HardenedBSD/sys/net/if_stf.c

/*	$KAME: if_stf.c,v 1.73 2001/12/03 11:08:30 keiichi Exp $	*/

/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * Copyright (C) 2000 WIDE Project.
 * Copyright (c) 2010 Hiroki Sato <hrs@FreeBSD.org>
 * Copyright (c) 2013 Ermal Luci <eri@FreeBSD.org>
 * Copyright (c) 2017-2021 Rubicon Communications, LLC (Netgate)
 * 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 project 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 PROJECT 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 PROJECT 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.
 */

/*
 * 6to4 interface, based on RFC3056.
 *
 * 6to4 interface is NOT capable of link-layer (I mean, IPv4) multicasting.
 * There is no address mapping defined from IPv6 multicast address to IPv4
 * address.  Therefore, we do not have IFF_MULTICAST on the interface.
 *
 * Due to the lack of address mapping for link-local addresses, we cannot
 * throw packets toward link-local addresses (fe80::x).  Also, we cannot throw
 * packets to link-local multicast addresses (ff02::x).
 *
 * Here are interesting symptoms due to the lack of link-local address:
 *
 * Unicast routing exchange:
 * - RIPng: Impossible.  Uses link-local multicast packet toward ff02::9,
 *   and link-local addresses as nexthop.
 * - OSPFv6: Impossible.  OSPFv6 assumes that there's link-local address
 *   assigned to the link, and makes use of them.  Also, HELLO packets use
 *   link-local multicast addresses (ff02::5 and ff02::6).
 * - BGP4+: Maybe.  You can only use global address as nexthop, and global
 *   address as TCP endpoint address.
 *
 * Multicast routing protocols:
 * - PIM: Hello packet cannot be used to discover adjacent PIM routers.
 *   Adjacent PIM routers must be configured manually (is it really spec-wise
 *   correct thing to do?).
 *
 * ICMPv6:
 * - Redirects cannot be used due to the lack of link-local address.
 *
 * stf interface does not have, and will not need, a link-local address.  
 * It seems to have no real benefit and does not help the above symptoms much.
 * Even if we assign link-locals to interface, we cannot really
 * use link-local unicast/multicast on top of 6to4 cloud (since there's no
 * encapsulation defined for link-local address), and the above analysis does
 * not change.  RFC3056 does not mandate the assignment of link-local address
 * either.
 *
 * 6to4 interface has security issues.  Refer to
 * http://playground.iijlab.net/i-d/draft-itojun-ipv6-transition-abuse-00.txt
 * for details.  The code tries to filter out some of malicious packets.
 * Note that there is no way to be 100% secure.
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/socket.h>
#include <sys/sockio.h>
#include <sys/mbuf.h>
#include <sys/endian.h>
#include <sys/errno.h>
#include <sys/kernel.h>
#include <sys/lock.h>
#include <sys/module.h>
#include <sys/priv.h>
#include <sys/proc.h>
#include <sys/queue.h>
#include <sys/sdt.h>
#include <sys/sysctl.h>
#include <machine/cpu.h>

#include <sys/malloc.h>

#include <net/if.h>
#include <net/if_var.h>
#include <net/if_private.h>
#include <net/if_clone.h>
#include <net/route.h>
#include <net/route/nhop.h>
#include <net/netisr.h>
#include <net/if_stf.h>
#include <net/if_types.h>
#include <net/vnet.h>

#include <netinet/in.h>
#include <netinet/in_fib.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netinet/ip_var.h>
#include <netinet/in_var.h>

#include <netinet/ip6.h>
#include <netinet6/in6_fib.h>
#include <netinet6/ip6_var.h>
#include <netinet6/in6_var.h>
#include <netinet/ip_ecn.h>

#include <netinet/ip_encap.h>

#include <machine/stdarg.h>

#include <net/bpf.h>

#include <security/mac/mac_framework.h>

SDT_PROVIDER_DEFINE(if_stf);
SDT_PROBE_DEFINE3(if_stf, , encapcheck, in, "struct mbuf *", "int", "int");
SDT_PROBE_DEFINE0(if_stf, , encapcheck, accept);
SDT_PROBE_DEFINE3(if_stf, , getsrcifa6, in, "struct ifnet *",
    "struct in6_addr *", "struct in6_addr *");
SDT_PROBE_DEFINE2(if_stf, , getsrcifa6, found, "struct in6_addr *",
    "struct in6_addr *");
SDT_PROBE_DEFINE0(if_stf, , getsrcifa6, notfound);

SDT_PROBE_DEFINE4(if_stf, , stf_output, in, "struct ifnet *", "struct mbuf *",
    "struct sockaddr *", "struct route *");
SDT_PROBE_DEFINE2(if_stf, , stf_output, error, "int", "int");
SDT_PROBE_DEFINE1(if_stf, , stf_output, out, "int");

SDT_PROBE_DEFINE3(if_stf, , checkaddr6, in, "struct stf_softc *",
    "struct in6_addr *", "struct ifnet *");
SDT_PROBE_DEFINE2(if_stf, , checkaddr6, out, "int", "int");

SDT_PROBE_DEFINE3(if_stf, , stf_input, in, "struct mbuf *", "int", "int");
SDT_PROBE_DEFINE2(if_stf, , stf_input, out, "int", "int");

SDT_PROBE_DEFINE3(if_stf, , ioctl, sv4net, "struct in_addr *",
    "struct in_addr *", "int");
SDT_PROBE_DEFINE1(if_stf, , ioctl, sdstv4, "struct in_addr *");
SDT_PROBE_DEFINE1(if_stf, , ioctl, ifaddr, "struct ifaddr *");

SDT_PROBE_DEFINE4(if_stf, , getin4addr_in6, out, "struct in6_addr *",
    "struct in6_addr *", "struct in6_addr *", "struct sockaddr_in *");

SDT_PROBE_DEFINE2(if_stf, , getin4addr, in, "struct in6_addr *", "struct in6_addr *");
SDT_PROBE_DEFINE1(if_stf, , getin4addr, out, "struct sockaddr_in *");

SYSCTL_DECL(_net_link);
static SYSCTL_NODE(_net_link, IFT_STF, stf, CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
    "6to4 Interface");

static int stf_permit_rfc1918 = 0;
SYSCTL_INT(_net_link_stf, OID_AUTO, permit_rfc1918, CTLFLAG_RWTUN,
    &stf_permit_rfc1918, 0, "Permit the use of private IPv4 addresses");

#define STFUNIT		0

#define IN6_IS_ADDR_6TO4(x)	(ntohs((x)->s6_addr16[0]) == 0x2002)

/*
 * XXX: Return a pointer with 16-bit aligned.  Don't cast it to
 * struct in_addr *; use bcopy() instead.
 */
#define GET_V4(x)	(&(x)->s6_addr16[1])

struct stf_softc {
	struct ifnet	*sc_ifp;
	in_addr_t	braddr;		/* Border relay IPv4 address */
	in_addr_t	srcv4_addr;	/* Our IPv4 WAN address */
	u_int		v4prefixlen;	/* How much of the v4 address to include in our address. */
	u_int		sc_fibnum;
	const struct encaptab *encap_cookie;
};
#define STF2IFP(sc)	((sc)->sc_ifp)

static const char stfname[] = "stf";

static MALLOC_DEFINE(M_STF, stfname, "6to4 Tunnel Interface");
static const int ip_stf_ttl = 40;

static int in_stf_input(struct mbuf *, int, int, void *);
static char *stfnames[] = {"stf0", "stf", "6to4", NULL};

static int stfmodevent(module_t, int, void *);
static int stf_encapcheck(const struct mbuf *, int, int, void *);
static int stf_getsrcifa6(struct ifnet *, struct in6_addr *, struct in6_addr *);
static int stf_output(struct ifnet *, struct mbuf *, const struct sockaddr *,
	struct route *);
static int isrfc1918addr(struct in_addr *);
static int stf_checkaddr4(struct stf_softc *, struct in_addr *,
	struct ifnet *);
static int stf_checkaddr6(struct stf_softc *, struct in6_addr *,
	struct ifnet *);
static struct sockaddr_in *stf_getin4addr_in6(struct stf_softc *,
	struct sockaddr_in *, struct in6_addr, struct in6_addr,
	struct in6_addr);
static struct sockaddr_in *stf_getin4addr(struct stf_softc *,
	struct sockaddr_in *, struct in6_addr, struct in6_addr);
static int stf_ioctl(struct ifnet *, u_long, caddr_t);

VNET_DEFINE_STATIC(struct if_clone *, stf_cloner);
#define V_stf_cloner	VNET(stf_cloner)

static const struct encap_config ipv4_encap_cfg = {
	.proto = IPPROTO_IPV6,
	.min_length = sizeof(struct ip),
	.exact_match = (sizeof(in_addr_t) << 3) + 8,
	.check = stf_encapcheck,
	.input = in_stf_input
};

static int
stf_clone_match(struct if_clone *ifc, const char *name)
{
	int i;

	for(i = 0; stfnames[i] != NULL; i++) {
		if (strcmp(stfnames[i], name) == 0)
			return (1);
	}

	return (0);
}

static int
stf_clone_create(struct if_clone *ifc, char *name, size_t len,
    struct ifc_data *ifd, struct ifnet **ifpp)
{
	char *dp;
	int err, unit, wildcard;
	struct stf_softc *sc;
	struct ifnet *ifp;

	err = ifc_name2unit(name, &unit);
	if (err != 0)
		return (err);
	wildcard = (unit < 0);

	/*
	 * We can only have one unit, but since unit allocation is
	 * already locked, we use it to keep from allocating extra
	 * interfaces.
	 */
	unit = STFUNIT;
	err = ifc_alloc_unit(ifc, &unit);
	if (err != 0)
		return (err);

	sc = malloc(sizeof(struct stf_softc), M_STF, M_WAITOK | M_ZERO);
	ifp = STF2IFP(sc) = if_alloc(IFT_STF);
	ifp->if_softc = sc;
	sc->sc_fibnum = curthread->td_proc->p_fibnum;

	/*
	 * Set the name manually rather then using if_initname because
	 * we don't conform to the default naming convention for interfaces.
	 * In the wildcard case, we need to update the name.
	 */
	if (wildcard) {
		for (dp = name; *dp != '\0'; dp++);
		if (snprintf(dp, len - (dp-name), "%d", unit) >
		    len - (dp-name) - 1) {
			/*
			 * This can only be a programmer error and
			 * there's no straightforward way to recover if
			 * it happens.
			 */
			panic("if_clone_create(): interface name too long");
		}
	}
	strlcpy(ifp->if_xname, name, IFNAMSIZ);
	ifp->if_dname = stfname;
	ifp->if_dunit = IF_DUNIT_NONE;

	sc->encap_cookie = ip_encap_attach(&ipv4_encap_cfg, sc, M_WAITOK);

	ifp->if_mtu    = IPV6_MMTU;
	ifp->if_ioctl  = stf_ioctl;
	ifp->if_output = stf_output;
	ifp->if_snd.ifq_maxlen = ifqmaxlen;
	if_attach(ifp);
	bpfattach(ifp, DLT_NULL, sizeof(u_int32_t));
	*ifpp = ifp;

	return (0);
}

static int
stf_clone_destroy(struct if_clone *ifc, struct ifnet *ifp, uint32_t flags)
{
	struct stf_softc *sc = ifp->if_softc;
	int err __unused;

	err = ip_encap_detach(sc->encap_cookie);
	KASSERT(err == 0, ("Unexpected error detaching encap_cookie"));
	bpfdetach(ifp);
	if_detach(ifp);
	if_free(ifp);

	free(sc, M_STF);
	ifc_free_unit(ifc, STFUNIT);

	return (0);
}

static void
vnet_stf_init(const void *unused __unused)
{
	struct if_clone_addreq req = {
		.match_f = stf_clone_match,
		.create_f = stf_clone_create,
		.destroy_f = stf_clone_destroy,
	};
	V_stf_cloner = ifc_attach_cloner(stfname, &req);
}
VNET_SYSINIT(vnet_stf_init, SI_SUB_PSEUDO, SI_ORDER_ANY, vnet_stf_init, NULL);

static void
vnet_stf_uninit(const void *unused __unused)
{
	if_clone_detach(V_stf_cloner);
	V_stf_cloner = NULL;
}
VNET_SYSUNINIT(vnet_stf_uninit, SI_SUB_PSEUDO, SI_ORDER_ANY, vnet_stf_uninit,
    NULL);

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

	switch (type) {
	case MOD_LOAD:
		/* Done in vnet_stf_init() */
		break;
	case MOD_UNLOAD:
		/* Done in vnet_stf_uninit() */
		break;
	default:
		return (EOPNOTSUPP);
	}

	return (0);
}

static moduledata_t stf_mod = {
	"if_stf",
	stfmodevent,
	0
};

DECLARE_MODULE(if_stf, stf_mod, SI_SUB_PSEUDO, SI_ORDER_ANY);
MODULE_VERSION(if_stf, 2);

static int
stf_encapcheck(const struct mbuf *m, int off, int proto, void *arg)
{
	struct ip ip;
	struct stf_softc *sc;
	struct in6_addr addr6, mask6;
	struct sockaddr_in sin4addr, sin4mask;

	SDT_PROBE3(if_stf, , encapcheck, in, m, off, proto);

	sc = (struct stf_softc *)arg;
	if (sc == NULL)
		return (0);

	if ((STF2IFP(sc)->if_flags & IFF_UP) == 0)
		return (0);

	/* IFF_LINK0 means "no decapsulation" */
	if ((STF2IFP(sc)->if_flags & IFF_LINK0) != 0)
		return (0);

	if (proto != IPPROTO_IPV6)
		return (0);

	m_copydata(m, 0, sizeof(ip), (caddr_t)&ip);

	if (ip.ip_v != 4)
		return (0);

	if (stf_getsrcifa6(STF2IFP(sc), &addr6, &mask6) != 0)
		return (0);

	if (sc->srcv4_addr != INADDR_ANY) {
		sin4addr.sin_addr.s_addr = sc->srcv4_addr;
		sin4addr.sin_family = AF_INET;
	} else
		if (stf_getin4addr(sc, &sin4addr, addr6, mask6) == NULL)
			return (0);

	if (sin4addr.sin_addr.s_addr != ip.ip_dst.s_addr)
		return (0);

	if (IN6_IS_ADDR_6TO4(&addr6)) {
		/*
		 * 6to4 (RFC 3056).
		 * Check if IPv4 src matches the IPv4 address derived
		 * from the local 6to4 address masked by prefixmask.
		 * success on: src = 10.1.1.1, ia6->ia_addr = 2002:0a00:.../24
		 * fail on: src = 10.1.1.1, ia6->ia_addr = 2002:0b00:.../24
		 */
		memcpy(&sin4mask.sin_addr, GET_V4(&mask6),
		    sizeof(sin4mask.sin_addr));
		if ((sin4addr.sin_addr.s_addr & sin4mask.sin_addr.s_addr) !=
		    (ip.ip_src.s_addr & sin4mask.sin_addr.s_addr))
			return (0);
	} else {
		/* 6rd (RFC 5569) */
		/*
		 * No restriction on the src address in the case of
		 * 6rd because the stf(4) interface always has a
		 * prefix which covers whole of IPv4 src address
		 * range.  So, stf_output() will catch all of
		 * 6rd-capsuled IPv4 traffic with suspicious inner dst
		 * IPv4 address (i.e. the IPv6 destination address is
		 * one the admin does not like to route to outside),
		 * and then it discard them silently.
		 */
	}

	SDT_PROBE0(if_stf, , encapcheck, accept);

	/* stf interface makes single side match only */
	return (32);
}

static int
stf_getsrcifa6(struct ifnet *ifp, struct in6_addr *addr, struct in6_addr *mask)
{
	struct ifaddr *ia;
	struct in_ifaddr *ia4;
	struct in6_addr addr6, mask6;
	struct sockaddr_in sin4;
	struct stf_softc *sc;
	struct in_addr in;

	NET_EPOCH_ASSERT();

	sc = ifp->if_softc;

	SDT_PROBE3(if_stf, , getsrcifa6, in, ifp, addr, mask);

	CK_STAILQ_FOREACH(ia, &ifp->if_addrhead, ifa_link) {
		if (ia->ifa_addr->sa_family != AF_INET6)
			continue;

		addr6 = *IFA_IN6(ia);
		mask6 = *IFA_MASKIN6(ia);
		if (sc->srcv4_addr != INADDR_ANY)
			bcopy(&sc->srcv4_addr, &in, sizeof(in));
		else {
			if (stf_getin4addr(sc, &sin4, addr6, mask6) == NULL)
				continue;
			bcopy(&sin4.sin_addr, &in, sizeof(in));
		}

		CK_LIST_FOREACH(ia4, INADDR_HASH(in.s_addr), ia_hash)
			if (ia4->ia_addr.sin_addr.s_addr == in.s_addr)
				break;
		if (ia4 == NULL)
			continue;

		*addr = addr6;
		*mask = mask6;

		SDT_PROBE2(if_stf, , getsrcifa6, found, addr, mask);

		return (0);
	}

	SDT_PROBE0(if_stf, , getsrcifa6, notfound);

	return (ENOENT);
}

static int
stf_output(struct ifnet *ifp, struct mbuf *m, const struct sockaddr *dst,
    struct route *ro)
{
	struct stf_softc *sc;
	const struct sockaddr_in6 *dst6;
	struct sockaddr_in dst4, src4;
	u_int8_t tos;
	struct ip *ip;
	struct ip6_hdr *ip6;
	struct in6_addr addr6, mask6;
	int error;

	SDT_PROBE4(if_stf, , stf_output, in, ifp, m, dst, ro);

#ifdef MAC
	error = mac_ifnet_check_transmit(ifp, m);
	if (error) {
		m_freem(m);
		SDT_PROBE2(if_stf, , stf_output, error, error, __LINE__);
		return (error);
	}
#endif

	sc = ifp->if_softc;
	dst6 = (const struct sockaddr_in6 *)dst;

	/* just in case */
	if ((ifp->if_flags & IFF_UP) == 0) {
		m_freem(m);
		if_inc_counter(ifp, IFCOUNTER_OERRORS, 1);
		SDT_PROBE2(if_stf, , stf_output, error, ENETDOWN, __LINE__);
		return (ENETDOWN);
	}

	/*
	 * If we don't have an ip4 address that match my inner ip6 address,
	 * we shouldn't generate output.  Without this check, we'll end up
	 * using wrong IPv4 source.
	 */
	if (stf_getsrcifa6(ifp, &addr6, &mask6) != 0) {
		m_freem(m);
		if_inc_counter(ifp, IFCOUNTER_OERRORS, 1);
		SDT_PROBE2(if_stf, , stf_output, error, ENETDOWN, __LINE__);
		return (ENETDOWN);
	}

	if (m->m_len < sizeof(*ip6)) {
		m = m_pullup(m, sizeof(*ip6));
		if (!m) {
			if_inc_counter(ifp, IFCOUNTER_OERRORS, 1);
			SDT_PROBE2(if_stf, , stf_output, error, ENOBUFS,
			    __LINE__);
			return (ENOBUFS);
		}
	}
	ip6 = mtod(m, struct ip6_hdr *);
	tos = IPV6_TRAFFIC_CLASS(ip6);

	/*
	 * Pickup the right outer dst addr from the list of candidates.
	 * ip6_dst has priority as it may be able to give us shorter IPv4 hops.
	 */
	if (stf_getin4addr_in6(sc, &dst4, addr6, mask6,
	    ip6->ip6_dst) == NULL) {
		if (sc->braddr != INADDR_ANY)
			dst4.sin_addr.s_addr = sc->braddr;
		else if (stf_getin4addr_in6(sc, &dst4, addr6, mask6,
		    dst6->sin6_addr) == NULL) {
			m_freem(m);
			if_inc_counter(ifp, IFCOUNTER_OERRORS, 1);
			SDT_PROBE2(if_stf, , stf_output, error, ENETUNREACH,
			    __LINE__);
			return (ENETUNREACH);
		}
	}

	if (bpf_peers_present(ifp->if_bpf)) {
		/*
		 * We need to prepend the address family as
		 * a four byte field.  Cons up a dummy header
		 * to pacify bpf.  This is safe because bpf
		 * will only read from the mbuf (i.e., it won't
		 * try to free it or keep a pointer a to it).
		 */
		u_int af = AF_INET6;
		bpf_mtap2(ifp->if_bpf, &af, sizeof(af), m);
	}

	M_PREPEND(m, sizeof(struct ip), M_NOWAIT);
	if (m == NULL) {
		if_inc_counter(ifp, IFCOUNTER_OERRORS, 1);
		SDT_PROBE2(if_stf, , stf_output, error, ENOBUFS, __LINE__);
		return (ENOBUFS);
	}
	ip = mtod(m, struct ip *);

	bzero(ip, sizeof(*ip));

	if (sc->srcv4_addr != INADDR_ANY)
		src4.sin_addr.s_addr = sc->srcv4_addr;
	else if (stf_getin4addr(sc, &src4, addr6, mask6) == NULL) {
		m_freem(m);
		if_inc_counter(ifp, IFCOUNTER_OERRORS, 1);
		SDT_PROBE2(if_stf, , stf_output, error, ENETUNREACH, __LINE__);
		return (ENETUNREACH);
	}
	bcopy(&src4.sin_addr, &ip->ip_src, sizeof(ip->ip_src));
	bcopy(&dst4.sin_addr, &ip->ip_dst, sizeof(ip->ip_dst));

	ip->ip_p = IPPROTO_IPV6;
	ip->ip_ttl = ip_stf_ttl;
	ip->ip_len = htons(m->m_pkthdr.len);
	if (ifp->if_flags & IFF_LINK1)
		ip_ecn_ingress(ECN_ALLOWED, &ip->ip_tos, &tos);
	else
		ip_ecn_ingress(ECN_NOCARE, &ip->ip_tos, &tos);

	M_SETFIB(m, sc->sc_fibnum);
	if_inc_counter(ifp, IFCOUNTER_OPACKETS, 1);
	error = ip_output(m, NULL, NULL, 0, NULL, NULL);

	SDT_PROBE1(if_stf, , stf_output, out, error);
	return (error);
}

static int
isrfc1918addr(struct in_addr *in)
{
	/*
	 * returns 1 if private address range:
	 * 10.0.0.0/8 172.16.0.0/12 192.168.0.0/16
	 */
	if (stf_permit_rfc1918 == 0 && (
	    (ntohl(in->s_addr) & 0xff000000) >> 24 == 10 ||
	    (ntohl(in->s_addr) & 0xfff00000) >> 16 == 172 * 256 + 16 ||
	    (ntohl(in->s_addr) & 0xffff0000) >> 16 == 192 * 256 + 168))
		return (1);

	return (0);
}

static int
stf_checkaddr4(struct stf_softc *sc, struct in_addr *in, struct ifnet *inifp)
{
	struct in_ifaddr *ia4;

	/*
	 * reject packets with the following address:
	 * 224.0.0.0/4 0.0.0.0/8 127.0.0.0/8 255.0.0.0/8
	 */
	if (IN_MULTICAST(ntohl(in->s_addr)))
		return (-1);
	switch ((ntohl(in->s_addr) & 0xff000000) >> 24) {
	case 0: case 127: case 255:
		return (-1);
	}

	/*
	 * reject packets with broadcast
	 */
	CK_STAILQ_FOREACH(ia4, &V_in_ifaddrhead, ia_link) {
		if ((ia4->ia_ifa.ifa_ifp->if_flags & IFF_BROADCAST) == 0)
			continue;
		if (in->s_addr == ia4->ia_broadaddr.sin_addr.s_addr) {
			return (-1);
		}
	}

	/*
	 * perform ingress filter
	 */
	if (sc && (STF2IFP(sc)->if_flags & IFF_LINK2) == 0 && inifp) {
		struct nhop_object *nh;

		NET_EPOCH_ASSERT();
		nh = fib4_lookup(sc->sc_fibnum, *in, 0, 0, 0);
		if (nh == NULL)
			return (-1);

		if (nh->nh_ifp != inifp)
			return (-1);
	}

	return (0);
}

static int
stf_checkaddr6(struct stf_softc *sc, struct in6_addr *in6, struct ifnet *inifp)
{
	SDT_PROBE3(if_stf, , checkaddr6, in, sc, in6, inifp);

	/*
	 * check 6to4 addresses
	 */
	if (IN6_IS_ADDR_6TO4(in6)) {
		struct in_addr in4;
		int ret;

		bcopy(GET_V4(in6), &in4, sizeof(in4));
		ret = stf_checkaddr4(sc, &in4, inifp);
		SDT_PROBE2(if_stf, , checkaddr6, out, ret, __LINE__);
		return (ret);
	}

	/*
	 * reject anything that look suspicious.  the test is implemented
	 * in ip6_input too, but we check here as well to
	 * (1) reject bad packets earlier, and
	 * (2) to be safe against future ip6_input change.
	 */
	if (IN6_IS_ADDR_V4COMPAT(in6)) {
		SDT_PROBE2(if_stf, , checkaddr6, out, -1, __LINE__);
		return (-1);
	}

	if (IN6_IS_ADDR_V4MAPPED(in6)) {
		SDT_PROBE2(if_stf, , checkaddr6, out, -1, __LINE__);
		return (-1);
	}

	SDT_PROBE2(if_stf, , checkaddr6, out, 0, __LINE__);
	return (0);
}

static int
in_stf_input(struct mbuf *m, int off, int proto, void *arg)
{
	struct stf_softc *sc = arg;
	struct ip ip;
	struct ip6_hdr *ip6;
	u_int8_t otos, itos;
	struct ifnet *ifp;
	struct nhop_object *nh;

	NET_EPOCH_ASSERT();

	SDT_PROBE3(if_stf, , stf_input, in, m, off, proto);

	if (proto != IPPROTO_IPV6) {
		m_freem(m);
		SDT_PROBE2(if_stf, , stf_input, out, IPPROTO_DONE, __LINE__);
		return (IPPROTO_DONE);
	}

	m_copydata(m, 0, sizeof(struct ip), (caddr_t)&ip);
	if (sc == NULL || (STF2IFP(sc)->if_flags & IFF_UP) == 0) {
		m_freem(m);
		SDT_PROBE2(if_stf, , stf_input, out, IPPROTO_DONE, __LINE__);
		return (IPPROTO_DONE);
	}

	ifp = STF2IFP(sc);

#ifdef MAC
	mac_ifnet_create_mbuf(ifp, m);
#endif

	/*
	 * perform sanity check against outer src/dst.
	 * for source, perform ingress filter as well.
	 */
	if (stf_checkaddr4(sc, &ip.ip_dst, NULL) < 0 ||
	    stf_checkaddr4(sc, &ip.ip_src, m->m_pkthdr.rcvif) < 0) {
		m_freem(m);
		SDT_PROBE2(if_stf, , stf_input, out, IPPROTO_DONE, __LINE__);
		return (IPPROTO_DONE);
	}

	otos = ip.ip_tos;
	m_adj(m, off);

	if (m->m_len < sizeof(*ip6)) {
		m = m_pullup(m, sizeof(*ip6));
		if (!m) {
			SDT_PROBE2(if_stf, , stf_input, out, IPPROTO_DONE,
			    __LINE__);
			return (IPPROTO_DONE);
		}
	}
	ip6 = mtod(m, struct ip6_hdr *);

	/*
	 * perform sanity check against inner src/dst.
	 * for source, perform ingress filter as well.
	 */
	if (stf_checkaddr6(sc, &ip6->ip6_dst, NULL) < 0 ||
	    stf_checkaddr6(sc, &ip6->ip6_src, m->m_pkthdr.rcvif) < 0) {
		m_freem(m);
		SDT_PROBE2(if_stf, , stf_input, out, IPPROTO_DONE, __LINE__);
		return (IPPROTO_DONE);
	}

	/*
	 * reject packets with private address range.
	 * (requirement from RFC3056 section 2 1st paragraph)
	 */
	if ((IN6_IS_ADDR_6TO4(&ip6->ip6_src) && isrfc1918addr(&ip.ip_src)) ||
	    (IN6_IS_ADDR_6TO4(&ip6->ip6_dst) && isrfc1918addr(&ip.ip_dst))) {
		m_freem(m);
		SDT_PROBE2(if_stf, , stf_input, out, IPPROTO_DONE, __LINE__);
		return (IPPROTO_DONE);
	}

	/*
	 * Ignore if the destination is the same stf interface because
	 * all of valid IPv6 outgoing traffic should go interfaces
	 * except for it.
	 */
	nh = fib6_lookup(sc->sc_fibnum, &ip6->ip6_dst, 0, 0, 0);
	if (nh == NULL) {
		m_free(m);
		SDT_PROBE2(if_stf, , stf_input, out, IPPROTO_DONE, __LINE__);
		return (IPPROTO_DONE);
	}
	if ((nh->nh_ifp == ifp) &&
	    (!IN6_ARE_ADDR_EQUAL(&ip6->ip6_src, &nh->gw6_sa.sin6_addr))) {
		m_free(m);
		SDT_PROBE2(if_stf, , stf_input, out, IPPROTO_DONE, __LINE__);
		return (IPPROTO_DONE);
	}

	itos = IPV6_TRAFFIC_CLASS(ip6);
	if ((ifp->if_flags & IFF_LINK1) != 0)
		ip_ecn_egress(ECN_ALLOWED, &otos, &itos);
	else
		ip_ecn_egress(ECN_NOCARE, &otos, &itos);
	ip6->ip6_flow &= ~htonl(0xff << 20);
	ip6->ip6_flow |= htonl((u_int32_t)itos << 20);

	m->m_pkthdr.rcvif = ifp;

	if (bpf_peers_present(ifp->if_bpf)) {
		/*
		 * We need to prepend the address family as
		 * a four byte field.  Cons up a dummy header
		 * to pacify bpf.  This is safe because bpf
		 * will only read from the mbuf (i.e., it won't
		 * try to free it or keep a pointer a to it).
		 */
		u_int32_t af = AF_INET6;
		bpf_mtap2(ifp->if_bpf, &af, sizeof(af), m);
	}

	/*
	 * Put the packet to the network layer input queue according to the
	 * specified address family.
	 * See net/if_gif.c for possible issues with packet processing
	 * reorder due to extra queueing.
	 */
	if_inc_counter(ifp, IFCOUNTER_IPACKETS, 1);
	if_inc_counter(ifp, IFCOUNTER_IBYTES, m->m_pkthdr.len);
	M_SETFIB(m, ifp->if_fib);
	netisr_dispatch(NETISR_IPV6, m);
	SDT_PROBE2(if_stf, , stf_input, out, IPPROTO_DONE, __LINE__);
	return (IPPROTO_DONE);
}

static struct sockaddr_in *
stf_getin4addr_in6(struct stf_softc *sc, struct sockaddr_in *sin,
    struct in6_addr addr6, struct in6_addr mask6, struct in6_addr in6)
{
       int i;
       struct sockaddr_in *out;

	/*
	* When (src addr & src mask) != (in6 & src mask),
	* the dst is not in the 6rd domain.  The IPv4 address must
	* not be used.
	*/
	for (i = 0; i < sizeof(addr6); i++) {
		if ((((u_char *)&addr6)[i] & ((u_char *)&mask6)[i]) !=
		    (((u_char *)&in6)[i] & ((u_char *)&mask6)[i])) {
			SDT_PROBE4(if_stf, , getin4addr_in6, out, &addr6,
			    &mask6, &in6, NULL);
			return (NULL);
		}
	}

	/* After the mask check, use in6 instead of addr6. */
	out = stf_getin4addr(sc, sin, in6, mask6);
	SDT_PROBE4(if_stf, , getin4addr_in6, out, &addr6, &mask6, &in6, out);
	return (out);
}

static struct sockaddr_in *
stf_getin4addr(struct stf_softc *sc, struct sockaddr_in *sin,
    struct in6_addr addr6, struct in6_addr mask6)
{
	struct in_addr *in;

	SDT_PROBE2(if_stf, , getin4addr, in, &addr6, &mask6);

	memset(sin, 0, sizeof(*sin));
	in = &sin->sin_addr;
	if (IN6_IS_ADDR_6TO4(&addr6)) {
		/* 6to4 (RFC 3056) */
		bcopy(GET_V4(&addr6), in, sizeof(*in));
		if (isrfc1918addr(in))
			return (NULL);
	} else {
		/* 6rd (RFC 5569) */
		in_addr_t v4prefix;
		uint8_t *v6 = (uint8_t*)&addr6;
		uint64_t v6prefix;
		u_int plen;
		u_int v4suffixlen;

		v4prefix = 0;
		if (sc->v4prefixlen < 32) {
			v4suffixlen = 32 - sc->v4prefixlen;
			v4prefix = ntohl(sc->srcv4_addr) &
			    (0xffffffffU << v4suffixlen);
		} else {
			MPASS(sc->v4prefixlen == 32);
			v4suffixlen = 32;
		}

		plen = in6_mask2len(&mask6, NULL);
		if (plen > 64)
			return (NULL);

		/* To make this simple we do not support prefixes longer than
		 * 64 bits. RFC5969 says "a 6rd delegated prefix SHOULD be /64
		 * or shorter." so this is a moderately safe assumption. */
		v6prefix = be64toh(*(uint64_t *)v6);

		/* Shift away the v6 prefix itself. */
		v6prefix <<= plen;
		v6prefix >>= plen;

		/* Now shift away everything after the v4 address. */
		v6prefix >>= 64 - plen - v4suffixlen;

		sin->sin_addr.s_addr = htonl(v4prefix | (uint32_t)v6prefix);
	}

	SDT_PROBE1(if_stf, , getin4addr, out, sin);

	return (sin);
}

static int
stf_ioctl(struct ifnet *ifp, u_long cmd, caddr_t data)
{
	struct ifaddr *ifa;
	struct ifdrv *ifd;
	struct ifreq *ifr;
	struct sockaddr_in sin4;
	struct stf_softc *sc_cur;
	struct stfv4args args;
	int error, mtu;

	error = 0;
	sc_cur = ifp->if_softc;

	switch (cmd) {
	case SIOCSDRVSPEC:
		ifd = (struct ifdrv *)data;
		error = priv_check(curthread, PRIV_NET_ADDIFADDR);
		if (error)
			break;
		if (ifd->ifd_cmd == STF6RD_SV4NET) {
			if (ifd->ifd_len != sizeof(args)) {
				error = EINVAL;
				break;
			}
			bzero(&args, sizeof(args));
			error = copyin(ifd->ifd_data, &args, ifd->ifd_len);
			if (error)
				break;

			if (args.v4_prefixlen < 1 || args.v4_prefixlen > 32) {
				error = EINVAL;
				break;
			}

			bcopy(&args.srcv4_addr, &sc_cur->srcv4_addr,
			    sizeof(sc_cur->srcv4_addr));
			sc_cur->v4prefixlen = args.v4_prefixlen;
			SDT_PROBE3(if_stf, , ioctl, sv4net, sc_cur->srcv4_addr,
			    sc_cur->srcv4_addr, sc_cur->v4prefixlen);
		} else if (ifd->ifd_cmd == STF6RD_SBR) {
			if (ifd->ifd_len != sizeof(args)) {
				error = EINVAL;
				break;
			}
			bzero(&args, sizeof(args));
			error = copyin(ifd->ifd_data, &args, ifd->ifd_len);
			if (error)
				break;
			sc_cur->braddr = args.braddr.s_addr;
			SDT_PROBE1(if_stf, , ioctl, sdstv4,
			    sc_cur->braddr);
		} else
			error = EINVAL;
		break;
	case SIOCGDRVSPEC:
		ifd = (struct ifdrv *)data;
		if (ifd->ifd_cmd != STF6RD_GV4NET) {
			error = EINVAL;
			break;
		}
		if (ifd->ifd_len != sizeof(args)) {
			error = EINVAL;
			break;
		}
		bzero(&args, sizeof(args));
		args.srcv4_addr.s_addr = sc_cur->srcv4_addr;
		args.braddr.s_addr = sc_cur->braddr;
		args.v4_prefixlen = sc_cur->v4prefixlen;
		error = copyout(&args, ifd->ifd_data, ifd->ifd_len);
		break;
	case SIOCSIFADDR:
		ifa = (struct ifaddr *)data;
		SDT_PROBE1(if_stf, , ioctl, ifaddr, ifa);
		if (ifa == NULL || ifa->ifa_addr->sa_family != AF_INET6) {
			error = EAFNOSUPPORT;
			break;
		}
		if (stf_getin4addr(sc_cur, &sin4,
		    satosin6(ifa->ifa_addr)->sin6_addr,
		    satosin6(ifa->ifa_netmask)->sin6_addr) == NULL) {
			error = EINVAL;
			break;
		}
		ifp->if_flags |= IFF_UP;
		ifp->if_drv_flags |= IFF_DRV_RUNNING;
		break;

	case SIOCADDMULTI:
	case SIOCDELMULTI:
		ifr = (struct ifreq *)data;
		if (ifr && ifr->ifr_addr.sa_family == AF_INET6)
			;
		else
			error = EAFNOSUPPORT;
		break;

	case SIOCGIFMTU:
		break;

	case SIOCSIFMTU:
		ifr = (struct ifreq *)data;
		mtu = ifr->ifr_mtu;
		/* RFC 4213 3.2 ideal world MTU */
		if (mtu < IPV6_MINMTU || mtu > IF_MAXMTU - 20)
			return (EINVAL);
		ifp->if_mtu = mtu;
		break;

	default:
		error = EINVAL;
		break;
	}

	return (error);
}