/*-
 * SPDX-License-Identifier: BSD-2-Clause
 *
 * Copyright (c) 2004 Andre Oppermann, Internet Business Solutions AG
 * 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.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR 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 AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <sys/cdefs.h>
#include "opt_ipfw.h"
#include "opt_inet.h"
#include "opt_inet6.h"
#ifndef INET
#error IPFIREWALL requires INET.
#endif /* INET */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/malloc.h>
#include <sys/mbuf.h>
#include <sys/module.h>
#include <sys/kernel.h>
#include <sys/lock.h>
#include <sys/rwlock.h>
#include <sys/socket.h>
#include <sys/sysctl.h>

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

#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netinet/ip_var.h>
#include <netinet/ip_fw.h>
#ifdef INET6
#include <netinet/ip6.h>
#include <netinet6/ip6_var.h>
#include <netinet6/scope6_var.h>
#endif

#include <netgraph/ng_ipfw.h>

#include <netpfil/ipfw/ip_fw_private.h>

#include <machine/in_cksum.h>

VNET_DEFINE_STATIC(int, fw_enable) = 1;
#define V_fw_enable     VNET(fw_enable)

#ifdef INET6
VNET_DEFINE_STATIC(int, fw6_enable) = 1;
#define V_fw6_enable    VNET(fw6_enable)
#endif

VNET_DEFINE_STATIC(int, fwlink_enable) = 0;
#define V_fwlink_enable VNET(fwlink_enable)

int ipfw_chg_hook(SYSCTL_HANDLER_ARGS);

/* Forward declarations. */
static int ipfw_divert(struct mbuf **, struct ip_fw_args *, bool);

#ifdef SYSCTL_NODE

SYSBEGIN(f1)

SYSCTL_DECL(_net_inet_ip_fw);
SYSCTL_PROC(_net_inet_ip_fw, OID_AUTO, enable,
    CTLFLAG_VNET | CTLTYPE_INT | CTLFLAG_RWTUN | CTLFLAG_NOFETCH | CTLFLAG_SECURE3 |
    CTLFLAG_NEEDGIANT, &VNET_NAME(fw_enable), 0, ipfw_chg_hook, "I",
    "Enable ipfw");
#ifdef INET6
SYSCTL_DECL(_net_inet6_ip6_fw);
SYSCTL_PROC(_net_inet6_ip6_fw, OID_AUTO, enable,
    CTLFLAG_VNET | CTLTYPE_INT | CTLFLAG_RWTUN | CTLFLAG_NOFETCH | CTLFLAG_SECURE3 |
    CTLFLAG_NEEDGIANT, &VNET_NAME(fw6_enable), 0, ipfw_chg_hook, "I",
    "Enable ipfw+6");
#endif /* INET6 */

SYSCTL_DECL(_net_link_ether);
SYSCTL_PROC(_net_link_ether, OID_AUTO, ipfw,
    CTLFLAG_VNET | CTLTYPE_INT | CTLFLAG_RWTUN | CTLFLAG_NOFETCH | CTLFLAG_SECURE3 |
    CTLFLAG_NEEDGIANT, &VNET_NAME(fwlink_enable), 0, ipfw_chg_hook, "I",
    "Pass ether pkts through firewall");

SYSEND

#endif /* SYSCTL_NODE */

/*
 * The pfilter hook to pass packets to ipfw_chk and then to
 * dummynet, divert, netgraph or other modules.
 * The packet may be consumed.
 */
static pfil_return_t
ipfw_check_packet(struct mbuf **m0, struct ifnet *ifp, int flags,
    void *ruleset __unused, struct inpcb *inp)
{
        struct ip_fw_args args;
        struct m_tag *tag;
        pfil_return_t ret;
        int ipfw;

        args.flags = (flags & PFIL_IN) ? IPFW_ARGS_IN : IPFW_ARGS_OUT;
        args.rule.pkt_mark = 0;
again:
        /*
         * extract and remove the tag if present. If we are left
         * with onepass, optimize the outgoing path.
         */
        tag = m_tag_locate(*m0, MTAG_IPFW_RULE, 0, NULL);
        if (tag != NULL) {
                args.rule = *((struct ipfw_rule_ref *)(tag+1));
                m_tag_delete(*m0, tag);
                if (args.rule.info & IPFW_ONEPASS)
                        return (PFIL_PASS);
                args.flags |= IPFW_ARGS_REF;
        }

        args.m = *m0;
        args.ifp = ifp;
        args.inp = inp;

        ipfw = ipfw_chk(&args);
        *m0 = args.m;

        KASSERT(*m0 != NULL || ipfw == IP_FW_DENY ||
            ipfw == IP_FW_NAT64, ("%s: m0 is NULL", __func__));

        ret = PFIL_PASS;
        switch (ipfw) {
        case IP_FW_PASS:
                /* next_hop may be set by ipfw_chk */
                if ((args.flags & (IPFW_ARGS_NH4 | IPFW_ARGS_NH4PTR |
                    IPFW_ARGS_NH6 | IPFW_ARGS_NH6PTR)) == 0)
                        break;
#if (!defined(INET6) && !defined(INET))
                ret = PFIL_DROPPED;
#else
            {
                void *psa;
                size_t len;
#ifdef INET
                if (args.flags & (IPFW_ARGS_NH4 | IPFW_ARGS_NH4PTR)) {
                        MPASS((args.flags & (IPFW_ARGS_NH4 |
                            IPFW_ARGS_NH4PTR)) != (IPFW_ARGS_NH4 |
                            IPFW_ARGS_NH4PTR));
                        MPASS((args.flags & (IPFW_ARGS_NH6 |
                            IPFW_ARGS_NH6PTR)) == 0);
                        len = sizeof(struct sockaddr_in);
                        psa = (args.flags & IPFW_ARGS_NH4) ?
                            &args.hopstore : args.next_hop;
                        if (in_localip(satosin(psa)->sin_addr))
                                (*m0)->m_flags |= M_FASTFWD_OURS;
                        (*m0)->m_flags |= M_IP_NEXTHOP;
                }
#endif /* INET */
#ifdef INET6
                if (args.flags & (IPFW_ARGS_NH6 | IPFW_ARGS_NH6PTR)) {
                        MPASS((args.flags & (IPFW_ARGS_NH6 |
                            IPFW_ARGS_NH6PTR)) != (IPFW_ARGS_NH6 |
                            IPFW_ARGS_NH6PTR));
                        MPASS((args.flags & (IPFW_ARGS_NH4 |
                            IPFW_ARGS_NH4PTR)) == 0);
                        len = sizeof(struct sockaddr_in6);
                        psa = args.next_hop6;
                        (*m0)->m_flags |= M_IP6_NEXTHOP;
                }
#endif /* INET6 */
                /*
                 * Incoming packets should not be tagged so we do not
                 * m_tag_find. Outgoing packets may be tagged, so we
                 * reuse the tag if present.
                 */
                tag = (flags & PFIL_IN) ? NULL :
                        m_tag_find(*m0, PACKET_TAG_IPFORWARD, NULL);
                if (tag != NULL) {
                        m_tag_unlink(*m0, tag);
                } else {
                        tag = m_tag_get(PACKET_TAG_IPFORWARD, len,
                            M_NOWAIT);
                        if (tag == NULL) {
                                ret = PFIL_DROPPED;
                                break;
                        }
                }
                if ((args.flags & IPFW_ARGS_NH6) == 0)
                        bcopy(psa, tag + 1, len);
                m_tag_prepend(*m0, tag);
                ret = PFIL_PASS;
#ifdef INET6
                /* IPv6 next hop needs additional handling */
                if (args.flags & (IPFW_ARGS_NH6 | IPFW_ARGS_NH6PTR)) {
                        struct sockaddr_in6 *sa6;

                        sa6 = satosin6(tag + 1);
                        if (args.flags & IPFW_ARGS_NH6) {
                                sa6->sin6_family = AF_INET6;
                                sa6->sin6_len = sizeof(*sa6);
                                sa6->sin6_addr = args.hopstore6.sin6_addr;
                                sa6->sin6_port = args.hopstore6.sin6_port;
                                sa6->sin6_scope_id =
                                    args.hopstore6.sin6_scope_id;
                        }
                        /*
                         * If nh6 address is link-local we should convert
                         * it to kernel internal form before doing any
                         * comparisons.
                         */
                        if (sa6_embedscope(sa6, V_ip6_use_defzone) != 0) {
                                ret = PFIL_DROPPED;
                                break;
                        }
                        if (in6_localip(&sa6->sin6_addr))
                                (*m0)->m_flags |= M_FASTFWD_OURS;
                }
#endif /* INET6 */
            }
#endif /* INET || INET6 */
                break;

        case IP_FW_DENY:
                ret = PFIL_DROPPED;
                break;

        case IP_FW_DUMMYNET:
                if (ip_dn_io_ptr == NULL) {
                        ret = PFIL_DROPPED;
                        break;
                }
                MPASS(args.flags & IPFW_ARGS_REF);
                if (args.flags & (IPFW_ARGS_IP4 | IPFW_ARGS_IP6))
                        (void )ip_dn_io_ptr(m0, &args);
                else {
                        ret = PFIL_DROPPED;
                        break;
                }
                /*
                 * XXX should read the return value.
                 * dummynet normally eats the packet and sets *m0=NULL
                 * unless the packet can be sent immediately. In this
                 * case args is updated and we should re-run the
                 * check without clearing args.
                 */
                if (*m0 != NULL)
                        goto again;
                ret = PFIL_CONSUMED;
                break;

        case IP_FW_TEE:
        case IP_FW_DIVERT:
                if (ip_divert_ptr == NULL) {
                        ret = PFIL_DROPPED;
                        break;
                }
                MPASS(args.flags & IPFW_ARGS_REF);
                (void )ipfw_divert(m0, &args, ipfw == IP_FW_TEE);
                /* continue processing for the original packet (tee). */
                if (*m0)
                        goto again;
                ret = PFIL_CONSUMED;
                break;

        case IP_FW_NGTEE:
        case IP_FW_NETGRAPH:
                if (ng_ipfw_input_p == NULL) {
                        ret = PFIL_DROPPED;
                        break;
                }
                MPASS(args.flags & IPFW_ARGS_REF);
                (void )ng_ipfw_input_p(m0, &args, ipfw == IP_FW_NGTEE);
                if (ipfw == IP_FW_NGTEE) /* ignore errors for NGTEE */
                        goto again;     /* continue with packet */
                ret = PFIL_CONSUMED;
                break;

        case IP_FW_NAT:
                /* honor one-pass in case of successful nat */
                if (V_fw_one_pass)
                        break;
                goto again;

        case IP_FW_REASS:
                goto again;             /* continue with packet */

        case IP_FW_NAT64:
                ret = PFIL_CONSUMED;
                break;

        default:
                KASSERT(0, ("%s: unknown retval", __func__));
        }

        if (ret != PFIL_PASS) {
                if (*m0)
                        FREE_PKT(*m0);
                *m0 = NULL;
        }

        return (ret);
}

/*
 * ipfw processing for ethernet packets (in and out), mbuf version.
 */
static pfil_return_t
ipfw_check_frame_mbuf(struct mbuf **m0, struct ifnet *ifp, const int flags,
    void *ruleset __unused, struct inpcb *inp)
{
        struct ip_fw_args args = {
                .flags = IPFW_ARGS_ETHER |
                    ((flags & PFIL_IN) ? IPFW_ARGS_IN : IPFW_ARGS_OUT),
                .ifp = ifp,
                .inp = inp,
        };
        struct m_tag *mtag;
        pfil_return_t ret;
        int ipfw;

again:
        /*
         * Fetch start point from rule, if any.
         * Remove the tag if present.
         */
        mtag = m_tag_locate(*m0, MTAG_IPFW_RULE, 0, NULL);
        if (mtag != NULL) {
                args.rule = *((struct ipfw_rule_ref *)(mtag+1));
                m_tag_delete(*m0, mtag);
                if (args.rule.info & IPFW_ONEPASS)
                        return (PFIL_PASS);
                args.flags |= IPFW_ARGS_REF;
        }
        args.m = *m0;

        ipfw = ipfw_chk(&args);
        *m0 = args.m;

        ret = PFIL_PASS;
        switch (ipfw) {
        case IP_FW_PASS:
                break;

        case IP_FW_DENY:
                ret = PFIL_DROPPED;
                break;

        case IP_FW_DUMMYNET:
                if (ip_dn_io_ptr == NULL) {
                        ret = PFIL_DROPPED;
                        break;
                }
                MPASS(args.flags & IPFW_ARGS_REF);
                ip_dn_io_ptr(m0, &args);
                return (PFIL_CONSUMED);

        case IP_FW_NGTEE:
        case IP_FW_NETGRAPH:
                if (ng_ipfw_input_p == NULL) {
                        ret = PFIL_DROPPED;
                        break;
                }
                MPASS(args.flags & IPFW_ARGS_REF);
                (void )ng_ipfw_input_p(m0, &args, ipfw == IP_FW_NGTEE);
                if (ipfw == IP_FW_NGTEE) /* ignore errors for NGTEE */
                        goto again;     /* continue with packet */
                ret = PFIL_CONSUMED;
                break;

        default:
                KASSERT(0, ("%s: unknown retval", __func__));
        }

        if (ret != PFIL_PASS) {
                if (*m0)
                        FREE_PKT(*m0);
                *m0 = NULL;
        }

        return (ret);
}

/*
 * ipfw processing for ethernet packets (in and out), memory pointer version,
 * two in/out accessors.
 */
static pfil_return_t
ipfw_check_frame_mem(void *mem, u_int len, int flags, struct ifnet *ifp,
    void *ruleset __unused, struct mbuf **m)
{
        struct ip_fw_args args = {
                .flags = len | IPFW_ARGS_ETHER |
                    ((flags & PFIL_IN) ? IPFW_ARGS_IN : IPFW_ARGS_OUT),
                .ifp = ifp,
                .mem = mem,
        };
        pfil_return_t ret;
        int ipfw;

        *m = NULL;
again:
        ipfw = ipfw_chk(&args);

        ret = PFIL_PASS;
        switch (ipfw) {
        case IP_FW_PASS:
                break;

        case IP_FW_DENY:
                ret = PFIL_DROPPED;
                break;

        case IP_FW_DUMMYNET:
                if (ip_dn_io_ptr == NULL) {
                        ret = PFIL_DROPPED;
                        break;
                }
                *m = m_devget(mem, len, 0, ifp, NULL);
                if (*m == NULL) {
                        ret = PFIL_DROPPED;
                        break;
                }
                MPASS(args.flags & IPFW_ARGS_REF);
                ip_dn_io_ptr(m, &args);
                return (PFIL_CONSUMED);

        case IP_FW_NGTEE:
        case IP_FW_NETGRAPH:
                if (ng_ipfw_input_p == NULL) {
                        ret = PFIL_DROPPED;
                        break;
                }
                *m = m_devget(mem, len, 0, ifp, NULL);
                if (*m == NULL) {
                        ret = PFIL_DROPPED;
                        break;
                }
                MPASS(args.flags & IPFW_ARGS_REF);
                (void )ng_ipfw_input_p(m, &args, ipfw == IP_FW_NGTEE);
                if (ipfw == IP_FW_NGTEE) /* ignore errors for NGTEE */
                        goto again;     /* continue with packet */
                ret = PFIL_CONSUMED;
                break;

        default:
                KASSERT(0, ("%s: unknown retval", __func__));
        }

        if (*m != NULL && ret == PFIL_PASS)
                ret = PFIL_REALLOCED;

        return (ret);
}

/* do the divert, return 1 on error 0 on success */
static int
ipfw_divert(struct mbuf **m0, struct ip_fw_args *args, bool tee)
{
        /*
         * ipfw_chk() has already tagged the packet with the divert tag.
         * If tee is set, copy packet and return original.
         * If not tee, consume packet and send it to divert socket.
         */
        struct mbuf *clone;
        struct ip *ip = mtod(*m0, struct ip *);
        struct m_tag *tag;

        /* Cloning needed for tee? */
        if (tee == false) {
                clone = *m0;    /* use the original mbuf */
                *m0 = NULL;
        } else {
                clone = m_dup(*m0, M_NOWAIT);
                /* If we cannot duplicate the mbuf, we sacrifice the divert
                 * chain and continue with the tee-ed packet.
                 */
                if (clone == NULL)
                        return 1;
        }

        /*
         * Divert listeners can normally handle non-fragmented packets,
         * but we can only reass in the non-tee case.
         * This means that listeners on a tee rule may get fragments,
         * and have to live with that.
         * Note that we now have the 'reass' ipfw option so if we care
         * we can do it before a 'tee'.
         */
        if (tee == false) switch (ip->ip_v) {
        case IPVERSION:
            if (ntohs(ip->ip_off) & (IP_MF | IP_OFFMASK)) {
                int hlen;
                struct mbuf *reass;

                reass = ip_reass(clone); /* Reassemble packet. */
                if (reass == NULL)
                        return 0; /* not an error */
                /* if reass = NULL then it was consumed by ip_reass */
                /*
                 * IP header checksum fixup after reassembly and leave header
                 * in network byte order.
                 */
                ip = mtod(reass, struct ip *);
                hlen = ip->ip_hl << 2;
                ip->ip_sum = 0;
                if (hlen == sizeof(struct ip))
                        ip->ip_sum = in_cksum_hdr(ip);
                else
                        ip->ip_sum = in_cksum(reass, hlen);
                clone = reass;
            }
            break;
#ifdef INET6
        case IPV6_VERSION >> 4:
            {
            struct ip6_hdr *const ip6 = mtod(clone, struct ip6_hdr *);

                if (ip6->ip6_nxt == IPPROTO_FRAGMENT) {
                        int nxt, off;

                        off = sizeof(struct ip6_hdr);
                        nxt = frag6_input(&clone, &off, 0);
                        if (nxt == IPPROTO_DONE)
                                return (0);
                }
                break;
            }
#endif
        }

        /* attach a tag to the packet with the reinject info */
        tag = m_tag_alloc(MTAG_IPFW_RULE, 0,
                    sizeof(struct ipfw_rule_ref), M_NOWAIT);
        if (tag == NULL) {
                FREE_PKT(clone);
                return 1;
        }
        *((struct ipfw_rule_ref *)(tag+1)) = args->rule;
        m_tag_prepend(clone, tag);

        /* Do the dirty job... */
        ip_divert_ptr(clone, args->flags & IPFW_ARGS_IN);
        return 0;
}

/*
 * attach or detach hooks for a given protocol family
 */
VNET_DEFINE_STATIC(pfil_hook_t, ipfw_inet_hook);
#define V_ipfw_inet_hook        VNET(ipfw_inet_hook)
#ifdef INET6
VNET_DEFINE_STATIC(pfil_hook_t, ipfw_inet6_hook);
#define V_ipfw_inet6_hook       VNET(ipfw_inet6_hook)
#endif
VNET_DEFINE_STATIC(pfil_hook_t, ipfw_link_hook);
#define V_ipfw_link_hook        VNET(ipfw_link_hook)

static void
ipfw_hook(int pf)
{
        struct pfil_hook_args pha = {
                .pa_version = PFIL_VERSION,
                .pa_flags = PFIL_IN | PFIL_OUT,
                .pa_modname = "ipfw",
        };
        pfil_hook_t *h;

        switch (pf) {
        case AF_INET:
                pha.pa_mbuf_chk = ipfw_check_packet;
                pha.pa_type = PFIL_TYPE_IP4;
                pha.pa_rulname = "default";
                h = &V_ipfw_inet_hook;
                break;
#ifdef INET6
        case AF_INET6:
                pha.pa_mbuf_chk = ipfw_check_packet;
                pha.pa_type = PFIL_TYPE_IP6;
                pha.pa_rulname = "default6";
                h = &V_ipfw_inet6_hook;
                break;
#endif
        case AF_LINK:
                pha.pa_mbuf_chk = ipfw_check_frame_mbuf;
                pha.pa_mem_chk = ipfw_check_frame_mem;
                pha.pa_type = PFIL_TYPE_ETHERNET;
                pha.pa_rulname = "default-link";
                h = &V_ipfw_link_hook;
                break;
        }

        *h = pfil_add_hook(&pha);
}

static void
ipfw_unhook(int pf)
{

        switch (pf) {
        case AF_INET:
                pfil_remove_hook(V_ipfw_inet_hook);
                break;
#ifdef INET6
        case AF_INET6:
                pfil_remove_hook(V_ipfw_inet6_hook);
                break;
#endif
        case AF_LINK:
                pfil_remove_hook(V_ipfw_link_hook);
                break;
        }
}

static int
ipfw_link(int pf, bool unlink)
{
        struct pfil_link_args pla;

        pla.pa_version = PFIL_VERSION;
        pla.pa_flags = PFIL_IN | PFIL_OUT | PFIL_HEADPTR | PFIL_HOOKPTR;
        if (unlink)
                pla.pa_flags |= PFIL_UNLINK;

        switch (pf) {
        case AF_INET:
                pla.pa_head = V_inet_pfil_head;
                pla.pa_hook = V_ipfw_inet_hook;
                break;
#ifdef INET6
        case AF_INET6:
                pla.pa_head = V_inet6_pfil_head;
                pla.pa_hook = V_ipfw_inet6_hook;
                break;
#endif
        case AF_LINK:
                pla.pa_head = V_link_pfil_head;
                pla.pa_hook = V_ipfw_link_hook;
                break;
        }

        return (pfil_link(&pla));
}

int
ipfw_attach_hooks(void)
{
        int error = 0;

        ipfw_hook(AF_INET);
        TUNABLE_INT_FETCH("net.inet.ip.fw.enable", &V_fw_enable);
        if (V_fw_enable && (error = ipfw_link(AF_INET, false)) != 0)
                printf("ipfw_hook() error\n");
#ifdef INET6
        ipfw_hook(AF_INET6);
        TUNABLE_INT_FETCH("net.inet6.ip6.fw.enable", &V_fw6_enable);
        if (V_fw6_enable && (error = ipfw_link(AF_INET6, false)) != 0)
                printf("ipfw6_hook() error\n");
#endif
        ipfw_hook(AF_LINK);
        TUNABLE_INT_FETCH("net.link.ether.ipfw", &V_fwlink_enable);
        if (V_fwlink_enable && (error = ipfw_link(AF_LINK, false)) != 0)
                printf("ipfw_link_hook() error\n");

        return (error);
}

void
ipfw_detach_hooks(void)
{

        ipfw_unhook(AF_INET);
#ifdef INET6
        ipfw_unhook(AF_INET6);
#endif
        ipfw_unhook(AF_LINK);
}

int
ipfw_chg_hook(SYSCTL_HANDLER_ARGS)
{
        int newval;
        int error;
        int af;

        if (arg1 == &V_fw_enable)
                af = AF_INET;
#ifdef INET6
        else if (arg1 == &V_fw6_enable)
                af = AF_INET6;
#endif
        else if (arg1 == &V_fwlink_enable)
                af = AF_LINK;
        else 
                return (EINVAL);

        newval = *(int *)arg1;
        /* Handle sysctl change */
        error = sysctl_handle_int(oidp, &newval, 0, req);

        if (error)
                return (error);

        /* Formalize new value */
        newval = (newval) ? 1 : 0;

        if (*(int *)arg1 == newval)
                return (0);

        error = ipfw_link(af, newval == 0 ? true : false);
        if (error)
                return (error);
        *(int *)arg1 = newval;

        return (0);
}
/* end of file */