1 // SPDX-License-Identifier: GPL-2.0-only 2 /* 3 * INET An implementation of the TCP/IP protocol suite for the LINUX 4 * operating system. INET is implemented using the BSD Socket 5 * interface as the means of communication with the user level. 6 * 7 * Implementation of the Transmission Control Protocol(TCP). 8 * 9 * Authors: Ross Biro 10 * Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG> 11 * Mark Evans, <evansmp@uhura.aston.ac.uk> 12 * Corey Minyard <wf-rch!minyard@relay.EU.net> 13 * Florian La Roche, <flla@stud.uni-sb.de> 14 * Charles Hedrick, <hedrick@klinzhai.rutgers.edu> 15 * Linus Torvalds, <torvalds@cs.helsinki.fi> 16 * Alan Cox, <gw4pts@gw4pts.ampr.org> 17 * Matthew Dillon, <dillon@apollo.west.oic.com> 18 * Arnt Gulbrandsen, <agulbra@nvg.unit.no> 19 * Jorge Cwik, <jorge@laser.satlink.net> 20 */ 21 22 /* 23 * Changes: Pedro Roque : Retransmit queue handled by TCP. 24 * : Fragmentation on mtu decrease 25 * : Segment collapse on retransmit 26 * : AF independence 27 * 28 * Linus Torvalds : send_delayed_ack 29 * David S. Miller : Charge memory using the right skb 30 * during syn/ack processing. 31 * David S. Miller : Output engine completely rewritten. 32 * Andrea Arcangeli: SYNACK carry ts_recent in tsecr. 33 * Cacophonix Gaul : draft-minshall-nagle-01 34 * J Hadi Salim : ECN support 35 * 36 */ 37 38 #define pr_fmt(fmt) "TCP: " fmt 39 40 #include <net/tcp.h> 41 #include <net/mptcp.h> 42 43 #include <linux/compiler.h> 44 #include <linux/gfp.h> 45 #include <linux/module.h> 46 #include <linux/static_key.h> 47 48 #include <trace/events/tcp.h> 49 50 /* Refresh clocks of a TCP socket, 51 * ensuring monotically increasing values. 52 */ 53 void tcp_mstamp_refresh(struct tcp_sock *tp) 54 { 55 u64 val = tcp_clock_ns(); 56 57 tp->tcp_clock_cache = val; 58 tp->tcp_mstamp = div_u64(val, NSEC_PER_USEC); 59 } 60 61 static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle, 62 int push_one, gfp_t gfp); 63 64 /* Account for new data that has been sent to the network. */ 65 static void tcp_event_new_data_sent(struct sock *sk, struct sk_buff *skb) 66 { 67 struct inet_connection_sock *icsk = inet_csk(sk); 68 struct tcp_sock *tp = tcp_sk(sk); 69 unsigned int prior_packets = tp->packets_out; 70 71 WRITE_ONCE(tp->snd_nxt, TCP_SKB_CB(skb)->end_seq); 72 73 __skb_unlink(skb, &sk->sk_write_queue); 74 tcp_rbtree_insert(&sk->tcp_rtx_queue, skb); 75 76 if (tp->highest_sack == NULL) 77 tp->highest_sack = skb; 78 79 tp->packets_out += tcp_skb_pcount(skb); 80 if (!prior_packets || icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) 81 tcp_rearm_rto(sk); 82 83 NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPORIGDATASENT, 84 tcp_skb_pcount(skb)); 85 tcp_check_space(sk); 86 } 87 88 /* SND.NXT, if window was not shrunk or the amount of shrunk was less than one 89 * window scaling factor due to loss of precision. 90 * If window has been shrunk, what should we make? It is not clear at all. 91 * Using SND.UNA we will fail to open window, SND.NXT is out of window. :-( 92 * Anything in between SND.UNA...SND.UNA+SND.WND also can be already 93 * invalid. OK, let's make this for now: 94 */ 95 static inline __u32 tcp_acceptable_seq(const struct sock *sk) 96 { 97 const struct tcp_sock *tp = tcp_sk(sk); 98 99 if (!before(tcp_wnd_end(tp), tp->snd_nxt) || 100 (tp->rx_opt.wscale_ok && 101 ((tp->snd_nxt - tcp_wnd_end(tp)) < (1 << tp->rx_opt.rcv_wscale)))) 102 return tp->snd_nxt; 103 else 104 return tcp_wnd_end(tp); 105 } 106 107 /* Calculate mss to advertise in SYN segment. 108 * RFC1122, RFC1063, draft-ietf-tcpimpl-pmtud-01 state that: 109 * 110 * 1. It is independent of path mtu. 111 * 2. Ideally, it is maximal possible segment size i.e. 65535-40. 112 * 3. For IPv4 it is reasonable to calculate it from maximal MTU of 113 * attached devices, because some buggy hosts are confused by 114 * large MSS. 115 * 4. We do not make 3, we advertise MSS, calculated from first 116 * hop device mtu, but allow to raise it to ip_rt_min_advmss. 117 * This may be overridden via information stored in routing table. 118 * 5. Value 65535 for MSS is valid in IPv6 and means "as large as possible, 119 * probably even Jumbo". 120 */ 121 static __u16 tcp_advertise_mss(struct sock *sk) 122 { 123 struct tcp_sock *tp = tcp_sk(sk); 124 const struct dst_entry *dst = __sk_dst_get(sk); 125 int mss = tp->advmss; 126 127 if (dst) { 128 unsigned int metric = dst_metric_advmss(dst); 129 130 if (metric < mss) { 131 mss = metric; 132 tp->advmss = mss; 133 } 134 } 135 136 return (__u16)mss; 137 } 138 139 /* RFC2861. Reset CWND after idle period longer RTO to "restart window". 140 * This is the first part of cwnd validation mechanism. 141 */ 142 void tcp_cwnd_restart(struct sock *sk, s32 delta) 143 { 144 struct tcp_sock *tp = tcp_sk(sk); 145 u32 restart_cwnd = tcp_init_cwnd(tp, __sk_dst_get(sk)); 146 u32 cwnd = tcp_snd_cwnd(tp); 147 148 tcp_ca_event(sk, CA_EVENT_CWND_RESTART); 149 150 tp->snd_ssthresh = tcp_current_ssthresh(sk); 151 restart_cwnd = min(restart_cwnd, cwnd); 152 153 while ((delta -= inet_csk(sk)->icsk_rto) > 0 && cwnd > restart_cwnd) 154 cwnd >>= 1; 155 tcp_snd_cwnd_set(tp, max(cwnd, restart_cwnd)); 156 tp->snd_cwnd_stamp = tcp_jiffies32; 157 tp->snd_cwnd_used = 0; 158 } 159 160 /* Congestion state accounting after a packet has been sent. */ 161 static void tcp_event_data_sent(struct tcp_sock *tp, 162 struct sock *sk) 163 { 164 struct inet_connection_sock *icsk = inet_csk(sk); 165 const u32 now = tcp_jiffies32; 166 167 if (tcp_packets_in_flight(tp) == 0) 168 tcp_ca_event(sk, CA_EVENT_TX_START); 169 170 /* If this is the first data packet sent in response to the 171 * previous received data, 172 * and it is a reply for ato after last received packet, 173 * increase pingpong count. 174 */ 175 if (before(tp->lsndtime, icsk->icsk_ack.lrcvtime) && 176 (u32)(now - icsk->icsk_ack.lrcvtime) < icsk->icsk_ack.ato) 177 inet_csk_inc_pingpong_cnt(sk); 178 179 tp->lsndtime = now; 180 } 181 182 /* Account for an ACK we sent. */ 183 static inline void tcp_event_ack_sent(struct sock *sk, unsigned int pkts, 184 u32 rcv_nxt) 185 { 186 struct tcp_sock *tp = tcp_sk(sk); 187 188 if (unlikely(tp->compressed_ack)) { 189 NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPACKCOMPRESSED, 190 tp->compressed_ack); 191 tp->compressed_ack = 0; 192 if (hrtimer_try_to_cancel(&tp->compressed_ack_timer) == 1) 193 __sock_put(sk); 194 } 195 196 if (unlikely(rcv_nxt != tp->rcv_nxt)) 197 return; /* Special ACK sent by DCTCP to reflect ECN */ 198 tcp_dec_quickack_mode(sk, pkts); 199 inet_csk_clear_xmit_timer(sk, ICSK_TIME_DACK); 200 } 201 202 /* Determine a window scaling and initial window to offer. 203 * Based on the assumption that the given amount of space 204 * will be offered. Store the results in the tp structure. 205 * NOTE: for smooth operation initial space offering should 206 * be a multiple of mss if possible. We assume here that mss >= 1. 207 * This MUST be enforced by all callers. 208 */ 209 void tcp_select_initial_window(const struct sock *sk, int __space, __u32 mss, 210 __u32 *rcv_wnd, __u32 *window_clamp, 211 int wscale_ok, __u8 *rcv_wscale, 212 __u32 init_rcv_wnd) 213 { 214 unsigned int space = (__space < 0 ? 0 : __space); 215 216 /* If no clamp set the clamp to the max possible scaled window */ 217 if (*window_clamp == 0) 218 (*window_clamp) = (U16_MAX << TCP_MAX_WSCALE); 219 space = min(*window_clamp, space); 220 221 /* Quantize space offering to a multiple of mss if possible. */ 222 if (space > mss) 223 space = rounddown(space, mss); 224 225 /* NOTE: offering an initial window larger than 32767 226 * will break some buggy TCP stacks. If the admin tells us 227 * it is likely we could be speaking with such a buggy stack 228 * we will truncate our initial window offering to 32K-1 229 * unless the remote has sent us a window scaling option, 230 * which we interpret as a sign the remote TCP is not 231 * misinterpreting the window field as a signed quantity. 232 */ 233 if (sock_net(sk)->ipv4.sysctl_tcp_workaround_signed_windows) 234 (*rcv_wnd) = min(space, MAX_TCP_WINDOW); 235 else 236 (*rcv_wnd) = min_t(u32, space, U16_MAX); 237 238 if (init_rcv_wnd) 239 *rcv_wnd = min(*rcv_wnd, init_rcv_wnd * mss); 240 241 *rcv_wscale = 0; 242 if (wscale_ok) { 243 /* Set window scaling on max possible window */ 244 space = max_t(u32, space, sock_net(sk)->ipv4.sysctl_tcp_rmem[2]); 245 space = max_t(u32, space, sysctl_rmem_max); 246 space = min_t(u32, space, *window_clamp); 247 *rcv_wscale = clamp_t(int, ilog2(space) - 15, 248 0, TCP_MAX_WSCALE); 249 } 250 /* Set the clamp no higher than max representable value */ 251 (*window_clamp) = min_t(__u32, U16_MAX << (*rcv_wscale), *window_clamp); 252 } 253 EXPORT_SYMBOL(tcp_select_initial_window); 254 255 /* Chose a new window to advertise, update state in tcp_sock for the 256 * socket, and return result with RFC1323 scaling applied. The return 257 * value can be stuffed directly into th->window for an outgoing 258 * frame. 259 */ 260 static u16 tcp_select_window(struct sock *sk) 261 { 262 struct tcp_sock *tp = tcp_sk(sk); 263 u32 old_win = tp->rcv_wnd; 264 u32 cur_win = tcp_receive_window(tp); 265 u32 new_win = __tcp_select_window(sk); 266 267 /* Never shrink the offered window */ 268 if (new_win < cur_win) { 269 /* Danger Will Robinson! 270 * Don't update rcv_wup/rcv_wnd here or else 271 * we will not be able to advertise a zero 272 * window in time. --DaveM 273 * 274 * Relax Will Robinson. 275 */ 276 if (new_win == 0) 277 NET_INC_STATS(sock_net(sk), 278 LINUX_MIB_TCPWANTZEROWINDOWADV); 279 new_win = ALIGN(cur_win, 1 << tp->rx_opt.rcv_wscale); 280 } 281 tp->rcv_wnd = new_win; 282 tp->rcv_wup = tp->rcv_nxt; 283 284 /* Make sure we do not exceed the maximum possible 285 * scaled window. 286 */ 287 if (!tp->rx_opt.rcv_wscale && 288 sock_net(sk)->ipv4.sysctl_tcp_workaround_signed_windows) 289 new_win = min(new_win, MAX_TCP_WINDOW); 290 else 291 new_win = min(new_win, (65535U << tp->rx_opt.rcv_wscale)); 292 293 /* RFC1323 scaling applied */ 294 new_win >>= tp->rx_opt.rcv_wscale; 295 296 /* If we advertise zero window, disable fast path. */ 297 if (new_win == 0) { 298 tp->pred_flags = 0; 299 if (old_win) 300 NET_INC_STATS(sock_net(sk), 301 LINUX_MIB_TCPTOZEROWINDOWADV); 302 } else if (old_win == 0) { 303 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFROMZEROWINDOWADV); 304 } 305 306 return new_win; 307 } 308 309 /* Packet ECN state for a SYN-ACK */ 310 static void tcp_ecn_send_synack(struct sock *sk, struct sk_buff *skb) 311 { 312 const struct tcp_sock *tp = tcp_sk(sk); 313 314 TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_CWR; 315 if (!(tp->ecn_flags & TCP_ECN_OK)) 316 TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_ECE; 317 else if (tcp_ca_needs_ecn(sk) || 318 tcp_bpf_ca_needs_ecn(sk)) 319 INET_ECN_xmit(sk); 320 } 321 322 /* Packet ECN state for a SYN. */ 323 static void tcp_ecn_send_syn(struct sock *sk, struct sk_buff *skb) 324 { 325 struct tcp_sock *tp = tcp_sk(sk); 326 bool bpf_needs_ecn = tcp_bpf_ca_needs_ecn(sk); 327 bool use_ecn = READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_ecn) == 1 || 328 tcp_ca_needs_ecn(sk) || bpf_needs_ecn; 329 330 if (!use_ecn) { 331 const struct dst_entry *dst = __sk_dst_get(sk); 332 333 if (dst && dst_feature(dst, RTAX_FEATURE_ECN)) 334 use_ecn = true; 335 } 336 337 tp->ecn_flags = 0; 338 339 if (use_ecn) { 340 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ECE | TCPHDR_CWR; 341 tp->ecn_flags = TCP_ECN_OK; 342 if (tcp_ca_needs_ecn(sk) || bpf_needs_ecn) 343 INET_ECN_xmit(sk); 344 } 345 } 346 347 static void tcp_ecn_clear_syn(struct sock *sk, struct sk_buff *skb) 348 { 349 if (READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_ecn_fallback)) 350 /* tp->ecn_flags are cleared at a later point in time when 351 * SYN ACK is ultimatively being received. 352 */ 353 TCP_SKB_CB(skb)->tcp_flags &= ~(TCPHDR_ECE | TCPHDR_CWR); 354 } 355 356 static void 357 tcp_ecn_make_synack(const struct request_sock *req, struct tcphdr *th) 358 { 359 if (inet_rsk(req)->ecn_ok) 360 th->ece = 1; 361 } 362 363 /* Set up ECN state for a packet on a ESTABLISHED socket that is about to 364 * be sent. 365 */ 366 static void tcp_ecn_send(struct sock *sk, struct sk_buff *skb, 367 struct tcphdr *th, int tcp_header_len) 368 { 369 struct tcp_sock *tp = tcp_sk(sk); 370 371 if (tp->ecn_flags & TCP_ECN_OK) { 372 /* Not-retransmitted data segment: set ECT and inject CWR. */ 373 if (skb->len != tcp_header_len && 374 !before(TCP_SKB_CB(skb)->seq, tp->snd_nxt)) { 375 INET_ECN_xmit(sk); 376 if (tp->ecn_flags & TCP_ECN_QUEUE_CWR) { 377 tp->ecn_flags &= ~TCP_ECN_QUEUE_CWR; 378 th->cwr = 1; 379 skb_shinfo(skb)->gso_type |= SKB_GSO_TCP_ECN; 380 } 381 } else if (!tcp_ca_needs_ecn(sk)) { 382 /* ACK or retransmitted segment: clear ECT|CE */ 383 INET_ECN_dontxmit(sk); 384 } 385 if (tp->ecn_flags & TCP_ECN_DEMAND_CWR) 386 th->ece = 1; 387 } 388 } 389 390 /* Constructs common control bits of non-data skb. If SYN/FIN is present, 391 * auto increment end seqno. 392 */ 393 static void tcp_init_nondata_skb(struct sk_buff *skb, u32 seq, u8 flags) 394 { 395 skb->ip_summed = CHECKSUM_PARTIAL; 396 397 TCP_SKB_CB(skb)->tcp_flags = flags; 398 399 tcp_skb_pcount_set(skb, 1); 400 401 TCP_SKB_CB(skb)->seq = seq; 402 if (flags & (TCPHDR_SYN | TCPHDR_FIN)) 403 seq++; 404 TCP_SKB_CB(skb)->end_seq = seq; 405 } 406 407 static inline bool tcp_urg_mode(const struct tcp_sock *tp) 408 { 409 return tp->snd_una != tp->snd_up; 410 } 411 412 #define OPTION_SACK_ADVERTISE BIT(0) 413 #define OPTION_TS BIT(1) 414 #define OPTION_MD5 BIT(2) 415 #define OPTION_WSCALE BIT(3) 416 #define OPTION_FAST_OPEN_COOKIE BIT(8) 417 #define OPTION_SMC BIT(9) 418 #define OPTION_MPTCP BIT(10) 419 420 static void smc_options_write(__be32 *ptr, u16 *options) 421 { 422 #if IS_ENABLED(CONFIG_SMC) 423 if (static_branch_unlikely(&tcp_have_smc)) { 424 if (unlikely(OPTION_SMC & *options)) { 425 *ptr++ = htonl((TCPOPT_NOP << 24) | 426 (TCPOPT_NOP << 16) | 427 (TCPOPT_EXP << 8) | 428 (TCPOLEN_EXP_SMC_BASE)); 429 *ptr++ = htonl(TCPOPT_SMC_MAGIC); 430 } 431 } 432 #endif 433 } 434 435 struct tcp_out_options { 436 u16 options; /* bit field of OPTION_* */ 437 u16 mss; /* 0 to disable */ 438 u8 ws; /* window scale, 0 to disable */ 439 u8 num_sack_blocks; /* number of SACK blocks to include */ 440 u8 hash_size; /* bytes in hash_location */ 441 u8 bpf_opt_len; /* length of BPF hdr option */ 442 __u8 *hash_location; /* temporary pointer, overloaded */ 443 __u32 tsval, tsecr; /* need to include OPTION_TS */ 444 struct tcp_fastopen_cookie *fastopen_cookie; /* Fast open cookie */ 445 struct mptcp_out_options mptcp; 446 }; 447 448 static void mptcp_options_write(struct tcphdr *th, __be32 *ptr, 449 struct tcp_sock *tp, 450 struct tcp_out_options *opts) 451 { 452 #if IS_ENABLED(CONFIG_MPTCP) 453 if (unlikely(OPTION_MPTCP & opts->options)) 454 mptcp_write_options(th, ptr, tp, &opts->mptcp); 455 #endif 456 } 457 458 #ifdef CONFIG_CGROUP_BPF 459 static int bpf_skops_write_hdr_opt_arg0(struct sk_buff *skb, 460 enum tcp_synack_type synack_type) 461 { 462 if (unlikely(!skb)) 463 return BPF_WRITE_HDR_TCP_CURRENT_MSS; 464 465 if (unlikely(synack_type == TCP_SYNACK_COOKIE)) 466 return BPF_WRITE_HDR_TCP_SYNACK_COOKIE; 467 468 return 0; 469 } 470 471 /* req, syn_skb and synack_type are used when writing synack */ 472 static void bpf_skops_hdr_opt_len(struct sock *sk, struct sk_buff *skb, 473 struct request_sock *req, 474 struct sk_buff *syn_skb, 475 enum tcp_synack_type synack_type, 476 struct tcp_out_options *opts, 477 unsigned int *remaining) 478 { 479 struct bpf_sock_ops_kern sock_ops; 480 int err; 481 482 if (likely(!BPF_SOCK_OPS_TEST_FLAG(tcp_sk(sk), 483 BPF_SOCK_OPS_WRITE_HDR_OPT_CB_FLAG)) || 484 !*remaining) 485 return; 486 487 /* *remaining has already been aligned to 4 bytes, so *remaining >= 4 */ 488 489 /* init sock_ops */ 490 memset(&sock_ops, 0, offsetof(struct bpf_sock_ops_kern, temp)); 491 492 sock_ops.op = BPF_SOCK_OPS_HDR_OPT_LEN_CB; 493 494 if (req) { 495 /* The listen "sk" cannot be passed here because 496 * it is not locked. It would not make too much 497 * sense to do bpf_setsockopt(listen_sk) based 498 * on individual connection request also. 499 * 500 * Thus, "req" is passed here and the cgroup-bpf-progs 501 * of the listen "sk" will be run. 502 * 503 * "req" is also used here for fastopen even the "sk" here is 504 * a fullsock "child" sk. It is to keep the behavior 505 * consistent between fastopen and non-fastopen on 506 * the bpf programming side. 507 */ 508 sock_ops.sk = (struct sock *)req; 509 sock_ops.syn_skb = syn_skb; 510 } else { 511 sock_owned_by_me(sk); 512 513 sock_ops.is_fullsock = 1; 514 sock_ops.sk = sk; 515 } 516 517 sock_ops.args[0] = bpf_skops_write_hdr_opt_arg0(skb, synack_type); 518 sock_ops.remaining_opt_len = *remaining; 519 /* tcp_current_mss() does not pass a skb */ 520 if (skb) 521 bpf_skops_init_skb(&sock_ops, skb, 0); 522 523 err = BPF_CGROUP_RUN_PROG_SOCK_OPS_SK(&sock_ops, sk); 524 525 if (err || sock_ops.remaining_opt_len == *remaining) 526 return; 527 528 opts->bpf_opt_len = *remaining - sock_ops.remaining_opt_len; 529 /* round up to 4 bytes */ 530 opts->bpf_opt_len = (opts->bpf_opt_len + 3) & ~3; 531 532 *remaining -= opts->bpf_opt_len; 533 } 534 535 static void bpf_skops_write_hdr_opt(struct sock *sk, struct sk_buff *skb, 536 struct request_sock *req, 537 struct sk_buff *syn_skb, 538 enum tcp_synack_type synack_type, 539 struct tcp_out_options *opts) 540 { 541 u8 first_opt_off, nr_written, max_opt_len = opts->bpf_opt_len; 542 struct bpf_sock_ops_kern sock_ops; 543 int err; 544 545 if (likely(!max_opt_len)) 546 return; 547 548 memset(&sock_ops, 0, offsetof(struct bpf_sock_ops_kern, temp)); 549 550 sock_ops.op = BPF_SOCK_OPS_WRITE_HDR_OPT_CB; 551 552 if (req) { 553 sock_ops.sk = (struct sock *)req; 554 sock_ops.syn_skb = syn_skb; 555 } else { 556 sock_owned_by_me(sk); 557 558 sock_ops.is_fullsock = 1; 559 sock_ops.sk = sk; 560 } 561 562 sock_ops.args[0] = bpf_skops_write_hdr_opt_arg0(skb, synack_type); 563 sock_ops.remaining_opt_len = max_opt_len; 564 first_opt_off = tcp_hdrlen(skb) - max_opt_len; 565 bpf_skops_init_skb(&sock_ops, skb, first_opt_off); 566 567 err = BPF_CGROUP_RUN_PROG_SOCK_OPS_SK(&sock_ops, sk); 568 569 if (err) 570 nr_written = 0; 571 else 572 nr_written = max_opt_len - sock_ops.remaining_opt_len; 573 574 if (nr_written < max_opt_len) 575 memset(skb->data + first_opt_off + nr_written, TCPOPT_NOP, 576 max_opt_len - nr_written); 577 } 578 #else 579 static void bpf_skops_hdr_opt_len(struct sock *sk, struct sk_buff *skb, 580 struct request_sock *req, 581 struct sk_buff *syn_skb, 582 enum tcp_synack_type synack_type, 583 struct tcp_out_options *opts, 584 unsigned int *remaining) 585 { 586 } 587 588 static void bpf_skops_write_hdr_opt(struct sock *sk, struct sk_buff *skb, 589 struct request_sock *req, 590 struct sk_buff *syn_skb, 591 enum tcp_synack_type synack_type, 592 struct tcp_out_options *opts) 593 { 594 } 595 #endif 596 597 /* Write previously computed TCP options to the packet. 598 * 599 * Beware: Something in the Internet is very sensitive to the ordering of 600 * TCP options, we learned this through the hard way, so be careful here. 601 * Luckily we can at least blame others for their non-compliance but from 602 * inter-operability perspective it seems that we're somewhat stuck with 603 * the ordering which we have been using if we want to keep working with 604 * those broken things (not that it currently hurts anybody as there isn't 605 * particular reason why the ordering would need to be changed). 606 * 607 * At least SACK_PERM as the first option is known to lead to a disaster 608 * (but it may well be that other scenarios fail similarly). 609 */ 610 static void tcp_options_write(struct tcphdr *th, struct tcp_sock *tp, 611 struct tcp_out_options *opts) 612 { 613 __be32 *ptr = (__be32 *)(th + 1); 614 u16 options = opts->options; /* mungable copy */ 615 616 if (unlikely(OPTION_MD5 & options)) { 617 *ptr++ = htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16) | 618 (TCPOPT_MD5SIG << 8) | TCPOLEN_MD5SIG); 619 /* overload cookie hash location */ 620 opts->hash_location = (__u8 *)ptr; 621 ptr += 4; 622 } 623 624 if (unlikely(opts->mss)) { 625 *ptr++ = htonl((TCPOPT_MSS << 24) | 626 (TCPOLEN_MSS << 16) | 627 opts->mss); 628 } 629 630 if (likely(OPTION_TS & options)) { 631 if (unlikely(OPTION_SACK_ADVERTISE & options)) { 632 *ptr++ = htonl((TCPOPT_SACK_PERM << 24) | 633 (TCPOLEN_SACK_PERM << 16) | 634 (TCPOPT_TIMESTAMP << 8) | 635 TCPOLEN_TIMESTAMP); 636 options &= ~OPTION_SACK_ADVERTISE; 637 } else { 638 *ptr++ = htonl((TCPOPT_NOP << 24) | 639 (TCPOPT_NOP << 16) | 640 (TCPOPT_TIMESTAMP << 8) | 641 TCPOLEN_TIMESTAMP); 642 } 643 *ptr++ = htonl(opts->tsval); 644 *ptr++ = htonl(opts->tsecr); 645 } 646 647 if (unlikely(OPTION_SACK_ADVERTISE & options)) { 648 *ptr++ = htonl((TCPOPT_NOP << 24) | 649 (TCPOPT_NOP << 16) | 650 (TCPOPT_SACK_PERM << 8) | 651 TCPOLEN_SACK_PERM); 652 } 653 654 if (unlikely(OPTION_WSCALE & options)) { 655 *ptr++ = htonl((TCPOPT_NOP << 24) | 656 (TCPOPT_WINDOW << 16) | 657 (TCPOLEN_WINDOW << 8) | 658 opts->ws); 659 } 660 661 if (unlikely(opts->num_sack_blocks)) { 662 struct tcp_sack_block *sp = tp->rx_opt.dsack ? 663 tp->duplicate_sack : tp->selective_acks; 664 int this_sack; 665 666 *ptr++ = htonl((TCPOPT_NOP << 24) | 667 (TCPOPT_NOP << 16) | 668 (TCPOPT_SACK << 8) | 669 (TCPOLEN_SACK_BASE + (opts->num_sack_blocks * 670 TCPOLEN_SACK_PERBLOCK))); 671 672 for (this_sack = 0; this_sack < opts->num_sack_blocks; 673 ++this_sack) { 674 *ptr++ = htonl(sp[this_sack].start_seq); 675 *ptr++ = htonl(sp[this_sack].end_seq); 676 } 677 678 tp->rx_opt.dsack = 0; 679 } 680 681 if (unlikely(OPTION_FAST_OPEN_COOKIE & options)) { 682 struct tcp_fastopen_cookie *foc = opts->fastopen_cookie; 683 u8 *p = (u8 *)ptr; 684 u32 len; /* Fast Open option length */ 685 686 if (foc->exp) { 687 len = TCPOLEN_EXP_FASTOPEN_BASE + foc->len; 688 *ptr = htonl((TCPOPT_EXP << 24) | (len << 16) | 689 TCPOPT_FASTOPEN_MAGIC); 690 p += TCPOLEN_EXP_FASTOPEN_BASE; 691 } else { 692 len = TCPOLEN_FASTOPEN_BASE + foc->len; 693 *p++ = TCPOPT_FASTOPEN; 694 *p++ = len; 695 } 696 697 memcpy(p, foc->val, foc->len); 698 if ((len & 3) == 2) { 699 p[foc->len] = TCPOPT_NOP; 700 p[foc->len + 1] = TCPOPT_NOP; 701 } 702 ptr += (len + 3) >> 2; 703 } 704 705 smc_options_write(ptr, &options); 706 707 mptcp_options_write(th, ptr, tp, opts); 708 } 709 710 static void smc_set_option(const struct tcp_sock *tp, 711 struct tcp_out_options *opts, 712 unsigned int *remaining) 713 { 714 #if IS_ENABLED(CONFIG_SMC) 715 if (static_branch_unlikely(&tcp_have_smc)) { 716 if (tp->syn_smc) { 717 if (*remaining >= TCPOLEN_EXP_SMC_BASE_ALIGNED) { 718 opts->options |= OPTION_SMC; 719 *remaining -= TCPOLEN_EXP_SMC_BASE_ALIGNED; 720 } 721 } 722 } 723 #endif 724 } 725 726 static void smc_set_option_cond(const struct tcp_sock *tp, 727 const struct inet_request_sock *ireq, 728 struct tcp_out_options *opts, 729 unsigned int *remaining) 730 { 731 #if IS_ENABLED(CONFIG_SMC) 732 if (static_branch_unlikely(&tcp_have_smc)) { 733 if (tp->syn_smc && ireq->smc_ok) { 734 if (*remaining >= TCPOLEN_EXP_SMC_BASE_ALIGNED) { 735 opts->options |= OPTION_SMC; 736 *remaining -= TCPOLEN_EXP_SMC_BASE_ALIGNED; 737 } 738 } 739 } 740 #endif 741 } 742 743 static void mptcp_set_option_cond(const struct request_sock *req, 744 struct tcp_out_options *opts, 745 unsigned int *remaining) 746 { 747 if (rsk_is_mptcp(req)) { 748 unsigned int size; 749 750 if (mptcp_synack_options(req, &size, &opts->mptcp)) { 751 if (*remaining >= size) { 752 opts->options |= OPTION_MPTCP; 753 *remaining -= size; 754 } 755 } 756 } 757 } 758 759 /* Compute TCP options for SYN packets. This is not the final 760 * network wire format yet. 761 */ 762 static unsigned int tcp_syn_options(struct sock *sk, struct sk_buff *skb, 763 struct tcp_out_options *opts, 764 struct tcp_md5sig_key **md5) 765 { 766 struct tcp_sock *tp = tcp_sk(sk); 767 unsigned int remaining = MAX_TCP_OPTION_SPACE; 768 struct tcp_fastopen_request *fastopen = tp->fastopen_req; 769 770 *md5 = NULL; 771 #ifdef CONFIG_TCP_MD5SIG 772 if (static_branch_unlikely(&tcp_md5_needed) && 773 rcu_access_pointer(tp->md5sig_info)) { 774 *md5 = tp->af_specific->md5_lookup(sk, sk); 775 if (*md5) { 776 opts->options |= OPTION_MD5; 777 remaining -= TCPOLEN_MD5SIG_ALIGNED; 778 } 779 } 780 #endif 781 782 /* We always get an MSS option. The option bytes which will be seen in 783 * normal data packets should timestamps be used, must be in the MSS 784 * advertised. But we subtract them from tp->mss_cache so that 785 * calculations in tcp_sendmsg are simpler etc. So account for this 786 * fact here if necessary. If we don't do this correctly, as a 787 * receiver we won't recognize data packets as being full sized when we 788 * should, and thus we won't abide by the delayed ACK rules correctly. 789 * SACKs don't matter, we never delay an ACK when we have any of those 790 * going out. */ 791 opts->mss = tcp_advertise_mss(sk); 792 remaining -= TCPOLEN_MSS_ALIGNED; 793 794 if (likely(READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_timestamps) && !*md5)) { 795 opts->options |= OPTION_TS; 796 opts->tsval = tcp_skb_timestamp(skb) + tp->tsoffset; 797 opts->tsecr = tp->rx_opt.ts_recent; 798 remaining -= TCPOLEN_TSTAMP_ALIGNED; 799 } 800 if (likely(READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_window_scaling))) { 801 opts->ws = tp->rx_opt.rcv_wscale; 802 opts->options |= OPTION_WSCALE; 803 remaining -= TCPOLEN_WSCALE_ALIGNED; 804 } 805 if (likely(READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_sack))) { 806 opts->options |= OPTION_SACK_ADVERTISE; 807 if (unlikely(!(OPTION_TS & opts->options))) 808 remaining -= TCPOLEN_SACKPERM_ALIGNED; 809 } 810 811 if (fastopen && fastopen->cookie.len >= 0) { 812 u32 need = fastopen->cookie.len; 813 814 need += fastopen->cookie.exp ? TCPOLEN_EXP_FASTOPEN_BASE : 815 TCPOLEN_FASTOPEN_BASE; 816 need = (need + 3) & ~3U; /* Align to 32 bits */ 817 if (remaining >= need) { 818 opts->options |= OPTION_FAST_OPEN_COOKIE; 819 opts->fastopen_cookie = &fastopen->cookie; 820 remaining -= need; 821 tp->syn_fastopen = 1; 822 tp->syn_fastopen_exp = fastopen->cookie.exp ? 1 : 0; 823 } 824 } 825 826 smc_set_option(tp, opts, &remaining); 827 828 if (sk_is_mptcp(sk)) { 829 unsigned int size; 830 831 if (mptcp_syn_options(sk, skb, &size, &opts->mptcp)) { 832 opts->options |= OPTION_MPTCP; 833 remaining -= size; 834 } 835 } 836 837 bpf_skops_hdr_opt_len(sk, skb, NULL, NULL, 0, opts, &remaining); 838 839 return MAX_TCP_OPTION_SPACE - remaining; 840 } 841 842 /* Set up TCP options for SYN-ACKs. */ 843 static unsigned int tcp_synack_options(const struct sock *sk, 844 struct request_sock *req, 845 unsigned int mss, struct sk_buff *skb, 846 struct tcp_out_options *opts, 847 const struct tcp_md5sig_key *md5, 848 struct tcp_fastopen_cookie *foc, 849 enum tcp_synack_type synack_type, 850 struct sk_buff *syn_skb) 851 { 852 struct inet_request_sock *ireq = inet_rsk(req); 853 unsigned int remaining = MAX_TCP_OPTION_SPACE; 854 855 #ifdef CONFIG_TCP_MD5SIG 856 if (md5) { 857 opts->options |= OPTION_MD5; 858 remaining -= TCPOLEN_MD5SIG_ALIGNED; 859 860 /* We can't fit any SACK blocks in a packet with MD5 + TS 861 * options. There was discussion about disabling SACK 862 * rather than TS in order to fit in better with old, 863 * buggy kernels, but that was deemed to be unnecessary. 864 */ 865 if (synack_type != TCP_SYNACK_COOKIE) 866 ireq->tstamp_ok &= !ireq->sack_ok; 867 } 868 #endif 869 870 /* We always send an MSS option. */ 871 opts->mss = mss; 872 remaining -= TCPOLEN_MSS_ALIGNED; 873 874 if (likely(ireq->wscale_ok)) { 875 opts->ws = ireq->rcv_wscale; 876 opts->options |= OPTION_WSCALE; 877 remaining -= TCPOLEN_WSCALE_ALIGNED; 878 } 879 if (likely(ireq->tstamp_ok)) { 880 opts->options |= OPTION_TS; 881 opts->tsval = tcp_skb_timestamp(skb) + tcp_rsk(req)->ts_off; 882 opts->tsecr = req->ts_recent; 883 remaining -= TCPOLEN_TSTAMP_ALIGNED; 884 } 885 if (likely(ireq->sack_ok)) { 886 opts->options |= OPTION_SACK_ADVERTISE; 887 if (unlikely(!ireq->tstamp_ok)) 888 remaining -= TCPOLEN_SACKPERM_ALIGNED; 889 } 890 if (foc != NULL && foc->len >= 0) { 891 u32 need = foc->len; 892 893 need += foc->exp ? TCPOLEN_EXP_FASTOPEN_BASE : 894 TCPOLEN_FASTOPEN_BASE; 895 need = (need + 3) & ~3U; /* Align to 32 bits */ 896 if (remaining >= need) { 897 opts->options |= OPTION_FAST_OPEN_COOKIE; 898 opts->fastopen_cookie = foc; 899 remaining -= need; 900 } 901 } 902 903 mptcp_set_option_cond(req, opts, &remaining); 904 905 smc_set_option_cond(tcp_sk(sk), ireq, opts, &remaining); 906 907 bpf_skops_hdr_opt_len((struct sock *)sk, skb, req, syn_skb, 908 synack_type, opts, &remaining); 909 910 return MAX_TCP_OPTION_SPACE - remaining; 911 } 912 913 /* Compute TCP options for ESTABLISHED sockets. This is not the 914 * final wire format yet. 915 */ 916 static unsigned int tcp_established_options(struct sock *sk, struct sk_buff *skb, 917 struct tcp_out_options *opts, 918 struct tcp_md5sig_key **md5) 919 { 920 struct tcp_sock *tp = tcp_sk(sk); 921 unsigned int size = 0; 922 unsigned int eff_sacks; 923 924 opts->options = 0; 925 926 *md5 = NULL; 927 #ifdef CONFIG_TCP_MD5SIG 928 if (static_branch_unlikely(&tcp_md5_needed) && 929 rcu_access_pointer(tp->md5sig_info)) { 930 *md5 = tp->af_specific->md5_lookup(sk, sk); 931 if (*md5) { 932 opts->options |= OPTION_MD5; 933 size += TCPOLEN_MD5SIG_ALIGNED; 934 } 935 } 936 #endif 937 938 if (likely(tp->rx_opt.tstamp_ok)) { 939 opts->options |= OPTION_TS; 940 opts->tsval = skb ? tcp_skb_timestamp(skb) + tp->tsoffset : 0; 941 opts->tsecr = tp->rx_opt.ts_recent; 942 size += TCPOLEN_TSTAMP_ALIGNED; 943 } 944 945 /* MPTCP options have precedence over SACK for the limited TCP 946 * option space because a MPTCP connection would be forced to 947 * fall back to regular TCP if a required multipath option is 948 * missing. SACK still gets a chance to use whatever space is 949 * left. 950 */ 951 if (sk_is_mptcp(sk)) { 952 unsigned int remaining = MAX_TCP_OPTION_SPACE - size; 953 unsigned int opt_size = 0; 954 955 if (mptcp_established_options(sk, skb, &opt_size, remaining, 956 &opts->mptcp)) { 957 opts->options |= OPTION_MPTCP; 958 size += opt_size; 959 } 960 } 961 962 eff_sacks = tp->rx_opt.num_sacks + tp->rx_opt.dsack; 963 if (unlikely(eff_sacks)) { 964 const unsigned int remaining = MAX_TCP_OPTION_SPACE - size; 965 if (unlikely(remaining < TCPOLEN_SACK_BASE_ALIGNED + 966 TCPOLEN_SACK_PERBLOCK)) 967 return size; 968 969 opts->num_sack_blocks = 970 min_t(unsigned int, eff_sacks, 971 (remaining - TCPOLEN_SACK_BASE_ALIGNED) / 972 TCPOLEN_SACK_PERBLOCK); 973 974 size += TCPOLEN_SACK_BASE_ALIGNED + 975 opts->num_sack_blocks * TCPOLEN_SACK_PERBLOCK; 976 } 977 978 if (unlikely(BPF_SOCK_OPS_TEST_FLAG(tp, 979 BPF_SOCK_OPS_WRITE_HDR_OPT_CB_FLAG))) { 980 unsigned int remaining = MAX_TCP_OPTION_SPACE - size; 981 982 bpf_skops_hdr_opt_len(sk, skb, NULL, NULL, 0, opts, &remaining); 983 984 size = MAX_TCP_OPTION_SPACE - remaining; 985 } 986 987 return size; 988 } 989 990 991 /* TCP SMALL QUEUES (TSQ) 992 * 993 * TSQ goal is to keep small amount of skbs per tcp flow in tx queues (qdisc+dev) 994 * to reduce RTT and bufferbloat. 995 * We do this using a special skb destructor (tcp_wfree). 996 * 997 * Its important tcp_wfree() can be replaced by sock_wfree() in the event skb 998 * needs to be reallocated in a driver. 999 * The invariant being skb->truesize subtracted from sk->sk_wmem_alloc 1000 * 1001 * Since transmit from skb destructor is forbidden, we use a tasklet 1002 * to process all sockets that eventually need to send more skbs. 1003 * We use one tasklet per cpu, with its own queue of sockets. 1004 */ 1005 struct tsq_tasklet { 1006 struct tasklet_struct tasklet; 1007 struct list_head head; /* queue of tcp sockets */ 1008 }; 1009 static DEFINE_PER_CPU(struct tsq_tasklet, tsq_tasklet); 1010 1011 static void tcp_tsq_write(struct sock *sk) 1012 { 1013 if ((1 << sk->sk_state) & 1014 (TCPF_ESTABLISHED | TCPF_FIN_WAIT1 | TCPF_CLOSING | 1015 TCPF_CLOSE_WAIT | TCPF_LAST_ACK)) { 1016 struct tcp_sock *tp = tcp_sk(sk); 1017 1018 if (tp->lost_out > tp->retrans_out && 1019 tcp_snd_cwnd(tp) > tcp_packets_in_flight(tp)) { 1020 tcp_mstamp_refresh(tp); 1021 tcp_xmit_retransmit_queue(sk); 1022 } 1023 1024 tcp_write_xmit(sk, tcp_current_mss(sk), tp->nonagle, 1025 0, GFP_ATOMIC); 1026 } 1027 } 1028 1029 static void tcp_tsq_handler(struct sock *sk) 1030 { 1031 bh_lock_sock(sk); 1032 if (!sock_owned_by_user(sk)) 1033 tcp_tsq_write(sk); 1034 else if (!test_and_set_bit(TCP_TSQ_DEFERRED, &sk->sk_tsq_flags)) 1035 sock_hold(sk); 1036 bh_unlock_sock(sk); 1037 } 1038 /* 1039 * One tasklet per cpu tries to send more skbs. 1040 * We run in tasklet context but need to disable irqs when 1041 * transferring tsq->head because tcp_wfree() might 1042 * interrupt us (non NAPI drivers) 1043 */ 1044 static void tcp_tasklet_func(struct tasklet_struct *t) 1045 { 1046 struct tsq_tasklet *tsq = from_tasklet(tsq, t, tasklet); 1047 LIST_HEAD(list); 1048 unsigned long flags; 1049 struct list_head *q, *n; 1050 struct tcp_sock *tp; 1051 struct sock *sk; 1052 1053 local_irq_save(flags); 1054 list_splice_init(&tsq->head, &list); 1055 local_irq_restore(flags); 1056 1057 list_for_each_safe(q, n, &list) { 1058 tp = list_entry(q, struct tcp_sock, tsq_node); 1059 list_del(&tp->tsq_node); 1060 1061 sk = (struct sock *)tp; 1062 smp_mb__before_atomic(); 1063 clear_bit(TSQ_QUEUED, &sk->sk_tsq_flags); 1064 1065 tcp_tsq_handler(sk); 1066 sk_free(sk); 1067 } 1068 } 1069 1070 #define TCP_DEFERRED_ALL (TCPF_TSQ_DEFERRED | \ 1071 TCPF_WRITE_TIMER_DEFERRED | \ 1072 TCPF_DELACK_TIMER_DEFERRED | \ 1073 TCPF_MTU_REDUCED_DEFERRED) 1074 /** 1075 * tcp_release_cb - tcp release_sock() callback 1076 * @sk: socket 1077 * 1078 * called from release_sock() to perform protocol dependent 1079 * actions before socket release. 1080 */ 1081 void tcp_release_cb(struct sock *sk) 1082 { 1083 unsigned long flags, nflags; 1084 1085 /* perform an atomic operation only if at least one flag is set */ 1086 do { 1087 flags = sk->sk_tsq_flags; 1088 if (!(flags & TCP_DEFERRED_ALL)) 1089 return; 1090 nflags = flags & ~TCP_DEFERRED_ALL; 1091 } while (cmpxchg(&sk->sk_tsq_flags, flags, nflags) != flags); 1092 1093 if (flags & TCPF_TSQ_DEFERRED) { 1094 tcp_tsq_write(sk); 1095 __sock_put(sk); 1096 } 1097 /* Here begins the tricky part : 1098 * We are called from release_sock() with : 1099 * 1) BH disabled 1100 * 2) sk_lock.slock spinlock held 1101 * 3) socket owned by us (sk->sk_lock.owned == 1) 1102 * 1103 * But following code is meant to be called from BH handlers, 1104 * so we should keep BH disabled, but early release socket ownership 1105 */ 1106 sock_release_ownership(sk); 1107 1108 if (flags & TCPF_WRITE_TIMER_DEFERRED) { 1109 tcp_write_timer_handler(sk); 1110 __sock_put(sk); 1111 } 1112 if (flags & TCPF_DELACK_TIMER_DEFERRED) { 1113 tcp_delack_timer_handler(sk); 1114 __sock_put(sk); 1115 } 1116 if (flags & TCPF_MTU_REDUCED_DEFERRED) { 1117 inet_csk(sk)->icsk_af_ops->mtu_reduced(sk); 1118 __sock_put(sk); 1119 } 1120 } 1121 EXPORT_SYMBOL(tcp_release_cb); 1122 1123 void __init tcp_tasklet_init(void) 1124 { 1125 int i; 1126 1127 for_each_possible_cpu(i) { 1128 struct tsq_tasklet *tsq = &per_cpu(tsq_tasklet, i); 1129 1130 INIT_LIST_HEAD(&tsq->head); 1131 tasklet_setup(&tsq->tasklet, tcp_tasklet_func); 1132 } 1133 } 1134 1135 /* 1136 * Write buffer destructor automatically called from kfree_skb. 1137 * We can't xmit new skbs from this context, as we might already 1138 * hold qdisc lock. 1139 */ 1140 void tcp_wfree(struct sk_buff *skb) 1141 { 1142 struct sock *sk = skb->sk; 1143 struct tcp_sock *tp = tcp_sk(sk); 1144 unsigned long flags, nval, oval; 1145 1146 /* Keep one reference on sk_wmem_alloc. 1147 * Will be released by sk_free() from here or tcp_tasklet_func() 1148 */ 1149 WARN_ON(refcount_sub_and_test(skb->truesize - 1, &sk->sk_wmem_alloc)); 1150 1151 /* If this softirq is serviced by ksoftirqd, we are likely under stress. 1152 * Wait until our queues (qdisc + devices) are drained. 1153 * This gives : 1154 * - less callbacks to tcp_write_xmit(), reducing stress (batches) 1155 * - chance for incoming ACK (processed by another cpu maybe) 1156 * to migrate this flow (skb->ooo_okay will be eventually set) 1157 */ 1158 if (refcount_read(&sk->sk_wmem_alloc) >= SKB_TRUESIZE(1) && this_cpu_ksoftirqd() == current) 1159 goto out; 1160 1161 for (oval = READ_ONCE(sk->sk_tsq_flags);; oval = nval) { 1162 struct tsq_tasklet *tsq; 1163 bool empty; 1164 1165 if (!(oval & TSQF_THROTTLED) || (oval & TSQF_QUEUED)) 1166 goto out; 1167 1168 nval = (oval & ~TSQF_THROTTLED) | TSQF_QUEUED; 1169 nval = cmpxchg(&sk->sk_tsq_flags, oval, nval); 1170 if (nval != oval) 1171 continue; 1172 1173 /* queue this socket to tasklet queue */ 1174 local_irq_save(flags); 1175 tsq = this_cpu_ptr(&tsq_tasklet); 1176 empty = list_empty(&tsq->head); 1177 list_add(&tp->tsq_node, &tsq->head); 1178 if (empty) 1179 tasklet_schedule(&tsq->tasklet); 1180 local_irq_restore(flags); 1181 return; 1182 } 1183 out: 1184 sk_free(sk); 1185 } 1186 1187 /* Note: Called under soft irq. 1188 * We can call TCP stack right away, unless socket is owned by user. 1189 */ 1190 enum hrtimer_restart tcp_pace_kick(struct hrtimer *timer) 1191 { 1192 struct tcp_sock *tp = container_of(timer, struct tcp_sock, pacing_timer); 1193 struct sock *sk = (struct sock *)tp; 1194 1195 tcp_tsq_handler(sk); 1196 sock_put(sk); 1197 1198 return HRTIMER_NORESTART; 1199 } 1200 1201 static void tcp_update_skb_after_send(struct sock *sk, struct sk_buff *skb, 1202 u64 prior_wstamp) 1203 { 1204 struct tcp_sock *tp = tcp_sk(sk); 1205 1206 if (sk->sk_pacing_status != SK_PACING_NONE) { 1207 unsigned long rate = sk->sk_pacing_rate; 1208 1209 /* Original sch_fq does not pace first 10 MSS 1210 * Note that tp->data_segs_out overflows after 2^32 packets, 1211 * this is a minor annoyance. 1212 */ 1213 if (rate != ~0UL && rate && tp->data_segs_out >= 10) { 1214 u64 len_ns = div64_ul((u64)skb->len * NSEC_PER_SEC, rate); 1215 u64 credit = tp->tcp_wstamp_ns - prior_wstamp; 1216 1217 /* take into account OS jitter */ 1218 len_ns -= min_t(u64, len_ns / 2, credit); 1219 tp->tcp_wstamp_ns += len_ns; 1220 } 1221 } 1222 list_move_tail(&skb->tcp_tsorted_anchor, &tp->tsorted_sent_queue); 1223 } 1224 1225 INDIRECT_CALLABLE_DECLARE(int ip_queue_xmit(struct sock *sk, struct sk_buff *skb, struct flowi *fl)); 1226 INDIRECT_CALLABLE_DECLARE(int inet6_csk_xmit(struct sock *sk, struct sk_buff *skb, struct flowi *fl)); 1227 INDIRECT_CALLABLE_DECLARE(void tcp_v4_send_check(struct sock *sk, struct sk_buff *skb)); 1228 1229 /* This routine actually transmits TCP packets queued in by 1230 * tcp_do_sendmsg(). This is used by both the initial 1231 * transmission and possible later retransmissions. 1232 * All SKB's seen here are completely headerless. It is our 1233 * job to build the TCP header, and pass the packet down to 1234 * IP so it can do the same plus pass the packet off to the 1235 * device. 1236 * 1237 * We are working here with either a clone of the original 1238 * SKB, or a fresh unique copy made by the retransmit engine. 1239 */ 1240 static int __tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, 1241 int clone_it, gfp_t gfp_mask, u32 rcv_nxt) 1242 { 1243 const struct inet_connection_sock *icsk = inet_csk(sk); 1244 struct inet_sock *inet; 1245 struct tcp_sock *tp; 1246 struct tcp_skb_cb *tcb; 1247 struct tcp_out_options opts; 1248 unsigned int tcp_options_size, tcp_header_size; 1249 struct sk_buff *oskb = NULL; 1250 struct tcp_md5sig_key *md5; 1251 struct tcphdr *th; 1252 u64 prior_wstamp; 1253 int err; 1254 1255 BUG_ON(!skb || !tcp_skb_pcount(skb)); 1256 tp = tcp_sk(sk); 1257 prior_wstamp = tp->tcp_wstamp_ns; 1258 tp->tcp_wstamp_ns = max(tp->tcp_wstamp_ns, tp->tcp_clock_cache); 1259 skb_set_delivery_time(skb, tp->tcp_wstamp_ns, true); 1260 if (clone_it) { 1261 oskb = skb; 1262 1263 tcp_skb_tsorted_save(oskb) { 1264 if (unlikely(skb_cloned(oskb))) 1265 skb = pskb_copy(oskb, gfp_mask); 1266 else 1267 skb = skb_clone(oskb, gfp_mask); 1268 } tcp_skb_tsorted_restore(oskb); 1269 1270 if (unlikely(!skb)) 1271 return -ENOBUFS; 1272 /* retransmit skbs might have a non zero value in skb->dev 1273 * because skb->dev is aliased with skb->rbnode.rb_left 1274 */ 1275 skb->dev = NULL; 1276 } 1277 1278 inet = inet_sk(sk); 1279 tcb = TCP_SKB_CB(skb); 1280 memset(&opts, 0, sizeof(opts)); 1281 1282 if (unlikely(tcb->tcp_flags & TCPHDR_SYN)) { 1283 tcp_options_size = tcp_syn_options(sk, skb, &opts, &md5); 1284 } else { 1285 tcp_options_size = tcp_established_options(sk, skb, &opts, 1286 &md5); 1287 /* Force a PSH flag on all (GSO) packets to expedite GRO flush 1288 * at receiver : This slightly improve GRO performance. 1289 * Note that we do not force the PSH flag for non GSO packets, 1290 * because they might be sent under high congestion events, 1291 * and in this case it is better to delay the delivery of 1-MSS 1292 * packets and thus the corresponding ACK packet that would 1293 * release the following packet. 1294 */ 1295 if (tcp_skb_pcount(skb) > 1) 1296 tcb->tcp_flags |= TCPHDR_PSH; 1297 } 1298 tcp_header_size = tcp_options_size + sizeof(struct tcphdr); 1299 1300 /* if no packet is in qdisc/device queue, then allow XPS to select 1301 * another queue. We can be called from tcp_tsq_handler() 1302 * which holds one reference to sk. 1303 * 1304 * TODO: Ideally, in-flight pure ACK packets should not matter here. 1305 * One way to get this would be to set skb->truesize = 2 on them. 1306 */ 1307 skb->ooo_okay = sk_wmem_alloc_get(sk) < SKB_TRUESIZE(1); 1308 1309 /* If we had to use memory reserve to allocate this skb, 1310 * this might cause drops if packet is looped back : 1311 * Other socket might not have SOCK_MEMALLOC. 1312 * Packets not looped back do not care about pfmemalloc. 1313 */ 1314 skb->pfmemalloc = 0; 1315 1316 skb_push(skb, tcp_header_size); 1317 skb_reset_transport_header(skb); 1318 1319 skb_orphan(skb); 1320 skb->sk = sk; 1321 skb->destructor = skb_is_tcp_pure_ack(skb) ? __sock_wfree : tcp_wfree; 1322 refcount_add(skb->truesize, &sk->sk_wmem_alloc); 1323 1324 skb_set_dst_pending_confirm(skb, sk->sk_dst_pending_confirm); 1325 1326 /* Build TCP header and checksum it. */ 1327 th = (struct tcphdr *)skb->data; 1328 th->source = inet->inet_sport; 1329 th->dest = inet->inet_dport; 1330 th->seq = htonl(tcb->seq); 1331 th->ack_seq = htonl(rcv_nxt); 1332 *(((__be16 *)th) + 6) = htons(((tcp_header_size >> 2) << 12) | 1333 tcb->tcp_flags); 1334 1335 th->check = 0; 1336 th->urg_ptr = 0; 1337 1338 /* The urg_mode check is necessary during a below snd_una win probe */ 1339 if (unlikely(tcp_urg_mode(tp) && before(tcb->seq, tp->snd_up))) { 1340 if (before(tp->snd_up, tcb->seq + 0x10000)) { 1341 th->urg_ptr = htons(tp->snd_up - tcb->seq); 1342 th->urg = 1; 1343 } else if (after(tcb->seq + 0xFFFF, tp->snd_nxt)) { 1344 th->urg_ptr = htons(0xFFFF); 1345 th->urg = 1; 1346 } 1347 } 1348 1349 skb_shinfo(skb)->gso_type = sk->sk_gso_type; 1350 if (likely(!(tcb->tcp_flags & TCPHDR_SYN))) { 1351 th->window = htons(tcp_select_window(sk)); 1352 tcp_ecn_send(sk, skb, th, tcp_header_size); 1353 } else { 1354 /* RFC1323: The window in SYN & SYN/ACK segments 1355 * is never scaled. 1356 */ 1357 th->window = htons(min(tp->rcv_wnd, 65535U)); 1358 } 1359 1360 tcp_options_write(th, tp, &opts); 1361 1362 #ifdef CONFIG_TCP_MD5SIG 1363 /* Calculate the MD5 hash, as we have all we need now */ 1364 if (md5) { 1365 sk_gso_disable(sk); 1366 tp->af_specific->calc_md5_hash(opts.hash_location, 1367 md5, sk, skb); 1368 } 1369 #endif 1370 1371 /* BPF prog is the last one writing header option */ 1372 bpf_skops_write_hdr_opt(sk, skb, NULL, NULL, 0, &opts); 1373 1374 INDIRECT_CALL_INET(icsk->icsk_af_ops->send_check, 1375 tcp_v6_send_check, tcp_v4_send_check, 1376 sk, skb); 1377 1378 if (likely(tcb->tcp_flags & TCPHDR_ACK)) 1379 tcp_event_ack_sent(sk, tcp_skb_pcount(skb), rcv_nxt); 1380 1381 if (skb->len != tcp_header_size) { 1382 tcp_event_data_sent(tp, sk); 1383 tp->data_segs_out += tcp_skb_pcount(skb); 1384 tp->bytes_sent += skb->len - tcp_header_size; 1385 } 1386 1387 if (after(tcb->end_seq, tp->snd_nxt) || tcb->seq == tcb->end_seq) 1388 TCP_ADD_STATS(sock_net(sk), TCP_MIB_OUTSEGS, 1389 tcp_skb_pcount(skb)); 1390 1391 tp->segs_out += tcp_skb_pcount(skb); 1392 skb_set_hash_from_sk(skb, sk); 1393 /* OK, its time to fill skb_shinfo(skb)->gso_{segs|size} */ 1394 skb_shinfo(skb)->gso_segs = tcp_skb_pcount(skb); 1395 skb_shinfo(skb)->gso_size = tcp_skb_mss(skb); 1396 1397 /* Leave earliest departure time in skb->tstamp (skb->skb_mstamp_ns) */ 1398 1399 /* Cleanup our debris for IP stacks */ 1400 memset(skb->cb, 0, max(sizeof(struct inet_skb_parm), 1401 sizeof(struct inet6_skb_parm))); 1402 1403 tcp_add_tx_delay(skb, tp); 1404 1405 err = INDIRECT_CALL_INET(icsk->icsk_af_ops->queue_xmit, 1406 inet6_csk_xmit, ip_queue_xmit, 1407 sk, skb, &inet->cork.fl); 1408 1409 if (unlikely(err > 0)) { 1410 tcp_enter_cwr(sk); 1411 err = net_xmit_eval(err); 1412 } 1413 if (!err && oskb) { 1414 tcp_update_skb_after_send(sk, oskb, prior_wstamp); 1415 tcp_rate_skb_sent(sk, oskb); 1416 } 1417 return err; 1418 } 1419 1420 static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it, 1421 gfp_t gfp_mask) 1422 { 1423 return __tcp_transmit_skb(sk, skb, clone_it, gfp_mask, 1424 tcp_sk(sk)->rcv_nxt); 1425 } 1426 1427 /* This routine just queues the buffer for sending. 1428 * 1429 * NOTE: probe0 timer is not checked, do not forget tcp_push_pending_frames, 1430 * otherwise socket can stall. 1431 */ 1432 static void tcp_queue_skb(struct sock *sk, struct sk_buff *skb) 1433 { 1434 struct tcp_sock *tp = tcp_sk(sk); 1435 1436 /* Advance write_seq and place onto the write_queue. */ 1437 WRITE_ONCE(tp->write_seq, TCP_SKB_CB(skb)->end_seq); 1438 __skb_header_release(skb); 1439 tcp_add_write_queue_tail(sk, skb); 1440 sk_wmem_queued_add(sk, skb->truesize); 1441 sk_mem_charge(sk, skb->truesize); 1442 } 1443 1444 /* Initialize TSO segments for a packet. */ 1445 static void tcp_set_skb_tso_segs(struct sk_buff *skb, unsigned int mss_now) 1446 { 1447 if (skb->len <= mss_now) { 1448 /* Avoid the costly divide in the normal 1449 * non-TSO case. 1450 */ 1451 tcp_skb_pcount_set(skb, 1); 1452 TCP_SKB_CB(skb)->tcp_gso_size = 0; 1453 } else { 1454 tcp_skb_pcount_set(skb, DIV_ROUND_UP(skb->len, mss_now)); 1455 TCP_SKB_CB(skb)->tcp_gso_size = mss_now; 1456 } 1457 } 1458 1459 /* Pcount in the middle of the write queue got changed, we need to do various 1460 * tweaks to fix counters 1461 */ 1462 static void tcp_adjust_pcount(struct sock *sk, const struct sk_buff *skb, int decr) 1463 { 1464 struct tcp_sock *tp = tcp_sk(sk); 1465 1466 tp->packets_out -= decr; 1467 1468 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED) 1469 tp->sacked_out -= decr; 1470 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) 1471 tp->retrans_out -= decr; 1472 if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST) 1473 tp->lost_out -= decr; 1474 1475 /* Reno case is special. Sigh... */ 1476 if (tcp_is_reno(tp) && decr > 0) 1477 tp->sacked_out -= min_t(u32, tp->sacked_out, decr); 1478 1479 if (tp->lost_skb_hint && 1480 before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(tp->lost_skb_hint)->seq) && 1481 (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) 1482 tp->lost_cnt_hint -= decr; 1483 1484 tcp_verify_left_out(tp); 1485 } 1486 1487 static bool tcp_has_tx_tstamp(const struct sk_buff *skb) 1488 { 1489 return TCP_SKB_CB(skb)->txstamp_ack || 1490 (skb_shinfo(skb)->tx_flags & SKBTX_ANY_TSTAMP); 1491 } 1492 1493 static void tcp_fragment_tstamp(struct sk_buff *skb, struct sk_buff *skb2) 1494 { 1495 struct skb_shared_info *shinfo = skb_shinfo(skb); 1496 1497 if (unlikely(tcp_has_tx_tstamp(skb)) && 1498 !before(shinfo->tskey, TCP_SKB_CB(skb2)->seq)) { 1499 struct skb_shared_info *shinfo2 = skb_shinfo(skb2); 1500 u8 tsflags = shinfo->tx_flags & SKBTX_ANY_TSTAMP; 1501 1502 shinfo->tx_flags &= ~tsflags; 1503 shinfo2->tx_flags |= tsflags; 1504 swap(shinfo->tskey, shinfo2->tskey); 1505 TCP_SKB_CB(skb2)->txstamp_ack = TCP_SKB_CB(skb)->txstamp_ack; 1506 TCP_SKB_CB(skb)->txstamp_ack = 0; 1507 } 1508 } 1509 1510 static void tcp_skb_fragment_eor(struct sk_buff *skb, struct sk_buff *skb2) 1511 { 1512 TCP_SKB_CB(skb2)->eor = TCP_SKB_CB(skb)->eor; 1513 TCP_SKB_CB(skb)->eor = 0; 1514 } 1515 1516 /* Insert buff after skb on the write or rtx queue of sk. */ 1517 static void tcp_insert_write_queue_after(struct sk_buff *skb, 1518 struct sk_buff *buff, 1519 struct sock *sk, 1520 enum tcp_queue tcp_queue) 1521 { 1522 if (tcp_queue == TCP_FRAG_IN_WRITE_QUEUE) 1523 __skb_queue_after(&sk->sk_write_queue, skb, buff); 1524 else 1525 tcp_rbtree_insert(&sk->tcp_rtx_queue, buff); 1526 } 1527 1528 /* Function to create two new TCP segments. Shrinks the given segment 1529 * to the specified size and appends a new segment with the rest of the 1530 * packet to the list. This won't be called frequently, I hope. 1531 * Remember, these are still headerless SKBs at this point. 1532 */ 1533 int tcp_fragment(struct sock *sk, enum tcp_queue tcp_queue, 1534 struct sk_buff *skb, u32 len, 1535 unsigned int mss_now, gfp_t gfp) 1536 { 1537 struct tcp_sock *tp = tcp_sk(sk); 1538 struct sk_buff *buff; 1539 int nsize, old_factor; 1540 long limit; 1541 int nlen; 1542 u8 flags; 1543 1544 if (WARN_ON(len > skb->len)) 1545 return -EINVAL; 1546 1547 nsize = skb_headlen(skb) - len; 1548 if (nsize < 0) 1549 nsize = 0; 1550 1551 /* tcp_sendmsg() can overshoot sk_wmem_queued by one full size skb. 1552 * We need some allowance to not penalize applications setting small 1553 * SO_SNDBUF values. 1554 * Also allow first and last skb in retransmit queue to be split. 1555 */ 1556 limit = sk->sk_sndbuf + 2 * SKB_TRUESIZE(GSO_LEGACY_MAX_SIZE); 1557 if (unlikely((sk->sk_wmem_queued >> 1) > limit && 1558 tcp_queue != TCP_FRAG_IN_WRITE_QUEUE && 1559 skb != tcp_rtx_queue_head(sk) && 1560 skb != tcp_rtx_queue_tail(sk))) { 1561 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPWQUEUETOOBIG); 1562 return -ENOMEM; 1563 } 1564 1565 if (skb_unclone_keeptruesize(skb, gfp)) 1566 return -ENOMEM; 1567 1568 /* Get a new skb... force flag on. */ 1569 buff = tcp_stream_alloc_skb(sk, nsize, gfp, true); 1570 if (!buff) 1571 return -ENOMEM; /* We'll just try again later. */ 1572 skb_copy_decrypted(buff, skb); 1573 mptcp_skb_ext_copy(buff, skb); 1574 1575 sk_wmem_queued_add(sk, buff->truesize); 1576 sk_mem_charge(sk, buff->truesize); 1577 nlen = skb->len - len - nsize; 1578 buff->truesize += nlen; 1579 skb->truesize -= nlen; 1580 1581 /* Correct the sequence numbers. */ 1582 TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len; 1583 TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq; 1584 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq; 1585 1586 /* PSH and FIN should only be set in the second packet. */ 1587 flags = TCP_SKB_CB(skb)->tcp_flags; 1588 TCP_SKB_CB(skb)->tcp_flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH); 1589 TCP_SKB_CB(buff)->tcp_flags = flags; 1590 TCP_SKB_CB(buff)->sacked = TCP_SKB_CB(skb)->sacked; 1591 tcp_skb_fragment_eor(skb, buff); 1592 1593 skb_split(skb, buff, len); 1594 1595 skb_set_delivery_time(buff, skb->tstamp, true); 1596 tcp_fragment_tstamp(skb, buff); 1597 1598 old_factor = tcp_skb_pcount(skb); 1599 1600 /* Fix up tso_factor for both original and new SKB. */ 1601 tcp_set_skb_tso_segs(skb, mss_now); 1602 tcp_set_skb_tso_segs(buff, mss_now); 1603 1604 /* Update delivered info for the new segment */ 1605 TCP_SKB_CB(buff)->tx = TCP_SKB_CB(skb)->tx; 1606 1607 /* If this packet has been sent out already, we must 1608 * adjust the various packet counters. 1609 */ 1610 if (!before(tp->snd_nxt, TCP_SKB_CB(buff)->end_seq)) { 1611 int diff = old_factor - tcp_skb_pcount(skb) - 1612 tcp_skb_pcount(buff); 1613 1614 if (diff) 1615 tcp_adjust_pcount(sk, skb, diff); 1616 } 1617 1618 /* Link BUFF into the send queue. */ 1619 __skb_header_release(buff); 1620 tcp_insert_write_queue_after(skb, buff, sk, tcp_queue); 1621 if (tcp_queue == TCP_FRAG_IN_RTX_QUEUE) 1622 list_add(&buff->tcp_tsorted_anchor, &skb->tcp_tsorted_anchor); 1623 1624 return 0; 1625 } 1626 1627 /* This is similar to __pskb_pull_tail(). The difference is that pulled 1628 * data is not copied, but immediately discarded. 1629 */ 1630 static int __pskb_trim_head(struct sk_buff *skb, int len) 1631 { 1632 struct skb_shared_info *shinfo; 1633 int i, k, eat; 1634 1635 eat = min_t(int, len, skb_headlen(skb)); 1636 if (eat) { 1637 __skb_pull(skb, eat); 1638 len -= eat; 1639 if (!len) 1640 return 0; 1641 } 1642 eat = len; 1643 k = 0; 1644 shinfo = skb_shinfo(skb); 1645 for (i = 0; i < shinfo->nr_frags; i++) { 1646 int size = skb_frag_size(&shinfo->frags[i]); 1647 1648 if (size <= eat) { 1649 skb_frag_unref(skb, i); 1650 eat -= size; 1651 } else { 1652 shinfo->frags[k] = shinfo->frags[i]; 1653 if (eat) { 1654 skb_frag_off_add(&shinfo->frags[k], eat); 1655 skb_frag_size_sub(&shinfo->frags[k], eat); 1656 eat = 0; 1657 } 1658 k++; 1659 } 1660 } 1661 shinfo->nr_frags = k; 1662 1663 skb->data_len -= len; 1664 skb->len = skb->data_len; 1665 return len; 1666 } 1667 1668 /* Remove acked data from a packet in the transmit queue. */ 1669 int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len) 1670 { 1671 u32 delta_truesize; 1672 1673 if (skb_unclone_keeptruesize(skb, GFP_ATOMIC)) 1674 return -ENOMEM; 1675 1676 delta_truesize = __pskb_trim_head(skb, len); 1677 1678 TCP_SKB_CB(skb)->seq += len; 1679 1680 if (delta_truesize) { 1681 skb->truesize -= delta_truesize; 1682 sk_wmem_queued_add(sk, -delta_truesize); 1683 if (!skb_zcopy_pure(skb)) 1684 sk_mem_uncharge(sk, delta_truesize); 1685 } 1686 1687 /* Any change of skb->len requires recalculation of tso factor. */ 1688 if (tcp_skb_pcount(skb) > 1) 1689 tcp_set_skb_tso_segs(skb, tcp_skb_mss(skb)); 1690 1691 return 0; 1692 } 1693 1694 /* Calculate MSS not accounting any TCP options. */ 1695 static inline int __tcp_mtu_to_mss(struct sock *sk, int pmtu) 1696 { 1697 const struct tcp_sock *tp = tcp_sk(sk); 1698 const struct inet_connection_sock *icsk = inet_csk(sk); 1699 int mss_now; 1700 1701 /* Calculate base mss without TCP options: 1702 It is MMS_S - sizeof(tcphdr) of rfc1122 1703 */ 1704 mss_now = pmtu - icsk->icsk_af_ops->net_header_len - sizeof(struct tcphdr); 1705 1706 /* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */ 1707 if (icsk->icsk_af_ops->net_frag_header_len) { 1708 const struct dst_entry *dst = __sk_dst_get(sk); 1709 1710 if (dst && dst_allfrag(dst)) 1711 mss_now -= icsk->icsk_af_ops->net_frag_header_len; 1712 } 1713 1714 /* Clamp it (mss_clamp does not include tcp options) */ 1715 if (mss_now > tp->rx_opt.mss_clamp) 1716 mss_now = tp->rx_opt.mss_clamp; 1717 1718 /* Now subtract optional transport overhead */ 1719 mss_now -= icsk->icsk_ext_hdr_len; 1720 1721 /* Then reserve room for full set of TCP options and 8 bytes of data */ 1722 mss_now = max(mss_now, 1723 READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_min_snd_mss)); 1724 return mss_now; 1725 } 1726 1727 /* Calculate MSS. Not accounting for SACKs here. */ 1728 int tcp_mtu_to_mss(struct sock *sk, int pmtu) 1729 { 1730 /* Subtract TCP options size, not including SACKs */ 1731 return __tcp_mtu_to_mss(sk, pmtu) - 1732 (tcp_sk(sk)->tcp_header_len - sizeof(struct tcphdr)); 1733 } 1734 EXPORT_SYMBOL(tcp_mtu_to_mss); 1735 1736 /* Inverse of above */ 1737 int tcp_mss_to_mtu(struct sock *sk, int mss) 1738 { 1739 const struct tcp_sock *tp = tcp_sk(sk); 1740 const struct inet_connection_sock *icsk = inet_csk(sk); 1741 int mtu; 1742 1743 mtu = mss + 1744 tp->tcp_header_len + 1745 icsk->icsk_ext_hdr_len + 1746 icsk->icsk_af_ops->net_header_len; 1747 1748 /* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */ 1749 if (icsk->icsk_af_ops->net_frag_header_len) { 1750 const struct dst_entry *dst = __sk_dst_get(sk); 1751 1752 if (dst && dst_allfrag(dst)) 1753 mtu += icsk->icsk_af_ops->net_frag_header_len; 1754 } 1755 return mtu; 1756 } 1757 EXPORT_SYMBOL(tcp_mss_to_mtu); 1758 1759 /* MTU probing init per socket */ 1760 void tcp_mtup_init(struct sock *sk) 1761 { 1762 struct tcp_sock *tp = tcp_sk(sk); 1763 struct inet_connection_sock *icsk = inet_csk(sk); 1764 struct net *net = sock_net(sk); 1765 1766 icsk->icsk_mtup.enabled = READ_ONCE(net->ipv4.sysctl_tcp_mtu_probing) > 1; 1767 icsk->icsk_mtup.search_high = tp->rx_opt.mss_clamp + sizeof(struct tcphdr) + 1768 icsk->icsk_af_ops->net_header_len; 1769 icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, READ_ONCE(net->ipv4.sysctl_tcp_base_mss)); 1770 icsk->icsk_mtup.probe_size = 0; 1771 if (icsk->icsk_mtup.enabled) 1772 icsk->icsk_mtup.probe_timestamp = tcp_jiffies32; 1773 } 1774 EXPORT_SYMBOL(tcp_mtup_init); 1775 1776 /* This function synchronize snd mss to current pmtu/exthdr set. 1777 1778 tp->rx_opt.user_mss is mss set by user by TCP_MAXSEG. It does NOT counts 1779 for TCP options, but includes only bare TCP header. 1780 1781 tp->rx_opt.mss_clamp is mss negotiated at connection setup. 1782 It is minimum of user_mss and mss received with SYN. 1783 It also does not include TCP options. 1784 1785 inet_csk(sk)->icsk_pmtu_cookie is last pmtu, seen by this function. 1786 1787 tp->mss_cache is current effective sending mss, including 1788 all tcp options except for SACKs. It is evaluated, 1789 taking into account current pmtu, but never exceeds 1790 tp->rx_opt.mss_clamp. 1791 1792 NOTE1. rfc1122 clearly states that advertised MSS 1793 DOES NOT include either tcp or ip options. 1794 1795 NOTE2. inet_csk(sk)->icsk_pmtu_cookie and tp->mss_cache 1796 are READ ONLY outside this function. --ANK (980731) 1797 */ 1798 unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu) 1799 { 1800 struct tcp_sock *tp = tcp_sk(sk); 1801 struct inet_connection_sock *icsk = inet_csk(sk); 1802 int mss_now; 1803 1804 if (icsk->icsk_mtup.search_high > pmtu) 1805 icsk->icsk_mtup.search_high = pmtu; 1806 1807 mss_now = tcp_mtu_to_mss(sk, pmtu); 1808 mss_now = tcp_bound_to_half_wnd(tp, mss_now); 1809 1810 /* And store cached results */ 1811 icsk->icsk_pmtu_cookie = pmtu; 1812 if (icsk->icsk_mtup.enabled) 1813 mss_now = min(mss_now, tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low)); 1814 tp->mss_cache = mss_now; 1815 1816 return mss_now; 1817 } 1818 EXPORT_SYMBOL(tcp_sync_mss); 1819 1820 /* Compute the current effective MSS, taking SACKs and IP options, 1821 * and even PMTU discovery events into account. 1822 */ 1823 unsigned int tcp_current_mss(struct sock *sk) 1824 { 1825 const struct tcp_sock *tp = tcp_sk(sk); 1826 const struct dst_entry *dst = __sk_dst_get(sk); 1827 u32 mss_now; 1828 unsigned int header_len; 1829 struct tcp_out_options opts; 1830 struct tcp_md5sig_key *md5; 1831 1832 mss_now = tp->mss_cache; 1833 1834 if (dst) { 1835 u32 mtu = dst_mtu(dst); 1836 if (mtu != inet_csk(sk)->icsk_pmtu_cookie) 1837 mss_now = tcp_sync_mss(sk, mtu); 1838 } 1839 1840 header_len = tcp_established_options(sk, NULL, &opts, &md5) + 1841 sizeof(struct tcphdr); 1842 /* The mss_cache is sized based on tp->tcp_header_len, which assumes 1843 * some common options. If this is an odd packet (because we have SACK 1844 * blocks etc) then our calculated header_len will be different, and 1845 * we have to adjust mss_now correspondingly */ 1846 if (header_len != tp->tcp_header_len) { 1847 int delta = (int) header_len - tp->tcp_header_len; 1848 mss_now -= delta; 1849 } 1850 1851 return mss_now; 1852 } 1853 1854 /* RFC2861, slow part. Adjust cwnd, after it was not full during one rto. 1855 * As additional protections, we do not touch cwnd in retransmission phases, 1856 * and if application hit its sndbuf limit recently. 1857 */ 1858 static void tcp_cwnd_application_limited(struct sock *sk) 1859 { 1860 struct tcp_sock *tp = tcp_sk(sk); 1861 1862 if (inet_csk(sk)->icsk_ca_state == TCP_CA_Open && 1863 sk->sk_socket && !test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) { 1864 /* Limited by application or receiver window. */ 1865 u32 init_win = tcp_init_cwnd(tp, __sk_dst_get(sk)); 1866 u32 win_used = max(tp->snd_cwnd_used, init_win); 1867 if (win_used < tcp_snd_cwnd(tp)) { 1868 tp->snd_ssthresh = tcp_current_ssthresh(sk); 1869 tcp_snd_cwnd_set(tp, (tcp_snd_cwnd(tp) + win_used) >> 1); 1870 } 1871 tp->snd_cwnd_used = 0; 1872 } 1873 tp->snd_cwnd_stamp = tcp_jiffies32; 1874 } 1875 1876 static void tcp_cwnd_validate(struct sock *sk, bool is_cwnd_limited) 1877 { 1878 const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops; 1879 struct tcp_sock *tp = tcp_sk(sk); 1880 1881 /* Track the maximum number of outstanding packets in each 1882 * window, and remember whether we were cwnd-limited then. 1883 */ 1884 if (!before(tp->snd_una, tp->max_packets_seq) || 1885 tp->packets_out > tp->max_packets_out || 1886 is_cwnd_limited) { 1887 tp->max_packets_out = tp->packets_out; 1888 tp->max_packets_seq = tp->snd_nxt; 1889 tp->is_cwnd_limited = is_cwnd_limited; 1890 } 1891 1892 if (tcp_is_cwnd_limited(sk)) { 1893 /* Network is feed fully. */ 1894 tp->snd_cwnd_used = 0; 1895 tp->snd_cwnd_stamp = tcp_jiffies32; 1896 } else { 1897 /* Network starves. */ 1898 if (tp->packets_out > tp->snd_cwnd_used) 1899 tp->snd_cwnd_used = tp->packets_out; 1900 1901 if (READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_slow_start_after_idle) && 1902 (s32)(tcp_jiffies32 - tp->snd_cwnd_stamp) >= inet_csk(sk)->icsk_rto && 1903 !ca_ops->cong_control) 1904 tcp_cwnd_application_limited(sk); 1905 1906 /* The following conditions together indicate the starvation 1907 * is caused by insufficient sender buffer: 1908 * 1) just sent some data (see tcp_write_xmit) 1909 * 2) not cwnd limited (this else condition) 1910 * 3) no more data to send (tcp_write_queue_empty()) 1911 * 4) application is hitting buffer limit (SOCK_NOSPACE) 1912 */ 1913 if (tcp_write_queue_empty(sk) && sk->sk_socket && 1914 test_bit(SOCK_NOSPACE, &sk->sk_socket->flags) && 1915 (1 << sk->sk_state) & (TCPF_ESTABLISHED | TCPF_CLOSE_WAIT)) 1916 tcp_chrono_start(sk, TCP_CHRONO_SNDBUF_LIMITED); 1917 } 1918 } 1919 1920 /* Minshall's variant of the Nagle send check. */ 1921 static bool tcp_minshall_check(const struct tcp_sock *tp) 1922 { 1923 return after(tp->snd_sml, tp->snd_una) && 1924 !after(tp->snd_sml, tp->snd_nxt); 1925 } 1926 1927 /* Update snd_sml if this skb is under mss 1928 * Note that a TSO packet might end with a sub-mss segment 1929 * The test is really : 1930 * if ((skb->len % mss) != 0) 1931 * tp->snd_sml = TCP_SKB_CB(skb)->end_seq; 1932 * But we can avoid doing the divide again given we already have 1933 * skb_pcount = skb->len / mss_now 1934 */ 1935 static void tcp_minshall_update(struct tcp_sock *tp, unsigned int mss_now, 1936 const struct sk_buff *skb) 1937 { 1938 if (skb->len < tcp_skb_pcount(skb) * mss_now) 1939 tp->snd_sml = TCP_SKB_CB(skb)->end_seq; 1940 } 1941 1942 /* Return false, if packet can be sent now without violation Nagle's rules: 1943 * 1. It is full sized. (provided by caller in %partial bool) 1944 * 2. Or it contains FIN. (already checked by caller) 1945 * 3. Or TCP_CORK is not set, and TCP_NODELAY is set. 1946 * 4. Or TCP_CORK is not set, and all sent packets are ACKed. 1947 * With Minshall's modification: all sent small packets are ACKed. 1948 */ 1949 static bool tcp_nagle_check(bool partial, const struct tcp_sock *tp, 1950 int nonagle) 1951 { 1952 return partial && 1953 ((nonagle & TCP_NAGLE_CORK) || 1954 (!nonagle && tp->packets_out && tcp_minshall_check(tp))); 1955 } 1956 1957 /* Return how many segs we'd like on a TSO packet, 1958 * depending on current pacing rate, and how close the peer is. 1959 * 1960 * Rationale is: 1961 * - For close peers, we rather send bigger packets to reduce 1962 * cpu costs, because occasional losses will be repaired fast. 1963 * - For long distance/rtt flows, we would like to get ACK clocking 1964 * with 1 ACK per ms. 1965 * 1966 * Use min_rtt to help adapt TSO burst size, with smaller min_rtt resulting 1967 * in bigger TSO bursts. We we cut the RTT-based allowance in half 1968 * for every 2^9 usec (aka 512 us) of RTT, so that the RTT-based allowance 1969 * is below 1500 bytes after 6 * ~500 usec = 3ms. 1970 */ 1971 static u32 tcp_tso_autosize(const struct sock *sk, unsigned int mss_now, 1972 int min_tso_segs) 1973 { 1974 unsigned long bytes; 1975 u32 r; 1976 1977 bytes = sk->sk_pacing_rate >> READ_ONCE(sk->sk_pacing_shift); 1978 1979 r = tcp_min_rtt(tcp_sk(sk)) >> sock_net(sk)->ipv4.sysctl_tcp_tso_rtt_log; 1980 if (r < BITS_PER_TYPE(sk->sk_gso_max_size)) 1981 bytes += sk->sk_gso_max_size >> r; 1982 1983 bytes = min_t(unsigned long, bytes, sk->sk_gso_max_size); 1984 1985 return max_t(u32, bytes / mss_now, min_tso_segs); 1986 } 1987 1988 /* Return the number of segments we want in the skb we are transmitting. 1989 * See if congestion control module wants to decide; otherwise, autosize. 1990 */ 1991 static u32 tcp_tso_segs(struct sock *sk, unsigned int mss_now) 1992 { 1993 const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops; 1994 u32 min_tso, tso_segs; 1995 1996 min_tso = ca_ops->min_tso_segs ? 1997 ca_ops->min_tso_segs(sk) : 1998 sock_net(sk)->ipv4.sysctl_tcp_min_tso_segs; 1999 2000 tso_segs = tcp_tso_autosize(sk, mss_now, min_tso); 2001 return min_t(u32, tso_segs, sk->sk_gso_max_segs); 2002 } 2003 2004 /* Returns the portion of skb which can be sent right away */ 2005 static unsigned int tcp_mss_split_point(const struct sock *sk, 2006 const struct sk_buff *skb, 2007 unsigned int mss_now, 2008 unsigned int max_segs, 2009 int nonagle) 2010 { 2011 const struct tcp_sock *tp = tcp_sk(sk); 2012 u32 partial, needed, window, max_len; 2013 2014 window = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq; 2015 max_len = mss_now * max_segs; 2016 2017 if (likely(max_len <= window && skb != tcp_write_queue_tail(sk))) 2018 return max_len; 2019 2020 needed = min(skb->len, window); 2021 2022 if (max_len <= needed) 2023 return max_len; 2024 2025 partial = needed % mss_now; 2026 /* If last segment is not a full MSS, check if Nagle rules allow us 2027 * to include this last segment in this skb. 2028 * Otherwise, we'll split the skb at last MSS boundary 2029 */ 2030 if (tcp_nagle_check(partial != 0, tp, nonagle)) 2031 return needed - partial; 2032 2033 return needed; 2034 } 2035 2036 /* Can at least one segment of SKB be sent right now, according to the 2037 * congestion window rules? If so, return how many segments are allowed. 2038 */ 2039 static inline unsigned int tcp_cwnd_test(const struct tcp_sock *tp, 2040 const struct sk_buff *skb) 2041 { 2042 u32 in_flight, cwnd, halfcwnd; 2043 2044 /* Don't be strict about the congestion window for the final FIN. */ 2045 if ((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) && 2046 tcp_skb_pcount(skb) == 1) 2047 return 1; 2048 2049 in_flight = tcp_packets_in_flight(tp); 2050 cwnd = tcp_snd_cwnd(tp); 2051 if (in_flight >= cwnd) 2052 return 0; 2053 2054 /* For better scheduling, ensure we have at least 2055 * 2 GSO packets in flight. 2056 */ 2057 halfcwnd = max(cwnd >> 1, 1U); 2058 return min(halfcwnd, cwnd - in_flight); 2059 } 2060 2061 /* Initialize TSO state of a skb. 2062 * This must be invoked the first time we consider transmitting 2063 * SKB onto the wire. 2064 */ 2065 static int tcp_init_tso_segs(struct sk_buff *skb, unsigned int mss_now) 2066 { 2067 int tso_segs = tcp_skb_pcount(skb); 2068 2069 if (!tso_segs || (tso_segs > 1 && tcp_skb_mss(skb) != mss_now)) { 2070 tcp_set_skb_tso_segs(skb, mss_now); 2071 tso_segs = tcp_skb_pcount(skb); 2072 } 2073 return tso_segs; 2074 } 2075 2076 2077 /* Return true if the Nagle test allows this packet to be 2078 * sent now. 2079 */ 2080 static inline bool tcp_nagle_test(const struct tcp_sock *tp, const struct sk_buff *skb, 2081 unsigned int cur_mss, int nonagle) 2082 { 2083 /* Nagle rule does not apply to frames, which sit in the middle of the 2084 * write_queue (they have no chances to get new data). 2085 * 2086 * This is implemented in the callers, where they modify the 'nonagle' 2087 * argument based upon the location of SKB in the send queue. 2088 */ 2089 if (nonagle & TCP_NAGLE_PUSH) 2090 return true; 2091 2092 /* Don't use the nagle rule for urgent data (or for the final FIN). */ 2093 if (tcp_urg_mode(tp) || (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)) 2094 return true; 2095 2096 if (!tcp_nagle_check(skb->len < cur_mss, tp, nonagle)) 2097 return true; 2098 2099 return false; 2100 } 2101 2102 /* Does at least the first segment of SKB fit into the send window? */ 2103 static bool tcp_snd_wnd_test(const struct tcp_sock *tp, 2104 const struct sk_buff *skb, 2105 unsigned int cur_mss) 2106 { 2107 u32 end_seq = TCP_SKB_CB(skb)->end_seq; 2108 2109 if (skb->len > cur_mss) 2110 end_seq = TCP_SKB_CB(skb)->seq + cur_mss; 2111 2112 return !after(end_seq, tcp_wnd_end(tp)); 2113 } 2114 2115 /* Trim TSO SKB to LEN bytes, put the remaining data into a new packet 2116 * which is put after SKB on the list. It is very much like 2117 * tcp_fragment() except that it may make several kinds of assumptions 2118 * in order to speed up the splitting operation. In particular, we 2119 * know that all the data is in scatter-gather pages, and that the 2120 * packet has never been sent out before (and thus is not cloned). 2121 */ 2122 static int tso_fragment(struct sock *sk, struct sk_buff *skb, unsigned int len, 2123 unsigned int mss_now, gfp_t gfp) 2124 { 2125 int nlen = skb->len - len; 2126 struct sk_buff *buff; 2127 u8 flags; 2128 2129 /* All of a TSO frame must be composed of paged data. */ 2130 if (skb->len != skb->data_len) 2131 return tcp_fragment(sk, TCP_FRAG_IN_WRITE_QUEUE, 2132 skb, len, mss_now, gfp); 2133 2134 buff = tcp_stream_alloc_skb(sk, 0, gfp, true); 2135 if (unlikely(!buff)) 2136 return -ENOMEM; 2137 skb_copy_decrypted(buff, skb); 2138 mptcp_skb_ext_copy(buff, skb); 2139 2140 sk_wmem_queued_add(sk, buff->truesize); 2141 sk_mem_charge(sk, buff->truesize); 2142 buff->truesize += nlen; 2143 skb->truesize -= nlen; 2144 2145 /* Correct the sequence numbers. */ 2146 TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len; 2147 TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq; 2148 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq; 2149 2150 /* PSH and FIN should only be set in the second packet. */ 2151 flags = TCP_SKB_CB(skb)->tcp_flags; 2152 TCP_SKB_CB(skb)->tcp_flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH); 2153 TCP_SKB_CB(buff)->tcp_flags = flags; 2154 2155 tcp_skb_fragment_eor(skb, buff); 2156 2157 skb_split(skb, buff, len); 2158 tcp_fragment_tstamp(skb, buff); 2159 2160 /* Fix up tso_factor for both original and new SKB. */ 2161 tcp_set_skb_tso_segs(skb, mss_now); 2162 tcp_set_skb_tso_segs(buff, mss_now); 2163 2164 /* Link BUFF into the send queue. */ 2165 __skb_header_release(buff); 2166 tcp_insert_write_queue_after(skb, buff, sk, TCP_FRAG_IN_WRITE_QUEUE); 2167 2168 return 0; 2169 } 2170 2171 /* Try to defer sending, if possible, in order to minimize the amount 2172 * of TSO splitting we do. View it as a kind of TSO Nagle test. 2173 * 2174 * This algorithm is from John Heffner. 2175 */ 2176 static bool tcp_tso_should_defer(struct sock *sk, struct sk_buff *skb, 2177 bool *is_cwnd_limited, 2178 bool *is_rwnd_limited, 2179 u32 max_segs) 2180 { 2181 const struct inet_connection_sock *icsk = inet_csk(sk); 2182 u32 send_win, cong_win, limit, in_flight; 2183 struct tcp_sock *tp = tcp_sk(sk); 2184 struct sk_buff *head; 2185 int win_divisor; 2186 s64 delta; 2187 2188 if (icsk->icsk_ca_state >= TCP_CA_Recovery) 2189 goto send_now; 2190 2191 /* Avoid bursty behavior by allowing defer 2192 * only if the last write was recent (1 ms). 2193 * Note that tp->tcp_wstamp_ns can be in the future if we have 2194 * packets waiting in a qdisc or device for EDT delivery. 2195 */ 2196 delta = tp->tcp_clock_cache - tp->tcp_wstamp_ns - NSEC_PER_MSEC; 2197 if (delta > 0) 2198 goto send_now; 2199 2200 in_flight = tcp_packets_in_flight(tp); 2201 2202 BUG_ON(tcp_skb_pcount(skb) <= 1); 2203 BUG_ON(tcp_snd_cwnd(tp) <= in_flight); 2204 2205 send_win = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq; 2206 2207 /* From in_flight test above, we know that cwnd > in_flight. */ 2208 cong_win = (tcp_snd_cwnd(tp) - in_flight) * tp->mss_cache; 2209 2210 limit = min(send_win, cong_win); 2211 2212 /* If a full-sized TSO skb can be sent, do it. */ 2213 if (limit >= max_segs * tp->mss_cache) 2214 goto send_now; 2215 2216 /* Middle in queue won't get any more data, full sendable already? */ 2217 if ((skb != tcp_write_queue_tail(sk)) && (limit >= skb->len)) 2218 goto send_now; 2219 2220 win_divisor = READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_tso_win_divisor); 2221 if (win_divisor) { 2222 u32 chunk = min(tp->snd_wnd, tcp_snd_cwnd(tp) * tp->mss_cache); 2223 2224 /* If at least some fraction of a window is available, 2225 * just use it. 2226 */ 2227 chunk /= win_divisor; 2228 if (limit >= chunk) 2229 goto send_now; 2230 } else { 2231 /* Different approach, try not to defer past a single 2232 * ACK. Receiver should ACK every other full sized 2233 * frame, so if we have space for more than 3 frames 2234 * then send now. 2235 */ 2236 if (limit > tcp_max_tso_deferred_mss(tp) * tp->mss_cache) 2237 goto send_now; 2238 } 2239 2240 /* TODO : use tsorted_sent_queue ? */ 2241 head = tcp_rtx_queue_head(sk); 2242 if (!head) 2243 goto send_now; 2244 delta = tp->tcp_clock_cache - head->tstamp; 2245 /* If next ACK is likely to come too late (half srtt), do not defer */ 2246 if ((s64)(delta - (u64)NSEC_PER_USEC * (tp->srtt_us >> 4)) < 0) 2247 goto send_now; 2248 2249 /* Ok, it looks like it is advisable to defer. 2250 * Three cases are tracked : 2251 * 1) We are cwnd-limited 2252 * 2) We are rwnd-limited 2253 * 3) We are application limited. 2254 */ 2255 if (cong_win < send_win) { 2256 if (cong_win <= skb->len) { 2257 *is_cwnd_limited = true; 2258 return true; 2259 } 2260 } else { 2261 if (send_win <= skb->len) { 2262 *is_rwnd_limited = true; 2263 return true; 2264 } 2265 } 2266 2267 /* If this packet won't get more data, do not wait. */ 2268 if ((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) || 2269 TCP_SKB_CB(skb)->eor) 2270 goto send_now; 2271 2272 return true; 2273 2274 send_now: 2275 return false; 2276 } 2277 2278 static inline void tcp_mtu_check_reprobe(struct sock *sk) 2279 { 2280 struct inet_connection_sock *icsk = inet_csk(sk); 2281 struct tcp_sock *tp = tcp_sk(sk); 2282 struct net *net = sock_net(sk); 2283 u32 interval; 2284 s32 delta; 2285 2286 interval = READ_ONCE(net->ipv4.sysctl_tcp_probe_interval); 2287 delta = tcp_jiffies32 - icsk->icsk_mtup.probe_timestamp; 2288 if (unlikely(delta >= interval * HZ)) { 2289 int mss = tcp_current_mss(sk); 2290 2291 /* Update current search range */ 2292 icsk->icsk_mtup.probe_size = 0; 2293 icsk->icsk_mtup.search_high = tp->rx_opt.mss_clamp + 2294 sizeof(struct tcphdr) + 2295 icsk->icsk_af_ops->net_header_len; 2296 icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss); 2297 2298 /* Update probe time stamp */ 2299 icsk->icsk_mtup.probe_timestamp = tcp_jiffies32; 2300 } 2301 } 2302 2303 static bool tcp_can_coalesce_send_queue_head(struct sock *sk, int len) 2304 { 2305 struct sk_buff *skb, *next; 2306 2307 skb = tcp_send_head(sk); 2308 tcp_for_write_queue_from_safe(skb, next, sk) { 2309 if (len <= skb->len) 2310 break; 2311 2312 if (unlikely(TCP_SKB_CB(skb)->eor) || 2313 tcp_has_tx_tstamp(skb) || 2314 !skb_pure_zcopy_same(skb, next)) 2315 return false; 2316 2317 len -= skb->len; 2318 } 2319 2320 return true; 2321 } 2322 2323 /* Create a new MTU probe if we are ready. 2324 * MTU probe is regularly attempting to increase the path MTU by 2325 * deliberately sending larger packets. This discovers routing 2326 * changes resulting in larger path MTUs. 2327 * 2328 * Returns 0 if we should wait to probe (no cwnd available), 2329 * 1 if a probe was sent, 2330 * -1 otherwise 2331 */ 2332 static int tcp_mtu_probe(struct sock *sk) 2333 { 2334 struct inet_connection_sock *icsk = inet_csk(sk); 2335 struct tcp_sock *tp = tcp_sk(sk); 2336 struct sk_buff *skb, *nskb, *next; 2337 struct net *net = sock_net(sk); 2338 int probe_size; 2339 int size_needed; 2340 int copy, len; 2341 int mss_now; 2342 int interval; 2343 2344 /* Not currently probing/verifying, 2345 * not in recovery, 2346 * have enough cwnd, and 2347 * not SACKing (the variable headers throw things off) 2348 */ 2349 if (likely(!icsk->icsk_mtup.enabled || 2350 icsk->icsk_mtup.probe_size || 2351 inet_csk(sk)->icsk_ca_state != TCP_CA_Open || 2352 tcp_snd_cwnd(tp) < 11 || 2353 tp->rx_opt.num_sacks || tp->rx_opt.dsack)) 2354 return -1; 2355 2356 /* Use binary search for probe_size between tcp_mss_base, 2357 * and current mss_clamp. if (search_high - search_low) 2358 * smaller than a threshold, backoff from probing. 2359 */ 2360 mss_now = tcp_current_mss(sk); 2361 probe_size = tcp_mtu_to_mss(sk, (icsk->icsk_mtup.search_high + 2362 icsk->icsk_mtup.search_low) >> 1); 2363 size_needed = probe_size + (tp->reordering + 1) * tp->mss_cache; 2364 interval = icsk->icsk_mtup.search_high - icsk->icsk_mtup.search_low; 2365 /* When misfortune happens, we are reprobing actively, 2366 * and then reprobe timer has expired. We stick with current 2367 * probing process by not resetting search range to its orignal. 2368 */ 2369 if (probe_size > tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_high) || 2370 interval < READ_ONCE(net->ipv4.sysctl_tcp_probe_threshold)) { 2371 /* Check whether enough time has elaplased for 2372 * another round of probing. 2373 */ 2374 tcp_mtu_check_reprobe(sk); 2375 return -1; 2376 } 2377 2378 /* Have enough data in the send queue to probe? */ 2379 if (tp->write_seq - tp->snd_nxt < size_needed) 2380 return -1; 2381 2382 if (tp->snd_wnd < size_needed) 2383 return -1; 2384 if (after(tp->snd_nxt + size_needed, tcp_wnd_end(tp))) 2385 return 0; 2386 2387 /* Do we need to wait to drain cwnd? With none in flight, don't stall */ 2388 if (tcp_packets_in_flight(tp) + 2 > tcp_snd_cwnd(tp)) { 2389 if (!tcp_packets_in_flight(tp)) 2390 return -1; 2391 else 2392 return 0; 2393 } 2394 2395 if (!tcp_can_coalesce_send_queue_head(sk, probe_size)) 2396 return -1; 2397 2398 /* We're allowed to probe. Build it now. */ 2399 nskb = tcp_stream_alloc_skb(sk, probe_size, GFP_ATOMIC, false); 2400 if (!nskb) 2401 return -1; 2402 sk_wmem_queued_add(sk, nskb->truesize); 2403 sk_mem_charge(sk, nskb->truesize); 2404 2405 skb = tcp_send_head(sk); 2406 skb_copy_decrypted(nskb, skb); 2407 mptcp_skb_ext_copy(nskb, skb); 2408 2409 TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(skb)->seq; 2410 TCP_SKB_CB(nskb)->end_seq = TCP_SKB_CB(skb)->seq + probe_size; 2411 TCP_SKB_CB(nskb)->tcp_flags = TCPHDR_ACK; 2412 2413 tcp_insert_write_queue_before(nskb, skb, sk); 2414 tcp_highest_sack_replace(sk, skb, nskb); 2415 2416 len = 0; 2417 tcp_for_write_queue_from_safe(skb, next, sk) { 2418 copy = min_t(int, skb->len, probe_size - len); 2419 skb_copy_bits(skb, 0, skb_put(nskb, copy), copy); 2420 2421 if (skb->len <= copy) { 2422 /* We've eaten all the data from this skb. 2423 * Throw it away. */ 2424 TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags; 2425 /* If this is the last SKB we copy and eor is set 2426 * we need to propagate it to the new skb. 2427 */ 2428 TCP_SKB_CB(nskb)->eor = TCP_SKB_CB(skb)->eor; 2429 tcp_skb_collapse_tstamp(nskb, skb); 2430 tcp_unlink_write_queue(skb, sk); 2431 tcp_wmem_free_skb(sk, skb); 2432 } else { 2433 TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags & 2434 ~(TCPHDR_FIN|TCPHDR_PSH); 2435 if (!skb_shinfo(skb)->nr_frags) { 2436 skb_pull(skb, copy); 2437 } else { 2438 __pskb_trim_head(skb, copy); 2439 tcp_set_skb_tso_segs(skb, mss_now); 2440 } 2441 TCP_SKB_CB(skb)->seq += copy; 2442 } 2443 2444 len += copy; 2445 2446 if (len >= probe_size) 2447 break; 2448 } 2449 tcp_init_tso_segs(nskb, nskb->len); 2450 2451 /* We're ready to send. If this fails, the probe will 2452 * be resegmented into mss-sized pieces by tcp_write_xmit(). 2453 */ 2454 if (!tcp_transmit_skb(sk, nskb, 1, GFP_ATOMIC)) { 2455 /* Decrement cwnd here because we are sending 2456 * effectively two packets. */ 2457 tcp_snd_cwnd_set(tp, tcp_snd_cwnd(tp) - 1); 2458 tcp_event_new_data_sent(sk, nskb); 2459 2460 icsk->icsk_mtup.probe_size = tcp_mss_to_mtu(sk, nskb->len); 2461 tp->mtu_probe.probe_seq_start = TCP_SKB_CB(nskb)->seq; 2462 tp->mtu_probe.probe_seq_end = TCP_SKB_CB(nskb)->end_seq; 2463 2464 return 1; 2465 } 2466 2467 return -1; 2468 } 2469 2470 static bool tcp_pacing_check(struct sock *sk) 2471 { 2472 struct tcp_sock *tp = tcp_sk(sk); 2473 2474 if (!tcp_needs_internal_pacing(sk)) 2475 return false; 2476 2477 if (tp->tcp_wstamp_ns <= tp->tcp_clock_cache) 2478 return false; 2479 2480 if (!hrtimer_is_queued(&tp->pacing_timer)) { 2481 hrtimer_start(&tp->pacing_timer, 2482 ns_to_ktime(tp->tcp_wstamp_ns), 2483 HRTIMER_MODE_ABS_PINNED_SOFT); 2484 sock_hold(sk); 2485 } 2486 return true; 2487 } 2488 2489 /* TCP Small Queues : 2490 * Control number of packets in qdisc/devices to two packets / or ~1 ms. 2491 * (These limits are doubled for retransmits) 2492 * This allows for : 2493 * - better RTT estimation and ACK scheduling 2494 * - faster recovery 2495 * - high rates 2496 * Alas, some drivers / subsystems require a fair amount 2497 * of queued bytes to ensure line rate. 2498 * One example is wifi aggregation (802.11 AMPDU) 2499 */ 2500 static bool tcp_small_queue_check(struct sock *sk, const struct sk_buff *skb, 2501 unsigned int factor) 2502 { 2503 unsigned long limit; 2504 2505 limit = max_t(unsigned long, 2506 2 * skb->truesize, 2507 sk->sk_pacing_rate >> READ_ONCE(sk->sk_pacing_shift)); 2508 if (sk->sk_pacing_status == SK_PACING_NONE) 2509 limit = min_t(unsigned long, limit, 2510 sock_net(sk)->ipv4.sysctl_tcp_limit_output_bytes); 2511 limit <<= factor; 2512 2513 if (static_branch_unlikely(&tcp_tx_delay_enabled) && 2514 tcp_sk(sk)->tcp_tx_delay) { 2515 u64 extra_bytes = (u64)sk->sk_pacing_rate * tcp_sk(sk)->tcp_tx_delay; 2516 2517 /* TSQ is based on skb truesize sum (sk_wmem_alloc), so we 2518 * approximate our needs assuming an ~100% skb->truesize overhead. 2519 * USEC_PER_SEC is approximated by 2^20. 2520 * do_div(extra_bytes, USEC_PER_SEC/2) is replaced by a right shift. 2521 */ 2522 extra_bytes >>= (20 - 1); 2523 limit += extra_bytes; 2524 } 2525 if (refcount_read(&sk->sk_wmem_alloc) > limit) { 2526 /* Always send skb if rtx queue is empty. 2527 * No need to wait for TX completion to call us back, 2528 * after softirq/tasklet schedule. 2529 * This helps when TX completions are delayed too much. 2530 */ 2531 if (tcp_rtx_queue_empty(sk)) 2532 return false; 2533 2534 set_bit(TSQ_THROTTLED, &sk->sk_tsq_flags); 2535 /* It is possible TX completion already happened 2536 * before we set TSQ_THROTTLED, so we must 2537 * test again the condition. 2538 */ 2539 smp_mb__after_atomic(); 2540 if (refcount_read(&sk->sk_wmem_alloc) > limit) 2541 return true; 2542 } 2543 return false; 2544 } 2545 2546 static void tcp_chrono_set(struct tcp_sock *tp, const enum tcp_chrono new) 2547 { 2548 const u32 now = tcp_jiffies32; 2549 enum tcp_chrono old = tp->chrono_type; 2550 2551 if (old > TCP_CHRONO_UNSPEC) 2552 tp->chrono_stat[old - 1] += now - tp->chrono_start; 2553 tp->chrono_start = now; 2554 tp->chrono_type = new; 2555 } 2556 2557 void tcp_chrono_start(struct sock *sk, const enum tcp_chrono type) 2558 { 2559 struct tcp_sock *tp = tcp_sk(sk); 2560 2561 /* If there are multiple conditions worthy of tracking in a 2562 * chronograph then the highest priority enum takes precedence 2563 * over the other conditions. So that if something "more interesting" 2564 * starts happening, stop the previous chrono and start a new one. 2565 */ 2566 if (type > tp->chrono_type) 2567 tcp_chrono_set(tp, type); 2568 } 2569 2570 void tcp_chrono_stop(struct sock *sk, const enum tcp_chrono type) 2571 { 2572 struct tcp_sock *tp = tcp_sk(sk); 2573 2574 2575 /* There are multiple conditions worthy of tracking in a 2576 * chronograph, so that the highest priority enum takes 2577 * precedence over the other conditions (see tcp_chrono_start). 2578 * If a condition stops, we only stop chrono tracking if 2579 * it's the "most interesting" or current chrono we are 2580 * tracking and starts busy chrono if we have pending data. 2581 */ 2582 if (tcp_rtx_and_write_queues_empty(sk)) 2583 tcp_chrono_set(tp, TCP_CHRONO_UNSPEC); 2584 else if (type == tp->chrono_type) 2585 tcp_chrono_set(tp, TCP_CHRONO_BUSY); 2586 } 2587 2588 /* This routine writes packets to the network. It advances the 2589 * send_head. This happens as incoming acks open up the remote 2590 * window for us. 2591 * 2592 * LARGESEND note: !tcp_urg_mode is overkill, only frames between 2593 * snd_up-64k-mss .. snd_up cannot be large. However, taking into 2594 * account rare use of URG, this is not a big flaw. 2595 * 2596 * Send at most one packet when push_one > 0. Temporarily ignore 2597 * cwnd limit to force at most one packet out when push_one == 2. 2598 2599 * Returns true, if no segments are in flight and we have queued segments, 2600 * but cannot send anything now because of SWS or another problem. 2601 */ 2602 static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle, 2603 int push_one, gfp_t gfp) 2604 { 2605 struct tcp_sock *tp = tcp_sk(sk); 2606 struct sk_buff *skb; 2607 unsigned int tso_segs, sent_pkts; 2608 int cwnd_quota; 2609 int result; 2610 bool is_cwnd_limited = false, is_rwnd_limited = false; 2611 u32 max_segs; 2612 2613 sent_pkts = 0; 2614 2615 tcp_mstamp_refresh(tp); 2616 if (!push_one) { 2617 /* Do MTU probing. */ 2618 result = tcp_mtu_probe(sk); 2619 if (!result) { 2620 return false; 2621 } else if (result > 0) { 2622 sent_pkts = 1; 2623 } 2624 } 2625 2626 max_segs = tcp_tso_segs(sk, mss_now); 2627 while ((skb = tcp_send_head(sk))) { 2628 unsigned int limit; 2629 2630 if (unlikely(tp->repair) && tp->repair_queue == TCP_SEND_QUEUE) { 2631 /* "skb_mstamp_ns" is used as a start point for the retransmit timer */ 2632 tp->tcp_wstamp_ns = tp->tcp_clock_cache; 2633 skb_set_delivery_time(skb, tp->tcp_wstamp_ns, true); 2634 list_move_tail(&skb->tcp_tsorted_anchor, &tp->tsorted_sent_queue); 2635 tcp_init_tso_segs(skb, mss_now); 2636 goto repair; /* Skip network transmission */ 2637 } 2638 2639 if (tcp_pacing_check(sk)) 2640 break; 2641 2642 tso_segs = tcp_init_tso_segs(skb, mss_now); 2643 BUG_ON(!tso_segs); 2644 2645 cwnd_quota = tcp_cwnd_test(tp, skb); 2646 if (!cwnd_quota) { 2647 if (push_one == 2) 2648 /* Force out a loss probe pkt. */ 2649 cwnd_quota = 1; 2650 else 2651 break; 2652 } 2653 2654 if (unlikely(!tcp_snd_wnd_test(tp, skb, mss_now))) { 2655 is_rwnd_limited = true; 2656 break; 2657 } 2658 2659 if (tso_segs == 1) { 2660 if (unlikely(!tcp_nagle_test(tp, skb, mss_now, 2661 (tcp_skb_is_last(sk, skb) ? 2662 nonagle : TCP_NAGLE_PUSH)))) 2663 break; 2664 } else { 2665 if (!push_one && 2666 tcp_tso_should_defer(sk, skb, &is_cwnd_limited, 2667 &is_rwnd_limited, max_segs)) 2668 break; 2669 } 2670 2671 limit = mss_now; 2672 if (tso_segs > 1 && !tcp_urg_mode(tp)) 2673 limit = tcp_mss_split_point(sk, skb, mss_now, 2674 min_t(unsigned int, 2675 cwnd_quota, 2676 max_segs), 2677 nonagle); 2678 2679 if (skb->len > limit && 2680 unlikely(tso_fragment(sk, skb, limit, mss_now, gfp))) 2681 break; 2682 2683 if (tcp_small_queue_check(sk, skb, 0)) 2684 break; 2685 2686 /* Argh, we hit an empty skb(), presumably a thread 2687 * is sleeping in sendmsg()/sk_stream_wait_memory(). 2688 * We do not want to send a pure-ack packet and have 2689 * a strange looking rtx queue with empty packet(s). 2690 */ 2691 if (TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq) 2692 break; 2693 2694 if (unlikely(tcp_transmit_skb(sk, skb, 1, gfp))) 2695 break; 2696 2697 repair: 2698 /* Advance the send_head. This one is sent out. 2699 * This call will increment packets_out. 2700 */ 2701 tcp_event_new_data_sent(sk, skb); 2702 2703 tcp_minshall_update(tp, mss_now, skb); 2704 sent_pkts += tcp_skb_pcount(skb); 2705 2706 if (push_one) 2707 break; 2708 } 2709 2710 if (is_rwnd_limited) 2711 tcp_chrono_start(sk, TCP_CHRONO_RWND_LIMITED); 2712 else 2713 tcp_chrono_stop(sk, TCP_CHRONO_RWND_LIMITED); 2714 2715 is_cwnd_limited |= (tcp_packets_in_flight(tp) >= tcp_snd_cwnd(tp)); 2716 if (likely(sent_pkts || is_cwnd_limited)) 2717 tcp_cwnd_validate(sk, is_cwnd_limited); 2718 2719 if (likely(sent_pkts)) { 2720 if (tcp_in_cwnd_reduction(sk)) 2721 tp->prr_out += sent_pkts; 2722 2723 /* Send one loss probe per tail loss episode. */ 2724 if (push_one != 2) 2725 tcp_schedule_loss_probe(sk, false); 2726 return false; 2727 } 2728 return !tp->packets_out && !tcp_write_queue_empty(sk); 2729 } 2730 2731 bool tcp_schedule_loss_probe(struct sock *sk, bool advancing_rto) 2732 { 2733 struct inet_connection_sock *icsk = inet_csk(sk); 2734 struct tcp_sock *tp = tcp_sk(sk); 2735 u32 timeout, rto_delta_us; 2736 int early_retrans; 2737 2738 /* Don't do any loss probe on a Fast Open connection before 3WHS 2739 * finishes. 2740 */ 2741 if (rcu_access_pointer(tp->fastopen_rsk)) 2742 return false; 2743 2744 early_retrans = READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_early_retrans); 2745 /* Schedule a loss probe in 2*RTT for SACK capable connections 2746 * not in loss recovery, that are either limited by cwnd or application. 2747 */ 2748 if ((early_retrans != 3 && early_retrans != 4) || 2749 !tp->packets_out || !tcp_is_sack(tp) || 2750 (icsk->icsk_ca_state != TCP_CA_Open && 2751 icsk->icsk_ca_state != TCP_CA_CWR)) 2752 return false; 2753 2754 /* Probe timeout is 2*rtt. Add minimum RTO to account 2755 * for delayed ack when there's one outstanding packet. If no RTT 2756 * sample is available then probe after TCP_TIMEOUT_INIT. 2757 */ 2758 if (tp->srtt_us) { 2759 timeout = usecs_to_jiffies(tp->srtt_us >> 2); 2760 if (tp->packets_out == 1) 2761 timeout += TCP_RTO_MIN; 2762 else 2763 timeout += TCP_TIMEOUT_MIN; 2764 } else { 2765 timeout = TCP_TIMEOUT_INIT; 2766 } 2767 2768 /* If the RTO formula yields an earlier time, then use that time. */ 2769 rto_delta_us = advancing_rto ? 2770 jiffies_to_usecs(inet_csk(sk)->icsk_rto) : 2771 tcp_rto_delta_us(sk); /* How far in future is RTO? */ 2772 if (rto_delta_us > 0) 2773 timeout = min_t(u32, timeout, usecs_to_jiffies(rto_delta_us)); 2774 2775 tcp_reset_xmit_timer(sk, ICSK_TIME_LOSS_PROBE, timeout, TCP_RTO_MAX); 2776 return true; 2777 } 2778 2779 /* Thanks to skb fast clones, we can detect if a prior transmit of 2780 * a packet is still in a qdisc or driver queue. 2781 * In this case, there is very little point doing a retransmit ! 2782 */ 2783 static bool skb_still_in_host_queue(struct sock *sk, 2784 const struct sk_buff *skb) 2785 { 2786 if (unlikely(skb_fclone_busy(sk, skb))) { 2787 set_bit(TSQ_THROTTLED, &sk->sk_tsq_flags); 2788 smp_mb__after_atomic(); 2789 if (skb_fclone_busy(sk, skb)) { 2790 NET_INC_STATS(sock_net(sk), 2791 LINUX_MIB_TCPSPURIOUS_RTX_HOSTQUEUES); 2792 return true; 2793 } 2794 } 2795 return false; 2796 } 2797 2798 /* When probe timeout (PTO) fires, try send a new segment if possible, else 2799 * retransmit the last segment. 2800 */ 2801 void tcp_send_loss_probe(struct sock *sk) 2802 { 2803 struct tcp_sock *tp = tcp_sk(sk); 2804 struct sk_buff *skb; 2805 int pcount; 2806 int mss = tcp_current_mss(sk); 2807 2808 /* At most one outstanding TLP */ 2809 if (tp->tlp_high_seq) 2810 goto rearm_timer; 2811 2812 tp->tlp_retrans = 0; 2813 skb = tcp_send_head(sk); 2814 if (skb && tcp_snd_wnd_test(tp, skb, mss)) { 2815 pcount = tp->packets_out; 2816 tcp_write_xmit(sk, mss, TCP_NAGLE_OFF, 2, GFP_ATOMIC); 2817 if (tp->packets_out > pcount) 2818 goto probe_sent; 2819 goto rearm_timer; 2820 } 2821 skb = skb_rb_last(&sk->tcp_rtx_queue); 2822 if (unlikely(!skb)) { 2823 WARN_ONCE(tp->packets_out, 2824 "invalid inflight: %u state %u cwnd %u mss %d\n", 2825 tp->packets_out, sk->sk_state, tcp_snd_cwnd(tp), mss); 2826 inet_csk(sk)->icsk_pending = 0; 2827 return; 2828 } 2829 2830 if (skb_still_in_host_queue(sk, skb)) 2831 goto rearm_timer; 2832 2833 pcount = tcp_skb_pcount(skb); 2834 if (WARN_ON(!pcount)) 2835 goto rearm_timer; 2836 2837 if ((pcount > 1) && (skb->len > (pcount - 1) * mss)) { 2838 if (unlikely(tcp_fragment(sk, TCP_FRAG_IN_RTX_QUEUE, skb, 2839 (pcount - 1) * mss, mss, 2840 GFP_ATOMIC))) 2841 goto rearm_timer; 2842 skb = skb_rb_next(skb); 2843 } 2844 2845 if (WARN_ON(!skb || !tcp_skb_pcount(skb))) 2846 goto rearm_timer; 2847 2848 if (__tcp_retransmit_skb(sk, skb, 1)) 2849 goto rearm_timer; 2850 2851 tp->tlp_retrans = 1; 2852 2853 probe_sent: 2854 /* Record snd_nxt for loss detection. */ 2855 tp->tlp_high_seq = tp->snd_nxt; 2856 2857 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPLOSSPROBES); 2858 /* Reset s.t. tcp_rearm_rto will restart timer from now */ 2859 inet_csk(sk)->icsk_pending = 0; 2860 rearm_timer: 2861 tcp_rearm_rto(sk); 2862 } 2863 2864 /* Push out any pending frames which were held back due to 2865 * TCP_CORK or attempt at coalescing tiny packets. 2866 * The socket must be locked by the caller. 2867 */ 2868 void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss, 2869 int nonagle) 2870 { 2871 /* If we are closed, the bytes will have to remain here. 2872 * In time closedown will finish, we empty the write queue and 2873 * all will be happy. 2874 */ 2875 if (unlikely(sk->sk_state == TCP_CLOSE)) 2876 return; 2877 2878 if (tcp_write_xmit(sk, cur_mss, nonagle, 0, 2879 sk_gfp_mask(sk, GFP_ATOMIC))) 2880 tcp_check_probe_timer(sk); 2881 } 2882 2883 /* Send _single_ skb sitting at the send head. This function requires 2884 * true push pending frames to setup probe timer etc. 2885 */ 2886 void tcp_push_one(struct sock *sk, unsigned int mss_now) 2887 { 2888 struct sk_buff *skb = tcp_send_head(sk); 2889 2890 BUG_ON(!skb || skb->len < mss_now); 2891 2892 tcp_write_xmit(sk, mss_now, TCP_NAGLE_PUSH, 1, sk->sk_allocation); 2893 } 2894 2895 /* This function returns the amount that we can raise the 2896 * usable window based on the following constraints 2897 * 2898 * 1. The window can never be shrunk once it is offered (RFC 793) 2899 * 2. We limit memory per socket 2900 * 2901 * RFC 1122: 2902 * "the suggested [SWS] avoidance algorithm for the receiver is to keep 2903 * RECV.NEXT + RCV.WIN fixed until: 2904 * RCV.BUFF - RCV.USER - RCV.WINDOW >= min(1/2 RCV.BUFF, MSS)" 2905 * 2906 * i.e. don't raise the right edge of the window until you can raise 2907 * it at least MSS bytes. 2908 * 2909 * Unfortunately, the recommended algorithm breaks header prediction, 2910 * since header prediction assumes th->window stays fixed. 2911 * 2912 * Strictly speaking, keeping th->window fixed violates the receiver 2913 * side SWS prevention criteria. The problem is that under this rule 2914 * a stream of single byte packets will cause the right side of the 2915 * window to always advance by a single byte. 2916 * 2917 * Of course, if the sender implements sender side SWS prevention 2918 * then this will not be a problem. 2919 * 2920 * BSD seems to make the following compromise: 2921 * 2922 * If the free space is less than the 1/4 of the maximum 2923 * space available and the free space is less than 1/2 mss, 2924 * then set the window to 0. 2925 * [ Actually, bsd uses MSS and 1/4 of maximal _window_ ] 2926 * Otherwise, just prevent the window from shrinking 2927 * and from being larger than the largest representable value. 2928 * 2929 * This prevents incremental opening of the window in the regime 2930 * where TCP is limited by the speed of the reader side taking 2931 * data out of the TCP receive queue. It does nothing about 2932 * those cases where the window is constrained on the sender side 2933 * because the pipeline is full. 2934 * 2935 * BSD also seems to "accidentally" limit itself to windows that are a 2936 * multiple of MSS, at least until the free space gets quite small. 2937 * This would appear to be a side effect of the mbuf implementation. 2938 * Combining these two algorithms results in the observed behavior 2939 * of having a fixed window size at almost all times. 2940 * 2941 * Below we obtain similar behavior by forcing the offered window to 2942 * a multiple of the mss when it is feasible to do so. 2943 * 2944 * Note, we don't "adjust" for TIMESTAMP or SACK option bytes. 2945 * Regular options like TIMESTAMP are taken into account. 2946 */ 2947 u32 __tcp_select_window(struct sock *sk) 2948 { 2949 struct inet_connection_sock *icsk = inet_csk(sk); 2950 struct tcp_sock *tp = tcp_sk(sk); 2951 /* MSS for the peer's data. Previous versions used mss_clamp 2952 * here. I don't know if the value based on our guesses 2953 * of peer's MSS is better for the performance. It's more correct 2954 * but may be worse for the performance because of rcv_mss 2955 * fluctuations. --SAW 1998/11/1 2956 */ 2957 int mss = icsk->icsk_ack.rcv_mss; 2958 int free_space = tcp_space(sk); 2959 int allowed_space = tcp_full_space(sk); 2960 int full_space, window; 2961 2962 if (sk_is_mptcp(sk)) 2963 mptcp_space(sk, &free_space, &allowed_space); 2964 2965 full_space = min_t(int, tp->window_clamp, allowed_space); 2966 2967 if (unlikely(mss > full_space)) { 2968 mss = full_space; 2969 if (mss <= 0) 2970 return 0; 2971 } 2972 if (free_space < (full_space >> 1)) { 2973 icsk->icsk_ack.quick = 0; 2974 2975 if (tcp_under_memory_pressure(sk)) 2976 tcp_adjust_rcv_ssthresh(sk); 2977 2978 /* free_space might become our new window, make sure we don't 2979 * increase it due to wscale. 2980 */ 2981 free_space = round_down(free_space, 1 << tp->rx_opt.rcv_wscale); 2982 2983 /* if free space is less than mss estimate, or is below 1/16th 2984 * of the maximum allowed, try to move to zero-window, else 2985 * tcp_clamp_window() will grow rcv buf up to tcp_rmem[2], and 2986 * new incoming data is dropped due to memory limits. 2987 * With large window, mss test triggers way too late in order 2988 * to announce zero window in time before rmem limit kicks in. 2989 */ 2990 if (free_space < (allowed_space >> 4) || free_space < mss) 2991 return 0; 2992 } 2993 2994 if (free_space > tp->rcv_ssthresh) 2995 free_space = tp->rcv_ssthresh; 2996 2997 /* Don't do rounding if we are using window scaling, since the 2998 * scaled window will not line up with the MSS boundary anyway. 2999 */ 3000 if (tp->rx_opt.rcv_wscale) { 3001 window = free_space; 3002 3003 /* Advertise enough space so that it won't get scaled away. 3004 * Import case: prevent zero window announcement if 3005 * 1<<rcv_wscale > mss. 3006 */ 3007 window = ALIGN(window, (1 << tp->rx_opt.rcv_wscale)); 3008 } else { 3009 window = tp->rcv_wnd; 3010 /* Get the largest window that is a nice multiple of mss. 3011 * Window clamp already applied above. 3012 * If our current window offering is within 1 mss of the 3013 * free space we just keep it. This prevents the divide 3014 * and multiply from happening most of the time. 3015 * We also don't do any window rounding when the free space 3016 * is too small. 3017 */ 3018 if (window <= free_space - mss || window > free_space) 3019 window = rounddown(free_space, mss); 3020 else if (mss == full_space && 3021 free_space > window + (full_space >> 1)) 3022 window = free_space; 3023 } 3024 3025 return window; 3026 } 3027 3028 void tcp_skb_collapse_tstamp(struct sk_buff *skb, 3029 const struct sk_buff *next_skb) 3030 { 3031 if (unlikely(tcp_has_tx_tstamp(next_skb))) { 3032 const struct skb_shared_info *next_shinfo = 3033 skb_shinfo(next_skb); 3034 struct skb_shared_info *shinfo = skb_shinfo(skb); 3035 3036 shinfo->tx_flags |= next_shinfo->tx_flags & SKBTX_ANY_TSTAMP; 3037 shinfo->tskey = next_shinfo->tskey; 3038 TCP_SKB_CB(skb)->txstamp_ack |= 3039 TCP_SKB_CB(next_skb)->txstamp_ack; 3040 } 3041 } 3042 3043 /* Collapses two adjacent SKB's during retransmission. */ 3044 static bool tcp_collapse_retrans(struct sock *sk, struct sk_buff *skb) 3045 { 3046 struct tcp_sock *tp = tcp_sk(sk); 3047 struct sk_buff *next_skb = skb_rb_next(skb); 3048 int next_skb_size; 3049 3050 next_skb_size = next_skb->len; 3051 3052 BUG_ON(tcp_skb_pcount(skb) != 1 || tcp_skb_pcount(next_skb) != 1); 3053 3054 if (next_skb_size && !tcp_skb_shift(skb, next_skb, 1, next_skb_size)) 3055 return false; 3056 3057 tcp_highest_sack_replace(sk, next_skb, skb); 3058 3059 /* Update sequence range on original skb. */ 3060 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(next_skb)->end_seq; 3061 3062 /* Merge over control information. This moves PSH/FIN etc. over */ 3063 TCP_SKB_CB(skb)->tcp_flags |= TCP_SKB_CB(next_skb)->tcp_flags; 3064 3065 /* All done, get rid of second SKB and account for it so 3066 * packet counting does not break. 3067 */ 3068 TCP_SKB_CB(skb)->sacked |= TCP_SKB_CB(next_skb)->sacked & TCPCB_EVER_RETRANS; 3069 TCP_SKB_CB(skb)->eor = TCP_SKB_CB(next_skb)->eor; 3070 3071 /* changed transmit queue under us so clear hints */ 3072 tcp_clear_retrans_hints_partial(tp); 3073 if (next_skb == tp->retransmit_skb_hint) 3074 tp->retransmit_skb_hint = skb; 3075 3076 tcp_adjust_pcount(sk, next_skb, tcp_skb_pcount(next_skb)); 3077 3078 tcp_skb_collapse_tstamp(skb, next_skb); 3079 3080 tcp_rtx_queue_unlink_and_free(next_skb, sk); 3081 return true; 3082 } 3083 3084 /* Check if coalescing SKBs is legal. */ 3085 static bool tcp_can_collapse(const struct sock *sk, const struct sk_buff *skb) 3086 { 3087 if (tcp_skb_pcount(skb) > 1) 3088 return false; 3089 if (skb_cloned(skb)) 3090 return false; 3091 /* Some heuristics for collapsing over SACK'd could be invented */ 3092 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED) 3093 return false; 3094 3095 return true; 3096 } 3097 3098 /* Collapse packets in the retransmit queue to make to create 3099 * less packets on the wire. This is only done on retransmission. 3100 */ 3101 static void tcp_retrans_try_collapse(struct sock *sk, struct sk_buff *to, 3102 int space) 3103 { 3104 struct tcp_sock *tp = tcp_sk(sk); 3105 struct sk_buff *skb = to, *tmp; 3106 bool first = true; 3107 3108 if (!READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_retrans_collapse)) 3109 return; 3110 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN) 3111 return; 3112 3113 skb_rbtree_walk_from_safe(skb, tmp) { 3114 if (!tcp_can_collapse(sk, skb)) 3115 break; 3116 3117 if (!tcp_skb_can_collapse(to, skb)) 3118 break; 3119 3120 space -= skb->len; 3121 3122 if (first) { 3123 first = false; 3124 continue; 3125 } 3126 3127 if (space < 0) 3128 break; 3129 3130 if (after(TCP_SKB_CB(skb)->end_seq, tcp_wnd_end(tp))) 3131 break; 3132 3133 if (!tcp_collapse_retrans(sk, to)) 3134 break; 3135 } 3136 } 3137 3138 /* This retransmits one SKB. Policy decisions and retransmit queue 3139 * state updates are done by the caller. Returns non-zero if an 3140 * error occurred which prevented the send. 3141 */ 3142 int __tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb, int segs) 3143 { 3144 struct inet_connection_sock *icsk = inet_csk(sk); 3145 struct tcp_sock *tp = tcp_sk(sk); 3146 unsigned int cur_mss; 3147 int diff, len, err; 3148 3149 3150 /* Inconclusive MTU probe */ 3151 if (icsk->icsk_mtup.probe_size) 3152 icsk->icsk_mtup.probe_size = 0; 3153 3154 if (skb_still_in_host_queue(sk, skb)) 3155 return -EBUSY; 3156 3157 if (before(TCP_SKB_CB(skb)->seq, tp->snd_una)) { 3158 if (unlikely(before(TCP_SKB_CB(skb)->end_seq, tp->snd_una))) { 3159 WARN_ON_ONCE(1); 3160 return -EINVAL; 3161 } 3162 if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq)) 3163 return -ENOMEM; 3164 } 3165 3166 if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk)) 3167 return -EHOSTUNREACH; /* Routing failure or similar. */ 3168 3169 cur_mss = tcp_current_mss(sk); 3170 3171 /* If receiver has shrunk his window, and skb is out of 3172 * new window, do not retransmit it. The exception is the 3173 * case, when window is shrunk to zero. In this case 3174 * our retransmit serves as a zero window probe. 3175 */ 3176 if (!before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp)) && 3177 TCP_SKB_CB(skb)->seq != tp->snd_una) 3178 return -EAGAIN; 3179 3180 len = cur_mss * segs; 3181 if (skb->len > len) { 3182 if (tcp_fragment(sk, TCP_FRAG_IN_RTX_QUEUE, skb, len, 3183 cur_mss, GFP_ATOMIC)) 3184 return -ENOMEM; /* We'll try again later. */ 3185 } else { 3186 if (skb_unclone_keeptruesize(skb, GFP_ATOMIC)) 3187 return -ENOMEM; 3188 3189 diff = tcp_skb_pcount(skb); 3190 tcp_set_skb_tso_segs(skb, cur_mss); 3191 diff -= tcp_skb_pcount(skb); 3192 if (diff) 3193 tcp_adjust_pcount(sk, skb, diff); 3194 if (skb->len < cur_mss) 3195 tcp_retrans_try_collapse(sk, skb, cur_mss); 3196 } 3197 3198 /* RFC3168, section 6.1.1.1. ECN fallback */ 3199 if ((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN_ECN) == TCPHDR_SYN_ECN) 3200 tcp_ecn_clear_syn(sk, skb); 3201 3202 /* Update global and local TCP statistics. */ 3203 segs = tcp_skb_pcount(skb); 3204 TCP_ADD_STATS(sock_net(sk), TCP_MIB_RETRANSSEGS, segs); 3205 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN) 3206 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSYNRETRANS); 3207 tp->total_retrans += segs; 3208 tp->bytes_retrans += skb->len; 3209 3210 /* make sure skb->data is aligned on arches that require it 3211 * and check if ack-trimming & collapsing extended the headroom 3212 * beyond what csum_start can cover. 3213 */ 3214 if (unlikely((NET_IP_ALIGN && ((unsigned long)skb->data & 3)) || 3215 skb_headroom(skb) >= 0xFFFF)) { 3216 struct sk_buff *nskb; 3217 3218 tcp_skb_tsorted_save(skb) { 3219 nskb = __pskb_copy(skb, MAX_TCP_HEADER, GFP_ATOMIC); 3220 if (nskb) { 3221 nskb->dev = NULL; 3222 err = tcp_transmit_skb(sk, nskb, 0, GFP_ATOMIC); 3223 } else { 3224 err = -ENOBUFS; 3225 } 3226 } tcp_skb_tsorted_restore(skb); 3227 3228 if (!err) { 3229 tcp_update_skb_after_send(sk, skb, tp->tcp_wstamp_ns); 3230 tcp_rate_skb_sent(sk, skb); 3231 } 3232 } else { 3233 err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC); 3234 } 3235 3236 /* To avoid taking spuriously low RTT samples based on a timestamp 3237 * for a transmit that never happened, always mark EVER_RETRANS 3238 */ 3239 TCP_SKB_CB(skb)->sacked |= TCPCB_EVER_RETRANS; 3240 3241 if (BPF_SOCK_OPS_TEST_FLAG(tp, BPF_SOCK_OPS_RETRANS_CB_FLAG)) 3242 tcp_call_bpf_3arg(sk, BPF_SOCK_OPS_RETRANS_CB, 3243 TCP_SKB_CB(skb)->seq, segs, err); 3244 3245 if (likely(!err)) { 3246 trace_tcp_retransmit_skb(sk, skb); 3247 } else if (err != -EBUSY) { 3248 NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPRETRANSFAIL, segs); 3249 } 3250 return err; 3251 } 3252 3253 int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb, int segs) 3254 { 3255 struct tcp_sock *tp = tcp_sk(sk); 3256 int err = __tcp_retransmit_skb(sk, skb, segs); 3257 3258 if (err == 0) { 3259 #if FASTRETRANS_DEBUG > 0 3260 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) { 3261 net_dbg_ratelimited("retrans_out leaked\n"); 3262 } 3263 #endif 3264 TCP_SKB_CB(skb)->sacked |= TCPCB_RETRANS; 3265 tp->retrans_out += tcp_skb_pcount(skb); 3266 } 3267 3268 /* Save stamp of the first (attempted) retransmit. */ 3269 if (!tp->retrans_stamp) 3270 tp->retrans_stamp = tcp_skb_timestamp(skb); 3271 3272 if (tp->undo_retrans < 0) 3273 tp->undo_retrans = 0; 3274 tp->undo_retrans += tcp_skb_pcount(skb); 3275 return err; 3276 } 3277 3278 /* This gets called after a retransmit timeout, and the initially 3279 * retransmitted data is acknowledged. It tries to continue 3280 * resending the rest of the retransmit queue, until either 3281 * we've sent it all or the congestion window limit is reached. 3282 */ 3283 void tcp_xmit_retransmit_queue(struct sock *sk) 3284 { 3285 const struct inet_connection_sock *icsk = inet_csk(sk); 3286 struct sk_buff *skb, *rtx_head, *hole = NULL; 3287 struct tcp_sock *tp = tcp_sk(sk); 3288 bool rearm_timer = false; 3289 u32 max_segs; 3290 int mib_idx; 3291 3292 if (!tp->packets_out) 3293 return; 3294 3295 rtx_head = tcp_rtx_queue_head(sk); 3296 skb = tp->retransmit_skb_hint ?: rtx_head; 3297 max_segs = tcp_tso_segs(sk, tcp_current_mss(sk)); 3298 skb_rbtree_walk_from(skb) { 3299 __u8 sacked; 3300 int segs; 3301 3302 if (tcp_pacing_check(sk)) 3303 break; 3304 3305 /* we could do better than to assign each time */ 3306 if (!hole) 3307 tp->retransmit_skb_hint = skb; 3308 3309 segs = tcp_snd_cwnd(tp) - tcp_packets_in_flight(tp); 3310 if (segs <= 0) 3311 break; 3312 sacked = TCP_SKB_CB(skb)->sacked; 3313 /* In case tcp_shift_skb_data() have aggregated large skbs, 3314 * we need to make sure not sending too bigs TSO packets 3315 */ 3316 segs = min_t(int, segs, max_segs); 3317 3318 if (tp->retrans_out >= tp->lost_out) { 3319 break; 3320 } else if (!(sacked & TCPCB_LOST)) { 3321 if (!hole && !(sacked & (TCPCB_SACKED_RETRANS|TCPCB_SACKED_ACKED))) 3322 hole = skb; 3323 continue; 3324 3325 } else { 3326 if (icsk->icsk_ca_state != TCP_CA_Loss) 3327 mib_idx = LINUX_MIB_TCPFASTRETRANS; 3328 else 3329 mib_idx = LINUX_MIB_TCPSLOWSTARTRETRANS; 3330 } 3331 3332 if (sacked & (TCPCB_SACKED_ACKED|TCPCB_SACKED_RETRANS)) 3333 continue; 3334 3335 if (tcp_small_queue_check(sk, skb, 1)) 3336 break; 3337 3338 if (tcp_retransmit_skb(sk, skb, segs)) 3339 break; 3340 3341 NET_ADD_STATS(sock_net(sk), mib_idx, tcp_skb_pcount(skb)); 3342 3343 if (tcp_in_cwnd_reduction(sk)) 3344 tp->prr_out += tcp_skb_pcount(skb); 3345 3346 if (skb == rtx_head && 3347 icsk->icsk_pending != ICSK_TIME_REO_TIMEOUT) 3348 rearm_timer = true; 3349 3350 } 3351 if (rearm_timer) 3352 tcp_reset_xmit_timer(sk, ICSK_TIME_RETRANS, 3353 inet_csk(sk)->icsk_rto, 3354 TCP_RTO_MAX); 3355 } 3356 3357 /* We allow to exceed memory limits for FIN packets to expedite 3358 * connection tear down and (memory) recovery. 3359 * Otherwise tcp_send_fin() could be tempted to either delay FIN 3360 * or even be forced to close flow without any FIN. 3361 * In general, we want to allow one skb per socket to avoid hangs 3362 * with edge trigger epoll() 3363 */ 3364 void sk_forced_mem_schedule(struct sock *sk, int size) 3365 { 3366 int amt; 3367 3368 if (size <= sk->sk_forward_alloc) 3369 return; 3370 amt = sk_mem_pages(size); 3371 sk->sk_forward_alloc += amt * SK_MEM_QUANTUM; 3372 sk_memory_allocated_add(sk, amt); 3373 3374 if (mem_cgroup_sockets_enabled && sk->sk_memcg) 3375 mem_cgroup_charge_skmem(sk->sk_memcg, amt, 3376 gfp_memcg_charge() | __GFP_NOFAIL); 3377 } 3378 3379 /* Send a FIN. The caller locks the socket for us. 3380 * We should try to send a FIN packet really hard, but eventually give up. 3381 */ 3382 void tcp_send_fin(struct sock *sk) 3383 { 3384 struct sk_buff *skb, *tskb, *tail = tcp_write_queue_tail(sk); 3385 struct tcp_sock *tp = tcp_sk(sk); 3386 3387 /* Optimization, tack on the FIN if we have one skb in write queue and 3388 * this skb was not yet sent, or we are under memory pressure. 3389 * Note: in the latter case, FIN packet will be sent after a timeout, 3390 * as TCP stack thinks it has already been transmitted. 3391 */ 3392 tskb = tail; 3393 if (!tskb && tcp_under_memory_pressure(sk)) 3394 tskb = skb_rb_last(&sk->tcp_rtx_queue); 3395 3396 if (tskb) { 3397 TCP_SKB_CB(tskb)->tcp_flags |= TCPHDR_FIN; 3398 TCP_SKB_CB(tskb)->end_seq++; 3399 tp->write_seq++; 3400 if (!tail) { 3401 /* This means tskb was already sent. 3402 * Pretend we included the FIN on previous transmit. 3403 * We need to set tp->snd_nxt to the value it would have 3404 * if FIN had been sent. This is because retransmit path 3405 * does not change tp->snd_nxt. 3406 */ 3407 WRITE_ONCE(tp->snd_nxt, tp->snd_nxt + 1); 3408 return; 3409 } 3410 } else { 3411 skb = alloc_skb_fclone(MAX_TCP_HEADER, sk->sk_allocation); 3412 if (unlikely(!skb)) 3413 return; 3414 3415 INIT_LIST_HEAD(&skb->tcp_tsorted_anchor); 3416 skb_reserve(skb, MAX_TCP_HEADER); 3417 sk_forced_mem_schedule(sk, skb->truesize); 3418 /* FIN eats a sequence byte, write_seq advanced by tcp_queue_skb(). */ 3419 tcp_init_nondata_skb(skb, tp->write_seq, 3420 TCPHDR_ACK | TCPHDR_FIN); 3421 tcp_queue_skb(sk, skb); 3422 } 3423 __tcp_push_pending_frames(sk, tcp_current_mss(sk), TCP_NAGLE_OFF); 3424 } 3425 3426 /* We get here when a process closes a file descriptor (either due to 3427 * an explicit close() or as a byproduct of exit()'ing) and there 3428 * was unread data in the receive queue. This behavior is recommended 3429 * by RFC 2525, section 2.17. -DaveM 3430 */ 3431 void tcp_send_active_reset(struct sock *sk, gfp_t priority) 3432 { 3433 struct sk_buff *skb; 3434 3435 TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTRSTS); 3436 3437 /* NOTE: No TCP options attached and we never retransmit this. */ 3438 skb = alloc_skb(MAX_TCP_HEADER, priority); 3439 if (!skb) { 3440 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED); 3441 return; 3442 } 3443 3444 /* Reserve space for headers and prepare control bits. */ 3445 skb_reserve(skb, MAX_TCP_HEADER); 3446 tcp_init_nondata_skb(skb, tcp_acceptable_seq(sk), 3447 TCPHDR_ACK | TCPHDR_RST); 3448 tcp_mstamp_refresh(tcp_sk(sk)); 3449 /* Send it off. */ 3450 if (tcp_transmit_skb(sk, skb, 0, priority)) 3451 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED); 3452 3453 /* skb of trace_tcp_send_reset() keeps the skb that caused RST, 3454 * skb here is different to the troublesome skb, so use NULL 3455 */ 3456 trace_tcp_send_reset(sk, NULL); 3457 } 3458 3459 /* Send a crossed SYN-ACK during socket establishment. 3460 * WARNING: This routine must only be called when we have already sent 3461 * a SYN packet that crossed the incoming SYN that caused this routine 3462 * to get called. If this assumption fails then the initial rcv_wnd 3463 * and rcv_wscale values will not be correct. 3464 */ 3465 int tcp_send_synack(struct sock *sk) 3466 { 3467 struct sk_buff *skb; 3468 3469 skb = tcp_rtx_queue_head(sk); 3470 if (!skb || !(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)) { 3471 pr_err("%s: wrong queue state\n", __func__); 3472 return -EFAULT; 3473 } 3474 if (!(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_ACK)) { 3475 if (skb_cloned(skb)) { 3476 struct sk_buff *nskb; 3477 3478 tcp_skb_tsorted_save(skb) { 3479 nskb = skb_copy(skb, GFP_ATOMIC); 3480 } tcp_skb_tsorted_restore(skb); 3481 if (!nskb) 3482 return -ENOMEM; 3483 INIT_LIST_HEAD(&nskb->tcp_tsorted_anchor); 3484 tcp_highest_sack_replace(sk, skb, nskb); 3485 tcp_rtx_queue_unlink_and_free(skb, sk); 3486 __skb_header_release(nskb); 3487 tcp_rbtree_insert(&sk->tcp_rtx_queue, nskb); 3488 sk_wmem_queued_add(sk, nskb->truesize); 3489 sk_mem_charge(sk, nskb->truesize); 3490 skb = nskb; 3491 } 3492 3493 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ACK; 3494 tcp_ecn_send_synack(sk, skb); 3495 } 3496 return tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC); 3497 } 3498 3499 /** 3500 * tcp_make_synack - Allocate one skb and build a SYNACK packet. 3501 * @sk: listener socket 3502 * @dst: dst entry attached to the SYNACK. It is consumed and caller 3503 * should not use it again. 3504 * @req: request_sock pointer 3505 * @foc: cookie for tcp fast open 3506 * @synack_type: Type of synack to prepare 3507 * @syn_skb: SYN packet just received. It could be NULL for rtx case. 3508 */ 3509 struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst, 3510 struct request_sock *req, 3511 struct tcp_fastopen_cookie *foc, 3512 enum tcp_synack_type synack_type, 3513 struct sk_buff *syn_skb) 3514 { 3515 struct inet_request_sock *ireq = inet_rsk(req); 3516 const struct tcp_sock *tp = tcp_sk(sk); 3517 struct tcp_md5sig_key *md5 = NULL; 3518 struct tcp_out_options opts; 3519 struct sk_buff *skb; 3520 int tcp_header_size; 3521 struct tcphdr *th; 3522 int mss; 3523 u64 now; 3524 3525 skb = alloc_skb(MAX_TCP_HEADER, GFP_ATOMIC); 3526 if (unlikely(!skb)) { 3527 dst_release(dst); 3528 return NULL; 3529 } 3530 /* Reserve space for headers. */ 3531 skb_reserve(skb, MAX_TCP_HEADER); 3532 3533 switch (synack_type) { 3534 case TCP_SYNACK_NORMAL: 3535 skb_set_owner_w(skb, req_to_sk(req)); 3536 break; 3537 case TCP_SYNACK_COOKIE: 3538 /* Under synflood, we do not attach skb to a socket, 3539 * to avoid false sharing. 3540 */ 3541 break; 3542 case TCP_SYNACK_FASTOPEN: 3543 /* sk is a const pointer, because we want to express multiple 3544 * cpu might call us concurrently. 3545 * sk->sk_wmem_alloc in an atomic, we can promote to rw. 3546 */ 3547 skb_set_owner_w(skb, (struct sock *)sk); 3548 break; 3549 } 3550 skb_dst_set(skb, dst); 3551 3552 mss = tcp_mss_clamp(tp, dst_metric_advmss(dst)); 3553 3554 memset(&opts, 0, sizeof(opts)); 3555 now = tcp_clock_ns(); 3556 #ifdef CONFIG_SYN_COOKIES 3557 if (unlikely(synack_type == TCP_SYNACK_COOKIE && ireq->tstamp_ok)) 3558 skb_set_delivery_time(skb, cookie_init_timestamp(req, now), 3559 true); 3560 else 3561 #endif 3562 { 3563 skb_set_delivery_time(skb, now, true); 3564 if (!tcp_rsk(req)->snt_synack) /* Timestamp first SYNACK */ 3565 tcp_rsk(req)->snt_synack = tcp_skb_timestamp_us(skb); 3566 } 3567 3568 #ifdef CONFIG_TCP_MD5SIG 3569 rcu_read_lock(); 3570 md5 = tcp_rsk(req)->af_specific->req_md5_lookup(sk, req_to_sk(req)); 3571 #endif 3572 skb_set_hash(skb, tcp_rsk(req)->txhash, PKT_HASH_TYPE_L4); 3573 /* bpf program will be interested in the tcp_flags */ 3574 TCP_SKB_CB(skb)->tcp_flags = TCPHDR_SYN | TCPHDR_ACK; 3575 tcp_header_size = tcp_synack_options(sk, req, mss, skb, &opts, md5, 3576 foc, synack_type, 3577 syn_skb) + sizeof(*th); 3578 3579 skb_push(skb, tcp_header_size); 3580 skb_reset_transport_header(skb); 3581 3582 th = (struct tcphdr *)skb->data; 3583 memset(th, 0, sizeof(struct tcphdr)); 3584 th->syn = 1; 3585 th->ack = 1; 3586 tcp_ecn_make_synack(req, th); 3587 th->source = htons(ireq->ir_num); 3588 th->dest = ireq->ir_rmt_port; 3589 skb->mark = ireq->ir_mark; 3590 skb->ip_summed = CHECKSUM_PARTIAL; 3591 th->seq = htonl(tcp_rsk(req)->snt_isn); 3592 /* XXX data is queued and acked as is. No buffer/window check */ 3593 th->ack_seq = htonl(tcp_rsk(req)->rcv_nxt); 3594 3595 /* RFC1323: The window in SYN & SYN/ACK segments is never scaled. */ 3596 th->window = htons(min(req->rsk_rcv_wnd, 65535U)); 3597 tcp_options_write(th, NULL, &opts); 3598 th->doff = (tcp_header_size >> 2); 3599 __TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTSEGS); 3600 3601 #ifdef CONFIG_TCP_MD5SIG 3602 /* Okay, we have all we need - do the md5 hash if needed */ 3603 if (md5) 3604 tcp_rsk(req)->af_specific->calc_md5_hash(opts.hash_location, 3605 md5, req_to_sk(req), skb); 3606 rcu_read_unlock(); 3607 #endif 3608 3609 bpf_skops_write_hdr_opt((struct sock *)sk, skb, req, syn_skb, 3610 synack_type, &opts); 3611 3612 skb_set_delivery_time(skb, now, true); 3613 tcp_add_tx_delay(skb, tp); 3614 3615 return skb; 3616 } 3617 EXPORT_SYMBOL(tcp_make_synack); 3618 3619 static void tcp_ca_dst_init(struct sock *sk, const struct dst_entry *dst) 3620 { 3621 struct inet_connection_sock *icsk = inet_csk(sk); 3622 const struct tcp_congestion_ops *ca; 3623 u32 ca_key = dst_metric(dst, RTAX_CC_ALGO); 3624 3625 if (ca_key == TCP_CA_UNSPEC) 3626 return; 3627 3628 rcu_read_lock(); 3629 ca = tcp_ca_find_key(ca_key); 3630 if (likely(ca && bpf_try_module_get(ca, ca->owner))) { 3631 bpf_module_put(icsk->icsk_ca_ops, icsk->icsk_ca_ops->owner); 3632 icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst); 3633 icsk->icsk_ca_ops = ca; 3634 } 3635 rcu_read_unlock(); 3636 } 3637 3638 /* Do all connect socket setups that can be done AF independent. */ 3639 static void tcp_connect_init(struct sock *sk) 3640 { 3641 const struct dst_entry *dst = __sk_dst_get(sk); 3642 struct tcp_sock *tp = tcp_sk(sk); 3643 __u8 rcv_wscale; 3644 u32 rcv_wnd; 3645 3646 /* We'll fix this up when we get a response from the other end. 3647 * See tcp_input.c:tcp_rcv_state_process case TCP_SYN_SENT. 3648 */ 3649 tp->tcp_header_len = sizeof(struct tcphdr); 3650 if (READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_timestamps)) 3651 tp->tcp_header_len += TCPOLEN_TSTAMP_ALIGNED; 3652 3653 #ifdef CONFIG_TCP_MD5SIG 3654 if (tp->af_specific->md5_lookup(sk, sk)) 3655 tp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED; 3656 #endif 3657 3658 /* If user gave his TCP_MAXSEG, record it to clamp */ 3659 if (tp->rx_opt.user_mss) 3660 tp->rx_opt.mss_clamp = tp->rx_opt.user_mss; 3661 tp->max_window = 0; 3662 tcp_mtup_init(sk); 3663 tcp_sync_mss(sk, dst_mtu(dst)); 3664 3665 tcp_ca_dst_init(sk, dst); 3666 3667 if (!tp->window_clamp) 3668 tp->window_clamp = dst_metric(dst, RTAX_WINDOW); 3669 tp->advmss = tcp_mss_clamp(tp, dst_metric_advmss(dst)); 3670 3671 tcp_initialize_rcv_mss(sk); 3672 3673 /* limit the window selection if the user enforce a smaller rx buffer */ 3674 if (sk->sk_userlocks & SOCK_RCVBUF_LOCK && 3675 (tp->window_clamp > tcp_full_space(sk) || tp->window_clamp == 0)) 3676 tp->window_clamp = tcp_full_space(sk); 3677 3678 rcv_wnd = tcp_rwnd_init_bpf(sk); 3679 if (rcv_wnd == 0) 3680 rcv_wnd = dst_metric(dst, RTAX_INITRWND); 3681 3682 tcp_select_initial_window(sk, tcp_full_space(sk), 3683 tp->advmss - (tp->rx_opt.ts_recent_stamp ? tp->tcp_header_len - sizeof(struct tcphdr) : 0), 3684 &tp->rcv_wnd, 3685 &tp->window_clamp, 3686 READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_window_scaling), 3687 &rcv_wscale, 3688 rcv_wnd); 3689 3690 tp->rx_opt.rcv_wscale = rcv_wscale; 3691 tp->rcv_ssthresh = tp->rcv_wnd; 3692 3693 sk->sk_err = 0; 3694 sock_reset_flag(sk, SOCK_DONE); 3695 tp->snd_wnd = 0; 3696 tcp_init_wl(tp, 0); 3697 tcp_write_queue_purge(sk); 3698 tp->snd_una = tp->write_seq; 3699 tp->snd_sml = tp->write_seq; 3700 tp->snd_up = tp->write_seq; 3701 WRITE_ONCE(tp->snd_nxt, tp->write_seq); 3702 3703 if (likely(!tp->repair)) 3704 tp->rcv_nxt = 0; 3705 else 3706 tp->rcv_tstamp = tcp_jiffies32; 3707 tp->rcv_wup = tp->rcv_nxt; 3708 WRITE_ONCE(tp->copied_seq, tp->rcv_nxt); 3709 3710 inet_csk(sk)->icsk_rto = tcp_timeout_init(sk); 3711 inet_csk(sk)->icsk_retransmits = 0; 3712 tcp_clear_retrans(tp); 3713 } 3714 3715 static void tcp_connect_queue_skb(struct sock *sk, struct sk_buff *skb) 3716 { 3717 struct tcp_sock *tp = tcp_sk(sk); 3718 struct tcp_skb_cb *tcb = TCP_SKB_CB(skb); 3719 3720 tcb->end_seq += skb->len; 3721 __skb_header_release(skb); 3722 sk_wmem_queued_add(sk, skb->truesize); 3723 sk_mem_charge(sk, skb->truesize); 3724 WRITE_ONCE(tp->write_seq, tcb->end_seq); 3725 tp->packets_out += tcp_skb_pcount(skb); 3726 } 3727 3728 /* Build and send a SYN with data and (cached) Fast Open cookie. However, 3729 * queue a data-only packet after the regular SYN, such that regular SYNs 3730 * are retransmitted on timeouts. Also if the remote SYN-ACK acknowledges 3731 * only the SYN sequence, the data are retransmitted in the first ACK. 3732 * If cookie is not cached or other error occurs, falls back to send a 3733 * regular SYN with Fast Open cookie request option. 3734 */ 3735 static int tcp_send_syn_data(struct sock *sk, struct sk_buff *syn) 3736 { 3737 struct inet_connection_sock *icsk = inet_csk(sk); 3738 struct tcp_sock *tp = tcp_sk(sk); 3739 struct tcp_fastopen_request *fo = tp->fastopen_req; 3740 int space, err = 0; 3741 struct sk_buff *syn_data; 3742 3743 tp->rx_opt.mss_clamp = tp->advmss; /* If MSS is not cached */ 3744 if (!tcp_fastopen_cookie_check(sk, &tp->rx_opt.mss_clamp, &fo->cookie)) 3745 goto fallback; 3746 3747 /* MSS for SYN-data is based on cached MSS and bounded by PMTU and 3748 * user-MSS. Reserve maximum option space for middleboxes that add 3749 * private TCP options. The cost is reduced data space in SYN :( 3750 */ 3751 tp->rx_opt.mss_clamp = tcp_mss_clamp(tp, tp->rx_opt.mss_clamp); 3752 /* Sync mss_cache after updating the mss_clamp */ 3753 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie); 3754 3755 space = __tcp_mtu_to_mss(sk, icsk->icsk_pmtu_cookie) - 3756 MAX_TCP_OPTION_SPACE; 3757 3758 space = min_t(size_t, space, fo->size); 3759 3760 /* limit to order-0 allocations */ 3761 space = min_t(size_t, space, SKB_MAX_HEAD(MAX_TCP_HEADER)); 3762 3763 syn_data = tcp_stream_alloc_skb(sk, space, sk->sk_allocation, false); 3764 if (!syn_data) 3765 goto fallback; 3766 memcpy(syn_data->cb, syn->cb, sizeof(syn->cb)); 3767 if (space) { 3768 int copied = copy_from_iter(skb_put(syn_data, space), space, 3769 &fo->data->msg_iter); 3770 if (unlikely(!copied)) { 3771 tcp_skb_tsorted_anchor_cleanup(syn_data); 3772 kfree_skb(syn_data); 3773 goto fallback; 3774 } 3775 if (copied != space) { 3776 skb_trim(syn_data, copied); 3777 space = copied; 3778 } 3779 skb_zcopy_set(syn_data, fo->uarg, NULL); 3780 } 3781 /* No more data pending in inet_wait_for_connect() */ 3782 if (space == fo->size) 3783 fo->data = NULL; 3784 fo->copied = space; 3785 3786 tcp_connect_queue_skb(sk, syn_data); 3787 if (syn_data->len) 3788 tcp_chrono_start(sk, TCP_CHRONO_BUSY); 3789 3790 err = tcp_transmit_skb(sk, syn_data, 1, sk->sk_allocation); 3791 3792 skb_set_delivery_time(syn, syn_data->skb_mstamp_ns, true); 3793 3794 /* Now full SYN+DATA was cloned and sent (or not), 3795 * remove the SYN from the original skb (syn_data) 3796 * we keep in write queue in case of a retransmit, as we 3797 * also have the SYN packet (with no data) in the same queue. 3798 */ 3799 TCP_SKB_CB(syn_data)->seq++; 3800 TCP_SKB_CB(syn_data)->tcp_flags = TCPHDR_ACK | TCPHDR_PSH; 3801 if (!err) { 3802 tp->syn_data = (fo->copied > 0); 3803 tcp_rbtree_insert(&sk->tcp_rtx_queue, syn_data); 3804 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPORIGDATASENT); 3805 goto done; 3806 } 3807 3808 /* data was not sent, put it in write_queue */ 3809 __skb_queue_tail(&sk->sk_write_queue, syn_data); 3810 tp->packets_out -= tcp_skb_pcount(syn_data); 3811 3812 fallback: 3813 /* Send a regular SYN with Fast Open cookie request option */ 3814 if (fo->cookie.len > 0) 3815 fo->cookie.len = 0; 3816 err = tcp_transmit_skb(sk, syn, 1, sk->sk_allocation); 3817 if (err) 3818 tp->syn_fastopen = 0; 3819 done: 3820 fo->cookie.len = -1; /* Exclude Fast Open option for SYN retries */ 3821 return err; 3822 } 3823 3824 /* Build a SYN and send it off. */ 3825 int tcp_connect(struct sock *sk) 3826 { 3827 struct tcp_sock *tp = tcp_sk(sk); 3828 struct sk_buff *buff; 3829 int err; 3830 3831 tcp_call_bpf(sk, BPF_SOCK_OPS_TCP_CONNECT_CB, 0, NULL); 3832 3833 if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk)) 3834 return -EHOSTUNREACH; /* Routing failure or similar. */ 3835 3836 tcp_connect_init(sk); 3837 3838 if (unlikely(tp->repair)) { 3839 tcp_finish_connect(sk, NULL); 3840 return 0; 3841 } 3842 3843 buff = tcp_stream_alloc_skb(sk, 0, sk->sk_allocation, true); 3844 if (unlikely(!buff)) 3845 return -ENOBUFS; 3846 3847 tcp_init_nondata_skb(buff, tp->write_seq++, TCPHDR_SYN); 3848 tcp_mstamp_refresh(tp); 3849 tp->retrans_stamp = tcp_time_stamp(tp); 3850 tcp_connect_queue_skb(sk, buff); 3851 tcp_ecn_send_syn(sk, buff); 3852 tcp_rbtree_insert(&sk->tcp_rtx_queue, buff); 3853 3854 /* Send off SYN; include data in Fast Open. */ 3855 err = tp->fastopen_req ? tcp_send_syn_data(sk, buff) : 3856 tcp_transmit_skb(sk, buff, 1, sk->sk_allocation); 3857 if (err == -ECONNREFUSED) 3858 return err; 3859 3860 /* We change tp->snd_nxt after the tcp_transmit_skb() call 3861 * in order to make this packet get counted in tcpOutSegs. 3862 */ 3863 WRITE_ONCE(tp->snd_nxt, tp->write_seq); 3864 tp->pushed_seq = tp->write_seq; 3865 buff = tcp_send_head(sk); 3866 if (unlikely(buff)) { 3867 WRITE_ONCE(tp->snd_nxt, TCP_SKB_CB(buff)->seq); 3868 tp->pushed_seq = TCP_SKB_CB(buff)->seq; 3869 } 3870 TCP_INC_STATS(sock_net(sk), TCP_MIB_ACTIVEOPENS); 3871 3872 /* Timer for repeating the SYN until an answer. */ 3873 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, 3874 inet_csk(sk)->icsk_rto, TCP_RTO_MAX); 3875 return 0; 3876 } 3877 EXPORT_SYMBOL(tcp_connect); 3878 3879 /* Send out a delayed ack, the caller does the policy checking 3880 * to see if we should even be here. See tcp_input.c:tcp_ack_snd_check() 3881 * for details. 3882 */ 3883 void tcp_send_delayed_ack(struct sock *sk) 3884 { 3885 struct inet_connection_sock *icsk = inet_csk(sk); 3886 int ato = icsk->icsk_ack.ato; 3887 unsigned long timeout; 3888 3889 if (ato > TCP_DELACK_MIN) { 3890 const struct tcp_sock *tp = tcp_sk(sk); 3891 int max_ato = HZ / 2; 3892 3893 if (inet_csk_in_pingpong_mode(sk) || 3894 (icsk->icsk_ack.pending & ICSK_ACK_PUSHED)) 3895 max_ato = TCP_DELACK_MAX; 3896 3897 /* Slow path, intersegment interval is "high". */ 3898 3899 /* If some rtt estimate is known, use it to bound delayed ack. 3900 * Do not use inet_csk(sk)->icsk_rto here, use results of rtt measurements 3901 * directly. 3902 */ 3903 if (tp->srtt_us) { 3904 int rtt = max_t(int, usecs_to_jiffies(tp->srtt_us >> 3), 3905 TCP_DELACK_MIN); 3906 3907 if (rtt < max_ato) 3908 max_ato = rtt; 3909 } 3910 3911 ato = min(ato, max_ato); 3912 } 3913 3914 ato = min_t(u32, ato, inet_csk(sk)->icsk_delack_max); 3915 3916 /* Stay within the limit we were given */ 3917 timeout = jiffies + ato; 3918 3919 /* Use new timeout only if there wasn't a older one earlier. */ 3920 if (icsk->icsk_ack.pending & ICSK_ACK_TIMER) { 3921 /* If delack timer is about to expire, send ACK now. */ 3922 if (time_before_eq(icsk->icsk_ack.timeout, jiffies + (ato >> 2))) { 3923 tcp_send_ack(sk); 3924 return; 3925 } 3926 3927 if (!time_before(timeout, icsk->icsk_ack.timeout)) 3928 timeout = icsk->icsk_ack.timeout; 3929 } 3930 icsk->icsk_ack.pending |= ICSK_ACK_SCHED | ICSK_ACK_TIMER; 3931 icsk->icsk_ack.timeout = timeout; 3932 sk_reset_timer(sk, &icsk->icsk_delack_timer, timeout); 3933 } 3934 3935 /* This routine sends an ack and also updates the window. */ 3936 void __tcp_send_ack(struct sock *sk, u32 rcv_nxt) 3937 { 3938 struct sk_buff *buff; 3939 3940 /* If we have been reset, we may not send again. */ 3941 if (sk->sk_state == TCP_CLOSE) 3942 return; 3943 3944 /* We are not putting this on the write queue, so 3945 * tcp_transmit_skb() will set the ownership to this 3946 * sock. 3947 */ 3948 buff = alloc_skb(MAX_TCP_HEADER, 3949 sk_gfp_mask(sk, GFP_ATOMIC | __GFP_NOWARN)); 3950 if (unlikely(!buff)) { 3951 struct inet_connection_sock *icsk = inet_csk(sk); 3952 unsigned long delay; 3953 3954 delay = TCP_DELACK_MAX << icsk->icsk_ack.retry; 3955 if (delay < TCP_RTO_MAX) 3956 icsk->icsk_ack.retry++; 3957 inet_csk_schedule_ack(sk); 3958 icsk->icsk_ack.ato = TCP_ATO_MIN; 3959 inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK, delay, TCP_RTO_MAX); 3960 return; 3961 } 3962 3963 /* Reserve space for headers and prepare control bits. */ 3964 skb_reserve(buff, MAX_TCP_HEADER); 3965 tcp_init_nondata_skb(buff, tcp_acceptable_seq(sk), TCPHDR_ACK); 3966 3967 /* We do not want pure acks influencing TCP Small Queues or fq/pacing 3968 * too much. 3969 * SKB_TRUESIZE(max(1 .. 66, MAX_TCP_HEADER)) is unfortunately ~784 3970 */ 3971 skb_set_tcp_pure_ack(buff); 3972 3973 /* Send it off, this clears delayed acks for us. */ 3974 __tcp_transmit_skb(sk, buff, 0, (__force gfp_t)0, rcv_nxt); 3975 } 3976 EXPORT_SYMBOL_GPL(__tcp_send_ack); 3977 3978 void tcp_send_ack(struct sock *sk) 3979 { 3980 __tcp_send_ack(sk, tcp_sk(sk)->rcv_nxt); 3981 } 3982 3983 /* This routine sends a packet with an out of date sequence 3984 * number. It assumes the other end will try to ack it. 3985 * 3986 * Question: what should we make while urgent mode? 3987 * 4.4BSD forces sending single byte of data. We cannot send 3988 * out of window data, because we have SND.NXT==SND.MAX... 3989 * 3990 * Current solution: to send TWO zero-length segments in urgent mode: 3991 * one is with SEG.SEQ=SND.UNA to deliver urgent pointer, another is 3992 * out-of-date with SND.UNA-1 to probe window. 3993 */ 3994 static int tcp_xmit_probe_skb(struct sock *sk, int urgent, int mib) 3995 { 3996 struct tcp_sock *tp = tcp_sk(sk); 3997 struct sk_buff *skb; 3998 3999 /* We don't queue it, tcp_transmit_skb() sets ownership. */ 4000 skb = alloc_skb(MAX_TCP_HEADER, 4001 sk_gfp_mask(sk, GFP_ATOMIC | __GFP_NOWARN)); 4002 if (!skb) 4003 return -1; 4004 4005 /* Reserve space for headers and set control bits. */ 4006 skb_reserve(skb, MAX_TCP_HEADER); 4007 /* Use a previous sequence. This should cause the other 4008 * end to send an ack. Don't queue or clone SKB, just 4009 * send it. 4010 */ 4011 tcp_init_nondata_skb(skb, tp->snd_una - !urgent, TCPHDR_ACK); 4012 NET_INC_STATS(sock_net(sk), mib); 4013 return tcp_transmit_skb(sk, skb, 0, (__force gfp_t)0); 4014 } 4015 4016 /* Called from setsockopt( ... TCP_REPAIR ) */ 4017 void tcp_send_window_probe(struct sock *sk) 4018 { 4019 if (sk->sk_state == TCP_ESTABLISHED) { 4020 tcp_sk(sk)->snd_wl1 = tcp_sk(sk)->rcv_nxt - 1; 4021 tcp_mstamp_refresh(tcp_sk(sk)); 4022 tcp_xmit_probe_skb(sk, 0, LINUX_MIB_TCPWINPROBE); 4023 } 4024 } 4025 4026 /* Initiate keepalive or window probe from timer. */ 4027 int tcp_write_wakeup(struct sock *sk, int mib) 4028 { 4029 struct tcp_sock *tp = tcp_sk(sk); 4030 struct sk_buff *skb; 4031 4032 if (sk->sk_state == TCP_CLOSE) 4033 return -1; 4034 4035 skb = tcp_send_head(sk); 4036 if (skb && before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp))) { 4037 int err; 4038 unsigned int mss = tcp_current_mss(sk); 4039 unsigned int seg_size = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq; 4040 4041 if (before(tp->pushed_seq, TCP_SKB_CB(skb)->end_seq)) 4042 tp->pushed_seq = TCP_SKB_CB(skb)->end_seq; 4043 4044 /* We are probing the opening of a window 4045 * but the window size is != 0 4046 * must have been a result SWS avoidance ( sender ) 4047 */ 4048 if (seg_size < TCP_SKB_CB(skb)->end_seq - TCP_SKB_CB(skb)->seq || 4049 skb->len > mss) { 4050 seg_size = min(seg_size, mss); 4051 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH; 4052 if (tcp_fragment(sk, TCP_FRAG_IN_WRITE_QUEUE, 4053 skb, seg_size, mss, GFP_ATOMIC)) 4054 return -1; 4055 } else if (!tcp_skb_pcount(skb)) 4056 tcp_set_skb_tso_segs(skb, mss); 4057 4058 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH; 4059 err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC); 4060 if (!err) 4061 tcp_event_new_data_sent(sk, skb); 4062 return err; 4063 } else { 4064 if (between(tp->snd_up, tp->snd_una + 1, tp->snd_una + 0xFFFF)) 4065 tcp_xmit_probe_skb(sk, 1, mib); 4066 return tcp_xmit_probe_skb(sk, 0, mib); 4067 } 4068 } 4069 4070 /* A window probe timeout has occurred. If window is not closed send 4071 * a partial packet else a zero probe. 4072 */ 4073 void tcp_send_probe0(struct sock *sk) 4074 { 4075 struct inet_connection_sock *icsk = inet_csk(sk); 4076 struct tcp_sock *tp = tcp_sk(sk); 4077 struct net *net = sock_net(sk); 4078 unsigned long timeout; 4079 int err; 4080 4081 err = tcp_write_wakeup(sk, LINUX_MIB_TCPWINPROBE); 4082 4083 if (tp->packets_out || tcp_write_queue_empty(sk)) { 4084 /* Cancel probe timer, if it is not required. */ 4085 icsk->icsk_probes_out = 0; 4086 icsk->icsk_backoff = 0; 4087 icsk->icsk_probes_tstamp = 0; 4088 return; 4089 } 4090 4091 icsk->icsk_probes_out++; 4092 if (err <= 0) { 4093 if (icsk->icsk_backoff < READ_ONCE(net->ipv4.sysctl_tcp_retries2)) 4094 icsk->icsk_backoff++; 4095 timeout = tcp_probe0_when(sk, TCP_RTO_MAX); 4096 } else { 4097 /* If packet was not sent due to local congestion, 4098 * Let senders fight for local resources conservatively. 4099 */ 4100 timeout = TCP_RESOURCE_PROBE_INTERVAL; 4101 } 4102 4103 timeout = tcp_clamp_probe0_to_user_timeout(sk, timeout); 4104 tcp_reset_xmit_timer(sk, ICSK_TIME_PROBE0, timeout, TCP_RTO_MAX); 4105 } 4106 4107 int tcp_rtx_synack(const struct sock *sk, struct request_sock *req) 4108 { 4109 const struct tcp_request_sock_ops *af_ops = tcp_rsk(req)->af_specific; 4110 struct flowi fl; 4111 int res; 4112 4113 /* Paired with WRITE_ONCE() in sock_setsockopt() */ 4114 if (READ_ONCE(sk->sk_txrehash) == SOCK_TXREHASH_ENABLED) 4115 tcp_rsk(req)->txhash = net_tx_rndhash(); 4116 res = af_ops->send_synack(sk, NULL, &fl, req, NULL, TCP_SYNACK_NORMAL, 4117 NULL); 4118 if (!res) { 4119 TCP_INC_STATS(sock_net(sk), TCP_MIB_RETRANSSEGS); 4120 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSYNRETRANS); 4121 if (unlikely(tcp_passive_fastopen(sk))) 4122 tcp_sk(sk)->total_retrans++; 4123 trace_tcp_retransmit_synack(sk, req); 4124 } 4125 return res; 4126 } 4127 EXPORT_SYMBOL(tcp_rtx_synack); 4128