/*- * 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. * * $FreeBSD: head/sys/netinet/tcp_syncache.c 159722 2006-06-18 11:48:03Z andre $ */ #include "opt_inet.h" #include "opt_inet6.h" #include "opt_ipsec.h" #include "opt_mac.h" #include "opt_tcpdebug.h" #include "opt_tcp_sack.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 #ifdef INET6 #include #include #include #include #include #endif #include #ifdef TCPDEBUG #include #endif #include #include #include #include #ifdef TCPDEBUG #include #endif #ifdef INET6 #include #endif #ifdef IPSEC #include #ifdef INET6 #include #endif #endif /*IPSEC*/ #ifdef FAST_IPSEC #include #ifdef INET6 #include #endif #include #endif /*FAST_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 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 *, struct mbuf *); static struct socket *syncache_socket(struct syncache *, struct socket *, struct mbuf *m); static void syncache_timer(void *); static void syncookie_init(void); static u_int32_t syncookie_generate(struct syncache *, u_int32_t *); static struct syncache *syncookie_lookup(struct in_conninfo *, struct tcphdr *, struct socket *); /* * Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies. * 3 retransmits corresponds to a timeout of (1 + 2 + 4 + 8 == 15) 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"); 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 SYNCACHE_TIMEOUT(sc, sch, co) do { \ (sc)->sc_rxmits++; \ (sc)->sc_rxttime = ticks + \ TCPTV_RTOBASE * tcp_backoff[(sc)->sc_rxmits - 1]; \ if ((sch)->sch_nextc > (sc)->sc_rxttime) \ (sch)->sch_nextc = (sc)->sc_rxttime; \ if (!TAILQ_EMPTY(&(sch)->sch_bucket) && !(co)) \ callout_reset(&(sch)->sch_timer, \ (sch)->sch_nextc - ticks, \ syncache_timer, (void *)(sch)); \ } while (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); 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); /* 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; } syncookie_init(); /* 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. */ 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--; syncache_free(sc); tcp_syncache.cache_count--; } /* * 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; /* NB: syncache_head has already been locked by the callout. */ SCH_LOCK_ASSERT(sch); 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 (sc->sc_rxttime >= tick) { if (sc->sc_rxttime < sch->sch_nextc) sch->sch_nextc = sc->sc_rxttime; continue; } if (sc->sc_rxmits > tcp_syncache.rexmt_limit) { syncache_drop(sc, sch); tcpstat.tcps_sc_stale++; continue; } (void) syncache_respond(sc, NULL); 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; sc = syncache_lookup(inc, &sch); /* returns locked sch */ SCH_LOCK_ASSERT(sch); if (sc == NULL) 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); tcpstat.tcps_sc_reset++; } done: 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; NET_ASSERT_GIANT(); 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 send a RST if the peer * retransmits the ACK, */ tcpstat.tcps_listendrop++; goto abort2; } #ifdef MAC SOCK_LOCK(so); mac_set_socket_peer_from_mbuf(m, so); SOCK_UNLOCK(so); #endif inp = sotoinpcb(so); INP_LOCK(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_pcbpolicy(sotoinpcb(lso)->inp_sp, inp->inp_sp)) printf("syncache_expand: could not copy policy\n"); #endif #ifdef FAST_IPSEC /* Copy old policy into new socket's. */ if (ipsec_copy_policy(sotoinpcb(lso)->inp_sp, inp->inp_sp)) printf("syncache_expand: 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 = ip_srcroute(m); 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->rcv_up = sc->sc_irs + 1; tp->rcv_wnd = sc->sc_wnd; tp->rcv_adv += tp->rcv_wnd; tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY); if (sc->sc_flags & SCF_NOOPT) tp->t_flags |= TF_NOOPT; 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_request_r_scale; } if (sc->sc_flags & SCF_TIMESTAMP) { tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP; tp->ts_recent = sc->sc_tsrecent; tp->ts_recent_age = ticks; } #ifdef TCP_SIGNATURE if (sc->sc_flags & SCF_SIGNATURE) tp->t_flags |= TF_SIGNATURE; #endif if (sc->sc_flags & SCF_SACK) { tp->sack_enable = 1; 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 > 1) tp->snd_cwnd = tp->t_maxseg; callout_reset(tp->tt_keep, tcp_keepinit, tcp_timer_keep, tp); INP_UNLOCK(inp); tcpstat.tcps_accepts++; return (so); abort: INP_UNLOCK(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 tcphdr *th, struct socket **lsop, struct mbuf *m) { struct syncache *sc; struct syncache_head *sch; struct socket *so; /* * Global TCP locks are held because we manipulate the PCB lists * and create a new socket. */ INP_INFO_WLOCK_ASSERT(&tcbinfo); 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. */ SCH_UNLOCK(sch); sch = NULL; if (!tcp_syncookies) goto failed; sc = syncookie_lookup(inc, th, *lsop); if (sc == NULL) goto failed; tcpstat.tcps_sc_recvcookie++; } else { /* Pull out the entry to unlock the bucket row. */ TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash); sch->sch_length--; SCH_UNLOCK(sch); } /* * If seg contains an ACK, but not for our SYN/ACK, send a RST. */ if (th->th_ack != sc->sc_iss + 1) goto failed; so = syncache_socket(sc, *lsop, m); if (so == NULL) { #if 0 resetandabort: /* XXXjlemon check this - is this correct? */ (void) tcp_respond(NULL, m, m, th, th->th_seq + tlen, (tcp_seq)0, TH_RST|TH_ACK); #endif m_freem(m); /* XXX: only needed for above */ tcpstat.tcps_sc_aborted++; if (sch != NULL) { syncache_insert(sc, sch); /* try again later */ sc = NULL; } goto failed; } else tcpstat.tcps_sc_completed++; *lsop = so; syncache_free(sc); return (1); failed: if (sc != NULL) syncache_free(sc); 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. */ int syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th, struct inpcb *inp, struct socket **lsop, struct mbuf *m) { 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; #ifdef INET6 int autoflowlabel = 0; #endif INP_INFO_WLOCK_ASSERT(&tcbinfo); INP_LOCK_ASSERT(inp); /* listen socket */ /* * 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; if (tp->t_flags & TF_NOOPT) sc->sc_flags = SCF_NOOPT; so = NULL; tp = NULL; INP_UNLOCK(inp); INP_INFO_WUNLOCK(&tcbinfo); /* * Remember the IP options, if any. */ #ifdef INET6 if (!inc->inc_isipv6) #endif ipopts = ip_srcroute(m); /* * 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?) */ sc = syncache_lookup(inc, &sch); /* returns locked entry */ SCH_LOCK_ASSERT(sch); if (sc != NULL) { 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) sc->sc_tsrecent = to->to_tsval; if (syncache_respond(sc, m) == 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++; sc = TAILQ_LAST(&sch->sch_bucket, sch_head); syncache_drop(sc, sch); SCH_UNLOCK(sch); sc = uma_zalloc(tcp_syncache.zone, M_NOWAIT | M_ZERO); if (sc == NULL) { if (ipopts) (void) m_free(ipopts); goto done; } } else SCH_UNLOCK(sch); /* * Fill in the syncache values. */ sc->sc_ipopts = ipopts; sc->sc_inc.inc_fport = inc->inc_fport; sc->sc_inc.inc_lport = inc->inc_lport; #ifdef INET6 sc->sc_inc.inc_isipv6 = inc->inc_isipv6; if (inc->inc_isipv6) { sc->sc_inc.inc6_faddr = inc->inc6_faddr; sc->sc_inc.inc6_laddr = inc->inc6_laddr; } else #endif { sc->sc_inc.inc_faddr = inc->inc_faddr; sc->sc_inc.inc_laddr = inc->inc_laddr; sc->sc_ip_tos = ip_tos; sc->sc_ip_ttl = ip_ttl; } sc->sc_irs = th->th_seq; sc->sc_flags = 0; sc->sc_peer_mss = to->to_flags & TOF_MSS ? to->to_mss : 0; sc->sc_flowlabel = 0; if (tcp_syncookies) { sc->sc_iss = syncookie_generate(sc, &flowtmp); #ifdef INET6 if (autoflowlabel) sc->sc_flowlabel = flowtmp & IPV6_FLOWLABEL_MASK; #endif } else { sc->sc_iss = arc4random(); #ifdef INET6 if (autoflowlabel) sc->sc_flowlabel = (htonl(ip6_randomflowlabel()) & IPV6_FLOWLABEL_MASK); #endif } /* * 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_tsrecent = to->to_tsval; sc->sc_flags |= SCF_TIMESTAMP; } if (to->to_flags & TOF_SCALE) { int wscale = 0; /* Compute proper scaling value from buffer space */ while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_hiwat) wscale++; sc->sc_request_r_scale = wscale; sc->sc_requested_s_scale = to->to_requested_s_scale; 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_SACK) sc->sc_flags |= SCF_SACK; /* * Do a standard 3-way handshake. */ if (syncache_respond(sc, m) == 0) { syncache_insert(sc, sch); /* locks and unlocks sch */ tcpstat.tcps_sndacks++; tcpstat.tcps_sndtotal++; } else { syncache_free(sc); tcpstat.tcps_sc_dropped++; } done: *lsop = NULL; return (1); } static int syncache_respond(struct syncache *sc, struct mbuf *m) { u_int8_t *optp; int optlen, error; u_int16_t tlen, hlen, mssopt; struct ip *ip = NULL; struct tcphdr *th; #ifdef INET6 struct ip6_hdr *ip6 = NULL; #endif #ifdef MAC struct inpcb *inp = NULL; #endif hlen = #ifdef INET6 (sc->sc_inc.inc_isipv6) ? sizeof(struct ip6_hdr) : #endif sizeof(struct ip); KASSERT((&sc->sc_inc) != NULL, ("syncache_respond with NULL in_conninfo pointer")); /* Determine MSS we advertize to other end of connection. */ mssopt = tcp_mssopt(&sc->sc_inc); /* Compute the size of the TCP options. */ if (sc->sc_flags & SCF_NOOPT) { optlen = 0; } else { optlen = TCPOLEN_MAXSEG + ((sc->sc_flags & SCF_WINSCALE) ? 4 : 0) + ((sc->sc_flags & SCF_TIMESTAMP) ? TCPOLEN_TSTAMP_APPA : 0); #ifdef TCP_SIGNATURE if (sc->sc_flags & SCF_SIGNATURE) optlen += TCPOLEN_SIGNATURE; #endif if (sc->sc_flags & SCF_SACK) optlen += TCPOLEN_SACK_PERMITTED; optlen = roundup2(optlen, 4); } tlen = hlen + sizeof(struct tcphdr) + optlen; /* * XXX: Assume that the entire packet will fit in a header mbuf. */ KASSERT(max_linkhdr + tlen <= MHLEN, ("syncache: mbuf too small")); /* Create the IP+TCP header from scratch. */ if (m) m_freem(m); m = m_gethdr(M_DONTWAIT, MT_DATA); if (m == NULL) return (ENOBUFS); m->m_data += max_linkhdr; m->m_len = tlen; m->m_pkthdr.len = tlen; m->m_pkthdr.rcvif = NULL; #ifdef MAC /* * For MAC look up the inpcb to get access to the label information. * We don't store the inpcb pointer in struct syncache to make locking * less complicated and to save locking operations. However for MAC * this gives a slight overhead as we have to do a full pcblookup here. */ INP_INFO_RLOCK(&tcbinfo); if (inp == NULL) { #ifdef INET6 /* && MAC */ if (sc->sc_inc.inc_isipv6) inp = in6_pcblookup_hash(&tcbinfo, &sc->sc_inc.inc6_laddr, sc->sc_inc.inc_lport, &sc->sc_inc.inc6_faddr, sc->sc_inc.inc_fport, 1, NULL); else #endif /* INET6 */ inp = in_pcblookup_hash(&tcbinfo, sc->sc_inc.inc_laddr, sc->sc_inc.inc_lport, sc->sc_inc.inc_faddr, sc->sc_inc.inc_fport, 1, NULL); if (inp == NULL) { m_freem(m); INP_INFO_RUNLOCK(&tcbinfo); return (ESHUTDOWN); } } INP_LOCK(inp); if (!inp->inp_socket->so_options & SO_ACCEPTCONN) { m_freem(m); INP_UNLOCK(inp); INP_INFO_RUNLOCK(&tcbinfo); return (ESHUTDOWN); } mac_create_mbuf_from_inpcb(inp, m); INP_UNLOCK(inp); INP_INFO_RUNLOCK(&tcbinfo); #endif /* MAC */ #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) + optlen) >> 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 (optlen != 0) { optp = (u_int8_t *)(th + 1); *optp++ = TCPOPT_MAXSEG; *optp++ = TCPOLEN_MAXSEG; *optp++ = (mssopt >> 8) & 0xff; *optp++ = mssopt & 0xff; if (sc->sc_flags & SCF_WINSCALE) { *((u_int32_t *)optp) = htonl(TCPOPT_NOP << 24 | TCPOPT_WINDOW << 16 | TCPOLEN_WINDOW << 8 | sc->sc_request_r_scale); optp += 4; } if (sc->sc_flags & SCF_TIMESTAMP) { u_int32_t *lp = (u_int32_t *)(optp); /* Form timestamp option per appendix A of RFC 1323. */ *lp++ = htonl(TCPOPT_TSTAMP_HDR); *lp++ = htonl(ticks); *lp = htonl(sc->sc_tsrecent); optp += TCPOLEN_TSTAMP_APPA; } #ifdef TCP_SIGNATURE /* * Handle TCP-MD5 passive opener response. */ if (sc->sc_flags & SCF_SIGNATURE) { u_int8_t *bp = optp; int i; *bp++ = TCPOPT_SIGNATURE; *bp++ = TCPOLEN_SIGNATURE; for (i = 0; i < TCP_SIGLEN; i++) *bp++ = 0; tcp_signature_compute(m, sizeof(struct ip), 0, optlen, optp + 2, IPSEC_DIR_OUTBOUND); optp += TCPOLEN_SIGNATURE; } #endif /* TCP_SIGNATURE */ if (sc->sc_flags & SCF_SACK) { *optp++ = TCPOPT_SACK_PERMITTED; *optp++ = TCPOLEN_SACK_PERMITTED; } { /* Pad TCP options to a 4 byte boundary */ int padlen = optlen - (optp - (u_int8_t *)(th + 1)); while (padlen-- > 0) *optp++ = TCPOPT_EOL; } } #ifdef INET6 if (sc->sc_inc.inc_isipv6) { th->th_sum = 0; th->th_sum = in6_cksum(m, IPPROTO_TCP, hlen, tlen - 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 - 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); } /* * cookie layers: * * |. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .| * | peer iss | * | MD5(laddr,faddr,secret,lport,fport) |. . . . . . .| * | 0 |(A)| | * (A): peer mss index */ /* * The values below are chosen to minimize the size of the tcp_secret * table, as well as providing roughly a 16 second lifetime for the cookie. */ #define SYNCOOKIE_WNDBITS 5 /* exposed bits for window indexing */ #define SYNCOOKIE_TIMESHIFT 1 /* scale ticks to window time units */ #define SYNCOOKIE_WNDMASK ((1 << SYNCOOKIE_WNDBITS) - 1) #define SYNCOOKIE_NSECRETS (1 << SYNCOOKIE_WNDBITS) #define SYNCOOKIE_TIMEOUT \ (hz * (1 << SYNCOOKIE_WNDBITS) / (1 << SYNCOOKIE_TIMESHIFT)) #define SYNCOOKIE_DATAMASK ((3 << SYNCOOKIE_WNDBITS) | SYNCOOKIE_WNDMASK) #define SYNCOOKIE_RLOCK(ts) (rw_rlock(&(ts).ts_rwmtx)) #define SYNCOOKIE_RUNLOCK(ts) (rw_runlock(&(ts).ts_rwmtx)) #define SYNCOOKIE_TRY_UPGRADE(ts) (rw_try_upgrade(&(ts).ts_rwmtx)) #define SYNCOOKIE_DOWNGRADE(ts) (rw_downgrade(&(ts).ts_rwmtx)) static struct { struct rwlock ts_rwmtx; u_int ts_expire; /* ticks */ u_int32_t ts_secbits[4]; } tcp_secret[SYNCOOKIE_NSECRETS]; static int tcp_msstab[] = { 0, 536, 1460, 8960 }; static MD5_CTX syn_ctx; #define MD5Add(v) MD5Update(&syn_ctx, (u_char *)&v, sizeof(v)) struct md5_add { u_int32_t laddr, faddr; u_int32_t secbits[4]; u_int16_t lport, fport; }; #ifdef CTASSERT CTASSERT(sizeof(struct md5_add) == 28); #endif /* * 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. * * However, since cookies have other problems, this may not be worth * worrying about. */ static void syncookie_init(void) { int idx; for (idx = 0; idx < SYNCOOKIE_NSECRETS; idx++) { rw_init(&(tcp_secret[idx].ts_rwmtx), "tcp_secret"); } } static u_int32_t syncookie_generate(struct syncache *sc, u_int32_t *flowid) { u_int32_t md5_buffer[4]; u_int32_t data; int idx, i; struct md5_add add; idx = ((ticks << SYNCOOKIE_TIMESHIFT) / hz) & SYNCOOKIE_WNDMASK; SYNCOOKIE_RLOCK(tcp_secret[idx]); if (tcp_secret[idx].ts_expire < time_uptime && SYNCOOKIE_TRY_UPGRADE(tcp_secret[idx]) ) { /* need write access */ for (i = 0; i < 4; i++) tcp_secret[idx].ts_secbits[i] = arc4random(); tcp_secret[idx].ts_expire = ticks + SYNCOOKIE_TIMEOUT; SYNCOOKIE_DOWNGRADE(tcp_secret[idx]); } for (data = sizeof(tcp_msstab) / sizeof(int) - 1; data > 0; data--) if (tcp_msstab[data] <= sc->sc_peer_mss) break; data = (data << SYNCOOKIE_WNDBITS) | idx; data ^= sc->sc_irs; /* peer's iss */ MD5Init(&syn_ctx); #ifdef INET6 if (sc->sc_inc.inc_isipv6) { MD5Add(sc->sc_inc.inc6_laddr); MD5Add(sc->sc_inc.inc6_faddr); add.laddr = 0; add.faddr = 0; } else #endif { add.laddr = sc->sc_inc.inc_laddr.s_addr; add.faddr = sc->sc_inc.inc_faddr.s_addr; } add.lport = sc->sc_inc.inc_lport; add.fport = sc->sc_inc.inc_fport; add.secbits[0] = tcp_secret[idx].ts_secbits[0]; add.secbits[1] = tcp_secret[idx].ts_secbits[1]; add.secbits[2] = tcp_secret[idx].ts_secbits[2]; add.secbits[3] = tcp_secret[idx].ts_secbits[3]; SYNCOOKIE_RUNLOCK(tcp_secret[idx]); MD5Add(add); MD5Final((u_char *)&md5_buffer, &syn_ctx); data ^= (md5_buffer[0] & ~SYNCOOKIE_WNDMASK); *flowid = md5_buffer[1]; return (data); } static struct syncache * syncookie_lookup(struct in_conninfo *inc, struct tcphdr *th, struct socket *so) { u_int32_t md5_buffer[4]; struct syncache *sc; u_int32_t data; int wnd, idx; struct md5_add add; data = (th->th_ack - 1) ^ (th->th_seq - 1); /* remove ISS */ idx = data & SYNCOOKIE_WNDMASK; SYNCOOKIE_RLOCK(tcp_secret[idx]); if (tcp_secret[idx].ts_expire < ticks || sototcpcb(so)->ts_recent + SYNCOOKIE_TIMEOUT < ticks) { SYNCOOKIE_RUNLOCK(tcp_secret[idx]); return (NULL); } MD5Init(&syn_ctx); #ifdef INET6 if (inc->inc_isipv6) { MD5Add(inc->inc6_laddr); MD5Add(inc->inc6_faddr); add.laddr = 0; add.faddr = 0; } else #endif { add.laddr = inc->inc_laddr.s_addr; add.faddr = inc->inc_faddr.s_addr; } add.lport = inc->inc_lport; add.fport = inc->inc_fport; add.secbits[0] = tcp_secret[idx].ts_secbits[0]; add.secbits[1] = tcp_secret[idx].ts_secbits[1]; add.secbits[2] = tcp_secret[idx].ts_secbits[2]; add.secbits[3] = tcp_secret[idx].ts_secbits[3]; SYNCOOKIE_RUNLOCK(tcp_secret[idx]); MD5Add(add); MD5Final((u_char *)&md5_buffer, &syn_ctx); data ^= md5_buffer[0]; if ((data & ~SYNCOOKIE_DATAMASK) != 0) return (NULL); data = data >> SYNCOOKIE_WNDBITS; sc = uma_zalloc(tcp_syncache.zone, M_NOWAIT | M_ZERO); if (sc == NULL) return (NULL); /* * Fill in the syncache values. * XXX: duplicate code from syncache_add */ sc->sc_ipopts = NULL; sc->sc_inc.inc_fport = inc->inc_fport; sc->sc_inc.inc_lport = inc->inc_lport; #ifdef INET6 sc->sc_inc.inc_isipv6 = inc->inc_isipv6; if (inc->inc_isipv6) { sc->sc_inc.inc6_faddr = inc->inc6_faddr; sc->sc_inc.inc6_laddr = inc->inc6_laddr; if (sotoinpcb(so)->in6p_flags & IN6P_AUTOFLOWLABEL) sc->sc_flowlabel = md5_buffer[1] & IPV6_FLOWLABEL_MASK; } else #endif { sc->sc_inc.inc_faddr = inc->inc_faddr; sc->sc_inc.inc_laddr = inc->inc_laddr; sc->sc_ip_ttl = sotoinpcb(so)->inp_ip_ttl; sc->sc_ip_tos = sotoinpcb(so)->inp_ip_tos; } sc->sc_irs = th->th_seq - 1; sc->sc_iss = th->th_ack - 1; wnd = sbspace(&so->so_rcv); wnd = imax(wnd, 0); wnd = imin(wnd, TCP_MAXWIN); sc->sc_wnd = wnd; sc->sc_flags = 0; sc->sc_rxmits = 0; sc->sc_peer_mss = tcp_msstab[data]; return (sc); }