/*      $NetBSD: tcp_input.c,v 1.441 2024/10/08 06:17:14 rin 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,
 * 2011 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code is derived from software contributed to The NetBSD Foundation
 * by Coyote Point Systems, Inc.
 * 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
 */

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: tcp_input.c,v 1.441 2024/10/08 06:17:14 rin Exp $");

#ifdef _KERNEL_OPT
#include "opt_inet.h"
#include "opt_ipsec.h"
#include "opt_inet_csum.h"
#include "opt_tcp_debug.h"
#endif

#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 <sys/cprng.h>

#include <net/if.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>

#if NARP > 0
#include <netinet/if_inarp.h>
#endif
#ifdef INET6
#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
#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/tcp_congctl.h>
#include <netinet/tcp_debug.h>
#include <netinet/tcp_syncache.h>

#ifdef INET6
#include "faith.h"
#if defined(NFAITH) && NFAITH > 0
#include <net/if_faith.h>
#endif
#endif

#ifdef IPSEC
#include <netipsec/ipsec.h>
#include <netipsec/key.h>
#ifdef INET6
#include <netipsec/ipsec6.h>
#endif
#endif  /* IPSEC*/

#include <netinet/tcp_vtw.h>

int     tcprexmtthresh = 3;
int     tcp_log_refused;

int     tcp_do_autorcvbuf = 1;
int     tcp_autorcvbuf_inc = 16 * 1024;
int     tcp_autorcvbuf_max = 256 * 1024;
int     tcp_msl = (TCPTV_MSL / PR_SLOWHZ);

int tcp_reass_maxqueuelen = 100;

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.
 */
static void
nd_hint(struct tcpcb *tp)
{
        struct route *ro = NULL;
        struct rtentry *rt;

        if (tp == NULL)
                return;

        ro = &tp->t_inpcb->inp_route;
        if (ro == NULL)
                return;

        rt = rtcache_validate(ro);
        if (rt == NULL)
                return;

        switch (tp->t_family) {
#if NARP > 0
        case AF_INET:
                arp_nud_hint(rt);
                break;
#endif
#ifdef INET6
        case AF_INET6:
                nd6_nud_hint(rt);
                break;
#endif
        }

        rtcache_unref(rt, ro);
}

/*
 * 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);
}

static void
tcp_urp_drop(struct tcphdr *th, int todrop, int *tiflags)
{
        if (th->th_urp > todrop) {
                th->th_urp -= todrop;
        } else {
                *tiflags &= ~TH_URG;
                th->th_urp = 0;
        }
}

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

extern struct evcnt tcp_hwcsum_ok;
extern struct evcnt tcp_hwcsum_bad;
extern struct evcnt tcp_hwcsum_data;
extern struct evcnt tcp_swcsum;
#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 void tcp4_log_refused(const struct ip *, const struct tcphdr *);
#ifdef INET6
static void tcp6_log_refused(const struct ip6_hdr *, const struct tcphdr *);
#endif

#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);
}

/*
 * Insert segment ti into reassembly queue of tcp with
 * control block tp.  Return TH_FIN if reassembly now includes
 * a segment with FIN.
 */
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
        net_stat_ref_t tcps;

        so = tp->t_inpcb->inp_socket;

        TCP_REASS_LOCK_CHECK(tp);

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

        m_claimm(m, &tcp_reass_mowner);

        rcvoobyte = tlen;
        /*
         * Copy these to local variables because the TCP header 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->ipqe_m, m);
                        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;
                        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) {
                        pkt_len += q->ipqe_len;
                        pkt_flags |= q->ipqe_flags;
                        pkt_seq = q->ipqe_seq;
                        m_cat(q->ipqe_m, m);
                        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 to 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();
                        _NET_STATINC_REF(tcps, TCP_STAT_RCVDUPPACK);
                        _NET_STATADD_REF(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);
                        goto out;
                }

                /*
                 * 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;
                }

                /*
                 * Received segment extends past the end of the fragment.
                 * Drop the overlapping bytes, merge the fragment and
                 * segment, and 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;
                        m_adj(m, overlap);
                        rcvpartdupbyte += overlap;
                        m_cat(q->ipqe_m, m);
                        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;
                }

                /*
                 * Received segment extends past the front of the fragment.
                 * Drop the overlapping bytes on the received packet. The
                 * packet will then be concatenated 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;
                        m_adj(m, -overlap);
                        pkt_len -= overlap;
                        rcvpartdupbyte += overlap;
                        TCP_REASS_COUNTER_INCR(&tcp_reass_overlapfront);
                        rcvoobyte -= overlap;
                }

                /*
                 * If the received segment immediately precedes this
                 * fragment then tack the fragment onto this segment
                 * and reinsert the data.
                 */
                if (q->ipqe_seq == pkt_seq + pkt_len) {
                        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 the 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:
        /* limit tcp segments per reassembly queue */
        if (tp->t_segqlen > tcp_reass_maxqueuelen) {
                TCP_STATINC(TCP_STAT_RCVMEMDROP);
                m_freem(m);
                goto out;
        }

        /*
         * Allocate a new queue entry (block) since the received segment
         * did not collapse onto any other out-of-order block. If it had
         * collapsed, tiqe would not be NULL and we would be reusing it.
         *
         * If the allocation fails, drop the packet.
         */
        if (tiqe == NULL) {
                tiqe = tcpipqent_alloc();
                if (tiqe == NULL) {
                        TCP_STATINC(TCP_STAT_RCVMEMDROP);
                        m_freem(m);
                        goto out;
                }
        }

        /*
         * Update the counters.
         */
        tp->t_rcvoopack++;
        tcps = TCP_STAT_GETREF();
        _NET_STATINC_REF(tcps, TCP_STAT_RCVOOPACK);
        _NET_STATADD_REF(tcps, TCP_STAT_RCVOOBYTE, rcvoobyte);
        if (rcvpartdupbyte) {
                _NET_STATINC_REF(tcps, TCP_STAT_RCVPARTDUPPACK);
                _NET_STATADD_REF(tcps, TCP_STAT_RCVPARTDUPBYTE,
                    rcvpartdupbyte);
        }
        TCP_STAT_PUTREF();

        /*
         * Insert the new fragment queue entry into both queues.
         */
        tiqe->ipqe_m = 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);
        } else {
                TAILQ_INSERT_AFTER(&tp->segq, p, tiqe, ipqe_q);
        }
        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)
                goto out;
        q = TAILQ_FIRST(&tp->segq);
        if (q == NULL || q->ipqe_seq != tp->rcv_nxt)
                goto out;
        if (tp->t_state == TCPS_SYN_RECEIVED && q->ipqe_len)
                goto out;

        tp->rcv_nxt += q->ipqe_len;
        pkt_flags = q->ipqe_flags & TH_FIN;
        nd_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);
        TCP_REASS_UNLOCK(tp);
        sorwakeup(so);
        return pkt_flags;

out:
        TCP_REASS_UNLOCK(tp);
        return 0;
}

#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

static void
tcp4_log_refused(const struct ip *ip, const struct tcphdr *th)
{
        char src[INET_ADDRSTRLEN];
        char dst[INET_ADDRSTRLEN];

        if (ip) {
                in_print(src, sizeof(src), &ip->ip_src);
                in_print(dst, sizeof(dst), &ip->ip_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));
}

#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) {
                in6_print(src, sizeof(src), &ip6->ip6_src);
                in6_print(dst, sizeof(dst), &ip6->ip6_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)
{
        struct ifnet *rcvif;
        int s;

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

        rcvif = m_get_rcvif(m, &s);
        if (__predict_false(rcvif == NULL))
                goto badcsum; /* XXX */

        switch (af) {
        case AF_INET:
                switch (m->m_pkthdr.csum_flags &
                        ((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(!(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;

#ifdef INET6
        case AF_INET6:
                switch (m->m_pkthdr.csum_flags &
                        ((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 */
        }
        m_put_rcvif(rcvif, &s);

        return 0;

badcsum:
        m_put_rcvif(rcvif, &s);
        TCP_STATINC(TCP_STAT_RCVBADSUM);
        return -1;
}

/*
 * When a packet arrives addressed to a vestigial tcpbp, we
 * nevertheless have to respond to it per the spec.
 *
 * This code is duplicated from the one in tcp_input().
 */
static void tcp_vtw_input(struct tcphdr *th, vestigial_inpcb_t *vp,
    struct mbuf *m, int tlen)
{
        int tiflags;
        int todrop;
        uint32_t t_flags = 0;
        net_stat_ref_t tcps;

        tiflags = th->th_flags;
        todrop  = vp->rcv_nxt - th->th_seq;

        if (todrop > 0) {
                if (tiflags & TH_SYN) {
                        tiflags &= ~TH_SYN;
                        th->th_seq++;
                        tcp_urp_drop(th, 1, &tiflags);
                        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.
                         */
                        t_flags |= TF_ACKNOW;
                        todrop = tlen;
                        tcps = TCP_STAT_GETREF();
                        _NET_STATINC_REF(tcps, TCP_STAT_RCVDUPPACK);
                        _NET_STATADD_REF(tcps, TCP_STAT_RCVDUPBYTE, todrop);
                        TCP_STAT_PUTREF();
                } else if ((tiflags & TH_RST) &&
                    th->th_seq != vp->rcv_nxt) {
                        /*
                         * Test for reset before adjusting the sequence
                         * number for overlapping data.
                         */
                        goto dropafterack_ratelim;
                } else {
                        tcps = TCP_STAT_GETREF();
                        _NET_STATINC_REF(tcps, TCP_STAT_RCVPARTDUPPACK);
                        _NET_STATADD_REF(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;
                tcp_urp_drop(th, todrop, &tiflags);
        }

        /*
         * If new data are received on a connection after the
         * user processes are gone, then RST the other end.
         */
        if (tlen) {
                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) - (vp->rcv_nxt + vp->rcv_wnd);

        if (todrop > 0) {
                TCP_STATINC(TCP_STAT_RCVPACKAFTERWIN);
                if (todrop >= tlen) {
                        /*
                         * The segment actually starts after the window.
                         * th->th_seq + tlen - vp->rcv_nxt - vp->rcv_wnd >= tlen
                         * th->th_seq - vp->rcv_nxt - vp->rcv_wnd >= 0
                         * th->th_seq >= vp->rcv_nxt + vp->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.
                         */
                        if ((tiflags & TH_SYN) &&
                            SEQ_GT(th->th_seq, vp->rcv_nxt)) {
                                /*
                                 * We only support this in the !NOFDREF case, which
                                 * is to say: not here.
                                 */
                                goto dropwithreset;
                        }

                        /*
                         * 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 (vp->rcv_wnd == 0 && th->th_seq == vp->rcv_nxt) {
                                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 (tiflags & TH_RST) {
                if (th->th_seq != vp->rcv_nxt)
                        goto dropafterack_ratelim;

                vtw_del(vp->ctl, vp->vtw);
                goto drop;
        }

        /*
         * If the ACK bit is off we drop the segment and return.
         */
        if ((tiflags & TH_ACK) == 0) {
                if (t_flags & TF_ACKNOW)
                        goto dropafterack;
                goto drop;
        }

        /*
         * In TIME_WAIT state the only thing that should arrive
         * is a retransmission of the remote FIN.  Acknowledge
         * it and restart the finack timer.
         */
        vtw_restart(vp);
        goto dropafterack;

dropafterack:
        /*
         * Generate an ACK dropping incoming segment if it occupies
         * sequence space, where the ACK reflects our state.
         */
        if (tiflags & TH_RST)
                goto drop;
        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:
        (void)tcp_respond(0, m, m, th, th->th_seq + tlen, th->th_ack, TH_ACK);
        return;

dropwithreset:
        /*
         * Generate a RST, dropping incoming segment.
         * Make ACK acceptable to originator of segment.
         */
        if (tiflags & TH_RST)
                goto drop;

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

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

        vestige.valid = 0;

        MCLAIM(m, &tcp_rx_mowner);

        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

        M_REGION_GET(th, struct tcphdr *, m, off, sizeof(struct tcphdr));
        if (th == NULL) {
                TCP_STATINC(TCP_STAT_RCVSHORT);
                return;
        }

        /*
         * Enforce alignment requirements that are violated in
         * some cases, see kern/50766 for details.
         */
        if (ACCESSIBLE_POINTER(th, struct tcphdr) == 0) {
                m = m_copyup(m, off + sizeof(struct tcphdr), 0);
                if (m == NULL) {
                        TCP_STATINC(TCP_STAT_RCVSHORT);
                        return;
                }
                th = (struct tcphdr *)(mtod(m, char *) + off);
        }
        KASSERT(ACCESSIBLE_POINTER(th, struct tcphdr));

        /*
         * Get IP and TCP header.
         * Note: IP leaves IP header in first mbuf.
         */
        ip = mtod(m, struct ip *);
#ifdef INET6
        ip6 = mtod(m, struct ip6_hdr *);
#endif
        switch (ip->ip_v) {
        case 4:
                af = AF_INET;
                iphlen = sizeof(struct ip);

                if (IN_MULTICAST(ip->ip_dst.s_addr) ||
                    in_broadcast(ip->ip_dst, m_get_rcvif_NOMPSAFE(m)))
                        goto drop;

                /* We do the checksum after PCB lookup... */
                len = ntohs(ip->ip_len);
                tlen = len - off;
                iptos = ip->ip_tos;
                break;
#ifdef INET6
        case 6:
                iphlen = sizeof(struct ip6_hdr);
                af = AF_INET6;

                /*
                 * 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 - off;
                iptos = (ntohl(ip6->ip6_flow) >> 20) & 0xff;
                break;
#endif
        default:
                m_freem(m);
                return;
        }


        /*
         * Check that TCP offset makes sense, pull out TCP options and
         * adjust length.
         */
        thlen = th->th_off << 2;
        if (thlen < sizeof(struct tcphdr) || thlen > tlen) {
                TCP_STATINC(TCP_STAT_RCVBADOFF);
                goto drop;
        }
        tlen -= thlen;

        if (thlen > sizeof(struct tcphdr)) {
                M_REGION_GET(th, struct tcphdr *, m, off, thlen);
                if (th == NULL) {
                        TCP_STATINC(TCP_STAT_RCVSHORT);
                        return;
                }
                KASSERT(ACCESSIBLE_POINTER(th, struct tcphdr));
                optlen = thlen - sizeof(struct tcphdr);
                optp = ((u_int8_t *)th) + sizeof(struct tcphdr);

                /*
                 * Do quick retrieval of timestamp options.
                 *
                 * If timestamp is the only option and it's formatted as
                 * recommended in RFC 1323 appendix A, we quickly get the
                 * values now and don't bother calling tcp_dooptions(),
                 * etc.
                 */
                if ((optlen == TCPOLEN_TSTAMP_APPA ||
                     (optlen > TCPOLEN_TSTAMP_APPA &&
                      optp[TCPOLEN_TSTAMP_APPA] == TCPOPT_EOL)) &&
                    be32dec(optp) == TCPOPT_TSTAMP_HDR &&
                    (th->th_flags & TH_SYN) == 0) {
                        opti.ts_present = 1;
                        opti.ts_val = be32dec(optp + 4);
                        opti.ts_ecr = be32dec(optp + 8);
                        optp = NULL;    /* we've parsed the options */
                }
        }
        tiflags = th->th_flags;

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

        /*
         * Locate pcb for segment.
         */
findpcb:
        inp = NULL;
        switch (af) {
        case AF_INET:
                inp = inpcb_lookup(&tcbtable, ip->ip_src, th->th_sport,
                    ip->ip_dst, th->th_dport, &vestige);
                if (inp == NULL && !vestige.valid) {
                        TCP_STATINC(TCP_STAT_PCBHASHMISS);
                        inp = inpcb_lookup_bound(&tcbtable, ip->ip_dst,
                            th->th_dport);
                }
#ifdef INET6
                if (inp == NULL && !vestige.valid) {
                        struct in6_addr s, d;

                        /* mapped addr case */
                        in6_in_2_v4mapin6(&ip->ip_src, &s);
                        in6_in_2_v4mapin6(&ip->ip_dst, &d);
                        inp = in6pcb_lookup(&tcbtable, &s,
                            th->th_sport, &d, th->th_dport, 0, &vestige);
                        if (inp == NULL && !vestige.valid) {
                                TCP_STATINC(TCP_STAT_PCBHASHMISS);
                                inp = in6pcb_lookup_bound(&tcbtable, &d,
                                    th->th_dport, 0);
                        }
                }
#endif
                if (inp == NULL && !vestige.valid) {
                        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)
                if (ipsec_used) {
                        if (inp && ipsec_in_reject(m, inp))
                                goto drop;
                }
#endif /*IPSEC*/
                break;
#ifdef INET6
        case AF_INET6:
            {
                int faith;

#if defined(NFAITH) && NFAITH > 0
                faith = faithprefix(&ip6->ip6_dst);
#else
                faith = 0;
#endif
                inp = in6pcb_lookup(&tcbtable, &ip6->ip6_src,
                    th->th_sport, &ip6->ip6_dst, th->th_dport, faith, &vestige);
                if (inp == NULL && !vestige.valid) {
                        TCP_STATINC(TCP_STAT_PCBHASHMISS);
                        inp = in6pcb_lookup_bound(&tcbtable, &ip6->ip6_dst,
                            th->th_dport, faith);
                }
                if (inp == NULL && !vestige.valid) {
                        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)
                if (ipsec_used && inp && ipsec_in_reject(m, inp))
                        goto drop;
#endif
                break;
            }
#endif
        }

        tcp_fields_to_host(th);

        /*
         * 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 (inp->inp_af == AF_INET && ip->ip_ttl < in4p_ip_minttl(inp))
                        goto drop;

                tp = intotcpcb(inp);
                so = inp->inp_socket;
        } else if (vestige.valid) {
                /* We do not support the resurrection of vtw tcpcps. */
                tcp_vtw_input(th, &vestige, m, tlen);
                m = NULL;
                goto drop;
        }

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

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

        /* 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 (inp->inp_af == AF_INET6 && (inp->inp_flags & IN6P_CONTROLOPTS)) {
                m_freem(inp->inp_options);
                inp->inp_options = NULL;
                ip6_savecontrol(inp, &inp->inp_options, ip6, m);
        }
#endif

        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 == NULL)
                                goto nosave;
                } else {
                        MGETHDR(tcp_saveti, M_DONTWAIT, MT_HEADER);
                        if (tcp_saveti == NULL)
                                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) {
                union syn_cache_sa src;
                union syn_cache_sa dst;

                KASSERT(tp->t_state == TCPS_LISTEN);

                memset(&src, 0, sizeof(src));
                memset(&dst, 0, sizeof(dst));
                switch (af) {
                case AF_INET:
                        src.sin.sin_len = sizeof(struct sockaddr_in);
                        src.sin.sin_family = AF_INET;
                        src.sin.sin_addr = ip->ip_src;
                        src.sin.sin_port = th->th_sport;

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

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

                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, 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.
                                         */
                                        inp = sotoinpcb(so);
                                        tp = intotcpcb(inp);
                                        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.
                         */

#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;
                                int s;
                                struct ifnet *rcvif = m_get_rcvif(m, &s);
                                if (rcvif == NULL)
                                        goto dropwithreset; /* XXX */
                                if ((ia6 = in6ifa_ifpwithaddr(rcvif,
                                    &ip6->ip6_dst)) &&
                                    (ia6->ia6_flags & IN6_IFF_DEPRECATED)) {
                                        tp = NULL;
                                        m_put_rcvif(rcvif, &s);
                                        goto dropwithreset;
                                }
                                m_put_rcvif(rcvif, &s);
                        }
#endif

                        /*
                         * LISTEN socket received a SYN from itself? This
                         * can't possibly be valid; drop the packet.
                         */
                        if (th->th_sport == th->th_dport) {
                                int eq = 0;

                                switch (af) {
                                case AF_INET:
                                        eq = in_hosteq(ip->ip_src, ip->ip_dst);
                                        break;
#ifdef INET6
                                case AF_INET6:
                                        eq = IN6_ARE_ADDR_EQUAL(&ip6->ip6_src,
                                            &ip6->ip6_dst);
                                        break;
#endif
                                }
                                if (eq) {
                                        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, off,
                            so, m, optp, optlen, &opti))
                                m = NULL;
                }

                goto drop;
        }

after_listen:
        /*
         * From here on, we're dealing with !LISTEN.
         */
        KASSERT(tp->t_state != TCPS_LISTEN);

        /*
         * 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, off, &opti) < 0)
                        goto drop;

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

        if (TCP_ECN_ALLOWED(tp)) {
                if (tiflags & TH_CWR) {
                        tp->t_flags &= ~TF_ECN_SND_ECE;
                }
                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;
                }
                /*
                 * 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_rtt is unsigned, we can test both
                 * at the same time.
                 *
                 * Note that ts_rtt is in units of slow ticks (500
                 * ms).  Since most earthbound RTTs are < 500 ms,
                 * observed values will have large quantization noise.
                 * Our smoothed RTT is then the fraction of observed
                 * samples that are 1 tick instead of 0 (times 500
                 * ms).
                 *
                 * ts_rtt is increased by 1 to denote a valid sample,
                 * with 0 indicating an invalid measurement.  This
                 * extra 1 must be removed when ts_rtt is used, or
                 * else an erroneous extra 500 ms will result.
                 */
                ts_rtt = TCP_TIMESTAMP(tp) - opti.ts_ecr + 1;
                if (ts_rtt > TCP_PAWS_IDLE)
                        ts_rtt = 0;
        } else {
                ts_rtt = 0;
        }

        /*
         * Fast path: check for the two common cases of a uni-directional
         * data transfer. If:
         *    o We are in the ESTABLISHED state, and
         *    o The packet has no control flags, and
         *    o The packet is in-sequence, and
         *    o The window didn't change, and
         *    o We are not retransmitting
         * It's a candidate.
         *
         * If the length (tlen) is zero and the ack moved forward, we're
         * the sender side of the transfer. Just free the data acked and
         * 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 - 1);
                                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();
                                _NET_STATINC_REF(tcps, TCP_STAT_PREDACK);
                                _NET_STATINC_REF(tcps, TCP_STAT_RCVACKPACK);
                                _NET_STATADD_REF(tcps, TCP_STAT_RCVACKBYTE,
                                    acked);
                                TCP_STAT_PUTREF();
                                nd_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;
                                /*
                                 * drag snd_wl2 along so only newer
                                 * ACKs can update the window size.
                                 * also avoids the state where snd_wl2
                                 * is eventually larger than th_ack and thus
                                 * blocking the window update mechanism and
                                 * the connection gets stuck for a loooong
                                 * time in the zero sized send window state.
                                 *
                                 * see PR/kern 55567
                                 */
                                tp->snd_wl2 = 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) {
                                        KERNEL_LOCK(1, NULL);
                                        (void)tcp_output(tp);
                                        KERNEL_UNLOCK_ONE(NULL);
                                }
                                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;

                        /*
                         * 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;

                        /*
                         * Pull rcv_up up to prevent seq wrap relative to
                         * rcv_nxt.
                         */
                        tp->rcv_up = tp->rcv_nxt;

                        /*
                         * Pull snd_wl1 up to prevent seq wrap relative to
                         * th_seq.
                         */
                        tp->snd_wl1 = th->th_seq;

                        tcps = TCP_STAT_GETREF();
                        _NET_STATINC_REF(tcps, TCP_STAT_PREDDAT);
                        _NET_STATINC_REF(tcps, TCP_STAT_RCVPACK);
                        _NET_STATADD_REF(tcps, TCP_STAT_RCVBYTE, tlen);
                        TCP_STAT_PUTREF();
                        nd_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 =
                                                    uimin(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, off + thlen);
                                sbappendstream(&so->so_rcv, m);
                        }
                        sorwakeup(so);
                        tcp_setup_ack(tp, th);
                        if (tp->t_flags & TF_ACKNOW) {
                                KERNEL_LOCK(1, NULL);
                                (void)tcp_output(tp);
                                KERNEL_UNLOCK_ONE(NULL);
                        }
                        m_freem(tcp_saveti);
                        return;
                }
        }

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

        /*
         * Calculate amount of space in receive window. 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;
                        if (inp->inp_af == AF_INET && in_localaddr(in4p_faddr(inp)))
                                ss = tcp_init_win_local;
#ifdef INET6
                        else if (inp->inp_af == AF_INET6 && in6_localaddr(&in6p_faddr(inp)))
                                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);
                        /*
                         * move tcp_established before soisconnected
                         * because upcall handler can drive tcp_output
                         * functionality.
                         * XXX we might call soisconnected at the end of
                         * all processing
                         */
                        tcp_established(tp);
                        soisconnected(so);
                        /* 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, NULL, tlen);
                        /*
                         * 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();
                        _NET_STATINC_REF(tcps, TCP_STAT_RCVPACKAFTERWIN);
                        _NET_STATADD_REF(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;
        }

        /*
         * From here on, we're dealing with !LISTEN and !SYN_SENT.
         */
        KASSERT(tp->t_state != TCPS_LISTEN &&
            tp->t_state != TCPS_SYN_SENT);

        /*
         * RFC1323 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();
                        _NET_STATINC_REF(tcps, TCP_STAT_RCVDUPPACK);
                        _NET_STATADD_REF(tcps, TCP_STAT_RCVDUPBYTE, tlen);
                        _NET_STATINC_REF(tcps, TCP_STAT_PAWSDROP);
                        TCP_STAT_PUTREF();
                        tcp_new_dsack(tp, th->th_seq, tlen);
                        goto dropafterack;
                }
        }

        /*
         * Check that at least some bytes of the segment are within the
         * receive window. If segment begins before rcv_nxt, drop leading
         * data (and SYN); if nothing left, just ack.
         */
        todrop = tp->rcv_nxt - th->th_seq;
        dupseg = false;
        if (todrop > 0) {
                if (tiflags & TH_SYN) {
                        tiflags &= ~TH_SYN;
                        th->th_seq++;
                        tcp_urp_drop(th, 1, &tiflags);
                        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();
                        _NET_STATINC_REF(tcps, TCP_STAT_RCVDUPPACK);
                        _NET_STATADD_REF(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();
                        _NET_STATINC_REF(tcps, TCP_STAT_RCVPARTDUPPACK);
                        _NET_STATADD_REF(tcps, TCP_STAT_RCVPARTDUPBYTE,
                            todrop);
                        TCP_STAT_PUTREF();
                }
                tcp_new_dsack(tp, th->th_seq, todrop);
                hdroptlen += todrop;    /* drop from head afterwards (m_adj) */
                th->th_seq += todrop;
                tlen -= todrop;
                tcp_urp_drop(th, todrop, &tiflags);
        }

        /*
         * If new data is 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 the segment ends after the 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 need to put the header fields back into
                         * network order.
                         */
                        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);
                                m_freem(tcp_saveti);
                                tcp_saveti = NULL;
                                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) {
                                KASSERT(todrop == tlen);
                                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:
         *    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.  RFC793 states (under Reset
         * 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);
                        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;
                goto drop;
        }

        /*
         * From here on, we're doing 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, NULL, tlen);
                tp->snd_wl1 = th->th_seq - 1;
                /* FALLTHROUGH */

        /*
         * In ESTABLISHED state: drop duplicate ACKs; ACK out of range
         * ACKs.  If the ack is in the range
         *      tp->snd_una < th->th_ack <= tp->snd_max
         * then advance tp->snd_una to th->th_ack and drop
         * data from the retransmission queue.  If this ACK reflects
         * more up to date window information we update our window information.
         */
        case TCPS_ESTABLISHED:
        case TCPS_FIN_WAIT_1:
        case TCPS_FIN_WAIT_2:
        case TCPS_CLOSE_WAIT:
        case TCPS_CLOSING:
        case TCPS_LAST_ACK:
        case TCPS_TIME_WAIT:
                if (SEQ_LEQ(th->th_ack, tp->snd_una)) {
                        if (tlen == 0 && !dupseg && tiwin == tp->snd_wnd) {
                                TCP_STATINC(TCP_STAT_RCVDUPACK);
                                /*
                                 * If we have outstanding data (other than
                                 * a window probe), this is a completely
                                 * duplicate ack (ie, window info didn't
                                 * change), the ack is the biggest we've
                                 * seen and we've seen exactly our rexmt
                                 * threshold of them, assume a packet
                                 * has been dropped and retransmit it.
                                 * Kludge snd_nxt & the congestion
                                 * window so we send only this one
                                 * packet.
                                 */
                                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 parameters.
                                         */
                                        if (tp->t_congctl->fast_retransmit(tp, th)) {
                                                /* False fast retransmit */
                                                break;
                                        }
                                        goto drop;
                                } else if (tp->t_dupacks > tcprexmtthresh) {
                                        tp->snd_cwnd += tp->t_segsz;
                                        KERNEL_LOCK(1, NULL);
                                        (void)tcp_output(tp);
                                        KERNEL_UNLOCK_ONE(NULL);
                                        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.
                 */
                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();
                _NET_STATINC_REF(tcps, TCP_STAT_RCVACKPACK);
                _NET_STATADD_REF(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 - 1);
                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);

                nd_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;
                        if (tp->snd_wnd > acked)
                                tp->snd_wnd -= acked;
                        else
                                tp->snd_wnd = 0;
                        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 * tp->t_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 * tp->t_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 &&
                    (so->so_options & SO_OOBINLINE) == 0)
                        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:

        /*
         * 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,
         * tcp_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) {
                /*
                 * Handle the common case:
                 *  o Segment is the next to be received, and
                 *  o The queue is empty, and
                 *  o The connection is established
                 * In this case, we avoid calling tcp_reass.
                 *
                 * tcp_setup_ack: set DELACK for segments received in order,
                 * but ack immediately when segments are out of order (so that
                 * fast retransmit can work).
                 */
                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();
                        _NET_STATINC_REF(tcps, TCP_STAT_RCVPACK);
                        _NET_STATADD_REF(tcps, TCP_STAT_RCVBYTE, tlen);
                        TCP_STAT_PUTREF();
                        nd_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;
                }

                /*
                 * 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 * tp->t_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 * tp->t_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)) {
                KERNEL_LOCK(1, NULL);
                (void)tcp_output(tp);
                KERNEL_UNLOCK_ONE(NULL);
        }
        m_freem(tcp_saveti);

        if (tp->t_state == TCPS_TIME_WAIT
            && (so->so_state & SS_NOFDREF)
            && (tp->t_inpcb || af != AF_INET || af != AF_INET6)
            && ((af == AF_INET ? tcp4_vtw_enable : tcp6_vtw_enable) & 1) != 0
            && TAILQ_EMPTY(&tp->segq)
            && vtw_add(af, tp)) {
                ;
        }
        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;
        }

dropafterack2:
        m_freem(m);
        tp->t_flags |= TF_ACKNOW;
        KERNEL_LOCK(1, NULL);
        (void)tcp_output(tp);
        KERNEL_UNLOCK_ONE(NULL);
        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;
        }

dropwithreset:
        /*
         * Generate a RST, dropping incoming segment.
         * Make ACK acceptable to originator of segment.
         */
        if (tiflags & TH_RST)
                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);
        }
        m_freem(tcp_saveti);
        return;

badcsum:
drop:
        /*
         * Drop space held by incoming segment and return.
         */
        if (tp) {
                so = tp->t_inpcb->inp_socket;
#ifdef TCP_DEBUG
                if (so && (so->so_options & SO_DEBUG) != 0)
                        tcp_trace(TA_DROP, ostate, tp, tcp_saveti, 0);
#endif
        }
        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 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 IPSEC
        union sockaddr_union dst;

        /* 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.
         */
        return KEY_LOOKUP_SA(&dst, IPPROTO_TCP, htonl(TCP_SIG_SPI), 0, 0);
#else
        return NULL;
#endif
}

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;
#ifdef INET6
        struct ip6_hdr *ip6;
        struct ip6_hdr_pseudo ip6pseudo;
#endif
        struct ippseudo ippseudo;
        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:
                MD5Init(&ctx);
                ip = mtod(m, struct 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));
                break;
#if INET6
        case 6:
                MD5Init(&ctx);
                ip6 = mtod(m, struct ip6_hdr *);
                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));
                break;
#endif
        default:
                return (-1);
        }

        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

/*
 * Parse and process tcp options.
 *
 * Returns -1 if this segment should be dropped.  (eg. wrong signature)
 * Otherwise returns 0.
 */
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;
                        memcpy(&mss, cp + 2, 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) {
                                char buf[INET6_ADDRSTRLEN];
                                struct ip *ip = mtod(m, struct ip *);
#ifdef INET6
                                struct ip6_hdr *ip6 = mtod(m, struct ip6_hdr *);
#endif

                                switch (ip->ip_v) {
                                case 4:
                                        in_print(buf, sizeof(buf),
                                            &ip->ip_src);
                                        break;
#ifdef INET6
                                case 6:
                                        in6_print(buf, sizeof(buf),
                                            &ip6->ip6_src);
                                        break;
#endif
                                default:
                                        strlcpy(buf, "(unknown)", sizeof(buf));
                                        break;
                                }

                                log(LOG_ERR, "TCP: invalid wscale %d from %s, "
                                    "assuming %d\n",
                                    tp->requested_s_scale, buf,
                                    TCP_MAX_WINSHIFT);
                                tp->requested_s_scale = TCP_MAX_WINSHIFT;
                        }
                        break;

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

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

#ifndef TCP_SIGNATURE
        return 0;
#else
        if (tp->t_flags & TF_SIGNATURE) {
                sav = tcp_signature_getsav(m);
                if (sav == NULL && tp->t_state == TCPS_LISTEN)
                        return (-1);
        }

        if ((sigp ? TF_SIGNATURE : 0) ^ (tp->t_flags & TF_SIGNATURE))
                goto out;

        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);
                        goto out;
                }
                tcp_fields_to_host(th);

                if (!consttime_memequal(sig, sigp, TCP_SIGLEN)) {
                        TCP_STATINC(TCP_STAT_BADSIG);
                        goto out;
                } else
                        TCP_STATINC(TCP_STAT_GOODSIG);

                key_sa_recordxfer(sav, m);
                KEY_SA_UNREF(&sav);
        }
        return 0;
out:
        if (sav != NULL)
                KEY_SA_UNREF(&sav);
        return -1;
#endif
}

/*
 * 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;
                        memmove(cp, cp + 1, (unsigned)(m->m_len - cnt - 1));
                        m->m_len--;
                        return;
                }
                cnt -= m->m_len;
                m = m->m_next;
                if (m == NULL)
                        break;
        }
        panic("tcp_pulloutofband");
}

/*
 * Collect new round-trip time estimate
 * and update averages and current timeout.
 *
 * rtt is in units of slow ticks (typically 500 ms) -- essentially the
 * difference of two timestamps.
 */
void
tcp_xmit_timer(struct tcpcb *tp, uint32_t rtt)
{
        int32_t delta;

        TCP_STATINC(TCP_STAT_RTTUPDATED);
        if (tp->t_srtt != 0) {
                /*
                 * Compute the amount to add to srtt for smoothing,
                 * *alpha, or 2^(-TCP_RTT_SHIFT).  Because
                 * srtt is stored in 1/32 slow ticks, we conceptually
                 * shift left 5 bits, subtract srtt to get the
                 * difference, and then shift right by TCP_RTT_SHIFT
                 * (3) to obtain 1/8 of the difference.
                 */
                delta = (rtt << 2) - (tp->t_srtt >> TCP_RTT_SHIFT);
                /* 
                 * This can never happen, because delta's lowest
                 * possible value is 1/8 of t_srtt.  But if it does,
                 * set srtt to some reasonable value, here chosen
                 * as 1/8 tick.
                 */
                if ((tp->t_srtt += delta) <= 0)
                        tp->t_srtt = 1 << 2;
                /*
                 * RFC2988 requires that rttvar be updated first.
                 * This code is compliant because "delta" is the old
                 * srtt minus the new observation (scaled).
                 *
                 * RFC2988 says:
                 *   rttvar = (1-beta) * rttvar + beta * |srtt-observed|
                 *
                 * delta is in units of 1/32 ticks, and has then been
                 * divided by 8.  This is equivalent to being in 1/16s
                 * units and divided by 4.  Subtract from it 1/4 of
                 * the existing rttvar to form the (signed) amount to
                 * adjust.
                 */
                if (delta < 0)
                        delta = -delta;
                delta -= (tp->t_rttvar >> TCP_RTTVAR_SHIFT);
                /*
                 * As with srtt, this should never happen.  There is
                 * no support in RFC2988 for this operation.  But 1/4s
                 * as rttvar when faced with something arguably wrong
                 * is ok.
                 */
                if ((tp->t_rttvar += delta) <= 0)
                        tp->t_rttvar = 1 << 2;

                /*
                 * If srtt exceeds .01 second, ensure we use the 'remote' MSL
                 * Problem is: it doesn't work.  Disabled by defaulting
                 * tcp_rttlocal to 0; see corresponding code in
                 * tcp_subr that selects local vs remote in a different way.
                 *
                 * The static branch prediction hint here should be removed
                 * when the rtt estimator is fixed and the rtt_enable code
                 * is turned back on.
                 */
                if (__predict_false(tcp_rttlocal) && tcp_msl_enable
                    && tp->t_srtt > tcp_msl_remote_threshold
                    && tp->t_msl  < tcp_msl_remote) {
                        tp->t_msl = MIN(tcp_msl_remote, TCP_MAXMSL);
                }
        } else {
                /*
                 * This is the first measurement.  Per RFC2988, 2.2,
                 * set rtt=R and srtt=R/2.
                 * For srtt, storage representation is 1/32 ticks,
                 * so shift left by 5.
                 * For rttvar, storage representation is 1/16 ticks,
                 * So shift left by 4, but then right by 1 to halve.
                 */
                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),
            uimax(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;
}