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>
43 #include <sys/kernel.h>
44 #include <sys/sysctl.h>
45 #include <sys/limits.h>
47 #include <sys/mutex.h>
48 #include <sys/malloc.h>
50 #include <sys/proc.h> /* for proc0 declaration */
51 #include <sys/random.h>
52 #include <sys/socket.h>
53 #include <sys/socketvar.h>
54 #include <sys/syslog.h>
55 #include <sys/ucred.h>
58 #include <crypto/siphash/siphash.h>
63 #include <net/route.h>
66 #include <netinet/in.h>
67 #include <netinet/in_systm.h>
68 #include <netinet/ip.h>
69 #include <netinet/in_var.h>
70 #include <netinet/in_pcb.h>
71 #include <netinet/ip_var.h>
72 #include <netinet/ip_options.h>
74 #include <netinet/ip6.h>
75 #include <netinet/icmp6.h>
76 #include <netinet6/nd6.h>
77 #include <netinet6/ip6_var.h>
78 #include <netinet6/in6_pcb.h>
80 #include <netinet/tcp.h>
82 #include <netinet/tcp_fastopen.h>
84 #include <netinet/tcp_fsm.h>
85 #include <netinet/tcp_seq.h>
86 #include <netinet/tcp_timer.h>
87 #include <netinet/tcp_var.h>
88 #include <netinet/tcp_syncache.h>
90 #include <netinet6/tcp6_var.h>
93 #include <netinet/toecore.h>
97 #include <netipsec/ipsec.h>
99 #include <netipsec/ipsec6.h>
101 #include <netipsec/key.h>
104 #include <machine/in_cksum.h>
106 #include <security/mac/mac_framework.h>
108 static VNET_DEFINE(int, tcp_syncookies) = 1;
109 #define V_tcp_syncookies VNET(tcp_syncookies)
110 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_RW,
111 &VNET_NAME(tcp_syncookies), 0,
112 "Use TCP SYN cookies if the syncache overflows");
114 static VNET_DEFINE(int, tcp_syncookiesonly) = 0;
115 #define V_tcp_syncookiesonly VNET(tcp_syncookiesonly)
116 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_RW,
117 &VNET_NAME(tcp_syncookiesonly), 0,
118 "Use only TCP SYN cookies");
121 #define ADDED_BY_TOE(sc) ((sc)->sc_tod != NULL)
124 static void syncache_drop(struct syncache *, struct syncache_head *);
125 static void syncache_free(struct syncache *);
126 static void syncache_insert(struct syncache *, struct syncache_head *);
127 static int syncache_respond(struct syncache *, const struct mbuf *);
128 static struct socket *syncache_socket(struct syncache *, struct socket *,
130 static int syncache_sysctl_count(SYSCTL_HANDLER_ARGS);
131 static void syncache_timeout(struct syncache *sc, struct syncache_head *sch,
133 static void syncache_timer(void *);
135 static uint32_t syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t,
136 uint8_t *, uintptr_t);
137 static tcp_seq syncookie_generate(struct syncache_head *, struct syncache *);
138 static struct syncache
139 *syncookie_lookup(struct in_conninfo *, struct syncache_head *,
140 struct syncache *, struct tcphdr *, struct tcpopt *,
142 static void syncookie_reseed(void *);
144 static int syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch,
145 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
150 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies.
151 * 3 retransmits corresponds to a timeout of 3 * (1 + 2 + 4 + 8) == 45 seconds,
152 * the odds are that the user has given up attempting to connect by then.
154 #define SYNCACHE_MAXREXMTS 3
156 /* Arbitrary values */
157 #define TCP_SYNCACHE_HASHSIZE 512
158 #define TCP_SYNCACHE_BUCKETLIMIT 30
160 static VNET_DEFINE(struct tcp_syncache, tcp_syncache);
161 #define V_tcp_syncache VNET(tcp_syncache)
163 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0,
166 SYSCTL_VNET_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_RDTUN,
167 &VNET_NAME(tcp_syncache.bucket_limit), 0,
168 "Per-bucket hash limit for syncache");
170 SYSCTL_VNET_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_RDTUN,
171 &VNET_NAME(tcp_syncache.cache_limit), 0,
172 "Overall entry limit for syncache");
174 SYSCTL_VNET_PROC(_net_inet_tcp_syncache, OID_AUTO, count, (CTLTYPE_UINT|CTLFLAG_RD),
175 NULL, 0, &syncache_sysctl_count, "IU",
176 "Current number of entries in syncache");
178 SYSCTL_VNET_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_RDTUN,
179 &VNET_NAME(tcp_syncache.hashsize), 0,
180 "Size of TCP syncache hashtable");
182 SYSCTL_VNET_UINT(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, CTLFLAG_RW,
183 &VNET_NAME(tcp_syncache.rexmt_limit), 0,
184 "Limit on SYN/ACK retransmissions");
186 VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1;
187 SYSCTL_VNET_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail,
188 CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0,
189 "Send reset on socket allocation failure");
191 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache");
193 #define SYNCACHE_HASH(inc, mask) \
194 ((V_tcp_syncache.hash_secret ^ \
195 (inc)->inc_faddr.s_addr ^ \
196 ((inc)->inc_faddr.s_addr >> 16) ^ \
197 (inc)->inc_fport ^ (inc)->inc_lport) & mask)
199 #define SYNCACHE_HASH6(inc, mask) \
200 ((V_tcp_syncache.hash_secret ^ \
201 (inc)->inc6_faddr.s6_addr32[0] ^ \
202 (inc)->inc6_faddr.s6_addr32[3] ^ \
203 (inc)->inc_fport ^ (inc)->inc_lport) & mask)
205 #define ENDPTS_EQ(a, b) ( \
206 (a)->ie_fport == (b)->ie_fport && \
207 (a)->ie_lport == (b)->ie_lport && \
208 (a)->ie_faddr.s_addr == (b)->ie_faddr.s_addr && \
209 (a)->ie_laddr.s_addr == (b)->ie_laddr.s_addr \
212 #define ENDPTS6_EQ(a, b) (memcmp(a, b, sizeof(*a)) == 0)
214 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx)
215 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx)
216 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED)
219 * Requires the syncache entry to be already removed from the bucket list.
222 syncache_free(struct syncache *sc)
226 (void) m_free(sc->sc_ipopts);
230 mac_syncache_destroy(&sc->sc_label);
233 uma_zfree(V_tcp_syncache.zone, sc);
241 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
242 V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT;
243 V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS;
244 V_tcp_syncache.hash_secret = arc4random();
246 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize",
247 &V_tcp_syncache.hashsize);
248 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit",
249 &V_tcp_syncache.bucket_limit);
250 if (!powerof2(V_tcp_syncache.hashsize) ||
251 V_tcp_syncache.hashsize == 0) {
252 printf("WARNING: syncache hash size is not a power of 2.\n");
253 V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
255 V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1;
258 V_tcp_syncache.cache_limit =
259 V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit;
260 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit",
261 &V_tcp_syncache.cache_limit);
263 /* Allocate the hash table. */
264 V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize *
265 sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO);
268 V_tcp_syncache.vnet = curvnet;
271 /* Initialize the hash buckets. */
272 for (i = 0; i < V_tcp_syncache.hashsize; i++) {
273 TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket);
274 mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head",
276 callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer,
277 &V_tcp_syncache.hashbase[i].sch_mtx, 0);
278 V_tcp_syncache.hashbase[i].sch_length = 0;
279 V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache;
282 /* Create the syncache entry zone. */
283 V_tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache),
284 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
285 V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone,
286 V_tcp_syncache.cache_limit);
288 /* Start the SYN cookie reseeder callout. */
289 callout_init(&V_tcp_syncache.secret.reseed, 1);
290 arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0);
291 arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0);
292 callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz,
293 syncookie_reseed, &V_tcp_syncache);
298 syncache_destroy(void)
300 struct syncache_head *sch;
301 struct syncache *sc, *nsc;
304 /* Cleanup hash buckets: stop timers, free entries, destroy locks. */
305 for (i = 0; i < V_tcp_syncache.hashsize; i++) {
307 sch = &V_tcp_syncache.hashbase[i];
308 callout_drain(&sch->sch_timer);
311 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc)
312 syncache_drop(sc, sch);
314 KASSERT(TAILQ_EMPTY(&sch->sch_bucket),
315 ("%s: sch->sch_bucket not empty", __func__));
316 KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0",
317 __func__, sch->sch_length));
318 mtx_destroy(&sch->sch_mtx);
321 KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0,
322 ("%s: cache_count not 0", __func__));
324 /* Free the allocated global resources. */
325 uma_zdestroy(V_tcp_syncache.zone);
326 free(V_tcp_syncache.hashbase, M_SYNCACHE);
328 callout_drain(&V_tcp_syncache.secret.reseed);
333 syncache_sysctl_count(SYSCTL_HANDLER_ARGS)
337 count = uma_zone_get_cur(V_tcp_syncache.zone);
338 return (sysctl_handle_int(oidp, &count, 0, req));
342 * Inserts a syncache entry into the specified bucket row.
343 * Locks and unlocks the syncache_head autonomously.
346 syncache_insert(struct syncache *sc, struct syncache_head *sch)
348 struct syncache *sc2;
353 * Make sure that we don't overflow the per-bucket limit.
354 * If the bucket is full, toss the oldest element.
356 if (sch->sch_length >= V_tcp_syncache.bucket_limit) {
357 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket),
358 ("sch->sch_length incorrect"));
359 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head);
360 syncache_drop(sc2, sch);
361 TCPSTAT_INC(tcps_sc_bucketoverflow);
364 /* Put it into the bucket. */
365 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash);
369 if (ADDED_BY_TOE(sc)) {
370 struct toedev *tod = sc->sc_tod;
372 tod->tod_syncache_added(tod, sc->sc_todctx);
376 /* Reinitialize the bucket row's timer. */
377 if (sch->sch_length == 1)
378 sch->sch_nextc = ticks + INT_MAX;
379 syncache_timeout(sc, sch, 1);
383 TCPSTAT_INC(tcps_sc_added);
387 * Remove and free entry from syncache bucket row.
388 * Expects locked syncache head.
391 syncache_drop(struct syncache *sc, struct syncache_head *sch)
394 SCH_LOCK_ASSERT(sch);
396 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
400 if (ADDED_BY_TOE(sc)) {
401 struct toedev *tod = sc->sc_tod;
403 tod->tod_syncache_removed(tod, sc->sc_todctx);
411 * Engage/reengage time on bucket row.
414 syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout)
416 sc->sc_rxttime = ticks +
417 TCPTV_RTOBASE * (tcp_syn_backoff[sc->sc_rxmits]);
419 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) {
420 sch->sch_nextc = sc->sc_rxttime;
422 callout_reset(&sch->sch_timer, sch->sch_nextc - ticks,
423 syncache_timer, (void *)sch);
428 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted.
429 * If we have retransmitted an entry the maximum number of times, expire it.
430 * One separate timer for each bucket row.
433 syncache_timer(void *xsch)
435 struct syncache_head *sch = (struct syncache_head *)xsch;
436 struct syncache *sc, *nsc;
440 CURVNET_SET(sch->sch_sc->vnet);
442 /* NB: syncache_head has already been locked by the callout. */
443 SCH_LOCK_ASSERT(sch);
446 * In the following cycle we may remove some entries and/or
447 * advance some timeouts, so re-initialize the bucket timer.
449 sch->sch_nextc = tick + INT_MAX;
451 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) {
453 * We do not check if the listen socket still exists
454 * and accept the case where the listen socket may be
455 * gone by the time we resend the SYN/ACK. We do
456 * not expect this to happens often. If it does,
457 * then the RST will be sent by the time the remote
458 * host does the SYN/ACK->ACK.
460 if (TSTMP_GT(sc->sc_rxttime, tick)) {
461 if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc))
462 sch->sch_nextc = sc->sc_rxttime;
465 if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) {
466 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
467 log(LOG_DEBUG, "%s; %s: Retransmits exhausted, "
468 "giving up and removing syncache entry\n",
472 syncache_drop(sc, sch);
473 TCPSTAT_INC(tcps_sc_stale);
476 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
477 log(LOG_DEBUG, "%s; %s: Response timeout, "
478 "retransmitting (%u) SYN|ACK\n",
479 s, __func__, sc->sc_rxmits);
483 (void) syncache_respond(sc, NULL);
484 TCPSTAT_INC(tcps_sc_retransmitted);
485 syncache_timeout(sc, sch, 0);
487 if (!TAILQ_EMPTY(&(sch)->sch_bucket))
488 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick,
489 syncache_timer, (void *)(sch));
494 * Find an entry in the syncache.
495 * Returns always with locked syncache_head plus a matching entry or NULL.
497 static struct syncache *
498 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp)
501 struct syncache_head *sch;
504 if (inc->inc_flags & INC_ISIPV6) {
505 sch = &V_tcp_syncache.hashbase[
506 SYNCACHE_HASH6(inc, V_tcp_syncache.hashmask)];
511 /* Circle through bucket row to find matching entry. */
512 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
513 if (ENDPTS6_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie))
519 sch = &V_tcp_syncache.hashbase[
520 SYNCACHE_HASH(inc, V_tcp_syncache.hashmask)];
525 /* Circle through bucket row to find matching entry. */
526 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
528 if (sc->sc_inc.inc_flags & INC_ISIPV6)
531 if (ENDPTS_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie))
535 SCH_LOCK_ASSERT(*schp);
536 return (NULL); /* always returns with locked sch */
540 * This function is called when we get a RST for a
541 * non-existent connection, so that we can see if the
542 * connection is in the syn cache. If it is, zap it.
545 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th)
548 struct syncache_head *sch;
551 sc = syncache_lookup(inc, &sch); /* returns locked sch */
552 SCH_LOCK_ASSERT(sch);
555 * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags.
556 * See RFC 793 page 65, section SEGMENT ARRIVES.
558 if (th->th_flags & (TH_ACK|TH_SYN|TH_FIN)) {
559 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
560 log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or "
561 "FIN flag set, segment ignored\n", s, __func__);
562 TCPSTAT_INC(tcps_badrst);
567 * No corresponding connection was found in syncache.
568 * If syncookies are enabled and possibly exclusively
569 * used, or we are under memory pressure, a valid RST
570 * may not find a syncache entry. In that case we're
571 * done and no SYN|ACK retransmissions will happen.
572 * Otherwise the RST was misdirected or spoofed.
575 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
576 log(LOG_DEBUG, "%s; %s: Spurious RST without matching "
577 "syncache entry (possibly syncookie only), "
578 "segment ignored\n", s, __func__);
579 TCPSTAT_INC(tcps_badrst);
584 * If the RST bit is set, check the sequence number to see
585 * if this is a valid reset segment.
587 * In all states except SYN-SENT, all reset (RST) segments
588 * are validated by checking their SEQ-fields. A reset is
589 * valid if its sequence number is in the window.
591 * The sequence number in the reset segment is normally an
592 * echo of our outgoing acknowlegement numbers, but some hosts
593 * send a reset with the sequence number at the rightmost edge
594 * of our receive window, and we have to handle this case.
596 if (SEQ_GEQ(th->th_seq, sc->sc_irs) &&
597 SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
598 syncache_drop(sc, sch);
599 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
600 log(LOG_DEBUG, "%s; %s: Our SYN|ACK was rejected, "
601 "connection attempt aborted by remote endpoint\n",
603 TCPSTAT_INC(tcps_sc_reset);
605 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
606 log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != "
607 "IRS %u (+WND %u), segment ignored\n",
608 s, __func__, th->th_seq, sc->sc_irs, sc->sc_wnd);
609 TCPSTAT_INC(tcps_badrst);
619 syncache_badack(struct in_conninfo *inc)
622 struct syncache_head *sch;
624 sc = syncache_lookup(inc, &sch); /* returns locked sch */
625 SCH_LOCK_ASSERT(sch);
627 syncache_drop(sc, sch);
628 TCPSTAT_INC(tcps_sc_badack);
634 syncache_unreach(struct in_conninfo *inc, struct tcphdr *th)
637 struct syncache_head *sch;
639 sc = syncache_lookup(inc, &sch); /* returns locked sch */
640 SCH_LOCK_ASSERT(sch);
644 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */
645 if (ntohl(th->th_seq) != sc->sc_iss)
649 * If we've rertransmitted 3 times and this is our second error,
650 * we remove the entry. Otherwise, we allow it to continue on.
651 * This prevents us from incorrectly nuking an entry during a
652 * spurious network outage.
656 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) {
657 sc->sc_flags |= SCF_UNREACH;
660 syncache_drop(sc, sch);
661 TCPSTAT_INC(tcps_sc_unreach);
667 * Build a new TCP socket structure from a syncache entry.
669 * On success return the newly created socket with its underlying inp locked.
671 static struct socket *
672 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m)
674 struct inpcb *inp = NULL;
680 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
683 * Ok, create the full blown connection, and set things up
684 * as they would have been set up if we had created the
685 * connection when the SYN arrived. If we can't create
686 * the connection, abort it.
688 so = sonewconn(lso, 0);
691 * Drop the connection; we will either send a RST or
692 * have the peer retransmit its SYN again after its
695 TCPSTAT_INC(tcps_listendrop);
696 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
697 log(LOG_DEBUG, "%s; %s: Socket create failed "
698 "due to limits or memory shortage\n",
705 mac_socketpeer_set_from_mbuf(m, so);
709 inp->inp_inc.inc_fibnum = so->so_fibnum;
712 * Exclusive pcbinfo lock is not required in syncache socket case even
713 * if two inpcb locks can be acquired simultaneously:
714 * - the inpcb in LISTEN state,
715 * - the newly created inp.
717 * In this case, an inp cannot be at same time in LISTEN state and
718 * just created by an accept() call.
720 INP_HASH_WLOCK(&V_tcbinfo);
722 /* Insert new socket into PCB hash list. */
723 inp->inp_inc.inc_flags = sc->sc_inc.inc_flags;
725 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
726 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
728 inp->inp_vflag &= ~INP_IPV6;
729 inp->inp_vflag |= INP_IPV4;
731 inp->inp_laddr = sc->sc_inc.inc_laddr;
737 * If there's an mbuf and it has a flowid, then let's initialise the
738 * inp with that particular flowid.
740 if (m != NULL && M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) {
741 inp->inp_flowid = m->m_pkthdr.flowid;
742 inp->inp_flowtype = M_HASHTYPE_GET(m);
746 * Install in the reservation hash table for now, but don't yet
747 * install a connection group since the full 4-tuple isn't yet
750 inp->inp_lport = sc->sc_inc.inc_lport;
751 if ((error = in_pcbinshash_nopcbgroup(inp)) != 0) {
753 * Undo the assignments above if we failed to
754 * put the PCB on the hash lists.
757 if (sc->sc_inc.inc_flags & INC_ISIPV6)
758 inp->in6p_laddr = in6addr_any;
761 inp->inp_laddr.s_addr = INADDR_ANY;
763 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
764 log(LOG_DEBUG, "%s; %s: in_pcbinshash failed "
769 INP_HASH_WUNLOCK(&V_tcbinfo);
773 /* Copy old policy into new socket's. */
774 if (ipsec_copy_policy(sotoinpcb(lso)->inp_sp, inp->inp_sp))
775 printf("syncache_socket: could not copy policy\n");
778 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
779 struct inpcb *oinp = sotoinpcb(lso);
780 struct in6_addr laddr6;
781 struct sockaddr_in6 sin6;
783 * Inherit socket options from the listening socket.
784 * Note that in6p_inputopts are not (and should not be)
785 * copied, since it stores previously received options and is
786 * used to detect if each new option is different than the
787 * previous one and hence should be passed to a user.
788 * If we copied in6p_inputopts, a user would not be able to
789 * receive options just after calling the accept system call.
791 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS;
792 if (oinp->in6p_outputopts)
793 inp->in6p_outputopts =
794 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT);
796 sin6.sin6_family = AF_INET6;
797 sin6.sin6_len = sizeof(sin6);
798 sin6.sin6_addr = sc->sc_inc.inc6_faddr;
799 sin6.sin6_port = sc->sc_inc.inc_fport;
800 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0;
801 laddr6 = inp->in6p_laddr;
802 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr))
803 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
804 if ((error = in6_pcbconnect_mbuf(inp, (struct sockaddr *)&sin6,
805 thread0.td_ucred, m)) != 0) {
806 inp->in6p_laddr = laddr6;
807 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
808 log(LOG_DEBUG, "%s; %s: in6_pcbconnect failed "
813 INP_HASH_WUNLOCK(&V_tcbinfo);
816 /* Override flowlabel from in6_pcbconnect. */
817 inp->inp_flow &= ~IPV6_FLOWLABEL_MASK;
818 inp->inp_flow |= sc->sc_flowlabel;
821 #if defined(INET) && defined(INET6)
826 struct in_addr laddr;
827 struct sockaddr_in sin;
829 inp->inp_options = (m) ? ip_srcroute(m) : NULL;
831 if (inp->inp_options == NULL) {
832 inp->inp_options = sc->sc_ipopts;
833 sc->sc_ipopts = NULL;
836 sin.sin_family = AF_INET;
837 sin.sin_len = sizeof(sin);
838 sin.sin_addr = sc->sc_inc.inc_faddr;
839 sin.sin_port = sc->sc_inc.inc_fport;
840 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero));
841 laddr = inp->inp_laddr;
842 if (inp->inp_laddr.s_addr == INADDR_ANY)
843 inp->inp_laddr = sc->sc_inc.inc_laddr;
844 if ((error = in_pcbconnect_mbuf(inp, (struct sockaddr *)&sin,
845 thread0.td_ucred, m)) != 0) {
846 inp->inp_laddr = laddr;
847 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
848 log(LOG_DEBUG, "%s; %s: in_pcbconnect failed "
853 INP_HASH_WUNLOCK(&V_tcbinfo);
858 INP_HASH_WUNLOCK(&V_tcbinfo);
860 tcp_state_change(tp, TCPS_SYN_RECEIVED);
861 tp->iss = sc->sc_iss;
862 tp->irs = sc->sc_irs;
865 tp->snd_wl1 = sc->sc_irs;
866 tp->snd_max = tp->iss + 1;
867 tp->snd_nxt = tp->iss + 1;
868 tp->rcv_up = sc->sc_irs + 1;
869 tp->rcv_wnd = sc->sc_wnd;
870 tp->rcv_adv += tp->rcv_wnd;
871 tp->last_ack_sent = tp->rcv_nxt;
873 tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY);
874 if (sc->sc_flags & SCF_NOOPT)
875 tp->t_flags |= TF_NOOPT;
877 if (sc->sc_flags & SCF_WINSCALE) {
878 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE;
879 tp->snd_scale = sc->sc_requested_s_scale;
880 tp->request_r_scale = sc->sc_requested_r_scale;
882 if (sc->sc_flags & SCF_TIMESTAMP) {
883 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP;
884 tp->ts_recent = sc->sc_tsreflect;
885 tp->ts_recent_age = tcp_ts_getticks();
886 tp->ts_offset = sc->sc_tsoff;
889 if (sc->sc_flags & SCF_SIGNATURE)
890 tp->t_flags |= TF_SIGNATURE;
892 if (sc->sc_flags & SCF_SACK)
893 tp->t_flags |= TF_SACK_PERMIT;
896 if (sc->sc_flags & SCF_ECN)
897 tp->t_flags |= TF_ECN_PERMIT;
900 * Set up MSS and get cached values from tcp_hostcache.
901 * This might overwrite some of the defaults we just set.
903 tcp_mss(tp, sc->sc_peer_mss);
906 * If the SYN,ACK was retransmitted, indicate that CWND to be
907 * limited to one segment in cc_conn_init().
908 * NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits.
910 if (sc->sc_rxmits > 1)
915 * Allow a TOE driver to install its hooks. Note that we hold the
916 * pcbinfo lock too and that prevents tcp_usr_accept from accepting a
917 * new connection before the TOE driver has done its thing.
919 if (ADDED_BY_TOE(sc)) {
920 struct toedev *tod = sc->sc_tod;
922 tod->tod_offload_socket(tod, sc->sc_todctx, so);
926 * Copy and activate timers.
928 tp->t_keepinit = sototcpcb(lso)->t_keepinit;
929 tp->t_keepidle = sototcpcb(lso)->t_keepidle;
930 tp->t_keepintvl = sototcpcb(lso)->t_keepintvl;
931 tp->t_keepcnt = sototcpcb(lso)->t_keepcnt;
932 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp));
934 TCPSTAT_INC(tcps_accepts);
946 * This function gets called when we receive an ACK for a
947 * socket in the LISTEN state. We look up the connection
948 * in the syncache, and if its there, we pull it out of
949 * the cache and turn it into a full-blown connection in
950 * the SYN-RECEIVED state.
952 * On syncache_socket() success the newly created socket
953 * has its underlying inp locked.
956 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
957 struct socket **lsop, struct mbuf *m)
960 struct syncache_head *sch;
965 * Global TCP locks are held because we manipulate the PCB lists
966 * and create a new socket.
968 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
969 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK,
970 ("%s: can handle only ACK", __func__));
972 sc = syncache_lookup(inc, &sch); /* returns locked sch */
973 SCH_LOCK_ASSERT(sch);
977 * Test code for syncookies comparing the syncache stored
978 * values with the reconstructed values from the cookie.
981 syncookie_cmp(inc, sch, sc, th, to, *lsop);
986 * There is no syncache entry, so see if this ACK is
987 * a returning syncookie. To do this, first:
988 * A. See if this socket has had a syncache entry dropped in
989 * the past. We don't want to accept a bogus syncookie
990 * if we've never received a SYN.
991 * B. check that the syncookie is valid. If it is, then
992 * cobble up a fake syncache entry, and return.
994 if (!V_tcp_syncookies) {
996 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
997 log(LOG_DEBUG, "%s; %s: Spurious ACK, "
998 "segment rejected (syncookies disabled)\n",
1002 bzero(&scs, sizeof(scs));
1003 sc = syncookie_lookup(inc, sch, &scs, th, to, *lsop);
1006 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1007 log(LOG_DEBUG, "%s; %s: Segment failed "
1008 "SYNCOOKIE authentication, segment rejected "
1009 "(probably spoofed)\n", s, __func__);
1013 /* Pull out the entry to unlock the bucket row. */
1014 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
1017 if (ADDED_BY_TOE(sc)) {
1018 struct toedev *tod = sc->sc_tod;
1020 tod->tod_syncache_removed(tod, sc->sc_todctx);
1027 * Segment validation:
1028 * ACK must match our initial sequence number + 1 (the SYN|ACK).
1030 if (th->th_ack != sc->sc_iss + 1) {
1031 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1032 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment "
1033 "rejected\n", s, __func__, th->th_ack, sc->sc_iss);
1038 * The SEQ must fall in the window starting at the received
1039 * initial receive sequence number + 1 (the SYN).
1041 if (SEQ_LEQ(th->th_seq, sc->sc_irs) ||
1042 SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
1043 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1044 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment "
1045 "rejected\n", s, __func__, th->th_seq, sc->sc_irs);
1050 * If timestamps were not negotiated during SYN/ACK they
1051 * must not appear on any segment during this session.
1053 if (!(sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) {
1054 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1055 log(LOG_DEBUG, "%s; %s: Timestamp not expected, "
1056 "segment rejected\n", s, __func__);
1061 * If timestamps were negotiated during SYN/ACK they should
1062 * appear on every segment during this session.
1063 * XXXAO: This is only informal as there have been unverified
1064 * reports of non-compliants stacks.
1066 if ((sc->sc_flags & SCF_TIMESTAMP) && !(to->to_flags & TOF_TS)) {
1067 if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1068 log(LOG_DEBUG, "%s; %s: Timestamp missing, "
1069 "no action\n", s, __func__);
1076 * If timestamps were negotiated the reflected timestamp
1077 * must be equal to what we actually sent in the SYN|ACK.
1079 if ((to->to_flags & TOF_TS) && to->to_tsecr != sc->sc_ts) {
1080 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
1081 log(LOG_DEBUG, "%s; %s: TSECR %u != TS %u, "
1082 "segment rejected\n",
1083 s, __func__, to->to_tsecr, sc->sc_ts);
1087 *lsop = syncache_socket(sc, *lsop, m);
1090 TCPSTAT_INC(tcps_sc_aborted);
1092 TCPSTAT_INC(tcps_sc_completed);
1094 /* how do we find the inp for the new socket? */
1099 if (sc != NULL && sc != &scs)
1109 syncache_tfo_expand(struct syncache *sc, struct socket **lsop, struct mbuf *m,
1110 uint64_t response_cookie)
1114 unsigned int *pending_counter;
1117 * Global TCP locks are held because we manipulate the PCB lists
1118 * and create a new socket.
1120 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
1122 pending_counter = intotcpcb(sotoinpcb(*lsop))->t_tfo_pending;
1123 *lsop = syncache_socket(sc, *lsop, m);
1124 if (*lsop == NULL) {
1125 TCPSTAT_INC(tcps_sc_aborted);
1126 atomic_subtract_int(pending_counter, 1);
1128 inp = sotoinpcb(*lsop);
1129 tp = intotcpcb(inp);
1130 tp->t_flags |= TF_FASTOPEN;
1131 tp->t_tfo_cookie = response_cookie;
1132 tp->snd_max = tp->iss;
1133 tp->snd_nxt = tp->iss;
1134 tp->t_tfo_pending = pending_counter;
1135 TCPSTAT_INC(tcps_sc_completed);
1138 #endif /* TCP_RFC7413 */
1141 * Given a LISTEN socket and an inbound SYN request, add
1142 * this to the syn cache, and send back a segment:
1143 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
1146 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN.
1147 * Doing so would require that we hold onto the data and deliver it
1148 * to the application. However, if we are the target of a SYN-flood
1149 * DoS attack, an attacker could send data which would eventually
1150 * consume all available buffer space if it were ACKed. By not ACKing
1151 * the data, we avoid this DoS scenario.
1153 * The exception to the above is when a SYN with a valid TCP Fast Open (TFO)
1154 * cookie is processed, V_tcp_fastopen_enabled set to true, and the
1155 * TCP_FASTOPEN socket option is set. In this case, a new socket is created
1156 * and returned via lsop, the mbuf is not freed so that tcp_input() can
1157 * queue its data to the socket, and 1 is returned to indicate the
1158 * TFO-socket-creation path was taken.
1161 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
1162 struct inpcb *inp, struct socket **lsop, struct mbuf *m, void *tod,
1167 struct syncache *sc = NULL;
1168 struct syncache_head *sch;
1169 struct mbuf *ipopts = NULL;
1171 int win, sb_hiwat, ip_ttl, ip_tos;
1175 int autoflowlabel = 0;
1178 struct label *maclabel;
1180 struct syncache scs;
1183 uint64_t tfo_response_cookie;
1184 int tfo_cookie_valid = 0;
1185 int tfo_response_cookie_valid = 0;
1188 INP_WLOCK_ASSERT(inp); /* listen socket */
1189 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN,
1190 ("%s: unexpected tcp flags", __func__));
1193 * Combine all so/tp operations very early to drop the INP lock as
1198 cred = crhold(so->so_cred);
1201 if ((inc->inc_flags & INC_ISIPV6) &&
1202 (inp->inp_flags & IN6P_AUTOFLOWLABEL))
1205 ip_ttl = inp->inp_ip_ttl;
1206 ip_tos = inp->inp_ip_tos;
1207 win = sbspace(&so->so_rcv);
1208 sb_hiwat = so->so_rcv.sb_hiwat;
1209 ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE));
1212 if (V_tcp_fastopen_enabled && (tp->t_flags & TF_FASTOPEN) &&
1213 (tp->t_tfo_pending != NULL) && (to->to_flags & TOF_FASTOPEN)) {
1215 * Limit the number of pending TFO connections to
1216 * approximately half of the queue limit. This prevents TFO
1217 * SYN floods from starving the service by filling the
1218 * listen queue with bogus TFO connections.
1220 if (atomic_fetchadd_int(tp->t_tfo_pending, 1) <=
1221 (so->so_qlimit / 2)) {
1224 result = tcp_fastopen_check_cookie(inc,
1225 to->to_tfo_cookie, to->to_tfo_len,
1226 &tfo_response_cookie);
1227 tfo_cookie_valid = (result > 0);
1228 tfo_response_cookie_valid = (result >= 0);
1230 atomic_subtract_int(tp->t_tfo_pending, 1);
1234 /* By the time we drop the lock these should no longer be used. */
1239 if (mac_syncache_init(&maclabel) != 0) {
1243 mac_syncache_create(maclabel, inp);
1246 if (!tfo_cookie_valid)
1251 * Remember the IP options, if any.
1254 if (!(inc->inc_flags & INC_ISIPV6))
1257 ipopts = (m) ? ip_srcroute(m) : NULL;
1263 * See if we already have an entry for this connection.
1264 * If we do, resend the SYN,ACK, and reset the retransmit timer.
1266 * XXX: should the syncache be re-initialized with the contents
1267 * of the new SYN here (which may have different options?)
1269 * XXX: We do not check the sequence number to see if this is a
1270 * real retransmit or a new connection attempt. The question is
1271 * how to handle such a case; either ignore it as spoofed, or
1272 * drop the current entry and create a new one?
1274 sc = syncache_lookup(inc, &sch); /* returns locked entry */
1275 SCH_LOCK_ASSERT(sch);
1278 if (tfo_cookie_valid)
1281 TCPSTAT_INC(tcps_sc_dupsyn);
1284 * If we were remembering a previous source route,
1285 * forget it and use the new one we've been given.
1288 (void) m_free(sc->sc_ipopts);
1289 sc->sc_ipopts = ipopts;
1292 * Update timestamp if present.
1294 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS))
1295 sc->sc_tsreflect = to->to_tsval;
1297 sc->sc_flags &= ~SCF_TIMESTAMP;
1300 * Since we have already unconditionally allocated label
1301 * storage, free it up. The syncache entry will already
1302 * have an initialized label we can use.
1304 mac_syncache_destroy(&maclabel);
1306 /* Retransmit SYN|ACK and reset retransmit count. */
1307 if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) {
1308 log(LOG_DEBUG, "%s; %s: Received duplicate SYN, "
1309 "resetting timer and retransmitting SYN|ACK\n",
1313 if (syncache_respond(sc, m) == 0) {
1315 syncache_timeout(sc, sch, 1);
1316 TCPSTAT_INC(tcps_sndacks);
1317 TCPSTAT_INC(tcps_sndtotal);
1324 if (tfo_cookie_valid) {
1325 bzero(&scs, sizeof(scs));
1331 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
1334 * The zone allocator couldn't provide more entries.
1335 * Treat this as if the cache was full; drop the oldest
1336 * entry and insert the new one.
1338 TCPSTAT_INC(tcps_sc_zonefail);
1339 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL)
1340 syncache_drop(sc, sch);
1341 sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
1343 if (V_tcp_syncookies) {
1344 bzero(&scs, sizeof(scs));
1349 (void) m_free(ipopts);
1357 if (!tfo_cookie_valid && tfo_response_cookie_valid)
1358 sc->sc_tfo_cookie = &tfo_response_cookie;
1362 * Fill in the syncache values.
1365 sc->sc_label = maclabel;
1369 sc->sc_ipopts = ipopts;
1370 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
1372 if (!(inc->inc_flags & INC_ISIPV6))
1375 sc->sc_ip_tos = ip_tos;
1376 sc->sc_ip_ttl = ip_ttl;
1380 sc->sc_todctx = todctx;
1382 sc->sc_irs = th->th_seq;
1383 sc->sc_iss = arc4random();
1385 sc->sc_flowlabel = 0;
1388 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN].
1389 * win was derived from socket earlier in the function.
1392 win = imin(win, TCP_MAXWIN);
1395 if (V_tcp_do_rfc1323) {
1397 * A timestamp received in a SYN makes
1398 * it ok to send timestamp requests and replies.
1400 if (to->to_flags & TOF_TS) {
1401 sc->sc_tsreflect = to->to_tsval;
1402 sc->sc_ts = tcp_ts_getticks();
1403 sc->sc_flags |= SCF_TIMESTAMP;
1405 if (to->to_flags & TOF_SCALE) {
1409 * Pick the smallest possible scaling factor that
1410 * will still allow us to scale up to sb_max, aka
1411 * kern.ipc.maxsockbuf.
1413 * We do this because there are broken firewalls that
1414 * will corrupt the window scale option, leading to
1415 * the other endpoint believing that our advertised
1416 * window is unscaled. At scale factors larger than
1417 * 5 the unscaled window will drop below 1500 bytes,
1418 * leading to serious problems when traversing these
1421 * With the default maxsockbuf of 256K, a scale factor
1422 * of 3 will be chosen by this algorithm. Those who
1423 * choose a larger maxsockbuf should watch out
1424 * for the compatiblity problems mentioned above.
1426 * RFC1323: The Window field in a SYN (i.e., a <SYN>
1427 * or <SYN,ACK>) segment itself is never scaled.
1429 while (wscale < TCP_MAX_WINSHIFT &&
1430 (TCP_MAXWIN << wscale) < sb_max)
1432 sc->sc_requested_r_scale = wscale;
1433 sc->sc_requested_s_scale = to->to_wscale;
1434 sc->sc_flags |= SCF_WINSCALE;
1437 #ifdef TCP_SIGNATURE
1439 * If listening socket requested TCP digests, and received SYN
1440 * contains the option, flag this in the syncache so that
1441 * syncache_respond() will do the right thing with the SYN+ACK.
1442 * XXX: Currently we always record the option by default and will
1443 * attempt to use it in syncache_respond().
1445 if (to->to_flags & TOF_SIGNATURE || ltflags & TF_SIGNATURE)
1446 sc->sc_flags |= SCF_SIGNATURE;
1448 if (to->to_flags & TOF_SACKPERM)
1449 sc->sc_flags |= SCF_SACK;
1450 if (to->to_flags & TOF_MSS)
1451 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */
1452 if (ltflags & TF_NOOPT)
1453 sc->sc_flags |= SCF_NOOPT;
1454 if ((th->th_flags & (TH_ECE|TH_CWR)) && V_tcp_do_ecn)
1455 sc->sc_flags |= SCF_ECN;
1457 if (V_tcp_syncookies)
1458 sc->sc_iss = syncookie_generate(sch, sc);
1460 if (autoflowlabel) {
1461 if (V_tcp_syncookies)
1462 sc->sc_flowlabel = sc->sc_iss;
1464 sc->sc_flowlabel = ip6_randomflowlabel();
1465 sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK;
1471 if (tfo_cookie_valid) {
1472 syncache_tfo_expand(sc, lsop, m, tfo_response_cookie);
1473 /* INP_WUNLOCK(inp) will be performed by the called */
1480 * Do a standard 3-way handshake.
1482 if (syncache_respond(sc, m) == 0) {
1483 if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs)
1485 else if (sc != &scs)
1486 syncache_insert(sc, sch); /* locks and unlocks sch */
1487 TCPSTAT_INC(tcps_sndacks);
1488 TCPSTAT_INC(tcps_sndtotal);
1492 TCPSTAT_INC(tcps_sc_dropped);
1507 mac_syncache_destroy(&maclabel);
1513 * Send SYN|ACK to the peer. Either in response to the peer's SYN,
1514 * i.e. m0 != NULL, or upon 3WHS ACK timeout, i.e. m0 == NULL.
1517 syncache_respond(struct syncache *sc, const struct mbuf *m0)
1519 struct ip *ip = NULL;
1521 struct tcphdr *th = NULL;
1522 int optlen, error = 0; /* Make compiler happy */
1523 u_int16_t hlen, tlen, mssopt;
1526 struct ip6_hdr *ip6 = NULL;
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
1638 if (sc->sc_flags & SCF_SIGNATURE)
1639 to.to_flags |= TOF_SIGNATURE;
1643 if (sc->sc_tfo_cookie) {
1644 to.to_flags |= TOF_FASTOPEN;
1645 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN;
1646 to.to_tfo_cookie = sc->sc_tfo_cookie;
1647 /* don't send cookie again when retransmitting response */
1648 sc->sc_tfo_cookie = NULL;
1651 optlen = tcp_addoptions(&to, (u_char *)(th + 1));
1653 /* Adjust headers by option size. */
1654 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
1656 m->m_pkthdr.len += optlen;
1658 #ifdef TCP_SIGNATURE
1659 if (sc->sc_flags & SCF_SIGNATURE)
1660 tcp_signature_compute(m, 0, 0, optlen,
1661 to.to_signature, IPSEC_DIR_OUTBOUND);
1664 if (sc->sc_inc.inc_flags & INC_ISIPV6)
1665 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen);
1668 ip->ip_len = htons(ntohs(ip->ip_len) + optlen);
1672 M_SETFIB(m, sc->sc_inc.inc_fibnum);
1673 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
1675 * If we have peer's SYN and it has a flowid, then let's assign it to
1676 * our SYN|ACK. ip6_output() and ip_output() will not assign flowid
1677 * to SYN|ACK due to lack of inp here.
1679 if (m0 != NULL && M_HASHTYPE_GET(m0) != M_HASHTYPE_NONE) {
1680 m->m_pkthdr.flowid = m0->m_pkthdr.flowid;
1681 M_HASHTYPE_SET(m, M_HASHTYPE_GET(m0));
1684 if (sc->sc_inc.inc_flags & INC_ISIPV6) {
1685 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
1686 th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen,
1688 ip6->ip6_hlim = in6_selecthlim(NULL, NULL);
1690 if (ADDED_BY_TOE(sc)) {
1691 struct toedev *tod = sc->sc_tod;
1693 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
1698 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL);
1701 #if defined(INET6) && defined(INET)
1706 m->m_pkthdr.csum_flags = CSUM_TCP;
1707 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
1708 htons(tlen + optlen - hlen + IPPROTO_TCP));
1710 if (ADDED_BY_TOE(sc)) {
1711 struct toedev *tod = sc->sc_tod;
1713 error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
1718 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL);
1725 * The purpose of syncookies is to handle spoofed SYN flooding DoS attacks
1726 * that exceed the capacity of the syncache by avoiding the storage of any
1727 * of the SYNs we receive. Syncookies defend against blind SYN flooding
1728 * attacks where the attacker does not have access to our responses.
1730 * Syncookies encode and include all necessary information about the
1731 * connection setup within the SYN|ACK that we send back. That way we
1732 * can avoid keeping any local state until the ACK to our SYN|ACK returns
1733 * (if ever). Normally the syncache and syncookies are running in parallel
1734 * with the latter taking over when the former is exhausted. When matching
1735 * syncache entry is found the syncookie is ignored.
1737 * The only reliable information persisting the 3WHS is our inital sequence
1738 * number ISS of 32 bits. Syncookies embed a cryptographically sufficient
1739 * strong hash (MAC) value and a few bits of TCP SYN options in the ISS
1740 * of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK
1741 * returns and signifies a legitimate connection if it matches the ACK.
1743 * The available space of 32 bits to store the hash and to encode the SYN
1744 * option information is very tight and we should have at least 24 bits for
1745 * the MAC to keep the number of guesses by blind spoofing reasonably high.
1747 * SYN option information we have to encode to fully restore a connection:
1748 * MSS: is imporant to chose an optimal segment size to avoid IP level
1749 * fragmentation along the path. The common MSS values can be encoded
1750 * in a 3-bit table. Uncommon values are captured by the next lower value
1751 * in the table leading to a slight increase in packetization overhead.
1752 * WSCALE: is necessary to allow large windows to be used for high delay-
1753 * bandwidth product links. Not scaling the window when it was initially
1754 * negotiated is bad for performance as lack of scaling further decreases
1755 * the apparent available send window. We only need to encode the WSCALE
1756 * we received from the remote end. Our end can be recalculated at any
1757 * time. The common WSCALE values can be encoded in a 3-bit table.
1758 * Uncommon values are captured by the next lower value in the table
1759 * making us under-estimate the available window size halving our
1760 * theoretically possible maximum throughput for that connection.
1761 * SACK: Greatly assists in packet loss recovery and requires 1 bit.
1762 * TIMESTAMP and SIGNATURE is not encoded because they are permanent options
1763 * that are included in all segments on a connection. We enable them when
1766 * Security of syncookies and attack vectors:
1768 * The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod)
1769 * together with the gloabl secret to make it unique per connection attempt.
1770 * Thus any change of any of those parameters results in a different MAC output
1771 * in an unpredictable way unless a collision is encountered. 24 bits of the
1772 * MAC are embedded into the ISS.
1774 * To prevent replay attacks two rotating global secrets are updated with a
1775 * new random value every 15 seconds. The life-time of a syncookie is thus
1778 * Vector 1: Attacking the secret. This requires finding a weakness in the
1779 * MAC itself or the way it is used here. The attacker can do a chosen plain
1780 * text attack by varying and testing the all parameters under his control.
1781 * The strength depends on the size and randomness of the secret, and the
1782 * cryptographic security of the MAC function. Due to the constant updating
1783 * of the secret the attacker has at most 29.999 seconds to find the secret
1784 * and launch spoofed connections. After that he has to start all over again.
1786 * Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC
1787 * size an average of 4,823 attempts are required for a 50% chance of success
1788 * to spoof a single syncookie (birthday collision paradox). However the
1789 * attacker is blind and doesn't know if one of his attempts succeeded unless
1790 * he has a side channel to interfere success from. A single connection setup
1791 * success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets.
1792 * This many attempts are required for each one blind spoofed connection. For
1793 * every additional spoofed connection he has to launch another N attempts.
1794 * Thus for a sustained rate 100 spoofed connections per second approximately
1795 * 1,800,000 packets per second would have to be sent.
1797 * NB: The MAC function should be fast so that it doesn't become a CPU
1798 * exhaustion attack vector itself.
1801 * RFC4987 TCP SYN Flooding Attacks and Common Mitigations
1802 * SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996
1803 * http://cr.yp.to/syncookies.html (overview)
1804 * http://cr.yp.to/syncookies/archive (details)
1807 * Schematic construction of a syncookie enabled Initial Sequence Number:
1809 * 12345678901234567890123456789012
1810 * |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP|
1812 * x 24 MAC (truncated)
1813 * W 3 Send Window Scale index
1815 * S 1 SACK permitted
1816 * P 1 Odd/even secret
1820 * Distribution and probability of certain MSS values. Those in between are
1821 * rounded down to the next lower one.
1822 * [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011]
1823 * .2% .3% 5% 7% 7% 20% 15% 45%
1825 static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 };
1828 * Distribution and probability of certain WSCALE values. We have to map the
1829 * (send) window scale (shift) option with a range of 0-14 from 4 bits into 3
1830 * bits based on prevalence of certain values. Where we don't have an exact
1831 * match for are rounded down to the next lower one letting us under-estimate
1832 * the true available window. At the moment this would happen only for the
1833 * very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer
1834 * and window size). The absence of the WSCALE option (no scaling in either
1835 * direction) is encoded with index zero.
1836 * [WSCALE values histograms, Allman, 2012]
1837 * X 10 10 35 5 6 14 10% by host
1838 * X 11 4 5 5 18 49 3% by connections
1840 static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 };
1843 * Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed
1844 * and good cryptographic properties.
1847 syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags,
1848 uint8_t *secbits, uintptr_t secmod)
1851 uint32_t siphash[2];
1853 SipHash24_Init(&ctx);
1854 SipHash_SetKey(&ctx, secbits);
1855 switch (inc->inc_flags & INC_ISIPV6) {
1858 SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr));
1859 SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr));
1864 SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr));
1865 SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr));
1869 SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport));
1870 SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport));
1871 SipHash_Update(&ctx, &irs, sizeof(irs));
1872 SipHash_Update(&ctx, &flags, sizeof(flags));
1873 SipHash_Update(&ctx, &secmod, sizeof(secmod));
1874 SipHash_Final((u_int8_t *)&siphash, &ctx);
1876 return (siphash[0] ^ siphash[1]);
1880 syncookie_generate(struct syncache_head *sch, struct syncache *sc)
1882 u_int i, mss, secbit, wscale;
1885 union syncookie cookie;
1887 SCH_LOCK_ASSERT(sch);
1891 /* Map our computed MSS into the 3-bit index. */
1892 mss = min(tcp_mssopt(&sc->sc_inc), max(sc->sc_peer_mss, V_tcp_minmss));
1893 for (i = sizeof(tcp_sc_msstab) / sizeof(*tcp_sc_msstab) - 1;
1894 tcp_sc_msstab[i] > mss && i > 0;
1897 cookie.flags.mss_idx = i;
1900 * Map the send window scale into the 3-bit index but only if
1901 * the wscale option was received.
1903 if (sc->sc_flags & SCF_WINSCALE) {
1904 wscale = sc->sc_requested_s_scale;
1905 for (i = sizeof(tcp_sc_wstab) / sizeof(*tcp_sc_wstab) - 1;
1906 tcp_sc_wstab[i] > wscale && i > 0;
1909 cookie.flags.wscale_idx = i;
1912 /* Can we do SACK? */
1913 if (sc->sc_flags & SCF_SACK)
1914 cookie.flags.sack_ok = 1;
1916 /* Which of the two secrets to use. */
1917 secbit = sch->sch_sc->secret.oddeven & 0x1;
1918 cookie.flags.odd_even = secbit;
1920 secbits = sch->sch_sc->secret.key[secbit];
1921 hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits,
1925 * Put the flags into the hash and XOR them to get better ISS number
1926 * variance. This doesn't enhance the cryptographic strength and is
1927 * done to prevent the 8 cookie bits from showing up directly on the
1931 iss |= cookie.cookie ^ (hash >> 24);
1933 /* Randomize the timestamp. */
1934 if (sc->sc_flags & SCF_TIMESTAMP) {
1935 sc->sc_ts = arc4random();
1936 sc->sc_tsoff = sc->sc_ts - tcp_ts_getticks();
1939 TCPSTAT_INC(tcps_sc_sendcookie);
1943 static struct syncache *
1944 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch,
1945 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
1951 int wnd, wscale = 0;
1952 union syncookie cookie;
1954 SCH_LOCK_ASSERT(sch);
1957 * Pull information out of SYN-ACK/ACK and revert sequence number
1960 ack = th->th_ack - 1;
1961 seq = th->th_seq - 1;
1964 * Unpack the flags containing enough information to restore the
1967 cookie.cookie = (ack & 0xff) ^ (ack >> 24);
1969 /* Which of the two secrets to use. */
1970 secbits = sch->sch_sc->secret.key[cookie.flags.odd_even];
1972 hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch);
1974 /* The recomputed hash matches the ACK if this was a genuine cookie. */
1975 if ((ack & ~0xff) != (hash & ~0xff))
1978 /* Fill in the syncache values. */
1980 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
1981 sc->sc_ipopts = NULL;
1986 switch (inc->inc_flags & INC_ISIPV6) {
1989 sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl;
1990 sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos;
1995 if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL)
1996 sc->sc_flowlabel = sc->sc_iss & IPV6_FLOWLABEL_MASK;
2001 sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx];
2003 /* We can simply recompute receive window scale we sent earlier. */
2004 while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max)
2007 /* Only use wscale if it was enabled in the orignal SYN. */
2008 if (cookie.flags.wscale_idx > 0) {
2009 sc->sc_requested_r_scale = wscale;
2010 sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx];
2011 sc->sc_flags |= SCF_WINSCALE;
2014 wnd = sbspace(&lso->so_rcv);
2016 wnd = imin(wnd, TCP_MAXWIN);
2019 if (cookie.flags.sack_ok)
2020 sc->sc_flags |= SCF_SACK;
2022 if (to->to_flags & TOF_TS) {
2023 sc->sc_flags |= SCF_TIMESTAMP;
2024 sc->sc_tsreflect = to->to_tsval;
2025 sc->sc_ts = to->to_tsecr;
2026 sc->sc_tsoff = to->to_tsecr - tcp_ts_getticks();
2029 if (to->to_flags & TOF_SIGNATURE)
2030 sc->sc_flags |= SCF_SIGNATURE;
2034 TCPSTAT_INC(tcps_sc_recvcookie);
2040 syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch,
2041 struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
2044 struct syncache scs, *scx;
2047 bzero(&scs, sizeof(scs));
2048 scx = syncookie_lookup(inc, sch, &scs, th, to, lso);
2050 if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL)
2054 if (sc->sc_peer_mss != scx->sc_peer_mss)
2055 log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n",
2056 s, __func__, sc->sc_peer_mss, scx->sc_peer_mss);
2058 if (sc->sc_requested_r_scale != scx->sc_requested_r_scale)
2059 log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n",
2060 s, __func__, sc->sc_requested_r_scale,
2061 scx->sc_requested_r_scale);
2063 if (sc->sc_requested_s_scale != scx->sc_requested_s_scale)
2064 log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n",
2065 s, __func__, sc->sc_requested_s_scale,
2066 scx->sc_requested_s_scale);
2068 if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK))
2069 log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__);
2076 #endif /* INVARIANTS */
2079 syncookie_reseed(void *arg)
2081 struct tcp_syncache *sc = arg;
2086 * Reseeding the secret doesn't have to be protected by a lock.
2087 * It only must be ensured that the new random values are visible
2088 * to all CPUs in a SMP environment. The atomic with release
2089 * semantics ensures that.
2091 secbit = (sc->secret.oddeven & 0x1) ? 0 : 1;
2092 secbits = sc->secret.key[secbit];
2093 arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0);
2094 atomic_add_rel_int(&sc->secret.oddeven, 1);
2096 /* Reschedule ourself. */
2097 callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz);
2101 * Returns the current number of syncache entries. This number
2102 * will probably change before you get around to calling
2106 syncache_pcbcount(void)
2108 struct syncache_head *sch;
2111 for (count = 0, i = 0; i < V_tcp_syncache.hashsize; i++) {
2112 /* No need to lock for a read. */
2113 sch = &V_tcp_syncache.hashbase[i];
2114 count += sch->sch_length;
2120 * Exports the syncache entries to userland so that netstat can display
2121 * them alongside the other sockets. This function is intended to be
2122 * called only from tcp_pcblist.
2124 * Due to concurrency on an active system, the number of pcbs exported
2125 * may have no relation to max_pcbs. max_pcbs merely indicates the
2126 * amount of space the caller allocated for this function to use.
2129 syncache_pcblist(struct sysctl_req *req, int max_pcbs, int *pcbs_exported)
2132 struct syncache *sc;
2133 struct syncache_head *sch;
2134 int count, error, i;
2136 for (count = 0, error = 0, i = 0; i < V_tcp_syncache.hashsize; i++) {
2137 sch = &V_tcp_syncache.hashbase[i];
2139 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
2140 if (count >= max_pcbs) {
2144 if (cr_cansee(req->td->td_ucred, sc->sc_cred) != 0)
2146 bzero(&xt, sizeof(xt));
2147 xt.xt_len = sizeof(xt);
2148 if (sc->sc_inc.inc_flags & INC_ISIPV6)
2149 xt.xt_inp.inp_vflag = INP_IPV6;
2151 xt.xt_inp.inp_vflag = INP_IPV4;
2152 bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, sizeof (struct in_conninfo));
2153 xt.xt_tp.t_inpcb = &xt.xt_inp;
2154 xt.xt_tp.t_state = TCPS_SYN_RECEIVED;
2155 xt.xt_socket.xso_protocol = IPPROTO_TCP;
2156 xt.xt_socket.xso_len = sizeof (struct xsocket);
2157 xt.xt_socket.so_type = SOCK_STREAM;
2158 xt.xt_socket.so_state = SS_ISCONNECTING;
2159 error = SYSCTL_OUT(req, &xt, sizeof xt);
2169 *pcbs_exported = count;