct tcp_sock *tp = tcp_sk(sk);
5027         int chunk = skb->len - hlen;
5028         int dma_cookie;
5029         int copied_early = 0;
5030 
5031         if (tp->ucopy.wakeup)
5032                 return 0;
5033 
5034         if (!tp->ucopy.dma_chan && tp->ucopy.pinned_list)
5035                 tp->ucopy.dma_chan = dma_find_channel(DMA_MEMCPY);
5036 
5037         if (tp->ucopy.dma_chan && skb_csum_unnecessary(skb)) {
5038 
5039                 dma_cookie = dma_skb_copy_datagram_iovec(tp->ucopy.dma_chan,
5040                                                          skb, hlen,
5041                                                          tp->ucopy.iov, chunk,
5042                                                          tp->ucopy.pinned_list);
5043 
5044                 if (dma_cookie < 0)
5045                         goto out;
5046 
5047                 tp->ucopy.dma_cookie = dma_cookie;
5048                 copied_early = 1;
5049 
5050                 tp->ucopy.len -= chunk;
5051                 tp->copied_seq += chunk;
5052                 tcp_rcv_space_adjust(sk);
5053 
5054                 if ((tp->ucopy.len == 0) ||
5055                     (tcp_flag_word(tcp_hdr(skb)) & TCP_FLAG_PSH) ||
5056                     (atomic_read(&sk->sk_rmem_alloc) > (sk->sk_rcvbuf >> 1))) {
5057                         tp->ucopy.wakeup = 1;
5058                         sk->sk_data_ready(sk, 0);
5059                 }
5060         } else if (chunk > 0) {
5061                 tp->ucopy.wakeup = 1;
5062                 sk->sk_data_ready(sk, 0);
5063         }
5064 out:
5065         return copied_early;
5066 }
5067 #endif /* CONFIG_NET_DMA */
5068 
5069 /* Does PAWS and seqno based validation of an incoming segment, flags will
5070  * play significant role here.
5071  */
5072 static int tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
5073                               struct tcphdr *th, int syn_inerr)
5074 {
5075         struct tcp_sock *tp = tcp_sk(sk);
5076 
5077         /* RFC1323: H1. Apply PAWS check first. */
5078         if (tcp_fast_parse_options(skb, th, tp) && tp->rx_opt.saw_tstamp &&
5079             tcp_paws_discard(sk, skb)) {
5080                 if (!th->rst) {
5081                         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);
5082                         tcp_send_dupack(sk, skb);
5083                         goto discard;
5084                 }
5085                 /* Reset is accepted even if it did not pass PAWS. */
5086         }
5087 
5088         /* Step 1: check sequence number */
5089         if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) {
5090                 /* RFC793, page 37: "In all states except SYN-SENT, all reset
5091                  * (RST) segments are validated by checking their SEQ-fields."
5092                  * And page 69: "If an incoming segment is not acceptable,
5093                  * an acknowledgment should be sent in reply (unless the RST
5094                  * bit is set, if so drop the segment and return)".
5095                  */
5096                 if (!th->rst)
5097                         tcp_send_dupack(sk, skb);
5098                 goto discard;
5099         }
5100 
5101         /* Step 2: check RST bit */
5102         if (th->rst) {
5103                 tcp_reset(sk);
5104                 goto discard;
5105         }
5106 
5107         /* ts_recent update must be made after we are sure that the packet
5108          * is in window.
5109          */
5110         tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
5111 
5112         /* step 3: check security and precedence [ignored] */
5113 
5114         /* step 4: Check for a SYN in window. */
5115         if (th->syn && !before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
5116                 if (syn_inerr)
5117                         TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS);
5118                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONSYN);
5119                 tcp_reset(sk);
5120                 return -1;
5121         }
5122 
5123         return 1;
5124 
5125 discard:
5126         __kfree_skb(skb);
5127         return 0;
5128 }
5129 
5130 /*
5131  *      TCP receive function for the ESTABLISHED state.
5132  *
5133  *      It is split into a fast path and a slow path. The fast path is
5134  *      disabled when:
5135  *      - A zero window was announced from us - zero window probing
5136  *        is only handled properly in the slow path.
5137  *      - Out of order segments arrived.
5138  *      - Urgent data is expected.
5139  *      - There is no buffer space left
5140  *      - Unexpected TCP flags/window values/header lengths are received
5141  *        (detected by checking the TCP header against pred_flags)
5142  *      - Data is sent in both directions. Fast path only supports pure senders
5143  *        or pure receivers (this means either the sequence number or the ack
5144  *        value must stay constant)
5145  *      - Unexpected TCP option.
5146  *
5147  *      When these conditions are not satisfied it drops into a standard
5148  *      receive procedure patterned after RFC793 to handle all cases.
5149  *      The first three cases are guaranteed by proper pred_flags setting,
5150  *      the rest is checked inline. Fast processing is turned on in
5151  *      tcp_data_queue when everything is OK.
5152  */
5153 int tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
5154                         struct tcphdr *th, unsigned len)
5155 {
5156         struct tcp_sock *tp = tcp_sk(sk);
5157         int res;
5158 
5159         /*
5160          *      Header prediction.
5161          *      The code loosely follows the one in the famous
5162          *      "30 instruction TCP receive" Van Jacobson mail.
5163          *
5164          *      Van's trick is to deposit buffers into socket queue
5165          *      on a device interrupt, to call tcp_recv function
5166          *      on the receive process context and checksum and copy
5167          *      the buffer to user space. smart...
5168          *
5169          *      Our current scheme is not silly either but we take the
5170          *      extra cost of the net_bh soft interrupt processing...
5171          *      We do checksum and copy also but from device to kernel.
5172          */
5173 
5174         tp->rx_opt.saw_tstamp = 0;
5175 
5176         /*      pred_flags is 0xS?10 << 16 + snd_wnd
5177          *      if header_prediction is to be made
5178          *      'S' will always be tp->tcp_header_len >> 2
5179          *      '?' will be 0 for the fast path, otherwise pred_flags is 0 to
5180          *  turn it off (when there are holes in the receive
5181          *       space for instance)
5182          *      PSH flag is ignored.
5183          */
5184 
5185         if ((tcp_flag_word(th) & TCP_HP_BITS) == tp->pred_flags &&
5186             TCP_SKB_CB(skb)->seq == tp->rcv_nxt &&
5187             !after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt)) {
5188                 int tcp_header_len = tp->tcp_header_len;
5189 
5190                 /* Timestamp header prediction: tcp_header_len
5191                  * is automatically equal to th->doff*4 due to pred_flags
5192                  * match.
5193                  */
5194 
5195                 /* Check timestamp */
5196                 if (tcp_header_len == sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) {
5197                         /* No? Slow path! */
5198                         if (!tcp_parse_aligned_timestamp(tp, th))
5199                                 goto slow_path;
5200 
5201                         /* If PAWS failed, check it more carefully in slow path */
5202                         if ((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) < 0)
5203                                 goto slow_path;
5204 
5205                         /* DO NOT update ts_recent here, if checksum fails
5206                          * and timestamp was corrupted part, it will result
5207                          * in a hung connection since we will drop all
5208                          * future packets due to the PAWS test.
5209                          */
5210                 }
5211 
5212                 if (len <= tcp_header_len) {
5213                         /* Bulk data transfer: sender */
5214                         if (len == tcp_header_len) {
5215                                 /* Predicted packet is in window by definition.
5216                                  * seq == rcv_nxt and rcv_wup <= rcv_nxt.
5217                                  * Hence, check seq<=rcv_wup reduces to:
5218                                  */
5219                                 if (tcp_header_len ==
5220                                     (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
5221                                     tp->rcv_nxt == tp->rcv_wup)
5222                                         tcp_store_ts_recent(tp);
5223 
5224                                 /* We know that such packets are checksummed
5225                                  * on entry.
5226                                  */
5227                                 tcp_ack(sk, skb, 0);
5228                                 __kfree_skb(skb);
5229                                 tcp_data_snd_check(sk);
5230                                 return 0;
5231                         } else { /* Header too small */
5232                                 TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS);
5233                                 goto discard;
5234                         }
5235                 } else {
5236                         int eaten = 0;
5237                         int copied_early = 0;
5238 
5239                         if (tp->copied_seq == tp->rcv_nxt &&
5240                             len - tcp_header_len <= tp->ucopy.len) {
5241 #ifdef CONFIG_NET_DMA
5242                                 if (tp->ucopy.task == current &&
5243                                     sock_owned_by_user(sk) &&
5244                                     tcp_dma_try_early_copy(sk, skb, tcp_header_len)) {
5245                                         copied_early = 1;
5246                                         eaten = 1;
5247                                 }
5248 #endif
5249                                 if (tp->ucopy.task == current &&
5250                                     sock_owned_by_user(sk) && !copied_early) {
5251                                         __set_current_state(TASK_RUNNING);
5252 
5253                                         if (!tcp_copy_to_iovec(sk, skb, tcp_header_len))
5254                                                 eaten = 1;
5255                                 }
5256                                 if (eaten) {
5257                                         /* Predicted packet is in window by definition.
5258                                          * seq == rcv_nxt and rcv_wup <= rcv_nxt.
5259                                          * Hence, check seq<=rcv_wup reduces to:
5260                                          */
5261                                         if (tcp_header_len ==
5262                                             (sizeof(struct tcphdr) +
5263                                              TCPOLEN_TSTAMP_ALIGNED) &&
5264                                             tp->rcv_nxt == tp->rcv_wup)
5265                                                 tcp_store_ts_recent(tp);
5266 
5267                                         tcp_rcv_rtt_measure_ts(sk, skb);
5268 
5269                                         __skb_pull(skb, tcp_header_len);
5270                                         tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
5271                                         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPHITSTOUSER);
5272                                 }
5273                                 if (copied_early)
5274                                         tcp_cleanup_rbuf(sk, skb->len);
5275                         }
5276                         if (!eaten) {
5277                                 if (tcp_checksum_complete_user(sk, skb))
5278                                         goto csum_error;
5279 
5280                                 /* Predicted packet is in window by definition.
5281                                  * seq == rcv_nxt and rcv_wup <= rcv_nxt.
5282                                  * Hence, check seq<=rcv_wup reduces to:
5283                                  */
5284                                 if (tcp_header_len ==
5285                                     (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
5286                                     tp->rcv_nxt == tp->rcv_wup)
5287                                         tcp_store_ts_recent(tp);
5288 
5289                                 tcp_rcv_rtt_measure_ts(sk, skb);
5290 
5291                                 if ((int)skb->truesize > sk->sk_forward_alloc)
5292                                         goto step5;
5293 
5294                                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPHITS);
5295 
5296                                 /* Bulk data transfer: receiver */
5297                                 __skb_pull(skb, tcp_header_len);
5298                                 __skb_queue_tail(&sk->sk_receive_queue, skb);
5299                                 skb_set_owner_r(skb, sk);
5300                                 tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
5301                         }
5302 
5303                         tcp_event_data_recv(sk, skb);
5304 
5305                         if (TCP_SKB_CB(skb)->ack_seq != tp->snd_una) {
5306                                 /* Well, only one small jumplet in fast path... */
5307                                 tcp_ack(sk, skb, FLAG_DATA);
5308                                 tcp_data_snd_check(sk);
5309                                 if (!inet_csk_ack_scheduled(sk))
5310                                         goto no_ack;
5311                         }
5312 
5313                         if (!copied_early || tp->rcv_nxt != tp->rcv_wup)
5314                                 __tcp_ack_snd_check(sk, 0);
5315 no_ack:
5316 #ifdef CONFIG_NET_DMA
5317                         if (copied_early)
5318                                 __skb_queue_tail(&sk->sk_async_wait_queue, skb);
5319                         else
5320 #endif
5321                         if (eaten)
5322                                 __kfree_skb(skb);
5323                         else
5324                                 sk->sk_data_ready(sk, 0);
5325                         return 0;
5326                 }
5327         }
5328 
5329 slow_path:
5330         if (len < (th->doff << 2) || tcp_checksum_complete_user(sk, skb))
5331                 goto csum_error;
5332 
5333         /*
5334          *      Standard slow path.
5335          */
5336 
5337         res = tcp_validate_incoming(sk, skb, th, 1);
5338         if (res <= 0)
5339                 return -res;
5340 
5341 step5:
5342         if (th->ack && tcp_ack(sk, skb, FLAG_SLOWPATH) < 0)
5343                 goto discard;
5344 
5345         tcp_rcv_rtt_measure_ts(sk, skb);
5346 
5347         /* Process urgent data. */
5348         tcp_urg(sk, skb, th);
5349 
5350         /* step 7: process the segment text */
5351         tcp_data_queue(sk, skb);
5352 
5353         tcp_data_snd_check(sk);
5354         tcp_ack_snd_check(sk);
5355         return 0;
5356 
5357 csum_error:
5358         TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS);
5359 
5360 discard:
5361         __kfree_skb(skb);
5362         return 0;
5363 }
5364 
5365 static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
5366                                          struct tcphdr *th, unsigned len)
5367 {
5368         struct tcp_sock *tp = tcp_sk(sk);
5369         struct inet_connection_sock *icsk = inet_csk(sk);
5370         int saved_clamp = tp->rx_opt.mss_clamp;
5371 
5372         tcp_parse_options(skb, &tp->rx_opt, 0);
5373 
5374         if (th->ack) {
5375                 /* rfc793:
5376                  * "If the state is SYN-SENT then
5377                  *    first check the ACK bit
5378                  *      If the ACK bit is set
5379                  *        If SEG.ACK =< ISS, or SEG.ACK > SND.NXT, send
5380                  *        a reset (unless the RST bit is set, if so drop
5381                  *        the segment and return)"
5382                  *
5383                  *  We do not send data with SYN, so that RFC-correct
5384                  *  test reduces to:
5385                  */
5386                 if (TCP_SKB_CB(skb)->ack_seq != tp->snd_nxt)
5387                         goto reset_and_undo;
5388 
5389                 if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
5390                     !between(tp->rx_opt.rcv_tsecr, tp->retrans_stamp,
5391                              tcp_time_stamp)) {
5392                         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSACTIVEREJECTED);
5393                         goto reset_and_undo;
5394                 }
5395 
5396                 /* Now ACK is acceptable.
5397                  *
5398                  * "If the RST bit is set
5399                  *    If the ACK was acceptable then signal the user "error:
5400                  *    connection reset", drop the segment, enter CLOSED state,
5401                  *    delete TCB, and return."
5402                  */
5403 
5404                 if (th->rst) {
5405                         tcp_reset(sk);
5406                         goto discard;
5407                 }
5408 
5409                 /* rfc793:
5410                  *   "fifth, if neither of the SYN or RST bits is set then
5411                  *    drop the segment and return."
5412                  *
5413                  *    See note below!
5414                  *                                        --ANK(990513)
5415                  */
5416                 if (!th->syn)
5417                         goto discard_and_undo;
5418 
5419                 /* rfc793:
5420                  *   "If the SYN bit is on ...
5421                  *    are acceptable then ...
5422                  *    (our SYN has been ACKed), change the connection
5423                  *    state to ESTABLISHED..."
5424                  */
5425 
5426                 TCP_ECN_rcv_synack(tp, th);
5427 
5428                 tp->snd_wl1 = TCP_SKB_CB(skb)->seq;
5429                 tcp_ack(sk, skb, FLAG_SLOWPATH);
5430 
5431                 /* Ok.. it's good. Set up sequence numbers and
5432                  * move to established.
5433                  */
5434                 tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
5435                 tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
5436 
5437                 /* RFC1323: The window in SYN & SYN/ACK segments is
5438                  * never scaled.
5439                  */
5440                 tp->snd_wnd = ntohs(th->window);
5441                 tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);
5442 
5443                 if (!tp->rx_opt.wscale_ok) {
5444                         tp->rx_opt.snd_wscale = tp->rx_opt.rcv_wscale = 0;
5445                         tp->window_clamp = min(tp->window_clamp, 65535U);
5446                 }
5447 
5448                 if (tp->rx_opt.saw_tstamp) {
5449                         tp->rx_opt.tstamp_ok       = 1;
5450                         tp->tcp_header_len =
5451                                 sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
5452                         tp->advmss          -= TCPOLEN_TSTAMP_ALIGNED;
5453                         tcp_store_ts_recent(tp);
5454                 } else {
5455                         tp->tcp_header_len = sizeof(struct tcphdr);
5456                 }
5457 
5458                 if (tcp_is_sack(tp) && sysctl_tcp_fack)
5459                         tcp_enable_fack(tp);
5460 
5461                 tcp_mtup_init(sk);
5462                 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
5463                 tcp_initialize_rcv_mss(sk);
5464 
5465                 /* Remember, tcp_poll() does not lock socket!
5466                  * Change state from SYN-SENT only after copied_seq
5467                  * is initialized. */
5468                 tp->copied_seq = tp->rcv_nxt;
5469                 smp_mb();
5470                 tcp_set_state(sk, TCP_ESTABLISHED);
5471 
5472                 security_inet_conn_established(sk, skb);
5473 
5474                 /* Make sure socket is routed, for correct metrics.  */
5475                 icsk->icsk_af_ops->rebuild_header(sk);
5476 
5477                 tcp_init_metrics(sk);
5478 
5479                 tcp_init_congestion_control(sk);
5480 
5481                 /* Prevent spurious tcp_cwnd_restart() on first data
5482                  * packet.
5483                  */
5484                 tp->lsndtime = tcp_time_stamp;
5485 
5486                 tcp_init_buffer_space(sk);
5487 
5488                 if (sock_flag(sk, SOCK_KEEPOPEN))
5489                         inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tp));
5490 
5491                 if (!tp->rx_opt.snd_wscale)
5492                         __tcp_fast_path_on(tp, tp->snd_wnd);
5493                 else
5494                         tp->pred_flags = 0;
5495 
5496                 if (!sock_flag(sk, SOCK_DEAD)) {
5497                         sk->sk_state_change(sk);
5498                         sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT);
5499                 }
5500 
5501                 if (sk->sk_write_pending ||
5502                     icsk->icsk_accept_queue.rskq_defer_accept ||
5503                     icsk->icsk_ack.pingpong) {
5504                         /* Save one ACK. Data will be ready after
5505                          * several ticks, if write_pending is set.
5506                          *
5507                          * It may be deleted, but with this feature tcpdumps
5508                          * look so _wonderfully_ clever, that I was not able
5509                          * to stand against the temptation 8)     --ANK
5510                          */
5511                         inet_csk_schedule_ack(sk);
5512                         icsk->icsk_ack.lrcvtime = tcp_time_stamp;
5513                         icsk->icsk_ack.ato       = TCP_ATO_MIN;
5514                         tcp_incr_quickack(sk);
5515                         tcp_enter_quickack_mode(sk);
5516                         inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
5517                                                   TCP_DELACK_MAX, TCP_RTO_MAX);
5518 
5519 discard:
5520                         __kfree_skb(skb);
5521                         return 0;
5522                 } else {
5523                         tcp_send_ack(sk);
5524                 }
5525                 return -1;
5526         }
5527 
5528         /* No ACK in the segment */
5529 
5530         if (th->rst) {
5531                 /* rfc793:
5532                  * "If the RST bit is set
5533                  *
5534                  *      Otherwise (no ACK) drop the segment and return."
5535                  */
5536 
5537                 goto discard_and_undo;
5538         }
5539 
5540         /* PAWS check. */
5541         if (tp->rx_opt.ts_recent_stamp && tp->rx_opt.saw_tstamp &&
5542             tcp_paws_reject(&tp->rx_opt, 0))
5543                 goto discard_and_undo;
5544 
5545         if (th->syn) {
5546                 /* We see SYN without ACK. It is attempt of
5547                  * simultaneous connect with crossed SYNs.
5548                  * Particularly, it can be connect to self.
5549                  */
5550                 tcp_set_state(sk, TCP_SYN_RECV);
5551 
5552                 if (tp->rx_opt.saw_tstamp) {
5553                         tp->rx_opt.tstamp_ok = 1;
5554                         tcp_store_ts_recent(tp);
5555                         tp->tcp_header_len =
5556                                 sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
5557                 } else {
5558                         tp->tcp_header_len = sizeof(struct tcphdr);
5559                 }
5560 
5561                 tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
5562                 tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
5563 
5564                 /* RFC1323: The window in SYN & SYN/ACK segments is
5565                  * never scaled.
5566                  */
5567                 tp->snd_wnd    = ntohs(th->window);
5568                 tp->snd_wl1    = TCP_SKB_CB(skb)->seq;
5569                 tp->max_window = tp->snd_wnd;
5570 
5571                 TCP_ECN_rcv_syn(tp, th);
5572 
5573                 tcp_mtup_init(sk);
5574                 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
5575                 tcp_initialize_rcv_mss(sk);
5576 
5577                 tcp_send_synack(sk);
5578 #if 0
5579                 /* Note, we could accept data and URG from this segment.
5580                  * There are no obstacles to make this.
5581                  *
5582                  * However, if we ignore data in ACKless segments sometimes,
5583                  * we have no reasons to accept it sometimes.
5584                  * Also, seems the code doing it in step6 of tcp_rcv_state_process
5585                  * is not flawless. So, discard packet for sanity.
5586                  * Uncomment this return to process the data.
5587                  */
5588                 return -1;
5589 #else
5590                 goto discard;
5591 #endif
5592         }
5593         /* "fifth, if neither of the SYN or RST bits is set then
5594          * drop the segment and return."
5595          */
5596 
5597 discard_and_undo:
5598         tcp_clear_options(&tp->rx_opt);
5599         tp->rx_opt.mss_clamp = saved_clamp;
5600         goto discard;
5601 
5602 reset_and_undo:
5603         tcp_clear_options(&tp->rx_opt);
5604         tp->rx_opt.mss_clamp = saved_clamp;
5605         return 1;
5606 }
5607 
5608 /*
5609  *      This function implements the receiving procedure of RFC 793 for
5610  *      all states except ESTABLISHED and TIME_WAIT.
5611  *      It's called from both tcp_v4_rcv and tcp_v6_rcv and should be
5612  *      address independent.
5613  */
5614 
5615 int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
5616                           struct tcphdr *th, unsigned len)
5617 {
5618         struct tcp_sock *tp = tcp_sk(sk);
5619         struct inet_connection_sock *icsk = inet_csk(sk);
5620         int queued = 0;
5621         int res;
5622 
5623         tp->rx_opt.saw_tstamp = 0;
5624 
5625         switch (sk->sk_state) {
5626         case TCP_CLOSE:
5627                 goto discard;
5628 
5629         case TCP_LISTEN:
5630                 if (th->ack)
5631                         return 1;
5632 
5633                 if (th->rst)
5634                         goto discard;
5635 
5636                 if (th->syn) {
5637                         if (th->fin)
5638                                 goto discard;
5639                         if (icsk->icsk_af_ops->conn_request(sk, skb) < 0)
5640                                 return 1;
5641 
5642                         /* Now we have several options: In theory there is
5643                          * nothing else in the frame. KA9Q has an option to
5644                          * send data with the syn, BSD accepts data with the
5645                          * syn up to the [to be] advertised window and
5646                          * Solaris 2.1 gives you a protocol error. For now
5647                          * we just ignore it, that fits the spec precisely
5648                          * and avoids incompatibilities. It would be nice in
5649                          * future to drop through and process the data.
5650                          *
5651                          * Now that TTCP is starting to be used we ought to
5652                          * queue this data.
5653                          * But, this leaves one open to an easy denial of
5654                          * service attack, and SYN cookies can't defend
5655                          * against this problem. So, we drop the data
5656                          * in the interest of security over speed unless
5657                          * it's still in use.
5658                          */
5659                         kfree_skb(skb);
5660                         return 0;
5661                 }
5662                 goto discard;
5663 
5664         case TCP_SYN_SENT:
5665                 queued = tcp_rcv_synsent_state_process(sk, skb, th, len);
5666                 if (queued >= 0)
5667                         return queued;
5668 
5669                 /* Do step6 onward by hand. */
5670                 tcp_urg(sk, skb, th);
5671                 __kfree_skb(skb);
5672                 tcp_data_snd_check(sk);
5673                 return 0;
5674         }
5675 
5676         res = tcp_validate_incoming(sk, skb, th, 0);
5677         if (res <= 0)
5678                 return -res;
5679 
5680         /* step 5: check the ACK field */
5681         if (th->ack) {
5682                 int acceptable = tcp_ack(sk, skb, FLAG_SLOWPATH) > 0;
5683 
5684                 switch (sk->sk_state) {
5685                 case TCP_SYN_RECV:
5686                         if (acceptable) {
5687                                 tp->copied_seq = tp->rcv_nxt;
5688                                 smp_mb();
5689                                 tcp_set_state(sk, TCP_ESTABLISHED);
5690                                 sk->sk_state_change(sk);
5691 
5692                                 /* Note, that this wakeup is only for marginal
5693                                  * crossed SYN case. Passively open sockets
5694                                  * are not waked up, because sk->sk_sleep ==
5695                                  * NULL and sk->sk_socket == NULL.
5696                                  */
5697                                 if (sk->sk_socket)
5698                                         sk_wake_async(sk,
5699                                                       SOCK_WAKE_IO, POLL_OUT);
5700 
5701                                 tp->snd_una = TCP_SKB_CB(skb)->ack_seq;
5702                                 tp->snd_wnd = ntohs(th->window) <<
5703                                               tp->rx_opt.snd_wscale;
5704                                 tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);
5705 
5706                                 /* tcp_ack considers this ACK as duplicate
5707                                  * and does not calculate rtt.
5708                                  * Force it here.
5709                                  */
5710                                 tcp_ack_update_rtt(sk, 0, 0);
5711 
5712                                 if (tp->rx_opt.tstamp_ok)
5713                                         tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;
5714 
5715                                 /* Make sure socket is routed, for
5716                                  * correct metrics.
5717                                  */
5718                                 icsk->icsk_af_ops->rebuild_header(sk);
5719 
5720                                 tcp_init_metrics(sk);
5721 
5722                                 tcp_init_congestion_control(sk);
5723 
5724                                 /* Prevent spurious tcp_cwnd_restart() on
5725                                  * first data packet.
5726                                  */
5727                                 tp->lsndtime = tcp_time_stamp;
5728 
5729                                 tcp_mtup_init(sk);
5730                                 tcp_initialize_rcv_mss(sk);
5731                                 tcp_init_buffer_space(sk);
5732                                 tcp_fast_path_on(tp);
5733                         } else {
5734                                 return 1;
5735                         }
5736                         break;
5737 
5738                 case TCP_FIN_WAIT1:
5739                         if (tp->snd_una == tp->write_seq) {
5740                                 tcp_set_state(sk, TCP_FIN_WAIT2);
5741                                 sk->sk_shutdown |= SEND_SHUTDOWN;
5742                                 dst_confirm(sk->sk_dst_cache);
5743 
5744                                 if (!sock_flag(sk, SOCK_DEAD))
5745                                         /* Wake up lingering close() */
5746                                         sk->sk_state_change(sk);
5747                                 else {
5748                                         int tmo;
5749 
5750                                         if (tp->linger2 < 0 ||
5751                                             (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
5752                                              after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt))) {
5753                                                 tcp_done(sk);
5754                                                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
5755                                                 return 1;
5756                                         }
5757 
5758                                         tmo = tcp_fin_time(sk);
5759                                         if (tmo > TCP_TIMEWAIT_LEN) {
5760                                                 inet_csk_reset_keepalive_timer(sk, tmo - TCP_TIMEWAIT_LEN);
5761                                         } else if (th->fin || sock_owned_by_user(sk)) {
5762                                                 /* Bad case. We could lose such FIN otherwise.
5763                                                  * It is not a big problem, but it looks confusing
5764                                                  * and not so rare event. We still can lose it now,
5765                                                  * if it spins in bh_lock_sock(), but it is really
5766                                                  * marginal case.
5767                                                  */
5768                                                 inet_csk_reset_keepalive_timer(sk, tmo);
5769                                         } else {
5770                                                 tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
5771                                                 goto discard;
5772                                         }
5773                                 }
5774                         }
5775                         break;
5776 
5777                 case TCP_CLOSING:
5778                         if (tp->snd_una == tp->write_seq) {
5779                                 tcp_time_wait(sk, TCP_TIME_WAIT, 0);
5780                                 goto discard;
5781                         }
5782                         break;
5783 
5784                 case TCP_LAST_ACK:
5785                         if (tp->snd_una == tp->write_seq) {
5786                                 tcp_update_metrics(sk);
5787                                 tcp_done(sk);
5788                                 goto discard;
5789                         }
5790                         break;
5791                 }
5792         } else
5793                 goto discard;
5794 
5795         /* step 6: check the URG bit */
5796         tcp_urg(sk, skb, th);
5797 
5798         /* step 7: process the segment text */
5799         switch (sk->sk_state) {
5800         case TCP_CLOSE_WAIT:
5801         case TCP_CLOSING:
5802         case TCP_LAST_ACK:
5803                 if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
5804                         break;
5805         case TCP_FIN_WAIT1:
5806         case TCP_FIN_WAIT2:
5807                 /* RFC 793 says to queue data in these states,
5808                  * RFC 1122 says we MUST send a reset.
5809                  * BSD 4.4 also does reset.
5810                  */
5811                 if (sk->sk_shutdown & RCV_SHUTDOWN) {
5812                         if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
5813                             after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) {
5814                                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
5815                                 tcp_reset(sk);
5816                                 return 1;
5817                         }
5818                 }
5819                 /* Fall through */
5820         case TCP_ESTABLISHED:
5821                 tcp_data_queue(sk, skb);
5822                 queued = 1;
5823                 break;
5824         }
5825 
5826         /* tcp_data could move socket to TIME-WAIT */
5827         if (sk->sk_state != TCP_CLOSE) {
5828                 tcp_data_snd_check(sk);
5829                 tcp_ack_snd_check(sk);
5830         }
5831 
5832         if (!queued) {
5833 discard:
5834                 __kfree_skb(skb);
5835         }
5836         return 0;
5837 }
5838 
5839 EXPORT_SYMBOL(sysctl_tcp_ecn);
5840 EXPORT_SYMBOL(sysctl_tcp_reordering);
5841 EXPORT_SYMBOL(sysctl_tcp_adv_win_scale);
5842 EXPORT_SYMBOL(tcp_parse_options);
5843 #ifdef CONFIG_TCP_MD5SIG
5844 EXPORT_SYMBOL(tcp_parse_md5sig_option);
5845 #endif
5846 EXPORT_SYMBOL(tcp_rcv_established);
5847 EXPORT_SYMBOL(tcp_rcv_state_process);
5848 EXPORT_SYMBOL(tcp_initialize_rcv_mss);
5849 

This page was automatically generated by LXR 0.3.1 (source).  •  Linux is a registered trademark of Linus Torvalds  •  Contact us