Add a new gre(4) driver, which could be used to create GRE (RFC1701)

and MOBILE (RFC2004) IP tunnels.

Obrained from:  NetBSD

1 files changed, 781 insertions, 0 deletions

diff --git a/sys/net/if_gre.c b/sys/net/if_gre.c
new file mode 100644
index 0000000..22d7e94
--- /dev/null
+++ b/sys/net/if_gre.c
@@ -0,0 +1,781 @@
+/*	$NetBSD: if_gre.c,v 1.42 2002/08/14 00:23:27 itojun Exp $ */
+/*	 $FreeBSD$ */
+
+/*
+ * 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 <sys/cdefs.h>
+__RCSID("@(#) $FreeBSD$");
+
+#include "opt_inet.h"
+#include "opt_ns.h"
+#include "bpf.h"
+
+#include <sys/param.h>
+#include <sys/kernel.h>
+#include <sys/malloc.h>
+#include <sys/mbuf.h>
+#include <sys/proc.h>
+#include <sys/protosw.h>
+#include <sys/socket.h>
+#include <sys/sockio.h>
+#include <sys/queue.h>
+#include <sys/sysctl.h>
+
+#include <machine/cpu.h>
+
+#include <net/ethernet.h>
+#include <net/if.h>
+#include <net/if_types.h>
+#include <net/netisr.h>
+#include <net/route.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
+
+#ifdef NS
+#include <netns/ns.h>
+#include <netns/ns_if.h>
+#endif
+
+#ifdef NETATALK
+#include <netatalk/at.h>
+#include <netatalk/at_var.h>
+#include <netatalk/at_extern.h>
+#endif
+
+#if NBPF > 0
+#include <sys/time.h>
+#include <net/bpf.h>
+#endif
+
+#include <net/net_osdep.h>
+#include <net/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"
+
+static MALLOC_DEFINE(M_GRE, GRENAME, "Generic Routing Encapsulation");
+
+struct gre_softc_head gre_softc_list;
+int ip_gre_ttl = GRE_TTL;
+
+int	gre_clone_create __P((struct if_clone *, int));
+void	gre_clone_destroy __P((struct ifnet *));
+
+struct if_clone gre_cloner =
+    IF_CLONE_INITIALIZER("gre", gre_clone_create, gre_clone_destroy, 0, IF_MAXUNIT);
+
+int gre_compute_route(struct gre_softc *sc);
+
+void	greattach __P((void));
+
+#ifdef INET
+extern struct domain inetdomain;
+static const struct protosw in_gre_protosw =
+{ SOCK_RAW,     &inetdomain,    IPPROTO_GRE,    PR_ATOMIC|PR_ADDR,
+  (pr_input_t*)gre_input, (pr_output_t*)rip_output, rip_ctlinput, rip_ctloutput,
+  0,
+  0,		0,		0,		0,
+  &rip_usrreqs
+};
+static const struct protosw in_mobile_protosw =
+{ SOCK_RAW,     &inetdomain,    IPPROTO_MOBILE, PR_ATOMIC|PR_ADDR,
+  (pr_input_t*)gre_mobile_input, (pr_output_t*)rip_output, rip_ctlinput, rip_ctloutput,
+  0,
+  0,		0,		0,		0,
+  &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 */
+void
+greattach(void)
+{
+
+	LIST_INIT(&gre_softc_list);
+	if_clone_attach(&gre_cloner);
+}
+
+int
+gre_clone_create(ifc, unit)
+	struct if_clone *ifc;
+	int unit;
+{
+	struct gre_softc *sc;
+
+	sc = malloc(sizeof(struct gre_softc), M_GRE, M_WAITOK);
+	memset(sc, 0, sizeof(struct gre_softc));
+
+	sc->sc_if.if_name = GRENAME;
+	sc->sc_if.if_softc = sc;
+	sc->sc_if.if_unit = unit;
+	sc->sc_if.if_snd.ifq_maxlen = 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->called = 0;
+	if_attach(&sc->sc_if);
+#if NBPF
+	bpfattach(&sc->sc_if, DLT_NULL, sizeof(u_int32_t));
+#endif
+	LIST_INSERT_HEAD(&gre_softc_list, sc, sc_list);
+	return (0);
+}
+
+void
+gre_clone_destroy(ifp)
+	struct ifnet *ifp;
+{
+	struct gre_softc *sc = ifp->if_softc;
+
+#ifdef INET
+	if (sc->encap != NULL)
+		encap_detach(sc->encap);
+#endif
+	LIST_REMOVE(sc, sc_list);
+#if NBPF
+	bpfdetach(ifp);
+#endif
+	if_detach(ifp);
+	free(sc, M_GRE);
+}
+
+/*
+ * The output routine. Takes a packet and encapsulates it in the protocol
+ * given by sc->g_proto. See also RFC 1701 and RFC 2004
+ */
+int
+gre_output(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_char osrc;
+	u_short etype = 0;
+	struct mobile_h mob_h;
+
+	/*
+	 * gre may cause infinite recursion calls when misconfigured.
+	 * We'll prevent this by introducing upper limit.
+	 */
+	if (++(sc->called) > max_gre_nesting) {
+		printf("%s: gre_output: recursively called too many "
+		       "times(%d)\n", if_name(&sc->sc_if), sc->called);
+		m_freem(m);
+		error = EIO;    /* is there better errno? */
+		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;
+	}
+
+	gh = NULL;
+	ip = NULL;
+	osrc = 0;
+
+#if NBPF
+	if (ifp->if_bpf) {
+		/* see comment of other if_foo.c files */
+		struct mbuf m0;
+		u_int32_t af = dst->sa_family;
+
+		m0.m_next = m;
+		m0.m_len = 4;
+		m0.m_data = (char *)&af;
+
+		bpf_mtap(ifp, &m0);
+	}
+#endif
+
+	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 diagrams shouldn't
+			 * be encapsulated.
+			 */
+			if ((ip->ip_off & IP_MF) != 0) {
+				_IF_DROP(&ifp->if_snd);
+				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_DONTWAIT, MT_HEADER);
+				if (m0 == NULL) {
+					_IF_DROP(&ifp->if_snd);
+					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 = ntohs(ip->ip_len) + msiz;
+		} else {  /* AF_INET */
+			_IF_DROP(&ifp->if_snd);
+			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;
+#ifdef NETATALK
+		case AF_APPLETALK:
+			etype = ETHERTYPE_ATALK;
+			break;
+#endif
+#ifdef NS
+		case AF_NS:
+			etype = ETHERTYPE_NS;
+			break;
+#endif
+		default:
+			_IF_DROP(&ifp->if_snd);
+			m_freem(m);
+			error = EAFNOSUPPORT;
+			goto end;
+		}
+		M_PREPEND(m, sizeof(struct greip), M_DONTWAIT);
+	} else {
+		_IF_DROP(&ifp->if_snd);
+		m_freem(m);
+		error = EINVAL;
+		goto end;
+	}
+
+	if (m == NULL) {	/* impossible */
+		_IF_DROP(&ifp->if_snd);
+		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 = ip_gre_ttl;
+		((struct ip*)gh)->ip_tos = ip->ip_tos;
+		((struct ip*)gh)->ip_id = ip->ip_id;
+		gh->gi_len = m->m_pkthdr.len;
+	}
+
+	ifp->if_opackets++;
+	ifp->if_obytes += m->m_pkthdr.len;
+	/* send it off */
+	error = ip_output(m, NULL, &sc->route, 0, NULL);
+  end:
+	sc->called = 0;
+	if (error)
+		ifp->if_oerrors++;
+	return (error);
+}
+
+int
+gre_ioctl(struct ifnet *ifp, u_long cmd, caddr_t data)
+{
+	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;
+	int s;
+	struct sockaddr_in si;
+	struct sockaddr *sa = NULL;
+	int error;
+	struct sockaddr_in sp, sm, dp, dm;
+
+	error = 0;
+
+	s = splnet();
+	switch (cmd) {
+	case SIOCSIFADDR:
+		ifp->if_flags |= IFF_UP;
+		break;
+	case SIOCSIFDSTADDR: 
+		break;
+	case SIOCSIFFLAGS:
+		if ((error = suser(curthread)) != 0)
+			break;
+		if ((ifr->ifr_flags & IFF_LINK0) != 0)
+			sc->g_proto = IPPROTO_GRE;
+		else
+			sc->g_proto = IPPROTO_MOBILE;
+		goto recompute;
+	case SIOCSIFMTU:
+		if ((error = suser(curthread)) != 0)
+			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:
+		if ((error = suser(curthread)) != 0)
+			break;
+		if (ifr == 0) {
+			error = EAFNOSUPPORT;
+			break;
+		}
+		switch (ifr->ifr_addr.sa_family) {
+#ifdef INET
+		case AF_INET:
+			break;
+#endif
+		default:
+			error = EAFNOSUPPORT;
+			break;
+		}
+		break;
+	case GRESPROTO:
+		if ((error = suser(curthread)) != 0)
+			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:
+		if ((error = suser(curthread)) != 0)
+			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)
+				printf("%s: unable to attach encap\n",
+				    if_name(&sc->sc_if));
+#endif
+			if (sc->route.ro_rt != 0) /* free old route */
+				RTFREE(sc->route.ro_rt);
+			if (gre_compute_route(sc) == 0)
+				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:
+		if ((error = suser(curthread)) != 0)
+			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:
+		if ((error = suser(curthread)) != 0)
+			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:
+		if ((error = suser(curthread)) != 0)
+			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;
+	}
+
+	splx(s);
+	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.
+ */
+int
+gre_compute_route(struct gre_softc *sc)
+{
+	struct route *ro;
+	u_int32_t a, b, c;
+
+	ro = &sc->route;
+
+	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
+	printf("%s: searching a route to %s", if_name(&sc->sc_if),
+	    inet_ntoa(((struct sockaddr_in *)&ro->ro_dst)->sin_addr));
+#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)
+			printf(" - no route found!\n");
+		else
+			printf(" - 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
+	printf(", choosing %s with gateway %s", if_name(ro->ro_rt->rt_ifp),
+	    inet_ntoa(((struct sockaddr_in *)(ro->ro_rt->rt_gateway))->sin_addr));
+	printf("\n");
+#endif
+
+	return 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);