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 if (treq->accecn_fail_mode & TCP_ACCECN_ACE_FAIL_SEND) 485 tcp_accecn_fail_mode_set(tp, TCP_ACCECN_ACE_FAIL_SEND); 486 if (treq->accecn_fail_mode & TCP_ACCECN_ACE_FAIL_RECV) 487 tcp_accecn_fail_mode_set(tp, TCP_ACCECN_ACE_FAIL_RECV); 488 tp->prev_ecnfield = treq->syn_ect_rcv; 489 tp->accecn_opt_demand = 1; 490 tcp_ecn_received_counters_payload(sk, skb); 491 } else { 492 if (inet_rsk(req)->ecn_ok && !tcp_ca_no_fallback_rfc3168(sk)) 493 tcp_ecn_mode_set(tp, TCP_ECN_MODE_RFC3168); 494 else 495 tcp_ecn_mode_set(tp, TCP_ECN_DISABLED); 496 } 497 } 498 499 void tcp_ca_openreq_child(struct sock *sk, const struct dst_entry *dst) 500 { 501 struct inet_connection_sock *icsk = inet_csk(sk); 502 u32 ca_key = dst_metric(dst, RTAX_CC_ALGO); 503 bool ca_got_dst = false; 504 505 if (ca_key != TCP_CA_UNSPEC) { 506 const struct tcp_congestion_ops *ca; 507 508 rcu_read_lock(); 509 ca = tcp_ca_find_key(ca_key); 510 if (likely(ca && bpf_try_module_get(ca, ca->owner))) { 511 icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst); 512 icsk->icsk_ca_ops = ca; 513 ca_got_dst = true; 514 } 515 rcu_read_unlock(); 516 } 517 518 /* If no valid choice made yet, assign current system default ca. */ 519 if (!ca_got_dst && 520 (!icsk->icsk_ca_setsockopt || 521 !bpf_try_module_get(icsk->icsk_ca_ops, icsk->icsk_ca_ops->owner))) 522 tcp_assign_congestion_control(sk); 523 524 tcp_set_ca_state(sk, TCP_CA_Open); 525 } 526 EXPORT_IPV6_MOD_GPL(tcp_ca_openreq_child); 527 528 static void smc_check_reset_syn_req(const struct tcp_sock *oldtp, 529 struct request_sock *req, 530 struct tcp_sock *newtp) 531 { 532 #if IS_ENABLED(CONFIG_SMC) 533 struct inet_request_sock *ireq; 534 535 if (static_branch_unlikely(&tcp_have_smc)) { 536 ireq = inet_rsk(req); 537 if (oldtp->syn_smc && !ireq->smc_ok) 538 newtp->syn_smc = 0; 539 } 540 #endif 541 } 542 543 /* This is not only more efficient than what we used to do, it eliminates 544 * a lot of code duplication between IPv4/IPv6 SYN recv processing. -DaveM 545 * 546 * Actually, we could lots of memory writes here. tp of listening 547 * socket contains all necessary default parameters. 548 */ 549 struct sock *tcp_create_openreq_child(const struct sock *sk, 550 struct request_sock *req, 551 struct sk_buff *skb) 552 { 553 struct sock *newsk = inet_csk_clone_lock(sk, req, GFP_ATOMIC); 554 const struct inet_request_sock *ireq = inet_rsk(req); 555 struct tcp_request_sock *treq = tcp_rsk(req); 556 struct inet_connection_sock *newicsk; 557 const struct tcp_sock *oldtp; 558 struct tcp_sock *newtp; 559 u32 seq; 560 561 if (!newsk) 562 return NULL; 563 564 newicsk = inet_csk(newsk); 565 newtp = tcp_sk(newsk); 566 oldtp = tcp_sk(sk); 567 568 smc_check_reset_syn_req(oldtp, req, newtp); 569 570 /* Now setup tcp_sock */ 571 newtp->pred_flags = 0; 572 573 seq = treq->rcv_isn + 1; 574 newtp->rcv_wup = seq; 575 WRITE_ONCE(newtp->copied_seq, seq); 576 WRITE_ONCE(newtp->rcv_nxt, seq); 577 newtp->segs_in = 1; 578 579 seq = treq->snt_isn + 1; 580 newtp->snd_sml = newtp->snd_una = seq; 581 WRITE_ONCE(newtp->snd_nxt, seq); 582 newtp->snd_up = seq; 583 584 INIT_LIST_HEAD(&newtp->tsq_node); 585 INIT_LIST_HEAD(&newtp->tsorted_sent_queue); 586 587 tcp_init_wl(newtp, treq->rcv_isn); 588 589 minmax_reset(&newtp->rtt_min, tcp_jiffies32, ~0U); 590 newicsk->icsk_ack.lrcvtime = tcp_jiffies32; 591 592 newtp->lsndtime = tcp_jiffies32; 593 newsk->sk_txhash = READ_ONCE(treq->txhash); 594 newtp->total_retrans = req->num_retrans; 595 596 tcp_init_xmit_timers(newsk); 597 WRITE_ONCE(newtp->write_seq, newtp->pushed_seq = treq->snt_isn + 1); 598 599 if (sock_flag(newsk, SOCK_KEEPOPEN)) 600 tcp_reset_keepalive_timer(newsk, keepalive_time_when(newtp)); 601 602 newtp->rx_opt.tstamp_ok = ireq->tstamp_ok; 603 newtp->rx_opt.sack_ok = ireq->sack_ok; 604 newtp->window_clamp = req->rsk_window_clamp; 605 newtp->rcv_ssthresh = req->rsk_rcv_wnd; 606 newtp->rcv_wnd = req->rsk_rcv_wnd; 607 newtp->rx_opt.wscale_ok = ireq->wscale_ok; 608 if (newtp->rx_opt.wscale_ok) { 609 newtp->rx_opt.snd_wscale = ireq->snd_wscale; 610 newtp->rx_opt.rcv_wscale = ireq->rcv_wscale; 611 } else { 612 newtp->rx_opt.snd_wscale = newtp->rx_opt.rcv_wscale = 0; 613 newtp->window_clamp = min(newtp->window_clamp, 65535U); 614 } 615 newtp->snd_wnd = ntohs(tcp_hdr(skb)->window) << newtp->rx_opt.snd_wscale; 616 newtp->max_window = newtp->snd_wnd; 617 618 if (newtp->rx_opt.tstamp_ok) { 619 newtp->tcp_usec_ts = treq->req_usec_ts; 620 newtp->rx_opt.ts_recent = req->ts_recent; 621 newtp->rx_opt.ts_recent_stamp = ktime_get_seconds(); 622 newtp->tcp_header_len = sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED; 623 } else { 624 newtp->tcp_usec_ts = 0; 625 newtp->rx_opt.ts_recent_stamp = 0; 626 newtp->tcp_header_len = sizeof(struct tcphdr); 627 } 628 if (req->num_timeout) { 629 newtp->total_rto = req->num_timeout; 630 newtp->undo_marker = treq->snt_isn; 631 if (newtp->tcp_usec_ts) { 632 newtp->retrans_stamp = treq->snt_synack; 633 newtp->total_rto_time = (u32)(tcp_clock_us() - 634 newtp->retrans_stamp) / USEC_PER_MSEC; 635 } else { 636 newtp->retrans_stamp = div_u64(treq->snt_synack, 637 USEC_PER_SEC / TCP_TS_HZ); 638 newtp->total_rto_time = tcp_clock_ms() - 639 newtp->retrans_stamp; 640 } 641 newtp->total_rto_recoveries = 1; 642 } 643 newtp->tsoffset = treq->ts_off; 644 #ifdef CONFIG_TCP_MD5SIG 645 newtp->md5sig_info = NULL; /*XXX*/ 646 #endif 647 #ifdef CONFIG_TCP_AO 648 newtp->ao_info = NULL; 649 650 if (tcp_rsk_used_ao(req)) { 651 struct tcp_ao_key *ao_key; 652 653 ao_key = treq->af_specific->ao_lookup(sk, req, tcp_rsk(req)->ao_keyid, -1); 654 if (ao_key) 655 newtp->tcp_header_len += tcp_ao_len_aligned(ao_key); 656 } 657 #endif 658 if (skb->len >= TCP_MSS_DEFAULT + newtp->tcp_header_len) 659 newicsk->icsk_ack.last_seg_size = skb->len - newtp->tcp_header_len; 660 newtp->rx_opt.mss_clamp = req->mss; 661 tcp_ecn_openreq_child(newsk, req, skb); 662 newtp->fastopen_req = NULL; 663 RCU_INIT_POINTER(newtp->fastopen_rsk, NULL); 664 665 newtp->bpf_chg_cc_inprogress = 0; 666 tcp_bpf_clone(sk, newsk); 667 668 __TCP_INC_STATS(sock_net(sk), TCP_MIB_PASSIVEOPENS); 669 670 xa_init_flags(&newsk->sk_user_frags, XA_FLAGS_ALLOC1); 671 672 return newsk; 673 } 674 EXPORT_SYMBOL(tcp_create_openreq_child); 675 676 /* 677 * Process an incoming packet for SYN_RECV sockets represented as a 678 * request_sock. Normally sk is the listener socket but for TFO it 679 * points to the child socket. 680 * 681 * XXX (TFO) - The current impl contains a special check for ack 682 * validation and inside tcp_v4_reqsk_send_ack(). Can we do better? 683 * 684 * We don't need to initialize tmp_opt.sack_ok as we don't use the results 685 * 686 * Note: If @fastopen is true, this can be called from process context. 687 * Otherwise, this is from BH context. 688 */ 689 690 struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb, 691 struct request_sock *req, 692 bool fastopen, bool *req_stolen, 693 enum skb_drop_reason *drop_reason) 694 { 695 struct tcp_options_received tmp_opt; 696 struct sock *child; 697 const struct tcphdr *th = tcp_hdr(skb); 698 __be32 flg = tcp_flag_word(th) & (TCP_FLAG_RST|TCP_FLAG_SYN|TCP_FLAG_ACK); 699 bool tsecr_reject = false; 700 bool paws_reject = false; 701 bool own_req; 702 703 tmp_opt.saw_tstamp = 0; 704 tmp_opt.accecn = 0; 705 if (th->doff > (sizeof(struct tcphdr)>>2)) { 706 tcp_parse_options(sock_net(sk), skb, &tmp_opt, 0, NULL); 707 708 if (tmp_opt.saw_tstamp) { 709 tmp_opt.ts_recent = req->ts_recent; 710 if (tmp_opt.rcv_tsecr) { 711 if (inet_rsk(req)->tstamp_ok && !fastopen) 712 tsecr_reject = !between(tmp_opt.rcv_tsecr, 713 tcp_rsk(req)->snt_tsval_first, 714 READ_ONCE(tcp_rsk(req)->snt_tsval_last)); 715 tmp_opt.rcv_tsecr -= tcp_rsk(req)->ts_off; 716 } 717 /* We do not store true stamp, but it is not required, 718 * it can be estimated (approximately) 719 * from another data. 720 */ 721 tmp_opt.ts_recent_stamp = ktime_get_seconds() - 722 tcp_reqsk_timeout(req) / HZ; 723 paws_reject = tcp_paws_reject(&tmp_opt, th->rst); 724 } 725 } 726 727 /* Check for pure retransmitted SYN. */ 728 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn && 729 flg == TCP_FLAG_SYN && 730 !paws_reject) { 731 /* 732 * RFC793 draws (Incorrectly! It was fixed in RFC1122) 733 * this case on figure 6 and figure 8, but formal 734 * protocol description says NOTHING. 735 * To be more exact, it says that we should send ACK, 736 * because this segment (at least, if it has no data) 737 * is out of window. 738 * 739 * CONCLUSION: RFC793 (even with RFC1122) DOES NOT 740 * describe SYN-RECV state. All the description 741 * is wrong, we cannot believe to it and should 742 * rely only on common sense and implementation 743 * experience. 744 * 745 * Enforce "SYN-ACK" according to figure 8, figure 6 746 * of RFC793, fixed by RFC1122. 747 * 748 * Note that even if there is new data in the SYN packet 749 * they will be thrown away too. 750 * 751 * Reset timer after retransmitting SYNACK, similar to 752 * the idea of fast retransmit in recovery. 753 */ 754 if (!tcp_oow_rate_limited(sock_net(sk), skb, 755 LINUX_MIB_TCPACKSKIPPEDSYNRECV, 756 &tcp_rsk(req)->last_oow_ack_time)) { 757 if (tcp_rsk(req)->accecn_ok) { 758 u8 ect_rcv = TCP_SKB_CB(skb)->ip_dsfield & 759 INET_ECN_MASK; 760 761 tcp_rsk(req)->syn_ect_rcv = ect_rcv; 762 if (tcp_accecn_ace(tcp_hdr(skb)) == 0x0) 763 tcp_rsk(req)->accecn_fail_mode |= TCP_ACCECN_ACE_FAIL_RECV; 764 } 765 if (!tcp_rtx_synack(sk, req)) { 766 unsigned long expires = jiffies; 767 768 if (req->num_retrans > 1 && tcp_rsk(req)->accecn_ok) 769 tcp_rsk(req)->accecn_fail_mode |= TCP_ACCECN_ACE_FAIL_SEND; 770 771 expires += tcp_reqsk_timeout(req); 772 if (!fastopen) 773 mod_timer_pending(&req->rsk_timer, 774 expires); 775 else 776 req->rsk_timer.expires = expires; 777 } 778 } 779 return NULL; 780 } 781 782 /* Further reproduces section "SEGMENT ARRIVES" 783 for state SYN-RECEIVED of RFC793. 784 It is broken, however, it does not work only 785 when SYNs are crossed. 786 787 You would think that SYN crossing is impossible here, since 788 we should have a SYN_SENT socket (from connect()) on our end, 789 but this is not true if the crossed SYNs were sent to both 790 ends by a malicious third party. We must defend against this, 791 and to do that we first verify the ACK (as per RFC793, page 792 36) and reset if it is invalid. Is this a true full defense? 793 To convince ourselves, let us consider a way in which the ACK 794 test can still pass in this 'malicious crossed SYNs' case. 795 Malicious sender sends identical SYNs (and thus identical sequence 796 numbers) to both A and B: 797 798 A: gets SYN, seq=7 799 B: gets SYN, seq=7 800 801 By our good fortune, both A and B select the same initial 802 send sequence number of seven :-) 803 804 A: sends SYN|ACK, seq=7, ack_seq=8 805 B: sends SYN|ACK, seq=7, ack_seq=8 806 807 So we are now A eating this SYN|ACK, ACK test passes. So 808 does sequence test, SYN is truncated, and thus we consider 809 it a bare ACK. 810 811 If icsk->icsk_accept_queue.rskq_defer_accept, we silently drop this 812 bare ACK. Otherwise, we create an established connection. Both 813 ends (listening sockets) accept the new incoming connection and try 814 to talk to each other. 8-) 815 816 Note: This case is both harmless, and rare. Possibility is about the 817 same as us discovering intelligent life on another plant tomorrow. 818 819 But generally, we should (RFC lies!) to accept ACK 820 from SYNACK both here and in tcp_rcv_state_process(). 821 tcp_rcv_state_process() does not, hence, we do not too. 822 823 Note that the case is absolutely generic: 824 we cannot optimize anything here without 825 violating protocol. All the checks must be made 826 before attempt to create socket. 827 */ 828 829 /* RFC793 page 36: "If the connection is in any non-synchronized state ... 830 * and the incoming segment acknowledges something not yet 831 * sent (the segment carries an unacceptable ACK) ... 832 * a reset is sent." 833 * 834 * Invalid ACK: reset will be sent by listening socket. 835 * Note that the ACK validity check for a Fast Open socket is done 836 * elsewhere and is checked directly against the child socket rather 837 * than req because user data may have been sent out. 838 */ 839 if ((flg & TCP_FLAG_ACK) && !fastopen && 840 (TCP_SKB_CB(skb)->ack_seq != 841 tcp_rsk(req)->snt_isn + 1)) 842 return sk; 843 844 /* RFC793: "first check sequence number". */ 845 846 if (paws_reject || tsecr_reject || 847 !tcp_in_window(TCP_SKB_CB(skb)->seq, 848 TCP_SKB_CB(skb)->end_seq, 849 tcp_rsk(req)->rcv_nxt, 850 tcp_rsk(req)->rcv_nxt + 851 tcp_synack_window(req))) { 852 /* Out of window: send ACK and drop. */ 853 if (!(flg & TCP_FLAG_RST) && 854 !tcp_oow_rate_limited(sock_net(sk), skb, 855 LINUX_MIB_TCPACKSKIPPEDSYNRECV, 856 &tcp_rsk(req)->last_oow_ack_time)) 857 req->rsk_ops->send_ack(sk, skb, req); 858 if (paws_reject) { 859 SKB_DR_SET(*drop_reason, TCP_RFC7323_PAWS); 860 NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED); 861 } else if (tsecr_reject) { 862 SKB_DR_SET(*drop_reason, TCP_RFC7323_TSECR); 863 NET_INC_STATS(sock_net(sk), LINUX_MIB_TSECRREJECTED); 864 } else { 865 SKB_DR_SET(*drop_reason, TCP_OVERWINDOW); 866 } 867 return NULL; 868 } 869 870 /* In sequence, PAWS is OK. */ 871 872 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn) { 873 /* Truncate SYN, it is out of window starting 874 at tcp_rsk(req)->rcv_isn + 1. */ 875 flg &= ~TCP_FLAG_SYN; 876 } 877 878 /* RFC793: "second check the RST bit" and 879 * "fourth, check the SYN bit" 880 */ 881 if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN)) { 882 TCP_INC_STATS(sock_net(sk), TCP_MIB_ATTEMPTFAILS); 883 goto embryonic_reset; 884 } 885 886 /* ACK sequence verified above, just make sure ACK is 887 * set. If ACK not set, just silently drop the packet. 888 * 889 * XXX (TFO) - if we ever allow "data after SYN", the 890 * following check needs to be removed. 891 */ 892 if (!(flg & TCP_FLAG_ACK)) 893 return NULL; 894 895 if (tcp_rsk(req)->accecn_ok && tmp_opt.accecn && 896 tcp_rsk(req)->saw_accecn_opt < TCP_ACCECN_OPT_COUNTER_SEEN) { 897 u8 saw_opt = tcp_accecn_option_init(skb, tmp_opt.accecn); 898 899 tcp_rsk(req)->saw_accecn_opt = saw_opt; 900 if (tcp_rsk(req)->saw_accecn_opt == TCP_ACCECN_OPT_FAIL_SEEN) { 901 u8 fail_mode = TCP_ACCECN_OPT_FAIL_RECV; 902 903 tcp_rsk(req)->accecn_fail_mode |= fail_mode; 904 } 905 } 906 907 /* For Fast Open no more processing is needed (sk is the 908 * child socket). 909 */ 910 if (fastopen) 911 return sk; 912 913 /* While TCP_DEFER_ACCEPT is active, drop bare ACK. */ 914 if (req->num_timeout < READ_ONCE(inet_csk(sk)->icsk_accept_queue.rskq_defer_accept) && 915 TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) { 916 inet_rsk(req)->acked = 1; 917 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDEFERACCEPTDROP); 918 return NULL; 919 } 920 921 /* OK, ACK is valid, create big socket and 922 * feed this segment to it. It will repeat all 923 * the tests. THIS SEGMENT MUST MOVE SOCKET TO 924 * ESTABLISHED STATE. If it will be dropped after 925 * socket is created, wait for troubles. 926 */ 927 child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL, 928 req, &own_req, NULL); 929 if (!child) 930 goto listen_overflow; 931 932 if (own_req && tmp_opt.saw_tstamp && 933 !after(TCP_SKB_CB(skb)->seq, tcp_rsk(req)->rcv_nxt)) 934 tcp_sk(child)->rx_opt.ts_recent = tmp_opt.rcv_tsval; 935 936 if (own_req && rsk_drop_req(req)) { 937 reqsk_queue_removed(&inet_csk(req->rsk_listener)->icsk_accept_queue, req); 938 inet_csk_reqsk_queue_drop_and_put(req->rsk_listener, req); 939 return child; 940 } 941 942 sock_rps_save_rxhash(child, skb); 943 tcp_synack_rtt_meas(child, req); 944 *req_stolen = !own_req; 945 return inet_csk_complete_hashdance(sk, child, req, own_req); 946 947 listen_overflow: 948 SKB_DR_SET(*drop_reason, TCP_LISTEN_OVERFLOW); 949 if (sk != req->rsk_listener) 950 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMIGRATEREQFAILURE); 951 952 if (!READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_abort_on_overflow)) { 953 inet_rsk(req)->acked = 1; 954 return NULL; 955 } 956 957 embryonic_reset: 958 if (!(flg & TCP_FLAG_RST)) { 959 /* Received a bad SYN pkt - for TFO We try not to reset 960 * the local connection unless it's really necessary to 961 * avoid becoming vulnerable to outside attack aiming at 962 * resetting legit local connections. 963 */ 964 req->rsk_ops->send_reset(sk, skb, SK_RST_REASON_INVALID_SYN); 965 } else if (fastopen) { /* received a valid RST pkt */ 966 reqsk_fastopen_remove(sk, req, true); 967 tcp_reset(sk, skb); 968 } 969 if (!fastopen) { 970 bool unlinked = inet_csk_reqsk_queue_drop(sk, req); 971 972 if (unlinked) 973 __NET_INC_STATS(sock_net(sk), LINUX_MIB_EMBRYONICRSTS); 974 *req_stolen = !unlinked; 975 } 976 return NULL; 977 } 978 EXPORT_IPV6_MOD(tcp_check_req); 979 980 /* 981 * Queue segment on the new socket if the new socket is active, 982 * otherwise we just shortcircuit this and continue with 983 * the new socket. 984 * 985 * For the vast majority of cases child->sk_state will be TCP_SYN_RECV 986 * when entering. But other states are possible due to a race condition 987 * where after __inet_lookup_established() fails but before the listener 988 * locked is obtained, other packets cause the same connection to 989 * be created. 990 */ 991 992 enum skb_drop_reason tcp_child_process(struct sock *parent, struct sock *child, 993 struct sk_buff *skb) 994 __releases(&((child)->sk_lock.slock)) 995 { 996 enum skb_drop_reason reason = SKB_NOT_DROPPED_YET; 997 int state = child->sk_state; 998 999 /* record sk_napi_id and sk_rx_queue_mapping of child. */ 1000 sk_mark_napi_id_set(child, skb); 1001 1002 tcp_segs_in(tcp_sk(child), skb); 1003 if (!sock_owned_by_user(child)) { 1004 reason = tcp_rcv_state_process(child, skb); 1005 /* Wakeup parent, send SIGIO */ 1006 if (state == TCP_SYN_RECV && child->sk_state != state) 1007 parent->sk_data_ready(parent); 1008 } else { 1009 /* Alas, it is possible again, because we do lookup 1010 * in main socket hash table and lock on listening 1011 * socket does not protect us more. 1012 */ 1013 __sk_add_backlog(child, skb); 1014 } 1015 1016 bh_unlock_sock(child); 1017 sock_put(child); 1018 return reason; 1019 } 1020 EXPORT_IPV6_MOD(tcp_child_process); 1021