/*
* skype.c
*
* Copyright (C) 2017-22 - ntop.org
*
* 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_SKYPE_TEAMS
#include "ndpi_api.h"
static int is_port(u_int16_t a, u_int16_t b, u_int16_t c) {
return(((a == c) || (b == c)) ? 1 : 0);
}
static int ndpi_check_skype_udp_again(struct ndpi_detection_module_struct *ndpi_struct, struct ndpi_flow_struct *flow) {
struct ndpi_packet_struct *packet = &ndpi_struct->packet;
u_int32_t payload_len = packet->payload_packet_len;
int i;
const uint8_t id_flags_iv_crc_len = 11;
const uint8_t crc_len = sizeof(flow->l4.udp.skype_crc);
const uint8_t crc_offset = id_flags_iv_crc_len - crc_len;
if (flow->packet_counter > 2)
{
/*
* Process only one packet after the initial packet received.
* This is required to prevent fals-positives with other protocols e.g. dnscrypt.
*/
return 0;
}
if ((payload_len >= id_flags_iv_crc_len) && (packet->payload[2] == 0x02 /* Payload flag */ )) {
u_int8_t detected = 1;
/* Check if both packets have the same CRC */
for (i = 0; i < crc_len && detected; i++) {
if (packet->payload[crc_offset + i] != flow->l4.udp.skype_crc[i])
detected = 0;
}
if (detected) {
ndpi_set_detected_protocol(ndpi_struct, flow, NDPI_PROTOCOL_SKYPE_TEAMS, NDPI_PROTOCOL_UNKNOWN, NDPI_CONFIDENCE_DPI);
flow->extra_packets_func = NULL;
/* Stop checking extra packets */
return 0;
}
}
/* Check more packets */
return 1;
}
static void ndpi_check_skype(struct ndpi_detection_module_struct *ndpi_struct, struct ndpi_flow_struct *flow) {
struct ndpi_packet_struct *packet = &ndpi_struct->packet;
// const u_int8_t *packet_payload = packet->payload;
u_int32_t payload_len = packet->payload_packet_len;
/* No need to do ntohl() with 0xFFFFFFFF */
if(packet->iph
&& ((packet->iph->daddr == 0xFFFFFFFF /* 255.255.255.255 */)
|| ((ntohl(packet->iph->daddr) & 0xFFFFFF00) == 0xE0000000 /* multicast */)
)) {
NDPI_EXCLUDE_PROTO(ndpi_struct, flow);
return;
}
if(flow->host_server_name[0] != '\0')
return;
// UDP check
if(packet->udp != NULL) {
flow->l4.udp.skype_packet_id++;
if(flow->l4.udp.skype_packet_id < 5) {
u_int16_t sport = ntohs(packet->udp->source);
u_int16_t dport = ntohs(packet->udp->dest);
/* skype-to-skype */
if(is_port(sport, dport, 1119) /* It can be confused with battle.net */
|| is_port(sport, dport, 80) /* No HTTP-like protocols UDP/80 */
) {
;
} else {
/* Too many false positives */
if(((payload_len == 3) && ((packet->payload[2] & 0x0F)== 0x0d))
||
((payload_len >= 16)
&& (((packet->payload[0] & 0xC0) >> 6) == 0x02 /* RTPv2 */
|| (((packet->payload[0] & 0xF0) >> 4) == 0 /* Zoom */)
|| (((packet->payload[0] & 0xF0) >> 4) == 0x07 /* Skype */)
)
&& (packet->payload[0] != 0x30) /* Avoid invalid SNMP detection */
&& (packet->payload[0] != 0x00) /* Avoid invalid CAPWAP detection */
&& (packet->payload[2] == 0x02))) {
if(is_port(sport, dport, 8801)) {
ndpi_set_detected_protocol(ndpi_struct, flow, NDPI_PROTOCOL_ZOOM, NDPI_PROTOCOL_UNKNOWN, NDPI_CONFIDENCE_DPI);
} else if (payload_len >= 16 && packet->payload[0] != 0x01) /* Avoid invalid Cisco HSRP detection / RADIUS */ {
ndpi_set_detected_protocol(ndpi_struct, flow, NDPI_PROTOCOL_SKYPE_CALL, NDPI_PROTOCOL_SKYPE_TEAMS, NDPI_CONFIDENCE_DPI);
}
}
if (flow->detected_protocol_stack[0] == NDPI_PROTOCOL_UNKNOWN) {
const uint8_t id_flags_iv_crc_len = 11;
const uint8_t crc_len = sizeof(flow->l4.udp.skype_crc);
const uint8_t crc_offset = id_flags_iv_crc_len - crc_len;
if ((payload_len >= id_flags_iv_crc_len)
&& (packet->payload[2] == 0x02 /* Payload flag */ )
&& (payload_len >= (crc_offset+crc_len))
&& (!flow->extra_packets_func)) {
flow->check_extra_packets = 1;
flow->max_extra_packets_to_check = 5;
flow->extra_packets_func = ndpi_check_skype_udp_again;
memcpy(flow->l4.udp.skype_crc, &packet->payload[crc_offset], crc_len);
return;
}
}
}
// return;
}
NDPI_EXCLUDE_PROTO(ndpi_struct, flow);
return;
// TCP check
} else if((packet->tcp != NULL)
/* As the TCP skype heuristic is weak, we need to make sure no other protocols overlap */
&& (flow->guessed_host_protocol_id == NDPI_PROTOCOL_UNKNOWN)
&& (flow->guessed_protocol_id == NDPI_PROTOCOL_UNKNOWN)) {
flow->l4.tcp.skype_packet_id++;
if(flow->l4.tcp.skype_packet_id < 3) {
; /* Too early */
} else if((flow->l4.tcp.skype_packet_id == 3)
/* We have seen the 3-way handshake */
&& flow->l4.tcp.seen_syn
&& flow->l4.tcp.seen_syn_ack
&& flow->l4.tcp.seen_ack) {
/* Disabled this logic as it's too weak and leads to false positives */
#if 0
if((payload_len == 8) || (payload_len == 3) || (payload_len == 17)) {
// printf("[SKYPE] payload_len=%u\n", payload_len);
/* printf("[SKYPE] %u/%u\n", ntohs(packet->tcp->source), ntohs(packet->tcp->dest)); */
NDPI_LOG_INFO(ndpi_struct, "found skype\n");
ndpi_set_detected_protocol(ndpi_struct, flow, NDPI_PROTOCOL_SKYPE_TEAMS_CALL, NDPI_PROTOCOL_SKYPE_TEAMS, NDPI_CONFIDENCE_DPI);
} else {
// printf("NO [SKYPE] payload_len=%u\n", payload_len);
}
/* printf("[SKYPE] [id: %u][len: %d]\n", flow->l4.tcp.skype_packet_id, payload_len); */
#endif
} else {
NDPI_EXCLUDE_PROTO(ndpi_struct, flow);
}
return;
}
}
void ndpi_search_skype(struct ndpi_detection_module_struct *ndpi_struct, struct ndpi_flow_struct *flow)
{
NDPI_LOG_DBG(ndpi_struct, "search skype\n");
/* skip marked packets */
if(flow->detected_protocol_stack[0] != NDPI_PROTOCOL_SKYPE_TEAMS)
ndpi_check_skype(ndpi_struct, flow);
}
void init_skype_dissector(struct ndpi_detection_module_struct *ndpi_struct, u_int32_t *id, NDPI_PROTOCOL_BITMASK *detection_bitmask)
{
ndpi_set_bitmask_protocol_detection("Skype", ndpi_struct, detection_bitmask, *id,
NDPI_PROTOCOL_SKYPE_TEAMS,
ndpi_search_skype,
NDPI_SELECTION_BITMASK_PROTOCOL_V4_V6_TCP_OR_UDP_WITH_PAYLOAD,
SAVE_DETECTION_BITMASK_AS_UNKNOWN,
ADD_TO_DETECTION_BITMASK);
*id += 1;
}