root/net/ipv4/tcp_fastopen.c

DEFINITIONS

1. tcp_fastopen_init_key_once
2. tcp_fastopen_ctx_free
3. tcp_fastopen_destroy_cipher
4. tcp_fastopen_ctx_destroy
5. tcp_fastopen_reset_cipher
6. __tcp_fastopen_cookie_gen_cipher
7. tcp_fastopen_cookie_gen
8. tcp_fastopen_add_skb
9. tcp_fastopen_cookie_gen_check
10. tcp_fastopen_create_child
11. tcp_fastopen_queue_check
12. tcp_fastopen_no_cookie
13. tcp_try_fastopen
14. tcp_fastopen_cookie_check
15. tcp_fastopen_defer_connect
16. tcp_fastopen_active_disable
17. tcp_fastopen_active_should_disable
18. tcp_fastopen_active_disable_ofo_check
19. tcp_fastopen_active_detect_blackhole

   1 // SPDX-License-Identifier: GPL-2.0
   2 #include <linux/crypto.h>
   3 #include <linux/err.h>
   4 #include <linux/init.h>
   5 #include <linux/kernel.h>
   6 #include <linux/list.h>
   7 #include <linux/tcp.h>
   8 #include <linux/rcupdate.h>
   9 #include <linux/rculist.h>
  10 #include <net/inetpeer.h>
  11 #include <net/tcp.h>
  12 
  13 void tcp_fastopen_init_key_once(struct net *net)
  14 {
  15         u8 key[TCP_FASTOPEN_KEY_LENGTH];
  16         struct tcp_fastopen_context *ctxt;
  17 
  18         rcu_read_lock();
  19         ctxt = rcu_dereference(net->ipv4.tcp_fastopen_ctx);
  20         if (ctxt) {
  21                 rcu_read_unlock();
  22                 return;
  23         }
  24         rcu_read_unlock();
  25 
  26         /* tcp_fastopen_reset_cipher publishes the new context
  27          * atomically, so we allow this race happening here.
  28          *
  29          * All call sites of tcp_fastopen_cookie_gen also check
  30          * for a valid cookie, so this is an acceptable risk.
  31          */
  32         get_random_bytes(key, sizeof(key));
  33         tcp_fastopen_reset_cipher(net, NULL, key, NULL);
  34 }
  35 
  36 static void tcp_fastopen_ctx_free(struct rcu_head *head)
  37 {
  38         struct tcp_fastopen_context *ctx =
  39             container_of(head, struct tcp_fastopen_context, rcu);
  40 
  41         kzfree(ctx);
  42 }
  43 
  44 void tcp_fastopen_destroy_cipher(struct sock *sk)
  45 {
  46         struct tcp_fastopen_context *ctx;
  47 
  48         ctx = rcu_dereference_protected(
  49                         inet_csk(sk)->icsk_accept_queue.fastopenq.ctx, 1);
  50         if (ctx)
  51                 call_rcu(&ctx->rcu, tcp_fastopen_ctx_free);
  52 }
  53 
  54 void tcp_fastopen_ctx_destroy(struct net *net)
  55 {
  56         struct tcp_fastopen_context *ctxt;
  57 
  58         spin_lock(&net->ipv4.tcp_fastopen_ctx_lock);
  59 
  60         ctxt = rcu_dereference_protected(net->ipv4.tcp_fastopen_ctx,
  61                                 lockdep_is_held(&net->ipv4.tcp_fastopen_ctx_lock));
  62         rcu_assign_pointer(net->ipv4.tcp_fastopen_ctx, NULL);
  63         spin_unlock(&net->ipv4.tcp_fastopen_ctx_lock);
  64 
  65         if (ctxt)
  66                 call_rcu(&ctxt->rcu, tcp_fastopen_ctx_free);
  67 }
  68 
  69 int tcp_fastopen_reset_cipher(struct net *net, struct sock *sk,
  70                               void *primary_key, void *backup_key)
  71 {
  72         struct tcp_fastopen_context *ctx, *octx;
  73         struct fastopen_queue *q;
  74         int err = 0;
  75 
  76         ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
  77         if (!ctx) {
  78                 err = -ENOMEM;
  79                 goto out;
  80         }
  81 
  82         ctx->key[0].key[0] = get_unaligned_le64(primary_key);
  83         ctx->key[0].key[1] = get_unaligned_le64(primary_key + 8);
  84         if (backup_key) {
  85                 ctx->key[1].key[0] = get_unaligned_le64(backup_key);
  86                 ctx->key[1].key[1] = get_unaligned_le64(backup_key + 8);
  87                 ctx->num = 2;
  88         } else {
  89                 ctx->num = 1;
  90         }
  91 
  92         spin_lock(&net->ipv4.tcp_fastopen_ctx_lock);
  93         if (sk) {
  94                 q = &inet_csk(sk)->icsk_accept_queue.fastopenq;
  95                 octx = rcu_dereference_protected(q->ctx,
  96                         lockdep_is_held(&net->ipv4.tcp_fastopen_ctx_lock));
  97                 rcu_assign_pointer(q->ctx, ctx);
  98         } else {
  99                 octx = rcu_dereference_protected(net->ipv4.tcp_fastopen_ctx,
 100                         lockdep_is_held(&net->ipv4.tcp_fastopen_ctx_lock));
 101                 rcu_assign_pointer(net->ipv4.tcp_fastopen_ctx, ctx);
 102         }
 103         spin_unlock(&net->ipv4.tcp_fastopen_ctx_lock);
 104 
 105         if (octx)
 106                 call_rcu(&octx->rcu, tcp_fastopen_ctx_free);
 107 out:
 108         return err;
 109 }
 110 
 111 static bool __tcp_fastopen_cookie_gen_cipher(struct request_sock *req,
 112                                              struct sk_buff *syn,
 113                                              const siphash_key_t *key,
 114                                              struct tcp_fastopen_cookie *foc)
 115 {
 116         BUILD_BUG_ON(TCP_FASTOPEN_COOKIE_SIZE != sizeof(u64));
 117 
 118         if (req->rsk_ops->family == AF_INET) {
 119                 const struct iphdr *iph = ip_hdr(syn);
 120 
 121                 foc->val[0] = cpu_to_le64(siphash(&iph->saddr,
 122                                           sizeof(iph->saddr) +
 123                                           sizeof(iph->daddr),
 124                                           key));
 125                 foc->len = TCP_FASTOPEN_COOKIE_SIZE;
 126                 return true;
 127         }
 128 #if IS_ENABLED(CONFIG_IPV6)
 129         if (req->rsk_ops->family == AF_INET6) {
 130                 const struct ipv6hdr *ip6h = ipv6_hdr(syn);
 131 
 132                 foc->val[0] = cpu_to_le64(siphash(&ip6h->saddr,
 133                                           sizeof(ip6h->saddr) +
 134                                           sizeof(ip6h->daddr),
 135                                           key));
 136                 foc->len = TCP_FASTOPEN_COOKIE_SIZE;
 137                 return true;
 138         }
 139 #endif
 140         return false;
 141 }
 142 
 143 /* Generate the fastopen cookie by applying SipHash to both the source and
 144  * destination addresses.
 145  */
 146 static void tcp_fastopen_cookie_gen(struct sock *sk,
 147                                     struct request_sock *req,
 148                                     struct sk_buff *syn,
 149                                     struct tcp_fastopen_cookie *foc)
 150 {
 151         struct tcp_fastopen_context *ctx;
 152 
 153         rcu_read_lock();
 154         ctx = tcp_fastopen_get_ctx(sk);
 155         if (ctx)
 156                 __tcp_fastopen_cookie_gen_cipher(req, syn, &ctx->key[0], foc);
 157         rcu_read_unlock();
 158 }
 159 
 160 /* If an incoming SYN or SYNACK frame contains a payload and/or FIN,
 161  * queue this additional data / FIN.
 162  */
 163 void tcp_fastopen_add_skb(struct sock *sk, struct sk_buff *skb)
 164 {
 165         struct tcp_sock *tp = tcp_sk(sk);
 166 
 167         if (TCP_SKB_CB(skb)->end_seq == tp->rcv_nxt)
 168                 return;
 169 
 170         skb = skb_clone(skb, GFP_ATOMIC);
 171         if (!skb)
 172                 return;
 173 
 174         skb_dst_drop(skb);
 175         /* segs_in has been initialized to 1 in tcp_create_openreq_child().
 176          * Hence, reset segs_in to 0 before calling tcp_segs_in()
 177          * to avoid double counting.  Also, tcp_segs_in() expects
 178          * skb->len to include the tcp_hdrlen.  Hence, it should
 179          * be called before __skb_pull().
 180          */
 181         tp->segs_in = 0;
 182         tcp_segs_in(tp, skb);
 183         __skb_pull(skb, tcp_hdrlen(skb));
 184         sk_forced_mem_schedule(sk, skb->truesize);
 185         skb_set_owner_r(skb, sk);
 186 
 187         TCP_SKB_CB(skb)->seq++;
 188         TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_SYN;
 189 
 190         tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
 191         __skb_queue_tail(&sk->sk_receive_queue, skb);
 192         tp->syn_data_acked = 1;
 193 
 194         /* u64_stats_update_begin(&tp->syncp) not needed here,
 195          * as we certainly are not changing upper 32bit value (0)
 196          */
 197         tp->bytes_received = skb->len;
 198 
 199         if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
 200                 tcp_fin(sk);
 201 }
 202 
 203 /* returns 0 - no key match, 1 for primary, 2 for backup */
 204 static int tcp_fastopen_cookie_gen_check(struct sock *sk,
 205                                          struct request_sock *req,
 206                                          struct sk_buff *syn,
 207                                          struct tcp_fastopen_cookie *orig,
 208                                          struct tcp_fastopen_cookie *valid_foc)
 209 {
 210         struct tcp_fastopen_cookie search_foc = { .len = -1 };
 211         struct tcp_fastopen_cookie *foc = valid_foc;
 212         struct tcp_fastopen_context *ctx;
 213         int i, ret = 0;
 214 
 215         rcu_read_lock();
 216         ctx = tcp_fastopen_get_ctx(sk);
 217         if (!ctx)
 218                 goto out;
 219         for (i = 0; i < tcp_fastopen_context_len(ctx); i++) {
 220                 __tcp_fastopen_cookie_gen_cipher(req, syn, &ctx->key[i], foc);
 221                 if (tcp_fastopen_cookie_match(foc, orig)) {
 222                         ret = i + 1;
 223                         goto out;
 224                 }
 225                 foc = &search_foc;
 226         }
 227 out:
 228         rcu_read_unlock();
 229         return ret;
 230 }
 231 
 232 static struct sock *tcp_fastopen_create_child(struct sock *sk,
 233                                               struct sk_buff *skb,
 234                                               struct request_sock *req)
 235 {
 236         struct tcp_sock *tp;
 237         struct request_sock_queue *queue = &inet_csk(sk)->icsk_accept_queue;
 238         struct sock *child;
 239         bool own_req;
 240 
 241         child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL,
 242                                                          NULL, &own_req);
 243         if (!child)
 244                 return NULL;
 245 
 246         spin_lock(&queue->fastopenq.lock);
 247         queue->fastopenq.qlen++;
 248         spin_unlock(&queue->fastopenq.lock);
 249 
 250         /* Initialize the child socket. Have to fix some values to take
 251          * into account the child is a Fast Open socket and is created
 252          * only out of the bits carried in the SYN packet.
 253          */
 254         tp = tcp_sk(child);
 255 
 256         rcu_assign_pointer(tp->fastopen_rsk, req);
 257         tcp_rsk(req)->tfo_listener = true;
 258 
 259         /* RFC1323: The window in SYN & SYN/ACK segments is never
 260          * scaled. So correct it appropriately.
 261          */
 262         tp->snd_wnd = ntohs(tcp_hdr(skb)->window);
 263         tp->max_window = tp->snd_wnd;
 264 
 265         /* Activate the retrans timer so that SYNACK can be retransmitted.
 266          * The request socket is not added to the ehash
 267          * because it's been added to the accept queue directly.
 268          */
 269         inet_csk_reset_xmit_timer(child, ICSK_TIME_RETRANS,
 270                                   TCP_TIMEOUT_INIT, TCP_RTO_MAX);
 271 
 272         refcount_set(&req->rsk_refcnt, 2);
 273 
 274         /* Now finish processing the fastopen child socket. */
 275         tcp_init_transfer(child, BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB);
 276 
 277         tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
 278 
 279         tcp_fastopen_add_skb(child, skb);
 280 
 281         tcp_rsk(req)->rcv_nxt = tp->rcv_nxt;
 282         tp->rcv_wup = tp->rcv_nxt;
 283         /* tcp_conn_request() is sending the SYNACK,
 284          * and queues the child into listener accept queue.
 285          */
 286         return child;
 287 }
 288 
 289 static bool tcp_fastopen_queue_check(struct sock *sk)
 290 {
 291         struct fastopen_queue *fastopenq;
 292 
 293         /* Make sure the listener has enabled fastopen, and we don't
 294          * exceed the max # of pending TFO requests allowed before trying
 295          * to validating the cookie in order to avoid burning CPU cycles
 296          * unnecessarily.
 297          *
 298          * XXX (TFO) - The implication of checking the max_qlen before
 299          * processing a cookie request is that clients can't differentiate
 300          * between qlen overflow causing Fast Open to be disabled
 301          * temporarily vs a server not supporting Fast Open at all.
 302          */
 303         fastopenq = &inet_csk(sk)->icsk_accept_queue.fastopenq;
 304         if (fastopenq->max_qlen == 0)
 305                 return false;
 306 
 307         if (fastopenq->qlen >= fastopenq->max_qlen) {
 308                 struct request_sock *req1;
 309                 spin_lock(&fastopenq->lock);
 310                 req1 = fastopenq->rskq_rst_head;
 311                 if (!req1 || time_after(req1->rsk_timer.expires, jiffies)) {
 312                         __NET_INC_STATS(sock_net(sk),
 313                                         LINUX_MIB_TCPFASTOPENLISTENOVERFLOW);
 314                         spin_unlock(&fastopenq->lock);
 315                         return false;
 316                 }
 317                 fastopenq->rskq_rst_head = req1->dl_next;
 318                 fastopenq->qlen--;
 319                 spin_unlock(&fastopenq->lock);
 320                 reqsk_put(req1);
 321         }
 322         return true;
 323 }
 324 
 325 static bool tcp_fastopen_no_cookie(const struct sock *sk,
 326                                    const struct dst_entry *dst,
 327                                    int flag)
 328 {
 329         return (sock_net(sk)->ipv4.sysctl_tcp_fastopen & flag) ||
 330                tcp_sk(sk)->fastopen_no_cookie ||
 331                (dst && dst_metric(dst, RTAX_FASTOPEN_NO_COOKIE));
 332 }
 333 
 334 /* Returns true if we should perform Fast Open on the SYN. The cookie (foc)
 335  * may be updated and return the client in the SYN-ACK later. E.g., Fast Open
 336  * cookie request (foc->len == 0).
 337  */
 338 struct sock *tcp_try_fastopen(struct sock *sk, struct sk_buff *skb,
 339                               struct request_sock *req,
 340                               struct tcp_fastopen_cookie *foc,
 341                               const struct dst_entry *dst)
 342 {
 343         bool syn_data = TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq + 1;
 344         int tcp_fastopen = sock_net(sk)->ipv4.sysctl_tcp_fastopen;
 345         struct tcp_fastopen_cookie valid_foc = { .len = -1 };
 346         struct sock *child;
 347         int ret = 0;
 348 
 349         if (foc->len == 0) /* Client requests a cookie */
 350                 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFASTOPENCOOKIEREQD);
 351 
 352         if (!((tcp_fastopen & TFO_SERVER_ENABLE) &&
 353               (syn_data || foc->len >= 0) &&
 354               tcp_fastopen_queue_check(sk))) {
 355                 foc->len = -1;
 356                 return NULL;
 357         }
 358 
 359         if (syn_data &&
 360             tcp_fastopen_no_cookie(sk, dst, TFO_SERVER_COOKIE_NOT_REQD))
 361                 goto fastopen;
 362 
 363         if (foc->len == 0) {
 364                 /* Client requests a cookie. */
 365                 tcp_fastopen_cookie_gen(sk, req, skb, &valid_foc);
 366         } else if (foc->len > 0) {
 367                 ret = tcp_fastopen_cookie_gen_check(sk, req, skb, foc,
 368                                                     &valid_foc);
 369                 if (!ret) {
 370                         NET_INC_STATS(sock_net(sk),
 371                                       LINUX_MIB_TCPFASTOPENPASSIVEFAIL);
 372                 } else {
 373                         /* Cookie is valid. Create a (full) child socket to
 374                          * accept the data in SYN before returning a SYN-ACK to
 375                          * ack the data. If we fail to create the socket, fall
 376                          * back and ack the ISN only but includes the same
 377                          * cookie.
 378                          *
 379                          * Note: Data-less SYN with valid cookie is allowed to
 380                          * send data in SYN_RECV state.
 381                          */
 382 fastopen:
 383                         child = tcp_fastopen_create_child(sk, skb, req);
 384                         if (child) {
 385                                 if (ret == 2) {
 386                                         valid_foc.exp = foc->exp;
 387                                         *foc = valid_foc;
 388                                         NET_INC_STATS(sock_net(sk),
 389                                                       LINUX_MIB_TCPFASTOPENPASSIVEALTKEY);
 390                                 } else {
 391                                         foc->len = -1;
 392                                 }
 393                                 NET_INC_STATS(sock_net(sk),
 394                                               LINUX_MIB_TCPFASTOPENPASSIVE);
 395                                 return child;
 396                         }
 397                         NET_INC_STATS(sock_net(sk),
 398                                       LINUX_MIB_TCPFASTOPENPASSIVEFAIL);
 399                 }
 400         }
 401         valid_foc.exp = foc->exp;
 402         *foc = valid_foc;
 403         return NULL;
 404 }
 405 
 406 bool tcp_fastopen_cookie_check(struct sock *sk, u16 *mss,
 407                                struct tcp_fastopen_cookie *cookie)
 408 {
 409         const struct dst_entry *dst;
 410 
 411         tcp_fastopen_cache_get(sk, mss, cookie);
 412 
 413         /* Firewall blackhole issue check */
 414         if (tcp_fastopen_active_should_disable(sk)) {
 415                 cookie->len = -1;
 416                 return false;
 417         }
 418 
 419         dst = __sk_dst_get(sk);
 420 
 421         if (tcp_fastopen_no_cookie(sk, dst, TFO_CLIENT_NO_COOKIE)) {
 422                 cookie->len = -1;
 423                 return true;
 424         }
 425         return cookie->len > 0;
 426 }
 427 
 428 /* This function checks if we want to defer sending SYN until the first
 429  * write().  We defer under the following conditions:
 430  * 1. fastopen_connect sockopt is set
 431  * 2. we have a valid cookie
 432  * Return value: return true if we want to defer until application writes data
 433  *               return false if we want to send out SYN immediately
 434  */
 435 bool tcp_fastopen_defer_connect(struct sock *sk, int *err)
 436 {
 437         struct tcp_fastopen_cookie cookie = { .len = 0 };
 438         struct tcp_sock *tp = tcp_sk(sk);
 439         u16 mss;
 440 
 441         if (tp->fastopen_connect && !tp->fastopen_req) {
 442                 if (tcp_fastopen_cookie_check(sk, &mss, &cookie)) {
 443                         inet_sk(sk)->defer_connect = 1;
 444                         return true;
 445                 }
 446 
 447                 /* Alloc fastopen_req in order for FO option to be included
 448                  * in SYN
 449                  */
 450                 tp->fastopen_req = kzalloc(sizeof(*tp->fastopen_req),
 451                                            sk->sk_allocation);
 452                 if (tp->fastopen_req)
 453                         tp->fastopen_req->cookie = cookie;
 454                 else
 455                         *err = -ENOBUFS;
 456         }
 457         return false;
 458 }
 459 EXPORT_SYMBOL(tcp_fastopen_defer_connect);
 460 
 461 /*
 462  * The following code block is to deal with middle box issues with TFO:
 463  * Middlebox firewall issues can potentially cause server's data being
 464  * blackholed after a successful 3WHS using TFO.
 465  * The proposed solution is to disable active TFO globally under the
 466  * following circumstances:
 467  *   1. client side TFO socket receives out of order FIN
 468  *   2. client side TFO socket receives out of order RST
 469  *   3. client side TFO socket has timed out three times consecutively during
 470  *      or after handshake
 471  * We disable active side TFO globally for 1hr at first. Then if it
 472  * happens again, we disable it for 2h, then 4h, 8h, ...
 473  * And we reset the timeout back to 1hr when we see a successful active
 474  * TFO connection with data exchanges.
 475  */
 476 
 477 /* Disable active TFO and record current jiffies and
 478  * tfo_active_disable_times
 479  */
 480 void tcp_fastopen_active_disable(struct sock *sk)
 481 {
 482         struct net *net = sock_net(sk);
 483 
 484         atomic_inc(&net->ipv4.tfo_active_disable_times);
 485         net->ipv4.tfo_active_disable_stamp = jiffies;
 486         NET_INC_STATS(net, LINUX_MIB_TCPFASTOPENBLACKHOLE);
 487 }
 488 
 489 /* Calculate timeout for tfo active disable
 490  * Return true if we are still in the active TFO disable period
 491  * Return false if timeout already expired and we should use active TFO
 492  */
 493 bool tcp_fastopen_active_should_disable(struct sock *sk)
 494 {
 495         unsigned int tfo_bh_timeout = sock_net(sk)->ipv4.sysctl_tcp_fastopen_blackhole_timeout;
 496         int tfo_da_times = atomic_read(&sock_net(sk)->ipv4.tfo_active_disable_times);
 497         unsigned long timeout;
 498         int multiplier;
 499 
 500         if (!tfo_da_times)
 501                 return false;
 502 
 503         /* Limit timout to max: 2^6 * initial timeout */
 504         multiplier = 1 << min(tfo_da_times - 1, 6);
 505         timeout = multiplier * tfo_bh_timeout * HZ;
 506         if (time_before(jiffies, sock_net(sk)->ipv4.tfo_active_disable_stamp + timeout))
 507                 return true;
 508 
 509         /* Mark check bit so we can check for successful active TFO
 510          * condition and reset tfo_active_disable_times
 511          */
 512         tcp_sk(sk)->syn_fastopen_ch = 1;
 513         return false;
 514 }
 515 
 516 /* Disable active TFO if FIN is the only packet in the ofo queue
 517  * and no data is received.
 518  * Also check if we can reset tfo_active_disable_times if data is
 519  * received successfully on a marked active TFO sockets opened on
 520  * a non-loopback interface
 521  */
 522 void tcp_fastopen_active_disable_ofo_check(struct sock *sk)
 523 {
 524         struct tcp_sock *tp = tcp_sk(sk);
 525         struct dst_entry *dst;
 526         struct sk_buff *skb;
 527 
 528         if (!tp->syn_fastopen)
 529                 return;
 530 
 531         if (!tp->data_segs_in) {
 532                 skb = skb_rb_first(&tp->out_of_order_queue);
 533                 if (skb && !skb_rb_next(skb)) {
 534                         if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) {
 535                                 tcp_fastopen_active_disable(sk);
 536                                 return;
 537                         }
 538                 }
 539         } else if (tp->syn_fastopen_ch &&
 540                    atomic_read(&sock_net(sk)->ipv4.tfo_active_disable_times)) {
 541                 dst = sk_dst_get(sk);
 542                 if (!(dst && dst->dev && (dst->dev->flags & IFF_LOOPBACK)))
 543                         atomic_set(&sock_net(sk)->ipv4.tfo_active_disable_times, 0);
 544                 dst_release(dst);
 545         }
 546 }
 547 
 548 void tcp_fastopen_active_detect_blackhole(struct sock *sk, bool expired)
 549 {
 550         u32 timeouts = inet_csk(sk)->icsk_retransmits;
 551         struct tcp_sock *tp = tcp_sk(sk);
 552 
 553         /* Broken middle-boxes may black-hole Fast Open connection during or
 554          * even after the handshake. Be extremely conservative and pause
 555          * Fast Open globally after hitting the third consecutive timeout or
 556          * exceeding the configured timeout limit.
 557          */
 558         if ((tp->syn_fastopen || tp->syn_data || tp->syn_data_acked) &&
 559             (timeouts == 2 || (timeouts < 2 && expired))) {
 560                 tcp_fastopen_active_disable(sk);
 561                 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFASTOPENACTIVEFAIL);
 562         }
 563 }