/*
 * Copyright (c) 1982, 1986, 1988 Regents of the University of California.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms are permitted
 * provided that the above copyright notice and this paragraph are
 * duplicated in all such forms and that any documentation,
 * advertising materials, and other materials related to such
 * distribution and use acknowledge that the software was developed
 * by the University of California, Berkeley.  The name of the
 * University may not be used to endorse or promote products derived
 * from this software without specific prior written permission.
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
 * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 *
 *      @(#)ip_input.c  7.6.1.4 (Berkeley) 2/17/89
 */

#include <sys/param.h>
#include <sys/mbuf.h>
#include <sys/domain.h>
#include <sys/protosw.h>
#include <sys/socket.h>
#include <errno.h>
#include <sys/time.h>
#include <sys/kernel.h>

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

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

#include "proto.h"

#ifndef IPFORWARDING
#ifdef GATEWAY
#define IPFORWARDING    1
#else /* GATEWAY */
#define IPFORWARDING    0
#endif /* GATEWAY */
#endif /* IPFORWARDING */

#ifndef IPSENDREDIRECTS
#define IPSENDREDIRECTS 1
#endif

int     ipprintfs = 0;
int     ipforwarding = IPFORWARDING;
extern  int in_interfaces;
int     ipsendredirects = IPSENDREDIRECTS;

u_char  ip_protox[IPPROTO_MAX];
int     ipqmaxlen = IFQ_MAXLEN;
struct  in_ifaddr *in_ifaddr;                   /* first inet address */

/*
 * 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.
 */
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;

/*
 * 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;
        static unsigned short id;

        enter_nlist("_ipstat", &ipstat);
        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;
        ipq.next = ipq.prev = &ipq;
        ip_id = ++id; /* XXXXX randomize this */
        ipintrq.ifq_maxlen = ipqmaxlen;
}

struct  ip *ip_reass();
struct  sockaddr_in ipaddr = { AF_INET };
struct  route ipforward_rt;

/*
 * Ip input routine.  Checksum and byte swap header.  If fragmented
 * try to reassamble.  If complete and fragment queue exists, discard.
 * Process options.  Pass to next level.
 */

void ipintr(void)
{
        register struct ip *ip;
        register struct mbuf *m;
        struct mbuf *m0;
        register int i;
        register struct ipq *fp;
        register struct in_ifaddr *ia;
        struct ifnet *ifp;
        int hlen;

next:
        /*
         * Get next datagram off input queue and get IP header
         * in first mbuf.
         */
        Forbid();       /* s = splimp(); */
        IF_DEQUEUEIF(&ipintrq, m, ifp);
        Permit();       /* splx(s); */
        if (m == 0)
                return;
        /*
         * If no IP addresses have been set yet but the interfaces
         * are receiving, can't do anything with incoming packets yet.
         */
        if (in_ifaddr == NULL)
                goto bad;
        ipstat.ips_total++;
        if ((m->m_off > MMAXOFF || m->m_len < sizeof (struct ip)) &&
            (m = m_pullup(m, sizeof (struct ip))) == 0) {
                ipstat.ips_toosmall++;
                goto next;
        }
        ip = mtod(m, struct ip *);
        hlen = ip->ip_hl << 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++;
                        goto next;
                }
                ip = mtod(m, struct ip *);
        }

        if (ip->ip_sum = in_cksum(m, hlen)) {
                ipstat.ips_badsum++;
                goto bad;
        }

        /*
         * Convert fields to host representation.
         */
        ip->ip_len = ntohs((u_short)ip->ip_len);
        if (ip->ip_len < hlen) {
                ipstat.ips_badlen++;
                goto bad;
        }
        ip->ip_id = ntohs(ip->ip_id);
        ip->ip_off = ntohs((u_short)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.
         */
        i = -(u_short)ip->ip_len;
        m0 = m;
        for (;;) {
                i += m->m_len;
                if (m->m_next == 0)
                        break;
                m = m->m_next;
        }
        if (i != 0) {
                if (i < 0) {
                        ipstat.ips_tooshort++;
                        m = m0;
                        goto bad;
                }
                if (i <= m->m_len)
                        m->m_len -= i;
                else
                        m_adj(m0, -i);
        }
        m = m0;

        /*
         * 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, ifp))
                goto next;

        /*
         * Check our list of addresses, to see if the packet is for us.
         */
        for (ia = in_ifaddr; ia; ia = ia->ia_next) {
#define satosin(sa)     ((struct sockaddr_in *)(sa))

                if (IA_SIN(ia)->sin_addr.s_addr == ip->ip_dst.s_addr)
                        goto ours;
                if (
#ifdef  DIRECTED_BROADCAST
                    ia->ia_ifp == ifp &&
#endif
                    (ia->ia_ifp->if_flags & IFF_BROADCAST)) {
                        u_long t;

                        if (satosin(&ia->ia_broadaddr)->sin_addr.s_addr ==
                            ip->ip_dst.s_addr)
                                goto ours;
                        if (ip->ip_dst.s_addr == ia->ia_netbroadcast.s_addr)
                                goto ours;
                        /*
                         * Look for all-0's host part (old broadcast addr),
                         * either for subnet or net.
                         */
                        t = ntohl(ip->ip_dst.s_addr);
                        if (t == ia->ia_subnet)
                                goto ours;
                        if (t == ia->ia_net)
                                goto ours;
                }
        }
        if (ip->ip_dst.s_addr == (u_long)INADDR_BROADCAST)
                goto ours;
        if (ip->ip_dst.s_addr == INADDR_ANY)
                goto ours;

        /*
         * Not for us; forward if possible and desirable.
         */
        if (ipforwarding == 0
//#ifndef GATEWAY
            || in_interfaces <= 1
//#endif
            ) {
                ipstat.ips_cantforward++;
                m_freem(m);
        } else
                ip_forward(m, ifp);
        goto next;

ours:
        /*
         * 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_DF) {
                /*
                 * Look for queue of fragments
                 * of this datagram.
                 */
                for (fp = ipq.next; fp != &ipq; 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;
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;
                ((struct ipasfrag *)ip)->ipf_mff = 0;
                if (ip->ip_off & IP_MF)
                        ((struct ipasfrag *)ip)->ipf_mff = 1;
                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 (((struct ipasfrag *)ip)->ipf_mff || ip->ip_off) {
                        ipstat.ips_fragments++;
                        ip = ip_reass((struct ipasfrag *)ip, fp);
                        if (ip == 0)
                                goto next;
                        m = dtom(ip);
                } else
                        if (fp)
                                ip_freef(fp);
        } else {
                ip->ip_len -= hlen;
        }

        /*
         * Switch out to protocol's input routine.
         */
        (*inetsw[ip_protox[ip->ip_p]].pr_input)(m, ifp);
        goto next;
bad:
        m_freem(m);
        goto next;
}

/*
 * 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.
 */
struct ip *
ip_reass(ip, fp)
        register struct ipasfrag *ip;
        register struct ipq *fp;
{
        register struct mbuf *m = dtom(ip);
        register struct ipasfrag *q;
        struct mbuf *t;
        int hlen = ip->ip_hl << 2;
        int i, next;

        /*
         * Presence of header sizes in mbufs
         * would confuse code below.
         */

        m->m_off += hlen;
        m->m_len -= hlen;

        /*
         * If first fragment to arrive, create a reassembly queue.
         */
        if (fp == 0) {
                if ((t = m_get(M_DONTWAIT, MT_FTABLE)) == NULL)
                        goto dropfrag;
                fp = mtod(t, struct ipq *);
                insque(fp, &ipq);
                fp->ipq_ttl = IPFRAGTTL;
                fp->ipq_p = ip->ip_p;
                fp->ipq_id = ip->ip_id;
                fp->ipq_next = fp->ipq_prev = (struct ipasfrag *)fp;
                fp->ipq_src = ((struct ip *)ip)->ip_src;
                fp->ipq_dst = ((struct ip *)ip)->ip_dst;
                q = (struct ipasfrag *)fp;
                goto insert;
        }

        /*
         * Find a segment which begins after this one does.
         */
        for (q = fp->ipq_next; q != (struct ipasfrag *)fp; q = q->ipf_next)
                if (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.
         */
        if (q->ipf_prev != (struct ipasfrag *)fp) {
                i = q->ipf_prev->ip_off + q->ipf_prev->ip_len - ip->ip_off;
                if (i > 0) {
                        if (i >= ip->ip_len)
                                goto dropfrag;
                        m_adj(dtom(ip), i);
                        ip->ip_off += i;
                        ip->ip_len -= i;
                }
        }

        /*
         * While we overlap succeeding segments trim them or,
         * if they are completely covered, dequeue them.
         */
        while (q != (struct ipasfrag *)fp && ip->ip_off + ip->ip_len > q->ip_off) {
                i = (ip->ip_off + ip->ip_len) - q->ip_off;
                if (i < q->ip_len) {
                        q->ip_len -= i;
                        q->ip_off += i;
                        m_adj(dtom(q), i);
                        break;
                }
                q = q->ipf_next;
                m_freem(dtom(q->ipf_prev));
                ip_deq(q->ipf_prev);
        }

insert:
        /*
         * Stick new segment in its place;
         * check for complete reassembly.
         */
        ip_enq(ip, q->ipf_prev);
        next = 0;
        for (q = fp->ipq_next; q != (struct ipasfrag *)fp; q = q->ipf_next) {
                if (q->ip_off != next)
                        return (0);
                next += q->ip_len;
        }
        if (q->ipf_prev->ipf_mff)
                return (0);

        /*
         * Reassembly is complete; concatenate fragments.
         */
        q = fp->ipq_next;
        m = dtom(q);
        t = m->m_next;
        m->m_next = 0;
        m_cat(m, t);
        q = q->ipf_next;
        while (q != (struct ipasfrag *)fp) {
                t = dtom(q);
                q = q->ipf_next;
                m_cat(m, t);
        }

        /*
         * Create header for new ip packet by
         * modifying header of first packet;
         * dequeue and discard fragment reassembly header.
         * Make header visible.
         */
        ip = fp->ipq_next;
        ip->ip_len = next;
        ((struct ip *)ip)->ip_src = fp->ipq_src;
        ((struct ip *)ip)->ip_dst = fp->ipq_dst;
        remque(fp);
        (void) m_free(dtom(fp));
        m = dtom(ip);
        m->m_len += (ip->ip_hl << 2);
        m->m_off -= (ip->ip_hl << 2);
        return ((struct ip *)ip);

dropfrag:
        ipstat.ips_fragdropped++;
        m_freem(m);
        return (0);
}

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

        for (q = fp->ipq_next; q != (struct ipasfrag *)fp; q = p) {
                p = q->ipf_next;
                ip_deq(q);
                m_freem(dtom(q));
        }
        remque(fp);
        (void) m_free(dtom(fp));
}

/*
 * Put an ip fragment on a reassembly chain.
 * Like insque, but pointers in middle of structure.
 */
void ip_enq(p, prev)
        register struct ipasfrag *p, *prev;
{

        p->ipf_prev = prev;
        p->ipf_next = prev->ipf_next;
        prev->ipf_next->ipf_prev = p;
        prev->ipf_next = p;
}

/*
 * To ip_enq as remque is to insque.
 */
void ip_deq(p)
        register struct ipasfrag *p;
{

        p->ipf_prev->ipf_next = p->ipf_next;
        p->ipf_next->ipf_prev = p->ipf_prev;
}

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

        fp = ipq.next;
        if (fp == 0) {
                Permit();       /* splx(s); */
                return;
        }
        while (fp != &ipq) {
                --fp->ipq_ttl;
                fp = fp->next;
                if (fp->prev->ipq_ttl == 0) {
                        ipstat.ips_fragtimeout++;
                        ip_freef(fp->prev);
                }
        }
        Permit();       /* splx(s); */
}

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

        while (ipq.next != &ipq) {
                ipstat.ips_fragdropped++;
                ip_freef(ipq.next);
        }
}

extern struct in_ifaddr *ifptoia();
struct in_ifaddr *ip_rtaddr();

/*
 * Do option processing on a datagram,
 * possibly discarding it if bad options
 * are encountered.
 */
int ip_dooptions(m, ifp)
        struct mbuf *m;
        struct ifnet *ifp;
{
        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;
    struct in_addr dummy;
        n_time ntime;

        cp = (u_char *)(ip + 1);
        cnt = (ip->ip_hl << 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 {
                        optlen = cp[IPOPT_OLEN];
                        if (optlen <= 0 || 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 on directly accessible net.
                 */
                case IPOPT_LSRR:
                case IPOPT_SSRR:
                        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;
                                }
                                /*
                                 * Loose routing, and not at next destination
                                 * yet; nothing to do except forward.
                                 */
                                break;
                        }
                        off--;                  /* 0 origin */
                        if (off > optlen - sizeof(struct in_addr)) {
                                /*
                                 * End of source route.  Should be for us.
                                 */
                                save_rte(cp, ip->ip_src);
                                break;
                        }
                        /*
                         * locate outgoing interface
                         */
                        bcopy((caddr_t)(cp + off), (caddr_t)&ipaddr.sin_addr,
                            sizeof(ipaddr.sin_addr));
                        if ((opt == IPOPT_SSRR &&
                            in_iaonnetof(in_netof(ipaddr.sin_addr)) == 0) ||
                            (ia = ip_rtaddr(ipaddr.sin_addr)) == 0) {
                                type = ICMP_UNREACH;
                                code = ICMP_UNREACH_SRCFAIL;
                                goto bad;
                        }
                        ip->ip_dst = ipaddr.sin_addr;
                        bcopy((caddr_t)&(IA_SIN(ia)->sin_addr),
                            (caddr_t)(cp + off), sizeof(struct in_addr));
                        cp[IPOPT_OFFSET] += sizeof(struct in_addr);
                        forward = 1;
                        break;

                case IPOPT_RR:
                        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 - sizeof(struct in_addr))
                                break;
                        bcopy((caddr_t)(&ip->ip_dst), (caddr_t)&ipaddr.sin_addr,
                            sizeof(ipaddr.sin_addr));
                        /*
                         * locate outgoing interface
                         */
                        if ((ia = ip_rtaddr(ipaddr.sin_addr)) == 0) {
                                type = ICMP_UNREACH;
                                code = ICMP_UNREACH_HOST;
                                goto bad;
                        }
                        bcopy((caddr_t)&(IA_SIN(ia)->sin_addr),
                            (caddr_t)(cp + off), 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 < 5)
                                goto bad;
                        if (ipt->ipt_ptr > ipt->ipt_len - sizeof (long)) {
                                if (++ipt->ipt_oflw == 0)
                                        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 + sizeof(n_time) +
                                    sizeof(struct in_addr) > ipt->ipt_len)
                                        goto bad;
                                ia = ifptoia(ifp);
                                bcopy((caddr_t)&IA_SIN(ia)->sin_addr,
                                    (caddr_t)sin, sizeof(struct in_addr));
                                ipt->ipt_ptr += sizeof(struct in_addr);
                                break;

                        case IPOPT_TS_PRESPEC:
                                if (ipt->ipt_ptr + sizeof(n_time) +
                                    sizeof(struct in_addr) > ipt->ipt_len)
                                        goto bad;
                                bcopy((caddr_t)sin, (caddr_t)&ipaddr.sin_addr,
                                    sizeof(struct in_addr));
                                if (ifa_ifwithaddr((struct sockaddr *)&ipaddr) == 0)
                                        continue;
                                ipt->ipt_ptr += sizeof(struct in_addr);
                                break;

                        default:
                                goto bad;
                        }
                        ntime = iptime();
                        bcopy((caddr_t)&ntime, (caddr_t)cp + ipt->ipt_ptr - 1,
                            sizeof(n_time));
                        ipt->ipt_ptr += sizeof(n_time);
                }
        }
        if (forward) {
                ip_forward(m, ifp);
                return (1);
        } else
                return (0);
bad:
        icmp_error(ip, type, code, ifp, dummy); /* dummy is a kludge */
        return (1);
}

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

        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_addr = dst;

                rtalloc(&ipforward_rt);
        }
        if (ipforward_rt.ro_rt == 0)
                return ((struct in_ifaddr *)0);
        /*
         * Find address associated with outgoing interface.
         */
        for (ia = in_ifaddr; ia; ia = ia->ia_next)
                if (ia->ia_ifp == ipforward_rt.ro_rt->rt_ifp)
                        break;
        return (ia);
}

/*
 * 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];
        if (ipprintfs)
                printf("save_rte: olen %d\n", olen);
        if (olen > sizeof(ip_srcrt) - (1 + sizeof(dst)))
                return;
        bcopy((caddr_t)option, (caddr_t)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_SOOPTS);
        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;
        if (ipprintfs)
                printf("ip_srcroute: nhops %d mlen %d", ip_nhops, m->m_len);

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

        /*
         * Copy option fields and padding (nop) to mbuf.
         */
        ip_srcrt.nop = IPOPT_NOP;
        ip_srcrt.srcopt[IPOPT_OFFSET] = IPOPT_MINOFF;
        bcopy((caddr_t)&ip_srcrt.nop,
            mtod(m, caddr_t) + sizeof(struct in_addr), 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) {
                if (ipprintfs)
                        printf(" %X", ntohl(*q));
                *q++ = *p--;
        }
        /*
         * Last hop goes to final destination.
         */
        *q = ip_srcrt.dst;
        if (ipprintfs)
                printf(" %X\n", ntohl(*q));
        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(ip, mopt)
        struct ip *ip;
        struct mbuf *mopt;
{
        register int i;
        register struct mbuf *m;
        register caddr_t opts;
        int olen;

        olen = (ip->ip_hl<<2) - sizeof (struct ip);
        m = dtom(ip);
        opts = (caddr_t)(ip + 1);
        if (mopt) {
                mopt->m_len = olen;
                mopt->m_off = MMINOFF;
                bcopy(opts, mtod(mopt, caddr_t), (unsigned)olen);
        }
        i = m->m_len - (sizeof (struct ip) + olen);
        bcopy(opts  + olen, opts, (unsigned)i);
        m->m_len -= olen;
        ip->ip_hl = sizeof(struct ip) >> 2;
}

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

/*
 * 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 (possibly because we have only a single external
 * network), 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.
 */

void ip_forward(m, ifp)
        struct mbuf *m;
        struct ifnet *ifp;
{
        register struct ip *ip = mtod(m, struct ip *);
        register int error, type = 0, code;
        register struct sockaddr_in *sin;
        struct mbuf *mcopy;
        struct in_addr dest;

        dest.s_addr = 0;
        if (ipprintfs)
                printf("forward: src %x dst %x ttl %x\n", ip->ip_src,
                        ip->ip_dst, ip->ip_ttl);
        if (in_canforward(ip->ip_dst) == 0) {
                ipstat.ips_cantforward++;
                m_freem(dtom(ip));
                return;
        }
        ip->ip_id = htons(ip->ip_id);
        if (ip->ip_ttl <= IPTTLDEC) {
                type = ICMP_TIMXCEED, code = ICMP_TIMXCEED_INTRANS;
                goto sendicmp;
        }
        ip->ip_ttl -= IPTTLDEC;

        /*
         * Save at most 64 bytes of the packet in case
         * we need to generate an ICMP message to the src.
         */
        mcopy = m_copy(dtom(ip), 0, imin((int)ip->ip_len, 64));

        sin = (struct sockaddr_in *)&ipforward_rt.ro_dst;
        if (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_addr = ip->ip_dst;

                rtalloc(&ipforward_rt);
        }
        /*
         * 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 modfied by a redirect.
         */
#define satosin(sa)     ((struct sockaddr_in *)(sa))
        if (ipforward_rt.ro_rt && ipforward_rt.ro_rt->rt_ifp == ifp &&
            (ipforward_rt.ro_rt->rt_flags & (RTF_DYNAMIC|RTF_MODIFIED)) == 0 &&
            satosin(&ipforward_rt.ro_rt->rt_dst)->sin_addr.s_addr != 0 &&
            ipsendredirects && ip->ip_hl == (sizeof(struct ip) >> 2)) {
                struct in_ifaddr *ia;
                u_long src = ntohl(ip->ip_src.s_addr);
                u_long dst = ntohl(ip->ip_dst.s_addr);

                if ((ia = ifptoia(ifp)) &&
                   (src & ia->ia_subnetmask) == ia->ia_subnet) {
                    if (ipforward_rt.ro_rt->rt_flags & RTF_GATEWAY)
                        dest = satosin(&ipforward_rt.ro_rt->rt_gateway)->sin_addr;
                    else
                        dest = ip->ip_dst;
                    /*
                     * If the destination is reached by a route to host,
                     * is on a subnet of a local net, or is directly
                     * on the attached net (!), use host redirect.
                     * (We may be the correct first hop for other subnets.)
                     */
                    type = ICMP_REDIRECT;
                    code = ICMP_REDIRECT_NET;
                    if ((ipforward_rt.ro_rt->rt_flags & RTF_HOST) ||
                       (ipforward_rt.ro_rt->rt_flags & RTF_GATEWAY) == 0)
                        code = ICMP_REDIRECT_HOST;
                    else for (ia = in_ifaddr; ia = ia->ia_next; )
                        if ((dst & ia->ia_netmask) == ia->ia_net) {
                            if (ia->ia_subnetmask != ia->ia_netmask)
                                    code = ICMP_REDIRECT_HOST;
                            break;
                        }
                    if (ipprintfs)
                        printf("redirect (%d) to %x\n", code, dest);
                }
        }

        error = ip_output(dtom(ip), (struct mbuf *)0, &ipforward_rt,
                IP_FORWARDING);
        if (error)
                ipstat.ips_cantforward++;
        else if (type)
                ipstat.ips_redirectsent++;
        else {
                if (mcopy)
                        m_freem(mcopy);
                ipstat.ips_forward++;
                return;
        }
        if (mcopy == NULL)
                return;
        ip = mtod(mcopy, struct ip *);
        type = ICMP_UNREACH;
        switch (error) {

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

        case ENETUNREACH:
        case ENETDOWN:
                if (in_localaddr(ip->ip_dst))
                        code = ICMP_UNREACH_HOST;
                else
                        code = ICMP_UNREACH_NET;
                break;

        case EMSGSIZE:
                code = ICMP_UNREACH_NEEDFRAG;
                break;

        case EPERM:
                code = ICMP_UNREACH_PORT;
                break;

        case ENOBUFS:
                type = ICMP_SOURCEQUENCH;
                break;

        case EHOSTDOWN:
        case EHOSTUNREACH:
                code = ICMP_UNREACH_HOST;
                break;
        }
sendicmp:
        icmp_error(ip, type, code, ifp, dest);
}
