xnu-6153.121.1.tar.gz

[apple/xnu.git] / bsd / netinet6 / frag6.c

/*
 * Copyright (c) 2000-2019 Apple Inc. All rights reserved.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
 *
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. The rights granted to you under the License
 * may not be used to create, or enable the creation or redistribution of,
 * unlawful or unlicensed copies of an Apple operating system, or to
 * circumvent, violate, or enable the circumvention or violation of, any
 * terms of an Apple operating system software license agreement.
 *
 * Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this file.
 *
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
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 *
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 */

/*      $FreeBSD: src/sys/netinet6/frag6.c,v 1.2.2.5 2001/07/03 11:01:50 ume Exp $      */
/*      $KAME: frag6.c,v 1.31 2001/05/17 13:45:34 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.
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/malloc.h>
#include <sys/mcache.h>
#include <sys/mbuf.h>
#include <sys/domain.h>
#include <sys/protosw.h>
#include <sys/socket.h>
#include <sys/errno.h>
#include <sys/time.h>
#include <sys/kernel.h>
#include <sys/syslog.h>
#include <kern/queue.h>
#include <kern/locks.h>

#include <net/if.h>
#include <net/route.h>

#include <netinet/in.h>
#include <netinet/in_var.h>
#include <netinet/ip.h>
#include <netinet/ip_var.h>
#include <netinet/ip6.h>
#include <netinet6/ip6_var.h>
#include <netinet/icmp6.h>

#include <net/net_osdep.h>
#include <dev/random/randomdev.h>

/*
 * Define it to get a correct behavior on per-interface statistics.
 */
#define IN6_IFSTAT_STRICT

MBUFQ_HEAD(fq6_head);

static void frag6_save_context(struct mbuf *, int);
static void frag6_scrub_context(struct mbuf *);
static int frag6_restore_context(struct mbuf *);

static void frag6_icmp6_paramprob_error(struct fq6_head *);
static void frag6_icmp6_timeex_error(struct fq6_head *);

static void frag6_enq(struct ip6asfrag *, struct ip6asfrag *);
static void frag6_deq(struct ip6asfrag *);
static void frag6_insque(struct ip6q *, struct ip6q *);
static void frag6_remque(struct ip6q *);
static void frag6_freef(struct ip6q *, struct fq6_head *, struct fq6_head *);

static int frag6_timeout_run;           /* frag6 timer is scheduled to run */
static void frag6_timeout(void *);
static void frag6_sched_timeout(void);

static struct ip6q *ip6q_alloc(int);
static void ip6q_free(struct ip6q *);
static void ip6q_updateparams(void);
static struct ip6asfrag *ip6af_alloc(int);
static void ip6af_free(struct ip6asfrag *);

decl_lck_mtx_data(static, ip6qlock);
static lck_attr_t       *ip6qlock_attr;
static lck_grp_t        *ip6qlock_grp;
static lck_grp_attr_t   *ip6qlock_grp_attr;

/* IPv6 fragment reassembly queues (protected by ip6qlock) */
static struct ip6q ip6q;                /* ip6 reassembly queues */
static int ip6_maxfragpackets;          /* max packets in reass queues */
static u_int32_t frag6_nfragpackets;    /* # of packets in reass queues */
static int ip6_maxfrags;                /* max fragments in reass queues */
static u_int32_t frag6_nfrags;          /* # of fragments in reass queues */
static u_int32_t ip6q_limit;            /* ip6q allocation limit */
static u_int32_t ip6q_count;            /* current # of allocated ip6q's */
static u_int32_t ip6af_limit;           /* ip6asfrag allocation limit */
static u_int32_t ip6af_count;           /* current # of allocated ip6asfrag's */

static int sysctl_maxfragpackets SYSCTL_HANDLER_ARGS;
static int sysctl_maxfrags SYSCTL_HANDLER_ARGS;

SYSCTL_DECL(_net_inet6_ip6);

SYSCTL_PROC(_net_inet6_ip6, IPV6CTL_MAXFRAGPACKETS, maxfragpackets,
    CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_LOCKED, &ip6_maxfragpackets, 0,
    sysctl_maxfragpackets, "I",
    "Maximum number of IPv6 fragment reassembly queue entries");

SYSCTL_UINT(_net_inet6_ip6, OID_AUTO, fragpackets,
    CTLFLAG_RD | CTLFLAG_LOCKED, &frag6_nfragpackets, 0,
    "Current number of IPv6 fragment reassembly queue entries");

SYSCTL_PROC(_net_inet6_ip6, IPV6CTL_MAXFRAGS, maxfrags,
    CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_LOCKED, &ip6_maxfrags, 0,
    sysctl_maxfrags, "I", "Maximum number of IPv6 fragments allowed");

/*
 * Initialise reassembly queue and fragment identifier.
 */
void
frag6_init(void)
{
        /* ip6q_alloc() uses mbufs for IPv6 fragment queue structures */
        _CASSERT(sizeof(struct ip6q) <= _MLEN);
        /* ip6af_alloc() uses mbufs for IPv6 fragment queue structures */
        _CASSERT(sizeof(struct ip6asfrag) <= _MLEN);

        /* IPv6 fragment reassembly queue lock */
        ip6qlock_grp_attr  = lck_grp_attr_alloc_init();
        ip6qlock_grp = lck_grp_alloc_init("ip6qlock", ip6qlock_grp_attr);
        ip6qlock_attr = lck_attr_alloc_init();
        lck_mtx_init(&ip6qlock, ip6qlock_grp, ip6qlock_attr);

        lck_mtx_lock(&ip6qlock);
        /* Initialize IPv6 reassembly queue. */
        ip6q.ip6q_next = ip6q.ip6q_prev = &ip6q;

        /* same limits as IPv4 */
        ip6_maxfragpackets = nmbclusters / 32;
        ip6_maxfrags = ip6_maxfragpackets * 2;
        ip6q_updateparams();
        lck_mtx_unlock(&ip6qlock);
}

static void
frag6_save_context(struct mbuf *m, int val)
{
        m->m_pkthdr.pkt_hdr = (void *)(uintptr_t)val;
}

static void
frag6_scrub_context(struct mbuf *m)
{
        m->m_pkthdr.pkt_hdr = NULL;
}

static int
frag6_restore_context(struct mbuf *m)
{
        return (int)m->m_pkthdr.pkt_hdr;
}

/*
 * Send any deferred ICMP param problem error messages; caller must not be
 * holding ip6qlock and is expected to have saved the per-packet parameter
 * value via frag6_save_context().
 */
static void
frag6_icmp6_paramprob_error(struct fq6_head *diq6)
{
        LCK_MTX_ASSERT(&ip6qlock, LCK_MTX_ASSERT_NOTOWNED);

        if (!MBUFQ_EMPTY(diq6)) {
                struct mbuf *merr, *merr_tmp;
                int param;
                MBUFQ_FOREACH_SAFE(merr, diq6, merr_tmp) {
                        MBUFQ_REMOVE(diq6, merr);
                        MBUFQ_NEXT(merr) = NULL;
                        param = frag6_restore_context(merr);
                        frag6_scrub_context(merr);
                        icmp6_error(merr, ICMP6_PARAM_PROB,
                            ICMP6_PARAMPROB_HEADER, param);
                }
        }
}

/*
 * Send any deferred ICMP time exceeded error messages;
 * caller must not be holding ip6qlock.
 */
static void
frag6_icmp6_timeex_error(struct fq6_head *diq6)
{
        LCK_MTX_ASSERT(&ip6qlock, LCK_MTX_ASSERT_NOTOWNED);

        if (!MBUFQ_EMPTY(diq6)) {
                struct mbuf *m, *m_tmp;
                MBUFQ_FOREACH_SAFE(m, diq6, m_tmp) {
                        MBUFQ_REMOVE(diq6, m);
                        MBUFQ_NEXT(m) = NULL;
                        icmp6_error_flag(m, ICMP6_TIME_EXCEEDED,
                            ICMP6_TIME_EXCEED_REASSEMBLY, 0, 0);
                }
        }
}

/*
 * In RFC2460, fragment and reassembly rule 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 the consistency.
 *
 * fragment rule (p20):
 *      (2) A Fragment header containing:
 *      The Next Header value that identifies the first header of
 *      the Fragmentable Part of the original packet.
 *              -> next header field is same for all fragments
 *
 * reassembly rule (p21):
 *      The Next Header field of the last header of the Unfragmentable
 *      Part 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 - noone is going to
 * send different fragment with different next header field.
 *
 * additional note (p22):
 *      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)
{
#pragma unused(proto)
        struct mbuf *m = *mp, *t;
        struct ip6_hdr *ip6;
        struct ip6_frag *ip6f;
        struct ip6q *q6;
        struct ip6asfrag *af6, *ip6af, *af6dwn;
        int offset = *offp, nxt, i, next;
        int first_frag = 0;
        int fragoff, frgpartlen;        /* must be larger than u_int16_t */
        struct ifnet *dstifp = NULL;
        u_int8_t ecn, ecn0;
        uint32_t csum, csum_flags;
        struct fq6_head diq6;
        int locked = 0;

        VERIFY(m->m_flags & M_PKTHDR);

        MBUFQ_INIT(&diq6);      /* for deferred ICMP param problem errors */

        /* Expect 32-bit aligned data pointer on strict-align platforms */
        MBUF_STRICT_DATA_ALIGNMENT_CHECK_32(m);

        ip6 = mtod(m, struct ip6_hdr *);
        IP6_EXTHDR_CHECK(m, offset, sizeof(struct ip6_frag), goto done);
        ip6f = (struct ip6_frag *)((caddr_t)ip6 + offset);

#ifdef IN6_IFSTAT_STRICT
        /* find the destination interface of the packet. */
        if (m->m_pkthdr.pkt_flags & PKTF_IFAINFO) {
                uint32_t idx;

                if (ip6_getdstifaddr_info(m, &idx, NULL) == 0) {
                        if (idx > 0 && idx <= if_index) {
                                ifnet_head_lock_shared();
                                dstifp = ifindex2ifnet[idx];
                                ifnet_head_done();
                        }
                }
        }
#endif /* IN6_IFSTAT_STRICT */

        /* we are violating the spec, this may not be the dst interface */
        if (dstifp == NULL) {
                dstifp = m->m_pkthdr.rcvif;
        }

        /* jumbo payload can't 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);
                m = NULL;
                goto done;
        }

        /*
         * check whether fragment packet's fragment length is
         * multiple of 8 octets.
         * sizeof(struct ip6_frag) == 8
         * sizeof(struct ip6_hdr) = 40
         */
        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);
                m = NULL;
                goto done;
        }

        /* If ip6_maxfragpackets or ip6_maxfrags is 0, never accept fragments */
        if (ip6_maxfragpackets == 0 || ip6_maxfrags == 0) {
                ip6stat.ip6s_fragments++;
                ip6stat.ip6s_fragdropped++;
                in6_ifstat_inc(dstifp, ifs6_reass_fail);
                m_freem(m);
                m = NULL;
                goto done;
        }

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

        /*
         * RFC 6946: Handle "atomic" fragments (offset and m bit set to 0)
         * upfront, unrelated to any reassembly.  Just skip the fragment header.
         */
        if ((ip6f->ip6f_offlg & ~IP6F_RESERVED_MASK) == 0) {
                /*
                 * Mark packet as reassembled.
                 * In ICMPv6 processing, we drop certain
                 * NDP messages that are not expected to
                 * have fragment header based on recommendations
                 * against security vulnerability as described in
                 * RFC 6980.
                 * Treat atomic fragments as re-assembled packets as well.
                 */
                m->m_pkthdr.pkt_flags |= PKTF_REASSEMBLED;
                ip6stat.ip6s_atmfrag_rcvd++;
                in6_ifstat_inc(dstifp, ifs6_atmfrag_rcvd);
                *offp = offset;
                return ip6f->ip6f_nxt;
        }

        /*
         * Leverage partial checksum offload for simple UDP/IP fragments,
         * as that is the most common case.
         *
         * Perform 1's complement adjustment of octets that got included/
         * excluded in the hardware-calculated checksum value.  Also take
         * care of any trailing bytes and subtract out their partial sum.
         */
        if (ip6f->ip6f_nxt == IPPROTO_UDP &&
            offset == (sizeof(*ip6) + sizeof(*ip6f)) &&
            (m->m_pkthdr.csum_flags &
            (CSUM_DATA_VALID | CSUM_PARTIAL | CSUM_PSEUDO_HDR)) ==
            (CSUM_DATA_VALID | CSUM_PARTIAL)) {
                uint32_t start = m->m_pkthdr.csum_rx_start;
                uint32_t ip_len = (sizeof(*ip6) + ntohs(ip6->ip6_plen));
                int32_t trailer = (m_pktlen(m) - ip_len);
                uint32_t swbytes = (uint32_t)trailer;

                csum = m->m_pkthdr.csum_rx_val;

                ASSERT(trailer >= 0);
                if (start != offset || trailer != 0) {
                        uint16_t s = 0, d = 0;

                        if (IN6_IS_SCOPE_EMBED(&ip6->ip6_src)) {
                                s = ip6->ip6_src.s6_addr16[1];
                                ip6->ip6_src.s6_addr16[1] = 0;
                        }
                        if (IN6_IS_SCOPE_EMBED(&ip6->ip6_dst)) {
                                d = ip6->ip6_dst.s6_addr16[1];
                                ip6->ip6_dst.s6_addr16[1] = 0;
                        }

                        /* callee folds in sum */
                        csum = m_adj_sum16(m, start, offset,
                            (ip_len - offset), csum);
                        if (offset > start) {
                                swbytes += (offset - start);
                        } else {
                                swbytes += (start - offset);
                        }

                        if (IN6_IS_SCOPE_EMBED(&ip6->ip6_src)) {
                                ip6->ip6_src.s6_addr16[1] = s;
                        }
                        if (IN6_IS_SCOPE_EMBED(&ip6->ip6_dst)) {
                                ip6->ip6_dst.s6_addr16[1] = d;
                        }
                }
                csum_flags = m->m_pkthdr.csum_flags;

                if (swbytes != 0) {
                        udp_in6_cksum_stats(swbytes);
                }
                if (trailer != 0) {
                        m_adj(m, -trailer);
                }
        } else {
                csum = 0;
                csum_flags = 0;
        }

        /* Invalidate checksum */
        m->m_pkthdr.csum_flags &= ~CSUM_DATA_VALID;

        ip6stat.ip6s_fragments++;
        in6_ifstat_inc(dstifp, ifs6_reass_reqd);

        lck_mtx_lock(&ip6qlock);
        locked = 1;

        for (q6 = ip6q.ip6q_next; q6 != &ip6q; q6 = q6->ip6q_next) {
                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)) {
                        break;
                }
        }

        if (q6 == &ip6q) {
                /*
                 * the first fragment to arrive, create a reassembly queue.
                 */
                first_frag = 1;

                q6 = ip6q_alloc(M_DONTWAIT);
                if (q6 == NULL) {
                        goto dropfrag;
                }

                frag6_insque(q6, &ip6q);
                frag6_nfragpackets++;

                /* ip6q_nxt will be filled afterwards, from 1st fragment */
                q6->ip6q_down   = q6->ip6q_up = (struct ip6asfrag *)q6;
#ifdef notyet
                q6->ip6q_nxtp   = (u_char *)nxtp;
#endif
                q6->ip6q_ident  = ip6f->ip6f_ident;
                q6->ip6q_ttl    = IPV6_FRAGTTL;
                q6->ip6q_src    = ip6->ip6_src;
                q6->ip6q_dst    = ip6->ip6_dst;
                q6->ip6q_ecn    =
                    (ntohl(ip6->ip6_flow) >> 20) & IPTOS_ECN_MASK;
                q6->ip6q_unfrglen = -1; /* The 1st fragment has not arrived. */

                q6->ip6q_nfrag = 0;

                /*
                 * If the first fragment has valid checksum offload
                 * info, the rest of fragments are eligible as well.
                 */
                if (csum_flags != 0) {
                        q6->ip6q_csum = csum;
                        q6->ip6q_csum_flags = csum_flags;
                }
        }

        /*
         * If it's the 1st fragment, record the length of the
         * unfragmentable part and the next header of the fragment header.
         */
        fragoff = ntohs(ip6f->ip6f_offlg & IP6F_OFF_MASK);
        if (fragoff == 0) {
                q6->ip6q_unfrglen = offset - sizeof(struct ip6_hdr) -
                    sizeof(struct ip6_frag);
                q6->ip6q_nxt = ip6f->ip6f_nxt;
        }

        /*
         * Check that the reassembled packet would not exceed 65535 bytes
         * in size.
         * If it would exceed, discard the fragment and return an ICMP error.
         */
        frgpartlen = sizeof(struct ip6_hdr) + ntohs(ip6->ip6_plen) - offset;
        if (q6->ip6q_unfrglen >= 0) {
                /* The 1st fragment has already arrived. */
                if (q6->ip6q_unfrglen + fragoff + frgpartlen > IPV6_MAXPACKET) {
                        lck_mtx_unlock(&ip6qlock);
                        locked = 0;
                        icmp6_error(m, ICMP6_PARAM_PROB, ICMP6_PARAMPROB_HEADER,
                            offset - sizeof(struct ip6_frag) +
                            offsetof(struct ip6_frag, ip6f_offlg));
                        m = NULL;
                        goto done;
                }
        } else if (fragoff + frgpartlen > IPV6_MAXPACKET) {
                lck_mtx_unlock(&ip6qlock);
                locked = 0;
                icmp6_error(m, ICMP6_PARAM_PROB, ICMP6_PARAMPROB_HEADER,
                    offset - sizeof(struct ip6_frag) +
                    offsetof(struct ip6_frag, ip6f_offlg));
                m = NULL;
                goto done;
        }
        /*
         * If it's the first fragment, do the above check for each
         * fragment already stored in the reassembly queue.
         */
        if (fragoff == 0) {
                for (af6 = q6->ip6q_down; af6 != (struct ip6asfrag *)q6;
                    af6 = af6dwn) {
                        af6dwn = af6->ip6af_down;

                        if (q6->ip6q_unfrglen + af6->ip6af_off + af6->ip6af_frglen >
                            IPV6_MAXPACKET) {
                                struct mbuf *merr = IP6_REASS_MBUF(af6);
                                struct ip6_hdr *ip6err;
                                int erroff = af6->ip6af_offset;

                                /* dequeue the fragment. */
                                frag6_deq(af6);
                                ip6af_free(af6);

                                /* 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;

                                frag6_save_context(merr,
                                    erroff - sizeof(struct ip6_frag) +
                                    offsetof(struct ip6_frag, ip6f_offlg));

                                MBUFQ_ENQUEUE(&diq6, merr);
                        }
                }
        }

        ip6af = ip6af_alloc(M_DONTWAIT);
        if (ip6af == NULL) {
                goto dropfrag;
        }

        ip6af->ip6af_mff = ip6f->ip6f_offlg & IP6F_MORE_FRAG;
        ip6af->ip6af_off = fragoff;
        ip6af->ip6af_frglen = frgpartlen;
        ip6af->ip6af_offset = offset;
        IP6_REASS_MBUF(ip6af) = m;

        if (first_frag) {
                af6 = (struct ip6asfrag *)q6;
                goto insert;
        }

        /*
         * 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 = (ntohl(ip6->ip6_flow) >> 20) & IPTOS_ECN_MASK;
        ecn0 = q6->ip6q_ecn;
        if (ecn == IPTOS_ECN_CE) {
                if (ecn0 == IPTOS_ECN_NOTECT) {
                        ip6af_free(ip6af);
                        goto dropfrag;
                }
                if (ecn0 != IPTOS_ECN_CE) {
                        q6->ip6q_ecn = IPTOS_ECN_CE;
                }
        }
        if (ecn == IPTOS_ECN_NOTECT && ecn0 != IPTOS_ECN_NOTECT) {
                ip6af_free(ip6af);
                goto dropfrag;
        }

        /*
         * Find a segment which begins after this one does.
         */
        for (af6 = q6->ip6q_down; af6 != (struct ip6asfrag *)q6;
            af6 = af6->ip6af_down) {
                if (af6->ip6af_off > ip6af->ip6af_off) {
                        break;
                }
        }

#if 0
        /*
         * If there is a preceding segment, it may provide some of
         * our data already.  If so, drop the data from the incoming
         * segment.  If it provides all of our data, drop us.
         *
         * If some of the data is dropped from the preceding
         * segment, then it's checksum is invalidated.
         */
        if (af6->ip6af_up != (struct ip6asfrag *)q6) {
                i = af6->ip6af_up->ip6af_off + af6->ip6af_up->ip6af_frglen
                    - ip6af->ip6af_off;
                if (i > 0) {
                        if (i >= ip6af->ip6af_frglen) {
                                goto dropfrag;
                        }
                        m_adj(IP6_REASS_MBUF(ip6af), i);
                        q6->ip6q_csum_flags = 0;
                        ip6af->ip6af_off += i;
                        ip6af->ip6af_frglen -= i;
                }
        }

        /*
         * While we overlap succeeding segments trim them or,
         * if they are completely covered, dequeue them.
         */
        while (af6 != (struct ip6asfrag *)q6 &&
            ip6af->ip6af_off + ip6af->ip6af_frglen > af6->ip6af_off) {
                i = (ip6af->ip6af_off + ip6af->ip6af_frglen) - af6->ip6af_off;
                if (i < af6->ip6af_frglen) {
                        af6->ip6af_frglen -= i;
                        af6->ip6af_off += i;
                        m_adj(IP6_REASS_MBUF(af6), i);
                        q6->ip6q_csum_flags = 0;
                        break;
                }
                af6 = af6->ip6af_down;
                m_freem(IP6_REASS_MBUF(af6->ip6af_up));
                frag6_deq(af6->ip6af_up);
        }
#else
        /*
         * If the incoming framgent overlaps some existing fragments in
         * the reassembly queue, drop it, since it is dangerous to override
         * existing fragments from a security point of view.
         * We don't know which fragment is the bad guy - here we trust
         * fragment that came in earlier, with no real reason.
         *
         * Note: due to changes after disabling this part, mbuf passed to
         * m_adj() below now does not meet the requirement.
         */
        if (af6->ip6af_up != (struct ip6asfrag *)q6) {
                i = af6->ip6af_up->ip6af_off + af6->ip6af_up->ip6af_frglen
                    - ip6af->ip6af_off;
                if (i > 0) {
#if 0                           /* suppress the noisy log */
                        log(LOG_ERR, "%d bytes of a fragment from %s "
                            "overlaps the previous fragment\n",
                            i, ip6_sprintf(&q6->ip6q_src));
#endif
                        ip6af_free(ip6af);
                        goto dropfrag;
                }
        }
        if (af6 != (struct ip6asfrag *)q6) {
                i = (ip6af->ip6af_off + ip6af->ip6af_frglen) - af6->ip6af_off;
                if (i > 0) {
#if 0                           /* suppress the noisy log */
                        log(LOG_ERR, "%d bytes of a fragment from %s "
                            "overlaps the succeeding fragment",
                            i, ip6_sprintf(&q6->ip6q_src));
#endif
                        ip6af_free(ip6af);
                        goto dropfrag;
                }
        }
#endif

        /*
         * If this fragment contains similar checksum offload info
         * as that of the existing ones, accumulate checksum.  Otherwise,
         * invalidate checksum offload info for the entire datagram.
         */
        if (csum_flags != 0 && csum_flags == q6->ip6q_csum_flags) {
                q6->ip6q_csum += csum;
        } else if (q6->ip6q_csum_flags != 0) {
                q6->ip6q_csum_flags = 0;
        }

insert:

        /*
         * Stick new segment in its place;
         * check for complete reassembly.
         * Move to front of packet queue, as we are
         * the most recently active fragmented packet.
         */
        frag6_enq(ip6af, af6->ip6af_up);
        frag6_nfrags++;
        q6->ip6q_nfrag++;
#if 0 /* xxx */
        if (q6 != ip6q.ip6q_next) {
                frag6_remque(q6);
                frag6_insque(q6, &ip6q);
        }
#endif
        next = 0;
        for (af6 = q6->ip6q_down; af6 != (struct ip6asfrag *)q6;
            af6 = af6->ip6af_down) {
                if (af6->ip6af_off != next) {
                        lck_mtx_unlock(&ip6qlock);
                        locked = 0;
                        m = NULL;
                        goto done;
                }
                next += af6->ip6af_frglen;
        }
        if (af6->ip6af_up->ip6af_mff) {
                lck_mtx_unlock(&ip6qlock);
                locked = 0;
                m = NULL;
                goto done;
        }

        /*
         * Reassembly is complete; concatenate fragments.
         */
        ip6af = q6->ip6q_down;
        t = m = IP6_REASS_MBUF(ip6af);
        af6 = ip6af->ip6af_down;
        frag6_deq(ip6af);
        while (af6 != (struct ip6asfrag *)q6) {
                af6dwn = af6->ip6af_down;
                frag6_deq(af6);
                while (t->m_next) {
                        t = t->m_next;
                }
                t->m_next = IP6_REASS_MBUF(af6);
                m_adj(t->m_next, af6->ip6af_offset);
                ip6af_free(af6);
                af6 = af6dwn;
        }

        /*
         * Store partial hardware checksum info from the fragment queue;
         * the receive start offset is set to 40 bytes (see code at the
         * top of this routine.)
         */
        if (q6->ip6q_csum_flags != 0) {
                csum = q6->ip6q_csum;

                ADDCARRY(csum);

                m->m_pkthdr.csum_rx_val = csum;
                m->m_pkthdr.csum_rx_start = sizeof(struct ip6_hdr);
                m->m_pkthdr.csum_flags = q6->ip6q_csum_flags;
        } else if ((m->m_pkthdr.rcvif->if_flags & IFF_LOOPBACK) ||
            (m->m_pkthdr.pkt_flags & PKTF_LOOP)) {
                /* loopback checksums are always OK */
                m->m_pkthdr.csum_data = 0xffff;
                m->m_pkthdr.csum_flags = CSUM_DATA_VALID | CSUM_PSEUDO_HDR;
        }

        /* adjust offset to point where the original next header starts */
        offset = ip6af->ip6af_offset - sizeof(struct ip6_frag);
        ip6af_free(ip6af);
        ip6 = mtod(m, struct ip6_hdr *);
        ip6->ip6_plen = htons((u_short)next + offset - sizeof(struct ip6_hdr));
        ip6->ip6_src = q6->ip6q_src;
        ip6->ip6_dst = q6->ip6q_dst;
        if (q6->ip6q_ecn == IPTOS_ECN_CE) {
                ip6->ip6_flow |= htonl(IPTOS_ECN_CE << 20);
        }

        nxt = q6->ip6q_nxt;
#ifdef notyet
        *q6->ip6q_nxtp = (u_char)(nxt & 0xff);
#endif

        /* Delete frag6 header */
        if (m->m_len >= offset + sizeof(struct ip6_frag)) {
                /* This is the only possible case with !PULLDOWN_TEST */
                ovbcopy((caddr_t)ip6, (caddr_t)ip6 + sizeof(struct ip6_frag),
                    offset);
                m->m_data += sizeof(struct ip6_frag);
                m->m_len -= sizeof(struct ip6_frag);
        } else {
                /* this comes with no copy if the boundary is on cluster */
                if ((t = m_split(m, offset, M_DONTWAIT)) == NULL) {
                        frag6_remque(q6);
                        frag6_nfragpackets--;
                        frag6_nfrags -= q6->ip6q_nfrag;
                        ip6q_free(q6);
                        goto dropfrag;
                }
                m_adj(t, sizeof(struct ip6_frag));
                m_cat(m, t);
        }

        /*
         * Store NXT to the original.
         */
        {
                char *prvnxtp = ip6_get_prevhdr(m, offset); /* XXX */
                *prvnxtp = nxt;
        }

        frag6_remque(q6);
        frag6_nfragpackets--;
        frag6_nfrags -= q6->ip6q_nfrag;
        ip6q_free(q6);

        if (m->m_flags & M_PKTHDR) {    /* Isn't it always true? */
                m_fixhdr(m);
                /*
                 * Mark packet as reassembled
                 * In ICMPv6 processing, we drop certain
                 * NDP messages that are not expected to
                 * have fragment header based on recommendations
                 * against security vulnerability as described in
                 * RFC 6980.
                 */
                m->m_pkthdr.pkt_flags |= PKTF_REASSEMBLED;
        }
        ip6stat.ip6s_reassembled++;

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

        /* arm the purge timer if not already and if there's work to do */
        frag6_sched_timeout();
        lck_mtx_unlock(&ip6qlock);
        in6_ifstat_inc(dstifp, ifs6_reass_ok);
        frag6_icmp6_paramprob_error(&diq6);
        VERIFY(MBUFQ_EMPTY(&diq6));
        return nxt;

done:
        VERIFY(m == NULL);
        if (!locked) {
                if (frag6_nfragpackets == 0) {
                        frag6_icmp6_paramprob_error(&diq6);
                        VERIFY(MBUFQ_EMPTY(&diq6));
                        return IPPROTO_DONE;
                }
                lck_mtx_lock(&ip6qlock);
        }
        /* arm the purge timer if not already and if there's work to do */
        frag6_sched_timeout();
        lck_mtx_unlock(&ip6qlock);
        frag6_icmp6_paramprob_error(&diq6);
        VERIFY(MBUFQ_EMPTY(&diq6));
        return IPPROTO_DONE;

dropfrag:
        ip6stat.ip6s_fragdropped++;
        /* arm the purge timer if not already and if there's work to do */
        frag6_sched_timeout();
        lck_mtx_unlock(&ip6qlock);
        in6_ifstat_inc(dstifp, ifs6_reass_fail);
        m_freem(m);
        frag6_icmp6_paramprob_error(&diq6);
        VERIFY(MBUFQ_EMPTY(&diq6));
        return IPPROTO_DONE;
}

/*
 * Free a fragment reassembly header and all
 * associated datagrams.
 */
void
frag6_freef(struct ip6q *q6, struct fq6_head *dfq6, struct fq6_head *diq6)
{
        struct ip6asfrag *af6, *down6;

        LCK_MTX_ASSERT(&ip6qlock, LCK_MTX_ASSERT_OWNED);

        for (af6 = q6->ip6q_down; af6 != (struct ip6asfrag *)q6;
            af6 = down6) {
                struct mbuf *m = IP6_REASS_MBUF(af6);

                down6 = af6->ip6af_down;
                frag6_deq(af6);

                /*
                 * Return ICMP time exceeded error for the 1st fragment.
                 * Just free other fragments.
                 */
                if (af6->ip6af_off == 0) {
                        struct ip6_hdr *ip6;

                        /* 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;

                        MBUFQ_ENQUEUE(diq6, m);
                } else {
                        MBUFQ_ENQUEUE(dfq6, m);
                }
                ip6af_free(af6);
        }
        frag6_remque(q6);
        frag6_nfragpackets--;
        frag6_nfrags -= q6->ip6q_nfrag;
        ip6q_free(q6);
}

/*
 * Put an ip fragment on a reassembly chain.
 * Like insque, but pointers in middle of structure.
 */
void
frag6_enq(struct ip6asfrag *af6, struct ip6asfrag *up6)
{
        LCK_MTX_ASSERT(&ip6qlock, LCK_MTX_ASSERT_OWNED);

        af6->ip6af_up = up6;
        af6->ip6af_down = up6->ip6af_down;
        up6->ip6af_down->ip6af_up = af6;
        up6->ip6af_down = af6;
}

/*
 * To frag6_enq as remque is to insque.
 */
void
frag6_deq(struct ip6asfrag *af6)
{
        LCK_MTX_ASSERT(&ip6qlock, LCK_MTX_ASSERT_OWNED);

        af6->ip6af_up->ip6af_down = af6->ip6af_down;
        af6->ip6af_down->ip6af_up = af6->ip6af_up;
}

void
frag6_insque(struct ip6q *new, struct ip6q *old)
{
        LCK_MTX_ASSERT(&ip6qlock, LCK_MTX_ASSERT_OWNED);

        new->ip6q_prev = old;
        new->ip6q_next = old->ip6q_next;
        old->ip6q_next->ip6q_prev = new;
        old->ip6q_next = new;
}

void
frag6_remque(struct ip6q *p6)
{
        LCK_MTX_ASSERT(&ip6qlock, LCK_MTX_ASSERT_OWNED);

        p6->ip6q_prev->ip6q_next = p6->ip6q_next;
        p6->ip6q_next->ip6q_prev = p6->ip6q_prev;
}

/*
 * IPv6 reassembling timer processing;
 * if a timer expires on a reassembly
 * queue, discard it.
 */
static void
frag6_timeout(void *arg)
{
#pragma unused(arg)
        struct fq6_head dfq6, diq6;
        struct ip6q *q6;

        MBUFQ_INIT(&dfq6);      /* for deferred frees */
        MBUFQ_INIT(&diq6);      /* for deferred ICMP time exceeded errors */

        /*
         * Update coarse-grained networking timestamp (in sec.); the idea
         * is to piggy-back on the timeout callout to update the counter
         * returnable via net_uptime().
         */
        net_update_uptime();

        lck_mtx_lock(&ip6qlock);
        q6 = ip6q.ip6q_next;
        if (q6) {
                while (q6 != &ip6q) {
                        --q6->ip6q_ttl;
                        q6 = q6->ip6q_next;
                        if (q6->ip6q_prev->ip6q_ttl == 0) {
                                ip6stat.ip6s_fragtimeout++;
                                /* XXX in6_ifstat_inc(ifp, ifs6_reass_fail) */
                                frag6_freef(q6->ip6q_prev, &dfq6, &diq6);
                        }
                }
        }
        /*
         * 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.
         */
        if (ip6_maxfragpackets >= 0) {
                while (frag6_nfragpackets > (unsigned)ip6_maxfragpackets &&
                    ip6q.ip6q_prev) {
                        ip6stat.ip6s_fragoverflow++;
                        /* XXX in6_ifstat_inc(ifp, ifs6_reass_fail) */
                        frag6_freef(ip6q.ip6q_prev, &dfq6, &diq6);
                }
        }
        /* re-arm the purge timer if there's work to do */
        frag6_timeout_run = 0;
        frag6_sched_timeout();
        lck_mtx_unlock(&ip6qlock);

        /* free fragments that need to be freed */
        if (!MBUFQ_EMPTY(&dfq6)) {
                MBUFQ_DRAIN(&dfq6);
        }

        frag6_icmp6_timeex_error(&diq6);

        VERIFY(MBUFQ_EMPTY(&dfq6));
        VERIFY(MBUFQ_EMPTY(&diq6));
}

static void
frag6_sched_timeout(void)
{
        LCK_MTX_ASSERT(&ip6qlock, LCK_MTX_ASSERT_OWNED);

        if (!frag6_timeout_run && frag6_nfragpackets > 0) {
                frag6_timeout_run = 1;
                timeout(frag6_timeout, NULL, hz);
        }
}

/*
 * Drain off all datagram fragments.
 */
void
frag6_drain(void)
{
        struct fq6_head dfq6, diq6;

        MBUFQ_INIT(&dfq6);      /* for deferred frees */
        MBUFQ_INIT(&diq6);      /* for deferred ICMP time exceeded errors */

        lck_mtx_lock(&ip6qlock);
        while (ip6q.ip6q_next != &ip6q) {
                ip6stat.ip6s_fragdropped++;
                /* XXX in6_ifstat_inc(ifp, ifs6_reass_fail) */
                frag6_freef(ip6q.ip6q_next, &dfq6, &diq6);
        }
        lck_mtx_unlock(&ip6qlock);

        /* free fragments that need to be freed */
        if (!MBUFQ_EMPTY(&dfq6)) {
                MBUFQ_DRAIN(&dfq6);
        }

        frag6_icmp6_timeex_error(&diq6);

        VERIFY(MBUFQ_EMPTY(&dfq6));
        VERIFY(MBUFQ_EMPTY(&diq6));
}

static struct ip6q *
ip6q_alloc(int how)
{
        struct mbuf *t;
        struct ip6q *q6;

        /*
         * See comments in ip6q_updateparams().  Keep the count separate
         * from frag6_nfragpackets since the latter represents the elements
         * already in the reassembly queues.
         */
        if (ip6q_limit > 0 && ip6q_count > ip6q_limit) {
                return NULL;
        }

        t = m_get(how, MT_FTABLE);
        if (t != NULL) {
                atomic_add_32(&ip6q_count, 1);
                q6 = mtod(t, struct ip6q *);
                bzero(q6, sizeof(*q6));
        } else {
                q6 = NULL;
        }
        return q6;
}

static void
ip6q_free(struct ip6q *q6)
{
        (void) m_free(dtom(q6));
        atomic_add_32(&ip6q_count, -1);
}

static struct ip6asfrag *
ip6af_alloc(int how)
{
        struct mbuf *t;
        struct ip6asfrag *af6;

        /*
         * See comments in ip6q_updateparams().  Keep the count separate
         * from frag6_nfrags since the latter represents the elements
         * already in the reassembly queues.
         */
        if (ip6af_limit > 0 && ip6af_count > ip6af_limit) {
                return NULL;
        }

        t = m_get(how, MT_FTABLE);
        if (t != NULL) {
                atomic_add_32(&ip6af_count, 1);
                af6 = mtod(t, struct ip6asfrag *);
                bzero(af6, sizeof(*af6));
        } else {
                af6 = NULL;
        }
        return af6;
}

static void
ip6af_free(struct ip6asfrag *af6)
{
        (void) m_free(dtom(af6));
        atomic_add_32(&ip6af_count, -1);
}

static void
ip6q_updateparams(void)
{
        LCK_MTX_ASSERT(&ip6qlock, LCK_MTX_ASSERT_OWNED);
        /*
         * -1 for unlimited allocation.
         */
        if (ip6_maxfragpackets < 0) {
                ip6q_limit = 0;
        }
        if (ip6_maxfrags < 0) {
                ip6af_limit = 0;
        }
        /*
         * Positive number for specific bound.
         */
        if (ip6_maxfragpackets > 0) {
                ip6q_limit = ip6_maxfragpackets;
        }
        if (ip6_maxfrags > 0) {
                ip6af_limit = ip6_maxfrags;
        }
        /*
         * Zero specifies no further fragment queue allocation -- set the
         * bound very low, but rely on implementation elsewhere to actually
         * prevent allocation and reclaim current queues.
         */
        if (ip6_maxfragpackets == 0) {
                ip6q_limit = 1;
        }
        if (ip6_maxfrags == 0) {
                ip6af_limit = 1;
        }
        /*
         * Arm the purge timer if not already and if there's work to do
         */
        frag6_sched_timeout();
}

static int
sysctl_maxfragpackets SYSCTL_HANDLER_ARGS
{
#pragma unused(arg1, arg2)
        int error, i;

        lck_mtx_lock(&ip6qlock);
        i = ip6_maxfragpackets;
        error = sysctl_handle_int(oidp, &i, 0, req);
        if (error || req->newptr == USER_ADDR_NULL) {
                goto done;
        }
        /* impose bounds */
        if (i < -1 || i > (nmbclusters / 4)) {
                error = EINVAL;
                goto done;
        }
        ip6_maxfragpackets = i;
        ip6q_updateparams();
done:
        lck_mtx_unlock(&ip6qlock);
        return error;
}

static int
sysctl_maxfrags SYSCTL_HANDLER_ARGS
{
#pragma unused(arg1, arg2)
        int error, i;

        lck_mtx_lock(&ip6qlock);
        i = ip6_maxfrags;
        error = sysctl_handle_int(oidp, &i, 0, req);
        if (error || req->newptr == USER_ADDR_NULL) {
                goto done;
        }
        /* impose bounds */
        if (i < -1 || i > (nmbclusters / 4)) {
                error = EINVAL;
                goto done;
        }
        ip6_maxfrags = i;
        ip6q_updateparams();    /* see if we need to arm timer */
done:
        lck_mtx_unlock(&ip6qlock);
        return error;
}