In m_pulldown(), before trying to prepend bytes to the subsequent mbuf,

[FreeBSD/FreeBSD.git] / sys / netinet / tcp_subr.c

/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * Copyright (c) 1982, 1986, 1988, 1990, 1993, 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_subr.c  8.2 (Berkeley) 5/24/95
 */

#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");

#include "opt_inet.h"
#include "opt_inet6.h"
#include "opt_ipsec.h"
#include "opt_tcpdebug.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/callout.h>
#include <sys/eventhandler.h>
#ifdef TCP_HHOOK
#include <sys/hhook.h>
#endif
#include <sys/kernel.h>
#ifdef TCP_HHOOK
#include <sys/khelp.h>
#endif
#include <sys/sysctl.h>
#include <sys/jail.h>
#include <sys/malloc.h>
#include <sys/refcount.h>
#include <sys/mbuf.h>
#ifdef INET6
#include <sys/domain.h>
#endif
#include <sys/priv.h>
#include <sys/proc.h>
#include <sys/sdt.h>
#include <sys/socket.h>
#include <sys/socketvar.h>
#include <sys/protosw.h>
#include <sys/random.h>

#include <vm/uma.h>

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

#include <netinet/in.h>
#include <netinet/in_fib.h>
#include <netinet/in_kdtrace.h>
#include <netinet/in_pcb.h>
#include <netinet/in_systm.h>
#include <netinet/in_var.h>
#include <netinet/ip.h>
#include <netinet/ip_icmp.h>
#include <netinet/ip_var.h>
#ifdef INET6
#include <netinet/icmp6.h>
#include <netinet/ip6.h>
#include <netinet6/in6_fib.h>
#include <netinet6/in6_pcb.h>
#include <netinet6/ip6_var.h>
#include <netinet6/scope6_var.h>
#include <netinet6/nd6.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_log_buf.h>
#include <netinet/tcp_syncache.h>
#include <netinet/tcp_hpts.h>
#include <netinet/cc/cc.h>
#ifdef INET6
#include <netinet6/tcp6_var.h>
#endif
#include <netinet/tcpip.h>
#include <netinet/tcp_fastopen.h>
#ifdef TCPPCAP
#include <netinet/tcp_pcap.h>
#endif
#ifdef TCPDEBUG
#include <netinet/tcp_debug.h>
#endif
#ifdef INET6
#include <netinet6/ip6protosw.h>
#endif
#ifdef TCP_OFFLOAD
#include <netinet/tcp_offload.h>
#endif

#include <netipsec/ipsec_support.h>

#include <machine/in_cksum.h>
#include <sys/md5.h>

#include <security/mac/mac_framework.h>

VNET_DEFINE(int, tcp_mssdflt) = TCP_MSS;
#ifdef INET6
VNET_DEFINE(int, tcp_v6mssdflt) = TCP6_MSS;
#endif

struct rwlock tcp_function_lock;

static int
sysctl_net_inet_tcp_mss_check(SYSCTL_HANDLER_ARGS)
{
        int error, new;

        new = V_tcp_mssdflt;
        error = sysctl_handle_int(oidp, &new, 0, req);
        if (error == 0 && req->newptr) {
                if (new < TCP_MINMSS)
                        error = EINVAL;
                else
                        V_tcp_mssdflt = new;
        }
        return (error);
}

SYSCTL_PROC(_net_inet_tcp, TCPCTL_MSSDFLT, mssdflt,
    CTLFLAG_VNET | CTLTYPE_INT | CTLFLAG_RW, &VNET_NAME(tcp_mssdflt), 0,
    &sysctl_net_inet_tcp_mss_check, "I",
    "Default TCP Maximum Segment Size");

#ifdef INET6
static int
sysctl_net_inet_tcp_mss_v6_check(SYSCTL_HANDLER_ARGS)
{
        int error, new;

        new = V_tcp_v6mssdflt;
        error = sysctl_handle_int(oidp, &new, 0, req);
        if (error == 0 && req->newptr) {
                if (new < TCP_MINMSS)
                        error = EINVAL;
                else
                        V_tcp_v6mssdflt = new;
        }
        return (error);
}

SYSCTL_PROC(_net_inet_tcp, TCPCTL_V6MSSDFLT, v6mssdflt,
    CTLFLAG_VNET | CTLTYPE_INT | CTLFLAG_RW, &VNET_NAME(tcp_v6mssdflt), 0,
    &sysctl_net_inet_tcp_mss_v6_check, "I",
   "Default TCP Maximum Segment Size for IPv6");
#endif /* INET6 */

/*
 * Minimum MSS we accept and use. This prevents DoS attacks where
 * we are forced to a ridiculous low MSS like 20 and send hundreds
 * of packets instead of one. The effect scales with the available
 * bandwidth and quickly saturates the CPU and network interface
 * with packet generation and sending. Set to zero to disable MINMSS
 * checking. This setting prevents us from sending too small packets.
 */
VNET_DEFINE(int, tcp_minmss) = TCP_MINMSS;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, minmss, CTLFLAG_VNET | CTLFLAG_RW,
     &VNET_NAME(tcp_minmss), 0,
    "Minimum TCP Maximum Segment Size");

VNET_DEFINE(int, tcp_do_rfc1323) = 1;
SYSCTL_INT(_net_inet_tcp, TCPCTL_DO_RFC1323, rfc1323, CTLFLAG_VNET | CTLFLAG_RW,
    &VNET_NAME(tcp_do_rfc1323), 0,
    "Enable rfc1323 (high performance TCP) extensions");

VNET_DEFINE(int, tcp_ts_offset_per_conn) = 1;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, ts_offset_per_conn, CTLFLAG_VNET | CTLFLAG_RW,
    &VNET_NAME(tcp_ts_offset_per_conn), 0,
    "Initialize TCP timestamps per connection instead of per host pair");

static int      tcp_log_debug = 0;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, log_debug, CTLFLAG_RW,
    &tcp_log_debug, 0, "Log errors caused by incoming TCP segments");

static int      tcp_tcbhashsize;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, tcbhashsize, CTLFLAG_RDTUN | CTLFLAG_NOFETCH,
    &tcp_tcbhashsize, 0, "Size of TCP control-block hashtable");

static int      do_tcpdrain = 1;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, do_tcpdrain, CTLFLAG_RW, &do_tcpdrain, 0,
    "Enable tcp_drain routine for extra help when low on mbufs");

SYSCTL_UINT(_net_inet_tcp, OID_AUTO, pcbcount, CTLFLAG_VNET | CTLFLAG_RD,
    &VNET_NAME(tcbinfo.ipi_count), 0, "Number of active PCBs");

VNET_DEFINE_STATIC(int, icmp_may_rst) = 1;
#define V_icmp_may_rst                  VNET(icmp_may_rst)
SYSCTL_INT(_net_inet_tcp, OID_AUTO, icmp_may_rst, CTLFLAG_VNET | CTLFLAG_RW,
    &VNET_NAME(icmp_may_rst), 0,
    "Certain ICMP unreachable messages may abort connections in SYN_SENT");

VNET_DEFINE_STATIC(int, tcp_isn_reseed_interval) = 0;
#define V_tcp_isn_reseed_interval       VNET(tcp_isn_reseed_interval)
SYSCTL_INT(_net_inet_tcp, OID_AUTO, isn_reseed_interval, CTLFLAG_VNET | CTLFLAG_RW,
    &VNET_NAME(tcp_isn_reseed_interval), 0,
    "Seconds between reseeding of ISN secret");

static int      tcp_soreceive_stream;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, soreceive_stream, CTLFLAG_RDTUN,
    &tcp_soreceive_stream, 0, "Using soreceive_stream for TCP sockets");

VNET_DEFINE(uma_zone_t, sack_hole_zone);
#define V_sack_hole_zone                VNET(sack_hole_zone)

#ifdef TCP_HHOOK
VNET_DEFINE(struct hhook_head *, tcp_hhh[HHOOK_TCP_LAST+1]);
#endif

#define TS_OFFSET_SECRET_LENGTH 32
VNET_DEFINE_STATIC(u_char, ts_offset_secret[TS_OFFSET_SECRET_LENGTH]);
#define V_ts_offset_secret      VNET(ts_offset_secret)

static int      tcp_default_fb_init(struct tcpcb *tp);
static void     tcp_default_fb_fini(struct tcpcb *tp, int tcb_is_purged);
static int      tcp_default_handoff_ok(struct tcpcb *tp);
static struct inpcb *tcp_notify(struct inpcb *, int);
static struct inpcb *tcp_mtudisc_notify(struct inpcb *, int);
static void tcp_mtudisc(struct inpcb *, int);
static char *   tcp_log_addr(struct in_conninfo *inc, struct tcphdr *th,
                    void *ip4hdr, const void *ip6hdr);


static struct tcp_function_block tcp_def_funcblk = {
        .tfb_tcp_block_name = "freebsd",
        .tfb_tcp_output = tcp_output,
        .tfb_tcp_do_segment = tcp_do_segment,
        .tfb_tcp_ctloutput = tcp_default_ctloutput,
        .tfb_tcp_handoff_ok = tcp_default_handoff_ok,
        .tfb_tcp_fb_init = tcp_default_fb_init,
        .tfb_tcp_fb_fini = tcp_default_fb_fini,
};

static int tcp_fb_cnt = 0;
struct tcp_funchead t_functions;
static struct tcp_function_block *tcp_func_set_ptr = &tcp_def_funcblk;

static struct tcp_function_block *
find_tcp_functions_locked(struct tcp_function_set *fs)
{
        struct tcp_function *f;
        struct tcp_function_block *blk=NULL;

        TAILQ_FOREACH(f, &t_functions, tf_next) {
                if (strcmp(f->tf_name, fs->function_set_name) == 0) {
                        blk = f->tf_fb;
                        break;
                }
        }
        return(blk);
}

static struct tcp_function_block *
find_tcp_fb_locked(struct tcp_function_block *blk, struct tcp_function **s)
{
        struct tcp_function_block *rblk=NULL;
        struct tcp_function *f;

        TAILQ_FOREACH(f, &t_functions, tf_next) {
                if (f->tf_fb == blk) {
                        rblk = blk;
                        if (s) {
                                *s = f;
                        }
                        break;
                }
        }
        return (rblk);
}

struct tcp_function_block *
find_and_ref_tcp_functions(struct tcp_function_set *fs)
{
        struct tcp_function_block *blk;
        
        rw_rlock(&tcp_function_lock);   
        blk = find_tcp_functions_locked(fs);
        if (blk)
                refcount_acquire(&blk->tfb_refcnt); 
        rw_runlock(&tcp_function_lock);
        return(blk);
}

struct tcp_function_block *
find_and_ref_tcp_fb(struct tcp_function_block *blk)
{
        struct tcp_function_block *rblk;
        
        rw_rlock(&tcp_function_lock);   
        rblk = find_tcp_fb_locked(blk, NULL);
        if (rblk) 
                refcount_acquire(&rblk->tfb_refcnt);
        rw_runlock(&tcp_function_lock);
        return(rblk);
}

static struct tcp_function_block *
find_and_ref_tcp_default_fb(void)
{
        struct tcp_function_block *rblk;

        rw_rlock(&tcp_function_lock);
        rblk = tcp_func_set_ptr;
        refcount_acquire(&rblk->tfb_refcnt);
        rw_runlock(&tcp_function_lock);
        return (rblk);
}

void
tcp_switch_back_to_default(struct tcpcb *tp)
{
        struct tcp_function_block *tfb;

        KASSERT(tp->t_fb != &tcp_def_funcblk,
            ("%s: called by the built-in default stack", __func__));

        /*
         * Release the old stack. This function will either find a new one
         * or panic.
         */
        if (tp->t_fb->tfb_tcp_fb_fini != NULL)
                (*tp->t_fb->tfb_tcp_fb_fini)(tp, 0);
        refcount_release(&tp->t_fb->tfb_refcnt);

        /*
         * Now, we'll find a new function block to use.
         * Start by trying the current user-selected
         * default, unless this stack is the user-selected
         * default.
         */
        tfb = find_and_ref_tcp_default_fb();
        if (tfb == tp->t_fb) {
                refcount_release(&tfb->tfb_refcnt);
                tfb = NULL;
        }
        /* Does the stack accept this connection? */
        if (tfb != NULL && tfb->tfb_tcp_handoff_ok != NULL &&
            (*tfb->tfb_tcp_handoff_ok)(tp)) {
                refcount_release(&tfb->tfb_refcnt);
                tfb = NULL;
        }
        /* Try to use that stack. */
        if (tfb != NULL) {
                /* Initialize the new stack. If it succeeds, we are done. */
                tp->t_fb = tfb;
                if (tp->t_fb->tfb_tcp_fb_init == NULL ||
                    (*tp->t_fb->tfb_tcp_fb_init)(tp) == 0)
                        return;

                /*
                 * Initialization failed. Release the reference count on
                 * the stack.
                 */
                refcount_release(&tfb->tfb_refcnt);
        }

        /*
         * If that wasn't feasible, use the built-in default
         * stack which is not allowed to reject anyone.
         */
        tfb = find_and_ref_tcp_fb(&tcp_def_funcblk);
        if (tfb == NULL) {
                /* there always should be a default */
                panic("Can't refer to tcp_def_funcblk");
        }
        if (tfb->tfb_tcp_handoff_ok != NULL) {
                if ((*tfb->tfb_tcp_handoff_ok) (tp)) {
                        /* The default stack cannot say no */
                        panic("Default stack rejects a new session?");
                }
        }
        tp->t_fb = tfb;
        if (tp->t_fb->tfb_tcp_fb_init != NULL &&
            (*tp->t_fb->tfb_tcp_fb_init)(tp)) {
                /* The default stack cannot fail */
                panic("Default stack initialization failed");
        }
}

static int
sysctl_net_inet_default_tcp_functions(SYSCTL_HANDLER_ARGS)
{
        int error=ENOENT;
        struct tcp_function_set fs;
        struct tcp_function_block *blk;

        memset(&fs, 0, sizeof(fs));
        rw_rlock(&tcp_function_lock);
        blk = find_tcp_fb_locked(tcp_func_set_ptr, NULL);
        if (blk) {
                /* Found him */
                strcpy(fs.function_set_name, blk->tfb_tcp_block_name);
                fs.pcbcnt = blk->tfb_refcnt;
        }
        rw_runlock(&tcp_function_lock); 
        error = sysctl_handle_string(oidp, fs.function_set_name,
                                     sizeof(fs.function_set_name), req);

        /* Check for error or no change */
        if (error != 0 || req->newptr == NULL)
                return(error);

        rw_wlock(&tcp_function_lock);
        blk = find_tcp_functions_locked(&fs);
        if ((blk == NULL) ||
            (blk->tfb_flags & TCP_FUNC_BEING_REMOVED)) { 
                error = ENOENT; 
                goto done;
        }
        tcp_func_set_ptr = blk;
done:
        rw_wunlock(&tcp_function_lock);
        return (error);
}

SYSCTL_PROC(_net_inet_tcp, OID_AUTO, functions_default,
            CTLTYPE_STRING | CTLFLAG_RW,
            NULL, 0, sysctl_net_inet_default_tcp_functions, "A",
            "Set/get the default TCP functions");

static int
sysctl_net_inet_list_available(SYSCTL_HANDLER_ARGS)
{
        int error, cnt, linesz;
        struct tcp_function *f;
        char *buffer, *cp;
        size_t bufsz, outsz;
        bool alias;

        cnt = 0;
        rw_rlock(&tcp_function_lock);
        TAILQ_FOREACH(f, &t_functions, tf_next) {
                cnt++;
        }
        rw_runlock(&tcp_function_lock);

        bufsz = (cnt+2) * ((TCP_FUNCTION_NAME_LEN_MAX * 2) + 13) + 1;
        buffer = malloc(bufsz, M_TEMP, M_WAITOK);

        error = 0;
        cp = buffer;

        linesz = snprintf(cp, bufsz, "\n%-32s%c %-32s %s\n", "Stack", 'D',
            "Alias", "PCB count");
        cp += linesz;
        bufsz -= linesz;
        outsz = linesz;

        rw_rlock(&tcp_function_lock);   
        TAILQ_FOREACH(f, &t_functions, tf_next) {
                alias = (f->tf_name != f->tf_fb->tfb_tcp_block_name);
                linesz = snprintf(cp, bufsz, "%-32s%c %-32s %u\n",
                    f->tf_fb->tfb_tcp_block_name,
                    (f->tf_fb == tcp_func_set_ptr) ? '*' : ' ',
                    alias ? f->tf_name : "-",
                    f->tf_fb->tfb_refcnt);
                if (linesz >= bufsz) {
                        error = EOVERFLOW;
                        break;
                }
                cp += linesz;
                bufsz -= linesz;
                outsz += linesz;
        }
        rw_runlock(&tcp_function_lock);
        if (error == 0)
                error = sysctl_handle_string(oidp, buffer, outsz + 1, req);
        free(buffer, M_TEMP);
        return (error);
}

SYSCTL_PROC(_net_inet_tcp, OID_AUTO, functions_available,
            CTLTYPE_STRING|CTLFLAG_RD,
            NULL, 0, sysctl_net_inet_list_available, "A",
            "list available TCP Function sets");

/*
 * Exports one (struct tcp_function_info) for each alias/name.
 */
static int
sysctl_net_inet_list_func_info(SYSCTL_HANDLER_ARGS)
{
        int cnt, error;
        struct tcp_function *f;
        struct tcp_function_info tfi;

        /*
         * We don't allow writes.
         */
        if (req->newptr != NULL)
                return (EINVAL);

        /*
         * Wire the old buffer so we can directly copy the functions to
         * user space without dropping the lock.
         */
        if (req->oldptr != NULL) {
                error = sysctl_wire_old_buffer(req, 0);
                if (error)
                        return (error);
        }

        /*
         * Walk the list and copy out matching entries. If INVARIANTS
         * is compiled in, also walk the list to verify the length of
         * the list matches what we have recorded.
         */
        rw_rlock(&tcp_function_lock);

        cnt = 0;
#ifndef INVARIANTS
        if (req->oldptr == NULL) {
                cnt = tcp_fb_cnt;
                goto skip_loop;
        }
#endif
        TAILQ_FOREACH(f, &t_functions, tf_next) {
#ifdef INVARIANTS
                cnt++;
#endif
                if (req->oldptr != NULL) {
                        bzero(&tfi, sizeof(tfi));
                        tfi.tfi_refcnt = f->tf_fb->tfb_refcnt;
                        tfi.tfi_id = f->tf_fb->tfb_id;
                        (void)strlcpy(tfi.tfi_alias, f->tf_name,
                            sizeof(tfi.tfi_alias));
                        (void)strlcpy(tfi.tfi_name,
                            f->tf_fb->tfb_tcp_block_name, sizeof(tfi.tfi_name));
                        error = SYSCTL_OUT(req, &tfi, sizeof(tfi));
                        /*
                         * Don't stop on error, as that is the
                         * mechanism we use to accumulate length
                         * information if the buffer was too short.
                         */
                }
        }
        KASSERT(cnt == tcp_fb_cnt,
            ("%s: cnt (%d) != tcp_fb_cnt (%d)", __func__, cnt, tcp_fb_cnt));
#ifndef INVARIANTS
skip_loop:
#endif
        rw_runlock(&tcp_function_lock);
        if (req->oldptr == NULL)
                error = SYSCTL_OUT(req, NULL,
                    (cnt + 1) * sizeof(struct tcp_function_info));

        return (error);
}

SYSCTL_PROC(_net_inet_tcp, OID_AUTO, function_info,
            CTLTYPE_OPAQUE | CTLFLAG_SKIP | CTLFLAG_RD | CTLFLAG_MPSAFE,
            NULL, 0, sysctl_net_inet_list_func_info, "S,tcp_function_info",
            "List TCP function block name-to-ID mappings");

/*
 * tfb_tcp_handoff_ok() function for the default stack.
 * Note that we'll basically try to take all comers.
 */
static int
tcp_default_handoff_ok(struct tcpcb *tp)
{

        return (0);
}

/*
 * tfb_tcp_fb_init() function for the default stack.
 *
 * This handles making sure we have appropriate timers set if you are
 * transitioning a socket that has some amount of setup done.
 *
 * The init() fuction from the default can *never* return non-zero i.e.
 * it is required to always succeed since it is the stack of last resort!
 */
static int
tcp_default_fb_init(struct tcpcb *tp)
{

        struct socket *so;

        INP_WLOCK_ASSERT(tp->t_inpcb);

        KASSERT(tp->t_state >= 0 && tp->t_state < TCPS_TIME_WAIT,
            ("%s: connection %p in unexpected state %d", __func__, tp,
            tp->t_state));

        /*
         * Nothing to do for ESTABLISHED or LISTEN states. And, we don't
         * know what to do for unexpected states (which includes TIME_WAIT).
         */
        if (tp->t_state <= TCPS_LISTEN || tp->t_state >= TCPS_TIME_WAIT)
                return (0);

        /*
         * Make sure some kind of transmission timer is set if there is
         * outstanding data.
         */
        so = tp->t_inpcb->inp_socket;
        if ((!TCPS_HAVEESTABLISHED(tp->t_state) || sbavail(&so->so_snd) ||
            tp->snd_una != tp->snd_max) && !(tcp_timer_active(tp, TT_REXMT) ||
            tcp_timer_active(tp, TT_PERSIST))) {
                /*
                 * If the session has established and it looks like it should
                 * be in the persist state, set the persist timer. Otherwise,
                 * set the retransmit timer.
                 */
                if (TCPS_HAVEESTABLISHED(tp->t_state) && tp->snd_wnd == 0 &&
                    (int32_t)(tp->snd_nxt - tp->snd_una) <
                    (int32_t)sbavail(&so->so_snd))
                        tcp_setpersist(tp);
                else
                        tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
        }

        /* All non-embryonic sessions get a keepalive timer. */
        if (!tcp_timer_active(tp, TT_KEEP))
                tcp_timer_activate(tp, TT_KEEP,
                    TCPS_HAVEESTABLISHED(tp->t_state) ? TP_KEEPIDLE(tp) :
                    TP_KEEPINIT(tp));

        return (0);
}

/*
 * tfb_tcp_fb_fini() function for the default stack.
 *
 * This changes state as necessary (or prudent) to prepare for another stack
 * to assume responsibility for the connection.
 */
static void
tcp_default_fb_fini(struct tcpcb *tp, int tcb_is_purged)
{

        INP_WLOCK_ASSERT(tp->t_inpcb);
        return;
}

/*
 * Target size of TCP PCB hash tables. Must be a power of two.
 *
 * Note that this can be overridden by the kernel environment
 * variable net.inet.tcp.tcbhashsize
 */
#ifndef TCBHASHSIZE
#define TCBHASHSIZE     0
#endif

/*
 * XXX
 * Callouts should be moved into struct tcp directly.  They are currently
 * separate because the tcpcb structure is exported to userland for sysctl
 * parsing purposes, which do not know about callouts.
 */
struct tcpcb_mem {
        struct  tcpcb           tcb;
        struct  tcp_timer       tt;
        struct  cc_var          ccv;
#ifdef TCP_HHOOK
        struct  osd             osd;
#endif
};

VNET_DEFINE_STATIC(uma_zone_t, tcpcb_zone);
#define V_tcpcb_zone                    VNET(tcpcb_zone)

MALLOC_DEFINE(M_TCPLOG, "tcplog", "TCP address and flags print buffers");
MALLOC_DEFINE(M_TCPFUNCTIONS, "tcpfunc", "TCP function set memory");

static struct mtx isn_mtx;

#define ISN_LOCK_INIT() mtx_init(&isn_mtx, "isn_mtx", NULL, MTX_DEF)
#define ISN_LOCK()      mtx_lock(&isn_mtx)
#define ISN_UNLOCK()    mtx_unlock(&isn_mtx)

/*
 * TCP initialization.
 */
static void
tcp_zone_change(void *tag)
{

        uma_zone_set_max(V_tcbinfo.ipi_zone, maxsockets);
        uma_zone_set_max(V_tcpcb_zone, maxsockets);
        tcp_tw_zone_change();
}

static int
tcp_inpcb_init(void *mem, int size, int flags)
{
        struct inpcb *inp = mem;

        INP_LOCK_INIT(inp, "inp", "tcpinp");
        return (0);
}

/*
 * Take a value and get the next power of 2 that doesn't overflow.
 * Used to size the tcp_inpcb hash buckets.
 */
static int
maketcp_hashsize(int size)
{
        int hashsize;

        /*
         * auto tune.
         * get the next power of 2 higher than maxsockets.
         */
        hashsize = 1 << fls(size);
        /* catch overflow, and just go one power of 2 smaller */
        if (hashsize < size) {
                hashsize = 1 << (fls(size) - 1);
        }
        return (hashsize);
}

static volatile int next_tcp_stack_id = 1;

/*
 * Register a TCP function block with the name provided in the names
 * array.  (Note that this function does NOT automatically register
 * blk->tfb_tcp_block_name as a stack name.  Therefore, you should
 * explicitly include blk->tfb_tcp_block_name in the list of names if
 * you wish to register the stack with that name.)
 *
 * Either all name registrations will succeed or all will fail.  If
 * a name registration fails, the function will update the num_names
 * argument to point to the array index of the name that encountered
 * the failure.
 *
 * Returns 0 on success, or an error code on failure.
 */
int
register_tcp_functions_as_names(struct tcp_function_block *blk, int wait,
    const char *names[], int *num_names)
{
        struct tcp_function *n;
        struct tcp_function_set fs;
        int error, i;

        KASSERT(names != NULL && *num_names > 0,
            ("%s: Called with 0-length name list", __func__));
        KASSERT(names != NULL, ("%s: Called with NULL name list", __func__));
        KASSERT(rw_initialized(&tcp_function_lock),
            ("%s: called too early", __func__));

        if ((blk->tfb_tcp_output == NULL) ||
            (blk->tfb_tcp_do_segment == NULL) ||
            (blk->tfb_tcp_ctloutput == NULL) ||
            (strlen(blk->tfb_tcp_block_name) == 0)) {
                /* 
                 * These functions are required and you
                 * need a name.
                 */
                *num_names = 0;
                return (EINVAL);
        }
        if (blk->tfb_tcp_timer_stop_all ||
            blk->tfb_tcp_timer_activate ||
            blk->tfb_tcp_timer_active ||
            blk->tfb_tcp_timer_stop) {
                /*
                 * If you define one timer function you 
                 * must have them all.
                 */
                if ((blk->tfb_tcp_timer_stop_all == NULL) ||
                    (blk->tfb_tcp_timer_activate == NULL) ||
                    (blk->tfb_tcp_timer_active == NULL) ||
                    (blk->tfb_tcp_timer_stop == NULL)) {
                        *num_names = 0;
                        return (EINVAL);
                }
        }

        if (blk->tfb_flags & TCP_FUNC_BEING_REMOVED) {
                *num_names = 0;
                return (EINVAL);
        }

        refcount_init(&blk->tfb_refcnt, 0);
        blk->tfb_id = atomic_fetchadd_int(&next_tcp_stack_id, 1);
        for (i = 0; i < *num_names; i++) {
                n = malloc(sizeof(struct tcp_function), M_TCPFUNCTIONS, wait);
                if (n == NULL) {
                        error = ENOMEM;
                        goto cleanup;
                }
                n->tf_fb = blk;

                (void)strlcpy(fs.function_set_name, names[i],
                    sizeof(fs.function_set_name));
                rw_wlock(&tcp_function_lock);
                if (find_tcp_functions_locked(&fs) != NULL) {
                        /* Duplicate name space not allowed */
                        rw_wunlock(&tcp_function_lock);
                        free(n, M_TCPFUNCTIONS);
                        error = EALREADY;
                        goto cleanup;
                }
                (void)strlcpy(n->tf_name, names[i], sizeof(n->tf_name));
                TAILQ_INSERT_TAIL(&t_functions, n, tf_next);
                tcp_fb_cnt++;
                rw_wunlock(&tcp_function_lock);
        }
        return(0);

cleanup:
        /*
         * Deregister the names we just added. Because registration failed
         * for names[i], we don't need to deregister that name.
         */
        *num_names = i;
        rw_wlock(&tcp_function_lock);
        while (--i >= 0) {
                TAILQ_FOREACH(n, &t_functions, tf_next) {
                        if (!strncmp(n->tf_name, names[i],
                            TCP_FUNCTION_NAME_LEN_MAX)) {
                                TAILQ_REMOVE(&t_functions, n, tf_next);
                                tcp_fb_cnt--;
                                n->tf_fb = NULL;
                                free(n, M_TCPFUNCTIONS);
                                break;
                        }
                }
        }
        rw_wunlock(&tcp_function_lock);
        return (error);
}

/*
 * Register a TCP function block using the name provided in the name
 * argument.
 *
 * Returns 0 on success, or an error code on failure.
 */
int
register_tcp_functions_as_name(struct tcp_function_block *blk, const char *name,
    int wait)
{
        const char *name_list[1];
        int num_names, rv;

        num_names = 1;
        if (name != NULL)
                name_list[0] = name;
        else
                name_list[0] = blk->tfb_tcp_block_name;
        rv = register_tcp_functions_as_names(blk, wait, name_list, &num_names);
        return (rv);
}

/*
 * Register a TCP function block using the name defined in
 * blk->tfb_tcp_block_name.
 *
 * Returns 0 on success, or an error code on failure.
 */
int
register_tcp_functions(struct tcp_function_block *blk, int wait)
{

        return (register_tcp_functions_as_name(blk, NULL, wait));
}

/*
 * Deregister all names associated with a function block. This
 * functionally removes the function block from use within the system.
 *
 * When called with a true quiesce argument, mark the function block
 * as being removed so no more stacks will use it and determine
 * whether the removal would succeed.
 *
 * When called with a false quiesce argument, actually attempt the
 * removal.
 *
 * When called with a force argument, attempt to switch all TCBs to
 * use the default stack instead of returning EBUSY.
 *
 * Returns 0 on success (or if the removal would succeed, or an error
 * code on failure.
 */
int
deregister_tcp_functions(struct tcp_function_block *blk, bool quiesce,
    bool force)
{
        struct tcp_function *f;

        if (blk == &tcp_def_funcblk) {
                /* You can't un-register the default */
                return (EPERM);
        }
        rw_wlock(&tcp_function_lock);
        if (blk == tcp_func_set_ptr) {
                /* You can't free the current default */
                rw_wunlock(&tcp_function_lock);
                return (EBUSY);
        }
        /* Mark the block so no more stacks can use it. */
        blk->tfb_flags |= TCP_FUNC_BEING_REMOVED;
        /*
         * If TCBs are still attached to the stack, attempt to switch them
         * to the default stack.
         */
        if (force && blk->tfb_refcnt) {
                struct inpcb *inp;
                struct tcpcb *tp;
                VNET_ITERATOR_DECL(vnet_iter);

                rw_wunlock(&tcp_function_lock);

                VNET_LIST_RLOCK();
                VNET_FOREACH(vnet_iter) {
                        CURVNET_SET(vnet_iter);
                        INP_INFO_WLOCK(&V_tcbinfo);
                        CK_LIST_FOREACH(inp, V_tcbinfo.ipi_listhead, inp_list) {
                                INP_WLOCK(inp);
                                if (inp->inp_flags & INP_TIMEWAIT) {
                                        INP_WUNLOCK(inp);
                                        continue;
                                }
                                tp = intotcpcb(inp);
                                if (tp == NULL || tp->t_fb != blk) {
                                        INP_WUNLOCK(inp);
                                        continue;
                                }
                                tcp_switch_back_to_default(tp);
                                INP_WUNLOCK(inp);
                        }
                        INP_INFO_WUNLOCK(&V_tcbinfo);
                        CURVNET_RESTORE();
                }
                VNET_LIST_RUNLOCK();

                rw_wlock(&tcp_function_lock);
        }
        if (blk->tfb_refcnt) {
                /* TCBs still attached. */
                rw_wunlock(&tcp_function_lock);
                return (EBUSY);
        }
        if (quiesce) {
                /* Skip removal. */
                rw_wunlock(&tcp_function_lock);
                return (0);
        }
        /* Remove any function names that map to this function block. */
        while (find_tcp_fb_locked(blk, &f) != NULL) {
                TAILQ_REMOVE(&t_functions, f, tf_next);
                tcp_fb_cnt--;
                f->tf_fb = NULL;
                free(f, M_TCPFUNCTIONS);
        }
        rw_wunlock(&tcp_function_lock);
        return (0);
}

void
tcp_init(void)
{
        const char *tcbhash_tuneable;
        int hashsize;

        tcbhash_tuneable = "net.inet.tcp.tcbhashsize";

#ifdef TCP_HHOOK
        if (hhook_head_register(HHOOK_TYPE_TCP, HHOOK_TCP_EST_IN,
            &V_tcp_hhh[HHOOK_TCP_EST_IN], HHOOK_NOWAIT|HHOOK_HEADISINVNET) != 0)
                printf("%s: WARNING: unable to register helper hook\n", __func__);
        if (hhook_head_register(HHOOK_TYPE_TCP, HHOOK_TCP_EST_OUT,
            &V_tcp_hhh[HHOOK_TCP_EST_OUT], HHOOK_NOWAIT|HHOOK_HEADISINVNET) != 0)
                printf("%s: WARNING: unable to register helper hook\n", __func__);
#endif
        hashsize = TCBHASHSIZE;
        TUNABLE_INT_FETCH(tcbhash_tuneable, &hashsize);
        if (hashsize == 0) {
                /*
                 * Auto tune the hash size based on maxsockets.
                 * A perfect hash would have a 1:1 mapping
                 * (hashsize = maxsockets) however it's been
                 * suggested that O(2) average is better.
                 */
                hashsize = maketcp_hashsize(maxsockets / 4);
                /*
                 * Our historical default is 512,
                 * do not autotune lower than this.
                 */
                if (hashsize < 512)
                        hashsize = 512;
                if (bootverbose && IS_DEFAULT_VNET(curvnet))
                        printf("%s: %s auto tuned to %d\n", __func__,
                            tcbhash_tuneable, hashsize);
        }
        /*
         * We require a hashsize to be a power of two.
         * Previously if it was not a power of two we would just reset it
         * back to 512, which could be a nasty surprise if you did not notice
         * the error message.
         * Instead what we do is clip it to the closest power of two lower
         * than the specified hash value.
         */
        if (!powerof2(hashsize)) {
                int oldhashsize = hashsize;

                hashsize = maketcp_hashsize(hashsize);
                /* prevent absurdly low value */
                if (hashsize < 16)
                        hashsize = 16;
                printf("%s: WARNING: TCB hash size not a power of 2, "
                    "clipped from %d to %d.\n", __func__, oldhashsize,
                    hashsize);
        }
        in_pcbinfo_init(&V_tcbinfo, "tcp", &V_tcb, hashsize, hashsize,
            "tcp_inpcb", tcp_inpcb_init, IPI_HASHFIELDS_4TUPLE);

        /*
         * These have to be type stable for the benefit of the timers.
         */
        V_tcpcb_zone = uma_zcreate("tcpcb", sizeof(struct tcpcb_mem),
            NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
        uma_zone_set_max(V_tcpcb_zone, maxsockets);
        uma_zone_set_warning(V_tcpcb_zone, "kern.ipc.maxsockets limit reached");

        tcp_tw_init();
        syncache_init();
        tcp_hc_init();

        TUNABLE_INT_FETCH("net.inet.tcp.sack.enable", &V_tcp_do_sack);
        V_sack_hole_zone = uma_zcreate("sackhole", sizeof(struct sackhole),
            NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);

        tcp_fastopen_init();

        /* Skip initialization of globals for non-default instances. */
        if (!IS_DEFAULT_VNET(curvnet))
                return;

        tcp_reass_global_init();

        /* XXX virtualize those bellow? */
        tcp_delacktime = TCPTV_DELACK;
        tcp_keepinit = TCPTV_KEEP_INIT;
        tcp_keepidle = TCPTV_KEEP_IDLE;
        tcp_keepintvl = TCPTV_KEEPINTVL;
        tcp_maxpersistidle = TCPTV_KEEP_IDLE;
        tcp_msl = TCPTV_MSL;
        tcp_rexmit_initial = TCPTV_RTOBASE;
        if (tcp_rexmit_initial < 1)
                tcp_rexmit_initial = 1;
        tcp_rexmit_min = TCPTV_MIN;
        if (tcp_rexmit_min < 1)
                tcp_rexmit_min = 1;
        tcp_persmin = TCPTV_PERSMIN;
        tcp_persmax = TCPTV_PERSMAX;
        tcp_rexmit_slop = TCPTV_CPU_VAR;
        tcp_finwait2_timeout = TCPTV_FINWAIT2_TIMEOUT;
        tcp_tcbhashsize = hashsize;

        /* Setup the tcp function block list */
        TAILQ_INIT(&t_functions);
        rw_init(&tcp_function_lock, "tcp_func_lock");
        register_tcp_functions(&tcp_def_funcblk, M_WAITOK);
#ifdef TCP_BLACKBOX
        /* Initialize the TCP logging data. */
        tcp_log_init();
#endif
        arc4rand(&V_ts_offset_secret, sizeof(V_ts_offset_secret), 0);

        if (tcp_soreceive_stream) {
#ifdef INET
                tcp_usrreqs.pru_soreceive = soreceive_stream;
#endif
#ifdef INET6
                tcp6_usrreqs.pru_soreceive = soreceive_stream;
#endif /* INET6 */
        }

#ifdef INET6
#define TCP_MINPROTOHDR (sizeof(struct ip6_hdr) + sizeof(struct tcphdr))
#else /* INET6 */
#define TCP_MINPROTOHDR (sizeof(struct tcpiphdr))
#endif /* INET6 */
        if (max_protohdr < TCP_MINPROTOHDR)
                max_protohdr = TCP_MINPROTOHDR;
        if (max_linkhdr + TCP_MINPROTOHDR > MHLEN)
                panic("tcp_init");
#undef TCP_MINPROTOHDR

        ISN_LOCK_INIT();
        EVENTHANDLER_REGISTER(shutdown_pre_sync, tcp_fini, NULL,
                SHUTDOWN_PRI_DEFAULT);
        EVENTHANDLER_REGISTER(maxsockets_change, tcp_zone_change, NULL,
                EVENTHANDLER_PRI_ANY);
#ifdef TCPPCAP
        tcp_pcap_init();
#endif
}

#ifdef VIMAGE
static void
tcp_destroy(void *unused __unused)
{
        int n;
#ifdef TCP_HHOOK
        int error;
#endif

        /*
         * All our processes are gone, all our sockets should be cleaned
         * up, which means, we should be past the tcp_discardcb() calls.
         * Sleep to let all tcpcb timers really disappear and cleanup.
         */
        for (;;) {
                INP_LIST_RLOCK(&V_tcbinfo);
                n = V_tcbinfo.ipi_count;
                INP_LIST_RUNLOCK(&V_tcbinfo);
                if (n == 0)
                        break;
                pause("tcpdes", hz / 10);
        }
        tcp_hc_destroy();
        syncache_destroy();
        tcp_tw_destroy();
        in_pcbinfo_destroy(&V_tcbinfo);
        /* tcp_discardcb() clears the sack_holes up. */
        uma_zdestroy(V_sack_hole_zone);
        uma_zdestroy(V_tcpcb_zone);

        /*
         * Cannot free the zone until all tcpcbs are released as we attach
         * the allocations to them.
         */
        tcp_fastopen_destroy();

#ifdef TCP_HHOOK
        error = hhook_head_deregister(V_tcp_hhh[HHOOK_TCP_EST_IN]);
        if (error != 0) {
                printf("%s: WARNING: unable to deregister helper hook "
                    "type=%d, id=%d: error %d returned\n", __func__,
                    HHOOK_TYPE_TCP, HHOOK_TCP_EST_IN, error);
        }
        error = hhook_head_deregister(V_tcp_hhh[HHOOK_TCP_EST_OUT]);
        if (error != 0) {
                printf("%s: WARNING: unable to deregister helper hook "
                    "type=%d, id=%d: error %d returned\n", __func__,
                    HHOOK_TYPE_TCP, HHOOK_TCP_EST_OUT, error);
        }
#endif
}
VNET_SYSUNINIT(tcp, SI_SUB_PROTO_DOMAIN, SI_ORDER_FOURTH, tcp_destroy, NULL);
#endif

void
tcp_fini(void *xtp)
{

}

/*
 * Fill in the IP and TCP headers for an outgoing packet, given the tcpcb.
 * tcp_template used to store this data in mbufs, but we now recopy it out
 * of the tcpcb each time to conserve mbufs.
 */
void
tcpip_fillheaders(struct inpcb *inp, void *ip_ptr, void *tcp_ptr)
{
        struct tcphdr *th = (struct tcphdr *)tcp_ptr;

        INP_WLOCK_ASSERT(inp);

#ifdef INET6
        if ((inp->inp_vflag & INP_IPV6) != 0) {
                struct ip6_hdr *ip6;

                ip6 = (struct ip6_hdr *)ip_ptr;
                ip6->ip6_flow = (ip6->ip6_flow & ~IPV6_FLOWINFO_MASK) |
                        (inp->inp_flow & IPV6_FLOWINFO_MASK);
                ip6->ip6_vfc = (ip6->ip6_vfc & ~IPV6_VERSION_MASK) |
                        (IPV6_VERSION & IPV6_VERSION_MASK);
                ip6->ip6_nxt = IPPROTO_TCP;
                ip6->ip6_plen = htons(sizeof(struct tcphdr));
                ip6->ip6_src = inp->in6p_laddr;
                ip6->ip6_dst = inp->in6p_faddr;
        }
#endif /* INET6 */
#if defined(INET6) && defined(INET)
        else
#endif
#ifdef INET
        {
                struct ip *ip;

                ip = (struct ip *)ip_ptr;
                ip->ip_v = IPVERSION;
                ip->ip_hl = 5;
                ip->ip_tos = inp->inp_ip_tos;
                ip->ip_len = 0;
                ip->ip_id = 0;
                ip->ip_off = 0;
                ip->ip_ttl = inp->inp_ip_ttl;
                ip->ip_sum = 0;
                ip->ip_p = IPPROTO_TCP;
                ip->ip_src = inp->inp_laddr;
                ip->ip_dst = inp->inp_faddr;
        }
#endif /* INET */
        th->th_sport = inp->inp_lport;
        th->th_dport = inp->inp_fport;
        th->th_seq = 0;
        th->th_ack = 0;
        th->th_x2 = 0;
        th->th_off = 5;
        th->th_flags = 0;
        th->th_win = 0;
        th->th_urp = 0;
        th->th_sum = 0;         /* in_pseudo() is called later for ipv4 */
}

/*
 * Create template to be used to send tcp packets on a connection.
 * Allocates an mbuf and fills in a skeletal tcp/ip header.  The only
 * use for this function is in keepalives, which use tcp_respond.
 */
struct tcptemp *
tcpip_maketemplate(struct inpcb *inp)
{
        struct tcptemp *t;

        t = malloc(sizeof(*t), M_TEMP, M_NOWAIT);
        if (t == NULL)
                return (NULL);
        tcpip_fillheaders(inp, (void *)&t->tt_ipgen, (void *)&t->tt_t);
        return (t);
}

/*
 * Send a single message to the TCP at address specified by
 * the given TCP/IP header.  If m == NULL, then we make a copy
 * of the tcpiphdr at th and send directly to the addressed host.
 * This is used to force keep alive messages out using the TCP
 * template for a connection.  If flags are given then we send
 * a message back to the TCP which originated the segment th,
 * and discard the mbuf containing it and any other attached mbufs.
 *
 * In any case the ack and sequence number of the transmitted
 * segment are as specified by the parameters.
 *
 * NOTE: If m != NULL, then th must point to *inside* the mbuf.
 */
void
tcp_respond(struct tcpcb *tp, void *ipgen, struct tcphdr *th, struct mbuf *m,
    tcp_seq ack, tcp_seq seq, int flags)
{
        struct tcpopt to;
        struct inpcb *inp;
        struct ip *ip;
        struct mbuf *optm;
        struct tcphdr *nth;
        u_char *optp;
#ifdef INET6
        struct ip6_hdr *ip6;
        int isipv6;
#endif /* INET6 */
        int optlen, tlen, win;
        bool incl_opts;

        KASSERT(tp != NULL || m != NULL, ("tcp_respond: tp and m both NULL"));

#ifdef INET6
        isipv6 = ((struct ip *)ipgen)->ip_v == (IPV6_VERSION >> 4);
        ip6 = ipgen;
#endif /* INET6 */
        ip = ipgen;

        if (tp != NULL) {
                inp = tp->t_inpcb;
                KASSERT(inp != NULL, ("tcp control block w/o inpcb"));
                INP_WLOCK_ASSERT(inp);
        } else
                inp = NULL;

        incl_opts = false;
        win = 0;
        if (tp != NULL) {
                if (!(flags & TH_RST)) {
                        win = sbspace(&inp->inp_socket->so_rcv);
                        if (win > TCP_MAXWIN << tp->rcv_scale)
                                win = TCP_MAXWIN << tp->rcv_scale;
                }
                if ((tp->t_flags & TF_NOOPT) == 0)
                        incl_opts = true;
        }
        if (m == NULL) {
                m = m_gethdr(M_NOWAIT, MT_DATA);
                if (m == NULL)
                        return;
                m->m_data += max_linkhdr;
#ifdef INET6
                if (isipv6) {
                        bcopy((caddr_t)ip6, mtod(m, caddr_t),
                              sizeof(struct ip6_hdr));
                        ip6 = mtod(m, struct ip6_hdr *);
                        nth = (struct tcphdr *)(ip6 + 1);
                } else
#endif /* INET6 */
                {
                        bcopy((caddr_t)ip, mtod(m, caddr_t), sizeof(struct ip));
                        ip = mtod(m, struct ip *);
                        nth = (struct tcphdr *)(ip + 1);
                }
                bcopy((caddr_t)th, (caddr_t)nth, sizeof(struct tcphdr));
                flags = TH_ACK;
        } else if (!M_WRITABLE(m)) {
                struct mbuf *n;

                /* Can't reuse 'm', allocate a new mbuf. */
                n = m_gethdr(M_NOWAIT, MT_DATA);
                if (n == NULL) {
                        m_freem(m);
                        return;
                }

                if (!m_dup_pkthdr(n, m, M_NOWAIT)) {
                        m_freem(m);
                        m_freem(n);
                        return;
                }

                n->m_data += max_linkhdr;
                /* m_len is set later */
#define xchg(a,b,type) { type t; t=a; a=b; b=t; }
#ifdef INET6
                if (isipv6) {
                        bcopy((caddr_t)ip6, mtod(n, caddr_t),
                              sizeof(struct ip6_hdr));
                        ip6 = mtod(n, struct ip6_hdr *);
                        xchg(ip6->ip6_dst, ip6->ip6_src, struct in6_addr);
                        nth = (struct tcphdr *)(ip6 + 1);
                } else
#endif /* INET6 */
                {
                        bcopy((caddr_t)ip, mtod(n, caddr_t), sizeof(struct ip));
                        ip = mtod(n, struct ip *);
                        xchg(ip->ip_dst.s_addr, ip->ip_src.s_addr, uint32_t);
                        nth = (struct tcphdr *)(ip + 1);
                }
                bcopy((caddr_t)th, (caddr_t)nth, sizeof(struct tcphdr));
                xchg(nth->th_dport, nth->th_sport, uint16_t);
                th = nth;
                m_freem(m);
                m = n;
        } else {
                /*
                 *  reuse the mbuf. 
                 * XXX MRT We inherit the FIB, which is lucky.
                 */
                m_freem(m->m_next);
                m->m_next = NULL;
                m->m_data = (caddr_t)ipgen;
                /* m_len is set later */
#ifdef INET6
                if (isipv6) {
                        xchg(ip6->ip6_dst, ip6->ip6_src, struct in6_addr);
                        nth = (struct tcphdr *)(ip6 + 1);
                } else
#endif /* INET6 */
                {
                        xchg(ip->ip_dst.s_addr, ip->ip_src.s_addr, uint32_t);
                        nth = (struct tcphdr *)(ip + 1);
                }
                if (th != nth) {
                        /*
                         * this is usually a case when an extension header
                         * exists between the IPv6 header and the
                         * TCP header.
                         */
                        nth->th_sport = th->th_sport;
                        nth->th_dport = th->th_dport;
                }
                xchg(nth->th_dport, nth->th_sport, uint16_t);
#undef xchg
        }
        tlen = 0;
#ifdef INET6
        if (isipv6)
                tlen = sizeof (struct ip6_hdr) + sizeof (struct tcphdr);
#endif
#if defined(INET) && defined(INET6)
        else
#endif
#ifdef INET
                tlen = sizeof (struct tcpiphdr);
#endif
#ifdef INVARIANTS
        m->m_len = 0;
        KASSERT(M_TRAILINGSPACE(m) >= tlen,
            ("Not enough trailing space for message (m=%p, need=%d, have=%ld)",
            m, tlen, (long)M_TRAILINGSPACE(m)));
#endif
        m->m_len = tlen;
        to.to_flags = 0;
        if (incl_opts) {
                /* Make sure we have room. */
                if (M_TRAILINGSPACE(m) < TCP_MAXOLEN) {
                        m->m_next = m_get(M_NOWAIT, MT_DATA);
                        if (m->m_next) {
                                optp = mtod(m->m_next, u_char *);
                                optm = m->m_next;
                        } else
                                incl_opts = false;
                } else {
                        optp = (u_char *) (nth + 1);
                        optm = m;
                }
        }
        if (incl_opts) {
                /* Timestamps. */
                if (tp->t_flags & TF_RCVD_TSTMP) {
                        to.to_tsval = tcp_ts_getticks() + tp->ts_offset;
                        to.to_tsecr = tp->ts_recent;
                        to.to_flags |= TOF_TS;
                }
#if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
                /* TCP-MD5 (RFC2385). */
                if (tp->t_flags & TF_SIGNATURE)
                        to.to_flags |= TOF_SIGNATURE;
#endif
                /* Add the options. */
                tlen += optlen = tcp_addoptions(&to, optp);

                /* Update m_len in the correct mbuf. */
                optm->m_len += optlen;
        } else
                optlen = 0;
#ifdef INET6
        if (isipv6) {
                ip6->ip6_flow = 0;
                ip6->ip6_vfc = IPV6_VERSION;
                ip6->ip6_nxt = IPPROTO_TCP;
                ip6->ip6_plen = htons(tlen - sizeof(*ip6));
        }
#endif
#if defined(INET) && defined(INET6)
        else
#endif
#ifdef INET
        {
                ip->ip_len = htons(tlen);
                ip->ip_ttl = V_ip_defttl;
                if (V_path_mtu_discovery)
                        ip->ip_off |= htons(IP_DF);
        }
#endif
        m->m_pkthdr.len = tlen;
        m->m_pkthdr.rcvif = NULL;
#ifdef MAC
        if (inp != NULL) {
                /*
                 * Packet is associated with a socket, so allow the
                 * label of the response to reflect the socket label.
                 */
                INP_WLOCK_ASSERT(inp);
                mac_inpcb_create_mbuf(inp, m);
        } else {
                /*
                 * Packet is not associated with a socket, so possibly
                 * update the label in place.
                 */
                mac_netinet_tcp_reply(m);
        }
#endif
        nth->th_seq = htonl(seq);
        nth->th_ack = htonl(ack);
        nth->th_x2 = 0;
        nth->th_off = (sizeof (struct tcphdr) + optlen) >> 2;
        nth->th_flags = flags;
        if (tp != NULL)
                nth->th_win = htons((u_short) (win >> tp->rcv_scale));
        else
                nth->th_win = htons((u_short)win);
        nth->th_urp = 0;

#if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
        if (to.to_flags & TOF_SIGNATURE) {
                if (!TCPMD5_ENABLED() ||
                    TCPMD5_OUTPUT(m, nth, to.to_signature) != 0) {
                        m_freem(m);
                        return;
                }
        }
#endif

        m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
#ifdef INET6
        if (isipv6) {
                m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
                nth->th_sum = in6_cksum_pseudo(ip6,
                    tlen - sizeof(struct ip6_hdr), IPPROTO_TCP, 0);
                ip6->ip6_hlim = in6_selecthlim(tp != NULL ? tp->t_inpcb :
                    NULL, NULL);
        }
#endif /* INET6 */
#if defined(INET6) && defined(INET)
        else
#endif
#ifdef INET
        {
                m->m_pkthdr.csum_flags = CSUM_TCP;
                nth->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
                    htons((u_short)(tlen - sizeof(struct ip) + ip->ip_p)));
        }
#endif /* INET */
#ifdef TCPDEBUG
        if (tp == NULL || (inp->inp_socket->so_options & SO_DEBUG))
                tcp_trace(TA_OUTPUT, 0, tp, mtod(m, void *), th, 0);
#endif
        TCP_PROBE3(debug__output, tp, th, m);
        if (flags & TH_RST)
                TCP_PROBE5(accept__refused, NULL, NULL, m, tp, nth);

#ifdef INET6
        if (isipv6) {
                TCP_PROBE5(send, NULL, tp, ip6, tp, nth);
                (void)ip6_output(m, NULL, NULL, 0, NULL, NULL, inp);
        }
#endif /* INET6 */
#if defined(INET) && defined(INET6)
        else
#endif
#ifdef INET
        {
                TCP_PROBE5(send, NULL, tp, ip, tp, nth);
                (void)ip_output(m, NULL, NULL, 0, NULL, inp);
        }
#endif
}

/*
 * Create a new TCP control block, making an
 * empty reassembly queue and hooking it to the argument
 * protocol control block.  The `inp' parameter must have
 * come from the zone allocator set up in tcp_init().
 */
struct tcpcb *
tcp_newtcpcb(struct inpcb *inp)
{
        struct tcpcb_mem *tm;
        struct tcpcb *tp;
#ifdef INET6
        int isipv6 = (inp->inp_vflag & INP_IPV6) != 0;
#endif /* INET6 */

        tm = uma_zalloc(V_tcpcb_zone, M_NOWAIT | M_ZERO);
        if (tm == NULL)
                return (NULL);
        tp = &tm->tcb;

        /* Initialise cc_var struct for this tcpcb. */
        tp->ccv = &tm->ccv;
        tp->ccv->type = IPPROTO_TCP;
        tp->ccv->ccvc.tcp = tp;
        rw_rlock(&tcp_function_lock);
        tp->t_fb = tcp_func_set_ptr;
        refcount_acquire(&tp->t_fb->tfb_refcnt);
        rw_runlock(&tcp_function_lock);
        /*
         * Use the current system default CC algorithm.
         */
        CC_LIST_RLOCK();
        KASSERT(!STAILQ_EMPTY(&cc_list), ("cc_list is empty!"));
        CC_ALGO(tp) = CC_DEFAULT();
        CC_LIST_RUNLOCK();

        if (CC_ALGO(tp)->cb_init != NULL)
                if (CC_ALGO(tp)->cb_init(tp->ccv) > 0) {
                        if (tp->t_fb->tfb_tcp_fb_fini)
                                (*tp->t_fb->tfb_tcp_fb_fini)(tp, 1);
                        refcount_release(&tp->t_fb->tfb_refcnt);
                        uma_zfree(V_tcpcb_zone, tm);
                        return (NULL);
                }

#ifdef TCP_HHOOK
        tp->osd = &tm->osd;
        if (khelp_init_osd(HELPER_CLASS_TCP, tp->osd)) {
                if (tp->t_fb->tfb_tcp_fb_fini)
                        (*tp->t_fb->tfb_tcp_fb_fini)(tp, 1);
                refcount_release(&tp->t_fb->tfb_refcnt);
                uma_zfree(V_tcpcb_zone, tm);
                return (NULL);
        }
#endif

#ifdef VIMAGE
        tp->t_vnet = inp->inp_vnet;
#endif
        tp->t_timers = &tm->tt;
        TAILQ_INIT(&tp->t_segq);
        tp->t_maxseg =
#ifdef INET6
                isipv6 ? V_tcp_v6mssdflt :
#endif /* INET6 */
                V_tcp_mssdflt;

        /* Set up our timeouts. */
        callout_init(&tp->t_timers->tt_rexmt, 1);
        callout_init(&tp->t_timers->tt_persist, 1);
        callout_init(&tp->t_timers->tt_keep, 1);
        callout_init(&tp->t_timers->tt_2msl, 1);
        callout_init(&tp->t_timers->tt_delack, 1);

        if (V_tcp_do_rfc1323)
                tp->t_flags = (TF_REQ_SCALE|TF_REQ_TSTMP);
        if (V_tcp_do_sack)
                tp->t_flags |= TF_SACK_PERMIT;
        TAILQ_INIT(&tp->snd_holes);
        /*
         * The tcpcb will hold a reference on its inpcb until tcp_discardcb()
         * is called.
         */
        in_pcbref(inp); /* Reference for tcpcb */
        tp->t_inpcb = inp;

        /*
         * Init srtt to TCPTV_SRTTBASE (0), so we can tell that we have no
         * rtt estimate.  Set rttvar so that srtt + 4 * rttvar gives
         * reasonable initial retransmit time.
         */
        tp->t_srtt = TCPTV_SRTTBASE;
        tp->t_rttvar = ((tcp_rexmit_initial - TCPTV_SRTTBASE) << TCP_RTTVAR_SHIFT) / 4;
        tp->t_rttmin = tcp_rexmit_min;
        tp->t_rxtcur = tcp_rexmit_initial;
        tp->snd_cwnd = TCP_MAXWIN << TCP_MAX_WINSHIFT;
        tp->snd_ssthresh = TCP_MAXWIN << TCP_MAX_WINSHIFT;
        tp->t_rcvtime = ticks;
        /*
         * IPv4 TTL initialization is necessary for an IPv6 socket as well,
         * because the socket may be bound to an IPv6 wildcard address,
         * which may match an IPv4-mapped IPv6 address.
         */
        inp->inp_ip_ttl = V_ip_defttl;
        inp->inp_ppcb = tp;
#ifdef TCPPCAP
        /*
         * Init the TCP PCAP queues.
         */
        tcp_pcap_tcpcb_init(tp);
#endif
#ifdef TCP_BLACKBOX
        /* Initialize the per-TCPCB log data. */
        tcp_log_tcpcbinit(tp);
#endif
        if (tp->t_fb->tfb_tcp_fb_init) {
                (*tp->t_fb->tfb_tcp_fb_init)(tp);
        }
        return (tp);            /* XXX */
}

/*
 * Switch the congestion control algorithm back to NewReno for any active
 * control blocks using an algorithm which is about to go away.
 * This ensures the CC framework can allow the unload to proceed without leaving
 * any dangling pointers which would trigger a panic.
 * Returning non-zero would inform the CC framework that something went wrong
 * and it would be unsafe to allow the unload to proceed. However, there is no
 * way for this to occur with this implementation so we always return zero.
 */
int
tcp_ccalgounload(struct cc_algo *unload_algo)
{
        struct cc_algo *tmpalgo;
        struct inpcb *inp;
        struct tcpcb *tp;
        VNET_ITERATOR_DECL(vnet_iter);

        /*
         * Check all active control blocks across all network stacks and change
         * any that are using "unload_algo" back to NewReno. If "unload_algo"
         * requires cleanup code to be run, call it.
         */
        VNET_LIST_RLOCK();
        VNET_FOREACH(vnet_iter) {
                CURVNET_SET(vnet_iter);
                INP_INFO_WLOCK(&V_tcbinfo);
                /*
                 * New connections already part way through being initialised
                 * with the CC algo we're removing will not race with this code
                 * because the INP_INFO_WLOCK is held during initialisation. We
                 * therefore don't enter the loop below until the connection
                 * list has stabilised.
                 */
                CK_LIST_FOREACH(inp, &V_tcb, inp_list) {
                        INP_WLOCK(inp);
                        /* Important to skip tcptw structs. */
                        if (!(inp->inp_flags & INP_TIMEWAIT) &&
                            (tp = intotcpcb(inp)) != NULL) {
                                /*
                                 * By holding INP_WLOCK here, we are assured
                                 * that the connection is not currently
                                 * executing inside the CC module's functions
                                 * i.e. it is safe to make the switch back to
                                 * NewReno.
                                 */
                                if (CC_ALGO(tp) == unload_algo) {
                                        tmpalgo = CC_ALGO(tp);
                                        if (tmpalgo->cb_destroy != NULL)
                                                tmpalgo->cb_destroy(tp->ccv);
                                        CC_DATA(tp) = NULL;
                                        /*
                                         * NewReno may allocate memory on
                                         * demand for certain stateful
                                         * configuration as needed, but is
                                         * coded to never fail on memory
                                         * allocation failure so it is a safe
                                         * fallback.
                                         */
                                        CC_ALGO(tp) = &newreno_cc_algo;
                                }
                        }
                        INP_WUNLOCK(inp);
                }
                INP_INFO_WUNLOCK(&V_tcbinfo);
                CURVNET_RESTORE();
        }
        VNET_LIST_RUNLOCK();

        return (0);
}

/*
 * Drop a TCP connection, reporting
 * the specified error.  If connection is synchronized,
 * then send a RST to peer.
 */
struct tcpcb *
tcp_drop(struct tcpcb *tp, int errno)
{
        struct socket *so = tp->t_inpcb->inp_socket;

        INP_INFO_LOCK_ASSERT(&V_tcbinfo);
        INP_WLOCK_ASSERT(tp->t_inpcb);

        if (TCPS_HAVERCVDSYN(tp->t_state)) {
                tcp_state_change(tp, TCPS_CLOSED);
                (void) tp->t_fb->tfb_tcp_output(tp);
                TCPSTAT_INC(tcps_drops);
        } else
                TCPSTAT_INC(tcps_conndrops);
        if (errno == ETIMEDOUT && tp->t_softerror)
                errno = tp->t_softerror;
        so->so_error = errno;
        return (tcp_close(tp));
}

void
tcp_discardcb(struct tcpcb *tp)
{
        struct inpcb *inp = tp->t_inpcb;
        struct socket *so = inp->inp_socket;
#ifdef INET6
        int isipv6 = (inp->inp_vflag & INP_IPV6) != 0;
#endif /* INET6 */
        int released __unused;

        INP_WLOCK_ASSERT(inp);

        /*
         * Make sure that all of our timers are stopped before we delete the
         * PCB.
         *
         * If stopping a timer fails, we schedule a discard function in same
         * callout, and the last discard function called will take care of
         * deleting the tcpcb.
         */
        tp->t_timers->tt_draincnt = 0;
        tcp_timer_stop(tp, TT_REXMT);
        tcp_timer_stop(tp, TT_PERSIST);
        tcp_timer_stop(tp, TT_KEEP);
        tcp_timer_stop(tp, TT_2MSL);
        tcp_timer_stop(tp, TT_DELACK);
        if (tp->t_fb->tfb_tcp_timer_stop_all) {
                /* 
                 * Call the stop-all function of the methods, 
                 * this function should call the tcp_timer_stop()
                 * method with each of the function specific timeouts.
                 * That stop will be called via the tfb_tcp_timer_stop()
                 * which should use the async drain function of the 
                 * callout system (see tcp_var.h).
                 */
                tp->t_fb->tfb_tcp_timer_stop_all(tp);
        }

        /*
         * If we got enough samples through the srtt filter,
         * save the rtt and rttvar in the routing entry.
         * 'Enough' is arbitrarily defined as 4 rtt samples.
         * 4 samples is enough for the srtt filter to converge
         * to within enough % of the correct value; fewer samples
         * and we could save a bogus rtt. The danger is not high
         * as tcp quickly recovers from everything.
         * XXX: Works very well but needs some more statistics!
         */
        if (tp->t_rttupdated >= 4) {
                struct hc_metrics_lite metrics;
                uint32_t ssthresh;

                bzero(&metrics, sizeof(metrics));
                /*
                 * Update the ssthresh always when the conditions below
                 * are satisfied. This gives us better new start value
                 * for the congestion avoidance for new connections.
                 * ssthresh is only set if packet loss occurred on a session.
                 *
                 * XXXRW: 'so' may be NULL here, and/or socket buffer may be
                 * being torn down.  Ideally this code would not use 'so'.
                 */
                ssthresh = tp->snd_ssthresh;
                if (ssthresh != 0 && ssthresh < so->so_snd.sb_hiwat / 2) {
                        /*
                         * convert the limit from user data bytes to
                         * packets then to packet data bytes.
                         */
                        ssthresh = (ssthresh + tp->t_maxseg / 2) / tp->t_maxseg;
                        if (ssthresh < 2)
                                ssthresh = 2;
                        ssthresh *= (tp->t_maxseg +
#ifdef INET6
                            (isipv6 ? sizeof (struct ip6_hdr) +
                                sizeof (struct tcphdr) :
#endif
                                sizeof (struct tcpiphdr)
#ifdef INET6
                            )
#endif
                            );
                } else
                        ssthresh = 0;
                metrics.rmx_ssthresh = ssthresh;

                metrics.rmx_rtt = tp->t_srtt;
                metrics.rmx_rttvar = tp->t_rttvar;
                metrics.rmx_cwnd = tp->snd_cwnd;
                metrics.rmx_sendpipe = 0;
                metrics.rmx_recvpipe = 0;

                tcp_hc_update(&inp->inp_inc, &metrics);
        }

        /* free the reassembly queue, if any */
        tcp_reass_flush(tp);

#ifdef TCP_OFFLOAD
        /* Disconnect offload device, if any. */
        if (tp->t_flags & TF_TOE)
                tcp_offload_detach(tp);
#endif
                
        tcp_free_sackholes(tp);

#ifdef TCPPCAP
        /* Free the TCP PCAP queues. */
        tcp_pcap_drain(&(tp->t_inpkts));
        tcp_pcap_drain(&(tp->t_outpkts));
#endif

        /* Allow the CC algorithm to clean up after itself. */
        if (CC_ALGO(tp)->cb_destroy != NULL)
                CC_ALGO(tp)->cb_destroy(tp->ccv);
        CC_DATA(tp) = NULL;

#ifdef TCP_HHOOK
        khelp_destroy_osd(tp->osd);
#endif

        CC_ALGO(tp) = NULL;
        inp->inp_ppcb = NULL;
        if (tp->t_timers->tt_draincnt == 0) {
                /* We own the last reference on tcpcb, let's free it. */
#ifdef TCP_BLACKBOX
                tcp_log_tcpcbfini(tp);
#endif
                TCPSTATES_DEC(tp->t_state);
                if (tp->t_fb->tfb_tcp_fb_fini)
                        (*tp->t_fb->tfb_tcp_fb_fini)(tp, 1);
                refcount_release(&tp->t_fb->tfb_refcnt);
                tp->t_inpcb = NULL;
                uma_zfree(V_tcpcb_zone, tp);
                released = in_pcbrele_wlocked(inp);
                KASSERT(!released, ("%s: inp %p should not have been released "
                        "here", __func__, inp));
        }
}

void
tcp_timer_discard(void *ptp)
{
        struct inpcb *inp;
        struct tcpcb *tp;
        struct epoch_tracker et;
        
        tp = (struct tcpcb *)ptp;
        CURVNET_SET(tp->t_vnet);
        INP_INFO_RLOCK_ET(&V_tcbinfo, et);
        inp = tp->t_inpcb;
        KASSERT(inp != NULL, ("%s: tp %p tp->t_inpcb == NULL",
                __func__, tp));
        INP_WLOCK(inp);
        KASSERT((tp->t_timers->tt_flags & TT_STOPPED) != 0,
                ("%s: tcpcb has to be stopped here", __func__));
        tp->t_timers->tt_draincnt--;
        if (tp->t_timers->tt_draincnt == 0) {
                /* We own the last reference on this tcpcb, let's free it. */
#ifdef TCP_BLACKBOX
                tcp_log_tcpcbfini(tp);
#endif
                TCPSTATES_DEC(tp->t_state);
                if (tp->t_fb->tfb_tcp_fb_fini)
                        (*tp->t_fb->tfb_tcp_fb_fini)(tp, 1);
                refcount_release(&tp->t_fb->tfb_refcnt);
                tp->t_inpcb = NULL;
                uma_zfree(V_tcpcb_zone, tp);
                if (in_pcbrele_wlocked(inp)) {
                        INP_INFO_RUNLOCK_ET(&V_tcbinfo, et);
                        CURVNET_RESTORE();
                        return;
                }
        }
        INP_WUNLOCK(inp);
        INP_INFO_RUNLOCK_ET(&V_tcbinfo, et);
        CURVNET_RESTORE();
}

/*
 * Attempt to close a TCP control block, marking it as dropped, and freeing
 * the socket if we hold the only reference.
 */
struct tcpcb *
tcp_close(struct tcpcb *tp)
{
        struct inpcb *inp = tp->t_inpcb;
        struct socket *so;

        INP_INFO_LOCK_ASSERT(&V_tcbinfo);
        INP_WLOCK_ASSERT(inp);

#ifdef TCP_OFFLOAD
        if (tp->t_state == TCPS_LISTEN)
                tcp_offload_listen_stop(tp);
#endif
        /*
         * This releases the TFO pending counter resource for TFO listen
         * sockets as well as passively-created TFO sockets that transition
         * from SYN_RECEIVED to CLOSED.
         */
        if (tp->t_tfo_pending) {
                tcp_fastopen_decrement_counter(tp->t_tfo_pending);
                tp->t_tfo_pending = NULL;
        }
        in_pcbdrop(inp);
        TCPSTAT_INC(tcps_closed);
        if (tp->t_state != TCPS_CLOSED)
                tcp_state_change(tp, TCPS_CLOSED);
        KASSERT(inp->inp_socket != NULL, ("tcp_close: inp_socket NULL"));
        so = inp->inp_socket;
        soisdisconnected(so);
        if (inp->inp_flags & INP_SOCKREF) {
                KASSERT(so->so_state & SS_PROTOREF,
                    ("tcp_close: !SS_PROTOREF"));
                inp->inp_flags &= ~INP_SOCKREF;
                INP_WUNLOCK(inp);
                SOCK_LOCK(so);
                so->so_state &= ~SS_PROTOREF;
                sofree(so);
                return (NULL);
        }
        return (tp);
}

void
tcp_drain(void)
{
        VNET_ITERATOR_DECL(vnet_iter);

        if (!do_tcpdrain)
                return;

        VNET_LIST_RLOCK_NOSLEEP();
        VNET_FOREACH(vnet_iter) {
                CURVNET_SET(vnet_iter);
                struct inpcb *inpb;
                struct tcpcb *tcpb;

        /*
         * Walk the tcpbs, if existing, and flush the reassembly queue,
         * if there is one...
         * XXX: The "Net/3" implementation doesn't imply that the TCP
         *      reassembly queue should be flushed, but in a situation
         *      where we're really low on mbufs, this is potentially
         *      useful.
         */
                INP_INFO_WLOCK(&V_tcbinfo);
                CK_LIST_FOREACH(inpb, V_tcbinfo.ipi_listhead, inp_list) {
                        INP_WLOCK(inpb);
                        if (inpb->inp_flags & INP_TIMEWAIT) {
                                INP_WUNLOCK(inpb);
                                continue;
                        }
                        if ((tcpb = intotcpcb(inpb)) != NULL) {
                                tcp_reass_flush(tcpb);
                                tcp_clean_sackreport(tcpb);
#ifdef TCP_BLACKBOX
                                tcp_log_drain(tcpb);
#endif
#ifdef TCPPCAP
                                if (tcp_pcap_aggressive_free) {
                                        /* Free the TCP PCAP queues. */
                                        tcp_pcap_drain(&(tcpb->t_inpkts));
                                        tcp_pcap_drain(&(tcpb->t_outpkts));
                                }
#endif
                        }
                        INP_WUNLOCK(inpb);
                }
                INP_INFO_WUNLOCK(&V_tcbinfo);
                CURVNET_RESTORE();
        }
        VNET_LIST_RUNLOCK_NOSLEEP();
}

/*
 * Notify a tcp user of an asynchronous error;
 * store error as soft error, but wake up user
 * (for now, won't do anything until can select for soft error).
 *
 * Do not wake up user since there currently is no mechanism for
 * reporting soft errors (yet - a kqueue filter may be added).
 */
static struct inpcb *
tcp_notify(struct inpcb *inp, int error)
{
        struct tcpcb *tp;

        INP_INFO_LOCK_ASSERT(&V_tcbinfo);
        INP_WLOCK_ASSERT(inp);

        if ((inp->inp_flags & INP_TIMEWAIT) ||
            (inp->inp_flags & INP_DROPPED))
                return (inp);

        tp = intotcpcb(inp);
        KASSERT(tp != NULL, ("tcp_notify: tp == NULL"));

        /*
         * Ignore some errors if we are hooked up.
         * If connection hasn't completed, has retransmitted several times,
         * and receives a second error, give up now.  This is better
         * than waiting a long time to establish a connection that
         * can never complete.
         */
        if (tp->t_state == TCPS_ESTABLISHED &&
            (error == EHOSTUNREACH || error == ENETUNREACH ||
             error == EHOSTDOWN)) {
                if (inp->inp_route.ro_rt) {
                        RTFREE(inp->inp_route.ro_rt);
                        inp->inp_route.ro_rt = (struct rtentry *)NULL;
                }
                return (inp);
        } else if (tp->t_state < TCPS_ESTABLISHED && tp->t_rxtshift > 3 &&
            tp->t_softerror) {
                tp = tcp_drop(tp, error);
                if (tp != NULL)
                        return (inp);
                else
                        return (NULL);
        } else {
                tp->t_softerror = error;
                return (inp);
        }
#if 0
        wakeup( &so->so_timeo);
        sorwakeup(so);
        sowwakeup(so);
#endif
}

static int
tcp_pcblist(SYSCTL_HANDLER_ARGS)
{
        int error, i, m, n, pcb_count;
        struct inpcb *inp, **inp_list;
        inp_gen_t gencnt;
        struct xinpgen xig;
        struct epoch_tracker et;

        /*
         * The process of preparing the TCB list is too time-consuming and
         * resource-intensive to repeat twice on every request.
         */
        if (req->oldptr == NULL) {
                n = V_tcbinfo.ipi_count +
                    counter_u64_fetch(V_tcps_states[TCPS_SYN_RECEIVED]);
                n += imax(n / 8, 10);
                req->oldidx = 2 * (sizeof xig) + n * sizeof(struct xtcpcb);
                return (0);
        }

        if (req->newptr != NULL)
                return (EPERM);

        /*
         * OK, now we're committed to doing something.
         */
        INP_LIST_RLOCK(&V_tcbinfo);
        gencnt = V_tcbinfo.ipi_gencnt;
        n = V_tcbinfo.ipi_count;
        INP_LIST_RUNLOCK(&V_tcbinfo);

        m = counter_u64_fetch(V_tcps_states[TCPS_SYN_RECEIVED]);

        error = sysctl_wire_old_buffer(req, 2 * (sizeof xig)
                + (n + m) * sizeof(struct xtcpcb));
        if (error != 0)
                return (error);

        bzero(&xig, sizeof(xig));
        xig.xig_len = sizeof xig;
        xig.xig_count = n + m;
        xig.xig_gen = gencnt;
        xig.xig_sogen = so_gencnt;
        error = SYSCTL_OUT(req, &xig, sizeof xig);
        if (error)
                return (error);

        error = syncache_pcblist(req, m, &pcb_count);
        if (error)
                return (error);

        inp_list = malloc(n * sizeof *inp_list, M_TEMP, M_WAITOK);

        INP_INFO_WLOCK(&V_tcbinfo);
        for (inp = CK_LIST_FIRST(V_tcbinfo.ipi_listhead), i = 0;
            inp != NULL && i < n; inp = CK_LIST_NEXT(inp, inp_list)) {
                INP_WLOCK(inp);
                if (inp->inp_gencnt <= gencnt) {
                        /*
                         * XXX: This use of cr_cansee(), introduced with
                         * TCP state changes, is not quite right, but for
                         * now, better than nothing.
                         */
                        if (inp->inp_flags & INP_TIMEWAIT) {
                                if (intotw(inp) != NULL)
                                        error = cr_cansee(req->td->td_ucred,
                                            intotw(inp)->tw_cred);
                                else
                                        error = EINVAL; /* Skip this inp. */
                        } else
                                error = cr_canseeinpcb(req->td->td_ucred, inp);
                        if (error == 0) {
                                in_pcbref(inp);
                                inp_list[i++] = inp;
                        }
                }
                INP_WUNLOCK(inp);
        }
        INP_INFO_WUNLOCK(&V_tcbinfo);
        n = i;

        error = 0;
        for (i = 0; i < n; i++) {
                inp = inp_list[i];
                INP_RLOCK(inp);
                if (inp->inp_gencnt <= gencnt) {
                        struct xtcpcb xt;

                        tcp_inptoxtp(inp, &xt);
                        INP_RUNLOCK(inp);
                        error = SYSCTL_OUT(req, &xt, sizeof xt);
                } else
                        INP_RUNLOCK(inp);
        }
        INP_INFO_RLOCK_ET(&V_tcbinfo, et);
        for (i = 0; i < n; i++) {
                inp = inp_list[i];
                INP_RLOCK(inp);
                if (!in_pcbrele_rlocked(inp))
                        INP_RUNLOCK(inp);
        }
        INP_INFO_RUNLOCK_ET(&V_tcbinfo, et);

        if (!error) {
                /*
                 * Give the user an updated idea of our state.
                 * If the generation differs from what we told
                 * her before, she knows that something happened
                 * while we were processing this request, and it
                 * might be necessary to retry.
                 */
                INP_LIST_RLOCK(&V_tcbinfo);
                xig.xig_gen = V_tcbinfo.ipi_gencnt;
                xig.xig_sogen = so_gencnt;
                xig.xig_count = V_tcbinfo.ipi_count + pcb_count;
                INP_LIST_RUNLOCK(&V_tcbinfo);
                error = SYSCTL_OUT(req, &xig, sizeof xig);
        }
        free(inp_list, M_TEMP);
        return (error);
}

SYSCTL_PROC(_net_inet_tcp, TCPCTL_PCBLIST, pcblist,
    CTLTYPE_OPAQUE | CTLFLAG_RD, NULL, 0,
    tcp_pcblist, "S,xtcpcb", "List of active TCP connections");

#ifdef INET
static int
tcp_getcred(SYSCTL_HANDLER_ARGS)
{
        struct xucred xuc;
        struct sockaddr_in addrs[2];
        struct inpcb *inp;
        int error;

        error = priv_check(req->td, PRIV_NETINET_GETCRED);
        if (error)
                return (error);
        error = SYSCTL_IN(req, addrs, sizeof(addrs));
        if (error)
                return (error);
        inp = in_pcblookup(&V_tcbinfo, addrs[1].sin_addr, addrs[1].sin_port,
            addrs[0].sin_addr, addrs[0].sin_port, INPLOOKUP_RLOCKPCB, NULL);
        if (inp != NULL) {
                if (inp->inp_socket == NULL)
                        error = ENOENT;
                if (error == 0)
                        error = cr_canseeinpcb(req->td->td_ucred, inp);
                if (error == 0)
                        cru2x(inp->inp_cred, &xuc);
                INP_RUNLOCK(inp);
        } else
                error = ENOENT;
        if (error == 0)
                error = SYSCTL_OUT(req, &xuc, sizeof(struct xucred));
        return (error);
}

SYSCTL_PROC(_net_inet_tcp, OID_AUTO, getcred,
    CTLTYPE_OPAQUE|CTLFLAG_RW|CTLFLAG_PRISON, 0, 0,
    tcp_getcred, "S,xucred", "Get the xucred of a TCP connection");
#endif /* INET */

#ifdef INET6
static int
tcp6_getcred(SYSCTL_HANDLER_ARGS)
{
        struct xucred xuc;
        struct sockaddr_in6 addrs[2];
        struct inpcb *inp;
        int error;
#ifdef INET
        int mapped = 0;
#endif

        error = priv_check(req->td, PRIV_NETINET_GETCRED);
        if (error)
                return (error);
        error = SYSCTL_IN(req, addrs, sizeof(addrs));
        if (error)
                return (error);
        if ((error = sa6_embedscope(&addrs[0], V_ip6_use_defzone)) != 0 ||
            (error = sa6_embedscope(&addrs[1], V_ip6_use_defzone)) != 0) {
                return (error);
        }
        if (IN6_IS_ADDR_V4MAPPED(&addrs[0].sin6_addr)) {
#ifdef INET
                if (IN6_IS_ADDR_V4MAPPED(&addrs[1].sin6_addr))
                        mapped = 1;
                else
#endif
                        return (EINVAL);
        }

#ifdef INET
        if (mapped == 1)
                inp = in_pcblookup(&V_tcbinfo,
                        *(struct in_addr *)&addrs[1].sin6_addr.s6_addr[12],
                        addrs[1].sin6_port,
                        *(struct in_addr *)&addrs[0].sin6_addr.s6_addr[12],
                        addrs[0].sin6_port, INPLOOKUP_RLOCKPCB, NULL);
        else
#endif
                inp = in6_pcblookup(&V_tcbinfo,
                        &addrs[1].sin6_addr, addrs[1].sin6_port,
                        &addrs[0].sin6_addr, addrs[0].sin6_port,
                        INPLOOKUP_RLOCKPCB, NULL);
        if (inp != NULL) {
                if (inp->inp_socket == NULL)
                        error = ENOENT;
                if (error == 0)
                        error = cr_canseeinpcb(req->td->td_ucred, inp);
                if (error == 0)
                        cru2x(inp->inp_cred, &xuc);
                INP_RUNLOCK(inp);
        } else
                error = ENOENT;
        if (error == 0)
                error = SYSCTL_OUT(req, &xuc, sizeof(struct xucred));
        return (error);
}

SYSCTL_PROC(_net_inet6_tcp6, OID_AUTO, getcred,
    CTLTYPE_OPAQUE|CTLFLAG_RW|CTLFLAG_PRISON, 0, 0,
    tcp6_getcred, "S,xucred", "Get the xucred of a TCP6 connection");
#endif /* INET6 */


#ifdef INET
void
tcp_ctlinput(int cmd, struct sockaddr *sa, void *vip)
{
        struct ip *ip = vip;
        struct tcphdr *th;
        struct in_addr faddr;
        struct inpcb *inp;
        struct tcpcb *tp;
        struct inpcb *(*notify)(struct inpcb *, int) = tcp_notify;
        struct icmp *icp;
        struct in_conninfo inc;
        struct epoch_tracker et;
        tcp_seq icmp_tcp_seq;
        int mtu;

        faddr = ((struct sockaddr_in *)sa)->sin_addr;
        if (sa->sa_family != AF_INET || faddr.s_addr == INADDR_ANY)
                return;

        if (cmd == PRC_MSGSIZE)
                notify = tcp_mtudisc_notify;
        else if (V_icmp_may_rst && (cmd == PRC_UNREACH_ADMIN_PROHIB ||
                cmd == PRC_UNREACH_PORT || cmd == PRC_UNREACH_PROTOCOL || 
                cmd == PRC_TIMXCEED_INTRANS) && ip)
                notify = tcp_drop_syn_sent;

        /*
         * Hostdead is ugly because it goes linearly through all PCBs.
         * XXX: We never get this from ICMP, otherwise it makes an
         * excellent DoS attack on machines with many connections.
         */
        else if (cmd == PRC_HOSTDEAD)
                ip = NULL;
        else if ((unsigned)cmd >= PRC_NCMDS || inetctlerrmap[cmd] == 0)
                return;

        if (ip == NULL) {
                in_pcbnotifyall(&V_tcbinfo, faddr, inetctlerrmap[cmd], notify);
                return;
        }

        icp = (struct icmp *)((caddr_t)ip - offsetof(struct icmp, icmp_ip));
        th = (struct tcphdr *)((caddr_t)ip + (ip->ip_hl << 2));
        INP_INFO_RLOCK_ET(&V_tcbinfo, et);
        inp = in_pcblookup(&V_tcbinfo, faddr, th->th_dport, ip->ip_src,
            th->th_sport, INPLOOKUP_WLOCKPCB, NULL);
        if (inp != NULL && PRC_IS_REDIRECT(cmd)) {
                /* signal EHOSTDOWN, as it flushes the cached route */
                inp = (*notify)(inp, EHOSTDOWN);
                goto out;
        }
        icmp_tcp_seq = th->th_seq;
        if (inp != NULL)  {
                if (!(inp->inp_flags & INP_TIMEWAIT) &&
                    !(inp->inp_flags & INP_DROPPED) &&
                    !(inp->inp_socket == NULL)) {
                        tp = intotcpcb(inp);
                        if (SEQ_GEQ(ntohl(icmp_tcp_seq), tp->snd_una) &&
                            SEQ_LT(ntohl(icmp_tcp_seq), tp->snd_max)) {
                                if (cmd == PRC_MSGSIZE) {
                                        /*
                                         * MTU discovery:
                                         * If we got a needfrag set the MTU
                                         * in the route to the suggested new
                                         * value (if given) and then notify.
                                         */
                                        mtu = ntohs(icp->icmp_nextmtu);
                                        /*
                                         * If no alternative MTU was
                                         * proposed, try the next smaller
                                         * one.
                                         */
                                        if (!mtu)
                                                mtu = ip_next_mtu(
                                                    ntohs(ip->ip_len), 1);
                                        if (mtu < V_tcp_minmss +
                                            sizeof(struct tcpiphdr))
                                                mtu = V_tcp_minmss +
                                                    sizeof(struct tcpiphdr);
                                        /*
                                         * Only process the offered MTU if it
                                         * is smaller than the current one.
                                         */
                                        if (mtu < tp->t_maxseg +
                                            sizeof(struct tcpiphdr)) {
                                                bzero(&inc, sizeof(inc));
                                                inc.inc_faddr = faddr;
                                                inc.inc_fibnum =
                                                    inp->inp_inc.inc_fibnum;
                                                tcp_hc_updatemtu(&inc, mtu);
                                                tcp_mtudisc(inp, mtu);
                                        }
                                } else
                                        inp = (*notify)(inp,
                                            inetctlerrmap[cmd]);
                        }
                }
        } else {
                bzero(&inc, sizeof(inc));
                inc.inc_fport = th->th_dport;
                inc.inc_lport = th->th_sport;
                inc.inc_faddr = faddr;
                inc.inc_laddr = ip->ip_src;
                syncache_unreach(&inc, icmp_tcp_seq);
        }
out:
        if (inp != NULL)
                INP_WUNLOCK(inp);
        INP_INFO_RUNLOCK_ET(&V_tcbinfo, et);
}
#endif /* INET */

#ifdef INET6
void
tcp6_ctlinput(int cmd, struct sockaddr *sa, void *d)
{
        struct in6_addr *dst;
        struct inpcb *(*notify)(struct inpcb *, int) = tcp_notify;
        struct ip6_hdr *ip6;
        struct mbuf *m;
        struct inpcb *inp;
        struct tcpcb *tp;
        struct icmp6_hdr *icmp6;
        struct ip6ctlparam *ip6cp = NULL;
        const struct sockaddr_in6 *sa6_src = NULL;
        struct in_conninfo inc;
        struct epoch_tracker et;
        struct tcp_ports {
                uint16_t th_sport;
                uint16_t th_dport;
        } t_ports;
        tcp_seq icmp_tcp_seq;
        unsigned int mtu;
        unsigned int off;

        if (sa->sa_family != AF_INET6 ||
            sa->sa_len != sizeof(struct sockaddr_in6))
                return;

        /* if the parameter is from icmp6, decode it. */
        if (d != NULL) {
                ip6cp = (struct ip6ctlparam *)d;
                icmp6 = ip6cp->ip6c_icmp6;
                m = ip6cp->ip6c_m;
                ip6 = ip6cp->ip6c_ip6;
                off = ip6cp->ip6c_off;
                sa6_src = ip6cp->ip6c_src;
                dst = ip6cp->ip6c_finaldst;
        } else {
                m = NULL;
                ip6 = NULL;
                off = 0;        /* fool gcc */
                sa6_src = &sa6_any;
                dst = NULL;
        }

        if (cmd == PRC_MSGSIZE)
                notify = tcp_mtudisc_notify;
        else if (V_icmp_may_rst && (cmd == PRC_UNREACH_ADMIN_PROHIB ||
                cmd == PRC_UNREACH_PORT || cmd == PRC_UNREACH_PROTOCOL || 
                cmd == PRC_TIMXCEED_INTRANS) && ip6 != NULL)
                notify = tcp_drop_syn_sent;

        /*
         * Hostdead is ugly because it goes linearly through all PCBs.
         * XXX: We never get this from ICMP, otherwise it makes an
         * excellent DoS attack on machines with many connections.
         */
        else if (cmd == PRC_HOSTDEAD)
                ip6 = NULL;
        else if ((unsigned)cmd >= PRC_NCMDS || inet6ctlerrmap[cmd] == 0)
                return;

        if (ip6 == NULL) {
                in6_pcbnotify(&V_tcbinfo, sa, 0,
                              (const struct sockaddr *)sa6_src,
                              0, cmd, NULL, notify);
                return;
        }

        /* Check if we can safely get the ports from the tcp hdr */
        if (m == NULL ||
            (m->m_pkthdr.len <
                (int32_t) (off + sizeof(struct tcp_ports)))) {
                return;
        }
        bzero(&t_ports, sizeof(struct tcp_ports));
        m_copydata(m, off, sizeof(struct tcp_ports), (caddr_t)&t_ports);
        INP_INFO_RLOCK_ET(&V_tcbinfo, et);
        inp = in6_pcblookup(&V_tcbinfo, &ip6->ip6_dst, t_ports.th_dport,
            &ip6->ip6_src, t_ports.th_sport, INPLOOKUP_WLOCKPCB, NULL);
        if (inp != NULL && PRC_IS_REDIRECT(cmd)) {
                /* signal EHOSTDOWN, as it flushes the cached route */
                inp = (*notify)(inp, EHOSTDOWN);
                goto out;
        }
        off += sizeof(struct tcp_ports);
        if (m->m_pkthdr.len < (int32_t) (off + sizeof(tcp_seq))) {
                goto out;
        }
        m_copydata(m, off, sizeof(tcp_seq), (caddr_t)&icmp_tcp_seq);
        if (inp != NULL)  {
                if (!(inp->inp_flags & INP_TIMEWAIT) &&
                    !(inp->inp_flags & INP_DROPPED) &&
                    !(inp->inp_socket == NULL)) {
                        tp = intotcpcb(inp);
                        if (SEQ_GEQ(ntohl(icmp_tcp_seq), tp->snd_una) &&
                            SEQ_LT(ntohl(icmp_tcp_seq), tp->snd_max)) {
                                if (cmd == PRC_MSGSIZE) {
                                        /*
                                         * MTU discovery:
                                         * If we got a needfrag set the MTU
                                         * in the route to the suggested new
                                         * value (if given) and then notify.
                                         */
                                        mtu = ntohl(icmp6->icmp6_mtu);
                                        /*
                                         * If no alternative MTU was
                                         * proposed, or the proposed
                                         * MTU was too small, set to
                                         * the min.
                                         */
                                        if (mtu < IPV6_MMTU)
                                                mtu = IPV6_MMTU - 8;
                                        bzero(&inc, sizeof(inc));
                                        inc.inc_fibnum = M_GETFIB(m);
                                        inc.inc_flags |= INC_ISIPV6;
                                        inc.inc6_faddr = *dst;
                                        if (in6_setscope(&inc.inc6_faddr,
                                                m->m_pkthdr.rcvif, NULL))
                                                goto out;
                                        /*
                                         * Only process the offered MTU if it
                                         * is smaller than the current one.
                                         */
                                        if (mtu < tp->t_maxseg +
                                            sizeof (struct tcphdr) +
                                            sizeof (struct ip6_hdr)) {
                                                tcp_hc_updatemtu(&inc, mtu);
                                                tcp_mtudisc(inp, mtu);
                                                ICMP6STAT_INC(icp6s_pmtuchg);
                                        }
                                } else
                                        inp = (*notify)(inp,
                                            inet6ctlerrmap[cmd]);
                        }
                }
        } else {
                bzero(&inc, sizeof(inc));
                inc.inc_fibnum = M_GETFIB(m);
                inc.inc_flags |= INC_ISIPV6;
                inc.inc_fport = t_ports.th_dport;
                inc.inc_lport = t_ports.th_sport;
                inc.inc6_faddr = *dst;
                inc.inc6_laddr = ip6->ip6_src;
                syncache_unreach(&inc, icmp_tcp_seq);
        }
out:
        if (inp != NULL)
                INP_WUNLOCK(inp);
        INP_INFO_RUNLOCK_ET(&V_tcbinfo, et);
}
#endif /* INET6 */

static uint32_t
tcp_keyed_hash(struct in_conninfo *inc, u_char *key, u_int len)
{
        MD5_CTX ctx;
        uint32_t hash[4];

        MD5Init(&ctx);
        MD5Update(&ctx, &inc->inc_fport, sizeof(uint16_t));
        MD5Update(&ctx, &inc->inc_lport, sizeof(uint16_t));
        switch (inc->inc_flags & INC_ISIPV6) {
#ifdef INET
        case 0:
                MD5Update(&ctx, &inc->inc_faddr, sizeof(struct in_addr));
                MD5Update(&ctx, &inc->inc_laddr, sizeof(struct in_addr));
                break;
#endif
#ifdef INET6
        case INC_ISIPV6:
                MD5Update(&ctx, &inc->inc6_faddr, sizeof(struct in6_addr));
                MD5Update(&ctx, &inc->inc6_laddr, sizeof(struct in6_addr));
                break;
#endif
        }
        MD5Update(&ctx, key, len);
        MD5Final((unsigned char *)hash, &ctx);

        return (hash[0]);
}

uint32_t
tcp_new_ts_offset(struct in_conninfo *inc)
{
        struct in_conninfo inc_store, *local_inc;

        if (!V_tcp_ts_offset_per_conn) {
                memcpy(&inc_store, inc, sizeof(struct in_conninfo));
                inc_store.inc_lport = 0;
                inc_store.inc_fport = 0;
                local_inc = &inc_store;
        } else {
                local_inc = inc;
        }
        return (tcp_keyed_hash(local_inc, V_ts_offset_secret,
            sizeof(V_ts_offset_secret)));
}

/*
 * Following is where TCP initial sequence number generation occurs.
 *
 * There are two places where we must use initial sequence numbers:
 * 1.  In SYN-ACK packets.
 * 2.  In SYN packets.
 *
 * All ISNs for SYN-ACK packets are generated by the syncache.  See
 * tcp_syncache.c for details.
 *
 * The ISNs in SYN packets must be monotonic; TIME_WAIT recycling
 * depends on this property.  In addition, these ISNs should be
 * unguessable so as to prevent connection hijacking.  To satisfy
 * the requirements of this situation, the algorithm outlined in
 * RFC 1948 is used, with only small modifications.
 *
 * Implementation details:
 *
 * Time is based off the system timer, and is corrected so that it
 * increases by one megabyte per second.  This allows for proper
 * recycling on high speed LANs while still leaving over an hour
 * before rollover.
 *
 * As reading the *exact* system time is too expensive to be done
 * whenever setting up a TCP connection, we increment the time
 * offset in two ways.  First, a small random positive increment
 * is added to isn_offset for each connection that is set up.
 * Second, the function tcp_isn_tick fires once per clock tick
 * and increments isn_offset as necessary so that sequence numbers
 * are incremented at approximately ISN_BYTES_PER_SECOND.  The
 * random positive increments serve only to ensure that the same
 * exact sequence number is never sent out twice (as could otherwise
 * happen when a port is recycled in less than the system tick
 * interval.)
 *
 * net.inet.tcp.isn_reseed_interval controls the number of seconds
 * between seeding of isn_secret.  This is normally set to zero,
 * as reseeding should not be necessary.
 *
 * Locking of the global variables isn_secret, isn_last_reseed, isn_offset,
 * isn_offset_old, and isn_ctx is performed using the ISN lock.  In
 * general, this means holding an exclusive (write) lock.
 */

#define ISN_BYTES_PER_SECOND 1048576
#define ISN_STATIC_INCREMENT 4096
#define ISN_RANDOM_INCREMENT (4096 - 1)
#define ISN_SECRET_LENGTH    32

VNET_DEFINE_STATIC(u_char, isn_secret[ISN_SECRET_LENGTH]);
VNET_DEFINE_STATIC(int, isn_last);
VNET_DEFINE_STATIC(int, isn_last_reseed);
VNET_DEFINE_STATIC(u_int32_t, isn_offset);
VNET_DEFINE_STATIC(u_int32_t, isn_offset_old);

#define V_isn_secret                    VNET(isn_secret)
#define V_isn_last                      VNET(isn_last)
#define V_isn_last_reseed               VNET(isn_last_reseed)
#define V_isn_offset                    VNET(isn_offset)
#define V_isn_offset_old                VNET(isn_offset_old)

tcp_seq
tcp_new_isn(struct in_conninfo *inc)
{
        tcp_seq new_isn;
        u_int32_t projected_offset;

        ISN_LOCK();
        /* Seed if this is the first use, reseed if requested. */
        if ((V_isn_last_reseed == 0) || ((V_tcp_isn_reseed_interval > 0) &&
             (((u_int)V_isn_last_reseed + (u_int)V_tcp_isn_reseed_interval*hz)
                < (u_int)ticks))) {
                arc4rand(&V_isn_secret, sizeof(V_isn_secret), 0);
                V_isn_last_reseed = ticks;
        }

        /* Compute the md5 hash and return the ISN. */
        new_isn = (tcp_seq)tcp_keyed_hash(inc, V_isn_secret,
            sizeof(V_isn_secret));
        V_isn_offset += ISN_STATIC_INCREMENT +
                (arc4random() & ISN_RANDOM_INCREMENT);
        if (ticks != V_isn_last) {
                projected_offset = V_isn_offset_old +
                    ISN_BYTES_PER_SECOND / hz * (ticks - V_isn_last);
                if (SEQ_GT(projected_offset, V_isn_offset))
                        V_isn_offset = projected_offset;
                V_isn_offset_old = V_isn_offset;
                V_isn_last = ticks;
        }
        new_isn += V_isn_offset;
        ISN_UNLOCK();
        return (new_isn);
}

/*
 * When a specific ICMP unreachable message is received and the
 * connection state is SYN-SENT, drop the connection.  This behavior
 * is controlled by the icmp_may_rst sysctl.
 */
struct inpcb *
tcp_drop_syn_sent(struct inpcb *inp, int errno)
{
        struct tcpcb *tp;

        INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
        INP_WLOCK_ASSERT(inp);

        if ((inp->inp_flags & INP_TIMEWAIT) ||
            (inp->inp_flags & INP_DROPPED))
                return (inp);

        tp = intotcpcb(inp);
        if (tp->t_state != TCPS_SYN_SENT)
                return (inp);

        if (IS_FASTOPEN(tp->t_flags))
                tcp_fastopen_disable_path(tp);
        
        tp = tcp_drop(tp, errno);
        if (tp != NULL)
                return (inp);
        else
                return (NULL);
}

/*
 * When `need fragmentation' ICMP is received, update our idea of the MSS
 * based on the new value. Also nudge TCP to send something, since we
 * know the packet we just sent was dropped.
 * This duplicates some code in the tcp_mss() function in tcp_input.c.
 */
static struct inpcb *
tcp_mtudisc_notify(struct inpcb *inp, int error)
{

        tcp_mtudisc(inp, -1);
        return (inp);
}

static void
tcp_mtudisc(struct inpcb *inp, int mtuoffer)
{
        struct tcpcb *tp;
        struct socket *so;

        INP_WLOCK_ASSERT(inp);
        if ((inp->inp_flags & INP_TIMEWAIT) ||
            (inp->inp_flags & INP_DROPPED))
                return;

        tp = intotcpcb(inp);
        KASSERT(tp != NULL, ("tcp_mtudisc: tp == NULL"));

        tcp_mss_update(tp, -1, mtuoffer, NULL, NULL);
  
        so = inp->inp_socket;
        SOCKBUF_LOCK(&so->so_snd);
        /* If the mss is larger than the socket buffer, decrease the mss. */
        if (so->so_snd.sb_hiwat < tp->t_maxseg)
                tp->t_maxseg = so->so_snd.sb_hiwat;
        SOCKBUF_UNLOCK(&so->so_snd);

        TCPSTAT_INC(tcps_mturesent);
        tp->t_rtttime = 0;
        tp->snd_nxt = tp->snd_una;
        tcp_free_sackholes(tp);
        tp->snd_recover = tp->snd_max;
        if (tp->t_flags & TF_SACK_PERMIT)
                EXIT_FASTRECOVERY(tp->t_flags);
        tp->t_fb->tfb_tcp_output(tp);
}

#ifdef INET
/*
 * Look-up the routing entry to the peer of this inpcb.  If no route
 * is found and it cannot be allocated, then return 0.  This routine
 * is called by TCP routines that access the rmx structure and by
 * tcp_mss_update to get the peer/interface MTU.
 */
uint32_t
tcp_maxmtu(struct in_conninfo *inc, struct tcp_ifcap *cap)
{
        struct nhop4_extended nh4;
        struct ifnet *ifp;
        uint32_t maxmtu = 0;

        KASSERT(inc != NULL, ("tcp_maxmtu with NULL in_conninfo pointer"));

        if (inc->inc_faddr.s_addr != INADDR_ANY) {

                if (fib4_lookup_nh_ext(inc->inc_fibnum, inc->inc_faddr,
                    NHR_REF, 0, &nh4) != 0)
                        return (0);

                ifp = nh4.nh_ifp;
                maxmtu = nh4.nh_mtu;

                /* Report additional interface capabilities. */
                if (cap != NULL) {
                        if (ifp->if_capenable & IFCAP_TSO4 &&
                            ifp->if_hwassist & CSUM_TSO) {
                                cap->ifcap |= CSUM_TSO;
                                cap->tsomax = ifp->if_hw_tsomax;
                                cap->tsomaxsegcount = ifp->if_hw_tsomaxsegcount;
                                cap->tsomaxsegsize = ifp->if_hw_tsomaxsegsize;
                        }
                }
                fib4_free_nh_ext(inc->inc_fibnum, &nh4);
        }
        return (maxmtu);
}
#endif /* INET */

#ifdef INET6
uint32_t
tcp_maxmtu6(struct in_conninfo *inc, struct tcp_ifcap *cap)
{
        struct nhop6_extended nh6;
        struct in6_addr dst6;
        uint32_t scopeid;
        struct ifnet *ifp;
        uint32_t maxmtu = 0;

        KASSERT(inc != NULL, ("tcp_maxmtu6 with NULL in_conninfo pointer"));

        if (inc->inc_flags & INC_IPV6MINMTU)
                return (IPV6_MMTU);

        if (!IN6_IS_ADDR_UNSPECIFIED(&inc->inc6_faddr)) {
                in6_splitscope(&inc->inc6_faddr, &dst6, &scopeid);
                if (fib6_lookup_nh_ext(inc->inc_fibnum, &dst6, scopeid, 0,
                    0, &nh6) != 0)
                        return (0);

                ifp = nh6.nh_ifp;
                maxmtu = nh6.nh_mtu;

                /* Report additional interface capabilities. */
                if (cap != NULL) {
                        if (ifp->if_capenable & IFCAP_TSO6 &&
                            ifp->if_hwassist & CSUM_TSO) {
                                cap->ifcap |= CSUM_TSO;
                                cap->tsomax = ifp->if_hw_tsomax;
                                cap->tsomaxsegcount = ifp->if_hw_tsomaxsegcount;
                                cap->tsomaxsegsize = ifp->if_hw_tsomaxsegsize;
                        }
                }
                fib6_free_nh_ext(inc->inc_fibnum, &nh6);
        }

        return (maxmtu);
}
#endif /* INET6 */

/*
 * Calculate effective SMSS per RFC5681 definition for a given TCP
 * connection at its current state, taking into account SACK and etc.
 */
u_int
tcp_maxseg(const struct tcpcb *tp)
{
        u_int optlen;

        if (tp->t_flags & TF_NOOPT)
                return (tp->t_maxseg);

        /*
         * Here we have a simplified code from tcp_addoptions(),
         * without a proper loop, and having most of paddings hardcoded.
         * We might make mistakes with padding here in some edge cases,
         * but this is harmless, since result of tcp_maxseg() is used
         * only in cwnd and ssthresh estimations.
         */
#define PAD(len)        ((((len) / 4) + !!((len) % 4)) * 4)
        if (TCPS_HAVEESTABLISHED(tp->t_state)) {
                if (tp->t_flags & TF_RCVD_TSTMP)
                        optlen = TCPOLEN_TSTAMP_APPA;
                else
                        optlen = 0;
#if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
                if (tp->t_flags & TF_SIGNATURE)
                        optlen += PAD(TCPOLEN_SIGNATURE);
#endif
                if ((tp->t_flags & TF_SACK_PERMIT) && tp->rcv_numsacks > 0) {
                        optlen += TCPOLEN_SACKHDR;
                        optlen += tp->rcv_numsacks * TCPOLEN_SACK;
                        optlen = PAD(optlen);
                }
        } else {
                if (tp->t_flags & TF_REQ_TSTMP)
                        optlen = TCPOLEN_TSTAMP_APPA;
                else
                        optlen = PAD(TCPOLEN_MAXSEG);
                if (tp->t_flags & TF_REQ_SCALE)
                        optlen += PAD(TCPOLEN_WINDOW);
#if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
                if (tp->t_flags & TF_SIGNATURE)
                        optlen += PAD(TCPOLEN_SIGNATURE);
#endif
                if (tp->t_flags & TF_SACK_PERMIT)
                        optlen += PAD(TCPOLEN_SACK_PERMITTED);
        }
#undef PAD
        optlen = min(optlen, TCP_MAXOLEN);
        return (tp->t_maxseg - optlen);
}

static int
sysctl_drop(SYSCTL_HANDLER_ARGS)
{
        /* addrs[0] is a foreign socket, addrs[1] is a local one. */
        struct sockaddr_storage addrs[2];
        struct inpcb *inp;
        struct tcpcb *tp;
        struct tcptw *tw;
        struct sockaddr_in *fin, *lin;
        struct epoch_tracker et;
#ifdef INET6
        struct sockaddr_in6 *fin6, *lin6;
#endif
        int error;

        inp = NULL;
        fin = lin = NULL;
#ifdef INET6
        fin6 = lin6 = NULL;
#endif
        error = 0;

        if (req->oldptr != NULL || req->oldlen != 0)
                return (EINVAL);
        if (req->newptr == NULL)
                return (EPERM);
        if (req->newlen < sizeof(addrs))
                return (ENOMEM);
        error = SYSCTL_IN(req, &addrs, sizeof(addrs));
        if (error)
                return (error);

        switch (addrs[0].ss_family) {
#ifdef INET6
        case AF_INET6:
                fin6 = (struct sockaddr_in6 *)&addrs[0];
                lin6 = (struct sockaddr_in6 *)&addrs[1];
                if (fin6->sin6_len != sizeof(struct sockaddr_in6) ||
                    lin6->sin6_len != sizeof(struct sockaddr_in6))
                        return (EINVAL);
                if (IN6_IS_ADDR_V4MAPPED(&fin6->sin6_addr)) {
                        if (!IN6_IS_ADDR_V4MAPPED(&lin6->sin6_addr))
                                return (EINVAL);
                        in6_sin6_2_sin_in_sock((struct sockaddr *)&addrs[0]);
                        in6_sin6_2_sin_in_sock((struct sockaddr *)&addrs[1]);
                        fin = (struct sockaddr_in *)&addrs[0];
                        lin = (struct sockaddr_in *)&addrs[1];
                        break;
                }
                error = sa6_embedscope(fin6, V_ip6_use_defzone);
                if (error)
                        return (error);
                error = sa6_embedscope(lin6, V_ip6_use_defzone);
                if (error)
                        return (error);
                break;
#endif
#ifdef INET
        case AF_INET:
                fin = (struct sockaddr_in *)&addrs[0];
                lin = (struct sockaddr_in *)&addrs[1];
                if (fin->sin_len != sizeof(struct sockaddr_in) ||
                    lin->sin_len != sizeof(struct sockaddr_in))
                        return (EINVAL);
                break;
#endif
        default:
                return (EINVAL);
        }
        INP_INFO_RLOCK_ET(&V_tcbinfo, et);
        switch (addrs[0].ss_family) {
#ifdef INET6
        case AF_INET6:
                inp = in6_pcblookup(&V_tcbinfo, &fin6->sin6_addr,
                    fin6->sin6_port, &lin6->sin6_addr, lin6->sin6_port,
                    INPLOOKUP_WLOCKPCB, NULL);
                break;
#endif
#ifdef INET
        case AF_INET:
                inp = in_pcblookup(&V_tcbinfo, fin->sin_addr, fin->sin_port,
                    lin->sin_addr, lin->sin_port, INPLOOKUP_WLOCKPCB, NULL);
                break;
#endif
        }
        if (inp != NULL) {
                if (inp->inp_flags & INP_TIMEWAIT) {
                        /*
                         * XXXRW: There currently exists a state where an
                         * inpcb is present, but its timewait state has been
                         * discarded.  For now, don't allow dropping of this
                         * type of inpcb.
                         */
                        tw = intotw(inp);
                        if (tw != NULL)
                                tcp_twclose(tw, 0);
                        else
                                INP_WUNLOCK(inp);
                } else if (!(inp->inp_flags & INP_DROPPED) &&
                           !(inp->inp_socket->so_options & SO_ACCEPTCONN)) {
                        tp = intotcpcb(inp);
                        tp = tcp_drop(tp, ECONNABORTED);
                        if (tp != NULL)
                                INP_WUNLOCK(inp);
                } else
                        INP_WUNLOCK(inp);
        } else
                error = ESRCH;
        INP_INFO_RUNLOCK_ET(&V_tcbinfo, et);
        return (error);
}

SYSCTL_PROC(_net_inet_tcp, TCPCTL_DROP, drop,
    CTLFLAG_VNET | CTLTYPE_STRUCT | CTLFLAG_WR | CTLFLAG_SKIP, NULL,
    0, sysctl_drop, "", "Drop TCP connection");

/*
 * Generate a standardized TCP log line for use throughout the
 * tcp subsystem.  Memory allocation is done with M_NOWAIT to
 * allow use in the interrupt context.
 *
 * NB: The caller MUST free(s, M_TCPLOG) the returned string.
 * NB: The function may return NULL if memory allocation failed.
 *
 * Due to header inclusion and ordering limitations the struct ip
 * and ip6_hdr pointers have to be passed as void pointers.
 */
char *
tcp_log_vain(struct in_conninfo *inc, struct tcphdr *th, void *ip4hdr,
    const void *ip6hdr)
{

        /* Is logging enabled? */
        if (tcp_log_in_vain == 0)
                return (NULL);

        return (tcp_log_addr(inc, th, ip4hdr, ip6hdr));
}

char *
tcp_log_addrs(struct in_conninfo *inc, struct tcphdr *th, void *ip4hdr,
    const void *ip6hdr)
{

        /* Is logging enabled? */
        if (tcp_log_debug == 0)
                return (NULL);

        return (tcp_log_addr(inc, th, ip4hdr, ip6hdr));
}

static char *
tcp_log_addr(struct in_conninfo *inc, struct tcphdr *th, void *ip4hdr,
    const void *ip6hdr)
{
        char *s, *sp;
        size_t size;
        struct ip *ip;
#ifdef INET6
        const struct ip6_hdr *ip6;

        ip6 = (const struct ip6_hdr *)ip6hdr;
#endif /* INET6 */
        ip = (struct ip *)ip4hdr;

        /*
         * The log line looks like this:
         * "TCP: [1.2.3.4]:50332 to [1.2.3.4]:80 tcpflags 0x2<SYN>"
         */
        size = sizeof("TCP: []:12345 to []:12345 tcpflags 0x2<>") +
            sizeof(PRINT_TH_FLAGS) + 1 +
#ifdef INET6
            2 * INET6_ADDRSTRLEN;
#else
            2 * INET_ADDRSTRLEN;
#endif /* INET6 */

        s = malloc(size, M_TCPLOG, M_ZERO|M_NOWAIT);
        if (s == NULL)
                return (NULL);

        strcat(s, "TCP: [");
        sp = s + strlen(s);

        if (inc && ((inc->inc_flags & INC_ISIPV6) == 0)) {
                inet_ntoa_r(inc->inc_faddr, sp);
                sp = s + strlen(s);
                sprintf(sp, "]:%i to [", ntohs(inc->inc_fport));
                sp = s + strlen(s);
                inet_ntoa_r(inc->inc_laddr, sp);
                sp = s + strlen(s);
                sprintf(sp, "]:%i", ntohs(inc->inc_lport));
#ifdef INET6
        } else if (inc) {
                ip6_sprintf(sp, &inc->inc6_faddr);
                sp = s + strlen(s);
                sprintf(sp, "]:%i to [", ntohs(inc->inc_fport));
                sp = s + strlen(s);
                ip6_sprintf(sp, &inc->inc6_laddr);
                sp = s + strlen(s);
                sprintf(sp, "]:%i", ntohs(inc->inc_lport));
        } else if (ip6 && th) {
                ip6_sprintf(sp, &ip6->ip6_src);
                sp = s + strlen(s);
                sprintf(sp, "]:%i to [", ntohs(th->th_sport));
                sp = s + strlen(s);
                ip6_sprintf(sp, &ip6->ip6_dst);
                sp = s + strlen(s);
                sprintf(sp, "]:%i", ntohs(th->th_dport));
#endif /* INET6 */
#ifdef INET
        } else if (ip && th) {
                inet_ntoa_r(ip->ip_src, sp);
                sp = s + strlen(s);
                sprintf(sp, "]:%i to [", ntohs(th->th_sport));
                sp = s + strlen(s);
                inet_ntoa_r(ip->ip_dst, sp);
                sp = s + strlen(s);
                sprintf(sp, "]:%i", ntohs(th->th_dport));
#endif /* INET */
        } else {
                free(s, M_TCPLOG);
                return (NULL);
        }
        sp = s + strlen(s);
        if (th)
                sprintf(sp, " tcpflags 0x%b", th->th_flags, PRINT_TH_FLAGS);
        if (*(s + size - 1) != '\0')
                panic("%s: string too long", __func__);
        return (s);
}

/*
 * A subroutine which makes it easy to track TCP state changes with DTrace.
 * This function shouldn't be called for t_state initializations that don't
 * correspond to actual TCP state transitions.
 */
void
tcp_state_change(struct tcpcb *tp, int newstate)
{
#if defined(KDTRACE_HOOKS)
        int pstate = tp->t_state;
#endif

        TCPSTATES_DEC(tp->t_state);
        TCPSTATES_INC(newstate);
        tp->t_state = newstate;
        TCP_PROBE6(state__change, NULL, tp, NULL, tp, NULL, pstate);
}

/*
 * Create an external-format (``xtcpcb'') structure using the information in
 * the kernel-format tcpcb structure pointed to by tp.  This is done to
 * reduce the spew of irrelevant information over this interface, to isolate
 * user code from changes in the kernel structure, and potentially to provide
 * information-hiding if we decide that some of this information should be
 * hidden from users.
 */
void
tcp_inptoxtp(const struct inpcb *inp, struct xtcpcb *xt)
{
        struct tcpcb *tp = intotcpcb(inp);
        sbintime_t now;

        bzero(xt, sizeof(*xt));
        if (inp->inp_flags & INP_TIMEWAIT) {
                xt->t_state = TCPS_TIME_WAIT;
        } else {
                xt->t_state = tp->t_state;
                xt->t_logstate = tp->t_logstate;
                xt->t_flags = tp->t_flags;
                xt->t_sndzerowin = tp->t_sndzerowin;
                xt->t_sndrexmitpack = tp->t_sndrexmitpack;
                xt->t_rcvoopack = tp->t_rcvoopack;

                now = getsbinuptime();
#define COPYTIMER(ttt)  do {                                            \
                if (callout_active(&tp->t_timers->ttt))                 \
                        xt->ttt = (tp->t_timers->ttt.c_time - now) /    \
                            SBT_1MS;                                    \
                else                                                    \
                        xt->ttt = 0;                                    \
} while (0)
                COPYTIMER(tt_delack);
                COPYTIMER(tt_rexmt);
                COPYTIMER(tt_persist);
                COPYTIMER(tt_keep);
                COPYTIMER(tt_2msl);
#undef COPYTIMER
                xt->t_rcvtime = 1000 * (ticks - tp->t_rcvtime) / hz;

                bcopy(tp->t_fb->tfb_tcp_block_name, xt->xt_stack,
                    TCP_FUNCTION_NAME_LEN_MAX);
#ifdef TCP_BLACKBOX
                (void)tcp_log_get_id(tp, xt->xt_logid);
#endif
        }

        xt->xt_len = sizeof(struct xtcpcb);
        in_pcbtoxinpcb(inp, &xt->xt_inp);
        if (inp->inp_socket == NULL)
                xt->xt_inp.xi_socket.xso_protocol = IPPROTO_TCP;
}