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

/*
 * Copyright (c) 2000 Apple Computer, Inc. All rights reserved.
 *
 * @APPLE_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. 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_LICENSE_HEADER_END@
 */
/*
 * Copyright (c) 1982, 1986, 1988, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *      @(#)ip_icmp.c   8.2 (Berkeley) 1/4/94
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/mbuf.h>
#include <sys/protosw.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <sys/kernel.h>
#include <sys/sysctl.h>

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

#define _IP_VHL
#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/in_var.h>
#include <netinet/ip.h>
#include <netinet/ip_icmp.h>
#include <netinet/ip_var.h>
#include <netinet/icmp_var.h>
#include <netinet/tcp.h>
#include <netinet/tcp_fsm.h>
#include <netinet/tcp_seq.h>
#include <netinet/tcp_timer.h>
#include <netinet/tcp_var.h>
#include <netinet/tcpip.h>

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

#if defined(NFAITH) && NFAITH > 0
#include "faith.h"
#include <net/if_types.h>
#endif

/*
 * ICMP routines: error generation, receive packet processing, and
 * routines to turnaround packets back to the originator, and
 * host table maintenance routines.
 */

static struct   icmpstat icmpstat;
SYSCTL_STRUCT(_net_inet_icmp, ICMPCTL_STATS, stats, CTLFLAG_RD,
        &icmpstat, icmpstat, "");

static int      icmpmaskrepl = 0;
SYSCTL_INT(_net_inet_icmp, ICMPCTL_MASKREPL, maskrepl, CTLFLAG_RW,
        &icmpmaskrepl, 0, "");

static int      icmptimestamp = 0;
SYSCTL_INT(_net_inet_icmp, ICMPCTL_TIMESTAMP, timestamp, CTLFLAG_RW,
        &icmptimestamp, 0, "");

static int      drop_redirect = 0;
SYSCTL_INT(_net_inet_icmp, OID_AUTO, drop_redirect, CTLFLAG_RW, 
        &drop_redirect, 0, "");

static int      log_redirect = 0;
SYSCTL_INT(_net_inet_icmp, OID_AUTO, log_redirect, CTLFLAG_RW, 
        &log_redirect, 0, "");

#if ICMP_BANDLIM 
 
/*    
 * ICMP error-response bandwidth limiting sysctl.  If not enabled, sysctl
 *      variable content is -1 and read-only.
 */     
    
static int      icmplim = 250;
SYSCTL_INT(_net_inet_icmp, ICMPCTL_ICMPLIM, icmplim, CTLFLAG_RW,
        &icmplim, 0, "");
#else

static int      icmplim = -1;
SYSCTL_INT(_net_inet_icmp, ICMPCTL_ICMPLIM, icmplim, CTLFLAG_RD,
        &icmplim, 0, "");
        
#endif 

/*
 * ICMP broadcast echo sysctl
 */

static int      icmpbmcastecho = 1;
SYSCTL_INT(_net_inet_icmp, OID_AUTO, bmcastecho, CTLFLAG_RW,
        &icmpbmcastecho, 0, "");


#if ICMPPRINTFS
int     icmpprintfs = 0;
#endif

static void     icmp_reflect(struct mbuf *);
static void     icmp_send(struct mbuf *, struct mbuf *);
static int      ip_next_mtu(int, int);

extern  struct protosw inetsw[];

/*
 * Generate an error packet of type error
 * in response to bad packet ip.
 */
void
icmp_error(
        struct mbuf *n,
        int type,
        int code,
        n_long dest,
        struct ifnet *destifp)
{
        register struct ip *oip = mtod(n, struct ip *), *nip;
        register unsigned oiplen = IP_VHL_HL(oip->ip_vhl) << 2;
        register struct icmp *icp;
        register struct mbuf *m;
        unsigned icmplen;

#if ICMPPRINTFS
        if (icmpprintfs)
                printf("icmp_error(%p, %x, %d)\n", oip, type, code);
#endif
        if (type != ICMP_REDIRECT)
                icmpstat.icps_error++;
        /*
         * Don't send error if not the first fragment of message.
         * Don't error if the old packet protocol was ICMP
         * error message, only known informational types.
         */
        if (oip->ip_off &~ (IP_MF|IP_DF))
                goto freeit;
        if (oip->ip_p == IPPROTO_ICMP && type != ICMP_REDIRECT &&
          n->m_len >= oiplen + ICMP_MINLEN &&
          !ICMP_INFOTYPE(((struct icmp *)((caddr_t)oip + oiplen))->icmp_type)) {
                icmpstat.icps_oldicmp++;
                goto freeit;
        }
        /* Don't send error in response to a multicast or broadcast packet */
        if (n->m_flags & (M_BCAST|M_MCAST))
                goto freeit;
        /*
         * First, formulate icmp message
         */
        m = m_gethdr(M_DONTWAIT, MT_HEADER);
        if (m == NULL)
                goto freeit;
        icmplen = min(oiplen + 8, oip->ip_len);
        if (icmplen < sizeof(struct ip)) {
                printf("icmp_error: bad length\n");
                m_free(m);
                goto freeit;
        }
        m->m_len = icmplen + ICMP_MINLEN;
        MH_ALIGN(m, m->m_len);
        icp = mtod(m, struct icmp *);
        if ((u_int)type > ICMP_MAXTYPE)
                panic("icmp_error");
        icmpstat.icps_outhist[type]++;
        icp->icmp_type = type;
        if (type == ICMP_REDIRECT)
                icp->icmp_gwaddr.s_addr = dest;
        else {
                icp->icmp_void = 0;
                /*
                 * The following assignments assume an overlay with the
                 * zeroed icmp_void field.
                 */
                if (type == ICMP_PARAMPROB) {
                        icp->icmp_pptr = code;
                        code = 0;
                } else if (type == ICMP_UNREACH &&
                        code == ICMP_UNREACH_NEEDFRAG && destifp) {
                        icp->icmp_nextmtu = htons(destifp->if_mtu);
                }
        }

        icp->icmp_code = code;
        m_copydata(n, 0, icmplen, (caddr_t)&icp->icmp_ip);
        nip = &icp->icmp_ip;

        /*
         * Convert fields to network representation.
         */
        HTONS(nip->ip_len);
        HTONS(nip->ip_off);

        /*
         * Now, copy old ip header (without options)
         * in front of icmp message.
         */
        if (m->m_data - sizeof(struct ip) < m->m_pktdat)
                panic("icmp len");
        m->m_data -= sizeof(struct ip);
        m->m_len += sizeof(struct ip);
        m->m_pkthdr.len = m->m_len;
        m->m_pkthdr.rcvif = n->m_pkthdr.rcvif;
        m->m_pkthdr.aux = NULL; /* for IPsec */
        nip = mtod(m, struct ip *);
        bcopy((caddr_t)oip, (caddr_t)nip, sizeof(struct ip));
        nip->ip_len = m->m_len;
        nip->ip_vhl = IP_VHL_BORING;
        nip->ip_p = IPPROTO_ICMP;
        nip->ip_tos = 0;
        icmp_reflect(m);

freeit:
        m_freem(n);
}

static struct sockaddr_in icmpsrc = { sizeof (struct sockaddr_in), AF_INET };
static struct sockaddr_in icmpdst = { sizeof (struct sockaddr_in), AF_INET };
static struct sockaddr_in icmpgw = { sizeof (struct sockaddr_in), AF_INET };

/*
 * Process a received ICMP message.
 */
void
icmp_input(m, hlen)
        register struct mbuf *m;
        int hlen;
{
        register struct icmp *icp;
        register struct ip *ip = mtod(m, struct ip *);
        int icmplen = ip->ip_len;
        register int i;
        struct in_ifaddr *ia;
        void (*ctlfunc)(int, struct sockaddr *, void *);
        int code;
        char ipv4str[MAX_IPv4_STR_LEN];

        /*
         * Locate icmp structure in mbuf, and check
         * that not corrupted and of at least minimum length.
         */
#if ICMPPRINTFS
        if (icmpprintfs) {
                char buf[MAX_IPv4_STR_LEN];

                printf("icmp_input from %s to %s, len %d\n",
                       inet_ntop(AF_INET, &ip->ip_src, buf, sizeof(buf)),
                       inet_ntop(AF_INET, &ip->ip_dst, ipv4str, sizeof(ipv4str)),
                       icmplen);
        }
#endif
        if (icmplen < ICMP_MINLEN) {
                icmpstat.icps_tooshort++;
                goto freeit;
        }
        i = hlen + min(icmplen, ICMP_ADVLENMIN);
        if (m->m_len < i && (m = m_pullup(m, i)) == 0)  {
                icmpstat.icps_tooshort++;
                return;
        }
        ip = mtod(m, struct ip *);
        m->m_len -= hlen;
        m->m_data += hlen;
        icp = mtod(m, struct icmp *);
        if (in_cksum(m, icmplen)) {
                icmpstat.icps_checksum++;
                goto freeit;
        }
        m->m_len += hlen;
        m->m_data -= hlen;

#if defined(NFAITH) && 0 < NFAITH
        if (m->m_pkthdr.rcvif && m->m_pkthdr.rcvif->if_type == IFT_FAITH) {
                /*
                 * Deliver very specific ICMP type only.
                 */
                switch (icp->icmp_type) {
                case ICMP_UNREACH:
                case ICMP_TIMXCEED:
                        break;
                default:
                        goto freeit;
                }
        }
#endif

#if ICMPPRINTFS
        if (icmpprintfs)
                printf("icmp_input, type %d code %d\n", icp->icmp_type,
                    icp->icmp_code);
#endif

        /*
         * Message type specific processing.
         */
        if (icp->icmp_type > ICMP_MAXTYPE)
                goto raw;
        icmpstat.icps_inhist[icp->icmp_type]++;
        code = icp->icmp_code;
        switch (icp->icmp_type) {

        case ICMP_UNREACH:
                switch (code) {
                        case ICMP_UNREACH_NET:
                        case ICMP_UNREACH_HOST:
                        case ICMP_UNREACH_SRCFAIL:
                        case ICMP_UNREACH_NET_UNKNOWN:
                        case ICMP_UNREACH_HOST_UNKNOWN:
                        case ICMP_UNREACH_ISOLATED:
                        case ICMP_UNREACH_TOSNET:
                        case ICMP_UNREACH_TOSHOST:
                        case ICMP_UNREACH_HOST_PRECEDENCE:
                        case ICMP_UNREACH_PRECEDENCE_CUTOFF:
                                code = PRC_UNREACH_NET;
                                break;

                        case ICMP_UNREACH_NEEDFRAG:
                                code = PRC_MSGSIZE;
                                break;

                        /*
                         * RFC 1122, Sections 3.2.2.1 and 4.2.3.9.
                         * Treat subcodes 2,3 as immediate RST
                         */
                        case ICMP_UNREACH_PROTOCOL:
                        case ICMP_UNREACH_PORT:
                                code = PRC_UNREACH_PORT;
                                break;

                        case ICMP_UNREACH_NET_PROHIB:
                        case ICMP_UNREACH_HOST_PROHIB:
                        case ICMP_UNREACH_FILTER_PROHIB:
                                code = PRC_UNREACH_ADMIN_PROHIB;
                                break;

                        default:
                                goto badcode;
                }
                goto deliver;

        case ICMP_TIMXCEED:
                if (code > 1)
                        goto badcode;
                code += PRC_TIMXCEED_INTRANS;
                goto deliver;

        case ICMP_PARAMPROB:
                if (code > 1)
                        goto badcode;
                code = PRC_PARAMPROB;
                goto deliver;

        case ICMP_SOURCEQUENCH:
                if (code)
                        goto badcode;
                code = PRC_QUENCH;
        deliver:
                /*
                 * Problem with datagram; advise higher level routines.
                 */
                if (icmplen < ICMP_ADVLENMIN || icmplen < ICMP_ADVLEN(icp) ||
                    IP_VHL_HL(icp->icmp_ip.ip_vhl) < (sizeof(struct ip) >> 2)) {
                        icmpstat.icps_badlen++;
                        goto freeit;
                }
                NTOHS(icp->icmp_ip.ip_len);
                /* Discard ICMP's in response to multicast packets */
                if (IN_MULTICAST(ntohl(icp->icmp_ip.ip_dst.s_addr)))
                        goto badcode;
#if ICMPPRINTFS
                if (icmpprintfs)
                        printf("deliver to protocol %d\n", icp->icmp_ip.ip_p);
#endif
                icmpsrc.sin_addr = icp->icmp_ip.ip_dst;
#if 1
                /*
                 * MTU discovery:
                 * If we got a needfrag and there is a host route to the
                 * original destination, and the MTU is not locked, then
                 * set the MTU in the route to the suggested new value
                 * (if given) and then notify as usual.  The ULPs will
                 * notice that the MTU has changed and adapt accordingly.
                 * If no new MTU was suggested, then we guess a new one
                 * less than the current value.  If the new MTU is 
                 * unreasonably small (defined by sysctl tcp_minmss), then
                 * we reset the MTU to the interface value and enable the
                 * lock bit, indicating that we are no longer doing MTU
                 * discovery.
                 */
                if (code == PRC_MSGSIZE) {
                        struct rtentry *rt;
                        int mtu;

                        rt = rtalloc1((struct sockaddr *)&icmpsrc, 0,
                                      RTF_CLONING | RTF_PRCLONING);
                        if (rt && (rt->rt_flags & RTF_HOST)
                            && !(rt->rt_rmx.rmx_locks & RTV_MTU)) {
                                mtu = ntohs(icp->icmp_nextmtu);
                                if (!mtu)
                                        mtu = ip_next_mtu(rt->rt_rmx.rmx_mtu,
                                                          1);
#if DEBUG_MTUDISC
                                printf("MTU for %s reduced to %d\n",
                                           inet_ntop(AF_INET, &icmpsrc.sin_addr, ipv4str,
                                                                 sizeof(ipv4str)),
                                           mtu);
#endif
                                if (mtu < max(296, (tcp_minmss + sizeof(struct tcpiphdr)))) {
                                        /* rt->rt_rmx.rmx_mtu =
                                                rt->rt_ifp->if_mtu; */
                                        rt->rt_rmx.rmx_locks |= RTV_MTU;
                                } else if (rt->rt_rmx.rmx_mtu > mtu) {
                                        rt->rt_rmx.rmx_mtu = mtu;
                                }
                        }
                        if (rt)
                                rtfree(rt);
                }

#endif
                /*
                 * XXX if the packet contains [IPv4 AH TCP], we can't make a
                 * notification to TCP layer.
                 */
                ctlfunc = ip_protox[icp->icmp_ip.ip_p]->pr_ctlinput;
                if (ctlfunc)
                        (*ctlfunc)(code, (struct sockaddr *)&icmpsrc,
                                   (void *)&icp->icmp_ip);
                break;

        badcode:
                icmpstat.icps_badcode++;
                break;

        case ICMP_ECHO:
                if (!icmpbmcastecho
                    && (m->m_flags & (M_MCAST | M_BCAST)) != 0) {
                        icmpstat.icps_bmcastecho++;
                        break;
                }
                icp->icmp_type = ICMP_ECHOREPLY;
#if ICMP_BANDLIM
                if (badport_bandlim(BANDLIM_ICMP_ECHO) < 0)
                        goto freeit;
                else
#endif
                        goto reflect;

        case ICMP_TSTAMP:

                if (icmptimestamp == 0)
                        break;

                if (!icmpbmcastecho
                    && (m->m_flags & (M_MCAST | M_BCAST)) != 0) {
                        icmpstat.icps_bmcasttstamp++;
                        break;
                }
                if (icmplen < ICMP_TSLEN) {
                        icmpstat.icps_badlen++;
                        break;
                }
                icp->icmp_type = ICMP_TSTAMPREPLY;
                icp->icmp_rtime = iptime();
                icp->icmp_ttime = icp->icmp_rtime;      /* bogus, do later! */
#if ICMP_BANDLIM
                if (badport_bandlim(BANDLIM_ICMP_TSTAMP) < 0)
                        goto freeit;
                else
#endif
                        goto reflect;

        case ICMP_MASKREQ:
#define satosin(sa)     ((struct sockaddr_in *)(sa))
                if (icmpmaskrepl == 0)
                        break;
                /*
                 * We are not able to respond with all ones broadcast
                 * unless we receive it over a point-to-point interface.
                 */
                if (icmplen < ICMP_MASKLEN)
                        break;
                switch (ip->ip_dst.s_addr) {

                case INADDR_BROADCAST:
                case INADDR_ANY:
                        icmpdst.sin_addr = ip->ip_src;
                        break;

                default:
                        icmpdst.sin_addr = ip->ip_dst;
                }
                ia = (struct in_ifaddr *)ifaof_ifpforaddr(
                            (struct sockaddr *)&icmpdst, m->m_pkthdr.rcvif);
                if (ia == 0)
                        break;
                if (ia->ia_ifp == 0) {
                        ifafree(&ia->ia_ifa);
                        ia = 0;
                        break;
                }
                icp->icmp_type = ICMP_MASKREPLY;
                icp->icmp_mask = ia->ia_sockmask.sin_addr.s_addr;
                if (ip->ip_src.s_addr == 0) {
                        if (ia->ia_ifp->if_flags & IFF_BROADCAST)
                            ip->ip_src = satosin(&ia->ia_broadaddr)->sin_addr;
                        else if (ia->ia_ifp->if_flags & IFF_POINTOPOINT)
                            ip->ip_src = satosin(&ia->ia_dstaddr)->sin_addr;
                }
                ifafree(&ia->ia_ifa);
reflect:
                ip->ip_len += hlen;     /* since ip_input deducts this */
                icmpstat.icps_reflect++;
                icmpstat.icps_outhist[icp->icmp_type]++;
                icmp_reflect(m);
                return;

        case ICMP_REDIRECT:
                if (log_redirect) {
                        u_long src, dst, gw;

                        src = ntohl(ip->ip_src.s_addr);
                        dst = ntohl(icp->icmp_ip.ip_dst.s_addr);
                        gw = ntohl(icp->icmp_gwaddr.s_addr);
                        printf("icmp redirect from %d.%d.%d.%d: "
                               "%d.%d.%d.%d => %d.%d.%d.%d\n",
                               (int)(src >> 24), (int)((src >> 16) & 0xff),
                               (int)((src >> 8) & 0xff), (int)(src & 0xff),
                               (int)(dst >> 24), (int)((dst >> 16) & 0xff),
                               (int)((dst >> 8) & 0xff), (int)(dst & 0xff),
                               (int)(gw >> 24), (int)((gw >> 16) & 0xff),
                               (int)((gw >> 8) & 0xff), (int)(gw & 0xff));
                }
                if (drop_redirect)
                        break;
                if (code > 3)
                        goto badcode;
                if (icmplen < ICMP_ADVLENMIN || icmplen < ICMP_ADVLEN(icp) ||
                    IP_VHL_HL(icp->icmp_ip.ip_vhl) < (sizeof(struct ip) >> 2)) {
                        icmpstat.icps_badlen++;
                        break;
                }
                /*
                 * Short circuit routing redirects to force
                 * immediate change in the kernel's routing
                 * tables.  The message is also handed to anyone
                 * listening on a raw socket (e.g. the routing
                 * daemon for use in updating its tables).
                 */
                icmpgw.sin_addr = ip->ip_src;
                icmpdst.sin_addr = icp->icmp_gwaddr;
#if     ICMPPRINTFS
                if (icmpprintfs) {
                        char buf[MAX_IPv4_STR_LEN];

                        printf("redirect dst %s to %s\n",
                               inet_ntop(AF_INET, &icp->icmp_ip.ip_dst, buf, sizeof(buf)),
                               inet_ntop(AF_INET, &icp->icmp_gwaddr, ipv4str,
                                                 sizeof(ipv4str)));
                }
#endif
                icmpsrc.sin_addr = icp->icmp_ip.ip_dst;
                rtredirect((struct sockaddr *)&icmpsrc,
                  (struct sockaddr *)&icmpdst,
                  (struct sockaddr *)0, RTF_GATEWAY | RTF_HOST,
                  (struct sockaddr *)&icmpgw, (struct rtentry **)0);
                pfctlinput(PRC_REDIRECT_HOST, (struct sockaddr *)&icmpsrc);
#if IPSEC
                key_sa_routechange((struct sockaddr *)&icmpsrc);
#endif
                break;

        /*
         * No kernel processing for the following;
         * just fall through to send to raw listener.
         */
        case ICMP_ECHOREPLY:
        case ICMP_ROUTERADVERT:
        case ICMP_ROUTERSOLICIT:
        case ICMP_TSTAMPREPLY:
        case ICMP_IREQREPLY:
        case ICMP_MASKREPLY:
        default:
                break;
        }

raw:
        rip_input(m, hlen);
        return;

freeit:
        m_freem(m);
}

/*
 * Reflect the ip packet back to the source
 */
static void
icmp_reflect(m)
        struct mbuf *m;
{
        register struct ip *ip = mtod(m, struct ip *);
        register struct in_ifaddr *ia;
        struct in_addr t;
        struct mbuf *opts = 0;
        int optlen = (IP_VHL_HL(ip->ip_vhl) << 2) - sizeof(struct ip);

        if (!in_canforward(ip->ip_src) &&
            ((ntohl(ip->ip_src.s_addr) & IN_CLASSA_NET) !=
             (IN_LOOPBACKNET << IN_CLASSA_NSHIFT))) {
                m_freem(m);     /* Bad return address */
                goto done;      /* Ip_output() will check for broadcast */
        }
        t = ip->ip_dst;
        ip->ip_dst = ip->ip_src;
        /*
         * If the incoming packet was addressed directly to us,
         * use dst as the src for the reply.  Otherwise (broadcast
         * or anonymous), use the address which corresponds
         * to the incoming interface.
         */
        lck_mtx_lock(rt_mtx);
        for (ia = in_ifaddrhead.tqh_first; ia; ia = ia->ia_link.tqe_next) {
                if (t.s_addr == IA_SIN(ia)->sin_addr.s_addr)
                        break;
                if (ia->ia_ifp && (ia->ia_ifp->if_flags & IFF_BROADCAST) &&
                    t.s_addr == satosin(&ia->ia_broadaddr)->sin_addr.s_addr)
                        break;
        }
        if (ia)
                ifaref(&ia->ia_ifa);
        icmpdst.sin_addr = t;
        if ((ia == (struct in_ifaddr *)0) && m->m_pkthdr.rcvif)
                ia = (struct in_ifaddr *)ifaof_ifpforaddr(
                        (struct sockaddr *)&icmpdst, m->m_pkthdr.rcvif);
        /*
         * The following happens if the packet was not addressed to us,
         * and was received on an interface with no IP address.
         */
        if (ia == (struct in_ifaddr *)0) {
                ia = in_ifaddrhead.tqh_first;
                if (ia == (struct in_ifaddr *)0) {/* no address yet, bail out */
                        m_freem(m);
                        lck_mtx_unlock(rt_mtx);
                        goto done;
                }
                ifaref(&ia->ia_ifa);
        }
        lck_mtx_unlock(rt_mtx);
        t = IA_SIN(ia)->sin_addr;
        ip->ip_src = t;
        ip->ip_ttl = ip_defttl;
        ifafree(&ia->ia_ifa);
        ia = NULL;

        if (optlen > 0) {
                register u_char *cp;
                int opt, cnt;
                u_int len;

                /*
                 * Retrieve any source routing from the incoming packet;
                 * add on any record-route or timestamp options.
                 */
                cp = (u_char *) (ip + 1);
                if ((opts = ip_srcroute()) == 0 &&
                    (opts = m_gethdr(M_DONTWAIT, MT_HEADER))) {
                        opts->m_len = sizeof(struct in_addr);
                        mtod(opts, struct in_addr *)->s_addr = 0;
                }
                if (opts) {
#if ICMPPRINTFS
                    if (icmpprintfs)
                            printf("icmp_reflect optlen %d rt %d => ",
                                optlen, opts->m_len);
#endif
                    for (cnt = optlen; cnt > 0; cnt -= len, cp += len) {
                            opt = cp[IPOPT_OPTVAL];
                            if (opt == IPOPT_EOL)
                                    break;
                            if (opt == IPOPT_NOP)
                                    len = 1;
                            else {
                                    if (cnt < IPOPT_OLEN + sizeof(*cp))
                                            break;
                                    len = cp[IPOPT_OLEN];
                                    if (len < IPOPT_OLEN + sizeof(*cp) ||
                                        len > cnt)
                                            break;
                            }
                            /*
                             * Should check for overflow, but it "can't happen"
                             */
                            if (opt == IPOPT_RR || opt == IPOPT_TS ||
                                opt == IPOPT_SECURITY) {
                                    bcopy((caddr_t)cp,
                                        mtod(opts, caddr_t) + opts->m_len, len);
                                    opts->m_len += len;
                            }
                    }
                    /* Terminate & pad, if necessary */
                    cnt = opts->m_len % 4;
                    if (cnt) {
                            for (; cnt < 4; cnt++) {
                                    *(mtod(opts, caddr_t) + opts->m_len) =
                                        IPOPT_EOL;
                                    opts->m_len++;
                            }
                    }
#if ICMPPRINTFS
                    if (icmpprintfs)
                            printf("%d\n", opts->m_len);
#endif
                }
                /*
                 * Now strip out original options by copying rest of first
                 * mbuf's data back, and adjust the IP length.
                 */
                ip->ip_len -= optlen;
                ip->ip_vhl = IP_VHL_BORING;
                m->m_len -= optlen;
                if (m->m_flags & M_PKTHDR)
                        m->m_pkthdr.len -= optlen;
                optlen += sizeof(struct ip);
                bcopy((caddr_t)ip + optlen, (caddr_t)(ip + 1),
                         (unsigned)(m->m_len - sizeof(struct ip)));
        }
        m->m_flags &= ~(M_BCAST|M_MCAST);
        icmp_send(m, opts);
done:
        if (opts)
                (void)m_free(opts);
}

/*
 * Send an icmp packet back to the ip level,
 * after supplying a checksum.
 */
static void
icmp_send(m, opts)
        register struct mbuf *m;
        struct mbuf *opts;
{
        register struct ip *ip = mtod(m, struct ip *);
        register int hlen;
        register struct icmp *icp;
        struct route ro;
        char ipv4str[MAX_IPv4_STR_LEN];

        hlen = IP_VHL_HL(ip->ip_vhl) << 2;
        m->m_data += hlen;
        m->m_len -= hlen;
        icp = mtod(m, struct icmp *);
        icp->icmp_cksum = 0;
        icp->icmp_cksum = in_cksum(m, ip->ip_len - hlen);
        m->m_data -= hlen;
        m->m_len += hlen;
        m->m_pkthdr.rcvif = 0;
        m->m_pkthdr.aux = NULL;
        m->m_pkthdr.csum_data = 0;
        m->m_pkthdr.csum_flags = 0;
#if ICMPPRINTFS
        if (icmpprintfs) {
                char buf[MAX_IPv4_STR_LEN];

                printf("icmp_send dst %s src %s\n",
                       inet_ntop(AF_INET, &ip->ip_dst, buf, sizeof(buf)),
                       inet_ntop(AF_INET, &ip->ip_src, ipv4str, sizeof(ipv4str)));
        }
#endif
        bzero(&ro, sizeof ro);
        (void) ip_output(m, opts, &ro, 0, NULL);
        if (ro.ro_rt)
                rtfree(ro.ro_rt);
}

n_time
iptime()
{
        struct timeval atv;
        u_long t;

        microtime(&atv);
        t = (atv.tv_sec % (24*60*60)) * 1000 + atv.tv_usec / 1000;
        return (htonl(t));
}

#if 1
/*
 * Return the next larger or smaller MTU plateau (table from RFC 1191)
 * given current value MTU.  If DIR is less than zero, a larger plateau
 * is returned; otherwise, a smaller value is returned.
 */
static int
ip_next_mtu(mtu, dir)
        int mtu;
        int dir;
{
        static int mtutab[] = {
                65535, 32000, 17914, 8166, 4352, 2002, 1492, 1006, 508, 296,
                68, 0
        };
        int i;

        for (i = 0; i < (sizeof mtutab) / (sizeof mtutab[0]); i++) {
                if (mtu >= mtutab[i])
                        break;
        }

        if (dir < 0) {
                if (i == 0) {
                        return 0;
                } else {
                        return mtutab[i - 1];
                }
        } else {
                if (mtutab[i] == 0) {
                        return 0;
                } else if(mtu > mtutab[i]) {
                        return mtutab[i];
                } else {
                        return mtutab[i + 1];
                }
        }
}
#endif

#if ICMP_BANDLIM

/*
 * badport_bandlim() - check for ICMP bandwidth limit
 *
 *      Return 0 if it is ok to send an ICMP error response, -1 if we have
 *      hit our bandwidth limit and it is not ok.  
 *
 *      If icmplim is <= 0, the feature is disabled and 0 is returned.
 *
 *      For now we separate the TCP and UDP subsystems w/ different 'which'
 *      values.  We may eventually remove this separation (and simplify the
 *      code further).
 *
 *      Note that the printing of the error message is delayed so we can
 *      properly print the icmp error rate that the system was trying to do
 *      (i.e. 22000/100 pps, etc...).  This can cause long delays in printing
 *      the 'final' error, but it doesn't make sense to solve the printing 
 *      delay with more complex code.
 */

int
badport_bandlim(int which)
{
        static struct timeval lticks[BANDLIM_MAX + 1];
        static int lpackets[BANDLIM_MAX + 1];
        struct timeval time;
        int secs;

        const char *bandlimittype[] = {
                "Limiting icmp unreach response",
                "Limiting icmp ping response",
                "Limiting icmp tstamp response",
                "Limiting closed port RST response",
                "Limiting open port RST response"
                };

        /*
         * Return ok status if feature disabled or argument out of
         * ranage.
         */

        if (icmplim <= 0 || which > BANDLIM_MAX || which < 0)
                return(0);

        getmicrouptime(&time);

        secs = time.tv_sec - lticks[which].tv_sec ;
                        
        /*
         * reset stats when cumulative delta exceeds one second.
         */

        if ((secs > 1) || (secs == 1 && (lticks[which].tv_usec > time.tv_usec))) { 
                if (lpackets[which] > icmplim) {
                        printf("%s from %d to %d packets per second\n",
                                bandlimittype[which],
                                lpackets[which],
                                icmplim
                        );
                }
                lticks[which].tv_sec = time.tv_sec;
                lticks[which].tv_usec = time.tv_usec;
                lpackets[which] = 0;
        }

        /*
         * bump packet count
         */

        if (++lpackets[which] > icmplim) {
                return(-1);
        }
        return(0);
}

#endif

#if __APPLE__

/*
 * Non-privileged ICMP socket operations
 * - send ICMP echo request
 * - all ICMP
 * - limited socket options
 */

#include <netinet/ip_icmp.h>
#include <netinet/in_pcb.h>

extern struct domain inetdomain;
extern u_long rip_sendspace;
extern u_long rip_recvspace;
extern struct inpcbinfo ripcbinfo;

int rip_abort(struct socket *);
int rip_bind(struct socket *, struct sockaddr *, struct proc *);
int rip_connect(struct socket *, struct sockaddr *, struct proc *);
int rip_detach(struct socket *);
int rip_disconnect(struct socket *);
int rip_shutdown(struct socket *);

__private_extern__ int icmp_dgram_send(struct socket *so, int flags, struct mbuf *m, struct sockaddr *nam, struct mbuf *control, struct proc *p);
__private_extern__ int icmp_dgram_attach(struct socket *so, int proto, struct proc *p);
__private_extern__ int icmp_dgram_ctloutput(struct socket *so, struct sockopt *sopt);

__private_extern__ struct pr_usrreqs icmp_dgram_usrreqs = {
        rip_abort, pru_accept_notsupp, icmp_dgram_attach, rip_bind, rip_connect,
        pru_connect2_notsupp, in_control, rip_detach, rip_disconnect,
        pru_listen_notsupp, in_setpeeraddr, pru_rcvd_notsupp,
        pru_rcvoob_notsupp, icmp_dgram_send, pru_sense_null, rip_shutdown,
        in_setsockaddr, sosend, soreceive, pru_sopoll_notsupp
};

/* Like rip_attach but without root privilege enforcement */
__private_extern__ int
icmp_dgram_attach(struct socket *so, int proto, struct proc *p)
{
        struct inpcb *inp;
        int error, s;

        inp = sotoinpcb(so);
        if (inp)
                panic("icmp_dgram_attach");

        error = soreserve(so, rip_sendspace, rip_recvspace);
        if (error)
                return error;
        s = splnet();
        error = in_pcballoc(so, &ripcbinfo, p);
        splx(s);
        if (error)
                return error;
        inp = (struct inpcb *)so->so_pcb;       
        inp->inp_vflag |= INP_IPV4;
        inp->inp_ip_p = IPPROTO_ICMP;
        inp->inp_ip_ttl = ip_defttl;
        return 0;
}

/*
 * Raw IP socket option processing.
 */
__private_extern__ int
icmp_dgram_ctloutput(struct socket *so, struct sockopt *sopt)
{
        struct  inpcb *inp = sotoinpcb(so);
        int     error, optval;

        if (sopt->sopt_level != IPPROTO_IP)
                return (EINVAL);

        switch (sopt->sopt_name) {
                case IP_OPTIONS:
                case IP_HDRINCL:
                case IP_TOS:
                case IP_TTL:
                case IP_RECVOPTS:
                case IP_RECVRETOPTS:
                case IP_RECVDSTADDR:
                case IP_RETOPTS:
                case IP_MULTICAST_IF:
                case IP_MULTICAST_TTL:
                case IP_MULTICAST_LOOP:
                case IP_ADD_MEMBERSHIP:
                case IP_DROP_MEMBERSHIP:
                case IP_MULTICAST_VIF:
                case IP_PORTRANGE:
                case IP_RECVIF:
                case IP_IPSEC_POLICY:
#if defined(NFAITH) && NFAITH > 0
                case IP_FAITH:
#endif
                case IP_STRIPHDR:
                case IP_RECVTTL:
                        error = rip_ctloutput(so, sopt);
                        break;
                
                default:
                        error = EINVAL;
                        break;
        }

        return (error);
}

__private_extern__ int
icmp_dgram_send(struct socket *so, int flags, struct mbuf *m, struct sockaddr *nam,
         struct mbuf *control, struct proc *p)
{
        struct ip *ip;
        struct inpcb *inp = sotoinpcb(so);
        int hlen;
        struct icmp *icp;
        struct in_ifaddr *ia = NULL;
        int icmplen;

        if ((inp->inp_flags & INP_HDRINCL) != 0) {
                /*
                 * This is not raw IP, we liberal only for fields TOS, id and TTL 
                 */
                ip = mtod(m, struct ip *);

                hlen = IP_VHL_HL(ip->ip_vhl) << 2;
                /* Some sanity checks */
                if (m->m_pkthdr.len < hlen + ICMP_MINLEN) {
                        goto bad;
                }
                /* Only IPv4 */
                if (IP_VHL_V(ip->ip_vhl) != 4)
                        goto bad;
                if (hlen < 20 || hlen > 40 || ip->ip_len != m->m_pkthdr.len)
                        goto bad;
                /* Bogus fragments can tie up peer resources */ 
                if (ip->ip_off != 0)
                        goto bad;
                /* Allow only ICMP even for user provided IP header */
                if (ip->ip_p != IPPROTO_ICMP)
                        goto bad;
                /* To prevent spoofing, specified source address must be one of ours */
                if (ip->ip_src.s_addr != INADDR_ANY) {
                        socket_unlock(so, 0);
                        lck_mtx_lock(rt_mtx);
                        if (TAILQ_EMPTY(&in_ifaddrhead)) {
                                lck_mtx_unlock(rt_mtx);
                                socket_lock(so, 0);
                                goto bad;
                        }
                        TAILQ_FOREACH(ia, &in_ifaddrhead, ia_link) {
                                if (IA_SIN(ia)->sin_addr.s_addr == ip->ip_src.s_addr) {
                                        lck_mtx_unlock(rt_mtx);
                                        socket_lock(so, 0);
                                        goto ours;
                                }
                        }
                        lck_mtx_unlock(rt_mtx);
                        socket_lock(so, 0);
                        goto bad;
                }
ours:
                /* Do not trust we got a valid checksum */
                ip->ip_sum = 0;
                
                icp = (struct icmp *)(((char *)m->m_data) + hlen);
                icmplen = m->m_pkthdr.len - hlen;
        } else {
                if ((icmplen = m->m_pkthdr.len) < ICMP_MINLEN) {
                        goto bad;
                }
                icp = mtod(m, struct icmp *);
        }
        /*
         * Allow only to send request types with code 0
         */
        if (icp->icmp_code != 0)
                goto bad;
        switch (icp->icmp_type) {
                case ICMP_ECHO:
                        break;
                case ICMP_TSTAMP:
                        if (icmplen != 20)
                                goto bad;
                        break;
                case ICMP_MASKREQ:
                        if (icmplen != 12)
                                goto bad;
                        break;
                default:
                        goto bad;
        }
        return rip_send(so, flags, m, nam, control, p);
bad:
        m_freem(m);
        return EINVAL;
}

#endif /* __APPLE__ */