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 /* 244 * Move a socket to time-wait or dead fin-wait-2 state. 245 */ 246 void tcp_time_wait(struct sock *sk, int state, int timeo) 247 { 248 const struct inet_connection_sock *icsk = inet_csk(sk); 249 const struct tcp_sock *tp = tcp_sk(sk); 250 struct net *net = sock_net(sk); 251 struct inet_timewait_sock *tw; 252 253 tw = inet_twsk_alloc(sk, &net->ipv4.tcp_death_row, state); 254 255 if (tw) { 256 struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw); 257 const int rto = (icsk->icsk_rto << 2) - (icsk->icsk_rto >> 1); 258 struct inet_sock *inet = inet_sk(sk); 259 260 tw->tw_transparent = inet->transparent; 261 tw->tw_mark = sk->sk_mark; 262 tw->tw_priority = sk->sk_priority; 263 tw->tw_rcv_wscale = tp->rx_opt.rcv_wscale; 264 tcptw->tw_rcv_nxt = tp->rcv_nxt; 265 tcptw->tw_snd_nxt = tp->snd_nxt; 266 tcptw->tw_rcv_wnd = tcp_receive_window(tp); 267 tcptw->tw_ts_recent = tp->rx_opt.ts_recent; 268 tcptw->tw_ts_recent_stamp = tp->rx_opt.ts_recent_stamp; 269 tcptw->tw_ts_offset = tp->tsoffset; 270 tcptw->tw_last_oow_ack_time = 0; 271 tcptw->tw_tx_delay = tp->tcp_tx_delay; 272 #if IS_ENABLED(CONFIG_IPV6) 273 if (tw->tw_family == PF_INET6) { 274 struct ipv6_pinfo *np = inet6_sk(sk); 275 276 tw->tw_v6_daddr = sk->sk_v6_daddr; 277 tw->tw_v6_rcv_saddr = sk->sk_v6_rcv_saddr; 278 tw->tw_tclass = np->tclass; 279 tw->tw_flowlabel = be32_to_cpu(np->flow_label & IPV6_FLOWLABEL_MASK); 280 tw->tw_txhash = sk->sk_txhash; 281 tw->tw_ipv6only = sk->sk_ipv6only; 282 } 283 #endif 284 285 #ifdef CONFIG_TCP_MD5SIG 286 /* 287 * The timewait bucket does not have the key DB from the 288 * sock structure. We just make a quick copy of the 289 * md5 key being used (if indeed we are using one) 290 * so the timewait ack generating code has the key. 291 */ 292 do { 293 tcptw->tw_md5_key = NULL; 294 if (static_branch_unlikely(&tcp_md5_needed)) { 295 struct tcp_md5sig_key *key; 296 297 key = tp->af_specific->md5_lookup(sk, sk); 298 if (key) { 299 tcptw->tw_md5_key = kmemdup(key, sizeof(*key), GFP_ATOMIC); 300 BUG_ON(tcptw->tw_md5_key && !tcp_alloc_md5sig_pool()); 301 } 302 } 303 } while (0); 304 #endif 305 306 /* Get the TIME_WAIT timeout firing. */ 307 if (timeo < rto) 308 timeo = rto; 309 310 if (state == TCP_TIME_WAIT) 311 timeo = TCP_TIMEWAIT_LEN; 312 313 /* tw_timer is pinned, so we need to make sure BH are disabled 314 * in following section, otherwise timer handler could run before 315 * we complete the initialization. 316 */ 317 local_bh_disable(); 318 inet_twsk_schedule(tw, timeo); 319 /* Linkage updates. 320 * Note that access to tw after this point is illegal. 321 */ 322 inet_twsk_hashdance(tw, sk, net->ipv4.tcp_death_row.hashinfo); 323 local_bh_enable(); 324 } else { 325 /* Sorry, if we're out of memory, just CLOSE this 326 * socket up. We've got bigger problems than 327 * non-graceful socket closings. 328 */ 329 NET_INC_STATS(net, LINUX_MIB_TCPTIMEWAITOVERFLOW); 330 } 331 332 tcp_update_metrics(sk); 333 tcp_done(sk); 334 } 335 EXPORT_SYMBOL(tcp_time_wait); 336 337 void tcp_twsk_destructor(struct sock *sk) 338 { 339 #ifdef CONFIG_TCP_MD5SIG 340 if (static_branch_unlikely(&tcp_md5_needed)) { 341 struct tcp_timewait_sock *twsk = tcp_twsk(sk); 342 343 if (twsk->tw_md5_key) 344 kfree_rcu(twsk->tw_md5_key, rcu); 345 } 346 #endif 347 } 348 EXPORT_SYMBOL_GPL(tcp_twsk_destructor); 349 350 void tcp_twsk_purge(struct list_head *net_exit_list, int family) 351 { 352 bool purged_once = false; 353 struct net *net; 354 355 list_for_each_entry(net, net_exit_list, exit_list) { 356 if (net->ipv4.tcp_death_row.hashinfo->pernet) { 357 /* Even if tw_refcount == 1, we must clean up kernel reqsk */ 358 inet_twsk_purge(net->ipv4.tcp_death_row.hashinfo, family); 359 } else if (!purged_once) { 360 /* The last refcount is decremented in tcp_sk_exit_batch() */ 361 if (refcount_read(&net->ipv4.tcp_death_row.tw_refcount) == 1) 362 continue; 363 364 inet_twsk_purge(&tcp_hashinfo, family); 365 purged_once = true; 366 } 367 } 368 } 369 EXPORT_SYMBOL_GPL(tcp_twsk_purge); 370 371 /* Warning : This function is called without sk_listener being locked. 372 * Be sure to read socket fields once, as their value could change under us. 373 */ 374 void tcp_openreq_init_rwin(struct request_sock *req, 375 const struct sock *sk_listener, 376 const struct dst_entry *dst) 377 { 378 struct inet_request_sock *ireq = inet_rsk(req); 379 const struct tcp_sock *tp = tcp_sk(sk_listener); 380 int full_space = tcp_full_space(sk_listener); 381 u32 window_clamp; 382 __u8 rcv_wscale; 383 u32 rcv_wnd; 384 int mss; 385 386 mss = tcp_mss_clamp(tp, dst_metric_advmss(dst)); 387 window_clamp = READ_ONCE(tp->window_clamp); 388 /* Set this up on the first call only */ 389 req->rsk_window_clamp = window_clamp ? : dst_metric(dst, RTAX_WINDOW); 390 391 /* limit the window selection if the user enforce a smaller rx buffer */ 392 if (sk_listener->sk_userlocks & SOCK_RCVBUF_LOCK && 393 (req->rsk_window_clamp > full_space || req->rsk_window_clamp == 0)) 394 req->rsk_window_clamp = full_space; 395 396 rcv_wnd = tcp_rwnd_init_bpf((struct sock *)req); 397 if (rcv_wnd == 0) 398 rcv_wnd = dst_metric(dst, RTAX_INITRWND); 399 else if (full_space < rcv_wnd * mss) 400 full_space = rcv_wnd * mss; 401 402 /* tcp_full_space because it is guaranteed to be the first packet */ 403 tcp_select_initial_window(sk_listener, full_space, 404 mss - (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0), 405 &req->rsk_rcv_wnd, 406 &req->rsk_window_clamp, 407 ireq->wscale_ok, 408 &rcv_wscale, 409 rcv_wnd); 410 ireq->rcv_wscale = rcv_wscale; 411 } 412 EXPORT_SYMBOL(tcp_openreq_init_rwin); 413 414 static void tcp_ecn_openreq_child(struct tcp_sock *tp, 415 const struct request_sock *req) 416 { 417 tp->ecn_flags = inet_rsk(req)->ecn_ok ? TCP_ECN_OK : 0; 418 } 419 420 void tcp_ca_openreq_child(struct sock *sk, const struct dst_entry *dst) 421 { 422 struct inet_connection_sock *icsk = inet_csk(sk); 423 u32 ca_key = dst_metric(dst, RTAX_CC_ALGO); 424 bool ca_got_dst = false; 425 426 if (ca_key != TCP_CA_UNSPEC) { 427 const struct tcp_congestion_ops *ca; 428 429 rcu_read_lock(); 430 ca = tcp_ca_find_key(ca_key); 431 if (likely(ca && bpf_try_module_get(ca, ca->owner))) { 432 icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst); 433 icsk->icsk_ca_ops = ca; 434 ca_got_dst = true; 435 } 436 rcu_read_unlock(); 437 } 438 439 /* If no valid choice made yet, assign current system default ca. */ 440 if (!ca_got_dst && 441 (!icsk->icsk_ca_setsockopt || 442 !bpf_try_module_get(icsk->icsk_ca_ops, icsk->icsk_ca_ops->owner))) 443 tcp_assign_congestion_control(sk); 444 445 tcp_set_ca_state(sk, TCP_CA_Open); 446 } 447 EXPORT_SYMBOL_GPL(tcp_ca_openreq_child); 448 449 static void smc_check_reset_syn_req(struct tcp_sock *oldtp, 450 struct request_sock *req, 451 struct tcp_sock *newtp) 452 { 453 #if IS_ENABLED(CONFIG_SMC) 454 struct inet_request_sock *ireq; 455 456 if (static_branch_unlikely(&tcp_have_smc)) { 457 ireq = inet_rsk(req); 458 if (oldtp->syn_smc && !ireq->smc_ok) 459 newtp->syn_smc = 0; 460 } 461 #endif 462 } 463 464 /* This is not only more efficient than what we used to do, it eliminates 465 * a lot of code duplication between IPv4/IPv6 SYN recv processing. -DaveM 466 * 467 * Actually, we could lots of memory writes here. tp of listening 468 * socket contains all necessary default parameters. 469 */ 470 struct sock *tcp_create_openreq_child(const struct sock *sk, 471 struct request_sock *req, 472 struct sk_buff *skb) 473 { 474 struct sock *newsk = inet_csk_clone_lock(sk, req, GFP_ATOMIC); 475 const struct inet_request_sock *ireq = inet_rsk(req); 476 struct tcp_request_sock *treq = tcp_rsk(req); 477 struct inet_connection_sock *newicsk; 478 struct tcp_sock *oldtp, *newtp; 479 u32 seq; 480 481 if (!newsk) 482 return NULL; 483 484 newicsk = inet_csk(newsk); 485 newtp = tcp_sk(newsk); 486 oldtp = tcp_sk(sk); 487 488 smc_check_reset_syn_req(oldtp, req, newtp); 489 490 /* Now setup tcp_sock */ 491 newtp->pred_flags = 0; 492 493 seq = treq->rcv_isn + 1; 494 newtp->rcv_wup = seq; 495 WRITE_ONCE(newtp->copied_seq, seq); 496 WRITE_ONCE(newtp->rcv_nxt, seq); 497 newtp->segs_in = 1; 498 499 seq = treq->snt_isn + 1; 500 newtp->snd_sml = newtp->snd_una = seq; 501 WRITE_ONCE(newtp->snd_nxt, seq); 502 newtp->snd_up = seq; 503 504 INIT_LIST_HEAD(&newtp->tsq_node); 505 INIT_LIST_HEAD(&newtp->tsorted_sent_queue); 506 507 tcp_init_wl(newtp, treq->rcv_isn); 508 509 minmax_reset(&newtp->rtt_min, tcp_jiffies32, ~0U); 510 newicsk->icsk_ack.lrcvtime = tcp_jiffies32; 511 512 newtp->lsndtime = tcp_jiffies32; 513 newsk->sk_txhash = treq->txhash; 514 newtp->total_retrans = req->num_retrans; 515 516 tcp_init_xmit_timers(newsk); 517 WRITE_ONCE(newtp->write_seq, newtp->pushed_seq = treq->snt_isn + 1); 518 519 if (sock_flag(newsk, SOCK_KEEPOPEN)) 520 inet_csk_reset_keepalive_timer(newsk, 521 keepalive_time_when(newtp)); 522 523 newtp->rx_opt.tstamp_ok = ireq->tstamp_ok; 524 newtp->rx_opt.sack_ok = ireq->sack_ok; 525 newtp->window_clamp = req->rsk_window_clamp; 526 newtp->rcv_ssthresh = req->rsk_rcv_wnd; 527 newtp->rcv_wnd = req->rsk_rcv_wnd; 528 newtp->rx_opt.wscale_ok = ireq->wscale_ok; 529 if (newtp->rx_opt.wscale_ok) { 530 newtp->rx_opt.snd_wscale = ireq->snd_wscale; 531 newtp->rx_opt.rcv_wscale = ireq->rcv_wscale; 532 } else { 533 newtp->rx_opt.snd_wscale = newtp->rx_opt.rcv_wscale = 0; 534 newtp->window_clamp = min(newtp->window_clamp, 65535U); 535 } 536 newtp->snd_wnd = ntohs(tcp_hdr(skb)->window) << newtp->rx_opt.snd_wscale; 537 newtp->max_window = newtp->snd_wnd; 538 539 if (newtp->rx_opt.tstamp_ok) { 540 newtp->rx_opt.ts_recent = req->ts_recent; 541 newtp->rx_opt.ts_recent_stamp = ktime_get_seconds(); 542 newtp->tcp_header_len = sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED; 543 } else { 544 newtp->rx_opt.ts_recent_stamp = 0; 545 newtp->tcp_header_len = sizeof(struct tcphdr); 546 } 547 if (req->num_timeout) { 548 newtp->undo_marker = treq->snt_isn; 549 newtp->retrans_stamp = div_u64(treq->snt_synack, 550 USEC_PER_SEC / TCP_TS_HZ); 551 } 552 newtp->tsoffset = treq->ts_off; 553 #ifdef CONFIG_TCP_MD5SIG 554 newtp->md5sig_info = NULL; /*XXX*/ 555 if (treq->af_specific->req_md5_lookup(sk, req_to_sk(req))) 556 newtp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED; 557 #endif 558 if (skb->len >= TCP_MSS_DEFAULT + newtp->tcp_header_len) 559 newicsk->icsk_ack.last_seg_size = skb->len - newtp->tcp_header_len; 560 newtp->rx_opt.mss_clamp = req->mss; 561 tcp_ecn_openreq_child(newtp, req); 562 newtp->fastopen_req = NULL; 563 RCU_INIT_POINTER(newtp->fastopen_rsk, NULL); 564 565 newtp->bpf_chg_cc_inprogress = 0; 566 tcp_bpf_clone(sk, newsk); 567 568 __TCP_INC_STATS(sock_net(sk), TCP_MIB_PASSIVEOPENS); 569 570 return newsk; 571 } 572 EXPORT_SYMBOL(tcp_create_openreq_child); 573 574 /* 575 * Process an incoming packet for SYN_RECV sockets represented as a 576 * request_sock. Normally sk is the listener socket but for TFO it 577 * points to the child socket. 578 * 579 * XXX (TFO) - The current impl contains a special check for ack 580 * validation and inside tcp_v4_reqsk_send_ack(). Can we do better? 581 * 582 * We don't need to initialize tmp_opt.sack_ok as we don't use the results 583 */ 584 585 struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb, 586 struct request_sock *req, 587 bool fastopen, bool *req_stolen) 588 { 589 struct tcp_options_received tmp_opt; 590 struct sock *child; 591 const struct tcphdr *th = tcp_hdr(skb); 592 __be32 flg = tcp_flag_word(th) & (TCP_FLAG_RST|TCP_FLAG_SYN|TCP_FLAG_ACK); 593 bool paws_reject = false; 594 bool own_req; 595 596 tmp_opt.saw_tstamp = 0; 597 if (th->doff > (sizeof(struct tcphdr)>>2)) { 598 tcp_parse_options(sock_net(sk), skb, &tmp_opt, 0, NULL); 599 600 if (tmp_opt.saw_tstamp) { 601 tmp_opt.ts_recent = req->ts_recent; 602 if (tmp_opt.rcv_tsecr) 603 tmp_opt.rcv_tsecr -= tcp_rsk(req)->ts_off; 604 /* We do not store true stamp, but it is not required, 605 * it can be estimated (approximately) 606 * from another data. 607 */ 608 tmp_opt.ts_recent_stamp = ktime_get_seconds() - reqsk_timeout(req, TCP_RTO_MAX) / HZ; 609 paws_reject = tcp_paws_reject(&tmp_opt, th->rst); 610 } 611 } 612 613 /* Check for pure retransmitted SYN. */ 614 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn && 615 flg == TCP_FLAG_SYN && 616 !paws_reject) { 617 /* 618 * RFC793 draws (Incorrectly! It was fixed in RFC1122) 619 * this case on figure 6 and figure 8, but formal 620 * protocol description says NOTHING. 621 * To be more exact, it says that we should send ACK, 622 * because this segment (at least, if it has no data) 623 * is out of window. 624 * 625 * CONCLUSION: RFC793 (even with RFC1122) DOES NOT 626 * describe SYN-RECV state. All the description 627 * is wrong, we cannot believe to it and should 628 * rely only on common sense and implementation 629 * experience. 630 * 631 * Enforce "SYN-ACK" according to figure 8, figure 6 632 * of RFC793, fixed by RFC1122. 633 * 634 * Note that even if there is new data in the SYN packet 635 * they will be thrown away too. 636 * 637 * Reset timer after retransmitting SYNACK, similar to 638 * the idea of fast retransmit in recovery. 639 */ 640 if (!tcp_oow_rate_limited(sock_net(sk), skb, 641 LINUX_MIB_TCPACKSKIPPEDSYNRECV, 642 &tcp_rsk(req)->last_oow_ack_time) && 643 644 !inet_rtx_syn_ack(sk, req)) { 645 unsigned long expires = jiffies; 646 647 expires += reqsk_timeout(req, TCP_RTO_MAX); 648 if (!fastopen) 649 mod_timer_pending(&req->rsk_timer, expires); 650 else 651 req->rsk_timer.expires = expires; 652 } 653 return NULL; 654 } 655 656 /* Further reproduces section "SEGMENT ARRIVES" 657 for state SYN-RECEIVED of RFC793. 658 It is broken, however, it does not work only 659 when SYNs are crossed. 660 661 You would think that SYN crossing is impossible here, since 662 we should have a SYN_SENT socket (from connect()) on our end, 663 but this is not true if the crossed SYNs were sent to both 664 ends by a malicious third party. We must defend against this, 665 and to do that we first verify the ACK (as per RFC793, page 666 36) and reset if it is invalid. Is this a true full defense? 667 To convince ourselves, let us consider a way in which the ACK 668 test can still pass in this 'malicious crossed SYNs' case. 669 Malicious sender sends identical SYNs (and thus identical sequence 670 numbers) to both A and B: 671 672 A: gets SYN, seq=7 673 B: gets SYN, seq=7 674 675 By our good fortune, both A and B select the same initial 676 send sequence number of seven :-) 677 678 A: sends SYN|ACK, seq=7, ack_seq=8 679 B: sends SYN|ACK, seq=7, ack_seq=8 680 681 So we are now A eating this SYN|ACK, ACK test passes. So 682 does sequence test, SYN is truncated, and thus we consider 683 it a bare ACK. 684 685 If icsk->icsk_accept_queue.rskq_defer_accept, we silently drop this 686 bare ACK. Otherwise, we create an established connection. Both 687 ends (listening sockets) accept the new incoming connection and try 688 to talk to each other. 8-) 689 690 Note: This case is both harmless, and rare. Possibility is about the 691 same as us discovering intelligent life on another plant tomorrow. 692 693 But generally, we should (RFC lies!) to accept ACK 694 from SYNACK both here and in tcp_rcv_state_process(). 695 tcp_rcv_state_process() does not, hence, we do not too. 696 697 Note that the case is absolutely generic: 698 we cannot optimize anything here without 699 violating protocol. All the checks must be made 700 before attempt to create socket. 701 */ 702 703 /* RFC793 page 36: "If the connection is in any non-synchronized state ... 704 * and the incoming segment acknowledges something not yet 705 * sent (the segment carries an unacceptable ACK) ... 706 * a reset is sent." 707 * 708 * Invalid ACK: reset will be sent by listening socket. 709 * Note that the ACK validity check for a Fast Open socket is done 710 * elsewhere and is checked directly against the child socket rather 711 * than req because user data may have been sent out. 712 */ 713 if ((flg & TCP_FLAG_ACK) && !fastopen && 714 (TCP_SKB_CB(skb)->ack_seq != 715 tcp_rsk(req)->snt_isn + 1)) 716 return sk; 717 718 /* Also, it would be not so bad idea to check rcv_tsecr, which 719 * is essentially ACK extension and too early or too late values 720 * should cause reset in unsynchronized states. 721 */ 722 723 /* RFC793: "first check sequence number". */ 724 725 if (paws_reject || !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq, 726 tcp_rsk(req)->rcv_nxt, tcp_rsk(req)->rcv_nxt + req->rsk_rcv_wnd)) { 727 /* Out of window: send ACK and drop. */ 728 if (!(flg & TCP_FLAG_RST) && 729 !tcp_oow_rate_limited(sock_net(sk), skb, 730 LINUX_MIB_TCPACKSKIPPEDSYNRECV, 731 &tcp_rsk(req)->last_oow_ack_time)) 732 req->rsk_ops->send_ack(sk, skb, req); 733 if (paws_reject) 734 __NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED); 735 return NULL; 736 } 737 738 /* In sequence, PAWS is OK. */ 739 740 if (tmp_opt.saw_tstamp && !after(TCP_SKB_CB(skb)->seq, tcp_rsk(req)->rcv_nxt)) 741 req->ts_recent = tmp_opt.rcv_tsval; 742 743 if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn) { 744 /* Truncate SYN, it is out of window starting 745 at tcp_rsk(req)->rcv_isn + 1. */ 746 flg &= ~TCP_FLAG_SYN; 747 } 748 749 /* RFC793: "second check the RST bit" and 750 * "fourth, check the SYN bit" 751 */ 752 if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN)) { 753 __TCP_INC_STATS(sock_net(sk), TCP_MIB_ATTEMPTFAILS); 754 goto embryonic_reset; 755 } 756 757 /* ACK sequence verified above, just make sure ACK is 758 * set. If ACK not set, just silently drop the packet. 759 * 760 * XXX (TFO) - if we ever allow "data after SYN", the 761 * following check needs to be removed. 762 */ 763 if (!(flg & TCP_FLAG_ACK)) 764 return NULL; 765 766 /* For Fast Open no more processing is needed (sk is the 767 * child socket). 768 */ 769 if (fastopen) 770 return sk; 771 772 /* While TCP_DEFER_ACCEPT is active, drop bare ACK. */ 773 if (req->num_timeout < inet_csk(sk)->icsk_accept_queue.rskq_defer_accept && 774 TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) { 775 inet_rsk(req)->acked = 1; 776 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDEFERACCEPTDROP); 777 return NULL; 778 } 779 780 /* OK, ACK is valid, create big socket and 781 * feed this segment to it. It will repeat all 782 * the tests. THIS SEGMENT MUST MOVE SOCKET TO 783 * ESTABLISHED STATE. If it will be dropped after 784 * socket is created, wait for troubles. 785 */ 786 child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL, 787 req, &own_req); 788 if (!child) 789 goto listen_overflow; 790 791 if (own_req && rsk_drop_req(req)) { 792 reqsk_queue_removed(&inet_csk(req->rsk_listener)->icsk_accept_queue, req); 793 inet_csk_reqsk_queue_drop_and_put(req->rsk_listener, req); 794 return child; 795 } 796 797 sock_rps_save_rxhash(child, skb); 798 tcp_synack_rtt_meas(child, req); 799 *req_stolen = !own_req; 800 return inet_csk_complete_hashdance(sk, child, req, own_req); 801 802 listen_overflow: 803 if (sk != req->rsk_listener) 804 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMIGRATEREQFAILURE); 805 806 if (!READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_abort_on_overflow)) { 807 inet_rsk(req)->acked = 1; 808 return NULL; 809 } 810 811 embryonic_reset: 812 if (!(flg & TCP_FLAG_RST)) { 813 /* Received a bad SYN pkt - for TFO We try not to reset 814 * the local connection unless it's really necessary to 815 * avoid becoming vulnerable to outside attack aiming at 816 * resetting legit local connections. 817 */ 818 req->rsk_ops->send_reset(sk, skb); 819 } else if (fastopen) { /* received a valid RST pkt */ 820 reqsk_fastopen_remove(sk, req, true); 821 tcp_reset(sk, skb); 822 } 823 if (!fastopen) { 824 bool unlinked = inet_csk_reqsk_queue_drop(sk, req); 825 826 if (unlinked) 827 __NET_INC_STATS(sock_net(sk), LINUX_MIB_EMBRYONICRSTS); 828 *req_stolen = !unlinked; 829 } 830 return NULL; 831 } 832 EXPORT_SYMBOL(tcp_check_req); 833 834 /* 835 * Queue segment on the new socket if the new socket is active, 836 * otherwise we just shortcircuit this and continue with 837 * the new socket. 838 * 839 * For the vast majority of cases child->sk_state will be TCP_SYN_RECV 840 * when entering. But other states are possible due to a race condition 841 * where after __inet_lookup_established() fails but before the listener 842 * locked is obtained, other packets cause the same connection to 843 * be created. 844 */ 845 846 int tcp_child_process(struct sock *parent, struct sock *child, 847 struct sk_buff *skb) 848 __releases(&((child)->sk_lock.slock)) 849 { 850 int ret = 0; 851 int state = child->sk_state; 852 853 /* record sk_napi_id and sk_rx_queue_mapping of child. */ 854 sk_mark_napi_id_set(child, skb); 855 856 tcp_segs_in(tcp_sk(child), skb); 857 if (!sock_owned_by_user(child)) { 858 ret = tcp_rcv_state_process(child, skb); 859 /* Wakeup parent, send SIGIO */ 860 if (state == TCP_SYN_RECV && child->sk_state != state) 861 parent->sk_data_ready(parent); 862 } else { 863 /* Alas, it is possible again, because we do lookup 864 * in main socket hash table and lock on listening 865 * socket does not protect us more. 866 */ 867 __sk_add_backlog(child, skb); 868 } 869 870 bh_unlock_sock(child); 871 sock_put(child); 872 return ret; 873 } 874 EXPORT_SYMBOL(tcp_child_process); 875