/*      $OpenBSD: tcp_input.c,v 1.468 2026/04/21 18:36:13 claudio Exp $ */
/*      $NetBSD: tcp_input.c,v 1.23 1996/02/13 23:43:44 christos Exp $  */

/*
 * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994
 *      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.
 * 3. 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.
 *
 *      @(#)COPYRIGHT   1.1 (NRL) 17 January 1995
 *
 * NRL grants permission for redistribution and use in source and binary
 * forms, with or without modification, of the software and documentation
 * created at NRL 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.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgements:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 *      This product includes software developed at the Information
 *      Technology Division, US Naval Research Laboratory.
 * 4. Neither the name of the NRL nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THE SOFTWARE PROVIDED BY NRL IS PROVIDED BY NRL 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 NRL 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.
 *
 * The views and conclusions contained in the software and documentation
 * are those of the authors and should not be interpreted as representing
 * official policies, either expressed or implied, of the US Naval
 * Research Laboratory (NRL).
 */

#include "pf.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/mbuf.h>
#include <sys/protosw.h>
#include <sys/socket.h>
#include <sys/timeout.h>
#include <sys/kernel.h>
#include <sys/pool.h>

#include <net/if.h>
#include <net/if_var.h>
#include <net/route.h>

#include <netinet/if_ether.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <netinet/in_pcb.h>
#include <netinet/ip_var.h>
#include <netinet6/ip6_var.h>
#include <netinet/tcp.h>
#include <netinet/tcp_fsm.h>
#include <netinet/tcp_seq.h>
#include <netinet/tcp_timer.h>
#include <netinet/tcp_var.h>
#include <netinet/tcp_debug.h>

#if NPF > 0
#include <net/pfvar.h>
#endif

#ifdef INET6
#include <netinet6/in6_var.h>
#include <netinet6/nd6.h>
#endif /* INET6 */

const int tcprexmtthresh = 3;

int tcp_rst_ppslim = 100;               /* 100pps */
int tcp_rst_ppslim_count = 0;
struct timeval tcp_rst_ppslim_last;

int tcp_ackdrop_ppslim = 100;           /* 100pps */
int tcp_ackdrop_ppslim_count = 0;
struct timeval tcp_ackdrop_ppslim_last;

#define TCP_PAWS_IDLE   TCP_TIME(24 * 24 * 60 * 60)

/* for modulo comparisons of timestamps */
#define TSTMP_LT(a,b)   ((int32_t)((a)-(b)) < 0)
#define TSTMP_GEQ(a,b)  ((int32_t)((a)-(b)) >= 0)

/* for TCP SACK comparisons */
#define SEQ_MIN(a,b)    (SEQ_LT(a,b) ? (a) : (b))
#define SEQ_MAX(a,b)    (SEQ_GT(a,b) ? (a) : (b))

#ifdef TCP_ECN
/*
 * ECN (Explicit Congestion Notification) support based on RFC3168
 * implementation note:
 *   snd_last is used to track a recovery phase.
 *   when cwnd is reduced, snd_last is set to snd_max.
 *   while snd_last > snd_una, the sender is in a recovery phase and
 *   its cwnd should not be reduced again.
 *   snd_last follows snd_una when not in a recovery phase.
 */
#endif

/*
 * Macro to compute ACK transmission behavior.  Delay the ACK unless
 * we have already delayed an ACK (must send an ACK every two segments).
 * We also ACK immediately if we received a PUSH and the ACK-on-PUSH
 * option is enabled or when the packet is coming from a loopback
 * interface.
 */
#define TCP_SETUP_ACK(tp, tiflags, m) \
do { \
        struct ifnet *ifp = NULL; \
        if (m && (m->m_flags & M_PKTHDR)) \
                ifp = if_get(m->m_pkthdr.ph_ifidx); \
        if (TCP_TIMER_ISARMED(tp, TCPT_DELACK) || \
            (atomic_load_int(&tcp_ack_on_push) && (tiflags) & TH_PUSH) || \
            (ifp && (ifp->if_flags & IFF_LOOPBACK))) \
                tp->t_flags |= TF_ACKNOW; \
        else \
                TCP_TIMER_ARM(tp, TCPT_DELACK, tcp_delack_msecs); \
        if_put(ifp); \
} while (0)

int      tcp_input_solocked(struct mbuf **, int *, int, int, struct socket **);
int      tcp_mss_adv(struct rtentry *, int);
int      tcp_flush_queue(struct tcpcb *);
void     tcp_sack_partialack(struct tcpcb *, struct tcphdr *);
void     tcp_newreno_partialack(struct tcpcb *, struct tcphdr *);

void     syn_cache_put(struct syn_cache *);
void     syn_cache_rm(struct syn_cache *);
int      syn_cache_respond(struct syn_cache *, struct mbuf *, uint64_t, int);
void     syn_cache_timer(void *);
void     syn_cache_insert(struct syn_cache *, struct tcpcb *);
void     syn_cache_reset(struct sockaddr *, struct sockaddr *,
                struct tcphdr *, u_int);
int      syn_cache_add(struct sockaddr *, struct sockaddr *, struct tcphdr *,
                unsigned int, struct socket *, struct mbuf *, u_char *, int,
                struct tcp_opt_info *, tcp_seq *, uint64_t, int);
struct socket *syn_cache_get(struct sockaddr *, struct sockaddr *,
                struct tcphdr *, unsigned int, unsigned int, struct socket *,
                struct mbuf *, uint64_t, int);
struct syn_cache *syn_cache_lookup(const struct sockaddr *,
                const struct sockaddr *, struct syn_cache_head **, u_int);

/*
 * Insert segment ti into reassembly queue of tcp with
 * control block tp.  Return TH_FIN if reassembly now includes
 * a segment with FIN.  The macro form does 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).
 */

int
tcp_reass(struct tcpcb *tp, struct tcphdr *th, struct mbuf *m, int *tlen)
{
        struct tcpqent *p, *q, *nq, *tiqe;

        /*
         * Allocate a new queue entry, before we throw away any data.
         * If we can't, just drop the packet.  XXX
         */
        tiqe = pool_get(&tcpqe_pool, PR_NOWAIT);
        if (tiqe == NULL) {
                tiqe = TAILQ_LAST(&tp->t_segq, tcpqehead);
                if (tiqe != NULL && th->th_seq == tp->rcv_nxt) {
                        /* Reuse last entry since new segment fills a hole */
                        m_freem(tiqe->tcpqe_m);
                        TAILQ_REMOVE(&tp->t_segq, tiqe, tcpqe_q);
                }
                if (tiqe == NULL || th->th_seq != tp->rcv_nxt) {
                        /* Flush segment queue for this connection */
                        tcp_freeq(tp);
                        tcpstat_inc(tcps_rcvmemdrop);
                        m_freem(m);
                        return (0);
                }
        }

        /*
         * Find a segment which begins after this one does.
         */
        for (p = NULL, q = TAILQ_FIRST(&tp->t_segq); q != NULL;
            p = q, q = TAILQ_NEXT(q, tcpqe_q))
                if (SEQ_GT(q->tcpqe_tcp->th_seq, th->th_seq))
                        break;

        /*
         * 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) {
                struct tcphdr *phdr = p->tcpqe_tcp;
                int i;

                /* conversion to int (in i) handles seq wraparound */
                i = phdr->th_seq + phdr->th_reseqlen - th->th_seq;
                if (i > 0) {
                        if (i >= *tlen) {
                                tcpstat_pkt(tcps_rcvduppack, tcps_rcvdupbyte,
                                    *tlen);
                                m_freem(m);
                                pool_put(&tcpqe_pool, tiqe);
                                return (0);
                        }
                        m_adj(m, i);
                        *tlen -= i;
                        th->th_seq += i;
                }
        }
        tcpstat_pkt(tcps_rcvoopack, tcps_rcvoobyte, *tlen);
        tp->t_rcvoopack++;

        /*
         * While we overlap succeeding segments trim them or,
         * if they are completely covered, dequeue them.
         */
        for (; q != NULL; q = nq) {
                struct tcphdr *qhdr = q->tcpqe_tcp;
                int i = (th->th_seq + *tlen) - qhdr->th_seq;

                if (i <= 0)
                        break;
                if (i < qhdr->th_reseqlen) {
                        qhdr->th_seq += i;
                        qhdr->th_reseqlen -= i;
                        m_adj(q->tcpqe_m, i);
                        break;
                }
                nq = TAILQ_NEXT(q, tcpqe_q);
                m_freem(q->tcpqe_m);
                TAILQ_REMOVE(&tp->t_segq, q, tcpqe_q);
                pool_put(&tcpqe_pool, q);
        }

        /* Insert the new segment queue entry into place. */
        tiqe->tcpqe_m = m;
        th->th_reseqlen = *tlen;
        tiqe->tcpqe_tcp = th;
        if (p == NULL) {
                TAILQ_INSERT_HEAD(&tp->t_segq, tiqe, tcpqe_q);
        } else {
                TAILQ_INSERT_AFTER(&tp->t_segq, p, tiqe, tcpqe_q);
        }

        if (th->th_seq != tp->rcv_nxt)
                return (0);

        return (tcp_flush_queue(tp));
}

int
tcp_flush_queue(struct tcpcb *tp)
{
        struct socket *so = tp->t_inpcb->inp_socket;
        struct tcpqent *q, *nq;
        int flags;

        /*
         * Present data to user, advancing rcv_nxt through
         * completed sequence space.
         */
        if (TCPS_HAVEESTABLISHED(tp->t_state) == 0)
                return (0);
        q = TAILQ_FIRST(&tp->t_segq);
        if (q == NULL || q->tcpqe_tcp->th_seq != tp->rcv_nxt)
                return (0);
        if (tp->t_state == TCPS_SYN_RECEIVED && q->tcpqe_tcp->th_reseqlen)
                return (0);
        do {
                tp->rcv_nxt += q->tcpqe_tcp->th_reseqlen;
                flags = q->tcpqe_tcp->th_flags & TH_FIN;

                nq = TAILQ_NEXT(q, tcpqe_q);
                TAILQ_REMOVE(&tp->t_segq, q, tcpqe_q);
                if (so->so_rcv.sb_state & SS_CANTRCVMORE)
                        m_freem(q->tcpqe_m);
                else {
                        mtx_enter(&so->so_rcv.sb_mtx);
                        sbappendstream(&so->so_rcv, q->tcpqe_m);
                        mtx_leave(&so->so_rcv.sb_mtx);
                }
                pool_put(&tcpqe_pool, q);
                q = nq;
        } while (q != NULL && q->tcpqe_tcp->th_seq == tp->rcv_nxt && !flags);
        sorwakeup(so);
        return (flags);
}

int
tcp_input(struct mbuf **mp, int *offp, int proto, int af, struct netstack *ns)
{
        if (ns == NULL)
                return tcp_input_solocked(mp, offp, proto, af, NULL);
        (*mp)->m_pkthdr.ph_cookie = (void *)(long)(*offp);
        switch (af) {
        case AF_INET:
                ml_enqueue(&ns->ns_tcp_ml, *mp);
                break;
#ifdef INET6
        case AF_INET6:
                ml_enqueue(&ns->ns_tcp6_ml, *mp);
                break;
#endif
        default:
                m_freemp(mp);
        }
        *mp = NULL;
        return IPPROTO_DONE;
}

void
tcp_input_mlist(struct mbuf_list *ml, int af)
{
        struct socket *so = NULL;
        struct mbuf *m;

        while ((m = ml_dequeue(ml)) != NULL) {
                int off, nxt;

                off = (long)m->m_pkthdr.ph_cookie;
                m->m_pkthdr.ph_cookie = NULL;
                nxt = tcp_input_solocked(&m, &off, IPPROTO_TCP, af, &so);
                KASSERT(nxt == IPPROTO_DONE);
        }

        in_pcbsounlock(NULL, so);
}

/*
 * TCP input routine, follows pages 65-76 of the
 * protocol specification dated September, 1981 very closely.
 */
int
tcp_input_solocked(struct mbuf **mp, int *offp, int proto, int af,
    struct socket **solocked)
{
        struct mbuf *m = *mp;
        int iphlen = *offp;
        struct ip *ip = NULL;
        struct inpcb *inp = NULL;
        u_int8_t *optp = NULL;
        int optlen = 0;
        int tlen, off;
        struct tcpcb *otp = NULL, *tp = NULL;
        int tiflags;
        struct socket *so = NULL;
        int todrop, acked, ourfinisacked;
        int hdroptlen = 0;
        short ostate;
        union {
                struct  tcpiphdr tcpip;
#ifdef INET6
                struct  tcpipv6hdr tcpip6;
#endif
                char    caddr;
        } saveti;
        tcp_seq iss, *reuse = NULL;
        uint64_t now;
        u_long tiwin;
        struct tcp_opt_info opti;
        struct tcphdr *th;
#ifdef INET6
        struct ip6_hdr *ip6 = NULL;
#endif /* INET6 */
        int do_ecn = 0;
#ifdef TCP_ECN
        u_char iptos;
#endif

        tcpstat_inc(tcps_rcvtotal);

        opti.ts_present = 0;
        opti.maxseg = 0;
        now = tcp_now();
#ifdef TCP_ECN
        do_ecn = atomic_load_int(&tcp_do_ecn);
#endif

        /*
         * RFC1122 4.2.3.10, p. 104: discard bcast/mcast SYN
         */
        if (m->m_flags & (M_BCAST|M_MCAST))
                goto drop;

        /*
         * Get IP and TCP header together in first mbuf.
         * Note: IP leaves IP header in first mbuf.
         */
        th = ip6_exthdr_get(mp, iphlen, sizeof(*th));
        if (th == NULL) {
                tcpstat_inc(tcps_rcvshort);
                return IPPROTO_DONE;
        }

        tlen = m->m_pkthdr.len - iphlen;
        switch (af) {
        case AF_INET:
                ip = mtod(m, struct ip *);
#ifdef TCP_ECN
                /* save ip_tos before clearing it for checksum */
                iptos = ip->ip_tos;
#endif
                break;
#ifdef INET6
        case AF_INET6:
                ip6 = mtod(m, struct ip6_hdr *);
#ifdef TCP_ECN
                iptos = (ntohl(ip6->ip6_flow) >> 20) & 0xff;
#endif

                /*
                 * 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;
                }

                /* Discard packets to multicast */
                if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst)) {
                        /* XXX stat */
                        goto drop;
                }
                break;
#endif
        default:
                unhandled_af(af);
        }

        /*
         * Checksum extended TCP header and data.
         */
        if ((m->m_pkthdr.csum_flags & M_TCP_CSUM_IN_OK) == 0) {
                int sum;

                if (m->m_pkthdr.csum_flags & M_TCP_CSUM_IN_BAD) {
                        tcpstat_inc(tcps_rcvbadsum);
                        goto drop;
                }
                tcpstat_inc(tcps_inswcsum);
                switch (af) {
                case AF_INET:
                        sum = in4_cksum(m, IPPROTO_TCP, iphlen, tlen);
                        break;
#ifdef INET6
                case AF_INET6:
                        sum = in6_cksum(m, IPPROTO_TCP, iphlen, tlen);
                        break;
#endif
                }
                if (sum != 0) {
                        tcpstat_inc(tcps_rcvbadsum);
                        goto drop;
                }
        }

        /*
         * 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_inc(tcps_rcvbadoff);
                goto drop;
        }
        tlen -= off;
        if (off > sizeof(struct tcphdr)) {
                th = ip6_exthdr_get(mp, iphlen, off);
                if (th == NULL) {
                        tcpstat_inc(tcps_rcvshort);
                        return IPPROTO_DONE;
                }
                optlen = off - sizeof(struct tcphdr);
                optp = (u_int8_t *)(th + 1);
                /*
                 * Do quick retrieval of timestamp options ("options
                 * prediction?").  If timestamp is the only option and it's
                 * formatted as recommended in RFC 1323 appendix A, we
                 * quickly get the values now and not bother calling
                 * tcp_dooptions(), etc.
                 */
                if ((optlen == TCPOLEN_TSTAMP_APPA ||
                     (optlen > TCPOLEN_TSTAMP_APPA &&
                      optp[TCPOLEN_TSTAMP_APPA] == TCPOPT_EOL)) &&
                     *(u_int32_t *)optp == htonl(TCPOPT_TSTAMP_HDR) &&
                     (th->th_flags & TH_SYN) == 0) {
                        opti.ts_present = 1;
                        opti.ts_val = ntohl(*(u_int32_t *)(optp + 4));
                        opti.ts_ecr = ntohl(*(u_int32_t *)(optp + 8));
                        optp = NULL;    /* we've parsed the options */
                }
        }
        tiflags = th->th_flags;

        /*
         * 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);

        if (th->th_dport == 0) {
                tcpstat_inc(tcps_noport);
                goto dropwithreset_ratelim;
        }

        /*
         * Locate pcb for segment.
         */
#if NPF > 0
        inp = pf_inp_lookup(m);
#endif
findpcb:
        if (inp == NULL) {
                switch (af) {
#ifdef INET6
                case AF_INET6:
                        inp = in6_pcblookup(&tcb6table, &ip6->ip6_src,
                            th->th_sport, &ip6->ip6_dst, th->th_dport,
                            m->m_pkthdr.ph_rtableid);
                        break;
#endif
                case AF_INET:
                        inp = in_pcblookup(&tcbtable, ip->ip_src,
                            th->th_sport, ip->ip_dst, th->th_dport,
                            m->m_pkthdr.ph_rtableid);
                        break;
                }
        }
        if (inp == NULL) {
                tcpstat_inc(tcps_pcbhashmiss);
                switch (af) {
#ifdef INET6
                case AF_INET6:
                        inp = in6_pcblookup_listen(&tcb6table, &ip6->ip6_dst,
                            th->th_dport, m, m->m_pkthdr.ph_rtableid);
                        break;
#endif
                case AF_INET:
                        inp = in_pcblookup_listen(&tcbtable, ip->ip_dst,
                            th->th_dport, m, m->m_pkthdr.ph_rtableid);
                        break;
                }
                /*
                 * 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.
                 */
        }
#ifdef IPSEC
        if (ipsec_in_use) {
                struct m_tag *mtag;
                struct tdb *tdb = NULL;
                int error;

                /* Find most recent IPsec tag */
                mtag = m_tag_find(m, PACKET_TAG_IPSEC_IN_DONE, NULL);
                if (mtag != NULL) {
                        struct tdb_ident *tdbi;

                        tdbi = (struct tdb_ident *)(mtag + 1);
                        tdb = gettdb(tdbi->rdomain, tdbi->spi,
                            &tdbi->dst, tdbi->proto);
                }
                error = ipsp_spd_lookup(m, af, iphlen, IPSP_DIRECTION_IN,
                    tdb, inp ? &inp->inp_seclevel : NULL, NULL, NULL);
                tdb_unref(tdb);
                if (error) {
                        tcpstat_inc(tcps_rcvnosec);
                        goto drop;
                }
        }
#endif /* IPSEC */

        if (inp == NULL) {
                tcpstat_inc(tcps_noport);
                goto dropwithreset_ratelim;
        }
        /*
         * Avoid needless lock and unlock operation when handling multiple
         * TCP packets from the same stream consecutively.
         */
        if (solocked != NULL && *solocked != NULL &&
            sotoinpcb(*solocked) == inp) {
                so = *solocked;
                *solocked = NULL;
        } else {
                if (solocked != NULL && *solocked != NULL) {
                        in_pcbsounlock(NULL, *solocked);
                        *solocked = NULL;
                }
                so = in_pcbsolock(inp);
        }
        if (so == NULL) {
                tcpstat_inc(tcps_closing);
                goto dropwithreset_ratelim;
        }
        KASSERT(sotoinpcb(inp->inp_socket) == inp);
        KASSERT(intotcpcb(inp) == NULL || intotcpcb(inp)->t_inpcb == inp);
        soassertlocked(inp->inp_socket);

        /* Check the minimum TTL for socket. */
        switch (af) {
        case AF_INET:
                if (inp->inp_ip_minttl && inp->inp_ip_minttl > ip->ip_ttl)
                        goto drop;
                break;
#ifdef INET6
        case AF_INET6:
                if (inp->inp_ip6_minhlim &&
                    inp->inp_ip6_minhlim > ip6->ip6_hlim)
                        goto drop;
                break;
#endif
        }

        tp = intotcpcb(inp);
        if (tp == NULL)
                goto dropwithreset_ratelim;
        if (tp->t_state == TCPS_CLOSED)
                goto drop;

        /* Unscale the window into a 32-bit value. */
        if ((tiflags & TH_SYN) == 0)
                tiwin = th->th_win << tp->snd_scale;
        else
                tiwin = th->th_win;

        if (so->so_options & (SO_DEBUG|SO_ACCEPTCONN)) {
                union syn_cache_sa src;
                union syn_cache_sa dst;

                bzero(&src, sizeof(src));
                bzero(&dst, sizeof(dst));
                switch (af) {
                case AF_INET:
                        src.sin.sin_len = sizeof(struct sockaddr_in);
                        src.sin.sin_family = AF_INET;
                        src.sin.sin_addr = ip->ip_src;
                        src.sin.sin_port = th->th_sport;

                        dst.sin.sin_len = sizeof(struct sockaddr_in);
                        dst.sin.sin_family = AF_INET;
                        dst.sin.sin_addr = ip->ip_dst;
                        dst.sin.sin_port = th->th_dport;
                        break;
#ifdef INET6
                case AF_INET6:
                        src.sin6.sin6_len = sizeof(struct sockaddr_in6);
                        src.sin6.sin6_family = AF_INET6;
                        src.sin6.sin6_addr = ip6->ip6_src;
                        src.sin6.sin6_port = th->th_sport;

                        dst.sin6.sin6_len = sizeof(struct sockaddr_in6);
                        dst.sin6.sin6_family = AF_INET6;
                        dst.sin6.sin6_addr = ip6->ip6_dst;
                        dst.sin6.sin6_port = th->th_dport;
                        break;
#endif /* INET6 */
                }

                if (so->so_options & SO_DEBUG) {
                        otp = tp;
                        ostate = tp->t_state;
                        switch (af) {
#ifdef INET6
                        case AF_INET6:
                                saveti.tcpip6.ti6_i = *ip6;
                                saveti.tcpip6.ti6_t = *th;
                                break;
#endif
                        case AF_INET:
                                memcpy(&saveti.tcpip.ti_i, ip, sizeof(*ip));
                                saveti.tcpip.ti_t = *th;
                                break;
                        }
                }
                if (so->so_options & SO_ACCEPTCONN) {
                        switch (tiflags & (TH_RST|TH_SYN|TH_ACK)) {

                        case TH_SYN|TH_ACK|TH_RST:
                        case TH_SYN|TH_RST:
                        case TH_ACK|TH_RST:
                        case TH_RST:
                                syn_cache_reset(&src.sa, &dst.sa, th,
                                    inp->inp_rtableid);
                                goto drop;

                        case TH_SYN|TH_ACK:
                                /*
                                 * Received a SYN,ACK.  This should
                                 * never happen while we are in
                                 * LISTEN.  Send an RST.
                                 */
                                goto badsyn;

                        case TH_ACK:
                                so = syn_cache_get(&src.sa, &dst.sa,
                                    th, iphlen, tlen, so, m, now, do_ecn);
                                if (so == NULL) {
                                        /*
                                         * We don't have a SYN for
                                         * this ACK; send an RST.
                                         */
                                        goto badsyn;
                                } else if (so == (struct socket *)(-1)) {
                                        /*
                                         * We were unable to create
                                         * the connection.  If the
                                         * 3-way handshake was
                                         * completed, and RST has
                                         * been sent to the peer.
                                         * Since the mbuf might be
                                         * in use for the reply,
                                         * do not free it.
                                         */
                                        so = NULL;
                                        m = *mp = NULL;
                                        goto drop;
                                } else {
                                        /*
                                         * We have created a
                                         * full-blown connection.
                                         */
                                        in_pcbunref(inp);
                                        /* syn_cache_get() has refcounted inp */
                                        inp = sotoinpcb(so);
                                        tp = intotcpcb(inp);
                                        if (tp == NULL)
                                                goto badsyn;    /*XXX*/
                                }
                                break;

                        default:
                                /*
                                 * None of RST, SYN or ACK was set.
                                 * This is an invalid packet for a
                                 * TCB in LISTEN state.  Send a RST.
                                 */
                                goto badsyn;

                        case TH_SYN:
                                /*
                                 * Received a SYN.
                                 */

                                /*
                                 * LISTEN socket received a SYN
                                 * from itself?  This can't possibly
                                 * be valid; drop the packet.
                                 */
                                if (th->th_dport == th->th_sport) {
                                        switch (af) {
#ifdef INET6
                                        case AF_INET6:
                                                if (IN6_ARE_ADDR_EQUAL(&ip6->ip6_src,
                                                    &ip6->ip6_dst)) {
                                                        tcpstat_inc(tcps_badsyn);
                                                        goto drop;
                                                }
                                                break;
#endif /* INET6 */
                                        case AF_INET:
                                                if (ip->ip_dst.s_addr == ip->ip_src.s_addr) {
                                                        tcpstat_inc(tcps_badsyn);
                                                        goto drop;
                                                }
                                                break;
                                        }
                                }

                                /*
                                 * SYN looks ok; create compressed TCP
                                 * state for it.
                                 */
                                if (so->so_qlen > so->so_qlimit ||
                                    syn_cache_add(&src.sa, &dst.sa, th, iphlen,
                                    so, m, optp, optlen, &opti, reuse, now,
                                    do_ecn) == -1) {
                                        tcpstat_inc(tcps_dropsyn);
                                        goto drop;
                                }
                                if (solocked != NULL)
                                        *solocked = so;
                                else
                                        in_pcbsounlock(inp, so);
                                in_pcbunref(inp);
                                return IPPROTO_DONE;
                        }
                }
        }

#ifdef DIAGNOSTIC
        /*
         * Should not happen now that all embryonic connections
         * are handled with compressed state.
         */
        if (tp->t_state == TCPS_LISTEN)
                panic("tcp_input: TCPS_LISTEN");
#endif

#if NPF > 0
        pf_inp_link(m, inp);
#endif

        /*
         * Segment received on connection.
         * Reset idle time and keep-alive timer.
         */
        tp->t_rcvtime = now;
        if (TCPS_HAVEESTABLISHED(tp->t_state))
                TCP_TIMER_ARM(tp, TCPT_KEEP, atomic_load_int(&tcp_keepidle));

        if (tp->sack_enable)
                tcp_del_sackholes(tp, th); /* Delete stale SACK holes */

        /*
         * Process options.
         */
        if (optp
#ifdef TCP_SIGNATURE
            || (tp->t_flags & TF_SIGNATURE)
#endif
            ) {
                if (tcp_dooptions(tp, optp, optlen, th, m, iphlen, &opti,
                    m->m_pkthdr.ph_rtableid, now))
                        goto drop;
        }

        if (opti.ts_present && opti.ts_ecr) {
                int32_t rtt_test;

                /* subtract out the tcp timestamp modulator */
                opti.ts_ecr -= tp->ts_modulate;

                /* make sure ts_ecr is sensible */
                rtt_test = now - opti.ts_ecr;
                if (rtt_test < 0 || rtt_test > TCP_RTT_MAX)
                        opti.ts_ecr = 0;
        }

#ifdef TCP_ECN
        /* if congestion experienced, set ECE bit in subsequent packets. */
        if ((iptos & IPTOS_ECN_MASK) == IPTOS_ECN_CE) {
                tp->t_flags |= TF_RCVD_CE;
                tcpstat_inc(tcps_ecn_rcvce);
        }
#endif
        /*
         * 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.
         */
        if (tp->t_state == TCPS_ESTABLISHED &&
#ifdef TCP_ECN
            (tiflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ECE|TH_CWR|TH_ACK)) == TH_ACK &&
#else
            (tiflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) == TH_ACK &&
#endif
            (!opti.ts_present || TSTMP_GEQ(opti.ts_val, 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.
                 * Fix from Braden, see Stevens p. 870
                 */
                if (opti.ts_present && SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
                        tp->ts_recent_age = now;
                        tp->ts_recent = opti.ts_val;
                }

                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 &&
                            tp->t_dupacks == 0) {
                                /*
                                 * this is a pure ack for outstanding data.
                                 */
                                tcpstat_inc(tcps_predack);
                                if (opti.ts_present && opti.ts_ecr)
                                        tcp_xmit_timer(tp, now - opti.ts_ecr);
                                else if (tp->t_rtttime &&
                                    SEQ_GT(th->th_ack, tp->t_rtseq))
                                        tcp_xmit_timer(tp, now - tp->t_rtttime);
                                acked = th->th_ack - tp->snd_una;
                                tcpstat_pkt(tcps_rcvackpack, tcps_rcvackbyte,
                                    acked);
                                tp->t_rcvacktime = now;

                                mtx_enter(&so->so_snd.sb_mtx);
                                sbdrop(&so->so_snd, acked);
                                mtx_leave(&so->so_snd.sb_mtx);

                                /*
                                 * If we had a pending ICMP message that
                                 * refers to data that have just been
                                 * acknowledged, disregard the recorded ICMP
                                 * message.
                                 */
                                if ((tp->t_flags & TF_PMTUD_PEND) &&
                                    SEQ_GT(th->th_ack, tp->t_pmtud_th_seq))
                                        tp->t_flags &= ~TF_PMTUD_PEND;

                                /*
                                 * Keep track of the largest chunk of data
                                 * acknowledged since last PMTU update
                                 */
                                if (tp->t_pmtud_mss_acked < acked)
                                        tp->t_pmtud_mss_acked = acked;

                                tp->snd_una = th->th_ack;
                                /* Pull snd_wl2 up to prevent seq wrap. */
                                tp->snd_wl2 = th->th_ack;
                                /*
                                 * We want snd_last to track snd_una so
                                 * as to avoid sequence wraparound problems
                                 * for very large transfers.
                                 */
#ifdef TCP_ECN
                                if (SEQ_GT(tp->snd_una, tp->snd_last))
#endif
                                tp->snd_last = tp->snd_una;
                                m_freem(m);

                                /*
                                 * 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.
                                 */
                                if (tp->snd_una == tp->snd_max)
                                        TCP_TIMER_DISARM(tp, TCPT_REXMT);
                                else if (TCP_TIMER_ISARMED(tp, TCPT_PERSIST) == 0)
                                        TCP_TIMER_ARM(tp, TCPT_REXMT, tp->t_rxtcur);

                                tcp_update_sndspace(tp);
                                if (sb_notify(&so->so_snd))
                                        sowwakeup(so);
                                if (so->so_snd.sb_cc ||
                                    tp->t_flags & TF_NEEDOUTPUT)
                                        (void) tcp_output(tp);
                                if (solocked != NULL)
                                        *solocked = so;
                                else
                                        in_pcbsounlock(inp, so);
                                in_pcbunref(inp);
                                return IPPROTO_DONE;
                        }
                } else if (th->th_ack == tp->snd_una &&
                    TAILQ_EMPTY(&tp->t_segq) &&
                    tlen <= sbspace(&so->so_rcv)) {
                        /*
                         * 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_inc(tcps_preddat);
                        tp->rcv_nxt += tlen;
                        /* Pull snd_wl1 and rcv_up up to prevent seq wrap. */
                        tp->snd_wl1 = th->th_seq;
                        /* Packet has most recent segment, no urgent exists. */
                        tp->rcv_up = tp->rcv_nxt;
                        tcpstat_pkt(tcps_rcvpack, tcps_rcvbyte, tlen);

                        TCP_SETUP_ACK(tp, tiflags, m);
                        /*
                         * Drop TCP, IP headers and TCP options then add data
                         * to socket buffer.
                         */
                        if (so->so_rcv.sb_state & SS_CANTRCVMORE)
                                m_freem(m);
                        else {
                                if (tp->t_srtt != 0 && tp->rfbuf_ts != 0 &&
                                    now - tp->rfbuf_ts > (tp->t_srtt >>
                                    (TCP_RTT_SHIFT + TCP_RTT_BASE_SHIFT))) {
                                        tcp_update_rcvspace(tp);
                                        /* Start over with next RTT. */
                                        tp->rfbuf_cnt = 0;
                                        tp->rfbuf_ts = 0;
                                } else
                                        tp->rfbuf_cnt += tlen;
                                m_adj(m, iphlen + off);
                                mtx_enter(&so->so_rcv.sb_mtx);
                                sbappendstream(&so->so_rcv, m);
                                mtx_leave(&so->so_rcv.sb_mtx);
                        }
                        sorwakeup(so);
                        if (tp->t_flags & (TF_ACKNOW|TF_NEEDOUTPUT))
                                (void) tcp_output(tp);
                        if (solocked != NULL)
                                *solocked = so;
                        else
                                in_pcbsounlock(inp, so);
                        in_pcbunref(inp);
                        return IPPROTO_DONE;
                }
        }

        /*
         * Compute mbuf offset to TCP data segment.
         */
        hdroptlen = iphlen + off;

        /*
         * 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 SYN/ACK, send an RST.
         *      if seg contains an ACK, but not for our SYN/ACK, send an RST
         */

        case TCPS_SYN_RECEIVED:
                if (tiflags & TH_ACK) {
                        if (tiflags & TH_SYN) {
                                tcpstat_inc(tcps_badsyn);
                                goto dropwithreset;
                        }
                        if (SEQ_LEQ(th->th_ack, tp->snd_una) ||
                            SEQ_GT(th->th_ack, tp->snd_max))
                                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 ((tiflags & TH_ACK) &&
                    (SEQ_LEQ(th->th_ack, tp->iss) ||
                     SEQ_GT(th->th_ack, tp->snd_max)))
                        goto dropwithreset;
                if (tiflags & TH_RST) {
#ifdef TCP_ECN
                        /* if ECN is enabled, fall back to non-ecn at rexmit */
                        if (do_ecn && !(tp->t_flags & TF_DISABLE_ECN))
                                goto drop;
#endif
                        if (tiflags & TH_ACK)
                                tp = tcp_drop(tp, ECONNREFUSED);
                        goto drop;
                }
                if ((tiflags & TH_SYN) == 0)
                        goto drop;
                if (tiflags & TH_ACK) {
                        tp->snd_una = th->th_ack;
                        if (SEQ_LT(tp->snd_nxt, tp->snd_una))
                                tp->snd_nxt = tp->snd_una;
                }
                TCP_TIMER_DISARM(tp, TCPT_REXMT);
                tp->irs = th->th_seq;
                tcp_mss(tp, opti.maxseg);
                /* Reset initial window to 1 segment for retransmit */
                if (tp->t_rxtshift > 0)
                        tp->snd_cwnd = tp->t_maxseg;
                tcp_rcvseqinit(tp);
                tp->t_flags |= TF_ACKNOW;
                /*
                 * If we've sent a SACK_PERMITTED option, and the peer
                 * also replied with one, then TF_SACK_PERMIT should have
                 * been set in tcp_dooptions().  If it was not, disable SACKs.
                 */
                if (tp->sack_enable)
                        tp->sack_enable = tp->t_flags & TF_SACK_PERMIT;
#ifdef TCP_ECN
                /*
                 * if ECE is set but CWR is not set for SYN-ACK, or
                 * both ECE and CWR are set for simultaneous open,
                 * peer is ECN capable.
                 */
                if (do_ecn) {
                        switch (tiflags & (TH_ACK|TH_ECE|TH_CWR)) {
                        case TH_ACK|TH_ECE:
                        case TH_ECE|TH_CWR:
                                tp->t_flags |= TF_ECN_PERMIT;
                                tiflags &= ~(TH_ECE|TH_CWR);
                                tcpstat_inc(tcps_ecn_accepts);
                        }
                }
#endif

                if (tiflags & TH_ACK && SEQ_GT(tp->snd_una, tp->iss)) {
                        tcpstat_inc(tcps_connects);
                        soisconnected(so);
                        tp->t_state = TCPS_ESTABLISHED;
                        TCP_TIMER_ARM(tp, TCPT_KEEP,
                            atomic_load_int(&tcp_keepidle));
                        /* 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;
                        }
                        tcp_flush_queue(tp);

                        /*
                         * if we didn't have to retransmit the SYN,
                         * use its rtt as our initial srtt & rtt var.
                         */
                        if (tp->t_rtttime)
                                tcp_xmit_timer(tp, now - tp->t_rtttime);
                        /*
                         * Since new data was acked (the SYN), open the
                         * congestion window by one MSS.  We do this
                         * here, because we won't go through the normal
                         * ACK processing below.  And since this is the
                         * start of the connection, we know we are in
                         * the exponential phase of slow-start.
                         */
                        tp->snd_cwnd += tp->t_maxseg;
                } else
                        tp->t_state = TCPS_SYN_RECEIVED;

#if 0
trimthenstep6:
#endif
                /*
                 * 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;
                        tiflags &= ~TH_FIN;
                        tcpstat_pkt(tcps_rcvpackafterwin, tcps_rcvbyteafterwin,
                            todrop);
                }
                tp->snd_wl1 = th->th_seq - 1;
                tp->rcv_up = th->th_seq;
                goto step6;
        /*
         * If a new connection request is received while in TIME_WAIT,
         * drop the old connection and start over if the if the
         * timestamp or the sequence numbers are above the previous
         * ones.
         */
        case TCPS_TIME_WAIT:
                if (((tiflags & (TH_SYN|TH_ACK)) == TH_SYN) &&
                    ((opti.ts_present &&
                    TSTMP_LT(tp->ts_recent, opti.ts_val)) ||
                    SEQ_GT(th->th_seq, tp->rcv_nxt))) {
#if NPF > 0
                        /*
                         * The socket will be recreated but the new state
                         * has already been linked to the socket.  Remove the
                         * link between old socket and new state.
                         */
                        pf_inp_unlink(inp);
#endif
                        /*
                        * Advance the iss by at least 32768, but
                        * clear the msb in order to make sure
                        * that SEG_LT(snd_nxt, iss).
                        */
                        iss = tp->snd_nxt +
                            ((arc4random() & 0x7fffffff) | 0x8000);
                        reuse = &iss;
                        tp = tcp_close(tp);
                        in_pcbsounlock(inp, so);
                        so = NULL;
                        in_pcbunref(inp);
                        inp = NULL;
                        goto findpcb;
                }
        }

        /*
         * States other than LISTEN or SYN_SENT.
         * First check timestamp, 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.
         *
         * RFC 1323 PAWS: If we have a timestamp reply on this segment
         * and it's less than opti.ts_recent, drop it.
         */
        if (opti.ts_present && (tiflags & TH_RST) == 0 && tp->ts_recent &&
            TSTMP_LT(opti.ts_val, tp->ts_recent)) {

                /* Check to see if ts_recent is over 24 days old.  */
                if (now - 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_pkt(tcps_rcvduppack, tcps_rcvdupbyte, tlen);
                        tcpstat_inc(tcps_pawsdrop);
                        if (tlen)
                                goto dropafterack;
                        goto drop;
                }
        }

        todrop = tp->rcv_nxt - th->th_seq;
        if (todrop > 0) {
                if (tiflags & TH_SYN) {
                        tiflags &= ~TH_SYN;
                        th->th_seq++;
                        if (th->th_urp > 1)
                                th->th_urp--;
                        else
                                tiflags &= ~TH_URG;
                        todrop--;
                }
                if (todrop > tlen ||
                    (todrop == tlen && (tiflags & TH_FIN) == 0)) {
                        /*
                         * Any valid FIN must be to the left of the
                         * window.  At this point, FIN must be a
                         * duplicate or out-of-sequence, so drop it.
                         */
                        tiflags &= ~TH_FIN;
                        /*
                         * Send ACK to resynchronize, and drop any data,
                         * but keep on processing for RST or ACK.
                         */
                        tp->t_flags |= TF_ACKNOW;
                        todrop = tlen;
                        tcpstat_pkt(tcps_rcvduppack, tcps_rcvdupbyte, todrop);
                } else {
                        tcpstat_pkt(tcps_rcvpartduppack, tcps_rcvpartdupbyte,
                            todrop);
                }
                hdroptlen += todrop;    /* drop from head afterwards */
                th->th_seq += todrop;
                tlen -= todrop;
                if (th->th_urp > todrop)
                        th->th_urp -= todrop;
                else {
                        tiflags &= ~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_inc(tcps_rcvafterclose);
                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_inc(tcps_rcvpackafterwin);
                if (todrop >= tlen) {
                        tcpstat_add(tcps_rcvbyteafterwin, tlen);
                        /*
                         * 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_inc(tcps_rcvwinprobe);
                        } else
                                goto dropafterack;
                } else
                        tcpstat_add(tcps_rcvbyteafterwin, todrop);
                m_adj(m, -todrop);
                tlen -= todrop;
                tiflags &= ~(TH_PUSH|TH_FIN);
        }

        /*
         * If last ACK falls within this segment's sequence numbers,
         * record its timestamp if it's more recent.
         * NOTE that the test is modified according to the latest
         * proposal of the tcplw@cray.com list (Braden 1993/04/26).
         */
        if (opti.ts_present && TSTMP_GEQ(opti.ts_val, tp->ts_recent) &&
            SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
                tp->ts_recent_age = now;
                tp->ts_recent = opti.ts_val;
        }

        /*
         * If the RST bit is set 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_WAIT2, CLOSE_WAIT STATES:
         *      Inform user that connection was reset, and close tcb.
         *    CLOSING, LAST_ACK, TIME_WAIT STATES
         *      Close the tcb.
         */
        if (tiflags & TH_RST) {
                if (th->th_seq != tp->last_ack_sent &&
                    th->th_seq != tp->rcv_nxt &&
                    th->th_seq != (tp->rcv_nxt + 1))
                        goto drop;

                switch (tp->t_state) {
                case TCPS_SYN_RECEIVED:
#ifdef TCP_ECN
                        /* if ECN is enabled, fall back to non-ecn at rexmit */
                        if (do_ecn && !(tp->t_flags & TF_DISABLE_ECN))
                                goto drop;
#endif
                        so->so_error = ECONNREFUSED;
                        goto close;

                case TCPS_ESTABLISHED:
                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_inc(tcps_drops);
                        tp = tcp_close(tp);
                        goto drop;
                case TCPS_CLOSING:
                case TCPS_LAST_ACK:
                case TCPS_TIME_WAIT:
                        tp = tcp_close(tp);
                        goto drop;
                }
        }

        /*
         * If a SYN is in the window, then this is an
         * error and we ACK and drop the packet.
         */
        if (tiflags & TH_SYN)
                goto dropafterack_ratelim;

        /*
         * If the ACK bit is off we drop the segment and return.
         */
        if ((tiflags & TH_ACK) == 0) {
                if (tp->t_flags & TF_ACKNOW)
                        goto dropafterack;
                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_inc(tcps_connects);
                soisconnected(so);
                tp->t_state = TCPS_ESTABLISHED;
                TCP_TIMER_ARM(tp, TCPT_KEEP, atomic_load_int(&tcp_keepidle));
                /* 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;
                        tiwin = th->th_win << tp->snd_scale;
                }
                tcp_flush_queue(tp);
                tp->snd_wl1 = th->th_seq - 1;
                /* fall into ... */

        /*
         * 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:
#ifdef TCP_ECN
                /*
                 * if we receive ECE and are not already in recovery phase,
                 * reduce cwnd by half but don't slow-start.
                 * advance snd_last to snd_max not to reduce cwnd again
                 * until all outstanding packets are acked.
                 */
                if (do_ecn && (tiflags & TH_ECE)) {
                        if ((tp->t_flags & TF_ECN_PERMIT) &&
                            SEQ_GEQ(tp->snd_una, tp->snd_last)) {
                                u_int win;

                                win = min(tp->snd_wnd, tp->snd_cwnd) / tp->t_maxseg;
                                if (win > 1) {
                                        tp->snd_ssthresh = win / 2 * tp->t_maxseg;
                                        tp->snd_cwnd = tp->snd_ssthresh;
                                        tp->snd_last = tp->snd_max;
                                        tp->t_flags |= TF_SEND_CWR;
                                        tcpstat_inc(tcps_cwr_ecn);
                                }
                        }
                        tcpstat_inc(tcps_ecn_rcvece);
                }
                /*
                 * if we receive CWR, we know that the peer has reduced
                 * its congestion window.  stop sending ecn-echo.
                 */
                if ((tiflags & TH_CWR)) {
                        tp->t_flags &= ~TF_RCVD_CE;
                        tcpstat_inc(tcps_ecn_rcvcwr);
                }
#endif /* TCP_ECN */

                if (SEQ_LEQ(th->th_ack, tp->snd_una)) {
                        /*
                         * Duplicate/old ACK processing.
                         * Increments t_dupacks:
                         *      Pure duplicate (same seq/ack/window, no data)
                         * Doesn't affect t_dupacks:
                         *      Data packets.
                         *      Normal window updates (window opens)
                         * Resets t_dupacks:
                         *      New data ACKed.
                         *      Window shrinks
                         *      Old ACK
                         */
                        if (tlen) {
                                /* Drop very old ACKs unless th_seq matches */
                                if (th->th_seq != tp->rcv_nxt &&
                                   SEQ_LT(th->th_ack,
                                   tp->snd_una - tp->max_sndwnd)) {
                                        tcpstat_inc(tcps_rcvacktooold);
                                        goto drop;
                                }
                                break;
                        }
                        /*
                         * If we get an old ACK, there is probably packet
                         * reordering going on.  Be conservative and reset
                         * t_dupacks so that we are less aggressive in
                         * doing a fast retransmit.
                         */
                        if (th->th_ack != tp->snd_una) {
                                tp->t_dupacks = 0;
                                break;
                        }
                        if (tiwin == tp->snd_wnd) {
                                tcpstat_inc(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
                                 * threshold 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 (TCP_TIMER_ISARMED(tp, TCPT_REXMT) == 0)
                                        tp->t_dupacks = 0;
                                else if (++tp->t_dupacks == tcprexmtthresh) {
                                        tcp_seq onxt = tp->snd_nxt;
                                        u_long win =
                                            ulmin(tp->snd_wnd, tp->snd_cwnd) /
                                                2 / tp->t_maxseg;

                                        if (SEQ_LT(th->th_ack, tp->snd_last)){
                                                /*
                                                 * False fast retx after
                                                 * timeout.  Do not cut window.
                                                 */
                                                tp->t_dupacks = 0;
                                                goto drop;
                                        }
                                        if (win < 2)
                                                win = 2;
                                        tp->snd_ssthresh = win * tp->t_maxseg;
                                        tp->snd_last = tp->snd_max;
                                        if (tp->sack_enable) {
                                                TCP_TIMER_DISARM(tp, TCPT_REXMT);
                                                tp->t_rtttime = 0;
#ifdef TCP_ECN
                                                tp->t_flags |= TF_SEND_CWR;
#endif
                                                tcpstat_inc(tcps_cwr_frecovery);
                                                tcpstat_inc(tcps_sack_recovery_episode);
                                                /*
                                                 * tcp_output() will send
                                                 * oldest SACK-eligible rtx.
                                                 */
                                                (void) tcp_output(tp);
                                                tp->snd_cwnd = tp->snd_ssthresh+
                                                   tp->t_maxseg * tp->t_dupacks;
                                                goto drop;
                                        }
                                        TCP_TIMER_DISARM(tp, TCPT_REXMT);
                                        tp->t_rtttime = 0;
                                        tp->snd_nxt = th->th_ack;
                                        tp->snd_cwnd = tp->t_maxseg;
#ifdef TCP_ECN
                                        tp->t_flags |= TF_SEND_CWR;
#endif
                                        tcpstat_inc(tcps_cwr_frecovery);
                                        tcpstat_inc(tcps_sndrexmitfast);
                                        (void) tcp_output(tp);

                                        tp->snd_cwnd = tp->snd_ssthresh +
                                            tp->t_maxseg * tp->t_dupacks;
                                        if (SEQ_GT(onxt, tp->snd_nxt))
                                                tp->snd_nxt = onxt;
                                        goto drop;
                                } else if (tp->t_dupacks > tcprexmtthresh) {
                                        tp->snd_cwnd += tp->t_maxseg;
                                        (void) tcp_output(tp);
                                        goto drop;
                                }
                        } else if (tiwin < tp->snd_wnd) {
                                /*
                                 * The window was retracted!  Previous dup
                                 * ACKs may have been due to packets arriving
                                 * after the shrunken window, not a missing
                                 * packet, so play it safe and reset t_dupacks
                                 */
                                tp->t_dupacks = 0;
                        }
                        break;
                }
                /*
                 * If the congestion window was inflated to account
                 * for the other side's cached packets, retract it.
                 */
                if (tp->t_dupacks >= tcprexmtthresh) {
                        /* Check for a partial ACK */
                        if (SEQ_LT(th->th_ack, tp->snd_last)) {
                                if (tp->sack_enable)
                                        tcp_sack_partialack(tp, th);
                                else
                                        tcp_newreno_partialack(tp, th);
                        } else {
                                /* Out of fast recovery */
                                tp->snd_cwnd = tp->snd_ssthresh;
                                if (tcp_seq_subtract(tp->snd_max, th->th_ack) <
                                    tp->snd_ssthresh)
                                        tp->snd_cwnd =
                                            tcp_seq_subtract(tp->snd_max,
                                            th->th_ack);
                                tp->t_dupacks = 0;
                        }
                } else {
                        /*
                         * Reset the duplicate ACK counter if we
                         * were not in fast recovery.
                         */
                        tp->t_dupacks = 0;
                }
                if (SEQ_GT(th->th_ack, tp->snd_max)) {
                        tcpstat_inc(tcps_rcvacktoomuch);
                        goto dropafterack_ratelim;
                }
                acked = th->th_ack - tp->snd_una;
                tcpstat_pkt(tcps_rcvackpack, tcps_rcvackbyte, acked);
                tp->t_rcvacktime = now;

                /*
                 * 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.
                 */
                if (opti.ts_present && opti.ts_ecr)
                        tcp_xmit_timer(tp, now - opti.ts_ecr);
                else if (tp->t_rtttime && SEQ_GT(th->th_ack, tp->t_rtseq))
                        tcp_xmit_timer(tp, now - tp->t_rtttime);

                /*
                 * 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) {
                        TCP_TIMER_DISARM(tp, TCPT_REXMT);
                        tp->t_flags |= TF_NEEDOUTPUT;
                } else if (TCP_TIMER_ISARMED(tp, TCPT_PERSIST) == 0)
                        TCP_TIMER_ARM(tp, TCPT_REXMT, tp->t_rxtcur);
                /*
                 * 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).
                 */
                {
                u_int cw = tp->snd_cwnd;
                u_int incr = tp->t_maxseg;

                if (cw > tp->snd_ssthresh)
                        incr = max(incr * incr / cw, 1);
                if (tp->t_dupacks < tcprexmtthresh)
                        tp->snd_cwnd = ulmin(cw + incr,
                            TCP_MAXWIN << tp->snd_scale);
                }
                if (acked > so->so_snd.sb_cc) {
                        if (tp->snd_wnd > so->so_snd.sb_cc)
                                tp->snd_wnd -= so->so_snd.sb_cc;
                        else
                                tp->snd_wnd = 0;
                        mtx_enter(&so->so_snd.sb_mtx);
                        sbdrop(&so->so_snd, (int)so->so_snd.sb_cc);
                        mtx_leave(&so->so_snd.sb_mtx);
                        ourfinisacked = 1;
                } else {
                        mtx_enter(&so->so_snd.sb_mtx);
                        sbdrop(&so->so_snd, acked);
                        mtx_leave(&so->so_snd.sb_mtx);
                        if (tp->snd_wnd > acked)
                                tp->snd_wnd -= acked;
                        else
                                tp->snd_wnd = 0;
                        ourfinisacked = 0;
                }

                tcp_update_sndspace(tp);
                if (sb_notify(&so->so_snd))
                        sowwakeup(so);

                /*
                 * If we had a pending ICMP message that referred to data
                 * that have just been acknowledged, disregard the recorded
                 * ICMP message.
                 */
                if ((tp->t_flags & TF_PMTUD_PEND) &&
                    SEQ_GT(th->th_ack, tp->t_pmtud_th_seq))
                        tp->t_flags &= ~TF_PMTUD_PEND;

                /*
                 * Keep track of the largest chunk of data acknowledged
                 * since last PMTU update
                 */
                if (tp->t_pmtud_mss_acked < acked)
                        tp->t_pmtud_mss_acked = acked;

                tp->snd_una = th->th_ack;
#ifdef TCP_ECN
                /* sync snd_last with snd_una */
                if (SEQ_GT(tp->snd_una, tp->snd_last))
                        tp->snd_last = tp->snd_una;
#endif
                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.
                                 */
                                if (so->so_rcv.sb_state & SS_CANTRCVMORE) {
                                        int maxidle;

                                        soisdisconnected(so);
                                        maxidle = TCPTV_KEEPCNT *
                                            atomic_load_int(&tcp_keepidle);
                                        TCP_TIMER_ARM(tp, TCPT_2MSL, maxidle);
                                }
                                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) {
                                tp->t_state = TCPS_TIME_WAIT;
                                tcp_canceltimers(tp);
                                TCP_TIMER_ARM(tp, TCPT_2MSL, 2 * TCPTV_MSL);
                                soisdisconnected(so);
                        }
                        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:
                        TCP_TIMER_ARM(tp, TCPT_2MSL, 2 * TCPTV_MSL);
                        goto dropafterack;
                }
        }

step6:
        /*
         * Update window information.
         * Don't look at window if no ACK: TAC's send garbage on first SYN.
         */
        if ((tiflags & 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_inc(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;
                tp->t_flags |= TF_NEEDOUTPUT;
        }

        /*
         * Process segments with URG.
         */
        if ((tiflags & TH_URG) && th->th_urp &&
            TCPS_HAVERCVDFIN(tp->t_state) == 0) {
                u_long urgent;

                /*
                 * 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.
                 */
                mtx_enter(&so->so_rcv.sb_mtx);
                urgent = th->th_urp + so->so_rcv.sb_cc;
                mtx_leave(&so->so_rcv.sb_mtx);

                if (urgent > sb_max) {
                        th->th_urp = 0;                 /* XXX */
                        tiflags &= ~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;
                        mtx_enter(&so->so_rcv.sb_mtx);
                        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 |= SS_RCVATMARK;
                        mtx_leave(&so->so_rcv.sb_mtx);
                        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_int16_t) tlen &&
                    (so->so_options & SO_OOBINLINE) == 0)
                        tcp_pulloutofband(so, th->th_urp, m, hdroptlen);
        } 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 */

        /*
         * 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 || (tiflags & TH_FIN)) &&
            TCPS_HAVERCVDFIN(tp->t_state) == 0) {
                tcp_seq laststart = th->th_seq;
                tcp_seq lastend = th->th_seq + tlen;

                if (th->th_seq == tp->rcv_nxt && TAILQ_EMPTY(&tp->t_segq) &&
                    tp->t_state == TCPS_ESTABLISHED) {
                        TCP_SETUP_ACK(tp, tiflags, m);
                        tp->rcv_nxt += tlen;
                        tiflags = th->th_flags & TH_FIN;
                        tcpstat_pkt(tcps_rcvpack, tcps_rcvbyte, tlen);
                        if (so->so_rcv.sb_state & SS_CANTRCVMORE)
                                m_freem(m);
                        else {
                                m_adj(m, hdroptlen);
                                mtx_enter(&so->so_rcv.sb_mtx);
                                sbappendstream(&so->so_rcv, m);
                                mtx_leave(&so->so_rcv.sb_mtx);
                        }
                        sorwakeup(so);
                } else {
                        m_adj(m, hdroptlen);
                        tiflags = tcp_reass(tp, th, m, &tlen);
                        tp->t_flags |= TF_ACKNOW;
                }
                if (tp->sack_enable)
                        tcp_update_sack_list(tp, laststart, lastend);

                /*
                 * variable len never referenced again in modern BSD,
                 * so why bother computing it ??
                 */
#if 0
                /*
                 * 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);
#endif /* 0 */
        } else {
                m_freem(m);
                tiflags &= ~TH_FIN;
        }

        /*
         * If FIN is received ACK the FIN and let the user know
         * that the connection is closing.  Ignore a FIN received before
         * the connection is fully established.
         */
        if ((tiflags & TH_FIN) && TCPS_HAVEESTABLISHED(tp->t_state)) {
                if (TCPS_HAVERCVDFIN(tp->t_state) == 0) {
                        socantrcvmore(so);
                        tp->t_flags |= TF_ACKNOW;
                        tp->rcv_nxt++;
                }
                switch (tp->t_state) {

                /*
                 * In ESTABLISHED STATE enter the CLOSE_WAIT state.
                 */
                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:
                        tp->t_state = TCPS_TIME_WAIT;
                        tcp_canceltimers(tp);
                        TCP_TIMER_ARM(tp, TCPT_2MSL, 2 * TCPTV_MSL);
                        soisdisconnected(so);
                        break;

                /*
                 * In TIME_WAIT state restart the 2 MSL time_wait timer.
                 */
                case TCPS_TIME_WAIT:
                        TCP_TIMER_ARM(tp, TCPT_2MSL, 2 * TCPTV_MSL);
                        break;
                }
        }
        if (otp)
                tcp_trace(TA_INPUT, ostate, tp, otp, &saveti.caddr, 0, tlen);

        /*
         * Return any desired output.
         */
        if (tp->t_flags & (TF_ACKNOW|TF_NEEDOUTPUT))
                (void) tcp_output(tp);
        if (solocked != NULL)
                *solocked = so;
        else
                in_pcbsounlock(inp, so);
        in_pcbunref(inp);
        return IPPROTO_DONE;

badsyn:
        /*
         * Received a bad SYN.  Increment counters and dropwithreset.
         */
        tcpstat_inc(tcps_badsyn);
        tp = NULL;
        goto dropwithreset;

dropafterack_ratelim:
        if (ppsratecheck(&tcp_ackdrop_ppslim_last, &tcp_ackdrop_ppslim_count,
            tcp_ackdrop_ppslim) == 0) {
                /* XXX stat */
                goto drop;
        }
        /* ...fall into dropafterack... */

dropafterack:
        /*
         * Generate an ACK dropping incoming segment if it occupies
         * sequence space, where the ACK reflects our state.
         */
        if (tiflags & TH_RST)
                goto drop;
        m_freem(m);
        tp->t_flags |= TF_ACKNOW;
        (void) tcp_output(tp);
        if (solocked != NULL)
                *solocked = so;
        else
                in_pcbsounlock(inp, so);
        in_pcbunref(inp);
        return IPPROTO_DONE;

dropwithreset_ratelim:
        /*
         * We may want to rate-limit RSTs in certain situations,
         * particularly if we are sending an RST in response to
         * an attempt to connect to or otherwise communicate with
         * a port for which we have no socket.
         */
        if (ppsratecheck(&tcp_rst_ppslim_last, &tcp_rst_ppslim_count,
            atomic_load_int(&tcp_rst_ppslim)) == 0) {
                /* XXX stat */
                goto drop;
        }
        /* ...fall into dropwithreset... */

dropwithreset:
        /*
         * Generate a RST, dropping incoming segment.
         * Make ACK acceptable to originator of segment.
         * Don't bother to respond to RST.
         */
        if (tiflags & TH_RST)
                goto drop;
        if (tiflags & TH_ACK) {
                tcp_respond(tp, mtod(m, caddr_t), th, (tcp_seq)0, th->th_ack,
                    TH_RST, m->m_pkthdr.ph_rtableid, now);
        } else {
                if (tiflags & TH_SYN)
                        tlen++;
                tcp_respond(tp, mtod(m, caddr_t), th, th->th_seq + tlen,
                    (tcp_seq)0, TH_RST|TH_ACK, m->m_pkthdr.ph_rtableid, now);
        }
        m_freem(m);
        in_pcbsounlock(inp, so);
        in_pcbunref(inp);
        return IPPROTO_DONE;

drop:
        /*
         * Drop space held by incoming segment and return.
         */
        if (otp)
                tcp_trace(TA_DROP, ostate, tp, otp, &saveti.caddr, 0, tlen);

        m_freem(m);
        in_pcbsounlock(inp, so);
        in_pcbunref(inp);
        return IPPROTO_DONE;
}

int
tcp_dooptions(struct tcpcb *tp, u_char *cp, int cnt, struct tcphdr *th,
    struct mbuf *m, int iphlen, struct tcp_opt_info *oi,
    u_int rtableid, uint64_t now)
{
        u_int16_t mss = 0;
        int opt, optlen;
#ifdef TCP_SIGNATURE
        caddr_t sigp = NULL;
        struct tdb *tdb = NULL;
#endif

        for (; cp && 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) {

                default:
                        continue;

                case TCPOPT_MAXSEG:
                        if (optlen != TCPOLEN_MAXSEG)
                                continue;
                        if (!(th->th_flags & TH_SYN))
                                continue;
                        if (TCPS_HAVERCVDSYN(tp->t_state))
                                continue;
                        memcpy(&mss, cp + 2, sizeof(mss));
                        mss = ntohs(mss);
                        oi->maxseg = mss;
                        break;

                case TCPOPT_WINDOW:
                        if (optlen != TCPOLEN_WINDOW)
                                continue;
                        if (!(th->th_flags & TH_SYN))
                                continue;
                        if (TCPS_HAVERCVDSYN(tp->t_state))
                                continue;
                        tp->t_flags |= TF_RCVD_SCALE;
                        tp->requested_s_scale = min(cp[2], TCP_MAX_WINSHIFT);
                        break;

                case TCPOPT_TIMESTAMP:
                        if (optlen != TCPOLEN_TIMESTAMP)
                                continue;
                        oi->ts_present = 1;
                        memcpy(&oi->ts_val, cp + 2, sizeof(oi->ts_val));
                        oi->ts_val = ntohl(oi->ts_val);
                        memcpy(&oi->ts_ecr, cp + 6, sizeof(oi->ts_ecr));
                        oi->ts_ecr = ntohl(oi->ts_ecr);

                        if (!(th->th_flags & TH_SYN))
                                continue;
                        if (TCPS_HAVERCVDSYN(tp->t_state))
                                continue;
                        /*
                         * A timestamp received in a SYN makes
                         * it ok to send timestamp requests and replies.
                         */
                        tp->t_flags |= TF_RCVD_TSTMP;
                        tp->ts_recent = oi->ts_val;
                        tp->ts_recent_age = now;
                        break;

                case TCPOPT_SACK_PERMITTED:
                        if (!tp->sack_enable || optlen!=TCPOLEN_SACK_PERMITTED)
                                continue;
                        if (!(th->th_flags & TH_SYN))
                                continue;
                        if (TCPS_HAVERCVDSYN(tp->t_state))
                                continue;
                        /* MUST only be set on SYN */
                        tp->t_flags |= TF_SACK_PERMIT;
                        break;
                case TCPOPT_SACK:
                        tcp_sack_option(tp, th, cp, optlen);
                        break;
#ifdef TCP_SIGNATURE
                case TCPOPT_SIGNATURE:
                        if (optlen != TCPOLEN_SIGNATURE)
                                continue;

                        if (sigp && timingsafe_bcmp(sigp, cp + 2, 16))
                                goto bad;

                        sigp = cp + 2;
                        break;
#endif /* TCP_SIGNATURE */
                }
        }

#ifdef TCP_SIGNATURE
        if (tp->t_flags & TF_SIGNATURE) {
                union sockaddr_union src, dst;

                memset(&src, 0, sizeof(union sockaddr_union));
                memset(&dst, 0, sizeof(union sockaddr_union));

                switch (tp->pf) {
                case 0:
                case AF_INET:
                        src.sa.sa_len = sizeof(struct sockaddr_in);
                        src.sa.sa_family = AF_INET;
                        src.sin.sin_addr = mtod(m, struct ip *)->ip_src;
                        dst.sa.sa_len = sizeof(struct sockaddr_in);
                        dst.sa.sa_family = AF_INET;
                        dst.sin.sin_addr = mtod(m, struct ip *)->ip_dst;
                        break;
#ifdef INET6
                case AF_INET6:
                        src.sa.sa_len = sizeof(struct sockaddr_in6);
                        src.sa.sa_family = AF_INET6;
                        src.sin6.sin6_addr = mtod(m, struct ip6_hdr *)->ip6_src;
                        dst.sa.sa_len = sizeof(struct sockaddr_in6);
                        dst.sa.sa_family = AF_INET6;
                        dst.sin6.sin6_addr = mtod(m, struct ip6_hdr *)->ip6_dst;
                        break;
#endif /* INET6 */
                }

                tdb = gettdbbysrcdst(rtable_l2(rtableid),
                    0, &src, &dst, IPPROTO_TCP);

                /*
                 * We don't have an SA for this peer, so we turn off
                 * TF_SIGNATURE on the listen socket
                 */
                if (tdb == NULL && tp->t_state == TCPS_LISTEN)
                        tp->t_flags &= ~TF_SIGNATURE;

        }

        if ((sigp ? TF_SIGNATURE : 0) ^ (tp->t_flags & TF_SIGNATURE)) {
                tcpstat_inc(tcps_rcvbadsig);
                goto bad;
        }

        if (sigp) {
                char sig[16];

                if (tdb == NULL) {
                        tcpstat_inc(tcps_rcvbadsig);
                        goto bad;
                }

                if (tcp_signature(tdb, tp->pf, m, th, iphlen, 1, sig) < 0)
                        goto bad;

                if (timingsafe_bcmp(sig, sigp, 16)) {
                        tcpstat_inc(tcps_rcvbadsig);
                        goto bad;
                }

                tcpstat_inc(tcps_rcvgoodsig);
        }

        tdb_unref(tdb);
#endif /* TCP_SIGNATURE */

        return (0);

#ifdef TCP_SIGNATURE
 bad:
        tdb_unref(tdb);
#endif
        return (-1);
}

u_long
tcp_seq_subtract(u_long a, u_long b)
{
        return ((long)(a - b));
}

/*
 * This function is called upon receipt of new valid data (while not in header
 * prediction mode), and it updates the ordered list of sacks.
 */
void
tcp_update_sack_list(struct tcpcb *tp, tcp_seq rcv_laststart,
    tcp_seq rcv_lastend)
{
        /*
         * First reported block MUST be the most recent one.  Subsequent
         * blocks SHOULD be in the order in which they arrived at the
         * receiver.  These two conditions make the implementation fully
         * compliant with RFC 2018.
         */
        int i, j = 0, count = 0, lastpos = -1;
        struct sackblk sack, firstsack, temp[MAX_SACK_BLKS];

        /* First clean up current list of sacks */
        for (i = 0; i < tp->rcv_numsacks; i++) {
                sack = tp->sackblks[i];
                if (sack.start == 0 && sack.end == 0) {
                        count++; /* count = number of blocks to be discarded */
                        continue;
                }
                if (SEQ_LEQ(sack.end, tp->rcv_nxt)) {
                        tp->sackblks[i].start = tp->sackblks[i].end = 0;
                        count++;
                } else {
                        temp[j].start = tp->sackblks[i].start;
                        temp[j++].end = tp->sackblks[i].end;
                }
        }
        tp->rcv_numsacks -= count;
        if (tp->rcv_numsacks == 0) { /* no sack blocks currently (fast path) */
                tcp_clean_sackreport(tp);
                if (SEQ_LT(tp->rcv_nxt, rcv_laststart)) {
                        /* ==> need first sack block */
                        tp->sackblks[0].start = rcv_laststart;
                        tp->sackblks[0].end = rcv_lastend;
                        tp->rcv_numsacks = 1;
                }
                return;
        }
        /* Otherwise, sack blocks are already present. */
        for (i = 0; i < tp->rcv_numsacks; i++)
                tp->sackblks[i] = temp[i]; /* first copy back sack list */
        if (SEQ_GEQ(tp->rcv_nxt, rcv_lastend))
                return;     /* sack list remains unchanged */
        /*
         * From here, segment just received should be (part of) the 1st sack.
         * Go through list, possibly coalescing sack block entries.
         */
        firstsack.start = rcv_laststart;
        firstsack.end = rcv_lastend;
        for (i = 0; i < tp->rcv_numsacks; i++) {
                sack = tp->sackblks[i];
                if (SEQ_LT(sack.end, firstsack.start) ||
                    SEQ_GT(sack.start, firstsack.end))
                        continue; /* no overlap */
                if (sack.start == firstsack.start && sack.end == firstsack.end){
                        /*
                         * identical block; delete it here since we will
                         * move it to the front of the list.
                         */
                        tp->sackblks[i].start = tp->sackblks[i].end = 0;
                        lastpos = i;    /* last posn with a zero entry */
                        continue;
                }
                if (SEQ_LEQ(sack.start, firstsack.start))
                        firstsack.start = sack.start; /* merge blocks */
                if (SEQ_GEQ(sack.end, firstsack.end))
                        firstsack.end = sack.end;     /* merge blocks */
                tp->sackblks[i].start = tp->sackblks[i].end = 0;
                lastpos = i;    /* last posn with a zero entry */
        }
        if (lastpos != -1) {    /* at least one merge */
                for (i = 0, j = 1; i < tp->rcv_numsacks; i++) {
                        sack = tp->sackblks[i];
                        if (sack.start == 0 && sack.end == 0)
                                continue;
                        temp[j++] = sack;
                }
                tp->rcv_numsacks = j; /* including first blk (added later) */
                for (i = 1; i < tp->rcv_numsacks; i++) /* now copy back */
                        tp->sackblks[i] = temp[i];
        } else {        /* no merges -- shift sacks by 1 */
                if (tp->rcv_numsacks < MAX_SACK_BLKS)
                        tp->rcv_numsacks++;
                for (i = tp->rcv_numsacks-1; i > 0; i--)
                        tp->sackblks[i] = tp->sackblks[i-1];
        }
        tp->sackblks[0] = firstsack;
        return;
}

/*
 * Process the TCP SACK option.  tp->snd_holes is an ordered list
 * of holes (oldest to newest, in terms of the sequence space).
 */
void
tcp_sack_option(struct tcpcb *tp, struct tcphdr *th, u_char *cp, int optlen)
{
        int tmp_olen;
        u_char *tmp_cp;
        struct sackhole *cur, *p, *temp;

        if (!tp->sack_enable)
                return;
        /* SACK without ACK doesn't make sense. */
        if ((th->th_flags & TH_ACK) == 0)
                return;
        /* Make sure the ACK on this segment is in [snd_una, snd_max]. */
        if (SEQ_LT(th->th_ack, tp->snd_una) ||
            SEQ_GT(th->th_ack, tp->snd_max))
                return;
        /* Note: TCPOLEN_SACK must be 2*sizeof(tcp_seq) */
        if (optlen <= 2 || (optlen - 2) % TCPOLEN_SACK != 0)
                return;
        /* Note: TCPOLEN_SACK must be 2*sizeof(tcp_seq) */
        tmp_cp = cp + 2;
        tmp_olen = optlen - 2;
        tcpstat_inc(tcps_sack_rcv_opts);
        if (tp->snd_numholes < 0)
                tp->snd_numholes = 0;
        if (tp->t_maxseg == 0)
                panic("tcp_sack_option"); /* Should never happen */
        while (tmp_olen > 0) {
                struct sackblk sack;

                memcpy(&sack.start, tmp_cp, sizeof(tcp_seq));
                sack.start = ntohl(sack.start);
                memcpy(&sack.end, tmp_cp + sizeof(tcp_seq), sizeof(tcp_seq));
                sack.end = ntohl(sack.end);
                tmp_olen -= TCPOLEN_SACK;
                tmp_cp += TCPOLEN_SACK;
                if (SEQ_LEQ(sack.end, sack.start))
                        continue; /* bad SACK fields */
                if (SEQ_LEQ(sack.end, tp->snd_una))
                        continue; /* old block */
                if (SEQ_GT(th->th_ack, tp->snd_una)) {
                        if (SEQ_LT(sack.start, th->th_ack))
                                continue;
                }
                if (SEQ_GT(sack.end, tp->snd_max))
                        continue;
                if (SEQ_LT(sack.start, tp->snd_una))
                        continue;
                if (tp->snd_holes == NULL) { /* first hole */
                        tp->snd_holes = (struct sackhole *)
                            pool_get(&sackhl_pool, PR_NOWAIT);
                        if (tp->snd_holes == NULL) {
                                /* ENOBUFS, so ignore SACKed block for now */
                                goto dropped;
                        }
                        cur = tp->snd_holes;
                        cur->start = th->th_ack;
                        cur->end = sack.start;
                        cur->rxmit = cur->start;
                        cur->next = NULL;
                        tp->snd_numholes = 1;
                        tp->rcv_lastsack = sack.end;
                        /*
                         * dups is at least one.  If more data has been
                         * SACKed, it can be greater than one.
                         */
                        cur->dups = min(tcprexmtthresh,
                            ((sack.end - cur->end)/tp->t_maxseg));
                        if (cur->dups < 1)
                                cur->dups = 1;
                        continue; /* with next sack block */
                }
                /* Go thru list of holes:  p = previous,  cur = current */
                p = cur = tp->snd_holes;
                while (cur) {
                        if (SEQ_LEQ(sack.end, cur->start))
                                /* SACKs data before the current hole */
                                break; /* no use going through more holes */
                        if (SEQ_GEQ(sack.start, cur->end)) {
                                /* SACKs data beyond the current hole */
                                cur->dups++;
                                if (((sack.end - cur->end)/tp->t_maxseg) >=
                                    tcprexmtthresh)
                                        cur->dups = tcprexmtthresh;
                                p = cur;
                                cur = cur->next;
                                continue;
                        }
                        if (SEQ_LEQ(sack.start, cur->start)) {
                                /* Data acks at least the beginning of hole */
                                if (SEQ_GEQ(sack.end, cur->end)) {
                                        /* Acks entire hole, so delete hole */
                                        if (p != cur) {
                                                p->next = cur->next;
                                                pool_put(&sackhl_pool, cur);
                                                cur = p->next;
                                        } else {
                                                cur = cur->next;
                                                pool_put(&sackhl_pool, p);
                                                p = cur;
                                                tp->snd_holes = p;
                                        }
                                        tp->snd_numholes--;
                                        continue;
                                }
                                /* otherwise, move start of hole forward */
                                cur->start = sack.end;
                                cur->rxmit = SEQ_MAX(cur->rxmit, cur->start);
                                p = cur;
                                cur = cur->next;
                                continue;
                        }
                        /* move end of hole backward */
                        if (SEQ_GEQ(sack.end, cur->end)) {
                                cur->end = sack.start;
                                cur->rxmit = SEQ_MIN(cur->rxmit, cur->end);
                                cur->dups++;
                                if (((sack.end - cur->end)/tp->t_maxseg) >=
                                    tcprexmtthresh)
                                        cur->dups = tcprexmtthresh;
                                p = cur;
                                cur = cur->next;
                                continue;
                        }
                        if (SEQ_LT(cur->start, sack.start) &&
                            SEQ_GT(cur->end, sack.end)) {
                                /*
                                 * ACKs some data in middle of a hole; need to
                                 * split current hole
                                 */
                                if (tp->snd_numholes >= TCP_SACKHOLE_LIMIT)
                                        goto dropped;
                                temp = (struct sackhole *)
                                    pool_get(&sackhl_pool, PR_NOWAIT);
                                if (temp == NULL)
                                        goto dropped; /* ENOBUFS */
                                temp->next = cur->next;
                                temp->start = sack.end;
                                temp->end = cur->end;
                                temp->dups = cur->dups;
                                temp->rxmit = SEQ_MAX(cur->rxmit, temp->start);
                                cur->end = sack.start;
                                cur->rxmit = SEQ_MIN(cur->rxmit, cur->end);
                                cur->dups++;
                                if (((sack.end - cur->end)/tp->t_maxseg) >=
                                        tcprexmtthresh)
                                        cur->dups = tcprexmtthresh;
                                cur->next = temp;
                                p = temp;
                                cur = p->next;
                                tp->snd_numholes++;
                        }
                }
                /* At this point, p points to the last hole on the list */
                if (p != NULL && SEQ_LT(tp->rcv_lastsack, sack.start)) {
                        /*
                         * Need to append new hole at end.
                         * Last hole is p (and it's not NULL).
                         */
                        if (tp->snd_numholes >= TCP_SACKHOLE_LIMIT)
                                goto dropped;
                        temp = (struct sackhole *)
                            pool_get(&sackhl_pool, PR_NOWAIT);
                        if (temp == NULL)
                                goto dropped; /* ENOBUFS */
                        temp->start = tp->rcv_lastsack;
                        temp->end = sack.start;
                        temp->dups = min(tcprexmtthresh,
                            ((sack.end - sack.start)/tp->t_maxseg));
                        if (temp->dups < 1)
                                temp->dups = 1;
                        temp->rxmit = temp->start;
                        temp->next = 0;
                        p->next = temp;
                        tp->rcv_lastsack = sack.end;
                        tp->snd_numholes++;
                }
        }
        return;
dropped:
        tcpstat_inc(tcps_sack_drop_opts);
}

/*
 * Delete stale (i.e, cumulatively ack'd) holes.  Hole is deleted only if
 * it is completely acked; otherwise, tcp_sack_option(), called from
 * tcp_dooptions(), will fix up the hole.
 */
void
tcp_del_sackholes(struct tcpcb *tp, struct tcphdr *th)
{
        if (tp->sack_enable && tp->t_state != TCPS_LISTEN) {
                /* max because this could be an older ack just arrived */
                tcp_seq lastack = SEQ_GT(th->th_ack, tp->snd_una) ?
                        th->th_ack : tp->snd_una;
                struct sackhole *cur = tp->snd_holes;
                struct sackhole *prev;
                while (cur)
                        if (SEQ_LEQ(cur->end, lastack)) {
                                prev = cur;
                                cur = cur->next;
                                pool_put(&sackhl_pool, prev);
                                tp->snd_numholes--;
                        } else if (SEQ_LT(cur->start, lastack)) {
                                cur->start = lastack;
                                if (SEQ_LT(cur->rxmit, cur->start))
                                        cur->rxmit = cur->start;
                                break;
                        } else
                                break;
                tp->snd_holes = cur;
        }
}

/*
 * Delete all receiver-side SACK information.
 */
void
tcp_clean_sackreport(struct tcpcb *tp)
{
        int i;

        tp->rcv_numsacks = 0;
        for (i = 0; i < MAX_SACK_BLKS; i++)
                tp->sackblks[i].start = tp->sackblks[i].end=0;

}

/*
 * Partial ack handling within a sack recovery episode.  When a partial ack
 * arrives, turn off retransmission timer, deflate the window, do not clear
 * tp->t_dupacks.
 */
void
tcp_sack_partialack(struct tcpcb *tp, struct tcphdr *th)
{
        /* Turn off retx. timer (will start again next segment) */
        TCP_TIMER_DISARM(tp, TCPT_REXMT);
        tp->t_rtttime = 0;
        /*
         * Partial window deflation.  This statement relies on the
         * fact that tp->snd_una has not been updated yet.
         */
        if (tp->snd_cwnd > (th->th_ack - tp->snd_una)) {
                tp->snd_cwnd -= th->th_ack - tp->snd_una;
                tp->snd_cwnd += tp->t_maxseg;
        } else
                tp->snd_cwnd = tp->t_maxseg;
        tp->snd_cwnd += tp->t_maxseg;
        tp->t_flags |= TF_NEEDOUTPUT;
}

/*
 * 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.
 */
void
tcp_pulloutofband(struct socket *so, u_int urgent, struct mbuf *m, int off)
{
        int cnt = off + urgent - 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;
                        memmove(cp, cp + 1, m->m_len - cnt - 1);
                        m->m_len--;
                        return;
                }
                cnt -= m->m_len;
                m = m->m_next;
                if (m == NULL)
                        break;
        }
        panic("tcp_pulloutofband");
}

/*
 * Collect new round-trip time estimate
 * and update averages and current timeout.
 */
void
tcp_xmit_timer(struct tcpcb *tp, int32_t rtt)
{
        int delta, rttmin;

        if (rtt < 0)
                rtt = 0;
        else if (rtt > TCP_RTT_MAX)
                rtt = TCP_RTT_MAX;

        tcpstat_inc(tcps_rttupdated);
        if (tp->t_srtt != 0) {
                /*
                 * delta is fixed point with 2 (TCP_RTT_BASE_SHIFT) bits
                 * after the binary point (scaled by 4), whereas
                 * srtt is stored as fixed point with 5 bits after the
                 * binary point (i.e., scaled by 32).  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).
                 */
                delta = (rtt << TCP_RTT_BASE_SHIFT) -
                    (tp->t_srtt >> TCP_RTT_SHIFT);
                if ((tp->t_srtt += delta) <= 0)
                        tp->t_srtt = 1 << TCP_RTT_BASE_SHIFT;
                /*
                 * 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);
                if ((tp->t_rttvar += delta) <= 0)
                        tp->t_rttvar = 1 << TCP_RTT_BASE_SHIFT;
        } 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 + 1) << (TCP_RTT_SHIFT + TCP_RTT_BASE_SHIFT);
                tp->t_rttvar = (rtt + 1) <<
                    (TCP_RTTVAR_SHIFT + TCP_RTT_BASE_SHIFT - 1);
        }
        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).
         */
        rttmin = min(max(tp->t_rttmin, rtt + 2 * (TCP_TIME(1) / hz)),
            TCPTV_REXMTMAX);
        TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp), rttmin, 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.
 *
 * NOTE: offer == -1 indicates that the maxseg size changed due to
 * Path MTU discovery.
 */
int
tcp_mss(struct tcpcb *tp, int offer)
{
        struct rtentry *rt;
        struct ifnet *ifp;
        int mss, mssopt, mssdflt, iphlen, do_rfc3390;
        u_int rtmtu;

        mss = mssopt = mssdflt = atomic_load_int(&tcp_mssdflt);

        rt = in_pcbrtentry(tp->t_inpcb);
        if (rt == NULL)
                goto out;

        ifp = if_get(rt->rt_ifidx);
        if (ifp == NULL)
                goto out;

        switch (tp->pf) {
        case AF_INET:
                iphlen = sizeof(struct ip);
                break;
#ifdef INET6
        case AF_INET6:
                iphlen = sizeof(struct ip6_hdr);
                break;
#endif
        default:
                unhandled_af(tp->pf);
        }

        /*
         * if there's an mtu associated with the route and we support
         * path MTU discovery for the underlying protocol family, use it.
         */
        rtmtu = atomic_load_int(&rt->rt_mtu);
        if (rtmtu) {
                /*
                 * One may wish to lower MSS to take into account options,
                 * especially security-related options.
                 */
                if (tp->pf == AF_INET6 && rtmtu < IPV6_MMTU) {
                        /*
                         * RFC2460 section 5, last paragraph: if path MTU is
                         * smaller than 1280, use 1280 as packet size and
                         * attach fragment header.
                         */
                        mss = IPV6_MMTU - iphlen - sizeof(struct ip6_frag) -
                            sizeof(struct tcphdr);
                } else {
                        mss = rtmtu - iphlen - sizeof(struct tcphdr);
                }
        } else if (ifp->if_flags & IFF_LOOPBACK) {
                mss = ifp->if_mtu - iphlen - sizeof(struct tcphdr);
        } else if (tp->pf == AF_INET) {
                if (atomic_load_int(&ip_mtudisc))
                        mss = ifp->if_mtu - iphlen - sizeof(struct tcphdr);
        }
#ifdef INET6
        else if (tp->pf == AF_INET6) {
                /*
                 * for IPv6, path MTU discovery is always turned on,
                 * or the node must use packet size <= 1280.
                 */
                mss = ifp->if_mtu - iphlen - sizeof(struct tcphdr);
        }
#endif /* INET6 */

        /* Calculate the value that we offer in TCPOPT_MAXSEG */
        if (offer != -1) {
                mssopt = ifp->if_mtu - iphlen - sizeof(struct tcphdr);
                mssopt = imax(mssopt, mssdflt);
        }
        if_put(ifp);
 out:
        /*
         * The current mss, t_maxseg, is initialized to the default value.
         * If we compute a smaller value, reduce the current mss.
         * If we compute a larger value, return it for use in sending
         * a max seg size option, but don't store it for use
         * unless we received an offer at least that large from peer.
         *
         * However, do not accept offers lower than the minimum of
         * the interface MTU and 216.
         */
        if (offer > 0)
                tp->t_peermss = offer;
        if (tp->t_peermss)
                mss = imin(mss, max(tp->t_peermss, 216));

        /* sanity - at least max opt. space */
        mss = imax(mss, 64);

        /*
         * 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;

        if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP &&
            (tp->t_flags & TF_RCVD_TSTMP) == TF_RCVD_TSTMP)
                mss -= TCPOLEN_TSTAMP_APPA;
#ifdef TCP_SIGNATURE
        if (tp->t_flags & TF_SIGNATURE)
                mss -= TCPOLEN_SIGLEN;
#endif

        do_rfc3390 = atomic_load_int(&tcp_do_rfc3390);
        if (offer == -1) {
                /* mss changed due to Path MTU discovery */
                tp->t_flags &= ~TF_PMTUD_PEND;
                tp->t_pmtud_mtu_sent = 0;
                tp->t_pmtud_mss_acked = 0;
                if (mss < tp->t_maxseg) {
                        /*
                         * Follow suggestion in RFC 2414 to reduce the
                         * congestion window by the ratio of the old
                         * segment size to the new segment size.
                         */
                        tp->snd_cwnd = ulmax((tp->snd_cwnd / tp->t_maxseg) *
                            mss, mss);
                }
        } else if (do_rfc3390 == 2) {
                /* increase initial window  */
                tp->snd_cwnd = ulmin(10 * mss, ulmax(2 * mss, 14600));
        } else if (do_rfc3390) {
                /* increase initial window  */
                tp->snd_cwnd = ulmin(4 * mss, ulmax(2 * mss, 4380));
        } else
                tp->snd_cwnd = mss;

        tp->t_maxseg = mss;

        return (offer != -1 ? mssopt : mss);
}

u_int
tcp_hdrsz(struct tcpcb *tp)
{
        u_int hlen;

        switch (tp->pf) {
#ifdef INET6
        case AF_INET6:
                hlen = sizeof(struct ip6_hdr);
                break;
#endif
        case AF_INET:
                hlen = sizeof(struct ip);
                break;
        default:
                hlen = 0;
                break;
        }
        hlen += sizeof(struct tcphdr);

        if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP &&
            (tp->t_flags & TF_RCVD_TSTMP) == TF_RCVD_TSTMP)
                hlen += TCPOLEN_TSTAMP_APPA;
#ifdef TCP_SIGNATURE
        if (tp->t_flags & TF_SIGNATURE)
                hlen += TCPOLEN_SIGLEN;
#endif
        return (hlen);
}

/*
 * Set connection variables based on the effective MSS.
 * We are passed the TCPCB for the actual connection.  If we
 * are the server, we are called by the compressed state engine
 * when the 3-way handshake is complete.  If we are the client,
 * we are called when we receive the SYN,ACK from the server.
 *
 * NOTE: The t_maxseg value must be initialized in the TCPCB
 * before this routine is called!
 */
void
tcp_mss_update(struct tcpcb *tp)
{
        int mss;
        u_long bufsize;
        struct rtentry *rt;
        struct socket *so;

        so = tp->t_inpcb->inp_socket;
        mss = tp->t_maxseg;

        rt = in_pcbrtentry(tp->t_inpcb);
        if (rt == NULL)
                return;

        mtx_enter(&so->so_snd.sb_mtx);
        bufsize = so->so_snd.sb_hiwat;
        if (bufsize < mss) {
                mtx_leave(&so->so_snd.sb_mtx);
                mss = bufsize;
                /* Update t_maxseg and t_maxopd */
                tcp_mss(tp, mss);
        } else {
                bufsize = roundup(bufsize, mss);
                if (bufsize > sb_max)
                        bufsize = sb_max;
                (void)sbreserve(&so->so_snd, bufsize);
                mtx_leave(&so->so_snd.sb_mtx);
        }

        mtx_enter(&so->so_rcv.sb_mtx);
        bufsize = so->so_rcv.sb_hiwat;
        if (bufsize > mss) {
                bufsize = roundup(bufsize, mss);
                if (bufsize > sb_max)
                        bufsize = sb_max;
                (void)sbreserve(&so->so_rcv, bufsize);
        }
        mtx_leave(&so->so_rcv.sb_mtx);
}

/*
 * When 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.
 */
void
tcp_newreno_partialack(struct tcpcb *tp, struct tcphdr *th)
{
        /*
         * snd_una has not been updated and the socket send buffer
         * not yet drained of the acked data, so we have to leave
         * snd_una as it was to get the correct data offset in
         * tcp_output().
         */
        tcp_seq onxt = tp->snd_nxt;
        u_long  ocwnd = tp->snd_cwnd;

        TCP_TIMER_DISARM(tp, TCPT_REXMT);
        tp->t_rtttime = 0;
        tp->snd_nxt = th->th_ack;
        /*
         * Set snd_cwnd to one segment beyond acknowledged offset
         * (tp->snd_una not yet updated when this function is called)
         */
        tp->snd_cwnd = tp->t_maxseg + (th->th_ack - tp->snd_una);
        (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.
         */
        if (tp->snd_cwnd > th->th_ack - tp->snd_una)
                tp->snd_cwnd -= th->th_ack - tp->snd_una;
        else
                tp->snd_cwnd = 0;
        tp->snd_cwnd += tp->t_maxseg;
}

int
tcp_mss_adv(struct rtentry *rt, int af)
{
        struct ifnet *ifp;
        int iphlen, mss, mssdflt;

        mssdflt = atomic_load_int(&tcp_mssdflt);

        if (rt == NULL)
                return mssdflt;

        ifp = if_get(rt->rt_ifidx);
        if (ifp == NULL)
                return mssdflt;

        switch (af) {
        case AF_INET:
                iphlen = sizeof(struct ip);
                break;
#ifdef INET6
        case AF_INET6:
                iphlen = sizeof(struct ip6_hdr);
                break;
#endif
        default:
                unhandled_af(af);
        }
        mss = ifp->if_mtu - iphlen - sizeof(struct tcphdr);
        if_put(ifp);

        return imax(mss, mssdflt);
}

/*
 * TCP compressed state engine.  Currently used to hold compressed
 * state for SYN_RECEIVED.
 */

/*
 * Locks used to protect global data and struct members:
 *      a       atomic operations
 *      N       net lock
 *      S       syn_cache_mtx           tcp syn cache global mutex
 */

/* syn hash parameters */
int     tcp_syn_hash_size = TCP_SYN_HASH_SIZE;  /* [S] size of hash table */
int     tcp_syn_cache_limit =                   /* [a] global entry limit */
            TCP_SYN_HASH_SIZE * TCP_SYN_BUCKET_SIZE;
int     tcp_syn_bucket_limit =                  /* [a] per bucket limit */
            3 * TCP_SYN_BUCKET_SIZE;
int     tcp_syn_use_limit = 100000;             /* [S] reseed after uses */

struct pool syn_cache_pool;
struct syn_cache_set tcp_syn_cache[2];          /* [S] */
int tcp_syn_cache_active;                       /* [S] */
struct mutex syn_cache_mtx = MUTEX_INITIALIZER(IPL_SOFTNET);

static inline uint32_t
syn_cache_hash(const struct sockaddr *src, const struct sockaddr *dst,
    uint32_t rand[])
{
        switch (src->sa_family) {
        case AF_INET: {
                uint32_t src_port = satosin_const(src)->sin_port;
                uint32_t dst_port = satosin_const(dst)->sin_port;
                const in_addr_t *src_addr =
                    &satosin_const(src)->sin_addr.s_addr;

                return ((((dst_port << 16) + src_port) ^ rand[4]) *
                    (*src_addr ^ rand[0]));
            }
#ifdef INET6
        case AF_INET6: {
                uint32_t src_port = satosin6_const(src)->sin6_port;
                uint32_t dst_port = satosin6_const(dst)->sin6_port;
                const uint32_t *src_addr6 =
                    satosin6_const(src)->sin6_addr.s6_addr32;

                return ((((dst_port << 16) + src_port) ^ rand[4]) *
                    (src_addr6[0] ^ rand[0]) *
                    (src_addr6[1] ^ rand[1]) *
                    (src_addr6[2] ^ rand[2]) *
                    (src_addr6[3] ^ rand[3]));
            }
#endif
        default:
                unhandled_af(src->sa_family);
        }
}

void
syn_cache_rm(struct syn_cache *sc)
{
        MUTEX_ASSERT_LOCKED(&syn_cache_mtx);

        TAILQ_REMOVE(&sc->sc_buckethead->sch_bucket, sc, sc_bucketq);
        in_pcbunref(sc->sc_inplisten);
        sc->sc_inplisten = NULL;
        LIST_REMOVE(sc, sc_tpq);
        refcnt_rele(&sc->sc_refcnt);
        sc->sc_buckethead->sch_length--;
        if (timeout_del(&sc->sc_timer))
                refcnt_rele(&sc->sc_refcnt);
        sc->sc_set->scs_count--;
}

void
syn_cache_put(struct syn_cache *sc)
{
        if (refcnt_rele(&sc->sc_refcnt) == 0)
                return;

        /* Dealing with last reference, no lock needed. */
        m_free(sc->sc_ipopts);
        rtfree(sc->sc_route.ro_rt);

        pool_put(&syn_cache_pool, sc);
}

void
syn_cache_init(void)
{
        int i;

        /* Initialize the hash buckets. */
        tcp_syn_cache[0].scs_buckethead = mallocarray(tcp_syn_hash_size,
            sizeof(struct syn_cache_head), M_SYNCACHE, M_WAITOK|M_ZERO);
        tcp_syn_cache[1].scs_buckethead = mallocarray(tcp_syn_hash_size,
            sizeof(struct syn_cache_head), M_SYNCACHE, M_WAITOK|M_ZERO);
        tcp_syn_cache[0].scs_size = tcp_syn_hash_size;
        tcp_syn_cache[1].scs_size = tcp_syn_hash_size;
        for (i = 0; i < tcp_syn_hash_size; i++) {
                TAILQ_INIT(&tcp_syn_cache[0].scs_buckethead[i].sch_bucket);
                TAILQ_INIT(&tcp_syn_cache[1].scs_buckethead[i].sch_bucket);
        }

        /* Initialize the syn cache pool. */
        pool_init(&syn_cache_pool, sizeof(struct syn_cache), 0, IPL_SOFTNET,
            0, "syncache", NULL);
}

void
syn_cache_insert(struct syn_cache *sc, struct tcpcb *tp)
{
        struct syn_cache_set *set;
        struct syn_cache_head *scp;
        struct syn_cache *sc2;
        int i;

        NET_ASSERT_LOCKED();
        MUTEX_ASSERT_LOCKED(&syn_cache_mtx);

        set = &tcp_syn_cache[tcp_syn_cache_active];

        /*
         * If there are no entries in the hash table, reinitialize
         * the hash secrets.  To avoid useless cache swaps and
         * reinitialization, use it until the limit is reached.
         * An empty cache is also the opportunity to resize the hash.
         */
        if (set->scs_count == 0 && set->scs_use <= 0) {
                set->scs_use = tcp_syn_use_limit;
                if (set->scs_size != tcp_syn_hash_size) {
                        scp = mallocarray(tcp_syn_hash_size, sizeof(struct
                            syn_cache_head), M_SYNCACHE, M_NOWAIT|M_ZERO);
                        if (scp == NULL) {
                                /* Try again next time. */
                                set->scs_use = 0;
                        } else {
                                free(set->scs_buckethead, M_SYNCACHE,
                                    set->scs_size *
                                    sizeof(struct syn_cache_head));
                                set->scs_buckethead = scp;
                                set->scs_size = tcp_syn_hash_size;
                                for (i = 0; i < tcp_syn_hash_size; i++)
                                        TAILQ_INIT(&scp[i].sch_bucket);
                        }
                }
                arc4random_buf(set->scs_random, sizeof(set->scs_random));
                tcpstat_inc(tcps_sc_seedrandom);
        }

        sc->sc_hash = syn_cache_hash(&sc->sc_src.sa, &sc->sc_dst.sa,
            set->scs_random);
        scp = &set->scs_buckethead[sc->sc_hash % set->scs_size];
        sc->sc_buckethead = scp;

        /*
         * Make sure that we don't overflow the per-bucket
         * limit or the total cache size limit.
         */
        if (scp->sch_length >= atomic_load_int(&tcp_syn_bucket_limit)) {
                tcpstat_inc(tcps_sc_bucketoverflow);
                /*
                 * Someone might attack our bucket hash function.  Reseed
                 * with random as soon as the passive syn cache gets empty.
                 */
                set->scs_use = 0;
                /*
                 * The bucket is full.  Toss the oldest element in the
                 * bucket.  This will be the first entry in the bucket.
                 */
                sc2 = TAILQ_FIRST(&scp->sch_bucket);
#ifdef DIAGNOSTIC
                /*
                 * This should never happen; we should always find an
                 * entry in our bucket.
                 */
                if (sc2 == NULL)
                        panic("%s: bucketoverflow: impossible", __func__);
#endif
                syn_cache_rm(sc2);
                syn_cache_put(sc2);
        } else if (set->scs_count >= atomic_load_int(&tcp_syn_cache_limit)) {
                struct syn_cache_head *scp2, *sce;

                tcpstat_inc(tcps_sc_overflowed);
                /*
                 * The cache is full.  Toss the oldest entry in the
                 * first non-empty bucket we can find.
                 *
                 * XXX We would really like to toss the oldest
                 * entry in the cache, but we hope that this
                 * condition doesn't happen very often.
                 */
                scp2 = scp;
                if (TAILQ_EMPTY(&scp2->sch_bucket)) {
                        sce = &set->scs_buckethead[set->scs_size];
                        for (++scp2; scp2 != scp; scp2++) {
                                if (scp2 >= sce)
                                        scp2 = &set->scs_buckethead[0];
                                if (! TAILQ_EMPTY(&scp2->sch_bucket))
                                        break;
                        }
#ifdef DIAGNOSTIC
                        /*
                         * This should never happen; we should always find a
                         * non-empty bucket.
                         */
                        if (scp2 == scp)
                                panic("%s: cacheoverflow: impossible",
                                    __func__);
#endif
                }
                sc2 = TAILQ_FIRST(&scp2->sch_bucket);
                syn_cache_rm(sc2);
                syn_cache_put(sc2);
        }

        /*
         * Initialize the entry's timer.  We don't estimate RTT
         * with SYNs, so each packet starts with the default RTT
         * and each timer step has a fixed timeout value.
         */
        sc->sc_rxttot = 0;
        sc->sc_rxtshift = 0;
        TCPT_RANGESET(sc->sc_rxtcur,
            TCPTV_SRTTDFLT * tcp_backoff[sc->sc_rxtshift], TCPTV_MIN,
            TCPTV_REXMTMAX);
        if (timeout_add_msec(&sc->sc_timer, sc->sc_rxtcur))
                refcnt_take(&sc->sc_refcnt);

        /* Link it from tcpcb entry */
        refcnt_take(&sc->sc_refcnt);
        LIST_INSERT_HEAD(&tp->t_sc, sc, sc_tpq);

        /* Put it into the bucket. */
        TAILQ_INSERT_TAIL(&scp->sch_bucket, sc, sc_bucketq);
        scp->sch_length++;
        sc->sc_set = set;
        set->scs_count++;
        set->scs_use--;

        tcpstat_inc(tcps_sc_added);

        /*
         * If the active cache has exceeded its use limit and
         * the passive syn cache is empty, exchange their roles.
         */
        if (set->scs_use <= 0 &&
            tcp_syn_cache[!tcp_syn_cache_active].scs_count == 0)
                tcp_syn_cache_active = !tcp_syn_cache_active;
}

/*
 * 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
 * that entry.
 */
void
syn_cache_timer(void *arg)
{
        struct syn_cache *sc = arg;
        struct inpcb *inp;
        struct socket *so;
        uint64_t now;
        int lastref, do_ecn = 0;

        mtx_enter(&syn_cache_mtx);
        inp = in_pcbref(sc->sc_inplisten);
        if (inp == NULL)
                goto freeit;

        if (__predict_false(sc->sc_rxtshift == TCP_MAXRXTSHIFT)) {
                /* Drop it -- too many retransmissions. */
                goto dropit;
        }

        /*
         * Compute the total amount of time this entry has
         * been on a queue.  If this entry has been on longer
         * than the keep alive timer would allow, expire it.
         */
        sc->sc_rxttot += sc->sc_rxtcur;
        if (sc->sc_rxttot >= atomic_load_int(&tcp_keepinit))
                goto dropit;

        /* Advance the timer back-off. */
        sc->sc_rxtshift++;
        TCPT_RANGESET(sc->sc_rxtcur,
            TCPTV_SRTTDFLT * tcp_backoff[sc->sc_rxtshift], TCPTV_MIN,
            TCPTV_REXMTMAX);
        if (timeout_add_msec(&sc->sc_timer, sc->sc_rxtcur))
                refcnt_take(&sc->sc_refcnt);
        mtx_leave(&syn_cache_mtx);

        NET_LOCK_SHARED();
        so = in_pcbsolock(inp);
        if (so != NULL) {
                now = tcp_now();
#ifdef TCP_ECN
                do_ecn = atomic_load_int(&tcp_do_ecn);
#endif
                (void) syn_cache_respond(sc, NULL, now, do_ecn);
                tcpstat_inc(tcps_sc_retransmitted);
        }
        in_pcbsounlock(inp, so);
        NET_UNLOCK_SHARED();

        in_pcbunref(inp);
        syn_cache_put(sc);
        return;

 dropit:
        tcpstat_inc(tcps_sc_timed_out);
        syn_cache_rm(sc);
        in_pcbunref(inp);
        /* Decrement reference of the timer and free object after remove. */
        lastref = refcnt_rele(&sc->sc_refcnt);
        KASSERT(lastref == 0);
        (void)lastref;
 freeit:
        mtx_leave(&syn_cache_mtx);
        syn_cache_put(sc);
}

/*
 * Remove syn cache created by the specified tcb entry,
 * because this does not make sense to keep them
 * (if there's no tcb entry, syn cache entry will never be used)
 */
void
syn_cache_cleanup(struct tcpcb *tp)
{
        struct syn_cache *sc, *nsc;

        NET_ASSERT_LOCKED();

        mtx_enter(&syn_cache_mtx);
        LIST_FOREACH_SAFE(sc, &tp->t_sc, sc_tpq, nsc) {
                KASSERT(sc->sc_inplisten == tp->t_inpcb);
                syn_cache_rm(sc);
                syn_cache_put(sc);
        }
        mtx_leave(&syn_cache_mtx);

        KASSERT(LIST_EMPTY(&tp->t_sc));
}

/*
 * Find an entry in the syn cache.
 */
struct syn_cache *
syn_cache_lookup(const struct sockaddr *src, const struct sockaddr *dst,
    struct syn_cache_head **headp, u_int rtableid)
{
        struct syn_cache_set *sets[2];
        struct syn_cache *sc;
        struct syn_cache_head *scp;
        u_int32_t hash;
        int i;

        NET_ASSERT_LOCKED();
        MUTEX_ASSERT_LOCKED(&syn_cache_mtx);

        /* Check the active cache first, the passive cache is likely empty. */
        sets[0] = &tcp_syn_cache[tcp_syn_cache_active];
        sets[1] = &tcp_syn_cache[!tcp_syn_cache_active];
        for (i = 0; i < 2; i++) {
                if (sets[i]->scs_count == 0)
                        continue;
                hash = syn_cache_hash(src, dst, sets[i]->scs_random);
                scp = &sets[i]->scs_buckethead[hash % sets[i]->scs_size];
                *headp = scp;
                TAILQ_FOREACH(sc, &scp->sch_bucket, sc_bucketq) {
                        if (sc->sc_hash != hash)
                                continue;
                        if (!bcmp(&sc->sc_src, src, src->sa_len) &&
                            !bcmp(&sc->sc_dst, dst, dst->sa_len) &&
                            rtable_l2(rtableid) == rtable_l2(sc->sc_rtableid))
                                return (sc);
                }
        }
        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 syn cache, and if its there, we pull it out of
 * the cache and turn it into a full-blown connection in
 * the SYN-RECEIVED state.
 *
 * The return values may not be immediately obvious, and their effects
 * can be subtle, so here they are:
 *
 *      NULL    SYN was not found in cache; caller should drop the
 *              packet and send an RST.
 *
 *      -1      We were unable to create the new connection, and are
 *              aborting it.  An ACK,RST is being sent to the peer
 *              (unless we got screwy sequence numbers; see below),
 *              because the 3-way handshake has been completed.  Caller
 *              should not free the mbuf, since we may be using it.  If
 *              we are not, we will free it.
 *
 *      Otherwise, the return value is a pointer to the new socket
 *      associated with the connection.
 */
struct socket *
syn_cache_get(struct sockaddr *src, struct sockaddr *dst, struct tcphdr *th,
    u_int hlen, u_int tlen, struct socket *so, struct mbuf *m, uint64_t now,
    int do_ecn)
{
        struct syn_cache *sc;
        struct syn_cache_head *scp;
        struct socket *listenso;
        struct inpcb *inp, *listeninp;
        struct tcpcb *tp = NULL;
        u_int rtableid;

        NET_ASSERT_LOCKED();

        inp = sotoinpcb(so);

        mtx_enter(&syn_cache_mtx);
        sc = syn_cache_lookup(src, dst, &scp, inp->inp_rtableid);
        if (sc == NULL) {
                mtx_leave(&syn_cache_mtx);
                in_pcbsounlock(inp, so);
                return (NULL);
        }

        /*
         * Verify the sequence and ack numbers.  Try getting the correct
         * response again.
         */
        if ((th->th_ack != sc->sc_iss + 1) ||
            SEQ_LEQ(th->th_seq, sc->sc_irs) ||
            SEQ_GT(th->th_seq, sc->sc_irs + 1 + sc->sc_win)) {
                refcnt_take(&sc->sc_refcnt);
                mtx_leave(&syn_cache_mtx);
                (void) syn_cache_respond(sc, m, now, do_ecn);
                in_pcbsounlock(inp, so);
                syn_cache_put(sc);
                return ((struct socket *)(-1));
        }

        /* Remove this cache entry */
        syn_cache_rm(sc);
        mtx_leave(&syn_cache_mtx);

        /*
         * 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.
         */
        listenso = so;
        listeninp = inp;
        inp = NULL;
        so = sonewconn(listenso, SS_ISCONNECTED, M_DONTWAIT);
        if (so == NULL)
                goto resetandabort;
        soassertlocked(so);
        /* inpcb does refcount socket, both so and inp cannot go away */
        inp = in_pcbref(sotoinpcb(so));
        tp = intotcpcb(inp);

#ifdef IPSEC
        /*
         * We need to copy the required security levels from the listen pcb.
         * Ditto for any other IPsec-related information.
         */
        inp->inp_seclevel = listeninp->inp_seclevel;
#endif /* IPSEC */
#ifdef INET6
        if (ISSET(inp->inp_flags, INP_IPV6)) {
                KASSERT(ISSET(listeninp->inp_flags, INP_IPV6));

                inp->inp_ipv6.ip6_hlim = listeninp->inp_ipv6.ip6_hlim;
                inp->inp_hops = listeninp->inp_hops;
        } else
#endif
        {
                KASSERT(!ISSET(listeninp->inp_flags, INP_IPV6));

                inp->inp_ip.ip_ttl = listeninp->inp_ip.ip_ttl;
                inp->inp_options = ip_srcroute(m);
                if (inp->inp_options == NULL) {
                        inp->inp_options = sc->sc_ipopts;
                        sc->sc_ipopts = NULL;
                }
        }

        /* inherit rtable from listening socket */
        rtableid = sc->sc_rtableid;
#if NPF > 0
        if (m->m_pkthdr.pf.flags & PF_TAG_DIVERTED) {
                struct pf_divert *divert;

                divert = pf_find_divert(m);
                KASSERT(divert != NULL);
                rtableid = divert->rdomain;
        }
#endif
        if (in_pcbset_addr(inp, src, dst, rtableid))
                goto resetandabort;

        /*
         * Give the new socket our cached route reference.
         */
        inp->inp_route = sc->sc_route;          /* struct assignment */
        sc->sc_route.ro_rt = NULL;

        tp->t_flags = intotcpcb(listeninp)->t_flags & (TF_NOPUSH|TF_NODELAY);
        if (sc->sc_request_r_scale != 15) {
                tp->requested_s_scale = sc->sc_requested_s_scale;
                tp->request_r_scale = sc->sc_request_r_scale;
                tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE;
        }
        if (ISSET(sc->sc_fixflags, SCF_TIMESTAMP))
                tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP;

        tp->t_template = tcp_template(tp);
        if (tp->t_template == NULL)
                goto abort;
        tp->sack_enable = ISSET(sc->sc_fixflags, SCF_SACK_PERMIT);
        tp->ts_modulate = sc->sc_modulate;
        tp->ts_recent = sc->sc_timestamp;
        tp->iss = sc->sc_iss;
        tp->irs = sc->sc_irs;
        tcp_sendseqinit(tp);
        tp->snd_last = tp->snd_una;
#ifdef TCP_ECN
        if (ISSET(sc->sc_fixflags, SCF_ECN_PERMIT)) {
                tp->t_flags |= TF_ECN_PERMIT;
                tcpstat_inc(tcps_ecn_accepts);
        }
#endif
        if (ISSET(sc->sc_fixflags, SCF_SACK_PERMIT))
                tp->t_flags |= TF_SACK_PERMIT;
#ifdef TCP_SIGNATURE
        if (ISSET(sc->sc_fixflags, SCF_SIGNATURE))
                tp->t_flags |= TF_SIGNATURE;
#endif
        tcp_rcvseqinit(tp);
        tp->t_state = TCPS_SYN_RECEIVED;
        tp->t_rcvtime = now;
        tp->t_sndtime = now;
        tp->t_rcvacktime = now;
        tp->t_sndacktime = now;
        TCP_TIMER_ARM(tp, TCPT_KEEP, atomic_load_int(&tcp_keepinit));
        tcpstat_inc(tcps_accepts);

        tcp_mss(tp, sc->sc_peermaxseg);  /* sets t_maxseg */
        if (sc->sc_peermaxseg)
                tcp_mss_update(tp);
        /* Reset initial window to 1 segment for retransmit */
        if (READ_ONCE(sc->sc_rxtshift) > 0)
                tp->snd_cwnd = tp->t_maxseg;
        tp->snd_wl1 = sc->sc_irs;
        tp->rcv_up = sc->sc_irs + 1;

        /*
         * 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;
        TCP_TIMER_ARM(tp, TCPT_REXMT, tp->t_rxtcur);
        if (sc->sc_win > 0 && SEQ_GT(tp->rcv_nxt + sc->sc_win, tp->rcv_adv))
                tp->rcv_adv = tp->rcv_nxt + sc->sc_win;
        tp->last_ack_sent = tp->rcv_nxt;

        in_pcbsounlock(listeninp, listenso);
        tcpstat_inc(tcps_sc_completed);
        syn_cache_put(sc);
        return (so);

resetandabort:
        tcp_respond(NULL, mtod(m, caddr_t), th, (tcp_seq)0, th->th_ack, TH_RST,
            m->m_pkthdr.ph_rtableid, now);
abort:
        if (tp != NULL)
                tp = tcp_drop(tp, ECONNABORTED);        /* destroys socket */
        in_pcbsounlock(inp, so);
        in_pcbsounlock(listeninp, listenso);
        in_pcbunref(inp);
        m_freem(m);
        syn_cache_put(sc);
        tcpstat_inc(tcps_sc_aborted);
        return ((struct socket *)(-1));
}

/*
 * 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
syn_cache_reset(struct sockaddr *src, struct sockaddr *dst, struct tcphdr *th,
    u_int rtableid)
{
        struct syn_cache *sc;
        struct syn_cache_head *scp;

        NET_ASSERT_LOCKED();

        mtx_enter(&syn_cache_mtx);
        sc = syn_cache_lookup(src, dst, &scp, rtableid);
        if (sc == NULL) {
                mtx_leave(&syn_cache_mtx);
                return;
        }
        if (SEQ_LT(th->th_seq, sc->sc_irs) ||
            SEQ_GT(th->th_seq, sc->sc_irs + 1)) {
                mtx_leave(&syn_cache_mtx);
                return;
        }
        syn_cache_rm(sc);
        mtx_leave(&syn_cache_mtx);
        tcpstat_inc(tcps_sc_reset);
        syn_cache_put(sc);
}

void
syn_cache_unreach(const struct sockaddr *src, const struct sockaddr *dst,
    struct tcphdr *th, u_int rtableid)
{
        struct syn_cache *sc;
        struct syn_cache_head *scp;

        NET_ASSERT_LOCKED();

        mtx_enter(&syn_cache_mtx);
        sc = syn_cache_lookup(src, dst, &scp, rtableid);
        if (sc == NULL) {
                mtx_leave(&syn_cache_mtx);
                return;
        }
        /* If the sequence number != sc_iss, then it's a bogus ICMP msg */
        if (ntohl (th->th_seq) != sc->sc_iss) {
                mtx_leave(&syn_cache_mtx);
                return;
        }

        /*
         * If we've retransmitted 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 (!ISSET(sc->sc_dynflags, SCF_UNREACH) || sc->sc_rxtshift < 3) {
                SET(sc->sc_dynflags, SCF_UNREACH);
                mtx_leave(&syn_cache_mtx);
                return;
        }

        syn_cache_rm(sc);
        mtx_leave(&syn_cache_mtx);
        tcpstat_inc(tcps_sc_unreach);
        syn_cache_put(sc);
}

/*
 * Given a LISTEN socket and an inbound SYN request, add
 * this to the syn cache, and send back a segment:
 *      <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
 * 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
syn_cache_add(struct sockaddr *src, struct sockaddr *dst, struct tcphdr *th,
    u_int iphlen, struct socket *so, struct mbuf *m, u_char *optp, int optlen,
    struct tcp_opt_info *oi, tcp_seq *issp, uint64_t now, int do_ecn)
{
        struct tcpcb tb, *tp;
        long win;
        struct syn_cache *sc;
        struct syn_cache_head *scp;
        struct mbuf *ipopts;
        struct rtentry *rt = NULL;

        soassertlocked(so);

        tp = sototcpcb(so);

        /*
         * RFC1122 4.2.3.10, p. 104: discard bcast/mcast SYN
         *
         * Note this check is performed in tcp_input() very early on.
         */

        /*
         * Initialize some local state.
         */
        win = sbspace(&so->so_rcv);
        if (win > TCP_MAXWIN)
                win = TCP_MAXWIN;

        bzero(&tb, sizeof(tb));
        if (optp
#ifdef TCP_SIGNATURE
            || (tp->t_flags & TF_SIGNATURE)
#endif
            ) {
                tb.pf = tp->pf;
                tb.sack_enable = tp->sack_enable;
                tb.t_flags = atomic_load_int(&tcp_do_rfc1323) ?
                    (TF_REQ_SCALE|TF_REQ_TSTMP) : 0;
#ifdef TCP_SIGNATURE
                if (tp->t_flags & TF_SIGNATURE)
                        tb.t_flags |= TF_SIGNATURE;
#endif
                tb.t_state = TCPS_LISTEN;
                if (tcp_dooptions(&tb, optp, optlen, th, m, iphlen, oi,
                    sotoinpcb(so)->inp_rtableid, now))
                        return (-1);
        }

        switch (src->sa_family) {
        case AF_INET:
                /*
                 * Remember the IP options, if any.
                 */
                ipopts = ip_srcroute(m);
                break;
        default:
                ipopts = NULL;
        }

        /*
         * See if we already have an entry for this connection.
         * If we do, resend the SYN,ACK.  We do not count this
         * as a retransmission (XXX though maybe we should).
         */
        mtx_enter(&syn_cache_mtx);
        sc = syn_cache_lookup(src, dst, &scp, sotoinpcb(so)->inp_rtableid);
        if (sc != NULL) {
                refcnt_take(&sc->sc_refcnt);
                mtx_leave(&syn_cache_mtx);
                tcpstat_inc(tcps_sc_dupesyn);
                if (ipopts) {
                        /*
                         * If we were remembering a previous source route,
                         * forget it and use the new one we've been given.
                         */
                        m_free(sc->sc_ipopts);
                        sc->sc_ipopts = ipopts;
                }
                sc->sc_timestamp = tb.ts_recent;
                if (syn_cache_respond(sc, m, now, do_ecn) == 0) {
                        tcpstat_inc(tcps_sndacks);
                        tcpstat_inc(tcps_sndtotal);
                }
                syn_cache_put(sc);
                return (0);
        }
        mtx_leave(&syn_cache_mtx);

        sc = pool_get(&syn_cache_pool, PR_NOWAIT|PR_ZERO);
        if (sc == NULL) {
                m_free(ipopts);
                return (-1);
        }
        refcnt_init_trace(&sc->sc_refcnt, DT_REFCNT_IDX_SYNCACHE);
        timeout_set_flags(&sc->sc_timer, syn_cache_timer, sc,
            KCLOCK_NONE, TIMEOUT_PROC | TIMEOUT_MPSAFE);

        /*
         * Fill in the cache, and put the necessary IP and TCP
         * options into the reply.
         */
        memcpy(&sc->sc_src, src, src->sa_len);
        memcpy(&sc->sc_dst, dst, dst->sa_len);
        sc->sc_rtableid = sotoinpcb(so)->inp_rtableid;
        switch (sc->sc_src.sa.sa_family) {
        case AF_INET:
                if (sc->sc_src.sin.sin_addr.s_addr != INADDR_ANY) {
                        rt = route_mpath(&sc->sc_route,
                            &sc->sc_src.sin.sin_addr,
                            &sc->sc_dst.sin.sin_addr, sc->sc_rtableid);
                }
                break;
#ifdef INET6
        case AF_INET6:
                if (!IN6_IS_ADDR_UNSPECIFIED(&sc->sc_src.sin6.sin6_addr)) {
                        rt = route6_mpath(&sc->sc_route,
                            &sc->sc_src.sin6.sin6_addr,
                            &sc->sc_dst.sin6.sin6_addr, sc->sc_rtableid);
                }
                break;
#endif
        }
        sc->sc_ipopts = ipopts;
        sc->sc_irs = th->th_seq;

        sc->sc_iss = issp ? *issp : arc4random();
        sc->sc_peermaxseg = oi->maxseg;
        sc->sc_ourmaxseg = tcp_mss_adv(rt, sc->sc_src.sa.sa_family);
        sc->sc_win = win;
        sc->sc_timestamp = tb.ts_recent;
        if ((tb.t_flags & (TF_REQ_TSTMP|TF_RCVD_TSTMP)) ==
            (TF_REQ_TSTMP|TF_RCVD_TSTMP)) {
                SET(sc->sc_fixflags, SCF_TIMESTAMP);
                sc->sc_modulate = arc4random();
        }
        if ((tb.t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
            (TF_RCVD_SCALE|TF_REQ_SCALE)) {
                sc->sc_requested_s_scale = tb.requested_s_scale;
                sc->sc_request_r_scale = 0;
                /*
                 * Pick the smallest possible scaling factor that
                 * will still allow us to scale up to sb_max.
                 *
                 * We do this because there are broken firewalls that
                 * will corrupt the window scale option, leading to
                 * the other endpoint believing that our advertised
                 * window is unscaled.  At scale factors larger than
                 * 5 the unscaled window will drop below 1500 bytes,
                 * leading to serious problems when traversing these
                 * broken firewalls.
                 *
                 * With the default sbmax of 256K, a scale factor
                 * of 3 will be chosen by this algorithm.  Those who
                 * choose a larger sbmax should watch out
                 * for the compatibility problems mentioned above.
                 *
                 * RFC1323: The Window field in a SYN (i.e., a <SYN>
                 * or <SYN,ACK>) segment itself is never scaled.
                 */
                while (sc->sc_request_r_scale < TCP_MAX_WINSHIFT &&
                    (TCP_MAXWIN << sc->sc_request_r_scale) < sb_max)
                        sc->sc_request_r_scale++;
        } else {
                sc->sc_requested_s_scale = 15;
                sc->sc_request_r_scale = 15;
        }
#ifdef TCP_ECN
        /*
         * if both ECE and CWR flag bits are set, peer is ECN capable.
         */
        if (do_ecn && (th->th_flags & (TH_ECE|TH_CWR)) == (TH_ECE|TH_CWR))
                SET(sc->sc_fixflags, SCF_ECN_PERMIT);
#endif
        /*
         * Set SCF_SACK_PERMIT if peer did send a SACK_PERMITTED option
         * (i.e., if tcp_dooptions() did set TF_SACK_PERMIT).
         */
        if (tb.sack_enable && (tb.t_flags & TF_SACK_PERMIT))
                SET(sc->sc_fixflags, SCF_SACK_PERMIT);
#ifdef TCP_SIGNATURE
        if (tb.t_flags & TF_SIGNATURE)
                SET(sc->sc_fixflags, SCF_SIGNATURE);
#endif
        sc->sc_inplisten = in_pcbref(tp->t_inpcb);
        if (syn_cache_respond(sc, m, now, do_ecn) == 0) {
                mtx_enter(&syn_cache_mtx);
                /*
                 * Socket lock prevents another insert after our
                 * syn_cache_lookup() and before syn_cache_insert().
                 */
                syn_cache_insert(sc, tp);
                mtx_leave(&syn_cache_mtx);
                tcpstat_inc(tcps_sndacks);
                tcpstat_inc(tcps_sndtotal);
        } else {
                in_pcbunref(sc->sc_inplisten);
                syn_cache_put(sc);
                tcpstat_inc(tcps_sc_dropped);
        }

        return (0);
}

int
syn_cache_respond(struct syn_cache *sc, struct mbuf *m, uint64_t now,
    int do_ecn)
{
        u_int8_t *optp;
        int optlen, error;
        u_int16_t tlen;
        struct ip *ip = NULL;
#ifdef INET6
        struct ip6_hdr *ip6 = NULL;
#endif
        struct tcphdr *th;
        u_int hlen;
        struct inpcb *inp;

        NET_ASSERT_LOCKED();

        switch (sc->sc_src.sa.sa_family) {
        case AF_INET:
                hlen = sizeof(struct ip);
                break;
#ifdef INET6
        case AF_INET6:
                hlen = sizeof(struct ip6_hdr);
                break;
#endif
        default:
                m_freem(m);
                return (EAFNOSUPPORT);
        }

        /* Compute the size of the TCP options. */
        optlen = 4 + (sc->sc_request_r_scale != 15 ? 4 : 0) +
            (ISSET(sc->sc_fixflags, SCF_SACK_PERMIT) ? 4 : 0) +
#ifdef TCP_SIGNATURE
            (ISSET(sc->sc_fixflags, SCF_SIGNATURE) ? TCPOLEN_SIGLEN : 0) +
#endif
            (ISSET(sc->sc_fixflags, SCF_TIMESTAMP) ? TCPOLEN_TSTAMP_APPA : 0);

        tlen = hlen + sizeof(struct tcphdr) + optlen;

        /*
         * Create the IP+TCP header from scratch.
         */
        m_freem(m);
#ifdef DIAGNOSTIC
        if (max_linkhdr + tlen > MCLBYTES)
                return (ENOBUFS);
#endif
        MGETHDR(m, M_DONTWAIT, MT_DATA);
        if (m && max_linkhdr + tlen > MHLEN) {
                MCLGET(m, M_DONTWAIT);
                if ((m->m_flags & M_EXT) == 0) {
                        m_freem(m);
                        m = NULL;
                }
        }
        if (m == NULL)
                return (ENOBUFS);

        /* Fixup the mbuf. */
        m->m_data += max_linkhdr;
        m->m_len = m->m_pkthdr.len = tlen;
        m->m_pkthdr.ph_ifidx = 0;
        m->m_pkthdr.ph_rtableid = sc->sc_rtableid;
        memset(mtod(m, u_char *), 0, tlen);

        switch (sc->sc_src.sa.sa_family) {
        case AF_INET:
                ip = mtod(m, struct ip *);
                ip->ip_dst = sc->sc_src.sin.sin_addr;
                ip->ip_src = sc->sc_dst.sin.sin_addr;
                ip->ip_p = IPPROTO_TCP;
                th = (struct tcphdr *)(ip + 1);
                th->th_dport = sc->sc_src.sin.sin_port;
                th->th_sport = sc->sc_dst.sin.sin_port;
                break;
#ifdef INET6
        case AF_INET6:
                ip6 = mtod(m, struct ip6_hdr *);
                ip6->ip6_dst = sc->sc_src.sin6.sin6_addr;
                ip6->ip6_src = sc->sc_dst.sin6.sin6_addr;
                ip6->ip6_nxt = IPPROTO_TCP;
                th = (struct tcphdr *)(ip6 + 1);
                th->th_dport = sc->sc_src.sin6.sin6_port;
                th->th_sport = sc->sc_dst.sin6.sin6_port;
                break;
#endif
        }

        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_flags = TH_SYN|TH_ACK;
#ifdef TCP_ECN
        /* Set ECE for SYN-ACK if peer supports ECN. */
        if (do_ecn && ISSET(sc->sc_fixflags, SCF_ECN_PERMIT))
                th->th_flags |= TH_ECE;
#endif
        th->th_win = htons(sc->sc_win);
        /* th_sum already 0 */
        /* th_urp already 0 */

        /* Tack on the TCP options. */
        optp = (u_int8_t *)(th + 1);
        *optp++ = TCPOPT_MAXSEG;
        *optp++ = 4;
        *optp++ = (sc->sc_ourmaxseg >> 8) & 0xff;
        *optp++ = sc->sc_ourmaxseg & 0xff;

        /* Include SACK_PERMIT_HDR option if peer has already done so. */
        if (ISSET(sc->sc_fixflags, SCF_SACK_PERMIT)) {
                *((u_int32_t *)optp) = htonl(TCPOPT_SACK_PERMIT_HDR);
                optp += 4;
        }

        if (sc->sc_request_r_scale != 15) {
                *((u_int32_t *)optp) = htonl(TCPOPT_NOP << 24 |
                    TCPOPT_WINDOW << 16 | TCPOLEN_WINDOW << 8 |
                    sc->sc_request_r_scale);
                optp += 4;
        }

        if (ISSET(sc->sc_fixflags, SCF_TIMESTAMP)) {
                u_int32_t *lp = (u_int32_t *)(optp);
                /* Form timestamp option as shown in appendix A of RFC 1323. */
                *lp++ = htonl(TCPOPT_TSTAMP_HDR);
                *lp++ = htonl(now + sc->sc_modulate);
                *lp   = htonl(sc->sc_timestamp);
                optp += TCPOLEN_TSTAMP_APPA;
        }

#ifdef TCP_SIGNATURE
        if (ISSET(sc->sc_fixflags, SCF_SIGNATURE)) {
                union sockaddr_union src, dst;
                struct tdb *tdb;

                bzero(&src, sizeof(union sockaddr_union));
                bzero(&dst, sizeof(union sockaddr_union));
                src.sa.sa_len = sc->sc_src.sa.sa_len;
                src.sa.sa_family = sc->sc_src.sa.sa_family;
                dst.sa.sa_len = sc->sc_dst.sa.sa_len;
                dst.sa.sa_family = sc->sc_dst.sa.sa_family;

                switch (sc->sc_src.sa.sa_family) {
                case 0: /*default to PF_INET*/
                case AF_INET:
                        src.sin.sin_addr = mtod(m, struct ip *)->ip_src;
                        dst.sin.sin_addr = mtod(m, struct ip *)->ip_dst;
                        break;
#ifdef INET6
                case AF_INET6:
                        src.sin6.sin6_addr = mtod(m, struct ip6_hdr *)->ip6_src;
                        dst.sin6.sin6_addr = mtod(m, struct ip6_hdr *)->ip6_dst;
                        break;
#endif /* INET6 */
                }

                tdb = gettdbbysrcdst(rtable_l2(sc->sc_rtableid),
                    0, &src, &dst, IPPROTO_TCP);
                if (tdb == NULL) {
                        m_freem(m);
                        return (EPERM);
                }

                /* Send signature option */
                *(optp++) = TCPOPT_SIGNATURE;
                *(optp++) = TCPOLEN_SIGNATURE;

                if (tcp_signature(tdb, sc->sc_src.sa.sa_family, m, th,
                    hlen, 0, optp) < 0) {
                        m_freem(m);
                        tdb_unref(tdb);
                        return (EINVAL);
                }
                tdb_unref(tdb);
                optp += 16;

                /* Pad options list to the next 32 bit boundary and
                 * terminate it.
                 */
                *optp++ = TCPOPT_NOP;
                *optp++ = TCPOPT_EOL;
        }
#endif /* TCP_SIGNATURE */

        SET(m->m_pkthdr.csum_flags, M_TCP_CSUM_OUT);

        /* use IPsec policy and ttl from listening socket, on SYN ACK */
        mtx_enter(&syn_cache_mtx);
        inp = in_pcbref(sc->sc_inplisten);
        mtx_leave(&syn_cache_mtx);

        /*
         * Fill in some straggling IP bits.  Note the stack expects
         * ip_len to be in host order, for convenience.
         */
        switch (sc->sc_src.sa.sa_family) {
        case AF_INET:
                ip->ip_len = htons(tlen);
                ip->ip_ttl = inp ?
                    inp->inp_ip.ip_ttl : atomic_load_int(&ip_defttl);
                if (inp != NULL)
                        ip->ip_tos = inp->inp_ip.ip_tos;

                error = ip_output(m, sc->sc_ipopts, &sc->sc_route,
                    (atomic_load_int(&ip_mtudisc) ? IP_MTUDISC : 0),  NULL,
                    inp ? &inp->inp_seclevel : NULL, 0);
                break;
#ifdef INET6
        case AF_INET6:
                ip6->ip6_vfc &= ~IPV6_VERSION_MASK;
                ip6->ip6_vfc |= IPV6_VERSION;
                /* ip6_plen will be updated in ip6_output() */
                ip6->ip6_hlim = in6_selecthlim(inp);
                /* leave flowlabel = 0, it is legal and require no state mgmt */

                error = ip6_output(m, NULL /*XXX*/, &sc->sc_route, 0,
                    NULL, inp ? &inp->inp_seclevel : NULL);
                break;
#endif
        }
        in_pcbunref(inp);
        return (error);
}

#ifndef SMALL_KERNEL
static int
tcp_softlro_check(struct mbuf *m, struct ether_extracted *ext)
{
        /* Don't merge packets with invalid TCP checksum. */
        if (!ISSET(m->m_pkthdr.csum_flags, M_TCP_CSUM_IN_OK))
                return 0;

        if (ext->ip4) {
                /* Don't merge packets with invalid IP header checksum. */
                if (!ISSET(m->m_pkthdr.csum_flags, M_IPV4_CSUM_IN_OK))
                        return 0;

                /* Don't merge IPv4 packets with IP options. */
                if (ext->iphlen != sizeof(struct ip))
                        return 0;
        }

        /* Check TCP protocol and header. */
        if (!ext->tcp)
                return 0;

        /* Don't merge empty TCP segments. */
        if (ext->paylen == 0)
                return 0;

        /* Just ACK and PUSH TCP flags are allowed. */
        if (ISSET(ext->tcp->th_flags, TH_ACK|TH_PUSH) != ext->tcp->th_flags)
                return 0;

        /* TCP ACK flag has to be set. */
        if (!ISSET(ext->tcp->th_flags, TH_ACK))
                return 0;

        /* Either no TCP options or timestamp as in RFC 1323 appendix A. */
        if (ext->tcphlen > sizeof(struct tcphdr)) {
                int optlen = ext->tcphlen - sizeof(struct tcphdr);
                uint8_t *optp = (uint8_t *)(ext->tcp + 1);

                /* Same logic as in TCP input quick retrieval. */
                if ((optlen != TCPOLEN_TSTAMP_APPA &&
                    (optlen <= TCPOLEN_TSTAMP_APPA ||
                    optp[TCPOLEN_TSTAMP_APPA] != TCPOPT_EOL)) ||
                    ((uint32_t *)optp)[0] != htonl(TCPOPT_TSTAMP_HDR))
                        return 0;
        }

        return 1;
}

static int
tcp_softlro_compare(struct ether_extracted *head, struct ether_extracted *tail)
{
        /* Don't merge packets inside and outside of VLANs */
        if (head->evh && tail->evh) {
                /* Don't merge packets of different VLANs */
                if (EVL_VLANOFTAG(head->evh->evl_tag) !=
                    EVL_VLANOFTAG(tail->evh->evl_tag))
                        return 0;

                /* Don't merge packets of different priorities */
                if (EVL_PRIOFTAG(head->evh->evl_tag) !=
                    EVL_PRIOFTAG(tail->evh->evl_tag))
                        return 0;
        } else if (head->evh || tail->evh)
                return 0;

        /* Check TCP ports. */
        if (head->tcp->th_sport != tail->tcp->th_sport ||
            head->tcp->th_dport != tail->tcp->th_dport)
                return 0;

        /* Check IP header. */
        if (head->ip4 && tail->ip4) {
                /* Check IPv4 addresses. */
                if (head->ip4->ip_src.s_addr != tail->ip4->ip_src.s_addr ||
                    head->ip4->ip_dst.s_addr != tail->ip4->ip_dst.s_addr)
                        return 0;

                /* Check max. IPv4 length. */
                if (head->iplen + tail->iplen > IP_MAXPACKET - max_linkhdr)
                        return 0;
        } else if (head->ip6 && tail->ip6) {
                /* Check IPv6 addresses. */
                if (!IN6_ARE_ADDR_EQUAL(&head->ip6->ip6_src,
                    &tail->ip6->ip6_src) ||
                    !IN6_ARE_ADDR_EQUAL(&head->ip6->ip6_dst,
                    &tail->ip6->ip6_dst))
                        return 0;

                /* Check max. IPv6 length. */
                if ((head->iplen - head->iphlen) +
                    (tail->iplen - tail->iphlen) > IPV6_MAXPACKET - max_linkhdr)
                        return 0;
        } else {
                /* Address family does not match. */
                return 0;
        }

        /* Check for contiguous segments. */
        if (ntohl(head->tcp->th_seq) + head->paylen != ntohl(tail->tcp->th_seq))
                return 0;

        /* Ignore segments with different TCP options. */
        if (head->tcphlen != tail->tcphlen)
                return 0;

        /* TCP timestamp options must match, type and length already checked. */
        if (head->tcphlen > sizeof(struct tcphdr)) {
                uint32_t *hoptp = (uint32_t *)(head->tcp + 1);
                uint32_t *toptp = (uint32_t *)(tail->tcp + 1);

                /* Tail timestamps must be more recent. */
                if (TSTMP_LT(ntohl(hoptp[1]), ntohl(toptp[1])) ||
                    TSTMP_LT(ntohl(hoptp[2]), ntohl(toptp[2])))
                        return 0;
        }

        return 1;
}

static void
tcp_softlro_concat(struct mbuf *mhead, struct ether_extracted *head,
    struct mbuf *mtail, struct ether_extracted *tail)
{
        struct mbuf *m;
        unsigned int hdrlen;

        /* Adjust IP header length. */
        if (head->ip4) {
                head->ip4->ip_len = htons(head->iplen + tail->paylen);
        } else if (head->ip6) {
                head->ip6->ip6_plen =
                    htons(head->iplen - head->iphlen + tail->paylen);
        }

        /* Combine TCP flags from head and tail. */
        if (ISSET(tail->tcp->th_flags, TH_PUSH))
                SET(head->tcp->th_flags, TH_PUSH);

        /* Adjust TCP header. */
        head->tcp->th_win = tail->tcp->th_win;
        head->tcp->th_ack = tail->tcp->th_ack;

        /* Use more recent timestamps from tail. */
        if (head->tcphlen > sizeof(struct tcphdr)) {
                uint32_t *hoptp = (uint32_t *)(head->tcp + 1);
                uint32_t *toptp = (uint32_t *)(tail->tcp + 1);

                hoptp[1] = toptp[1];
                hoptp[2] = toptp[2];
        }

        /* Calculate header length of tail packet. */
        hdrlen = sizeof(*tail->eh);
        if (tail->evh)
                hdrlen = sizeof(*tail->evh);
        hdrlen += tail->iphlen;
        hdrlen += tail->tcphlen;

        /* Skip protocol headers in tail. */
        m_adj(mtail, hdrlen);
        CLR(mtail->m_flags, M_PKTHDR);

        /* Concatenate */
        for (m = mhead; m->m_next != NULL; m = m->m_next)
                ;
        m->m_next = mtail;
        mhead->m_pkthdr.len += tail->paylen;

        /* Flag mbuf as TSO packet with MSS. */
        if (!ISSET(mhead->m_pkthdr.csum_flags, M_TCP_TSO)) {
                /* Set CSUM_OUT flags in case of forwarding. */
                SET(mhead->m_pkthdr.csum_flags, M_TCP_CSUM_OUT);
                head->tcp->th_sum = 0;
                if (head->ip4) {
                        SET(mhead->m_pkthdr.csum_flags, M_IPV4_CSUM_OUT);
                        head->ip4->ip_sum = 0;
                }

                SET(mhead->m_pkthdr.csum_flags, M_TCP_TSO);
                mhead->m_pkthdr.ph_mss = head->paylen;
                tcpstat_inc(tcps_inswlro);
                tcpstat_inc(tcps_inpktlro);     /* count head */
        }
        mhead->m_pkthdr.ph_mss = MAX(mhead->m_pkthdr.ph_mss, tail->paylen);
        tcpstat_inc(tcps_inpktlro);     /* count tail */
}

void
tcp_softlro_glue(struct mbuf_list *ml, struct mbuf *mtail, struct ifnet *ifp)
{
        struct ether_extracted head, tail;
        struct mbuf *mhead;

        if (!ISSET(ifp->if_xflags, IFXF_LRO))
                goto dontmerge;

        mtail->m_pkthdr.ph_mss = 0;

        ether_extract_headers(mtail, &tail);

        if (tail.tcp) {
                int tcpdatalen;

                /* Remove possible ethernet padding at the end. */
                tcpdatalen = tail.iplen - tail.iphlen - tail.tcphlen;
                if (tcpdatalen < tail.paylen ) {
                        m_adj(mtail, tcpdatalen - tail.paylen);
                        tail.paylen = tcpdatalen;
                }
        }

        if (!tcp_softlro_check(mtail, &tail))
                goto dontmerge;

        mtail->m_pkthdr.ph_mss = tail.paylen;

        for (mhead = ml->ml_head; mhead != NULL; mhead = mhead->m_nextpkt) {
                /* This packet has been checked and was not mergable before. */
                if (mhead->m_pkthdr.ph_mss == 0)
                        continue;

                /* Use RSS hash to skip packets of different connections. */
                if (ISSET(mhead->m_pkthdr.csum_flags, M_FLOWID) &&
                    ISSET(mtail->m_pkthdr.csum_flags, M_FLOWID) &&
                    mhead->m_pkthdr.ph_flowid != mtail->m_pkthdr.ph_flowid)
                        continue;

                /* Don't merge packets inside and outside of VLANs */
                if (ISSET(mhead->m_flags, M_VLANTAG) !=
                    ISSET(mtail->m_flags, M_VLANTAG))
                        continue;

                if (ISSET(mhead->m_flags, M_VLANTAG)) {
                        /* Don't merge packets of different VLANs */
                        if (EVL_VLANOFTAG(mhead->m_pkthdr.ether_vtag) !=
                            EVL_VLANOFTAG(mtail->m_pkthdr.ether_vtag))
                                continue;

                        /* Don't merge packets of different priorities */
                        if (EVL_PRIOFTAG(mhead->m_pkthdr.ether_vtag) !=
                            EVL_PRIOFTAG(mtail->m_pkthdr.ether_vtag))
                                continue;
                }

                ether_extract_headers(mhead, &head);
                if (!tcp_softlro_compare(&head, &tail))
                        continue;

                tcp_softlro_concat(mhead, &head, mtail, &tail);
                return;
        }
 dontmerge:
        ml_enqueue(ml, mtail);
}
#endif