/*      $NetBSD: if_gre.c,v 1.42 2002/08/14 00:23:27 itojun Exp $ */
/*      $FreeBSD: src/sys/net/if_gre.c,v 1.9.2.3 2003/01/23 21:06:44 sam Exp $ */

/*
 * Copyright (c) 1998 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code is derived from software contributed to The NetBSD Foundation
 * by Heiko W.Rupp <hwr@pilhuhn.de>
 *
 * 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. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *        This product includes software developed by the NetBSD
 *        Foundation, Inc. and its contributors.
 * 4. Neither the name of The NetBSD Foundation 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 NETBSD FOUNDATION, INC. 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 FOUNDATION 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.
 */

/*
 * Encapsulate L3 protocols into IP
 * See RFC 1701 and 1702 for more details.
 * If_gre is compatible with Cisco GRE tunnels, so you can
 * have a NetBSD box as the other end of a tunnel interface of a Cisco
 * router. See gre(4) for more details.
 * Also supported:  IP in IP encaps (proto 55) as of RFC 2004
 */

#include "opt_inet.h"

#include <sys/param.h>
#include <sys/kernel.h>
#include <sys/bus.h>
#include <sys/malloc.h>
#include <sys/mbuf.h>
#include <sys/proc.h>
#include <sys/caps.h>
#include <sys/protosw.h>
#include <sys/socket.h>
#include <sys/sockio.h>
#include <sys/sysctl.h>
#include <sys/systm.h>
#include <sys/thread2.h>

#include <net/ethernet.h>
#include <net/if.h>
#include <net/if_types.h>
#include <net/ifq_var.h>
#include <net/route.h>
#include <net/if_clone.h>
#include <net/netmsg2.h>
#include <net/netisr2.h>

#ifdef INET
#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/in_var.h>
#include <netinet/ip.h>
#include <netinet/ip_gre.h>
#include <netinet/ip_var.h>
#include <netinet/ip_encap.h>
#else
#error "Huh? if_gre without inet?"
#endif

#include <net/bpf.h>

#include <net/net_osdep.h>
#include "if_gre.h"

/*
 * It is not easy to calculate the right value for a GRE MTU.
 * We leave this task to the admin and use the same default that
 * other vendors use.
 */
#define GREMTU  1476

#define GRENAME "gre"

#define MTAG_GRE        1709049137 /* mtag cookie for nesting check */

static MALLOC_DEFINE(M_GRE, GRENAME, "Generic Routing Encapsulation");

struct gre_softc_head gre_softc_list;

static int      gre_clone_create(struct if_clone *, int, caddr_t, caddr_t);
static int      gre_clone_destroy(struct ifnet *);
static int      gre_ioctl(struct ifnet *, u_long, caddr_t, struct ucred *);
static int      gre_output(struct ifnet *, struct mbuf *, struct sockaddr *,
                    struct rtentry *rt);

static struct if_clone gre_cloner = IF_CLONE_INITIALIZER("gre",
    gre_clone_create, gre_clone_destroy, 0, IF_MAXUNIT);

static int      gre_compute_route(struct gre_softc *sc, struct route *);
static int      gre_check_route(struct gre_softc *sc);

static void     greattach(void);

#ifdef INET

extern struct domain inetdomain;

static const struct protosw in_gre_protosw =
    {
        .pr_type = SOCK_RAW,
        .pr_domain = &inetdomain,
        .pr_protocol = IPPROTO_GRE,
        .pr_flags = PR_ATOMIC|PR_ADDR,

        .pr_input = gre_input,
        .pr_output = rip_output,
        .pr_ctlinput = NULL,
        .pr_ctloutput = rip_ctloutput,

        .pr_ctlport = NULL,
        .pr_usrreqs = &rip_usrreqs
    };

static const struct protosw in_mobile_protosw =
    {
        .pr_type = SOCK_RAW,
        .pr_domain = &inetdomain,
        .pr_protocol = IPPROTO_MOBILE,
        .pr_flags = PR_ATOMIC|PR_ADDR,

        .pr_input = gre_mobile_input,
        .pr_output = rip_output,
        .pr_ctlinput = NULL,
        .pr_ctloutput = rip_ctloutput,

        .pr_ctlport = NULL,
        .pr_usrreqs = &rip_usrreqs
    };

#endif

SYSCTL_DECL(_net_link);
SYSCTL_NODE(_net_link, IFT_OTHER, gre, CTLFLAG_RW, 0,
    "Generic Routing Encapsulation");
#ifndef MAX_GRE_NEST
/*
 * This macro controls the default upper limitation on nesting of gre tunnels.
 * Since, setting a large value to this macro with a careless configuration
 * may introduce system crash, we don't allow any nestings by default.
 * If you need to configure nested gre tunnels, you can define this macro
 * in your kernel configuration file.  However, if you do so, please be
 * careful to configure the tunnels so that it won't make a loop.
 */
#define MAX_GRE_NEST 1
#endif
static int max_gre_nesting = MAX_GRE_NEST;
SYSCTL_INT(_net_link_gre, OID_AUTO, max_nesting, CTLFLAG_RW,
    &max_gre_nesting, 0, "Max nested tunnels");

/* ARGSUSED */
static void
greattach(void)
{

        LIST_INIT(&gre_softc_list);
        if_clone_attach(&gre_cloner);
}

static int
gre_clone_create(struct if_clone *ifc, int unit,
                 caddr_t params __unused, caddr_t data __unused)
{
        struct gre_softc *sc;

        sc = kmalloc(sizeof(struct gre_softc), M_GRE, M_WAITOK);
        memset(sc, 0, sizeof(struct gre_softc));

        sc->sc_if.if_softc = sc;
        if_initname(&(sc->sc_if), GRENAME, unit);
        ifq_set_maxlen(&sc->sc_if.if_snd, IFQ_MAXLEN);
        sc->sc_if.if_type = IFT_OTHER;
        sc->sc_if.if_addrlen = 0;
        sc->sc_if.if_hdrlen = 24; /* IP + GRE */
        sc->sc_if.if_mtu = GREMTU;
        sc->sc_if.if_flags = IFF_POINTOPOINT|IFF_MULTICAST;
        sc->sc_if.if_output = gre_output;
        sc->sc_if.if_ioctl = gre_ioctl;
        sc->g_dst.s_addr = sc->g_src.s_addr = INADDR_ANY;
        sc->g_proto = IPPROTO_GRE;
        sc->sc_if.if_flags |= IFF_LINK0;
        sc->encap = NULL;
        sc->route_pcpu = kmalloc(netisr_ncpus * sizeof(struct route), M_GRE,
            M_WAITOK | M_ZERO);
        if_attach(&sc->sc_if, NULL);
        bpfattach(&sc->sc_if, DLT_NULL, sizeof(u_int32_t));
        LIST_INSERT_HEAD(&gre_softc_list, sc, sc_list);
        return (0);
}

static int
gre_clone_destroy(struct ifnet *ifp)
{
        struct gre_softc *sc = ifp->if_softc;
        int cpu;

#ifdef INET
        if (sc->encap != NULL)
                encap_detach(sc->encap);
#endif
        LIST_REMOVE(sc, sc_list);
        bpfdetach(ifp);
        if_detach(ifp);

        for (cpu = 0; cpu < netisr_ncpus; ++cpu) {
                if (sc->route_pcpu[cpu].ro_rt != NULL) {
                        rtfree_async(sc->route_pcpu[cpu].ro_rt);
                        sc->route_pcpu[cpu].ro_rt = NULL;
                }
        }
        kfree(sc->route_pcpu, M_GRE);
        kfree(sc, M_GRE);

        return 0;
}

/*
 * The output routine. Takes a packet and encapsulates it in the protocol
 * given by sc->g_proto. See also RFC 1701 and RFC 2004
 */
static int
gre_output_serialized(struct ifnet *ifp, struct mbuf *m, struct sockaddr *dst,
                      struct rtentry *rt)
{
        int error = 0;
        struct gre_softc *sc = ifp->if_softc;
        struct greip *gh;
        struct ip *ip;
        u_short etype = 0;
        struct mobile_h mob_h;
        struct route *ro;
        struct sockaddr_in *ro_dst;

        ASSERT_NETISR_NCPUS(mycpuid);

        error = if_tunnel_check_nesting(ifp, m, MTAG_GRE, max_gre_nesting);
        if (error != 0) {
                m_freem(m);
                goto end;
        }

        if ((ifp->if_flags & (IFF_UP | IFF_RUNNING)) == 0 ||
            sc->g_src.s_addr == INADDR_ANY || sc->g_dst.s_addr == INADDR_ANY) {
                m_freem(m);
                error = ENETDOWN;
                goto end;
        }

        ro = &sc->route_pcpu[mycpuid];
        ro_dst = (struct sockaddr_in *)&ro->ro_dst;
        if (ro->ro_rt != NULL &&
            ((ro->ro_rt->rt_flags & RTF_UP) == 0 ||
             ro_dst->sin_addr.s_addr != sc->g_dst.s_addr)) {
                RTFREE(ro->ro_rt);
                ro->ro_rt = NULL;
        }
        if (ro->ro_rt == NULL) {
                error = gre_compute_route(sc, ro);
                if (error) {
                        m_freem(m);
                        goto end;
                }
        }

        gh = NULL;
        ip = NULL;

        if (ifp->if_bpf) {
                bpf_gettoken();
                if (ifp->if_bpf) {
                        uint32_t af = dst->sa_family;

                        bpf_ptap(ifp->if_bpf, m, &af, sizeof(af));
                }
                bpf_reltoken();
        }

        m->m_flags &= ~(M_BCAST|M_MCAST);

        if (sc->g_proto == IPPROTO_MOBILE) {
                if (dst->sa_family == AF_INET) {
                        struct mbuf *m0;
                        int msiz;

                        ip = mtod(m, struct ip *);

                        /*
                         * RFC2004 specifies that fragmented datagrams shouldn't
                         * be encapsulated.
                         */
                        if (ip->ip_off & htons(IP_MF | IP_OFFMASK)) {
                                m_freem(m);
                                error = EINVAL;    /* is there better errno? */
                                goto end;
                        }
                        memset(&mob_h, 0, MOB_H_SIZ_L);
                        mob_h.proto = (ip->ip_p) << 8;
                        mob_h.odst = ip->ip_dst.s_addr;
                        ip->ip_dst.s_addr = sc->g_dst.s_addr;

                        /*
                         * If the packet comes from our host, we only change
                         * the destination address in the IP header.
                         * Else we also need to save and change the source
                         */
                        if (in_hosteq(ip->ip_src, sc->g_src)) {
                                msiz = MOB_H_SIZ_S;
                        } else {
                                mob_h.proto |= MOB_H_SBIT;
                                mob_h.osrc = ip->ip_src.s_addr;
                                ip->ip_src.s_addr = sc->g_src.s_addr;
                                msiz = MOB_H_SIZ_L;
                        }
                        mob_h.proto = htons(mob_h.proto);
                        mob_h.hcrc = gre_in_cksum((u_short *)&mob_h, msiz);

                        if ((m->m_data - msiz) < m->m_pktdat) {
                                /* need new mbuf */
                                MGETHDR(m0, M_NOWAIT, MT_HEADER);
                                if (m0 == NULL) {
                                        m_freem(m);
                                        error = ENOBUFS;
                                        goto end;
                                }
                                m0->m_next = m;
                                m->m_data += sizeof(struct ip);
                                m->m_len -= sizeof(struct ip);
                                m0->m_pkthdr.len = m->m_pkthdr.len + msiz;
                                m0->m_len = msiz + sizeof(struct ip);
                                m0->m_data += max_linkhdr;
                                memcpy(mtod(m0, caddr_t), (caddr_t)ip,
                                       sizeof(struct ip));
                                m = m0;
                        } else {  /* we have some space left in the old one */
                                m->m_data -= msiz;
                                m->m_len += msiz;
                                m->m_pkthdr.len += msiz;
                                bcopy(ip, mtod(m, caddr_t),
                                        sizeof(struct ip));
                        }
                        ip = mtod(m, struct ip *);
                        memcpy((caddr_t)(ip + 1), &mob_h, (unsigned)msiz);
                        ip->ip_len = htons(ntohs(ip->ip_len) + msiz);
                } else {  /* AF_INET */
                        m_freem(m);
                        error = EINVAL;
                        goto end;
                }
        } else if (sc->g_proto == IPPROTO_GRE) {
                switch (dst->sa_family) {
                case AF_INET:
                        ip = mtod(m, struct ip *);
                        etype = ETHERTYPE_IP;
                        break;
                default:
                        m_freem(m);
                        error = EAFNOSUPPORT;
                        goto end;
                }
                M_PREPEND(m, sizeof(struct greip), M_NOWAIT);
        } else {
                m_freem(m);
                error = EINVAL;
                goto end;
        }

        if (m == NULL) {        /* impossible */
                error = ENOBUFS;
                goto end;
        }

        gh = mtod(m, struct greip *);
        if (sc->g_proto == IPPROTO_GRE) {
                /* we don't have any GRE flags for now */

                memset((void *)&gh->gi_g, 0, sizeof(struct gre_h));
                gh->gi_ptype = htons(etype);
        }

        gh->gi_pr = sc->g_proto;
        if (sc->g_proto != IPPROTO_MOBILE) {
                gh->gi_src = sc->g_src;
                gh->gi_dst = sc->g_dst;
                ((struct ip*)gh)->ip_hl = (sizeof(struct ip)) >> 2;
                ((struct ip*)gh)->ip_ttl = GRE_TTL;
                ((struct ip*)gh)->ip_tos = ip->ip_tos;
                ((struct ip*)gh)->ip_id = ip->ip_id;
                gh->gi_len = htons(m->m_pkthdr.len);
        }

        IFNET_STAT_INC(ifp, opackets, 1);
        IFNET_STAT_INC(ifp, obytes, m->m_pkthdr.len);
        /* send it off */
        error = ip_output(m, NULL, ro, IP_DEBUGROUTE, NULL, NULL);
  end:
        if (error)
                IFNET_STAT_INC(ifp, oerrors, 1);
        return (error);
}

static int
gre_output(struct ifnet *ifp, struct mbuf *m, struct sockaddr *dst,
           struct rtentry *rt)
{
        struct ifaltq_subque *ifsq = ifq_get_subq_default(&ifp->if_snd);
        int error;

        ifsq_serialize_hw(ifsq);
        error = gre_output_serialized(ifp, m, dst, rt);
        ifsq_deserialize_hw(ifsq);

        return error;
}

static int
gre_ioctl(struct ifnet *ifp, u_long cmd, caddr_t data, struct ucred *cr)
{
        struct ifreq *ifr = (struct ifreq *)data;
        struct if_laddrreq *lifr = (struct if_laddrreq *)data;
        struct in_aliasreq *aifr = (struct in_aliasreq *)data;
        struct gre_softc *sc = ifp->if_softc;
        struct sockaddr_in si;
        struct sockaddr *sa = NULL;
        int error;
        struct sockaddr_in sp, sm, dp, dm;

        error = 0;

        crit_enter();
        switch (cmd) {
        case SIOCSIFADDR:
                ifp->if_flags |= IFF_UP;
                break;
        case SIOCSIFDSTADDR:
                break;
        case SIOCSIFFLAGS:
                error = caps_priv_check(cr, SYSCAP_RESTRICTEDROOT |
                                            __SYSCAP_NULLCRED);
                if (error)
                        break;
                if ((ifr->ifr_flags & IFF_LINK0) != 0)
                        sc->g_proto = IPPROTO_GRE;
                else
                        sc->g_proto = IPPROTO_MOBILE;
                goto recompute;
        case SIOCSIFMTU:
                error = caps_priv_check(cr, SYSCAP_RESTRICTEDROOT |
                                            __SYSCAP_NULLCRED);
                if (error)
                        break;
                if (ifr->ifr_mtu < 576) {
                        error = EINVAL;
                        break;
                }
                ifp->if_mtu = ifr->ifr_mtu;
                break;
        case SIOCGIFMTU:
                ifr->ifr_mtu = sc->sc_if.if_mtu;
                break;
        case SIOCADDMULTI:
        case SIOCDELMULTI:
                error = caps_priv_check(cr, SYSCAP_RESTRICTEDROOT |
                                            __SYSCAP_NULLCRED);
                if (error)
                        break;
                if (ifr == NULL) {
                        error = EAFNOSUPPORT;
                        break;
                }
                switch (ifr->ifr_addr.sa_family) {
#ifdef INET
                case AF_INET:
                        break;
#endif
                default:
                        error = EAFNOSUPPORT;
                        break;
                }
                break;
        case GRESPROTO:
                error = caps_priv_check(cr, SYSCAP_RESTRICTEDROOT |
                                            __SYSCAP_NULLCRED);
                if (error)
                        break;
                sc->g_proto = ifr->ifr_flags;
                switch (sc->g_proto) {
                case IPPROTO_GRE:
                        ifp->if_flags |= IFF_LINK0;
                        break;
                case IPPROTO_MOBILE:
                        ifp->if_flags &= ~IFF_LINK0;
                        break;
                default:
                        error = EPROTONOSUPPORT;
                        break;
                }
                goto recompute;
        case GREGPROTO:
                ifr->ifr_flags = sc->g_proto;
                break;
        case GRESADDRS:
        case GRESADDRD:
                error = caps_priv_check(cr, SYSCAP_RESTRICTEDROOT |
                                            __SYSCAP_NULLCRED);
                if (error)
                        break;
                /*
                 * set tunnel endpoints, compute a less specific route
                 * to the remote end and mark if as up
                 */
                sa = &ifr->ifr_addr;
                if (cmd == GRESADDRS)
                        sc->g_src = (satosin(sa))->sin_addr;
                if (cmd == GRESADDRD)
                        sc->g_dst = (satosin(sa))->sin_addr;
        recompute:
#ifdef INET
                if (sc->encap != NULL) {
                        encap_detach(sc->encap);
                        sc->encap = NULL;
                }
#endif
                if ((sc->g_src.s_addr != INADDR_ANY) &&
                    (sc->g_dst.s_addr != INADDR_ANY)) {
                        bzero(&sp, sizeof(sp));
                        bzero(&sm, sizeof(sm));
                        bzero(&dp, sizeof(dp));
                        bzero(&dm, sizeof(dm));
                        sp.sin_len = sm.sin_len = dp.sin_len = dm.sin_len =
                            sizeof(struct sockaddr_in);
                        sp.sin_family = sm.sin_family = dp.sin_family =
                            dm.sin_family = AF_INET;
                        sp.sin_addr = sc->g_src;
                        dp.sin_addr = sc->g_dst;
                        sm.sin_addr.s_addr = dm.sin_addr.s_addr =
                            INADDR_BROADCAST;
#ifdef INET
                        sc->encap = encap_attach(AF_INET, sc->g_proto,
                            sintosa(&sp), sintosa(&sm), sintosa(&dp),
                            sintosa(&dm), (sc->g_proto == IPPROTO_GRE) ?
                                &in_gre_protosw : &in_mobile_protosw, sc);
                        if (sc->encap == NULL)
                                kprintf("%s: unable to attach encap\n",
                                    if_name(&sc->sc_if));
#endif
                        ifnet_deserialize_all(ifp);
                        error = gre_check_route(sc);
                        ifnet_serialize_all(ifp);
                        if (!error)
                                ifp->if_flags |= IFF_RUNNING;
                        else
                                ifp->if_flags &= ~IFF_RUNNING;
                }
                break;
        case GREGADDRS:
                memset(&si, 0, sizeof(si));
                si.sin_family = AF_INET;
                si.sin_len = sizeof(struct sockaddr_in);
                si.sin_addr.s_addr = sc->g_src.s_addr;
                sa = sintosa(&si);
                ifr->ifr_addr = *sa;
                break;
        case GREGADDRD:
                memset(&si, 0, sizeof(si));
                si.sin_family = AF_INET;
                si.sin_len = sizeof(struct sockaddr_in);
                si.sin_addr.s_addr = sc->g_dst.s_addr;
                sa = sintosa(&si);
                ifr->ifr_addr = *sa;
                break;
        case SIOCSIFPHYADDR:
                error = caps_priv_check(cr, SYSCAP_RESTRICTEDROOT |
                                            __SYSCAP_NULLCRED);
                if (error)
                        break;
                if (aifr->ifra_addr.sin_family != AF_INET ||
                    aifr->ifra_dstaddr.sin_family != AF_INET)
                {
                        error = EAFNOSUPPORT;
                        break;
                }
                if (aifr->ifra_addr.sin_len != sizeof(si) ||
                    aifr->ifra_dstaddr.sin_len != sizeof(si))
                {
                        error = EINVAL;
                        break;
                }
                sc->g_src = aifr->ifra_addr.sin_addr;
                sc->g_dst = aifr->ifra_dstaddr.sin_addr;
                goto recompute;
        case SIOCSLIFPHYADDR:
                error = caps_priv_check(cr, SYSCAP_RESTRICTEDROOT |
                                            __SYSCAP_NULLCRED);
                if (error)
                        break;
                if (lifr->addr.ss_family != AF_INET ||
                    lifr->dstaddr.ss_family != AF_INET) {
                        error = EAFNOSUPPORT;
                        break;
                }
                if (lifr->addr.ss_len != sizeof(si) ||
                    lifr->dstaddr.ss_len != sizeof(si)) {
                        error = EINVAL;
                        break;
                }
                sc->g_src = (satosin((struct sockadrr *)&lifr->addr))->sin_addr;
                sc->g_dst =
                    (satosin((struct sockadrr *)&lifr->dstaddr))->sin_addr;
                goto recompute;
        case SIOCDIFPHYADDR:
                error = caps_priv_check(cr, SYSCAP_RESTRICTEDROOT |
                                            __SYSCAP_NULLCRED);
                if (error)
                        break;
                sc->g_src.s_addr = INADDR_ANY;
                sc->g_dst.s_addr = INADDR_ANY;
                goto recompute;
        case SIOCGLIFPHYADDR:
                if (sc->g_src.s_addr == INADDR_ANY ||
                    sc->g_dst.s_addr == INADDR_ANY) {
                        error = EADDRNOTAVAIL;
                        break;
                }
                memset(&si, 0, sizeof(si));
                si.sin_family = AF_INET;
                si.sin_len = sizeof(struct sockaddr_in);
                si.sin_addr.s_addr = sc->g_src.s_addr;
                memcpy(&lifr->addr, &si, sizeof(si));
                si.sin_addr.s_addr = sc->g_dst.s_addr;
                memcpy(&lifr->dstaddr, &si, sizeof(si));
                break;
        case SIOCGIFPSRCADDR:
                if (sc->g_src.s_addr == INADDR_ANY) {
                        error = EADDRNOTAVAIL;
                        break;
                }
                memset(&si, 0, sizeof(si));
                si.sin_family = AF_INET;
                si.sin_len = sizeof(struct sockaddr_in);
                si.sin_addr.s_addr = sc->g_src.s_addr;
                bcopy(&si, &ifr->ifr_addr, sizeof(ifr->ifr_addr));
                break;
        case SIOCGIFPDSTADDR:
                if (sc->g_dst.s_addr == INADDR_ANY) {
                        error = EADDRNOTAVAIL;
                        break;
                }
                memset(&si, 0, sizeof(si));
                si.sin_family = AF_INET;
                si.sin_len = sizeof(struct sockaddr_in);
                si.sin_addr.s_addr = sc->g_dst.s_addr;
                bcopy(&si, &ifr->ifr_addr, sizeof(ifr->ifr_addr));
                break;
        default:
                error = EINVAL;
                break;
        }

        crit_exit();
        return (error);
}

/*
 * computes a route to our destination that is not the one
 * which would be taken by ip_output(), as this one will loop back to
 * us. If the interface is p2p as  a--->b, then a routing entry exists
 * If we now send a packet to b (e.g. ping b), this will come down here
 * gets src=a, dst=b tacked on and would from ip_ouput() sent back to
 * if_gre.
 * Goal here is to compute a route to b that is less specific than
 * a-->b. We know that this one exists as in normal operation we have
 * at least a default route which matches.
 */
static int
gre_compute_route(struct gre_softc *sc, struct route *ro)
{
#ifdef DIAGNOSTIC
        char abuf[INET_ADDRSTRLEN];
#endif
        u_int32_t a, b, c;

        ASSERT_NETISR_NCPUS(mycpuid);
        KASSERT(ro == &sc->route_pcpu[mycpuid], ("route mismatch"));
        KASSERT(ro->ro_rt == NULL, ("rtentry not freed"));

        memset(ro, 0, sizeof(struct route));
        ((struct sockaddr_in *)&ro->ro_dst)->sin_addr = sc->g_dst;
        ro->ro_dst.sa_family = AF_INET;
        ro->ro_dst.sa_len = sizeof(ro->ro_dst);

        /*
         * toggle last bit, so our interface is not found, but a less
         * specific route. I'd rather like to specify a shorter mask,
         * but this is not possible. Should work though. XXX
         * there is a simpler way ...
         */
        if ((sc->sc_if.if_flags & IFF_LINK1) == 0) {
                a = ntohl(sc->g_dst.s_addr);
                b = a & 0x01;
                c = a & 0xfffffffe;
                b = b ^ 0x01;
                a = b | c;
                ((struct sockaddr_in *)&ro->ro_dst)->sin_addr.s_addr
                    = htonl(a);
        }

#ifdef DIAGNOSTIC
        kprintf("%s: searching a route to %s", if_name(&sc->sc_if),
            kinet_ntoa(((struct sockaddr_in *)&ro->ro_dst)->sin_addr, abuf));
#endif

        rtalloc(ro);

        /*
         * check if this returned a route at all and this route is no
         * recursion to ourself
         */
        if (ro->ro_rt == NULL || ro->ro_rt->rt_ifp->if_softc == sc) {
#ifdef DIAGNOSTIC
                if (ro->ro_rt == NULL)
                        kprintf(" - no route found!\n");
                else
                        kprintf(" - route loops back to ourself!\n");
#endif
                return EADDRNOTAVAIL;
        }

        /*
         * now change it back - else ip_output will just drop
         * the route and search one to this interface ...
         */
        if ((sc->sc_if.if_flags & IFF_LINK1) == 0)
                ((struct sockaddr_in *)&ro->ro_dst)->sin_addr = sc->g_dst;

#ifdef DIAGNOSTIC
        kprintf(", choosing %s with gateway %s", if_name(ro->ro_rt->rt_ifp),
            kinet_ntoa(
                ((struct sockaddr_in *)(ro->ro_rt->rt_gateway))->sin_addr, abuf));
        kprintf("\n");
#endif

        return 0;
}

static void
gre_check_route_handler(netmsg_t msg)
{
        struct gre_softc *sc = msg->base.lmsg.u.ms_resultp;
        struct route *ro;
        int error;

        ASSERT_NETISR0;

        ro = &sc->route_pcpu[mycpuid];
        if (ro->ro_rt != NULL) {
                RTFREE(ro->ro_rt);
                ro->ro_rt = NULL;
        }
        error = gre_compute_route(sc, ro);

        netisr_replymsg(&msg->base, error);
}

static int
gre_check_route(struct gre_softc *sc)
{
        struct netmsg_base msg;

        netmsg_init(&msg, NULL, &curthread->td_msgport, MSGF_PRIORITY,
            gre_check_route_handler);
        msg.lmsg.u.ms_resultp = sc;

        return (netisr_domsg(&msg, 0));
}

/*
 * do a checksum of a buffer - much like in_cksum, which operates on
 * mbufs.
 */
u_short
gre_in_cksum(u_short *p, u_int len)
{
        u_int sum = 0;
        int nwords = len >> 1;

        while (nwords-- != 0)
                sum += *p++;

        if (len & 1) {
                union {
                        u_short w;
                        u_char c[2];
                } u;
                u.c[0] = *(u_char *)p;
                u.c[1] = 0;
                sum += u.w;
        }

        /* end-around-carry */
        sum = (sum >> 16) + (sum & 0xffff);
        sum += (sum >> 16);
        return (~sum);
}

static int
gremodevent(module_t mod, int type, void *data)
{

        switch (type) {
        case MOD_LOAD:
                greattach();
                break;
        case MOD_UNLOAD:
                if_clone_detach(&gre_cloner);

                while (!LIST_EMPTY(&gre_softc_list))
                        gre_clone_destroy(&LIST_FIRST(&gre_softc_list)->sc_if);

                break;
        }
        return 0;
}

static moduledata_t gre_mod = {
        "if_gre",
        gremodevent,
        0
};

DECLARE_MODULE(if_gre, gre_mod, SI_SUB_PSEUDO, SI_ORDER_ANY);
MODULE_VERSION(if_gre, 1);