No empty .Rs/.Re

[netbsd-mini2440.git] / sys / netinet / tcp_input.c

/*      $NetBSD: tcp_input.c,v 1.298 2009/07/18 23:09:53 minskim Exp $  */

/*
 * Copyright (C) 1995, 1996, 1997, and 1998 WIDE Project.
 * 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 project 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 PROJECT 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 PROJECT 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).
 */

/*-
 * Copyright (c) 1997, 1998, 1999, 2001, 2005, 2006 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code is derived from software contributed to The NetBSD Foundation
 * by Jason R. Thorpe and Kevin M. Lahey of the Numerical Aerospace Simulation
 * Facility, NASA Ames Research Center.
 * This code is derived from software contributed to The NetBSD Foundation
 * by Charles M. Hannum.
 * This code is derived from software contributed to The NetBSD Foundation
 * by Rui Paulo.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. 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 FOUNDATION 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 (c) 1982, 1986, 1988, 1990, 1993, 1994, 1995
 *      The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 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.
 *
 *      @(#)tcp_input.c 8.12 (Berkeley) 5/24/95
 */

/*
 *      TODO list for SYN cache stuff:
 *
 *      Find room for a "state" field, which is needed to keep a
 *      compressed state for TIME_WAIT TCBs.  It's been noted already
 *      that this is fairly important for very high-volume web and
 *      mail servers, which use a large number of short-lived
 *      connections.
 */

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: tcp_input.c,v 1.298 2009/07/18 23:09:53 minskim Exp $");

#include "opt_inet.h"
#include "opt_ipsec.h"
#include "opt_inet_csum.h"
#include "opt_tcp_debug.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/malloc.h>
#include <sys/mbuf.h>
#include <sys/protosw.h>
#include <sys/socket.h>
#include <sys/socketvar.h>
#include <sys/errno.h>
#include <sys/syslog.h>
#include <sys/pool.h>
#include <sys/domain.h>
#include <sys/kernel.h>
#ifdef TCP_SIGNATURE
#include <sys/md5.h>
#endif
#include <sys/lwp.h> /* for lwp0 */

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

#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netinet/in_pcb.h>
#include <netinet/in_var.h>
#include <netinet/ip_var.h>
#include <netinet/in_offload.h>

#ifdef INET6
#ifndef INET
#include <netinet/in.h>
#endif
#include <netinet/ip6.h>
#include <netinet6/ip6_var.h>
#include <netinet6/in6_pcb.h>
#include <netinet6/ip6_var.h>
#include <netinet6/in6_var.h>
#include <netinet/icmp6.h>
#include <netinet6/nd6.h>
#ifdef TCP_SIGNATURE
#include <netinet6/scope6_var.h>
#endif
#endif

#ifndef INET6
/* always need ip6.h for IP6_EXTHDR_GET */
#include <netinet/ip6.h>
#endif

#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_private.h>
#include <netinet/tcpip.h>
#include <netinet/tcp_congctl.h>
#include <netinet/tcp_debug.h>

#include <machine/stdarg.h>

#ifdef IPSEC
#include <netinet6/ipsec.h>
#include <netinet6/ipsec_private.h>
#include <netkey/key.h>
#endif /*IPSEC*/
#ifdef INET6
#include "faith.h"
#if defined(NFAITH) && NFAITH > 0
#include <net/if_faith.h>
#endif
#endif  /* IPSEC */

#ifdef FAST_IPSEC
#include <netipsec/ipsec.h>
#include <netipsec/ipsec_var.h>
#include <netipsec/ipsec_private.h>
#include <netipsec/key.h>
#ifdef INET6
#include <netipsec/ipsec6.h>
#endif
#endif  /* FAST_IPSEC*/

int     tcprexmtthresh = 3;
int     tcp_log_refused;

int     tcp_do_autorcvbuf = 0;
int     tcp_autorcvbuf_inc = 16 * 1024;
int     tcp_autorcvbuf_max = 256 * 1024;
int     tcp_msl = (TCPTV_MSL / PR_SLOWHZ);

static int tcp_rst_ppslim_count = 0;
static struct timeval tcp_rst_ppslim_last;
static int tcp_ackdrop_ppslim_count = 0;
static struct timeval tcp_ackdrop_ppslim_last;

#define TCP_PAWS_IDLE   (24U * 24 * 60 * 60 * PR_SLOWHZ)

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

/*
 * Neighbor Discovery, Neighbor Unreachability Detection Upper layer hint.
 */
#ifdef INET6
static inline void
nd6_hint(struct tcpcb *tp)
{
        struct rtentry *rt;

        if (tp != NULL && tp->t_in6pcb != NULL && tp->t_family == AF_INET6 &&
            (rt = rtcache_validate(&tp->t_in6pcb->in6p_route)) != NULL)
                nd6_nud_hint(rt, NULL, 0);
}
#else
static inline void
nd6_hint(struct tcpcb *tp)
{
}
#endif

/*
 * 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.
 */
static void
tcp_setup_ack(struct tcpcb *tp, const struct tcphdr *th)
{

        if (tp->t_flags & TF_DELACK ||
            (tcp_ack_on_push && th->th_flags & TH_PUSH))
                tp->t_flags |= TF_ACKNOW;
        else
                TCP_SET_DELACK(tp);
}

static void
icmp_check(struct tcpcb *tp, const struct tcphdr *th, int acked)
{

        /*
         * 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;
}

/*
 * Convert TCP protocol fields to host order for easier processing.
 */
static void
tcp_fields_to_host(struct tcphdr *th)
{

        NTOHL(th->th_seq);
        NTOHL(th->th_ack);
        NTOHS(th->th_win);
        NTOHS(th->th_urp);
}

/*
 * ... and reverse the above.
 */
static void
tcp_fields_to_net(struct tcphdr *th)
{

        HTONL(th->th_seq);
        HTONL(th->th_ack);
        HTONS(th->th_win);
        HTONS(th->th_urp);
}

#ifdef TCP_CSUM_COUNTERS
#include <sys/device.h>

#if defined(INET)
extern struct evcnt tcp_hwcsum_ok;
extern struct evcnt tcp_hwcsum_bad;
extern struct evcnt tcp_hwcsum_data;
extern struct evcnt tcp_swcsum;
#endif /* defined(INET) */
#if defined(INET6)
extern struct evcnt tcp6_hwcsum_ok;
extern struct evcnt tcp6_hwcsum_bad;
extern struct evcnt tcp6_hwcsum_data;
extern struct evcnt tcp6_swcsum;
#endif /* defined(INET6) */

#define TCP_CSUM_COUNTER_INCR(ev)       (ev)->ev_count++

#else

#define TCP_CSUM_COUNTER_INCR(ev)       /* nothing */

#endif /* TCP_CSUM_COUNTERS */

#ifdef TCP_REASS_COUNTERS
#include <sys/device.h>

extern struct evcnt tcp_reass_;
extern struct evcnt tcp_reass_empty;
extern struct evcnt tcp_reass_iteration[8];
extern struct evcnt tcp_reass_prependfirst;
extern struct evcnt tcp_reass_prepend;
extern struct evcnt tcp_reass_insert;
extern struct evcnt tcp_reass_inserttail;
extern struct evcnt tcp_reass_append;
extern struct evcnt tcp_reass_appendtail;
extern struct evcnt tcp_reass_overlaptail;
extern struct evcnt tcp_reass_overlapfront;
extern struct evcnt tcp_reass_segdup;
extern struct evcnt tcp_reass_fragdup;

#define TCP_REASS_COUNTER_INCR(ev)      (ev)->ev_count++

#else

#define TCP_REASS_COUNTER_INCR(ev)      /* nothing */

#endif /* TCP_REASS_COUNTERS */

static int tcp_reass(struct tcpcb *, const struct tcphdr *, struct mbuf *,
    int *);
static int tcp_dooptions(struct tcpcb *, const u_char *, int,
    struct tcphdr *, struct mbuf *, int, struct tcp_opt_info *);

#ifdef INET
static void tcp4_log_refused(const struct ip *, const struct tcphdr *);
#endif
#ifdef INET6
static void tcp6_log_refused(const struct ip6_hdr *, const struct tcphdr *);
#endif

#define TRAVERSE(x) while ((x)->m_next) (x) = (x)->m_next

#if defined(MBUFTRACE)
struct mowner tcp_reass_mowner = MOWNER_INIT("tcp", "reass");
#endif /* defined(MBUFTRACE) */

static struct pool tcpipqent_pool;

void
tcpipqent_init(void)
{

        pool_init(&tcpipqent_pool, sizeof(struct ipqent), 0, 0, 0, "tcpipqepl",
            NULL, IPL_VM);
}

struct ipqent *
tcpipqent_alloc(void)
{
        struct ipqent *ipqe;
        int s;

        s = splvm();
        ipqe = pool_get(&tcpipqent_pool, PR_NOWAIT);
        splx(s);

        return ipqe;
}

void
tcpipqent_free(struct ipqent *ipqe)
{
        int s;

        s = splvm();
        pool_put(&tcpipqent_pool, ipqe);
        splx(s);
}

static int
tcp_reass(struct tcpcb *tp, const struct tcphdr *th, struct mbuf *m, int *tlen)
{
        struct ipqent *p, *q, *nq, *tiqe = NULL;
        struct socket *so = NULL;
        int pkt_flags;
        tcp_seq pkt_seq;
        unsigned pkt_len;
        u_long rcvpartdupbyte = 0;
        u_long rcvoobyte;
#ifdef TCP_REASS_COUNTERS
        u_int count = 0;
#endif
        uint64_t *tcps;

        if (tp->t_inpcb)
                so = tp->t_inpcb->inp_socket;
#ifdef INET6
        else if (tp->t_in6pcb)
                so = tp->t_in6pcb->in6p_socket;
#endif

        TCP_REASS_LOCK_CHECK(tp);

        /*
         * Call with th==0 after become established to
         * force pre-ESTABLISHED data up to user socket.
         */
        if (th == 0)
                goto present;

        m_claimm(m, &tcp_reass_mowner);

        rcvoobyte = *tlen;
        /*
         * Copy these to local variables because the tcpiphdr
         * gets munged while we are collapsing mbufs.
         */
        pkt_seq = th->th_seq;
        pkt_len = *tlen;
        pkt_flags = th->th_flags;

        TCP_REASS_COUNTER_INCR(&tcp_reass_);

        if ((p = TAILQ_LAST(&tp->segq, ipqehead)) != NULL) {
                /*
                 * When we miss a packet, the vast majority of time we get
                 * packets that follow it in order.  So optimize for that.
                 */
                if (pkt_seq == p->ipqe_seq + p->ipqe_len) {
                        p->ipqe_len += pkt_len;
                        p->ipqe_flags |= pkt_flags;
                        m_cat(p->ipre_mlast, m);
                        TRAVERSE(p->ipre_mlast);
                        m = NULL;
                        tiqe = p;
                        TAILQ_REMOVE(&tp->timeq, p, ipqe_timeq);
                        TCP_REASS_COUNTER_INCR(&tcp_reass_appendtail);
                        goto skip_replacement;
                }
                /*
                 * While we're here, if the pkt is completely beyond
                 * anything we have, just insert it at the tail.
                 */
                if (SEQ_GT(pkt_seq, p->ipqe_seq + p->ipqe_len)) {
                        TCP_REASS_COUNTER_INCR(&tcp_reass_inserttail);
                        goto insert_it;
                }
        }

        q = TAILQ_FIRST(&tp->segq);

        if (q != NULL) {
                /*
                 * If this segment immediately precedes the first out-of-order
                 * block, simply slap the segment in front of it and (mostly)
                 * skip the complicated logic.
                 */
                if (pkt_seq + pkt_len == q->ipqe_seq) {
                        q->ipqe_seq = pkt_seq;
                        q->ipqe_len += pkt_len;
                        q->ipqe_flags |= pkt_flags;
                        m_cat(m, q->ipqe_m);
                        q->ipqe_m = m;
                        q->ipre_mlast = m; /* last mbuf may have changed */
                        TRAVERSE(q->ipre_mlast);
                        tiqe = q;
                        TAILQ_REMOVE(&tp->timeq, q, ipqe_timeq);
                        TCP_REASS_COUNTER_INCR(&tcp_reass_prependfirst);
                        goto skip_replacement;
                }
        } else {
                TCP_REASS_COUNTER_INCR(&tcp_reass_empty);
        }

        /*
         * Find a segment which begins after this one does.
         */
        for (p = NULL; q != NULL; q = nq) {
                nq = TAILQ_NEXT(q, ipqe_q);
#ifdef TCP_REASS_COUNTERS
                count++;
#endif
                /*
                 * If the received segment is just right after this
                 * fragment, merge the two together and then check
                 * for further overlaps.
                 */
                if (q->ipqe_seq + q->ipqe_len == pkt_seq) {
#ifdef TCPREASS_DEBUG
                        printf("tcp_reass[%p]: concat %u:%u(%u) to %u:%u(%u)\n",
                               tp, pkt_seq, pkt_seq + pkt_len, pkt_len,
                               q->ipqe_seq, q->ipqe_seq + q->ipqe_len, q->ipqe_len);
#endif
                        pkt_len += q->ipqe_len;
                        pkt_flags |= q->ipqe_flags;
                        pkt_seq = q->ipqe_seq;
                        m_cat(q->ipre_mlast, m);
                        TRAVERSE(q->ipre_mlast);
                        m = q->ipqe_m;
                        TCP_REASS_COUNTER_INCR(&tcp_reass_append);
                        goto free_ipqe;
                }
                /*
                 * If the received segment is completely past this
                 * fragment, we need to go the next fragment.
                 */
                if (SEQ_LT(q->ipqe_seq + q->ipqe_len, pkt_seq)) {
                        p = q;
                        continue;
                }
                /*
                 * If the fragment is past the received segment,
                 * it (or any following) can't be concatenated.
                 */
                if (SEQ_GT(q->ipqe_seq, pkt_seq + pkt_len)) {
                        TCP_REASS_COUNTER_INCR(&tcp_reass_insert);
                        break;
                }

                /*
                 * We've received all the data in this segment before.
                 * mark it as a duplicate and return.
                 */
                if (SEQ_LEQ(q->ipqe_seq, pkt_seq) &&
                    SEQ_GEQ(q->ipqe_seq + q->ipqe_len, pkt_seq + pkt_len)) {
                        tcps = TCP_STAT_GETREF();
                        tcps[TCP_STAT_RCVDUPPACK]++;
                        tcps[TCP_STAT_RCVDUPBYTE] += pkt_len;
                        TCP_STAT_PUTREF();
                        tcp_new_dsack(tp, pkt_seq, pkt_len);
                        m_freem(m);
                        if (tiqe != NULL) {
                                tcpipqent_free(tiqe);
                        }
                        TCP_REASS_COUNTER_INCR(&tcp_reass_segdup);
                        return (0);
                }
                /*
                 * Received segment completely overlaps this fragment
                 * so we drop the fragment (this keeps the temporal
                 * ordering of segments correct).
                 */
                if (SEQ_GEQ(q->ipqe_seq, pkt_seq) &&
                    SEQ_LEQ(q->ipqe_seq + q->ipqe_len, pkt_seq + pkt_len)) {
                        rcvpartdupbyte += q->ipqe_len;
                        m_freem(q->ipqe_m);
                        TCP_REASS_COUNTER_INCR(&tcp_reass_fragdup);
                        goto free_ipqe;
                }
                /*
                 * RX'ed segment extends past the end of the
                 * fragment.  Drop the overlapping bytes.  Then
                 * merge the fragment and segment then treat as
                 * a longer received packet.
                 */
                if (SEQ_LT(q->ipqe_seq, pkt_seq) &&
                    SEQ_GT(q->ipqe_seq + q->ipqe_len, pkt_seq))  {
                        int overlap = q->ipqe_seq + q->ipqe_len - pkt_seq;
#ifdef TCPREASS_DEBUG
                        printf("tcp_reass[%p]: trim starting %d bytes of %u:%u(%u)\n",
                               tp, overlap,
                               pkt_seq, pkt_seq + pkt_len, pkt_len);
#endif
                        m_adj(m, overlap);
                        rcvpartdupbyte += overlap;
                        m_cat(q->ipre_mlast, m);
                        TRAVERSE(q->ipre_mlast);
                        m = q->ipqe_m;
                        pkt_seq = q->ipqe_seq;
                        pkt_len += q->ipqe_len - overlap;
                        rcvoobyte -= overlap;
                        TCP_REASS_COUNTER_INCR(&tcp_reass_overlaptail);
                        goto free_ipqe;
                }
                /*
                 * RX'ed segment extends past the front of the
                 * fragment.  Drop the overlapping bytes on the
                 * received packet.  The packet will then be
                 * contatentated with this fragment a bit later.
                 */
                if (SEQ_GT(q->ipqe_seq, pkt_seq) &&
                    SEQ_LT(q->ipqe_seq, pkt_seq + pkt_len))  {
                        int overlap = pkt_seq + pkt_len - q->ipqe_seq;
#ifdef TCPREASS_DEBUG
                        printf("tcp_reass[%p]: trim trailing %d bytes of %u:%u(%u)\n",
                               tp, overlap,
                               pkt_seq, pkt_seq + pkt_len, pkt_len);
#endif
                        m_adj(m, -overlap);
                        pkt_len -= overlap;
                        rcvpartdupbyte += overlap;
                        TCP_REASS_COUNTER_INCR(&tcp_reass_overlapfront);
                        rcvoobyte -= overlap;
                }
                /*
                 * If the received segment immediates precedes this
                 * fragment then tack the fragment onto this segment
                 * and reinsert the data.
                 */
                if (q->ipqe_seq == pkt_seq + pkt_len) {
#ifdef TCPREASS_DEBUG
                        printf("tcp_reass[%p]: append %u:%u(%u) to %u:%u(%u)\n",
                               tp, q->ipqe_seq, q->ipqe_seq + q->ipqe_len, q->ipqe_len,
                               pkt_seq, pkt_seq + pkt_len, pkt_len);
#endif
                        pkt_len += q->ipqe_len;
                        pkt_flags |= q->ipqe_flags;
                        m_cat(m, q->ipqe_m);
                        TAILQ_REMOVE(&tp->segq, q, ipqe_q);
                        TAILQ_REMOVE(&tp->timeq, q, ipqe_timeq);
                        tp->t_segqlen--;
                        KASSERT(tp->t_segqlen >= 0);
                        KASSERT(tp->t_segqlen != 0 ||
                            (TAILQ_EMPTY(&tp->segq) &&
                            TAILQ_EMPTY(&tp->timeq)));
                        if (tiqe == NULL) {
                                tiqe = q;
                        } else {
                                tcpipqent_free(q);
                        }
                        TCP_REASS_COUNTER_INCR(&tcp_reass_prepend);
                        break;
                }
                /*
                 * If the fragment is before the segment, remember it.
                 * When this loop is terminated, p will contain the
                 * pointer to fragment that is right before the received
                 * segment.
                 */
                if (SEQ_LEQ(q->ipqe_seq, pkt_seq))
                        p = q;

                continue;

                /*
                 * This is a common operation.  It also will allow
                 * to save doing a malloc/free in most instances.
                 */
          free_ipqe:
                TAILQ_REMOVE(&tp->segq, q, ipqe_q);
                TAILQ_REMOVE(&tp->timeq, q, ipqe_timeq);
                tp->t_segqlen--;
                KASSERT(tp->t_segqlen >= 0);
                KASSERT(tp->t_segqlen != 0 ||
                    (TAILQ_EMPTY(&tp->segq) && TAILQ_EMPTY(&tp->timeq)));
                if (tiqe == NULL) {
                        tiqe = q;
                } else {
                        tcpipqent_free(q);
                }
        }

#ifdef TCP_REASS_COUNTERS
        if (count > 7)
                TCP_REASS_COUNTER_INCR(&tcp_reass_iteration[0]);
        else if (count > 0)
                TCP_REASS_COUNTER_INCR(&tcp_reass_iteration[count]);
#endif

    insert_it:

        /*
         * Allocate a new queue entry since the received segment did not
         * collapse onto any other out-of-order block; thus we are allocating
         * a new block.  If it had collapsed, tiqe would not be NULL and
         * we would be reusing it.
         * XXX If we can't, just drop the packet.  XXX
         */
        if (tiqe == NULL) {
                tiqe = tcpipqent_alloc();
                if (tiqe == NULL) {
                        TCP_STATINC(TCP_STAT_RCVMEMDROP);
                        m_freem(m);
                        return (0);
                }
        }

        /*
         * Update the counters.
         */
        tcps = TCP_STAT_GETREF();
        tcps[TCP_STAT_RCVOOPACK]++;
        tcps[TCP_STAT_RCVOOBYTE] += rcvoobyte;
        if (rcvpartdupbyte) {
            tcps[TCP_STAT_RCVPARTDUPPACK]++;
            tcps[TCP_STAT_RCVPARTDUPBYTE] += rcvpartdupbyte;
        }
        TCP_STAT_PUTREF();

        /*
         * Insert the new fragment queue entry into both queues.
         */
        tiqe->ipqe_m = m;
        tiqe->ipre_mlast = m;
        tiqe->ipqe_seq = pkt_seq;
        tiqe->ipqe_len = pkt_len;
        tiqe->ipqe_flags = pkt_flags;
        if (p == NULL) {
                TAILQ_INSERT_HEAD(&tp->segq, tiqe, ipqe_q);
#ifdef TCPREASS_DEBUG
                if (tiqe->ipqe_seq != tp->rcv_nxt)
                        printf("tcp_reass[%p]: insert %u:%u(%u) at front\n",
                               tp, pkt_seq, pkt_seq + pkt_len, pkt_len);
#endif
        } else {
                TAILQ_INSERT_AFTER(&tp->segq, p, tiqe, ipqe_q);
#ifdef TCPREASS_DEBUG
                printf("tcp_reass[%p]: insert %u:%u(%u) after %u:%u(%u)\n",
                       tp, pkt_seq, pkt_seq + pkt_len, pkt_len,
                       p->ipqe_seq, p->ipqe_seq + p->ipqe_len, p->ipqe_len);
#endif
        }
        tp->t_segqlen++;

skip_replacement:

        TAILQ_INSERT_HEAD(&tp->timeq, tiqe, ipqe_timeq);

present:
        /*
         * Present data to user, advancing rcv_nxt through
         * completed sequence space.
         */
        if (TCPS_HAVEESTABLISHED(tp->t_state) == 0)
                return (0);
        q = TAILQ_FIRST(&tp->segq);
        if (q == NULL || q->ipqe_seq != tp->rcv_nxt)
                return (0);
        if (tp->t_state == TCPS_SYN_RECEIVED && q->ipqe_len)
                return (0);

        tp->rcv_nxt += q->ipqe_len;
        pkt_flags = q->ipqe_flags & TH_FIN;
        nd6_hint(tp);

        TAILQ_REMOVE(&tp->segq, q, ipqe_q);
        TAILQ_REMOVE(&tp->timeq, q, ipqe_timeq);
        tp->t_segqlen--;
        KASSERT(tp->t_segqlen >= 0);
        KASSERT(tp->t_segqlen != 0 ||
            (TAILQ_EMPTY(&tp->segq) && TAILQ_EMPTY(&tp->timeq)));
        if (so->so_state & SS_CANTRCVMORE)
                m_freem(q->ipqe_m);
        else
                sbappendstream(&so->so_rcv, q->ipqe_m);
        tcpipqent_free(q);
        sorwakeup(so);
        return (pkt_flags);
}

#ifdef INET6
int
tcp6_input(struct mbuf **mp, int *offp, int proto)
{
        struct mbuf *m = *mp;

        /*
         * draft-itojun-ipv6-tcp-to-anycast
         * better place to put this in?
         */
        if (m->m_flags & M_ANYCAST6) {
                struct ip6_hdr *ip6;
                if (m->m_len < sizeof(struct ip6_hdr)) {
                        if ((m = m_pullup(m, sizeof(struct ip6_hdr))) == NULL) {
                                TCP_STATINC(TCP_STAT_RCVSHORT);
                                return IPPROTO_DONE;
                        }
                }
                ip6 = mtod(m, struct ip6_hdr *);
                icmp6_error(m, ICMP6_DST_UNREACH, ICMP6_DST_UNREACH_ADDR,
                    (char *)&ip6->ip6_dst - (char *)ip6);
                return IPPROTO_DONE;
        }

        tcp_input(m, *offp, proto);
        return IPPROTO_DONE;
}
#endif

#ifdef INET
static void
tcp4_log_refused(const struct ip *ip, const struct tcphdr *th)
{
        char src[4*sizeof "123"];
        char dst[4*sizeof "123"];

        if (ip) {
                strlcpy(src, inet_ntoa(ip->ip_src), sizeof(src));
                strlcpy(dst, inet_ntoa(ip->ip_dst), sizeof(dst));
        }
        else {
                strlcpy(src, "(unknown)", sizeof(src));
                strlcpy(dst, "(unknown)", sizeof(dst));
        }
        log(LOG_INFO,
            "Connection attempt to TCP %s:%d from %s:%d\n",
            dst, ntohs(th->th_dport),
            src, ntohs(th->th_sport));
}
#endif

#ifdef INET6
static void
tcp6_log_refused(const struct ip6_hdr *ip6, const struct tcphdr *th)
{
        char src[INET6_ADDRSTRLEN];
        char dst[INET6_ADDRSTRLEN];

        if (ip6) {
                strlcpy(src, ip6_sprintf(&ip6->ip6_src), sizeof(src));
                strlcpy(dst, ip6_sprintf(&ip6->ip6_dst), sizeof(dst));
        }
        else {
                strlcpy(src, "(unknown v6)", sizeof(src));
                strlcpy(dst, "(unknown v6)", sizeof(dst));
        }
        log(LOG_INFO,
            "Connection attempt to TCP [%s]:%d from [%s]:%d\n",
            dst, ntohs(th->th_dport),
            src, ntohs(th->th_sport));
}
#endif

/*
 * Checksum extended TCP header and data.
 */
int
tcp_input_checksum(int af, struct mbuf *m, const struct tcphdr *th,
    int toff, int off, int tlen)
{

        /*
         * XXX it's better to record and check if this mbuf is
         * already checked.
         */

        switch (af) {
#ifdef INET
        case AF_INET:
                switch (m->m_pkthdr.csum_flags &
                        ((m->m_pkthdr.rcvif->if_csum_flags_rx & M_CSUM_TCPv4) |
                         M_CSUM_TCP_UDP_BAD | M_CSUM_DATA)) {
                case M_CSUM_TCPv4|M_CSUM_TCP_UDP_BAD:
                        TCP_CSUM_COUNTER_INCR(&tcp_hwcsum_bad);
                        goto badcsum;

                case M_CSUM_TCPv4|M_CSUM_DATA: {
                        u_int32_t hw_csum = m->m_pkthdr.csum_data;

                        TCP_CSUM_COUNTER_INCR(&tcp_hwcsum_data);
                        if (m->m_pkthdr.csum_flags & M_CSUM_NO_PSEUDOHDR) {
                                const struct ip *ip =
                                    mtod(m, const struct ip *);

                                hw_csum = in_cksum_phdr(ip->ip_src.s_addr,
                                    ip->ip_dst.s_addr,
                                    htons(hw_csum + tlen + off + IPPROTO_TCP));
                        }
                        if ((hw_csum ^ 0xffff) != 0)
                                goto badcsum;
                        break;
                }

                case M_CSUM_TCPv4:
                        /* Checksum was okay. */
                        TCP_CSUM_COUNTER_INCR(&tcp_hwcsum_ok);
                        break;

                default:
                        /*
                         * Must compute it ourselves.  Maybe skip checksum
                         * on loopback interfaces.
                         */
                        if (__predict_true(!(m->m_pkthdr.rcvif->if_flags &
                                             IFF_LOOPBACK) ||
                                           tcp_do_loopback_cksum)) {
                                TCP_CSUM_COUNTER_INCR(&tcp_swcsum);
                                if (in4_cksum(m, IPPROTO_TCP, toff,
                                              tlen + off) != 0)
                                        goto badcsum;
                        }
                        break;
                }
                break;
#endif /* INET4 */

#ifdef INET6
        case AF_INET6:
                switch (m->m_pkthdr.csum_flags &
                        ((m->m_pkthdr.rcvif->if_csum_flags_rx & M_CSUM_TCPv6) |
                         M_CSUM_TCP_UDP_BAD | M_CSUM_DATA)) {
                case M_CSUM_TCPv6|M_CSUM_TCP_UDP_BAD:
                        TCP_CSUM_COUNTER_INCR(&tcp6_hwcsum_bad);
                        goto badcsum;

#if 0 /* notyet */
                case M_CSUM_TCPv6|M_CSUM_DATA:
#endif

                case M_CSUM_TCPv6:
                        /* Checksum was okay. */
                        TCP_CSUM_COUNTER_INCR(&tcp6_hwcsum_ok);
                        break;

                default:
                        /*
                         * Must compute it ourselves.  Maybe skip checksum
                         * on loopback interfaces.
                         */
                        if (__predict_true((m->m_flags & M_LOOP) == 0 ||
                            tcp_do_loopback_cksum)) {
                                TCP_CSUM_COUNTER_INCR(&tcp6_swcsum);
                                if (in6_cksum(m, IPPROTO_TCP, toff,
                                    tlen + off) != 0)
                                        goto badcsum;
                        }
                }
                break;
#endif /* INET6 */
        }

        return 0;

badcsum:
        TCP_STATINC(TCP_STAT_RCVBADSUM);
        return -1;
}

/*
 * TCP input routine, follows pages 65-76 of RFC 793 very closely.
 */
void
tcp_input(struct mbuf *m, ...)
{
        struct tcphdr *th;
        struct ip *ip;
        struct inpcb *inp;
#ifdef INET6
        struct ip6_hdr *ip6;
        struct in6pcb *in6p;
#endif
        u_int8_t *optp = NULL;
        int optlen = 0;
        int len, tlen, toff, hdroptlen = 0;
        struct tcpcb *tp = 0;
        int tiflags;
        struct socket *so = NULL;
        int todrop, dupseg, acked, ourfinisacked, needoutput = 0;
#ifdef TCP_DEBUG
        short ostate = 0;
#endif
        u_long tiwin;
        struct tcp_opt_info opti;
        int off, iphlen;
        va_list ap;
        int af;         /* af on the wire */
        struct mbuf *tcp_saveti = NULL;
        uint32_t ts_rtt;
        uint8_t iptos;
        uint64_t *tcps;

        MCLAIM(m, &tcp_rx_mowner);
        va_start(ap, m);
        toff = va_arg(ap, int);
        (void)va_arg(ap, int);          /* ignore value, advance ap */
        va_end(ap);

        TCP_STATINC(TCP_STAT_RCVTOTAL);

        memset(&opti, 0, sizeof(opti));
        opti.ts_present = 0;
        opti.maxseg = 0;

        /*
         * RFC1122 4.2.3.10, p. 104: discard bcast/mcast SYN.
         *
         * TCP is, by definition, unicast, so we reject all
         * multicast outright.
         *
         * Note, there are additional src/dst address checks in
         * the AF-specific code below.
         */
        if (m->m_flags & (M_BCAST|M_MCAST)) {
                /* XXX stat */
                goto drop;
        }
#ifdef INET6
        if (m->m_flags & M_ANYCAST6) {
                /* XXX stat */
                goto drop;
        }
#endif

        /*
         * Get IP and TCP header.
         * Note: IP leaves IP header in first mbuf.
         */
        ip = mtod(m, struct ip *);
#ifdef INET6
        ip6 = NULL;
#endif
        switch (ip->ip_v) {
#ifdef INET
        case 4:
                af = AF_INET;
                iphlen = sizeof(struct ip);
                ip = mtod(m, struct ip *);
                IP6_EXTHDR_GET(th, struct tcphdr *, m, toff,
                        sizeof(struct tcphdr));
                if (th == NULL) {
                        TCP_STATINC(TCP_STAT_RCVSHORT);
                        return;
                }
                /* We do the checksum after PCB lookup... */
                len = ntohs(ip->ip_len);
                tlen = len - toff;
                iptos = ip->ip_tos;
                break;
#endif
#ifdef INET6
        case 6:
                ip = NULL;
                iphlen = sizeof(struct ip6_hdr);
                af = AF_INET6;
                ip6 = mtod(m, struct ip6_hdr *);
                IP6_EXTHDR_GET(th, struct tcphdr *, m, toff,
                        sizeof(struct tcphdr));
                if (th == NULL) {
                        TCP_STATINC(TCP_STAT_RCVSHORT);
                        return;
                }

                /* Be proactive about malicious use of IPv4 mapped address */
                if (IN6_IS_ADDR_V4MAPPED(&ip6->ip6_src) ||
                    IN6_IS_ADDR_V4MAPPED(&ip6->ip6_dst)) {
                        /* XXX stat */
                        goto drop;
                }

                /*
                 * 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;
                }

                /*
                 * Make sure destination address is not multicast.
                 * Source address checked in ip6_input().
                 */
                if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst)) {
                        /* XXX stat */
                        goto drop;
                }

                /* We do the checksum after PCB lookup... */
                len = m->m_pkthdr.len;
                tlen = len - toff;
                iptos = (ntohl(ip6->ip6_flow) >> 20) & 0xff;
                break;
#endif
        default:
                m_freem(m);
                return;
        }

        KASSERT(TCP_HDR_ALIGNED_P(th));

        /*
         * 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) {
                TCP_STATINC(TCP_STAT_RCVBADOFF);
                goto drop;
        }
        tlen -= off;

        /*
         * tcp_input() has been modified to use tlen to mean the TCP data
         * length throughout the function.  Other functions can use
         * m->m_pkthdr.len as the basis for calculating the TCP data length.
         * rja
         */

        if (off > sizeof (struct tcphdr)) {
                IP6_EXTHDR_GET(th, struct tcphdr *, m, toff, off);
                if (th == NULL) {
                        TCP_STATINC(TCP_STAT_RCVSHORT);
                        return;
                }
                /*
                 * NOTE: ip/ip6 will not be affected by m_pulldown()
                 * (as they're before toff) and we don't need to update those.
                 */
                KASSERT(TCP_HDR_ALIGNED_P(th));
                optlen = off - sizeof (struct tcphdr);
                optp = ((u_int8_t *)th) + sizeof(struct tcphdr);
                /*
                 * 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;

        /*
         * Locate pcb for segment.
         */
findpcb:
        inp = NULL;
#ifdef INET6
        in6p = NULL;
#endif
        switch (af) {
#ifdef INET
        case AF_INET:
                inp = in_pcblookup_connect(&tcbtable, ip->ip_src, th->th_sport,
                    ip->ip_dst, th->th_dport);
                if (inp == 0) {
                        TCP_STATINC(TCP_STAT_PCBHASHMISS);
                        inp = in_pcblookup_bind(&tcbtable, ip->ip_dst, th->th_dport);
                }
#ifdef INET6
                if (inp == 0) {
                        struct in6_addr s, d;

                        /* mapped addr case */
                        memset(&s, 0, sizeof(s));
                        s.s6_addr16[5] = htons(0xffff);
                        bcopy(&ip->ip_src, &s.s6_addr32[3], sizeof(ip->ip_src));
                        memset(&d, 0, sizeof(d));
                        d.s6_addr16[5] = htons(0xffff);
                        bcopy(&ip->ip_dst, &d.s6_addr32[3], sizeof(ip->ip_dst));
                        in6p = in6_pcblookup_connect(&tcbtable, &s,
                            th->th_sport, &d, th->th_dport, 0);
                        if (in6p == 0) {
                                TCP_STATINC(TCP_STAT_PCBHASHMISS);
                                in6p = in6_pcblookup_bind(&tcbtable, &d,
                                    th->th_dport, 0);
                        }
                }
#endif
#ifndef INET6
                if (inp == 0)
#else
                if (inp == 0 && in6p == 0)
#endif
                {
                        TCP_STATINC(TCP_STAT_NOPORT);
                        if (tcp_log_refused &&
                            (tiflags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN) {
                                tcp4_log_refused(ip, th);
                        }
                        tcp_fields_to_host(th);
                        goto dropwithreset_ratelim;
                }
#if defined(IPSEC) || defined(FAST_IPSEC)
                if (inp && (inp->inp_socket->so_options & SO_ACCEPTCONN) == 0 &&
                    ipsec4_in_reject(m, inp)) {
                        IPSEC_STATINC(IPSEC_STAT_IN_POLVIO);
                        goto drop;
                }
#ifdef INET6
                else if (in6p &&
                    (in6p->in6p_socket->so_options & SO_ACCEPTCONN) == 0 &&
                    ipsec6_in_reject_so(m, in6p->in6p_socket)) {
                        IPSEC_STATINC(IPSEC_STAT_IN_POLVIO);
                        goto drop;
                }
#endif
#endif /*IPSEC*/
                break;
#endif /*INET*/
#ifdef INET6
        case AF_INET6:
            {
                int faith;

#if defined(NFAITH) && NFAITH > 0
                faith = faithprefix(&ip6->ip6_dst);
#else
                faith = 0;
#endif
                in6p = in6_pcblookup_connect(&tcbtable, &ip6->ip6_src,
                    th->th_sport, &ip6->ip6_dst, th->th_dport, faith);
                if (in6p == NULL) {
                        TCP_STATINC(TCP_STAT_PCBHASHMISS);
                        in6p = in6_pcblookup_bind(&tcbtable, &ip6->ip6_dst,
                                th->th_dport, faith);
                }
                if (in6p == NULL) {
                        TCP_STATINC(TCP_STAT_NOPORT);
                        if (tcp_log_refused &&
                            (tiflags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN) {
                                tcp6_log_refused(ip6, th);
                        }
                        tcp_fields_to_host(th);
                        goto dropwithreset_ratelim;
                }
#if defined(IPSEC) || defined(FAST_IPSEC)
                if ((in6p->in6p_socket->so_options & SO_ACCEPTCONN) == 0 &&
                    ipsec6_in_reject(m, in6p)) {
                        IPSEC6_STATINC(IPSEC_STAT_IN_POLVIO);
                        goto drop;
                }
#endif /*IPSEC*/
                break;
            }
#endif
        }

        /*
         * 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.
         */
        tp = NULL;
        so = NULL;
        if (inp) {
                /* Check the minimum TTL for socket. */
                if (ip->ip_ttl < inp->inp_ip_minttl)
                        goto drop;

                tp = intotcpcb(inp);
                so = inp->inp_socket;
        }
#ifdef INET6
        else if (in6p) {
                tp = in6totcpcb(in6p);
                so = in6p->in6p_socket;
        }
#endif
        if (tp == 0) {
                tcp_fields_to_host(th);
                goto dropwithreset_ratelim;
        }
        if (tp->t_state == TCPS_CLOSED)
                goto drop;

        KASSERT(so->so_lock == softnet_lock);
        KASSERT(solocked(so));

        /*
         * Checksum extended TCP header and data.
         */
        if (tcp_input_checksum(af, m, th, toff, off, tlen))
                goto badcsum;

        tcp_fields_to_host(th);

        /* 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;

#ifdef INET6
        /* save packet options if user wanted */
        if (in6p && (in6p->in6p_flags & IN6P_CONTROLOPTS)) {
                if (in6p->in6p_options) {
                        m_freem(in6p->in6p_options);
                        in6p->in6p_options = 0;
                }
                KASSERT(ip6 != NULL);
                ip6_savecontrol(in6p, &in6p->in6p_options, ip6, m);
        }
#endif

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

                memset(&src, 0, sizeof(src));
                memset(&dst, 0, sizeof(dst));
                switch (af) {
#ifdef INET
                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;
#endif
#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 */
                default:
                        goto badsyn;    /*sanity*/
                }

                if (so->so_options & SO_DEBUG) {
#ifdef TCP_DEBUG
                        ostate = tp->t_state;
#endif

                        tcp_saveti = NULL;
                        if (iphlen + sizeof(struct tcphdr) > MHLEN)
                                goto nosave;

                        if (m->m_len > iphlen && (m->m_flags & M_EXT) == 0) {
                                tcp_saveti = m_copym(m, 0, iphlen, M_DONTWAIT);
                                if (!tcp_saveti)
                                        goto nosave;
                        } else {
                                MGETHDR(tcp_saveti, M_DONTWAIT, MT_HEADER);
                                if (!tcp_saveti)
                                        goto nosave;
                                MCLAIM(m, &tcp_mowner);
                                tcp_saveti->m_len = iphlen;
                                m_copydata(m, 0, iphlen,
                                    mtod(tcp_saveti, void *));
                        }

                        if (M_TRAILINGSPACE(tcp_saveti) < sizeof(struct tcphdr)) {
                                m_freem(tcp_saveti);
                                tcp_saveti = NULL;
                        } else {
                                tcp_saveti->m_len += sizeof(struct tcphdr);
                                memcpy(mtod(tcp_saveti, char *) + iphlen, th,
                                    sizeof(struct tcphdr));
                        }
        nosave:;
                }
                if (so->so_options & SO_ACCEPTCONN) {
                        if ((tiflags & (TH_RST|TH_ACK|TH_SYN)) != TH_SYN) {
                                if (tiflags & TH_RST) {
                                        syn_cache_reset(&src.sa, &dst.sa, th);
                                } else if ((tiflags & (TH_ACK|TH_SYN)) ==
                                    (TH_ACK|TH_SYN)) {
                                        /*
                                         * Received a SYN,ACK.  This should
                                         * never happen while we are in
                                         * LISTEN.  Send an RST.
                                         */
                                        goto badsyn;
                                } else if (tiflags & TH_ACK) {
                                        so = syn_cache_get(&src.sa, &dst.sa,
                                                th, toff, tlen, so, m);
                                        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.
                                                 */
                                                m = NULL;
                                        } else {
                                                /*
                                                 * We have created a
                                                 * full-blown connection.
                                                 */
                                                tp = NULL;
                                                inp = NULL;
#ifdef INET6
                                                in6p = NULL;
#endif
                                                switch (so->so_proto->pr_domain->dom_family) {
#ifdef INET
                                                case AF_INET:
                                                        inp = sotoinpcb(so);
                                                        tp = intotcpcb(inp);
                                                        break;
#endif
#ifdef INET6
                                                case AF_INET6:
                                                        in6p = sotoin6pcb(so);
                                                        tp = in6totcpcb(in6p);
                                                        break;
#endif
                                                }
                                                if (tp == NULL)
                                                        goto badsyn;    /*XXX*/
                                                tiwin <<= tp->snd_scale;
                                                goto after_listen;
                                        }
                                } else {
                                        /*
                                         * None of RST, SYN or ACK was set.
                                         * This is an invalid packet for a
                                         * TCB in LISTEN state.  Send a RST.
                                         */
                                        goto badsyn;
                                }
                        } else {
                                /*
                                 * Received a SYN.
                                 *
                                 * RFC1122 4.2.3.10, p. 104: discard bcast/mcast SYN
                                 */
                                if (m->m_flags & (M_BCAST|M_MCAST))
                                        goto drop;

                                switch (af) {
#ifdef INET6
                                case AF_INET6:
                                        if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst))
                                                goto drop;
                                        break;
#endif /* INET6 */
                                case AF_INET:
                                        if (IN_MULTICAST(ip->ip_dst.s_addr) ||
                                            in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
                                                goto drop;
                                break;
                                }

#ifdef INET6
                                /*
                                 * If deprecated address is forbidden, we do
                                 * not accept SYN to deprecated interface
                                 * address to prevent any new inbound
                                 * connection from getting established.
                                 * When we do not accept SYN, we send a TCP
                                 * RST, with deprecated source address (instead
                                 * of dropping it).  We compromise it as it is
                                 * much better for peer to send a RST, and
                                 * RST will be the final packet for the
                                 * exchange.
                                 *
                                 * If we do not forbid deprecated addresses, we
                                 * accept the SYN packet.  RFC2462 does not
                                 * suggest dropping SYN in this case.
                                 * If we decipher RFC2462 5.5.4, it says like
                                 * this:
                                 * 1. use of deprecated addr with existing
                                 *    communication is okay - "SHOULD continue
                                 *    to be used"
                                 * 2. use of it with new communication:
                                 *   (2a) "SHOULD NOT be used if alternate
                                 *        address with sufficient scope is
                                 *        available"
                                 *   (2b) nothing mentioned otherwise.
                                 * Here we fall into (2b) case as we have no
                                 * choice in our source address selection - we
                                 * must obey the peer.
                                 *
                                 * The wording in RFC2462 is confusing, and
                                 * there are multiple description text for
                                 * deprecated address handling - worse, they
                                 * are not exactly the same.  I believe 5.5.4
                                 * is the best one, so we follow 5.5.4.
                                 */
                                if (af == AF_INET6 && !ip6_use_deprecated) {
                                        struct in6_ifaddr *ia6;
                                        if ((ia6 = in6ifa_ifpwithaddr(m->m_pkthdr.rcvif,
                                            &ip6->ip6_dst)) &&
                                            (ia6->ia6_flags & IN6_IFF_DEPRECATED)) {
                                                tp = NULL;
                                                goto dropwithreset;
                                        }
                                }
#endif

#if defined(IPSEC) || defined(FAST_IPSEC)
                                switch (af) {
#ifdef INET
                                case AF_INET:
                                        if (ipsec4_in_reject_so(m, so)) {
                                                IPSEC_STATINC(IPSEC_STAT_IN_POLVIO);
                                                tp = NULL;
                                                goto dropwithreset;
                                        }
                                        break;
#endif
#ifdef INET6
                                case AF_INET6:
                                        if (ipsec6_in_reject_so(m, so)) {
                                                IPSEC6_STATINC(IPSEC_STAT_IN_POLVIO);
                                                tp = NULL;
                                                goto dropwithreset;
                                        }
                                        break;
#endif /*INET6*/
                                }
#endif /*IPSEC*/

                                /*
                                 * LISTEN socket received a SYN
                                 * from itself?  This can't possibly
                                 * be valid; drop the packet.
                                 */
                                if (th->th_sport == th->th_dport) {
                                        int i;

                                        switch (af) {
#ifdef INET
                                        case AF_INET:
                                                i = in_hosteq(ip->ip_src, ip->ip_dst);
                                                break;
#endif
#ifdef INET6
                                        case AF_INET6:
                                                i = IN6_ARE_ADDR_EQUAL(&ip6->ip6_src, &ip6->ip6_dst);
                                                break;
#endif
                                        default:
                                                i = 1;
                                        }
                                        if (i) {
                                                TCP_STATINC(TCP_STAT_BADSYN);
                                                goto drop;
                                        }
                                }

                                /*
                                 * SYN looks ok; create compressed TCP
                                 * state for it.
                                 */
                                if (so->so_qlen <= so->so_qlimit &&
                                    syn_cache_add(&src.sa, &dst.sa, th, tlen,
                                                so, m, optp, optlen, &opti))
                                        m = NULL;
                        }
                        goto drop;
                }
        }

after_listen:
#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

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

        /*
         * Process options.
         */
#ifdef TCP_SIGNATURE
        if (optp || (tp->t_flags & TF_SIGNATURE))
#else
        if (optp)
#endif
                if (tcp_dooptions(tp, optp, optlen, th, m, toff, &opti) < 0)
                        goto drop;

        if (TCP_SACK_ENABLED(tp)) {
                tcp_del_sackholes(tp, th);
        }

        if (TCP_ECN_ALLOWED(tp)) {
                switch (iptos & IPTOS_ECN_MASK) {
                case IPTOS_ECN_CE:
                        tp->t_flags |= TF_ECN_SND_ECE;
                        TCP_STATINC(TCP_STAT_ECN_CE);
                        break;
                case IPTOS_ECN_ECT0:
                        TCP_STATINC(TCP_STAT_ECN_ECT);
                        break;
                case IPTOS_ECN_ECT1:
                        /* XXX: ignore for now -- rpaulo */
                        break;
                }

                if (tiflags & TH_CWR)
                        tp->t_flags &= ~TF_ECN_SND_ECE;

                /*
                 * Congestion experienced.
                 * Ignore if we are already trying to recover.
                 */
                if ((tiflags & TH_ECE) && SEQ_GEQ(tp->snd_una, tp->snd_recover))
                        tp->t_congctl->cong_exp(tp);
        }

        if (opti.ts_present && opti.ts_ecr) {
                /*
                 * Calculate the RTT from the returned time stamp and the
                 * connection's time base.  If the time stamp is later than
                 * the current time, or is extremely old, fall back to non-1323
                 * RTT calculation.  Since ts_ecr is unsigned, we can test both
                 * at the same time.
                 */
                ts_rtt = TCP_TIMESTAMP(tp) - opti.ts_ecr + 1;
                if (ts_rtt > TCP_PAWS_IDLE)
                        ts_rtt = 0;
        } else {
                ts_rtt = 0;
        }

        /*
         * 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 &&
            (tiflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ECE|TH_CWR|TH_ACK))
                == TH_ACK &&
            (!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.
                 * NOTE that the test is modified according to the latest
                 * proposal of the tcplw@cray.com list (Braden 1993/04/26).
                 *
                 * note that we already know
                 *      TSTMP_GEQ(opti.ts_val, tp->ts_recent)
                 */
                if (opti.ts_present &&
                    SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
                        tp->ts_recent_age = tcp_now;
                        tp->ts_recent = opti.ts_val;
                }

                if (tlen == 0) {
                        /* Ack prediction. */
                        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_partialacks < 0) {
                                /*
                                 * this is a pure ack for outstanding data.
                                 */
                                if (ts_rtt)
                                        tcp_xmit_timer(tp, ts_rtt);
                                else if (tp->t_rtttime &&
                                    SEQ_GT(th->th_ack, tp->t_rtseq))
                                        tcp_xmit_timer(tp,
                                          tcp_now - tp->t_rtttime);
                                acked = th->th_ack - tp->snd_una;
                                tcps = TCP_STAT_GETREF();
                                tcps[TCP_STAT_PREDACK]++;
                                tcps[TCP_STAT_RCVACKPACK]++;
                                tcps[TCP_STAT_RCVACKBYTE] += acked;
                                TCP_STAT_PUTREF();
                                nd6_hint(tp);

                                if (acked > (tp->t_lastoff - tp->t_inoff))
                                        tp->t_lastm = NULL;
                                sbdrop(&so->so_snd, acked);
                                tp->t_lastoff -= acked;

                                icmp_check(tp, th, acked);

                                tp->snd_una = th->th_ack;
                                tp->snd_fack = tp->snd_una;
                                if (SEQ_LT(tp->snd_high, tp->snd_una))
                                        tp->snd_high = 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/selnotify/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);

                                sowwakeup(so);
                                if (so->so_snd.sb_cc)
                                        (void) tcp_output(tp);
                                if (tcp_saveti)
                                        m_freem(tcp_saveti);
                                return;
                        }
                } else if (th->th_ack == tp->snd_una &&
                    TAILQ_FIRST(&tp->segq) == NULL &&
                    tlen <= sbspace(&so->so_rcv)) {
                        int newsize = 0;        /* automatic sockbuf scaling */

                        /*
                         * this is a pure, in-sequence data packet
                         * with nothing on the reassembly queue and
                         * we have enough buffer space to take it.
                         */
                        tp->rcv_nxt += tlen;
                        tcps = TCP_STAT_GETREF();
                        tcps[TCP_STAT_PREDDAT]++;
                        tcps[TCP_STAT_RCVPACK]++;
                        tcps[TCP_STAT_RCVBYTE] += tlen;
                        TCP_STAT_PUTREF();
                        nd6_hint(tp);

                /*
                 * Automatic sizing enables the performance of large buffers
                 * and most of the efficiency of small ones by only allocating
                 * space when it is needed.
                 *
                 * On the receive side the socket buffer memory is only rarely
                 * used to any significant extent.  This allows us to be much
                 * more aggressive in scaling the receive socket buffer.  For
                 * the case that the buffer space is actually used to a large
                 * extent and we run out of kernel memory we can simply drop
                 * the new segments; TCP on the sender will just retransmit it
                 * later.  Setting the buffer size too big may only consume too
                 * much kernel memory if the application doesn't read() from
                 * the socket or packet loss or reordering makes use of the
                 * reassembly queue.
                 *
                 * The criteria to step up the receive buffer one notch are:
                 *  1. the number of bytes received during the time it takes
                 *     one timestamp to be reflected back to us (the RTT);
                 *  2. received bytes per RTT is within seven eighth of the
                 *     current socket buffer size;
                 *  3. receive buffer size has not hit maximal automatic size;
                 *
                 * This algorithm does one step per RTT at most and only if
                 * we receive a bulk stream w/o packet losses or reorderings.
                 * Shrinking the buffer during idle times is not necessary as
                 * it doesn't consume any memory when idle.
                 *
                 * TODO: Only step up if the application is actually serving
                 * the buffer to better manage the socket buffer resources.
                 */
                        if (tcp_do_autorcvbuf &&
                            opti.ts_ecr &&
                            (so->so_rcv.sb_flags & SB_AUTOSIZE)) {
                                if (opti.ts_ecr > tp->rfbuf_ts &&
                                    opti.ts_ecr - tp->rfbuf_ts < PR_SLOWHZ) {
                                        if (tp->rfbuf_cnt >
                                            (so->so_rcv.sb_hiwat / 8 * 7) &&
                                            so->so_rcv.sb_hiwat <
                                            tcp_autorcvbuf_max) {
                                                newsize =
                                                    min(so->so_rcv.sb_hiwat +
                                                    tcp_autorcvbuf_inc,
                                                    tcp_autorcvbuf_max);
                                        }
                                        /* Start over with next RTT. */
                                        tp->rfbuf_ts = 0;
                                        tp->rfbuf_cnt = 0;
                                } else
                                        tp->rfbuf_cnt += tlen;  /* add up */
                        }

                        /*
                         * Drop TCP, IP headers and TCP options then add data
                         * to socket buffer.
                         */
                        if (so->so_state & SS_CANTRCVMORE)
                                m_freem(m);
                        else {
                                /*
                                 * Set new socket buffer size.
                                 * Give up when limit is reached.
                                 */
                                if (newsize)
                                        if (!sbreserve(&so->so_rcv,
                                            newsize, so))
                                                so->so_rcv.sb_flags &= ~SB_AUTOSIZE;
                                m_adj(m, toff + off);
                                sbappendstream(&so->so_rcv, m);
                        }
                        sorwakeup(so);
                        tcp_setup_ack(tp, th);
                        if (tp->t_flags & TF_ACKNOW)
                                (void) tcp_output(tp);
                        if (tcp_saveti)
                                m_freem(tcp_saveti);
                        return;
                }
        }

        /*
         * Compute mbuf offset to TCP data segment.
         */
        hdroptlen = toff + 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));
        }

        /* Reset receive buffer auto scaling when not in bulk receive mode. */
        tp->rfbuf_ts = 0;
        tp->rfbuf_cnt = 0;

        switch (tp->t_state) {
        /*
         * 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 seg contains a ECE and ECN support is enabled, the stream
         *          is ECN capable.
         *      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) {
                        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;
                        if (SEQ_LT(tp->snd_high, tp->snd_una))
                                tp->snd_high = tp->snd_una;
                        TCP_TIMER_DISARM(tp, TCPT_REXMT);

                        if ((tiflags & TH_ECE) && tcp_do_ecn) {
                                tp->t_flags |= TF_ECN_PERMIT;
                                TCP_STATINC(TCP_STAT_ECN_SHS);
                        }

                }
                tp->irs = th->th_seq;
                tcp_rcvseqinit(tp);
                tp->t_flags |= TF_ACKNOW;
                tcp_mss_from_peer(tp, opti.maxseg);

                /*
                 * Initialize the initial congestion window.  If we
                 * had to retransmit the SYN, we must initialize cwnd
                 * to 1 segment (i.e. the Loss Window).
                 */
                if (tp->t_flags & TF_SYN_REXMT)
                        tp->snd_cwnd = tp->t_peermss;
                else {
                        int ss = tcp_init_win;
#ifdef INET
                        if (inp != NULL && in_localaddr(inp->inp_faddr))
                                ss = tcp_init_win_local;
#endif
#ifdef INET6
                        if (in6p != NULL && in6_localaddr(&in6p->in6p_faddr))
                                ss = tcp_init_win_local;
#endif
                        tp->snd_cwnd = TCP_INITIAL_WINDOW(ss, tp->t_peermss);
                }

                tcp_rmx_rtt(tp);
                if (tiflags & TH_ACK) {
                        TCP_STATINC(TCP_STAT_CONNECTS);
                        soisconnected(so);
                        tcp_established(tp);
                        /* 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_REASS_LOCK(tp);
                        (void) tcp_reass(tp, NULL, (struct mbuf *)0, &tlen);
                        TCP_REASS_UNLOCK(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, tcp_now - tp->t_rtttime);
                } else
                        tp->t_state = TCPS_SYN_RECEIVED;

                /*
                 * 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;
                        tcps = TCP_STAT_GETREF();
                        tcps[TCP_STAT_RCVPACKAFTERWIN]++;
                        tcps[TCP_STAT_RCVBYTEAFTERWIN] += todrop;
                        TCP_STAT_PUTREF();
                }
                tp->snd_wl1 = th->th_seq - 1;
                tp->rcv_up = th->th_seq;
                goto step6;

        /*
         * If the state is SYN_RECEIVED:
         *      If seg contains an ACK, but not for our SYN, drop the input
         *      and generate an RST.  See page 36, rfc793
         */
        case TCPS_SYN_RECEIVED:
                if ((tiflags & TH_ACK) &&
                    (SEQ_LEQ(th->th_ack, tp->iss) ||
                     SEQ_GT(th->th_ack, tp->snd_max)))
                        goto dropwithreset;
                break;
        }

        /*
         * 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 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 (tcp_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 {
                        tcps = TCP_STAT_GETREF();
                        tcps[TCP_STAT_RCVDUPPACK]++;
                        tcps[TCP_STAT_RCVDUPBYTE] += tlen;
                        tcps[TCP_STAT_PAWSDROP]++;
                        TCP_STAT_PUTREF();
                        tcp_new_dsack(tp, th->th_seq, tlen);
                        goto dropafterack;
                }
        }

        todrop = tp->rcv_nxt - th->th_seq;
        dupseg = false;
        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;
                                th->th_urp = 0;
                        }
                        todrop--;
                }
                if (todrop > tlen ||
                    (todrop == tlen && (tiflags & TH_FIN) == 0)) {
                        /*
                         * Any valid FIN or RST must be to the left of the
                         * window.  At this point the FIN or RST must be a
                         * duplicate or out of sequence; drop it.
                         */
                        if (tiflags & TH_RST)
                                goto drop;
                        tiflags &= ~(TH_FIN|TH_RST);
                        /*
                         * Send an ACK to resynchronize and drop any data.
                         * But keep on processing for RST or ACK.
                         */
                        tp->t_flags |= TF_ACKNOW;
                        todrop = tlen;
                        dupseg = true;
                        tcps = TCP_STAT_GETREF();
                        tcps[TCP_STAT_RCVDUPPACK]++;
                        tcps[TCP_STAT_RCVDUPBYTE] += todrop;
                        TCP_STAT_PUTREF();
                } else if ((tiflags & TH_RST) &&
                           th->th_seq != tp->rcv_nxt) {
                        /*
                         * Test for reset before adjusting the sequence
                         * number for overlapping data.
                         */
                        goto dropafterack_ratelim;
                } else {
                        tcps = TCP_STAT_GETREF();
                        tcps[TCP_STAT_RCVPARTDUPPACK]++;
                        tcps[TCP_STAT_RCVPARTDUPBYTE] += todrop;
                        TCP_STAT_PUTREF();
                }
                tcp_new_dsack(tp, th->th_seq, 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);
                TCP_STATINC(TCP_STAT_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) {
                TCP_STATINC(TCP_STAT_RCVPACKAFTERWIN);
                if (todrop >= tlen) {
                        /*
                         * The segment actually starts after the window.
                         * th->th_seq + tlen - tp->rcv_nxt - tp->rcv_wnd >= tlen
                         * th->th_seq - tp->rcv_nxt - tp->rcv_wnd >= 0
                         * th->th_seq >= tp->rcv_nxt + tp->rcv_wnd
                         */
                        TCP_STATADD(TCP_STAT_RCVBYTEAFTERWIN, tlen);
                        /*
                         * If a new connection request is received
                         * while in TIME_WAIT, drop the old connection
                         * and start over if the sequence numbers
                         * are above the previous ones.
                         *
                         * NOTE: We will checksum the packet again, and
                         * so we need to put the header fields back into
                         * network order!
                         * XXX This kind of sucks, but we don't expect
                         * XXX this to happen very often, so maybe it
                         * XXX doesn't matter so much.
                         */
                        if (tiflags & TH_SYN &&
                            tp->t_state == TCPS_TIME_WAIT &&
                            SEQ_GT(th->th_seq, tp->rcv_nxt)) {
                                tp = tcp_close(tp);
                                tcp_fields_to_net(th);
                                goto findpcb;
                        }
                        /*
                         * If window is closed can only take segments at
                         * window edge, and have to drop data and PUSH from
                         * incoming segments.  Continue processing, but
                         * remember to ack.  Otherwise, drop segment
                         * and (if not RST) ack.
                         */
                        if (tp->rcv_wnd == 0 && th->th_seq == tp->rcv_nxt) {
                                tp->t_flags |= TF_ACKNOW;
                                TCP_STATINC(TCP_STAT_RCVWINPROBE);
                        } else
                                goto dropafterack;
                } else
                        TCP_STATADD(TCP_STAT_RCVBYTEAFTERWIN, todrop);
                m_adj(m, -todrop);
                tlen -= todrop;
                tiflags &= ~(TH_PUSH|TH_FIN);
        }

        /*
         * If last ACK falls within this segment's sequence numbers,
         *  record the timestamp.
         * NOTE: 
         * 1) That the test incorporates suggestions from the latest
         *    proposal of the tcplw@cray.com list (Braden 1993/04/26).
         * 2) That updating only on newer timestamps interferes with
         *    our earlier PAWS tests, so this check should be solely
         *    predicated on the sequence space of this segment.
         * 3) That we modify the segment boundary check to be 
         *        Last.ACK.Sent <= SEG.SEQ + SEG.Len  
         *    instead of RFC1323's
         *        Last.ACK.Sent < SEG.SEQ + SEG.Len,
         *    This modified check allows us to overcome RFC1323's
         *    limitations as described in Stevens TCP/IP Illustrated
         *    Vol. 2 p.869. In such cases, we can still calculate the
         *    RTT correctly when RCV.NXT == Last.ACK.Sent.
         */
        if (opti.ts_present &&
            SEQ_LEQ(th->th_seq, tp->last_ack_sent) &&
            SEQ_LEQ(tp->last_ack_sent, th->th_seq + tlen +
                    ((tiflags & (TH_SYN|TH_FIN)) != 0))) {
                tp->ts_recent_age = tcp_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->rcv_nxt)
                        goto dropafterack_ratelim;

                switch (tp->t_state) {
                case TCPS_SYN_RECEIVED:
                        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;
                        TCP_STATINC(TCP_STAT_DROPS);
                        tp = tcp_close(tp);
                        goto drop;

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

        /*
         * Since we've covered the SYN-SENT and SYN-RECEIVED states above
         * we must be in a synchronized state.  RFC791 states (under RST
         * generation) that any unacceptable segment (an out-of-order SYN
         * qualifies) received in a synchronized state must elicit only an
         * empty acknowledgment segment ... and the connection remains in
         * the same state.
         */
        if (tiflags & TH_SYN) {
                if (tp->rcv_nxt == th->th_seq) {
                        tcp_respond(tp, m, m, th, (tcp_seq)0, th->th_ack - 1,
                            TH_ACK);
                        if (tcp_saveti)
                                m_freem(tcp_saveti);
                        return;
                }

                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 if the ack ACKs our SYN then enter
         * ESTABLISHED state and continue processing, otherwise
         * send an RST.
         */
        case TCPS_SYN_RECEIVED:
                if (SEQ_GT(tp->snd_una, th->th_ack) ||
                    SEQ_GT(th->th_ack, tp->snd_max))
                        goto dropwithreset;
                TCP_STATINC(TCP_STAT_CONNECTS);
                soisconnected(so);
                tcp_established(tp);
                /* 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;
                }
                TCP_REASS_LOCK(tp);
                (void) tcp_reass(tp, NULL, (struct mbuf *)0, &tlen);
                TCP_REASS_UNLOCK(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:

                if (SEQ_LEQ(th->th_ack, tp->snd_una)) {
                        if (tlen == 0 && !dupseg && tiwin == tp->snd_wnd) {
                                TCP_STATINC(TCP_STAT_RCVDUPPACK);
                                /*
                                 * If we have outstanding data (other than
                                 * a window probe), this is a completely
                                 * duplicate ack (ie, window info didn't
                                 * change), the ack is the biggest we've
                                 * seen and we've seen exactly our rexmt
                                 * threshhold of them, assume a packet
                                 * has been dropped and retransmit it.
                                 * Kludge snd_nxt & the congestion
                                 * window so we send only this one
                                 * packet.
                                 */
                                if (TCP_TIMER_ISARMED(tp, TCPT_REXMT) == 0 ||
                                    th->th_ack != tp->snd_una)
                                        tp->t_dupacks = 0;
                                else if (tp->t_partialacks < 0 &&
                                         (++tp->t_dupacks == tcprexmtthresh ||
                                         TCP_FACK_FASTRECOV(tp))) {
                                        /*
                                         * Do the fast retransmit, and adjust
                                         * congestion control paramenters.
                                         */
                                        if (tp->t_congctl->fast_retransmit(tp, th)) {
                                                /* False fast retransmit */
                                                break;
                                        } else
                                                goto drop;
                                } else if (tp->t_dupacks > tcprexmtthresh) {
                                        tp->snd_cwnd += tp->t_segsz;
                                        (void) tcp_output(tp);
                                        goto drop;
                                }
                        } else {
                                /*
                                 * If the ack appears to be very old, only
                                 * allow data that is in-sequence.  This
                                 * makes it somewhat more difficult to insert
                                 * forged data by guessing sequence numbers.
                                 * Sent an ack to try to update the send
                                 * sequence number on the other side.
                                 */
                                if (tlen && th->th_seq != tp->rcv_nxt &&
                                    SEQ_LT(th->th_ack,
                                    tp->snd_una - tp->max_sndwnd))
                                        goto dropafterack;
                        }
                        break;
                }
                /*
                 * If the congestion window was inflated to account
                 * for the other side's cached packets, retract it.
                 */
                /* XXX: make SACK have his own congestion control
                 * struct -- rpaulo */
                if (TCP_SACK_ENABLED(tp))
                        tcp_sack_newack(tp, th);
                else
                        tp->t_congctl->fast_retransmit_newack(tp, th);
                if (SEQ_GT(th->th_ack, tp->snd_max)) {
                        TCP_STATINC(TCP_STAT_RCVACKTOOMUCH);
                        goto dropafterack;
                }
                acked = th->th_ack - tp->snd_una;
                tcps = TCP_STAT_GETREF();
                tcps[TCP_STAT_RCVACKPACK]++;
                tcps[TCP_STAT_RCVACKBYTE] += acked;
                TCP_STAT_PUTREF();

                /*
                 * 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 (ts_rtt)
                        tcp_xmit_timer(tp, ts_rtt);
                else if (tp->t_rtttime && SEQ_GT(th->th_ack, tp->t_rtseq))
                        tcp_xmit_timer(tp, tcp_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);
                        needoutput = 1;
                } else if (TCP_TIMER_ISARMED(tp, TCPT_PERSIST) == 0)
                        TCP_TIMER_ARM(tp, TCPT_REXMT, tp->t_rxtcur);

                /*
                 * New data has been acked, adjust the congestion window.
                 */
                tp->t_congctl->newack(tp, th);

                nd6_hint(tp);
                if (acked > so->so_snd.sb_cc) {
                        tp->snd_wnd -= so->so_snd.sb_cc;
                        sbdrop(&so->so_snd, (int)so->so_snd.sb_cc);
                        ourfinisacked = 1;
                } else {
                        if (acked > (tp->t_lastoff - tp->t_inoff))
                                tp->t_lastm = NULL;
                        sbdrop(&so->so_snd, acked);
                        tp->t_lastoff -= acked;
                        tp->snd_wnd -= acked;
                        ourfinisacked = 0;
                }
                sowwakeup(so);

                icmp_check(tp, th, acked);

                tp->snd_una = th->th_ack;
                if (SEQ_GT(tp->snd_una, tp->snd_fack))
                        tp->snd_fack = tp->snd_una;
                if (SEQ_LT(tp->snd_nxt, tp->snd_una))
                        tp->snd_nxt = tp->snd_una;
                if (SEQ_LT(tp->snd_high, tp->snd_una))
                        tp->snd_high = 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_state & SS_CANTRCVMORE) {
                                        soisdisconnected(so);
                                        if (tp->t_maxidle > 0)
                                                TCP_TIMER_ARM(tp, TCPT_2MSL,
                                                    tp->t_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 * PR_SLOWHZ * tcp_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 * PR_SLOWHZ * tcp_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)
                        TCP_STATINC(TCP_STAT_RCVWINUPD);
                tp->snd_wnd = tiwin;
                tp->snd_wl1 = th->th_seq;
                tp->snd_wl2 = th->th_ack;
                if (tp->snd_wnd > tp->max_sndwnd)
                        tp->max_sndwnd = tp->snd_wnd;
                needoutput = 1;
        }

        /*
         * Process segments with URG.
         */
        if ((tiflags & TH_URG) && th->th_urp &&
            TCPS_HAVERCVDFIN(tp->t_state) == 0) {
                /*
                 * This is a kludge, but if we receive and accept
                 * random urgent pointers, we'll crash in
                 * soreceive.  It's hard to imagine someone
                 * actually wanting to send this much urgent data.
                 */
                if (th->th_urp + so->so_rcv.sb_cc > sb_max) {
                        th->th_urp = 0;                 /* XXX */
                        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;
                        so->so_oobmark = so->so_rcv.sb_cc +
                            (tp->rcv_up - tp->rcv_nxt) - 1;
                        if (so->so_oobmark == 0)
                                so->so_state |= SS_RCVATMARK;
                        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
#ifdef SO_OOBINLINE
                     && (so->so_options & SO_OOBINLINE) == 0
#endif
                     )
                        tcp_pulloutofband(so, th, 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 acknowledgement 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) {
                /*
                 * 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).
                 */
                /* NOTE: this was TCP_REASS() macro, but used only once */
                TCP_REASS_LOCK(tp);
                if (th->th_seq == tp->rcv_nxt &&
                    TAILQ_FIRST(&tp->segq) == NULL &&
                    tp->t_state == TCPS_ESTABLISHED) {
                        tcp_setup_ack(tp, th);
                        tp->rcv_nxt += tlen;
                        tiflags = th->th_flags & TH_FIN;
                        tcps = TCP_STAT_GETREF();
                        tcps[TCP_STAT_RCVPACK]++;
                        tcps[TCP_STAT_RCVBYTE] += tlen;
                        TCP_STAT_PUTREF();
                        nd6_hint(tp);
                        if (so->so_state & SS_CANTRCVMORE)
                                m_freem(m);
                        else {
                                m_adj(m, hdroptlen);
                                sbappendstream(&(so)->so_rcv, m);
                        }
                        TCP_REASS_UNLOCK(tp);
                        sorwakeup(so);
                } else {
                        m_adj(m, hdroptlen);
                        tiflags = tcp_reass(tp, th, m, &tlen);
                        tp->t_flags |= TF_ACKNOW;
                        TCP_REASS_UNLOCK(tp);
                }

                /*
                 * Note the amount of data that peer has sent into
                 * our window, in order to estimate the sender's
                 * buffer size.
                 */
                len = so->so_rcv.sb_hiwat - (tp->rcv_adv - tp->rcv_nxt);
        } else {
                m_freem(m);
                m = NULL;
                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 * PR_SLOWHZ * tcp_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 * PR_SLOWHZ * tcp_msl);
                        break;
                }
        }
#ifdef TCP_DEBUG
        if (so->so_options & SO_DEBUG)
                tcp_trace(TA_INPUT, ostate, tp, tcp_saveti, 0);
#endif

        /*
         * Return any desired output.
         */
        if (needoutput || (tp->t_flags & TF_ACKNOW)) {
                (void) tcp_output(tp);
        }
        if (tcp_saveti)
                m_freem(tcp_saveti);
        return;

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

dropafterack:
        /*
         * Generate an ACK dropping incoming segment if it occupies
         * sequence space, where the ACK reflects our state.
         */
        if (tiflags & TH_RST)
                goto drop;
        goto dropafterack2;

dropafterack_ratelim:
        /*
         * We may want to rate-limit ACKs against SYN/RST attack.
         */
        if (ppsratecheck(&tcp_ackdrop_ppslim_last, &tcp_ackdrop_ppslim_count,
            tcp_ackdrop_ppslim) == 0) {
                /* XXX stat */
                goto drop;
        }
        /* ...fall into dropafterack2... */

dropafterack2:
        m_freem(m);
        tp->t_flags |= TF_ACKNOW;
        (void) tcp_output(tp);
        if (tcp_saveti)
                m_freem(tcp_saveti);
        return;

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,
            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.
         */
        if (tiflags & TH_RST)
                goto drop;

        switch (af) {
#ifdef INET6
        case AF_INET6:
                /* For following calls to tcp_respond */
                if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst))
                        goto drop;
                break;
#endif /* INET6 */
        case AF_INET:
                if (IN_MULTICAST(ip->ip_dst.s_addr) ||
                    in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
                        goto drop;
        }

        if (tiflags & TH_ACK)
                (void)tcp_respond(tp, m, m, th, (tcp_seq)0, th->th_ack, TH_RST);
        else {
                if (tiflags & TH_SYN)
                        tlen++;
                (void)tcp_respond(tp, m, m, th, th->th_seq + tlen, (tcp_seq)0,
                    TH_RST|TH_ACK);
        }
        if (tcp_saveti)
                m_freem(tcp_saveti);
        return;

badcsum:
drop:
        /*
         * Drop space held by incoming segment and return.
         */
        if (tp) {
                if (tp->t_inpcb)
                        so = tp->t_inpcb->inp_socket;
#ifdef INET6
                else if (tp->t_in6pcb)
                        so = tp->t_in6pcb->in6p_socket;
#endif
                else
                        so = NULL;
#ifdef TCP_DEBUG
                if (so && (so->so_options & SO_DEBUG) != 0)
                        tcp_trace(TA_DROP, ostate, tp, tcp_saveti, 0);
#endif
        }
        if (tcp_saveti)
                m_freem(tcp_saveti);
        m_freem(m);
        return;
}

#ifdef TCP_SIGNATURE
int
tcp_signature_apply(void *fstate, void *data, u_int len)
{

        MD5Update(fstate, (u_char *)data, len);
        return (0);
}

struct secasvar *
tcp_signature_getsav(struct mbuf *m, struct tcphdr *th)
{
        struct secasvar *sav;
#ifdef FAST_IPSEC
        union sockaddr_union dst;
#endif
        struct ip *ip;
        struct ip6_hdr *ip6;

        ip = mtod(m, struct ip *);
        switch (ip->ip_v) {
        case 4:
                ip = mtod(m, struct ip *);
                ip6 = NULL;
                break;
        case 6:
                ip = NULL;
                ip6 = mtod(m, struct ip6_hdr *);
                break;
        default:
                return (NULL);
        }

#ifdef FAST_IPSEC
        /* Extract the destination from the IP header in the mbuf. */
        memset(&dst, 0, sizeof(union sockaddr_union));
        if (ip !=NULL) {
                dst.sa.sa_len = sizeof(struct sockaddr_in);
                dst.sa.sa_family = AF_INET;
                dst.sin.sin_addr = ip->ip_dst;
        } else {
                dst.sa.sa_len = sizeof(struct sockaddr_in6);
                dst.sa.sa_family = AF_INET6;
                dst.sin6.sin6_addr = ip6->ip6_dst;
        }

        /*
         * Look up an SADB entry which matches the address of the peer.
         */
        sav = KEY_ALLOCSA(&dst, IPPROTO_TCP, htonl(TCP_SIG_SPI));
#else
        if (ip)
                sav = key_allocsa(AF_INET, (void *)&ip->ip_src,
                    (void *)&ip->ip_dst, IPPROTO_TCP,
                    htonl(TCP_SIG_SPI), 0, 0);
        else
                sav = key_allocsa(AF_INET6, (void *)&ip6->ip6_src,
                    (void *)&ip6->ip6_dst, IPPROTO_TCP,
                    htonl(TCP_SIG_SPI), 0, 0);
#endif

        return (sav);   /* freesav must be performed by caller */
}

int
tcp_signature(struct mbuf *m, struct tcphdr *th, int thoff,
    struct secasvar *sav, char *sig)
{
        MD5_CTX ctx;
        struct ip *ip;
        struct ipovly *ipovly;
        struct ip6_hdr *ip6;
        struct ippseudo ippseudo;
        struct ip6_hdr_pseudo ip6pseudo;
        struct tcphdr th0;
        int l, tcphdrlen;

        if (sav == NULL)
                return (-1);

        tcphdrlen = th->th_off * 4;

        switch (mtod(m, struct ip *)->ip_v) {
        case 4:
                ip = mtod(m, struct ip *);
                ip6 = NULL;
                break;
        case 6:
                ip = NULL;
                ip6 = mtod(m, struct ip6_hdr *);
                break;
        default:
                return (-1);
        }

        MD5Init(&ctx);

        if (ip) {
                memset(&ippseudo, 0, sizeof(ippseudo));
                ipovly = (struct ipovly *)ip;
                ippseudo.ippseudo_src = ipovly->ih_src;
                ippseudo.ippseudo_dst = ipovly->ih_dst;
                ippseudo.ippseudo_pad = 0;
                ippseudo.ippseudo_p = IPPROTO_TCP;
                ippseudo.ippseudo_len = htons(m->m_pkthdr.len - thoff);
                MD5Update(&ctx, (char *)&ippseudo, sizeof(ippseudo));
        } else {
                memset(&ip6pseudo, 0, sizeof(ip6pseudo));
                ip6pseudo.ip6ph_src = ip6->ip6_src;
                in6_clearscope(&ip6pseudo.ip6ph_src);
                ip6pseudo.ip6ph_dst = ip6->ip6_dst;
                in6_clearscope(&ip6pseudo.ip6ph_dst);
                ip6pseudo.ip6ph_len = htons(m->m_pkthdr.len - thoff);
                ip6pseudo.ip6ph_nxt = IPPROTO_TCP;
                MD5Update(&ctx, (char *)&ip6pseudo, sizeof(ip6pseudo));
        }

        th0 = *th;
        th0.th_sum = 0;
        MD5Update(&ctx, (char *)&th0, sizeof(th0));

        l = m->m_pkthdr.len - thoff - tcphdrlen;
        if (l > 0)
                m_apply(m, thoff + tcphdrlen,
                    m->m_pkthdr.len - thoff - tcphdrlen,
                    tcp_signature_apply, &ctx);

        MD5Update(&ctx, _KEYBUF(sav->key_auth), _KEYLEN(sav->key_auth));
        MD5Final(sig, &ctx);

        return (0);
}
#endif

static int
tcp_dooptions(struct tcpcb *tp, const u_char *cp, int cnt,
    struct tcphdr *th,
    struct mbuf *m, int toff, struct tcp_opt_info *oi)
{
        u_int16_t mss;
        int opt, optlen = 0;
#ifdef TCP_SIGNATURE
        void *sigp = NULL;
        char sigbuf[TCP_SIGLEN];
        struct secasvar *sav = 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;
                        bcopy(cp + 2, &mss, sizeof(mss));
                        oi->maxseg = ntohs(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 = cp[2];
                        if (tp->requested_s_scale > TCP_MAX_WINSHIFT) {
#if 0   /*XXX*/
                                char *p;

                                if (ip)
                                        p = ntohl(ip->ip_src);
#ifdef INET6
                                else if (ip6)
                                        p = ip6_sprintf(&ip6->ip6_src);
#endif
                                else
                                        p = "(unknown)";
                                log(LOG_ERR, "TCP: invalid wscale %d from %s, "
                                    "assuming %d\n",
                                    tp->requested_s_scale, p,
                                    TCP_MAX_WINSHIFT);
#else
                                log(LOG_ERR, "TCP: invalid wscale %d, "
                                    "assuming %d\n",
                                    tp->requested_s_scale,
                                    TCP_MAX_WINSHIFT);
#endif
                                tp->requested_s_scale = TCP_MAX_WINSHIFT;
                        }
                        break;

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

                case TCPOPT_SACK_PERMITTED:
                        if (optlen != TCPOLEN_SACK_PERMITTED)
                                continue;
                        if (!(th->th_flags & TH_SYN))
                                continue;
                        if (TCPS_HAVERCVDSYN(tp->t_state))
                                continue;
                        if (tcp_do_sack) {
                                tp->t_flags |= TF_SACK_PERMIT;
                                tp->t_flags |= TF_WILL_SACK;
                        }
                        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 && memcmp(sigp, cp + 2, TCP_SIGLEN))
                                return (-1);

                        sigp = sigbuf;
                        memcpy(sigbuf, cp + 2, TCP_SIGLEN);
                        tp->t_flags |= TF_SIGNATURE;
                        break;
#endif
                }
        }

#ifdef TCP_SIGNATURE
        if (tp->t_flags & TF_SIGNATURE) {

                sav = tcp_signature_getsav(m, th);

                if (sav == NULL && tp->t_state == TCPS_LISTEN)
                        return (-1);
        }

        if ((sigp ? TF_SIGNATURE : 0) ^ (tp->t_flags & TF_SIGNATURE)) {
                if (sav == NULL)
                        return (-1);
#ifdef FAST_IPSEC
                KEY_FREESAV(&sav);
#else
                key_freesav(sav);
#endif
                return (-1);
        }

        if (sigp) {
                char sig[TCP_SIGLEN];

                tcp_fields_to_net(th);
                if (tcp_signature(m, th, toff, sav, sig) < 0) {
                        tcp_fields_to_host(th);
                        if (sav == NULL)
                                return (-1);
#ifdef FAST_IPSEC
                        KEY_FREESAV(&sav);
#else
                        key_freesav(sav);
#endif
                        return (-1);
                }
                tcp_fields_to_host(th);

                if (memcmp(sig, sigp, TCP_SIGLEN)) {
                        TCP_STATINC(TCP_STAT_BADSIG);
                        if (sav == NULL)
                                return (-1);
#ifdef FAST_IPSEC
                        KEY_FREESAV(&sav);
#else
                        key_freesav(sav);
#endif
                        return (-1);
                } else
                        TCP_STATINC(TCP_STAT_GOODSIG);

                key_sa_recordxfer(sav, m);
#ifdef FAST_IPSEC
                KEY_FREESAV(&sav);
#else
                key_freesav(sav);
#endif
        }
#endif

        return (0);
}

/*
 * 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, struct tcphdr *th,
    struct mbuf *m, int off)
{
        int cnt = off + th->th_urp - 1;

        while (cnt >= 0) {
                if (m->m_len > cnt) {
                        char *cp = mtod(m, char *) + cnt;
                        struct tcpcb *tp = sototcpcb(so);

                        tp->t_iobc = *cp;
                        tp->t_oobflags |= TCPOOB_HAVEDATA;
                        bcopy(cp+1, cp, (unsigned)(m->m_len - cnt - 1));
                        m->m_len--;
                        return;
                }
                cnt -= m->m_len;
                m = m->m_next;
                if (m == 0)
                        break;
        }
        panic("tcp_pulloutofband");
}

/*
 * Collect new round-trip time estimate
 * and update averages and current timeout.
 */
void
tcp_xmit_timer(struct tcpcb *tp, uint32_t rtt)
{
        int32_t delta;

        TCP_STATINC(TCP_STAT_RTTUPDATED);
        if (tp->t_srtt != 0) {
                /*
                 * srtt is stored as fixed point with 3 bits after the
                 * binary point (i.e., scaled by 8).  The following magic
                 * is equivalent to the smoothing algorithm in rfc793 with
                 * an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed
                 * point).  Adjust rtt to origin 0.
                 */
                delta = (rtt << 2) - (tp->t_srtt >> TCP_RTT_SHIFT);
                if ((tp->t_srtt += delta) <= 0)
                        tp->t_srtt = 1 << 2;
                /*
                 * 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 2 bits after the
                 * binary point (scaled by 4).  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 << 2;
        } else {
                /*
                 * No rtt measurement yet - use the unsmoothed rtt.
                 * Set the variance to half the rtt (so our first
                 * retransmit happens at 3*rtt).
                 */
                tp->t_srtt = rtt << (TCP_RTT_SHIFT + 2);
                tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT + 2 - 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).
         */
        TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp),
            max(tp->t_rttmin, rtt + 2), TCPTV_REXMTMAX);

        /*
         * We received an ack for a packet that wasn't retransmitted;
         * it is probably safe to discard any error indications we've
         * received recently.  This isn't quite right, but close enough
         * for now (a route might have failed after we sent a segment,
         * and the return path might not be symmetrical).
         */
        tp->t_softerror = 0;
}


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

u_long  syn_cache_count;
u_int32_t syn_hash1, syn_hash2;

#define SYN_HASH(sa, sp, dp) \
        ((((sa)->s_addr^syn_hash1)*(((((u_int32_t)(dp))<<16) + \
                                     ((u_int32_t)(sp)))^syn_hash2)))
#ifndef INET6
#define SYN_HASHALL(hash, src, dst) \
do {                                                                    \
        hash = SYN_HASH(&((const struct sockaddr_in *)(src))->sin_addr, \
                ((const struct sockaddr_in *)(src))->sin_port,          \
                ((const struct sockaddr_in *)(dst))->sin_port);         \
} while (/*CONSTCOND*/ 0)
#else
#define SYN_HASH6(sa, sp, dp) \
        ((((sa)->s6_addr32[0] ^ (sa)->s6_addr32[3] ^ syn_hash1) * \
          (((((u_int32_t)(dp))<<16) + ((u_int32_t)(sp)))^syn_hash2)) \
         & 0x7fffffff)

#define SYN_HASHALL(hash, src, dst) \
do {                                                                    \
        switch ((src)->sa_family) {                                     \
        case AF_INET:                                                   \
                hash = SYN_HASH(&((const struct sockaddr_in *)(src))->sin_addr, \
                        ((const struct sockaddr_in *)(src))->sin_port,  \
                        ((const struct sockaddr_in *)(dst))->sin_port); \
                break;                                                  \
        case AF_INET6:                                                  \
                hash = SYN_HASH6(&((const struct sockaddr_in6 *)(src))->sin6_addr, \
                        ((const struct sockaddr_in6 *)(src))->sin6_port,        \
                        ((const struct sockaddr_in6 *)(dst))->sin6_port);       \
                break;                                                  \
        default:                                                        \
                hash = 0;                                               \
        }                                                               \
} while (/*CONSTCOND*/0)
#endif /* INET6 */

static struct pool syn_cache_pool;

/*
 * We don't estimate RTT with SYNs, so each packet starts with the default
 * RTT and each timer step has a fixed timeout value.
 */
#define SYN_CACHE_TIMER_ARM(sc)                                         \
do {                                                                    \
        TCPT_RANGESET((sc)->sc_rxtcur,                                  \
            TCPTV_SRTTDFLT * tcp_backoff[(sc)->sc_rxtshift], TCPTV_MIN, \
            TCPTV_REXMTMAX);                                            \
        callout_reset(&(sc)->sc_timer,                                  \
            (sc)->sc_rxtcur * (hz / PR_SLOWHZ), syn_cache_timer, (sc)); \
} while (/*CONSTCOND*/0)

#define SYN_CACHE_TIMESTAMP(sc) (tcp_now - (sc)->sc_timebase)

static inline void
syn_cache_rm(struct syn_cache *sc)
{
        TAILQ_REMOVE(&tcp_syn_cache[sc->sc_bucketidx].sch_bucket,
            sc, sc_bucketq);
        sc->sc_tp = NULL;
        LIST_REMOVE(sc, sc_tpq);
        tcp_syn_cache[sc->sc_bucketidx].sch_length--;
        callout_stop(&sc->sc_timer);
        syn_cache_count--;
}

static inline void
syn_cache_put(struct syn_cache *sc)
{
        if (sc->sc_ipopts)
                (void) m_free(sc->sc_ipopts);
        rtcache_free(&sc->sc_route);
        if (callout_invoking(&sc->sc_timer))
                sc->sc_flags |= SCF_DEAD;
        else {
                callout_destroy(&sc->sc_timer);
                pool_put(&syn_cache_pool, sc);
        }
}

void
syn_cache_init(void)
{
        int i;

        pool_init(&syn_cache_pool, sizeof(struct syn_cache), 0, 0, 0,
            "synpl", NULL, IPL_SOFTNET);

        /* Initialize the hash buckets. */
        for (i = 0; i < tcp_syn_cache_size; i++)
                TAILQ_INIT(&tcp_syn_cache[i].sch_bucket);
}

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

        /*
         * If there are no entries in the hash table, reinitialize
         * the hash secrets.
         */
        if (syn_cache_count == 0) {
                syn_hash1 = arc4random();
                syn_hash2 = arc4random();
        }

        SYN_HASHALL(sc->sc_hash, &sc->sc_src.sa, &sc->sc_dst.sa);
        sc->sc_bucketidx = sc->sc_hash % tcp_syn_cache_size;
        scp = &tcp_syn_cache[sc->sc_bucketidx];

        /*
         * Make sure that we don't overflow the per-bucket
         * limit or the total cache size limit.
         */
        s = splsoftnet();
        if (scp->sch_length >= tcp_syn_bucket_limit) {
                TCP_STATINC(TCP_STAT_SC_BUCKETOVERFLOW);
                /*
                 * 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("syn_cache_insert: bucketoverflow: impossible");
#endif
                syn_cache_rm(sc2);
                syn_cache_put(sc2);     /* calls pool_put but see spl above */
        } else if (syn_cache_count >= tcp_syn_cache_limit) {
                struct syn_cache_head *scp2, *sce;

                TCP_STATINC(TCP_STAT_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 = &tcp_syn_cache[tcp_syn_cache_size];
                        for (++scp2; scp2 != scp; scp2++) {
                                if (scp2 >= sce)
                                        scp2 = &tcp_syn_cache[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("syn_cache_insert: cacheoverflow: "
                                    "impossible");
#endif
                }
                sc2 = TAILQ_FIRST(&scp2->sch_bucket);
                syn_cache_rm(sc2);
                syn_cache_put(sc2);     /* calls pool_put but see spl above */
        }

        /*
         * Initialize the entry's timer.
         */
        sc->sc_rxttot = 0;
        sc->sc_rxtshift = 0;
        SYN_CACHE_TIMER_ARM(sc);

        /* Link it from tcpcb entry */
        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++;
        syn_cache_count++;

        TCP_STATINC(TCP_STAT_SC_ADDED);
        splx(s);
}

/*
 * 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;

        mutex_enter(softnet_lock);
        KERNEL_LOCK(1, NULL);
        callout_ack(&sc->sc_timer);

        if (__predict_false(sc->sc_flags & SCF_DEAD)) {
                TCP_STATINC(TCP_STAT_SC_DELAYED_FREE);
                callout_destroy(&sc->sc_timer);
                pool_put(&syn_cache_pool, sc);
                KERNEL_UNLOCK_ONE(NULL);
                mutex_exit(softnet_lock);
                return;
        }

        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 >= tcp_keepinit)
                goto dropit;

        TCP_STATINC(TCP_STAT_SC_RETRANSMITTED);
        (void) syn_cache_respond(sc, NULL);

        /* Advance the timer back-off. */
        sc->sc_rxtshift++;
        SYN_CACHE_TIMER_ARM(sc);

        KERNEL_UNLOCK_ONE(NULL);
        mutex_exit(softnet_lock);
        return;

 dropit:
        TCP_STATINC(TCP_STAT_SC_TIMED_OUT);
        syn_cache_rm(sc);
        syn_cache_put(sc);      /* calls pool_put but see spl above */
        KERNEL_UNLOCK_ONE(NULL);
        mutex_exit(softnet_lock);
}

/*
 * 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;
        int s;

        s = splsoftnet();

        for (sc = LIST_FIRST(&tp->t_sc); sc != NULL; sc = nsc) {
                nsc = LIST_NEXT(sc, sc_tpq);

#ifdef DIAGNOSTIC
                if (sc->sc_tp != tp)
                        panic("invalid sc_tp in syn_cache_cleanup");
#endif
                syn_cache_rm(sc);
                syn_cache_put(sc);      /* calls pool_put but see spl above */
        }
        /* just for safety */
        LIST_INIT(&tp->t_sc);

        splx(s);
}

/*
 * 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)
{
        struct syn_cache *sc;
        struct syn_cache_head *scp;
        u_int32_t hash;
        int s;

        SYN_HASHALL(hash, src, dst);

        scp = &tcp_syn_cache[hash % tcp_syn_cache_size];
        *headp = scp;
        s = splsoftnet();
        for (sc = TAILQ_FIRST(&scp->sch_bucket); sc != NULL;
             sc = TAILQ_NEXT(sc, sc_bucketq)) {
                if (sc->sc_hash != hash)
                        continue;
                if (!memcmp(&sc->sc_src, src, src->sa_len) &&
                    !memcmp(&sc->sc_dst, dst, dst->sa_len)) {
                        splx(s);
                        return (sc);
                }
        }
        splx(s);
        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 screwey sequence numbners; 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, unsigned int hlen, unsigned int tlen,
    struct socket *so, struct mbuf *m)
{
        struct syn_cache *sc;
        struct syn_cache_head *scp;
        struct inpcb *inp = NULL;
#ifdef INET6
        struct in6pcb *in6p = NULL;
#endif
        struct tcpcb *tp = 0;
        struct mbuf *am;
        int s;
        struct socket *oso;

        s = splsoftnet();
        if ((sc = syn_cache_lookup(src, dst, &scp)) == NULL) {
                splx(s);
                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)) {
                (void) syn_cache_respond(sc, m);
                splx(s);
                return ((struct socket *)(-1));
        }

        /* Remove this cache entry */
        syn_cache_rm(sc);
        splx(s);

        /*
         * 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.
         */
        /*
         * inp still has the OLD in_pcb stuff, set the
         * v6-related flags on the new guy, too.   This is
         * done particularly for the case where an AF_INET6
         * socket is bound only to a port, and a v4 connection
         * comes in on that port.
         * we also copy the flowinfo from the original pcb
         * to the new one.
         */
        oso = so;
        so = sonewconn(so, SS_ISCONNECTED);
        if (so == NULL)
                goto resetandabort;

        switch (so->so_proto->pr_domain->dom_family) {
#ifdef INET
        case AF_INET:
                inp = sotoinpcb(so);
                break;
#endif
#ifdef INET6
        case AF_INET6:
                in6p = sotoin6pcb(so);
                break;
#endif
        }
        switch (src->sa_family) {
#ifdef INET
        case AF_INET:
                if (inp) {
                        inp->inp_laddr = ((struct sockaddr_in *)dst)->sin_addr;
                        inp->inp_lport = ((struct sockaddr_in *)dst)->sin_port;
                        inp->inp_options = ip_srcroute();
                        in_pcbstate(inp, INP_BOUND);
                        if (inp->inp_options == NULL) {
                                inp->inp_options = sc->sc_ipopts;
                                sc->sc_ipopts = NULL;
                        }
                }
#ifdef INET6
                else if (in6p) {
                        /* IPv4 packet to AF_INET6 socket */
                        memset(&in6p->in6p_laddr, 0, sizeof(in6p->in6p_laddr));
                        in6p->in6p_laddr.s6_addr16[5] = htons(0xffff);
                        bcopy(&((struct sockaddr_in *)dst)->sin_addr,
                                &in6p->in6p_laddr.s6_addr32[3],
                                sizeof(((struct sockaddr_in *)dst)->sin_addr));
                        in6p->in6p_lport = ((struct sockaddr_in *)dst)->sin_port;
                        in6totcpcb(in6p)->t_family = AF_INET;
                        if (sotoin6pcb(oso)->in6p_flags & IN6P_IPV6_V6ONLY)
                                in6p->in6p_flags |= IN6P_IPV6_V6ONLY;
                        else
                                in6p->in6p_flags &= ~IN6P_IPV6_V6ONLY;
                        in6_pcbstate(in6p, IN6P_BOUND);
                }
#endif
                break;
#endif
#ifdef INET6
        case AF_INET6:
                if (in6p) {
                        in6p->in6p_laddr = ((struct sockaddr_in6 *)dst)->sin6_addr;
                        in6p->in6p_lport = ((struct sockaddr_in6 *)dst)->sin6_port;
                        in6_pcbstate(in6p, IN6P_BOUND);
                }
                break;
#endif
        }
#ifdef INET6
        if (in6p && in6totcpcb(in6p)->t_family == AF_INET6 && sotoinpcb(oso)) {
                struct in6pcb *oin6p = sotoin6pcb(oso);
                /* inherit socket options from the listening socket */
                in6p->in6p_flags |= (oin6p->in6p_flags & IN6P_CONTROLOPTS);
                if (in6p->in6p_flags & IN6P_CONTROLOPTS) {
                        m_freem(in6p->in6p_options);
                        in6p->in6p_options = 0;
                }
                ip6_savecontrol(in6p, &in6p->in6p_options,
                        mtod(m, struct ip6_hdr *), m);
        }
#endif

#if defined(IPSEC) || defined(FAST_IPSEC)
        /*
         * we make a copy of policy, instead of sharing the policy,
         * for better behavior in terms of SA lookup and dead SA removal.
         */
        if (inp) {
                /* copy old policy into new socket's */
                if (ipsec_copy_pcbpolicy(sotoinpcb(oso)->inp_sp, inp->inp_sp))
                        printf("tcp_input: could not copy policy\n");
        }
#ifdef INET6
        else if (in6p) {
                /* copy old policy into new socket's */
                if (ipsec_copy_pcbpolicy(sotoin6pcb(oso)->in6p_sp,
                    in6p->in6p_sp))
                        printf("tcp_input: could not copy policy\n");
        }
#endif
#endif

        /*
         * Give the new socket our cached route reference.
         */
        if (inp) {
                rtcache_copy(&inp->inp_route, &sc->sc_route);
                rtcache_free(&sc->sc_route);
        }
#ifdef INET6
        else {
                rtcache_copy(&in6p->in6p_route, &sc->sc_route);
                rtcache_free(&sc->sc_route);
        }
#endif

        am = m_get(M_DONTWAIT, MT_SONAME);      /* XXX */
        if (am == NULL)
                goto resetandabort;
        MCLAIM(am, &tcp_mowner);
        am->m_len = src->sa_len;
        bcopy(src, mtod(am, void *), src->sa_len);
        if (inp) {
                if (in_pcbconnect(inp, am, &lwp0)) {
                        (void) m_free(am);
                        goto resetandabort;
                }
        }
#ifdef INET6
        else if (in6p) {
                if (src->sa_family == AF_INET) {
                        /* IPv4 packet to AF_INET6 socket */
                        struct sockaddr_in6 *sin6;
                        sin6 = mtod(am, struct sockaddr_in6 *);
                        am->m_len = sizeof(*sin6);
                        memset(sin6, 0, sizeof(*sin6));
                        sin6->sin6_family = AF_INET6;
                        sin6->sin6_len = sizeof(*sin6);
                        sin6->sin6_port = ((struct sockaddr_in *)src)->sin_port;
                        sin6->sin6_addr.s6_addr16[5] = htons(0xffff);
                        bcopy(&((struct sockaddr_in *)src)->sin_addr,
                                &sin6->sin6_addr.s6_addr32[3],
                                sizeof(sin6->sin6_addr.s6_addr32[3]));
                }
                if (in6_pcbconnect(in6p, am, NULL)) {
                        (void) m_free(am);
                        goto resetandabort;
                }
        }
#endif
        else {
                (void) m_free(am);
                goto resetandabort;
        }
        (void) m_free(am);

        if (inp)
                tp = intotcpcb(inp);
#ifdef INET6
        else if (in6p)
                tp = in6totcpcb(in6p);
#endif
        else
                tp = NULL;
        tp->t_flags = sototcpcb(oso)->t_flags & 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->snd_scale = sc->sc_requested_s_scale;
                tp->rcv_scale = sc->sc_request_r_scale;
                tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE;
        }
        if (sc->sc_flags & SCF_TIMESTAMP)
                tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP;
        tp->ts_timebase = sc->sc_timebase;

        tp->t_template = tcp_template(tp);
        if (tp->t_template == 0) {
                tp = tcp_drop(tp, ENOBUFS);     /* destroys socket */
                so = NULL;
                m_freem(m);
                goto abort;
        }

        tp->iss = sc->sc_iss;
        tp->irs = sc->sc_irs;
        tcp_sendseqinit(tp);
        tcp_rcvseqinit(tp);
        tp->t_state = TCPS_SYN_RECEIVED;
        TCP_TIMER_ARM(tp, TCPT_KEEP, tp->t_keepinit);
        TCP_STATINC(TCP_STAT_ACCEPTS);

        if ((sc->sc_flags & SCF_SACK_PERMIT) && tcp_do_sack)
                tp->t_flags |= TF_WILL_SACK;

        if ((sc->sc_flags & SCF_ECN_PERMIT) && tcp_do_ecn)
                tp->t_flags |= TF_ECN_PERMIT;

#ifdef TCP_SIGNATURE
        if (sc->sc_flags & SCF_SIGNATURE)
                tp->t_flags |= TF_SIGNATURE;
#endif

        /* Initialize tp->t_ourmss before we deal with the peer's! */
        tp->t_ourmss = sc->sc_ourmaxseg;
        tcp_mss_from_peer(tp, sc->sc_peermaxseg);

        /*
         * Initialize the initial congestion window.  If we
         * had to retransmit the SYN,ACK, we must initialize cwnd
         * to 1 segment (i.e. the Loss Window).
         */
        if (sc->sc_rxtshift)
                tp->snd_cwnd = tp->t_peermss;
        else {
                int ss = tcp_init_win;
#ifdef INET
                if (inp != NULL && in_localaddr(inp->inp_faddr))
                        ss = tcp_init_win_local;
#endif
#ifdef INET6
                if (in6p != NULL && in6_localaddr(&in6p->in6p_faddr))
                        ss = tcp_init_win_local;
#endif
                tp->snd_cwnd = TCP_INITIAL_WINDOW(ss, tp->t_peermss);
        }

        tcp_rmx_rtt(tp);
        tp->snd_wl1 = sc->sc_irs;
        tp->rcv_up = sc->sc_irs + 1;

        /*
         * This is what whould 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;
        tp->t_partialacks = -1;
        tp->t_dupacks = 0;

        TCP_STATINC(TCP_STAT_SC_COMPLETED);
        s = splsoftnet();
        syn_cache_put(sc);
        splx(s);
        return (so);

resetandabort:
        (void)tcp_respond(NULL, m, m, th, (tcp_seq)0, th->th_ack, TH_RST);
abort:
        if (so != NULL) {
                (void) soqremque(so, 1);
                (void) soabort(so);
                mutex_enter(softnet_lock);
        }
        s = splsoftnet();
        syn_cache_put(sc);
        splx(s);
        TCP_STATINC(TCP_STAT_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)
{
        struct syn_cache *sc;
        struct syn_cache_head *scp;
        int s = splsoftnet();

        if ((sc = syn_cache_lookup(src, dst, &scp)) == NULL) {
                splx(s);
                return;
        }
        if (SEQ_LT(th->th_seq, sc->sc_irs) ||
            SEQ_GT(th->th_seq, sc->sc_irs+1)) {
                splx(s);
                return;
        }
        syn_cache_rm(sc);
        TCP_STATINC(TCP_STAT_SC_RESET);
        syn_cache_put(sc);      /* calls pool_put but see spl above */
        splx(s);
}

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

        s = splsoftnet();
        if ((sc = syn_cache_lookup(src, dst, &scp)) == NULL) {
                splx(s);
                return;
        }
        /* If the sequence number != sc_iss, then it's a bogus ICMP msg */
        if (ntohl (th->th_seq) != sc->sc_iss) {
                splx(s);
                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 ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxtshift < 3) {
                sc->sc_flags |= SCF_UNREACH;
                splx(s);
                return;
        }

        syn_cache_rm(sc);
        TCP_STATINC(TCP_STAT_SC_UNREACH);
        syn_cache_put(sc);      /* calls pool_put but see spl above */
        splx(s);
}

/*
 * 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,
    unsigned int hlen, struct socket *so, struct mbuf *m, u_char *optp,
    int optlen, struct tcp_opt_info *oi)
{
        struct tcpcb tb, *tp;
        long win;
        struct syn_cache *sc;
        struct syn_cache_head *scp;
        struct mbuf *ipopts;
        struct tcp_opt_info opti;
        int s;

        tp = sototcpcb(so);

        memset(&opti, 0, sizeof(opti));

        /*
         * 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;

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

#ifdef TCP_SIGNATURE
        if (optp || (tp->t_flags & TF_SIGNATURE))
#else
        if (optp)
#endif
        {
                tb.t_flags = tcp_do_rfc1323 ? (TF_REQ_SCALE|TF_REQ_TSTMP) : 0;
#ifdef TCP_SIGNATURE
                tb.t_flags |= (tp->t_flags & TF_SIGNATURE);
#endif
                tb.t_state = TCPS_LISTEN;
                if (tcp_dooptions(&tb, optp, optlen, th, m, m->m_pkthdr.len -
                    sizeof(struct tcphdr) - optlen - hlen, oi) < 0)
                        return (0);
        } else
                tb.t_flags = 0;

        /*
         * 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).
         */
        if ((sc = syn_cache_lookup(src, dst, &scp)) != NULL) {
                TCP_STATINC(TCP_STAT_SC_DUPESYN);
                if (ipopts) {
                        /*
                         * If we were remembering a previous source route,
                         * forget it and use the new one we've been given.
                         */
                        if (sc->sc_ipopts)
                                (void) m_free(sc->sc_ipopts);
                        sc->sc_ipopts = ipopts;
                }
                sc->sc_timestamp = tb.ts_recent;
                if (syn_cache_respond(sc, m) == 0) {
                        uint64_t *tcps = TCP_STAT_GETREF();
                        tcps[TCP_STAT_SNDACKS]++;
                        tcps[TCP_STAT_SNDTOTAL]++;
                        TCP_STAT_PUTREF();
                }
                return (1);
        }

        s = splsoftnet();
        sc = pool_get(&syn_cache_pool, PR_NOWAIT);
        splx(s);
        if (sc == NULL) {
                if (ipopts)
                        (void) m_free(ipopts);
                return (0);
        }

        /*
         * Fill in the cache, and put the necessary IP and TCP
         * options into the reply.
         */
        memset(sc, 0, sizeof(struct syn_cache));
        callout_init(&sc->sc_timer, CALLOUT_MPSAFE);
        bcopy(src, &sc->sc_src, src->sa_len);
        bcopy(dst, &sc->sc_dst, dst->sa_len);
        sc->sc_flags = 0;
        sc->sc_ipopts = ipopts;
        sc->sc_irs = th->th_seq;
        switch (src->sa_family) {
#ifdef INET
        case AF_INET:
            {
                struct sockaddr_in *srcin = (void *) src;
                struct sockaddr_in *dstin = (void *) dst;

                sc->sc_iss = tcp_new_iss1(&dstin->sin_addr,
                    &srcin->sin_addr, dstin->sin_port,
                    srcin->sin_port, sizeof(dstin->sin_addr), 0);
                break;
            }
#endif /* INET */
#ifdef INET6
        case AF_INET6:
            {
                struct sockaddr_in6 *srcin6 = (void *) src;
                struct sockaddr_in6 *dstin6 = (void *) dst;

                sc->sc_iss = tcp_new_iss1(&dstin6->sin6_addr,
                    &srcin6->sin6_addr, dstin6->sin6_port,
                    srcin6->sin6_port, sizeof(dstin6->sin6_addr), 0);
                break;
            }
#endif /* INET6 */
        }
        sc->sc_peermaxseg = oi->maxseg;
        sc->sc_ourmaxseg = tcp_mss_to_advertise(m->m_flags & M_PKTHDR ?
                                                m->m_pkthdr.rcvif : NULL,
                                                sc->sc_src.sa.sa_family);
        sc->sc_win = win;
        sc->sc_timebase = tcp_now - 1;  /* see tcp_newtcpcb() */
        sc->sc_timestamp = tb.ts_recent;
        if ((tb.t_flags & (TF_REQ_TSTMP|TF_RCVD_TSTMP)) ==
            (TF_REQ_TSTMP|TF_RCVD_TSTMP))
                sc->sc_flags |= SCF_TIMESTAMP;
        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 compatiblity 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;
        }
        if ((tb.t_flags & TF_SACK_PERMIT) && tcp_do_sack)
                sc->sc_flags |= SCF_SACK_PERMIT;

        /*
         * ECN setup packet recieved.
         */
        if ((th->th_flags & (TH_ECE|TH_CWR)) && tcp_do_ecn)
                sc->sc_flags |= SCF_ECN_PERMIT;

#ifdef TCP_SIGNATURE
        if (tb.t_flags & TF_SIGNATURE)
                sc->sc_flags |= SCF_SIGNATURE;
#endif
        sc->sc_tp = tp;
        if (syn_cache_respond(sc, m) == 0) {
                uint64_t *tcps = TCP_STAT_GETREF();
                tcps[TCP_STAT_SNDACKS]++;
                tcps[TCP_STAT_SNDTOTAL]++;
                TCP_STAT_PUTREF();
                syn_cache_insert(sc, tp);
        } else {
                s = splsoftnet();
                syn_cache_put(sc);
                splx(s);
                TCP_STATINC(TCP_STAT_SC_DROPPED);
        }
        return (1);
}

int
syn_cache_respond(struct syn_cache *sc, struct mbuf *m)
{
#ifdef INET6
        struct rtentry *rt;
#endif
        struct route *ro;
        u_int8_t *optp;
        int optlen, error;
        u_int16_t tlen;
        struct ip *ip = NULL;
#ifdef INET6
        struct ip6_hdr *ip6 = NULL;
#endif
        struct tcpcb *tp = NULL;
        struct tcphdr *th;
        u_int hlen;
        struct socket *so;

        ro = &sc->sc_route;
        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:
                if (m)
                        m_freem(m);
                return (EAFNOSUPPORT);
        }

        /* Compute the size of the TCP options. */
        optlen = 4 + (sc->sc_request_r_scale != 15 ? 4 : 0) +
            ((sc->sc_flags & SCF_SACK_PERMIT) ? (TCPOLEN_SACK_PERMITTED + 2) : 0) +
#ifdef TCP_SIGNATURE
            ((sc->sc_flags & SCF_SIGNATURE) ? (TCPOLEN_SIGNATURE + 2) : 0) +
#endif
            ((sc->sc_flags & SCF_TIMESTAMP) ? TCPOLEN_TSTAMP_APPA : 0);

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

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

        /* Fixup the mbuf. */
        m->m_data += max_linkhdr;
        m->m_len = m->m_pkthdr.len = tlen;
        if (sc->sc_tp) {
                tp = sc->sc_tp;
                if (tp->t_inpcb)
                        so = tp->t_inpcb->inp_socket;
#ifdef INET6
                else if (tp->t_in6pcb)
                        so = tp->t_in6pcb->in6p_socket;
#endif
                else
                        so = NULL;
        } else
                so = NULL;
        m->m_pkthdr.rcvif = NULL;
        memset(mtod(m, u_char *), 0, tlen);

        switch (sc->sc_src.sa.sa_family) {
        case AF_INET:
                ip = mtod(m, struct ip *);
                ip->ip_v = 4;
                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_vfc = IPV6_VERSION;
                ip6->ip6_dst = sc->sc_src.sin6.sin6_addr;
                ip6->ip6_src = sc->sc_dst.sin6.sin6_addr;
                ip6->ip6_nxt = IPPROTO_TCP;
                /* ip6_plen will be updated in ip6_output() */
                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
        default:
                th = NULL;
        }

        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;
        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;

        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 (sc->sc_flags & 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(SYN_CACHE_TIMESTAMP(sc));
                *lp   = htonl(sc->sc_timestamp);
                optp += TCPOLEN_TSTAMP_APPA;
        }

        if (sc->sc_flags & SCF_SACK_PERMIT) {
                u_int8_t *p = optp;

                /* Let the peer know that we will SACK. */
                p[0] = TCPOPT_SACK_PERMITTED;
                p[1] = 2;
                p[2] = TCPOPT_NOP;
                p[3] = TCPOPT_NOP;
                optp += 4;
        }

        /*
         * Send ECN SYN-ACK setup packet.
         * Routes can be asymetric, so, even if we receive a packet
         * with ECE and CWR set, we must not assume no one will block
         * the ECE packet we are about to send.
         */
        if ((sc->sc_flags & SCF_ECN_PERMIT) && tp &&
            SEQ_GEQ(tp->snd_nxt, tp->snd_max)) {
                th->th_flags |= TH_ECE;
                TCP_STATINC(TCP_STAT_ECN_SHS);

                /*
                 * draft-ietf-tcpm-ecnsyn-00.txt
                 *
                 * "[...] a TCP node MAY respond to an ECN-setup
                 * SYN packet by setting ECT in the responding
                 * ECN-setup SYN/ACK packet, indicating to routers 
                 * that the SYN/ACK packet is ECN-Capable.
                 * This allows a congested router along the path
                 * to mark the packet instead of dropping the
                 * packet as an indication of congestion."
                 *
                 * "[...] There can be a great benefit in setting
                 * an ECN-capable codepoint in SYN/ACK packets [...]
                 * Congestion is  most likely to occur in
                 * the server-to-client direction.  As a result,
                 * setting an ECN-capable codepoint in SYN/ACK
                 * packets can reduce the occurence of three-second
                 * retransmit timeouts resulting from the drop
                 * of SYN/ACK packets."
                 *
                 * Page 4 and 6, January 2006.
                 */

                switch (sc->sc_src.sa.sa_family) {
#ifdef INET
                case AF_INET:
                        ip->ip_tos |= IPTOS_ECN_ECT0;
                        break;
#endif
#ifdef INET6
                case AF_INET6:
                        ip6->ip6_flow |= htonl(IPTOS_ECN_ECT0 << 20);
                        break;
#endif
                }
                TCP_STATINC(TCP_STAT_ECN_ECT);
        }

#ifdef TCP_SIGNATURE
        if (sc->sc_flags & SCF_SIGNATURE) {
                struct secasvar *sav;
                u_int8_t *sigp;

                sav = tcp_signature_getsav(m, th);

                if (sav == NULL) {
                        if (m)
                                m_freem(m);
                        return (EPERM);
                }

                *optp++ = TCPOPT_SIGNATURE;
                *optp++ = TCPOLEN_SIGNATURE;
                sigp = optp;
                memset(optp, 0, TCP_SIGLEN);
                optp += TCP_SIGLEN;
                *optp++ = TCPOPT_NOP;
                *optp++ = TCPOPT_EOL;

                (void)tcp_signature(m, th, hlen, sav, sigp);

                key_sa_recordxfer(sav, m);
#ifdef FAST_IPSEC
                KEY_FREESAV(&sav);
#else
                key_freesav(sav);
#endif
        }
#endif

        /* Compute the packet's checksum. */
        switch (sc->sc_src.sa.sa_family) {
        case AF_INET:
                ip->ip_len = htons(tlen - hlen);
                th->th_sum = 0;
                th->th_sum = in4_cksum(m, IPPROTO_TCP, hlen, tlen - hlen);
                break;
#ifdef INET6
        case AF_INET6:
                ip6->ip6_plen = htons(tlen - hlen);
                th->th_sum = 0;
                th->th_sum = in6_cksum(m, IPPROTO_TCP, hlen, tlen - hlen);
                break;
#endif
        }

        /*
         * 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) {
#ifdef INET
        case AF_INET:
                ip->ip_len = htons(tlen);
                ip->ip_ttl = ip_defttl;
                /* XXX tos? */
                break;
#endif
#ifdef INET6
        case AF_INET6:
                ip6->ip6_vfc &= ~IPV6_VERSION_MASK;
                ip6->ip6_vfc |= IPV6_VERSION;
                ip6->ip6_plen = htons(tlen - hlen);
                /* ip6_hlim will be initialized afterwards */
                /* XXX flowlabel? */
                break;
#endif
        }

        /* XXX use IPsec policy on listening socket, on SYN ACK */
        tp = sc->sc_tp;

        switch (sc->sc_src.sa.sa_family) {
#ifdef INET
        case AF_INET:
                error = ip_output(m, sc->sc_ipopts, ro,
                    (ip_mtudisc ? IP_MTUDISC : 0),
                    (struct ip_moptions *)NULL, so);
                break;
#endif
#ifdef INET6
        case AF_INET6:
                ip6->ip6_hlim = in6_selecthlim(NULL,
                                (rt = rtcache_validate(ro)) != NULL ? rt->rt_ifp
                                                                    : NULL);

                error = ip6_output(m, NULL /*XXX*/, ro, 0, NULL, so, NULL);
                break;
#endif
        default:
                error = EAFNOSUPPORT;
                break;
        }
        return (error);
}