/*      $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/stdarg.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 <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);
}