1 // SPDX-License-Identifier: GPL-2.0 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 /* 23 * Changes: 24 * Pedro Roque : Fast Retransmit/Recovery. 25 * Two receive queues. 26 * Retransmit queue handled by TCP. 27 * Better retransmit timer handling. 28 * New congestion avoidance. 29 * Header prediction. 30 * Variable renaming. 31 * 32 * Eric : Fast Retransmit. 33 * Randy Scott : MSS option defines. 34 * Eric Schenk : Fixes to slow start algorithm. 35 * Eric Schenk : Yet another double ACK bug. 36 * Eric Schenk : Delayed ACK bug fixes. 37 * Eric Schenk : Floyd style fast retrans war avoidance. 38 * David S. Miller : Don't allow zero congestion window. 39 * Eric Schenk : Fix retransmitter so that it sends 40 * next packet on ack of previous packet. 41 * Andi Kleen : Moved open_request checking here 42 * and process RSTs for open_requests. 43 * Andi Kleen : Better prune_queue, and other fixes. 44 * Andrey Savochkin: Fix RTT measurements in the presence of 45 * timestamps. 46 * Andrey Savochkin: Check sequence numbers correctly when 47 * removing SACKs due to in sequence incoming 48 * data segments. 49 * Andi Kleen: Make sure we never ack data there is not 50 * enough room for. Also make this condition 51 * a fatal error if it might still happen. 52 * Andi Kleen: Add tcp_measure_rcv_mss to make 53 * connections with MSS<min(MTU,ann. MSS) 54 * work without delayed acks. 55 * Andi Kleen: Process packets with PSH set in the 56 * fast path. 57 * J Hadi Salim: ECN support 58 * Andrei Gurtov, 59 * Pasi Sarolahti, 60 * Panu Kuhlberg: Experimental audit of TCP (re)transmission 61 * engine. Lots of bugs are found. 62 * Pasi Sarolahti: F-RTO for dealing with spurious RTOs 63 */ 64 65 #define pr_fmt(fmt) "TCP: " fmt 66 67 #include <linux/mm.h> 68 #include <linux/slab.h> 69 #include <linux/module.h> 70 #include <linux/sysctl.h> 71 #include <linux/kernel.h> 72 #include <linux/prefetch.h> 73 #include <net/dst.h> 74 #include <net/tcp.h> 75 #include <net/inet_common.h> 76 #include <linux/ipsec.h> 77 #include <asm/unaligned.h> 78 #include <linux/errqueue.h> 79 #include <trace/events/tcp.h> 80 #include <linux/jump_label_ratelimit.h> 81 #include <net/busy_poll.h> 82 #include <net/mptcp.h> 83 84 int sysctl_tcp_max_orphans __read_mostly = NR_FILE; 85 86 #define FLAG_DATA 0x01 /* Incoming frame contained data. */ 87 #define FLAG_WIN_UPDATE 0x02 /* Incoming ACK was a window update. */ 88 #define FLAG_DATA_ACKED 0x04 /* This ACK acknowledged new data. */ 89 #define FLAG_RETRANS_DATA_ACKED 0x08 /* "" "" some of which was retransmitted. */ 90 #define FLAG_SYN_ACKED 0x10 /* This ACK acknowledged SYN. */ 91 #define FLAG_DATA_SACKED 0x20 /* New SACK. */ 92 #define FLAG_ECE 0x40 /* ECE in this ACK */ 93 #define FLAG_LOST_RETRANS 0x80 /* This ACK marks some retransmission lost */ 94 #define FLAG_SLOWPATH 0x100 /* Do not skip RFC checks for window update.*/ 95 #define FLAG_ORIG_SACK_ACKED 0x200 /* Never retransmitted data are (s)acked */ 96 #define FLAG_SND_UNA_ADVANCED 0x400 /* Snd_una was changed (!= FLAG_DATA_ACKED) */ 97 #define FLAG_DSACKING_ACK 0x800 /* SACK blocks contained D-SACK info */ 98 #define FLAG_SET_XMIT_TIMER 0x1000 /* Set TLP or RTO timer */ 99 #define FLAG_SACK_RENEGING 0x2000 /* snd_una advanced to a sacked seq */ 100 #define FLAG_UPDATE_TS_RECENT 0x4000 /* tcp_replace_ts_recent() */ 101 #define FLAG_NO_CHALLENGE_ACK 0x8000 /* do not call tcp_send_challenge_ack() */ 102 #define FLAG_ACK_MAYBE_DELAYED 0x10000 /* Likely a delayed ACK */ 103 #define FLAG_DSACK_TLP 0x20000 /* DSACK for tail loss probe */ 104 105 #define FLAG_ACKED (FLAG_DATA_ACKED|FLAG_SYN_ACKED) 106 #define FLAG_NOT_DUP (FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED) 107 #define FLAG_CA_ALERT (FLAG_DATA_SACKED|FLAG_ECE|FLAG_DSACKING_ACK) 108 #define FLAG_FORWARD_PROGRESS (FLAG_ACKED|FLAG_DATA_SACKED) 109 110 #define TCP_REMNANT (TCP_FLAG_FIN|TCP_FLAG_URG|TCP_FLAG_SYN|TCP_FLAG_PSH) 111 #define TCP_HP_BITS (~(TCP_RESERVED_BITS|TCP_FLAG_PSH)) 112 113 #define REXMIT_NONE 0 /* no loss recovery to do */ 114 #define REXMIT_LOST 1 /* retransmit packets marked lost */ 115 #define REXMIT_NEW 2 /* FRTO-style transmit of unsent/new packets */ 116 117 #if IS_ENABLED(CONFIG_TLS_DEVICE) 118 static DEFINE_STATIC_KEY_DEFERRED_FALSE(clean_acked_data_enabled, HZ); 119 120 void clean_acked_data_enable(struct inet_connection_sock *icsk, 121 void (*cad)(struct sock *sk, u32 ack_seq)) 122 { 123 icsk->icsk_clean_acked = cad; 124 static_branch_deferred_inc(&clean_acked_data_enabled); 125 } 126 EXPORT_SYMBOL_GPL(clean_acked_data_enable); 127 128 void clean_acked_data_disable(struct inet_connection_sock *icsk) 129 { 130 static_branch_slow_dec_deferred(&clean_acked_data_enabled); 131 icsk->icsk_clean_acked = NULL; 132 } 133 EXPORT_SYMBOL_GPL(clean_acked_data_disable); 134 135 void clean_acked_data_flush(void) 136 { 137 static_key_deferred_flush(&clean_acked_data_enabled); 138 } 139 EXPORT_SYMBOL_GPL(clean_acked_data_flush); 140 #endif 141 142 #ifdef CONFIG_CGROUP_BPF 143 static void bpf_skops_parse_hdr(struct sock *sk, struct sk_buff *skb) 144 { 145 bool unknown_opt = tcp_sk(sk)->rx_opt.saw_unknown && 146 BPF_SOCK_OPS_TEST_FLAG(tcp_sk(sk), 147 BPF_SOCK_OPS_PARSE_UNKNOWN_HDR_OPT_CB_FLAG); 148 bool parse_all_opt = BPF_SOCK_OPS_TEST_FLAG(tcp_sk(sk), 149 BPF_SOCK_OPS_PARSE_ALL_HDR_OPT_CB_FLAG); 150 struct bpf_sock_ops_kern sock_ops; 151 152 if (likely(!unknown_opt && !parse_all_opt)) 153 return; 154 155 /* The skb will be handled in the 156 * bpf_skops_established() or 157 * bpf_skops_write_hdr_opt(). 158 */ 159 switch (sk->sk_state) { 160 case TCP_SYN_RECV: 161 case TCP_SYN_SENT: 162 case TCP_LISTEN: 163 return; 164 } 165 166 sock_owned_by_me(sk); 167 168 memset(&sock_ops, 0, offsetof(struct bpf_sock_ops_kern, temp)); 169 sock_ops.op = BPF_SOCK_OPS_PARSE_HDR_OPT_CB; 170 sock_ops.is_fullsock = 1; 171 sock_ops.sk = sk; 172 bpf_skops_init_skb(&sock_ops, skb, tcp_hdrlen(skb)); 173 174 BPF_CGROUP_RUN_PROG_SOCK_OPS(&sock_ops); 175 } 176 177 static void bpf_skops_established(struct sock *sk, int bpf_op, 178 struct sk_buff *skb) 179 { 180 struct bpf_sock_ops_kern sock_ops; 181 182 sock_owned_by_me(sk); 183 184 memset(&sock_ops, 0, offsetof(struct bpf_sock_ops_kern, temp)); 185 sock_ops.op = bpf_op; 186 sock_ops.is_fullsock = 1; 187 sock_ops.sk = sk; 188 /* sk with TCP_REPAIR_ON does not have skb in tcp_finish_connect */ 189 if (skb) 190 bpf_skops_init_skb(&sock_ops, skb, tcp_hdrlen(skb)); 191 192 BPF_CGROUP_RUN_PROG_SOCK_OPS(&sock_ops); 193 } 194 #else 195 static void bpf_skops_parse_hdr(struct sock *sk, struct sk_buff *skb) 196 { 197 } 198 199 static void bpf_skops_established(struct sock *sk, int bpf_op, 200 struct sk_buff *skb) 201 { 202 } 203 #endif 204 205 static void tcp_gro_dev_warn(struct sock *sk, const struct sk_buff *skb, 206 unsigned int len) 207 { 208 static bool __once __read_mostly; 209 210 if (!__once) { 211 struct net_device *dev; 212 213 __once = true; 214 215 rcu_read_lock(); 216 dev = dev_get_by_index_rcu(sock_net(sk), skb->skb_iif); 217 if (!dev || len >= dev->mtu) 218 pr_warn("%s: Driver has suspect GRO implementation, TCP performance may be compromised.\n", 219 dev ? dev->name : "Unknown driver"); 220 rcu_read_unlock(); 221 } 222 } 223 224 /* Adapt the MSS value used to make delayed ack decision to the 225 * real world. 226 */ 227 static void tcp_measure_rcv_mss(struct sock *sk, const struct sk_buff *skb) 228 { 229 struct inet_connection_sock *icsk = inet_csk(sk); 230 const unsigned int lss = icsk->icsk_ack.last_seg_size; 231 unsigned int len; 232 233 icsk->icsk_ack.last_seg_size = 0; 234 235 /* skb->len may jitter because of SACKs, even if peer 236 * sends good full-sized frames. 237 */ 238 len = skb_shinfo(skb)->gso_size ? : skb->len; 239 if (len >= icsk->icsk_ack.rcv_mss) { 240 icsk->icsk_ack.rcv_mss = min_t(unsigned int, len, 241 tcp_sk(sk)->advmss); 242 /* Account for possibly-removed options */ 243 if (unlikely(len > icsk->icsk_ack.rcv_mss + 244 MAX_TCP_OPTION_SPACE)) 245 tcp_gro_dev_warn(sk, skb, len); 246 } else { 247 /* Otherwise, we make more careful check taking into account, 248 * that SACKs block is variable. 249 * 250 * "len" is invariant segment length, including TCP header. 251 */ 252 len += skb->data - skb_transport_header(skb); 253 if (len >= TCP_MSS_DEFAULT + sizeof(struct tcphdr) || 254 /* If PSH is not set, packet should be 255 * full sized, provided peer TCP is not badly broken. 256 * This observation (if it is correct 8)) allows 257 * to handle super-low mtu links fairly. 258 */ 259 (len >= TCP_MIN_MSS + sizeof(struct tcphdr) && 260 !(tcp_flag_word(tcp_hdr(skb)) & TCP_REMNANT))) { 261 /* Subtract also invariant (if peer is RFC compliant), 262 * tcp header plus fixed timestamp option length. 263 * Resulting "len" is MSS free of SACK jitter. 264 */ 265 len -= tcp_sk(sk)->tcp_header_len; 266 icsk->icsk_ack.last_seg_size = len; 267 if (len == lss) { 268 icsk->icsk_ack.rcv_mss = len; 269 return; 270 } 271 } 272 if (icsk->icsk_ack.pending & ICSK_ACK_PUSHED) 273 icsk->icsk_ack.pending |= ICSK_ACK_PUSHED2; 274 icsk->icsk_ack.pending |= ICSK_ACK_PUSHED; 275 } 276 } 277 278 static void tcp_incr_quickack(struct sock *sk, unsigned int max_quickacks) 279 { 280 struct inet_connection_sock *icsk = inet_csk(sk); 281 unsigned int quickacks = tcp_sk(sk)->rcv_wnd / (2 * icsk->icsk_ack.rcv_mss); 282 283 if (quickacks == 0) 284 quickacks = 2; 285 quickacks = min(quickacks, max_quickacks); 286 if (quickacks > icsk->icsk_ack.quick) 287 icsk->icsk_ack.quick = quickacks; 288 } 289 290 void tcp_enter_quickack_mode(struct sock *sk, unsigned int max_quickacks) 291 { 292 struct inet_connection_sock *icsk = inet_csk(sk); 293 294 tcp_incr_quickack(sk, max_quickacks); 295 inet_csk_exit_pingpong_mode(sk); 296 icsk->icsk_ack.ato = TCP_ATO_MIN; 297 } 298 EXPORT_SYMBOL(tcp_enter_quickack_mode); 299 300 /* Send ACKs quickly, if "quick" count is not exhausted 301 * and the session is not interactive. 302 */ 303 304 static bool tcp_in_quickack_mode(struct sock *sk) 305 { 306 const struct inet_connection_sock *icsk = inet_csk(sk); 307 const struct dst_entry *dst = __sk_dst_get(sk); 308 309 return (dst && dst_metric(dst, RTAX_QUICKACK)) || 310 (icsk->icsk_ack.quick && !inet_csk_in_pingpong_mode(sk)); 311 } 312 313 static void tcp_ecn_queue_cwr(struct tcp_sock *tp) 314 { 315 if (tp->ecn_flags & TCP_ECN_OK) 316 tp->ecn_flags |= TCP_ECN_QUEUE_CWR; 317 } 318 319 static void tcp_ecn_accept_cwr(struct sock *sk, const struct sk_buff *skb) 320 { 321 if (tcp_hdr(skb)->cwr) { 322 tcp_sk(sk)->ecn_flags &= ~TCP_ECN_DEMAND_CWR; 323 324 /* If the sender is telling us it has entered CWR, then its 325 * cwnd may be very low (even just 1 packet), so we should ACK 326 * immediately. 327 */ 328 if (TCP_SKB_CB(skb)->seq != TCP_SKB_CB(skb)->end_seq) 329 inet_csk(sk)->icsk_ack.pending |= ICSK_ACK_NOW; 330 } 331 } 332 333 static void tcp_ecn_withdraw_cwr(struct tcp_sock *tp) 334 { 335 tp->ecn_flags &= ~TCP_ECN_QUEUE_CWR; 336 } 337 338 static void __tcp_ecn_check_ce(struct sock *sk, const struct sk_buff *skb) 339 { 340 struct tcp_sock *tp = tcp_sk(sk); 341 342 switch (TCP_SKB_CB(skb)->ip_dsfield & INET_ECN_MASK) { 343 case INET_ECN_NOT_ECT: 344 /* Funny extension: if ECT is not set on a segment, 345 * and we already seen ECT on a previous segment, 346 * it is probably a retransmit. 347 */ 348 if (tp->ecn_flags & TCP_ECN_SEEN) 349 tcp_enter_quickack_mode(sk, 2); 350 break; 351 case INET_ECN_CE: 352 if (tcp_ca_needs_ecn(sk)) 353 tcp_ca_event(sk, CA_EVENT_ECN_IS_CE); 354 355 if (!(tp->ecn_flags & TCP_ECN_DEMAND_CWR)) { 356 /* Better not delay acks, sender can have a very low cwnd */ 357 tcp_enter_quickack_mode(sk, 2); 358 tp->ecn_flags |= TCP_ECN_DEMAND_CWR; 359 } 360 tp->ecn_flags |= TCP_ECN_SEEN; 361 break; 362 default: 363 if (tcp_ca_needs_ecn(sk)) 364 tcp_ca_event(sk, CA_EVENT_ECN_NO_CE); 365 tp->ecn_flags |= TCP_ECN_SEEN; 366 break; 367 } 368 } 369 370 static void tcp_ecn_check_ce(struct sock *sk, const struct sk_buff *skb) 371 { 372 if (tcp_sk(sk)->ecn_flags & TCP_ECN_OK) 373 __tcp_ecn_check_ce(sk, skb); 374 } 375 376 static void tcp_ecn_rcv_synack(struct tcp_sock *tp, const struct tcphdr *th) 377 { 378 if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || th->cwr)) 379 tp->ecn_flags &= ~TCP_ECN_OK; 380 } 381 382 static void tcp_ecn_rcv_syn(struct tcp_sock *tp, const struct tcphdr *th) 383 { 384 if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || !th->cwr)) 385 tp->ecn_flags &= ~TCP_ECN_OK; 386 } 387 388 static bool tcp_ecn_rcv_ecn_echo(const struct tcp_sock *tp, const struct tcphdr *th) 389 { 390 if (th->ece && !th->syn && (tp->ecn_flags & TCP_ECN_OK)) 391 return true; 392 return false; 393 } 394 395 /* Buffer size and advertised window tuning. 396 * 397 * 1. Tuning sk->sk_sndbuf, when connection enters established state. 398 */ 399 400 static void tcp_sndbuf_expand(struct sock *sk) 401 { 402 const struct tcp_sock *tp = tcp_sk(sk); 403 const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops; 404 int sndmem, per_mss; 405 u32 nr_segs; 406 407 /* Worst case is non GSO/TSO : each frame consumes one skb 408 * and skb->head is kmalloced using power of two area of memory 409 */ 410 per_mss = max_t(u32, tp->rx_opt.mss_clamp, tp->mss_cache) + 411 MAX_TCP_HEADER + 412 SKB_DATA_ALIGN(sizeof(struct skb_shared_info)); 413 414 per_mss = roundup_pow_of_two(per_mss) + 415 SKB_DATA_ALIGN(sizeof(struct sk_buff)); 416 417 nr_segs = max_t(u32, TCP_INIT_CWND, tcp_snd_cwnd(tp)); 418 nr_segs = max_t(u32, nr_segs, tp->reordering + 1); 419 420 /* Fast Recovery (RFC 5681 3.2) : 421 * Cubic needs 1.7 factor, rounded to 2 to include 422 * extra cushion (application might react slowly to EPOLLOUT) 423 */ 424 sndmem = ca_ops->sndbuf_expand ? ca_ops->sndbuf_expand(sk) : 2; 425 sndmem *= nr_segs * per_mss; 426 427 if (sk->sk_sndbuf < sndmem) 428 WRITE_ONCE(sk->sk_sndbuf, 429 min(sndmem, sock_net(sk)->ipv4.sysctl_tcp_wmem[2])); 430 } 431 432 /* 2. Tuning advertised window (window_clamp, rcv_ssthresh) 433 * 434 * All tcp_full_space() is split to two parts: "network" buffer, allocated 435 * forward and advertised in receiver window (tp->rcv_wnd) and 436 * "application buffer", required to isolate scheduling/application 437 * latencies from network. 438 * window_clamp is maximal advertised window. It can be less than 439 * tcp_full_space(), in this case tcp_full_space() - window_clamp 440 * is reserved for "application" buffer. The less window_clamp is 441 * the smoother our behaviour from viewpoint of network, but the lower 442 * throughput and the higher sensitivity of the connection to losses. 8) 443 * 444 * rcv_ssthresh is more strict window_clamp used at "slow start" 445 * phase to predict further behaviour of this connection. 446 * It is used for two goals: 447 * - to enforce header prediction at sender, even when application 448 * requires some significant "application buffer". It is check #1. 449 * - to prevent pruning of receive queue because of misprediction 450 * of receiver window. Check #2. 451 * 452 * The scheme does not work when sender sends good segments opening 453 * window and then starts to feed us spaghetti. But it should work 454 * in common situations. Otherwise, we have to rely on queue collapsing. 455 */ 456 457 /* Slow part of check#2. */ 458 static int __tcp_grow_window(const struct sock *sk, const struct sk_buff *skb, 459 unsigned int skbtruesize) 460 { 461 struct tcp_sock *tp = tcp_sk(sk); 462 /* Optimize this! */ 463 int truesize = tcp_win_from_space(sk, skbtruesize) >> 1; 464 int window = tcp_win_from_space(sk, sock_net(sk)->ipv4.sysctl_tcp_rmem[2]) >> 1; 465 466 while (tp->rcv_ssthresh <= window) { 467 if (truesize <= skb->len) 468 return 2 * inet_csk(sk)->icsk_ack.rcv_mss; 469 470 truesize >>= 1; 471 window >>= 1; 472 } 473 return 0; 474 } 475 476 /* Even if skb appears to have a bad len/truesize ratio, TCP coalescing 477 * can play nice with us, as sk_buff and skb->head might be either 478 * freed or shared with up to MAX_SKB_FRAGS segments. 479 * Only give a boost to drivers using page frag(s) to hold the frame(s), 480 * and if no payload was pulled in skb->head before reaching us. 481 */ 482 static u32 truesize_adjust(bool adjust, const struct sk_buff *skb) 483 { 484 u32 truesize = skb->truesize; 485 486 if (adjust && !skb_headlen(skb)) { 487 truesize -= SKB_TRUESIZE(skb_end_offset(skb)); 488 /* paranoid check, some drivers might be buggy */ 489 if (unlikely((int)truesize < (int)skb->len)) 490 truesize = skb->truesize; 491 } 492 return truesize; 493 } 494 495 static void tcp_grow_window(struct sock *sk, const struct sk_buff *skb, 496 bool adjust) 497 { 498 struct tcp_sock *tp = tcp_sk(sk); 499 int room; 500 501 room = min_t(int, tp->window_clamp, tcp_space(sk)) - tp->rcv_ssthresh; 502 503 if (room <= 0) 504 return; 505 506 /* Check #1 */ 507 if (!tcp_under_memory_pressure(sk)) { 508 unsigned int truesize = truesize_adjust(adjust, skb); 509 int incr; 510 511 /* Check #2. Increase window, if skb with such overhead 512 * will fit to rcvbuf in future. 513 */ 514 if (tcp_win_from_space(sk, truesize) <= skb->len) 515 incr = 2 * tp->advmss; 516 else 517 incr = __tcp_grow_window(sk, skb, truesize); 518 519 if (incr) { 520 incr = max_t(int, incr, 2 * skb->len); 521 tp->rcv_ssthresh += min(room, incr); 522 inet_csk(sk)->icsk_ack.quick |= 1; 523 } 524 } else { 525 /* Under pressure: 526 * Adjust rcv_ssthresh according to reserved mem 527 */ 528 tcp_adjust_rcv_ssthresh(sk); 529 } 530 } 531 532 /* 3. Try to fixup all. It is made immediately after connection enters 533 * established state. 534 */ 535 static void tcp_init_buffer_space(struct sock *sk) 536 { 537 int tcp_app_win = sock_net(sk)->ipv4.sysctl_tcp_app_win; 538 struct tcp_sock *tp = tcp_sk(sk); 539 int maxwin; 540 541 if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK)) 542 tcp_sndbuf_expand(sk); 543 544 tcp_mstamp_refresh(tp); 545 tp->rcvq_space.time = tp->tcp_mstamp; 546 tp->rcvq_space.seq = tp->copied_seq; 547 548 maxwin = tcp_full_space(sk); 549 550 if (tp->window_clamp >= maxwin) { 551 tp->window_clamp = maxwin; 552 553 if (tcp_app_win && maxwin > 4 * tp->advmss) 554 tp->window_clamp = max(maxwin - 555 (maxwin >> tcp_app_win), 556 4 * tp->advmss); 557 } 558 559 /* Force reservation of one segment. */ 560 if (tcp_app_win && 561 tp->window_clamp > 2 * tp->advmss && 562 tp->window_clamp + tp->advmss > maxwin) 563 tp->window_clamp = max(2 * tp->advmss, maxwin - tp->advmss); 564 565 tp->rcv_ssthresh = min(tp->rcv_ssthresh, tp->window_clamp); 566 tp->snd_cwnd_stamp = tcp_jiffies32; 567 tp->rcvq_space.space = min3(tp->rcv_ssthresh, tp->rcv_wnd, 568 (u32)TCP_INIT_CWND * tp->advmss); 569 } 570 571 /* 4. Recalculate window clamp after socket hit its memory bounds. */ 572 static void tcp_clamp_window(struct sock *sk) 573 { 574 struct tcp_sock *tp = tcp_sk(sk); 575 struct inet_connection_sock *icsk = inet_csk(sk); 576 struct net *net = sock_net(sk); 577 578 icsk->icsk_ack.quick = 0; 579 580 if (sk->sk_rcvbuf < net->ipv4.sysctl_tcp_rmem[2] && 581 !(sk->sk_userlocks & SOCK_RCVBUF_LOCK) && 582 !tcp_under_memory_pressure(sk) && 583 sk_memory_allocated(sk) < sk_prot_mem_limits(sk, 0)) { 584 WRITE_ONCE(sk->sk_rcvbuf, 585 min(atomic_read(&sk->sk_rmem_alloc), 586 net->ipv4.sysctl_tcp_rmem[2])); 587 } 588 if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf) 589 tp->rcv_ssthresh = min(tp->window_clamp, 2U * tp->advmss); 590 } 591 592 /* Initialize RCV_MSS value. 593 * RCV_MSS is an our guess about MSS used by the peer. 594 * We haven't any direct information about the MSS. 595 * It's better to underestimate the RCV_MSS rather than overestimate. 596 * Overestimations make us ACKing less frequently than needed. 597 * Underestimations are more easy to detect and fix by tcp_measure_rcv_mss(). 598 */ 599 void tcp_initialize_rcv_mss(struct sock *sk) 600 { 601 const struct tcp_sock *tp = tcp_sk(sk); 602 unsigned int hint = min_t(unsigned int, tp->advmss, tp->mss_cache); 603 604 hint = min(hint, tp->rcv_wnd / 2); 605 hint = min(hint, TCP_MSS_DEFAULT); 606 hint = max(hint, TCP_MIN_MSS); 607 608 inet_csk(sk)->icsk_ack.rcv_mss = hint; 609 } 610 EXPORT_SYMBOL(tcp_initialize_rcv_mss); 611 612 /* Receiver "autotuning" code. 613 * 614 * The algorithm for RTT estimation w/o timestamps is based on 615 * Dynamic Right-Sizing (DRS) by Wu Feng and Mike Fisk of LANL. 616 * <https://public.lanl.gov/radiant/pubs.html#DRS> 617 * 618 * More detail on this code can be found at 619 * <http://staff.psc.edu/jheffner/>, 620 * though this reference is out of date. A new paper 621 * is pending. 622 */ 623 static void tcp_rcv_rtt_update(struct tcp_sock *tp, u32 sample, int win_dep) 624 { 625 u32 new_sample = tp->rcv_rtt_est.rtt_us; 626 long m = sample; 627 628 if (new_sample != 0) { 629 /* If we sample in larger samples in the non-timestamp 630 * case, we could grossly overestimate the RTT especially 631 * with chatty applications or bulk transfer apps which 632 * are stalled on filesystem I/O. 633 * 634 * Also, since we are only going for a minimum in the 635 * non-timestamp case, we do not smooth things out 636 * else with timestamps disabled convergence takes too 637 * long. 638 */ 639 if (!win_dep) { 640 m -= (new_sample >> 3); 641 new_sample += m; 642 } else { 643 m <<= 3; 644 if (m < new_sample) 645 new_sample = m; 646 } 647 } else { 648 /* No previous measure. */ 649 new_sample = m << 3; 650 } 651 652 tp->rcv_rtt_est.rtt_us = new_sample; 653 } 654 655 static inline void tcp_rcv_rtt_measure(struct tcp_sock *tp) 656 { 657 u32 delta_us; 658 659 if (tp->rcv_rtt_est.time == 0) 660 goto new_measure; 661 if (before(tp->rcv_nxt, tp->rcv_rtt_est.seq)) 662 return; 663 delta_us = tcp_stamp_us_delta(tp->tcp_mstamp, tp->rcv_rtt_est.time); 664 if (!delta_us) 665 delta_us = 1; 666 tcp_rcv_rtt_update(tp, delta_us, 1); 667 668 new_measure: 669 tp->rcv_rtt_est.seq = tp->rcv_nxt + tp->rcv_wnd; 670 tp->rcv_rtt_est.time = tp->tcp_mstamp; 671 } 672 673 static inline void tcp_rcv_rtt_measure_ts(struct sock *sk, 674 const struct sk_buff *skb) 675 { 676 struct tcp_sock *tp = tcp_sk(sk); 677 678 if (tp->rx_opt.rcv_tsecr == tp->rcv_rtt_last_tsecr) 679 return; 680 tp->rcv_rtt_last_tsecr = tp->rx_opt.rcv_tsecr; 681 682 if (TCP_SKB_CB(skb)->end_seq - 683 TCP_SKB_CB(skb)->seq >= inet_csk(sk)->icsk_ack.rcv_mss) { 684 u32 delta = tcp_time_stamp(tp) - tp->rx_opt.rcv_tsecr; 685 u32 delta_us; 686 687 if (likely(delta < INT_MAX / (USEC_PER_SEC / TCP_TS_HZ))) { 688 if (!delta) 689 delta = 1; 690 delta_us = delta * (USEC_PER_SEC / TCP_TS_HZ); 691 tcp_rcv_rtt_update(tp, delta_us, 0); 692 } 693 } 694 } 695 696 /* 697 * This function should be called every time data is copied to user space. 698 * It calculates the appropriate TCP receive buffer space. 699 */ 700 void tcp_rcv_space_adjust(struct sock *sk) 701 { 702 struct tcp_sock *tp = tcp_sk(sk); 703 u32 copied; 704 int time; 705 706 trace_tcp_rcv_space_adjust(sk); 707 708 tcp_mstamp_refresh(tp); 709 time = tcp_stamp_us_delta(tp->tcp_mstamp, tp->rcvq_space.time); 710 if (time < (tp->rcv_rtt_est.rtt_us >> 3) || tp->rcv_rtt_est.rtt_us == 0) 711 return; 712 713 /* Number of bytes copied to user in last RTT */ 714 copied = tp->copied_seq - tp->rcvq_space.seq; 715 if (copied <= tp->rcvq_space.space) 716 goto new_measure; 717 718 /* A bit of theory : 719 * copied = bytes received in previous RTT, our base window 720 * To cope with packet losses, we need a 2x factor 721 * To cope with slow start, and sender growing its cwin by 100 % 722 * every RTT, we need a 4x factor, because the ACK we are sending 723 * now is for the next RTT, not the current one : 724 * <prev RTT . ><current RTT .. ><next RTT .... > 725 */ 726 727 if (sock_net(sk)->ipv4.sysctl_tcp_moderate_rcvbuf && 728 !(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) { 729 int rcvmem, rcvbuf; 730 u64 rcvwin, grow; 731 732 /* minimal window to cope with packet losses, assuming 733 * steady state. Add some cushion because of small variations. 734 */ 735 rcvwin = ((u64)copied << 1) + 16 * tp->advmss; 736 737 /* Accommodate for sender rate increase (eg. slow start) */ 738 grow = rcvwin * (copied - tp->rcvq_space.space); 739 do_div(grow, tp->rcvq_space.space); 740 rcvwin += (grow << 1); 741 742 rcvmem = SKB_TRUESIZE(tp->advmss + MAX_TCP_HEADER); 743 while (tcp_win_from_space(sk, rcvmem) < tp->advmss) 744 rcvmem += 128; 745 746 do_div(rcvwin, tp->advmss); 747 rcvbuf = min_t(u64, rcvwin * rcvmem, 748 sock_net(sk)->ipv4.sysctl_tcp_rmem[2]); 749 if (rcvbuf > sk->sk_rcvbuf) { 750 WRITE_ONCE(sk->sk_rcvbuf, rcvbuf); 751 752 /* Make the window clamp follow along. */ 753 tp->window_clamp = tcp_win_from_space(sk, rcvbuf); 754 } 755 } 756 tp->rcvq_space.space = copied; 757 758 new_measure: 759 tp->rcvq_space.seq = tp->copied_seq; 760 tp->rcvq_space.time = tp->tcp_mstamp; 761 } 762 763 /* There is something which you must keep in mind when you analyze the 764 * behavior of the tp->ato delayed ack timeout interval. When a 765 * connection starts up, we want to ack as quickly as possible. The 766 * problem is that "good" TCP's do slow start at the beginning of data 767 * transmission. The means that until we send the first few ACK's the 768 * sender will sit on his end and only queue most of his data, because 769 * he can only send snd_cwnd unacked packets at any given time. For 770 * each ACK we send, he increments snd_cwnd and transmits more of his 771 * queue. -DaveM 772 */ 773 static void tcp_event_data_recv(struct sock *sk, struct sk_buff *skb) 774 { 775 struct tcp_sock *tp = tcp_sk(sk); 776 struct inet_connection_sock *icsk = inet_csk(sk); 777 u32 now; 778 779 inet_csk_schedule_ack(sk); 780 781 tcp_measure_rcv_mss(sk, skb); 782 783 tcp_rcv_rtt_measure(tp); 784 785 now = tcp_jiffies32; 786 787 if (!icsk->icsk_ack.ato) { 788 /* The _first_ data packet received, initialize 789 * delayed ACK engine. 790 */ 791 tcp_incr_quickack(sk, TCP_MAX_QUICKACKS); 792 icsk->icsk_ack.ato = TCP_ATO_MIN; 793 } else { 794 int m = now - icsk->icsk_ack.lrcvtime; 795 796 if (m <= TCP_ATO_MIN / 2) { 797 /* The fastest case is the first. */ 798 icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + TCP_ATO_MIN / 2; 799 } else if (m < icsk->icsk_ack.ato) { 800 icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + m; 801 if (icsk->icsk_ack.ato > icsk->icsk_rto) 802 icsk->icsk_ack.ato = icsk->icsk_rto; 803 } else if (m > icsk->icsk_rto) { 804 /* Too long gap. Apparently sender failed to 805 * restart window, so that we send ACKs quickly. 806 */ 807 tcp_incr_quickack(sk, TCP_MAX_QUICKACKS); 808 sk_mem_reclaim(sk); 809 } 810 } 811 icsk->icsk_ack.lrcvtime = now; 812 813 tcp_ecn_check_ce(sk, skb); 814 815 if (skb->len >= 128) 816 tcp_grow_window(sk, skb, true); 817 } 818 819 /* Called to compute a smoothed rtt estimate. The data fed to this 820 * routine either comes from timestamps, or from segments that were 821 * known _not_ to have been retransmitted [see Karn/Partridge 822 * Proceedings SIGCOMM 87]. The algorithm is from the SIGCOMM 88 823 * piece by Van Jacobson. 824 * NOTE: the next three routines used to be one big routine. 825 * To save cycles in the RFC 1323 implementation it was better to break 826 * it up into three procedures. -- erics 827 */ 828 static void tcp_rtt_estimator(struct sock *sk, long mrtt_us) 829 { 830 struct tcp_sock *tp = tcp_sk(sk); 831 long m = mrtt_us; /* RTT */ 832 u32 srtt = tp->srtt_us; 833 834 /* The following amusing code comes from Jacobson's 835 * article in SIGCOMM '88. Note that rtt and mdev 836 * are scaled versions of rtt and mean deviation. 837 * This is designed to be as fast as possible 838 * m stands for "measurement". 839 * 840 * On a 1990 paper the rto value is changed to: 841 * RTO = rtt + 4 * mdev 842 * 843 * Funny. This algorithm seems to be very broken. 844 * These formulae increase RTO, when it should be decreased, increase 845 * too slowly, when it should be increased quickly, decrease too quickly 846 * etc. I guess in BSD RTO takes ONE value, so that it is absolutely 847 * does not matter how to _calculate_ it. Seems, it was trap 848 * that VJ failed to avoid. 8) 849 */ 850 if (srtt != 0) { 851 m -= (srtt >> 3); /* m is now error in rtt est */ 852 srtt += m; /* rtt = 7/8 rtt + 1/8 new */ 853 if (m < 0) { 854 m = -m; /* m is now abs(error) */ 855 m -= (tp->mdev_us >> 2); /* similar update on mdev */ 856 /* This is similar to one of Eifel findings. 857 * Eifel blocks mdev updates when rtt decreases. 858 * This solution is a bit different: we use finer gain 859 * for mdev in this case (alpha*beta). 860 * Like Eifel it also prevents growth of rto, 861 * but also it limits too fast rto decreases, 862 * happening in pure Eifel. 863 */ 864 if (m > 0) 865 m >>= 3; 866 } else { 867 m -= (tp->mdev_us >> 2); /* similar update on mdev */ 868 } 869 tp->mdev_us += m; /* mdev = 3/4 mdev + 1/4 new */ 870 if (tp->mdev_us > tp->mdev_max_us) { 871 tp->mdev_max_us = tp->mdev_us; 872 if (tp->mdev_max_us > tp->rttvar_us) 873 tp->rttvar_us = tp->mdev_max_us; 874 } 875 if (after(tp->snd_una, tp->rtt_seq)) { 876 if (tp->mdev_max_us < tp->rttvar_us) 877 tp->rttvar_us -= (tp->rttvar_us - tp->mdev_max_us) >> 2; 878 tp->rtt_seq = tp->snd_nxt; 879 tp->mdev_max_us = tcp_rto_min_us(sk); 880 881 tcp_bpf_rtt(sk); 882 } 883 } else { 884 /* no previous measure. */ 885 srtt = m << 3; /* take the measured time to be rtt */ 886 tp->mdev_us = m << 1; /* make sure rto = 3*rtt */ 887 tp->rttvar_us = max(tp->mdev_us, tcp_rto_min_us(sk)); 888 tp->mdev_max_us = tp->rttvar_us; 889 tp->rtt_seq = tp->snd_nxt; 890 891 tcp_bpf_rtt(sk); 892 } 893 tp->srtt_us = max(1U, srtt); 894 } 895 896 static void tcp_update_pacing_rate(struct sock *sk) 897 { 898 const struct tcp_sock *tp = tcp_sk(sk); 899 u64 rate; 900 901 /* set sk_pacing_rate to 200 % of current rate (mss * cwnd / srtt) */ 902 rate = (u64)tp->mss_cache * ((USEC_PER_SEC / 100) << 3); 903 904 /* current rate is (cwnd * mss) / srtt 905 * In Slow Start [1], set sk_pacing_rate to 200 % the current rate. 906 * In Congestion Avoidance phase, set it to 120 % the current rate. 907 * 908 * [1] : Normal Slow Start condition is (tp->snd_cwnd < tp->snd_ssthresh) 909 * If snd_cwnd >= (tp->snd_ssthresh / 2), we are approaching 910 * end of slow start and should slow down. 911 */ 912 if (tcp_snd_cwnd(tp) < tp->snd_ssthresh / 2) 913 rate *= sock_net(sk)->ipv4.sysctl_tcp_pacing_ss_ratio; 914 else 915 rate *= sock_net(sk)->ipv4.sysctl_tcp_pacing_ca_ratio; 916 917 rate *= max(tcp_snd_cwnd(tp), tp->packets_out); 918 919 if (likely(tp->srtt_us)) 920 do_div(rate, tp->srtt_us); 921 922 /* WRITE_ONCE() is needed because sch_fq fetches sk_pacing_rate 923 * without any lock. We want to make sure compiler wont store 924 * intermediate values in this location. 925 */ 926 WRITE_ONCE(sk->sk_pacing_rate, min_t(u64, rate, 927 sk->sk_max_pacing_rate)); 928 } 929 930 /* Calculate rto without backoff. This is the second half of Van Jacobson's 931 * routine referred to above. 932 */ 933 static void tcp_set_rto(struct sock *sk) 934 { 935 const struct tcp_sock *tp = tcp_sk(sk); 936 /* Old crap is replaced with new one. 8) 937 * 938 * More seriously: 939 * 1. If rtt variance happened to be less 50msec, it is hallucination. 940 * It cannot be less due to utterly erratic ACK generation made 941 * at least by solaris and freebsd. "Erratic ACKs" has _nothing_ 942 * to do with delayed acks, because at cwnd>2 true delack timeout 943 * is invisible. Actually, Linux-2.4 also generates erratic 944 * ACKs in some circumstances. 945 */ 946 inet_csk(sk)->icsk_rto = __tcp_set_rto(tp); 947 948 /* 2. Fixups made earlier cannot be right. 949 * If we do not estimate RTO correctly without them, 950 * all the algo is pure shit and should be replaced 951 * with correct one. It is exactly, which we pretend to do. 952 */ 953 954 /* NOTE: clamping at TCP_RTO_MIN is not required, current algo 955 * guarantees that rto is higher. 956 */ 957 tcp_bound_rto(sk); 958 } 959 960 __u32 tcp_init_cwnd(const struct tcp_sock *tp, const struct dst_entry *dst) 961 { 962 __u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0); 963 964 if (!cwnd) 965 cwnd = TCP_INIT_CWND; 966 return min_t(__u32, cwnd, tp->snd_cwnd_clamp); 967 } 968 969 struct tcp_sacktag_state { 970 /* Timestamps for earliest and latest never-retransmitted segment 971 * that was SACKed. RTO needs the earliest RTT to stay conservative, 972 * but congestion control should still get an accurate delay signal. 973 */ 974 u64 first_sackt; 975 u64 last_sackt; 976 u32 reord; 977 u32 sack_delivered; 978 int flag; 979 unsigned int mss_now; 980 struct rate_sample *rate; 981 }; 982 983 /* Take a notice that peer is sending D-SACKs. Skip update of data delivery 984 * and spurious retransmission information if this DSACK is unlikely caused by 985 * sender's action: 986 * - DSACKed sequence range is larger than maximum receiver's window. 987 * - Total no. of DSACKed segments exceed the total no. of retransmitted segs. 988 */ 989 static u32 tcp_dsack_seen(struct tcp_sock *tp, u32 start_seq, 990 u32 end_seq, struct tcp_sacktag_state *state) 991 { 992 u32 seq_len, dup_segs = 1; 993 994 if (!before(start_seq, end_seq)) 995 return 0; 996 997 seq_len = end_seq - start_seq; 998 /* Dubious DSACK: DSACKed range greater than maximum advertised rwnd */ 999 if (seq_len > tp->max_window) 1000 return 0; 1001 if (seq_len > tp->mss_cache) 1002 dup_segs = DIV_ROUND_UP(seq_len, tp->mss_cache); 1003 else if (tp->tlp_high_seq && tp->tlp_high_seq == end_seq) 1004 state->flag |= FLAG_DSACK_TLP; 1005 1006 tp->dsack_dups += dup_segs; 1007 /* Skip the DSACK if dup segs weren't retransmitted by sender */ 1008 if (tp->dsack_dups > tp->total_retrans) 1009 return 0; 1010 1011 tp->rx_opt.sack_ok |= TCP_DSACK_SEEN; 1012 /* We increase the RACK ordering window in rounds where we receive 1013 * DSACKs that may have been due to reordering causing RACK to trigger 1014 * a spurious fast recovery. Thus RACK ignores DSACKs that happen 1015 * without having seen reordering, or that match TLP probes (TLP 1016 * is timer-driven, not triggered by RACK). 1017 */ 1018 if (tp->reord_seen && !(state->flag & FLAG_DSACK_TLP)) 1019 tp->rack.dsack_seen = 1; 1020 1021 state->flag |= FLAG_DSACKING_ACK; 1022 /* A spurious retransmission is delivered */ 1023 state->sack_delivered += dup_segs; 1024 1025 return dup_segs; 1026 } 1027 1028 /* It's reordering when higher sequence was delivered (i.e. sacked) before 1029 * some lower never-retransmitted sequence ("low_seq"). The maximum reordering 1030 * distance is approximated in full-mss packet distance ("reordering"). 1031 */ 1032 static void tcp_check_sack_reordering(struct sock *sk, const u32 low_seq, 1033 const int ts) 1034 { 1035 struct tcp_sock *tp = tcp_sk(sk); 1036 const u32 mss = tp->mss_cache; 1037 u32 fack, metric; 1038 1039 fack = tcp_highest_sack_seq(tp); 1040 if (!before(low_seq, fack)) 1041 return; 1042 1043 metric = fack - low_seq; 1044 if ((metric > tp->reordering * mss) && mss) { 1045 #if FASTRETRANS_DEBUG > 1 1046 pr_debug("Disorder%d %d %u f%u s%u rr%d\n", 1047 tp->rx_opt.sack_ok, inet_csk(sk)->icsk_ca_state, 1048 tp->reordering, 1049 0, 1050 tp->sacked_out, 1051 tp->undo_marker ? tp->undo_retrans : 0); 1052 #endif 1053 tp->reordering = min_t(u32, (metric + mss - 1) / mss, 1054 READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_max_reordering)); 1055 } 1056 1057 /* This exciting event is worth to be remembered. 8) */ 1058 tp->reord_seen++; 1059 NET_INC_STATS(sock_net(sk), 1060 ts ? LINUX_MIB_TCPTSREORDER : LINUX_MIB_TCPSACKREORDER); 1061 } 1062 1063 /* This must be called before lost_out or retrans_out are updated 1064 * on a new loss, because we want to know if all skbs previously 1065 * known to be lost have already been retransmitted, indicating 1066 * that this newly lost skb is our next skb to retransmit. 1067 */ 1068 static void tcp_verify_retransmit_hint(struct tcp_sock *tp, struct sk_buff *skb) 1069 { 1070 if ((!tp->retransmit_skb_hint && tp->retrans_out >= tp->lost_out) || 1071 (tp->retransmit_skb_hint && 1072 before(TCP_SKB_CB(skb)->seq, 1073 TCP_SKB_CB(tp->retransmit_skb_hint)->seq))) 1074 tp->retransmit_skb_hint = skb; 1075 } 1076 1077 /* Sum the number of packets on the wire we have marked as lost, and 1078 * notify the congestion control module that the given skb was marked lost. 1079 */ 1080 static void tcp_notify_skb_loss_event(struct tcp_sock *tp, const struct sk_buff *skb) 1081 { 1082 tp->lost += tcp_skb_pcount(skb); 1083 } 1084 1085 void tcp_mark_skb_lost(struct sock *sk, struct sk_buff *skb) 1086 { 1087 __u8 sacked = TCP_SKB_CB(skb)->sacked; 1088 struct tcp_sock *tp = tcp_sk(sk); 1089 1090 if (sacked & TCPCB_SACKED_ACKED) 1091 return; 1092 1093 tcp_verify_retransmit_hint(tp, skb); 1094 if (sacked & TCPCB_LOST) { 1095 if (sacked & TCPCB_SACKED_RETRANS) { 1096 /* Account for retransmits that are lost again */ 1097 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS; 1098 tp->retrans_out -= tcp_skb_pcount(skb); 1099 NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPLOSTRETRANSMIT, 1100 tcp_skb_pcount(skb)); 1101 tcp_notify_skb_loss_event(tp, skb); 1102 } 1103 } else { 1104 tp->lost_out += tcp_skb_pcount(skb); 1105 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST; 1106 tcp_notify_skb_loss_event(tp, skb); 1107 } 1108 } 1109 1110 /* Updates the delivered and delivered_ce counts */ 1111 static void tcp_count_delivered(struct tcp_sock *tp, u32 delivered, 1112 bool ece_ack) 1113 { 1114 tp->delivered += delivered; 1115 if (ece_ack) 1116 tp->delivered_ce += delivered; 1117 } 1118 1119 /* This procedure tags the retransmission queue when SACKs arrive. 1120 * 1121 * We have three tag bits: SACKED(S), RETRANS(R) and LOST(L). 1122 * Packets in queue with these bits set are counted in variables 1123 * sacked_out, retrans_out and lost_out, correspondingly. 1124 * 1125 * Valid combinations are: 1126 * Tag InFlight Description 1127 * 0 1 - orig segment is in flight. 1128 * S 0 - nothing flies, orig reached receiver. 1129 * L 0 - nothing flies, orig lost by net. 1130 * R 2 - both orig and retransmit are in flight. 1131 * L|R 1 - orig is lost, retransmit is in flight. 1132 * S|R 1 - orig reached receiver, retrans is still in flight. 1133 * (L|S|R is logically valid, it could occur when L|R is sacked, 1134 * but it is equivalent to plain S and code short-curcuits it to S. 1135 * L|S is logically invalid, it would mean -1 packet in flight 8)) 1136 * 1137 * These 6 states form finite state machine, controlled by the following events: 1138 * 1. New ACK (+SACK) arrives. (tcp_sacktag_write_queue()) 1139 * 2. Retransmission. (tcp_retransmit_skb(), tcp_xmit_retransmit_queue()) 1140 * 3. Loss detection event of two flavors: 1141 * A. Scoreboard estimator decided the packet is lost. 1142 * A'. Reno "three dupacks" marks head of queue lost. 1143 * B. SACK arrives sacking SND.NXT at the moment, when the 1144 * segment was retransmitted. 1145 * 4. D-SACK added new rule: D-SACK changes any tag to S. 1146 * 1147 * It is pleasant to note, that state diagram turns out to be commutative, 1148 * so that we are allowed not to be bothered by order of our actions, 1149 * when multiple events arrive simultaneously. (see the function below). 1150 * 1151 * Reordering detection. 1152 * -------------------- 1153 * Reordering metric is maximal distance, which a packet can be displaced 1154 * in packet stream. With SACKs we can estimate it: 1155 * 1156 * 1. SACK fills old hole and the corresponding segment was not 1157 * ever retransmitted -> reordering. Alas, we cannot use it 1158 * when segment was retransmitted. 1159 * 2. The last flaw is solved with D-SACK. D-SACK arrives 1160 * for retransmitted and already SACKed segment -> reordering.. 1161 * Both of these heuristics are not used in Loss state, when we cannot 1162 * account for retransmits accurately. 1163 * 1164 * SACK block validation. 1165 * ---------------------- 1166 * 1167 * SACK block range validation checks that the received SACK block fits to 1168 * the expected sequence limits, i.e., it is between SND.UNA and SND.NXT. 1169 * Note that SND.UNA is not included to the range though being valid because 1170 * it means that the receiver is rather inconsistent with itself reporting 1171 * SACK reneging when it should advance SND.UNA. Such SACK block this is 1172 * perfectly valid, however, in light of RFC2018 which explicitly states 1173 * that "SACK block MUST reflect the newest segment. Even if the newest 1174 * segment is going to be discarded ...", not that it looks very clever 1175 * in case of head skb. Due to potentional receiver driven attacks, we 1176 * choose to avoid immediate execution of a walk in write queue due to 1177 * reneging and defer head skb's loss recovery to standard loss recovery 1178 * procedure that will eventually trigger (nothing forbids us doing this). 1179 * 1180 * Implements also blockage to start_seq wrap-around. Problem lies in the 1181 * fact that though start_seq (s) is before end_seq (i.e., not reversed), 1182 * there's no guarantee that it will be before snd_nxt (n). The problem 1183 * happens when start_seq resides between end_seq wrap (e_w) and snd_nxt 1184 * wrap (s_w): 1185 * 1186 * <- outs wnd -> <- wrapzone -> 1187 * u e n u_w e_w s n_w 1188 * | | | | | | | 1189 * |<------------+------+----- TCP seqno space --------------+---------->| 1190 * ...-- <2^31 ->| |<--------... 1191 * ...---- >2^31 ------>| |<--------... 1192 * 1193 * Current code wouldn't be vulnerable but it's better still to discard such 1194 * crazy SACK blocks. Doing this check for start_seq alone closes somewhat 1195 * similar case (end_seq after snd_nxt wrap) as earlier reversed check in 1196 * snd_nxt wrap -> snd_una region will then become "well defined", i.e., 1197 * equal to the ideal case (infinite seqno space without wrap caused issues). 1198 * 1199 * With D-SACK the lower bound is extended to cover sequence space below 1200 * SND.UNA down to undo_marker, which is the last point of interest. Yet 1201 * again, D-SACK block must not to go across snd_una (for the same reason as 1202 * for the normal SACK blocks, explained above). But there all simplicity 1203 * ends, TCP might receive valid D-SACKs below that. As long as they reside 1204 * fully below undo_marker they do not affect behavior in anyway and can 1205 * therefore be safely ignored. In rare cases (which are more or less 1206 * theoretical ones), the D-SACK will nicely cross that boundary due to skb 1207 * fragmentation and packet reordering past skb's retransmission. To consider 1208 * them correctly, the acceptable range must be extended even more though 1209 * the exact amount is rather hard to quantify. However, tp->max_window can 1210 * be used as an exaggerated estimate. 1211 */ 1212 static bool tcp_is_sackblock_valid(struct tcp_sock *tp, bool is_dsack, 1213 u32 start_seq, u32 end_seq) 1214 { 1215 /* Too far in future, or reversed (interpretation is ambiguous) */ 1216 if (after(end_seq, tp->snd_nxt) || !before(start_seq, end_seq)) 1217 return false; 1218 1219 /* Nasty start_seq wrap-around check (see comments above) */ 1220 if (!before(start_seq, tp->snd_nxt)) 1221 return false; 1222 1223 /* In outstanding window? ...This is valid exit for D-SACKs too. 1224 * start_seq == snd_una is non-sensical (see comments above) 1225 */ 1226 if (after(start_seq, tp->snd_una)) 1227 return true; 1228 1229 if (!is_dsack || !tp->undo_marker) 1230 return false; 1231 1232 /* ...Then it's D-SACK, and must reside below snd_una completely */ 1233 if (after(end_seq, tp->snd_una)) 1234 return false; 1235 1236 if (!before(start_seq, tp->undo_marker)) 1237 return true; 1238 1239 /* Too old */ 1240 if (!after(end_seq, tp->undo_marker)) 1241 return false; 1242 1243 /* Undo_marker boundary crossing (overestimates a lot). Known already: 1244 * start_seq < undo_marker and end_seq >= undo_marker. 1245 */ 1246 return !before(start_seq, end_seq - tp->max_window); 1247 } 1248 1249 static bool tcp_check_dsack(struct sock *sk, const struct sk_buff *ack_skb, 1250 struct tcp_sack_block_wire *sp, int num_sacks, 1251 u32 prior_snd_una, struct tcp_sacktag_state *state) 1252 { 1253 struct tcp_sock *tp = tcp_sk(sk); 1254 u32 start_seq_0 = get_unaligned_be32(&sp[0].start_seq); 1255 u32 end_seq_0 = get_unaligned_be32(&sp[0].end_seq); 1256 u32 dup_segs; 1257 1258 if (before(start_seq_0, TCP_SKB_CB(ack_skb)->ack_seq)) { 1259 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKRECV); 1260 } else if (num_sacks > 1) { 1261 u32 end_seq_1 = get_unaligned_be32(&sp[1].end_seq); 1262 u32 start_seq_1 = get_unaligned_be32(&sp[1].start_seq); 1263 1264 if (after(end_seq_0, end_seq_1) || before(start_seq_0, start_seq_1)) 1265 return false; 1266 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKOFORECV); 1267 } else { 1268 return false; 1269 } 1270 1271 dup_segs = tcp_dsack_seen(tp, start_seq_0, end_seq_0, state); 1272 if (!dup_segs) { /* Skip dubious DSACK */ 1273 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKIGNOREDDUBIOUS); 1274 return false; 1275 } 1276 1277 NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPDSACKRECVSEGS, dup_segs); 1278 1279 /* D-SACK for already forgotten data... Do dumb counting. */ 1280 if (tp->undo_marker && tp->undo_retrans > 0 && 1281 !after(end_seq_0, prior_snd_una) && 1282 after(end_seq_0, tp->undo_marker)) 1283 tp->undo_retrans = max_t(int, 0, tp->undo_retrans - dup_segs); 1284 1285 return true; 1286 } 1287 1288 /* Check if skb is fully within the SACK block. In presence of GSO skbs, 1289 * the incoming SACK may not exactly match but we can find smaller MSS 1290 * aligned portion of it that matches. Therefore we might need to fragment 1291 * which may fail and creates some hassle (caller must handle error case 1292 * returns). 1293 * 1294 * FIXME: this could be merged to shift decision code 1295 */ 1296 static int tcp_match_skb_to_sack(struct sock *sk, struct sk_buff *skb, 1297 u32 start_seq, u32 end_seq) 1298 { 1299 int err; 1300 bool in_sack; 1301 unsigned int pkt_len; 1302 unsigned int mss; 1303 1304 in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) && 1305 !before(end_seq, TCP_SKB_CB(skb)->end_seq); 1306 1307 if (tcp_skb_pcount(skb) > 1 && !in_sack && 1308 after(TCP_SKB_CB(skb)->end_seq, start_seq)) { 1309 mss = tcp_skb_mss(skb); 1310 in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq); 1311 1312 if (!in_sack) { 1313 pkt_len = start_seq - TCP_SKB_CB(skb)->seq; 1314 if (pkt_len < mss) 1315 pkt_len = mss; 1316 } else { 1317 pkt_len = end_seq - TCP_SKB_CB(skb)->seq; 1318 if (pkt_len < mss) 1319 return -EINVAL; 1320 } 1321 1322 /* Round if necessary so that SACKs cover only full MSSes 1323 * and/or the remaining small portion (if present) 1324 */ 1325 if (pkt_len > mss) { 1326 unsigned int new_len = (pkt_len / mss) * mss; 1327 if (!in_sack && new_len < pkt_len) 1328 new_len += mss; 1329 pkt_len = new_len; 1330 } 1331 1332 if (pkt_len >= skb->len && !in_sack) 1333 return 0; 1334 1335 err = tcp_fragment(sk, TCP_FRAG_IN_RTX_QUEUE, skb, 1336 pkt_len, mss, GFP_ATOMIC); 1337 if (err < 0) 1338 return err; 1339 } 1340 1341 return in_sack; 1342 } 1343 1344 /* Mark the given newly-SACKed range as such, adjusting counters and hints. */ 1345 static u8 tcp_sacktag_one(struct sock *sk, 1346 struct tcp_sacktag_state *state, u8 sacked, 1347 u32 start_seq, u32 end_seq, 1348 int dup_sack, int pcount, 1349 u64 xmit_time) 1350 { 1351 struct tcp_sock *tp = tcp_sk(sk); 1352 1353 /* Account D-SACK for retransmitted packet. */ 1354 if (dup_sack && (sacked & TCPCB_RETRANS)) { 1355 if (tp->undo_marker && tp->undo_retrans > 0 && 1356 after(end_seq, tp->undo_marker)) 1357 tp->undo_retrans = max_t(int, 0, tp->undo_retrans - pcount); 1358 if ((sacked & TCPCB_SACKED_ACKED) && 1359 before(start_seq, state->reord)) 1360 state->reord = start_seq; 1361 } 1362 1363 /* Nothing to do; acked frame is about to be dropped (was ACKed). */ 1364 if (!after(end_seq, tp->snd_una)) 1365 return sacked; 1366 1367 if (!(sacked & TCPCB_SACKED_ACKED)) { 1368 tcp_rack_advance(tp, sacked, end_seq, xmit_time); 1369 1370 if (sacked & TCPCB_SACKED_RETRANS) { 1371 /* If the segment is not tagged as lost, 1372 * we do not clear RETRANS, believing 1373 * that retransmission is still in flight. 1374 */ 1375 if (sacked & TCPCB_LOST) { 1376 sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS); 1377 tp->lost_out -= pcount; 1378 tp->retrans_out -= pcount; 1379 } 1380 } else { 1381 if (!(sacked & TCPCB_RETRANS)) { 1382 /* New sack for not retransmitted frame, 1383 * which was in hole. It is reordering. 1384 */ 1385 if (before(start_seq, 1386 tcp_highest_sack_seq(tp)) && 1387 before(start_seq, state->reord)) 1388 state->reord = start_seq; 1389 1390 if (!after(end_seq, tp->high_seq)) 1391 state->flag |= FLAG_ORIG_SACK_ACKED; 1392 if (state->first_sackt == 0) 1393 state->first_sackt = xmit_time; 1394 state->last_sackt = xmit_time; 1395 } 1396 1397 if (sacked & TCPCB_LOST) { 1398 sacked &= ~TCPCB_LOST; 1399 tp->lost_out -= pcount; 1400 } 1401 } 1402 1403 sacked |= TCPCB_SACKED_ACKED; 1404 state->flag |= FLAG_DATA_SACKED; 1405 tp->sacked_out += pcount; 1406 /* Out-of-order packets delivered */ 1407 state->sack_delivered += pcount; 1408 1409 /* Lost marker hint past SACKed? Tweak RFC3517 cnt */ 1410 if (tp->lost_skb_hint && 1411 before(start_seq, TCP_SKB_CB(tp->lost_skb_hint)->seq)) 1412 tp->lost_cnt_hint += pcount; 1413 } 1414 1415 /* D-SACK. We can detect redundant retransmission in S|R and plain R 1416 * frames and clear it. undo_retrans is decreased above, L|R frames 1417 * are accounted above as well. 1418 */ 1419 if (dup_sack && (sacked & TCPCB_SACKED_RETRANS)) { 1420 sacked &= ~TCPCB_SACKED_RETRANS; 1421 tp->retrans_out -= pcount; 1422 } 1423 1424 return sacked; 1425 } 1426 1427 /* Shift newly-SACKed bytes from this skb to the immediately previous 1428 * already-SACKed sk_buff. Mark the newly-SACKed bytes as such. 1429 */ 1430 static bool tcp_shifted_skb(struct sock *sk, struct sk_buff *prev, 1431 struct sk_buff *skb, 1432 struct tcp_sacktag_state *state, 1433 unsigned int pcount, int shifted, int mss, 1434 bool dup_sack) 1435 { 1436 struct tcp_sock *tp = tcp_sk(sk); 1437 u32 start_seq = TCP_SKB_CB(skb)->seq; /* start of newly-SACKed */ 1438 u32 end_seq = start_seq + shifted; /* end of newly-SACKed */ 1439 1440 BUG_ON(!pcount); 1441 1442 /* Adjust counters and hints for the newly sacked sequence 1443 * range but discard the return value since prev is already 1444 * marked. We must tag the range first because the seq 1445 * advancement below implicitly advances 1446 * tcp_highest_sack_seq() when skb is highest_sack. 1447 */ 1448 tcp_sacktag_one(sk, state, TCP_SKB_CB(skb)->sacked, 1449 start_seq, end_seq, dup_sack, pcount, 1450 tcp_skb_timestamp_us(skb)); 1451 tcp_rate_skb_delivered(sk, skb, state->rate); 1452 1453 if (skb == tp->lost_skb_hint) 1454 tp->lost_cnt_hint += pcount; 1455 1456 TCP_SKB_CB(prev)->end_seq += shifted; 1457 TCP_SKB_CB(skb)->seq += shifted; 1458 1459 tcp_skb_pcount_add(prev, pcount); 1460 WARN_ON_ONCE(tcp_skb_pcount(skb) < pcount); 1461 tcp_skb_pcount_add(skb, -pcount); 1462 1463 /* When we're adding to gso_segs == 1, gso_size will be zero, 1464 * in theory this shouldn't be necessary but as long as DSACK 1465 * code can come after this skb later on it's better to keep 1466 * setting gso_size to something. 1467 */ 1468 if (!TCP_SKB_CB(prev)->tcp_gso_size) 1469 TCP_SKB_CB(prev)->tcp_gso_size = mss; 1470 1471 /* CHECKME: To clear or not to clear? Mimics normal skb currently */ 1472 if (tcp_skb_pcount(skb) <= 1) 1473 TCP_SKB_CB(skb)->tcp_gso_size = 0; 1474 1475 /* Difference in this won't matter, both ACKed by the same cumul. ACK */ 1476 TCP_SKB_CB(prev)->sacked |= (TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS); 1477 1478 if (skb->len > 0) { 1479 BUG_ON(!tcp_skb_pcount(skb)); 1480 NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKSHIFTED); 1481 return false; 1482 } 1483 1484 /* Whole SKB was eaten :-) */ 1485 1486 if (skb == tp->retransmit_skb_hint) 1487 tp->retransmit_skb_hint = prev; 1488 if (skb == tp->lost_skb_hint) { 1489 tp->lost_skb_hint = prev; 1490 tp->lost_cnt_hint -= tcp_skb_pcount(prev); 1491 } 1492 1493 TCP_SKB_CB(prev)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags; 1494 TCP_SKB_CB(prev)->eor = TCP_SKB_CB(skb)->eor; 1495 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) 1496 TCP_SKB_CB(prev)->end_seq++; 1497 1498 if (skb == tcp_highest_sack(sk)) 1499 tcp_advance_highest_sack(sk, skb); 1500 1501 tcp_skb_collapse_tstamp(prev, skb); 1502 if (unlikely(TCP_SKB_CB(prev)->tx.delivered_mstamp)) 1503 TCP_SKB_CB(prev)->tx.delivered_mstamp = 0; 1504 1505 tcp_rtx_queue_unlink_and_free(skb, sk); 1506 1507 NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKMERGED); 1508 1509 return true; 1510 } 1511 1512 /* I wish gso_size would have a bit more sane initialization than 1513 * something-or-zero which complicates things 1514 */ 1515 static int tcp_skb_seglen(const struct sk_buff *skb) 1516 { 1517 return tcp_skb_pcount(skb) == 1 ? skb->len : tcp_skb_mss(skb); 1518 } 1519 1520 /* Shifting pages past head area doesn't work */ 1521 static int skb_can_shift(const struct sk_buff *skb) 1522 { 1523 return !skb_headlen(skb) && skb_is_nonlinear(skb); 1524 } 1525 1526 int tcp_skb_shift(struct sk_buff *to, struct sk_buff *from, 1527 int pcount, int shiftlen) 1528 { 1529 /* TCP min gso_size is 8 bytes (TCP_MIN_GSO_SIZE) 1530 * Since TCP_SKB_CB(skb)->tcp_gso_segs is 16 bits, we need 1531 * to make sure not storing more than 65535 * 8 bytes per skb, 1532 * even if current MSS is bigger. 1533 */ 1534 if (unlikely(to->len + shiftlen >= 65535 * TCP_MIN_GSO_SIZE)) 1535 return 0; 1536 if (unlikely(tcp_skb_pcount(to) + pcount > 65535)) 1537 return 0; 1538 return skb_shift(to, from, shiftlen); 1539 } 1540 1541 /* Try collapsing SACK blocks spanning across multiple skbs to a single 1542 * skb. 1543 */ 1544 static struct sk_buff *tcp_shift_skb_data(struct sock *sk, struct sk_buff *skb, 1545 struct tcp_sacktag_state *state, 1546 u32 start_seq, u32 end_seq, 1547 bool dup_sack) 1548 { 1549 struct tcp_sock *tp = tcp_sk(sk); 1550 struct sk_buff *prev; 1551 int mss; 1552 int pcount = 0; 1553 int len; 1554 int in_sack; 1555 1556 /* Normally R but no L won't result in plain S */ 1557 if (!dup_sack && 1558 (TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_RETRANS)) == TCPCB_SACKED_RETRANS) 1559 goto fallback; 1560 if (!skb_can_shift(skb)) 1561 goto fallback; 1562 /* This frame is about to be dropped (was ACKed). */ 1563 if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una)) 1564 goto fallback; 1565 1566 /* Can only happen with delayed DSACK + discard craziness */ 1567 prev = skb_rb_prev(skb); 1568 if (!prev) 1569 goto fallback; 1570 1571 if ((TCP_SKB_CB(prev)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED) 1572 goto fallback; 1573 1574 if (!tcp_skb_can_collapse(prev, skb)) 1575 goto fallback; 1576 1577 in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) && 1578 !before(end_seq, TCP_SKB_CB(skb)->end_seq); 1579 1580 if (in_sack) { 1581 len = skb->len; 1582 pcount = tcp_skb_pcount(skb); 1583 mss = tcp_skb_seglen(skb); 1584 1585 /* TODO: Fix DSACKs to not fragment already SACKed and we can 1586 * drop this restriction as unnecessary 1587 */ 1588 if (mss != tcp_skb_seglen(prev)) 1589 goto fallback; 1590 } else { 1591 if (!after(TCP_SKB_CB(skb)->end_seq, start_seq)) 1592 goto noop; 1593 /* CHECKME: This is non-MSS split case only?, this will 1594 * cause skipped skbs due to advancing loop btw, original 1595 * has that feature too 1596 */ 1597 if (tcp_skb_pcount(skb) <= 1) 1598 goto noop; 1599 1600 in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq); 1601 if (!in_sack) { 1602 /* TODO: head merge to next could be attempted here 1603 * if (!after(TCP_SKB_CB(skb)->end_seq, end_seq)), 1604 * though it might not be worth of the additional hassle 1605 * 1606 * ...we can probably just fallback to what was done 1607 * previously. We could try merging non-SACKed ones 1608 * as well but it probably isn't going to buy off 1609 * because later SACKs might again split them, and 1610 * it would make skb timestamp tracking considerably 1611 * harder problem. 1612 */ 1613 goto fallback; 1614 } 1615 1616 len = end_seq - TCP_SKB_CB(skb)->seq; 1617 BUG_ON(len < 0); 1618 BUG_ON(len > skb->len); 1619 1620 /* MSS boundaries should be honoured or else pcount will 1621 * severely break even though it makes things bit trickier. 1622 * Optimize common case to avoid most of the divides 1623 */ 1624 mss = tcp_skb_mss(skb); 1625 1626 /* TODO: Fix DSACKs to not fragment already SACKed and we can 1627 * drop this restriction as unnecessary 1628 */ 1629 if (mss != tcp_skb_seglen(prev)) 1630 goto fallback; 1631 1632 if (len == mss) { 1633 pcount = 1; 1634 } else if (len < mss) { 1635 goto noop; 1636 } else { 1637 pcount = len / mss; 1638 len = pcount * mss; 1639 } 1640 } 1641 1642 /* tcp_sacktag_one() won't SACK-tag ranges below snd_una */ 1643 if (!after(TCP_SKB_CB(skb)->seq + len, tp->snd_una)) 1644 goto fallback; 1645 1646 if (!tcp_skb_shift(prev, skb, pcount, len)) 1647 goto fallback; 1648 if (!tcp_shifted_skb(sk, prev, skb, state, pcount, len, mss, dup_sack)) 1649 goto out; 1650 1651 /* Hole filled allows collapsing with the next as well, this is very 1652 * useful when hole on every nth skb pattern happens 1653 */ 1654 skb = skb_rb_next(prev); 1655 if (!skb) 1656 goto out; 1657 1658 if (!skb_can_shift(skb) || 1659 ((TCP_SKB_CB(skb)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED) || 1660 (mss != tcp_skb_seglen(skb))) 1661 goto out; 1662 1663 if (!tcp_skb_can_collapse(prev, skb)) 1664 goto out; 1665 len = skb->len; 1666 pcount = tcp_skb_pcount(skb); 1667 if (tcp_skb_shift(prev, skb, pcount, len)) 1668 tcp_shifted_skb(sk, prev, skb, state, pcount, 1669 len, mss, 0); 1670 1671 out: 1672 return prev; 1673 1674 noop: 1675 return skb; 1676 1677 fallback: 1678 NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKSHIFTFALLBACK); 1679 return NULL; 1680 } 1681 1682 static struct sk_buff *tcp_sacktag_walk(struct sk_buff *skb, struct sock *sk, 1683 struct tcp_sack_block *next_dup, 1684 struct tcp_sacktag_state *state, 1685 u32 start_seq, u32 end_seq, 1686 bool dup_sack_in) 1687 { 1688 struct tcp_sock *tp = tcp_sk(sk); 1689 struct sk_buff *tmp; 1690 1691 skb_rbtree_walk_from(skb) { 1692 int in_sack = 0; 1693 bool dup_sack = dup_sack_in; 1694 1695 /* queue is in-order => we can short-circuit the walk early */ 1696 if (!before(TCP_SKB_CB(skb)->seq, end_seq)) 1697 break; 1698 1699 if (next_dup && 1700 before(TCP_SKB_CB(skb)->seq, next_dup->end_seq)) { 1701 in_sack = tcp_match_skb_to_sack(sk, skb, 1702 next_dup->start_seq, 1703 next_dup->end_seq); 1704 if (in_sack > 0) 1705 dup_sack = true; 1706 } 1707 1708 /* skb reference here is a bit tricky to get right, since 1709 * shifting can eat and free both this skb and the next, 1710 * so not even _safe variant of the loop is enough. 1711 */ 1712 if (in_sack <= 0) { 1713 tmp = tcp_shift_skb_data(sk, skb, state, 1714 start_seq, end_seq, dup_sack); 1715 if (tmp) { 1716 if (tmp != skb) { 1717 skb = tmp; 1718 continue; 1719 } 1720 1721 in_sack = 0; 1722 } else { 1723 in_sack = tcp_match_skb_to_sack(sk, skb, 1724 start_seq, 1725 end_seq); 1726 } 1727 } 1728 1729 if (unlikely(in_sack < 0)) 1730 break; 1731 1732 if (in_sack) { 1733 TCP_SKB_CB(skb)->sacked = 1734 tcp_sacktag_one(sk, 1735 state, 1736 TCP_SKB_CB(skb)->sacked, 1737 TCP_SKB_CB(skb)->seq, 1738 TCP_SKB_CB(skb)->end_seq, 1739 dup_sack, 1740 tcp_skb_pcount(skb), 1741 tcp_skb_timestamp_us(skb)); 1742 tcp_rate_skb_delivered(sk, skb, state->rate); 1743 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED) 1744 list_del_init(&skb->tcp_tsorted_anchor); 1745 1746 if (!before(TCP_SKB_CB(skb)->seq, 1747 tcp_highest_sack_seq(tp))) 1748 tcp_advance_highest_sack(sk, skb); 1749 } 1750 } 1751 return skb; 1752 } 1753 1754 static struct sk_buff *tcp_sacktag_bsearch(struct sock *sk, u32 seq) 1755 { 1756 struct rb_node *parent, **p = &sk->tcp_rtx_queue.rb_node; 1757 struct sk_buff *skb; 1758 1759 while (*p) { 1760 parent = *p; 1761 skb = rb_to_skb(parent); 1762 if (before(seq, TCP_SKB_CB(skb)->seq)) { 1763 p = &parent->rb_left; 1764 continue; 1765 } 1766 if (!before(seq, TCP_SKB_CB(skb)->end_seq)) { 1767 p = &parent->rb_right; 1768 continue; 1769 } 1770 return skb; 1771 } 1772 return NULL; 1773 } 1774 1775 static struct sk_buff *tcp_sacktag_skip(struct sk_buff *skb, struct sock *sk, 1776 u32 skip_to_seq) 1777 { 1778 if (skb && after(TCP_SKB_CB(skb)->seq, skip_to_seq)) 1779 return skb; 1780 1781 return tcp_sacktag_bsearch(sk, skip_to_seq); 1782 } 1783 1784 static struct sk_buff *tcp_maybe_skipping_dsack(struct sk_buff *skb, 1785 struct sock *sk, 1786 struct tcp_sack_block *next_dup, 1787 struct tcp_sacktag_state *state, 1788 u32 skip_to_seq) 1789 { 1790 if (!next_dup) 1791 return skb; 1792 1793 if (before(next_dup->start_seq, skip_to_seq)) { 1794 skb = tcp_sacktag_skip(skb, sk, next_dup->start_seq); 1795 skb = tcp_sacktag_walk(skb, sk, NULL, state, 1796 next_dup->start_seq, next_dup->end_seq, 1797 1); 1798 } 1799 1800 return skb; 1801 } 1802 1803 static int tcp_sack_cache_ok(const struct tcp_sock *tp, const struct tcp_sack_block *cache) 1804 { 1805 return cache < tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache); 1806 } 1807 1808 static int 1809 tcp_sacktag_write_queue(struct sock *sk, const struct sk_buff *ack_skb, 1810 u32 prior_snd_una, struct tcp_sacktag_state *state) 1811 { 1812 struct tcp_sock *tp = tcp_sk(sk); 1813 const unsigned char *ptr = (skb_transport_header(ack_skb) + 1814 TCP_SKB_CB(ack_skb)->sacked); 1815 struct tcp_sack_block_wire *sp_wire = (struct tcp_sack_block_wire *)(ptr+2); 1816 struct tcp_sack_block sp[TCP_NUM_SACKS]; 1817 struct tcp_sack_block *cache; 1818 struct sk_buff *skb; 1819 int num_sacks = min(TCP_NUM_SACKS, (ptr[1] - TCPOLEN_SACK_BASE) >> 3); 1820 int used_sacks; 1821 bool found_dup_sack = false; 1822 int i, j; 1823 int first_sack_index; 1824 1825 state->flag = 0; 1826 state->reord = tp->snd_nxt; 1827 1828 if (!tp->sacked_out) 1829 tcp_highest_sack_reset(sk); 1830 1831 found_dup_sack = tcp_check_dsack(sk, ack_skb, sp_wire, 1832 num_sacks, prior_snd_una, state); 1833 1834 /* Eliminate too old ACKs, but take into 1835 * account more or less fresh ones, they can 1836 * contain valid SACK info. 1837 */ 1838 if (before(TCP_SKB_CB(ack_skb)->ack_seq, prior_snd_una - tp->max_window)) 1839 return 0; 1840 1841 if (!tp->packets_out) 1842 goto out; 1843 1844 used_sacks = 0; 1845 first_sack_index = 0; 1846 for (i = 0; i < num_sacks; i++) { 1847 bool dup_sack = !i && found_dup_sack; 1848 1849 sp[used_sacks].start_seq = get_unaligned_be32(&sp_wire[i].start_seq); 1850 sp[used_sacks].end_seq = get_unaligned_be32(&sp_wire[i].end_seq); 1851 1852 if (!tcp_is_sackblock_valid(tp, dup_sack, 1853 sp[used_sacks].start_seq, 1854 sp[used_sacks].end_seq)) { 1855 int mib_idx; 1856 1857 if (dup_sack) { 1858 if (!tp->undo_marker) 1859 mib_idx = LINUX_MIB_TCPDSACKIGNOREDNOUNDO; 1860 else 1861 mib_idx = LINUX_MIB_TCPDSACKIGNOREDOLD; 1862 } else { 1863 /* Don't count olds caused by ACK reordering */ 1864 if ((TCP_SKB_CB(ack_skb)->ack_seq != tp->snd_una) && 1865 !after(sp[used_sacks].end_seq, tp->snd_una)) 1866 continue; 1867 mib_idx = LINUX_MIB_TCPSACKDISCARD; 1868 } 1869 1870 NET_INC_STATS(sock_net(sk), mib_idx); 1871 if (i == 0) 1872 first_sack_index = -1; 1873 continue; 1874 } 1875 1876 /* Ignore very old stuff early */ 1877 if (!after(sp[used_sacks].end_seq, prior_snd_una)) { 1878 if (i == 0) 1879 first_sack_index = -1; 1880 continue; 1881 } 1882 1883 used_sacks++; 1884 } 1885 1886 /* order SACK blocks to allow in order walk of the retrans queue */ 1887 for (i = used_sacks - 1; i > 0; i--) { 1888 for (j = 0; j < i; j++) { 1889 if (after(sp[j].start_seq, sp[j + 1].start_seq)) { 1890 swap(sp[j], sp[j + 1]); 1891 1892 /* Track where the first SACK block goes to */ 1893 if (j == first_sack_index) 1894 first_sack_index = j + 1; 1895 } 1896 } 1897 } 1898 1899 state->mss_now = tcp_current_mss(sk); 1900 skb = NULL; 1901 i = 0; 1902 1903 if (!tp->sacked_out) { 1904 /* It's already past, so skip checking against it */ 1905 cache = tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache); 1906 } else { 1907 cache = tp->recv_sack_cache; 1908 /* Skip empty blocks in at head of the cache */ 1909 while (tcp_sack_cache_ok(tp, cache) && !cache->start_seq && 1910 !cache->end_seq) 1911 cache++; 1912 } 1913 1914 while (i < used_sacks) { 1915 u32 start_seq = sp[i].start_seq; 1916 u32 end_seq = sp[i].end_seq; 1917 bool dup_sack = (found_dup_sack && (i == first_sack_index)); 1918 struct tcp_sack_block *next_dup = NULL; 1919 1920 if (found_dup_sack && ((i + 1) == first_sack_index)) 1921 next_dup = &sp[i + 1]; 1922 1923 /* Skip too early cached blocks */ 1924 while (tcp_sack_cache_ok(tp, cache) && 1925 !before(start_seq, cache->end_seq)) 1926 cache++; 1927 1928 /* Can skip some work by looking recv_sack_cache? */ 1929 if (tcp_sack_cache_ok(tp, cache) && !dup_sack && 1930 after(end_seq, cache->start_seq)) { 1931 1932 /* Head todo? */ 1933 if (before(start_seq, cache->start_seq)) { 1934 skb = tcp_sacktag_skip(skb, sk, start_seq); 1935 skb = tcp_sacktag_walk(skb, sk, next_dup, 1936 state, 1937 start_seq, 1938 cache->start_seq, 1939 dup_sack); 1940 } 1941 1942 /* Rest of the block already fully processed? */ 1943 if (!after(end_seq, cache->end_seq)) 1944 goto advance_sp; 1945 1946 skb = tcp_maybe_skipping_dsack(skb, sk, next_dup, 1947 state, 1948 cache->end_seq); 1949 1950 /* ...tail remains todo... */ 1951 if (tcp_highest_sack_seq(tp) == cache->end_seq) { 1952 /* ...but better entrypoint exists! */ 1953 skb = tcp_highest_sack(sk); 1954 if (!skb) 1955 break; 1956 cache++; 1957 goto walk; 1958 } 1959 1960 skb = tcp_sacktag_skip(skb, sk, cache->end_seq); 1961 /* Check overlap against next cached too (past this one already) */ 1962 cache++; 1963 continue; 1964 } 1965 1966 if (!before(start_seq, tcp_highest_sack_seq(tp))) { 1967 skb = tcp_highest_sack(sk); 1968 if (!skb) 1969 break; 1970 } 1971 skb = tcp_sacktag_skip(skb, sk, start_seq); 1972 1973 walk: 1974 skb = tcp_sacktag_walk(skb, sk, next_dup, state, 1975 start_seq, end_seq, dup_sack); 1976 1977 advance_sp: 1978 i++; 1979 } 1980 1981 /* Clear the head of the cache sack blocks so we can skip it next time */ 1982 for (i = 0; i < ARRAY_SIZE(tp->recv_sack_cache) - used_sacks; i++) { 1983 tp->recv_sack_cache[i].start_seq = 0; 1984 tp->recv_sack_cache[i].end_seq = 0; 1985 } 1986 for (j = 0; j < used_sacks; j++) 1987 tp->recv_sack_cache[i++] = sp[j]; 1988 1989 if (inet_csk(sk)->icsk_ca_state != TCP_CA_Loss || tp->undo_marker) 1990 tcp_check_sack_reordering(sk, state->reord, 0); 1991 1992 tcp_verify_left_out(tp); 1993 out: 1994 1995 #if FASTRETRANS_DEBUG > 0 1996 WARN_ON((int)tp->sacked_out < 0); 1997 WARN_ON((int)tp->lost_out < 0); 1998 WARN_ON((int)tp->retrans_out < 0); 1999 WARN_ON((int)tcp_packets_in_flight(tp) < 0); 2000 #endif 2001 return state->flag; 2002 } 2003 2004 /* Limits sacked_out so that sum with lost_out isn't ever larger than 2005 * packets_out. Returns false if sacked_out adjustement wasn't necessary. 2006 */ 2007 static bool tcp_limit_reno_sacked(struct tcp_sock *tp) 2008 { 2009 u32 holes; 2010 2011 holes = max(tp->lost_out, 1U); 2012 holes = min(holes, tp->packets_out); 2013 2014 if ((tp->sacked_out + holes) > tp->packets_out) { 2015 tp->sacked_out = tp->packets_out - holes; 2016 return true; 2017 } 2018 return false; 2019 } 2020 2021 /* If we receive more dupacks than we expected counting segments 2022 * in assumption of absent reordering, interpret this as reordering. 2023 * The only another reason could be bug in receiver TCP. 2024 */ 2025 static void tcp_check_reno_reordering(struct sock *sk, const int addend) 2026 { 2027 struct tcp_sock *tp = tcp_sk(sk); 2028 2029 if (!tcp_limit_reno_sacked(tp)) 2030 return; 2031 2032 tp->reordering = min_t(u32, tp->packets_out + addend, 2033 READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_max_reordering)); 2034 tp->reord_seen++; 2035 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRENOREORDER); 2036 } 2037 2038 /* Emulate SACKs for SACKless connection: account for a new dupack. */ 2039 2040 static void tcp_add_reno_sack(struct sock *sk, int num_dupack, bool ece_ack) 2041 { 2042 if (num_dupack) { 2043 struct tcp_sock *tp = tcp_sk(sk); 2044 u32 prior_sacked = tp->sacked_out; 2045 s32 delivered; 2046 2047 tp->sacked_out += num_dupack; 2048 tcp_check_reno_reordering(sk, 0); 2049 delivered = tp->sacked_out - prior_sacked; 2050 if (delivered > 0) 2051 tcp_count_delivered(tp, delivered, ece_ack); 2052 tcp_verify_left_out(tp); 2053 } 2054 } 2055 2056 /* Account for ACK, ACKing some data in Reno Recovery phase. */ 2057 2058 static void tcp_remove_reno_sacks(struct sock *sk, int acked, bool ece_ack) 2059 { 2060 struct tcp_sock *tp = tcp_sk(sk); 2061 2062 if (acked > 0) { 2063 /* One ACK acked hole. The rest eat duplicate ACKs. */ 2064 tcp_count_delivered(tp, max_t(int, acked - tp->sacked_out, 1), 2065 ece_ack); 2066 if (acked - 1 >= tp->sacked_out) 2067 tp->sacked_out = 0; 2068 else 2069 tp->sacked_out -= acked - 1; 2070 } 2071 tcp_check_reno_reordering(sk, acked); 2072 tcp_verify_left_out(tp); 2073 } 2074 2075 static inline void tcp_reset_reno_sack(struct tcp_sock *tp) 2076 { 2077 tp->sacked_out = 0; 2078 } 2079 2080 void tcp_clear_retrans(struct tcp_sock *tp) 2081 { 2082 tp->retrans_out = 0; 2083 tp->lost_out = 0; 2084 tp->undo_marker = 0; 2085 tp->undo_retrans = -1; 2086 tp->sacked_out = 0; 2087 } 2088 2089 static inline void tcp_init_undo(struct tcp_sock *tp) 2090 { 2091 tp->undo_marker = tp->snd_una; 2092 /* Retransmission still in flight may cause DSACKs later. */ 2093 tp->undo_retrans = tp->retrans_out ? : -1; 2094 } 2095 2096 static bool tcp_is_rack(const struct sock *sk) 2097 { 2098 return READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_recovery) & 2099 TCP_RACK_LOSS_DETECTION; 2100 } 2101 2102 /* If we detect SACK reneging, forget all SACK information 2103 * and reset tags completely, otherwise preserve SACKs. If receiver 2104 * dropped its ofo queue, we will know this due to reneging detection. 2105 */ 2106 static void tcp_timeout_mark_lost(struct sock *sk) 2107 { 2108 struct tcp_sock *tp = tcp_sk(sk); 2109 struct sk_buff *skb, *head; 2110 bool is_reneg; /* is receiver reneging on SACKs? */ 2111 2112 head = tcp_rtx_queue_head(sk); 2113 is_reneg = head && (TCP_SKB_CB(head)->sacked & TCPCB_SACKED_ACKED); 2114 if (is_reneg) { 2115 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSACKRENEGING); 2116 tp->sacked_out = 0; 2117 /* Mark SACK reneging until we recover from this loss event. */ 2118 tp->is_sack_reneg = 1; 2119 } else if (tcp_is_reno(tp)) { 2120 tcp_reset_reno_sack(tp); 2121 } 2122 2123 skb = head; 2124 skb_rbtree_walk_from(skb) { 2125 if (is_reneg) 2126 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED; 2127 else if (tcp_is_rack(sk) && skb != head && 2128 tcp_rack_skb_timeout(tp, skb, 0) > 0) 2129 continue; /* Don't mark recently sent ones lost yet */ 2130 tcp_mark_skb_lost(sk, skb); 2131 } 2132 tcp_verify_left_out(tp); 2133 tcp_clear_all_retrans_hints(tp); 2134 } 2135 2136 /* Enter Loss state. */ 2137 void tcp_enter_loss(struct sock *sk) 2138 { 2139 const struct inet_connection_sock *icsk = inet_csk(sk); 2140 struct tcp_sock *tp = tcp_sk(sk); 2141 struct net *net = sock_net(sk); 2142 bool new_recovery = icsk->icsk_ca_state < TCP_CA_Recovery; 2143 u8 reordering; 2144 2145 tcp_timeout_mark_lost(sk); 2146 2147 /* Reduce ssthresh if it has not yet been made inside this window. */ 2148 if (icsk->icsk_ca_state <= TCP_CA_Disorder || 2149 !after(tp->high_seq, tp->snd_una) || 2150 (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) { 2151 tp->prior_ssthresh = tcp_current_ssthresh(sk); 2152 tp->prior_cwnd = tcp_snd_cwnd(tp); 2153 tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk); 2154 tcp_ca_event(sk, CA_EVENT_LOSS); 2155 tcp_init_undo(tp); 2156 } 2157 tcp_snd_cwnd_set(tp, tcp_packets_in_flight(tp) + 1); 2158 tp->snd_cwnd_cnt = 0; 2159 tp->snd_cwnd_stamp = tcp_jiffies32; 2160 2161 /* Timeout in disordered state after receiving substantial DUPACKs 2162 * suggests that the degree of reordering is over-estimated. 2163 */ 2164 reordering = READ_ONCE(net->ipv4.sysctl_tcp_reordering); 2165 if (icsk->icsk_ca_state <= TCP_CA_Disorder && 2166 tp->sacked_out >= reordering) 2167 tp->reordering = min_t(unsigned int, tp->reordering, 2168 reordering); 2169 2170 tcp_set_ca_state(sk, TCP_CA_Loss); 2171 tp->high_seq = tp->snd_nxt; 2172 tcp_ecn_queue_cwr(tp); 2173 2174 /* F-RTO RFC5682 sec 3.1 step 1: retransmit SND.UNA if no previous 2175 * loss recovery is underway except recurring timeout(s) on 2176 * the same SND.UNA (sec 3.2). Disable F-RTO on path MTU probing 2177 */ 2178 tp->frto = net->ipv4.sysctl_tcp_frto && 2179 (new_recovery || icsk->icsk_retransmits) && 2180 !inet_csk(sk)->icsk_mtup.probe_size; 2181 } 2182 2183 /* If ACK arrived pointing to a remembered SACK, it means that our 2184 * remembered SACKs do not reflect real state of receiver i.e. 2185 * receiver _host_ is heavily congested (or buggy). 2186 * 2187 * To avoid big spurious retransmission bursts due to transient SACK 2188 * scoreboard oddities that look like reneging, we give the receiver a 2189 * little time (max(RTT/2, 10ms)) to send us some more ACKs that will 2190 * restore sanity to the SACK scoreboard. If the apparent reneging 2191 * persists until this RTO then we'll clear the SACK scoreboard. 2192 */ 2193 static bool tcp_check_sack_reneging(struct sock *sk, int flag) 2194 { 2195 if (flag & FLAG_SACK_RENEGING) { 2196 struct tcp_sock *tp = tcp_sk(sk); 2197 unsigned long delay = max(usecs_to_jiffies(tp->srtt_us >> 4), 2198 msecs_to_jiffies(10)); 2199 2200 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, 2201 delay, TCP_RTO_MAX); 2202 return true; 2203 } 2204 return false; 2205 } 2206 2207 /* Heurestics to calculate number of duplicate ACKs. There's no dupACKs 2208 * counter when SACK is enabled (without SACK, sacked_out is used for 2209 * that purpose). 2210 * 2211 * With reordering, holes may still be in flight, so RFC3517 recovery 2212 * uses pure sacked_out (total number of SACKed segments) even though 2213 * it violates the RFC that uses duplicate ACKs, often these are equal 2214 * but when e.g. out-of-window ACKs or packet duplication occurs, 2215 * they differ. Since neither occurs due to loss, TCP should really 2216 * ignore them. 2217 */ 2218 static inline int tcp_dupack_heuristics(const struct tcp_sock *tp) 2219 { 2220 return tp->sacked_out + 1; 2221 } 2222 2223 /* Linux NewReno/SACK/ECN state machine. 2224 * -------------------------------------- 2225 * 2226 * "Open" Normal state, no dubious events, fast path. 2227 * "Disorder" In all the respects it is "Open", 2228 * but requires a bit more attention. It is entered when 2229 * we see some SACKs or dupacks. It is split of "Open" 2230 * mainly to move some processing from fast path to slow one. 2231 * "CWR" CWND was reduced due to some Congestion Notification event. 2232 * It can be ECN, ICMP source quench, local device congestion. 2233 * "Recovery" CWND was reduced, we are fast-retransmitting. 2234 * "Loss" CWND was reduced due to RTO timeout or SACK reneging. 2235 * 2236 * tcp_fastretrans_alert() is entered: 2237 * - each incoming ACK, if state is not "Open" 2238 * - when arrived ACK is unusual, namely: 2239 * * SACK 2240 * * Duplicate ACK. 2241 * * ECN ECE. 2242 * 2243 * Counting packets in flight is pretty simple. 2244 * 2245 * in_flight = packets_out - left_out + retrans_out 2246 * 2247 * packets_out is SND.NXT-SND.UNA counted in packets. 2248 * 2249 * retrans_out is number of retransmitted segments. 2250 * 2251 * left_out is number of segments left network, but not ACKed yet. 2252 * 2253 * left_out = sacked_out + lost_out 2254 * 2255 * sacked_out: Packets, which arrived to receiver out of order 2256 * and hence not ACKed. With SACKs this number is simply 2257 * amount of SACKed data. Even without SACKs 2258 * it is easy to give pretty reliable estimate of this number, 2259 * counting duplicate ACKs. 2260 * 2261 * lost_out: Packets lost by network. TCP has no explicit 2262 * "loss notification" feedback from network (for now). 2263 * It means that this number can be only _guessed_. 2264 * Actually, it is the heuristics to predict lossage that 2265 * distinguishes different algorithms. 2266 * 2267 * F.e. after RTO, when all the queue is considered as lost, 2268 * lost_out = packets_out and in_flight = retrans_out. 2269 * 2270 * Essentially, we have now a few algorithms detecting 2271 * lost packets. 2272 * 2273 * If the receiver supports SACK: 2274 * 2275 * RFC6675/3517: It is the conventional algorithm. A packet is 2276 * considered lost if the number of higher sequence packets 2277 * SACKed is greater than or equal the DUPACK thoreshold 2278 * (reordering). This is implemented in tcp_mark_head_lost and 2279 * tcp_update_scoreboard. 2280 * 2281 * RACK (draft-ietf-tcpm-rack-01): it is a newer algorithm 2282 * (2017-) that checks timing instead of counting DUPACKs. 2283 * Essentially a packet is considered lost if it's not S/ACKed 2284 * after RTT + reordering_window, where both metrics are 2285 * dynamically measured and adjusted. This is implemented in 2286 * tcp_rack_mark_lost. 2287 * 2288 * If the receiver does not support SACK: 2289 * 2290 * NewReno (RFC6582): in Recovery we assume that one segment 2291 * is lost (classic Reno). While we are in Recovery and 2292 * a partial ACK arrives, we assume that one more packet 2293 * is lost (NewReno). This heuristics are the same in NewReno 2294 * and SACK. 2295 * 2296 * Really tricky (and requiring careful tuning) part of algorithm 2297 * is hidden in functions tcp_time_to_recover() and tcp_xmit_retransmit_queue(). 2298 * The first determines the moment _when_ we should reduce CWND and, 2299 * hence, slow down forward transmission. In fact, it determines the moment 2300 * when we decide that hole is caused by loss, rather than by a reorder. 2301 * 2302 * tcp_xmit_retransmit_queue() decides, _what_ we should retransmit to fill 2303 * holes, caused by lost packets. 2304 * 2305 * And the most logically complicated part of algorithm is undo 2306 * heuristics. We detect false retransmits due to both too early 2307 * fast retransmit (reordering) and underestimated RTO, analyzing 2308 * timestamps and D-SACKs. When we detect that some segments were 2309 * retransmitted by mistake and CWND reduction was wrong, we undo 2310 * window reduction and abort recovery phase. This logic is hidden 2311 * inside several functions named tcp_try_undo_<something>. 2312 */ 2313 2314 /* This function decides, when we should leave Disordered state 2315 * and enter Recovery phase, reducing congestion window. 2316 * 2317 * Main question: may we further continue forward transmission 2318 * with the same cwnd? 2319 */ 2320 static bool tcp_time_to_recover(struct sock *sk, int flag) 2321 { 2322 struct tcp_sock *tp = tcp_sk(sk); 2323 2324 /* Trick#1: The loss is proven. */ 2325 if (tp->lost_out) 2326 return true; 2327 2328 /* Not-A-Trick#2 : Classic rule... */ 2329 if (!tcp_is_rack(sk) && tcp_dupack_heuristics(tp) > tp->reordering) 2330 return true; 2331 2332 return false; 2333 } 2334 2335 /* Detect loss in event "A" above by marking head of queue up as lost. 2336 * For RFC3517 SACK, a segment is considered lost if it 2337 * has at least tp->reordering SACKed seqments above it; "packets" refers to 2338 * the maximum SACKed segments to pass before reaching this limit. 2339 */ 2340 static void tcp_mark_head_lost(struct sock *sk, int packets, int mark_head) 2341 { 2342 struct tcp_sock *tp = tcp_sk(sk); 2343 struct sk_buff *skb; 2344 int cnt; 2345 /* Use SACK to deduce losses of new sequences sent during recovery */ 2346 const u32 loss_high = tp->snd_nxt; 2347 2348 WARN_ON(packets > tp->packets_out); 2349 skb = tp->lost_skb_hint; 2350 if (skb) { 2351 /* Head already handled? */ 2352 if (mark_head && after(TCP_SKB_CB(skb)->seq, tp->snd_una)) 2353 return; 2354 cnt = tp->lost_cnt_hint; 2355 } else { 2356 skb = tcp_rtx_queue_head(sk); 2357 cnt = 0; 2358 } 2359 2360 skb_rbtree_walk_from(skb) { 2361 /* TODO: do this better */ 2362 /* this is not the most efficient way to do this... */ 2363 tp->lost_skb_hint = skb; 2364 tp->lost_cnt_hint = cnt; 2365 2366 if (after(TCP_SKB_CB(skb)->end_seq, loss_high)) 2367 break; 2368 2369 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED) 2370 cnt += tcp_skb_pcount(skb); 2371 2372 if (cnt > packets) 2373 break; 2374 2375 if (!(TCP_SKB_CB(skb)->sacked & TCPCB_LOST)) 2376 tcp_mark_skb_lost(sk, skb); 2377 2378 if (mark_head) 2379 break; 2380 } 2381 tcp_verify_left_out(tp); 2382 } 2383 2384 /* Account newly detected lost packet(s) */ 2385 2386 static void tcp_update_scoreboard(struct sock *sk, int fast_rexmit) 2387 { 2388 struct tcp_sock *tp = tcp_sk(sk); 2389 2390 if (tcp_is_sack(tp)) { 2391 int sacked_upto = tp->sacked_out - tp->reordering; 2392 if (sacked_upto >= 0) 2393 tcp_mark_head_lost(sk, sacked_upto, 0); 2394 else if (fast_rexmit) 2395 tcp_mark_head_lost(sk, 1, 1); 2396 } 2397 } 2398 2399 static bool tcp_tsopt_ecr_before(const struct tcp_sock *tp, u32 when) 2400 { 2401 return tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr && 2402 before(tp->rx_opt.rcv_tsecr, when); 2403 } 2404 2405 /* skb is spurious retransmitted if the returned timestamp echo 2406 * reply is prior to the skb transmission time 2407 */ 2408 static bool tcp_skb_spurious_retrans(const struct tcp_sock *tp, 2409 const struct sk_buff *skb) 2410 { 2411 return (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS) && 2412 tcp_tsopt_ecr_before(tp, tcp_skb_timestamp(skb)); 2413 } 2414 2415 /* Nothing was retransmitted or returned timestamp is less 2416 * than timestamp of the first retransmission. 2417 */ 2418 static inline bool tcp_packet_delayed(const struct tcp_sock *tp) 2419 { 2420 return tp->retrans_stamp && 2421 tcp_tsopt_ecr_before(tp, tp->retrans_stamp); 2422 } 2423 2424 /* Undo procedures. */ 2425 2426 /* We can clear retrans_stamp when there are no retransmissions in the 2427 * window. It would seem that it is trivially available for us in 2428 * tp->retrans_out, however, that kind of assumptions doesn't consider 2429 * what will happen if errors occur when sending retransmission for the 2430 * second time. ...It could the that such segment has only 2431 * TCPCB_EVER_RETRANS set at the present time. It seems that checking 2432 * the head skb is enough except for some reneging corner cases that 2433 * are not worth the effort. 2434 * 2435 * Main reason for all this complexity is the fact that connection dying 2436 * time now depends on the validity of the retrans_stamp, in particular, 2437 * that successive retransmissions of a segment must not advance 2438 * retrans_stamp under any conditions. 2439 */ 2440 static bool tcp_any_retrans_done(const struct sock *sk) 2441 { 2442 const struct tcp_sock *tp = tcp_sk(sk); 2443 struct sk_buff *skb; 2444 2445 if (tp->retrans_out) 2446 return true; 2447 2448 skb = tcp_rtx_queue_head(sk); 2449 if (unlikely(skb && TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS)) 2450 return true; 2451 2452 return false; 2453 } 2454 2455 static void DBGUNDO(struct sock *sk, const char *msg) 2456 { 2457 #if FASTRETRANS_DEBUG > 1 2458 struct tcp_sock *tp = tcp_sk(sk); 2459 struct inet_sock *inet = inet_sk(sk); 2460 2461 if (sk->sk_family == AF_INET) { 2462 pr_debug("Undo %s %pI4/%u c%u l%u ss%u/%u p%u\n", 2463 msg, 2464 &inet->inet_daddr, ntohs(inet->inet_dport), 2465 tcp_snd_cwnd(tp), tcp_left_out(tp), 2466 tp->snd_ssthresh, tp->prior_ssthresh, 2467 tp->packets_out); 2468 } 2469 #if IS_ENABLED(CONFIG_IPV6) 2470 else if (sk->sk_family == AF_INET6) { 2471 pr_debug("Undo %s %pI6/%u c%u l%u ss%u/%u p%u\n", 2472 msg, 2473 &sk->sk_v6_daddr, ntohs(inet->inet_dport), 2474 tcp_snd_cwnd(tp), tcp_left_out(tp), 2475 tp->snd_ssthresh, tp->prior_ssthresh, 2476 tp->packets_out); 2477 } 2478 #endif 2479 #endif 2480 } 2481 2482 static void tcp_undo_cwnd_reduction(struct sock *sk, bool unmark_loss) 2483 { 2484 struct tcp_sock *tp = tcp_sk(sk); 2485 2486 if (unmark_loss) { 2487 struct sk_buff *skb; 2488 2489 skb_rbtree_walk(skb, &sk->tcp_rtx_queue) { 2490 TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST; 2491 } 2492 tp->lost_out = 0; 2493 tcp_clear_all_retrans_hints(tp); 2494 } 2495 2496 if (tp->prior_ssthresh) { 2497 const struct inet_connection_sock *icsk = inet_csk(sk); 2498 2499 tcp_snd_cwnd_set(tp, icsk->icsk_ca_ops->undo_cwnd(sk)); 2500 2501 if (tp->prior_ssthresh > tp->snd_ssthresh) { 2502 tp->snd_ssthresh = tp->prior_ssthresh; 2503 tcp_ecn_withdraw_cwr(tp); 2504 } 2505 } 2506 tp->snd_cwnd_stamp = tcp_jiffies32; 2507 tp->undo_marker = 0; 2508 tp->rack.advanced = 1; /* Force RACK to re-exam losses */ 2509 } 2510 2511 static inline bool tcp_may_undo(const struct tcp_sock *tp) 2512 { 2513 return tp->undo_marker && (!tp->undo_retrans || tcp_packet_delayed(tp)); 2514 } 2515 2516 /* People celebrate: "We love our President!" */ 2517 static bool tcp_try_undo_recovery(struct sock *sk) 2518 { 2519 struct tcp_sock *tp = tcp_sk(sk); 2520 2521 if (tcp_may_undo(tp)) { 2522 int mib_idx; 2523 2524 /* Happy end! We did not retransmit anything 2525 * or our original transmission succeeded. 2526 */ 2527 DBGUNDO(sk, inet_csk(sk)->icsk_ca_state == TCP_CA_Loss ? "loss" : "retrans"); 2528 tcp_undo_cwnd_reduction(sk, false); 2529 if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss) 2530 mib_idx = LINUX_MIB_TCPLOSSUNDO; 2531 else 2532 mib_idx = LINUX_MIB_TCPFULLUNDO; 2533 2534 NET_INC_STATS(sock_net(sk), mib_idx); 2535 } else if (tp->rack.reo_wnd_persist) { 2536 tp->rack.reo_wnd_persist--; 2537 } 2538 if (tp->snd_una == tp->high_seq && tcp_is_reno(tp)) { 2539 /* Hold old state until something *above* high_seq 2540 * is ACKed. For Reno it is MUST to prevent false 2541 * fast retransmits (RFC2582). SACK TCP is safe. */ 2542 if (!tcp_any_retrans_done(sk)) 2543 tp->retrans_stamp = 0; 2544 return true; 2545 } 2546 tcp_set_ca_state(sk, TCP_CA_Open); 2547 tp->is_sack_reneg = 0; 2548 return false; 2549 } 2550 2551 /* Try to undo cwnd reduction, because D-SACKs acked all retransmitted data */ 2552 static bool tcp_try_undo_dsack(struct sock *sk) 2553 { 2554 struct tcp_sock *tp = tcp_sk(sk); 2555 2556 if (tp->undo_marker && !tp->undo_retrans) { 2557 tp->rack.reo_wnd_persist = min(TCP_RACK_RECOVERY_THRESH, 2558 tp->rack.reo_wnd_persist + 1); 2559 DBGUNDO(sk, "D-SACK"); 2560 tcp_undo_cwnd_reduction(sk, false); 2561 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKUNDO); 2562 return true; 2563 } 2564 return false; 2565 } 2566 2567 /* Undo during loss recovery after partial ACK or using F-RTO. */ 2568 static bool tcp_try_undo_loss(struct sock *sk, bool frto_undo) 2569 { 2570 struct tcp_sock *tp = tcp_sk(sk); 2571 2572 if (frto_undo || tcp_may_undo(tp)) { 2573 tcp_undo_cwnd_reduction(sk, true); 2574 2575 DBGUNDO(sk, "partial loss"); 2576 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPLOSSUNDO); 2577 if (frto_undo) 2578 NET_INC_STATS(sock_net(sk), 2579 LINUX_MIB_TCPSPURIOUSRTOS); 2580 inet_csk(sk)->icsk_retransmits = 0; 2581 if (frto_undo || tcp_is_sack(tp)) { 2582 tcp_set_ca_state(sk, TCP_CA_Open); 2583 tp->is_sack_reneg = 0; 2584 } 2585 return true; 2586 } 2587 return false; 2588 } 2589 2590 /* The cwnd reduction in CWR and Recovery uses the PRR algorithm in RFC 6937. 2591 * It computes the number of packets to send (sndcnt) based on packets newly 2592 * delivered: 2593 * 1) If the packets in flight is larger than ssthresh, PRR spreads the 2594 * cwnd reductions across a full RTT. 2595 * 2) Otherwise PRR uses packet conservation to send as much as delivered. 2596 * But when SND_UNA is acked without further losses, 2597 * slow starts cwnd up to ssthresh to speed up the recovery. 2598 */ 2599 static void tcp_init_cwnd_reduction(struct sock *sk) 2600 { 2601 struct tcp_sock *tp = tcp_sk(sk); 2602 2603 tp->high_seq = tp->snd_nxt; 2604 tp->tlp_high_seq = 0; 2605 tp->snd_cwnd_cnt = 0; 2606 tp->prior_cwnd = tcp_snd_cwnd(tp); 2607 tp->prr_delivered = 0; 2608 tp->prr_out = 0; 2609 tp->snd_ssthresh = inet_csk(sk)->icsk_ca_ops->ssthresh(sk); 2610 tcp_ecn_queue_cwr(tp); 2611 } 2612 2613 void tcp_cwnd_reduction(struct sock *sk, int newly_acked_sacked, int newly_lost, int flag) 2614 { 2615 struct tcp_sock *tp = tcp_sk(sk); 2616 int sndcnt = 0; 2617 int delta = tp->snd_ssthresh - tcp_packets_in_flight(tp); 2618 2619 if (newly_acked_sacked <= 0 || WARN_ON_ONCE(!tp->prior_cwnd)) 2620 return; 2621 2622 tp->prr_delivered += newly_acked_sacked; 2623 if (delta < 0) { 2624 u64 dividend = (u64)tp->snd_ssthresh * tp->prr_delivered + 2625 tp->prior_cwnd - 1; 2626 sndcnt = div_u64(dividend, tp->prior_cwnd) - tp->prr_out; 2627 } else { 2628 sndcnt = max_t(int, tp->prr_delivered - tp->prr_out, 2629 newly_acked_sacked); 2630 if (flag & FLAG_SND_UNA_ADVANCED && !newly_lost) 2631 sndcnt++; 2632 sndcnt = min(delta, sndcnt); 2633 } 2634 /* Force a fast retransmit upon entering fast recovery */ 2635 sndcnt = max(sndcnt, (tp->prr_out ? 0 : 1)); 2636 tcp_snd_cwnd_set(tp, tcp_packets_in_flight(tp) + sndcnt); 2637 } 2638 2639 static inline void tcp_end_cwnd_reduction(struct sock *sk) 2640 { 2641 struct tcp_sock *tp = tcp_sk(sk); 2642 2643 if (inet_csk(sk)->icsk_ca_ops->cong_control) 2644 return; 2645 2646 /* Reset cwnd to ssthresh in CWR or Recovery (unless it's undone) */ 2647 if (tp->snd_ssthresh < TCP_INFINITE_SSTHRESH && 2648 (inet_csk(sk)->icsk_ca_state == TCP_CA_CWR || tp->undo_marker)) { 2649 tcp_snd_cwnd_set(tp, tp->snd_ssthresh); 2650 tp->snd_cwnd_stamp = tcp_jiffies32; 2651 } 2652 tcp_ca_event(sk, CA_EVENT_COMPLETE_CWR); 2653 } 2654 2655 /* Enter CWR state. Disable cwnd undo since congestion is proven with ECN */ 2656 void tcp_enter_cwr(struct sock *sk) 2657 { 2658 struct tcp_sock *tp = tcp_sk(sk); 2659 2660 tp->prior_ssthresh = 0; 2661 if (inet_csk(sk)->icsk_ca_state < TCP_CA_CWR) { 2662 tp->undo_marker = 0; 2663 tcp_init_cwnd_reduction(sk); 2664 tcp_set_ca_state(sk, TCP_CA_CWR); 2665 } 2666 } 2667 EXPORT_SYMBOL(tcp_enter_cwr); 2668 2669 static void tcp_try_keep_open(struct sock *sk) 2670 { 2671 struct tcp_sock *tp = tcp_sk(sk); 2672 int state = TCP_CA_Open; 2673 2674 if (tcp_left_out(tp) || tcp_any_retrans_done(sk)) 2675 state = TCP_CA_Disorder; 2676 2677 if (inet_csk(sk)->icsk_ca_state != state) { 2678 tcp_set_ca_state(sk, state); 2679 tp->high_seq = tp->snd_nxt; 2680 } 2681 } 2682 2683 static void tcp_try_to_open(struct sock *sk, int flag) 2684 { 2685 struct tcp_sock *tp = tcp_sk(sk); 2686 2687 tcp_verify_left_out(tp); 2688 2689 if (!tcp_any_retrans_done(sk)) 2690 tp->retrans_stamp = 0; 2691 2692 if (flag & FLAG_ECE) 2693 tcp_enter_cwr(sk); 2694 2695 if (inet_csk(sk)->icsk_ca_state != TCP_CA_CWR) { 2696 tcp_try_keep_open(sk); 2697 } 2698 } 2699 2700 static void tcp_mtup_probe_failed(struct sock *sk) 2701 { 2702 struct inet_connection_sock *icsk = inet_csk(sk); 2703 2704 icsk->icsk_mtup.search_high = icsk->icsk_mtup.probe_size - 1; 2705 icsk->icsk_mtup.probe_size = 0; 2706 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMTUPFAIL); 2707 } 2708 2709 static void tcp_mtup_probe_success(struct sock *sk) 2710 { 2711 struct tcp_sock *tp = tcp_sk(sk); 2712 struct inet_connection_sock *icsk = inet_csk(sk); 2713 u64 val; 2714 2715 tp->prior_ssthresh = tcp_current_ssthresh(sk); 2716 2717 val = (u64)tcp_snd_cwnd(tp) * tcp_mss_to_mtu(sk, tp->mss_cache); 2718 do_div(val, icsk->icsk_mtup.probe_size); 2719 DEBUG_NET_WARN_ON_ONCE((u32)val != val); 2720 tcp_snd_cwnd_set(tp, max_t(u32, 1U, val)); 2721 2722 tp->snd_cwnd_cnt = 0; 2723 tp->snd_cwnd_stamp = tcp_jiffies32; 2724 tp->snd_ssthresh = tcp_current_ssthresh(sk); 2725 2726 icsk->icsk_mtup.search_low = icsk->icsk_mtup.probe_size; 2727 icsk->icsk_mtup.probe_size = 0; 2728 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie); 2729 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMTUPSUCCESS); 2730 } 2731 2732 /* Do a simple retransmit without using the backoff mechanisms in 2733 * tcp_timer. This is used for path mtu discovery. 2734 * The socket is already locked here. 2735 */ 2736 void tcp_simple_retransmit(struct sock *sk) 2737 { 2738 const struct inet_connection_sock *icsk = inet_csk(sk); 2739 struct tcp_sock *tp = tcp_sk(sk); 2740 struct sk_buff *skb; 2741 int mss; 2742 2743 /* A fastopen SYN request is stored as two separate packets within 2744 * the retransmit queue, this is done by tcp_send_syn_data(). 2745 * As a result simply checking the MSS of the frames in the queue 2746 * will not work for the SYN packet. 2747 * 2748 * Us being here is an indication of a path MTU issue so we can 2749 * assume that the fastopen SYN was lost and just mark all the 2750 * frames in the retransmit queue as lost. We will use an MSS of 2751 * -1 to mark all frames as lost, otherwise compute the current MSS. 2752 */ 2753 if (tp->syn_data && sk->sk_state == TCP_SYN_SENT) 2754 mss = -1; 2755 else 2756 mss = tcp_current_mss(sk); 2757 2758 skb_rbtree_walk(skb, &sk->tcp_rtx_queue) { 2759 if (tcp_skb_seglen(skb) > mss) 2760 tcp_mark_skb_lost(sk, skb); 2761 } 2762 2763 tcp_clear_retrans_hints_partial(tp); 2764 2765 if (!tp->lost_out) 2766 return; 2767 2768 if (tcp_is_reno(tp)) 2769 tcp_limit_reno_sacked(tp); 2770 2771 tcp_verify_left_out(tp); 2772 2773 /* Don't muck with the congestion window here. 2774 * Reason is that we do not increase amount of _data_ 2775 * in network, but units changed and effective 2776 * cwnd/ssthresh really reduced now. 2777 */ 2778 if (icsk->icsk_ca_state != TCP_CA_Loss) { 2779 tp->high_seq = tp->snd_nxt; 2780 tp->snd_ssthresh = tcp_current_ssthresh(sk); 2781 tp->prior_ssthresh = 0; 2782 tp->undo_marker = 0; 2783 tcp_set_ca_state(sk, TCP_CA_Loss); 2784 } 2785 tcp_xmit_retransmit_queue(sk); 2786 } 2787 EXPORT_SYMBOL(tcp_simple_retransmit); 2788 2789 void tcp_enter_recovery(struct sock *sk, bool ece_ack) 2790 { 2791 struct tcp_sock *tp = tcp_sk(sk); 2792 int mib_idx; 2793 2794 if (tcp_is_reno(tp)) 2795 mib_idx = LINUX_MIB_TCPRENORECOVERY; 2796 else 2797 mib_idx = LINUX_MIB_TCPSACKRECOVERY; 2798 2799 NET_INC_STATS(sock_net(sk), mib_idx); 2800 2801 tp->prior_ssthresh = 0; 2802 tcp_init_undo(tp); 2803 2804 if (!tcp_in_cwnd_reduction(sk)) { 2805 if (!ece_ack) 2806 tp->prior_ssthresh = tcp_current_ssthresh(sk); 2807 tcp_init_cwnd_reduction(sk); 2808 } 2809 tcp_set_ca_state(sk, TCP_CA_Recovery); 2810 } 2811 2812 /* Process an ACK in CA_Loss state. Move to CA_Open if lost data are 2813 * recovered or spurious. Otherwise retransmits more on partial ACKs. 2814 */ 2815 static void tcp_process_loss(struct sock *sk, int flag, int num_dupack, 2816 int *rexmit) 2817 { 2818 struct tcp_sock *tp = tcp_sk(sk); 2819 bool recovered = !before(tp->snd_una, tp->high_seq); 2820 2821 if ((flag & FLAG_SND_UNA_ADVANCED || rcu_access_pointer(tp->fastopen_rsk)) && 2822 tcp_try_undo_loss(sk, false)) 2823 return; 2824 2825 if (tp->frto) { /* F-RTO RFC5682 sec 3.1 (sack enhanced version). */ 2826 /* Step 3.b. A timeout is spurious if not all data are 2827 * lost, i.e., never-retransmitted data are (s)acked. 2828 */ 2829 if ((flag & FLAG_ORIG_SACK_ACKED) && 2830 tcp_try_undo_loss(sk, true)) 2831 return; 2832 2833 if (after(tp->snd_nxt, tp->high_seq)) { 2834 if (flag & FLAG_DATA_SACKED || num_dupack) 2835 tp->frto = 0; /* Step 3.a. loss was real */ 2836 } else if (flag & FLAG_SND_UNA_ADVANCED && !recovered) { 2837 tp->high_seq = tp->snd_nxt; 2838 /* Step 2.b. Try send new data (but deferred until cwnd 2839 * is updated in tcp_ack()). Otherwise fall back to 2840 * the conventional recovery. 2841 */ 2842 if (!tcp_write_queue_empty(sk) && 2843 after(tcp_wnd_end(tp), tp->snd_nxt)) { 2844 *rexmit = REXMIT_NEW; 2845 return; 2846 } 2847 tp->frto = 0; 2848 } 2849 } 2850 2851 if (recovered) { 2852 /* F-RTO RFC5682 sec 3.1 step 2.a and 1st part of step 3.a */ 2853 tcp_try_undo_recovery(sk); 2854 return; 2855 } 2856 if (tcp_is_reno(tp)) { 2857 /* A Reno DUPACK means new data in F-RTO step 2.b above are 2858 * delivered. Lower inflight to clock out (re)tranmissions. 2859 */ 2860 if (after(tp->snd_nxt, tp->high_seq) && num_dupack) 2861 tcp_add_reno_sack(sk, num_dupack, flag & FLAG_ECE); 2862 else if (flag & FLAG_SND_UNA_ADVANCED) 2863 tcp_reset_reno_sack(tp); 2864 } 2865 *rexmit = REXMIT_LOST; 2866 } 2867 2868 static bool tcp_force_fast_retransmit(struct sock *sk) 2869 { 2870 struct tcp_sock *tp = tcp_sk(sk); 2871 2872 return after(tcp_highest_sack_seq(tp), 2873 tp->snd_una + tp->reordering * tp->mss_cache); 2874 } 2875 2876 /* Undo during fast recovery after partial ACK. */ 2877 static bool tcp_try_undo_partial(struct sock *sk, u32 prior_snd_una, 2878 bool *do_lost) 2879 { 2880 struct tcp_sock *tp = tcp_sk(sk); 2881 2882 if (tp->undo_marker && tcp_packet_delayed(tp)) { 2883 /* Plain luck! Hole if filled with delayed 2884 * packet, rather than with a retransmit. Check reordering. 2885 */ 2886 tcp_check_sack_reordering(sk, prior_snd_una, 1); 2887 2888 /* We are getting evidence that the reordering degree is higher 2889 * than we realized. If there are no retransmits out then we 2890 * can undo. Otherwise we clock out new packets but do not 2891 * mark more packets lost or retransmit more. 2892 */ 2893 if (tp->retrans_out) 2894 return true; 2895 2896 if (!tcp_any_retrans_done(sk)) 2897 tp->retrans_stamp = 0; 2898 2899 DBGUNDO(sk, "partial recovery"); 2900 tcp_undo_cwnd_reduction(sk, true); 2901 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPPARTIALUNDO); 2902 tcp_try_keep_open(sk); 2903 } else { 2904 /* Partial ACK arrived. Force fast retransmit. */ 2905 *do_lost = tcp_force_fast_retransmit(sk); 2906 } 2907 return false; 2908 } 2909 2910 static void tcp_identify_packet_loss(struct sock *sk, int *ack_flag) 2911 { 2912 struct tcp_sock *tp = tcp_sk(sk); 2913 2914 if (tcp_rtx_queue_empty(sk)) 2915 return; 2916 2917 if (unlikely(tcp_is_reno(tp))) { 2918 tcp_newreno_mark_lost(sk, *ack_flag & FLAG_SND_UNA_ADVANCED); 2919 } else if (tcp_is_rack(sk)) { 2920 u32 prior_retrans = tp->retrans_out; 2921 2922 if (tcp_rack_mark_lost(sk)) 2923 *ack_flag &= ~FLAG_SET_XMIT_TIMER; 2924 if (prior_retrans > tp->retrans_out) 2925 *ack_flag |= FLAG_LOST_RETRANS; 2926 } 2927 } 2928 2929 /* Process an event, which can update packets-in-flight not trivially. 2930 * Main goal of this function is to calculate new estimate for left_out, 2931 * taking into account both packets sitting in receiver's buffer and 2932 * packets lost by network. 2933 * 2934 * Besides that it updates the congestion state when packet loss or ECN 2935 * is detected. But it does not reduce the cwnd, it is done by the 2936 * congestion control later. 2937 * 2938 * It does _not_ decide what to send, it is made in function 2939 * tcp_xmit_retransmit_queue(). 2940 */ 2941 static void tcp_fastretrans_alert(struct sock *sk, const u32 prior_snd_una, 2942 int num_dupack, int *ack_flag, int *rexmit) 2943 { 2944 struct inet_connection_sock *icsk = inet_csk(sk); 2945 struct tcp_sock *tp = tcp_sk(sk); 2946 int fast_rexmit = 0, flag = *ack_flag; 2947 bool ece_ack = flag & FLAG_ECE; 2948 bool do_lost = num_dupack || ((flag & FLAG_DATA_SACKED) && 2949 tcp_force_fast_retransmit(sk)); 2950 2951 if (!tp->packets_out && tp->sacked_out) 2952 tp->sacked_out = 0; 2953 2954 /* Now state machine starts. 2955 * A. ECE, hence prohibit cwnd undoing, the reduction is required. */ 2956 if (ece_ack) 2957 tp->prior_ssthresh = 0; 2958 2959 /* B. In all the states check for reneging SACKs. */ 2960 if (tcp_check_sack_reneging(sk, flag)) 2961 return; 2962 2963 /* C. Check consistency of the current state. */ 2964 tcp_verify_left_out(tp); 2965 2966 /* D. Check state exit conditions. State can be terminated 2967 * when high_seq is ACKed. */ 2968 if (icsk->icsk_ca_state == TCP_CA_Open) { 2969 WARN_ON(tp->retrans_out != 0 && !tp->syn_data); 2970 tp->retrans_stamp = 0; 2971 } else if (!before(tp->snd_una, tp->high_seq)) { 2972 switch (icsk->icsk_ca_state) { 2973 case TCP_CA_CWR: 2974 /* CWR is to be held something *above* high_seq 2975 * is ACKed for CWR bit to reach receiver. */ 2976 if (tp->snd_una != tp->high_seq) { 2977 tcp_end_cwnd_reduction(sk); 2978 tcp_set_ca_state(sk, TCP_CA_Open); 2979 } 2980 break; 2981 2982 case TCP_CA_Recovery: 2983 if (tcp_is_reno(tp)) 2984 tcp_reset_reno_sack(tp); 2985 if (tcp_try_undo_recovery(sk)) 2986 return; 2987 tcp_end_cwnd_reduction(sk); 2988 break; 2989 } 2990 } 2991 2992 /* E. Process state. */ 2993 switch (icsk->icsk_ca_state) { 2994 case TCP_CA_Recovery: 2995 if (!(flag & FLAG_SND_UNA_ADVANCED)) { 2996 if (tcp_is_reno(tp)) 2997 tcp_add_reno_sack(sk, num_dupack, ece_ack); 2998 } else if (tcp_try_undo_partial(sk, prior_snd_una, &do_lost)) 2999 return; 3000 3001 if (tcp_try_undo_dsack(sk)) 3002 tcp_try_keep_open(sk); 3003 3004 tcp_identify_packet_loss(sk, ack_flag); 3005 if (icsk->icsk_ca_state != TCP_CA_Recovery) { 3006 if (!tcp_time_to_recover(sk, flag)) 3007 return; 3008 /* Undo reverts the recovery state. If loss is evident, 3009 * starts a new recovery (e.g. reordering then loss); 3010 */ 3011 tcp_enter_recovery(sk, ece_ack); 3012 } 3013 break; 3014 case TCP_CA_Loss: 3015 tcp_process_loss(sk, flag, num_dupack, rexmit); 3016 tcp_identify_packet_loss(sk, ack_flag); 3017 if (!(icsk->icsk_ca_state == TCP_CA_Open || 3018 (*ack_flag & FLAG_LOST_RETRANS))) 3019 return; 3020 /* Change state if cwnd is undone or retransmits are lost */ 3021 fallthrough; 3022 default: 3023 if (tcp_is_reno(tp)) { 3024 if (flag & FLAG_SND_UNA_ADVANCED) 3025 tcp_reset_reno_sack(tp); 3026 tcp_add_reno_sack(sk, num_dupack, ece_ack); 3027 } 3028 3029 if (icsk->icsk_ca_state <= TCP_CA_Disorder) 3030 tcp_try_undo_dsack(sk); 3031 3032 tcp_identify_packet_loss(sk, ack_flag); 3033 if (!tcp_time_to_recover(sk, flag)) { 3034 tcp_try_to_open(sk, flag); 3035 return; 3036 } 3037 3038 /* MTU probe failure: don't reduce cwnd */ 3039 if (icsk->icsk_ca_state < TCP_CA_CWR && 3040 icsk->icsk_mtup.probe_size && 3041 tp->snd_una == tp->mtu_probe.probe_seq_start) { 3042 tcp_mtup_probe_failed(sk); 3043 /* Restores the reduction we did in tcp_mtup_probe() */ 3044 tcp_snd_cwnd_set(tp, tcp_snd_cwnd(tp) + 1); 3045 tcp_simple_retransmit(sk); 3046 return; 3047 } 3048 3049 /* Otherwise enter Recovery state */ 3050 tcp_enter_recovery(sk, ece_ack); 3051 fast_rexmit = 1; 3052 } 3053 3054 if (!tcp_is_rack(sk) && do_lost) 3055 tcp_update_scoreboard(sk, fast_rexmit); 3056 *rexmit = REXMIT_LOST; 3057 } 3058 3059 static void tcp_update_rtt_min(struct sock *sk, u32 rtt_us, const int flag) 3060 { 3061 u32 wlen = sock_net(sk)->ipv4.sysctl_tcp_min_rtt_wlen * HZ; 3062 struct tcp_sock *tp = tcp_sk(sk); 3063 3064 if ((flag & FLAG_ACK_MAYBE_DELAYED) && rtt_us > tcp_min_rtt(tp)) { 3065 /* If the remote keeps returning delayed ACKs, eventually 3066 * the min filter would pick it up and overestimate the 3067 * prop. delay when it expires. Skip suspected delayed ACKs. 3068 */ 3069 return; 3070 } 3071 minmax_running_min(&tp->rtt_min, wlen, tcp_jiffies32, 3072 rtt_us ? : jiffies_to_usecs(1)); 3073 } 3074 3075 static bool tcp_ack_update_rtt(struct sock *sk, const int flag, 3076 long seq_rtt_us, long sack_rtt_us, 3077 long ca_rtt_us, struct rate_sample *rs) 3078 { 3079 const struct tcp_sock *tp = tcp_sk(sk); 3080 3081 /* Prefer RTT measured from ACK's timing to TS-ECR. This is because 3082 * broken middle-boxes or peers may corrupt TS-ECR fields. But 3083 * Karn's algorithm forbids taking RTT if some retransmitted data 3084 * is acked (RFC6298). 3085 */ 3086 if (seq_rtt_us < 0) 3087 seq_rtt_us = sack_rtt_us; 3088 3089 /* RTTM Rule: A TSecr value received in a segment is used to 3090 * update the averaged RTT measurement only if the segment 3091 * acknowledges some new data, i.e., only if it advances the 3092 * left edge of the send window. 3093 * See draft-ietf-tcplw-high-performance-00, section 3.3. 3094 */ 3095 if (seq_rtt_us < 0 && tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr && 3096 flag & FLAG_ACKED) { 3097 u32 delta = tcp_time_stamp(tp) - tp->rx_opt.rcv_tsecr; 3098 3099 if (likely(delta < INT_MAX / (USEC_PER_SEC / TCP_TS_HZ))) { 3100 if (!delta) 3101 delta = 1; 3102 seq_rtt_us = delta * (USEC_PER_SEC / TCP_TS_HZ); 3103 ca_rtt_us = seq_rtt_us; 3104 } 3105 } 3106 rs->rtt_us = ca_rtt_us; /* RTT of last (S)ACKed packet (or -1) */ 3107 if (seq_rtt_us < 0) 3108 return false; 3109 3110 /* ca_rtt_us >= 0 is counting on the invariant that ca_rtt_us is 3111 * always taken together with ACK, SACK, or TS-opts. Any negative 3112 * values will be skipped with the seq_rtt_us < 0 check above. 3113 */ 3114 tcp_update_rtt_min(sk, ca_rtt_us, flag); 3115 tcp_rtt_estimator(sk, seq_rtt_us); 3116 tcp_set_rto(sk); 3117 3118 /* RFC6298: only reset backoff on valid RTT measurement. */ 3119 inet_csk(sk)->icsk_backoff = 0; 3120 return true; 3121 } 3122 3123 /* Compute time elapsed between (last) SYNACK and the ACK completing 3WHS. */ 3124 void tcp_synack_rtt_meas(struct sock *sk, struct request_sock *req) 3125 { 3126 struct rate_sample rs; 3127 long rtt_us = -1L; 3128 3129 if (req && !req->num_retrans && tcp_rsk(req)->snt_synack) 3130 rtt_us = tcp_stamp_us_delta(tcp_clock_us(), tcp_rsk(req)->snt_synack); 3131 3132 tcp_ack_update_rtt(sk, FLAG_SYN_ACKED, rtt_us, -1L, rtt_us, &rs); 3133 } 3134 3135 3136 static void tcp_cong_avoid(struct sock *sk, u32 ack, u32 acked) 3137 { 3138 const struct inet_connection_sock *icsk = inet_csk(sk); 3139 3140 icsk->icsk_ca_ops->cong_avoid(sk, ack, acked); 3141 tcp_sk(sk)->snd_cwnd_stamp = tcp_jiffies32; 3142 } 3143 3144 /* Restart timer after forward progress on connection. 3145 * RFC2988 recommends to restart timer to now+rto. 3146 */ 3147 void tcp_rearm_rto(struct sock *sk) 3148 { 3149 const struct inet_connection_sock *icsk = inet_csk(sk); 3150 struct tcp_sock *tp = tcp_sk(sk); 3151 3152 /* If the retrans timer is currently being used by Fast Open 3153 * for SYN-ACK retrans purpose, stay put. 3154 */ 3155 if (rcu_access_pointer(tp->fastopen_rsk)) 3156 return; 3157 3158 if (!tp->packets_out) { 3159 inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS); 3160 } else { 3161 u32 rto = inet_csk(sk)->icsk_rto; 3162 /* Offset the time elapsed after installing regular RTO */ 3163 if (icsk->icsk_pending == ICSK_TIME_REO_TIMEOUT || 3164 icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) { 3165 s64 delta_us = tcp_rto_delta_us(sk); 3166 /* delta_us may not be positive if the socket is locked 3167 * when the retrans timer fires and is rescheduled. 3168 */ 3169 rto = usecs_to_jiffies(max_t(int, delta_us, 1)); 3170 } 3171 tcp_reset_xmit_timer(sk, ICSK_TIME_RETRANS, rto, 3172 TCP_RTO_MAX); 3173 } 3174 } 3175 3176 /* Try to schedule a loss probe; if that doesn't work, then schedule an RTO. */ 3177 static void tcp_set_xmit_timer(struct sock *sk) 3178 { 3179 if (!tcp_schedule_loss_probe(sk, true)) 3180 tcp_rearm_rto(sk); 3181 } 3182 3183 /* If we get here, the whole TSO packet has not been acked. */ 3184 static u32 tcp_tso_acked(struct sock *sk, struct sk_buff *skb) 3185 { 3186 struct tcp_sock *tp = tcp_sk(sk); 3187 u32 packets_acked; 3188 3189 BUG_ON(!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una)); 3190 3191 packets_acked = tcp_skb_pcount(skb); 3192 if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq)) 3193 return 0; 3194 packets_acked -= tcp_skb_pcount(skb); 3195 3196 if (packets_acked) { 3197 BUG_ON(tcp_skb_pcount(skb) == 0); 3198 BUG_ON(!before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)); 3199 } 3200 3201 return packets_acked; 3202 } 3203 3204 static void tcp_ack_tstamp(struct sock *sk, struct sk_buff *skb, 3205 const struct sk_buff *ack_skb, u32 prior_snd_una) 3206 { 3207 const struct skb_shared_info *shinfo; 3208 3209 /* Avoid cache line misses to get skb_shinfo() and shinfo->tx_flags */ 3210 if (likely(!TCP_SKB_CB(skb)->txstamp_ack)) 3211 return; 3212 3213 shinfo = skb_shinfo(skb); 3214 if (!before(shinfo->tskey, prior_snd_una) && 3215 before(shinfo->tskey, tcp_sk(sk)->snd_una)) { 3216 tcp_skb_tsorted_save(skb) { 3217 __skb_tstamp_tx(skb, ack_skb, NULL, sk, SCM_TSTAMP_ACK); 3218 } tcp_skb_tsorted_restore(skb); 3219 } 3220 } 3221 3222 /* Remove acknowledged frames from the retransmission queue. If our packet 3223 * is before the ack sequence we can discard it as it's confirmed to have 3224 * arrived at the other end. 3225 */ 3226 static int tcp_clean_rtx_queue(struct sock *sk, const struct sk_buff *ack_skb, 3227 u32 prior_fack, u32 prior_snd_una, 3228 struct tcp_sacktag_state *sack, bool ece_ack) 3229 { 3230 const struct inet_connection_sock *icsk = inet_csk(sk); 3231 u64 first_ackt, last_ackt; 3232 struct tcp_sock *tp = tcp_sk(sk); 3233 u32 prior_sacked = tp->sacked_out; 3234 u32 reord = tp->snd_nxt; /* lowest acked un-retx un-sacked seq */ 3235 struct sk_buff *skb, *next; 3236 bool fully_acked = true; 3237 long sack_rtt_us = -1L; 3238 long seq_rtt_us = -1L; 3239 long ca_rtt_us = -1L; 3240 u32 pkts_acked = 0; 3241 bool rtt_update; 3242 int flag = 0; 3243 3244 first_ackt = 0; 3245 3246 for (skb = skb_rb_first(&sk->tcp_rtx_queue); skb; skb = next) { 3247 struct tcp_skb_cb *scb = TCP_SKB_CB(skb); 3248 const u32 start_seq = scb->seq; 3249 u8 sacked = scb->sacked; 3250 u32 acked_pcount; 3251 3252 /* Determine how many packets and what bytes were acked, tso and else */ 3253 if (after(scb->end_seq, tp->snd_una)) { 3254 if (tcp_skb_pcount(skb) == 1 || 3255 !after(tp->snd_una, scb->seq)) 3256 break; 3257 3258 acked_pcount = tcp_tso_acked(sk, skb); 3259 if (!acked_pcount) 3260 break; 3261 fully_acked = false; 3262 } else { 3263 acked_pcount = tcp_skb_pcount(skb); 3264 } 3265 3266 if (unlikely(sacked & TCPCB_RETRANS)) { 3267 if (sacked & TCPCB_SACKED_RETRANS) 3268 tp->retrans_out -= acked_pcount; 3269 flag |= FLAG_RETRANS_DATA_ACKED; 3270 } else if (!(sacked & TCPCB_SACKED_ACKED)) { 3271 last_ackt = tcp_skb_timestamp_us(skb); 3272 WARN_ON_ONCE(last_ackt == 0); 3273 if (!first_ackt) 3274 first_ackt = last_ackt; 3275 3276 if (before(start_seq, reord)) 3277 reord = start_seq; 3278 if (!after(scb->end_seq, tp->high_seq)) 3279 flag |= FLAG_ORIG_SACK_ACKED; 3280 } 3281 3282 if (sacked & TCPCB_SACKED_ACKED) { 3283 tp->sacked_out -= acked_pcount; 3284 } else if (tcp_is_sack(tp)) { 3285 tcp_count_delivered(tp, acked_pcount, ece_ack); 3286 if (!tcp_skb_spurious_retrans(tp, skb)) 3287 tcp_rack_advance(tp, sacked, scb->end_seq, 3288 tcp_skb_timestamp_us(skb)); 3289 } 3290 if (sacked & TCPCB_LOST) 3291 tp->lost_out -= acked_pcount; 3292 3293 tp->packets_out -= acked_pcount; 3294 pkts_acked += acked_pcount; 3295 tcp_rate_skb_delivered(sk, skb, sack->rate); 3296 3297 /* Initial outgoing SYN's get put onto the write_queue 3298 * just like anything else we transmit. It is not 3299 * true data, and if we misinform our callers that 3300 * this ACK acks real data, we will erroneously exit 3301 * connection startup slow start one packet too 3302 * quickly. This is severely frowned upon behavior. 3303 */ 3304 if (likely(!(scb->tcp_flags & TCPHDR_SYN))) { 3305 flag |= FLAG_DATA_ACKED; 3306 } else { 3307 flag |= FLAG_SYN_ACKED; 3308 tp->retrans_stamp = 0; 3309 } 3310 3311 if (!fully_acked) 3312 break; 3313 3314 tcp_ack_tstamp(sk, skb, ack_skb, prior_snd_una); 3315 3316 next = skb_rb_next(skb); 3317 if (unlikely(skb == tp->retransmit_skb_hint)) 3318 tp->retransmit_skb_hint = NULL; 3319 if (unlikely(skb == tp->lost_skb_hint)) 3320 tp->lost_skb_hint = NULL; 3321 tcp_highest_sack_replace(sk, skb, next); 3322 tcp_rtx_queue_unlink_and_free(skb, sk); 3323 } 3324 3325 if (!skb) 3326 tcp_chrono_stop(sk, TCP_CHRONO_BUSY); 3327 3328 if (likely(between(tp->snd_up, prior_snd_una, tp->snd_una))) 3329 tp->snd_up = tp->snd_una; 3330 3331 if (skb) { 3332 tcp_ack_tstamp(sk, skb, ack_skb, prior_snd_una); 3333 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED) 3334 flag |= FLAG_SACK_RENEGING; 3335 } 3336 3337 if (likely(first_ackt) && !(flag & FLAG_RETRANS_DATA_ACKED)) { 3338 seq_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, first_ackt); 3339 ca_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, last_ackt); 3340 3341 if (pkts_acked == 1 && fully_acked && !prior_sacked && 3342 (tp->snd_una - prior_snd_una) < tp->mss_cache && 3343 sack->rate->prior_delivered + 1 == tp->delivered && 3344 !(flag & (FLAG_CA_ALERT | FLAG_SYN_ACKED))) { 3345 /* Conservatively mark a delayed ACK. It's typically 3346 * from a lone runt packet over the round trip to 3347 * a receiver w/o out-of-order or CE events. 3348 */ 3349 flag |= FLAG_ACK_MAYBE_DELAYED; 3350 } 3351 } 3352 if (sack->first_sackt) { 3353 sack_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, sack->first_sackt); 3354 ca_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, sack->last_sackt); 3355 } 3356 rtt_update = tcp_ack_update_rtt(sk, flag, seq_rtt_us, sack_rtt_us, 3357 ca_rtt_us, sack->rate); 3358 3359 if (flag & FLAG_ACKED) { 3360 flag |= FLAG_SET_XMIT_TIMER; /* set TLP or RTO timer */ 3361 if (unlikely(icsk->icsk_mtup.probe_size && 3362 !after(tp->mtu_probe.probe_seq_end, tp->snd_una))) { 3363 tcp_mtup_probe_success(sk); 3364 } 3365 3366 if (tcp_is_reno(tp)) { 3367 tcp_remove_reno_sacks(sk, pkts_acked, ece_ack); 3368 3369 /* If any of the cumulatively ACKed segments was 3370 * retransmitted, non-SACK case cannot confirm that 3371 * progress was due to original transmission due to 3372 * lack of TCPCB_SACKED_ACKED bits even if some of 3373 * the packets may have been never retransmitted. 3374 */ 3375 if (flag & FLAG_RETRANS_DATA_ACKED) 3376 flag &= ~FLAG_ORIG_SACK_ACKED; 3377 } else { 3378 int delta; 3379 3380 /* Non-retransmitted hole got filled? That's reordering */ 3381 if (before(reord, prior_fack)) 3382 tcp_check_sack_reordering(sk, reord, 0); 3383 3384 delta = prior_sacked - tp->sacked_out; 3385 tp->lost_cnt_hint -= min(tp->lost_cnt_hint, delta); 3386 } 3387 } else if (skb && rtt_update && sack_rtt_us >= 0 && 3388 sack_rtt_us > tcp_stamp_us_delta(tp->tcp_mstamp, 3389 tcp_skb_timestamp_us(skb))) { 3390 /* Do not re-arm RTO if the sack RTT is measured from data sent 3391 * after when the head was last (re)transmitted. Otherwise the 3392 * timeout may continue to extend in loss recovery. 3393 */ 3394 flag |= FLAG_SET_XMIT_TIMER; /* set TLP or RTO timer */ 3395 } 3396 3397 if (icsk->icsk_ca_ops->pkts_acked) { 3398 struct ack_sample sample = { .pkts_acked = pkts_acked, 3399 .rtt_us = sack->rate->rtt_us }; 3400 3401 sample.in_flight = tp->mss_cache * 3402 (tp->delivered - sack->rate->prior_delivered); 3403 icsk->icsk_ca_ops->pkts_acked(sk, &sample); 3404 } 3405 3406 #if FASTRETRANS_DEBUG > 0 3407 WARN_ON((int)tp->sacked_out < 0); 3408 WARN_ON((int)tp->lost_out < 0); 3409 WARN_ON((int)tp->retrans_out < 0); 3410 if (!tp->packets_out && tcp_is_sack(tp)) { 3411 icsk = inet_csk(sk); 3412 if (tp->lost_out) { 3413 pr_debug("Leak l=%u %d\n", 3414 tp->lost_out, icsk->icsk_ca_state); 3415 tp->lost_out = 0; 3416 } 3417 if (tp->sacked_out) { 3418 pr_debug("Leak s=%u %d\n", 3419 tp->sacked_out, icsk->icsk_ca_state); 3420 tp->sacked_out = 0; 3421 } 3422 if (tp->retrans_out) { 3423 pr_debug("Leak r=%u %d\n", 3424 tp->retrans_out, icsk->icsk_ca_state); 3425 tp->retrans_out = 0; 3426 } 3427 } 3428 #endif 3429 return flag; 3430 } 3431 3432 static void tcp_ack_probe(struct sock *sk) 3433 { 3434 struct inet_connection_sock *icsk = inet_csk(sk); 3435 struct sk_buff *head = tcp_send_head(sk); 3436 const struct tcp_sock *tp = tcp_sk(sk); 3437 3438 /* Was it a usable window open? */ 3439 if (!head) 3440 return; 3441 if (!after(TCP_SKB_CB(head)->end_seq, tcp_wnd_end(tp))) { 3442 icsk->icsk_backoff = 0; 3443 icsk->icsk_probes_tstamp = 0; 3444 inet_csk_clear_xmit_timer(sk, ICSK_TIME_PROBE0); 3445 /* Socket must be waked up by subsequent tcp_data_snd_check(). 3446 * This function is not for random using! 3447 */ 3448 } else { 3449 unsigned long when = tcp_probe0_when(sk, TCP_RTO_MAX); 3450 3451 when = tcp_clamp_probe0_to_user_timeout(sk, when); 3452 tcp_reset_xmit_timer(sk, ICSK_TIME_PROBE0, when, TCP_RTO_MAX); 3453 } 3454 } 3455 3456 static inline bool tcp_ack_is_dubious(const struct sock *sk, const int flag) 3457 { 3458 return !(flag & FLAG_NOT_DUP) || (flag & FLAG_CA_ALERT) || 3459 inet_csk(sk)->icsk_ca_state != TCP_CA_Open; 3460 } 3461 3462 /* Decide wheather to run the increase function of congestion control. */ 3463 static inline bool tcp_may_raise_cwnd(const struct sock *sk, const int flag) 3464 { 3465 /* If reordering is high then always grow cwnd whenever data is 3466 * delivered regardless of its ordering. Otherwise stay conservative 3467 * and only grow cwnd on in-order delivery (RFC5681). A stretched ACK w/ 3468 * new SACK or ECE mark may first advance cwnd here and later reduce 3469 * cwnd in tcp_fastretrans_alert() based on more states. 3470 */ 3471 if (tcp_sk(sk)->reordering > 3472 READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_reordering)) 3473 return flag & FLAG_FORWARD_PROGRESS; 3474 3475 return flag & FLAG_DATA_ACKED; 3476 } 3477 3478 /* The "ultimate" congestion control function that aims to replace the rigid 3479 * cwnd increase and decrease control (tcp_cong_avoid,tcp_*cwnd_reduction). 3480 * It's called toward the end of processing an ACK with precise rate 3481 * information. All transmission or retransmission are delayed afterwards. 3482 */ 3483 static void tcp_cong_control(struct sock *sk, u32 ack, u32 acked_sacked, 3484 int flag, const struct rate_sample *rs) 3485 { 3486 const struct inet_connection_sock *icsk = inet_csk(sk); 3487 3488 if (icsk->icsk_ca_ops->cong_control) { 3489 icsk->icsk_ca_ops->cong_control(sk, rs); 3490 return; 3491 } 3492 3493 if (tcp_in_cwnd_reduction(sk)) { 3494 /* Reduce cwnd if state mandates */ 3495 tcp_cwnd_reduction(sk, acked_sacked, rs->losses, flag); 3496 } else if (tcp_may_raise_cwnd(sk, flag)) { 3497 /* Advance cwnd if state allows */ 3498 tcp_cong_avoid(sk, ack, acked_sacked); 3499 } 3500 tcp_update_pacing_rate(sk); 3501 } 3502 3503 /* Check that window update is acceptable. 3504 * The function assumes that snd_una<=ack<=snd_next. 3505 */ 3506 static inline bool tcp_may_update_window(const struct tcp_sock *tp, 3507 const u32 ack, const u32 ack_seq, 3508 const u32 nwin) 3509 { 3510 return after(ack, tp->snd_una) || 3511 after(ack_seq, tp->snd_wl1) || 3512 (ack_seq == tp->snd_wl1 && nwin > tp->snd_wnd); 3513 } 3514 3515 /* If we update tp->snd_una, also update tp->bytes_acked */ 3516 static void tcp_snd_una_update(struct tcp_sock *tp, u32 ack) 3517 { 3518 u32 delta = ack - tp->snd_una; 3519 3520 sock_owned_by_me((struct sock *)tp); 3521 tp->bytes_acked += delta; 3522 tp->snd_una = ack; 3523 } 3524 3525 /* If we update tp->rcv_nxt, also update tp->bytes_received */ 3526 static void tcp_rcv_nxt_update(struct tcp_sock *tp, u32 seq) 3527 { 3528 u32 delta = seq - tp->rcv_nxt; 3529 3530 sock_owned_by_me((struct sock *)tp); 3531 tp->bytes_received += delta; 3532 WRITE_ONCE(tp->rcv_nxt, seq); 3533 } 3534 3535 /* Update our send window. 3536 * 3537 * Window update algorithm, described in RFC793/RFC1122 (used in linux-2.2 3538 * and in FreeBSD. NetBSD's one is even worse.) is wrong. 3539 */ 3540 static int tcp_ack_update_window(struct sock *sk, const struct sk_buff *skb, u32 ack, 3541 u32 ack_seq) 3542 { 3543 struct tcp_sock *tp = tcp_sk(sk); 3544 int flag = 0; 3545 u32 nwin = ntohs(tcp_hdr(skb)->window); 3546 3547 if (likely(!tcp_hdr(skb)->syn)) 3548 nwin <<= tp->rx_opt.snd_wscale; 3549 3550 if (tcp_may_update_window(tp, ack, ack_seq, nwin)) { 3551 flag |= FLAG_WIN_UPDATE; 3552 tcp_update_wl(tp, ack_seq); 3553 3554 if (tp->snd_wnd != nwin) { 3555 tp->snd_wnd = nwin; 3556 3557 /* Note, it is the only place, where 3558 * fast path is recovered for sending TCP. 3559 */ 3560 tp->pred_flags = 0; 3561 tcp_fast_path_check(sk); 3562 3563 if (!tcp_write_queue_empty(sk)) 3564 tcp_slow_start_after_idle_check(sk); 3565 3566 if (nwin > tp->max_window) { 3567 tp->max_window = nwin; 3568 tcp_sync_mss(sk, inet_csk(sk)->icsk_pmtu_cookie); 3569 } 3570 } 3571 } 3572 3573 tcp_snd_una_update(tp, ack); 3574 3575 return flag; 3576 } 3577 3578 static bool __tcp_oow_rate_limited(struct net *net, int mib_idx, 3579 u32 *last_oow_ack_time) 3580 { 3581 if (*last_oow_ack_time) { 3582 s32 elapsed = (s32)(tcp_jiffies32 - *last_oow_ack_time); 3583 3584 if (0 <= elapsed && elapsed < net->ipv4.sysctl_tcp_invalid_ratelimit) { 3585 NET_INC_STATS(net, mib_idx); 3586 return true; /* rate-limited: don't send yet! */ 3587 } 3588 } 3589 3590 *last_oow_ack_time = tcp_jiffies32; 3591 3592 return false; /* not rate-limited: go ahead, send dupack now! */ 3593 } 3594 3595 /* Return true if we're currently rate-limiting out-of-window ACKs and 3596 * thus shouldn't send a dupack right now. We rate-limit dupacks in 3597 * response to out-of-window SYNs or ACKs to mitigate ACK loops or DoS 3598 * attacks that send repeated SYNs or ACKs for the same connection. To 3599 * do this, we do not send a duplicate SYNACK or ACK if the remote 3600 * endpoint is sending out-of-window SYNs or pure ACKs at a high rate. 3601 */ 3602 bool tcp_oow_rate_limited(struct net *net, const struct sk_buff *skb, 3603 int mib_idx, u32 *last_oow_ack_time) 3604 { 3605 /* Data packets without SYNs are not likely part of an ACK loop. */ 3606 if ((TCP_SKB_CB(skb)->seq != TCP_SKB_CB(skb)->end_seq) && 3607 !tcp_hdr(skb)->syn) 3608 return false; 3609 3610 return __tcp_oow_rate_limited(net, mib_idx, last_oow_ack_time); 3611 } 3612 3613 /* RFC 5961 7 [ACK Throttling] */ 3614 static void tcp_send_challenge_ack(struct sock *sk) 3615 { 3616 /* unprotected vars, we dont care of overwrites */ 3617 static u32 challenge_timestamp; 3618 static unsigned int challenge_count; 3619 struct tcp_sock *tp = tcp_sk(sk); 3620 struct net *net = sock_net(sk); 3621 u32 count, now; 3622 3623 /* First check our per-socket dupack rate limit. */ 3624 if (__tcp_oow_rate_limited(net, 3625 LINUX_MIB_TCPACKSKIPPEDCHALLENGE, 3626 &tp->last_oow_ack_time)) 3627 return; 3628 3629 /* Then check host-wide RFC 5961 rate limit. */ 3630 now = jiffies / HZ; 3631 if (now != challenge_timestamp) { 3632 u32 ack_limit = net->ipv4.sysctl_tcp_challenge_ack_limit; 3633 u32 half = (ack_limit + 1) >> 1; 3634 3635 challenge_timestamp = now; 3636 WRITE_ONCE(challenge_count, half + prandom_u32_max(ack_limit)); 3637 } 3638 count = READ_ONCE(challenge_count); 3639 if (count > 0) { 3640 WRITE_ONCE(challenge_count, count - 1); 3641 NET_INC_STATS(net, LINUX_MIB_TCPCHALLENGEACK); 3642 tcp_send_ack(sk); 3643 } 3644 } 3645 3646 static void tcp_store_ts_recent(struct tcp_sock *tp) 3647 { 3648 tp->rx_opt.ts_recent = tp->rx_opt.rcv_tsval; 3649 tp->rx_opt.ts_recent_stamp = ktime_get_seconds(); 3650 } 3651 3652 static void tcp_replace_ts_recent(struct tcp_sock *tp, u32 seq) 3653 { 3654 if (tp->rx_opt.saw_tstamp && !after(seq, tp->rcv_wup)) { 3655 /* PAWS bug workaround wrt. ACK frames, the PAWS discard 3656 * extra check below makes sure this can only happen 3657 * for pure ACK frames. -DaveM 3658 * 3659 * Not only, also it occurs for expired timestamps. 3660 */ 3661 3662 if (tcp_paws_check(&tp->rx_opt, 0)) 3663 tcp_store_ts_recent(tp); 3664 } 3665 } 3666 3667 /* This routine deals with acks during a TLP episode and ends an episode by 3668 * resetting tlp_high_seq. Ref: TLP algorithm in draft-ietf-tcpm-rack 3669 */ 3670 static void tcp_process_tlp_ack(struct sock *sk, u32 ack, int flag) 3671 { 3672 struct tcp_sock *tp = tcp_sk(sk); 3673 3674 if (before(ack, tp->tlp_high_seq)) 3675 return; 3676 3677 if (!tp->tlp_retrans) { 3678 /* TLP of new data has been acknowledged */ 3679 tp->tlp_high_seq = 0; 3680 } else if (flag & FLAG_DSACK_TLP) { 3681 /* This DSACK means original and TLP probe arrived; no loss */ 3682 tp->tlp_high_seq = 0; 3683 } else if (after(ack, tp->tlp_high_seq)) { 3684 /* ACK advances: there was a loss, so reduce cwnd. Reset 3685 * tlp_high_seq in tcp_init_cwnd_reduction() 3686 */ 3687 tcp_init_cwnd_reduction(sk); 3688 tcp_set_ca_state(sk, TCP_CA_CWR); 3689 tcp_end_cwnd_reduction(sk); 3690 tcp_try_keep_open(sk); 3691 NET_INC_STATS(sock_net(sk), 3692 LINUX_MIB_TCPLOSSPROBERECOVERY); 3693 } else if (!(flag & (FLAG_SND_UNA_ADVANCED | 3694 FLAG_NOT_DUP | FLAG_DATA_SACKED))) { 3695 /* Pure dupack: original and TLP probe arrived; no loss */ 3696 tp->tlp_high_seq = 0; 3697 } 3698 } 3699 3700 static inline void tcp_in_ack_event(struct sock *sk, u32 flags) 3701 { 3702 const struct inet_connection_sock *icsk = inet_csk(sk); 3703 3704 if (icsk->icsk_ca_ops->in_ack_event) 3705 icsk->icsk_ca_ops->in_ack_event(sk, flags); 3706 } 3707 3708 /* Congestion control has updated the cwnd already. So if we're in 3709 * loss recovery then now we do any new sends (for FRTO) or 3710 * retransmits (for CA_Loss or CA_recovery) that make sense. 3711 */ 3712 static void tcp_xmit_recovery(struct sock *sk, int rexmit) 3713 { 3714 struct tcp_sock *tp = tcp_sk(sk); 3715 3716 if (rexmit == REXMIT_NONE || sk->sk_state == TCP_SYN_SENT) 3717 return; 3718 3719 if (unlikely(rexmit == REXMIT_NEW)) { 3720 __tcp_push_pending_frames(sk, tcp_current_mss(sk), 3721 TCP_NAGLE_OFF); 3722 if (after(tp->snd_nxt, tp->high_seq)) 3723 return; 3724 tp->frto = 0; 3725 } 3726 tcp_xmit_retransmit_queue(sk); 3727 } 3728 3729 /* Returns the number of packets newly acked or sacked by the current ACK */ 3730 static u32 tcp_newly_delivered(struct sock *sk, u32 prior_delivered, int flag) 3731 { 3732 const struct net *net = sock_net(sk); 3733 struct tcp_sock *tp = tcp_sk(sk); 3734 u32 delivered; 3735 3736 delivered = tp->delivered - prior_delivered; 3737 NET_ADD_STATS(net, LINUX_MIB_TCPDELIVERED, delivered); 3738 if (flag & FLAG_ECE) 3739 NET_ADD_STATS(net, LINUX_MIB_TCPDELIVEREDCE, delivered); 3740 3741 return delivered; 3742 } 3743 3744 /* This routine deals with incoming acks, but not outgoing ones. */ 3745 static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag) 3746 { 3747 struct inet_connection_sock *icsk = inet_csk(sk); 3748 struct tcp_sock *tp = tcp_sk(sk); 3749 struct tcp_sacktag_state sack_state; 3750 struct rate_sample rs = { .prior_delivered = 0 }; 3751 u32 prior_snd_una = tp->snd_una; 3752 bool is_sack_reneg = tp->is_sack_reneg; 3753 u32 ack_seq = TCP_SKB_CB(skb)->seq; 3754 u32 ack = TCP_SKB_CB(skb)->ack_seq; 3755 int num_dupack = 0; 3756 int prior_packets = tp->packets_out; 3757 u32 delivered = tp->delivered; 3758 u32 lost = tp->lost; 3759 int rexmit = REXMIT_NONE; /* Flag to (re)transmit to recover losses */ 3760 u32 prior_fack; 3761 3762 sack_state.first_sackt = 0; 3763 sack_state.rate = &rs; 3764 sack_state.sack_delivered = 0; 3765 3766 /* We very likely will need to access rtx queue. */ 3767 prefetch(sk->tcp_rtx_queue.rb_node); 3768 3769 /* If the ack is older than previous acks 3770 * then we can probably ignore it. 3771 */ 3772 if (before(ack, prior_snd_una)) { 3773 /* RFC 5961 5.2 [Blind Data Injection Attack].[Mitigation] */ 3774 if (before(ack, prior_snd_una - tp->max_window)) { 3775 if (!(flag & FLAG_NO_CHALLENGE_ACK)) 3776 tcp_send_challenge_ack(sk); 3777 return -SKB_DROP_REASON_TCP_TOO_OLD_ACK; 3778 } 3779 goto old_ack; 3780 } 3781 3782 /* If the ack includes data we haven't sent yet, discard 3783 * this segment (RFC793 Section 3.9). 3784 */ 3785 if (after(ack, tp->snd_nxt)) 3786 return -SKB_DROP_REASON_TCP_ACK_UNSENT_DATA; 3787 3788 if (after(ack, prior_snd_una)) { 3789 flag |= FLAG_SND_UNA_ADVANCED; 3790 icsk->icsk_retransmits = 0; 3791 3792 #if IS_ENABLED(CONFIG_TLS_DEVICE) 3793 if (static_branch_unlikely(&clean_acked_data_enabled.key)) 3794 if (icsk->icsk_clean_acked) 3795 icsk->icsk_clean_acked(sk, ack); 3796 #endif 3797 } 3798 3799 prior_fack = tcp_is_sack(tp) ? tcp_highest_sack_seq(tp) : tp->snd_una; 3800 rs.prior_in_flight = tcp_packets_in_flight(tp); 3801 3802 /* ts_recent update must be made after we are sure that the packet 3803 * is in window. 3804 */ 3805 if (flag & FLAG_UPDATE_TS_RECENT) 3806 tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq); 3807 3808 if ((flag & (FLAG_SLOWPATH | FLAG_SND_UNA_ADVANCED)) == 3809 FLAG_SND_UNA_ADVANCED) { 3810 /* Window is constant, pure forward advance. 3811 * No more checks are required. 3812 * Note, we use the fact that SND.UNA>=SND.WL2. 3813 */ 3814 tcp_update_wl(tp, ack_seq); 3815 tcp_snd_una_update(tp, ack); 3816 flag |= FLAG_WIN_UPDATE; 3817 3818 tcp_in_ack_event(sk, CA_ACK_WIN_UPDATE); 3819 3820 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPHPACKS); 3821 } else { 3822 u32 ack_ev_flags = CA_ACK_SLOWPATH; 3823 3824 if (ack_seq != TCP_SKB_CB(skb)->end_seq) 3825 flag |= FLAG_DATA; 3826 else 3827 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPPUREACKS); 3828 3829 flag |= tcp_ack_update_window(sk, skb, ack, ack_seq); 3830 3831 if (TCP_SKB_CB(skb)->sacked) 3832 flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una, 3833 &sack_state); 3834 3835 if (tcp_ecn_rcv_ecn_echo(tp, tcp_hdr(skb))) { 3836 flag |= FLAG_ECE; 3837 ack_ev_flags |= CA_ACK_ECE; 3838 } 3839 3840 if (sack_state.sack_delivered) 3841 tcp_count_delivered(tp, sack_state.sack_delivered, 3842 flag & FLAG_ECE); 3843 3844 if (flag & FLAG_WIN_UPDATE) 3845 ack_ev_flags |= CA_ACK_WIN_UPDATE; 3846 3847 tcp_in_ack_event(sk, ack_ev_flags); 3848 } 3849 3850 /* This is a deviation from RFC3168 since it states that: 3851 * "When the TCP data sender is ready to set the CWR bit after reducing 3852 * the congestion window, it SHOULD set the CWR bit only on the first 3853 * new data packet that it transmits." 3854 * We accept CWR on pure ACKs to be more robust 3855 * with widely-deployed TCP implementations that do this. 3856 */ 3857 tcp_ecn_accept_cwr(sk, skb); 3858 3859 /* We passed data and got it acked, remove any soft error 3860 * log. Something worked... 3861 */ 3862 sk->sk_err_soft = 0; 3863 icsk->icsk_probes_out = 0; 3864 tp->rcv_tstamp = tcp_jiffies32; 3865 if (!prior_packets) 3866 goto no_queue; 3867 3868 /* See if we can take anything off of the retransmit queue. */ 3869 flag |= tcp_clean_rtx_queue(sk, skb, prior_fack, prior_snd_una, 3870 &sack_state, flag & FLAG_ECE); 3871 3872 tcp_rack_update_reo_wnd(sk, &rs); 3873 3874 if (tp->tlp_high_seq) 3875 tcp_process_tlp_ack(sk, ack, flag); 3876 3877 if (tcp_ack_is_dubious(sk, flag)) { 3878 if (!(flag & (FLAG_SND_UNA_ADVANCED | 3879 FLAG_NOT_DUP | FLAG_DSACKING_ACK))) { 3880 num_dupack = 1; 3881 /* Consider if pure acks were aggregated in tcp_add_backlog() */ 3882 if (!(flag & FLAG_DATA)) 3883 num_dupack = max_t(u16, 1, skb_shinfo(skb)->gso_segs); 3884 } 3885 tcp_fastretrans_alert(sk, prior_snd_una, num_dupack, &flag, 3886 &rexmit); 3887 } 3888 3889 /* If needed, reset TLP/RTO timer when RACK doesn't set. */ 3890 if (flag & FLAG_SET_XMIT_TIMER) 3891 tcp_set_xmit_timer(sk); 3892 3893 if ((flag & FLAG_FORWARD_PROGRESS) || !(flag & FLAG_NOT_DUP)) 3894 sk_dst_confirm(sk); 3895 3896 delivered = tcp_newly_delivered(sk, delivered, flag); 3897 lost = tp->lost - lost; /* freshly marked lost */ 3898 rs.is_ack_delayed = !!(flag & FLAG_ACK_MAYBE_DELAYED); 3899 tcp_rate_gen(sk, delivered, lost, is_sack_reneg, sack_state.rate); 3900 tcp_cong_control(sk, ack, delivered, flag, sack_state.rate); 3901 tcp_xmit_recovery(sk, rexmit); 3902 return 1; 3903 3904 no_queue: 3905 /* If data was DSACKed, see if we can undo a cwnd reduction. */ 3906 if (flag & FLAG_DSACKING_ACK) { 3907 tcp_fastretrans_alert(sk, prior_snd_una, num_dupack, &flag, 3908 &rexmit); 3909 tcp_newly_delivered(sk, delivered, flag); 3910 } 3911 /* If this ack opens up a zero window, clear backoff. It was 3912 * being used to time the probes, and is probably far higher than 3913 * it needs to be for normal retransmission. 3914 */ 3915 tcp_ack_probe(sk); 3916 3917 if (tp->tlp_high_seq) 3918 tcp_process_tlp_ack(sk, ack, flag); 3919 return 1; 3920 3921 old_ack: 3922 /* If data was SACKed, tag it and see if we should send more data. 3923 * If data was DSACKed, see if we can undo a cwnd reduction. 3924 */ 3925 if (TCP_SKB_CB(skb)->sacked) { 3926 flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una, 3927 &sack_state); 3928 tcp_fastretrans_alert(sk, prior_snd_una, num_dupack, &flag, 3929 &rexmit); 3930 tcp_newly_delivered(sk, delivered, flag); 3931 tcp_xmit_recovery(sk, rexmit); 3932 } 3933 3934 return 0; 3935 } 3936 3937 static void tcp_parse_fastopen_option(int len, const unsigned char *cookie, 3938 bool syn, struct tcp_fastopen_cookie *foc, 3939 bool exp_opt) 3940 { 3941 /* Valid only in SYN or SYN-ACK with an even length. */ 3942 if (!foc || !syn || len < 0 || (len & 1)) 3943 return; 3944 3945 if (len >= TCP_FASTOPEN_COOKIE_MIN && 3946 len <= TCP_FASTOPEN_COOKIE_MAX) 3947 memcpy(foc->val, cookie, len); 3948 else if (len != 0) 3949 len = -1; 3950 foc->len = len; 3951 foc->exp = exp_opt; 3952 } 3953 3954 static bool smc_parse_options(const struct tcphdr *th, 3955 struct tcp_options_received *opt_rx, 3956 const unsigned char *ptr, 3957 int opsize) 3958 { 3959 #if IS_ENABLED(CONFIG_SMC) 3960 if (static_branch_unlikely(&tcp_have_smc)) { 3961 if (th->syn && !(opsize & 1) && 3962 opsize >= TCPOLEN_EXP_SMC_BASE && 3963 get_unaligned_be32(ptr) == TCPOPT_SMC_MAGIC) { 3964 opt_rx->smc_ok = 1; 3965 return true; 3966 } 3967 } 3968 #endif 3969 return false; 3970 } 3971 3972 /* Try to parse the MSS option from the TCP header. Return 0 on failure, clamped 3973 * value on success. 3974 */ 3975 static u16 tcp_parse_mss_option(const struct tcphdr *th, u16 user_mss) 3976 { 3977 const unsigned char *ptr = (const unsigned char *)(th + 1); 3978 int length = (th->doff * 4) - sizeof(struct tcphdr); 3979 u16 mss = 0; 3980 3981 while (length > 0) { 3982 int opcode = *ptr++; 3983 int opsize; 3984 3985 switch (opcode) { 3986 case TCPOPT_EOL: 3987 return mss; 3988 case TCPOPT_NOP: /* Ref: RFC 793 section 3.1 */ 3989 length--; 3990 continue; 3991 default: 3992 if (length < 2) 3993 return mss; 3994 opsize = *ptr++; 3995 if (opsize < 2) /* "silly options" */ 3996 return mss; 3997 if (opsize > length) 3998 return mss; /* fail on partial options */ 3999 if (opcode == TCPOPT_MSS && opsize == TCPOLEN_MSS) { 4000 u16 in_mss = get_unaligned_be16(ptr); 4001 4002 if (in_mss) { 4003 if (user_mss && user_mss < in_mss) 4004 in_mss = user_mss; 4005 mss = in_mss; 4006 } 4007 } 4008 ptr += opsize - 2; 4009 length -= opsize; 4010 } 4011 } 4012 return mss; 4013 } 4014 4015 /* Look for tcp options. Normally only called on SYN and SYNACK packets. 4016 * But, this can also be called on packets in the established flow when 4017 * the fast version below fails. 4018 */ 4019 void tcp_parse_options(const struct net *net, 4020 const struct sk_buff *skb, 4021 struct tcp_options_received *opt_rx, int estab, 4022 struct tcp_fastopen_cookie *foc) 4023 { 4024 const unsigned char *ptr; 4025 const struct tcphdr *th = tcp_hdr(skb); 4026 int length = (th->doff * 4) - sizeof(struct tcphdr); 4027 4028 ptr = (const unsigned char *)(th + 1); 4029 opt_rx->saw_tstamp = 0; 4030 opt_rx->saw_unknown = 0; 4031 4032 while (length > 0) { 4033 int opcode = *ptr++; 4034 int opsize; 4035 4036 switch (opcode) { 4037 case TCPOPT_EOL: 4038 return; 4039 case TCPOPT_NOP: /* Ref: RFC 793 section 3.1 */ 4040 length--; 4041 continue; 4042 default: 4043 if (length < 2) 4044 return; 4045 opsize = *ptr++; 4046 if (opsize < 2) /* "silly options" */ 4047 return; 4048 if (opsize > length) 4049 return; /* don't parse partial options */ 4050 switch (opcode) { 4051 case TCPOPT_MSS: 4052 if (opsize == TCPOLEN_MSS && th->syn && !estab) { 4053 u16 in_mss = get_unaligned_be16(ptr); 4054 if (in_mss) { 4055 if (opt_rx->user_mss && 4056 opt_rx->user_mss < in_mss) 4057 in_mss = opt_rx->user_mss; 4058 opt_rx->mss_clamp = in_mss; 4059 } 4060 } 4061 break; 4062 case TCPOPT_WINDOW: 4063 if (opsize == TCPOLEN_WINDOW && th->syn && 4064 !estab && READ_ONCE(net->ipv4.sysctl_tcp_window_scaling)) { 4065 __u8 snd_wscale = *(__u8 *)ptr; 4066 opt_rx->wscale_ok = 1; 4067 if (snd_wscale > TCP_MAX_WSCALE) { 4068 net_info_ratelimited("%s: Illegal window scaling value %d > %u received\n", 4069 __func__, 4070 snd_wscale, 4071 TCP_MAX_WSCALE); 4072 snd_wscale = TCP_MAX_WSCALE; 4073 } 4074 opt_rx->snd_wscale = snd_wscale; 4075 } 4076 break; 4077 case TCPOPT_TIMESTAMP: 4078 if ((opsize == TCPOLEN_TIMESTAMP) && 4079 ((estab && opt_rx->tstamp_ok) || 4080 (!estab && READ_ONCE(net->ipv4.sysctl_tcp_timestamps)))) { 4081 opt_rx->saw_tstamp = 1; 4082 opt_rx->rcv_tsval = get_unaligned_be32(ptr); 4083 opt_rx->rcv_tsecr = get_unaligned_be32(ptr + 4); 4084 } 4085 break; 4086 case TCPOPT_SACK_PERM: 4087 if (opsize == TCPOLEN_SACK_PERM && th->syn && 4088 !estab && READ_ONCE(net->ipv4.sysctl_tcp_sack)) { 4089 opt_rx->sack_ok = TCP_SACK_SEEN; 4090 tcp_sack_reset(opt_rx); 4091 } 4092 break; 4093 4094 case TCPOPT_SACK: 4095 if ((opsize >= (TCPOLEN_SACK_BASE + TCPOLEN_SACK_PERBLOCK)) && 4096 !((opsize - TCPOLEN_SACK_BASE) % TCPOLEN_SACK_PERBLOCK) && 4097 opt_rx->sack_ok) { 4098 TCP_SKB_CB(skb)->sacked = (ptr - 2) - (unsigned char *)th; 4099 } 4100 break; 4101 #ifdef CONFIG_TCP_MD5SIG 4102 case TCPOPT_MD5SIG: 4103 /* 4104 * The MD5 Hash has already been 4105 * checked (see tcp_v{4,6}_do_rcv()). 4106 */ 4107 break; 4108 #endif 4109 case TCPOPT_FASTOPEN: 4110 tcp_parse_fastopen_option( 4111 opsize - TCPOLEN_FASTOPEN_BASE, 4112 ptr, th->syn, foc, false); 4113 break; 4114 4115 case TCPOPT_EXP: 4116 /* Fast Open option shares code 254 using a 4117 * 16 bits magic number. 4118 */ 4119 if (opsize >= TCPOLEN_EXP_FASTOPEN_BASE && 4120 get_unaligned_be16(ptr) == 4121 TCPOPT_FASTOPEN_MAGIC) { 4122 tcp_parse_fastopen_option(opsize - 4123 TCPOLEN_EXP_FASTOPEN_BASE, 4124 ptr + 2, th->syn, foc, true); 4125 break; 4126 } 4127 4128 if (smc_parse_options(th, opt_rx, ptr, opsize)) 4129 break; 4130 4131 opt_rx->saw_unknown = 1; 4132 break; 4133 4134 default: 4135 opt_rx->saw_unknown = 1; 4136 } 4137 ptr += opsize-2; 4138 length -= opsize; 4139 } 4140 } 4141 } 4142 EXPORT_SYMBOL(tcp_parse_options); 4143 4144 static bool tcp_parse_aligned_timestamp(struct tcp_sock *tp, const struct tcphdr *th) 4145 { 4146 const __be32 *ptr = (const __be32 *)(th + 1); 4147 4148 if (*ptr == htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16) 4149 | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP)) { 4150 tp->rx_opt.saw_tstamp = 1; 4151 ++ptr; 4152 tp->rx_opt.rcv_tsval = ntohl(*ptr); 4153 ++ptr; 4154 if (*ptr) 4155 tp->rx_opt.rcv_tsecr = ntohl(*ptr) - tp->tsoffset; 4156 else 4157 tp->rx_opt.rcv_tsecr = 0; 4158 return true; 4159 } 4160 return false; 4161 } 4162 4163 /* Fast parse options. This hopes to only see timestamps. 4164 * If it is wrong it falls back on tcp_parse_options(). 4165 */ 4166 static bool tcp_fast_parse_options(const struct net *net, 4167 const struct sk_buff *skb, 4168 const struct tcphdr *th, struct tcp_sock *tp) 4169 { 4170 /* In the spirit of fast parsing, compare doff directly to constant 4171 * values. Because equality is used, short doff can be ignored here. 4172 */ 4173 if (th->doff == (sizeof(*th) / 4)) { 4174 tp->rx_opt.saw_tstamp = 0; 4175 return false; 4176 } else if (tp->rx_opt.tstamp_ok && 4177 th->doff == ((sizeof(*th) + TCPOLEN_TSTAMP_ALIGNED) / 4)) { 4178 if (tcp_parse_aligned_timestamp(tp, th)) 4179 return true; 4180 } 4181 4182 tcp_parse_options(net, skb, &tp->rx_opt, 1, NULL); 4183 if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr) 4184 tp->rx_opt.rcv_tsecr -= tp->tsoffset; 4185 4186 return true; 4187 } 4188 4189 #ifdef CONFIG_TCP_MD5SIG 4190 /* 4191 * Parse MD5 Signature option 4192 */ 4193 const u8 *tcp_parse_md5sig_option(const struct tcphdr *th) 4194 { 4195 int length = (th->doff << 2) - sizeof(*th); 4196 const u8 *ptr = (const u8 *)(th + 1); 4197 4198 /* If not enough data remaining, we can short cut */ 4199 while (length >= TCPOLEN_MD5SIG) { 4200 int opcode = *ptr++; 4201 int opsize; 4202 4203 switch (opcode) { 4204 case TCPOPT_EOL: 4205 return NULL; 4206 case TCPOPT_NOP: 4207 length--; 4208 continue; 4209 default: 4210 opsize = *ptr++; 4211 if (opsize < 2 || opsize > length) 4212 return NULL; 4213 if (opcode == TCPOPT_MD5SIG) 4214 return opsize == TCPOLEN_MD5SIG ? ptr : NULL; 4215 } 4216 ptr += opsize - 2; 4217 length -= opsize; 4218 } 4219 return NULL; 4220 } 4221 EXPORT_SYMBOL(tcp_parse_md5sig_option); 4222 #endif 4223 4224 /* Sorry, PAWS as specified is broken wrt. pure-ACKs -DaveM 4225 * 4226 * It is not fatal. If this ACK does _not_ change critical state (seqs, window) 4227 * it can pass through stack. So, the following predicate verifies that 4228 * this segment is not used for anything but congestion avoidance or 4229 * fast retransmit. Moreover, we even are able to eliminate most of such 4230 * second order effects, if we apply some small "replay" window (~RTO) 4231 * to timestamp space. 4232 * 4233 * All these measures still do not guarantee that we reject wrapped ACKs 4234 * on networks with high bandwidth, when sequence space is recycled fastly, 4235 * but it guarantees that such events will be very rare and do not affect 4236 * connection seriously. This doesn't look nice, but alas, PAWS is really 4237 * buggy extension. 4238 * 4239 * [ Later note. Even worse! It is buggy for segments _with_ data. RFC 4240 * states that events when retransmit arrives after original data are rare. 4241 * It is a blatant lie. VJ forgot about fast retransmit! 8)8) It is 4242 * the biggest problem on large power networks even with minor reordering. 4243 * OK, let's give it small replay window. If peer clock is even 1hz, it is safe 4244 * up to bandwidth of 18Gigabit/sec. 8) ] 4245 */ 4246 4247 static int tcp_disordered_ack(const struct sock *sk, const struct sk_buff *skb) 4248 { 4249 const struct tcp_sock *tp = tcp_sk(sk); 4250 const struct tcphdr *th = tcp_hdr(skb); 4251 u32 seq = TCP_SKB_CB(skb)->seq; 4252 u32 ack = TCP_SKB_CB(skb)->ack_seq; 4253 4254 return (/* 1. Pure ACK with correct sequence number. */ 4255 (th->ack && seq == TCP_SKB_CB(skb)->end_seq && seq == tp->rcv_nxt) && 4256 4257 /* 2. ... and duplicate ACK. */ 4258 ack == tp->snd_una && 4259 4260 /* 3. ... and does not update window. */ 4261 !tcp_may_update_window(tp, ack, seq, ntohs(th->window) << tp->rx_opt.snd_wscale) && 4262 4263 /* 4. ... and sits in replay window. */ 4264 (s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) <= (inet_csk(sk)->icsk_rto * 1024) / HZ); 4265 } 4266 4267 static inline bool tcp_paws_discard(const struct sock *sk, 4268 const struct sk_buff *skb) 4269 { 4270 const struct tcp_sock *tp = tcp_sk(sk); 4271 4272 return !tcp_paws_check(&tp->rx_opt, TCP_PAWS_WINDOW) && 4273 !tcp_disordered_ack(sk, skb); 4274 } 4275 4276 /* Check segment sequence number for validity. 4277 * 4278 * Segment controls are considered valid, if the segment 4279 * fits to the window after truncation to the window. Acceptability 4280 * of data (and SYN, FIN, of course) is checked separately. 4281 * See tcp_data_queue(), for example. 4282 * 4283 * Also, controls (RST is main one) are accepted using RCV.WUP instead 4284 * of RCV.NXT. Peer still did not advance his SND.UNA when we 4285 * delayed ACK, so that hisSND.UNA<=ourRCV.WUP. 4286 * (borrowed from freebsd) 4287 */ 4288 4289 static inline bool tcp_sequence(const struct tcp_sock *tp, u32 seq, u32 end_seq) 4290 { 4291 return !before(end_seq, tp->rcv_wup) && 4292 !after(seq, tp->rcv_nxt + tcp_receive_window(tp)); 4293 } 4294 4295 /* When we get a reset we do this. */ 4296 void tcp_reset(struct sock *sk, struct sk_buff *skb) 4297 { 4298 trace_tcp_receive_reset(sk); 4299 4300 /* mptcp can't tell us to ignore reset pkts, 4301 * so just ignore the return value of mptcp_incoming_options(). 4302 */ 4303 if (sk_is_mptcp(sk)) 4304 mptcp_incoming_options(sk, skb); 4305 4306 /* We want the right error as BSD sees it (and indeed as we do). */ 4307 switch (sk->sk_state) { 4308 case TCP_SYN_SENT: 4309 sk->sk_err = ECONNREFUSED; 4310 break; 4311 case TCP_CLOSE_WAIT: 4312 sk->sk_err = EPIPE; 4313 break; 4314 case TCP_CLOSE: 4315 return; 4316 default: 4317 sk->sk_err = ECONNRESET; 4318 } 4319 /* This barrier is coupled with smp_rmb() in tcp_poll() */ 4320 smp_wmb(); 4321 4322 tcp_write_queue_purge(sk); 4323 tcp_done(sk); 4324 4325 if (!sock_flag(sk, SOCK_DEAD)) 4326 sk_error_report(sk); 4327 } 4328 4329 /* 4330 * Process the FIN bit. This now behaves as it is supposed to work 4331 * and the FIN takes effect when it is validly part of sequence 4332 * space. Not before when we get holes. 4333 * 4334 * If we are ESTABLISHED, a received fin moves us to CLOSE-WAIT 4335 * (and thence onto LAST-ACK and finally, CLOSE, we never enter 4336 * TIME-WAIT) 4337 * 4338 * If we are in FINWAIT-1, a received FIN indicates simultaneous 4339 * close and we go into CLOSING (and later onto TIME-WAIT) 4340 * 4341 * If we are in FINWAIT-2, a received FIN moves us to TIME-WAIT. 4342 */ 4343 void tcp_fin(struct sock *sk) 4344 { 4345 struct tcp_sock *tp = tcp_sk(sk); 4346 4347 inet_csk_schedule_ack(sk); 4348 4349 sk->sk_shutdown |= RCV_SHUTDOWN; 4350 sock_set_flag(sk, SOCK_DONE); 4351 4352 switch (sk->sk_state) { 4353 case TCP_SYN_RECV: 4354 case TCP_ESTABLISHED: 4355 /* Move to CLOSE_WAIT */ 4356 tcp_set_state(sk, TCP_CLOSE_WAIT); 4357 inet_csk_enter_pingpong_mode(sk); 4358 break; 4359 4360 case TCP_CLOSE_WAIT: 4361 case TCP_CLOSING: 4362 /* Received a retransmission of the FIN, do 4363 * nothing. 4364 */ 4365 break; 4366 case TCP_LAST_ACK: 4367 /* RFC793: Remain in the LAST-ACK state. */ 4368 break; 4369 4370 case TCP_FIN_WAIT1: 4371 /* This case occurs when a simultaneous close 4372 * happens, we must ack the received FIN and 4373 * enter the CLOSING state. 4374 */ 4375 tcp_send_ack(sk); 4376 tcp_set_state(sk, TCP_CLOSING); 4377 break; 4378 case TCP_FIN_WAIT2: 4379 /* Received a FIN -- send ACK and enter TIME_WAIT. */ 4380 tcp_send_ack(sk); 4381 tcp_time_wait(sk, TCP_TIME_WAIT, 0); 4382 break; 4383 default: 4384 /* Only TCP_LISTEN and TCP_CLOSE are left, in these 4385 * cases we should never reach this piece of code. 4386 */ 4387 pr_err("%s: Impossible, sk->sk_state=%d\n", 4388 __func__, sk->sk_state); 4389 break; 4390 } 4391 4392 /* It _is_ possible, that we have something out-of-order _after_ FIN. 4393 * Probably, we should reset in this case. For now drop them. 4394 */ 4395 skb_rbtree_purge(&tp->out_of_order_queue); 4396 if (tcp_is_sack(tp)) 4397 tcp_sack_reset(&tp->rx_opt); 4398 sk_mem_reclaim(sk); 4399 4400 if (!sock_flag(sk, SOCK_DEAD)) { 4401 sk->sk_state_change(sk); 4402 4403 /* Do not send POLL_HUP for half duplex close. */ 4404 if (sk->sk_shutdown == SHUTDOWN_MASK || 4405 sk->sk_state == TCP_CLOSE) 4406 sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_HUP); 4407 else 4408 sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_IN); 4409 } 4410 } 4411 4412 static inline bool tcp_sack_extend(struct tcp_sack_block *sp, u32 seq, 4413 u32 end_seq) 4414 { 4415 if (!after(seq, sp->end_seq) && !after(sp->start_seq, end_seq)) { 4416 if (before(seq, sp->start_seq)) 4417 sp->start_seq = seq; 4418 if (after(end_seq, sp->end_seq)) 4419 sp->end_seq = end_seq; 4420 return true; 4421 } 4422 return false; 4423 } 4424 4425 static void tcp_dsack_set(struct sock *sk, u32 seq, u32 end_seq) 4426 { 4427 struct tcp_sock *tp = tcp_sk(sk); 4428 4429 if (tcp_is_sack(tp) && sock_net(sk)->ipv4.sysctl_tcp_dsack) { 4430 int mib_idx; 4431 4432 if (before(seq, tp->rcv_nxt)) 4433 mib_idx = LINUX_MIB_TCPDSACKOLDSENT; 4434 else 4435 mib_idx = LINUX_MIB_TCPDSACKOFOSENT; 4436 4437 NET_INC_STATS(sock_net(sk), mib_idx); 4438 4439 tp->rx_opt.dsack = 1; 4440 tp->duplicate_sack[0].start_seq = seq; 4441 tp->duplicate_sack[0].end_seq = end_seq; 4442 } 4443 } 4444 4445 static void tcp_dsack_extend(struct sock *sk, u32 seq, u32 end_seq) 4446 { 4447 struct tcp_sock *tp = tcp_sk(sk); 4448 4449 if (!tp->rx_opt.dsack) 4450 tcp_dsack_set(sk, seq, end_seq); 4451 else 4452 tcp_sack_extend(tp->duplicate_sack, seq, end_seq); 4453 } 4454 4455 static void tcp_rcv_spurious_retrans(struct sock *sk, const struct sk_buff *skb) 4456 { 4457 /* When the ACK path fails or drops most ACKs, the sender would 4458 * timeout and spuriously retransmit the same segment repeatedly. 4459 * The receiver remembers and reflects via DSACKs. Leverage the 4460 * DSACK state and change the txhash to re-route speculatively. 4461 */ 4462 if (TCP_SKB_CB(skb)->seq == tcp_sk(sk)->duplicate_sack[0].start_seq && 4463 sk_rethink_txhash(sk)) 4464 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDUPLICATEDATAREHASH); 4465 } 4466 4467 static void tcp_send_dupack(struct sock *sk, const struct sk_buff *skb) 4468 { 4469 struct tcp_sock *tp = tcp_sk(sk); 4470 4471 if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq && 4472 before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) { 4473 NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOST); 4474 tcp_enter_quickack_mode(sk, TCP_MAX_QUICKACKS); 4475 4476 if (tcp_is_sack(tp) && sock_net(sk)->ipv4.sysctl_tcp_dsack) { 4477 u32 end_seq = TCP_SKB_CB(skb)->end_seq; 4478 4479 tcp_rcv_spurious_retrans(sk, skb); 4480 if (after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) 4481 end_seq = tp->rcv_nxt; 4482 tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, end_seq); 4483 } 4484 } 4485 4486 tcp_send_ack(sk); 4487 } 4488 4489 /* These routines update the SACK block as out-of-order packets arrive or 4490 * in-order packets close up the sequence space. 4491 */ 4492 static void tcp_sack_maybe_coalesce(struct tcp_sock *tp) 4493 { 4494 int this_sack; 4495 struct tcp_sack_block *sp = &tp->selective_acks[0]; 4496 struct tcp_sack_block *swalk = sp + 1; 4497 4498 /* See if the recent change to the first SACK eats into 4499 * or hits the sequence space of other SACK blocks, if so coalesce. 4500 */ 4501 for (this_sack = 1; this_sack < tp->rx_opt.num_sacks;) { 4502 if (tcp_sack_extend(sp, swalk->start_seq, swalk->end_seq)) { 4503 int i; 4504 4505 /* Zap SWALK, by moving every further SACK up by one slot. 4506 * Decrease num_sacks. 4507 */ 4508 tp->rx_opt.num_sacks--; 4509 for (i = this_sack; i < tp->rx_opt.num_sacks; i++) 4510 sp[i] = sp[i + 1]; 4511 continue; 4512 } 4513 this_sack++; 4514 swalk++; 4515 } 4516 } 4517 4518 static void tcp_sack_compress_send_ack(struct sock *sk) 4519 { 4520 struct tcp_sock *tp = tcp_sk(sk); 4521 4522 if (!tp->compressed_ack) 4523 return; 4524 4525 if (hrtimer_try_to_cancel(&tp->compressed_ack_timer) == 1) 4526 __sock_put(sk); 4527 4528 /* Since we have to send one ack finally, 4529 * substract one from tp->compressed_ack to keep 4530 * LINUX_MIB_TCPACKCOMPRESSED accurate. 4531 */ 4532 NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPACKCOMPRESSED, 4533 tp->compressed_ack - 1); 4534 4535 tp->compressed_ack = 0; 4536 tcp_send_ack(sk); 4537 } 4538 4539 /* Reasonable amount of sack blocks included in TCP SACK option 4540 * The max is 4, but this becomes 3 if TCP timestamps are there. 4541 * Given that SACK packets might be lost, be conservative and use 2. 4542 */ 4543 #define TCP_SACK_BLOCKS_EXPECTED 2 4544 4545 static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq) 4546 { 4547 struct tcp_sock *tp = tcp_sk(sk); 4548 struct tcp_sack_block *sp = &tp->selective_acks[0]; 4549 int cur_sacks = tp->rx_opt.num_sacks; 4550 int this_sack; 4551 4552 if (!cur_sacks) 4553 goto new_sack; 4554 4555 for (this_sack = 0; this_sack < cur_sacks; this_sack++, sp++) { 4556 if (tcp_sack_extend(sp, seq, end_seq)) { 4557 if (this_sack >= TCP_SACK_BLOCKS_EXPECTED) 4558 tcp_sack_compress_send_ack(sk); 4559 /* Rotate this_sack to the first one. */ 4560 for (; this_sack > 0; this_sack--, sp--) 4561 swap(*sp, *(sp - 1)); 4562 if (cur_sacks > 1) 4563 tcp_sack_maybe_coalesce(tp); 4564 return; 4565 } 4566 } 4567 4568 if (this_sack >= TCP_SACK_BLOCKS_EXPECTED) 4569 tcp_sack_compress_send_ack(sk); 4570 4571 /* Could not find an adjacent existing SACK, build a new one, 4572 * put it at the front, and shift everyone else down. We 4573 * always know there is at least one SACK present already here. 4574 * 4575 * If the sack array is full, forget about the last one. 4576 */ 4577 if (this_sack >= TCP_NUM_SACKS) { 4578 this_sack--; 4579 tp->rx_opt.num_sacks--; 4580 sp--; 4581 } 4582 for (; this_sack > 0; this_sack--, sp--) 4583 *sp = *(sp - 1); 4584 4585 new_sack: 4586 /* Build the new head SACK, and we're done. */ 4587 sp->start_seq = seq; 4588 sp->end_seq = end_seq; 4589 tp->rx_opt.num_sacks++; 4590 } 4591 4592 /* RCV.NXT advances, some SACKs should be eaten. */ 4593 4594 static void tcp_sack_remove(struct tcp_sock *tp) 4595 { 4596 struct tcp_sack_block *sp = &tp->selective_acks[0]; 4597 int num_sacks = tp->rx_opt.num_sacks; 4598 int this_sack; 4599 4600 /* Empty ofo queue, hence, all the SACKs are eaten. Clear. */ 4601 if (RB_EMPTY_ROOT(&tp->out_of_order_queue)) { 4602 tp->rx_opt.num_sacks = 0; 4603 return; 4604 } 4605 4606 for (this_sack = 0; this_sack < num_sacks;) { 4607 /* Check if the start of the sack is covered by RCV.NXT. */ 4608 if (!before(tp->rcv_nxt, sp->start_seq)) { 4609 int i; 4610 4611 /* RCV.NXT must cover all the block! */ 4612 WARN_ON(before(tp->rcv_nxt, sp->end_seq)); 4613 4614 /* Zap this SACK, by moving forward any other SACKS. */ 4615 for (i = this_sack+1; i < num_sacks; i++) 4616 tp->selective_acks[i-1] = tp->selective_acks[i]; 4617 num_sacks--; 4618 continue; 4619 } 4620 this_sack++; 4621 sp++; 4622 } 4623 tp->rx_opt.num_sacks = num_sacks; 4624 } 4625 4626 /** 4627 * tcp_try_coalesce - try to merge skb to prior one 4628 * @sk: socket 4629 * @to: prior buffer 4630 * @from: buffer to add in queue 4631 * @fragstolen: pointer to boolean 4632 * 4633 * Before queueing skb @from after @to, try to merge them 4634 * to reduce overall memory use and queue lengths, if cost is small. 4635 * Packets in ofo or receive queues can stay a long time. 4636 * Better try to coalesce them right now to avoid future collapses. 4637 * Returns true if caller should free @from instead of queueing it 4638 */ 4639 static bool tcp_try_coalesce(struct sock *sk, 4640 struct sk_buff *to, 4641 struct sk_buff *from, 4642 bool *fragstolen) 4643 { 4644 int delta; 4645 4646 *fragstolen = false; 4647 4648 /* Its possible this segment overlaps with prior segment in queue */ 4649 if (TCP_SKB_CB(from)->seq != TCP_SKB_CB(to)->end_seq) 4650 return false; 4651 4652 if (!mptcp_skb_can_collapse(to, from)) 4653 return false; 4654 4655 #ifdef CONFIG_TLS_DEVICE 4656 if (from->decrypted != to->decrypted) 4657 return false; 4658 #endif 4659 4660 if (!skb_try_coalesce(to, from, fragstolen, &delta)) 4661 return false; 4662 4663 atomic_add(delta, &sk->sk_rmem_alloc); 4664 sk_mem_charge(sk, delta); 4665 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVCOALESCE); 4666 TCP_SKB_CB(to)->end_seq = TCP_SKB_CB(from)->end_seq; 4667 TCP_SKB_CB(to)->ack_seq = TCP_SKB_CB(from)->ack_seq; 4668 TCP_SKB_CB(to)->tcp_flags |= TCP_SKB_CB(from)->tcp_flags; 4669 4670 if (TCP_SKB_CB(from)->has_rxtstamp) { 4671 TCP_SKB_CB(to)->has_rxtstamp = true; 4672 to->tstamp = from->tstamp; 4673 skb_hwtstamps(to)->hwtstamp = skb_hwtstamps(from)->hwtstamp; 4674 } 4675 4676 return true; 4677 } 4678 4679 static bool tcp_ooo_try_coalesce(struct sock *sk, 4680 struct sk_buff *to, 4681 struct sk_buff *from, 4682 bool *fragstolen) 4683 { 4684 bool res = tcp_try_coalesce(sk, to, from, fragstolen); 4685 4686 /* In case tcp_drop_reason() is called later, update to->gso_segs */ 4687 if (res) { 4688 u32 gso_segs = max_t(u16, 1, skb_shinfo(to)->gso_segs) + 4689 max_t(u16, 1, skb_shinfo(from)->gso_segs); 4690 4691 skb_shinfo(to)->gso_segs = min_t(u32, gso_segs, 0xFFFF); 4692 } 4693 return res; 4694 } 4695 4696 static void tcp_drop_reason(struct sock *sk, struct sk_buff *skb, 4697 enum skb_drop_reason reason) 4698 { 4699 sk_drops_add(sk, skb); 4700 kfree_skb_reason(skb, reason); 4701 } 4702 4703 /* This one checks to see if we can put data from the 4704 * out_of_order queue into the receive_queue. 4705 */ 4706 static void tcp_ofo_queue(struct sock *sk) 4707 { 4708 struct tcp_sock *tp = tcp_sk(sk); 4709 __u32 dsack_high = tp->rcv_nxt; 4710 bool fin, fragstolen, eaten; 4711 struct sk_buff *skb, *tail; 4712 struct rb_node *p; 4713 4714 p = rb_first(&tp->out_of_order_queue); 4715 while (p) { 4716 skb = rb_to_skb(p); 4717 if (after(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) 4718 break; 4719 4720 if (before(TCP_SKB_CB(skb)->seq, dsack_high)) { 4721 __u32 dsack = dsack_high; 4722 if (before(TCP_SKB_CB(skb)->end_seq, dsack_high)) 4723 dsack_high = TCP_SKB_CB(skb)->end_seq; 4724 tcp_dsack_extend(sk, TCP_SKB_CB(skb)->seq, dsack); 4725 } 4726 p = rb_next(p); 4727 rb_erase(&skb->rbnode, &tp->out_of_order_queue); 4728 4729 if (unlikely(!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))) { 4730 tcp_drop_reason(sk, skb, SKB_DROP_REASON_TCP_OFO_DROP); 4731 continue; 4732 } 4733 4734 tail = skb_peek_tail(&sk->sk_receive_queue); 4735 eaten = tail && tcp_try_coalesce(sk, tail, skb, &fragstolen); 4736 tcp_rcv_nxt_update(tp, TCP_SKB_CB(skb)->end_seq); 4737 fin = TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN; 4738 if (!eaten) 4739 __skb_queue_tail(&sk->sk_receive_queue, skb); 4740 else 4741 kfree_skb_partial(skb, fragstolen); 4742 4743 if (unlikely(fin)) { 4744 tcp_fin(sk); 4745 /* tcp_fin() purges tp->out_of_order_queue, 4746 * so we must end this loop right now. 4747 */ 4748 break; 4749 } 4750 } 4751 } 4752 4753 static bool tcp_prune_ofo_queue(struct sock *sk); 4754 static int tcp_prune_queue(struct sock *sk); 4755 4756 static int tcp_try_rmem_schedule(struct sock *sk, struct sk_buff *skb, 4757 unsigned int size) 4758 { 4759 if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf || 4760 !sk_rmem_schedule(sk, skb, size)) { 4761 4762 if (tcp_prune_queue(sk) < 0) 4763 return -1; 4764 4765 while (!sk_rmem_schedule(sk, skb, size)) { 4766 if (!tcp_prune_ofo_queue(sk)) 4767 return -1; 4768 } 4769 } 4770 return 0; 4771 } 4772 4773 static void tcp_data_queue_ofo(struct sock *sk, struct sk_buff *skb) 4774 { 4775 struct tcp_sock *tp = tcp_sk(sk); 4776 struct rb_node **p, *parent; 4777 struct sk_buff *skb1; 4778 u32 seq, end_seq; 4779 bool fragstolen; 4780 4781 tcp_ecn_check_ce(sk, skb); 4782 4783 if (unlikely(tcp_try_rmem_schedule(sk, skb, skb->truesize))) { 4784 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFODROP); 4785 sk->sk_data_ready(sk); 4786 tcp_drop_reason(sk, skb, SKB_DROP_REASON_PROTO_MEM); 4787 return; 4788 } 4789 4790 /* Disable header prediction. */ 4791 tp->pred_flags = 0; 4792 inet_csk_schedule_ack(sk); 4793 4794 tp->rcv_ooopack += max_t(u16, 1, skb_shinfo(skb)->gso_segs); 4795 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFOQUEUE); 4796 seq = TCP_SKB_CB(skb)->seq; 4797 end_seq = TCP_SKB_CB(skb)->end_seq; 4798 4799 p = &tp->out_of_order_queue.rb_node; 4800 if (RB_EMPTY_ROOT(&tp->out_of_order_queue)) { 4801 /* Initial out of order segment, build 1 SACK. */ 4802 if (tcp_is_sack(tp)) { 4803 tp->rx_opt.num_sacks = 1; 4804 tp->selective_acks[0].start_seq = seq; 4805 tp->selective_acks[0].end_seq = end_seq; 4806 } 4807 rb_link_node(&skb->rbnode, NULL, p); 4808 rb_insert_color(&skb->rbnode, &tp->out_of_order_queue); 4809 tp->ooo_last_skb = skb; 4810 goto end; 4811 } 4812 4813 /* In the typical case, we are adding an skb to the end of the list. 4814 * Use of ooo_last_skb avoids the O(Log(N)) rbtree lookup. 4815 */ 4816 if (tcp_ooo_try_coalesce(sk, tp->ooo_last_skb, 4817 skb, &fragstolen)) { 4818 coalesce_done: 4819 /* For non sack flows, do not grow window to force DUPACK 4820 * and trigger fast retransmit. 4821 */ 4822 if (tcp_is_sack(tp)) 4823 tcp_grow_window(sk, skb, true); 4824 kfree_skb_partial(skb, fragstolen); 4825 skb = NULL; 4826 goto add_sack; 4827 } 4828 /* Can avoid an rbtree lookup if we are adding skb after ooo_last_skb */ 4829 if (!before(seq, TCP_SKB_CB(tp->ooo_last_skb)->end_seq)) { 4830 parent = &tp->ooo_last_skb->rbnode; 4831 p = &parent->rb_right; 4832 goto insert; 4833 } 4834 4835 /* Find place to insert this segment. Handle overlaps on the way. */ 4836 parent = NULL; 4837 while (*p) { 4838 parent = *p; 4839 skb1 = rb_to_skb(parent); 4840 if (before(seq, TCP_SKB_CB(skb1)->seq)) { 4841 p = &parent->rb_left; 4842 continue; 4843 } 4844 if (before(seq, TCP_SKB_CB(skb1)->end_seq)) { 4845 if (!after(end_seq, TCP_SKB_CB(skb1)->end_seq)) { 4846 /* All the bits are present. Drop. */ 4847 NET_INC_STATS(sock_net(sk), 4848 LINUX_MIB_TCPOFOMERGE); 4849 tcp_drop_reason(sk, skb, 4850 SKB_DROP_REASON_TCP_OFOMERGE); 4851 skb = NULL; 4852 tcp_dsack_set(sk, seq, end_seq); 4853 goto add_sack; 4854 } 4855 if (after(seq, TCP_SKB_CB(skb1)->seq)) { 4856 /* Partial overlap. */ 4857 tcp_dsack_set(sk, seq, TCP_SKB_CB(skb1)->end_seq); 4858 } else { 4859 /* skb's seq == skb1's seq and skb covers skb1. 4860 * Replace skb1 with skb. 4861 */ 4862 rb_replace_node(&skb1->rbnode, &skb->rbnode, 4863 &tp->out_of_order_queue); 4864 tcp_dsack_extend(sk, 4865 TCP_SKB_CB(skb1)->seq, 4866 TCP_SKB_CB(skb1)->end_seq); 4867 NET_INC_STATS(sock_net(sk), 4868 LINUX_MIB_TCPOFOMERGE); 4869 tcp_drop_reason(sk, skb1, 4870 SKB_DROP_REASON_TCP_OFOMERGE); 4871 goto merge_right; 4872 } 4873 } else if (tcp_ooo_try_coalesce(sk, skb1, 4874 skb, &fragstolen)) { 4875 goto coalesce_done; 4876 } 4877 p = &parent->rb_right; 4878 } 4879 insert: 4880 /* Insert segment into RB tree. */ 4881 rb_link_node(&skb->rbnode, parent, p); 4882 rb_insert_color(&skb->rbnode, &tp->out_of_order_queue); 4883 4884 merge_right: 4885 /* Remove other segments covered by skb. */ 4886 while ((skb1 = skb_rb_next(skb)) != NULL) { 4887 if (!after(end_seq, TCP_SKB_CB(skb1)->seq)) 4888 break; 4889 if (before(end_seq, TCP_SKB_CB(skb1)->end_seq)) { 4890 tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq, 4891 end_seq); 4892 break; 4893 } 4894 rb_erase(&skb1->rbnode, &tp->out_of_order_queue); 4895 tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq, 4896 TCP_SKB_CB(skb1)->end_seq); 4897 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFOMERGE); 4898 tcp_drop_reason(sk, skb1, SKB_DROP_REASON_TCP_OFOMERGE); 4899 } 4900 /* If there is no skb after us, we are the last_skb ! */ 4901 if (!skb1) 4902 tp->ooo_last_skb = skb; 4903 4904 add_sack: 4905 if (tcp_is_sack(tp)) 4906 tcp_sack_new_ofo_skb(sk, seq, end_seq); 4907 end: 4908 if (skb) { 4909 /* For non sack flows, do not grow window to force DUPACK 4910 * and trigger fast retransmit. 4911 */ 4912 if (tcp_is_sack(tp)) 4913 tcp_grow_window(sk, skb, false); 4914 skb_condense(skb); 4915 skb_set_owner_r(skb, sk); 4916 } 4917 } 4918 4919 static int __must_check tcp_queue_rcv(struct sock *sk, struct sk_buff *skb, 4920 bool *fragstolen) 4921 { 4922 int eaten; 4923 struct sk_buff *tail = skb_peek_tail(&sk->sk_receive_queue); 4924 4925 eaten = (tail && 4926 tcp_try_coalesce(sk, tail, 4927 skb, fragstolen)) ? 1 : 0; 4928 tcp_rcv_nxt_update(tcp_sk(sk), TCP_SKB_CB(skb)->end_seq); 4929 if (!eaten) { 4930 __skb_queue_tail(&sk->sk_receive_queue, skb); 4931 skb_set_owner_r(skb, sk); 4932 } 4933 return eaten; 4934 } 4935 4936 int tcp_send_rcvq(struct sock *sk, struct msghdr *msg, size_t size) 4937 { 4938 struct sk_buff *skb; 4939 int err = -ENOMEM; 4940 int data_len = 0; 4941 bool fragstolen; 4942 4943 if (size == 0) 4944 return 0; 4945 4946 if (size > PAGE_SIZE) { 4947 int npages = min_t(size_t, size >> PAGE_SHIFT, MAX_SKB_FRAGS); 4948 4949 data_len = npages << PAGE_SHIFT; 4950 size = data_len + (size & ~PAGE_MASK); 4951 } 4952 skb = alloc_skb_with_frags(size - data_len, data_len, 4953 PAGE_ALLOC_COSTLY_ORDER, 4954 &err, sk->sk_allocation); 4955 if (!skb) 4956 goto err; 4957 4958 skb_put(skb, size - data_len); 4959 skb->data_len = data_len; 4960 skb->len = size; 4961 4962 if (tcp_try_rmem_schedule(sk, skb, skb->truesize)) { 4963 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVQDROP); 4964 goto err_free; 4965 } 4966 4967 err = skb_copy_datagram_from_iter(skb, 0, &msg->msg_iter, size); 4968 if (err) 4969 goto err_free; 4970 4971 TCP_SKB_CB(skb)->seq = tcp_sk(sk)->rcv_nxt; 4972 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq + size; 4973 TCP_SKB_CB(skb)->ack_seq = tcp_sk(sk)->snd_una - 1; 4974 4975 if (tcp_queue_rcv(sk, skb, &fragstolen)) { 4976 WARN_ON_ONCE(fragstolen); /* should not happen */ 4977 __kfree_skb(skb); 4978 } 4979 return size; 4980 4981 err_free: 4982 kfree_skb(skb); 4983 err: 4984 return err; 4985 4986 } 4987 4988 void tcp_data_ready(struct sock *sk) 4989 { 4990 if (tcp_epollin_ready(sk, sk->sk_rcvlowat) || sock_flag(sk, SOCK_DONE)) 4991 sk->sk_data_ready(sk); 4992 } 4993 4994 static void tcp_data_queue(struct sock *sk, struct sk_buff *skb) 4995 { 4996 struct tcp_sock *tp = tcp_sk(sk); 4997 enum skb_drop_reason reason; 4998 bool fragstolen; 4999 int eaten; 5000 5001 /* If a subflow has been reset, the packet should not continue 5002 * to be processed, drop the packet. 5003 */ 5004 if (sk_is_mptcp(sk) && !mptcp_incoming_options(sk, skb)) { 5005 __kfree_skb(skb); 5006 return; 5007 } 5008 5009 if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq) { 5010 __kfree_skb(skb); 5011 return; 5012 } 5013 skb_dst_drop(skb); 5014 __skb_pull(skb, tcp_hdr(skb)->doff * 4); 5015 5016 reason = SKB_DROP_REASON_NOT_SPECIFIED; 5017 tp->rx_opt.dsack = 0; 5018 5019 /* Queue data for delivery to the user. 5020 * Packets in sequence go to the receive queue. 5021 * Out of sequence packets to the out_of_order_queue. 5022 */ 5023 if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt) { 5024 if (tcp_receive_window(tp) == 0) { 5025 reason = SKB_DROP_REASON_TCP_ZEROWINDOW; 5026 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPZEROWINDOWDROP); 5027 goto out_of_window; 5028 } 5029 5030 /* Ok. In sequence. In window. */ 5031 queue_and_out: 5032 if (skb_queue_len(&sk->sk_receive_queue) == 0) 5033 sk_forced_mem_schedule(sk, skb->truesize); 5034 else if (tcp_try_rmem_schedule(sk, skb, skb->truesize)) { 5035 reason = SKB_DROP_REASON_PROTO_MEM; 5036 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVQDROP); 5037 sk->sk_data_ready(sk); 5038 goto drop; 5039 } 5040 5041 eaten = tcp_queue_rcv(sk, skb, &fragstolen); 5042 if (skb->len) 5043 tcp_event_data_recv(sk, skb); 5044 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) 5045 tcp_fin(sk); 5046 5047 if (!RB_EMPTY_ROOT(&tp->out_of_order_queue)) { 5048 tcp_ofo_queue(sk); 5049 5050 /* RFC5681. 4.2. SHOULD send immediate ACK, when 5051 * gap in queue is filled. 5052 */ 5053 if (RB_EMPTY_ROOT(&tp->out_of_order_queue)) 5054 inet_csk(sk)->icsk_ack.pending |= ICSK_ACK_NOW; 5055 } 5056 5057 if (tp->rx_opt.num_sacks) 5058 tcp_sack_remove(tp); 5059 5060 tcp_fast_path_check(sk); 5061 5062 if (eaten > 0) 5063 kfree_skb_partial(skb, fragstolen); 5064 if (!sock_flag(sk, SOCK_DEAD)) 5065 tcp_data_ready(sk); 5066 return; 5067 } 5068 5069 if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) { 5070 tcp_rcv_spurious_retrans(sk, skb); 5071 /* A retransmit, 2nd most common case. Force an immediate ack. */ 5072 reason = SKB_DROP_REASON_TCP_OLD_DATA; 5073 NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOST); 5074 tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq); 5075 5076 out_of_window: 5077 tcp_enter_quickack_mode(sk, TCP_MAX_QUICKACKS); 5078 inet_csk_schedule_ack(sk); 5079 drop: 5080 tcp_drop_reason(sk, skb, reason); 5081 return; 5082 } 5083 5084 /* Out of window. F.e. zero window probe. */ 5085 if (!before(TCP_SKB_CB(skb)->seq, 5086 tp->rcv_nxt + tcp_receive_window(tp))) { 5087 reason = SKB_DROP_REASON_TCP_OVERWINDOW; 5088 goto out_of_window; 5089 } 5090 5091 if (before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) { 5092 /* Partial packet, seq < rcv_next < end_seq */ 5093 tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, tp->rcv_nxt); 5094 5095 /* If window is closed, drop tail of packet. But after 5096 * remembering D-SACK for its head made in previous line. 5097 */ 5098 if (!tcp_receive_window(tp)) { 5099 reason = SKB_DROP_REASON_TCP_ZEROWINDOW; 5100 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPZEROWINDOWDROP); 5101 goto out_of_window; 5102 } 5103 goto queue_and_out; 5104 } 5105 5106 tcp_data_queue_ofo(sk, skb); 5107 } 5108 5109 static struct sk_buff *tcp_skb_next(struct sk_buff *skb, struct sk_buff_head *list) 5110 { 5111 if (list) 5112 return !skb_queue_is_last(list, skb) ? skb->next : NULL; 5113 5114 return skb_rb_next(skb); 5115 } 5116 5117 static struct sk_buff *tcp_collapse_one(struct sock *sk, struct sk_buff *skb, 5118 struct sk_buff_head *list, 5119 struct rb_root *root) 5120 { 5121 struct sk_buff *next = tcp_skb_next(skb, list); 5122 5123 if (list) 5124 __skb_unlink(skb, list); 5125 else 5126 rb_erase(&skb->rbnode, root); 5127 5128 __kfree_skb(skb); 5129 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVCOLLAPSED); 5130 5131 return next; 5132 } 5133 5134 /* Insert skb into rb tree, ordered by TCP_SKB_CB(skb)->seq */ 5135 void tcp_rbtree_insert(struct rb_root *root, struct sk_buff *skb) 5136 { 5137 struct rb_node **p = &root->rb_node; 5138 struct rb_node *parent = NULL; 5139 struct sk_buff *skb1; 5140 5141 while (*p) { 5142 parent = *p; 5143 skb1 = rb_to_skb(parent); 5144 if (before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb1)->seq)) 5145 p = &parent->rb_left; 5146 else 5147 p = &parent->rb_right; 5148 } 5149 rb_link_node(&skb->rbnode, parent, p); 5150 rb_insert_color(&skb->rbnode, root); 5151 } 5152 5153 /* Collapse contiguous sequence of skbs head..tail with 5154 * sequence numbers start..end. 5155 * 5156 * If tail is NULL, this means until the end of the queue. 5157 * 5158 * Segments with FIN/SYN are not collapsed (only because this 5159 * simplifies code) 5160 */ 5161 static void 5162 tcp_collapse(struct sock *sk, struct sk_buff_head *list, struct rb_root *root, 5163 struct sk_buff *head, struct sk_buff *tail, u32 start, u32 end) 5164 { 5165 struct sk_buff *skb = head, *n; 5166 struct sk_buff_head tmp; 5167 bool end_of_skbs; 5168 5169 /* First, check that queue is collapsible and find 5170 * the point where collapsing can be useful. 5171 */ 5172 restart: 5173 for (end_of_skbs = true; skb != NULL && skb != tail; skb = n) { 5174 n = tcp_skb_next(skb, list); 5175 5176 /* No new bits? It is possible on ofo queue. */ 5177 if (!before(start, TCP_SKB_CB(skb)->end_seq)) { 5178 skb = tcp_collapse_one(sk, skb, list, root); 5179 if (!skb) 5180 break; 5181 goto restart; 5182 } 5183 5184 /* The first skb to collapse is: 5185 * - not SYN/FIN and 5186 * - bloated or contains data before "start" or 5187 * overlaps to the next one and mptcp allow collapsing. 5188 */ 5189 if (!(TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)) && 5190 (tcp_win_from_space(sk, skb->truesize) > skb->len || 5191 before(TCP_SKB_CB(skb)->seq, start))) { 5192 end_of_skbs = false; 5193 break; 5194 } 5195 5196 if (n && n != tail && mptcp_skb_can_collapse(skb, n) && 5197 TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(n)->seq) { 5198 end_of_skbs = false; 5199 break; 5200 } 5201 5202 /* Decided to skip this, advance start seq. */ 5203 start = TCP_SKB_CB(skb)->end_seq; 5204 } 5205 if (end_of_skbs || 5206 (TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN))) 5207 return; 5208 5209 __skb_queue_head_init(&tmp); 5210 5211 while (before(start, end)) { 5212 int copy = min_t(int, SKB_MAX_ORDER(0, 0), end - start); 5213 struct sk_buff *nskb; 5214 5215 nskb = alloc_skb(copy, GFP_ATOMIC); 5216 if (!nskb) 5217 break; 5218 5219 memcpy(nskb->cb, skb->cb, sizeof(skb->cb)); 5220 #ifdef CONFIG_TLS_DEVICE 5221 nskb->decrypted = skb->decrypted; 5222 #endif 5223 TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(nskb)->end_seq = start; 5224 if (list) 5225 __skb_queue_before(list, skb, nskb); 5226 else 5227 __skb_queue_tail(&tmp, nskb); /* defer rbtree insertion */ 5228 skb_set_owner_r(nskb, sk); 5229 mptcp_skb_ext_move(nskb, skb); 5230 5231 /* Copy data, releasing collapsed skbs. */ 5232 while (copy > 0) { 5233 int offset = start - TCP_SKB_CB(skb)->seq; 5234 int size = TCP_SKB_CB(skb)->end_seq - start; 5235 5236 BUG_ON(offset < 0); 5237 if (size > 0) { 5238 size = min(copy, size); 5239 if (skb_copy_bits(skb, offset, skb_put(nskb, size), size)) 5240 BUG(); 5241 TCP_SKB_CB(nskb)->end_seq += size; 5242 copy -= size; 5243 start += size; 5244 } 5245 if (!before(start, TCP_SKB_CB(skb)->end_seq)) { 5246 skb = tcp_collapse_one(sk, skb, list, root); 5247 if (!skb || 5248 skb == tail || 5249 !mptcp_skb_can_collapse(nskb, skb) || 5250 (TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN))) 5251 goto end; 5252 #ifdef CONFIG_TLS_DEVICE 5253 if (skb->decrypted != nskb->decrypted) 5254 goto end; 5255 #endif 5256 } 5257 } 5258 } 5259 end: 5260 skb_queue_walk_safe(&tmp, skb, n) 5261 tcp_rbtree_insert(root, skb); 5262 } 5263 5264 /* Collapse ofo queue. Algorithm: select contiguous sequence of skbs 5265 * and tcp_collapse() them until all the queue is collapsed. 5266 */ 5267 static void tcp_collapse_ofo_queue(struct sock *sk) 5268 { 5269 struct tcp_sock *tp = tcp_sk(sk); 5270 u32 range_truesize, sum_tiny = 0; 5271 struct sk_buff *skb, *head; 5272 u32 start, end; 5273 5274 skb = skb_rb_first(&tp->out_of_order_queue); 5275 new_range: 5276 if (!skb) { 5277 tp->ooo_last_skb = skb_rb_last(&tp->out_of_order_queue); 5278 return; 5279 } 5280 start = TCP_SKB_CB(skb)->seq; 5281 end = TCP_SKB_CB(skb)->end_seq; 5282 range_truesize = skb->truesize; 5283 5284 for (head = skb;;) { 5285 skb = skb_rb_next(skb); 5286 5287 /* Range is terminated when we see a gap or when 5288 * we are at the queue end. 5289 */ 5290 if (!skb || 5291 after(TCP_SKB_CB(skb)->seq, end) || 5292 before(TCP_SKB_CB(skb)->end_seq, start)) { 5293 /* Do not attempt collapsing tiny skbs */ 5294 if (range_truesize != head->truesize || 5295 end - start >= SKB_WITH_OVERHEAD(SK_MEM_QUANTUM)) { 5296 tcp_collapse(sk, NULL, &tp->out_of_order_queue, 5297 head, skb, start, end); 5298 } else { 5299 sum_tiny += range_truesize; 5300 if (sum_tiny > sk->sk_rcvbuf >> 3) 5301 return; 5302 } 5303 goto new_range; 5304 } 5305 5306 range_truesize += skb->truesize; 5307 if (unlikely(before(TCP_SKB_CB(skb)->seq, start))) 5308 start = TCP_SKB_CB(skb)->seq; 5309 if (after(TCP_SKB_CB(skb)->end_seq, end)) 5310 end = TCP_SKB_CB(skb)->end_seq; 5311 } 5312 } 5313 5314 /* 5315 * Clean the out-of-order queue to make room. 5316 * We drop high sequences packets to : 5317 * 1) Let a chance for holes to be filled. 5318 * 2) not add too big latencies if thousands of packets sit there. 5319 * (But if application shrinks SO_RCVBUF, we could still end up 5320 * freeing whole queue here) 5321 * 3) Drop at least 12.5 % of sk_rcvbuf to avoid malicious attacks. 5322 * 5323 * Return true if queue has shrunk. 5324 */ 5325 static bool tcp_prune_ofo_queue(struct sock *sk) 5326 { 5327 struct tcp_sock *tp = tcp_sk(sk); 5328 struct rb_node *node, *prev; 5329 int goal; 5330 5331 if (RB_EMPTY_ROOT(&tp->out_of_order_queue)) 5332 return false; 5333 5334 NET_INC_STATS(sock_net(sk), LINUX_MIB_OFOPRUNED); 5335 goal = sk->sk_rcvbuf >> 3; 5336 node = &tp->ooo_last_skb->rbnode; 5337 do { 5338 prev = rb_prev(node); 5339 rb_erase(node, &tp->out_of_order_queue); 5340 goal -= rb_to_skb(node)->truesize; 5341 tcp_drop_reason(sk, rb_to_skb(node), 5342 SKB_DROP_REASON_TCP_OFO_QUEUE_PRUNE); 5343 if (!prev || goal <= 0) { 5344 sk_mem_reclaim(sk); 5345 if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf && 5346 !tcp_under_memory_pressure(sk)) 5347 break; 5348 goal = sk->sk_rcvbuf >> 3; 5349 } 5350 node = prev; 5351 } while (node); 5352 tp->ooo_last_skb = rb_to_skb(prev); 5353 5354 /* Reset SACK state. A conforming SACK implementation will 5355 * do the same at a timeout based retransmit. When a connection 5356 * is in a sad state like this, we care only about integrity 5357 * of the connection not performance. 5358 */ 5359 if (tp->rx_opt.sack_ok) 5360 tcp_sack_reset(&tp->rx_opt); 5361 return true; 5362 } 5363 5364 /* Reduce allocated memory if we can, trying to get 5365 * the socket within its memory limits again. 5366 * 5367 * Return less than zero if we should start dropping frames 5368 * until the socket owning process reads some of the data 5369 * to stabilize the situation. 5370 */ 5371 static int tcp_prune_queue(struct sock *sk) 5372 { 5373 struct tcp_sock *tp = tcp_sk(sk); 5374 5375 NET_INC_STATS(sock_net(sk), LINUX_MIB_PRUNECALLED); 5376 5377 if (atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf) 5378 tcp_clamp_window(sk); 5379 else if (tcp_under_memory_pressure(sk)) 5380 tcp_adjust_rcv_ssthresh(sk); 5381 5382 if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf) 5383 return 0; 5384 5385 tcp_collapse_ofo_queue(sk); 5386 if (!skb_queue_empty(&sk->sk_receive_queue)) 5387 tcp_collapse(sk, &sk->sk_receive_queue, NULL, 5388 skb_peek(&sk->sk_receive_queue), 5389 NULL, 5390 tp->copied_seq, tp->rcv_nxt); 5391 sk_mem_reclaim(sk); 5392 5393 if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf) 5394 return 0; 5395 5396 /* Collapsing did not help, destructive actions follow. 5397 * This must not ever occur. */ 5398 5399 tcp_prune_ofo_queue(sk); 5400 5401 if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf) 5402 return 0; 5403 5404 /* If we are really being abused, tell the caller to silently 5405 * drop receive data on the floor. It will get retransmitted 5406 * and hopefully then we'll have sufficient space. 5407 */ 5408 NET_INC_STATS(sock_net(sk), LINUX_MIB_RCVPRUNED); 5409 5410 /* Massive buffer overcommit. */ 5411 tp->pred_flags = 0; 5412 return -1; 5413 } 5414 5415 static bool tcp_should_expand_sndbuf(struct sock *sk) 5416 { 5417 const struct tcp_sock *tp = tcp_sk(sk); 5418 5419 /* If the user specified a specific send buffer setting, do 5420 * not modify it. 5421 */ 5422 if (sk->sk_userlocks & SOCK_SNDBUF_LOCK) 5423 return false; 5424 5425 /* If we are under global TCP memory pressure, do not expand. */ 5426 if (tcp_under_memory_pressure(sk)) { 5427 int unused_mem = sk_unused_reserved_mem(sk); 5428 5429 /* Adjust sndbuf according to reserved mem. But make sure 5430 * it never goes below SOCK_MIN_SNDBUF. 5431 * See sk_stream_moderate_sndbuf() for more details. 5432 */ 5433 if (unused_mem > SOCK_MIN_SNDBUF) 5434 WRITE_ONCE(sk->sk_sndbuf, unused_mem); 5435 5436 return false; 5437 } 5438 5439 /* If we are under soft global TCP memory pressure, do not expand. */ 5440 if (sk_memory_allocated(sk) >= sk_prot_mem_limits(sk, 0)) 5441 return false; 5442 5443 /* If we filled the congestion window, do not expand. */ 5444 if (tcp_packets_in_flight(tp) >= tcp_snd_cwnd(tp)) 5445 return false; 5446 5447 return true; 5448 } 5449 5450 static void tcp_new_space(struct sock *sk) 5451 { 5452 struct tcp_sock *tp = tcp_sk(sk); 5453 5454 if (tcp_should_expand_sndbuf(sk)) { 5455 tcp_sndbuf_expand(sk); 5456 tp->snd_cwnd_stamp = tcp_jiffies32; 5457 } 5458 5459 INDIRECT_CALL_1(sk->sk_write_space, sk_stream_write_space, sk); 5460 } 5461 5462 /* Caller made space either from: 5463 * 1) Freeing skbs in rtx queues (after tp->snd_una has advanced) 5464 * 2) Sent skbs from output queue (and thus advancing tp->snd_nxt) 5465 * 5466 * We might be able to generate EPOLLOUT to the application if: 5467 * 1) Space consumed in output/rtx queues is below sk->sk_sndbuf/2 5468 * 2) notsent amount (tp->write_seq - tp->snd_nxt) became 5469 * small enough that tcp_stream_memory_free() decides it 5470 * is time to generate EPOLLOUT. 5471 */ 5472 void tcp_check_space(struct sock *sk) 5473 { 5474 /* pairs with tcp_poll() */ 5475 smp_mb(); 5476 if (sk->sk_socket && 5477 test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) { 5478 tcp_new_space(sk); 5479 if (!test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) 5480 tcp_chrono_stop(sk, TCP_CHRONO_SNDBUF_LIMITED); 5481 } 5482 } 5483 5484 static inline void tcp_data_snd_check(struct sock *sk) 5485 { 5486 tcp_push_pending_frames(sk); 5487 tcp_check_space(sk); 5488 } 5489 5490 /* 5491 * Check if sending an ack is needed. 5492 */ 5493 static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible) 5494 { 5495 struct tcp_sock *tp = tcp_sk(sk); 5496 unsigned long rtt, delay; 5497 5498 /* More than one full frame received... */ 5499 if (((tp->rcv_nxt - tp->rcv_wup) > inet_csk(sk)->icsk_ack.rcv_mss && 5500 /* ... and right edge of window advances far enough. 5501 * (tcp_recvmsg() will send ACK otherwise). 5502 * If application uses SO_RCVLOWAT, we want send ack now if 5503 * we have not received enough bytes to satisfy the condition. 5504 */ 5505 (tp->rcv_nxt - tp->copied_seq < sk->sk_rcvlowat || 5506 __tcp_select_window(sk) >= tp->rcv_wnd)) || 5507 /* We ACK each frame or... */ 5508 tcp_in_quickack_mode(sk) || 5509 /* Protocol state mandates a one-time immediate ACK */ 5510 inet_csk(sk)->icsk_ack.pending & ICSK_ACK_NOW) { 5511 send_now: 5512 tcp_send_ack(sk); 5513 return; 5514 } 5515 5516 if (!ofo_possible || RB_EMPTY_ROOT(&tp->out_of_order_queue)) { 5517 tcp_send_delayed_ack(sk); 5518 return; 5519 } 5520 5521 if (!tcp_is_sack(tp) || 5522 tp->compressed_ack >= sock_net(sk)->ipv4.sysctl_tcp_comp_sack_nr) 5523 goto send_now; 5524 5525 if (tp->compressed_ack_rcv_nxt != tp->rcv_nxt) { 5526 tp->compressed_ack_rcv_nxt = tp->rcv_nxt; 5527 tp->dup_ack_counter = 0; 5528 } 5529 if (tp->dup_ack_counter < TCP_FASTRETRANS_THRESH) { 5530 tp->dup_ack_counter++; 5531 goto send_now; 5532 } 5533 tp->compressed_ack++; 5534 if (hrtimer_is_queued(&tp->compressed_ack_timer)) 5535 return; 5536 5537 /* compress ack timer : 5 % of rtt, but no more than tcp_comp_sack_delay_ns */ 5538 5539 rtt = tp->rcv_rtt_est.rtt_us; 5540 if (tp->srtt_us && tp->srtt_us < rtt) 5541 rtt = tp->srtt_us; 5542 5543 delay = min_t(unsigned long, sock_net(sk)->ipv4.sysctl_tcp_comp_sack_delay_ns, 5544 rtt * (NSEC_PER_USEC >> 3)/20); 5545 sock_hold(sk); 5546 hrtimer_start_range_ns(&tp->compressed_ack_timer, ns_to_ktime(delay), 5547 sock_net(sk)->ipv4.sysctl_tcp_comp_sack_slack_ns, 5548 HRTIMER_MODE_REL_PINNED_SOFT); 5549 } 5550 5551 static inline void tcp_ack_snd_check(struct sock *sk) 5552 { 5553 if (!inet_csk_ack_scheduled(sk)) { 5554 /* We sent a data segment already. */ 5555 return; 5556 } 5557 __tcp_ack_snd_check(sk, 1); 5558 } 5559 5560 /* 5561 * This routine is only called when we have urgent data 5562 * signaled. Its the 'slow' part of tcp_urg. It could be 5563 * moved inline now as tcp_urg is only called from one 5564 * place. We handle URGent data wrong. We have to - as 5565 * BSD still doesn't use the correction from RFC961. 5566 * For 1003.1g we should support a new option TCP_STDURG to permit 5567 * either form (or just set the sysctl tcp_stdurg). 5568 */ 5569 5570 static void tcp_check_urg(struct sock *sk, const struct tcphdr *th) 5571 { 5572 struct tcp_sock *tp = tcp_sk(sk); 5573 u32 ptr = ntohs(th->urg_ptr); 5574 5575 if (ptr && !READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_stdurg)) 5576 ptr--; 5577 ptr += ntohl(th->seq); 5578 5579 /* Ignore urgent data that we've already seen and read. */ 5580 if (after(tp->copied_seq, ptr)) 5581 return; 5582 5583 /* Do not replay urg ptr. 5584 * 5585 * NOTE: interesting situation not covered by specs. 5586 * Misbehaving sender may send urg ptr, pointing to segment, 5587 * which we already have in ofo queue. We are not able to fetch 5588 * such data and will stay in TCP_URG_NOTYET until will be eaten 5589 * by recvmsg(). Seems, we are not obliged to handle such wicked 5590 * situations. But it is worth to think about possibility of some 5591 * DoSes using some hypothetical application level deadlock. 5592 */ 5593 if (before(ptr, tp->rcv_nxt)) 5594 return; 5595 5596 /* Do we already have a newer (or duplicate) urgent pointer? */ 5597 if (tp->urg_data && !after(ptr, tp->urg_seq)) 5598 return; 5599 5600 /* Tell the world about our new urgent pointer. */ 5601 sk_send_sigurg(sk); 5602 5603 /* We may be adding urgent data when the last byte read was 5604 * urgent. To do this requires some care. We cannot just ignore 5605 * tp->copied_seq since we would read the last urgent byte again 5606 * as data, nor can we alter copied_seq until this data arrives 5607 * or we break the semantics of SIOCATMARK (and thus sockatmark()) 5608 * 5609 * NOTE. Double Dutch. Rendering to plain English: author of comment 5610 * above did something sort of send("A", MSG_OOB); send("B", MSG_OOB); 5611 * and expect that both A and B disappear from stream. This is _wrong_. 5612 * Though this happens in BSD with high probability, this is occasional. 5613 * Any application relying on this is buggy. Note also, that fix "works" 5614 * only in this artificial test. Insert some normal data between A and B and we will 5615 * decline of BSD again. Verdict: it is better to remove to trap 5616 * buggy users. 5617 */ 5618 if (tp->urg_seq == tp->copied_seq && tp->urg_data && 5619 !sock_flag(sk, SOCK_URGINLINE) && tp->copied_seq != tp->rcv_nxt) { 5620 struct sk_buff *skb = skb_peek(&sk->sk_receive_queue); 5621 tp->copied_seq++; 5622 if (skb && !before(tp->copied_seq, TCP_SKB_CB(skb)->end_seq)) { 5623 __skb_unlink(skb, &sk->sk_receive_queue); 5624 __kfree_skb(skb); 5625 } 5626 } 5627 5628 WRITE_ONCE(tp->urg_data, TCP_URG_NOTYET); 5629 WRITE_ONCE(tp->urg_seq, ptr); 5630 5631 /* Disable header prediction. */ 5632 tp->pred_flags = 0; 5633 } 5634 5635 /* This is the 'fast' part of urgent handling. */ 5636 static void tcp_urg(struct sock *sk, struct sk_buff *skb, const struct tcphdr *th) 5637 { 5638 struct tcp_sock *tp = tcp_sk(sk); 5639 5640 /* Check if we get a new urgent pointer - normally not. */ 5641 if (unlikely(th->urg)) 5642 tcp_check_urg(sk, th); 5643 5644 /* Do we wait for any urgent data? - normally not... */ 5645 if (unlikely(tp->urg_data == TCP_URG_NOTYET)) { 5646 u32 ptr = tp->urg_seq - ntohl(th->seq) + (th->doff * 4) - 5647 th->syn; 5648 5649 /* Is the urgent pointer pointing into this packet? */ 5650 if (ptr < skb->len) { 5651 u8 tmp; 5652 if (skb_copy_bits(skb, ptr, &tmp, 1)) 5653 BUG(); 5654 WRITE_ONCE(tp->urg_data, TCP_URG_VALID | tmp); 5655 if (!sock_flag(sk, SOCK_DEAD)) 5656 sk->sk_data_ready(sk); 5657 } 5658 } 5659 } 5660 5661 /* Accept RST for rcv_nxt - 1 after a FIN. 5662 * When tcp connections are abruptly terminated from Mac OSX (via ^C), a 5663 * FIN is sent followed by a RST packet. The RST is sent with the same 5664 * sequence number as the FIN, and thus according to RFC 5961 a challenge 5665 * ACK should be sent. However, Mac OSX rate limits replies to challenge 5666 * ACKs on the closed socket. In addition middleboxes can drop either the 5667 * challenge ACK or a subsequent RST. 5668 */ 5669 static bool tcp_reset_check(const struct sock *sk, const struct sk_buff *skb) 5670 { 5671 struct tcp_sock *tp = tcp_sk(sk); 5672 5673 return unlikely(TCP_SKB_CB(skb)->seq == (tp->rcv_nxt - 1) && 5674 (1 << sk->sk_state) & (TCPF_CLOSE_WAIT | TCPF_LAST_ACK | 5675 TCPF_CLOSING)); 5676 } 5677 5678 /* Does PAWS and seqno based validation of an incoming segment, flags will 5679 * play significant role here. 5680 */ 5681 static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb, 5682 const struct tcphdr *th, int syn_inerr) 5683 { 5684 struct tcp_sock *tp = tcp_sk(sk); 5685 SKB_DR(reason); 5686 5687 /* RFC1323: H1. Apply PAWS check first. */ 5688 if (tcp_fast_parse_options(sock_net(sk), skb, th, tp) && 5689 tp->rx_opt.saw_tstamp && 5690 tcp_paws_discard(sk, skb)) { 5691 if (!th->rst) { 5692 NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED); 5693 if (!tcp_oow_rate_limited(sock_net(sk), skb, 5694 LINUX_MIB_TCPACKSKIPPEDPAWS, 5695 &tp->last_oow_ack_time)) 5696 tcp_send_dupack(sk, skb); 5697 SKB_DR_SET(reason, TCP_RFC7323_PAWS); 5698 goto discard; 5699 } 5700 /* Reset is accepted even if it did not pass PAWS. */ 5701 } 5702 5703 /* Step 1: check sequence number */ 5704 if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) { 5705 /* RFC793, page 37: "In all states except SYN-SENT, all reset 5706 * (RST) segments are validated by checking their SEQ-fields." 5707 * And page 69: "If an incoming segment is not acceptable, 5708 * an acknowledgment should be sent in reply (unless the RST 5709 * bit is set, if so drop the segment and return)". 5710 */ 5711 if (!th->rst) { 5712 if (th->syn) 5713 goto syn_challenge; 5714 if (!tcp_oow_rate_limited(sock_net(sk), skb, 5715 LINUX_MIB_TCPACKSKIPPEDSEQ, 5716 &tp->last_oow_ack_time)) 5717 tcp_send_dupack(sk, skb); 5718 } else if (tcp_reset_check(sk, skb)) { 5719 goto reset; 5720 } 5721 SKB_DR_SET(reason, TCP_INVALID_SEQUENCE); 5722 goto discard; 5723 } 5724 5725 /* Step 2: check RST bit */ 5726 if (th->rst) { 5727 /* RFC 5961 3.2 (extend to match against (RCV.NXT - 1) after a 5728 * FIN and SACK too if available): 5729 * If seq num matches RCV.NXT or (RCV.NXT - 1) after a FIN, or 5730 * the right-most SACK block, 5731 * then 5732 * RESET the connection 5733 * else 5734 * Send a challenge ACK 5735 */ 5736 if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt || 5737 tcp_reset_check(sk, skb)) 5738 goto reset; 5739 5740 if (tcp_is_sack(tp) && tp->rx_opt.num_sacks > 0) { 5741 struct tcp_sack_block *sp = &tp->selective_acks[0]; 5742 int max_sack = sp[0].end_seq; 5743 int this_sack; 5744 5745 for (this_sack = 1; this_sack < tp->rx_opt.num_sacks; 5746 ++this_sack) { 5747 max_sack = after(sp[this_sack].end_seq, 5748 max_sack) ? 5749 sp[this_sack].end_seq : max_sack; 5750 } 5751 5752 if (TCP_SKB_CB(skb)->seq == max_sack) 5753 goto reset; 5754 } 5755 5756 /* Disable TFO if RST is out-of-order 5757 * and no data has been received 5758 * for current active TFO socket 5759 */ 5760 if (tp->syn_fastopen && !tp->data_segs_in && 5761 sk->sk_state == TCP_ESTABLISHED) 5762 tcp_fastopen_active_disable(sk); 5763 tcp_send_challenge_ack(sk); 5764 SKB_DR_SET(reason, TCP_RESET); 5765 goto discard; 5766 } 5767 5768 /* step 3: check security and precedence [ignored] */ 5769 5770 /* step 4: Check for a SYN 5771 * RFC 5961 4.2 : Send a challenge ack 5772 */ 5773 if (th->syn) { 5774 syn_challenge: 5775 if (syn_inerr) 5776 TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS); 5777 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSYNCHALLENGE); 5778 tcp_send_challenge_ack(sk); 5779 SKB_DR_SET(reason, TCP_INVALID_SYN); 5780 goto discard; 5781 } 5782 5783 bpf_skops_parse_hdr(sk, skb); 5784 5785 return true; 5786 5787 discard: 5788 tcp_drop_reason(sk, skb, reason); 5789 return false; 5790 5791 reset: 5792 tcp_reset(sk, skb); 5793 __kfree_skb(skb); 5794 return false; 5795 } 5796 5797 /* 5798 * TCP receive function for the ESTABLISHED state. 5799 * 5800 * It is split into a fast path and a slow path. The fast path is 5801 * disabled when: 5802 * - A zero window was announced from us - zero window probing 5803 * is only handled properly in the slow path. 5804 * - Out of order segments arrived. 5805 * - Urgent data is expected. 5806 * - There is no buffer space left 5807 * - Unexpected TCP flags/window values/header lengths are received 5808 * (detected by checking the TCP header against pred_flags) 5809 * - Data is sent in both directions. Fast path only supports pure senders 5810 * or pure receivers (this means either the sequence number or the ack 5811 * value must stay constant) 5812 * - Unexpected TCP option. 5813 * 5814 * When these conditions are not satisfied it drops into a standard 5815 * receive procedure patterned after RFC793 to handle all cases. 5816 * The first three cases are guaranteed by proper pred_flags setting, 5817 * the rest is checked inline. Fast processing is turned on in 5818 * tcp_data_queue when everything is OK. 5819 */ 5820 void tcp_rcv_established(struct sock *sk, struct sk_buff *skb) 5821 { 5822 enum skb_drop_reason reason = SKB_DROP_REASON_NOT_SPECIFIED; 5823 const struct tcphdr *th = (const struct tcphdr *)skb->data; 5824 struct tcp_sock *tp = tcp_sk(sk); 5825 unsigned int len = skb->len; 5826 5827 /* TCP congestion window tracking */ 5828 trace_tcp_probe(sk, skb); 5829 5830 tcp_mstamp_refresh(tp); 5831 if (unlikely(!rcu_access_pointer(sk->sk_rx_dst))) 5832 inet_csk(sk)->icsk_af_ops->sk_rx_dst_set(sk, skb); 5833 /* 5834 * Header prediction. 5835 * The code loosely follows the one in the famous 5836 * "30 instruction TCP receive" Van Jacobson mail. 5837 * 5838 * Van's trick is to deposit buffers into socket queue 5839 * on a device interrupt, to call tcp_recv function 5840 * on the receive process context and checksum and copy 5841 * the buffer to user space. smart... 5842 * 5843 * Our current scheme is not silly either but we take the 5844 * extra cost of the net_bh soft interrupt processing... 5845 * We do checksum and copy also but from device to kernel. 5846 */ 5847 5848 tp->rx_opt.saw_tstamp = 0; 5849 5850 /* pred_flags is 0xS?10 << 16 + snd_wnd 5851 * if header_prediction is to be made 5852 * 'S' will always be tp->tcp_header_len >> 2 5853 * '?' will be 0 for the fast path, otherwise pred_flags is 0 to 5854 * turn it off (when there are holes in the receive 5855 * space for instance) 5856 * PSH flag is ignored. 5857 */ 5858 5859 if ((tcp_flag_word(th) & TCP_HP_BITS) == tp->pred_flags && 5860 TCP_SKB_CB(skb)->seq == tp->rcv_nxt && 5861 !after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt)) { 5862 int tcp_header_len = tp->tcp_header_len; 5863 5864 /* Timestamp header prediction: tcp_header_len 5865 * is automatically equal to th->doff*4 due to pred_flags 5866 * match. 5867 */ 5868 5869 /* Check timestamp */ 5870 if (tcp_header_len == sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) { 5871 /* No? Slow path! */ 5872 if (!tcp_parse_aligned_timestamp(tp, th)) 5873 goto slow_path; 5874 5875 /* If PAWS failed, check it more carefully in slow path */ 5876 if ((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) < 0) 5877 goto slow_path; 5878 5879 /* DO NOT update ts_recent here, if checksum fails 5880 * and timestamp was corrupted part, it will result 5881 * in a hung connection since we will drop all 5882 * future packets due to the PAWS test. 5883 */ 5884 } 5885 5886 if (len <= tcp_header_len) { 5887 /* Bulk data transfer: sender */ 5888 if (len == tcp_header_len) { 5889 /* Predicted packet is in window by definition. 5890 * seq == rcv_nxt and rcv_wup <= rcv_nxt. 5891 * Hence, check seq<=rcv_wup reduces to: 5892 */ 5893 if (tcp_header_len == 5894 (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) && 5895 tp->rcv_nxt == tp->rcv_wup) 5896 tcp_store_ts_recent(tp); 5897 5898 /* We know that such packets are checksummed 5899 * on entry. 5900 */ 5901 tcp_ack(sk, skb, 0); 5902 __kfree_skb(skb); 5903 tcp_data_snd_check(sk); 5904 /* When receiving pure ack in fast path, update 5905 * last ts ecr directly instead of calling 5906 * tcp_rcv_rtt_measure_ts() 5907 */ 5908 tp->rcv_rtt_last_tsecr = tp->rx_opt.rcv_tsecr; 5909 return; 5910 } else { /* Header too small */ 5911 reason = SKB_DROP_REASON_PKT_TOO_SMALL; 5912 TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS); 5913 goto discard; 5914 } 5915 } else { 5916 int eaten = 0; 5917 bool fragstolen = false; 5918 5919 if (tcp_checksum_complete(skb)) 5920 goto csum_error; 5921 5922 if ((int)skb->truesize > sk->sk_forward_alloc) 5923 goto step5; 5924 5925 /* Predicted packet is in window by definition. 5926 * seq == rcv_nxt and rcv_wup <= rcv_nxt. 5927 * Hence, check seq<=rcv_wup reduces to: 5928 */ 5929 if (tcp_header_len == 5930 (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) && 5931 tp->rcv_nxt == tp->rcv_wup) 5932 tcp_store_ts_recent(tp); 5933 5934 tcp_rcv_rtt_measure_ts(sk, skb); 5935 5936 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPHPHITS); 5937 5938 /* Bulk data transfer: receiver */ 5939 skb_dst_drop(skb); 5940 __skb_pull(skb, tcp_header_len); 5941 eaten = tcp_queue_rcv(sk, skb, &fragstolen); 5942 5943 tcp_event_data_recv(sk, skb); 5944 5945 if (TCP_SKB_CB(skb)->ack_seq != tp->snd_una) { 5946 /* Well, only one small jumplet in fast path... */ 5947 tcp_ack(sk, skb, FLAG_DATA); 5948 tcp_data_snd_check(sk); 5949 if (!inet_csk_ack_scheduled(sk)) 5950 goto no_ack; 5951 } else { 5952 tcp_update_wl(tp, TCP_SKB_CB(skb)->seq); 5953 } 5954 5955 __tcp_ack_snd_check(sk, 0); 5956 no_ack: 5957 if (eaten) 5958 kfree_skb_partial(skb, fragstolen); 5959 tcp_data_ready(sk); 5960 return; 5961 } 5962 } 5963 5964 slow_path: 5965 if (len < (th->doff << 2) || tcp_checksum_complete(skb)) 5966 goto csum_error; 5967 5968 if (!th->ack && !th->rst && !th->syn) { 5969 reason = SKB_DROP_REASON_TCP_FLAGS; 5970 goto discard; 5971 } 5972 5973 /* 5974 * Standard slow path. 5975 */ 5976 5977 if (!tcp_validate_incoming(sk, skb, th, 1)) 5978 return; 5979 5980 step5: 5981 reason = tcp_ack(sk, skb, FLAG_SLOWPATH | FLAG_UPDATE_TS_RECENT); 5982 if ((int)reason < 0) { 5983 reason = -reason; 5984 goto discard; 5985 } 5986 tcp_rcv_rtt_measure_ts(sk, skb); 5987 5988 /* Process urgent data. */ 5989 tcp_urg(sk, skb, th); 5990 5991 /* step 7: process the segment text */ 5992 tcp_data_queue(sk, skb); 5993 5994 tcp_data_snd_check(sk); 5995 tcp_ack_snd_check(sk); 5996 return; 5997 5998 csum_error: 5999 reason = SKB_DROP_REASON_TCP_CSUM; 6000 trace_tcp_bad_csum(skb); 6001 TCP_INC_STATS(sock_net(sk), TCP_MIB_CSUMERRORS); 6002 TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS); 6003 6004 discard: 6005 tcp_drop_reason(sk, skb, reason); 6006 } 6007 EXPORT_SYMBOL(tcp_rcv_established); 6008 6009 void tcp_init_transfer(struct sock *sk, int bpf_op, struct sk_buff *skb) 6010 { 6011 struct inet_connection_sock *icsk = inet_csk(sk); 6012 struct tcp_sock *tp = tcp_sk(sk); 6013 6014 tcp_mtup_init(sk); 6015 icsk->icsk_af_ops->rebuild_header(sk); 6016 tcp_init_metrics(sk); 6017 6018 /* Initialize the congestion window to start the transfer. 6019 * Cut cwnd down to 1 per RFC5681 if SYN or SYN-ACK has been 6020 * retransmitted. In light of RFC6298 more aggressive 1sec 6021 * initRTO, we only reset cwnd when more than 1 SYN/SYN-ACK 6022 * retransmission has occurred. 6023 */ 6024 if (tp->total_retrans > 1 && tp->undo_marker) 6025 tcp_snd_cwnd_set(tp, 1); 6026 else 6027 tcp_snd_cwnd_set(tp, tcp_init_cwnd(tp, __sk_dst_get(sk))); 6028 tp->snd_cwnd_stamp = tcp_jiffies32; 6029 6030 bpf_skops_established(sk, bpf_op, skb); 6031 /* Initialize congestion control unless BPF initialized it already: */ 6032 if (!icsk->icsk_ca_initialized) 6033 tcp_init_congestion_control(sk); 6034 tcp_init_buffer_space(sk); 6035 } 6036 6037 void tcp_finish_connect(struct sock *sk, struct sk_buff *skb) 6038 { 6039 struct tcp_sock *tp = tcp_sk(sk); 6040 struct inet_connection_sock *icsk = inet_csk(sk); 6041 6042 tcp_set_state(sk, TCP_ESTABLISHED); 6043 icsk->icsk_ack.lrcvtime = tcp_jiffies32; 6044 6045 if (skb) { 6046 icsk->icsk_af_ops->sk_rx_dst_set(sk, skb); 6047 security_inet_conn_established(sk, skb); 6048 sk_mark_napi_id(sk, skb); 6049 } 6050 6051 tcp_init_transfer(sk, BPF_SOCK_OPS_ACTIVE_ESTABLISHED_CB, skb); 6052 6053 /* Prevent spurious tcp_cwnd_restart() on first data 6054 * packet. 6055 */ 6056 tp->lsndtime = tcp_jiffies32; 6057 6058 if (sock_flag(sk, SOCK_KEEPOPEN)) 6059 inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tp)); 6060 6061 if (!tp->rx_opt.snd_wscale) 6062 __tcp_fast_path_on(tp, tp->snd_wnd); 6063 else 6064 tp->pred_flags = 0; 6065 } 6066 6067 static bool tcp_rcv_fastopen_synack(struct sock *sk, struct sk_buff *synack, 6068 struct tcp_fastopen_cookie *cookie) 6069 { 6070 struct tcp_sock *tp = tcp_sk(sk); 6071 struct sk_buff *data = tp->syn_data ? tcp_rtx_queue_head(sk) : NULL; 6072 u16 mss = tp->rx_opt.mss_clamp, try_exp = 0; 6073 bool syn_drop = false; 6074 6075 if (mss == tp->rx_opt.user_mss) { 6076 struct tcp_options_received opt; 6077 6078 /* Get original SYNACK MSS value if user MSS sets mss_clamp */ 6079 tcp_clear_options(&opt); 6080 opt.user_mss = opt.mss_clamp = 0; 6081 tcp_parse_options(sock_net(sk), synack, &opt, 0, NULL); 6082 mss = opt.mss_clamp; 6083 } 6084 6085 if (!tp->syn_fastopen) { 6086 /* Ignore an unsolicited cookie */ 6087 cookie->len = -1; 6088 } else if (tp->total_retrans) { 6089 /* SYN timed out and the SYN-ACK neither has a cookie nor 6090 * acknowledges data. Presumably the remote received only 6091 * the retransmitted (regular) SYNs: either the original 6092 * SYN-data or the corresponding SYN-ACK was dropped. 6093 */ 6094 syn_drop = (cookie->len < 0 && data); 6095 } else if (cookie->len < 0 && !tp->syn_data) { 6096 /* We requested a cookie but didn't get it. If we did not use 6097 * the (old) exp opt format then try so next time (try_exp=1). 6098 * Otherwise we go back to use the RFC7413 opt (try_exp=2). 6099 */ 6100 try_exp = tp->syn_fastopen_exp ? 2 : 1; 6101 } 6102 6103 tcp_fastopen_cache_set(sk, mss, cookie, syn_drop, try_exp); 6104 6105 if (data) { /* Retransmit unacked data in SYN */ 6106 if (tp->total_retrans) 6107 tp->fastopen_client_fail = TFO_SYN_RETRANSMITTED; 6108 else 6109 tp->fastopen_client_fail = TFO_DATA_NOT_ACKED; 6110 skb_rbtree_walk_from(data) 6111 tcp_mark_skb_lost(sk, data); 6112 tcp_xmit_retransmit_queue(sk); 6113 NET_INC_STATS(sock_net(sk), 6114 LINUX_MIB_TCPFASTOPENACTIVEFAIL); 6115 return true; 6116 } 6117 tp->syn_data_acked = tp->syn_data; 6118 if (tp->syn_data_acked) { 6119 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFASTOPENACTIVE); 6120 /* SYN-data is counted as two separate packets in tcp_ack() */ 6121 if (tp->delivered > 1) 6122 --tp->delivered; 6123 } 6124 6125 tcp_fastopen_add_skb(sk, synack); 6126 6127 return false; 6128 } 6129 6130 static void smc_check_reset_syn(struct tcp_sock *tp) 6131 { 6132 #if IS_ENABLED(CONFIG_SMC) 6133 if (static_branch_unlikely(&tcp_have_smc)) { 6134 if (tp->syn_smc && !tp->rx_opt.smc_ok) 6135 tp->syn_smc = 0; 6136 } 6137 #endif 6138 } 6139 6140 static void tcp_try_undo_spurious_syn(struct sock *sk) 6141 { 6142 struct tcp_sock *tp = tcp_sk(sk); 6143 u32 syn_stamp; 6144 6145 /* undo_marker is set when SYN or SYNACK times out. The timeout is 6146 * spurious if the ACK's timestamp option echo value matches the 6147 * original SYN timestamp. 6148 */ 6149 syn_stamp = tp->retrans_stamp; 6150 if (tp->undo_marker && syn_stamp && tp->rx_opt.saw_tstamp && 6151 syn_stamp == tp->rx_opt.rcv_tsecr) 6152 tp->undo_marker = 0; 6153 } 6154 6155 static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb, 6156 const struct tcphdr *th) 6157 { 6158 struct inet_connection_sock *icsk = inet_csk(sk); 6159 struct tcp_sock *tp = tcp_sk(sk); 6160 struct tcp_fastopen_cookie foc = { .len = -1 }; 6161 int saved_clamp = tp->rx_opt.mss_clamp; 6162 bool fastopen_fail; 6163 SKB_DR(reason); 6164 6165 tcp_parse_options(sock_net(sk), skb, &tp->rx_opt, 0, &foc); 6166 if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr) 6167 tp->rx_opt.rcv_tsecr -= tp->tsoffset; 6168 6169 if (th->ack) { 6170 /* rfc793: 6171 * "If the state is SYN-SENT then 6172 * first check the ACK bit 6173 * If the ACK bit is set 6174 * If SEG.ACK =< ISS, or SEG.ACK > SND.NXT, send 6175 * a reset (unless the RST bit is set, if so drop 6176 * the segment and return)" 6177 */ 6178 if (!after(TCP_SKB_CB(skb)->ack_seq, tp->snd_una) || 6179 after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt)) { 6180 /* Previous FIN/ACK or RST/ACK might be ignored. */ 6181 if (icsk->icsk_retransmits == 0) 6182 inet_csk_reset_xmit_timer(sk, 6183 ICSK_TIME_RETRANS, 6184 TCP_TIMEOUT_MIN, TCP_RTO_MAX); 6185 goto reset_and_undo; 6186 } 6187 6188 if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr && 6189 !between(tp->rx_opt.rcv_tsecr, tp->retrans_stamp, 6190 tcp_time_stamp(tp))) { 6191 NET_INC_STATS(sock_net(sk), 6192 LINUX_MIB_PAWSACTIVEREJECTED); 6193 goto reset_and_undo; 6194 } 6195 6196 /* Now ACK is acceptable. 6197 * 6198 * "If the RST bit is set 6199 * If the ACK was acceptable then signal the user "error: 6200 * connection reset", drop the segment, enter CLOSED state, 6201 * delete TCB, and return." 6202 */ 6203 6204 if (th->rst) { 6205 tcp_reset(sk, skb); 6206 consume: 6207 __kfree_skb(skb); 6208 return 0; 6209 } 6210 6211 /* rfc793: 6212 * "fifth, if neither of the SYN or RST bits is set then 6213 * drop the segment and return." 6214 * 6215 * See note below! 6216 * --ANK(990513) 6217 */ 6218 if (!th->syn) { 6219 SKB_DR_SET(reason, TCP_FLAGS); 6220 goto discard_and_undo; 6221 } 6222 /* rfc793: 6223 * "If the SYN bit is on ... 6224 * are acceptable then ... 6225 * (our SYN has been ACKed), change the connection 6226 * state to ESTABLISHED..." 6227 */ 6228 6229 tcp_ecn_rcv_synack(tp, th); 6230 6231 tcp_init_wl(tp, TCP_SKB_CB(skb)->seq); 6232 tcp_try_undo_spurious_syn(sk); 6233 tcp_ack(sk, skb, FLAG_SLOWPATH); 6234 6235 /* Ok.. it's good. Set up sequence numbers and 6236 * move to established. 6237 */ 6238 WRITE_ONCE(tp->rcv_nxt, TCP_SKB_CB(skb)->seq + 1); 6239 tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1; 6240 6241 /* RFC1323: The window in SYN & SYN/ACK segments is 6242 * never scaled. 6243 */ 6244 tp->snd_wnd = ntohs(th->window); 6245 6246 if (!tp->rx_opt.wscale_ok) { 6247 tp->rx_opt.snd_wscale = tp->rx_opt.rcv_wscale = 0; 6248 tp->window_clamp = min(tp->window_clamp, 65535U); 6249 } 6250 6251 if (tp->rx_opt.saw_tstamp) { 6252 tp->rx_opt.tstamp_ok = 1; 6253 tp->tcp_header_len = 6254 sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED; 6255 tp->advmss -= TCPOLEN_TSTAMP_ALIGNED; 6256 tcp_store_ts_recent(tp); 6257 } else { 6258 tp->tcp_header_len = sizeof(struct tcphdr); 6259 } 6260 6261 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie); 6262 tcp_initialize_rcv_mss(sk); 6263 6264 /* Remember, tcp_poll() does not lock socket! 6265 * Change state from SYN-SENT only after copied_seq 6266 * is initialized. */ 6267 WRITE_ONCE(tp->copied_seq, tp->rcv_nxt); 6268 6269 smc_check_reset_syn(tp); 6270 6271 smp_mb(); 6272 6273 tcp_finish_connect(sk, skb); 6274 6275 fastopen_fail = (tp->syn_fastopen || tp->syn_data) && 6276 tcp_rcv_fastopen_synack(sk, skb, &foc); 6277 6278 if (!sock_flag(sk, SOCK_DEAD)) { 6279 sk->sk_state_change(sk); 6280 sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT); 6281 } 6282 if (fastopen_fail) 6283 return -1; 6284 if (sk->sk_write_pending || 6285 icsk->icsk_accept_queue.rskq_defer_accept || 6286 inet_csk_in_pingpong_mode(sk)) { 6287 /* Save one ACK. Data will be ready after 6288 * several ticks, if write_pending is set. 6289 * 6290 * It may be deleted, but with this feature tcpdumps 6291 * look so _wonderfully_ clever, that I was not able 6292 * to stand against the temptation 8) --ANK 6293 */ 6294 inet_csk_schedule_ack(sk); 6295 tcp_enter_quickack_mode(sk, TCP_MAX_QUICKACKS); 6296 inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK, 6297 TCP_DELACK_MAX, TCP_RTO_MAX); 6298 goto consume; 6299 } 6300 tcp_send_ack(sk); 6301 return -1; 6302 } 6303 6304 /* No ACK in the segment */ 6305 6306 if (th->rst) { 6307 /* rfc793: 6308 * "If the RST bit is set 6309 * 6310 * Otherwise (no ACK) drop the segment and return." 6311 */ 6312 SKB_DR_SET(reason, TCP_RESET); 6313 goto discard_and_undo; 6314 } 6315 6316 /* PAWS check. */ 6317 if (tp->rx_opt.ts_recent_stamp && tp->rx_opt.saw_tstamp && 6318 tcp_paws_reject(&tp->rx_opt, 0)) { 6319 SKB_DR_SET(reason, TCP_RFC7323_PAWS); 6320 goto discard_and_undo; 6321 } 6322 if (th->syn) { 6323 /* We see SYN without ACK. It is attempt of 6324 * simultaneous connect with crossed SYNs. 6325 * Particularly, it can be connect to self. 6326 */ 6327 tcp_set_state(sk, TCP_SYN_RECV); 6328 6329 if (tp->rx_opt.saw_tstamp) { 6330 tp->rx_opt.tstamp_ok = 1; 6331 tcp_store_ts_recent(tp); 6332 tp->tcp_header_len = 6333 sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED; 6334 } else { 6335 tp->tcp_header_len = sizeof(struct tcphdr); 6336 } 6337 6338 WRITE_ONCE(tp->rcv_nxt, TCP_SKB_CB(skb)->seq + 1); 6339 WRITE_ONCE(tp->copied_seq, tp->rcv_nxt); 6340 tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1; 6341 6342 /* RFC1323: The window in SYN & SYN/ACK segments is 6343 * never scaled. 6344 */ 6345 tp->snd_wnd = ntohs(th->window); 6346 tp->snd_wl1 = TCP_SKB_CB(skb)->seq; 6347 tp->max_window = tp->snd_wnd; 6348 6349 tcp_ecn_rcv_syn(tp, th); 6350 6351 tcp_mtup_init(sk); 6352 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie); 6353 tcp_initialize_rcv_mss(sk); 6354 6355 tcp_send_synack(sk); 6356 #if 0 6357 /* Note, we could accept data and URG from this segment. 6358 * There are no obstacles to make this (except that we must 6359 * either change tcp_recvmsg() to prevent it from returning data 6360 * before 3WHS completes per RFC793, or employ TCP Fast Open). 6361 * 6362 * However, if we ignore data in ACKless segments sometimes, 6363 * we have no reasons to accept it sometimes. 6364 * Also, seems the code doing it in step6 of tcp_rcv_state_process 6365 * is not flawless. So, discard packet for sanity. 6366 * Uncomment this return to process the data. 6367 */ 6368 return -1; 6369 #else 6370 goto consume; 6371 #endif 6372 } 6373 /* "fifth, if neither of the SYN or RST bits is set then 6374 * drop the segment and return." 6375 */ 6376 6377 discard_and_undo: 6378 tcp_clear_options(&tp->rx_opt); 6379 tp->rx_opt.mss_clamp = saved_clamp; 6380 tcp_drop_reason(sk, skb, reason); 6381 return 0; 6382 6383 reset_and_undo: 6384 tcp_clear_options(&tp->rx_opt); 6385 tp->rx_opt.mss_clamp = saved_clamp; 6386 return 1; 6387 } 6388 6389 static void tcp_rcv_synrecv_state_fastopen(struct sock *sk) 6390 { 6391 struct request_sock *req; 6392 6393 /* If we are still handling the SYNACK RTO, see if timestamp ECR allows 6394 * undo. If peer SACKs triggered fast recovery, we can't undo here. 6395 */ 6396 if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss) 6397 tcp_try_undo_loss(sk, false); 6398 6399 /* Reset rtx states to prevent spurious retransmits_timed_out() */ 6400 tcp_sk(sk)->retrans_stamp = 0; 6401 inet_csk(sk)->icsk_retransmits = 0; 6402 6403 /* Once we leave TCP_SYN_RECV or TCP_FIN_WAIT_1, 6404 * we no longer need req so release it. 6405 */ 6406 req = rcu_dereference_protected(tcp_sk(sk)->fastopen_rsk, 6407 lockdep_sock_is_held(sk)); 6408 reqsk_fastopen_remove(sk, req, false); 6409 6410 /* Re-arm the timer because data may have been sent out. 6411 * This is similar to the regular data transmission case 6412 * when new data has just been ack'ed. 6413 * 6414 * (TFO) - we could try to be more aggressive and 6415 * retransmitting any data sooner based on when they 6416 * are sent out. 6417 */ 6418 tcp_rearm_rto(sk); 6419 } 6420 6421 /* 6422 * This function implements the receiving procedure of RFC 793 for 6423 * all states except ESTABLISHED and TIME_WAIT. 6424 * It's called from both tcp_v4_rcv and tcp_v6_rcv and should be 6425 * address independent. 6426 */ 6427 6428 int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb) 6429 { 6430 struct tcp_sock *tp = tcp_sk(sk); 6431 struct inet_connection_sock *icsk = inet_csk(sk); 6432 const struct tcphdr *th = tcp_hdr(skb); 6433 struct request_sock *req; 6434 int queued = 0; 6435 bool acceptable; 6436 SKB_DR(reason); 6437 6438 switch (sk->sk_state) { 6439 case TCP_CLOSE: 6440 SKB_DR_SET(reason, TCP_CLOSE); 6441 goto discard; 6442 6443 case TCP_LISTEN: 6444 if (th->ack) 6445 return 1; 6446 6447 if (th->rst) { 6448 SKB_DR_SET(reason, TCP_RESET); 6449 goto discard; 6450 } 6451 if (th->syn) { 6452 if (th->fin) { 6453 SKB_DR_SET(reason, TCP_FLAGS); 6454 goto discard; 6455 } 6456 /* It is possible that we process SYN packets from backlog, 6457 * so we need to make sure to disable BH and RCU right there. 6458 */ 6459 rcu_read_lock(); 6460 local_bh_disable(); 6461 acceptable = icsk->icsk_af_ops->conn_request(sk, skb) >= 0; 6462 local_bh_enable(); 6463 rcu_read_unlock(); 6464 6465 if (!acceptable) 6466 return 1; 6467 consume_skb(skb); 6468 return 0; 6469 } 6470 SKB_DR_SET(reason, TCP_FLAGS); 6471 goto discard; 6472 6473 case TCP_SYN_SENT: 6474 tp->rx_opt.saw_tstamp = 0; 6475 tcp_mstamp_refresh(tp); 6476 queued = tcp_rcv_synsent_state_process(sk, skb, th); 6477 if (queued >= 0) 6478 return queued; 6479 6480 /* Do step6 onward by hand. */ 6481 tcp_urg(sk, skb, th); 6482 __kfree_skb(skb); 6483 tcp_data_snd_check(sk); 6484 return 0; 6485 } 6486 6487 tcp_mstamp_refresh(tp); 6488 tp->rx_opt.saw_tstamp = 0; 6489 req = rcu_dereference_protected(tp->fastopen_rsk, 6490 lockdep_sock_is_held(sk)); 6491 if (req) { 6492 bool req_stolen; 6493 6494 WARN_ON_ONCE(sk->sk_state != TCP_SYN_RECV && 6495 sk->sk_state != TCP_FIN_WAIT1); 6496 6497 if (!tcp_check_req(sk, skb, req, true, &req_stolen)) { 6498 SKB_DR_SET(reason, TCP_FASTOPEN); 6499 goto discard; 6500 } 6501 } 6502 6503 if (!th->ack && !th->rst && !th->syn) { 6504 SKB_DR_SET(reason, TCP_FLAGS); 6505 goto discard; 6506 } 6507 if (!tcp_validate_incoming(sk, skb, th, 0)) 6508 return 0; 6509 6510 /* step 5: check the ACK field */ 6511 acceptable = tcp_ack(sk, skb, FLAG_SLOWPATH | 6512 FLAG_UPDATE_TS_RECENT | 6513 FLAG_NO_CHALLENGE_ACK) > 0; 6514 6515 if (!acceptable) { 6516 if (sk->sk_state == TCP_SYN_RECV) 6517 return 1; /* send one RST */ 6518 tcp_send_challenge_ack(sk); 6519 SKB_DR_SET(reason, TCP_OLD_ACK); 6520 goto discard; 6521 } 6522 switch (sk->sk_state) { 6523 case TCP_SYN_RECV: 6524 tp->delivered++; /* SYN-ACK delivery isn't tracked in tcp_ack */ 6525 if (!tp->srtt_us) 6526 tcp_synack_rtt_meas(sk, req); 6527 6528 if (req) { 6529 tcp_rcv_synrecv_state_fastopen(sk); 6530 } else { 6531 tcp_try_undo_spurious_syn(sk); 6532 tp->retrans_stamp = 0; 6533 tcp_init_transfer(sk, BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB, 6534 skb); 6535 WRITE_ONCE(tp->copied_seq, tp->rcv_nxt); 6536 } 6537 smp_mb(); 6538 tcp_set_state(sk, TCP_ESTABLISHED); 6539 sk->sk_state_change(sk); 6540 6541 /* Note, that this wakeup is only for marginal crossed SYN case. 6542 * Passively open sockets are not waked up, because 6543 * sk->sk_sleep == NULL and sk->sk_socket == NULL. 6544 */ 6545 if (sk->sk_socket) 6546 sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT); 6547 6548 tp->snd_una = TCP_SKB_CB(skb)->ack_seq; 6549 tp->snd_wnd = ntohs(th->window) << tp->rx_opt.snd_wscale; 6550 tcp_init_wl(tp, TCP_SKB_CB(skb)->seq); 6551 6552 if (tp->rx_opt.tstamp_ok) 6553 tp->advmss -= TCPOLEN_TSTAMP_ALIGNED; 6554 6555 if (!inet_csk(sk)->icsk_ca_ops->cong_control) 6556 tcp_update_pacing_rate(sk); 6557 6558 /* Prevent spurious tcp_cwnd_restart() on first data packet */ 6559 tp->lsndtime = tcp_jiffies32; 6560 6561 tcp_initialize_rcv_mss(sk); 6562 tcp_fast_path_on(tp); 6563 break; 6564 6565 case TCP_FIN_WAIT1: { 6566 int tmo; 6567 6568 if (req) 6569 tcp_rcv_synrecv_state_fastopen(sk); 6570 6571 if (tp->snd_una != tp->write_seq) 6572 break; 6573 6574 tcp_set_state(sk, TCP_FIN_WAIT2); 6575 sk->sk_shutdown |= SEND_SHUTDOWN; 6576 6577 sk_dst_confirm(sk); 6578 6579 if (!sock_flag(sk, SOCK_DEAD)) { 6580 /* Wake up lingering close() */ 6581 sk->sk_state_change(sk); 6582 break; 6583 } 6584 6585 if (tp->linger2 < 0) { 6586 tcp_done(sk); 6587 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONDATA); 6588 return 1; 6589 } 6590 if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq && 6591 after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) { 6592 /* Receive out of order FIN after close() */ 6593 if (tp->syn_fastopen && th->fin) 6594 tcp_fastopen_active_disable(sk); 6595 tcp_done(sk); 6596 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONDATA); 6597 return 1; 6598 } 6599 6600 tmo = tcp_fin_time(sk); 6601 if (tmo > TCP_TIMEWAIT_LEN) { 6602 inet_csk_reset_keepalive_timer(sk, tmo - TCP_TIMEWAIT_LEN); 6603 } else if (th->fin || sock_owned_by_user(sk)) { 6604 /* Bad case. We could lose such FIN otherwise. 6605 * It is not a big problem, but it looks confusing 6606 * and not so rare event. We still can lose it now, 6607 * if it spins in bh_lock_sock(), but it is really 6608 * marginal case. 6609 */ 6610 inet_csk_reset_keepalive_timer(sk, tmo); 6611 } else { 6612 tcp_time_wait(sk, TCP_FIN_WAIT2, tmo); 6613 goto consume; 6614 } 6615 break; 6616 } 6617 6618 case TCP_CLOSING: 6619 if (tp->snd_una == tp->write_seq) { 6620 tcp_time_wait(sk, TCP_TIME_WAIT, 0); 6621 goto consume; 6622 } 6623 break; 6624 6625 case TCP_LAST_ACK: 6626 if (tp->snd_una == tp->write_seq) { 6627 tcp_update_metrics(sk); 6628 tcp_done(sk); 6629 goto consume; 6630 } 6631 break; 6632 } 6633 6634 /* step 6: check the URG bit */ 6635 tcp_urg(sk, skb, th); 6636 6637 /* step 7: process the segment text */ 6638 switch (sk->sk_state) { 6639 case TCP_CLOSE_WAIT: 6640 case TCP_CLOSING: 6641 case TCP_LAST_ACK: 6642 if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) { 6643 /* If a subflow has been reset, the packet should not 6644 * continue to be processed, drop the packet. 6645 */ 6646 if (sk_is_mptcp(sk) && !mptcp_incoming_options(sk, skb)) 6647 goto discard; 6648 break; 6649 } 6650 fallthrough; 6651 case TCP_FIN_WAIT1: 6652 case TCP_FIN_WAIT2: 6653 /* RFC 793 says to queue data in these states, 6654 * RFC 1122 says we MUST send a reset. 6655 * BSD 4.4 also does reset. 6656 */ 6657 if (sk->sk_shutdown & RCV_SHUTDOWN) { 6658 if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq && 6659 after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) { 6660 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONDATA); 6661 tcp_reset(sk, skb); 6662 return 1; 6663 } 6664 } 6665 fallthrough; 6666 case TCP_ESTABLISHED: 6667 tcp_data_queue(sk, skb); 6668 queued = 1; 6669 break; 6670 } 6671 6672 /* tcp_data could move socket to TIME-WAIT */ 6673 if (sk->sk_state != TCP_CLOSE) { 6674 tcp_data_snd_check(sk); 6675 tcp_ack_snd_check(sk); 6676 } 6677 6678 if (!queued) { 6679 discard: 6680 tcp_drop_reason(sk, skb, reason); 6681 } 6682 return 0; 6683 6684 consume: 6685 __kfree_skb(skb); 6686 return 0; 6687 } 6688 EXPORT_SYMBOL(tcp_rcv_state_process); 6689 6690 static inline void pr_drop_req(struct request_sock *req, __u16 port, int family) 6691 { 6692 struct inet_request_sock *ireq = inet_rsk(req); 6693 6694 if (family == AF_INET) 6695 net_dbg_ratelimited("drop open request from %pI4/%u\n", 6696 &ireq->ir_rmt_addr, port); 6697 #if IS_ENABLED(CONFIG_IPV6) 6698 else if (family == AF_INET6) 6699 net_dbg_ratelimited("drop open request from %pI6/%u\n", 6700 &ireq->ir_v6_rmt_addr, port); 6701 #endif 6702 } 6703 6704 /* RFC3168 : 6.1.1 SYN packets must not have ECT/ECN bits set 6705 * 6706 * If we receive a SYN packet with these bits set, it means a 6707 * network is playing bad games with TOS bits. In order to 6708 * avoid possible false congestion notifications, we disable 6709 * TCP ECN negotiation. 6710 * 6711 * Exception: tcp_ca wants ECN. This is required for DCTCP 6712 * congestion control: Linux DCTCP asserts ECT on all packets, 6713 * including SYN, which is most optimal solution; however, 6714 * others, such as FreeBSD do not. 6715 * 6716 * Exception: At least one of the reserved bits of the TCP header (th->res1) is 6717 * set, indicating the use of a future TCP extension (such as AccECN). See 6718 * RFC8311 §4.3 which updates RFC3168 to allow the development of such 6719 * extensions. 6720 */ 6721 static void tcp_ecn_create_request(struct request_sock *req, 6722 const struct sk_buff *skb, 6723 const struct sock *listen_sk, 6724 const struct dst_entry *dst) 6725 { 6726 const struct tcphdr *th = tcp_hdr(skb); 6727 const struct net *net = sock_net(listen_sk); 6728 bool th_ecn = th->ece && th->cwr; 6729 bool ect, ecn_ok; 6730 u32 ecn_ok_dst; 6731 6732 if (!th_ecn) 6733 return; 6734 6735 ect = !INET_ECN_is_not_ect(TCP_SKB_CB(skb)->ip_dsfield); 6736 ecn_ok_dst = dst_feature(dst, DST_FEATURE_ECN_MASK); 6737 ecn_ok = READ_ONCE(net->ipv4.sysctl_tcp_ecn) || ecn_ok_dst; 6738 6739 if (((!ect || th->res1) && ecn_ok) || tcp_ca_needs_ecn(listen_sk) || 6740 (ecn_ok_dst & DST_FEATURE_ECN_CA) || 6741 tcp_bpf_ca_needs_ecn((struct sock *)req)) 6742 inet_rsk(req)->ecn_ok = 1; 6743 } 6744 6745 static void tcp_openreq_init(struct request_sock *req, 6746 const struct tcp_options_received *rx_opt, 6747 struct sk_buff *skb, const struct sock *sk) 6748 { 6749 struct inet_request_sock *ireq = inet_rsk(req); 6750 6751 req->rsk_rcv_wnd = 0; /* So that tcp_send_synack() knows! */ 6752 tcp_rsk(req)->rcv_isn = TCP_SKB_CB(skb)->seq; 6753 tcp_rsk(req)->rcv_nxt = TCP_SKB_CB(skb)->seq + 1; 6754 tcp_rsk(req)->snt_synack = 0; 6755 tcp_rsk(req)->last_oow_ack_time = 0; 6756 req->mss = rx_opt->mss_clamp; 6757 req->ts_recent = rx_opt->saw_tstamp ? rx_opt->rcv_tsval : 0; 6758 ireq->tstamp_ok = rx_opt->tstamp_ok; 6759 ireq->sack_ok = rx_opt->sack_ok; 6760 ireq->snd_wscale = rx_opt->snd_wscale; 6761 ireq->wscale_ok = rx_opt->wscale_ok; 6762 ireq->acked = 0; 6763 ireq->ecn_ok = 0; 6764 ireq->ir_rmt_port = tcp_hdr(skb)->source; 6765 ireq->ir_num = ntohs(tcp_hdr(skb)->dest); 6766 ireq->ir_mark = inet_request_mark(sk, skb); 6767 #if IS_ENABLED(CONFIG_SMC) 6768 ireq->smc_ok = rx_opt->smc_ok && !(tcp_sk(sk)->smc_hs_congested && 6769 tcp_sk(sk)->smc_hs_congested(sk)); 6770 #endif 6771 } 6772 6773 struct request_sock *inet_reqsk_alloc(const struct request_sock_ops *ops, 6774 struct sock *sk_listener, 6775 bool attach_listener) 6776 { 6777 struct request_sock *req = reqsk_alloc(ops, sk_listener, 6778 attach_listener); 6779 6780 if (req) { 6781 struct inet_request_sock *ireq = inet_rsk(req); 6782 6783 ireq->ireq_opt = NULL; 6784 #if IS_ENABLED(CONFIG_IPV6) 6785 ireq->pktopts = NULL; 6786 #endif 6787 atomic64_set(&ireq->ir_cookie, 0); 6788 ireq->ireq_state = TCP_NEW_SYN_RECV; 6789 write_pnet(&ireq->ireq_net, sock_net(sk_listener)); 6790 ireq->ireq_family = sk_listener->sk_family; 6791 req->timeout = TCP_TIMEOUT_INIT; 6792 } 6793 6794 return req; 6795 } 6796 EXPORT_SYMBOL(inet_reqsk_alloc); 6797 6798 /* 6799 * Return true if a syncookie should be sent 6800 */ 6801 static bool tcp_syn_flood_action(const struct sock *sk, const char *proto) 6802 { 6803 struct request_sock_queue *queue = &inet_csk(sk)->icsk_accept_queue; 6804 const char *msg = "Dropping request"; 6805 struct net *net = sock_net(sk); 6806 bool want_cookie = false; 6807 u8 syncookies; 6808 6809 syncookies = READ_ONCE(net->ipv4.sysctl_tcp_syncookies); 6810 6811 #ifdef CONFIG_SYN_COOKIES 6812 if (syncookies) { 6813 msg = "Sending cookies"; 6814 want_cookie = true; 6815 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPREQQFULLDOCOOKIES); 6816 } else 6817 #endif 6818 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPREQQFULLDROP); 6819 6820 if (!queue->synflood_warned && syncookies != 2 && 6821 xchg(&queue->synflood_warned, 1) == 0) 6822 net_info_ratelimited("%s: Possible SYN flooding on port %d. %s. Check SNMP counters.\n", 6823 proto, sk->sk_num, msg); 6824 6825 return want_cookie; 6826 } 6827 6828 static void tcp_reqsk_record_syn(const struct sock *sk, 6829 struct request_sock *req, 6830 const struct sk_buff *skb) 6831 { 6832 if (tcp_sk(sk)->save_syn) { 6833 u32 len = skb_network_header_len(skb) + tcp_hdrlen(skb); 6834 struct saved_syn *saved_syn; 6835 u32 mac_hdrlen; 6836 void *base; 6837 6838 if (tcp_sk(sk)->save_syn == 2) { /* Save full header. */ 6839 base = skb_mac_header(skb); 6840 mac_hdrlen = skb_mac_header_len(skb); 6841 len += mac_hdrlen; 6842 } else { 6843 base = skb_network_header(skb); 6844 mac_hdrlen = 0; 6845 } 6846 6847 saved_syn = kmalloc(struct_size(saved_syn, data, len), 6848 GFP_ATOMIC); 6849 if (saved_syn) { 6850 saved_syn->mac_hdrlen = mac_hdrlen; 6851 saved_syn->network_hdrlen = skb_network_header_len(skb); 6852 saved_syn->tcp_hdrlen = tcp_hdrlen(skb); 6853 memcpy(saved_syn->data, base, len); 6854 req->saved_syn = saved_syn; 6855 } 6856 } 6857 } 6858 6859 /* If a SYN cookie is required and supported, returns a clamped MSS value to be 6860 * used for SYN cookie generation. 6861 */ 6862 u16 tcp_get_syncookie_mss(struct request_sock_ops *rsk_ops, 6863 const struct tcp_request_sock_ops *af_ops, 6864 struct sock *sk, struct tcphdr *th) 6865 { 6866 struct tcp_sock *tp = tcp_sk(sk); 6867 u16 mss; 6868 6869 if (READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_syncookies) != 2 && 6870 !inet_csk_reqsk_queue_is_full(sk)) 6871 return 0; 6872 6873 if (!tcp_syn_flood_action(sk, rsk_ops->slab_name)) 6874 return 0; 6875 6876 if (sk_acceptq_is_full(sk)) { 6877 NET_INC_STATS(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS); 6878 return 0; 6879 } 6880 6881 mss = tcp_parse_mss_option(th, tp->rx_opt.user_mss); 6882 if (!mss) 6883 mss = af_ops->mss_clamp; 6884 6885 return mss; 6886 } 6887 EXPORT_SYMBOL_GPL(tcp_get_syncookie_mss); 6888 6889 int tcp_conn_request(struct request_sock_ops *rsk_ops, 6890 const struct tcp_request_sock_ops *af_ops, 6891 struct sock *sk, struct sk_buff *skb) 6892 { 6893 struct tcp_fastopen_cookie foc = { .len = -1 }; 6894 __u32 isn = TCP_SKB_CB(skb)->tcp_tw_isn; 6895 struct tcp_options_received tmp_opt; 6896 struct tcp_sock *tp = tcp_sk(sk); 6897 struct net *net = sock_net(sk); 6898 struct sock *fastopen_sk = NULL; 6899 struct request_sock *req; 6900 bool want_cookie = false; 6901 struct dst_entry *dst; 6902 struct flowi fl; 6903 u8 syncookies; 6904 6905 syncookies = READ_ONCE(net->ipv4.sysctl_tcp_syncookies); 6906 6907 /* TW buckets are converted to open requests without 6908 * limitations, they conserve resources and peer is 6909 * evidently real one. 6910 */ 6911 if ((syncookies == 2 || inet_csk_reqsk_queue_is_full(sk)) && !isn) { 6912 want_cookie = tcp_syn_flood_action(sk, rsk_ops->slab_name); 6913 if (!want_cookie) 6914 goto drop; 6915 } 6916 6917 if (sk_acceptq_is_full(sk)) { 6918 NET_INC_STATS(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS); 6919 goto drop; 6920 } 6921 6922 req = inet_reqsk_alloc(rsk_ops, sk, !want_cookie); 6923 if (!req) 6924 goto drop; 6925 6926 req->syncookie = want_cookie; 6927 tcp_rsk(req)->af_specific = af_ops; 6928 tcp_rsk(req)->ts_off = 0; 6929 #if IS_ENABLED(CONFIG_MPTCP) 6930 tcp_rsk(req)->is_mptcp = 0; 6931 #endif 6932 6933 tcp_clear_options(&tmp_opt); 6934 tmp_opt.mss_clamp = af_ops->mss_clamp; 6935 tmp_opt.user_mss = tp->rx_opt.user_mss; 6936 tcp_parse_options(sock_net(sk), skb, &tmp_opt, 0, 6937 want_cookie ? NULL : &foc); 6938 6939 if (want_cookie && !tmp_opt.saw_tstamp) 6940 tcp_clear_options(&tmp_opt); 6941 6942 if (IS_ENABLED(CONFIG_SMC) && want_cookie) 6943 tmp_opt.smc_ok = 0; 6944 6945 tmp_opt.tstamp_ok = tmp_opt.saw_tstamp; 6946 tcp_openreq_init(req, &tmp_opt, skb, sk); 6947 inet_rsk(req)->no_srccheck = inet_sk(sk)->transparent; 6948 6949 /* Note: tcp_v6_init_req() might override ir_iif for link locals */ 6950 inet_rsk(req)->ir_iif = inet_request_bound_dev_if(sk, skb); 6951 6952 dst = af_ops->route_req(sk, skb, &fl, req); 6953 if (!dst) 6954 goto drop_and_free; 6955 6956 if (tmp_opt.tstamp_ok) 6957 tcp_rsk(req)->ts_off = af_ops->init_ts_off(net, skb); 6958 6959 if (!want_cookie && !isn) { 6960 int max_syn_backlog = READ_ONCE(net->ipv4.sysctl_max_syn_backlog); 6961 6962 /* Kill the following clause, if you dislike this way. */ 6963 if (!syncookies && 6964 (max_syn_backlog - inet_csk_reqsk_queue_len(sk) < 6965 (max_syn_backlog >> 2)) && 6966 !tcp_peer_is_proven(req, dst)) { 6967 /* Without syncookies last quarter of 6968 * backlog is filled with destinations, 6969 * proven to be alive. 6970 * It means that we continue to communicate 6971 * to destinations, already remembered 6972 * to the moment of synflood. 6973 */ 6974 pr_drop_req(req, ntohs(tcp_hdr(skb)->source), 6975 rsk_ops->family); 6976 goto drop_and_release; 6977 } 6978 6979 isn = af_ops->init_seq(skb); 6980 } 6981 6982 tcp_ecn_create_request(req, skb, sk, dst); 6983 6984 if (want_cookie) { 6985 isn = cookie_init_sequence(af_ops, sk, skb, &req->mss); 6986 if (!tmp_opt.tstamp_ok) 6987 inet_rsk(req)->ecn_ok = 0; 6988 } 6989 6990 tcp_rsk(req)->snt_isn = isn; 6991 tcp_rsk(req)->txhash = net_tx_rndhash(); 6992 tcp_rsk(req)->syn_tos = TCP_SKB_CB(skb)->ip_dsfield; 6993 tcp_openreq_init_rwin(req, sk, dst); 6994 sk_rx_queue_set(req_to_sk(req), skb); 6995 if (!want_cookie) { 6996 tcp_reqsk_record_syn(sk, req, skb); 6997 fastopen_sk = tcp_try_fastopen(sk, skb, req, &foc, dst); 6998 } 6999 if (fastopen_sk) { 7000 af_ops->send_synack(fastopen_sk, dst, &fl, req, 7001 &foc, TCP_SYNACK_FASTOPEN, skb); 7002 /* Add the child socket directly into the accept queue */ 7003 if (!inet_csk_reqsk_queue_add(sk, req, fastopen_sk)) { 7004 reqsk_fastopen_remove(fastopen_sk, req, false); 7005 bh_unlock_sock(fastopen_sk); 7006 sock_put(fastopen_sk); 7007 goto drop_and_free; 7008 } 7009 sk->sk_data_ready(sk); 7010 bh_unlock_sock(fastopen_sk); 7011 sock_put(fastopen_sk); 7012 } else { 7013 tcp_rsk(req)->tfo_listener = false; 7014 if (!want_cookie) { 7015 req->timeout = tcp_timeout_init((struct sock *)req); 7016 inet_csk_reqsk_queue_hash_add(sk, req, req->timeout); 7017 } 7018 af_ops->send_synack(sk, dst, &fl, req, &foc, 7019 !want_cookie ? TCP_SYNACK_NORMAL : 7020 TCP_SYNACK_COOKIE, 7021 skb); 7022 if (want_cookie) { 7023 reqsk_free(req); 7024 return 0; 7025 } 7026 } 7027 reqsk_put(req); 7028 return 0; 7029 7030 drop_and_release: 7031 dst_release(dst); 7032 drop_and_free: 7033 __reqsk_free(req); 7034 drop: 7035 tcp_listendrop(sk); 7036 return 0; 7037 } 7038 EXPORT_SYMBOL(tcp_conn_request); 7039