/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * Copyright (c) 1982, 1986, 1988, 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.
 */

/*
 * Ethernet address resolution protocol.
 * TODO:
 *      add "inuse/lock" bit (or ref. count) along with valid bit
 */

#include "opt_inet.h"

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

#include <net/if.h>
#include <net/if_var.h>
#include <net/if_dl.h>
#include <net/if_private.h>
#include <net/if_types.h>
#include <net/if_bridgevar.h>
#include <net/netisr.h>
#include <net/ethernet.h>
#include <net/route.h>
#include <net/route/nhop.h>
#include <net/vnet.h>

#include <netinet/in.h>
#include <netinet/in_fib.h>
#include <netinet/in_var.h>
#include <net/if_llatbl.h>
#include <netinet/if_ether.h>
#ifdef INET
#include <netinet/ip_carp.h>
#endif

#include <security/mac/mac_framework.h>

#define SIN(s) ((const struct sockaddr_in *)(s))

static struct timeval arp_lastlog;
static int arp_curpps;
static int arp_maxpps = 1;

/* Simple ARP state machine */
enum arp_llinfo_state {
        ARP_LLINFO_INCOMPLETE = 0, /* No LLE data */
        ARP_LLINFO_REACHABLE,   /* LLE is valid */
        ARP_LLINFO_VERIFY,      /* LLE is valid, need refresh */
        ARP_LLINFO_DELETED,     /* LLE is deleted */
};

SYSCTL_DECL(_net_link_ether);
static SYSCTL_NODE(_net_link_ether, PF_INET, inet,
    CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
    "");
static SYSCTL_NODE(_net_link_ether, PF_ARP, arp,
    CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
    "");

/* timer values */
VNET_DEFINE_STATIC(int, arpt_keep) = (20*60);   /* once resolved, good for 20
                                                 * minutes */
VNET_DEFINE_STATIC(int, arp_maxtries) = 5;
VNET_DEFINE_STATIC(int, arp_proxyall) = 0;
VNET_DEFINE_STATIC(int, arpt_down) = 20;        /* keep incomplete entries for
                                                 * 20 seconds */
VNET_DEFINE_STATIC(int, arpt_rexmit) = 1;       /* retransmit arp entries, sec*/
VNET_PCPUSTAT_DEFINE(struct arpstat, arpstat);  /* ARP statistics, see if_arp.h */
VNET_PCPUSTAT_SYSINIT(arpstat);

#ifdef VIMAGE
VNET_PCPUSTAT_SYSUNINIT(arpstat);
#endif /* VIMAGE */

VNET_DEFINE_STATIC(int, arp_maxhold) = 16;

#define V_arpt_keep             VNET(arpt_keep)
#define V_arpt_down             VNET(arpt_down)
#define V_arpt_rexmit           VNET(arpt_rexmit)
#define V_arp_maxtries          VNET(arp_maxtries)
#define V_arp_proxyall          VNET(arp_proxyall)
#define V_arp_maxhold           VNET(arp_maxhold)

SYSCTL_INT(_net_link_ether_inet, OID_AUTO, max_age, CTLFLAG_VNET | CTLFLAG_RW,
        &VNET_NAME(arpt_keep), 0,
        "ARP entry lifetime in seconds");
SYSCTL_INT(_net_link_ether_inet, OID_AUTO, maxtries, CTLFLAG_VNET | CTLFLAG_RW,
        &VNET_NAME(arp_maxtries), 0,
        "ARP resolution attempts before returning error");
SYSCTL_INT(_net_link_ether_inet, OID_AUTO, proxyall, CTLFLAG_VNET | CTLFLAG_RW,
        &VNET_NAME(arp_proxyall), 0,
        "Enable proxy ARP for all suitable requests");
SYSCTL_INT(_net_link_ether_inet, OID_AUTO, wait, CTLFLAG_VNET | CTLFLAG_RW,
        &VNET_NAME(arpt_down), 0,
        "Incomplete ARP entry lifetime in seconds");
SYSCTL_VNET_PCPUSTAT(_net_link_ether_arp, OID_AUTO, stats, struct arpstat,
    arpstat, "ARP statistics (struct arpstat, net/if_arp.h)");
SYSCTL_INT(_net_link_ether_inet, OID_AUTO, maxhold, CTLFLAG_VNET | CTLFLAG_RW,
        &VNET_NAME(arp_maxhold), 0,
        "Number of packets to hold per ARP entry");
SYSCTL_INT(_net_link_ether_inet, OID_AUTO, max_log_per_second,
        CTLFLAG_RW, &arp_maxpps, 0,
        "Maximum number of remotely triggered ARP messages that can be "
        "logged per second");

/*
 * Due to the exponential backoff algorithm used for the interval between GARP
 * retransmissions, the maximum number of retransmissions is limited for
 * sanity. This limit corresponds to a maximum interval between retransmissions
 * of 2^16 seconds ~= 18 hours.
 *
 * Making this limit more dynamic is more complicated than worthwhile,
 * especially since sending out GARPs spaced days apart would be of little
 * use. A maximum dynamic limit would look something like:
 *
 * const int max = fls(INT_MAX / hz) - 1;
 */
#define MAX_GARP_RETRANSMITS 16
static int sysctl_garp_rexmit(SYSCTL_HANDLER_ARGS);
VNET_DEFINE_STATIC(int, garp_rexmit_count) = 0; /* GARP retransmission setting. */
#define V_garp_rexmit_count     VNET(garp_rexmit_count)

SYSCTL_PROC(_net_link_ether_inet, OID_AUTO, garp_rexmit_count,
    CTLTYPE_INT|CTLFLAG_RW|CTLFLAG_MPSAFE|CTLFLAG_VNET,
    &VNET_NAME(garp_rexmit_count), 0, sysctl_garp_rexmit, "I",
    "Number of times to retransmit GARP packets;"
    " 0 to disable, maximum of 16");

VNET_DEFINE_STATIC(int, arp_log_level) = LOG_INFO;      /* Min. log(9) level. */
#define V_arp_log_level         VNET(arp_log_level)
SYSCTL_INT(_net_link_ether_arp, OID_AUTO, log_level, CTLFLAG_VNET | CTLFLAG_RW,
        &VNET_NAME(arp_log_level), 0,
        "Minimum log(9) level for recording rate limited arp log messages. "
        "The higher will be log more (emerg=0, info=6 (default), debug=7).");
#define ARP_LOG(pri, ...)       do {                                    \
        if ((pri) <= V_arp_log_level &&                                 \
            ppsratecheck(&arp_lastlog, &arp_curpps, arp_maxpps))        \
                log((pri), "arp: " __VA_ARGS__);                        \
} while (0)

static void     arpintr(struct mbuf *);
static void     arptimer(void *);
#ifdef INET
static void     in_arpinput(struct mbuf *);
#endif

static void arp_check_update_lle(struct arphdr *ah, struct in_addr isaddr,
    struct ifnet *ifp, int bridged, struct llentry *la);
static void arp_mark_lle_reachable(struct llentry *la, struct ifnet *ifp);
static void arp_iflladdr(void *arg __unused, struct ifnet *ifp);

static eventhandler_tag iflladdr_tag;

static const struct netisr_handler arp_nh = {
        .nh_name = "arp",
        .nh_handler = arpintr,
        .nh_proto = NETISR_ARP,
        .nh_policy = NETISR_POLICY_SOURCE,
};

/*
 * Timeout routine.  Age arp_tab entries periodically.
 */
static void
arptimer(void *arg)
{
        struct llentry *lle = (struct llentry *)arg;
        struct ifnet *ifp;

        if (lle->la_flags & LLE_STATIC) {
                return;
        }
        LLE_WLOCK(lle);
        if (callout_pending(&lle->lle_timer)) {
                /*
                 * Here we are a bit odd here in the treatment of
                 * active/pending. If the pending bit is set, it got
                 * rescheduled before I ran. The active
                 * bit we ignore, since if it was stopped
                 * in ll_tablefree() and was currently running
                 * it would have return 0 so the code would
                 * not have deleted it since the callout could
                 * not be stopped so we want to go through
                 * with the delete here now. If the callout
                 * was restarted, the pending bit will be back on and
                 * we just want to bail since the callout_reset would
                 * return 1 and our reference would have been removed
                 * by arpresolve() below.
                 */
                LLE_WUNLOCK(lle);
                return;
        }
        ifp = lle->lle_tbl->llt_ifp;
        CURVNET_SET(ifp->if_vnet);

        switch (lle->ln_state) {
        case ARP_LLINFO_REACHABLE:

                /*
                 * Expiration time is approaching.
                 * Request usage feedback from the datapath.
                 * Change state and re-schedule ourselves.
                 */
                llentry_request_feedback(lle);
                lle->ln_state = ARP_LLINFO_VERIFY;
                callout_schedule(&lle->lle_timer, hz * V_arpt_rexmit);
                LLE_WUNLOCK(lle);
                CURVNET_RESTORE();
                return;
        case ARP_LLINFO_VERIFY:
                if (llentry_get_hittime(lle) > 0 && lle->la_preempt > 0) {
                        /* Entry was used, issue refresh request */
                        struct epoch_tracker et;
                        struct in_addr dst;

                        dst = lle->r_l3addr.addr4;
                        lle->la_preempt--;
                        callout_schedule(&lle->lle_timer, hz * V_arpt_rexmit);
                        LLE_WUNLOCK(lle);
                        NET_EPOCH_ENTER(et);
                        arprequest(ifp, NULL, &dst, NULL);
                        NET_EPOCH_EXIT(et);
                        CURVNET_RESTORE();
                        return;
                }
                /* Nothing happened. Reschedule if not too late */
                if (lle->la_expire > time_uptime) {
                        callout_schedule(&lle->lle_timer, hz * V_arpt_rexmit);
                        LLE_WUNLOCK(lle);
                        CURVNET_RESTORE();
                        return;
                }
                break;
        case ARP_LLINFO_INCOMPLETE:
        case ARP_LLINFO_DELETED:
                break;
        }

        if ((lle->la_flags & LLE_DELETED) == 0) {
                int evt;

                if (lle->la_flags & LLE_VALID)
                        evt = LLENTRY_EXPIRED;
                else
                        evt = LLENTRY_TIMEDOUT;
                EVENTHANDLER_INVOKE(lle_event, lle, evt);
        }

        callout_stop(&lle->lle_timer);

        /* XXX: LOR avoidance. We still have ref on lle. */
        LLE_WUNLOCK(lle);
        LLTABLE_LOCK(LLTABLE(ifp));
        LLE_WLOCK(lle);

        /* Guard against race with other llentry_free(). */
        if (lle->la_flags & LLE_LINKED) {
                LLE_REMREF(lle);
                lltable_unlink_entry(lle->lle_tbl, lle);
        }
        LLTABLE_UNLOCK(LLTABLE(ifp));

        size_t pkts_dropped = llentry_free(lle);

        ARPSTAT_ADD(dropped, pkts_dropped);
        ARPSTAT_INC(timeouts);

        CURVNET_RESTORE();
}

/*
 * Stores link-layer header for @ifp in format suitable for if_output()
 * into buffer @buf. Resulting header length is stored in @bufsize.
 *
 * Returns 0 on success.
 */
static int
arp_fillheader(struct ifnet *ifp, struct arphdr *ah, int bcast, u_char *buf,
    size_t *bufsize)
{
        struct if_encap_req ereq;
        int error;

        bzero(buf, *bufsize);
        bzero(&ereq, sizeof(ereq));
        ereq.buf = buf;
        ereq.bufsize = *bufsize;
        ereq.rtype = IFENCAP_LL;
        ereq.family = AF_ARP;
        ereq.lladdr = ar_tha(ah);
        ereq.hdata = (u_char *)ah;
        if (bcast)
                ereq.flags = IFENCAP_FLAG_BROADCAST;
        error = ifp->if_requestencap(ifp, &ereq);
        if (error == 0)
                *bufsize = ereq.bufsize;

        return (error);
}

/*
 * Broadcast an ARP request. Caller specifies:
 *      - arp header source ip address
 *      - arp header target ip address
 *      - arp header source ethernet address
 */
static int
arprequest_internal(struct ifnet *ifp, const struct in_addr *sip,
    const struct in_addr *tip, u_char *enaddr)
{
        struct mbuf *m;
        struct arphdr *ah;
        struct sockaddr sa;
        u_char *carpaddr = NULL;
        uint8_t linkhdr[LLE_MAX_LINKHDR];
        size_t linkhdrsize;
        struct route ro;
        int error;

        NET_EPOCH_ASSERT();

        if (sip == NULL) {
                /*
                 * The caller did not supply a source address, try to find
                 * a compatible one among those assigned to this interface.
                 */
                struct ifaddr *ifa;

                CK_STAILQ_FOREACH(ifa, &ifp->if_addrhead, ifa_link) {
                        if (ifa->ifa_addr->sa_family != AF_INET)
                                continue;

                        if (ifa->ifa_carp) {
                                if ((*carp_iamatch_p)(ifa, &carpaddr) == 0)
                                        continue;
                                sip = &IA_SIN(ifa)->sin_addr;
                        } else {
                                carpaddr = NULL;
                                sip = &IA_SIN(ifa)->sin_addr;
                        }

                        if (0 == ((sip->s_addr ^ tip->s_addr) &
                            IA_MASKSIN(ifa)->sin_addr.s_addr))
                                break;  /* found it. */
                }
                if (sip == NULL) {
                        printf("%s: cannot find matching address\n", __func__);
                        return (EADDRNOTAVAIL);
                }
        }
        if (enaddr == NULL)
                enaddr = carpaddr ? carpaddr : (u_char *)IF_LLADDR(ifp);

        if ((m = m_gethdr(M_NOWAIT, MT_DATA)) == NULL)
                return (ENOMEM);
        m->m_len = sizeof(*ah) + 2 * sizeof(struct in_addr) +
                2 * ifp->if_addrlen;
        m->m_pkthdr.len = m->m_len;
        M_ALIGN(m, m->m_len);
        ah = mtod(m, struct arphdr *);
        bzero((caddr_t)ah, m->m_len);
#ifdef MAC
        mac_netinet_arp_send(ifp, m);
#endif
        ah->ar_pro = htons(ETHERTYPE_IP);
        ah->ar_hln = ifp->if_addrlen;           /* hardware address length */
        ah->ar_pln = sizeof(struct in_addr);    /* protocol address length */
        ah->ar_op = htons(ARPOP_REQUEST);
        bcopy(enaddr, ar_sha(ah), ah->ar_hln);
        bcopy(sip, ar_spa(ah), ah->ar_pln);
        bcopy(tip, ar_tpa(ah), ah->ar_pln);
        sa.sa_family = AF_ARP;
        sa.sa_len = 2;

        /* Calculate link header for sending frame */
        bzero(&ro, sizeof(ro));
        linkhdrsize = sizeof(linkhdr);
        error = arp_fillheader(ifp, ah, 1, linkhdr, &linkhdrsize);
        if (error != 0 && error != EAFNOSUPPORT) {
                m_freem(m);
                ARP_LOG(LOG_ERR, "Failed to calculate ARP header on %s: %d\n",
                    if_name(ifp), error);
                return (error);
        }

        ro.ro_prepend = linkhdr;
        ro.ro_plen = linkhdrsize;
        ro.ro_flags = 0;

        m->m_flags |= M_BCAST;
        m_clrprotoflags(m);     /* Avoid confusing lower layers. */
        error = (*ifp->if_output)(ifp, m, &sa, &ro);
        ARPSTAT_INC(txrequests);
        if (error) {
                ARPSTAT_INC(txerrors);
                ARP_LOG(LOG_DEBUG, "Failed to send ARP packet on %s: %d\n",
                    if_name(ifp), error);
        }
        return (error);
}

void
arprequest(struct ifnet *ifp, const struct in_addr *sip,
    const struct in_addr *tip, u_char *enaddr)
{

        (void) arprequest_internal(ifp, sip, tip, enaddr);
}

/*
 * Resolve an IP address into an ethernet address - heavy version.
 * Used internally by arpresolve().
 * We have already checked that we can't use an existing lle without
 * modification so we have to acquire an LLE_EXCLUSIVE lle lock.
 *
 * On success, desten and pflags are filled in and the function returns 0;
 * If the packet must be held pending resolution, we return EWOULDBLOCK
 * On other errors, we return the corresponding error code.
 * Note that m_freem() handles NULL.
 */
static int
arpresolve_full(struct ifnet *ifp, int is_gw, int flags, struct mbuf *m,
        const struct sockaddr *dst, u_char *desten, uint32_t *pflags,
        struct llentry **plle)
{
        struct llentry *la = NULL, *la_tmp;
        int error, renew;
        char *lladdr;
        int ll_len;

        NET_EPOCH_ASSERT();

        if (pflags != NULL)
                *pflags = 0;
        if (plle != NULL)
                *plle = NULL;

        if ((flags & LLE_CREATE) == 0)
                la = lla_lookup(LLTABLE(ifp), LLE_EXCLUSIVE, dst);
        if (la == NULL && (ifp->if_flags & (IFF_NOARP | IFF_STATICARP)) == 0) {
                la = lltable_alloc_entry(LLTABLE(ifp), 0, dst);
                if (la == NULL) {
                        char addrbuf[INET_ADDRSTRLEN];

                        log(LOG_DEBUG,
                            "arpresolve: can't allocate llinfo for %s on %s\n",
                            inet_ntoa_r(SIN(dst)->sin_addr, addrbuf),
                            if_name(ifp));
                        m_freem(m);
                        return (EINVAL);
                }

                LLTABLE_LOCK(LLTABLE(ifp));
                LLE_WLOCK(la);
                la_tmp = lla_lookup(LLTABLE(ifp), LLE_EXCLUSIVE, dst);
                /* Prefer ANY existing lle over newly-created one */
                if (la_tmp == NULL)
                        lltable_link_entry(LLTABLE(ifp), la);
                LLTABLE_UNLOCK(LLTABLE(ifp));
                if (la_tmp != NULL) {
                        lltable_free_entry(LLTABLE(ifp), la);
                        la = la_tmp;
                }
        }
        if (la == NULL) {
                m_freem(m);
                return (EINVAL);
        }

        if ((la->la_flags & LLE_VALID) &&
            ((la->la_flags & LLE_STATIC) || la->la_expire > time_uptime)) {
                if (flags & LLE_ADDRONLY) {
                        lladdr = la->ll_addr;
                        ll_len = ifp->if_addrlen;
                } else {
                        lladdr = la->r_linkdata;
                        ll_len = la->r_hdrlen;
                }
                bcopy(lladdr, desten, ll_len);

                /* Notify LLE code that the entry was used by datapath */
                llentry_provide_feedback(la);
                if (pflags != NULL)
                        *pflags = la->la_flags & (LLE_VALID|LLE_IFADDR);
                if (plle) {
                        LLE_ADDREF(la);
                        *plle = la;
                }
                LLE_WUNLOCK(la);
                return (0);
        }

        renew = (la->la_asked == 0 || la->la_expire != time_uptime);

        /*
         * There is an arptab entry, but no ethernet address
         * response yet.  Add the mbuf to the list, dropping
         * the oldest packet if we have exceeded the system
         * setting.
         */
        if (m != NULL) {
                size_t dropped = lltable_append_entry_queue(la, m, V_arp_maxhold);
                ARPSTAT_ADD(dropped, dropped);
        }

        /*
         * Return EWOULDBLOCK if we have tried less than arp_maxtries. It
         * will be masked by ether_output(). Return EHOSTDOWN/EHOSTUNREACH
         * if we have already sent arp_maxtries ARP requests. Retransmit the
         * ARP request, but not faster than one request per second.
         */
        if (la->la_asked < V_arp_maxtries)
                error = EWOULDBLOCK;    /* First request. */
        else
                error = is_gw != 0 ? EHOSTUNREACH : EHOSTDOWN;

        if (renew) {
                int canceled, e;

                LLE_ADDREF(la);
                la->la_expire = time_uptime;
                canceled = callout_reset(&la->lle_timer, hz * V_arpt_down,
                    arptimer, la);
                if (canceled)
                        LLE_REMREF(la);
                la->la_asked++;
                LLE_WUNLOCK(la);
                e = arprequest_internal(ifp, NULL, &SIN(dst)->sin_addr, NULL);
                /*
                 * Only overwrite 'error' in case of error; in case of success
                 * the proper return value was already set above.
                 */
                if (e != 0)
                        return (e);
                return (error);
        }

        LLE_WUNLOCK(la);
        return (error);
}

/*
 * Lookups link header based on an IP address.
 * On input:
 *    ifp is the interface we use
 *    is_gw != 0 if @dst represents gateway to some destination
 *    m is the mbuf. May be NULL if we don't have a packet.
 *    dst is the next hop,
 *    desten is the storage to put LL header.
 *    flags returns subset of lle flags: LLE_VALID | LLE_IFADDR
 *
 * On success, full/partial link header and flags are filled in and
 * the function returns 0.
 * If the packet must be held pending resolution, we return EWOULDBLOCK
 * On other errors, we return the corresponding error code.
 * Note that m_freem() handles NULL.
 */
int
arpresolve(struct ifnet *ifp, int is_gw, struct mbuf *m,
        const struct sockaddr *dst, u_char *desten, uint32_t *pflags,
        struct llentry **plle)
{
        struct llentry *la = NULL;

        NET_EPOCH_ASSERT();

        if (pflags != NULL)
                *pflags = 0;
        if (plle != NULL)
                *plle = NULL;

        if (m != NULL) {
                if (m->m_flags & M_BCAST) {
                        /* broadcast */
                        (void)memcpy(desten,
                            ifp->if_broadcastaddr, ifp->if_addrlen);
                        return (0);
                }
                if (m->m_flags & M_MCAST) {
                        /* multicast */
                        ETHER_MAP_IP_MULTICAST(&SIN(dst)->sin_addr, desten);
                        return (0);
                }
        }

        la = lla_lookup(LLTABLE(ifp), plle ? LLE_EXCLUSIVE : LLE_UNLOCKED, dst);
        if (la != NULL && (la->r_flags & RLLE_VALID) != 0) {
                /* Entry found, let's copy lle info */
                bcopy(la->r_linkdata, desten, la->r_hdrlen);
                if (pflags != NULL)
                        *pflags = LLE_VALID | (la->r_flags & RLLE_IFADDR);
                /* Notify the LLE handling code that the entry was used. */
                llentry_provide_feedback(la);
                if (plle) {
                        LLE_ADDREF(la);
                        *plle = la;
                        LLE_WUNLOCK(la);
                }
                return (0);
        }
        if (plle && la)
                LLE_WUNLOCK(la);

        return (arpresolve_full(ifp, is_gw, la == NULL ? LLE_CREATE : 0, m, dst,
            desten, pflags, plle));
}

/*
 * Common length and type checks are done here,
 * then the protocol-specific routine is called.
 */
static void
arpintr(struct mbuf *m)
{
        struct arphdr *ar;
        struct ifnet *ifp;
        char *layer;
        int hlen;

        ifp = m->m_pkthdr.rcvif;

        if (m->m_len < sizeof(struct arphdr) &&
            ((m = m_pullup(m, sizeof(struct arphdr))) == NULL)) {
                ARP_LOG(LOG_NOTICE, "packet with short header received on %s\n",
                    if_name(ifp));
                return;
        }
        ar = mtod(m, struct arphdr *);

        /* Check if length is sufficient */
        if (m->m_len <  arphdr_len(ar)) {
                m = m_pullup(m, arphdr_len(ar));
                if (m == NULL) {
                        ARP_LOG(LOG_NOTICE, "short packet received on %s\n",
                            if_name(ifp));
                        return;
                }
                ar = mtod(m, struct arphdr *);
        }

        hlen = 0;
        layer = "";
        switch (ntohs(ar->ar_hrd)) {
        case ARPHRD_ETHER:
                hlen = ETHER_ADDR_LEN; /* RFC 826 */
                layer = "ethernet";
                break;
        case ARPHRD_IEEE802:
                hlen = ETHER_ADDR_LEN;
                layer = "ieee802";
                break;
        case ARPHRD_INFINIBAND:
                hlen = 20;      /* RFC 4391, INFINIBAND_ALEN */
                layer = "infiniband";
                break;
        case ARPHRD_IEEE1394:
                hlen = 0; /* SHALL be 16 */ /* RFC 2734 */
                layer = "firewire";

                /*
                 * Restrict too long hardware addresses.
                 * Currently we are capable of handling 20-byte
                 * addresses ( sizeof(lle->ll_addr) )
                 */
                if (ar->ar_hln >= 20)
                        hlen = 16;
                break;
        default:
                ARP_LOG(LOG_NOTICE,
                    "packet with unknown hardware format 0x%02d received on "
                    "%s\n", ntohs(ar->ar_hrd), if_name(ifp));
                m_freem(m);
                return;
        }

        if (hlen != 0 && hlen != ar->ar_hln) {
                ARP_LOG(LOG_NOTICE,
                    "packet with invalid %s address length %d received on %s\n",
                    layer, ar->ar_hln, if_name(ifp));
                m_freem(m);
                return;
        }

        ARPSTAT_INC(received);
        switch (ntohs(ar->ar_pro)) {
#ifdef INET
        case ETHERTYPE_IP:
                in_arpinput(m);
                return;
#endif
        }
        m_freem(m);
}

#ifdef INET
/*
 * ARP for Internet protocols on 10 Mb/s Ethernet.
 * Algorithm is that given in RFC 826.
 * In addition, a sanity check is performed on the sender
 * protocol address, to catch impersonators.
 * We no longer handle negotiations for use of trailer protocol:
 * Formerly, ARP replied for protocol type ETHERTYPE_TRAIL sent
 * along with IP replies if we wanted trailers sent to us,
 * and also sent them in response to IP replies.
 * This allowed either end to announce the desire to receive
 * trailer packets.
 * We no longer reply to requests for ETHERTYPE_TRAIL protocol either,
 * but formerly didn't normally send requests.
 */
static int log_arp_wrong_iface = 1;
static int log_arp_movements = 1;
static int log_arp_permanent_modify = 1;
static int allow_multicast = 0;

SYSCTL_INT(_net_link_ether_inet, OID_AUTO, log_arp_wrong_iface, CTLFLAG_RW,
        &log_arp_wrong_iface, 0,
        "log arp packets arriving on the wrong interface");
SYSCTL_INT(_net_link_ether_inet, OID_AUTO, log_arp_movements, CTLFLAG_RW,
        &log_arp_movements, 0,
        "log arp replies from MACs different than the one in the cache");
SYSCTL_INT(_net_link_ether_inet, OID_AUTO, log_arp_permanent_modify, CTLFLAG_RW,
        &log_arp_permanent_modify, 0,
        "log arp replies from MACs different than the one in the permanent arp entry");
SYSCTL_INT(_net_link_ether_inet, OID_AUTO, allow_multicast, CTLFLAG_RW,
        &allow_multicast, 0, "accept multicast addresses");

static void
in_arpinput(struct mbuf *m)
{
        struct arphdr *ah;
        struct ifnet *ifp = m->m_pkthdr.rcvif;
        struct llentry *la = NULL, *la_tmp;
        struct ifaddr *ifa;
        struct in_ifaddr *ia;
        struct sockaddr sa;
        struct in_addr isaddr, itaddr, myaddr;
        u_int8_t *enaddr = NULL;
        int op;
        int bridged = 0, is_bridge = 0;
        int carped;
        struct sockaddr_in sin;
        struct sockaddr *dst;
        struct nhop_object *nh;
        uint8_t linkhdr[LLE_MAX_LINKHDR];
        struct route ro;
        size_t linkhdrsize;
        int lladdr_off;
        int error;
        char addrbuf[INET_ADDRSTRLEN];

        NET_EPOCH_ASSERT();

        sin.sin_len = sizeof(struct sockaddr_in);
        sin.sin_family = AF_INET;
        sin.sin_addr.s_addr = 0;

        if (ifp->if_bridge)
                bridged = 1;
        if (ifp->if_type == IFT_BRIDGE)
                is_bridge = 1;

        /*
         * We already have checked that mbuf contains enough contiguous data
         * to hold entire arp message according to the arp header.
         */
        ah = mtod(m, struct arphdr *);

        /*
         * ARP is only for IPv4 so we can reject packets with
         * a protocol length not equal to an IPv4 address.
         */
        if (ah->ar_pln != sizeof(struct in_addr)) {
                ARP_LOG(LOG_NOTICE, "requested protocol length != %zu\n",
                    sizeof(struct in_addr));
                goto drop;
        }

        if (allow_multicast == 0 && ETHER_IS_MULTICAST(ar_sha(ah))) {
                ARP_LOG(LOG_NOTICE, "%*D is multicast\n",
                    ifp->if_addrlen, (u_char *)ar_sha(ah), ":");
                goto drop;
        }

        op = ntohs(ah->ar_op);
        (void)memcpy(&isaddr, ar_spa(ah), sizeof (isaddr));
        (void)memcpy(&itaddr, ar_tpa(ah), sizeof (itaddr));

        if (op == ARPOP_REPLY)
                ARPSTAT_INC(rxreplies);

        /*
         * For a bridge, we want to check the address irrespective
         * of the receive interface. (This will change slightly
         * when we have clusters of interfaces).
         */
        CK_LIST_FOREACH(ia, INADDR_HASH(itaddr.s_addr), ia_hash) {
                if (((bridged && bridge_same_p(ia->ia_ifp->if_bridge, ifp->if_bridge)) ||
                    ia->ia_ifp == ifp) &&
                    itaddr.s_addr == ia->ia_addr.sin_addr.s_addr &&
                    (ia->ia_ifa.ifa_carp == NULL ||
                    (*carp_iamatch_p)(&ia->ia_ifa, &enaddr))) {
                        ifa_ref(&ia->ia_ifa);
                        goto match;
                }
        }
        CK_LIST_FOREACH(ia, INADDR_HASH(isaddr.s_addr), ia_hash)
                if (((bridged && bridge_same_p(ia->ia_ifp->if_bridge, ifp->if_bridge)) ||
                    ia->ia_ifp == ifp) &&
                    isaddr.s_addr == ia->ia_addr.sin_addr.s_addr) {
                        ifa_ref(&ia->ia_ifa);
                        goto match;
                }

#define BDG_MEMBER_MATCHES_ARP(addr, ifp, ia)                           \
  (bridge_get_softc_p(ia->ia_ifp) == ifp->if_softc &&                   \
  !bcmp(IF_LLADDR(ia->ia_ifp), IF_LLADDR(ifp), ifp->if_addrlen) &&      \
  addr == ia->ia_addr.sin_addr.s_addr)
        /*
         * Check the case when bridge shares its MAC address with
         * some of its children, so packets are claimed by bridge
         * itself (bridge_input() does it first), but they are really
         * meant to be destined to the bridge member.
         */
        if (is_bridge) {
                CK_LIST_FOREACH(ia, INADDR_HASH(itaddr.s_addr), ia_hash) {
                        if (BDG_MEMBER_MATCHES_ARP(itaddr.s_addr, ifp, ia)) {
                                ifa_ref(&ia->ia_ifa);
                                ifp = ia->ia_ifp;
                                goto match;
                        }
                }
        }
#undef BDG_MEMBER_MATCHES_ARP

        /*
         * No match, use the first inet address on the receive interface
         * as a dummy address for the rest of the function.
         */
        CK_STAILQ_FOREACH(ifa, &ifp->if_addrhead, ifa_link)
                if (ifa->ifa_addr->sa_family == AF_INET &&
                    (ifa->ifa_carp == NULL ||
                    (*carp_iamatch_p)(ifa, &enaddr))) {
                        ia = ifatoia(ifa);
                        ifa_ref(ifa);
                        goto match;
                }

        /*
         * If bridging, fall back to using any inet address.
         */
        if (!bridged || (ia = CK_STAILQ_FIRST(&V_in_ifaddrhead)) == NULL)
                goto drop;
        ifa_ref(&ia->ia_ifa);
match:
        if (!enaddr)
                enaddr = (u_int8_t *)IF_LLADDR(ifp);
        carped = (ia->ia_ifa.ifa_carp != NULL);
        myaddr = ia->ia_addr.sin_addr;
        ifa_free(&ia->ia_ifa);
        if (!bcmp(ar_sha(ah), enaddr, ifp->if_addrlen))
                goto drop;      /* it's from me, ignore it. */
        if (!bcmp(ar_sha(ah), ifp->if_broadcastaddr, ifp->if_addrlen)) {
                ARP_LOG(LOG_NOTICE, "link address is broadcast for IP address "
                    "%s!\n", inet_ntoa_r(isaddr, addrbuf));
                goto drop;
        }

        if (ifp->if_addrlen != ah->ar_hln) {
                ARP_LOG(LOG_WARNING, "from %*D: addr len: new %d, "
                    "i/f %d (ignored)\n", ifp->if_addrlen,
                    (u_char *) ar_sha(ah), ":", ah->ar_hln,
                    ifp->if_addrlen);
                goto drop;
        }

        /*
         * Warn if another host is using the same IP address, but only if the
         * IP address isn't 0.0.0.0, which is used for DHCP only, in which
         * case we suppress the warning to avoid false positive complaints of
         * potential misconfiguration.
         */
        if (!bridged && !carped && isaddr.s_addr == myaddr.s_addr &&
            myaddr.s_addr != 0) {
                ARP_LOG(LOG_ERR, "%*D is using my IP address %s on %s!\n",
                   ifp->if_addrlen, (u_char *)ar_sha(ah), ":",
                   inet_ntoa_r(isaddr, addrbuf), ifp->if_xname);
                itaddr = myaddr;
                ARPSTAT_INC(dupips);
                goto reply;
        }
        if (ifp->if_flags & IFF_STATICARP)
                goto reply;

        bzero(&sin, sizeof(sin));
        sin.sin_len = sizeof(struct sockaddr_in);
        sin.sin_family = AF_INET;
        sin.sin_addr = isaddr;
        dst = (struct sockaddr *)&sin;
        la = lla_lookup(LLTABLE(ifp), LLE_EXCLUSIVE, dst);
        if (la != NULL)
                arp_check_update_lle(ah, isaddr, ifp, bridged, la);
        else if (itaddr.s_addr == myaddr.s_addr) {
                /*
                 * Request/reply to our address, but no lle exists yet.
                 * Calculate full link prepend to use in lle.
                 */
                linkhdrsize = sizeof(linkhdr);
                if (lltable_calc_llheader(ifp, AF_INET, ar_sha(ah), linkhdr,
                    &linkhdrsize, &lladdr_off) != 0)
                        goto reply;

                /* Allocate new entry */
                la = lltable_alloc_entry(LLTABLE(ifp), 0, dst);
                if (la == NULL) {
                        /*
                         * lle creation may fail if source address belongs
                         * to non-directly connected subnet. However, we
                         * will try to answer the request instead of dropping
                         * frame.
                         */
                        goto reply;
                }
                lltable_set_entry_addr(ifp, la, linkhdr, linkhdrsize,
                    lladdr_off);

                LLTABLE_LOCK(LLTABLE(ifp));
                LLE_WLOCK(la);
                la_tmp = lla_lookup(LLTABLE(ifp), LLE_EXCLUSIVE, dst);

                /*
                 * Check if lle still does not exists.
                 * If it does, that means that we either
                 * 1) have configured it explicitly, via
                 * 1a) 'arp -s' static entry or
                 * 1b) interface address static record
                 * or
                 * 2) it was the result of sending first packet to-host
                 * or
                 * 3) it was another arp reply packet we handled in
                 * different thread.
                 *
                 * In all cases except 3) we definitely need to prefer
                 * existing lle. For the sake of simplicity, prefer any
                 * existing lle over newly-create one.
                 */
                if (la_tmp == NULL)
                        lltable_link_entry(LLTABLE(ifp), la);
                LLTABLE_UNLOCK(LLTABLE(ifp));

                if (la_tmp == NULL) {
                        arp_mark_lle_reachable(la, ifp);
                        LLE_WUNLOCK(la);
                } else {
                        /* Free newly-create entry and handle packet */
                        lltable_free_entry(LLTABLE(ifp), la);
                        la = la_tmp;
                        la_tmp = NULL;
                        arp_check_update_lle(ah, isaddr, ifp, bridged, la);
                        /* arp_check_update_lle() returns @la unlocked */
                }
                la = NULL;
        }
reply:
        if (op != ARPOP_REQUEST)
                goto drop;
        ARPSTAT_INC(rxrequests);

        if (itaddr.s_addr == myaddr.s_addr) {
                /* Shortcut.. the receiving interface is the target. */
                (void)memcpy(ar_tha(ah), ar_sha(ah), ah->ar_hln);
                (void)memcpy(ar_sha(ah), enaddr, ah->ar_hln);
        } else {
                /*
                 * Destination address is not ours. Check if
                 * proxyarp entry exists or proxyarp is turned on globally.
                 */
                struct llentry *lle;

                sin.sin_addr = itaddr;
                lle = lla_lookup(LLTABLE(ifp), 0, (struct sockaddr *)&sin);

                if ((lle != NULL) && (lle->la_flags & LLE_PUB)) {
                        (void)memcpy(ar_tha(ah), ar_sha(ah), ah->ar_hln);
                        (void)memcpy(ar_sha(ah), lle->ll_addr, ah->ar_hln);
                        LLE_RUNLOCK(lle);
                } else {
                        if (lle != NULL)
                                LLE_RUNLOCK(lle);

                        if (!V_arp_proxyall)
                                goto drop;

                        NET_EPOCH_ASSERT();
                        nh = fib4_lookup(ifp->if_fib, itaddr, 0, 0, 0);
                        if (nh == NULL)
                                goto drop;

                        /*
                         * Don't send proxies for nodes on the same interface
                         * as this one came out of, or we'll get into a fight
                         * over who claims what Ether address.
                         */
                        if (nh->nh_ifp == ifp)
                                goto drop;

                        (void)memcpy(ar_tha(ah), ar_sha(ah), ah->ar_hln);
                        (void)memcpy(ar_sha(ah), enaddr, ah->ar_hln);

                        /*
                         * Also check that the node which sent the ARP packet
                         * is on the interface we expect it to be on. This
                         * avoids ARP chaos if an interface is connected to the
                         * wrong network.
                         */

                        nh = fib4_lookup(ifp->if_fib, isaddr, 0, 0, 0);
                        if (nh == NULL)
                                goto drop;
                        if (nh->nh_ifp != ifp) {
                                ARP_LOG(LOG_INFO, "proxy: ignoring request"
                                    " from %s via %s\n",
                                    inet_ntoa_r(isaddr, addrbuf),
                                    ifp->if_xname);
                                goto drop;
                        }

#ifdef DEBUG_PROXY
                        printf("arp: proxying for %s\n",
                            inet_ntoa_r(itaddr, addrbuf));
#endif
                }
        }

        if (itaddr.s_addr == myaddr.s_addr &&
            IN_LINKLOCAL(ntohl(itaddr.s_addr))) {
                /* RFC 3927 link-local IPv4; always reply by broadcast. */
#ifdef DEBUG_LINKLOCAL
                printf("arp: sending reply for link-local addr %s\n",
                    inet_ntoa_r(itaddr, addrbuf));
#endif
                m->m_flags |= M_BCAST;
                m->m_flags &= ~M_MCAST;
        } else {
                /* default behaviour; never reply by broadcast. */
                m->m_flags &= ~(M_BCAST|M_MCAST);
        }
        (void)memcpy(ar_tpa(ah), ar_spa(ah), ah->ar_pln);
        (void)memcpy(ar_spa(ah), &itaddr, ah->ar_pln);
        ah->ar_op = htons(ARPOP_REPLY);
        ah->ar_pro = htons(ETHERTYPE_IP); /* let's be sure! */
        m->m_len = sizeof(*ah) + (2 * ah->ar_pln) + (2 * ah->ar_hln);
        m->m_pkthdr.len = m->m_len;
        m->m_pkthdr.rcvif = NULL;
        sa.sa_family = AF_ARP;
        sa.sa_len = 2;

        /* Calculate link header for sending frame */
        bzero(&ro, sizeof(ro));
        linkhdrsize = sizeof(linkhdr);
        error = arp_fillheader(ifp, ah, 0, linkhdr, &linkhdrsize);

        /*
         * arp_fillheader() may fail due to lack of support inside encap request
         * routing. This is not necessary an error, AF_ARP can/should be handled
         * by if_output().
         */
        if (error != 0 && error != EAFNOSUPPORT) {
                ARP_LOG(LOG_ERR, "Failed to calculate ARP header on %s: %d\n",
                    if_name(ifp), error);
                goto drop;
        }

        ro.ro_prepend = linkhdr;
        ro.ro_plen = linkhdrsize;
        ro.ro_flags = 0;

        m_clrprotoflags(m);     /* Avoid confusing lower layers. */
        (*ifp->if_output)(ifp, m, &sa, &ro);
        ARPSTAT_INC(txreplies);
        return;

drop:
        m_freem(m);
}
#endif

static struct mbuf *
arp_grab_holdchain(struct llentry *la)
{
        struct mbuf *chain;

        LLE_WLOCK_ASSERT(la);

        chain = la->la_hold;
        la->la_hold = NULL;
        la->la_numheld = 0;

        return (chain);
}

static void
arp_flush_holdchain(struct ifnet *ifp, struct llentry *la, struct mbuf *chain)
{
        struct mbuf *m_hold, *m_hold_next;
        struct sockaddr_in sin;

        NET_EPOCH_ASSERT();

        struct route ro = {
                .ro_prepend = la->r_linkdata,
                .ro_plen = la->r_hdrlen,
        };

        lltable_fill_sa_entry(la, (struct sockaddr *)&sin);

        for (m_hold = chain; m_hold != NULL; m_hold = m_hold_next) {
                m_hold_next = m_hold->m_nextpkt;
                m_hold->m_nextpkt = NULL;
                /* Avoid confusing lower layers. */
                m_clrprotoflags(m_hold);
                (*ifp->if_output)(ifp, m_hold, (struct sockaddr *)&sin, &ro);
        }
}

/*
 * Checks received arp data against existing @la.
 * Updates lle state/performs notification if necessary.
 */
static void
arp_check_update_lle(struct arphdr *ah, struct in_addr isaddr, struct ifnet *ifp,
    int bridged, struct llentry *la)
{
        uint8_t linkhdr[LLE_MAX_LINKHDR];
        size_t linkhdrsize;
        int lladdr_off;
        char addrbuf[INET_ADDRSTRLEN];

        LLE_WLOCK_ASSERT(la);

        /* the following is not an error when doing bridging */
        if (!bridged && la->lle_tbl->llt_ifp != ifp) {
                if (log_arp_wrong_iface)
                        ARP_LOG(LOG_WARNING, "%s is on %s "
                            "but got reply from %*D on %s\n",
                            inet_ntoa_r(isaddr, addrbuf),
                            la->lle_tbl->llt_ifp->if_xname,
                            ifp->if_addrlen, (u_char *)ar_sha(ah), ":",
                            ifp->if_xname);
                LLE_WUNLOCK(la);
                return;
        }
        if ((la->la_flags & LLE_VALID) &&
            bcmp(ar_sha(ah), la->ll_addr, ifp->if_addrlen)) {
                if (la->la_flags & LLE_STATIC) {
                        LLE_WUNLOCK(la);
                        if (log_arp_permanent_modify)
                                ARP_LOG(LOG_ERR,
                                    "%*D attempts to modify "
                                    "permanent entry for %s on %s\n",
                                    ifp->if_addrlen,
                                    (u_char *)ar_sha(ah), ":",
                                    inet_ntoa_r(isaddr, addrbuf),
                                    ifp->if_xname);
                        return;
                }
                if (log_arp_movements) {
                        ARP_LOG(LOG_INFO, "%s moved from %*D "
                            "to %*D on %s\n",
                            inet_ntoa_r(isaddr, addrbuf),
                            ifp->if_addrlen,
                            (u_char *)la->ll_addr, ":",
                            ifp->if_addrlen, (u_char *)ar_sha(ah), ":",
                            ifp->if_xname);
                }
        }

        /* Calculate full link prepend to use in lle */
        linkhdrsize = sizeof(linkhdr);
        if (lltable_calc_llheader(ifp, AF_INET, ar_sha(ah), linkhdr,
            &linkhdrsize, &lladdr_off) != 0) {
                LLE_WUNLOCK(la);
                return;
        }

        /* Check if something has changed */
        if (memcmp(la->r_linkdata, linkhdr, linkhdrsize) != 0 ||
            (la->la_flags & LLE_VALID) == 0) {
                /* Try to perform LLE update */
                if (lltable_try_set_entry_addr(ifp, la, linkhdr, linkhdrsize,
                    lladdr_off) == 0) {
                        LLE_WUNLOCK(la);
                        return;
                }

                /* Clear fast path feedback request if set */
                llentry_mark_used(la);
        }

        arp_mark_lle_reachable(la, ifp);

        /*
         * The packets are all freed within the call to the output
         * routine.
         *
         * NB: The lock MUST be released before the call to the
         * output routine.
         */
        if (la->la_hold != NULL) {
                struct mbuf *chain;

                chain = arp_grab_holdchain(la);
                LLE_WUNLOCK(la);
                arp_flush_holdchain(ifp, la, chain);
        } else
                LLE_WUNLOCK(la);
}

static void
arp_mark_lle_reachable(struct llentry *la, struct ifnet *ifp)
{
        int canceled, wtime;

        LLE_WLOCK_ASSERT(la);

        la->ln_state = ARP_LLINFO_REACHABLE;
        EVENTHANDLER_INVOKE(lle_event, la, LLENTRY_RESOLVED);

        if ((ifp->if_flags & IFF_STICKYARP) != 0)
                la->la_flags |= LLE_STATIC;

        if (!(la->la_flags & LLE_STATIC)) {
                LLE_ADDREF(la);
                la->la_expire = time_uptime + V_arpt_keep;
                wtime = V_arpt_keep - V_arp_maxtries * V_arpt_rexmit;
                if (wtime < 0)
                        wtime = V_arpt_keep;
                canceled = callout_reset(&la->lle_timer,
                    hz * wtime, arptimer, la);
                if (canceled)
                        LLE_REMREF(la);
        }
        la->la_asked = 0;
        la->la_preempt = V_arp_maxtries;
}

/*
 * Add permanent link-layer record for given interface address.
 */
static __noinline void
arp_add_ifa_lle(struct ifnet *ifp, const struct sockaddr *dst)
{
        struct llentry *lle, *lle_tmp;

        /*
         * Interface address LLE record is considered static
         * because kernel code relies on LLE_STATIC flag to check
         * if these entries can be rewriten by arp updates.
         */
        lle = lltable_alloc_entry(LLTABLE(ifp), LLE_IFADDR | LLE_STATIC, dst);
        if (lle == NULL) {
                log(LOG_INFO, "arp_ifinit: cannot create arp "
                    "entry for interface address\n");
                return;
        }

        LLTABLE_LOCK(LLTABLE(ifp));
        LLE_WLOCK(lle);
        /* Unlink any entry if exists */
        lle_tmp = lla_lookup(LLTABLE(ifp), LLE_EXCLUSIVE, dst);
        if (lle_tmp != NULL)
                lltable_unlink_entry(LLTABLE(ifp), lle_tmp);

        lltable_link_entry(LLTABLE(ifp), lle);
        LLTABLE_UNLOCK(LLTABLE(ifp));

        if (lle_tmp != NULL)
                EVENTHANDLER_INVOKE(lle_event, lle_tmp, LLENTRY_EXPIRED);

        EVENTHANDLER_INVOKE(lle_event, lle, LLENTRY_RESOLVED);
        LLE_WUNLOCK(lle);
        if (lle_tmp != NULL)
                lltable_free_entry(LLTABLE(ifp), lle_tmp);
}

/*
 * Handle the garp_rexmit_count. Like sysctl_handle_int(), but limits the range
 * of valid values.
 */
static int
sysctl_garp_rexmit(SYSCTL_HANDLER_ARGS)
{
        int error;
        int rexmit_count = *(int *)arg1;

        error = sysctl_handle_int(oidp, &rexmit_count, 0, req);

        /* Enforce limits on any new value that may have been set. */
        if (!error && req->newptr) {
                /* A new value was set. */
                if (rexmit_count < 0) {
                        rexmit_count = 0;
                } else if (rexmit_count > MAX_GARP_RETRANSMITS) {
                        rexmit_count = MAX_GARP_RETRANSMITS;
                }
                *(int *)arg1 = rexmit_count;
        }

        return (error);
}

/*
 * Retransmit a Gratuitous ARP (GARP) and, if necessary, schedule a callout to
 * retransmit it again. A pending callout owns a reference to the ifa.
 */
static void
garp_rexmit(void *arg)
{
        struct epoch_tracker et;
        struct in_ifaddr *ia = arg;

        if (callout_pending(&ia->ia_garp_timer) ||
            !callout_active(&ia->ia_garp_timer)) {
                IF_ADDR_WUNLOCK(ia->ia_ifa.ifa_ifp);
                ifa_free(&ia->ia_ifa);
                return;
        }

        NET_EPOCH_ENTER(et);
        CURVNET_SET(ia->ia_ifa.ifa_ifp->if_vnet);

        /*
         * Drop lock while the ARP request is generated.
         */
        IF_ADDR_WUNLOCK(ia->ia_ifa.ifa_ifp);

        arprequest(ia->ia_ifa.ifa_ifp, &IA_SIN(ia)->sin_addr,
            &IA_SIN(ia)->sin_addr, IF_LLADDR(ia->ia_ifa.ifa_ifp));

        /*
         * Increment the count of retransmissions. If the count has reached the
         * maximum value, stop sending the GARP packets. Otherwise, schedule
         * the callout to retransmit another GARP packet.
         */
        ++ia->ia_garp_count;
        if (ia->ia_garp_count >= V_garp_rexmit_count) {
                ifa_free(&ia->ia_ifa);
        } else {
                int rescheduled;
                IF_ADDR_WLOCK(ia->ia_ifa.ifa_ifp);
                rescheduled = callout_reset(&ia->ia_garp_timer,
                    (1 << ia->ia_garp_count) * hz,
                    garp_rexmit, ia);
                IF_ADDR_WUNLOCK(ia->ia_ifa.ifa_ifp);
                if (rescheduled) {
                        ifa_free(&ia->ia_ifa);
                }
        }

        CURVNET_RESTORE();
        NET_EPOCH_EXIT(et);
}

/*
 * Start the GARP retransmit timer.
 *
 * A single GARP is always transmitted when an IPv4 address is added
 * to an interface and that is usually sufficient. However, in some
 * circumstances, such as when a shared address is passed between
 * cluster nodes, this single GARP may occasionally be dropped or
 * lost. This can lead to neighbors on the network link working with a
 * stale ARP cache and sending packets destined for that address to
 * the node that previously owned the address, which may not respond.
 *
 * To avoid this situation, GARP retransmits can be enabled by setting
 * the net.link.ether.inet.garp_rexmit_count sysctl to a value greater
 * than zero. The setting represents the maximum number of
 * retransmissions. The interval between retransmissions is calculated
 * using an exponential backoff algorithm, doubling each time, so the
 * retransmission intervals are: {1, 2, 4, 8, 16, ...} (seconds).
 */
static void
garp_timer_start(struct ifaddr *ifa)
{
        struct in_ifaddr *ia = (struct in_ifaddr *) ifa;

        IF_ADDR_WLOCK(ia->ia_ifa.ifa_ifp);
        ia->ia_garp_count = 0;
        if (callout_reset(&ia->ia_garp_timer, (1 << ia->ia_garp_count) * hz,
            garp_rexmit, ia) == 0) {
                ifa_ref(ifa);
        }
        IF_ADDR_WUNLOCK(ia->ia_ifa.ifa_ifp);
}

void
arp_ifinit(struct ifnet *ifp, struct ifaddr *ifa)
{
        struct epoch_tracker et;
        const struct sockaddr_in *dst_in;
        const struct sockaddr *dst;

        if (ifa->ifa_carp != NULL)
                return;

        dst = ifa->ifa_addr;
        dst_in = (const struct sockaddr_in *)dst;

        if (ntohl(dst_in->sin_addr.s_addr) == INADDR_ANY)
                return;
        NET_EPOCH_ENTER(et);
        arp_announce_ifaddr(ifp, dst_in->sin_addr, IF_LLADDR(ifp));
        NET_EPOCH_EXIT(et);
        if (V_garp_rexmit_count > 0) {
                garp_timer_start(ifa);
        }

        arp_add_ifa_lle(ifp, dst);
}

void
arp_announce_ifaddr(struct ifnet *ifp, struct in_addr addr, u_char *enaddr)
{

        if (ntohl(addr.s_addr) != INADDR_ANY)
                arprequest(ifp, &addr, &addr, enaddr);
}

/*
 * Sends gratuitous ARPs for each ifaddr to notify other
 * nodes about the address change.
 */
static __noinline void
arp_handle_ifllchange(struct ifnet *ifp)
{
        struct ifaddr *ifa;

        CK_STAILQ_FOREACH(ifa, &ifp->if_addrhead, ifa_link) {
                if (ifa->ifa_addr->sa_family == AF_INET)
                        arp_ifinit(ifp, ifa);
        }
}

/*
 * A handler for interface link layer address change event.
 */
static void
arp_iflladdr(void *arg __unused, struct ifnet *ifp)
{
        /* if_bridge can update its lladdr during if_vmove(), after we've done
         * with in_ifdetach(). XXXGL: needs to be fixed. */
        if (ifp->if_inet == NULL)
                return;

        lltable_update_ifaddr(LLTABLE(ifp));

        if ((ifp->if_flags & IFF_UP) != 0)
                arp_handle_ifllchange(ifp);
}

static void
vnet_arp_init(void)
{

        if (IS_DEFAULT_VNET(curvnet)) {
                netisr_register(&arp_nh);
                iflladdr_tag = EVENTHANDLER_REGISTER(iflladdr_event,
                    arp_iflladdr, NULL, EVENTHANDLER_PRI_ANY);
        }
#ifdef VIMAGE
        else
                netisr_register_vnet(&arp_nh);
#endif
}
VNET_SYSINIT(vnet_arp_init, SI_SUB_PROTO_DOMAIN, SI_ORDER_SECOND,
    vnet_arp_init, NULL);

#ifdef VIMAGE
/*
 * We have to unregister ARP along with IP otherwise we risk doing INADDR_HASH
 * lookups after destroying the hash.  Ideally this would go on SI_ORDER_3.5.
 */
static void
vnet_arp_destroy(__unused void *arg)
{

        netisr_unregister_vnet(&arp_nh);
}
VNET_SYSUNINIT(vnet_arp_uninit, SI_SUB_PROTO_DOMAIN, SI_ORDER_THIRD,
    vnet_arp_destroy, NULL);
#endif