xnu-4570.20.62.tar.gz

[apple/xnu.git] / bsd / netinet6 / in6_src.c

/*
 * Copyright (c) 2000-2016 Apple Inc. All rights reserved.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
 *
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. The rights granted to you under the License
 * may not be used to create, or enable the creation or redistribution of,
 * unlawful or unlicensed copies of an Apple operating system, or to
 * circumvent, violate, or enable the circumvention or violation of, any
 * terms of an Apple operating system software license agreement.
 *
 * Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this file.
 *
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
 */

/*
 * 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. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. 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 <sys/param.h>
#include <sys/systm.h>
#include <sys/malloc.h>
#include <sys/mbuf.h>
#include <sys/protosw.h>
#include <sys/socket.h>
#include <sys/socketvar.h>
#include <sys/errno.h>
#include <sys/time.h>
#include <sys/proc.h>
#include <sys/sysctl.h>
#include <sys/kauth.h>
#include <sys/priv.h>
#include <kern/locks.h>

#include <net/if.h>
#include <net/if_types.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/scope6_var.h>
#include <netinet6/nd6.h>

#include <net/net_osdep.h>

#include "loop.h"

SYSCTL_DECL(_net_inet6_ip6);

static int ip6_select_srcif_debug = 0;
SYSCTL_INT(_net_inet6_ip6, OID_AUTO, select_srcif_debug,
        CTLFLAG_RW | CTLFLAG_LOCKED, &ip6_select_srcif_debug, 0,
        "log source interface selection debug info");

static int ip6_select_srcaddr_debug = 0;
SYSCTL_INT(_net_inet6_ip6, OID_AUTO, select_srcaddr_debug,
        CTLFLAG_RW | CTLFLAG_LOCKED, &ip6_select_srcaddr_debug, 0,
        "log source address selection debug info");

static int ip6_select_src_expensive_secondary_if = 0;
SYSCTL_INT(_net_inet6_ip6, OID_AUTO, select_src_expensive_secondary_if,
        CTLFLAG_RW | CTLFLAG_LOCKED, &ip6_select_src_expensive_secondary_if, 0,
        "allow source interface selection to use expensive secondaries");

static int ip6_select_src_strong_end = 1;
SYSCTL_INT(_net_inet6_ip6, OID_AUTO, select_src_strong_end,
        CTLFLAG_RW | CTLFLAG_LOCKED, &ip6_select_src_strong_end, 0,
        "limit source address selection to outgoing interface");

#define ADDR_LABEL_NOTAPP (-1)
struct in6_addrpolicy defaultaddrpolicy;

int ip6_prefer_tempaddr = 1;
#ifdef ENABLE_ADDRSEL
extern lck_mtx_t *addrsel_mutex;
#define ADDRSEL_LOCK()          lck_mtx_lock(addrsel_mutex)
#define ADDRSEL_UNLOCK()        lck_mtx_unlock(addrsel_mutex)
#else
#define ADDRSEL_LOCK()
#define ADDRSEL_UNLOCK()
#endif

static int selectroute(struct sockaddr_in6 *, struct sockaddr_in6 *,
        struct ip6_pktopts *, struct ip6_moptions *, struct in6_ifaddr **,
        struct route_in6 *, struct ifnet **, struct rtentry **, int, int,
        struct ip6_out_args *ip6oa);
static int in6_selectif(struct sockaddr_in6 *, struct ip6_pktopts *,
        struct ip6_moptions *, struct route_in6 *ro,
        struct ip6_out_args *, struct ifnet **);
static void init_policy_queue(void);
static int add_addrsel_policyent(const struct in6_addrpolicy *);
#ifdef ENABLE_ADDRSEL
static int delete_addrsel_policyent(const struct in6_addrpolicy *);
#endif
static int walk_addrsel_policy(int (*)(const struct in6_addrpolicy *, void *),
        void *);
static int dump_addrsel_policyent(const struct in6_addrpolicy *, void *);
static struct in6_addrpolicy *match_addrsel_policy(struct sockaddr_in6 *);
void addrsel_policy_init(void);

#define SASEL_DO_DBG(inp) \
        (ip6_select_srcaddr_debug && (inp) != NULL && \
            (inp)->inp_socket != NULL && \
            ((inp)->inp_socket->so_options & SO_DEBUG))

#define SASEL_LOG(fmt, ...) \
do { \
        if (srcsel_debug) \
                printf("%s:%d " fmt "\n",\
                    __FUNCTION__, __LINE__, ##__VA_ARGS__); \
} while (0); \

/*
 * 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.
 */
#define REPLACE(r) do {\
        SASEL_LOG("REPLACE r %d ia %s ifp1 %s\n", \
            (r), s_src, ifp1->if_xname); \
        srcrule = (r); \
        goto replace; \
} while (0)

#define NEXTSRC(r) do {\
        SASEL_LOG("NEXTSRC r %d ia %s ifp1 %s\n", \
            (r), s_src, ifp1->if_xname); \
        goto next;              /* XXX: we can't use 'continue' here */ \
} while (0)

#define BREAK(r) do { \
        SASEL_LOG("BREAK r %d ia %s ifp1 %s\n", \
            (r), s_src, ifp1->if_xname); \
        srcrule = (r); \
        goto out;               /* XXX: we can't use 'break' here */ \
} while (0)

struct in6_addr *
in6_selectsrc_core(struct sockaddr_in6 *dstsock, uint32_t hint_mask,
    struct ifnet *ifp, int srcsel_debug, struct in6_addr *src_storage,
    struct ifnet **sifp, int *errorp, struct ifaddr **ifapp)
{
        u_int32_t odstzone;
        int bestrule = IP6S_SRCRULE_0;
        struct in6_addrpolicy *dst_policy = NULL, *best_policy = NULL;
        struct in6_addr dst;
        struct in6_ifaddr *ia = NULL, *ia_best = NULL;
        char s_src[MAX_IPv6_STR_LEN] = {0};
        char s_dst[MAX_IPv6_STR_LEN] = {0};
        const struct in6_addr *tmp = NULL;
        int dst_scope = -1, best_scope = -1, best_matchlen = -1;
        uint64_t secs = net_uptime();
        VERIFY(dstsock != NULL);
        VERIFY(src_storage != NULL);
        VERIFY(ifp != NULL);

        if (sifp != NULL)
                *sifp = NULL;

        if (ifapp != NULL)
                *ifapp = NULL;

        dst = dstsock->sin6_addr; /* make a copy for local operation */

        if (srcsel_debug) {
                (void) inet_ntop(AF_INET6, &dst, s_dst, sizeof (s_src));

                tmp = &in6addr_any;
                (void) inet_ntop(AF_INET6, tmp, s_src, sizeof (s_src));
                printf("%s out src %s dst %s ifp %s\n",
                    __func__, s_src, s_dst, ifp->if_xname);
        }

        *errorp = in6_setscope(&dst, ifp, &odstzone);
        if (*errorp != 0) {
                src_storage = NULL;
                goto done;
        }

        lck_rw_lock_shared(&in6_ifaddr_rwlock);
        for (ia = in6_ifaddrs; ia; ia = ia->ia_next) {
                int new_scope = -1, new_matchlen = -1;
                struct in6_addrpolicy *new_policy = NULL;
                u_int32_t srczone = 0, osrczone, dstzone;
                struct in6_addr src;
                struct ifnet *ifp1 = ia->ia_ifp;
                int srcrule;

                if (srcsel_debug)
                        (void) inet_ntop(AF_INET6, &ia->ia_addr.sin6_addr,
                            s_src, sizeof (s_src));

                IFA_LOCK(&ia->ia_ifa);

                /*
                 * XXX By default we are strong end system and will
                 * limit candidate set of source address to the ones
                 * configured on the outgoing interface.
                 */
                if (ip6_select_src_strong_end &&
                    ifp1 != ifp) {
                        SASEL_LOG("NEXT ia %s ifp1 %s address is not on outgoing "
                            "interface \n", s_src, ifp1->if_xname);
                        goto next;
                }

                /*
                 * We'll never take an address that breaks the scope zone
                 * of the destination. We also skip an address if its zone
                 * does not contain the outgoing interface.
                 * XXX: we should probably use sin6_scope_id here.
                 */
                if (in6_setscope(&dst, ifp1, &dstzone) ||
                    odstzone != dstzone) {
                        SASEL_LOG("NEXT ia %s ifp1 %s odstzone %d != dstzone %d\n",
                            s_src, ifp1->if_xname, odstzone, dstzone);
                        goto next;
                }
                src = ia->ia_addr.sin6_addr;
                if (in6_setscope(&src, ifp, &osrczone) ||
                    in6_setscope(&src, ifp1, &srczone) ||
                    osrczone != srczone) {
                        SASEL_LOG("NEXT ia %s ifp1 %s osrczone %d != srczone %d\n",
                            s_src, ifp1->if_xname, osrczone, srczone);
                        goto next;
                }
                /* avoid unusable addresses */
                if ((ia->ia6_flags &
                    (IN6_IFF_NOTREADY | IN6_IFF_ANYCAST | IN6_IFF_DETACHED))) {
                        SASEL_LOG("NEXT ia %s ifp1 %s ia6_flags 0x%x\n",
                            s_src, ifp1->if_xname, ia->ia6_flags);
                        goto next;
                }
                if (!ip6_use_deprecated && IFA6_IS_DEPRECATED(ia, secs)) {
                        SASEL_LOG("NEXT ia %s ifp1 %s IFA6_IS_DEPRECATED\n",
                            s_src, ifp1->if_xname);
                        goto next;
                }
                if (!nd6_optimistic_dad &&
                    (ia->ia6_flags & IN6_IFF_OPTIMISTIC) != 0) {
                        SASEL_LOG("NEXT ia %s ifp1 %s IN6_IFF_OPTIMISTIC\n",
                            s_src, ifp1->if_xname);
                        goto next;
                }
                /* Rule 1: Prefer same address */
                if (IN6_ARE_ADDR_EQUAL(&dst, &ia->ia_addr.sin6_addr))
                        BREAK(IP6S_SRCRULE_1); /* there should be no better candidate */

                if (ia_best == NULL)
                        REPLACE(IP6S_SRCRULE_0);

                /* Rule 2: Prefer appropriate scope */
                if (dst_scope < 0)
                        dst_scope = in6_addrscope(&dst);
                new_scope = in6_addrscope(&ia->ia_addr.sin6_addr);
                if (IN6_ARE_SCOPE_CMP(best_scope, new_scope) < 0) {
                        if (IN6_ARE_SCOPE_CMP(best_scope, dst_scope) < 0)
                                REPLACE(IP6S_SRCRULE_2);
                        NEXTSRC(IP6S_SRCRULE_2);
                } else if (IN6_ARE_SCOPE_CMP(new_scope, best_scope) < 0) {
                        if (IN6_ARE_SCOPE_CMP(new_scope, dst_scope) < 0)
                                NEXTSRC(IP6S_SRCRULE_2);
                        REPLACE(IP6S_SRCRULE_2);
                }

                /*
                 * Rule 3: Avoid deprecated addresses.  Note that the case of
                 * !ip6_use_deprecated is already rejected above.
                 */
                if (!IFA6_IS_DEPRECATED(ia_best, secs) &&
                    IFA6_IS_DEPRECATED(ia, secs))
                        NEXTSRC(IP6S_SRCRULE_3);
                if (IFA6_IS_DEPRECATED(ia_best, secs) &&
                    !IFA6_IS_DEPRECATED(ia, secs))
                        REPLACE(IP6S_SRCRULE_3);

                /*
                 * RFC 4429 says that optimistic addresses are equivalent to
                 * deprecated addresses, so avoid them here.
                 */
                if ((ia_best->ia6_flags & IN6_IFF_OPTIMISTIC) == 0 &&
                    (ia->ia6_flags & IN6_IFF_OPTIMISTIC) != 0)
                        NEXTSRC(IP6S_SRCRULE_3);
                if ((ia_best->ia6_flags & IN6_IFF_OPTIMISTIC) != 0 &&
                    (ia->ia6_flags & IN6_IFF_OPTIMISTIC) == 0)
                        REPLACE(IP6S_SRCRULE_3);

                /* Rule 4: Prefer home addresses */
                /*
                 * XXX: This is a TODO.  We should probably merge the MIP6
                 * case above.
                 */

                /* Rule 5: Prefer outgoing interface */
                /*
                 * XXX By default we are strong end with source address
                 * selection. That means all address selection candidate
                 * addresses will be the ones hosted on the outgoing interface
                 * making the following check redundant.
                 */
                if (ip6_select_src_strong_end == 0) {
                        if (ia_best->ia_ifp == ifp && ia->ia_ifp != ifp)
                                NEXTSRC(IP6S_SRCRULE_5);
                        if (ia_best->ia_ifp != ifp && ia->ia_ifp == ifp)
                                REPLACE(IP6S_SRCRULE_5);
                }

                /*
                 * Rule 6: Prefer matching label
                 * Note that best_policy should be non-NULL here.
                 */
                if (dst_policy == NULL)
                        dst_policy = in6_addrsel_lookup_policy(dstsock);
                if (dst_policy->label != ADDR_LABEL_NOTAPP) {
                        new_policy = in6_addrsel_lookup_policy(&ia->ia_addr);
                        if (dst_policy->label == best_policy->label &&
                            dst_policy->label != new_policy->label)
                                NEXTSRC(IP6S_SRCRULE_6);
                        if (dst_policy->label != best_policy->label &&
                            dst_policy->label == new_policy->label)
                                REPLACE(IP6S_SRCRULE_6);
                }

                /*
                 * Rule 7: Prefer temporary addresses.
                 * We allow users to reverse the logic by configuring
                 * a sysctl variable, so that transparency conscious users can
                 * always prefer stable addresses.
                 */
                if (!(ia_best->ia6_flags & IN6_IFF_TEMPORARY) &&
                    (ia->ia6_flags & IN6_IFF_TEMPORARY)) {
                        if (hint_mask & IPV6_SRCSEL_HINT_PREFER_TMPADDR)
                                REPLACE(IP6S_SRCRULE_7);
                        else
                                NEXTSRC(IP6S_SRCRULE_7);
                }
                if ((ia_best->ia6_flags & IN6_IFF_TEMPORARY) &&
                    !(ia->ia6_flags & IN6_IFF_TEMPORARY)) {
                        if (hint_mask & IPV6_SRCSEL_HINT_PREFER_TMPADDR)
                                NEXTSRC(IP6S_SRCRULE_7);
                        else
                                REPLACE(IP6S_SRCRULE_7);
                }

                /*
                 * Rule 7x: prefer addresses on alive interfaces.
                 * This is a KAME specific rule.
                 */
                if ((ia_best->ia_ifp->if_flags & IFF_UP) &&
                    !(ia->ia_ifp->if_flags & IFF_UP))
                        NEXTSRC(IP6S_SRCRULE_7x);
                if (!(ia_best->ia_ifp->if_flags & IFF_UP) &&
                    (ia->ia_ifp->if_flags & IFF_UP))
                        REPLACE(IP6S_SRCRULE_7x);

                /*
                 * Rule 8: Use longest matching prefix.
                 */
                new_matchlen = in6_matchlen(&ia->ia_addr.sin6_addr, &dst);
                if (best_matchlen < new_matchlen)
                        REPLACE(IP6S_SRCRULE_8);
                if (new_matchlen < best_matchlen)
                        NEXTSRC(IP6S_SRCRULE_8);

                /*
                 * Last resort: just keep the current candidate.
                 * Or, do we need more rules?
                 */
                if (ifp1 != ifp && (ifp1->if_eflags & IFEF_EXPENSIVE) &&
                    ip6_select_src_expensive_secondary_if == 0) {
                        SASEL_LOG("NEXT ia %s ifp1 %s IFEF_EXPENSIVE\n",
                            s_src, ifp1->if_xname);
                        ip6stat.ip6s_sources_skip_expensive_secondary_if++;
                        goto next;
                }
                SASEL_LOG("NEXT ia %s ifp1 %s last resort\n",
                    s_src, ifp1->if_xname);
                IFA_UNLOCK(&ia->ia_ifa);
                continue;

replace:
                /*
                 * Ignore addresses on secondary interfaces that are marked
                 * expensive
                 */
                if (ifp1 != ifp && (ifp1->if_eflags & IFEF_EXPENSIVE) &&
                    ip6_select_src_expensive_secondary_if == 0) {
                        SASEL_LOG("NEXT ia %s ifp1 %s IFEF_EXPENSIVE\n",
                            s_src, ifp1->if_xname);
                        ip6stat.ip6s_sources_skip_expensive_secondary_if++;
                        goto next;
                }
                bestrule = srcrule;
                best_scope = (new_scope >= 0 ? new_scope :
                    in6_addrscope(&ia->ia_addr.sin6_addr));
                best_policy = (new_policy ? new_policy :
                    in6_addrsel_lookup_policy(&ia->ia_addr));
                best_matchlen = (new_matchlen >= 0 ? new_matchlen :
                    in6_matchlen(&ia->ia_addr.sin6_addr, &dst));
                SASEL_LOG("NEXT ia %s ifp1 %s best_scope %d new_scope %d dst_scope %d\n",
                    s_src, ifp1->if_xname, best_scope, new_scope, dst_scope);
                IFA_ADDREF_LOCKED(&ia->ia_ifa); /* for ia_best */
                IFA_UNLOCK(&ia->ia_ifa);
                if (ia_best != NULL)
                        IFA_REMREF(&ia_best->ia_ifa);
                ia_best = ia;
                continue;

next:
                IFA_UNLOCK(&ia->ia_ifa);
                continue;

out:
                IFA_ADDREF_LOCKED(&ia->ia_ifa); /* for ia_best */
                IFA_UNLOCK(&ia->ia_ifa);
                if (ia_best != NULL)
                        IFA_REMREF(&ia_best->ia_ifa);
                ia_best = ia;
                break;
        }

        lck_rw_done(&in6_ifaddr_rwlock);

        if ((ia = ia_best) == NULL) {
                if (*errorp == 0)
                        *errorp = EADDRNOTAVAIL;
                src_storage = NULL;
                goto done;
        }

        if (sifp != NULL) {
                *sifp = ia->ia_ifa.ifa_ifp;
                ifnet_reference(*sifp);
        }

        IFA_LOCK_SPIN(&ia->ia_ifa);
        if (bestrule < IP6S_SRCRULE_COUNT)
                ip6stat.ip6s_sources_rule[bestrule]++;
        *src_storage = satosin6(&ia->ia_addr)->sin6_addr;
        IFA_UNLOCK(&ia->ia_ifa);

        if (ifapp != NULL)
                *ifapp = &ia->ia_ifa;
        else
                IFA_REMREF(&ia->ia_ifa);

done:
        if (srcsel_debug) {
                (void) inet_ntop(AF_INET6, &dst, s_dst, sizeof (s_src));

                tmp = (src_storage != NULL) ? src_storage : &in6addr_any;
                (void) inet_ntop(AF_INET6, tmp, s_src, sizeof (s_src));

                printf("%s out src %s dst %s dst_scope %d best_scope %d\n",
                    __func__, s_src, s_dst, dst_scope, best_scope);
        }

        return (src_storage);
}

/*
 * Regardless of error, it will return an ifp with a reference held if the
 * caller provides a non-NULL ifpp.  The caller is responsible for checking
 * if the returned ifp is valid and release its reference at all times.
 */
struct in6_addr *
in6_selectsrc(struct sockaddr_in6 *dstsock, struct ip6_pktopts *opts,
    struct inpcb *inp, struct route_in6 *ro,
    struct ifnet **ifpp, struct in6_addr *src_storage, unsigned int ifscope,
    int *errorp)
{
        struct ifnet *ifp = NULL;
        struct in6_pktinfo *pi = NULL;
        struct ip6_moptions *mopts;
        struct ip6_out_args ip6oa = { ifscope, { 0 }, IP6OAF_SELECT_SRCIF, 0,
            SO_TC_UNSPEC, _NET_SERVICE_TYPE_UNSPEC };
        boolean_t inp_debug = FALSE;
        uint32_t hint_mask = 0;
        int prefer_tempaddr = 0;
        struct ifnet *sifp = NULL;

        *errorp = 0;
        if (ifpp != NULL)
                *ifpp = NULL;

        if (inp != NULL) {
                inp_debug = SASEL_DO_DBG(inp);
                mopts = inp->in6p_moptions;
                if (INP_NO_CELLULAR(inp))
                        ip6oa.ip6oa_flags |= IP6OAF_NO_CELLULAR;
                if (INP_NO_EXPENSIVE(inp))
                        ip6oa.ip6oa_flags |= IP6OAF_NO_EXPENSIVE;
                if (INP_AWDL_UNRESTRICTED(inp))
                        ip6oa.ip6oa_flags |= IP6OAF_AWDL_UNRESTRICTED;
                if (INP_INTCOPROC_ALLOWED(inp))
                        ip6oa.ip6oa_flags |= IP6OAF_INTCOPROC_ALLOWED;
        } else {
                mopts = NULL;
                /* Allow the kernel to retransmit packets. */
                ip6oa.ip6oa_flags |= IP6OAF_INTCOPROC_ALLOWED |
                    IP6OAF_AWDL_UNRESTRICTED;
        }

        if (ip6oa.ip6oa_boundif != IFSCOPE_NONE)
                ip6oa.ip6oa_flags |= IP6OAF_BOUND_IF;

        /*
         * If the source address is explicitly specified by the caller,
         * check if the requested source address is indeed a unicast address
         * assigned to the node, and can be used as the packet's source
         * address.  If everything is okay, use the address as source.
         */
        if (opts && (pi = opts->ip6po_pktinfo) &&
            !IN6_IS_ADDR_UNSPECIFIED(&pi->ipi6_addr)) {
                struct sockaddr_in6 srcsock;
                struct in6_ifaddr *ia6;

                /* get the outgoing interface */
                if ((*errorp = in6_selectif(dstsock, opts, mopts, ro, &ip6oa,
                    &ifp)) != 0) {
                        src_storage = NULL;
                        goto done;
                }

                /*
                 * determine the appropriate zone id of the source based on
                 * the zone of the destination and the outgoing interface.
                 * If the specified address is ambiguous wrt the scope zone,
                 * the interface must be specified; otherwise, ifa_ifwithaddr()
                 * will fail matching the address.
                 */
                bzero(&srcsock, sizeof (srcsock));
                srcsock.sin6_family = AF_INET6;
                srcsock.sin6_len = sizeof (srcsock);
                srcsock.sin6_addr = pi->ipi6_addr;
                if (ifp != NULL) {
                        *errorp = in6_setscope(&srcsock.sin6_addr, ifp, NULL);
                        if (*errorp != 0) {
                                src_storage = NULL;
                                goto done;
                        }
                }
                ia6 = (struct in6_ifaddr *)ifa_ifwithaddr((struct sockaddr *)
                    (&srcsock));
                if (ia6 == NULL) {
                        *errorp = EADDRNOTAVAIL;
                        src_storage = NULL;
                        goto done;
                }
                IFA_LOCK_SPIN(&ia6->ia_ifa);
                if ((ia6->ia6_flags & (IN6_IFF_ANYCAST | IN6_IFF_NOTREADY)) ||
                    (inp && inp_restricted_send(inp, ia6->ia_ifa.ifa_ifp))) {
                        IFA_UNLOCK(&ia6->ia_ifa);
                        IFA_REMREF(&ia6->ia_ifa);
                        *errorp = EHOSTUNREACH;
                        src_storage = NULL;
                        goto done;
                }

                *src_storage = satosin6(&ia6->ia_addr)->sin6_addr;
                IFA_UNLOCK(&ia6->ia_ifa);
                IFA_REMREF(&ia6->ia_ifa);
                goto done;
        }

        /*
         * Otherwise, if the socket has already bound the source, just use it.
         */
        if (inp != NULL && !IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr)) {
                src_storage = &inp->in6p_laddr;
                goto done;
        }

        /*
         * If the address is not specified, choose the best one based on
         * the outgoing interface and the destination address.
         */
        /* get the outgoing interface */
        if ((*errorp = in6_selectif(dstsock, opts, mopts, ro, &ip6oa,
            &ifp)) != 0) {
                src_storage = NULL;
                goto done;
        }

        VERIFY(ifp != NULL);

        if (opts == NULL ||
            opts->ip6po_prefer_tempaddr == IP6PO_TEMPADDR_SYSTEM) {
                prefer_tempaddr = ip6_prefer_tempaddr;
        } else if (opts->ip6po_prefer_tempaddr == IP6PO_TEMPADDR_NOTPREFER) {
                prefer_tempaddr = 0;
        } else
                prefer_tempaddr = 1;

        if (prefer_tempaddr)
                hint_mask |= IPV6_SRCSEL_HINT_PREFER_TMPADDR;

        if (in6_selectsrc_core(dstsock, hint_mask, ifp, inp_debug, src_storage,
            &sifp, errorp, NULL) == NULL) {
                src_storage = NULL;
                goto done;
        }

        VERIFY(sifp != NULL);

        if (inp && inp_restricted_send(inp, sifp)) {
                src_storage = NULL;
                *errorp = EHOSTUNREACH;
                ifnet_release(sifp);
                goto done;
        } else {
                ifnet_release(sifp);
        }

done:
        if (ifpp != NULL) {
                /* if ifp is non-NULL, refcnt held in in6_selectif() */
                *ifpp = ifp;
        } else if (ifp != NULL) {
                ifnet_release(ifp);
        }
        return (src_storage);
}

/*
 * Given a source IPv6 address (and route, if available), determine the best
 * interface to send the packet from.  Checking for (and updating) the
 * ROF_SRCIF_SELECTED flag in the pcb-supplied route placeholder is done
 * without any locks, based on the assumption that in the event this is
 * called from ip6_output(), the output operation is single-threaded per-pcb,
 * i.e. for any given pcb there can only be one thread performing output at
 * the IPv6 layer.
 *
 * This routine is analogous to in_selectsrcif() for IPv4.  Regardless of
 * error, it will return an ifp with a reference held if the caller provides
 * a non-NULL retifp.  The caller is responsible for checking if the
 * returned ifp is valid and release its reference at all times.
 *
 * clone - meaningful only for bsdi and freebsd
 */
static int
selectroute(struct sockaddr_in6 *srcsock, struct sockaddr_in6 *dstsock,
    struct ip6_pktopts *opts, struct ip6_moptions *mopts,
    struct in6_ifaddr **retsrcia, struct route_in6 *ro,
    struct ifnet **retifp, struct rtentry **retrt, int clone,
    int norouteok, struct ip6_out_args *ip6oa)
{
        int error = 0;
        struct ifnet *ifp = NULL, *ifp0 = NULL;
        struct route_in6 *route = NULL;
        struct sockaddr_in6 *sin6_next;
        struct in6_pktinfo *pi = NULL;
        struct in6_addr *dst = &dstsock->sin6_addr;
        struct ifaddr *ifa = NULL;
        char s_src[MAX_IPv6_STR_LEN], s_dst[MAX_IPv6_STR_LEN];
        boolean_t select_srcif, proxied_ifa = FALSE, local_dst = FALSE;
        unsigned int ifscope = ((ip6oa != NULL) ?
            ip6oa->ip6oa_boundif : IFSCOPE_NONE);

        if (retifp != NULL)
                *retifp = NULL;

        if (retrt != NULL)
                *retrt = NULL;

        if (ip6_select_srcif_debug) {
                struct in6_addr src;
                src = (srcsock != NULL) ? srcsock->sin6_addr : in6addr_any;
                (void) inet_ntop(AF_INET6, &src, s_src, sizeof (s_src));
                (void) inet_ntop(AF_INET6, dst, s_dst, sizeof (s_dst));
        }

        /*
         * If the destination address is UNSPECIFIED addr, bail out.
         */
        if (IN6_IS_ADDR_UNSPECIFIED(dst)) {
                error = EHOSTUNREACH;
                goto done;
        }

        /*
         * Perform source interface selection only if Scoped Routing
         * is enabled and a source address that isn't unspecified.
         */
        select_srcif = (srcsock != NULL &&
            !IN6_IS_ADDR_UNSPECIFIED(&srcsock->sin6_addr));

        if (ip6_select_srcif_debug) {
                printf("%s src %s dst %s ifscope %d select_srcif %d\n",
                    __func__, s_src, s_dst, ifscope, select_srcif);
        }

        /* If the caller specified the outgoing interface explicitly, use it */
        if (opts != NULL && (pi = opts->ip6po_pktinfo) != NULL &&
            pi->ipi6_ifindex != 0) {
                /*
                 * If IPV6_PKTINFO takes precedence over IPV6_BOUND_IF.
                 */
                ifscope = pi->ipi6_ifindex;
                ifnet_head_lock_shared();
                /* ifp may be NULL if detached or out of range */
                ifp = ifp0 =
                    ((ifscope <= if_index) ? ifindex2ifnet[ifscope] : NULL);
                ifnet_head_done();
                if (norouteok || retrt == NULL || IN6_IS_ADDR_MULTICAST(dst)) {
                        /*
                         * We do not have to check or get the route for
                         * multicast.  If the caller didn't ask/care for
                         * the route and we have no interface to use,
                         * it's an error.
                         */
                        if (ifp == NULL)
                                error = EHOSTUNREACH;
                        goto done;
                } else {
                        goto getsrcif;
                }
        }

        /*
         * If the destination address is a multicast address and the outgoing
         * interface for the address is specified by the caller, use it.
         */
        if (IN6_IS_ADDR_MULTICAST(dst) && mopts != NULL) {
                IM6O_LOCK(mopts);
                if ((ifp = ifp0 = mopts->im6o_multicast_ifp) != NULL) {
                        IM6O_UNLOCK(mopts);
                        goto done; /* we do not need a route for multicast. */
                }
                IM6O_UNLOCK(mopts);
        }

getsrcif:
        /*
         * If the outgoing interface was not set via IPV6_BOUND_IF or
         * IPV6_PKTINFO, use the scope ID in the destination address.
         */
        if (ifscope == IFSCOPE_NONE)
                ifscope = dstsock->sin6_scope_id;

        /*
         * Perform source interface selection; the source IPv6 address
         * must belong to one of the addresses of the interface used
         * by the route.  For performance reasons, do this only if
         * there is no route, or if the routing table has changed,
         * or if we haven't done source interface selection on this
         * route (for this PCB instance) before.
         */
        if (!select_srcif) {
                goto getroute;
        } else if (!ROUTE_UNUSABLE(ro) && ro->ro_srcia != NULL &&
            (ro->ro_flags & ROF_SRCIF_SELECTED)) {
                if (ro->ro_rt->rt_ifp->if_flags & IFF_LOOPBACK)
                        local_dst = TRUE;
                ifa = ro->ro_srcia;
                IFA_ADDREF(ifa);        /* for caller */
                goto getroute;
        }

        /*
         * Given the source IPv6 address, find a suitable source interface
         * to use for transmission; if a scope ID has been specified,
         * optimize the search by looking at the addresses only for that
         * interface.  This is still suboptimal, however, as we need to
         * traverse the per-interface list.
         */
        if (ifscope != IFSCOPE_NONE || (ro != NULL && ro->ro_rt != NULL)) {
                unsigned int scope = ifscope;
                struct ifnet *rt_ifp;

                rt_ifp = (ro->ro_rt != NULL) ? ro->ro_rt->rt_ifp : NULL;

                /*
                 * If no scope is specified and the route is stale (pointing
                 * to a defunct interface) use the current primary interface;
                 * this happens when switching between interfaces configured
                 * with the same IPv6 address.  Otherwise pick up the scope
                 * information from the route; the ULP may have looked up a
                 * correct route and we just need to verify it here and mark
                 * it with the ROF_SRCIF_SELECTED flag below.
                 */
                if (scope == IFSCOPE_NONE) {
                        scope = rt_ifp->if_index;
                        if (scope != get_primary_ifscope(AF_INET6) &&
                            ROUTE_UNUSABLE(ro))
                                scope = get_primary_ifscope(AF_INET6);
                }

                ifa = (struct ifaddr *)
                    ifa_foraddr6_scoped(&srcsock->sin6_addr, scope);

                /*
                 * If we are forwarding and proxying prefix(es), see if the
                 * source address is one of ours and is a proxied address;
                 * if so, use it.
                 */
                if (ifa == NULL && ip6_forwarding && nd6_prproxy) {
                        ifa = (struct ifaddr *)
                            ifa_foraddr6(&srcsock->sin6_addr);
                        if (ifa != NULL && !(proxied_ifa =
                            nd6_prproxy_ifaddr((struct in6_ifaddr *)ifa))) {
                                IFA_REMREF(ifa);
                                ifa = NULL;
                        }
                }

                if (ip6_select_srcif_debug && ifa != NULL) {
                        if (ro->ro_rt != NULL) {
                                printf("%s %s->%s ifscope %d->%d ifa_if %s "
                                    "ro_if %s\n",
                                    __func__,
                                    s_src, s_dst, ifscope,
                                    scope, if_name(ifa->ifa_ifp),
                                    if_name(rt_ifp));
                        } else {
                                printf("%s %s->%s ifscope %d->%d ifa_if %s\n",
                                    __func__,
                                    s_src, s_dst, ifscope, scope,
                                    if_name(ifa->ifa_ifp));
                        }
                }
        }

        /*
         * Slow path; search for an interface having the corresponding source
         * IPv6 address if the scope was not specified by the caller, and:
         *
         *   1) There currently isn't any route, or,
         *   2) The interface used by the route does not own that source
         *      IPv6 address; in this case, the route will get blown away
         *      and we'll do a more specific scoped search using the newly
         *      found interface.
         */
        if (ifa == NULL && ifscope == IFSCOPE_NONE) {
                struct ifaddr *ifadst;

                /* Check if the destination address is one of ours */
                ifadst = (struct ifaddr *)ifa_foraddr6(&dstsock->sin6_addr);
                if (ifadst != NULL) {
                        local_dst = TRUE;
                        IFA_REMREF(ifadst);
                }

                ifa = (struct ifaddr *)ifa_foraddr6(&srcsock->sin6_addr);

                if (ip6_select_srcif_debug && ifa != NULL) {
                        printf("%s %s->%s ifscope %d ifa_if %s\n",
                            __func__,
                            s_src, s_dst, ifscope, if_name(ifa->ifa_ifp));
                } else if (ip6_select_srcif_debug) {
                        printf("%s %s->%s ifscope %d ifa_if NULL\n",
                            __func__,
                            s_src, s_dst, ifscope);
                }
        }

getroute:
        if (ifa != NULL && !proxied_ifa && !local_dst)
                ifscope = ifa->ifa_ifp->if_index;

        /*
         * If the next hop address for the packet is specified by the caller,
         * use it as the gateway.
         */
        if (opts != NULL && opts->ip6po_nexthop != NULL) {
                struct route_in6 *ron;

                sin6_next = satosin6(opts->ip6po_nexthop);

                /* at this moment, we only support AF_INET6 next hops */
                if (sin6_next->sin6_family != AF_INET6) {
                        error = EAFNOSUPPORT; /* or should we proceed? */
                        goto done;
                }

                /*
                 * If the next hop is an IPv6 address, then the node identified
                 * by that address must be a neighbor of the sending host.
                 */
                ron = &opts->ip6po_nextroute;
                if (ron->ro_rt != NULL)
                        RT_LOCK(ron->ro_rt);
                if (ROUTE_UNUSABLE(ron) || (ron->ro_rt != NULL &&
                    (!(ron->ro_rt->rt_flags & RTF_LLINFO) ||
                    (select_srcif && (ifa == NULL ||
                    (ifa->ifa_ifp != ron->ro_rt->rt_ifp && !proxied_ifa))))) ||
                    !IN6_ARE_ADDR_EQUAL(&satosin6(&ron->ro_dst)->sin6_addr,
                    &sin6_next->sin6_addr)) {
                        if (ron->ro_rt != NULL)
                                RT_UNLOCK(ron->ro_rt);

                        ROUTE_RELEASE(ron);
                        *satosin6(&ron->ro_dst) = *sin6_next;
                }
                if (ron->ro_rt == NULL) {
                        rtalloc_scoped((struct route *)ron, ifscope);
                        if (ron->ro_rt != NULL)
                                RT_LOCK(ron->ro_rt);
                        if (ROUTE_UNUSABLE(ron) ||
                            !(ron->ro_rt->rt_flags & RTF_LLINFO) ||
                            !IN6_ARE_ADDR_EQUAL(&satosin6(rt_key(ron->ro_rt))->
                            sin6_addr, &sin6_next->sin6_addr)) {
                                if (ron->ro_rt != NULL)
                                        RT_UNLOCK(ron->ro_rt);

                                ROUTE_RELEASE(ron);
                                error = EHOSTUNREACH;
                                goto done;
                        }
                }
                route = ron;
                ifp = ifp0 = ron->ro_rt->rt_ifp;

                /*
                 * When cloning is required, try to allocate a route to the
                 * destination so that the caller can store path MTU
                 * information.
                 */
                if (!clone) {
                        if (select_srcif) {
                                /* Keep the route locked */
                                goto validateroute;
                        }
                        RT_UNLOCK(ron->ro_rt);
                        goto done;
                }
                RT_UNLOCK(ron->ro_rt);
        }

        /*
         * Use a cached route if it exists and is valid, else try to allocate
         * a new one.  Note that we should check the address family of the
         * cached destination, in case of sharing the cache with IPv4.
         */
        if (ro == NULL)
                goto done;
        if (ro->ro_rt != NULL)
                RT_LOCK_SPIN(ro->ro_rt);
        if (ROUTE_UNUSABLE(ro) || (ro->ro_rt != NULL &&
            (satosin6(&ro->ro_dst)->sin6_family != AF_INET6 ||
            !IN6_ARE_ADDR_EQUAL(&satosin6(&ro->ro_dst)->sin6_addr, dst) ||
            (select_srcif && (ifa == NULL ||
            (ifa->ifa_ifp != ro->ro_rt->rt_ifp && !proxied_ifa)))))) {
                if (ro->ro_rt != NULL)
                        RT_UNLOCK(ro->ro_rt);

                ROUTE_RELEASE(ro);
        }
        if (ro->ro_rt == NULL) {
                struct sockaddr_in6 *sa6;

                if (ro->ro_rt != NULL)
                        RT_UNLOCK(ro->ro_rt);
                /* No route yet, so try to acquire one */
                bzero(&ro->ro_dst, sizeof (struct sockaddr_in6));
                sa6 = (struct sockaddr_in6 *)&ro->ro_dst;
                sa6->sin6_family = AF_INET6;
                sa6->sin6_len = sizeof (struct sockaddr_in6);
                sa6->sin6_addr = *dst;
                if (IN6_IS_ADDR_MULTICAST(dst)) {
                        ro->ro_rt = rtalloc1_scoped(
                            &((struct route *)ro)->ro_dst, 0, 0, ifscope);
                } else {
                        rtalloc_scoped((struct route *)ro, ifscope);
                }
                if (ro->ro_rt != NULL)
                        RT_LOCK_SPIN(ro->ro_rt);
        }

        /*
         * Do not care about the result if we have the nexthop
         * explicitly specified (in case we're asked to clone.)
         */
        if (opts != NULL && opts->ip6po_nexthop != NULL) {
                if (ro->ro_rt != NULL)
                        RT_UNLOCK(ro->ro_rt);
                goto done;
        }

        if (ro->ro_rt != NULL) {
                RT_LOCK_ASSERT_HELD(ro->ro_rt);
                ifp = ifp0 = ro->ro_rt->rt_ifp;
        } else {
                error = EHOSTUNREACH;
        }
        route = ro;

validateroute:
        if (select_srcif) {
                boolean_t has_route = (route != NULL && route->ro_rt != NULL);
                boolean_t srcif_selected = FALSE;

                if (has_route)
                        RT_LOCK_ASSERT_HELD(route->ro_rt);
                /*
                 * If there is a non-loopback route with the wrong interface,
                 * or if there is no interface configured with such an address,
                 * blow it away.  Except for local/loopback, we look for one
                 * with a matching interface scope/index.
                 */
                if (has_route && (ifa == NULL ||
                    (ifa->ifa_ifp != ifp && ifp != lo_ifp) ||
                    !(route->ro_rt->rt_flags & RTF_UP))) {
                        /*
                         * If the destination address belongs to a proxied
                         * prefix, relax the requirement and allow the packet
                         * to come out of the proxy interface with the source
                         * address of the real interface.
                         */
                        if (ifa != NULL && proxied_ifa &&
                            (route->ro_rt->rt_flags & (RTF_UP|RTF_PROXY)) ==
                            (RTF_UP|RTF_PROXY)) {
                                srcif_selected = TRUE;
                        } else {
                                if (ip6_select_srcif_debug) {
                                        if (ifa != NULL) {
                                                printf("%s->%s ifscope %d "
                                                    "ro_if %s != ifa_if %s "
                                                    "(cached route cleared)\n",
                                                    s_src, s_dst,
                                                    ifscope, if_name(ifp),
                                                    if_name(ifa->ifa_ifp));
                                        } else {
                                                printf("%s->%s ifscope %d "
                                                    "ro_if %s (no ifa_if "
                                                    "found)\n", s_src, s_dst,
                                                    ifscope, if_name(ifp));
                                        }
                                }
                                RT_UNLOCK(route->ro_rt);
                                ROUTE_RELEASE(route);
                                error = EHOSTUNREACH;
                                /* Undo the settings done above */
                                route = NULL;
                                ifp = NULL;     /* ditch ifp; keep ifp0 */
                                has_route = FALSE;
                        }
                } else if (has_route) {
                        srcif_selected = TRUE;
                }

                if (srcif_selected) {
                        VERIFY(has_route);
                        if (ifa != route->ro_srcia ||
                            !(route->ro_flags & ROF_SRCIF_SELECTED)) {
                                RT_CONVERT_LOCK(route->ro_rt);
                                if (ifa != NULL)
                                        IFA_ADDREF(ifa); /* for route_in6 */
                                if (route->ro_srcia != NULL)
                                        IFA_REMREF(route->ro_srcia);
                                route->ro_srcia = ifa;
                                route->ro_flags |= ROF_SRCIF_SELECTED;
                                RT_GENID_SYNC(route->ro_rt);
                        }
                        RT_UNLOCK(route->ro_rt);
                }
        } else {
                if (ro->ro_rt != NULL)
                        RT_UNLOCK(ro->ro_rt);
                if (ifp != NULL && opts != NULL &&
                    opts->ip6po_pktinfo != NULL &&
                    opts->ip6po_pktinfo->ipi6_ifindex != 0) {
                        /*
                         * Check if the outgoing interface conflicts with the
                         * interface specified by ipi6_ifindex (if specified).
                         * Note that loopback interface is always okay.
                         * (this may happen when we are sending a packet to
                         * one of our own addresses.)
                         */
                        if (!(ifp->if_flags & IFF_LOOPBACK) && ifp->if_index !=
                            opts->ip6po_pktinfo->ipi6_ifindex) {
                                error = EHOSTUNREACH;
                                goto done;
                        }
                }
        }

done:
        /*
         * Check for interface restrictions.
         */
#define CHECK_RESTRICTIONS(_ip6oa, _ifp)                        \
        ((((_ip6oa)->ip6oa_flags & IP6OAF_NO_CELLULAR) &&       \
            IFNET_IS_CELLULAR(_ifp)) ||                         \
        (((_ip6oa)->ip6oa_flags & IP6OAF_NO_EXPENSIVE) &&       \
            IFNET_IS_EXPENSIVE(_ifp)) ||                        \
        (!((_ip6oa)->ip6oa_flags & IP6OAF_INTCOPROC_ALLOWED) && \
            IFNET_IS_INTCOPROC(_ifp)) ||                        \
        (!((_ip6oa)->ip6oa_flags & IP6OAF_AWDL_UNRESTRICTED) && \
            IFNET_IS_AWDL_RESTRICTED(_ifp)))

        if (error == 0 && ip6oa != NULL &&
            ((ifp && CHECK_RESTRICTIONS(ip6oa, ifp)) ||
            (route && route->ro_rt &&
            CHECK_RESTRICTIONS(ip6oa, route->ro_rt->rt_ifp)))) {
                if (route != NULL && route->ro_rt != NULL) {
                        ROUTE_RELEASE(route);
                        route = NULL;
                }
                ifp = NULL;     /* ditch ifp; keep ifp0 */
                error = EHOSTUNREACH;
                ip6oa->ip6oa_retflags |= IP6OARF_IFDENIED;
        }
#undef CHECK_RESTRICTIONS

        /*
         * If the interface is disabled for IPv6, then ENETDOWN error.
         */
        if (error == 0 &&
            ifp != NULL && (ifp->if_eflags & IFEF_IPV6_DISABLED)) {
                error = ENETDOWN;
        }

        if (ifp == NULL && (route == NULL || route->ro_rt == NULL)) {
                /*
                 * This can happen if the caller did not pass a cached route
                 * nor any other hints.  We treat this case an error.
                 */
                error = EHOSTUNREACH;
        }
        if (error == EHOSTUNREACH || error == ENETDOWN)
                ip6stat.ip6s_noroute++;

        /*
         * We'll return ifp regardless of error, so pick it up from ifp0
         * in case it was nullified above.  Caller is responsible for
         * releasing the ifp if it is non-NULL.
         */
        ifp = ifp0;
        if (retifp != NULL) {
                if (ifp != NULL)
                        ifnet_reference(ifp);   /* for caller */
                *retifp = ifp;
        }

        if (retsrcia != NULL) {
                if (ifa != NULL)
                        IFA_ADDREF(ifa);        /* for caller */
                *retsrcia = (struct in6_ifaddr *)ifa;
        }

        if (error == 0) {
                if (retrt != NULL && route != NULL)
                        *retrt = route->ro_rt;  /* ro_rt may be NULL */
        }
        if (ip6_select_srcif_debug) {
                printf("%s %s->%s ifscope %d ifa_if %s ro_if %s (error=%d)\n",
                    __func__,
                    s_src, s_dst, ifscope,
                    (ifa != NULL) ? if_name(ifa->ifa_ifp) : "NONE",
                    (ifp != NULL) ? if_name(ifp) : "NONE", error);
        }

        if (ifa != NULL)
                IFA_REMREF(ifa);

        return (error);
}

/*
 * Regardless of error, it will return an ifp with a reference held if the
 * caller provides a non-NULL retifp.  The caller is responsible for checking
 * if the returned ifp is valid and release its reference at all times.
 */
int
in6_selectif(struct sockaddr_in6 *dstsock, struct ip6_pktopts *opts,
    struct ip6_moptions *mopts, struct route_in6 *ro,
    struct ip6_out_args *ip6oa, struct ifnet **retifp)
{
        int err = 0;
        struct route_in6 sro;
        struct rtentry *rt = NULL;

        if (ro == NULL) {
                bzero(&sro, sizeof (sro));
                ro = &sro;
        }

        if ((err = selectroute(NULL, dstsock, opts, mopts, NULL, ro, retifp,
            &rt, 0, 1, ip6oa)) != 0)
                goto done;

        /*
         * do not use a rejected or black hole route.
         * XXX: this check should be done in the L2 output routine.
         * However, if we skipped this check here, we'd see the following
         * scenario:
         * - install a rejected route for a scoped address prefix
         *   (like fe80::/10)
         * - send a packet to a destination that matches the scoped prefix,
         *   with ambiguity about the scope zone.
         * - pick the outgoing interface from the route, and disambiguate the
         *   scope zone with the interface.
         * - ip6_output() would try to get another route with the "new"
         *   destination, which may be valid.
         * - we'd see no error on output.
         * Although this may not be very harmful, it should still be confusing.
         * We thus reject the case here.
         */
        if (rt && (rt->rt_flags & (RTF_REJECT | RTF_BLACKHOLE))) {
                err = ((rt->rt_flags & RTF_HOST) ? EHOSTUNREACH : ENETUNREACH);
                goto done;
        }

        /*
         * Adjust the "outgoing" interface.  If we're going to loop the packet
         * back to ourselves, the ifp would be the loopback interface.
         * However, we'd rather know the interface associated to the
         * destination address (which should probably be one of our own
         * addresses.)
         */
        if (rt != NULL && rt->rt_ifa != NULL && rt->rt_ifa->ifa_ifp != NULL &&
            retifp != NULL) {
                ifnet_reference(rt->rt_ifa->ifa_ifp);
                if (*retifp != NULL)
                        ifnet_release(*retifp);
                *retifp = rt->rt_ifa->ifa_ifp;
        }

done:
        if (ro == &sro) {
                VERIFY(rt == NULL || rt == ro->ro_rt);
                ROUTE_RELEASE(ro);
        }

        /*
         * retifp might point to a valid ifp with a reference held;
         * caller is responsible for releasing it if non-NULL.
         */
        return (err);
}

/*
 * Regardless of error, it will return an ifp with a reference held if the
 * caller provides a non-NULL retifp.  The caller is responsible for checking
 * if the returned ifp is valid and release its reference at all times.
 *
 * clone - meaningful only for bsdi and freebsd
 */
int
in6_selectroute(struct sockaddr_in6 *srcsock, struct sockaddr_in6 *dstsock,
    struct ip6_pktopts *opts, struct ip6_moptions *mopts,
    struct in6_ifaddr **retsrcia, struct route_in6 *ro, struct ifnet **retifp,
    struct rtentry **retrt, int clone, struct ip6_out_args *ip6oa)
{

        return (selectroute(srcsock, dstsock, opts, mopts, retsrcia, ro, retifp,
            retrt, clone, 0, ip6oa));
}

/*
 * 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)
{
        if (in6p && in6p->in6p_hops >= 0) {
                return (in6p->in6p_hops);
        } else if (NULL != ifp) {
                u_int8_t chlim;
                struct nd_ifinfo *ndi = ND_IFINFO(ifp);
                if (ndi && ndi->initialized) {
                        /* access chlim without lock, for performance */
                        chlim = ndi->chlim;
                } else {
                        chlim = ip6_defhlim;
                }
                return (chlim);
        }

        return (ip6_defhlim);
}

/*
 * XXX: this is borrowed from in6_pcbbind(). If possible, we should
 * share this function by all *bsd*...
 */
int
in6_pcbsetport(struct in6_addr *laddr, struct inpcb *inp, struct proc *p,
    int locked)
{
#pragma unused(laddr)
        struct socket *so = inp->inp_socket;
        u_int16_t lport = 0, first, last, *lastport;
        int count, error = 0, wild = 0;
        bool found;
        struct inpcbinfo *pcbinfo = inp->inp_pcbinfo;
        kauth_cred_t cred;
        if (!locked) { /* Make sure we don't run into a deadlock: 4052373 */
                if (!lck_rw_try_lock_exclusive(pcbinfo->ipi_lock)) {
                        socket_unlock(inp->inp_socket, 0);
                        lck_rw_lock_exclusive(pcbinfo->ipi_lock);
                        socket_lock(inp->inp_socket, 0);
                }

                /*
                 * Check if a local port was assigned to the inp while
                 * this thread was waiting for the pcbinfo lock
                 */
                if (inp->inp_lport != 0) {
                        VERIFY(inp->inp_flags2 & INP2_INHASHLIST);
                        lck_rw_done(pcbinfo->ipi_lock);

                        /*
                         * It is not an error if another thread allocated
                         * a port
                         */
                        return (0);
                }
        }

        /* XXX: this is redundant when called from in6_pcbbind */
        if ((so->so_options & (SO_REUSEADDR|SO_REUSEPORT)) == 0)
                wild = INPLOOKUP_WILDCARD;

        if (inp->inp_flags & INP_HIGHPORT) {
                first = ipport_hifirstauto;     /* sysctl */
                last  = ipport_hilastauto;
                lastport = &pcbinfo->ipi_lasthi;
        } else if (inp->inp_flags & INP_LOWPORT) {
                cred = kauth_cred_proc_ref(p);
                error = priv_check_cred(cred, PRIV_NETINET_RESERVEDPORT, 0);
                kauth_cred_unref(&cred);
                if (error != 0) {
                        if (!locked)
                                lck_rw_done(pcbinfo->ipi_lock);
                        return (error);
                }
                first = ipport_lowfirstauto;    /* 1023 */
                last  = ipport_lowlastauto;     /* 600 */
                lastport = &pcbinfo->ipi_lastlow;
        } else {
                first = ipport_firstauto;       /* sysctl */
                last  = ipport_lastauto;
                lastport = &pcbinfo->ipi_lastport;
        }
        /*
         * Simple check to ensure all ports are not used up causing
         * a deadlock here.
         *
         * We split the two cases (up and down) so that the direction
         * is not being tested on each round of the loop.
         */
        if (first > last) {
                /*
                 * counting down
                 */
                count = first - last;
                found = false;

                do {
                        if (count-- < 0) {      /* completely used? */
                                /*
                                 * Undo any address bind that may have
                                 * occurred above.
                                 */
                                inp->in6p_laddr = in6addr_any;
                                inp->in6p_last_outifp = NULL;
                                if (!locked)
                                        lck_rw_done(pcbinfo->ipi_lock);
                                return (EAGAIN);
                        }
                        --*lastport;
                        if (*lastport > first || *lastport < last)
                                *lastport = first;
                        lport = htons(*lastport);

                        found = in6_pcblookup_local(pcbinfo, &inp->in6p_laddr,
                            lport, wild) == NULL;
                } while (!found);
        } else {
                /* counting up */
                count = last - first;
                found = false;

                do {
                        if (count-- < 0) {      /* completely used? */
                                /*
                                 * Undo any address bind that may have
                                 * occurred above.
                                 */
                                inp->in6p_laddr = in6addr_any;
                                inp->in6p_last_outifp = NULL;
                                if (!locked)
                                        lck_rw_done(pcbinfo->ipi_lock);
                                return (EAGAIN);
                        }
                        ++*lastport;
                        if (*lastport < first || *lastport > last)
                                *lastport = first;
                        lport = htons(*lastport);

                        found = in6_pcblookup_local(pcbinfo, &inp->in6p_laddr,
                            lport, wild) == NULL;
                } while (!found);
        }

        inp->inp_lport = lport;
        inp->inp_flags |= INP_ANONPORT;

        if (in_pcbinshash(inp, 1) != 0) {
                inp->in6p_laddr = in6addr_any;
                inp->in6p_last_outifp = NULL;

                inp->inp_lport = 0;
                inp->inp_flags &= ~INP_ANONPORT;
                if (!locked)
                        lck_rw_done(pcbinfo->ipi_lock);
                return (EAGAIN);
        }

        if (!locked)
                lck_rw_done(pcbinfo->ipi_lock);
        return (0);
}

/*
 * 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);
}

void
addrsel_policy_init(void)
{
        /*
         * Default address selection policy based on RFC 6724.
         */
        static const struct in6_addrpolicy defaddrsel[] = {
                /* Loopback -- prefix=::1/128, precedence=50, label=0 */
                {
                        .addr = {
                                .sin6_family = AF_INET6,
                                .sin6_addr   = IN6ADDR_LOOPBACK_INIT,
                                .sin6_len    = sizeof (struct sockaddr_in6)
                        },
                        .addrmask = {
                                .sin6_family = AF_INET6,
                                .sin6_addr   = IN6MASK128,
                                .sin6_len    = sizeof (struct sockaddr_in6)
                        },
                        .preced   = 50,
                        .label    = 0
                },

                /* Unspecified -- prefix=::/0, precedence=40, label=1 */
                {
                        .addr = {
                                .sin6_family = AF_INET6,
                                .sin6_addr   = IN6ADDR_ANY_INIT,
                                .sin6_len    = sizeof (struct sockaddr_in6)
                        },
                        .addrmask = {
                                .sin6_family = AF_INET6,
                                .sin6_addr   = IN6MASK0,
                                .sin6_len    = sizeof (struct sockaddr_in6)
                        },
                        .preced   = 40,
                        .label    = 1
                },

                /* IPv4 Mapped -- prefix=::ffff:0:0/96, precedence=35, label=4 */
                {
                        .addr = {
                                .sin6_family = AF_INET6,
                                .sin6_addr   = IN6ADDR_V4MAPPED_INIT,
                                .sin6_len    = sizeof (struct sockaddr_in6)
                        },
                        .addrmask = {
                                .sin6_family = AF_INET6,
                                .sin6_addr   = IN6MASK96,
                                .sin6_len    = sizeof (struct sockaddr_in6)
                        },
                        .preced   = 35,
                        .label    = 4
                },

                /* 6to4 -- prefix=2002::/16, precedence=30, label=2 */
                {
                        .addr = {
                                .sin6_family = AF_INET6,
                                .sin6_addr   = {{{ 0x20, 0x02 }}},
                                .sin6_len    = sizeof (struct sockaddr_in6)
                        },
                        .addrmask = {
                                .sin6_family = AF_INET6,
                                .sin6_addr   = IN6MASK16,
                                .sin6_len    = sizeof (struct sockaddr_in6)
                        },
                        .preced   = 30,
                        .label    = 2
                },

                /* Teredo -- prefix=2001::/32, precedence=5, label=5 */
                {
                        .addr = {
                                .sin6_family = AF_INET6,
                                .sin6_addr   = {{{ 0x20, 0x01 }}},
                                .sin6_len    = sizeof (struct sockaddr_in6)
                        },
                        .addrmask = {
                                .sin6_family = AF_INET6,
                                .sin6_addr   = IN6MASK32,
                                .sin6_len    = sizeof (struct sockaddr_in6)
                        },
                        .preced   = 5,
                        .label    = 5
                },

                /* Unique Local (ULA) -- prefix=fc00::/7, precedence=3, label=13 */
                {
                        .addr = {
                                .sin6_family = AF_INET6,
                                .sin6_addr   = {{{ 0xfc }}},
                                .sin6_len    = sizeof (struct sockaddr_in6)
                        },
                        .addrmask = {
                                .sin6_family = AF_INET6,
                                .sin6_addr   = IN6MASK7,
                                .sin6_len    = sizeof (struct sockaddr_in6)
                        },
                        .preced   = 3,
                        .label    = 13
                },

                /* IPv4 Compatible -- prefix=::/96, precedence=1, label=3 */
                {
                        .addr = {
                                .sin6_family = AF_INET6,
                                .sin6_addr = IN6ADDR_ANY_INIT,
                                .sin6_len    = sizeof (struct sockaddr_in6)
                        },
                        .addrmask = {
                                .sin6_family = AF_INET6,
                                .sin6_addr = IN6MASK96,
                                .sin6_len    = sizeof (struct sockaddr_in6)
                        },
                        .preced   = 1,
                        .label    = 3
                },

                /* Site-local (deprecated) -- prefix=fec0::/10, precedence=1, label=11 */
                {
                        .addr = {
                                .sin6_family = AF_INET6,
                                .sin6_addr = {{{ 0xfe, 0xc0 }}},
                                .sin6_len    = sizeof (struct sockaddr_in6)
                        },
                        .addrmask = {
                                .sin6_family = AF_INET6,
                                .sin6_addr = IN6MASK16,
                                .sin6_len    = sizeof (struct sockaddr_in6)
                        },
                        .preced   = 1,
                        .label    = 11
                },

                /* 6bone (deprecated) -- prefix=3ffe::/16, precedence=1, label=12 */
                {
                        .addr = {
                                .sin6_family = AF_INET6,
                                .sin6_addr = {{{ 0x3f, 0xfe }}},
                                .sin6_len    = sizeof (struct sockaddr_in6)
                        },
                        .addrmask = {
                                .sin6_family = AF_INET6,
                                .sin6_addr = IN6MASK16,
                                .sin6_len    = sizeof (struct sockaddr_in6)
                        },
                        .preced   = 1,
                        .label    = 12
                },
        };
        int i;

        init_policy_queue();

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

        for (i = 0; i < sizeof (defaddrsel) / sizeof (defaddrsel[0]); i++)
                add_addrsel_policyent(&defaddrsel[i]);

}

struct in6_addrpolicy *
in6_addrsel_lookup_policy(struct sockaddr_in6 *key)
{
        struct in6_addrpolicy *match = NULL;

        ADDRSEL_LOCK();
        match = match_addrsel_policy(key);

        if (match == NULL)
                match = &defaultaddrpolicy;
        else
                match->use++;
        ADDRSEL_UNLOCK();

        return (match);
}

static struct in6_addrpolicy *
match_addrsel_policy(struct sockaddr_in6 *key)
{
        struct addrsel_policyent *pent;
        struct in6_addrpolicy *bestpol = NULL, *pol;
        int matchlen, bestmatchlen = -1;
        u_char *mp, *ep, *k, *p, m;

        TAILQ_FOREACH(pent, &addrsel_policytab, ape_entry) {
                matchlen = 0;

                pol = &pent->ape_policy;
                mp = (u_char *)&pol->addrmask.sin6_addr;
                ep = mp + 16;   /* XXX: scope field? */
                k = (u_char *)&key->sin6_addr;
                p = (u_char *)&pol->addr.sin6_addr;
                for (; mp < ep && *mp; mp++, k++, p++) {
                        m = *mp;
                        if ((*k & m) != *p)
                                goto next; /* not match */
                        if (m == 0xff) /* short cut for a typical case */
                                matchlen += 8;
                        else {
                                while (m >= 0x80) {
                                        matchlen++;
                                        m <<= 1;
                                }
                        }
                }

                /* matched.  check if this is better than the current best. */
                if (bestpol == NULL ||
                    matchlen > bestmatchlen) {
                        bestpol = pol;
                        bestmatchlen = matchlen;
                }

        next:
                continue;
        }

        return (bestpol);
}

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

        MALLOC(new, struct addrsel_policyent *, sizeof (*new), M_IFADDR,
            M_WAITOK);

        ADDRSEL_LOCK();

        /* duplication check */
        TAILQ_FOREACH(pol, &addrsel_policytab, ape_entry) {
                if (IN6_ARE_ADDR_EQUAL(&newpolicy->addr.sin6_addr,
                    &pol->ape_policy.addr.sin6_addr) &&
                    IN6_ARE_ADDR_EQUAL(&newpolicy->addrmask.sin6_addr,
                    &pol->ape_policy.addrmask.sin6_addr)) {
                        ADDRSEL_UNLOCK();
                        FREE(new, M_IFADDR);
                        return (EEXIST);        /* or override it? */
                }
        }

        bzero(new, sizeof (*new));

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

        TAILQ_INSERT_TAIL(&addrsel_policytab, new, ape_entry);
        ADDRSEL_UNLOCK();

        return (0);
}
#ifdef ENABLE_ADDRSEL
static int
delete_addrsel_policyent(const struct in6_addrpolicy *key)
{
        struct addrsel_policyent *pol;


        ADDRSEL_LOCK();

        /* search for the entry in the table */
        TAILQ_FOREACH(pol, &addrsel_policytab, ape_entry) {
                if (IN6_ARE_ADDR_EQUAL(&key->addr.sin6_addr,
                    &pol->ape_policy.addr.sin6_addr) &&
                    IN6_ARE_ADDR_EQUAL(&key->addrmask.sin6_addr,
                    &pol->ape_policy.addrmask.sin6_addr)) {
                        break;
                }
        }
        if (pol == NULL) {
                ADDRSEL_UNLOCK();
                return (ESRCH);
        }

        TAILQ_REMOVE(&addrsel_policytab, pol, ape_entry);
        FREE(pol, M_IFADDR);
        pol = NULL;
        ADDRSEL_UNLOCK();

        return (0);
}
#endif /* ENABLE_ADDRSEL */

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

        ADDRSEL_LOCK();
        TAILQ_FOREACH(pol, &addrsel_policytab, ape_entry) {
                if ((error = (*callback)(&pol->ape_policy, w)) != 0) {
                        ADDRSEL_UNLOCK();
                        return (error);
                }
        }
        ADDRSEL_UNLOCK();
        return (error);
}
/*
 * Subroutines to manage the address selection policy table via sysctl.
 */
struct walkarg {
        struct sysctl_req *w_req;
};


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

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

        return (error);
}

static int
in6_src_sysctl SYSCTL_HANDLER_ARGS
{
#pragma unused(oidp, arg1, arg2)
struct walkarg w;

        if (req->newptr)
                return (EPERM);
        bzero(&w, sizeof (w));
        w.w_req = req;

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


SYSCTL_NODE(_net_inet6_ip6, IPV6CTL_ADDRCTLPOLICY, addrctlpolicy,
        CTLFLAG_RD | CTLFLAG_LOCKED, in6_src_sysctl, "");
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 */

        bcopy(data, &ent0, sizeof (ent0));

        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:
#ifdef ENABLE_ADDRSEL
                return (add_addrsel_policyent(&ent0));
#else
                return (ENOTSUP);
#endif
        case SIOCDADDRCTL_POLICY:
#ifdef ENABLE_ADDRSEL
                return (delete_addrsel_policyent(&ent0));
#else
                return (ENOTSUP);
#endif
        }

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

/*
 * 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,
    struct in6pcb *in6p, struct ifnet **ifpp, struct ip6_pktopts *opt)
{
        struct ifnet *ifp = NULL;
        u_int32_t scopeid;
        struct ip6_pktopts *optp = NULL;

        *in6 = sin6->sin6_addr;
        scopeid = sin6->sin6_scope_id;
        if (ifpp != NULL)
                *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) || IN6_IS_ADDR_MC_INTFACELOCAL(in6)) {
                struct in6_pktinfo *pi;
                struct ifnet *im6o_multicast_ifp = NULL;

                if (in6p != NULL && IN6_IS_ADDR_MULTICAST(in6) &&
                    in6p->in6p_moptions != NULL) {
                        IM6O_LOCK(in6p->in6p_moptions);
                        im6o_multicast_ifp =
                            in6p->in6p_moptions->im6o_multicast_ifp;
                        IM6O_UNLOCK(in6p->in6p_moptions);
                }

                if (opt != NULL)
                        optp = opt;
                else if (in6p != NULL)
                        optp = in6p->in6p_outputopts;
                /*
                 * KAME assumption: link id == interface id
                 */
                if (in6p != NULL && optp != NULL &&
                    (pi = optp->ip6po_pktinfo) != NULL &&
                    pi->ipi6_ifindex != 0) {
                        /* ifp is needed here if only we're returning it */
                        if (ifpp != NULL) {
                                ifnet_head_lock_shared();
                                ifp = ifindex2ifnet[pi->ipi6_ifindex];
                                ifnet_head_done();
                        }
                        in6->s6_addr16[1] = htons(pi->ipi6_ifindex);
                } else if (in6p != NULL && IN6_IS_ADDR_MULTICAST(in6) &&
                    in6p->in6p_moptions != NULL && im6o_multicast_ifp != NULL) {
                        ifp = im6o_multicast_ifp;
                        in6->s6_addr16[1] = htons(ifp->if_index);
                } else if (scopeid != 0) {
                        /*
                         * Since scopeid is unsigned, we only have to check it
                         * against if_index (ifnet_head_lock not needed since
                         * if_index is an ever-increasing integer.)
                         */
                        if (if_index < scopeid)
                                return (ENXIO);  /* XXX EINVAL? */

                        /* ifp is needed here only if we're returning it */
                        if (ifpp != NULL) {
                                ifnet_head_lock_shared();
                                ifp = ifindex2ifnet[scopeid];
                                ifnet_head_done();
                        }
                        /* XXX assignment to 16bit from 32bit variable */
                        in6->s6_addr16[1] = htons(scopeid & 0xffff);
                }

                if (ifpp != NULL) {
                        if (ifp != NULL)
                                ifnet_reference(ifp);   /* for caller */
                        *ifpp = ifp;
                }
        }

        return (0);
}

/*
 * 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 scopeid;

        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
                 */
                scopeid = ntohs(sin6->sin6_addr.s6_addr16[1]);
                if (scopeid) {
                        /*
                         * sanity check
                         *
                         * Since scopeid is unsigned, we only have to check it
                         * against if_index
                         */
                        if (if_index < scopeid)
                                return (ENXIO);
                        if (ifp && ifp->if_index != scopeid)
                                return (ENXIO);
                        sin6->sin6_addr.s6_addr16[1] = 0;
                        sin6->sin6_scope_id = scopeid;
                }
        }

        return (0);
}