/*- * Copyright (c) 2001 McAfee, Inc. * Copyright (c) 2006 Andre Oppermann, Internet Business Solutions AG * All rights reserved. * * This software was developed for the FreeBSD Project by Jonathan Lemon * and McAfee Research, the Security Research Division of McAfee, Inc. under * DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the * DARPA CHATS research program. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF * SUCH DAMAGE. */ #include __FBSDID("$FreeBSD$"); #include "opt_inet.h" #include "opt_inet6.h" #include "opt_ipsec.h" #include "opt_mac.h" #include #include #include #include #include #include #include #include #include #include #include /* for proc0 declaration */ #include #include #include #include #include #include #include #include #include #include #include #include #include #include #ifdef INET6 #include #include #include #include #include #endif #include #include #include #include #include #include #include #ifdef INET6 #include #endif #ifdef IPSEC #include #ifdef INET6 #include #endif #include #endif /*IPSEC*/ #include #include static int tcp_syncookies = 1; SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_RW, &tcp_syncookies, 0, "Use TCP SYN cookies if the syncache overflows"); static int tcp_syncookiesonly = 0; SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_RW, &tcp_syncookiesonly, 0, "Use only TCP SYN cookies"); #define SYNCOOKIE_SECRET_SIZE 8 /* dwords */ #define SYNCOOKIE_LIFETIME 16 /* seconds */ struct syncache { TAILQ_ENTRY(syncache) sc_hash; struct in_conninfo sc_inc; /* addresses */ int sc_rxttime; /* retransmit time */ u_int16_t sc_rxmits; /* retransmit counter */ u_int32_t sc_tsreflect; /* timestamp to reflect */ u_int32_t sc_ts; /* our timestamp to send */ u_int32_t sc_tsoff; /* ts offset w/ syncookies */ u_int32_t sc_flowlabel; /* IPv6 flowlabel */ tcp_seq sc_irs; /* seq from peer */ tcp_seq sc_iss; /* our ISS */ struct mbuf *sc_ipopts; /* source route */ u_int16_t sc_peer_mss; /* peer's MSS */ u_int16_t sc_wnd; /* advertised window */ u_int8_t sc_ip_ttl; /* IPv4 TTL */ u_int8_t sc_ip_tos; /* IPv4 TOS */ u_int8_t sc_requested_s_scale:4, sc_requested_r_scale:4; u_int8_t sc_flags; #define SCF_NOOPT 0x01 /* no TCP options */ #define SCF_WINSCALE 0x02 /* negotiated window scaling */ #define SCF_TIMESTAMP 0x04 /* negotiated timestamps */ /* MSS is implicit */ #define SCF_UNREACH 0x10 /* icmp unreachable received */ #define SCF_SIGNATURE 0x20 /* send MD5 digests */ #define SCF_SACK 0x80 /* send SACK option */ #ifndef TCP_OFFLOAD_DISABLE struct toe_usrreqs *sc_tu; /* TOE operations */ void *sc_toepcb; /* TOE protocol block */ #endif #ifdef MAC struct label *sc_label; /* MAC label reference */ #endif }; #ifdef TCP_OFFLOAD_DISABLE #define TOEPCB_ISSET(sc) (0) #else #define TOEPCB_ISSET(sc) ((sc)->sc_toepcb != NULL) #endif struct syncache_head { struct mtx sch_mtx; TAILQ_HEAD(sch_head, syncache) sch_bucket; struct callout sch_timer; int sch_nextc; u_int sch_length; u_int sch_oddeven; u_int32_t sch_secbits_odd[SYNCOOKIE_SECRET_SIZE]; u_int32_t sch_secbits_even[SYNCOOKIE_SECRET_SIZE]; u_int sch_reseed; /* time_uptime, seconds */ }; static void syncache_drop(struct syncache *, struct syncache_head *); static void syncache_free(struct syncache *); static void syncache_insert(struct syncache *, struct syncache_head *); struct syncache *syncache_lookup(struct in_conninfo *, struct syncache_head **); static int syncache_respond(struct syncache *); static struct socket *syncache_socket(struct syncache *, struct socket *, struct mbuf *m); static void syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout); static void syncache_timer(void *); static void syncookie_generate(struct syncache_head *, struct syncache *, u_int32_t *); static struct syncache *syncookie_lookup(struct in_conninfo *, struct syncache_head *, struct syncache *, struct tcpopt *, struct tcphdr *, struct socket *); /* * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies. * 3 retransmits corresponds to a timeout of 3 * (1 + 2 + 4 + 8) == 45 seconds, * the odds are that the user has given up attempting to connect by then. */ #define SYNCACHE_MAXREXMTS 3 /* Arbitrary values */ #define TCP_SYNCACHE_HASHSIZE 512 #define TCP_SYNCACHE_BUCKETLIMIT 30 struct tcp_syncache { struct syncache_head *hashbase; uma_zone_t zone; u_int hashsize; u_int hashmask; u_int bucket_limit; u_int cache_count; /* XXX: unprotected */ u_int cache_limit; u_int rexmt_limit; u_int hash_secret; }; static struct tcp_syncache tcp_syncache; SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0, "TCP SYN cache"); SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_RDTUN, &tcp_syncache.bucket_limit, 0, "Per-bucket hash limit for syncache"); SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_RDTUN, &tcp_syncache.cache_limit, 0, "Overall entry limit for syncache"); SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_RD, &tcp_syncache.cache_count, 0, "Current number of entries in syncache"); SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_RDTUN, &tcp_syncache.hashsize, 0, "Size of TCP syncache hashtable"); SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, CTLFLAG_RW, &tcp_syncache.rexmt_limit, 0, "Limit on SYN/ACK retransmissions"); int tcp_sc_rst_sock_fail = 1; SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail, CTLFLAG_RW, &tcp_sc_rst_sock_fail, 0, "Send reset on socket allocation failure"); static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache"); #define SYNCACHE_HASH(inc, mask) \ ((tcp_syncache.hash_secret ^ \ (inc)->inc_faddr.s_addr ^ \ ((inc)->inc_faddr.s_addr >> 16) ^ \ (inc)->inc_fport ^ (inc)->inc_lport) & mask) #define SYNCACHE_HASH6(inc, mask) \ ((tcp_syncache.hash_secret ^ \ (inc)->inc6_faddr.s6_addr32[0] ^ \ (inc)->inc6_faddr.s6_addr32[3] ^ \ (inc)->inc_fport ^ (inc)->inc_lport) & mask) #define ENDPTS_EQ(a, b) ( \ (a)->ie_fport == (b)->ie_fport && \ (a)->ie_lport == (b)->ie_lport && \ (a)->ie_faddr.s_addr == (b)->ie_faddr.s_addr && \ (a)->ie_laddr.s_addr == (b)->ie_laddr.s_addr \ ) #define ENDPTS6_EQ(a, b) (memcmp(a, b, sizeof(*a)) == 0) #define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx) #define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx) #define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED) /* * Requires the syncache entry to be already removed from the bucket list. */ static void syncache_free(struct syncache *sc) { if (sc->sc_ipopts) (void) m_free(sc->sc_ipopts); #ifdef MAC mac_syncache_destroy(&sc->sc_label); #endif uma_zfree(tcp_syncache.zone, sc); } void syncache_init(void) { int i; tcp_syncache.cache_count = 0; tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT; tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS; tcp_syncache.hash_secret = arc4random(); TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize", &tcp_syncache.hashsize); TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit", &tcp_syncache.bucket_limit); if (!powerof2(tcp_syncache.hashsize) || tcp_syncache.hashsize == 0) { printf("WARNING: syncache hash size is not a power of 2.\n"); tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE; } tcp_syncache.hashmask = tcp_syncache.hashsize - 1; /* Set limits. */ tcp_syncache.cache_limit = tcp_syncache.hashsize * tcp_syncache.bucket_limit; TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit", &tcp_syncache.cache_limit); /* Allocate the hash table. */ MALLOC(tcp_syncache.hashbase, struct syncache_head *, tcp_syncache.hashsize * sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO); /* Initialize the hash buckets. */ for (i = 0; i < tcp_syncache.hashsize; i++) { TAILQ_INIT(&tcp_syncache.hashbase[i].sch_bucket); mtx_init(&tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head", NULL, MTX_DEF); callout_init_mtx(&tcp_syncache.hashbase[i].sch_timer, &tcp_syncache.hashbase[i].sch_mtx, 0); tcp_syncache.hashbase[i].sch_length = 0; } /* Create the syncache entry zone. */ tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache), NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0); uma_zone_set_max(tcp_syncache.zone, tcp_syncache.cache_limit); } /* * Inserts a syncache entry into the specified bucket row. * Locks and unlocks the syncache_head autonomously. */ static void syncache_insert(struct syncache *sc, struct syncache_head *sch) { struct syncache *sc2; SCH_LOCK(sch); /* * Make sure that we don't overflow the per-bucket limit. * If the bucket is full, toss the oldest element. */ if (sch->sch_length >= tcp_syncache.bucket_limit) { KASSERT(!TAILQ_EMPTY(&sch->sch_bucket), ("sch->sch_length incorrect")); sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head); syncache_drop(sc2, sch); tcpstat.tcps_sc_bucketoverflow++; } /* Put it into the bucket. */ TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash); sch->sch_length++; /* Reinitialize the bucket row's timer. */ if (sch->sch_length == 1) sch->sch_nextc = ticks + INT_MAX; syncache_timeout(sc, sch, 1); SCH_UNLOCK(sch); tcp_syncache.cache_count++; tcpstat.tcps_sc_added++; } /* * Remove and free entry from syncache bucket row. * Expects locked syncache head. */ static void syncache_drop(struct syncache *sc, struct syncache_head *sch) { SCH_LOCK_ASSERT(sch); TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); sch->sch_length--; #ifndef TCP_OFFLOAD_DISABLE if (sc->sc_tu) sc->sc_tu->tu_syncache_event(TOE_SC_DROP, sc->sc_toepcb); #endif syncache_free(sc); tcp_syncache.cache_count--; } /* * Engage/reengage time on bucket row. */ static void syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout) { sc->sc_rxttime = ticks + TCPTV_RTOBASE * (tcp_backoff[sc->sc_rxmits]); sc->sc_rxmits++; if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) { sch->sch_nextc = sc->sc_rxttime; if (docallout) callout_reset(&sch->sch_timer, sch->sch_nextc - ticks, syncache_timer, (void *)sch); } } /* * Walk the timer queues, looking for SYN,ACKs that need to be retransmitted. * If we have retransmitted an entry the maximum number of times, expire it. * One separate timer for each bucket row. */ static void syncache_timer(void *xsch) { struct syncache_head *sch = (struct syncache_head *)xsch; struct syncache *sc, *nsc; int tick = ticks; char *s; /* NB: syncache_head has already been locked by the callout. */ SCH_LOCK_ASSERT(sch); /* * In the following cycle we may remove some entries and/or * advance some timeouts, so re-initialize the bucket timer. */ sch->sch_nextc = tick + INT_MAX; TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) { /* * We do not check if the listen socket still exists * and accept the case where the listen socket may be * gone by the time we resend the SYN/ACK. We do * not expect this to happens often. If it does, * then the RST will be sent by the time the remote * host does the SYN/ACK->ACK. */ if (TSTMP_GT(sc->sc_rxttime, tick)) { if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) sch->sch_nextc = sc->sc_rxttime; continue; } if (sc->sc_rxmits > tcp_syncache.rexmt_limit) { if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { log(LOG_DEBUG, "%s; %s: Retransmits exhausted, " "giving up and removing syncache entry\n", s, __func__); free(s, M_TCPLOG); } syncache_drop(sc, sch); tcpstat.tcps_sc_stale++; continue; } if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { log(LOG_DEBUG, "%s; %s: Response timeout, " "retransmitting (%u) SYN|ACK\n", s, __func__, sc->sc_rxmits); free(s, M_TCPLOG); } (void) syncache_respond(sc); tcpstat.tcps_sc_retransmitted++; syncache_timeout(sc, sch, 0); } if (!TAILQ_EMPTY(&(sch)->sch_bucket)) callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick, syncache_timer, (void *)(sch)); } /* * Find an entry in the syncache. * Returns always with locked syncache_head plus a matching entry or NULL. */ struct syncache * syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp) { struct syncache *sc; struct syncache_head *sch; #ifdef INET6 if (inc->inc_isipv6) { sch = &tcp_syncache.hashbase[ SYNCACHE_HASH6(inc, tcp_syncache.hashmask)]; *schp = sch; SCH_LOCK(sch); /* Circle through bucket row to find matching entry. */ TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { if (ENDPTS6_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie)) return (sc); } } else #endif { sch = &tcp_syncache.hashbase[ SYNCACHE_HASH(inc, tcp_syncache.hashmask)]; *schp = sch; SCH_LOCK(sch); /* Circle through bucket row to find matching entry. */ TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { #ifdef INET6 if (sc->sc_inc.inc_isipv6) continue; #endif if (ENDPTS_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie)) return (sc); } } SCH_LOCK_ASSERT(*schp); return (NULL); /* always returns with locked sch */ } /* * This function is called when we get a RST for a * non-existent connection, so that we can see if the * connection is in the syn cache. If it is, zap it. */ void syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th) { struct syncache *sc; struct syncache_head *sch; char *s = NULL; sc = syncache_lookup(inc, &sch); /* returns locked sch */ SCH_LOCK_ASSERT(sch); /* * Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags. * See RFC 793 page 65, section SEGMENT ARRIVES. */ if (th->th_flags & (TH_ACK|TH_SYN|TH_FIN)) { if ((s = tcp_log_addrs(inc, th, NULL, NULL))) log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or " "FIN flag set, segment ignored\n", s, __func__); tcpstat.tcps_badrst++; goto done; } /* * No corresponding connection was found in syncache. * If syncookies are enabled and possibly exclusively * used, or we are under memory pressure, a valid RST * may not find a syncache entry. In that case we're * done and no SYN|ACK retransmissions will happen. * Otherwise the the RST was misdirected or spoofed. */ if (sc == NULL) { if ((s = tcp_log_addrs(inc, th, NULL, NULL))) log(LOG_DEBUG, "%s; %s: Spurious RST without matching " "syncache entry (possibly syncookie only), " "segment ignored\n", s, __func__); tcpstat.tcps_badrst++; goto done; } /* * If the RST bit is set, check the sequence number to see * if this is a valid reset segment. * RFC 793 page 37: * In all states except SYN-SENT, all reset (RST) segments * are validated by checking their SEQ-fields. A reset is * valid if its sequence number is in the window. * * The sequence number in the reset segment is normally an * echo of our outgoing acknowlegement numbers, but some hosts * send a reset with the sequence number at the rightmost edge * of our receive window, and we have to handle this case. */ if (SEQ_GEQ(th->th_seq, sc->sc_irs) && SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) { syncache_drop(sc, sch); if ((s = tcp_log_addrs(inc, th, NULL, NULL))) log(LOG_DEBUG, "%s; %s: Our SYN|ACK was rejected, " "connection attempt aborted by remote endpoint\n", s, __func__); tcpstat.tcps_sc_reset++; } else if ((s = tcp_log_addrs(inc, th, NULL, NULL))) { log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != IRS %u " "(+WND %u), segment ignored\n", s, __func__, th->th_seq, sc->sc_irs, sc->sc_wnd); tcpstat.tcps_badrst++; } done: if (s != NULL) free(s, M_TCPLOG); SCH_UNLOCK(sch); } void syncache_badack(struct in_conninfo *inc) { struct syncache *sc; struct syncache_head *sch; sc = syncache_lookup(inc, &sch); /* returns locked sch */ SCH_LOCK_ASSERT(sch); if (sc != NULL) { syncache_drop(sc, sch); tcpstat.tcps_sc_badack++; } SCH_UNLOCK(sch); } void syncache_unreach(struct in_conninfo *inc, struct tcphdr *th) { struct syncache *sc; struct syncache_head *sch; sc = syncache_lookup(inc, &sch); /* returns locked sch */ SCH_LOCK_ASSERT(sch); if (sc == NULL) goto done; /* If the sequence number != sc_iss, then it's a bogus ICMP msg */ if (ntohl(th->th_seq) != sc->sc_iss) goto done; /* * If we've rertransmitted 3 times and this is our second error, * we remove the entry. Otherwise, we allow it to continue on. * This prevents us from incorrectly nuking an entry during a * spurious network outage. * * See tcp_notify(). */ if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) { sc->sc_flags |= SCF_UNREACH; goto done; } syncache_drop(sc, sch); tcpstat.tcps_sc_unreach++; done: SCH_UNLOCK(sch); } /* * Build a new TCP socket structure from a syncache entry. */ static struct socket * syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m) { struct inpcb *inp = NULL; struct socket *so; struct tcpcb *tp; char *s; INP_INFO_WLOCK_ASSERT(&tcbinfo); /* * Ok, create the full blown connection, and set things up * as they would have been set up if we had created the * connection when the SYN arrived. If we can't create * the connection, abort it. */ so = sonewconn(lso, SS_ISCONNECTED); if (so == NULL) { /* * Drop the connection; we will either send a RST or * have the peer retransmit its SYN again after its * RTO and try again. */ tcpstat.tcps_listendrop++; if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) { log(LOG_DEBUG, "%s; %s: Socket create failed " "due to limits or memory shortage\n", s, __func__); free(s, M_TCPLOG); } goto abort2; } #ifdef MAC SOCK_LOCK(so); mac_socketpeer_set_from_mbuf(m, so); SOCK_UNLOCK(so); #endif inp = sotoinpcb(so); INP_WLOCK(inp); /* Insert new socket into PCB hash list. */ inp->inp_inc.inc_isipv6 = sc->sc_inc.inc_isipv6; #ifdef INET6 if (sc->sc_inc.inc_isipv6) { inp->in6p_laddr = sc->sc_inc.inc6_laddr; } else { inp->inp_vflag &= ~INP_IPV6; inp->inp_vflag |= INP_IPV4; #endif inp->inp_laddr = sc->sc_inc.inc_laddr; #ifdef INET6 } #endif inp->inp_lport = sc->sc_inc.inc_lport; if (in_pcbinshash(inp) != 0) { /* * Undo the assignments above if we failed to * put the PCB on the hash lists. */ #ifdef INET6 if (sc->sc_inc.inc_isipv6) inp->in6p_laddr = in6addr_any; else #endif inp->inp_laddr.s_addr = INADDR_ANY; inp->inp_lport = 0; goto abort; } #ifdef IPSEC /* Copy old policy into new socket's. */ if (ipsec_copy_policy(sotoinpcb(lso)->inp_sp, inp->inp_sp)) printf("syncache_socket: could not copy policy\n"); #endif #ifdef INET6 if (sc->sc_inc.inc_isipv6) { struct inpcb *oinp = sotoinpcb(lso); struct in6_addr laddr6; struct sockaddr_in6 sin6; /* * Inherit socket options from the listening socket. * Note that in6p_inputopts are not (and should not be) * copied, since it stores previously received options and is * used to detect if each new option is different than the * previous one and hence should be passed to a user. * If we copied in6p_inputopts, a user would not be able to * receive options just after calling the accept system call. */ inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS; if (oinp->in6p_outputopts) inp->in6p_outputopts = ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT); sin6.sin6_family = AF_INET6; sin6.sin6_len = sizeof(sin6); sin6.sin6_addr = sc->sc_inc.inc6_faddr; sin6.sin6_port = sc->sc_inc.inc_fport; sin6.sin6_flowinfo = sin6.sin6_scope_id = 0; laddr6 = inp->in6p_laddr; if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr)) inp->in6p_laddr = sc->sc_inc.inc6_laddr; if (in6_pcbconnect(inp, (struct sockaddr *)&sin6, thread0.td_ucred)) { inp->in6p_laddr = laddr6; goto abort; } /* Override flowlabel from in6_pcbconnect. */ inp->in6p_flowinfo &= ~IPV6_FLOWLABEL_MASK; inp->in6p_flowinfo |= sc->sc_flowlabel; } else #endif { struct in_addr laddr; struct sockaddr_in sin; inp->inp_options = (m) ? ip_srcroute(m) : NULL; if (inp->inp_options == NULL) { inp->inp_options = sc->sc_ipopts; sc->sc_ipopts = NULL; } sin.sin_family = AF_INET; sin.sin_len = sizeof(sin); sin.sin_addr = sc->sc_inc.inc_faddr; sin.sin_port = sc->sc_inc.inc_fport; bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero)); laddr = inp->inp_laddr; if (inp->inp_laddr.s_addr == INADDR_ANY) inp->inp_laddr = sc->sc_inc.inc_laddr; if (in_pcbconnect(inp, (struct sockaddr *)&sin, thread0.td_ucred)) { inp->inp_laddr = laddr; goto abort; } } tp = intotcpcb(inp); tp->t_state = TCPS_SYN_RECEIVED; tp->iss = sc->sc_iss; tp->irs = sc->sc_irs; tcp_rcvseqinit(tp); tcp_sendseqinit(tp); tp->snd_wl1 = sc->sc_irs; tp->snd_max = tp->iss + 1; tp->snd_nxt = tp->iss + 1; tp->rcv_up = sc->sc_irs + 1; tp->rcv_wnd = sc->sc_wnd; tp->rcv_adv += tp->rcv_wnd; tp->last_ack_sent = tp->rcv_nxt; tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY); if (sc->sc_flags & SCF_NOOPT) tp->t_flags |= TF_NOOPT; else { if (sc->sc_flags & SCF_WINSCALE) { tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE; tp->snd_scale = sc->sc_requested_s_scale; tp->request_r_scale = sc->sc_requested_r_scale; } if (sc->sc_flags & SCF_TIMESTAMP) { tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP; tp->ts_recent = sc->sc_tsreflect; tp->ts_recent_age = ticks; tp->ts_offset = sc->sc_tsoff; } #ifdef TCP_SIGNATURE if (sc->sc_flags & SCF_SIGNATURE) tp->t_flags |= TF_SIGNATURE; #endif if (sc->sc_flags & SCF_SACK) tp->t_flags |= TF_SACK_PERMIT; } /* * Set up MSS and get cached values from tcp_hostcache. * This might overwrite some of the defaults we just set. */ tcp_mss(tp, sc->sc_peer_mss); /* * If the SYN,ACK was retransmitted, reset cwnd to 1 segment. */ if (sc->sc_rxmits) tp->snd_cwnd = tp->t_maxseg; tcp_timer_activate(tp, TT_KEEP, tcp_keepinit); INP_WUNLOCK(inp); tcpstat.tcps_accepts++; return (so); abort: INP_WUNLOCK(inp); abort2: if (so != NULL) soabort(so); return (NULL); } /* * This function gets called when we receive an ACK for a * socket in the LISTEN state. We look up the connection * in the syncache, and if its there, we pull it out of * the cache and turn it into a full-blown connection in * the SYN-RECEIVED state. */ int syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, struct socket **lsop, struct mbuf *m) { struct syncache *sc; struct syncache_head *sch; struct syncache scs; char *s; /* * Global TCP locks are held because we manipulate the PCB lists * and create a new socket. */ INP_INFO_WLOCK_ASSERT(&tcbinfo); KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK, ("%s: can handle only ACK", __func__)); sc = syncache_lookup(inc, &sch); /* returns locked sch */ SCH_LOCK_ASSERT(sch); if (sc == NULL) { /* * There is no syncache entry, so see if this ACK is * a returning syncookie. To do this, first: * A. See if this socket has had a syncache entry dropped in * the past. We don't want to accept a bogus syncookie * if we've never received a SYN. * B. check that the syncookie is valid. If it is, then * cobble up a fake syncache entry, and return. */ if (!tcp_syncookies) { SCH_UNLOCK(sch); if ((s = tcp_log_addrs(inc, th, NULL, NULL))) log(LOG_DEBUG, "%s; %s: Spurious ACK, " "segment rejected (syncookies disabled)\n", s, __func__); goto failed; } bzero(&scs, sizeof(scs)); sc = syncookie_lookup(inc, sch, &scs, to, th, *lsop); SCH_UNLOCK(sch); if (sc == NULL) { if ((s = tcp_log_addrs(inc, th, NULL, NULL))) log(LOG_DEBUG, "%s; %s: Segment failed " "SYNCOOKIE authentication, segment rejected " "(probably spoofed)\n", s, __func__); goto failed; } } else { /* Pull out the entry to unlock the bucket row. */ TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); sch->sch_length--; tcp_syncache.cache_count--; SCH_UNLOCK(sch); } /* * Segment validation: * ACK must match our initial sequence number + 1 (the SYN|ACK). */ if (th->th_ack != sc->sc_iss + 1 && !TOEPCB_ISSET(sc)) { if ((s = tcp_log_addrs(inc, th, NULL, NULL))) log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment " "rejected\n", s, __func__, th->th_ack, sc->sc_iss); goto failed; } /* * The SEQ must match the received initial receive sequence * number + 1 (the SYN) because we didn't ACK any data that * may have come with the SYN. */ if (th->th_seq != sc->sc_irs + 1 && !TOEPCB_ISSET(sc)) { if ((s = tcp_log_addrs(inc, th, NULL, NULL))) log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment " "rejected\n", s, __func__, th->th_seq, sc->sc_irs); goto failed; } if (!(sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) { if ((s = tcp_log_addrs(inc, th, NULL, NULL))) log(LOG_DEBUG, "%s; %s: Timestamp not expected, " "segment rejected\n", s, __func__); goto failed; } /* * If timestamps were negotiated the reflected timestamp * must be equal to what we actually sent in the SYN|ACK. */ if ((to->to_flags & TOF_TS) && to->to_tsecr != sc->sc_ts && !TOEPCB_ISSET(sc)) { if ((s = tcp_log_addrs(inc, th, NULL, NULL))) log(LOG_DEBUG, "%s; %s: TSECR %u != TS %u, " "segment rejected\n", s, __func__, to->to_tsecr, sc->sc_ts); goto failed; } *lsop = syncache_socket(sc, *lsop, m); if (*lsop == NULL) tcpstat.tcps_sc_aborted++; else tcpstat.tcps_sc_completed++; if (sc != &scs) syncache_free(sc); return (1); failed: if (sc != NULL && sc != &scs) syncache_free(sc); if (s != NULL) free(s, M_TCPLOG); *lsop = NULL; return (0); } /* * Given a LISTEN socket and an inbound SYN request, add * this to the syn cache, and send back a segment: * * to the source. * * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN. * Doing so would require that we hold onto the data and deliver it * to the application. However, if we are the target of a SYN-flood * DoS attack, an attacker could send data which would eventually * consume all available buffer space if it were ACKed. By not ACKing * the data, we avoid this DoS scenario. */ static void _syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, struct inpcb *inp, struct socket **lsop, struct mbuf *m, struct toe_usrreqs *tu, void *toepcb) { struct tcpcb *tp; struct socket *so; struct syncache *sc = NULL; struct syncache_head *sch; struct mbuf *ipopts = NULL; u_int32_t flowtmp; int win, sb_hiwat, ip_ttl, ip_tos, noopt; char *s; #ifdef INET6 int autoflowlabel = 0; #endif #ifdef MAC struct label *maclabel; #endif struct syncache scs; INP_INFO_WLOCK_ASSERT(&tcbinfo); INP_WLOCK_ASSERT(inp); /* listen socket */ KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN, ("%s: unexpected tcp flags", __func__)); /* * Combine all so/tp operations very early to drop the INP lock as * soon as possible. */ so = *lsop; tp = sototcpcb(so); #ifdef INET6 if (inc->inc_isipv6 && (inp->in6p_flags & IN6P_AUTOFLOWLABEL)) autoflowlabel = 1; #endif ip_ttl = inp->inp_ip_ttl; ip_tos = inp->inp_ip_tos; win = sbspace(&so->so_rcv); sb_hiwat = so->so_rcv.sb_hiwat; noopt = (tp->t_flags & TF_NOOPT); so = NULL; tp = NULL; #ifdef MAC if (mac_syncache_init(&maclabel) != 0) { INP_WUNLOCK(inp); INP_INFO_WUNLOCK(&tcbinfo); goto done; } else mac_syncache_create(maclabel, inp); #endif INP_WUNLOCK(inp); INP_INFO_WUNLOCK(&tcbinfo); /* * Remember the IP options, if any. */ #ifdef INET6 if (!inc->inc_isipv6) #endif ipopts = (m) ? ip_srcroute(m) : NULL; /* * See if we already have an entry for this connection. * If we do, resend the SYN,ACK, and reset the retransmit timer. * * XXX: should the syncache be re-initialized with the contents * of the new SYN here (which may have different options?) * * XXX: We do not check the sequence number to see if this is a * real retransmit or a new connection attempt. The question is * how to handle such a case; either ignore it as spoofed, or * drop the current entry and create a new one? */ sc = syncache_lookup(inc, &sch); /* returns locked entry */ SCH_LOCK_ASSERT(sch); if (sc != NULL) { #ifndef TCP_OFFLOAD_DISABLE if (sc->sc_tu) sc->sc_tu->tu_syncache_event(TOE_SC_ENTRY_PRESENT, sc->sc_toepcb); #endif tcpstat.tcps_sc_dupsyn++; if (ipopts) { /* * If we were remembering a previous source route, * forget it and use the new one we've been given. */ if (sc->sc_ipopts) (void) m_free(sc->sc_ipopts); sc->sc_ipopts = ipopts; } /* * Update timestamp if present. */ if ((sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) sc->sc_tsreflect = to->to_tsval; else sc->sc_flags &= ~SCF_TIMESTAMP; #ifdef MAC /* * Since we have already unconditionally allocated label * storage, free it up. The syncache entry will already * have an initialized label we can use. */ mac_syncache_destroy(&maclabel); KASSERT(sc->sc_label != NULL, ("%s: label not initialized", __func__)); #endif /* Retransmit SYN|ACK and reset retransmit count. */ if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) { log(LOG_DEBUG, "%s; %s: Received duplicate SYN, " "resetting timer and retransmitting SYN|ACK\n", s, __func__); free(s, M_TCPLOG); } if (!TOEPCB_ISSET(sc) && syncache_respond(sc) == 0) { sc->sc_rxmits = 0; syncache_timeout(sc, sch, 1); tcpstat.tcps_sndacks++; tcpstat.tcps_sndtotal++; } SCH_UNLOCK(sch); goto done; } sc = uma_zalloc(tcp_syncache.zone, M_NOWAIT | M_ZERO); if (sc == NULL) { /* * The zone allocator couldn't provide more entries. * Treat this as if the cache was full; drop the oldest * entry and insert the new one. */ tcpstat.tcps_sc_zonefail++; if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL) syncache_drop(sc, sch); sc = uma_zalloc(tcp_syncache.zone, M_NOWAIT | M_ZERO); if (sc == NULL) { if (tcp_syncookies) { bzero(&scs, sizeof(scs)); sc = &scs; } else { SCH_UNLOCK(sch); if (ipopts) (void) m_free(ipopts); goto done; } } } /* * Fill in the syncache values. */ #ifdef MAC sc->sc_label = maclabel; #endif sc->sc_ipopts = ipopts; bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); #ifdef INET6 if (!inc->inc_isipv6) #endif { sc->sc_ip_tos = ip_tos; sc->sc_ip_ttl = ip_ttl; } #ifndef TCP_OFFLOAD_DISABLE sc->sc_tu = tu; sc->sc_toepcb = toepcb; #endif sc->sc_irs = th->th_seq; sc->sc_iss = arc4random(); sc->sc_flags = 0; sc->sc_flowlabel = 0; /* * Initial receive window: clip sbspace to [0 .. TCP_MAXWIN]. * win was derived from socket earlier in the function. */ win = imax(win, 0); win = imin(win, TCP_MAXWIN); sc->sc_wnd = win; if (tcp_do_rfc1323) { /* * A timestamp received in a SYN makes * it ok to send timestamp requests and replies. */ if (to->to_flags & TOF_TS) { sc->sc_tsreflect = to->to_tsval; sc->sc_ts = ticks; sc->sc_flags |= SCF_TIMESTAMP; } if (to->to_flags & TOF_SCALE) { int wscale = 0; /* * Pick the smallest possible scaling factor that * will still allow us to scale up to sb_max, aka * kern.ipc.maxsockbuf. * * We do this because there are broken firewalls that * will corrupt the window scale option, leading to * the other endpoint believing that our advertised * window is unscaled. At scale factors larger than * 5 the unscaled window will drop below 1500 bytes, * leading to serious problems when traversing these * broken firewalls. * * With the default maxsockbuf of 256K, a scale factor * of 3 will be chosen by this algorithm. Those who * choose a larger maxsockbuf should watch out * for the compatiblity problems mentioned above. * * RFC1323: The Window field in a SYN (i.e., a * or ) segment itself is never scaled. */ while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max) wscale++; sc->sc_requested_r_scale = wscale; sc->sc_requested_s_scale = to->to_wscale; sc->sc_flags |= SCF_WINSCALE; } } #ifdef TCP_SIGNATURE /* * If listening socket requested TCP digests, and received SYN * contains the option, flag this in the syncache so that * syncache_respond() will do the right thing with the SYN+ACK. * XXX: Currently we always record the option by default and will * attempt to use it in syncache_respond(). */ if (to->to_flags & TOF_SIGNATURE) sc->sc_flags |= SCF_SIGNATURE; #endif if (to->to_flags & TOF_SACKPERM) sc->sc_flags |= SCF_SACK; if (to->to_flags & TOF_MSS) sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */ if (noopt) sc->sc_flags |= SCF_NOOPT; if (tcp_syncookies) { syncookie_generate(sch, sc, &flowtmp); #ifdef INET6 if (autoflowlabel) sc->sc_flowlabel = flowtmp; #endif } else { #ifdef INET6 if (autoflowlabel) sc->sc_flowlabel = (htonl(ip6_randomflowlabel()) & IPV6_FLOWLABEL_MASK); #endif } SCH_UNLOCK(sch); /* * Do a standard 3-way handshake. */ if (TOEPCB_ISSET(sc) || syncache_respond(sc) == 0) { if (tcp_syncookies && tcp_syncookiesonly && sc != &scs) syncache_free(sc); else if (sc != &scs) syncache_insert(sc, sch); /* locks and unlocks sch */ tcpstat.tcps_sndacks++; tcpstat.tcps_sndtotal++; } else { if (sc != &scs) syncache_free(sc); tcpstat.tcps_sc_dropped++; } done: #ifdef MAC if (sc == &scs) mac_syncache_destroy(&maclabel); #endif if (m) { *lsop = NULL; m_freem(m); } return; } static int syncache_respond(struct syncache *sc) { struct ip *ip = NULL; struct mbuf *m; struct tcphdr *th; int optlen, error; u_int16_t hlen, tlen, mssopt; struct tcpopt to; #ifdef INET6 struct ip6_hdr *ip6 = NULL; #endif hlen = #ifdef INET6 (sc->sc_inc.inc_isipv6) ? sizeof(struct ip6_hdr) : #endif sizeof(struct ip); tlen = hlen + sizeof(struct tcphdr); /* Determine MSS we advertize to other end of connection. */ mssopt = tcp_mssopt(&sc->sc_inc); if (sc->sc_peer_mss) mssopt = max( min(sc->sc_peer_mss, mssopt), tcp_minmss); /* XXX: Assume that the entire packet will fit in a header mbuf. */ KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN, ("syncache: mbuf too small")); /* Create the IP+TCP header from scratch. */ m = m_gethdr(M_DONTWAIT, MT_DATA); if (m == NULL) return (ENOBUFS); #ifdef MAC mac_syncache_create_mbuf(sc->sc_label, m); #endif m->m_data += max_linkhdr; m->m_len = tlen; m->m_pkthdr.len = tlen; m->m_pkthdr.rcvif = NULL; #ifdef INET6 if (sc->sc_inc.inc_isipv6) { ip6 = mtod(m, struct ip6_hdr *); ip6->ip6_vfc = IPV6_VERSION; ip6->ip6_nxt = IPPROTO_TCP; ip6->ip6_src = sc->sc_inc.inc6_laddr; ip6->ip6_dst = sc->sc_inc.inc6_faddr; ip6->ip6_plen = htons(tlen - hlen); /* ip6_hlim is set after checksum */ ip6->ip6_flow &= ~IPV6_FLOWLABEL_MASK; ip6->ip6_flow |= sc->sc_flowlabel; th = (struct tcphdr *)(ip6 + 1); } else #endif { ip = mtod(m, struct ip *); ip->ip_v = IPVERSION; ip->ip_hl = sizeof(struct ip) >> 2; ip->ip_len = tlen; ip->ip_id = 0; ip->ip_off = 0; ip->ip_sum = 0; ip->ip_p = IPPROTO_TCP; ip->ip_src = sc->sc_inc.inc_laddr; ip->ip_dst = sc->sc_inc.inc_faddr; ip->ip_ttl = sc->sc_ip_ttl; ip->ip_tos = sc->sc_ip_tos; /* * See if we should do MTU discovery. Route lookups are * expensive, so we will only unset the DF bit if: * * 1) path_mtu_discovery is disabled * 2) the SCF_UNREACH flag has been set */ if (path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0)) ip->ip_off |= IP_DF; th = (struct tcphdr *)(ip + 1); } th->th_sport = sc->sc_inc.inc_lport; th->th_dport = sc->sc_inc.inc_fport; th->th_seq = htonl(sc->sc_iss); th->th_ack = htonl(sc->sc_irs + 1); th->th_off = sizeof(struct tcphdr) >> 2; th->th_x2 = 0; th->th_flags = TH_SYN|TH_ACK; th->th_win = htons(sc->sc_wnd); th->th_urp = 0; /* Tack on the TCP options. */ if ((sc->sc_flags & SCF_NOOPT) == 0) { to.to_flags = 0; to.to_mss = mssopt; to.to_flags = TOF_MSS; if (sc->sc_flags & SCF_WINSCALE) { to.to_wscale = sc->sc_requested_r_scale; to.to_flags |= TOF_SCALE; } if (sc->sc_flags & SCF_TIMESTAMP) { /* Virgin timestamp or TCP cookie enhanced one. */ to.to_tsval = sc->sc_ts; to.to_tsecr = sc->sc_tsreflect; to.to_flags |= TOF_TS; } if (sc->sc_flags & SCF_SACK) to.to_flags |= TOF_SACKPERM; #ifdef TCP_SIGNATURE if (sc->sc_flags & SCF_SIGNATURE) to.to_flags |= TOF_SIGNATURE; #endif optlen = tcp_addoptions(&to, (u_char *)(th + 1)); /* Adjust headers by option size. */ th->th_off = (sizeof(struct tcphdr) + optlen) >> 2; m->m_len += optlen; m->m_pkthdr.len += optlen; #ifdef TCP_SIGNATURE if (sc->sc_flags & SCF_SIGNATURE) tcp_signature_compute(m, sizeof(struct ip), 0, optlen, to.to_signature, IPSEC_DIR_OUTBOUND); #endif #ifdef INET6 if (sc->sc_inc.inc_isipv6) ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen); else #endif ip->ip_len += optlen; } else optlen = 0; #ifdef INET6 if (sc->sc_inc.inc_isipv6) { th->th_sum = 0; th->th_sum = in6_cksum(m, IPPROTO_TCP, hlen, tlen + optlen - hlen); ip6->ip6_hlim = in6_selecthlim(NULL, NULL); error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL); } else #endif { th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, htons(tlen + optlen - hlen + IPPROTO_TCP)); m->m_pkthdr.csum_flags = CSUM_TCP; m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL); } return (error); } void syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, struct inpcb *inp, struct socket **lsop, struct mbuf *m) { _syncache_add(inc, to, th, inp, lsop, m, NULL, NULL); } void syncache_offload_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, struct inpcb *inp, struct socket **lsop, struct toe_usrreqs *tu, void *toepcb) { INP_INFO_WLOCK(&tcbinfo); INP_WLOCK(inp); _syncache_add(inc, to, th, inp, lsop, NULL, tu, toepcb); } /* * The purpose of SYN cookies is to avoid keeping track of all SYN's we * receive and to be able to handle SYN floods from bogus source addresses * (where we will never receive any reply). SYN floods try to exhaust all * our memory and available slots in the SYN cache table to cause a denial * of service to legitimate users of the local host. * * The idea of SYN cookies is to encode and include all necessary information * about the connection setup state within the SYN-ACK we send back and thus * to get along without keeping any local state until the ACK to the SYN-ACK * arrives (if ever). Everything we need to know should be available from * the information we encoded in the SYN-ACK. * * More information about the theory behind SYN cookies and its first * discussion and specification can be found at: * http://cr.yp.to/syncookies.html (overview) * http://cr.yp.to/syncookies/archive (gory details) * * This implementation extends the orginal idea and first implementation * of FreeBSD by using not only the initial sequence number field to store * information but also the timestamp field if present. This way we can * keep track of the entire state we need to know to recreate the session in * its original form. Almost all TCP speakers implement RFC1323 timestamps * these days. For those that do not we still have to live with the known * shortcomings of the ISN only SYN cookies. * * Cookie layers: * * Initial sequence number we send: * 31|................................|0 * DDDDDDDDDDDDDDDDDDDDDDDDDMMMRRRP * D = MD5 Digest (first dword) * M = MSS index * R = Rotation of secret * P = Odd or Even secret * * The MD5 Digest is computed with over following parameters: * a) randomly rotated secret * b) struct in_conninfo containing the remote/local ip/port (IPv4&IPv6) * c) the received initial sequence number from remote host * d) the rotation offset and odd/even bit * * Timestamp we send: * 31|................................|0 * DDDDDDDDDDDDDDDDDDDDDDSSSSRRRRA5 * D = MD5 Digest (third dword) (only as filler) * S = Requested send window scale * R = Requested receive window scale * A = SACK allowed * 5 = TCP-MD5 enabled (not implemented yet) * XORed with MD5 Digest (forth dword) * * The timestamp isn't cryptographically secure and doesn't need to be. * The double use of the MD5 digest dwords ties it to a specific remote/ * local host/port, remote initial sequence number and our local time * limited secret. A received timestamp is reverted (XORed) and then * the contained MD5 dword is compared to the computed one to ensure the * timestamp belongs to the SYN-ACK we sent. The other parameters may * have been tampered with but this isn't different from supplying bogus * values in the SYN in the first place. * * Some problems with SYN cookies remain however: * Consider the problem of a recreated (and retransmitted) cookie. If the * original SYN was accepted, the connection is established. The second * SYN is inflight, and if it arrives with an ISN that falls within the * receive window, the connection is killed. * * Notes: * A heuristic to determine when to accept syn cookies is not necessary. * An ACK flood would cause the syncookie verification to be attempted, * but a SYN flood causes syncookies to be generated. Both are of equal * cost, so there's no point in trying to optimize the ACK flood case. * Also, if you don't process certain ACKs for some reason, then all someone * would have to do is launch a SYN and ACK flood at the same time, which * would stop cookie verification and defeat the entire purpose of syncookies. */ static int tcp_sc_msstab[] = { 0, 256, 468, 536, 996, 1452, 1460, 8960 }; static void syncookie_generate(struct syncache_head *sch, struct syncache *sc, u_int32_t *flowlabel) { MD5_CTX ctx; u_int32_t md5_buffer[MD5_DIGEST_LENGTH / sizeof(u_int32_t)]; u_int32_t data; u_int32_t *secbits; u_int off, pmss, mss; int i; SCH_LOCK_ASSERT(sch); /* Which of the two secrets to use. */ secbits = sch->sch_oddeven ? sch->sch_secbits_odd : sch->sch_secbits_even; /* Reseed secret if too old. */ if (sch->sch_reseed < time_uptime) { sch->sch_oddeven = sch->sch_oddeven ? 0 : 1; /* toggle */ secbits = sch->sch_oddeven ? sch->sch_secbits_odd : sch->sch_secbits_even; for (i = 0; i < SYNCOOKIE_SECRET_SIZE; i++) secbits[i] = arc4random(); sch->sch_reseed = time_uptime + SYNCOOKIE_LIFETIME; } /* Secret rotation offset. */ off = sc->sc_iss & 0x7; /* iss was randomized before */ /* Maximum segment size calculation. */ pmss = max( min(sc->sc_peer_mss, tcp_mssopt(&sc->sc_inc)), tcp_minmss); for (mss = sizeof(tcp_sc_msstab) / sizeof(int) - 1; mss > 0; mss--) if (tcp_sc_msstab[mss] <= pmss) break; /* Fold parameters and MD5 digest into the ISN we will send. */ data = sch->sch_oddeven;/* odd or even secret, 1 bit */ data |= off << 1; /* secret offset, derived from iss, 3 bits */ data |= mss << 4; /* mss, 3 bits */ MD5Init(&ctx); MD5Update(&ctx, ((u_int8_t *)secbits) + off, SYNCOOKIE_SECRET_SIZE * sizeof(*secbits) - off); MD5Update(&ctx, secbits, off); MD5Update(&ctx, &sc->sc_inc, sizeof(sc->sc_inc)); MD5Update(&ctx, &sc->sc_irs, sizeof(sc->sc_irs)); MD5Update(&ctx, &data, sizeof(data)); MD5Final((u_int8_t *)&md5_buffer, &ctx); data |= (md5_buffer[0] << 7); sc->sc_iss = data; #ifdef INET6 *flowlabel = md5_buffer[1] & IPV6_FLOWLABEL_MASK; #endif /* Additional parameters are stored in the timestamp if present. */ if (sc->sc_flags & SCF_TIMESTAMP) { data = ((sc->sc_flags & SCF_SIGNATURE) ? 1 : 0); /* TCP-MD5, 1 bit */ data |= ((sc->sc_flags & SCF_SACK) ? 1 : 0) << 1; /* SACK, 1 bit */ data |= sc->sc_requested_s_scale << 2; /* SWIN scale, 4 bits */ data |= sc->sc_requested_r_scale << 6; /* RWIN scale, 4 bits */ data |= md5_buffer[2] << 10; /* more digest bits */ data ^= md5_buffer[3]; sc->sc_ts = data; sc->sc_tsoff = data - ticks; /* after XOR */ } tcpstat.tcps_sc_sendcookie++; return; } static struct syncache * syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch, struct syncache *sc, struct tcpopt *to, struct tcphdr *th, struct socket *so) { MD5_CTX ctx; u_int32_t md5_buffer[MD5_DIGEST_LENGTH / sizeof(u_int32_t)]; u_int32_t data = 0; u_int32_t *secbits; tcp_seq ack, seq; int off, mss, wnd, flags; SCH_LOCK_ASSERT(sch); /* * Pull information out of SYN-ACK/ACK and * revert sequence number advances. */ ack = th->th_ack - 1; seq = th->th_seq - 1; off = (ack >> 1) & 0x7; mss = (ack >> 4) & 0x7; flags = ack & 0x7f; /* Which of the two secrets to use. */ secbits = (flags & 0x1) ? sch->sch_secbits_odd : sch->sch_secbits_even; /* * The secret wasn't updated for the lifetime of a syncookie, * so this SYN-ACK/ACK is either too old (replay) or totally bogus. */ if (sch->sch_reseed < time_uptime) { return (NULL); } /* Recompute the digest so we can compare it. */ MD5Init(&ctx); MD5Update(&ctx, ((u_int8_t *)secbits) + off, SYNCOOKIE_SECRET_SIZE * sizeof(*secbits) - off); MD5Update(&ctx, secbits, off); MD5Update(&ctx, inc, sizeof(*inc)); MD5Update(&ctx, &seq, sizeof(seq)); MD5Update(&ctx, &flags, sizeof(flags)); MD5Final((u_int8_t *)&md5_buffer, &ctx); /* Does the digest part of or ACK'ed ISS match? */ if ((ack & (~0x7f)) != (md5_buffer[0] << 7)) return (NULL); /* Does the digest part of our reflected timestamp match? */ if (to->to_flags & TOF_TS) { data = md5_buffer[3] ^ to->to_tsecr; if ((data & (~0x3ff)) != (md5_buffer[2] << 10)) return (NULL); } /* Fill in the syncache values. */ bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo)); sc->sc_ipopts = NULL; sc->sc_irs = seq; sc->sc_iss = ack; #ifdef INET6 if (inc->inc_isipv6) { if (sotoinpcb(so)->in6p_flags & IN6P_AUTOFLOWLABEL) sc->sc_flowlabel = md5_buffer[1] & IPV6_FLOWLABEL_MASK; } else #endif { sc->sc_ip_ttl = sotoinpcb(so)->inp_ip_ttl; sc->sc_ip_tos = sotoinpcb(so)->inp_ip_tos; } /* Additional parameters that were encoded in the timestamp. */ if (data) { sc->sc_flags |= SCF_TIMESTAMP; sc->sc_tsreflect = to->to_tsval; sc->sc_ts = to->to_tsecr; sc->sc_tsoff = to->to_tsecr - ticks; sc->sc_flags |= (data & 0x1) ? SCF_SIGNATURE : 0; sc->sc_flags |= ((data >> 1) & 0x1) ? SCF_SACK : 0; sc->sc_requested_s_scale = min((data >> 2) & 0xf, TCP_MAX_WINSHIFT); sc->sc_requested_r_scale = min((data >> 6) & 0xf, TCP_MAX_WINSHIFT); if (sc->sc_requested_s_scale || sc->sc_requested_r_scale) sc->sc_flags |= SCF_WINSCALE; } else sc->sc_flags |= SCF_NOOPT; wnd = sbspace(&so->so_rcv); wnd = imax(wnd, 0); wnd = imin(wnd, TCP_MAXWIN); sc->sc_wnd = wnd; sc->sc_rxmits = 0; sc->sc_peer_mss = tcp_sc_msstab[mss]; tcpstat.tcps_sc_recvcookie++; return (sc); } /* * Returns the current number of syncache entries. This number * will probably change before you get around to calling * syncache_pcblist. */ int syncache_pcbcount(void) { struct syncache_head *sch; int count, i; for (count = 0, i = 0; i < tcp_syncache.hashsize; i++) { /* No need to lock for a read. */ sch = &tcp_syncache.hashbase[i]; count += sch->sch_length; } return count; } /* * Exports the syncache entries to userland so that netstat can display * them alongside the other sockets. This function is intended to be * called only from tcp_pcblist. * * Due to concurrency on an active system, the number of pcbs exported * may have no relation to max_pcbs. max_pcbs merely indicates the * amount of space the caller allocated for this function to use. */ int syncache_pcblist(struct sysctl_req *req, int max_pcbs, int *pcbs_exported) { struct xtcpcb xt; struct syncache *sc; struct syncache_head *sch; int count, error, i; for (count = 0, error = 0, i = 0; i < tcp_syncache.hashsize; i++) { sch = &tcp_syncache.hashbase[i]; SCH_LOCK(sch); TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) { if (count >= max_pcbs) { SCH_UNLOCK(sch); goto exit; } bzero(&xt, sizeof(xt)); xt.xt_len = sizeof(xt); if (sc->sc_inc.inc_isipv6) xt.xt_inp.inp_vflag = INP_IPV6; else xt.xt_inp.inp_vflag = INP_IPV4; bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, sizeof (struct in_conninfo)); xt.xt_tp.t_inpcb = &xt.xt_inp; xt.xt_tp.t_state = TCPS_SYN_RECEIVED; xt.xt_socket.xso_protocol = IPPROTO_TCP; xt.xt_socket.xso_len = sizeof (struct xsocket); xt.xt_socket.so_type = SOCK_STREAM; xt.xt_socket.so_state = SS_ISCONNECTING; error = SYSCTL_OUT(req, &xt, sizeof xt); if (error) { SCH_UNLOCK(sch); goto exit; } count++; } SCH_UNLOCK(sch); } exit: *pcbs_exported = count; return error; }