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_minisocks.c,v 1.15 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 #include <linux/config.h> 24 #include <linux/mm.h> 25 #include <linux/module.h> 26 #include <linux/sysctl.h> 27 #include <linux/workqueue.h> 28 #include <net/tcp.h> 29 #include <net/inet_common.h> 30 #include <net/xfrm.h> 31 32 #ifdef CONFIG_SYSCTL 33 #define SYNC_INIT 0 /* let the user enable it */ 34 #else 35 #define SYNC_INIT 1 36 #endif 37 38 int sysctl_tcp_syncookies = SYNC_INIT; 39 int sysctl_tcp_abort_on_overflow; 40 41 struct inet_timewait_death_row tcp_death_row = { 42 .sysctl_max_tw_buckets = NR_FILE * 2, 43 .period = TCP_TIMEWAIT_LEN / INET_TWDR_TWKILL_SLOTS, 44 .death_lock = SPIN_LOCK_UNLOCKED, 45 .hashinfo = &tcp_hashinfo, 46 .tw_timer = TIMER_INITIALIZER(inet_twdr_hangman, 0, 47 (unsigned long)&tcp_death_row), 48 .twkill_work = __WORK_INITIALIZER(tcp_death_row.twkill_work, 49 inet_twdr_twkill_work, 50 &tcp_death_row), 51 /* Short-time timewait calendar */ 52 53 .twcal_hand = -1, 54 .twcal_timer = TIMER_INITIALIZER(inet_twdr_twcal_tick, 0, 55 (unsigned long)&tcp_death_row), 56 }; 57 58 EXPORT_SYMBOL_GPL(tcp_death_row); 59 60 static __inline__ int tcp_in_window(u32 seq, u32 end_seq, u32 s_win, u32 e_win) 61 { 62 if (seq == s_win) 63 return 1; 64 if (after(end_seq, s_win) && before(seq, e_win)) 65 return 1; 66 return (seq == e_win && seq == end_seq); 67 } 68 69 /* 70 * * Main purpose of TIME-WAIT state is to close connection gracefully, 71 * when one of ends sits in LAST-ACK or CLOSING retransmitting FIN 72 * (and, probably, tail of data) and one or more our ACKs are lost. 73 * * What is TIME-WAIT timeout? It is associated with maximal packet 74 * lifetime in the internet, which results in wrong conclusion, that 75 * it is set to catch "old duplicate segments" wandering out of their path. 76 * It is not quite correct. This timeout is calculated so that it exceeds 77 * maximal retransmission timeout enough to allow to lose one (or more) 78 * segments sent by peer and our ACKs. This time may be calculated from RTO. 79 * * When TIME-WAIT socket receives RST, it means that another end 80 * finally closed and we are allowed to kill TIME-WAIT too. 81 * * Second purpose of TIME-WAIT is catching old duplicate segments. 82 * Well, certainly it is pure paranoia, but if we load TIME-WAIT 83 * with this semantics, we MUST NOT kill TIME-WAIT state with RSTs. 84 * * If we invented some more clever way to catch duplicates 85 * (f.e. based on PAWS), we could truncate TIME-WAIT to several RTOs. 86 * 87 * The algorithm below is based on FORMAL INTERPRETATION of RFCs. 88 * When you compare it to RFCs, please, read section SEGMENT ARRIVES 89 * from the very beginning. 90 * 91 * NOTE. With recycling (and later with fin-wait-2) TW bucket 92 * is _not_ stateless. It means, that strictly speaking we must 93 * spinlock it. I do not want! Well, probability of misbehaviour 94 * is ridiculously low and, seems, we could use some mb() tricks 95 * to avoid misread sequence numbers, states etc. --ANK 96 */ 97 enum tcp_tw_status 98 tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb, 99 const struct tcphdr *th) 100 { 101 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw); 102 struct tcp_options_received tmp_opt; 103 int paws_reject = 0; 104 105 tmp_opt.saw_tstamp = 0; 106 if (th->doff > (sizeof(*th) >> 2) && tcptw->tw_ts_recent_stamp) { 107 tcp_parse_options(skb, &tmp_opt, 0); 108 109 if (tmp_opt.saw_tstamp) { 110 tmp_opt.ts_recent = tcptw->tw_ts_recent; 111 tmp_opt.ts_recent_stamp = tcptw->tw_ts_recent_stamp; 112 paws_reject = tcp_paws_check(&tmp_opt, th->rst); 113 } 114 } 115 116 if (tw->tw_substate == TCP_FIN_WAIT2) { 117 /* Just repeat all the checks of tcp_rcv_state_process() */ 118 119 /* Out of window, send ACK */ 120 if (paws_reject || 121 !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq, 122 tcptw->tw_rcv_nxt, 123 tcptw->tw_rcv_nxt + tcptw->tw_rcv_wnd)) 124 return TCP_TW_ACK; 125 126 if (th->rst) 127 goto kill; 128 129 if (th->syn && !before(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt)) 130 goto kill_with_rst; 131 132 /* Dup ACK? */ 133 if (!after(TCP_SKB_CB(skb)->end_seq, tcptw->tw_rcv_nxt) || 134 TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq) { 135 inet_twsk_put(tw); 136 return TCP_TW_SUCCESS; 137 } 138 139 /* New data or FIN. If new data arrive after half-duplex close, 140 * reset. 141 */ 142 if (!th->fin || 143 TCP_SKB_CB(skb)->end_seq != tcptw->tw_rcv_nxt + 1) { 144 kill_with_rst: 145 inet_twsk_deschedule(tw, &tcp_death_row); 146 inet_twsk_put(tw); 147 return TCP_TW_RST; 148 } 149 150 /* FIN arrived, enter true time-wait state. */ 151 tw->tw_substate = TCP_TIME_WAIT; 152 tcptw->tw_rcv_nxt = TCP_SKB_CB(skb)->end_seq; 153 if (tmp_opt.saw_tstamp) { 154 tcptw->tw_ts_recent_stamp = xtime.tv_sec; 155 tcptw->tw_ts_recent = tmp_opt.rcv_tsval; 156 } 157 158 /* I am shamed, but failed to make it more elegant. 159 * Yes, it is direct reference to IP, which is impossible 160 * to generalize to IPv6. Taking into account that IPv6 161 * do not understand recycling in any case, it not 162 * a big problem in practice. --ANK */ 163 if (tw->tw_family == AF_INET && 164 tcp_death_row.sysctl_tw_recycle && tcptw->tw_ts_recent_stamp && 165 tcp_v4_tw_remember_stamp(tw)) 166 inet_twsk_schedule(tw, &tcp_death_row, tw->tw_timeout, 167 TCP_TIMEWAIT_LEN); 168 else 169 inet_twsk_schedule(tw, &tcp_death_row, TCP_TIMEWAIT_LEN, 170 TCP_TIMEWAIT_LEN); 171 return TCP_TW_ACK; 172 } 173 174 /* 175 * Now real TIME-WAIT state. 176 * 177 * RFC 1122: 178 * "When a connection is [...] on TIME-WAIT state [...] 179 * [a TCP] MAY accept a new SYN from the remote TCP to 180 * reopen the connection directly, if it: 181 * 182 * (1) assigns its initial sequence number for the new 183 * connection to be larger than the largest sequence 184 * number it used on the previous connection incarnation, 185 * and 186 * 187 * (2) returns to TIME-WAIT state if the SYN turns out 188 * to be an old duplicate". 189 */ 190 191 if (!paws_reject && 192 (TCP_SKB_CB(skb)->seq == tcptw->tw_rcv_nxt && 193 (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq || th->rst))) { 194 /* In window segment, it may be only reset or bare ack. */ 195 196 if (th->rst) { 197 /* This is TIME_WAIT assassination, in two flavors. 198 * Oh well... nobody has a sufficient solution to this 199 * protocol bug yet. 200 */ 201 if (sysctl_tcp_rfc1337 == 0) { 202 kill: 203 inet_twsk_deschedule(tw, &tcp_death_row); 204 inet_twsk_put(tw); 205 return TCP_TW_SUCCESS; 206 } 207 } 208 inet_twsk_schedule(tw, &tcp_death_row, TCP_TIMEWAIT_LEN, 209 TCP_TIMEWAIT_LEN); 210 211 if (tmp_opt.saw_tstamp) { 212 tcptw->tw_ts_recent = tmp_opt.rcv_tsval; 213 tcptw->tw_ts_recent_stamp = xtime.tv_sec; 214 } 215 216 inet_twsk_put(tw); 217 return TCP_TW_SUCCESS; 218 } 219 220 /* Out of window segment. 221 222 All the segments are ACKed immediately. 223 224 The only exception is new SYN. We accept it, if it is 225 not old duplicate and we are not in danger to be killed 226 by delayed old duplicates. RFC check is that it has 227 newer sequence number works at rates <40Mbit/sec. 228 However, if paws works, it is reliable AND even more, 229 we even may relax silly seq space cutoff. 230 231 RED-PEN: we violate main RFC requirement, if this SYN will appear 232 old duplicate (i.e. we receive RST in reply to SYN-ACK), 233 we must return socket to time-wait state. It is not good, 234 but not fatal yet. 235 */ 236 237 if (th->syn && !th->rst && !th->ack && !paws_reject && 238 (after(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt) || 239 (tmp_opt.saw_tstamp && 240 (s32)(tcptw->tw_ts_recent - tmp_opt.rcv_tsval) < 0))) { 241 u32 isn = tcptw->tw_snd_nxt + 65535 + 2; 242 if (isn == 0) 243 isn++; 244 TCP_SKB_CB(skb)->when = isn; 245 return TCP_TW_SYN; 246 } 247 248 if (paws_reject) 249 NET_INC_STATS_BH(LINUX_MIB_PAWSESTABREJECTED); 250 251 if(!th->rst) { 252 /* In this case we must reset the TIMEWAIT timer. 253 * 254 * If it is ACKless SYN it may be both old duplicate 255 * and new good SYN with random sequence number <rcv_nxt. 256 * Do not reschedule in the last case. 257 */ 258 if (paws_reject || th->ack) 259 inet_twsk_schedule(tw, &tcp_death_row, TCP_TIMEWAIT_LEN, 260 TCP_TIMEWAIT_LEN); 261 262 /* Send ACK. Note, we do not put the bucket, 263 * it will be released by caller. 264 */ 265 return TCP_TW_ACK; 266 } 267 inet_twsk_put(tw); 268 return TCP_TW_SUCCESS; 269 } 270 271 /* 272 * Move a socket to time-wait or dead fin-wait-2 state. 273 */ 274 void tcp_time_wait(struct sock *sk, int state, int timeo) 275 { 276 struct inet_timewait_sock *tw = NULL; 277 const struct inet_connection_sock *icsk = inet_csk(sk); 278 const struct tcp_sock *tp = tcp_sk(sk); 279 int recycle_ok = 0; 280 281 if (tcp_death_row.sysctl_tw_recycle && tp->rx_opt.ts_recent_stamp) 282 recycle_ok = icsk->icsk_af_ops->remember_stamp(sk); 283 284 if (tcp_death_row.tw_count < tcp_death_row.sysctl_max_tw_buckets) 285 tw = inet_twsk_alloc(sk, state); 286 287 if (tw != NULL) { 288 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw); 289 const int rto = (icsk->icsk_rto << 2) - (icsk->icsk_rto >> 1); 290 291 tw->tw_rcv_wscale = tp->rx_opt.rcv_wscale; 292 tcptw->tw_rcv_nxt = tp->rcv_nxt; 293 tcptw->tw_snd_nxt = tp->snd_nxt; 294 tcptw->tw_rcv_wnd = tcp_receive_window(tp); 295 tcptw->tw_ts_recent = tp->rx_opt.ts_recent; 296 tcptw->tw_ts_recent_stamp = tp->rx_opt.ts_recent_stamp; 297 298 #if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE) 299 if (tw->tw_family == PF_INET6) { 300 struct ipv6_pinfo *np = inet6_sk(sk); 301 struct inet6_timewait_sock *tw6; 302 303 tw->tw_ipv6_offset = inet6_tw_offset(sk->sk_prot); 304 tw6 = inet6_twsk((struct sock *)tw); 305 ipv6_addr_copy(&tw6->tw_v6_daddr, &np->daddr); 306 ipv6_addr_copy(&tw6->tw_v6_rcv_saddr, &np->rcv_saddr); 307 tw->tw_ipv6only = np->ipv6only; 308 } 309 #endif 310 /* Linkage updates. */ 311 __inet_twsk_hashdance(tw, sk, &tcp_hashinfo); 312 313 /* Get the TIME_WAIT timeout firing. */ 314 if (timeo < rto) 315 timeo = rto; 316 317 if (recycle_ok) { 318 tw->tw_timeout = rto; 319 } else { 320 tw->tw_timeout = TCP_TIMEWAIT_LEN; 321 if (state == TCP_TIME_WAIT) 322 timeo = TCP_TIMEWAIT_LEN; 323 } 324 325 inet_twsk_schedule(tw, &tcp_death_row, timeo, 326 TCP_TIMEWAIT_LEN); 327 inet_twsk_put(tw); 328 } else { 329 /* Sorry, if we're out of memory, just CLOSE this 330 * socket up. We've got bigger problems than 331 * non-graceful socket closings. 332 */ 333 if (net_ratelimit()) 334 printk(KERN_INFO "TCP: time wait bucket table overflow\n"); 335 } 336 337 tcp_update_metrics(sk); 338 tcp_done(sk); 339 } 340 341 /* This is not only more efficient than what we used to do, it eliminates 342 * a lot of code duplication between IPv4/IPv6 SYN recv processing. -DaveM 343 * 344 * Actually, we could lots of memory writes here. tp of listening 345 * socket contains all necessary default parameters. 346 */ 347 struct sock *tcp_create_openreq_child(struct sock *sk, struct request_sock *req, struct sk_buff *skb) 348 { 349 struct sock *newsk = inet_csk_clone(sk, req, GFP_ATOMIC); 350 351 if (newsk != NULL) { 352 const struct inet_request_sock *ireq = inet_rsk(req); 353 struct tcp_request_sock *treq = tcp_rsk(req); 354 struct inet_connection_sock *newicsk = inet_csk(sk); 355 struct tcp_sock *newtp; 356 357 /* Now setup tcp_sock */ 358 newtp = tcp_sk(newsk); 359 newtp->pred_flags = 0; 360 newtp->rcv_nxt = treq->rcv_isn + 1; 361 newtp->snd_nxt = newtp->snd_una = newtp->snd_sml = treq->snt_isn + 1; 362 363 tcp_prequeue_init(newtp); 364 365 tcp_init_wl(newtp, treq->snt_isn, treq->rcv_isn); 366 367 newtp->srtt = 0; 368 newtp->mdev = TCP_TIMEOUT_INIT; 369 newicsk->icsk_rto = TCP_TIMEOUT_INIT; 370 371 newtp->packets_out = 0; 372 newtp->left_out = 0; 373 newtp->retrans_out = 0; 374 newtp->sacked_out = 0; 375 newtp->fackets_out = 0; 376 newtp->snd_ssthresh = 0x7fffffff; 377 378 /* So many TCP implementations out there (incorrectly) count the 379 * initial SYN frame in their delayed-ACK and congestion control 380 * algorithms that we must have the following bandaid to talk 381 * efficiently to them. -DaveM 382 */ 383 newtp->snd_cwnd = 2; 384 newtp->snd_cwnd_cnt = 0; 385 newtp->bytes_acked = 0; 386 387 newtp->frto_counter = 0; 388 newtp->frto_highmark = 0; 389 390 newicsk->icsk_ca_ops = &tcp_init_congestion_ops; 391 392 tcp_set_ca_state(newsk, TCP_CA_Open); 393 tcp_init_xmit_timers(newsk); 394 skb_queue_head_init(&newtp->out_of_order_queue); 395 newtp->rcv_wup = treq->rcv_isn + 1; 396 newtp->write_seq = treq->snt_isn + 1; 397 newtp->pushed_seq = newtp->write_seq; 398 newtp->copied_seq = treq->rcv_isn + 1; 399 400 newtp->rx_opt.saw_tstamp = 0; 401 402 newtp->rx_opt.dsack = 0; 403 newtp->rx_opt.eff_sacks = 0; 404 405 newtp->rx_opt.num_sacks = 0; 406 newtp->urg_data = 0; 407 408 if (sock_flag(newsk, SOCK_KEEPOPEN)) 409 inet_csk_reset_keepalive_timer(newsk, 410 keepalive_time_when(newtp)); 411 412 newtp->rx_opt.tstamp_ok = ireq->tstamp_ok; 413 if((newtp->rx_opt.sack_ok = ireq->sack_ok) != 0) { 414 if (sysctl_tcp_fack) 415 newtp->rx_opt.sack_ok |= 2; 416 } 417 newtp->window_clamp = req->window_clamp; 418 newtp->rcv_ssthresh = req->rcv_wnd; 419 newtp->rcv_wnd = req->rcv_wnd; 420 newtp->rx_opt.wscale_ok = ireq->wscale_ok; 421 if (newtp->rx_opt.wscale_ok) { 422 newtp->rx_opt.snd_wscale = ireq->snd_wscale; 423 newtp->rx_opt.rcv_wscale = ireq->rcv_wscale; 424 } else { 425 newtp->rx_opt.snd_wscale = newtp->rx_opt.rcv_wscale = 0; 426 newtp->window_clamp = min(newtp->window_clamp, 65535U); 427 } 428 newtp->snd_wnd = ntohs(skb->h.th->window) << newtp->rx_opt.snd_wscale; 429 newtp->max_window = newtp->snd_wnd; 430 431 if (newtp->rx_opt.tstamp_ok) { 432 newtp->rx_opt.ts_recent = req->ts_recent; 433 newtp->rx_opt.ts_recent_stamp = xtime.tv_sec; 434 newtp->tcp_header_len = sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED; 435 } else { 436 newtp->rx_opt.ts_recent_stamp = 0; 437 newtp->tcp_header_len = sizeof(struct tcphdr); 438 } 439 if (skb->len >= TCP_MIN_RCVMSS+newtp->tcp_header_len) 440 newicsk->icsk_ack.last_seg_size = skb->len - newtp->tcp_header_len; 441 newtp->rx_opt.mss_clamp = req->mss; 442 TCP_ECN_openreq_child(newtp, req); 443 if (newtp->ecn_flags&TCP_ECN_OK) 444 sock_set_flag(newsk, SOCK_NO_LARGESEND); 445 446 TCP_INC_STATS_BH(TCP_MIB_PASSIVEOPENS); 447 } 448 return newsk; 449 } 450 451 /* 452 * Process an incoming packet for SYN_RECV sockets represented 453 * as a request_sock. 454 */ 455 456 struct sock *tcp_check_req(struct sock *sk,struct sk_buff *skb, 457 struct request_sock *req, 458 struct request_sock **prev) 459 { 460 struct tcphdr *th = skb->h.th; 461 u32 flg = tcp_flag_word(th) & (TCP_FLAG_RST|TCP_FLAG_SYN|TCP_FLAG_ACK); 462 int paws_reject = 0; 463 struct tcp_options_received tmp_opt; 464 struct sock *child; 465 466 tmp_opt.saw_tstamp = 0; 467 if (th->doff > (sizeof(struct tcphdr)>>2)) { 468 tcp_parse_options(skb, &tmp_opt, 0); 469 470 if (tmp_opt.saw_tstamp) { 471 tmp_opt.ts_recent = req->ts_recent; 472 /* We do not store true stamp, but it is not required, 473 * it can be estimated (approximately) 474 * from another data. 475 */ 476 tmp_opt.ts_recent_stamp = xtime.tv_sec - ((TCP_TIMEOUT_INIT/HZ)<<req->retrans); 477 paws_reject = tcp_paws_check(&tmp_opt, th->rst); 478 } 479 } 480 481 /* Check for pure retransmitted SYN. */ 482 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn && 483 flg == TCP_FLAG_SYN && 484 !paws_reject) { 485 /* 486 * RFC793 draws (Incorrectly! It was fixed in RFC1122) 487 * this case on figure 6 and figure 8, but formal 488 * protocol description says NOTHING. 489 * To be more exact, it says that we should send ACK, 490 * because this segment (at least, if it has no data) 491 * is out of window. 492 * 493 * CONCLUSION: RFC793 (even with RFC1122) DOES NOT 494 * describe SYN-RECV state. All the description 495 * is wrong, we cannot believe to it and should 496 * rely only on common sense and implementation 497 * experience. 498 * 499 * Enforce "SYN-ACK" according to figure 8, figure 6 500 * of RFC793, fixed by RFC1122. 501 */ 502 req->rsk_ops->rtx_syn_ack(sk, req, NULL); 503 return NULL; 504 } 505 506 /* Further reproduces section "SEGMENT ARRIVES" 507 for state SYN-RECEIVED of RFC793. 508 It is broken, however, it does not work only 509 when SYNs are crossed. 510 511 You would think that SYN crossing is impossible here, since 512 we should have a SYN_SENT socket (from connect()) on our end, 513 but this is not true if the crossed SYNs were sent to both 514 ends by a malicious third party. We must defend against this, 515 and to do that we first verify the ACK (as per RFC793, page 516 36) and reset if it is invalid. Is this a true full defense? 517 To convince ourselves, let us consider a way in which the ACK 518 test can still pass in this 'malicious crossed SYNs' case. 519 Malicious sender sends identical SYNs (and thus identical sequence 520 numbers) to both A and B: 521 522 A: gets SYN, seq=7 523 B: gets SYN, seq=7 524 525 By our good fortune, both A and B select the same initial 526 send sequence number of seven :-) 527 528 A: sends SYN|ACK, seq=7, ack_seq=8 529 B: sends SYN|ACK, seq=7, ack_seq=8 530 531 So we are now A eating this SYN|ACK, ACK test passes. So 532 does sequence test, SYN is truncated, and thus we consider 533 it a bare ACK. 534 535 If icsk->icsk_accept_queue.rskq_defer_accept, we silently drop this 536 bare ACK. Otherwise, we create an established connection. Both 537 ends (listening sockets) accept the new incoming connection and try 538 to talk to each other. 8-) 539 540 Note: This case is both harmless, and rare. Possibility is about the 541 same as us discovering intelligent life on another plant tomorrow. 542 543 But generally, we should (RFC lies!) to accept ACK 544 from SYNACK both here and in tcp_rcv_state_process(). 545 tcp_rcv_state_process() does not, hence, we do not too. 546 547 Note that the case is absolutely generic: 548 we cannot optimize anything here without 549 violating protocol. All the checks must be made 550 before attempt to create socket. 551 */ 552 553 /* RFC793 page 36: "If the connection is in any non-synchronized state ... 554 * and the incoming segment acknowledges something not yet 555 * sent (the segment carries an unacceptable ACK) ... 556 * a reset is sent." 557 * 558 * Invalid ACK: reset will be sent by listening socket 559 */ 560 if ((flg & TCP_FLAG_ACK) && 561 (TCP_SKB_CB(skb)->ack_seq != tcp_rsk(req)->snt_isn + 1)) 562 return sk; 563 564 /* Also, it would be not so bad idea to check rcv_tsecr, which 565 * is essentially ACK extension and too early or too late values 566 * should cause reset in unsynchronized states. 567 */ 568 569 /* RFC793: "first check sequence number". */ 570 571 if (paws_reject || !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq, 572 tcp_rsk(req)->rcv_isn + 1, tcp_rsk(req)->rcv_isn + 1 + req->rcv_wnd)) { 573 /* Out of window: send ACK and drop. */ 574 if (!(flg & TCP_FLAG_RST)) 575 req->rsk_ops->send_ack(skb, req); 576 if (paws_reject) 577 NET_INC_STATS_BH(LINUX_MIB_PAWSESTABREJECTED); 578 return NULL; 579 } 580 581 /* In sequence, PAWS is OK. */ 582 583 if (tmp_opt.saw_tstamp && !after(TCP_SKB_CB(skb)->seq, tcp_rsk(req)->rcv_isn + 1)) 584 req->ts_recent = tmp_opt.rcv_tsval; 585 586 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn) { 587 /* Truncate SYN, it is out of window starting 588 at tcp_rsk(req)->rcv_isn + 1. */ 589 flg &= ~TCP_FLAG_SYN; 590 } 591 592 /* RFC793: "second check the RST bit" and 593 * "fourth, check the SYN bit" 594 */ 595 if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN)) 596 goto embryonic_reset; 597 598 /* ACK sequence verified above, just make sure ACK is 599 * set. If ACK not set, just silently drop the packet. 600 */ 601 if (!(flg & TCP_FLAG_ACK)) 602 return NULL; 603 604 /* If TCP_DEFER_ACCEPT is set, drop bare ACK. */ 605 if (inet_csk(sk)->icsk_accept_queue.rskq_defer_accept && 606 TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) { 607 inet_rsk(req)->acked = 1; 608 return NULL; 609 } 610 611 /* OK, ACK is valid, create big socket and 612 * feed this segment to it. It will repeat all 613 * the tests. THIS SEGMENT MUST MOVE SOCKET TO 614 * ESTABLISHED STATE. If it will be dropped after 615 * socket is created, wait for troubles. 616 */ 617 child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, 618 req, NULL); 619 if (child == NULL) 620 goto listen_overflow; 621 622 inet_csk_reqsk_queue_unlink(sk, req, prev); 623 inet_csk_reqsk_queue_removed(sk, req); 624 625 inet_csk_reqsk_queue_add(sk, req, child); 626 return child; 627 628 listen_overflow: 629 if (!sysctl_tcp_abort_on_overflow) { 630 inet_rsk(req)->acked = 1; 631 return NULL; 632 } 633 634 embryonic_reset: 635 NET_INC_STATS_BH(LINUX_MIB_EMBRYONICRSTS); 636 if (!(flg & TCP_FLAG_RST)) 637 req->rsk_ops->send_reset(skb); 638 639 inet_csk_reqsk_queue_drop(sk, req, prev); 640 return NULL; 641 } 642 643 /* 644 * Queue segment on the new socket if the new socket is active, 645 * otherwise we just shortcircuit this and continue with 646 * the new socket. 647 */ 648 649 int tcp_child_process(struct sock *parent, struct sock *child, 650 struct sk_buff *skb) 651 { 652 int ret = 0; 653 int state = child->sk_state; 654 655 if (!sock_owned_by_user(child)) { 656 ret = tcp_rcv_state_process(child, skb, skb->h.th, skb->len); 657 658 /* Wakeup parent, send SIGIO */ 659 if (state == TCP_SYN_RECV && child->sk_state != state) 660 parent->sk_data_ready(parent, 0); 661 } else { 662 /* Alas, it is possible again, because we do lookup 663 * in main socket hash table and lock on listening 664 * socket does not protect us more. 665 */ 666 sk_add_backlog(child, skb); 667 } 668 669 bh_unlock_sock(child); 670 sock_put(child); 671 return ret; 672 } 673 674 EXPORT_SYMBOL(tcp_check_req); 675 EXPORT_SYMBOL(tcp_child_process); 676 EXPORT_SYMBOL(tcp_create_openreq_child); 677 EXPORT_SYMBOL(tcp_timewait_state_process); 678