[apple/xnu.git] / bsd / netinet / ip_input.c

/*
 * Copyright (c) 2000-2013 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
 * limitations under the License.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
 */
/*
 * 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. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. 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
 */
/*
 * NOTICE: This file was modified by SPARTA, Inc. in 2007 to introduce
 * support for mandatory and extensible security protections.  This notice
 * is included in support of clause 2.2 (b) of the Apple Public License,
 * Version 2.0.
 */

#define _IP_VHL

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/mbuf.h>
#include <sys/malloc.h>
#include <sys/domain.h>
#include <sys/protosw.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <sys/kernel.h>
#include <sys/syslog.h>
#include <sys/sysctl.h>
#include <sys/mcache.h>
#include <sys/socketvar.h>
#include <sys/kdebug.h>
#include <mach/mach_time.h>
#include <mach/sdt.h>

#include <machine/endian.h>
#include <dev/random/randomdev.h>

#include <kern/queue.h>
#include <kern/locks.h>
#include <libkern/OSAtomic.h>

#include <pexpert/pexpert.h>

#include <net/if.h>
#include <net/if_var.h>
#include <net/if_dl.h>
#include <net/route.h>
#include <net/kpi_protocol.h>
#include <net/ntstat.h>
#include <net/dlil.h>
#include <net/classq/classq.h>
#if PF
#include <net/pfvar.h>
#endif /* PF */

#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/in_var.h>
#include <netinet/in_arp.h>
#include <netinet/ip.h>
#include <netinet/in_pcb.h>
#include <netinet/ip_var.h>
#include <netinet/ip_icmp.h>
#include <netinet/ip_fw.h>
#include <netinet/ip_divert.h>
#include <netinet/kpi_ipfilter_var.h>
#include <netinet/udp.h>
#include <netinet/udp_var.h>
#include <netinet/bootp.h>
#include <netinet/lro_ext.h>

#if DUMMYNET
#include <netinet/ip_dummynet.h>
#endif /* DUMMYNET */

#if CONFIG_MACF_NET
#include <security/mac_framework.h>
#endif /* CONFIG_MACF_NET */

#if IPSEC
#include <netinet6/ipsec.h>
#include <netkey/key.h>
#endif /* IPSEC */

#define DBG_LAYER_BEG           NETDBG_CODE(DBG_NETIP, 0)
#define DBG_LAYER_END           NETDBG_CODE(DBG_NETIP, 2)
#define DBG_FNC_IP_INPUT        NETDBG_CODE(DBG_NETIP, (2 << 8))

#if IPSEC
extern int ipsec_bypass;
extern lck_mtx_t *sadb_mutex;

lck_grp_t       *sadb_stat_mutex_grp;
lck_grp_attr_t  *sadb_stat_mutex_grp_attr;
lck_attr_t      *sadb_stat_mutex_attr;
decl_lck_mtx_data(, sadb_stat_mutex_data);
lck_mtx_t       *sadb_stat_mutex = &sadb_stat_mutex_data;
#endif /* IPSEC */

MBUFQ_HEAD(fq_head);

static int frag_timeout_run;            /* frag timer is scheduled to run */
static void frag_timeout(void *);
static void frag_sched_timeout(void);

static struct ipq *ipq_alloc(int);
static void ipq_free(struct ipq *);
static void ipq_updateparams(void);

decl_lck_mtx_data(static, ipqlock);
static lck_attr_t       *ipqlock_attr;
static lck_grp_t        *ipqlock_grp;
static lck_grp_attr_t   *ipqlock_grp_attr;

/* Packet reassembly stuff */
#define IPREASS_NHASH_LOG2      6
#define IPREASS_NHASH           (1 << IPREASS_NHASH_LOG2)
#define IPREASS_HMASK           (IPREASS_NHASH - 1)
#define IPREASS_HASH(x, y) \
        (((((x) & 0xF) | ((((x) >> 8) & 0xF) << 4)) ^ (y)) & IPREASS_HMASK)

/* IP fragment reassembly queues (protected by ipqlock) */
static TAILQ_HEAD(ipqhead, ipq) ipq[IPREASS_NHASH]; /* ip reassembly queues */
static int maxnipq;                     /* max packets in reass queues */
static u_int32_t maxfragsperpacket;     /* max frags/packet in reass queues */
static u_int32_t nipq;                  /* # of packets in reass queues */
static u_int32_t ipq_limit;             /* ipq allocation limit */
static u_int32_t ipq_count;             /* current # of allocated ipq's */

static int sysctl_ipforwarding SYSCTL_HANDLER_ARGS;
static int sysctl_maxnipq SYSCTL_HANDLER_ARGS;
static int sysctl_maxfragsperpacket SYSCTL_HANDLER_ARGS;

int ipforwarding = 0;
SYSCTL_PROC(_net_inet_ip, IPCTL_FORWARDING, forwarding,
        CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_LOCKED, &ipforwarding, 0,
        sysctl_ipforwarding, "I", "Enable IP forwarding between interfaces");

static int ipsendredirects = 1; /* XXX */
SYSCTL_INT(_net_inet_ip, IPCTL_SENDREDIRECTS, redirect,
        CTLFLAG_RW | CTLFLAG_LOCKED, &ipsendredirects, 0,
        "Enable sending IP redirects");

int ip_defttl = IPDEFTTL;
SYSCTL_INT(_net_inet_ip, IPCTL_DEFTTL, ttl, CTLFLAG_RW | CTLFLAG_LOCKED,
        &ip_defttl, 0, "Maximum TTL on IP packets");

static int ip_dosourceroute = 0;
SYSCTL_INT(_net_inet_ip, IPCTL_SOURCEROUTE, sourceroute,
        CTLFLAG_RW | CTLFLAG_LOCKED, &ip_dosourceroute, 0,
        "Enable forwarding source routed IP packets");

static int ip_acceptsourceroute = 0;
SYSCTL_INT(_net_inet_ip, IPCTL_ACCEPTSOURCEROUTE, accept_sourceroute,
        CTLFLAG_RW | CTLFLAG_LOCKED, &ip_acceptsourceroute, 0,
        "Enable accepting source routed IP packets");

static int ip_sendsourcequench = 0;
SYSCTL_INT(_net_inet_ip, OID_AUTO, sendsourcequench,
        CTLFLAG_RW | CTLFLAG_LOCKED, &ip_sendsourcequench, 0,
        "Enable the transmission of source quench packets");

SYSCTL_PROC(_net_inet_ip, OID_AUTO, maxfragpackets,
        CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_LOCKED, &maxnipq, 0, sysctl_maxnipq,
        "I", "Maximum number of IPv4 fragment reassembly queue entries");

SYSCTL_UINT(_net_inet_ip, OID_AUTO, fragpackets, CTLFLAG_RD | CTLFLAG_LOCKED,
        &nipq, 0, "Current number of IPv4 fragment reassembly queue entries");

SYSCTL_PROC(_net_inet_ip, OID_AUTO, maxfragsperpacket,
        CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_LOCKED, &maxfragsperpacket, 0,
        sysctl_maxfragsperpacket, "I",
        "Maximum number of IPv4 fragments allowed per packet");

int ip_doscopedroute = 1;
SYSCTL_INT(_net_inet_ip, OID_AUTO, scopedroute, CTLFLAG_RD | CTLFLAG_LOCKED,
        &ip_doscopedroute, 0, "Enable IPv4 scoped routing");

static uint32_t ip_adj_clear_hwcksum = 0;
SYSCTL_UINT(_net_inet_ip, OID_AUTO, adj_clear_hwcksum,
        CTLFLAG_RW | CTLFLAG_LOCKED, &ip_adj_clear_hwcksum, 0,
        "Invalidate hwcksum info when adjusting length");

/*
 * XXX - Setting ip_checkinterface mostly implements the receive side of
 * the Strong ES model described in RFC 1122, but since the routing table
 * and transmit implementation do not implement the Strong ES model,
 * setting this to 1 results in an odd hybrid.
 *
 * XXX - ip_checkinterface currently must be disabled if you use ipnat
 * to translate the destination address to another local interface.
 *
 * XXX - ip_checkinterface must be disabled if you add IP aliases
 * to the loopback interface instead of the interface where the
 * packets for those addresses are received.
 */
static int ip_checkinterface = 0;
SYSCTL_INT(_net_inet_ip, OID_AUTO, check_interface, CTLFLAG_RW | CTLFLAG_LOCKED,
        &ip_checkinterface, 0, "Verify packet arrives on correct interface");

#if DIAGNOSTIC
static int ipprintfs = 0;
#endif

struct protosw *ip_protox[IPPROTO_MAX];

static lck_grp_attr_t   *in_ifaddr_rwlock_grp_attr;
static lck_grp_t        *in_ifaddr_rwlock_grp;
static lck_attr_t       *in_ifaddr_rwlock_attr;
decl_lck_rw_data(, in_ifaddr_rwlock_data);
lck_rw_t                *in_ifaddr_rwlock = &in_ifaddr_rwlock_data;

/* Protected by in_ifaddr_rwlock */
struct in_ifaddrhead in_ifaddrhead;             /* first inet address */
struct in_ifaddrhashhead *in_ifaddrhashtbl;     /* inet addr hash table  */

#define INADDR_NHASH    61
static u_int32_t inaddr_nhash;                  /* hash table size */
static u_int32_t inaddr_hashp;                  /* next largest prime */

static int ip_getstat SYSCTL_HANDLER_ARGS;
struct ipstat ipstat;
SYSCTL_PROC(_net_inet_ip, IPCTL_STATS, stats,
        CTLTYPE_STRUCT | CTLFLAG_RD | CTLFLAG_LOCKED,
        0, 0, ip_getstat, "S,ipstat",
        "IP statistics (struct ipstat, netinet/ip_var.h)");

#if IPCTL_DEFMTU
SYSCTL_INT(_net_inet_ip, IPCTL_DEFMTU, mtu, CTLFLAG_RW | CTLFLAG_LOCKED,
        &ip_mtu, 0, "Default MTU");
#endif /* IPCTL_DEFMTU */

#if IPSTEALTH
static int      ipstealth = 0;
SYSCTL_INT(_net_inet_ip, OID_AUTO, stealth, CTLFLAG_RW | CTLFLAG_LOCKED,
        &ipstealth, 0, "");
#endif /* IPSTEALTH */

/* Firewall hooks */
#if IPFIREWALL
ip_fw_chk_t *ip_fw_chk_ptr;
int fw_enable = 1;
int fw_bypass = 1;
int fw_one_pass = 0;
#endif /* IPFIREWALL */

#if DUMMYNET
ip_dn_io_t *ip_dn_io_ptr;
#endif /* DUMMYNET */

SYSCTL_NODE(_net_inet_ip, OID_AUTO, linklocal,
        CTLFLAG_RW | CTLFLAG_LOCKED, 0, "link local");

struct ip_linklocal_stat ip_linklocal_stat;
SYSCTL_STRUCT(_net_inet_ip_linklocal, OID_AUTO, stat,
        CTLFLAG_RD | CTLFLAG_LOCKED, &ip_linklocal_stat, ip_linklocal_stat,
        "Number of link local packets with TTL less than 255");

SYSCTL_NODE(_net_inet_ip_linklocal, OID_AUTO, in,
        CTLFLAG_RW | CTLFLAG_LOCKED, 0, "link local input");

int ip_linklocal_in_allowbadttl = 1;
SYSCTL_INT(_net_inet_ip_linklocal_in, OID_AUTO, allowbadttl,
        CTLFLAG_RW | CTLFLAG_LOCKED, &ip_linklocal_in_allowbadttl, 0,
        "Allow incoming link local packets with TTL less than 255");


/*
 * We need to save the IP options in case a protocol wants to respond
 * to an incoming packet over the same route if the packet got here
 * using IP source routing.  This allows connection establishment and
 * maintenance when the remote end is on a network that is not known
 * to us.
 */
static int      ip_nhops = 0;
static  struct ip_srcrt {
        struct  in_addr dst;                    /* final destination */
        char    nop;                            /* one NOP to align */
        char    srcopt[IPOPT_OFFSET + 1];       /* OPTVAL, OLEN and OFFSET */
        struct  in_addr route[MAX_IPOPTLEN / sizeof (struct in_addr)];
} ip_srcrt;

static void in_ifaddrhashtbl_init(void);
static void save_rte(u_char *, struct in_addr);
static int ip_dooptions(struct mbuf *, int, struct sockaddr_in *);
static void ip_forward(struct mbuf *, int, struct sockaddr_in *);
static void frag_freef(struct ipqhead *, struct ipq *);
#if IPDIVERT
#ifdef IPDIVERT_44
static struct mbuf *ip_reass(struct mbuf *, u_int32_t *, u_int16_t *);
#else /* !IPDIVERT_44 */
static struct mbuf *ip_reass(struct mbuf *, u_int16_t *, u_int16_t *);
#endif /* !IPDIVERT_44 */
#else /* !IPDIVERT */
static struct mbuf *ip_reass(struct mbuf *);
#endif /* !IPDIVERT */
static void ip_fwd_route_copyout(struct ifnet *, struct route *);
static void ip_fwd_route_copyin(struct ifnet *, struct route *);
static inline u_short ip_cksum(struct mbuf *, int);

int ip_use_randomid = 1;
SYSCTL_INT(_net_inet_ip, OID_AUTO, random_id, CTLFLAG_RW | CTLFLAG_LOCKED,
        &ip_use_randomid, 0, "Randomize IP packets IDs");

/*
 * On platforms which require strict alignment (currently for anything but
 * i386 or x86_64), check if the IP header pointer is 32-bit aligned; if not,
 * copy the contents of the mbuf chain into a new chain, and free the original
 * one.  Create some head room in the first mbuf of the new chain, in case
 * it's needed later on.
 */
#if defined(__i386__) || defined(__x86_64__)
#define IP_HDR_ALIGNMENT_FIXUP(_m, _ifp, _action) do { } while (0)
#else /* !__i386__ && !__x86_64__ */
#define IP_HDR_ALIGNMENT_FIXUP(_m, _ifp, _action) do {                  \
        if (!IP_HDR_ALIGNED_P(mtod(_m, caddr_t))) {                     \
                struct mbuf *_n;                                        \
                struct ifnet *__ifp = (_ifp);                           \
                atomic_add_64(&(__ifp)->if_alignerrs, 1);               \
                if (((_m)->m_flags & M_PKTHDR) &&                       \
                    (_m)->m_pkthdr.pkt_hdr != NULL)                     \
                        (_m)->m_pkthdr.pkt_hdr = NULL;                  \
                _n = m_defrag_offset(_m, max_linkhdr, M_NOWAIT);        \
                if (_n == NULL) {                                       \
                        atomic_add_32(&ipstat.ips_toosmall, 1);         \
                        m_freem(_m);                                    \
                        (_m) = NULL;                                    \
                        _action;                                        \
                } else {                                                \
                        VERIFY(_n != (_m));                             \
                        (_m) = _n;                                      \
                }                                                       \
        }                                                               \
} while (0)
#endif /* !__i386__ && !__x86_64__ */

/*
 * GRE input handler function, settable via ip_gre_register_input() for PPTP.
 */
static gre_input_func_t gre_input_func;

/*
 * IP initialization: fill in IP protocol switch table.
 * All protocols not implemented in kernel go to raw IP protocol handler.
 */
void
ip_init(struct protosw *pp, struct domain *dp)
{
        static int ip_initialized = 0;
        struct protosw *pr;
        struct timeval tv;
        int i;

        domain_proto_mtx_lock_assert_held();
        VERIFY((pp->pr_flags & (PR_INITIALIZED|PR_ATTACHED)) == PR_ATTACHED);

        /* ipq_alloc() uses mbufs for IP fragment queue structures */
        _CASSERT(sizeof (struct ipq) <= _MLEN);

        /*
         * Some ioctls (e.g. SIOCAIFADDR) use ifaliasreq struct, which is
         * interchangeable with in_aliasreq; they must have the same size.
         */
        _CASSERT(sizeof (struct ifaliasreq) == sizeof (struct in_aliasreq));

        if (ip_initialized)
                return;
        ip_initialized = 1;

        PE_parse_boot_argn("net.inet.ip.scopedroute",
            &ip_doscopedroute, sizeof (ip_doscopedroute));

        in_ifaddr_init();

        in_ifaddr_rwlock_grp_attr = lck_grp_attr_alloc_init();
        in_ifaddr_rwlock_grp = lck_grp_alloc_init("in_ifaddr_rwlock",
            in_ifaddr_rwlock_grp_attr);
        in_ifaddr_rwlock_attr = lck_attr_alloc_init();
        lck_rw_init(in_ifaddr_rwlock, in_ifaddr_rwlock_grp,
            in_ifaddr_rwlock_attr);

        TAILQ_INIT(&in_ifaddrhead);
        in_ifaddrhashtbl_init();

        ip_moptions_init();

        pr = pffindproto_locked(PF_INET, IPPROTO_RAW, SOCK_RAW);
        if (pr == NULL) {
                panic("%s: Unable to find [PF_INET,IPPROTO_RAW,SOCK_RAW]\n",
                    __func__);
                /* NOTREACHED */
        }

        /* Initialize the entire ip_protox[] array to IPPROTO_RAW. */
        for (i = 0; i < IPPROTO_MAX; i++)
                ip_protox[i] = pr;
        /*
         * Cycle through IP protocols and put them into the appropriate place
         * in ip_protox[], skipping protocols IPPROTO_{IP,RAW}.
         */
        VERIFY(dp == inetdomain && dp->dom_family == PF_INET);
        TAILQ_FOREACH(pr, &dp->dom_protosw, pr_entry) {
                VERIFY(pr->pr_domain == dp);
                if (pr->pr_protocol != 0 && pr->pr_protocol != IPPROTO_RAW) {
                        /* Be careful to only index valid IP protocols. */
                        if (pr->pr_protocol < IPPROTO_MAX)
                                ip_protox[pr->pr_protocol] = pr;
                }
        }

        /* IP fragment reassembly queue lock */
        ipqlock_grp_attr  = lck_grp_attr_alloc_init();
        ipqlock_grp = lck_grp_alloc_init("ipqlock", ipqlock_grp_attr);
        ipqlock_attr = lck_attr_alloc_init();
        lck_mtx_init(&ipqlock, ipqlock_grp, ipqlock_attr);

        lck_mtx_lock(&ipqlock);
        /* Initialize IP reassembly queue. */
        for (i = 0; i < IPREASS_NHASH; i++)
                TAILQ_INIT(&ipq[i]);

        maxnipq = nmbclusters / 32;
        maxfragsperpacket = 128; /* enough for 64k in 512 byte fragments */
        ipq_updateparams();
        lck_mtx_unlock(&ipqlock);

        getmicrotime(&tv);
        ip_id = RandomULong() ^ tv.tv_usec;
        ip_initid();

        ipf_init();

#if IPSEC
        sadb_stat_mutex_grp_attr = lck_grp_attr_alloc_init();
        sadb_stat_mutex_grp = lck_grp_alloc_init("sadb_stat",
            sadb_stat_mutex_grp_attr);
        sadb_stat_mutex_attr = lck_attr_alloc_init();
        lck_mtx_init(sadb_stat_mutex, sadb_stat_mutex_grp,
            sadb_stat_mutex_attr);

#endif
        arp_init();
}

/*
 * Initialize IPv4 source address hash table.
 */
static void
in_ifaddrhashtbl_init(void)
{
        int i, k, p;

        if (in_ifaddrhashtbl != NULL)
                return;

        PE_parse_boot_argn("inaddr_nhash", &inaddr_nhash,
            sizeof (inaddr_nhash));
        if (inaddr_nhash == 0)
                inaddr_nhash = INADDR_NHASH;

        MALLOC(in_ifaddrhashtbl, struct in_ifaddrhashhead *,
            inaddr_nhash * sizeof (*in_ifaddrhashtbl),
            M_IFADDR, M_WAITOK | M_ZERO);
        if (in_ifaddrhashtbl == NULL)
                panic("in_ifaddrhashtbl_init allocation failed");

        /*
         * Generate the next largest prime greater than inaddr_nhash.
         */
        k = (inaddr_nhash % 2 == 0) ? inaddr_nhash + 1 : inaddr_nhash + 2;
        for (;;) {
                p = 1;
                for (i = 3; i * i <= k; i += 2) {
                        if (k % i == 0)
                                p = 0;
                }
                if (p == 1)
                        break;
                k += 2;
        }
        inaddr_hashp = k;
}

u_int32_t
inaddr_hashval(u_int32_t key)
{
        /*
         * The hash index is the computed prime times the key modulo
         * the hash size, as documented in "Introduction to Algorithms"
         * (Cormen, Leiserson, Rivest).
         */
        if (inaddr_nhash > 1)
                return ((key * inaddr_hashp) % inaddr_nhash);
        else
                return (0);
}

void
ip_proto_dispatch_in_wrapper(struct mbuf *m, int hlen, u_int8_t proto)
{
        ip_proto_dispatch_in(m, hlen, proto, 0);
}

__private_extern__ void
ip_proto_dispatch_in(struct mbuf *m, int hlen, u_int8_t proto,
    ipfilter_t inject_ipfref)
{
        struct ipfilter *filter;
        int seen = (inject_ipfref == NULL);
        int     changed_header = 0;
        struct ip *ip;
        void (*pr_input)(struct mbuf *, int len);

        if (!TAILQ_EMPTY(&ipv4_filters)) {
                ipf_ref();
                TAILQ_FOREACH(filter, &ipv4_filters, ipf_link) {
                        if (seen == 0) {
                                if ((struct ipfilter *)inject_ipfref == filter)
                                        seen = 1;
                        } else if (filter->ipf_filter.ipf_input) {
                                errno_t result;

                                if (changed_header == 0) {
                                        /*
                                         * Perform IP header alignment fixup,
                                         * if needed, before passing packet
                                         * into filter(s).
                                         */
                                        IP_HDR_ALIGNMENT_FIXUP(m,
                                            m->m_pkthdr.rcvif, ipf_unref());

                                        /* ipf_unref() already called */
                                        if (m == NULL)
                                                return;

                                        changed_header = 1;
                                        ip = mtod(m, struct ip *);
                                        ip->ip_len = htons(ip->ip_len + hlen);
                                        ip->ip_off = htons(ip->ip_off);
                                        ip->ip_sum = 0;
                                        ip->ip_sum = ip_cksum_hdr_in(m, hlen);
                                }
                                result = filter->ipf_filter.ipf_input(
                                    filter->ipf_filter.cookie, (mbuf_t *)&m,
                                    hlen, proto);
                                if (result == EJUSTRETURN) {
                                        ipf_unref();
                                        return;
                                }
                                if (result != 0) {
                                        ipf_unref();
                                        m_freem(m);
                                        return;
                                }
                        }
                }
                ipf_unref();
        }

        /* Perform IP header alignment fixup (post-filters), if needed */
        IP_HDR_ALIGNMENT_FIXUP(m, m->m_pkthdr.rcvif, return);

        /*
         * If there isn't a specific lock for the protocol
         * we're about to call, use the generic lock for AF_INET.
         * otherwise let the protocol deal with its own locking
         */
        ip = mtod(m, struct ip *);

        if (changed_header) {
                ip->ip_len = ntohs(ip->ip_len) - hlen;
                ip->ip_off = ntohs(ip->ip_off);
        }

        if ((pr_input = ip_protox[ip->ip_p]->pr_input) == NULL) {
                m_freem(m);
        } else if (!(ip_protox[ip->ip_p]->pr_flags & PR_PROTOLOCK)) {
                lck_mtx_lock(inet_domain_mutex);
                pr_input(m, hlen);
                lck_mtx_unlock(inet_domain_mutex);
        } else {
                pr_input(m, hlen);
        }
}

/*
 * Ip input routine.  Checksum and byte swap header.  If fragmented
 * try to reassemble.  Process options.  Pass to next level.
 */
void
ip_input(struct mbuf *m)
{
        struct ip *ip;
        struct in_ifaddr *ia = NULL;
        unsigned int hlen, checkif;
        u_short sum = 0;
        struct in_addr pkt_dst;
#if IPFIREWALL
        int i;
        u_int32_t div_info = 0;         /* packet divert/tee info */
#endif
#if IPFIREWALL || DUMMYNET
        struct ip_fw_args args;
        struct m_tag    *tag;
#endif
        ipfilter_t inject_filter_ref = NULL;
        struct ifnet *inifp;

        /* Check if the mbuf is still valid after interface filter processing */
        MBUF_INPUT_CHECK(m, m->m_pkthdr.rcvif);
        inifp = m->m_pkthdr.rcvif;
        VERIFY(inifp != NULL);

        /* Perform IP header alignment fixup, if needed */
        IP_HDR_ALIGNMENT_FIXUP(m, inifp, goto bad);

        m->m_pkthdr.pkt_flags &= ~PKTF_FORWARDED;

#if IPFIREWALL || DUMMYNET
        bzero(&args, sizeof (struct ip_fw_args));

        /*
         * Don't bother searching for tag(s) if there's none.
         */
        if (SLIST_EMPTY(&m->m_pkthdr.tags))
                goto ipfw_tags_done;

        /* Grab info from mtags prepended to the chain */
#if DUMMYNET
        if ((tag = m_tag_locate(m, KERNEL_MODULE_TAG_ID,
            KERNEL_TAG_TYPE_DUMMYNET, NULL)) != NULL) {
                struct dn_pkt_tag *dn_tag;

                dn_tag = (struct dn_pkt_tag *)(tag+1);
                args.fwa_ipfw_rule = dn_tag->dn_ipfw_rule;
                args.fwa_pf_rule = dn_tag->dn_pf_rule;

                m_tag_delete(m, tag);
        }
#endif /* DUMMYNET */

#if IPDIVERT
        if ((tag = m_tag_locate(m, KERNEL_MODULE_TAG_ID,
            KERNEL_TAG_TYPE_DIVERT, NULL)) != NULL) {
                struct divert_tag *div_tag;

                div_tag = (struct divert_tag *)(tag+1);
                args.fwa_divert_rule = div_tag->cookie;

                m_tag_delete(m, tag);
        }
#endif

        if ((tag = m_tag_locate(m, KERNEL_MODULE_TAG_ID,
            KERNEL_TAG_TYPE_IPFORWARD, NULL)) != NULL) {
                struct ip_fwd_tag *ipfwd_tag;

                ipfwd_tag = (struct ip_fwd_tag *)(tag+1);
                args.fwa_next_hop = ipfwd_tag->next_hop;

                m_tag_delete(m, tag);
        }

#if     DIAGNOSTIC
        if (m == NULL || !(m->m_flags & M_PKTHDR))
                panic("ip_input no HDR");
#endif

#if DUMMYNET
        if (args.fwa_ipfw_rule || args.fwa_pf_rule) {
                /* dummynet already filtered us */
                ip = mtod(m, struct ip *);
                hlen = IP_VHL_HL(ip->ip_vhl) << 2;
                inject_filter_ref = ipf_get_inject_filter(m);
#if IPFIREWALL
                if (args.fwa_ipfw_rule)
                        goto iphack;
#endif /* IPFIREWALL */
                if (args.fwa_pf_rule)
                        goto check_with_pf;
        }
#endif /* DUMMYNET */
ipfw_tags_done:
#endif /* IPFIREWALL || DUMMYNET */

        /*
         * No need to process packet twice if we've already seen it.
         */
        if (!SLIST_EMPTY(&m->m_pkthdr.tags))
                inject_filter_ref = ipf_get_inject_filter(m);
        if (inject_filter_ref != NULL) {
                ip = mtod(m, struct ip *);
                hlen = IP_VHL_HL(ip->ip_vhl) << 2;

                DTRACE_IP6(receive, struct mbuf *, m, struct inpcb *, NULL,
                    struct ip *, ip, struct ifnet *, inifp,
                    struct ip *, ip, struct ip6_hdr *, NULL);

                ip->ip_len = ntohs(ip->ip_len) - hlen;
                ip->ip_off = ntohs(ip->ip_off);
                ip_proto_dispatch_in(m, hlen, ip->ip_p, inject_filter_ref);
                return;
        }

        OSAddAtomic(1, &ipstat.ips_total);
        if (m->m_pkthdr.len < sizeof (struct ip))
                goto tooshort;

        if (m->m_len < sizeof (struct ip) &&
            (m = m_pullup(m, sizeof (struct ip))) == NULL) {
                OSAddAtomic(1, &ipstat.ips_toosmall);
                return;
        }
        ip = mtod(m, struct ip *);

        KERNEL_DEBUG(DBG_LAYER_BEG, ip->ip_dst.s_addr, ip->ip_src.s_addr,
            ip->ip_p, ip->ip_off, ip->ip_len);

        if (IP_VHL_V(ip->ip_vhl) != IPVERSION) {
                OSAddAtomic(1, &ipstat.ips_badvers);
                goto bad;
        }

        hlen = IP_VHL_HL(ip->ip_vhl) << 2;
        if (hlen < sizeof (struct ip)) {        /* minimum header length */
                OSAddAtomic(1, &ipstat.ips_badhlen);
                goto bad;
        }
        if (hlen > m->m_len) {
                if ((m = m_pullup(m, hlen)) == NULL) {
                        OSAddAtomic(1, &ipstat.ips_badhlen);
                        return;
                }
                ip = mtod(m, struct ip *);
        }

        /* 127/8 must not appear on wire - RFC1122 */
        if ((ntohl(ip->ip_dst.s_addr) >> IN_CLASSA_NSHIFT) == IN_LOOPBACKNET ||
            (ntohl(ip->ip_src.s_addr) >> IN_CLASSA_NSHIFT) == IN_LOOPBACKNET) {
                /*
                 * Allow for the following exceptions:
                 *
                 *   1. If the packet was sent to loopback (i.e. rcvif
                 *      would have been set earlier at output time.)
                 *
                 *   2. If the packet was sent out on loopback from a local
                 *      source address which belongs to a non-loopback
                 *      interface (i.e. rcvif may not necessarily be a
                 *      loopback interface, hence the test for PKTF_LOOP.)
                 *      Unlike IPv6, there is no interface scope ID, and
                 *      therefore we don't care so much about PKTF_IFINFO.
                 */
                if (!(inifp->if_flags & IFF_LOOPBACK) &&
                    !(m->m_pkthdr.pkt_flags & PKTF_LOOP)) {
                        OSAddAtomic(1, &ipstat.ips_badaddr);
                        goto bad;
                }
        }

        /* IPv4 Link-Local Addresses as defined in RFC3927 */
        if ((IN_LINKLOCAL(ntohl(ip->ip_dst.s_addr)) ||
            IN_LINKLOCAL(ntohl(ip->ip_src.s_addr)))) {
                ip_linklocal_stat.iplls_in_total++;
                if (ip->ip_ttl != MAXTTL) {
                        OSAddAtomic(1, &ip_linklocal_stat.iplls_in_badttl);
                        /* Silently drop link local traffic with bad TTL */
                        if (!ip_linklocal_in_allowbadttl)
                                goto bad;
                }
        }

        sum = ip_cksum(m, hlen);
        if (sum) {
                goto bad;
        }

        DTRACE_IP6(receive, struct mbuf *, m, struct inpcb *, NULL,
            struct ip *, ip, struct ifnet *, inifp,
            struct ip *, ip, struct ip6_hdr *, NULL);

        /*
         * Naively assume we can attribute inbound data to the route we would
         * use to send to this destination. Asymetric routing breaks this
         * assumption, but it still allows us to account for traffic from
         * a remote node in the routing table.
         * this has a very significant performance impact so we bypass
         * if nstat_collect is disabled. We may also bypass if the
         * protocol is tcp in the future because tcp will have a route that
         * we can use to attribute the data to. That does mean we would not
         * account for forwarded tcp traffic.
         */
        if (nstat_collect) {
                struct rtentry *rt =
                    ifnet_cached_rtlookup_inet(inifp, ip->ip_src);
                if (rt != NULL) {
                        nstat_route_rx(rt, 1, m->m_pkthdr.len, 0);
                        rtfree(rt);
                }
        }

        /*
         * Convert fields to host representation.
         */
#if BYTE_ORDER != BIG_ENDIAN
        NTOHS(ip->ip_len);
#endif

        if (ip->ip_len < hlen) {
                OSAddAtomic(1, &ipstat.ips_badlen);
                goto bad;
        }

#if BYTE_ORDER != BIG_ENDIAN
        NTOHS(ip->ip_off);
#endif
        /*
         * Check that the amount of data in the buffers
         * is as at least much as the IP header would have us expect.
         * Trim mbufs if longer than we expect.
         * Drop packet if shorter than we expect.
         */
        if (m->m_pkthdr.len < ip->ip_len) {
tooshort:
                OSAddAtomic(1, &ipstat.ips_tooshort);
                goto bad;
        }
        if (m->m_pkthdr.len > ip->ip_len) {
                /*
                 * Invalidate hardware checksum info if ip_adj_clear_hwcksum
                 * is set; useful to handle buggy drivers.  Note that this
                 * should not be enabled by default, as we may get here due
                 * to link-layer padding.
                 */
                if (ip_adj_clear_hwcksum &&
                    (m->m_pkthdr.csum_flags & CSUM_DATA_VALID) &&
                    !(inifp->if_flags & IFF_LOOPBACK) &&
                    !(m->m_pkthdr.pkt_flags & PKTF_LOOP)) {
                        m->m_pkthdr.csum_flags &= ~CSUM_DATA_VALID;
                        m->m_pkthdr.csum_data = 0;
                        ipstat.ips_adj_hwcsum_clr++;
                }

                ipstat.ips_adj++;
                if (m->m_len == m->m_pkthdr.len) {
                        m->m_len = ip->ip_len;
                        m->m_pkthdr.len = ip->ip_len;
                } else
                        m_adj(m, ip->ip_len - m->m_pkthdr.len);
        }

        /* for consistency */
        m->m_pkthdr.pkt_proto = ip->ip_p;

#if DUMMYNET
check_with_pf:
#endif
#if PF
        /* Invoke inbound packet filter */
        if (PF_IS_ENABLED) {
                int error;
#if DUMMYNET
                error = pf_af_hook(inifp, NULL, &m, AF_INET, TRUE, &args);
#else
                error = pf_af_hook(inifp, NULL, &m, AF_INET, TRUE, NULL);
#endif /* DUMMYNET */
                if (error != 0 || m == NULL) {
                        if (m != NULL) {
                                panic("%s: unexpected packet %p\n",
                                    __func__, m);
                                /* NOTREACHED */
                        }
                        /* Already freed by callee */
                        return;
                }
                ip = mtod(m, struct ip *);
                hlen = IP_VHL_HL(ip->ip_vhl) << 2;
        }
#endif /* PF */

#if IPSEC
        if (ipsec_bypass == 0 && ipsec_gethist(m, NULL))
                goto pass;
#endif

#if IPFIREWALL
#if DUMMYNET
iphack:
#endif /* DUMMYNET */
        /*
         * Check if we want to allow this packet to be processed.
         * Consider it to be bad if not.
         */
        if (fw_enable && IPFW_LOADED) {
#if IPFIREWALL_FORWARD
                /*
                 * If we've been forwarded from the output side, then
                 * skip the firewall a second time
                 */
                if (args.fwa_next_hop)
                        goto ours;
#endif  /* IPFIREWALL_FORWARD */

                args.fwa_m = m;

                i = ip_fw_chk_ptr(&args);
                m = args.fwa_m;

                if ((i & IP_FW_PORT_DENY_FLAG) || m == NULL) { /* drop */
                        if (m)
                                m_freem(m);
                        return;
                }
                ip = mtod(m, struct ip *); /* just in case m changed */

                if (i == 0 && args.fwa_next_hop == NULL) { /* common case */
                        goto pass;
                }
#if DUMMYNET
                if (DUMMYNET_LOADED && (i & IP_FW_PORT_DYNT_FLAG) != 0) {
                        /* Send packet to the appropriate pipe */
                        ip_dn_io_ptr(m, i&0xffff, DN_TO_IP_IN, &args,
                            DN_CLIENT_IPFW);
                        return;
                }
#endif /* DUMMYNET */
#if IPDIVERT
                if (i != 0 && (i & IP_FW_PORT_DYNT_FLAG) == 0) {
                        /* Divert or tee packet */
                        div_info = i;
                        goto ours;
                }
#endif
#if IPFIREWALL_FORWARD
                if (i == 0 && args.fwa_next_hop != NULL) {
                        goto pass;
                }
#endif
                /*
                 * if we get here, the packet must be dropped
                 */
                m_freem(m);
                return;
        }
#endif /* IPFIREWALL */
#if IPSEC | IPFIREWALL
pass:
#endif
        /*
         * Process options and, if not destined for us,
         * ship it on.  ip_dooptions returns 1 when an
         * error was detected (causing an icmp message
         * to be sent and the original packet to be freed).
         */
        ip_nhops = 0;           /* for source routed packets */
#if IPFIREWALL
        if (hlen > sizeof (struct ip) &&
            ip_dooptions(m, 0, args.fwa_next_hop)) {
#else /* !IPFIREWALL */
        if (hlen > sizeof (struct ip) && ip_dooptions(m, 0, NULL)) {
#endif /* !IPFIREWALL */
                return;
        }

        /*
         * Check our list of addresses, to see if the packet is for us.
         * If we don't have any addresses, assume any unicast packet
         * we receive might be for us (and let the upper layers deal
         * with it).
         */
        if (TAILQ_EMPTY(&in_ifaddrhead) && !(m->m_flags & (M_MCAST|M_BCAST))) {
                ip_setdstifaddr_info(m, inifp->if_index, NULL);
                goto ours;
        }

        /*
         * Cache the destination address of the packet; this may be
         * changed by use of 'ipfw fwd'.
         */
#if IPFIREWALL
        pkt_dst = args.fwa_next_hop == NULL ?
            ip->ip_dst : args.fwa_next_hop->sin_addr;
#else /* !IPFIREWALL */
        pkt_dst = ip->ip_dst;
#endif /* !IPFIREWALL */

        /*
         * Enable a consistency check between the destination address
         * and the arrival interface for a unicast packet (the RFC 1122
         * strong ES model) if IP forwarding is disabled and the packet
         * is not locally generated and the packet is not subject to
         * 'ipfw fwd'.
         *
         * XXX - Checking also should be disabled if the destination
         * address is ipnat'ed to a different interface.
         *
         * XXX - Checking is incompatible with IP aliases added
         * to the loopback interface instead of the interface where
         * the packets are received.
         */
        checkif = ip_checkinterface && (ipforwarding == 0) &&
            !(inifp->if_flags & IFF_LOOPBACK) &&
            !(m->m_pkthdr.pkt_flags & PKTF_LOOP)
#if IPFIREWALL
            && (args.fwa_next_hop == NULL);
#else /* !IPFIREWALL */
                ;
#endif /* !IPFIREWALL */

        /*
         * Check for exact addresses in the hash bucket.
         */
        lck_rw_lock_shared(in_ifaddr_rwlock);
        TAILQ_FOREACH(ia, INADDR_HASH(pkt_dst.s_addr), ia_hash) {
                /*
                 * If the address matches, verify that the packet
                 * arrived via the correct interface if checking is
                 * enabled.
                 */
                if (IA_SIN(ia)->sin_addr.s_addr == pkt_dst.s_addr &&
                    (!checkif || ia->ia_ifp == inifp)) {
                        ip_setdstifaddr_info(m, 0, ia);
                        lck_rw_done(in_ifaddr_rwlock);
                        goto ours;
                }
        }
        lck_rw_done(in_ifaddr_rwlock);

        /*
         * Check for broadcast addresses.
         *
         * Only accept broadcast packets that arrive via the matching
         * interface.  Reception of forwarded directed broadcasts would be
         * handled via ip_forward() and ether_frameout() with the loopback
         * into the stack for SIMPLEX interfaces handled by ether_frameout().
         */
        if (inifp->if_flags & IFF_BROADCAST) {
                struct ifaddr *ifa;

                ifnet_lock_shared(inifp);
                TAILQ_FOREACH(ifa, &inifp->if_addrhead, ifa_link) {
                        if (ifa->ifa_addr->sa_family != AF_INET) {
                                continue;
                        }
                        ia = ifatoia(ifa);
                        if (satosin(&ia->ia_broadaddr)->sin_addr.s_addr ==
                            pkt_dst.s_addr || ia->ia_netbroadcast.s_addr ==
                            pkt_dst.s_addr) {
                                ip_setdstifaddr_info(m, 0, ia);
                                ifnet_lock_done(inifp);
                                goto ours;
                        }
                }
                ifnet_lock_done(inifp);
        }

        if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr))) {
                struct in_multi *inm;
                /*
                 * See if we belong to the destination multicast group on the
                 * arrival interface.
                 */
                in_multihead_lock_shared();
                IN_LOOKUP_MULTI(&ip->ip_dst, inifp, inm);
                in_multihead_lock_done();
                if (inm == NULL) {
                        OSAddAtomic(1, &ipstat.ips_notmember);
                        m_freem(m);
                        return;
                }
                ip_setdstifaddr_info(m, inifp->if_index, NULL);
                INM_REMREF(inm);
                goto ours;
        }
        if (ip->ip_dst.s_addr == (u_int32_t)INADDR_BROADCAST ||
            ip->ip_dst.s_addr == INADDR_ANY) {
                ip_setdstifaddr_info(m, inifp->if_index, NULL);
                goto ours;
        }

        /* Allow DHCP/BootP responses through */
        if ((inifp->if_eflags & IFEF_AUTOCONFIGURING) &&
            hlen == sizeof (struct ip) && ip->ip_p == IPPROTO_UDP) {
                struct udpiphdr *ui;

                if (m->m_len < sizeof (struct udpiphdr) &&
                    (m = m_pullup(m, sizeof (struct udpiphdr))) == NULL) {
                        OSAddAtomic(1, &udpstat.udps_hdrops);
                        return;
                }
                ui = mtod(m, struct udpiphdr *);
                if (ntohs(ui->ui_dport) == IPPORT_BOOTPC) {
                        ip_setdstifaddr_info(m, inifp->if_index, NULL);
                        goto ours;
                }
                ip = mtod(m, struct ip *); /* in case it changed */
        }

        /*
         * Not for us; forward if possible and desirable.
         */
        if (ipforwarding == 0) {
                OSAddAtomic(1, &ipstat.ips_cantforward);
                m_freem(m);
        } else {
#if IPFIREWALL
                ip_forward(m, 0, args.fwa_next_hop);
#else
                ip_forward(m, 0, NULL);
#endif
        }
        return;

ours:
        /*
         * If offset or IP_MF are set, must reassemble.
         */
        if (ip->ip_off & ~(IP_DF | IP_RF)) {
                /*
                 * ip_reass() will return a different mbuf, and update
                 * the divert info in div_info and args.fwa_divert_rule.
                 */
#if IPDIVERT
                m = ip_reass(m, (u_int16_t *)&div_info, &args.fwa_divert_rule);
#else
                m = ip_reass(m);
#endif
                if (m == NULL)
                        return;
                ip = mtod(m, struct ip *);
                /* Get the header length of the reassembled packet */
                hlen = IP_VHL_HL(ip->ip_vhl) << 2;
#if IPDIVERT
                /* Restore original checksum before diverting packet */
                if (div_info != 0) {
#if BYTE_ORDER != BIG_ENDIAN
                        HTONS(ip->ip_len);
                        HTONS(ip->ip_off);
#endif
                        ip->ip_sum = 0;
                        ip->ip_sum = ip_cksum_hdr_in(m, hlen);
#if BYTE_ORDER != BIG_ENDIAN
                        NTOHS(ip->ip_off);
                        NTOHS(ip->ip_len);
#endif
                }
#endif
        }

        /*
         * Further protocols expect the packet length to be w/o the
         * IP header.
         */
        ip->ip_len -= hlen;

#if IPDIVERT
        /*
         * Divert or tee packet to the divert protocol if required.
         *
         * If div_info is zero then cookie should be too, so we shouldn't
         * need to clear them here.  Assume divert_packet() does so also.
         */
        if (div_info != 0) {
                struct mbuf *clone = NULL;

                /* Clone packet if we're doing a 'tee' */
                if (div_info & IP_FW_PORT_TEE_FLAG)
                        clone = m_dup(m, M_DONTWAIT);

                /* Restore packet header fields to original values */
                ip->ip_len += hlen;

#if BYTE_ORDER != BIG_ENDIAN
                HTONS(ip->ip_len);
                HTONS(ip->ip_off);
#endif
                /* Deliver packet to divert input routine */
                OSAddAtomic(1, &ipstat.ips_delivered);
                divert_packet(m, 1, div_info & 0xffff, args.fwa_divert_rule);

                /* If 'tee', continue with original packet */
                if (clone == NULL) {
                        return;
                }
                m = clone;
                ip = mtod(m, struct ip *);
        }
#endif

#if 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 (ipsec_bypass == 0 && (ip_protox[ip->ip_p]->pr_flags & PR_LASTHDR)) {
                if (ipsec4_in_reject(m, NULL)) {
                        IPSEC_STAT_INCREMENT(ipsecstat.in_polvio);
                        goto bad;
                }
        }
#endif /* IPSEC */

        /*
         * Switch out to protocol's input routine.
         */
        OSAddAtomic(1, &ipstat.ips_delivered);

#if IPFIREWALL
        if (args.fwa_next_hop && ip->ip_p == IPPROTO_TCP) {
                /* TCP needs IPFORWARD info if available */
                struct m_tag *fwd_tag;
                struct ip_fwd_tag *ipfwd_tag;

                fwd_tag = m_tag_create(KERNEL_MODULE_TAG_ID,
                    KERNEL_TAG_TYPE_IPFORWARD, sizeof (*ipfwd_tag),
                    M_NOWAIT, m);
                if (fwd_tag == NULL)
                        goto bad;

                ipfwd_tag = (struct ip_fwd_tag *)(fwd_tag+1);
                ipfwd_tag->next_hop = args.fwa_next_hop;

                m_tag_prepend(m, fwd_tag);

                KERNEL_DEBUG(DBG_LAYER_END, ip->ip_dst.s_addr,
                    ip->ip_src.s_addr, ip->ip_p, ip->ip_off, ip->ip_len);

                /* TCP deals with its own locking */
                ip_proto_dispatch_in(m, hlen, ip->ip_p, 0);
        } else {
                KERNEL_DEBUG(DBG_LAYER_END, ip->ip_dst.s_addr,
                    ip->ip_src.s_addr, ip->ip_p, ip->ip_off, ip->ip_len);

                if ((sw_lro) && (ip->ip_p == IPPROTO_TCP)) {
                        m = tcp_lro(m, hlen);
                        if (m == NULL)
                                return;
                }

                ip_proto_dispatch_in(m, hlen, ip->ip_p, 0);
        }
#else /* !IPFIREWALL */
        if ((sw_lro) && (ip->ip_p == IPPROTO_TCP)) {
                m = tcp_lro(m, hlen);
                if (m == NULL)
                        return;
        }
        ip_proto_dispatch_in(m, hlen, ip->ip_p, 0);
#endif /* !IPFIREWALL */
        return;

bad:
        KERNEL_DEBUG(DBG_LAYER_END, 0, 0, 0, 0, 0);
        m_freem(m);
}

static void
ipq_updateparams(void)
{
        lck_mtx_assert(&ipqlock, LCK_MTX_ASSERT_OWNED);
        /*
         * -1 for unlimited allocation.
         */
        if (maxnipq < 0)
                ipq_limit = 0;
        /*
         * Positive number for specific bound.
         */
        if (maxnipq > 0)
                ipq_limit = maxnipq;
        /*
         * 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 (maxnipq == 0)
                ipq_limit = 1;
        /*
         * Arm the purge timer if not already and if there's work to do
         */
        frag_sched_timeout();
}

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

        lck_mtx_lock(&ipqlock);
        i = maxnipq;
        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;
        }
        maxnipq = i;
        ipq_updateparams();
done:
        lck_mtx_unlock(&ipqlock);
        return (error);
}

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

        lck_mtx_lock(&ipqlock);
        i = maxfragsperpacket;
        error = sysctl_handle_int(oidp, &i, 0, req);
        if (error || req->newptr == USER_ADDR_NULL)
                goto done;
        maxfragsperpacket = i;
        ipq_updateparams();     /* see if we need to arm timer */
done:
        lck_mtx_unlock(&ipqlock);
        return (error);
}

/*
 * Take incoming datagram fragment and try to reassemble it into
 * whole datagram.  If a chain for reassembly of this datagram already
 * exists, then it is given as fp; otherwise have to make a chain.
 *
 * When IPDIVERT enabled, keep additional state with each packet that
 * tells us if we need to divert or tee the packet we're building.
 *
 * The IP header is *NOT* adjusted out of iplen.
 */
static struct mbuf *
#if IPDIVERT
ip_reass(struct mbuf *m,
#ifdef IPDIVERT_44
    u_int32_t *divinfo,
#else /* IPDIVERT_44 */
    u_int16_t *divinfo,
#endif /* IPDIVERT_44 */
    u_int16_t *divcookie)
#else /* IPDIVERT */
ip_reass(struct mbuf *m)
#endif /* IPDIVERT */
{
        struct ip *ip;
        struct mbuf *p, *q, *nq, *t;
        struct ipq *fp = NULL;
        struct ipqhead *head;
        int i, hlen, next;
        u_int8_t ecn, ecn0;
        uint32_t csum, csum_flags;
        uint16_t hash;
        struct fq_head dfq;

        MBUFQ_INIT(&dfq);       /* for deferred frees */

        /* If maxnipq or maxfragsperpacket is 0, never accept fragments. */
        if (maxnipq == 0 || maxfragsperpacket == 0) {
                ipstat.ips_fragments++;
                ipstat.ips_fragdropped++;
                m_freem(m);
                if (nipq > 0) {
                        lck_mtx_lock(&ipqlock);
                        frag_sched_timeout();   /* purge stale fragments */
                        lck_mtx_unlock(&ipqlock);
                }
                return (NULL);
        }

        ip = mtod(m, struct ip *);
        hlen = IP_VHL_HL(ip->ip_vhl) << 2;

        lck_mtx_lock(&ipqlock);

        hash = IPREASS_HASH(ip->ip_src.s_addr, ip->ip_id);
        head = &ipq[hash];

        /*
         * Look for queue of fragments
         * of this datagram.
         */
        TAILQ_FOREACH(fp, head, ipq_list) {
                if (ip->ip_id == fp->ipq_id &&
                    ip->ip_src.s_addr == fp->ipq_src.s_addr &&
                    ip->ip_dst.s_addr == fp->ipq_dst.s_addr &&
#if CONFIG_MACF_NET
                    mac_ipq_label_compare(m, fp) &&
#endif
                    ip->ip_p == fp->ipq_p)
                        goto found;
        }

        fp = NULL;

        /*
         * Attempt to trim the number of allocated fragment queues if it
         * exceeds the administrative limit.
         */
        if ((nipq > (unsigned)maxnipq) && (maxnipq > 0)) {
                /*
                 * drop something from the tail of the current queue
                 * before proceeding further
                 */
                struct ipq *fq = TAILQ_LAST(head, ipqhead);
                if (fq == NULL) {   /* gak */
                        for (i = 0; i < IPREASS_NHASH; i++) {
                                struct ipq *r = TAILQ_LAST(&ipq[i], ipqhead);
                                if (r) {
                                        ipstat.ips_fragtimeout += r->ipq_nfrags;
                                        frag_freef(&ipq[i], r);
                                        break;
                                }
                        }
                } else {
                        ipstat.ips_fragtimeout += fq->ipq_nfrags;
                        frag_freef(head, fq);
                }
        }

found:
        /*
         * Leverage partial checksum offload for IP fragments.  Narrow down
         * the scope to cover only UDP without IP options, as that is the
         * most common case.
         *
         * Perform 1's complement adjustment of octets that got included/
         * excluded in the hardware-calculated checksum value.  Ignore cases
         * where the value includes or excludes the IP header span, as the
         * sum for those octets would already be 0xffff and thus no-op.
         */
        if (ip->ip_p == IPPROTO_UDP && hlen == sizeof (struct ip) &&
            (m->m_pkthdr.csum_flags &
            (CSUM_DATA_VALID | CSUM_PARTIAL | CSUM_PSEUDO_HDR)) ==
            (CSUM_DATA_VALID | CSUM_PARTIAL)) {
                uint32_t start;

                start = m->m_pkthdr.csum_rx_start;
                csum = m->m_pkthdr.csum_rx_val;

                if (start != 0 && start != hlen) {
#if BYTE_ORDER != BIG_ENDIAN
                        if (start < hlen) {
                                HTONS(ip->ip_len);
                                HTONS(ip->ip_off);
                        }
#endif
                        /* callee folds in sum */
                        csum = m_adj_sum16(m, start, hlen, csum);
#if BYTE_ORDER != BIG_ENDIAN
                        if (start < hlen) {
                                NTOHS(ip->ip_off);
                                NTOHS(ip->ip_len);
                        }
#endif
                }
                csum_flags = m->m_pkthdr.csum_flags;
        } else {
                csum = 0;
                csum_flags = 0;
        }

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

        ipstat.ips_fragments++;

        /*
         * Adjust ip_len to not reflect header,
         * convert offset of this to bytes.
         */
        ip->ip_len -= hlen;
        if (ip->ip_off & IP_MF) {
                /*
                 * Make sure that fragments have a data length
                 * that's a non-zero multiple of 8 bytes.
                 */
                if (ip->ip_len == 0 || (ip->ip_len & 0x7) != 0) {
                        OSAddAtomic(1, &ipstat.ips_toosmall);
                        /*
                         * Reassembly queue may have been found if previous
                         * fragments were valid; given that this one is bad,
                         * we need to drop it.  Make sure to set fp to NULL
                         * if not already, since we don't want to decrement
                         * ipq_nfrags as it doesn't include this packet.
                         */
                        fp = NULL;
                        goto dropfrag;
                }
                m->m_flags |= M_FRAG;
        } else {
                /* Clear the flag in case packet comes from loopback */
                m->m_flags &= ~M_FRAG;
        }
        ip->ip_off <<= 3;

        m->m_pkthdr.pkt_hdr = ip;

        /* Previous ip_reass() started here. */
        /*
         * Presence of header sizes in mbufs
         * would confuse code below.
         */
        m->m_data += hlen;
        m->m_len -= hlen;

        /*
         * If first fragment to arrive, create a reassembly queue.
         */
        if (fp == NULL) {
                fp = ipq_alloc(M_DONTWAIT);
                if (fp == NULL)
                        goto dropfrag;
#if CONFIG_MACF_NET
                if (mac_ipq_label_init(fp, M_NOWAIT) != 0) {
                        ipq_free(fp);
                        fp = NULL;
                        goto dropfrag;
                }
                mac_ipq_label_associate(m, fp);
#endif
                TAILQ_INSERT_HEAD(head, fp, ipq_list);
                nipq++;
                fp->ipq_nfrags = 1;
                fp->ipq_ttl = IPFRAGTTL;
                fp->ipq_p = ip->ip_p;
                fp->ipq_id = ip->ip_id;
                fp->ipq_src = ip->ip_src;
                fp->ipq_dst = ip->ip_dst;
                fp->ipq_frags = m;
                m->m_nextpkt = NULL;
                /*
                 * If the first fragment has valid checksum offload
                 * info, the rest of fragments are eligible as well.
                 */
                if (csum_flags != 0) {
                        fp->ipq_csum = csum;
                        fp->ipq_csum_flags = csum_flags;
                }
#if IPDIVERT
                /*
                 * Transfer firewall instructions to the fragment structure.
                 * Only trust info in the fragment at offset 0.
                 */
                if (ip->ip_off == 0) {
#ifdef IPDIVERT_44
                        fp->ipq_div_info = *divinfo;
#else
                        fp->ipq_divert = *divinfo;
#endif
                        fp->ipq_div_cookie = *divcookie;
                }
                *divinfo = 0;
                *divcookie = 0;
#endif /* IPDIVERT */
                m = NULL;       /* nothing to return */
                goto done;
        } else {
                fp->ipq_nfrags++;
#if CONFIG_MACF_NET
                mac_ipq_label_update(m, fp);
#endif
        }

#define GETIP(m)        ((struct ip *)((m)->m_pkthdr.pkt_hdr))

        /*
         * 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 = ip->ip_tos & IPTOS_ECN_MASK;
        ecn0 = GETIP(fp->ipq_frags)->ip_tos & IPTOS_ECN_MASK;
        if (ecn == IPTOS_ECN_CE) {
                if (ecn0 == IPTOS_ECN_NOTECT)
                        goto dropfrag;
                if (ecn0 != IPTOS_ECN_CE)
                        GETIP(fp->ipq_frags)->ip_tos |= IPTOS_ECN_CE;
        }
        if (ecn == IPTOS_ECN_NOTECT && ecn0 != IPTOS_ECN_NOTECT)
                goto dropfrag;

        /*
         * Find a segment which begins after this one does.
         */
        for (p = NULL, q = fp->ipq_frags; q; p = q, q = q->m_nextpkt)
                if (GETIP(q)->ip_off > ip->ip_off)
                        break;

        /*
         * 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, otherwise
         * stick new segment in the proper place.
         *
         * If some of the data is dropped from the preceding
         * segment, then it's checksum is invalidated.
         */
        if (p) {
                i = GETIP(p)->ip_off + GETIP(p)->ip_len - ip->ip_off;
                if (i > 0) {
                        if (i >= ip->ip_len)
                                goto dropfrag;
                        m_adj(m, i);
                        fp->ipq_csum_flags = 0;
                        ip->ip_off += i;
                        ip->ip_len -= i;
                }
                m->m_nextpkt = p->m_nextpkt;
                p->m_nextpkt = m;
        } else {
                m->m_nextpkt = fp->ipq_frags;
                fp->ipq_frags = m;
        }

        /*
         * While we overlap succeeding segments trim them or,
         * if they are completely covered, dequeue them.
         */
        for (; q != NULL && ip->ip_off + ip->ip_len > GETIP(q)->ip_off;
            q = nq) {
                i = (ip->ip_off + ip->ip_len) - GETIP(q)->ip_off;
                if (i < GETIP(q)->ip_len) {
                        GETIP(q)->ip_len -= i;
                        GETIP(q)->ip_off += i;
                        m_adj(q, i);
                        fp->ipq_csum_flags = 0;
                        break;
                }
                nq = q->m_nextpkt;
                m->m_nextpkt = nq;
                ipstat.ips_fragdropped++;
                fp->ipq_nfrags--;
                /* defer freeing until after lock is dropped */
                MBUFQ_ENQUEUE(&dfq, q);
        }

        /*
         * 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 == fp->ipq_csum_flags)
                fp->ipq_csum += csum;
        else if (fp->ipq_csum_flags != 0)
                fp->ipq_csum_flags = 0;

#if IPDIVERT
        /*
         * Transfer firewall instructions to the fragment structure.
         * Only trust info in the fragment at offset 0.
         */
        if (ip->ip_off == 0) {
#ifdef IPDIVERT_44
                fp->ipq_div_info = *divinfo;
#else
                fp->ipq_divert = *divinfo;
#endif
                fp->ipq_div_cookie = *divcookie;
        }
        *divinfo = 0;
        *divcookie = 0;
#endif /* IPDIVERT */

        /*
         * Check for complete reassembly and perform frag per packet
         * limiting.
         *
         * Frag limiting is performed here so that the nth frag has
         * a chance to complete the packet before we drop the packet.
         * As a result, n+1 frags are actually allowed per packet, but
         * only n will ever be stored. (n = maxfragsperpacket.)
         *
         */
        next = 0;
        for (p = NULL, q = fp->ipq_frags; q; p = q, q = q->m_nextpkt) {
                if (GETIP(q)->ip_off != next) {
                        if (fp->ipq_nfrags > maxfragsperpacket) {
                                ipstat.ips_fragdropped += fp->ipq_nfrags;
                                frag_freef(head, fp);
                        }
                        m = NULL;       /* nothing to return */
                        goto done;
                }
                next += GETIP(q)->ip_len;
        }
        /* Make sure the last packet didn't have the IP_MF flag */
        if (p->m_flags & M_FRAG) {
                if (fp->ipq_nfrags > maxfragsperpacket) {
                        ipstat.ips_fragdropped += fp->ipq_nfrags;
                        frag_freef(head, fp);
                }
                m = NULL;               /* nothing to return */
                goto done;
        }

        /*
         * Reassembly is complete.  Make sure the packet is a sane size.
         */
        q = fp->ipq_frags;
        ip = GETIP(q);
        if (next + (IP_VHL_HL(ip->ip_vhl) << 2) > IP_MAXPACKET) {
                ipstat.ips_toolong++;
                ipstat.ips_fragdropped += fp->ipq_nfrags;
                frag_freef(head, fp);
                m = NULL;               /* nothing to return */
                goto done;
        }

        /*
         * Concatenate fragments.
         */
        m = q;
        t = m->m_next;
        m->m_next = NULL;
        m_cat(m, t);
        nq = q->m_nextpkt;
        q->m_nextpkt = NULL;
        for (q = nq; q != NULL; q = nq) {
                nq = q->m_nextpkt;
                q->m_nextpkt = NULL;
                m_cat(m, q);
        }

        /*
         * Store partial hardware checksum info from the fragment queue;
         * the receive start offset is set to 20 bytes (see code at the
         * top of this routine.)
         */
        if (fp->ipq_csum_flags != 0) {
                csum = fp->ipq_csum;

                ADDCARRY(csum);

                m->m_pkthdr.csum_rx_val = csum;
                m->m_pkthdr.csum_rx_start = sizeof (struct ip);
                m->m_pkthdr.csum_flags = fp->ipq_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_PARTIAL;
                m->m_pkthdr.csum_flags =
                    CSUM_DATA_VALID | CSUM_PSEUDO_HDR |
                    CSUM_IP_CHECKED | CSUM_IP_VALID;
        }

#if IPDIVERT
        /*
         * Extract firewall instructions from the fragment structure.
         */
#ifdef IPDIVERT_44
        *divinfo = fp->ipq_div_info;
#else
        *divinfo = fp->ipq_divert;
#endif
        *divcookie = fp->ipq_div_cookie;
#endif /* IPDIVERT */

#if CONFIG_MACF_NET
        mac_mbuf_label_associate_ipq(fp, m);
        mac_ipq_label_destroy(fp);
#endif
        /*
         * Create header for new ip packet by modifying header of first
         * packet; dequeue and discard fragment reassembly header.
         * Make header visible.
         */
        ip->ip_len = (IP_VHL_HL(ip->ip_vhl) << 2) + next;
        ip->ip_src = fp->ipq_src;
        ip->ip_dst = fp->ipq_dst;

        fp->ipq_frags = NULL;   /* return to caller as 'm' */
        frag_freef(head, fp);
        fp = NULL;

        m->m_len += (IP_VHL_HL(ip->ip_vhl) << 2);
        m->m_data -= (IP_VHL_HL(ip->ip_vhl) << 2);
        /* some debugging cruft by sklower, below, will go away soon */
        if (m->m_flags & M_PKTHDR)      /* XXX this should be done elsewhere */
                m_fixhdr(m);
        ipstat.ips_reassembled++;

        /* arm the purge timer if not already and if there's work to do */
        frag_sched_timeout();
        lck_mtx_unlock(&ipqlock);
        /* perform deferred free (if needed) now that lock is dropped */
        if (!MBUFQ_EMPTY(&dfq))
                MBUFQ_DRAIN(&dfq);
        VERIFY(MBUFQ_EMPTY(&dfq));
        return (m);

done:
        VERIFY(m == NULL);
        /* arm the purge timer if not already and if there's work to do */
        frag_sched_timeout();
        lck_mtx_unlock(&ipqlock);
        /* perform deferred free (if needed) */
        if (!MBUFQ_EMPTY(&dfq))
                MBUFQ_DRAIN(&dfq);
        VERIFY(MBUFQ_EMPTY(&dfq));
        return (NULL);

dropfrag:
#if IPDIVERT
        *divinfo = 0;
        *divcookie = 0;
#endif /* IPDIVERT */
        ipstat.ips_fragdropped++;
        if (fp != NULL)
                fp->ipq_nfrags--;
        /* arm the purge timer if not already and if there's work to do */
        frag_sched_timeout();
        lck_mtx_unlock(&ipqlock);
        m_freem(m);
        /* perform deferred free (if needed) */
        if (!MBUFQ_EMPTY(&dfq))
                MBUFQ_DRAIN(&dfq);
        VERIFY(MBUFQ_EMPTY(&dfq));
        return (NULL);
#undef GETIP
}

/*
 * Free a fragment reassembly header and all
 * associated datagrams.
 */
static void
frag_freef(struct ipqhead *fhp, struct ipq *fp)
{
        lck_mtx_assert(&ipqlock, LCK_MTX_ASSERT_OWNED);

        fp->ipq_nfrags = 0;
        if (fp->ipq_frags != NULL) {
                m_freem_list(fp->ipq_frags);
                fp->ipq_frags = NULL;
        }
        TAILQ_REMOVE(fhp, fp, ipq_list);
        nipq--;
        ipq_free(fp);
}

/*
 * IP reassembly timer processing
 */
static void
frag_timeout(void *arg)
{
#pragma unused(arg)
        struct ipq *fp;
        int i;

        /*
         * 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(&ipqlock);
        for (i = 0; i < IPREASS_NHASH; i++) {
                for (fp = TAILQ_FIRST(&ipq[i]); fp; ) {
                        struct ipq *fpp;

                        fpp = fp;
                        fp = TAILQ_NEXT(fp, ipq_list);
                        if (--fpp->ipq_ttl == 0) {
                                ipstat.ips_fragtimeout += fpp->ipq_nfrags;
                                frag_freef(&ipq[i], fpp);
                        }
                }
        }
        /*
         * 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 (maxnipq >= 0 && nipq > (unsigned)maxnipq) {
                for (i = 0; i < IPREASS_NHASH; i++) {
                        while (nipq > (unsigned)maxnipq &&
                            !TAILQ_EMPTY(&ipq[i])) {
                                ipstat.ips_fragdropped +=
                                    TAILQ_FIRST(&ipq[i])->ipq_nfrags;
                                frag_freef(&ipq[i], TAILQ_FIRST(&ipq[i]));
                        }
                }
        }
        /* re-arm the purge timer if there's work to do */
        frag_timeout_run = 0;
        frag_sched_timeout();
        lck_mtx_unlock(&ipqlock);
}

static void
frag_sched_timeout(void)
{
        lck_mtx_assert(&ipqlock, LCK_MTX_ASSERT_OWNED);

        if (!frag_timeout_run && nipq > 0) {
                frag_timeout_run = 1;
                timeout(frag_timeout, NULL, hz);
        }
}

/*
 * Drain off all datagram fragments.
 */
static void
frag_drain(void)
{
        int i;

        lck_mtx_lock(&ipqlock);
        for (i = 0; i < IPREASS_NHASH; i++) {
                while (!TAILQ_EMPTY(&ipq[i])) {
                        ipstat.ips_fragdropped +=
                            TAILQ_FIRST(&ipq[i])->ipq_nfrags;
                        frag_freef(&ipq[i], TAILQ_FIRST(&ipq[i]));
                }
        }
        lck_mtx_unlock(&ipqlock);
}

static struct ipq *
ipq_alloc(int how)
{
        struct mbuf *t;
        struct ipq *fp;

        /*
         * See comments in ipq_updateparams().  Keep the count separate
         * from nipq since the latter represents the elements already
         * in the reassembly queues.
         */
        if (ipq_limit > 0 && ipq_count > ipq_limit)
                return (NULL);

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

static void
ipq_free(struct ipq *fp)
{
        (void) m_free(dtom(fp));
        atomic_add_32(&ipq_count, -1);
}

/*
 * Drain callback
 */
void
ip_drain(void)
{
        frag_drain();           /* fragments */
        in_rtqdrain();          /* protocol cloned routes */
        in_arpdrain(NULL);      /* cloned routes: ARP */
}

/*
 * Do option processing on a datagram,
 * possibly discarding it if bad options are encountered,
 * or forwarding it if source-routed.
 * The pass argument is used when operating in the IPSTEALTH
 * mode to tell what options to process:
 * [LS]SRR (pass 0) or the others (pass 1).
 * The reason for as many as two passes is that when doing IPSTEALTH,
 * non-routing options should be processed only if the packet is for us.
 * Returns 1 if packet has been forwarded/freed,
 * 0 if the packet should be processed further.
 */
static int
ip_dooptions(struct mbuf *m, int pass, struct sockaddr_in *next_hop)
{
#pragma unused(pass)
        struct ip *ip = mtod(m, struct ip *);
        u_char *cp;
        struct ip_timestamp *ipt;
        struct in_ifaddr *ia;
        int opt, optlen, cnt, off, code, type = ICMP_PARAMPROB, forward = 0;
        struct in_addr *sin, dst;
        n_time ntime;
        struct sockaddr_in ipaddr = {
            sizeof (ipaddr), AF_INET, 0, { 0 }, { 0, } };

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

        dst = ip->ip_dst;
        cp = (u_char *)(ip + 1);
        cnt = (IP_VHL_HL(ip->ip_vhl) << 2) - sizeof (struct ip);
        for (; cnt > 0; cnt -= optlen, cp += optlen) {
                opt = cp[IPOPT_OPTVAL];
                if (opt == IPOPT_EOL)
                        break;
                if (opt == IPOPT_NOP)
                        optlen = 1;
                else {
                        if (cnt < IPOPT_OLEN + sizeof (*cp)) {
                                code = &cp[IPOPT_OLEN] - (u_char *)ip;
                                goto bad;
                        }
                        optlen = cp[IPOPT_OLEN];
                        if (optlen < IPOPT_OLEN + sizeof (*cp) ||
                            optlen > cnt) {
                                code = &cp[IPOPT_OLEN] - (u_char *)ip;
                                goto bad;
                        }
                }
                switch (opt) {

                default:
                        break;

                /*
                 * Source routing with record.
                 * Find interface with current destination address.
                 * If none on this machine then drop if strictly routed,
                 * or do nothing if loosely routed.
                 * Record interface address and bring up next address
                 * component.  If strictly routed make sure next
                 * address is on directly accessible net.
                 */
                case IPOPT_LSRR:
                case IPOPT_SSRR:
                        if (optlen < IPOPT_OFFSET + sizeof (*cp)) {
                                code = &cp[IPOPT_OLEN] - (u_char *)ip;
                                goto bad;
                        }
                        if ((off = cp[IPOPT_OFFSET]) < IPOPT_MINOFF) {
                                code = &cp[IPOPT_OFFSET] - (u_char *)ip;
                                goto bad;
                        }
                        ipaddr.sin_addr = ip->ip_dst;
                        ia = (struct in_ifaddr *)ifa_ifwithaddr(SA(&ipaddr));
                        if (ia == NULL) {
                                if (opt == IPOPT_SSRR) {
                                        type = ICMP_UNREACH;
                                        code = ICMP_UNREACH_SRCFAIL;
                                        goto bad;
                                }
                                if (!ip_dosourceroute)
                                        goto nosourcerouting;
                                /*
                                 * Loose routing, and not at next destination
                                 * yet; nothing to do except forward.
                                 */
                                break;
                        } else {
                                IFA_REMREF(&ia->ia_ifa);
                                ia = NULL;
                        }
                        off--;                  /* 0 origin */
                        if (off > optlen - (int)sizeof (struct in_addr)) {
                                /*
                                 * End of source route.  Should be for us.
                                 */
                                if (!ip_acceptsourceroute)
                                        goto nosourcerouting;
                                save_rte(cp, ip->ip_src);
                                break;
                        }

                        if (!ip_dosourceroute) {
                                if (ipforwarding) {
                                        char buf[MAX_IPv4_STR_LEN];
                                        char buf2[MAX_IPv4_STR_LEN];
                                        /*
                                         * Acting as a router, so generate ICMP
                                         */
nosourcerouting:
                                        log(LOG_WARNING,
                                            "attempted source route from %s "
                                            "to %s\n",
                                            inet_ntop(AF_INET, &ip->ip_src,
                                            buf, sizeof (buf)),
                                            inet_ntop(AF_INET, &ip->ip_dst,
                                            buf2, sizeof (buf2)));
                                        type = ICMP_UNREACH;
                                        code = ICMP_UNREACH_SRCFAIL;
                                        goto bad;
                                } else {
                                        /*
                                         * Not acting as a router,
                                         * so silently drop.
                                         */
                                        OSAddAtomic(1, &ipstat.ips_cantforward);
                                        m_freem(m);
                                        return (1);
                                }
                        }

                        /*
                         * locate outgoing interface
                         */
                        (void) memcpy(&ipaddr.sin_addr, cp + off,
                            sizeof (ipaddr.sin_addr));

                        if (opt == IPOPT_SSRR) {
#define INA     struct in_ifaddr *
                                if ((ia = (INA)ifa_ifwithdstaddr(
                                    SA(&ipaddr))) == NULL) {
                                        ia = (INA)ifa_ifwithnet(SA(&ipaddr));
                                }
                        } else {
                                ia = ip_rtaddr(ipaddr.sin_addr);
                        }
                        if (ia == NULL) {
                                type = ICMP_UNREACH;
                                code = ICMP_UNREACH_SRCFAIL;
                                goto bad;
                        }
                        ip->ip_dst = ipaddr.sin_addr;
                        IFA_LOCK(&ia->ia_ifa);
                        (void) memcpy(cp + off, &(IA_SIN(ia)->sin_addr),
                            sizeof (struct in_addr));
                        IFA_UNLOCK(&ia->ia_ifa);
                        IFA_REMREF(&ia->ia_ifa);
                        ia = NULL;
                        cp[IPOPT_OFFSET] += sizeof (struct in_addr);
                        /*
                         * Let ip_intr's mcast routing check handle mcast pkts
                         */
                        forward = !IN_MULTICAST(ntohl(ip->ip_dst.s_addr));
                        break;

                case IPOPT_RR:
                        if (optlen < IPOPT_OFFSET + sizeof (*cp)) {
                                code = &cp[IPOPT_OFFSET] - (u_char *)ip;
                                goto bad;
                        }
                        if ((off = cp[IPOPT_OFFSET]) < IPOPT_MINOFF) {
                                code = &cp[IPOPT_OFFSET] - (u_char *)ip;
                                goto bad;
                        }
                        /*
                         * If no space remains, ignore.
                         */
                        off--;                  /* 0 origin */
                        if (off > optlen - (int)sizeof (struct in_addr))
                                break;
                        (void) memcpy(&ipaddr.sin_addr, &ip->ip_dst,
                            sizeof (ipaddr.sin_addr));
                        /*
                         * locate outgoing interface; if we're the destination,
                         * use the incoming interface (should be same).
                         */
                        if ((ia = (INA)ifa_ifwithaddr(SA(&ipaddr))) == NULL) {
                                if ((ia = ip_rtaddr(ipaddr.sin_addr)) == NULL) {
                                        type = ICMP_UNREACH;
                                        code = ICMP_UNREACH_HOST;
                                        goto bad;
                                }
                        }
                        IFA_LOCK(&ia->ia_ifa);
                        (void) memcpy(cp + off, &(IA_SIN(ia)->sin_addr),
                            sizeof (struct in_addr));
                        IFA_UNLOCK(&ia->ia_ifa);
                        IFA_REMREF(&ia->ia_ifa);
                        ia = NULL;
                        cp[IPOPT_OFFSET] += sizeof (struct in_addr);
                        break;

                case IPOPT_TS:
                        code = cp - (u_char *)ip;
                        ipt = (struct ip_timestamp *)(void *)cp;
                        if (ipt->ipt_len < 4 || ipt->ipt_len > 40) {
                                code = (u_char *)&ipt->ipt_len - (u_char *)ip;
                                goto bad;
                        }
                        if (ipt->ipt_ptr < 5) {
                                code = (u_char *)&ipt->ipt_ptr - (u_char *)ip;
                                goto bad;
                        }
                        if (ipt->ipt_ptr >
                            ipt->ipt_len - (int)sizeof (int32_t)) {
                                if (++ipt->ipt_oflw == 0) {
                                        code = (u_char *)&ipt->ipt_ptr -
                                            (u_char *)ip;
                                        goto bad;
                                }
                                break;
                        }
                        sin = (struct in_addr *)(void *)(cp + ipt->ipt_ptr - 1);
                        switch (ipt->ipt_flg) {

                        case IPOPT_TS_TSONLY:
                                break;

                        case IPOPT_TS_TSANDADDR:
                                if (ipt->ipt_ptr - 1 + sizeof (n_time) +
                                    sizeof (struct in_addr) > ipt->ipt_len) {
                                        code = (u_char *)&ipt->ipt_ptr -
                                            (u_char *)ip;
                                        goto bad;
                                }
                                ipaddr.sin_addr = dst;
                                ia = (INA)ifaof_ifpforaddr(SA(&ipaddr),
                                    m->m_pkthdr.rcvif);
                                if (ia == NULL)
                                        continue;
                                IFA_LOCK(&ia->ia_ifa);
                                (void) memcpy(sin, &IA_SIN(ia)->sin_addr,
                                    sizeof (struct in_addr));
                                IFA_UNLOCK(&ia->ia_ifa);
                                ipt->ipt_ptr += sizeof (struct in_addr);
                                IFA_REMREF(&ia->ia_ifa);
                                ia = NULL;
                                break;

                        case IPOPT_TS_PRESPEC:
                                if (ipt->ipt_ptr - 1 + sizeof (n_time) +
                                    sizeof (struct in_addr) > ipt->ipt_len) {
                                        code = (u_char *)&ipt->ipt_ptr -
                                            (u_char *)ip;
                                        goto bad;
                                }
                                (void) memcpy(&ipaddr.sin_addr, sin,
                                    sizeof (struct in_addr));
                                if ((ia = (struct in_ifaddr *)ifa_ifwithaddr(
                                    SA(&ipaddr))) == NULL)
                                        continue;
                                IFA_REMREF(&ia->ia_ifa);
                                ia = NULL;
                                ipt->ipt_ptr += sizeof (struct in_addr);
                                break;

                        default:
                                /* XXX can't take &ipt->ipt_flg */
                                code = (u_char *)&ipt->ipt_ptr -
                                    (u_char *)ip + 1;
                                goto bad;
                        }
                        ntime = iptime();
                        (void) memcpy(cp + ipt->ipt_ptr - 1, &ntime,
                            sizeof (n_time));
                        ipt->ipt_ptr += sizeof (n_time);
                }
        }
        if (forward && ipforwarding) {
                ip_forward(m, 1, next_hop);
                return (1);
        }
        return (0);
bad:
        /* XXX icmp_error adds in hdr length */
        ip->ip_len -= IP_VHL_HL(ip->ip_vhl) << 2;
        icmp_error(m, type, code, 0, 0);
        OSAddAtomic(1, &ipstat.ips_badoptions);
        return (1);
}

/*
 * Check for the presence of the IP Router Alert option [RFC2113]
 * in the header of an IPv4 datagram.
 *
 * This call is not intended for use from the forwarding path; it is here
 * so that protocol domains may check for the presence of the option.
 * Given how FreeBSD's IPv4 stack is currently structured, the Router Alert
 * option does not have much relevance to the implementation, though this
 * may change in future.
 * Router alert options SHOULD be passed if running in IPSTEALTH mode and
 * we are not the endpoint.
 * Length checks on individual options should already have been peformed
 * by ip_dooptions() therefore they are folded under DIAGNOSTIC here.
 *
 * Return zero if not present or options are invalid, non-zero if present.
 */
int
ip_checkrouteralert(struct mbuf *m)
{
        struct ip *ip = mtod(m, struct ip *);
        u_char *cp;
        int opt, optlen, cnt, found_ra;

        found_ra = 0;
        cp = (u_char *)(ip + 1);
        cnt = (IP_VHL_HL(ip->ip_vhl) << 2) - sizeof (struct ip);
        for (; cnt > 0; cnt -= optlen, cp += optlen) {
                opt = cp[IPOPT_OPTVAL];
                if (opt == IPOPT_EOL)
                        break;
                if (opt == IPOPT_NOP)
                        optlen = 1;
                else {
#ifdef DIAGNOSTIC
                        if (cnt < IPOPT_OLEN + sizeof (*cp))
                                break;
#endif
                        optlen = cp[IPOPT_OLEN];
#ifdef DIAGNOSTIC
                        if (optlen < IPOPT_OLEN + sizeof (*cp) || optlen > cnt)
                                break;
#endif
                }
                switch (opt) {
                case IPOPT_RA:
#ifdef DIAGNOSTIC
                        if (optlen != IPOPT_OFFSET + sizeof (uint16_t) ||
                            (*((uint16_t *)(void *)&cp[IPOPT_OFFSET]) != 0))
                                break;
                        else
#endif
                                found_ra = 1;
                        break;
                default:
                        break;
                }
        }

        return (found_ra);
}

/*
 * Given address of next destination (final or next hop),
 * return internet address info of interface to be used to get there.
 */
struct in_ifaddr *
ip_rtaddr(struct in_addr dst)
{
        struct sockaddr_in *sin;
        struct ifaddr *rt_ifa;
        struct route ro;

        bzero(&ro, sizeof (ro));
        sin = SIN(&ro.ro_dst);
        sin->sin_family = AF_INET;
        sin->sin_len = sizeof (*sin);
        sin->sin_addr = dst;

        rtalloc_ign(&ro, RTF_PRCLONING);
        if (ro.ro_rt == NULL) {
                ROUTE_RELEASE(&ro);
                return (NULL);
        }

        RT_LOCK(ro.ro_rt);
        if ((rt_ifa = ro.ro_rt->rt_ifa) != NULL)
                IFA_ADDREF(rt_ifa);
        RT_UNLOCK(ro.ro_rt);
        ROUTE_RELEASE(&ro);

        return ((struct in_ifaddr *)rt_ifa);
}

/*
 * Save incoming source route for use in replies,
 * to be picked up later by ip_srcroute if the receiver is interested.
 */
void
save_rte(u_char *option, struct in_addr dst)
{
        unsigned olen;

        olen = option[IPOPT_OLEN];
#if DIAGNOSTIC
        if (ipprintfs)
                printf("save_rte: olen %d\n", olen);
#endif
        if (olen > sizeof (ip_srcrt) - (1 + sizeof (dst)))
                return;
        bcopy(option, ip_srcrt.srcopt, olen);
        ip_nhops = (olen - IPOPT_OFFSET - 1) / sizeof (struct in_addr);
        ip_srcrt.dst = dst;
}

/*
 * Retrieve incoming source route for use in replies,
 * in the same form used by setsockopt.
 * The first hop is placed before the options, will be removed later.
 */
struct mbuf *
ip_srcroute(void)
{
        struct in_addr *p, *q;
        struct mbuf *m;

        if (ip_nhops == 0)
                return (NULL);

        m = m_get(M_DONTWAIT, MT_HEADER);
        if (m == NULL)
                return (NULL);

#define OPTSIZ  (sizeof (ip_srcrt.nop) + sizeof (ip_srcrt.srcopt))

        /* length is (nhops+1)*sizeof(addr) + sizeof(nop + srcrt header) */
        m->m_len = ip_nhops * sizeof (struct in_addr) +
            sizeof (struct in_addr) + OPTSIZ;
#if DIAGNOSTIC
        if (ipprintfs)
                printf("ip_srcroute: nhops %d mlen %d", ip_nhops, m->m_len);
#endif

        /*
         * First save first hop for return route
         */
        p = &ip_srcrt.route[ip_nhops - 1];
        *(mtod(m, struct in_addr *)) = *p--;
#if DIAGNOSTIC
        if (ipprintfs)
                printf(" hops %lx",
                    (u_int32_t)ntohl(mtod(m, struct in_addr *)->s_addr));
#endif

        /*
         * Copy option fields and padding (nop) to mbuf.
         */
        ip_srcrt.nop = IPOPT_NOP;
        ip_srcrt.srcopt[IPOPT_OFFSET] = IPOPT_MINOFF;
        (void) memcpy(mtod(m, caddr_t) + sizeof (struct in_addr),
            &ip_srcrt.nop, OPTSIZ);
        q = (struct in_addr *)(void *)(mtod(m, caddr_t) +
            sizeof (struct in_addr) + OPTSIZ);
#undef OPTSIZ
        /*
         * Record return path as an IP source route,
         * reversing the path (pointers are now aligned).
         */
        while (p >= ip_srcrt.route) {
#if DIAGNOSTIC
                if (ipprintfs)
                        printf(" %lx", (u_int32_t)ntohl(q->s_addr));
#endif
                *q++ = *p--;
        }
        /*
         * Last hop goes to final destination.
         */
        *q = ip_srcrt.dst;
#if DIAGNOSTIC
        if (ipprintfs)
                printf(" %lx\n", (u_int32_t)ntohl(q->s_addr));
#endif
        return (m);
}

/*
 * Strip out IP options, at higher
 * level protocol in the kernel.
 * Second argument is buffer to which options
 * will be moved, and return value is their length.
 * XXX should be deleted; last arg currently ignored.
 */
void
ip_stripoptions(struct mbuf *m, struct mbuf *mopt)
{
#pragma unused(mopt)
        int i;
        struct ip *ip = mtod(m, struct ip *);
        caddr_t opts;
        int olen;

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

        olen = (IP_VHL_HL(ip->ip_vhl) << 2) - sizeof (struct ip);
        opts = (caddr_t)(ip + 1);
        i = m->m_len - (sizeof (struct ip) + olen);
        bcopy(opts + olen, opts, (unsigned)i);
        m->m_len -= olen;
        if (m->m_flags & M_PKTHDR)
                m->m_pkthdr.len -= olen;
        ip->ip_vhl = IP_MAKE_VHL(IPVERSION, sizeof (struct ip) >> 2);
}

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

static int
sysctl_ipforwarding SYSCTL_HANDLER_ARGS
{
#pragma unused(arg1, arg2)
        int i, was_ipforwarding = ipforwarding;

        i = sysctl_handle_int(oidp, oidp->oid_arg1, oidp->oid_arg2, req);
        if (i != 0 || req->newptr == USER_ADDR_NULL)
                return (i);

        if (was_ipforwarding && !ipforwarding) {
                /* clean up IPv4 forwarding cached routes */
                ifnet_head_lock_shared();
                for (i = 0; i <= if_index; i++) {
                        struct ifnet *ifp = ifindex2ifnet[i];
                        if (ifp != NULL) {
                                lck_mtx_lock(&ifp->if_cached_route_lock);
                                ROUTE_RELEASE(&ifp->if_fwd_route);
                                bzero(&ifp->if_fwd_route,
                                    sizeof (ifp->if_fwd_route));
                                lck_mtx_unlock(&ifp->if_cached_route_lock);
                        }
                }
                ifnet_head_done();
        }

        return (0);
}

/*
 * Similar to inp_route_{copyout,copyin} routines except that these copy
 * out the cached IPv4 forwarding route from struct ifnet instead of the
 * inpcb.  See comments for those routines for explanations.
 */
static void
ip_fwd_route_copyout(struct ifnet *ifp, struct route *dst)
{
        struct route *src = &ifp->if_fwd_route;

        lck_mtx_lock_spin(&ifp->if_cached_route_lock);
        lck_mtx_convert_spin(&ifp->if_cached_route_lock);

        /* Minor sanity check */
        if (src->ro_rt != NULL && rt_key(src->ro_rt)->sa_family != AF_INET)
                panic("%s: wrong or corrupted route: %p", __func__, src);

        route_copyout(dst, src, sizeof (*dst));

        lck_mtx_unlock(&ifp->if_cached_route_lock);
}

static void
ip_fwd_route_copyin(struct ifnet *ifp, struct route *src)
{
        struct route *dst = &ifp->if_fwd_route;

        lck_mtx_lock_spin(&ifp->if_cached_route_lock);
        lck_mtx_convert_spin(&ifp->if_cached_route_lock);

        /* Minor sanity check */
        if (src->ro_rt != NULL && rt_key(src->ro_rt)->sa_family != AF_INET)
                panic("%s: wrong or corrupted route: %p", __func__, src);

        if (ifp->if_fwd_cacheok)
                route_copyin(src, dst, sizeof (*src));

        lck_mtx_unlock(&ifp->if_cached_route_lock);
}

/*
 * Forward a packet.  If some error occurs return the sender
 * an icmp packet.  Note we can't always generate a meaningful
 * icmp message because icmp doesn't have a large enough repertoire
 * of codes and types.
 *
 * If not forwarding, just drop the packet.  This could be confusing
 * if ipforwarding was zero but some routing protocol was advancing
 * us as a gateway to somewhere.  However, we must let the routing
 * protocol deal with that.
 *
 * The srcrt parameter indicates whether the packet is being forwarded
 * via a source route.
 */
static void
ip_forward(struct mbuf *m, int srcrt, struct sockaddr_in *next_hop)
{
#if !IPFIREWALL
#pragma unused(next_hop)
#endif
        struct ip *ip = mtod(m, struct ip *);
        struct sockaddr_in *sin;
        struct rtentry *rt;
        struct route fwd_rt;
        int error, type = 0, code = 0;
        struct mbuf *mcopy;
        n_long dest;
        struct in_addr pkt_dst;
        u_int32_t nextmtu = 0, len;
        struct ip_out_args ipoa = { IFSCOPE_NONE, { 0 }, 0, 0 };
        struct ifnet *rcvifp = m->m_pkthdr.rcvif;
#if IPSEC
        struct secpolicy *sp = NULL;
        int ipsecerror;
#endif /* IPSEC */
#if PF
        struct pf_mtag *pf_mtag;
#endif /* PF */

        dest = 0;
#if IPFIREWALL
        /*
         * Cache the destination address of the packet; this may be
         * changed by use of 'ipfw fwd'.
         */
        pkt_dst = ((next_hop != NULL) ? next_hop->sin_addr : ip->ip_dst);
#else /* !IPFIREWALL */
        pkt_dst = ip->ip_dst;
#endif /* !IPFIREWALL */

#if DIAGNOSTIC
        if (ipprintfs)
                printf("forward: src %lx dst %lx ttl %x\n",
                    (u_int32_t)ip->ip_src.s_addr, (u_int32_t)pkt_dst.s_addr,
                    ip->ip_ttl);
#endif

        if (m->m_flags & (M_BCAST|M_MCAST) || !in_canforward(pkt_dst)) {
                OSAddAtomic(1, &ipstat.ips_cantforward);
                m_freem(m);
                return;
        }
#if IPSTEALTH
        if (!ipstealth) {
#endif /* IPSTEALTH */
                if (ip->ip_ttl <= IPTTLDEC) {
                        icmp_error(m, ICMP_TIMXCEED, ICMP_TIMXCEED_INTRANS,
                            dest, 0);
                        return;
                }
#if IPSTEALTH
        }
#endif /* IPSTEALTH */

#if PF
        pf_mtag = pf_find_mtag(m);
        if (pf_mtag != NULL && pf_mtag->pftag_rtableid != IFSCOPE_NONE) {
                ipoa.ipoa_boundif = pf_mtag->pftag_rtableid;
                ipoa.ipoa_flags |= IPOAF_BOUND_IF;
        }
#endif /* PF */

        ip_fwd_route_copyout(rcvifp, &fwd_rt);

        sin = SIN(&fwd_rt.ro_dst);
        if (ROUTE_UNUSABLE(&fwd_rt) || pkt_dst.s_addr != sin->sin_addr.s_addr) {
                ROUTE_RELEASE(&fwd_rt);

                sin->sin_family = AF_INET;
                sin->sin_len = sizeof (*sin);
                sin->sin_addr = pkt_dst;

                rtalloc_scoped_ign(&fwd_rt, RTF_PRCLONING, ipoa.ipoa_boundif);
                if (fwd_rt.ro_rt == NULL) {
                        icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_HOST, dest, 0);
                        goto done;
                }
        }
        rt = fwd_rt.ro_rt;

        /*
         * Save the IP header and at most 8 bytes of the payload,
         * in case we need to generate an ICMP message to the src.
         *
         * We don't use m_copy() because it might return a reference
         * to a shared cluster. Both this function and ip_output()
         * assume exclusive access to the IP header in `m', so any
         * data in a cluster may change before we reach icmp_error().
         */
        MGET(mcopy, M_DONTWAIT, m->m_type);
        if (mcopy != NULL) {
                M_COPY_PKTHDR(mcopy, m);
                mcopy->m_len = imin((IP_VHL_HL(ip->ip_vhl) << 2) + 8,
                    (int)ip->ip_len);
                m_copydata(m, 0, mcopy->m_len, mtod(mcopy, caddr_t));
        }

#if IPSTEALTH
        if (!ipstealth) {
#endif /* IPSTEALTH */
                ip->ip_ttl -= IPTTLDEC;
#if IPSTEALTH
        }
#endif /* IPSTEALTH */

        /*
         * If forwarding packet using same interface that it came in on,
         * perhaps should send a redirect to sender to shortcut a hop.
         * Only send redirect if source is sending directly to us,
         * and if packet was not source routed (or has any options).
         * Also, don't send redirect if forwarding using a default route
         * or a route modified by a redirect.
         */
        RT_LOCK_SPIN(rt);
        if (rt->rt_ifp == m->m_pkthdr.rcvif &&
            !(rt->rt_flags & (RTF_DYNAMIC|RTF_MODIFIED)) &&
            satosin(rt_key(rt))->sin_addr.s_addr != INADDR_ANY &&
            ipsendredirects && !srcrt && rt->rt_ifa != NULL) {
                struct in_ifaddr *ia = (struct in_ifaddr *)rt->rt_ifa;
                u_int32_t src = ntohl(ip->ip_src.s_addr);

                /* Become a regular mutex */
                RT_CONVERT_LOCK(rt);
                IFA_LOCK_SPIN(&ia->ia_ifa);
                if ((src & ia->ia_subnetmask) == ia->ia_subnet) {
                        if (rt->rt_flags & RTF_GATEWAY)
                                dest = satosin(rt->rt_gateway)->sin_addr.s_addr;
                        else
                                dest = pkt_dst.s_addr;
                        /*
                         * Router requirements says to only send
                         * host redirects.
                         */
                        type = ICMP_REDIRECT;
                        code = ICMP_REDIRECT_HOST;
#if DIAGNOSTIC
                        if (ipprintfs)
                                printf("redirect (%d) to %lx\n", code,
                                    (u_int32_t)dest);
#endif
                }
                IFA_UNLOCK(&ia->ia_ifa);
        }
        RT_UNLOCK(rt);

#if IPFIREWALL
        if (next_hop != NULL) {
                /* Pass IPFORWARD info if available */
                struct m_tag *tag;
                struct ip_fwd_tag *ipfwd_tag;

                tag = m_tag_create(KERNEL_MODULE_TAG_ID,
                    KERNEL_TAG_TYPE_IPFORWARD,
                    sizeof (*ipfwd_tag), M_NOWAIT, m);
                if (tag == NULL) {
                        error = ENOBUFS;
                        m_freem(m);
                        goto done;
                }

                ipfwd_tag = (struct ip_fwd_tag *)(tag+1);
                ipfwd_tag->next_hop = next_hop;

                m_tag_prepend(m, tag);
        }
#endif /* IPFIREWALL */

        /* Mark this packet as being forwarded from another interface */
        m->m_pkthdr.pkt_flags |= PKTF_FORWARDED;
        len = m_pktlen(m);

        error = ip_output(m, NULL, &fwd_rt, IP_FORWARDING | IP_OUTARGS,
            NULL, &ipoa);

        /* Refresh rt since the route could have changed while in IP */
        rt = fwd_rt.ro_rt;

        if (error != 0) {
                OSAddAtomic(1, &ipstat.ips_cantforward);
        } else {
                /*
                 * Increment stats on the source interface; the ones
                 * for destination interface has been taken care of
                 * during output above by virtue of PKTF_FORWARDED.
                 */
                rcvifp->if_fpackets++;
                rcvifp->if_fbytes += len;

                OSAddAtomic(1, &ipstat.ips_forward);
                if (type != 0) {
                        OSAddAtomic(1, &ipstat.ips_redirectsent);
                } else {
                        if (mcopy != NULL) {
                                /*
                                 * If we didn't have to go thru ipflow and
                                 * the packet was successfully consumed by
                                 * ip_output, the mcopy is rather a waste;
                                 * this could be further optimized.
                                 */
                                m_freem(mcopy);
                        }
                        goto done;
                }
        }
        if (mcopy == NULL)
                goto done;

        switch (error) {
        case 0:                         /* forwarded, but need redirect */
                /* type, code set above */
                break;

        case ENETUNREACH:               /* shouldn't happen, checked above */
        case EHOSTUNREACH:
        case ENETDOWN:
        case EHOSTDOWN:
        default:
                type = ICMP_UNREACH;
                code = ICMP_UNREACH_HOST;
                break;

        case EMSGSIZE:
                type = ICMP_UNREACH;
                code = ICMP_UNREACH_NEEDFRAG;

                if (rt == NULL) {
                        break;
                } else {
                        RT_LOCK_SPIN(rt);
                        if (rt->rt_ifp != NULL)
                                nextmtu = rt->rt_ifp->if_mtu;
                        RT_UNLOCK(rt);
                }
#ifdef IPSEC
                if (ipsec_bypass)
                        break;

                /*
                 * If the packet is routed over IPsec tunnel, tell the
                 * originator the tunnel MTU.
                 *      tunnel MTU = if MTU - sizeof(IP) - ESP/AH hdrsiz
                 * XXX quickhack!!!
                 */
                sp = ipsec4_getpolicybyaddr(mcopy, IPSEC_DIR_OUTBOUND,
                    IP_FORWARDING, &ipsecerror);

                if (sp == NULL)
                        break;

                /*
                 * find the correct route for outer IPv4
                 * header, compute tunnel MTU.
                 */
                nextmtu = 0;

                if (sp->req != NULL &&
                    sp->req->saidx.mode == IPSEC_MODE_TUNNEL) {
                        struct secasindex saidx;
                        struct secasvar *sav;
                        struct route *ro;
                        struct ip *ipm;
                        int ipsechdr;

                        /* count IPsec header size */
                        ipsechdr = ipsec_hdrsiz(sp);

                        ipm = mtod(mcopy, struct ip *);
                        bcopy(&sp->req->saidx, &saidx, sizeof (saidx));
                        saidx.mode = sp->req->saidx.mode;
                        saidx.reqid = sp->req->saidx.reqid;
                        sin = SIN(&saidx.src);
                        if (sin->sin_len == 0) {
                                sin->sin_len = sizeof (*sin);
                                sin->sin_family = AF_INET;
                                sin->sin_port = IPSEC_PORT_ANY;
                                bcopy(&ipm->ip_src, &sin->sin_addr,
                                    sizeof (sin->sin_addr));
                        }
                        sin = SIN(&saidx.dst);
                        if (sin->sin_len == 0) {
                                sin->sin_len = sizeof (*sin);
                                sin->sin_family = AF_INET;
                                sin->sin_port = IPSEC_PORT_ANY;
                                bcopy(&ipm->ip_dst, &sin->sin_addr,
                                    sizeof (sin->sin_addr));
                        }
                        sav = key_allocsa_policy(&saidx);
                        if (sav != NULL) {
                                lck_mtx_lock(sadb_mutex);
                                if (sav->sah != NULL) {
                                        ro = &sav->sah->sa_route;
                                        if (ro->ro_rt != NULL) {
                                                RT_LOCK(ro->ro_rt);
                                                if (ro->ro_rt->rt_ifp != NULL) {
                                                        nextmtu = ro->ro_rt->
                                                            rt_ifp->if_mtu;
                                                        nextmtu -= ipsechdr;
                                                }
                                                RT_UNLOCK(ro->ro_rt);
                                        }
                                }
                                key_freesav(sav, KEY_SADB_LOCKED);
                                lck_mtx_unlock(sadb_mutex);
                        }
                }
                key_freesp(sp, KEY_SADB_UNLOCKED);
#endif /* IPSEC */
                break;

        case ENOBUFS:
                /*
                 * A router should not generate ICMP_SOURCEQUENCH as
                 * required in RFC1812 Requirements for IP Version 4 Routers.
                 * Source quench could be a big problem under DoS attacks,
                 * or if the underlying interface is rate-limited.
                 * Those who need source quench packets may re-enable them
                 * via the net.inet.ip.sendsourcequench sysctl.
                 */
                if (ip_sendsourcequench == 0) {
                        m_freem(mcopy);
                        goto done;
                } else {
                        type = ICMP_SOURCEQUENCH;
                        code = 0;
                }
                break;

        case EACCES:                    /* ipfw denied packet */
                m_freem(mcopy);
                goto done;
        }

        if (type == ICMP_UNREACH && code == ICMP_UNREACH_NEEDFRAG)
                OSAddAtomic(1, &ipstat.ips_cantfrag);

        icmp_error(mcopy, type, code, dest, nextmtu);
done:
        ip_fwd_route_copyin(rcvifp, &fwd_rt);
}

int
ip_savecontrol(struct inpcb *inp, struct mbuf **mp, struct ip *ip,
    struct mbuf *m)
{
        *mp = NULL;
        if (inp->inp_socket->so_options & SO_TIMESTAMP) {
                struct timeval tv;

                getmicrotime(&tv);
                mp = sbcreatecontrol_mbuf((caddr_t)&tv, sizeof (tv),
                    SCM_TIMESTAMP, SOL_SOCKET, mp);
                if (*mp == NULL) {
                        goto no_mbufs;
                }
        }
        if (inp->inp_socket->so_options & SO_TIMESTAMP_MONOTONIC) {
                uint64_t time;

                time = mach_absolute_time();
                mp = sbcreatecontrol_mbuf((caddr_t)&time, sizeof (time),
                    SCM_TIMESTAMP_MONOTONIC, SOL_SOCKET, mp);
                if (*mp == NULL) {
                        goto no_mbufs;
                }
        }
        if (inp->inp_flags & INP_RECVDSTADDR) {
                mp = sbcreatecontrol_mbuf((caddr_t)&ip->ip_dst,
                    sizeof (struct in_addr), IP_RECVDSTADDR, IPPROTO_IP, mp);
                if (*mp == NULL) {
                        goto no_mbufs;
                }
        }
#ifdef notyet
        /*
         * XXX
         * Moving these out of udp_input() made them even more broken
         * than they already were.
         */
        /* options were tossed already */
        if (inp->inp_flags & INP_RECVOPTS) {
                mp = sbcreatecontrol_mbuf((caddr_t)opts_deleted_above,
                    sizeof (struct in_addr), IP_RECVOPTS, IPPROTO_IP, mp);
                if (*mp == NULL) {
                        goto no_mbufs;
                }
        }
        /* ip_srcroute doesn't do what we want here, need to fix */
        if (inp->inp_flags & INP_RECVRETOPTS) {
                mp = sbcreatecontrol_mbuf((caddr_t)ip_srcroute(),
                    sizeof (struct in_addr), IP_RECVRETOPTS, IPPROTO_IP, mp);
                if (*mp == NULL) {
                        goto no_mbufs;
                }
        }
#endif /* notyet */
        if (inp->inp_flags & INP_RECVIF) {
                struct ifnet *ifp;
                uint8_t sdlbuf[SOCK_MAXADDRLEN + 1];
                struct sockaddr_dl *sdl2 = SDL(&sdlbuf);

                /*
                 * Make sure to accomodate the largest possible
                 * size of SA(if_lladdr)->sa_len.
                 */
                _CASSERT(sizeof (sdlbuf) == (SOCK_MAXADDRLEN + 1));

                ifnet_head_lock_shared();
                if ((ifp = m->m_pkthdr.rcvif) != NULL &&
                    ifp->if_index && (ifp->if_index <= if_index)) {
                        struct ifaddr *ifa = ifnet_addrs[ifp->if_index - 1];
                        struct sockaddr_dl *sdp;

                        if (!ifa || !ifa->ifa_addr)
                                goto makedummy;

                        IFA_LOCK_SPIN(ifa);
                        sdp = SDL(ifa->ifa_addr);
                        /*
                         * Change our mind and don't try copy.
                         */
                        if (sdp->sdl_family != AF_LINK) {
                                IFA_UNLOCK(ifa);
                                goto makedummy;
                        }
                        /* the above _CASSERT ensures sdl_len fits in sdlbuf */
                        bcopy(sdp, sdl2, sdp->sdl_len);
                        IFA_UNLOCK(ifa);
                } else {
makedummy:
                        sdl2->sdl_len =
                            offsetof(struct sockaddr_dl, sdl_data[0]);
                        sdl2->sdl_family = AF_LINK;
                        sdl2->sdl_index = 0;
                        sdl2->sdl_nlen = sdl2->sdl_alen = sdl2->sdl_slen = 0;
                }
                ifnet_head_done();
                mp = sbcreatecontrol_mbuf((caddr_t)sdl2, sdl2->sdl_len,
                    IP_RECVIF, IPPROTO_IP, mp);
                if (*mp == NULL) {
                        goto no_mbufs;
                }
        }
        if (inp->inp_flags & INP_RECVTTL) {
                mp = sbcreatecontrol_mbuf((caddr_t)&ip->ip_ttl,
                    sizeof (ip->ip_ttl), IP_RECVTTL, IPPROTO_IP, mp);
                if (*mp == NULL) {
                        goto no_mbufs;
                }
        }
        if (inp->inp_socket->so_flags & SOF_RECV_TRAFFIC_CLASS) {
                int tc = m_get_traffic_class(m);

                mp = sbcreatecontrol_mbuf((caddr_t)&tc, sizeof (tc),
                    SO_TRAFFIC_CLASS, SOL_SOCKET, mp);
                if (*mp == NULL) {
                        goto no_mbufs;
                }
        }
        if (inp->inp_flags & INP_PKTINFO) {
                struct in_pktinfo pi;

                bzero(&pi, sizeof (struct in_pktinfo));
                bcopy(&ip->ip_dst, &pi.ipi_addr, sizeof (struct in_addr));
                pi.ipi_ifindex = (m != NULL && m->m_pkthdr.rcvif != NULL) ?
                    m->m_pkthdr.rcvif->if_index : 0;

                mp = sbcreatecontrol_mbuf((caddr_t)&pi,
                    sizeof (struct in_pktinfo), IP_RECVPKTINFO, IPPROTO_IP, mp);
                if (*mp == NULL) {
                        goto no_mbufs;
                }
        }
        return (0);

no_mbufs:
        ipstat.ips_pktdropcntrl++;
        return (ENOBUFS);
}

static inline u_short
ip_cksum(struct mbuf *m, int hlen)
{
        u_short sum;

        if (m->m_pkthdr.csum_flags & CSUM_IP_CHECKED) {
                sum = !(m->m_pkthdr.csum_flags & CSUM_IP_VALID);
        } else if (!(m->m_pkthdr.rcvif->if_flags & IFF_LOOPBACK) &&
            !(m->m_pkthdr.pkt_flags & PKTF_LOOP)) {
                /*
                 * The packet arrived on an interface which isn't capable
                 * of performing IP header checksum; compute it now.
                 */
                sum = ip_cksum_hdr_in(m, hlen);
        } else {
                sum = 0;
                m->m_pkthdr.csum_flags |= (CSUM_DATA_VALID | CSUM_PSEUDO_HDR |
                    CSUM_IP_CHECKED | CSUM_IP_VALID);
                m->m_pkthdr.csum_data = 0xffff;
        }

        if (sum != 0)
                OSAddAtomic(1, &ipstat.ips_badsum);

        return (sum);
}

static int
ip_getstat SYSCTL_HANDLER_ARGS
{
#pragma unused(oidp, arg1, arg2)
        if (req->oldptr == USER_ADDR_NULL)
                req->oldlen = (size_t)sizeof (struct ipstat);

        return (SYSCTL_OUT(req, &ipstat, MIN(sizeof (ipstat), req->oldlen)));
}

void
ip_setsrcifaddr_info(struct mbuf *m, uint32_t src_idx, struct in_ifaddr *ia)
{
        VERIFY(m->m_flags & M_PKTHDR);

        /*
         * If the source ifaddr is specified, pick up the information
         * from there; otherwise just grab the passed-in ifindex as the
         * caller may not have the ifaddr available.
         */
        if (ia != NULL) {
                m->m_pkthdr.pkt_flags |= PKTF_IFAINFO;
                m->m_pkthdr.src_ifindex = ia->ia_ifp->if_index;
        } else {
                m->m_pkthdr.src_ifindex = src_idx;
                if (src_idx != 0)
                        m->m_pkthdr.pkt_flags |= PKTF_IFAINFO;
        }
}

void
ip_setdstifaddr_info(struct mbuf *m, uint32_t dst_idx, struct in_ifaddr *ia)
{
        VERIFY(m->m_flags & M_PKTHDR);

        /*
         * If the destination ifaddr is specified, pick up the information
         * from there; otherwise just grab the passed-in ifindex as the
         * caller may not have the ifaddr available.
         */
        if (ia != NULL) {
                m->m_pkthdr.pkt_flags |= PKTF_IFAINFO;
                m->m_pkthdr.dst_ifindex = ia->ia_ifp->if_index;
        } else {
                m->m_pkthdr.dst_ifindex = dst_idx;
                if (dst_idx != 0)
                        m->m_pkthdr.pkt_flags |= PKTF_IFAINFO;
        }
}

int
ip_getsrcifaddr_info(struct mbuf *m, uint32_t *src_idx, uint32_t *iaf)
{
        VERIFY(m->m_flags & M_PKTHDR);

        if (!(m->m_pkthdr.pkt_flags & PKTF_IFAINFO))
                return (-1);

        if (src_idx != NULL)
                *src_idx = m->m_pkthdr.src_ifindex;

        if (iaf != NULL)
                *iaf = 0;

        return (0);
}

int
ip_getdstifaddr_info(struct mbuf *m, uint32_t *dst_idx, uint32_t *iaf)
{
        VERIFY(m->m_flags & M_PKTHDR);

        if (!(m->m_pkthdr.pkt_flags & PKTF_IFAINFO))
                return (-1);

        if (dst_idx != NULL)
                *dst_idx = m->m_pkthdr.dst_ifindex;

        if (iaf != NULL)
                *iaf = 0;

        return (0);
}

/*
 * Protocol input handler for IPPROTO_GRE.
 */
void
gre_input(struct mbuf *m, int off)
{
        gre_input_func_t fn = gre_input_func;

        /*
         * If there is a registered GRE input handler, pass mbuf to it.
         */
        if (fn != NULL) {
                lck_mtx_unlock(inet_domain_mutex);
                m = fn(m, off, (mtod(m, struct ip *))->ip_p);
                lck_mtx_lock(inet_domain_mutex);
        }

        /*
         * If no matching tunnel that is up is found, we inject
         * the mbuf to raw ip socket to see if anyone picks it up.
         */
        if (m != NULL)
                rip_input(m, off);
}

/*
 * Private KPI for PPP/PPTP.
 */
int
ip_gre_register_input(gre_input_func_t fn)
{
        lck_mtx_lock(inet_domain_mutex);
        gre_input_func = fn;
        lck_mtx_unlock(inet_domain_mutex);

        return (0);
}