/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * Copyright (C) 1995, 1996, 1997, and 1998 WIDE Project.
 * All rights reserved.
 * Copyright (c) 2019 Netflix, Inc.
 *
 * 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.
 *
 *      $KAME: frag6.c,v 1.33 2002/01/07 11:34:48 kjc Exp $
 */

#include "opt_rss.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/domain.h>
#include <sys/eventhandler.h>
#include <sys/hash.h>
#include <sys/kernel.h>
#include <sys/malloc.h>
#include <sys/mbuf.h>
#include <sys/protosw.h>
#include <sys/queue.h>
#include <sys/socket.h>
#include <sys/sysctl.h>
#include <sys/syslog.h>

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

#include <netinet/in.h>
#include <netinet/in_var.h>
#include <netinet/ip6.h>
#include <netinet6/ip6_var.h>
#include <netinet/icmp6.h>
#include <netinet/in_systm.h>   /* For ECN definitions. */
#include <netinet/ip.h>         /* For ECN definitions. */

#ifdef MAC
#include <security/mac/mac_framework.h>
#endif

/*
 * A "big picture" of how IPv6 fragment queues are all linked together.
 *
 * struct ip6qbucket ip6qb[...];                        hashed buckets
 * ||||||||
 * |
 * +--- TAILQ(struct ip6q, packets) *q6;                tailq entries holding
 *      ||||||||                                        fragmented packets
 *      |                                               (1 per original packet)
 *      |
 *      +--- TAILQ(struct ip6asfrag, ip6q_frags) *af6;  tailq entries of IPv6
 *           |                                   *ip6af;fragment packets
 *           |                                          for one original packet
 *           + *mbuf
 */

/* Reassembly headers are stored in hash buckets. */
#define IP6REASS_NHASH_LOG2     10
#define IP6REASS_NHASH          (1 << IP6REASS_NHASH_LOG2)
#define IP6REASS_HMASK          (IP6REASS_NHASH - 1)

TAILQ_HEAD(ip6qhead, ip6q);
struct ip6qbucket {
        struct ip6qhead packets;
        struct mtx      lock;
        int             count;
};

struct ip6asfrag {
        TAILQ_ENTRY(ip6asfrag) ip6af_tq;
        struct mbuf     *ip6af_m;
        int             ip6af_offset;   /* Offset in ip6af_m to next header. */
        int             ip6af_frglen;   /* Fragmentable part length. */
        int             ip6af_off;      /* Fragment offset. */
        bool            ip6af_mff;      /* More fragment bit in frag off. */
};

static MALLOC_DEFINE(M_FRAG6, "frag6", "IPv6 fragment reassembly header");

#ifdef VIMAGE
/* A flag to indicate if IPv6 fragmentation is initialized. */
VNET_DEFINE_STATIC(bool,                frag6_on);
#define V_frag6_on                      VNET(frag6_on)
#endif

/* System wide (global) maximum and count of packets in reassembly queues. */
static int ip6_maxfrags;
static u_int __exclusive_cache_line frag6_nfrags;

/* Maximum and current packets in per-VNET reassembly queue. */
VNET_DEFINE_STATIC(int,                 ip6_maxfragpackets);
VNET_DEFINE_STATIC(volatile u_int,      frag6_nfragpackets);
#define V_ip6_maxfragpackets            VNET(ip6_maxfragpackets)
#define V_frag6_nfragpackets            VNET(frag6_nfragpackets)

/* Maximum per-VNET reassembly timeout (milliseconds) */
VNET_DEFINE_STATIC(u_int,               ip6_fraglifetime) = IPV6_DEFFRAGTTL;
#define V_ip6_fraglifetime              VNET(ip6_fraglifetime)

/* Maximum per-VNET reassembly queues per bucket and fragments per packet. */
VNET_DEFINE_STATIC(int,                 ip6_maxfragbucketsize);
VNET_DEFINE_STATIC(int,                 ip6_maxfragsperpacket);
#define V_ip6_maxfragbucketsize         VNET(ip6_maxfragbucketsize)
#define V_ip6_maxfragsperpacket         VNET(ip6_maxfragsperpacket)

/* Per-VNET reassembly queue buckets. */
VNET_DEFINE_STATIC(struct ip6qbucket,   ip6qb[IP6REASS_NHASH]);
VNET_DEFINE_STATIC(uint32_t,            ip6qb_hashseed);
#define V_ip6qb                         VNET(ip6qb)
#define V_ip6qb_hashseed                VNET(ip6qb_hashseed)

#define IP6QB_LOCK(_b)          mtx_lock(&V_ip6qb[(_b)].lock)
#define IP6QB_TRYLOCK(_b)       mtx_trylock(&V_ip6qb[(_b)].lock)
#define IP6QB_LOCK_ASSERT(_b)   mtx_assert(&V_ip6qb[(_b)].lock, MA_OWNED)
#define IP6QB_UNLOCK(_b)        mtx_unlock(&V_ip6qb[(_b)].lock)
#define IP6QB_HEAD(_b)          (&V_ip6qb[(_b)].packets)

/*
 * By default, limit the number of IP6 fragments across all reassembly
 * queues to  1/32 of the total number of mbuf clusters.
 *
 * Limit the total number of reassembly queues per VNET to the
 * IP6 fragment limit, but ensure the limit will not allow any bucket
 * to grow above 100 items. (The bucket limit is
 * IP_MAXFRAGPACKETS / (IPREASS_NHASH / 2), so the 50 is the correct
 * multiplier to reach a 100-item limit.)
 * The 100-item limit was chosen as brief testing seems to show that
 * this produces "reasonable" performance on some subset of systems
 * under DoS attack.
 */
#define IP6_MAXFRAGS            (nmbclusters / 32)
#define IP6_MAXFRAGPACKETS      (imin(IP6_MAXFRAGS, IP6REASS_NHASH * 50))

/* Interval between periodic reassembly queue inspections */
#define IP6_CALLOUT_INTERVAL_MS 500

/*
 * Sysctls and helper function.
 */
SYSCTL_DECL(_net_inet6_ip6);

SYSCTL_UINT(_net_inet6_ip6, OID_AUTO, frag6_nfrags,
        CTLFLAG_RD, &frag6_nfrags, 0,
        "Global number of IPv6 fragments across all reassembly queues.");

static void
frag6_set_bucketsize(void)
{
        int i;

        if ((i = V_ip6_maxfragpackets) > 0)
                V_ip6_maxfragbucketsize = imax(i / (IP6REASS_NHASH / 2), 1);
}

SYSCTL_INT(_net_inet6_ip6, IPV6CTL_MAXFRAGS, maxfrags,
        CTLFLAG_RW, &ip6_maxfrags, 0,
        "Maximum allowed number of outstanding IPv6 packet fragments. "
        "A value of 0 means no fragmented packets will be accepted, while "
        "a value of -1 means no limit");

static int
sysctl_ip6_maxfragpackets(SYSCTL_HANDLER_ARGS)
{
        int error, val;

        val = V_ip6_maxfragpackets;
        error = sysctl_handle_int(oidp, &val, 0, req);
        if (error != 0 || !req->newptr)
                return (error);
        V_ip6_maxfragpackets = val;
        frag6_set_bucketsize();
        return (0);
}
SYSCTL_PROC(_net_inet6_ip6, IPV6CTL_MAXFRAGPACKETS, maxfragpackets,
        CTLFLAG_VNET | CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
        NULL, 0, sysctl_ip6_maxfragpackets, "I",
        "Default maximum number of outstanding fragmented IPv6 packets. "
        "A value of 0 means no fragmented packets will be accepted, while a "
        "a value of -1 means no limit");
SYSCTL_UINT(_net_inet6_ip6, OID_AUTO, frag6_nfragpackets,
        CTLFLAG_VNET | CTLFLAG_RD,
        __DEVOLATILE(u_int *, &VNET_NAME(frag6_nfragpackets)), 0,
        "Per-VNET number of IPv6 fragments across all reassembly queues.");
SYSCTL_INT(_net_inet6_ip6, IPV6CTL_MAXFRAGSPERPACKET, maxfragsperpacket,
        CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(ip6_maxfragsperpacket), 0,
        "Maximum allowed number of fragments per packet");
SYSCTL_INT(_net_inet6_ip6, IPV6CTL_MAXFRAGBUCKETSIZE, maxfragbucketsize,
        CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(ip6_maxfragbucketsize), 0,
        "Maximum number of reassembly queues per hash bucket");

static int
frag6_milli_to_callout_ticks(int ms)
{
        return (ms / IP6_CALLOUT_INTERVAL_MS);
}

static int
frag6_callout_ticks_to_milli(int ms)
{
        return (ms * IP6_CALLOUT_INTERVAL_MS);
}

_Static_assert(sizeof(((struct ip6q *)NULL)->ip6q_ttl) >= 2,
    "ip6q_ttl field is not large enough");

static int
sysctl_ip6_fraglifetime(SYSCTL_HANDLER_ARGS)
{
        int error, val;

        val = V_ip6_fraglifetime;
        error = sysctl_handle_int(oidp, &val, 0, req);
        if (error != 0 || !req->newptr)
                return (error);
        if (val <= 0)
                val = IPV6_DEFFRAGTTL;

        if (frag6_milli_to_callout_ticks(val) >= 65536)
                val = frag6_callout_ticks_to_milli(65535);
#ifdef VIMAGE
        if (!IS_DEFAULT_VNET(curvnet)) {
                CURVNET_SET(vnet0);
                int host_val = V_ip6_fraglifetime;
                CURVNET_RESTORE();

                if (val > host_val)
                        val = host_val;
        }
#endif
        V_ip6_fraglifetime = val;
        return (0);
}
SYSCTL_PROC(_net_inet6_ip6, OID_AUTO, fraglifetime_ms,
        CTLFLAG_VNET | CTLTYPE_UINT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
        NULL, 0, sysctl_ip6_fraglifetime, "I",
        "Fragment lifetime, in milliseconds");

/*
 * Remove the IPv6 fragmentation header from the mbuf.
 */
int
ip6_deletefraghdr(struct mbuf *m, int offset, int wait __unused)
{
        struct ip6_hdr *ip6;

        KASSERT(m->m_len >= offset + sizeof(struct ip6_frag),
            ("%s: ext headers not contigous in mbuf %p m_len %d >= "
            "offset %d + %zu\n", __func__, m, m->m_len, offset,
            sizeof(struct ip6_frag)));

        /* Delete frag6 header. */
        ip6 = mtod(m, struct ip6_hdr *);
        bcopy(ip6, (char *)ip6 + sizeof(struct ip6_frag), offset);
        m->m_data += sizeof(struct ip6_frag);
        m->m_len -= sizeof(struct ip6_frag);
        m->m_flags |= M_FRAGMENTED;

        return (0);
}

static void
frag6_rmqueue(struct ip6q *q6, uint32_t bucket)
{
        IP6QB_LOCK_ASSERT(bucket);

        TAILQ_REMOVE(IP6QB_HEAD(bucket), q6, ip6q_tq);
        V_ip6qb[bucket].count--;
#ifdef MAC
        mac_ip6q_destroy(q6);
#endif
        free(q6, M_FRAG6);
        atomic_subtract_int(&V_frag6_nfragpackets, 1);
}

/*
 * Free a fragment reassembly header and all associated datagrams.
 */
static void
frag6_freef(struct ip6q *q6, uint32_t bucket)
{
        struct ip6_hdr *ip6;
        struct ip6asfrag *af6;
        struct mbuf *m;

        IP6QB_LOCK_ASSERT(bucket);

        while ((af6 = TAILQ_FIRST(&q6->ip6q_frags)) != NULL) {
                m = af6->ip6af_m;
                TAILQ_REMOVE(&q6->ip6q_frags, af6, ip6af_tq);

                /*
                 * Return ICMP time exceeded error for the 1st fragment.
                 * Just free other fragments.
                 */
                if (af6->ip6af_off == 0 && m->m_pkthdr.rcvif != NULL) {
                        /* Adjust pointer. */
                        ip6 = mtod(m, struct ip6_hdr *);

                        /* Restore source and destination addresses. */
                        ip6->ip6_src = q6->ip6q_src;
                        ip6->ip6_dst = q6->ip6q_dst;

                        icmp6_error(m, ICMP6_TIME_EXCEEDED,
                            ICMP6_TIME_EXCEED_REASSEMBLY, 0);
                } else
                        m_freem(m);

                free(af6, M_FRAG6);
        }

        atomic_subtract_int(&frag6_nfrags, q6->ip6q_nfrag);
        frag6_rmqueue(q6, bucket);
}

/*
 * Drain off all datagram fragments belonging to
 * the given network interface.
 */
static void
frag6_cleanup(void *arg __unused, struct ifnet *ifp)
{
        struct ip6qhead *head;
        struct ip6q *q6;
        struct ip6asfrag *af6;
        uint32_t bucket;

        KASSERT(ifp != NULL, ("%s: ifp is NULL", __func__));

        CURVNET_SET_QUIET(ifp->if_vnet);
#ifdef VIMAGE
        /*
         * Skip processing if IPv6 reassembly is not initialised or
         * torn down by frag6_destroy().
         */
        if (!V_frag6_on) {
                CURVNET_RESTORE();
                return;
        }
#endif

        for (bucket = 0; bucket < IP6REASS_NHASH; bucket++) {
                IP6QB_LOCK(bucket);
                head = IP6QB_HEAD(bucket);
                /* Scan fragment list. */
                TAILQ_FOREACH(q6, head, ip6q_tq) {
                        TAILQ_FOREACH(af6, &q6->ip6q_frags, ip6af_tq) {
                                /* Clear no longer valid rcvif pointer. */
                                if (af6->ip6af_m->m_pkthdr.rcvif == ifp)
                                        af6->ip6af_m->m_pkthdr.rcvif = NULL;
                        }
                }
                IP6QB_UNLOCK(bucket);
        }
        CURVNET_RESTORE();
}
EVENTHANDLER_DEFINE(ifnet_departure_event, frag6_cleanup, NULL, 0);

/*
 * Like in RFC2460, in RFC8200, fragment and reassembly rules do not agree with
 * each other, in terms of next header field handling in fragment header.
 * While the sender will use the same value for all of the fragmented packets,
 * receiver is suggested not to check for consistency.
 *
 * Fragment rules (p18,p19):
 *      (2)  A Fragment header containing:
 *      The Next Header value that identifies the first header
 *      after the Per-Fragment headers of the original packet.
 *              -> next header field is same for all fragments
 *
 * Reassembly rule (p20):
 *      The Next Header field of the last header of the Per-Fragment
 *      headers is obtained from the Next Header field of the first
 *      fragment's Fragment header.
 *              -> should grab it from the first fragment only
 *
 * The following note also contradicts with fragment rule - no one is going to
 * send different fragment with different next header field.
 *
 * Additional note (p22) [not an error]:
 *      The Next Header values in the Fragment headers of different
 *      fragments of the same original packet may differ.  Only the value
 *      from the Offset zero fragment packet is used for reassembly.
 *              -> should grab it from the first fragment only
 *
 * There is no explicit reason given in the RFC.  Historical reason maybe?
 */
/*
 * Fragment input.
 */
int
frag6_input(struct mbuf **mp, int *offp, int proto)
{
        struct mbuf *m, *t;
        struct ip6_hdr *ip6;
        struct ip6_frag *ip6f;
        struct ip6qhead *head;
        struct ip6q *q6;
        struct ip6asfrag *af6, *ip6af, *af6tmp;
        struct in6_ifaddr *ia6;
        struct ifnet *dstifp, *srcifp;
        uint32_t hashkey[(sizeof(struct in6_addr) * 2 +
                    sizeof(ip6f->ip6f_ident)) / sizeof(uint32_t)];
        uint32_t bucket, *hashkeyp;
        int fragoff, frgpartlen;        /* Must be larger than uint16_t. */
        int nxt, offset, plen;
        uint8_t ecn, ecn0;
        bool only_frag;
#ifdef RSS
        struct ip6_direct_ctx *ip6dc;
        struct m_tag *mtag;
#endif

        m = *mp;
        offset = *offp;

        M_ASSERTPKTHDR(m);

        if (m->m_len < offset + sizeof(struct ip6_frag)) {
                m = m_pullup(m, offset + sizeof(struct ip6_frag));
                if (m == NULL) {
                        IP6STAT_INC(ip6s_exthdrtoolong);
                        *mp = NULL;
                        return (IPPROTO_DONE);
                }
        }
        ip6 = mtod(m, struct ip6_hdr *);

        dstifp = NULL;
        /* Find the destination interface of the packet. */
        ia6 = in6ifa_ifwithaddr(&ip6->ip6_dst, 0 /* XXX */, false);
        if (ia6 != NULL)
                dstifp = ia6->ia_ifp;

        /* Jumbo payload cannot contain a fragment header. */
        if (ip6->ip6_plen == 0) {
                icmp6_error(m, ICMP6_PARAM_PROB, ICMP6_PARAMPROB_HEADER, offset);
                in6_ifstat_inc(dstifp, ifs6_reass_fail);
                *mp = NULL;
                return (IPPROTO_DONE);
        }

        /*
         * Check whether fragment packet's fragment length is a
         * multiple of 8 octets (unless it is the last one).
         * sizeof(struct ip6_frag) == 8
         * sizeof(struct ip6_hdr) = 40
         */
        ip6f = (struct ip6_frag *)((caddr_t)ip6 + offset);
        if ((ip6f->ip6f_offlg & IP6F_MORE_FRAG) &&
            (((ntohs(ip6->ip6_plen) - offset) & 0x7) != 0)) {
                icmp6_error(m, ICMP6_PARAM_PROB, ICMP6_PARAMPROB_HEADER,
                    offsetof(struct ip6_hdr, ip6_plen));
                in6_ifstat_inc(dstifp, ifs6_reass_fail);
                *mp = NULL;
                return (IPPROTO_DONE);
        }

        IP6STAT_INC(ip6s_fragments);
        in6_ifstat_inc(dstifp, ifs6_reass_reqd);

        /*
         * Handle "atomic" fragments (offset and m bit set to 0) upfront,
         * unrelated to any reassembly.  We need to remove the frag hdr
         * which is ugly.
         * See RFC 6946 and section 4.5 of RFC 8200.
         */
        if ((ip6f->ip6f_offlg & ~IP6F_RESERVED_MASK) == 0) {
                IP6STAT_INC(ip6s_atomicfrags);
                nxt = ip6f->ip6f_nxt;
                /*
                 * Set nxt(-hdr field value) to the original value.
                 * We cannot just set ip6->ip6_nxt as there might be
                 * an unfragmentable part with extension headers and
                 * we must update the last one.
                 */
                m_copyback(m, ip6_get_prevhdr(m, offset), sizeof(uint8_t),
                    (caddr_t)&nxt);
                ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) -
                    sizeof(struct ip6_frag));
                if (ip6_deletefraghdr(m, offset, M_NOWAIT) != 0)
                        goto dropfrag2;
                m->m_pkthdr.len -= sizeof(struct ip6_frag);
                in6_ifstat_inc(dstifp, ifs6_reass_ok);
                *mp = m;
                return (nxt);
        }

        /* Offset now points to data portion. */
        offset += sizeof(struct ip6_frag);

        /* Get fragment length and discard 0-byte fragments. */
        frgpartlen = sizeof(struct ip6_hdr) + ntohs(ip6->ip6_plen) - offset;
        if (frgpartlen == 0) {
                icmp6_error(m, ICMP6_PARAM_PROB, ICMP6_PARAMPROB_HEADER,
                    offsetof(struct ip6_hdr, ip6_plen));
                in6_ifstat_inc(dstifp, ifs6_reass_fail);
                IP6STAT_INC(ip6s_fragdropped);
                *mp = NULL;
                return (IPPROTO_DONE);
        }

        /*
         * Enforce upper bound on number of fragments for the entire system.
         * If maxfrag is 0, never accept fragments.
         * If maxfrag is -1, accept all fragments without limitation.
         */
        if (ip6_maxfrags < 0)
                ;
        else if (atomic_load_int(&frag6_nfrags) >= (u_int)ip6_maxfrags)
                goto dropfrag2;

        /*
         * Validate that a full header chain to the ULP is present in the
         * packet containing the first fragment as per RFC RFC7112 and
         * RFC 8200 pages 18,19:
         * The first fragment packet is composed of:
         * (3)  Extension headers, if any, and the Upper-Layer header.  These
         *      headers must be in the first fragment.  ...
         */
        fragoff = ntohs(ip6f->ip6f_offlg & IP6F_OFF_MASK);
        /* XXX TODO.  thj has D16851 open for this. */
        /* Send ICMPv6 4,3 in case of violation. */

        /* Store receive network interface pointer for later. */
        srcifp = m->m_pkthdr.rcvif;

        /* Generate a hash value for fragment bucket selection. */
        hashkeyp = hashkey;
        memcpy(hashkeyp, &ip6->ip6_src, sizeof(struct in6_addr));
        hashkeyp += sizeof(struct in6_addr) / sizeof(*hashkeyp);
        memcpy(hashkeyp, &ip6->ip6_dst, sizeof(struct in6_addr));
        hashkeyp += sizeof(struct in6_addr) / sizeof(*hashkeyp);
        *hashkeyp = ip6f->ip6f_ident;
        bucket = jenkins_hash32(hashkey, nitems(hashkey), V_ip6qb_hashseed);
        bucket &= IP6REASS_HMASK;
        IP6QB_LOCK(bucket);
        head = IP6QB_HEAD(bucket);

        TAILQ_FOREACH(q6, head, ip6q_tq)
                if (ip6f->ip6f_ident == q6->ip6q_ident &&
                    IN6_ARE_ADDR_EQUAL(&ip6->ip6_src, &q6->ip6q_src) &&
                    IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst, &q6->ip6q_dst)
#ifdef MAC
                    && mac_ip6q_match(m, q6)
#endif
                    )
                        break;

        only_frag = false;
        if (q6 == NULL) {
                /* A first fragment to arrive creates a reassembly queue. */
                only_frag = true;

                /*
                 * Enforce upper bound on number of fragmented packets
                 * for which we attempt reassembly;
                 * If maxfragpackets is 0, never accept fragments.
                 * If maxfragpackets is -1, accept all fragments without
                 * limitation.
                 */
                if (V_ip6_maxfragpackets < 0)
                        ;
                else if (V_ip6qb[bucket].count >= V_ip6_maxfragbucketsize ||
                    atomic_load_int(&V_frag6_nfragpackets) >=
                    (u_int)V_ip6_maxfragpackets)
                        goto dropfrag;

                /* Allocate IPv6 fragement packet queue entry. */
                q6 = malloc(sizeof(struct ip6q), M_FRAG6, M_NOWAIT | M_ZERO);
                if (q6 == NULL)
                        goto dropfrag;
#ifdef MAC
                if (mac_ip6q_init(q6, M_NOWAIT) != 0) {
                        free(q6, M_FRAG6);
                        goto dropfrag;
                }
                mac_ip6q_create(m, q6);
#endif
                atomic_add_int(&V_frag6_nfragpackets, 1);

                /* ip6q_nxt will be filled afterwards, from 1st fragment. */
                TAILQ_INIT(&q6->ip6q_frags);
                q6->ip6q_ident  = ip6f->ip6f_ident;
                q6->ip6q_ttl    = frag6_milli_to_callout_ticks(V_ip6_fraglifetime);
                q6->ip6q_src    = ip6->ip6_src;
                q6->ip6q_dst    = ip6->ip6_dst;
                q6->ip6q_ecn    = IPV6_ECN(ip6);
                q6->ip6q_unfrglen = -1; /* The 1st fragment has not arrived. */

                /* Add the fragemented packet to the bucket. */
                TAILQ_INSERT_HEAD(head, q6, ip6q_tq);
                V_ip6qb[bucket].count++;
        }

        /*
         * If it is the 1st fragment, record the length of the
         * unfragmentable part and the next header of the fragment header.
         * Assume the first 1st fragement to arrive will be correct.
         * We do not have any duplicate checks here yet so another packet
         * with fragoff == 0 could come and overwrite the ip6q_unfrglen
         * and worse, the next header, at any time.
         */
        if (fragoff == 0 && q6->ip6q_unfrglen == -1) {
                q6->ip6q_unfrglen = offset - sizeof(struct ip6_hdr) -
                    sizeof(struct ip6_frag);
                q6->ip6q_nxt = ip6f->ip6f_nxt;
                /* XXX ECN? */
        }

        /*
         * Check that the reassembled packet would not exceed 65535 bytes
         * in size.
         * If it would exceed, discard the fragment and return an ICMP error.
         */
        if (q6->ip6q_unfrglen >= 0) {
                /* The 1st fragment has already arrived. */
                if (q6->ip6q_unfrglen + fragoff + frgpartlen > IPV6_MAXPACKET) {
                        if (only_frag)
                                frag6_rmqueue(q6, bucket);
                        IP6QB_UNLOCK(bucket);
                        icmp6_error(m, ICMP6_PARAM_PROB, ICMP6_PARAMPROB_HEADER,
                            offset - sizeof(struct ip6_frag) +
                            offsetof(struct ip6_frag, ip6f_offlg));
                        *mp = NULL;
                        return (IPPROTO_DONE);
                }
        } else if (fragoff + frgpartlen > IPV6_MAXPACKET) {
                if (only_frag)
                        frag6_rmqueue(q6, bucket);
                IP6QB_UNLOCK(bucket);
                icmp6_error(m, ICMP6_PARAM_PROB, ICMP6_PARAMPROB_HEADER,
                    offset - sizeof(struct ip6_frag) +
                    offsetof(struct ip6_frag, ip6f_offlg));
                *mp = NULL;
                return (IPPROTO_DONE);
        }

        /*
         * If it is the first fragment, do the above check for each
         * fragment already stored in the reassembly queue.
         */
        if (fragoff == 0 && !only_frag) {
                TAILQ_FOREACH_SAFE(af6, &q6->ip6q_frags, ip6af_tq, af6tmp) {
                        if (q6->ip6q_unfrglen + af6->ip6af_off +
                            af6->ip6af_frglen > IPV6_MAXPACKET) {
                                struct ip6_hdr *ip6err;
                                struct mbuf *merr;
                                int erroff;

                                merr = af6->ip6af_m;
                                erroff = af6->ip6af_offset;

                                /* Dequeue the fragment. */
                                TAILQ_REMOVE(&q6->ip6q_frags, af6, ip6af_tq);
                                q6->ip6q_nfrag--;
                                atomic_subtract_int(&frag6_nfrags, 1);
                                free(af6, M_FRAG6);

                                /* Set a valid receive interface pointer. */
                                merr->m_pkthdr.rcvif = srcifp;

                                /* Adjust pointer. */
                                ip6err = mtod(merr, struct ip6_hdr *);

                                /*
                                 * Restore source and destination addresses
                                 * in the erroneous IPv6 header.
                                 */
                                ip6err->ip6_src = q6->ip6q_src;
                                ip6err->ip6_dst = q6->ip6q_dst;

                                icmp6_error(merr, ICMP6_PARAM_PROB,
                                    ICMP6_PARAMPROB_HEADER,
                                    erroff - sizeof(struct ip6_frag) +
                                    offsetof(struct ip6_frag, ip6f_offlg));
                        }
                }
        }

        /* Allocate an IPv6 fragement queue entry for this fragmented part. */
        ip6af = malloc(sizeof(struct ip6asfrag), M_FRAG6, M_NOWAIT | M_ZERO);
        if (ip6af == NULL)
                goto dropfrag;
        ip6af->ip6af_mff = (ip6f->ip6f_offlg & IP6F_MORE_FRAG) ? true : false;
        ip6af->ip6af_off = fragoff;
        ip6af->ip6af_frglen = frgpartlen;
        ip6af->ip6af_offset = offset;
        ip6af->ip6af_m = m;

        if (only_frag) {
                /*
                 * Do a manual insert rather than a hard-to-understand cast
                 * to a different type relying on data structure order to work.
                 */
                TAILQ_INSERT_HEAD(&q6->ip6q_frags, ip6af, ip6af_tq);
                goto postinsert;
        }

        /* Do duplicate, condition, and boundry checks. */
        /*
         * Handle ECN by comparing this segment with the first one;
         * if CE is set, do not lose CE.
         * Drop if CE and not-ECT are mixed for the same packet.
         */
        ecn = IPV6_ECN(ip6);
        ecn0 = q6->ip6q_ecn;
        if (ecn == IPTOS_ECN_CE) {
                if (ecn0 == IPTOS_ECN_NOTECT) {
                        free(ip6af, M_FRAG6);
                        goto dropfrag;
                }
                if (ecn0 != IPTOS_ECN_CE)
                        q6->ip6q_ecn = IPTOS_ECN_CE;
        }
        if (ecn == IPTOS_ECN_NOTECT && ecn0 != IPTOS_ECN_NOTECT) {
                free(ip6af, M_FRAG6);
                goto dropfrag;
        }

        /* Find a fragmented part which begins after this one does. */
        TAILQ_FOREACH(af6, &q6->ip6q_frags, ip6af_tq)
                if (af6->ip6af_off > ip6af->ip6af_off)
                        break;

        /*
         * If the incoming framgent overlaps some existing fragments in
         * the reassembly queue, drop both the new fragment and the
         * entire reassembly queue.  However, if the new fragment
         * is an exact duplicate of an existing fragment, only silently
         * drop the existing fragment and leave the fragmentation queue
         * unchanged, as allowed by the RFC.  (RFC 8200, 4.5)
         */
        if (af6 != NULL)
                af6tmp = TAILQ_PREV(af6, ip6fraghead, ip6af_tq);
        else
                af6tmp = TAILQ_LAST(&q6->ip6q_frags, ip6fraghead);
        if (af6tmp != NULL) {
                if (af6tmp->ip6af_off + af6tmp->ip6af_frglen -
                    ip6af->ip6af_off > 0) {
                        if (af6tmp->ip6af_off != ip6af->ip6af_off ||
                            af6tmp->ip6af_frglen != ip6af->ip6af_frglen)
                                frag6_freef(q6, bucket);
                        free(ip6af, M_FRAG6);
                        goto dropfrag;
                }
        }
        if (af6 != NULL) {
                if (ip6af->ip6af_off + ip6af->ip6af_frglen -
                    af6->ip6af_off > 0) {
                        if (af6->ip6af_off != ip6af->ip6af_off ||
                            af6->ip6af_frglen != ip6af->ip6af_frglen)
                                frag6_freef(q6, bucket);
                        free(ip6af, M_FRAG6);
                        goto dropfrag;
                }
        }

#ifdef MAC
        mac_ip6q_update(m, q6);
#endif

        /*
         * Stick new segment in its place; check for complete reassembly.
         * If not complete, check fragment limit.  Move to front of packet
         * queue, as we are the most recently active fragmented packet.
         */
        if (af6 != NULL)
                TAILQ_INSERT_BEFORE(af6, ip6af, ip6af_tq);
        else
                TAILQ_INSERT_TAIL(&q6->ip6q_frags, ip6af, ip6af_tq);
postinsert:
        atomic_add_int(&frag6_nfrags, 1);
        q6->ip6q_nfrag++;

        plen = 0;
        TAILQ_FOREACH(af6, &q6->ip6q_frags, ip6af_tq) {
                if (af6->ip6af_off != plen) {
                        if (q6->ip6q_nfrag > V_ip6_maxfragsperpacket) {
                                IP6STAT_ADD(ip6s_fragdropped, q6->ip6q_nfrag);
                                frag6_freef(q6, bucket);
                        }
                        IP6QB_UNLOCK(bucket);
                        *mp = NULL;
                        return (IPPROTO_DONE);
                }
                plen += af6->ip6af_frglen;
        }
        af6 = TAILQ_LAST(&q6->ip6q_frags, ip6fraghead);
        if (af6->ip6af_mff) {
                if (q6->ip6q_nfrag > V_ip6_maxfragsperpacket) {
                        IP6STAT_ADD(ip6s_fragdropped, q6->ip6q_nfrag);
                        frag6_freef(q6, bucket);
                }
                IP6QB_UNLOCK(bucket);
                *mp = NULL;
                return (IPPROTO_DONE);
        }

        /* Reassembly is complete; concatenate fragments. */
        ip6af = TAILQ_FIRST(&q6->ip6q_frags);
        t = m = ip6af->ip6af_m;
        TAILQ_REMOVE(&q6->ip6q_frags, ip6af, ip6af_tq);
        while ((af6 = TAILQ_FIRST(&q6->ip6q_frags)) != NULL) {
                m->m_pkthdr.csum_flags &=
                    af6->ip6af_m->m_pkthdr.csum_flags;
                m->m_pkthdr.csum_data +=
                    af6->ip6af_m->m_pkthdr.csum_data;

                TAILQ_REMOVE(&q6->ip6q_frags, af6, ip6af_tq);
                t = m_last(t);
                m_adj(af6->ip6af_m, af6->ip6af_offset);
                m_demote_pkthdr(af6->ip6af_m);
                m_cat(t, af6->ip6af_m);
                free(af6, M_FRAG6);
        }

        while (m->m_pkthdr.csum_data & 0xffff0000)
                m->m_pkthdr.csum_data = (m->m_pkthdr.csum_data & 0xffff) +
                    (m->m_pkthdr.csum_data >> 16);

        /* Adjust offset to point where the original next header starts. */
        offset = ip6af->ip6af_offset - sizeof(struct ip6_frag);
        free(ip6af, M_FRAG6);
        if ((u_int)plen + (u_int)offset - sizeof(struct ip6_hdr) >
            IPV6_MAXPACKET) {
                frag6_freef(q6, bucket);
                goto dropfrag;
        }
        ip6 = mtod(m, struct ip6_hdr *);
        ip6->ip6_plen = htons((u_short)plen + offset - sizeof(struct ip6_hdr));
        if (q6->ip6q_ecn == IPTOS_ECN_CE)
                ip6->ip6_flow |= htonl(IPTOS_ECN_CE << 20);
        nxt = q6->ip6q_nxt;

        ip6_deletefraghdr(m, offset, M_NOWAIT);

        /* Set nxt(-hdr field value) to the original value. */
        m_copyback(m, ip6_get_prevhdr(m, offset), sizeof(uint8_t),
            (caddr_t)&nxt);

#ifdef MAC
        mac_ip6q_reassemble(q6, m);
#endif
        atomic_subtract_int(&frag6_nfrags, q6->ip6q_nfrag);
        frag6_rmqueue(q6, bucket);

        if (m->m_flags & M_PKTHDR) { /* Isn't it always true? */

                plen = 0;
                for (t = m; t; t = t->m_next)
                        plen += t->m_len;
                m->m_pkthdr.len = plen;
                /* Set a valid receive interface pointer. */
                m->m_pkthdr.rcvif = srcifp;
        }

#ifdef RSS
        mtag = m_tag_alloc(MTAG_ABI_IPV6, IPV6_TAG_DIRECT, sizeof(*ip6dc),
            M_NOWAIT);
        if (mtag == NULL)
                goto dropfrag;

        ip6dc = (struct ip6_direct_ctx *)(mtag + 1);
        ip6dc->ip6dc_nxt = nxt;
        ip6dc->ip6dc_off = offset;

        m_tag_prepend(m, mtag);
#endif

        IP6QB_UNLOCK(bucket);
        IP6STAT_INC(ip6s_reassembled);
        in6_ifstat_inc(dstifp, ifs6_reass_ok);

#ifdef RSS
        /* Queue/dispatch for reprocessing. */
        netisr_dispatch(NETISR_IPV6_DIRECT, m);
        *mp = NULL;
        return (IPPROTO_DONE);
#endif

        /* Tell launch routine the next header. */
        *mp = m;
        *offp = offset;

        return (nxt);

dropfrag:
        IP6QB_UNLOCK(bucket);
dropfrag2:
        in6_ifstat_inc(dstifp, ifs6_reass_fail);
        IP6STAT_INC(ip6s_fragdropped);
        m_freem(m);
        *mp = NULL;
        return (IPPROTO_DONE);
}

/*
 * IPv6 reassembling timer processing;
 * if a timer expires on a reassembly queue, discard it.
 */
static struct callout frag6_callout;
static void
frag6_slowtimo(void *arg __unused)
{
        VNET_ITERATOR_DECL(vnet_iter);
        struct ip6qhead *head;
        struct ip6q *q6, *q6tmp;
        uint32_t bucket;

        if (atomic_load_int(&frag6_nfrags) == 0)
                goto done;

        VNET_LIST_RLOCK_NOSLEEP();
        VNET_FOREACH(vnet_iter) {
                CURVNET_SET(vnet_iter);
                for (bucket = 0; bucket < IP6REASS_NHASH; bucket++) {
                        if (V_ip6qb[bucket].count == 0)
                                continue;
                        IP6QB_LOCK(bucket);
                        head = IP6QB_HEAD(bucket);
                        TAILQ_FOREACH_SAFE(q6, head, ip6q_tq, q6tmp)
                                if (--q6->ip6q_ttl == 0) {
                                        IP6STAT_ADD(ip6s_fragtimeout,
                                                q6->ip6q_nfrag);
                                        /* XXX in6_ifstat_inc(ifp, ifs6_reass_fail) */
                                        frag6_freef(q6, bucket);
                                }
                        /*
                         * If we are over the maximum number of fragments
                         * (due to the limit being lowered), drain off
                         * enough to get down to the new limit.
                         * Note that we drain all reassembly queues if
                         * maxfragpackets is 0 (fragmentation is disabled),
                         * and do not enforce a limit when maxfragpackets
                         * is negative.
                         */
                        while ((V_ip6_maxfragpackets == 0 ||
                            (V_ip6_maxfragpackets > 0 &&
                            V_ip6qb[bucket].count > V_ip6_maxfragbucketsize)) &&
                            (q6 = TAILQ_LAST(head, ip6qhead)) != NULL) {
                                IP6STAT_ADD(ip6s_fragoverflow, q6->ip6q_nfrag);
                                /* XXX in6_ifstat_inc(ifp, ifs6_reass_fail) */
                                frag6_freef(q6, bucket);
                        }
                        IP6QB_UNLOCK(bucket);
                }
                /*
                 * If we are still over the maximum number of fragmented
                 * packets, drain off enough to get down to the new limit.
                 */
                bucket = 0;
                while (V_ip6_maxfragpackets >= 0 &&
                    atomic_load_int(&V_frag6_nfragpackets) >
                    (u_int)V_ip6_maxfragpackets) {
                        IP6QB_LOCK(bucket);
                        q6 = TAILQ_LAST(IP6QB_HEAD(bucket), ip6qhead);
                        if (q6 != NULL) {
                                IP6STAT_ADD(ip6s_fragoverflow, q6->ip6q_nfrag);
                                /* XXX in6_ifstat_inc(ifp, ifs6_reass_fail) */
                                frag6_freef(q6, bucket);
                        }
                        IP6QB_UNLOCK(bucket);
                        bucket = (bucket + 1) % IP6REASS_NHASH;
                }
                CURVNET_RESTORE();
        }
        VNET_LIST_RUNLOCK_NOSLEEP();
done:
        callout_reset_sbt(&frag6_callout, SBT_1MS * IP6_CALLOUT_INTERVAL_MS,
            SBT_1MS * 10, frag6_slowtimo, NULL, 0);
}

static void
frag6_slowtimo_init(void *arg __unused)
{

        callout_init(&frag6_callout, 1);
        callout_reset_sbt(&frag6_callout, SBT_1MS * IP6_CALLOUT_INTERVAL_MS,
            SBT_1MS * 10, frag6_slowtimo, NULL, 0);
}
SYSINIT(frag6, SI_SUB_VNET_DONE, SI_ORDER_ANY, frag6_slowtimo_init, NULL);

/*
 * Eventhandler to adjust limits in case nmbclusters change.
 */
static void
frag6_change(void *tag)
{
        VNET_ITERATOR_DECL(vnet_iter);

        ip6_maxfrags = IP6_MAXFRAGS;
        VNET_LIST_RLOCK_NOSLEEP();
        VNET_FOREACH(vnet_iter) {
                CURVNET_SET(vnet_iter);
                V_ip6_maxfragpackets = IP6_MAXFRAGPACKETS;
                frag6_set_bucketsize();
                CURVNET_RESTORE();
        }
        VNET_LIST_RUNLOCK_NOSLEEP();
}

/*
 * Initialise reassembly queue and fragment identifier.
 */
void
frag6_init(void)
{
        uint32_t bucket;

        V_ip6_maxfragpackets = IP6_MAXFRAGPACKETS;
        frag6_set_bucketsize();
        for (bucket = 0; bucket < IP6REASS_NHASH; bucket++) {
                TAILQ_INIT(IP6QB_HEAD(bucket));
                mtx_init(&V_ip6qb[bucket].lock, "ip6qb", NULL, MTX_DEF);
                V_ip6qb[bucket].count = 0;
        }
        V_ip6qb_hashseed = arc4random();
        V_ip6_maxfragsperpacket = 64;
#ifdef VIMAGE
        V_frag6_on = true;
#endif
        if (!IS_DEFAULT_VNET(curvnet))
                return;

        ip6_maxfrags = IP6_MAXFRAGS;
        EVENTHANDLER_REGISTER(nmbclusters_change,
            frag6_change, NULL, EVENTHANDLER_PRI_ANY);
}

/*
 * Drain off all datagram fragments.
 */
static void
frag6_drain_one(void)
{
        struct ip6q *q6;
        uint32_t bucket;

        for (bucket = 0; bucket < IP6REASS_NHASH; bucket++) {
                IP6QB_LOCK(bucket);
                while ((q6 = TAILQ_FIRST(IP6QB_HEAD(bucket))) != NULL) {
                        IP6STAT_INC(ip6s_fragdropped);
                        /* XXX in6_ifstat_inc(ifp, ifs6_reass_fail) */
                        frag6_freef(q6, bucket);
                }
                IP6QB_UNLOCK(bucket);
        }
}

void
frag6_drain(void *arg __unused, int flags __unused)
{
        VNET_ITERATOR_DECL(vnet_iter);

        VNET_LIST_RLOCK_NOSLEEP();
        VNET_FOREACH(vnet_iter) {
                CURVNET_SET(vnet_iter);
                frag6_drain_one();
                CURVNET_RESTORE();
        }
        VNET_LIST_RUNLOCK_NOSLEEP();
}

#ifdef VIMAGE
/*
 * Clear up IPv6 reassembly structures.
 */
void
frag6_destroy(void)
{
        uint32_t bucket;

        frag6_drain_one();
        V_frag6_on = false;
        for (bucket = 0; bucket < IP6REASS_NHASH; bucket++) {
                KASSERT(V_ip6qb[bucket].count == 0,
                    ("%s: V_ip6qb[%d] (%p) count not 0 (%d)", __func__,
                    bucket, &V_ip6qb[bucket], V_ip6qb[bucket].count));
                mtx_destroy(&V_ip6qb[bucket].lock);
        }
}
#endif