/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * 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.
 */

#include "opt_inet.h"
#include "opt_inet6.h"

/* For debugging we want counters and BB logging */
/* #define TCP_REASS_COUNTERS 1 */
/* #define TCP_REASS_LOGGING 1 */

#include <sys/param.h>
#include <sys/kernel.h>
#include <sys/eventhandler.h>
#include <sys/malloc.h>
#include <sys/mbuf.h>
#include <sys/socket.h>
#include <sys/socketvar.h>
#include <sys/sysctl.h>
#include <sys/syslog.h>
#include <sys/systm.h>

#include <vm/uma.h>

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

#include <netinet/in.h>
#include <netinet/in_pcb.h>
#include <netinet/in_systm.h>
#include <netinet/in_var.h>
#include <netinet/ip.h>
#include <netinet/ip_var.h>
#include <netinet/ip_options.h>
#include <netinet/ip6.h>
#include <netinet6/in6_pcb.h>
#include <netinet6/ip6_var.h>
#include <netinet6/nd6.h>
#include <netinet/tcp.h>
#include <netinet/tcp_fsm.h>
#include <netinet/tcp_seq.h>
#include <netinet/tcp_timer.h>
#include <netinet/tcp_var.h>
#ifdef TCP_REASS_LOGGING
#include <netinet/tcp_log_buf.h>
#include <netinet/tcp_hpts.h>
#endif
#include <netinet/tcpip.h>

#define TCP_R_LOG_ADD           1
#define TCP_R_LOG_LIMIT_REACHED 2
#define TCP_R_LOG_APPEND        3
#define TCP_R_LOG_PREPEND       4
#define TCP_R_LOG_REPLACE       5
#define TCP_R_LOG_MERGE_INTO    6
#define TCP_R_LOG_NEW_ENTRY     7
#define TCP_R_LOG_READ          8
#define TCP_R_LOG_ZERO          9
#define TCP_R_LOG_DUMP          10
#define TCP_R_LOG_TRIM          11

static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, reass,
    CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
    "TCP Segment Reassembly Queue");

static SYSCTL_NODE(_net_inet_tcp_reass, OID_AUTO, stats,
    CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
    "TCP Segment Reassembly stats");

static int tcp_reass_maxseg = 0;
SYSCTL_INT(_net_inet_tcp_reass, OID_AUTO, maxsegments, CTLFLAG_RDTUN,
    &tcp_reass_maxseg, 0,
    "Global maximum number of TCP Segments in Reassembly Queue");

static uma_zone_t tcp_reass_zone;
SYSCTL_UMA_CUR(_net_inet_tcp_reass, OID_AUTO, cursegments, 0,
    &tcp_reass_zone,
    "Global number of TCP Segments currently in Reassembly Queue");

static u_int tcp_reass_maxqueuelen = 100;
SYSCTL_UINT(_net_inet_tcp_reass, OID_AUTO, maxqueuelen, CTLFLAG_RWTUN,
    &tcp_reass_maxqueuelen, 0,
    "Maximum number of TCP Segments per Reassembly Queue");

static int tcp_new_limits = 0;
SYSCTL_INT(_net_inet_tcp_reass, OID_AUTO, new_limit, CTLFLAG_RWTUN,
    &tcp_new_limits, 0,
    "Do we use the new limit method we are discussing?");

static u_int tcp_reass_queue_guard = 16;
SYSCTL_UINT(_net_inet_tcp_reass, OID_AUTO, queueguard, CTLFLAG_RWTUN,
    &tcp_reass_queue_guard, 16,
    "Number of TCP Segments in Reassembly Queue where we flip over to guard mode");

#ifdef TCP_REASS_COUNTERS

counter_u64_t reass_entry;
SYSCTL_COUNTER_U64(_net_inet_tcp_reass_stats, OID_AUTO, entry, CTLFLAG_RD,
    &reass_entry, "A segment entered reassembly ");

counter_u64_t reass_path1;
SYSCTL_COUNTER_U64(_net_inet_tcp_reass_stats, OID_AUTO, path1, CTLFLAG_RD,
    &reass_path1, "Took path 1");

counter_u64_t reass_path2;
SYSCTL_COUNTER_U64(_net_inet_tcp_reass_stats, OID_AUTO, path2, CTLFLAG_RD,
    &reass_path2, "Took path 2");

counter_u64_t reass_path3;
SYSCTL_COUNTER_U64(_net_inet_tcp_reass_stats, OID_AUTO, path3, CTLFLAG_RD,
    &reass_path3, "Took path 3");

counter_u64_t reass_path4;
SYSCTL_COUNTER_U64(_net_inet_tcp_reass_stats, OID_AUTO, path4, CTLFLAG_RD,
    &reass_path4, "Took path 4");

counter_u64_t reass_path5;
SYSCTL_COUNTER_U64(_net_inet_tcp_reass_stats, OID_AUTO, path5, CTLFLAG_RD,
    &reass_path5, "Took path 5");

counter_u64_t reass_path6;
SYSCTL_COUNTER_U64(_net_inet_tcp_reass_stats, OID_AUTO, path6, CTLFLAG_RD,
    &reass_path6, "Took path 6");

counter_u64_t reass_path7;
SYSCTL_COUNTER_U64(_net_inet_tcp_reass_stats, OID_AUTO, path7, CTLFLAG_RD,
    &reass_path7, "Took path 7");

counter_u64_t reass_fullwalk;
SYSCTL_COUNTER_U64(_net_inet_tcp_reass_stats, OID_AUTO, fullwalk, CTLFLAG_RD,
    &reass_fullwalk, "Took a full walk ");

counter_u64_t reass_nospace;
SYSCTL_COUNTER_U64(_net_inet_tcp_reass_stats, OID_AUTO, nospace, CTLFLAG_RD,
    &reass_nospace, "Had no mbuf capacity ");

counter_u64_t merge_fwd;
SYSCTL_COUNTER_U64(_net_inet_tcp_reass_stats, OID_AUTO, merge_fwd, CTLFLAG_RD,
    &merge_fwd, "Ran merge fwd");

counter_u64_t merge_into;
SYSCTL_COUNTER_U64(_net_inet_tcp_reass_stats, OID_AUTO, merge_into, CTLFLAG_RD,
    &merge_into, "Ran merge into");

counter_u64_t tcp_zero_input;
SYSCTL_COUNTER_U64(_net_inet_tcp_reass_stats, OID_AUTO, zero_input, CTLFLAG_RD,
    &tcp_zero_input, "The reassembly buffer saw a zero len segment etc");

#endif

/* Initialize TCP reassembly queue */
static void
tcp_reass_zone_change(void *tag)
{

        /* Set the zone limit and read back the effective value. */
        tcp_reass_maxseg = nmbclusters / 16;
        tcp_reass_maxseg = uma_zone_set_max(tcp_reass_zone,
            tcp_reass_maxseg);
}

#ifdef TCP_REASS_LOGGING

static void
tcp_log_reassm(struct tcpcb *tp, struct tseg_qent *q, struct tseg_qent *p,
    tcp_seq seq, int len, uint8_t action, int instance)
{
        struct socket *so = tptosocket(tp);
        uint32_t cts;
        struct timeval tv;

        if (tp->t_logstate != TCP_LOG_STATE_OFF) {
                union tcp_log_stackspecific log;

                memset(&log, 0, sizeof(log));
                cts = tcp_get_usecs(&tv);
                log.u_bbr.flex1 = seq;
                log.u_bbr.cur_del_rate = (uint64_t)q;
                log.u_bbr.delRate = (uint64_t)p;
                if (q != NULL) {
                        log.u_bbr.flex2 = q->tqe_start;
                        log.u_bbr.flex3 = q->tqe_len;
                        log.u_bbr.flex4 = q->tqe_mbuf_cnt;
                        log.u_bbr.hptsi_gain = q->tqe_flags;
                }
                if (p != NULL)  {
                        log.u_bbr.flex5 = p->tqe_start;
                        log.u_bbr.pkts_out = p->tqe_len;
                        log.u_bbr.epoch = p->tqe_mbuf_cnt;
                        log.u_bbr.cwnd_gain = p->tqe_flags;
                }
                log.u_bbr.flex6 = tp->t_segqmbuflen;
                log.u_bbr.flex7 = instance;
                log.u_bbr.flex8 = action;
                log.u_bbr.timeStamp = cts;
                TCP_LOG_EVENTP(tp, NULL, &so->so_rcv, &so->so_snd,
                    TCP_LOG_REASS, 0,
                    len, &log, false, &tv);
        }
}

static void
tcp_reass_log_dump(struct tcpcb *tp)
{
        struct tseg_qent *q;

        if (tp->t_logstate != TCP_LOG_STATE_OFF) {
                TAILQ_FOREACH(q, &tp->t_segq, tqe_q) {
                        tcp_log_reassm(tp, q, NULL, q->tqe_start, q->tqe_len, TCP_R_LOG_DUMP, 0);
                }
        };
}

static void
tcp_reass_log_new_in(struct tcpcb *tp, tcp_seq seq, int len, struct mbuf *m,
    int logval, struct tseg_qent *q)
{
        int cnt;
        struct mbuf *t;

        cnt = 0;
        t = m;
        while (t) {
                cnt += t->m_len;
                t = t->m_next;
        }
        tcp_log_reassm(tp, q, NULL, seq, len, logval, cnt);
}

#endif

void
tcp_reass_global_init(void)
{

        tcp_reass_maxseg = nmbclusters / 16;
        TUNABLE_INT_FETCH("net.inet.tcp.reass.maxsegments",
            &tcp_reass_maxseg);
        tcp_reass_zone = uma_zcreate("tcpreass", sizeof (struct tseg_qent),
            NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
        /* Set the zone limit and read back the effective value. */
        tcp_reass_maxseg = uma_zone_set_max(tcp_reass_zone,
            tcp_reass_maxseg);
#ifdef TCP_REASS_COUNTERS
        reass_path1 = counter_u64_alloc(M_WAITOK);
        reass_path2 = counter_u64_alloc(M_WAITOK);
        reass_path3 = counter_u64_alloc(M_WAITOK);
        reass_path4 = counter_u64_alloc(M_WAITOK);
        reass_path5 = counter_u64_alloc(M_WAITOK);
        reass_path6 = counter_u64_alloc(M_WAITOK);
        reass_path7 = counter_u64_alloc(M_WAITOK);
        reass_fullwalk = counter_u64_alloc(M_WAITOK);
        reass_nospace = counter_u64_alloc(M_WAITOK);
        reass_entry = counter_u64_alloc(M_WAITOK);
        merge_fwd = counter_u64_alloc(M_WAITOK);
        merge_into = counter_u64_alloc(M_WAITOK);
        tcp_zero_input = counter_u64_alloc(M_WAITOK);
#endif
        EVENTHANDLER_REGISTER(nmbclusters_change,
            tcp_reass_zone_change, NULL, EVENTHANDLER_PRI_ANY);

}

void
tcp_reass_flush(struct tcpcb *tp)
{
        struct tseg_qent *qe;

        INP_WLOCK_ASSERT(tptoinpcb(tp));

        while ((qe = TAILQ_FIRST(&tp->t_segq)) != NULL) {
                TAILQ_REMOVE(&tp->t_segq, qe, tqe_q);
                m_freem(qe->tqe_m);
                uma_zfree(tcp_reass_zone, qe);
                tp->t_segqlen--;
        }
        tp->t_segqmbuflen = 0;
        KASSERT((tp->t_segqlen == 0),
            ("TCP reass queue %p segment count is %d instead of 0 after flush.",
            tp, tp->t_segqlen));
}

static void
tcp_reass_append(struct tcpcb *tp, struct tseg_qent *last,
    struct mbuf *m, struct tcphdr *th, int tlen,
    struct mbuf *mlast, int lenofoh)
{

#ifdef TCP_REASS_LOGGING
        tcp_log_reassm(tp, last, NULL, th->th_seq, tlen, TCP_R_LOG_APPEND, 0);
#endif
        last->tqe_len += tlen;
        last->tqe_m->m_pkthdr.len += tlen;
        /* Preserve the FIN bit if its there */
        last->tqe_flags |= (tcp_get_flags(th) & TH_FIN);
        last->tqe_last->m_next = m;
        last->tqe_last = mlast;
        last->tqe_mbuf_cnt += lenofoh;
        tp->t_rcvoopack++;
        TCPSTAT_INC(tcps_rcvoopack);
        TCPSTAT_ADD(tcps_rcvoobyte, tlen);
#ifdef TCP_REASS_LOGGING
        tcp_reass_log_new_in(tp, last->tqe_start, lenofoh, last->tqe_m,
                             TCP_R_LOG_APPEND,
                             last);
#endif
}

static void
tcp_reass_prepend(struct tcpcb *tp, struct tseg_qent *first, struct mbuf *m, struct tcphdr *th,
                  int tlen, struct mbuf *mlast, int lenofoh)
{
        int i;

#ifdef TCP_REASS_LOGGING
        tcp_log_reassm(tp, first, NULL, th->th_seq, tlen, TCP_R_LOG_PREPEND, 0);
#endif
        if (SEQ_GT((th->th_seq + tlen), first->tqe_start)) {
                /* The new data overlaps into the old */
                i = (th->th_seq + tlen) - first->tqe_start;
#ifdef TCP_REASS_LOGGING
                tcp_log_reassm(tp, first, NULL, 0, i, TCP_R_LOG_TRIM, 1);
#endif
                m_adj(first->tqe_m, i);
                first->tqe_len -= i;
                first->tqe_start += i;
        }
        /* Ok now setup our chain to point to the old first */
        mlast->m_next = first->tqe_m;
        first->tqe_m = m;
        first->tqe_len += tlen;
        first->tqe_start = th->th_seq;
        first->tqe_m->m_pkthdr.len = first->tqe_len;
        first->tqe_mbuf_cnt += lenofoh;
        tp->t_rcvoopack++;
        TCPSTAT_INC(tcps_rcvoopack);
        TCPSTAT_ADD(tcps_rcvoobyte, tlen);
#ifdef TCP_REASS_LOGGING
        tcp_reass_log_new_in(tp, first->tqe_start, lenofoh, first->tqe_m,
                             TCP_R_LOG_PREPEND,
                             first);
#endif
}

static void
tcp_reass_replace(struct tcpcb *tp, struct tseg_qent *q, struct mbuf *m,
    tcp_seq seq, int len, struct mbuf *mlast, int mbufoh, uint16_t flags)
{
        /*
         * Free the data in q, and replace
         * it with the new segment.
         */
        int len_dif;

#ifdef TCP_REASS_LOGGING
        tcp_log_reassm(tp, q, NULL, seq, len, TCP_R_LOG_REPLACE, 0);
#endif
        m_freem(q->tqe_m);
        KASSERT(tp->t_segqmbuflen >= q->tqe_mbuf_cnt,
                ("Tp:%p seg queue goes negative", tp));
        tp->t_segqmbuflen -= q->tqe_mbuf_cnt;
        q->tqe_mbuf_cnt = mbufoh;
        q->tqe_m = m;
        q->tqe_last = mlast;
        q->tqe_start = seq;
        if (len > q->tqe_len)
                len_dif = len - q->tqe_len;
        else
                len_dif = 0;
        tp->t_rcvoopack++;
        TCPSTAT_INC(tcps_rcvoopack);
        TCPSTAT_ADD(tcps_rcvoobyte, len_dif);
        q->tqe_len = len;
        q->tqe_flags = (flags & TH_FIN);
        q->tqe_m->m_pkthdr.len = q->tqe_len;
        tp->t_segqmbuflen += mbufoh;

}

static void
tcp_reass_merge_into(struct tcpcb *tp, struct tseg_qent *ent,
    struct tseg_qent *q)
{
        /*
         * Merge q into ent and free q from the list.
         */
#ifdef TCP_REASS_LOGGING
        tcp_log_reassm(tp, q, ent, 0, 0, TCP_R_LOG_MERGE_INTO, 0);
#endif
#ifdef TCP_REASS_COUNTERS
        counter_u64_add(merge_into, 1);
#endif
        ent->tqe_last->m_next = q->tqe_m;
        ent->tqe_last = q->tqe_last;
        ent->tqe_len += q->tqe_len;
        ent->tqe_mbuf_cnt += q->tqe_mbuf_cnt;
        ent->tqe_m->m_pkthdr.len += q->tqe_len;
        ent->tqe_flags |= (q->tqe_flags & TH_FIN);
        TAILQ_REMOVE(&tp->t_segq, q, tqe_q);
        uma_zfree(tcp_reass_zone, q);
        tp->t_segqlen--;

}

static void
tcp_reass_merge_forward(struct tcpcb *tp, struct tseg_qent *ent)
{
        struct tseg_qent *q, *qtmp;
        int i;
        tcp_seq max;
        /*
         * Given an entry merge forward anyplace
         * that ent overlaps forward.
         */

        max = ent->tqe_start + ent->tqe_len;
        q = TAILQ_NEXT(ent, tqe_q);
        if (q == NULL) {
                /* Nothing left */
                return;
        }
        TAILQ_FOREACH_FROM_SAFE(q, &tp->t_segq, tqe_q, qtmp) {
                if (SEQ_GT(q->tqe_start, max)) {
                        /* Beyond q */
                        break;
                }
                /* We have some or all that are overlapping */
                if (SEQ_GEQ(max, (q->tqe_start + q->tqe_len))) {
                        /* It consumes it all */
                        tp->t_segqmbuflen -= q->tqe_mbuf_cnt;
                        m_freem(q->tqe_m);
                        TAILQ_REMOVE(&tp->t_segq, q, tqe_q);
                        uma_zfree(tcp_reass_zone, q);
                        tp->t_segqlen--;
                        continue;
                }
                /*
                 * Trim the q entry to dovetail to this one
                 * and then merge q into ent updating max
                 * in the process.
                 */
                i = max - q->tqe_start;
#ifdef TCP_REASS_LOGGING
                tcp_log_reassm(tp, q, NULL, 0, i, TCP_R_LOG_TRIM, 2);
#endif
                m_adj(q->tqe_m, i);
                q->tqe_len -= i;
                q->tqe_start += i;
                tcp_reass_merge_into(tp, ent, q);
                max = ent->tqe_start + ent->tqe_len;
        }
#ifdef TCP_REASS_COUNTERS
        counter_u64_add(merge_fwd, 1);
#endif
}

static int
tcp_reass_overhead_of_chain(struct mbuf *m, struct mbuf **mlast)
{
        int len = MSIZE;

        if (m->m_flags & M_EXT)
                len += m->m_ext.ext_size;
        while (m->m_next != NULL) {
                m = m->m_next;
                len += MSIZE;
                if (m->m_flags & M_EXT)
                        len += m->m_ext.ext_size;
        }
        *mlast = m;
        return (len);
}

/*
 * NOTE!!! the new tcp-reassembly code *must not* use
 * m_adj() with a negative index. That alters the chain
 * of mbufs (by possibly chopping trailing mbufs). At
 * the front of tcp_reass we count the mbuf overhead
 * and setup the tail pointer. If we use m_adj(m, -5)
 * we could corrupt the tail pointer. Currently the
 * code only uses m_adj(m, postive-num). If this
 * changes appropriate changes to update mlast would
 * be needed.
 */
int
tcp_reass(struct tcpcb *tp, struct tcphdr *th, tcp_seq *seq_start,
          int *tlenp, struct mbuf *m)
{
        struct tseg_qent *q, *last, *first;
        struct tseg_qent *p = NULL;
        struct tseg_qent *nq = NULL;
        struct tseg_qent *te = NULL;
        struct mbuf *mlast = NULL;
        struct inpcb *inp = tptoinpcb(tp);
        struct socket *so = tptosocket(tp);
        struct sockbuf *sb = &so->so_rcv;
        char *s = NULL;
        int flags, i, lenofoh;

        INP_WLOCK_ASSERT(inp);
        /*
         * XXX: tcp_reass() is rather inefficient with its data structures
         * and should be rewritten (see NetBSD for optimizations).
         */

        KASSERT(th == NULL || (seq_start != NULL && tlenp != NULL),
                ("tcp_reass called with illegal parameter combination "
                 "(tp=%p, th=%p, seq_start=%p, tlenp=%p, m=%p)",
                 tp, th, seq_start, tlenp, m));
        /*
         * Call with th==NULL after become established to
         * force pre-ESTABLISHED data up to user socket.
         */
        if (th == NULL)
                goto present;
        KASSERT(SEQ_GEQ(th->th_seq, tp->rcv_nxt),
                ("Attempt to add old entry to reassembly queue (th=%p, tp=%p)",
                 th, tp));
#ifdef TCP_REASS_LOGGING
        tcp_reass_log_new_in(tp, th->th_seq, *tlenp, m, TCP_R_LOG_ADD, NULL);
#endif
#ifdef TCP_REASS_COUNTERS
        counter_u64_add(reass_entry, 1);
#endif
        /*
         * Check for zero length data.
         */
        if ((*tlenp == 0) && ((tcp_get_flags(th) & TH_FIN) == 0)) {
                /*
                 * A zero length segment does no
                 * one any good. We could check
                 * the rcv_nxt <-> rcv_wnd but thats
                 * already done for us by the caller.
                 */
strip_fin:
#ifdef TCP_REASS_COUNTERS
                counter_u64_add(tcp_zero_input, 1);
#endif
                m_freem(m);
#ifdef TCP_REASS_LOGGING
                tcp_reass_log_dump(tp);
#endif
                return (0);
        } else if ((*tlenp == 0) &&
                   (tcp_get_flags(th) & TH_FIN) &&
                   !TCPS_HAVEESTABLISHED(tp->t_state)) {
                /*
                 * We have not established, and we
                 * have a FIN and no data. Lets treat
                 * this as the same as if the FIN were
                 * not present. We don't want to save
                 * the FIN bit in a reassembly buffer
                 * we want to get established first before
                 * we do that (the peer will retransmit).
                 */
                goto strip_fin;
        }
        /*
         * Will it fit?
         */
        lenofoh = tcp_reass_overhead_of_chain(m, &mlast);
        if ((th->th_seq != tp->rcv_nxt || !TCPS_HAVEESTABLISHED(tp->t_state)) &&
            (sb->sb_mbcnt + tp->t_segqmbuflen + lenofoh) > sb->sb_mbmax) {
                /* No room */
                TCPSTAT_INC(tcps_rcvreassfull);
#ifdef TCP_REASS_COUNTERS
                counter_u64_add(reass_nospace, 1);
#endif
#ifdef TCP_REASS_LOGGING
                tcp_log_reassm(tp, NULL, NULL, th->th_seq, lenofoh, TCP_R_LOG_LIMIT_REACHED, 0);
#endif
                if ((s = tcp_log_addrs(&inp->inp_inc, th, NULL, NULL))) {
                        log(LOG_DEBUG, "%s; %s: mbuf count limit reached, "
                            "segment dropped\n", s, __func__);
                        free(s, M_TCPLOG);
                }
                m_freem(m);
                *tlenp = 0;
#ifdef TCP_REASS_LOGGING
                tcp_reass_log_dump(tp);
#endif
                return (0);
        }
        /*
         * First lets deal with two common cases, the
         * segment appends to the back of our collected
         * segments. Or the segment is the next in line.
         */
        last = TAILQ_LAST_FAST(&tp->t_segq, tseg_qent, tqe_q);
        if (last != NULL) {
                if ((tcp_get_flags(th) & TH_FIN) &&
                    SEQ_LT((th->th_seq + *tlenp), (last->tqe_start + last->tqe_len))) {
                        /*
                         * Someone is trying to game us, dump
                         * the segment.
                         */
                        *tlenp = 0;
                        m_freem(m);
                        return (0);
                }
                if ((SEQ_GEQ(th->th_seq, last->tqe_start)) &&
                    (SEQ_GEQ((last->tqe_start + last->tqe_len), th->th_seq))) {
                        /* Common case, trailing segment is added */
                        /**
                         *                                 +--last
                         *                                 v
                         *  reassembly buffer |---|  |---| |---|
                         *  new segment                       |---|
                         */
#ifdef TCP_REASS_COUNTERS
                        counter_u64_add(reass_path1, 1);
#endif
                        if (SEQ_GT((last->tqe_start + last->tqe_len), th->th_seq)) {
                                i = (last->tqe_start + last->tqe_len) - th->th_seq;
                                if (i < *tlenp) {
#ifdef TCP_REASS_LOGGING
                                        tcp_log_reassm(tp, last, NULL, 0, i, TCP_R_LOG_TRIM, 3);
                                        th->th_seq += i;
#endif
                                        m_adj(m, i);
                                        *tlenp -= i;
                                } else {
                                        /* Complete overlap */
                                        TCPSTAT_INC(tcps_rcvduppack);
                                        TCPSTAT_ADD(tcps_rcvdupbyte, *tlenp);
                                        m_freem(m);
                                        *tlenp = last->tqe_len;
                                        *seq_start = last->tqe_start;
                                        return (0);
                                }
                        }
                        if (last->tqe_flags & TH_FIN) {
                                /*
                                 * We have data after the FIN on the last?
                                 */
                                *tlenp = 0;
                                m_freem(m);
                                return(0);
                        }
                        tcp_reass_append(tp, last, m, th, *tlenp, mlast, lenofoh);
                        tp->t_segqmbuflen += lenofoh;
                        *seq_start = last->tqe_start;
                        *tlenp = last->tqe_len;
                        return (0);
                } else if (SEQ_GT(th->th_seq, (last->tqe_start + last->tqe_len))) {
                        /*
                         * Second common case, we missed
                         * another one and have something more
                         * for the end.
                         */
                        /**
                         *                                 +--last
                         *                                 v
                         *  reassembly buffer |---|  |---| |---|
                         *  new segment                           |---|
                         */
                        if (last->tqe_flags & TH_FIN) {
                                /*
                                 * We have data after the FIN on the last?
                                 */
                                *tlenp = 0;
                                m_freem(m);
                                return(0);
                        }
#ifdef TCP_REASS_COUNTERS
                        counter_u64_add(reass_path2, 1);
#endif
                        p = last;
                        goto new_entry;
                }
        } else {
                /* First segment (it's NULL). */
                goto new_entry;
        }
        first = TAILQ_FIRST(&tp->t_segq);
        if (SEQ_LT(th->th_seq, first->tqe_start) &&
            SEQ_GEQ((th->th_seq + *tlenp),first->tqe_start) &&
            SEQ_LT((th->th_seq + *tlenp), (first->tqe_start + first->tqe_len))) {
                /*
                 * The head of the queue is prepended by this and
                 * it may be the one I want most.
                 */
                /**
                 *       first-------+
                 *                   v
                 *  rea:             |---|  |---| |---|
                 *  new:         |---|
                 * Note the case we do not deal with here is:
                 *   rea=     |---|   |---|   |---|
                 *   new=  |----|
                 * Due to the fact that it could be
                 *   new   |--------------------|
                 * And we might need to merge forward.
                 */
#ifdef INVARIANTS
                struct mbuf *firstmbuf;
#endif

#ifdef TCP_REASS_COUNTERS
                counter_u64_add(reass_path3, 1);
#endif
                if (SEQ_LT(th->th_seq, tp->rcv_nxt)) {
                        /*
                         * The resend was even before
                         * what we have. We need to trim it.
                         * Note TSNH (it should be trimmed
                         * before the call to tcp_reass()).
                         */
#ifdef INVARIANTS
                        panic("th->th_seq:%u rcv_nxt:%u tp:%p not pre-trimmed",
                              th->th_seq, tp->rcv_nxt, tp);
#else
                        i = tp->rcv_nxt - th->th_seq;
#ifdef TCP_REASS_LOGGING
                        tcp_log_reassm(tp, first, NULL, 0, i, TCP_R_LOG_TRIM, 4);
#endif
                        m_adj(m, i);
                        th->th_seq += i;
                        *tlenp -= i;
#endif
                }
#ifdef INVARIANTS
                firstmbuf = first->tqe_m;
#endif
                tcp_reass_prepend(tp, first, m, th, *tlenp, mlast, lenofoh);
#ifdef INVARIANTS
                if (firstmbuf == first->tqe_m) {
                        panic("First stayed same m:%p foobar:%p first->tqe_m:%p tp:%p first:%p",
                              m, firstmbuf, first->tqe_m, tp, first);
                } else if (first->tqe_m != m) {
                        panic("First did not change to m:%p foobar:%p first->tqe_m:%p tp:%p first:%p",
                              m, firstmbuf, first->tqe_m, tp, first);
                }
#endif
                tp->t_segqmbuflen += lenofoh;
                *seq_start = first->tqe_start;
                *tlenp = first->tqe_len;
                goto present;
        } else if (SEQ_LT((th->th_seq + *tlenp), first->tqe_start)) {
                /* New segment is before our earliest segment. */
                /**
                 *           first---->+
                 *                      v
                 *  rea=                |---| ....
                 *  new"         |---|
                 *
                 */
                goto new_entry;
        }
        /*
         * Find a segment which begins after this one does.
         */
#ifdef TCP_REASS_COUNTERS
        counter_u64_add(reass_fullwalk, 1);
#endif
        TAILQ_FOREACH(q, &tp->t_segq, tqe_q) {
                if (SEQ_GT(q->tqe_start, th->th_seq))
                        break;
        }
        p = TAILQ_PREV(q, tsegqe_head, tqe_q);
        /**
         * Now is this fit just in-between only?
         * i.e.:
         *      p---+        +----q
         *          v        v
         *     res= |--|     |--|    |--|
         *     nee       |-|
         */
        if (SEQ_LT((th->th_seq + *tlenp), q->tqe_start) &&
            ((p == NULL) || (SEQ_GT(th->th_seq, (p->tqe_start + p->tqe_len))))) {
                /* Yep no overlap */
                goto new_entry;
        }
        /**
         * If we reach here we have some (possibly all) overlap
         * such as:
         *     res=     |--|     |--|    |--|
         *     new=  |----|
         * or  new=  |-----------------|
         * or  new=      |--------|
         * or  new=            |---|
         * or  new=            |-----------|
         */
        if ((p != NULL) &&
            (SEQ_LEQ(th->th_seq, (p->tqe_start + p->tqe_len)))) {
                /* conversion to int (in i) handles seq wraparound */

#ifdef TCP_REASS_COUNTERS
                counter_u64_add(reass_path4, 1);
#endif
                i = p->tqe_start + p->tqe_len - th->th_seq;
                if (i >= 0) {
                        if (i >= *tlenp) {
                                /**
                                 *       prev seg---->+
                                 *                    v
                                 *  reassembly buffer |---|
                                 *  new segment        |-|
                                 */
                                TCPSTAT_INC(tcps_rcvduppack);
                                TCPSTAT_ADD(tcps_rcvdupbyte, *tlenp);
                                *tlenp = p->tqe_len;
                                *seq_start = p->tqe_start;
                                m_freem(m);
                                /*
                                 * Try to present any queued data
                                 * at the left window edge to the user.
                                 * This is needed after the 3-WHS
                                 * completes. Note this probably
                                 * will not work and we will return.
                                 */
                                return (0);
                        }
                        if (i > 0) {
                                /**
                                 *       prev seg---->+
                                 *                    v
                                 *  reassembly buffer |---|
                                 *  new segment         |-----|
                                 */
#ifdef TCP_REASS_COUNTERS
                                counter_u64_add(reass_path5, 1);
#endif
#ifdef TCP_REASS_LOGGING
                                tcp_log_reassm(tp, p, NULL, 0, i, TCP_R_LOG_TRIM, 5);
#endif
                                m_adj(m, i);
                                *tlenp -= i;
                                th->th_seq += i;
                        }
                }
                if (th->th_seq == (p->tqe_start + p->tqe_len)) {
                        /*
                         * If dovetails in with this one
                         * append it.
                         */
                        /**
                         *       prev seg---->+
                         *                    v
                         *  reassembly buffer |--|     |---|
                         *  new segment          |--|
                         * (note: it was trimmed above if it overlapped)
                         */
                        tcp_reass_append(tp, p, m, th, *tlenp, mlast, lenofoh);
                        tp->t_segqmbuflen += lenofoh;
                } else {
#ifdef INVARIANTS
                        panic("Impossible cut th_seq:%u p->seq:%u(%d) p:%p tp:%p",
                              th->th_seq, p->tqe_start, p->tqe_len,
                              p, tp);
#endif
                        *tlenp = 0;
                        m_freem(m);
                        return (0);
                }
                q = p;
        } else {
                /*
                 * The new data runs over the
                 * top of previously sack'd data (in q).
                 * It may be partially overlapping, or
                 * it may overlap the entire segment.
                 */
#ifdef TCP_REASS_COUNTERS
                counter_u64_add(reass_path6, 1);
#endif
                if (SEQ_GEQ((th->th_seq + *tlenp), (q->tqe_start + q->tqe_len))) {
                        /* It consumes it all */
                        /**
                         *             next seg---->+
                         *                          v
                         *  reassembly buffer |--|     |---|
                         *  new segment              |----------|
                         */
#ifdef TCP_REASS_COUNTERS
                        counter_u64_add(reass_path7, 1);
#endif
                        tcp_reass_replace(tp, q, m, th->th_seq, *tlenp, mlast, lenofoh, tcp_get_flags(th));
                } else {
                        /*
                         * We just need to prepend the data
                         * to this. It does not overrun
                         * the end.
                         */
                        /**
                         *                next seg---->+
                         *                             v
                         *  reassembly buffer |--|     |---|
                         *  new segment                   |----------|
                         */
                        tcp_reass_prepend(tp, q, m, th, *tlenp, mlast, lenofoh);
                        tp->t_segqmbuflen += lenofoh;
                }
        }
        /* Now does it go further than that? */
        tcp_reass_merge_forward(tp, q);
        *seq_start = q->tqe_start;
        *tlenp = q->tqe_len;
        goto present;

        /*
         * When we reach here we can't combine it
         * with any existing segment.
         *
         * Limit the number of segments that can be queued to reduce the
         * potential for mbuf exhaustion. For best performance, we want to be
         * able to queue a full window's worth of segments. The size of the
         * socket receive buffer determines our advertised window and grows
         * automatically when socket buffer autotuning is enabled. Use it as the
         * basis for our queue limit.
         *
         * However, allow the user to specify a ceiling for the number of
         * segments in each queue.
         *
         * Always let the missing segment through which caused this queue.
         * NB: Access to the socket buffer is left intentionally unlocked as we
         * can tolerate stale information here.
         *
         * XXXLAS: Using sbspace(so->so_rcv) instead of so->so_rcv.sb_hiwat
         * should work but causes packets to be dropped when they shouldn't.
         * Investigate why and re-evaluate the below limit after the behaviour
         * is understood.
         */
new_entry:
        if (th->th_seq == tp->rcv_nxt && TCPS_HAVEESTABLISHED(tp->t_state)) {
                tp->rcv_nxt += *tlenp;
                flags = tcp_get_flags(th) & TH_FIN;
                TCPSTAT_INC(tcps_rcvoopack);
                TCPSTAT_ADD(tcps_rcvoobyte, *tlenp);
                SOCK_RECVBUF_LOCK(so);
                if (so->so_rcv.sb_state & SBS_CANTRCVMORE) {
                        m_freem(m);
                } else {
                        sbappendstream_locked(&so->so_rcv, m, 0);
                }
                tp->t_flags |= TF_WAKESOR;
                return (flags);
        }
        if (tcp_new_limits) {
                if ((tp->t_segqlen > tcp_reass_queue_guard) &&
                    (*tlenp < MSIZE)) {
                        /*
                         * This is really a lie, we are not full but
                         * are getting a segment that is above
                         * guard threshold. If it is and its below
                         * a mbuf size (256) we drop it if it
                         * can't fill in some place.
                         */
                        TCPSTAT_INC(tcps_rcvreassfull);
                        *tlenp = 0;
                        if ((s = tcp_log_addrs(&inp->inp_inc, th, NULL, NULL))) {
                                log(LOG_DEBUG, "%s; %s: queue limit reached, "
                                    "segment dropped\n", s, __func__);
                                free(s, M_TCPLOG);
                        }
                        m_freem(m);
#ifdef TCP_REASS_LOGGING
                        tcp_reass_log_dump(tp);
#endif
                        return (0);
                }
        } else {
                if (tp->t_segqlen >= min((so->so_rcv.sb_hiwat / tp->t_maxseg) + 1,
                                         tcp_reass_maxqueuelen)) {
                        TCPSTAT_INC(tcps_rcvreassfull);
                        *tlenp = 0;
                        if ((s = tcp_log_addrs(&inp->inp_inc, th, NULL, NULL))) {
                                log(LOG_DEBUG, "%s; %s: queue limit reached, "
                                    "segment dropped\n", s, __func__);
                                free(s, M_TCPLOG);
                        }
                        m_freem(m);
#ifdef TCP_REASS_LOGGING
                        tcp_reass_log_dump(tp);
#endif
                        return (0);
                }
        }
        /*
         * Allocate a new queue entry. If we can't, or hit the zone limit
         * just drop the pkt.
         */
        te = uma_zalloc(tcp_reass_zone, M_NOWAIT);
        if (te == NULL) {
                TCPSTAT_INC(tcps_rcvmemdrop);
                m_freem(m);
                *tlenp = 0;
                if ((s = tcp_log_addrs(&inp->inp_inc, th, NULL, NULL))) {
                        log(LOG_DEBUG, "%s; %s: global zone limit "
                            "reached, segment dropped\n", s, __func__);
                        free(s, M_TCPLOG);
                }
                return (0);
        }
        tp->t_segqlen++;
        tp->t_rcvoopack++;
        TCPSTAT_INC(tcps_rcvoopack);
        TCPSTAT_ADD(tcps_rcvoobyte, *tlenp);
        /* Insert the new segment queue entry into place. */
        te->tqe_m = m;
        te->tqe_flags = tcp_get_flags(th);
        te->tqe_len = *tlenp;
        te->tqe_start = th->th_seq;
        te->tqe_last = mlast;
        te->tqe_mbuf_cnt = lenofoh;
        tp->t_segqmbuflen += te->tqe_mbuf_cnt;
        if (p == NULL) {
                TAILQ_INSERT_HEAD(&tp->t_segq, te, tqe_q);
        } else {
                TAILQ_INSERT_AFTER(&tp->t_segq, p, te, tqe_q);
        }
#ifdef TCP_REASS_LOGGING
        tcp_reass_log_new_in(tp, th->th_seq, *tlenp, m, TCP_R_LOG_NEW_ENTRY, te);
#endif
present:
        /*
         * Present data to user, advancing rcv_nxt through
         * completed sequence space.
         */
        if (!TCPS_HAVEESTABLISHED(tp->t_state))
                return (0);
        q = TAILQ_FIRST(&tp->t_segq);
        KASSERT(q == NULL || SEQ_GEQ(q->tqe_start, tp->rcv_nxt),
                ("Reassembly queue for %p has stale entry at head", tp));
        if (!q || q->tqe_start != tp->rcv_nxt) {
#ifdef TCP_REASS_LOGGING
                tcp_reass_log_dump(tp);
#endif
                return (0);
        }
        SOCK_RECVBUF_LOCK(so);
        do {
                tp->rcv_nxt += q->tqe_len;
                flags = q->tqe_flags & TH_FIN;
                nq = TAILQ_NEXT(q, tqe_q);
                TAILQ_REMOVE(&tp->t_segq, q, tqe_q);
                if (so->so_rcv.sb_state & SBS_CANTRCVMORE) {
                        m_freem(q->tqe_m);
                } else {
#ifdef TCP_REASS_LOGGING
                        tcp_reass_log_new_in(tp, q->tqe_start, q->tqe_len, q->tqe_m, TCP_R_LOG_READ, q);
                        if (th != NULL) {
                                tcp_log_reassm(tp, q, NULL, th->th_seq, *tlenp, TCP_R_LOG_READ, 1);
                        } else {
                                tcp_log_reassm(tp, q, NULL, 0, 0, TCP_R_LOG_READ, 1);
                        }
#endif
                        sbappendstream_locked(&so->so_rcv, q->tqe_m, 0);
                }
#ifdef TCP_REASS_LOGGING
                if (th != NULL) {
                        tcp_log_reassm(tp, q, NULL, th->th_seq, *tlenp, TCP_R_LOG_READ, 2);
                } else {
                        tcp_log_reassm(tp, q, NULL, 0, 0, TCP_R_LOG_READ, 2);
                }
#endif
                KASSERT(tp->t_segqmbuflen >= q->tqe_mbuf_cnt,
                        ("tp:%p seg queue goes negative", tp));
                tp->t_segqmbuflen -= q->tqe_mbuf_cnt;
                uma_zfree(tcp_reass_zone, q);
                tp->t_segqlen--;
                q = nq;
        } while (q && q->tqe_start == tp->rcv_nxt);
        if (TAILQ_EMPTY(&tp->t_segq) &&
            (tp->t_segqmbuflen != 0)) {
#ifdef INVARIANTS
                panic("tp:%p segq:%p len:%d queue empty",
                      tp, &tp->t_segq, tp->t_segqmbuflen);
#else
#ifdef TCP_REASS_LOGGING
                if (th != NULL) {
                        tcp_log_reassm(tp, NULL, NULL, th->th_seq, *tlenp, TCP_R_LOG_ZERO, 0);
                } else {
                        tcp_log_reassm(tp, NULL, NULL, 0, 0, TCP_R_LOG_ZERO, 0);
                }
#endif
                tp->t_segqmbuflen = 0;
#endif
        }
#ifdef TCP_REASS_LOGGING
        tcp_reass_log_dump(tp);
#endif
        tp->t_flags |= TF_WAKESOR;
        return (flags);
}