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/xfrm.h> 24 #include <net/busy_poll.h> 25 #include <net/rstreason.h> 26 27 static bool tcp_in_window(u32 seq, u32 end_seq, u32 s_win, u32 e_win) 28 { 29 if (seq == s_win) 30 return true; 31 if (after(end_seq, s_win) && before(seq, e_win)) 32 return true; 33 return seq == e_win && seq == end_seq; 34 } 35 36 static enum tcp_tw_status 37 tcp_timewait_check_oow_rate_limit(struct inet_timewait_sock *tw, 38 const struct sk_buff *skb, int mib_idx) 39 { 40 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw); 41 42 if (!tcp_oow_rate_limited(twsk_net(tw), skb, mib_idx, 43 &tcptw->tw_last_oow_ack_time)) { 44 /* Send ACK. Note, we do not put the bucket, 45 * it will be released by caller. 46 */ 47 return TCP_TW_ACK_OOW; 48 } 49 50 /* We are rate-limiting, so just release the tw sock and drop skb. */ 51 inet_twsk_put(tw); 52 return TCP_TW_SUCCESS; 53 } 54 55 static void twsk_rcv_nxt_update(struct tcp_timewait_sock *tcptw, u32 seq, 56 u32 rcv_nxt) 57 { 58 #ifdef CONFIG_TCP_AO 59 struct tcp_ao_info *ao; 60 61 ao = rcu_dereference(tcptw->ao_info); 62 if (unlikely(ao && seq < rcv_nxt)) 63 WRITE_ONCE(ao->rcv_sne, ao->rcv_sne + 1); 64 #endif 65 WRITE_ONCE(tcptw->tw_rcv_nxt, seq); 66 } 67 68 /* 69 * * Main purpose of TIME-WAIT state is to close connection gracefully, 70 * when one of ends sits in LAST-ACK or CLOSING retransmitting FIN 71 * (and, probably, tail of data) and one or more our ACKs are lost. 72 * * What is TIME-WAIT timeout? It is associated with maximal packet 73 * lifetime in the internet, which results in wrong conclusion, that 74 * it is set to catch "old duplicate segments" wandering out of their path. 75 * It is not quite correct. This timeout is calculated so that it exceeds 76 * maximal retransmission timeout enough to allow to lose one (or more) 77 * segments sent by peer and our ACKs. This time may be calculated from RTO. 78 * * When TIME-WAIT socket receives RST, it means that another end 79 * finally closed and we are allowed to kill TIME-WAIT too. 80 * * Second purpose of TIME-WAIT is catching old duplicate segments. 81 * Well, certainly it is pure paranoia, but if we load TIME-WAIT 82 * with this semantics, we MUST NOT kill TIME-WAIT state with RSTs. 83 * * If we invented some more clever way to catch duplicates 84 * (f.e. based on PAWS), we could truncate TIME-WAIT to several RTOs. 85 * 86 * The algorithm below is based on FORMAL INTERPRETATION of RFCs. 87 * When you compare it to RFCs, please, read section SEGMENT ARRIVES 88 * from the very beginning. 89 * 90 * NOTE. With recycling (and later with fin-wait-2) TW bucket 91 * is _not_ stateless. It means, that strictly speaking we must 92 * spinlock it. I do not want! Well, probability of misbehaviour 93 * is ridiculously low and, seems, we could use some mb() tricks 94 * to avoid misread sequence numbers, states etc. --ANK 95 * 96 * We don't need to initialize tmp_out.sack_ok as we don't use the results 97 */ 98 enum tcp_tw_status 99 tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb, 100 const struct tcphdr *th, u32 *tw_isn, 101 enum skb_drop_reason *drop_reason) 102 { 103 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw); 104 u32 rcv_nxt = READ_ONCE(tcptw->tw_rcv_nxt); 105 struct tcp_options_received tmp_opt; 106 bool paws_reject = false; 107 int ts_recent_stamp; 108 109 tmp_opt.saw_tstamp = 0; 110 ts_recent_stamp = READ_ONCE(tcptw->tw_ts_recent_stamp); 111 if (th->doff > (sizeof(*th) >> 2) && ts_recent_stamp) { 112 tcp_parse_options(twsk_net(tw), skb, &tmp_opt, 0, NULL); 113 114 if (tmp_opt.saw_tstamp) { 115 if (tmp_opt.rcv_tsecr) 116 tmp_opt.rcv_tsecr -= tcptw->tw_ts_offset; 117 tmp_opt.ts_recent = READ_ONCE(tcptw->tw_ts_recent); 118 tmp_opt.ts_recent_stamp = ts_recent_stamp; 119 paws_reject = tcp_paws_reject(&tmp_opt, th->rst); 120 } 121 } 122 123 if (READ_ONCE(tw->tw_substate) == TCP_FIN_WAIT2) { 124 /* Just repeat all the checks of tcp_rcv_state_process() */ 125 126 /* Out of window, send ACK */ 127 if (paws_reject || 128 !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq, 129 rcv_nxt, 130 rcv_nxt + tcptw->tw_rcv_wnd)) 131 return tcp_timewait_check_oow_rate_limit( 132 tw, skb, LINUX_MIB_TCPACKSKIPPEDFINWAIT2); 133 134 if (th->rst) 135 goto kill; 136 137 if (th->syn && !before(TCP_SKB_CB(skb)->seq, rcv_nxt)) 138 return TCP_TW_RST; 139 140 /* Dup ACK? */ 141 if (!th->ack || 142 !after(TCP_SKB_CB(skb)->end_seq, rcv_nxt) || 143 TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq) { 144 inet_twsk_put(tw); 145 return TCP_TW_SUCCESS; 146 } 147 148 /* New data or FIN. If new data arrive after half-duplex close, 149 * reset. 150 */ 151 if (!th->fin || 152 TCP_SKB_CB(skb)->end_seq != rcv_nxt + 1) 153 return TCP_TW_RST; 154 155 /* FIN arrived, enter true time-wait state. */ 156 WRITE_ONCE(tw->tw_substate, TCP_TIME_WAIT); 157 twsk_rcv_nxt_update(tcptw, TCP_SKB_CB(skb)->end_seq, 158 rcv_nxt); 159 160 if (tmp_opt.saw_tstamp) { 161 u64 ts = tcp_clock_ms(); 162 163 WRITE_ONCE(tw->tw_entry_stamp, ts); 164 WRITE_ONCE(tcptw->tw_ts_recent_stamp, 165 div_u64(ts, MSEC_PER_SEC)); 166 WRITE_ONCE(tcptw->tw_ts_recent, 167 tmp_opt.rcv_tsval); 168 } 169 170 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN); 171 return TCP_TW_ACK; 172 } 173 174 /* 175 * Now real TIME-WAIT state. 176 * 177 * RFC 1122: 178 * "When a connection is [...] on TIME-WAIT state [...] 179 * [a TCP] MAY accept a new SYN from the remote TCP to 180 * reopen the connection directly, if it: 181 * 182 * (1) assigns its initial sequence number for the new 183 * connection to be larger than the largest sequence 184 * number it used on the previous connection incarnation, 185 * and 186 * 187 * (2) returns to TIME-WAIT state if the SYN turns out 188 * to be an old duplicate". 189 */ 190 191 if (!paws_reject && 192 (TCP_SKB_CB(skb)->seq == rcv_nxt && 193 (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq || th->rst))) { 194 /* In window segment, it may be only reset or bare ack. */ 195 196 if (th->rst) { 197 /* This is TIME_WAIT assassination, in two flavors. 198 * Oh well... nobody has a sufficient solution to this 199 * protocol bug yet. 200 */ 201 if (!READ_ONCE(twsk_net(tw)->ipv4.sysctl_tcp_rfc1337)) { 202 kill: 203 inet_twsk_deschedule_put(tw); 204 return TCP_TW_SUCCESS; 205 } 206 } else { 207 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN); 208 } 209 210 if (tmp_opt.saw_tstamp) { 211 WRITE_ONCE(tcptw->tw_ts_recent, 212 tmp_opt.rcv_tsval); 213 WRITE_ONCE(tcptw->tw_ts_recent_stamp, 214 ktime_get_seconds()); 215 } 216 217 inet_twsk_put(tw); 218 return TCP_TW_SUCCESS; 219 } 220 221 /* Out of window segment. 222 223 All the segments are ACKed immediately. 224 225 The only exception is new SYN. We accept it, if it is 226 not old duplicate and we are not in danger to be killed 227 by delayed old duplicates. RFC check is that it has 228 newer sequence number works at rates <40Mbit/sec. 229 However, if paws works, it is reliable AND even more, 230 we even may relax silly seq space cutoff. 231 232 RED-PEN: we violate main RFC requirement, if this SYN will appear 233 old duplicate (i.e. we receive RST in reply to SYN-ACK), 234 we must return socket to time-wait state. It is not good, 235 but not fatal yet. 236 */ 237 238 if (th->syn && !th->rst && !th->ack && !paws_reject && 239 (after(TCP_SKB_CB(skb)->seq, rcv_nxt) || 240 (tmp_opt.saw_tstamp && 241 (s32)(READ_ONCE(tcptw->tw_ts_recent) - tmp_opt.rcv_tsval) < 0))) { 242 u32 isn = tcptw->tw_snd_nxt + 65535 + 2; 243 if (isn == 0) 244 isn++; 245 *tw_isn = isn; 246 return TCP_TW_SYN; 247 } 248 249 if (paws_reject) { 250 *drop_reason = SKB_DROP_REASON_TCP_RFC7323_TW_PAWS; 251 __NET_INC_STATS(twsk_net(tw), LINUX_MIB_PAWS_TW_REJECTED); 252 } 253 254 if (!th->rst) { 255 /* In this case we must reset the TIMEWAIT timer. 256 * 257 * If it is ACKless SYN it may be both old duplicate 258 * and new good SYN with random sequence number <rcv_nxt. 259 * Do not reschedule in the last case. 260 */ 261 if (paws_reject || th->ack) 262 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN); 263 264 return tcp_timewait_check_oow_rate_limit( 265 tw, skb, LINUX_MIB_TCPACKSKIPPEDTIMEWAIT); 266 } 267 inet_twsk_put(tw); 268 return TCP_TW_SUCCESS; 269 } 270 EXPORT_IPV6_MOD(tcp_timewait_state_process); 271 272 static void tcp_time_wait_init(struct sock *sk, struct tcp_timewait_sock *tcptw) 273 { 274 #ifdef CONFIG_TCP_MD5SIG 275 const struct tcp_sock *tp = tcp_sk(sk); 276 struct tcp_md5sig_key *key; 277 278 /* 279 * The timewait bucket does not have the key DB from the 280 * sock structure. We just make a quick copy of the 281 * md5 key being used (if indeed we are using one) 282 * so the timewait ack generating code has the key. 283 */ 284 tcptw->tw_md5_key = NULL; 285 if (!static_branch_unlikely(&tcp_md5_needed.key)) 286 return; 287 288 key = tp->af_specific->md5_lookup(sk, sk); 289 if (key) { 290 tcptw->tw_md5_key = kmemdup(key, sizeof(*key), GFP_ATOMIC); 291 if (!tcptw->tw_md5_key) 292 return; 293 if (!static_key_fast_inc_not_disabled(&tcp_md5_needed.key.key)) 294 goto out_free; 295 tcp_md5_add_sigpool(); 296 } 297 return; 298 out_free: 299 WARN_ON_ONCE(1); 300 kfree(tcptw->tw_md5_key); 301 tcptw->tw_md5_key = NULL; 302 #endif 303 } 304 305 /* 306 * Move a socket to time-wait or dead fin-wait-2 state. 307 */ 308 void tcp_time_wait(struct sock *sk, int state, int timeo) 309 { 310 const struct inet_connection_sock *icsk = inet_csk(sk); 311 struct tcp_sock *tp = tcp_sk(sk); 312 struct net *net = sock_net(sk); 313 struct inet_timewait_sock *tw; 314 315 tw = inet_twsk_alloc(sk, &net->ipv4.tcp_death_row, state); 316 317 if (tw) { 318 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw); 319 const int rto = (icsk->icsk_rto << 2) - (icsk->icsk_rto >> 1); 320 321 tw->tw_transparent = inet_test_bit(TRANSPARENT, sk); 322 tw->tw_mark = sk->sk_mark; 323 tw->tw_priority = READ_ONCE(sk->sk_priority); 324 tw->tw_rcv_wscale = tp->rx_opt.rcv_wscale; 325 /* refreshed when we enter true TIME-WAIT state */ 326 tw->tw_entry_stamp = tcp_time_stamp_ms(tp); 327 tcptw->tw_rcv_nxt = tp->rcv_nxt; 328 tcptw->tw_snd_nxt = tp->snd_nxt; 329 tcptw->tw_rcv_wnd = tcp_receive_window(tp); 330 tcptw->tw_ts_recent = tp->rx_opt.ts_recent; 331 tcptw->tw_ts_recent_stamp = tp->rx_opt.ts_recent_stamp; 332 tcptw->tw_ts_offset = tp->tsoffset; 333 tw->tw_usec_ts = tp->tcp_usec_ts; 334 tcptw->tw_last_oow_ack_time = 0; 335 tcptw->tw_tx_delay = tp->tcp_tx_delay; 336 tw->tw_txhash = sk->sk_txhash; 337 tw->tw_tx_queue_mapping = sk->sk_tx_queue_mapping; 338 #ifdef CONFIG_SOCK_RX_QUEUE_MAPPING 339 tw->tw_rx_queue_mapping = sk->sk_rx_queue_mapping; 340 #endif 341 #if IS_ENABLED(CONFIG_IPV6) 342 if (tw->tw_family == PF_INET6) { 343 struct ipv6_pinfo *np = inet6_sk(sk); 344 345 tw->tw_v6_daddr = sk->sk_v6_daddr; 346 tw->tw_v6_rcv_saddr = sk->sk_v6_rcv_saddr; 347 tw->tw_tclass = np->tclass; 348 tw->tw_flowlabel = be32_to_cpu(np->flow_label & IPV6_FLOWLABEL_MASK); 349 tw->tw_ipv6only = sk->sk_ipv6only; 350 } 351 #endif 352 353 tcp_time_wait_init(sk, tcptw); 354 tcp_ao_time_wait(tcptw, tp); 355 356 /* Get the TIME_WAIT timeout firing. */ 357 if (timeo < rto) 358 timeo = rto; 359 360 if (state == TCP_TIME_WAIT) 361 timeo = TCP_TIMEWAIT_LEN; 362 363 /* Linkage updates. 364 * Note that access to tw after this point is illegal. 365 */ 366 inet_twsk_hashdance_schedule(tw, sk, net->ipv4.tcp_death_row.hashinfo, timeo); 367 } else { 368 /* Sorry, if we're out of memory, just CLOSE this 369 * socket up. We've got bigger problems than 370 * non-graceful socket closings. 371 */ 372 NET_INC_STATS(net, LINUX_MIB_TCPTIMEWAITOVERFLOW); 373 } 374 375 tcp_update_metrics(sk); 376 tcp_done(sk); 377 } 378 EXPORT_SYMBOL(tcp_time_wait); 379 380 #ifdef CONFIG_TCP_MD5SIG 381 static void tcp_md5_twsk_free_rcu(struct rcu_head *head) 382 { 383 struct tcp_md5sig_key *key; 384 385 key = container_of(head, struct tcp_md5sig_key, rcu); 386 kfree(key); 387 static_branch_slow_dec_deferred(&tcp_md5_needed); 388 tcp_md5_release_sigpool(); 389 } 390 #endif 391 392 void tcp_twsk_destructor(struct sock *sk) 393 { 394 #ifdef CONFIG_TCP_MD5SIG 395 if (static_branch_unlikely(&tcp_md5_needed.key)) { 396 struct tcp_timewait_sock *twsk = tcp_twsk(sk); 397 398 if (twsk->tw_md5_key) 399 call_rcu(&twsk->tw_md5_key->rcu, tcp_md5_twsk_free_rcu); 400 } 401 #endif 402 tcp_ao_destroy_sock(sk, true); 403 } 404 405 void tcp_twsk_purge(struct list_head *net_exit_list) 406 { 407 bool purged_once = false; 408 struct net *net; 409 410 list_for_each_entry(net, net_exit_list, exit_list) { 411 if (net->ipv4.tcp_death_row.hashinfo->pernet) { 412 /* Even if tw_refcount == 1, we must clean up kernel reqsk */ 413 inet_twsk_purge(net->ipv4.tcp_death_row.hashinfo); 414 } else if (!purged_once) { 415 inet_twsk_purge(&tcp_hashinfo); 416 purged_once = true; 417 } 418 } 419 } 420 421 /* Warning : This function is called without sk_listener being locked. 422 * Be sure to read socket fields once, as their value could change under us. 423 */ 424 void tcp_openreq_init_rwin(struct request_sock *req, 425 const struct sock *sk_listener, 426 const struct dst_entry *dst) 427 { 428 struct inet_request_sock *ireq = inet_rsk(req); 429 const struct tcp_sock *tp = tcp_sk(sk_listener); 430 int full_space = tcp_full_space(sk_listener); 431 u32 window_clamp; 432 __u8 rcv_wscale; 433 u32 rcv_wnd; 434 int mss; 435 436 mss = tcp_mss_clamp(tp, dst_metric_advmss(dst)); 437 window_clamp = READ_ONCE(tp->window_clamp); 438 /* Set this up on the first call only */ 439 req->rsk_window_clamp = window_clamp ? : dst_metric(dst, RTAX_WINDOW); 440 441 /* limit the window selection if the user enforce a smaller rx buffer */ 442 if (sk_listener->sk_userlocks & SOCK_RCVBUF_LOCK && 443 (req->rsk_window_clamp > full_space || req->rsk_window_clamp == 0)) 444 req->rsk_window_clamp = full_space; 445 446 rcv_wnd = tcp_rwnd_init_bpf((struct sock *)req); 447 if (rcv_wnd == 0) 448 rcv_wnd = dst_metric(dst, RTAX_INITRWND); 449 else if (full_space < rcv_wnd * mss) 450 full_space = rcv_wnd * mss; 451 452 /* tcp_full_space because it is guaranteed to be the first packet */ 453 tcp_select_initial_window(sk_listener, full_space, 454 mss - (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0), 455 &req->rsk_rcv_wnd, 456 &req->rsk_window_clamp, 457 ireq->wscale_ok, 458 &rcv_wscale, 459 rcv_wnd); 460 ireq->rcv_wscale = rcv_wscale; 461 } 462 463 static void tcp_ecn_openreq_child(struct tcp_sock *tp, 464 const struct request_sock *req) 465 { 466 tcp_ecn_mode_set(tp, inet_rsk(req)->ecn_ok ? 467 TCP_ECN_MODE_RFC3168 : 468 TCP_ECN_DISABLED); 469 } 470 471 void tcp_ca_openreq_child(struct sock *sk, const struct dst_entry *dst) 472 { 473 struct inet_connection_sock *icsk = inet_csk(sk); 474 u32 ca_key = dst_metric(dst, RTAX_CC_ALGO); 475 bool ca_got_dst = false; 476 477 if (ca_key != TCP_CA_UNSPEC) { 478 const struct tcp_congestion_ops *ca; 479 480 rcu_read_lock(); 481 ca = tcp_ca_find_key(ca_key); 482 if (likely(ca && bpf_try_module_get(ca, ca->owner))) { 483 icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst); 484 icsk->icsk_ca_ops = ca; 485 ca_got_dst = true; 486 } 487 rcu_read_unlock(); 488 } 489 490 /* If no valid choice made yet, assign current system default ca. */ 491 if (!ca_got_dst && 492 (!icsk->icsk_ca_setsockopt || 493 !bpf_try_module_get(icsk->icsk_ca_ops, icsk->icsk_ca_ops->owner))) 494 tcp_assign_congestion_control(sk); 495 496 tcp_set_ca_state(sk, TCP_CA_Open); 497 } 498 EXPORT_IPV6_MOD_GPL(tcp_ca_openreq_child); 499 500 static void smc_check_reset_syn_req(const struct tcp_sock *oldtp, 501 struct request_sock *req, 502 struct tcp_sock *newtp) 503 { 504 #if IS_ENABLED(CONFIG_SMC) 505 struct inet_request_sock *ireq; 506 507 if (static_branch_unlikely(&tcp_have_smc)) { 508 ireq = inet_rsk(req); 509 if (oldtp->syn_smc && !ireq->smc_ok) 510 newtp->syn_smc = 0; 511 } 512 #endif 513 } 514 515 /* This is not only more efficient than what we used to do, it eliminates 516 * a lot of code duplication between IPv4/IPv6 SYN recv processing. -DaveM 517 * 518 * Actually, we could lots of memory writes here. tp of listening 519 * socket contains all necessary default parameters. 520 */ 521 struct sock *tcp_create_openreq_child(const struct sock *sk, 522 struct request_sock *req, 523 struct sk_buff *skb) 524 { 525 struct sock *newsk = inet_csk_clone_lock(sk, req, GFP_ATOMIC); 526 const struct inet_request_sock *ireq = inet_rsk(req); 527 struct tcp_request_sock *treq = tcp_rsk(req); 528 struct inet_connection_sock *newicsk; 529 const struct tcp_sock *oldtp; 530 struct tcp_sock *newtp; 531 u32 seq; 532 533 if (!newsk) 534 return NULL; 535 536 newicsk = inet_csk(newsk); 537 newtp = tcp_sk(newsk); 538 oldtp = tcp_sk(sk); 539 540 smc_check_reset_syn_req(oldtp, req, newtp); 541 542 /* Now setup tcp_sock */ 543 newtp->pred_flags = 0; 544 545 seq = treq->rcv_isn + 1; 546 newtp->rcv_wup = seq; 547 WRITE_ONCE(newtp->copied_seq, seq); 548 WRITE_ONCE(newtp->rcv_nxt, seq); 549 newtp->segs_in = 1; 550 551 seq = treq->snt_isn + 1; 552 newtp->snd_sml = newtp->snd_una = seq; 553 WRITE_ONCE(newtp->snd_nxt, seq); 554 newtp->snd_up = seq; 555 556 INIT_LIST_HEAD(&newtp->tsq_node); 557 INIT_LIST_HEAD(&newtp->tsorted_sent_queue); 558 559 tcp_init_wl(newtp, treq->rcv_isn); 560 561 minmax_reset(&newtp->rtt_min, tcp_jiffies32, ~0U); 562 newicsk->icsk_ack.lrcvtime = tcp_jiffies32; 563 564 newtp->lsndtime = tcp_jiffies32; 565 newsk->sk_txhash = READ_ONCE(treq->txhash); 566 newtp->total_retrans = req->num_retrans; 567 568 tcp_init_xmit_timers(newsk); 569 WRITE_ONCE(newtp->write_seq, newtp->pushed_seq = treq->snt_isn + 1); 570 571 if (sock_flag(newsk, SOCK_KEEPOPEN)) 572 tcp_reset_keepalive_timer(newsk, keepalive_time_when(newtp)); 573 574 newtp->rx_opt.tstamp_ok = ireq->tstamp_ok; 575 newtp->rx_opt.sack_ok = ireq->sack_ok; 576 newtp->window_clamp = req->rsk_window_clamp; 577 newtp->rcv_ssthresh = req->rsk_rcv_wnd; 578 newtp->rcv_wnd = req->rsk_rcv_wnd; 579 newtp->rx_opt.wscale_ok = ireq->wscale_ok; 580 if (newtp->rx_opt.wscale_ok) { 581 newtp->rx_opt.snd_wscale = ireq->snd_wscale; 582 newtp->rx_opt.rcv_wscale = ireq->rcv_wscale; 583 } else { 584 newtp->rx_opt.snd_wscale = newtp->rx_opt.rcv_wscale = 0; 585 newtp->window_clamp = min(newtp->window_clamp, 65535U); 586 } 587 newtp->snd_wnd = ntohs(tcp_hdr(skb)->window) << newtp->rx_opt.snd_wscale; 588 newtp->max_window = newtp->snd_wnd; 589 590 if (newtp->rx_opt.tstamp_ok) { 591 newtp->tcp_usec_ts = treq->req_usec_ts; 592 newtp->rx_opt.ts_recent = req->ts_recent; 593 newtp->rx_opt.ts_recent_stamp = ktime_get_seconds(); 594 newtp->tcp_header_len = sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED; 595 } else { 596 newtp->tcp_usec_ts = 0; 597 newtp->rx_opt.ts_recent_stamp = 0; 598 newtp->tcp_header_len = sizeof(struct tcphdr); 599 } 600 if (req->num_timeout) { 601 newtp->total_rto = req->num_timeout; 602 newtp->undo_marker = treq->snt_isn; 603 if (newtp->tcp_usec_ts) { 604 newtp->retrans_stamp = treq->snt_synack; 605 newtp->total_rto_time = (u32)(tcp_clock_us() - 606 newtp->retrans_stamp) / USEC_PER_MSEC; 607 } else { 608 newtp->retrans_stamp = div_u64(treq->snt_synack, 609 USEC_PER_SEC / TCP_TS_HZ); 610 newtp->total_rto_time = tcp_clock_ms() - 611 newtp->retrans_stamp; 612 } 613 newtp->total_rto_recoveries = 1; 614 } 615 newtp->tsoffset = treq->ts_off; 616 #ifdef CONFIG_TCP_MD5SIG 617 newtp->md5sig_info = NULL; /*XXX*/ 618 #endif 619 #ifdef CONFIG_TCP_AO 620 newtp->ao_info = NULL; 621 622 if (tcp_rsk_used_ao(req)) { 623 struct tcp_ao_key *ao_key; 624 625 ao_key = treq->af_specific->ao_lookup(sk, req, tcp_rsk(req)->ao_keyid, -1); 626 if (ao_key) 627 newtp->tcp_header_len += tcp_ao_len_aligned(ao_key); 628 } 629 #endif 630 if (skb->len >= TCP_MSS_DEFAULT + newtp->tcp_header_len) 631 newicsk->icsk_ack.last_seg_size = skb->len - newtp->tcp_header_len; 632 newtp->rx_opt.mss_clamp = req->mss; 633 tcp_ecn_openreq_child(newtp, req); 634 newtp->fastopen_req = NULL; 635 RCU_INIT_POINTER(newtp->fastopen_rsk, NULL); 636 637 newtp->bpf_chg_cc_inprogress = 0; 638 tcp_bpf_clone(sk, newsk); 639 640 __TCP_INC_STATS(sock_net(sk), TCP_MIB_PASSIVEOPENS); 641 642 xa_init_flags(&newsk->sk_user_frags, XA_FLAGS_ALLOC1); 643 644 return newsk; 645 } 646 EXPORT_SYMBOL(tcp_create_openreq_child); 647 648 /* 649 * Process an incoming packet for SYN_RECV sockets represented as a 650 * request_sock. Normally sk is the listener socket but for TFO it 651 * points to the child socket. 652 * 653 * XXX (TFO) - The current impl contains a special check for ack 654 * validation and inside tcp_v4_reqsk_send_ack(). Can we do better? 655 * 656 * We don't need to initialize tmp_opt.sack_ok as we don't use the results 657 * 658 * Note: If @fastopen is true, this can be called from process context. 659 * Otherwise, this is from BH context. 660 */ 661 662 struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb, 663 struct request_sock *req, 664 bool fastopen, bool *req_stolen, 665 enum skb_drop_reason *drop_reason) 666 { 667 struct tcp_options_received tmp_opt; 668 struct sock *child; 669 const struct tcphdr *th = tcp_hdr(skb); 670 __be32 flg = tcp_flag_word(th) & (TCP_FLAG_RST|TCP_FLAG_SYN|TCP_FLAG_ACK); 671 bool tsecr_reject = false; 672 bool paws_reject = false; 673 bool own_req; 674 675 tmp_opt.saw_tstamp = 0; 676 if (th->doff > (sizeof(struct tcphdr)>>2)) { 677 tcp_parse_options(sock_net(sk), skb, &tmp_opt, 0, NULL); 678 679 if (tmp_opt.saw_tstamp) { 680 tmp_opt.ts_recent = req->ts_recent; 681 if (tmp_opt.rcv_tsecr) { 682 if (inet_rsk(req)->tstamp_ok && !fastopen) 683 tsecr_reject = !between(tmp_opt.rcv_tsecr, 684 tcp_rsk(req)->snt_tsval_first, 685 READ_ONCE(tcp_rsk(req)->snt_tsval_last)); 686 tmp_opt.rcv_tsecr -= tcp_rsk(req)->ts_off; 687 } 688 /* We do not store true stamp, but it is not required, 689 * it can be estimated (approximately) 690 * from another data. 691 */ 692 tmp_opt.ts_recent_stamp = ktime_get_seconds() - reqsk_timeout(req, TCP_RTO_MAX) / HZ; 693 paws_reject = tcp_paws_reject(&tmp_opt, th->rst); 694 } 695 } 696 697 /* Check for pure retransmitted SYN. */ 698 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn && 699 flg == TCP_FLAG_SYN && 700 !paws_reject) { 701 /* 702 * RFC793 draws (Incorrectly! It was fixed in RFC1122) 703 * this case on figure 6 and figure 8, but formal 704 * protocol description says NOTHING. 705 * To be more exact, it says that we should send ACK, 706 * because this segment (at least, if it has no data) 707 * is out of window. 708 * 709 * CONCLUSION: RFC793 (even with RFC1122) DOES NOT 710 * describe SYN-RECV state. All the description 711 * is wrong, we cannot believe to it and should 712 * rely only on common sense and implementation 713 * experience. 714 * 715 * Enforce "SYN-ACK" according to figure 8, figure 6 716 * of RFC793, fixed by RFC1122. 717 * 718 * Note that even if there is new data in the SYN packet 719 * they will be thrown away too. 720 * 721 * Reset timer after retransmitting SYNACK, similar to 722 * the idea of fast retransmit in recovery. 723 */ 724 if (!tcp_oow_rate_limited(sock_net(sk), skb, 725 LINUX_MIB_TCPACKSKIPPEDSYNRECV, 726 &tcp_rsk(req)->last_oow_ack_time) && 727 728 !tcp_rtx_synack(sk, req)) { 729 unsigned long expires = jiffies; 730 731 expires += reqsk_timeout(req, TCP_RTO_MAX); 732 if (!fastopen) 733 mod_timer_pending(&req->rsk_timer, expires); 734 else 735 req->rsk_timer.expires = expires; 736 } 737 return NULL; 738 } 739 740 /* Further reproduces section "SEGMENT ARRIVES" 741 for state SYN-RECEIVED of RFC793. 742 It is broken, however, it does not work only 743 when SYNs are crossed. 744 745 You would think that SYN crossing is impossible here, since 746 we should have a SYN_SENT socket (from connect()) on our end, 747 but this is not true if the crossed SYNs were sent to both 748 ends by a malicious third party. We must defend against this, 749 and to do that we first verify the ACK (as per RFC793, page 750 36) and reset if it is invalid. Is this a true full defense? 751 To convince ourselves, let us consider a way in which the ACK 752 test can still pass in this 'malicious crossed SYNs' case. 753 Malicious sender sends identical SYNs (and thus identical sequence 754 numbers) to both A and B: 755 756 A: gets SYN, seq=7 757 B: gets SYN, seq=7 758 759 By our good fortune, both A and B select the same initial 760 send sequence number of seven :-) 761 762 A: sends SYN|ACK, seq=7, ack_seq=8 763 B: sends SYN|ACK, seq=7, ack_seq=8 764 765 So we are now A eating this SYN|ACK, ACK test passes. So 766 does sequence test, SYN is truncated, and thus we consider 767 it a bare ACK. 768 769 If icsk->icsk_accept_queue.rskq_defer_accept, we silently drop this 770 bare ACK. Otherwise, we create an established connection. Both 771 ends (listening sockets) accept the new incoming connection and try 772 to talk to each other. 8-) 773 774 Note: This case is both harmless, and rare. Possibility is about the 775 same as us discovering intelligent life on another plant tomorrow. 776 777 But generally, we should (RFC lies!) to accept ACK 778 from SYNACK both here and in tcp_rcv_state_process(). 779 tcp_rcv_state_process() does not, hence, we do not too. 780 781 Note that the case is absolutely generic: 782 we cannot optimize anything here without 783 violating protocol. All the checks must be made 784 before attempt to create socket. 785 */ 786 787 /* RFC793 page 36: "If the connection is in any non-synchronized state ... 788 * and the incoming segment acknowledges something not yet 789 * sent (the segment carries an unacceptable ACK) ... 790 * a reset is sent." 791 * 792 * Invalid ACK: reset will be sent by listening socket. 793 * Note that the ACK validity check for a Fast Open socket is done 794 * elsewhere and is checked directly against the child socket rather 795 * than req because user data may have been sent out. 796 */ 797 if ((flg & TCP_FLAG_ACK) && !fastopen && 798 (TCP_SKB_CB(skb)->ack_seq != 799 tcp_rsk(req)->snt_isn + 1)) 800 return sk; 801 802 /* RFC793: "first check sequence number". */ 803 804 if (paws_reject || tsecr_reject || 805 !tcp_in_window(TCP_SKB_CB(skb)->seq, 806 TCP_SKB_CB(skb)->end_seq, 807 tcp_rsk(req)->rcv_nxt, 808 tcp_rsk(req)->rcv_nxt + 809 tcp_synack_window(req))) { 810 /* Out of window: send ACK and drop. */ 811 if (!(flg & TCP_FLAG_RST) && 812 !tcp_oow_rate_limited(sock_net(sk), skb, 813 LINUX_MIB_TCPACKSKIPPEDSYNRECV, 814 &tcp_rsk(req)->last_oow_ack_time)) 815 req->rsk_ops->send_ack(sk, skb, req); 816 if (paws_reject) { 817 SKB_DR_SET(*drop_reason, TCP_RFC7323_PAWS); 818 NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED); 819 } else if (tsecr_reject) { 820 SKB_DR_SET(*drop_reason, TCP_RFC7323_TSECR); 821 NET_INC_STATS(sock_net(sk), LINUX_MIB_TSECRREJECTED); 822 } else { 823 SKB_DR_SET(*drop_reason, TCP_OVERWINDOW); 824 } 825 return NULL; 826 } 827 828 /* In sequence, PAWS is OK. */ 829 830 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn) { 831 /* Truncate SYN, it is out of window starting 832 at tcp_rsk(req)->rcv_isn + 1. */ 833 flg &= ~TCP_FLAG_SYN; 834 } 835 836 /* RFC793: "second check the RST bit" and 837 * "fourth, check the SYN bit" 838 */ 839 if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN)) { 840 TCP_INC_STATS(sock_net(sk), TCP_MIB_ATTEMPTFAILS); 841 goto embryonic_reset; 842 } 843 844 /* ACK sequence verified above, just make sure ACK is 845 * set. If ACK not set, just silently drop the packet. 846 * 847 * XXX (TFO) - if we ever allow "data after SYN", the 848 * following check needs to be removed. 849 */ 850 if (!(flg & TCP_FLAG_ACK)) 851 return NULL; 852 853 /* For Fast Open no more processing is needed (sk is the 854 * child socket). 855 */ 856 if (fastopen) 857 return sk; 858 859 /* While TCP_DEFER_ACCEPT is active, drop bare ACK. */ 860 if (req->num_timeout < READ_ONCE(inet_csk(sk)->icsk_accept_queue.rskq_defer_accept) && 861 TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) { 862 inet_rsk(req)->acked = 1; 863 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDEFERACCEPTDROP); 864 return NULL; 865 } 866 867 /* OK, ACK is valid, create big socket and 868 * feed this segment to it. It will repeat all 869 * the tests. THIS SEGMENT MUST MOVE SOCKET TO 870 * ESTABLISHED STATE. If it will be dropped after 871 * socket is created, wait for troubles. 872 */ 873 child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL, 874 req, &own_req); 875 if (!child) 876 goto listen_overflow; 877 878 if (own_req && tmp_opt.saw_tstamp && 879 !after(TCP_SKB_CB(skb)->seq, tcp_rsk(req)->rcv_nxt)) 880 tcp_sk(child)->rx_opt.ts_recent = tmp_opt.rcv_tsval; 881 882 if (own_req && rsk_drop_req(req)) { 883 reqsk_queue_removed(&inet_csk(req->rsk_listener)->icsk_accept_queue, req); 884 inet_csk_reqsk_queue_drop_and_put(req->rsk_listener, req); 885 return child; 886 } 887 888 sock_rps_save_rxhash(child, skb); 889 tcp_synack_rtt_meas(child, req); 890 *req_stolen = !own_req; 891 return inet_csk_complete_hashdance(sk, child, req, own_req); 892 893 listen_overflow: 894 SKB_DR_SET(*drop_reason, TCP_LISTEN_OVERFLOW); 895 if (sk != req->rsk_listener) 896 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMIGRATEREQFAILURE); 897 898 if (!READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_abort_on_overflow)) { 899 inet_rsk(req)->acked = 1; 900 return NULL; 901 } 902 903 embryonic_reset: 904 if (!(flg & TCP_FLAG_RST)) { 905 /* Received a bad SYN pkt - for TFO We try not to reset 906 * the local connection unless it's really necessary to 907 * avoid becoming vulnerable to outside attack aiming at 908 * resetting legit local connections. 909 */ 910 req->rsk_ops->send_reset(sk, skb, SK_RST_REASON_INVALID_SYN); 911 } else if (fastopen) { /* received a valid RST pkt */ 912 reqsk_fastopen_remove(sk, req, true); 913 tcp_reset(sk, skb); 914 } 915 if (!fastopen) { 916 bool unlinked = inet_csk_reqsk_queue_drop(sk, req); 917 918 if (unlinked) 919 __NET_INC_STATS(sock_net(sk), LINUX_MIB_EMBRYONICRSTS); 920 *req_stolen = !unlinked; 921 } 922 return NULL; 923 } 924 EXPORT_IPV6_MOD(tcp_check_req); 925 926 /* 927 * Queue segment on the new socket if the new socket is active, 928 * otherwise we just shortcircuit this and continue with 929 * the new socket. 930 * 931 * For the vast majority of cases child->sk_state will be TCP_SYN_RECV 932 * when entering. But other states are possible due to a race condition 933 * where after __inet_lookup_established() fails but before the listener 934 * locked is obtained, other packets cause the same connection to 935 * be created. 936 */ 937 938 enum skb_drop_reason tcp_child_process(struct sock *parent, struct sock *child, 939 struct sk_buff *skb) 940 __releases(&((child)->sk_lock.slock)) 941 { 942 enum skb_drop_reason reason = SKB_NOT_DROPPED_YET; 943 int state = child->sk_state; 944 945 /* record sk_napi_id and sk_rx_queue_mapping of child. */ 946 sk_mark_napi_id_set(child, skb); 947 948 tcp_segs_in(tcp_sk(child), skb); 949 if (!sock_owned_by_user(child)) { 950 reason = tcp_rcv_state_process(child, skb); 951 /* Wakeup parent, send SIGIO */ 952 if (state == TCP_SYN_RECV && child->sk_state != state) 953 parent->sk_data_ready(parent); 954 } else { 955 /* Alas, it is possible again, because we do lookup 956 * in main socket hash table and lock on listening 957 * socket does not protect us more. 958 */ 959 __sk_add_backlog(child, skb); 960 } 961 962 bh_unlock_sock(child); 963 sock_put(child); 964 return reason; 965 } 966 EXPORT_IPV6_MOD(tcp_child_process); 967