source: lib/protocols_transport.c @ 7e8a25a

/*
 * This file is part of libtrace
 *
 * Copyright (c) 2007,2008,2009,2010 The University of Waikato, Hamilton, 
 * New Zealand.
 *
 * Authors: Daniel Lawson 
 *          Perry Lorier
 *          Shane Alcock 
 *          
 * All rights reserved.
 *
 * This code has been developed by the University of Waikato WAND 
 * research group. For further information please see http://www.wand.net.nz/
 *
 * libtrace is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * libtrace is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with libtrace; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 * $Id$
 *
 */


#include "libtrace.h"
#include "protocols.h"
#include <assert.h>
#include <stdlib.h>
#include <stdio.h> // fprintf

/* This file contains all the protocol decoding functions for transport layer
 * protocols. This includes functions for access port numbers.
 *
 * Supported protocols include (but are not limited to):
 *      TCP
 *      UDP
 *      ICMP
 */

/* Get the size of the payload as it was in the original packet, i.e. prior
 * to any truncation.
 *
 * Basically, wire length minus the packet headers.
 *
 * Currently only supports IP (v4 and v6) and TCP, UDP and ICMP. Will return
 * 0 if an unsupported protocol header is encountered, or if one of the 
 * headers is truncated.
 */
DLLEXPORT size_t trace_get_payload_length(const libtrace_packet_t *packet) {

        void *layer;
        uint16_t ethertype;
        uint8_t proto;
        uint32_t rem;
        libtrace_ip_t *ip;
        libtrace_ip6_t *ip6;
        libtrace_tcp_t *tcp;
        size_t len = 0;

        

        layer = trace_get_layer3(packet, &ethertype, &rem);

        if (!layer)
                return 0;
        switch (ethertype) {
                case TRACE_ETHERTYPE_IP:
                        ip = (libtrace_ip_t *)layer;
                        if (rem < sizeof(libtrace_ip_t))
                                return 0;
                        len = ntohs(ip->ip_len) - (4 * ip->ip_hl);
                
                        /* Deal with v6 within v4 */
                        if (ip->ip_p == TRACE_IPPROTO_IPV6)
                                len -= sizeof(libtrace_ip6_t);
                        
                        break;
                case TRACE_ETHERTYPE_IPV6:
                        ip6 = (libtrace_ip6_t *)layer;
                        if (rem < sizeof(libtrace_ip6_t))
                                return 0;
                        len = ntohs(ip6->plen);
                        break;
                default:
                        return 0;
        }

        layer = trace_get_transport(packet, &proto, &rem);
        if (!layer)
                return 0;
        
        switch(proto) {
                case TRACE_IPPROTO_TCP:
                        if (rem < sizeof(libtrace_tcp_t))
                                return 0;
                        tcp = (libtrace_tcp_t *)layer;
                        len -= (4 * tcp->doff);
                        break;
                case TRACE_IPPROTO_UDP:
                        len -= sizeof(libtrace_udp_t);
                        break;
                case TRACE_IPPROTO_ICMP:
                        len -= sizeof(libtrace_icmp_t);
                        break;
                
                default:
                        return 0;
        }

        return len;

}

DLLEXPORT void *trace_get_transport(const libtrace_packet_t *packet, 
                uint8_t *proto,
                uint32_t *remaining
                ) 
{
        uint8_t dummy_proto;
        uint16_t ethertype;
        uint32_t dummy_remaining;
        void *transport;

        if (!proto) proto=&dummy_proto;

        if (!remaining) remaining=&dummy_remaining;

        transport = trace_get_layer3(packet,&ethertype,remaining);

        if (!transport || *remaining == 0)
                return NULL;

        switch (ethertype) {
                case TRACE_ETHERTYPE_IP: /* IPv4 */
                        transport=trace_get_payload_from_ip(
                                (libtrace_ip_t*)transport, proto, remaining);
                        /* IPv6 */
                        if (transport && *proto == TRACE_IPPROTO_IPV6) {
                                transport=trace_get_payload_from_ip6(
                                 (libtrace_ip6_t*)transport, proto,remaining);
                        }
                        return transport;
                case TRACE_ETHERTYPE_IPV6: /* IPv6 */
                        return trace_get_payload_from_ip6(
                                (libtrace_ip6_t*)transport, proto, remaining);
                        
        }

        *proto=0;
        return NULL;
}

DLLEXPORT libtrace_tcp_t *trace_get_tcp(libtrace_packet_t *packet) {
        uint8_t proto;
        uint32_t rem = 0;
        libtrace_tcp_t *tcp;

        tcp=(libtrace_tcp_t*)trace_get_transport(packet,&proto,&rem);

        if (!tcp || proto != TRACE_IPPROTO_TCP)
                return NULL;

        /* We should return NULL if there isn't a full TCP header, because the
         * caller has no way of telling how much of a TCP header we have
         * returned - use trace_get_transport() if you want to deal with
         * partial headers 
         *
         * NOTE: We're not going to insist that all the TCP options are present
         * as well, because lots of traces are snapped after 20 bytes of TCP
         * header and I don't really want to break libtrace programs that
         * use this function to process those traces */

        if (rem < sizeof(libtrace_tcp_t))
                return NULL;

        return (libtrace_tcp_t*)tcp;
}

DLLEXPORT libtrace_tcp_t *trace_get_tcp_from_ip(libtrace_ip_t *ip, uint32_t *remaining)
{
        libtrace_tcp_t *tcpptr = 0;

        if (ip->ip_p == TRACE_IPPROTO_TCP)  {
                tcpptr = (libtrace_tcp_t *)
                        trace_get_payload_from_ip(ip, NULL, remaining);
        }

        return tcpptr;
}

DLLEXPORT libtrace_udp_t *trace_get_udp(libtrace_packet_t *packet) {
        uint8_t proto;
        uint32_t rem = 0;
        libtrace_udp_t *udp;

        udp=(libtrace_udp_t*)trace_get_transport(packet,&proto,&rem);

        if (!udp || proto != TRACE_IPPROTO_UDP)
                return NULL;

        /* Make sure we return a full UDP header as the caller has no way of
         * telling how much of the packet is remaining */
        if (rem < sizeof(libtrace_udp_t))
                return NULL;

        return udp;
}

DLLEXPORT libtrace_udp_t *trace_get_udp_from_ip(libtrace_ip_t *ip, uint32_t *remaining)
{
        libtrace_udp_t *udpptr = 0;

        if (ip->ip_p == TRACE_IPPROTO_UDP) {
                udpptr = (libtrace_udp_t *)
                        trace_get_payload_from_ip(ip, NULL, remaining);
        }

        return udpptr;
}

DLLEXPORT libtrace_icmp_t *trace_get_icmp(libtrace_packet_t *packet) {
        uint8_t proto;
        uint32_t rem = 0;
        libtrace_icmp_t *icmp;

        icmp=(libtrace_icmp_t*)trace_get_transport(packet,&proto,&rem);

        if (!icmp || proto != TRACE_IPPROTO_ICMP)
                return NULL;

        /* Make sure we return a full ICMP header as the caller has no way of
         * telling how much of the packet is remaining */
        if (rem < sizeof(libtrace_icmp_t))
                return NULL;

        return icmp;
}

DLLEXPORT libtrace_icmp_t *trace_get_icmp_from_ip(libtrace_ip_t *ip, uint32_t *remaining)
{
        libtrace_icmp_t *icmpptr = 0;

        if (ip->ip_p == TRACE_IPPROTO_ICMP)  {
                icmpptr = (libtrace_icmp_t *)trace_get_payload_from_ip(ip, 
                                NULL, remaining);
        }

        return icmpptr;
}

DLLEXPORT void *trace_get_payload_from_udp(libtrace_udp_t *udp, uint32_t *remaining)
{
        if (remaining) {
                if (*remaining < sizeof(libtrace_udp_t)) {
                        *remaining = 0;
                        return NULL;
                }
                *remaining-=sizeof(libtrace_udp_t);
        }
        return (void*)((char*)udp+sizeof(libtrace_udp_t));
}

DLLEXPORT void *trace_get_payload_from_tcp(libtrace_tcp_t *tcp, uint32_t *remaining)
{
        unsigned int dlen = tcp->doff*4;
        if (remaining) {
                if (*remaining < dlen) {
                        *remaining = 0;
                        return NULL;
                }
                *remaining-=dlen;
        }
        return (void *)((char *)tcp+dlen);
}

DLLEXPORT void *trace_get_payload_from_icmp(libtrace_icmp_t *icmp, uint32_t *remaining)
{
        if (remaining) {
                if (*remaining < sizeof(libtrace_icmp_t)) {
                        *remaining = 0;
                        return NULL;
                }
                *remaining-=sizeof(libtrace_icmp_t);
        }
        return (char*)icmp+sizeof(libtrace_icmp_t);
}

/* Return the source port
 */
DLLEXPORT uint16_t trace_get_source_port(const libtrace_packet_t *packet)
{
        uint32_t remaining;
        uint8_t proto;
        const struct ports_t *port = 
                (const struct ports_t*)trace_get_transport((libtrace_packet_t*)packet,
                        &proto, &remaining);

        /* Snapped too early */
        if (remaining<2)
                return 0;

        /* ICMP *technically* doesn't have ports */
        if (proto == TRACE_IPPROTO_ICMP)
                return 0;

        if (port)
                return ntohs(port->src);
        else
                return 0;
}

/* Same as get_source_port except use the destination port */
DLLEXPORT uint16_t trace_get_destination_port(const libtrace_packet_t *packet)
{
        uint32_t remaining;
        uint8_t proto;
        struct ports_t *port = 
                (struct ports_t*)trace_get_transport((libtrace_packet_t*)packet,
                        &proto, &remaining);
        /* Snapped too early */
        if (remaining<4)
                return 0;
        
        /* ICMP *technically* doesn't have ports */
        if (proto == TRACE_IPPROTO_ICMP)
                return 0;

        if (port)
                return ntohs(port->dst);
        else
                return 0;
}