freebsd-nq/sys/netipsec/ipsec_output.c

/*-
 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
 *
 * Copyright (c) 2002, 2003 Sam Leffler, Errno Consulting
 * Copyright (c) 2016 Andrey V. Elsukov <ae@FreeBSD.org>
 * 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.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR 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 AUTHOR 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.
 *
 * $FreeBSD$
 */

/*
 * IPsec output processing.
 */
#include "opt_inet.h"
#include "opt_inet6.h"
#include "opt_ipsec.h"
#include "opt_sctp.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/mbuf.h>
#include <sys/domain.h>
#include <sys/protosw.h>
#include <sys/socket.h>
#include <sys/errno.h>
#include <sys/hhook.h>
#include <sys/syslog.h>

#include <net/if.h>
#include <net/if_enc.h>
#include <net/if_var.h>
#include <net/vnet.h>

#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netinet/ip_var.h>
#include <netinet/in_var.h>
#include <netinet/ip_ecn.h>
#ifdef INET6
#include <netinet6/ip6_ecn.h>
#endif
#include <netinet/ip_icmp.h>
#include <netinet/tcp_var.h>

#include <netinet/ip6.h>
#ifdef INET6
#include <netinet6/ip6_var.h>
#include <netinet6/scope6_var.h>
#endif
#include <netinet/in_pcb.h>
#ifdef INET6
#include <netinet/icmp6.h>
#endif
#if defined(SCTP) || defined(SCTP_SUPPORT)
#include <netinet/sctp_crc32.h>
#endif

#include <netinet/udp.h>
#include <netipsec/ah.h>
#include <netipsec/esp.h>
#include <netipsec/ipsec.h>
#ifdef INET6
#include <netipsec/ipsec6.h>
#endif
#include <netipsec/ah_var.h>
#include <netipsec/esp_var.h>
#include <netipsec/ipcomp_var.h>

#include <netipsec/xform.h>

#include <netipsec/key.h>
#include <netipsec/keydb.h>
#include <netipsec/key_debug.h>

#include <machine/in_cksum.h>

#define	IPSEC_OSTAT_INC(proto, name)	do {		\
	if ((proto) == IPPROTO_ESP)	\
		ESPSTAT_INC(esps_##name);	\
	else if ((proto) == IPPROTO_AH)\
		AHSTAT_INC(ahs_##name);		\
	else					\
		IPCOMPSTAT_INC(ipcomps_##name);	\
} while (0)

static int ipsec_encap(struct mbuf **mp, struct secasindex *saidx);
static size_t ipsec_get_pmtu(struct secasvar *sav);

#ifdef INET
static struct secasvar *
ipsec4_allocsa(struct mbuf *m, struct secpolicy *sp, u_int *pidx, int *error)
{
	struct secasindex *saidx, tmpsaidx;
	struct ipsecrequest *isr;
	struct sockaddr_in *sin;
	struct secasvar *sav;
	struct ip *ip;

	/*
	 * Check system global policy controls.
	 */
next:
	isr = sp->req[*pidx];
	if ((isr->saidx.proto == IPPROTO_ESP && !V_esp_enable) ||
	    (isr->saidx.proto == IPPROTO_AH && !V_ah_enable) ||
	    (isr->saidx.proto == IPPROTO_IPCOMP && !V_ipcomp_enable)) {
		DPRINTF(("%s: IPsec outbound packet dropped due"
			" to policy (check your sysctls)\n", __func__));
		IPSEC_OSTAT_INC(isr->saidx.proto, pdrops);
		*error = EHOSTUNREACH;
		return (NULL);
	}
	/*
	 * Craft SA index to search for proper SA.  Note that
	 * we only initialize unspecified SA peers for transport
	 * mode; for tunnel mode they must already be filled in.
	 */
	if (isr->saidx.mode == IPSEC_MODE_TRANSPORT) {
		saidx = &tmpsaidx;
		*saidx = isr->saidx;
		ip = mtod(m, struct ip *);
		if (saidx->src.sa.sa_len == 0) {
			sin = &saidx->src.sin;
			sin->sin_len = sizeof(*sin);
			sin->sin_family = AF_INET;
			sin->sin_port = IPSEC_PORT_ANY;
			sin->sin_addr = ip->ip_src;
		}
		if (saidx->dst.sa.sa_len == 0) {
			sin = &saidx->dst.sin;
			sin->sin_len = sizeof(*sin);
			sin->sin_family = AF_INET;
			sin->sin_port = IPSEC_PORT_ANY;
			sin->sin_addr = ip->ip_dst;
		}
	} else
		saidx = &sp->req[*pidx]->saidx;
	/*
	 * Lookup SA and validate it.
	 */
	sav = key_allocsa_policy(sp, saidx, error);
	if (sav == NULL) {
		IPSECSTAT_INC(ips_out_nosa);
		if (*error != 0)
			return (NULL);
		if (ipsec_get_reqlevel(sp, *pidx) != IPSEC_LEVEL_REQUIRE) {
			/*
			 * We have no SA and policy that doesn't require
			 * this IPsec transform, thus we can continue w/o
			 * IPsec processing, i.e. return EJUSTRETURN.
			 * But first check if there is some bundled transform.
			 */
			if (sp->tcount > ++(*pidx))
				goto next;
			*error = EJUSTRETURN;
		}
		return (NULL);
	}
	IPSEC_ASSERT(sav->tdb_xform != NULL, ("SA with NULL tdb_xform"));
	return (sav);
}

/*
 * IPsec output logic for IPv4.
 */
static int
ipsec4_perform_request(struct mbuf *m, struct secpolicy *sp,
    struct inpcb *inp, u_int idx)
{
	struct ipsec_ctx_data ctx;
	union sockaddr_union *dst;
	struct secasvar *sav;
	struct ip *ip;
	int error, i, off;

	IPSEC_ASSERT(idx < sp->tcount, ("Wrong IPsec request index %d", idx));

	/*
	 * We hold the reference to SP. Content of SP couldn't be changed.
	 * Craft secasindex and do lookup for suitable SA.
	 * Then do encapsulation if needed and call xform's output.
	 * We need to store SP in the xform callback parameters.
	 * In xform callback we will extract SP and it can be used to
	 * determine next transform. At the end of transform we can
	 * release reference to SP.
	 */
	sav = ipsec4_allocsa(m, sp, &idx, &error);
	if (sav == NULL) {
		if (error == EJUSTRETURN) { /* No IPsec required */
			key_freesp(&sp);
			return (error);
		}
		goto bad;
	}
	/*
	 * XXXAE: most likely ip_sum at this point is wrong.
	 */
	IPSEC_INIT_CTX(&ctx, &m, inp, sav, AF_INET, IPSEC_ENC_BEFORE);
	if ((error = ipsec_run_hhooks(&ctx, HHOOK_TYPE_IPSEC_OUT)) != 0)
		goto bad;

	ip = mtod(m, struct ip *);
	dst = &sav->sah->saidx.dst;
	/* Do the appropriate encapsulation, if necessary */
	if (sp->req[idx]->saidx.mode == IPSEC_MODE_TUNNEL || /* Tunnel requ'd */
	    dst->sa.sa_family != AF_INET ||	    /* PF mismatch */
	    (dst->sa.sa_family == AF_INET &&	    /* Proxy */
	     dst->sin.sin_addr.s_addr != INADDR_ANY &&
	     dst->sin.sin_addr.s_addr != ip->ip_dst.s_addr)) {
		/* Fix IPv4 header checksum and length */
		ip->ip_len = htons(m->m_pkthdr.len);
		ip->ip_sum = 0;
		ip->ip_sum = in_cksum(m, ip->ip_hl << 2);
		error = ipsec_encap(&m, &sav->sah->saidx);
		if (error != 0) {
			DPRINTF(("%s: encapsulation for SPI 0x%08x failed "
			    "with error %d\n", __func__, ntohl(sav->spi),
			    error));
			/* XXXAE: IPSEC_OSTAT_INC(tunnel); */
			goto bad;
		}
		inp = NULL;
	}

	IPSEC_INIT_CTX(&ctx, &m, inp, sav, dst->sa.sa_family, IPSEC_ENC_AFTER);
	if ((error = ipsec_run_hhooks(&ctx, HHOOK_TYPE_IPSEC_OUT)) != 0)
		goto bad;

	/*
	 * Dispatch to the appropriate IPsec transform logic.  The
	 * packet will be returned for transmission after crypto
	 * processing, etc. are completed.
	 *
	 * NB: m & sav are ``passed to caller'' who's responsible for
	 *     reclaiming their resources.
	 */
	switch(dst->sa.sa_family) {
	case AF_INET:
		ip = mtod(m, struct ip *);
		i = ip->ip_hl << 2;
		off = offsetof(struct ip, ip_p);
		break;
#ifdef INET6
	case AF_INET6:
		i = sizeof(struct ip6_hdr);
		off = offsetof(struct ip6_hdr, ip6_nxt);
		break;
#endif /* INET6 */
	default:
		DPRINTF(("%s: unsupported protocol family %u\n",
		    __func__, dst->sa.sa_family));
		error = EPFNOSUPPORT;
		IPSEC_OSTAT_INC(sav->sah->saidx.proto, nopf);
		goto bad;
	}
	error = (*sav->tdb_xform->xf_output)(m, sp, sav, idx, i, off);
	return (error);
bad:
	IPSECSTAT_INC(ips_out_inval);
	if (m != NULL)
		m_freem(m);
	if (sav != NULL)
		key_freesav(&sav);
	key_freesp(&sp);
	return (error);
}

int
ipsec4_process_packet(struct mbuf *m, struct secpolicy *sp,
    struct inpcb *inp)
{

	return (ipsec4_perform_request(m, sp, inp, 0));
}

int
ipsec4_check_pmtu(struct mbuf *m, struct secpolicy *sp, int forwarding)
{
	struct secasvar *sav;
	struct ip *ip;
	size_t hlen, pmtu;
	uint32_t idx;
	int error;

	/* Don't check PMTU if the frame won't have DF bit set. */
	if (!V_ip4_ipsec_dfbit)
		return (0);
	if (V_ip4_ipsec_dfbit == 1)
		goto setdf;

	/* V_ip4_ipsec_dfbit > 1 - we will copy it from inner header. */
	ip = mtod(m, struct ip *);
	if (!(ip->ip_off & htons(IP_DF)))
		return (0);

setdf:
	idx = sp->tcount - 1;
	sav = ipsec4_allocsa(m, sp, &idx, &error);
	if (sav == NULL) {
		key_freesp(&sp);
		/*
		 * No matching SA was found and SADB_ACQUIRE message was generated.
		 * Since we have matched a SP to this packet drop it silently.
		 */
		if (error == 0)
			error = EINPROGRESS;
		if (error != EJUSTRETURN)
			m_freem(m);

		return (error);
	}

	pmtu = ipsec_get_pmtu(sav);
	if (pmtu == 0) {
		key_freesav(&sav);
		return (0);
	}

	hlen = ipsec_hdrsiz_internal(sp);
	key_freesav(&sav);

	if (m_length(m, NULL) + hlen > pmtu) {
		/*
		 * If we're forwarding generate ICMP message here,
		 * so that it contains pmtu subtracted by header size.
		 * Set error to EINPROGRESS, in order for the frame
		 * to be dropped silently.
		 */
		if (forwarding) {
			if (pmtu > hlen)
				icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_NEEDFRAG,
				    0, pmtu - hlen);
			else
				m_freem(m);

			key_freesp(&sp);
			return (EINPROGRESS); /* Pretend that we consumed it. */
		} else {
			m_freem(m);
			key_freesp(&sp);
			return (EMSGSIZE);
		}
	}

	return (0);
}

static int
ipsec4_common_output(struct mbuf *m, struct inpcb *inp, int forwarding)
{
	struct secpolicy *sp;
	int error;

	/* Lookup for the corresponding outbound security policy */
	sp = ipsec4_checkpolicy(m, inp, &error, !forwarding);
	if (sp == NULL) {
		if (error == -EINVAL) {
			/* Discarded by policy. */
			m_freem(m);
			return (EACCES);
		}
		return (0); /* No IPsec required. */
	}

	/*
	 * Usually we have to have tunnel mode IPsec security policy
	 * when we are forwarding a packet. Otherwise we could not handle
	 * encrypted replies, because they are not destined for us. But
	 * some users are doing source address translation for forwarded
	 * packets, and thus, even if they are forwarded, the replies will
	 * return back to us.
	 */
	if (!forwarding) {
		/*
		 * Do delayed checksums now because we send before
		 * this is done in the normal processing path.
		 */
		if (m->m_pkthdr.csum_flags & CSUM_DELAY_DATA) {
			in_delayed_cksum(m);
			m->m_pkthdr.csum_flags &= ~CSUM_DELAY_DATA;
		}
#if defined(SCTP) || defined(SCTP_SUPPORT)
		if (m->m_pkthdr.csum_flags & CSUM_SCTP) {
			struct ip *ip;

			ip = mtod(m, struct ip *);
			sctp_delayed_cksum(m, (uint32_t)(ip->ip_hl << 2));
			m->m_pkthdr.csum_flags &= ~CSUM_SCTP;
		}
#endif
	}
	/* NB: callee frees mbuf and releases reference to SP */
	error = ipsec4_check_pmtu(m, sp, forwarding);
	if (error != 0) {
		if (error == EJUSTRETURN)
			return (0);

		return (error);
	}

	error = ipsec4_process_packet(m, sp, inp);
	if (error == EJUSTRETURN) {
		/*
		 * We had a SP with a level of 'use' and no SA. We
		 * will just continue to process the packet without
		 * IPsec processing and return without error.
		 */
		return (0);
	}
	if (error == 0)
		return (EINPROGRESS); /* consumed by IPsec */
	return (error);
}

/*
 * IPSEC_OUTPUT() method implementation for IPv4.
 * 0 - no IPsec handling needed
 * other values - mbuf consumed by IPsec.
 */
int
ipsec4_output(struct mbuf *m, struct inpcb *inp)
{

	/*
	 * If the packet is resubmitted to ip_output (e.g. after
	 * AH, ESP, etc. processing), there will be a tag to bypass
	 * the lookup and related policy checking.
	 */
	if (m_tag_find(m, PACKET_TAG_IPSEC_OUT_DONE, NULL) != NULL)
		return (0);

	return (ipsec4_common_output(m, inp, 0));
}

/*
 * IPSEC_FORWARD() method implementation for IPv4.
 * 0 - no IPsec handling needed
 * other values - mbuf consumed by IPsec.
 */
int
ipsec4_forward(struct mbuf *m)
{

	/*
	 * Check if this packet has an active inbound SP and needs to be
	 * dropped instead of forwarded.
	 */
	if (ipsec4_in_reject(m, NULL) != 0) {
		m_freem(m);
		return (EACCES);
	}
	return (ipsec4_common_output(m, NULL, 1));
}
#endif

#ifdef INET6
static int
in6_sa_equal_addrwithscope(const struct sockaddr_in6 *sa,
    const struct in6_addr *ia)
{
	struct in6_addr ia2;

	if (IN6_IS_SCOPE_LINKLOCAL(&sa->sin6_addr)) {
		memcpy(&ia2, &sa->sin6_addr, sizeof(ia2));
		ia2.s6_addr16[1] = htons(sa->sin6_scope_id);
		return (IN6_ARE_ADDR_EQUAL(ia, &ia2));
	}
	return (IN6_ARE_ADDR_EQUAL(&sa->sin6_addr, ia));
}

static struct secasvar *
ipsec6_allocsa(struct mbuf *m, struct secpolicy *sp, u_int *pidx, int *error)
{
	struct secasindex *saidx, tmpsaidx;
	struct ipsecrequest *isr;
	struct sockaddr_in6 *sin6;
	struct secasvar *sav;
	struct ip6_hdr *ip6;

	/*
	 * Check system global policy controls.
	 */
next:
	isr = sp->req[*pidx];
	if ((isr->saidx.proto == IPPROTO_ESP && !V_esp_enable) ||
	    (isr->saidx.proto == IPPROTO_AH && !V_ah_enable) ||
	    (isr->saidx.proto == IPPROTO_IPCOMP && !V_ipcomp_enable)) {
		DPRINTF(("%s: IPsec outbound packet dropped due"
			" to policy (check your sysctls)\n", __func__));
		IPSEC_OSTAT_INC(isr->saidx.proto, pdrops);
		*error = EHOSTUNREACH;
		return (NULL);
	}
	/*
	 * Craft SA index to search for proper SA.  Note that
	 * we only fillin unspecified SA peers for transport
	 * mode; for tunnel mode they must already be filled in.
	 */
	if (isr->saidx.mode == IPSEC_MODE_TRANSPORT) {
		saidx = &tmpsaidx;
		*saidx = isr->saidx;
		ip6 = mtod(m, struct ip6_hdr *);
		if (saidx->src.sin6.sin6_len == 0) {
			sin6 = (struct sockaddr_in6 *)&saidx->src;
			sin6->sin6_len = sizeof(*sin6);
			sin6->sin6_family = AF_INET6;
			sin6->sin6_port = IPSEC_PORT_ANY;
			sin6->sin6_addr = ip6->ip6_src;
			if (IN6_IS_SCOPE_LINKLOCAL(&ip6->ip6_src)) {
				/* fix scope id for comparing SPD */
				sin6->sin6_addr.s6_addr16[1] = 0;
				sin6->sin6_scope_id =
				    ntohs(ip6->ip6_src.s6_addr16[1]);
			}
		}
		if (saidx->dst.sin6.sin6_len == 0) {
			sin6 = (struct sockaddr_in6 *)&saidx->dst;
			sin6->sin6_len = sizeof(*sin6);
			sin6->sin6_family = AF_INET6;
			sin6->sin6_port = IPSEC_PORT_ANY;
			sin6->sin6_addr = ip6->ip6_dst;
			if (IN6_IS_SCOPE_LINKLOCAL(&ip6->ip6_dst)) {
				/* fix scope id for comparing SPD */
				sin6->sin6_addr.s6_addr16[1] = 0;
				sin6->sin6_scope_id =
				    ntohs(ip6->ip6_dst.s6_addr16[1]);
			}
		}
	} else
		saidx = &sp->req[*pidx]->saidx;
	/*
	 * Lookup SA and validate it.
	 */
	sav = key_allocsa_policy(sp, saidx, error);
	if (sav == NULL) {
		IPSEC6STAT_INC(ips_out_nosa);
		if (*error != 0)
			return (NULL);
		if (ipsec_get_reqlevel(sp, *pidx) != IPSEC_LEVEL_REQUIRE) {
			/*
			 * We have no SA and policy that doesn't require
			 * this IPsec transform, thus we can continue w/o
			 * IPsec processing, i.e. return EJUSTRETURN.
			 * But first check if there is some bundled transform.
			 */
			if (sp->tcount > ++(*pidx))
				goto next;
			*error = EJUSTRETURN;
		}
		return (NULL);
	}
	IPSEC_ASSERT(sav->tdb_xform != NULL, ("SA with NULL tdb_xform"));
	return (sav);
}

/*
 * IPsec output logic for IPv6.
 */
static int
ipsec6_perform_request(struct mbuf *m, struct secpolicy *sp,
    struct inpcb *inp, u_int idx)
{
	struct ipsec_ctx_data ctx;
	union sockaddr_union *dst;
	struct secasvar *sav;
	struct ip6_hdr *ip6;
	int error, i, off;

	IPSEC_ASSERT(idx < sp->tcount, ("Wrong IPsec request index %d", idx));

	sav = ipsec6_allocsa(m, sp, &idx, &error);
	if (sav == NULL) {
		if (error == EJUSTRETURN) { /* No IPsec required */
			key_freesp(&sp);
			return (error);
		}
		goto bad;
	}

	/* Fix IP length in case if it is not set yet. */
	ip6 = mtod(m, struct ip6_hdr *);
	ip6->ip6_plen = htons(m->m_pkthdr.len - sizeof(*ip6));

	IPSEC_INIT_CTX(&ctx, &m, inp, sav, AF_INET6, IPSEC_ENC_BEFORE);
	if ((error = ipsec_run_hhooks(&ctx, HHOOK_TYPE_IPSEC_OUT)) != 0)
		goto bad;

	ip6 = mtod(m, struct ip6_hdr *); /* pfil can change mbuf */
	dst = &sav->sah->saidx.dst;

	/* Do the appropriate encapsulation, if necessary */
	if (sp->req[idx]->saidx.mode == IPSEC_MODE_TUNNEL || /* Tunnel requ'd */
	    dst->sa.sa_family != AF_INET6 ||        /* PF mismatch */
	    ((dst->sa.sa_family == AF_INET6) &&
	     (!IN6_IS_ADDR_UNSPECIFIED(&dst->sin6.sin6_addr)) &&
	     (!in6_sa_equal_addrwithscope(&dst->sin6, &ip6->ip6_dst)))) {
		if (m->m_pkthdr.len - sizeof(*ip6) > IPV6_MAXPACKET) {
			/* No jumbogram support. */
			error = ENXIO;   /*XXX*/
			goto bad;
		}
		error = ipsec_encap(&m, &sav->sah->saidx);
		if (error != 0) {
			DPRINTF(("%s: encapsulation for SPI 0x%08x failed "
			    "with error %d\n", __func__, ntohl(sav->spi),
			    error));
			/* XXXAE: IPSEC_OSTAT_INC(tunnel); */
			goto bad;
		}
		inp = NULL;
	}

	IPSEC_INIT_CTX(&ctx, &m, inp, sav, dst->sa.sa_family, IPSEC_ENC_AFTER);
	if ((error = ipsec_run_hhooks(&ctx, HHOOK_TYPE_IPSEC_OUT)) != 0)
		goto bad;

	switch(dst->sa.sa_family) {
#ifdef INET
	case AF_INET:
		{
		struct ip *ip;
		ip = mtod(m, struct ip *);
		i = ip->ip_hl << 2;
		off = offsetof(struct ip, ip_p);
		}
		break;
#endif /* AF_INET */
	case AF_INET6:
		i = sizeof(struct ip6_hdr);
		off = offsetof(struct ip6_hdr, ip6_nxt);
		break;
	default:
		DPRINTF(("%s: unsupported protocol family %u\n",
				 __func__, dst->sa.sa_family));
		error = EPFNOSUPPORT;
		IPSEC_OSTAT_INC(sav->sah->saidx.proto, nopf);
		goto bad;
	}
	error = (*sav->tdb_xform->xf_output)(m, sp, sav, idx, i, off);
	return (error);
bad:
	IPSEC6STAT_INC(ips_out_inval);
	if (m != NULL)
		m_freem(m);
	if (sav != NULL)
		key_freesav(&sav);
	key_freesp(&sp);
	return (error);
}

int
ipsec6_process_packet(struct mbuf *m, struct secpolicy *sp,
    struct inpcb *inp)
{

	return (ipsec6_perform_request(m, sp, inp, 0));
}

/*
 * IPv6 implementation is based on IPv4 implementation.
 */
int
ipsec6_check_pmtu(struct mbuf *m, struct secpolicy *sp, int forwarding)
{
	struct secasvar *sav;
	size_t hlen, pmtu;
	uint32_t idx;
	int error;

	/*
	 * According to RFC8200 L3 fragmentation is supposed to be done only on
	 * locally generated packets. During L3 forwarding packets that are too
	 * big are always supposed to be dropped, with an ICMPv6 packet being
	 * sent back.
	 */
	if (!forwarding)
		return (0);

	idx = sp->tcount - 1;
	sav = ipsec6_allocsa(m, sp, &idx, &error);
	if (sav == NULL) {
		key_freesp(&sp);
		/*
		 * No matching SA was found and SADB_ACQUIRE message was generated.
		 * Since we have matched a SP to this packet drop it silently.
		 */
		if (error == 0)
			error = EINPROGRESS;
		if (error != EJUSTRETURN)
			m_freem(m);

		return (error);
	}

	pmtu = ipsec_get_pmtu(sav);
	if (pmtu == 0) {
		key_freesav(&sav);
		return (0);
	}

	hlen = ipsec_hdrsiz_internal(sp);
	key_freesav(&sav);

	if (m_length(m, NULL) + hlen > pmtu) {
		/*
		 * If we're forwarding generate ICMPv6 message here,
		 * so that it contains pmtu subtracted by header size.
		 * Set error to EINPROGRESS, in order for the frame
		 * to be dropped silently.
		 */
		if (forwarding) {
			if (pmtu > hlen)
				icmp6_error(m, ICMP6_PACKET_TOO_BIG, 0, pmtu - hlen);
			else
				m_freem(m);

			key_freesp(&sp);
			return (EINPROGRESS); /* Pretend that we consumed it. */
		}
	}

	return (0);
}

static int
ipsec6_common_output(struct mbuf *m, struct inpcb *inp, int forwarding)
{
	struct secpolicy *sp;
	int error;

	/* Lookup for the corresponding outbound security policy */
	sp = ipsec6_checkpolicy(m, inp, &error, !forwarding);
	if (sp == NULL) {
		if (error == -EINVAL) {
			/* Discarded by policy. */
			m_freem(m);
			return (EACCES);
		}
		return (0); /* No IPsec required. */
	}

	if (!forwarding) {
		/*
		 * Do delayed checksums now because we send before
		 * this is done in the normal processing path.
		 */
		if (m->m_pkthdr.csum_flags & CSUM_DELAY_DATA_IPV6) {
			in6_delayed_cksum(m, m->m_pkthdr.len -
			    sizeof(struct ip6_hdr), sizeof(struct ip6_hdr));
			m->m_pkthdr.csum_flags &= ~CSUM_DELAY_DATA_IPV6;
		}
#if defined(SCTP) || defined(SCTP_SUPPORT)
		if (m->m_pkthdr.csum_flags & CSUM_SCTP_IPV6) {
			sctp_delayed_cksum(m, sizeof(struct ip6_hdr));
			m->m_pkthdr.csum_flags &= ~CSUM_SCTP_IPV6;
		}
#endif
	}

	error = ipsec6_check_pmtu(m, sp, forwarding);
	if (error != 0) {
		if (error == EJUSTRETURN)
			return (0);

		return (error);
	}

	/* NB: callee frees mbuf and releases reference to SP */
	error = ipsec6_process_packet(m, sp, inp);
	if (error == EJUSTRETURN) {
		/*
		 * We had a SP with a level of 'use' and no SA. We
		 * will just continue to process the packet without
		 * IPsec processing and return without error.
		 */
		return (0);
	}
	if (error == 0)
		return (EINPROGRESS); /* consumed by IPsec */
	return (error);
}

/*
 * IPSEC_OUTPUT() method implementation for IPv6.
 * 0 - no IPsec handling needed
 * other values - mbuf consumed by IPsec.
 */
int
ipsec6_output(struct mbuf *m, struct inpcb *inp)
{

	/*
	 * If the packet is resubmitted to ip_output (e.g. after
	 * AH, ESP, etc. processing), there will be a tag to bypass
	 * the lookup and related policy checking.
	 */
	if (m_tag_find(m, PACKET_TAG_IPSEC_OUT_DONE, NULL) != NULL)
		return (0);

	return (ipsec6_common_output(m, inp, 0));
}

/*
 * IPSEC_FORWARD() method implementation for IPv6.
 * 0 - no IPsec handling needed
 * other values - mbuf consumed by IPsec.
 */
int
ipsec6_forward(struct mbuf *m)
{

	/*
	 * Check if this packet has an active inbound SP and needs to be
	 * dropped instead of forwarded.
	 */
	if (ipsec6_in_reject(m, NULL) != 0) {
		m_freem(m);
		return (EACCES);
	}
	return (ipsec6_common_output(m, NULL, 1));
}
#endif /* INET6 */

int
ipsec_process_done(struct mbuf *m, struct secpolicy *sp, struct secasvar *sav,
    u_int idx)
{
	struct epoch_tracker et;
	struct xform_history *xh;
	struct secasindex *saidx;
	struct m_tag *mtag;
	int error;

	saidx = &sav->sah->saidx;
	switch (saidx->dst.sa.sa_family) {
#ifdef INET
	case AF_INET:
		/* Fix the header length, for AH processing. */
		mtod(m, struct ip *)->ip_len = htons(m->m_pkthdr.len);
		break;
#endif /* INET */
#ifdef INET6
	case AF_INET6:
		/* Fix the header length, for AH processing. */
		if (m->m_pkthdr.len < sizeof (struct ip6_hdr)) {
			error = ENXIO;
			goto bad;
		}
		if (m->m_pkthdr.len - sizeof (struct ip6_hdr) > IPV6_MAXPACKET) {
			/* No jumbogram support. */
			error = ENXIO;	/*?*/
			goto bad;
		}
		mtod(m, struct ip6_hdr *)->ip6_plen =
			htons(m->m_pkthdr.len - sizeof(struct ip6_hdr));
		break;
#endif /* INET6 */
	default:
		DPRINTF(("%s: unknown protocol family %u\n", __func__,
		    saidx->dst.sa.sa_family));
		error = ENXIO;
		goto bad;
	}

	/*
	 * Add a record of what we've done to the packet.
	 */
	mtag = m_tag_get(PACKET_TAG_IPSEC_OUT_DONE, sizeof(*xh), M_NOWAIT);
	if (mtag == NULL) {
		DPRINTF(("%s: could not get packet tag\n", __func__));
		error = ENOMEM;
		goto bad;
	}

	xh = (struct xform_history *)(mtag + 1);
	xh->dst = saidx->dst;
	xh->proto = saidx->proto;
	xh->mode = saidx->mode;
	xh->spi = sav->spi;
	m_tag_prepend(m, mtag);

	key_sa_recordxfer(sav, m);		/* record data transfer */

	/*
	 * If there's another (bundled) SA to apply, do so.
	 * Note that this puts a burden on the kernel stack size.
	 * If this is a problem we'll need to introduce a queue
	 * to set the packet on so we can unwind the stack before
	 * doing further processing.
	 */
	if (++idx < sp->tcount) {
		switch (saidx->dst.sa.sa_family) {
#ifdef INET
		case AF_INET:
			key_freesav(&sav);
			IPSECSTAT_INC(ips_out_bundlesa);
			return (ipsec4_perform_request(m, sp, NULL, idx));
			/* NOTREACHED */
#endif
#ifdef INET6
		case AF_INET6:
			key_freesav(&sav);
			IPSEC6STAT_INC(ips_out_bundlesa);
			return (ipsec6_perform_request(m, sp, NULL, idx));
			/* NOTREACHED */
#endif /* INET6 */
		default:
			DPRINTF(("%s: unknown protocol family %u\n", __func__,
			    saidx->dst.sa.sa_family));
			error = EPFNOSUPPORT;
			goto bad;
		}
	}

	key_freesp(&sp), sp = NULL;	/* Release reference to SP */
#ifdef INET
	/*
	 * Do UDP encapsulation if SA requires it.
	 */
	if (sav->natt != NULL) {
		error = udp_ipsec_output(m, sav);
		if (error != 0)
			goto bad;
	}
#endif /* INET */
	/*
	 * We're done with IPsec processing, transmit the packet using the
	 * appropriate network protocol (IP or IPv6).
	 */
	NET_EPOCH_ENTER(et);
	switch (saidx->dst.sa.sa_family) {
#ifdef INET
	case AF_INET:
		key_freesav(&sav);
		error = ip_output(m, NULL, NULL, IP_RAWOUTPUT, NULL, NULL);
		break;
#endif /* INET */
#ifdef INET6
	case AF_INET6:
		key_freesav(&sav);
		error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL);
		break;
#endif /* INET6 */
	default:
		panic("ipsec_process_done");
	}
	NET_EPOCH_EXIT(et);
	return (error);
bad:
	m_freem(m);
	key_freesav(&sav);
	if (sp != NULL)
		key_freesp(&sp);
	return (error);
}

/*
 * ipsec_prepend() is optimized version of M_PREPEND().
 * ipsec_encap() is called by IPsec output routine for tunnel mode SA.
 * It is expected that after IP encapsulation some IPsec transform will
 * be performed. Each IPsec transform inserts its variable length header
 * just after outer IP header using m_makespace(). If given mbuf has not
 * enough free space at the beginning, we allocate new mbuf and reserve
 * some space at the beginning and at the end.
 * This helps avoid allocating of new mbuf and data copying in m_makespace(),
 * we place outer header in the middle of mbuf's data with reserved leading
 * and trailing space:
 *	[ LEADINGSPACE ][ Outer IP header ][ TRAILINGSPACE ]
 * LEADINGSPACE will be used to add ethernet header, TRAILINGSPACE will
 * be used to inject AH/ESP/IPCOMP header.
 */
#define	IPSEC_TRAILINGSPACE	(sizeof(struct udphdr) +/* NAT-T */	\
    max(sizeof(struct newesp) + EALG_MAX_BLOCK_LEN,	/* ESP + IV */	\
	sizeof(struct newah) + HASH_MAX_LEN		/* AH + ICV */))
static struct mbuf *
ipsec_prepend(struct mbuf *m, int len, int how)
{
	struct mbuf *n;

	M_ASSERTPKTHDR(m);
	IPSEC_ASSERT(len < MHLEN, ("wrong length"));
	if (M_LEADINGSPACE(m) >= len) {
		/* No need to allocate new mbuf. */
		m->m_data -= len;
		m->m_len += len;
		m->m_pkthdr.len += len;
		return (m);
	}
	n = m_gethdr(how, m->m_type);
	if (n == NULL) {
		m_freem(m);
		return (NULL);
	}
	m_move_pkthdr(n, m);
	n->m_next = m;
	if (len + IPSEC_TRAILINGSPACE < M_SIZE(n))
		m_align(n, len + IPSEC_TRAILINGSPACE);
	n->m_len = len;
	n->m_pkthdr.len += len;
	return (n);
}

static size_t
ipsec_get_pmtu(struct secasvar *sav)
{
	union sockaddr_union *dst;
	struct in_conninfo inc;
	size_t pmtu;

	dst = &sav->sah->saidx.dst;
	memset(&inc, 0, sizeof(inc));

	switch (dst->sa.sa_family) {
#ifdef INET
	case AF_INET:
		inc.inc_faddr = satosin(&dst->sa)->sin_addr;
		break;
#endif
#ifdef INET6
	case AF_INET6:
		inc.inc6_faddr = satosin6(&dst->sa)->sin6_addr;
		inc.inc_flags |= INC_ISIPV6;
		break;
#endif
	default:
		return (0);
	}

	pmtu = tcp_hc_getmtu(&inc);
	if (pmtu != 0)
		return (pmtu);

	/* No entry in hostcache. Assume that PMTU is equal to link's MTU */
	switch (dst->sa.sa_family) {
#ifdef INET
	case AF_INET:
		pmtu = tcp_maxmtu(&inc, NULL);
		break;
#endif
#ifdef INET6
	case AF_INET6:
		pmtu = tcp_maxmtu6(&inc, NULL);
		break;
#endif
	default:
		return (0);
	}
	if (pmtu == 0)
		return (0);

	tcp_hc_updatemtu(&inc, pmtu);

	return (pmtu);
}

static int
ipsec_encap(struct mbuf **mp, struct secasindex *saidx)
{
#ifdef INET6
	struct ip6_hdr *ip6;
#endif
	struct ip *ip;
	int setdf;
	uint8_t itos, proto;

	ip = mtod(*mp, struct ip *);
	switch (ip->ip_v) {
#ifdef INET
	case IPVERSION:
		proto = IPPROTO_IPIP;
		/*
		 * Collect IP_DF state from the inner header
		 * and honor system-wide control of how to handle it.
		 */
		switch (V_ip4_ipsec_dfbit) {
		case 0:	/* clear in outer header */
		case 1:	/* set in outer header */
			setdf = V_ip4_ipsec_dfbit;
			break;
		default:/* propagate to outer header */
			setdf = (ip->ip_off & htons(IP_DF)) != 0;
		}
		itos = ip->ip_tos;
		break;
#endif
#ifdef INET6
	case (IPV6_VERSION >> 4):
		proto = IPPROTO_IPV6;
		ip6 = mtod(*mp, struct ip6_hdr *);
		itos = (ntohl(ip6->ip6_flow) >> 20) & 0xff;
		setdf = V_ip4_ipsec_dfbit ? 1: 0;
		/* scoped address handling */
		in6_clearscope(&ip6->ip6_src);
		in6_clearscope(&ip6->ip6_dst);
		break;
#endif
	default:
		return (EAFNOSUPPORT);
	}
	switch (saidx->dst.sa.sa_family) {
#ifdef INET
	case AF_INET:
		if (saidx->src.sa.sa_family != AF_INET ||
		    saidx->src.sin.sin_addr.s_addr == INADDR_ANY ||
		    saidx->dst.sin.sin_addr.s_addr == INADDR_ANY)
			return (EINVAL);
		*mp = ipsec_prepend(*mp, sizeof(struct ip), M_NOWAIT);
		if (*mp == NULL)
			return (ENOBUFS);
		ip = mtod(*mp, struct ip *);
		ip->ip_v = IPVERSION;
		ip->ip_hl = sizeof(struct ip) >> 2;
		ip->ip_p = proto;
		ip->ip_len = htons((*mp)->m_pkthdr.len);
		ip->ip_ttl = V_ip_defttl;
		ip->ip_sum = 0;
		ip->ip_off = setdf ? htons(IP_DF): 0;
		ip->ip_src = saidx->src.sin.sin_addr;
		ip->ip_dst = saidx->dst.sin.sin_addr;
		ip_ecn_ingress(V_ip4_ipsec_ecn, &ip->ip_tos, &itos);
		ip_fillid(ip);
		break;
#endif /* INET */
#ifdef INET6
	case AF_INET6:
		if (saidx->src.sa.sa_family != AF_INET6 ||
		    IN6_IS_ADDR_UNSPECIFIED(&saidx->src.sin6.sin6_addr) ||
		    IN6_IS_ADDR_UNSPECIFIED(&saidx->dst.sin6.sin6_addr))
			return (EINVAL);
		*mp = ipsec_prepend(*mp, sizeof(struct ip6_hdr), M_NOWAIT);
		if (*mp == NULL)
			return (ENOBUFS);
		ip6 = mtod(*mp, struct ip6_hdr *);
		ip6->ip6_flow = 0;
		ip6->ip6_vfc = IPV6_VERSION;
		ip6->ip6_hlim = V_ip6_defhlim;
		ip6->ip6_nxt = proto;
		ip6->ip6_dst = saidx->dst.sin6.sin6_addr;
		/* For link-local address embed scope zone id */
		if (IN6_IS_SCOPE_LINKLOCAL(&ip6->ip6_dst))
			ip6->ip6_dst.s6_addr16[1] =
			    htons(saidx->dst.sin6.sin6_scope_id & 0xffff);
		ip6->ip6_src = saidx->src.sin6.sin6_addr;
		if (IN6_IS_SCOPE_LINKLOCAL(&ip6->ip6_src))
			ip6->ip6_src.s6_addr16[1] =
			    htons(saidx->src.sin6.sin6_scope_id & 0xffff);
		ip6->ip6_plen = htons((*mp)->m_pkthdr.len - sizeof(*ip6));
		ip_ecn_ingress(V_ip6_ipsec_ecn, &proto, &itos);
		ip6->ip6_flow |= htonl((uint32_t)proto << 20);
		break;
#endif /* INET6 */
	default:
		return (EAFNOSUPPORT);
	}
	(*mp)->m_flags &= ~(M_BCAST | M_MCAST);
	return (0);
}