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 26 static bool tcp_in_window(u32 seq, u32 end_seq, u32 s_win, u32 e_win) 27 { 28 if (seq == s_win) 29 return true; 30 if (after(end_seq, s_win) && before(seq, e_win)) 31 return true; 32 return seq == e_win && seq == end_seq; 33 } 34 35 static enum tcp_tw_status 36 tcp_timewait_check_oow_rate_limit(struct inet_timewait_sock *tw, 37 const struct sk_buff *skb, int mib_idx) 38 { 39 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw); 40 41 if (!tcp_oow_rate_limited(twsk_net(tw), skb, mib_idx, 42 &tcptw->tw_last_oow_ack_time)) { 43 /* Send ACK. Note, we do not put the bucket, 44 * it will be released by caller. 45 */ 46 return TCP_TW_ACK; 47 } 48 49 /* We are rate-limiting, so just release the tw sock and drop skb. */ 50 inet_twsk_put(tw); 51 return TCP_TW_SUCCESS; 52 } 53 54 /* 55 * * Main purpose of TIME-WAIT state is to close connection gracefully, 56 * when one of ends sits in LAST-ACK or CLOSING retransmitting FIN 57 * (and, probably, tail of data) and one or more our ACKs are lost. 58 * * What is TIME-WAIT timeout? It is associated with maximal packet 59 * lifetime in the internet, which results in wrong conclusion, that 60 * it is set to catch "old duplicate segments" wandering out of their path. 61 * It is not quite correct. This timeout is calculated so that it exceeds 62 * maximal retransmission timeout enough to allow to lose one (or more) 63 * segments sent by peer and our ACKs. This time may be calculated from RTO. 64 * * When TIME-WAIT socket receives RST, it means that another end 65 * finally closed and we are allowed to kill TIME-WAIT too. 66 * * Second purpose of TIME-WAIT is catching old duplicate segments. 67 * Well, certainly it is pure paranoia, but if we load TIME-WAIT 68 * with this semantics, we MUST NOT kill TIME-WAIT state with RSTs. 69 * * If we invented some more clever way to catch duplicates 70 * (f.e. based on PAWS), we could truncate TIME-WAIT to several RTOs. 71 * 72 * The algorithm below is based on FORMAL INTERPRETATION of RFCs. 73 * When you compare it to RFCs, please, read section SEGMENT ARRIVES 74 * from the very beginning. 75 * 76 * NOTE. With recycling (and later with fin-wait-2) TW bucket 77 * is _not_ stateless. It means, that strictly speaking we must 78 * spinlock it. I do not want! Well, probability of misbehaviour 79 * is ridiculously low and, seems, we could use some mb() tricks 80 * to avoid misread sequence numbers, states etc. --ANK 81 * 82 * We don't need to initialize tmp_out.sack_ok as we don't use the results 83 */ 84 enum tcp_tw_status 85 tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb, 86 const struct tcphdr *th) 87 { 88 struct tcp_options_received tmp_opt; 89 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw); 90 bool paws_reject = false; 91 92 tmp_opt.saw_tstamp = 0; 93 if (th->doff > (sizeof(*th) >> 2) && tcptw->tw_ts_recent_stamp) { 94 tcp_parse_options(twsk_net(tw), skb, &tmp_opt, 0, NULL); 95 96 if (tmp_opt.saw_tstamp) { 97 if (tmp_opt.rcv_tsecr) 98 tmp_opt.rcv_tsecr -= tcptw->tw_ts_offset; 99 tmp_opt.ts_recent = tcptw->tw_ts_recent; 100 tmp_opt.ts_recent_stamp = tcptw->tw_ts_recent_stamp; 101 paws_reject = tcp_paws_reject(&tmp_opt, th->rst); 102 } 103 } 104 105 if (tw->tw_substate == TCP_FIN_WAIT2) { 106 /* Just repeat all the checks of tcp_rcv_state_process() */ 107 108 /* Out of window, send ACK */ 109 if (paws_reject || 110 !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq, 111 tcptw->tw_rcv_nxt, 112 tcptw->tw_rcv_nxt + tcptw->tw_rcv_wnd)) 113 return tcp_timewait_check_oow_rate_limit( 114 tw, skb, LINUX_MIB_TCPACKSKIPPEDFINWAIT2); 115 116 if (th->rst) 117 goto kill; 118 119 if (th->syn && !before(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt)) 120 return TCP_TW_RST; 121 122 /* Dup ACK? */ 123 if (!th->ack || 124 !after(TCP_SKB_CB(skb)->end_seq, tcptw->tw_rcv_nxt) || 125 TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq) { 126 inet_twsk_put(tw); 127 return TCP_TW_SUCCESS; 128 } 129 130 /* New data or FIN. If new data arrive after half-duplex close, 131 * reset. 132 */ 133 if (!th->fin || 134 TCP_SKB_CB(skb)->end_seq != tcptw->tw_rcv_nxt + 1) 135 return TCP_TW_RST; 136 137 /* FIN arrived, enter true time-wait state. */ 138 tw->tw_substate = TCP_TIME_WAIT; 139 tcptw->tw_rcv_nxt = TCP_SKB_CB(skb)->end_seq; 140 if (tmp_opt.saw_tstamp) { 141 tcptw->tw_ts_recent_stamp = ktime_get_seconds(); 142 tcptw->tw_ts_recent = tmp_opt.rcv_tsval; 143 } 144 145 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN); 146 return TCP_TW_ACK; 147 } 148 149 /* 150 * Now real TIME-WAIT state. 151 * 152 * RFC 1122: 153 * "When a connection is [...] on TIME-WAIT state [...] 154 * [a TCP] MAY accept a new SYN from the remote TCP to 155 * reopen the connection directly, if it: 156 * 157 * (1) assigns its initial sequence number for the new 158 * connection to be larger than the largest sequence 159 * number it used on the previous connection incarnation, 160 * and 161 * 162 * (2) returns to TIME-WAIT state if the SYN turns out 163 * to be an old duplicate". 164 */ 165 166 if (!paws_reject && 167 (TCP_SKB_CB(skb)->seq == tcptw->tw_rcv_nxt && 168 (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq || th->rst))) { 169 /* In window segment, it may be only reset or bare ack. */ 170 171 if (th->rst) { 172 /* This is TIME_WAIT assassination, in two flavors. 173 * Oh well... nobody has a sufficient solution to this 174 * protocol bug yet. 175 */ 176 if (!READ_ONCE(twsk_net(tw)->ipv4.sysctl_tcp_rfc1337)) { 177 kill: 178 inet_twsk_deschedule_put(tw); 179 return TCP_TW_SUCCESS; 180 } 181 } else { 182 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN); 183 } 184 185 if (tmp_opt.saw_tstamp) { 186 tcptw->tw_ts_recent = tmp_opt.rcv_tsval; 187 tcptw->tw_ts_recent_stamp = ktime_get_seconds(); 188 } 189 190 inet_twsk_put(tw); 191 return TCP_TW_SUCCESS; 192 } 193 194 /* Out of window segment. 195 196 All the segments are ACKed immediately. 197 198 The only exception is new SYN. We accept it, if it is 199 not old duplicate and we are not in danger to be killed 200 by delayed old duplicates. RFC check is that it has 201 newer sequence number works at rates <40Mbit/sec. 202 However, if paws works, it is reliable AND even more, 203 we even may relax silly seq space cutoff. 204 205 RED-PEN: we violate main RFC requirement, if this SYN will appear 206 old duplicate (i.e. we receive RST in reply to SYN-ACK), 207 we must return socket to time-wait state. It is not good, 208 but not fatal yet. 209 */ 210 211 if (th->syn && !th->rst && !th->ack && !paws_reject && 212 (after(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt) || 213 (tmp_opt.saw_tstamp && 214 (s32)(tcptw->tw_ts_recent - tmp_opt.rcv_tsval) < 0))) { 215 u32 isn = tcptw->tw_snd_nxt + 65535 + 2; 216 if (isn == 0) 217 isn++; 218 TCP_SKB_CB(skb)->tcp_tw_isn = isn; 219 return TCP_TW_SYN; 220 } 221 222 if (paws_reject) 223 __NET_INC_STATS(twsk_net(tw), LINUX_MIB_PAWSESTABREJECTED); 224 225 if (!th->rst) { 226 /* In this case we must reset the TIMEWAIT timer. 227 * 228 * If it is ACKless SYN it may be both old duplicate 229 * and new good SYN with random sequence number <rcv_nxt. 230 * Do not reschedule in the last case. 231 */ 232 if (paws_reject || th->ack) 233 inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN); 234 235 return tcp_timewait_check_oow_rate_limit( 236 tw, skb, LINUX_MIB_TCPACKSKIPPEDTIMEWAIT); 237 } 238 inet_twsk_put(tw); 239 return TCP_TW_SUCCESS; 240 } 241 EXPORT_SYMBOL(tcp_timewait_state_process); 242 243 static void tcp_time_wait_init(struct sock *sk, struct tcp_timewait_sock *tcptw) 244 { 245 #ifdef CONFIG_TCP_MD5SIG 246 const struct tcp_sock *tp = tcp_sk(sk); 247 struct tcp_md5sig_key *key; 248 249 /* 250 * The timewait bucket does not have the key DB from the 251 * sock structure. We just make a quick copy of the 252 * md5 key being used (if indeed we are using one) 253 * so the timewait ack generating code has the key. 254 */ 255 tcptw->tw_md5_key = NULL; 256 if (!static_branch_unlikely(&tcp_md5_needed.key)) 257 return; 258 259 key = tp->af_specific->md5_lookup(sk, sk); 260 if (key) { 261 tcptw->tw_md5_key = kmemdup(key, sizeof(*key), GFP_ATOMIC); 262 if (!tcptw->tw_md5_key) 263 return; 264 if (!tcp_alloc_md5sig_pool()) 265 goto out_free; 266 if (!static_key_fast_inc_not_disabled(&tcp_md5_needed.key.key)) 267 goto out_free; 268 } 269 return; 270 out_free: 271 WARN_ON_ONCE(1); 272 kfree(tcptw->tw_md5_key); 273 tcptw->tw_md5_key = NULL; 274 #endif 275 } 276 277 /* 278 * Move a socket to time-wait or dead fin-wait-2 state. 279 */ 280 void tcp_time_wait(struct sock *sk, int state, int timeo) 281 { 282 const struct inet_connection_sock *icsk = inet_csk(sk); 283 const struct tcp_sock *tp = tcp_sk(sk); 284 struct net *net = sock_net(sk); 285 struct inet_timewait_sock *tw; 286 287 tw = inet_twsk_alloc(sk, &net->ipv4.tcp_death_row, state); 288 289 if (tw) { 290 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw); 291 const int rto = (icsk->icsk_rto << 2) - (icsk->icsk_rto >> 1); 292 struct inet_sock *inet = inet_sk(sk); 293 294 tw->tw_transparent = inet->transparent; 295 tw->tw_mark = sk->sk_mark; 296 tw->tw_priority = sk->sk_priority; 297 tw->tw_rcv_wscale = tp->rx_opt.rcv_wscale; 298 tcptw->tw_rcv_nxt = tp->rcv_nxt; 299 tcptw->tw_snd_nxt = tp->snd_nxt; 300 tcptw->tw_rcv_wnd = tcp_receive_window(tp); 301 tcptw->tw_ts_recent = tp->rx_opt.ts_recent; 302 tcptw->tw_ts_recent_stamp = tp->rx_opt.ts_recent_stamp; 303 tcptw->tw_ts_offset = tp->tsoffset; 304 tcptw->tw_last_oow_ack_time = 0; 305 tcptw->tw_tx_delay = tp->tcp_tx_delay; 306 #if IS_ENABLED(CONFIG_IPV6) 307 if (tw->tw_family == PF_INET6) { 308 struct ipv6_pinfo *np = inet6_sk(sk); 309 310 tw->tw_v6_daddr = sk->sk_v6_daddr; 311 tw->tw_v6_rcv_saddr = sk->sk_v6_rcv_saddr; 312 tw->tw_tclass = np->tclass; 313 tw->tw_flowlabel = be32_to_cpu(np->flow_label & IPV6_FLOWLABEL_MASK); 314 tw->tw_txhash = sk->sk_txhash; 315 tw->tw_ipv6only = sk->sk_ipv6only; 316 } 317 #endif 318 319 tcp_time_wait_init(sk, tcptw); 320 321 /* Get the TIME_WAIT timeout firing. */ 322 if (timeo < rto) 323 timeo = rto; 324 325 if (state == TCP_TIME_WAIT) 326 timeo = TCP_TIMEWAIT_LEN; 327 328 /* tw_timer is pinned, so we need to make sure BH are disabled 329 * in following section, otherwise timer handler could run before 330 * we complete the initialization. 331 */ 332 local_bh_disable(); 333 inet_twsk_schedule(tw, timeo); 334 /* Linkage updates. 335 * Note that access to tw after this point is illegal. 336 */ 337 inet_twsk_hashdance(tw, sk, net->ipv4.tcp_death_row.hashinfo); 338 local_bh_enable(); 339 } else { 340 /* Sorry, if we're out of memory, just CLOSE this 341 * socket up. We've got bigger problems than 342 * non-graceful socket closings. 343 */ 344 NET_INC_STATS(net, LINUX_MIB_TCPTIMEWAITOVERFLOW); 345 } 346 347 tcp_update_metrics(sk); 348 tcp_done(sk); 349 } 350 EXPORT_SYMBOL(tcp_time_wait); 351 352 void tcp_twsk_destructor(struct sock *sk) 353 { 354 #ifdef CONFIG_TCP_MD5SIG 355 if (static_branch_unlikely(&tcp_md5_needed.key)) { 356 struct tcp_timewait_sock *twsk = tcp_twsk(sk); 357 358 if (twsk->tw_md5_key) { 359 kfree_rcu(twsk->tw_md5_key, rcu); 360 static_branch_slow_dec_deferred(&tcp_md5_needed); 361 } 362 } 363 #endif 364 } 365 EXPORT_SYMBOL_GPL(tcp_twsk_destructor); 366 367 void tcp_twsk_purge(struct list_head *net_exit_list, int family) 368 { 369 bool purged_once = false; 370 struct net *net; 371 372 list_for_each_entry(net, net_exit_list, exit_list) { 373 if (net->ipv4.tcp_death_row.hashinfo->pernet) { 374 /* Even if tw_refcount == 1, we must clean up kernel reqsk */ 375 inet_twsk_purge(net->ipv4.tcp_death_row.hashinfo, family); 376 } else if (!purged_once) { 377 /* The last refcount is decremented in tcp_sk_exit_batch() */ 378 if (refcount_read(&net->ipv4.tcp_death_row.tw_refcount) == 1) 379 continue; 380 381 inet_twsk_purge(&tcp_hashinfo, family); 382 purged_once = true; 383 } 384 } 385 } 386 EXPORT_SYMBOL_GPL(tcp_twsk_purge); 387 388 /* Warning : This function is called without sk_listener being locked. 389 * Be sure to read socket fields once, as their value could change under us. 390 */ 391 void tcp_openreq_init_rwin(struct request_sock *req, 392 const struct sock *sk_listener, 393 const struct dst_entry *dst) 394 { 395 struct inet_request_sock *ireq = inet_rsk(req); 396 const struct tcp_sock *tp = tcp_sk(sk_listener); 397 int full_space = tcp_full_space(sk_listener); 398 u32 window_clamp; 399 __u8 rcv_wscale; 400 u32 rcv_wnd; 401 int mss; 402 403 mss = tcp_mss_clamp(tp, dst_metric_advmss(dst)); 404 window_clamp = READ_ONCE(tp->window_clamp); 405 /* Set this up on the first call only */ 406 req->rsk_window_clamp = window_clamp ? : dst_metric(dst, RTAX_WINDOW); 407 408 /* limit the window selection if the user enforce a smaller rx buffer */ 409 if (sk_listener->sk_userlocks & SOCK_RCVBUF_LOCK && 410 (req->rsk_window_clamp > full_space || req->rsk_window_clamp == 0)) 411 req->rsk_window_clamp = full_space; 412 413 rcv_wnd = tcp_rwnd_init_bpf((struct sock *)req); 414 if (rcv_wnd == 0) 415 rcv_wnd = dst_metric(dst, RTAX_INITRWND); 416 else if (full_space < rcv_wnd * mss) 417 full_space = rcv_wnd * mss; 418 419 /* tcp_full_space because it is guaranteed to be the first packet */ 420 tcp_select_initial_window(sk_listener, full_space, 421 mss - (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0), 422 &req->rsk_rcv_wnd, 423 &req->rsk_window_clamp, 424 ireq->wscale_ok, 425 &rcv_wscale, 426 rcv_wnd); 427 ireq->rcv_wscale = rcv_wscale; 428 } 429 EXPORT_SYMBOL(tcp_openreq_init_rwin); 430 431 static void tcp_ecn_openreq_child(struct tcp_sock *tp, 432 const struct request_sock *req) 433 { 434 tp->ecn_flags = inet_rsk(req)->ecn_ok ? TCP_ECN_OK : 0; 435 } 436 437 void tcp_ca_openreq_child(struct sock *sk, const struct dst_entry *dst) 438 { 439 struct inet_connection_sock *icsk = inet_csk(sk); 440 u32 ca_key = dst_metric(dst, RTAX_CC_ALGO); 441 bool ca_got_dst = false; 442 443 if (ca_key != TCP_CA_UNSPEC) { 444 const struct tcp_congestion_ops *ca; 445 446 rcu_read_lock(); 447 ca = tcp_ca_find_key(ca_key); 448 if (likely(ca && bpf_try_module_get(ca, ca->owner))) { 449 icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst); 450 icsk->icsk_ca_ops = ca; 451 ca_got_dst = true; 452 } 453 rcu_read_unlock(); 454 } 455 456 /* If no valid choice made yet, assign current system default ca. */ 457 if (!ca_got_dst && 458 (!icsk->icsk_ca_setsockopt || 459 !bpf_try_module_get(icsk->icsk_ca_ops, icsk->icsk_ca_ops->owner))) 460 tcp_assign_congestion_control(sk); 461 462 tcp_set_ca_state(sk, TCP_CA_Open); 463 } 464 EXPORT_SYMBOL_GPL(tcp_ca_openreq_child); 465 466 static void smc_check_reset_syn_req(struct tcp_sock *oldtp, 467 struct request_sock *req, 468 struct tcp_sock *newtp) 469 { 470 #if IS_ENABLED(CONFIG_SMC) 471 struct inet_request_sock *ireq; 472 473 if (static_branch_unlikely(&tcp_have_smc)) { 474 ireq = inet_rsk(req); 475 if (oldtp->syn_smc && !ireq->smc_ok) 476 newtp->syn_smc = 0; 477 } 478 #endif 479 } 480 481 /* This is not only more efficient than what we used to do, it eliminates 482 * a lot of code duplication between IPv4/IPv6 SYN recv processing. -DaveM 483 * 484 * Actually, we could lots of memory writes here. tp of listening 485 * socket contains all necessary default parameters. 486 */ 487 struct sock *tcp_create_openreq_child(const struct sock *sk, 488 struct request_sock *req, 489 struct sk_buff *skb) 490 { 491 struct sock *newsk = inet_csk_clone_lock(sk, req, GFP_ATOMIC); 492 const struct inet_request_sock *ireq = inet_rsk(req); 493 struct tcp_request_sock *treq = tcp_rsk(req); 494 struct inet_connection_sock *newicsk; 495 struct tcp_sock *oldtp, *newtp; 496 u32 seq; 497 498 if (!newsk) 499 return NULL; 500 501 newicsk = inet_csk(newsk); 502 newtp = tcp_sk(newsk); 503 oldtp = tcp_sk(sk); 504 505 smc_check_reset_syn_req(oldtp, req, newtp); 506 507 /* Now setup tcp_sock */ 508 newtp->pred_flags = 0; 509 510 seq = treq->rcv_isn + 1; 511 newtp->rcv_wup = seq; 512 WRITE_ONCE(newtp->copied_seq, seq); 513 WRITE_ONCE(newtp->rcv_nxt, seq); 514 newtp->segs_in = 1; 515 516 seq = treq->snt_isn + 1; 517 newtp->snd_sml = newtp->snd_una = seq; 518 WRITE_ONCE(newtp->snd_nxt, seq); 519 newtp->snd_up = seq; 520 521 INIT_LIST_HEAD(&newtp->tsq_node); 522 INIT_LIST_HEAD(&newtp->tsorted_sent_queue); 523 524 tcp_init_wl(newtp, treq->rcv_isn); 525 526 minmax_reset(&newtp->rtt_min, tcp_jiffies32, ~0U); 527 newicsk->icsk_ack.lrcvtime = tcp_jiffies32; 528 529 newtp->lsndtime = tcp_jiffies32; 530 newsk->sk_txhash = treq->txhash; 531 newtp->total_retrans = req->num_retrans; 532 533 tcp_init_xmit_timers(newsk); 534 WRITE_ONCE(newtp->write_seq, newtp->pushed_seq = treq->snt_isn + 1); 535 536 if (sock_flag(newsk, SOCK_KEEPOPEN)) 537 inet_csk_reset_keepalive_timer(newsk, 538 keepalive_time_when(newtp)); 539 540 newtp->rx_opt.tstamp_ok = ireq->tstamp_ok; 541 newtp->rx_opt.sack_ok = ireq->sack_ok; 542 newtp->window_clamp = req->rsk_window_clamp; 543 newtp->rcv_ssthresh = req->rsk_rcv_wnd; 544 newtp->rcv_wnd = req->rsk_rcv_wnd; 545 newtp->rx_opt.wscale_ok = ireq->wscale_ok; 546 if (newtp->rx_opt.wscale_ok) { 547 newtp->rx_opt.snd_wscale = ireq->snd_wscale; 548 newtp->rx_opt.rcv_wscale = ireq->rcv_wscale; 549 } else { 550 newtp->rx_opt.snd_wscale = newtp->rx_opt.rcv_wscale = 0; 551 newtp->window_clamp = min(newtp->window_clamp, 65535U); 552 } 553 newtp->snd_wnd = ntohs(tcp_hdr(skb)->window) << newtp->rx_opt.snd_wscale; 554 newtp->max_window = newtp->snd_wnd; 555 556 if (newtp->rx_opt.tstamp_ok) { 557 newtp->rx_opt.ts_recent = req->ts_recent; 558 newtp->rx_opt.ts_recent_stamp = ktime_get_seconds(); 559 newtp->tcp_header_len = sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED; 560 } else { 561 newtp->rx_opt.ts_recent_stamp = 0; 562 newtp->tcp_header_len = sizeof(struct tcphdr); 563 } 564 if (req->num_timeout) { 565 newtp->undo_marker = treq->snt_isn; 566 newtp->retrans_stamp = div_u64(treq->snt_synack, 567 USEC_PER_SEC / TCP_TS_HZ); 568 } 569 newtp->tsoffset = treq->ts_off; 570 #ifdef CONFIG_TCP_MD5SIG 571 newtp->md5sig_info = NULL; /*XXX*/ 572 if (treq->af_specific->req_md5_lookup(sk, req_to_sk(req))) 573 newtp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED; 574 #endif 575 if (skb->len >= TCP_MSS_DEFAULT + newtp->tcp_header_len) 576 newicsk->icsk_ack.last_seg_size = skb->len - newtp->tcp_header_len; 577 newtp->rx_opt.mss_clamp = req->mss; 578 tcp_ecn_openreq_child(newtp, req); 579 newtp->fastopen_req = NULL; 580 RCU_INIT_POINTER(newtp->fastopen_rsk, NULL); 581 582 newtp->bpf_chg_cc_inprogress = 0; 583 tcp_bpf_clone(sk, newsk); 584 585 __TCP_INC_STATS(sock_net(sk), TCP_MIB_PASSIVEOPENS); 586 587 return newsk; 588 } 589 EXPORT_SYMBOL(tcp_create_openreq_child); 590 591 /* 592 * Process an incoming packet for SYN_RECV sockets represented as a 593 * request_sock. Normally sk is the listener socket but for TFO it 594 * points to the child socket. 595 * 596 * XXX (TFO) - The current impl contains a special check for ack 597 * validation and inside tcp_v4_reqsk_send_ack(). Can we do better? 598 * 599 * We don't need to initialize tmp_opt.sack_ok as we don't use the results 600 * 601 * Note: If @fastopen is true, this can be called from process context. 602 * Otherwise, this is from BH context. 603 */ 604 605 struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb, 606 struct request_sock *req, 607 bool fastopen, bool *req_stolen) 608 { 609 struct tcp_options_received tmp_opt; 610 struct sock *child; 611 const struct tcphdr *th = tcp_hdr(skb); 612 __be32 flg = tcp_flag_word(th) & (TCP_FLAG_RST|TCP_FLAG_SYN|TCP_FLAG_ACK); 613 bool paws_reject = false; 614 bool own_req; 615 616 tmp_opt.saw_tstamp = 0; 617 if (th->doff > (sizeof(struct tcphdr)>>2)) { 618 tcp_parse_options(sock_net(sk), skb, &tmp_opt, 0, NULL); 619 620 if (tmp_opt.saw_tstamp) { 621 tmp_opt.ts_recent = req->ts_recent; 622 if (tmp_opt.rcv_tsecr) 623 tmp_opt.rcv_tsecr -= tcp_rsk(req)->ts_off; 624 /* We do not store true stamp, but it is not required, 625 * it can be estimated (approximately) 626 * from another data. 627 */ 628 tmp_opt.ts_recent_stamp = ktime_get_seconds() - reqsk_timeout(req, TCP_RTO_MAX) / HZ; 629 paws_reject = tcp_paws_reject(&tmp_opt, th->rst); 630 } 631 } 632 633 /* Check for pure retransmitted SYN. */ 634 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn && 635 flg == TCP_FLAG_SYN && 636 !paws_reject) { 637 /* 638 * RFC793 draws (Incorrectly! It was fixed in RFC1122) 639 * this case on figure 6 and figure 8, but formal 640 * protocol description says NOTHING. 641 * To be more exact, it says that we should send ACK, 642 * because this segment (at least, if it has no data) 643 * is out of window. 644 * 645 * CONCLUSION: RFC793 (even with RFC1122) DOES NOT 646 * describe SYN-RECV state. All the description 647 * is wrong, we cannot believe to it and should 648 * rely only on common sense and implementation 649 * experience. 650 * 651 * Enforce "SYN-ACK" according to figure 8, figure 6 652 * of RFC793, fixed by RFC1122. 653 * 654 * Note that even if there is new data in the SYN packet 655 * they will be thrown away too. 656 * 657 * Reset timer after retransmitting SYNACK, similar to 658 * the idea of fast retransmit in recovery. 659 */ 660 if (!tcp_oow_rate_limited(sock_net(sk), skb, 661 LINUX_MIB_TCPACKSKIPPEDSYNRECV, 662 &tcp_rsk(req)->last_oow_ack_time) && 663 664 !inet_rtx_syn_ack(sk, req)) { 665 unsigned long expires = jiffies; 666 667 expires += reqsk_timeout(req, TCP_RTO_MAX); 668 if (!fastopen) 669 mod_timer_pending(&req->rsk_timer, expires); 670 else 671 req->rsk_timer.expires = expires; 672 } 673 return NULL; 674 } 675 676 /* Further reproduces section "SEGMENT ARRIVES" 677 for state SYN-RECEIVED of RFC793. 678 It is broken, however, it does not work only 679 when SYNs are crossed. 680 681 You would think that SYN crossing is impossible here, since 682 we should have a SYN_SENT socket (from connect()) on our end, 683 but this is not true if the crossed SYNs were sent to both 684 ends by a malicious third party. We must defend against this, 685 and to do that we first verify the ACK (as per RFC793, page 686 36) and reset if it is invalid. Is this a true full defense? 687 To convince ourselves, let us consider a way in which the ACK 688 test can still pass in this 'malicious crossed SYNs' case. 689 Malicious sender sends identical SYNs (and thus identical sequence 690 numbers) to both A and B: 691 692 A: gets SYN, seq=7 693 B: gets SYN, seq=7 694 695 By our good fortune, both A and B select the same initial 696 send sequence number of seven :-) 697 698 A: sends SYN|ACK, seq=7, ack_seq=8 699 B: sends SYN|ACK, seq=7, ack_seq=8 700 701 So we are now A eating this SYN|ACK, ACK test passes. So 702 does sequence test, SYN is truncated, and thus we consider 703 it a bare ACK. 704 705 If icsk->icsk_accept_queue.rskq_defer_accept, we silently drop this 706 bare ACK. Otherwise, we create an established connection. Both 707 ends (listening sockets) accept the new incoming connection and try 708 to talk to each other. 8-) 709 710 Note: This case is both harmless, and rare. Possibility is about the 711 same as us discovering intelligent life on another plant tomorrow. 712 713 But generally, we should (RFC lies!) to accept ACK 714 from SYNACK both here and in tcp_rcv_state_process(). 715 tcp_rcv_state_process() does not, hence, we do not too. 716 717 Note that the case is absolutely generic: 718 we cannot optimize anything here without 719 violating protocol. All the checks must be made 720 before attempt to create socket. 721 */ 722 723 /* RFC793 page 36: "If the connection is in any non-synchronized state ... 724 * and the incoming segment acknowledges something not yet 725 * sent (the segment carries an unacceptable ACK) ... 726 * a reset is sent." 727 * 728 * Invalid ACK: reset will be sent by listening socket. 729 * Note that the ACK validity check for a Fast Open socket is done 730 * elsewhere and is checked directly against the child socket rather 731 * than req because user data may have been sent out. 732 */ 733 if ((flg & TCP_FLAG_ACK) && !fastopen && 734 (TCP_SKB_CB(skb)->ack_seq != 735 tcp_rsk(req)->snt_isn + 1)) 736 return sk; 737 738 /* Also, it would be not so bad idea to check rcv_tsecr, which 739 * is essentially ACK extension and too early or too late values 740 * should cause reset in unsynchronized states. 741 */ 742 743 /* RFC793: "first check sequence number". */ 744 745 if (paws_reject || !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq, 746 tcp_rsk(req)->rcv_nxt, tcp_rsk(req)->rcv_nxt + req->rsk_rcv_wnd)) { 747 /* Out of window: send ACK and drop. */ 748 if (!(flg & TCP_FLAG_RST) && 749 !tcp_oow_rate_limited(sock_net(sk), skb, 750 LINUX_MIB_TCPACKSKIPPEDSYNRECV, 751 &tcp_rsk(req)->last_oow_ack_time)) 752 req->rsk_ops->send_ack(sk, skb, req); 753 if (paws_reject) 754 NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED); 755 return NULL; 756 } 757 758 /* In sequence, PAWS is OK. */ 759 760 if (tmp_opt.saw_tstamp && !after(TCP_SKB_CB(skb)->seq, tcp_rsk(req)->rcv_nxt)) 761 req->ts_recent = tmp_opt.rcv_tsval; 762 763 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn) { 764 /* Truncate SYN, it is out of window starting 765 at tcp_rsk(req)->rcv_isn + 1. */ 766 flg &= ~TCP_FLAG_SYN; 767 } 768 769 /* RFC793: "second check the RST bit" and 770 * "fourth, check the SYN bit" 771 */ 772 if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN)) { 773 TCP_INC_STATS(sock_net(sk), TCP_MIB_ATTEMPTFAILS); 774 goto embryonic_reset; 775 } 776 777 /* ACK sequence verified above, just make sure ACK is 778 * set. If ACK not set, just silently drop the packet. 779 * 780 * XXX (TFO) - if we ever allow "data after SYN", the 781 * following check needs to be removed. 782 */ 783 if (!(flg & TCP_FLAG_ACK)) 784 return NULL; 785 786 /* For Fast Open no more processing is needed (sk is the 787 * child socket). 788 */ 789 if (fastopen) 790 return sk; 791 792 /* While TCP_DEFER_ACCEPT is active, drop bare ACK. */ 793 if (req->num_timeout < inet_csk(sk)->icsk_accept_queue.rskq_defer_accept && 794 TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) { 795 inet_rsk(req)->acked = 1; 796 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDEFERACCEPTDROP); 797 return NULL; 798 } 799 800 /* OK, ACK is valid, create big socket and 801 * feed this segment to it. It will repeat all 802 * the tests. THIS SEGMENT MUST MOVE SOCKET TO 803 * ESTABLISHED STATE. If it will be dropped after 804 * socket is created, wait for troubles. 805 */ 806 child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL, 807 req, &own_req); 808 if (!child) 809 goto listen_overflow; 810 811 if (own_req && rsk_drop_req(req)) { 812 reqsk_queue_removed(&inet_csk(req->rsk_listener)->icsk_accept_queue, req); 813 inet_csk_reqsk_queue_drop_and_put(req->rsk_listener, req); 814 return child; 815 } 816 817 sock_rps_save_rxhash(child, skb); 818 tcp_synack_rtt_meas(child, req); 819 *req_stolen = !own_req; 820 return inet_csk_complete_hashdance(sk, child, req, own_req); 821 822 listen_overflow: 823 if (sk != req->rsk_listener) 824 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMIGRATEREQFAILURE); 825 826 if (!READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_abort_on_overflow)) { 827 inet_rsk(req)->acked = 1; 828 return NULL; 829 } 830 831 embryonic_reset: 832 if (!(flg & TCP_FLAG_RST)) { 833 /* Received a bad SYN pkt - for TFO We try not to reset 834 * the local connection unless it's really necessary to 835 * avoid becoming vulnerable to outside attack aiming at 836 * resetting legit local connections. 837 */ 838 req->rsk_ops->send_reset(sk, skb); 839 } else if (fastopen) { /* received a valid RST pkt */ 840 reqsk_fastopen_remove(sk, req, true); 841 tcp_reset(sk, skb); 842 } 843 if (!fastopen) { 844 bool unlinked = inet_csk_reqsk_queue_drop(sk, req); 845 846 if (unlinked) 847 __NET_INC_STATS(sock_net(sk), LINUX_MIB_EMBRYONICRSTS); 848 *req_stolen = !unlinked; 849 } 850 return NULL; 851 } 852 EXPORT_SYMBOL(tcp_check_req); 853 854 /* 855 * Queue segment on the new socket if the new socket is active, 856 * otherwise we just shortcircuit this and continue with 857 * the new socket. 858 * 859 * For the vast majority of cases child->sk_state will be TCP_SYN_RECV 860 * when entering. But other states are possible due to a race condition 861 * where after __inet_lookup_established() fails but before the listener 862 * locked is obtained, other packets cause the same connection to 863 * be created. 864 */ 865 866 int tcp_child_process(struct sock *parent, struct sock *child, 867 struct sk_buff *skb) 868 __releases(&((child)->sk_lock.slock)) 869 { 870 int ret = 0; 871 int state = child->sk_state; 872 873 /* record sk_napi_id and sk_rx_queue_mapping of child. */ 874 sk_mark_napi_id_set(child, skb); 875 876 tcp_segs_in(tcp_sk(child), skb); 877 if (!sock_owned_by_user(child)) { 878 ret = tcp_rcv_state_process(child, skb); 879 /* Wakeup parent, send SIGIO */ 880 if (state == TCP_SYN_RECV && child->sk_state != state) 881 parent->sk_data_ready(parent); 882 } else { 883 /* Alas, it is possible again, because we do lookup 884 * in main socket hash table and lock on listening 885 * socket does not protect us more. 886 */ 887 __sk_add_backlog(child, skb); 888 } 889 890 bh_unlock_sock(child); 891 sock_put(child); 892 return ret; 893 } 894 EXPORT_SYMBOL(tcp_child_process); 895