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; 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 tp->ecn_flags = inet_rsk(req)->ecn_ok ? TCP_ECN_OK : 0; 465 } 466 467 void tcp_ca_openreq_child(struct sock *sk, const struct dst_entry *dst) 468 { 469 struct inet_connection_sock *icsk = inet_csk(sk); 470 u32 ca_key = dst_metric(dst, RTAX_CC_ALGO); 471 bool ca_got_dst = false; 472 473 if (ca_key != TCP_CA_UNSPEC) { 474 const struct tcp_congestion_ops *ca; 475 476 rcu_read_lock(); 477 ca = tcp_ca_find_key(ca_key); 478 if (likely(ca && bpf_try_module_get(ca, ca->owner))) { 479 icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst); 480 icsk->icsk_ca_ops = ca; 481 ca_got_dst = true; 482 } 483 rcu_read_unlock(); 484 } 485 486 /* If no valid choice made yet, assign current system default ca. */ 487 if (!ca_got_dst && 488 (!icsk->icsk_ca_setsockopt || 489 !bpf_try_module_get(icsk->icsk_ca_ops, icsk->icsk_ca_ops->owner))) 490 tcp_assign_congestion_control(sk); 491 492 tcp_set_ca_state(sk, TCP_CA_Open); 493 } 494 EXPORT_IPV6_MOD_GPL(tcp_ca_openreq_child); 495 496 static void smc_check_reset_syn_req(const struct tcp_sock *oldtp, 497 struct request_sock *req, 498 struct tcp_sock *newtp) 499 { 500 #if IS_ENABLED(CONFIG_SMC) 501 struct inet_request_sock *ireq; 502 503 if (static_branch_unlikely(&tcp_have_smc)) { 504 ireq = inet_rsk(req); 505 if (oldtp->syn_smc && !ireq->smc_ok) 506 newtp->syn_smc = 0; 507 } 508 #endif 509 } 510 511 /* This is not only more efficient than what we used to do, it eliminates 512 * a lot of code duplication between IPv4/IPv6 SYN recv processing. -DaveM 513 * 514 * Actually, we could lots of memory writes here. tp of listening 515 * socket contains all necessary default parameters. 516 */ 517 struct sock *tcp_create_openreq_child(const struct sock *sk, 518 struct request_sock *req, 519 struct sk_buff *skb) 520 { 521 struct sock *newsk = inet_csk_clone_lock(sk, req, GFP_ATOMIC); 522 const struct inet_request_sock *ireq = inet_rsk(req); 523 struct tcp_request_sock *treq = tcp_rsk(req); 524 struct inet_connection_sock *newicsk; 525 const struct tcp_sock *oldtp; 526 struct tcp_sock *newtp; 527 u32 seq; 528 529 if (!newsk) 530 return NULL; 531 532 newicsk = inet_csk(newsk); 533 newtp = tcp_sk(newsk); 534 oldtp = tcp_sk(sk); 535 536 smc_check_reset_syn_req(oldtp, req, newtp); 537 538 /* Now setup tcp_sock */ 539 newtp->pred_flags = 0; 540 541 seq = treq->rcv_isn + 1; 542 newtp->rcv_wup = seq; 543 WRITE_ONCE(newtp->copied_seq, seq); 544 WRITE_ONCE(newtp->rcv_nxt, seq); 545 newtp->segs_in = 1; 546 547 seq = treq->snt_isn + 1; 548 newtp->snd_sml = newtp->snd_una = seq; 549 WRITE_ONCE(newtp->snd_nxt, seq); 550 newtp->snd_up = seq; 551 552 INIT_LIST_HEAD(&newtp->tsq_node); 553 INIT_LIST_HEAD(&newtp->tsorted_sent_queue); 554 555 tcp_init_wl(newtp, treq->rcv_isn); 556 557 minmax_reset(&newtp->rtt_min, tcp_jiffies32, ~0U); 558 newicsk->icsk_ack.lrcvtime = tcp_jiffies32; 559 560 newtp->lsndtime = tcp_jiffies32; 561 newsk->sk_txhash = READ_ONCE(treq->txhash); 562 newtp->total_retrans = req->num_retrans; 563 564 tcp_init_xmit_timers(newsk); 565 WRITE_ONCE(newtp->write_seq, newtp->pushed_seq = treq->snt_isn + 1); 566 567 if (sock_flag(newsk, SOCK_KEEPOPEN)) 568 tcp_reset_keepalive_timer(newsk, keepalive_time_when(newtp)); 569 570 newtp->rx_opt.tstamp_ok = ireq->tstamp_ok; 571 newtp->rx_opt.sack_ok = ireq->sack_ok; 572 newtp->window_clamp = req->rsk_window_clamp; 573 newtp->rcv_ssthresh = req->rsk_rcv_wnd; 574 newtp->rcv_wnd = req->rsk_rcv_wnd; 575 newtp->rx_opt.wscale_ok = ireq->wscale_ok; 576 if (newtp->rx_opt.wscale_ok) { 577 newtp->rx_opt.snd_wscale = ireq->snd_wscale; 578 newtp->rx_opt.rcv_wscale = ireq->rcv_wscale; 579 } else { 580 newtp->rx_opt.snd_wscale = newtp->rx_opt.rcv_wscale = 0; 581 newtp->window_clamp = min(newtp->window_clamp, 65535U); 582 } 583 newtp->snd_wnd = ntohs(tcp_hdr(skb)->window) << newtp->rx_opt.snd_wscale; 584 newtp->max_window = newtp->snd_wnd; 585 586 if (newtp->rx_opt.tstamp_ok) { 587 newtp->tcp_usec_ts = treq->req_usec_ts; 588 newtp->rx_opt.ts_recent = req->ts_recent; 589 newtp->rx_opt.ts_recent_stamp = ktime_get_seconds(); 590 newtp->tcp_header_len = sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED; 591 } else { 592 newtp->tcp_usec_ts = 0; 593 newtp->rx_opt.ts_recent_stamp = 0; 594 newtp->tcp_header_len = sizeof(struct tcphdr); 595 } 596 if (req->num_timeout) { 597 newtp->total_rto = req->num_timeout; 598 newtp->undo_marker = treq->snt_isn; 599 if (newtp->tcp_usec_ts) { 600 newtp->retrans_stamp = treq->snt_synack; 601 newtp->total_rto_time = (u32)(tcp_clock_us() - 602 newtp->retrans_stamp) / USEC_PER_MSEC; 603 } else { 604 newtp->retrans_stamp = div_u64(treq->snt_synack, 605 USEC_PER_SEC / TCP_TS_HZ); 606 newtp->total_rto_time = tcp_clock_ms() - 607 newtp->retrans_stamp; 608 } 609 newtp->total_rto_recoveries = 1; 610 } 611 newtp->tsoffset = treq->ts_off; 612 #ifdef CONFIG_TCP_MD5SIG 613 newtp->md5sig_info = NULL; /*XXX*/ 614 #endif 615 #ifdef CONFIG_TCP_AO 616 newtp->ao_info = NULL; 617 618 if (tcp_rsk_used_ao(req)) { 619 struct tcp_ao_key *ao_key; 620 621 ao_key = treq->af_specific->ao_lookup(sk, req, tcp_rsk(req)->ao_keyid, -1); 622 if (ao_key) 623 newtp->tcp_header_len += tcp_ao_len_aligned(ao_key); 624 } 625 #endif 626 if (skb->len >= TCP_MSS_DEFAULT + newtp->tcp_header_len) 627 newicsk->icsk_ack.last_seg_size = skb->len - newtp->tcp_header_len; 628 newtp->rx_opt.mss_clamp = req->mss; 629 tcp_ecn_openreq_child(newtp, req); 630 newtp->fastopen_req = NULL; 631 RCU_INIT_POINTER(newtp->fastopen_rsk, NULL); 632 633 newtp->bpf_chg_cc_inprogress = 0; 634 tcp_bpf_clone(sk, newsk); 635 636 __TCP_INC_STATS(sock_net(sk), TCP_MIB_PASSIVEOPENS); 637 638 xa_init_flags(&newsk->sk_user_frags, XA_FLAGS_ALLOC1); 639 640 return newsk; 641 } 642 EXPORT_SYMBOL(tcp_create_openreq_child); 643 644 /* 645 * Process an incoming packet for SYN_RECV sockets represented as a 646 * request_sock. Normally sk is the listener socket but for TFO it 647 * points to the child socket. 648 * 649 * XXX (TFO) - The current impl contains a special check for ack 650 * validation and inside tcp_v4_reqsk_send_ack(). Can we do better? 651 * 652 * We don't need to initialize tmp_opt.sack_ok as we don't use the results 653 * 654 * Note: If @fastopen is true, this can be called from process context. 655 * Otherwise, this is from BH context. 656 */ 657 658 struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb, 659 struct request_sock *req, 660 bool fastopen, bool *req_stolen, 661 enum skb_drop_reason *drop_reason) 662 { 663 struct tcp_options_received tmp_opt; 664 struct sock *child; 665 const struct tcphdr *th = tcp_hdr(skb); 666 __be32 flg = tcp_flag_word(th) & (TCP_FLAG_RST|TCP_FLAG_SYN|TCP_FLAG_ACK); 667 bool tsecr_reject = false; 668 bool paws_reject = false; 669 bool own_req; 670 671 tmp_opt.saw_tstamp = 0; 672 if (th->doff > (sizeof(struct tcphdr)>>2)) { 673 tcp_parse_options(sock_net(sk), skb, &tmp_opt, 0, NULL); 674 675 if (tmp_opt.saw_tstamp) { 676 tmp_opt.ts_recent = req->ts_recent; 677 if (tmp_opt.rcv_tsecr) { 678 if (inet_rsk(req)->tstamp_ok && !fastopen) 679 tsecr_reject = !between(tmp_opt.rcv_tsecr, 680 tcp_rsk(req)->snt_tsval_first, 681 READ_ONCE(tcp_rsk(req)->snt_tsval_last)); 682 tmp_opt.rcv_tsecr -= tcp_rsk(req)->ts_off; 683 } 684 /* We do not store true stamp, but it is not required, 685 * it can be estimated (approximately) 686 * from another data. 687 */ 688 tmp_opt.ts_recent_stamp = ktime_get_seconds() - reqsk_timeout(req, TCP_RTO_MAX) / HZ; 689 paws_reject = tcp_paws_reject(&tmp_opt, th->rst); 690 } 691 } 692 693 /* Check for pure retransmitted SYN. */ 694 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn && 695 flg == TCP_FLAG_SYN && 696 !paws_reject) { 697 /* 698 * RFC793 draws (Incorrectly! It was fixed in RFC1122) 699 * this case on figure 6 and figure 8, but formal 700 * protocol description says NOTHING. 701 * To be more exact, it says that we should send ACK, 702 * because this segment (at least, if it has no data) 703 * is out of window. 704 * 705 * CONCLUSION: RFC793 (even with RFC1122) DOES NOT 706 * describe SYN-RECV state. All the description 707 * is wrong, we cannot believe to it and should 708 * rely only on common sense and implementation 709 * experience. 710 * 711 * Enforce "SYN-ACK" according to figure 8, figure 6 712 * of RFC793, fixed by RFC1122. 713 * 714 * Note that even if there is new data in the SYN packet 715 * they will be thrown away too. 716 * 717 * Reset timer after retransmitting SYNACK, similar to 718 * the idea of fast retransmit in recovery. 719 */ 720 if (!tcp_oow_rate_limited(sock_net(sk), skb, 721 LINUX_MIB_TCPACKSKIPPEDSYNRECV, 722 &tcp_rsk(req)->last_oow_ack_time) && 723 724 !inet_rtx_syn_ack(sk, req)) { 725 unsigned long expires = jiffies; 726 727 expires += reqsk_timeout(req, TCP_RTO_MAX); 728 if (!fastopen) 729 mod_timer_pending(&req->rsk_timer, expires); 730 else 731 req->rsk_timer.expires = expires; 732 } 733 return NULL; 734 } 735 736 /* Further reproduces section "SEGMENT ARRIVES" 737 for state SYN-RECEIVED of RFC793. 738 It is broken, however, it does not work only 739 when SYNs are crossed. 740 741 You would think that SYN crossing is impossible here, since 742 we should have a SYN_SENT socket (from connect()) on our end, 743 but this is not true if the crossed SYNs were sent to both 744 ends by a malicious third party. We must defend against this, 745 and to do that we first verify the ACK (as per RFC793, page 746 36) and reset if it is invalid. Is this a true full defense? 747 To convince ourselves, let us consider a way in which the ACK 748 test can still pass in this 'malicious crossed SYNs' case. 749 Malicious sender sends identical SYNs (and thus identical sequence 750 numbers) to both A and B: 751 752 A: gets SYN, seq=7 753 B: gets SYN, seq=7 754 755 By our good fortune, both A and B select the same initial 756 send sequence number of seven :-) 757 758 A: sends SYN|ACK, seq=7, ack_seq=8 759 B: sends SYN|ACK, seq=7, ack_seq=8 760 761 So we are now A eating this SYN|ACK, ACK test passes. So 762 does sequence test, SYN is truncated, and thus we consider 763 it a bare ACK. 764 765 If icsk->icsk_accept_queue.rskq_defer_accept, we silently drop this 766 bare ACK. Otherwise, we create an established connection. Both 767 ends (listening sockets) accept the new incoming connection and try 768 to talk to each other. 8-) 769 770 Note: This case is both harmless, and rare. Possibility is about the 771 same as us discovering intelligent life on another plant tomorrow. 772 773 But generally, we should (RFC lies!) to accept ACK 774 from SYNACK both here and in tcp_rcv_state_process(). 775 tcp_rcv_state_process() does not, hence, we do not too. 776 777 Note that the case is absolutely generic: 778 we cannot optimize anything here without 779 violating protocol. All the checks must be made 780 before attempt to create socket. 781 */ 782 783 /* RFC793 page 36: "If the connection is in any non-synchronized state ... 784 * and the incoming segment acknowledges something not yet 785 * sent (the segment carries an unacceptable ACK) ... 786 * a reset is sent." 787 * 788 * Invalid ACK: reset will be sent by listening socket. 789 * Note that the ACK validity check for a Fast Open socket is done 790 * elsewhere and is checked directly against the child socket rather 791 * than req because user data may have been sent out. 792 */ 793 if ((flg & TCP_FLAG_ACK) && !fastopen && 794 (TCP_SKB_CB(skb)->ack_seq != 795 tcp_rsk(req)->snt_isn + 1)) 796 return sk; 797 798 /* RFC793: "first check sequence number". */ 799 800 if (paws_reject || tsecr_reject || 801 !tcp_in_window(TCP_SKB_CB(skb)->seq, 802 TCP_SKB_CB(skb)->end_seq, 803 tcp_rsk(req)->rcv_nxt, 804 tcp_rsk(req)->rcv_nxt + 805 tcp_synack_window(req))) { 806 /* Out of window: send ACK and drop. */ 807 if (!(flg & TCP_FLAG_RST) && 808 !tcp_oow_rate_limited(sock_net(sk), skb, 809 LINUX_MIB_TCPACKSKIPPEDSYNRECV, 810 &tcp_rsk(req)->last_oow_ack_time)) 811 req->rsk_ops->send_ack(sk, skb, req); 812 if (paws_reject) { 813 SKB_DR_SET(*drop_reason, TCP_RFC7323_PAWS); 814 NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED); 815 } else if (tsecr_reject) { 816 SKB_DR_SET(*drop_reason, TCP_RFC7323_TSECR); 817 NET_INC_STATS(sock_net(sk), LINUX_MIB_TSECRREJECTED); 818 } else { 819 SKB_DR_SET(*drop_reason, TCP_OVERWINDOW); 820 } 821 return NULL; 822 } 823 824 /* In sequence, PAWS is OK. */ 825 826 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn) { 827 /* Truncate SYN, it is out of window starting 828 at tcp_rsk(req)->rcv_isn + 1. */ 829 flg &= ~TCP_FLAG_SYN; 830 } 831 832 /* RFC793: "second check the RST bit" and 833 * "fourth, check the SYN bit" 834 */ 835 if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN)) { 836 TCP_INC_STATS(sock_net(sk), TCP_MIB_ATTEMPTFAILS); 837 goto embryonic_reset; 838 } 839 840 /* ACK sequence verified above, just make sure ACK is 841 * set. If ACK not set, just silently drop the packet. 842 * 843 * XXX (TFO) - if we ever allow "data after SYN", the 844 * following check needs to be removed. 845 */ 846 if (!(flg & TCP_FLAG_ACK)) 847 return NULL; 848 849 /* For Fast Open no more processing is needed (sk is the 850 * child socket). 851 */ 852 if (fastopen) 853 return sk; 854 855 /* While TCP_DEFER_ACCEPT is active, drop bare ACK. */ 856 if (req->num_timeout < READ_ONCE(inet_csk(sk)->icsk_accept_queue.rskq_defer_accept) && 857 TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) { 858 inet_rsk(req)->acked = 1; 859 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDEFERACCEPTDROP); 860 return NULL; 861 } 862 863 /* OK, ACK is valid, create big socket and 864 * feed this segment to it. It will repeat all 865 * the tests. THIS SEGMENT MUST MOVE SOCKET TO 866 * ESTABLISHED STATE. If it will be dropped after 867 * socket is created, wait for troubles. 868 */ 869 child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL, 870 req, &own_req); 871 if (!child) 872 goto listen_overflow; 873 874 if (own_req && tmp_opt.saw_tstamp && 875 !after(TCP_SKB_CB(skb)->seq, tcp_rsk(req)->rcv_nxt)) 876 tcp_sk(child)->rx_opt.ts_recent = tmp_opt.rcv_tsval; 877 878 if (own_req && rsk_drop_req(req)) { 879 reqsk_queue_removed(&inet_csk(req->rsk_listener)->icsk_accept_queue, req); 880 inet_csk_reqsk_queue_drop_and_put(req->rsk_listener, req); 881 return child; 882 } 883 884 sock_rps_save_rxhash(child, skb); 885 tcp_synack_rtt_meas(child, req); 886 *req_stolen = !own_req; 887 return inet_csk_complete_hashdance(sk, child, req, own_req); 888 889 listen_overflow: 890 SKB_DR_SET(*drop_reason, TCP_LISTEN_OVERFLOW); 891 if (sk != req->rsk_listener) 892 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMIGRATEREQFAILURE); 893 894 if (!READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_abort_on_overflow)) { 895 inet_rsk(req)->acked = 1; 896 return NULL; 897 } 898 899 embryonic_reset: 900 if (!(flg & TCP_FLAG_RST)) { 901 /* Received a bad SYN pkt - for TFO We try not to reset 902 * the local connection unless it's really necessary to 903 * avoid becoming vulnerable to outside attack aiming at 904 * resetting legit local connections. 905 */ 906 req->rsk_ops->send_reset(sk, skb, SK_RST_REASON_INVALID_SYN); 907 } else if (fastopen) { /* received a valid RST pkt */ 908 reqsk_fastopen_remove(sk, req, true); 909 tcp_reset(sk, skb); 910 } 911 if (!fastopen) { 912 bool unlinked = inet_csk_reqsk_queue_drop(sk, req); 913 914 if (unlinked) 915 __NET_INC_STATS(sock_net(sk), LINUX_MIB_EMBRYONICRSTS); 916 *req_stolen = !unlinked; 917 } 918 return NULL; 919 } 920 EXPORT_IPV6_MOD(tcp_check_req); 921 922 /* 923 * Queue segment on the new socket if the new socket is active, 924 * otherwise we just shortcircuit this and continue with 925 * the new socket. 926 * 927 * For the vast majority of cases child->sk_state will be TCP_SYN_RECV 928 * when entering. But other states are possible due to a race condition 929 * where after __inet_lookup_established() fails but before the listener 930 * locked is obtained, other packets cause the same connection to 931 * be created. 932 */ 933 934 enum skb_drop_reason tcp_child_process(struct sock *parent, struct sock *child, 935 struct sk_buff *skb) 936 __releases(&((child)->sk_lock.slock)) 937 { 938 enum skb_drop_reason reason = SKB_NOT_DROPPED_YET; 939 int state = child->sk_state; 940 941 /* record sk_napi_id and sk_rx_queue_mapping of child. */ 942 sk_mark_napi_id_set(child, skb); 943 944 tcp_segs_in(tcp_sk(child), skb); 945 if (!sock_owned_by_user(child)) { 946 reason = tcp_rcv_state_process(child, skb); 947 /* Wakeup parent, send SIGIO */ 948 if (state == TCP_SYN_RECV && child->sk_state != state) 949 parent->sk_data_ready(parent); 950 } else { 951 /* Alas, it is possible again, because we do lookup 952 * in main socket hash table and lock on listening 953 * socket does not protect us more. 954 */ 955 __sk_add_backlog(child, skb); 956 } 957 958 bh_unlock_sock(child); 959 sock_put(child); 960 return reason; 961 } 962 EXPORT_IPV6_MOD(tcp_child_process); 963