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 tcp_md5_add_sigpool(); 316 } 317 return; 318 out_free: 319 WARN_ON_ONCE(1); 320 kfree(tcptw->tw_md5_key); 321 tcptw->tw_md5_key = NULL; 322 #endif 323 } 324 325 /* 326 * Move a socket to time-wait or dead fin-wait-2 state. 327 */ 328 void tcp_time_wait(struct sock *sk, int state, int timeo) 329 { 330 const struct inet_connection_sock *icsk = inet_csk(sk); 331 struct tcp_sock *tp = tcp_sk(sk); 332 struct net *net = sock_net(sk); 333 struct inet_timewait_sock *tw; 334 335 tw = inet_twsk_alloc(sk, &net->ipv4.tcp_death_row, state); 336 337 if (tw) { 338 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw); 339 const int rto = (icsk->icsk_rto << 2) - (icsk->icsk_rto >> 1); 340 341 tw->tw_transparent = inet_test_bit(TRANSPARENT, sk); 342 tw->tw_mark = sk->sk_mark; 343 tw->tw_priority = READ_ONCE(sk->sk_priority); 344 tw->tw_rcv_wscale = tp->rx_opt.rcv_wscale; 345 /* refreshed when we enter true TIME-WAIT state */ 346 tw->tw_entry_stamp = tcp_time_stamp_ms(tp); 347 tcptw->tw_rcv_nxt = tp->rcv_nxt; 348 tcptw->tw_snd_nxt = tp->snd_nxt; 349 tcptw->tw_rcv_wnd = tcp_receive_window(tp); 350 tcptw->tw_ts_recent = tp->rx_opt.ts_recent; 351 tcptw->tw_ts_recent_stamp = tp->rx_opt.ts_recent_stamp; 352 tcptw->tw_ts_offset = tp->tsoffset; 353 tw->tw_usec_ts = tp->tcp_usec_ts; 354 tcptw->tw_last_oow_ack_time = 0; 355 tcptw->tw_tx_delay = tp->tcp_tx_delay; 356 tw->tw_txhash = sk->sk_txhash; 357 tw->tw_tx_queue_mapping = sk->sk_tx_queue_mapping; 358 #ifdef CONFIG_SOCK_RX_QUEUE_MAPPING 359 tw->tw_rx_queue_mapping = sk->sk_rx_queue_mapping; 360 #endif 361 #if IS_ENABLED(CONFIG_IPV6) 362 if (tw->tw_family == PF_INET6) { 363 struct ipv6_pinfo *np = inet6_sk(sk); 364 365 tw->tw_v6_daddr = sk->sk_v6_daddr; 366 tw->tw_v6_rcv_saddr = sk->sk_v6_rcv_saddr; 367 tw->tw_tclass = np->tclass; 368 tw->tw_flowlabel = be32_to_cpu(np->flow_label & IPV6_FLOWLABEL_MASK); 369 tw->tw_ipv6only = sk->sk_ipv6only; 370 } 371 #endif 372 373 tcp_time_wait_init(sk, tcptw); 374 tcp_ao_time_wait(tcptw, tp); 375 376 /* Get the TIME_WAIT timeout firing. */ 377 if (timeo < rto) 378 timeo = rto; 379 380 if (state == TCP_TIME_WAIT) 381 timeo = TCP_TIMEWAIT_LEN; 382 383 /* Linkage updates. 384 * Note that access to tw after this point is illegal. 385 */ 386 inet_twsk_hashdance_schedule(tw, sk, net->ipv4.tcp_death_row.hashinfo, timeo); 387 } else { 388 /* Sorry, if we're out of memory, just CLOSE this 389 * socket up. We've got bigger problems than 390 * non-graceful socket closings. 391 */ 392 NET_INC_STATS(net, LINUX_MIB_TCPTIMEWAITOVERFLOW); 393 } 394 395 tcp_update_metrics(sk); 396 tcp_done(sk); 397 } 398 EXPORT_SYMBOL(tcp_time_wait); 399 400 void tcp_twsk_destructor(struct sock *sk) 401 { 402 #ifdef CONFIG_TCP_MD5SIG 403 if (static_branch_unlikely(&tcp_md5_needed.key)) { 404 struct tcp_timewait_sock *twsk = tcp_twsk(sk); 405 406 if (twsk->tw_md5_key) { 407 kfree(twsk->tw_md5_key); 408 static_branch_slow_dec_deferred(&tcp_md5_needed); 409 tcp_md5_release_sigpool(); 410 } 411 } 412 #endif 413 tcp_ao_destroy_sock(sk, true); 414 psp_twsk_assoc_free(inet_twsk(sk)); 415 } 416 417 void tcp_twsk_purge(struct list_head *net_exit_list) 418 { 419 bool purged_once = false; 420 struct net *net; 421 422 list_for_each_entry(net, net_exit_list, exit_list) { 423 if (net->ipv4.tcp_death_row.hashinfo->pernet) { 424 /* Even if tw_refcount == 1, we must clean up kernel reqsk */ 425 inet_twsk_purge(net->ipv4.tcp_death_row.hashinfo); 426 } else if (!purged_once) { 427 inet_twsk_purge(&tcp_hashinfo); 428 purged_once = true; 429 } 430 } 431 } 432 433 /* Warning : This function is called without sk_listener being locked. 434 * Be sure to read socket fields once, as their value could change under us. 435 */ 436 void tcp_openreq_init_rwin(struct request_sock *req, 437 const struct sock *sk_listener, 438 const struct dst_entry *dst) 439 { 440 struct inet_request_sock *ireq = inet_rsk(req); 441 const struct tcp_sock *tp = tcp_sk(sk_listener); 442 int full_space = tcp_full_space(sk_listener); 443 u32 window_clamp; 444 __u8 rcv_wscale; 445 u32 rcv_wnd; 446 int mss; 447 448 mss = tcp_mss_clamp(tp, dst_metric_advmss(dst)); 449 window_clamp = READ_ONCE(tp->window_clamp); 450 /* Set this up on the first call only */ 451 req->rsk_window_clamp = window_clamp ? : dst_metric(dst, RTAX_WINDOW); 452 453 /* limit the window selection if the user enforce a smaller rx buffer */ 454 if (sk_listener->sk_userlocks & SOCK_RCVBUF_LOCK && 455 (req->rsk_window_clamp > full_space || req->rsk_window_clamp == 0)) 456 req->rsk_window_clamp = full_space; 457 458 rcv_wnd = tcp_rwnd_init_bpf((struct sock *)req); 459 if (rcv_wnd == 0) 460 rcv_wnd = dst_metric(dst, RTAX_INITRWND); 461 else if (full_space < rcv_wnd * mss) 462 full_space = rcv_wnd * mss; 463 464 /* tcp_full_space because it is guaranteed to be the first packet */ 465 tcp_select_initial_window(sk_listener, full_space, 466 mss - (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0), 467 &req->rsk_rcv_wnd, 468 &req->rsk_window_clamp, 469 ireq->wscale_ok, 470 &rcv_wscale, 471 rcv_wnd); 472 ireq->rcv_wscale = rcv_wscale; 473 } 474 475 static void tcp_ecn_openreq_child(struct sock *sk, 476 const struct request_sock *req, 477 const struct sk_buff *skb) 478 { 479 const struct tcp_request_sock *treq = tcp_rsk(req); 480 struct tcp_sock *tp = tcp_sk(sk); 481 482 if (treq->accecn_ok) { 483 tcp_ecn_mode_set(tp, TCP_ECN_MODE_ACCECN); 484 tp->syn_ect_snt = treq->syn_ect_snt; 485 tcp_accecn_third_ack(sk, skb, treq->syn_ect_snt); 486 tp->saw_accecn_opt = treq->saw_accecn_opt; 487 tp->prev_ecnfield = treq->syn_ect_rcv; 488 tp->accecn_opt_demand = 1; 489 tcp_ecn_received_counters_payload(sk, skb); 490 } else { 491 tcp_ecn_mode_set(tp, inet_rsk(req)->ecn_ok ? 492 TCP_ECN_MODE_RFC3168 : 493 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 EXPORT_IPV6_MOD_GPL(tcp_ca_openreq_child); 525 526 static void smc_check_reset_syn_req(const struct tcp_sock *oldtp, 527 struct request_sock *req, 528 struct tcp_sock *newtp) 529 { 530 #if IS_ENABLED(CONFIG_SMC) 531 struct inet_request_sock *ireq; 532 533 if (static_branch_unlikely(&tcp_have_smc)) { 534 ireq = inet_rsk(req); 535 if (oldtp->syn_smc && !ireq->smc_ok) 536 newtp->syn_smc = 0; 537 } 538 #endif 539 } 540 541 /* This is not only more efficient than what we used to do, it eliminates 542 * a lot of code duplication between IPv4/IPv6 SYN recv processing. -DaveM 543 * 544 * Actually, we could lots of memory writes here. tp of listening 545 * socket contains all necessary default parameters. 546 */ 547 struct sock *tcp_create_openreq_child(const struct sock *sk, 548 struct request_sock *req, 549 struct sk_buff *skb) 550 { 551 struct sock *newsk = inet_csk_clone_lock(sk, req, GFP_ATOMIC); 552 const struct inet_request_sock *ireq = inet_rsk(req); 553 struct tcp_request_sock *treq = tcp_rsk(req); 554 struct inet_connection_sock *newicsk; 555 const struct tcp_sock *oldtp; 556 struct tcp_sock *newtp; 557 u32 seq; 558 559 if (!newsk) 560 return NULL; 561 562 newicsk = inet_csk(newsk); 563 newtp = tcp_sk(newsk); 564 oldtp = tcp_sk(sk); 565 566 smc_check_reset_syn_req(oldtp, req, newtp); 567 568 /* Now setup tcp_sock */ 569 newtp->pred_flags = 0; 570 571 seq = treq->rcv_isn + 1; 572 newtp->rcv_wup = seq; 573 WRITE_ONCE(newtp->copied_seq, seq); 574 WRITE_ONCE(newtp->rcv_nxt, seq); 575 newtp->segs_in = 1; 576 577 seq = treq->snt_isn + 1; 578 newtp->snd_sml = newtp->snd_una = seq; 579 WRITE_ONCE(newtp->snd_nxt, seq); 580 newtp->snd_up = seq; 581 582 INIT_LIST_HEAD(&newtp->tsq_node); 583 INIT_LIST_HEAD(&newtp->tsorted_sent_queue); 584 585 tcp_init_wl(newtp, treq->rcv_isn); 586 587 minmax_reset(&newtp->rtt_min, tcp_jiffies32, ~0U); 588 newicsk->icsk_ack.lrcvtime = tcp_jiffies32; 589 590 newtp->lsndtime = tcp_jiffies32; 591 newsk->sk_txhash = READ_ONCE(treq->txhash); 592 newtp->total_retrans = req->num_retrans; 593 594 tcp_init_xmit_timers(newsk); 595 WRITE_ONCE(newtp->write_seq, newtp->pushed_seq = treq->snt_isn + 1); 596 597 if (sock_flag(newsk, SOCK_KEEPOPEN)) 598 tcp_reset_keepalive_timer(newsk, keepalive_time_when(newtp)); 599 600 newtp->rx_opt.tstamp_ok = ireq->tstamp_ok; 601 newtp->rx_opt.sack_ok = ireq->sack_ok; 602 newtp->window_clamp = req->rsk_window_clamp; 603 newtp->rcv_ssthresh = req->rsk_rcv_wnd; 604 newtp->rcv_wnd = 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 EXPORT_SYMBOL(tcp_create_openreq_child); 673 674 /* 675 * Process an incoming packet for SYN_RECV sockets represented as a 676 * request_sock. Normally sk is the listener socket but for TFO it 677 * points to the child socket. 678 * 679 * XXX (TFO) - The current impl contains a special check for ack 680 * validation and inside tcp_v4_reqsk_send_ack(). Can we do better? 681 * 682 * We don't need to initialize tmp_opt.sack_ok as we don't use the results 683 * 684 * Note: If @fastopen is true, this can be called from process context. 685 * Otherwise, this is from BH context. 686 */ 687 688 struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb, 689 struct request_sock *req, 690 bool fastopen, bool *req_stolen, 691 enum skb_drop_reason *drop_reason) 692 { 693 struct tcp_options_received tmp_opt; 694 struct sock *child; 695 const struct tcphdr *th = tcp_hdr(skb); 696 __be32 flg = tcp_flag_word(th) & (TCP_FLAG_RST|TCP_FLAG_SYN|TCP_FLAG_ACK); 697 bool tsecr_reject = false; 698 bool paws_reject = false; 699 bool own_req; 700 701 tmp_opt.saw_tstamp = 0; 702 tmp_opt.accecn = 0; 703 if (th->doff > (sizeof(struct tcphdr)>>2)) { 704 tcp_parse_options(sock_net(sk), skb, &tmp_opt, 0, NULL); 705 706 if (tmp_opt.saw_tstamp) { 707 tmp_opt.ts_recent = req->ts_recent; 708 if (tmp_opt.rcv_tsecr) { 709 if (inet_rsk(req)->tstamp_ok && !fastopen) 710 tsecr_reject = !between(tmp_opt.rcv_tsecr, 711 tcp_rsk(req)->snt_tsval_first, 712 READ_ONCE(tcp_rsk(req)->snt_tsval_last)); 713 tmp_opt.rcv_tsecr -= tcp_rsk(req)->ts_off; 714 } 715 /* We do not store true stamp, but it is not required, 716 * it can be estimated (approximately) 717 * from another data. 718 */ 719 tmp_opt.ts_recent_stamp = ktime_get_seconds() - reqsk_timeout(req, TCP_RTO_MAX) / 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) && 754 755 !tcp_rtx_synack(sk, req)) { 756 unsigned long expires = jiffies; 757 758 expires += reqsk_timeout(req, TCP_RTO_MAX); 759 if (!fastopen) 760 mod_timer_pending(&req->rsk_timer, expires); 761 else 762 req->rsk_timer.expires = expires; 763 } 764 return NULL; 765 } 766 767 /* Further reproduces section "SEGMENT ARRIVES" 768 for state SYN-RECEIVED of RFC793. 769 It is broken, however, it does not work only 770 when SYNs are crossed. 771 772 You would think that SYN crossing is impossible here, since 773 we should have a SYN_SENT socket (from connect()) on our end, 774 but this is not true if the crossed SYNs were sent to both 775 ends by a malicious third party. We must defend against this, 776 and to do that we first verify the ACK (as per RFC793, page 777 36) and reset if it is invalid. Is this a true full defense? 778 To convince ourselves, let us consider a way in which the ACK 779 test can still pass in this 'malicious crossed SYNs' case. 780 Malicious sender sends identical SYNs (and thus identical sequence 781 numbers) to both A and B: 782 783 A: gets SYN, seq=7 784 B: gets SYN, seq=7 785 786 By our good fortune, both A and B select the same initial 787 send sequence number of seven :-) 788 789 A: sends SYN|ACK, seq=7, ack_seq=8 790 B: sends SYN|ACK, seq=7, ack_seq=8 791 792 So we are now A eating this SYN|ACK, ACK test passes. So 793 does sequence test, SYN is truncated, and thus we consider 794 it a bare ACK. 795 796 If icsk->icsk_accept_queue.rskq_defer_accept, we silently drop this 797 bare ACK. Otherwise, we create an established connection. Both 798 ends (listening sockets) accept the new incoming connection and try 799 to talk to each other. 8-) 800 801 Note: This case is both harmless, and rare. Possibility is about the 802 same as us discovering intelligent life on another plant tomorrow. 803 804 But generally, we should (RFC lies!) to accept ACK 805 from SYNACK both here and in tcp_rcv_state_process(). 806 tcp_rcv_state_process() does not, hence, we do not too. 807 808 Note that the case is absolutely generic: 809 we cannot optimize anything here without 810 violating protocol. All the checks must be made 811 before attempt to create socket. 812 */ 813 814 /* RFC793 page 36: "If the connection is in any non-synchronized state ... 815 * and the incoming segment acknowledges something not yet 816 * sent (the segment carries an unacceptable ACK) ... 817 * a reset is sent." 818 * 819 * Invalid ACK: reset will be sent by listening socket. 820 * Note that the ACK validity check for a Fast Open socket is done 821 * elsewhere and is checked directly against the child socket rather 822 * than req because user data may have been sent out. 823 */ 824 if ((flg & TCP_FLAG_ACK) && !fastopen && 825 (TCP_SKB_CB(skb)->ack_seq != 826 tcp_rsk(req)->snt_isn + 1)) 827 return sk; 828 829 /* RFC793: "first check sequence number". */ 830 831 if (paws_reject || tsecr_reject || 832 !tcp_in_window(TCP_SKB_CB(skb)->seq, 833 TCP_SKB_CB(skb)->end_seq, 834 tcp_rsk(req)->rcv_nxt, 835 tcp_rsk(req)->rcv_nxt + 836 tcp_synack_window(req))) { 837 /* Out of window: send ACK and drop. */ 838 if (!(flg & TCP_FLAG_RST) && 839 !tcp_oow_rate_limited(sock_net(sk), skb, 840 LINUX_MIB_TCPACKSKIPPEDSYNRECV, 841 &tcp_rsk(req)->last_oow_ack_time)) 842 req->rsk_ops->send_ack(sk, skb, req); 843 if (paws_reject) { 844 SKB_DR_SET(*drop_reason, TCP_RFC7323_PAWS); 845 NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED); 846 } else if (tsecr_reject) { 847 SKB_DR_SET(*drop_reason, TCP_RFC7323_TSECR); 848 NET_INC_STATS(sock_net(sk), LINUX_MIB_TSECRREJECTED); 849 } else { 850 SKB_DR_SET(*drop_reason, TCP_OVERWINDOW); 851 } 852 return NULL; 853 } 854 855 /* In sequence, PAWS is OK. */ 856 857 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn) { 858 /* Truncate SYN, it is out of window starting 859 at tcp_rsk(req)->rcv_isn + 1. */ 860 flg &= ~TCP_FLAG_SYN; 861 } 862 863 /* RFC793: "second check the RST bit" and 864 * "fourth, check the SYN bit" 865 */ 866 if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN)) { 867 TCP_INC_STATS(sock_net(sk), TCP_MIB_ATTEMPTFAILS); 868 goto embryonic_reset; 869 } 870 871 /* ACK sequence verified above, just make sure ACK is 872 * set. If ACK not set, just silently drop the packet. 873 * 874 * XXX (TFO) - if we ever allow "data after SYN", the 875 * following check needs to be removed. 876 */ 877 if (!(flg & TCP_FLAG_ACK)) 878 return NULL; 879 880 if (tcp_rsk(req)->accecn_ok && tmp_opt.accecn && 881 tcp_rsk(req)->saw_accecn_opt < TCP_ACCECN_OPT_COUNTER_SEEN) { 882 u8 saw_opt = tcp_accecn_option_init(skb, tmp_opt.accecn); 883 884 tcp_rsk(req)->saw_accecn_opt = saw_opt; 885 if (tcp_rsk(req)->saw_accecn_opt == TCP_ACCECN_OPT_FAIL_SEEN) { 886 u8 fail_mode = TCP_ACCECN_OPT_FAIL_RECV; 887 888 tcp_rsk(req)->accecn_fail_mode |= fail_mode; 889 } 890 } 891 892 /* For Fast Open no more processing is needed (sk is the 893 * child socket). 894 */ 895 if (fastopen) 896 return sk; 897 898 /* While TCP_DEFER_ACCEPT is active, drop bare ACK. */ 899 if (req->num_timeout < READ_ONCE(inet_csk(sk)->icsk_accept_queue.rskq_defer_accept) && 900 TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) { 901 inet_rsk(req)->acked = 1; 902 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDEFERACCEPTDROP); 903 return NULL; 904 } 905 906 /* OK, ACK is valid, create big socket and 907 * feed this segment to it. It will repeat all 908 * the tests. THIS SEGMENT MUST MOVE SOCKET TO 909 * ESTABLISHED STATE. If it will be dropped after 910 * socket is created, wait for troubles. 911 */ 912 child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL, 913 req, &own_req); 914 if (!child) 915 goto listen_overflow; 916 917 if (own_req && tmp_opt.saw_tstamp && 918 !after(TCP_SKB_CB(skb)->seq, tcp_rsk(req)->rcv_nxt)) 919 tcp_sk(child)->rx_opt.ts_recent = tmp_opt.rcv_tsval; 920 921 if (own_req && rsk_drop_req(req)) { 922 reqsk_queue_removed(&inet_csk(req->rsk_listener)->icsk_accept_queue, req); 923 inet_csk_reqsk_queue_drop_and_put(req->rsk_listener, req); 924 return child; 925 } 926 927 sock_rps_save_rxhash(child, skb); 928 tcp_synack_rtt_meas(child, req); 929 *req_stolen = !own_req; 930 return inet_csk_complete_hashdance(sk, child, req, own_req); 931 932 listen_overflow: 933 SKB_DR_SET(*drop_reason, TCP_LISTEN_OVERFLOW); 934 if (sk != req->rsk_listener) 935 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMIGRATEREQFAILURE); 936 937 if (!READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_abort_on_overflow)) { 938 inet_rsk(req)->acked = 1; 939 return NULL; 940 } 941 942 embryonic_reset: 943 if (!(flg & TCP_FLAG_RST)) { 944 /* Received a bad SYN pkt - for TFO We try not to reset 945 * the local connection unless it's really necessary to 946 * avoid becoming vulnerable to outside attack aiming at 947 * resetting legit local connections. 948 */ 949 req->rsk_ops->send_reset(sk, skb, SK_RST_REASON_INVALID_SYN); 950 } else if (fastopen) { /* received a valid RST pkt */ 951 reqsk_fastopen_remove(sk, req, true); 952 tcp_reset(sk, skb); 953 } 954 if (!fastopen) { 955 bool unlinked = inet_csk_reqsk_queue_drop(sk, req); 956 957 if (unlinked) 958 __NET_INC_STATS(sock_net(sk), LINUX_MIB_EMBRYONICRSTS); 959 *req_stolen = !unlinked; 960 } 961 return NULL; 962 } 963 EXPORT_IPV6_MOD(tcp_check_req); 964 965 /* 966 * Queue segment on the new socket if the new socket is active, 967 * otherwise we just shortcircuit this and continue with 968 * the new socket. 969 * 970 * For the vast majority of cases child->sk_state will be TCP_SYN_RECV 971 * when entering. But other states are possible due to a race condition 972 * where after __inet_lookup_established() fails but before the listener 973 * locked is obtained, other packets cause the same connection to 974 * be created. 975 */ 976 977 enum skb_drop_reason tcp_child_process(struct sock *parent, struct sock *child, 978 struct sk_buff *skb) 979 __releases(&((child)->sk_lock.slock)) 980 { 981 enum skb_drop_reason reason = SKB_NOT_DROPPED_YET; 982 int state = child->sk_state; 983 984 /* record sk_napi_id and sk_rx_queue_mapping of child. */ 985 sk_mark_napi_id_set(child, skb); 986 987 tcp_segs_in(tcp_sk(child), skb); 988 if (!sock_owned_by_user(child)) { 989 reason = tcp_rcv_state_process(child, skb); 990 /* Wakeup parent, send SIGIO */ 991 if (state == TCP_SYN_RECV && child->sk_state != state) 992 parent->sk_data_ready(parent); 993 } else { 994 /* Alas, it is possible again, because we do lookup 995 * in main socket hash table and lock on listening 996 * socket does not protect us more. 997 */ 998 __sk_add_backlog(child, skb); 999 } 1000 1001 bh_unlock_sock(child); 1002 sock_put(child); 1003 return reason; 1004 } 1005 EXPORT_IPV6_MOD(tcp_child_process); 1006