2 * Copyright (c) 2001 McAfee, Inc.
3 * Copyright (c) 2006,2013 Andre Oppermann, Internet Business Solutions AG
6 * This software was developed for the FreeBSD Project by Jonathan Lemon
7 * and McAfee Research, the Security Research Division of McAfee, Inc. under
8 * DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the
9 * DARPA CHATS research program. [2001 McAfee, Inc.]
11 * Redistribution and use in source and binary forms, with or without
12 * modification, are permitted provided that the following conditions
14 * 1. Redistributions of source code must retain the above copyright
15 * notice, this list of conditions and the following disclaimer.
16 * 2. Redistributions in binary form must reproduce the above copyright
17 * notice, this list of conditions and the following disclaimer in the
18 * documentation and/or other materials provided with the distribution.
20 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
21 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
22 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
23 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
24 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
25 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
26 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
27 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
28 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
29 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
33 #include <sys/cdefs.h>
34 __FBSDID("$FreeBSD$");
37 #include "opt_inet6.h"
38 #include "opt_ipsec.h"
39 #include "opt_pcbgroup.h"
41 #include <sys/param.h>
42 #include <sys/systm.h>
44 #include <sys/refcount.h>
45 #include <sys/kernel.h>
46 #include <sys/sysctl.h>
47 #include <sys/limits.h>
49 #include <sys/mutex.h>
50 #include <sys/malloc.h>
52 #include <sys/proc.h> /* for proc0 declaration */
53 #include <sys/random.h>
54 #include <sys/socket.h>
55 #include <sys/socketvar.h>
56 #include <sys/syslog.h>
57 #include <sys/ucred.h>
60 #include <crypto/siphash/siphash.h>
65 #include <net/if_var.h>
66 #include <net/route.h>
69 #include <netinet/in.h>
70 #include <netinet/in_systm.h>
71 #include <netinet/ip.h>
72 #include <netinet/in_var.h>
73 #include <netinet/in_pcb.h>
74 #include <netinet/ip_var.h>
75 #include <netinet/ip_options.h>
77 #include <netinet/ip6.h>
78 #include <netinet/icmp6.h>
79 #include <netinet6/nd6.h>
80 #include <netinet6/ip6_var.h>
81 #include <netinet6/in6_pcb.h>
83 #include <netinet/tcp.h>
85 #include <netinet/tcp_fastopen.h>
87 #include <netinet/tcp_fsm.h>
88 #include <netinet/tcp_seq.h>
89 #include <netinet/tcp_timer.h>
90 #include <netinet/tcp_var.h>
91 #include <netinet/tcp_syncache.h>
93 #include <netinet6/tcp6_var.h>
96 #include <netinet/toecore.h>
100 #include <netipsec/ipsec.h>
102 #include <netipsec/ipsec6.h>
104 #include <netipsec/key.h>
107 #include <machine/in_cksum.h>
109 #include <security/mac/mac_framework.h>
111 static VNET_DEFINE(int, tcp_syncookies) = 1;
112 #define V_tcp_syncookies VNET(tcp_syncookies)
113 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_VNET | CTLFLAG_RW,
114 &VNET_NAME(tcp_syncookies), 0,
115 "Use TCP SYN cookies if the syncache overflows");
117 static VNET_DEFINE(int, tcp_syncookiesonly) = 0;
118 #define V_tcp_syncookiesonly VNET(tcp_syncookiesonly)
119 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_VNET | CTLFLAG_RW,
120 &VNET_NAME(tcp_syncookiesonly), 0,
121 "Use only TCP SYN cookies");
124 #define ADDED_BY_TOE(sc) ((sc)->sc_tod != NULL)
127 static void syncache_drop(struct syncache *, struct syncache_head *);
128 static void syncache_free(struct syncache *);
129 static void syncache_insert(struct syncache *, struct syncache_head *);
130 static int syncache_respond(struct syncache *, struct syncache_head *, int,
131 const struct mbuf *);
132 static struct socket *syncache_socket(struct syncache *, struct socket *,
134 static void syncache_timeout(struct syncache *sc, struct syncache_head *sch,
136 static void syncache_timer(void *);
138 static uint32_t syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t,
139 uint8_t *, uintptr_t);
140 static tcp_seq syncookie_generate(struct syncache_head *, struct syncache *);
141 static struct syncache
142 *syncookie_lookup(struct in_conninfo *, struct syncache_head *,
143 struct syncache *, struct tcphdr *, struct tcpopt *,
145 static void syncookie_reseed(void *);
147 static int syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch,
148 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
153 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies.
154 * 3 retransmits corresponds to a timeout of 3 * (1 + 2 + 4 + 8) == 45 seconds,
155 * the odds are that the user has given up attempting to connect by then.
157 #define SYNCACHE_MAXREXMTS 3
159 /* Arbitrary values */
160 #define TCP_SYNCACHE_HASHSIZE 512
161 #define TCP_SYNCACHE_BUCKETLIMIT 30
163 static VNET_DEFINE(struct tcp_syncache, tcp_syncache);
164 #define V_tcp_syncache VNET(tcp_syncache)
166 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0,
169 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_VNET | CTLFLAG_RDTUN,
170 &VNET_NAME(tcp_syncache.bucket_limit), 0,
171 "Per-bucket hash limit for syncache");
173 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_VNET | CTLFLAG_RDTUN,
174 &VNET_NAME(tcp_syncache.cache_limit), 0,
175 "Overall entry limit for syncache");
177 SYSCTL_UMA_CUR(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_VNET,
178 &VNET_NAME(tcp_syncache.zone), "Current number of entries in syncache");
180 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_VNET | CTLFLAG_RDTUN,
181 &VNET_NAME(tcp_syncache.hashsize), 0,
182 "Size of TCP syncache hashtable");
184 SYSCTL_UINT(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, CTLFLAG_VNET | CTLFLAG_RW,
185 &VNET_NAME(tcp_syncache.rexmt_limit), 0,
186 "Limit on SYN/ACK retransmissions");
188 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1;
189 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail,
190 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0,
191 "Send reset on socket allocation failure");
193 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache");
195 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx)
196 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx)
197 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED)
200 * Requires the syncache entry to be already removed from the bucket list.
203 syncache_free(struct syncache *sc)
207 (void) m_free(sc->sc_ipopts);
211 mac_syncache_destroy(&sc->sc_label);
214 uma_zfree(V_tcp_syncache.zone, sc);
222 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
223 V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT;
224 V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS;
225 V_tcp_syncache.hash_secret = arc4random();
227 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize",
228 &V_tcp_syncache.hashsize);
229 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit",
230 &V_tcp_syncache.bucket_limit);
231 if (!powerof2(V_tcp_syncache.hashsize) ||
232 V_tcp_syncache.hashsize == 0) {
233 printf("WARNING: syncache hash size is not a power of 2.\n");
234 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
236 V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1;
239 V_tcp_syncache.cache_limit =
240 V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit;
241 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit",
242 &V_tcp_syncache.cache_limit);
244 /* Allocate the hash table. */
245 V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize *
246 sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO);
249 V_tcp_syncache.vnet = curvnet;
252 /* Initialize the hash buckets. */
253 for (i = 0; i < V_tcp_syncache.hashsize; i++) {
254 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket);
255 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head",
257 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer,
258 &V_tcp_syncache.hashbase[i].sch_mtx, 0);
259 V_tcp_syncache.hashbase[i].sch_length = 0;
260 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache;
263 /* Create the syncache entry zone. */
264 V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache),
265 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
266 V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone,
267 V_tcp_syncache.cache_limit);
269 /* Start the SYN cookie reseeder callout. */
270 callout_init(&V_tcp_syncache.secret.reseed, 1);
271 arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0);
272 arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0);
273 callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz,
274 syncookie_reseed, &V_tcp_syncache);
279 syncache_destroy(void)
281 struct syncache_head *sch;
282 struct syncache *sc, *nsc;
286 * Stop the re-seed timer before freeing resources. No need to
287 * possibly schedule it another time.
289 callout_drain(&V_tcp_syncache.secret.reseed);
291 /* Cleanup hash buckets: stop timers, free entries, destroy locks. */
292 for (i = 0; i < V_tcp_syncache.hashsize; i++) {
294 sch = &V_tcp_syncache.hashbase[i];
295 callout_drain(&sch->sch_timer);
298 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc)
299 syncache_drop(sc, sch);
301 KASSERT(TAILQ_EMPTY(&sch->sch_bucket),
302 ("%s: sch->sch_bucket not empty", __func__));
303 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0",
304 __func__, sch->sch_length));
305 mtx_destroy(&sch->sch_mtx);
308 KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0,
309 ("%s: cache_count not 0", __func__));
311 /* Free the allocated global resources. */
312 uma_zdestroy(V_tcp_syncache.zone);
313 free(V_tcp_syncache.hashbase, M_SYNCACHE);
318 * Inserts a syncache entry into the specified bucket row.
319 * Locks and unlocks the syncache_head autonomously.
322 syncache_insert(struct syncache *sc, struct syncache_head *sch)
324 struct syncache *sc2;
329 * Make sure that we don't overflow the per-bucket limit.
330 * If the bucket is full, toss the oldest element.
332 if (sch->sch_length >= V_tcp_syncache.bucket_limit) {
333 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket),
334 ("sch->sch_length incorrect"));
335 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head);
336 syncache_drop(sc2, sch);
337 TCPSTAT_INC(tcps_sc_bucketoverflow);
340 /* Put it into the bucket. */
341 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash);
345 if (ADDED_BY_TOE(sc)) {
346 struct toedev *tod = sc->sc_tod;
348 tod->tod_syncache_added(tod, sc->sc_todctx);
352 /* Reinitialize the bucket row's timer. */
353 if (sch->sch_length == 1)
354 sch->sch_nextc = ticks + INT_MAX;
355 syncache_timeout(sc, sch, 1);
359 TCPSTATES_INC(TCPS_SYN_RECEIVED);
360 TCPSTAT_INC(tcps_sc_added);
364 * Remove and free entry from syncache bucket row.
365 * Expects locked syncache head.
368 syncache_drop(struct syncache *sc, struct syncache_head *sch)
371 SCH_LOCK_ASSERT(sch);
373 TCPSTATES_DEC(TCPS_SYN_RECEIVED);
374 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
378 if (ADDED_BY_TOE(sc)) {
379 struct toedev *tod = sc->sc_tod;
381 tod->tod_syncache_removed(tod, sc->sc_todctx);
389 * Engage/reengage time on bucket row.
392 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout)
394 sc->sc_rxttime = ticks +
395 TCPTV_RTOBASE * (tcp_syn_backoff[sc->sc_rxmits]);
397 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) {
398 sch->sch_nextc = sc->sc_rxttime;
400 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks,
401 syncache_timer, (void *)sch);
406 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted.
407 * If we have retransmitted an entry the maximum number of times, expire it.
408 * One separate timer for each bucket row.
411 syncache_timer(void *xsch)
413 struct syncache_head *sch = (struct syncache_head *)xsch;
414 struct syncache *sc, *nsc;
418 CURVNET_SET(sch->sch_sc->vnet);
420 /* NB: syncache_head has already been locked by the callout. */
421 SCH_LOCK_ASSERT(sch);
424 * In the following cycle we may remove some entries and/or
425 * advance some timeouts, so re-initialize the bucket timer.
427 sch->sch_nextc = tick + INT_MAX;
429 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) {
431 * We do not check if the listen socket still exists
432 * and accept the case where the listen socket may be
433 * gone by the time we resend the SYN/ACK. We do
434 * not expect this to happens often. If it does,
435 * then the RST will be sent by the time the remote
436 * host does the SYN/ACK->ACK.
438 if (TSTMP_GT(sc->sc_rxttime, tick)) {
439 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc))
440 sch->sch_nextc = sc->sc_rxttime;
443 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) {
444 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
445 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, "
446 "giving up and removing syncache entry\n",
450 syncache_drop(sc, sch);
451 TCPSTAT_INC(tcps_sc_stale);
454 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
455 log(LOG_DEBUG, "%s; %s: Response timeout, "
456 "retransmitting (%u) SYN|ACK\n",
457 s, __func__, sc->sc_rxmits);
461 syncache_respond(sc, sch, 1, NULL);
462 TCPSTAT_INC(tcps_sc_retransmitted);
463 syncache_timeout(sc, sch, 0);
465 if (!TAILQ_EMPTY(&(sch)->sch_bucket))
466 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick,
467 syncache_timer, (void *)(sch));
472 * Find an entry in the syncache.
473 * Returns always with locked syncache_head plus a matching entry or NULL.
475 static struct syncache *
476 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp)
479 struct syncache_head *sch;
483 * The hash is built on foreign port + local port + foreign address.
484 * We rely on the fact that struct in_conninfo starts with 16 bits
485 * of foreign port, then 16 bits of local port then followed by 128
486 * bits of foreign address. In case of IPv4 address, the first 3
487 * 32-bit words of the address always are zeroes.
489 hash = jenkins_hash32((uint32_t *)&inc->inc_ie, 5,
490 V_tcp_syncache.hash_secret) & V_tcp_syncache.hashmask;
492 sch = &V_tcp_syncache.hashbase[hash];
496 /* Circle through bucket row to find matching entry. */
497 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash)
498 if (bcmp(&inc->inc_ie, &sc->sc_inc.inc_ie,
499 sizeof(struct in_endpoints)) == 0)
502 return (sc); /* Always returns with locked sch. */
506 * This function is called when we get a RST for a
507 * non-existent connection, so that we can see if the
508 * connection is in the syn cache. If it is, zap it.
511 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th)
514 struct syncache_head *sch;
517 sc = syncache_lookup(inc, &sch); /* returns locked sch */
518 SCH_LOCK_ASSERT(sch);
521 * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags.
522 * See RFC 793 page 65, section SEGMENT ARRIVES.
524 if (th->th_flags & (TH_ACK|TH_SYN|TH_FIN)) {
525 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
526 log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or "
527 "FIN flag set, segment ignored\n", s, __func__);
528 TCPSTAT_INC(tcps_badrst);
533 * No corresponding connection was found in syncache.
534 * If syncookies are enabled and possibly exclusively
535 * used, or we are under memory pressure, a valid RST
536 * may not find a syncache entry. In that case we're
537 * done and no SYN|ACK retransmissions will happen.
538 * Otherwise the RST was misdirected or spoofed.
541 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
542 log(LOG_DEBUG, "%s; %s: Spurious RST without matching "
543 "syncache entry (possibly syncookie only), "
544 "segment ignored\n", s, __func__);
545 TCPSTAT_INC(tcps_badrst);
550 * If the RST bit is set, check the sequence number to see
551 * if this is a valid reset segment.
553 * In all states except SYN-SENT, all reset (RST) segments
554 * are validated by checking their SEQ-fields. A reset is
555 * valid if its sequence number is in the window.
557 * The sequence number in the reset segment is normally an
558 * echo of our outgoing acknowlegement numbers, but some hosts
559 * send a reset with the sequence number at the rightmost edge
560 * of our receive window, and we have to handle this case.
562 if (SEQ_GEQ(th->th_seq, sc->sc_irs) &&
563 SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
564 syncache_drop(sc, sch);
565 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
566 log(LOG_DEBUG, "%s; %s: Our SYN|ACK was rejected, "
567 "connection attempt aborted by remote endpoint\n",
569 TCPSTAT_INC(tcps_sc_reset);
571 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
572 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != "
573 "IRS %u (+WND %u), segment ignored\n",
574 s, __func__, th->th_seq, sc->sc_irs, sc->sc_wnd);
575 TCPSTAT_INC(tcps_badrst);
585 syncache_badack(struct in_conninfo *inc)
588 struct syncache_head *sch;
590 sc = syncache_lookup(inc, &sch); /* returns locked sch */
591 SCH_LOCK_ASSERT(sch);
593 syncache_drop(sc, sch);
594 TCPSTAT_INC(tcps_sc_badack);
600 syncache_unreach(struct in_conninfo *inc, struct tcphdr *th)
603 struct syncache_head *sch;
605 sc = syncache_lookup(inc, &sch); /* returns locked sch */
606 SCH_LOCK_ASSERT(sch);
610 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */
611 if (ntohl(th->th_seq) != sc->sc_iss)
615 * If we've rertransmitted 3 times and this is our second error,
616 * we remove the entry. Otherwise, we allow it to continue on.
617 * This prevents us from incorrectly nuking an entry during a
618 * spurious network outage.
622 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) {
623 sc->sc_flags |= SCF_UNREACH;
626 syncache_drop(sc, sch);
627 TCPSTAT_INC(tcps_sc_unreach);
633 * Build a new TCP socket structure from a syncache entry.
635 * On success return the newly created socket with its underlying inp locked.
637 static struct socket *
638 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m)
640 struct tcp_function_block *blk;
641 struct inpcb *inp = NULL;
647 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
650 * Ok, create the full blown connection, and set things up
651 * as they would have been set up if we had created the
652 * connection when the SYN arrived. If we can't create
653 * the connection, abort it.
655 so = sonewconn(lso, 0);
658 * Drop the connection; we will either send a RST or
659 * have the peer retransmit its SYN again after its
662 TCPSTAT_INC(tcps_listendrop);
663 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
664 log(LOG_DEBUG, "%s; %s: Socket create failed "
665 "due to limits or memory shortage\n",
672 mac_socketpeer_set_from_mbuf(m, so);
676 inp->inp_inc.inc_fibnum = so->so_fibnum;
679 * Exclusive pcbinfo lock is not required in syncache socket case even
680 * if two inpcb locks can be acquired simultaneously:
681 * - the inpcb in LISTEN state,
682 * - the newly created inp.
684 * In this case, an inp cannot be at same time in LISTEN state and
685 * just created by an accept() call.
687 INP_HASH_WLOCK(&V_tcbinfo);
689 /* Insert new socket into PCB hash list. */
690 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags;
692 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
693 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
695 inp->inp_vflag &= ~INP_IPV6;
696 inp->inp_vflag |= INP_IPV4;
698 inp->inp_laddr = sc->sc_inc.inc_laddr;
704 * If there's an mbuf and it has a flowid, then let's initialise the
705 * inp with that particular flowid.
707 if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) {
708 inp->inp_flowid = m->m_pkthdr.flowid;
709 inp->inp_flowtype = M_HASHTYPE_GET(m);
713 * Install in the reservation hash table for now, but don't yet
714 * install a connection group since the full 4-tuple isn't yet
717 inp->inp_lport = sc->sc_inc.inc_lport;
718 if ((error = in_pcbinshash_nopcbgroup(inp)) != 0) {
720 * Undo the assignments above if we failed to
721 * put the PCB on the hash lists.
724 if (sc->sc_inc.inc_flags & INC_ISIPV6)
725 inp->in6p_laddr = in6addr_any;
728 inp->inp_laddr.s_addr = INADDR_ANY;
730 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
731 log(LOG_DEBUG, "%s; %s: in_pcbinshash failed "
736 INP_HASH_WUNLOCK(&V_tcbinfo);
740 /* Copy old policy into new socket's. */
741 if (ipsec_copy_policy(sotoinpcb(lso)->inp_sp, inp->inp_sp))
742 printf("syncache_socket: could not copy policy\n");
745 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
746 struct inpcb *oinp = sotoinpcb(lso);
747 struct in6_addr laddr6;
748 struct sockaddr_in6 sin6;
750 * Inherit socket options from the listening socket.
751 * Note that in6p_inputopts are not (and should not be)
752 * copied, since it stores previously received options and is
753 * used to detect if each new option is different than the
754 * previous one and hence should be passed to a user.
755 * If we copied in6p_inputopts, a user would not be able to
756 * receive options just after calling the accept system call.
758 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS;
759 if (oinp->in6p_outputopts)
760 inp->in6p_outputopts =
761 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT);
763 sin6.sin6_family = AF_INET6;
764 sin6.sin6_len = sizeof(sin6);
765 sin6.sin6_addr = sc->sc_inc.inc6_faddr;
766 sin6.sin6_port = sc->sc_inc.inc_fport;
767 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0;
768 laddr6 = inp->in6p_laddr;
769 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr))
770 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
771 if ((error = in6_pcbconnect_mbuf(inp, (struct sockaddr *)&sin6,
772 thread0.td_ucred, m)) != 0) {
773 inp->in6p_laddr = laddr6;
774 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
775 log(LOG_DEBUG, "%s; %s: in6_pcbconnect failed "
780 INP_HASH_WUNLOCK(&V_tcbinfo);
783 /* Override flowlabel from in6_pcbconnect. */
784 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK;
785 inp->inp_flow |= sc->sc_flowlabel;
788 #if defined(INET) && defined(INET6)
793 struct in_addr laddr;
794 struct sockaddr_in sin;
796 inp->inp_options = (m) ? ip_srcroute(m) : NULL;
798 if (inp->inp_options == NULL) {
799 inp->inp_options = sc->sc_ipopts;
800 sc->sc_ipopts = NULL;
803 sin.sin_family = AF_INET;
804 sin.sin_len = sizeof(sin);
805 sin.sin_addr = sc->sc_inc.inc_faddr;
806 sin.sin_port = sc->sc_inc.inc_fport;
807 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero));
808 laddr = inp->inp_laddr;
809 if (inp->inp_laddr.s_addr == INADDR_ANY)
810 inp->inp_laddr = sc->sc_inc.inc_laddr;
811 if ((error = in_pcbconnect_mbuf(inp, (struct sockaddr *)&sin,
812 thread0.td_ucred, m)) != 0) {
813 inp->inp_laddr = laddr;
814 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
815 log(LOG_DEBUG, "%s; %s: in_pcbconnect failed "
820 INP_HASH_WUNLOCK(&V_tcbinfo);
825 INP_HASH_WUNLOCK(&V_tcbinfo);
827 tcp_state_change(tp, TCPS_SYN_RECEIVED);
828 tp->iss = sc->sc_iss;
829 tp->irs = sc->sc_irs;
832 blk = sototcpcb(lso)->t_fb;
833 if (blk != tp->t_fb) {
835 * Our parents t_fb was not the default,
836 * we need to release our ref on tp->t_fb and
837 * pickup one on the new entry.
839 struct tcp_function_block *rblk;
841 rblk = find_and_ref_tcp_fb(blk);
842 KASSERT(rblk != NULL,
843 ("cannot find blk %p out of syncache?", blk));
844 if (tp->t_fb->tfb_tcp_fb_fini)
845 (*tp->t_fb->tfb_tcp_fb_fini)(tp, 0);
846 refcount_release(&tp->t_fb->tfb_refcnt);
848 if (tp->t_fb->tfb_tcp_fb_init) {
849 (*tp->t_fb->tfb_tcp_fb_init)(tp);
852 tp->snd_wl1 = sc->sc_irs;
853 tp->snd_max = tp->iss + 1;
854 tp->snd_nxt = tp->iss + 1;
855 tp->rcv_up = sc->sc_irs + 1;
856 tp->rcv_wnd = sc->sc_wnd;
857 tp->rcv_adv += tp->rcv_wnd;
858 tp->last_ack_sent = tp->rcv_nxt;
860 tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY);
861 if (sc->sc_flags & SCF_NOOPT)
862 tp->t_flags |= TF_NOOPT;
864 if (sc->sc_flags & SCF_WINSCALE) {
865 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE;
866 tp->snd_scale = sc->sc_requested_s_scale;
867 tp->request_r_scale = sc->sc_requested_r_scale;
869 if (sc->sc_flags & SCF_TIMESTAMP) {
870 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP;
871 tp->ts_recent = sc->sc_tsreflect;
872 tp->ts_recent_age = tcp_ts_getticks();
873 tp->ts_offset = sc->sc_tsoff;
876 if (sc->sc_flags & SCF_SIGNATURE)
877 tp->t_flags |= TF_SIGNATURE;
879 if (sc->sc_flags & SCF_SACK)
880 tp->t_flags |= TF_SACK_PERMIT;
883 if (sc->sc_flags & SCF_ECN)
884 tp->t_flags |= TF_ECN_PERMIT;
887 * Set up MSS and get cached values from tcp_hostcache.
888 * This might overwrite some of the defaults we just set.
890 tcp_mss(tp, sc->sc_peer_mss);
893 * If the SYN,ACK was retransmitted, indicate that CWND to be
894 * limited to one segment in cc_conn_init().
895 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits.
897 if (sc->sc_rxmits > 1)
902 * Allow a TOE driver to install its hooks. Note that we hold the
903 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a
904 * new connection before the TOE driver has done its thing.
906 if (ADDED_BY_TOE(sc)) {
907 struct toedev *tod = sc->sc_tod;
909 tod->tod_offload_socket(tod, sc->sc_todctx, so);
913 * Copy and activate timers.
915 tp->t_keepinit = sototcpcb(lso)->t_keepinit;
916 tp->t_keepidle = sototcpcb(lso)->t_keepidle;
917 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl;
918 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt;
919 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp));
923 TCPSTAT_INC(tcps_accepts);
935 * This function gets called when we receive an ACK for a
936 * socket in the LISTEN state. We look up the connection
937 * in the syncache, and if its there, we pull it out of
938 * the cache and turn it into a full-blown connection in
939 * the SYN-RECEIVED state.
941 * On syncache_socket() success the newly created socket
942 * has its underlying inp locked.
945 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
946 struct socket **lsop, struct mbuf *m)
949 struct syncache_head *sch;
954 * Global TCP locks are held because we manipulate the PCB lists
955 * and create a new socket.
957 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
958 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK,
959 ("%s: can handle only ACK", __func__));
961 sc = syncache_lookup(inc, &sch); /* returns locked sch */
962 SCH_LOCK_ASSERT(sch);
966 * Test code for syncookies comparing the syncache stored
967 * values with the reconstructed values from the cookie.
970 syncookie_cmp(inc, sch, sc, th, to, *lsop);
975 * There is no syncache entry, so see if this ACK is
976 * a returning syncookie. To do this, first:
977 * A. See if this socket has had a syncache entry dropped in
978 * the past. We don't want to accept a bogus syncookie
979 * if we've never received a SYN.
980 * B. check that the syncookie is valid. If it is, then
981 * cobble up a fake syncache entry, and return.
983 if (!V_tcp_syncookies) {
985 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
986 log(LOG_DEBUG, "%s; %s: Spurious ACK, "
987 "segment rejected (syncookies disabled)\n",
991 bzero(&scs, sizeof(scs));
992 sc = syncookie_lookup(inc, sch, &scs, th, to, *lsop);
995 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
996 log(LOG_DEBUG, "%s; %s: Segment failed "
997 "SYNCOOKIE authentication, segment rejected "
998 "(probably spoofed)\n", s, __func__);
1003 * Pull out the entry to unlock the bucket row.
1005 * NOTE: We must decrease TCPS_SYN_RECEIVED count here, not
1006 * tcp_state_change(). The tcpcb is not existent at this
1007 * moment. A new one will be allocated via syncache_socket->
1008 * sonewconn->tcp_usr_attach in TCPS_CLOSED state, then
1009 * syncache_socket() will change it to TCPS_SYN_RECEIVED.
1011 TCPSTATES_DEC(TCPS_SYN_RECEIVED);
1012 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
1015 if (ADDED_BY_TOE(sc)) {
1016 struct toedev *tod = sc->sc_tod;
1018 tod->tod_syncache_removed(tod, sc->sc_todctx);
1025 * Segment validation:
1026 * ACK must match our initial sequence number + 1 (the SYN|ACK).
1028 if (th->th_ack != sc->sc_iss + 1) {
1029 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1030 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment "
1031 "rejected\n", s, __func__, th->th_ack, sc->sc_iss);
1036 * The SEQ must fall in the window starting at the received
1037 * initial receive sequence number + 1 (the SYN).
1039 if (SEQ_LEQ(th->th_seq, sc->sc_irs) ||
1040 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
1041 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1042 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment "
1043 "rejected\n", s, __func__, th->th_seq, sc->sc_irs);
1048 * If timestamps were not negotiated during SYN/ACK they
1049 * must not appear on any segment during this session.
1051 if (!(sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) {
1052 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1053 log(LOG_DEBUG, "%s; %s: Timestamp not expected, "
1054 "segment rejected\n", s, __func__);
1059 * If timestamps were negotiated during SYN/ACK they should
1060 * appear on every segment during this session.
1061 * XXXAO: This is only informal as there have been unverified
1062 * reports of non-compliants stacks.
1064 if ((sc->sc_flags & SCF_TIMESTAMP) && !(to->to_flags & TOF_TS)) {
1065 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1066 log(LOG_DEBUG, "%s; %s: Timestamp missing, "
1067 "no action\n", s, __func__);
1074 * If timestamps were negotiated the reflected timestamp
1075 * must be equal to what we actually sent in the SYN|ACK.
1077 if ((to->to_flags & TOF_TS) && to->to_tsecr != sc->sc_ts) {
1078 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1079 log(LOG_DEBUG, "%s; %s: TSECR %u != TS %u, "
1080 "segment rejected\n",
1081 s, __func__, to->to_tsecr, sc->sc_ts);
1085 *lsop = syncache_socket(sc, *lsop, m);
1088 TCPSTAT_INC(tcps_sc_aborted);
1090 TCPSTAT_INC(tcps_sc_completed);
1092 /* how do we find the inp for the new socket? */
1097 if (sc != NULL && sc != &scs)
1107 syncache_tfo_expand(struct syncache *sc, struct socket **lsop, struct mbuf *m,
1108 uint64_t response_cookie)
1112 unsigned int *pending_counter;
1115 * Global TCP locks are held because we manipulate the PCB lists
1116 * and create a new socket.
1118 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
1120 pending_counter = intotcpcb(sotoinpcb(*lsop))->t_tfo_pending;
1121 *lsop = syncache_socket(sc, *lsop, m);
1122 if (*lsop == NULL) {
1123 TCPSTAT_INC(tcps_sc_aborted);
1124 atomic_subtract_int(pending_counter, 1);
1126 inp = sotoinpcb(*lsop);
1127 tp = intotcpcb(inp);
1128 tp->t_flags |= TF_FASTOPEN;
1129 tp->t_tfo_cookie = response_cookie;
1130 tp->snd_max = tp->iss;
1131 tp->snd_nxt = tp->iss;
1132 tp->t_tfo_pending = pending_counter;
1133 TCPSTAT_INC(tcps_sc_completed);
1136 #endif /* TCP_RFC7413 */
1139 * Given a LISTEN socket and an inbound SYN request, add
1140 * this to the syn cache, and send back a segment:
1141 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
1144 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN.
1145 * Doing so would require that we hold onto the data and deliver it
1146 * to the application. However, if we are the target of a SYN-flood
1147 * DoS attack, an attacker could send data which would eventually
1148 * consume all available buffer space if it were ACKed. By not ACKing
1149 * the data, we avoid this DoS scenario.
1151 * The exception to the above is when a SYN with a valid TCP Fast Open (TFO)
1152 * cookie is processed, V_tcp_fastopen_enabled set to true, and the
1153 * TCP_FASTOPEN socket option is set. In this case, a new socket is created
1154 * and returned via lsop, the mbuf is not freed so that tcp_input() can
1155 * queue its data to the socket, and 1 is returned to indicate the
1156 * TFO-socket-creation path was taken.
1159 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
1160 struct inpcb *inp, struct socket **lsop, struct mbuf *m, void *tod,
1165 struct syncache *sc = NULL;
1166 struct syncache_head *sch;
1167 struct mbuf *ipopts = NULL;
1169 int win, sb_hiwat, ip_ttl, ip_tos;
1173 int autoflowlabel = 0;
1176 struct label *maclabel;
1178 struct syncache scs;
1181 uint64_t tfo_response_cookie;
1182 int tfo_cookie_valid = 0;
1183 int tfo_response_cookie_valid = 0;
1186 INP_WLOCK_ASSERT(inp); /* listen socket */
1187 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN,
1188 ("%s: unexpected tcp flags", __func__));
1191 * Combine all so/tp operations very early to drop the INP lock as
1196 cred = crhold(so->so_cred);
1199 if ((inc->inc_flags & INC_ISIPV6) &&
1200 (inp->inp_flags & IN6P_AUTOFLOWLABEL))
1203 ip_ttl = inp->inp_ip_ttl;
1204 ip_tos = inp->inp_ip_tos;
1205 win = sbspace(&so->so_rcv);
1206 sb_hiwat = so->so_rcv.sb_hiwat;
1207 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE));
1210 if (V_tcp_fastopen_enabled && (tp->t_flags & TF_FASTOPEN) &&
1211 (tp->t_tfo_pending != NULL) && (to->to_flags & TOF_FASTOPEN)) {
1213 * Limit the number of pending TFO connections to
1214 * approximately half of the queue limit. This prevents TFO
1215 * SYN floods from starving the service by filling the
1216 * listen queue with bogus TFO connections.
1218 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <=
1219 (so->so_qlimit / 2)) {
1222 result = tcp_fastopen_check_cookie(inc,
1223 to->to_tfo_cookie, to->to_tfo_len,
1224 &tfo_response_cookie);
1225 tfo_cookie_valid = (result > 0);
1226 tfo_response_cookie_valid = (result >= 0);
1228 atomic_subtract_int(tp->t_tfo_pending, 1);
1232 /* By the time we drop the lock these should no longer be used. */
1237 if (mac_syncache_init(&maclabel) != 0) {
1241 mac_syncache_create(maclabel, inp);
1244 if (!tfo_cookie_valid)
1249 * Remember the IP options, if any.
1252 if (!(inc->inc_flags & INC_ISIPV6))
1255 ipopts = (m) ? ip_srcroute(m) : NULL;
1261 * See if we already have an entry for this connection.
1262 * If we do, resend the SYN,ACK, and reset the retransmit timer.
1264 * XXX: should the syncache be re-initialized with the contents
1265 * of the new SYN here (which may have different options?)
1267 * XXX: We do not check the sequence number to see if this is a
1268 * real retransmit or a new connection attempt. The question is
1269 * how to handle such a case; either ignore it as spoofed, or
1270 * drop the current entry and create a new one?
1272 sc = syncache_lookup(inc, &sch); /* returns locked entry */
1273 SCH_LOCK_ASSERT(sch);
1276 if (tfo_cookie_valid)
1279 TCPSTAT_INC(tcps_sc_dupsyn);
1282 * If we were remembering a previous source route,
1283 * forget it and use the new one we've been given.
1286 (void) m_free(sc->sc_ipopts);
1287 sc->sc_ipopts = ipopts;
1290 * Update timestamp if present.
1292 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS))
1293 sc->sc_tsreflect = to->to_tsval;
1295 sc->sc_flags &= ~SCF_TIMESTAMP;
1298 * Since we have already unconditionally allocated label
1299 * storage, free it up. The syncache entry will already
1300 * have an initialized label we can use.
1302 mac_syncache_destroy(&maclabel);
1304 /* Retransmit SYN|ACK and reset retransmit count. */
1305 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) {
1306 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, "
1307 "resetting timer and retransmitting SYN|ACK\n",
1311 if (syncache_respond(sc, sch, 1, m) == 0) {
1313 syncache_timeout(sc, sch, 1);
1314 TCPSTAT_INC(tcps_sndacks);
1315 TCPSTAT_INC(tcps_sndtotal);
1322 if (tfo_cookie_valid) {
1323 bzero(&scs, sizeof(scs));
1329 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
1332 * The zone allocator couldn't provide more entries.
1333 * Treat this as if the cache was full; drop the oldest
1334 * entry and insert the new one.
1336 TCPSTAT_INC(tcps_sc_zonefail);
1337 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL)
1338 syncache_drop(sc, sch);
1339 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
1341 if (V_tcp_syncookies) {
1342 bzero(&scs, sizeof(scs));
1347 (void) m_free(ipopts);
1355 if (!tfo_cookie_valid && tfo_response_cookie_valid)
1356 sc->sc_tfo_cookie = &tfo_response_cookie;
1360 * Fill in the syncache values.
1363 sc->sc_label = maclabel;
1367 sc->sc_ipopts = ipopts;
1368 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
1370 if (!(inc->inc_flags & INC_ISIPV6))
1373 sc->sc_ip_tos = ip_tos;
1374 sc->sc_ip_ttl = ip_ttl;
1378 sc->sc_todctx = todctx;
1380 sc->sc_irs = th->th_seq;
1381 sc->sc_iss = arc4random();
1383 sc->sc_flowlabel = 0;
1386 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN].
1387 * win was derived from socket earlier in the function.
1390 win = imin(win, TCP_MAXWIN);
1393 if (V_tcp_do_rfc1323) {
1395 * A timestamp received in a SYN makes
1396 * it ok to send timestamp requests and replies.
1398 if (to->to_flags & TOF_TS) {
1399 sc->sc_tsreflect = to->to_tsval;
1400 sc->sc_ts = tcp_ts_getticks();
1401 sc->sc_flags |= SCF_TIMESTAMP;
1403 if (to->to_flags & TOF_SCALE) {
1407 * Pick the smallest possible scaling factor that
1408 * will still allow us to scale up to sb_max, aka
1409 * kern.ipc.maxsockbuf.
1411 * We do this because there are broken firewalls that
1412 * will corrupt the window scale option, leading to
1413 * the other endpoint believing that our advertised
1414 * window is unscaled. At scale factors larger than
1415 * 5 the unscaled window will drop below 1500 bytes,
1416 * leading to serious problems when traversing these
1419 * With the default maxsockbuf of 256K, a scale factor
1420 * of 3 will be chosen by this algorithm. Those who
1421 * choose a larger maxsockbuf should watch out
1422 * for the compatibility problems mentioned above.
1424 * RFC1323: The Window field in a SYN (i.e., a <SYN>
1425 * or <SYN,ACK>) segment itself is never scaled.
1427 while (wscale < TCP_MAX_WINSHIFT &&
1428 (TCP_MAXWIN << wscale) < sb_max)
1430 sc->sc_requested_r_scale = wscale;
1431 sc->sc_requested_s_scale = to->to_wscale;
1432 sc->sc_flags |= SCF_WINSCALE;
1435 #ifdef TCP_SIGNATURE
1437 * If listening socket requested TCP digests, OR received SYN
1438 * contains the option, flag this in the syncache so that
1439 * syncache_respond() will do the right thing with the SYN+ACK.
1441 if (to->to_flags & TOF_SIGNATURE || ltflags & TF_SIGNATURE)
1442 sc->sc_flags |= SCF_SIGNATURE;
1444 if (to->to_flags & TOF_SACKPERM)
1445 sc->sc_flags |= SCF_SACK;
1446 if (to->to_flags & TOF_MSS)
1447 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */
1448 if (ltflags & TF_NOOPT)
1449 sc->sc_flags |= SCF_NOOPT;
1450 if ((th->th_flags & (TH_ECE|TH_CWR)) && V_tcp_do_ecn)
1451 sc->sc_flags |= SCF_ECN;
1453 if (V_tcp_syncookies)
1454 sc->sc_iss = syncookie_generate(sch, sc);
1456 if (autoflowlabel) {
1457 if (V_tcp_syncookies)
1458 sc->sc_flowlabel = sc->sc_iss;
1460 sc->sc_flowlabel = ip6_randomflowlabel();
1461 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK;
1467 if (tfo_cookie_valid) {
1468 syncache_tfo_expand(sc, lsop, m, tfo_response_cookie);
1469 /* INP_WUNLOCK(inp) will be performed by the called */
1476 * Do a standard 3-way handshake.
1478 if (syncache_respond(sc, sch, 0, m) == 0) {
1479 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs)
1481 else if (sc != &scs)
1482 syncache_insert(sc, sch); /* locks and unlocks sch */
1483 TCPSTAT_INC(tcps_sndacks);
1484 TCPSTAT_INC(tcps_sndtotal);
1488 TCPSTAT_INC(tcps_sc_dropped);
1503 mac_syncache_destroy(&maclabel);
1509 * Send SYN|ACK to the peer. Either in response to the peer's SYN,
1510 * i.e. m0 != NULL, or upon 3WHS ACK timeout, i.e. m0 == NULL.
1513 syncache_respond(struct syncache *sc, struct syncache_head *sch, int locked,
1514 const struct mbuf *m0)
1516 struct ip *ip = NULL;
1518 struct tcphdr *th = NULL;
1519 int optlen, error = 0; /* Make compiler happy */
1520 u_int16_t hlen, tlen, mssopt;
1523 struct ip6_hdr *ip6 = NULL;
1525 #ifdef TCP_SIGNATURE
1526 struct secasvar *sav;
1531 (sc->sc_inc.inc_flags & INC_ISIPV6) ? sizeof(struct ip6_hdr) :
1534 tlen = hlen + sizeof(struct tcphdr);
1536 /* Determine MSS we advertize to other end of connection. */
1537 mssopt = tcp_mssopt(&sc->sc_inc);
1538 if (sc->sc_peer_mss)
1539 mssopt = max( min(sc->sc_peer_mss, mssopt), V_tcp_minmss);
1541 /* XXX: Assume that the entire packet will fit in a header mbuf. */
1542 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN,
1543 ("syncache: mbuf too small"));
1545 /* Create the IP+TCP header from scratch. */
1546 m = m_gethdr(M_NOWAIT, MT_DATA);
1550 mac_syncache_create_mbuf(sc->sc_label, m);
1552 m->m_data += max_linkhdr;
1554 m->m_pkthdr.len = tlen;
1555 m->m_pkthdr.rcvif = NULL;
1558 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
1559 ip6 = mtod(m, struct ip6_hdr *);
1560 ip6->ip6_vfc = IPV6_VERSION;
1561 ip6->ip6_nxt = IPPROTO_TCP;
1562 ip6->ip6_src = sc->sc_inc.inc6_laddr;
1563 ip6->ip6_dst = sc->sc_inc.inc6_faddr;
1564 ip6->ip6_plen = htons(tlen - hlen);
1565 /* ip6_hlim is set after checksum */
1566 ip6->ip6_flow &= ~IPV6_FLOWLABEL_MASK;
1567 ip6->ip6_flow |= sc->sc_flowlabel;
1569 th = (struct tcphdr *)(ip6 + 1);
1572 #if defined(INET6) && defined(INET)
1577 ip = mtod(m, struct ip *);
1578 ip->ip_v = IPVERSION;
1579 ip->ip_hl = sizeof(struct ip) >> 2;
1580 ip->ip_len = htons(tlen);
1584 ip->ip_p = IPPROTO_TCP;
1585 ip->ip_src = sc->sc_inc.inc_laddr;
1586 ip->ip_dst = sc->sc_inc.inc_faddr;
1587 ip->ip_ttl = sc->sc_ip_ttl;
1588 ip->ip_tos = sc->sc_ip_tos;
1591 * See if we should do MTU discovery. Route lookups are
1592 * expensive, so we will only unset the DF bit if:
1594 * 1) path_mtu_discovery is disabled
1595 * 2) the SCF_UNREACH flag has been set
1597 if (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0))
1598 ip->ip_off |= htons(IP_DF);
1600 th = (struct tcphdr *)(ip + 1);
1603 th->th_sport = sc->sc_inc.inc_lport;
1604 th->th_dport = sc->sc_inc.inc_fport;
1606 th->th_seq = htonl(sc->sc_iss);
1607 th->th_ack = htonl(sc->sc_irs + 1);
1608 th->th_off = sizeof(struct tcphdr) >> 2;
1610 th->th_flags = TH_SYN|TH_ACK;
1611 th->th_win = htons(sc->sc_wnd);
1614 if (sc->sc_flags & SCF_ECN) {
1615 th->th_flags |= TH_ECE;
1616 TCPSTAT_INC(tcps_ecn_shs);
1619 /* Tack on the TCP options. */
1620 if ((sc->sc_flags & SCF_NOOPT) == 0) {
1624 to.to_flags = TOF_MSS;
1625 if (sc->sc_flags & SCF_WINSCALE) {
1626 to.to_wscale = sc->sc_requested_r_scale;
1627 to.to_flags |= TOF_SCALE;
1629 if (sc->sc_flags & SCF_TIMESTAMP) {
1630 /* Virgin timestamp or TCP cookie enhanced one. */
1631 to.to_tsval = sc->sc_ts;
1632 to.to_tsecr = sc->sc_tsreflect;
1633 to.to_flags |= TOF_TS;
1635 if (sc->sc_flags & SCF_SACK)
1636 to.to_flags |= TOF_SACKPERM;
1637 #ifdef TCP_SIGNATURE
1639 if (sc->sc_flags & SCF_SIGNATURE) {
1640 sav = tcp_get_sav(m, IPSEC_DIR_OUTBOUND);
1642 to.to_flags |= TOF_SIGNATURE;
1646 * We've got SCF_SIGNATURE flag
1647 * inherited from listening socket,
1648 * but no SADB key for given source
1649 * address. Assume signature is not
1650 * required and remove signature flag
1651 * instead of silently dropping
1656 sc->sc_flags &= ~SCF_SIGNATURE;
1664 if (sc->sc_tfo_cookie) {
1665 to.to_flags |= TOF_FASTOPEN;
1666 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN;
1667 to.to_tfo_cookie = sc->sc_tfo_cookie;
1668 /* don't send cookie again when retransmitting response */
1669 sc->sc_tfo_cookie = NULL;
1672 optlen = tcp_addoptions(&to, (u_char *)(th + 1));
1674 /* Adjust headers by option size. */
1675 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
1677 m->m_pkthdr.len += optlen;
1679 #ifdef TCP_SIGNATURE
1680 if (sc->sc_flags & SCF_SIGNATURE)
1681 tcp_signature_do_compute(m, 0, optlen,
1682 to.to_signature, sav);
1685 if (sc->sc_inc.inc_flags & INC_ISIPV6)
1686 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen);
1689 ip->ip_len = htons(ntohs(ip->ip_len) + optlen);
1693 M_SETFIB(m, sc->sc_inc.inc_fibnum);
1694 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
1696 * If we have peer's SYN and it has a flowid, then let's assign it to
1697 * our SYN|ACK. ip6_output() and ip_output() will not assign flowid
1698 * to SYN|ACK due to lack of inp here.
1700 if (m0 != NULL && M_HASHTYPE_GET(m0) != M_HASHTYPE_NONE) {
1701 m->m_pkthdr.flowid = m0->m_pkthdr.flowid;
1702 M_HASHTYPE_SET(m, M_HASHTYPE_GET(m0));
1705 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
1706 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
1707 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen,
1709 ip6->ip6_hlim = in6_selecthlim(NULL, NULL);
1711 if (ADDED_BY_TOE(sc)) {
1712 struct toedev *tod = sc->sc_tod;
1714 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
1719 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL);
1722 #if defined(INET6) && defined(INET)
1727 m->m_pkthdr.csum_flags = CSUM_TCP;
1728 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
1729 htons(tlen + optlen - hlen + IPPROTO_TCP));
1731 if (ADDED_BY_TOE(sc)) {
1732 struct toedev *tod = sc->sc_tod;
1734 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
1739 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL);
1746 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks
1747 * that exceed the capacity of the syncache by avoiding the storage of any
1748 * of the SYNs we receive. Syncookies defend against blind SYN flooding
1749 * attacks where the attacker does not have access to our responses.
1751 * Syncookies encode and include all necessary information about the
1752 * connection setup within the SYN|ACK that we send back. That way we
1753 * can avoid keeping any local state until the ACK to our SYN|ACK returns
1754 * (if ever). Normally the syncache and syncookies are running in parallel
1755 * with the latter taking over when the former is exhausted. When matching
1756 * syncache entry is found the syncookie is ignored.
1758 * The only reliable information persisting the 3WHS is our initial sequence
1759 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient
1760 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS
1761 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK
1762 * returns and signifies a legitimate connection if it matches the ACK.
1764 * The available space of 32 bits to store the hash and to encode the SYN
1765 * option information is very tight and we should have at least 24 bits for
1766 * the MAC to keep the number of guesses by blind spoofing reasonably high.
1768 * SYN option information we have to encode to fully restore a connection:
1769 * MSS: is imporant to chose an optimal segment size to avoid IP level
1770 * fragmentation along the path. The common MSS values can be encoded
1771 * in a 3-bit table. Uncommon values are captured by the next lower value
1772 * in the table leading to a slight increase in packetization overhead.
1773 * WSCALE: is necessary to allow large windows to be used for high delay-
1774 * bandwidth product links. Not scaling the window when it was initially
1775 * negotiated is bad for performance as lack of scaling further decreases
1776 * the apparent available send window. We only need to encode the WSCALE
1777 * we received from the remote end. Our end can be recalculated at any
1778 * time. The common WSCALE values can be encoded in a 3-bit table.
1779 * Uncommon values are captured by the next lower value in the table
1780 * making us under-estimate the available window size halving our
1781 * theoretically possible maximum throughput for that connection.
1782 * SACK: Greatly assists in packet loss recovery and requires 1 bit.
1783 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options
1784 * that are included in all segments on a connection. We enable them when
1787 * Security of syncookies and attack vectors:
1789 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod)
1790 * together with the gloabl secret to make it unique per connection attempt.
1791 * Thus any change of any of those parameters results in a different MAC output
1792 * in an unpredictable way unless a collision is encountered. 24 bits of the
1793 * MAC are embedded into the ISS.
1795 * To prevent replay attacks two rotating global secrets are updated with a
1796 * new random value every 15 seconds. The life-time of a syncookie is thus
1799 * Vector 1: Attacking the secret. This requires finding a weakness in the
1800 * MAC itself or the way it is used here. The attacker can do a chosen plain
1801 * text attack by varying and testing the all parameters under his control.
1802 * The strength depends on the size and randomness of the secret, and the
1803 * cryptographic security of the MAC function. Due to the constant updating
1804 * of the secret the attacker has at most 29.999 seconds to find the secret
1805 * and launch spoofed connections. After that he has to start all over again.
1807 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC
1808 * size an average of 4,823 attempts are required for a 50% chance of success
1809 * to spoof a single syncookie (birthday collision paradox). However the
1810 * attacker is blind and doesn't know if one of his attempts succeeded unless
1811 * he has a side channel to interfere success from. A single connection setup
1812 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets.
1813 * This many attempts are required for each one blind spoofed connection. For
1814 * every additional spoofed connection he has to launch another N attempts.
1815 * Thus for a sustained rate 100 spoofed connections per second approximately
1816 * 1,800,000 packets per second would have to be sent.
1818 * NB: The MAC function should be fast so that it doesn't become a CPU
1819 * exhaustion attack vector itself.
1822 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations
1823 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996
1824 * http://cr.yp.to/syncookies.html (overview)
1825 * http://cr.yp.to/syncookies/archive (details)
1828 * Schematic construction of a syncookie enabled Initial Sequence Number:
1830 * 12345678901234567890123456789012
1831 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP|
1833 * x 24 MAC (truncated)
1834 * W 3 Send Window Scale index
1836 * S 1 SACK permitted
1837 * P 1 Odd/even secret
1841 * Distribution and probability of certain MSS values. Those in between are
1842 * rounded down to the next lower one.
1843 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011]
1844 * .2% .3% 5% 7% 7% 20% 15% 45%
1846 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 };
1849 * Distribution and probability of certain WSCALE values. We have to map the
1850 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3
1851 * bits based on prevalence of certain values. Where we don't have an exact
1852 * match for are rounded down to the next lower one letting us under-estimate
1853 * the true available window. At the moment this would happen only for the
1854 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer
1855 * and window size). The absence of the WSCALE option (no scaling in either
1856 * direction) is encoded with index zero.
1857 * [WSCALE values histograms, Allman, 2012]
1858 * X 10 10 35 5 6 14 10% by host
1859 * X 11 4 5 5 18 49 3% by connections
1861 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 };
1864 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed
1865 * and good cryptographic properties.
1868 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags,
1869 uint8_t *secbits, uintptr_t secmod)
1872 uint32_t siphash[2];
1874 SipHash24_Init(&ctx);
1875 SipHash_SetKey(&ctx, secbits);
1876 switch (inc->inc_flags & INC_ISIPV6) {
1879 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr));
1880 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr));
1885 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr));
1886 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr));
1890 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport));
1891 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport));
1892 SipHash_Update(&ctx, &irs, sizeof(irs));
1893 SipHash_Update(&ctx, &flags, sizeof(flags));
1894 SipHash_Update(&ctx, &secmod, sizeof(secmod));
1895 SipHash_Final((u_int8_t *)&siphash, &ctx);
1897 return (siphash[0] ^ siphash[1]);
1901 syncookie_generate(struct syncache_head *sch, struct syncache *sc)
1903 u_int i, mss, secbit, wscale;
1906 union syncookie cookie;
1908 SCH_LOCK_ASSERT(sch);
1912 /* Map our computed MSS into the 3-bit index. */
1913 mss = min(tcp_mssopt(&sc->sc_inc), max(sc->sc_peer_mss, V_tcp_minmss));
1914 for (i = nitems(tcp_sc_msstab) - 1; tcp_sc_msstab[i] > mss && i > 0;
1917 cookie.flags.mss_idx = i;
1920 * Map the send window scale into the 3-bit index but only if
1921 * the wscale option was received.
1923 if (sc->sc_flags & SCF_WINSCALE) {
1924 wscale = sc->sc_requested_s_scale;
1925 for (i = nitems(tcp_sc_wstab) - 1;
1926 tcp_sc_wstab[i] > wscale && i > 0;
1929 cookie.flags.wscale_idx = i;
1932 /* Can we do SACK? */
1933 if (sc->sc_flags & SCF_SACK)
1934 cookie.flags.sack_ok = 1;
1936 /* Which of the two secrets to use. */
1937 secbit = sch->sch_sc->secret.oddeven & 0x1;
1938 cookie.flags.odd_even = secbit;
1940 secbits = sch->sch_sc->secret.key[secbit];
1941 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits,
1945 * Put the flags into the hash and XOR them to get better ISS number
1946 * variance. This doesn't enhance the cryptographic strength and is
1947 * done to prevent the 8 cookie bits from showing up directly on the
1951 iss |= cookie.cookie ^ (hash >> 24);
1953 /* Randomize the timestamp. */
1954 if (sc->sc_flags & SCF_TIMESTAMP) {
1955 sc->sc_ts = arc4random();
1956 sc->sc_tsoff = sc->sc_ts - tcp_ts_getticks();
1959 TCPSTAT_INC(tcps_sc_sendcookie);
1963 static struct syncache *
1964 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch,
1965 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
1971 int wnd, wscale = 0;
1972 union syncookie cookie;
1974 SCH_LOCK_ASSERT(sch);
1977 * Pull information out of SYN-ACK/ACK and revert sequence number
1980 ack = th->th_ack - 1;
1981 seq = th->th_seq - 1;
1984 * Unpack the flags containing enough information to restore the
1987 cookie.cookie = (ack & 0xff) ^ (ack >> 24);
1989 /* Which of the two secrets to use. */
1990 secbits = sch->sch_sc->secret.key[cookie.flags.odd_even];
1992 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch);
1994 /* The recomputed hash matches the ACK if this was a genuine cookie. */
1995 if ((ack & ~0xff) != (hash & ~0xff))
1998 /* Fill in the syncache values. */
2000 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
2001 sc->sc_ipopts = NULL;
2006 switch (inc->inc_flags & INC_ISIPV6) {
2009 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl;
2010 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos;
2015 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL)
2016 sc->sc_flowlabel = sc->sc_iss & IPV6_FLOWLABEL_MASK;
2021 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx];
2023 /* We can simply recompute receive window scale we sent earlier. */
2024 while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max)
2027 /* Only use wscale if it was enabled in the orignal SYN. */
2028 if (cookie.flags.wscale_idx > 0) {
2029 sc->sc_requested_r_scale = wscale;
2030 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx];
2031 sc->sc_flags |= SCF_WINSCALE;
2034 wnd = sbspace(&lso->so_rcv);
2036 wnd = imin(wnd, TCP_MAXWIN);
2039 if (cookie.flags.sack_ok)
2040 sc->sc_flags |= SCF_SACK;
2042 if (to->to_flags & TOF_TS) {
2043 sc->sc_flags |= SCF_TIMESTAMP;
2044 sc->sc_tsreflect = to->to_tsval;
2045 sc->sc_ts = to->to_tsecr;
2046 sc->sc_tsoff = to->to_tsecr - tcp_ts_getticks();
2049 if (to->to_flags & TOF_SIGNATURE)
2050 sc->sc_flags |= SCF_SIGNATURE;
2054 TCPSTAT_INC(tcps_sc_recvcookie);
2060 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch,
2061 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
2064 struct syncache scs, *scx;
2067 bzero(&scs, sizeof(scs));
2068 scx = syncookie_lookup(inc, sch, &scs, th, to, lso);
2070 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL)
2074 if (sc->sc_peer_mss != scx->sc_peer_mss)
2075 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n",
2076 s, __func__, sc->sc_peer_mss, scx->sc_peer_mss);
2078 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale)
2079 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n",
2080 s, __func__, sc->sc_requested_r_scale,
2081 scx->sc_requested_r_scale);
2083 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale)
2084 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n",
2085 s, __func__, sc->sc_requested_s_scale,
2086 scx->sc_requested_s_scale);
2088 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK))
2089 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__);
2096 #endif /* INVARIANTS */
2099 syncookie_reseed(void *arg)
2101 struct tcp_syncache *sc = arg;
2106 * Reseeding the secret doesn't have to be protected by a lock.
2107 * It only must be ensured that the new random values are visible
2108 * to all CPUs in a SMP environment. The atomic with release
2109 * semantics ensures that.
2111 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1;
2112 secbits = sc->secret.key[secbit];
2113 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0);
2114 atomic_add_rel_int(&sc->secret.oddeven, 1);
2116 /* Reschedule ourself. */
2117 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz);
2121 * Exports the syncache entries to userland so that netstat can display
2122 * them alongside the other sockets. This function is intended to be
2123 * called only from tcp_pcblist.
2125 * Due to concurrency on an active system, the number of pcbs exported
2126 * may have no relation to max_pcbs. max_pcbs merely indicates the
2127 * amount of space the caller allocated for this function to use.
2130 syncache_pcblist(struct sysctl_req *req, int max_pcbs, int *pcbs_exported)
2133 struct syncache *sc;
2134 struct syncache_head *sch;
2135 int count, error, i;
2137 for (count = 0, error = 0, i = 0; i < V_tcp_syncache.hashsize; i++) {
2138 sch = &V_tcp_syncache.hashbase[i];
2140 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
2141 if (count >= max_pcbs) {
2145 if (cr_cansee(req->td->td_ucred, sc->sc_cred) != 0)
2147 bzero(&xt, sizeof(xt));
2148 xt.xt_len = sizeof(xt);
2149 if (sc->sc_inc.inc_flags & INC_ISIPV6)
2150 xt.xt_inp.inp_vflag = INP_IPV6;
2152 xt.xt_inp.inp_vflag = INP_IPV4;
2153 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, sizeof (struct in_conninfo));
2154 xt.xt_tp.t_inpcb = &xt.xt_inp;
2155 xt.xt_tp.t_state = TCPS_SYN_RECEIVED;
2156 xt.xt_socket.xso_protocol = IPPROTO_TCP;
2157 xt.xt_socket.xso_len = sizeof (struct xsocket);
2158 xt.xt_socket.so_type = SOCK_STREAM;
2159 xt.xt_socket.so_state = SS_ISCONNECTING;
2160 error = SYSCTL_OUT(req, &xt, sizeof xt);
2170 *pcbs_exported = count;