kernel - Fix races created by a comedy of circumstansces (3)

[dragonfly.git] / sys / netinet6 / ip6_input.c

/*      $FreeBSD: src/sys/netinet6/ip6_input.c,v 1.11.2.15 2003/01/24 05:11:35 sam Exp $        */
/*      $KAME: ip6_input.c,v 1.259 2002/01/21 04:58:09 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.
 */

/*
 * Copyright (c) 1982, 1986, 1988, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *      @(#)ip_input.c  8.2 (Berkeley) 1/4/94
 */

#include "opt_ip6fw.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/socketvar.h>
#include <sys/errno.h>
#include <sys/time.h>
#include <sys/kernel.h>
#include <sys/syslog.h>
#include <sys/proc.h>
#include <sys/priv.h>

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

#include <sys/thread2.h>
#include <sys/msgport2.h>
#include <net/netmsg2.h>
#include <net/netisr2.h>

#include <netinet/in.h>
#include <netinet/in_systm.h>
#ifdef INET
#include <netinet/ip.h>
#include <netinet/ip_icmp.h>
#endif /* INET */
#include <netinet/ip6.h>
#include <netinet6/in6_var.h>
#include <netinet6/ip6_var.h>
#include <netinet/in_pcb.h>
#include <netinet/icmp6.h>
#include <netinet6/scope6_var.h>
#include <netinet6/in6_ifattach.h>
#include <netinet6/nd6.h>

#ifdef IPSEC
#include <netinet6/ipsec.h>
#ifdef INET6
#include <netinet6/ipsec6.h>
#endif
#endif

#ifdef FAST_IPSEC
#include <netproto/ipsec/ipsec.h>
#include <netproto/ipsec/ipsec6.h>
#define IPSEC
#endif /* FAST_IPSEC */

#include <net/ip6fw/ip6_fw.h>

#include <netinet6/ip6protosw.h>

#include <net/net_osdep.h>

extern struct domain inet6domain;
extern struct protosw inet6sw[];

u_char ip6_protox[IPPROTO_MAX];
struct in6_ifaddr *in6_ifaddr;

int ip6_forward_srcrt;                  /* XXX */
int ip6_sourcecheck;                    /* XXX */
int ip6_sourcecheck_interval;           /* XXX */

int ip6_ours_check_algorithm;

struct pfil_head inet6_pfil_hook;

/* firewall hooks */
ip6_fw_chk_t *ip6_fw_chk_ptr;
ip6_fw_ctl_t *ip6_fw_ctl_ptr;
int ip6_fw_enable = 1;

struct ip6stat ip6stat;

static void ip6_init2 (void *);
static struct ip6aux *ip6_setdstifaddr (struct mbuf *, struct in6_ifaddr *);
static int ip6_hopopts_input (u_int32_t *, u_int32_t *, struct mbuf **, int *);
static void ip6_input(netmsg_t msg);
#ifdef PULLDOWN_TEST
static struct mbuf *ip6_pullexthdr (struct mbuf *, size_t, int);
#endif
static void transport6_processing_handler(netmsg_t netmsg);

/*
 * IP6 initialization: fill in IP6 protocol switch table.
 * All protocols not implemented in kernel go to raw IP6 protocol handler.
 */
void
ip6_init(void)
{
        struct protosw *pr;
        int i;
        struct timeval tv;

        pr = pffindproto(PF_INET6, IPPROTO_RAW, SOCK_RAW);
        if (pr == NULL)
                panic("ip6_init");
        for (i = 0; i < IPPROTO_MAX; i++)
                ip6_protox[i] = pr - inet6sw;
        for (pr = inet6domain.dom_protosw;
            pr < inet6domain.dom_protoswNPROTOSW; pr++)
                if (pr->pr_domain->dom_family == PF_INET6 &&
                    pr->pr_protocol && pr->pr_protocol != IPPROTO_RAW)
                        ip6_protox[pr->pr_protocol] = pr - inet6sw;

        inet6_pfil_hook.ph_type = PFIL_TYPE_AF;
        inet6_pfil_hook.ph_af = AF_INET6;
        if ((i = pfil_head_register(&inet6_pfil_hook)) != 0) {
                kprintf("%s: WARNING: unable to register pfil hook, "
                        "error %d\n", __func__, i);
        }

        netisr_register(NETISR_IPV6, ip6_input, NULL); /* XXX hashfn */
        scope6_init();
        addrsel_policy_init();
        nd6_init();
        frag6_init();
        /*
         * in many cases, random() here does NOT return random number
         * as initialization during bootstrap time occur in fixed order.
         */
        microtime(&tv);
        ip6_flow_seq = krandom() ^ tv.tv_usec;
        microtime(&tv);
        ip6_desync_factor = (krandom() ^ tv.tv_usec) % MAX_TEMP_DESYNC_FACTOR;
}

static void
ip6_init2(void *dummy)
{
        nd6_timer_init();
        in6_tmpaddrtimer_init();
}

/* cheat */
/* This must be after route_init(), which is now SI_ORDER_THIRD */
SYSINIT(netinet6init2, SI_SUB_PROTO_DOMAIN, SI_ORDER_MIDDLE, ip6_init2, NULL);

extern struct   route_in6 ip6_forward_rt;

static void
ip6_input(netmsg_t msg)
{
        struct mbuf *m = msg->packet.nm_packet;
        struct ip6_hdr *ip6;
        int off = sizeof(struct ip6_hdr), nest;
        u_int32_t plen;
        u_int32_t rtalert = ~0;
        int nxt, ours = 0, rh_present = 0;
        struct ifnet *deliverifp = NULL;
        struct in6_addr odst;
        int srcrt = 0;

#ifdef IPSEC
        /*
         * should the inner packet be considered authentic?
         * see comment in ah4_input().
         */
        if (m) {
                m->m_flags &= ~M_AUTHIPHDR;
                m->m_flags &= ~M_AUTHIPDGM;
        }
#endif

        /*
         * make sure we don't have onion peering information into m_aux.
         */
        ip6_delaux(m);

        /*
         * mbuf statistics
         */
        if (m->m_flags & M_EXT) {
                if (m->m_next)
                        ip6stat.ip6s_mext2m++;
                else
                        ip6stat.ip6s_mext1++;
        } else {
#define M2MMAX  NELEM(ip6stat.ip6s_m2m)
                if (m->m_next) {
                        if (m->m_flags & M_LOOP) {
                                ip6stat.ip6s_m2m[loif[0].if_index]++; /* XXX */
                        } else if (m->m_pkthdr.rcvif->if_index < M2MMAX)
                                ip6stat.ip6s_m2m[m->m_pkthdr.rcvif->if_index]++;
                        else
                                ip6stat.ip6s_m2m[0]++;
                } else
                        ip6stat.ip6s_m1++;
#undef M2MMAX
        }

        in6_ifstat_inc(m->m_pkthdr.rcvif, ifs6_in_receive);
        ip6stat.ip6s_total++;

#ifndef PULLDOWN_TEST
        /*
         * L2 bridge code and some other code can return mbuf chain
         * that does not conform to KAME requirement.  too bad.
         * XXX: fails to join if interface MTU > MCLBYTES.  jumbogram?
         */
        if (m && m->m_next != NULL && m->m_pkthdr.len < MCLBYTES) {
                struct mbuf *n;

                n = m_getb(m->m_pkthdr.len, M_NOWAIT, MT_HEADER, M_PKTHDR);
                if (n == NULL)
                        goto bad;
                M_MOVE_PKTHDR(n, m);

                m_copydata(m, 0, n->m_pkthdr.len, mtod(n, caddr_t));
                n->m_len = n->m_pkthdr.len;
                m_freem(m);
                m = n;
        }
        IP6_EXTHDR_CHECK_VOIDRET(m, 0, sizeof(struct ip6_hdr));
#endif

        if (m->m_len < sizeof(struct ip6_hdr)) {
                struct ifnet *inifp;
                inifp = m->m_pkthdr.rcvif;
                if ((m = m_pullup(m, sizeof(struct ip6_hdr))) == NULL) {
                        ip6stat.ip6s_toosmall++;
                        in6_ifstat_inc(inifp, ifs6_in_hdrerr);
                        goto bad2;
                }
        }

        ip6 = mtod(m, struct ip6_hdr *);

        if ((ip6->ip6_vfc & IPV6_VERSION_MASK) != IPV6_VERSION) {
                ip6stat.ip6s_badvers++;
                in6_ifstat_inc(m->m_pkthdr.rcvif, ifs6_in_hdrerr);
                goto bad;
        }

        /*
         * Run through list of hooks for input packets.
         *
         * NB: Beware of the destination address changing
         *     (e.g. by NAT rewriting). When this happens,
         *     tell ip6_forward to do the right thing.
         */
        if (pfil_has_hooks(&inet6_pfil_hook)) {
                odst = ip6->ip6_dst;
                if (pfil_run_hooks(&inet6_pfil_hook, &m,
                    m->m_pkthdr.rcvif, PFIL_IN)) {
                        goto bad2;
                }
                if (m == NULL)                  /* consumed by filter */
                        goto bad2;
                ip6 = mtod(m, struct ip6_hdr *);
                srcrt = !IN6_ARE_ADDR_EQUAL(&odst, &ip6->ip6_dst);
        }

        ip6stat.ip6s_nxthist[ip6->ip6_nxt]++;

#ifdef ALTQ
        if (altq_input != NULL && (*altq_input)(m, AF_INET6) == 0) {
                /* packet is dropped by traffic conditioner */
                return;
        }
#endif

        /*
         * Check with the firewall...
         */
        if (ip6_fw_enable && ip6_fw_chk_ptr) {
                u_short port = 0;
                /* If ipfw says divert, we have to just drop packet */
                /* use port as a dummy argument */
                if ((*ip6_fw_chk_ptr)(&ip6, NULL, &port, &m)) {
                        m_freem(m);
                        m = NULL;
                }
                if (!m)
                        goto bad2;
        }

        /*
         * Check against address spoofing/corruption.
         */
        if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_src) ||
            IN6_IS_ADDR_UNSPECIFIED(&ip6->ip6_dst)) {
                /*
                 * XXX: "badscope" is not very suitable for a multicast source.
                 */
                ip6stat.ip6s_badscope++;
                in6_ifstat_inc(m->m_pkthdr.rcvif, ifs6_in_addrerr);
                goto bad;
        }
        if ((IN6_IS_ADDR_LOOPBACK(&ip6->ip6_src) ||
             IN6_IS_ADDR_LOOPBACK(&ip6->ip6_dst)) &&
            (m->m_pkthdr.rcvif->if_flags & IFF_LOOPBACK) == 0) {
                ip6stat.ip6s_badscope++;
                in6_ifstat_inc(m->m_pkthdr.rcvif, ifs6_in_addrerr);
                goto bad;
        }

        /*
         * The following check is not documented in specs.  A malicious
         * party may be able to use IPv4 mapped addr to confuse tcp/udp stack
         * and bypass security checks (act as if it was from 127.0.0.1 by using
         * IPv6 src ::ffff:127.0.0.1).  Be cautious.
         *
         * This check chokes if we are in an SIIT cloud.  As none of BSDs
         * support IPv4-less kernel compilation, we cannot support SIIT
         * environment at all.  So, it makes more sense for us to reject any
         * malicious packets for non-SIIT environment, than try to do a
         * partial support for SIIT environment.
         */
        if (IN6_IS_ADDR_V4MAPPED(&ip6->ip6_src) ||
            IN6_IS_ADDR_V4MAPPED(&ip6->ip6_dst)) {
                ip6stat.ip6s_badscope++;
                in6_ifstat_inc(m->m_pkthdr.rcvif, ifs6_in_addrerr);
                goto bad;
        }
#if 0
        /*
         * Reject packets with IPv4 compatible addresses (auto tunnel).
         *
         * The code forbids auto tunnel relay case in RFC1933 (the check is
         * stronger than RFC1933).  We may want to re-enable it if mech-xx
         * is revised to forbid relaying case.
         */
        if (IN6_IS_ADDR_V4COMPAT(&ip6->ip6_src) ||
            IN6_IS_ADDR_V4COMPAT(&ip6->ip6_dst)) {
                ip6stat.ip6s_badscope++;
                in6_ifstat_inc(m->m_pkthdr.rcvif, ifs6_in_addrerr);
                goto bad;
        }
#endif

        /* drop packets if interface ID portion is already filled */
        if ((m->m_pkthdr.rcvif->if_flags & IFF_LOOPBACK) == 0) {
                if (IN6_IS_SCOPE_LINKLOCAL(&ip6->ip6_src) &&
                    ip6->ip6_src.s6_addr16[1]) {
                        ip6stat.ip6s_badscope++;
                        goto bad;
                }
                if ((IN6_IS_ADDR_MC_INTFACELOCAL(&ip6->ip6_dst) ||
                     IN6_IS_SCOPE_LINKLOCAL(&ip6->ip6_dst)) &&
                    ip6->ip6_dst.s6_addr16[1]) {
                        ip6stat.ip6s_badscope++;
                        goto bad;
                }
        }

        if (IN6_IS_SCOPE_LINKLOCAL(&ip6->ip6_src))
                ip6->ip6_src.s6_addr16[1]
                        = htons(m->m_pkthdr.rcvif->if_index);
        if (IN6_IS_SCOPE_LINKLOCAL(&ip6->ip6_dst))
                ip6->ip6_dst.s6_addr16[1]
                        = htons(m->m_pkthdr.rcvif->if_index);

        /*
         * Multicast check
         *
         * WARNING!  For general subnet proxying the interface hw will
         *           likely filter out the multicast solicitations, so
         *           the interface must be in promiscuous mode.
         */
        if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst)) {
                ours = 1;
                in6_ifstat_inc(m->m_pkthdr.rcvif, ifs6_in_mcast);
                deliverifp = m->m_pkthdr.rcvif;
                goto hbhcheck;
        }

        /*
         *  Unicast check
         */
        if (ip6_forward_rt.ro_rt != NULL &&
            (ip6_forward_rt.ro_rt->rt_flags & RTF_UP) &&
            IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst,
            &((struct sockaddr_in6 *)(&ip6_forward_rt.ro_dst))->sin6_addr)) {
                ip6stat.ip6s_forward_cachehit++;
        } else {
                struct sockaddr_in6 *dst6;

                if (ip6_forward_rt.ro_rt) {
                        /* route is down or destination is different */
                        ip6stat.ip6s_forward_cachemiss++;
                        RTFREE(ip6_forward_rt.ro_rt);
                        ip6_forward_rt.ro_rt = 0;
                }

                bzero(&ip6_forward_rt.ro_dst, sizeof(struct sockaddr_in6));
                dst6 = &ip6_forward_rt.ro_dst;
                dst6->sin6_len = sizeof(struct sockaddr_in6);
                dst6->sin6_family = AF_INET6;
                dst6->sin6_addr = ip6->ip6_dst;

                rtalloc_ign((struct route *)&ip6_forward_rt, RTF_PRCLONING);
        }

#define rt6_key(r) ((struct sockaddr_in6 *)((r)->rt_nodes->rn_key))

        /*
         * Accept the packet if the forwarding interface to the destination
         * according to the routing table is the loopback interface,
         * unless the associated route has a gateway.
         * Note that this approach causes to accept a packet if there is a
         * route to the loopback interface for the destination of the packet.
         * But we think it's even useful in some situations, e.g. when using
         * a special daemon which wants to intercept the packet.
         *
         * XXX: some OSes automatically make a cloned route for the destination
         * of an outgoing packet.  If the outgoing interface of the packet
         * is a loopback one, the kernel would consider the packet to be
         * accepted, even if we have no such address assinged on the interface.
         * We check the cloned flag of the route entry to reject such cases,
         * assuming that route entries for our own addresses are not made by
         * cloning (it should be true because in6_addloop explicitly installs
         * the host route).  However, we might have to do an explicit check
         * while it would be less efficient.  Or, should we rather install a
         * reject route for such a case?
         */
        if (ip6_forward_rt.ro_rt &&
            (ip6_forward_rt.ro_rt->rt_flags &
             (RTF_HOST|RTF_GATEWAY)) == RTF_HOST &&
#ifdef RTF_WASCLONED
            !(ip6_forward_rt.ro_rt->rt_flags & RTF_WASCLONED) &&
#endif
#ifdef RTF_CLONED
            !(ip6_forward_rt.ro_rt->rt_flags & RTF_CLONED) &&
#endif
#if 0
            /*
             * The check below is redundant since the comparison of
             * the destination and the key of the rtentry has
             * already done through looking up the routing table.
             */
            IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst,
                                &rt6_key(ip6_forward_rt.ro_rt)->sin6_addr)
#endif
            ip6_forward_rt.ro_rt->rt_ifp->if_type == IFT_LOOP) {
                struct in6_ifaddr *ia6 =
                        (struct in6_ifaddr *)ip6_forward_rt.ro_rt->rt_ifa;

                /*
                 * record address information into m_aux.
                 */
                ip6_setdstifaddr(m, ia6);

                /*
                 * packets to a tentative, duplicated, or somehow invalid
                 * address must not be accepted.
                 */
                if (!(ia6->ia6_flags & IN6_IFF_NOTREADY)) {
                        /* this address is ready */
                        ours = 1;
                        deliverifp = ia6->ia_ifp;       /* correct? */
                        /* Count the packet in the ip address stats */
                        IFA_STAT_INC(&ia6->ia_ifa, ipackets, 1);
                        IFA_STAT_INC(&ia6->ia_ifa, ibytes, m->m_pkthdr.len);
                        goto hbhcheck;
                } else {
                        /* address is not ready, so discard the packet. */
                        nd6log((LOG_INFO,
                            "ip6_input: packet to an unready address %s->%s\n",
                            ip6_sprintf(&ip6->ip6_src),
                            ip6_sprintf(&ip6->ip6_dst)));

                        goto bad;
                }
        }

        /*
         * FAITH (Firewall Aided Internet Translator)
         */
        if (ip6_keepfaith) {
                if (ip6_forward_rt.ro_rt && ip6_forward_rt.ro_rt->rt_ifp
                 && ip6_forward_rt.ro_rt->rt_ifp->if_type == IFT_FAITH) {
                        /* XXX do we need more sanity checks? */
                        ours = 1;
                        deliverifp = ip6_forward_rt.ro_rt->rt_ifp; /* faith */
                        goto hbhcheck;
                }
        }

        /*
         * Now there is no reason to process the packet if it's not our own
         * and we're not a router.
         */
        if (!ip6_forwarding) {
                ip6stat.ip6s_cantforward++;
                in6_ifstat_inc(m->m_pkthdr.rcvif, ifs6_in_discard);
                goto bad;
        }

hbhcheck:
        /*
         * record address information into m_aux, if we don't have one yet.
         * note that we are unable to record it, if the address is not listed
         * as our interface address (e.g. multicast addresses, addresses
         * within FAITH prefixes and such).
         */
        if (deliverifp && !ip6_getdstifaddr(m)) {
                struct in6_ifaddr *ia6;

                ia6 = in6_ifawithifp(deliverifp, &ip6->ip6_dst);
                if (ia6) {
                        if (!ip6_setdstifaddr(m, ia6)) {
                                /*
                                 * XXX maybe we should drop the packet here,
                                 * as we could not provide enough information
                                 * to the upper layers.
                                 */
                        }
                }
        }

        /*
         * Process Hop-by-Hop options header if it's contained.
         * m may be modified in ip6_hopopts_input().
         * If a JumboPayload option is included, plen will also be modified.
         */
        plen = (u_int32_t)ntohs(ip6->ip6_plen);
        if (ip6->ip6_nxt == IPPROTO_HOPOPTS) {
                struct ip6_hbh *hbh;

                if (ip6_hopopts_input(&plen, &rtalert, &m, &off)) {
#if 0   /*touches NULL pointer*/
                        in6_ifstat_inc(m->m_pkthdr.rcvif, ifs6_in_discard);
#endif
                        goto bad2;      /* m have already been freed */
                }

                /* adjust pointer */
                ip6 = mtod(m, struct ip6_hdr *);

                /*
                 * if the payload length field is 0 and the next header field
                 * indicates Hop-by-Hop Options header, then a Jumbo Payload
                 * option MUST be included.
                 */
                if (ip6->ip6_plen == 0 && plen == 0) {
                        /*
                         * Note that if a valid jumbo payload option is
                         * contained, ip6_hoptops_input() must set a valid
                         * (non-zero) payload length to the variable plen.
                         */
                        ip6stat.ip6s_badoptions++;
                        in6_ifstat_inc(m->m_pkthdr.rcvif, ifs6_in_discard);
                        in6_ifstat_inc(m->m_pkthdr.rcvif, ifs6_in_hdrerr);
                        icmp6_error(m, ICMP6_PARAM_PROB,
                                    ICMP6_PARAMPROB_HEADER,
                                    (caddr_t)&ip6->ip6_plen - (caddr_t)ip6);
                        goto bad2;
                }
#ifndef PULLDOWN_TEST
                /* ip6_hopopts_input() ensures that mbuf is contiguous */
                hbh = (struct ip6_hbh *)(ip6 + 1);
#else
                IP6_EXTHDR_GET(hbh, struct ip6_hbh *, m, sizeof(struct ip6_hdr),
                        sizeof(struct ip6_hbh));
                if (hbh == NULL) {
                        ip6stat.ip6s_tooshort++;
                        goto bad2;
                }
#endif
                nxt = hbh->ip6h_nxt;

                /*
                 * If we are acting as a router and the packet contains a
                 * router alert option, see if we know the option value.
                 * Currently, we only support the option value for MLD, in which
                 * case we should pass the packet to the multicast routing
                 * daemon.
                 */
                if (rtalert != ~0 && ip6_forwarding) {
                        switch (rtalert) {
                        case IP6OPT_RTALERT_MLD:
                                ours = 1;
                                break;
                        default:
                                /*
                                 * RFC2711 requires unrecognized values must be
                                 * silently ignored.
                                 */
                                break;
                        }
                }
        } else
                nxt = ip6->ip6_nxt;

        /*
         * Check that the amount of data in the buffers
         * is as at least much as the IPv6 header would have us expect.
         * Trim mbufs if longer than we expect.
         * Drop packet if shorter than we expect.
         */
        if (m->m_pkthdr.len - sizeof(struct ip6_hdr) < plen) {
                ip6stat.ip6s_tooshort++;
                in6_ifstat_inc(m->m_pkthdr.rcvif, ifs6_in_truncated);
                goto bad;
        }
        if (m->m_pkthdr.len > sizeof(struct ip6_hdr) + plen) {
                if (m->m_len == m->m_pkthdr.len) {
                        m->m_len = sizeof(struct ip6_hdr) + plen;
                        m->m_pkthdr.len = sizeof(struct ip6_hdr) + plen;
                } else
                        m_adj(m, sizeof(struct ip6_hdr) + plen - m->m_pkthdr.len);
        }

        /*
         * Forward if desirable.
         */
        if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst)) {
                /*
                 * If we are acting as a multicast router, all
                 * incoming multicast packets are passed to the
                 * kernel-level multicast forwarding function.
                 * The packet is returned (relatively) intact; if
                 * ip6_mforward() returns a non-zero value, the packet
                 * must be discarded, else it may be accepted below.
                 */
                if (ip6_mrouter && ip6_mforward(ip6, m->m_pkthdr.rcvif, m)) {
                        ip6stat.ip6s_cantforward++;
                        goto bad;
                }
                if (!ours)
                        goto bad;
        } else if (!ours) {
                ip6_forward(m, srcrt);
                goto bad2;
        }       

        ip6 = mtod(m, struct ip6_hdr *);

        /*
         * Malicious party may be able to use IPv4 mapped addr to confuse
         * tcp/udp stack and bypass security checks (act as if it was from
         * 127.0.0.1 by using IPv6 src ::ffff:127.0.0.1).  Be cautious.
         *
         * For SIIT end node behavior, you may want to disable the check.
         * However, you will  become vulnerable to attacks using IPv4 mapped
         * source.
         */
        if (IN6_IS_ADDR_V4MAPPED(&ip6->ip6_src) ||
            IN6_IS_ADDR_V4MAPPED(&ip6->ip6_dst)) {
                ip6stat.ip6s_badscope++;
                in6_ifstat_inc(m->m_pkthdr.rcvif, ifs6_in_addrerr);
                goto bad;
        }

        /*
         * Tell launch routine the next header
         */
        ip6stat.ip6s_delivered++;
        in6_ifstat_inc(deliverifp, ifs6_in_deliver);
        nest = 0;

        rh_present = 0;
        while (nxt != IPPROTO_DONE) {
                struct protosw *sw6;

                if (ip6_hdrnestlimit && (++nest > ip6_hdrnestlimit)) {
                        ip6stat.ip6s_toomanyhdr++;
                        in6_ifstat_inc(m->m_pkthdr.rcvif, ifs6_in_hdrerr);
                        goto bad;
                }

                /*
                 * protection against faulty packet - there should be
                 * more sanity checks in header chain processing.
                 */
                if (m->m_pkthdr.len < off) {
                        ip6stat.ip6s_tooshort++;
                        in6_ifstat_inc(m->m_pkthdr.rcvif, ifs6_in_truncated);
                        goto bad;
                }

#if 0
                /*
                 * do we need to do it for every header?  yeah, other
                 * functions can play with it (like re-allocate and copy).
                 */
                mhist = ip6_addaux(m);
                if (mhist && M_TRAILINGSPACE(mhist) >= sizeof(nxt)) {
                        hist = mtod(mhist, caddr_t) + mhist->m_len;
                        bcopy(&nxt, hist, sizeof(nxt));
                        mhist->m_len += sizeof(nxt);
                } else {
                        ip6stat.ip6s_toomanyhdr++;
                        goto bad;
                }
#endif

                if (nxt == IPPROTO_ROUTING) {
                        if (rh_present++) {
                                in6_ifstat_inc(m->m_pkthdr.rcvif,
                                    ifs6_in_hdrerr);
                                ip6stat.ip6s_badoptions++;
                                goto bad;
                        }
                }

                sw6 = &inet6sw[ip6_protox[nxt]];
#ifdef IPSEC
                /*
                 * 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 ((sw6->pr_flags & PR_LASTHDR) && ipsec6_in_reject(m, NULL)) {
                        ipsec6stat.in_polvio++;
                        goto bad;
                }
#endif
                /*
                 * If this is a terminal header forward to the port, otherwise
                 * process synchronously for more headers.
                 */
                if (sw6->pr_flags & PR_LASTHDR) {
                        struct netmsg_packet *pmsg;
                        lwkt_port_t port;

                        port = netisr_cpuport(0); /* XXX */
                        KKASSERT(port != NULL);
                        pmsg = &m->m_hdr.mh_netmsg;
                        netmsg_init(&pmsg->base, NULL,
                                    &netisr_apanic_rport,
                                    0, transport6_processing_handler);
                        pmsg->nm_packet = m;
                        pmsg->nm_nxt = nxt;
                        pmsg->base.lmsg.u.ms_result = off;
                        lwkt_sendmsg(port, &pmsg->base.lmsg);
                        /* done with m */
                        nxt = IPPROTO_DONE;
                } else {
                        nxt = sw6->pr_input(&m, &off, nxt);
                }
        }
        goto bad2;
bad:
        m_freem(m);
bad2:
        ;
        /* msg was embedded in the mbuf, do not reply! */
}

/*
 * We have to call the pr_input() function from the correct protocol
 * thread.  The sw6->pr_soport() request at the end of ip6_input()
 * returns the port and we forward a netmsg to the port to execute
 * this function.
 */
static void
transport6_processing_handler(netmsg_t netmsg)
{
        struct netmsg_packet *pmsg = (struct netmsg_packet *)netmsg;
        struct protosw *sw6;
        int hlen;
        int nxt;

        sw6 = &inet6sw[ip6_protox[pmsg->nm_nxt]];
        hlen = pmsg->base.lmsg.u.ms_result;

        nxt = sw6->pr_input(&pmsg->nm_packet, &hlen, pmsg->nm_nxt);
        KKASSERT(nxt == IPPROTO_DONE);
        /* netmsg was embedded in the mbuf, do not reply! */
}

/*
 * set/grab in6_ifaddr correspond to IPv6 destination address.
 * XXX backward compatibility wrapper
 */
static struct ip6aux *
ip6_setdstifaddr(struct mbuf *m, struct in6_ifaddr *ia6)
{
        struct ip6aux *n;

        n = ip6_addaux(m);
        if (n)
                n->ip6a_dstia6 = ia6;
        return n;       /* NULL if failed to set */
}

struct in6_ifaddr *
ip6_getdstifaddr(struct mbuf *m)
{
        struct ip6aux *n;

        n = ip6_findaux(m);
        if (n)
                return n->ip6a_dstia6;
        else
                return NULL;
}

/*
 * Hop-by-Hop options header processing. If a valid jumbo payload option is
 * included, the real payload length will be stored in plenp.
 */
static int
ip6_hopopts_input(u_int32_t *plenp,
                  u_int32_t *rtalertp,/* XXX: should be stored more smart way */
                  struct mbuf **mp,
                  int *offp)
{
        struct mbuf *m = *mp;
        int off = *offp, hbhlen;
        struct ip6_hbh *hbh;

        /* validation of the length of the header */
#ifndef PULLDOWN_TEST
        IP6_EXTHDR_CHECK(m, off, sizeof(*hbh), -1);
        hbh = (struct ip6_hbh *)(mtod(m, caddr_t) + off);
        hbhlen = (hbh->ip6h_len + 1) << 3;

        IP6_EXTHDR_CHECK(m, off, hbhlen, -1);
        hbh = (struct ip6_hbh *)(mtod(m, caddr_t) + off);
#else
        IP6_EXTHDR_GET(hbh, struct ip6_hbh *, m,
                sizeof(struct ip6_hdr), sizeof(struct ip6_hbh));
        if (hbh == NULL) {
                ip6stat.ip6s_tooshort++;
                return -1;
        }
        hbhlen = (hbh->ip6h_len + 1) << 3;
        IP6_EXTHDR_GET(hbh, struct ip6_hbh *, m, sizeof(struct ip6_hdr),
                hbhlen);
        if (hbh == NULL) {
                ip6stat.ip6s_tooshort++;
                return -1;
        }
#endif
        off += hbhlen;
        hbhlen -= sizeof(struct ip6_hbh);

        if (ip6_process_hopopts(m, (u_int8_t *)hbh + sizeof(struct ip6_hbh),
                                hbhlen, rtalertp, plenp) < 0)
                return (-1);

        *offp = off;
        *mp = m;
        return (0);
}

/*
 * Search header for all Hop-by-hop options and process each option.
 * This function is separate from ip6_hopopts_input() in order to
 * handle a case where the sending node itself process its hop-by-hop
 * options header. In such a case, the function is called from ip6_output().
 *
 * The function assumes that hbh header is located right after the IPv6 header
 * (RFC2460 p7), opthead is pointer into data content in m, and opthead to
 * opthead + hbhlen is located in continuous memory region.
 */
int
ip6_process_hopopts(struct mbuf *m, u_int8_t *opthead, int hbhlen,
                    u_int32_t *rtalertp, u_int32_t *plenp)
{
        struct ip6_hdr *ip6;
        int optlen = 0;
        u_int8_t *opt = opthead;
        u_int16_t rtalert_val;
        u_int32_t jumboplen;
        const int erroff = sizeof(struct ip6_hdr) + sizeof(struct ip6_hbh);

        for (; hbhlen > 0; hbhlen -= optlen, opt += optlen) {
                switch (*opt) {
                case IP6OPT_PAD1:
                        optlen = 1;
                        break;
                case IP6OPT_PADN:
                        if (hbhlen < IP6OPT_MINLEN) {
                                ip6stat.ip6s_toosmall++;
                                goto bad;
                        }
                        optlen = *(opt + 1) + 2;
                        break;
                case IP6OPT_RTALERT:
                        /* XXX may need check for alignment */
                        if (hbhlen < IP6OPT_RTALERT_LEN) {
                                ip6stat.ip6s_toosmall++;
                                goto bad;
                        }
                        if (*(opt + 1) != IP6OPT_RTALERT_LEN - 2) {
                                /* XXX stat */
                                icmp6_error(m, ICMP6_PARAM_PROB,
                                    ICMP6_PARAMPROB_HEADER,
                                    erroff + opt + 1 - opthead);
                                return (-1);
                        }
                        optlen = IP6OPT_RTALERT_LEN;
                        bcopy((caddr_t)(opt + 2), (caddr_t)&rtalert_val, 2);
                        *rtalertp = ntohs(rtalert_val);
                        break;
                case IP6OPT_JUMBO:
                        /* XXX may need check for alignment */
                        if (hbhlen < IP6OPT_JUMBO_LEN) {
                                ip6stat.ip6s_toosmall++;
                                goto bad;
                        }
                        if (*(opt + 1) != IP6OPT_JUMBO_LEN - 2) {
                                /* XXX stat */
                                icmp6_error(m, ICMP6_PARAM_PROB,
                                    ICMP6_PARAMPROB_HEADER,
                                    erroff + opt + 1 - opthead);
                                return (-1);
                        }
                        optlen = IP6OPT_JUMBO_LEN;

                        /*
                         * IPv6 packets that have non 0 payload length
                         * must not contain a jumbo payload option.
                         */
                        ip6 = mtod(m, struct ip6_hdr *);
                        if (ip6->ip6_plen) {
                                ip6stat.ip6s_badoptions++;
                                icmp6_error(m, ICMP6_PARAM_PROB,
                                    ICMP6_PARAMPROB_HEADER,
                                    erroff + opt - opthead);
                                return (-1);
                        }

                        /*
                         * We may see jumbolen in unaligned location, so
                         * we'd need to perform bcopy().
                         */
                        bcopy(opt + 2, &jumboplen, sizeof(jumboplen));
                        jumboplen = (u_int32_t)htonl(jumboplen);

#if 1
                        /*
                         * if there are multiple jumbo payload options,
                         * *plenp will be non-zero and the packet will be
                         * rejected.
                         * the behavior may need some debate in ipngwg -
                         * multiple options does not make sense, however,
                         * there's no explicit mention in specification.
                         */
                        if (*plenp != 0) {
                                ip6stat.ip6s_badoptions++;
                                icmp6_error(m, ICMP6_PARAM_PROB,
                                    ICMP6_PARAMPROB_HEADER,
                                    erroff + opt + 2 - opthead);
                                return (-1);
                        }
#endif

                        /*
                         * jumbo payload length must be larger than 65535.
                         */
                        if (jumboplen <= IPV6_MAXPACKET) {
                                ip6stat.ip6s_badoptions++;
                                icmp6_error(m, ICMP6_PARAM_PROB,
                                    ICMP6_PARAMPROB_HEADER,
                                    erroff + opt + 2 - opthead);
                                return (-1);
                        }
                        *plenp = jumboplen;

                        break;
                default:                /* unknown option */
                        if (hbhlen < IP6OPT_MINLEN) {
                                ip6stat.ip6s_toosmall++;
                                goto bad;
                        }
                        optlen = ip6_unknown_opt(opt, m,
                            erroff + opt - opthead);
                        if (optlen == -1)
                                return (-1);
                        optlen += 2;
                        break;
                }
        }

        return (0);

bad:
        m_freem(m);
        return (-1);
}

/*
 * Unknown option processing.
 * The third argument `off' is the offset from the IPv6 header to the option,
 * which is necessary if the IPv6 header the and option header and IPv6 header
 * is not continuous in order to return an ICMPv6 error.
 */
int
ip6_unknown_opt(u_int8_t *optp, struct mbuf *m, int off)
{
        struct ip6_hdr *ip6;

        switch (IP6OPT_TYPE(*optp)) {
        case IP6OPT_TYPE_SKIP: /* ignore the option */
                return ((int)*(optp + 1));
        case IP6OPT_TYPE_DISCARD:       /* silently discard */
                m_freem(m);
                return (-1);
        case IP6OPT_TYPE_FORCEICMP: /* send ICMP even if multicasted */
                ip6stat.ip6s_badoptions++;
                icmp6_error(m, ICMP6_PARAM_PROB, ICMP6_PARAMPROB_OPTION, off);
                return (-1);
        case IP6OPT_TYPE_ICMP: /* send ICMP if not multicasted */
                ip6stat.ip6s_badoptions++;
                ip6 = mtod(m, struct ip6_hdr *);
                if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
                    (m->m_flags & (M_BCAST|M_MCAST)))
                        m_freem(m);
                else
                        icmp6_error(m, ICMP6_PARAM_PROB,
                                    ICMP6_PARAMPROB_OPTION, off);
                return (-1);
        }

        m_freem(m);             /* XXX: NOTREACHED */
        return (-1);
}

/*
 * Create the "control" list for this pcb.
 * The function will not modify mbuf chain at all.
 *
 * with KAME mbuf chain restriction:
 * The routine will be called from upper layer handlers like tcp6_input().
 * Thus the routine assumes that the caller (tcp6_input) have already
 * called IP6_EXTHDR_CHECK() and all the extension headers are located in the
 * very first mbuf on the mbuf chain.
 */
void
ip6_savecontrol(struct inpcb *in6p, struct mbuf **mp, struct ip6_hdr *ip6,
                struct mbuf *m)
{
        #define IS2292(x, y)    ((in6p->in6p_flags & IN6P_RFC2292) ? (x) : (y))
        struct thread *td = curthread;  /* XXX */
        int privileged = 0;


        if (priv_check(td, PRIV_ROOT) == 0)
                privileged++;

#ifdef SO_TIMESTAMP
        if (in6p->in6p_socket->so_options & SO_TIMESTAMP) {
                struct timeval tv;

                microtime(&tv);
                *mp = sbcreatecontrol((caddr_t)&tv, sizeof(tv),
                    SCM_TIMESTAMP, SOL_SOCKET);
                if (*mp) {
                        mp = &(*mp)->m_next;
                }
        }
#endif

        /* RFC 2292 sec. 5 */
        if (in6p->in6p_flags & IN6P_PKTINFO) {
                struct in6_pktinfo pi6;

                bcopy(&ip6->ip6_dst, &pi6.ipi6_addr, sizeof(struct in6_addr));
                in6_clearscope(&pi6.ipi6_addr); /* XXX */
                pi6.ipi6_ifindex = (m && m->m_pkthdr.rcvif) ?
                    m->m_pkthdr.rcvif->if_index : 0;
                *mp = sbcreatecontrol((caddr_t)&pi6, sizeof(struct in6_pktinfo),
                    IS2292(IPV6_2292PKTINFO, IPV6_PKTINFO), IPPROTO_IPV6);
                if (*mp)
                        mp = &(*mp)->m_next;
        }

        if (in6p->in6p_flags & IN6P_HOPLIMIT) {
                int hlim = ip6->ip6_hlim & 0xff;

                *mp = sbcreatecontrol((caddr_t)&hlim, sizeof(int),
                    IS2292(IPV6_2292HOPLIMIT, IPV6_HOPLIMIT), IPPROTO_IPV6);
                if (*mp)
                        mp = &(*mp)->m_next;
        }

        if ((in6p->in6p_flags & IN6P_TCLASS) != 0) {
                u_int32_t flowinfo;
                int tclass;

                flowinfo = (u_int32_t)ntohl(ip6->ip6_flow & IPV6_FLOWINFO_MASK);
                flowinfo >>= 20;

                tclass = flowinfo & 0xff;
                *mp = sbcreatecontrol((caddr_t) &tclass, sizeof(tclass),
                    IPV6_TCLASS, IPPROTO_IPV6);
                if (*mp)
                        mp = &(*mp)->m_next;
        }

        /*
         * IPV6_HOPOPTS socket option. We require super-user privilege
         * for the option, but it might be too strict, since there might
         * be some hop-by-hop options which can be returned to normal user.
         * See RFC 2292 section 6.
         */
        if ((in6p->in6p_flags & IN6P_HOPOPTS) && privileged) {
                /*
                 * Check if a hop-by-hop options header is contatined in the
                 * received packet, and if so, store the options as ancillary
                 * data. Note that a hop-by-hop options header must be
                 * just after the IPv6 header, which is assured through the
                 * IPv6 input processing.
                 */
                struct ip6_hdr *ip6 = mtod(m, struct ip6_hdr *);
                if (ip6->ip6_nxt == IPPROTO_HOPOPTS) {
                        struct ip6_hbh *hbh;
                        int hbhlen = 0;
#ifdef PULLDOWN_TEST
                        struct mbuf *ext;
#endif

#ifndef PULLDOWN_TEST
                        hbh = (struct ip6_hbh *)(ip6 + 1);
                        hbhlen = (hbh->ip6h_len + 1) << 3;
#else
                        ext = ip6_pullexthdr(m, sizeof(struct ip6_hdr),
                            ip6->ip6_nxt);
                        if (ext == NULL) {
                                ip6stat.ip6s_tooshort++;
                                return;
                        }
                        hbh = mtod(ext, struct ip6_hbh *);
                        hbhlen = (hbh->ip6h_len + 1) << 3;
                        if (hbhlen != ext->m_len) {
                                m_freem(ext);
                                ip6stat.ip6s_tooshort++;
                                return;
                        }
#endif

                        /*
                         * XXX: We copy the whole header even if a
                         * jumbo payload option is included, the option which
                         * is to be removed before returning according to
                         * RFC 2292.
                         * Note: this constraint is removed in 2292bis.
                         */
                        *mp = sbcreatecontrol((caddr_t)hbh, hbhlen,
                            IS2292(IPV6_2292HOPOPTS, IPV6_HOPOPTS),
                            IPPROTO_IPV6);
                        if (*mp)
                                mp = &(*mp)->m_next;
#ifdef PULLDOWN_TEST
                        m_freem(ext);
#endif
                }
        }

        /* IPV6_DSTOPTS and IPV6_RTHDR socket options */
        if ((in6p->in6p_flags & (IN6P_DSTOPTS | IN6P_RTHDRDSTOPTS)) != 0) {
                int proto, off, nxt;

                /*
                 * go through the header chain to see if a routing header is
                 * contained in the packet. We need this information to store
                 * destination options headers (if any) properly.
                 * XXX: performance issue. We should record this info when
                 * processing extension headers in incoming routine.
                 * (todo) use m_aux?
                 */
                proto = IPPROTO_IPV6;
                off = 0;
                nxt = -1;
                while (1) {
                        int newoff;

                        newoff = ip6_nexthdr(m, off, proto, &nxt);
                        if (newoff < 0)
                                break;
                        if (newoff < off) /* invalid, check for safety */
                                break;
                        if ((proto = nxt) == IPPROTO_ROUTING)
                                break;
                        off = newoff;
                }
        }

        if ((in6p->in6p_flags &
             (IN6P_RTHDR | IN6P_DSTOPTS | IN6P_RTHDRDSTOPTS)) != 0) {
                struct ip6_hdr *ip6 = mtod(m, struct ip6_hdr *);
                int nxt = ip6->ip6_nxt, off = sizeof(struct ip6_hdr);

                /*
                 * Search for destination options headers or routing
                 * header(s) through the header chain, and stores each
                 * header as ancillary data.
                 * Note that the order of the headers remains in
                 * the chain of ancillary data.
                 */
                while (1) {     /* is explicit loop prevention necessary? */
                        struct ip6_ext *ip6e = NULL;
                        int elen;
#ifdef PULLDOWN_TEST
                        struct mbuf *ext = NULL;
#endif

                        /*
                         * if it is not an extension header, don't try to
                         * pull it from the chain.
                         */
                        switch (nxt) {
                        case IPPROTO_DSTOPTS:
                        case IPPROTO_ROUTING:
                        case IPPROTO_HOPOPTS:
                        case IPPROTO_AH: /* is it possible? */
                                break;
                        default:
                                goto loopend;
                        }

#ifndef PULLDOWN_TEST
                        if (off + sizeof(*ip6e) > m->m_len)
                                goto loopend;
                        ip6e = (struct ip6_ext *)(mtod(m, caddr_t) + off);
                        if (nxt == IPPROTO_AH)
                                elen = (ip6e->ip6e_len + 2) << 2;
                        else
                                elen = (ip6e->ip6e_len + 1) << 3;
                        if (off + elen > m->m_len)
                                goto loopend;
#else
                        ext = ip6_pullexthdr(m, off, nxt);
                        if (ext == NULL) {
                                ip6stat.ip6s_tooshort++;
                                return;
                        }
                        ip6e = mtod(ext, struct ip6_ext *);
                        if (nxt == IPPROTO_AH)
                                elen = (ip6e->ip6e_len + 2) << 2;
                        else
                                elen = (ip6e->ip6e_len + 1) << 3;
                        if (elen != ext->m_len) {
                                m_freem(ext);
                                ip6stat.ip6s_tooshort++;
                                return;
                        }
#endif

                        switch (nxt) {
                        case IPPROTO_DSTOPTS:
                                if ((in6p->in6p_flags & IN6P_DSTOPTS) == 0)
                                        break;

                                /*
                                 * We also require super-user privilege for
                                 * the option.  See comments on IN6_HOPOPTS.
                                 */
                                if (!privileged)
                                        break;

                                *mp = sbcreatecontrol((caddr_t)ip6e, elen,
                                    IS2292(IPV6_2292DSTOPTS, IPV6_DSTOPTS),
                                    IPPROTO_IPV6);
                                if (*mp)
                                        mp = &(*mp)->m_next;
                                break;
                        case IPPROTO_ROUTING:
                                if (!(in6p->in6p_flags & IN6P_RTHDR))
                                        break;

                                *mp = sbcreatecontrol((caddr_t)ip6e, elen,
                                    IS2292(IPV6_2292RTHDR, IPV6_RTHDR),
                                    IPPROTO_IPV6);
                                if (*mp)
                                        mp = &(*mp)->m_next;
                                break;
                        case IPPROTO_HOPOPTS:
                        case IPPROTO_AH: /* is it possible? */
                                break;

                        default:
                                /*
                                 * other cases have been filtered in the above.
                                 * none will visit this case.  here we supply
                                 * the code just in case (nxt overwritten or
                                 * other cases).
                                 */
#ifdef PULLDOWN_TEST
                                m_freem(ext);
#endif
                                goto loopend;

                        }

                        /* proceed with the next header. */
                        off += elen;
                        nxt = ip6e->ip6e_nxt;
                        ip6e = NULL;
#ifdef PULLDOWN_TEST
                        m_freem(ext);
                        ext = NULL;
#endif
                }
          loopend:
                ;
        }
#undef IS2292
}

void
ip6_notify_pmtu(struct inpcb *in6p, struct sockaddr_in6 *dst, u_int32_t *mtu)
{
        struct socket *so;
        struct mbuf *m_mtu;
        struct ip6_mtuinfo mtuctl;

        so =  in6p->inp_socket;

        if (mtu == NULL)
                return;

#ifdef DIAGNOSTIC
        if (so == NULL)         /* I believe this is impossible */
                panic("ip6_notify_pmtu: socket is NULL");
#endif

        bzero(&mtuctl, sizeof(mtuctl)); /* zero-clear for safety */
        mtuctl.ip6m_mtu = *mtu;
        mtuctl.ip6m_addr = *dst;

        if ((m_mtu = sbcreatecontrol((caddr_t)&mtuctl, sizeof(mtuctl),
            IPV6_PATHMTU, IPPROTO_IPV6)) == NULL)
                return;

        lwkt_gettoken(&so->so_rcv.ssb_token);
        if (sbappendaddr(&so->so_rcv.sb, (struct sockaddr *)dst, NULL, m_mtu)
            == 0) {
                m_freem(m_mtu);
                /* XXX: should count statistics */
        } else {
                sorwakeup(so);
        }
        lwkt_reltoken(&so->so_rcv.ssb_token);
}

#ifdef PULLDOWN_TEST
/*
 * pull single extension header from mbuf chain.  returns single mbuf that
 * contains the result, or NULL on error.
 */
static struct mbuf *
ip6_pullexthdr(struct mbuf *m, size_t off, int nxt)
{
        struct ip6_ext ip6e;
        size_t elen;
        struct mbuf *n;

#ifdef DIAGNOSTIC
        switch (nxt) {
        case IPPROTO_DSTOPTS:
        case IPPROTO_ROUTING:
        case IPPROTO_HOPOPTS:
        case IPPROTO_AH: /* is it possible? */
                break;
        default:
                kprintf("ip6_pullexthdr: invalid nxt=%d\n", nxt);
        }
#endif

        m_copydata(m, off, sizeof(ip6e), (caddr_t)&ip6e);
        if (nxt == IPPROTO_AH)
                elen = (ip6e.ip6e_len + 2) << 2;
        else
                elen = (ip6e.ip6e_len + 1) << 3;

        n = m_getb(elen, M_NOWAIT, MT_DATA, 0);
        if (n == NULL)
                return NULL;
        n->m_len = 0;

        if (elen >= M_TRAILINGSPACE(n)) {
                m_free(n);
                return NULL;
        }

        m_copydata(m, off, elen, mtod(n, caddr_t));
        n->m_len = elen;
        return n;
}
#endif

/*
 * Get pointer to the previous header followed by the header
 * currently processed.
 * XXX: This function supposes that
 *      M includes all headers,
 *      the next header field and the header length field of each header
 *      are valid, and
 *      the sum of each header length equals to OFF.
 * Because of these assumptions, this function must be called very
 * carefully. Moreover, it will not be used in the near future when
 * we develop `neater' mechanism to process extension headers.
 */
char *
ip6_get_prevhdr(struct mbuf *m, int off)
{
        struct ip6_hdr *ip6 = mtod(m, struct ip6_hdr *);

        if (off == sizeof(struct ip6_hdr))
                return (&ip6->ip6_nxt);
        else {
                int len, nxt;
                struct ip6_ext *ip6e = NULL;

                nxt = ip6->ip6_nxt;
                len = sizeof(struct ip6_hdr);
                while (len < off) {
                        ip6e = (struct ip6_ext *)(mtod(m, caddr_t) + len);

                        switch (nxt) {
                        case IPPROTO_FRAGMENT:
                                len += sizeof(struct ip6_frag);
                                break;
                        case IPPROTO_AH:
                                len += (ip6e->ip6e_len + 2) << 2;
                                break;
                        default:
                                len += (ip6e->ip6e_len + 1) << 3;
                                break;
                        }
                        nxt = ip6e->ip6e_nxt;
                }
                if (ip6e)
                        return (&ip6e->ip6e_nxt);
                else
                        return NULL;
        }
}

/*
 * get next header offset.  m will be retained.
 */
int
ip6_nexthdr(struct mbuf *m, int off, int proto, int *nxtp)
{
        struct ip6_hdr ip6;
        struct ip6_ext ip6e;
        struct ip6_frag fh;

        /* just in case */
        if (m == NULL)
                panic("ip6_nexthdr: m == NULL");
        if ((m->m_flags & M_PKTHDR) == 0 || m->m_pkthdr.len < off)
                return -1;

        switch (proto) {
        case IPPROTO_IPV6:
                if (m->m_pkthdr.len < off + sizeof(ip6))
                        return -1;
                m_copydata(m, off, sizeof(ip6), (caddr_t)&ip6);
                if (nxtp)
                        *nxtp = ip6.ip6_nxt;
                off += sizeof(ip6);
                return off;

        case IPPROTO_FRAGMENT:
                /*
                 * terminate parsing if it is not the first fragment,
                 * it does not make sense to parse through it.
                 */
                if (m->m_pkthdr.len < off + sizeof(fh))
                        return -1;
                m_copydata(m, off, sizeof(fh), (caddr_t)&fh);
                /* IP6F_OFF_MASK = 0xfff8(BigEndian), 0xf8ff(LittleEndian) */
                if (fh.ip6f_offlg & IP6F_OFF_MASK)
                        return -1;
                if (nxtp)
                        *nxtp = fh.ip6f_nxt;
                off += sizeof(struct ip6_frag);
                return off;

        case IPPROTO_AH:
                if (m->m_pkthdr.len < off + sizeof(ip6e))
                        return -1;
                m_copydata(m, off, sizeof(ip6e), (caddr_t)&ip6e);
                if (nxtp)
                        *nxtp = ip6e.ip6e_nxt;
                off += (ip6e.ip6e_len + 2) << 2;
                return off;

        case IPPROTO_HOPOPTS:
        case IPPROTO_ROUTING:
        case IPPROTO_DSTOPTS:
                if (m->m_pkthdr.len < off + sizeof(ip6e))
                        return -1;
                m_copydata(m, off, sizeof(ip6e), (caddr_t)&ip6e);
                if (nxtp)
                        *nxtp = ip6e.ip6e_nxt;
                off += (ip6e.ip6e_len + 1) << 3;
                return off;

        case IPPROTO_NONE:
        case IPPROTO_ESP:
        case IPPROTO_IPCOMP:
                /* give up */
                return -1;

        default:
                return -1;
        }

        return -1;
}

/*
 * get offset for the last header in the chain.  m will be kept untainted.
 */
int
ip6_lasthdr(struct mbuf *m, int off, int proto, int *nxtp)
{
        int newoff;
        int nxt;

        if (!nxtp) {
                nxt = -1;
                nxtp = &nxt;
        }
        while (1) {
                newoff = ip6_nexthdr(m, off, proto, nxtp);
                if (newoff < 0)
                        return off;
                else if (newoff < off)
                        return -1;      /* invalid */
                else if (newoff == off)
                        return newoff;

                off = newoff;
                proto = *nxtp;
        }
}

struct ip6aux *
ip6_addaux(struct mbuf *m)
{
        struct m_tag *mtag;

        mtag = m_tag_find(m, PACKET_TAG_IPV6_INPUT, NULL);
        if (!mtag) {
                mtag = m_tag_get(PACKET_TAG_IPV6_INPUT, sizeof(struct ip6aux),
                    M_NOWAIT);
                if (mtag)
                        m_tag_prepend(m, mtag);
        }
        if (mtag)
                bzero(m_tag_data(mtag), sizeof(struct ip6aux));
        return mtag ? (struct ip6aux *)m_tag_data(mtag) : NULL;
}

struct ip6aux *
ip6_findaux(struct mbuf *m)
{
        struct m_tag *mtag;

        mtag = m_tag_find(m, PACKET_TAG_IPV6_INPUT, NULL);
        return mtag ? (struct ip6aux *)m_tag_data(mtag) : NULL;
}

void
ip6_delaux(struct mbuf *m)
{
        struct m_tag *mtag;

        mtag = m_tag_find(m, PACKET_TAG_IPV6_INPUT, NULL);
        if (mtag)
                m_tag_delete(m, mtag);
}

/*
 * System control for IP6
 */

u_char  inet6ctlerrmap[PRC_NCMDS] = {
        0,              0,              0,              0,
        0,              EMSGSIZE,       EHOSTDOWN,      EHOSTUNREACH,
        EHOSTUNREACH,   EHOSTUNREACH,   ECONNREFUSED,   ECONNREFUSED,
        EMSGSIZE,       EHOSTUNREACH,   0,              0,
        0,              0,              0,              0,
        ENOPROTOOPT
};