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.
6 * Implementation of the Transmission Control Protocol(TCP).
8 * Version: $Id: tcp_minisocks.c,v 1.1.1.1 2005/04/11 02:51:13 jack Exp $
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>
23 #include <linux/config.h>
25 #include <linux/sysctl.h>
27 #include <net/inet_common.h>
30 #define SYNC_INIT 0 /* let the user enable it */
35 int sysctl_tcp_tw_recycle = 0;
36 int sysctl_tcp_max_tw_buckets = NR_FILE*2;
38 int sysctl_tcp_syncookies = SYNC_INIT;
39 int sysctl_tcp_abort_on_overflow = 0;
41 static __inline__ int tcp_in_window(u32 seq, u32 end_seq, u32 s_win, u32 e_win)
45 if (after(end_seq, s_win) && before(seq, e_win))
47 return (seq == e_win && seq == end_seq);
50 /* New-style handling of TIME_WAIT sockets. */
55 /* Must be called with locally disabled BHs. */
56 void tcp_timewait_kill(struct tcp_tw_bucket *tw)
58 struct tcp_ehash_bucket *ehead;
59 struct tcp_bind_hashbucket *bhead;
60 struct tcp_bind_bucket *tb;
62 /* Unlink from established hashes. */
63 ehead = &tcp_ehash[tw->hashent];
64 write_lock(&ehead->lock);
66 write_unlock(&ehead->lock);
70 tw->next->pprev = tw->pprev;
71 *(tw->pprev) = tw->next;
73 write_unlock(&ehead->lock);
75 /* Disassociate with bind bucket. */
76 bhead = &tcp_bhash[tcp_bhashfn(tw->num)];
77 spin_lock(&bhead->lock);
80 tw->bind_next->bind_pprev = tw->bind_pprev;
81 *(tw->bind_pprev) = tw->bind_next;
83 if (tb->owners == NULL) {
85 tb->next->pprev = tb->pprev;
86 *(tb->pprev) = tb->next;
87 kmem_cache_free(tcp_bucket_cachep, tb);
89 spin_unlock(&bhead->lock);
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));
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.
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.
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
128 tcp_timewait_state_process(struct tcp_tw_bucket *tw, struct sk_buff *skb,
129 struct tcphdr *th, unsigned len)
135 if (th->doff > (sizeof(struct tcphdr)>>2) && tw->ts_recent_stamp) {
136 tcp_parse_options(skb, &tp, 0);
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);
145 if (tw->substate == TCP_FIN_WAIT2) {
146 /* Just repeat all the checks of tcp_rcv_state_process() */
148 /* Out of window, send ACK */
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))
157 if (th->syn && !before(TCP_SKB_CB(skb)->seq, tw->rcv_nxt))
161 if (!after(TCP_SKB_CB(skb)->end_seq, tw->rcv_nxt) ||
162 TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq) {
164 return TCP_TW_SUCCESS;
167 /* New data or FIN. If new data arrive after half-duplex close,
170 if (!th->fin || TCP_SKB_CB(skb)->end_seq != tw->rcv_nxt+1) {
172 tcp_tw_deschedule(tw);
173 tcp_timewait_kill(tw);
178 /* FIN arrived, enter true time-wait state. */
179 tw->substate = TCP_TIME_WAIT;
180 tw->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
182 tw->ts_recent_stamp = xtime.tv_sec;
183 tw->ts_recent = tp.rcv_tsval;
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);
196 tcp_tw_schedule(tw, TCP_TIMEWAIT_LEN);
201 * Now real TIME-WAIT state.
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:
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,
213 * (2) returns to TIME-WAIT state if the SYN turns out
214 * to be an old duplicate".
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. */
223 /* This is TIME_WAIT assasination, in two flavors.
224 * Oh well... nobody has a sufficient solution to this
227 if (sysctl_tcp_rfc1337 == 0) {
229 tcp_tw_deschedule(tw);
230 tcp_timewait_kill(tw);
232 return TCP_TW_SUCCESS;
235 tcp_tw_schedule(tw, TCP_TIMEWAIT_LEN);
238 tw->ts_recent = tp.rcv_tsval;
239 tw->ts_recent_stamp = xtime.tv_sec;
243 return TCP_TW_SUCCESS;
246 /* Out of window segment.
248 All the segments are ACKed immediately.
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.
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,
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;
269 TCP_SKB_CB(skb)->when = isn;
274 NET_INC_STATS_BH(PAWSEstabRejected);
277 /* In this case we must reset the TIMEWAIT timer.
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.
283 if (paws_reject || th->ack)
284 tcp_tw_schedule(tw, TCP_TIMEWAIT_LEN);
286 /* Send ACK. Note, we do not put the bucket,
287 * it will be released by caller.
292 return TCP_TW_SUCCESS;
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
300 static void __tcp_tw_hashdance(struct sock *sk, struct tcp_tw_bucket *tw)
302 struct tcp_ehash_bucket *ehead = &tcp_ehash[sk->hashent];
303 struct tcp_bind_hashbucket *bhead;
304 struct sock **head, *sktw;
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.
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);
320 write_lock(&ehead->lock);
322 /* Step 2: Remove SK from established hash. */
325 sk->next->pprev = sk->pprev;
326 *sk->pprev = sk->next;
328 sock_prot_dec_use(sk->prot);
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;
338 atomic_inc(&tw->refcnt);
340 write_unlock(&ehead->lock);
344 * Move a socket to time-wait or dead fin-wait-2 state.
346 void tcp_time_wait(struct sock *sk, int state, int timeo)
348 struct tcp_tw_bucket *tw = NULL;
349 struct tcp_opt *tp = &(sk->tp_pinfo.af_tcp);
352 if (sysctl_tcp_tw_recycle && tp->ts_recent_stamp)
353 recycle_ok = tp->af_specific->remember_stamp(sk);
355 if (tcp_tw_count < sysctl_tcp_max_tw_buckets)
356 tw = kmem_cache_alloc(tcp_timewait_cachep, SLAB_ATOMIC);
359 int rto = (tp->rto<<2) - (tp->rto>>1);
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;
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);
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;
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));
393 /* Linkage updates. */
394 __tcp_tw_hashdance(sk, tw);
396 /* Get the TIME_WAIT timeout firing. */
403 tw->timeout = TCP_TIMEWAIT_LEN;
404 if (state == TCP_TIME_WAIT)
405 timeo = TCP_TIMEWAIT_LEN;
408 tcp_tw_schedule(tw, timeo);
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.
416 printk(KERN_INFO "TCP: time wait bucket table overflow\n");
419 tcp_update_metrics(sk);
423 /* Kill off TIME_WAIT sockets once their lifetime has expired. */
424 static int tcp_tw_death_row_slot = 0;
426 static void tcp_twkill(unsigned long);
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 };
432 static void SMP_TIMER_NAME(tcp_twkill)(unsigned long dummy)
434 struct tcp_tw_bucket *tw;
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.
443 spin_lock(&tw_death_lock);
445 if (tcp_tw_count == 0)
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 tw->pprev_death = NULL;
451 spin_unlock(&tw_death_lock);
453 tcp_timewait_kill(tw);
458 spin_lock(&tw_death_lock);
460 tcp_tw_death_row_slot =
461 ((tcp_tw_death_row_slot + 1) & (TCP_TWKILL_SLOTS - 1));
463 if ((tcp_tw_count -= killed) != 0)
464 mod_timer(&tcp_tw_timer, jiffies+TCP_TWKILL_PERIOD);
465 net_statistics[smp_processor_id()*2].TimeWaited += killed;
467 spin_unlock(&tw_death_lock);
470 SMP_TIMER_DEFINE(tcp_twkill, tcp_twkill_task);
472 /* These are always called from BH context. See callers in
473 * tcp_input.c to verify this.
476 /* This is for handling early-kills of TIME_WAIT sockets. */
477 void tcp_tw_deschedule(struct tcp_tw_bucket *tw)
479 spin_lock(&tw_death_lock);
480 if (tw->pprev_death) {
482 tw->next_death->pprev_death = tw->pprev_death;
483 *tw->pprev_death = tw->next_death;
484 tw->pprev_death = NULL;
486 if (--tcp_tw_count == 0)
487 del_timer(&tcp_tw_timer);
489 spin_unlock(&tw_death_lock);
492 /* Short-time timewait calendar */
494 static int tcp_twcal_hand = -1;
495 static int tcp_twcal_jiffie;
496 static void tcp_twcal_tick(unsigned long);
497 static struct timer_list tcp_twcal_timer = {function: tcp_twcal_tick};
498 static struct tcp_tw_bucket *tcp_twcal_row[TCP_TW_RECYCLE_SLOTS];
500 void tcp_tw_schedule(struct tcp_tw_bucket *tw, int timeo)
502 struct tcp_tw_bucket **tpp;
505 /* timeout := RTO * 3.5
507 * 3.5 = 1+2+0.5 to wait for two retransmits.
509 * RATIONALE: if FIN arrived and we entered TIME-WAIT state,
510 * our ACK acking that FIN can be lost. If N subsequent retransmitted
511 * FINs (or previous seqments) are lost (probability of such event
512 * is p^(N+1), where p is probability to lose single packet and
513 * time to detect the loss is about RTO*(2^N - 1) with exponential
514 * backoff). Normal timewait length is calculated so, that we
515 * waited at least for one retransmitted FIN (maximal RTO is 120sec).
516 * [ BTW Linux. following BSD, violates this requirement waiting
517 * only for 60sec, we should wait at least for 240 secs.
518 * Well, 240 consumes too much of resources 8)
520 * This interval is not reduced to catch old duplicate and
521 * responces to our wandering segments living for two MSLs.
522 * However, if we use PAWS to detect
523 * old duplicates, we can reduce the interval to bounds required
524 * by RTO, rather than MSL. So, if peer understands PAWS, we
525 * kill tw bucket after 3.5*RTO (it is important that this number
526 * is greater than TS tick!) and detect old duplicates with help
529 slot = (timeo + (1<<TCP_TW_RECYCLE_TICK) - 1) >> TCP_TW_RECYCLE_TICK;
531 spin_lock(&tw_death_lock);
533 /* Unlink it, if it was scheduled */
534 if (tw->pprev_death) {
536 tw->next_death->pprev_death = tw->pprev_death;
537 *tw->pprev_death = tw->next_death;
538 tw->pprev_death = NULL;
541 atomic_inc(&tw->refcnt);
543 if (slot >= TCP_TW_RECYCLE_SLOTS) {
544 /* Schedule to slow timer */
545 if (timeo >= TCP_TIMEWAIT_LEN) {
546 slot = TCP_TWKILL_SLOTS-1;
548 slot = (timeo + TCP_TWKILL_PERIOD-1) / TCP_TWKILL_PERIOD;
549 if (slot >= TCP_TWKILL_SLOTS)
550 slot = TCP_TWKILL_SLOTS-1;
552 tw->ttd = jiffies + timeo;
553 slot = (tcp_tw_death_row_slot + slot) & (TCP_TWKILL_SLOTS - 1);
554 tpp = &tcp_tw_death_row[slot];
556 tw->ttd = jiffies + (slot<<TCP_TW_RECYCLE_TICK);
558 if (tcp_twcal_hand < 0) {
560 tcp_twcal_jiffie = jiffies;
561 tcp_twcal_timer.expires = tcp_twcal_jiffie + (slot<<TCP_TW_RECYCLE_TICK);
562 add_timer(&tcp_twcal_timer);
564 if ((long)(tcp_twcal_timer.expires - jiffies) > (slot<<TCP_TW_RECYCLE_TICK))
565 mod_timer(&tcp_twcal_timer, jiffies + (slot<<TCP_TW_RECYCLE_TICK));
566 slot = (tcp_twcal_hand + slot)&(TCP_TW_RECYCLE_SLOTS-1);
568 tpp = &tcp_twcal_row[slot];
571 if((tw->next_death = *tpp) != NULL)
572 (*tpp)->pprev_death = &tw->next_death;
574 tw->pprev_death = tpp;
576 if (tcp_tw_count++ == 0)
577 mod_timer(&tcp_tw_timer, jiffies+TCP_TWKILL_PERIOD);
578 spin_unlock(&tw_death_lock);
581 void SMP_TIMER_NAME(tcp_twcal_tick)(unsigned long dummy)
585 unsigned long now = jiffies;
589 spin_lock(&tw_death_lock);
590 if (tcp_twcal_hand < 0)
593 slot = tcp_twcal_hand;
594 j = tcp_twcal_jiffie;
596 for (n=0; n<TCP_TW_RECYCLE_SLOTS; n++) {
597 if ((long)(j - now) <= 0) {
598 struct tcp_tw_bucket *tw;
600 while((tw = tcp_twcal_row[slot]) != NULL) {
601 tcp_twcal_row[slot] = tw->next_death;
602 tw->pprev_death = NULL;
604 tcp_timewait_kill(tw);
611 tcp_twcal_jiffie = j;
612 tcp_twcal_hand = slot;
615 if (tcp_twcal_row[slot] != NULL) {
616 mod_timer(&tcp_twcal_timer, j);
620 j += (1<<TCP_TW_RECYCLE_TICK);
621 slot = (slot+1)&(TCP_TW_RECYCLE_SLOTS-1);
626 if ((tcp_tw_count -= killed) == 0)
627 del_timer(&tcp_tw_timer);
628 net_statistics[smp_processor_id()*2].TimeWaitKilled += killed;
629 spin_unlock(&tw_death_lock);
632 SMP_TIMER_DEFINE(tcp_twcal_tick, tcp_twcal_tasklet);
635 /* This is not only more efficient than what we used to do, it eliminates
636 * a lot of code duplication between IPv4/IPv6 SYN recv processing. -DaveM
638 * Actually, we could lots of memory writes here. tp of listening
639 * socket contains all necessary default parameters.
641 struct sock *tcp_create_openreq_child(struct sock *sk, struct open_request *req, struct sk_buff *skb)
643 struct sock *newsk = sk_alloc(PF_INET, GFP_ATOMIC, 0);
646 struct tcp_opt *newtp;
648 struct sk_filter *filter;
651 memcpy(newsk, sk, sizeof(*newsk));
652 newsk->state = TCP_SYN_RECV;
658 /* Clone the TCP header template */
659 newsk->dport = req->rmt_port;
661 sock_lock_init(newsk);
664 newsk->dst_lock = RW_LOCK_UNLOCKED;
665 atomic_set(&newsk->rmem_alloc, 0);
666 skb_queue_head_init(&newsk->receive_queue);
667 atomic_set(&newsk->wmem_alloc, 0);
668 skb_queue_head_init(&newsk->write_queue);
669 atomic_set(&newsk->omem_alloc, 0);
670 newsk->wmem_queued = 0;
671 newsk->forward_alloc = 0;
674 newsk->userlocks = sk->userlocks & ~SOCK_BINDPORT_LOCK;
676 newsk->backlog.head = newsk->backlog.tail = NULL;
677 newsk->callback_lock = RW_LOCK_UNLOCKED;
678 skb_queue_head_init(&newsk->error_queue);
679 newsk->write_space = tcp_write_space;
681 if ((filter = newsk->filter) != NULL)
682 sk_filter_charge(newsk, filter);
685 /* Now setup tcp_opt */
686 newtp = &(newsk->tp_pinfo.af_tcp);
687 newtp->pred_flags = 0;
688 newtp->rcv_nxt = req->rcv_isn + 1;
689 newtp->snd_nxt = req->snt_isn + 1;
690 newtp->snd_una = req->snt_isn + 1;
691 newtp->snd_sml = req->snt_isn + 1;
693 tcp_prequeue_init(newtp);
695 tcp_init_wl(newtp, req->snt_isn, req->rcv_isn);
697 newtp->retransmits = 0;
700 newtp->mdev = TCP_TIMEOUT_INIT;
701 newtp->rto = TCP_TIMEOUT_INIT;
703 newtp->packets_out = 0;
705 newtp->retrans_out = 0;
706 newtp->sacked_out = 0;
707 newtp->fackets_out = 0;
708 newtp->snd_ssthresh = 0x7fffffff;
710 /* So many TCP implementations out there (incorrectly) count the
711 * initial SYN frame in their delayed-ACK and congestion control
712 * algorithms that we must have the following bandaid to talk
713 * efficiently to them. -DaveM
716 newtp->snd_cwnd_cnt = 0;
718 newtp->frto_counter = 0;
719 newtp->frto_highmark = 0;
721 newtp->ca_state = TCP_CA_Open;
722 tcp_init_xmit_timers(newsk);
723 skb_queue_head_init(&newtp->out_of_order_queue);
724 newtp->send_head = NULL;
725 newtp->rcv_wup = req->rcv_isn + 1;
726 newtp->write_seq = req->snt_isn + 1;
727 newtp->pushed_seq = newtp->write_seq;
728 newtp->copied_seq = req->rcv_isn + 1;
730 newtp->saw_tstamp = 0;
733 newtp->eff_sacks = 0;
735 newtp->probes_out = 0;
736 newtp->num_sacks = 0;
738 newtp->listen_opt = NULL;
739 newtp->accept_queue = newtp->accept_queue_tail = NULL;
740 /* Deinitialize syn_wait_lock to trap illegal accesses. */
741 memset(&newtp->syn_wait_lock, 0, sizeof(newtp->syn_wait_lock));
743 /* Back to base struct sock members. */
746 atomic_set(&newsk->refcnt, 2);
747 #ifdef INET_REFCNT_DEBUG
748 atomic_inc(&inet_sock_nr);
750 atomic_inc(&tcp_sockets_allocated);
753 tcp_reset_keepalive_timer(newsk, keepalive_time_when(newtp));
754 newsk->socket = NULL;
757 newtp->tstamp_ok = req->tstamp_ok;
758 if((newtp->sack_ok = req->sack_ok) != 0) {
762 newtp->window_clamp = req->window_clamp;
763 newtp->rcv_ssthresh = req->rcv_wnd;
764 newtp->rcv_wnd = req->rcv_wnd;
765 newtp->wscale_ok = req->wscale_ok;
766 if (newtp->wscale_ok) {
767 newtp->snd_wscale = req->snd_wscale;
768 newtp->rcv_wscale = req->rcv_wscale;
770 newtp->snd_wscale = newtp->rcv_wscale = 0;
771 newtp->window_clamp = min(newtp->window_clamp, 65535U);
773 newtp->snd_wnd = ntohs(skb->h.th->window) << newtp->snd_wscale;
774 newtp->max_window = newtp->snd_wnd;
776 if (newtp->tstamp_ok) {
777 newtp->ts_recent = req->ts_recent;
778 newtp->ts_recent_stamp = xtime.tv_sec;
779 newtp->tcp_header_len = sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
781 newtp->ts_recent_stamp = 0;
782 newtp->tcp_header_len = sizeof(struct tcphdr);
784 if (skb->len >= TCP_MIN_RCVMSS+newtp->tcp_header_len)
785 newtp->ack.last_seg_size = skb->len-newtp->tcp_header_len;
786 newtp->mss_clamp = req->mss;
787 TCP_ECN_openreq_child(newtp, req);
789 TCP_INC_STATS_BH(TcpPassiveOpens);
795 * Process an incoming packet for SYN_RECV sockets represented
796 * as an open_request.
799 struct sock *tcp_check_req(struct sock *sk,struct sk_buff *skb,
800 struct open_request *req,
801 struct open_request **prev)
803 struct tcphdr *th = skb->h.th;
804 struct tcp_opt *tp = &(sk->tp_pinfo.af_tcp);
805 u32 flg = tcp_flag_word(th) & (TCP_FLAG_RST|TCP_FLAG_SYN|TCP_FLAG_ACK);
811 if (th->doff > (sizeof(struct tcphdr)>>2)) {
812 tcp_parse_options(skb, &ttp, 0);
814 if (ttp.saw_tstamp) {
815 ttp.ts_recent = req->ts_recent;
816 /* We do not store true stamp, but it is not required,
817 * it can be estimated (approximately)
820 ttp.ts_recent_stamp = xtime.tv_sec - ((TCP_TIMEOUT_INIT/HZ)<<req->retrans);
821 paws_reject = tcp_paws_check(&ttp, th->rst);
825 /* Check for pure retransmitted SYN. */
826 if (TCP_SKB_CB(skb)->seq == req->rcv_isn &&
827 flg == TCP_FLAG_SYN &&
830 * RFC793 draws (Incorrectly! It was fixed in RFC1122)
831 * this case on figure 6 and figure 8, but formal
832 * protocol description says NOTHING.
833 * To be more exact, it says that we should send ACK,
834 * because this segment (at least, if it has no data)
837 * CONCLUSION: RFC793 (even with RFC1122) DOES NOT
838 * describe SYN-RECV state. All the description
839 * is wrong, we cannot believe to it and should
840 * rely only on common sense and implementation
843 * Enforce "SYN-ACK" according to figure 8, figure 6
844 * of RFC793, fixed by RFC1122.
846 req->class->rtx_syn_ack(sk, req, NULL);
850 /* Further reproduces section "SEGMENT ARRIVES"
851 for state SYN-RECEIVED of RFC793.
852 It is broken, however, it does not work only
853 when SYNs are crossed.
855 You would think that SYN crossing is impossible here, since
856 we should have a SYN_SENT socket (from connect()) on our end,
857 but this is not true if the crossed SYNs were sent to both
858 ends by a malicious third party. We must defend against this,
859 and to do that we first verify the ACK (as per RFC793, page
860 36) and reset if it is invalid. Is this a true full defense?
861 To convince ourselves, let us consider a way in which the ACK
862 test can still pass in this 'malicious crossed SYNs' case.
863 Malicious sender sends identical SYNs (and thus identical sequence
864 numbers) to both A and B:
869 By our good fortune, both A and B select the same initial
870 send sequence number of seven :-)
872 A: sends SYN|ACK, seq=7, ack_seq=8
873 B: sends SYN|ACK, seq=7, ack_seq=8
875 So we are now A eating this SYN|ACK, ACK test passes. So
876 does sequence test, SYN is truncated, and thus we consider
879 If tp->defer_accept, we silently drop this bare ACK. Otherwise,
880 we create an established connection. Both ends (listening sockets)
881 accept the new incoming connection and try to talk to each other. 8-)
883 Note: This case is both harmless, and rare. Possibility is about the
884 same as us discovering intelligent life on another plant tomorrow.
886 But generally, we should (RFC lies!) to accept ACK
887 from SYNACK both here and in tcp_rcv_state_process().
888 tcp_rcv_state_process() does not, hence, we do not too.
890 Note that the case is absolutely generic:
891 we cannot optimize anything here without
892 violating protocol. All the checks must be made
893 before attempt to create socket.
896 /* RFC793 page 36: "If the connection is in any non-synchronized state ...
897 * and the incoming segment acknowledges something not yet
898 * sent (the segment carries an unaccaptable ACK) ...
901 * Invalid ACK: reset will be sent by listening socket
903 if ((flg & TCP_FLAG_ACK) &&
904 (TCP_SKB_CB(skb)->ack_seq != req->snt_isn+1))
907 /* Also, it would be not so bad idea to check rcv_tsecr, which
908 * is essentially ACK extension and too early or too late values
909 * should cause reset in unsynchronized states.
912 /* RFC793: "first check sequence number". */
914 if (paws_reject || !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq,
915 req->rcv_isn+1, req->rcv_isn+1+req->rcv_wnd)) {
916 /* Out of window: send ACK and drop. */
917 if (!(flg & TCP_FLAG_RST))
918 req->class->send_ack(skb, req);
920 NET_INC_STATS_BH(PAWSEstabRejected);
924 /* In sequence, PAWS is OK. */
926 if (ttp.saw_tstamp && !after(TCP_SKB_CB(skb)->seq, req->rcv_isn+1))
927 req->ts_recent = ttp.rcv_tsval;
929 if (TCP_SKB_CB(skb)->seq == req->rcv_isn) {
930 /* Truncate SYN, it is out of window starting
931 at req->rcv_isn+1. */
932 flg &= ~TCP_FLAG_SYN;
935 /* RFC793: "second check the RST bit" and
936 * "fourth, check the SYN bit"
938 if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN))
939 goto embryonic_reset;
941 /* If TCP_DEFER_ACCEPT is set, drop bare ACK. */
942 if (tp->defer_accept && TCP_SKB_CB(skb)->end_seq == req->rcv_isn+1) {
947 /* OK, ACK is valid, create big socket and
948 * feed this segment to it. It will repeat all
949 * the tests. THIS SEGMENT MUST MOVE SOCKET TO
950 * ESTABLISHED STATE. If it will be dropped after
951 * socket is created, wait for troubles.
953 child = tp->af_specific->syn_recv_sock(sk, skb, req, NULL);
955 goto listen_overflow;
957 tcp_synq_unlink(tp, req, prev);
958 tcp_synq_removed(sk, req);
960 tcp_acceptq_queue(sk, req, child);
964 if (!sysctl_tcp_abort_on_overflow) {
970 NET_INC_STATS_BH(EmbryonicRsts);
971 if (!(flg & TCP_FLAG_RST))
972 req->class->send_reset(skb);
974 tcp_synq_drop(sk, req, prev);
979 * Queue segment on the new socket if the new socket is active,
980 * otherwise we just shortcircuit this and continue with
984 int tcp_child_process(struct sock *parent, struct sock *child,
988 int state = child->state;
990 if (child->lock.users == 0) {
991 ret = tcp_rcv_state_process(child, skb, skb->h.th, skb->len);
993 /* Wakeup parent, send SIGIO */
994 if (state == TCP_SYN_RECV && child->state != state)
995 parent->data_ready(parent, 0);
997 /* Alas, it is possible again, because we do lookup
998 * in main socket hash table and lock on listening
999 * socket does not protect us more.
1001 sk_add_backlog(child, skb);
1004 bh_unlock_sock(child);