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ip_input.c

//==========================================================================
//
//      src/sys/netinet/ip_input.c
//
//==========================================================================
//####BSDCOPYRIGHTBEGIN####
//
// -------------------------------------------
//
// Portions of this software may have been derived from OpenBSD, 
// FreeBSD or other sources, and are covered by the appropriate
// copyright disclaimers included herein.
//
// Portions created by Red Hat are
// Copyright (C) 2002 Red Hat, Inc. All Rights Reserved.
//
// -------------------------------------------
//
//####BSDCOPYRIGHTEND####
//==========================================================================

/*
 * Copyright (c) 1982, 1986, 1988, 1993
 *    The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *    This product includes software developed by the University of
 *    California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *    @(#)ip_input.c    8.2 (Berkeley) 1/4/94
 * $FreeBSD: src/sys/netinet/ip_input.c,v 1.130.2.25 2001/08/29 21:41:37 jesper Exp $
 */

#define     _IP_VHL

#include <sys/param.h>
#include <sys/mbuf.h>
#include <sys/malloc.h>
#include <sys/domain.h>
#include <sys/protosw.h>
#include <sys/socket.h>

#include <net/if.h>
#include <net/if_var.h>
#include <net/if_dl.h>
#include <net/route.h>
#include <net/netisr.h>
#include <net/intrq.h>

#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/in_var.h>
#include <netinet/ip.h>
#include <netinet/in_pcb.h>
#include <netinet/ip_var.h>
#include <netinet/ip_icmp.h>

#include <sys/socketvar.h>

#include <netinet/ip_fw.h>

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

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

int rsvp_on = 0;
static int ip_rsvp_on;
struct socket *ip_rsvpd;

int   ipforwarding = 0;
static int  ipsendredirects = 1; /* XXX */
int   ip_defttl = IPDEFTTL;
static int  ip_dosourceroute = 0;
static int  ip_acceptsourceroute = 0;
static int  ip_keepfaith = 0;
static int  ip_nfragpackets = 0;
static int  ip_maxfragpackets;      /* initialized in ip_init() */

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

#ifdef DIAGNOSTIC
static int  ipprintfs = 0;
#endif

extern      struct domain inetdomain;
extern      struct protosw inetsw[];
u_char      ip_protox[IPPROTO_MAX];
static int  ipqmaxlen = IFQ_MAXLEN;
struct      in_ifaddrhead in_ifaddrhead; /* first inet address */
struct ipstat ipstat;

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

static struct ipq ipq[IPREASS_NHASH];
static int    nipq = 0;         /* total # of reass queues */
static int    maxnipq;
const  int    ipintrq_present = 1;

#ifdef IPSTEALTH
static int  ipstealth = 0;
#endif


/* Firewall hooks */
ip_fw_chk_t *ip_fw_chk_ptr;
ip_fw_ctl_t *ip_fw_ctl_ptr;
int fw_enable = 1 ;

#ifdef DUMMYNET
ip_dn_ctl_t *ip_dn_ctl_ptr;
#endif

int (*fr_checkp) __P((struct ip *, int, struct ifnet *, int, struct mbuf **)) = NULL;


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

struct sockaddr_in *ip_fw_fwd_addr;

static void save_rte __P((u_char *, struct in_addr));
static int  ip_dooptions __P((struct mbuf *));
#ifdef NATPT
       void ip_forward __P((struct mbuf *, int));
#else
static void ip_forward __P((struct mbuf *, int));
#endif
static void ip_freef __P((struct ipq *));
#ifdef IPDIVERT
static struct     mbuf *ip_reass __P((struct mbuf *,
                  struct ipq *, struct ipq *, u_int32_t *, u_int16_t *));
#else
static struct     mbuf *ip_reass __P((struct mbuf *, struct ipq *, struct ipq *));
#endif
static struct     in_ifaddr *ip_rtaddr __P((struct in_addr));
static void ipintr __P((void));

#ifdef NATPT
extern      int               ip6_protocol_tr;
int   natpt_in4         __P((struct mbuf *, struct mbuf **));
extern      void ip6_forward  __P((struct mbuf *, int));
#endif      /* NATPT */

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

      TAILQ_INIT(&in_ifaddrhead);
      pr = pffindproto(PF_INET, IPPROTO_RAW, SOCK_RAW);
      if (pr == 0)
            panic("ip_init");
      for (i = 0; i < IPPROTO_MAX; i++)
            ip_protox[i] = pr - inetsw;
      for (pr = inetdomain.dom_protosw;
          pr < inetdomain.dom_protoswNPROTOSW; pr++)
            if (pr->pr_domain->dom_family == PF_INET &&
                pr->pr_protocol && pr->pr_protocol != IPPROTO_RAW)
                  ip_protox[pr->pr_protocol] = pr - inetsw;

      for (i = 0; i < IPREASS_NHASH; i++)
          ipq[i].next = ipq[i].prev = &ipq[i];

      maxnipq = nmbclusters / 4;
      ip_maxfragpackets = nmbclusters / 4;

#ifndef RANDOM_IP_ID
      ip_id = time_second & 0xffff;
#endif
      ipintrq.ifq_maxlen = ipqmaxlen;

      register_netisr(NETISR_IP, ipintr);
}

static struct     sockaddr_in ipaddr = { sizeof(ipaddr), AF_INET };
static struct     route ipforward_rt;

/*
 * Ip input routine.  Checksum and byte swap header.  If fragmented
 * try to reassemble.  Process options.  Pass to next level.
 */
void
ip_input(struct mbuf *m)
{
      struct ip *ip;
      struct ipq *fp;
      struct in_ifaddr *ia = NULL;
      int    i, hlen, mff, checkif;
      u_short sum;
      u_int16_t divert_cookie;            /* firewall cookie */
      struct in_addr pkt_dst;
#ifdef IPDIVERT
      u_int32_t divert_info = 0;          /* packet divert/tee info */
#endif
      struct ip_fw_chain *rule = NULL;

#ifdef IPDIVERT
      /* Get and reset firewall cookie */
      divert_cookie = ip_divert_cookie;
      ip_divert_cookie = 0;
#else
      divert_cookie = 0;
#endif

#if defined(IPFIREWALL) && defined(DUMMYNET)
        /*
         * dummynet packet are prepended a vestigial mbuf with
         * m_type = MT_DUMMYNET and m_data pointing to the matching
         * rule.
         */
        if (m->m_type == MT_DUMMYNET) {
            rule = (struct ip_fw_chain *)(m->m_data) ;
            m = m->m_next ;
            ip = mtod(m, struct ip *);
            hlen = IP_VHL_HL(ip->ip_vhl) << 2;
            goto iphack ;
        } else
            rule = NULL ;
#endif

#ifdef      DIAGNOSTIC
      if (m == NULL || (m->m_flags & M_PKTHDR) == 0)
            panic("ip_input no HDR");
#endif
      ipstat.ips_total++;

      if (m->m_pkthdr.len < sizeof(struct ip))
            goto tooshort;

      if (m->m_len < sizeof (struct ip) &&
          (m = m_pullup(m, sizeof (struct ip))) == 0) {
            ipstat.ips_toosmall++;
            return;
      }
      ip = mtod(m, struct ip *);

      if (IP_VHL_V(ip->ip_vhl) != IPVERSION) {
            ipstat.ips_badvers++;
            goto bad;
      }

      hlen = IP_VHL_HL(ip->ip_vhl) << 2;
      if (hlen < sizeof(struct ip)) {     /* minimum header length */
            ipstat.ips_badhlen++;
            goto bad;
      }
      if (hlen > m->m_len) {
            if ((m = m_pullup(m, hlen)) == 0) {
                  ipstat.ips_badhlen++;
                  return;
            }
            ip = mtod(m, struct ip *);
      }

      /* 127/8 must not appear on wire - RFC1122 */
      if ((ntohl(ip->ip_dst.s_addr) >> IN_CLASSA_NSHIFT) == IN_LOOPBACKNET ||
          (ntohl(ip->ip_src.s_addr) >> IN_CLASSA_NSHIFT) == IN_LOOPBACKNET) {
            if ((m->m_pkthdr.rcvif->if_flags & IFF_LOOPBACK) == 0) {
                  ipstat.ips_badaddr++;
                  goto bad;
            }
      }

      if (m->m_pkthdr.csum_flags & CSUM_IP_CHECKED) {
            sum = !(m->m_pkthdr.csum_flags & CSUM_IP_VALID);
      } else {
            if (hlen == sizeof(struct ip)) {
                  sum = in_cksum_hdr(ip);
            } else {
                  sum = in_cksum(m, hlen);
            }
      }
      if (sum) {
            ipstat.ips_badsum++;
            goto bad;
      }

#ifdef ALTQ
      if (altq_input != NULL && (*altq_input)(m, AF_INET) == 0)
            /* packet is dropped by traffic conditioner */
            return;
#endif
      /*
       * Convert fields to host representation.
       */
      NTOHS(ip->ip_len);
      if (ip->ip_len < hlen) {
            ipstat.ips_badlen++;
            goto bad;
      }
      NTOHS(ip->ip_off);

      /*
       * Check that the amount of data in the buffers
       * is as at least much as the IP header would have us expect.
       * Trim mbufs if longer than we expect.
       * Drop packet if shorter than we expect.
       */
      if (m->m_pkthdr.len < ip->ip_len) {
tooshort:
            ipstat.ips_tooshort++;
            goto bad;
      }
      if (m->m_pkthdr.len > ip->ip_len) {
            if (m->m_len == m->m_pkthdr.len) {
                  m->m_len = ip->ip_len;
                  m->m_pkthdr.len = ip->ip_len;
            } else
                  m_adj(m, ip->ip_len - m->m_pkthdr.len);
      }

#ifdef IPSEC
      if (ipsec_getnhist(m))
            goto pass;
#endif

      /*
       * IpHack's section.
       * Right now when no processing on packet has done
       * and it is still fresh out of network we do our black
       * deals with it.
       * - Firewall: deny/allow/divert
       * - Xlate: translate packet's addr/port (NAT).
       * - Pipe: pass pkt through dummynet.
       * - Wrap: fake packet's addr/port <unimpl.>
       * - Encapsulate: put it in another IP and send out. <unimp.>
       */

#if defined(IPFIREWALL) && defined(DUMMYNET)
iphack:
#endif
      /*
       * Check if we want to allow this packet to be processed.
       * Consider it to be bad if not.
       */
      if (fr_checkp) {
            struct      mbuf  *m1 = m;

            if ((*fr_checkp)(ip, hlen, m->m_pkthdr.rcvif, 0, &m1) || !m1)
                  return;
            ip = mtod(m = m1, struct ip *);
      }
      if (fw_enable && ip_fw_chk_ptr) {
#ifdef IPFIREWALL_FORWARD
            /*
             * If we've been forwarded from the output side, then
             * skip the firewall a second time
             */
            if (ip_fw_fwd_addr)
                  goto ours;
#endif      /* IPFIREWALL_FORWARD */
            /*
             * See the comment in ip_output for the return values
             * produced by the firewall.
             */
            i = (*ip_fw_chk_ptr)(&ip,
                hlen, NULL, &divert_cookie, &m, &rule, &ip_fw_fwd_addr);
            if ( (i & IP_FW_PORT_DENY_FLAG) || m == NULL) { /* drop */
                        if (m)
                                m_freem(m);
                  return ;
                }
            ip = mtod(m, struct ip *); /* just in case m changed */
            if (i == 0 && ip_fw_fwd_addr == NULL)     /* common case */
                  goto pass;
#ifdef DUMMYNET
                if ((i & IP_FW_PORT_DYNT_FLAG) != 0) {
                        /* Send packet to the appropriate pipe */
                        dummynet_io(i&0xffff,DN_TO_IP_IN,m,NULL,NULL,0, rule,
                            0);
                  return;
            }
#endif
#ifdef IPDIVERT
            if (i != 0 && (i & IP_FW_PORT_DYNT_FLAG) == 0) {
                  /* Divert or tee packet */
                  divert_info = i;
                  goto ours;
            }
#endif
#ifdef IPFIREWALL_FORWARD
            if (i == 0 && ip_fw_fwd_addr != NULL)
                  goto pass;
#endif
            /*
             * if we get here, the packet must be dropped
             */
            m_freem(m);
            return;
      }
pass:

      /*
       * Process options and, if not destined for us,
       * ship it on.  ip_dooptions returns 1 when an
       * error was detected (causing an icmp message
       * to be sent and the original packet to be freed).
       */
      ip_nhops = 0;           /* for source routed packets */
      if (hlen > sizeof (struct ip) && ip_dooptions(m)) {
#ifdef IPFIREWALL_FORWARD
            ip_fw_fwd_addr = NULL;
#endif
            return;
      }

        /* greedy RSVP, snatches any PATH packet of the RSVP protocol and no
         * matter if it is destined to another node, or whether it is 
         * a multicast one, RSVP wants it! and prevents it from being forwarded
         * anywhere else. Also checks if the rsvp daemon is running before
       * grabbing the packet.
         */
      if (rsvp_on && ip->ip_p==IPPROTO_RSVP) 
            goto ours;

#ifdef NATPT
      /*
       * NATPT (Network Address Translation - Protocol Translation)
       */
      if (ip6_protocol_tr) {
            struct mbuf *m1 = NULL;

            switch (natpt_in4(m, &m1)) {
            case IPPROTO_IP:  /* this packet is not changed */
                  goto checkaddresses;

            case IPPROTO_IPV4:
                  ip_forward(m1, 0);
                  break;

            case IPPROTO_IPV6:
                  ip6_forward(m1, 1);
                  break;

            case IPPROTO_DONE:      /* discard without free */
                  return;

            case IPPROTO_MAX: /* discard this packet  */
            default:
                  break;
            }

            if (m != m1)
                  m_freem(m);

            return;
      }
checkaddresses:;
#endif

      /*
       * Check our list of addresses, to see if the packet is for us.
       * If we don't have any addresses, assume any unicast packet
       * we receive might be for us (and let the upper layers deal
       * with it).
       */
      if (TAILQ_EMPTY(&in_ifaddrhead) &&
          (m->m_flags & (M_MCAST|M_BCAST)) == 0)
            goto ours;

      /*
       * Cache the destination address of the packet; this may be
       * changed by use of 'ipfw fwd'.
       */
      pkt_dst = ip_fw_fwd_addr == NULL ?
          ip->ip_dst : ip_fw_fwd_addr->sin_addr;

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

      TAILQ_FOREACH(ia, &in_ifaddrhead, ia_link) {
#define     satosin(sa) ((struct sockaddr_in *)(sa))

#ifdef BOOTP_COMPAT
            if (IA_SIN(ia)->sin_addr.s_addr == INADDR_ANY)
                  goto ours;
#endif
            /*
             * If the address matches, verify that the packet
             * arrived via the correct interface if checking is
             * enabled.
             */
            if (IA_SIN(ia)->sin_addr.s_addr == pkt_dst.s_addr && 
                (!checkif || ia->ia_ifp == m->m_pkthdr.rcvif))
                  goto ours;
            /*
             * Only accept broadcast packets that arrive via the
             * matching interface.  Reception of forwarded directed
             * broadcasts would be handled via ip_forward() and
             * ether_output() with the loopback into the stack for
             * SIMPLEX interfaces handled by ether_output().
             */
            if (ia->ia_ifp == m->m_pkthdr.rcvif &&
                ia->ia_ifp && ia->ia_ifp->if_flags & IFF_BROADCAST) {
                  if (satosin(&ia->ia_broadaddr)->sin_addr.s_addr ==
                      pkt_dst.s_addr)
                        goto ours;
                  if (ia->ia_netbroadcast.s_addr == pkt_dst.s_addr)
                        goto ours;
            }
      }
      if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr))) {
            struct in_multi *inm;
            if (ip_mrouter) {
                  /*
                   * If we are acting as a multicast router, all
                   * incoming multicast packets are passed to the
                   * kernel-level multicast forwarding function.
                   * The packet is returned (relatively) intact; if
                   * ip_mforward() returns a non-zero value, the packet
                   * must be discarded, else it may be accepted below.
                   */
                  if (ip_mforward(ip, m->m_pkthdr.rcvif, m, 0) != 0) {
                        ipstat.ips_cantforward++;
                        m_freem(m);
                        return;
                  }

                  /*
                   * The process-level routing demon needs to receive
                   * all multicast IGMP packets, whether or not this
                   * host belongs to their destination groups.
                   */
                  if (ip->ip_p == IPPROTO_IGMP)
                        goto ours;
                  ipstat.ips_forward++;
            }
            /*
             * See if we belong to the destination multicast group on the
             * arrival interface.
             */
            IN_LOOKUP_MULTI(ip->ip_dst, m->m_pkthdr.rcvif, inm);
            if (inm == NULL) {
                  ipstat.ips_notmember++;
                  m_freem(m);
                  return;
            }
            goto ours;
      }
      if (ip->ip_dst.s_addr == (u_long)INADDR_BROADCAST)
            goto ours;
      if (ip->ip_dst.s_addr == INADDR_ANY)
            goto ours;

#if defined(NFAITH) && 0 < NFAITH
      /*
       * FAITH(Firewall Aided Internet Translator)
       */
      if (m->m_pkthdr.rcvif && m->m_pkthdr.rcvif->if_type == IFT_FAITH) {
            if (ip_keepfaith) {
                  if (ip->ip_p == IPPROTO_TCP || ip->ip_p == IPPROTO_ICMP) 
                        goto ours;
            }
            m_freem(m);
            return;
      }
#endif
      /*
       * Not for us; forward if possible and desirable.
       */
      if (ipforwarding == 0) {
            ipstat.ips_cantforward++;
            m_freem(m);
      } else
            ip_forward(m, 0);
#ifdef IPFIREWALL_FORWARD
      ip_fw_fwd_addr = NULL;
#endif
      return;

ours:
      /* Count the packet in the ip address stats */
      if (ia != NULL) {
            ia->ia_ifa.if_ipackets++;
            ia->ia_ifa.if_ibytes += m->m_pkthdr.len;
      }

      /*
       * If offset or IP_MF are set, must reassemble.
       * Otherwise, nothing need be done.
       * (We could look in the reassembly queue to see
       * if the packet was previously fragmented,
       * but it's not worth the time; just let them time out.)
       */
      if (ip->ip_off & (IP_MF | IP_OFFMASK | IP_RF)) {

#if 0 /*
       * Reassembly should be able to treat a mbuf cluster, for later
       * operation of contiguous protocol headers on the cluster. (KAME)
       */
            if (m->m_flags & M_EXT) {           /* XXX */
                  if ((m = m_pullup(m, hlen)) == 0) {
                        ipstat.ips_toosmall++;
#ifdef IPFIREWALL_FORWARD
                        ip_fw_fwd_addr = NULL;
#endif
                        return;
                  }
                  ip = mtod(m, struct ip *);
            }
#endif
            sum = IPREASS_HASH(ip->ip_src.s_addr, ip->ip_id);
            /*
             * Look for queue of fragments
             * of this datagram.
             */
            for (fp = ipq[sum].next; fp != &ipq[sum]; fp = fp->next)
                  if (ip->ip_id == fp->ipq_id &&
                      ip->ip_src.s_addr == fp->ipq_src.s_addr &&
                      ip->ip_dst.s_addr == fp->ipq_dst.s_addr &&
                      ip->ip_p == fp->ipq_p)
                        goto found;

            fp = 0;

            /* check if there's a place for the new queue */
            if (nipq > maxnipq) {
                /*
                 * drop something from the tail of the current queue
                 * before proceeding further
                 */
                if (ipq[sum].prev == &ipq[sum]) {   /* gak */
                  for (i = 0; i < IPREASS_NHASH; i++) {
                      if (ipq[i].prev != &ipq[i]) {
                        ip_freef(ipq[i].prev);
                        break;
                      }
                  }
                } else
                  ip_freef(ipq[sum].prev);
            }
found:
            /*
             * Adjust ip_len to not reflect header,
             * set ip_mff if more fragments are expected,
             * convert offset of this to bytes.
             */
            ip->ip_len -= hlen;
            mff = (ip->ip_off & IP_MF) != 0;
            if (mff) {
                    /*
                     * Make sure that fragments have a data length
                   * that's a non-zero multiple of 8 bytes.
                     */
                  if (ip->ip_len == 0 || (ip->ip_len & 0x7) != 0) {
                        ipstat.ips_toosmall++; /* XXX */
                        goto bad;
                  }
                  m->m_flags |= M_FRAG;
            }
            ip->ip_off <<= 3;

            /*
             * If datagram marked as having more fragments
             * or if this is not the first fragment,
             * attempt reassembly; if it succeeds, proceed.
             */
            if (mff || ip->ip_off) {
                  ipstat.ips_fragments++;
                  m->m_pkthdr.header = ip;
#ifdef IPDIVERT
                  m = ip_reass(m,
                      fp, &ipq[sum], &divert_info, &divert_cookie);
#else
                  m = ip_reass(m, fp, &ipq[sum]);
#endif
                  if (m == 0) {
#ifdef IPFIREWALL_FORWARD
                        ip_fw_fwd_addr = NULL;
#endif
                        return;
                  }
                  ipstat.ips_reassembled++;
                  ip = mtod(m, struct ip *);
                  /* Get the header length of the reassembled packet */
                  hlen = IP_VHL_HL(ip->ip_vhl) << 2;
#ifdef IPDIVERT
                  /* Restore original checksum before diverting packet */
                  if (divert_info != 0) {
                        ip->ip_len += hlen;
                        HTONS(ip->ip_len);
                        HTONS(ip->ip_off);
                        ip->ip_sum = 0;
                        if (hlen == sizeof(struct ip))
                              ip->ip_sum = in_cksum_hdr(ip);
                        else
                              ip->ip_sum = in_cksum(m, hlen);
                        NTOHS(ip->ip_off);
                        NTOHS(ip->ip_len);
                        ip->ip_len -= hlen;
                  }
#endif
            } else
                  if (fp)
                        ip_freef(fp);
      } else
            ip->ip_len -= hlen;

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

            /* Clone packet if we're doing a 'tee' */
            if ((divert_info & IP_FW_PORT_TEE_FLAG) != 0)
                  clone = m_dup(m, M_DONTWAIT);

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

            /* Deliver packet to divert input routine */
            ip_divert_cookie = divert_cookie;
            divert_packet(m, 1, divert_info & 0xffff);
            ipstat.ips_delivered++;

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

#ifdef IPSEC
      /*
       * enforce IPsec policy checking if we are seeing last header.
       * note that we do not visit this with protocols with pcb layer
       * code - like udp/tcp/raw ip.
       */
      if ((inetsw[ip_protox[ip->ip_p]].pr_flags & PR_LASTHDR) != 0 &&
          ipsec4_in_reject(m, NULL)) {
            ipsecstat.in_polvio++;
            goto bad;
      }
#endif

      /*
       * Switch out to protocol's input routine.
       */
      ipstat.ips_delivered++;
    {
      int off = hlen;

      (*inetsw[ip_protox[ip->ip_p]].pr_input)(m, off);
#ifdef      IPFIREWALL_FORWARD
      ip_fw_fwd_addr = NULL;  /* tcp needed it */
#endif
      return;
    }
bad:
#ifdef      IPFIREWALL_FORWARD
      ip_fw_fwd_addr = NULL;
#endif
      m_freem(m);
}

/*
 * IP software interrupt routine - to go away sometime soon
 */
static void
ipintr(void)
{
      int s;
      struct mbuf *m;

      while(1) {
            s = splimp();
            IF_DEQUEUE(&ipintrq, m);
            splx(s);
            if (m == 0)
                  return;
            ip_input(m);
      }
}

/*
 * Take incoming datagram fragment and try to reassemble it into
 * whole datagram.  If a chain for reassembly of this datagram already
 * exists, then it is given as fp; otherwise have to make a chain.
 *
 * When IPDIVERT enabled, keep additional state with each packet that
 * tells us if we need to divert or tee the packet we're building.
 */

static struct mbuf *
#ifdef IPDIVERT
ip_reass(m, fp, where, divinfo, divcookie)
#else
ip_reass(m, fp, where)
#endif
      register struct mbuf *m;
      register struct ipq *fp;
      struct   ipq    *where;
#ifdef IPDIVERT
      u_int32_t *divinfo;
      u_int16_t *divcookie;
#endif
{
      struct ip *ip = mtod(m, struct ip *);
      register struct mbuf *p = 0, *q, *nq;
      struct mbuf *t;
      int hlen = IP_VHL_HL(ip->ip_vhl) << 2;
      int i, next;

      /*
       * Presence of header sizes in mbufs
       * would confuse code below.
       */
      m->m_data += hlen;
      m->m_len -= hlen;

      /*
       * If first fragment to arrive, create a reassembly queue.
       */
      if (fp == 0) {
            /*
             * Enforce upper bound on number of fragmented packets
             * for which we attempt reassembly;
             * If maxfrag is 0, never accept fragments.
             * If maxfrag is -1, accept all fragments without limitation.
             */
            if ((ip_maxfragpackets >= 0) && (ip_nfragpackets >= ip_maxfragpackets))
                  goto dropfrag;
            ip_nfragpackets++;
            if ((t = m_get(M_DONTWAIT, MT_FTABLE)) == NULL)
                  goto dropfrag;
            fp = mtod(t, struct ipq *);
            insque(fp, where);
            nipq++;
            fp->ipq_ttl = IPFRAGTTL;
            fp->ipq_p = ip->ip_p;
            fp->ipq_id = ip->ip_id;
            fp->ipq_src = ip->ip_src;
            fp->ipq_dst = ip->ip_dst;
            fp->ipq_frags = m;
            m->m_nextpkt = NULL;
#ifdef IPDIVERT
            fp->ipq_div_info = 0;
            fp->ipq_div_cookie = 0;
#endif
            goto inserted;
      }

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

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

      /*
       * If there is a preceding segment, it may provide some of
       * our data already.  If so, drop the data from the incoming
       * segment.  If it provides all of our data, drop us, otherwise
       * stick new segment in the proper place.
       *
       * If some of the data is dropped from the the preceding
       * segment, then it's checksum is invalidated.
       */
      if (p) {
            i = GETIP(p)->ip_off + GETIP(p)->ip_len - ip->ip_off;
            if (i > 0) {
                  if (i >= ip->ip_len)
                        goto dropfrag;
                  m_adj(m, i);
                  m->m_pkthdr.csum_flags = 0;
                  ip->ip_off += i;
                  ip->ip_len -= i;
            }
            m->m_nextpkt = p->m_nextpkt;
            p->m_nextpkt = m;
      } else {
            m->m_nextpkt = fp->ipq_frags;
            fp->ipq_frags = m;
      }

      /*
       * While we overlap succeeding segments trim them or,
       * if they are completely covered, dequeue them.
       */
      for (; q != NULL && ip->ip_off + ip->ip_len > GETIP(q)->ip_off;
           q = nq) {
            i = (ip->ip_off + ip->ip_len) -
                GETIP(q)->ip_off;
            if (i < GETIP(q)->ip_len) {
                  GETIP(q)->ip_len -= i;
                  GETIP(q)->ip_off += i;
                  m_adj(q, i);
                  q->m_pkthdr.csum_flags = 0;
                  break;
            }
            nq = q->m_nextpkt;
            m->m_nextpkt = nq;
            m_freem(q);
      }

inserted:

#ifdef IPDIVERT
      /*
       * Transfer firewall instructions to the fragment structure.
       * Any fragment diverting causes the whole packet to divert.
       */
      fp->ipq_div_info = *divinfo;
      fp->ipq_div_cookie = *divcookie;
      *divinfo = 0;
      *divcookie = 0;
#endif

      /*
       * Check for complete reassembly.
       */
      next = 0;
      for (p = NULL, q = fp->ipq_frags; q; p = q, q = q->m_nextpkt) {
            if (GETIP(q)->ip_off != next)
                  return (0);
            next += GETIP(q)->ip_len;
      }
      /* Make sure the last packet didn't have the IP_MF flag */
      if (p->m_flags & M_FRAG)
            return (0);

      /*
       * Reassembly is complete.  Make sure the packet is a sane size.
       */
      q = fp->ipq_frags;
      ip = GETIP(q);
      if (next + (IP_VHL_HL(ip->ip_vhl) << 2) > IP_MAXPACKET) {
            ipstat.ips_toolong++;
            ip_freef(fp);
            return (0);
      }

      /*
       * Concatenate fragments.
       */
      m = q;
      t = m->m_next;
      m->m_next = 0;
      m_cat(m, t);
      nq = q->m_nextpkt;
      q->m_nextpkt = 0;
      for (q = nq; q != NULL; q = nq) {
            nq = q->m_nextpkt;
            q->m_nextpkt = NULL;
            m->m_pkthdr.csum_flags &= q->m_pkthdr.csum_flags;
            m->m_pkthdr.csum_data += q->m_pkthdr.csum_data;
            m_cat(m, q);
      }

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

      /*
       * Create header for new ip packet by
       * modifying header of first packet;
       * dequeue and discard fragment reassembly header.
       * Make header visible.
       */
      ip->ip_len = next;
      ip->ip_src = fp->ipq_src;
      ip->ip_dst = fp->ipq_dst;
      remque(fp);
      nipq--;
      (void) m_free(dtom(fp));
      ip_nfragpackets--;
      m->m_len += (IP_VHL_HL(ip->ip_vhl) << 2);
      m->m_data -= (IP_VHL_HL(ip->ip_vhl) << 2);
      /* some debugging cruft by sklower, below, will go away soon */
      if (m->m_flags & M_PKTHDR) { /* XXX this should be done elsewhere */
            register int plen = 0;
            for (t = m; t; t = t->m_next)
                  plen += t->m_len;
            m->m_pkthdr.len = plen;
      }
      return (m);

dropfrag:
#ifdef IPDIVERT
      *divinfo = 0;
      *divcookie = 0;
#endif
      ipstat.ips_fragdropped++;
      m_freem(m);
      return (0);

#undef GETIP
}

/*
 * Free a fragment reassembly header and all
 * associated datagrams.
 */
static void
ip_freef(fp)
      struct ipq *fp;
{
      register struct mbuf *q;

      while (fp->ipq_frags) {
            q = fp->ipq_frags;
            fp->ipq_frags = q->m_nextpkt;
            m_freem(q);
      }
      remque(fp);
      (void) m_free(dtom(fp));
      ip_nfragpackets--;
      nipq--;
}

/*
 * IP timer processing;
 * if a timer expires on a reassembly
 * queue, discard it.
 */
void
ip_slowtimo()
{
      register struct ipq *fp;
      int s = splnet();
      int i;

      for (i = 0; i < IPREASS_NHASH; i++) {
            fp = ipq[i].next;
            if (fp == 0)
                  continue;
            while (fp != &ipq[i]) {
                  --fp->ipq_ttl;
                  fp = fp->next;
                  if (fp->prev->ipq_ttl == 0) {
                        ipstat.ips_fragtimeout++;
                        ip_freef(fp->prev);
                  }
            }
      }
      /*
       * If we are over the maximum number of fragments
       * (due to the limit being lowered), drain off
       * enough to get down to the new limit.
       */
      for (i = 0; i < IPREASS_NHASH; i++) {
            if (ip_maxfragpackets >= 0) {
                  while ((ip_nfragpackets > ip_maxfragpackets) &&
                        (ipq[i].next != &ipq[i])) {
                        ipstat.ips_fragdropped++;
                        ip_freef(ipq[i].next);
                  }
            }
      }
      ipflow_slowtimo();
      splx(s);
}

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

      for (i = 0; i < IPREASS_NHASH; i++) {
            while (ipq[i].next != &ipq[i]) {
                  ipstat.ips_fragdropped++;
                  ip_freef(ipq[i].next);
            }
      }
      in_rtqdrain();
}

/*
 * Do option processing on a datagram,
 * possibly discarding it if bad options are encountered,
 * or forwarding it if source-routed.
 * Returns 1 if packet has been forwarded/freed,
 * 0 if the packet should be processed further.
 */
static int
ip_dooptions(m)
      struct mbuf *m;
{
      register struct ip *ip = mtod(m, struct ip *);
      register u_char *cp;
      register struct ip_timestamp *ipt;
      register struct in_ifaddr *ia;
      int opt, optlen, cnt, off, code, type = ICMP_PARAMPROB, forward = 0;
      struct in_addr *sin, dst;
      n_time ntime;

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

            default:
                  break;

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

                  if (!ip_dosourceroute) {
                        if (ipforwarding) {
                              char buf[16]; /* aaa.bbb.ccc.ddd\0 */
                              /*
                               * Acting as a router, so generate ICMP
                               */
nosourcerouting:
                              strcpy(buf, inet_ntoa(ip->ip_dst));
                              log(LOG_WARNING, 
                                  "attempted source route from %s to %s\n",
                                  inet_ntoa(ip->ip_src), buf);
                              type = ICMP_UNREACH;
                              code = ICMP_UNREACH_SRCFAIL;
                              goto bad;
                        } else {
                              /*
                               * Not acting as a router, so silently drop.
                               */
                              ipstat.ips_cantforward++;
                              m_freem(m);
                              return (1);
                        }
                  }

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

                  if (opt == IPOPT_SSRR) {
#define     INA   struct in_ifaddr *
#define     SA    struct sockaddr *
                      if ((ia = (INA)ifa_ifwithdstaddr((SA)&ipaddr)) == 0)
                        ia = (INA)ifa_ifwithnet((SA)&ipaddr);
                  } else
                        ia = ip_rtaddr(ipaddr.sin_addr);
                  if (ia == 0) {
                        type = ICMP_UNREACH;
                        code = ICMP_UNREACH_SRCFAIL;
                        goto bad;
                  }
                  ip->ip_dst = ipaddr.sin_addr;
                  (void)memcpy(cp + off, &(IA_SIN(ia)->sin_addr),
                      sizeof(struct in_addr));
                  cp[IPOPT_OFFSET] += sizeof(struct in_addr);
                  /*
                   * Let ip_intr's mcast routing check handle mcast pkts
                   */
                  forward = !IN_MULTICAST(ntohl(ip->ip_dst.s_addr));
                  break;

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

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

                  case IPOPT_TS_TSONLY:
                        break;

                  case IPOPT_TS_TSANDADDR:
                        if (ipt->ipt_ptr - 1 + sizeof(n_time) +
                            sizeof(struct in_addr) > ipt->ipt_len) {
                              code = (u_char *)&ipt->ipt_ptr -
                                  (u_char *)ip;
                              goto bad;
                        }
                        ipaddr.sin_addr = dst;
                        ia = (INA)ifaof_ifpforaddr((SA)&ipaddr,
                                              m->m_pkthdr.rcvif);
                        if (ia == 0)
                              continue;
                        (void)memcpy(sin, &IA_SIN(ia)->sin_addr,
                            sizeof(struct in_addr));
                        ipt->ipt_ptr += sizeof(struct in_addr);
                        break;

                  case IPOPT_TS_PRESPEC:
                        if (ipt->ipt_ptr - 1 + sizeof(n_time) +
                            sizeof(struct in_addr) > ipt->ipt_len) {
                              code = (u_char *)&ipt->ipt_ptr -
                                  (u_char *)ip;
                              goto bad;
                        }
                        (void)memcpy(&ipaddr.sin_addr, sin,
                            sizeof(struct in_addr));
                        if (ifa_ifwithaddr((SA)&ipaddr) == 0)
                              continue;
                        ipt->ipt_ptr += sizeof(struct in_addr);
                        break;

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

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

      sin = (struct sockaddr_in *) &ipforward_rt.ro_dst;

      if (ipforward_rt.ro_rt == 0 || dst.s_addr != sin->sin_addr.s_addr) {
            if (ipforward_rt.ro_rt) {
                  RTFREE(ipforward_rt.ro_rt);
                  ipforward_rt.ro_rt = 0;
            }
            sin->sin_family = AF_INET;
            sin->sin_len = sizeof(*sin);
            sin->sin_addr = dst;

            rtalloc_ign(&ipforward_rt, RTF_PRCLONING);
      }
      if (ipforward_rt.ro_rt == 0)
            return ((struct in_ifaddr *)0);
      return ((struct in_ifaddr *) ipforward_rt.ro_rt->rt_ifa);
}

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

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

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

      if (ip_nhops == 0)
            return ((struct mbuf *)0);
      m = m_get(M_DONTWAIT, MT_HEADER);
      if (m == 0)
            return ((struct mbuf *)0);

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

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

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

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

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

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

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

/*
 * Forward a packet.  If some error occurs return the sender
 * an icmp packet.  Note we can't always generate a meaningful
 * icmp message because icmp doesn't have a large enough repertoire
 * of codes and types.
 *
 * If not forwarding, just drop the packet.  This could be confusing
 * if ipforwarding was zero but some routing protocol was advancing
 * us as a gateway to somewhere.  However, we must let the routing
 * protocol deal with that.
 *
 * The srcrt parameter indicates whether the packet is being forwarded
 * via a source route.
 */
#ifdef NATPT
void
#else
static void
#endif
ip_forward(m, srcrt)
      struct mbuf *m;
      int srcrt;
{
      register struct ip *ip = mtod(m, struct ip *);
      register struct sockaddr_in *sin;
      register struct rtentry *rt;
      int error, type = 0, code = 0;
      struct mbuf *mcopy;
      n_long dest;
      struct ifnet *destifp;
#ifdef IPSEC
      struct ifnet dummyifp;
#endif

      dest = 0;
#ifdef DIAGNOSTIC
      if (ipprintfs)
            printf("forward: src %lx dst %lx ttl %x\n",
                (u_long)ip->ip_src.s_addr, (u_long)ip->ip_dst.s_addr,
                ip->ip_ttl);
#endif


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

      sin = (struct sockaddr_in *)&ipforward_rt.ro_dst;
      if ((rt = ipforward_rt.ro_rt) == 0 ||
          ip->ip_dst.s_addr != sin->sin_addr.s_addr) {
            if (ipforward_rt.ro_rt) {
                  RTFREE(ipforward_rt.ro_rt);
                  ipforward_rt.ro_rt = 0;
            }
            sin->sin_family = AF_INET;
            sin->sin_len = sizeof(*sin);
            sin->sin_addr = ip->ip_dst;

            rtalloc_ign(&ipforward_rt, RTF_PRCLONING);
            if (ipforward_rt.ro_rt == 0) {
                  icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_HOST, dest, 0);
                  return;
            }
            rt = ipforward_rt.ro_rt;
      }

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

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

      /*
       * If forwarding packet using same interface that it came in on,
       * perhaps should send a redirect to sender to shortcut a hop.
       * Only send redirect if source is sending directly to us,
       * and if packet was not source routed (or has any options).
       * Also, don't send redirect if forwarding using a default route
       * or a route modified by a redirect.
       */
#define     satosin(sa) ((struct sockaddr_in *)(sa))
      if (rt->rt_ifp == m->m_pkthdr.rcvif &&
          (rt->rt_flags & (RTF_DYNAMIC|RTF_MODIFIED)) == 0 &&
          satosin(rt_key(rt))->sin_addr.s_addr != 0 &&
          ipsendredirects && !srcrt) {
#define     RTA(rt)     ((struct in_ifaddr *)(rt->rt_ifa))
            u_long src = ntohl(ip->ip_src.s_addr);

            if (RTA(rt) &&
                (src & RTA(rt)->ia_subnetmask) == RTA(rt)->ia_subnet) {
                if (rt->rt_flags & RTF_GATEWAY)
                  dest = satosin(rt->rt_gateway)->sin_addr.s_addr;
                else
                  dest = ip->ip_dst.s_addr;
                /* Router requirements says to only send host redirects */
                type = ICMP_REDIRECT;
                code = ICMP_REDIRECT_HOST;
#ifdef DIAGNOSTIC
                if (ipprintfs)
                    printf("redirect (%d) to %lx\n", code, (u_long)dest);
#endif
            }
      }

      error = ip_output(m, (struct mbuf *)0, &ipforward_rt, 
                    IP_FORWARDING, 0);
      if (error)
            ipstat.ips_cantforward++;
      else {
            ipstat.ips_forward++;
            if (type)
                  ipstat.ips_redirectsent++;
            else {
                  if (mcopy) {
                        ipflow_create(&ipforward_rt, mcopy);
                        m_freem(mcopy);
                  }
                  return;
            }
      }
      if (mcopy == NULL)
            return;
      destifp = NULL;

      switch (error) {

      case 0:                       /* forwarded, but need redirect */
            /* type, code set above */
            break;

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

      case EMSGSIZE:
            type = ICMP_UNREACH;
            code = ICMP_UNREACH_NEEDFRAG;
#ifndef IPSEC
            if (ipforward_rt.ro_rt)
                  destifp = ipforward_rt.ro_rt->rt_ifp;
#else
            /*
             * If the packet is routed over IPsec tunnel, tell the
             * originator the tunnel MTU.
             *    tunnel MTU = if MTU - sizeof(IP) - ESP/AH hdrsiz
             * XXX quickhack!!!
             */
            if (ipforward_rt.ro_rt) {
                  struct secpolicy *sp = NULL;
                  int ipsecerror;
                  int ipsechdr;
                  struct route *ro;

                  sp = ipsec4_getpolicybyaddr(mcopy,
                                        IPSEC_DIR_OUTBOUND,
                                              IP_FORWARDING,
                                              &ipsecerror);

                  if (sp == NULL)
                        destifp = ipforward_rt.ro_rt->rt_ifp;
                  else {
                        /* count IPsec header size */
                        ipsechdr = ipsec4_hdrsiz(mcopy,
                                           IPSEC_DIR_OUTBOUND,
                                           NULL);

                        /*
                         * find the correct route for outer IPv4
                         * header, compute tunnel MTU.
                         *
                         * XXX BUG ALERT
                         * The "dummyifp" code relies upon the fact
                         * that icmp_error() touches only ifp->if_mtu.
                         */
                        /*XXX*/
                        destifp = NULL;
                        if (sp->req != NULL
                         && sp->req->sav != NULL
                         && sp->req->sav->sah != NULL) {
                              ro = &sp->req->sav->sah->sa_route;
                              if (ro->ro_rt && ro->ro_rt->rt_ifp) {
                                    dummyifp.if_mtu =
                                        ro->ro_rt->rt_ifp->if_mtu;
                                    dummyifp.if_mtu -= ipsechdr;
                                    destifp = &dummyifp;
                              }
                        }

                        key_freesp(sp);
                  }
            }
#endif /*IPSEC*/
            ipstat.ips_cantfrag++;
            break;

      case ENOBUFS:
#ifdef ALTQ
            /*
             * don't generate ICMP_SOURCEQUENCH
             * (RFC1812 Requirements for IP Version 4 Routers)
             */
            if (mcopy)
                  m_freem(mcopy);
            return;
#else
            type = ICMP_SOURCEQUENCH;
            code = 0;
            break;
#endif

      case EACCES:                  /* ipfw denied packet */
            m_freem(mcopy);
            return;
      }
      icmp_error(mcopy, type, code, dest, destifp);
}

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

            microtime(&tv);
            *mp = sbcreatecontrol((caddr_t) &tv, sizeof(tv),
                  SCM_TIMESTAMP, SOL_SOCKET);
            if (*mp)
                  mp = &(*mp)->m_next;
      }
      if (inp->inp_flags & INP_RECVDSTADDR) {
            *mp = sbcreatecontrol((caddr_t) &ip->ip_dst,
                sizeof(struct in_addr), IP_RECVDSTADDR, IPPROTO_IP);
            if (*mp)
                  mp = &(*mp)->m_next;
      }
#ifdef notyet
      /* XXX
       * Moving these out of udp_input() made them even more broken
       * than they already were.
       */
      /* options were tossed already */
      if (inp->inp_flags & INP_RECVOPTS) {
            *mp = sbcreatecontrol((caddr_t) opts_deleted_above,
                sizeof(struct in_addr), IP_RECVOPTS, IPPROTO_IP);
            if (*mp)
                  mp = &(*mp)->m_next;
      }
      /* ip_srcroute doesn't do what we want here, need to fix */
      if (inp->inp_flags & INP_RECVRETOPTS) {
            *mp = sbcreatecontrol((caddr_t) ip_srcroute(),
                sizeof(struct in_addr), IP_RECVRETOPTS, IPPROTO_IP);
            if (*mp)
                  mp = &(*mp)->m_next;
      }
#endif
      if (inp->inp_flags & INP_RECVIF) {
            struct ifnet *ifp;
            struct sdlbuf {
                  struct sockaddr_dl sdl;
                  u_char      pad[32];
            } sdlbuf;
            struct sockaddr_dl *sdp;
            struct sockaddr_dl *sdl2 = &sdlbuf.sdl;

            if (((ifp = m->m_pkthdr.rcvif)) 
            && ( ifp->if_index && (ifp->if_index <= if_index))) {
                  sdp = (struct sockaddr_dl *)(ifnet_addrs
                              [ifp->if_index - 1]->ifa_addr);
                  /*
                   * Change our mind and don't try copy.
                   */
                  if ((sdp->sdl_family != AF_LINK)
                  || (sdp->sdl_len > sizeof(sdlbuf))) {
                        goto makedummy;
                  }
                  bcopy(sdp, sdl2, sdp->sdl_len);
            } else {
makedummy:  
                  sdl2->sdl_len
                        = offsetof(struct sockaddr_dl, sdl_data[0]);
                  sdl2->sdl_family = AF_LINK;
                  sdl2->sdl_index = 0;
                  sdl2->sdl_nlen = sdl2->sdl_alen = sdl2->sdl_slen = 0;
            }
            *mp = sbcreatecontrol((caddr_t) sdl2, sdl2->sdl_len,
                  IP_RECVIF, IPPROTO_IP);
            if (*mp)
                  mp = &(*mp)->m_next;
      }
}

int
ip_rsvp_init(struct socket *so)
{
      if (so->so_type != SOCK_RAW ||
          so->so_proto->pr_protocol != IPPROTO_RSVP)
        return EOPNOTSUPP;

      if (ip_rsvpd != NULL)
        return EADDRINUSE;

      ip_rsvpd = so;
      /*
       * This may seem silly, but we need to be sure we don't over-increment
       * the RSVP counter, in case something slips up.
       */
      if (!ip_rsvp_on) {
            ip_rsvp_on = 1;
            rsvp_on++;
      }

      return 0;
}

int
ip_rsvp_done(void)
{
      ip_rsvpd = NULL;
      /*
       * This may seem silly, but we need to be sure we don't over-decrement
       * the RSVP counter, in case something slips up.
       */
      if (ip_rsvp_on) {
            ip_rsvp_on = 0;
            rsvp_on--;
      }
      return 0;
}

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