1 /* 2 * INET An implementation of the TCP/IP protocol suite for the LINUX 3 * operating system. INET is implemented using the BSD Socket 4 * interface as the means of communication with the user level. 5 * 6 * Implementation of the Transmission Control Protocol(TCP). 7 * 8 * Authors: Ross Biro 9 * Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG> 10 * Mark Evans, <evansmp@uhura.aston.ac.uk> 11 * Corey Minyard <wf-rch!minyard@relay.EU.net> 12 * Florian La Roche, <flla@stud.uni-sb.de> 13 * Charles Hedrick, <hedrick@klinzhai.rutgers.edu> 14 * Linus Torvalds, <torvalds@cs.helsinki.fi> 15 * Alan Cox, <gw4pts@gw4pts.ampr.org> 16 * Matthew Dillon, <dillon@apollo.west.oic.com> 17 * Arnt Gulbrandsen, <agulbra@nvg.unit.no> 18 * Jorge Cwik, <jorge@laser.satlink.net> 19 */ 20 21 #include <linux/mm.h> 22 #include <linux/module.h> 23 #include <linux/slab.h> 24 #include <linux/sysctl.h> 25 #include <linux/workqueue.h> 26 #include <linux/static_key.h> 27 #include <net/tcp.h> 28 #include <net/inet_common.h> 29 #include <net/xfrm.h> 30 #include <net/busy_poll.h> 31 32 static bool tcp_in_window(u32 seq, u32 end_seq, u32 s_win, u32 e_win) 33 { 34 if (seq == s_win) 35 return true; 36 if (after(end_seq, s_win) && before(seq, e_win)) 37 return true; 38 return seq == e_win && seq == end_seq; 39 } 40 41 static enum tcp_tw_status 42 tcp_timewait_check_oow_rate_limit(struct inet_timewait_sock *tw, 43 const struct sk_buff *skb, int mib_idx) 44 { 45 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw); 46 47 if (!tcp_oow_rate_limited(twsk_net(tw), skb, mib_idx, 48 &tcptw->tw_last_oow_ack_time)) { 49 /* Send ACK. Note, we do not put the bucket, 50 * it will be released by caller. 51 */ 52 return TCP_TW_ACK; 53 } 54 55 /* We are rate-limiting, so just release the tw sock and drop skb. */ 56 inet_twsk_put(tw); 57 return TCP_TW_SUCCESS; 58 } 59 60 /* 61 * * Main purpose of TIME-WAIT state is to close connection gracefully, 62 * when one of ends sits in LAST-ACK or CLOSING retransmitting FIN 63 * (and, probably, tail of data) and one or more our ACKs are lost. 64 * * What is TIME-WAIT timeout? It is associated with maximal packet 65 * lifetime in the internet, which results in wrong conclusion, that 66 * it is set to catch "old duplicate segments" wandering out of their path. 67 * It is not quite correct. This timeout is calculated so that it exceeds 68 * maximal retransmission timeout enough to allow to lose one (or more) 69 * segments sent by peer and our ACKs. This time may be calculated from RTO. 70 * * When TIME-WAIT socket receives RST, it means that another end 71 * finally closed and we are allowed to kill TIME-WAIT too. 72 * * Second purpose of TIME-WAIT is catching old duplicate segments. 73 * Well, certainly it is pure paranoia, but if we load TIME-WAIT 74 * with this semantics, we MUST NOT kill TIME-WAIT state with RSTs. 75 * * If we invented some more clever way to catch duplicates 76 * (f.e. based on PAWS), we could truncate TIME-WAIT to several RTOs. 77 * 78 * The algorithm below is based on FORMAL INTERPRETATION of RFCs. 79 * When you compare it to RFCs, please, read section SEGMENT ARRIVES 80 * from the very beginning. 81 * 82 * NOTE. With recycling (and later with fin-wait-2) TW bucket 83 * is _not_ stateless. It means, that strictly speaking we must 84 * spinlock it. I do not want! Well, probability of misbehaviour 85 * is ridiculously low and, seems, we could use some mb() tricks 86 * to avoid misread sequence numbers, states etc. --ANK 87 * 88 * We don't need to initialize tmp_out.sack_ok as we don't use the results 89 */ 90 enum tcp_tw_status 91 tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb, 92 const struct tcphdr *th) 93 { 94 struct tcp_options_received tmp_opt; 95 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw); 96 bool paws_reject = false; 97 98 tmp_opt.saw_tstamp = 0; 99 if (th->doff > (sizeof(*th) >> 2) && tcptw->tw_ts_recent_stamp) { 100 tcp_parse_options(twsk_net(tw), skb, &tmp_opt, 0, NULL); 101 102 if (tmp_opt.saw_tstamp) { 103 if (tmp_opt.rcv_tsecr) 104 tmp_opt.rcv_tsecr -= tcptw->tw_ts_offset; 105 tmp_opt.ts_recent = tcptw->tw_ts_recent; 106 tmp_opt.ts_recent_stamp = tcptw->tw_ts_recent_stamp; 107 paws_reject = tcp_paws_reject(&tmp_opt, th->rst); 108 } 109 } 110 111 if (tw->tw_substate == TCP_FIN_WAIT2) { 112 /* Just repeat all the checks of tcp_rcv_state_process() */ 113 114 /* Out of window, send ACK */ 115 if (paws_reject || 116 !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq, 117 tcptw->tw_rcv_nxt, 118 tcptw->tw_rcv_nxt + tcptw->tw_rcv_wnd)) 119 return tcp_timewait_check_oow_rate_limit( 120 tw, skb, LINUX_MIB_TCPACKSKIPPEDFINWAIT2); 121 122 if (th->rst) 123 goto kill; 124 125 if (th->syn && !before(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt)) 126 return TCP_TW_RST; 127 128 /* Dup ACK? */ 129 if (!th->ack || 130 !after(TCP_SKB_CB(skb)->end_seq, tcptw->tw_rcv_nxt) || 131 TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq) { 132 inet_twsk_put(tw); 133 return TCP_TW_SUCCESS; 134 } 135 136 /* New data or FIN. If new data arrive after half-duplex close, 137 * reset. 138 */ 139 if (!th->fin || 140 TCP_SKB_CB(skb)->end_seq != tcptw->tw_rcv_nxt + 1) 141 return TCP_TW_RST; 142 143 /* FIN arrived, enter true time-wait state. */ 144 tw->tw_substate = TCP_TIME_WAIT; 145 tcptw->tw_rcv_nxt = TCP_SKB_CB(skb)->end_seq; 146 if (tmp_opt.saw_tstamp) { 147 tcptw->tw_ts_recent_stamp = get_seconds(); 148 tcptw->tw_ts_recent = tmp_opt.rcv_tsval; 149 } 150 151 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN); 152 return TCP_TW_ACK; 153 } 154 155 /* 156 * Now real TIME-WAIT state. 157 * 158 * RFC 1122: 159 * "When a connection is [...] on TIME-WAIT state [...] 160 * [a TCP] MAY accept a new SYN from the remote TCP to 161 * reopen the connection directly, if it: 162 * 163 * (1) assigns its initial sequence number for the new 164 * connection to be larger than the largest sequence 165 * number it used on the previous connection incarnation, 166 * and 167 * 168 * (2) returns to TIME-WAIT state if the SYN turns out 169 * to be an old duplicate". 170 */ 171 172 if (!paws_reject && 173 (TCP_SKB_CB(skb)->seq == tcptw->tw_rcv_nxt && 174 (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq || th->rst))) { 175 /* In window segment, it may be only reset or bare ack. */ 176 177 if (th->rst) { 178 /* This is TIME_WAIT assassination, in two flavors. 179 * Oh well... nobody has a sufficient solution to this 180 * protocol bug yet. 181 */ 182 if (twsk_net(tw)->ipv4.sysctl_tcp_rfc1337 == 0) { 183 kill: 184 inet_twsk_deschedule_put(tw); 185 return TCP_TW_SUCCESS; 186 } 187 } 188 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN); 189 190 if (tmp_opt.saw_tstamp) { 191 tcptw->tw_ts_recent = tmp_opt.rcv_tsval; 192 tcptw->tw_ts_recent_stamp = get_seconds(); 193 } 194 195 inet_twsk_put(tw); 196 return TCP_TW_SUCCESS; 197 } 198 199 /* Out of window segment. 200 201 All the segments are ACKed immediately. 202 203 The only exception is new SYN. We accept it, if it is 204 not old duplicate and we are not in danger to be killed 205 by delayed old duplicates. RFC check is that it has 206 newer sequence number works at rates <40Mbit/sec. 207 However, if paws works, it is reliable AND even more, 208 we even may relax silly seq space cutoff. 209 210 RED-PEN: we violate main RFC requirement, if this SYN will appear 211 old duplicate (i.e. we receive RST in reply to SYN-ACK), 212 we must return socket to time-wait state. It is not good, 213 but not fatal yet. 214 */ 215 216 if (th->syn && !th->rst && !th->ack && !paws_reject && 217 (after(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt) || 218 (tmp_opt.saw_tstamp && 219 (s32)(tcptw->tw_ts_recent - tmp_opt.rcv_tsval) < 0))) { 220 u32 isn = tcptw->tw_snd_nxt + 65535 + 2; 221 if (isn == 0) 222 isn++; 223 TCP_SKB_CB(skb)->tcp_tw_isn = isn; 224 return TCP_TW_SYN; 225 } 226 227 if (paws_reject) 228 __NET_INC_STATS(twsk_net(tw), LINUX_MIB_PAWSESTABREJECTED); 229 230 if (!th->rst) { 231 /* In this case we must reset the TIMEWAIT timer. 232 * 233 * If it is ACKless SYN it may be both old duplicate 234 * and new good SYN with random sequence number <rcv_nxt. 235 * Do not reschedule in the last case. 236 */ 237 if (paws_reject || th->ack) 238 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN); 239 240 return tcp_timewait_check_oow_rate_limit( 241 tw, skb, LINUX_MIB_TCPACKSKIPPEDTIMEWAIT); 242 } 243 inet_twsk_put(tw); 244 return TCP_TW_SUCCESS; 245 } 246 EXPORT_SYMBOL(tcp_timewait_state_process); 247 248 /* 249 * Move a socket to time-wait or dead fin-wait-2 state. 250 */ 251 void tcp_time_wait(struct sock *sk, int state, int timeo) 252 { 253 const struct inet_connection_sock *icsk = inet_csk(sk); 254 const struct tcp_sock *tp = tcp_sk(sk); 255 struct inet_timewait_sock *tw; 256 struct inet_timewait_death_row *tcp_death_row = &sock_net(sk)->ipv4.tcp_death_row; 257 258 tw = inet_twsk_alloc(sk, tcp_death_row, state); 259 260 if (tw) { 261 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw); 262 const int rto = (icsk->icsk_rto << 2) - (icsk->icsk_rto >> 1); 263 struct inet_sock *inet = inet_sk(sk); 264 265 tw->tw_transparent = inet->transparent; 266 tw->tw_rcv_wscale = tp->rx_opt.rcv_wscale; 267 tcptw->tw_rcv_nxt = tp->rcv_nxt; 268 tcptw->tw_snd_nxt = tp->snd_nxt; 269 tcptw->tw_rcv_wnd = tcp_receive_window(tp); 270 tcptw->tw_ts_recent = tp->rx_opt.ts_recent; 271 tcptw->tw_ts_recent_stamp = tp->rx_opt.ts_recent_stamp; 272 tcptw->tw_ts_offset = tp->tsoffset; 273 tcptw->tw_last_oow_ack_time = 0; 274 275 #if IS_ENABLED(CONFIG_IPV6) 276 if (tw->tw_family == PF_INET6) { 277 struct ipv6_pinfo *np = inet6_sk(sk); 278 279 tw->tw_v6_daddr = sk->sk_v6_daddr; 280 tw->tw_v6_rcv_saddr = sk->sk_v6_rcv_saddr; 281 tw->tw_tclass = np->tclass; 282 tw->tw_flowlabel = be32_to_cpu(np->flow_label & IPV6_FLOWLABEL_MASK); 283 tw->tw_ipv6only = sk->sk_ipv6only; 284 } 285 #endif 286 287 #ifdef CONFIG_TCP_MD5SIG 288 /* 289 * The timewait bucket does not have the key DB from the 290 * sock structure. We just make a quick copy of the 291 * md5 key being used (if indeed we are using one) 292 * so the timewait ack generating code has the key. 293 */ 294 do { 295 struct tcp_md5sig_key *key; 296 tcptw->tw_md5_key = NULL; 297 key = tp->af_specific->md5_lookup(sk, sk); 298 if (key) { 299 tcptw->tw_md5_key = kmemdup(key, sizeof(*key), GFP_ATOMIC); 300 BUG_ON(tcptw->tw_md5_key && !tcp_alloc_md5sig_pool()); 301 } 302 } while (0); 303 #endif 304 305 /* Get the TIME_WAIT timeout firing. */ 306 if (timeo < rto) 307 timeo = rto; 308 309 tw->tw_timeout = TCP_TIMEWAIT_LEN; 310 if (state == TCP_TIME_WAIT) 311 timeo = TCP_TIMEWAIT_LEN; 312 313 inet_twsk_schedule(tw, timeo); 314 /* Linkage updates. */ 315 __inet_twsk_hashdance(tw, sk, &tcp_hashinfo); 316 inet_twsk_put(tw); 317 } else { 318 /* Sorry, if we're out of memory, just CLOSE this 319 * socket up. We've got bigger problems than 320 * non-graceful socket closings. 321 */ 322 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPTIMEWAITOVERFLOW); 323 } 324 325 tcp_update_metrics(sk); 326 tcp_done(sk); 327 } 328 329 void tcp_twsk_destructor(struct sock *sk) 330 { 331 #ifdef CONFIG_TCP_MD5SIG 332 struct tcp_timewait_sock *twsk = tcp_twsk(sk); 333 334 if (twsk->tw_md5_key) 335 kfree_rcu(twsk->tw_md5_key, rcu); 336 #endif 337 } 338 EXPORT_SYMBOL_GPL(tcp_twsk_destructor); 339 340 /* Warning : This function is called without sk_listener being locked. 341 * Be sure to read socket fields once, as their value could change under us. 342 */ 343 void tcp_openreq_init_rwin(struct request_sock *req, 344 const struct sock *sk_listener, 345 const struct dst_entry *dst) 346 { 347 struct inet_request_sock *ireq = inet_rsk(req); 348 const struct tcp_sock *tp = tcp_sk(sk_listener); 349 int full_space = tcp_full_space(sk_listener); 350 u32 window_clamp; 351 __u8 rcv_wscale; 352 u32 rcv_wnd; 353 int mss; 354 355 mss = tcp_mss_clamp(tp, dst_metric_advmss(dst)); 356 window_clamp = READ_ONCE(tp->window_clamp); 357 /* Set this up on the first call only */ 358 req->rsk_window_clamp = window_clamp ? : dst_metric(dst, RTAX_WINDOW); 359 360 /* limit the window selection if the user enforce a smaller rx buffer */ 361 if (sk_listener->sk_userlocks & SOCK_RCVBUF_LOCK && 362 (req->rsk_window_clamp > full_space || req->rsk_window_clamp == 0)) 363 req->rsk_window_clamp = full_space; 364 365 rcv_wnd = tcp_rwnd_init_bpf((struct sock *)req); 366 if (rcv_wnd == 0) 367 rcv_wnd = dst_metric(dst, RTAX_INITRWND); 368 else if (full_space < rcv_wnd * mss) 369 full_space = rcv_wnd * mss; 370 371 /* tcp_full_space because it is guaranteed to be the first packet */ 372 tcp_select_initial_window(sk_listener, full_space, 373 mss - (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0), 374 &req->rsk_rcv_wnd, 375 &req->rsk_window_clamp, 376 ireq->wscale_ok, 377 &rcv_wscale, 378 rcv_wnd); 379 ireq->rcv_wscale = rcv_wscale; 380 } 381 EXPORT_SYMBOL(tcp_openreq_init_rwin); 382 383 static void tcp_ecn_openreq_child(struct tcp_sock *tp, 384 const struct request_sock *req) 385 { 386 tp->ecn_flags = inet_rsk(req)->ecn_ok ? TCP_ECN_OK : 0; 387 } 388 389 void tcp_ca_openreq_child(struct sock *sk, const struct dst_entry *dst) 390 { 391 struct inet_connection_sock *icsk = inet_csk(sk); 392 u32 ca_key = dst_metric(dst, RTAX_CC_ALGO); 393 bool ca_got_dst = false; 394 395 if (ca_key != TCP_CA_UNSPEC) { 396 const struct tcp_congestion_ops *ca; 397 398 rcu_read_lock(); 399 ca = tcp_ca_find_key(ca_key); 400 if (likely(ca && try_module_get(ca->owner))) { 401 icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst); 402 icsk->icsk_ca_ops = ca; 403 ca_got_dst = true; 404 } 405 rcu_read_unlock(); 406 } 407 408 /* If no valid choice made yet, assign current system default ca. */ 409 if (!ca_got_dst && 410 (!icsk->icsk_ca_setsockopt || 411 !try_module_get(icsk->icsk_ca_ops->owner))) 412 tcp_assign_congestion_control(sk); 413 414 tcp_set_ca_state(sk, TCP_CA_Open); 415 } 416 EXPORT_SYMBOL_GPL(tcp_ca_openreq_child); 417 418 static void smc_check_reset_syn_req(struct tcp_sock *oldtp, 419 struct request_sock *req, 420 struct tcp_sock *newtp) 421 { 422 #if IS_ENABLED(CONFIG_SMC) 423 struct inet_request_sock *ireq; 424 425 if (static_branch_unlikely(&tcp_have_smc)) { 426 ireq = inet_rsk(req); 427 if (oldtp->syn_smc && !ireq->smc_ok) 428 newtp->syn_smc = 0; 429 } 430 #endif 431 } 432 433 /* This is not only more efficient than what we used to do, it eliminates 434 * a lot of code duplication between IPv4/IPv6 SYN recv processing. -DaveM 435 * 436 * Actually, we could lots of memory writes here. tp of listening 437 * socket contains all necessary default parameters. 438 */ 439 struct sock *tcp_create_openreq_child(const struct sock *sk, 440 struct request_sock *req, 441 struct sk_buff *skb) 442 { 443 struct sock *newsk = inet_csk_clone_lock(sk, req, GFP_ATOMIC); 444 445 if (newsk) { 446 const struct inet_request_sock *ireq = inet_rsk(req); 447 struct tcp_request_sock *treq = tcp_rsk(req); 448 struct inet_connection_sock *newicsk = inet_csk(newsk); 449 struct tcp_sock *newtp = tcp_sk(newsk); 450 struct tcp_sock *oldtp = tcp_sk(sk); 451 452 smc_check_reset_syn_req(oldtp, req, newtp); 453 454 /* Now setup tcp_sock */ 455 newtp->pred_flags = 0; 456 457 newtp->rcv_wup = newtp->copied_seq = 458 newtp->rcv_nxt = treq->rcv_isn + 1; 459 newtp->segs_in = 1; 460 461 newtp->snd_sml = newtp->snd_una = 462 newtp->snd_nxt = newtp->snd_up = treq->snt_isn + 1; 463 464 INIT_LIST_HEAD(&newtp->tsq_node); 465 INIT_LIST_HEAD(&newtp->tsorted_sent_queue); 466 467 tcp_init_wl(newtp, treq->rcv_isn); 468 469 newtp->srtt_us = 0; 470 newtp->mdev_us = jiffies_to_usecs(TCP_TIMEOUT_INIT); 471 minmax_reset(&newtp->rtt_min, tcp_jiffies32, ~0U); 472 newicsk->icsk_rto = TCP_TIMEOUT_INIT; 473 newicsk->icsk_ack.lrcvtime = tcp_jiffies32; 474 475 newtp->packets_out = 0; 476 newtp->retrans_out = 0; 477 newtp->sacked_out = 0; 478 newtp->fackets_out = 0; 479 newtp->snd_ssthresh = TCP_INFINITE_SSTHRESH; 480 newtp->tlp_high_seq = 0; 481 newtp->lsndtime = tcp_jiffies32; 482 newsk->sk_txhash = treq->txhash; 483 newtp->last_oow_ack_time = 0; 484 newtp->total_retrans = req->num_retrans; 485 486 /* So many TCP implementations out there (incorrectly) count the 487 * initial SYN frame in their delayed-ACK and congestion control 488 * algorithms that we must have the following bandaid to talk 489 * efficiently to them. -DaveM 490 */ 491 newtp->snd_cwnd = TCP_INIT_CWND; 492 newtp->snd_cwnd_cnt = 0; 493 494 /* There's a bubble in the pipe until at least the first ACK. */ 495 newtp->app_limited = ~0U; 496 497 tcp_init_xmit_timers(newsk); 498 newtp->write_seq = newtp->pushed_seq = treq->snt_isn + 1; 499 500 newtp->rx_opt.saw_tstamp = 0; 501 502 newtp->rx_opt.dsack = 0; 503 newtp->rx_opt.num_sacks = 0; 504 505 newtp->urg_data = 0; 506 507 if (sock_flag(newsk, SOCK_KEEPOPEN)) 508 inet_csk_reset_keepalive_timer(newsk, 509 keepalive_time_when(newtp)); 510 511 newtp->rx_opt.tstamp_ok = ireq->tstamp_ok; 512 if ((newtp->rx_opt.sack_ok = ireq->sack_ok) != 0) { 513 if (sock_net(sk)->ipv4.sysctl_tcp_fack) 514 tcp_enable_fack(newtp); 515 } 516 newtp->window_clamp = req->rsk_window_clamp; 517 newtp->rcv_ssthresh = req->rsk_rcv_wnd; 518 newtp->rcv_wnd = req->rsk_rcv_wnd; 519 newtp->rx_opt.wscale_ok = ireq->wscale_ok; 520 if (newtp->rx_opt.wscale_ok) { 521 newtp->rx_opt.snd_wscale = ireq->snd_wscale; 522 newtp->rx_opt.rcv_wscale = ireq->rcv_wscale; 523 } else { 524 newtp->rx_opt.snd_wscale = newtp->rx_opt.rcv_wscale = 0; 525 newtp->window_clamp = min(newtp->window_clamp, 65535U); 526 } 527 newtp->snd_wnd = (ntohs(tcp_hdr(skb)->window) << 528 newtp->rx_opt.snd_wscale); 529 newtp->max_window = newtp->snd_wnd; 530 531 if (newtp->rx_opt.tstamp_ok) { 532 newtp->rx_opt.ts_recent = req->ts_recent; 533 newtp->rx_opt.ts_recent_stamp = get_seconds(); 534 newtp->tcp_header_len = sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED; 535 } else { 536 newtp->rx_opt.ts_recent_stamp = 0; 537 newtp->tcp_header_len = sizeof(struct tcphdr); 538 } 539 newtp->tsoffset = treq->ts_off; 540 #ifdef CONFIG_TCP_MD5SIG 541 newtp->md5sig_info = NULL; /*XXX*/ 542 if (newtp->af_specific->md5_lookup(sk, newsk)) 543 newtp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED; 544 #endif 545 if (skb->len >= TCP_MSS_DEFAULT + newtp->tcp_header_len) 546 newicsk->icsk_ack.last_seg_size = skb->len - newtp->tcp_header_len; 547 newtp->rx_opt.mss_clamp = req->mss; 548 tcp_ecn_openreq_child(newtp, req); 549 newtp->fastopen_req = NULL; 550 newtp->fastopen_rsk = NULL; 551 newtp->syn_data_acked = 0; 552 newtp->rack.mstamp = 0; 553 newtp->rack.advanced = 0; 554 newtp->rack.reo_wnd_steps = 1; 555 newtp->rack.last_delivered = 0; 556 newtp->rack.reo_wnd_persist = 0; 557 newtp->rack.dsack_seen = 0; 558 559 __TCP_INC_STATS(sock_net(sk), TCP_MIB_PASSIVEOPENS); 560 } 561 return newsk; 562 } 563 EXPORT_SYMBOL(tcp_create_openreq_child); 564 565 /* 566 * Process an incoming packet for SYN_RECV sockets represented as a 567 * request_sock. Normally sk is the listener socket but for TFO it 568 * points to the child socket. 569 * 570 * XXX (TFO) - The current impl contains a special check for ack 571 * validation and inside tcp_v4_reqsk_send_ack(). Can we do better? 572 * 573 * We don't need to initialize tmp_opt.sack_ok as we don't use the results 574 */ 575 576 struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb, 577 struct request_sock *req, 578 bool fastopen) 579 { 580 struct tcp_options_received tmp_opt; 581 struct sock *child; 582 const struct tcphdr *th = tcp_hdr(skb); 583 __be32 flg = tcp_flag_word(th) & (TCP_FLAG_RST|TCP_FLAG_SYN|TCP_FLAG_ACK); 584 bool paws_reject = false; 585 bool own_req; 586 587 tmp_opt.saw_tstamp = 0; 588 if (th->doff > (sizeof(struct tcphdr)>>2)) { 589 tcp_parse_options(sock_net(sk), skb, &tmp_opt, 0, NULL); 590 591 if (tmp_opt.saw_tstamp) { 592 tmp_opt.ts_recent = req->ts_recent; 593 if (tmp_opt.rcv_tsecr) 594 tmp_opt.rcv_tsecr -= tcp_rsk(req)->ts_off; 595 /* We do not store true stamp, but it is not required, 596 * it can be estimated (approximately) 597 * from another data. 598 */ 599 tmp_opt.ts_recent_stamp = get_seconds() - ((TCP_TIMEOUT_INIT/HZ)<<req->num_timeout); 600 paws_reject = tcp_paws_reject(&tmp_opt, th->rst); 601 } 602 } 603 604 /* Check for pure retransmitted SYN. */ 605 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn && 606 flg == TCP_FLAG_SYN && 607 !paws_reject) { 608 /* 609 * RFC793 draws (Incorrectly! It was fixed in RFC1122) 610 * this case on figure 6 and figure 8, but formal 611 * protocol description says NOTHING. 612 * To be more exact, it says that we should send ACK, 613 * because this segment (at least, if it has no data) 614 * is out of window. 615 * 616 * CONCLUSION: RFC793 (even with RFC1122) DOES NOT 617 * describe SYN-RECV state. All the description 618 * is wrong, we cannot believe to it and should 619 * rely only on common sense and implementation 620 * experience. 621 * 622 * Enforce "SYN-ACK" according to figure 8, figure 6 623 * of RFC793, fixed by RFC1122. 624 * 625 * Note that even if there is new data in the SYN packet 626 * they will be thrown away too. 627 * 628 * Reset timer after retransmitting SYNACK, similar to 629 * the idea of fast retransmit in recovery. 630 */ 631 if (!tcp_oow_rate_limited(sock_net(sk), skb, 632 LINUX_MIB_TCPACKSKIPPEDSYNRECV, 633 &tcp_rsk(req)->last_oow_ack_time) && 634 635 !inet_rtx_syn_ack(sk, req)) { 636 unsigned long expires = jiffies; 637 638 expires += min(TCP_TIMEOUT_INIT << req->num_timeout, 639 TCP_RTO_MAX); 640 if (!fastopen) 641 mod_timer_pending(&req->rsk_timer, expires); 642 else 643 req->rsk_timer.expires = expires; 644 } 645 return NULL; 646 } 647 648 /* Further reproduces section "SEGMENT ARRIVES" 649 for state SYN-RECEIVED of RFC793. 650 It is broken, however, it does not work only 651 when SYNs are crossed. 652 653 You would think that SYN crossing is impossible here, since 654 we should have a SYN_SENT socket (from connect()) on our end, 655 but this is not true if the crossed SYNs were sent to both 656 ends by a malicious third party. We must defend against this, 657 and to do that we first verify the ACK (as per RFC793, page 658 36) and reset if it is invalid. Is this a true full defense? 659 To convince ourselves, let us consider a way in which the ACK 660 test can still pass in this 'malicious crossed SYNs' case. 661 Malicious sender sends identical SYNs (and thus identical sequence 662 numbers) to both A and B: 663 664 A: gets SYN, seq=7 665 B: gets SYN, seq=7 666 667 By our good fortune, both A and B select the same initial 668 send sequence number of seven :-) 669 670 A: sends SYN|ACK, seq=7, ack_seq=8 671 B: sends SYN|ACK, seq=7, ack_seq=8 672 673 So we are now A eating this SYN|ACK, ACK test passes. So 674 does sequence test, SYN is truncated, and thus we consider 675 it a bare ACK. 676 677 If icsk->icsk_accept_queue.rskq_defer_accept, we silently drop this 678 bare ACK. Otherwise, we create an established connection. Both 679 ends (listening sockets) accept the new incoming connection and try 680 to talk to each other. 8-) 681 682 Note: This case is both harmless, and rare. Possibility is about the 683 same as us discovering intelligent life on another plant tomorrow. 684 685 But generally, we should (RFC lies!) to accept ACK 686 from SYNACK both here and in tcp_rcv_state_process(). 687 tcp_rcv_state_process() does not, hence, we do not too. 688 689 Note that the case is absolutely generic: 690 we cannot optimize anything here without 691 violating protocol. All the checks must be made 692 before attempt to create socket. 693 */ 694 695 /* RFC793 page 36: "If the connection is in any non-synchronized state ... 696 * and the incoming segment acknowledges something not yet 697 * sent (the segment carries an unacceptable ACK) ... 698 * a reset is sent." 699 * 700 * Invalid ACK: reset will be sent by listening socket. 701 * Note that the ACK validity check for a Fast Open socket is done 702 * elsewhere and is checked directly against the child socket rather 703 * than req because user data may have been sent out. 704 */ 705 if ((flg & TCP_FLAG_ACK) && !fastopen && 706 (TCP_SKB_CB(skb)->ack_seq != 707 tcp_rsk(req)->snt_isn + 1)) 708 return sk; 709 710 /* Also, it would be not so bad idea to check rcv_tsecr, which 711 * is essentially ACK extension and too early or too late values 712 * should cause reset in unsynchronized states. 713 */ 714 715 /* RFC793: "first check sequence number". */ 716 717 if (paws_reject || !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq, 718 tcp_rsk(req)->rcv_nxt, tcp_rsk(req)->rcv_nxt + req->rsk_rcv_wnd)) { 719 /* Out of window: send ACK and drop. */ 720 if (!(flg & TCP_FLAG_RST) && 721 !tcp_oow_rate_limited(sock_net(sk), skb, 722 LINUX_MIB_TCPACKSKIPPEDSYNRECV, 723 &tcp_rsk(req)->last_oow_ack_time)) 724 req->rsk_ops->send_ack(sk, skb, req); 725 if (paws_reject) 726 __NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED); 727 return NULL; 728 } 729 730 /* In sequence, PAWS is OK. */ 731 732 if (tmp_opt.saw_tstamp && !after(TCP_SKB_CB(skb)->seq, tcp_rsk(req)->rcv_nxt)) 733 req->ts_recent = tmp_opt.rcv_tsval; 734 735 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn) { 736 /* Truncate SYN, it is out of window starting 737 at tcp_rsk(req)->rcv_isn + 1. */ 738 flg &= ~TCP_FLAG_SYN; 739 } 740 741 /* RFC793: "second check the RST bit" and 742 * "fourth, check the SYN bit" 743 */ 744 if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN)) { 745 __TCP_INC_STATS(sock_net(sk), TCP_MIB_ATTEMPTFAILS); 746 goto embryonic_reset; 747 } 748 749 /* ACK sequence verified above, just make sure ACK is 750 * set. If ACK not set, just silently drop the packet. 751 * 752 * XXX (TFO) - if we ever allow "data after SYN", the 753 * following check needs to be removed. 754 */ 755 if (!(flg & TCP_FLAG_ACK)) 756 return NULL; 757 758 /* For Fast Open no more processing is needed (sk is the 759 * child socket). 760 */ 761 if (fastopen) 762 return sk; 763 764 /* While TCP_DEFER_ACCEPT is active, drop bare ACK. */ 765 if (req->num_timeout < inet_csk(sk)->icsk_accept_queue.rskq_defer_accept && 766 TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) { 767 inet_rsk(req)->acked = 1; 768 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDEFERACCEPTDROP); 769 return NULL; 770 } 771 772 /* OK, ACK is valid, create big socket and 773 * feed this segment to it. It will repeat all 774 * the tests. THIS SEGMENT MUST MOVE SOCKET TO 775 * ESTABLISHED STATE. If it will be dropped after 776 * socket is created, wait for troubles. 777 */ 778 child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL, 779 req, &own_req); 780 if (!child) 781 goto listen_overflow; 782 783 sock_rps_save_rxhash(child, skb); 784 tcp_synack_rtt_meas(child, req); 785 return inet_csk_complete_hashdance(sk, child, req, own_req); 786 787 listen_overflow: 788 if (!sock_net(sk)->ipv4.sysctl_tcp_abort_on_overflow) { 789 inet_rsk(req)->acked = 1; 790 return NULL; 791 } 792 793 embryonic_reset: 794 if (!(flg & TCP_FLAG_RST)) { 795 /* Received a bad SYN pkt - for TFO We try not to reset 796 * the local connection unless it's really necessary to 797 * avoid becoming vulnerable to outside attack aiming at 798 * resetting legit local connections. 799 */ 800 req->rsk_ops->send_reset(sk, skb); 801 } else if (fastopen) { /* received a valid RST pkt */ 802 reqsk_fastopen_remove(sk, req, true); 803 tcp_reset(sk); 804 } 805 if (!fastopen) { 806 inet_csk_reqsk_queue_drop(sk, req); 807 __NET_INC_STATS(sock_net(sk), LINUX_MIB_EMBRYONICRSTS); 808 } 809 return NULL; 810 } 811 EXPORT_SYMBOL(tcp_check_req); 812 813 /* 814 * Queue segment on the new socket if the new socket is active, 815 * otherwise we just shortcircuit this and continue with 816 * the new socket. 817 * 818 * For the vast majority of cases child->sk_state will be TCP_SYN_RECV 819 * when entering. But other states are possible due to a race condition 820 * where after __inet_lookup_established() fails but before the listener 821 * locked is obtained, other packets cause the same connection to 822 * be created. 823 */ 824 825 int tcp_child_process(struct sock *parent, struct sock *child, 826 struct sk_buff *skb) 827 { 828 int ret = 0; 829 int state = child->sk_state; 830 831 /* record NAPI ID of child */ 832 sk_mark_napi_id(child, skb); 833 834 tcp_segs_in(tcp_sk(child), skb); 835 if (!sock_owned_by_user(child)) { 836 ret = tcp_rcv_state_process(child, skb); 837 /* Wakeup parent, send SIGIO */ 838 if (state == TCP_SYN_RECV && child->sk_state != state) 839 parent->sk_data_ready(parent); 840 } else { 841 /* Alas, it is possible again, because we do lookup 842 * in main socket hash table and lock on listening 843 * socket does not protect us more. 844 */ 845 __sk_add_backlog(child, skb); 846 } 847 848 bh_unlock_sock(child); 849 sock_put(child); 850 return ret; 851 } 852 EXPORT_SYMBOL(tcp_child_process); 853