1 // SPDX-License-Identifier: GPL-2.0-only 2 /* 3 * INET An implementation of the TCP/IP protocol suite for the LINUX 4 * operating system. INET is implemented using the BSD Socket 5 * interface as the means of communication with the user level. 6 * 7 * Implementation of the Transmission Control Protocol(TCP). 8 * 9 * Authors: Ross Biro 10 * Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG> 11 * Mark Evans, <evansmp@uhura.aston.ac.uk> 12 * Corey Minyard <wf-rch!minyard@relay.EU.net> 13 * Florian La Roche, <flla@stud.uni-sb.de> 14 * Charles Hedrick, <hedrick@klinzhai.rutgers.edu> 15 * Linus Torvalds, <torvalds@cs.helsinki.fi> 16 * Alan Cox, <gw4pts@gw4pts.ampr.org> 17 * Matthew Dillon, <dillon@apollo.west.oic.com> 18 * Arnt Gulbrandsen, <agulbra@nvg.unit.no> 19 * Jorge Cwik, <jorge@laser.satlink.net> 20 */ 21 22 #include <net/tcp.h> 23 #include <net/tcp_ecn.h> 24 #include <net/xfrm.h> 25 #include <net/busy_poll.h> 26 #include <net/rstreason.h> 27 #include <net/psp.h> 28 29 static bool tcp_in_window(u32 seq, u32 end_seq, u32 s_win, u32 e_win) 30 { 31 if (seq == s_win) 32 return true; 33 if (after(end_seq, s_win) && before(seq, e_win)) 34 return true; 35 return seq == e_win && seq == end_seq; 36 } 37 38 static enum tcp_tw_status 39 tcp_timewait_check_oow_rate_limit(struct inet_timewait_sock *tw, 40 const struct sk_buff *skb, int mib_idx) 41 { 42 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw); 43 44 if (!tcp_oow_rate_limited(twsk_net(tw), skb, mib_idx, 45 &tcptw->tw_last_oow_ack_time)) { 46 /* Send ACK. Note, we do not put the bucket, 47 * it will be released by caller. 48 */ 49 return TCP_TW_ACK_OOW; 50 } 51 52 /* We are rate-limiting, so just release the tw sock and drop skb. */ 53 inet_twsk_put(tw); 54 return TCP_TW_SUCCESS; 55 } 56 57 static void twsk_rcv_nxt_update(struct tcp_timewait_sock *tcptw, u32 seq, 58 u32 rcv_nxt) 59 { 60 #ifdef CONFIG_TCP_AO 61 struct tcp_ao_info *ao; 62 63 ao = rcu_dereference(tcptw->ao_info); 64 if (unlikely(ao && seq < rcv_nxt)) 65 WRITE_ONCE(ao->rcv_sne, ao->rcv_sne + 1); 66 #endif 67 WRITE_ONCE(tcptw->tw_rcv_nxt, seq); 68 } 69 70 /* 71 * * Main purpose of TIME-WAIT state is to close connection gracefully, 72 * when one of ends sits in LAST-ACK or CLOSING retransmitting FIN 73 * (and, probably, tail of data) and one or more our ACKs are lost. 74 * * What is TIME-WAIT timeout? It is associated with maximal packet 75 * lifetime in the internet, which results in wrong conclusion, that 76 * it is set to catch "old duplicate segments" wandering out of their path. 77 * It is not quite correct. This timeout is calculated so that it exceeds 78 * maximal retransmission timeout enough to allow to lose one (or more) 79 * segments sent by peer and our ACKs. This time may be calculated from RTO. 80 * * When TIME-WAIT socket receives RST, it means that another end 81 * finally closed and we are allowed to kill TIME-WAIT too. 82 * * Second purpose of TIME-WAIT is catching old duplicate segments. 83 * Well, certainly it is pure paranoia, but if we load TIME-WAIT 84 * with this semantics, we MUST NOT kill TIME-WAIT state with RSTs. 85 * * If we invented some more clever way to catch duplicates 86 * (f.e. based on PAWS), we could truncate TIME-WAIT to several RTOs. 87 * 88 * The algorithm below is based on FORMAL INTERPRETATION of RFCs. 89 * When you compare it to RFCs, please, read section SEGMENT ARRIVES 90 * from the very beginning. 91 * 92 * NOTE. With recycling (and later with fin-wait-2) TW bucket 93 * is _not_ stateless. It means, that strictly speaking we must 94 * spinlock it. I do not want! Well, probability of misbehaviour 95 * is ridiculously low and, seems, we could use some mb() tricks 96 * to avoid misread sequence numbers, states etc. --ANK 97 * 98 * We don't need to initialize tmp_out.sack_ok as we don't use the results 99 */ 100 enum tcp_tw_status 101 tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb, 102 const struct tcphdr *th, u32 *tw_isn, 103 enum skb_drop_reason *drop_reason) 104 { 105 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw); 106 u32 rcv_nxt = READ_ONCE(tcptw->tw_rcv_nxt); 107 struct tcp_options_received tmp_opt; 108 enum skb_drop_reason psp_drop; 109 bool paws_reject = false; 110 int ts_recent_stamp; 111 112 /* Instead of dropping immediately, wait to see what value is 113 * returned. We will accept a non psp-encapsulated syn in the 114 * case where TCP_TW_SYN is returned. 115 */ 116 psp_drop = psp_twsk_rx_policy_check(tw, skb); 117 118 tmp_opt.saw_tstamp = 0; 119 ts_recent_stamp = READ_ONCE(tcptw->tw_ts_recent_stamp); 120 if (th->doff > (sizeof(*th) >> 2) && ts_recent_stamp) { 121 tcp_parse_options(twsk_net(tw), skb, &tmp_opt, 0, NULL); 122 123 if (tmp_opt.saw_tstamp) { 124 if (tmp_opt.rcv_tsecr) 125 tmp_opt.rcv_tsecr -= tcptw->tw_ts_offset; 126 tmp_opt.ts_recent = READ_ONCE(tcptw->tw_ts_recent); 127 tmp_opt.ts_recent_stamp = ts_recent_stamp; 128 paws_reject = tcp_paws_reject(&tmp_opt, th->rst); 129 } 130 } 131 132 if (READ_ONCE(tw->tw_substate) == TCP_FIN_WAIT2) { 133 /* Just repeat all the checks of tcp_rcv_state_process() */ 134 135 if (psp_drop) 136 goto out_put; 137 138 /* Out of window, send ACK */ 139 if (paws_reject || 140 !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq, 141 rcv_nxt, 142 rcv_nxt + tcptw->tw_rcv_wnd)) 143 return tcp_timewait_check_oow_rate_limit( 144 tw, skb, LINUX_MIB_TCPACKSKIPPEDFINWAIT2); 145 146 if (th->rst) 147 goto kill; 148 149 if (th->syn && !before(TCP_SKB_CB(skb)->seq, rcv_nxt)) 150 return TCP_TW_RST; 151 152 /* Dup ACK? */ 153 if (!th->ack || 154 !after(TCP_SKB_CB(skb)->end_seq, rcv_nxt) || 155 TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq) { 156 inet_twsk_put(tw); 157 return TCP_TW_SUCCESS; 158 } 159 160 /* New data or FIN. If new data arrive after half-duplex close, 161 * reset. 162 */ 163 if (!th->fin || 164 TCP_SKB_CB(skb)->end_seq != rcv_nxt + 1) 165 return TCP_TW_RST; 166 167 /* FIN arrived, enter true time-wait state. */ 168 WRITE_ONCE(tw->tw_substate, TCP_TIME_WAIT); 169 twsk_rcv_nxt_update(tcptw, TCP_SKB_CB(skb)->end_seq, 170 rcv_nxt); 171 172 if (tmp_opt.saw_tstamp) { 173 u64 ts = tcp_clock_ms(); 174 175 WRITE_ONCE(tw->tw_entry_stamp, ts); 176 WRITE_ONCE(tcptw->tw_ts_recent_stamp, 177 div_u64(ts, MSEC_PER_SEC)); 178 WRITE_ONCE(tcptw->tw_ts_recent, 179 tmp_opt.rcv_tsval); 180 } 181 182 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN); 183 return TCP_TW_ACK; 184 } 185 186 /* 187 * Now real TIME-WAIT state. 188 * 189 * RFC 1122: 190 * "When a connection is [...] on TIME-WAIT state [...] 191 * [a TCP] MAY accept a new SYN from the remote TCP to 192 * reopen the connection directly, if it: 193 * 194 * (1) assigns its initial sequence number for the new 195 * connection to be larger than the largest sequence 196 * number it used on the previous connection incarnation, 197 * and 198 * 199 * (2) returns to TIME-WAIT state if the SYN turns out 200 * to be an old duplicate". 201 */ 202 203 if (!paws_reject && 204 (TCP_SKB_CB(skb)->seq == rcv_nxt && 205 (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq || th->rst))) { 206 /* In window segment, it may be only reset or bare ack. */ 207 208 if (psp_drop) 209 goto out_put; 210 211 if (th->rst) { 212 /* This is TIME_WAIT assassination, in two flavors. 213 * Oh well... nobody has a sufficient solution to this 214 * protocol bug yet. 215 */ 216 if (!READ_ONCE(twsk_net(tw)->ipv4.sysctl_tcp_rfc1337)) { 217 kill: 218 inet_twsk_deschedule_put(tw); 219 return TCP_TW_SUCCESS; 220 } 221 } else { 222 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN); 223 } 224 225 if (tmp_opt.saw_tstamp) { 226 WRITE_ONCE(tcptw->tw_ts_recent, 227 tmp_opt.rcv_tsval); 228 WRITE_ONCE(tcptw->tw_ts_recent_stamp, 229 ktime_get_seconds()); 230 } 231 232 inet_twsk_put(tw); 233 return TCP_TW_SUCCESS; 234 } 235 236 /* Out of window segment. 237 238 All the segments are ACKed immediately. 239 240 The only exception is new SYN. We accept it, if it is 241 not old duplicate and we are not in danger to be killed 242 by delayed old duplicates. RFC check is that it has 243 newer sequence number works at rates <40Mbit/sec. 244 However, if paws works, it is reliable AND even more, 245 we even may relax silly seq space cutoff. 246 247 RED-PEN: we violate main RFC requirement, if this SYN will appear 248 old duplicate (i.e. we receive RST in reply to SYN-ACK), 249 we must return socket to time-wait state. It is not good, 250 but not fatal yet. 251 */ 252 253 if (th->syn && !th->rst && !th->ack && !paws_reject && 254 (after(TCP_SKB_CB(skb)->seq, rcv_nxt) || 255 (tmp_opt.saw_tstamp && 256 (s32)(READ_ONCE(tcptw->tw_ts_recent) - tmp_opt.rcv_tsval) < 0))) { 257 u32 isn = tcptw->tw_snd_nxt + 65535 + 2; 258 if (isn == 0) 259 isn++; 260 *tw_isn = isn; 261 return TCP_TW_SYN; 262 } 263 264 if (psp_drop) 265 goto out_put; 266 267 if (paws_reject) { 268 *drop_reason = SKB_DROP_REASON_TCP_RFC7323_TW_PAWS; 269 __NET_INC_STATS(twsk_net(tw), LINUX_MIB_PAWS_TW_REJECTED); 270 } 271 272 if (!th->rst) { 273 /* In this case we must reset the TIMEWAIT timer. 274 * 275 * If it is ACKless SYN it may be both old duplicate 276 * and new good SYN with random sequence number <rcv_nxt. 277 * Do not reschedule in the last case. 278 */ 279 if (paws_reject || th->ack) 280 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN); 281 282 return tcp_timewait_check_oow_rate_limit( 283 tw, skb, LINUX_MIB_TCPACKSKIPPEDTIMEWAIT); 284 } 285 286 out_put: 287 inet_twsk_put(tw); 288 return TCP_TW_SUCCESS; 289 } 290 EXPORT_IPV6_MOD(tcp_timewait_state_process); 291 292 static void tcp_time_wait_init(struct sock *sk, struct tcp_timewait_sock *tcptw) 293 { 294 #ifdef CONFIG_TCP_MD5SIG 295 const struct tcp_sock *tp = tcp_sk(sk); 296 struct tcp_md5sig_key *key; 297 298 /* 299 * The timewait bucket does not have the key DB from the 300 * sock structure. We just make a quick copy of the 301 * md5 key being used (if indeed we are using one) 302 * so the timewait ack generating code has the key. 303 */ 304 tcptw->tw_md5_key = NULL; 305 if (!static_branch_unlikely(&tcp_md5_needed.key)) 306 return; 307 308 key = tp->af_specific->md5_lookup(sk, sk); 309 if (key) { 310 tcptw->tw_md5_key = kmemdup(key, sizeof(*key), GFP_ATOMIC); 311 if (!tcptw->tw_md5_key) 312 return; 313 if (!static_key_fast_inc_not_disabled(&tcp_md5_needed.key.key)) 314 goto out_free; 315 } 316 return; 317 out_free: 318 WARN_ON_ONCE(1); 319 kfree(tcptw->tw_md5_key); 320 tcptw->tw_md5_key = NULL; 321 #endif 322 } 323 324 /* 325 * Move a socket to time-wait or dead fin-wait-2 state. 326 */ 327 void tcp_time_wait(struct sock *sk, int state, int timeo) 328 { 329 const struct inet_connection_sock *icsk = inet_csk(sk); 330 struct tcp_sock *tp = tcp_sk(sk); 331 struct net *net = sock_net(sk); 332 struct inet_timewait_sock *tw; 333 334 tw = inet_twsk_alloc(sk, &net->ipv4.tcp_death_row, state); 335 336 if (tw) { 337 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw); 338 const int rto = (icsk->icsk_rto << 2) - (icsk->icsk_rto >> 1); 339 340 tw->tw_mark = sk->sk_mark; 341 tw->tw_priority = READ_ONCE(sk->sk_priority); 342 tw->tw_rcv_wscale = tp->rx_opt.rcv_wscale; 343 /* refreshed when we enter true TIME-WAIT state */ 344 tw->tw_entry_stamp = tcp_time_stamp_ms(tp); 345 tcptw->tw_rcv_nxt = tp->rcv_nxt; 346 tcptw->tw_snd_nxt = tp->snd_nxt; 347 tcptw->tw_rcv_wnd = tcp_receive_window(tp); 348 tcptw->tw_ts_recent = tp->rx_opt.ts_recent; 349 tcptw->tw_ts_recent_stamp = tp->rx_opt.ts_recent_stamp; 350 tcptw->tw_ts_offset = tp->tsoffset; 351 tw->tw_usec_ts = tp->tcp_usec_ts; 352 tcptw->tw_last_oow_ack_time = 0; 353 tcptw->tw_tx_delay = tp->tcp_tx_delay; 354 tw->tw_txhash = sk->sk_txhash; 355 tw->tw_tx_queue_mapping = sk->sk_tx_queue_mapping; 356 #ifdef CONFIG_SOCK_RX_QUEUE_MAPPING 357 tw->tw_rx_queue_mapping = sk->sk_rx_queue_mapping; 358 #endif 359 #if IS_ENABLED(CONFIG_IPV6) 360 if (tw->tw_family == PF_INET6) { 361 struct ipv6_pinfo *np = inet6_sk(sk); 362 363 tw->tw_v6_daddr = sk->sk_v6_daddr; 364 tw->tw_v6_rcv_saddr = sk->sk_v6_rcv_saddr; 365 tw->tw_tclass = np->tclass; 366 tw->tw_flowlabel = be32_to_cpu(np->flow_label & IPV6_FLOWLABEL_MASK); 367 tw->tw_ipv6only = sk->sk_ipv6only; 368 } 369 #endif 370 371 tcp_time_wait_init(sk, tcptw); 372 tcp_ao_time_wait(tcptw, tp); 373 374 /* Get the TIME_WAIT timeout firing. */ 375 if (timeo < rto) 376 timeo = rto; 377 378 if (state == TCP_TIME_WAIT) 379 timeo = TCP_TIMEWAIT_LEN; 380 381 /* Linkage updates. 382 * Note that access to tw after this point is illegal. 383 */ 384 inet_twsk_hashdance_schedule(tw, sk, net->ipv4.tcp_death_row.hashinfo, timeo); 385 } else { 386 /* Sorry, if we're out of memory, just CLOSE this 387 * socket up. We've got bigger problems than 388 * non-graceful socket closings. 389 */ 390 NET_INC_STATS(net, LINUX_MIB_TCPTIMEWAITOVERFLOW); 391 } 392 393 tcp_update_metrics(sk); 394 tcp_done(sk); 395 } 396 EXPORT_SYMBOL(tcp_time_wait); 397 398 void tcp_twsk_destructor(struct sock *sk) 399 { 400 #ifdef CONFIG_TCP_MD5SIG 401 if (static_branch_unlikely(&tcp_md5_needed.key)) { 402 struct tcp_timewait_sock *twsk = tcp_twsk(sk); 403 404 if (twsk->tw_md5_key) { 405 kfree(twsk->tw_md5_key); 406 static_branch_slow_dec_deferred(&tcp_md5_needed); 407 } 408 } 409 #endif 410 tcp_ao_destroy_sock(sk, true); 411 psp_twsk_assoc_free(inet_twsk(sk)); 412 } 413 414 void tcp_twsk_purge(struct list_head *net_exit_list) 415 { 416 bool purged_once = false; 417 struct net *net; 418 419 list_for_each_entry(net, net_exit_list, exit_list) { 420 if (net->ipv4.tcp_death_row.hashinfo->pernet) { 421 /* Even if tw_refcount == 1, we must clean up kernel reqsk */ 422 inet_twsk_purge(net->ipv4.tcp_death_row.hashinfo); 423 } else if (!purged_once) { 424 inet_twsk_purge(&tcp_hashinfo); 425 purged_once = true; 426 } 427 } 428 } 429 430 /* Warning : This function is called without sk_listener being locked. 431 * Be sure to read socket fields once, as their value could change under us. 432 */ 433 void tcp_openreq_init_rwin(struct request_sock *req, 434 const struct sock *sk_listener, 435 const struct dst_entry *dst) 436 { 437 struct inet_request_sock *ireq = inet_rsk(req); 438 const struct tcp_sock *tp = tcp_sk(sk_listener); 439 int full_space = tcp_full_space(sk_listener); 440 u32 window_clamp; 441 __u8 rcv_wscale; 442 u32 rcv_wnd; 443 int mss; 444 445 mss = tcp_mss_clamp(tp, dst_metric_advmss(dst)); 446 window_clamp = READ_ONCE(tp->window_clamp); 447 /* Set this up on the first call only */ 448 req->rsk_window_clamp = window_clamp ? : dst_metric(dst, RTAX_WINDOW); 449 450 /* limit the window selection if the user enforce a smaller rx buffer */ 451 if (sk_listener->sk_userlocks & SOCK_RCVBUF_LOCK && 452 (req->rsk_window_clamp > full_space || req->rsk_window_clamp == 0)) 453 req->rsk_window_clamp = full_space; 454 455 rcv_wnd = tcp_rwnd_init_bpf((struct sock *)req); 456 if (rcv_wnd == 0) 457 rcv_wnd = dst_metric(dst, RTAX_INITRWND); 458 else if (full_space < rcv_wnd * mss) 459 full_space = rcv_wnd * mss; 460 461 /* tcp_full_space because it is guaranteed to be the first packet */ 462 tcp_select_initial_window(sk_listener, full_space, 463 mss - (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0), 464 &req->rsk_rcv_wnd, 465 &req->rsk_window_clamp, 466 ireq->wscale_ok, 467 &rcv_wscale, 468 rcv_wnd); 469 ireq->rcv_wscale = rcv_wscale; 470 } 471 472 static void tcp_ecn_openreq_child(struct sock *sk, 473 const struct request_sock *req, 474 const struct sk_buff *skb) 475 { 476 const struct tcp_request_sock *treq = tcp_rsk(req); 477 struct tcp_sock *tp = tcp_sk(sk); 478 479 if (treq->accecn_ok) { 480 tcp_ecn_mode_set(tp, TCP_ECN_MODE_ACCECN); 481 tp->syn_ect_snt = treq->syn_ect_snt; 482 tcp_accecn_third_ack(sk, skb, treq->syn_ect_snt); 483 tp->saw_accecn_opt = treq->saw_accecn_opt; 484 tp->prev_ecnfield = treq->syn_ect_rcv; 485 tp->accecn_opt_demand = 1; 486 tcp_ecn_received_counters_payload(sk, skb); 487 } else { 488 tcp_ecn_mode_set(tp, inet_rsk(req)->ecn_ok ? 489 TCP_ECN_MODE_RFC3168 : 490 TCP_ECN_DISABLED); 491 } 492 } 493 494 void tcp_ca_openreq_child(struct sock *sk, const struct dst_entry *dst) 495 { 496 struct inet_connection_sock *icsk = inet_csk(sk); 497 u32 ca_key = dst_metric(dst, RTAX_CC_ALGO); 498 bool ca_got_dst = false; 499 500 if (ca_key != TCP_CA_UNSPEC) { 501 const struct tcp_congestion_ops *ca; 502 503 rcu_read_lock(); 504 ca = tcp_ca_find_key(ca_key); 505 if (likely(ca && bpf_try_module_get(ca, ca->owner))) { 506 icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst); 507 icsk->icsk_ca_ops = ca; 508 ca_got_dst = true; 509 } 510 rcu_read_unlock(); 511 } 512 513 /* If no valid choice made yet, assign current system default ca. */ 514 if (!ca_got_dst && 515 (!icsk->icsk_ca_setsockopt || 516 !bpf_try_module_get(icsk->icsk_ca_ops, icsk->icsk_ca_ops->owner))) 517 tcp_assign_congestion_control(sk); 518 519 tcp_set_ca_state(sk, TCP_CA_Open); 520 } 521 EXPORT_IPV6_MOD_GPL(tcp_ca_openreq_child); 522 523 static void smc_check_reset_syn_req(const struct tcp_sock *oldtp, 524 struct request_sock *req, 525 struct tcp_sock *newtp) 526 { 527 #if IS_ENABLED(CONFIG_SMC) 528 struct inet_request_sock *ireq; 529 530 if (static_branch_unlikely(&tcp_have_smc)) { 531 ireq = inet_rsk(req); 532 if (oldtp->syn_smc && !ireq->smc_ok) 533 newtp->syn_smc = 0; 534 } 535 #endif 536 } 537 538 /* This is not only more efficient than what we used to do, it eliminates 539 * a lot of code duplication between IPv4/IPv6 SYN recv processing. -DaveM 540 * 541 * Actually, we could lots of memory writes here. tp of listening 542 * socket contains all necessary default parameters. 543 */ 544 struct sock *tcp_create_openreq_child(const struct sock *sk, 545 struct request_sock *req, 546 struct sk_buff *skb) 547 { 548 struct sock *newsk = inet_csk_clone_lock(sk, req, GFP_ATOMIC); 549 const struct inet_request_sock *ireq = inet_rsk(req); 550 struct tcp_request_sock *treq = tcp_rsk(req); 551 struct inet_connection_sock *newicsk; 552 const struct tcp_sock *oldtp; 553 struct tcp_sock *newtp; 554 u32 seq; 555 556 if (!newsk) 557 return NULL; 558 559 newicsk = inet_csk(newsk); 560 newtp = tcp_sk(newsk); 561 oldtp = tcp_sk(sk); 562 563 smc_check_reset_syn_req(oldtp, req, newtp); 564 565 /* Now setup tcp_sock */ 566 newtp->pred_flags = 0; 567 568 seq = treq->rcv_isn + 1; 569 newtp->rcv_wup = seq; 570 WRITE_ONCE(newtp->copied_seq, seq); 571 WRITE_ONCE(newtp->rcv_nxt, seq); 572 newtp->segs_in = 1; 573 574 seq = treq->snt_isn + 1; 575 newtp->snd_sml = newtp->snd_una = seq; 576 WRITE_ONCE(newtp->snd_nxt, seq); 577 newtp->snd_up = seq; 578 579 INIT_LIST_HEAD(&newtp->tsq_node); 580 INIT_LIST_HEAD(&newtp->tsorted_sent_queue); 581 582 tcp_init_wl(newtp, treq->rcv_isn); 583 584 minmax_reset(&newtp->rtt_min, tcp_jiffies32, ~0U); 585 newicsk->icsk_ack.lrcvtime = tcp_jiffies32; 586 587 newtp->lsndtime = tcp_jiffies32; 588 newsk->sk_txhash = READ_ONCE(treq->txhash); 589 newtp->total_retrans = req->num_retrans; 590 591 tcp_init_xmit_timers(newsk); 592 WRITE_ONCE(newtp->write_seq, newtp->pushed_seq = treq->snt_isn + 1); 593 594 if (sock_flag(newsk, SOCK_KEEPOPEN)) 595 tcp_reset_keepalive_timer(newsk, keepalive_time_when(newtp)); 596 597 newtp->rx_opt.tstamp_ok = ireq->tstamp_ok; 598 newtp->rx_opt.sack_ok = ireq->sack_ok; 599 newtp->window_clamp = req->rsk_window_clamp; 600 newtp->rcv_ssthresh = req->rsk_rcv_wnd; 601 newtp->rcv_wnd = req->rsk_rcv_wnd; 602 newtp->rx_opt.wscale_ok = ireq->wscale_ok; 603 if (newtp->rx_opt.wscale_ok) { 604 newtp->rx_opt.snd_wscale = ireq->snd_wscale; 605 newtp->rx_opt.rcv_wscale = ireq->rcv_wscale; 606 } else { 607 newtp->rx_opt.snd_wscale = newtp->rx_opt.rcv_wscale = 0; 608 newtp->window_clamp = min(newtp->window_clamp, 65535U); 609 } 610 newtp->snd_wnd = ntohs(tcp_hdr(skb)->window) << newtp->rx_opt.snd_wscale; 611 newtp->max_window = newtp->snd_wnd; 612 613 if (newtp->rx_opt.tstamp_ok) { 614 newtp->tcp_usec_ts = treq->req_usec_ts; 615 newtp->rx_opt.ts_recent = req->ts_recent; 616 newtp->rx_opt.ts_recent_stamp = ktime_get_seconds(); 617 newtp->tcp_header_len = sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED; 618 } else { 619 newtp->tcp_usec_ts = 0; 620 newtp->rx_opt.ts_recent_stamp = 0; 621 newtp->tcp_header_len = sizeof(struct tcphdr); 622 } 623 if (req->num_timeout) { 624 newtp->total_rto = req->num_timeout; 625 newtp->undo_marker = treq->snt_isn; 626 if (newtp->tcp_usec_ts) { 627 newtp->retrans_stamp = treq->snt_synack; 628 newtp->total_rto_time = (u32)(tcp_clock_us() - 629 newtp->retrans_stamp) / USEC_PER_MSEC; 630 } else { 631 newtp->retrans_stamp = div_u64(treq->snt_synack, 632 USEC_PER_SEC / TCP_TS_HZ); 633 newtp->total_rto_time = tcp_clock_ms() - 634 newtp->retrans_stamp; 635 } 636 newtp->total_rto_recoveries = 1; 637 } 638 newtp->tsoffset = treq->ts_off; 639 #ifdef CONFIG_TCP_MD5SIG 640 newtp->md5sig_info = NULL; /*XXX*/ 641 #endif 642 #ifdef CONFIG_TCP_AO 643 newtp->ao_info = NULL; 644 645 if (tcp_rsk_used_ao(req)) { 646 struct tcp_ao_key *ao_key; 647 648 ao_key = treq->af_specific->ao_lookup(sk, req, tcp_rsk(req)->ao_keyid, -1); 649 if (ao_key) 650 newtp->tcp_header_len += tcp_ao_len_aligned(ao_key); 651 } 652 #endif 653 if (skb->len >= TCP_MSS_DEFAULT + newtp->tcp_header_len) 654 newicsk->icsk_ack.last_seg_size = skb->len - newtp->tcp_header_len; 655 newtp->rx_opt.mss_clamp = req->mss; 656 tcp_ecn_openreq_child(newsk, req, skb); 657 newtp->fastopen_req = NULL; 658 RCU_INIT_POINTER(newtp->fastopen_rsk, NULL); 659 660 newtp->bpf_chg_cc_inprogress = 0; 661 tcp_bpf_clone(sk, newsk); 662 663 __TCP_INC_STATS(sock_net(sk), TCP_MIB_PASSIVEOPENS); 664 665 xa_init_flags(&newsk->sk_user_frags, XA_FLAGS_ALLOC1); 666 667 return newsk; 668 } 669 EXPORT_SYMBOL(tcp_create_openreq_child); 670 671 /* 672 * Process an incoming packet for SYN_RECV sockets represented as a 673 * request_sock. Normally sk is the listener socket but for TFO it 674 * points to the child socket. 675 * 676 * XXX (TFO) - The current impl contains a special check for ack 677 * validation and inside tcp_v4_reqsk_send_ack(). Can we do better? 678 * 679 * We don't need to initialize tmp_opt.sack_ok as we don't use the results 680 * 681 * Note: If @fastopen is true, this can be called from process context. 682 * Otherwise, this is from BH context. 683 */ 684 685 struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb, 686 struct request_sock *req, 687 bool fastopen, bool *req_stolen, 688 enum skb_drop_reason *drop_reason) 689 { 690 struct tcp_options_received tmp_opt; 691 struct sock *child; 692 const struct tcphdr *th = tcp_hdr(skb); 693 __be32 flg = tcp_flag_word(th) & (TCP_FLAG_RST|TCP_FLAG_SYN|TCP_FLAG_ACK); 694 bool tsecr_reject = false; 695 bool paws_reject = false; 696 bool own_req; 697 698 tmp_opt.saw_tstamp = 0; 699 tmp_opt.accecn = 0; 700 if (th->doff > (sizeof(struct tcphdr)>>2)) { 701 tcp_parse_options(sock_net(sk), skb, &tmp_opt, 0, NULL); 702 703 if (tmp_opt.saw_tstamp) { 704 tmp_opt.ts_recent = req->ts_recent; 705 if (tmp_opt.rcv_tsecr) { 706 if (inet_rsk(req)->tstamp_ok && !fastopen) 707 tsecr_reject = !between(tmp_opt.rcv_tsecr, 708 tcp_rsk(req)->snt_tsval_first, 709 READ_ONCE(tcp_rsk(req)->snt_tsval_last)); 710 tmp_opt.rcv_tsecr -= tcp_rsk(req)->ts_off; 711 } 712 /* We do not store true stamp, but it is not required, 713 * it can be estimated (approximately) 714 * from another data. 715 */ 716 tmp_opt.ts_recent_stamp = ktime_get_seconds() - 717 tcp_reqsk_timeout(req) / HZ; 718 paws_reject = tcp_paws_reject(&tmp_opt, th->rst); 719 } 720 } 721 722 /* Check for pure retransmitted SYN. */ 723 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn && 724 flg == TCP_FLAG_SYN && 725 !paws_reject) { 726 /* 727 * RFC793 draws (Incorrectly! It was fixed in RFC1122) 728 * this case on figure 6 and figure 8, but formal 729 * protocol description says NOTHING. 730 * To be more exact, it says that we should send ACK, 731 * because this segment (at least, if it has no data) 732 * is out of window. 733 * 734 * CONCLUSION: RFC793 (even with RFC1122) DOES NOT 735 * describe SYN-RECV state. All the description 736 * is wrong, we cannot believe to it and should 737 * rely only on common sense and implementation 738 * experience. 739 * 740 * Enforce "SYN-ACK" according to figure 8, figure 6 741 * of RFC793, fixed by RFC1122. 742 * 743 * Note that even if there is new data in the SYN packet 744 * they will be thrown away too. 745 * 746 * Reset timer after retransmitting SYNACK, similar to 747 * the idea of fast retransmit in recovery. 748 */ 749 if (!tcp_oow_rate_limited(sock_net(sk), skb, 750 LINUX_MIB_TCPACKSKIPPEDSYNRECV, 751 &tcp_rsk(req)->last_oow_ack_time) && 752 753 !tcp_rtx_synack(sk, req)) { 754 unsigned long expires = jiffies; 755 756 expires += tcp_reqsk_timeout(req); 757 if (!fastopen) 758 mod_timer_pending(&req->rsk_timer, expires); 759 else 760 req->rsk_timer.expires = expires; 761 } 762 return NULL; 763 } 764 765 /* Further reproduces section "SEGMENT ARRIVES" 766 for state SYN-RECEIVED of RFC793. 767 It is broken, however, it does not work only 768 when SYNs are crossed. 769 770 You would think that SYN crossing is impossible here, since 771 we should have a SYN_SENT socket (from connect()) on our end, 772 but this is not true if the crossed SYNs were sent to both 773 ends by a malicious third party. We must defend against this, 774 and to do that we first verify the ACK (as per RFC793, page 775 36) and reset if it is invalid. Is this a true full defense? 776 To convince ourselves, let us consider a way in which the ACK 777 test can still pass in this 'malicious crossed SYNs' case. 778 Malicious sender sends identical SYNs (and thus identical sequence 779 numbers) to both A and B: 780 781 A: gets SYN, seq=7 782 B: gets SYN, seq=7 783 784 By our good fortune, both A and B select the same initial 785 send sequence number of seven :-) 786 787 A: sends SYN|ACK, seq=7, ack_seq=8 788 B: sends SYN|ACK, seq=7, ack_seq=8 789 790 So we are now A eating this SYN|ACK, ACK test passes. So 791 does sequence test, SYN is truncated, and thus we consider 792 it a bare ACK. 793 794 If icsk->icsk_accept_queue.rskq_defer_accept, we silently drop this 795 bare ACK. Otherwise, we create an established connection. Both 796 ends (listening sockets) accept the new incoming connection and try 797 to talk to each other. 8-) 798 799 Note: This case is both harmless, and rare. Possibility is about the 800 same as us discovering intelligent life on another plant tomorrow. 801 802 But generally, we should (RFC lies!) to accept ACK 803 from SYNACK both here and in tcp_rcv_state_process(). 804 tcp_rcv_state_process() does not, hence, we do not too. 805 806 Note that the case is absolutely generic: 807 we cannot optimize anything here without 808 violating protocol. All the checks must be made 809 before attempt to create socket. 810 */ 811 812 /* RFC793 page 36: "If the connection is in any non-synchronized state ... 813 * and the incoming segment acknowledges something not yet 814 * sent (the segment carries an unacceptable ACK) ... 815 * a reset is sent." 816 * 817 * Invalid ACK: reset will be sent by listening socket. 818 * Note that the ACK validity check for a Fast Open socket is done 819 * elsewhere and is checked directly against the child socket rather 820 * than req because user data may have been sent out. 821 */ 822 if ((flg & TCP_FLAG_ACK) && !fastopen && 823 (TCP_SKB_CB(skb)->ack_seq != 824 tcp_rsk(req)->snt_isn + 1)) 825 return sk; 826 827 /* RFC793: "first check sequence number". */ 828 829 if (paws_reject || tsecr_reject || 830 !tcp_in_window(TCP_SKB_CB(skb)->seq, 831 TCP_SKB_CB(skb)->end_seq, 832 tcp_rsk(req)->rcv_nxt, 833 tcp_rsk(req)->rcv_nxt + 834 tcp_synack_window(req))) { 835 /* Out of window: send ACK and drop. */ 836 if (!(flg & TCP_FLAG_RST) && 837 !tcp_oow_rate_limited(sock_net(sk), skb, 838 LINUX_MIB_TCPACKSKIPPEDSYNRECV, 839 &tcp_rsk(req)->last_oow_ack_time)) 840 req->rsk_ops->send_ack(sk, skb, req); 841 if (paws_reject) { 842 SKB_DR_SET(*drop_reason, TCP_RFC7323_PAWS); 843 NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED); 844 } else if (tsecr_reject) { 845 SKB_DR_SET(*drop_reason, TCP_RFC7323_TSECR); 846 NET_INC_STATS(sock_net(sk), LINUX_MIB_TSECRREJECTED); 847 } else { 848 SKB_DR_SET(*drop_reason, TCP_OVERWINDOW); 849 } 850 return NULL; 851 } 852 853 /* In sequence, PAWS is OK. */ 854 855 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn) { 856 /* Truncate SYN, it is out of window starting 857 at tcp_rsk(req)->rcv_isn + 1. */ 858 flg &= ~TCP_FLAG_SYN; 859 } 860 861 /* RFC793: "second check the RST bit" and 862 * "fourth, check the SYN bit" 863 */ 864 if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN)) { 865 TCP_INC_STATS(sock_net(sk), TCP_MIB_ATTEMPTFAILS); 866 goto embryonic_reset; 867 } 868 869 /* ACK sequence verified above, just make sure ACK is 870 * set. If ACK not set, just silently drop the packet. 871 * 872 * XXX (TFO) - if we ever allow "data after SYN", the 873 * following check needs to be removed. 874 */ 875 if (!(flg & TCP_FLAG_ACK)) 876 return NULL; 877 878 if (tcp_rsk(req)->accecn_ok && tmp_opt.accecn && 879 tcp_rsk(req)->saw_accecn_opt < TCP_ACCECN_OPT_COUNTER_SEEN) { 880 u8 saw_opt = tcp_accecn_option_init(skb, tmp_opt.accecn); 881 882 tcp_rsk(req)->saw_accecn_opt = saw_opt; 883 if (tcp_rsk(req)->saw_accecn_opt == TCP_ACCECN_OPT_FAIL_SEEN) { 884 u8 fail_mode = TCP_ACCECN_OPT_FAIL_RECV; 885 886 tcp_rsk(req)->accecn_fail_mode |= fail_mode; 887 } 888 } 889 890 /* For Fast Open no more processing is needed (sk is the 891 * child socket). 892 */ 893 if (fastopen) 894 return sk; 895 896 /* While TCP_DEFER_ACCEPT is active, drop bare ACK. */ 897 if (req->num_timeout < READ_ONCE(inet_csk(sk)->icsk_accept_queue.rskq_defer_accept) && 898 TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) { 899 inet_rsk(req)->acked = 1; 900 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDEFERACCEPTDROP); 901 return NULL; 902 } 903 904 /* OK, ACK is valid, create big socket and 905 * feed this segment to it. It will repeat all 906 * the tests. THIS SEGMENT MUST MOVE SOCKET TO 907 * ESTABLISHED STATE. If it will be dropped after 908 * socket is created, wait for troubles. 909 */ 910 child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL, 911 req, &own_req); 912 if (!child) 913 goto listen_overflow; 914 915 if (own_req && tmp_opt.saw_tstamp && 916 !after(TCP_SKB_CB(skb)->seq, tcp_rsk(req)->rcv_nxt)) 917 tcp_sk(child)->rx_opt.ts_recent = tmp_opt.rcv_tsval; 918 919 if (own_req && rsk_drop_req(req)) { 920 reqsk_queue_removed(&inet_csk(req->rsk_listener)->icsk_accept_queue, req); 921 inet_csk_reqsk_queue_drop_and_put(req->rsk_listener, req); 922 return child; 923 } 924 925 sock_rps_save_rxhash(child, skb); 926 tcp_synack_rtt_meas(child, req); 927 *req_stolen = !own_req; 928 return inet_csk_complete_hashdance(sk, child, req, own_req); 929 930 listen_overflow: 931 SKB_DR_SET(*drop_reason, TCP_LISTEN_OVERFLOW); 932 if (sk != req->rsk_listener) 933 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMIGRATEREQFAILURE); 934 935 if (!READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_abort_on_overflow)) { 936 inet_rsk(req)->acked = 1; 937 return NULL; 938 } 939 940 embryonic_reset: 941 if (!(flg & TCP_FLAG_RST)) { 942 /* Received a bad SYN pkt - for TFO We try not to reset 943 * the local connection unless it's really necessary to 944 * avoid becoming vulnerable to outside attack aiming at 945 * resetting legit local connections. 946 */ 947 req->rsk_ops->send_reset(sk, skb, SK_RST_REASON_INVALID_SYN); 948 } else if (fastopen) { /* received a valid RST pkt */ 949 reqsk_fastopen_remove(sk, req, true); 950 tcp_reset(sk, skb); 951 } 952 if (!fastopen) { 953 bool unlinked = inet_csk_reqsk_queue_drop(sk, req); 954 955 if (unlinked) 956 __NET_INC_STATS(sock_net(sk), LINUX_MIB_EMBRYONICRSTS); 957 *req_stolen = !unlinked; 958 } 959 return NULL; 960 } 961 EXPORT_IPV6_MOD(tcp_check_req); 962 963 /* 964 * Queue segment on the new socket if the new socket is active, 965 * otherwise we just shortcircuit this and continue with 966 * the new socket. 967 * 968 * For the vast majority of cases child->sk_state will be TCP_SYN_RECV 969 * when entering. But other states are possible due to a race condition 970 * where after __inet_lookup_established() fails but before the listener 971 * locked is obtained, other packets cause the same connection to 972 * be created. 973 */ 974 975 enum skb_drop_reason tcp_child_process(struct sock *parent, struct sock *child, 976 struct sk_buff *skb) 977 __releases(&((child)->sk_lock.slock)) 978 { 979 enum skb_drop_reason reason = SKB_NOT_DROPPED_YET; 980 int state = child->sk_state; 981 982 /* record sk_napi_id and sk_rx_queue_mapping of child. */ 983 sk_mark_napi_id_set(child, skb); 984 985 tcp_segs_in(tcp_sk(child), skb); 986 if (!sock_owned_by_user(child)) { 987 reason = tcp_rcv_state_process(child, skb); 988 /* Wakeup parent, send SIGIO */ 989 if (state == TCP_SYN_RECV && child->sk_state != state) 990 parent->sk_data_ready(parent); 991 } else { 992 /* Alas, it is possible again, because we do lookup 993 * in main socket hash table and lock on listening 994 * socket does not protect us more. 995 */ 996 __sk_add_backlog(child, skb); 997 } 998 999 bh_unlock_sock(child); 1000 sock_put(child); 1001 return reason; 1002 } 1003 EXPORT_IPV6_MOD(tcp_child_process); 1004