/*      $FreeBSD: src/sys/netinet6/in6_src.c,v 1.1.2.3 2002/02/26 18:02:06 ume Exp $    */
/*      $KAME: in6_src.c,v 1.37 2001/03/29 05:34:31 itojun Exp $        */

/*
 * Copyright (C) 1995, 1996, 1997, and 1998 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.
 */

/*
 * Copyright (c) 1982, 1986, 1991, 1993
 *      The Regents of the University of California.  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 University 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 REGENTS 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 REGENTS 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.
 *
 *      @(#)in_pcb.c    8.2 (Berkeley) 1/4/94
 */

#include "opt_inet.h"
#include "opt_inet6.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/jail.h>
#include <sys/kernel.h>
#include <sys/malloc.h>
#include <sys/mbuf.h>
#include <sys/protosw.h>
#include <sys/socket.h>
#include <sys/socketvar.h>
#include <sys/sockio.h>
#include <sys/sysctl.h>
#include <sys/errno.h>
#include <sys/time.h>
#include <sys/proc.h>
#include <sys/caps.h>

#include <net/if.h>
#include <net/route.h>

#include <netinet/in.h>
#include <netinet/in_var.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netinet/in_pcb.h>
#include <netinet6/in6_var.h>
#include <netinet/ip6.h>
#include <netinet6/in6_pcb.h>
#include <netinet6/ip6_var.h>
#include <netinet6/nd6.h>
#ifdef ENABLE_DEFAULT_SCOPE
#include <netinet6/scope6_var.h>
#endif

#include <net/net_osdep.h>

#define ADDR_LABEL_NOTAPP (-1)
struct in6_addrpolicy defaultaddrpolicy;

static void     init_policy_queue(void);
static int      add_addrsel_policyent(struct in6_addrpolicy *);
static int      delete_addrsel_policyent(struct in6_addrpolicy *);
static int      walk_addrsel_policy(int (*)(struct in6_addrpolicy *, void *),
                                    void *);
static int      dump_addrsel_policyent(struct in6_addrpolicy *, void *);


/*
 * Return an IPv6 address, which is the most appropriate for a given
 * destination and user specified options.
 * If necessary, this function lookups the routing table and returns
 * an entry to the caller for later use.
 */
struct in6_addr *
in6_selectsrc(struct sockaddr_in6 *dstsock, struct ip6_pktopts *opts,
              struct ip6_moptions *mopts, struct route_in6 *ro,
              struct in6_addr *laddr, int *errorp, struct thread *td)
{
        struct sockaddr_in6 jsin6;
        struct ucred *cred = NULL;
        struct in6_addr *dst;
        struct in6_ifaddr *ia6 = NULL;
        struct in6_pktinfo *pi = NULL;
        int jailed = 0;

        if (td && td->td_proc && td->td_proc->p_ucred)
                cred = td->td_proc->p_ucred;
        if (cred && cred->cr_prison)
                jailed = 1;
        jsin6.sin6_family = AF_INET6;
        dst = &dstsock->sin6_addr;
        *errorp = 0;

        /*
         * If the source address is explicitly specified by the caller,
         * use it.
         */
        if (opts && (pi = opts->ip6po_pktinfo) &&
            !IN6_IS_ADDR_UNSPECIFIED(&pi->ipi6_addr)) {
                jsin6.sin6_addr = pi->ipi6_addr;
                if (jailed && !jailed_ip(cred->cr_prison,
                    (struct sockaddr *)&jsin6)) {
                        return(0);
                } else {
                        return (&pi->ipi6_addr);
                }
        }

        /*
         * If the source address is not specified but the socket(if any)
         * is already bound, use the bound address.
         */
        if (laddr && !IN6_IS_ADDR_UNSPECIFIED(laddr)) {
                jsin6.sin6_addr = *laddr;
                if (jailed && !jailed_ip(cred->cr_prison,
                    (struct sockaddr *)&jsin6)) {
                        return(0);
                } else {
                        return (laddr);
                }
        }

        /*
         * If the caller doesn't specify the source address but
         * the outgoing interface, use an address associated with
         * the interface.
         */
        if (pi && pi->ipi6_ifindex) {
                /* XXX boundary check is assumed to be already done. */
                ia6 = in6_ifawithscope(ifindex2ifnet[pi->ipi6_ifindex],
                                       dst, cred);

                if (ia6 && jailed) {
                        jsin6.sin6_addr = (&ia6->ia_addr)->sin6_addr;
                        if (!jailed_ip(cred->cr_prison,
                                (struct sockaddr *)&jsin6))
                                ia6 = NULL;
                }

                if (ia6 == NULL) {
                        *errorp = EADDRNOTAVAIL;
                        return (0);
                }
                return (&satosin6(&ia6->ia_addr)->sin6_addr);
        }

        /*
         * If the destination address is a link-local unicast address or
         * a multicast address, and if the outgoing interface is specified
         * by the sin6_scope_id filed, use an address associated with the
         * interface.
         * XXX: We're now trying to define more specific semantics of
         *      sin6_scope_id field, so this part will be rewritten in
         *      the near future.
         */
        if ((IN6_IS_ADDR_LINKLOCAL(dst) || IN6_IS_ADDR_MULTICAST(dst)) &&
            dstsock->sin6_scope_id) {
                /*
                 * I'm not sure if boundary check for scope_id is done
                 * somewhere...
                 */
                if (dstsock->sin6_scope_id < 0 ||
                    if_index < dstsock->sin6_scope_id) {
                        *errorp = ENXIO; /* XXX: better error? */
                        return (0);
                }
                ia6 = in6_ifawithscope(ifindex2ifnet[dstsock->sin6_scope_id],
                                       dst, cred);

                if (ia6 && jailed) {
                        jsin6.sin6_addr = (&ia6->ia_addr)->sin6_addr;
                        if (!jailed_ip(cred->cr_prison,
                                (struct sockaddr *)&jsin6))
                                ia6 = NULL;
                }

                if (ia6 == NULL) {
                        *errorp = EADDRNOTAVAIL;
                        return (0);
                }
                return (&satosin6(&ia6->ia_addr)->sin6_addr);
        }

        /*
         * If the destination address is a multicast address and
         * the outgoing interface for the address is specified
         * by the caller, use an address associated with the interface.
         * There is a sanity check here; if the destination has node-local
         * scope, the outgoing interfacde should be a loopback address.
         * Even if the outgoing interface is not specified, we also
         * choose a loopback interface as the outgoing interface.
         */
        if (!jailed && IN6_IS_ADDR_MULTICAST(dst)) {
                struct ifnet *ifp = mopts ? mopts->im6o_multicast_ifp : NULL;

                if (ifp == NULL && IN6_IS_ADDR_MC_INTFACELOCAL(dst)) {
                        ifp = loif;
                }

                if (ifp) {
                        ia6 = in6_ifawithscope(ifp, dst, cred);
                        if (ia6 == NULL) {
                                *errorp = EADDRNOTAVAIL;
                                return (0);
                        }
                        return (&satosin6(&ia6->ia_addr)->sin6_addr);
                }
        }

        /*
         * If the next hop address for the packet is specified
         * by caller, use an address associated with the route
         * to the next hop.
         */
        {
                struct sockaddr_in6 *sin6_next;
                struct rtentry *rt;

                if (opts && opts->ip6po_nexthop) {
                        sin6_next = satosin6(opts->ip6po_nexthop);
                        rt = nd6_lookup(&sin6_next->sin6_addr, 1, NULL);
                        if (rt) {
                                ia6 = in6_ifawithscope(rt->rt_ifp, dst, cred);
                                if (ia6 == NULL)
                                        ia6 = ifatoia6(rt->rt_ifa);
                        }
                        if (ia6 && jailed) {
                                jsin6.sin6_addr = (&ia6->ia_addr)->sin6_addr;
                                if (!jailed_ip(cred->cr_prison,
                                        (struct sockaddr *)&jsin6))
                                        ia6 = NULL;
                        }

                        if (ia6 == NULL) {
                                *errorp = EADDRNOTAVAIL;
                                return (0);
                        }
                        return (&satosin6(&ia6->ia_addr)->sin6_addr);
                }
        }

        /*
         * If route is known or can be allocated now,
         * our src addr is taken from the i/f, else punt.
         */
        if (ro) {
                if (ro->ro_rt &&
                    (!(ro->ro_rt->rt_flags & RTF_UP) ||
                     satosin6(&ro->ro_dst)->sin6_family != AF_INET6 ||
                     !IN6_ARE_ADDR_EQUAL(&satosin6(&ro->ro_dst)->sin6_addr,
                                         dst))) {
                        RTFREE(ro->ro_rt);
                        ro->ro_rt = NULL;
                }
                if (ro->ro_rt == NULL || ro->ro_rt->rt_ifp == NULL) {
                        struct sockaddr_in6 *sa6;

                        /* No route yet, so try to acquire one */
                        bzero(&ro->ro_dst, sizeof(struct sockaddr_in6));
                        sa6 = &ro->ro_dst;
                        sa6->sin6_family = AF_INET6;
                        sa6->sin6_len = sizeof(struct sockaddr_in6);
                        sa6->sin6_addr = *dst;
                        sa6->sin6_scope_id = dstsock->sin6_scope_id;
                        if (!jailed && IN6_IS_ADDR_MULTICAST(dst)) {
                                ro->ro_rt =
                                  rtpurelookup((struct sockaddr *)&ro->ro_dst);
                        } else {
                                rtalloc((struct route *)ro);
                        }
                }

                /*
                 * in_pcbconnect() checks out IFF_LOOPBACK to skip using
                 * the address. But we don't know why it does so.
                 * It is necessary to ensure the scope even for lo0
                 * so doesn't check out IFF_LOOPBACK.
                 */

                if (ro->ro_rt) {
                        ia6 = in6_ifawithscope(ro->ro_rt->rt_ifa->ifa_ifp, dst, cred);
                        if (ia6 && jailed) {
                                jsin6.sin6_addr = (&ia6->ia_addr)->sin6_addr;
                                if (!jailed_ip(cred->cr_prison,
                                        (struct sockaddr *)&jsin6))
                                        ia6 = NULL;
                        }

                        if (ia6 == NULL) /* xxx scope error ?*/
                                ia6 = ifatoia6(ro->ro_rt->rt_ifa);

                        if (ia6 && jailed) {
                                jsin6.sin6_addr = (&ia6->ia_addr)->sin6_addr;
                                if (!jailed_ip(cred->cr_prison,
                                        (struct sockaddr *)&jsin6))
                                        ia6 = NULL;
                        }
                }
                if (ia6 == NULL) {
                        *errorp = EHOSTUNREACH; /* no route */
                        return (0);
                }
                return (&satosin6(&ia6->ia_addr)->sin6_addr);
        }

        *errorp = EADDRNOTAVAIL;
        return (0);
}

/*
 * Default hop limit selection. The precedence is as follows:
 * 1. Hoplimit value specified via ioctl.
 * 2. (If the outgoing interface is detected) the current
 *     hop limit of the interface specified by router advertisement.
 * 3. The system default hoplimit.
*/
int
in6_selecthlim(struct in6pcb *in6p, struct ifnet *ifp)
{
        int hlim;

        if (in6p && in6p->in6p_hops >= 0) {
                return (in6p->in6p_hops);
        } else if (ifp) {
                hlim = ND_IFINFO(ifp)->chlim;
                if (hlim < ip6_minhlim)
                        hlim = ip6_minhlim;
        } else {
                hlim = ip6_defhlim;
        }
        return (hlim);
}

static boolean_t
in6_pcbporthash_update(struct inpcbportinfo *portinfo,
    struct inpcb *inp, u_short lport, struct ucred *cred, int wild)
{
        struct inpcbporthead *porthash;

        /*
         * This has to be atomic.  If the porthash is shared across multiple
         * protocol threads, e.g. tcp and udp, then the token must be held.
         */
        porthash = in_pcbporthash_head(portinfo, lport);
        GET_PORTHASH_TOKEN(porthash);

        if (in6_pcblookup_local(porthash, &inp->in6p_laddr, lport,
            wild, cred) != NULL) {
                REL_PORTHASH_TOKEN(porthash);
                return FALSE;
        }
        inp->inp_lport = lport;
        in_pcbinsporthash(porthash, inp);

        REL_PORTHASH_TOKEN(porthash);
        return TRUE;
}

/*
 * XXX: this is borrowed from in6_pcbbind(). If possible, we should
 * share this function by all *bsd*...
 */
int
in6_pcbsetlport(struct in6_addr *laddr, struct inpcb *inp, struct thread *td)
{
#if 0
        struct socket *so = inp->inp_socket;
#endif
        uint16_t lport, first, last, step, first0, last0;
        int count, error = 0, wild = 0;
        struct inpcbinfo *pcbinfo = inp->inp_pcbinfo;
        struct inpcbportinfo *portinfo;
        struct ucred *cred = NULL;
        int portinfo_first, portinfo_idx;
        uint32_t cut;

#if 0
        /* XXX: this is redundant when called from in6_pcbbind */
        if ((so->so_options & (SO_REUSEADDR|SO_REUSEPORT)) == 0)
                wild = INPLOOKUP_WILDCARD;
#endif
        /*
         * We force matches against wildcard ports in order to
         * avoid auto-assigning lport to such ports, which would
         * cause problems for same-machine connect()s.
         */
        wild = INPLOOKUP_WILDCARD;
        if (td->td_proc && td->td_proc->p_ucred)
                cred = td->td_proc->p_ucred;

        inp->inp_flags |= INP_ANONPORT;

        step = pcbinfo->portinfo_cnt;
        portinfo_first = mycpuid % pcbinfo->portinfo_cnt;
        portinfo_idx = portinfo_first;

        if (inp->inp_flags & INP_HIGHPORT) {
                first0 = ipport_hifirstauto;    /* sysctl */
                last0  = ipport_hilastauto;
        } else if (inp->inp_flags & INP_LOWPORT) {
                error = caps_priv_check_td(td, SYSCAP_RESTRICTEDROOT);
                if (error)
                        return error;
                first0 = ipport_lowfirstauto;   /* 1023 */
                last0  = ipport_lowlastauto;    /* 600 */
        } else {
                first0 = ipport_firstauto;      /* sysctl */
                last0  = ipport_lastauto;
        }
        if (first0 > last0) {
                lport = last0;
                last0 = first0;
                first0 = lport;
        }
        KKASSERT(last0 >= first0);

        cut = karc4random();
loop:
        portinfo = &pcbinfo->portinfo[portinfo_idx];
        first = first0;
        last = last0;

        /*
         * Simple check to ensure all ports are not used up causing
         * a deadlock here.
         */
        in_pcbportrange(&last, &first, portinfo->offset, step);
        lport = last - first;
        count = lport / step;

        lport = rounddown(cut % lport, step) + first;
        KKASSERT(lport % step == portinfo->offset);

        for (;;) {
                if (count-- < 0) {      /* completely used? */
                        error = EAGAIN;
                        break;
                }

                if (__predict_false(lport < first || lport > last)) {
                        lport = first;
                        KKASSERT(lport % step == portinfo->offset);
                }

                if (in6_pcbporthash_update(portinfo, inp, htons(lport),
                    cred, wild)) {
                        error = 0;
                        break;
                }

                lport += step;
                KKASSERT(lport % step == portinfo->offset);
        }

        if (error) {
                /* Try next portinfo */
                portinfo_idx++;
                portinfo_idx %= pcbinfo->portinfo_cnt;
                if (portinfo_idx != portinfo_first)
                        goto loop;

                /* Undo any address bind that may have occurred above. */
                inp->in6p_laddr = kin6addr_any;
        }
        return error;
}

/*
 * Generate kernel-internal form (scopeid embedded into s6_addr16[1]).
 * If the address scope of is link-local, embed the interface index in the
 * address.  The routine determines our precedence
 * between advanced API scope/interface specification and basic API
 * specification.
 *
 * This function should be nuked in the future, when we get rid of embedded
 * scopeid thing.
 *
 * XXX actually, it is over-specification to return ifp against sin6_scope_id.
 * there can be multiple interfaces that belong to a particular scope zone
 * (in specification, we have 1:N mapping between a scope zone and interfaces).
 * we may want to change the function to return something other than ifp.
 */
int
in6_embedscope(struct in6_addr *in6,
               const struct sockaddr_in6 *sin6,
#ifdef HAVE_NRL_INPCB
               struct inpcb *in6p,
#define in6p_outputopts inp_outputopts6
#define in6p_moptions   inp_moptions6
#else
               struct in6pcb *in6p,
#endif
               struct ifnet **ifpp)
{
        struct ifnet *ifp = NULL;
        u_int32_t scopeid;

        *in6 = sin6->sin6_addr;
        scopeid = sin6->sin6_scope_id;
        if (ifpp)
                *ifpp = NULL;

        /*
         * don't try to read sin6->sin6_addr beyond here, since the caller may
         * ask us to overwrite existing sockaddr_in6
         */

#ifdef ENABLE_DEFAULT_SCOPE
        if (scopeid == 0)
                scopeid = scope6_addr2default(in6);
#endif

        if (IN6_IS_SCOPE_LINKLOCAL(in6)) {
                struct in6_pktinfo *pi;

                /*
                 * KAME assumption: link id == interface id
                 */

                if (in6p && in6p->in6p_outputopts &&
                    (pi = in6p->in6p_outputopts->ip6po_pktinfo) &&
                    pi->ipi6_ifindex) {
                        ifp = ifindex2ifnet[pi->ipi6_ifindex];
                        in6->s6_addr16[1] = htons(pi->ipi6_ifindex);
                } else if (in6p && IN6_IS_ADDR_MULTICAST(in6) &&
                           in6p->in6p_moptions &&
                           in6p->in6p_moptions->im6o_multicast_ifp) {
                        ifp = in6p->in6p_moptions->im6o_multicast_ifp;
                        in6->s6_addr16[1] = htons(ifp->if_index);
                } else if (scopeid) {
                        /* boundary check */
                        if (scopeid < 0 || if_index < scopeid)
                                return ENXIO;  /* XXX EINVAL? */
                        ifp = ifindex2ifnet[scopeid];
                        /* XXX assignment to 16bit from 32bit variable */
                        in6->s6_addr16[1] = htons(scopeid & 0xffff);
                }

                if (ifpp)
                        *ifpp = ifp;
        }

        return 0;
}
#ifdef HAVE_NRL_INPCB
#undef in6p_outputopts
#undef in6p_moptions
#endif

/*
 * generate standard sockaddr_in6 from embedded form.
 * touches sin6_addr and sin6_scope_id only.
 *
 * this function should be nuked in the future, when we get rid of
 * embedded scopeid thing.
 */
int
in6_recoverscope(struct sockaddr_in6 *sin6, const struct in6_addr *in6,
                 struct ifnet *ifp)
{
        u_int32_t zoneid;

        sin6->sin6_addr = *in6;

        /*
         * don't try to read *in6 beyond here, since the caller may
         * ask us to overwrite existing sockaddr_in6
         */

        sin6->sin6_scope_id = 0;
        if (IN6_IS_SCOPE_LINKLOCAL(in6) || IN6_IS_ADDR_MC_INTFACELOCAL(in6)) {
                /*
                 * KAME assumption: link id == interface id
                 */
                zoneid = ntohs(sin6->sin6_addr.s6_addr16[1]);
                if (zoneid) {
                        /* sanity check */
                        if (zoneid < 0 || if_index < zoneid)
                                return ENXIO;
                        if (ifp && ifp->if_index != zoneid)
                                return ENXIO;
                        sin6->sin6_addr.s6_addr16[1] = 0;
                        sin6->sin6_scope_id = zoneid;
                }
        }

        return 0;
}

/*
 * just clear the embedded scope identifier.
 */
void
in6_clearscope(struct in6_addr *addr)
{
        if (IN6_IS_SCOPE_LINKLOCAL(addr) || IN6_IS_ADDR_MC_INTFACELOCAL(addr))
                addr->s6_addr16[1] = 0;
}

void
addrsel_policy_init(void)
{

        init_policy_queue();

        /* initialize the "last resort" policy */
        bzero(&defaultaddrpolicy, sizeof(defaultaddrpolicy));
        defaultaddrpolicy.label = ADDR_LABEL_NOTAPP;
}

/*
 * Subroutines to manage the address selection policy table via sysctl.
 */
struct walkarg {
        struct sysctl_req *w_req;
};

static int in6_src_sysctl(SYSCTL_HANDLER_ARGS);
SYSCTL_DECL(_net_inet6_ip6);
SYSCTL_NODE(_net_inet6_ip6, IPV6CTL_ADDRCTLPOLICY, addrctlpolicy,
        CTLFLAG_RD, in6_src_sysctl, "Address selection policy");

static int
in6_src_sysctl(SYSCTL_HANDLER_ARGS)
{
        struct walkarg w;

        if (req->newptr)
                return EPERM;

        bzero(&w, sizeof(w));
        w.w_req = req;

        return (walk_addrsel_policy(dump_addrsel_policyent, &w));
}

int
in6_src_ioctl(u_long cmd, caddr_t data)
{
        int i;
        struct in6_addrpolicy ent0;

        if (cmd != SIOCAADDRCTL_POLICY && cmd != SIOCDADDRCTL_POLICY)
                return (EOPNOTSUPP); /* check for safety */

        ent0 = *(struct in6_addrpolicy *)data;

        if (ent0.label == ADDR_LABEL_NOTAPP)
                return (EINVAL);
        /* check if the prefix mask is consecutive. */
        if (in6_mask2len(&ent0.addrmask.sin6_addr, NULL) < 0)
                return (EINVAL);
        /* clear trailing garbages (if any) of the prefix address. */
        for (i = 0; i < 4; i++) {
                ent0.addr.sin6_addr.s6_addr32[i] &=
                        ent0.addrmask.sin6_addr.s6_addr32[i];
        }
        ent0.use = 0;

        switch (cmd) {
        case SIOCAADDRCTL_POLICY:
                return (add_addrsel_policyent(&ent0));
        case SIOCDADDRCTL_POLICY:
                return (delete_addrsel_policyent(&ent0));
        }

        return (0);             /* XXX: compromise compilers */
}

/*
 * The followings are implementation of the policy table using a
 * simple tail queue.
 * XXX such details should be hidden.
 * XXX implementation using binary tree should be more efficient.
 */
struct addrsel_policyent {
        TAILQ_ENTRY(addrsel_policyent) ape_entry;
        struct in6_addrpolicy ape_policy;
};

TAILQ_HEAD(addrsel_policyhead, addrsel_policyent);

struct addrsel_policyhead addrsel_policytab;

static void
init_policy_queue(void)
{
        TAILQ_INIT(&addrsel_policytab);
}

static int
add_addrsel_policyent(struct in6_addrpolicy *newpolicy)
{
        struct addrsel_policyent *new, *pol;

        /* duplication check */
        for (pol = TAILQ_FIRST(&addrsel_policytab); pol;
             pol = TAILQ_NEXT(pol, ape_entry)) {
                if (SA6_ARE_ADDR_EQUAL(&newpolicy->addr,
                                       &pol->ape_policy.addr) &&
                    SA6_ARE_ADDR_EQUAL(&newpolicy->addrmask,
                                       &pol->ape_policy.addrmask)) {
                        return (EEXIST);        /* or override it? */
                }
        }

        new = kmalloc(sizeof(*new), M_IFADDR, M_WAITOK | M_ZERO);

        /* XXX: should validate entry */
        new->ape_policy = *newpolicy;

        TAILQ_INSERT_TAIL(&addrsel_policytab, new, ape_entry);

        return (0);
}

static int
delete_addrsel_policyent(struct in6_addrpolicy *key)
{
        struct addrsel_policyent *pol;

        /* search for the entry in the table */
        for (pol = TAILQ_FIRST(&addrsel_policytab); pol;
             pol = TAILQ_NEXT(pol, ape_entry)) {
                if (SA6_ARE_ADDR_EQUAL(&key->addr, &pol->ape_policy.addr) &&
                    SA6_ARE_ADDR_EQUAL(&key->addrmask,
                                       &pol->ape_policy.addrmask)) {
                        break;
                }
        }
        if (pol == NULL)
                return (ESRCH);

        TAILQ_REMOVE(&addrsel_policytab, pol, ape_entry);
        kfree(pol, M_IFADDR);

        return (0);
}

static int
walk_addrsel_policy(int(*callback)(struct in6_addrpolicy *, void *), void *w)
{
        struct addrsel_policyent *pol;
        int error = 0;

        for (pol = TAILQ_FIRST(&addrsel_policytab); pol;
             pol = TAILQ_NEXT(pol, ape_entry)) {
                if ((error = (*callback)(&pol->ape_policy, w)) != 0)
                        return (error);
        }

        return (error);
}

static int
dump_addrsel_policyent(struct in6_addrpolicy *pol, void *arg)
{
        int error = 0;
        struct walkarg *w = arg;

        error = SYSCTL_OUT(w->w_req, pol, sizeof(*pol));

        return (error);
}