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_SYMBOL(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_SYMBOL_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 EXPORT_SYMBOL(tcp_openreq_init_rwin); 461 462 static void tcp_ecn_openreq_child(struct tcp_sock *tp, 463 const struct request_sock *req) 464 { 465 tp->ecn_flags = inet_rsk(req)->ecn_ok ? TCP_ECN_OK : 0; 466 } 467 468 void tcp_ca_openreq_child(struct sock *sk, const struct dst_entry *dst) 469 { 470 struct inet_connection_sock *icsk = inet_csk(sk); 471 u32 ca_key = dst_metric(dst, RTAX_CC_ALGO); 472 bool ca_got_dst = false; 473 474 if (ca_key != TCP_CA_UNSPEC) { 475 const struct tcp_congestion_ops *ca; 476 477 rcu_read_lock(); 478 ca = tcp_ca_find_key(ca_key); 479 if (likely(ca && bpf_try_module_get(ca, ca->owner))) { 480 icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst); 481 icsk->icsk_ca_ops = ca; 482 ca_got_dst = true; 483 } 484 rcu_read_unlock(); 485 } 486 487 /* If no valid choice made yet, assign current system default ca. */ 488 if (!ca_got_dst && 489 (!icsk->icsk_ca_setsockopt || 490 !bpf_try_module_get(icsk->icsk_ca_ops, icsk->icsk_ca_ops->owner))) 491 tcp_assign_congestion_control(sk); 492 493 tcp_set_ca_state(sk, TCP_CA_Open); 494 } 495 EXPORT_SYMBOL_GPL(tcp_ca_openreq_child); 496 497 static void smc_check_reset_syn_req(const struct tcp_sock *oldtp, 498 struct request_sock *req, 499 struct tcp_sock *newtp) 500 { 501 #if IS_ENABLED(CONFIG_SMC) 502 struct inet_request_sock *ireq; 503 504 if (static_branch_unlikely(&tcp_have_smc)) { 505 ireq = inet_rsk(req); 506 if (oldtp->syn_smc && !ireq->smc_ok) 507 newtp->syn_smc = 0; 508 } 509 #endif 510 } 511 512 /* This is not only more efficient than what we used to do, it eliminates 513 * a lot of code duplication between IPv4/IPv6 SYN recv processing. -DaveM 514 * 515 * Actually, we could lots of memory writes here. tp of listening 516 * socket contains all necessary default parameters. 517 */ 518 struct sock *tcp_create_openreq_child(const struct sock *sk, 519 struct request_sock *req, 520 struct sk_buff *skb) 521 { 522 struct sock *newsk = inet_csk_clone_lock(sk, req, GFP_ATOMIC); 523 const struct inet_request_sock *ireq = inet_rsk(req); 524 struct tcp_request_sock *treq = tcp_rsk(req); 525 struct inet_connection_sock *newicsk; 526 const struct tcp_sock *oldtp; 527 struct tcp_sock *newtp; 528 u32 seq; 529 530 if (!newsk) 531 return NULL; 532 533 newicsk = inet_csk(newsk); 534 newtp = tcp_sk(newsk); 535 oldtp = tcp_sk(sk); 536 537 smc_check_reset_syn_req(oldtp, req, newtp); 538 539 /* Now setup tcp_sock */ 540 newtp->pred_flags = 0; 541 542 seq = treq->rcv_isn + 1; 543 newtp->rcv_wup = seq; 544 WRITE_ONCE(newtp->copied_seq, seq); 545 WRITE_ONCE(newtp->rcv_nxt, seq); 546 newtp->segs_in = 1; 547 548 seq = treq->snt_isn + 1; 549 newtp->snd_sml = newtp->snd_una = seq; 550 WRITE_ONCE(newtp->snd_nxt, seq); 551 newtp->snd_up = seq; 552 553 INIT_LIST_HEAD(&newtp->tsq_node); 554 INIT_LIST_HEAD(&newtp->tsorted_sent_queue); 555 556 tcp_init_wl(newtp, treq->rcv_isn); 557 558 minmax_reset(&newtp->rtt_min, tcp_jiffies32, ~0U); 559 newicsk->icsk_ack.lrcvtime = tcp_jiffies32; 560 561 newtp->lsndtime = tcp_jiffies32; 562 newsk->sk_txhash = READ_ONCE(treq->txhash); 563 newtp->total_retrans = req->num_retrans; 564 565 tcp_init_xmit_timers(newsk); 566 WRITE_ONCE(newtp->write_seq, newtp->pushed_seq = treq->snt_isn + 1); 567 568 if (sock_flag(newsk, SOCK_KEEPOPEN)) 569 tcp_reset_keepalive_timer(newsk, keepalive_time_when(newtp)); 570 571 newtp->rx_opt.tstamp_ok = ireq->tstamp_ok; 572 newtp->rx_opt.sack_ok = ireq->sack_ok; 573 newtp->window_clamp = req->rsk_window_clamp; 574 newtp->rcv_ssthresh = req->rsk_rcv_wnd; 575 newtp->rcv_wnd = req->rsk_rcv_wnd; 576 newtp->rx_opt.wscale_ok = ireq->wscale_ok; 577 if (newtp->rx_opt.wscale_ok) { 578 newtp->rx_opt.snd_wscale = ireq->snd_wscale; 579 newtp->rx_opt.rcv_wscale = ireq->rcv_wscale; 580 } else { 581 newtp->rx_opt.snd_wscale = newtp->rx_opt.rcv_wscale = 0; 582 newtp->window_clamp = min(newtp->window_clamp, 65535U); 583 } 584 newtp->snd_wnd = ntohs(tcp_hdr(skb)->window) << newtp->rx_opt.snd_wscale; 585 newtp->max_window = newtp->snd_wnd; 586 587 if (newtp->rx_opt.tstamp_ok) { 588 newtp->tcp_usec_ts = treq->req_usec_ts; 589 newtp->rx_opt.ts_recent = READ_ONCE(req->ts_recent); 590 newtp->rx_opt.ts_recent_stamp = ktime_get_seconds(); 591 newtp->tcp_header_len = sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED; 592 } else { 593 newtp->tcp_usec_ts = 0; 594 newtp->rx_opt.ts_recent_stamp = 0; 595 newtp->tcp_header_len = sizeof(struct tcphdr); 596 } 597 if (req->num_timeout) { 598 newtp->total_rto = req->num_timeout; 599 newtp->undo_marker = treq->snt_isn; 600 if (newtp->tcp_usec_ts) { 601 newtp->retrans_stamp = treq->snt_synack; 602 newtp->total_rto_time = (u32)(tcp_clock_us() - 603 newtp->retrans_stamp) / USEC_PER_MSEC; 604 } else { 605 newtp->retrans_stamp = div_u64(treq->snt_synack, 606 USEC_PER_SEC / TCP_TS_HZ); 607 newtp->total_rto_time = tcp_clock_ms() - 608 newtp->retrans_stamp; 609 } 610 newtp->total_rto_recoveries = 1; 611 } 612 newtp->tsoffset = treq->ts_off; 613 #ifdef CONFIG_TCP_MD5SIG 614 newtp->md5sig_info = NULL; /*XXX*/ 615 #endif 616 #ifdef CONFIG_TCP_AO 617 newtp->ao_info = NULL; 618 619 if (tcp_rsk_used_ao(req)) { 620 struct tcp_ao_key *ao_key; 621 622 ao_key = treq->af_specific->ao_lookup(sk, req, tcp_rsk(req)->ao_keyid, -1); 623 if (ao_key) 624 newtp->tcp_header_len += tcp_ao_len_aligned(ao_key); 625 } 626 #endif 627 if (skb->len >= TCP_MSS_DEFAULT + newtp->tcp_header_len) 628 newicsk->icsk_ack.last_seg_size = skb->len - newtp->tcp_header_len; 629 newtp->rx_opt.mss_clamp = req->mss; 630 tcp_ecn_openreq_child(newtp, req); 631 newtp->fastopen_req = NULL; 632 RCU_INIT_POINTER(newtp->fastopen_rsk, NULL); 633 634 newtp->bpf_chg_cc_inprogress = 0; 635 tcp_bpf_clone(sk, newsk); 636 637 __TCP_INC_STATS(sock_net(sk), TCP_MIB_PASSIVEOPENS); 638 639 xa_init_flags(&newsk->sk_user_frags, XA_FLAGS_ALLOC1); 640 641 return newsk; 642 } 643 EXPORT_SYMBOL(tcp_create_openreq_child); 644 645 /* 646 * Process an incoming packet for SYN_RECV sockets represented as a 647 * request_sock. Normally sk is the listener socket but for TFO it 648 * points to the child socket. 649 * 650 * XXX (TFO) - The current impl contains a special check for ack 651 * validation and inside tcp_v4_reqsk_send_ack(). Can we do better? 652 * 653 * We don't need to initialize tmp_opt.sack_ok as we don't use the results 654 * 655 * Note: If @fastopen is true, this can be called from process context. 656 * Otherwise, this is from BH context. 657 */ 658 659 struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb, 660 struct request_sock *req, 661 bool fastopen, bool *req_stolen) 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 paws_reject = false; 668 bool own_req; 669 670 tmp_opt.saw_tstamp = 0; 671 if (th->doff > (sizeof(struct tcphdr)>>2)) { 672 tcp_parse_options(sock_net(sk), skb, &tmp_opt, 0, NULL); 673 674 if (tmp_opt.saw_tstamp) { 675 tmp_opt.ts_recent = READ_ONCE(req->ts_recent); 676 if (tmp_opt.rcv_tsecr) 677 tmp_opt.rcv_tsecr -= tcp_rsk(req)->ts_off; 678 /* We do not store true stamp, but it is not required, 679 * it can be estimated (approximately) 680 * from another data. 681 */ 682 tmp_opt.ts_recent_stamp = ktime_get_seconds() - reqsk_timeout(req, TCP_RTO_MAX) / HZ; 683 paws_reject = tcp_paws_reject(&tmp_opt, th->rst); 684 } 685 } 686 687 /* Check for pure retransmitted SYN. */ 688 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn && 689 flg == TCP_FLAG_SYN && 690 !paws_reject) { 691 /* 692 * RFC793 draws (Incorrectly! It was fixed in RFC1122) 693 * this case on figure 6 and figure 8, but formal 694 * protocol description says NOTHING. 695 * To be more exact, it says that we should send ACK, 696 * because this segment (at least, if it has no data) 697 * is out of window. 698 * 699 * CONCLUSION: RFC793 (even with RFC1122) DOES NOT 700 * describe SYN-RECV state. All the description 701 * is wrong, we cannot believe to it and should 702 * rely only on common sense and implementation 703 * experience. 704 * 705 * Enforce "SYN-ACK" according to figure 8, figure 6 706 * of RFC793, fixed by RFC1122. 707 * 708 * Note that even if there is new data in the SYN packet 709 * they will be thrown away too. 710 * 711 * Reset timer after retransmitting SYNACK, similar to 712 * the idea of fast retransmit in recovery. 713 */ 714 if (!tcp_oow_rate_limited(sock_net(sk), skb, 715 LINUX_MIB_TCPACKSKIPPEDSYNRECV, 716 &tcp_rsk(req)->last_oow_ack_time) && 717 718 !inet_rtx_syn_ack(sk, req)) { 719 unsigned long expires = jiffies; 720 721 expires += reqsk_timeout(req, TCP_RTO_MAX); 722 if (!fastopen) 723 mod_timer_pending(&req->rsk_timer, expires); 724 else 725 req->rsk_timer.expires = expires; 726 } 727 return NULL; 728 } 729 730 /* Further reproduces section "SEGMENT ARRIVES" 731 for state SYN-RECEIVED of RFC793. 732 It is broken, however, it does not work only 733 when SYNs are crossed. 734 735 You would think that SYN crossing is impossible here, since 736 we should have a SYN_SENT socket (from connect()) on our end, 737 but this is not true if the crossed SYNs were sent to both 738 ends by a malicious third party. We must defend against this, 739 and to do that we first verify the ACK (as per RFC793, page 740 36) and reset if it is invalid. Is this a true full defense? 741 To convince ourselves, let us consider a way in which the ACK 742 test can still pass in this 'malicious crossed SYNs' case. 743 Malicious sender sends identical SYNs (and thus identical sequence 744 numbers) to both A and B: 745 746 A: gets SYN, seq=7 747 B: gets SYN, seq=7 748 749 By our good fortune, both A and B select the same initial 750 send sequence number of seven :-) 751 752 A: sends SYN|ACK, seq=7, ack_seq=8 753 B: sends SYN|ACK, seq=7, ack_seq=8 754 755 So we are now A eating this SYN|ACK, ACK test passes. So 756 does sequence test, SYN is truncated, and thus we consider 757 it a bare ACK. 758 759 If icsk->icsk_accept_queue.rskq_defer_accept, we silently drop this 760 bare ACK. Otherwise, we create an established connection. Both 761 ends (listening sockets) accept the new incoming connection and try 762 to talk to each other. 8-) 763 764 Note: This case is both harmless, and rare. Possibility is about the 765 same as us discovering intelligent life on another plant tomorrow. 766 767 But generally, we should (RFC lies!) to accept ACK 768 from SYNACK both here and in tcp_rcv_state_process(). 769 tcp_rcv_state_process() does not, hence, we do not too. 770 771 Note that the case is absolutely generic: 772 we cannot optimize anything here without 773 violating protocol. All the checks must be made 774 before attempt to create socket. 775 */ 776 777 /* RFC793 page 36: "If the connection is in any non-synchronized state ... 778 * and the incoming segment acknowledges something not yet 779 * sent (the segment carries an unacceptable ACK) ... 780 * a reset is sent." 781 * 782 * Invalid ACK: reset will be sent by listening socket. 783 * Note that the ACK validity check for a Fast Open socket is done 784 * elsewhere and is checked directly against the child socket rather 785 * than req because user data may have been sent out. 786 */ 787 if ((flg & TCP_FLAG_ACK) && !fastopen && 788 (TCP_SKB_CB(skb)->ack_seq != 789 tcp_rsk(req)->snt_isn + 1)) 790 return sk; 791 792 /* Also, it would be not so bad idea to check rcv_tsecr, which 793 * is essentially ACK extension and too early or too late values 794 * should cause reset in unsynchronized states. 795 */ 796 797 /* RFC793: "first check sequence number". */ 798 799 if (paws_reject || !tcp_in_window(TCP_SKB_CB(skb)->seq, 800 TCP_SKB_CB(skb)->end_seq, 801 tcp_rsk(req)->rcv_nxt, 802 tcp_rsk(req)->rcv_nxt + 803 tcp_synack_window(req))) { 804 /* Out of window: send ACK and drop. */ 805 if (!(flg & TCP_FLAG_RST) && 806 !tcp_oow_rate_limited(sock_net(sk), skb, 807 LINUX_MIB_TCPACKSKIPPEDSYNRECV, 808 &tcp_rsk(req)->last_oow_ack_time)) 809 req->rsk_ops->send_ack(sk, skb, req); 810 if (paws_reject) 811 NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED); 812 return NULL; 813 } 814 815 /* In sequence, PAWS is OK. */ 816 817 /* TODO: We probably should defer ts_recent change once 818 * we take ownership of @req. 819 */ 820 if (tmp_opt.saw_tstamp && !after(TCP_SKB_CB(skb)->seq, tcp_rsk(req)->rcv_nxt)) 821 WRITE_ONCE(req->ts_recent, tmp_opt.rcv_tsval); 822 823 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn) { 824 /* Truncate SYN, it is out of window starting 825 at tcp_rsk(req)->rcv_isn + 1. */ 826 flg &= ~TCP_FLAG_SYN; 827 } 828 829 /* RFC793: "second check the RST bit" and 830 * "fourth, check the SYN bit" 831 */ 832 if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN)) { 833 TCP_INC_STATS(sock_net(sk), TCP_MIB_ATTEMPTFAILS); 834 goto embryonic_reset; 835 } 836 837 /* ACK sequence verified above, just make sure ACK is 838 * set. If ACK not set, just silently drop the packet. 839 * 840 * XXX (TFO) - if we ever allow "data after SYN", the 841 * following check needs to be removed. 842 */ 843 if (!(flg & TCP_FLAG_ACK)) 844 return NULL; 845 846 /* For Fast Open no more processing is needed (sk is the 847 * child socket). 848 */ 849 if (fastopen) 850 return sk; 851 852 /* While TCP_DEFER_ACCEPT is active, drop bare ACK. */ 853 if (req->num_timeout < READ_ONCE(inet_csk(sk)->icsk_accept_queue.rskq_defer_accept) && 854 TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) { 855 inet_rsk(req)->acked = 1; 856 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDEFERACCEPTDROP); 857 return NULL; 858 } 859 860 /* OK, ACK is valid, create big socket and 861 * feed this segment to it. It will repeat all 862 * the tests. THIS SEGMENT MUST MOVE SOCKET TO 863 * ESTABLISHED STATE. If it will be dropped after 864 * socket is created, wait for troubles. 865 */ 866 child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL, 867 req, &own_req); 868 if (!child) 869 goto listen_overflow; 870 871 if (own_req && rsk_drop_req(req)) { 872 reqsk_queue_removed(&inet_csk(req->rsk_listener)->icsk_accept_queue, req); 873 inet_csk_reqsk_queue_drop_and_put(req->rsk_listener, req); 874 return child; 875 } 876 877 sock_rps_save_rxhash(child, skb); 878 tcp_synack_rtt_meas(child, req); 879 *req_stolen = !own_req; 880 return inet_csk_complete_hashdance(sk, child, req, own_req); 881 882 listen_overflow: 883 if (sk != req->rsk_listener) 884 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMIGRATEREQFAILURE); 885 886 if (!READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_abort_on_overflow)) { 887 inet_rsk(req)->acked = 1; 888 return NULL; 889 } 890 891 embryonic_reset: 892 if (!(flg & TCP_FLAG_RST)) { 893 /* Received a bad SYN pkt - for TFO We try not to reset 894 * the local connection unless it's really necessary to 895 * avoid becoming vulnerable to outside attack aiming at 896 * resetting legit local connections. 897 */ 898 req->rsk_ops->send_reset(sk, skb, SK_RST_REASON_INVALID_SYN); 899 } else if (fastopen) { /* received a valid RST pkt */ 900 reqsk_fastopen_remove(sk, req, true); 901 tcp_reset(sk, skb); 902 } 903 if (!fastopen) { 904 bool unlinked = inet_csk_reqsk_queue_drop(sk, req); 905 906 if (unlinked) 907 __NET_INC_STATS(sock_net(sk), LINUX_MIB_EMBRYONICRSTS); 908 *req_stolen = !unlinked; 909 } 910 return NULL; 911 } 912 EXPORT_SYMBOL(tcp_check_req); 913 914 /* 915 * Queue segment on the new socket if the new socket is active, 916 * otherwise we just shortcircuit this and continue with 917 * the new socket. 918 * 919 * For the vast majority of cases child->sk_state will be TCP_SYN_RECV 920 * when entering. But other states are possible due to a race condition 921 * where after __inet_lookup_established() fails but before the listener 922 * locked is obtained, other packets cause the same connection to 923 * be created. 924 */ 925 926 enum skb_drop_reason tcp_child_process(struct sock *parent, struct sock *child, 927 struct sk_buff *skb) 928 __releases(&((child)->sk_lock.slock)) 929 { 930 enum skb_drop_reason reason = SKB_NOT_DROPPED_YET; 931 int state = child->sk_state; 932 933 /* record sk_napi_id and sk_rx_queue_mapping of child. */ 934 sk_mark_napi_id_set(child, skb); 935 936 tcp_segs_in(tcp_sk(child), skb); 937 if (!sock_owned_by_user(child)) { 938 reason = tcp_rcv_state_process(child, skb); 939 /* Wakeup parent, send SIGIO */ 940 if (state == TCP_SYN_RECV && child->sk_state != state) 941 parent->sk_data_ready(parent); 942 } else { 943 /* Alas, it is possible again, because we do lookup 944 * in main socket hash table and lock on listening 945 * socket does not protect us more. 946 */ 947 __sk_add_backlog(child, skb); 948 } 949 950 bh_unlock_sock(child); 951 sock_put(child); 952 return reason; 953 } 954 EXPORT_SYMBOL(tcp_child_process); 955