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 1.14.2.1 2002/03/05 04:30:08 davem Exp $
   9  *
  10  * Authors:     Ross Biro, <bir7@leland.Stanford.Edu>
  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/sysctl.h>
  26 #include <net/tcp.h>
  27 #include <net/inet_common.h>
  28
  29 #ifdef CONFIG_SYSCTL
  30 #define SYNC_INIT 0 /* let the user enable it */
  31 #else
  32 #define SYNC_INIT 1
  33 #endif
  34
  35 int sysctl_tcp_tw_recycle = 0;
  36 int sysctl_tcp_max_tw_buckets = NR_FILE*2;
  37
  38 int sysctl_tcp_syncookies = SYNC_INIT;
  39 int sysctl_tcp_abort_on_overflow = 0;
  40
  41 static __inline__ int tcp_in_window(u32 seq, u32 end_seq, u32 s_win, u32 e_win)
  42 {
  43         if (seq == s_win)
  44                 return 1;
  45         if (after(end_seq, s_win) && before(seq, e_win))
  46                 return 1;
  47         return (seq == e_win && seq == end_seq);
  48 }
  49
  50 /* New-style handling of TIME_WAIT sockets. */
  51
  52 int tcp_tw_count = 0;
  53
  54
  55 /* Must be called with locally disabled BHs. */
  56 void tcp_timewait_kill(struct tcp_tw_bucket *tw)
  57 {
  58         struct tcp_ehash_bucket *ehead;
  59         struct tcp_bind_hashbucket *bhead;
  60         struct tcp_bind_bucket *tb;
  61
  62         /* Unlink from established hashes. */
  63         ehead = &tcp_ehash[tw->hashent];
  64         write_lock(&ehead->lock);
  65         if (!tw->pprev) {
  66                 write_unlock(&ehead->lock);
  67                 return;
  68         }
  69         if(tw->next)
  70                 tw->next->pprev = tw->pprev;
  71         *(tw->pprev) = tw->next;
  72         tw->pprev = NULL;
  73         write_unlock(&ehead->lock);
  74
  75         /* Disassociate with bind bucket. */
  76         bhead = &tcp_bhash[tcp_bhashfn(tw->num)];
  77         spin_lock(&bhead->lock);
  78         tb = tw->tb;
  79         if(tw->bind_next)
  80                 tw->bind_next->bind_pprev = tw->bind_pprev;
  81         *(tw->bind_pprev) = tw->bind_next;
  82         tw->tb = NULL;
  83         if (tb->owners == NULL) {
  84                 if (tb->next)
  85                         tb->next->pprev = tb->pprev;
  86                 *(tb->pprev) = tb->next;
  87                 kmem_cache_free(tcp_bucket_cachep, tb);
  88         }
  89         spin_unlock(&bhead->lock);
  90
  91 #ifdef INET_REFCNT_DEBUG
  92         if (atomic_read(&tw->refcnt) != 1) {
  93                 printk(KERN_DEBUG "tw_bucket %p refcnt=%d\n", tw, atomic_read(&tw->refcnt));
  94         }
  95 #endif
  96         tcp_tw_put(tw);
  97 }
  98
  99 /*
 100  * * Main purpose of TIME-WAIT state is to close connection gracefully,
 101  *   when one of ends sits in LAST-ACK or CLOSING retransmitting FIN
 102  *   (and, probably, tail of data) and one or more our ACKs are lost.
 103  * * What is TIME-WAIT timeout? It is associated with maximal packet
 104  *   lifetime in the internet, which results in wrong conclusion, that
 105  *   it is set to catch "old duplicate segments" wandering out of their path.
 106  *   It is not quite correct. This timeout is calculated so that it exceeds
 107  *   maximal retransmission timeout enough to allow to lose one (or more)
 108  *   segments sent by peer and our ACKs. This time may be calculated from RTO.
 109  * * When TIME-WAIT socket receives RST, it means that another end
 110  *   finally closed and we are allowed to kill TIME-WAIT too.
 111  * * Second purpose of TIME-WAIT is catching old duplicate segments.
 112  *   Well, certainly it is pure paranoia, but if we load TIME-WAIT
 113  *   with this semantics, we MUST NOT kill TIME-WAIT state with RSTs.
 114  * * If we invented some more clever way to catch duplicates
 115  *   (f.e. based on PAWS), we could truncate TIME-WAIT to several RTOs.
 116  *
 117  * The algorithm below is based on FORMAL INTERPRETATION of RFCs.
 118  * When you compare it to RFCs, please, read section SEGMENT ARRIVES
 119  * from the very beginning.
 120  *
 121  * NOTE. With recycling (and later with fin-wait-2) TW bucket
 122  * is _not_ stateless. It means, that strictly speaking we must
 123  * spinlock it. I do not want! Well, probability of misbehaviour
 124  * is ridiculously low and, seems, we could use some mb() tricks
 125  * to avoid misread sequence numbers, states etc.  --ANK
 126  */
 127 enum tcp_tw_status
 128 tcp_timewait_state_process(struct tcp_tw_bucket *tw, struct sk_buff *skb,
 129                            struct tcphdr *th, unsigned len)
 130 {
 131         struct tcp_opt tp;
 132         int paws_reject = 0;
 133
 134         tp.saw_tstamp = 0;
 135         if (th->doff > (sizeof(struct tcphdr)>>2) && tw->ts_recent_stamp) {
 136                 tcp_parse_options(skb, &tp, 0);
 137
 138                 if (tp.saw_tstamp) {
 139                         tp.ts_recent = tw->ts_recent;
 140                         tp.ts_recent_stamp = tw->ts_recent_stamp;
 141                         paws_reject = tcp_paws_check(&tp, th->rst);
 142                 }
 143         }
 144
 145         if (tw->substate == TCP_FIN_WAIT2) {
 146                 /* Just repeat all the checks of tcp_rcv_state_process() */
 147
 148                 /* Out of window, send ACK */
 149                 if (paws_reject ||
 150                     !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq,
 151                                    tw->rcv_nxt, tw->rcv_nxt + tw->rcv_wnd))
 152                         return TCP_TW_ACK;
 153
 154                 if (th->rst)
 155                         goto kill;
 156
 157                 if (th->syn && !before(TCP_SKB_CB(skb)->seq, tw->rcv_nxt))
 158                         goto kill_with_rst;
 159
 160                 /* Dup ACK? */
 161                 if (!after(TCP_SKB_CB(skb)->end_seq, tw->rcv_nxt) ||
 162                     TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq) {
 163                         tcp_tw_put(tw);
 164                         return TCP_TW_SUCCESS;
 165                 }
 166
 167                 /* New data or FIN. If new data arrive after half-duplex close,
 168                  * reset.
 169                  */
 170                 if (!th->fin || TCP_SKB_CB(skb)->end_seq != tw->rcv_nxt+1) {
 171 kill_with_rst:
 172                         tcp_tw_deschedule(tw);
 173                         tcp_timewait_kill(tw);
 174                         tcp_tw_put(tw);
 175                         return TCP_TW_RST;
 176                 }
 177
 178                 /* FIN arrived, enter true time-wait state. */
 179                 tw->substate = TCP_TIME_WAIT;
 180                 tw->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
 181                 if (tp.saw_tstamp) {
 182                         tw->ts_recent_stamp = xtime.tv_sec;
 183                         tw->ts_recent = tp.rcv_tsval;
 184                 }
 185
 186                 /* I am shamed, but failed to make it more elegant.
 187                  * Yes, it is direct reference to IP, which is impossible
 188                  * to generalize to IPv6. Taking into account that IPv6
 189                  * do not undertsnad recycling in any case, it not
 190                  * a big problem in practice. --ANK */
 191                 if (tw->family == AF_INET &&
 192                     sysctl_tcp_tw_recycle && tw->ts_recent_stamp &&
 193                     tcp_v4_tw_remember_stamp(tw))
 194                         tcp_tw_schedule(tw, tw->timeout);
 195                 else
 196                         tcp_tw_schedule(tw, TCP_TIMEWAIT_LEN);
 197                 return TCP_TW_ACK;
 198         }
 199
 200         /*
 201          *      Now real TIME-WAIT state.
 202          *
 203          *      RFC 1122:
 204          *      "When a connection is [...] on TIME-WAIT state [...]
 205          *      [a TCP] MAY accept a new SYN from the remote TCP to
 206          *      reopen the connection directly, if it:
 207          *
 208          *      (1)  assigns its initial sequence number for the new
 209          *      connection to be larger than the largest sequence
 210          *      number it used on the previous connection incarnation,
 211          *      and
 212          *
 213          *      (2)  returns to TIME-WAIT state if the SYN turns out
 214          *      to be an old duplicate".
 215          */
 216
 217         if (!paws_reject &&
 218             (TCP_SKB_CB(skb)->seq == tw->rcv_nxt &&
 219              (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq || th->rst))) {
 220                 /* In window segment, it may be only reset or bare ack. */
 221
 222                 if (th->rst) {
 223                         /* This is TIME_WAIT assasination, in two flavors.
 224                          * Oh well... nobody has a sufficient solution to this
 225                          * protocol bug yet.
 226                          */
 227                         if (sysctl_tcp_rfc1337 == 0) {
 228 kill:
 229                                 tcp_tw_deschedule(tw);
 230                                 tcp_timewait_kill(tw);
 231                                 tcp_tw_put(tw);
 232                                 return TCP_TW_SUCCESS;
 233                         }
 234                 }
 235                 tcp_tw_schedule(tw, TCP_TIMEWAIT_LEN);
 236
 237                 if (tp.saw_tstamp) {
 238                         tw->ts_recent = tp.rcv_tsval;
 239                         tw->ts_recent_stamp = xtime.tv_sec;
 240                 }
 241
 242                 tcp_tw_put(tw);
 243                 return TCP_TW_SUCCESS;
 244         }
 245
 246         /* Out of window segment.
 247
 248            All the segments are ACKed immediately.
 249
 250            The only exception is new SYN. We accept it, if it is
 251            not old duplicate and we are not in danger to be killed
 252            by delayed old duplicates. RFC check is that it has
 253            newer sequence number works at rates <40Mbit/sec.
 254            However, if paws works, it is reliable AND even more,
 255            we even may relax silly seq space cutoff.
 256
 257            RED-PEN: we violate main RFC requirement, if this SYN will appear
 258            old duplicate (i.e. we receive RST in reply to SYN-ACK),
 259            we must return socket to time-wait state. It is not good,
 260            but not fatal yet.
 261          */
 262
 263         if (th->syn && !th->rst && !th->ack && !paws_reject &&
 264             (after(TCP_SKB_CB(skb)->seq, tw->rcv_nxt) ||
 265              (tp.saw_tstamp && (s32)(tw->ts_recent - tp.rcv_tsval) < 0))) {
 266                 u32 isn = tw->snd_nxt+65535+2;
 267                 if (isn == 0)
 268                         isn++;
 269                 TCP_SKB_CB(skb)->when = isn;
 270                 return TCP_TW_SYN;
 271         }
 272
 273         if (paws_reject)
 274                 NET_INC_STATS_BH(PAWSEstabRejected);
 275
 276         if(!th->rst) {
 277                 /* In this case we must reset the TIMEWAIT timer.
 278                  *
 279                  * If it is ACKless SYN it may be both old duplicate
 280                  * and new good SYN with random sequence number <rcv_nxt.
 281                  * Do not reschedule in the last case.
 282                  */
 283                 if (paws_reject || th->ack)
 284                         tcp_tw_schedule(tw, TCP_TIMEWAIT_LEN);
 285
 286                 /* Send ACK. Note, we do not put the bucket,
 287                  * it will be released by caller.
 288                  */
 289                 return TCP_TW_ACK;
 290         }
 291         tcp_tw_put(tw);
 292         return TCP_TW_SUCCESS;
 293 }
 294
 295 /* Enter the time wait state.  This is called with locally disabled BH.
 296  * Essentially we whip up a timewait bucket, copy the
 297  * relevant info into it from the SK, and mess with hash chains
 298  * and list linkage.
 299  */
 300 static void __tcp_tw_hashdance(struct sock *sk, struct tcp_tw_bucket *tw)
 301 {
 302         struct tcp_ehash_bucket *ehead = &tcp_ehash[sk->hashent];
 303         struct tcp_bind_hashbucket *bhead;
 304         struct sock **head, *sktw;
 305
 306         /* Step 1: Put TW into bind hash. Original socket stays there too.
 307            Note, that any socket with sk->num!=0 MUST be bound in binding
 308            cache, even if it is closed.
 309          */
 310         bhead = &tcp_bhash[tcp_bhashfn(sk->num)];
 311         spin_lock(&bhead->lock);
 312         tw->tb = (struct tcp_bind_bucket *)sk->prev;
 313         BUG_TRAP(sk->prev!=NULL);
 314         if ((tw->bind_next = tw->tb->owners) != NULL)
 315                 tw->tb->owners->bind_pprev = &tw->bind_next;
 316         tw->tb->owners = (struct sock*)tw;
 317         tw->bind_pprev = &tw->tb->owners;
 318         spin_unlock(&bhead->lock);
 319
 320         write_lock(&ehead->lock);
 321
 322         /* Step 2: Remove SK from established hash. */
 323         if (sk->pprev) {
 324                 if(sk->next)
 325                         sk->next->pprev = sk->pprev;
 326                 *sk->pprev = sk->next;
 327                 sk->pprev = NULL;
 328                 sock_prot_dec_use(sk->prot);
 329         }
 330
 331         /* Step 3: Hash TW into TIMEWAIT half of established hash table. */
 332         head = &(ehead + tcp_ehash_size)->chain;
 333         sktw = (struct sock *)tw;
 334         if((sktw->next = *head) != NULL)
 335                 (*head)->pprev = &sktw->next;
 336         *head = sktw;
 337         sktw->pprev = head;
 338         atomic_inc(&tw->refcnt);
 339
 340         write_unlock(&ehead->lock);
 341 }
 342
 343 /*
 344  * Move a socket to time-wait or dead fin-wait-2 state.
 345  */
 346 void tcp_time_wait(struct sock *sk, int state, int timeo)
 347 {
 348         struct tcp_tw_bucket *tw = NULL;
 349         struct tcp_opt *tp = &(sk->tp_pinfo.af_tcp);
 350         int recycle_ok = 0;
 351
 352         if (sysctl_tcp_tw_recycle && tp->ts_recent_stamp)
 353                 recycle_ok = tp->af_specific->remember_stamp(sk);
 354
 355         if (tcp_tw_count < sysctl_tcp_max_tw_buckets)
 356                 tw = kmem_cache_alloc(tcp_timewait_cachep, SLAB_ATOMIC);
 357
 358         if(tw != NULL) {
 359                 int rto = (tp->rto<<2) - (tp->rto>>1);
 360
 361                 /* Give us an identity. */
 362                 tw->daddr       = sk->daddr;
 363                 tw->rcv_saddr   = sk->rcv_saddr;
 364                 tw->bound_dev_if= sk->bound_dev_if;
 365                 tw->num         = sk->num;
 366                 tw->state       = TCP_TIME_WAIT;
 367                 tw->substate    = state;
 368                 tw->sport       = sk->sport;
 369                 tw->dport       = sk->dport;
 370                 tw->family      = sk->family;
 371                 tw->reuse       = sk->reuse;
 372                 tw->rcv_wscale  = tp->rcv_wscale;
 373                 atomic_set(&tw->refcnt, 1);
 374
 375                 tw->hashent     = sk->hashent;
 376                 tw->rcv_nxt     = tp->rcv_nxt;
 377                 tw->snd_nxt     = tp->snd_nxt;
 378                 tw->rcv_wnd     = tcp_receive_window(tp);
 379                 tw->ts_recent   = tp->ts_recent;
 380                 tw->ts_recent_stamp= tp->ts_recent_stamp;
 381                 tw->pprev_death = NULL;
 382
 383 #if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
 384                 if(tw->family == PF_INET6) {
 385                         memcpy(&tw->v6_daddr,
 386                                &sk->net_pinfo.af_inet6.daddr,
 387                                sizeof(struct in6_addr));
 388                         memcpy(&tw->v6_rcv_saddr,
 389                                &sk->net_pinfo.af_inet6.rcv_saddr,
 390                                sizeof(struct in6_addr));
 391                 }
 392 #endif
 393                 /* Linkage updates. */
 394                 __tcp_tw_hashdance(sk, tw);
 395
 396                 /* Get the TIME_WAIT timeout firing. */
 397                 if (timeo < rto)
 398                         timeo = rto;
 399
 400                 if (recycle_ok) {
 401                         tw->timeout = rto;
 402                 } else {
 403                         tw->timeout = TCP_TIMEWAIT_LEN;
 404                         if (state == TCP_TIME_WAIT)
 405                                 timeo = TCP_TIMEWAIT_LEN;
 406                 }
 407
 408                 tcp_tw_schedule(tw, timeo);
 409                 tcp_tw_put(tw);
 410         } else {
 411                 /* Sorry, if we're out of memory, just CLOSE this
 412                  * socket up.  We've got bigger problems than
 413                  * non-graceful socket closings.
 414                  */
 415                 if (net_ratelimit())
 416                         printk(KERN_INFO "TCP: time wait bucket table overflow\n");
 417         }
 418
 419         tcp_update_metrics(sk);
 420         tcp_done(sk);
 421 }
 422
 423 /* Kill off TIME_WAIT sockets once their lifetime has expired. */
 424 static int tcp_tw_death_row_slot = 0;
 425
 426 static void tcp_twkill(unsigned long);
 427
 428 static struct tcp_tw_bucket *tcp_tw_death_row[TCP_TWKILL_SLOTS];
 429 static spinlock_t tw_death_lock = SPIN_LOCK_UNLOCKED;
 430 static struct timer_list tcp_tw_timer = { function: tcp_twkill };
 431
 432 static void SMP_TIMER_NAME(tcp_twkill)(unsigned long dummy)
 433 {
 434         struct tcp_tw_bucket *tw;
 435         int killed = 0;
 436
 437         /* NOTE: compare this to previous version where lock
 438          * was released after detaching chain. It was racy,
 439          * because tw buckets are scheduled in not serialized context
 440          * in 2.3 (with netfilter), and with softnet it is common, because
 441          * soft irqs are not sequenced.
 442          */
 443         spin_lock(&tw_death_lock);
 444
 445         if (tcp_tw_count == 0)
 446                 goto out;
 447
 448         while((tw = tcp_tw_death_row[tcp_tw_death_row_slot]) != NULL) {
 449                 tcp_tw_death_row[tcp_tw_death_row_slot] = tw->next_death;
 450                 if (tw->next_death)
 451                         tw->next_death->pprev_death = tw->pprev_death;
 452                 tw->pprev_death = NULL;
 453                 spin_unlock(&tw_death_lock);
 454
 455                 tcp_timewait_kill(tw);
 456                 tcp_tw_put(tw);
 457
 458                 killed++;
 459
 460                 spin_lock(&tw_death_lock);
 461         }
 462         tcp_tw_death_row_slot =
 463                 ((tcp_tw_death_row_slot + 1) & (TCP_TWKILL_SLOTS - 1));
 464
 465         if ((tcp_tw_count -= killed) != 0)
 466                 mod_timer(&tcp_tw_timer, jiffies+TCP_TWKILL_PERIOD);
 467         net_statistics[smp_processor_id()*2].TimeWaited += killed;
 468 out:
 469         spin_unlock(&tw_death_lock);
 470 }
 471
 472 SMP_TIMER_DEFINE(tcp_twkill, tcp_twkill_task);
 473
 474 /* These are always called from BH context.  See callers in
 475  * tcp_input.c to verify this.
 476  */
 477
 478 /* This is for handling early-kills of TIME_WAIT sockets. */
 479 void tcp_tw_deschedule(struct tcp_tw_bucket *tw)
 480 {
 481         spin_lock(&tw_death_lock);
 482         if (tw->pprev_death) {
 483                 if(tw->next_death)
 484                         tw->next_death->pprev_death = tw->pprev_death;
 485                 *tw->pprev_death = tw->next_death;
 486                 tw->pprev_death = NULL;
 487                 tcp_tw_put(tw);
 488                 if (--tcp_tw_count == 0)
 489                         del_timer(&tcp_tw_timer);
 490         }
 491         spin_unlock(&tw_death_lock);
 492 }
 493
 494 /* Short-time timewait calendar */
 495
 496 static int tcp_twcal_hand = -1;
 497 static int tcp_twcal_jiffie;
 498 static void tcp_twcal_tick(unsigned long);
 499 static struct timer_list tcp_twcal_timer = {function: tcp_twcal_tick};
 500 static struct tcp_tw_bucket *tcp_twcal_row[TCP_TW_RECYCLE_SLOTS];
 501
 502 void tcp_tw_schedule(struct tcp_tw_bucket *tw, int timeo)
 503 {
 504         struct tcp_tw_bucket **tpp;
 505         int slot;
 506
 507         /* timeout := RTO * 3.5
 508          *
 509          * 3.5 = 1+2+0.5 to wait for two retransmits.
 510          *
 511          * RATIONALE: if FIN arrived and we entered TIME-WAIT state,
 512          * our ACK acking that FIN can be lost. If N subsequent retransmitted
 513          * FINs (or previous seqments) are lost (probability of such event
 514          * is p^(N+1), where p is probability to lose single packet and
 515          * time to detect the loss is about RTO*(2^N - 1) with exponential
 516          * backoff). Normal timewait length is calculated so, that we
 517          * waited at least for one retransmitted FIN (maximal RTO is 120sec).
 518          * [ BTW Linux. following BSD, violates this requirement waiting
 519          *   only for 60sec, we should wait at least for 240 secs.
 520          *   Well, 240 consumes too much of resources 8)
 521          * ]
 522          * This interval is not reduced to catch old duplicate and
 523          * responces to our wandering segments living for two MSLs.
 524          * However, if we use PAWS to detect
 525          * old duplicates, we can reduce the interval to bounds required
 526          * by RTO, rather than MSL. So, if peer understands PAWS, we
 527          * kill tw bucket after 3.5*RTO (it is important that this number
 528          * is greater than TS tick!) and detect old duplicates with help
 529          * of PAWS.
 530          */
 531         slot = (timeo + (1<<TCP_TW_RECYCLE_TICK) - 1) >> TCP_TW_RECYCLE_TICK;
 532
 533         spin_lock(&tw_death_lock);
 534
 535         /* Unlink it, if it was scheduled */
 536         if (tw->pprev_death) {
 537                 if(tw->next_death)
 538                         tw->next_death->pprev_death = tw->pprev_death;
 539                 *tw->pprev_death = tw->next_death;
 540                 tw->pprev_death = NULL;
 541                 tcp_tw_count--;
 542         } else
 543                 atomic_inc(&tw->refcnt);
 544
 545         if (slot >= TCP_TW_RECYCLE_SLOTS) {
 546                 /* Schedule to slow timer */
 547                 if (timeo >= TCP_TIMEWAIT_LEN) {
 548                         slot = TCP_TWKILL_SLOTS-1;
 549                 } else {
 550                         slot = (timeo + TCP_TWKILL_PERIOD-1) / TCP_TWKILL_PERIOD;
 551                         if (slot >= TCP_TWKILL_SLOTS)
 552                                 slot = TCP_TWKILL_SLOTS-1;
 553                 }
 554                 tw->ttd = jiffies + timeo;
 555                 slot = (tcp_tw_death_row_slot + slot) & (TCP_TWKILL_SLOTS - 1);
 556                 tpp = &tcp_tw_death_row[slot];
 557         } else {
 558                 tw->ttd = jiffies + (slot<<TCP_TW_RECYCLE_TICK);
 559
 560                 if (tcp_twcal_hand < 0) {
 561                         tcp_twcal_hand = 0;
 562                         tcp_twcal_jiffie = jiffies;
 563                         tcp_twcal_timer.expires = tcp_twcal_jiffie + (slot<<TCP_TW_RECYCLE_TICK);
 564                         add_timer(&tcp_twcal_timer);
 565                 } else {
 566                         if ((long)(tcp_twcal_timer.expires - jiffies) > (slot<<TCP_TW_RECYCLE_TICK))
 567                                 mod_timer(&tcp_twcal_timer, jiffies + (slot<<TCP_TW_RECYCLE_TICK));
 568                         slot = (tcp_twcal_hand + slot)&(TCP_TW_RECYCLE_SLOTS-1);
 569                 }
 570                 tpp = &tcp_twcal_row[slot];
 571         }
 572
 573         if((tw->next_death = *tpp) != NULL)
 574                 (*tpp)->pprev_death = &tw->next_death;
 575         *tpp = tw;
 576         tw->pprev_death = tpp;
 577
 578         if (tcp_tw_count++ == 0)
 579                 mod_timer(&tcp_tw_timer, jiffies+TCP_TWKILL_PERIOD);
 580         spin_unlock(&tw_death_lock);
 581 }
 582
 583 void SMP_TIMER_NAME(tcp_twcal_tick)(unsigned long dummy)
 584 {
 585         int n, slot;
 586         unsigned long j;
 587         unsigned long now = jiffies;
 588         int killed = 0;
 589         int adv = 0;
 590
 591         spin_lock(&tw_death_lock);
 592         if (tcp_twcal_hand < 0)
 593                 goto out;
 594
 595         slot = tcp_twcal_hand;
 596         j = tcp_twcal_jiffie;
 597
 598         for (n=0; n<TCP_TW_RECYCLE_SLOTS; n++) {
 599                 if ((long)(j - now) <= 0) {
 600                         struct tcp_tw_bucket *tw;
 601
 602                         while((tw = tcp_twcal_row[slot]) != NULL) {
 603                                 tcp_twcal_row[slot] = tw->next_death;
 604                                 tw->pprev_death = NULL;
 605
 606                                 tcp_timewait_kill(tw);
 607                                 tcp_tw_put(tw);
 608                                 killed++;
 609                         }
 610                 } else {
 611                         if (!adv) {
 612                                 adv = 1;
 613                                 tcp_twcal_jiffie = j;
 614                                 tcp_twcal_hand = slot;
 615                         }
 616
 617                         if (tcp_twcal_row[slot] != NULL) {
 618                                 mod_timer(&tcp_twcal_timer, j);
 619                                 goto out;
 620                         }
 621                 }
 622                 j += (1<<TCP_TW_RECYCLE_TICK);
 623                 slot = (slot+1)&(TCP_TW_RECYCLE_SLOTS-1);
 624         }
 625         tcp_twcal_hand = -1;
 626
 627 out:
 628         if ((tcp_tw_count -= killed) == 0)
 629                 del_timer(&tcp_tw_timer);
 630         net_statistics[smp_processor_id()*2].TimeWaitKilled += killed;
 631         spin_unlock(&tw_death_lock);
 632 }
 633
 634 SMP_TIMER_DEFINE(tcp_twcal_tick, tcp_twcal_tasklet);
 635
 636
 637 /* This is not only more efficient than what we used to do, it eliminates
 638  * a lot of code duplication between IPv4/IPv6 SYN recv processing. -DaveM
 639  *
 640  * Actually, we could lots of memory writes here. tp of listening
 641  * socket contains all necessary default parameters.
 642  */
 643 struct sock *tcp_create_openreq_child(struct sock *sk, struct open_request *req, struct sk_buff *skb)
 644 {
 645         struct sock *newsk = sk_alloc(PF_INET, GFP_ATOMIC, 0);
 646
 647         if(newsk != NULL) {
 648                 struct tcp_opt *newtp;
 649 #ifdef CONFIG_FILTER
 650                 struct sk_filter *filter;
 651 #endif
 652
 653                 memcpy(newsk, sk, sizeof(*newsk));
 654                 newsk->state = TCP_SYN_RECV;
 655
 656                 /* SANITY */
 657                 newsk->pprev = NULL;
 658                 newsk->prev = NULL;
 659
 660                 /* Clone the TCP header template */
 661                 newsk->dport = req->rmt_port;
 662
 663                 sock_lock_init(newsk);
 664                 bh_lock_sock(newsk);
 665
 666                 newsk->dst_lock = RW_LOCK_UNLOCKED;
 667                 atomic_set(&newsk->rmem_alloc, 0);
 668                 skb_queue_head_init(&newsk->receive_queue);
 669                 atomic_set(&newsk->wmem_alloc, 0);
 670                 skb_queue_head_init(&newsk->write_queue);
 671                 atomic_set(&newsk->omem_alloc, 0);
 672                 newsk->wmem_queued = 0;
 673                 newsk->forward_alloc = 0;
 674
 675                 newsk->done = 0;
 676                 newsk->userlocks = sk->userlocks & ~SOCK_BINDPORT_LOCK;
 677                 newsk->proc = 0;
 678                 newsk->backlog.head = newsk->backlog.tail = NULL;
 679                 newsk->callback_lock = RW_LOCK_UNLOCKED;
 680                 skb_queue_head_init(&newsk->error_queue);
 681                 newsk->write_space = tcp_write_space;
 682 #ifdef CONFIG_FILTER
 683                 if ((filter = newsk->filter) != NULL)
 684                         sk_filter_charge(newsk, filter);
 685 #endif
 686
 687                 /* Now setup tcp_opt */
 688                 newtp = &(newsk->tp_pinfo.af_tcp);
 689                 newtp->pred_flags = 0;
 690                 newtp->rcv_nxt = req->rcv_isn + 1;
 691                 newtp->snd_nxt = req->snt_isn + 1;
 692                 newtp->snd_una = req->snt_isn + 1;
 693                 newtp->snd_sml = req->snt_isn + 1;
 694
 695                 tcp_prequeue_init(newtp);
 696
 697                 tcp_init_wl(newtp, req->snt_isn, req->rcv_isn);
 698
 699                 newtp->retransmits = 0;
 700                 newtp->backoff = 0;
 701                 newtp->srtt = 0;
 702                 newtp->mdev = TCP_TIMEOUT_INIT;
 703                 newtp->rto = TCP_TIMEOUT_INIT;
 704
 705                 newtp->packets_out = 0;
 706                 newtp->left_out = 0;
 707                 newtp->retrans_out = 0;
 708                 newtp->sacked_out = 0;
 709                 newtp->fackets_out = 0;
 710                 newtp->snd_ssthresh = 0x7fffffff;
 711
 712                 /* So many TCP implementations out there (incorrectly) count the
 713                  * initial SYN frame in their delayed-ACK and congestion control
 714                  * algorithms that we must have the following bandaid to talk
 715                  * efficiently to them.  -DaveM
 716                  */
 717                 newtp->snd_cwnd = 2;
 718                 newtp->snd_cwnd_cnt = 0;
 719
 720                 newtp->frto_counter = 0;
 721                 newtp->frto_highmark = 0;
 722
 723                 tcp_set_ca_state(newtp, TCP_CA_Open);
 724                 tcp_init_xmit_timers(newsk);
 725                 skb_queue_head_init(&newtp->out_of_order_queue);
 726                 newtp->send_head = NULL;
 727                 newtp->rcv_wup = req->rcv_isn + 1;
 728                 newtp->write_seq = req->snt_isn + 1;
 729                 newtp->pushed_seq = newtp->write_seq;
 730                 newtp->copied_seq = req->rcv_isn + 1;
 731
 732                 newtp->saw_tstamp = 0;
 733
 734                 newtp->dsack = 0;
 735                 newtp->eff_sacks = 0;
 736
 737                 newtp->probes_out = 0;
 738                 newtp->num_sacks = 0;
 739                 newtp->urg_data = 0;
 740                 newtp->listen_opt = NULL;
 741                 newtp->accept_queue = newtp->accept_queue_tail = NULL;
 742                 /* Deinitialize syn_wait_lock to trap illegal accesses. */
 743                 memset(&newtp->syn_wait_lock, 0, sizeof(newtp->syn_wait_lock));
 744
 745                 /* Back to base struct sock members. */
 746                 newsk->err = 0;
 747                 newsk->priority = 0;
 748                 atomic_set(&newsk->refcnt, 2);
 749 #ifdef INET_REFCNT_DEBUG
 750                 atomic_inc(&inet_sock_nr);
 751 #endif
 752                 atomic_inc(&tcp_sockets_allocated);
 753
 754                 if (newsk->keepopen)
 755                         tcp_reset_keepalive_timer(newsk, keepalive_time_when(newtp));
 756                 newsk->socket = NULL;
 757                 newsk->sleep = NULL;
 758
 759                 newtp->tstamp_ok = req->tstamp_ok;
 760                 if((newtp->sack_ok = req->sack_ok) != 0) {
 761                         if (sysctl_tcp_fack)
 762                                 newtp->sack_ok |= 2;
 763                 }
 764                 newtp->window_clamp = req->window_clamp;
 765                 newtp->rcv_ssthresh = req->rcv_wnd;
 766                 newtp->rcv_wnd = req->rcv_wnd;
 767                 newtp->wscale_ok = req->wscale_ok;
 768                 if (newtp->wscale_ok) {
 769                         newtp->snd_wscale = req->snd_wscale;
 770                         newtp->rcv_wscale = req->rcv_wscale;
 771                 } else {
 772                         newtp->snd_wscale = newtp->rcv_wscale = 0;
 773                         newtp->window_clamp = min(newtp->window_clamp, 65535U);
 774                 }
 775                 newtp->snd_wnd = ntohs(skb->h.th->window) << newtp->snd_wscale;
 776                 newtp->max_window = newtp->snd_wnd;
 777
 778                 if (newtp->tstamp_ok) {
 779                         newtp->ts_recent = req->ts_recent;
 780                         newtp->ts_recent_stamp = xtime.tv_sec;
 781                         newtp->tcp_header_len = sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
 782                 } else {
 783                         newtp->ts_recent_stamp = 0;
 784                         newtp->tcp_header_len = sizeof(struct tcphdr);
 785                 }
 786                 if (skb->len >= TCP_MIN_RCVMSS+newtp->tcp_header_len)
 787                         newtp->ack.last_seg_size = skb->len-newtp->tcp_header_len;
 788                 newtp->mss_clamp = req->mss;
 789                 TCP_ECN_openreq_child(newtp, req);
 790
 791                 tcp_ca_init(newtp);
 792                 TCP_INC_STATS_BH(TcpPassiveOpens);
 793         }
 794         return newsk;
 795 }
 796
 797 /*
 798  *      Process an incoming packet for SYN_RECV sockets represented
 799  *      as an open_request.
 800  */
 801
 802 struct sock *tcp_check_req(struct sock *sk,struct sk_buff *skb,
 803                            struct open_request *req,
 804                            struct open_request **prev)
 805 {
 806         struct tcphdr *th = skb->h.th;
 807         struct tcp_opt *tp = &(sk->tp_pinfo.af_tcp);
 808         u32 flg = tcp_flag_word(th) & (TCP_FLAG_RST|TCP_FLAG_SYN|TCP_FLAG_ACK);
 809         int paws_reject = 0;
 810         struct tcp_opt ttp;
 811         struct sock *child;
 812
 813         ttp.saw_tstamp = 0;
 814         if (th->doff > (sizeof(struct tcphdr)>>2)) {
 815                 tcp_parse_options(skb, &ttp, 0);
 816
 817                 if (ttp.saw_tstamp) {
 818                         ttp.ts_recent = req->ts_recent;
 819                         /* We do not store true stamp, but it is not required,
 820                          * it can be estimated (approximately)
 821                          * from another data.
 822                          */
 823                         ttp.ts_recent_stamp = xtime.tv_sec - ((TCP_TIMEOUT_INIT/HZ)<<req->retrans);
 824                         paws_reject = tcp_paws_check(&ttp, th->rst);
 825                 }
 826         }
 827
 828         /* Check for pure retransmitted SYN. */
 829         if (TCP_SKB_CB(skb)->seq == req->rcv_isn &&
 830             flg == TCP_FLAG_SYN &&
 831             !paws_reject) {
 832                 /*
 833                  * RFC793 draws (Incorrectly! It was fixed in RFC1122)
 834                  * this case on figure 6 and figure 8, but formal
 835                  * protocol description says NOTHING.
 836                  * To be more exact, it says that we should send ACK,
 837                  * because this segment (at least, if it has no data)
 838                  * is out of window.
 839                  *
 840                  *  CONCLUSION: RFC793 (even with RFC1122) DOES NOT
 841                  *  describe SYN-RECV state. All the description
 842                  *  is wrong, we cannot believe to it and should
 843                  *  rely only on common sense and implementation
 844                  *  experience.
 845                  *
 846                  * Enforce "SYN-ACK" according to figure 8, figure 6
 847                  * of RFC793, fixed by RFC1122.
 848                  */
 849                 req->class->rtx_syn_ack(sk, req, NULL);
 850                 return NULL;
 851         }
 852
 853         /* Further reproduces section "SEGMENT ARRIVES"
 854            for state SYN-RECEIVED of RFC793.
 855            It is broken, however, it does not work only
 856            when SYNs are crossed.
 857
 858            You would think that SYN crossing is impossible here, since
 859            we should have a SYN_SENT socket (from connect()) on our end,
 860            but this is not true if the crossed SYNs were sent to both
 861            ends by a malicious third party.  We must defend against this,
 862            and to do that we first verify the ACK (as per RFC793, page
 863            36) and reset if it is invalid.  Is this a true full defense?
 864            To convince ourselves, let us consider a way in which the ACK
 865            test can still pass in this 'malicious crossed SYNs' case.
 866            Malicious sender sends identical SYNs (and thus identical sequence
 867            numbers) to both A and B:
 868
 869                 A: gets SYN, seq=7
 870                 B: gets SYN, seq=7
 871
 872            By our good fortune, both A and B select the same initial
 873            send sequence number of seven :-)
 874
 875                 A: sends SYN|ACK, seq=7, ack_seq=8
 876                 B: sends SYN|ACK, seq=7, ack_seq=8
 877
 878            So we are now A eating this SYN|ACK, ACK test passes.  So
 879            does sequence test, SYN is truncated, and thus we consider
 880            it a bare ACK.
 881
 882            If tp->defer_accept, we silently drop this bare ACK.  Otherwise,
 883            we create an established connection.  Both ends (listening sockets)
 884            accept the new incoming connection and try to talk to each other. 8-)
 885
 886            Note: This case is both harmless, and rare.  Possibility is about the
 887            same as us discovering intelligent life on another plant tomorrow.
 888
 889            But generally, we should (RFC lies!) to accept ACK
 890            from SYNACK both here and in tcp_rcv_state_process().
 891            tcp_rcv_state_process() does not, hence, we do not too.
 892
 893            Note that the case is absolutely generic:
 894            we cannot optimize anything here without
 895            violating protocol. All the checks must be made
 896            before attempt to create socket.
 897          */
 898
 899         /* RFC793 page 36: "If the connection is in any non-synchronized state ...
 900          *                  and the incoming segment acknowledges something not yet
 901          *                  sent (the segment carries an unaccaptable ACK) ...
 902          *                  a reset is sent."
 903          *
 904          * Invalid ACK: reset will be sent by listening socket
 905          */
 906         if ((flg & TCP_FLAG_ACK) &&
 907             (TCP_SKB_CB(skb)->ack_seq != req->snt_isn+1))
 908                 return sk;
 909
 910         /* Also, it would be not so bad idea to check rcv_tsecr, which
 911          * is essentially ACK extension and too early or too late values
 912          * should cause reset in unsynchronized states.
 913          */
 914
 915         /* RFC793: "first check sequence number". */
 916
 917         if (paws_reject || !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq,
 918                                           req->rcv_isn+1, req->rcv_isn+1+req->rcv_wnd)) {
 919                 /* Out of window: send ACK and drop. */
 920                 if (!(flg & TCP_FLAG_RST))
 921                         req->class->send_ack(skb, req);
 922                 if (paws_reject)
 923                         NET_INC_STATS_BH(PAWSEstabRejected);
 924                 return NULL;
 925         }
 926
 927         /* In sequence, PAWS is OK. */
 928
 929         if (ttp.saw_tstamp && !after(TCP_SKB_CB(skb)->seq, req->rcv_isn+1))
 930                 req->ts_recent = ttp.rcv_tsval;
 931
 932         if (TCP_SKB_CB(skb)->seq == req->rcv_isn) {
 933                 /* Truncate SYN, it is out of window starting
 934                    at req->rcv_isn+1. */
 935                 flg &= ~TCP_FLAG_SYN;
 936         }
 937
 938         /* RFC793: "second check the RST bit" and
 939          *         "fourth, check the SYN bit"
 940          */
 941         if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN))
 942                 goto embryonic_reset;
 943
 944         /* ACK sequence verified above, just make sure ACK is
 945          * set.  If ACK not set, just silently drop the packet.
 946          */
 947         if (!(flg & TCP_FLAG_ACK))
 948                 return NULL;
 949
 950         /* If TCP_DEFER_ACCEPT is set, drop bare ACK. */
 951         if (tp->defer_accept && TCP_SKB_CB(skb)->end_seq == req->rcv_isn+1) {
 952                 req->acked = 1;
 953                 return NULL;
 954         }
 955
 956         /* OK, ACK is valid, create big socket and
 957          * feed this segment to it. It will repeat all
 958          * the tests. THIS SEGMENT MUST MOVE SOCKET TO
 959          * ESTABLISHED STATE. If it will be dropped after
 960          * socket is created, wait for troubles.
 961          */
 962         child = tp->af_specific->syn_recv_sock(sk, skb, req, NULL);
 963         if (child == NULL)
 964                 goto listen_overflow;
 965
 966         tcp_synq_unlink(tp, req, prev);
 967         tcp_synq_removed(sk, req);
 968
 969         tcp_acceptq_queue(sk, req, child);
 970         return child;
 971
 972 listen_overflow:
 973         if (!sysctl_tcp_abort_on_overflow) {
 974                 req->acked = 1;
 975                 return NULL;
 976         }
 977
 978 embryonic_reset:
 979         NET_INC_STATS_BH(EmbryonicRsts);
 980         if (!(flg & TCP_FLAG_RST))
 981                 req->class->send_reset(skb);
 982
 983         tcp_synq_drop(sk, req, prev);
 984         return NULL;
 985 }
 986
 987 /*
 988  * Queue segment on the new socket if the new socket is active,
 989  * otherwise we just shortcircuit this and continue with
 990  * the new socket.
 991  */
 992
 993 int tcp_child_process(struct sock *parent, struct sock *child,
 994                       struct sk_buff *skb)
 995 {
 996         int ret = 0;
 997         int state = child->state;
 998
 999         if (child->lock.users == 0) {
1000                 ret = tcp_rcv_state_process(child, skb, skb->h.th, skb->len);
1001
1002                 /* Wakeup parent, send SIGIO */
1003                 if (state == TCP_SYN_RECV && child->state != state)
1004                         parent->data_ready(parent, 0);
1005         } else {
1006                 /* Alas, it is possible again, because we do lookup
1007                  * in main socket hash table and lock on listening
1008                  * socket does not protect us more.
1009                  */
1010                 sk_add_backlog(child, skb);
1011         }
1012
1013         bh_unlock_sock(child);
1014         sock_put(child);
1015         return ret;
1016 }