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