/* * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994, 1995 * The Regents of the University of California. All rights reserved. * * 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. * 4. Neither the name of the University nor the names of its contributors * may be used to endorse or promote products derived from this software * without specific prior written permission. * * THIS SOFTWARE IS PROVIDED BY THE REGENTS 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 REGENTS 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. * * @(#)tcp_input.c 8.12 (Berkeley) 5/24/95 * $FreeBSD$ */ #include "opt_ipfw.h" /* for ipfw_fwd */ #include "opt_inet.h" #include "opt_inet6.h" #include "opt_ipsec.h" #include "opt_mac.h" #include "opt_tcpdebug.h" #include "opt_tcp_input.h" #include "opt_tcp_sack.h" #include #include #include #include #include #include /* for proc0 declaration */ #include #include #include #include #include #include #include #include /* before tcp_seq.h, for tcp_random18() */ #include #include #include #include #include #include #include #include #include /* for ICMP_BANDLIM */ #include /* for ICMP_BANDLIM */ #include #include #include #include #include #include #include #include #include #include #include #include #include #ifdef TCPDEBUG #include #endif /* TCPDEBUG */ #ifdef FAST_IPSEC #include #include #endif /*FAST_IPSEC*/ #ifdef IPSEC #include #include #include #endif /*IPSEC*/ #include static const int tcprexmtthresh = 3; struct tcpstat tcpstat; SYSCTL_STRUCT(_net_inet_tcp, TCPCTL_STATS, stats, CTLFLAG_RW, &tcpstat , tcpstat, "TCP statistics (struct tcpstat, netinet/tcp_var.h)"); static int log_in_vain = 0; SYSCTL_INT(_net_inet_tcp, OID_AUTO, log_in_vain, CTLFLAG_RW, &log_in_vain, 0, "Log all incoming TCP connections"); static int blackhole = 0; SYSCTL_INT(_net_inet_tcp, OID_AUTO, blackhole, CTLFLAG_RW, &blackhole, 0, "Do not send RST when dropping refused connections"); int tcp_delack_enabled = 1; SYSCTL_INT(_net_inet_tcp, OID_AUTO, delayed_ack, CTLFLAG_RW, &tcp_delack_enabled, 0, "Delay ACK to try and piggyback it onto a data packet"); #ifdef TCP_DROP_SYNFIN static int drop_synfin = 0; SYSCTL_INT(_net_inet_tcp, OID_AUTO, drop_synfin, CTLFLAG_RW, &drop_synfin, 0, "Drop TCP packets with SYN+FIN set"); #endif static int tcp_do_rfc3042 = 1; SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc3042, CTLFLAG_RW, &tcp_do_rfc3042, 0, "Enable RFC 3042 (Limited Transmit)"); static int tcp_do_rfc3390 = 1; SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc3390, CTLFLAG_RW, &tcp_do_rfc3390, 0, "Enable RFC 3390 (Increasing TCP's Initial Congestion Window)"); SYSCTL_NODE(_net_inet_tcp, OID_AUTO, reass, CTLFLAG_RW, 0, "TCP Segment Reassembly Queue"); static int tcp_reass_maxseg = 0; SYSCTL_INT(_net_inet_tcp_reass, OID_AUTO, maxsegments, CTLFLAG_RDTUN, &tcp_reass_maxseg, 0, "Global maximum number of TCP Segments in Reassembly Queue"); int tcp_reass_qsize = 0; SYSCTL_INT(_net_inet_tcp_reass, OID_AUTO, cursegments, CTLFLAG_RD, &tcp_reass_qsize, 0, "Global number of TCP Segments currently in Reassembly Queue"); static int tcp_reass_maxqlen = 48; SYSCTL_INT(_net_inet_tcp_reass, OID_AUTO, maxqlen, CTLFLAG_RW, &tcp_reass_maxqlen, 0, "Maximum number of TCP Segments per individual Reassembly Queue"); static int tcp_reass_overflows = 0; SYSCTL_INT(_net_inet_tcp_reass, OID_AUTO, overflows, CTLFLAG_RD, &tcp_reass_overflows, 0, "Global number of TCP Segment Reassembly Queue Overflows"); static int tcp_sack_recovery_initburst = 3; SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, initburst, CTLFLAG_RW, &tcp_sack_recovery_initburst, 0, "Initial Number of Rexmits when sack recovery is set up"); struct inpcbhead tcb; #define tcb6 tcb /* for KAME src sync over BSD*'s */ struct inpcbinfo tcbinfo; struct mtx *tcbinfo_mtx; static void tcp_dooptions(struct tcpcb *, struct tcpopt *, u_char *, int, int, struct tcphdr *); static void tcp_pulloutofband(struct socket *, struct tcphdr *, struct mbuf *, int); static int tcp_reass(struct tcpcb *, struct tcphdr *, int *, struct mbuf *); static void tcp_xmit_timer(struct tcpcb *, int); static void tcp_newreno_partial_ack(struct tcpcb *, struct tcphdr *); static int tcp_timewait(struct tcptw *, struct tcpopt *, struct tcphdr *, struct mbuf *, int); /* Neighbor Discovery, Neighbor Unreachability Detection Upper layer hint. */ #ifdef INET6 #define ND6_HINT(tp) \ do { \ if ((tp) && (tp)->t_inpcb && \ ((tp)->t_inpcb->inp_vflag & INP_IPV6) != 0) \ nd6_nud_hint(NULL, NULL, 0); \ } while (0) #else #define ND6_HINT(tp) #endif /* * Indicate whether this ack should be delayed. We can delay the ack if * - there is no delayed ack timer in progress and * - our last ack wasn't a 0-sized window. We never want to delay * the ack that opens up a 0-sized window and * - delayed acks are enabled or * - this is a half-synchronized T/TCP connection. */ #define DELAY_ACK(tp) \ ((!callout_active(tp->tt_delack) && \ (tp->t_flags & TF_RXWIN0SENT) == 0) && \ (tcp_delack_enabled || (tp->t_flags & TF_NEEDSYN))) /* Initialize TCP reassembly queue */ uma_zone_t tcp_reass_zone; void tcp_reass_init() { tcp_reass_maxseg = nmbclusters / 16; TUNABLE_INT_FETCH("net.inet.tcp.reass.maxsegments", &tcp_reass_maxseg); tcp_reass_zone = uma_zcreate("tcpreass", sizeof (struct tseg_qent), NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, UMA_ZONE_NOFREE); uma_zone_set_max(tcp_reass_zone, tcp_reass_maxseg); } static int tcp_reass(tp, th, tlenp, m) register struct tcpcb *tp; register struct tcphdr *th; int *tlenp; struct mbuf *m; { struct tseg_qent *q; struct tseg_qent *p = NULL; struct tseg_qent *nq; struct tseg_qent *te = NULL; struct socket *so = tp->t_inpcb->inp_socket; int flags; /* * XXX: tcp_reass() is rather inefficient with its data structures * and should be rewritten (see NetBSD for optimizations). While * doing that it should move to its own file tcp_reass.c. */ /* * Call with th==0 after become established to * force pre-ESTABLISHED data up to user socket. */ if (th == 0) goto present; /* * Limit the number of segments in the reassembly queue to prevent * holding on to too many segments (and thus running out of mbufs). * Make sure to let the missing segment through which caused this * queue. Always keep one global queue entry spare to be able to * process the missing segment. */ if (th->th_seq != tp->rcv_nxt && (tcp_reass_qsize + 1 >= tcp_reass_maxseg || tp->t_segqlen >= tcp_reass_maxqlen)) { tcp_reass_overflows++; tcpstat.tcps_rcvmemdrop++; m_freem(m); return (0); } /* * Allocate a new queue entry. If we can't, or hit the zone limit * just drop the pkt. */ te = uma_zalloc(tcp_reass_zone, M_NOWAIT); if (te == NULL) { tcpstat.tcps_rcvmemdrop++; m_freem(m); return (0); } tp->t_segqlen++; tcp_reass_qsize++; /* * Find a segment which begins after this one does. */ LIST_FOREACH(q, &tp->t_segq, tqe_q) { if (SEQ_GT(q->tqe_th->th_seq, th->th_seq)) break; p = q; } /* * If there is a preceding segment, it may provide some of * our data already. If so, drop the data from the incoming * segment. If it provides all of our data, drop us. */ if (p != NULL) { register int i; /* conversion to int (in i) handles seq wraparound */ i = p->tqe_th->th_seq + p->tqe_len - th->th_seq; if (i > 0) { if (i >= *tlenp) { tcpstat.tcps_rcvduppack++; tcpstat.tcps_rcvdupbyte += *tlenp; m_freem(m); uma_zfree(tcp_reass_zone, te); tp->t_segqlen--; tcp_reass_qsize--; /* * Try to present any queued data * at the left window edge to the user. * This is needed after the 3-WHS * completes. */ goto present; /* ??? */ } m_adj(m, i); *tlenp -= i; th->th_seq += i; } } tcpstat.tcps_rcvoopack++; tcpstat.tcps_rcvoobyte += *tlenp; /* * While we overlap succeeding segments trim them or, * if they are completely covered, dequeue them. */ while (q) { register int i = (th->th_seq + *tlenp) - q->tqe_th->th_seq; if (i <= 0) break; if (i < q->tqe_len) { q->tqe_th->th_seq += i; q->tqe_len -= i; m_adj(q->tqe_m, i); break; } nq = LIST_NEXT(q, tqe_q); LIST_REMOVE(q, tqe_q); m_freem(q->tqe_m); uma_zfree(tcp_reass_zone, q); tp->t_segqlen--; tcp_reass_qsize--; q = nq; } /* Insert the new segment queue entry into place. */ te->tqe_m = m; te->tqe_th = th; te->tqe_len = *tlenp; if (p == NULL) { LIST_INSERT_HEAD(&tp->t_segq, te, tqe_q); } else { LIST_INSERT_AFTER(p, te, tqe_q); } present: /* * Present data to user, advancing rcv_nxt through * completed sequence space. */ if (!TCPS_HAVEESTABLISHED(tp->t_state)) return (0); q = LIST_FIRST(&tp->t_segq); if (!q || q->tqe_th->th_seq != tp->rcv_nxt) return (0); SOCKBUF_LOCK(&so->so_rcv); do { tp->rcv_nxt += q->tqe_len; flags = q->tqe_th->th_flags & TH_FIN; nq = LIST_NEXT(q, tqe_q); LIST_REMOVE(q, tqe_q); /* Unlocked read. */ if (so->so_rcv.sb_state & SBS_CANTRCVMORE) m_freem(q->tqe_m); else sbappendstream_locked(&so->so_rcv, q->tqe_m); uma_zfree(tcp_reass_zone, q); tp->t_segqlen--; tcp_reass_qsize--; q = nq; } while (q && q->tqe_th->th_seq == tp->rcv_nxt); ND6_HINT(tp); sorwakeup_locked(so); return (flags); } /* * TCP input routine, follows pages 65-76 of the * protocol specification dated September, 1981 very closely. */ #ifdef INET6 int tcp6_input(mp, offp, proto) struct mbuf **mp; int *offp, proto; { register struct mbuf *m = *mp; struct in6_ifaddr *ia6; IP6_EXTHDR_CHECK(m, *offp, sizeof(struct tcphdr), IPPROTO_DONE); /* * draft-itojun-ipv6-tcp-to-anycast * better place to put this in? */ ia6 = ip6_getdstifaddr(m); if (ia6 && (ia6->ia6_flags & IN6_IFF_ANYCAST)) { struct ip6_hdr *ip6; ip6 = mtod(m, struct ip6_hdr *); icmp6_error(m, ICMP6_DST_UNREACH, ICMP6_DST_UNREACH_ADDR, (caddr_t)&ip6->ip6_dst - (caddr_t)ip6); return IPPROTO_DONE; } tcp_input(m, *offp); return IPPROTO_DONE; } #endif void tcp_input(m, off0) register struct mbuf *m; int off0; { register struct tcphdr *th; register struct ip *ip = NULL; register struct ipovly *ipov; register struct inpcb *inp = NULL; u_char *optp = NULL; int optlen = 0; int len, tlen, off; int drop_hdrlen; register struct tcpcb *tp = 0; register int thflags; struct socket *so = 0; int todrop, acked, ourfinisacked, needoutput = 0; u_long tiwin; struct tcpopt to; /* options in this segment */ int headlocked = 0; #ifdef IPFIREWALL_FORWARD struct m_tag *fwd_tag; #endif int rstreason; /* For badport_bandlim accounting purposes */ struct ip6_hdr *ip6 = NULL; #ifdef INET6 int isipv6; #else const int isipv6 = 0; #endif #ifdef TCPDEBUG /* * The size of tcp_saveipgen must be the size of the max ip header, * now IPv6. */ u_char tcp_saveipgen[40]; struct tcphdr tcp_savetcp; short ostate = 0; #endif #ifdef INET6 isipv6 = (mtod(m, struct ip *)->ip_v == 6) ? 1 : 0; #endif bzero((char *)&to, sizeof(to)); tcpstat.tcps_rcvtotal++; if (isipv6) { #ifdef INET6 /* IP6_EXTHDR_CHECK() is already done at tcp6_input() */ ip6 = mtod(m, struct ip6_hdr *); tlen = sizeof(*ip6) + ntohs(ip6->ip6_plen) - off0; if (in6_cksum(m, IPPROTO_TCP, off0, tlen)) { tcpstat.tcps_rcvbadsum++; goto drop; } th = (struct tcphdr *)((caddr_t)ip6 + off0); /* * Be proactive about unspecified IPv6 address in source. * As we use all-zero to indicate unbounded/unconnected pcb, * unspecified IPv6 address can be used to confuse us. * * Note that packets with unspecified IPv6 destination is * already dropped in ip6_input. */ if (IN6_IS_ADDR_UNSPECIFIED(&ip6->ip6_src)) { /* XXX stat */ goto drop; } #else th = NULL; /* XXX: avoid compiler warning */ #endif } else { /* * Get IP and TCP header together in first mbuf. * Note: IP leaves IP header in first mbuf. */ if (off0 > sizeof (struct ip)) { ip_stripoptions(m, (struct mbuf *)0); off0 = sizeof(struct ip); } if (m->m_len < sizeof (struct tcpiphdr)) { if ((m = m_pullup(m, sizeof (struct tcpiphdr))) == 0) { tcpstat.tcps_rcvshort++; return; } } ip = mtod(m, struct ip *); ipov = (struct ipovly *)ip; th = (struct tcphdr *)((caddr_t)ip + off0); tlen = ip->ip_len; if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID) { if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR) th->th_sum = m->m_pkthdr.csum_data; else th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, htonl(m->m_pkthdr.csum_data + ip->ip_len + IPPROTO_TCP)); th->th_sum ^= 0xffff; #ifdef TCPDEBUG ipov->ih_len = (u_short)tlen; ipov->ih_len = htons(ipov->ih_len); #endif } else { /* * Checksum extended TCP header and data. */ len = sizeof (struct ip) + tlen; bzero(ipov->ih_x1, sizeof(ipov->ih_x1)); ipov->ih_len = (u_short)tlen; ipov->ih_len = htons(ipov->ih_len); th->th_sum = in_cksum(m, len); } if (th->th_sum) { tcpstat.tcps_rcvbadsum++; goto drop; } #ifdef INET6 /* Re-initialization for later version check */ ip->ip_v = IPVERSION; #endif } /* * Check that TCP offset makes sense, * pull out TCP options and adjust length. XXX */ off = th->th_off << 2; if (off < sizeof (struct tcphdr) || off > tlen) { tcpstat.tcps_rcvbadoff++; goto drop; } tlen -= off; /* tlen is used instead of ti->ti_len */ if (off > sizeof (struct tcphdr)) { if (isipv6) { #ifdef INET6 IP6_EXTHDR_CHECK(m, off0, off, ); ip6 = mtod(m, struct ip6_hdr *); th = (struct tcphdr *)((caddr_t)ip6 + off0); #endif } else { if (m->m_len < sizeof(struct ip) + off) { if ((m = m_pullup(m, sizeof (struct ip) + off)) == 0) { tcpstat.tcps_rcvshort++; return; } ip = mtod(m, struct ip *); ipov = (struct ipovly *)ip; th = (struct tcphdr *)((caddr_t)ip + off0); } } optlen = off - sizeof (struct tcphdr); optp = (u_char *)(th + 1); } thflags = th->th_flags; #ifdef TCP_DROP_SYNFIN /* * If the drop_synfin option is enabled, drop all packets with * both the SYN and FIN bits set. This prevents e.g. nmap from * identifying the TCP/IP stack. * * This is a violation of the TCP specification. */ if (drop_synfin && (thflags & (TH_SYN|TH_FIN)) == (TH_SYN|TH_FIN)) goto drop; #endif /* * Convert TCP protocol specific fields to host format. */ th->th_seq = ntohl(th->th_seq); th->th_ack = ntohl(th->th_ack); th->th_win = ntohs(th->th_win); th->th_urp = ntohs(th->th_urp); /* * Delay dropping TCP, IP headers, IPv6 ext headers, and TCP options, * until after ip6_savecontrol() is called and before other functions * which don't want those proto headers. * Because ip6_savecontrol() is going to parse the mbuf to * search for data to be passed up to user-land, it wants mbuf * parameters to be unchanged. * XXX: the call of ip6_savecontrol() has been obsoleted based on * latest version of the advanced API (20020110). */ drop_hdrlen = off0 + off; /* * Locate pcb for segment. */ INP_INFO_WLOCK(&tcbinfo); headlocked = 1; findpcb: #ifdef IPFIREWALL_FORWARD /* Grab info from PACKET_TAG_IPFORWARD tag prepended to the chain. */ fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL); if (fwd_tag != NULL && isipv6 == 0) { /* IPv6 support is not yet */ struct sockaddr_in *next_hop; next_hop = (struct sockaddr_in *)(fwd_tag+1); /* * Transparently forwarded. Pretend to be the destination. * already got one like this? */ inp = in_pcblookup_hash(&tcbinfo, ip->ip_src, th->th_sport, ip->ip_dst, th->th_dport, 0, m->m_pkthdr.rcvif); if (!inp) { /* It's new. Try to find the ambushing socket. */ inp = in_pcblookup_hash(&tcbinfo, ip->ip_src, th->th_sport, next_hop->sin_addr, next_hop->sin_port ? ntohs(next_hop->sin_port) : th->th_dport, 1, m->m_pkthdr.rcvif); } /* Remove the tag from the packet. We don't need it anymore. */ m_tag_delete(m, fwd_tag); } else { #endif /* IPFIREWALL_FORWARD */ if (isipv6) { #ifdef INET6 inp = in6_pcblookup_hash(&tcbinfo, &ip6->ip6_src, th->th_sport, &ip6->ip6_dst, th->th_dport, 1, m->m_pkthdr.rcvif); #endif } else inp = in_pcblookup_hash(&tcbinfo, ip->ip_src, th->th_sport, ip->ip_dst, th->th_dport, 1, m->m_pkthdr.rcvif); #ifdef IPFIREWALL_FORWARD } #endif /* IPFIREWALL_FORWARD */ #if defined(IPSEC) || defined(FAST_IPSEC) #ifdef INET6 if (isipv6) { if (inp != NULL && ipsec6_in_reject(m, inp)) { #ifdef IPSEC ipsec6stat.in_polvio++; #endif goto drop; } } else #endif /* INET6 */ if (inp != NULL && ipsec4_in_reject(m, inp)) { #ifdef IPSEC ipsecstat.in_polvio++; #endif goto drop; } #endif /*IPSEC || FAST_IPSEC*/ /* * If the state is CLOSED (i.e., TCB does not exist) then * all data in the incoming segment is discarded. * If the TCB exists but is in CLOSED state, it is embryonic, * but should either do a listen or a connect soon. */ if (inp == NULL) { if (log_in_vain) { #ifdef INET6 char dbuf[INET6_ADDRSTRLEN+2], sbuf[INET6_ADDRSTRLEN+2]; #else char dbuf[4*sizeof "123"], sbuf[4*sizeof "123"]; #endif if (isipv6) { #ifdef INET6 strcpy(dbuf, "["); strcpy(sbuf, "["); strcat(dbuf, ip6_sprintf(&ip6->ip6_dst)); strcat(sbuf, ip6_sprintf(&ip6->ip6_src)); strcat(dbuf, "]"); strcat(sbuf, "]"); #endif } else { strcpy(dbuf, inet_ntoa(ip->ip_dst)); strcpy(sbuf, inet_ntoa(ip->ip_src)); } switch (log_in_vain) { case 1: if ((thflags & TH_SYN) == 0) break; /* FALLTHROUGH */ case 2: log(LOG_INFO, "Connection attempt to TCP %s:%d " "from %s:%d flags:0x%02x\n", dbuf, ntohs(th->th_dport), sbuf, ntohs(th->th_sport), thflags); break; default: break; } } if (blackhole) { switch (blackhole) { case 1: if (thflags & TH_SYN) goto drop; break; case 2: goto drop; default: goto drop; } } rstreason = BANDLIM_RST_CLOSEDPORT; goto dropwithreset; } INP_LOCK(inp); if (inp->inp_vflag & INP_TIMEWAIT) { /* * The only option of relevance is TOF_CC, and only if * present in a SYN segment. See tcp_timewait(). */ if (thflags & TH_SYN) tcp_dooptions((struct tcpcb *)NULL, &to, optp, optlen, 1, th); if (tcp_timewait((struct tcptw *)inp->inp_ppcb, &to, th, m, tlen)) goto findpcb; /* * tcp_timewait unlocks inp. */ INP_INFO_WUNLOCK(&tcbinfo); return; } tp = intotcpcb(inp); if (tp == 0) { INP_UNLOCK(inp); rstreason = BANDLIM_RST_CLOSEDPORT; goto dropwithreset; } if (tp->t_state == TCPS_CLOSED) goto drop; /* Unscale the window into a 32-bit value. */ if ((thflags & TH_SYN) == 0) tiwin = th->th_win << tp->snd_scale; else tiwin = th->th_win; #ifdef MAC INP_LOCK_ASSERT(inp); if (mac_check_inpcb_deliver(inp, m)) goto drop; #endif so = inp->inp_socket; #ifdef TCPDEBUG if (so->so_options & SO_DEBUG) { ostate = tp->t_state; if (isipv6) bcopy((char *)ip6, (char *)tcp_saveipgen, sizeof(*ip6)); else bcopy((char *)ip, (char *)tcp_saveipgen, sizeof(*ip)); tcp_savetcp = *th; } #endif if (so->so_options & SO_ACCEPTCONN) { struct in_conninfo inc; #ifdef INET6 inc.inc_isipv6 = isipv6; #endif if (isipv6) { inc.inc6_faddr = ip6->ip6_src; inc.inc6_laddr = ip6->ip6_dst; } else { inc.inc_faddr = ip->ip_src; inc.inc_laddr = ip->ip_dst; } inc.inc_fport = th->th_sport; inc.inc_lport = th->th_dport; /* * If the state is LISTEN then ignore segment if it contains * a RST. If the segment contains an ACK then it is bad and * send a RST. If it does not contain a SYN then it is not * interesting; drop it. * * If the state is SYN_RECEIVED (syncache) and seg contains * an ACK, but not for our SYN/ACK, send a RST. If the seg * contains a RST, check the sequence number to see if it * is a valid reset segment. */ if ((thflags & (TH_RST|TH_ACK|TH_SYN)) != TH_SYN) { if ((thflags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK) { if (!syncache_expand(&inc, th, &so, m)) { /* * No syncache entry, or ACK was not * for our SYN/ACK. Send a RST. */ tcpstat.tcps_badsyn++; rstreason = BANDLIM_RST_OPENPORT; goto dropwithreset; } if (so == NULL) { /* * Could not complete 3-way handshake, * connection is being closed down, and * syncache will free mbuf. */ INP_UNLOCK(inp); INP_INFO_WUNLOCK(&tcbinfo); return; } /* * Socket is created in state SYN_RECEIVED. * Continue processing segment. */ INP_UNLOCK(inp); inp = sotoinpcb(so); INP_LOCK(inp); tp = intotcpcb(inp); /* * This is what would have happened in * tcp_output() when the SYN,ACK was sent. */ tp->snd_up = tp->snd_una; tp->snd_max = tp->snd_nxt = tp->iss + 1; tp->last_ack_sent = tp->rcv_nxt; /* * RFC1323: The window in SYN & SYN/ACK * segments is never scaled. */ tp->snd_wnd = tiwin; /* unscaled */ goto after_listen; } if (thflags & TH_RST) { syncache_chkrst(&inc, th); goto drop; } if (thflags & TH_ACK) { syncache_badack(&inc); tcpstat.tcps_badsyn++; rstreason = BANDLIM_RST_OPENPORT; goto dropwithreset; } goto drop; } /* * Segment's flags are (SYN) or (SYN|FIN). */ #ifdef INET6 /* * If deprecated address is forbidden, * we do not accept SYN to deprecated interface * address to prevent any new inbound connection from * getting established. * When we do not accept SYN, we send a TCP RST, * with deprecated source address (instead of dropping * it). We compromise it as it is much better for peer * to send a RST, and RST will be the final packet * for the exchange. * * If we do not forbid deprecated addresses, we accept * the SYN packet. RFC2462 does not suggest dropping * SYN in this case. * If we decipher RFC2462 5.5.4, it says like this: * 1. use of deprecated addr with existing * communication is okay - "SHOULD continue to be * used" * 2. use of it with new communication: * (2a) "SHOULD NOT be used if alternate address * with sufficient scope is available" * (2b) nothing mentioned otherwise. * Here we fall into (2b) case as we have no choice in * our source address selection - we must obey the peer. * * The wording in RFC2462 is confusing, and there are * multiple description text for deprecated address * handling - worse, they are not exactly the same. * I believe 5.5.4 is the best one, so we follow 5.5.4. */ if (isipv6 && !ip6_use_deprecated) { struct in6_ifaddr *ia6; if ((ia6 = ip6_getdstifaddr(m)) && (ia6->ia6_flags & IN6_IFF_DEPRECATED)) { INP_UNLOCK(inp); tp = NULL; rstreason = BANDLIM_RST_OPENPORT; goto dropwithreset; } } #endif /* * If it is from this socket, drop it, it must be forged. * Don't bother responding if the destination was a broadcast. */ if (th->th_dport == th->th_sport) { if (isipv6) { if (IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst, &ip6->ip6_src)) goto drop; } else { if (ip->ip_dst.s_addr == ip->ip_src.s_addr) goto drop; } } /* * RFC1122 4.2.3.10, p. 104: discard bcast/mcast SYN * * Note that it is quite possible to receive unicast * link-layer packets with a broadcast IP address. Use * in_broadcast() to find them. */ if (m->m_flags & (M_BCAST|M_MCAST)) goto drop; if (isipv6) { if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) || IN6_IS_ADDR_MULTICAST(&ip6->ip6_src)) goto drop; } else { if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) || IN_MULTICAST(ntohl(ip->ip_src.s_addr)) || ip->ip_src.s_addr == htonl(INADDR_BROADCAST) || in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif)) goto drop; } /* * SYN appears to be valid; create compressed TCP state * for syncache, or perform t/tcp connection. */ if (so->so_qlen <= so->so_qlimit) { #ifdef TCPDEBUG if (so->so_options & SO_DEBUG) tcp_trace(TA_INPUT, ostate, tp, (void *)tcp_saveipgen, &tcp_savetcp, 0); #endif tcp_dooptions(tp, &to, optp, optlen, 1, th); if (!syncache_add(&inc, &to, th, &so, m)) goto drop; if (so == NULL) { /* * Entry added to syncache, mbuf used to * send SYN,ACK packet. */ KASSERT(headlocked, ("headlocked")); INP_UNLOCK(inp); INP_INFO_WUNLOCK(&tcbinfo); return; } /* * Segment passed TAO tests. */ INP_UNLOCK(inp); inp = sotoinpcb(so); INP_LOCK(inp); tp = intotcpcb(inp); tp->snd_wnd = tiwin; tp->t_starttime = ticks; tp->t_state = TCPS_ESTABLISHED; /* * T/TCP logic: * If there is a FIN or if there is data, then * delay SYN,ACK(SYN) in the hope of piggy-backing * it on a response segment. Otherwise must send * ACK now in case the other side is slow starting. */ if (thflags & TH_FIN || tlen != 0) tp->t_flags |= (TF_DELACK | TF_NEEDSYN); else tp->t_flags |= (TF_ACKNOW | TF_NEEDSYN); tcpstat.tcps_connects++; soisconnected(so); goto trimthenstep6; } goto drop; } after_listen: KASSERT(headlocked, ("tcp_input(): after_listen head is not locked")); INP_LOCK_ASSERT(inp); /* XXX temp debugging */ /* should not happen - syncache should pick up these connections */ if (tp->t_state == TCPS_LISTEN) panic("tcp_input: TCPS_LISTEN"); /* * This is the second part of the MSS DoS prevention code (after * minmss on the sending side) and it deals with too many too small * tcp packets in a too short timeframe (1 second). * * For every full second we count the number of received packets * and bytes. If we get a lot of packets per second for this connection * (tcp_minmssoverload) we take a closer look at it and compute the * average packet size for the past second. If that is less than * tcp_minmss we get too many packets with very small payload which * is not good and burdens our system (and every packet generates * a wakeup to the process connected to our socket). We can reasonable * expect this to be small packet DoS attack to exhaust our CPU * cycles. * * Care has to be taken for the minimum packet overload value. This * value defines the minimum number of packets per second before we * start to worry. This must not be too low to avoid killing for * example interactive connections with many small packets like * telnet or SSH. * * Setting either tcp_minmssoverload or tcp_minmss to "0" disables * this check. * * Account for packet if payload packet, skip over ACK, etc. */ if (tcp_minmss && tcp_minmssoverload && tp->t_state == TCPS_ESTABLISHED && tlen > 0) { if (tp->rcv_second > ticks) { tp->rcv_pps++; tp->rcv_byps += tlen + off; if (tp->rcv_pps > tcp_minmssoverload) { if ((tp->rcv_byps / tp->rcv_pps) < tcp_minmss) { printf("too many small tcp packets from " "%s:%u, av. %lubyte/packet, " "dropping connection\n", #ifdef INET6 isipv6 ? ip6_sprintf(&inp->inp_inc.inc6_faddr) : #endif inet_ntoa(inp->inp_inc.inc_faddr), inp->inp_inc.inc_fport, tp->rcv_byps / tp->rcv_pps); tp = tcp_drop(tp, ECONNRESET); tcpstat.tcps_minmssdrops++; goto drop; } } } else { tp->rcv_second = ticks + hz; tp->rcv_pps = 1; tp->rcv_byps = tlen + off; } } /* * Segment received on connection. * Reset idle time and keep-alive timer. */ tp->t_rcvtime = ticks; if (TCPS_HAVEESTABLISHED(tp->t_state)) callout_reset(tp->tt_keep, tcp_keepidle, tcp_timer_keep, tp); /* * Process options only when we get SYN/ACK back. The SYN case * for incoming connections is handled in tcp_syncache. * XXX this is traditional behavior, may need to be cleaned up. */ tcp_dooptions(tp, &to, optp, optlen, thflags & TH_SYN, th); if (thflags & TH_SYN) { if (to.to_flags & TOF_SCALE) { tp->t_flags |= TF_RCVD_SCALE; tp->requested_s_scale = to.to_requested_s_scale; } if (to.to_flags & TOF_TS) { tp->t_flags |= TF_RCVD_TSTMP; tp->ts_recent = to.to_tsval; tp->ts_recent_age = ticks; } if (to.to_flags & TOF_MSS) tcp_mss(tp, to.to_mss); if (tp->sack_enable) { if (!(to.to_flags & TOF_SACK)) tp->sack_enable = 0; else tp->t_flags |= TF_SACK_PERMIT; } } if (tp->sack_enable) { /* Delete stale (cumulatively acked) SACK holes */ tcp_del_sackholes(tp, th); tp->rcv_laststart = th->th_seq; /* last recv'd segment*/ tp->rcv_lastend = th->th_seq + tlen; } /* * Header prediction: check for the two common cases * of a uni-directional data xfer. If the packet has * no control flags, is in-sequence, the window didn't * change and we're not retransmitting, it's a * candidate. If the length is zero and the ack moved * forward, we're the sender side of the xfer. Just * free the data acked & wake any higher level process * that was blocked waiting for space. If the length * is non-zero and the ack didn't move, we're the * receiver side. If we're getting packets in-order * (the reassembly queue is empty), add the data to * the socket buffer and note that we need a delayed ack. * Make sure that the hidden state-flags are also off. * Since we check for TCPS_ESTABLISHED above, it can only * be TH_NEEDSYN. */ if (tp->t_state == TCPS_ESTABLISHED && (thflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) == TH_ACK && ((tp->t_flags & (TF_NEEDSYN|TF_NEEDFIN)) == 0) && ((to.to_flags & TOF_TS) == 0 || TSTMP_GEQ(to.to_tsval, tp->ts_recent)) && th->th_seq == tp->rcv_nxt && tiwin && tiwin == tp->snd_wnd && tp->snd_nxt == tp->snd_max) { /* * If last ACK falls within this segment's sequence numbers, * record the timestamp. * NOTE that the test is modified according to the latest * proposal of the tcplw@cray.com list (Braden 1993/04/26). */ if ((to.to_flags & TOF_TS) != 0 && SEQ_LEQ(th->th_seq, tp->last_ack_sent)) { tp->ts_recent_age = ticks; tp->ts_recent = to.to_tsval; } if (tlen == 0) { if (SEQ_GT(th->th_ack, tp->snd_una) && SEQ_LEQ(th->th_ack, tp->snd_max) && tp->snd_cwnd >= tp->snd_wnd && ((!tcp_do_newreno && !tp->sack_enable && tp->t_dupacks < tcprexmtthresh) || ((tcp_do_newreno || tp->sack_enable) && !IN_FASTRECOVERY(tp)))) { KASSERT(headlocked, ("headlocked")); INP_INFO_WUNLOCK(&tcbinfo); /* * this is a pure ack for outstanding data. */ ++tcpstat.tcps_predack; /* * "bad retransmit" recovery */ if (tp->t_rxtshift == 1 && ticks < tp->t_badrxtwin) { ++tcpstat.tcps_sndrexmitbad; tp->snd_cwnd = tp->snd_cwnd_prev; tp->snd_ssthresh = tp->snd_ssthresh_prev; tp->snd_recover = tp->snd_recover_prev; if (tp->t_flags & TF_WASFRECOVERY) ENTER_FASTRECOVERY(tp); tp->snd_nxt = tp->snd_max; tp->t_badrxtwin = 0; } /* * Recalculate the transmit timer / rtt. * * Some boxes send broken timestamp replies * during the SYN+ACK phase, ignore * timestamps of 0 or we could calculate a * huge RTT and blow up the retransmit timer. */ if ((to.to_flags & TOF_TS) != 0 && to.to_tsecr) { tcp_xmit_timer(tp, ticks - to.to_tsecr + 1); } else if (tp->t_rtttime && SEQ_GT(th->th_ack, tp->t_rtseq)) { tcp_xmit_timer(tp, ticks - tp->t_rtttime); } tcp_xmit_bandwidth_limit(tp, th->th_ack); acked = th->th_ack - tp->snd_una; tcpstat.tcps_rcvackpack++; tcpstat.tcps_rcvackbyte += acked; sbdrop(&so->so_snd, acked); if (SEQ_GT(tp->snd_una, tp->snd_recover) && SEQ_LEQ(th->th_ack, tp->snd_recover)) tp->snd_recover = th->th_ack - 1; tp->snd_una = th->th_ack; /* * pull snd_wl2 up to prevent seq wrap relative * to th_ack. */ tp->snd_wl2 = th->th_ack; tp->t_dupacks = 0; m_freem(m); ND6_HINT(tp); /* some progress has been done */ /* * If all outstanding data are acked, stop * retransmit timer, otherwise restart timer * using current (possibly backed-off) value. * If process is waiting for space, * wakeup/selwakeup/signal. If data * are ready to send, let tcp_output * decide between more output or persist. #ifdef TCPDEBUG if (so->so_options & SO_DEBUG) tcp_trace(TA_INPUT, ostate, tp, (void *)tcp_saveipgen, &tcp_savetcp, 0); #endif */ if (tp->snd_una == tp->snd_max) callout_stop(tp->tt_rexmt); else if (!callout_active(tp->tt_persist)) callout_reset(tp->tt_rexmt, tp->t_rxtcur, tcp_timer_rexmt, tp); sowwakeup(so); if (so->so_snd.sb_cc) (void) tcp_output(tp); goto check_delack; } } else if (th->th_ack == tp->snd_una && LIST_EMPTY(&tp->t_segq) && tlen <= sbspace(&so->so_rcv)) { KASSERT(headlocked, ("headlocked")); INP_INFO_WUNLOCK(&tcbinfo); /* * this is a pure, in-sequence data packet * with nothing on the reassembly queue and * we have enough buffer space to take it. */ /* Clean receiver SACK report if present */ if (tp->sack_enable && tp->rcv_numsacks) tcp_clean_sackreport(tp); ++tcpstat.tcps_preddat; tp->rcv_nxt += tlen; /* * Pull snd_wl1 up to prevent seq wrap relative to * th_seq. */ tp->snd_wl1 = th->th_seq; /* * Pull rcv_up up to prevent seq wrap relative to * rcv_nxt. */ tp->rcv_up = tp->rcv_nxt; tcpstat.tcps_rcvpack++; tcpstat.tcps_rcvbyte += tlen; ND6_HINT(tp); /* some progress has been done */ /* #ifdef TCPDEBUG if (so->so_options & SO_DEBUG) tcp_trace(TA_INPUT, ostate, tp, (void *)tcp_saveipgen, &tcp_savetcp, 0); #endif * Add data to socket buffer. */ /* Unlocked read. */ SOCKBUF_LOCK(&so->so_rcv); if (so->so_rcv.sb_state & SBS_CANTRCVMORE) { m_freem(m); } else { m_adj(m, drop_hdrlen); /* delayed header drop */ sbappendstream_locked(&so->so_rcv, m); } sorwakeup_locked(so); if (DELAY_ACK(tp)) { tp->t_flags |= TF_DELACK; } else { tp->t_flags |= TF_ACKNOW; tcp_output(tp); } goto check_delack; } } /* * Calculate amount of space in receive window, * and then do TCP input processing. * Receive window is amount of space in rcv queue, * but not less than advertised window. */ { int win; win = sbspace(&so->so_rcv); if (win < 0) win = 0; tp->rcv_wnd = imax(win, (int)(tp->rcv_adv - tp->rcv_nxt)); } switch (tp->t_state) { /* * If the state is SYN_RECEIVED: * if seg contains an ACK, but not for our SYN/ACK, send a RST. */ case TCPS_SYN_RECEIVED: if ((thflags & TH_ACK) && (SEQ_LEQ(th->th_ack, tp->snd_una) || SEQ_GT(th->th_ack, tp->snd_max))) { rstreason = BANDLIM_RST_OPENPORT; goto dropwithreset; } break; /* * If the state is SYN_SENT: * if seg contains an ACK, but not for our SYN, drop the input. * if seg contains a RST, then drop the connection. * if seg does not contain SYN, then drop it. * Otherwise this is an acceptable SYN segment * initialize tp->rcv_nxt and tp->irs * if seg contains ack then advance tp->snd_una * if SYN has been acked change to ESTABLISHED else SYN_RCVD state * arrange for segment to be acked (eventually) * continue processing rest of data/controls, beginning with URG */ case TCPS_SYN_SENT: if ((thflags & TH_ACK) && (SEQ_LEQ(th->th_ack, tp->iss) || SEQ_GT(th->th_ack, tp->snd_max))) { rstreason = BANDLIM_UNLIMITED; goto dropwithreset; } if (thflags & TH_RST) { if (thflags & TH_ACK) tp = tcp_drop(tp, ECONNREFUSED); goto drop; } if ((thflags & TH_SYN) == 0) goto drop; tp->snd_wnd = th->th_win; /* initial send window */ tp->irs = th->th_seq; tcp_rcvseqinit(tp); if (thflags & TH_ACK) { tcpstat.tcps_connects++; soisconnected(so); #ifdef MAC SOCK_LOCK(so); mac_set_socket_peer_from_mbuf(m, so); SOCK_UNLOCK(so); #endif /* Do window scaling on this connection? */ if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) == (TF_RCVD_SCALE|TF_REQ_SCALE)) { tp->snd_scale = tp->requested_s_scale; tp->rcv_scale = tp->request_r_scale; } tp->rcv_adv += tp->rcv_wnd; tp->snd_una++; /* SYN is acked */ /* * If there's data, delay ACK; if there's also a FIN * ACKNOW will be turned on later. */ if (DELAY_ACK(tp) && tlen != 0) callout_reset(tp->tt_delack, tcp_delacktime, tcp_timer_delack, tp); else tp->t_flags |= TF_ACKNOW; /* * Received in SYN_SENT[*] state. * Transitions: * SYN_SENT --> ESTABLISHED * SYN_SENT* --> FIN_WAIT_1 */ tp->t_starttime = ticks; if (tp->t_flags & TF_NEEDFIN) { tp->t_state = TCPS_FIN_WAIT_1; tp->t_flags &= ~TF_NEEDFIN; thflags &= ~TH_SYN; } else { tp->t_state = TCPS_ESTABLISHED; callout_reset(tp->tt_keep, tcp_keepidle, tcp_timer_keep, tp); } } else { /* * Received initial SYN in SYN-SENT[*] state => * simultaneous open. If segment contains CC option * and there is a cached CC, apply TAO test. * If it succeeds, connection is * half-synchronized. * Otherwise, do 3-way handshake: * SYN-SENT -> SYN-RECEIVED * SYN-SENT* -> SYN-RECEIVED* * If there was no CC option, clear cached CC value. */ tp->t_flags |= TF_ACKNOW; callout_stop(tp->tt_rexmt); tp->t_state = TCPS_SYN_RECEIVED; } trimthenstep6: KASSERT(headlocked, ("tcp_input(): trimthenstep6 head is not locked")); INP_LOCK_ASSERT(inp); /* * Advance th->th_seq to correspond to first data byte. * If data, trim to stay within window, * dropping FIN if necessary. */ th->th_seq++; if (tlen > tp->rcv_wnd) { todrop = tlen - tp->rcv_wnd; m_adj(m, -todrop); tlen = tp->rcv_wnd; thflags &= ~TH_FIN; tcpstat.tcps_rcvpackafterwin++; tcpstat.tcps_rcvbyteafterwin += todrop; } tp->snd_wl1 = th->th_seq - 1; tp->rcv_up = th->th_seq; /* * Client side of transaction: already sent SYN and data. * If the remote host used T/TCP to validate the SYN, * our data will be ACK'd; if so, enter normal data segment * processing in the middle of step 5, ack processing. * Otherwise, goto step 6. */ if (thflags & TH_ACK) goto process_ACK; goto step6; /* * If the state is LAST_ACK or CLOSING or TIME_WAIT: * do normal processing. * * NB: Leftover from RFC1644 T/TCP. Cases to be reused later. */ case TCPS_LAST_ACK: case TCPS_CLOSING: case TCPS_TIME_WAIT: KASSERT(tp->t_state != TCPS_TIME_WAIT, ("timewait")); break; /* continue normal processing */ } /* * States other than LISTEN or SYN_SENT. * First check the RST flag and sequence number since reset segments * are exempt from the timestamp and connection count tests. This * fixes a bug introduced by the Stevens, vol. 2, p. 960 bugfix * below which allowed reset segments in half the sequence space * to fall though and be processed (which gives forged reset * segments with a random sequence number a 50 percent chance of * killing a connection). * Then check timestamp, if present. * Then check the connection count, if present. * Then check that at least some bytes of segment are within * receive window. If segment begins before rcv_nxt, * drop leading data (and SYN); if nothing left, just ack. * * * 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. * Note: this does not take into account delayed ACKs, so * we should test against last_ack_sent instead of rcv_nxt. * 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. * Note 2: Paul Watson's paper "Slipping in the Window" has shown * that brute force RST attacks are possible. To combat this, * we use a much stricter check while in the ESTABLISHED state, * only accepting RSTs where the sequence number is equal to * last_ack_sent. In all other states (the states in which a * RST is more likely), the more permissive check is used. * If we have multiple segments in flight, the intial reset * segment sequence numbers will be to the left of last_ack_sent, * but they will eventually catch up. * In any case, it never made sense to trim reset segments to * fit the receive window since RFC 1122 says: * 4.2.2.12 RST Segment: RFC-793 Section 3.4 * * A TCP SHOULD allow a received RST segment to include data. * * DISCUSSION * It has been suggested that a RST segment could contain * ASCII text that encoded and explained the cause of the * RST. No standard has yet been established for such * data. * * If the reset segment passes the sequence number test examine * the state: * SYN_RECEIVED STATE: * If passive open, return to LISTEN state. * If active open, inform user that connection was refused. * ESTABLISHED, FIN_WAIT_1, FIN_WAIT_2, CLOSE_WAIT STATES: * Inform user that connection was reset, and close tcb. * CLOSING, LAST_ACK STATES: * Close the tcb. * TIME_WAIT STATE: * Drop the segment - see Stevens, vol. 2, p. 964 and * RFC 1337. */ if (thflags & TH_RST) { if (SEQ_GEQ(th->th_seq, tp->last_ack_sent) && SEQ_LT(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) { switch (tp->t_state) { case TCPS_SYN_RECEIVED: so->so_error = ECONNREFUSED; goto close; case TCPS_ESTABLISHED: if (tp->last_ack_sent != th->th_seq) { tcpstat.tcps_badrst++; goto drop; } case TCPS_FIN_WAIT_1: case TCPS_FIN_WAIT_2: case TCPS_CLOSE_WAIT: so->so_error = ECONNRESET; close: tp->t_state = TCPS_CLOSED; tcpstat.tcps_drops++; tp = tcp_close(tp); break; case TCPS_CLOSING: case TCPS_LAST_ACK: tp = tcp_close(tp); break; case TCPS_TIME_WAIT: KASSERT(tp->t_state != TCPS_TIME_WAIT, ("timewait")); break; } } goto drop; } /* * RFC 1323 PAWS: If we have a timestamp reply on this segment * and it's less than ts_recent, drop it. */ if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent && TSTMP_LT(to.to_tsval, tp->ts_recent)) { /* Check to see if ts_recent is over 24 days old. */ if ((int)(ticks - tp->ts_recent_age) > TCP_PAWS_IDLE) { /* * Invalidate ts_recent. If this segment updates * ts_recent, the age will be reset later and ts_recent * will get a valid value. If it does not, setting * ts_recent to zero will at least satisfy the * requirement that zero be placed in the timestamp * echo reply when ts_recent isn't valid. The * age isn't reset until we get a valid ts_recent * because we don't want out-of-order segments to be * dropped when ts_recent is old. */ tp->ts_recent = 0; } else { tcpstat.tcps_rcvduppack++; tcpstat.tcps_rcvdupbyte += tlen; tcpstat.tcps_pawsdrop++; if (tlen) goto dropafterack; goto drop; } } /* * In the SYN-RECEIVED state, validate that the packet belongs to * this connection before trimming the data to fit the receive * window. Check the sequence number versus IRS since we know * the sequence numbers haven't wrapped. This is a partial fix * for the "LAND" DoS attack. */ if (tp->t_state == TCPS_SYN_RECEIVED && SEQ_LT(th->th_seq, tp->irs)) { rstreason = BANDLIM_RST_OPENPORT; goto dropwithreset; } todrop = tp->rcv_nxt - th->th_seq; if (todrop > 0) { if (thflags & TH_SYN) { thflags &= ~TH_SYN; th->th_seq++; if (th->th_urp > 1) th->th_urp--; else thflags &= ~TH_URG; todrop--; } /* * Following if statement from Stevens, vol. 2, p. 960. */ if (todrop > tlen || (todrop == tlen && (thflags & TH_FIN) == 0)) { /* * Any valid FIN must be to the left of the window. * At this point the FIN must be a duplicate or out * of sequence; drop it. */ thflags &= ~TH_FIN; /* * Send an ACK to resynchronize and drop any data. * But keep on processing for RST or ACK. */ tp->t_flags |= TF_ACKNOW; todrop = tlen; tcpstat.tcps_rcvduppack++; tcpstat.tcps_rcvdupbyte += todrop; } else { tcpstat.tcps_rcvpartduppack++; tcpstat.tcps_rcvpartdupbyte += todrop; } drop_hdrlen += todrop; /* drop from the top afterwards */ th->th_seq += todrop; tlen -= todrop; if (th->th_urp > todrop) th->th_urp -= todrop; else { thflags &= ~TH_URG; th->th_urp = 0; } } /* * If new data are received on a connection after the * user processes are gone, then RST the other end. */ if ((so->so_state & SS_NOFDREF) && tp->t_state > TCPS_CLOSE_WAIT && tlen) { tp = tcp_close(tp); tcpstat.tcps_rcvafterclose++; rstreason = BANDLIM_UNLIMITED; goto dropwithreset; } /* * If segment ends after window, drop trailing data * (and PUSH and FIN); if nothing left, just ACK. */ todrop = (th->th_seq+tlen) - (tp->rcv_nxt+tp->rcv_wnd); if (todrop > 0) { tcpstat.tcps_rcvpackafterwin++; if (todrop >= tlen) { tcpstat.tcps_rcvbyteafterwin += tlen; /* * If a new connection request is received * while in TIME_WAIT, drop the old connection * and start over if the sequence numbers * are above the previous ones. */ KASSERT(tp->t_state != TCPS_TIME_WAIT, ("timewait")); if (thflags & TH_SYN && tp->t_state == TCPS_TIME_WAIT && SEQ_GT(th->th_seq, tp->rcv_nxt)) { tp = tcp_close(tp); goto findpcb; } /* * If window is closed can only take segments at * window edge, and have to drop data and PUSH from * incoming segments. Continue processing, but * remember to ack. Otherwise, drop segment * and ack. */ if (tp->rcv_wnd == 0 && th->th_seq == tp->rcv_nxt) { tp->t_flags |= TF_ACKNOW; tcpstat.tcps_rcvwinprobe++; } else goto dropafterack; } else tcpstat.tcps_rcvbyteafterwin += todrop; m_adj(m, -todrop); tlen -= todrop; thflags &= ~(TH_PUSH|TH_FIN); } /* * If last ACK falls within this segment's sequence numbers, * record its timestamp. * NOTE that the test is modified according to the latest * proposal of the tcplw@cray.com list (Braden 1993/04/26). */ if ((to.to_flags & TOF_TS) != 0 && SEQ_LEQ(th->th_seq, tp->last_ack_sent)) { tp->ts_recent_age = ticks; tp->ts_recent = to.to_tsval; } /* * If a SYN is in the window, then this is an * error and we send an RST and drop the connection. */ if (thflags & TH_SYN) { tp = tcp_drop(tp, ECONNRESET); rstreason = BANDLIM_UNLIMITED; goto drop; } /* * If the ACK bit is off: if in SYN-RECEIVED state or SENDSYN * flag is on (half-synchronized state), then queue data for * later processing; else drop segment and return. */ if ((thflags & TH_ACK) == 0) { if (tp->t_state == TCPS_SYN_RECEIVED || (tp->t_flags & TF_NEEDSYN)) goto step6; else goto drop; } /* * Ack processing. */ switch (tp->t_state) { /* * In SYN_RECEIVED state, the ack ACKs our SYN, so enter * ESTABLISHED state and continue processing. * The ACK was checked above. */ case TCPS_SYN_RECEIVED: tcpstat.tcps_connects++; soisconnected(so); /* Do window scaling? */ if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) == (TF_RCVD_SCALE|TF_REQ_SCALE)) { tp->snd_scale = tp->requested_s_scale; tp->rcv_scale = tp->request_r_scale; } /* * Make transitions: * SYN-RECEIVED -> ESTABLISHED * SYN-RECEIVED* -> FIN-WAIT-1 */ tp->t_starttime = ticks; if (tp->t_flags & TF_NEEDFIN) { tp->t_state = TCPS_FIN_WAIT_1; tp->t_flags &= ~TF_NEEDFIN; } else { tp->t_state = TCPS_ESTABLISHED; callout_reset(tp->tt_keep, tcp_keepidle, tcp_timer_keep, tp); } /* * If segment contains data or ACK, will call tcp_reass() * later; if not, do so now to pass queued data to user. */ if (tlen == 0 && (thflags & TH_FIN) == 0) (void) tcp_reass(tp, (struct tcphdr *)0, 0, (struct mbuf *)0); tp->snd_wl1 = th->th_seq - 1; /* FALLTHROUGH */ /* * In ESTABLISHED state: drop duplicate ACKs; ACK out of range * ACKs. If the ack is in the range * tp->snd_una < th->th_ack <= tp->snd_max * then advance tp->snd_una to th->th_ack and drop * data from the retransmission queue. If this ACK reflects * more up to date window information we update our window information. */ case TCPS_ESTABLISHED: case TCPS_FIN_WAIT_1: case TCPS_FIN_WAIT_2: case TCPS_CLOSE_WAIT: case TCPS_CLOSING: case TCPS_LAST_ACK: case TCPS_TIME_WAIT: KASSERT(tp->t_state != TCPS_TIME_WAIT, ("timewait")); if (SEQ_LEQ(th->th_ack, tp->snd_una)) { if (tlen == 0 && tiwin == tp->snd_wnd) { tcpstat.tcps_rcvdupack++; /* * If we have outstanding data (other than * a window probe), this is a completely * duplicate ack (ie, window info didn't * change), the ack is the biggest we've * seen and we've seen exactly our rexmt * threshhold of them, assume a packet * has been dropped and retransmit it. * Kludge snd_nxt & the congestion * window so we send only this one * packet. * * We know we're losing at the current * window size so do congestion avoidance * (set ssthresh to half the current window * and pull our congestion window back to * the new ssthresh). * * Dup acks mean that packets have left the * network (they're now cached at the receiver) * so bump cwnd by the amount in the receiver * to keep a constant cwnd packets in the * network. */ if (!callout_active(tp->tt_rexmt) || th->th_ack != tp->snd_una) tp->t_dupacks = 0; else if (++tp->t_dupacks > tcprexmtthresh || ((tcp_do_newreno || tp->sack_enable) && IN_FASTRECOVERY(tp))) { tp->snd_cwnd += tp->t_maxseg; (void) tcp_output(tp); goto drop; } else if (tp->t_dupacks == tcprexmtthresh) { tcp_seq onxt = tp->snd_nxt; u_int win; /* * If we're doing sack, check to * see if we're already in sack * recovery. If we're not doing sack, * check to see if we're in newreno * recovery. */ if (tp->sack_enable) { if (IN_FASTRECOVERY(tp)) { tp->t_dupacks = 0; break; } } else if (tcp_do_newreno) { if (SEQ_LEQ(th->th_ack, tp->snd_recover)) { tp->t_dupacks = 0; break; } } win = min(tp->snd_wnd, tp->snd_cwnd) / 2 / tp->t_maxseg; if (win < 2) win = 2; tp->snd_ssthresh = win * tp->t_maxseg; ENTER_FASTRECOVERY(tp); tp->snd_recover = tp->snd_max; callout_stop(tp->tt_rexmt); tp->t_rtttime = 0; if (tp->sack_enable) { tcpstat.tcps_sack_recovery_episode++; tp->sack_newdata = tp->snd_nxt; tp->snd_cwnd = tp->t_maxseg * tcp_sack_recovery_initburst; (void) tcp_output(tp); tp->snd_cwnd += tp->snd_ssthresh; goto drop; } tp->snd_nxt = th->th_ack; tp->snd_cwnd = tp->t_maxseg; (void) tcp_output(tp); KASSERT(tp->snd_limited <= 2, ("tp->snd_limited too big")); tp->snd_cwnd = tp->snd_ssthresh + tp->t_maxseg * (tp->t_dupacks - tp->snd_limited); if (SEQ_GT(onxt, tp->snd_nxt)) tp->snd_nxt = onxt; goto drop; } else if (tcp_do_rfc3042) { u_long oldcwnd = tp->snd_cwnd; tcp_seq oldsndmax = tp->snd_max; u_int sent; KASSERT(tp->t_dupacks == 1 || tp->t_dupacks == 2, ("dupacks not 1 or 2")); if (tp->t_dupacks == 1) tp->snd_limited = 0; tp->snd_cwnd = (tp->snd_nxt - tp->snd_una) + (tp->t_dupacks - tp->snd_limited) * tp->t_maxseg; (void) tcp_output(tp); sent = tp->snd_max - oldsndmax; if (sent > tp->t_maxseg) { KASSERT((tp->t_dupacks == 2 && tp->snd_limited == 0) || (sent == tp->t_maxseg + 1 && tp->t_flags & TF_SENTFIN), ("sent too much")); tp->snd_limited = 2; } else if (sent > 0) ++tp->snd_limited; tp->snd_cwnd = oldcwnd; goto drop; } } else tp->t_dupacks = 0; break; } KASSERT(SEQ_GT(th->th_ack, tp->snd_una), ("th_ack <= snd_una")); /* * If the congestion window was inflated to account * for the other side's cached packets, retract it. */ if (tcp_do_newreno || tp->sack_enable) { if (IN_FASTRECOVERY(tp)) { if (SEQ_LT(th->th_ack, tp->snd_recover)) { if (tp->sack_enable) tcp_sack_partialack(tp, th); else tcp_newreno_partial_ack(tp, th); } else { /* * Out of fast recovery. * Window inflation should have left us * with approximately snd_ssthresh * outstanding data. * But in case we would be inclined to * send a burst, better to do it via * the slow start mechanism. */ if (SEQ_GT(th->th_ack + tp->snd_ssthresh, tp->snd_max)) tp->snd_cwnd = tp->snd_max - th->th_ack + tp->t_maxseg; else tp->snd_cwnd = tp->snd_ssthresh; } } } else { if (tp->t_dupacks >= tcprexmtthresh && tp->snd_cwnd > tp->snd_ssthresh) tp->snd_cwnd = tp->snd_ssthresh; } tp->t_dupacks = 0; if (SEQ_GT(th->th_ack, tp->snd_max)) { tcpstat.tcps_rcvacktoomuch++; goto dropafterack; } /* * If we reach this point, ACK is not a duplicate, * i.e., it ACKs something we sent. */ if (tp->t_flags & TF_NEEDSYN) { /* * T/TCP: Connection was half-synchronized, and our * SYN has been ACK'd (so connection is now fully * synchronized). Go to non-starred state, * increment snd_una for ACK of SYN, and check if * we can do window scaling. */ tp->t_flags &= ~TF_NEEDSYN; tp->snd_una++; /* Do window scaling? */ if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) == (TF_RCVD_SCALE|TF_REQ_SCALE)) { tp->snd_scale = tp->requested_s_scale; tp->rcv_scale = tp->request_r_scale; } } process_ACK: KASSERT(headlocked, ("tcp_input(): process_ACK head is not locked")); INP_LOCK_ASSERT(inp); acked = th->th_ack - tp->snd_una; tcpstat.tcps_rcvackpack++; tcpstat.tcps_rcvackbyte += acked; /* * If we just performed our first retransmit, and the ACK * arrives within our recovery window, then it was a mistake * to do the retransmit in the first place. Recover our * original cwnd and ssthresh, and proceed to transmit where * we left off. */ if (tp->t_rxtshift == 1 && ticks < tp->t_badrxtwin) { ++tcpstat.tcps_sndrexmitbad; tp->snd_cwnd = tp->snd_cwnd_prev; tp->snd_ssthresh = tp->snd_ssthresh_prev; tp->snd_recover = tp->snd_recover_prev; if (tp->t_flags & TF_WASFRECOVERY) ENTER_FASTRECOVERY(tp); tp->snd_nxt = tp->snd_max; tp->t_badrxtwin = 0; /* XXX probably not required */ } /* * If we have a timestamp reply, update smoothed * round trip time. If no timestamp is present but * transmit timer is running and timed sequence * number was acked, update smoothed round trip time. * Since we now have an rtt measurement, cancel the * timer backoff (cf., Phil Karn's retransmit alg.). * Recompute the initial retransmit timer. * * Some boxes send broken timestamp replies * during the SYN+ACK phase, ignore * timestamps of 0 or we could calculate a * huge RTT and blow up the retransmit timer. */ if ((to.to_flags & TOF_TS) != 0 && to.to_tsecr) { tcp_xmit_timer(tp, ticks - to.to_tsecr + 1); } else if (tp->t_rtttime && SEQ_GT(th->th_ack, tp->t_rtseq)) { tcp_xmit_timer(tp, ticks - tp->t_rtttime); } tcp_xmit_bandwidth_limit(tp, th->th_ack); /* * If all outstanding data is acked, stop retransmit * timer and remember to restart (more output or persist). * If there is more data to be acked, restart retransmit * timer, using current (possibly backed-off) value. */ if (th->th_ack == tp->snd_max) { callout_stop(tp->tt_rexmt); needoutput = 1; } else if (!callout_active(tp->tt_persist)) callout_reset(tp->tt_rexmt, tp->t_rxtcur, tcp_timer_rexmt, tp); /* * If no data (only SYN) was ACK'd, * skip rest of ACK processing. */ if (acked == 0) goto step6; /* * When new data is acked, open the congestion window. * If the window gives us less than ssthresh packets * in flight, open exponentially (maxseg per packet). * Otherwise open linearly: maxseg per window * (maxseg^2 / cwnd per packet). */ if ((!tcp_do_newreno && !tp->sack_enable) || !IN_FASTRECOVERY(tp)) { register u_int cw = tp->snd_cwnd; register u_int incr = tp->t_maxseg; if (cw > tp->snd_ssthresh) incr = incr * incr / cw; tp->snd_cwnd = min(cw+incr, TCP_MAXWIN<snd_scale); } SOCKBUF_LOCK(&so->so_snd); if (acked > so->so_snd.sb_cc) { tp->snd_wnd -= so->so_snd.sb_cc; sbdrop_locked(&so->so_snd, (int)so->so_snd.sb_cc); ourfinisacked = 1; } else { sbdrop_locked(&so->so_snd, acked); tp->snd_wnd -= acked; ourfinisacked = 0; } sowwakeup_locked(so); /* detect una wraparound */ if ((tcp_do_newreno || tp->sack_enable) && !IN_FASTRECOVERY(tp) && SEQ_GT(tp->snd_una, tp->snd_recover) && SEQ_LEQ(th->th_ack, tp->snd_recover)) tp->snd_recover = th->th_ack - 1; if ((tcp_do_newreno || tp->sack_enable) && IN_FASTRECOVERY(tp) && SEQ_GEQ(th->th_ack, tp->snd_recover)) EXIT_FASTRECOVERY(tp); tp->snd_una = th->th_ack; if (tp->sack_enable) { if (SEQ_GT(tp->snd_una, tp->snd_recover)) tp->snd_recover = tp->snd_una; } if (SEQ_LT(tp->snd_nxt, tp->snd_una)) tp->snd_nxt = tp->snd_una; switch (tp->t_state) { /* * In FIN_WAIT_1 STATE in addition to the processing * for the ESTABLISHED state if our FIN is now acknowledged * then enter FIN_WAIT_2. */ case TCPS_FIN_WAIT_1: if (ourfinisacked) { /* * If we can't receive any more * data, then closing user can proceed. * Starting the timer is contrary to the * specification, but if we don't get a FIN * we'll hang forever. */ /* XXXjl * we should release the tp also, and use a * compressed state. */ if (so->so_rcv.sb_state & SBS_CANTRCVMORE) { soisdisconnected(so); callout_reset(tp->tt_2msl, tcp_maxidle, tcp_timer_2msl, tp); } tp->t_state = TCPS_FIN_WAIT_2; } break; /* * In CLOSING STATE in addition to the processing for * the ESTABLISHED state if the ACK acknowledges our FIN * then enter the TIME-WAIT state, otherwise ignore * the segment. */ case TCPS_CLOSING: if (ourfinisacked) { KASSERT(headlocked, ("headlocked")); tcp_twstart(tp); INP_INFO_WUNLOCK(&tcbinfo); m_freem(m); return; } break; /* * In LAST_ACK, we may still be waiting for data to drain * and/or to be acked, as well as for the ack of our FIN. * If our FIN is now acknowledged, delete the TCB, * enter the closed state and return. */ case TCPS_LAST_ACK: if (ourfinisacked) { tp = tcp_close(tp); goto drop; } break; /* * In TIME_WAIT state the only thing that should arrive * is a retransmission of the remote FIN. Acknowledge * it and restart the finack timer. */ case TCPS_TIME_WAIT: KASSERT(tp->t_state != TCPS_TIME_WAIT, ("timewait")); callout_reset(tp->tt_2msl, 2 * tcp_msl, tcp_timer_2msl, tp); goto dropafterack; } } step6: KASSERT(headlocked, ("tcp_input(): step6 head is not locked")); INP_LOCK_ASSERT(inp); /* * Update window information. * Don't look at window if no ACK: TAC's send garbage on first SYN. */ if ((thflags & TH_ACK) && (SEQ_LT(tp->snd_wl1, th->th_seq) || (tp->snd_wl1 == th->th_seq && (SEQ_LT(tp->snd_wl2, th->th_ack) || (tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd))))) { /* keep track of pure window updates */ if (tlen == 0 && tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd) tcpstat.tcps_rcvwinupd++; tp->snd_wnd = tiwin; tp->snd_wl1 = th->th_seq; tp->snd_wl2 = th->th_ack; if (tp->snd_wnd > tp->max_sndwnd) tp->max_sndwnd = tp->snd_wnd; needoutput = 1; } /* * Process segments with URG. */ if ((thflags & TH_URG) && th->th_urp && TCPS_HAVERCVDFIN(tp->t_state) == 0) { /* * This is a kludge, but if we receive and accept * random urgent pointers, we'll crash in * soreceive. It's hard to imagine someone * actually wanting to send this much urgent data. */ if (th->th_urp + so->so_rcv.sb_cc > sb_max) { th->th_urp = 0; /* XXX */ thflags &= ~TH_URG; /* XXX */ goto dodata; /* XXX */ } /* * If this segment advances the known urgent pointer, * then mark the data stream. This should not happen * in CLOSE_WAIT, CLOSING, LAST_ACK or TIME_WAIT STATES since * a FIN has been received from the remote side. * In these states we ignore the URG. * * According to RFC961 (Assigned Protocols), * the urgent pointer points to the last octet * of urgent data. We continue, however, * to consider it to indicate the first octet * of data past the urgent section as the original * spec states (in one of two places). */ if (SEQ_GT(th->th_seq+th->th_urp, tp->rcv_up)) { tp->rcv_up = th->th_seq + th->th_urp; SOCKBUF_LOCK(&so->so_rcv); so->so_oobmark = so->so_rcv.sb_cc + (tp->rcv_up - tp->rcv_nxt) - 1; if (so->so_oobmark == 0) so->so_rcv.sb_state |= SBS_RCVATMARK; SOCKBUF_UNLOCK(&so->so_rcv); sohasoutofband(so); tp->t_oobflags &= ~(TCPOOB_HAVEDATA | TCPOOB_HADDATA); } /* * Remove out of band data so doesn't get presented to user. * This can happen independent of advancing the URG pointer, * but if two URG's are pending at once, some out-of-band * data may creep in... ick. */ if (th->th_urp <= (u_long)tlen && !(so->so_options & SO_OOBINLINE)) { /* hdr drop is delayed */ tcp_pulloutofband(so, th, m, drop_hdrlen); } } else { /* * If no out of band data is expected, * pull receive urgent pointer along * with the receive window. */ if (SEQ_GT(tp->rcv_nxt, tp->rcv_up)) tp->rcv_up = tp->rcv_nxt; } dodata: /* XXX */ KASSERT(headlocked, ("tcp_input(): dodata head is not locked")); INP_LOCK_ASSERT(inp); /* * Process the segment text, merging it into the TCP sequencing queue, * and arranging for acknowledgment of receipt if necessary. * This process logically involves adjusting tp->rcv_wnd as data * is presented to the user (this happens in tcp_usrreq.c, * case PRU_RCVD). If a FIN has already been received on this * connection then we just ignore the text. */ if ((tlen || (thflags & TH_FIN)) && TCPS_HAVERCVDFIN(tp->t_state) == 0) { m_adj(m, drop_hdrlen); /* delayed header drop */ /* * Insert segment which includes th into TCP reassembly queue * with control block tp. Set thflags to whether reassembly now * includes a segment with FIN. This handles the common case * inline (segment is the next to be received on an established * connection, and the queue is empty), avoiding linkage into * and removal from the queue and repetition of various * conversions. * Set DELACK for segments received in order, but ack * immediately when segments are out of order (so * fast retransmit can work). */ if (th->th_seq == tp->rcv_nxt && LIST_EMPTY(&tp->t_segq) && TCPS_HAVEESTABLISHED(tp->t_state)) { if (DELAY_ACK(tp)) tp->t_flags |= TF_DELACK; else tp->t_flags |= TF_ACKNOW; tp->rcv_nxt += tlen; thflags = th->th_flags & TH_FIN; tcpstat.tcps_rcvpack++; tcpstat.tcps_rcvbyte += tlen; ND6_HINT(tp); /* Unlocked read. */ SOCKBUF_LOCK(&so->so_rcv); if (so->so_rcv.sb_state & SBS_CANTRCVMORE) m_freem(m); else sbappendstream_locked(&so->so_rcv, m); sorwakeup_locked(so); } else { thflags = tcp_reass(tp, th, &tlen, m); tp->t_flags |= TF_ACKNOW; } if (tp->sack_enable) tcp_update_sack_list(tp); /* * Note the amount of data that peer has sent into * our window, in order to estimate the sender's * buffer size. */ len = so->so_rcv.sb_hiwat - (tp->rcv_adv - tp->rcv_nxt); } else { m_freem(m); thflags &= ~TH_FIN; } /* * If FIN is received ACK the FIN and let the user know * that the connection is closing. */ if (thflags & TH_FIN) { if (TCPS_HAVERCVDFIN(tp->t_state) == 0) { socantrcvmore(so); /* * If connection is half-synchronized * (ie NEEDSYN flag on) then delay ACK, * so it may be piggybacked when SYN is sent. * Otherwise, since we received a FIN then no * more input can be expected, send ACK now. */ if (tp->t_flags & TF_NEEDSYN) tp->t_flags |= TF_DELACK; else tp->t_flags |= TF_ACKNOW; tp->rcv_nxt++; } switch (tp->t_state) { /* * In SYN_RECEIVED and ESTABLISHED STATES * enter the CLOSE_WAIT state. */ case TCPS_SYN_RECEIVED: tp->t_starttime = ticks; /*FALLTHROUGH*/ case TCPS_ESTABLISHED: tp->t_state = TCPS_CLOSE_WAIT; break; /* * If still in FIN_WAIT_1 STATE FIN has not been acked so * enter the CLOSING state. */ case TCPS_FIN_WAIT_1: tp->t_state = TCPS_CLOSING; break; /* * In FIN_WAIT_2 state enter the TIME_WAIT state, * starting the time-wait timer, turning off the other * standard timers. */ case TCPS_FIN_WAIT_2: KASSERT(headlocked == 1, ("headlocked should be 1")); tcp_twstart(tp); INP_INFO_WUNLOCK(&tcbinfo); return; /* * In TIME_WAIT state restart the 2 MSL time_wait timer. */ case TCPS_TIME_WAIT: KASSERT(tp->t_state != TCPS_TIME_WAIT, ("timewait")); callout_reset(tp->tt_2msl, 2 * tcp_msl, tcp_timer_2msl, tp); break; } } INP_INFO_WUNLOCK(&tcbinfo); #ifdef TCPDEBUG if (so->so_options & SO_DEBUG) tcp_trace(TA_INPUT, ostate, tp, (void *)tcp_saveipgen, &tcp_savetcp, 0); #endif /* * Return any desired output. */ if (needoutput || (tp->t_flags & TF_ACKNOW)) (void) tcp_output(tp); check_delack: INP_LOCK_ASSERT(inp); if (tp->t_flags & TF_DELACK) { tp->t_flags &= ~TF_DELACK; callout_reset(tp->tt_delack, tcp_delacktime, tcp_timer_delack, tp); } INP_UNLOCK(inp); return; dropafterack: /* * Generate an ACK dropping incoming segment if it occupies * sequence space, where the ACK reflects our state. * * We can now skip the test for the RST flag since all * paths to this code happen after packets containing * RST have been dropped. * * In the SYN-RECEIVED state, don't send an ACK unless the * segment we received passes the SYN-RECEIVED ACK test. * If it fails send a RST. This breaks the loop in the * "LAND" DoS attack, and also prevents an ACK storm * between two listening ports that have been sent forged * SYN segments, each with the source address of the other. */ if (tp->t_state == TCPS_SYN_RECEIVED && (thflags & TH_ACK) && (SEQ_GT(tp->snd_una, th->th_ack) || SEQ_GT(th->th_ack, tp->snd_max)) ) { rstreason = BANDLIM_RST_OPENPORT; goto dropwithreset; } #ifdef TCPDEBUG if (so->so_options & SO_DEBUG) tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen, &tcp_savetcp, 0); #endif KASSERT(headlocked, ("headlocked should be 1")); INP_INFO_WUNLOCK(&tcbinfo); m_freem(m); tp->t_flags |= TF_ACKNOW; (void) tcp_output(tp); INP_UNLOCK(inp); return; dropwithreset: /* * Generate a RST, dropping incoming segment. * Make ACK acceptable to originator of segment. * Don't bother to respond if destination was broadcast/multicast. */ if ((thflags & TH_RST) || m->m_flags & (M_BCAST|M_MCAST)) goto drop; if (isipv6) { if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) || IN6_IS_ADDR_MULTICAST(&ip6->ip6_src)) goto drop; } else { if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) || IN_MULTICAST(ntohl(ip->ip_src.s_addr)) || ip->ip_src.s_addr == htonl(INADDR_BROADCAST) || in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif)) goto drop; } /* IPv6 anycast check is done at tcp6_input() */ /* * Perform bandwidth limiting. */ if (badport_bandlim(rstreason) < 0) goto drop; #ifdef TCPDEBUG if (tp == 0 || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG)) tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen, &tcp_savetcp, 0); #endif if (thflags & TH_ACK) /* mtod() below is safe as long as hdr dropping is delayed */ tcp_respond(tp, mtod(m, void *), th, m, (tcp_seq)0, th->th_ack, TH_RST); else { if (thflags & TH_SYN) tlen++; /* mtod() below is safe as long as hdr dropping is delayed */ tcp_respond(tp, mtod(m, void *), th, m, th->th_seq+tlen, (tcp_seq)0, TH_RST|TH_ACK); } if (tp) INP_UNLOCK(inp); if (headlocked) INP_INFO_WUNLOCK(&tcbinfo); return; drop: /* * Drop space held by incoming segment and return. */ #ifdef TCPDEBUG if (tp == 0 || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG)) tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen, &tcp_savetcp, 0); #endif if (tp) INP_UNLOCK(inp); m_freem(m); if (headlocked) INP_INFO_WUNLOCK(&tcbinfo); return; } /* * Parse TCP options and place in tcpopt. */ static void tcp_dooptions(tp, to, cp, cnt, is_syn, th) struct tcpcb *tp; struct tcpopt *to; u_char *cp; int cnt; int is_syn; struct tcphdr *th; { int opt, optlen; to->to_flags = 0; for (; cnt > 0; cnt -= optlen, cp += optlen) { opt = cp[0]; if (opt == TCPOPT_EOL) break; if (opt == TCPOPT_NOP) optlen = 1; else { if (cnt < 2) break; optlen = cp[1]; if (optlen < 2 || optlen > cnt) break; } switch (opt) { case TCPOPT_MAXSEG: if (optlen != TCPOLEN_MAXSEG) continue; if (!is_syn) continue; to->to_flags |= TOF_MSS; bcopy((char *)cp + 2, (char *)&to->to_mss, sizeof(to->to_mss)); to->to_mss = ntohs(to->to_mss); break; case TCPOPT_WINDOW: if (optlen != TCPOLEN_WINDOW) continue; if (! is_syn) continue; to->to_flags |= TOF_SCALE; to->to_requested_s_scale = min(cp[2], TCP_MAX_WINSHIFT); break; case TCPOPT_TIMESTAMP: if (optlen != TCPOLEN_TIMESTAMP) continue; to->to_flags |= TOF_TS; bcopy((char *)cp + 2, (char *)&to->to_tsval, sizeof(to->to_tsval)); to->to_tsval = ntohl(to->to_tsval); bcopy((char *)cp + 6, (char *)&to->to_tsecr, sizeof(to->to_tsecr)); to->to_tsecr = ntohl(to->to_tsecr); break; #ifdef TCP_SIGNATURE /* * XXX In order to reply to a host which has set the * TCP_SIGNATURE option in its initial SYN, we have to * record the fact that the option was observed here * for the syncache code to perform the correct response. */ case TCPOPT_SIGNATURE: if (optlen != TCPOLEN_SIGNATURE) continue; to->to_flags |= (TOF_SIGNATURE | TOF_SIGLEN); break; #endif case TCPOPT_SACK_PERMITTED: if (!tcp_do_sack || optlen != TCPOLEN_SACK_PERMITTED) continue; if (is_syn) { /* MUST only be set on SYN */ to->to_flags |= TOF_SACK; } break; case TCPOPT_SACK: if (!tp || tcp_sack_option(tp, th, cp, optlen)) continue; break; default: continue; } } } /* * Pull out of band byte out of a segment so * it doesn't appear in the user's data queue. * It is still reflected in the segment length for * sequencing purposes. */ static void tcp_pulloutofband(so, th, m, off) struct socket *so; struct tcphdr *th; register struct mbuf *m; int off; /* delayed to be droped hdrlen */ { int cnt = off + th->th_urp - 1; while (cnt >= 0) { if (m->m_len > cnt) { char *cp = mtod(m, caddr_t) + cnt; struct tcpcb *tp = sototcpcb(so); tp->t_iobc = *cp; tp->t_oobflags |= TCPOOB_HAVEDATA; bcopy(cp+1, cp, (unsigned)(m->m_len - cnt - 1)); m->m_len--; if (m->m_flags & M_PKTHDR) m->m_pkthdr.len--; return; } cnt -= m->m_len; m = m->m_next; if (m == 0) break; } panic("tcp_pulloutofband"); } /* * Collect new round-trip time estimate * and update averages and current timeout. */ static void tcp_xmit_timer(tp, rtt) register struct tcpcb *tp; int rtt; { register int delta; tcpstat.tcps_rttupdated++; tp->t_rttupdated++; if (tp->t_srtt != 0) { /* * srtt is stored as fixed point with 5 bits after the * binary point (i.e., scaled by 8). The following magic * is equivalent to the smoothing algorithm in rfc793 with * an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed * point). Adjust rtt to origin 0. */ delta = ((rtt - 1) << TCP_DELTA_SHIFT) - (tp->t_srtt >> (TCP_RTT_SHIFT - TCP_DELTA_SHIFT)); if ((tp->t_srtt += delta) <= 0) tp->t_srtt = 1; /* * We accumulate a smoothed rtt variance (actually, a * smoothed mean difference), then set the retransmit * timer to smoothed rtt + 4 times the smoothed variance. * rttvar is stored as fixed point with 4 bits after the * binary point (scaled by 16). The following is * equivalent to rfc793 smoothing with an alpha of .75 * (rttvar = rttvar*3/4 + |delta| / 4). This replaces * rfc793's wired-in beta. */ if (delta < 0) delta = -delta; delta -= tp->t_rttvar >> (TCP_RTTVAR_SHIFT - TCP_DELTA_SHIFT); if ((tp->t_rttvar += delta) <= 0) tp->t_rttvar = 1; if (tp->t_rttbest > tp->t_srtt + tp->t_rttvar) tp->t_rttbest = tp->t_srtt + tp->t_rttvar; } else { /* * No rtt measurement yet - use the unsmoothed rtt. * Set the variance to half the rtt (so our first * retransmit happens at 3*rtt). */ tp->t_srtt = rtt << TCP_RTT_SHIFT; tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1); tp->t_rttbest = tp->t_srtt + tp->t_rttvar; } tp->t_rtttime = 0; tp->t_rxtshift = 0; /* * the retransmit should happen at rtt + 4 * rttvar. * Because of the way we do the smoothing, srtt and rttvar * will each average +1/2 tick of bias. When we compute * the retransmit timer, we want 1/2 tick of rounding and * 1 extra tick because of +-1/2 tick uncertainty in the * firing of the timer. The bias will give us exactly the * 1.5 tick we need. But, because the bias is * statistical, we have to test that we don't drop below * the minimum feasible timer (which is 2 ticks). */ TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp), max(tp->t_rttmin, rtt + 2), TCPTV_REXMTMAX); /* * We received an ack for a packet that wasn't retransmitted; * it is probably safe to discard any error indications we've * received recently. This isn't quite right, but close enough * for now (a route might have failed after we sent a segment, * and the return path might not be symmetrical). */ tp->t_softerror = 0; } /* * Determine a reasonable value for maxseg size. * If the route is known, check route for mtu. * If none, use an mss that can be handled on the outgoing * interface without forcing IP to fragment; if bigger than * an mbuf cluster (MCLBYTES), round down to nearest multiple of MCLBYTES * to utilize large mbufs. If no route is found, route has no mtu, * or the destination isn't local, use a default, hopefully conservative * size (usually 512 or the default IP max size, but no more than the mtu * of the interface), as we can't discover anything about intervening * gateways or networks. We also initialize the congestion/slow start * window to be a single segment if the destination isn't local. * While looking at the routing entry, we also initialize other path-dependent * parameters from pre-set or cached values in the routing entry. * * Also take into account the space needed for options that we * send regularly. Make maxseg shorter by that amount to assure * that we can send maxseg amount of data even when the options * are present. Store the upper limit of the length of options plus * data in maxopd. * * * In case of T/TCP, we call this routine during implicit connection * setup as well (offer = -1), to initialize maxseg from the cached * MSS of our peer. * * NOTE that this routine is only called when we process an incoming * segment. Outgoing SYN/ACK MSS settings are handled in tcp_mssopt(). */ void tcp_mss(tp, offer) struct tcpcb *tp; int offer; { int rtt, mss; u_long bufsize; u_long maxmtu; struct inpcb *inp = tp->t_inpcb; struct socket *so; struct hc_metrics_lite metrics; int origoffer = offer; #ifdef INET6 int isipv6 = ((inp->inp_vflag & INP_IPV6) != 0) ? 1 : 0; size_t min_protoh = isipv6 ? sizeof (struct ip6_hdr) + sizeof (struct tcphdr) : sizeof (struct tcpiphdr); #else const size_t min_protoh = sizeof(struct tcpiphdr); #endif /* initialize */ #ifdef INET6 if (isipv6) { maxmtu = tcp_maxmtu6(&inp->inp_inc); tp->t_maxopd = tp->t_maxseg = tcp_v6mssdflt; } else #endif { maxmtu = tcp_maxmtu(&inp->inp_inc); tp->t_maxopd = tp->t_maxseg = tcp_mssdflt; } so = inp->inp_socket; /* * no route to sender, stay with default mss and return */ if (maxmtu == 0) return; /* what have we got? */ switch (offer) { case 0: /* * Offer == 0 means that there was no MSS on the SYN * segment, in this case we use tcp_mssdflt. */ offer = #ifdef INET6 isipv6 ? tcp_v6mssdflt : #endif tcp_mssdflt; break; case -1: /* * Offer == -1 means that we didn't receive SYN yet. */ /* FALLTHROUGH */ default: /* * Prevent DoS attack with too small MSS. Round up * to at least minmss. */ offer = max(offer, tcp_minmss); /* * Sanity check: make sure that maxopd will be large * enough to allow some data on segments even if the * all the option space is used (40bytes). Otherwise * funny things may happen in tcp_output. */ offer = max(offer, 64); } /* * rmx information is now retrieved from tcp_hostcache */ tcp_hc_get(&inp->inp_inc, &metrics); /* * if there's a discovered mtu int tcp hostcache, use it * else, use the link mtu. */ if (metrics.rmx_mtu) mss = min(metrics.rmx_mtu, maxmtu) - min_protoh; else { #ifdef INET6 if (isipv6) { mss = maxmtu - min_protoh; if (!path_mtu_discovery && !in6_localaddr(&inp->in6p_faddr)) mss = min(mss, tcp_v6mssdflt); } else #endif { mss = maxmtu - min_protoh; if (!path_mtu_discovery && !in_localaddr(inp->inp_faddr)) mss = min(mss, tcp_mssdflt); } } mss = min(mss, offer); /* * maxopd stores the maximum length of data AND options * in a segment; maxseg is the amount of data in a normal * segment. We need to store this value (maxopd) apart * from maxseg, because now every segment carries options * and thus we normally have somewhat less data in segments. */ tp->t_maxopd = mss; /* * origoffer==-1 indicates, that no segments were received yet. * In this case we just guess. */ if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP && (origoffer == -1 || (tp->t_flags & TF_RCVD_TSTMP) == TF_RCVD_TSTMP)) mss -= TCPOLEN_TSTAMP_APPA; tp->t_maxseg = mss; #if (MCLBYTES & (MCLBYTES - 1)) == 0 if (mss > MCLBYTES) mss &= ~(MCLBYTES-1); #else if (mss > MCLBYTES) mss = mss / MCLBYTES * MCLBYTES; #endif tp->t_maxseg = mss; /* * If there's a pipesize, change the socket buffer to that size, * don't change if sb_hiwat is different than default (then it * has been changed on purpose with setsockopt). * Make the socket buffers an integral number of mss units; * if the mss is larger than the socket buffer, decrease the mss. */ SOCKBUF_LOCK(&so->so_snd); if ((so->so_snd.sb_hiwat == tcp_sendspace) && metrics.rmx_sendpipe) bufsize = metrics.rmx_sendpipe; else bufsize = so->so_snd.sb_hiwat; if (bufsize < mss) mss = bufsize; else { bufsize = roundup(bufsize, mss); if (bufsize > sb_max) bufsize = sb_max; if (bufsize > so->so_snd.sb_hiwat) (void)sbreserve_locked(&so->so_snd, bufsize, so, NULL); } SOCKBUF_UNLOCK(&so->so_snd); tp->t_maxseg = mss; SOCKBUF_LOCK(&so->so_rcv); if ((so->so_rcv.sb_hiwat == tcp_recvspace) && metrics.rmx_recvpipe) bufsize = metrics.rmx_recvpipe; else bufsize = so->so_rcv.sb_hiwat; if (bufsize > mss) { bufsize = roundup(bufsize, mss); if (bufsize > sb_max) bufsize = sb_max; if (bufsize > so->so_rcv.sb_hiwat) (void)sbreserve_locked(&so->so_rcv, bufsize, so, NULL); } SOCKBUF_UNLOCK(&so->so_rcv); /* * While we're here, check the others too */ if (tp->t_srtt == 0 && (rtt = metrics.rmx_rtt)) { tp->t_srtt = rtt; tp->t_rttbest = tp->t_srtt + TCP_RTT_SCALE; tcpstat.tcps_usedrtt++; if (metrics.rmx_rttvar) { tp->t_rttvar = metrics.rmx_rttvar; tcpstat.tcps_usedrttvar++; } else { /* default variation is +- 1 rtt */ tp->t_rttvar = tp->t_srtt * TCP_RTTVAR_SCALE / TCP_RTT_SCALE; } TCPT_RANGESET(tp->t_rxtcur, ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1, tp->t_rttmin, TCPTV_REXMTMAX); } if (metrics.rmx_ssthresh) { /* * There's some sort of gateway or interface * buffer limit on the path. Use this to set * the slow start threshhold, but set the * threshold to no less than 2*mss. */ tp->snd_ssthresh = max(2 * mss, metrics.rmx_ssthresh); tcpstat.tcps_usedssthresh++; } if (metrics.rmx_bandwidth) tp->snd_bandwidth = metrics.rmx_bandwidth; /* * Set the slow-start flight size depending on whether this * is a local network or not. * * Extend this so we cache the cwnd too and retrieve it here. * Make cwnd even bigger than RFC3390 suggests but only if we * have previous experience with the remote host. Be careful * not make cwnd bigger than remote receive window or our own * send socket buffer. Maybe put some additional upper bound * on the retrieved cwnd. Should do incremental updates to * hostcache when cwnd collapses so next connection doesn't * overloads the path again. * * RFC3390 says only do this if SYN or SYN/ACK didn't got lost. * We currently check only in syncache_socket for that. */ #define TCP_METRICS_CWND #ifdef TCP_METRICS_CWND if (metrics.rmx_cwnd) tp->snd_cwnd = max(mss, min(metrics.rmx_cwnd / 2, min(tp->snd_wnd, so->so_snd.sb_hiwat))); else #endif if (tcp_do_rfc3390) tp->snd_cwnd = min(4 * mss, max(2 * mss, 4380)); #ifdef INET6 else if ((isipv6 && in6_localaddr(&inp->in6p_faddr)) || (!isipv6 && in_localaddr(inp->inp_faddr))) #else else if (in_localaddr(inp->inp_faddr)) #endif tp->snd_cwnd = mss * ss_fltsz_local; else tp->snd_cwnd = mss * ss_fltsz; } /* * Determine the MSS option to send on an outgoing SYN. */ int tcp_mssopt(inc) struct in_conninfo *inc; { int mss = 0; u_long maxmtu = 0; u_long thcmtu = 0; size_t min_protoh; #ifdef INET6 int isipv6 = inc->inc_isipv6 ? 1 : 0; #endif KASSERT(inc != NULL, ("tcp_mssopt with NULL in_conninfo pointer")); #ifdef INET6 if (isipv6) { mss = tcp_v6mssdflt; maxmtu = tcp_maxmtu6(inc); thcmtu = tcp_hc_getmtu(inc); /* IPv4 and IPv6 */ min_protoh = sizeof(struct ip6_hdr) + sizeof(struct tcphdr); } else #endif { mss = tcp_mssdflt; maxmtu = tcp_maxmtu(inc); thcmtu = tcp_hc_getmtu(inc); /* IPv4 and IPv6 */ min_protoh = sizeof(struct tcpiphdr); } if (maxmtu && thcmtu) mss = min(maxmtu, thcmtu) - min_protoh; else if (maxmtu || thcmtu) mss = max(maxmtu, thcmtu) - min_protoh; return (mss); } /* * On a partial ack arrives, force the retransmission of the * next unacknowledged segment. Do not clear tp->t_dupacks. * By setting snd_nxt to ti_ack, this forces retransmission timer to * be started again. */ static void tcp_newreno_partial_ack(tp, th) struct tcpcb *tp; struct tcphdr *th; { tcp_seq onxt = tp->snd_nxt; u_long ocwnd = tp->snd_cwnd; callout_stop(tp->tt_rexmt); tp->t_rtttime = 0; tp->snd_nxt = th->th_ack; /* * Set snd_cwnd to one segment beyond acknowledged offset. * (tp->snd_una has not yet been updated when this function is called.) */ tp->snd_cwnd = tp->t_maxseg + (th->th_ack - tp->snd_una); tp->t_flags |= TF_ACKNOW; (void) tcp_output(tp); tp->snd_cwnd = ocwnd; if (SEQ_GT(onxt, tp->snd_nxt)) tp->snd_nxt = onxt; /* * Partial window deflation. Relies on fact that tp->snd_una * not updated yet. */ tp->snd_cwnd -= (th->th_ack - tp->snd_una - tp->t_maxseg); } /* * Returns 1 if the TIME_WAIT state was killed and we should start over, * looking for a pcb in the listen state. Returns 0 otherwise. */ static int tcp_timewait(tw, to, th, m, tlen) struct tcptw *tw; struct tcpopt *to; struct tcphdr *th; struct mbuf *m; int tlen; { int thflags; tcp_seq seq; #ifdef INET6 int isipv6 = (mtod(m, struct ip *)->ip_v == 6) ? 1 : 0; #else const int isipv6 = 0; #endif thflags = th->th_flags; /* * NOTE: for FIN_WAIT_2 (to be added later), * must validate sequence number before accepting RST */ /* * If the segment contains RST: * Drop the segment - see Stevens, vol. 2, p. 964 and * RFC 1337. */ if (thflags & TH_RST) goto drop; #if 0 /* PAWS not needed at the moment */ /* * RFC 1323 PAWS: If we have a timestamp reply on this segment * and it's less than ts_recent, drop it. */ if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent && TSTMP_LT(to.to_tsval, tp->ts_recent)) { if ((thflags & TH_ACK) == 0) goto drop; goto ack; } /* * ts_recent is never updated because we never accept new segments. */ #endif /* * If a new connection request is received * while in TIME_WAIT, drop the old connection * and start over if the sequence numbers * are above the previous ones. */ if ((thflags & TH_SYN) && SEQ_GT(th->th_seq, tw->rcv_nxt)) { (void) tcp_twclose(tw, 0); return (1); } /* * Drop the the segment if it does not contain an ACK. */ if ((thflags & TH_ACK) == 0) goto drop; /* * Reset the 2MSL timer if this is a duplicate FIN. */ if (thflags & TH_FIN) { seq = th->th_seq + tlen + (thflags & TH_SYN ? 1 : 0); if (seq + 1 == tw->rcv_nxt) tcp_timer_2msl_reset(tw, 2 * tcp_msl); } /* * Acknowledge the segment if it has data or is not a duplicate ACK. */ if (thflags != TH_ACK || tlen != 0 || th->th_seq != tw->rcv_nxt || th->th_ack != tw->snd_nxt) tcp_twrespond(tw, TH_ACK); goto drop; /* * Generate a RST, dropping incoming segment. * Make ACK acceptable to originator of segment. * Don't bother to respond if destination was broadcast/multicast. */ if (m->m_flags & (M_BCAST|M_MCAST)) goto drop; if (isipv6) { struct ip6_hdr *ip6; /* IPv6 anycast check is done at tcp6_input() */ ip6 = mtod(m, struct ip6_hdr *); if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) || IN6_IS_ADDR_MULTICAST(&ip6->ip6_src)) goto drop; } else { struct ip *ip; ip = mtod(m, struct ip *); if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) || IN_MULTICAST(ntohl(ip->ip_src.s_addr)) || ip->ip_src.s_addr == htonl(INADDR_BROADCAST) || in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif)) goto drop; } if (thflags & TH_ACK) { tcp_respond(NULL, mtod(m, void *), th, m, 0, th->th_ack, TH_RST); } else { seq = th->th_seq + (thflags & TH_SYN ? 1 : 0); tcp_respond(NULL, mtod(m, void *), th, m, seq, 0, TH_RST|TH_ACK); } INP_UNLOCK(tw->tw_inpcb); return (0); drop: INP_UNLOCK(tw->tw_inpcb); m_freem(m); return (0); }