/*
* dns.c
*
* Copyright (C) 2012-18 - ntop.org
*
* This file is part of nDPI, an open source deep packet inspection
* library based on the OpenDPI and PACE technology by ipoque GmbH
*
* nDPI is free software: you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* nDPI 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 Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with nDPI. If not, see <http://www.gnu.org/licenses/>.
*
*/
#include "ndpi_protocol_ids.h"
#define NDPI_CURRENT_PROTO NDPI_PROTOCOL_DNS
#include "ndpi_api.h"
#define FLAGS_MASK 0x8000
/* #define DNS_DEBUG 1 */
/* *********************************************** */
static u_int16_t get16(int *i, const u_int8_t *payload) {
u_int16_t v = *(u_int16_t*)&payload[*i];
(*i) += 2;
return(ntohs(v));
}
/* *********************************************** */
static u_int getNameLength(u_int i, const u_int8_t *payload, u_int payloadLen) {
if(payload[i] == 0x00)
return(1);
else if(payload[i] == 0xC0)
return(2);
else {
u_int8_t len = payload[i];
u_int8_t off = len + 1;
if(off == 0) /* Bad packet */
return(0);
else
return(off + getNameLength(i+off, payload, payloadLen));
}
}
/*
allowed chars for dns names A-Z 0-9 _ -
Perl script for generation map:
my @M;
for(my $ch=0; $ch < 256; $ch++) {
$M[$ch >> 5] |= 1 << ($ch & 0x1f) if chr($ch) =~ /[a-z0-9_-]/i;
}
print join(',', map { sprintf "0x%08x",$_ } @M),"\n";
*/
static uint32_t dns_validchar[8] = {
0x00000000,0x03ff2000,0x87fffffe,0x07fffffe,0,0,0,0
};
/* *********************************************** */
void ndpi_search_dns(struct ndpi_detection_module_struct *ndpi_struct, struct ndpi_flow_struct *flow) {
int x, payload_offset;
u_int8_t is_query;
u_int16_t s_port = 0, d_port = 0;
NDPI_LOG_DBG(ndpi_struct, "search DNS\n");
if(flow->packet.udp != NULL) {
s_port = ntohs(flow->packet.udp->source);
d_port = ntohs(flow->packet.udp->dest);
payload_offset = 0;
} else if(flow->packet.tcp != NULL) /* pkt size > 512 bytes */ {
s_port = ntohs(flow->packet.tcp->source);
d_port = ntohs(flow->packet.tcp->dest);
payload_offset = 2;
} else {
NDPI_EXCLUDE_PROTO(ndpi_struct, flow);
return;
}
x = payload_offset;
if((s_port == 53 || d_port == 53 || d_port == 5355)
&& (flow->packet.payload_packet_len > sizeof(struct ndpi_dns_packet_header)+x)) {
struct ndpi_dns_packet_header dns_header;
int invalid = 0;
memcpy(&dns_header, (struct ndpi_dns_packet_header*) &flow->packet.payload[x], sizeof(struct ndpi_dns_packet_header));
dns_header.tr_id = ntohs(dns_header.tr_id);
dns_header.flags = ntohs(dns_header.flags);
dns_header.num_queries = ntohs(dns_header.num_queries);
dns_header.num_answers = ntohs(dns_header.num_answers);
dns_header.authority_rrs = ntohs(dns_header.authority_rrs);
dns_header.additional_rrs = ntohs(dns_header.additional_rrs);
x += sizeof(struct ndpi_dns_packet_header);
/* 0x0000 QUERY */
if((dns_header.flags & FLAGS_MASK) == 0x0000)
is_query = 1;
/* 0x8000 RESPONSE */
else if((dns_header.flags & FLAGS_MASK) == 0x8000)
is_query = 0;
else
invalid = 1;
if(!invalid) {
int j = 0, max_len, off;
if(is_query) {
/* DNS Request */
if((dns_header.num_queries > 0) && (dns_header.num_queries <= NDPI_MAX_DNS_REQUESTS)
&& (((dns_header.flags & 0x2800) == 0x2800 /* Dynamic DNS Update */)
|| ((dns_header.num_answers == 0) && (dns_header.authority_rrs == 0)))) {
/* This is a good query */
if(dns_header.num_queries > 0) {
while(x < flow->packet.payload_packet_len) {
if(flow->packet.payload[x] == '\0') {
x++;
flow->protos.dns.query_type = get16(&x, flow->packet.payload);
#ifdef DNS_DEBUG
NDPI_LOG_DBG2(ndpi_struct, "query_type=%2d\n", flow->protos.dns.query_type);
#endif
break;
} else
x++;
}
}
} else
invalid = 1;
} else {
/* DNS Reply */
flow->protos.dns.reply_code = dns_header.flags & 0x0F;
if((dns_header.num_queries > 0) && (dns_header.num_queries <= NDPI_MAX_DNS_REQUESTS) /* Don't assume that num_queries must be zero */
&& (((dns_header.num_answers > 0) && (dns_header.num_answers <= NDPI_MAX_DNS_REQUESTS))
|| ((dns_header.authority_rrs > 0) && (dns_header.authority_rrs <= NDPI_MAX_DNS_REQUESTS))
|| ((dns_header.additional_rrs > 0) && (dns_header.additional_rrs <= NDPI_MAX_DNS_REQUESTS)))
) {
/* This is a good reply: we dissect it both for request and response */
/* Leave the statement below commented necessary in case of call to ndpi_get_partial_detection() */
/* if(ndpi_struct->dns_dont_dissect_response == 0) */ {
x++;
if(flow->packet.payload[x] != '\0') {
while((x < flow->packet.payload_packet_len)
&& (flow->packet.payload[x] != '\0')) {
x++;
}
x++;
}
x += 4;
if(dns_header.num_answers > 0) {
u_int16_t rsp_type;
u_int16_t num;
for(num = 0; num < dns_header.num_answers; num++) {
u_int16_t data_len;
if((x+6) >= flow->packet.payload_packet_len) {
break;
}
if((data_len = getNameLength(x, flow->packet.payload, flow->packet.payload_packet_len)) == 0) {
break;
} else
x += data_len;
rsp_type = get16(&x, flow->packet.payload);
flow->protos.dns.rsp_type = rsp_type;
/* here x points to the response "class" field */
if((x+12) <= flow->packet.payload_packet_len) {
x += 6;
data_len = get16(&x, flow->packet.payload);
if(((x + data_len) <= flow->packet.payload_packet_len)
&& (((rsp_type == 0x1) && (data_len == 4)) /* A */
#ifdef NDPI_DETECTION_SUPPORT_IPV6
|| ((rsp_type == 0x1c) && (data_len == 16)) /* AAAA */
#endif
)) {
memcpy(&flow->protos.dns.rsp_addr, flow->packet.payload + x, data_len);
}
}
break;
}
}
}
} else
invalid = 1;
}
if(invalid) {
NDPI_EXCLUDE_PROTO(ndpi_struct, flow);
return;
}
/* extract host name server */
max_len = sizeof(flow->host_server_name)-1;
off = sizeof(struct ndpi_dns_packet_header) + payload_offset;
while(j < max_len && off < flow->packet.payload_packet_len && flow->packet.payload[off] != '\0') {
uint8_t c,cl = flow->packet.payload[off++];
if( (cl & 0xc0) != 0 || // we not support compressed names in query
off + cl >= flow->packet.payload_packet_len) {
j = 0; break;
}
if(j && j < max_len) flow->host_server_name[j++] = '.';
while(j < max_len && cl != 0) {
c = flow->packet.payload[off++];
flow->host_server_name[j++] = dns_validchar[c >> 5] & (1 << (c & 0x1f)) ? c:'_';
cl--;
}
}
flow->host_server_name[j] = '\0';
if(is_query && (ndpi_struct->dns_dont_dissect_response == 0)) {
// dpi_set_detected_protocol(ndpi_struct, flow, (d_port == 5355) ? NDPI_PROTOCOL_LLMNR : NDPI_PROTOCOL_DNS, NDPI_PROTOCOL_UNKNOWN);
return; /* The response will set the verdict */
}
flow->protos.dns.num_queries = (u_int8_t)dns_header.num_queries,
flow->protos.dns.num_answers = (u_int8_t) (dns_header.num_answers + dns_header.authority_rrs + dns_header.additional_rrs);
if(j > 0) {
ndpi_protocol_match_result ret_match;
ndpi_match_host_subprotocol(ndpi_struct, flow,
(char *)flow->host_server_name,
strlen((const char*)flow->host_server_name),
&ret_match,
NDPI_PROTOCOL_DNS);
}
#ifdef DNS_DEBUG
NDPI_LOG_DBG2(ndpi_struct, "[num_queries=%d][num_answers=%d][reply_code=%u][rsp_type=%u][host_server_name=%s]\n",
flow->protos.dns.num_queries, flow->protos.dns.num_answers,
flow->protos.dns.reply_code, flow->protos.dns.rsp_type, flow->host_server_name
);
#endif
if(flow->packet.detected_protocol_stack[0] == NDPI_PROTOCOL_UNKNOWN) {
/**
Do not set the protocol with DNS if ndpi_match_host_subprotocol() has
matched a subprotocol
**/
NDPI_LOG_INFO(ndpi_struct, "found DNS\n");
ndpi_set_detected_protocol(ndpi_struct, flow, (d_port == 5355) ? NDPI_PROTOCOL_LLMNR : NDPI_PROTOCOL_DNS, NDPI_PROTOCOL_UNKNOWN);
} else {
NDPI_EXCLUDE_PROTO(ndpi_struct, flow);
}
}
}
}
void init_dns_dissector(struct ndpi_detection_module_struct *ndpi_struct, u_int32_t *id, NDPI_PROTOCOL_BITMASK *detection_bitmask)
{
ndpi_set_bitmask_protocol_detection("DNS", ndpi_struct, detection_bitmask, *id,
NDPI_PROTOCOL_DNS,
ndpi_search_dns,
NDPI_SELECTION_BITMASK_PROTOCOL_V4_V6_TCP_OR_UDP_WITH_PAYLOAD_WITHOUT_RETRANSMISSION,
SAVE_DETECTION_BITMASK_AS_UNKNOWN,
ADD_TO_DETECTION_BITMASK);
*id += 1;
}