xref: /src/sys/netinet6/nd6_nbr.c

/*	$NetBSD: nd6_nbr.c,v 1.170 2019/08/29 16:26:43 roy Exp $	*/
/*	$KAME: nd6_nbr.c,v 1.61 2001/02/10 16:06:14 jinmei Exp $	*/

/*
 * Copyright (C) 1995, 1996, 1997, and 1998 WIDE Project.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the project nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE PROJECT AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: nd6_nbr.c,v 1.170 2019/08/29 16:26:43 roy Exp $");

#ifdef _KERNEL_OPT
#include "opt_inet.h"
#include "opt_net_mpsafe.h"
#endif

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kmem.h>
#include <sys/mbuf.h>
#include <sys/socket.h>
#include <sys/socketvar.h>
#include <sys/sockio.h>
#include <sys/time.h>
#include <sys/kernel.h>
#include <sys/errno.h>
#include <sys/ioctl.h>
#include <sys/syslog.h>
#include <sys/queue.h>
#include <sys/callout.h>
#include <sys/cprng.h>

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

#include <netinet/in.h>
#include <netinet/in_var.h>
#include <netinet6/in6_var.h>
#include <netinet6/in6_ifattach.h>
#include <netinet/ip6.h>
#include <netinet6/ip6_var.h>
#include <netinet6/scope6_var.h>
#include <netinet6/nd6.h>
#include <netinet/icmp6.h>
#include <netinet6/icmp6_private.h>

#include "carp.h"
#if NCARP > 0
#include <netinet/ip_carp.h>
#endif

struct dadq;
static struct dadq *nd6_dad_find(struct ifaddr *, struct nd_opt_nonce *, bool *);
static bool nd6_dad_ownnonce(struct ifaddr *, struct nd_opt_nonce *nonce);
static void nd6_dad_starttimer(struct dadq *, int);
static void nd6_dad_destroytimer(struct dadq *);
static void nd6_dad_timer(struct dadq *);
static void nd6_dad_ns_output(struct dadq *, struct ifaddr *);
static void nd6_dad_input(struct ifaddr *, struct nd_opt_nonce *,
    const struct sockaddr_dl *);
static void nd6_dad_duplicated(struct ifaddr *, struct dadq *,
    const struct sockaddr_dl *);

static int dad_maxtry = 15;	/* max # of *tries* to transmit DAD packet */

/*
 * Input a Neighbor Solicitation Message.
 *
 * Based on RFC 2461
 * Based on RFC 2462 (duplicate address detection)
 */
void
nd6_ns_input(struct mbuf *m, int off, int icmp6len)
{
	struct ifnet *ifp;
	struct ip6_hdr *ip6 = mtod(m, struct ip6_hdr *);
	struct nd_neighbor_solicit *nd_ns;
	struct in6_addr saddr6 = ip6->ip6_src;
	struct in6_addr daddr6 = ip6->ip6_dst;
	struct in6_addr taddr6;
	struct in6_addr myaddr6;
	char *lladdr = NULL;
	struct ifaddr *ifa = NULL;
	int lladdrlen = 0;
	int anycast = 0, proxy = 0, tentative = 0;
	int router = ip6_forwarding;
	int tlladdr;
	union nd_opts ndopts;
	const struct sockaddr_dl *proxydl = NULL;
	struct psref psref;
	struct psref psref_ia;
	char ip6buf[INET6_ADDRSTRLEN], ip6buf2[INET6_ADDRSTRLEN];

	ifp = m_get_rcvif_psref(m, &psref);
	if (ifp == NULL)
		goto freeit;

	IP6_EXTHDR_GET(nd_ns, struct nd_neighbor_solicit *, m, off, icmp6len);
	if (nd_ns == NULL) {
		ICMP6_STATINC(ICMP6_STAT_TOOSHORT);
		m_put_rcvif_psref(ifp, &psref);
		return;
	}
	ip6 = mtod(m, struct ip6_hdr *); /* adjust pointer for safety */
	taddr6 = nd_ns->nd_ns_target;
	if (in6_setscope(&taddr6, ifp, NULL) != 0)
		goto bad;

	if (ip6->ip6_hlim != 255) {
		nd6log(LOG_ERR, "invalid hlim (%d) from %s to %s on %s\n",
		    ip6->ip6_hlim, IN6_PRINT(ip6buf, &ip6->ip6_src),
		    IN6_PRINT(ip6buf2, &ip6->ip6_dst), if_name(ifp));
		goto bad;
	}

	if (IN6_IS_ADDR_UNSPECIFIED(&saddr6)) {
		/* dst has to be a solicited node multicast address. */
		/* don't check ifindex portion */
		if (daddr6.s6_addr16[0] == IPV6_ADDR_INT16_MLL &&
		    daddr6.s6_addr32[1] == 0 &&
		    daddr6.s6_addr32[2] == IPV6_ADDR_INT32_ONE &&
		    daddr6.s6_addr8[12] == 0xff) {
			; /* good */
		} else {
			nd6log(LOG_INFO, "bad DAD packet (wrong ip6 dst)\n");
			goto bad;
		}
	} else {
		struct sockaddr_in6 ssin6;

		/*
		 * Make sure the source address is from a neighbor's address.
		 */
		sockaddr_in6_init(&ssin6, &saddr6, 0, 0, 0);
		if (nd6_is_addr_neighbor(&ssin6, ifp) == 0) {
			nd6log(LOG_INFO,
			    "NS packet from non-neighbor %s on %s\n",
			    IN6_PRINT(ip6buf, &saddr6), if_name(ifp));
			goto bad;
		}
	}

	if (IN6_IS_ADDR_MULTICAST(&taddr6)) {
		nd6log(LOG_INFO, "bad NS target (multicast)\n");
		goto bad;
	}

	icmp6len -= sizeof(*nd_ns);
	nd6_option_init(nd_ns + 1, icmp6len, &ndopts);
	if (nd6_options(&ndopts) < 0) {
		nd6log(LOG_INFO, "invalid ND option, ignored\n");
		/* nd6_options have incremented stats */
		goto freeit;
	}

	if (ndopts.nd_opts_src_lladdr) {
		lladdr = (char *)(ndopts.nd_opts_src_lladdr + 1);
		lladdrlen = ndopts.nd_opts_src_lladdr->nd_opt_len << 3;
	}

	if (IN6_IS_ADDR_UNSPECIFIED(&ip6->ip6_src) && lladdr) {
		nd6log(LOG_INFO,
		    "bad DAD packet (link-layer address option)\n");
		goto bad;
	}

	/*
	 * Attaching target link-layer address to the NA?
	 * (RFC 2461 7.2.4)
	 *
	 * NS IP dst is multicast			MUST add
	 * Otherwise					MAY be omitted
	 *
	 * In this implementation, we omit the target link-layer address
	 * in the "MAY" case.
	 */
#if 0 /* too much! */
	ifa = (struct ifaddr *)in6ifa_ifpwithaddr(ifp, &daddr6);
	if (ifa && (((struct in6_ifaddr *)ifa)->ia6_flags & IN6_IFF_ANYCAST))
		tlladdr = 0;
	else
#endif
	if (!IN6_IS_ADDR_MULTICAST(&daddr6))
		tlladdr = 0;
	else
		tlladdr = 1;

	/*
	 * Target address (taddr6) must be either:
	 * (1) Valid unicast/anycast address for my receiving interface,
	 * (2) Unicast address for which I'm offering proxy service, or
	 * (3) "tentative" address on which DAD is being performed.
	 */
	/* (1) and (3) check. */
#if NCARP > 0
	if (ifp->if_carp && ifp->if_type != IFT_CARP) {
		int s = pserialize_read_enter();
		ifa = carp_iamatch6(ifp->if_carp, &taddr6);
		if (ifa != NULL)
			ifa_acquire(ifa, &psref_ia);
		pserialize_read_exit(s);
	} else
		ifa = NULL;
	if (!ifa)
		ifa = (struct ifaddr *)in6ifa_ifpwithaddr_psref(ifp, &taddr6,
		    &psref_ia);
#else
	ifa = (struct ifaddr *)in6ifa_ifpwithaddr_psref(ifp, &taddr6,
	    &psref_ia);
#endif

	/* (2) check. */
	if (ifa == NULL) {
		struct rtentry *rt;
		struct sockaddr_in6 tsin6;

		sockaddr_in6_init(&tsin6, &taddr6, 0, 0, 0);

		rt = rtalloc1(sin6tosa(&tsin6), 0);
		if (rt && (rt->rt_flags & RTF_ANNOUNCE) != 0 &&
		    rt->rt_gateway->sa_family == AF_LINK) {
			/*
			 * proxy NDP for single entry
			 */
			ifa = (struct ifaddr *)in6ifa_ifpforlinklocal_psref(ifp,
				IN6_IFF_NOTREADY|IN6_IFF_ANYCAST, &psref_ia);
			if (ifa) {
				proxy = 1;
				proxydl = satocsdl(rt->rt_gateway);
				router = 0;	/* XXX */
			}
		}
		if (rt)
			rt_unref(rt);
	}
	if (ifa == NULL) {
		/*
		 * We've got an NS packet, and we don't have that address
		 * assigned for us.  We MUST silently ignore it.
		 * See RFC2461 7.2.3.
		 */
		goto freeit;
	}
	myaddr6 = *IFA_IN6(ifa);
	anycast = ((struct in6_ifaddr *)ifa)->ia6_flags & IN6_IFF_ANYCAST;
	tentative = ((struct in6_ifaddr *)ifa)->ia6_flags & IN6_IFF_TENTATIVE;
	if (((struct in6_ifaddr *)ifa)->ia6_flags & IN6_IFF_DUPLICATED)
		goto freeit;

	if (lladdr && ((ifp->if_addrlen + 2 + 7) & ~7) != lladdrlen) {
		nd6log(LOG_INFO, "lladdrlen mismatch for %s "
		    "(if %d, NS packet %d)\n",
		    IN6_PRINT(ip6buf, &taddr6),
		    ifp->if_addrlen, lladdrlen - 2);
		goto bad;
	}

	if (IN6_ARE_ADDR_EQUAL(&myaddr6, &saddr6)) {
		nd6log(LOG_INFO, "duplicate IP6 address %s\n",
		    IN6_PRINT(ip6buf, &saddr6));
		goto freeit;
	}

	/*
	 * We have neighbor solicitation packet, with target address equals to
	 * one of my tentative address.
	 *
	 * src addr	how to process?
	 * ---		---
	 * multicast	of course, invalid (rejected in ip6_input)
	 * unicast	somebody is doing address resolution -> ignore
	 * unspec	dup address detection
	 *
	 * The processing is defined in RFC 2462.
	 */
	if (tentative) {
		/*
		 * If source address is unspecified address, it is for
		 * duplicate address detection.
		 *
		 * If not, the packet is for addess resolution;
		 * silently ignore it.
		 */
		if (IN6_IS_ADDR_UNSPECIFIED(&saddr6)) {
			struct sockaddr_dl sdl, *sdlp;

			if (lladdr != NULL)
				sdlp = sockaddr_dl_init(&sdl, sizeof(sdl),
				    ifp->if_index, ifp->if_type,
				    NULL, 0, lladdr, lladdrlen);
			else
				sdlp = NULL;
			nd6_dad_input(ifa, ndopts.nd_opts_nonce, sdlp);
		}
		goto freeit;
	}

	/*
	 * It looks that sender is performing DAD.
	 * Check that the nonce is not being used by the same address
	 * on another interface.
	 */
	if (IN6_IS_ADDR_UNSPECIFIED(&saddr6) && ndopts.nd_opts_nonce != NULL) {
		if (nd6_dad_ownnonce(ifa, ndopts.nd_opts_nonce))
			goto freeit;
	}

	ifa_release(ifa, &psref_ia);
	ifa = NULL;

	/*
	 * If the source address is unspecified address, entries must not
	 * be created or updated.
	 * It looks that sender is performing DAD.  Output NA toward
	 * all-node multicast address, to tell the sender that I'm using
	 * the address.
	 * S bit ("solicited") must be zero.
	 */
	if (IN6_IS_ADDR_UNSPECIFIED(&saddr6)) {
		struct in6_addr in6_all;

		in6_all = in6addr_linklocal_allnodes;
		if (in6_setscope(&in6_all, ifp, NULL) != 0)
			goto bad;
		nd6_na_output(ifp, &in6_all, &taddr6,
		    ((anycast || proxy || !tlladdr) ? 0 : ND_NA_FLAG_OVERRIDE) |
		    (ip6_forwarding ? ND_NA_FLAG_ROUTER : 0),
		    tlladdr, (const struct sockaddr *)proxydl);
		goto freeit;
	}

	nd6_cache_lladdr(ifp, &saddr6, lladdr, lladdrlen, ND_NEIGHBOR_SOLICIT, 0);

	nd6_na_output(ifp, &saddr6, &taddr6,
	    ((anycast || proxy || !tlladdr) ? 0 : ND_NA_FLAG_OVERRIDE) |
	    (router ? ND_NA_FLAG_ROUTER : 0) | ND_NA_FLAG_SOLICITED,
	    tlladdr, (const struct sockaddr *)proxydl);
 freeit:
	ifa_release(ifa, &psref_ia);
	m_put_rcvif_psref(ifp, &psref);
	m_freem(m);
	return;

 bad:
	nd6log(LOG_ERR, "src=%s\n", IN6_PRINT(ip6buf, &saddr6));
	nd6log(LOG_ERR, "dst=%s\n", IN6_PRINT(ip6buf, &daddr6));
	nd6log(LOG_ERR, "tgt=%s\n", IN6_PRINT(ip6buf, &taddr6));
	ICMP6_STATINC(ICMP6_STAT_BADNS);
	ifa_release(ifa, &psref_ia);
	m_put_rcvif_psref(ifp, &psref);
	m_freem(m);
}

/*
 * Output a Neighbor Solicitation Message. Caller specifies:
 *	- ICMP6 header source IP6 address
 *	- ND6 header target IP6 address
 *	- ND6 header source datalink address
 *
 * Based on RFC 2461
 * Based on RFC 2462 (duplicate address detection)
 */
void
nd6_ns_output(struct ifnet *ifp, const struct in6_addr *daddr6,
    const struct in6_addr *taddr6,
    struct in6_addr *hsrc,
    uint8_t *nonce		/* duplicate address detection */)
{
	struct mbuf *m;
	struct ip6_hdr *ip6;
	struct nd_neighbor_solicit *nd_ns;
	struct in6_addr *src, src_in;
	struct ip6_moptions im6o;
	int icmp6len;
	int maxlen;
	const void *mac;
	struct route ro;

	if (IN6_IS_ADDR_MULTICAST(taddr6))
		return;

	memset(&ro, 0, sizeof(ro));

	/* estimate the size of message */
	maxlen = sizeof(*ip6) + sizeof(*nd_ns);
	maxlen += (sizeof(struct nd_opt_hdr) + ifp->if_addrlen + 7) & ~7;
	KASSERTMSG(max_linkhdr + maxlen <= MCLBYTES,
	    "max_linkhdr + maxlen > MCLBYTES (%d + %d > %d)",
	    max_linkhdr, maxlen, MCLBYTES);

	MGETHDR(m, M_DONTWAIT, MT_DATA);
	if (m && max_linkhdr + maxlen >= MHLEN) {
		MCLGET(m, M_DONTWAIT);
		if ((m->m_flags & M_EXT) == 0) {
			m_free(m);
			m = NULL;
		}
	}
	if (m == NULL)
		return;
	m_reset_rcvif(m);

	if (daddr6 == NULL || IN6_IS_ADDR_MULTICAST(daddr6)) {
		m->m_flags |= M_MCAST;
		im6o.im6o_multicast_if_index = if_get_index(ifp);
		im6o.im6o_multicast_hlim = 255;
		im6o.im6o_multicast_loop = 0;
	}

	icmp6len = sizeof(*nd_ns);
	m->m_pkthdr.len = m->m_len = sizeof(*ip6) + icmp6len;
	m->m_data += max_linkhdr;	/* or m_align() equivalent? */

	/* fill neighbor solicitation packet */
	ip6 = mtod(m, struct ip6_hdr *);
	ip6->ip6_flow = 0;
	ip6->ip6_vfc &= ~IPV6_VERSION_MASK;
	ip6->ip6_vfc |= IPV6_VERSION;
	/* ip6->ip6_plen will be set later */
	ip6->ip6_nxt = IPPROTO_ICMPV6;
	ip6->ip6_hlim = 255;
	if (daddr6)
		ip6->ip6_dst = *daddr6;
	else {
		ip6->ip6_dst.s6_addr16[0] = IPV6_ADDR_INT16_MLL;
		ip6->ip6_dst.s6_addr16[1] = 0;
		ip6->ip6_dst.s6_addr32[1] = 0;
		ip6->ip6_dst.s6_addr32[2] = IPV6_ADDR_INT32_ONE;
		ip6->ip6_dst.s6_addr32[3] = taddr6->s6_addr32[3];
		ip6->ip6_dst.s6_addr8[12] = 0xff;
		if (in6_setscope(&ip6->ip6_dst, ifp, NULL) != 0)
			goto bad;
	}
	if (nonce == NULL) {
		int s;
		/*
		 * RFC2461 7.2.2:
		 * "If the source address of the packet prompting the
		 * solicitation is the same as one of the addresses assigned
		 * to the outgoing interface, that address SHOULD be placed
		 * in the IP Source Address of the outgoing solicitation.
		 * Otherwise, any one of the addresses assigned to the
		 * interface should be used."
		 *
		 * We use the source address for the prompting packet
		 * (hsrc), if:
		 * - hsrc is given from the caller (by giving "ln"), and
		 * - hsrc belongs to the outgoing interface.
		 * Otherwise, we perform the source address selection as usual.
		 */
		s = pserialize_read_enter();
		if (hsrc && in6ifa_ifpwithaddr(ifp, hsrc)) {
			pserialize_read_exit(s);
			src = hsrc;
		} else {
			int error;
			struct sockaddr_in6 dst_sa;

			pserialize_read_exit(s);

			sockaddr_in6_init(&dst_sa, &ip6->ip6_dst, 0, 0, 0);

			error = in6_selectsrc(&dst_sa, NULL,
			    NULL, &ro, NULL, NULL, NULL, &src_in);
			if (error != 0) {
				char ip6buf[INET6_ADDRSTRLEN];
				nd6log(LOG_DEBUG, "source can't be "
				    "determined: dst=%s, error=%d\n",
				    IN6_PRINT(ip6buf, &dst_sa.sin6_addr),
				    error);
				pserialize_read_exit(s);
				goto bad;
			}
			src = &src_in;
		}
	} else {
		/*
		 * Source address for DAD packet must always be IPv6
		 * unspecified address. (0::0)
		 * We actually don't have to 0-clear the address (we did it
		 * above), but we do so here explicitly to make the intention
		 * clearer.
		 */
		memset(&src_in, 0, sizeof(src_in));
		src = &src_in;
	}
	ip6->ip6_src = *src;
	nd_ns = (struct nd_neighbor_solicit *)(ip6 + 1);
	nd_ns->nd_ns_type = ND_NEIGHBOR_SOLICIT;
	nd_ns->nd_ns_code = 0;
	nd_ns->nd_ns_reserved = 0;
	nd_ns->nd_ns_target = *taddr6;
	in6_clearscope(&nd_ns->nd_ns_target); /* XXX */

	/*
	 * Add source link-layer address option.
	 *
	 *				spec		implementation
	 *				---		---
	 * DAD packet			MUST NOT	do not add the option
	 * there's no link layer address:
	 *				impossible	do not add the option
	 * there's link layer address:
	 *	Multicast NS		MUST add one	add the option
	 *	Unicast NS		SHOULD add one	add the option
	 */
	if (nonce == NULL && (mac = nd6_ifptomac(ifp))) {
		int optlen = sizeof(struct nd_opt_hdr) + ifp->if_addrlen;
		struct nd_opt_hdr *nd_opt = (struct nd_opt_hdr *)(nd_ns + 1);
		/* 8 byte alignments... */
		optlen = (optlen + 7) & ~7;

		m->m_pkthdr.len += optlen;
		m->m_len += optlen;
		icmp6len += optlen;
		memset((void *)nd_opt, 0, optlen);
		nd_opt->nd_opt_type = ND_OPT_SOURCE_LINKADDR;
		nd_opt->nd_opt_len = optlen >> 3;
		memcpy((void *)(nd_opt + 1), mac, ifp->if_addrlen);
	}

	/* Add a nonce option (RFC 3971) to detect looped back NS messages.
	 * This behavior is documented in RFC 7527. */
	if (nonce != NULL) {
		int optlen = sizeof(struct nd_opt_hdr) + ND_OPT_NONCE_LEN;
		struct nd_opt_hdr *nd_opt = (struct nd_opt_hdr *)(nd_ns + 1);

		/* 8-byte alignment is required. */
		optlen = (optlen + 7) & ~7;
		m->m_pkthdr.len += optlen;
		m->m_len += optlen;
		icmp6len += optlen;
		memset(nd_opt, 0, optlen);
		nd_opt->nd_opt_type = ND_OPT_NONCE;
		nd_opt->nd_opt_len = optlen >> 3;
		memcpy(nd_opt + 1, nonce, ND_OPT_NONCE_LEN);
	}

	ip6->ip6_plen = htons((u_int16_t)icmp6len);
	nd_ns->nd_ns_cksum = 0;
	nd_ns->nd_ns_cksum =
	    in6_cksum(m, IPPROTO_ICMPV6, sizeof(*ip6), icmp6len);

	ip6_output(m, NULL, &ro, nonce != NULL ? IPV6_UNSPECSRC : 0,
	    &im6o, NULL, NULL);
	icmp6_ifstat_inc(ifp, ifs6_out_msg);
	icmp6_ifstat_inc(ifp, ifs6_out_neighborsolicit);
	ICMP6_STATINC(ICMP6_STAT_OUTHIST + ND_NEIGHBOR_SOLICIT);

	rtcache_free(&ro);
	return;

  bad:
	rtcache_free(&ro);
	m_freem(m);
	return;
}

/*
 * Neighbor advertisement input handling.
 *
 * Based on RFC 2461
 * Based on RFC 2462 (duplicate address detection)
 *
 * the following items are not implemented yet:
 * - proxy advertisement delay rule (RFC2461 7.2.8, last paragraph, SHOULD)
 * - anycast advertisement delay rule (RFC2461 7.2.7, SHOULD)
 */
void
nd6_na_input(struct mbuf *m, int off, int icmp6len)
{
	struct ifnet *ifp;
	struct ip6_hdr *ip6 = mtod(m, struct ip6_hdr *);
	struct nd_neighbor_advert *nd_na;
	struct in6_addr saddr6 = ip6->ip6_src;
	struct in6_addr daddr6 = ip6->ip6_dst;
	struct in6_addr taddr6;
	int flags;
	int is_router;
	int is_solicited;
	int is_override;
	char *lladdr = NULL;
	int lladdrlen = 0;
	struct ifaddr *ifa;
	struct llentry *ln = NULL;
	union nd_opts ndopts;
	struct sockaddr_in6 ssin6;
	bool rt_announce;
	bool checklink = false;
	struct psref psref;
	struct psref psref_ia;
	char ip6buf[INET6_ADDRSTRLEN], ip6buf2[INET6_ADDRSTRLEN];

	ifp = m_get_rcvif_psref(m, &psref);
	if (ifp == NULL)
		goto freeit;

	if (ip6->ip6_hlim != 255) {
		nd6log(LOG_ERR,
		    "invalid hlim (%d) from %s to %s on %s\n",
		    ip6->ip6_hlim, IN6_PRINT(ip6buf, &ip6->ip6_src),
		    IN6_PRINT(ip6buf2, &ip6->ip6_dst), if_name(ifp));
		goto bad;
	}

	IP6_EXTHDR_GET(nd_na, struct nd_neighbor_advert *, m, off, icmp6len);
	if (nd_na == NULL) {
		m_put_rcvif_psref(ifp, &psref);
		ICMP6_STATINC(ICMP6_STAT_TOOSHORT);
		return;
	}

	flags = nd_na->nd_na_flags_reserved;
	is_router = ((flags & ND_NA_FLAG_ROUTER) != 0);
	is_solicited = ((flags & ND_NA_FLAG_SOLICITED) != 0);
	is_override = ((flags & ND_NA_FLAG_OVERRIDE) != 0);

	taddr6 = nd_na->nd_na_target;
	if (in6_setscope(&taddr6, ifp, NULL)) {
		goto bad;
	}

	if (IN6_IS_ADDR_MULTICAST(&taddr6)) {
		nd6log(LOG_ERR, "invalid target address %s\n",
		    IN6_PRINT(ip6buf, &taddr6));
		goto bad;
	}
	if (is_solicited && IN6_IS_ADDR_MULTICAST(&daddr6)) {
		nd6log(LOG_ERR, "a solicited adv is multicasted\n");
		goto bad;
	}

	icmp6len -= sizeof(*nd_na);
	nd6_option_init(nd_na + 1, icmp6len, &ndopts);
	if (nd6_options(&ndopts) < 0) {
		nd6log(LOG_INFO, "invalid ND option, ignored\n");
		/* nd6_options have incremented stats */
		goto freeit;
	}

	if (ndopts.nd_opts_tgt_lladdr != NULL) {
		struct ifnet *ifp_ll;
		struct psref psref_ll;

		lladdr = (char *)(ndopts.nd_opts_tgt_lladdr + 1);
		lladdrlen = ndopts.nd_opts_tgt_lladdr->nd_opt_len << 3;

		if (lladdr && ((ifp->if_addrlen + 2 + 7) & ~7) != lladdrlen) {
			nd6log(LOG_INFO, "lladdrlen mismatch for %s "
			    "(if %d, NA packet %d)\n", IN6_PRINT(ip6buf, &taddr6),
			    ifp->if_addrlen, lladdrlen - 2);
			goto bad;
		}

		ifp_ll = if_get_bylla(lladdr, ifp->if_addrlen, &psref_ll);
		if (ifp_ll != NULL) {
			/* it's from me, ignore it. */
			if_put(ifp_ll, &psref_ll);
			goto freeit;
		}
	}

	ifa = (struct ifaddr *)in6ifa_ifpwithaddr_psref(ifp, &taddr6, &psref_ia);

	/*
	 * Target address matches one of my interface address.
	 *
	 * If my address is tentative, this means that there's somebody
	 * already using the same address as mine.  This indicates DAD failure.
	 * This is defined in RFC 2462.
	 *
	 * Otherwise, process as defined in RFC 2461.
	 */
	if (ifa) {
		if (((struct in6_ifaddr *)ifa)->ia6_flags & IN6_IFF_TENTATIVE) {
			struct sockaddr_dl sdl, *sdlp;

			if (lladdr != NULL)
				sdlp = sockaddr_dl_init(&sdl, sizeof(sdl),
				    ifp->if_index, ifp->if_type,
				    NULL, 0, lladdr, lladdrlen);
			else
				sdlp = NULL;
			nd6_dad_input(ifa, NULL, sdlp);
		} else
			log(LOG_ERR,
			    "nd6_na_input: duplicate IP6 address %s\n",
			    IN6_PRINT(ip6buf, &taddr6));
		ifa_release(ifa, &psref_ia);
		ifa = NULL;
		goto freeit;
	}

	/*
	 * Make sure the source address is from a neighbor's address.
	 */
	sockaddr_in6_init(&ssin6, &saddr6, 0, 0, 0);
	if (nd6_is_addr_neighbor(&ssin6, ifp) == 0) {
		nd6log(LOG_INFO, "ND packet from non-neighbor %s on %s\n",
		    IN6_PRINT(ip6buf, &saddr6), if_name(ifp));
		goto bad;
	}

	/*
	 * If no neighbor cache entry is found, NA SHOULD silently be
	 * discarded.
	 */
	ln = nd6_lookup(&taddr6, ifp, true);
	if (ln == NULL)
		goto freeit;

	rt_announce = false;
	if (ln->ln_state == ND6_LLINFO_INCOMPLETE) {
		/*
		 * If the link-layer has address, and no lladdr option came,
		 * discard the packet.
		 */
		if (ifp->if_addrlen && !lladdr)
			goto freeit;

		/*
		 * Record link-layer address, and update the state.
		 */
		memcpy(&ln->ll_addr, lladdr, ifp->if_addrlen);
		ln->la_flags |= LLE_VALID;
		rt_announce = true;
		if (is_solicited) {
			ln->ln_state = ND6_LLINFO_REACHABLE;
			ln->ln_byhint = 0;
			if (!ND6_LLINFO_PERMANENT(ln)) {
				nd6_llinfo_settimer(ln,
				    ND_IFINFO(ln->lle_tbl->llt_ifp)->reachable * hz);
			}
		} else {
			ln->ln_state = ND6_LLINFO_STALE;
			nd6_llinfo_settimer(ln, nd6_gctimer * hz);
		}
		if ((ln->ln_router = is_router) != 0) {
			/*
			 * This means a router's state has changed from
			 * non-reachable to probably reachable, and might
			 * affect the status of associated prefixes..
			 */
			checklink = true;
		}
	} else {
		bool llchange;

		/*
		 * Check if the link-layer address has changed or not.
		 */
		if (lladdr == NULL)
			llchange = false;
		else {
			if (ln->la_flags & LLE_VALID) {
				if (memcmp(lladdr, &ln->ll_addr, ifp->if_addrlen))
					llchange = rt_announce = true;
				else
					llchange = false;
			} else
				llchange = rt_announce = true;
		}

		/*
		 * This is VERY complex.  Look at it with care.
		 *
		 * override solicit lladdr llchange	action
		 *					(L: record lladdr)
		 *
		 *	0	0	n	--	(2c)
		 *	0	0	y	n	(2b) L
		 *	0	0	y	y	(1)    REACHABLE->STALE
		 *	0	1	n	--	(2c)   *->REACHABLE
		 *	0	1	y	n	(2b) L *->REACHABLE
		 *	0	1	y	y	(1)    REACHABLE->STALE
		 *	1	0	n	--	(2a)
		 *	1	0	y	n	(2a) L
		 *	1	0	y	y	(2a) L *->STALE
		 *	1	1	n	--	(2a)   *->REACHABLE
		 *	1	1	y	n	(2a) L *->REACHABLE
		 *	1	1	y	y	(2a) L *->REACHABLE
		 */
		if (!is_override && lladdr != NULL && llchange) { /* (1) */
			/*
			 * If state is REACHABLE, make it STALE.
			 * no other updates should be done.
			 */
			if (ln->ln_state == ND6_LLINFO_REACHABLE) {
				ln->ln_state = ND6_LLINFO_STALE;
				nd6_llinfo_settimer(ln, nd6_gctimer * hz);
			}
			goto freeit;
		} else if (is_override				   /* (2a) */
		    || (!is_override && lladdr != NULL && !llchange) /* (2b) */
		    || lladdr == NULL) {			   /* (2c) */
			/*
			 * Update link-local address, if any.
			 */
			if (lladdr != NULL) {
				memcpy(&ln->ll_addr, lladdr, ifp->if_addrlen);
				ln->la_flags |= LLE_VALID;
			}

			/*
			 * If solicited, make the state REACHABLE.
			 * If not solicited and the link-layer address was
			 * changed, make it STALE.
			 */
			if (is_solicited) {
				ln->ln_state = ND6_LLINFO_REACHABLE;
				ln->ln_byhint = 0;
				if (!ND6_LLINFO_PERMANENT(ln)) {
					nd6_llinfo_settimer(ln,
					    ND_IFINFO(ifp)->reachable * hz);
				}
			} else {
				if (lladdr && llchange) {
					ln->ln_state = ND6_LLINFO_STALE;
					nd6_llinfo_settimer(ln,
					    nd6_gctimer * hz);
				}
			}
		}

		if (ln->ln_router && !is_router) {
			/*
			 * The peer dropped the router flag.
			 * Remove the sender from the Default Router List and
			 * update the Destination Cache entries.
			 */
			const struct in6_addr *in6 = &ln->r_l3addr.addr6;
			struct nd_defrouter *dr;
			struct sockaddr_in6 sin6;

			/*
			 * Userland really has no business with NA messages.
			 * However, RFC 4861 6.2.5 only says departing routers
			 * *SHOULD* send RA with lifetime of zero and *MUST*
			 * send all subsequent NA messages if the router flag
			 * unset.
			 *
			 * To help userland avoid the expensive process of
			 * parsing NA messages, send RTM_CHANGE without a
			 * lladdr in the gateway.
			 * This is different from the intial RTM_ADD also
			 * without a lladdr in the gateway and RTM_DELETE.
			 */
			sockaddr_in6_init(&sin6, in6, 0, 0, 0);
			rt_clonedmsg(RTM_CHANGE, sin6tosa(&sin6), NULL,
			    ln->lle_tbl->llt_ifp);
			rt_announce = true;

			ND6_WLOCK();
			dr = nd6_defrouter_lookup(in6, ln->lle_tbl->llt_ifp);
			if (dr)
				nd6_defrtrlist_del(dr, NULL);
			else if (!ip6_forwarding) {
				/*
				 * Even if the neighbor is not in the default
				 * router list, the neighbor may be used
				 * as a next hop for some destinations
				 * (e.g. redirect case). So we must
				 * call nd6_rt_flush explicitly.
				 */
				nd6_rt_flush(&ip6->ip6_src, ln->lle_tbl->llt_ifp);
			}
			ND6_UNLOCK();
		}
		ln->ln_router = is_router;
	}
        /*
	 * XXX: does this matter?
	 * rt->rt_flags &= ~RTF_REJECT;
	 */
	ln->ln_asked = 0;
	nd6_llinfo_release_pkts(ln, ifp);

	if (rt_announce) {
		struct sockaddr_in6 sin6;

		sockaddr_in6_init(&sin6, &ln->r_l3addr.addr6, 0, 0, 0);
		rt_clonedmsg(RTM_CHANGE, sin6tosa(&sin6),
		    (char *)&ln->ll_addr, ln->lle_tbl->llt_ifp);
	}

 freeit:
	if (ln != NULL)
		LLE_WUNLOCK(ln);

	if (checklink) {
		ND6_WLOCK();
		nd6_pfxlist_onlink_check();
		ND6_UNLOCK();
	}

	m_put_rcvif_psref(ifp, &psref);
	m_freem(m);
	return;

 bad:
	if (ln != NULL)
		LLE_WUNLOCK(ln);

	ICMP6_STATINC(ICMP6_STAT_BADNA);
	m_put_rcvif_psref(ifp, &psref);
	m_freem(m);
}

/*
 * Neighbor advertisement output handling.
 *
 * Based on RFC 2461
 *
 * the following items are not implemented yet:
 * - proxy advertisement delay rule (RFC2461 7.2.8, last paragraph, SHOULD)
 * - anycast advertisement delay rule (RFC2461 7.2.7, SHOULD)
 */
void
nd6_na_output(
	struct ifnet *ifp,
	const struct in6_addr *daddr6_0,
	const struct in6_addr *taddr6,
	u_long flags,
	int tlladdr,		/* 1 if include target link-layer address */
	const struct sockaddr *sdl0)	/* sockaddr_dl (= proxy NA) or NULL */
{
	struct mbuf *m;
	struct ip6_hdr *ip6;
	struct nd_neighbor_advert *nd_na;
	struct ip6_moptions im6o;
	struct sockaddr *dst;
	union {
		struct sockaddr		dst;
		struct sockaddr_in6	dst6;
	} u;
	struct in6_addr daddr6;
	int icmp6len, maxlen, error;
	const void *mac;
	struct route ro;

	mac = NULL;
	memset(&ro, 0, sizeof(ro));

	daddr6 = *daddr6_0;	/* make a local copy for modification */

	/* estimate the size of message */
	maxlen = sizeof(*ip6) + sizeof(*nd_na);
	maxlen += (sizeof(struct nd_opt_hdr) + ifp->if_addrlen + 7) & ~7;
	KASSERTMSG(max_linkhdr + maxlen <= MCLBYTES,
	    "max_linkhdr + maxlen > MCLBYTES (%d + %d > %d)",
	    max_linkhdr, maxlen, MCLBYTES);

	MGETHDR(m, M_DONTWAIT, MT_DATA);
	if (m && max_linkhdr + maxlen >= MHLEN) {
		MCLGET(m, M_DONTWAIT);
		if ((m->m_flags & M_EXT) == 0) {
			m_free(m);
			m = NULL;
		}
	}
	if (m == NULL)
		return;
	m_reset_rcvif(m);

	if (IN6_IS_ADDR_MULTICAST(&daddr6)) {
		m->m_flags |= M_MCAST;
		im6o.im6o_multicast_if_index = if_get_index(ifp);
		im6o.im6o_multicast_hlim = 255;
		im6o.im6o_multicast_loop = 0;
	}

	icmp6len = sizeof(*nd_na);
	m->m_pkthdr.len = m->m_len = sizeof(struct ip6_hdr) + icmp6len;
	m->m_data += max_linkhdr;	/* or m_align() equivalent? */

	/* fill neighbor advertisement packet */
	ip6 = mtod(m, struct ip6_hdr *);
	ip6->ip6_flow = 0;
	ip6->ip6_vfc &= ~IPV6_VERSION_MASK;
	ip6->ip6_vfc |= IPV6_VERSION;
	ip6->ip6_nxt = IPPROTO_ICMPV6;
	ip6->ip6_hlim = 255;
	if (IN6_IS_ADDR_UNSPECIFIED(&daddr6)) {
		/* reply to DAD */
		daddr6.s6_addr16[0] = IPV6_ADDR_INT16_MLL;
		daddr6.s6_addr16[1] = 0;
		daddr6.s6_addr32[1] = 0;
		daddr6.s6_addr32[2] = 0;
		daddr6.s6_addr32[3] = IPV6_ADDR_INT32_ONE;
		if (in6_setscope(&daddr6, ifp, NULL))
			goto bad;

		flags &= ~ND_NA_FLAG_SOLICITED;
	}
	ip6->ip6_dst = daddr6;
	sockaddr_in6_init(&u.dst6, &daddr6, 0, 0, 0);
	dst = &u.dst;
	if (rtcache_setdst(&ro, dst) != 0)
		goto bad;

	/*
	 * Select a source whose scope is the same as that of the dest.
	 */
	error = in6_selectsrc(satosin6(dst), NULL, NULL, &ro, NULL, NULL, NULL,
	    &ip6->ip6_src);
	if (error != 0) {
		char ip6buf[INET6_ADDRSTRLEN];
		nd6log(LOG_DEBUG, "source can't be "
		    "determined: dst=%s, error=%d\n",
		    IN6_PRINT(ip6buf, &satocsin6(dst)->sin6_addr), error);
		goto bad;
	}
	nd_na = (struct nd_neighbor_advert *)(ip6 + 1);
	nd_na->nd_na_type = ND_NEIGHBOR_ADVERT;
	nd_na->nd_na_code = 0;
	nd_na->nd_na_target = *taddr6;
	in6_clearscope(&nd_na->nd_na_target); /* XXX */

	/*
	 * "tlladdr" indicates NS's condition for adding tlladdr or not.
	 * see nd6_ns_input() for details.
	 * Basically, if NS packet is sent to unicast/anycast addr,
	 * target lladdr option SHOULD NOT be included.
	 */
	if (tlladdr) {
		/*
		 * sdl0 != NULL indicates proxy NA.  If we do proxy, use
		 * lladdr in sdl0.  If we are not proxying (sending NA for
		 * my address) use lladdr configured for the interface.
		 */
		if (sdl0 == NULL)
			mac = nd6_ifptomac(ifp);
		else if (sdl0->sa_family == AF_LINK) {
			const struct sockaddr_dl *sdl;
			sdl = satocsdl(sdl0);
			if (sdl->sdl_alen == ifp->if_addrlen)
				mac = CLLADDR(sdl);
		}
	}
	if (tlladdr && mac) {
		int optlen = sizeof(struct nd_opt_hdr) + ifp->if_addrlen;
		struct nd_opt_hdr *nd_opt = (struct nd_opt_hdr *)(nd_na + 1);

		/* roundup to 8 bytes alignment! */
		optlen = (optlen + 7) & ~7;

		m->m_pkthdr.len += optlen;
		m->m_len += optlen;
		icmp6len += optlen;
		memset((void *)nd_opt, 0, optlen);
		nd_opt->nd_opt_type = ND_OPT_TARGET_LINKADDR;
		nd_opt->nd_opt_len = optlen >> 3;
		memcpy((void *)(nd_opt + 1), mac, ifp->if_addrlen);
	} else
		flags &= ~ND_NA_FLAG_OVERRIDE;

	ip6->ip6_plen = htons((u_int16_t)icmp6len);
	nd_na->nd_na_flags_reserved = flags;
	nd_na->nd_na_cksum = 0;
	nd_na->nd_na_cksum =
	    in6_cksum(m, IPPROTO_ICMPV6, sizeof(struct ip6_hdr), icmp6len);

	ip6_output(m, NULL, NULL, 0, &im6o, NULL, NULL);

	icmp6_ifstat_inc(ifp, ifs6_out_msg);
	icmp6_ifstat_inc(ifp, ifs6_out_neighboradvert);
	ICMP6_STATINC(ICMP6_STAT_OUTHIST + ND_NEIGHBOR_ADVERT);

	rtcache_free(&ro);
	return;

  bad:
	rtcache_free(&ro);
	m_freem(m);
	return;
}

const void *
nd6_ifptomac(const struct ifnet *ifp)
{
	switch (ifp->if_type) {
	case IFT_ARCNET:
	case IFT_ETHER:
	case IFT_FDDI:
	case IFT_IEEE1394:
	case IFT_PROPVIRTUAL:
	case IFT_CARP:
	case IFT_L2VLAN:
	case IFT_IEEE80211:
		return CLLADDR(ifp->if_sadl);
	default:
		return NULL;
	}
}

TAILQ_HEAD(dadq_head, dadq);
struct dadq {
	TAILQ_ENTRY(dadq) dad_list;
	struct ifaddr *dad_ifa;
	int dad_count;			/* max NS to send */
	int dad_ns_tcount;		/* # of trials to send NS */
	int dad_ns_ocount;		/* NS sent so far */
	int dad_ns_lcount;		/* looped back NS */
	struct callout dad_timer_ch;
#define	ND_OPT_NONCE_STORE	3	/* dad_count should not exceed this */
	/*
	 * The default ip6_dad_count is 1 as specified by RFC 4862 and
	 * practically must users won't exceed this.
	 * A storage of 3 is defaulted to here, in-case the administrator wants
	 * to match the equivalent behaviour in our ARP implementation.
	 * This constraint could be removed by sending the on wire nonce as
	 * hmac(key, dad_ns_ocount), but that would increase the nonce size
	 * sent on the wire.
	 */
	uint8_t dad_nonce[ND_OPT_NONCE_STORE][ND_OPT_NONCE_LEN];
};

static struct dadq_head dadq;
static int dad_init = 0;
static kmutex_t nd6_dad_lock;

static struct dadq *
nd6_dad_find(struct ifaddr *ifa, struct nd_opt_nonce *nonce, bool *found_nonce)
{
	struct in6_addr *myaddr6, *dadaddr6;
	bool match_ifa;
	struct dadq *dp;
	int i, nonce_max;

	KASSERT(mutex_owned(&nd6_dad_lock));
	KASSERT(ifa != NULL);

	myaddr6 = IFA_IN6(ifa);
	if (nonce != NULL &&
	    nonce->nd_opt_nonce_len != (ND_OPT_NONCE_LEN + 2) / 8)
		nonce = NULL;
	match_ifa = nonce == NULL || found_nonce == NULL || *found_nonce == false;
	if (found_nonce != NULL)
		*found_nonce = false;

	TAILQ_FOREACH(dp, &dadq, dad_list) {
		if (match_ifa) {
			if (dp->dad_ifa != ifa)
				continue;
		} else {
			dadaddr6 = IFA_IN6(dp->dad_ifa);
			if (!IN6_ARE_ADDR_EQUAL(myaddr6, dadaddr6))
				continue;
		}

		if (nonce == NULL)
			break;

		nonce_max = MIN(dp->dad_ns_ocount, ND_OPT_NONCE_STORE);
		for (i = 0; i < nonce_max; i++) {
			if (memcmp(nonce->nd_opt_nonce,
			    dp->dad_nonce[i],
			    ND_OPT_NONCE_LEN) == 0)
				break;
		}
		if (i < nonce_max) {
			char ip6buf[INET6_ADDRSTRLEN];

			*found_nonce = true;
			log(LOG_DEBUG,
			    "%s: detected a looped back NS message for %s\n",
			    ifa->ifa_ifp ? if_name(ifa->ifa_ifp) : "???",
			    IN6_PRINT(ip6buf, myaddr6));
			dp->dad_ns_lcount++;
			continue;
		}

		break;
	}
	return dp;
}

static bool
nd6_dad_ownnonce(struct ifaddr *ifa, struct nd_opt_nonce *nonce)
{
	bool found_nonce = true;

	mutex_enter(&nd6_dad_lock);
	nd6_dad_find(ifa, nonce, &found_nonce);
	mutex_exit(&nd6_dad_lock);

	return found_nonce;
}

static void
nd6_dad_starttimer(struct dadq *dp, int ticks)
{

	callout_reset(&dp->dad_timer_ch, ticks,
	    (void (*)(void *))nd6_dad_timer, dp);
}

static void
nd6_dad_stoptimer(struct dadq *dp)
{

	KASSERT(mutex_owned(&nd6_dad_lock));

	TAILQ_REMOVE(&dadq, dp, dad_list);
	/* Tell the timer that dp is being destroyed. */
	dp->dad_ifa = NULL;
	callout_halt(&dp->dad_timer_ch, &nd6_dad_lock);
}

static void
nd6_dad_destroytimer(struct dadq *dp)
{

	KASSERT(dp->dad_ifa == NULL);
	callout_destroy(&dp->dad_timer_ch);
	kmem_intr_free(dp, sizeof(*dp));
}

/*
 * Start Duplicate Address Detection (DAD) for specified interface address.
 *
 * Note that callout is used when xtick > 0 and not when xtick == 0.
 *
 * xtick: minimum delay ticks for IFF_UP event
 */
void
nd6_dad_start(struct ifaddr *ifa, int xtick)
{
	struct in6_ifaddr *ia = (struct in6_ifaddr *)ifa;
	struct dadq *dp;
	char ip6buf[INET6_ADDRSTRLEN];

	if (!dad_init) {
		TAILQ_INIT(&dadq);
		mutex_init(&nd6_dad_lock, MUTEX_DEFAULT, IPL_NONE);
		dad_init++;
	}

	/*
	 * If we don't need DAD, don't do it.
	 * There are several cases:
	 * - DAD is disabled
	 * - the interface address is anycast
	 */
	if (!(ia->ia6_flags & IN6_IFF_TENTATIVE)) {
		log(LOG_DEBUG,
			"nd6_dad_start: called with non-tentative address "
			"%s(%s)\n",
			IN6_PRINT(ip6buf, &ia->ia_addr.sin6_addr),
			ifa->ifa_ifp ? if_name(ifa->ifa_ifp) : "???");
		return;
	}
	if (ia->ia6_flags & IN6_IFF_ANYCAST || !ip6_dad_enabled()) {
		ia->ia6_flags &= ~IN6_IFF_TENTATIVE;
		rt_addrmsg(RTM_NEWADDR, ifa);
		return;
	}
	KASSERT(ifa->ifa_ifp != NULL);
	if (!(ifa->ifa_ifp->if_flags & IFF_UP))
		return;

	dp = kmem_intr_alloc(sizeof(*dp), KM_NOSLEEP);

	mutex_enter(&nd6_dad_lock);
	if (nd6_dad_find(ifa, NULL, NULL) != NULL) {
		mutex_exit(&nd6_dad_lock);
		/* DAD already in progress */
		if (dp != NULL)
			kmem_intr_free(dp, sizeof(*dp));
		return;
	}

	if (dp == NULL) {
		mutex_exit(&nd6_dad_lock);
		log(LOG_ERR, "nd6_dad_start: memory allocation failed for "
			"%s(%s)\n",
			IN6_PRINT(ip6buf, &ia->ia_addr.sin6_addr),
			ifa->ifa_ifp ? if_name(ifa->ifa_ifp) : "???");
		return;
	}

	/*
	 * Send NS packet for DAD, ip6_dad_count times.
	 * Note that we must delay the first transmission, if this is the
	 * first packet to be sent from the interface after interface
	 * (re)initialization.
	 */
	callout_init(&dp->dad_timer_ch, CALLOUT_MPSAFE);
	dp->dad_ifa = ifa;
	ifaref(ifa);	/* just for safety */
	dp->dad_count = ip6_dad_count;
	dp->dad_ns_ocount = dp->dad_ns_tcount = 0;
	dp->dad_ns_lcount = 0;
	TAILQ_INSERT_TAIL(&dadq, (struct dadq *)dp, dad_list);

	nd6log(LOG_DEBUG, "%s: starting DAD for %s\n", if_name(ifa->ifa_ifp),
	    IN6_PRINT(ip6buf, &ia->ia_addr.sin6_addr));

	if (xtick == 0) {
		nd6_dad_ns_output(dp, ifa);
		nd6_dad_starttimer(dp,
		    (long)ND_IFINFO(ifa->ifa_ifp)->retrans * hz / 1000);
	} else
		nd6_dad_starttimer(dp, xtick);
	mutex_exit(&nd6_dad_lock);
}

/*
 * terminate DAD unconditionally.  used for address removals.
 */
void
nd6_dad_stop(struct ifaddr *ifa)
{
	struct dadq *dp;

	if (!dad_init)
		return;

	mutex_enter(&nd6_dad_lock);
	dp = nd6_dad_find(ifa, NULL, NULL);
	if (dp == NULL) {
		mutex_exit(&nd6_dad_lock);
		/* DAD wasn't started yet */
		return;
	}

	/* Prevent the timer from running anymore. */
	nd6_dad_stoptimer(dp);

	mutex_exit(&nd6_dad_lock);

	nd6_dad_destroytimer(dp);
	ifafree(ifa);
}

static void
nd6_dad_timer(struct dadq *dp)
{
	struct ifaddr *ifa;
	struct in6_ifaddr *ia;
	char ip6buf[INET6_ADDRSTRLEN];
	bool need_free = false;

	KERNEL_LOCK_UNLESS_NET_MPSAFE();
	mutex_enter(&nd6_dad_lock);

	ifa = dp->dad_ifa;
	if (ifa == NULL) {
		/* dp is being destroyed by someone.  Do nothing. */
		goto done;
	}

	ia = (struct in6_ifaddr *)ifa;
	if (ia->ia6_flags & IN6_IFF_DUPLICATED) {
		log(LOG_ERR, "nd6_dad_timer: called with duplicate address "
			"%s(%s)\n",
			IN6_PRINT(ip6buf, &ia->ia_addr.sin6_addr),
			ifa->ifa_ifp ? if_name(ifa->ifa_ifp) : "???");
		goto done;
	}
	if ((ia->ia6_flags & IN6_IFF_TENTATIVE) == 0) {
		log(LOG_ERR, "nd6_dad_timer: called with non-tentative address "
			"%s(%s)\n",
			IN6_PRINT(ip6buf, &ia->ia_addr.sin6_addr),
			ifa->ifa_ifp ? if_name(ifa->ifa_ifp) : "???");
		goto done;
	}

	/* timeouted with IFF_{RUNNING,UP} check */
	if (dp->dad_ns_tcount > dad_maxtry) {
		nd6log(LOG_INFO, "%s: could not run DAD, driver problem?\n",
			if_name(ifa->ifa_ifp));

		nd6_dad_stoptimer(dp);
		need_free = true;
		goto done;
	}

	/* Need more checks? */
	if (dp->dad_ns_ocount < dp->dad_count) {
		/*
		 * We have more NS to go.  Send NS packet for DAD.
		 */
		nd6_dad_ns_output(dp, ifa);
		nd6_dad_starttimer(dp,
		    (long)ND_IFINFO(ifa->ifa_ifp)->retrans * hz / 1000);
	} else {
		/*
		 * We are done with DAD.  No NA came, no NS came.
		 * No duplicate address found.
		 */
		ia->ia6_flags &= ~IN6_IFF_TENTATIVE;
		rt_addrmsg(RTM_NEWADDR, ifa);

		nd6log(LOG_DEBUG,
		    "%s: DAD complete for %s - no duplicates found\n",
		    if_name(ifa->ifa_ifp),
		    IN6_PRINT(ip6buf, &ia->ia_addr.sin6_addr));

		nd6_dad_stoptimer(dp);
		need_free = true;
	}
done:
	mutex_exit(&nd6_dad_lock);

	if (need_free) {
		nd6_dad_destroytimer(dp);
		KASSERT(ifa != NULL);
		ifafree(ifa);
	}

	KERNEL_UNLOCK_UNLESS_NET_MPSAFE();
}

static void
nd6_dad_duplicated(struct ifaddr *ifa, struct dadq *dp,
    const struct sockaddr_dl *from)
{
	struct in6_ifaddr *ia;
	struct ifnet *ifp;
	char ip6buf[INET6_ADDRSTRLEN], llabuf[LLA_ADDRSTRLEN], *llastr;

	KASSERT(mutex_owned(&nd6_dad_lock));
	KASSERT(ifa != NULL);

	ifp = ifa->ifa_ifp;
	ia = (struct in6_ifaddr *)ifa;

	ia->ia6_flags &= ~IN6_IFF_TENTATIVE;
	ia->ia6_flags |= IN6_IFF_DUPLICATED;

	if (__predict_false(from == NULL))
		llastr = NULL;
	else
		llastr = lla_snprintf(llabuf, sizeof(llabuf),
		    CLLADDR(from), from->sdl_alen);

	log(LOG_ERR, "%s: DAD duplicate address %s from %s\n",
	    if_name(ifp), IN6_PRINT(ip6buf, &ia->ia_addr.sin6_addr), llastr);

	/* Inform the routing socket that DAD has completed */
	rt_addrmsg_src(RTM_NEWADDR, ifa, (const struct sockaddr *)from);

	/*
	 * If the address is a link-local address formed from an interface
	 * identifier based on the hardware address which is supposed to be
	 * uniquely assigned (e.g., EUI-64 for an Ethernet interface), IP
	 * operation on the interface SHOULD be disabled.
	 * [rfc2462bis-03 Section 5.4.5]
	 */
	if (IN6_IS_ADDR_LINKLOCAL(&ia->ia_addr.sin6_addr)) {
		struct in6_addr in6;

		/*
		 * To avoid over-reaction, we only apply this logic when we are
		 * very sure that hardware addresses are supposed to be unique.
		 */
		switch (ifp->if_type) {
		case IFT_ETHER:
		case IFT_FDDI:
		case IFT_ATM:
		case IFT_IEEE1394:
		case IFT_IEEE80211:
			in6 = ia->ia_addr.sin6_addr;
			if (in6_get_hw_ifid(ifp, &in6) == 0 &&
			    IN6_ARE_ADDR_EQUAL(&ia->ia_addr.sin6_addr, &in6)) {
				ND_IFINFO(ifp)->flags |= ND6_IFF_IFDISABLED;
				log(LOG_ERR, "%s: possible hardware address "
				    "duplication detected, disable IPv6\n",
				    if_name(ifp));
			}
			break;
		}
	}
}

static void
nd6_dad_ns_output(struct dadq *dp, struct ifaddr *ifa)
{
	struct in6_ifaddr *ia = (struct in6_ifaddr *)ifa;
	struct ifnet *ifp = ifa->ifa_ifp;
	uint8_t *nonce;

	dp->dad_ns_tcount++;
	if ((ifp->if_flags & IFF_UP) == 0) {
#if 0
		printf("%s: interface down?\n", if_name(ifp));
#endif
		return;
	}
	if ((ifp->if_flags & IFF_RUNNING) == 0) {
#if 0
		printf("%s: interface not running?\n", if_name(ifp));
#endif
		return;
	}

	dp->dad_ns_tcount = 0;
	nonce = dp->dad_nonce[dp->dad_ns_ocount % ND_OPT_NONCE_STORE];
	cprng_fast(nonce, ND_OPT_NONCE_LEN);
	dp->dad_ns_ocount++;

	nd6_ns_output(ifp, NULL, &ia->ia_addr.sin6_addr, NULL, nonce);
}

static void
nd6_dad_input(struct ifaddr *ifa, struct nd_opt_nonce *nonce,
    const struct sockaddr_dl *from)
{
	struct dadq *dp;
	bool found_nonce = false;

	KASSERT(ifa != NULL);

	mutex_enter(&nd6_dad_lock);
	dp = nd6_dad_find(ifa, nonce, &found_nonce);
	if (!found_nonce) {
		nd6_dad_duplicated(ifa, dp, from);
		if (dp != NULL)
			nd6_dad_stoptimer(dp);
	}
	mutex_exit(&nd6_dad_lock);
	if (dp != NULL) {
		nd6_dad_destroytimer(dp);
		ifafree(ifa);
	}
}