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 } 290 291 static void tcp_time_wait_init(struct sock *sk, struct tcp_timewait_sock *tcptw) 292 { 293 #ifdef CONFIG_TCP_MD5SIG 294 const struct tcp_sock *tp = tcp_sk(sk); 295 struct tcp_md5sig_key *key; 296 297 /* 298 * The timewait bucket does not have the key DB from the 299 * sock structure. We just make a quick copy of the 300 * md5 key being used (if indeed we are using one) 301 * so the timewait ack generating code has the key. 302 */ 303 tcptw->tw_md5_key = NULL; 304 if (!static_branch_unlikely(&tcp_md5_needed.key)) 305 return; 306 307 key = tp->af_specific->md5_lookup(sk, sk); 308 if (key) { 309 tcptw->tw_md5_key = kmemdup(key, sizeof(*key), GFP_ATOMIC); 310 if (!tcptw->tw_md5_key) 311 return; 312 if (!static_key_fast_inc_not_disabled(&tcp_md5_needed.key.key)) 313 goto out_free; 314 } 315 return; 316 out_free: 317 WARN_ON_ONCE(1); 318 kfree(tcptw->tw_md5_key); 319 tcptw->tw_md5_key = NULL; 320 #endif 321 } 322 323 /* 324 * Move a socket to time-wait or dead fin-wait-2 state. 325 */ 326 void tcp_time_wait(struct sock *sk, int state, int timeo) 327 { 328 const struct inet_connection_sock *icsk = inet_csk(sk); 329 struct tcp_sock *tp = tcp_sk(sk); 330 struct net *net = sock_net(sk); 331 struct inet_timewait_sock *tw; 332 333 tw = inet_twsk_alloc(sk, &net->ipv4.tcp_death_row, state); 334 335 if (tw) { 336 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw); 337 const int rto = (icsk->icsk_rto << 2) - (icsk->icsk_rto >> 1); 338 339 tw->tw_mark = sk->sk_mark; 340 tw->tw_priority = READ_ONCE(sk->sk_priority); 341 tw->tw_rcv_wscale = tp->rx_opt.rcv_wscale; 342 /* refreshed when we enter true TIME-WAIT state */ 343 tw->tw_entry_stamp = tcp_time_stamp_ms(tp); 344 tcptw->tw_rcv_nxt = tp->rcv_nxt; 345 tcptw->tw_snd_nxt = tp->snd_nxt; 346 tcptw->tw_rcv_wnd = tcp_receive_window(tp); 347 tcptw->tw_ts_recent = tp->rx_opt.ts_recent; 348 tcptw->tw_ts_recent_stamp = tp->rx_opt.ts_recent_stamp; 349 tcptw->tw_ts_offset = tp->tsoffset; 350 tw->tw_usec_ts = tp->tcp_usec_ts; 351 tcptw->tw_last_oow_ack_time = 0; 352 tcptw->tw_tx_delay = tp->tcp_tx_delay; 353 tw->tw_txhash = sk->sk_txhash; 354 tw->tw_tx_queue_mapping = sk->sk_tx_queue_mapping; 355 #ifdef CONFIG_SOCK_RX_QUEUE_MAPPING 356 tw->tw_rx_queue_mapping = sk->sk_rx_queue_mapping; 357 #endif 358 #if IS_ENABLED(CONFIG_IPV6) 359 if (tw->tw_family == PF_INET6) { 360 struct ipv6_pinfo *np = inet6_sk(sk); 361 362 tw->tw_v6_daddr = sk->sk_v6_daddr; 363 tw->tw_v6_rcv_saddr = sk->sk_v6_rcv_saddr; 364 tw->tw_tclass = np->tclass; 365 tw->tw_flowlabel = be32_to_cpu(np->flow_label & IPV6_FLOWLABEL_MASK); 366 tw->tw_ipv6only = sk->sk_ipv6only; 367 } 368 #endif 369 370 tcp_time_wait_init(sk, tcptw); 371 tcp_ao_time_wait(tcptw, tp); 372 373 /* Get the TIME_WAIT timeout firing. */ 374 if (timeo < rto) 375 timeo = rto; 376 377 if (state == TCP_TIME_WAIT) 378 timeo = TCP_TIMEWAIT_LEN; 379 380 /* Linkage updates. 381 * Note that access to tw after this point is illegal. 382 */ 383 inet_twsk_hashdance_schedule(tw, sk, net->ipv4.tcp_death_row.hashinfo, timeo); 384 } else { 385 /* Sorry, if we're out of memory, just CLOSE this 386 * socket up. We've got bigger problems than 387 * non-graceful socket closings. 388 */ 389 NET_INC_STATS(net, LINUX_MIB_TCPTIMEWAITOVERFLOW); 390 } 391 392 tcp_update_metrics(sk); 393 tcp_done(sk); 394 } 395 396 void tcp_twsk_destructor(struct sock *sk) 397 { 398 #ifdef CONFIG_TCP_MD5SIG 399 if (static_branch_unlikely(&tcp_md5_needed.key)) { 400 struct tcp_timewait_sock *twsk = tcp_twsk(sk); 401 402 if (twsk->tw_md5_key) { 403 kfree(twsk->tw_md5_key); 404 static_branch_slow_dec_deferred(&tcp_md5_needed); 405 } 406 } 407 #endif 408 tcp_ao_destroy_sock(sk, true); 409 psp_twsk_assoc_free(inet_twsk(sk)); 410 } 411 412 void tcp_twsk_purge(struct list_head *net_exit_list) 413 { 414 bool purged_once = false; 415 struct net *net; 416 417 list_for_each_entry(net, net_exit_list, exit_list) { 418 if (net->ipv4.tcp_death_row.hashinfo->pernet) { 419 /* Even if tw_refcount == 1, we must clean up kernel reqsk */ 420 inet_twsk_purge(net->ipv4.tcp_death_row.hashinfo); 421 } else if (!purged_once) { 422 inet_twsk_purge(&tcp_hashinfo); 423 purged_once = true; 424 } 425 } 426 } 427 428 /* Warning : This function is called without sk_listener being locked. 429 * Be sure to read socket fields once, as their value could change under us. 430 */ 431 void tcp_openreq_init_rwin(struct request_sock *req, 432 const struct sock *sk_listener, 433 const struct dst_entry *dst) 434 { 435 struct inet_request_sock *ireq = inet_rsk(req); 436 const struct tcp_sock *tp = tcp_sk(sk_listener); 437 int full_space = tcp_full_space(sk_listener); 438 u32 window_clamp; 439 __u8 rcv_wscale; 440 u32 rcv_wnd; 441 int mss; 442 443 mss = tcp_mss_clamp(tp, dst_metric_advmss(dst)); 444 window_clamp = READ_ONCE(tp->window_clamp); 445 /* Set this up on the first call only */ 446 req->rsk_window_clamp = window_clamp ? : dst_metric(dst, RTAX_WINDOW); 447 448 /* limit the window selection if the user enforce a smaller rx buffer */ 449 if (sk_listener->sk_userlocks & SOCK_RCVBUF_LOCK && 450 (req->rsk_window_clamp > full_space || req->rsk_window_clamp == 0)) 451 req->rsk_window_clamp = full_space; 452 453 rcv_wnd = tcp_rwnd_init_bpf((struct sock *)req); 454 if (rcv_wnd == 0) 455 rcv_wnd = dst_metric(dst, RTAX_INITRWND); 456 else if (full_space < rcv_wnd * mss) 457 full_space = rcv_wnd * mss; 458 459 /* tcp_full_space because it is guaranteed to be the first packet */ 460 tcp_select_initial_window(sk_listener, full_space, 461 mss - (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0), 462 &req->rsk_rcv_wnd, 463 &req->rsk_window_clamp, 464 ireq->wscale_ok, 465 &rcv_wscale, 466 rcv_wnd); 467 ireq->rcv_wscale = rcv_wscale; 468 } 469 470 static void tcp_ecn_openreq_child(struct sock *sk, 471 const struct request_sock *req, 472 const struct sk_buff *skb) 473 { 474 const struct tcp_request_sock *treq = tcp_rsk(req); 475 struct tcp_sock *tp = tcp_sk(sk); 476 477 if (treq->accecn_ok) { 478 tcp_ecn_mode_set(tp, TCP_ECN_MODE_ACCECN); 479 tp->syn_ect_snt = treq->syn_ect_snt; 480 tcp_accecn_third_ack(sk, skb, treq->syn_ect_snt); 481 tp->saw_accecn_opt = treq->saw_accecn_opt; 482 if (treq->accecn_fail_mode & TCP_ACCECN_ACE_FAIL_SEND) 483 tcp_accecn_fail_mode_set(tp, TCP_ACCECN_ACE_FAIL_SEND); 484 if (treq->accecn_fail_mode & TCP_ACCECN_ACE_FAIL_RECV) 485 tcp_accecn_fail_mode_set(tp, TCP_ACCECN_ACE_FAIL_RECV); 486 tp->prev_ecnfield = treq->syn_ect_rcv; 487 tp->accecn_opt_demand = 1; 488 tcp_ecn_received_counters_payload(sk, skb); 489 } else { 490 if (inet_rsk(req)->ecn_ok && !tcp_ca_no_fallback_rfc3168(sk)) 491 tcp_ecn_mode_set(tp, TCP_ECN_MODE_RFC3168); 492 else 493 tcp_ecn_mode_set(tp, TCP_ECN_DISABLED); 494 } 495 } 496 497 void tcp_ca_openreq_child(struct sock *sk, const struct dst_entry *dst) 498 { 499 struct inet_connection_sock *icsk = inet_csk(sk); 500 u32 ca_key = dst_metric(dst, RTAX_CC_ALGO); 501 bool ca_got_dst = false; 502 503 if (ca_key != TCP_CA_UNSPEC) { 504 const struct tcp_congestion_ops *ca; 505 506 rcu_read_lock(); 507 ca = tcp_ca_find_key(ca_key); 508 if (likely(ca && bpf_try_module_get(ca, ca->owner))) { 509 icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst); 510 icsk->icsk_ca_ops = ca; 511 ca_got_dst = true; 512 } 513 rcu_read_unlock(); 514 } 515 516 /* If no valid choice made yet, assign current system default ca. */ 517 if (!ca_got_dst && 518 (!icsk->icsk_ca_setsockopt || 519 !bpf_try_module_get(icsk->icsk_ca_ops, icsk->icsk_ca_ops->owner))) 520 tcp_assign_congestion_control(sk); 521 522 tcp_set_ca_state(sk, TCP_CA_Open); 523 } 524 525 static void smc_check_reset_syn_req(const struct tcp_sock *oldtp, 526 struct request_sock *req, 527 struct tcp_sock *newtp) 528 { 529 #if IS_ENABLED(CONFIG_SMC) 530 struct inet_request_sock *ireq; 531 532 if (static_branch_unlikely(&tcp_have_smc)) { 533 ireq = inet_rsk(req); 534 if (oldtp->syn_smc && !ireq->smc_ok) 535 newtp->syn_smc = 0; 536 } 537 #endif 538 } 539 540 /* This is not only more efficient than what we used to do, it eliminates 541 * a lot of code duplication between IPv4/IPv6 SYN recv processing. -DaveM 542 * 543 * Actually, we could lots of memory writes here. tp of listening 544 * socket contains all necessary default parameters. 545 */ 546 struct sock *tcp_create_openreq_child(const struct sock *sk, 547 struct request_sock *req, 548 struct sk_buff *skb) 549 { 550 struct sock *newsk = inet_csk_clone_lock(sk, req, GFP_ATOMIC); 551 const struct inet_request_sock *ireq = inet_rsk(req); 552 struct tcp_request_sock *treq = tcp_rsk(req); 553 struct inet_connection_sock *newicsk; 554 const struct tcp_sock *oldtp; 555 struct tcp_sock *newtp; 556 u32 seq; 557 558 if (!newsk) 559 return NULL; 560 561 newicsk = inet_csk(newsk); 562 newtp = tcp_sk(newsk); 563 oldtp = tcp_sk(sk); 564 565 smc_check_reset_syn_req(oldtp, req, newtp); 566 567 /* Now setup tcp_sock */ 568 newtp->pred_flags = 0; 569 570 seq = treq->rcv_isn + 1; 571 newtp->rcv_wup = seq; 572 WRITE_ONCE(newtp->copied_seq, seq); 573 WRITE_ONCE(newtp->rcv_nxt, seq); 574 newtp->segs_in = 1; 575 576 seq = treq->snt_isn + 1; 577 newtp->snd_sml = newtp->snd_una = seq; 578 WRITE_ONCE(newtp->snd_nxt, seq); 579 newtp->snd_up = seq; 580 581 INIT_LIST_HEAD(&newtp->tsq_node); 582 INIT_LIST_HEAD(&newtp->tsorted_sent_queue); 583 584 tcp_init_wl(newtp, treq->rcv_isn); 585 586 minmax_reset(&newtp->rtt_min, tcp_jiffies32, ~0U); 587 newicsk->icsk_ack.lrcvtime = tcp_jiffies32; 588 589 newtp->lsndtime = tcp_jiffies32; 590 newsk->sk_txhash = READ_ONCE(treq->txhash); 591 newtp->total_retrans = req->num_retrans; 592 593 tcp_init_xmit_timers(newsk); 594 WRITE_ONCE(newtp->write_seq, newtp->pushed_seq = treq->snt_isn + 1); 595 596 if (sock_flag(newsk, SOCK_KEEPOPEN)) 597 tcp_reset_keepalive_timer(newsk, keepalive_time_when(newtp)); 598 599 newtp->rx_opt.tstamp_ok = ireq->tstamp_ok; 600 newtp->rx_opt.sack_ok = ireq->sack_ok; 601 newtp->window_clamp = req->rsk_window_clamp; 602 newtp->rcv_ssthresh = req->rsk_rcv_wnd; 603 newtp->rcv_wnd = req->rsk_rcv_wnd; 604 newtp->rcv_mwnd_seq = newtp->rcv_wup + req->rsk_rcv_wnd; 605 newtp->rx_opt.wscale_ok = ireq->wscale_ok; 606 if (newtp->rx_opt.wscale_ok) { 607 newtp->rx_opt.snd_wscale = ireq->snd_wscale; 608 newtp->rx_opt.rcv_wscale = ireq->rcv_wscale; 609 } else { 610 newtp->rx_opt.snd_wscale = newtp->rx_opt.rcv_wscale = 0; 611 newtp->window_clamp = min(newtp->window_clamp, 65535U); 612 } 613 newtp->snd_wnd = ntohs(tcp_hdr(skb)->window) << newtp->rx_opt.snd_wscale; 614 newtp->max_window = newtp->snd_wnd; 615 616 if (newtp->rx_opt.tstamp_ok) { 617 newtp->tcp_usec_ts = treq->req_usec_ts; 618 newtp->rx_opt.ts_recent = req->ts_recent; 619 newtp->rx_opt.ts_recent_stamp = ktime_get_seconds(); 620 newtp->tcp_header_len = sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED; 621 } else { 622 newtp->tcp_usec_ts = 0; 623 newtp->rx_opt.ts_recent_stamp = 0; 624 newtp->tcp_header_len = sizeof(struct tcphdr); 625 } 626 if (req->num_timeout) { 627 newtp->total_rto = req->num_timeout; 628 newtp->undo_marker = treq->snt_isn; 629 if (newtp->tcp_usec_ts) { 630 newtp->retrans_stamp = treq->snt_synack; 631 newtp->total_rto_time = (u32)(tcp_clock_us() - 632 newtp->retrans_stamp) / USEC_PER_MSEC; 633 } else { 634 newtp->retrans_stamp = div_u64(treq->snt_synack, 635 USEC_PER_SEC / TCP_TS_HZ); 636 newtp->total_rto_time = tcp_clock_ms() - 637 newtp->retrans_stamp; 638 } 639 newtp->total_rto_recoveries = 1; 640 } 641 newtp->tsoffset = treq->ts_off; 642 #ifdef CONFIG_TCP_MD5SIG 643 newtp->md5sig_info = NULL; /*XXX*/ 644 #endif 645 #ifdef CONFIG_TCP_AO 646 newtp->ao_info = NULL; 647 648 if (tcp_rsk_used_ao(req)) { 649 struct tcp_ao_key *ao_key; 650 651 ao_key = treq->af_specific->ao_lookup(sk, req, tcp_rsk(req)->ao_keyid, -1); 652 if (ao_key) 653 newtp->tcp_header_len += tcp_ao_len_aligned(ao_key); 654 } 655 #endif 656 if (skb->len >= TCP_MSS_DEFAULT + newtp->tcp_header_len) 657 newicsk->icsk_ack.last_seg_size = skb->len - newtp->tcp_header_len; 658 newtp->rx_opt.mss_clamp = req->mss; 659 tcp_ecn_openreq_child(newsk, req, skb); 660 newtp->fastopen_req = NULL; 661 RCU_INIT_POINTER(newtp->fastopen_rsk, NULL); 662 663 newtp->bpf_chg_cc_inprogress = 0; 664 tcp_bpf_clone(sk, newsk); 665 666 __TCP_INC_STATS(sock_net(sk), TCP_MIB_PASSIVEOPENS); 667 668 xa_init_flags(&newsk->sk_user_frags, XA_FLAGS_ALLOC1); 669 670 return newsk; 671 } 672 673 /* 674 * Process an incoming packet for SYN_RECV sockets represented as a 675 * request_sock. Normally sk is the listener socket but for TFO it 676 * points to the child socket. 677 * 678 * XXX (TFO) - The current impl contains a special check for ack 679 * validation and inside tcp_v4_reqsk_send_ack(). Can we do better? 680 * 681 * We don't need to initialize tmp_opt.sack_ok as we don't use the results 682 * 683 * Note: If @fastopen is true, this can be called from process context. 684 * Otherwise, this is from BH context. 685 */ 686 687 struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb, 688 struct request_sock *req, 689 bool fastopen, bool *req_stolen, 690 enum skb_drop_reason *drop_reason) 691 { 692 struct tcp_options_received tmp_opt; 693 struct sock *child; 694 const struct tcphdr *th = tcp_hdr(skb); 695 __be32 flg = tcp_flag_word(th) & (TCP_FLAG_RST|TCP_FLAG_SYN|TCP_FLAG_ACK); 696 bool tsecr_reject = false; 697 bool paws_reject = false; 698 bool own_req; 699 700 tmp_opt.saw_tstamp = 0; 701 tmp_opt.accecn = 0; 702 if (th->doff > (sizeof(struct tcphdr)>>2)) { 703 tcp_parse_options(sock_net(sk), skb, &tmp_opt, 0, NULL); 704 705 if (tmp_opt.saw_tstamp) { 706 tmp_opt.ts_recent = req->ts_recent; 707 if (tmp_opt.rcv_tsecr) { 708 if (inet_rsk(req)->tstamp_ok && !fastopen) 709 tsecr_reject = !between(tmp_opt.rcv_tsecr, 710 tcp_rsk(req)->snt_tsval_first, 711 READ_ONCE(tcp_rsk(req)->snt_tsval_last)); 712 tmp_opt.rcv_tsecr -= tcp_rsk(req)->ts_off; 713 } 714 /* We do not store true stamp, but it is not required, 715 * it can be estimated (approximately) 716 * from another data. 717 */ 718 tmp_opt.ts_recent_stamp = ktime_get_seconds() - 719 tcp_reqsk_timeout(req) / HZ; 720 paws_reject = tcp_paws_reject(&tmp_opt, th->rst); 721 } 722 } 723 724 /* Check for pure retransmitted SYN. */ 725 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn && 726 flg == TCP_FLAG_SYN && 727 !paws_reject) { 728 /* 729 * RFC793 draws (Incorrectly! It was fixed in RFC1122) 730 * this case on figure 6 and figure 8, but formal 731 * protocol description says NOTHING. 732 * To be more exact, it says that we should send ACK, 733 * because this segment (at least, if it has no data) 734 * is out of window. 735 * 736 * CONCLUSION: RFC793 (even with RFC1122) DOES NOT 737 * describe SYN-RECV state. All the description 738 * is wrong, we cannot believe to it and should 739 * rely only on common sense and implementation 740 * experience. 741 * 742 * Enforce "SYN-ACK" according to figure 8, figure 6 743 * of RFC793, fixed by RFC1122. 744 * 745 * Note that even if there is new data in the SYN packet 746 * they will be thrown away too. 747 * 748 * Reset timer after retransmitting SYNACK, similar to 749 * the idea of fast retransmit in recovery. 750 */ 751 if (!tcp_oow_rate_limited(sock_net(sk), skb, 752 LINUX_MIB_TCPACKSKIPPEDSYNRECV, 753 &tcp_rsk(req)->last_oow_ack_time)) { 754 if (tcp_rsk(req)->accecn_ok) { 755 u8 ect_rcv = TCP_SKB_CB(skb)->ip_dsfield & 756 INET_ECN_MASK; 757 758 tcp_rsk(req)->syn_ect_rcv = ect_rcv; 759 if (tcp_accecn_ace(tcp_hdr(skb)) == 0x0) 760 tcp_rsk(req)->accecn_fail_mode |= TCP_ACCECN_ACE_FAIL_RECV; 761 } 762 if (!tcp_rtx_synack(sk, req)) { 763 unsigned long expires = jiffies; 764 765 if (req->num_retrans > 1 && tcp_rsk(req)->accecn_ok) 766 tcp_rsk(req)->accecn_fail_mode |= TCP_ACCECN_ACE_FAIL_SEND; 767 768 expires += tcp_reqsk_timeout(req); 769 if (!fastopen) 770 mod_timer_pending(&req->rsk_timer, 771 expires); 772 else 773 req->rsk_timer.expires = expires; 774 } 775 } 776 return NULL; 777 } 778 779 /* Further reproduces section "SEGMENT ARRIVES" 780 for state SYN-RECEIVED of RFC793. 781 It is broken, however, it does not work only 782 when SYNs are crossed. 783 784 You would think that SYN crossing is impossible here, since 785 we should have a SYN_SENT socket (from connect()) on our end, 786 but this is not true if the crossed SYNs were sent to both 787 ends by a malicious third party. We must defend against this, 788 and to do that we first verify the ACK (as per RFC793, page 789 36) and reset if it is invalid. Is this a true full defense? 790 To convince ourselves, let us consider a way in which the ACK 791 test can still pass in this 'malicious crossed SYNs' case. 792 Malicious sender sends identical SYNs (and thus identical sequence 793 numbers) to both A and B: 794 795 A: gets SYN, seq=7 796 B: gets SYN, seq=7 797 798 By our good fortune, both A and B select the same initial 799 send sequence number of seven :-) 800 801 A: sends SYN|ACK, seq=7, ack_seq=8 802 B: sends SYN|ACK, seq=7, ack_seq=8 803 804 So we are now A eating this SYN|ACK, ACK test passes. So 805 does sequence test, SYN is truncated, and thus we consider 806 it a bare ACK. 807 808 If icsk->icsk_accept_queue.rskq_defer_accept, we silently drop this 809 bare ACK. Otherwise, we create an established connection. Both 810 ends (listening sockets) accept the new incoming connection and try 811 to talk to each other. 8-) 812 813 Note: This case is both harmless, and rare. Possibility is about the 814 same as us discovering intelligent life on another plant tomorrow. 815 816 But generally, we should (RFC lies!) to accept ACK 817 from SYNACK both here and in tcp_rcv_state_process(). 818 tcp_rcv_state_process() does not, hence, we do not too. 819 820 Note that the case is absolutely generic: 821 we cannot optimize anything here without 822 violating protocol. All the checks must be made 823 before attempt to create socket. 824 */ 825 826 /* RFC793 page 36: "If the connection is in any non-synchronized state ... 827 * and the incoming segment acknowledges something not yet 828 * sent (the segment carries an unacceptable ACK) ... 829 * a reset is sent." 830 * 831 * Invalid ACK: reset will be sent by listening socket. 832 * Note that the ACK validity check for a Fast Open socket is done 833 * elsewhere and is checked directly against the child socket rather 834 * than req because user data may have been sent out. 835 */ 836 if ((flg & TCP_FLAG_ACK) && !(flg & TCP_FLAG_RST) && !fastopen && 837 (TCP_SKB_CB(skb)->ack_seq != 838 tcp_rsk(req)->snt_isn + 1)) 839 return sk; 840 841 /* RFC793: "first check sequence number". */ 842 843 if (paws_reject || tsecr_reject || 844 !tcp_in_window(TCP_SKB_CB(skb)->seq, 845 TCP_SKB_CB(skb)->end_seq, 846 tcp_rsk(req)->rcv_nxt, 847 tcp_rsk(req)->rcv_nxt + 848 tcp_synack_window(req))) { 849 /* Out of window: send ACK and drop. */ 850 if (!(flg & TCP_FLAG_RST) && 851 !tcp_oow_rate_limited(sock_net(sk), skb, 852 LINUX_MIB_TCPACKSKIPPEDSYNRECV, 853 &tcp_rsk(req)->last_oow_ack_time)) 854 req->rsk_ops->send_ack(sk, skb, req); 855 if (paws_reject) { 856 SKB_DR_SET(*drop_reason, TCP_RFC7323_PAWS); 857 NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED); 858 } else if (tsecr_reject) { 859 SKB_DR_SET(*drop_reason, TCP_RFC7323_TSECR); 860 NET_INC_STATS(sock_net(sk), LINUX_MIB_TSECRREJECTED); 861 } else { 862 SKB_DR_SET(*drop_reason, TCP_OVERWINDOW); 863 } 864 return NULL; 865 } 866 867 /* In sequence, PAWS is OK. */ 868 869 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn) { 870 /* Truncate SYN, it is out of window starting 871 at tcp_rsk(req)->rcv_isn + 1. */ 872 flg &= ~TCP_FLAG_SYN; 873 } 874 875 /* RFC 5961 section 3.2, as clarified by RFC 9293 section 876 * 3.10.7.4, requires a challenge ACK for a non-exact 877 * in-window RST in SYN-RECEIVED. 878 */ 879 if ((flg & TCP_FLAG_RST) && 880 TCP_SKB_CB(skb)->seq != tcp_rsk(req)->rcv_nxt) { 881 tcp_reqsk_send_challenge_ack(sk, skb, req); 882 return NULL; 883 } 884 885 /* RFC793: "second check the RST bit" and 886 * "fourth, check the SYN bit" 887 */ 888 if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN)) { 889 TCP_INC_STATS(sock_net(sk), TCP_MIB_ATTEMPTFAILS); 890 goto embryonic_reset; 891 } 892 893 /* ACK sequence verified above, just make sure ACK is 894 * set. If ACK not set, just silently drop the packet. 895 * 896 * XXX (TFO) - if we ever allow "data after SYN", the 897 * following check needs to be removed. 898 */ 899 if (!(flg & TCP_FLAG_ACK)) 900 return NULL; 901 902 if (tcp_rsk(req)->accecn_ok && tmp_opt.accecn && 903 tcp_rsk(req)->saw_accecn_opt < TCP_ACCECN_OPT_COUNTER_SEEN) { 904 u8 saw_opt = tcp_accecn_option_init(skb, tmp_opt.accecn); 905 906 tcp_rsk(req)->saw_accecn_opt = saw_opt; 907 if (tcp_rsk(req)->saw_accecn_opt == TCP_ACCECN_OPT_FAIL_SEEN) { 908 u8 fail_mode = TCP_ACCECN_OPT_FAIL_RECV; 909 910 tcp_rsk(req)->accecn_fail_mode |= fail_mode; 911 } 912 } 913 914 /* For Fast Open no more processing is needed (sk is the 915 * child socket). 916 */ 917 if (fastopen) 918 return sk; 919 920 /* While TCP_DEFER_ACCEPT is active, drop bare ACK. */ 921 if (req->num_timeout < READ_ONCE(inet_csk(sk)->icsk_accept_queue.rskq_defer_accept) && 922 TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) { 923 inet_rsk(req)->acked = 1; 924 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDEFERACCEPTDROP); 925 return NULL; 926 } 927 928 /* OK, ACK is valid, create big socket and 929 * feed this segment to it. It will repeat all 930 * the tests. THIS SEGMENT MUST MOVE SOCKET TO 931 * ESTABLISHED STATE. If it will be dropped after 932 * socket is created, wait for troubles. 933 */ 934 child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL, 935 req, &own_req, NULL); 936 if (!child) 937 goto listen_overflow; 938 939 if (own_req && tmp_opt.saw_tstamp && 940 !after(TCP_SKB_CB(skb)->seq, tcp_rsk(req)->rcv_nxt)) 941 tcp_sk(child)->rx_opt.ts_recent = tmp_opt.rcv_tsval; 942 943 if (own_req && rsk_drop_req(req)) { 944 reqsk_queue_removed(&inet_csk(req->rsk_listener)->icsk_accept_queue, req); 945 inet_csk_reqsk_queue_drop_and_put(req->rsk_listener, req); 946 return child; 947 } 948 949 sock_rps_save_rxhash(child, skb); 950 tcp_synack_rtt_meas(child, req); 951 *req_stolen = !own_req; 952 return inet_csk_complete_hashdance(sk, child, req, own_req); 953 954 listen_overflow: 955 SKB_DR_SET(*drop_reason, TCP_LISTEN_OVERFLOW); 956 if (sk != req->rsk_listener) 957 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMIGRATEREQFAILURE); 958 959 if (!READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_abort_on_overflow)) { 960 inet_rsk(req)->acked = 1; 961 return NULL; 962 } 963 964 embryonic_reset: 965 if (!(flg & TCP_FLAG_RST)) { 966 /* Received a bad SYN pkt - for TFO We try not to reset 967 * the local connection unless it's really necessary to 968 * avoid becoming vulnerable to outside attack aiming at 969 * resetting legit local connections. 970 */ 971 req->rsk_ops->send_reset(sk, skb, SK_RST_REASON_INVALID_SYN); 972 } else if (fastopen) { /* received a valid RST pkt */ 973 reqsk_fastopen_remove(sk, req, true); 974 tcp_reset(sk, skb); 975 } 976 if (!fastopen) { 977 bool unlinked = inet_csk_reqsk_queue_drop(sk, req); 978 979 if (unlinked) 980 __NET_INC_STATS(sock_net(sk), LINUX_MIB_EMBRYONICRSTS); 981 *req_stolen = !unlinked; 982 } 983 return NULL; 984 } 985 986 /* 987 * Queue segment on the new socket if the new socket is active, 988 * otherwise we just shortcircuit this and continue with 989 * the new socket. 990 * 991 * For the vast majority of cases child->sk_state will be TCP_SYN_RECV 992 * when entering. But other states are possible due to a race condition 993 * where after __inet_lookup_established() fails but before the listener 994 * locked is obtained, other packets cause the same connection to 995 * be created. 996 */ 997 998 enum skb_drop_reason tcp_child_process(struct sock *parent, struct sock *child, 999 struct sk_buff *skb) 1000 __releases(&((child)->sk_lock.slock)) 1001 { 1002 enum skb_drop_reason reason = SKB_NOT_DROPPED_YET; 1003 int state = child->sk_state; 1004 1005 /* record sk_napi_id and sk_rx_queue_mapping of child. */ 1006 sk_mark_napi_id_set(child, skb); 1007 1008 tcp_segs_in(tcp_sk(child), skb); 1009 if (!sock_owned_by_user(child)) { 1010 reason = tcp_rcv_state_process(child, skb); 1011 /* Wakeup parent, send SIGIO */ 1012 if (state == TCP_SYN_RECV && child->sk_state != state) 1013 READ_ONCE(parent->sk_data_ready)(parent); 1014 } else { 1015 /* Alas, it is possible again, because we do lookup 1016 * in main socket hash table and lock on listening 1017 * socket does not protect us more. 1018 */ 1019 __sk_add_backlog(child, skb); 1020 } 1021 1022 bh_unlock_sock(child); 1023 1024 return reason; 1025 } 1026