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

/*
 * Copyright (c) 2000-2019 Apple Inc. All rights reserved.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
 *
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. The rights granted to you under the License
 * may not be used to create, or enable the creation or redistribution of,
 * unlawful or unlicensed copies of an Apple operating system, or to
 * circumvent, violate, or enable the circumvention or violation of, any
 * terms of an Apple operating system software license agreement.
 *
 * Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this file.
 *
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
 */
/*
 * Copyright (c) 1982, 1986, 1988, 1990, 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_output.c 8.3 (Berkeley) 1/21/94
 */
/*
 * NOTICE: This file was modified by SPARTA, Inc. in 2005 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/kernel.h>
#include <sys/malloc.h>
#include <sys/mbuf.h>
#include <sys/protosw.h>
#include <sys/socket.h>
#include <sys/socketvar.h>
#include <kern/locks.h>
#include <sys/sysctl.h>
#include <sys/mcache.h>
#include <sys/kdebug.h>

#include <machine/endian.h>
#include <pexpert/pexpert.h>
#include <mach/sdt.h>

#include <libkern/OSAtomic.h>
#include <libkern/OSByteOrder.h>

#include <net/if.h>
#include <net/if_dl.h>
#include <net/if_types.h>
#include <net/route.h>
#include <net/ntstat.h>
#include <net/net_osdep.h>
#include <net/dlil.h>
#include <net/net_perf.h>

#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netinet/in_pcb.h>
#include <netinet/in_var.h>
#include <netinet/ip_var.h>
#include <netinet/kpi_ipfilter_var.h>
#include <netinet/in_tclass.h>
#include <netinet/udp.h>

#include <netinet6/nd6.h>

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

#define DBG_LAYER_BEG           NETDBG_CODE(DBG_NETIP, 1)
#define DBG_LAYER_END           NETDBG_CODE(DBG_NETIP, 3)
#define DBG_FNC_IP_OUTPUT       NETDBG_CODE(DBG_NETIP, (1 << 8) | 1)
#define DBG_FNC_IPSEC4_OUTPUT   NETDBG_CODE(DBG_NETIP, (2 << 8) | 1)

#if IPSEC
#include <netinet6/ipsec.h>
#include <netkey/key.h>
#if IPSEC_DEBUG
#include <netkey/key_debug.h>
#else
#define KEYDEBUG(lev, arg)
#endif
#endif /* IPSEC */

#if NECP
#include <net/necp.h>
#endif /* NECP */

#if IPFIREWALL
#include <netinet/ip_fw.h>
#if IPDIVERT
#include <netinet/ip_divert.h>
#endif /* IPDIVERT */
#endif /* IPFIREWALL */

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

#if PF
#include <net/pfvar.h>
#endif /* PF */

#if IPFIREWALL_FORWARD && IPFIREWALL_FORWARD_DEBUG
#define print_ip(a)     \
        printf("%ld.%ld.%ld.%ld", (ntohl(a.s_addr) >> 24) & 0xFF,       \
            (ntohl(a.s_addr) >> 16) & 0xFF,                             \
            (ntohl(a.s_addr) >> 8) & 0xFF,                              \
            (ntohl(a.s_addr)) & 0xFF);
#endif /* IPFIREWALL_FORWARD && IPFIREWALL_FORWARD_DEBUG */

u_short ip_id;

static int sysctl_reset_ip_output_stats SYSCTL_HANDLER_ARGS;
static int sysctl_ip_output_measure_bins SYSCTL_HANDLER_ARGS;
static int sysctl_ip_output_getperf SYSCTL_HANDLER_ARGS;
static void ip_out_cksum_stats(int, u_int32_t);
static struct mbuf *ip_insertoptions(struct mbuf *, struct mbuf *, int *);
static int ip_optcopy(struct ip *, struct ip *);
static int ip_pcbopts(int, struct mbuf **, struct mbuf *);
static void imo_trace(struct ip_moptions *, int);
static void ip_mloopback(struct ifnet *, struct ifnet *, struct mbuf *,
    struct sockaddr_in *, int);
static struct ifaddr *in_selectsrcif(struct ip *, struct route *, unsigned int);

extern struct ip_linklocal_stat ip_linklocal_stat;

/* temporary: for testing */
#if IPSEC
extern int ipsec_bypass;
#endif

static int ip_maxchainsent = 0;
SYSCTL_INT(_net_inet_ip, OID_AUTO, maxchainsent,
    CTLFLAG_RW | CTLFLAG_LOCKED, &ip_maxchainsent, 0,
    "use dlil_output_list");
#if DEBUG
static int forge_ce = 0;
SYSCTL_INT(_net_inet_ip, OID_AUTO, forge_ce,
    CTLFLAG_RW | CTLFLAG_LOCKED, &forge_ce, 0,
    "Forge ECN CE");
#endif /* DEBUG */

static int ip_select_srcif_debug = 0;
SYSCTL_INT(_net_inet_ip, OID_AUTO, select_srcif_debug,
    CTLFLAG_RW | CTLFLAG_LOCKED, &ip_select_srcif_debug, 0,
    "log source interface selection debug info");

static int ip_output_measure = 0;
SYSCTL_PROC(_net_inet_ip, OID_AUTO, output_perf,
    CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_LOCKED,
    &ip_output_measure, 0, sysctl_reset_ip_output_stats, "I",
    "Do time measurement");

static uint64_t ip_output_measure_bins = 0;
SYSCTL_PROC(_net_inet_ip, OID_AUTO, output_perf_bins,
    CTLTYPE_QUAD | CTLFLAG_RW | CTLFLAG_LOCKED, &ip_output_measure_bins, 0,
    sysctl_ip_output_measure_bins, "I",
    "bins for chaining performance data histogram");

static net_perf_t net_perf;
SYSCTL_PROC(_net_inet_ip, OID_AUTO, output_perf_data,
    CTLTYPE_STRUCT | CTLFLAG_RD | CTLFLAG_LOCKED,
    0, 0, sysctl_ip_output_getperf, "S,net_perf",
    "IP output performance data (struct net_perf, net/net_perf.h)");

__private_extern__ int rfc6864 = 1;
SYSCTL_INT(_net_inet_ip, OID_AUTO, rfc6864, CTLFLAG_RW | CTLFLAG_LOCKED,
    &rfc6864, 0, "updated ip id field behavior");

#define IMO_TRACE_HIST_SIZE     32      /* size of trace history */

/* For gdb */
__private_extern__ unsigned int imo_trace_hist_size = IMO_TRACE_HIST_SIZE;

struct ip_moptions_dbg {
        struct ip_moptions      imo;                    /* ip_moptions */
        u_int16_t               imo_refhold_cnt;        /* # of IMO_ADDREF */
        u_int16_t               imo_refrele_cnt;        /* # of IMO_REMREF */
        /*
         * Alloc and free callers.
         */
        ctrace_t                imo_alloc;
        ctrace_t                imo_free;
        /*
         * Circular lists of IMO_ADDREF and IMO_REMREF callers.
         */
        ctrace_t                imo_refhold[IMO_TRACE_HIST_SIZE];
        ctrace_t                imo_refrele[IMO_TRACE_HIST_SIZE];
};

#if DEBUG
static unsigned int imo_debug = 1;      /* debugging (enabled) */
#else
static unsigned int imo_debug;          /* debugging (disabled) */
#endif /* !DEBUG */
static unsigned int imo_size;           /* size of zone element */
static struct zone *imo_zone;           /* zone for ip_moptions */

#define IMO_ZONE_MAX            64              /* maximum elements in zone */
#define IMO_ZONE_NAME           "ip_moptions"   /* zone name */

/*
 * IP output.  The packet in mbuf chain m contains a skeletal IP
 * header (with len, off, ttl, proto, tos, src, dst).
 * The mbuf chain containing the packet will be freed.
 * The mbuf opt, if present, will not be freed.
 */
int
ip_output(struct mbuf *m0, struct mbuf *opt, struct route *ro, int flags,
    struct ip_moptions *imo, struct ip_out_args *ipoa)
{
        return ip_output_list(m0, 0, opt, ro, flags, imo, ipoa);
}

/*
 * IP output.  The packet in mbuf chain m contains a skeletal IP
 * header (with len, off, ttl, proto, tos, src, dst).
 * The mbuf chain containing the packet will be freed.
 * The mbuf opt, if present, will not be freed.
 *
 * Route ro MUST be non-NULL; if ro->ro_rt is valid, route lookup would be
 * skipped and ro->ro_rt would be used.  Otherwise the result of route
 * lookup is stored in ro->ro_rt.
 *
 * In the IP forwarding case, the packet will arrive with options already
 * inserted, so must have a NULL opt pointer.
 */
int
ip_output_list(struct mbuf *m0, int packetchain, struct mbuf *opt,
    struct route *ro, int flags, struct ip_moptions *imo,
    struct ip_out_args *ipoa)
{
        struct ip *ip;
        struct ifnet *ifp = NULL;               /* not refcnt'd */
        struct mbuf *m = m0, *prevnxt = NULL, **mppn = &prevnxt;
        int hlen = sizeof(struct ip);
        int len = 0, error = 0;
        struct sockaddr_in *dst = NULL;
        struct in_ifaddr *ia = NULL, *src_ia = NULL;
        struct in_addr pkt_dst;
        struct ipf_pktopts *ippo = NULL;
        ipfilter_t inject_filter_ref = NULL;
        struct mbuf *packetlist;
        uint32_t sw_csum, pktcnt = 0, scnt = 0, bytecnt = 0;
        uint32_t packets_processed = 0;
        unsigned int ifscope = IFSCOPE_NONE;
        struct flowadv *adv = NULL;
        struct timeval start_tv;
#if IPSEC
        struct socket *so = NULL;
        struct secpolicy *sp = NULL;
#endif /* IPSEC */
#if NECP
        necp_kernel_policy_result necp_result = 0;
        necp_kernel_policy_result_parameter necp_result_parameter;
        necp_kernel_policy_id necp_matched_policy_id = 0;
#endif /* NECP */
#if IPFIREWALL
        int ipfwoff;
        struct sockaddr_in *next_hop_from_ipfwd_tag = NULL;
#endif /* IPFIREWALL */
#if IPFIREWALL || DUMMYNET
        struct m_tag *tag;
#endif /* IPFIREWALL || DUMMYNET */
#if DUMMYNET
        struct ip_out_args saved_ipoa;
        struct sockaddr_in dst_buf;
#endif /* DUMMYNET */
        struct {
#if IPSEC
                struct ipsec_output_state ipsec_state;
#endif /* IPSEC */
#if NECP
                struct route necp_route;
#endif /* NECP */
#if IPFIREWALL || DUMMYNET
                struct ip_fw_args args;
#endif /* IPFIREWALL || DUMMYNET */
#if IPFIREWALL_FORWARD
                struct route sro_fwd;
#endif /* IPFIREWALL_FORWARD */
#if DUMMYNET
                struct route saved_route;
#endif /* DUMMYNET */
                struct ipf_pktopts ipf_pktopts;
        } ipobz;
#define ipsec_state     ipobz.ipsec_state
#define necp_route      ipobz.necp_route
#define args            ipobz.args
#define sro_fwd         ipobz.sro_fwd
#define saved_route     ipobz.saved_route
#define ipf_pktopts     ipobz.ipf_pktopts
        union {
                struct {
                        boolean_t select_srcif : 1;     /* set once */
                        boolean_t srcbound : 1;         /* set once */
                        boolean_t nocell : 1;           /* set once */
                        boolean_t isbroadcast : 1;
                        boolean_t didfilter : 1;
                        boolean_t noexpensive : 1;      /* set once */
                        boolean_t noconstrained : 1;      /* set once */
                        boolean_t awdl_unrestricted : 1;        /* set once */
#if IPFIREWALL_FORWARD
                        boolean_t fwd_rewrite_src : 1;
#endif /* IPFIREWALL_FORWARD */
                };
                uint32_t raw;
        } ipobf = { .raw = 0 };

        int interface_mtu = 0;

/*
 * Here we check for restrictions when sending frames.
 * N.B.: IPv4 over internal co-processor interfaces is not allowed.
 */
#define IP_CHECK_RESTRICTIONS(_ifp, _ipobf)                             \
        (((_ipobf).nocell && IFNET_IS_CELLULAR(_ifp)) ||                \
         ((_ipobf).noexpensive && IFNET_IS_EXPENSIVE(_ifp)) ||          \
         ((_ipobf).noconstrained && IFNET_IS_CONSTRAINED(_ifp)) ||      \
          (IFNET_IS_INTCOPROC(_ifp)) ||                                 \
         (!(_ipobf).awdl_unrestricted && IFNET_IS_AWDL_RESTRICTED(_ifp)))

        if (ip_output_measure) {
                net_perf_start_time(&net_perf, &start_tv);
        }
        KERNEL_DEBUG(DBG_FNC_IP_OUTPUT | DBG_FUNC_START, 0, 0, 0, 0, 0);

        VERIFY(m0->m_flags & M_PKTHDR);
        packetlist = m0;

        /* zero out {ipsec_state, args, sro_fwd, saved_route, ipf_pktops} */
        bzero(&ipobz, sizeof(ipobz));
        ippo = &ipf_pktopts;

#if IPFIREWALL || DUMMYNET
        if (SLIST_EMPTY(&m0->m_pkthdr.tags)) {
                goto ipfw_tags_done;
        }

        /* Grab info from mtags prepended to the chain */
#if DUMMYNET
        if ((tag = m_tag_locate(m0, 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;
                opt = NULL;
                saved_route = dn_tag->dn_ro;
                ro = &saved_route;

                imo = NULL;
                bcopy(&dn_tag->dn_dst, &dst_buf, sizeof(dst_buf));
                dst = &dst_buf;
                ifp = dn_tag->dn_ifp;
                flags = dn_tag->dn_flags;
                if ((dn_tag->dn_flags & IP_OUTARGS)) {
                        saved_ipoa = dn_tag->dn_ipoa;
                        ipoa = &saved_ipoa;
                }

                m_tag_delete(m0, tag);
        }
#endif /* DUMMYNET */

#if IPDIVERT
        if ((tag = m_tag_locate(m0, 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(m0, tag);
        }
#endif /* IPDIVERT */

#if IPFIREWALL
        if ((tag = m_tag_locate(m0, KERNEL_MODULE_TAG_ID,
            KERNEL_TAG_TYPE_IPFORWARD, NULL)) != NULL) {
                struct ip_fwd_tag       *ipfwd_tag;

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

                m_tag_delete(m0, tag);
        }
#endif /* IPFIREWALL */

ipfw_tags_done:
#endif /* IPFIREWALL || DUMMYNET */

        m = m0;
        m->m_pkthdr.pkt_flags &= ~(PKTF_LOOP | PKTF_IFAINFO);

#if IPSEC
        if (ipsec_bypass == 0 && !(flags & IP_NOIPSEC)) {
                /* If packet is bound to an interface, check bound policies */
                if ((flags & IP_OUTARGS) && (ipoa != NULL) &&
                    (ipoa->ipoa_flags & IPOAF_BOUND_IF) &&
                    ipoa->ipoa_boundif != IFSCOPE_NONE) {
                        if (ipsec4_getpolicybyinterface(m, IPSEC_DIR_OUTBOUND,
                            &flags, ipoa, &sp) != 0) {
                                goto bad;
                        }
                }
        }
#endif /* IPSEC */

        VERIFY(ro != NULL);

        if (flags & IP_OUTARGS) {
                /*
                 * In the forwarding case, only the ifscope value is used,
                 * as source interface selection doesn't take place.
                 */
                if ((ipobf.select_srcif = (!(flags & IP_FORWARDING) &&
                    (ipoa->ipoa_flags & IPOAF_SELECT_SRCIF)))) {
                        ipf_pktopts.ippo_flags |= IPPOF_SELECT_SRCIF;
                }

                if ((ipoa->ipoa_flags & IPOAF_BOUND_IF) &&
                    ipoa->ipoa_boundif != IFSCOPE_NONE) {
                        ifscope = ipoa->ipoa_boundif;
                        ipf_pktopts.ippo_flags |=
                            (IPPOF_BOUND_IF | (ifscope << IPPOF_SHIFT_IFSCOPE));
                }

                /* double negation needed for bool bit field */
                ipobf.srcbound = !!(ipoa->ipoa_flags & IPOAF_BOUND_SRCADDR);
                if (ipobf.srcbound) {
                        ipf_pktopts.ippo_flags |= IPPOF_BOUND_SRCADDR;
                }
        } else {
                ipobf.select_srcif = FALSE;
                ipobf.srcbound = FALSE;
                ifscope = IFSCOPE_NONE;
                if (flags & IP_OUTARGS) {
                        ipoa->ipoa_boundif = IFSCOPE_NONE;
                        ipoa->ipoa_flags &= ~(IPOAF_SELECT_SRCIF |
                            IPOAF_BOUND_IF | IPOAF_BOUND_SRCADDR);
                }
        }

        if (flags & IP_OUTARGS) {
                if (ipoa->ipoa_flags & IPOAF_NO_CELLULAR) {
                        ipobf.nocell = TRUE;
                        ipf_pktopts.ippo_flags |= IPPOF_NO_IFT_CELLULAR;
                }
                if (ipoa->ipoa_flags & IPOAF_NO_EXPENSIVE) {
                        ipobf.noexpensive = TRUE;
                        ipf_pktopts.ippo_flags |= IPPOF_NO_IFF_EXPENSIVE;
                }
                if (ipoa->ipoa_flags & IPOAF_NO_CONSTRAINED) {
                        ipobf.noconstrained = TRUE;
                        ipf_pktopts.ippo_flags |= IPPOF_NO_IFF_CONSTRAINED;
                }
                if (ipoa->ipoa_flags & IPOAF_AWDL_UNRESTRICTED) {
                        ipobf.awdl_unrestricted = TRUE;
                }
                adv = &ipoa->ipoa_flowadv;
                adv->code = FADV_SUCCESS;
                ipoa->ipoa_retflags = 0;
        }

#if IPSEC
        if (ipsec_bypass == 0 && !(flags & IP_NOIPSEC)) {
                so = ipsec_getsocket(m);
                if (so != NULL) {
                        (void) ipsec_setsocket(m, NULL);
                }
        }
#endif /* IPSEC */

#if DUMMYNET
        if (args.fwa_ipfw_rule != NULL || args.fwa_pf_rule != NULL) {
                /* dummynet already saw us */
                ip = mtod(m, struct ip *);
                hlen = IP_VHL_HL(ip->ip_vhl) << 2;
                pkt_dst = ip->ip_dst;
                if (ro->ro_rt != NULL) {
                        RT_LOCK_SPIN(ro->ro_rt);
                        ia = (struct in_ifaddr *)ro->ro_rt->rt_ifa;
                        if (ia) {
                                /* Become a regular mutex */
                                RT_CONVERT_LOCK(ro->ro_rt);
                                IFA_ADDREF(&ia->ia_ifa);
                        }
                        RT_UNLOCK(ro->ro_rt);
                }

#if IPFIREWALL
                if (args.fwa_ipfw_rule != NULL) {
                        goto skip_ipsec;
                }
#endif /* IPFIREWALL  */
                if (args.fwa_pf_rule != NULL) {
                        goto sendit;
                }
        }
#endif /* DUMMYNET */

loopit:
        packets_processed++;
        ipobf.isbroadcast = FALSE;
        ipobf.didfilter = FALSE;
#if IPFIREWALL_FORWARD
        ipobf.fwd_rewrite_src = FALSE;
#endif /* IPFIREWALL_FORWARD */

        VERIFY(m->m_flags & M_PKTHDR);
        /*
         * No need to proccess packet twice if we've already seen it.
         */
        if (!SLIST_EMPTY(&m->m_pkthdr.tags)) {
                inject_filter_ref = ipf_get_inject_filter(m);
        } else {
                inject_filter_ref = NULL;
        }

        if (opt) {
                m = ip_insertoptions(m, opt, &len);
                hlen = len;
                /* Update the chain */
                if (m != m0) {
                        if (m0 == packetlist) {
                                packetlist = m;
                        }
                        m0 = m;
                }
        }
        ip = mtod(m, struct ip *);

#if IPFIREWALL
        /*
         * rdar://8542331
         *
         * When dealing with a packet chain, we need to reset "next_hop"
         * because "dst" may have been changed to the gateway address below
         * for the previous packet of the chain. This could cause the route
         * to be inavertandly changed to the route to the gateway address
         * (instead of the route to the destination).
         */
        args.fwa_next_hop = next_hop_from_ipfwd_tag;
        pkt_dst = args.fwa_next_hop ? args.fwa_next_hop->sin_addr : ip->ip_dst;
#else /* !IPFIREWALL */
        pkt_dst = ip->ip_dst;
#endif /* !IPFIREWALL */

        /*
         * We must not send if the packet is destined to network zero.
         * RFC1122 3.2.1.3 (a) and (b).
         */
        if (IN_ZERONET(ntohl(pkt_dst.s_addr))) {
                error = EHOSTUNREACH;
                goto bad;
        }

        /*
         * Fill in IP header.
         */
        if (!(flags & (IP_FORWARDING | IP_RAWOUTPUT))) {
                ip->ip_vhl = IP_MAKE_VHL(IPVERSION, hlen >> 2);
                ip->ip_off &= IP_DF;
                if (rfc6864 && IP_OFF_IS_ATOMIC(ip->ip_off)) {
                        // Per RFC6864, value of ip_id is undefined for atomic ip packets
                        ip->ip_id = 0;
                } else {
                        ip->ip_id = ip_randomid();
                }
                OSAddAtomic(1, &ipstat.ips_localout);
        } else {
                hlen = IP_VHL_HL(ip->ip_vhl) << 2;
        }

#if DEBUG
        /* For debugging, we let the stack forge congestion */
        if (forge_ce != 0 &&
            ((ip->ip_tos & IPTOS_ECN_MASK) == IPTOS_ECN_ECT1 ||
            (ip->ip_tos & IPTOS_ECN_MASK) == IPTOS_ECN_ECT0)) {
                ip->ip_tos = (ip->ip_tos & ~IPTOS_ECN_MASK) | IPTOS_ECN_CE;
                forge_ce--;
        }
#endif /* DEBUG */

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

        dst = SIN(&ro->ro_dst);

        /*
         * If there is a cached route,
         * check that it is to the same destination
         * and is still up.  If not, free it and try again.
         * The address family should also be checked in case of sharing the
         * cache with IPv6.
         */

        if (ro->ro_rt != NULL) {
                if (ROUTE_UNUSABLE(ro) && ip->ip_src.s_addr != INADDR_ANY &&
                    !(flags & (IP_ROUTETOIF | IP_FORWARDING))) {
                        src_ia = ifa_foraddr(ip->ip_src.s_addr);
                        if (src_ia == NULL) {
                                error = EADDRNOTAVAIL;
                                goto bad;
                        }
                        IFA_REMREF(&src_ia->ia_ifa);
                        src_ia = NULL;
                }
                /*
                 * Test rt_flags without holding rt_lock for performance
                 * reasons; if the route is down it will hopefully be
                 * caught by the layer below (since it uses this route
                 * as a hint) or during the next transmit.
                 */
                if (ROUTE_UNUSABLE(ro) || dst->sin_family != AF_INET ||
                    dst->sin_addr.s_addr != pkt_dst.s_addr) {
                        ROUTE_RELEASE(ro);
                }

                /*
                 * If we're doing source interface selection, we may not
                 * want to use this route; only synch up the generation
                 * count otherwise.
                 */
                if (!ipobf.select_srcif && ro->ro_rt != NULL &&
                    RT_GENID_OUTOFSYNC(ro->ro_rt)) {
                        RT_GENID_SYNC(ro->ro_rt);
                }
        }
        if (ro->ro_rt == NULL) {
                bzero(dst, sizeof(*dst));
                dst->sin_family = AF_INET;
                dst->sin_len = sizeof(*dst);
                dst->sin_addr = pkt_dst;
        }
        /*
         * If routing to interface only,
         * short circuit routing lookup.
         */
        if (flags & IP_ROUTETOIF) {
                if (ia != NULL) {
                        IFA_REMREF(&ia->ia_ifa);
                }
                if ((ia = ifatoia(ifa_ifwithdstaddr(sintosa(dst)))) == NULL) {
                        ia = ifatoia(ifa_ifwithnet(sintosa(dst)));
                        if (ia == NULL) {
                                OSAddAtomic(1, &ipstat.ips_noroute);
                                error = ENETUNREACH;
                                /* XXX IPv6 APN fallback notification?? */
                                goto bad;
                        }
                }
                ifp = ia->ia_ifp;
                ip->ip_ttl = 1;
                ipobf.isbroadcast = in_broadcast(dst->sin_addr, ifp);
                /*
                 * For consistency with other cases below.  Loopback
                 * multicast case is handled separately by ip_mloopback().
                 */
                if ((ifp->if_flags & IFF_LOOPBACK) &&
                    !IN_MULTICAST(ntohl(pkt_dst.s_addr))) {
                        m->m_pkthdr.rcvif = ifp;
                        ip_setsrcifaddr_info(m, ifp->if_index, NULL);
                        ip_setdstifaddr_info(m, ifp->if_index, NULL);
                }
        } else if (IN_MULTICAST(ntohl(pkt_dst.s_addr)) &&
            imo != NULL && (ifp = imo->imo_multicast_ifp) != NULL) {
                /*
                 * Bypass the normal routing lookup for multicast
                 * packets if the interface is specified.
                 */
                ipobf.isbroadcast = FALSE;
                if (ia != NULL) {
                        IFA_REMREF(&ia->ia_ifa);
                }

                /* Macro takes reference on ia */
                IFP_TO_IA(ifp, ia);
        } else {
                struct ifaddr *ia0 = NULL;
                boolean_t cloneok = FALSE;
                /*
                 * Perform source interface selection; the source IP address
                 * must belong to one of the addresses of the interface used
                 * by the route.  For performance reasons, do this only if
                 * there is no route, or if the routing table has changed,
                 * or if we haven't done source interface selection on this
                 * route (for this PCB instance) before.
                 */
                if (ipobf.select_srcif &&
                    ip->ip_src.s_addr != INADDR_ANY && (ROUTE_UNUSABLE(ro) ||
                    !(ro->ro_flags & ROF_SRCIF_SELECTED))) {
                        /* Find the source interface */
                        ia0 = in_selectsrcif(ip, ro, ifscope);

                        /*
                         * If the source address belongs to a restricted
                         * interface and the caller forbids our using
                         * interfaces of such type, pretend that there is no
                         * route.
                         */
                        if (ia0 != NULL &&
                            IP_CHECK_RESTRICTIONS(ia0->ifa_ifp, ipobf)) {
                                IFA_REMREF(ia0);
                                ia0 = NULL;
                                error = EHOSTUNREACH;
                                if (flags & IP_OUTARGS) {
                                        ipoa->ipoa_retflags |= IPOARF_IFDENIED;
                                }
                                goto bad;
                        }

                        /*
                         * If the source address is spoofed (in the case of
                         * IP_RAWOUTPUT on an unbounded socket), or if this
                         * is destined for local/loopback, just let it go out
                         * using the interface of the route.  Otherwise,
                         * there's no interface having such an address,
                         * so bail out.
                         */
                        if (ia0 == NULL && (!(flags & IP_RAWOUTPUT) ||
                            ipobf.srcbound) && ifscope != lo_ifp->if_index) {
                                error = EADDRNOTAVAIL;
                                goto bad;
                        }

                        /*
                         * If the caller didn't explicitly specify the scope,
                         * pick it up from the source interface.  If the cached
                         * route was wrong and was blown away as part of source
                         * interface selection, don't mask out RTF_PRCLONING
                         * since that route may have been allocated by the ULP,
                         * unless the IP header was created by the caller or
                         * the destination is IPv4 LLA.  The check for the
                         * latter is needed because IPv4 LLAs are never scoped
                         * in the current implementation, and we don't want to
                         * replace the resolved IPv4 LLA route with one whose
                         * gateway points to that of the default gateway on
                         * the primary interface of the system.
                         */
                        if (ia0 != NULL) {
                                if (ifscope == IFSCOPE_NONE) {
                                        ifscope = ia0->ifa_ifp->if_index;
                                }
                                cloneok = (!(flags & IP_RAWOUTPUT) &&
                                    !(IN_LINKLOCAL(ntohl(ip->ip_dst.s_addr))));
                        }
                }

                /*
                 * If this is the case, we probably don't want to allocate
                 * a protocol-cloned route since we didn't get one from the
                 * ULP.  This lets TCP do its thing, while not burdening
                 * forwarding or ICMP with the overhead of cloning a route.
                 * Of course, we still want to do any cloning requested by
                 * the link layer, as this is probably required in all cases
                 * for correct operation (as it is for ARP).
                 */
                if (ro->ro_rt == NULL) {
                        unsigned long ign = RTF_PRCLONING;
                        /*
                         * We make an exception here: if the destination
                         * address is INADDR_BROADCAST, allocate a protocol-
                         * cloned host route so that we end up with a route
                         * marked with the RTF_BROADCAST flag.  Otherwise,
                         * we would end up referring to the default route,
                         * instead of creating a cloned host route entry.
                         * That would introduce inconsistencies between ULPs
                         * that allocate a route and those that don't.  The
                         * RTF_BROADCAST route is important since we'd want
                         * to send out undirected IP broadcast packets using
                         * link-level broadcast address. Another exception
                         * is for ULP-created routes that got blown away by
                         * source interface selection (see above).
                         *
                         * These exceptions will no longer be necessary when
                         * the RTF_PRCLONING scheme is no longer present.
                         */
                        if (cloneok || dst->sin_addr.s_addr == INADDR_BROADCAST) {
                                ign &= ~RTF_PRCLONING;
                        }

                        /*
                         * Loosen the route lookup criteria if the ifscope
                         * corresponds to the loopback interface; this is
                         * needed to support Application Layer Gateways
                         * listening on loopback, in conjunction with packet
                         * filter redirection rules.  The final source IP
                         * address will be rewritten by the packet filter
                         * prior to the RFC1122 loopback check below.
                         */
                        if (ifscope == lo_ifp->if_index) {
                                rtalloc_ign(ro, ign);
                        } else {
                                rtalloc_scoped_ign(ro, ign, ifscope);
                        }

                        /*
                         * If the route points to a cellular/expensive interface
                         * and the caller forbids our using interfaces of such type,
                         * pretend that there is no route.
                         */
                        if (ro->ro_rt != NULL) {
                                RT_LOCK_SPIN(ro->ro_rt);
                                if (IP_CHECK_RESTRICTIONS(ro->ro_rt->rt_ifp,
                                    ipobf)) {
                                        RT_UNLOCK(ro->ro_rt);
                                        ROUTE_RELEASE(ro);
                                        if (flags & IP_OUTARGS) {
                                                ipoa->ipoa_retflags |=
                                                    IPOARF_IFDENIED;
                                        }
                                } else {
                                        RT_UNLOCK(ro->ro_rt);
                                }
                        }
                }

                if (ro->ro_rt == NULL) {
                        OSAddAtomic(1, &ipstat.ips_noroute);
                        error = EHOSTUNREACH;
                        if (ia0 != NULL) {
                                IFA_REMREF(ia0);
                                ia0 = NULL;
                        }
                        goto bad;
                }

                if (ia != NULL) {
                        IFA_REMREF(&ia->ia_ifa);
                }
                RT_LOCK_SPIN(ro->ro_rt);
                ia = ifatoia(ro->ro_rt->rt_ifa);
                if (ia != NULL) {
                        /* Become a regular mutex */
                        RT_CONVERT_LOCK(ro->ro_rt);
                        IFA_ADDREF(&ia->ia_ifa);
                }
                /*
                 * Note: ia_ifp may not be the same as rt_ifp; the latter
                 * is what we use for determining outbound i/f, mtu, etc.
                 */
                ifp = ro->ro_rt->rt_ifp;
                ro->ro_rt->rt_use++;
                if (ro->ro_rt->rt_flags & RTF_GATEWAY) {
                        dst = SIN(ro->ro_rt->rt_gateway);
                }
                if (ro->ro_rt->rt_flags & RTF_HOST) {
                        /* double negation needed for bool bit field */
                        ipobf.isbroadcast =
                            !!(ro->ro_rt->rt_flags & RTF_BROADCAST);
                } else {
                        /* Become a regular mutex */
                        RT_CONVERT_LOCK(ro->ro_rt);
                        ipobf.isbroadcast = in_broadcast(dst->sin_addr, ifp);
                }
                /*
                 * For consistency with IPv6, as well as to ensure that
                 * IP_RECVIF is set correctly for packets that are sent
                 * to one of the local addresses.  ia (rt_ifa) would have
                 * been fixed up by rt_setif for local routes.  This
                 * would make it appear as if the packet arrives on the
                 * interface which owns the local address.  Loopback
                 * multicast case is handled separately by ip_mloopback().
                 */
                if (ia != NULL && (ifp->if_flags & IFF_LOOPBACK) &&
                    !IN_MULTICAST(ntohl(pkt_dst.s_addr))) {
                        uint32_t srcidx;

                        m->m_pkthdr.rcvif = ia->ia_ifa.ifa_ifp;

                        if (ia0 != NULL) {
                                srcidx = ia0->ifa_ifp->if_index;
                        } else if ((ro->ro_flags & ROF_SRCIF_SELECTED) &&
                            ro->ro_srcia != NULL) {
                                srcidx = ro->ro_srcia->ifa_ifp->if_index;
                        } else {
                                srcidx = 0;
                        }

                        ip_setsrcifaddr_info(m, srcidx, NULL);
                        ip_setdstifaddr_info(m, 0, ia);
                }
                RT_UNLOCK(ro->ro_rt);
                if (ia0 != NULL) {
                        IFA_REMREF(ia0);
                        ia0 = NULL;
                }
        }

        if (IN_MULTICAST(ntohl(pkt_dst.s_addr))) {
                struct ifnet *srcifp = NULL;
                struct in_multi *inm;
                u_int32_t vif = 0;
                u_int8_t ttl = IP_DEFAULT_MULTICAST_TTL;
                u_int8_t loop = IP_DEFAULT_MULTICAST_LOOP;

                m->m_flags |= M_MCAST;
                /*
                 * IP destination address is multicast.  Make sure "dst"
                 * still points to the address in "ro".  (It may have been
                 * changed to point to a gateway address, above.)
                 */
                dst = SIN(&ro->ro_dst);
                /*
                 * See if the caller provided any multicast options
                 */
                if (imo != NULL) {
                        IMO_LOCK(imo);
                        vif = imo->imo_multicast_vif;
                        ttl = imo->imo_multicast_ttl;
                        loop = imo->imo_multicast_loop;
                        if (!(flags & IP_RAWOUTPUT)) {
                                ip->ip_ttl = ttl;
                        }
                        if (imo->imo_multicast_ifp != NULL) {
                                ifp = imo->imo_multicast_ifp;
                        }
                        IMO_UNLOCK(imo);
                } else if (!(flags & IP_RAWOUTPUT)) {
                        vif = -1;
                        ip->ip_ttl = ttl;
                }
                /*
                 * Confirm that the outgoing interface supports multicast.
                 */
                if (imo == NULL || vif == -1) {
                        if (!(ifp->if_flags & IFF_MULTICAST)) {
                                OSAddAtomic(1, &ipstat.ips_noroute);
                                error = ENETUNREACH;
                                goto bad;
                        }
                }
                /*
                 * If source address not specified yet, use address
                 * of outgoing interface.
                 */
                if (ip->ip_src.s_addr == INADDR_ANY) {
                        struct in_ifaddr *ia1;
                        lck_rw_lock_shared(in_ifaddr_rwlock);
                        TAILQ_FOREACH(ia1, &in_ifaddrhead, ia_link) {
                                IFA_LOCK_SPIN(&ia1->ia_ifa);
                                if (ia1->ia_ifp == ifp) {
                                        ip->ip_src = IA_SIN(ia1)->sin_addr;
                                        srcifp = ifp;
                                        IFA_UNLOCK(&ia1->ia_ifa);
                                        break;
                                }
                                IFA_UNLOCK(&ia1->ia_ifa);
                        }
                        lck_rw_done(in_ifaddr_rwlock);
                        if (ip->ip_src.s_addr == INADDR_ANY) {
                                error = ENETUNREACH;
                                goto bad;
                        }
                }

                in_multihead_lock_shared();
                IN_LOOKUP_MULTI(&pkt_dst, ifp, inm);
                in_multihead_lock_done();
                if (inm != NULL && (imo == NULL || loop)) {
                        /*
                         * If we belong to the destination multicast group
                         * on the outgoing interface, and the caller did not
                         * forbid loopback, loop back a copy.
                         */
                        if (!TAILQ_EMPTY(&ipv4_filters)
#if NECP
                            && !necp_packet_should_skip_filters(m)
#endif // NECP
                            ) {
                                struct ipfilter *filter;
                                int seen = (inject_filter_ref == NULL);

                                if (imo != NULL) {
                                        ipf_pktopts.ippo_flags |=
                                            IPPOF_MCAST_OPTS;
                                        ipf_pktopts.ippo_mcast_ifnet = ifp;
                                        ipf_pktopts.ippo_mcast_ttl = ttl;
                                        ipf_pktopts.ippo_mcast_loop = loop;
                                }

                                ipf_ref();

                                /*
                                 * 4135317 - always pass network byte
                                 * order to filter
                                 */
#if BYTE_ORDER != BIG_ENDIAN
                                HTONS(ip->ip_len);
                                HTONS(ip->ip_off);
#endif
                                TAILQ_FOREACH(filter, &ipv4_filters, ipf_link) {
                                        if (seen == 0) {
                                                if ((struct ipfilter *)
                                                    inject_filter_ref == filter) {
                                                        seen = 1;
                                                }
                                        } else if (filter->ipf_filter.
                                            ipf_output != NULL) {
                                                errno_t result;
                                                result = filter->ipf_filter.
                                                    ipf_output(filter->
                                                    ipf_filter.cookie,
                                                    (mbuf_t *)&m, ippo);
                                                if (result == EJUSTRETURN) {
                                                        ipf_unref();
                                                        INM_REMREF(inm);
                                                        goto done;
                                                }
                                                if (result != 0) {
                                                        ipf_unref();
                                                        INM_REMREF(inm);
                                                        goto bad;
                                                }
                                        }
                                }

                                /* set back to host byte order */
                                ip = mtod(m, struct ip *);
#if BYTE_ORDER != BIG_ENDIAN
                                NTOHS(ip->ip_len);
                                NTOHS(ip->ip_off);
#endif
                                ipf_unref();
                                ipobf.didfilter = TRUE;
                        }
                        ip_mloopback(srcifp, ifp, m, dst, hlen);
                }
                if (inm != NULL) {
                        INM_REMREF(inm);
                }
                /*
                 * Multicasts with a time-to-live of zero may be looped-
                 * back, above, but must not be transmitted on a network.
                 * Also, multicasts addressed to the loopback interface
                 * are not sent -- the above call to ip_mloopback() will
                 * loop back a copy if this host actually belongs to the
                 * destination group on the loopback interface.
                 */
                if (ip->ip_ttl == 0 || ifp->if_flags & IFF_LOOPBACK) {
                        m_freem(m);
                        goto done;
                }

                goto sendit;
        }
        /*
         * If source address not specified yet, use address
         * of outgoing interface.
         */
        if (ip->ip_src.s_addr == INADDR_ANY) {
                IFA_LOCK_SPIN(&ia->ia_ifa);
                ip->ip_src = IA_SIN(ia)->sin_addr;
                IFA_UNLOCK(&ia->ia_ifa);
#if IPFIREWALL_FORWARD
                /*
                 * Keep note that we did this - if the firewall changes
                 * the next-hop, our interface may change, changing the
                 * default source IP. It's a shame so much effort happens
                 * twice. Oh well.
                 */
                ipobf.fwd_rewrite_src = TRUE;
#endif /* IPFIREWALL_FORWARD */
        }

        /*
         * Look for broadcast address and
         * and verify user is allowed to send
         * such a packet.
         */
        if (ipobf.isbroadcast) {
                if (!(ifp->if_flags & IFF_BROADCAST)) {
                        error = EADDRNOTAVAIL;
                        goto bad;
                }
                if (!(flags & IP_ALLOWBROADCAST)) {
                        error = EACCES;
                        goto bad;
                }
                /* don't allow broadcast messages to be fragmented */
                if ((u_short)ip->ip_len > ifp->if_mtu) {
                        error = EMSGSIZE;
                        goto bad;
                }
                m->m_flags |= M_BCAST;
        } else {
                m->m_flags &= ~M_BCAST;
        }

sendit:
#if PF
        /* Invoke outbound packet filter */
        if (PF_IS_ENABLED) {
                int rc;

                m0 = m; /* Save for later */
#if DUMMYNET
                args.fwa_m = m;
                args.fwa_next_hop = dst;
                args.fwa_oif = ifp;
                args.fwa_ro = ro;
                args.fwa_dst = dst;
                args.fwa_oflags = flags;
                if (flags & IP_OUTARGS) {
                        args.fwa_ipoa = ipoa;
                }
                rc = pf_af_hook(ifp, mppn, &m, AF_INET, FALSE, &args);
#else /* DUMMYNET */
                rc = pf_af_hook(ifp, mppn, &m, AF_INET, FALSE, NULL);
#endif /* DUMMYNET */
                if (rc != 0 || m == NULL) {
                        /* Move to the next packet */
                        m = *mppn;

                        /* Skip ahead if first packet in list got dropped */
                        if (packetlist == m0) {
                                packetlist = m;
                        }

                        if (m != NULL) {
                                m0 = m;
                                /* Next packet in the chain */
                                goto loopit;
                        } else if (packetlist != NULL) {
                                /* No more packet; send down the chain */
                                goto sendchain;
                        }
                        /* Nothing left; we're done */
                        goto done;
                }
                m0 = m;
                ip = mtod(m, struct ip *);
                pkt_dst = ip->ip_dst;
                hlen = IP_VHL_HL(ip->ip_vhl) << 2;
        }
#endif /* PF */
        /*
         * Force IP TTL to 255 following draft-ietf-zeroconf-ipv4-linklocal.txt
         */
        if (IN_LINKLOCAL(ntohl(ip->ip_src.s_addr)) ||
            IN_LINKLOCAL(ntohl(ip->ip_dst.s_addr))) {
                ip_linklocal_stat.iplls_out_total++;
                if (ip->ip_ttl != MAXTTL) {
                        ip_linklocal_stat.iplls_out_badttl++;
                        ip->ip_ttl = MAXTTL;
                }
        }

        if (!ipobf.didfilter &&
            !TAILQ_EMPTY(&ipv4_filters)
#if NECP
            && !necp_packet_should_skip_filters(m)
#endif // NECP
            ) {
                struct ipfilter *filter;
                int seen = (inject_filter_ref == NULL);
                ipf_pktopts.ippo_flags &= ~IPPOF_MCAST_OPTS;

                /*
                 * Check that a TSO frame isn't passed to a filter.
                 * This could happen if a filter is inserted while
                 * TCP is sending the TSO packet.
                 */
                if (m->m_pkthdr.csum_flags & CSUM_TSO_IPV4) {
                        error = EMSGSIZE;
                        goto bad;
                }

                ipf_ref();

                /* 4135317 - always pass network byte order to filter */
#if BYTE_ORDER != BIG_ENDIAN
                HTONS(ip->ip_len);
                HTONS(ip->ip_off);
#endif
                TAILQ_FOREACH(filter, &ipv4_filters, ipf_link) {
                        if (seen == 0) {
                                if ((struct ipfilter *)inject_filter_ref ==
                                    filter) {
                                        seen = 1;
                                }
                        } else if (filter->ipf_filter.ipf_output) {
                                errno_t result;
                                result = filter->ipf_filter.
                                    ipf_output(filter->ipf_filter.cookie,
                                    (mbuf_t *)&m, ippo);
                                if (result == EJUSTRETURN) {
                                        ipf_unref();
                                        goto done;
                                }
                                if (result != 0) {
                                        ipf_unref();
                                        goto bad;
                                }
                        }
                }
                /* set back to host byte order */
                ip = mtod(m, struct ip *);
#if BYTE_ORDER != BIG_ENDIAN
                NTOHS(ip->ip_len);
                NTOHS(ip->ip_off);
#endif
                ipf_unref();
        }

#if NECP
        /* Process Network Extension Policy. Will Pass, Drop, or Rebind packet. */
        necp_matched_policy_id = necp_ip_output_find_policy_match(m,
            flags, (flags & IP_OUTARGS) ? ipoa : NULL, ro ? ro->ro_rt : NULL, &necp_result, &necp_result_parameter);
        if (necp_matched_policy_id) {
                necp_mark_packet_from_ip(m, necp_matched_policy_id);
                switch (necp_result) {
                case NECP_KERNEL_POLICY_RESULT_PASS:
                        /* Check if the interface is allowed */
                        if (!necp_packet_is_allowed_over_interface(m, ifp)) {
                                error = EHOSTUNREACH;
                                OSAddAtomic(1, &ipstat.ips_necp_policy_drop);
                                goto bad;
                        }
                        goto skip_ipsec;
                case NECP_KERNEL_POLICY_RESULT_DROP:
                case NECP_KERNEL_POLICY_RESULT_SOCKET_DIVERT:
                        /* Flow divert packets should be blocked at the IP layer */
                        error = EHOSTUNREACH;
                        OSAddAtomic(1, &ipstat.ips_necp_policy_drop);
                        goto bad;
                case NECP_KERNEL_POLICY_RESULT_IP_TUNNEL: {
                        /* Verify that the packet is being routed to the tunnel */
                        struct ifnet *policy_ifp = necp_get_ifnet_from_result_parameter(&necp_result_parameter);
                        if (policy_ifp == ifp) {
                                /* Check if the interface is allowed */
                                if (!necp_packet_is_allowed_over_interface(m, ifp)) {
                                        error = EHOSTUNREACH;
                                        OSAddAtomic(1, &ipstat.ips_necp_policy_drop);
                                        goto bad;
                                }
                                goto skip_ipsec;
                        } else {
                                if (necp_packet_can_rebind_to_ifnet(m, policy_ifp, &necp_route, AF_INET)) {
                                        /* Check if the interface is allowed */
                                        if (!necp_packet_is_allowed_over_interface(m, policy_ifp)) {
                                                error = EHOSTUNREACH;
                                                OSAddAtomic(1, &ipstat.ips_necp_policy_drop);
                                                goto bad;
                                        }

                                        /* Set ifp to the tunnel interface, since it is compatible with the packet */
                                        ifp = policy_ifp;
                                        ro = &necp_route;
                                        goto skip_ipsec;
                                } else {
                                        error = ENETUNREACH;
                                        OSAddAtomic(1, &ipstat.ips_necp_policy_drop);
                                        goto bad;
                                }
                        }
                }
                default:
                        break;
                }
        }
        /* Catch-all to check if the interface is allowed */
        if (!necp_packet_is_allowed_over_interface(m, ifp)) {
                error = EHOSTUNREACH;
                OSAddAtomic(1, &ipstat.ips_necp_policy_drop);
                goto bad;
        }
#endif /* NECP */

#if IPSEC
        if (ipsec_bypass != 0 || (flags & IP_NOIPSEC)) {
                goto skip_ipsec;
        }

        KERNEL_DEBUG(DBG_FNC_IPSEC4_OUTPUT | DBG_FUNC_START, 0, 0, 0, 0, 0);

        if (sp == NULL) {
                /* get SP for this packet */
                if (so != NULL) {
                        sp = ipsec4_getpolicybysock(m, IPSEC_DIR_OUTBOUND,
                            so, &error);
                } else {
                        sp = ipsec4_getpolicybyaddr(m, IPSEC_DIR_OUTBOUND,
                            flags, &error);
                }
                if (sp == NULL) {
                        IPSEC_STAT_INCREMENT(ipsecstat.out_inval);
                        KERNEL_DEBUG(DBG_FNC_IPSEC4_OUTPUT | DBG_FUNC_END,
                            0, 0, 0, 0, 0);
                        goto bad;
                }
        }

        error = 0;

        /* check policy */
        switch (sp->policy) {
        case IPSEC_POLICY_DISCARD:
        case IPSEC_POLICY_GENERATE:
                /*
                 * This packet is just discarded.
                 */
                IPSEC_STAT_INCREMENT(ipsecstat.out_polvio);
                KERNEL_DEBUG(DBG_FNC_IPSEC4_OUTPUT | DBG_FUNC_END,
                    1, 0, 0, 0, 0);
                goto bad;

        case IPSEC_POLICY_BYPASS:
        case IPSEC_POLICY_NONE:
                /* no need to do IPsec. */
                KERNEL_DEBUG(DBG_FNC_IPSEC4_OUTPUT | DBG_FUNC_END,
                    2, 0, 0, 0, 0);
                goto skip_ipsec;

        case IPSEC_POLICY_IPSEC:
                if (sp->req == NULL) {
                        /* acquire a policy */
                        error = key_spdacquire(sp);
                        KERNEL_DEBUG(DBG_FNC_IPSEC4_OUTPUT | DBG_FUNC_END,
                            3, 0, 0, 0, 0);
                        goto bad;
                }
                if (sp->ipsec_if) {
                        /* Verify the redirect to ipsec interface */
                        if (sp->ipsec_if == ifp) {
                                goto skip_ipsec;
                        }
                        goto bad;
                }
                break;

        case IPSEC_POLICY_ENTRUST:
        default:
                printf("ip_output: Invalid policy found. %d\n", sp->policy);
        }
        {
                ipsec_state.m = m;
                if (flags & IP_ROUTETOIF) {
                        bzero(&ipsec_state.ro, sizeof(ipsec_state.ro));
                } else {
                        route_copyout((struct route *)&ipsec_state.ro, ro, sizeof(struct route));
                }
                ipsec_state.dst = SA(dst);

                ip->ip_sum = 0;

                /*
                 * XXX
                 * delayed checksums are not currently compatible with IPsec
                 */
                if (m->m_pkthdr.csum_flags & CSUM_DELAY_DATA) {
                        in_delayed_cksum(m);
                }

#if BYTE_ORDER != BIG_ENDIAN
                HTONS(ip->ip_len);
                HTONS(ip->ip_off);
#endif

                DTRACE_IP6(send, struct mbuf *, m, struct inpcb *, NULL,
                    struct ip *, ip, struct ifnet *, ifp,
                    struct ip *, ip, struct ip6_hdr *, NULL);

                error = ipsec4_output(&ipsec_state, sp, flags);
                if (ipsec_state.tunneled == 6) {
                        m0 = m = NULL;
                        error = 0;
                        goto bad;
                }

                m0 = m = ipsec_state.m;

#if DUMMYNET
                /*
                 * If we're about to use the route in ipsec_state
                 * and this came from dummynet, cleaup now.
                 */
                if (ro == &saved_route &&
                    (!(flags & IP_ROUTETOIF) || ipsec_state.tunneled)) {
                        ROUTE_RELEASE(ro);
                }
#endif /* DUMMYNET */

                if (flags & IP_ROUTETOIF) {
                        /*
                         * if we have tunnel mode SA, we may need to ignore
                         * IP_ROUTETOIF.
                         */
                        if (ipsec_state.tunneled) {
                                flags &= ~IP_ROUTETOIF;
                                ro = (struct route *)&ipsec_state.ro;
                        }
                } else {
                        ro = (struct route *)&ipsec_state.ro;
                }
                dst = SIN(ipsec_state.dst);
                if (error) {
                        /* mbuf is already reclaimed in ipsec4_output. */
                        m0 = NULL;
                        switch (error) {
                        case EHOSTUNREACH:
                        case ENETUNREACH:
                        case EMSGSIZE:
                        case ENOBUFS:
                        case ENOMEM:
                                break;
                        default:
                                printf("ip4_output (ipsec): error code %d\n", error);
                        /* FALLTHRU */
                        case ENOENT:
                                /* don't show these error codes to the user */
                                error = 0;
                                break;
                        }
                        KERNEL_DEBUG(DBG_FNC_IPSEC4_OUTPUT | DBG_FUNC_END,
                            4, 0, 0, 0, 0);
                        goto bad;
                }
        }

        /* be sure to update variables that are affected by ipsec4_output() */
        ip = mtod(m, struct ip *);

#ifdef _IP_VHL
        hlen = IP_VHL_HL(ip->ip_vhl) << 2;
#else /* !_IP_VHL */
        hlen = ip->ip_hl << 2;
#endif /* !_IP_VHL */
        /* Check that there wasn't a route change and src is still valid */
        if (ROUTE_UNUSABLE(ro)) {
                ROUTE_RELEASE(ro);
                VERIFY(src_ia == NULL);
                if (ip->ip_src.s_addr != INADDR_ANY &&
                    !(flags & (IP_ROUTETOIF | IP_FORWARDING)) &&
                    (src_ia = ifa_foraddr(ip->ip_src.s_addr)) == NULL) {
                        error = EADDRNOTAVAIL;
                        KERNEL_DEBUG(DBG_FNC_IPSEC4_OUTPUT | DBG_FUNC_END,
                            5, 0, 0, 0, 0);
                        goto bad;
                }
                if (src_ia != NULL) {
                        IFA_REMREF(&src_ia->ia_ifa);
                        src_ia = NULL;
                }
        }

        if (ro->ro_rt == NULL) {
                if (!(flags & IP_ROUTETOIF)) {
                        printf("%s: can't update route after "
                            "IPsec processing\n", __func__);
                        error = EHOSTUNREACH;   /* XXX */
                        KERNEL_DEBUG(DBG_FNC_IPSEC4_OUTPUT | DBG_FUNC_END,
                            6, 0, 0, 0, 0);
                        goto bad;
                }
        } else {
                if (ia != NULL) {
                        IFA_REMREF(&ia->ia_ifa);
                }
                RT_LOCK_SPIN(ro->ro_rt);
                ia = ifatoia(ro->ro_rt->rt_ifa);
                if (ia != NULL) {
                        /* Become a regular mutex */
                        RT_CONVERT_LOCK(ro->ro_rt);
                        IFA_ADDREF(&ia->ia_ifa);
                }
                ifp = ro->ro_rt->rt_ifp;
                RT_UNLOCK(ro->ro_rt);
        }

        /* make it flipped, again. */
#if BYTE_ORDER != BIG_ENDIAN
        NTOHS(ip->ip_len);
        NTOHS(ip->ip_off);
#endif
        KERNEL_DEBUG(DBG_FNC_IPSEC4_OUTPUT | DBG_FUNC_END,
            7, 0xff, 0xff, 0xff, 0xff);

        /* Pass to filters again */
        if (!TAILQ_EMPTY(&ipv4_filters)
#if NECP
            && !necp_packet_should_skip_filters(m)
#endif // NECP
            ) {
                struct ipfilter *filter;

                ipf_pktopts.ippo_flags &= ~IPPOF_MCAST_OPTS;

                /*
                 * Check that a TSO frame isn't passed to a filter.
                 * This could happen if a filter is inserted while
                 * TCP is sending the TSO packet.
                 */
                if (m->m_pkthdr.csum_flags & CSUM_TSO_IPV4) {
                        error = EMSGSIZE;
                        goto bad;
                }

                ipf_ref();

                /* 4135317 - always pass network byte order to filter */
#if BYTE_ORDER != BIG_ENDIAN
                HTONS(ip->ip_len);
                HTONS(ip->ip_off);
#endif
                TAILQ_FOREACH(filter, &ipv4_filters, ipf_link) {
                        if (filter->ipf_filter.ipf_output) {
                                errno_t result;
                                result = filter->ipf_filter.
                                    ipf_output(filter->ipf_filter.cookie,
                                    (mbuf_t *)&m, ippo);
                                if (result == EJUSTRETURN) {
                                        ipf_unref();
                                        goto done;
                                }
                                if (result != 0) {
                                        ipf_unref();
                                        goto bad;
                                }
                        }
                }
                /* set back to host byte order */
                ip = mtod(m, struct ip *);
#if BYTE_ORDER != BIG_ENDIAN
                NTOHS(ip->ip_len);
                NTOHS(ip->ip_off);
#endif
                ipf_unref();
        }
skip_ipsec:
#endif /* IPSEC */

#if IPFIREWALL
        /*
         * Check with the firewall...
         * but not if we are already being fwd'd from a firewall.
         */
        if (fw_enable && IPFW_LOADED && !args.fwa_next_hop) {
                struct sockaddr_in *old = dst;

                args.fwa_m = m;
                args.fwa_next_hop = dst;
                args.fwa_oif = ifp;
                ipfwoff = ip_fw_chk_ptr(&args);
                m = args.fwa_m;
                dst = args.fwa_next_hop;

                /*
                 * On return we must do the following:
                 *   IP_FW_PORT_DENY_FLAG         -> drop the pkt (XXX new)
                 *   1<=off<= 0xffff              -> DIVERT
                 *   (off & IP_FW_PORT_DYNT_FLAG) -> send to a DUMMYNET pipe
                 *   (off & IP_FW_PORT_TEE_FLAG)  -> TEE the packet
                 *   dst != old                   -> IPFIREWALL_FORWARD
                 *   off==0, dst==old             -> accept
                 * If some of the above modules is not compiled in, then
                 * we should't have to check the corresponding condition
                 * (because the ipfw control socket should not accept
                 * unsupported rules), but better play safe and drop
                 * packets in case of doubt.
                 */
                m0 = m;
                if ((ipfwoff & IP_FW_PORT_DENY_FLAG) || m == NULL) {
                        if (m) {
                                m_freem(m);
                        }
                        error = EACCES;
                        goto done;
                }
                ip = mtod(m, struct ip *);

                if (ipfwoff == 0 && dst == old) {       /* common case */
                        goto pass;
                }
#if DUMMYNET
                if (DUMMYNET_LOADED && (ipfwoff & IP_FW_PORT_DYNT_FLAG) != 0) {
                        /*
                         * pass the pkt to dummynet. Need to include
                         * pipe number, m, ifp, ro, dst because these are
                         * not recomputed in the next pass.
                         * All other parameters have been already used and
                         * so they are not needed anymore.
                         * XXX note: if the ifp or ro entry are deleted
                         * while a pkt is in dummynet, we are in trouble!
                         */
                        args.fwa_ro = ro;
                        args.fwa_dst = dst;
                        args.fwa_oflags = flags;
                        if (flags & IP_OUTARGS) {
                                args.fwa_ipoa = ipoa;
                        }

                        error = ip_dn_io_ptr(m, ipfwoff & 0xffff, DN_TO_IP_OUT,
                            &args, DN_CLIENT_IPFW);
                        goto done;
                }
#endif /* DUMMYNET */
#if IPDIVERT
                if (ipfwoff != 0 && (ipfwoff & IP_FW_PORT_DYNT_FLAG) == 0) {
                        struct mbuf *clone = NULL;

                        /* Clone packet if we're doing a 'tee' */
                        if ((ipfwoff & IP_FW_PORT_TEE_FLAG) != 0) {
                                clone = m_dup(m, M_DONTWAIT);
                        }
                        /*
                         * XXX
                         * delayed checksums are not currently compatible
                         * with divert sockets.
                         */
                        if (m->m_pkthdr.csum_flags & CSUM_DELAY_DATA) {
                                in_delayed_cksum(m);
                        }

                        /* Restore packet header fields to original values */

#if BYTE_ORDER != BIG_ENDIAN
                        HTONS(ip->ip_len);
                        HTONS(ip->ip_off);
#endif

                        /* Deliver packet to divert input routine */
                        divert_packet(m, 0, ipfwoff & 0xffff,
                            args.fwa_divert_rule);

                        /* If 'tee', continue with original packet */
                        if (clone != NULL) {
                                m0 = m = clone;
                                ip = mtod(m, struct ip *);
                                goto pass;
                        }
                        goto done;
                }
#endif /* IPDIVERT */
#if IPFIREWALL_FORWARD
                /*
                 * Here we check dst to make sure it's directly reachable on
                 * the interface we previously thought it was.
                 * If it isn't (which may be likely in some situations) we have
                 * to re-route it (ie, find a route for the next-hop and the
                 * associated interface) and set them here. This is nested
                 * forwarding which in most cases is undesirable, except where
                 * such control is nigh impossible. So we do it here.
                 * And I'm babbling.
                 */
                if (ipfwoff == 0 && old != dst) {
                        struct in_ifaddr *ia_fw;
                        struct route *ro_fwd = &sro_fwd;

#if IPFIREWALL_FORWARD_DEBUG
                        printf("IPFIREWALL_FORWARD: New dst ip: ");
                        print_ip(dst->sin_addr);
                        printf("\n");
#endif /* IPFIREWALL_FORWARD_DEBUG */
                        /*
                         * We need to figure out if we have been forwarded
                         * to a local socket. If so then we should somehow
                         * "loop back" to ip_input, and get directed to the
                         * PCB as if we had received this packet. This is
                         * because it may be dificult to identify the packets
                         * you want to forward until they are being output
                         * and have selected an interface. (e.g. locally
                         * initiated packets) If we used the loopback inteface,
                         * we would not be able to control what happens
                         * as the packet runs through ip_input() as
                         * it is done through a ISR.
                         */
                        lck_rw_lock_shared(in_ifaddr_rwlock);
                        TAILQ_FOREACH(ia_fw, &in_ifaddrhead, ia_link) {
                                /*
                                 * If the addr to forward to is one
                                 * of ours, we pretend to
                                 * be the destination for this packet.
                                 */
                                IFA_LOCK_SPIN(&ia_fw->ia_ifa);
                                if (IA_SIN(ia_fw)->sin_addr.s_addr ==
                                    dst->sin_addr.s_addr) {
                                        IFA_UNLOCK(&ia_fw->ia_ifa);
                                        break;
                                }
                                IFA_UNLOCK(&ia_fw->ia_ifa);
                        }
                        lck_rw_done(in_ifaddr_rwlock);
                        if (ia_fw) {
                                /* tell ip_input "dont filter" */
                                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) {
                                        error = ENOBUFS;
                                        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);

                                if (m->m_pkthdr.rcvif == NULL) {
                                        m->m_pkthdr.rcvif = lo_ifp;
                                }

#if BYTE_ORDER != BIG_ENDIAN
                                HTONS(ip->ip_len);
                                HTONS(ip->ip_off);
#endif
                                mbuf_outbound_finalize(m, PF_INET, 0);

                                /*
                                 * we need to call dlil_output to run filters
                                 * and resync to avoid recursion loops.
                                 */
                                if (lo_ifp) {
                                        dlil_output(lo_ifp, PF_INET, m, NULL,
                                            SA(dst), 0, adv);
                                } else {
                                        printf("%s: no loopback ifp for "
                                            "forwarding!!!\n", __func__);
                                }
                                goto done;
                        }
                        /*
                         * Some of the logic for this was nicked from above.
                         *
                         * This rewrites the cached route in a local PCB.
                         * Is this what we want to do?
                         */
                        ROUTE_RELEASE(ro_fwd);
                        bcopy(dst, &ro_fwd->ro_dst, sizeof(*dst));

                        rtalloc_ign(ro_fwd, RTF_PRCLONING, false);

                        if (ro_fwd->ro_rt == NULL) {
                                OSAddAtomic(1, &ipstat.ips_noroute);
                                error = EHOSTUNREACH;
                                goto bad;
                        }

                        RT_LOCK_SPIN(ro_fwd->ro_rt);
                        ia_fw = ifatoia(ro_fwd->ro_rt->rt_ifa);
                        if (ia_fw != NULL) {
                                /* Become a regular mutex */
                                RT_CONVERT_LOCK(ro_fwd->ro_rt);
                                IFA_ADDREF(&ia_fw->ia_ifa);
                        }
                        ifp = ro_fwd->ro_rt->rt_ifp;
                        ro_fwd->ro_rt->rt_use++;
                        if (ro_fwd->ro_rt->rt_flags & RTF_GATEWAY) {
                                dst = SIN(ro_fwd->ro_rt->rt_gateway);
                        }
                        if (ro_fwd->ro_rt->rt_flags & RTF_HOST) {
                                /* double negation needed for bool bit field */
                                ipobf.isbroadcast =
                                    !!(ro_fwd->ro_rt->rt_flags & RTF_BROADCAST);
                        } else {
                                /* Become a regular mutex */
                                RT_CONVERT_LOCK(ro_fwd->ro_rt);
                                ipobf.isbroadcast =
                                    in_broadcast(dst->sin_addr, ifp);
                        }
                        RT_UNLOCK(ro_fwd->ro_rt);
                        ROUTE_RELEASE(ro);
                        ro->ro_rt = ro_fwd->ro_rt;
                        ro_fwd->ro_rt = NULL;
                        dst = SIN(&ro_fwd->ro_dst);

                        /*
                         * If we added a default src ip earlier,
                         * which would have been gotten from the-then
                         * interface, do it again, from the new one.
                         */
                        if (ia_fw != NULL) {
                                if (ipobf.fwd_rewrite_src) {
                                        IFA_LOCK_SPIN(&ia_fw->ia_ifa);
                                        ip->ip_src = IA_SIN(ia_fw)->sin_addr;
                                        IFA_UNLOCK(&ia_fw->ia_ifa);
                                }
                                IFA_REMREF(&ia_fw->ia_ifa);
                        }
                        goto pass;
                }
#endif /* IPFIREWALL_FORWARD */
                /*
                 * if we get here, none of the above matches, and
                 * we have to drop the pkt
                 */
                m_freem(m);
                error = EACCES; /* not sure this is the right error msg */
                goto done;
        }

pass:
#endif /* IPFIREWALL */

        /* 127/8 must not appear on wire - RFC1122 */
        if (!(ifp->if_flags & IFF_LOOPBACK) &&
            ((ntohl(ip->ip_src.s_addr) >> IN_CLASSA_NSHIFT) == IN_LOOPBACKNET ||
            (ntohl(ip->ip_dst.s_addr) >> IN_CLASSA_NSHIFT) == IN_LOOPBACKNET)) {
                OSAddAtomic(1, &ipstat.ips_badaddr);
                error = EADDRNOTAVAIL;
                goto bad;
        }

        if (ipoa != NULL) {
                u_int8_t dscp = ip->ip_tos >> IPTOS_DSCP_SHIFT;

                error = set_packet_qos(m, ifp,
                    ipoa->ipoa_flags & IPOAF_QOSMARKING_ALLOWED ? TRUE : FALSE,
                    ipoa->ipoa_sotc, ipoa->ipoa_netsvctype, &dscp);
                if (error == 0) {
                        ip->ip_tos &= IPTOS_ECN_MASK;
                        ip->ip_tos |= dscp << IPTOS_DSCP_SHIFT;
                } else {
                        printf("%s if_dscp_for_mbuf() error %d\n", __func__, error);
                        error = 0;
                }
        }

        ip_output_checksum(ifp, m, (IP_VHL_HL(ip->ip_vhl) << 2),
            ip->ip_len, &sw_csum);

        interface_mtu = ifp->if_mtu;

        if (INTF_ADJUST_MTU_FOR_CLAT46(ifp)) {
                interface_mtu = IN6_LINKMTU(ifp);
                /* Further adjust the size for CLAT46 expansion */
                interface_mtu -= CLAT46_HDR_EXPANSION_OVERHD;
        }

        /*
         * If small enough for interface, or the interface will take
         * care of the fragmentation for us, can just send directly.
         */
        if ((u_short)ip->ip_len <= interface_mtu || TSO_IPV4_OK(ifp, m) ||
            (!(ip->ip_off & IP_DF) && (ifp->if_hwassist & CSUM_FRAGMENT))) {
#if BYTE_ORDER != BIG_ENDIAN
                HTONS(ip->ip_len);
                HTONS(ip->ip_off);
#endif

                ip->ip_sum = 0;
                if (sw_csum & CSUM_DELAY_IP) {
                        ip->ip_sum = ip_cksum_hdr_out(m, hlen);
                        sw_csum &= ~CSUM_DELAY_IP;
                        m->m_pkthdr.csum_flags &= ~CSUM_DELAY_IP;
                }

#if IPSEC
                /* clean ipsec history once it goes out of the node */
                if (ipsec_bypass == 0 && !(flags & IP_NOIPSEC)) {
                        ipsec_delaux(m);
                }
#endif /* IPSEC */
                if ((m->m_pkthdr.csum_flags & CSUM_TSO_IPV4) &&
                    (m->m_pkthdr.tso_segsz > 0)) {
                        scnt += m->m_pkthdr.len / m->m_pkthdr.tso_segsz;
                } else {
                        scnt++;
                }

                if (packetchain == 0) {
                        if (ro->ro_rt != NULL && nstat_collect) {
                                nstat_route_tx(ro->ro_rt, scnt,
                                    m->m_pkthdr.len, 0);
                        }

                        error = dlil_output(ifp, PF_INET, m, ro->ro_rt,
                            SA(dst), 0, adv);
                        if (dlil_verbose && error) {
                                printf("dlil_output error on interface %s: %d\n",
                                    ifp->if_xname, error);
                        }
                        scnt = 0;
                        goto done;
                } else {
                        /*
                         * packet chaining allows us to reuse the
                         * route for all packets
                         */
                        bytecnt += m->m_pkthdr.len;
                        mppn = &m->m_nextpkt;
                        m = m->m_nextpkt;
                        if (m == NULL) {
#if PF
sendchain:
#endif /* PF */
                                if (pktcnt > ip_maxchainsent) {
                                        ip_maxchainsent = pktcnt;
                                }
                                if (ro->ro_rt != NULL && nstat_collect) {
                                        nstat_route_tx(ro->ro_rt, scnt,
                                            bytecnt, 0);
                                }

                                error = dlil_output(ifp, PF_INET, packetlist,
                                    ro->ro_rt, SA(dst), 0, adv);
                                if (dlil_verbose && error) {
                                        printf("dlil_output error on interface %s: %d\n",
                                            ifp->if_xname, error);
                                }
                                pktcnt = 0;
                                scnt = 0;
                                bytecnt = 0;
                                goto done;
                        }
                        m0 = m;
                        pktcnt++;
                        goto loopit;
                }
        }

        VERIFY(interface_mtu != 0);
        /*
         * Too large for interface; fragment if possible.
         * Must be able to put at least 8 bytes per fragment.
         * Balk when DF bit is set or the interface didn't support TSO.
         */
        if ((ip->ip_off & IP_DF) || pktcnt > 0 ||
            (m->m_pkthdr.csum_flags & CSUM_TSO_IPV4)) {
                error = EMSGSIZE;
                /*
                 * This case can happen if the user changed the MTU
                 * of an interface after enabling IP on it.  Because
                 * most netifs don't keep track of routes pointing to
                 * them, there is no way for one to update all its
                 * routes when the MTU is changed.
                 */
                if (ro->ro_rt) {
                        RT_LOCK_SPIN(ro->ro_rt);
                        if ((ro->ro_rt->rt_flags & (RTF_UP | RTF_HOST)) &&
                            !(ro->ro_rt->rt_rmx.rmx_locks & RTV_MTU) &&
                            (ro->ro_rt->rt_rmx.rmx_mtu > interface_mtu)) {
                                ro->ro_rt->rt_rmx.rmx_mtu = interface_mtu;
                        }
                        RT_UNLOCK(ro->ro_rt);
                }
                if (pktcnt > 0) {
                        m0 = packetlist;
                }
                OSAddAtomic(1, &ipstat.ips_cantfrag);
                goto bad;
        }

        /*
         * XXX Only TCP seems to be passing a list of packets here.
         * The following issue is limited to UDP datagrams with 0 checksum.
         * For now limit it to the case when single packet is passed down.
         */
        if (packetchain == 0 && IS_INTF_CLAT46(ifp)) {
                /*
                 * If it is a UDP packet that has checksum set to 0
                 * and is also not being offloaded, compute a full checksum
                 * and update the UDP checksum.
                 */
                if (ip->ip_p == IPPROTO_UDP &&
                    !(m->m_pkthdr.csum_flags & (CSUM_UDP | CSUM_PARTIAL))) {
                        struct udphdr *uh = NULL;

                        if (m->m_len < hlen + sizeof(struct udphdr)) {
                                m = m_pullup(m, hlen + sizeof(struct udphdr));
                                if (m == NULL) {
                                        error = ENOBUFS;
                                        m0 = m;
                                        goto bad;
                                }
                                m0 = m;
                                ip = mtod(m, struct ip *);
                        }
                        /*
                         * Get UDP header and if checksum is 0, then compute the full
                         * checksum.
                         */
                        uh = (struct udphdr *)(void *)((caddr_t)ip + hlen);
                        if (uh->uh_sum == 0) {
                                uh->uh_sum = inet_cksum(m, IPPROTO_UDP, hlen,
                                    ip->ip_len - hlen);
                                if (uh->uh_sum == 0) {
                                        uh->uh_sum = 0xffff;
                                }
                        }
                }
        }

        error = ip_fragment(m, ifp, interface_mtu, sw_csum);
        if (error != 0) {
                m0 = m = NULL;
                goto bad;
        }

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

        for (m = m0; m; m = m0) {
                m0 = m->m_nextpkt;
                m->m_nextpkt = 0;
#if IPSEC
                /* clean ipsec history once it goes out of the node */
                if (ipsec_bypass == 0 && !(flags & IP_NOIPSEC)) {
                        ipsec_delaux(m);
                }
#endif /* IPSEC */
                if (error == 0) {
                        if ((packetchain != 0) && (pktcnt > 0)) {
                                panic("%s: mix of packet in packetlist is "
                                    "wrong=%p", __func__, packetlist);
                                /* NOTREACHED */
                        }
                        if (ro->ro_rt != NULL && nstat_collect) {
                                nstat_route_tx(ro->ro_rt, 1,
                                    m->m_pkthdr.len, 0);
                        }
                        error = dlil_output(ifp, PF_INET, m, ro->ro_rt,
                            SA(dst), 0, adv);
                        if (dlil_verbose && error) {
                                printf("dlil_output error on interface %s: %d\n",
                                    ifp->if_xname, error);
                        }
                } else {
                        m_freem(m);
                }
        }

        if (error == 0) {
                OSAddAtomic(1, &ipstat.ips_fragmented);
        }

done:
        if (ia != NULL) {
                IFA_REMREF(&ia->ia_ifa);
                ia = NULL;
        }
#if IPSEC
        ROUTE_RELEASE(&ipsec_state.ro);
        if (sp != NULL) {
                KEYDEBUG(KEYDEBUG_IPSEC_STAMP,
                    printf("DP ip_output call free SP:%x\n", sp));
                key_freesp(sp, KEY_SADB_UNLOCKED);
        }
#endif /* IPSEC */
#if NECP
        ROUTE_RELEASE(&necp_route);
#endif /* NECP */
#if DUMMYNET
        ROUTE_RELEASE(&saved_route);
#endif /* DUMMYNET */
#if IPFIREWALL_FORWARD
        ROUTE_RELEASE(&sro_fwd);
#endif /* IPFIREWALL_FORWARD */

        KERNEL_DEBUG(DBG_FNC_IP_OUTPUT | DBG_FUNC_END, error, 0, 0, 0, 0);
        if (ip_output_measure) {
                net_perf_measure_time(&net_perf, &start_tv, packets_processed);
                net_perf_histogram(&net_perf, packets_processed);
        }
        return error;
bad:
        if (pktcnt > 0) {
                m0 = packetlist;
        }
        m_freem_list(m0);
        goto done;

#undef ipsec_state
#undef args
#undef sro_fwd
#undef saved_route
#undef ipf_pktopts
#undef IP_CHECK_RESTRICTIONS
}

int
ip_fragment(struct mbuf *m, struct ifnet *ifp, unsigned long mtu, int sw_csum)
{
        struct ip *ip, *mhip;
        int len, hlen, mhlen, firstlen, off, error = 0;
        struct mbuf **mnext = &m->m_nextpkt, *m0;
        int nfrags = 1;

        ip = mtod(m, struct ip *);
#ifdef _IP_VHL
        hlen = IP_VHL_HL(ip->ip_vhl) << 2;
#else /* !_IP_VHL */
        hlen = ip->ip_hl << 2;
#endif /* !_IP_VHL */

#ifdef INET6
        /*
         * We need to adjust the fragment sizes to account
         * for IPv6 fragment header if it needs to be translated
         * from IPv4 to IPv6.
         */
        if (IS_INTF_CLAT46(ifp)) {
                mtu -= sizeof(struct ip6_frag);
        }

#endif
        firstlen = len = (mtu - hlen) & ~7;
        if (len < 8) {
                m_freem(m);
                return EMSGSIZE;
        }

        /*
         * if the interface will not calculate checksums on
         * fragmented packets, then do it here.
         */
        if ((m->m_pkthdr.csum_flags & CSUM_DELAY_DATA) &&
            !(ifp->if_hwassist & CSUM_IP_FRAGS)) {
                in_delayed_cksum(m);
        }

        /*
         * Loop through length of segment after first fragment,
         * make new header and copy data of each part and link onto chain.
         */
        m0 = m;
        mhlen = sizeof(struct ip);
        for (off = hlen + len; off < (u_short)ip->ip_len; off += len) {
                MGETHDR(m, M_DONTWAIT, MT_HEADER);      /* MAC-OK */
                if (m == NULL) {
                        error = ENOBUFS;
                        OSAddAtomic(1, &ipstat.ips_odropped);
                        goto sendorfree;
                }
                m->m_flags |= (m0->m_flags & M_MCAST) | M_FRAG;
                m->m_data += max_linkhdr;
                mhip = mtod(m, struct ip *);
                *mhip = *ip;
                if (hlen > sizeof(struct ip)) {
                        mhlen = ip_optcopy(ip, mhip) + sizeof(struct ip);
                        mhip->ip_vhl = IP_MAKE_VHL(IPVERSION, mhlen >> 2);
                }
                m->m_len = mhlen;
                mhip->ip_off = ((off - hlen) >> 3) + (ip->ip_off & ~IP_MF);
                if (ip->ip_off & IP_MF) {
                        mhip->ip_off |= IP_MF;
                }
                if (off + len >= (u_short)ip->ip_len) {
                        len = (u_short)ip->ip_len - off;
                } else {
                        mhip->ip_off |= IP_MF;
                }
                mhip->ip_len = htons((u_short)(len + mhlen));
                m->m_next = m_copy(m0, off, len);
                if (m->m_next == NULL) {
                        (void) m_free(m);
                        error = ENOBUFS;        /* ??? */
                        OSAddAtomic(1, &ipstat.ips_odropped);
                        goto sendorfree;
                }
                m->m_pkthdr.len = mhlen + len;
                m->m_pkthdr.rcvif = NULL;
                m->m_pkthdr.csum_flags = m0->m_pkthdr.csum_flags;

                M_COPY_CLASSIFIER(m, m0);
                M_COPY_PFTAG(m, m0);

#if CONFIG_MACF_NET
                mac_netinet_fragment(m0, m);
#endif /* CONFIG_MACF_NET */

#if BYTE_ORDER != BIG_ENDIAN
                HTONS(mhip->ip_off);
#endif

                mhip->ip_sum = 0;
                if (sw_csum & CSUM_DELAY_IP) {
                        mhip->ip_sum = ip_cksum_hdr_out(m, mhlen);
                        m->m_pkthdr.csum_flags &= ~CSUM_DELAY_IP;
                }
                *mnext = m;
                mnext = &m->m_nextpkt;
                nfrags++;
        }
        OSAddAtomic(nfrags, &ipstat.ips_ofragments);

        /* set first/last markers for fragment chain */
        m->m_flags |= M_LASTFRAG;
        m0->m_flags |= M_FIRSTFRAG | M_FRAG;
        m0->m_pkthdr.csum_data = nfrags;

        /*
         * Update first fragment by trimming what's been copied out
         * and updating header, then send each fragment (in order).
         */
        m = m0;
        m_adj(m, hlen + firstlen - (u_short)ip->ip_len);
        m->m_pkthdr.len = hlen + firstlen;
        ip->ip_len = htons((u_short)m->m_pkthdr.len);
        ip->ip_off |= IP_MF;

#if BYTE_ORDER != BIG_ENDIAN
        HTONS(ip->ip_off);
#endif

        ip->ip_sum = 0;
        if (sw_csum & CSUM_DELAY_IP) {
                ip->ip_sum = ip_cksum_hdr_out(m, hlen);
                m->m_pkthdr.csum_flags &= ~CSUM_DELAY_IP;
        }
sendorfree:
        if (error) {
                m_freem_list(m0);
        }

        return error;
}

static void
ip_out_cksum_stats(int proto, u_int32_t len)
{
        switch (proto) {
        case IPPROTO_TCP:
                tcp_out_cksum_stats(len);
                break;
        case IPPROTO_UDP:
                udp_out_cksum_stats(len);
                break;
        default:
                /* keep only TCP or UDP stats for now */
                break;
        }
}

/*
 * Process a delayed payload checksum calculation (outbound path.)
 *
 * hoff is the number of bytes beyond the mbuf data pointer which
 * points to the IP header.
 *
 * Returns a bitmask representing all the work done in software.
 */
uint32_t
in_finalize_cksum(struct mbuf *m, uint32_t hoff, uint32_t csum_flags)
{
        unsigned char buf[15 << 2] __attribute__((aligned(8)));
        struct ip *ip;
        uint32_t offset, _hlen, mlen, hlen, len, sw_csum;
        uint16_t csum, ip_len;

        _CASSERT(sizeof(csum) == sizeof(uint16_t));
        VERIFY(m->m_flags & M_PKTHDR);

        sw_csum = (csum_flags & m->m_pkthdr.csum_flags);

        if ((sw_csum &= (CSUM_DELAY_IP | CSUM_DELAY_DATA)) == 0) {
                goto done;
        }

        mlen = m->m_pkthdr.len;                         /* total mbuf len */

        /* sanity check (need at least simple IP header) */
        if (mlen < (hoff + sizeof(*ip))) {
                panic("%s: mbuf %p pkt len (%u) < hoff+ip_hdr "
                    "(%u+%u)\n", __func__, m, mlen, hoff,
                    (uint32_t)sizeof(*ip));
                /* NOTREACHED */
        }

        /*
         * In case the IP header is not contiguous, or not 32-bit aligned,
         * or if we're computing the IP header checksum, copy it to a local
         * buffer.  Copy only the simple IP header here (IP options case
         * is handled below.)
         */
        if ((sw_csum & CSUM_DELAY_IP) || (hoff + sizeof(*ip)) > m->m_len ||
            !IP_HDR_ALIGNED_P(mtod(m, caddr_t) + hoff)) {
                m_copydata(m, hoff, sizeof(*ip), (caddr_t)buf);
                ip = (struct ip *)(void *)buf;
                _hlen = sizeof(*ip);
        } else {
                ip = (struct ip *)(void *)(m->m_data + hoff);
                _hlen = 0;
        }

        hlen = IP_VHL_HL(ip->ip_vhl) << 2;              /* IP header len */

        /* sanity check */
        if (mlen < (hoff + hlen)) {
                panic("%s: mbuf %p pkt too short (%d) for IP header (%u), "
                    "hoff %u", __func__, m, mlen, hlen, hoff);
                /* NOTREACHED */
        }

        /*
         * We could be in the context of an IP or interface filter; in the
         * former case, ip_len would be in host (correct) order while for
         * the latter it would be in network order.  Because of this, we
         * attempt to interpret the length field by comparing it against
         * the actual packet length.  If the comparison fails, byte swap
         * the length and check again.  If it still fails, use the actual
         * packet length.  This also covers the trailing bytes case.
         */
        ip_len = ip->ip_len;
        if (ip_len != (mlen - hoff)) {
                ip_len = OSSwapInt16(ip_len);
                if (ip_len != (mlen - hoff)) {
                        printf("%s: mbuf 0x%llx proto %d IP len %d (%x) "
                            "[swapped %d (%x)] doesn't match actual packet "
                            "length; %d is used instead\n", __func__,
                            (uint64_t)VM_KERNEL_ADDRPERM(m), ip->ip_p,
                            ip->ip_len, ip->ip_len, ip_len, ip_len,
                            (mlen - hoff));
                        ip_len = mlen - hoff;
                }
        }

        len = ip_len - hlen;                            /* csum span */

        if (sw_csum & CSUM_DELAY_DATA) {
                uint16_t ulpoff;

                /*
                 * offset is added to the lower 16-bit value of csum_data,
                 * which is expected to contain the ULP offset; therefore
                 * CSUM_PARTIAL offset adjustment must be undone.
                 */
                if ((m->m_pkthdr.csum_flags & (CSUM_PARTIAL | CSUM_DATA_VALID)) ==
                    (CSUM_PARTIAL | CSUM_DATA_VALID)) {
                        /*
                         * Get back the original ULP offset (this will
                         * undo the CSUM_PARTIAL logic in ip_output.)
                         */
                        m->m_pkthdr.csum_data = (m->m_pkthdr.csum_tx_stuff -
                            m->m_pkthdr.csum_tx_start);
                }

                ulpoff = (m->m_pkthdr.csum_data & 0xffff); /* ULP csum offset */
                offset = hoff + hlen;                   /* ULP header */

                if (mlen < (ulpoff + sizeof(csum))) {
                        panic("%s: mbuf %p pkt len (%u) proto %d invalid ULP "
                            "cksum offset (%u) cksum flags 0x%x\n", __func__,
                            m, mlen, ip->ip_p, ulpoff, m->m_pkthdr.csum_flags);
                        /* NOTREACHED */
                }

                csum = inet_cksum(m, 0, offset, len);

                /* Update stats */
                ip_out_cksum_stats(ip->ip_p, len);

                /* RFC1122 4.1.3.4 */
                if (csum == 0 &&
                    (m->m_pkthdr.csum_flags & (CSUM_UDP | CSUM_ZERO_INVERT))) {
                        csum = 0xffff;
                }

                /* Insert the checksum in the ULP csum field */
                offset += ulpoff;
                if (offset + sizeof(csum) > m->m_len) {
                        m_copyback(m, offset, sizeof(csum), &csum);
                } else if (IP_HDR_ALIGNED_P(mtod(m, char *) + hoff)) {
                        *(uint16_t *)(void *)(mtod(m, char *) + offset) = csum;
                } else {
                        bcopy(&csum, (mtod(m, char *) + offset), sizeof(csum));
                }
                m->m_pkthdr.csum_flags &= ~(CSUM_DELAY_DATA | CSUM_DATA_VALID |
                    CSUM_PARTIAL | CSUM_ZERO_INVERT);
        }

        if (sw_csum & CSUM_DELAY_IP) {
                /* IP header must be in the local buffer */
                VERIFY(_hlen == sizeof(*ip));
                if (_hlen != hlen) {
                        VERIFY(hlen <= sizeof(buf));
                        m_copydata(m, hoff, hlen, (caddr_t)buf);
                        ip = (struct ip *)(void *)buf;
                        _hlen = hlen;
                }

                /*
                 * Compute the IP header checksum as if the IP length
                 * is the length which we believe is "correct"; see
                 * how ip_len gets calculated above.  Note that this
                 * is done on the local copy and not on the real one.
                 */
                ip->ip_len = htons(ip_len);
                ip->ip_sum = 0;
                csum = in_cksum_hdr_opt(ip);

                /* Update stats */
                ipstat.ips_snd_swcsum++;
                ipstat.ips_snd_swcsum_bytes += hlen;

                /*
                 * Insert only the checksum in the existing IP header
                 * csum field; all other fields are left unchanged.
                 */
                offset = hoff + offsetof(struct ip, ip_sum);
                if (offset + sizeof(csum) > m->m_len) {
                        m_copyback(m, offset, sizeof(csum), &csum);
                } else if (IP_HDR_ALIGNED_P(mtod(m, char *) + hoff)) {
                        *(uint16_t *)(void *)(mtod(m, char *) + offset) = csum;
                } else {
                        bcopy(&csum, (mtod(m, char *) + offset), sizeof(csum));
                }
                m->m_pkthdr.csum_flags &= ~CSUM_DELAY_IP;
        }

done:
        return sw_csum;
}

/*
 * Insert IP options into preformed packet.
 * Adjust IP destination as required for IP source routing,
 * as indicated by a non-zero in_addr at the start of the options.
 *
 * XXX This routine assumes that the packet has no options in place.
 */
static struct mbuf *
ip_insertoptions(struct mbuf *m, struct mbuf *opt, int *phlen)
{
        struct ipoption *p = mtod(opt, struct ipoption *);
        struct mbuf *n;
        struct ip *ip = mtod(m, struct ip *);
        unsigned optlen;

        optlen = opt->m_len - sizeof(p->ipopt_dst);
        if (optlen + (u_short)ip->ip_len > IP_MAXPACKET) {
                return m;             /* XXX should fail */
        }
        if (p->ipopt_dst.s_addr) {
                ip->ip_dst = p->ipopt_dst;
        }
        if (m->m_flags & M_EXT || m->m_data - optlen < m->m_pktdat) {
                MGETHDR(n, M_DONTWAIT, MT_HEADER);      /* MAC-OK */
                if (n == NULL) {
                        return m;
                }
                n->m_pkthdr.rcvif = 0;
#if CONFIG_MACF_NET
                mac_mbuf_label_copy(m, n);
#endif /* CONFIG_MACF_NET */
                n->m_pkthdr.len = m->m_pkthdr.len + optlen;
                m->m_len -= sizeof(struct ip);
                m->m_data += sizeof(struct ip);
                n->m_next = m;
                m = n;
                m->m_len = optlen + sizeof(struct ip);
                m->m_data += max_linkhdr;
                (void) memcpy(mtod(m, void *), ip, sizeof(struct ip));
        } else {
                m->m_data -= optlen;
                m->m_len += optlen;
                m->m_pkthdr.len += optlen;
                ovbcopy((caddr_t)ip, mtod(m, caddr_t), sizeof(struct ip));
        }
        ip = mtod(m, struct ip *);
        bcopy(p->ipopt_list, ip + 1, optlen);
        *phlen = sizeof(struct ip) + optlen;
        ip->ip_vhl = IP_MAKE_VHL(IPVERSION, *phlen >> 2);
        ip->ip_len += optlen;
        return m;
}

/*
 * Copy options from ip to jp,
 * omitting those not copied during fragmentation.
 */
static int
ip_optcopy(struct ip *ip, struct ip *jp)
{
        u_char *cp, *dp;
        int opt, optlen, cnt;

        cp = (u_char *)(ip + 1);
        dp = (u_char *)(jp + 1);
        cnt = (IP_VHL_HL(ip->ip_vhl) << 2) - sizeof(struct ip);
        for (; cnt > 0; cnt -= optlen, cp += optlen) {
                opt = cp[0];
                if (opt == IPOPT_EOL) {
                        break;
                }
                if (opt == IPOPT_NOP) {
                        /* Preserve for IP mcast tunnel's LSRR alignment. */
                        *dp++ = IPOPT_NOP;
                        optlen = 1;
                        continue;
                }
#if DIAGNOSTIC
                if (cnt < IPOPT_OLEN + sizeof(*cp)) {
                        panic("malformed IPv4 option passed to ip_optcopy");
                        /* NOTREACHED */
                }
#endif
                optlen = cp[IPOPT_OLEN];
#if DIAGNOSTIC
                if (optlen < IPOPT_OLEN + sizeof(*cp) || optlen > cnt) {
                        panic("malformed IPv4 option passed to ip_optcopy");
                        /* NOTREACHED */
                }
#endif
                /* bogus lengths should have been caught by ip_dooptions */
                if (optlen > cnt) {
                        optlen = cnt;
                }
                if (IPOPT_COPIED(opt)) {
                        bcopy(cp, dp, optlen);
                        dp += optlen;
                }
        }
        for (optlen = dp - (u_char *)(jp + 1); optlen & 0x3; optlen++) {
                *dp++ = IPOPT_EOL;
        }
        return optlen;
}

/*
 * IP socket option processing.
 */
int
ip_ctloutput(struct socket *so, struct sockopt *sopt)
{
        struct  inpcb *inp = sotoinpcb(so);
        int     error, optval;
        lck_mtx_t *mutex_held = NULL;

        error = optval = 0;
        if (sopt->sopt_level != IPPROTO_IP) {
                return EINVAL;
        }

        switch (sopt->sopt_dir) {
        case SOPT_SET:
                mutex_held = socket_getlock(so, PR_F_WILLUNLOCK);
                /*
                 *  Wait if we are in the middle of ip_output
                 *  as we unlocked the socket there and don't
                 *  want to overwrite the IP options
                 */
                if (inp->inp_sndinprog_cnt > 0) {
                        inp->inp_sndingprog_waiters++;

                        while (inp->inp_sndinprog_cnt > 0) {
                                msleep(&inp->inp_sndinprog_cnt, mutex_held,
                                    PSOCK | PCATCH, "inp_sndinprog_cnt", NULL);
                        }
                        inp->inp_sndingprog_waiters--;
                }
                switch (sopt->sopt_name) {
#ifdef notyet
                case IP_RETOPTS:
#endif
                case IP_OPTIONS: {
                        struct mbuf *m;

                        if (sopt->sopt_valsize > MLEN) {
                                error = EMSGSIZE;
                                break;
                        }
                        MGET(m, sopt->sopt_p != kernproc ? M_WAIT : M_DONTWAIT,
                            MT_HEADER);
                        if (m == NULL) {
                                error = ENOBUFS;
                                break;
                        }
                        m->m_len = sopt->sopt_valsize;
                        error = sooptcopyin(sopt, mtod(m, char *),
                            m->m_len, m->m_len);
                        if (error) {
                                m_freem(m);
                                break;
                        }

                        return ip_pcbopts(sopt->sopt_name,
                                   &inp->inp_options, m);
                }

                case IP_TOS:
                case IP_TTL:
                case IP_RECVOPTS:
                case IP_RECVRETOPTS:
                case IP_RECVDSTADDR:
                case IP_RECVIF:
                case IP_RECVTTL:
                case IP_RECVPKTINFO:
                case IP_RECVTOS:
                        error = sooptcopyin(sopt, &optval, sizeof(optval),
                            sizeof(optval));
                        if (error) {
                                break;
                        }

                        switch (sopt->sopt_name) {
                        case IP_TOS:
                                inp->inp_ip_tos = optval;
                                break;

                        case IP_TTL:
                                inp->inp_ip_ttl = optval;
                                break;
#define OPTSET(bit) \
        if (optval) \
                inp->inp_flags |= bit; \
        else \
                inp->inp_flags &= ~bit;

                        case IP_RECVOPTS:
                                OPTSET(INP_RECVOPTS);
                                break;

                        case IP_RECVRETOPTS:
                                OPTSET(INP_RECVRETOPTS);
                                break;

                        case IP_RECVDSTADDR:
                                OPTSET(INP_RECVDSTADDR);
                                break;

                        case IP_RECVIF:
                                OPTSET(INP_RECVIF);
                                break;

                        case IP_RECVTTL:
                                OPTSET(INP_RECVTTL);
                                break;

                        case IP_RECVPKTINFO:
                                OPTSET(INP_PKTINFO);
                                break;

                        case IP_RECVTOS:
                                OPTSET(INP_RECVTOS);
                                break;
 #undef OPTSET
                        }
                        break;
                /*
                 * Multicast socket options are processed by the in_mcast
                 * module.
                 */
                case IP_MULTICAST_IF:
                case IP_MULTICAST_IFINDEX:
                case IP_MULTICAST_VIF:
                case IP_MULTICAST_TTL:
                case IP_MULTICAST_LOOP:
                case IP_ADD_MEMBERSHIP:
                case IP_DROP_MEMBERSHIP:
                case IP_ADD_SOURCE_MEMBERSHIP:
                case IP_DROP_SOURCE_MEMBERSHIP:
                case IP_BLOCK_SOURCE:
                case IP_UNBLOCK_SOURCE:
                case IP_MSFILTER:
                case MCAST_JOIN_GROUP:
                case MCAST_LEAVE_GROUP:
                case MCAST_JOIN_SOURCE_GROUP:
                case MCAST_LEAVE_SOURCE_GROUP:
                case MCAST_BLOCK_SOURCE:
                case MCAST_UNBLOCK_SOURCE:
                        error = inp_setmoptions(inp, sopt);
                        break;

                case IP_PORTRANGE:
                        error = sooptcopyin(sopt, &optval, sizeof(optval),
                            sizeof(optval));
                        if (error) {
                                break;
                        }

                        switch (optval) {
                        case IP_PORTRANGE_DEFAULT:
                                inp->inp_flags &= ~(INP_LOWPORT);
                                inp->inp_flags &= ~(INP_HIGHPORT);
                                break;

                        case IP_PORTRANGE_HIGH:
                                inp->inp_flags &= ~(INP_LOWPORT);
                                inp->inp_flags |= INP_HIGHPORT;
                                break;

                        case IP_PORTRANGE_LOW:
                                inp->inp_flags &= ~(INP_HIGHPORT);
                                inp->inp_flags |= INP_LOWPORT;
                                break;

                        default:
                                error = EINVAL;
                                break;
                        }
                        break;

#if IPSEC
                case IP_IPSEC_POLICY: {
                        caddr_t req = NULL;
                        size_t len = 0;
                        int priv;
                        struct mbuf *m;
                        int optname;

                        if ((error = soopt_getm(sopt, &m)) != 0) { /* XXX */
                                break;
                        }
                        if ((error = soopt_mcopyin(sopt, m)) != 0) { /* XXX */
                                break;
                        }
                        priv = (proc_suser(sopt->sopt_p) == 0);
                        if (m) {
                                req = mtod(m, caddr_t);
                                len = m->m_len;
                        }
                        optname = sopt->sopt_name;
                        error = ipsec4_set_policy(inp, optname, req, len, priv);
                        m_freem(m);
                        break;
                }
#endif /* IPSEC */

#if TRAFFIC_MGT
                case IP_TRAFFIC_MGT_BACKGROUND: {
                        unsigned background = 0;

                        error = sooptcopyin(sopt, &background,
                            sizeof(background), sizeof(background));
                        if (error) {
                                break;
                        }

                        if (background) {
                                socket_set_traffic_mgt_flags_locked(so,
                                    TRAFFIC_MGT_SO_BACKGROUND);
                        } else {
                                socket_clear_traffic_mgt_flags_locked(so,
                                    TRAFFIC_MGT_SO_BACKGROUND);
                        }

                        break;
                }
#endif /* TRAFFIC_MGT */

                /*
                 * On a multihomed system, scoped routing can be used to
                 * restrict the source interface used for sending packets.
                 * The socket option IP_BOUND_IF binds a particular AF_INET
                 * socket to an interface such that data sent on the socket
                 * is restricted to that interface.  This is unlike the
                 * SO_DONTROUTE option where the routing table is bypassed;
                 * therefore it allows for a greater flexibility and control
                 * over the system behavior, and does not place any restriction
                 * on the destination address type (e.g.  unicast, multicast,
                 * or broadcast if applicable) or whether or not the host is
                 * directly reachable.  Note that in the multicast transmit
                 * case, IP_MULTICAST_{IF,IFINDEX} takes precedence over
                 * IP_BOUND_IF, since the former practically bypasses the
                 * routing table; in this case, IP_BOUND_IF sets the default
                 * interface used for sending multicast packets in the absence
                 * of an explicit multicast transmit interface.
                 */
                case IP_BOUND_IF:
                        /* This option is settable only for IPv4 */
                        if (!(inp->inp_vflag & INP_IPV4)) {
                                error = EINVAL;
                                break;
                        }

                        error = sooptcopyin(sopt, &optval, sizeof(optval),
                            sizeof(optval));

                        if (error) {
                                break;
                        }

                        error = inp_bindif(inp, optval, NULL);
                        break;

                case IP_NO_IFT_CELLULAR:
                        /* This option is settable only for IPv4 */
                        if (!(inp->inp_vflag & INP_IPV4)) {
                                error = EINVAL;
                                break;
                        }

                        error = sooptcopyin(sopt, &optval, sizeof(optval),
                            sizeof(optval));

                        if (error) {
                                break;
                        }

                        /* once set, it cannot be unset */
                        if (!optval && INP_NO_CELLULAR(inp)) {
                                error = EINVAL;
                                break;
                        }

                        error = so_set_restrictions(so,
                            SO_RESTRICT_DENY_CELLULAR);
                        break;

                case IP_OUT_IF:
                        /* This option is not settable */
                        error = EINVAL;
                        break;

                default:
                        error = ENOPROTOOPT;
                        break;
                }
                break;

        case SOPT_GET:
                switch (sopt->sopt_name) {
                case IP_OPTIONS:
                case IP_RETOPTS:
                        if (inp->inp_options) {
                                error = sooptcopyout(sopt,
                                    mtod(inp->inp_options, char *),
                                    inp->inp_options->m_len);
                        } else {
                                sopt->sopt_valsize = 0;
                        }
                        break;

                case IP_TOS:
                case IP_TTL:
                case IP_RECVOPTS:
                case IP_RECVRETOPTS:
                case IP_RECVDSTADDR:
                case IP_RECVIF:
                case IP_RECVTTL:
                case IP_PORTRANGE:
                case IP_RECVPKTINFO:
                case IP_RECVTOS:
                        switch (sopt->sopt_name) {
                        case IP_TOS:
                                optval = inp->inp_ip_tos;
                                break;

                        case IP_TTL:
                                optval = inp->inp_ip_ttl;
                                break;

#define OPTBIT(bit)     (inp->inp_flags & bit ? 1 : 0)

                        case IP_RECVOPTS:
                                optval = OPTBIT(INP_RECVOPTS);
                                break;

                        case IP_RECVRETOPTS:
                                optval = OPTBIT(INP_RECVRETOPTS);
                                break;

                        case IP_RECVDSTADDR:
                                optval = OPTBIT(INP_RECVDSTADDR);
                                break;

                        case IP_RECVIF:
                                optval = OPTBIT(INP_RECVIF);
                                break;

                        case IP_RECVTTL:
                                optval = OPTBIT(INP_RECVTTL);
                                break;

                        case IP_PORTRANGE:
                                if (inp->inp_flags & INP_HIGHPORT) {
                                        optval = IP_PORTRANGE_HIGH;
                                } else if (inp->inp_flags & INP_LOWPORT) {
                                        optval = IP_PORTRANGE_LOW;
                                } else {
                                        optval = 0;
                                }
                                break;

                        case IP_RECVPKTINFO:
                                optval = OPTBIT(INP_PKTINFO);
                                break;

                        case IP_RECVTOS:
                                optval = OPTBIT(INP_RECVTOS);
                                break;
                        }
                        error = sooptcopyout(sopt, &optval, sizeof(optval));
                        break;

                case IP_MULTICAST_IF:
                case IP_MULTICAST_IFINDEX:
                case IP_MULTICAST_VIF:
                case IP_MULTICAST_TTL:
                case IP_MULTICAST_LOOP:
                case IP_MSFILTER:
                        error = inp_getmoptions(inp, sopt);
                        break;

#if IPSEC
                case IP_IPSEC_POLICY: {
                        error = 0; /* This option is no longer supported */
                        break;
                }
#endif /* IPSEC */

#if TRAFFIC_MGT
                case IP_TRAFFIC_MGT_BACKGROUND: {
                        unsigned background = (so->so_flags1 &
                            SOF1_TRAFFIC_MGT_SO_BACKGROUND) ? 1 : 0;
                        return sooptcopyout(sopt, &background,
                                   sizeof(background));
                }
#endif /* TRAFFIC_MGT */

                case IP_BOUND_IF:
                        if (inp->inp_flags & INP_BOUND_IF) {
                                optval = inp->inp_boundifp->if_index;
                        }
                        error = sooptcopyout(sopt, &optval, sizeof(optval));
                        break;

                case IP_NO_IFT_CELLULAR:
                        optval = INP_NO_CELLULAR(inp) ? 1 : 0;
                        error = sooptcopyout(sopt, &optval, sizeof(optval));
                        break;

                case IP_OUT_IF:
                        optval = (inp->inp_last_outifp != NULL) ?
                            inp->inp_last_outifp->if_index : 0;
                        error = sooptcopyout(sopt, &optval, sizeof(optval));
                        break;

                default:
                        error = ENOPROTOOPT;
                        break;
                }
                break;
        }
        return error;
}

/*
 * Set up IP options in pcb for insertion in output packets.
 * Store in mbuf with pointer in pcbopt, adding pseudo-option
 * with destination address if source routed.
 */
static int
ip_pcbopts(int optname, struct mbuf **pcbopt, struct mbuf *m)
{
#pragma unused(optname)
        int cnt, optlen;
        u_char *cp;
        u_char opt;

        /* turn off any old options */
        if (*pcbopt) {
                (void) m_free(*pcbopt);
        }
        *pcbopt = 0;
        if (m == (struct mbuf *)0 || m->m_len == 0) {
                /*
                 * Only turning off any previous options.
                 */
                if (m) {
                        (void) m_free(m);
                }
                return 0;
        }

        if (m->m_len % sizeof(int32_t)) {
                goto bad;
        }

        /*
         * IP first-hop destination address will be stored before
         * actual options; move other options back
         * and clear it when none present.
         */
        if (m->m_data + m->m_len + sizeof(struct in_addr) >= &m->m_dat[MLEN]) {
                goto bad;
        }
        cnt = m->m_len;
        m->m_len += sizeof(struct in_addr);
        cp = mtod(m, u_char *) + sizeof(struct in_addr);
        ovbcopy(mtod(m, caddr_t), (caddr_t)cp, (unsigned)cnt);
        bzero(mtod(m, caddr_t), sizeof(struct in_addr));

        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)) {
                                goto bad;
                        }
                        optlen = cp[IPOPT_OLEN];
                        if (optlen < IPOPT_OLEN + sizeof(*cp) || optlen > cnt) {
                                goto bad;
                        }
                }
                switch (opt) {
                default:
                        break;

                case IPOPT_LSRR:
                case IPOPT_SSRR:
                        /*
                         * user process specifies route as:
                         *      ->A->B->C->D
                         * D must be our final destination (but we can't
                         * check that since we may not have connected yet).
                         * A is first hop destination, which doesn't appear in
                         * actual IP option, but is stored before the options.
                         */
                        if (optlen < IPOPT_MINOFF - 1 + sizeof(struct in_addr)) {
                                goto bad;
                        }
                        m->m_len -= sizeof(struct in_addr);
                        cnt -= sizeof(struct in_addr);
                        optlen -= sizeof(struct in_addr);
                        cp[IPOPT_OLEN] = optlen;
                        /*
                         * Move first hop before start of options.
                         */
                        bcopy((caddr_t)&cp[IPOPT_OFFSET + 1], mtod(m, caddr_t),
                            sizeof(struct in_addr));
                        /*
                         * Then copy rest of options back
                         * to close up the deleted entry.
                         */
                        ovbcopy((caddr_t)(&cp[IPOPT_OFFSET + 1] +
                            sizeof(struct in_addr)),
                            (caddr_t)&cp[IPOPT_OFFSET + 1],
                            (unsigned)cnt - (IPOPT_MINOFF - 1));
                        break;
                }
        }
        if (m->m_len > MAX_IPOPTLEN + sizeof(struct in_addr)) {
                goto bad;
        }
        *pcbopt = m;
        return 0;

bad:
        (void) m_free(m);
        return EINVAL;
}

void
ip_moptions_init(void)
{
        PE_parse_boot_argn("ifa_debug", &imo_debug, sizeof(imo_debug));

        imo_size = (imo_debug == 0) ? sizeof(struct ip_moptions) :
            sizeof(struct ip_moptions_dbg);

        imo_zone = zinit(imo_size, IMO_ZONE_MAX * imo_size, 0,
            IMO_ZONE_NAME);
        if (imo_zone == NULL) {
                panic("%s: failed allocating %s", __func__, IMO_ZONE_NAME);
                /* NOTREACHED */
        }
        zone_change(imo_zone, Z_EXPAND, TRUE);
}

void
imo_addref(struct ip_moptions *imo, int locked)
{
        if (!locked) {
                IMO_LOCK(imo);
        } else {
                IMO_LOCK_ASSERT_HELD(imo);
        }

        if (++imo->imo_refcnt == 0) {
                panic("%s: imo %p wraparound refcnt\n", __func__, imo);
                /* NOTREACHED */
        } else if (imo->imo_trace != NULL) {
                (*imo->imo_trace)(imo, TRUE);
        }

        if (!locked) {
                IMO_UNLOCK(imo);
        }
}

void
imo_remref(struct ip_moptions *imo)
{
        int i;

        IMO_LOCK(imo);
        if (imo->imo_refcnt == 0) {
                panic("%s: imo %p negative refcnt", __func__, imo);
                /* NOTREACHED */
        } else if (imo->imo_trace != NULL) {
                (*imo->imo_trace)(imo, FALSE);
        }

        --imo->imo_refcnt;
        if (imo->imo_refcnt > 0) {
                IMO_UNLOCK(imo);
                return;
        }

        for (i = 0; i < imo->imo_num_memberships; ++i) {
                struct in_mfilter *imf;

                imf = imo->imo_mfilters ? &imo->imo_mfilters[i] : NULL;
                if (imf != NULL) {
                        imf_leave(imf);
                }

                (void) in_leavegroup(imo->imo_membership[i], imf);

                if (imf != NULL) {
                        imf_purge(imf);
                }

                INM_REMREF(imo->imo_membership[i]);
                imo->imo_membership[i] = NULL;
        }
        imo->imo_num_memberships = 0;
        if (imo->imo_mfilters != NULL) {
                FREE(imo->imo_mfilters, M_INMFILTER);
                imo->imo_mfilters = NULL;
        }
        if (imo->imo_membership != NULL) {
                FREE(imo->imo_membership, M_IPMOPTS);
                imo->imo_membership = NULL;
        }
        IMO_UNLOCK(imo);

        lck_mtx_destroy(&imo->imo_lock, ifa_mtx_grp);

        if (!(imo->imo_debug & IFD_ALLOC)) {
                panic("%s: imo %p cannot be freed", __func__, imo);
                /* NOTREACHED */
        }
        zfree(imo_zone, imo);
}

static void
imo_trace(struct ip_moptions *imo, int refhold)
{
        struct ip_moptions_dbg *imo_dbg = (struct ip_moptions_dbg *)imo;
        ctrace_t *tr;
        u_int32_t idx;
        u_int16_t *cnt;

        if (!(imo->imo_debug & IFD_DEBUG)) {
                panic("%s: imo %p has no debug structure", __func__, imo);
                /* NOTREACHED */
        }
        if (refhold) {
                cnt = &imo_dbg->imo_refhold_cnt;
                tr = imo_dbg->imo_refhold;
        } else {
                cnt = &imo_dbg->imo_refrele_cnt;
                tr = imo_dbg->imo_refrele;
        }

        idx = atomic_add_16_ov(cnt, 1) % IMO_TRACE_HIST_SIZE;
        ctrace_record(&tr[idx]);
}

struct ip_moptions *
ip_allocmoptions(int how)
{
        struct ip_moptions *imo;

        imo = (how == M_WAITOK) ? zalloc(imo_zone) : zalloc_noblock(imo_zone);
        if (imo != NULL) {
                bzero(imo, imo_size);
                lck_mtx_init(&imo->imo_lock, ifa_mtx_grp, ifa_mtx_attr);
                imo->imo_debug |= IFD_ALLOC;
                if (imo_debug != 0) {
                        imo->imo_debug |= IFD_DEBUG;
                        imo->imo_trace = imo_trace;
                }
                IMO_ADDREF(imo);
        }

        return imo;
}

/*
 * Routine called from ip_output() to loop back a copy of an IP multicast
 * packet to the input queue of a specified interface.  Note that this
 * calls the output routine of the loopback "driver", but with an interface
 * pointer that might NOT be a loopback interface -- evil, but easier than
 * replicating that code here.
 */
static void
ip_mloopback(struct ifnet *srcifp, struct ifnet *origifp, struct mbuf *m,
    struct sockaddr_in *dst, int hlen)
{
        struct mbuf *copym;
        struct ip *ip;

        if (lo_ifp == NULL) {
                return;
        }

        /*
         * Copy the packet header as it's needed for the checksum
         * Make sure to deep-copy IP header portion in case the data
         * is in an mbuf cluster, so that we can safely override the IP
         * header portion later.
         */
        copym = m_copym_mode(m, 0, M_COPYALL, M_DONTWAIT, M_COPYM_COPY_HDR);
        if (copym != NULL && ((copym->m_flags & M_EXT) || copym->m_len < hlen)) {
                copym = m_pullup(copym, hlen);
        }

        if (copym == NULL) {
                return;
        }

        /*
         * We don't bother to fragment if the IP length is greater
         * than the interface's MTU.  Can this possibly matter?
         */
        ip = mtod(copym, struct ip *);
#if BYTE_ORDER != BIG_ENDIAN
        HTONS(ip->ip_len);
        HTONS(ip->ip_off);
#endif
        ip->ip_sum = 0;
        ip->ip_sum = ip_cksum_hdr_out(copym, hlen);

        /*
         * Mark checksum as valid unless receive checksum offload is
         * disabled; if so, compute checksum in software.  If the
         * interface itself is lo0, this will be overridden by if_loop.
         */
        if (hwcksum_rx) {
                copym->m_pkthdr.csum_flags &= ~(CSUM_PARTIAL | CSUM_ZERO_INVERT);
                copym->m_pkthdr.csum_flags |=
                    CSUM_DATA_VALID | CSUM_PSEUDO_HDR;
                copym->m_pkthdr.csum_data = 0xffff;
        } else if (copym->m_pkthdr.csum_flags & CSUM_DELAY_DATA) {
#if BYTE_ORDER != BIG_ENDIAN
                NTOHS(ip->ip_len);
#endif
                in_delayed_cksum(copym);
#if BYTE_ORDER != BIG_ENDIAN
                HTONS(ip->ip_len);
#endif
        }

        /*
         * Stuff the 'real' ifp into the pkthdr, to be used in matching
         * in ip_input(); we need the loopback ifp/dl_tag passed as args
         * to make the loopback driver compliant with the data link
         * requirements.
         */
        copym->m_pkthdr.rcvif = origifp;

        /*
         * Also record the source interface (which owns the source address).
         * This is basically a stripped down version of ifa_foraddr().
         */
        if (srcifp == NULL) {
                struct in_ifaddr *ia;

                lck_rw_lock_shared(in_ifaddr_rwlock);
                TAILQ_FOREACH(ia, INADDR_HASH(ip->ip_src.s_addr), ia_hash) {
                        IFA_LOCK_SPIN(&ia->ia_ifa);
                        if (IA_SIN(ia)->sin_addr.s_addr == ip->ip_src.s_addr) {
                                srcifp = ia->ia_ifp;
                                IFA_UNLOCK(&ia->ia_ifa);
                                break;
                        }
                        IFA_UNLOCK(&ia->ia_ifa);
                }
                lck_rw_done(in_ifaddr_rwlock);
        }
        if (srcifp != NULL) {
                ip_setsrcifaddr_info(copym, srcifp->if_index, NULL);
        }
        ip_setdstifaddr_info(copym, origifp->if_index, NULL);

        dlil_output(lo_ifp, PF_INET, copym, NULL, SA(dst), 0, NULL);
}

/*
 * Given a source IP address (and route, if available), determine the best
 * interface to send the packet from.  Checking for (and updating) the
 * ROF_SRCIF_SELECTED flag in the pcb-supplied route placeholder is done
 * without any locks based on the assumption that ip_output() is single-
 * threaded per-pcb, i.e. for any given pcb there can only be one thread
 * performing output at the IP layer.
 *
 * This routine is analogous to in6_selectroute() for IPv6.
 */
static struct ifaddr *
in_selectsrcif(struct ip *ip, struct route *ro, unsigned int ifscope)
{
        struct ifaddr *ifa = NULL;
        struct in_addr src = ip->ip_src;
        struct in_addr dst = ip->ip_dst;
        struct ifnet *rt_ifp;
        char s_src[MAX_IPv4_STR_LEN], s_dst[MAX_IPv4_STR_LEN];

        VERIFY(src.s_addr != INADDR_ANY);

        if (ip_select_srcif_debug) {
                (void) inet_ntop(AF_INET, &src.s_addr, s_src, sizeof(s_src));
                (void) inet_ntop(AF_INET, &dst.s_addr, s_dst, sizeof(s_dst));
        }

        if (ro->ro_rt != NULL) {
                RT_LOCK(ro->ro_rt);
        }

        rt_ifp = (ro->ro_rt != NULL) ? ro->ro_rt->rt_ifp : NULL;

        /*
         * Given the source IP address, find a suitable source interface
         * to use for transmission; if the caller has specified a scope,
         * optimize the search by looking at the addresses only for that
         * interface.  This is still suboptimal, however, as we need to
         * traverse the per-interface list.
         */
        if (ifscope != IFSCOPE_NONE || ro->ro_rt != NULL) {
                unsigned int scope = ifscope;

                /*
                 * If no scope is specified and the route is stale (pointing
                 * to a defunct interface) use the current primary interface;
                 * this happens when switching between interfaces configured
                 * with the same IP address.  Otherwise pick up the scope
                 * information from the route; the ULP may have looked up a
                 * correct route and we just need to verify it here and mark
                 * it with the ROF_SRCIF_SELECTED flag below.
                 */
                if (scope == IFSCOPE_NONE) {
                        scope = rt_ifp->if_index;
                        if (scope != get_primary_ifscope(AF_INET) &&
                            ROUTE_UNUSABLE(ro)) {
                                scope = get_primary_ifscope(AF_INET);
                        }
                }

                ifa = (struct ifaddr *)ifa_foraddr_scoped(src.s_addr, scope);

                if (ifa == NULL && ip->ip_p != IPPROTO_UDP &&
                    ip->ip_p != IPPROTO_TCP && ipforwarding) {
                        /*
                         * If forwarding is enabled, and if the packet isn't
                         * TCP or UDP, check if the source address belongs
                         * to one of our own interfaces; if so, demote the
                         * interface scope and do a route lookup right below.
                         */
                        ifa = (struct ifaddr *)ifa_foraddr(src.s_addr);
                        if (ifa != NULL) {
                                IFA_REMREF(ifa);
                                ifa = NULL;
                                ifscope = IFSCOPE_NONE;
                        }
                }

                if (ip_select_srcif_debug && ifa != NULL) {
                        if (ro->ro_rt != NULL) {
                                printf("%s->%s ifscope %d->%d ifa_if %s "
                                    "ro_if %s\n", s_src, s_dst, ifscope,
                                    scope, if_name(ifa->ifa_ifp),
                                    if_name(rt_ifp));
                        } else {
                                printf("%s->%s ifscope %d->%d ifa_if %s\n",
                                    s_src, s_dst, ifscope, scope,
                                    if_name(ifa->ifa_ifp));
                        }
                }
        }

        /*
         * Slow path; search for an interface having the corresponding source
         * IP address if the scope was not specified by the caller, and:
         *
         *   1) There currently isn't any route, or,
         *   2) The interface used by the route does not own that source
         *      IP address; in this case, the route will get blown away
         *      and we'll do a more specific scoped search using the newly
         *      found interface.
         */
        if (ifa == NULL && ifscope == IFSCOPE_NONE) {
                ifa = (struct ifaddr *)ifa_foraddr(src.s_addr);

                /*
                 * If we have the IP address, but not the route, we don't
                 * really know whether or not it belongs to the correct
                 * interface (it could be shared across multiple interfaces.)
                 * The only way to find out is to do a route lookup.
                 */
                if (ifa != NULL && ro->ro_rt == NULL) {
                        struct rtentry *rt;
                        struct sockaddr_in sin;
                        struct ifaddr *oifa = NULL;

                        bzero(&sin, sizeof(sin));
                        sin.sin_family = AF_INET;
                        sin.sin_len = sizeof(sin);
                        sin.sin_addr = dst;

                        lck_mtx_lock(rnh_lock);
                        if ((rt = rt_lookup(TRUE, SA(&sin), NULL,
                            rt_tables[AF_INET], IFSCOPE_NONE)) != NULL) {
                                RT_LOCK(rt);
                                /*
                                 * If the route uses a different interface,
                                 * use that one instead.  The IP address of
                                 * the ifaddr that we pick up here is not
                                 * relevant.
                                 */
                                if (ifa->ifa_ifp != rt->rt_ifp) {
                                        oifa = ifa;
                                        ifa = rt->rt_ifa;
                                        IFA_ADDREF(ifa);
                                        RT_UNLOCK(rt);
                                } else {
                                        RT_UNLOCK(rt);
                                }
                                rtfree_locked(rt);
                        }
                        lck_mtx_unlock(rnh_lock);

                        if (oifa != NULL) {
                                struct ifaddr *iifa;

                                /*
                                 * See if the interface pointed to by the
                                 * route is configured with the source IP
                                 * address of the packet.
                                 */
                                iifa = (struct ifaddr *)ifa_foraddr_scoped(
                                        src.s_addr, ifa->ifa_ifp->if_index);

                                if (iifa != NULL) {
                                        /*
                                         * Found it; drop the original one
                                         * as well as the route interface
                                         * address, and use this instead.
                                         */
                                        IFA_REMREF(oifa);
                                        IFA_REMREF(ifa);
                                        ifa = iifa;
                                } else if (!ipforwarding ||
                                    (rt->rt_flags & RTF_GATEWAY)) {
                                        /*
                                         * This interface doesn't have that
                                         * source IP address; drop the route
                                         * interface address and just use the
                                         * original one, and let the caller
                                         * do a scoped route lookup.
                                         */
                                        IFA_REMREF(ifa);
                                        ifa = oifa;
                                } else {
                                        /*
                                         * Forwarding is enabled and the source
                                         * address belongs to one of our own
                                         * interfaces which isn't the outgoing
                                         * interface, and we have a route, and
                                         * the destination is on a network that
                                         * is directly attached (onlink); drop
                                         * the original one and use the route
                                         * interface address instead.
                                         */
                                        IFA_REMREF(oifa);
                                }
                        }
                } else if (ifa != NULL && ro->ro_rt != NULL &&
                    !(ro->ro_rt->rt_flags & RTF_GATEWAY) &&
                    ifa->ifa_ifp != ro->ro_rt->rt_ifp && ipforwarding) {
                        /*
                         * Forwarding is enabled and the source address belongs
                         * to one of our own interfaces which isn't the same
                         * as the interface used by the known route; drop the
                         * original one and use the route interface address.
                         */
                        IFA_REMREF(ifa);
                        ifa = ro->ro_rt->rt_ifa;
                        IFA_ADDREF(ifa);
                }

                if (ip_select_srcif_debug && ifa != NULL) {
                        printf("%s->%s ifscope %d ifa_if %s\n",
                            s_src, s_dst, ifscope, if_name(ifa->ifa_ifp));
                }
        }

        if (ro->ro_rt != NULL) {
                RT_LOCK_ASSERT_HELD(ro->ro_rt);
        }
        /*
         * If there is a non-loopback route with the wrong interface, or if
         * there is no interface configured with such an address, blow it
         * away.  Except for local/loopback, we look for one with a matching
         * interface scope/index.
         */
        if (ro->ro_rt != NULL &&
            (ifa == NULL || (ifa->ifa_ifp != rt_ifp && rt_ifp != lo_ifp) ||
            !(ro->ro_rt->rt_flags & RTF_UP))) {
                if (ip_select_srcif_debug) {
                        if (ifa != NULL) {
                                printf("%s->%s ifscope %d ro_if %s != "
                                    "ifa_if %s (cached route cleared)\n",
                                    s_src, s_dst, ifscope, if_name(rt_ifp),
                                    if_name(ifa->ifa_ifp));
                        } else {
                                printf("%s->%s ifscope %d ro_if %s "
                                    "(no ifa_if found)\n",
                                    s_src, s_dst, ifscope, if_name(rt_ifp));
                        }
                }

                RT_UNLOCK(ro->ro_rt);
                ROUTE_RELEASE(ro);

                /*
                 * If the destination is IPv4 LLA and the route's interface
                 * doesn't match the source interface, then the source IP
                 * address is wrong; it most likely belongs to the primary
                 * interface associated with the IPv4 LL subnet.  Drop the
                 * packet rather than letting it go out and return an error
                 * to the ULP.  This actually applies not only to IPv4 LL
                 * but other shared subnets; for now we explicitly test only
                 * for the former case and save the latter for future.
                 */
                if (IN_LINKLOCAL(ntohl(dst.s_addr)) &&
                    !IN_LINKLOCAL(ntohl(src.s_addr)) && ifa != NULL) {
                        IFA_REMREF(ifa);
                        ifa = NULL;
                }
        }

        if (ip_select_srcif_debug && ifa == NULL) {
                printf("%s->%s ifscope %d (neither ro_if/ifa_if found)\n",
                    s_src, s_dst, ifscope);
        }

        /*
         * If there is a route, mark it accordingly.  If there isn't one,
         * we'll get here again during the next transmit (possibly with a
         * route) and the flag will get set at that point.  For IPv4 LLA
         * destination, mark it only if the route has been fully resolved;
         * otherwise we want to come back here again when the route points
         * to the interface over which the ARP reply arrives on.
         */
        if (ro->ro_rt != NULL && (!IN_LINKLOCAL(ntohl(dst.s_addr)) ||
            (ro->ro_rt->rt_gateway->sa_family == AF_LINK &&
            SDL(ro->ro_rt->rt_gateway)->sdl_alen != 0))) {
                if (ifa != NULL) {
                        IFA_ADDREF(ifa);        /* for route */
                }
                if (ro->ro_srcia != NULL) {
                        IFA_REMREF(ro->ro_srcia);
                }
                ro->ro_srcia = ifa;
                ro->ro_flags |= ROF_SRCIF_SELECTED;
                RT_GENID_SYNC(ro->ro_rt);
        }

        if (ro->ro_rt != NULL) {
                RT_UNLOCK(ro->ro_rt);
        }

        return ifa;
}

/*
 * @brief       Given outgoing interface it determines what checksum needs
 *      to be computed in software and what needs to be offloaded to the
 *      interface.
 *
 * @param       ifp Pointer to the outgoing interface
 * @param       m Pointer to the packet
 * @param       hlen IP header length
 * @param       ip_len Total packet size i.e. headers + data payload
 * @param       sw_csum Pointer to a software checksum flag set
 *
 * @return      void
 */
void
ip_output_checksum(struct ifnet *ifp, struct mbuf *m, int hlen, int ip_len,
    uint32_t *sw_csum)
{
        int tso = TSO_IPV4_OK(ifp, m);
        uint32_t hwcap = ifp->if_hwassist;

        m->m_pkthdr.csum_flags |= CSUM_IP;

        if (!hwcksum_tx) {
                /* do all in software; hardware checksum offload is disabled */
                *sw_csum = (CSUM_DELAY_DATA | CSUM_DELAY_IP) &
                    m->m_pkthdr.csum_flags;
        } else {
                /* do in software what the hardware cannot */
                *sw_csum = m->m_pkthdr.csum_flags &
                    ~IF_HWASSIST_CSUM_FLAGS(hwcap);
        }

        if (hlen != sizeof(struct ip)) {
                *sw_csum |= ((CSUM_DELAY_DATA | CSUM_DELAY_IP) &
                    m->m_pkthdr.csum_flags);
        } else if (!(*sw_csum & CSUM_DELAY_DATA) && (hwcap & CSUM_PARTIAL)) {
                int interface_mtu = ifp->if_mtu;

                if (INTF_ADJUST_MTU_FOR_CLAT46(ifp)) {
                        interface_mtu = IN6_LINKMTU(ifp);
                        /* Further adjust the size for CLAT46 expansion */
                        interface_mtu -= CLAT46_HDR_EXPANSION_OVERHD;
                }

                /*
                 * Partial checksum offload, if non-IP fragment, and TCP only
                 * (no UDP support, as the hardware may not be able to convert
                 * +0 to -0 (0xffff) per RFC1122 4.1.3.4. unless the interface
                 * supports "invert zero" capability.)
                 */
                if (hwcksum_tx && !tso &&
                    ((m->m_pkthdr.csum_flags & CSUM_TCP) ||
                    ((hwcap & CSUM_ZERO_INVERT) &&
                    (m->m_pkthdr.csum_flags & CSUM_ZERO_INVERT))) &&
                    ip_len <= interface_mtu) {
                        uint16_t start = sizeof(struct ip);
                        uint16_t ulpoff = m->m_pkthdr.csum_data & 0xffff;
                        m->m_pkthdr.csum_flags |=
                            (CSUM_DATA_VALID | CSUM_PARTIAL);
                        m->m_pkthdr.csum_tx_stuff = (ulpoff + start);
                        m->m_pkthdr.csum_tx_start = start;
                        /* do IP hdr chksum in software */
                        *sw_csum = CSUM_DELAY_IP;
                } else {
                        *sw_csum |= (CSUM_DELAY_DATA & m->m_pkthdr.csum_flags);
                }
        }

        if (*sw_csum & CSUM_DELAY_DATA) {
                in_delayed_cksum(m);
                *sw_csum &= ~CSUM_DELAY_DATA;
        }

        if (hwcksum_tx) {
                /*
                 * Drop off bits that aren't supported by hardware;
                 * also make sure to preserve non-checksum related bits.
                 */
                m->m_pkthdr.csum_flags =
                    ((m->m_pkthdr.csum_flags &
                    (IF_HWASSIST_CSUM_FLAGS(hwcap) | CSUM_DATA_VALID)) |
                    (m->m_pkthdr.csum_flags & ~IF_HWASSIST_CSUM_MASK));
        } else {
                /* drop all bits; hardware checksum offload is disabled */
                m->m_pkthdr.csum_flags = 0;
        }
}

/*
 * GRE protocol output for PPP/PPTP
 */
int
ip_gre_output(struct mbuf *m)
{
        struct route ro;
        int error;

        bzero(&ro, sizeof(ro));

        error = ip_output(m, NULL, &ro, 0, NULL, NULL);

        ROUTE_RELEASE(&ro);

        return error;
}

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

        i = ip_output_measure;
        error = sysctl_handle_int(oidp, &i, 0, req);
        if (error || req->newptr == USER_ADDR_NULL) {
                goto done;
        }
        /* impose bounds */
        if (i < 0 || i > 1) {
                error = EINVAL;
                goto done;
        }
        if (ip_output_measure != i && i == 1) {
                net_perf_initialize(&net_perf, ip_output_measure_bins);
        }
        ip_output_measure = i;
done:
        return error;
}

static int
sysctl_ip_output_measure_bins SYSCTL_HANDLER_ARGS
{
#pragma unused(arg1, arg2)
        int error;
        uint64_t i;

        i = ip_output_measure_bins;
        error = sysctl_handle_quad(oidp, &i, 0, req);
        if (error || req->newptr == USER_ADDR_NULL) {
                goto done;
        }
        /* validate data */
        if (!net_perf_validate_bins(i)) {
                error = EINVAL;
                goto done;
        }
        ip_output_measure_bins = i;
done:
        return error;
}

static int
sysctl_ip_output_getperf 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, &net_perf, MIN(sizeof(net_perf), req->oldlen));
}