xref: /src/sys/netinet/ip_encap.c

/*	$NetBSD: ip_encap.c,v 1.74 2020/08/22 01:43:07 riastradh Exp $	*/
/*	$KAME: ip_encap.c,v 1.73 2001/10/02 08:30:58 itojun Exp $	*/

/*
 * Copyright (C) 1995, 1996, 1997, and 1998 WIDE Project.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the project nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE PROJECT AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */
/*
 * My grandfather said that there's a devil inside tunnelling technology...
 *
 * We have surprisingly many protocols that want packets with IP protocol
 * #4 or #41.  Here's a list of protocols that want protocol #41:
 *	RFC1933 configured tunnel
 *	RFC1933 automatic tunnel
 *	RFC2401 IPsec tunnel
 *	RFC2473 IPv6 generic packet tunnelling
 *	RFC2529 6over4 tunnel
 *	RFC3056 6to4 tunnel
 *	isatap tunnel
 *	mobile-ip6 (uses RFC2473)
 * Here's a list of protocol that want protocol #4:
 *	RFC1853 IPv4-in-IPv4 tunnelling
 *	RFC2003 IPv4 encapsulation within IPv4
 *	RFC2344 reverse tunnelling for mobile-ip4
 *	RFC2401 IPsec tunnel
 * Well, what can I say.  They impose different en/decapsulation mechanism
 * from each other, so they need separate protocol handler.  The only one
 * we can easily determine by protocol # is IPsec, which always has
 * AH/ESP/IPComp header right after outer IP header.
 *
 * So, clearly good old protosw does not work for protocol #4 and #41.
 * The code will let you match protocol via src/dst address pair.
 */
/* XXX is M_NETADDR correct? */

/*
 * With USE_RADIX the code will use radix table for tunnel lookup, for
 * tunnels registered with encap_attach() with a addr/mask pair.
 * Faster on machines with thousands of tunnel registerations (= interfaces).
 *
 * The code assumes that radix table code can handle non-continuous netmask,
 * as it will pass radix table memory region with (src + dst) sockaddr pair.
 */
#define USE_RADIX

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: ip_encap.c,v 1.74 2020/08/22 01:43:07 riastradh Exp $");

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

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/socket.h>
#include <sys/socketvar.h> /* for softnet_lock */
#include <sys/sockio.h>
#include <sys/mbuf.h>
#include <sys/errno.h>
#include <sys/queue.h>
#include <sys/kmem.h>
#include <sys/mutex.h>
#include <sys/condvar.h>
#include <sys/psref.h>
#include <sys/pslist.h>

#include <net/if.h>

#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netinet/ip_var.h>
#include <netinet/ip_encap.h>
#ifdef MROUTING
#include <netinet/ip_mroute.h>
#endif /* MROUTING */

#ifdef INET6
#include <netinet/ip6.h>
#include <netinet6/ip6_var.h>
#include <netinet6/ip6protosw.h> /* for struct ip6ctlparam */
#include <netinet6/in6_var.h>
#include <netinet6/in6_pcb.h>
#include <netinet/icmp6.h>
#endif

#ifdef NET_MPSAFE
#define ENCAP_MPSAFE	1
#endif

enum direction { INBOUND, OUTBOUND };

#ifdef INET
static struct encaptab *encap4_lookup(struct mbuf *, int, int, enum direction,
    struct psref *);
#endif
#ifdef INET6
static struct encaptab *encap6_lookup(struct mbuf *, int, int, enum direction,
    struct psref *);
#endif
static int encap_add(struct encaptab *);
static int encap_remove(struct encaptab *);
static void encap_afcheck(int, const struct sockaddr *, const struct sockaddr *);
#ifdef USE_RADIX
static struct radix_node_head *encap_rnh(int);
static int mask_matchlen(const struct sockaddr *);
#else
static int mask_match(const struct encaptab *, const struct sockaddr *,
		const struct sockaddr *);
#endif

/*
 * In encap[46]_lookup(), ep->func can sleep(e.g. rtalloc1) while walking
 * encap_table. So, it cannot use pserialize_read_enter()
 */
static struct {
	struct pslist_head	list;
	pserialize_t		psz;
	struct psref_class	*elem_class; /* for the element of et_list */
} encaptab  __cacheline_aligned = {
	.list = PSLIST_INITIALIZER,
};
#define encap_table encaptab.list

static struct {
	kmutex_t	lock;
	kcondvar_t	cv;
	struct lwp	*busy;
} encap_whole __cacheline_aligned;

#ifdef USE_RADIX
struct radix_node_head *encap_head[2];	/* 0 for AF_INET, 1 for AF_INET6 */
static bool encap_head_updating = false;
#endif

static bool encap_initialized = false;
/*
 * must be done before other encap interfaces initialization.
 */
void
encapinit(void)
{

	if (encap_initialized)
		return;

	encaptab.psz = pserialize_create();
	encaptab.elem_class = psref_class_create("encapelem", IPL_SOFTNET);

	mutex_init(&encap_whole.lock, MUTEX_DEFAULT, IPL_NONE);
	cv_init(&encap_whole.cv, "ip_encap cv");
	encap_whole.busy = NULL;

	encap_initialized = true;
}

void
encap_init(void)
{
	static int initialized = 0;

	if (initialized)
		return;
	initialized++;
#if 0
	/*
	 * we cannot use LIST_INIT() here, since drivers may want to call
	 * encap_attach(), on driver attach.  encap_init() will be called
	 * on AF_INET{,6} initialization, which happens after driver
	 * initialization - using LIST_INIT() here can nuke encap_attach()
	 * from drivers.
	 */
	PSLIST_INIT(&encap_table);
#endif

#ifdef USE_RADIX
	/*
	 * initialize radix lookup table when the radix subsystem is inited.
	 */
	rn_delayedinit((void *)&encap_head[0],
	    sizeof(struct sockaddr_pack) << 3);
#ifdef INET6
	rn_delayedinit((void *)&encap_head[1],
	    sizeof(struct sockaddr_pack) << 3);
#endif
#endif
}

#ifdef INET
static struct encaptab *
encap4_lookup(struct mbuf *m, int off, int proto, enum direction dir,
    struct psref *match_psref)
{
	struct ip *ip;
	struct ip_pack4 pack;
	struct encaptab *ep, *match;
	int prio, matchprio;
	int s;
#ifdef USE_RADIX
	struct radix_node_head *rnh = encap_rnh(AF_INET);
	struct radix_node *rn;
#endif

	KASSERT(m->m_len >= sizeof(*ip));

	ip = mtod(m, struct ip *);

	memset(&pack, 0, sizeof(pack));
	pack.p.sp_len = sizeof(pack);
	pack.mine.sin_family = pack.yours.sin_family = AF_INET;
	pack.mine.sin_len = pack.yours.sin_len = sizeof(struct sockaddr_in);
	if (dir == INBOUND) {
		pack.mine.sin_addr = ip->ip_dst;
		pack.yours.sin_addr = ip->ip_src;
	} else {
		pack.mine.sin_addr = ip->ip_src;
		pack.yours.sin_addr = ip->ip_dst;
	}

	match = NULL;
	matchprio = 0;

	s = pserialize_read_enter();
#ifdef USE_RADIX
	if (encap_head_updating) {
		/*
		 * Update in progress. Do nothing.
		 */
		pserialize_read_exit(s);
		return NULL;
	}

	rn = rnh->rnh_matchaddr((void *)&pack, rnh);
	if (rn && (rn->rn_flags & RNF_ROOT) == 0) {
		struct encaptab *encapp = (struct encaptab *)rn;

		psref_acquire(match_psref, &encapp->psref,
		    encaptab.elem_class);
		match = encapp;
		matchprio = mask_matchlen(match->srcmask) +
		    mask_matchlen(match->dstmask);
	}
#endif
	PSLIST_READER_FOREACH(ep, &encap_table, struct encaptab, chain) {
		struct psref elem_psref;

		if (ep->af != AF_INET)
			continue;
		if (ep->proto >= 0 && ep->proto != proto)
			continue;

		psref_acquire(&elem_psref, &ep->psref,
		    encaptab.elem_class);
		if (ep->func) {
			pserialize_read_exit(s);
			/* ep->func is sleepable. e.g. rtalloc1 */
			prio = (*ep->func)(m, off, proto, ep->arg);
			s = pserialize_read_enter();
		} else {
#ifdef USE_RADIX
			psref_release(&elem_psref, &ep->psref,
			    encaptab.elem_class);
			continue;
#else
			prio = mask_match(ep, (struct sockaddr *)&pack.mine,
			    (struct sockaddr *)&pack.yours);
#endif
		}

		/*
		 * We prioritize the matches by using bit length of the
		 * matches.  mask_match() and user-supplied matching function
		 * should return the bit length of the matches (for example,
		 * if both src/dst are matched for IPv4, 64 should be returned).
		 * 0 or negative return value means "it did not match".
		 *
		 * The question is, since we have two "mask" portion, we
		 * cannot really define total order between entries.
		 * For example, which of these should be preferred?
		 * mask_match() returns 48 (32 + 16) for both of them.
		 *	src=3ffe::/16, dst=3ffe:501::/32
		 *	src=3ffe:501::/32, dst=3ffe::/16
		 *
		 * We need to loop through all the possible candidates
		 * to get the best match - the search takes O(n) for
		 * n attachments (i.e. interfaces).
		 *
		 * For radix-based lookup, I guess source takes precedence.
		 * See rn_{refines,lexobetter} for the correct answer.
		 */
		if (prio <= 0) {
			psref_release(&elem_psref, &ep->psref,
			    encaptab.elem_class);
			continue;
		}
		if (prio > matchprio) {
			/* release last matched ep */
			if (match != NULL)
				psref_release(match_psref, &match->psref,
				    encaptab.elem_class);

			psref_copy(match_psref, &elem_psref,
			    encaptab.elem_class);
			matchprio = prio;
			match = ep;
		}
		KASSERTMSG((match == NULL) || psref_held(&match->psref,
			encaptab.elem_class),
		    "current match = %p, but not hold its psref", match);

		psref_release(&elem_psref, &ep->psref,
		    encaptab.elem_class);
	}
	pserialize_read_exit(s);

	return match;
}

void
encap4_input(struct mbuf *m, int off, int proto)
{
	const struct encapsw *esw;
	struct encaptab *match;
	struct psref match_psref;

	match = encap4_lookup(m, off, proto, INBOUND, &match_psref);
	if (match) {
		/* found a match, "match" has the best one */
		esw = match->esw;
		if (esw && esw->encapsw4.pr_input) {
			(*esw->encapsw4.pr_input)(m, off, proto, match->arg);
			psref_release(&match_psref, &match->psref,
			    encaptab.elem_class);
		} else {
			psref_release(&match_psref, &match->psref,
			    encaptab.elem_class);
			m_freem(m);
		}
		return;
	}

	/* last resort: inject to raw socket */
	SOFTNET_LOCK_IF_NET_MPSAFE();
	rip_input(m, off, proto);
	SOFTNET_UNLOCK_IF_NET_MPSAFE();
}
#endif

#ifdef INET6
static struct encaptab *
encap6_lookup(struct mbuf *m, int off, int proto, enum direction dir,
    struct psref *match_psref)
{
	struct ip6_hdr *ip6;
	struct ip_pack6 pack;
	int prio, matchprio;
	int s;
	struct encaptab *ep, *match;
#ifdef USE_RADIX
	struct radix_node_head *rnh = encap_rnh(AF_INET6);
	struct radix_node *rn;
#endif

	KASSERT(m->m_len >= sizeof(*ip6));

	ip6 = mtod(m, struct ip6_hdr *);

	memset(&pack, 0, sizeof(pack));
	pack.p.sp_len = sizeof(pack);
	pack.mine.sin6_family = pack.yours.sin6_family = AF_INET6;
	pack.mine.sin6_len = pack.yours.sin6_len = sizeof(struct sockaddr_in6);
	if (dir == INBOUND) {
		pack.mine.sin6_addr = ip6->ip6_dst;
		pack.yours.sin6_addr = ip6->ip6_src;
	} else {
		pack.mine.sin6_addr = ip6->ip6_src;
		pack.yours.sin6_addr = ip6->ip6_dst;
	}

	match = NULL;
	matchprio = 0;

	s = pserialize_read_enter();
#ifdef USE_RADIX
	if (encap_head_updating) {
		/*
		 * Update in progress. Do nothing.
		 */
		pserialize_read_exit(s);
		return NULL;
	}

	rn = rnh->rnh_matchaddr((void *)&pack, rnh);
	if (rn && (rn->rn_flags & RNF_ROOT) == 0) {
		struct encaptab *encapp = (struct encaptab *)rn;

		psref_acquire(match_psref, &encapp->psref,
		    encaptab.elem_class);
		match = encapp;
		matchprio = mask_matchlen(match->srcmask) +
		    mask_matchlen(match->dstmask);
	}
#endif
	PSLIST_READER_FOREACH(ep, &encap_table, struct encaptab, chain) {
		struct psref elem_psref;

		if (ep->af != AF_INET6)
			continue;
		if (ep->proto >= 0 && ep->proto != proto)
			continue;

		psref_acquire(&elem_psref, &ep->psref,
		    encaptab.elem_class);

		if (ep->func) {
			pserialize_read_exit(s);
			/* ep->func is sleepable. e.g. rtalloc1 */
			prio = (*ep->func)(m, off, proto, ep->arg);
			s = pserialize_read_enter();
		} else {
#ifdef USE_RADIX
			psref_release(&elem_psref, &ep->psref,
			    encaptab.elem_class);
			continue;
#else
			prio = mask_match(ep, (struct sockaddr *)&pack.mine,
			    (struct sockaddr *)&pack.yours);
#endif
		}

		/* see encap4_lookup() for issues here */
		if (prio <= 0) {
			psref_release(&elem_psref, &ep->psref,
			    encaptab.elem_class);
			continue;
		}
		if (prio > matchprio) {
			/* release last matched ep */
			if (match != NULL)
				psref_release(match_psref, &match->psref,
				    encaptab.elem_class);

			psref_copy(match_psref, &elem_psref,
			    encaptab.elem_class);
			matchprio = prio;
			match = ep;
		}
		KASSERTMSG((match == NULL) || psref_held(&match->psref,
			encaptab.elem_class),
		    "current match = %p, but not hold its psref", match);

		psref_release(&elem_psref, &ep->psref,
		    encaptab.elem_class);
	}
	pserialize_read_exit(s);

	return match;
}

int
encap6_input(struct mbuf **mp, int *offp, int proto)
{
	struct mbuf *m = *mp;
	const struct encapsw *esw;
	struct encaptab *match;
	struct psref match_psref;
	int rv;

	match = encap6_lookup(m, *offp, proto, INBOUND, &match_psref);

	if (match) {
		/* found a match */
		esw = match->esw;
		if (esw && esw->encapsw6.pr_input) {
			int ret;
			ret = (*esw->encapsw6.pr_input)(mp, offp, proto,
			    match->arg);
			psref_release(&match_psref, &match->psref,
			    encaptab.elem_class);
			return ret;
		} else {
			psref_release(&match_psref, &match->psref,
			    encaptab.elem_class);
			m_freem(m);
			return IPPROTO_DONE;
		}
	}

	/* last resort: inject to raw socket */
	SOFTNET_LOCK_IF_NET_MPSAFE();
	rv = rip6_input(mp, offp, proto);
	SOFTNET_UNLOCK_IF_NET_MPSAFE();
	return rv;
}
#endif

/*
 * XXX
 * The encaptab list and the rnh radix tree must be manipulated atomically.
 */
static int
encap_add(struct encaptab *ep)
{
#ifdef USE_RADIX
	struct radix_node_head *rnh = encap_rnh(ep->af);
#endif

	KASSERT(encap_lock_held());

#ifdef USE_RADIX
	if (!ep->func && rnh) {
		/* Disable access to the radix tree for reader. */
		encap_head_updating = true;
		/* Wait for all readers to drain. */
		pserialize_perform(encaptab.psz);

		if (!rnh->rnh_addaddr((void *)ep->addrpack,
		    (void *)ep->maskpack, rnh, ep->nodes)) {
			encap_head_updating = false;
			return EEXIST;
		}

		/*
		 * The ep added to the radix tree must be skipped while
		 * encap[46]_lookup walks encaptab list. In other words,
		 * encap_add() does not need to care whether the ep has
		 * been added encaptab list or not yet.
		 * So, we can re-enable access to the radix tree for now.
		 */
		encap_head_updating = false;
	}
#endif
	PSLIST_WRITER_INSERT_HEAD(&encap_table, ep, chain);

	return 0;
}

/*
 * XXX
 * The encaptab list and the rnh radix tree must be manipulated atomically.
 */
static int
encap_remove(struct encaptab *ep)
{
#ifdef USE_RADIX
	struct radix_node_head *rnh = encap_rnh(ep->af);
#endif
	int error = 0;

	KASSERT(encap_lock_held());

#ifdef USE_RADIX
	if (!ep->func && rnh) {
		/* Disable access to the radix tree for reader. */
		encap_head_updating = true;
		/* Wait for all readers to drain. */
		pserialize_perform(encaptab.psz);

		if (!rnh->rnh_deladdr((void *)ep->addrpack,
		    (void *)ep->maskpack, rnh))
			error = ESRCH;

		/*
		 * The ep added to the radix tree must be skipped while
		 * encap[46]_lookup walks encaptab list. In other words,
		 * encap_add() does not need to care whether the ep has
		 * been added encaptab list or not yet.
		 * So, we can re-enable access to the radix tree for now.
		 */
		encap_head_updating = false;
	}
#endif
	PSLIST_WRITER_REMOVE(ep, chain);

	return error;
}

static void
encap_afcheck(int af, const struct sockaddr *sp, const struct sockaddr *dp)
{

	KASSERT(sp != NULL && dp != NULL);
	KASSERT(sp->sa_len == dp->sa_len);
	KASSERT(af == sp->sa_family && af == dp->sa_family);

	socklen_t len __diagused = sockaddr_getsize_by_family(af);
	KASSERT(len != 0 && len == sp->sa_len && len == dp->sa_len);
}

/*
 * sp (src ptr) is always my side, and dp (dst ptr) is always remote side.
 * length of mask (sm and dm) is assumed to be same as sp/dp.
 * Return value will be necessary as input (cookie) for encap_detach().
 */
const struct encaptab *
encap_attach(int af, int proto,
    const struct sockaddr *sp, const struct sockaddr *sm,
    const struct sockaddr *dp, const struct sockaddr *dm,
    const struct encapsw *esw, void *arg)
{
	struct encaptab *ep;
	int error;
	int pss;
	size_t l;
	struct ip_pack4 *pack4;
#ifdef INET6
	struct ip_pack6 *pack6;
#endif
#ifndef ENCAP_MPSAFE
	int s;

	s = splsoftnet();
#endif

	ASSERT_SLEEPABLE();

	/* sanity check on args */
	encap_afcheck(af, sp, dp);

	/* check if anyone have already attached with exactly same config */
	pss = pserialize_read_enter();
	PSLIST_READER_FOREACH(ep, &encap_table, struct encaptab, chain) {
		if (ep->af != af)
			continue;
		if (ep->proto != proto)
			continue;
		if (ep->func)
			continue;

		KASSERT(ep->src != NULL);
		KASSERT(ep->dst != NULL);
		KASSERT(ep->srcmask != NULL);
		KASSERT(ep->dstmask != NULL);

		if (ep->src->sa_len != sp->sa_len ||
		    memcmp(ep->src, sp, sp->sa_len) != 0 ||
		    memcmp(ep->srcmask, sm, sp->sa_len) != 0)
			continue;
		if (ep->dst->sa_len != dp->sa_len ||
		    memcmp(ep->dst, dp, dp->sa_len) != 0 ||
		    memcmp(ep->dstmask, dm, dp->sa_len) != 0)
			continue;

		error = EEXIST;
		pserialize_read_exit(pss);
		goto fail;
	}
	pserialize_read_exit(pss);

	switch (af) {
	case AF_INET:
		l = sizeof(*pack4);
		break;
#ifdef INET6
	case AF_INET6:
		l = sizeof(*pack6);
		break;
#endif
	default:
		goto fail;
	}

	/* M_NETADDR ok? */
	ep = kmem_zalloc(sizeof(*ep), KM_SLEEP);
	ep->addrpack = kmem_zalloc(l, KM_SLEEP);
	ep->maskpack = kmem_zalloc(l, KM_SLEEP);

	ep->af = af;
	ep->proto = proto;
	ep->addrpack->sa_len = l & 0xff;
	ep->maskpack->sa_len = l & 0xff;
	switch (af) {
	case AF_INET:
		pack4 = (struct ip_pack4 *)ep->addrpack;
		ep->src = (struct sockaddr *)&pack4->mine;
		ep->dst = (struct sockaddr *)&pack4->yours;
		pack4 = (struct ip_pack4 *)ep->maskpack;
		ep->srcmask = (struct sockaddr *)&pack4->mine;
		ep->dstmask = (struct sockaddr *)&pack4->yours;
		break;
#ifdef INET6
	case AF_INET6:
		pack6 = (struct ip_pack6 *)ep->addrpack;
		ep->src = (struct sockaddr *)&pack6->mine;
		ep->dst = (struct sockaddr *)&pack6->yours;
		pack6 = (struct ip_pack6 *)ep->maskpack;
		ep->srcmask = (struct sockaddr *)&pack6->mine;
		ep->dstmask = (struct sockaddr *)&pack6->yours;
		break;
#endif
	}

	memcpy(ep->src, sp, sp->sa_len);
	memcpy(ep->srcmask, sm, sp->sa_len);
	memcpy(ep->dst, dp, dp->sa_len);
	memcpy(ep->dstmask, dm, dp->sa_len);
	ep->esw = esw;
	ep->arg = arg;
	psref_target_init(&ep->psref, encaptab.elem_class);

	error = encap_add(ep);
	if (error)
		goto gc;

	error = 0;
#ifndef ENCAP_MPSAFE
	splx(s);
#endif
	return ep;

gc:
	if (ep->addrpack)
		kmem_free(ep->addrpack, l);
	if (ep->maskpack)
		kmem_free(ep->maskpack, l);
	if (ep)
		kmem_free(ep, sizeof(*ep));
fail:
#ifndef ENCAP_MPSAFE
	splx(s);
#endif
	return NULL;
}

const struct encaptab *
encap_attach_func(int af, int proto,
    int (*func)(struct mbuf *, int, int, void *),
    const struct encapsw *esw, void *arg)
{
	struct encaptab *ep;
	int error;
#ifndef ENCAP_MPSAFE
	int s;

	s = splsoftnet();
#endif

	ASSERT_SLEEPABLE();

	/* sanity check on args */
	KASSERT(func != NULL);
	KASSERT(af == AF_INET
#ifdef INET6
	    || af == AF_INET6
#endif
	);

	ep = kmem_alloc(sizeof(*ep), KM_SLEEP);
	memset(ep, 0, sizeof(*ep));

	ep->af = af;
	ep->proto = proto;
	ep->func = func;
	ep->esw = esw;
	ep->arg = arg;
	psref_target_init(&ep->psref, encaptab.elem_class);

	error = encap_add(ep);
	if (error)
		goto gc;

	error = 0;
#ifndef ENCAP_MPSAFE
	splx(s);
#endif
	return ep;

gc:
	kmem_free(ep, sizeof(*ep));
#ifndef ENCAP_MPSAFE
	splx(s);
#endif
	return NULL;
}

/* XXX encap4_ctlinput() is necessary if we set DF=1 on outer IPv4 header */

#ifdef INET6
void *
encap6_ctlinput(int cmd, const struct sockaddr *sa, void *d0)
{
	void *d = d0;
	struct ip6_hdr *ip6;
	struct mbuf *m;
	int off;
	struct ip6ctlparam *ip6cp = NULL;
	int nxt;
	int s;
	struct encaptab *ep;
	const struct encapsw *esw;

	if (sa->sa_family != AF_INET6 ||
	    sa->sa_len != sizeof(struct sockaddr_in6))
		return NULL;

	if ((unsigned)cmd >= PRC_NCMDS)
		return NULL;
	if (cmd == PRC_HOSTDEAD)
		d = NULL;
	else if (cmd == PRC_MSGSIZE)
		; /* special code is present, see below */
	else if (inet6ctlerrmap[cmd] == 0)
		return NULL;

	/* if the parameter is from icmp6, decode it. */
	if (d != NULL) {
		ip6cp = (struct ip6ctlparam *)d;
		m = ip6cp->ip6c_m;
		ip6 = ip6cp->ip6c_ip6;
		off = ip6cp->ip6c_off;
		nxt = ip6cp->ip6c_nxt;

		if (ip6 && cmd == PRC_MSGSIZE) {
			int valid = 0;
			struct encaptab *match;
			struct psref elem_psref;

			/*
		 	* Check to see if we have a valid encap configuration.
		 	*/
			match = encap6_lookup(m, off, nxt, OUTBOUND,
			    &elem_psref);
			if (match) {
				valid++;
				psref_release(&elem_psref, &match->psref,
				    encaptab.elem_class);
			}

			/*
		 	* Depending on the value of "valid" and routing table
		 	* size (mtudisc_{hi,lo}wat), we will:
		 	* - recalcurate the new MTU and create the
		 	*   corresponding routing entry, or
		 	* - ignore the MTU change notification.
		 	*/
			icmp6_mtudisc_update((struct ip6ctlparam *)d, valid);
		}
	} else {
		m = NULL;
		ip6 = NULL;
		nxt = -1;
	}

	/* inform all listeners */

	s = pserialize_read_enter();
	PSLIST_READER_FOREACH(ep, &encap_table, struct encaptab, chain) {
		struct psref elem_psref;

		if (ep->af != AF_INET6)
			continue;
		if (ep->proto >= 0 && ep->proto != nxt)
			continue;

		/* should optimize by looking at address pairs */

		/* XXX need to pass ep->arg or ep itself to listeners */
		psref_acquire(&elem_psref, &ep->psref,
		    encaptab.elem_class);
		esw = ep->esw;
		if (esw && esw->encapsw6.pr_ctlinput) {
			pserialize_read_exit(s);
			/* pr_ctlinput is sleepable. e.g. rtcache_free */
			(*esw->encapsw6.pr_ctlinput)(cmd, sa, d, ep->arg);
			s = pserialize_read_enter();
		}
		psref_release(&elem_psref, &ep->psref,
		    encaptab.elem_class);
	}
	pserialize_read_exit(s);

	rip6_ctlinput(cmd, sa, d0);
	return NULL;
}
#endif

int
encap_detach(const struct encaptab *cookie)
{
	const struct encaptab *ep = cookie;
	struct encaptab *p;
	int error;

	KASSERT(encap_lock_held());

	PSLIST_WRITER_FOREACH(p, &encap_table, struct encaptab, chain) {
		if (p == ep) {
			error = encap_remove(p);
			if (error)
				return error;
			else
				break;
		}
	}
	if (p == NULL)
		return ENOENT;

	pserialize_perform(encaptab.psz);
	psref_target_destroy(&p->psref,
	    encaptab.elem_class);
	if (!ep->func) {
		kmem_free(p->addrpack, ep->addrpack->sa_len);
		kmem_free(p->maskpack, ep->maskpack->sa_len);
	}
	kmem_free(p, sizeof(*p));

	return 0;
}

#ifdef USE_RADIX
static struct radix_node_head *
encap_rnh(int af)
{

	switch (af) {
	case AF_INET:
		return encap_head[0];
#ifdef INET6
	case AF_INET6:
		return encap_head[1];
#endif
	default:
		return NULL;
	}
}

static int
mask_matchlen(const struct sockaddr *sa)
{
	const char *p, *ep;
	int l;

	p = (const char *)sa;
	ep = p + sa->sa_len;
	p += 2;	/* sa_len + sa_family */

	l = 0;
	while (p < ep) {
		l += (*p ? 8 : 0);	/* estimate */
		p++;
	}
	return l;
}
#endif

#ifndef USE_RADIX
static int
mask_match(const struct encaptab *ep,
	   const struct sockaddr *sp,
	   const struct sockaddr *dp)
{
	struct sockaddr_storage s;
	struct sockaddr_storage d;
	int i;
	const u_int8_t *p, *q;
	u_int8_t *r;
	int matchlen;

	KASSERTMSG(ep->func == NULL, "wrong encaptab passed to mask_match");

	if (sp->sa_len > sizeof(s) || dp->sa_len > sizeof(d))
		return 0;
	if (sp->sa_family != ep->af || dp->sa_family != ep->af)
		return 0;
	if (sp->sa_len != ep->src->sa_len || dp->sa_len != ep->dst->sa_len)
		return 0;

	matchlen = 0;

	p = (const u_int8_t *)sp;
	q = (const u_int8_t *)ep->srcmask;
	r = (u_int8_t *)&s;
	for (i = 0 ; i < sp->sa_len; i++) {
		r[i] = p[i] & q[i];
		/* XXX estimate */
		matchlen += (q[i] ? 8 : 0);
	}

	p = (const u_int8_t *)dp;
	q = (const u_int8_t *)ep->dstmask;
	r = (u_int8_t *)&d;
	for (i = 0 ; i < dp->sa_len; i++) {
		r[i] = p[i] & q[i];
		/* XXX rough estimate */
		matchlen += (q[i] ? 8 : 0);
	}

	/* need to overwrite len/family portion as we don't compare them */
	s.ss_len = sp->sa_len;
	s.ss_family = sp->sa_family;
	d.ss_len = dp->sa_len;
	d.ss_family = dp->sa_family;

	if (memcmp(&s, ep->src, ep->src->sa_len) == 0 &&
	    memcmp(&d, ep->dst, ep->dst->sa_len) == 0) {
		return matchlen;
	} else
		return 0;
}
#endif

int
encap_lock_enter(void)
{
	int error;

	mutex_enter(&encap_whole.lock);
	while (encap_whole.busy != NULL) {
		error = cv_wait_sig(&encap_whole.cv, &encap_whole.lock);
		if (error) {
			mutex_exit(&encap_whole.lock);
			return error;
		}
	}
	KASSERT(encap_whole.busy == NULL);
	encap_whole.busy = curlwp;
	mutex_exit(&encap_whole.lock);

	return 0;
}

void
encap_lock_exit(void)
{

	mutex_enter(&encap_whole.lock);
	KASSERT(encap_whole.busy == curlwp);
	encap_whole.busy = NULL;
	cv_broadcast(&encap_whole.cv);
	mutex_exit(&encap_whole.lock);
}

bool
encap_lock_held(void)
{

	return (encap_whole.busy == curlwp);
}