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 undertsnad 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 assasination, 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 tcp_sock *tp = tcp_sk(sk); 278 int recycle_ok = 0; 279 280 if (tcp_death_row.sysctl_tw_recycle && tp->rx_opt.ts_recent_stamp) 281 recycle_ok = tp->af_specific->remember_stamp(sk); 282 283 if (tcp_death_row.tw_count < tcp_death_row.sysctl_max_tw_buckets) 284 tw = inet_twsk_alloc(sk, state); 285 286 if (tw != NULL) { 287 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw); 288 const struct inet_connection_sock *icsk = inet_csk(sk); 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 tcp6_timewait_sock *tcp6tw = tcp6_twsk((struct sock *)tw); 302 303 ipv6_addr_copy(&tcp6tw->tw_v6_daddr, &np->daddr); 304 ipv6_addr_copy(&tcp6tw->tw_v6_rcv_saddr, &np->rcv_saddr); 305 tw->tw_ipv6only = np->ipv6only; 306 } 307 #endif 308 /* Linkage updates. */ 309 __inet_twsk_hashdance(tw, sk, &tcp_hashinfo); 310 311 /* Get the TIME_WAIT timeout firing. */ 312 if (timeo < rto) 313 timeo = rto; 314 315 if (recycle_ok) { 316 tw->tw_timeout = rto; 317 } else { 318 tw->tw_timeout = TCP_TIMEWAIT_LEN; 319 if (state == TCP_TIME_WAIT) 320 timeo = TCP_TIMEWAIT_LEN; 321 } 322 323 inet_twsk_schedule(tw, &tcp_death_row, timeo, 324 TCP_TIMEWAIT_LEN); 325 inet_twsk_put(tw); 326 } else { 327 /* Sorry, if we're out of memory, just CLOSE this 328 * socket up. We've got bigger problems than 329 * non-graceful socket closings. 330 */ 331 if (net_ratelimit()) 332 printk(KERN_INFO "TCP: time wait bucket table overflow\n"); 333 } 334 335 tcp_update_metrics(sk); 336 tcp_done(sk); 337 } 338 339 /* This is not only more efficient than what we used to do, it eliminates 340 * a lot of code duplication between IPv4/IPv6 SYN recv processing. -DaveM 341 * 342 * Actually, we could lots of memory writes here. tp of listening 343 * socket contains all necessary default parameters. 344 */ 345 struct sock *tcp_create_openreq_child(struct sock *sk, struct request_sock *req, struct sk_buff *skb) 346 { 347 struct sock *newsk = inet_csk_clone(sk, req, GFP_ATOMIC); 348 349 if (newsk != NULL) { 350 const struct inet_request_sock *ireq = inet_rsk(req); 351 struct tcp_request_sock *treq = tcp_rsk(req); 352 struct inet_connection_sock *newicsk = inet_csk(sk); 353 struct tcp_sock *newtp; 354 355 /* Now setup tcp_sock */ 356 newtp = tcp_sk(newsk); 357 newtp->pred_flags = 0; 358 newtp->rcv_nxt = treq->rcv_isn + 1; 359 newtp->snd_nxt = newtp->snd_una = newtp->snd_sml = treq->snt_isn + 1; 360 361 tcp_prequeue_init(newtp); 362 363 tcp_init_wl(newtp, treq->snt_isn, treq->rcv_isn); 364 365 newtp->srtt = 0; 366 newtp->mdev = TCP_TIMEOUT_INIT; 367 newicsk->icsk_rto = TCP_TIMEOUT_INIT; 368 369 newtp->packets_out = 0; 370 newtp->left_out = 0; 371 newtp->retrans_out = 0; 372 newtp->sacked_out = 0; 373 newtp->fackets_out = 0; 374 newtp->snd_ssthresh = 0x7fffffff; 375 376 /* So many TCP implementations out there (incorrectly) count the 377 * initial SYN frame in their delayed-ACK and congestion control 378 * algorithms that we must have the following bandaid to talk 379 * efficiently to them. -DaveM 380 */ 381 newtp->snd_cwnd = 2; 382 newtp->snd_cwnd_cnt = 0; 383 384 newtp->frto_counter = 0; 385 newtp->frto_highmark = 0; 386 387 newicsk->icsk_ca_ops = &tcp_reno; 388 389 tcp_set_ca_state(newsk, TCP_CA_Open); 390 tcp_init_xmit_timers(newsk); 391 skb_queue_head_init(&newtp->out_of_order_queue); 392 newtp->rcv_wup = treq->rcv_isn + 1; 393 newtp->write_seq = treq->snt_isn + 1; 394 newtp->pushed_seq = newtp->write_seq; 395 newtp->copied_seq = treq->rcv_isn + 1; 396 397 newtp->rx_opt.saw_tstamp = 0; 398 399 newtp->rx_opt.dsack = 0; 400 newtp->rx_opt.eff_sacks = 0; 401 402 newtp->rx_opt.num_sacks = 0; 403 newtp->urg_data = 0; 404 405 if (sock_flag(newsk, SOCK_KEEPOPEN)) 406 inet_csk_reset_keepalive_timer(newsk, 407 keepalive_time_when(newtp)); 408 409 newtp->rx_opt.tstamp_ok = ireq->tstamp_ok; 410 if((newtp->rx_opt.sack_ok = ireq->sack_ok) != 0) { 411 if (sysctl_tcp_fack) 412 newtp->rx_opt.sack_ok |= 2; 413 } 414 newtp->window_clamp = req->window_clamp; 415 newtp->rcv_ssthresh = req->rcv_wnd; 416 newtp->rcv_wnd = req->rcv_wnd; 417 newtp->rx_opt.wscale_ok = ireq->wscale_ok; 418 if (newtp->rx_opt.wscale_ok) { 419 newtp->rx_opt.snd_wscale = ireq->snd_wscale; 420 newtp->rx_opt.rcv_wscale = ireq->rcv_wscale; 421 } else { 422 newtp->rx_opt.snd_wscale = newtp->rx_opt.rcv_wscale = 0; 423 newtp->window_clamp = min(newtp->window_clamp, 65535U); 424 } 425 newtp->snd_wnd = ntohs(skb->h.th->window) << newtp->rx_opt.snd_wscale; 426 newtp->max_window = newtp->snd_wnd; 427 428 if (newtp->rx_opt.tstamp_ok) { 429 newtp->rx_opt.ts_recent = req->ts_recent; 430 newtp->rx_opt.ts_recent_stamp = xtime.tv_sec; 431 newtp->tcp_header_len = sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED; 432 } else { 433 newtp->rx_opt.ts_recent_stamp = 0; 434 newtp->tcp_header_len = sizeof(struct tcphdr); 435 } 436 if (skb->len >= TCP_MIN_RCVMSS+newtp->tcp_header_len) 437 newicsk->icsk_ack.last_seg_size = skb->len - newtp->tcp_header_len; 438 newtp->rx_opt.mss_clamp = req->mss; 439 TCP_ECN_openreq_child(newtp, req); 440 if (newtp->ecn_flags&TCP_ECN_OK) 441 sock_set_flag(newsk, SOCK_NO_LARGESEND); 442 443 TCP_INC_STATS_BH(TCP_MIB_PASSIVEOPENS); 444 } 445 return newsk; 446 } 447 448 /* 449 * Process an incoming packet for SYN_RECV sockets represented 450 * as a request_sock. 451 */ 452 453 struct sock *tcp_check_req(struct sock *sk,struct sk_buff *skb, 454 struct request_sock *req, 455 struct request_sock **prev) 456 { 457 struct tcphdr *th = skb->h.th; 458 struct tcp_sock *tp = tcp_sk(sk); 459 u32 flg = tcp_flag_word(th) & (TCP_FLAG_RST|TCP_FLAG_SYN|TCP_FLAG_ACK); 460 int paws_reject = 0; 461 struct tcp_options_received tmp_opt; 462 struct sock *child; 463 464 tmp_opt.saw_tstamp = 0; 465 if (th->doff > (sizeof(struct tcphdr)>>2)) { 466 tcp_parse_options(skb, &tmp_opt, 0); 467 468 if (tmp_opt.saw_tstamp) { 469 tmp_opt.ts_recent = req->ts_recent; 470 /* We do not store true stamp, but it is not required, 471 * it can be estimated (approximately) 472 * from another data. 473 */ 474 tmp_opt.ts_recent_stamp = xtime.tv_sec - ((TCP_TIMEOUT_INIT/HZ)<<req->retrans); 475 paws_reject = tcp_paws_check(&tmp_opt, th->rst); 476 } 477 } 478 479 /* Check for pure retransmitted SYN. */ 480 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn && 481 flg == TCP_FLAG_SYN && 482 !paws_reject) { 483 /* 484 * RFC793 draws (Incorrectly! It was fixed in RFC1122) 485 * this case on figure 6 and figure 8, but formal 486 * protocol description says NOTHING. 487 * To be more exact, it says that we should send ACK, 488 * because this segment (at least, if it has no data) 489 * is out of window. 490 * 491 * CONCLUSION: RFC793 (even with RFC1122) DOES NOT 492 * describe SYN-RECV state. All the description 493 * is wrong, we cannot believe to it and should 494 * rely only on common sense and implementation 495 * experience. 496 * 497 * Enforce "SYN-ACK" according to figure 8, figure 6 498 * of RFC793, fixed by RFC1122. 499 */ 500 req->rsk_ops->rtx_syn_ack(sk, req, NULL); 501 return NULL; 502 } 503 504 /* Further reproduces section "SEGMENT ARRIVES" 505 for state SYN-RECEIVED of RFC793. 506 It is broken, however, it does not work only 507 when SYNs are crossed. 508 509 You would think that SYN crossing is impossible here, since 510 we should have a SYN_SENT socket (from connect()) on our end, 511 but this is not true if the crossed SYNs were sent to both 512 ends by a malicious third party. We must defend against this, 513 and to do that we first verify the ACK (as per RFC793, page 514 36) and reset if it is invalid. Is this a true full defense? 515 To convince ourselves, let us consider a way in which the ACK 516 test can still pass in this 'malicious crossed SYNs' case. 517 Malicious sender sends identical SYNs (and thus identical sequence 518 numbers) to both A and B: 519 520 A: gets SYN, seq=7 521 B: gets SYN, seq=7 522 523 By our good fortune, both A and B select the same initial 524 send sequence number of seven :-) 525 526 A: sends SYN|ACK, seq=7, ack_seq=8 527 B: sends SYN|ACK, seq=7, ack_seq=8 528 529 So we are now A eating this SYN|ACK, ACK test passes. So 530 does sequence test, SYN is truncated, and thus we consider 531 it a bare ACK. 532 533 If icsk->icsk_accept_queue.rskq_defer_accept, we silently drop this 534 bare ACK. Otherwise, we create an established connection. Both 535 ends (listening sockets) accept the new incoming connection and try 536 to talk to each other. 8-) 537 538 Note: This case is both harmless, and rare. Possibility is about the 539 same as us discovering intelligent life on another plant tomorrow. 540 541 But generally, we should (RFC lies!) to accept ACK 542 from SYNACK both here and in tcp_rcv_state_process(). 543 tcp_rcv_state_process() does not, hence, we do not too. 544 545 Note that the case is absolutely generic: 546 we cannot optimize anything here without 547 violating protocol. All the checks must be made 548 before attempt to create socket. 549 */ 550 551 /* RFC793 page 36: "If the connection is in any non-synchronized state ... 552 * and the incoming segment acknowledges something not yet 553 * sent (the segment carries an unaccaptable ACK) ... 554 * a reset is sent." 555 * 556 * Invalid ACK: reset will be sent by listening socket 557 */ 558 if ((flg & TCP_FLAG_ACK) && 559 (TCP_SKB_CB(skb)->ack_seq != tcp_rsk(req)->snt_isn + 1)) 560 return sk; 561 562 /* Also, it would be not so bad idea to check rcv_tsecr, which 563 * is essentially ACK extension and too early or too late values 564 * should cause reset in unsynchronized states. 565 */ 566 567 /* RFC793: "first check sequence number". */ 568 569 if (paws_reject || !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq, 570 tcp_rsk(req)->rcv_isn + 1, tcp_rsk(req)->rcv_isn + 1 + req->rcv_wnd)) { 571 /* Out of window: send ACK and drop. */ 572 if (!(flg & TCP_FLAG_RST)) 573 req->rsk_ops->send_ack(skb, req); 574 if (paws_reject) 575 NET_INC_STATS_BH(LINUX_MIB_PAWSESTABREJECTED); 576 return NULL; 577 } 578 579 /* In sequence, PAWS is OK. */ 580 581 if (tmp_opt.saw_tstamp && !after(TCP_SKB_CB(skb)->seq, tcp_rsk(req)->rcv_isn + 1)) 582 req->ts_recent = tmp_opt.rcv_tsval; 583 584 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn) { 585 /* Truncate SYN, it is out of window starting 586 at tcp_rsk(req)->rcv_isn + 1. */ 587 flg &= ~TCP_FLAG_SYN; 588 } 589 590 /* RFC793: "second check the RST bit" and 591 * "fourth, check the SYN bit" 592 */ 593 if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN)) 594 goto embryonic_reset; 595 596 /* ACK sequence verified above, just make sure ACK is 597 * set. If ACK not set, just silently drop the packet. 598 */ 599 if (!(flg & TCP_FLAG_ACK)) 600 return NULL; 601 602 /* If TCP_DEFER_ACCEPT is set, drop bare ACK. */ 603 if (inet_csk(sk)->icsk_accept_queue.rskq_defer_accept && 604 TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) { 605 inet_rsk(req)->acked = 1; 606 return NULL; 607 } 608 609 /* OK, ACK is valid, create big socket and 610 * feed this segment to it. It will repeat all 611 * the tests. THIS SEGMENT MUST MOVE SOCKET TO 612 * ESTABLISHED STATE. If it will be dropped after 613 * socket is created, wait for troubles. 614 */ 615 child = tp->af_specific->syn_recv_sock(sk, skb, req, NULL); 616 if (child == NULL) 617 goto listen_overflow; 618 619 inet_csk_reqsk_queue_unlink(sk, req, prev); 620 inet_csk_reqsk_queue_removed(sk, req); 621 622 inet_csk_reqsk_queue_add(sk, req, child); 623 return child; 624 625 listen_overflow: 626 if (!sysctl_tcp_abort_on_overflow) { 627 inet_rsk(req)->acked = 1; 628 return NULL; 629 } 630 631 embryonic_reset: 632 NET_INC_STATS_BH(LINUX_MIB_EMBRYONICRSTS); 633 if (!(flg & TCP_FLAG_RST)) 634 req->rsk_ops->send_reset(skb); 635 636 inet_csk_reqsk_queue_drop(sk, req, prev); 637 return NULL; 638 } 639 640 /* 641 * Queue segment on the new socket if the new socket is active, 642 * otherwise we just shortcircuit this and continue with 643 * the new socket. 644 */ 645 646 int tcp_child_process(struct sock *parent, struct sock *child, 647 struct sk_buff *skb) 648 { 649 int ret = 0; 650 int state = child->sk_state; 651 652 if (!sock_owned_by_user(child)) { 653 ret = tcp_rcv_state_process(child, skb, skb->h.th, skb->len); 654 655 /* Wakeup parent, send SIGIO */ 656 if (state == TCP_SYN_RECV && child->sk_state != state) 657 parent->sk_data_ready(parent, 0); 658 } else { 659 /* Alas, it is possible again, because we do lookup 660 * in main socket hash table and lock on listening 661 * socket does not protect us more. 662 */ 663 sk_add_backlog(child, skb); 664 } 665 666 bh_unlock_sock(child); 667 sock_put(child); 668 return ret; 669 } 670 671 EXPORT_SYMBOL(tcp_check_req); 672 EXPORT_SYMBOL(tcp_child_process); 673 EXPORT_SYMBOL(tcp_create_openreq_child); 674 EXPORT_SYMBOL(tcp_timewait_state_process); 675