net/ipv4/tcp_minisocks.c

   1 /*
   2  * INET         An implementation of the TCP/IP protocol suite for the LINUX
   3  *              operating system.  INET is implemented using the  BSD Socket
   4  *              interface as the means of communication with the user level.
   5  *
   6  *              Implementation of the Transmission Control Protocol(TCP).
   7  *
   8  * Version:     $Id: tcp_minisocks.c,v 1.15 2002/02/01 22:01:04 davem Exp $
   9  *
  10  * Authors:     Ross Biro
  11  *              Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
  12  *              Mark Evans, <evansmp@uhura.aston.ac.uk>
  13  *              Corey Minyard <wf-rch!minyard@relay.EU.net>
  14  *              Florian La Roche, <flla@stud.uni-sb.de>
  15  *              Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
  16  *              Linus Torvalds, <torvalds@cs.helsinki.fi>
  17  *              Alan Cox, <gw4pts@gw4pts.ampr.org>
  18  *              Matthew Dillon, <dillon@apollo.west.oic.com>
  19  *              Arnt Gulbrandsen, <agulbra@nvg.unit.no>
  20  *              Jorge Cwik, <jorge@laser.satlink.net>
  21  */
  22
  23 #include <linux/config.h>
  24 #include <linux/mm.h>
  25 #include <linux/module.h>
  26 #include <linux/sysctl.h>
  27 #include <linux/workqueue.h>
  28 #include <linux/vs_limit.h>
  29 #include <linux/vs_socket.h>
  30 #include <net/tcp.h>
  31 #include <net/inet_common.h>
  32 #include <net/xfrm.h>
  33
  34 #include <linux/vs_limit.h>
  35 #include <linux/vs_socket.h>
  36 #include <linux/vs_context.h>
  37
  38 #ifdef CONFIG_SYSCTL
  39 #define SYNC_INIT 0 /* let the user enable it */
  40 #else
  41 #define SYNC_INIT 1
  42 #endif
  43
  44 int sysctl_tcp_tw_recycle;
  45 int sysctl_tcp_max_tw_buckets = NR_FILE*2;
  46
  47 int sysctl_tcp_syncookies = SYNC_INIT;
  48 int sysctl_tcp_abort_on_overflow;
  49
  50 static void tcp_tw_schedule(struct tcp_tw_bucket *tw, int timeo);
  51
  52 static __inline__ int tcp_in_window(u32 seq, u32 end_seq, u32 s_win, u32 e_win)
  53 {
  54         if (seq == s_win)
  55                 return 1;
  56         if (after(end_seq, s_win) && before(seq, e_win))
  57                 return 1;
  58         return (seq == e_win && seq == end_seq);
  59 }
  60
  61 /* New-style handling of TIME_WAIT sockets. */
  62
  63 int tcp_tw_count;
  64
  65
  66 /* Must be called with locally disabled BHs. */
  67 static void tcp_timewait_kill(struct tcp_tw_bucket *tw)
  68 {
  69         struct tcp_ehash_bucket *ehead;
  70         struct tcp_bind_hashbucket *bhead;
  71         struct tcp_bind_bucket *tb;
  72
  73         /* Unlink from established hashes. */
  74         ehead = &tcp_ehash[tw->tw_hashent];
  75         write_lock(&ehead->lock);
  76         if (hlist_unhashed(&tw->tw_node)) {
  77                 write_unlock(&ehead->lock);
  78                 return;
  79         }
  80         __hlist_del(&tw->tw_node);
  81         sk_node_init(&tw->tw_node);
  82         write_unlock(&ehead->lock);
  83
  84         /* Disassociate with bind bucket. */
  85         bhead = &tcp_bhash[tcp_bhashfn(tw->tw_num)];
  86         spin_lock(&bhead->lock);
  87         tb = tw->tw_tb;
  88         __hlist_del(&tw->tw_bind_node);
  89         tw->tw_tb = NULL;
  90         tcp_bucket_destroy(tb);
  91         spin_unlock(&bhead->lock);
  92
  93 #ifdef INET_REFCNT_DEBUG
  94         if (atomic_read(&tw->tw_refcnt) != 1) {
  95                 printk(KERN_DEBUG "tw_bucket %p refcnt=%d\n", tw,
  96                        atomic_read(&tw->tw_refcnt));
  97         }
  98 #endif
  99         tcp_tw_put(tw);
 100 }
 101
 102 /*
 103  * * Main purpose of TIME-WAIT state is to close connection gracefully,
 104  *   when one of ends sits in LAST-ACK or CLOSING retransmitting FIN
 105  *   (and, probably, tail of data) and one or more our ACKs are lost.
 106  * * What is TIME-WAIT timeout? It is associated with maximal packet
 107  *   lifetime in the internet, which results in wrong conclusion, that
 108  *   it is set to catch "old duplicate segments" wandering out of their path.
 109  *   It is not quite correct. This timeout is calculated so that it exceeds
 110  *   maximal retransmission timeout enough to allow to lose one (or more)
 111  *   segments sent by peer and our ACKs. This time may be calculated from RTO.
 112  * * When TIME-WAIT socket receives RST, it means that another end
 113  *   finally closed and we are allowed to kill TIME-WAIT too.
 114  * * Second purpose of TIME-WAIT is catching old duplicate segments.
 115  *   Well, certainly it is pure paranoia, but if we load TIME-WAIT
 116  *   with this semantics, we MUST NOT kill TIME-WAIT state with RSTs.
 117  * * If we invented some more clever way to catch duplicates
 118  *   (f.e. based on PAWS), we could truncate TIME-WAIT to several RTOs.
 119  *
 120  * The algorithm below is based on FORMAL INTERPRETATION of RFCs.
 121  * When you compare it to RFCs, please, read section SEGMENT ARRIVES
 122  * from the very beginning.
 123  *
 124  * NOTE. With recycling (and later with fin-wait-2) TW bucket
 125  * is _not_ stateless. It means, that strictly speaking we must
 126  * spinlock it. I do not want! Well, probability of misbehaviour
 127  * is ridiculously low and, seems, we could use some mb() tricks
 128  * to avoid misread sequence numbers, states etc.  --ANK
 129  */
 130 enum tcp_tw_status
 131 tcp_timewait_state_process(struct tcp_tw_bucket *tw, struct sk_buff *skb,
 132                            struct tcphdr *th, unsigned len)
 133 {
 134         struct tcp_options_received tmp_opt;
 135         int paws_reject = 0;
 136
 137         tmp_opt.saw_tstamp = 0;
 138         if (th->doff > (sizeof(struct tcphdr) >> 2) && tw->tw_ts_recent_stamp) {
 139                 tcp_parse_options(skb, &tmp_opt, 0);
 140
 141                 if (tmp_opt.saw_tstamp) {
 142                         tmp_opt.ts_recent          = tw->tw_ts_recent;
 143                         tmp_opt.ts_recent_stamp = tw->tw_ts_recent_stamp;
 144                         paws_reject = tcp_paws_check(&tmp_opt, th->rst);
 145                 }
 146         }
 147
 148         if (tw->tw_substate == TCP_FIN_WAIT2) {
 149                 /* Just repeat all the checks of tcp_rcv_state_process() */
 150
 151                 /* Out of window, send ACK */
 152                 if (paws_reject ||
 153                     !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq,
 154                                    tw->tw_rcv_nxt,
 155                                    tw->tw_rcv_nxt + tw->tw_rcv_wnd))
 156                         return TCP_TW_ACK;
 157
 158                 if (th->rst)
 159                         goto kill;
 160
 161                 if (th->syn && !before(TCP_SKB_CB(skb)->seq, tw->tw_rcv_nxt))
 162                         goto kill_with_rst;
 163
 164                 /* Dup ACK? */
 165                 if (!after(TCP_SKB_CB(skb)->end_seq, tw->tw_rcv_nxt) ||
 166                     TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq) {
 167                         tcp_tw_put(tw);
 168                         return TCP_TW_SUCCESS;
 169                 }
 170
 171                 /* New data or FIN. If new data arrive after half-duplex close,
 172                  * reset.
 173                  */
 174                 if (!th->fin ||
 175                     TCP_SKB_CB(skb)->end_seq != tw->tw_rcv_nxt + 1) {
 176 kill_with_rst:
 177                         tcp_tw_deschedule(tw);
 178                         tcp_tw_put(tw);
 179                         return TCP_TW_RST;
 180                 }
 181
 182                 /* FIN arrived, enter true time-wait state. */
 183                 tw->tw_substate = TCP_TIME_WAIT;
 184                 tw->tw_rcv_nxt  = TCP_SKB_CB(skb)->end_seq;
 185                 if (tmp_opt.saw_tstamp) {
 186                         tw->tw_ts_recent_stamp  = xtime.tv_sec;
 187                         tw->tw_ts_recent        = tmp_opt.rcv_tsval;
 188                 }
 189
 190                 /* I am shamed, but failed to make it more elegant.
 191                  * Yes, it is direct reference to IP, which is impossible
 192                  * to generalize to IPv6. Taking into account that IPv6
 193                  * do not undertsnad recycling in any case, it not
 194                  * a big problem in practice. --ANK */
 195                 if (tw->tw_family == AF_INET &&
 196                     sysctl_tcp_tw_recycle && tw->tw_ts_recent_stamp &&
 197                     tcp_v4_tw_remember_stamp(tw))
 198                         tcp_tw_schedule(tw, tw->tw_timeout);
 199                 else
 200                         tcp_tw_schedule(tw, TCP_TIMEWAIT_LEN);
 201                 return TCP_TW_ACK;
 202         }
 203
 204         /*
 205          *      Now real TIME-WAIT state.
 206          *
 207          *      RFC 1122:
 208          *      "When a connection is [...] on TIME-WAIT state [...]
 209          *      [a TCP] MAY accept a new SYN from the remote TCP to
 210          *      reopen the connection directly, if it:
 211          *
 212          *      (1)  assigns its initial sequence number for the new
 213          *      connection to be larger than the largest sequence
 214          *      number it used on the previous connection incarnation,
 215          *      and
 216          *
 217          *      (2)  returns to TIME-WAIT state if the SYN turns out
 218          *      to be an old duplicate".
 219          */
 220
 221         if (!paws_reject &&
 222             (TCP_SKB_CB(skb)->seq == tw->tw_rcv_nxt &&
 223              (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq || th->rst))) {
 224                 /* In window segment, it may be only reset or bare ack. */
 225
 226                 if (th->rst) {
 227                         /* This is TIME_WAIT assasination, in two flavors.
 228                          * Oh well... nobody has a sufficient solution to this
 229                          * protocol bug yet.
 230                          */
 231                         if (sysctl_tcp_rfc1337 == 0) {
 232 kill:
 233                                 tcp_tw_deschedule(tw);
 234                                 tcp_tw_put(tw);
 235                                 return TCP_TW_SUCCESS;
 236                         }
 237                 }
 238                 tcp_tw_schedule(tw, TCP_TIMEWAIT_LEN);
 239
 240                 if (tmp_opt.saw_tstamp) {
 241                         tw->tw_ts_recent        = tmp_opt.rcv_tsval;
 242                         tw->tw_ts_recent_stamp  = xtime.tv_sec;
 243                 }
 244
 245                 tcp_tw_put(tw);
 246                 return TCP_TW_SUCCESS;
 247         }
 248
 249         /* Out of window segment.
 250
 251            All the segments are ACKed immediately.
 252
 253            The only exception is new SYN. We accept it, if it is
 254            not old duplicate and we are not in danger to be killed
 255            by delayed old duplicates. RFC check is that it has
 256            newer sequence number works at rates <40Mbit/sec.
 257            However, if paws works, it is reliable AND even more,
 258            we even may relax silly seq space cutoff.
 259
 260            RED-PEN: we violate main RFC requirement, if this SYN will appear
 261            old duplicate (i.e. we receive RST in reply to SYN-ACK),
 262            we must return socket to time-wait state. It is not good,
 263            but not fatal yet.
 264          */
 265
 266         if (th->syn && !th->rst && !th->ack && !paws_reject &&
 267             (after(TCP_SKB_CB(skb)->seq, tw->tw_rcv_nxt) ||
 268              (tmp_opt.saw_tstamp && (s32)(tw->tw_ts_recent - tmp_opt.rcv_tsval) < 0))) {
 269                 u32 isn = tw->tw_snd_nxt + 65535 + 2;
 270                 if (isn == 0)
 271                         isn++;
 272                 TCP_SKB_CB(skb)->when = isn;
 273                 return TCP_TW_SYN;
 274         }
 275
 276         if (paws_reject)
 277                 NET_INC_STATS_BH(LINUX_MIB_PAWSESTABREJECTED);
 278
 279         if(!th->rst) {
 280                 /* In this case we must reset the TIMEWAIT timer.
 281                  *
 282                  * If it is ACKless SYN it may be both old duplicate
 283                  * and new good SYN with random sequence number <rcv_nxt.
 284                  * Do not reschedule in the last case.
 285                  */
 286                 if (paws_reject || th->ack)
 287                         tcp_tw_schedule(tw, TCP_TIMEWAIT_LEN);
 288
 289                 /* Send ACK. Note, we do not put the bucket,
 290                  * it will be released by caller.
 291                  */
 292                 return TCP_TW_ACK;
 293         }
 294         tcp_tw_put(tw);
 295         return TCP_TW_SUCCESS;
 296 }
 297
 298 /* Enter the time wait state.  This is called with locally disabled BH.
 299  * Essentially we whip up a timewait bucket, copy the
 300  * relevant info into it from the SK, and mess with hash chains
 301  * and list linkage.
 302  */
 303 static void __tcp_tw_hashdance(struct sock *sk, struct tcp_tw_bucket *tw)
 304 {
 305         struct tcp_ehash_bucket *ehead = &tcp_ehash[sk->sk_hashent];
 306         struct tcp_bind_hashbucket *bhead;
 307
 308         /* Step 1: Put TW into bind hash. Original socket stays there too.
 309            Note, that any socket with inet_sk(sk)->num != 0 MUST be bound in
 310            binding cache, even if it is closed.
 311          */
 312         bhead = &tcp_bhash[tcp_bhashfn(inet_sk(sk)->num)];
 313         spin_lock(&bhead->lock);
 314         tw->tw_tb = tcp_sk(sk)->bind_hash;
 315         BUG_TRAP(tcp_sk(sk)->bind_hash);
 316         tw_add_bind_node(tw, &tw->tw_tb->owners);
 317         spin_unlock(&bhead->lock);
 318
 319         write_lock(&ehead->lock);
 320
 321         /* Step 2: Remove SK from established hash. */
 322         if (__sk_del_node_init(sk))
 323                 sock_prot_dec_use(sk->sk_prot);
 324
 325         /* Step 3: Hash TW into TIMEWAIT half of established hash table. */
 326         tw_add_node(tw, &(ehead + tcp_ehash_size)->chain);
 327         atomic_inc(&tw->tw_refcnt);
 328
 329         write_unlock(&ehead->lock);
 330 }
 331
 332 /*
 333  * Move a socket to time-wait or dead fin-wait-2 state.
 334  */
 335 void tcp_time_wait(struct sock *sk, int state, int timeo)
 336 {
 337         struct tcp_tw_bucket *tw = NULL;
 338         struct tcp_sock *tp = tcp_sk(sk);
 339         int recycle_ok = 0;
 340
 341         if (sysctl_tcp_tw_recycle && tp->rx_opt.ts_recent_stamp)
 342                 recycle_ok = tp->af_specific->remember_stamp(sk);
 343
 344         if (tcp_tw_count < sysctl_tcp_max_tw_buckets)
 345                 tw = kmem_cache_alloc(tcp_timewait_cachep, SLAB_ATOMIC);
 346
 347         if(tw != NULL) {
 348                 struct inet_sock *inet = inet_sk(sk);
 349                 int rto = (tp->rto<<2) - (tp->rto>>1);
 350
 351                 /* Give us an identity. */
 352                 tw->tw_daddr            = inet->daddr;
 353                 tw->tw_rcv_saddr        = inet->rcv_saddr;
 354                 tw->tw_bound_dev_if     = sk->sk_bound_dev_if;
 355                 tw->tw_num              = inet->num;
 356                 tw->tw_state            = TCP_TIME_WAIT;
 357                 tw->tw_substate         = state;
 358                 tw->tw_sport            = inet->sport;
 359                 tw->tw_dport            = inet->dport;
 360                 tw->tw_family           = sk->sk_family;
 361                 tw->tw_reuse            = sk->sk_reuse;
 362                 tw->tw_rcv_wscale       = tp->rx_opt.rcv_wscale;
 363                 atomic_set(&tw->tw_refcnt, 1);
 364
 365                 tw->tw_hashent          = sk->sk_hashent;
 366                 tw->tw_rcv_nxt          = tp->rcv_nxt;
 367                 tw->tw_snd_nxt          = tp->snd_nxt;
 368                 tw->tw_rcv_wnd          = tcp_receive_window(tp);
 369                 tw->tw_ts_recent        = tp->rx_opt.ts_recent;
 370                 tw->tw_ts_recent_stamp  = tp->rx_opt.ts_recent_stamp;
 371                 tw_dead_node_init(tw);
 372
 373                 tw->tw_xid              = sk->sk_xid;
 374                 tw->tw_vx_info          = NULL;
 375                 tw->tw_nid              = sk->sk_nid;
 376                 tw->tw_nx_info          = NULL;
 377
 378 #if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
 379                 if (tw->tw_family == PF_INET6) {
 380                         struct ipv6_pinfo *np = inet6_sk(sk);
 381
 382                         ipv6_addr_copy(&tw->tw_v6_daddr, &np->daddr);
 383                         ipv6_addr_copy(&tw->tw_v6_rcv_saddr, &np->rcv_saddr);
 384                         tw->tw_v6_ipv6only = np->ipv6only;
 385                 } else {
 386                         memset(&tw->tw_v6_daddr, 0, sizeof(tw->tw_v6_daddr));
 387                         memset(&tw->tw_v6_rcv_saddr, 0, sizeof(tw->tw_v6_rcv_saddr));
 388                         tw->tw_v6_ipv6only = 0;
 389                 }
 390 #endif
 391                 /* Linkage updates. */
 392                 __tcp_tw_hashdance(sk, tw);
 393
 394                 /* Get the TIME_WAIT timeout firing. */
 395                 if (timeo < rto)
 396                         timeo = rto;
 397
 398                 if (recycle_ok) {
 399                         tw->tw_timeout = rto;
 400                 } else {
 401                         tw->tw_timeout = TCP_TIMEWAIT_LEN;
 402                         if (state == TCP_TIME_WAIT)
 403                                 timeo = TCP_TIMEWAIT_LEN;
 404                 }
 405
 406                 tcp_tw_schedule(tw, timeo);
 407                 tcp_tw_put(tw);
 408         } else {
 409                 /* Sorry, if we're out of memory, just CLOSE this
 410                  * socket up.  We've got bigger problems than
 411                  * non-graceful socket closings.
 412                  */
 413                 if (net_ratelimit())
 414                         printk(KERN_INFO "TCP: time wait bucket table overflow\n");
 415         }
 416
 417         tcp_update_metrics(sk);
 418         tcp_done(sk);
 419 }
 420
 421 /* Kill off TIME_WAIT sockets once their lifetime has expired. */
 422 static int tcp_tw_death_row_slot;
 423
 424 static void tcp_twkill(unsigned long);
 425
 426 /* TIME_WAIT reaping mechanism. */
 427 #define TCP_TWKILL_SLOTS        8       /* Please keep this a power of 2. */
 428 #define TCP_TWKILL_PERIOD       (TCP_TIMEWAIT_LEN/TCP_TWKILL_SLOTS)
 429
 430 #define TCP_TWKILL_QUOTA        100
 431
 432 static struct hlist_head tcp_tw_death_row[TCP_TWKILL_SLOTS];
 433 static DEFINE_SPINLOCK(tw_death_lock);
 434 static struct timer_list tcp_tw_timer = TIMER_INITIALIZER(tcp_twkill, 0, 0);
 435 static void twkill_work(void *);
 436 static DECLARE_WORK(tcp_twkill_work, twkill_work, NULL);
 437 static u32 twkill_thread_slots;
 438
 439 /* Returns non-zero if quota exceeded.  */
 440 static int tcp_do_twkill_work(int slot, unsigned int quota)
 441 {
 442         struct tcp_tw_bucket *tw;
 443         struct hlist_node *node;
 444         unsigned int killed;
 445         int ret;
 446
 447         /* NOTE: compare this to previous version where lock
 448          * was released after detaching chain. It was racy,
 449          * because tw buckets are scheduled in not serialized context
 450          * in 2.3 (with netfilter), and with softnet it is common, because
 451          * soft irqs are not sequenced.
 452          */
 453         killed = 0;
 454         ret = 0;
 455 rescan:
 456         tw_for_each_inmate(tw, node, &tcp_tw_death_row[slot]) {
 457                 __tw_del_dead_node(tw);
 458                 spin_unlock(&tw_death_lock);
 459                 tcp_timewait_kill(tw);
 460                 tcp_tw_put(tw);
 461                 killed++;
 462                 spin_lock(&tw_death_lock);
 463                 if (killed > quota) {
 464                         ret = 1;
 465                         break;
 466                 }
 467
 468                 /* While we dropped tw_death_lock, another cpu may have
 469                  * killed off the next TW bucket in the list, therefore
 470                  * do a fresh re-read of the hlist head node with the
 471                  * lock reacquired.  We still use the hlist traversal
 472                  * macro in order to get the prefetches.
 473                  */
 474                 goto rescan;
 475         }
 476
 477         tcp_tw_count -= killed;
 478         NET_ADD_STATS_BH(LINUX_MIB_TIMEWAITED, killed);
 479
 480         return ret;
 481 }
 482
 483 static void tcp_twkill(unsigned long dummy)
 484 {
 485         int need_timer, ret;
 486
 487         spin_lock(&tw_death_lock);
 488
 489         if (tcp_tw_count == 0)
 490                 goto out;
 491
 492         need_timer = 0;
 493         ret = tcp_do_twkill_work(tcp_tw_death_row_slot, TCP_TWKILL_QUOTA);
 494         if (ret) {
 495                 twkill_thread_slots |= (1 << tcp_tw_death_row_slot);
 496                 mb();
 497                 schedule_work(&tcp_twkill_work);
 498                 need_timer = 1;
 499         } else {
 500                 /* We purged the entire slot, anything left?  */
 501                 if (tcp_tw_count)
 502                         need_timer = 1;
 503         }
 504         tcp_tw_death_row_slot =
 505                 ((tcp_tw_death_row_slot + 1) & (TCP_TWKILL_SLOTS - 1));
 506         if (need_timer)
 507                 mod_timer(&tcp_tw_timer, jiffies + TCP_TWKILL_PERIOD);
 508 out:
 509         spin_unlock(&tw_death_lock);
 510 }
 511
 512 extern void twkill_slots_invalid(void);
 513
 514 static void twkill_work(void *dummy)
 515 {
 516         int i;
 517
 518         if ((TCP_TWKILL_SLOTS - 1) > (sizeof(twkill_thread_slots) * 8))
 519                 twkill_slots_invalid();
 520
 521         while (twkill_thread_slots) {
 522                 spin_lock_bh(&tw_death_lock);
 523                 for (i = 0; i < TCP_TWKILL_SLOTS; i++) {
 524                         if (!(twkill_thread_slots & (1 << i)))
 525                                 continue;
 526
 527                         while (tcp_do_twkill_work(i, TCP_TWKILL_QUOTA) != 0) {
 528                                 if (need_resched()) {
 529                                         spin_unlock_bh(&tw_death_lock);
 530                                         schedule();
 531                                         spin_lock_bh(&tw_death_lock);
 532                                 }
 533                         }
 534
 535                         twkill_thread_slots &= ~(1 << i);
 536                 }
 537                 spin_unlock_bh(&tw_death_lock);
 538         }
 539 }
 540
 541 /* These are always called from BH context.  See callers in
 542  * tcp_input.c to verify this.
 543  */
 544
 545 /* This is for handling early-kills of TIME_WAIT sockets. */
 546 void tcp_tw_deschedule(struct tcp_tw_bucket *tw)
 547 {
 548         spin_lock(&tw_death_lock);
 549         if (tw_del_dead_node(tw)) {
 550                 tcp_tw_put(tw);
 551                 if (--tcp_tw_count == 0)
 552                         del_timer(&tcp_tw_timer);
 553         }
 554         spin_unlock(&tw_death_lock);
 555         tcp_timewait_kill(tw);
 556 }
 557
 558 /* Short-time timewait calendar */
 559
 560 static int tcp_twcal_hand = -1;
 561 static int tcp_twcal_jiffie;
 562 static void tcp_twcal_tick(unsigned long);
 563 static struct timer_list tcp_twcal_timer =
 564                 TIMER_INITIALIZER(tcp_twcal_tick, 0, 0);
 565 static struct hlist_head tcp_twcal_row[TCP_TW_RECYCLE_SLOTS];
 566
 567 static void tcp_tw_schedule(struct tcp_tw_bucket *tw, int timeo)
 568 {
 569         struct hlist_head *list;
 570         int slot;
 571
 572         /* timeout := RTO * 3.5
 573          *
 574          * 3.5 = 1+2+0.5 to wait for two retransmits.
 575          *
 576          * RATIONALE: if FIN arrived and we entered TIME-WAIT state,
 577          * our ACK acking that FIN can be lost. If N subsequent retransmitted
 578          * FINs (or previous seqments) are lost (probability of such event
 579          * is p^(N+1), where p is probability to lose single packet and
 580          * time to detect the loss is about RTO*(2^N - 1) with exponential
 581          * backoff). Normal timewait length is calculated so, that we
 582          * waited at least for one retransmitted FIN (maximal RTO is 120sec).
 583          * [ BTW Linux. following BSD, violates this requirement waiting
 584          *   only for 60sec, we should wait at least for 240 secs.
 585          *   Well, 240 consumes too much of resources 8)
 586          * ]
 587          * This interval is not reduced to catch old duplicate and
 588          * responces to our wandering segments living for two MSLs.
 589          * However, if we use PAWS to detect
 590          * old duplicates, we can reduce the interval to bounds required
 591          * by RTO, rather than MSL. So, if peer understands PAWS, we
 592          * kill tw bucket after 3.5*RTO (it is important that this number
 593          * is greater than TS tick!) and detect old duplicates with help
 594          * of PAWS.
 595          */
 596         slot = (timeo + (1<<TCP_TW_RECYCLE_TICK) - 1) >> TCP_TW_RECYCLE_TICK;
 597
 598         spin_lock(&tw_death_lock);
 599
 600         /* Unlink it, if it was scheduled */
 601         if (tw_del_dead_node(tw))
 602                 tcp_tw_count--;
 603         else
 604                 atomic_inc(&tw->tw_refcnt);
 605
 606         if (slot >= TCP_TW_RECYCLE_SLOTS) {
 607                 /* Schedule to slow timer */
 608                 if (timeo >= TCP_TIMEWAIT_LEN) {
 609                         slot = TCP_TWKILL_SLOTS-1;
 610                 } else {
 611                         slot = (timeo + TCP_TWKILL_PERIOD-1) / TCP_TWKILL_PERIOD;
 612                         if (slot >= TCP_TWKILL_SLOTS)
 613                                 slot = TCP_TWKILL_SLOTS-1;
 614                 }
 615                 tw->tw_ttd = jiffies + timeo;
 616                 slot = (tcp_tw_death_row_slot + slot) & (TCP_TWKILL_SLOTS - 1);
 617                 list = &tcp_tw_death_row[slot];
 618         } else {
 619                 tw->tw_ttd = jiffies + (slot << TCP_TW_RECYCLE_TICK);
 620
 621                 if (tcp_twcal_hand < 0) {
 622                         tcp_twcal_hand = 0;
 623                         tcp_twcal_jiffie = jiffies;
 624                         tcp_twcal_timer.expires = tcp_twcal_jiffie + (slot<<TCP_TW_RECYCLE_TICK);
 625                         add_timer(&tcp_twcal_timer);
 626                 } else {
 627                         if (time_after(tcp_twcal_timer.expires, jiffies + (slot<<TCP_TW_RECYCLE_TICK)))
 628                                 mod_timer(&tcp_twcal_timer, jiffies + (slot<<TCP_TW_RECYCLE_TICK));
 629                         slot = (tcp_twcal_hand + slot)&(TCP_TW_RECYCLE_SLOTS-1);
 630                 }
 631                 list = &tcp_twcal_row[slot];
 632         }
 633
 634         hlist_add_head(&tw->tw_death_node, list);
 635
 636         if (tcp_tw_count++ == 0)
 637                 mod_timer(&tcp_tw_timer, jiffies+TCP_TWKILL_PERIOD);
 638         spin_unlock(&tw_death_lock);
 639 }
 640
 641 void tcp_twcal_tick(unsigned long dummy)
 642 {
 643         int n, slot;
 644         unsigned long j;
 645         unsigned long now = jiffies;
 646         int killed = 0;
 647         int adv = 0;
 648
 649         spin_lock(&tw_death_lock);
 650         if (tcp_twcal_hand < 0)
 651                 goto out;
 652
 653         slot = tcp_twcal_hand;
 654         j = tcp_twcal_jiffie;
 655
 656         for (n=0; n<TCP_TW_RECYCLE_SLOTS; n++) {
 657                 if (time_before_eq(j, now)) {
 658                         struct hlist_node *node, *safe;
 659                         struct tcp_tw_bucket *tw;
 660
 661                         tw_for_each_inmate_safe(tw, node, safe,
 662                                            &tcp_twcal_row[slot]) {
 663                                 __tw_del_dead_node(tw);
 664                                 tcp_timewait_kill(tw);
 665                                 tcp_tw_put(tw);
 666                                 killed++;
 667                         }
 668                 } else {
 669                         if (!adv) {
 670                                 adv = 1;
 671                                 tcp_twcal_jiffie = j;
 672                                 tcp_twcal_hand = slot;
 673                         }
 674
 675                         if (!hlist_empty(&tcp_twcal_row[slot])) {
 676                                 mod_timer(&tcp_twcal_timer, j);
 677                                 goto out;
 678                         }
 679                 }
 680                 j += (1<<TCP_TW_RECYCLE_TICK);
 681                 slot = (slot+1)&(TCP_TW_RECYCLE_SLOTS-1);
 682         }
 683         tcp_twcal_hand = -1;
 684
 685 out:
 686         if ((tcp_tw_count -= killed) == 0)
 687                 del_timer(&tcp_tw_timer);
 688         NET_ADD_STATS_BH(LINUX_MIB_TIMEWAITKILLED, killed);
 689         spin_unlock(&tw_death_lock);
 690 }
 691
 692 /* This is not only more efficient than what we used to do, it eliminates
 693  * a lot of code duplication between IPv4/IPv6 SYN recv processing. -DaveM
 694  *
 695  * Actually, we could lots of memory writes here. tp of listening
 696  * socket contains all necessary default parameters.
 697  */
 698 struct sock *tcp_create_openreq_child(struct sock *sk, struct open_request *req, struct sk_buff *skb)
 699 {
 700         /* allocate the newsk from the same slab of the master sock,
 701          * if not, at sk_free time we'll try to free it from the wrong
 702          * slabcache (i.e. is it TCPv4 or v6?), this is handled thru sk->sk_prot -acme */
 703         struct sock *newsk = sk_alloc(PF_INET, GFP_ATOMIC, sk->sk_prot, 0);
 704
 705         if(newsk != NULL) {
 706                 struct tcp_sock *newtp;
 707                 struct sk_filter *filter;
 708
 709                 memcpy(newsk, sk, sizeof(struct tcp_sock));
 710                 newsk->sk_state = TCP_SYN_RECV;
 711
 712                 /* SANITY */
 713                 sock_vx_init(newsk);
 714                 sock_nx_init(newsk);
 715                 sk_node_init(&newsk->sk_node);
 716                 tcp_sk(newsk)->bind_hash = NULL;
 717
 718                 /* Clone the TCP header template */
 719                 inet_sk(newsk)->dport = req->rmt_port;
 720
 721                 sock_lock_init(newsk);
 722                 bh_lock_sock(newsk);
 723
 724                 rwlock_init(&newsk->sk_dst_lock);
 725                 atomic_set(&newsk->sk_rmem_alloc, 0);
 726                 skb_queue_head_init(&newsk->sk_receive_queue);
 727                 atomic_set(&newsk->sk_wmem_alloc, 0);
 728                 skb_queue_head_init(&newsk->sk_write_queue);
 729                 atomic_set(&newsk->sk_omem_alloc, 0);
 730                 newsk->sk_wmem_queued = 0;
 731                 newsk->sk_forward_alloc = 0;
 732
 733                 sock_reset_flag(newsk, SOCK_DONE);
 734                 newsk->sk_userlocks = sk->sk_userlocks & ~SOCK_BINDPORT_LOCK;
 735                 newsk->sk_backlog.head = newsk->sk_backlog.tail = NULL;
 736                 newsk->sk_send_head = NULL;
 737                 rwlock_init(&newsk->sk_callback_lock);
 738                 skb_queue_head_init(&newsk->sk_error_queue);
 739                 newsk->sk_write_space = sk_stream_write_space;
 740
 741                 if ((filter = newsk->sk_filter) != NULL)
 742                         sk_filter_charge(newsk, filter);
 743
 744                 if (sk->sk_create_child)
 745                         sk->sk_create_child(sk, newsk);
 746
 747                 if (unlikely(xfrm_sk_clone_policy(newsk))) {
 748                         /* It is still raw copy of parent, so invalidate
 749                          * destructor and make plain sk_free() */
 750                         newsk->sk_destruct = NULL;
 751                         sk_free(newsk);
 752                         return NULL;
 753                 }
 754
 755                 /* Now setup tcp_sock */
 756                 newtp = tcp_sk(newsk);
 757                 newtp->pred_flags = 0;
 758                 newtp->rcv_nxt = req->rcv_isn + 1;
 759                 newtp->snd_nxt = req->snt_isn + 1;
 760                 newtp->snd_una = req->snt_isn + 1;
 761                 newtp->snd_sml = req->snt_isn + 1;
 762
 763                 tcp_prequeue_init(newtp);
 764
 765                 tcp_init_wl(newtp, req->snt_isn, req->rcv_isn);
 766
 767                 newtp->retransmits = 0;
 768                 newtp->backoff = 0;
 769                 newtp->srtt = 0;
 770                 newtp->mdev = TCP_TIMEOUT_INIT;
 771                 newtp->rto = TCP_TIMEOUT_INIT;
 772
 773                 newtp->packets_out = 0;
 774                 newtp->left_out = 0;
 775                 newtp->retrans_out = 0;
 776                 newtp->sacked_out = 0;
 777                 newtp->fackets_out = 0;
 778                 newtp->snd_ssthresh = 0x7fffffff;
 779
 780                 /* So many TCP implementations out there (incorrectly) count the
 781                  * initial SYN frame in their delayed-ACK and congestion control
 782                  * algorithms that we must have the following bandaid to talk
 783                  * efficiently to them.  -DaveM
 784                  */
 785                 newtp->snd_cwnd = 2;
 786                 newtp->snd_cwnd_cnt = 0;
 787
 788                 newtp->frto_counter = 0;
 789                 newtp->frto_highmark = 0;
 790
 791                 tcp_set_ca_state(newtp, TCP_CA_Open);
 792                 tcp_init_xmit_timers(newsk);
 793                 skb_queue_head_init(&newtp->out_of_order_queue);
 794                 newtp->rcv_wup = req->rcv_isn + 1;
 795                 newtp->write_seq = req->snt_isn + 1;
 796                 newtp->pushed_seq = newtp->write_seq;
 797                 newtp->copied_seq = req->rcv_isn + 1;
 798
 799                 newtp->rx_opt.saw_tstamp = 0;
 800
 801                 newtp->rx_opt.dsack = 0;
 802                 newtp->rx_opt.eff_sacks = 0;
 803
 804                 newtp->probes_out = 0;
 805                 newtp->rx_opt.num_sacks = 0;
 806                 newtp->urg_data = 0;
 807                 newtp->listen_opt = NULL;
 808                 newtp->accept_queue = newtp->accept_queue_tail = NULL;
 809                 /* Deinitialize syn_wait_lock to trap illegal accesses. */
 810                 memset(&newtp->syn_wait_lock, 0, sizeof(newtp->syn_wait_lock));
 811
 812                 /* Back to base struct sock members. */
 813                 newsk->sk_err = 0;
 814                 newsk->sk_priority = 0;
 815                 atomic_set(&newsk->sk_refcnt, 2);
 816
 817                 set_vx_info(&newsk->sk_vx_info, sk->sk_vx_info);
 818                 newsk->sk_xid = sk->sk_xid;
 819                 vx_sock_inc(newsk);
 820                 set_nx_info(&newsk->sk_nx_info, sk->sk_nx_info);
 821                 newsk->sk_nid = sk->sk_nid;
 822 #ifdef INET_REFCNT_DEBUG
 823                 atomic_inc(&inet_sock_nr);
 824 #endif
 825                 atomic_inc(&tcp_sockets_allocated);
 826
 827                 if (sock_flag(newsk, SOCK_KEEPOPEN))
 828                         tcp_reset_keepalive_timer(newsk,
 829                                                   keepalive_time_when(newtp));
 830                 newsk->sk_socket = NULL;
 831                 newsk->sk_sleep = NULL;
 832
 833                 newtp->rx_opt.tstamp_ok = req->tstamp_ok;
 834                 if((newtp->rx_opt.sack_ok = req->sack_ok) != 0) {
 835                         if (sysctl_tcp_fack)
 836                                 newtp->rx_opt.sack_ok |= 2;
 837                 }
 838                 newtp->window_clamp = req->window_clamp;
 839                 newtp->rcv_ssthresh = req->rcv_wnd;
 840                 newtp->rcv_wnd = req->rcv_wnd;
 841                 newtp->rx_opt.wscale_ok = req->wscale_ok;
 842                 if (newtp->rx_opt.wscale_ok) {
 843                         newtp->rx_opt.snd_wscale = req->snd_wscale;
 844                         newtp->rx_opt.rcv_wscale = req->rcv_wscale;
 845                 } else {
 846                         newtp->rx_opt.snd_wscale = newtp->rx_opt.rcv_wscale = 0;
 847                         newtp->window_clamp = min(newtp->window_clamp, 65535U);
 848                 }
 849                 newtp->snd_wnd = ntohs(skb->h.th->window) << newtp->rx_opt.snd_wscale;
 850                 newtp->max_window = newtp->snd_wnd;
 851
 852                 if (newtp->rx_opt.tstamp_ok) {
 853                         newtp->rx_opt.ts_recent = req->ts_recent;
 854                         newtp->rx_opt.ts_recent_stamp = xtime.tv_sec;
 855                         newtp->tcp_header_len = sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
 856                 } else {
 857                         newtp->rx_opt.ts_recent_stamp = 0;
 858                         newtp->tcp_header_len = sizeof(struct tcphdr);
 859                 }
 860                 if (skb->len >= TCP_MIN_RCVMSS+newtp->tcp_header_len)
 861                         newtp->ack.last_seg_size = skb->len-newtp->tcp_header_len;
 862                 newtp->rx_opt.mss_clamp = req->mss;
 863                 TCP_ECN_openreq_child(newtp, req);
 864                 if (newtp->ecn_flags&TCP_ECN_OK)
 865                         sock_set_flag(newsk, SOCK_NO_LARGESEND);
 866
 867                 tcp_ca_init(newtp);
 868
 869                 TCP_INC_STATS_BH(TCP_MIB_PASSIVEOPENS);
 870         }
 871         return newsk;
 872 }
 873
 874 /*
 875  *      Process an incoming packet for SYN_RECV sockets represented
 876  *      as an open_request.
 877  */
 878
 879 struct sock *tcp_check_req(struct sock *sk,struct sk_buff *skb,
 880                            struct open_request *req,
 881                            struct open_request **prev)
 882 {
 883         struct tcphdr *th = skb->h.th;
 884         struct tcp_sock *tp = tcp_sk(sk);
 885         u32 flg = tcp_flag_word(th) & (TCP_FLAG_RST|TCP_FLAG_SYN|TCP_FLAG_ACK);
 886         int paws_reject = 0;
 887         struct tcp_options_received tmp_opt;
 888         struct sock *child;
 889
 890         tmp_opt.saw_tstamp = 0;
 891         if (th->doff > (sizeof(struct tcphdr)>>2)) {
 892                 tcp_parse_options(skb, &tmp_opt, 0);
 893
 894                 if (tmp_opt.saw_tstamp) {
 895                         tmp_opt.ts_recent = req->ts_recent;
 896                         /* We do not store true stamp, but it is not required,
 897                          * it can be estimated (approximately)
 898                          * from another data.
 899                          */
 900                         tmp_opt.ts_recent_stamp = xtime.tv_sec - ((TCP_TIMEOUT_INIT/HZ)<<req->retrans);
 901                         paws_reject = tcp_paws_check(&tmp_opt, th->rst);
 902                 }
 903         }
 904
 905         /* Check for pure retransmitted SYN. */
 906         if (TCP_SKB_CB(skb)->seq == req->rcv_isn &&
 907             flg == TCP_FLAG_SYN &&
 908             !paws_reject) {
 909                 /*
 910                  * RFC793 draws (Incorrectly! It was fixed in RFC1122)
 911                  * this case on figure 6 and figure 8, but formal
 912                  * protocol description says NOTHING.
 913                  * To be more exact, it says that we should send ACK,
 914                  * because this segment (at least, if it has no data)
 915                  * is out of window.
 916                  *
 917                  *  CONCLUSION: RFC793 (even with RFC1122) DOES NOT
 918                  *  describe SYN-RECV state. All the description
 919                  *  is wrong, we cannot believe to it and should
 920                  *  rely only on common sense and implementation
 921                  *  experience.
 922                  *
 923                  * Enforce "SYN-ACK" according to figure 8, figure 6
 924                  * of RFC793, fixed by RFC1122.
 925                  */
 926                 req->class->rtx_syn_ack(sk, req, NULL);
 927                 return NULL;
 928         }
 929
 930         /* Further reproduces section "SEGMENT ARRIVES"
 931            for state SYN-RECEIVED of RFC793.
 932            It is broken, however, it does not work only
 933            when SYNs are crossed.
 934
 935            You would think that SYN crossing is impossible here, since
 936            we should have a SYN_SENT socket (from connect()) on our end,
 937            but this is not true if the crossed SYNs were sent to both
 938            ends by a malicious third party.  We must defend against this,
 939            and to do that we first verify the ACK (as per RFC793, page
 940            36) and reset if it is invalid.  Is this a true full defense?
 941            To convince ourselves, let us consider a way in which the ACK
 942            test can still pass in this 'malicious crossed SYNs' case.
 943            Malicious sender sends identical SYNs (and thus identical sequence
 944            numbers) to both A and B:
 945
 946                 A: gets SYN, seq=7
 947                 B: gets SYN, seq=7
 948
 949            By our good fortune, both A and B select the same initial
 950            send sequence number of seven :-)
 951
 952                 A: sends SYN|ACK, seq=7, ack_seq=8
 953                 B: sends SYN|ACK, seq=7, ack_seq=8
 954
 955            So we are now A eating this SYN|ACK, ACK test passes.  So
 956            does sequence test, SYN is truncated, and thus we consider
 957            it a bare ACK.
 958
 959            If tp->defer_accept, we silently drop this bare ACK.  Otherwise,
 960            we create an established connection.  Both ends (listening sockets)
 961            accept the new incoming connection and try to talk to each other. 8-)
 962
 963            Note: This case is both harmless, and rare.  Possibility is about the
 964            same as us discovering intelligent life on another plant tomorrow.
 965
 966            But generally, we should (RFC lies!) to accept ACK
 967            from SYNACK both here and in tcp_rcv_state_process().
 968            tcp_rcv_state_process() does not, hence, we do not too.
 969
 970            Note that the case is absolutely generic:
 971            we cannot optimize anything here without
 972            violating protocol. All the checks must be made
 973            before attempt to create socket.
 974          */
 975
 976         /* RFC793 page 36: "If the connection is in any non-synchronized state ...
 977          *                  and the incoming segment acknowledges something not yet
 978          *                  sent (the segment carries an unaccaptable ACK) ...
 979          *                  a reset is sent."
 980          *
 981          * Invalid ACK: reset will be sent by listening socket
 982          */
 983         if ((flg & TCP_FLAG_ACK) &&
 984             (TCP_SKB_CB(skb)->ack_seq != req->snt_isn+1))
 985                 return sk;
 986
 987         /* Also, it would be not so bad idea to check rcv_tsecr, which
 988          * is essentially ACK extension and too early or too late values
 989          * should cause reset in unsynchronized states.
 990          */
 991
 992         /* RFC793: "first check sequence number". */
 993
 994         if (paws_reject || !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq,
 995                                           req->rcv_isn+1, req->rcv_isn+1+req->rcv_wnd)) {
 996                 /* Out of window: send ACK and drop. */
 997                 if (!(flg & TCP_FLAG_RST))
 998                         req->class->send_ack(skb, req);
 999                 if (paws_reject)
1000                         NET_INC_STATS_BH(LINUX_MIB_PAWSESTABREJECTED);
1001                 return NULL;
1002         }
1003
1004         /* In sequence, PAWS is OK. */
1005
1006         if (tmp_opt.saw_tstamp && !after(TCP_SKB_CB(skb)->seq, req->rcv_isn+1))
1007                         req->ts_recent = tmp_opt.rcv_tsval;
1008
1009                 if (TCP_SKB_CB(skb)->seq == req->rcv_isn) {
1010                         /* Truncate SYN, it is out of window starting
1011                            at req->rcv_isn+1. */
1012                         flg &= ~TCP_FLAG_SYN;
1013                 }
1014
1015                 /* RFC793: "second check the RST bit" and
1016                  *         "fourth, check the SYN bit"
1017                  */
1018                 if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN))
1019                         goto embryonic_reset;
1020
1021                 /* ACK sequence verified above, just make sure ACK is
1022                  * set.  If ACK not set, just silently drop the packet.
1023                  */
1024                 if (!(flg & TCP_FLAG_ACK))
1025                         return NULL;
1026
1027                 /* If TCP_DEFER_ACCEPT is set, drop bare ACK. */
1028                 if (tp->defer_accept && TCP_SKB_CB(skb)->end_seq == req->rcv_isn+1) {
1029                         req->acked = 1;
1030                         return NULL;
1031                 }
1032
1033                 /* OK, ACK is valid, create big socket and
1034                  * feed this segment to it. It will repeat all
1035                  * the tests. THIS SEGMENT MUST MOVE SOCKET TO
1036                  * ESTABLISHED STATE. If it will be dropped after
1037                  * socket is created, wait for troubles.
1038                  */
1039                 child = tp->af_specific->syn_recv_sock(sk, skb, req, NULL);
1040                 if (child == NULL)
1041                         goto listen_overflow;
1042
1043                 tcp_synq_unlink(tp, req, prev);
1044                 tcp_synq_removed(sk, req);
1045
1046                 tcp_acceptq_queue(sk, req, child);
1047                 return child;
1048
1049         listen_overflow:
1050                 if (!sysctl_tcp_abort_on_overflow) {
1051                         req->acked = 1;
1052                         return NULL;
1053                 }
1054
1055         embryonic_reset:
1056                 NET_INC_STATS_BH(LINUX_MIB_EMBRYONICRSTS);
1057                 if (!(flg & TCP_FLAG_RST))
1058                         req->class->send_reset(skb);
1059
1060                 tcp_synq_drop(sk, req, prev);
1061                 return NULL;
1062 }
1063
1064 /*
1065  * Queue segment on the new socket if the new socket is active,
1066  * otherwise we just shortcircuit this and continue with
1067  * the new socket.
1068  */
1069
1070 int tcp_child_process(struct sock *parent, struct sock *child,
1071                       struct sk_buff *skb)
1072 {
1073         int ret = 0;
1074         int state = child->sk_state;
1075
1076         if (!sock_owned_by_user(child)) {
1077                 ret = tcp_rcv_state_process(child, skb, skb->h.th, skb->len);
1078
1079                 /* Wakeup parent, send SIGIO */
1080                 if (state == TCP_SYN_RECV && child->sk_state != state)
1081                         parent->sk_data_ready(parent, 0);
1082         } else {
1083                 /* Alas, it is possible again, because we do lookup
1084                  * in main socket hash table and lock on listening
1085                  * socket does not protect us more.
1086                  */
1087                 sk_add_backlog(child, skb);
1088         }
1089
1090         bh_unlock_sock(child);
1091         sock_put(child);
1092         return ret;
1093 }
1094
1095 EXPORT_SYMBOL(tcp_check_req);
1096 EXPORT_SYMBOL(tcp_child_process);
1097 EXPORT_SYMBOL(tcp_create_openreq_child);
1098 EXPORT_SYMBOL(tcp_timewait_state_process);
1099 EXPORT_SYMBOL(tcp_tw_deschedule);