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/*
ettercap -- dissector for multicast DNS
This program 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.
This program 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 this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
*/
#include <ec.h>
#include <ec_dissect.h>
#include <ec_resolv.h>
FUNC_DECODER(dissector_mdns);
void mdns_init(void);
static void handle_ipv4_record(char* name, char* ptr);
static void handle_ipv6_record(char* name, char* ptr);
static void handle_srv_record(char* name, char* port_ptr, struct packet_object *po);
static const char local_tcp[] = "._tcp.local";
static const char local_udp[] = "._udp.local";
/************************************************/
void __init mdns_init(void)
{
dissect_add("mdns", APP_LAYER_UDP, 5353, dissector_mdns);
}
FUNC_DECODER(dissector_mdns)
{
uint16_t questions = 0;
uint16_t records = 0;
unsigned char* start = NULL;
char name[NS_MAXDNAME];
DECLARE_DISP_PTR_END(ptr, end);
// unused param supression
(void)buf;
(void)buflen;
(void)len;
// skip packets which are not useful
if (PACKET->DATA.len <= 12)
return NULL;
PACKET->PASSIVE.flags |= FP_HOST_LOCAL;
questions = ntohs(*((uint16_t*)ptr + 4));
hook_point(HOOK_PROTO_MDNS, PACKET);
if (questions > 0)
{
//skip packets with questions for now. Makes parsing easier
return NULL;
}
records += ntohs(*((uint16_t*)(ptr + 6)));
records += ntohs(*((uint16_t*)(ptr + 8)));
records += ntohs(*((uint16_t*)(ptr + 10)));
if (records == 0)
{
// there is nothing to parse
return NULL;
}
if ((ptr + 12) >= end)
{
// not enough data
return NULL;
}
// store the start for dns records pointers
start = ptr;
ptr += 12;
// loop over all the records
for ( ; records > 0; --records)
{
uint16_t type = 0;
uint16_t length = 0;
uint16_t name_len = dn_expand(start, end, ptr, name, sizeof(name));
if ((ptr + name_len + 10) >= end)
{
return NULL;
}
ptr += name_len;
type = ntohs(*((uint16_t*)(ptr)));
length = ntohs(*((uint16_t*)(ptr + 8)));
if ((ptr + 10 + length) >= end)
{
return NULL;
}
ptr += 10;
switch (type)
{
case ns_t_a: // A host IPv4
handle_ipv4_record(name, (char*)ptr);
break;
case ns_t_aaaa: // AAAA (Host IPv6 Address)
handle_ipv6_record(name, (char*)ptr);
break;
case ns_t_srv: // Service
handle_srv_record(name, (char*)ptr + 4, PACKET);
break;
default:
//various other types should hit here: TXT, HINFO, etc.
break;
}
// skip over the rest of the record
ptr += length;
}
return NULL;
}
static void handle_ipv4_record(char* name, char* ptr)
{
uint32_t addr;
struct ip_addr ip;
NS_GET32(addr, ptr);
addr = htonl(addr);
ip_addr_init(&ip, AF_INET, (u_char *)&addr);
/* insert the answer in the resolv cache */
resolv_cache_insert_passive(&ip, name);
}
static void handle_ipv6_record(char* name, char* ptr)
{
uint16_t addr[8];
struct ip_addr ip;
int i = 0;
for (i=0; i<8; i++) {
NS_GET16(addr[i], ptr);
addr[i] = htons(addr[i]);
}
ip_addr_init(&ip, AF_INET6, (u_char *)&addr);
/* insert the answer in the resolv cache */
resolv_cache_insert_passive(&ip, name);
}
static void handle_srv_record(char* name, char* port_ptr, struct packet_object *po)
{
uint16_t port;
NS_GET16(port, port_ptr);
port = ntohs(port);
if (strlen(name) > sizeof(local_tcp))
{
int name_offset = strlen(name) - (sizeof(local_tcp) - 1);
if (strncmp(name + name_offset, local_tcp, sizeof(local_tcp) - 1) == 0)
{
PACKET->DISSECTOR.advertised_proto = NL_TYPE_TCP;
}
else if (strncmp(name + name_offset, local_udp, sizeof(local_udp) - 1) == 0)
{
PACKET->DISSECTOR.advertised_proto = NL_TYPE_UDP;
}
PACKET->DISSECTOR.advertised_port = port;
}
}
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