/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * 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.
 *
 *      $KAME: in6_src.c,v 1.132 2003/08/26 04:42:27 keiichi Exp $
 */

/*-
 * 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.
 */

#include "opt_inet.h"
#include "opt_inet6.h"
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/lock.h>
#include <sys/malloc.h>
#include <sys/mbuf.h>
#include <sys/priv.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/jail.h>
#include <sys/kernel.h>
#include <sys/rmlock.h>
#include <sys/sx.h>

#include <net/if.h>
#include <net/if_var.h>
#include <net/if_dl.h>
#include <net/if_private.h>
#include <net/route.h>
#include <net/route/nhop.h>
#include <net/if_llatbl.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 <netinet/ip_var.h>
#include <netinet/udp.h>
#include <netinet/udp_var.h>

#include <netinet6/in6_var.h>
#include <netinet/ip6.h>
#include <netinet6/in6_fib.h>
#include <netinet6/in6_pcb.h>
#include <netinet6/ip6_var.h>
#include <netinet6/scope6_var.h>
#include <netinet6/nd6.h>

static struct mtx addrsel_lock;
#define ADDRSEL_LOCK_INIT()     mtx_init(&addrsel_lock, "addrsel_lock", NULL, MTX_DEF)
#define ADDRSEL_LOCK()          mtx_lock(&addrsel_lock)
#define ADDRSEL_UNLOCK()        mtx_unlock(&addrsel_lock)
#define ADDRSEL_LOCK_ASSERT()   mtx_assert(&addrsel_lock, MA_OWNED)

static struct sx addrsel_sxlock;
#define ADDRSEL_SXLOCK_INIT()   sx_init(&addrsel_sxlock, "addrsel_sxlock")
#define ADDRSEL_SLOCK()         sx_slock(&addrsel_sxlock)
#define ADDRSEL_SUNLOCK()       sx_sunlock(&addrsel_sxlock)
#define ADDRSEL_XLOCK()         sx_xlock(&addrsel_sxlock)
#define ADDRSEL_XUNLOCK()       sx_xunlock(&addrsel_sxlock)

#define ADDR_LABEL_NOTAPP (-1)
VNET_DEFINE_STATIC(struct in6_addrpolicy, defaultaddrpolicy);
#define V_defaultaddrpolicy             VNET(defaultaddrpolicy)

VNET_DEFINE(int, ip6_prefer_tempaddr) = 0;

static int selectroute(struct sockaddr_in6 *, struct ip6_pktopts *,
        struct ip6_moptions *, struct route_in6 *, struct ifnet **,
        struct nhop_object **, int, u_int, uint32_t);
static int in6_selectif(struct sockaddr_in6 *, struct ip6_pktopts *,
        struct ip6_moptions *, struct ifnet **,
        struct ifnet *, u_int);
static int in6_selectsrc(uint32_t, struct sockaddr_in6 *,
        struct ip6_pktopts *, struct ip6_moptions *, struct inpcb *,
        struct ucred *, struct ifnet **, struct in6_addr *);

static struct in6_addrpolicy *lookup_addrsel_policy(struct sockaddr_in6 *);

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 *);
static struct in6_addrpolicy *match_addrsel_policy(struct sockaddr_in6 *);

/*
 * 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 {\
        IP6STAT_INC2(ip6s_sources_rule, (r)); \
        /* { \
        char ip6buf[INET6_ADDRSTRLEN], ip6b[INET6_ADDRSTRLEN]; \
        printf("in6_selectsrc: replace %s with %s by %d\n", ia_best ? ip6_sprintf(ip6buf, &ia_best->ia_addr.sin6_addr) : "none", ip6_sprintf(ip6b, &ia->ia_addr.sin6_addr), (r)); \
        } */ \
        goto replace; \
} while(0)
#define NEXT(r) do {\
        /* { \
        char ip6buf[INET6_ADDRSTRLEN], ip6b[INET6_ADDRSTRLEN]; \
        printf("in6_selectsrc: keep %s against %s by %d\n", ia_best ? ip6_sprintf(ip6buf, &ia_best->ia_addr.sin6_addr) : "none", ip6_sprintf(ip6b, &ia->ia_addr.sin6_addr), (r)); \
        } */ \
        goto next;              /* XXX: we can't use 'continue' here */ \
} while(0)
#define BREAK(r) do { \
        IP6STAT_INC2(ip6s_sources_rule, (r)); \
        goto out;               /* XXX: we can't use 'break' here */ \
} while(0)

static int
in6_selectsrc(uint32_t fibnum, struct sockaddr_in6 *dstsock,
    struct ip6_pktopts *opts, struct ip6_moptions *mopts, struct inpcb *inp,
    struct ucred *cred, struct ifnet **ifpp, struct in6_addr *srcp)
{
        struct rm_priotracker in6_ifa_tracker;
        struct in6_addr dst, tmp;
        struct ifnet *ifp = NULL, *oifp = NULL;
        struct in6_ifaddr *ia = NULL, *ia_best = NULL;
        struct in6_pktinfo *pi = NULL;
        int dst_scope = -1, best_scope = -1, best_matchlen = -1;
        struct in6_addrpolicy *dst_policy = NULL, *best_policy = NULL;
        u_int32_t odstzone;
        int prefer_tempaddr;
        int error;

        NET_EPOCH_ASSERT();
        KASSERT(srcp != NULL, ("%s: srcp is NULL", __func__));

        dst = dstsock->sin6_addr; /* make a copy for local operation */
        if (ifpp) {
                /*
                 * Save a possibly passed in ifp for in6_selectsrc. Only
                 * neighbor discovery code should use this feature, where
                 * we may know the interface but not the FIB number holding
                 * the connected subnet in case someone deleted it from the
                 * default FIB and we need to check the interface.
                 */
                if (*ifpp != NULL)
                        oifp = *ifpp;
                *ifpp = NULL;
        }

        /*
         * 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)) {
                /* get the outgoing interface */
                if ((error = in6_selectif(dstsock, opts, mopts, &ifp, oifp,
                    fibnum))
                    != 0)
                        return (error);

                /*
                 * 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.
                 */
                tmp = pi->ipi6_addr;
                if (ifp) {
                        error = in6_setscope(&tmp, ifp, &odstzone);
                        if (error)
                                return (error);
                }
                if (cred != NULL && (error = prison_local_ip6(cred,
                    &tmp, (inp->inp_flags & IN6P_IPV6_V6ONLY) != 0)) != 0)
                        return (error);

                /*
                 * If IPV6_BINDANY socket option is set, we allow to specify
                 * non local addresses as source address in IPV6_PKTINFO
                 * ancillary data.
                 */
                if ((inp->inp_flags & INP_BINDANY) == 0) {
                        ia = in6ifa_ifwithaddr(&tmp, 0 /* XXX */, false);
                        if (ia == NULL || (ia->ia6_flags & (IN6_IFF_ANYCAST |
                            IN6_IFF_NOTREADY)))
                                return (EADDRNOTAVAIL);
                        bcopy(&ia->ia_addr.sin6_addr, srcp, sizeof(*srcp));
                } else
                        bcopy(&tmp, srcp, sizeof(*srcp));
                pi->ipi6_addr = tmp; /* XXX: this overrides pi */
                if (ifpp)
                        *ifpp = ifp;
                return (0);
        }

        /*
         * Otherwise, if the socket has already bound the source, just use it.
         */
        if (inp != NULL && !IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr)) {
                if (cred != NULL &&
                    (error = prison_local_ip6(cred, &inp->in6p_laddr,
                    ((inp->inp_flags & IN6P_IPV6_V6ONLY) != 0))) != 0)
                        return (error);
                bcopy(&inp->in6p_laddr, srcp, sizeof(*srcp));
                return (0);
        }

        /*
         * Bypass source address selection and use the primary jail IP
         * if requested.
         */
        if (cred != NULL && !prison_saddrsel_ip6(cred, srcp))
                return (0);

        /*
         * If the address is not specified, choose the best one based on
         * the outgoing interface and the destination address.
         */
        /* get the outgoing interface */
        if ((error = in6_selectif(dstsock, opts, mopts, &ifp, oifp,
            (inp != NULL) ? inp->inp_inc.inc_fibnum : fibnum)) != 0)
                return (error);

#ifdef DIAGNOSTIC
        if (ifp == NULL)        /* this should not happen */
                panic("in6_selectsrc: NULL ifp");
#endif
        error = in6_setscope(&dst, ifp, &odstzone);
        if (error)
                return (error);

        IN6_IFADDR_RLOCK(&in6_ifa_tracker);
        CK_STAILQ_FOREACH(ia, &V_in6_ifaddrhead, ia_link) {
                int new_scope = -1, new_matchlen = -1;
                struct in6_addrpolicy *new_policy = NULL;
                u_int32_t srczone, osrczone, dstzone;
                struct in6_addr src;
                struct ifnet *ifp1 = ia->ia_ifp;

                /*
                 * 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) {
                        continue;
                }
                src = ia->ia_addr.sin6_addr;
                if (in6_setscope(&src, ifp, &osrczone) ||
                    in6_setscope(&src, ifp1, &srczone) ||
                    osrczone != srczone) {
                        continue;
                }

                /* avoid unusable addresses */
                if ((ia->ia6_flags &
                     (IN6_IFF_NOTREADY | IN6_IFF_ANYCAST | IN6_IFF_DETACHED))) {
                                continue;
                }
                if (!V_ip6_use_deprecated && IFA6_IS_DEPRECATED(ia))
                        continue;

                /* If jailed only take addresses of the jail into account. */
                if (cred != NULL &&
                    prison_check_ip6(cred, &ia->ia_addr.sin6_addr) != 0)
                        continue;

                /* Rule 1: Prefer same address */
                if (IN6_ARE_ADDR_EQUAL(&dst, &ia->ia_addr.sin6_addr)) {
                        ia_best = ia;
                        BREAK(1); /* there should be no better candidate */
                }

                if (ia_best == NULL)
                        REPLACE(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(2);
                        NEXT(2);
                } else if (IN6_ARE_SCOPE_CMP(new_scope, best_scope) < 0) {
                        if (IN6_ARE_SCOPE_CMP(new_scope, dst_scope) < 0)
                                NEXT(2);
                        REPLACE(2);
                }

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

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

                /* Rule 5: Prefer outgoing interface */
                if (!(ifp->if_inet6->nd_flags & ND6_IFF_NO_PREFER_IFACE)) {
                        if (ia_best->ia_ifp == ifp && ia->ia_ifp != ifp)
                                NEXT(5);
                        if (ia_best->ia_ifp != ifp && ia->ia_ifp == ifp)
                                REPLACE(5);
                }

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

                /*
                 * Rule 7: Prefer public addresses.
                 * We allow users to reverse the logic by configuring
                 * a sysctl variable, so that privacy conscious users can
                 * always prefer temporary addresses.
                 */
                if (opts == NULL ||
                    opts->ip6po_prefer_tempaddr == IP6PO_TEMPADDR_SYSTEM) {
                        prefer_tempaddr = V_ip6_prefer_tempaddr;
                } else if (opts->ip6po_prefer_tempaddr ==
                    IP6PO_TEMPADDR_NOTPREFER) {
                        prefer_tempaddr = 0;
                } else
                        prefer_tempaddr = 1;
                if (!(ia_best->ia6_flags & IN6_IFF_TEMPORARY) &&
                    (ia->ia6_flags & IN6_IFF_TEMPORARY)) {
                        if (prefer_tempaddr)
                                REPLACE(7);
                        else
                                NEXT(7);
                }
                if ((ia_best->ia6_flags & IN6_IFF_TEMPORARY) &&
                    !(ia->ia6_flags & IN6_IFF_TEMPORARY)) {
                        if (prefer_tempaddr)
                                NEXT(7);
                        else
                                REPLACE(7);
                }

                /*
                 * Rule 8: 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))
                        NEXT(8);
                if (!(ia_best->ia_ifp->if_flags & IFF_UP) &&
                    (ia->ia_ifp->if_flags & IFF_UP))
                        REPLACE(8);

                /*
                 * Rule 9: prefer address with better virtual status.
                 */
                if (ifa_preferred(&ia_best->ia_ifa, &ia->ia_ifa))
                        REPLACE(9);
                if (ifa_preferred(&ia->ia_ifa, &ia_best->ia_ifa))
                        NEXT(9);

                /*
                 * Rule 10: prefer address with `prefer_source' flag.
                 */
                if ((ia_best->ia6_flags & IN6_IFF_PREFER_SOURCE) == 0 &&
                    (ia->ia6_flags & IN6_IFF_PREFER_SOURCE) != 0)
                        REPLACE(10);
                if ((ia_best->ia6_flags & IN6_IFF_PREFER_SOURCE) != 0 &&
                    (ia->ia6_flags & IN6_IFF_PREFER_SOURCE) == 0)
                        NEXT(10);

                /*
                 * Rule 14: Use longest matching prefix.
                 * Note: in the address selection draft, this rule is
                 * documented as "Rule 8".  However, since it is also
                 * documented that this rule can be overridden, we assign
                 * a large number so that it is easy to assign smaller numbers
                 * to more preferred rules.
                 */
                new_matchlen = in6_matchlen(&ia->ia_addr.sin6_addr, &dst);
                if (best_matchlen < new_matchlen)
                        REPLACE(14);
                if (new_matchlen < best_matchlen)
                        NEXT(14);

                /* Rule 15 is reserved. */

                /*
                 * Last resort: just keep the current candidate.
                 * Or, do we need more rules?
                 */
                continue;

          replace:
                ia_best = ia;
                best_scope = (new_scope >= 0 ? new_scope :
                              in6_addrscope(&ia_best->ia_addr.sin6_addr));
                best_policy = (new_policy ? new_policy :
                               lookup_addrsel_policy(&ia_best->ia_addr));
                best_matchlen = (new_matchlen >= 0 ? new_matchlen :
                                 in6_matchlen(&ia_best->ia_addr.sin6_addr,
                                              &dst));

          next:
                continue;

          out:
                break;
        }

        if ((ia = ia_best) == NULL) {
                IN6_IFADDR_RUNLOCK(&in6_ifa_tracker);
                IP6STAT_INC(ip6s_sources_none);
                return (EADDRNOTAVAIL);
        }

        /*
         * At this point at least one of the addresses belonged to the jail
         * but it could still be, that we want to further restrict it, e.g.
         * theoratically IN6_IS_ADDR_LOOPBACK.
         * It must not be IN6_IS_ADDR_UNSPECIFIED anymore.
         * prison_local_ip6() will fix an IN6_IS_ADDR_LOOPBACK but should
         * let all others previously selected pass.
         * Use tmp to not change ::1 on lo0 to the primary jail address.
         */
        tmp = ia->ia_addr.sin6_addr;
        if (cred != NULL && prison_local_ip6(cred, &tmp, (inp != NULL &&
            (inp->inp_flags & IN6P_IPV6_V6ONLY) != 0)) != 0) {
                IN6_IFADDR_RUNLOCK(&in6_ifa_tracker);
                IP6STAT_INC(ip6s_sources_none);
                return (EADDRNOTAVAIL);
        }

        if (ifpp)
                *ifpp = ifp;

        bcopy(&tmp, srcp, sizeof(*srcp));
        if (ia->ia_ifp == ifp)
                IP6STAT_INC2(ip6s_sources_sameif, best_scope);
        else
                IP6STAT_INC2(ip6s_sources_otherif, best_scope);
        if (dst_scope == best_scope)
                IP6STAT_INC2(ip6s_sources_samescope, best_scope);
        else
                IP6STAT_INC2(ip6s_sources_otherscope, best_scope);
        if (IFA6_IS_DEPRECATED(ia))
                IP6STAT_INC2(ip6s_sources_deprecated, best_scope);
        IN6_IFADDR_RUNLOCK(&in6_ifa_tracker);
        return (0);
}

/*
 * Select source address based on @inp, @dstsock and @opts.
 * Stores selected address to @srcp. If @scope_ambiguous is set,
 * embed scope from selected outgoing interface. If @hlim pointer
 * is provided, stores calculated hop limit there.
 * Returns 0 on success.
 */
int
in6_selectsrc_socket(struct sockaddr_in6 *dstsock, struct ip6_pktopts *opts,
    struct inpcb *inp, struct ucred *cred, int scope_ambiguous,
    struct in6_addr *srcp, int *hlim)
{
        struct ifnet *retifp;
        uint32_t fibnum;
        int error;

        INP_LOCK_ASSERT(inp);

        fibnum = inp->inp_inc.inc_fibnum;
        retifp = NULL;

        error = in6_selectsrc(fibnum, dstsock, opts, inp->in6p_moptions,
            inp, cred, &retifp, srcp);
        if (error != 0)
                return (error);

        if (hlim != NULL)
                *hlim = in6_selecthlim(inp, retifp);

        if (retifp == NULL || scope_ambiguous == 0)
                return (0);

        /*
         * Application should provide a proper zone ID or the use of
         * default zone IDs should be enabled.  Unfortunately, some
         * applications do not behave as it should, so we need a
         * workaround.  Even if an appropriate ID is not determined
         * (when it's required), if we can determine the outgoing
         * interface. determine the zone ID based on the interface.
         */
        error = in6_setscope(&dstsock->sin6_addr, retifp, NULL);

        return (error);
}

/*
 * Select source address based on @fibnum, @dst and @scopeid.
 * Stores selected address to @srcp.
 * Returns 0 on success.
 *
 * Used by non-socket based consumers
 */
int
in6_selectsrc_addr(uint32_t fibnum, const struct in6_addr *dst,
    uint32_t scopeid, struct ifnet *ifp, struct in6_addr *srcp,
    int *hlim)
{
        struct ifnet *retifp;
        struct sockaddr_in6 dst_sa;
        int error;

        retifp = ifp;
        bzero(&dst_sa, sizeof(dst_sa));
        dst_sa.sin6_family = AF_INET6;
        dst_sa.sin6_len = sizeof(dst_sa);
        dst_sa.sin6_addr = *dst;
        dst_sa.sin6_scope_id = scopeid;
        sa6_embedscope(&dst_sa, 0);

        error = in6_selectsrc(fibnum, &dst_sa, NULL, NULL,
            NULL, NULL, &retifp, srcp);
        if (hlim != NULL)
                *hlim = in6_selecthlim(NULL, retifp);

        return (error);
}

/*
 * Select source address based on @fibnum, @dst and @mopts.
 * Stores selected address to @srcp.
 * Returns 0 on success.
 *
 * Used by non-socket based consumers (ND code mostly)
 */
int
in6_selectsrc_nbr(uint32_t fibnum, const struct in6_addr *dst,
    struct ip6_moptions *mopts, struct ifnet *ifp, struct in6_addr *srcp)
{
        struct sockaddr_in6 dst_sa;
        struct ifnet *retifp;
        int error;

        retifp = ifp;
        bzero(&dst_sa, sizeof(dst_sa));
        dst_sa.sin6_family = AF_INET6;
        dst_sa.sin6_len = sizeof(dst_sa);
        dst_sa.sin6_addr = *dst;
        dst_sa.sin6_scope_id = ntohs(in6_getscope(dst));
        sa6_embedscope(&dst_sa, 0);

        error = in6_selectsrc(fibnum, &dst_sa, NULL, mopts,
            NULL, NULL, &retifp, srcp);
        return (error);
}

static struct nhop_object *
cache_route(uint32_t fibnum, const struct sockaddr_in6 *dst, struct route_in6 *ro,
    uint32_t flowid)
{
        /*
         * 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.
         * Assumes that 'struct route_in6' is exclusively locked.
         */
        if (ro->ro_nh != NULL && (
            !NH_IS_VALID(ro->ro_nh) || ro->ro_dst.sin6_family != AF_INET6 ||
            !IN6_ARE_ADDR_EQUAL(&ro->ro_dst.sin6_addr, &dst->sin6_addr)))
                RO_NHFREE(ro);

        if (ro->ro_nh == NULL) {
                ro->ro_dst = *dst;

                const struct in6_addr *paddr;
                struct in6_addr unscoped_addr;
                uint32_t scopeid = 0;
                if (IN6_IS_SCOPE_LINKLOCAL(&dst->sin6_addr)) {
                        in6_splitscope(&dst->sin6_addr, &unscoped_addr, &scopeid);
                        paddr = &unscoped_addr;
                } else
                        paddr = &dst->sin6_addr;
                ro->ro_nh = fib6_lookup(fibnum, paddr, scopeid, NHR_REF, flowid);
        }
        return (ro->ro_nh);
}

static struct nhop_object *
lookup_route(uint32_t fibnum, struct sockaddr_in6 *dst, struct route_in6 *ro,
    struct ip6_pktopts *opts, uint32_t flowid)
{
        struct nhop_object *nh = NULL;

        /*
         * If the next hop address for the packet is specified by the caller,
         * use it as the gateway.
         */
        if (opts && opts->ip6po_nexthop) {
                struct route_in6 *ron = &opts->ip6po_nextroute;
                struct sockaddr_in6 *sin6_next = satosin6(opts->ip6po_nexthop);

                nh = cache_route(fibnum, sin6_next, ron, flowid);

                /*
                 * The node identified by that address must be a
                 * neighbor of the sending host.
                 */
                if (nh != NULL && (nh->nh_flags & NHF_GATEWAY) != 0)
                        nh = NULL;
        } else if (ro != NULL) {
                nh = cache_route(fibnum, dst, ro, flowid);
                if (nh == NULL)
                        return (NULL);

                /*
                 * Check if the outgoing interface conflicts with
                 * the interface specified by ipi6_ifindex (if specified).
                 */
                struct in6_pktinfo *pi;
                if (opts && (pi = opts->ip6po_pktinfo) != NULL && pi->ipi6_ifindex) {
                        if (nh->nh_aifp->if_index != pi->ipi6_ifindex)
                                nh = NULL;
                }
        }

        return (nh);
}

/*
 * Finds outgoing nexthop or the outgoing interface for the
 * @dstsock.
 * Return 0 on success and stores the lookup result in @retnh and @retifp
 */
static int
selectroute(struct sockaddr_in6 *dstsock, struct ip6_pktopts *opts,
    struct ip6_moptions *mopts, struct route_in6 *ro,
    struct ifnet **retifp, struct nhop_object **retnh, int norouteok,
    u_int fibnum, uint32_t flowid)
{
        int error = 0;
        struct ifnet *ifp = NULL;
        struct in6_pktinfo *pi = NULL;
        struct in6_addr *dst = &dstsock->sin6_addr;

        /* If the caller specify the outgoing interface explicitly, use it. */
        if (opts && (pi = opts->ip6po_pktinfo) != NULL && pi->ipi6_ifindex) {
                /* XXX boundary check is assumed to be already done. */
                ifp = ifnet_byindex(pi->ipi6_ifindex);
                if (ifp != NULL && (norouteok || IN6_IS_ADDR_MULTICAST(dst))) {
                        /*
                         * we do not have to check or get the route for
                         * multicast.
                         */
                        goto done;
                } else
                        goto getroute;
        }
        /*
         * 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 && (ifp = mopts->im6o_multicast_ifp) != NULL) {
                goto done; /* we do not need a route for multicast. */
        }
        /*
         * If destination address is LLA or link- or node-local multicast,
         * use it's embedded scope zone id to determine outgoing interface.
         */
        if (IN6_IS_ADDR_MC_LINKLOCAL(dst) ||
            IN6_IS_ADDR_MC_NODELOCAL(dst)) {
                uint32_t zoneid = ntohs(in6_getscope(dst));
                if (zoneid > 0) {
                        ifp = in6_getlinkifnet(zoneid);
                        goto done;
                }
        }

  getroute:;
        struct nhop_object *nh = lookup_route(fibnum, dstsock, ro, opts, flowid);
        if (nh != NULL) {
                *retifp = nh->nh_aifp;
                error = 0;
        } else {
                *retifp = NULL;
                IP6STAT_INC(ip6s_noroute);
                error = EHOSTUNREACH;
        }
        *retnh = nh;
        return (error);

  done:
        if (ifp == 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)
                IP6STAT_INC(ip6s_noroute);

        *retifp = ifp;
        *retnh = NULL;

        return (error);
}

static int
in6_selectif(struct sockaddr_in6 *dstsock, struct ip6_pktopts *opts,
    struct ip6_moptions *mopts, struct ifnet **retifp,
    struct ifnet *oifp, u_int fibnum)
{
        int error;
        struct route_in6 sro;
        struct nhop_object *nh = NULL;
        uint16_t nh_flags;

        KASSERT(retifp != NULL, ("%s: retifp is NULL", __func__));

        bzero(&sro, sizeof(sro));
        nh_flags = 0;

        error = selectroute(dstsock, opts, mopts, &sro, retifp, &nh, 1, fibnum, 0);

        if (nh != NULL)
                nh_flags = nh->nh_flags;
        if (nh != NULL && nh == sro.ro_nh)
                NH_FREE(nh);

        if (error != 0) {
                /* Help ND. See oifp comment in in6_selectsrc(). */
                if (oifp != NULL && fibnum == RT_DEFAULT_FIB) {
                        *retifp = oifp;
                        error = 0;
                }
                return (error);
        }

        /*
         * 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 (nh_flags & (NHF_REJECT | NHF_BLACKHOLE)) {
                error = (nh_flags & NHF_HOST ? EHOSTUNREACH : ENETUNREACH);
                return (error);
        }

        return (0);
}

/* Public wrapper function to selectroute(). */
int
in6_selectroute(struct sockaddr_in6 *dstsock, struct ip6_pktopts *opts,
    struct ip6_moptions *mopts, struct route_in6 *ro,
    struct ifnet **retifp, struct nhop_object **retnh, u_int fibnum, uint32_t flowid)
{
        MPASS(retifp != NULL);
        MPASS(retnh != NULL);

        return (selectroute(dstsock, opts, mopts, ro, retifp,
            retnh, 0, fibnum, flowid));
}

/*
 * 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 inpcb *inp, struct ifnet *ifp)
{

        if (inp && inp->in6p_hops >= 0)
                return (inp->in6p_hops);
        else if (ifp)
                return (ifp->if_inet6->nd_curhoplimit);
        else if (inp && !IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_faddr)) {
                struct nhop_object *nh;
                struct in6_addr dst;
                uint32_t fibnum, scopeid;
                int hlim;

                fibnum = inp->inp_inc.inc_fibnum;
                in6_splitscope(&inp->in6p_faddr, &dst, &scopeid);
                nh = fib6_lookup(fibnum, &dst, scopeid, 0, 0);
                if (nh != NULL) {
                        hlim = nh->nh_ifp->if_inet6->nd_curhoplimit;
                        return (hlim);
                }
        }
        return (V_ip6_defhlim);
}

void
addrsel_policy_init(void)
{

        init_policy_queue();

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

        if (!IS_DEFAULT_VNET(curvnet))
                return;

        ADDRSEL_LOCK_INIT();
        ADDRSEL_SXLOCK_INIT();
}

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

        ADDRSEL_LOCK();
        match = match_addrsel_policy(key);

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

        return (match);
}

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

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)
{
        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. */
        IN6_MASK_ADDR(&ent0.addr.sin6_addr, &ent0.addrmask.sin6_addr);
        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);

VNET_DEFINE_STATIC(struct addrsel_policyhead, addrsel_policytab);
#define V_addrsel_policytab             VNET(addrsel_policytab)

static void
init_policy_queue(void)
{

        TAILQ_INIT(&V_addrsel_policytab);
}

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

        new = malloc(sizeof(*new), M_IFADDR,
               M_WAITOK);
        ADDRSEL_XLOCK();
        ADDRSEL_LOCK();

        /* duplication check */
        TAILQ_FOREACH(pol, &V_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();
                        ADDRSEL_XUNLOCK();
                        free(new, M_IFADDR);
                        return (EEXIST);        /* or override it? */
                }
        }

        bzero(new, sizeof(*new));

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

        TAILQ_INSERT_TAIL(&V_addrsel_policytab, new, ape_entry);
        ADDRSEL_UNLOCK();
        ADDRSEL_XUNLOCK();

        return (0);
}

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

        ADDRSEL_XLOCK();
        ADDRSEL_LOCK();

        /* search for the entry in the table */
        TAILQ_FOREACH(pol, &V_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();
                ADDRSEL_XUNLOCK();
                return (ESRCH);
        }

        TAILQ_REMOVE(&V_addrsel_policytab, pol, ape_entry);
        ADDRSEL_UNLOCK();
        ADDRSEL_XUNLOCK();
        free(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;

        ADDRSEL_SLOCK();
        TAILQ_FOREACH(pol, &V_addrsel_policytab, ape_entry) {
                if ((error = (*callback)(&pol->ape_policy, w)) != 0) {
                        ADDRSEL_SUNLOCK();
                        return (error);
                }
        }
        ADDRSEL_SUNLOCK();
        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);
}

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, &V_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);
}