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 * Version: $Id: tcp_input.c,v 1.243 2002/02/01 22:01:04 davem Exp $ 9 * 10 * Authors: Ross Biro 11 * Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG> 12 * Mark Evans, <evansmp@uhura.aston.ac.uk> 13 * Corey Minyard <wf-rch!minyard@relay.EU.net> 14 * Florian La Roche, <flla@stud.uni-sb.de> 15 * Charles Hedrick, <hedrick@klinzhai.rutgers.edu> 16 * Linus Torvalds, <torvalds@cs.helsinki.fi> 17 * Alan Cox, <gw4pts@gw4pts.ampr.org> 18 * Matthew Dillon, <dillon@apollo.west.oic.com> 19 * Arnt Gulbrandsen, <agulbra@nvg.unit.no> 20 * Jorge Cwik, <jorge@laser.satlink.net> 21 */ 22 23 /* 24 * Changes: 25 * Pedro Roque : Fast Retransmit/Recovery. 26 * Two receive queues. 27 * Retransmit queue handled by TCP. 28 * Better retransmit timer handling. 29 * New congestion avoidance. 30 * Header prediction. 31 * Variable renaming. 32 * 33 * Eric : Fast Retransmit. 34 * Randy Scott : MSS option defines. 35 * Eric Schenk : Fixes to slow start algorithm. 36 * Eric Schenk : Yet another double ACK bug. 37 * Eric Schenk : Delayed ACK bug fixes. 38 * Eric Schenk : Floyd style fast retrans war avoidance. 39 * David S. Miller : Don't allow zero congestion window. 40 * Eric Schenk : Fix retransmitter so that it sends 41 * next packet on ack of previous packet. 42 * Andi Kleen : Moved open_request checking here 43 * and process RSTs for open_requests. 44 * Andi Kleen : Better prune_queue, and other fixes. 45 * Andrey Savochkin: Fix RTT measurements in the presnce of 46 * timestamps. 47 * Andrey Savochkin: Check sequence numbers correctly when 48 * removing SACKs due to in sequence incoming 49 * data segments. 50 * Andi Kleen: Make sure we never ack data there is not 51 * enough room for. Also make this condition 52 * a fatal error if it might still happen. 53 * Andi Kleen: Add tcp_measure_rcv_mss to make 54 * connections with MSS<min(MTU,ann. MSS) 55 * work without delayed acks. 56 * Andi Kleen: Process packets with PSH set in the 57 * fast path. 58 * J Hadi Salim: ECN support 59 * Andrei Gurtov, 60 * Pasi Sarolahti, 61 * Panu Kuhlberg: Experimental audit of TCP (re)transmission 62 * engine. Lots of bugs are found. 63 * Pasi Sarolahti: F-RTO for dealing with spurious RTOs 64 */ 65 66 #include <linux/config.h> 67 #include <linux/mm.h> 68 #include <linux/module.h> 69 #include <linux/sysctl.h> 70 #include <net/tcp.h> 71 #include <net/inet_common.h> 72 #include <linux/ipsec.h> 73 #include <asm/unaligned.h> 74 75 int sysctl_tcp_timestamps = 1; 76 int sysctl_tcp_window_scaling = 1; 77 int sysctl_tcp_sack = 1; 78 int sysctl_tcp_fack = 1; 79 int sysctl_tcp_reordering = TCP_FASTRETRANS_THRESH; 80 int sysctl_tcp_ecn; 81 int sysctl_tcp_dsack = 1; 82 int sysctl_tcp_app_win = 31; 83 int sysctl_tcp_adv_win_scale = 2; 84 85 int sysctl_tcp_stdurg; 86 int sysctl_tcp_rfc1337; 87 int sysctl_tcp_max_orphans = NR_FILE; 88 int sysctl_tcp_frto; 89 int sysctl_tcp_nometrics_save; 90 91 int sysctl_tcp_moderate_rcvbuf = 1; 92 93 #define FLAG_DATA 0x01 /* Incoming frame contained data. */ 94 #define FLAG_WIN_UPDATE 0x02 /* Incoming ACK was a window update. */ 95 #define FLAG_DATA_ACKED 0x04 /* This ACK acknowledged new data. */ 96 #define FLAG_RETRANS_DATA_ACKED 0x08 /* "" "" some of which was retransmitted. */ 97 #define FLAG_SYN_ACKED 0x10 /* This ACK acknowledged SYN. */ 98 #define FLAG_DATA_SACKED 0x20 /* New SACK. */ 99 #define FLAG_ECE 0x40 /* ECE in this ACK */ 100 #define FLAG_DATA_LOST 0x80 /* SACK detected data lossage. */ 101 #define FLAG_SLOWPATH 0x100 /* Do not skip RFC checks for window update.*/ 102 103 #define FLAG_ACKED (FLAG_DATA_ACKED|FLAG_SYN_ACKED) 104 #define FLAG_NOT_DUP (FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED) 105 #define FLAG_CA_ALERT (FLAG_DATA_SACKED|FLAG_ECE) 106 #define FLAG_FORWARD_PROGRESS (FLAG_ACKED|FLAG_DATA_SACKED) 107 108 #define IsReno(tp) ((tp)->rx_opt.sack_ok == 0) 109 #define IsFack(tp) ((tp)->rx_opt.sack_ok & 2) 110 #define IsDSack(tp) ((tp)->rx_opt.sack_ok & 4) 111 112 #define TCP_REMNANT (TCP_FLAG_FIN|TCP_FLAG_URG|TCP_FLAG_SYN|TCP_FLAG_PSH) 113 114 /* Adapt the MSS value used to make delayed ack decision to the 115 * real world. 116 */ 117 static inline void tcp_measure_rcv_mss(struct sock *sk, 118 const struct sk_buff *skb) 119 { 120 struct inet_connection_sock *icsk = inet_csk(sk); 121 const unsigned int lss = icsk->icsk_ack.last_seg_size; 122 unsigned int len; 123 124 icsk->icsk_ack.last_seg_size = 0; 125 126 /* skb->len may jitter because of SACKs, even if peer 127 * sends good full-sized frames. 128 */ 129 len = skb->len; 130 if (len >= icsk->icsk_ack.rcv_mss) { 131 icsk->icsk_ack.rcv_mss = len; 132 } else { 133 /* Otherwise, we make more careful check taking into account, 134 * that SACKs block is variable. 135 * 136 * "len" is invariant segment length, including TCP header. 137 */ 138 len += skb->data - skb->h.raw; 139 if (len >= TCP_MIN_RCVMSS + sizeof(struct tcphdr) || 140 /* If PSH is not set, packet should be 141 * full sized, provided peer TCP is not badly broken. 142 * This observation (if it is correct 8)) allows 143 * to handle super-low mtu links fairly. 144 */ 145 (len >= TCP_MIN_MSS + sizeof(struct tcphdr) && 146 !(tcp_flag_word(skb->h.th)&TCP_REMNANT))) { 147 /* Subtract also invariant (if peer is RFC compliant), 148 * tcp header plus fixed timestamp option length. 149 * Resulting "len" is MSS free of SACK jitter. 150 */ 151 len -= tcp_sk(sk)->tcp_header_len; 152 icsk->icsk_ack.last_seg_size = len; 153 if (len == lss) { 154 icsk->icsk_ack.rcv_mss = len; 155 return; 156 } 157 } 158 icsk->icsk_ack.pending |= ICSK_ACK_PUSHED; 159 } 160 } 161 162 static void tcp_incr_quickack(struct sock *sk) 163 { 164 struct inet_connection_sock *icsk = inet_csk(sk); 165 unsigned quickacks = tcp_sk(sk)->rcv_wnd / (2 * icsk->icsk_ack.rcv_mss); 166 167 if (quickacks==0) 168 quickacks=2; 169 if (quickacks > icsk->icsk_ack.quick) 170 icsk->icsk_ack.quick = min(quickacks, TCP_MAX_QUICKACKS); 171 } 172 173 void tcp_enter_quickack_mode(struct sock *sk) 174 { 175 struct inet_connection_sock *icsk = inet_csk(sk); 176 tcp_incr_quickack(sk); 177 icsk->icsk_ack.pingpong = 0; 178 icsk->icsk_ack.ato = TCP_ATO_MIN; 179 } 180 181 /* Send ACKs quickly, if "quick" count is not exhausted 182 * and the session is not interactive. 183 */ 184 185 static inline int tcp_in_quickack_mode(const struct sock *sk) 186 { 187 const struct inet_connection_sock *icsk = inet_csk(sk); 188 return icsk->icsk_ack.quick && !icsk->icsk_ack.pingpong; 189 } 190 191 /* Buffer size and advertised window tuning. 192 * 193 * 1. Tuning sk->sk_sndbuf, when connection enters established state. 194 */ 195 196 static void tcp_fixup_sndbuf(struct sock *sk) 197 { 198 int sndmem = tcp_sk(sk)->rx_opt.mss_clamp + MAX_TCP_HEADER + 16 + 199 sizeof(struct sk_buff); 200 201 if (sk->sk_sndbuf < 3 * sndmem) 202 sk->sk_sndbuf = min(3 * sndmem, sysctl_tcp_wmem[2]); 203 } 204 205 /* 2. Tuning advertised window (window_clamp, rcv_ssthresh) 206 * 207 * All tcp_full_space() is split to two parts: "network" buffer, allocated 208 * forward and advertised in receiver window (tp->rcv_wnd) and 209 * "application buffer", required to isolate scheduling/application 210 * latencies from network. 211 * window_clamp is maximal advertised window. It can be less than 212 * tcp_full_space(), in this case tcp_full_space() - window_clamp 213 * is reserved for "application" buffer. The less window_clamp is 214 * the smoother our behaviour from viewpoint of network, but the lower 215 * throughput and the higher sensitivity of the connection to losses. 8) 216 * 217 * rcv_ssthresh is more strict window_clamp used at "slow start" 218 * phase to predict further behaviour of this connection. 219 * It is used for two goals: 220 * - to enforce header prediction at sender, even when application 221 * requires some significant "application buffer". It is check #1. 222 * - to prevent pruning of receive queue because of misprediction 223 * of receiver window. Check #2. 224 * 225 * The scheme does not work when sender sends good segments opening 226 * window and then starts to feed us spagetti. But it should work 227 * in common situations. Otherwise, we have to rely on queue collapsing. 228 */ 229 230 /* Slow part of check#2. */ 231 static int __tcp_grow_window(const struct sock *sk, struct tcp_sock *tp, 232 const struct sk_buff *skb) 233 { 234 /* Optimize this! */ 235 int truesize = tcp_win_from_space(skb->truesize)/2; 236 int window = tcp_full_space(sk)/2; 237 238 while (tp->rcv_ssthresh <= window) { 239 if (truesize <= skb->len) 240 return 2 * inet_csk(sk)->icsk_ack.rcv_mss; 241 242 truesize >>= 1; 243 window >>= 1; 244 } 245 return 0; 246 } 247 248 static inline void tcp_grow_window(struct sock *sk, struct tcp_sock *tp, 249 struct sk_buff *skb) 250 { 251 /* Check #1 */ 252 if (tp->rcv_ssthresh < tp->window_clamp && 253 (int)tp->rcv_ssthresh < tcp_space(sk) && 254 !tcp_memory_pressure) { 255 int incr; 256 257 /* Check #2. Increase window, if skb with such overhead 258 * will fit to rcvbuf in future. 259 */ 260 if (tcp_win_from_space(skb->truesize) <= skb->len) 261 incr = 2*tp->advmss; 262 else 263 incr = __tcp_grow_window(sk, tp, skb); 264 265 if (incr) { 266 tp->rcv_ssthresh = min(tp->rcv_ssthresh + incr, tp->window_clamp); 267 inet_csk(sk)->icsk_ack.quick |= 1; 268 } 269 } 270 } 271 272 /* 3. Tuning rcvbuf, when connection enters established state. */ 273 274 static void tcp_fixup_rcvbuf(struct sock *sk) 275 { 276 struct tcp_sock *tp = tcp_sk(sk); 277 int rcvmem = tp->advmss + MAX_TCP_HEADER + 16 + sizeof(struct sk_buff); 278 279 /* Try to select rcvbuf so that 4 mss-sized segments 280 * will fit to window and correspoding skbs will fit to our rcvbuf. 281 * (was 3; 4 is minimum to allow fast retransmit to work.) 282 */ 283 while (tcp_win_from_space(rcvmem) < tp->advmss) 284 rcvmem += 128; 285 if (sk->sk_rcvbuf < 4 * rcvmem) 286 sk->sk_rcvbuf = min(4 * rcvmem, sysctl_tcp_rmem[2]); 287 } 288 289 /* 4. Try to fixup all. It is made iimediately after connection enters 290 * established state. 291 */ 292 static void tcp_init_buffer_space(struct sock *sk) 293 { 294 struct tcp_sock *tp = tcp_sk(sk); 295 int maxwin; 296 297 if (!(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) 298 tcp_fixup_rcvbuf(sk); 299 if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK)) 300 tcp_fixup_sndbuf(sk); 301 302 tp->rcvq_space.space = tp->rcv_wnd; 303 304 maxwin = tcp_full_space(sk); 305 306 if (tp->window_clamp >= maxwin) { 307 tp->window_clamp = maxwin; 308 309 if (sysctl_tcp_app_win && maxwin > 4 * tp->advmss) 310 tp->window_clamp = max(maxwin - 311 (maxwin >> sysctl_tcp_app_win), 312 4 * tp->advmss); 313 } 314 315 /* Force reservation of one segment. */ 316 if (sysctl_tcp_app_win && 317 tp->window_clamp > 2 * tp->advmss && 318 tp->window_clamp + tp->advmss > maxwin) 319 tp->window_clamp = max(2 * tp->advmss, maxwin - tp->advmss); 320 321 tp->rcv_ssthresh = min(tp->rcv_ssthresh, tp->window_clamp); 322 tp->snd_cwnd_stamp = tcp_time_stamp; 323 } 324 325 /* 5. Recalculate window clamp after socket hit its memory bounds. */ 326 static void tcp_clamp_window(struct sock *sk, struct tcp_sock *tp) 327 { 328 struct inet_connection_sock *icsk = inet_csk(sk); 329 struct sk_buff *skb; 330 unsigned int app_win = tp->rcv_nxt - tp->copied_seq; 331 int ofo_win = 0; 332 333 icsk->icsk_ack.quick = 0; 334 335 skb_queue_walk(&tp->out_of_order_queue, skb) { 336 ofo_win += skb->len; 337 } 338 339 /* If overcommit is due to out of order segments, 340 * do not clamp window. Try to expand rcvbuf instead. 341 */ 342 if (ofo_win) { 343 if (sk->sk_rcvbuf < sysctl_tcp_rmem[2] && 344 !(sk->sk_userlocks & SOCK_RCVBUF_LOCK) && 345 !tcp_memory_pressure && 346 atomic_read(&tcp_memory_allocated) < sysctl_tcp_mem[0]) 347 sk->sk_rcvbuf = min(atomic_read(&sk->sk_rmem_alloc), 348 sysctl_tcp_rmem[2]); 349 } 350 if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf) { 351 app_win += ofo_win; 352 if (atomic_read(&sk->sk_rmem_alloc) >= 2 * sk->sk_rcvbuf) 353 app_win >>= 1; 354 if (app_win > icsk->icsk_ack.rcv_mss) 355 app_win -= icsk->icsk_ack.rcv_mss; 356 app_win = max(app_win, 2U*tp->advmss); 357 358 tp->rcv_ssthresh = min(tp->window_clamp, 2U*tp->advmss); 359 } 360 } 361 362 /* Receiver "autotuning" code. 363 * 364 * The algorithm for RTT estimation w/o timestamps is based on 365 * Dynamic Right-Sizing (DRS) by Wu Feng and Mike Fisk of LANL. 366 * <http://www.lanl.gov/radiant/website/pubs/drs/lacsi2001.ps> 367 * 368 * More detail on this code can be found at 369 * <http://www.psc.edu/~jheffner/senior_thesis.ps>, 370 * though this reference is out of date. A new paper 371 * is pending. 372 */ 373 static void tcp_rcv_rtt_update(struct tcp_sock *tp, u32 sample, int win_dep) 374 { 375 u32 new_sample = tp->rcv_rtt_est.rtt; 376 long m = sample; 377 378 if (m == 0) 379 m = 1; 380 381 if (new_sample != 0) { 382 /* If we sample in larger samples in the non-timestamp 383 * case, we could grossly overestimate the RTT especially 384 * with chatty applications or bulk transfer apps which 385 * are stalled on filesystem I/O. 386 * 387 * Also, since we are only going for a minimum in the 388 * non-timestamp case, we do not smoothe things out 389 * else with timestamps disabled convergance takes too 390 * long. 391 */ 392 if (!win_dep) { 393 m -= (new_sample >> 3); 394 new_sample += m; 395 } else if (m < new_sample) 396 new_sample = m << 3; 397 } else { 398 /* No previous mesaure. */ 399 new_sample = m << 3; 400 } 401 402 if (tp->rcv_rtt_est.rtt != new_sample) 403 tp->rcv_rtt_est.rtt = new_sample; 404 } 405 406 static inline void tcp_rcv_rtt_measure(struct tcp_sock *tp) 407 { 408 if (tp->rcv_rtt_est.time == 0) 409 goto new_measure; 410 if (before(tp->rcv_nxt, tp->rcv_rtt_est.seq)) 411 return; 412 tcp_rcv_rtt_update(tp, 413 jiffies - tp->rcv_rtt_est.time, 414 1); 415 416 new_measure: 417 tp->rcv_rtt_est.seq = tp->rcv_nxt + tp->rcv_wnd; 418 tp->rcv_rtt_est.time = tcp_time_stamp; 419 } 420 421 static inline void tcp_rcv_rtt_measure_ts(struct sock *sk, const struct sk_buff *skb) 422 { 423 struct tcp_sock *tp = tcp_sk(sk); 424 if (tp->rx_opt.rcv_tsecr && 425 (TCP_SKB_CB(skb)->end_seq - 426 TCP_SKB_CB(skb)->seq >= inet_csk(sk)->icsk_ack.rcv_mss)) 427 tcp_rcv_rtt_update(tp, tcp_time_stamp - tp->rx_opt.rcv_tsecr, 0); 428 } 429 430 /* 431 * This function should be called every time data is copied to user space. 432 * It calculates the appropriate TCP receive buffer space. 433 */ 434 void tcp_rcv_space_adjust(struct sock *sk) 435 { 436 struct tcp_sock *tp = tcp_sk(sk); 437 int time; 438 int space; 439 440 if (tp->rcvq_space.time == 0) 441 goto new_measure; 442 443 time = tcp_time_stamp - tp->rcvq_space.time; 444 if (time < (tp->rcv_rtt_est.rtt >> 3) || 445 tp->rcv_rtt_est.rtt == 0) 446 return; 447 448 space = 2 * (tp->copied_seq - tp->rcvq_space.seq); 449 450 space = max(tp->rcvq_space.space, space); 451 452 if (tp->rcvq_space.space != space) { 453 int rcvmem; 454 455 tp->rcvq_space.space = space; 456 457 if (sysctl_tcp_moderate_rcvbuf) { 458 int new_clamp = space; 459 460 /* Receive space grows, normalize in order to 461 * take into account packet headers and sk_buff 462 * structure overhead. 463 */ 464 space /= tp->advmss; 465 if (!space) 466 space = 1; 467 rcvmem = (tp->advmss + MAX_TCP_HEADER + 468 16 + sizeof(struct sk_buff)); 469 while (tcp_win_from_space(rcvmem) < tp->advmss) 470 rcvmem += 128; 471 space *= rcvmem; 472 space = min(space, sysctl_tcp_rmem[2]); 473 if (space > sk->sk_rcvbuf) { 474 sk->sk_rcvbuf = space; 475 476 /* Make the window clamp follow along. */ 477 tp->window_clamp = new_clamp; 478 } 479 } 480 } 481 482 new_measure: 483 tp->rcvq_space.seq = tp->copied_seq; 484 tp->rcvq_space.time = tcp_time_stamp; 485 } 486 487 /* There is something which you must keep in mind when you analyze the 488 * behavior of the tp->ato delayed ack timeout interval. When a 489 * connection starts up, we want to ack as quickly as possible. The 490 * problem is that "good" TCP's do slow start at the beginning of data 491 * transmission. The means that until we send the first few ACK's the 492 * sender will sit on his end and only queue most of his data, because 493 * he can only send snd_cwnd unacked packets at any given time. For 494 * each ACK we send, he increments snd_cwnd and transmits more of his 495 * queue. -DaveM 496 */ 497 static void tcp_event_data_recv(struct sock *sk, struct tcp_sock *tp, struct sk_buff *skb) 498 { 499 struct inet_connection_sock *icsk = inet_csk(sk); 500 u32 now; 501 502 inet_csk_schedule_ack(sk); 503 504 tcp_measure_rcv_mss(sk, skb); 505 506 tcp_rcv_rtt_measure(tp); 507 508 now = tcp_time_stamp; 509 510 if (!icsk->icsk_ack.ato) { 511 /* The _first_ data packet received, initialize 512 * delayed ACK engine. 513 */ 514 tcp_incr_quickack(sk); 515 icsk->icsk_ack.ato = TCP_ATO_MIN; 516 } else { 517 int m = now - icsk->icsk_ack.lrcvtime; 518 519 if (m <= TCP_ATO_MIN/2) { 520 /* The fastest case is the first. */ 521 icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + TCP_ATO_MIN / 2; 522 } else if (m < icsk->icsk_ack.ato) { 523 icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + m; 524 if (icsk->icsk_ack.ato > icsk->icsk_rto) 525 icsk->icsk_ack.ato = icsk->icsk_rto; 526 } else if (m > icsk->icsk_rto) { 527 /* Too long gap. Apparently sender falled to 528 * restart window, so that we send ACKs quickly. 529 */ 530 tcp_incr_quickack(sk); 531 sk_stream_mem_reclaim(sk); 532 } 533 } 534 icsk->icsk_ack.lrcvtime = now; 535 536 TCP_ECN_check_ce(tp, skb); 537 538 if (skb->len >= 128) 539 tcp_grow_window(sk, tp, skb); 540 } 541 542 /* Called to compute a smoothed rtt estimate. The data fed to this 543 * routine either comes from timestamps, or from segments that were 544 * known _not_ to have been retransmitted [see Karn/Partridge 545 * Proceedings SIGCOMM 87]. The algorithm is from the SIGCOMM 88 546 * piece by Van Jacobson. 547 * NOTE: the next three routines used to be one big routine. 548 * To save cycles in the RFC 1323 implementation it was better to break 549 * it up into three procedures. -- erics 550 */ 551 static void tcp_rtt_estimator(struct sock *sk, const __u32 mrtt, u32 *usrtt) 552 { 553 struct tcp_sock *tp = tcp_sk(sk); 554 const struct inet_connection_sock *icsk = inet_csk(sk); 555 long m = mrtt; /* RTT */ 556 557 /* The following amusing code comes from Jacobson's 558 * article in SIGCOMM '88. Note that rtt and mdev 559 * are scaled versions of rtt and mean deviation. 560 * This is designed to be as fast as possible 561 * m stands for "measurement". 562 * 563 * On a 1990 paper the rto value is changed to: 564 * RTO = rtt + 4 * mdev 565 * 566 * Funny. This algorithm seems to be very broken. 567 * These formulae increase RTO, when it should be decreased, increase 568 * too slowly, when it should be incresed fastly, decrease too fastly 569 * etc. I guess in BSD RTO takes ONE value, so that it is absolutely 570 * does not matter how to _calculate_ it. Seems, it was trap 571 * that VJ failed to avoid. 8) 572 */ 573 if(m == 0) 574 m = 1; 575 if (tp->srtt != 0) { 576 m -= (tp->srtt >> 3); /* m is now error in rtt est */ 577 tp->srtt += m; /* rtt = 7/8 rtt + 1/8 new */ 578 if (m < 0) { 579 m = -m; /* m is now abs(error) */ 580 m -= (tp->mdev >> 2); /* similar update on mdev */ 581 /* This is similar to one of Eifel findings. 582 * Eifel blocks mdev updates when rtt decreases. 583 * This solution is a bit different: we use finer gain 584 * for mdev in this case (alpha*beta). 585 * Like Eifel it also prevents growth of rto, 586 * but also it limits too fast rto decreases, 587 * happening in pure Eifel. 588 */ 589 if (m > 0) 590 m >>= 3; 591 } else { 592 m -= (tp->mdev >> 2); /* similar update on mdev */ 593 } 594 tp->mdev += m; /* mdev = 3/4 mdev + 1/4 new */ 595 if (tp->mdev > tp->mdev_max) { 596 tp->mdev_max = tp->mdev; 597 if (tp->mdev_max > tp->rttvar) 598 tp->rttvar = tp->mdev_max; 599 } 600 if (after(tp->snd_una, tp->rtt_seq)) { 601 if (tp->mdev_max < tp->rttvar) 602 tp->rttvar -= (tp->rttvar-tp->mdev_max)>>2; 603 tp->rtt_seq = tp->snd_nxt; 604 tp->mdev_max = TCP_RTO_MIN; 605 } 606 } else { 607 /* no previous measure. */ 608 tp->srtt = m<<3; /* take the measured time to be rtt */ 609 tp->mdev = m<<1; /* make sure rto = 3*rtt */ 610 tp->mdev_max = tp->rttvar = max(tp->mdev, TCP_RTO_MIN); 611 tp->rtt_seq = tp->snd_nxt; 612 } 613 614 if (icsk->icsk_ca_ops->rtt_sample) 615 icsk->icsk_ca_ops->rtt_sample(sk, *usrtt); 616 } 617 618 /* Calculate rto without backoff. This is the second half of Van Jacobson's 619 * routine referred to above. 620 */ 621 static inline void tcp_set_rto(struct sock *sk) 622 { 623 const struct tcp_sock *tp = tcp_sk(sk); 624 /* Old crap is replaced with new one. 8) 625 * 626 * More seriously: 627 * 1. If rtt variance happened to be less 50msec, it is hallucination. 628 * It cannot be less due to utterly erratic ACK generation made 629 * at least by solaris and freebsd. "Erratic ACKs" has _nothing_ 630 * to do with delayed acks, because at cwnd>2 true delack timeout 631 * is invisible. Actually, Linux-2.4 also generates erratic 632 * ACKs in some curcumstances. 633 */ 634 inet_csk(sk)->icsk_rto = (tp->srtt >> 3) + tp->rttvar; 635 636 /* 2. Fixups made earlier cannot be right. 637 * If we do not estimate RTO correctly without them, 638 * all the algo is pure shit and should be replaced 639 * with correct one. It is exaclty, which we pretend to do. 640 */ 641 } 642 643 /* NOTE: clamping at TCP_RTO_MIN is not required, current algo 644 * guarantees that rto is higher. 645 */ 646 static inline void tcp_bound_rto(struct sock *sk) 647 { 648 if (inet_csk(sk)->icsk_rto > TCP_RTO_MAX) 649 inet_csk(sk)->icsk_rto = TCP_RTO_MAX; 650 } 651 652 /* Save metrics learned by this TCP session. 653 This function is called only, when TCP finishes successfully 654 i.e. when it enters TIME-WAIT or goes from LAST-ACK to CLOSE. 655 */ 656 void tcp_update_metrics(struct sock *sk) 657 { 658 struct tcp_sock *tp = tcp_sk(sk); 659 struct dst_entry *dst = __sk_dst_get(sk); 660 661 if (sysctl_tcp_nometrics_save) 662 return; 663 664 dst_confirm(dst); 665 666 if (dst && (dst->flags&DST_HOST)) { 667 const struct inet_connection_sock *icsk = inet_csk(sk); 668 int m; 669 670 if (icsk->icsk_backoff || !tp->srtt) { 671 /* This session failed to estimate rtt. Why? 672 * Probably, no packets returned in time. 673 * Reset our results. 674 */ 675 if (!(dst_metric_locked(dst, RTAX_RTT))) 676 dst->metrics[RTAX_RTT-1] = 0; 677 return; 678 } 679 680 m = dst_metric(dst, RTAX_RTT) - tp->srtt; 681 682 /* If newly calculated rtt larger than stored one, 683 * store new one. Otherwise, use EWMA. Remember, 684 * rtt overestimation is always better than underestimation. 685 */ 686 if (!(dst_metric_locked(dst, RTAX_RTT))) { 687 if (m <= 0) 688 dst->metrics[RTAX_RTT-1] = tp->srtt; 689 else 690 dst->metrics[RTAX_RTT-1] -= (m>>3); 691 } 692 693 if (!(dst_metric_locked(dst, RTAX_RTTVAR))) { 694 if (m < 0) 695 m = -m; 696 697 /* Scale deviation to rttvar fixed point */ 698 m >>= 1; 699 if (m < tp->mdev) 700 m = tp->mdev; 701 702 if (m >= dst_metric(dst, RTAX_RTTVAR)) 703 dst->metrics[RTAX_RTTVAR-1] = m; 704 else 705 dst->metrics[RTAX_RTTVAR-1] -= 706 (dst->metrics[RTAX_RTTVAR-1] - m)>>2; 707 } 708 709 if (tp->snd_ssthresh >= 0xFFFF) { 710 /* Slow start still did not finish. */ 711 if (dst_metric(dst, RTAX_SSTHRESH) && 712 !dst_metric_locked(dst, RTAX_SSTHRESH) && 713 (tp->snd_cwnd >> 1) > dst_metric(dst, RTAX_SSTHRESH)) 714 dst->metrics[RTAX_SSTHRESH-1] = tp->snd_cwnd >> 1; 715 if (!dst_metric_locked(dst, RTAX_CWND) && 716 tp->snd_cwnd > dst_metric(dst, RTAX_CWND)) 717 dst->metrics[RTAX_CWND-1] = tp->snd_cwnd; 718 } else if (tp->snd_cwnd > tp->snd_ssthresh && 719 icsk->icsk_ca_state == TCP_CA_Open) { 720 /* Cong. avoidance phase, cwnd is reliable. */ 721 if (!dst_metric_locked(dst, RTAX_SSTHRESH)) 722 dst->metrics[RTAX_SSTHRESH-1] = 723 max(tp->snd_cwnd >> 1, tp->snd_ssthresh); 724 if (!dst_metric_locked(dst, RTAX_CWND)) 725 dst->metrics[RTAX_CWND-1] = (dst->metrics[RTAX_CWND-1] + tp->snd_cwnd) >> 1; 726 } else { 727 /* Else slow start did not finish, cwnd is non-sense, 728 ssthresh may be also invalid. 729 */ 730 if (!dst_metric_locked(dst, RTAX_CWND)) 731 dst->metrics[RTAX_CWND-1] = (dst->metrics[RTAX_CWND-1] + tp->snd_ssthresh) >> 1; 732 if (dst->metrics[RTAX_SSTHRESH-1] && 733 !dst_metric_locked(dst, RTAX_SSTHRESH) && 734 tp->snd_ssthresh > dst->metrics[RTAX_SSTHRESH-1]) 735 dst->metrics[RTAX_SSTHRESH-1] = tp->snd_ssthresh; 736 } 737 738 if (!dst_metric_locked(dst, RTAX_REORDERING)) { 739 if (dst->metrics[RTAX_REORDERING-1] < tp->reordering && 740 tp->reordering != sysctl_tcp_reordering) 741 dst->metrics[RTAX_REORDERING-1] = tp->reordering; 742 } 743 } 744 } 745 746 /* Numbers are taken from RFC2414. */ 747 __u32 tcp_init_cwnd(struct tcp_sock *tp, struct dst_entry *dst) 748 { 749 __u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0); 750 751 if (!cwnd) { 752 if (tp->mss_cache > 1460) 753 cwnd = 2; 754 else 755 cwnd = (tp->mss_cache > 1095) ? 3 : 4; 756 } 757 return min_t(__u32, cwnd, tp->snd_cwnd_clamp); 758 } 759 760 /* Initialize metrics on socket. */ 761 762 static void tcp_init_metrics(struct sock *sk) 763 { 764 struct tcp_sock *tp = tcp_sk(sk); 765 struct dst_entry *dst = __sk_dst_get(sk); 766 767 if (dst == NULL) 768 goto reset; 769 770 dst_confirm(dst); 771 772 if (dst_metric_locked(dst, RTAX_CWND)) 773 tp->snd_cwnd_clamp = dst_metric(dst, RTAX_CWND); 774 if (dst_metric(dst, RTAX_SSTHRESH)) { 775 tp->snd_ssthresh = dst_metric(dst, RTAX_SSTHRESH); 776 if (tp->snd_ssthresh > tp->snd_cwnd_clamp) 777 tp->snd_ssthresh = tp->snd_cwnd_clamp; 778 } 779 if (dst_metric(dst, RTAX_REORDERING) && 780 tp->reordering != dst_metric(dst, RTAX_REORDERING)) { 781 tp->rx_opt.sack_ok &= ~2; 782 tp->reordering = dst_metric(dst, RTAX_REORDERING); 783 } 784 785 if (dst_metric(dst, RTAX_RTT) == 0) 786 goto reset; 787 788 if (!tp->srtt && dst_metric(dst, RTAX_RTT) < (TCP_TIMEOUT_INIT << 3)) 789 goto reset; 790 791 /* Initial rtt is determined from SYN,SYN-ACK. 792 * The segment is small and rtt may appear much 793 * less than real one. Use per-dst memory 794 * to make it more realistic. 795 * 796 * A bit of theory. RTT is time passed after "normal" sized packet 797 * is sent until it is ACKed. In normal curcumstances sending small 798 * packets force peer to delay ACKs and calculation is correct too. 799 * The algorithm is adaptive and, provided we follow specs, it 800 * NEVER underestimate RTT. BUT! If peer tries to make some clever 801 * tricks sort of "quick acks" for time long enough to decrease RTT 802 * to low value, and then abruptly stops to do it and starts to delay 803 * ACKs, wait for troubles. 804 */ 805 if (dst_metric(dst, RTAX_RTT) > tp->srtt) { 806 tp->srtt = dst_metric(dst, RTAX_RTT); 807 tp->rtt_seq = tp->snd_nxt; 808 } 809 if (dst_metric(dst, RTAX_RTTVAR) > tp->mdev) { 810 tp->mdev = dst_metric(dst, RTAX_RTTVAR); 811 tp->mdev_max = tp->rttvar = max(tp->mdev, TCP_RTO_MIN); 812 } 813 tcp_set_rto(sk); 814 tcp_bound_rto(sk); 815 if (inet_csk(sk)->icsk_rto < TCP_TIMEOUT_INIT && !tp->rx_opt.saw_tstamp) 816 goto reset; 817 tp->snd_cwnd = tcp_init_cwnd(tp, dst); 818 tp->snd_cwnd_stamp = tcp_time_stamp; 819 return; 820 821 reset: 822 /* Play conservative. If timestamps are not 823 * supported, TCP will fail to recalculate correct 824 * rtt, if initial rto is too small. FORGET ALL AND RESET! 825 */ 826 if (!tp->rx_opt.saw_tstamp && tp->srtt) { 827 tp->srtt = 0; 828 tp->mdev = tp->mdev_max = tp->rttvar = TCP_TIMEOUT_INIT; 829 inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT; 830 } 831 } 832 833 static void tcp_update_reordering(struct sock *sk, const int metric, 834 const int ts) 835 { 836 struct tcp_sock *tp = tcp_sk(sk); 837 if (metric > tp->reordering) { 838 tp->reordering = min(TCP_MAX_REORDERING, metric); 839 840 /* This exciting event is worth to be remembered. 8) */ 841 if (ts) 842 NET_INC_STATS_BH(LINUX_MIB_TCPTSREORDER); 843 else if (IsReno(tp)) 844 NET_INC_STATS_BH(LINUX_MIB_TCPRENOREORDER); 845 else if (IsFack(tp)) 846 NET_INC_STATS_BH(LINUX_MIB_TCPFACKREORDER); 847 else 848 NET_INC_STATS_BH(LINUX_MIB_TCPSACKREORDER); 849 #if FASTRETRANS_DEBUG > 1 850 printk(KERN_DEBUG "Disorder%d %d %u f%u s%u rr%d\n", 851 tp->rx_opt.sack_ok, inet_csk(sk)->icsk_ca_state, 852 tp->reordering, 853 tp->fackets_out, 854 tp->sacked_out, 855 tp->undo_marker ? tp->undo_retrans : 0); 856 #endif 857 /* Disable FACK yet. */ 858 tp->rx_opt.sack_ok &= ~2; 859 } 860 } 861 862 /* This procedure tags the retransmission queue when SACKs arrive. 863 * 864 * We have three tag bits: SACKED(S), RETRANS(R) and LOST(L). 865 * Packets in queue with these bits set are counted in variables 866 * sacked_out, retrans_out and lost_out, correspondingly. 867 * 868 * Valid combinations are: 869 * Tag InFlight Description 870 * 0 1 - orig segment is in flight. 871 * S 0 - nothing flies, orig reached receiver. 872 * L 0 - nothing flies, orig lost by net. 873 * R 2 - both orig and retransmit are in flight. 874 * L|R 1 - orig is lost, retransmit is in flight. 875 * S|R 1 - orig reached receiver, retrans is still in flight. 876 * (L|S|R is logically valid, it could occur when L|R is sacked, 877 * but it is equivalent to plain S and code short-curcuits it to S. 878 * L|S is logically invalid, it would mean -1 packet in flight 8)) 879 * 880 * These 6 states form finite state machine, controlled by the following events: 881 * 1. New ACK (+SACK) arrives. (tcp_sacktag_write_queue()) 882 * 2. Retransmission. (tcp_retransmit_skb(), tcp_xmit_retransmit_queue()) 883 * 3. Loss detection event of one of three flavors: 884 * A. Scoreboard estimator decided the packet is lost. 885 * A'. Reno "three dupacks" marks head of queue lost. 886 * A''. Its FACK modfication, head until snd.fack is lost. 887 * B. SACK arrives sacking data transmitted after never retransmitted 888 * hole was sent out. 889 * C. SACK arrives sacking SND.NXT at the moment, when the 890 * segment was retransmitted. 891 * 4. D-SACK added new rule: D-SACK changes any tag to S. 892 * 893 * It is pleasant to note, that state diagram turns out to be commutative, 894 * so that we are allowed not to be bothered by order of our actions, 895 * when multiple events arrive simultaneously. (see the function below). 896 * 897 * Reordering detection. 898 * -------------------- 899 * Reordering metric is maximal distance, which a packet can be displaced 900 * in packet stream. With SACKs we can estimate it: 901 * 902 * 1. SACK fills old hole and the corresponding segment was not 903 * ever retransmitted -> reordering. Alas, we cannot use it 904 * when segment was retransmitted. 905 * 2. The last flaw is solved with D-SACK. D-SACK arrives 906 * for retransmitted and already SACKed segment -> reordering.. 907 * Both of these heuristics are not used in Loss state, when we cannot 908 * account for retransmits accurately. 909 */ 910 static int 911 tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb, u32 prior_snd_una) 912 { 913 const struct inet_connection_sock *icsk = inet_csk(sk); 914 struct tcp_sock *tp = tcp_sk(sk); 915 unsigned char *ptr = ack_skb->h.raw + TCP_SKB_CB(ack_skb)->sacked; 916 struct tcp_sack_block *sp = (struct tcp_sack_block *)(ptr+2); 917 int num_sacks = (ptr[1] - TCPOLEN_SACK_BASE)>>3; 918 int reord = tp->packets_out; 919 int prior_fackets; 920 u32 lost_retrans = 0; 921 int flag = 0; 922 int i; 923 924 if (!tp->sacked_out) 925 tp->fackets_out = 0; 926 prior_fackets = tp->fackets_out; 927 928 for (i=0; i<num_sacks; i++, sp++) { 929 struct sk_buff *skb; 930 __u32 start_seq = ntohl(sp->start_seq); 931 __u32 end_seq = ntohl(sp->end_seq); 932 int fack_count = 0; 933 int dup_sack = 0; 934 935 /* Check for D-SACK. */ 936 if (i == 0) { 937 u32 ack = TCP_SKB_CB(ack_skb)->ack_seq; 938 939 if (before(start_seq, ack)) { 940 dup_sack = 1; 941 tp->rx_opt.sack_ok |= 4; 942 NET_INC_STATS_BH(LINUX_MIB_TCPDSACKRECV); 943 } else if (num_sacks > 1 && 944 !after(end_seq, ntohl(sp[1].end_seq)) && 945 !before(start_seq, ntohl(sp[1].start_seq))) { 946 dup_sack = 1; 947 tp->rx_opt.sack_ok |= 4; 948 NET_INC_STATS_BH(LINUX_MIB_TCPDSACKOFORECV); 949 } 950 951 /* D-SACK for already forgotten data... 952 * Do dumb counting. */ 953 if (dup_sack && 954 !after(end_seq, prior_snd_una) && 955 after(end_seq, tp->undo_marker)) 956 tp->undo_retrans--; 957 958 /* Eliminate too old ACKs, but take into 959 * account more or less fresh ones, they can 960 * contain valid SACK info. 961 */ 962 if (before(ack, prior_snd_una - tp->max_window)) 963 return 0; 964 } 965 966 /* Event "B" in the comment above. */ 967 if (after(end_seq, tp->high_seq)) 968 flag |= FLAG_DATA_LOST; 969 970 sk_stream_for_retrans_queue(skb, sk) { 971 int in_sack, pcount; 972 u8 sacked; 973 974 /* The retransmission queue is always in order, so 975 * we can short-circuit the walk early. 976 */ 977 if (!before(TCP_SKB_CB(skb)->seq, end_seq)) 978 break; 979 980 in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) && 981 !before(end_seq, TCP_SKB_CB(skb)->end_seq); 982 983 pcount = tcp_skb_pcount(skb); 984 985 if (pcount > 1 && !in_sack && 986 after(TCP_SKB_CB(skb)->end_seq, start_seq)) { 987 unsigned int pkt_len; 988 989 in_sack = !after(start_seq, 990 TCP_SKB_CB(skb)->seq); 991 992 if (!in_sack) 993 pkt_len = (start_seq - 994 TCP_SKB_CB(skb)->seq); 995 else 996 pkt_len = (end_seq - 997 TCP_SKB_CB(skb)->seq); 998 if (tcp_fragment(sk, skb, pkt_len, skb_shinfo(skb)->tso_size)) 999 break; 1000 pcount = tcp_skb_pcount(skb); 1001 } 1002 1003 fack_count += pcount; 1004 1005 sacked = TCP_SKB_CB(skb)->sacked; 1006 1007 /* Account D-SACK for retransmitted packet. */ 1008 if ((dup_sack && in_sack) && 1009 (sacked & TCPCB_RETRANS) && 1010 after(TCP_SKB_CB(skb)->end_seq, tp->undo_marker)) 1011 tp->undo_retrans--; 1012 1013 /* The frame is ACKed. */ 1014 if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una)) { 1015 if (sacked&TCPCB_RETRANS) { 1016 if ((dup_sack && in_sack) && 1017 (sacked&TCPCB_SACKED_ACKED)) 1018 reord = min(fack_count, reord); 1019 } else { 1020 /* If it was in a hole, we detected reordering. */ 1021 if (fack_count < prior_fackets && 1022 !(sacked&TCPCB_SACKED_ACKED)) 1023 reord = min(fack_count, reord); 1024 } 1025 1026 /* Nothing to do; acked frame is about to be dropped. */ 1027 continue; 1028 } 1029 1030 if ((sacked&TCPCB_SACKED_RETRANS) && 1031 after(end_seq, TCP_SKB_CB(skb)->ack_seq) && 1032 (!lost_retrans || after(end_seq, lost_retrans))) 1033 lost_retrans = end_seq; 1034 1035 if (!in_sack) 1036 continue; 1037 1038 if (!(sacked&TCPCB_SACKED_ACKED)) { 1039 if (sacked & TCPCB_SACKED_RETRANS) { 1040 /* If the segment is not tagged as lost, 1041 * we do not clear RETRANS, believing 1042 * that retransmission is still in flight. 1043 */ 1044 if (sacked & TCPCB_LOST) { 1045 TCP_SKB_CB(skb)->sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS); 1046 tp->lost_out -= tcp_skb_pcount(skb); 1047 tp->retrans_out -= tcp_skb_pcount(skb); 1048 } 1049 } else { 1050 /* New sack for not retransmitted frame, 1051 * which was in hole. It is reordering. 1052 */ 1053 if (!(sacked & TCPCB_RETRANS) && 1054 fack_count < prior_fackets) 1055 reord = min(fack_count, reord); 1056 1057 if (sacked & TCPCB_LOST) { 1058 TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST; 1059 tp->lost_out -= tcp_skb_pcount(skb); 1060 } 1061 } 1062 1063 TCP_SKB_CB(skb)->sacked |= TCPCB_SACKED_ACKED; 1064 flag |= FLAG_DATA_SACKED; 1065 tp->sacked_out += tcp_skb_pcount(skb); 1066 1067 if (fack_count > tp->fackets_out) 1068 tp->fackets_out = fack_count; 1069 } else { 1070 if (dup_sack && (sacked&TCPCB_RETRANS)) 1071 reord = min(fack_count, reord); 1072 } 1073 1074 /* D-SACK. We can detect redundant retransmission 1075 * in S|R and plain R frames and clear it. 1076 * undo_retrans is decreased above, L|R frames 1077 * are accounted above as well. 1078 */ 1079 if (dup_sack && 1080 (TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_RETRANS)) { 1081 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS; 1082 tp->retrans_out -= tcp_skb_pcount(skb); 1083 } 1084 } 1085 } 1086 1087 /* Check for lost retransmit. This superb idea is 1088 * borrowed from "ratehalving". Event "C". 1089 * Later note: FACK people cheated me again 8), 1090 * we have to account for reordering! Ugly, 1091 * but should help. 1092 */ 1093 if (lost_retrans && icsk->icsk_ca_state == TCP_CA_Recovery) { 1094 struct sk_buff *skb; 1095 1096 sk_stream_for_retrans_queue(skb, sk) { 1097 if (after(TCP_SKB_CB(skb)->seq, lost_retrans)) 1098 break; 1099 if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una)) 1100 continue; 1101 if ((TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_RETRANS) && 1102 after(lost_retrans, TCP_SKB_CB(skb)->ack_seq) && 1103 (IsFack(tp) || 1104 !before(lost_retrans, 1105 TCP_SKB_CB(skb)->ack_seq + tp->reordering * 1106 tp->mss_cache))) { 1107 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS; 1108 tp->retrans_out -= tcp_skb_pcount(skb); 1109 1110 if (!(TCP_SKB_CB(skb)->sacked&(TCPCB_LOST|TCPCB_SACKED_ACKED))) { 1111 tp->lost_out += tcp_skb_pcount(skb); 1112 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST; 1113 flag |= FLAG_DATA_SACKED; 1114 NET_INC_STATS_BH(LINUX_MIB_TCPLOSTRETRANSMIT); 1115 } 1116 } 1117 } 1118 } 1119 1120 tp->left_out = tp->sacked_out + tp->lost_out; 1121 1122 if ((reord < tp->fackets_out) && icsk->icsk_ca_state != TCP_CA_Loss) 1123 tcp_update_reordering(sk, ((tp->fackets_out + 1) - reord), 0); 1124 1125 #if FASTRETRANS_DEBUG > 0 1126 BUG_TRAP((int)tp->sacked_out >= 0); 1127 BUG_TRAP((int)tp->lost_out >= 0); 1128 BUG_TRAP((int)tp->retrans_out >= 0); 1129 BUG_TRAP((int)tcp_packets_in_flight(tp) >= 0); 1130 #endif 1131 return flag; 1132 } 1133 1134 /* RTO occurred, but do not yet enter loss state. Instead, transmit two new 1135 * segments to see from the next ACKs whether any data was really missing. 1136 * If the RTO was spurious, new ACKs should arrive. 1137 */ 1138 void tcp_enter_frto(struct sock *sk) 1139 { 1140 const struct inet_connection_sock *icsk = inet_csk(sk); 1141 struct tcp_sock *tp = tcp_sk(sk); 1142 struct sk_buff *skb; 1143 1144 tp->frto_counter = 1; 1145 1146 if (icsk->icsk_ca_state <= TCP_CA_Disorder || 1147 tp->snd_una == tp->high_seq || 1148 (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) { 1149 tp->prior_ssthresh = tcp_current_ssthresh(sk); 1150 tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk); 1151 tcp_ca_event(sk, CA_EVENT_FRTO); 1152 } 1153 1154 /* Have to clear retransmission markers here to keep the bookkeeping 1155 * in shape, even though we are not yet in Loss state. 1156 * If something was really lost, it is eventually caught up 1157 * in tcp_enter_frto_loss. 1158 */ 1159 tp->retrans_out = 0; 1160 tp->undo_marker = tp->snd_una; 1161 tp->undo_retrans = 0; 1162 1163 sk_stream_for_retrans_queue(skb, sk) { 1164 TCP_SKB_CB(skb)->sacked &= ~TCPCB_RETRANS; 1165 } 1166 tcp_sync_left_out(tp); 1167 1168 tcp_set_ca_state(sk, TCP_CA_Open); 1169 tp->frto_highmark = tp->snd_nxt; 1170 } 1171 1172 /* Enter Loss state after F-RTO was applied. Dupack arrived after RTO, 1173 * which indicates that we should follow the traditional RTO recovery, 1174 * i.e. mark everything lost and do go-back-N retransmission. 1175 */ 1176 static void tcp_enter_frto_loss(struct sock *sk) 1177 { 1178 struct tcp_sock *tp = tcp_sk(sk); 1179 struct sk_buff *skb; 1180 int cnt = 0; 1181 1182 tp->sacked_out = 0; 1183 tp->lost_out = 0; 1184 tp->fackets_out = 0; 1185 1186 sk_stream_for_retrans_queue(skb, sk) { 1187 cnt += tcp_skb_pcount(skb); 1188 TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST; 1189 if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED)) { 1190 1191 /* Do not mark those segments lost that were 1192 * forward transmitted after RTO 1193 */ 1194 if (!after(TCP_SKB_CB(skb)->end_seq, 1195 tp->frto_highmark)) { 1196 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST; 1197 tp->lost_out += tcp_skb_pcount(skb); 1198 } 1199 } else { 1200 tp->sacked_out += tcp_skb_pcount(skb); 1201 tp->fackets_out = cnt; 1202 } 1203 } 1204 tcp_sync_left_out(tp); 1205 1206 tp->snd_cwnd = tp->frto_counter + tcp_packets_in_flight(tp)+1; 1207 tp->snd_cwnd_cnt = 0; 1208 tp->snd_cwnd_stamp = tcp_time_stamp; 1209 tp->undo_marker = 0; 1210 tp->frto_counter = 0; 1211 1212 tp->reordering = min_t(unsigned int, tp->reordering, 1213 sysctl_tcp_reordering); 1214 tcp_set_ca_state(sk, TCP_CA_Loss); 1215 tp->high_seq = tp->frto_highmark; 1216 TCP_ECN_queue_cwr(tp); 1217 } 1218 1219 void tcp_clear_retrans(struct tcp_sock *tp) 1220 { 1221 tp->left_out = 0; 1222 tp->retrans_out = 0; 1223 1224 tp->fackets_out = 0; 1225 tp->sacked_out = 0; 1226 tp->lost_out = 0; 1227 1228 tp->undo_marker = 0; 1229 tp->undo_retrans = 0; 1230 } 1231 1232 /* Enter Loss state. If "how" is not zero, forget all SACK information 1233 * and reset tags completely, otherwise preserve SACKs. If receiver 1234 * dropped its ofo queue, we will know this due to reneging detection. 1235 */ 1236 void tcp_enter_loss(struct sock *sk, int how) 1237 { 1238 const struct inet_connection_sock *icsk = inet_csk(sk); 1239 struct tcp_sock *tp = tcp_sk(sk); 1240 struct sk_buff *skb; 1241 int cnt = 0; 1242 1243 /* Reduce ssthresh if it has not yet been made inside this window. */ 1244 if (icsk->icsk_ca_state <= TCP_CA_Disorder || tp->snd_una == tp->high_seq || 1245 (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) { 1246 tp->prior_ssthresh = tcp_current_ssthresh(sk); 1247 tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk); 1248 tcp_ca_event(sk, CA_EVENT_LOSS); 1249 } 1250 tp->snd_cwnd = 1; 1251 tp->snd_cwnd_cnt = 0; 1252 tp->snd_cwnd_stamp = tcp_time_stamp; 1253 1254 tcp_clear_retrans(tp); 1255 1256 /* Push undo marker, if it was plain RTO and nothing 1257 * was retransmitted. */ 1258 if (!how) 1259 tp->undo_marker = tp->snd_una; 1260 1261 sk_stream_for_retrans_queue(skb, sk) { 1262 cnt += tcp_skb_pcount(skb); 1263 if (TCP_SKB_CB(skb)->sacked&TCPCB_RETRANS) 1264 tp->undo_marker = 0; 1265 TCP_SKB_CB(skb)->sacked &= (~TCPCB_TAGBITS)|TCPCB_SACKED_ACKED; 1266 if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED) || how) { 1267 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED; 1268 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST; 1269 tp->lost_out += tcp_skb_pcount(skb); 1270 } else { 1271 tp->sacked_out += tcp_skb_pcount(skb); 1272 tp->fackets_out = cnt; 1273 } 1274 } 1275 tcp_sync_left_out(tp); 1276 1277 tp->reordering = min_t(unsigned int, tp->reordering, 1278 sysctl_tcp_reordering); 1279 tcp_set_ca_state(sk, TCP_CA_Loss); 1280 tp->high_seq = tp->snd_nxt; 1281 TCP_ECN_queue_cwr(tp); 1282 } 1283 1284 static int tcp_check_sack_reneging(struct sock *sk) 1285 { 1286 struct sk_buff *skb; 1287 1288 /* If ACK arrived pointing to a remembered SACK, 1289 * it means that our remembered SACKs do not reflect 1290 * real state of receiver i.e. 1291 * receiver _host_ is heavily congested (or buggy). 1292 * Do processing similar to RTO timeout. 1293 */ 1294 if ((skb = skb_peek(&sk->sk_write_queue)) != NULL && 1295 (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) { 1296 struct inet_connection_sock *icsk = inet_csk(sk); 1297 NET_INC_STATS_BH(LINUX_MIB_TCPSACKRENEGING); 1298 1299 tcp_enter_loss(sk, 1); 1300 icsk->icsk_retransmits++; 1301 tcp_retransmit_skb(sk, skb_peek(&sk->sk_write_queue)); 1302 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, 1303 icsk->icsk_rto, TCP_RTO_MAX); 1304 return 1; 1305 } 1306 return 0; 1307 } 1308 1309 static inline int tcp_fackets_out(struct tcp_sock *tp) 1310 { 1311 return IsReno(tp) ? tp->sacked_out+1 : tp->fackets_out; 1312 } 1313 1314 static inline int tcp_skb_timedout(struct sock *sk, struct sk_buff *skb) 1315 { 1316 return (tcp_time_stamp - TCP_SKB_CB(skb)->when > inet_csk(sk)->icsk_rto); 1317 } 1318 1319 static inline int tcp_head_timedout(struct sock *sk, struct tcp_sock *tp) 1320 { 1321 return tp->packets_out && 1322 tcp_skb_timedout(sk, skb_peek(&sk->sk_write_queue)); 1323 } 1324 1325 /* Linux NewReno/SACK/FACK/ECN state machine. 1326 * -------------------------------------- 1327 * 1328 * "Open" Normal state, no dubious events, fast path. 1329 * "Disorder" In all the respects it is "Open", 1330 * but requires a bit more attention. It is entered when 1331 * we see some SACKs or dupacks. It is split of "Open" 1332 * mainly to move some processing from fast path to slow one. 1333 * "CWR" CWND was reduced due to some Congestion Notification event. 1334 * It can be ECN, ICMP source quench, local device congestion. 1335 * "Recovery" CWND was reduced, we are fast-retransmitting. 1336 * "Loss" CWND was reduced due to RTO timeout or SACK reneging. 1337 * 1338 * tcp_fastretrans_alert() is entered: 1339 * - each incoming ACK, if state is not "Open" 1340 * - when arrived ACK is unusual, namely: 1341 * * SACK 1342 * * Duplicate ACK. 1343 * * ECN ECE. 1344 * 1345 * Counting packets in flight is pretty simple. 1346 * 1347 * in_flight = packets_out - left_out + retrans_out 1348 * 1349 * packets_out is SND.NXT-SND.UNA counted in packets. 1350 * 1351 * retrans_out is number of retransmitted segments. 1352 * 1353 * left_out is number of segments left network, but not ACKed yet. 1354 * 1355 * left_out = sacked_out + lost_out 1356 * 1357 * sacked_out: Packets, which arrived to receiver out of order 1358 * and hence not ACKed. With SACKs this number is simply 1359 * amount of SACKed data. Even without SACKs 1360 * it is easy to give pretty reliable estimate of this number, 1361 * counting duplicate ACKs. 1362 * 1363 * lost_out: Packets lost by network. TCP has no explicit 1364 * "loss notification" feedback from network (for now). 1365 * It means that this number can be only _guessed_. 1366 * Actually, it is the heuristics to predict lossage that 1367 * distinguishes different algorithms. 1368 * 1369 * F.e. after RTO, when all the queue is considered as lost, 1370 * lost_out = packets_out and in_flight = retrans_out. 1371 * 1372 * Essentially, we have now two algorithms counting 1373 * lost packets. 1374 * 1375 * FACK: It is the simplest heuristics. As soon as we decided 1376 * that something is lost, we decide that _all_ not SACKed 1377 * packets until the most forward SACK are lost. I.e. 1378 * lost_out = fackets_out - sacked_out and left_out = fackets_out. 1379 * It is absolutely correct estimate, if network does not reorder 1380 * packets. And it loses any connection to reality when reordering 1381 * takes place. We use FACK by default until reordering 1382 * is suspected on the path to this destination. 1383 * 1384 * NewReno: when Recovery is entered, we assume that one segment 1385 * is lost (classic Reno). While we are in Recovery and 1386 * a partial ACK arrives, we assume that one more packet 1387 * is lost (NewReno). This heuristics are the same in NewReno 1388 * and SACK. 1389 * 1390 * Imagine, that's all! Forget about all this shamanism about CWND inflation 1391 * deflation etc. CWND is real congestion window, never inflated, changes 1392 * only according to classic VJ rules. 1393 * 1394 * Really tricky (and requiring careful tuning) part of algorithm 1395 * is hidden in functions tcp_time_to_recover() and tcp_xmit_retransmit_queue(). 1396 * The first determines the moment _when_ we should reduce CWND and, 1397 * hence, slow down forward transmission. In fact, it determines the moment 1398 * when we decide that hole is caused by loss, rather than by a reorder. 1399 * 1400 * tcp_xmit_retransmit_queue() decides, _what_ we should retransmit to fill 1401 * holes, caused by lost packets. 1402 * 1403 * And the most logically complicated part of algorithm is undo 1404 * heuristics. We detect false retransmits due to both too early 1405 * fast retransmit (reordering) and underestimated RTO, analyzing 1406 * timestamps and D-SACKs. When we detect that some segments were 1407 * retransmitted by mistake and CWND reduction was wrong, we undo 1408 * window reduction and abort recovery phase. This logic is hidden 1409 * inside several functions named tcp_try_undo_<something>. 1410 */ 1411 1412 /* This function decides, when we should leave Disordered state 1413 * and enter Recovery phase, reducing congestion window. 1414 * 1415 * Main question: may we further continue forward transmission 1416 * with the same cwnd? 1417 */ 1418 static int tcp_time_to_recover(struct sock *sk, struct tcp_sock *tp) 1419 { 1420 __u32 packets_out; 1421 1422 /* Trick#1: The loss is proven. */ 1423 if (tp->lost_out) 1424 return 1; 1425 1426 /* Not-A-Trick#2 : Classic rule... */ 1427 if (tcp_fackets_out(tp) > tp->reordering) 1428 return 1; 1429 1430 /* Trick#3 : when we use RFC2988 timer restart, fast 1431 * retransmit can be triggered by timeout of queue head. 1432 */ 1433 if (tcp_head_timedout(sk, tp)) 1434 return 1; 1435 1436 /* Trick#4: It is still not OK... But will it be useful to delay 1437 * recovery more? 1438 */ 1439 packets_out = tp->packets_out; 1440 if (packets_out <= tp->reordering && 1441 tp->sacked_out >= max_t(__u32, packets_out/2, sysctl_tcp_reordering) && 1442 !tcp_may_send_now(sk, tp)) { 1443 /* We have nothing to send. This connection is limited 1444 * either by receiver window or by application. 1445 */ 1446 return 1; 1447 } 1448 1449 return 0; 1450 } 1451 1452 /* If we receive more dupacks than we expected counting segments 1453 * in assumption of absent reordering, interpret this as reordering. 1454 * The only another reason could be bug in receiver TCP. 1455 */ 1456 static void tcp_check_reno_reordering(struct sock *sk, const int addend) 1457 { 1458 struct tcp_sock *tp = tcp_sk(sk); 1459 u32 holes; 1460 1461 holes = max(tp->lost_out, 1U); 1462 holes = min(holes, tp->packets_out); 1463 1464 if ((tp->sacked_out + holes) > tp->packets_out) { 1465 tp->sacked_out = tp->packets_out - holes; 1466 tcp_update_reordering(sk, tp->packets_out + addend, 0); 1467 } 1468 } 1469 1470 /* Emulate SACKs for SACKless connection: account for a new dupack. */ 1471 1472 static void tcp_add_reno_sack(struct sock *sk) 1473 { 1474 struct tcp_sock *tp = tcp_sk(sk); 1475 tp->sacked_out++; 1476 tcp_check_reno_reordering(sk, 0); 1477 tcp_sync_left_out(tp); 1478 } 1479 1480 /* Account for ACK, ACKing some data in Reno Recovery phase. */ 1481 1482 static void tcp_remove_reno_sacks(struct sock *sk, struct tcp_sock *tp, int acked) 1483 { 1484 if (acked > 0) { 1485 /* One ACK acked hole. The rest eat duplicate ACKs. */ 1486 if (acked-1 >= tp->sacked_out) 1487 tp->sacked_out = 0; 1488 else 1489 tp->sacked_out -= acked-1; 1490 } 1491 tcp_check_reno_reordering(sk, acked); 1492 tcp_sync_left_out(tp); 1493 } 1494 1495 static inline void tcp_reset_reno_sack(struct tcp_sock *tp) 1496 { 1497 tp->sacked_out = 0; 1498 tp->left_out = tp->lost_out; 1499 } 1500 1501 /* Mark head of queue up as lost. */ 1502 static void tcp_mark_head_lost(struct sock *sk, struct tcp_sock *tp, 1503 int packets, u32 high_seq) 1504 { 1505 struct sk_buff *skb; 1506 int cnt = packets; 1507 1508 BUG_TRAP(cnt <= tp->packets_out); 1509 1510 sk_stream_for_retrans_queue(skb, sk) { 1511 cnt -= tcp_skb_pcount(skb); 1512 if (cnt < 0 || after(TCP_SKB_CB(skb)->end_seq, high_seq)) 1513 break; 1514 if (!(TCP_SKB_CB(skb)->sacked&TCPCB_TAGBITS)) { 1515 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST; 1516 tp->lost_out += tcp_skb_pcount(skb); 1517 } 1518 } 1519 tcp_sync_left_out(tp); 1520 } 1521 1522 /* Account newly detected lost packet(s) */ 1523 1524 static void tcp_update_scoreboard(struct sock *sk, struct tcp_sock *tp) 1525 { 1526 if (IsFack(tp)) { 1527 int lost = tp->fackets_out - tp->reordering; 1528 if (lost <= 0) 1529 lost = 1; 1530 tcp_mark_head_lost(sk, tp, lost, tp->high_seq); 1531 } else { 1532 tcp_mark_head_lost(sk, tp, 1, tp->high_seq); 1533 } 1534 1535 /* New heuristics: it is possible only after we switched 1536 * to restart timer each time when something is ACKed. 1537 * Hence, we can detect timed out packets during fast 1538 * retransmit without falling to slow start. 1539 */ 1540 if (tcp_head_timedout(sk, tp)) { 1541 struct sk_buff *skb; 1542 1543 sk_stream_for_retrans_queue(skb, sk) { 1544 if (tcp_skb_timedout(sk, skb) && 1545 !(TCP_SKB_CB(skb)->sacked&TCPCB_TAGBITS)) { 1546 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST; 1547 tp->lost_out += tcp_skb_pcount(skb); 1548 } 1549 } 1550 tcp_sync_left_out(tp); 1551 } 1552 } 1553 1554 /* CWND moderation, preventing bursts due to too big ACKs 1555 * in dubious situations. 1556 */ 1557 static inline void tcp_moderate_cwnd(struct tcp_sock *tp) 1558 { 1559 tp->snd_cwnd = min(tp->snd_cwnd, 1560 tcp_packets_in_flight(tp)+tcp_max_burst(tp)); 1561 tp->snd_cwnd_stamp = tcp_time_stamp; 1562 } 1563 1564 /* Decrease cwnd each second ack. */ 1565 static void tcp_cwnd_down(struct sock *sk) 1566 { 1567 const struct inet_connection_sock *icsk = inet_csk(sk); 1568 struct tcp_sock *tp = tcp_sk(sk); 1569 int decr = tp->snd_cwnd_cnt + 1; 1570 1571 tp->snd_cwnd_cnt = decr&1; 1572 decr >>= 1; 1573 1574 if (decr && tp->snd_cwnd > icsk->icsk_ca_ops->min_cwnd(sk)) 1575 tp->snd_cwnd -= decr; 1576 1577 tp->snd_cwnd = min(tp->snd_cwnd, tcp_packets_in_flight(tp)+1); 1578 tp->snd_cwnd_stamp = tcp_time_stamp; 1579 } 1580 1581 /* Nothing was retransmitted or returned timestamp is less 1582 * than timestamp of the first retransmission. 1583 */ 1584 static inline int tcp_packet_delayed(struct tcp_sock *tp) 1585 { 1586 return !tp->retrans_stamp || 1587 (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr && 1588 (__s32)(tp->rx_opt.rcv_tsecr - tp->retrans_stamp) < 0); 1589 } 1590 1591 /* Undo procedures. */ 1592 1593 #if FASTRETRANS_DEBUG > 1 1594 static void DBGUNDO(struct sock *sk, struct tcp_sock *tp, const char *msg) 1595 { 1596 struct inet_sock *inet = inet_sk(sk); 1597 printk(KERN_DEBUG "Undo %s %u.%u.%u.%u/%u c%u l%u ss%u/%u p%u\n", 1598 msg, 1599 NIPQUAD(inet->daddr), ntohs(inet->dport), 1600 tp->snd_cwnd, tp->left_out, 1601 tp->snd_ssthresh, tp->prior_ssthresh, 1602 tp->packets_out); 1603 } 1604 #else 1605 #define DBGUNDO(x...) do { } while (0) 1606 #endif 1607 1608 static void tcp_undo_cwr(struct sock *sk, const int undo) 1609 { 1610 struct tcp_sock *tp = tcp_sk(sk); 1611 1612 if (tp->prior_ssthresh) { 1613 const struct inet_connection_sock *icsk = inet_csk(sk); 1614 1615 if (icsk->icsk_ca_ops->undo_cwnd) 1616 tp->snd_cwnd = icsk->icsk_ca_ops->undo_cwnd(sk); 1617 else 1618 tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh<<1); 1619 1620 if (undo && tp->prior_ssthresh > tp->snd_ssthresh) { 1621 tp->snd_ssthresh = tp->prior_ssthresh; 1622 TCP_ECN_withdraw_cwr(tp); 1623 } 1624 } else { 1625 tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh); 1626 } 1627 tcp_moderate_cwnd(tp); 1628 tp->snd_cwnd_stamp = tcp_time_stamp; 1629 } 1630 1631 static inline int tcp_may_undo(struct tcp_sock *tp) 1632 { 1633 return tp->undo_marker && 1634 (!tp->undo_retrans || tcp_packet_delayed(tp)); 1635 } 1636 1637 /* People celebrate: "We love our President!" */ 1638 static int tcp_try_undo_recovery(struct sock *sk, struct tcp_sock *tp) 1639 { 1640 if (tcp_may_undo(tp)) { 1641 /* Happy end! We did not retransmit anything 1642 * or our original transmission succeeded. 1643 */ 1644 DBGUNDO(sk, tp, inet_csk(sk)->icsk_ca_state == TCP_CA_Loss ? "loss" : "retrans"); 1645 tcp_undo_cwr(sk, 1); 1646 if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss) 1647 NET_INC_STATS_BH(LINUX_MIB_TCPLOSSUNDO); 1648 else 1649 NET_INC_STATS_BH(LINUX_MIB_TCPFULLUNDO); 1650 tp->undo_marker = 0; 1651 } 1652 if (tp->snd_una == tp->high_seq && IsReno(tp)) { 1653 /* Hold old state until something *above* high_seq 1654 * is ACKed. For Reno it is MUST to prevent false 1655 * fast retransmits (RFC2582). SACK TCP is safe. */ 1656 tcp_moderate_cwnd(tp); 1657 return 1; 1658 } 1659 tcp_set_ca_state(sk, TCP_CA_Open); 1660 return 0; 1661 } 1662 1663 /* Try to undo cwnd reduction, because D-SACKs acked all retransmitted data */ 1664 static void tcp_try_undo_dsack(struct sock *sk, struct tcp_sock *tp) 1665 { 1666 if (tp->undo_marker && !tp->undo_retrans) { 1667 DBGUNDO(sk, tp, "D-SACK"); 1668 tcp_undo_cwr(sk, 1); 1669 tp->undo_marker = 0; 1670 NET_INC_STATS_BH(LINUX_MIB_TCPDSACKUNDO); 1671 } 1672 } 1673 1674 /* Undo during fast recovery after partial ACK. */ 1675 1676 static int tcp_try_undo_partial(struct sock *sk, struct tcp_sock *tp, 1677 int acked) 1678 { 1679 /* Partial ACK arrived. Force Hoe's retransmit. */ 1680 int failed = IsReno(tp) || tp->fackets_out>tp->reordering; 1681 1682 if (tcp_may_undo(tp)) { 1683 /* Plain luck! Hole if filled with delayed 1684 * packet, rather than with a retransmit. 1685 */ 1686 if (tp->retrans_out == 0) 1687 tp->retrans_stamp = 0; 1688 1689 tcp_update_reordering(sk, tcp_fackets_out(tp) + acked, 1); 1690 1691 DBGUNDO(sk, tp, "Hoe"); 1692 tcp_undo_cwr(sk, 0); 1693 NET_INC_STATS_BH(LINUX_MIB_TCPPARTIALUNDO); 1694 1695 /* So... Do not make Hoe's retransmit yet. 1696 * If the first packet was delayed, the rest 1697 * ones are most probably delayed as well. 1698 */ 1699 failed = 0; 1700 } 1701 return failed; 1702 } 1703 1704 /* Undo during loss recovery after partial ACK. */ 1705 static int tcp_try_undo_loss(struct sock *sk, struct tcp_sock *tp) 1706 { 1707 if (tcp_may_undo(tp)) { 1708 struct sk_buff *skb; 1709 sk_stream_for_retrans_queue(skb, sk) { 1710 TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST; 1711 } 1712 DBGUNDO(sk, tp, "partial loss"); 1713 tp->lost_out = 0; 1714 tp->left_out = tp->sacked_out; 1715 tcp_undo_cwr(sk, 1); 1716 NET_INC_STATS_BH(LINUX_MIB_TCPLOSSUNDO); 1717 inet_csk(sk)->icsk_retransmits = 0; 1718 tp->undo_marker = 0; 1719 if (!IsReno(tp)) 1720 tcp_set_ca_state(sk, TCP_CA_Open); 1721 return 1; 1722 } 1723 return 0; 1724 } 1725 1726 static inline void tcp_complete_cwr(struct sock *sk) 1727 { 1728 struct tcp_sock *tp = tcp_sk(sk); 1729 tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh); 1730 tp->snd_cwnd_stamp = tcp_time_stamp; 1731 tcp_ca_event(sk, CA_EVENT_COMPLETE_CWR); 1732 } 1733 1734 static void tcp_try_to_open(struct sock *sk, struct tcp_sock *tp, int flag) 1735 { 1736 tp->left_out = tp->sacked_out; 1737 1738 if (tp->retrans_out == 0) 1739 tp->retrans_stamp = 0; 1740 1741 if (flag&FLAG_ECE) 1742 tcp_enter_cwr(sk); 1743 1744 if (inet_csk(sk)->icsk_ca_state != TCP_CA_CWR) { 1745 int state = TCP_CA_Open; 1746 1747 if (tp->left_out || tp->retrans_out || tp->undo_marker) 1748 state = TCP_CA_Disorder; 1749 1750 if (inet_csk(sk)->icsk_ca_state != state) { 1751 tcp_set_ca_state(sk, state); 1752 tp->high_seq = tp->snd_nxt; 1753 } 1754 tcp_moderate_cwnd(tp); 1755 } else { 1756 tcp_cwnd_down(sk); 1757 } 1758 } 1759 1760 /* Process an event, which can update packets-in-flight not trivially. 1761 * Main goal of this function is to calculate new estimate for left_out, 1762 * taking into account both packets sitting in receiver's buffer and 1763 * packets lost by network. 1764 * 1765 * Besides that it does CWND reduction, when packet loss is detected 1766 * and changes state of machine. 1767 * 1768 * It does _not_ decide what to send, it is made in function 1769 * tcp_xmit_retransmit_queue(). 1770 */ 1771 static void 1772 tcp_fastretrans_alert(struct sock *sk, u32 prior_snd_una, 1773 int prior_packets, int flag) 1774 { 1775 struct inet_connection_sock *icsk = inet_csk(sk); 1776 struct tcp_sock *tp = tcp_sk(sk); 1777 int is_dupack = (tp->snd_una == prior_snd_una && !(flag&FLAG_NOT_DUP)); 1778 1779 /* Some technical things: 1780 * 1. Reno does not count dupacks (sacked_out) automatically. */ 1781 if (!tp->packets_out) 1782 tp->sacked_out = 0; 1783 /* 2. SACK counts snd_fack in packets inaccurately. */ 1784 if (tp->sacked_out == 0) 1785 tp->fackets_out = 0; 1786 1787 /* Now state machine starts. 1788 * A. ECE, hence prohibit cwnd undoing, the reduction is required. */ 1789 if (flag&FLAG_ECE) 1790 tp->prior_ssthresh = 0; 1791 1792 /* B. In all the states check for reneging SACKs. */ 1793 if (tp->sacked_out && tcp_check_sack_reneging(sk)) 1794 return; 1795 1796 /* C. Process data loss notification, provided it is valid. */ 1797 if ((flag&FLAG_DATA_LOST) && 1798 before(tp->snd_una, tp->high_seq) && 1799 icsk->icsk_ca_state != TCP_CA_Open && 1800 tp->fackets_out > tp->reordering) { 1801 tcp_mark_head_lost(sk, tp, tp->fackets_out-tp->reordering, tp->high_seq); 1802 NET_INC_STATS_BH(LINUX_MIB_TCPLOSS); 1803 } 1804 1805 /* D. Synchronize left_out to current state. */ 1806 tcp_sync_left_out(tp); 1807 1808 /* E. Check state exit conditions. State can be terminated 1809 * when high_seq is ACKed. */ 1810 if (icsk->icsk_ca_state == TCP_CA_Open) { 1811 if (!sysctl_tcp_frto) 1812 BUG_TRAP(tp->retrans_out == 0); 1813 tp->retrans_stamp = 0; 1814 } else if (!before(tp->snd_una, tp->high_seq)) { 1815 switch (icsk->icsk_ca_state) { 1816 case TCP_CA_Loss: 1817 icsk->icsk_retransmits = 0; 1818 if (tcp_try_undo_recovery(sk, tp)) 1819 return; 1820 break; 1821 1822 case TCP_CA_CWR: 1823 /* CWR is to be held something *above* high_seq 1824 * is ACKed for CWR bit to reach receiver. */ 1825 if (tp->snd_una != tp->high_seq) { 1826 tcp_complete_cwr(sk); 1827 tcp_set_ca_state(sk, TCP_CA_Open); 1828 } 1829 break; 1830 1831 case TCP_CA_Disorder: 1832 tcp_try_undo_dsack(sk, tp); 1833 if (!tp->undo_marker || 1834 /* For SACK case do not Open to allow to undo 1835 * catching for all duplicate ACKs. */ 1836 IsReno(tp) || tp->snd_una != tp->high_seq) { 1837 tp->undo_marker = 0; 1838 tcp_set_ca_state(sk, TCP_CA_Open); 1839 } 1840 break; 1841 1842 case TCP_CA_Recovery: 1843 if (IsReno(tp)) 1844 tcp_reset_reno_sack(tp); 1845 if (tcp_try_undo_recovery(sk, tp)) 1846 return; 1847 tcp_complete_cwr(sk); 1848 break; 1849 } 1850 } 1851 1852 /* F. Process state. */ 1853 switch (icsk->icsk_ca_state) { 1854 case TCP_CA_Recovery: 1855 if (prior_snd_una == tp->snd_una) { 1856 if (IsReno(tp) && is_dupack) 1857 tcp_add_reno_sack(sk); 1858 } else { 1859 int acked = prior_packets - tp->packets_out; 1860 if (IsReno(tp)) 1861 tcp_remove_reno_sacks(sk, tp, acked); 1862 is_dupack = tcp_try_undo_partial(sk, tp, acked); 1863 } 1864 break; 1865 case TCP_CA_Loss: 1866 if (flag&FLAG_DATA_ACKED) 1867 icsk->icsk_retransmits = 0; 1868 if (!tcp_try_undo_loss(sk, tp)) { 1869 tcp_moderate_cwnd(tp); 1870 tcp_xmit_retransmit_queue(sk); 1871 return; 1872 } 1873 if (icsk->icsk_ca_state != TCP_CA_Open) 1874 return; 1875 /* Loss is undone; fall through to processing in Open state. */ 1876 default: 1877 if (IsReno(tp)) { 1878 if (tp->snd_una != prior_snd_una) 1879 tcp_reset_reno_sack(tp); 1880 if (is_dupack) 1881 tcp_add_reno_sack(sk); 1882 } 1883 1884 if (icsk->icsk_ca_state == TCP_CA_Disorder) 1885 tcp_try_undo_dsack(sk, tp); 1886 1887 if (!tcp_time_to_recover(sk, tp)) { 1888 tcp_try_to_open(sk, tp, flag); 1889 return; 1890 } 1891 1892 /* Otherwise enter Recovery state */ 1893 1894 if (IsReno(tp)) 1895 NET_INC_STATS_BH(LINUX_MIB_TCPRENORECOVERY); 1896 else 1897 NET_INC_STATS_BH(LINUX_MIB_TCPSACKRECOVERY); 1898 1899 tp->high_seq = tp->snd_nxt; 1900 tp->prior_ssthresh = 0; 1901 tp->undo_marker = tp->snd_una; 1902 tp->undo_retrans = tp->retrans_out; 1903 1904 if (icsk->icsk_ca_state < TCP_CA_CWR) { 1905 if (!(flag&FLAG_ECE)) 1906 tp->prior_ssthresh = tcp_current_ssthresh(sk); 1907 tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk); 1908 TCP_ECN_queue_cwr(tp); 1909 } 1910 1911 tp->snd_cwnd_cnt = 0; 1912 tcp_set_ca_state(sk, TCP_CA_Recovery); 1913 } 1914 1915 if (is_dupack || tcp_head_timedout(sk, tp)) 1916 tcp_update_scoreboard(sk, tp); 1917 tcp_cwnd_down(sk); 1918 tcp_xmit_retransmit_queue(sk); 1919 } 1920 1921 /* Read draft-ietf-tcplw-high-performance before mucking 1922 * with this code. (Superceeds RFC1323) 1923 */ 1924 static void tcp_ack_saw_tstamp(struct sock *sk, u32 *usrtt, int flag) 1925 { 1926 /* RTTM Rule: A TSecr value received in a segment is used to 1927 * update the averaged RTT measurement only if the segment 1928 * acknowledges some new data, i.e., only if it advances the 1929 * left edge of the send window. 1930 * 1931 * See draft-ietf-tcplw-high-performance-00, section 3.3. 1932 * 1998/04/10 Andrey V. Savochkin <saw@msu.ru> 1933 * 1934 * Changed: reset backoff as soon as we see the first valid sample. 1935 * If we do not, we get strongly overstimated rto. With timestamps 1936 * samples are accepted even from very old segments: f.e., when rtt=1 1937 * increases to 8, we retransmit 5 times and after 8 seconds delayed 1938 * answer arrives rto becomes 120 seconds! If at least one of segments 1939 * in window is lost... Voila. --ANK (010210) 1940 */ 1941 struct tcp_sock *tp = tcp_sk(sk); 1942 const __u32 seq_rtt = tcp_time_stamp - tp->rx_opt.rcv_tsecr; 1943 tcp_rtt_estimator(sk, seq_rtt, usrtt); 1944 tcp_set_rto(sk); 1945 inet_csk(sk)->icsk_backoff = 0; 1946 tcp_bound_rto(sk); 1947 } 1948 1949 static void tcp_ack_no_tstamp(struct sock *sk, u32 seq_rtt, u32 *usrtt, int flag) 1950 { 1951 /* We don't have a timestamp. Can only use 1952 * packets that are not retransmitted to determine 1953 * rtt estimates. Also, we must not reset the 1954 * backoff for rto until we get a non-retransmitted 1955 * packet. This allows us to deal with a situation 1956 * where the network delay has increased suddenly. 1957 * I.e. Karn's algorithm. (SIGCOMM '87, p5.) 1958 */ 1959 1960 if (flag & FLAG_RETRANS_DATA_ACKED) 1961 return; 1962 1963 tcp_rtt_estimator(sk, seq_rtt, usrtt); 1964 tcp_set_rto(sk); 1965 inet_csk(sk)->icsk_backoff = 0; 1966 tcp_bound_rto(sk); 1967 } 1968 1969 static inline void tcp_ack_update_rtt(struct sock *sk, const int flag, 1970 const s32 seq_rtt, u32 *usrtt) 1971 { 1972 const struct tcp_sock *tp = tcp_sk(sk); 1973 /* Note that peer MAY send zero echo. In this case it is ignored. (rfc1323) */ 1974 if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr) 1975 tcp_ack_saw_tstamp(sk, usrtt, flag); 1976 else if (seq_rtt >= 0) 1977 tcp_ack_no_tstamp(sk, seq_rtt, usrtt, flag); 1978 } 1979 1980 static inline void tcp_cong_avoid(struct sock *sk, u32 ack, u32 rtt, 1981 u32 in_flight, int good) 1982 { 1983 const struct inet_connection_sock *icsk = inet_csk(sk); 1984 icsk->icsk_ca_ops->cong_avoid(sk, ack, rtt, in_flight, good); 1985 tcp_sk(sk)->snd_cwnd_stamp = tcp_time_stamp; 1986 } 1987 1988 /* Restart timer after forward progress on connection. 1989 * RFC2988 recommends to restart timer to now+rto. 1990 */ 1991 1992 static inline void tcp_ack_packets_out(struct sock *sk, struct tcp_sock *tp) 1993 { 1994 if (!tp->packets_out) { 1995 inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS); 1996 } else { 1997 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, inet_csk(sk)->icsk_rto, TCP_RTO_MAX); 1998 } 1999 } 2000 2001 static int tcp_tso_acked(struct sock *sk, struct sk_buff *skb, 2002 __u32 now, __s32 *seq_rtt) 2003 { 2004 struct tcp_sock *tp = tcp_sk(sk); 2005 struct tcp_skb_cb *scb = TCP_SKB_CB(skb); 2006 __u32 seq = tp->snd_una; 2007 __u32 packets_acked; 2008 int acked = 0; 2009 2010 /* If we get here, the whole TSO packet has not been 2011 * acked. 2012 */ 2013 BUG_ON(!after(scb->end_seq, seq)); 2014 2015 packets_acked = tcp_skb_pcount(skb); 2016 if (tcp_trim_head(sk, skb, seq - scb->seq)) 2017 return 0; 2018 packets_acked -= tcp_skb_pcount(skb); 2019 2020 if (packets_acked) { 2021 __u8 sacked = scb->sacked; 2022 2023 acked |= FLAG_DATA_ACKED; 2024 if (sacked) { 2025 if (sacked & TCPCB_RETRANS) { 2026 if (sacked & TCPCB_SACKED_RETRANS) 2027 tp->retrans_out -= packets_acked; 2028 acked |= FLAG_RETRANS_DATA_ACKED; 2029 *seq_rtt = -1; 2030 } else if (*seq_rtt < 0) 2031 *seq_rtt = now - scb->when; 2032 if (sacked & TCPCB_SACKED_ACKED) 2033 tp->sacked_out -= packets_acked; 2034 if (sacked & TCPCB_LOST) 2035 tp->lost_out -= packets_acked; 2036 if (sacked & TCPCB_URG) { 2037 if (tp->urg_mode && 2038 !before(seq, tp->snd_up)) 2039 tp->urg_mode = 0; 2040 } 2041 } else if (*seq_rtt < 0) 2042 *seq_rtt = now - scb->when; 2043 2044 if (tp->fackets_out) { 2045 __u32 dval = min(tp->fackets_out, packets_acked); 2046 tp->fackets_out -= dval; 2047 } 2048 tp->packets_out -= packets_acked; 2049 2050 BUG_ON(tcp_skb_pcount(skb) == 0); 2051 BUG_ON(!before(scb->seq, scb->end_seq)); 2052 } 2053 2054 return acked; 2055 } 2056 2057 2058 /* Remove acknowledged frames from the retransmission queue. */ 2059 static int tcp_clean_rtx_queue(struct sock *sk, __s32 *seq_rtt_p, s32 *seq_usrtt) 2060 { 2061 struct tcp_sock *tp = tcp_sk(sk); 2062 struct sk_buff *skb; 2063 __u32 now = tcp_time_stamp; 2064 int acked = 0; 2065 __s32 seq_rtt = -1; 2066 struct timeval usnow; 2067 u32 pkts_acked = 0; 2068 2069 if (seq_usrtt) 2070 do_gettimeofday(&usnow); 2071 2072 while ((skb = skb_peek(&sk->sk_write_queue)) && 2073 skb != sk->sk_send_head) { 2074 struct tcp_skb_cb *scb = TCP_SKB_CB(skb); 2075 __u8 sacked = scb->sacked; 2076 2077 /* If our packet is before the ack sequence we can 2078 * discard it as it's confirmed to have arrived at 2079 * the other end. 2080 */ 2081 if (after(scb->end_seq, tp->snd_una)) { 2082 if (tcp_skb_pcount(skb) > 1 && 2083 after(tp->snd_una, scb->seq)) 2084 acked |= tcp_tso_acked(sk, skb, 2085 now, &seq_rtt); 2086 break; 2087 } 2088 2089 /* Initial outgoing SYN's get put onto the write_queue 2090 * just like anything else we transmit. It is not 2091 * true data, and if we misinform our callers that 2092 * this ACK acks real data, we will erroneously exit 2093 * connection startup slow start one packet too 2094 * quickly. This is severely frowned upon behavior. 2095 */ 2096 if (!(scb->flags & TCPCB_FLAG_SYN)) { 2097 acked |= FLAG_DATA_ACKED; 2098 ++pkts_acked; 2099 } else { 2100 acked |= FLAG_SYN_ACKED; 2101 tp->retrans_stamp = 0; 2102 } 2103 2104 if (sacked) { 2105 if (sacked & TCPCB_RETRANS) { 2106 if(sacked & TCPCB_SACKED_RETRANS) 2107 tp->retrans_out -= tcp_skb_pcount(skb); 2108 acked |= FLAG_RETRANS_DATA_ACKED; 2109 seq_rtt = -1; 2110 } else if (seq_rtt < 0) 2111 seq_rtt = now - scb->when; 2112 if (seq_usrtt) { 2113 struct timeval tv; 2114 2115 skb_get_timestamp(skb, &tv); 2116 *seq_usrtt = (usnow.tv_sec - tv.tv_sec) * 1000000 2117 + (usnow.tv_usec - tv.tv_usec); 2118 } 2119 2120 if (sacked & TCPCB_SACKED_ACKED) 2121 tp->sacked_out -= tcp_skb_pcount(skb); 2122 if (sacked & TCPCB_LOST) 2123 tp->lost_out -= tcp_skb_pcount(skb); 2124 if (sacked & TCPCB_URG) { 2125 if (tp->urg_mode && 2126 !before(scb->end_seq, tp->snd_up)) 2127 tp->urg_mode = 0; 2128 } 2129 } else if (seq_rtt < 0) 2130 seq_rtt = now - scb->when; 2131 tcp_dec_pcount_approx(&tp->fackets_out, skb); 2132 tcp_packets_out_dec(tp, skb); 2133 __skb_unlink(skb, &sk->sk_write_queue); 2134 sk_stream_free_skb(sk, skb); 2135 } 2136 2137 if (acked&FLAG_ACKED) { 2138 const struct inet_connection_sock *icsk = inet_csk(sk); 2139 tcp_ack_update_rtt(sk, acked, seq_rtt, seq_usrtt); 2140 tcp_ack_packets_out(sk, tp); 2141 2142 if (icsk->icsk_ca_ops->pkts_acked) 2143 icsk->icsk_ca_ops->pkts_acked(sk, pkts_acked); 2144 } 2145 2146 #if FASTRETRANS_DEBUG > 0 2147 BUG_TRAP((int)tp->sacked_out >= 0); 2148 BUG_TRAP((int)tp->lost_out >= 0); 2149 BUG_TRAP((int)tp->retrans_out >= 0); 2150 if (!tp->packets_out && tp->rx_opt.sack_ok) { 2151 const struct inet_connection_sock *icsk = inet_csk(sk); 2152 if (tp->lost_out) { 2153 printk(KERN_DEBUG "Leak l=%u %d\n", 2154 tp->lost_out, icsk->icsk_ca_state); 2155 tp->lost_out = 0; 2156 } 2157 if (tp->sacked_out) { 2158 printk(KERN_DEBUG "Leak s=%u %d\n", 2159 tp->sacked_out, icsk->icsk_ca_state); 2160 tp->sacked_out = 0; 2161 } 2162 if (tp->retrans_out) { 2163 printk(KERN_DEBUG "Leak r=%u %d\n", 2164 tp->retrans_out, icsk->icsk_ca_state); 2165 tp->retrans_out = 0; 2166 } 2167 } 2168 #endif 2169 *seq_rtt_p = seq_rtt; 2170 return acked; 2171 } 2172 2173 static void tcp_ack_probe(struct sock *sk) 2174 { 2175 const struct tcp_sock *tp = tcp_sk(sk); 2176 struct inet_connection_sock *icsk = inet_csk(sk); 2177 2178 /* Was it a usable window open? */ 2179 2180 if (!after(TCP_SKB_CB(sk->sk_send_head)->end_seq, 2181 tp->snd_una + tp->snd_wnd)) { 2182 icsk->icsk_backoff = 0; 2183 inet_csk_clear_xmit_timer(sk, ICSK_TIME_PROBE0); 2184 /* Socket must be waked up by subsequent tcp_data_snd_check(). 2185 * This function is not for random using! 2186 */ 2187 } else { 2188 inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0, 2189 min(icsk->icsk_rto << icsk->icsk_backoff, TCP_RTO_MAX), 2190 TCP_RTO_MAX); 2191 } 2192 } 2193 2194 static inline int tcp_ack_is_dubious(const struct sock *sk, const int flag) 2195 { 2196 return (!(flag & FLAG_NOT_DUP) || (flag & FLAG_CA_ALERT) || 2197 inet_csk(sk)->icsk_ca_state != TCP_CA_Open); 2198 } 2199 2200 static inline int tcp_may_raise_cwnd(const struct sock *sk, const int flag) 2201 { 2202 const struct tcp_sock *tp = tcp_sk(sk); 2203 return (!(flag & FLAG_ECE) || tp->snd_cwnd < tp->snd_ssthresh) && 2204 !((1 << inet_csk(sk)->icsk_ca_state) & (TCPF_CA_Recovery | TCPF_CA_CWR)); 2205 } 2206 2207 /* Check that window update is acceptable. 2208 * The function assumes that snd_una<=ack<=snd_next. 2209 */ 2210 static inline int tcp_may_update_window(const struct tcp_sock *tp, const u32 ack, 2211 const u32 ack_seq, const u32 nwin) 2212 { 2213 return (after(ack, tp->snd_una) || 2214 after(ack_seq, tp->snd_wl1) || 2215 (ack_seq == tp->snd_wl1 && nwin > tp->snd_wnd)); 2216 } 2217 2218 /* Update our send window. 2219 * 2220 * Window update algorithm, described in RFC793/RFC1122 (used in linux-2.2 2221 * and in FreeBSD. NetBSD's one is even worse.) is wrong. 2222 */ 2223 static int tcp_ack_update_window(struct sock *sk, struct tcp_sock *tp, 2224 struct sk_buff *skb, u32 ack, u32 ack_seq) 2225 { 2226 int flag = 0; 2227 u32 nwin = ntohs(skb->h.th->window); 2228 2229 if (likely(!skb->h.th->syn)) 2230 nwin <<= tp->rx_opt.snd_wscale; 2231 2232 if (tcp_may_update_window(tp, ack, ack_seq, nwin)) { 2233 flag |= FLAG_WIN_UPDATE; 2234 tcp_update_wl(tp, ack, ack_seq); 2235 2236 if (tp->snd_wnd != nwin) { 2237 tp->snd_wnd = nwin; 2238 2239 /* Note, it is the only place, where 2240 * fast path is recovered for sending TCP. 2241 */ 2242 tp->pred_flags = 0; 2243 tcp_fast_path_check(sk, tp); 2244 2245 if (nwin > tp->max_window) { 2246 tp->max_window = nwin; 2247 tcp_sync_mss(sk, tp->pmtu_cookie); 2248 } 2249 } 2250 } 2251 2252 tp->snd_una = ack; 2253 2254 return flag; 2255 } 2256 2257 static void tcp_process_frto(struct sock *sk, u32 prior_snd_una) 2258 { 2259 struct tcp_sock *tp = tcp_sk(sk); 2260 2261 tcp_sync_left_out(tp); 2262 2263 if (tp->snd_una == prior_snd_una || 2264 !before(tp->snd_una, tp->frto_highmark)) { 2265 /* RTO was caused by loss, start retransmitting in 2266 * go-back-N slow start 2267 */ 2268 tcp_enter_frto_loss(sk); 2269 return; 2270 } 2271 2272 if (tp->frto_counter == 1) { 2273 /* First ACK after RTO advances the window: allow two new 2274 * segments out. 2275 */ 2276 tp->snd_cwnd = tcp_packets_in_flight(tp) + 2; 2277 } else { 2278 /* Also the second ACK after RTO advances the window. 2279 * The RTO was likely spurious. Reduce cwnd and continue 2280 * in congestion avoidance 2281 */ 2282 tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh); 2283 tcp_moderate_cwnd(tp); 2284 } 2285 2286 /* F-RTO affects on two new ACKs following RTO. 2287 * At latest on third ACK the TCP behavor is back to normal. 2288 */ 2289 tp->frto_counter = (tp->frto_counter + 1) % 3; 2290 } 2291 2292 /* This routine deals with incoming acks, but not outgoing ones. */ 2293 static int tcp_ack(struct sock *sk, struct sk_buff *skb, int flag) 2294 { 2295 struct inet_connection_sock *icsk = inet_csk(sk); 2296 struct tcp_sock *tp = tcp_sk(sk); 2297 u32 prior_snd_una = tp->snd_una; 2298 u32 ack_seq = TCP_SKB_CB(skb)->seq; 2299 u32 ack = TCP_SKB_CB(skb)->ack_seq; 2300 u32 prior_in_flight; 2301 s32 seq_rtt; 2302 s32 seq_usrtt = 0; 2303 int prior_packets; 2304 2305 /* If the ack is newer than sent or older than previous acks 2306 * then we can probably ignore it. 2307 */ 2308 if (after(ack, tp->snd_nxt)) 2309 goto uninteresting_ack; 2310 2311 if (before(ack, prior_snd_una)) 2312 goto old_ack; 2313 2314 if (!(flag&FLAG_SLOWPATH) && after(ack, prior_snd_una)) { 2315 /* Window is constant, pure forward advance. 2316 * No more checks are required. 2317 * Note, we use the fact that SND.UNA>=SND.WL2. 2318 */ 2319 tcp_update_wl(tp, ack, ack_seq); 2320 tp->snd_una = ack; 2321 flag |= FLAG_WIN_UPDATE; 2322 2323 tcp_ca_event(sk, CA_EVENT_FAST_ACK); 2324 2325 NET_INC_STATS_BH(LINUX_MIB_TCPHPACKS); 2326 } else { 2327 if (ack_seq != TCP_SKB_CB(skb)->end_seq) 2328 flag |= FLAG_DATA; 2329 else 2330 NET_INC_STATS_BH(LINUX_MIB_TCPPUREACKS); 2331 2332 flag |= tcp_ack_update_window(sk, tp, skb, ack, ack_seq); 2333 2334 if (TCP_SKB_CB(skb)->sacked) 2335 flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una); 2336 2337 if (TCP_ECN_rcv_ecn_echo(tp, skb->h.th)) 2338 flag |= FLAG_ECE; 2339 2340 tcp_ca_event(sk, CA_EVENT_SLOW_ACK); 2341 } 2342 2343 /* We passed data and got it acked, remove any soft error 2344 * log. Something worked... 2345 */ 2346 sk->sk_err_soft = 0; 2347 tp->rcv_tstamp = tcp_time_stamp; 2348 prior_packets = tp->packets_out; 2349 if (!prior_packets) 2350 goto no_queue; 2351 2352 prior_in_flight = tcp_packets_in_flight(tp); 2353 2354 /* See if we can take anything off of the retransmit queue. */ 2355 flag |= tcp_clean_rtx_queue(sk, &seq_rtt, 2356 icsk->icsk_ca_ops->rtt_sample ? &seq_usrtt : NULL); 2357 2358 if (tp->frto_counter) 2359 tcp_process_frto(sk, prior_snd_una); 2360 2361 if (tcp_ack_is_dubious(sk, flag)) { 2362 /* Advanve CWND, if state allows this. */ 2363 if ((flag & FLAG_DATA_ACKED) && tcp_may_raise_cwnd(sk, flag)) 2364 tcp_cong_avoid(sk, ack, seq_rtt, prior_in_flight, 0); 2365 tcp_fastretrans_alert(sk, prior_snd_una, prior_packets, flag); 2366 } else { 2367 if ((flag & FLAG_DATA_ACKED)) 2368 tcp_cong_avoid(sk, ack, seq_rtt, prior_in_flight, 1); 2369 } 2370 2371 if ((flag & FLAG_FORWARD_PROGRESS) || !(flag&FLAG_NOT_DUP)) 2372 dst_confirm(sk->sk_dst_cache); 2373 2374 return 1; 2375 2376 no_queue: 2377 icsk->icsk_probes_out = 0; 2378 2379 /* If this ack opens up a zero window, clear backoff. It was 2380 * being used to time the probes, and is probably far higher than 2381 * it needs to be for normal retransmission. 2382 */ 2383 if (sk->sk_send_head) 2384 tcp_ack_probe(sk); 2385 return 1; 2386 2387 old_ack: 2388 if (TCP_SKB_CB(skb)->sacked) 2389 tcp_sacktag_write_queue(sk, skb, prior_snd_una); 2390 2391 uninteresting_ack: 2392 SOCK_DEBUG(sk, "Ack %u out of %u:%u\n", ack, tp->snd_una, tp->snd_nxt); 2393 return 0; 2394 } 2395 2396 2397 /* Look for tcp options. Normally only called on SYN and SYNACK packets. 2398 * But, this can also be called on packets in the established flow when 2399 * the fast version below fails. 2400 */ 2401 void tcp_parse_options(struct sk_buff *skb, struct tcp_options_received *opt_rx, int estab) 2402 { 2403 unsigned char *ptr; 2404 struct tcphdr *th = skb->h.th; 2405 int length=(th->doff*4)-sizeof(struct tcphdr); 2406 2407 ptr = (unsigned char *)(th + 1); 2408 opt_rx->saw_tstamp = 0; 2409 2410 while(length>0) { 2411 int opcode=*ptr++; 2412 int opsize; 2413 2414 switch (opcode) { 2415 case TCPOPT_EOL: 2416 return; 2417 case TCPOPT_NOP: /* Ref: RFC 793 section 3.1 */ 2418 length--; 2419 continue; 2420 default: 2421 opsize=*ptr++; 2422 if (opsize < 2) /* "silly options" */ 2423 return; 2424 if (opsize > length) 2425 return; /* don't parse partial options */ 2426 switch(opcode) { 2427 case TCPOPT_MSS: 2428 if(opsize==TCPOLEN_MSS && th->syn && !estab) { 2429 u16 in_mss = ntohs(get_unaligned((__u16 *)ptr)); 2430 if (in_mss) { 2431 if (opt_rx->user_mss && opt_rx->user_mss < in_mss) 2432 in_mss = opt_rx->user_mss; 2433 opt_rx->mss_clamp = in_mss; 2434 } 2435 } 2436 break; 2437 case TCPOPT_WINDOW: 2438 if(opsize==TCPOLEN_WINDOW && th->syn && !estab) 2439 if (sysctl_tcp_window_scaling) { 2440 __u8 snd_wscale = *(__u8 *) ptr; 2441 opt_rx->wscale_ok = 1; 2442 if (snd_wscale > 14) { 2443 if(net_ratelimit()) 2444 printk(KERN_INFO "tcp_parse_options: Illegal window " 2445 "scaling value %d >14 received.\n", 2446 snd_wscale); 2447 snd_wscale = 14; 2448 } 2449 opt_rx->snd_wscale = snd_wscale; 2450 } 2451 break; 2452 case TCPOPT_TIMESTAMP: 2453 if(opsize==TCPOLEN_TIMESTAMP) { 2454 if ((estab && opt_rx->tstamp_ok) || 2455 (!estab && sysctl_tcp_timestamps)) { 2456 opt_rx->saw_tstamp = 1; 2457 opt_rx->rcv_tsval = ntohl(get_unaligned((__u32 *)ptr)); 2458 opt_rx->rcv_tsecr = ntohl(get_unaligned((__u32 *)(ptr+4))); 2459 } 2460 } 2461 break; 2462 case TCPOPT_SACK_PERM: 2463 if(opsize==TCPOLEN_SACK_PERM && th->syn && !estab) { 2464 if (sysctl_tcp_sack) { 2465 opt_rx->sack_ok = 1; 2466 tcp_sack_reset(opt_rx); 2467 } 2468 } 2469 break; 2470 2471 case TCPOPT_SACK: 2472 if((opsize >= (TCPOLEN_SACK_BASE + TCPOLEN_SACK_PERBLOCK)) && 2473 !((opsize - TCPOLEN_SACK_BASE) % TCPOLEN_SACK_PERBLOCK) && 2474 opt_rx->sack_ok) { 2475 TCP_SKB_CB(skb)->sacked = (ptr - 2) - (unsigned char *)th; 2476 } 2477 }; 2478 ptr+=opsize-2; 2479 length-=opsize; 2480 }; 2481 } 2482 } 2483 2484 /* Fast parse options. This hopes to only see timestamps. 2485 * If it is wrong it falls back on tcp_parse_options(). 2486 */ 2487 static inline int tcp_fast_parse_options(struct sk_buff *skb, struct tcphdr *th, 2488 struct tcp_sock *tp) 2489 { 2490 if (th->doff == sizeof(struct tcphdr)>>2) { 2491 tp->rx_opt.saw_tstamp = 0; 2492 return 0; 2493 } else if (tp->rx_opt.tstamp_ok && 2494 th->doff == (sizeof(struct tcphdr)>>2)+(TCPOLEN_TSTAMP_ALIGNED>>2)) { 2495 __u32 *ptr = (__u32 *)(th + 1); 2496 if (*ptr == ntohl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16) 2497 | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP)) { 2498 tp->rx_opt.saw_tstamp = 1; 2499 ++ptr; 2500 tp->rx_opt.rcv_tsval = ntohl(*ptr); 2501 ++ptr; 2502 tp->rx_opt.rcv_tsecr = ntohl(*ptr); 2503 return 1; 2504 } 2505 } 2506 tcp_parse_options(skb, &tp->rx_opt, 1); 2507 return 1; 2508 } 2509 2510 static inline void tcp_store_ts_recent(struct tcp_sock *tp) 2511 { 2512 tp->rx_opt.ts_recent = tp->rx_opt.rcv_tsval; 2513 tp->rx_opt.ts_recent_stamp = xtime.tv_sec; 2514 } 2515 2516 static inline void tcp_replace_ts_recent(struct tcp_sock *tp, u32 seq) 2517 { 2518 if (tp->rx_opt.saw_tstamp && !after(seq, tp->rcv_wup)) { 2519 /* PAWS bug workaround wrt. ACK frames, the PAWS discard 2520 * extra check below makes sure this can only happen 2521 * for pure ACK frames. -DaveM 2522 * 2523 * Not only, also it occurs for expired timestamps. 2524 */ 2525 2526 if((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) >= 0 || 2527 xtime.tv_sec >= tp->rx_opt.ts_recent_stamp + TCP_PAWS_24DAYS) 2528 tcp_store_ts_recent(tp); 2529 } 2530 } 2531 2532 /* Sorry, PAWS as specified is broken wrt. pure-ACKs -DaveM 2533 * 2534 * It is not fatal. If this ACK does _not_ change critical state (seqs, window) 2535 * it can pass through stack. So, the following predicate verifies that 2536 * this segment is not used for anything but congestion avoidance or 2537 * fast retransmit. Moreover, we even are able to eliminate most of such 2538 * second order effects, if we apply some small "replay" window (~RTO) 2539 * to timestamp space. 2540 * 2541 * All these measures still do not guarantee that we reject wrapped ACKs 2542 * on networks with high bandwidth, when sequence space is recycled fastly, 2543 * but it guarantees that such events will be very rare and do not affect 2544 * connection seriously. This doesn't look nice, but alas, PAWS is really 2545 * buggy extension. 2546 * 2547 * [ Later note. Even worse! It is buggy for segments _with_ data. RFC 2548 * states that events when retransmit arrives after original data are rare. 2549 * It is a blatant lie. VJ forgot about fast retransmit! 8)8) It is 2550 * the biggest problem on large power networks even with minor reordering. 2551 * OK, let's give it small replay window. If peer clock is even 1hz, it is safe 2552 * up to bandwidth of 18Gigabit/sec. 8) ] 2553 */ 2554 2555 static int tcp_disordered_ack(const struct sock *sk, const struct sk_buff *skb) 2556 { 2557 struct tcp_sock *tp = tcp_sk(sk); 2558 struct tcphdr *th = skb->h.th; 2559 u32 seq = TCP_SKB_CB(skb)->seq; 2560 u32 ack = TCP_SKB_CB(skb)->ack_seq; 2561 2562 return (/* 1. Pure ACK with correct sequence number. */ 2563 (th->ack && seq == TCP_SKB_CB(skb)->end_seq && seq == tp->rcv_nxt) && 2564 2565 /* 2. ... and duplicate ACK. */ 2566 ack == tp->snd_una && 2567 2568 /* 3. ... and does not update window. */ 2569 !tcp_may_update_window(tp, ack, seq, ntohs(th->window) << tp->rx_opt.snd_wscale) && 2570 2571 /* 4. ... and sits in replay window. */ 2572 (s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) <= (inet_csk(sk)->icsk_rto * 1024) / HZ); 2573 } 2574 2575 static inline int tcp_paws_discard(const struct sock *sk, const struct sk_buff *skb) 2576 { 2577 const struct tcp_sock *tp = tcp_sk(sk); 2578 return ((s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) > TCP_PAWS_WINDOW && 2579 xtime.tv_sec < tp->rx_opt.ts_recent_stamp + TCP_PAWS_24DAYS && 2580 !tcp_disordered_ack(sk, skb)); 2581 } 2582 2583 /* Check segment sequence number for validity. 2584 * 2585 * Segment controls are considered valid, if the segment 2586 * fits to the window after truncation to the window. Acceptability 2587 * of data (and SYN, FIN, of course) is checked separately. 2588 * See tcp_data_queue(), for example. 2589 * 2590 * Also, controls (RST is main one) are accepted using RCV.WUP instead 2591 * of RCV.NXT. Peer still did not advance his SND.UNA when we 2592 * delayed ACK, so that hisSND.UNA<=ourRCV.WUP. 2593 * (borrowed from freebsd) 2594 */ 2595 2596 static inline int tcp_sequence(struct tcp_sock *tp, u32 seq, u32 end_seq) 2597 { 2598 return !before(end_seq, tp->rcv_wup) && 2599 !after(seq, tp->rcv_nxt + tcp_receive_window(tp)); 2600 } 2601 2602 /* When we get a reset we do this. */ 2603 static void tcp_reset(struct sock *sk) 2604 { 2605 /* We want the right error as BSD sees it (and indeed as we do). */ 2606 switch (sk->sk_state) { 2607 case TCP_SYN_SENT: 2608 sk->sk_err = ECONNREFUSED; 2609 break; 2610 case TCP_CLOSE_WAIT: 2611 sk->sk_err = EPIPE; 2612 break; 2613 case TCP_CLOSE: 2614 return; 2615 default: 2616 sk->sk_err = ECONNRESET; 2617 } 2618 2619 if (!sock_flag(sk, SOCK_DEAD)) 2620 sk->sk_error_report(sk); 2621 2622 tcp_done(sk); 2623 } 2624 2625 /* 2626 * Process the FIN bit. This now behaves as it is supposed to work 2627 * and the FIN takes effect when it is validly part of sequence 2628 * space. Not before when we get holes. 2629 * 2630 * If we are ESTABLISHED, a received fin moves us to CLOSE-WAIT 2631 * (and thence onto LAST-ACK and finally, CLOSE, we never enter 2632 * TIME-WAIT) 2633 * 2634 * If we are in FINWAIT-1, a received FIN indicates simultaneous 2635 * close and we go into CLOSING (and later onto TIME-WAIT) 2636 * 2637 * If we are in FINWAIT-2, a received FIN moves us to TIME-WAIT. 2638 */ 2639 static void tcp_fin(struct sk_buff *skb, struct sock *sk, struct tcphdr *th) 2640 { 2641 struct tcp_sock *tp = tcp_sk(sk); 2642 2643 inet_csk_schedule_ack(sk); 2644 2645 sk->sk_shutdown |= RCV_SHUTDOWN; 2646 sock_set_flag(sk, SOCK_DONE); 2647 2648 switch (sk->sk_state) { 2649 case TCP_SYN_RECV: 2650 case TCP_ESTABLISHED: 2651 /* Move to CLOSE_WAIT */ 2652 tcp_set_state(sk, TCP_CLOSE_WAIT); 2653 inet_csk(sk)->icsk_ack.pingpong = 1; 2654 break; 2655 2656 case TCP_CLOSE_WAIT: 2657 case TCP_CLOSING: 2658 /* Received a retransmission of the FIN, do 2659 * nothing. 2660 */ 2661 break; 2662 case TCP_LAST_ACK: 2663 /* RFC793: Remain in the LAST-ACK state. */ 2664 break; 2665 2666 case TCP_FIN_WAIT1: 2667 /* This case occurs when a simultaneous close 2668 * happens, we must ack the received FIN and 2669 * enter the CLOSING state. 2670 */ 2671 tcp_send_ack(sk); 2672 tcp_set_state(sk, TCP_CLOSING); 2673 break; 2674 case TCP_FIN_WAIT2: 2675 /* Received a FIN -- send ACK and enter TIME_WAIT. */ 2676 tcp_send_ack(sk); 2677 tcp_time_wait(sk, TCP_TIME_WAIT, 0); 2678 break; 2679 default: 2680 /* Only TCP_LISTEN and TCP_CLOSE are left, in these 2681 * cases we should never reach this piece of code. 2682 */ 2683 printk(KERN_ERR "%s: Impossible, sk->sk_state=%d\n", 2684 __FUNCTION__, sk->sk_state); 2685 break; 2686 }; 2687 2688 /* It _is_ possible, that we have something out-of-order _after_ FIN. 2689 * Probably, we should reset in this case. For now drop them. 2690 */ 2691 __skb_queue_purge(&tp->out_of_order_queue); 2692 if (tp->rx_opt.sack_ok) 2693 tcp_sack_reset(&tp->rx_opt); 2694 sk_stream_mem_reclaim(sk); 2695 2696 if (!sock_flag(sk, SOCK_DEAD)) { 2697 sk->sk_state_change(sk); 2698 2699 /* Do not send POLL_HUP for half duplex close. */ 2700 if (sk->sk_shutdown == SHUTDOWN_MASK || 2701 sk->sk_state == TCP_CLOSE) 2702 sk_wake_async(sk, 1, POLL_HUP); 2703 else 2704 sk_wake_async(sk, 1, POLL_IN); 2705 } 2706 } 2707 2708 static __inline__ int 2709 tcp_sack_extend(struct tcp_sack_block *sp, u32 seq, u32 end_seq) 2710 { 2711 if (!after(seq, sp->end_seq) && !after(sp->start_seq, end_seq)) { 2712 if (before(seq, sp->start_seq)) 2713 sp->start_seq = seq; 2714 if (after(end_seq, sp->end_seq)) 2715 sp->end_seq = end_seq; 2716 return 1; 2717 } 2718 return 0; 2719 } 2720 2721 static inline void tcp_dsack_set(struct tcp_sock *tp, u32 seq, u32 end_seq) 2722 { 2723 if (tp->rx_opt.sack_ok && sysctl_tcp_dsack) { 2724 if (before(seq, tp->rcv_nxt)) 2725 NET_INC_STATS_BH(LINUX_MIB_TCPDSACKOLDSENT); 2726 else 2727 NET_INC_STATS_BH(LINUX_MIB_TCPDSACKOFOSENT); 2728 2729 tp->rx_opt.dsack = 1; 2730 tp->duplicate_sack[0].start_seq = seq; 2731 tp->duplicate_sack[0].end_seq = end_seq; 2732 tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + 1, 4 - tp->rx_opt.tstamp_ok); 2733 } 2734 } 2735 2736 static inline void tcp_dsack_extend(struct tcp_sock *tp, u32 seq, u32 end_seq) 2737 { 2738 if (!tp->rx_opt.dsack) 2739 tcp_dsack_set(tp, seq, end_seq); 2740 else 2741 tcp_sack_extend(tp->duplicate_sack, seq, end_seq); 2742 } 2743 2744 static void tcp_send_dupack(struct sock *sk, struct sk_buff *skb) 2745 { 2746 struct tcp_sock *tp = tcp_sk(sk); 2747 2748 if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq && 2749 before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) { 2750 NET_INC_STATS_BH(LINUX_MIB_DELAYEDACKLOST); 2751 tcp_enter_quickack_mode(sk); 2752 2753 if (tp->rx_opt.sack_ok && sysctl_tcp_dsack) { 2754 u32 end_seq = TCP_SKB_CB(skb)->end_seq; 2755 2756 if (after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) 2757 end_seq = tp->rcv_nxt; 2758 tcp_dsack_set(tp, TCP_SKB_CB(skb)->seq, end_seq); 2759 } 2760 } 2761 2762 tcp_send_ack(sk); 2763 } 2764 2765 /* These routines update the SACK block as out-of-order packets arrive or 2766 * in-order packets close up the sequence space. 2767 */ 2768 static void tcp_sack_maybe_coalesce(struct tcp_sock *tp) 2769 { 2770 int this_sack; 2771 struct tcp_sack_block *sp = &tp->selective_acks[0]; 2772 struct tcp_sack_block *swalk = sp+1; 2773 2774 /* See if the recent change to the first SACK eats into 2775 * or hits the sequence space of other SACK blocks, if so coalesce. 2776 */ 2777 for (this_sack = 1; this_sack < tp->rx_opt.num_sacks; ) { 2778 if (tcp_sack_extend(sp, swalk->start_seq, swalk->end_seq)) { 2779 int i; 2780 2781 /* Zap SWALK, by moving every further SACK up by one slot. 2782 * Decrease num_sacks. 2783 */ 2784 tp->rx_opt.num_sacks--; 2785 tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + tp->rx_opt.dsack, 4 - tp->rx_opt.tstamp_ok); 2786 for(i=this_sack; i < tp->rx_opt.num_sacks; i++) 2787 sp[i] = sp[i+1]; 2788 continue; 2789 } 2790 this_sack++, swalk++; 2791 } 2792 } 2793 2794 static __inline__ void tcp_sack_swap(struct tcp_sack_block *sack1, struct tcp_sack_block *sack2) 2795 { 2796 __u32 tmp; 2797 2798 tmp = sack1->start_seq; 2799 sack1->start_seq = sack2->start_seq; 2800 sack2->start_seq = tmp; 2801 2802 tmp = sack1->end_seq; 2803 sack1->end_seq = sack2->end_seq; 2804 sack2->end_seq = tmp; 2805 } 2806 2807 static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq) 2808 { 2809 struct tcp_sock *tp = tcp_sk(sk); 2810 struct tcp_sack_block *sp = &tp->selective_acks[0]; 2811 int cur_sacks = tp->rx_opt.num_sacks; 2812 int this_sack; 2813 2814 if (!cur_sacks) 2815 goto new_sack; 2816 2817 for (this_sack=0; this_sack<cur_sacks; this_sack++, sp++) { 2818 if (tcp_sack_extend(sp, seq, end_seq)) { 2819 /* Rotate this_sack to the first one. */ 2820 for (; this_sack>0; this_sack--, sp--) 2821 tcp_sack_swap(sp, sp-1); 2822 if (cur_sacks > 1) 2823 tcp_sack_maybe_coalesce(tp); 2824 return; 2825 } 2826 } 2827 2828 /* Could not find an adjacent existing SACK, build a new one, 2829 * put it at the front, and shift everyone else down. We 2830 * always know there is at least one SACK present already here. 2831 * 2832 * If the sack array is full, forget about the last one. 2833 */ 2834 if (this_sack >= 4) { 2835 this_sack--; 2836 tp->rx_opt.num_sacks--; 2837 sp--; 2838 } 2839 for(; this_sack > 0; this_sack--, sp--) 2840 *sp = *(sp-1); 2841 2842 new_sack: 2843 /* Build the new head SACK, and we're done. */ 2844 sp->start_seq = seq; 2845 sp->end_seq = end_seq; 2846 tp->rx_opt.num_sacks++; 2847 tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + tp->rx_opt.dsack, 4 - tp->rx_opt.tstamp_ok); 2848 } 2849 2850 /* RCV.NXT advances, some SACKs should be eaten. */ 2851 2852 static void tcp_sack_remove(struct tcp_sock *tp) 2853 { 2854 struct tcp_sack_block *sp = &tp->selective_acks[0]; 2855 int num_sacks = tp->rx_opt.num_sacks; 2856 int this_sack; 2857 2858 /* Empty ofo queue, hence, all the SACKs are eaten. Clear. */ 2859 if (skb_queue_empty(&tp->out_of_order_queue)) { 2860 tp->rx_opt.num_sacks = 0; 2861 tp->rx_opt.eff_sacks = tp->rx_opt.dsack; 2862 return; 2863 } 2864 2865 for(this_sack = 0; this_sack < num_sacks; ) { 2866 /* Check if the start of the sack is covered by RCV.NXT. */ 2867 if (!before(tp->rcv_nxt, sp->start_seq)) { 2868 int i; 2869 2870 /* RCV.NXT must cover all the block! */ 2871 BUG_TRAP(!before(tp->rcv_nxt, sp->end_seq)); 2872 2873 /* Zap this SACK, by moving forward any other SACKS. */ 2874 for (i=this_sack+1; i < num_sacks; i++) 2875 tp->selective_acks[i-1] = tp->selective_acks[i]; 2876 num_sacks--; 2877 continue; 2878 } 2879 this_sack++; 2880 sp++; 2881 } 2882 if (num_sacks != tp->rx_opt.num_sacks) { 2883 tp->rx_opt.num_sacks = num_sacks; 2884 tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + tp->rx_opt.dsack, 4 - tp->rx_opt.tstamp_ok); 2885 } 2886 } 2887 2888 /* This one checks to see if we can put data from the 2889 * out_of_order queue into the receive_queue. 2890 */ 2891 static void tcp_ofo_queue(struct sock *sk) 2892 { 2893 struct tcp_sock *tp = tcp_sk(sk); 2894 __u32 dsack_high = tp->rcv_nxt; 2895 struct sk_buff *skb; 2896 2897 while ((skb = skb_peek(&tp->out_of_order_queue)) != NULL) { 2898 if (after(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) 2899 break; 2900 2901 if (before(TCP_SKB_CB(skb)->seq, dsack_high)) { 2902 __u32 dsack = dsack_high; 2903 if (before(TCP_SKB_CB(skb)->end_seq, dsack_high)) 2904 dsack_high = TCP_SKB_CB(skb)->end_seq; 2905 tcp_dsack_extend(tp, TCP_SKB_CB(skb)->seq, dsack); 2906 } 2907 2908 if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) { 2909 SOCK_DEBUG(sk, "ofo packet was already received \n"); 2910 __skb_unlink(skb, &tp->out_of_order_queue); 2911 __kfree_skb(skb); 2912 continue; 2913 } 2914 SOCK_DEBUG(sk, "ofo requeuing : rcv_next %X seq %X - %X\n", 2915 tp->rcv_nxt, TCP_SKB_CB(skb)->seq, 2916 TCP_SKB_CB(skb)->end_seq); 2917 2918 __skb_unlink(skb, &tp->out_of_order_queue); 2919 __skb_queue_tail(&sk->sk_receive_queue, skb); 2920 tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq; 2921 if(skb->h.th->fin) 2922 tcp_fin(skb, sk, skb->h.th); 2923 } 2924 } 2925 2926 static int tcp_prune_queue(struct sock *sk); 2927 2928 static void tcp_data_queue(struct sock *sk, struct sk_buff *skb) 2929 { 2930 struct tcphdr *th = skb->h.th; 2931 struct tcp_sock *tp = tcp_sk(sk); 2932 int eaten = -1; 2933 2934 if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq) 2935 goto drop; 2936 2937 __skb_pull(skb, th->doff*4); 2938 2939 TCP_ECN_accept_cwr(tp, skb); 2940 2941 if (tp->rx_opt.dsack) { 2942 tp->rx_opt.dsack = 0; 2943 tp->rx_opt.eff_sacks = min_t(unsigned int, tp->rx_opt.num_sacks, 2944 4 - tp->rx_opt.tstamp_ok); 2945 } 2946 2947 /* Queue data for delivery to the user. 2948 * Packets in sequence go to the receive queue. 2949 * Out of sequence packets to the out_of_order_queue. 2950 */ 2951 if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt) { 2952 if (tcp_receive_window(tp) == 0) 2953 goto out_of_window; 2954 2955 /* Ok. In sequence. In window. */ 2956 if (tp->ucopy.task == current && 2957 tp->copied_seq == tp->rcv_nxt && tp->ucopy.len && 2958 sock_owned_by_user(sk) && !tp->urg_data) { 2959 int chunk = min_t(unsigned int, skb->len, 2960 tp->ucopy.len); 2961 2962 __set_current_state(TASK_RUNNING); 2963 2964 local_bh_enable(); 2965 if (!skb_copy_datagram_iovec(skb, 0, tp->ucopy.iov, chunk)) { 2966 tp->ucopy.len -= chunk; 2967 tp->copied_seq += chunk; 2968 eaten = (chunk == skb->len && !th->fin); 2969 tcp_rcv_space_adjust(sk); 2970 } 2971 local_bh_disable(); 2972 } 2973 2974 if (eaten <= 0) { 2975 queue_and_out: 2976 if (eaten < 0 && 2977 (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf || 2978 !sk_stream_rmem_schedule(sk, skb))) { 2979 if (tcp_prune_queue(sk) < 0 || 2980 !sk_stream_rmem_schedule(sk, skb)) 2981 goto drop; 2982 } 2983 sk_stream_set_owner_r(skb, sk); 2984 __skb_queue_tail(&sk->sk_receive_queue, skb); 2985 } 2986 tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq; 2987 if(skb->len) 2988 tcp_event_data_recv(sk, tp, skb); 2989 if(th->fin) 2990 tcp_fin(skb, sk, th); 2991 2992 if (!skb_queue_empty(&tp->out_of_order_queue)) { 2993 tcp_ofo_queue(sk); 2994 2995 /* RFC2581. 4.2. SHOULD send immediate ACK, when 2996 * gap in queue is filled. 2997 */ 2998 if (skb_queue_empty(&tp->out_of_order_queue)) 2999 inet_csk(sk)->icsk_ack.pingpong = 0; 3000 } 3001 3002 if (tp->rx_opt.num_sacks) 3003 tcp_sack_remove(tp); 3004 3005 tcp_fast_path_check(sk, tp); 3006 3007 if (eaten > 0) 3008 __kfree_skb(skb); 3009 else if (!sock_flag(sk, SOCK_DEAD)) 3010 sk->sk_data_ready(sk, 0); 3011 return; 3012 } 3013 3014 if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) { 3015 /* A retransmit, 2nd most common case. Force an immediate ack. */ 3016 NET_INC_STATS_BH(LINUX_MIB_DELAYEDACKLOST); 3017 tcp_dsack_set(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq); 3018 3019 out_of_window: 3020 tcp_enter_quickack_mode(sk); 3021 inet_csk_schedule_ack(sk); 3022 drop: 3023 __kfree_skb(skb); 3024 return; 3025 } 3026 3027 /* Out of window. F.e. zero window probe. */ 3028 if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt + tcp_receive_window(tp))) 3029 goto out_of_window; 3030 3031 tcp_enter_quickack_mode(sk); 3032 3033 if (before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) { 3034 /* Partial packet, seq < rcv_next < end_seq */ 3035 SOCK_DEBUG(sk, "partial packet: rcv_next %X seq %X - %X\n", 3036 tp->rcv_nxt, TCP_SKB_CB(skb)->seq, 3037 TCP_SKB_CB(skb)->end_seq); 3038 3039 tcp_dsack_set(tp, TCP_SKB_CB(skb)->seq, tp->rcv_nxt); 3040 3041 /* If window is closed, drop tail of packet. But after 3042 * remembering D-SACK for its head made in previous line. 3043 */ 3044 if (!tcp_receive_window(tp)) 3045 goto out_of_window; 3046 goto queue_and_out; 3047 } 3048 3049 TCP_ECN_check_ce(tp, skb); 3050 3051 if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf || 3052 !sk_stream_rmem_schedule(sk, skb)) { 3053 if (tcp_prune_queue(sk) < 0 || 3054 !sk_stream_rmem_schedule(sk, skb)) 3055 goto drop; 3056 } 3057 3058 /* Disable header prediction. */ 3059 tp->pred_flags = 0; 3060 inet_csk_schedule_ack(sk); 3061 3062 SOCK_DEBUG(sk, "out of order segment: rcv_next %X seq %X - %X\n", 3063 tp->rcv_nxt, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq); 3064 3065 sk_stream_set_owner_r(skb, sk); 3066 3067 if (!skb_peek(&tp->out_of_order_queue)) { 3068 /* Initial out of order segment, build 1 SACK. */ 3069 if (tp->rx_opt.sack_ok) { 3070 tp->rx_opt.num_sacks = 1; 3071 tp->rx_opt.dsack = 0; 3072 tp->rx_opt.eff_sacks = 1; 3073 tp->selective_acks[0].start_seq = TCP_SKB_CB(skb)->seq; 3074 tp->selective_acks[0].end_seq = 3075 TCP_SKB_CB(skb)->end_seq; 3076 } 3077 __skb_queue_head(&tp->out_of_order_queue,skb); 3078 } else { 3079 struct sk_buff *skb1 = tp->out_of_order_queue.prev; 3080 u32 seq = TCP_SKB_CB(skb)->seq; 3081 u32 end_seq = TCP_SKB_CB(skb)->end_seq; 3082 3083 if (seq == TCP_SKB_CB(skb1)->end_seq) { 3084 __skb_append(skb1, skb, &tp->out_of_order_queue); 3085 3086 if (!tp->rx_opt.num_sacks || 3087 tp->selective_acks[0].end_seq != seq) 3088 goto add_sack; 3089 3090 /* Common case: data arrive in order after hole. */ 3091 tp->selective_acks[0].end_seq = end_seq; 3092 return; 3093 } 3094 3095 /* Find place to insert this segment. */ 3096 do { 3097 if (!after(TCP_SKB_CB(skb1)->seq, seq)) 3098 break; 3099 } while ((skb1 = skb1->prev) != 3100 (struct sk_buff*)&tp->out_of_order_queue); 3101 3102 /* Do skb overlap to previous one? */ 3103 if (skb1 != (struct sk_buff*)&tp->out_of_order_queue && 3104 before(seq, TCP_SKB_CB(skb1)->end_seq)) { 3105 if (!after(end_seq, TCP_SKB_CB(skb1)->end_seq)) { 3106 /* All the bits are present. Drop. */ 3107 __kfree_skb(skb); 3108 tcp_dsack_set(tp, seq, end_seq); 3109 goto add_sack; 3110 } 3111 if (after(seq, TCP_SKB_CB(skb1)->seq)) { 3112 /* Partial overlap. */ 3113 tcp_dsack_set(tp, seq, TCP_SKB_CB(skb1)->end_seq); 3114 } else { 3115 skb1 = skb1->prev; 3116 } 3117 } 3118 __skb_insert(skb, skb1, skb1->next, &tp->out_of_order_queue); 3119 3120 /* And clean segments covered by new one as whole. */ 3121 while ((skb1 = skb->next) != 3122 (struct sk_buff*)&tp->out_of_order_queue && 3123 after(end_seq, TCP_SKB_CB(skb1)->seq)) { 3124 if (before(end_seq, TCP_SKB_CB(skb1)->end_seq)) { 3125 tcp_dsack_extend(tp, TCP_SKB_CB(skb1)->seq, end_seq); 3126 break; 3127 } 3128 __skb_unlink(skb1, &tp->out_of_order_queue); 3129 tcp_dsack_extend(tp, TCP_SKB_CB(skb1)->seq, TCP_SKB_CB(skb1)->end_seq); 3130 __kfree_skb(skb1); 3131 } 3132 3133 add_sack: 3134 if (tp->rx_opt.sack_ok) 3135 tcp_sack_new_ofo_skb(sk, seq, end_seq); 3136 } 3137 } 3138 3139 /* Collapse contiguous sequence of skbs head..tail with 3140 * sequence numbers start..end. 3141 * Segments with FIN/SYN are not collapsed (only because this 3142 * simplifies code) 3143 */ 3144 static void 3145 tcp_collapse(struct sock *sk, struct sk_buff_head *list, 3146 struct sk_buff *head, struct sk_buff *tail, 3147 u32 start, u32 end) 3148 { 3149 struct sk_buff *skb; 3150 3151 /* First, check that queue is collapsable and find 3152 * the point where collapsing can be useful. */ 3153 for (skb = head; skb != tail; ) { 3154 /* No new bits? It is possible on ofo queue. */ 3155 if (!before(start, TCP_SKB_CB(skb)->end_seq)) { 3156 struct sk_buff *next = skb->next; 3157 __skb_unlink(skb, list); 3158 __kfree_skb(skb); 3159 NET_INC_STATS_BH(LINUX_MIB_TCPRCVCOLLAPSED); 3160 skb = next; 3161 continue; 3162 } 3163 3164 /* The first skb to collapse is: 3165 * - not SYN/FIN and 3166 * - bloated or contains data before "start" or 3167 * overlaps to the next one. 3168 */ 3169 if (!skb->h.th->syn && !skb->h.th->fin && 3170 (tcp_win_from_space(skb->truesize) > skb->len || 3171 before(TCP_SKB_CB(skb)->seq, start) || 3172 (skb->next != tail && 3173 TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb->next)->seq))) 3174 break; 3175 3176 /* Decided to skip this, advance start seq. */ 3177 start = TCP_SKB_CB(skb)->end_seq; 3178 skb = skb->next; 3179 } 3180 if (skb == tail || skb->h.th->syn || skb->h.th->fin) 3181 return; 3182 3183 while (before(start, end)) { 3184 struct sk_buff *nskb; 3185 int header = skb_headroom(skb); 3186 int copy = SKB_MAX_ORDER(header, 0); 3187 3188 /* Too big header? This can happen with IPv6. */ 3189 if (copy < 0) 3190 return; 3191 if (end-start < copy) 3192 copy = end-start; 3193 nskb = alloc_skb(copy+header, GFP_ATOMIC); 3194 if (!nskb) 3195 return; 3196 skb_reserve(nskb, header); 3197 memcpy(nskb->head, skb->head, header); 3198 nskb->nh.raw = nskb->head + (skb->nh.raw-skb->head); 3199 nskb->h.raw = nskb->head + (skb->h.raw-skb->head); 3200 nskb->mac.raw = nskb->head + (skb->mac.raw-skb->head); 3201 memcpy(nskb->cb, skb->cb, sizeof(skb->cb)); 3202 TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(nskb)->end_seq = start; 3203 __skb_insert(nskb, skb->prev, skb, list); 3204 sk_stream_set_owner_r(nskb, sk); 3205 3206 /* Copy data, releasing collapsed skbs. */ 3207 while (copy > 0) { 3208 int offset = start - TCP_SKB_CB(skb)->seq; 3209 int size = TCP_SKB_CB(skb)->end_seq - start; 3210 3211 if (offset < 0) BUG(); 3212 if (size > 0) { 3213 size = min(copy, size); 3214 if (skb_copy_bits(skb, offset, skb_put(nskb, size), size)) 3215 BUG(); 3216 TCP_SKB_CB(nskb)->end_seq += size; 3217 copy -= size; 3218 start += size; 3219 } 3220 if (!before(start, TCP_SKB_CB(skb)->end_seq)) { 3221 struct sk_buff *next = skb->next; 3222 __skb_unlink(skb, list); 3223 __kfree_skb(skb); 3224 NET_INC_STATS_BH(LINUX_MIB_TCPRCVCOLLAPSED); 3225 skb = next; 3226 if (skb == tail || skb->h.th->syn || skb->h.th->fin) 3227 return; 3228 } 3229 } 3230 } 3231 } 3232 3233 /* Collapse ofo queue. Algorithm: select contiguous sequence of skbs 3234 * and tcp_collapse() them until all the queue is collapsed. 3235 */ 3236 static void tcp_collapse_ofo_queue(struct sock *sk) 3237 { 3238 struct tcp_sock *tp = tcp_sk(sk); 3239 struct sk_buff *skb = skb_peek(&tp->out_of_order_queue); 3240 struct sk_buff *head; 3241 u32 start, end; 3242 3243 if (skb == NULL) 3244 return; 3245 3246 start = TCP_SKB_CB(skb)->seq; 3247 end = TCP_SKB_CB(skb)->end_seq; 3248 head = skb; 3249 3250 for (;;) { 3251 skb = skb->next; 3252 3253 /* Segment is terminated when we see gap or when 3254 * we are at the end of all the queue. */ 3255 if (skb == (struct sk_buff *)&tp->out_of_order_queue || 3256 after(TCP_SKB_CB(skb)->seq, end) || 3257 before(TCP_SKB_CB(skb)->end_seq, start)) { 3258 tcp_collapse(sk, &tp->out_of_order_queue, 3259 head, skb, start, end); 3260 head = skb; 3261 if (skb == (struct sk_buff *)&tp->out_of_order_queue) 3262 break; 3263 /* Start new segment */ 3264 start = TCP_SKB_CB(skb)->seq; 3265 end = TCP_SKB_CB(skb)->end_seq; 3266 } else { 3267 if (before(TCP_SKB_CB(skb)->seq, start)) 3268 start = TCP_SKB_CB(skb)->seq; 3269 if (after(TCP_SKB_CB(skb)->end_seq, end)) 3270 end = TCP_SKB_CB(skb)->end_seq; 3271 } 3272 } 3273 } 3274 3275 /* Reduce allocated memory if we can, trying to get 3276 * the socket within its memory limits again. 3277 * 3278 * Return less than zero if we should start dropping frames 3279 * until the socket owning process reads some of the data 3280 * to stabilize the situation. 3281 */ 3282 static int tcp_prune_queue(struct sock *sk) 3283 { 3284 struct tcp_sock *tp = tcp_sk(sk); 3285 3286 SOCK_DEBUG(sk, "prune_queue: c=%x\n", tp->copied_seq); 3287 3288 NET_INC_STATS_BH(LINUX_MIB_PRUNECALLED); 3289 3290 if (atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf) 3291 tcp_clamp_window(sk, tp); 3292 else if (tcp_memory_pressure) 3293 tp->rcv_ssthresh = min(tp->rcv_ssthresh, 4U * tp->advmss); 3294 3295 tcp_collapse_ofo_queue(sk); 3296 tcp_collapse(sk, &sk->sk_receive_queue, 3297 sk->sk_receive_queue.next, 3298 (struct sk_buff*)&sk->sk_receive_queue, 3299 tp->copied_seq, tp->rcv_nxt); 3300 sk_stream_mem_reclaim(sk); 3301 3302 if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf) 3303 return 0; 3304 3305 /* Collapsing did not help, destructive actions follow. 3306 * This must not ever occur. */ 3307 3308 /* First, purge the out_of_order queue. */ 3309 if (!skb_queue_empty(&tp->out_of_order_queue)) { 3310 NET_INC_STATS_BH(LINUX_MIB_OFOPRUNED); 3311 __skb_queue_purge(&tp->out_of_order_queue); 3312 3313 /* Reset SACK state. A conforming SACK implementation will 3314 * do the same at a timeout based retransmit. When a connection 3315 * is in a sad state like this, we care only about integrity 3316 * of the connection not performance. 3317 */ 3318 if (tp->rx_opt.sack_ok) 3319 tcp_sack_reset(&tp->rx_opt); 3320 sk_stream_mem_reclaim(sk); 3321 } 3322 3323 if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf) 3324 return 0; 3325 3326 /* If we are really being abused, tell the caller to silently 3327 * drop receive data on the floor. It will get retransmitted 3328 * and hopefully then we'll have sufficient space. 3329 */ 3330 NET_INC_STATS_BH(LINUX_MIB_RCVPRUNED); 3331 3332 /* Massive buffer overcommit. */ 3333 tp->pred_flags = 0; 3334 return -1; 3335 } 3336 3337 3338 /* RFC2861, slow part. Adjust cwnd, after it was not full during one rto. 3339 * As additional protections, we do not touch cwnd in retransmission phases, 3340 * and if application hit its sndbuf limit recently. 3341 */ 3342 void tcp_cwnd_application_limited(struct sock *sk) 3343 { 3344 struct tcp_sock *tp = tcp_sk(sk); 3345 3346 if (inet_csk(sk)->icsk_ca_state == TCP_CA_Open && 3347 sk->sk_socket && !test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) { 3348 /* Limited by application or receiver window. */ 3349 u32 win_used = max(tp->snd_cwnd_used, 2U); 3350 if (win_used < tp->snd_cwnd) { 3351 tp->snd_ssthresh = tcp_current_ssthresh(sk); 3352 tp->snd_cwnd = (tp->snd_cwnd + win_used) >> 1; 3353 } 3354 tp->snd_cwnd_used = 0; 3355 } 3356 tp->snd_cwnd_stamp = tcp_time_stamp; 3357 } 3358 3359 static inline int tcp_should_expand_sndbuf(struct sock *sk, struct tcp_sock *tp) 3360 { 3361 /* If the user specified a specific send buffer setting, do 3362 * not modify it. 3363 */ 3364 if (sk->sk_userlocks & SOCK_SNDBUF_LOCK) 3365 return 0; 3366 3367 /* If we are under global TCP memory pressure, do not expand. */ 3368 if (tcp_memory_pressure) 3369 return 0; 3370 3371 /* If we are under soft global TCP memory pressure, do not expand. */ 3372 if (atomic_read(&tcp_memory_allocated) >= sysctl_tcp_mem[0]) 3373 return 0; 3374 3375 /* If we filled the congestion window, do not expand. */ 3376 if (tp->packets_out >= tp->snd_cwnd) 3377 return 0; 3378 3379 return 1; 3380 } 3381 3382 /* When incoming ACK allowed to free some skb from write_queue, 3383 * we remember this event in flag SOCK_QUEUE_SHRUNK and wake up socket 3384 * on the exit from tcp input handler. 3385 * 3386 * PROBLEM: sndbuf expansion does not work well with largesend. 3387 */ 3388 static void tcp_new_space(struct sock *sk) 3389 { 3390 struct tcp_sock *tp = tcp_sk(sk); 3391 3392 if (tcp_should_expand_sndbuf(sk, tp)) { 3393 int sndmem = max_t(u32, tp->rx_opt.mss_clamp, tp->mss_cache) + 3394 MAX_TCP_HEADER + 16 + sizeof(struct sk_buff), 3395 demanded = max_t(unsigned int, tp->snd_cwnd, 3396 tp->reordering + 1); 3397 sndmem *= 2*demanded; 3398 if (sndmem > sk->sk_sndbuf) 3399 sk->sk_sndbuf = min(sndmem, sysctl_tcp_wmem[2]); 3400 tp->snd_cwnd_stamp = tcp_time_stamp; 3401 } 3402 3403 sk->sk_write_space(sk); 3404 } 3405 3406 static inline void tcp_check_space(struct sock *sk) 3407 { 3408 if (sock_flag(sk, SOCK_QUEUE_SHRUNK)) { 3409 sock_reset_flag(sk, SOCK_QUEUE_SHRUNK); 3410 if (sk->sk_socket && 3411 test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) 3412 tcp_new_space(sk); 3413 } 3414 } 3415 3416 static __inline__ void tcp_data_snd_check(struct sock *sk, struct tcp_sock *tp) 3417 { 3418 tcp_push_pending_frames(sk, tp); 3419 tcp_check_space(sk); 3420 } 3421 3422 /* 3423 * Check if sending an ack is needed. 3424 */ 3425 static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible) 3426 { 3427 struct tcp_sock *tp = tcp_sk(sk); 3428 3429 /* More than one full frame received... */ 3430 if (((tp->rcv_nxt - tp->rcv_wup) > inet_csk(sk)->icsk_ack.rcv_mss 3431 /* ... and right edge of window advances far enough. 3432 * (tcp_recvmsg() will send ACK otherwise). Or... 3433 */ 3434 && __tcp_select_window(sk) >= tp->rcv_wnd) || 3435 /* We ACK each frame or... */ 3436 tcp_in_quickack_mode(sk) || 3437 /* We have out of order data. */ 3438 (ofo_possible && 3439 skb_peek(&tp->out_of_order_queue))) { 3440 /* Then ack it now */ 3441 tcp_send_ack(sk); 3442 } else { 3443 /* Else, send delayed ack. */ 3444 tcp_send_delayed_ack(sk); 3445 } 3446 } 3447 3448 static __inline__ void tcp_ack_snd_check(struct sock *sk) 3449 { 3450 if (!inet_csk_ack_scheduled(sk)) { 3451 /* We sent a data segment already. */ 3452 return; 3453 } 3454 __tcp_ack_snd_check(sk, 1); 3455 } 3456 3457 /* 3458 * This routine is only called when we have urgent data 3459 * signalled. Its the 'slow' part of tcp_urg. It could be 3460 * moved inline now as tcp_urg is only called from one 3461 * place. We handle URGent data wrong. We have to - as 3462 * BSD still doesn't use the correction from RFC961. 3463 * For 1003.1g we should support a new option TCP_STDURG to permit 3464 * either form (or just set the sysctl tcp_stdurg). 3465 */ 3466 3467 static void tcp_check_urg(struct sock * sk, struct tcphdr * th) 3468 { 3469 struct tcp_sock *tp = tcp_sk(sk); 3470 u32 ptr = ntohs(th->urg_ptr); 3471 3472 if (ptr && !sysctl_tcp_stdurg) 3473 ptr--; 3474 ptr += ntohl(th->seq); 3475 3476 /* Ignore urgent data that we've already seen and read. */ 3477 if (after(tp->copied_seq, ptr)) 3478 return; 3479 3480 /* Do not replay urg ptr. 3481 * 3482 * NOTE: interesting situation not covered by specs. 3483 * Misbehaving sender may send urg ptr, pointing to segment, 3484 * which we already have in ofo queue. We are not able to fetch 3485 * such data and will stay in TCP_URG_NOTYET until will be eaten 3486 * by recvmsg(). Seems, we are not obliged to handle such wicked 3487 * situations. But it is worth to think about possibility of some 3488 * DoSes using some hypothetical application level deadlock. 3489 */ 3490 if (before(ptr, tp->rcv_nxt)) 3491 return; 3492 3493 /* Do we already have a newer (or duplicate) urgent pointer? */ 3494 if (tp->urg_data && !after(ptr, tp->urg_seq)) 3495 return; 3496 3497 /* Tell the world about our new urgent pointer. */ 3498 sk_send_sigurg(sk); 3499 3500 /* We may be adding urgent data when the last byte read was 3501 * urgent. To do this requires some care. We cannot just ignore 3502 * tp->copied_seq since we would read the last urgent byte again 3503 * as data, nor can we alter copied_seq until this data arrives 3504 * or we break the sematics of SIOCATMARK (and thus sockatmark()) 3505 * 3506 * NOTE. Double Dutch. Rendering to plain English: author of comment 3507 * above did something sort of send("A", MSG_OOB); send("B", MSG_OOB); 3508 * and expect that both A and B disappear from stream. This is _wrong_. 3509 * Though this happens in BSD with high probability, this is occasional. 3510 * Any application relying on this is buggy. Note also, that fix "works" 3511 * only in this artificial test. Insert some normal data between A and B and we will 3512 * decline of BSD again. Verdict: it is better to remove to trap 3513 * buggy users. 3514 */ 3515 if (tp->urg_seq == tp->copied_seq && tp->urg_data && 3516 !sock_flag(sk, SOCK_URGINLINE) && 3517 tp->copied_seq != tp->rcv_nxt) { 3518 struct sk_buff *skb = skb_peek(&sk->sk_receive_queue); 3519 tp->copied_seq++; 3520 if (skb && !before(tp->copied_seq, TCP_SKB_CB(skb)->end_seq)) { 3521 __skb_unlink(skb, &sk->sk_receive_queue); 3522 __kfree_skb(skb); 3523 } 3524 } 3525 3526 tp->urg_data = TCP_URG_NOTYET; 3527 tp->urg_seq = ptr; 3528 3529 /* Disable header prediction. */ 3530 tp->pred_flags = 0; 3531 } 3532 3533 /* This is the 'fast' part of urgent handling. */ 3534 static void tcp_urg(struct sock *sk, struct sk_buff *skb, struct tcphdr *th) 3535 { 3536 struct tcp_sock *tp = tcp_sk(sk); 3537 3538 /* Check if we get a new urgent pointer - normally not. */ 3539 if (th->urg) 3540 tcp_check_urg(sk,th); 3541 3542 /* Do we wait for any urgent data? - normally not... */ 3543 if (tp->urg_data == TCP_URG_NOTYET) { 3544 u32 ptr = tp->urg_seq - ntohl(th->seq) + (th->doff * 4) - 3545 th->syn; 3546 3547 /* Is the urgent pointer pointing into this packet? */ 3548 if (ptr < skb->len) { 3549 u8 tmp; 3550 if (skb_copy_bits(skb, ptr, &tmp, 1)) 3551 BUG(); 3552 tp->urg_data = TCP_URG_VALID | tmp; 3553 if (!sock_flag(sk, SOCK_DEAD)) 3554 sk->sk_data_ready(sk, 0); 3555 } 3556 } 3557 } 3558 3559 static int tcp_copy_to_iovec(struct sock *sk, struct sk_buff *skb, int hlen) 3560 { 3561 struct tcp_sock *tp = tcp_sk(sk); 3562 int chunk = skb->len - hlen; 3563 int err; 3564 3565 local_bh_enable(); 3566 if (skb->ip_summed==CHECKSUM_UNNECESSARY) 3567 err = skb_copy_datagram_iovec(skb, hlen, tp->ucopy.iov, chunk); 3568 else 3569 err = skb_copy_and_csum_datagram_iovec(skb, hlen, 3570 tp->ucopy.iov); 3571 3572 if (!err) { 3573 tp->ucopy.len -= chunk; 3574 tp->copied_seq += chunk; 3575 tcp_rcv_space_adjust(sk); 3576 } 3577 3578 local_bh_disable(); 3579 return err; 3580 } 3581 3582 static int __tcp_checksum_complete_user(struct sock *sk, struct sk_buff *skb) 3583 { 3584 int result; 3585 3586 if (sock_owned_by_user(sk)) { 3587 local_bh_enable(); 3588 result = __tcp_checksum_complete(skb); 3589 local_bh_disable(); 3590 } else { 3591 result = __tcp_checksum_complete(skb); 3592 } 3593 return result; 3594 } 3595 3596 static __inline__ int 3597 tcp_checksum_complete_user(struct sock *sk, struct sk_buff *skb) 3598 { 3599 return skb->ip_summed != CHECKSUM_UNNECESSARY && 3600 __tcp_checksum_complete_user(sk, skb); 3601 } 3602 3603 /* 3604 * TCP receive function for the ESTABLISHED state. 3605 * 3606 * It is split into a fast path and a slow path. The fast path is 3607 * disabled when: 3608 * - A zero window was announced from us - zero window probing 3609 * is only handled properly in the slow path. 3610 * - Out of order segments arrived. 3611 * - Urgent data is expected. 3612 * - There is no buffer space left 3613 * - Unexpected TCP flags/window values/header lengths are received 3614 * (detected by checking the TCP header against pred_flags) 3615 * - Data is sent in both directions. Fast path only supports pure senders 3616 * or pure receivers (this means either the sequence number or the ack 3617 * value must stay constant) 3618 * - Unexpected TCP option. 3619 * 3620 * When these conditions are not satisfied it drops into a standard 3621 * receive procedure patterned after RFC793 to handle all cases. 3622 * The first three cases are guaranteed by proper pred_flags setting, 3623 * the rest is checked inline. Fast processing is turned on in 3624 * tcp_data_queue when everything is OK. 3625 */ 3626 int tcp_rcv_established(struct sock *sk, struct sk_buff *skb, 3627 struct tcphdr *th, unsigned len) 3628 { 3629 struct tcp_sock *tp = tcp_sk(sk); 3630 3631 /* 3632 * Header prediction. 3633 * The code loosely follows the one in the famous 3634 * "30 instruction TCP receive" Van Jacobson mail. 3635 * 3636 * Van's trick is to deposit buffers into socket queue 3637 * on a device interrupt, to call tcp_recv function 3638 * on the receive process context and checksum and copy 3639 * the buffer to user space. smart... 3640 * 3641 * Our current scheme is not silly either but we take the 3642 * extra cost of the net_bh soft interrupt processing... 3643 * We do checksum and copy also but from device to kernel. 3644 */ 3645 3646 tp->rx_opt.saw_tstamp = 0; 3647 3648 /* pred_flags is 0xS?10 << 16 + snd_wnd 3649 * if header_predition is to be made 3650 * 'S' will always be tp->tcp_header_len >> 2 3651 * '?' will be 0 for the fast path, otherwise pred_flags is 0 to 3652 * turn it off (when there are holes in the receive 3653 * space for instance) 3654 * PSH flag is ignored. 3655 */ 3656 3657 if ((tcp_flag_word(th) & TCP_HP_BITS) == tp->pred_flags && 3658 TCP_SKB_CB(skb)->seq == tp->rcv_nxt) { 3659 int tcp_header_len = tp->tcp_header_len; 3660 3661 /* Timestamp header prediction: tcp_header_len 3662 * is automatically equal to th->doff*4 due to pred_flags 3663 * match. 3664 */ 3665 3666 /* Check timestamp */ 3667 if (tcp_header_len == sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) { 3668 __u32 *ptr = (__u32 *)(th + 1); 3669 3670 /* No? Slow path! */ 3671 if (*ptr != ntohl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16) 3672 | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP)) 3673 goto slow_path; 3674 3675 tp->rx_opt.saw_tstamp = 1; 3676 ++ptr; 3677 tp->rx_opt.rcv_tsval = ntohl(*ptr); 3678 ++ptr; 3679 tp->rx_opt.rcv_tsecr = ntohl(*ptr); 3680 3681 /* If PAWS failed, check it more carefully in slow path */ 3682 if ((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) < 0) 3683 goto slow_path; 3684 3685 /* DO NOT update ts_recent here, if checksum fails 3686 * and timestamp was corrupted part, it will result 3687 * in a hung connection since we will drop all 3688 * future packets due to the PAWS test. 3689 */ 3690 } 3691 3692 if (len <= tcp_header_len) { 3693 /* Bulk data transfer: sender */ 3694 if (len == tcp_header_len) { 3695 /* Predicted packet is in window by definition. 3696 * seq == rcv_nxt and rcv_wup <= rcv_nxt. 3697 * Hence, check seq<=rcv_wup reduces to: 3698 */ 3699 if (tcp_header_len == 3700 (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) && 3701 tp->rcv_nxt == tp->rcv_wup) 3702 tcp_store_ts_recent(tp); 3703 3704 tcp_rcv_rtt_measure_ts(sk, skb); 3705 3706 /* We know that such packets are checksummed 3707 * on entry. 3708 */ 3709 tcp_ack(sk, skb, 0); 3710 __kfree_skb(skb); 3711 tcp_data_snd_check(sk, tp); 3712 return 0; 3713 } else { /* Header too small */ 3714 TCP_INC_STATS_BH(TCP_MIB_INERRS); 3715 goto discard; 3716 } 3717 } else { 3718 int eaten = 0; 3719 3720 if (tp->ucopy.task == current && 3721 tp->copied_seq == tp->rcv_nxt && 3722 len - tcp_header_len <= tp->ucopy.len && 3723 sock_owned_by_user(sk)) { 3724 __set_current_state(TASK_RUNNING); 3725 3726 if (!tcp_copy_to_iovec(sk, skb, tcp_header_len)) { 3727 /* Predicted packet is in window by definition. 3728 * seq == rcv_nxt and rcv_wup <= rcv_nxt. 3729 * Hence, check seq<=rcv_wup reduces to: 3730 */ 3731 if (tcp_header_len == 3732 (sizeof(struct tcphdr) + 3733 TCPOLEN_TSTAMP_ALIGNED) && 3734 tp->rcv_nxt == tp->rcv_wup) 3735 tcp_store_ts_recent(tp); 3736 3737 tcp_rcv_rtt_measure_ts(sk, skb); 3738 3739 __skb_pull(skb, tcp_header_len); 3740 tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq; 3741 NET_INC_STATS_BH(LINUX_MIB_TCPHPHITSTOUSER); 3742 eaten = 1; 3743 } 3744 } 3745 if (!eaten) { 3746 if (tcp_checksum_complete_user(sk, skb)) 3747 goto csum_error; 3748 3749 /* Predicted packet is in window by definition. 3750 * seq == rcv_nxt and rcv_wup <= rcv_nxt. 3751 * Hence, check seq<=rcv_wup reduces to: 3752 */ 3753 if (tcp_header_len == 3754 (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) && 3755 tp->rcv_nxt == tp->rcv_wup) 3756 tcp_store_ts_recent(tp); 3757 3758 tcp_rcv_rtt_measure_ts(sk, skb); 3759 3760 if ((int)skb->truesize > sk->sk_forward_alloc) 3761 goto step5; 3762 3763 NET_INC_STATS_BH(LINUX_MIB_TCPHPHITS); 3764 3765 /* Bulk data transfer: receiver */ 3766 __skb_pull(skb,tcp_header_len); 3767 __skb_queue_tail(&sk->sk_receive_queue, skb); 3768 sk_stream_set_owner_r(skb, sk); 3769 tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq; 3770 } 3771 3772 tcp_event_data_recv(sk, tp, skb); 3773 3774 if (TCP_SKB_CB(skb)->ack_seq != tp->snd_una) { 3775 /* Well, only one small jumplet in fast path... */ 3776 tcp_ack(sk, skb, FLAG_DATA); 3777 tcp_data_snd_check(sk, tp); 3778 if (!inet_csk_ack_scheduled(sk)) 3779 goto no_ack; 3780 } 3781 3782 __tcp_ack_snd_check(sk, 0); 3783 no_ack: 3784 if (eaten) 3785 __kfree_skb(skb); 3786 else 3787 sk->sk_data_ready(sk, 0); 3788 return 0; 3789 } 3790 } 3791 3792 slow_path: 3793 if (len < (th->doff<<2) || tcp_checksum_complete_user(sk, skb)) 3794 goto csum_error; 3795 3796 /* 3797 * RFC1323: H1. Apply PAWS check first. 3798 */ 3799 if (tcp_fast_parse_options(skb, th, tp) && tp->rx_opt.saw_tstamp && 3800 tcp_paws_discard(sk, skb)) { 3801 if (!th->rst) { 3802 NET_INC_STATS_BH(LINUX_MIB_PAWSESTABREJECTED); 3803 tcp_send_dupack(sk, skb); 3804 goto discard; 3805 } 3806 /* Resets are accepted even if PAWS failed. 3807 3808 ts_recent update must be made after we are sure 3809 that the packet is in window. 3810 */ 3811 } 3812 3813 /* 3814 * Standard slow path. 3815 */ 3816 3817 if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) { 3818 /* RFC793, page 37: "In all states except SYN-SENT, all reset 3819 * (RST) segments are validated by checking their SEQ-fields." 3820 * And page 69: "If an incoming segment is not acceptable, 3821 * an acknowledgment should be sent in reply (unless the RST bit 3822 * is set, if so drop the segment and return)". 3823 */ 3824 if (!th->rst) 3825 tcp_send_dupack(sk, skb); 3826 goto discard; 3827 } 3828 3829 if(th->rst) { 3830 tcp_reset(sk); 3831 goto discard; 3832 } 3833 3834 tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq); 3835 3836 if (th->syn && !before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) { 3837 TCP_INC_STATS_BH(TCP_MIB_INERRS); 3838 NET_INC_STATS_BH(LINUX_MIB_TCPABORTONSYN); 3839 tcp_reset(sk); 3840 return 1; 3841 } 3842 3843 step5: 3844 if(th->ack) 3845 tcp_ack(sk, skb, FLAG_SLOWPATH); 3846 3847 tcp_rcv_rtt_measure_ts(sk, skb); 3848 3849 /* Process urgent data. */ 3850 tcp_urg(sk, skb, th); 3851 3852 /* step 7: process the segment text */ 3853 tcp_data_queue(sk, skb); 3854 3855 tcp_data_snd_check(sk, tp); 3856 tcp_ack_snd_check(sk); 3857 return 0; 3858 3859 csum_error: 3860 TCP_INC_STATS_BH(TCP_MIB_INERRS); 3861 3862 discard: 3863 __kfree_skb(skb); 3864 return 0; 3865 } 3866 3867 static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb, 3868 struct tcphdr *th, unsigned len) 3869 { 3870 struct tcp_sock *tp = tcp_sk(sk); 3871 int saved_clamp = tp->rx_opt.mss_clamp; 3872 3873 tcp_parse_options(skb, &tp->rx_opt, 0); 3874 3875 if (th->ack) { 3876 struct inet_connection_sock *icsk; 3877 /* rfc793: 3878 * "If the state is SYN-SENT then 3879 * first check the ACK bit 3880 * If the ACK bit is set 3881 * If SEG.ACK =< ISS, or SEG.ACK > SND.NXT, send 3882 * a reset (unless the RST bit is set, if so drop 3883 * the segment and return)" 3884 * 3885 * We do not send data with SYN, so that RFC-correct 3886 * test reduces to: 3887 */ 3888 if (TCP_SKB_CB(skb)->ack_seq != tp->snd_nxt) 3889 goto reset_and_undo; 3890 3891 if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr && 3892 !between(tp->rx_opt.rcv_tsecr, tp->retrans_stamp, 3893 tcp_time_stamp)) { 3894 NET_INC_STATS_BH(LINUX_MIB_PAWSACTIVEREJECTED); 3895 goto reset_and_undo; 3896 } 3897 3898 /* Now ACK is acceptable. 3899 * 3900 * "If the RST bit is set 3901 * If the ACK was acceptable then signal the user "error: 3902 * connection reset", drop the segment, enter CLOSED state, 3903 * delete TCB, and return." 3904 */ 3905 3906 if (th->rst) { 3907 tcp_reset(sk); 3908 goto discard; 3909 } 3910 3911 /* rfc793: 3912 * "fifth, if neither of the SYN or RST bits is set then 3913 * drop the segment and return." 3914 * 3915 * See note below! 3916 * --ANK(990513) 3917 */ 3918 if (!th->syn) 3919 goto discard_and_undo; 3920 3921 /* rfc793: 3922 * "If the SYN bit is on ... 3923 * are acceptable then ... 3924 * (our SYN has been ACKed), change the connection 3925 * state to ESTABLISHED..." 3926 */ 3927 3928 TCP_ECN_rcv_synack(tp, th); 3929 if (tp->ecn_flags&TCP_ECN_OK) 3930 sock_set_flag(sk, SOCK_NO_LARGESEND); 3931 3932 tp->snd_wl1 = TCP_SKB_CB(skb)->seq; 3933 tcp_ack(sk, skb, FLAG_SLOWPATH); 3934 3935 /* Ok.. it's good. Set up sequence numbers and 3936 * move to established. 3937 */ 3938 tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1; 3939 tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1; 3940 3941 /* RFC1323: The window in SYN & SYN/ACK segments is 3942 * never scaled. 3943 */ 3944 tp->snd_wnd = ntohs(th->window); 3945 tcp_init_wl(tp, TCP_SKB_CB(skb)->ack_seq, TCP_SKB_CB(skb)->seq); 3946 3947 if (!tp->rx_opt.wscale_ok) { 3948 tp->rx_opt.snd_wscale = tp->rx_opt.rcv_wscale = 0; 3949 tp->window_clamp = min(tp->window_clamp, 65535U); 3950 } 3951 3952 if (tp->rx_opt.saw_tstamp) { 3953 tp->rx_opt.tstamp_ok = 1; 3954 tp->tcp_header_len = 3955 sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED; 3956 tp->advmss -= TCPOLEN_TSTAMP_ALIGNED; 3957 tcp_store_ts_recent(tp); 3958 } else { 3959 tp->tcp_header_len = sizeof(struct tcphdr); 3960 } 3961 3962 if (tp->rx_opt.sack_ok && sysctl_tcp_fack) 3963 tp->rx_opt.sack_ok |= 2; 3964 3965 tcp_sync_mss(sk, tp->pmtu_cookie); 3966 tcp_initialize_rcv_mss(sk); 3967 3968 /* Remember, tcp_poll() does not lock socket! 3969 * Change state from SYN-SENT only after copied_seq 3970 * is initialized. */ 3971 tp->copied_seq = tp->rcv_nxt; 3972 mb(); 3973 tcp_set_state(sk, TCP_ESTABLISHED); 3974 3975 /* Make sure socket is routed, for correct metrics. */ 3976 tp->af_specific->rebuild_header(sk); 3977 3978 tcp_init_metrics(sk); 3979 3980 tcp_init_congestion_control(sk); 3981 3982 /* Prevent spurious tcp_cwnd_restart() on first data 3983 * packet. 3984 */ 3985 tp->lsndtime = tcp_time_stamp; 3986 3987 tcp_init_buffer_space(sk); 3988 3989 if (sock_flag(sk, SOCK_KEEPOPEN)) 3990 inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tp)); 3991 3992 if (!tp->rx_opt.snd_wscale) 3993 __tcp_fast_path_on(tp, tp->snd_wnd); 3994 else 3995 tp->pred_flags = 0; 3996 3997 if (!sock_flag(sk, SOCK_DEAD)) { 3998 sk->sk_state_change(sk); 3999 sk_wake_async(sk, 0, POLL_OUT); 4000 } 4001 4002 icsk = inet_csk(sk); 4003 4004 if (sk->sk_write_pending || 4005 icsk->icsk_accept_queue.rskq_defer_accept || 4006 icsk->icsk_ack.pingpong) { 4007 /* Save one ACK. Data will be ready after 4008 * several ticks, if write_pending is set. 4009 * 4010 * It may be deleted, but with this feature tcpdumps 4011 * look so _wonderfully_ clever, that I was not able 4012 * to stand against the temptation 8) --ANK 4013 */ 4014 inet_csk_schedule_ack(sk); 4015 icsk->icsk_ack.lrcvtime = tcp_time_stamp; 4016 icsk->icsk_ack.ato = TCP_ATO_MIN; 4017 tcp_incr_quickack(sk); 4018 tcp_enter_quickack_mode(sk); 4019 inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK, 4020 TCP_DELACK_MAX, TCP_RTO_MAX); 4021 4022 discard: 4023 __kfree_skb(skb); 4024 return 0; 4025 } else { 4026 tcp_send_ack(sk); 4027 } 4028 return -1; 4029 } 4030 4031 /* No ACK in the segment */ 4032 4033 if (th->rst) { 4034 /* rfc793: 4035 * "If the RST bit is set 4036 * 4037 * Otherwise (no ACK) drop the segment and return." 4038 */ 4039 4040 goto discard_and_undo; 4041 } 4042 4043 /* PAWS check. */ 4044 if (tp->rx_opt.ts_recent_stamp && tp->rx_opt.saw_tstamp && tcp_paws_check(&tp->rx_opt, 0)) 4045 goto discard_and_undo; 4046 4047 if (th->syn) { 4048 /* We see SYN without ACK. It is attempt of 4049 * simultaneous connect with crossed SYNs. 4050 * Particularly, it can be connect to self. 4051 */ 4052 tcp_set_state(sk, TCP_SYN_RECV); 4053 4054 if (tp->rx_opt.saw_tstamp) { 4055 tp->rx_opt.tstamp_ok = 1; 4056 tcp_store_ts_recent(tp); 4057 tp->tcp_header_len = 4058 sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED; 4059 } else { 4060 tp->tcp_header_len = sizeof(struct tcphdr); 4061 } 4062 4063 tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1; 4064 tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1; 4065 4066 /* RFC1323: The window in SYN & SYN/ACK segments is 4067 * never scaled. 4068 */ 4069 tp->snd_wnd = ntohs(th->window); 4070 tp->snd_wl1 = TCP_SKB_CB(skb)->seq; 4071 tp->max_window = tp->snd_wnd; 4072 4073 TCP_ECN_rcv_syn(tp, th); 4074 if (tp->ecn_flags&TCP_ECN_OK) 4075 sock_set_flag(sk, SOCK_NO_LARGESEND); 4076 4077 tcp_sync_mss(sk, tp->pmtu_cookie); 4078 tcp_initialize_rcv_mss(sk); 4079 4080 4081 tcp_send_synack(sk); 4082 #if 0 4083 /* Note, we could accept data and URG from this segment. 4084 * There are no obstacles to make this. 4085 * 4086 * However, if we ignore data in ACKless segments sometimes, 4087 * we have no reasons to accept it sometimes. 4088 * Also, seems the code doing it in step6 of tcp_rcv_state_process 4089 * is not flawless. So, discard packet for sanity. 4090 * Uncomment this return to process the data. 4091 */ 4092 return -1; 4093 #else 4094 goto discard; 4095 #endif 4096 } 4097 /* "fifth, if neither of the SYN or RST bits is set then 4098 * drop the segment and return." 4099 */ 4100 4101 discard_and_undo: 4102 tcp_clear_options(&tp->rx_opt); 4103 tp->rx_opt.mss_clamp = saved_clamp; 4104 goto discard; 4105 4106 reset_and_undo: 4107 tcp_clear_options(&tp->rx_opt); 4108 tp->rx_opt.mss_clamp = saved_clamp; 4109 return 1; 4110 } 4111 4112 4113 /* 4114 * This function implements the receiving procedure of RFC 793 for 4115 * all states except ESTABLISHED and TIME_WAIT. 4116 * It's called from both tcp_v4_rcv and tcp_v6_rcv and should be 4117 * address independent. 4118 */ 4119 4120 int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb, 4121 struct tcphdr *th, unsigned len) 4122 { 4123 struct tcp_sock *tp = tcp_sk(sk); 4124 int queued = 0; 4125 4126 tp->rx_opt.saw_tstamp = 0; 4127 4128 switch (sk->sk_state) { 4129 case TCP_CLOSE: 4130 goto discard; 4131 4132 case TCP_LISTEN: 4133 if(th->ack) 4134 return 1; 4135 4136 if(th->rst) 4137 goto discard; 4138 4139 if(th->syn) { 4140 if(tp->af_specific->conn_request(sk, skb) < 0) 4141 return 1; 4142 4143 /* Now we have several options: In theory there is 4144 * nothing else in the frame. KA9Q has an option to 4145 * send data with the syn, BSD accepts data with the 4146 * syn up to the [to be] advertised window and 4147 * Solaris 2.1 gives you a protocol error. For now 4148 * we just ignore it, that fits the spec precisely 4149 * and avoids incompatibilities. It would be nice in 4150 * future to drop through and process the data. 4151 * 4152 * Now that TTCP is starting to be used we ought to 4153 * queue this data. 4154 * But, this leaves one open to an easy denial of 4155 * service attack, and SYN cookies can't defend 4156 * against this problem. So, we drop the data 4157 * in the interest of security over speed. 4158 */ 4159 goto discard; 4160 } 4161 goto discard; 4162 4163 case TCP_SYN_SENT: 4164 queued = tcp_rcv_synsent_state_process(sk, skb, th, len); 4165 if (queued >= 0) 4166 return queued; 4167 4168 /* Do step6 onward by hand. */ 4169 tcp_urg(sk, skb, th); 4170 __kfree_skb(skb); 4171 tcp_data_snd_check(sk, tp); 4172 return 0; 4173 } 4174 4175 if (tcp_fast_parse_options(skb, th, tp) && tp->rx_opt.saw_tstamp && 4176 tcp_paws_discard(sk, skb)) { 4177 if (!th->rst) { 4178 NET_INC_STATS_BH(LINUX_MIB_PAWSESTABREJECTED); 4179 tcp_send_dupack(sk, skb); 4180 goto discard; 4181 } 4182 /* Reset is accepted even if it did not pass PAWS. */ 4183 } 4184 4185 /* step 1: check sequence number */ 4186 if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) { 4187 if (!th->rst) 4188 tcp_send_dupack(sk, skb); 4189 goto discard; 4190 } 4191 4192 /* step 2: check RST bit */ 4193 if(th->rst) { 4194 tcp_reset(sk); 4195 goto discard; 4196 } 4197 4198 tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq); 4199 4200 /* step 3: check security and precedence [ignored] */ 4201 4202 /* step 4: 4203 * 4204 * Check for a SYN in window. 4205 */ 4206 if (th->syn && !before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) { 4207 NET_INC_STATS_BH(LINUX_MIB_TCPABORTONSYN); 4208 tcp_reset(sk); 4209 return 1; 4210 } 4211 4212 /* step 5: check the ACK field */ 4213 if (th->ack) { 4214 int acceptable = tcp_ack(sk, skb, FLAG_SLOWPATH); 4215 4216 switch(sk->sk_state) { 4217 case TCP_SYN_RECV: 4218 if (acceptable) { 4219 tp->copied_seq = tp->rcv_nxt; 4220 mb(); 4221 tcp_set_state(sk, TCP_ESTABLISHED); 4222 sk->sk_state_change(sk); 4223 4224 /* Note, that this wakeup is only for marginal 4225 * crossed SYN case. Passively open sockets 4226 * are not waked up, because sk->sk_sleep == 4227 * NULL and sk->sk_socket == NULL. 4228 */ 4229 if (sk->sk_socket) { 4230 sk_wake_async(sk,0,POLL_OUT); 4231 } 4232 4233 tp->snd_una = TCP_SKB_CB(skb)->ack_seq; 4234 tp->snd_wnd = ntohs(th->window) << 4235 tp->rx_opt.snd_wscale; 4236 tcp_init_wl(tp, TCP_SKB_CB(skb)->ack_seq, 4237 TCP_SKB_CB(skb)->seq); 4238 4239 /* tcp_ack considers this ACK as duplicate 4240 * and does not calculate rtt. 4241 * Fix it at least with timestamps. 4242 */ 4243 if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr && 4244 !tp->srtt) 4245 tcp_ack_saw_tstamp(sk, NULL, 0); 4246 4247 if (tp->rx_opt.tstamp_ok) 4248 tp->advmss -= TCPOLEN_TSTAMP_ALIGNED; 4249 4250 /* Make sure socket is routed, for 4251 * correct metrics. 4252 */ 4253 tp->af_specific->rebuild_header(sk); 4254 4255 tcp_init_metrics(sk); 4256 4257 tcp_init_congestion_control(sk); 4258 4259 /* Prevent spurious tcp_cwnd_restart() on 4260 * first data packet. 4261 */ 4262 tp->lsndtime = tcp_time_stamp; 4263 4264 tcp_initialize_rcv_mss(sk); 4265 tcp_init_buffer_space(sk); 4266 tcp_fast_path_on(tp); 4267 } else { 4268 return 1; 4269 } 4270 break; 4271 4272 case TCP_FIN_WAIT1: 4273 if (tp->snd_una == tp->write_seq) { 4274 tcp_set_state(sk, TCP_FIN_WAIT2); 4275 sk->sk_shutdown |= SEND_SHUTDOWN; 4276 dst_confirm(sk->sk_dst_cache); 4277 4278 if (!sock_flag(sk, SOCK_DEAD)) 4279 /* Wake up lingering close() */ 4280 sk->sk_state_change(sk); 4281 else { 4282 int tmo; 4283 4284 if (tp->linger2 < 0 || 4285 (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq && 4286 after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt))) { 4287 tcp_done(sk); 4288 NET_INC_STATS_BH(LINUX_MIB_TCPABORTONDATA); 4289 return 1; 4290 } 4291 4292 tmo = tcp_fin_time(sk); 4293 if (tmo > TCP_TIMEWAIT_LEN) { 4294 inet_csk_reset_keepalive_timer(sk, tmo - TCP_TIMEWAIT_LEN); 4295 } else if (th->fin || sock_owned_by_user(sk)) { 4296 /* Bad case. We could lose such FIN otherwise. 4297 * It is not a big problem, but it looks confusing 4298 * and not so rare event. We still can lose it now, 4299 * if it spins in bh_lock_sock(), but it is really 4300 * marginal case. 4301 */ 4302 inet_csk_reset_keepalive_timer(sk, tmo); 4303 } else { 4304 tcp_time_wait(sk, TCP_FIN_WAIT2, tmo); 4305 goto discard; 4306 } 4307 } 4308 } 4309 break; 4310 4311 case TCP_CLOSING: 4312 if (tp->snd_una == tp->write_seq) { 4313 tcp_time_wait(sk, TCP_TIME_WAIT, 0); 4314 goto discard; 4315 } 4316 break; 4317 4318 case TCP_LAST_ACK: 4319 if (tp->snd_una == tp->write_seq) { 4320 tcp_update_metrics(sk); 4321 tcp_done(sk); 4322 goto discard; 4323 } 4324 break; 4325 } 4326 } else 4327 goto discard; 4328 4329 /* step 6: check the URG bit */ 4330 tcp_urg(sk, skb, th); 4331 4332 /* step 7: process the segment text */ 4333 switch (sk->sk_state) { 4334 case TCP_CLOSE_WAIT: 4335 case TCP_CLOSING: 4336 case TCP_LAST_ACK: 4337 if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) 4338 break; 4339 case TCP_FIN_WAIT1: 4340 case TCP_FIN_WAIT2: 4341 /* RFC 793 says to queue data in these states, 4342 * RFC 1122 says we MUST send a reset. 4343 * BSD 4.4 also does reset. 4344 */ 4345 if (sk->sk_shutdown & RCV_SHUTDOWN) { 4346 if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq && 4347 after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) { 4348 NET_INC_STATS_BH(LINUX_MIB_TCPABORTONDATA); 4349 tcp_reset(sk); 4350 return 1; 4351 } 4352 } 4353 /* Fall through */ 4354 case TCP_ESTABLISHED: 4355 tcp_data_queue(sk, skb); 4356 queued = 1; 4357 break; 4358 } 4359 4360 /* tcp_data could move socket to TIME-WAIT */ 4361 if (sk->sk_state != TCP_CLOSE) { 4362 tcp_data_snd_check(sk, tp); 4363 tcp_ack_snd_check(sk); 4364 } 4365 4366 if (!queued) { 4367 discard: 4368 __kfree_skb(skb); 4369 } 4370 return 0; 4371 } 4372 4373 EXPORT_SYMBOL(sysctl_tcp_ecn); 4374 EXPORT_SYMBOL(sysctl_tcp_reordering); 4375 EXPORT_SYMBOL(tcp_parse_options); 4376 EXPORT_SYMBOL(tcp_rcv_established); 4377 EXPORT_SYMBOL(tcp_rcv_state_process); 4378