src/ip_output.c

/* SPDX-License-Identifier: BSD-3-Clause */
/*
 * Copyright (c) 1982, 1986, 1988, 1990, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *	@(#)ip_output.c	8.3 (Berkeley) 1/21/94
 * ip_output.c,v 1.9 1994/11/16 10:17:10 jkh Exp
 */

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

#include "slirp.h"

/* Number of packets queued before we start sending
 * (to prevent allocing too many mbufs) */
#define IF_THRESH 10

/*
 * IP output.  The packet in mbuf chain m contains a skeletal IP
 * header (with len, off, ttl, proto, tos, src, dst).
 * The mbuf chain containing the packet will be freed.
 * The mbuf opt, if present, will not be freed.
 */
int ip_output(struct socket *so, struct mbuf *m0)
{
    Slirp *slirp = m0->slirp;
    M_DUP_DEBUG(slirp, m0, 0, 0);

    register struct ip *ip;
    register struct mbuf *m = m0;
    register int hlen = sizeof(struct ip);
    int len, off, error = 0;

    DEBUG_CALL("ip_output");
    DEBUG_ARG("so = %p", so);
    DEBUG_ARG("m0 = %p", m0);

    ip = mtod(m, struct ip *);
    /*
     * Fill in IP header.
     */
    ip->ip_v = IPVERSION;
    ip->ip_off &= IP_DF;
    ip->ip_id = htons(slirp->ip_id++);
    ip->ip_hl = hlen >> 2;

    /*
     * If small enough for interface, can just send directly.
     */
    if ((uint16_t)ip->ip_len <= slirp->if_mtu) {
        ip->ip_len = htons((uint16_t)ip->ip_len);
        ip->ip_off = htons((uint16_t)ip->ip_off);
        ip->ip_sum = 0;
        ip->ip_sum = cksum(m, hlen);

        if_output(so, m);
        goto done;
    }

    /*
     * Too large for interface; fragment if possible.
     * Must be able to put at least 8 bytes per fragment.
     */
    if (ip->ip_off & IP_DF) {
        error = -1;
        goto bad;
    }

    len = (slirp->if_mtu - hlen) & ~7; /* ip databytes per packet */
    if (len < 8) {
        error = -1;
        goto bad;
    }

    {
        int mhlen, firstlen = len;
        struct mbuf **mnext = &m->m_nextpkt;

        /*
         * Loop through length of segment after first fragment,
         * make new header and copy data of each part and link onto chain.
         */
        m0 = m;
        mhlen = sizeof(struct ip);
        for (off = hlen + len; off < (uint16_t)ip->ip_len; off += len) {
            register struct ip *mhip;
            m = m_get(slirp);
            if (m == NULL) {
                error = -1;
                goto sendorfree;
            }
            m->m_data += IF_MAXLINKHDR;
            mhip = mtod(m, struct ip *);
            *mhip = *ip;

            m->m_len = mhlen;
            mhip->ip_off = ((off - hlen) >> 3) + (ip->ip_off & ~IP_MF);
            if (ip->ip_off & IP_MF)
                mhip->ip_off |= IP_MF;
            if (off + len >= (uint16_t)ip->ip_len)
                len = (uint16_t)ip->ip_len - off;
            else
                mhip->ip_off |= IP_MF;
            mhip->ip_len = htons((uint16_t)(len + mhlen));

            if (m_copy(m, m0, off, len) < 0) {
                error = -1;
                goto sendorfree;
            }

            mhip->ip_off = htons((uint16_t)mhip->ip_off);
            mhip->ip_sum = 0;
            mhip->ip_sum = cksum(m, mhlen);
            *mnext = m;
            mnext = &m->m_nextpkt;
        }
        /*
         * Update first fragment by trimming what's been copied out
         * and updating header, then send each fragment (in order).
         */
        m = m0;
        m_adj(m, hlen + firstlen - (uint16_t)ip->ip_len);
        ip->ip_len = htons((uint16_t)m->m_len);
        ip->ip_off = htons((uint16_t)(ip->ip_off | IP_MF));
        ip->ip_sum = 0;
        ip->ip_sum = cksum(m, hlen);
    sendorfree:
        for (m = m0; m; m = m0) {
            m0 = m->m_nextpkt;
            m->m_nextpkt = NULL;
            if (error == 0)
                if_output(so, m);
            else
                m_free(m);
        }
    }

done:
    return (error);

bad:
    m_free(m0);
    goto done;
}