/*      $OpenBSD: ipsec_input.c,v 1.63 2003/02/20 18:35:43 deraadt Exp $        */
/*-
 * The authors of this code are John Ioannidis (ji@tla.org),
 * Angelos D. Keromytis (kermit@csd.uch.gr) and
 * Niels Provos (provos@physnet.uni-hamburg.de).
 *
 * This code was written by John Ioannidis for BSD/OS in Athens, Greece,
 * in November 1995.
 *
 * Ported to OpenBSD and NetBSD, with additional transforms, in December 1996,
 * by Angelos D. Keromytis.
 *
 * Additional transforms and features in 1997 and 1998 by Angelos D. Keromytis
 * and Niels Provos.
 *
 * Additional features in 1999 by Angelos D. Keromytis.
 *
 * Copyright (C) 1995, 1996, 1997, 1998, 1999 by John Ioannidis,
 * Angelos D. Keromytis and Niels Provos.
 * Copyright (c) 2001, Angelos D. Keromytis.
 * Copyright (c) 2016 Andrey V. Elsukov <ae@FreeBSD.org>
 *
 * Permission to use, copy, and modify this software with or without fee
 * is hereby granted, provided that this entire notice is included in
 * all copies of any software which is or includes a copy or
 * modification of this software.
 * You may use this code under the GNU public license if you so wish. Please
 * contribute changes back to the authors under this freer than GPL license
 * so that we may further the use of strong encryption without limitations to
 * all.
 *
 * THIS SOFTWARE IS BEING PROVIDED "AS IS", WITHOUT ANY EXPRESS OR
 * IMPLIED WARRANTY. IN PARTICULAR, NONE OF THE AUTHORS MAKES ANY
 * REPRESENTATION OR WARRANTY OF ANY KIND CONCERNING THE
 * MERCHANTABILITY OF THIS SOFTWARE OR ITS FITNESS FOR ANY PARTICULAR
 * PURPOSE.
 */

/*
 * IPsec input processing.
 */

#include <sys/cdefs.h>
#include "opt_inet.h"
#include "opt_inet6.h"
#include "opt_ipsec.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/malloc.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/stdarg.h>
#include <sys/syslog.h>

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

#include <netinet/in.h>
#include <netinet/in_pcb.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netinet/ip_var.h>
#include <netinet/ip_icmp.h>
#include <netinet/in_var.h>
#include <netinet/tcp_var.h>

#include <netinet/ip6.h>
#ifdef INET6
#include <netinet6/ip6_var.h>
#endif
#include <netinet/in_pcb.h>
#ifdef INET6
#include <netinet/icmp6.h>
#endif

#include <netipsec/ipsec.h>
#ifdef INET6
#include <netipsec/ipsec6.h>
#endif
#include <netipsec/ipsec_support.h>
#include <netipsec/ah_var.h>
#include <netipsec/esp.h>
#include <netipsec/esp_var.h>
#include <netipsec/ipcomp_var.h>
#include <netipsec/ipsec_offload.h>

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

#include <netipsec/xform.h>

#include <machine/in_cksum.h>

#define IPSEC_ISTAT(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)

/*
 * ipsec_common_input gets called when an IPsec-protected packet
 * is received by IPv4 or IPv6.  Its job is to find the right SA
 * and call the appropriate transform.  The transform callback
 * takes care of further processing (like ingress filtering).
 */
static int
ipsec_common_input(struct mbuf *m, int skip, int protoff, int af, int sproto)
{
        IPSEC_DEBUG_DECLARE(char buf[IPSEC_ADDRSTRLEN]);
        union sockaddr_union dst_address;
        struct secasvar *sav;
        uint32_t spi;
        int error;

        IPSEC_ISTAT(sproto, input);

        IPSEC_ASSERT(m != NULL, ("null packet"));

        IPSEC_ASSERT(sproto == IPPROTO_ESP || sproto == IPPROTO_AH ||
                sproto == IPPROTO_IPCOMP,
                ("unexpected security protocol %u", sproto));

        if ((sproto == IPPROTO_ESP && !V_esp_enable) ||
            (sproto == IPPROTO_AH && !V_ah_enable) ||
            (sproto == IPPROTO_IPCOMP && !V_ipcomp_enable)) {
                m_freem(m);
                IPSEC_ISTAT(sproto, pdrops);
                return EOPNOTSUPP;
        }

        if (m->m_pkthdr.len - skip < 2 * sizeof (u_int32_t)) {
                m_freem(m);
                IPSEC_ISTAT(sproto, hdrops);
                DPRINTF(("%s: packet too small\n", __func__));
                return EINVAL;
        }

        /* Retrieve the SPI from the relevant IPsec header */
        if (sproto == IPPROTO_ESP)
                m_copydata(m, skip, sizeof(u_int32_t), (caddr_t) &spi);
        else if (sproto == IPPROTO_AH)
                m_copydata(m, skip + sizeof(u_int32_t), sizeof(u_int32_t),
                    (caddr_t) &spi);
        else if (sproto == IPPROTO_IPCOMP) {
                u_int16_t cpi;
                m_copydata(m, skip + sizeof(u_int16_t), sizeof(u_int16_t),
                    (caddr_t) &cpi);
                spi = ntohl(htons(cpi));
        }

        /*
         * Find the SA and (indirectly) call the appropriate
         * kernel crypto routine. The resulting mbuf chain is a valid
         * IP packet ready to go through input processing.
         */
        bzero(&dst_address, sizeof (dst_address));
        dst_address.sa.sa_family = af;
        switch (af) {
#ifdef INET
        case AF_INET:
                dst_address.sin.sin_len = sizeof(struct sockaddr_in);
                m_copydata(m, offsetof(struct ip, ip_dst),
                    sizeof(struct in_addr),
                    (caddr_t) &dst_address.sin.sin_addr);
                break;
#endif /* INET */
#ifdef INET6
        case AF_INET6:
                dst_address.sin6.sin6_len = sizeof(struct sockaddr_in6);
                m_copydata(m, offsetof(struct ip6_hdr, ip6_dst),
                    sizeof(struct in6_addr),
                    (caddr_t) &dst_address.sin6.sin6_addr);
                /* We keep addresses in SADB without embedded scope id */
                if (IN6_IS_SCOPE_LINKLOCAL(&dst_address.sin6.sin6_addr)) {
                        /* XXX: sa6_recoverscope() */
                        dst_address.sin6.sin6_scope_id =
                            ntohs(dst_address.sin6.sin6_addr.s6_addr16[1]);
                        dst_address.sin6.sin6_addr.s6_addr16[1] = 0;
                }
                break;
#endif /* INET6 */
        default:
                DPRINTF(("%s: unsupported protocol family %u\n", __func__, af));
                m_freem(m);
                IPSEC_ISTAT(sproto, nopf);
                return EPFNOSUPPORT;
        }

        /* NB: only pass dst since key_allocsa follows RFC2401 */
        sav = key_allocsa(&dst_address, sproto, spi);
        if (sav == NULL) {
                DPRINTF(("%s: no key association found for SA %s/%08lx/%u\n",
                    __func__, ipsec_address(&dst_address, buf, sizeof(buf)),
                    (u_long) ntohl(spi), sproto));
                IPSEC_ISTAT(sproto, notdb);
                m_freem(m);
                return ENOENT;
        }

        if (sav->tdb_xform == NULL) {
                DPRINTF(("%s: attempted to use uninitialized SA %s/%08lx/%u\n",
                    __func__, ipsec_address(&dst_address, buf, sizeof(buf)),
                    (u_long) ntohl(spi), sproto));
                IPSEC_ISTAT(sproto, noxform);
                key_freesav(&sav);
                m_freem(m);
                return ENXIO;
        }

        /*
         * Call appropriate transform and return -- callback takes care of
         * everything else.
         */
        error = (*sav->tdb_xform->xf_input)(m, sav, skip, protoff);
        return (error);
}

#ifdef INET
/*
 * IPSEC_INPUT() method implementation for IPv4.
 *  0 - Permitted by inbound security policy for further processing.
 *  EACCES - Forbidden by inbound security policy.
 *  EINPROGRESS - consumed by IPsec.
 */
int
ipsec4_input(struct mbuf *m, int offset, int proto)
{
        int error;

        error = ipsec_accel_input(m, offset, proto);
        if (error != ENXIO)
                return (error);

        switch (proto) {
        case IPPROTO_AH:
        case IPPROTO_ESP:
        case IPPROTO_IPCOMP:
                /* Do inbound IPsec processing for AH/ESP/IPCOMP */
                ipsec_common_input(m, offset,
                    offsetof(struct ip, ip_p), AF_INET, proto);
                return (EINPROGRESS); /* mbuf consumed by IPsec */
        default:
                /*
                 * Protocols with further headers get their IPsec treatment
                 * within the protocol specific processing.
                 */
                switch (proto) {
                case IPPROTO_ICMP:
                case IPPROTO_IGMP:
                case IPPROTO_IPV4:
                case IPPROTO_IPV6:
                case IPPROTO_RSVP:
                case IPPROTO_GRE:
                case IPPROTO_MOBILE:
                case IPPROTO_ETHERIP:
                case IPPROTO_PIM:
                case IPPROTO_SCTP:
                        break;
                default:
                        return (0);
                }
        };
        /*
         * Enforce IPsec policy checking if we are seeing last header.
         */
        if (ipsec4_in_reject(m, NULL) != 0) {
                /* Forbidden by inbound security policy */
                m_freem(m);
                return (EACCES);
        }
        return (0);
}

int
ipsec4_ctlinput(ipsec_ctlinput_param_t param)
{
        struct icmp *icp = param.icmp;
        struct ip *ip = &icp->icmp_ip;
        struct sockaddr_in icmpsrc = {
                .sin_len = sizeof(struct sockaddr_in),
                .sin_family = AF_INET,
                .sin_addr = ip->ip_dst,
        };
        struct in_conninfo inc;
        struct secasvar *sav;
        uint32_t pmtu, spi;
        uint32_t max_pmtu;
        uint8_t proto;

        pmtu = ntohs(icp->icmp_nextmtu);

        if (pmtu < V_ip4_ipsec_min_pmtu)
                return (EINVAL);

        proto = ip->ip_p;
        if (proto != IPPROTO_ESP && proto != IPPROTO_AH &&
            proto != IPPROTO_IPCOMP)
                return (EINVAL);

        memcpy(&spi, (caddr_t)ip + (ip->ip_hl << 2), sizeof(spi));
        sav = key_allocsa((union sockaddr_union *)&icmpsrc, proto, spi);
        if (sav == NULL)
                return (ENOENT);

        key_freesav(&sav);

        memset(&inc, 0, sizeof(inc));
        inc.inc_faddr = ip->ip_dst;

        /* Update pmtu only if its smaller than the current one. */
        max_pmtu = tcp_hc_getmtu(&inc);
        if (max_pmtu == 0)
                max_pmtu = tcp_maxmtu(&inc, NULL);

        if (pmtu < max_pmtu)
                tcp_hc_updatemtu(&inc, pmtu);

        return (0);
}

/*
 * IPsec input callback for INET protocols.
 * This routine is called as the transform callback.
 * Takes care of filtering and other sanity checks on
 * the processed packet.
 */
int
ipsec4_common_input_cb(struct mbuf *m, struct secasvar *sav, int skip,
    int protoff, struct rm_priotracker *sahtree_tracker)
{
        IPSEC_DEBUG_DECLARE(char buf[IPSEC_ADDRSTRLEN]);
        struct epoch_tracker et;
        struct ipsec_ctx_data ctx;
        struct xform_history *xh;
        struct secasindex *saidx;
        struct m_tag *mtag;
        struct ip *ip;
        int error, prot, af, sproto, isr_prot;

        IPSEC_ASSERT(sav != NULL, ("null SA"));
        IPSEC_ASSERT(sav->sah != NULL, ("null SAH"));
        saidx = &sav->sah->saidx;
        af = saidx->dst.sa.sa_family;
        IPSEC_ASSERT(af == AF_INET, ("unexpected af %u", af));
        sproto = saidx->proto;
        IPSEC_ASSERT(sproto == IPPROTO_ESP || sproto == IPPROTO_AH ||
                sproto == IPPROTO_IPCOMP,
                ("unexpected security protocol %u", sproto));

        if (skip != 0) {
                /*
                 * Fix IPv4 header
                 */
                if (m->m_len < skip && (m = m_pullup(m, skip)) == NULL) {
                        DPRINTF(("%s: processing failed for SA %s/%08lx\n",
                            __func__, ipsec_address(&sav->sah->saidx.dst,
                            buf, sizeof(buf)), (u_long) ntohl(sav->spi)));
                        IPSEC_ISTAT(sproto, hdrops);
                        error = ENOBUFS;
                        goto bad_noepoch;
                }

                ip = mtod(m, struct ip *);
                ip->ip_len = htons(m->m_pkthdr.len);
                ip->ip_sum = 0;
                ip->ip_sum = in_cksum(m, ip->ip_hl << 2);
        } else {
                ip = mtod(m, struct ip *);
        }
        prot = ip->ip_p;
        /*
         * Check that we have NAT-T enabled and apply transport mode
         * decapsulation NAT procedure (RFC3948).
         * Do this before invoking into the PFIL.
         */
        if (sav->natt != NULL &&
            (prot == IPPROTO_UDP || prot == IPPROTO_TCP))
                udp_ipsec_adjust_cksum(m, sav, prot, skip);

        /*
         * Needed for ipsec_run_hooks and netisr_queue_src
         */
        NET_EPOCH_ENTER(et);

        IPSEC_INIT_CTX(&ctx, &m, NULL, sav, AF_INET, IPSEC_ENC_BEFORE);
        if ((error = ipsec_run_hhooks(&ctx, HHOOK_TYPE_IPSEC_IN)) != 0)
                goto bad;
        ip = mtod(m, struct ip *);      /* update pointer */

        /* IP-in-IP encapsulation */
        if (prot == IPPROTO_IPIP &&
            saidx->mode != IPSEC_MODE_TRANSPORT) {
                if (m->m_pkthdr.len - skip < sizeof(struct ip)) {
                        IPSEC_ISTAT(sproto, hdrops);
                        error = EINVAL;
                        goto bad;
                }
                /* enc0: strip outer IPv4 header */
                m_striphdr(m, 0, ip->ip_hl << 2);
        }
#ifdef INET6
        /* IPv6-in-IP encapsulation. */
        else if (prot == IPPROTO_IPV6 &&
            saidx->mode != IPSEC_MODE_TRANSPORT) {
                if (m->m_pkthdr.len - skip < sizeof(struct ip6_hdr)) {
                        IPSEC_ISTAT(sproto, hdrops);
                        error = EINVAL;
                        goto bad;
                }
                /* enc0: strip IPv4 header, keep IPv6 header only */
                m_striphdr(m, 0, ip->ip_hl << 2);
        }
#endif /* INET6 */
        else if (prot != IPPROTO_IPV6 && saidx->mode == IPSEC_MODE_ANY) {
                /*
                 * When mode is wildcard, inner protocol is IPv6 and
                 * we have no INET6 support - drop this packet a bit later.
                 * In other cases we assume transport mode. Set prot to
                 * correctly choose netisr.
                 */
                prot = IPPROTO_IPIP;
        }

        /*
         * Record what we've done to the packet (under what SA it was
         * processed).
         */
        if (sproto != IPPROTO_IPCOMP) {
                mtag = m_tag_get(PACKET_TAG_IPSEC_IN_DONE,
                    sizeof(struct xform_history), M_NOWAIT);
                if (mtag == NULL) {
                        DPRINTF(("%s: failed to get tag\n", __func__));
                        IPSEC_ISTAT(sproto, hdrops);
                        error = ENOMEM;
                        goto bad;
                }

                xh = (struct xform_history *)(mtag + 1);
                bcopy(&saidx->dst, &xh->dst, saidx->dst.sa.sa_len);
                xh->spi = sav->spi;
                xh->proto = sproto;
                xh->mode = saidx->mode;
                m_tag_prepend(m, mtag);
        }

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

        /*
         * In transport mode requeue decrypted mbuf back to IPv4 protocol
         * handler. This is necessary to correctly expose rcvif.
         */
        if (saidx->mode == IPSEC_MODE_TRANSPORT)
                prot = IPPROTO_IPIP;
        /*
         * Re-dispatch via software interrupt.
         */
        switch (prot) {
        case IPPROTO_IPIP:
                isr_prot = NETISR_IP;
                af = AF_INET;
                break;
#ifdef INET6
        case IPPROTO_IPV6:
                isr_prot = NETISR_IPV6;
                af = AF_INET6;
                break;
#endif
        default:
                DPRINTF(("%s: cannot handle inner ip proto %d\n",
                            __func__, prot));
                IPSEC_ISTAT(sproto, nopf);
                error = EPFNOSUPPORT;
                goto bad;
        }

        IPSEC_INIT_CTX(&ctx, &m, NULL, sav, af, IPSEC_ENC_AFTER);
        if ((error = ipsec_run_hhooks(&ctx, HHOOK_TYPE_IPSEC_IN)) != 0)
                goto bad;

        /* Handle virtual tunneling interfaces */
        if (saidx->mode == IPSEC_MODE_TUNNEL)
                error = ipsec_if_input(m, sav, af, sahtree_tracker);
        else
                ipsec_sahtree_runlock(sahtree_tracker);
        if (error == 0) {
                error = netisr_queue_src(isr_prot, (uintptr_t)sav->spi, m);
                if (error) {
                        IPSEC_ISTAT(sproto, qfull);
                        DPRINTF(("%s: queue full; proto %u packet dropped\n",
                            __func__, sproto));
                }
        }
        NET_EPOCH_EXIT(et);
        key_freesav(&sav);
        return (error);
bad:
        NET_EPOCH_EXIT(et);
bad_noepoch:
        ipsec_sahtree_runlock(sahtree_tracker);
        key_freesav(&sav);
        if (m != NULL)
                m_freem(m);
        return (error);
}
#endif /* INET */

#ifdef INET6
static bool
ipsec6_lasthdr(int proto)
{

        switch (proto) {
        case IPPROTO_IPV4:
        case IPPROTO_IPV6:
        case IPPROTO_GRE:
        case IPPROTO_ICMPV6:
        case IPPROTO_ETHERIP:
        case IPPROTO_PIM:
        case IPPROTO_SCTP:
                return (true);
        default:
                return (false);
        };
}

/*
 * IPSEC_INPUT() method implementation for IPv6.
 *  0 - Permitted by inbound security policy for further processing.
 *  EACCES - Forbidden by inbound security policy.
 *  EINPROGRESS - consumed by IPsec.
 */
int
ipsec6_input(struct mbuf *m, int offset, int proto)
{
        int error;

        error = ipsec_accel_input(m, offset, proto);
        if (error != ENXIO)
                return (error);
                
        switch (proto) {
        case IPPROTO_AH:
        case IPPROTO_ESP:
        case IPPROTO_IPCOMP:
                /* Do inbound IPsec processing for AH/ESP/IPCOMP */
                ipsec_common_input(m, offset,
                    offsetof(struct ip6_hdr, ip6_nxt), AF_INET6, proto);
                return (EINPROGRESS); /* mbuf consumed by IPsec */
        default:
                /*
                 * Protocols with further headers get their IPsec treatment
                 * within the protocol specific processing.
                 */
                if (!ipsec6_lasthdr(proto))
                        return (0);
                /* FALLTHROUGH */
        };
        /*
         * Enforce IPsec policy checking if we are seeing last header.
         */
        if (ipsec6_in_reject(m, NULL) != 0) {
                /* Forbidden by inbound security policy */
                m_freem(m);
                return (EACCES);
        }
        return (0);
}

int
ipsec6_ctlinput(ipsec_ctlinput_param_t param)
{
        return (0);
}

extern ipproto_input_t  *ip6_protox[];

/*
 * IPsec input callback, called by the transform callback. Takes care of
 * filtering and other sanity checks on the processed packet.
 */
int
ipsec6_common_input_cb(struct mbuf *m, struct secasvar *sav, int skip,
    int protoff, struct rm_priotracker *sahtree_tracker)
{
        IPSEC_DEBUG_DECLARE(char buf[IPSEC_ADDRSTRLEN]);
        struct epoch_tracker et;
        struct ipsec_ctx_data ctx;
        struct xform_history *xh;
        struct secasindex *saidx;
        struct ip6_hdr *ip6;
        struct m_tag *mtag;
        int prot, af, sproto;
        int nxt, isr_prot;
        int error, nest;
        uint8_t nxt8;

        IPSEC_ASSERT(sav != NULL, ("null SA"));
        IPSEC_ASSERT(sav->sah != NULL, ("null SAH"));
        saidx = &sav->sah->saidx;
        af = saidx->dst.sa.sa_family;
        IPSEC_ASSERT(af == AF_INET6, ("unexpected af %u", af));
        sproto = saidx->proto;
        IPSEC_ASSERT(sproto == IPPROTO_ESP || sproto == IPPROTO_AH ||
                sproto == IPPROTO_IPCOMP,
                ("unexpected security protocol %u", sproto));

        NET_EPOCH_ENTER(et);

        /* Fix IPv6 header */
        if (m->m_len < sizeof(struct ip6_hdr) &&
            (m = m_pullup(m, sizeof(struct ip6_hdr))) == NULL) {
                DPRINTF(("%s: processing failed for SA %s/%08lx\n",
                    __func__, ipsec_address(&sav->sah->saidx.dst, buf,
                    sizeof(buf)), (u_long) ntohl(sav->spi)));

                IPSEC_ISTAT(sproto, hdrops);
                error = EACCES;
                goto bad;
        }

        IPSEC_INIT_CTX(&ctx, &m, NULL, sav, af, IPSEC_ENC_BEFORE);
        if ((error = ipsec_run_hhooks(&ctx, HHOOK_TYPE_IPSEC_IN)) != 0)
                goto bad;

        ip6 = mtod(m, struct ip6_hdr *);
        ip6->ip6_plen = htons(m->m_pkthdr.len - sizeof(struct ip6_hdr));

        /* Save protocol */
        m_copydata(m, protoff, 1, &nxt8);
        prot = nxt8;

        /*
         * Check that we have NAT-T enabled and apply transport mode
         * decapsulation NAT procedure (RFC3948).
         * Do this before invoking into the PFIL.
         */
        if (sav->natt != NULL &&
            (prot == IPPROTO_UDP || prot == IPPROTO_TCP))
                udp_ipsec_adjust_cksum(m, sav, prot, skip);

        /* IPv6-in-IP encapsulation */
        if (prot == IPPROTO_IPV6 &&
            saidx->mode != IPSEC_MODE_TRANSPORT) {
                if (m->m_pkthdr.len - skip < sizeof(struct ip6_hdr)) {
                        IPSEC_ISTAT(sproto, hdrops);
                        error = EINVAL;
                        goto bad;
                }
                /* ip6n will now contain the inner IPv6 header. */
                m_striphdr(m, 0, skip);
                skip = 0;
        }
#ifdef INET
        /* IP-in-IP encapsulation */
        else if (prot == IPPROTO_IPIP &&
            saidx->mode != IPSEC_MODE_TRANSPORT) {
                if (m->m_pkthdr.len - skip < sizeof(struct ip)) {
                        IPSEC_ISTAT(sproto, hdrops);
                        error = EINVAL;
                        goto bad;
                }
                /* ipn will now contain the inner IPv4 header */
                m_striphdr(m, 0, skip);
                skip = 0;
        }
#endif /* INET */
        else {
                prot = IPPROTO_IPV6; /* for correct BPF processing */
        }

        /*
         * Record what we've done to the packet (under what SA it was
         * processed).
         */
        if (sproto != IPPROTO_IPCOMP) {
                mtag = m_tag_get(PACKET_TAG_IPSEC_IN_DONE,
                    sizeof(struct xform_history), M_NOWAIT);
                if (mtag == NULL) {
                        DPRINTF(("%s: failed to get tag\n", __func__));
                        IPSEC_ISTAT(sproto, hdrops);
                        error = ENOMEM;
                        goto bad;
                }

                xh = (struct xform_history *)(mtag + 1);
                bcopy(&saidx->dst, &xh->dst, saidx->dst.sa.sa_len);
                xh->spi = sav->spi;
                xh->proto = sproto;
                xh->mode = saidx->mode;
                m_tag_prepend(m, mtag);
        }

        key_sa_recordxfer(sav, m);

#ifdef INET
        if (prot == IPPROTO_IPIP)
                af = AF_INET;
        else
#endif
                af = AF_INET6;
        IPSEC_INIT_CTX(&ctx, &m, NULL, sav, af, IPSEC_ENC_AFTER);
        if ((error = ipsec_run_hhooks(&ctx, HHOOK_TYPE_IPSEC_IN)) != 0)
                goto bad;
        if (skip == 0) {
                /*
                 * We stripped outer IPv6 header.
                 * Now we should requeue decrypted packet via netisr.
                 */
                switch (prot) {
#ifdef INET
                case IPPROTO_IPIP:
                        isr_prot = NETISR_IP;
                        break;
#endif
                case IPPROTO_IPV6:
                        isr_prot = NETISR_IPV6;
                        break;
                default:
                        DPRINTF(("%s: cannot handle inner ip proto %d\n",
                            __func__, prot));
                        IPSEC_ISTAT(sproto, nopf);
                        error = EPFNOSUPPORT;
                        goto bad;
                }
                /* Handle virtual tunneling interfaces */
                if (saidx->mode == IPSEC_MODE_TUNNEL)
                        error = ipsec_if_input(m, sav, af, sahtree_tracker);
                else
                        ipsec_sahtree_runlock(sahtree_tracker);
                if (error == 0) {
                        error = netisr_queue_src(isr_prot,
                            (uintptr_t)sav->spi, m);
                        if (error) {
                                IPSEC_ISTAT(sproto, qfull);
                                DPRINTF(("%s: queue full; proto %u packet"
                                    " dropped\n", __func__, sproto));
                        }
                }
                NET_EPOCH_EXIT(et);
                key_freesav(&sav);
                return (error);
        }

        ipsec_sahtree_runlock(sahtree_tracker);

        /*
         * See the end of ip6_input for this logic.
         * IPPROTO_IPV[46] case will be processed just like other ones
         */
        nest = 0;
        nxt = nxt8;
        while (nxt != IPPROTO_DONE) {
                if (V_ip6_hdrnestlimit && (++nest > V_ip6_hdrnestlimit)) {
                        IP6STAT_INC(ip6s_toomanyhdr);
                        error = EINVAL;
                        goto bad;
                }

                /*
                 * Protection against faulty packet - there should be
                 * more sanity checks in header chain processing.
                 */
                if (m->m_pkthdr.len < skip) {
                        IP6STAT_INC(ip6s_tooshort);
                        in6_ifstat_inc(m->m_pkthdr.rcvif, ifs6_in_truncated);
                        error = EINVAL;
                        goto bad;
                }
                /*
                 * Enforce IPsec policy checking if we are seeing last header.
                 * note that we do not visit this with protocols with pcb layer
                 * code - like udp/tcp/raw ip.
                 */
                if (ipsec6_lasthdr(nxt) && ipsec6_in_reject(m, NULL)) {
                        error = EINVAL;
                        goto bad;
                }
                nxt = ip6_protox[nxt](&m, &skip, nxt);
        }
        NET_EPOCH_EXIT(et);
        key_freesav(&sav);
        return (0);
bad:
        NET_EPOCH_EXIT(et);
        ipsec_sahtree_runlock(sahtree_tracker);
        key_freesav(&sav);
        if (m)
                m_freem(m);
        return (error);
}
#endif /* INET6 */