/*
* rtp.c
*
* Copyright (C) 2009-11 - ipoque GmbH
* Copyright (C) 2011-22 - 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_RTP
#include "ndpi_api.h"
#include "ndpi_private.h"
#define RTP_MIN_HEADER 12
#define RTCP_MIN_HEADER 8
/* https://www.iana.org/assignments/rtp-parameters/rtp-parameters.xhtml */
int is_valid_rtp_payload_type(uint8_t type)
{
if(!(type <= 34 || (type >= 96 && type <= 127)))
return 0;
return 1;
}
u_int8_t rtp_get_stream_type(u_int8_t payloadType, ndpi_multimedia_flow_type *s_type)
{
switch(payloadType) {
case 0: /* G.711 u-Law */
case 3: /* GSM 6.10 */
case 4: /* G.723.1 */
case 8: /* G.711 A-Law */
case 9: /* G.722 */
case 13: /* Comfort Noise */
case 96: /* Dynamic RTP */
case 97: /* Redundant Audio Data Payload */
case 98: /* DynamicRTP-Type-98 (Zoom) */
case 101: /* DTMF */
case 103: /* SILK Narrowband */
case 104: /* SILK Wideband */
case 111: /* Siren */
case 112: /* G.722.1 */
case 114: /* RT Audio Wideband */
case 115: /* RT Audio Narrowband */
case 116: /* G.726 */
case 117: /* G.722 */
case 118: /* Comfort Noise Wideband */
*s_type = ndpi_multimedia_audio_flow;
return(1);
case 34: /* H.263 [MS-H26XPF] */
case 121: /* RT Video */
case 122: /* H.264 [MS-H264PF] */
case 123: /* H.264 FEC [MS-H264PF] */
case 127: /* x-data */
*s_type = ndpi_multimedia_video_flow;
return(1);
default:
*s_type = ndpi_multimedia_unknown_flow;
return(0);
}
}
static int is_valid_rtcp_payload_type(uint8_t type) {
return (type >= 192 && type <= 213);
}
int is_rtp_or_rtcp(struct ndpi_detection_module_struct *ndpi_struct,
const u_int8_t *payload, u_int16_t payload_len, u_int16_t *seq)
{
u_int8_t csrc_count, ext_header;
u_int16_t ext_len;
u_int32_t min_len;
if(payload_len < 2)
return NO_RTP_RTCP;
if((payload[0] & 0xC0) != 0x80) { /* Version 2 */
NDPI_LOG_DBG(ndpi_struct, "Not version 2\n");
return NO_RTP_RTCP;
}
if(is_valid_rtp_payload_type(payload[1] & 0x7F) &&
payload_len >= RTP_MIN_HEADER) {
/* RTP */
csrc_count = payload[0] & 0x0F;
ext_header = !!(payload[0] & 0x10);
min_len = RTP_MIN_HEADER + 4 * csrc_count + 4 * ext_header;
if(ext_header) {
if(min_len > payload_len) {
NDPI_LOG_DBG(ndpi_struct, "Too short (a) %d vs %d\n", min_len, payload_len);
return NO_RTP_RTCP;
}
ext_len = ntohs(*(unsigned short *)&payload[min_len - 2]);
min_len += ext_len * 4;
}
if(min_len > payload_len) {
NDPI_LOG_DBG(ndpi_struct, "Too short (b) %d vs %d\n", min_len, payload_len);
return NO_RTP_RTCP;
}
/* Check on padding doesn't work because:
* we may have multiple RTP packets in the same TCP/UDP datagram
* with SRTP, padding_length field is encrypted */
if(seq)
*seq = ntohs(*(unsigned short *)&payload[2]);
return IS_RTP;
} else if(is_valid_rtcp_payload_type(payload[1]) &&
payload_len >= RTCP_MIN_HEADER) {
min_len = (ntohs(*(unsigned short *)&payload[2]) + 1) * 4;
if(min_len > payload_len) {
NDPI_LOG_DBG(ndpi_struct, "Too short (c) %d vs %d\n", min_len, payload_len);
return NO_RTP_RTCP;
}
return IS_RTCP;
}
NDPI_LOG_DBG(ndpi_struct, "not RTP/RTCP\n");
return NO_RTP_RTCP;
}
static void ndpi_int_rtp_add_connection(struct ndpi_detection_module_struct *ndpi_struct,
struct ndpi_flow_struct *flow,
u_int16_t proto)
{
ndpi_set_detected_protocol(ndpi_struct, flow,
NDPI_PROTOCOL_UNKNOWN, proto,
NDPI_CONFIDENCE_DPI);
if(ndpi_struct->cfg.rtp_search_for_stun) {
/* It makes sense to look for STUN only if we didn't capture the entire flow,
from the beginning */
if(!(flow->l4_proto == IPPROTO_TCP && ndpi_seen_flow_beginning(flow))) {
NDPI_LOG_DBG(ndpi_struct, "Enabling (STUN) extra dissection\n");
switch_extra_dissection_to_stun(ndpi_struct, flow);
}
}
}
/* *************************************************************** */
static void ndpi_rtp_search(struct ndpi_detection_module_struct *ndpi_struct,
struct ndpi_flow_struct *flow) {
u_int8_t is_rtp;
struct ndpi_packet_struct *packet = &ndpi_struct->packet;
const u_int8_t *payload = packet->payload;
u_int16_t payload_len = packet->payload_packet_len;
u_int16_t seq;
if(packet->tcp != NULL) {
payload += 2; /* Skip the length field */
payload_len -= 2;
}
NDPI_LOG_DBG(ndpi_struct, "search RTP (stage %d/%d)\n", flow->rtp_stage, flow->rtcp_stage);
/* * Let some "unknown" packets at the beginning:
* search for 3/4 consecutive RTP/RTCP packets.
* Wait a little longer (4 vs 3 pkts) for RTCP to try to tell if there are only
* RTCP packets in the flow or if RTP/RTCP are multiplexed together */
if(flow->packet_counter > 3 &&
flow->rtp_stage == 0 &&
flow->rtcp_stage == 0) {
NDPI_EXCLUDE_PROTO(ndpi_struct, flow);
NDPI_EXCLUDE_PROTO_EXT(ndpi_struct, flow, NDPI_PROTOCOL_RTCP);
return;
}
is_rtp = is_rtp_or_rtcp(ndpi_struct, payload, payload_len, &seq);
if(is_rtp == IS_RTP) {
if(flow->rtp_stage == 2) {
if(flow->l4.udp.line_pkts[0] >= 2 && flow->l4.udp.line_pkts[1] >= 2) {
/* It seems that it is a LINE stuff; let its dissector to evaluate */
} else if(flow->l4.udp.epicgames_stage > 0) {
/* It seems that it is a EpicGames stuff; let its dissector to evaluate */
} else if(flow->rtp_seq_set[packet->packet_direction] &&
flow->rtp_seq[packet->packet_direction] == seq) {
/* Simple heuristic to avoid false positives. tradeoff between:
* consecutive RTP packets should have different sequence number
* we should handle duplicated traffic */
NDPI_LOG_DBG(ndpi_struct, "Same seq on consecutive pkts\n");
flow->rtp_stage = 0;
flow->rtcp_stage = 0;
NDPI_EXCLUDE_PROTO(ndpi_struct, flow);
NDPI_EXCLUDE_PROTO_EXT(ndpi_struct, flow, NDPI_PROTOCOL_RTCP);
} else {
rtp_get_stream_type(payload[1] & 0x7F, &flow->flow_multimedia_type);
NDPI_LOG_INFO(ndpi_struct, "Found RTP\n");
ndpi_int_rtp_add_connection(ndpi_struct, flow, NDPI_PROTOCOL_RTP);
}
return;
}
if(flow->rtp_stage == 0) {
flow->rtp_seq[packet->packet_direction] = seq;
flow->rtp_seq_set[packet->packet_direction] = 1;
}
flow->rtp_stage += 1;
} else if(is_rtp == IS_RTCP && flow->rtp_stage > 0) {
/* RTCP after (some) RTP. Keep looking for RTP */
} else if(is_rtp == IS_RTCP && flow->rtp_stage == 0) {
if(flow->rtcp_stage == 3) {
NDPI_LOG_INFO(ndpi_struct, "Found RTCP\n");
ndpi_int_rtp_add_connection(ndpi_struct, flow, NDPI_PROTOCOL_RTCP);
return;
}
flow->rtcp_stage += 1;
} else {
if(flow->rtp_stage || flow->rtcp_stage) {
u_int32_t unused;
u_int16_t app_proto = NDPI_PROTOCOL_UNKNOWN;
/* TODO: we should switch to the demultiplexing-code in stun dissector */
if(is_stun(ndpi_struct, flow, &app_proto) != 0 &&
!is_dtls(packet->payload, packet->payload_packet_len, &unused)) {
flow->rtp_stage = 0;
flow->rtcp_stage = 0;
NDPI_EXCLUDE_PROTO(ndpi_struct, flow);
NDPI_EXCLUDE_PROTO_EXT(ndpi_struct, flow, NDPI_PROTOCOL_RTCP);
}
} else if(flow->packet_counter > 3) {
NDPI_EXCLUDE_PROTO(ndpi_struct, flow);
NDPI_EXCLUDE_PROTO_EXT(ndpi_struct, flow, NDPI_PROTOCOL_RTCP);
}
}
}
/* *************************************************************** */
/* https://datatracker.ietf.org/doc/html/rfc4571
* message format for RTP/RTCP over TCP:
* 0 1 2 3
* 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
* ---------------------------------------------------------------
* | LENGTH | RTP or RTCP packet ... |
* ---------------------------------------------------------------
*/
static void ndpi_search_rtp_tcp(struct ndpi_detection_module_struct *ndpi_struct,
struct ndpi_flow_struct *flow)
{
struct ndpi_packet_struct *packet = &ndpi_struct->packet;
const u_int8_t *payload = packet->payload;
if(packet->payload_packet_len < 4){ /* (2) len field + (2) min rtp/rtcp*/
NDPI_EXCLUDE_PROTO(ndpi_struct, flow);
NDPI_EXCLUDE_PROTO_EXT(ndpi_struct, flow, NDPI_PROTOCOL_RTCP);
return;
}
u_int16_t len = ntohs(get_u_int16_t(payload, 0));
if(len + sizeof(len) != packet->payload_packet_len) { /*fragmented packets are not handled*/
NDPI_EXCLUDE_PROTO(ndpi_struct, flow);
NDPI_EXCLUDE_PROTO_EXT(ndpi_struct, flow, NDPI_PROTOCOL_RTCP);
} else {
ndpi_rtp_search(ndpi_struct, flow);
}
}
/* *************************************************************** */
static void ndpi_search_rtp_udp(struct ndpi_detection_module_struct *ndpi_struct,
struct ndpi_flow_struct *flow)
{
struct ndpi_packet_struct *packet = &ndpi_struct->packet;
u_int16_t source = ntohs(packet->udp->source);
u_int16_t dest = ntohs(packet->udp->dest);
/*
* XXX: not sure if rtp/rtcp over tcp will also mix with Ethereum
* for now, will not add it unitl we have a false positive.
*/
if((source == 30303) || (dest == 30303 /* Avoid to mix it with Ethereum that looks alike */)
|| (dest == 5355 /* LLMNR_PORT */)
|| (dest == 5353 /* MDNS_PORT */)
|| (dest == 9600 /* FINS_PORT */)
|| (dest <= 1023)){
NDPI_EXCLUDE_PROTO(ndpi_struct, flow);
NDPI_EXCLUDE_PROTO_EXT(ndpi_struct, flow, NDPI_PROTOCOL_RTCP);
return;
}
ndpi_rtp_search(ndpi_struct, flow);
}
/* *************************************************************** */
static void ndpi_search_rtp(struct ndpi_detection_module_struct *ndpi_struct, struct ndpi_flow_struct *flow)
{
struct ndpi_packet_struct *packet = &ndpi_struct->packet;
if(packet->tcp != NULL) {
ndpi_search_rtp_tcp(ndpi_struct, flow);
} else {
ndpi_search_rtp_udp(ndpi_struct, flow);
}
}
/* *************************************************************** */
void init_rtp_dissector(struct ndpi_detection_module_struct *ndpi_struct,
u_int32_t *id) {
ndpi_set_bitmask_protocol_detection("RTP", ndpi_struct, *id,
NDPI_PROTOCOL_RTP,
ndpi_search_rtp,
NDPI_SELECTION_BITMASK_PROTOCOL_V4_V6_TCP_OR_UDP_WITH_PAYLOAD_WITHOUT_RETRANSMISSION,
SAVE_DETECTION_BITMASK_AS_UNKNOWN,
ADD_TO_DETECTION_BITMASK);
*id += 1;
}