/* SPDX-License-Identifier: BSD-3-Clause */
/*
 * 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. 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
 * ip_input.c,v 1.11 1994/11/16 10:17:08 jkh Exp
 */

/*
 * Changes and additions relating to SLiRP are
 * Copyright (c) 1995 Danny Gasparovski.
 */

#include "slirp.h"
#include "ip_icmp.h"

static struct ip *ip_reass(Slirp *slirp, struct ip *ip, struct ipq *fp);
static void ip_freef(Slirp *slirp, struct ipq *fp);
static void ip_enq(register struct ipasfrag *p,
                   register struct ipasfrag *prev);
static void ip_deq(register struct ipasfrag *p);

/*
 * IP initialization: fill in IP protocol switch table.
 * All protocols not implemented in kernel go to raw IP protocol handler.
 */
void
ip_init(Slirp *slirp)
{
    slirp->ipq.ip_link.next = slirp->ipq.ip_link.prev = &slirp->ipq.ip_link;
    udp_init(slirp);
    tcp_init(slirp);
    icmp_init(slirp);
}

void ip_cleanup(Slirp *slirp)
{
    udp_cleanup(slirp);
    tcp_cleanup(slirp);
    icmp_cleanup(slirp);
}

/*
 * 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)
{
        Slirp *slirp = m->slirp;
        register struct ip *ip;
        int hlen;

        if (!slirp->in_enabled) {
                goto bad;
        }

        DEBUG_CALL("ip_input");
        DEBUG_ARG("m = %p", m);
        DEBUG_ARG("m_len = %d", m->m_len);

        if (m->m_len < sizeof (struct ip)) {
                goto bad;
        }

        ip = mtod(m, struct ip *);

        if (ip->ip_v != IPVERSION) {
                goto bad;
        }

        hlen = ip->ip_hl << 2;
        if (hlen<sizeof(struct ip ) || hlen>m->m_len) {/* min header length */
          goto bad;                                  /* or packet too short */
        }

        /* keep ip header intact for ICMP reply
         * ip->ip_sum = cksum(m, hlen);
         * if (ip->ip_sum) {
         */
        if(cksum(m,hlen)) {
          goto bad;
        }

        /*
         * Convert fields to host representation.
         */
        NTOHS(ip->ip_len);
        if (ip->ip_len < hlen) {
                goto bad;
        }
        NTOHS(ip->ip_id);
        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_len < ip->ip_len) {
                goto bad;
        }

        /* Should drop packet if mbuf too long? hmmm... */
        if (m->m_len > ip->ip_len)
           m_adj(m, ip->ip_len - m->m_len);

        /* check ip_ttl for a correct ICMP reply */
        if (ip->ip_ttl == 0) {
            icmp_send_error(m, ICMP_TIMXCEED, ICMP_TIMXCEED_INTRANS, 0, "ttl");
            goto bad;
        }

        /*
         * 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.)
         *
         * XXX This should fail, don't fragment yet
         */
        if (ip->ip_off &~ IP_DF) {
          register struct ipq *fp;
      struct qlink *l;
                /*
                 * Look for queue of fragments
                 * of this datagram.
                 */
                for (l = slirp->ipq.ip_link.next; l != &slirp->ipq.ip_link;
                     l = l->next) {
            fp = container_of(l, struct ipq, ip_link);
            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 = NULL;
        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;
                if (ip->ip_off & IP_MF)
                  ip->ip_tos |= 1;
                else
                  ip->ip_tos &= ~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 (ip->ip_tos & 1 || ip->ip_off) {
                        ip = ip_reass(slirp, ip, fp);
                        if (ip == NULL)
                                return;
                        m = dtom(slirp, ip);
                } else
                        if (fp)
                           ip_freef(slirp, fp);

        } else
                ip->ip_len -= hlen;

        /*
         * Switch out to protocol's input routine.
         */
        switch (ip->ip_p) {
         case IPPROTO_TCP:
                tcp_input(m, hlen, (struct socket *)NULL, AF_INET);
                break;
         case IPPROTO_UDP:
                udp_input(m, hlen);
                break;
         case IPPROTO_ICMP:
                icmp_input(m, hlen);
                break;
         default:
                m_free(m);
        }
        return;
bad:
        m_free(m);
}

#define iptofrag(P) ((struct ipasfrag *)(((char*)(P)) - sizeof(struct qlink)))
#define fragtoip(P) ((struct ip*)(((char*)(P)) + sizeof(struct qlink)))
/*
 * 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.
 */
static struct ip *
ip_reass(Slirp *slirp, struct ip *ip, struct ipq *fp)
{
        register struct mbuf *m = dtom(slirp, ip);
        register struct ipasfrag *q;
        int hlen = ip->ip_hl << 2;
        int i, next;

        DEBUG_CALL("ip_reass");
        DEBUG_ARG("ip = %p", ip);
        DEBUG_ARG("fp = %p", fp);
        DEBUG_ARG("m = %p", m);

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

        /*
         * If first fragment to arrive, create a reassembly queue.
         */
        if (fp == NULL) {
          struct mbuf *t = m_get(slirp);

          if (t == NULL) {
              goto dropfrag;
          }
          fp = mtod(t, struct ipq *);
          insque(&fp->ip_link, &slirp->ipq.ip_link);
          fp->ipq_ttl = IPFRAGTTL;
          fp->ipq_p = ip->ip_p;
          fp->ipq_id = ip->ip_id;
          fp->frag_link.next = fp->frag_link.prev = &fp->frag_link;
          fp->ipq_src = ip->ip_src;
          fp->ipq_dst = ip->ip_dst;
          q = (struct ipasfrag *)fp;
          goto insert;
        }

        /*
         * Find a segment which begins after this one does.
         */
        for (q = fp->frag_link.next; q != (struct ipasfrag *)&fp->frag_link;
            q = q->ipf_next)
                if (q->ipf_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 != &fp->frag_link) {
        struct ipasfrag *pq = q->ipf_prev;
                i = pq->ipf_off + pq->ipf_len - ip->ip_off;
                if (i > 0) {
                        if (i >= ip->ip_len)
                                goto dropfrag;
                        m_adj(dtom(slirp, 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->frag_link &&
            ip->ip_off + ip->ip_len > q->ipf_off) {
                i = (ip->ip_off + ip->ip_len) - q->ipf_off;
                if (i < q->ipf_len) {
                        q->ipf_len -= i;
                        q->ipf_off += i;
                        m_adj(dtom(slirp, q), i);
                        break;
                }
                q = q->ipf_next;
                m_free(dtom(slirp, q->ipf_prev));
                ip_deq(q->ipf_prev);
        }

insert:
        /*
         * Stick new segment in its place;
         * check for complete reassembly.
         */
        ip_enq(iptofrag(ip), q->ipf_prev);
        next = 0;
        for (q = fp->frag_link.next; q != (struct ipasfrag*)&fp->frag_link;
            q = q->ipf_next) {
                if (q->ipf_off != next)
                        return NULL;
                next += q->ipf_len;
        }
        if (((struct ipasfrag *)(q->ipf_prev))->ipf_tos & 1)
                return NULL;

        /*
         * Reassembly is complete; concatenate fragments.
         */
    q = fp->frag_link.next;
        m = dtom(slirp, q);

        q = (struct ipasfrag *) q->ipf_next;
        while (q != (struct ipasfrag*)&fp->frag_link) {
          struct mbuf *t = dtom(slirp, q);
          q = (struct ipasfrag *) 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.
         */
        q = fp->frag_link.next;

        /*
         * If the fragments concatenated to an mbuf that's
         * bigger than the total size of the fragment, then and
         * m_ext buffer was alloced. But fp->ipq_next points to
         * the old buffer (in the mbuf), so we must point ip
         * into the new buffer.
         */
        if (m->m_flags & M_EXT) {
          int delta = (char *)q - m->m_dat;
          q = (struct ipasfrag *)(m->m_ext + delta);
        }

    ip = fragtoip(q);
        ip->ip_len = next;
        ip->ip_tos &= ~1;
        ip->ip_src = fp->ipq_src;
        ip->ip_dst = fp->ipq_dst;
        remque(&fp->ip_link);
        (void) m_free(dtom(slirp, fp));
        m->m_len += (ip->ip_hl << 2);
        m->m_data -= (ip->ip_hl << 2);

        return ip;

dropfrag:
        m_free(m);
        return NULL;
}

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

        for (q = fp->frag_link.next; q != (struct ipasfrag*)&fp->frag_link; q = p) {
                p = q->ipf_next;
                ip_deq(q);
                m_free(dtom(slirp, q));
        }
        remque(&fp->ip_link);
        (void) m_free(dtom(slirp, fp));
}

/*
 * Put an ip fragment on a reassembly chain.
 * Like insque, but pointers in middle of structure.
 */
static void
ip_enq(register struct ipasfrag *p, register struct ipasfrag *prev)
{
        DEBUG_CALL("ip_enq");
        DEBUG_ARG("prev = %p", prev);
        p->ipf_prev =  prev;
        p->ipf_next = prev->ipf_next;
        ((struct ipasfrag *)(prev->ipf_next))->ipf_prev = p;
        prev->ipf_next = p;
}

/*
 * To ip_enq as remque is to insque.
 */
static void
ip_deq(register struct ipasfrag *p)
{
        ((struct ipasfrag *)(p->ipf_prev))->ipf_next = p->ipf_next;
        ((struct ipasfrag *)(p->ipf_next))->ipf_prev = p->ipf_prev;
}

/*
 * IP timer processing;
 * if a timer expires on a reassembly
 * queue, discard it.
 */
void
ip_slowtimo(Slirp *slirp)
{
    struct qlink *l;

        DEBUG_CALL("ip_slowtimo");

    l = slirp->ipq.ip_link.next;

        if (l == NULL)
           return;

    while (l != &slirp->ipq.ip_link) {
        struct ipq *fp = container_of(l, struct ipq, ip_link);
        l = l->next;
                if (--fp->ipq_ttl == 0) {
                        ip_freef(slirp, fp);
                }
    }
}

/*
 * 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(register struct mbuf *m, struct mbuf *mopt)
{
        register int i;
        struct ip *ip = mtod(m, struct ip *);
        register char *opts;
        int olen;

        olen = (ip->ip_hl<<2) - sizeof (struct ip);
        opts = (char *)(ip + 1);
        i = m->m_len - (sizeof (struct ip) + olen);
        memcpy(opts, opts  + olen, (unsigned)i);
        m->m_len -= olen;

        ip->ip_hl = sizeof(struct ip) >> 2;
}