ed(1): simplify by using arc4random_buf().

[freebsd-src.git] / sys / net / if_stf.c

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

/*-
 * Copyright (C) 2000 WIDE Project.
 * 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/errno.h>
#include <sys/kernel.h>
#include <sys/lock.h>
#include <sys/module.h>
#include <sys/protosw.h>
#include <sys/proc.h>
#include <sys/queue.h>
#include <sys/rmlock.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_clone.h>
#include <net/route.h>
#include <net/netisr.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/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>

SYSCTL_DECL(_net_link);
static SYSCTL_NODE(_net_link, IFT_STF, stf, CTLFLAG_RW, 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;
        struct mtx      sc_ro_mtx;
        u_int   sc_fibnum;
        const struct encaptab *encap_cookie;
};
#define STF2IFP(sc)     ((sc)->sc_ifp)

static const char stfname[] = "stf";

/*
 * Note that mutable fields in the softc are not currently locked.
 * We do lock sc_ro in stf_output though.
 */
static MALLOC_DEFINE(M_STF, stfname, "6to4 Tunnel Interface");
static const int ip_stf_ttl = 40;

extern  struct domain inetdomain;
static int in_stf_input(struct mbuf **, int *, int);
static struct protosw in_stf_protosw = {
        .pr_type =              SOCK_RAW,
        .pr_domain =            &inetdomain,
        .pr_protocol =          IPPROTO_IPV6,
        .pr_flags =             PR_ATOMIC|PR_ADDR,
        .pr_input =             in_stf_input,
        .pr_output =            rip_output,
        .pr_ctloutput =         rip_ctloutput,
        .pr_usrreqs =           &rip_usrreqs
};

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 int stf_ioctl(struct ifnet *, u_long, caddr_t);

static int stf_clone_match(struct if_clone *, const char *);
static int stf_clone_create(struct if_clone *, char *, size_t, caddr_t);
static int stf_clone_destroy(struct if_clone *, struct ifnet *);
static struct if_clone *stf_cloner;

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, caddr_t params)
{
        int err, unit;
        struct stf_softc *sc;
        struct ifnet *ifp;

        /*
         * 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);
        if (ifp == NULL) {
                free(sc, M_STF);
                ifc_free_unit(ifc, unit);
                return (ENOSPC);
        }
        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.
         */
        strlcpy(ifp->if_xname, name, IFNAMSIZ);
        ifp->if_dname = stfname;
        ifp->if_dunit = IF_DUNIT_NONE;

        mtx_init(&(sc)->sc_ro_mtx, "stf ro", NULL, MTX_DEF);
        sc->encap_cookie = encap_attach_func(AF_INET, IPPROTO_IPV6,
            stf_encapcheck, &in_stf_protosw, sc);
        if (sc->encap_cookie == NULL) {
                if_printf(ifp, "attach failed\n");
                free(sc, M_STF);
                ifc_free_unit(ifc, unit);
                return (ENOMEM);
        }

        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));
        return (0);
}

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

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

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

        return (0);
}

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

        switch (type) {
        case MOD_LOAD:
                stf_cloner = if_clone_advanced(stfname, 0, stf_clone_match,
                    stf_clone_create, stf_clone_destroy);
                break;
        case MOD_UNLOAD:
                if_clone_detach(stf_cloner);
                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);

static int
stf_encapcheck(const struct mbuf *m, int off, int proto, void *arg)
{
        struct ip ip;
        struct stf_softc *sc;
        struct in_addr a, b, mask;
        struct in6_addr addr6, mask6;

        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;

        /* LINTED const cast */
        m_copydata((struct mbuf *)(uintptr_t)m, 0, sizeof(ip), (caddr_t)&ip);

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

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

        /*
         * check if IPv4 dst matches the IPv4 address derived from the
         * local 6to4 address.
         * success on: dst = 10.1.1.1, ia6->ia_addr = 2002:0a01:0101:...
         */
        if (bcmp(GET_V4(&addr6), &ip.ip_dst, sizeof(ip.ip_dst)) != 0)
                return 0;

        /*
         * 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
         */
        bzero(&a, sizeof(a));
        bcopy(GET_V4(&addr6), &a, sizeof(a));
        bcopy(GET_V4(&mask6), &mask, sizeof(mask));
        a.s_addr &= mask.s_addr;
        b = ip.ip_src;
        b.s_addr &= mask.s_addr;
        if (a.s_addr != b.s_addr)
                return 0;

        /* 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_ifaddr *ia6;
        struct sockaddr_in6 *sin6;
        struct in_addr in;

        if_addr_rlock(ifp);
        TAILQ_FOREACH(ia, &ifp->if_addrhead, ifa_link) {
                if (ia->ifa_addr->sa_family != AF_INET6)
                        continue;
                sin6 = (struct sockaddr_in6 *)ia->ifa_addr;
                if (!IN6_IS_ADDR_6TO4(&sin6->sin6_addr))
                        continue;

                bcopy(GET_V4(&sin6->sin6_addr), &in, sizeof(in));
                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;

                ia6 = (struct in6_ifaddr *)ia;

                *addr = sin6->sin6_addr;
                *mask = ia6->ia_prefixmask.sin6_addr;
                if_addr_runlock(ifp);
                return (0);
        }
        if_addr_runlock(ifp);

        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 in_addr in4;
        const void *ptr;
        u_int8_t tos;
        struct ip *ip;
        struct ip6_hdr *ip6;
        struct in6_addr addr6, mask6;
        int error;

#ifdef MAC
        error = mac_ifnet_check_transmit(ifp, m);
        if (error) {
                m_freem(m);
                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);
                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);
                return ENETDOWN;
        }

        if (m->m_len < sizeof(*ip6)) {
                m = m_pullup(m, sizeof(*ip6));
                if (!m) {
                        if_inc_counter(ifp, IFCOUNTER_OERRORS, 1);
                        return ENOBUFS;
                }
        }
        ip6 = mtod(m, struct ip6_hdr *);
        tos = (ntohl(ip6->ip6_flow) >> 20) & 0xff;

        /*
         * 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.
         */
        ptr = NULL;
        if (IN6_IS_ADDR_6TO4(&ip6->ip6_dst))
                ptr = GET_V4(&ip6->ip6_dst);
        else if (IN6_IS_ADDR_6TO4(&dst6->sin6_addr))
                ptr = GET_V4(&dst6->sin6_addr);
        else {
                m_freem(m);
                if_inc_counter(ifp, IFCOUNTER_OERRORS, 1);
                return ENETUNREACH;
        }
        bcopy(ptr, &in4, sizeof(in4));

        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);
                return ENOBUFS;
        }
        ip = mtod(m, struct ip *);

        bzero(ip, sizeof(*ip));

        bcopy(GET_V4(&addr6), &ip->ip_src, sizeof(ip->ip_src));
        bcopy(&in4, &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);

        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 rm_priotracker in_ifa_tracker;
        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 private address range.
         * (requirement from RFC3056 section 2 1st paragraph)
         */
        if (isrfc1918addr(in))
                return -1;

        /*
         * reject packets with broadcast
         */
        IN_IFADDR_RLOCK(&in_ifa_tracker);
        TAILQ_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) {
                        IN_IFADDR_RUNLOCK(&in_ifa_tracker);
                        return -1;
                }
        }
        IN_IFADDR_RUNLOCK(&in_ifa_tracker);

        /*
         * perform ingress filter
         */
        if (sc && (STF2IFP(sc)->if_flags & IFF_LINK2) == 0 && inifp) {
                struct nhop4_basic nh4;

                if (fib4_lookup_nh_basic(sc->sc_fibnum, *in, 0, 0, &nh4) != 0)
                        return (-1);

                if (nh4.nh_ifp != inifp)
                        return (-1);
        }

        return 0;
}

static int
stf_checkaddr6(struct stf_softc *sc, struct in6_addr *in6, struct ifnet *inifp)
{
        /*
         * check 6to4 addresses
         */
        if (IN6_IS_ADDR_6TO4(in6)) {
                struct in_addr in4;
                bcopy(GET_V4(in6), &in4, sizeof(in4));
                return stf_checkaddr4(sc, &in4, inifp);
        }

        /*
         * 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) || IN6_IS_ADDR_V4MAPPED(in6))
                return -1;

        return 0;
}

static int
in_stf_input(struct mbuf **mp, int *offp, int proto)
{
        struct stf_softc *sc;
        struct ip *ip;
        struct ip6_hdr *ip6;
        struct mbuf *m;
        u_int8_t otos, itos;
        struct ifnet *ifp;
        int off;

        m = *mp;
        off = *offp;

        if (proto != IPPROTO_IPV6) {
                m_freem(m);
                return (IPPROTO_DONE);
        }

        ip = mtod(m, struct ip *);

        sc = (struct stf_softc *)encap_getarg(m);

        if (sc == NULL || (STF2IFP(sc)->if_flags & IFF_UP) == 0) {
                m_freem(m);
                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);
                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)
                        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);
                return (IPPROTO_DONE);
        }

        itos = (ntohl(ip6->ip6_flow) >> 20) & 0xff;
        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);
        return (IPPROTO_DONE);
}

static int
stf_ioctl(struct ifnet *ifp, u_long cmd, caddr_t data)
{
        struct ifaddr *ifa;
        struct ifreq *ifr;
        struct sockaddr_in6 *sin6;
        struct in_addr addr;
        int error, mtu;

        error = 0;
        switch (cmd) {
        case SIOCSIFADDR:
                ifa = (struct ifaddr *)data;
                if (ifa == NULL || ifa->ifa_addr->sa_family != AF_INET6) {
                        error = EAFNOSUPPORT;
                        break;
                }
                sin6 = (struct sockaddr_in6 *)ifa->ifa_addr;
                if (!IN6_IS_ADDR_6TO4(&sin6->sin6_addr)) {
                        error = EINVAL;
                        break;
                }
                bcopy(GET_V4(&sin6->sin6_addr), &addr, sizeof(addr));
                if (isrfc1918addr(&addr)) {
                        error = EINVAL;
                        break;
                }

                ifp->if_flags |= IFF_UP;
                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;
}