2 * Copyright (c) 2001 McAfee, Inc.
3 * Copyright (c) 2006 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.
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
36 #include "opt_inet6.h"
37 #include "opt_ipsec.h"
40 #include <sys/param.h>
41 #include <sys/systm.h>
42 #include <sys/kernel.h>
43 #include <sys/sysctl.h>
45 #include <sys/mutex.h>
46 #include <sys/malloc.h>
49 #include <sys/proc.h> /* for proc0 declaration */
50 #include <sys/random.h>
51 #include <sys/socket.h>
52 #include <sys/socketvar.h>
53 #include <sys/syslog.h>
58 #include <net/route.h>
60 #include <netinet/in.h>
61 #include <netinet/in_systm.h>
62 #include <netinet/ip.h>
63 #include <netinet/in_var.h>
64 #include <netinet/in_pcb.h>
65 #include <netinet/ip_var.h>
66 #include <netinet/ip_options.h>
68 #include <netinet/ip6.h>
69 #include <netinet/icmp6.h>
70 #include <netinet6/nd6.h>
71 #include <netinet6/ip6_var.h>
72 #include <netinet6/in6_pcb.h>
74 #include <netinet/tcp.h>
75 #include <netinet/tcp_fsm.h>
76 #include <netinet/tcp_seq.h>
77 #include <netinet/tcp_timer.h>
78 #include <netinet/tcp_var.h>
80 #include <netinet6/tcp6_var.h>
84 #include <netinet6/ipsec.h>
86 #include <netinet6/ipsec6.h>
91 #include <netipsec/ipsec.h>
93 #include <netipsec/ipsec6.h>
95 #include <netipsec/key.h>
98 #include <machine/in_cksum.h>
100 #include <security/mac/mac_framework.h>
102 static int tcp_syncookies = 1;
103 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_RW,
105 "Use TCP SYN cookies if the syncache overflows");
107 static int tcp_syncookiesonly = 0;
108 SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_RW,
109 &tcp_syncookiesonly, 0,
110 "Use only TCP SYN cookies");
112 #define SYNCOOKIE_SECRET_SIZE 8 /* dwords */
113 #define SYNCOOKIE_LIFETIME 16 /* seconds */
116 TAILQ_ENTRY(syncache) sc_hash;
117 struct in_conninfo sc_inc; /* addresses */
118 u_long sc_rxttime; /* retransmit time */
119 u_int16_t sc_rxmits; /* retransmit counter */
121 u_int32_t sc_tsreflect; /* timestamp to reflect */
122 u_int32_t sc_ts; /* our timestamp to send */
123 u_int32_t sc_tsoff; /* ts offset w/ syncookies */
124 u_int32_t sc_flowlabel; /* IPv6 flowlabel */
125 tcp_seq sc_irs; /* seq from peer */
126 tcp_seq sc_iss; /* our ISS */
127 struct mbuf *sc_ipopts; /* source route */
129 u_int16_t sc_peer_mss; /* peer's MSS */
130 u_int16_t sc_wnd; /* advertised window */
131 u_int8_t sc_ip_ttl; /* IPv4 TTL */
132 u_int8_t sc_ip_tos; /* IPv4 TOS */
133 u_int8_t sc_requested_s_scale:4,
134 sc_requested_r_scale:4;
136 #define SCF_NOOPT 0x01 /* no TCP options */
137 #define SCF_WINSCALE 0x02 /* negotiated window scaling */
138 #define SCF_TIMESTAMP 0x04 /* negotiated timestamps */
139 /* MSS is implicit */
140 #define SCF_UNREACH 0x10 /* icmp unreachable received */
141 #define SCF_SIGNATURE 0x20 /* send MD5 digests */
142 #define SCF_SACK 0x80 /* send SACK option */
144 struct label *sc_label; /* MAC label reference */
148 struct syncache_head {
150 TAILQ_HEAD(sch_head, syncache) sch_bucket;
151 struct callout sch_timer;
155 u_int32_t sch_secbits_odd[SYNCOOKIE_SECRET_SIZE];
156 u_int32_t sch_secbits_even[SYNCOOKIE_SECRET_SIZE];
157 u_int sch_reseed; /* time_uptime, seconds */
160 static void syncache_drop(struct syncache *, struct syncache_head *);
161 static void syncache_free(struct syncache *);
162 static void syncache_insert(struct syncache *, struct syncache_head *);
163 struct syncache *syncache_lookup(struct in_conninfo *, struct syncache_head **);
164 static int syncache_respond(struct syncache *);
165 static struct socket *syncache_socket(struct syncache *, struct socket *,
167 static void syncache_timer(void *);
168 static void syncookie_generate(struct syncache_head *, struct syncache *,
170 static struct syncache
171 *syncookie_lookup(struct in_conninfo *, struct syncache_head *,
172 struct syncache *, struct tcpopt *, struct tcphdr *,
176 * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies.
177 * 3 retransmits corresponds to a timeout of (1 + 2 + 4 + 8 == 15) seconds,
178 * the odds are that the user has given up attempting to connect by then.
180 #define SYNCACHE_MAXREXMTS 3
182 /* Arbitrary values */
183 #define TCP_SYNCACHE_HASHSIZE 512
184 #define TCP_SYNCACHE_BUCKETLIMIT 30
186 struct tcp_syncache {
187 struct syncache_head *hashbase;
192 u_int cache_count; /* XXX: unprotected */
197 static struct tcp_syncache tcp_syncache;
199 SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0, "TCP SYN cache");
201 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_RDTUN,
202 &tcp_syncache.bucket_limit, 0, "Per-bucket hash limit for syncache");
204 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_RDTUN,
205 &tcp_syncache.cache_limit, 0, "Overall entry limit for syncache");
207 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_RD,
208 &tcp_syncache.cache_count, 0, "Current number of entries in syncache");
210 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_RDTUN,
211 &tcp_syncache.hashsize, 0, "Size of TCP syncache hashtable");
213 SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, CTLFLAG_RW,
214 &tcp_syncache.rexmt_limit, 0, "Limit on SYN/ACK retransmissions");
216 static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache");
218 #define SYNCACHE_HASH(inc, mask) \
219 ((tcp_syncache.hash_secret ^ \
220 (inc)->inc_faddr.s_addr ^ \
221 ((inc)->inc_faddr.s_addr >> 16) ^ \
222 (inc)->inc_fport ^ (inc)->inc_lport) & mask)
224 #define SYNCACHE_HASH6(inc, mask) \
225 ((tcp_syncache.hash_secret ^ \
226 (inc)->inc6_faddr.s6_addr32[0] ^ \
227 (inc)->inc6_faddr.s6_addr32[3] ^ \
228 (inc)->inc_fport ^ (inc)->inc_lport) & mask)
230 #define ENDPTS_EQ(a, b) ( \
231 (a)->ie_fport == (b)->ie_fport && \
232 (a)->ie_lport == (b)->ie_lport && \
233 (a)->ie_faddr.s_addr == (b)->ie_faddr.s_addr && \
234 (a)->ie_laddr.s_addr == (b)->ie_laddr.s_addr \
237 #define ENDPTS6_EQ(a, b) (memcmp(a, b, sizeof(*a)) == 0)
239 #define SYNCACHE_TIMEOUT(sc, sch, co) do { \
241 (sc)->sc_rxttime = ticks + \
242 TCPTV_RTOBASE * tcp_backoff[(sc)->sc_rxmits - 1]; \
243 if ((sch)->sch_nextc > (sc)->sc_rxttime) \
244 (sch)->sch_nextc = (sc)->sc_rxttime; \
245 if (!TAILQ_EMPTY(&(sch)->sch_bucket) && !(co)) \
246 callout_reset(&(sch)->sch_timer, \
247 (sch)->sch_nextc - ticks, \
248 syncache_timer, (void *)(sch)); \
251 #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx)
252 #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx)
253 #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED)
256 * Requires the syncache entry to be already removed from the bucket list.
259 syncache_free(struct syncache *sc)
262 (void) m_free(sc->sc_ipopts);
264 mac_destroy_syncache(&sc->sc_label);
267 uma_zfree(tcp_syncache.zone, sc);
275 tcp_syncache.cache_count = 0;
276 tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
277 tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT;
278 tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS;
279 tcp_syncache.hash_secret = arc4random();
281 TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize",
282 &tcp_syncache.hashsize);
283 TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit",
284 &tcp_syncache.bucket_limit);
285 if (!powerof2(tcp_syncache.hashsize) || tcp_syncache.hashsize == 0) {
286 printf("WARNING: syncache hash size is not a power of 2.\n");
287 tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
289 tcp_syncache.hashmask = tcp_syncache.hashsize - 1;
292 tcp_syncache.cache_limit =
293 tcp_syncache.hashsize * tcp_syncache.bucket_limit;
294 TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit",
295 &tcp_syncache.cache_limit);
297 /* Allocate the hash table. */
298 MALLOC(tcp_syncache.hashbase, struct syncache_head *,
299 tcp_syncache.hashsize * sizeof(struct syncache_head),
300 M_SYNCACHE, M_WAITOK | M_ZERO);
302 /* Initialize the hash buckets. */
303 for (i = 0; i < tcp_syncache.hashsize; i++) {
304 TAILQ_INIT(&tcp_syncache.hashbase[i].sch_bucket);
305 mtx_init(&tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head",
307 callout_init_mtx(&tcp_syncache.hashbase[i].sch_timer,
308 &tcp_syncache.hashbase[i].sch_mtx, 0);
309 tcp_syncache.hashbase[i].sch_length = 0;
312 /* Create the syncache entry zone. */
313 tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache),
314 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
315 uma_zone_set_max(tcp_syncache.zone, tcp_syncache.cache_limit);
319 * Inserts a syncache entry into the specified bucket row.
320 * Locks and unlocks the syncache_head autonomously.
323 syncache_insert(struct syncache *sc, struct syncache_head *sch)
325 struct syncache *sc2;
330 * Make sure that we don't overflow the per-bucket limit.
331 * If the bucket is full, toss the oldest element.
333 if (sch->sch_length >= tcp_syncache.bucket_limit) {
334 KASSERT(!TAILQ_EMPTY(&sch->sch_bucket),
335 ("sch->sch_length incorrect"));
336 sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head);
337 syncache_drop(sc2, sch);
338 tcpstat.tcps_sc_bucketoverflow++;
341 /* Put it into the bucket. */
342 TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash);
345 /* Reinitialize the bucket row's timer. */
346 SYNCACHE_TIMEOUT(sc, sch, 1);
350 tcp_syncache.cache_count++;
351 tcpstat.tcps_sc_added++;
355 * Remove and free entry from syncache bucket row.
356 * Expects locked syncache head.
359 syncache_drop(struct syncache *sc, struct syncache_head *sch)
362 SCH_LOCK_ASSERT(sch);
364 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
368 tcp_syncache.cache_count--;
372 * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted.
373 * If we have retransmitted an entry the maximum number of times, expire it.
374 * One separate timer for each bucket row.
377 syncache_timer(void *xsch)
379 struct syncache_head *sch = (struct syncache_head *)xsch;
380 struct syncache *sc, *nsc;
384 /* NB: syncache_head has already been locked by the callout. */
385 SCH_LOCK_ASSERT(sch);
387 TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) {
389 * We do not check if the listen socket still exists
390 * and accept the case where the listen socket may be
391 * gone by the time we resend the SYN/ACK. We do
392 * not expect this to happens often. If it does,
393 * then the RST will be sent by the time the remote
394 * host does the SYN/ACK->ACK.
396 if (sc->sc_rxttime >= tick) {
397 if (sc->sc_rxttime < sch->sch_nextc)
398 sch->sch_nextc = sc->sc_rxttime;
402 if (sc->sc_rxmits > tcp_syncache.rexmt_limit) {
403 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
404 log(LOG_DEBUG, "%s; %s: Response timeout\n",
408 syncache_drop(sc, sch);
409 tcpstat.tcps_sc_stale++;
413 (void) syncache_respond(sc);
414 tcpstat.tcps_sc_retransmitted++;
415 SYNCACHE_TIMEOUT(sc, sch, 0);
417 if (!TAILQ_EMPTY(&(sch)->sch_bucket))
418 callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick,
419 syncache_timer, (void *)(sch));
423 * Find an entry in the syncache.
424 * Returns always with locked syncache_head plus a matching entry or NULL.
427 syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp)
430 struct syncache_head *sch;
433 if (inc->inc_isipv6) {
434 sch = &tcp_syncache.hashbase[
435 SYNCACHE_HASH6(inc, tcp_syncache.hashmask)];
440 /* Circle through bucket row to find matching entry. */
441 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
442 if (ENDPTS6_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie))
448 sch = &tcp_syncache.hashbase[
449 SYNCACHE_HASH(inc, tcp_syncache.hashmask)];
454 /* Circle through bucket row to find matching entry. */
455 TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
457 if (sc->sc_inc.inc_isipv6)
460 if (ENDPTS_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie))
464 SCH_LOCK_ASSERT(*schp);
465 return (NULL); /* always returns with locked sch */
469 * This function is called when we get a RST for a
470 * non-existent connection, so that we can see if the
471 * connection is in the syn cache. If it is, zap it.
474 syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th)
477 struct syncache_head *sch;
479 sc = syncache_lookup(inc, &sch); /* returns locked sch */
480 SCH_LOCK_ASSERT(sch);
485 * If the RST bit is set, check the sequence number to see
486 * if this is a valid reset segment.
488 * In all states except SYN-SENT, all reset (RST) segments
489 * are validated by checking their SEQ-fields. A reset is
490 * valid if its sequence number is in the window.
492 * The sequence number in the reset segment is normally an
493 * echo of our outgoing acknowlegement numbers, but some hosts
494 * send a reset with the sequence number at the rightmost edge
495 * of our receive window, and we have to handle this case.
497 if (SEQ_GEQ(th->th_seq, sc->sc_irs) &&
498 SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
499 syncache_drop(sc, sch);
500 tcpstat.tcps_sc_reset++;
507 syncache_badack(struct in_conninfo *inc)
510 struct syncache_head *sch;
512 sc = syncache_lookup(inc, &sch); /* returns locked sch */
513 SCH_LOCK_ASSERT(sch);
515 syncache_drop(sc, sch);
516 tcpstat.tcps_sc_badack++;
522 syncache_unreach(struct in_conninfo *inc, struct tcphdr *th)
525 struct syncache_head *sch;
527 sc = syncache_lookup(inc, &sch); /* returns locked sch */
528 SCH_LOCK_ASSERT(sch);
532 /* If the sequence number != sc_iss, then it's a bogus ICMP msg */
533 if (ntohl(th->th_seq) != sc->sc_iss)
537 * If we've rertransmitted 3 times and this is our second error,
538 * we remove the entry. Otherwise, we allow it to continue on.
539 * This prevents us from incorrectly nuking an entry during a
540 * spurious network outage.
544 if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) {
545 sc->sc_flags |= SCF_UNREACH;
548 syncache_drop(sc, sch);
549 tcpstat.tcps_sc_unreach++;
555 * Build a new TCP socket structure from a syncache entry.
557 static struct socket *
558 syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m)
560 struct inpcb *inp = NULL;
566 INP_INFO_WLOCK_ASSERT(&tcbinfo);
569 * Ok, create the full blown connection, and set things up
570 * as they would have been set up if we had created the
571 * connection when the SYN arrived. If we can't create
572 * the connection, abort it.
574 so = sonewconn(lso, SS_ISCONNECTED);
577 * Drop the connection; we will either send a RST or
578 * have the peer retransmit its SYN again after its
581 tcpstat.tcps_listendrop++;
582 if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
583 log(LOG_DEBUG, "%s; %s: Socket create failed "
584 "due to limits or memory shortage\n",
592 mac_set_socket_peer_from_mbuf(m, so);
599 /* Insert new socket into PCB hash list. */
600 inp->inp_inc.inc_isipv6 = sc->sc_inc.inc_isipv6;
602 if (sc->sc_inc.inc_isipv6) {
603 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
605 inp->inp_vflag &= ~INP_IPV6;
606 inp->inp_vflag |= INP_IPV4;
608 inp->inp_laddr = sc->sc_inc.inc_laddr;
612 inp->inp_lport = sc->sc_inc.inc_lport;
613 if (in_pcbinshash(inp) != 0) {
615 * Undo the assignments above if we failed to
616 * put the PCB on the hash lists.
619 if (sc->sc_inc.inc_isipv6)
620 inp->in6p_laddr = in6addr_any;
623 inp->inp_laddr.s_addr = INADDR_ANY;
628 /* Copy old policy into new socket's. */
629 if (ipsec_copy_pcbpolicy(sotoinpcb(lso)->inp_sp, inp->inp_sp))
630 printf("syncache_socket: could not copy policy\n");
633 /* Copy old policy into new socket's. */
634 if (ipsec_copy_policy(sotoinpcb(lso)->inp_sp, inp->inp_sp))
635 printf("syncache_socket: could not copy policy\n");
638 if (sc->sc_inc.inc_isipv6) {
639 struct inpcb *oinp = sotoinpcb(lso);
640 struct in6_addr laddr6;
641 struct sockaddr_in6 sin6;
643 * Inherit socket options from the listening socket.
644 * Note that in6p_inputopts are not (and should not be)
645 * copied, since it stores previously received options and is
646 * used to detect if each new option is different than the
647 * previous one and hence should be passed to a user.
648 * If we copied in6p_inputopts, a user would not be able to
649 * receive options just after calling the accept system call.
651 inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS;
652 if (oinp->in6p_outputopts)
653 inp->in6p_outputopts =
654 ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT);
656 sin6.sin6_family = AF_INET6;
657 sin6.sin6_len = sizeof(sin6);
658 sin6.sin6_addr = sc->sc_inc.inc6_faddr;
659 sin6.sin6_port = sc->sc_inc.inc_fport;
660 sin6.sin6_flowinfo = sin6.sin6_scope_id = 0;
661 laddr6 = inp->in6p_laddr;
662 if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr))
663 inp->in6p_laddr = sc->sc_inc.inc6_laddr;
664 if (in6_pcbconnect(inp, (struct sockaddr *)&sin6,
666 inp->in6p_laddr = laddr6;
669 /* Override flowlabel from in6_pcbconnect. */
670 inp->in6p_flowinfo &= ~IPV6_FLOWLABEL_MASK;
671 inp->in6p_flowinfo |= sc->sc_flowlabel;
675 struct in_addr laddr;
676 struct sockaddr_in sin;
678 inp->inp_options = ip_srcroute(m);
679 if (inp->inp_options == NULL) {
680 inp->inp_options = sc->sc_ipopts;
681 sc->sc_ipopts = NULL;
684 sin.sin_family = AF_INET;
685 sin.sin_len = sizeof(sin);
686 sin.sin_addr = sc->sc_inc.inc_faddr;
687 sin.sin_port = sc->sc_inc.inc_fport;
688 bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero));
689 laddr = inp->inp_laddr;
690 if (inp->inp_laddr.s_addr == INADDR_ANY)
691 inp->inp_laddr = sc->sc_inc.inc_laddr;
692 if (in_pcbconnect(inp, (struct sockaddr *)&sin,
694 inp->inp_laddr = laddr;
699 tp->t_state = TCPS_SYN_RECEIVED;
700 tp->iss = sc->sc_iss;
701 tp->irs = sc->sc_irs;
704 tp->snd_wl1 = sc->sc_irs;
705 tp->snd_max = tp->iss + 1;
706 tp->snd_nxt = tp->iss + 1;
707 tp->rcv_up = sc->sc_irs + 1;
708 tp->rcv_wnd = sc->sc_wnd;
709 tp->rcv_adv += tp->rcv_wnd;
710 tp->last_ack_sent = tp->rcv_nxt;
712 tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY);
713 if (sc->sc_flags & SCF_NOOPT)
714 tp->t_flags |= TF_NOOPT;
716 if (sc->sc_flags & SCF_WINSCALE) {
717 tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE;
718 tp->snd_scale = sc->sc_requested_s_scale;
719 tp->request_r_scale = sc->sc_requested_r_scale;
721 if (sc->sc_flags & SCF_TIMESTAMP) {
722 tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP;
723 tp->ts_recent = sc->sc_tsreflect;
724 tp->ts_recent_age = ticks;
725 tp->ts_offset = sc->sc_tsoff;
728 if (sc->sc_flags & SCF_SIGNATURE)
729 tp->t_flags |= TF_SIGNATURE;
731 if (sc->sc_flags & SCF_SACK)
732 tp->t_flags |= TF_SACK_PERMIT;
736 * Set up MSS and get cached values from tcp_hostcache.
737 * This might overwrite some of the defaults we just set.
739 tcp_mss(tp, sc->sc_peer_mss);
742 * If the SYN,ACK was retransmitted, reset cwnd to 1 segment.
744 if (sc->sc_rxmits > 1)
745 tp->snd_cwnd = tp->t_maxseg;
746 tcp_timer_activate(tp, TT_KEEP, tcp_keepinit);
750 tcpstat.tcps_accepts++;
762 * This function gets called when we receive an ACK for a
763 * socket in the LISTEN state. We look up the connection
764 * in the syncache, and if its there, we pull it out of
765 * the cache and turn it into a full-blown connection in
766 * the SYN-RECEIVED state.
769 syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
770 struct socket **lsop, struct mbuf *m)
773 struct syncache_head *sch;
778 * Global TCP locks are held because we manipulate the PCB lists
779 * and create a new socket.
781 INP_INFO_WLOCK_ASSERT(&tcbinfo);
782 KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK,
783 ("%s: can handle only ACK", __func__));
785 sc = syncache_lookup(inc, &sch); /* returns locked sch */
786 SCH_LOCK_ASSERT(sch);
789 * There is no syncache entry, so see if this ACK is
790 * a returning syncookie. To do this, first:
791 * A. See if this socket has had a syncache entry dropped in
792 * the past. We don't want to accept a bogus syncookie
793 * if we've never received a SYN.
794 * B. check that the syncookie is valid. If it is, then
795 * cobble up a fake syncache entry, and return.
797 if (!tcp_syncookies) {
799 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
800 log(LOG_DEBUG, "%s; %s: Spurious ACK\n",
804 bzero(&scs, sizeof(scs));
805 sc = syncookie_lookup(inc, sch, &scs, to, th, *lsop);
808 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
809 log(LOG_DEBUG, "%s; %s: Segment failed "
810 "SYNCOOKIE authentication\n",
814 tcpstat.tcps_sc_recvcookie++;
816 /* Pull out the entry to unlock the bucket row. */
817 TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
819 tcp_syncache.cache_count--;
824 * Segment validation:
825 * ACK must match our initial sequence number + 1 (the SYN|ACK).
827 if (th->th_ack != sc->sc_iss + 1) {
828 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
829 log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u\n",
830 s, __func__, th->th_ack, sc->sc_iss);
834 * The SEQ must match the received initial receive sequence
835 * number + 1 (the SYN) because we didn't ACK any data that
836 * may have come with the SYN.
838 if (th->th_seq != sc->sc_irs + 1) {
839 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
840 log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u\n",
841 s, __func__, th->th_ack, sc->sc_iss);
845 * If timestamps were present in the SYN and we accepted
846 * them in our SYN|ACK we require them to be present from
847 * now on. And vice versa.
849 if ((sc->sc_flags & SCF_TIMESTAMP) && !(to->to_flags & TOF_TS)) {
850 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
851 log(LOG_DEBUG, "%s; %s: Timestamp missing\n",
855 if (!(sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) {
856 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
857 log(LOG_DEBUG, "%s; %s: Timestamp not expected\n",
862 * If timestamps were negotiated the reflected timestamp
863 * must be equal to what we actually sent in the SYN|ACK.
865 if ((to->to_flags & TOF_TS) && to->to_tsecr != sc->sc_ts) {
866 if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
867 log(LOG_DEBUG, "%s; %s: TSECR %u != TS %u\n",
868 s, __func__, to->to_tsecr, sc->sc_ts);
872 *lsop = syncache_socket(sc, *lsop, m);
875 tcpstat.tcps_sc_aborted++;
877 tcpstat.tcps_sc_completed++;
883 if (sc != NULL && sc != &scs)
892 * Given a LISTEN socket and an inbound SYN request, add
893 * this to the syn cache, and send back a segment:
894 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
897 * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN.
898 * Doing so would require that we hold onto the data and deliver it
899 * to the application. However, if we are the target of a SYN-flood
900 * DoS attack, an attacker could send data which would eventually
901 * consume all available buffer space if it were ACKed. By not ACKing
902 * the data, we avoid this DoS scenario.
905 syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
906 struct inpcb *inp, struct socket **lsop, struct mbuf *m)
910 struct syncache *sc = NULL;
911 struct syncache_head *sch;
912 struct mbuf *ipopts = NULL;
914 int win, sb_hiwat, ip_ttl, ip_tos, noopt;
916 int autoflowlabel = 0;
919 struct label *maclabel;
923 INP_INFO_WLOCK_ASSERT(&tcbinfo);
924 INP_LOCK_ASSERT(inp); /* listen socket */
927 * Combine all so/tp operations very early to drop the INP lock as
934 if (inc->inc_isipv6 &&
935 (inp->in6p_flags & IN6P_AUTOFLOWLABEL))
938 ip_ttl = inp->inp_ip_ttl;
939 ip_tos = inp->inp_ip_tos;
940 win = sbspace(&so->so_rcv);
941 sb_hiwat = so->so_rcv.sb_hiwat;
942 noopt = (tp->t_flags & TF_NOOPT);
948 if (mac_init_syncache(&maclabel) != 0) {
950 INP_INFO_WUNLOCK(&tcbinfo);
953 mac_init_syncache_from_inpcb(maclabel, inp);
956 INP_INFO_WUNLOCK(&tcbinfo);
959 * Remember the IP options, if any.
962 if (!inc->inc_isipv6)
964 ipopts = ip_srcroute(m);
967 * See if we already have an entry for this connection.
968 * If we do, resend the SYN,ACK, and reset the retransmit timer.
970 * XXX: should the syncache be re-initialized with the contents
971 * of the new SYN here (which may have different options?)
973 sc = syncache_lookup(inc, &sch); /* returns locked entry */
974 SCH_LOCK_ASSERT(sch);
976 tcpstat.tcps_sc_dupsyn++;
979 * If we were remembering a previous source route,
980 * forget it and use the new one we've been given.
983 (void) m_free(sc->sc_ipopts);
984 sc->sc_ipopts = ipopts;
987 * Update timestamp if present.
989 if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS))
990 sc->sc_tsreflect = to->to_tsval;
992 sc->sc_flags &= ~SCF_TIMESTAMP;
995 * Since we have already unconditionally allocated label
996 * storage, free it up. The syncache entry will already
997 * have an initialized label we can use.
999 mac_destroy_syncache(&maclabel);
1000 KASSERT(sc->sc_label != NULL,
1001 ("%s: label not initialized", __func__));
1003 if (syncache_respond(sc) == 0) {
1004 SYNCACHE_TIMEOUT(sc, sch, 1);
1005 tcpstat.tcps_sndacks++;
1006 tcpstat.tcps_sndtotal++;
1012 sc = uma_zalloc(tcp_syncache.zone, M_NOWAIT | M_ZERO);
1015 * The zone allocator couldn't provide more entries.
1016 * Treat this as if the cache was full; drop the oldest
1017 * entry and insert the new one.
1019 tcpstat.tcps_sc_zonefail++;
1020 if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL)
1021 syncache_drop(sc, sch);
1022 sc = uma_zalloc(tcp_syncache.zone, M_NOWAIT | M_ZERO);
1024 if (tcp_syncookies) {
1025 bzero(&scs, sizeof(scs));
1030 (void) m_free(ipopts);
1037 * Fill in the syncache values.
1040 sc->sc_label = maclabel;
1042 sc->sc_ipopts = ipopts;
1043 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
1045 if (!inc->inc_isipv6)
1048 sc->sc_ip_tos = ip_tos;
1049 sc->sc_ip_ttl = ip_ttl;
1052 sc->sc_irs = th->th_seq;
1053 sc->sc_iss = arc4random();
1055 sc->sc_flowlabel = 0;
1058 * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN].
1059 * win was derived from socket earlier in the function.
1062 win = imin(win, TCP_MAXWIN);
1065 if (tcp_do_rfc1323) {
1067 * A timestamp received in a SYN makes
1068 * it ok to send timestamp requests and replies.
1070 if (to->to_flags & TOF_TS) {
1071 sc->sc_tsreflect = to->to_tsval;
1073 sc->sc_flags |= SCF_TIMESTAMP;
1075 if (to->to_flags & TOF_SCALE) {
1079 * Compute proper scaling value from buffer space.
1080 * Leave enough room for the socket buffer to grow
1081 * with auto sizing. This allows us to scale the
1082 * receive buffer over a wide range while not losing
1083 * any efficiency or fine granularity.
1085 * RFC1323: The Window field in a SYN (i.e., a <SYN>
1086 * or <SYN,ACK>) segment itself is never scaled.
1088 while (wscale < TCP_MAX_WINSHIFT &&
1089 (0x1 << wscale) < tcp_minmss)
1091 sc->sc_requested_r_scale = wscale;
1092 sc->sc_requested_s_scale = to->to_wscale;
1093 sc->sc_flags |= SCF_WINSCALE;
1096 #ifdef TCP_SIGNATURE
1098 * If listening socket requested TCP digests, and received SYN
1099 * contains the option, flag this in the syncache so that
1100 * syncache_respond() will do the right thing with the SYN+ACK.
1101 * XXX: Currently we always record the option by default and will
1102 * attempt to use it in syncache_respond().
1104 if (to->to_flags & TOF_SIGNATURE)
1105 sc->sc_flags |= SCF_SIGNATURE;
1107 if (to->to_flags & TOF_SACK)
1108 sc->sc_flags |= SCF_SACK;
1109 if (to->to_flags & TOF_MSS)
1110 sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */
1112 sc->sc_flags |= SCF_NOOPT;
1114 if (tcp_syncookies) {
1115 syncookie_generate(sch, sc, &flowtmp);
1118 sc->sc_flowlabel = flowtmp;
1124 (htonl(ip6_randomflowlabel()) & IPV6_FLOWLABEL_MASK);
1130 * Do a standard 3-way handshake.
1132 if (syncache_respond(sc) == 0) {
1133 if (tcp_syncookies && tcp_syncookiesonly && sc != &scs)
1135 else if (sc != &scs)
1136 syncache_insert(sc, sch); /* locks and unlocks sch */
1137 tcpstat.tcps_sndacks++;
1138 tcpstat.tcps_sndtotal++;
1142 tcpstat.tcps_sc_dropped++;
1148 mac_destroy_syncache(&maclabel);
1156 syncache_respond(struct syncache *sc)
1158 struct ip *ip = NULL;
1162 u_int16_t hlen, tlen, mssopt;
1165 struct ip6_hdr *ip6 = NULL;
1170 (sc->sc_inc.inc_isipv6) ? sizeof(struct ip6_hdr) :
1173 tlen = hlen + sizeof(struct tcphdr);
1175 /* Determine MSS we advertize to other end of connection. */
1176 mssopt = tcp_mssopt(&sc->sc_inc);
1177 if (sc->sc_peer_mss)
1178 mssopt = max( min(sc->sc_peer_mss, mssopt), tcp_minmss);
1180 /* XXX: Assume that the entire packet will fit in a header mbuf. */
1181 KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN,
1182 ("syncache: mbuf too small"));
1184 /* Create the IP+TCP header from scratch. */
1185 m = m_gethdr(M_DONTWAIT, MT_DATA);
1189 mac_create_mbuf_from_syncache(sc->sc_label, m);
1191 m->m_data += max_linkhdr;
1193 m->m_pkthdr.len = tlen;
1194 m->m_pkthdr.rcvif = NULL;
1197 if (sc->sc_inc.inc_isipv6) {
1198 ip6 = mtod(m, struct ip6_hdr *);
1199 ip6->ip6_vfc = IPV6_VERSION;
1200 ip6->ip6_nxt = IPPROTO_TCP;
1201 ip6->ip6_src = sc->sc_inc.inc6_laddr;
1202 ip6->ip6_dst = sc->sc_inc.inc6_faddr;
1203 ip6->ip6_plen = htons(tlen - hlen);
1204 /* ip6_hlim is set after checksum */
1205 ip6->ip6_flow &= ~IPV6_FLOWLABEL_MASK;
1206 ip6->ip6_flow |= sc->sc_flowlabel;
1208 th = (struct tcphdr *)(ip6 + 1);
1212 ip = mtod(m, struct ip *);
1213 ip->ip_v = IPVERSION;
1214 ip->ip_hl = sizeof(struct ip) >> 2;
1219 ip->ip_p = IPPROTO_TCP;
1220 ip->ip_src = sc->sc_inc.inc_laddr;
1221 ip->ip_dst = sc->sc_inc.inc_faddr;
1222 ip->ip_ttl = sc->sc_ip_ttl;
1223 ip->ip_tos = sc->sc_ip_tos;
1226 * See if we should do MTU discovery. Route lookups are
1227 * expensive, so we will only unset the DF bit if:
1229 * 1) path_mtu_discovery is disabled
1230 * 2) the SCF_UNREACH flag has been set
1232 if (path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0))
1233 ip->ip_off |= IP_DF;
1235 th = (struct tcphdr *)(ip + 1);
1237 th->th_sport = sc->sc_inc.inc_lport;
1238 th->th_dport = sc->sc_inc.inc_fport;
1240 th->th_seq = htonl(sc->sc_iss);
1241 th->th_ack = htonl(sc->sc_irs + 1);
1242 th->th_off = sizeof(struct tcphdr) >> 2;
1244 th->th_flags = TH_SYN|TH_ACK;
1245 th->th_win = htons(sc->sc_wnd);
1248 /* Tack on the TCP options. */
1249 if ((sc->sc_flags & SCF_NOOPT) == 0) {
1253 to.to_flags = TOF_MSS;
1254 if (sc->sc_flags & SCF_WINSCALE) {
1255 to.to_wscale = sc->sc_requested_r_scale;
1256 to.to_flags |= TOF_SCALE;
1258 if (sc->sc_flags & SCF_TIMESTAMP) {
1259 /* Virgin timestamp or TCP cookie enhanced one. */
1260 to.to_tsval = sc->sc_ts;
1261 to.to_tsecr = sc->sc_tsreflect;
1262 to.to_flags |= TOF_TS;
1264 if (sc->sc_flags & SCF_SACK)
1265 to.to_flags |= TOF_SACKPERM;
1266 #ifdef TCP_SIGNATURE
1267 if (sc->sc_flags & SCF_SIGNATURE)
1268 to.to_flags |= TOF_SIGNATURE;
1270 optlen = tcp_addoptions(&to, (u_char *)(th + 1));
1272 #ifdef TCP_SIGNATURE
1273 tcp_signature_compute(m, sizeof(struct ip), 0, optlen,
1274 to.to_signature, IPSEC_DIR_OUTBOUND);
1277 /* Adjust headers by option size. */
1278 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
1280 m->m_pkthdr.len += optlen;
1282 if (sc->sc_inc.inc_isipv6)
1283 ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen);
1286 ip->ip_len += optlen;
1291 if (sc->sc_inc.inc_isipv6) {
1293 th->th_sum = in6_cksum(m, IPPROTO_TCP, hlen,
1294 tlen + optlen - hlen);
1295 ip6->ip6_hlim = in6_selecthlim(NULL, NULL);
1296 error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL);
1300 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
1301 htons(tlen + optlen - hlen + IPPROTO_TCP));
1302 m->m_pkthdr.csum_flags = CSUM_TCP;
1303 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
1304 error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL);
1310 * The purpose of SYN cookies is to avoid keeping track of all SYN's we
1311 * receive and to be able to handle SYN floods from bogus source addresses
1312 * (where we will never receive any reply). SYN floods try to exhaust all
1313 * our memory and available slots in the SYN cache table to cause a denial
1314 * of service to legitimate users of the local host.
1316 * The idea of SYN cookies is to encode and include all necessary information
1317 * about the connection setup state within the SYN-ACK we send back and thus
1318 * to get along without keeping any local state until the ACK to the SYN-ACK
1319 * arrives (if ever). Everything we need to know should be available from
1320 * the information we encoded in the SYN-ACK.
1322 * More information about the theory behind SYN cookies and its first
1323 * discussion and specification can be found at:
1324 * http://cr.yp.to/syncookies.html (overview)
1325 * http://cr.yp.to/syncookies/archive (gory details)
1327 * This implementation extends the orginal idea and first implementation
1328 * of FreeBSD by using not only the initial sequence number field to store
1329 * information but also the timestamp field if present. This way we can
1330 * keep track of the entire state we need to know to recreate the session in
1331 * its original form. Almost all TCP speakers implement RFC1323 timestamps
1332 * these days. For those that do not we still have to live with the known
1333 * shortcomings of the ISN only SYN cookies.
1337 * Initial sequence number we send:
1338 * 31|................................|0
1339 * DDDDDDDDDDDDDDDDDDDDDDDDDMMMRRRP
1340 * D = MD5 Digest (first dword)
1342 * R = Rotation of secret
1343 * P = Odd or Even secret
1345 * The MD5 Digest is computed with over following parameters:
1346 * a) randomly rotated secret
1347 * b) struct in_conninfo containing the remote/local ip/port (IPv4&IPv6)
1348 * c) the received initial sequence number from remote host
1349 * d) the rotation offset and odd/even bit
1351 * Timestamp we send:
1352 * 31|................................|0
1353 * DDDDDDDDDDDDDDDDDDDDDDSSSSRRRRA5
1354 * D = MD5 Digest (third dword) (only as filler)
1355 * S = Requested send window scale
1356 * R = Requested receive window scale
1358 * 5 = TCP-MD5 enabled (not implemented yet)
1359 * XORed with MD5 Digest (forth dword)
1361 * The timestamp isn't cryptographically secure and doesn't need to be.
1362 * The double use of the MD5 digest dwords ties it to a specific remote/
1363 * local host/port, remote initial sequence number and our local time
1364 * limited secret. A received timestamp is reverted (XORed) and then
1365 * the contained MD5 dword is compared to the computed one to ensure the
1366 * timestamp belongs to the SYN-ACK we sent. The other parameters may
1367 * have been tampered with but this isn't different from supplying bogus
1368 * values in the SYN in the first place.
1370 * Some problems with SYN cookies remain however:
1371 * Consider the problem of a recreated (and retransmitted) cookie. If the
1372 * original SYN was accepted, the connection is established. The second
1373 * SYN is inflight, and if it arrives with an ISN that falls within the
1374 * receive window, the connection is killed.
1377 * A heuristic to determine when to accept syn cookies is not necessary.
1378 * An ACK flood would cause the syncookie verification to be attempted,
1379 * but a SYN flood causes syncookies to be generated. Both are of equal
1380 * cost, so there's no point in trying to optimize the ACK flood case.
1381 * Also, if you don't process certain ACKs for some reason, then all someone
1382 * would have to do is launch a SYN and ACK flood at the same time, which
1383 * would stop cookie verification and defeat the entire purpose of syncookies.
1385 static int tcp_sc_msstab[] = { 0, 256, 468, 536, 996, 1452, 1460, 8960 };
1388 syncookie_generate(struct syncache_head *sch, struct syncache *sc,
1389 u_int32_t *flowlabel)
1392 u_int32_t md5_buffer[MD5_DIGEST_LENGTH / sizeof(u_int32_t)];
1395 u_int off, pmss, mss;
1398 SCH_LOCK_ASSERT(sch);
1400 /* Which of the two secrets to use. */
1401 secbits = sch->sch_oddeven ?
1402 sch->sch_secbits_odd : sch->sch_secbits_even;
1404 /* Reseed secret if too old. */
1405 if (sch->sch_reseed < time_uptime) {
1406 sch->sch_oddeven = sch->sch_oddeven ? 0 : 1; /* toggle */
1407 secbits = sch->sch_oddeven ?
1408 sch->sch_secbits_odd : sch->sch_secbits_even;
1409 for (i = 0; i < SYNCOOKIE_SECRET_SIZE; i++)
1410 secbits[i] = arc4random();
1411 sch->sch_reseed = time_uptime + SYNCOOKIE_LIFETIME;
1414 /* Secret rotation offset. */
1415 off = sc->sc_iss & 0x7; /* iss was randomized before */
1417 /* Maximum segment size calculation. */
1418 pmss = max( min(sc->sc_peer_mss, tcp_mssopt(&sc->sc_inc)), tcp_minmss);
1419 for (mss = sizeof(tcp_sc_msstab) / sizeof(int) - 1; mss > 0; mss--)
1420 if (tcp_sc_msstab[mss] <= pmss)
1423 /* Fold parameters and MD5 digest into the ISN we will send. */
1424 data = sch->sch_oddeven;/* odd or even secret, 1 bit */
1425 data |= off << 1; /* secret offset, derived from iss, 3 bits */
1426 data |= mss << 4; /* mss, 3 bits */
1429 MD5Update(&ctx, ((u_int8_t *)secbits) + off,
1430 SYNCOOKIE_SECRET_SIZE * sizeof(*secbits) - off);
1431 MD5Update(&ctx, secbits, off);
1432 MD5Update(&ctx, &sc->sc_inc, sizeof(sc->sc_inc));
1433 MD5Update(&ctx, &sc->sc_irs, sizeof(sc->sc_irs));
1434 MD5Update(&ctx, &data, sizeof(data));
1435 MD5Final((u_int8_t *)&md5_buffer, &ctx);
1437 data |= (md5_buffer[0] << 7);
1441 *flowlabel = md5_buffer[1] & IPV6_FLOWLABEL_MASK;
1444 /* Additional parameters are stored in the timestamp if present. */
1445 if (sc->sc_flags & SCF_TIMESTAMP) {
1446 data = ((sc->sc_flags & SCF_SIGNATURE) ? 1 : 0); /* TCP-MD5, 1 bit */
1447 data |= ((sc->sc_flags & SCF_SACK) ? 1 : 0) << 1; /* SACK, 1 bit */
1448 data |= sc->sc_requested_s_scale << 2; /* SWIN scale, 4 bits */
1449 data |= sc->sc_requested_r_scale << 6; /* RWIN scale, 4 bits */
1450 data |= md5_buffer[2] << 10; /* more digest bits */
1451 data ^= md5_buffer[3];
1453 sc->sc_tsoff = data - ticks; /* after XOR */
1459 static struct syncache *
1460 syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch,
1461 struct syncache *sc, struct tcpopt *to, struct tcphdr *th,
1465 u_int32_t md5_buffer[MD5_DIGEST_LENGTH / sizeof(u_int32_t)];
1469 int off, mss, wnd, flags;
1471 SCH_LOCK_ASSERT(sch);
1474 * Pull information out of SYN-ACK/ACK and
1475 * revert sequence number advances.
1477 ack = th->th_ack - 1;
1478 seq = th->th_seq - 1;
1479 off = (ack >> 1) & 0x7;
1480 mss = (ack >> 4) & 0x7;
1483 /* Which of the two secrets to use. */
1484 secbits = (flags & 0x1) ? sch->sch_secbits_odd : sch->sch_secbits_even;
1487 * The secret wasn't updated for the lifetime of a syncookie,
1488 * so this SYN-ACK/ACK is either too old (replay) or totally bogus.
1490 if (sch->sch_reseed < time_uptime) {
1494 /* Recompute the digest so we can compare it. */
1496 MD5Update(&ctx, ((u_int8_t *)secbits) + off,
1497 SYNCOOKIE_SECRET_SIZE * sizeof(*secbits) - off);
1498 MD5Update(&ctx, secbits, off);
1499 MD5Update(&ctx, inc, sizeof(*inc));
1500 MD5Update(&ctx, &seq, sizeof(seq));
1501 MD5Update(&ctx, &flags, sizeof(flags));
1502 MD5Final((u_int8_t *)&md5_buffer, &ctx);
1504 /* Does the digest part of or ACK'ed ISS match? */
1505 if ((ack & (~0x7f)) != (md5_buffer[0] << 7))
1508 /* Does the digest part of our reflected timestamp match? */
1509 if (to->to_flags & TOF_TS) {
1510 data = md5_buffer[3] ^ to->to_tsecr;
1511 if ((data & (~0x3ff)) != (md5_buffer[2] << 10))
1515 /* Fill in the syncache values. */
1516 bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
1517 sc->sc_ipopts = NULL;
1523 if (inc->inc_isipv6) {
1524 if (sotoinpcb(so)->in6p_flags & IN6P_AUTOFLOWLABEL)
1525 sc->sc_flowlabel = md5_buffer[1] & IPV6_FLOWLABEL_MASK;
1529 sc->sc_ip_ttl = sotoinpcb(so)->inp_ip_ttl;
1530 sc->sc_ip_tos = sotoinpcb(so)->inp_ip_tos;
1533 /* Additional parameters that were encoded in the timestamp. */
1535 sc->sc_flags |= SCF_TIMESTAMP;
1536 sc->sc_tsreflect = to->to_tsval;
1537 sc->sc_ts = to->to_tsecr;
1538 sc->sc_tsoff = to->to_tsecr - ticks;
1539 sc->sc_flags |= (data & 0x1) ? SCF_SIGNATURE : 0;
1540 sc->sc_flags |= ((data >> 1) & 0x1) ? SCF_SACK : 0;
1541 sc->sc_requested_s_scale = min((data >> 2) & 0xf,
1543 sc->sc_requested_r_scale = min((data >> 6) & 0xf,
1545 if (sc->sc_requested_s_scale || sc->sc_requested_r_scale)
1546 sc->sc_flags |= SCF_WINSCALE;
1548 sc->sc_flags |= SCF_NOOPT;
1550 wnd = sbspace(&so->so_rcv);
1552 wnd = imin(wnd, TCP_MAXWIN);
1556 sc->sc_peer_mss = tcp_sc_msstab[mss];