/*      $OpenBSD: tcp_timer.c,v 1.88 2025/09/17 17:29:14 bluhm Exp $    */
/*      $NetBSD: tcp_timer.c,v 1.14 1996/02/13 23:44:09 christos Exp $  */

/*
 * Copyright (c) 1982, 1986, 1988, 1990, 1993
 *      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_timer.c 8.1 (Berkeley) 6/10/93
 */

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

#include <net/route.h>

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

/*
 * Locks used to protect struct members in this file:
 *      T       tcp_timer_mtx           global tcp timer data structures
 */

int     tcp_always_keepalive;
int     tcp_keepinit = TCPTV_KEEPINIT;
int     tcp_keepidle = TCPTV_KEEPIDLE;
int     tcp_keepintvl = TCPTV_KEEPINTVL;
int     tcp_keepinit_sec = TCPTV_KEEPINIT / TCP_TIME(1);
int     tcp_keepidle_sec = TCPTV_KEEPIDLE / TCP_TIME(1);
int     tcp_keepintvl_sec = TCPTV_KEEPINTVL / TCP_TIME(1);
int     tcp_maxpersistidle = TCPTV_KEEPIDLE;    /* max idle time in persist */
int     tcp_delack_msecs = TCP_DELACK_MSECS;    /* time to delay the ACK */

void    tcp_timer_rexmt(void *);
void    tcp_timer_persist(void *);
void    tcp_timer_keep(void *);
void    tcp_timer_2msl(void *);
void    tcp_timer_delack(void *);

const tcp_timer_func_t tcp_timer_funcs[TCPT_NTIMERS] = {
        tcp_timer_rexmt,
        tcp_timer_persist,
        tcp_timer_keep,
        tcp_timer_2msl,
        tcp_timer_delack,
};

static inline int
tcp_timer_enter(struct inpcb *inp, struct socket **so, struct tcpcb **tp,
    u_int timer)
{
        KASSERT(timer < TCPT_NTIMERS);

        NET_LOCK_SHARED();
        *so = in_pcbsolock(inp);
        if (*so == NULL) {
                *tp = NULL;
                return -1;
        }
        *tp = intotcpcb(inp);
        /* Ignore canceled timeouts or timeouts that have been rescheduled. */
        if (*tp == NULL || !ISSET((*tp)->t_flags, TF_TIMER << timer) ||
            timeout_pending(&(*tp)->t_timer[timer]))
                return -1;
        CLR((*tp)->t_flags, TF_TIMER << timer);

        return 0;
}

static inline void
tcp_timer_leave(struct inpcb *inp, struct socket *so)
{
        in_pcbsounlock(inp, so);
        NET_UNLOCK_SHARED();
        in_pcbunref(inp);
}

/*
 * Callout to process delayed ACKs for a TCPCB.
 */
void
tcp_timer_delack(void *arg)
{
        struct inpcb *inp = arg;
        struct socket *so;
        struct tcpcb *otp = NULL, *tp;
        short ostate;

        /*
         * If tcp_output() wasn't able to transmit the ACK
         * for whatever reason, it will restart the delayed
         * ACK callout.
         */
        if (tcp_timer_enter(inp, &so, &tp, TCPT_DELACK))
                goto out;

        if (so->so_options & SO_DEBUG) {
                otp = tp;
                ostate = tp->t_state;
        }
        tp->t_flags |= TF_ACKNOW;
        (void) tcp_output(tp);
        if (otp)
                tcp_trace(TA_TIMER, ostate, tp, otp, NULL, TCPT_DELACK, 0);
 out:
        tcp_timer_leave(inp, so);
}

/*
 * Tcp protocol timeout routine called every 500 ms.
 * Updates the timers in all active tcb's and
 * causes finite state machine actions if timers expire.
 */
void
tcp_slowtimo(void)
{
        mtx_enter(&tcp_timer_mtx);
        tcp_iss += TCP_ISSINCR2/PR_SLOWHZ;              /* increment iss */
        mtx_leave(&tcp_timer_mtx);
}

/*
 * Cancel all timers for TCP tp.
 */
void
tcp_canceltimers(struct tcpcb *tp)
{
        int i;

        for (i = 0; i < TCPT_NTIMERS; i++)
                TCP_TIMER_DISARM(tp, i);
}

const int tcp_backoff[TCP_MAXRXTSHIFT + 1] =
    { 1, 2, 4, 8, 16, 32, 64, 64, 64, 64, 64, 64, 64 };

const int tcp_totbackoff = 511; /* sum of tcp_backoff[] */

/*
 * TCP timer processing.
 */

void    tcp_timer_freesack(struct tcpcb *);

void
tcp_timer_freesack(struct tcpcb *tp)
{
        struct sackhole *p, *q;
        /*
         * Free SACK holes for 2MSL and REXMT timers.
         */
        q = tp->snd_holes;
        while (q != NULL) {
                p = q;
                q = q->next;
                pool_put(&sackhl_pool, p);
        }
        tp->snd_holes = 0;
}

void
tcp_timer_rexmt(void *arg)
{
        struct inpcb *inp = arg;
        struct socket *so;
        struct tcpcb *otp = NULL, *tp;
        short ostate;
        uint32_t rto;

        if (tcp_timer_enter(inp, &so, &tp, TCPT_REXMT))
                goto out;

        if ((tp->t_flags & TF_PMTUD_PEND) &&
            SEQ_GEQ(tp->t_pmtud_th_seq, tp->snd_una) &&
            SEQ_LT(tp->t_pmtud_th_seq, (int)(tp->snd_una + tp->t_maxseg))) {
                struct sockaddr_in sin;
                struct icmp icmp;
                u_int rtableid;

                /* TF_PMTUD_PEND is set in tcp_ctlinput() which is IPv4 only */
                KASSERT(!ISSET(inp->inp_flags, INP_IPV6));
                tp->t_flags &= ~TF_PMTUD_PEND;

                rtableid = inp->inp_rtableid;

                /* XXX create fake icmp message with relevant entries */
                icmp.icmp_nextmtu = tp->t_pmtud_nextmtu;
                icmp.icmp_ip.ip_len = tp->t_pmtud_ip_len;
                icmp.icmp_ip.ip_hl = tp->t_pmtud_ip_hl;
                icmp.icmp_ip.ip_dst = inp->inp_faddr;

                /*
                 * Notify all connections to the same peer about
                 * new mss and trigger retransmit.
                 */
                bzero(&sin, sizeof(sin));
                sin.sin_len = sizeof(sin);
                sin.sin_family = AF_INET;
                sin.sin_addr = inp->inp_faddr;

                in_pcbsounlock(inp, so);
                in_pcbunref(inp);

                icmp_mtudisc(&icmp, rtableid);
                in_pcbnotifyall(&tcbtable, &sin, rtableid, EMSGSIZE,
                    tcp_mtudisc);

                NET_UNLOCK_SHARED();
                return;
        }

        tcp_timer_freesack(tp);
        if (++tp->t_rxtshift > TCP_MAXRXTSHIFT) {
                tp->t_rxtshift = TCP_MAXRXTSHIFT;
                tcpstat_inc(tcps_timeoutdrop);
                tp = tcp_drop(tp, tp->t_softerror ?
                    tp->t_softerror : ETIMEDOUT);
                goto out;
        }
        if (so->so_options & SO_DEBUG) {
                otp = tp;
                ostate = tp->t_state;
        }
        tcpstat_inc(tcps_rexmttimeo);
        rto = TCP_REXMTVAL(tp);
        if (rto < tp->t_rttmin)
                rto = tp->t_rttmin;
        TCPT_RANGESET(tp->t_rxtcur,
            rto * tcp_backoff[tp->t_rxtshift],
            tp->t_rttmin, TCPTV_REXMTMAX);
        TCP_TIMER_ARM(tp, TCPT_REXMT, tp->t_rxtcur);

        /*
         * If we are losing and we are trying path MTU discovery,
         * try turning it off.  This will avoid black holes in
         * the network which suppress or fail to send "packet
         * too big" ICMP messages.  We should ideally do
         * lots more sophisticated searching to find the right
         * value here...
         */
        if (atomic_load_int(&ip_mtudisc) &&
            TCPS_HAVEESTABLISHED(tp->t_state) &&
            tp->t_rxtshift > TCP_MAXRXTSHIFT / 6) {
                struct rtentry *rt = NULL;

                /* No data to send means path mtu is not a problem */
                if (!READ_ONCE(so->so_snd.sb_cc))
                        goto leave;

                rt = in_pcbrtentry(inp);
                /* Check if path MTU discovery is disabled already */
                if (rt && (rt->rt_flags & RTF_HOST) &&
                    (rt->rt_locks & RTV_MTU))
                        goto leave;

                rt = NULL;
                switch(tp->pf) {
#ifdef INET6
                case PF_INET6:
                        /*
                         * We can not turn off path MTU for IPv6.
                         * Do nothing for now, maybe lower to
                         * minimum MTU.
                         */
                        break;
#endif
                case PF_INET:
                        rt = icmp_mtudisc_clone(inp->inp_faddr,
                            inp->inp_rtableid, 0);
                        break;
                }
                if (rt != NULL) {
                        /* Disable path MTU discovery */
                        if ((rt->rt_locks & RTV_MTU) == 0) {
                                rt->rt_locks |= RTV_MTU;
                                in_pcbrtchange(inp, 0);
                        }

                        rtfree(rt);
                }
        leave:
                ;
        }

        /*
         * If losing, let the lower level know and try for
         * a better route.  Also, if we backed off this far,
         * our srtt estimate is probably bogus.  Clobber it
         * so we'll take the next rtt measurement as our srtt;
         * move the current srtt into rttvar to keep the current
         * retransmit times until then.
         */
        if (tp->t_rxtshift > TCP_MAXRXTSHIFT / 4) {
                in_losing(inp);
                tp->t_rttvar += (tp->t_srtt >> TCP_RTT_SHIFT);
                tp->t_srtt = 0;
        }
        tp->snd_nxt = tp->snd_una;
        /*
         * Note:  We overload snd_last to function also as the
         * snd_last variable described in RFC 2582
         */
        tp->snd_last = tp->snd_max;
        /*
         * If timing a segment in this window, stop the timer.
         */
        tp->t_rtttime = 0;
#ifdef TCP_ECN
        /*
         * if ECN is enabled, there might be a broken firewall which
         * blocks ecn packets.  fall back to non-ecn.
         */
        if ((tp->t_state == TCPS_SYN_SENT || tp->t_state == TCPS_SYN_RECEIVED)
            && atomic_load_int(&tcp_do_ecn) && !(tp->t_flags & TF_DISABLE_ECN))
                tp->t_flags |= TF_DISABLE_ECN;
#endif
        /*
         * Close the congestion window down to one segment
         * (we'll open it by one segment for each ack we get).
         * Since we probably have a window's worth of unacked
         * data accumulated, this "slow start" keeps us from
         * dumping all that data as back-to-back packets (which
         * might overwhelm an intermediate gateway).
         *
         * There are two phases to the opening: Initially we
         * open by one mss on each ack.  This makes the window
         * size increase exponentially with time.  If the
         * window is larger than the path can handle, this
         * exponential growth results in dropped packet(s)
         * almost immediately.  To get more time between
         * drops but still "push" the network to take advantage
         * of improving conditions, we switch from exponential
         * to linear window opening at some threshold size.
         * For a threshold, we use half the current window
         * size, truncated to a multiple of the mss.
         *
         * (the minimum cwnd that will give us exponential
         * growth is 2 mss.  We don't allow the threshold
         * to go below this.)
         */
        {
                u_long win;

                win = ulmin(tp->snd_wnd, tp->snd_cwnd) / 2 / tp->t_maxseg;
                if (win < 2)
                        win = 2;
                tp->snd_cwnd = tp->t_maxseg;
                tp->snd_ssthresh = win * tp->t_maxseg;
                tp->t_dupacks = 0;
#ifdef TCP_ECN
                tp->snd_last = tp->snd_max;
                tp->t_flags |= TF_SEND_CWR;
#endif
#if 1 /* TCP_ECN */
                tcpstat_inc(tcps_cwr_timeout);
#endif
        }
        (void) tcp_output(tp);
        if (otp)
                tcp_trace(TA_TIMER, ostate, tp, otp, NULL, TCPT_REXMT, 0);
 out:
        tcp_timer_leave(inp, so);
}

void
tcp_timer_persist(void *arg)
{
        struct inpcb *inp = arg;
        struct socket *so;
        struct tcpcb *otp = NULL, *tp;
        short ostate;
        uint64_t now;
        uint32_t rto;

        if (tcp_timer_enter(inp, &so, &tp, TCPT_PERSIST))
                goto out;

        if (TCP_TIMER_ISARMED(tp, TCPT_REXMT))
                goto out;

        if (so->so_options & SO_DEBUG) {
                otp = tp;
                ostate = tp->t_state;
        }
        tcpstat_inc(tcps_persisttimeo);
        /*
         * Hack: if the peer is dead/unreachable, we do not
         * time out if the window is closed.  After a full
         * backoff, drop the connection if the idle time
         * (no responses to probes) reaches the maximum
         * backoff that we would use if retransmitting.
         */
        rto = TCP_REXMTVAL(tp);
        if (rto < tp->t_rttmin)
                rto = tp->t_rttmin;
        now = tcp_now();
        if (tp->t_rxtshift == TCP_MAXRXTSHIFT &&
            ((now - tp->t_rcvtime) >= tcp_maxpersistidle ||
            (now - tp->t_rcvtime) >= rto * tcp_totbackoff)) {
                tcpstat_inc(tcps_persistdrop);
                tp = tcp_drop(tp, ETIMEDOUT);
                goto out;
        }
        tcp_setpersist(tp);
        tp->t_force = 1;
        (void) tcp_output(tp);
        tp->t_force = 0;
        if (otp)
                tcp_trace(TA_TIMER, ostate, tp, otp, NULL, TCPT_PERSIST, 0);
 out:
        tcp_timer_leave(inp, so);
}

void
tcp_timer_keep(void *arg)
{
        struct inpcb *inp = arg;
        struct socket *so;
        struct tcpcb *otp = NULL, *tp;
        short ostate;

        if (tcp_timer_enter(inp, &so, &tp, TCPT_KEEP))
                goto out;

        if (so->so_options & SO_DEBUG) {
                otp = tp;
                ostate = tp->t_state;
        }
        tcpstat_inc(tcps_keeptimeo);
        if (TCPS_HAVEESTABLISHED(tp->t_state) == 0) {
                tcpstat_inc(tcps_keepdrops);
                tp = tcp_drop(tp, ETIMEDOUT);
                goto out;
        }
        if ((atomic_load_int(&tcp_always_keepalive) ||
            so->so_options & SO_KEEPALIVE) &&
            tp->t_state <= TCPS_CLOSING) {
                int keepidle, keepintvl, maxidle;
                uint64_t now;

                keepidle = atomic_load_int(&tcp_keepidle);
                keepintvl = atomic_load_int(&tcp_keepintvl);
                maxidle = TCPTV_KEEPCNT * keepintvl;
                now = tcp_now();
                if ((maxidle > 0) &&
                    ((now - tp->t_rcvtime) >= keepidle + maxidle)) {
                        tcpstat_inc(tcps_keepdrops);
                        tp = tcp_drop(tp, ETIMEDOUT);
                        goto out;
                }
                /*
                 * Send a packet designed to force a response
                 * if the peer is up and reachable:
                 * either an ACK if the connection is still alive,
                 * or an RST if the peer has closed the connection
                 * due to timeout or reboot.
                 * Using sequence number tp->snd_una-1
                 * causes the transmitted zero-length segment
                 * to lie outside the receive window;
                 * by the protocol spec, this requires the
                 * correspondent TCP to respond.
                 */
                tcpstat_inc(tcps_keepprobe);
                tcp_respond(tp, mtod(tp->t_template, caddr_t),
                    NULL, tp->rcv_nxt, tp->snd_una - 1, 0, 0, now);
                TCP_TIMER_ARM(tp, TCPT_KEEP, keepintvl);
        } else
                TCP_TIMER_ARM(tp, TCPT_KEEP, atomic_load_int(&tcp_keepidle));
        if (otp)
                tcp_trace(TA_TIMER, ostate, tp, otp, NULL, TCPT_KEEP, 0);
 out:
        tcp_timer_leave(inp, so);
}

void
tcp_timer_2msl(void *arg)
{
        struct inpcb *inp = arg;
        struct socket *so;
        struct tcpcb *otp = NULL, *tp;
        short ostate;
        uint64_t now;
        int keepintvl, maxidle;

        if (tcp_timer_enter(inp, &so, &tp, TCPT_2MSL))
                goto out;

        if (so->so_options & SO_DEBUG) {
                otp = tp;
                ostate = tp->t_state;
        }
        tcp_timer_freesack(tp);

        keepintvl = atomic_load_int(&tcp_keepintvl);
        maxidle = TCPTV_KEEPCNT * keepintvl;
        now = tcp_now();
        if (tp->t_state != TCPS_TIME_WAIT &&
            ((maxidle == 0) || ((now - tp->t_rcvtime) <= maxidle)))
                TCP_TIMER_ARM(tp, TCPT_2MSL, keepintvl);
        else
                tp = tcp_close(tp);
        if (otp)
                tcp_trace(TA_TIMER, ostate, tp, otp, NULL, TCPT_2MSL, 0);
 out:
        tcp_timer_leave(inp, so);
}