/*
* dns.c
*
* Copyright (C) 2012-21 - 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
#define DNS_PORT 53
#define LLMNR_PORT 5355
#define MDNS_PORT 5353
static void ndpi_search_dns(struct ndpi_detection_module_struct *ndpi_struct,
struct ndpi_flow_struct *flow);
/* *********************************************** */
static void ndpi_check_dns_type(struct ndpi_detection_module_struct *ndpi_struct,
struct ndpi_flow_struct *flow,
u_int16_t dns_type) {
/* https://en.wikipedia.org/wiki/List_of_DNS_record_types */
switch(dns_type) {
/* Obsolete record types */
case 3:
case 4:
case 254:
case 7:
case 8:
case 9:
case 14:
case 253:
case 11:
case 33:
case 10:
case 38:
case 30:
case 25:
case 24:
case 13:
case 17:
case 19:
case 20:
case 21:
case 22:
case 23:
case 26:
case 31:
case 32:
case 34:
case 42:
case 40:
case 27:
case 100:
case 101:
case 102:
case 103:
case 99:
case 56:
case 57:
case 58:
case 104:
case 105:
case 106:
case 107:
case 259:
ndpi_set_risk(flow, NDPI_DNS_SUSPICIOUS_TRAFFIC);
break;
}
}
/* *********************************************** */
static u_int16_t checkPort(u_int16_t port) {
switch(port) {
case DNS_PORT:
return(NDPI_PROTOCOL_DNS);
break;
case LLMNR_PORT:
return(NDPI_PROTOCOL_LLMNR);
break;
case MDNS_PORT:
return(NDPI_PROTOCOL_MDNS);
break;
}
return(0);
}
/* *********************************************** */
static u_int16_t checkDNSSubprotocol(u_int16_t sport, u_int16_t dport) {
u_int16_t rc = checkPort(sport);
if(rc == 0)
return(checkPort(dport));
else
return(rc);
}
/* *********************************************** */
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(i >= payloadLen)
return(0);
else 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
};
/* *********************************************** */
static int search_valid_dns(struct ndpi_detection_module_struct *ndpi_struct,
struct ndpi_flow_struct *flow,
struct ndpi_dns_packet_header *dns_header,
int payload_offset, u_int8_t *is_query) {
int x = payload_offset;
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 {
ndpi_set_risk(flow, NDPI_MALFORMED_PACKET);
return(1 /* invalid */);
}
if(*is_query) {
/* DNS Request */
if((dns_header->num_queries > 0) && (dns_header->num_queries <= NDPI_MAX_DNS_REQUESTS)
// && (dns_header->num_answers == 0)
&& (((dns_header->flags & 0x2800) == 0x2800 /* Dynamic DNS Update */)
|| (dns_header->flags == 0x00) /* Standard Query */
|| ((dns_header->num_answers == 0) && (dns_header->authority_rrs == 0)))) {
/* This is a good query */
while(x+2 < 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);
printf("[DNS] [request] query_type=%d\n", flow->protos.dns.query_type);
#endif
break;
} else
x++;
}
} else {
ndpi_set_risk(flow, NDPI_MALFORMED_PACKET);
return(1 /* invalid */);
}
} 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() */
x++;
if(x < flow->packet.payload_packet_len && 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;
if((x+2) >= flow->packet.payload_packet_len) {
break;
}
rsp_type = get16(&x, flow->packet.payload);
#ifdef DNS_DEBUG
printf("[DNS] [response] response_type=%d\n", rsp_type);
#endif
ndpi_check_dns_type(ndpi_struct, flow, rsp_type);
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) {
// printf("[rsp_type: %u][data_len: %u]\n", rsp_type, data_len);
if(rsp_type == 0x05 /* CNAME */) {
x += data_len;
continue; /* Skip CNAME */
}
if((((rsp_type == 0x1) && (data_len == 4)) /* A */
|| ((rsp_type == 0x1c) && (data_len == 16)) /* AAAA */
)) {
memcpy(&flow->protos.dns.rsp_addr, flow->packet.payload + x, data_len);
}
}
}
break;
}
}
if((flow->packet.detected_protocol_stack[0] == NDPI_PROTOCOL_DNS)
|| (flow->packet.detected_protocol_stack[1] == NDPI_PROTOCOL_DNS)) {
/* Request already set the protocol */
// flow->extra_packets_func = NULL; /* Removed so the caller can keep dissecting DNS flows */
} else {
/* We missed the request */
u_int16_t s_port = flow->packet.udp ? ntohs(flow->packet.udp->source) : ntohs(flow->packet.tcp->source);
ndpi_set_detected_protocol(ndpi_struct, flow, checkPort(s_port), NDPI_PROTOCOL_UNKNOWN);
}
}
}
/* Valid */
return(0);
}
/* *********************************************** */
static int search_dns_again(struct ndpi_detection_module_struct *ndpi_struct, struct ndpi_flow_struct *flow) {
/* possibly dissect the DNS reply */
ndpi_search_dns(ndpi_struct, flow);
/* Possibly more processing */
return(1);
}
/* *********************************************** */
static void ndpi_search_dns(struct ndpi_detection_module_struct *ndpi_struct, struct ndpi_flow_struct *flow) {
int 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;
}
if(((s_port == DNS_PORT) || (d_port == DNS_PORT)
|| (s_port == MDNS_PORT) || (d_port == MDNS_PORT)
|| (d_port == LLMNR_PORT))
&& (flow->packet.payload_packet_len > sizeof(struct ndpi_dns_packet_header)+payload_offset)) {
struct ndpi_dns_packet_header dns_header;
int j = 0, max_len, off;
int invalid = search_valid_dns(ndpi_struct, flow, &dns_header, payload_offset, &is_query);
ndpi_protocol ret;
u_int num_queries, idx;
ret.master_protocol = NDPI_PROTOCOL_UNKNOWN;
ret.app_protocol = (d_port == LLMNR_PORT) ? NDPI_PROTOCOL_LLMNR : ((d_port == MDNS_PORT) ? NDPI_PROTOCOL_MDNS : NDPI_PROTOCOL_DNS);
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;
/* Before continuing let's dissect the following queries to see if they are valid */
for(idx=off, num_queries=0; (num_queries < dns_header.num_queries) && (idx < flow->packet.payload_packet_len);) {
u_int16_t i, tot_len = 0;
for(i=idx; i<flow->packet.payload_packet_len;) {
u_int8_t name_len = flow->packet.payload[i]; /* Lenght of the individual name blocks aaa.bbb.com */
if(name_len == 0) {
tot_len++; /* \0 */
/* End of query */
break;
} else if((name_len & 0xC0) == 0xC0) {
name_len = 1;
}
#ifdef DNS_DEBUG
printf("[DNS] [name_len: %u]\n", name_len);
#endif
i += name_len+1, tot_len += name_len+1;
} /* for */
#ifdef DNS_DEBUG
printf("[DNS] [tot_len: %u]\n\n", tot_len);
#endif
if(((i+4) > flow->packet.payload_packet_len)
|| ((flow->packet.payload[i+1] == 0x0) && (flow->packet.payload[i+2] == 0x0)) /* Query type cannot be 0 */
|| (tot_len > 253)
)
{
/* Invalid */
#ifdef DNS_DEBUG
printf("[DNS] Invalid query len [%u >= %u]\n", i+4, flow->packet.payload_packet_len);
#endif
ndpi_set_risk(flow, NDPI_MALFORMED_PACKET);
break;
} else
idx += tot_len+4, num_queries++;
} /* for */
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)) {
u_int32_t shift;
c = flow->packet.payload[off++];
shift = ((u_int32_t) 1) << (c & 0x1f);
flow->host_server_name[j++] = tolower((dns_validchar[c >> 5] & shift) ? c : '_');
cl--;
}
}
flow->host_server_name[j] = '\0';
if(j > 0) {
ndpi_protocol_match_result ret_match;
ndpi_check_dga_name(ndpi_struct, flow, (char*)flow->host_server_name, 1);
ret.app_protocol = ndpi_match_host_subprotocol(ndpi_struct, flow,
(char *)flow->host_server_name,
strlen((const char*)flow->host_server_name),
&ret_match,
NDPI_PROTOCOL_DNS);
if(ret_match.protocol_category != NDPI_PROTOCOL_CATEGORY_UNSPECIFIED)
flow->category = ret_match.protocol_category;
if(ret.app_protocol == NDPI_PROTOCOL_UNKNOWN)
ret.master_protocol = checkDNSSubprotocol(s_port, d_port);
else
ret.master_protocol = NDPI_PROTOCOL_DNS;
}
/* Report if this is a DNS query or reply */
flow->protos.dns.is_query = is_query;
if(is_query) {
/* In this case we say that the protocol has been detected just to let apps carry on with their activities */
ndpi_set_detected_protocol(ndpi_struct, flow, ret.app_protocol, ret.master_protocol);
/* This is necessary to inform the core to call this dissector again */
flow->check_extra_packets = 1;
/* Don't use just 1 as in TCP DNS more packets could be returned (e.g. ACK). */
flow->max_extra_packets_to_check = 5;
flow->extra_packets_func = search_dns_again;
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);
#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, ret.app_protocol, ret.master_protocol);
} else {
if((flow->packet.detected_protocol_stack[0] == NDPI_PROTOCOL_DNS)
|| (flow->packet.detected_protocol_stack[1] == NDPI_PROTOCOL_DNS))
;
else
NDPI_EXCLUDE_PROTO(ndpi_struct, flow);
}
}
if(flow->packet_counter > 3)
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;
}