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