/*
* openvpn.c
*
* Copyright (C) 2011-21 - 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_OPENVPN
#include "ndpi_api.h"
/*
* OpenVPN TCP / UDP Detection - 128/160 hmac
*
* Detection based upon these openvpn protocol properties:
* - opcode
* - packet ID
* - session ID
*
* Two (good) packets are needed to perform detection.
* - First packet from client: save session ID
* - Second packet from server: report saved session ID
*
* TODO
* - Support PSK only mode (instead of TLS)
* - Support PSK + TLS mode (PSK used for early authentication)
* - TLS certificate extraction
*
*/
#define P_CONTROL_HARD_RESET_CLIENT_V1 (0x01 << 3)
#define P_CONTROL_HARD_RESET_CLIENT_V2 (0x07 << 3)
#define P_CONTROL_HARD_RESET_SERVER_V1 (0x02 << 3)
#define P_CONTROL_HARD_RESET_SERVER_V2 (0x08 << 3)
#define P_OPCODE_MASK 0xF8
#define P_SHA1_HMAC_SIZE 20
#define P_HMAC_128 16 // (RSA-)MD5, (RSA-)MD4, ..others
#define P_HMAC_160 20 // (RSA-|DSA-)SHA(1), ..others, SHA1 is openvpn default
#define P_HARD_RESET_PACKET_ID_OFFSET(hmac_size) (9 + hmac_size)
#define P_PACKET_ID_ARRAY_LEN_OFFSET(hmac_size) (P_HARD_RESET_PACKET_ID_OFFSET(hmac_size) + 8)
#define P_HARD_RESET_CLIENT_MAX_COUNT 5
static
#ifndef WIN32
inline
#endif
u_int32_t get_packet_id(const u_int8_t * payload, u_int8_t hms) {
return(ntohl(*(u_int32_t*)(payload + P_HARD_RESET_PACKET_ID_OFFSET(hms))));
}
static
#ifndef WIN32
inline
#endif
int8_t check_pkid_and_detect_hmac_size(const u_int8_t * payload) {
// try to guess
if(get_packet_id(payload, P_HMAC_160) == 1)
return P_HMAC_160;
if(get_packet_id(payload, P_HMAC_128) == 1)
return P_HMAC_128;
return(-1);
}
void ndpi_search_openvpn(struct ndpi_detection_module_struct* ndpi_struct,
struct ndpi_flow_struct* flow) {
struct ndpi_packet_struct* packet = &flow->packet;
const u_int8_t * ovpn_payload = packet->payload;
const u_int8_t * session_remote;
u_int8_t opcode;
u_int8_t alen;
int8_t hmac_size;
int8_t failed = 0;
/* No u_ */int16_t ovpn_payload_len = packet->payload_packet_len;
if(ovpn_payload_len >= 40) {
// skip openvpn TCP transport packet size
if(packet->tcp != NULL)
ovpn_payload += 2, ovpn_payload_len -= 2;;
opcode = ovpn_payload[0] & P_OPCODE_MASK;
if(packet->udp) {
#ifdef DEBUG
printf("[packet_id: %u][opcode: %u][Packet ID: %d][%u <-> %u][len: %u]\n",
flow->num_processed_pkts,
opcode, check_pkid_and_detect_hmac_size(ovpn_payload),
htons(packet->udp->source), htons(packet->udp->dest), ovpn_payload_len);
#endif
if(
(flow->num_processed_pkts == 1)
&& (
((ovpn_payload_len == 112)
&& ((opcode == 168) || (opcode == 192))
)
|| ((ovpn_payload_len == 80)
&& ((opcode == 184) || (opcode == 88) || (opcode == 160) || (opcode == 168) || (opcode == 200)))
)) {
NDPI_LOG_INFO(ndpi_struct,"found openvpn\n");
ndpi_set_detected_protocol(ndpi_struct, flow, NDPI_PROTOCOL_OPENVPN, NDPI_PROTOCOL_UNKNOWN);
return;
}
}
if(flow->ovpn_counter < P_HARD_RESET_CLIENT_MAX_COUNT && (opcode == P_CONTROL_HARD_RESET_CLIENT_V1 ||
opcode == P_CONTROL_HARD_RESET_CLIENT_V2)) {
if(check_pkid_and_detect_hmac_size(ovpn_payload) > 0) {
memcpy(flow->ovpn_session_id, ovpn_payload+1, 8);
NDPI_LOG_DBG2(ndpi_struct,
"session key: %02x%02x%02x%02x%02x%02x%02x%02x\n",
flow->ovpn_session_id[0], flow->ovpn_session_id[1], flow->ovpn_session_id[2], flow->ovpn_session_id[3],
flow->ovpn_session_id[4], flow->ovpn_session_id[5], flow->ovpn_session_id[6], flow->ovpn_session_id[7]);
}
} else if(flow->ovpn_counter >= 1 && flow->ovpn_counter <= P_HARD_RESET_CLIENT_MAX_COUNT &&
(opcode == P_CONTROL_HARD_RESET_SERVER_V1 || opcode == P_CONTROL_HARD_RESET_SERVER_V2)) {
hmac_size = check_pkid_and_detect_hmac_size(ovpn_payload);
if(hmac_size > 0) {
u_int16_t offset = P_PACKET_ID_ARRAY_LEN_OFFSET(hmac_size);
alen = ovpn_payload[offset];
if (alen > 0) {
offset += 1 + alen * 4;
if((offset+8) <= ovpn_payload_len) {
session_remote = &ovpn_payload[offset];
if(memcmp(flow->ovpn_session_id, session_remote, 8) == 0) {
NDPI_LOG_INFO(ndpi_struct,"found openvpn\n");
ndpi_set_detected_protocol(ndpi_struct, flow, NDPI_PROTOCOL_OPENVPN, NDPI_PROTOCOL_UNKNOWN);
return;
} else {
NDPI_LOG_DBG2(ndpi_struct,
"key mismatch: %02x%02x%02x%02x%02x%02x%02x%02x\n",
session_remote[0], session_remote[1], session_remote[2], session_remote[3],
session_remote[4], session_remote[5], session_remote[6], session_remote[7]);
failed = 1;
}
} else
failed = 1;
} else
failed = 1;
} else
failed = 1;
} else
failed = 1;
flow->ovpn_counter++;
if(failed)
NDPI_EXCLUDE_PROTO(ndpi_struct, flow);
}
if(flow->packet_counter > 5)
NDPI_EXCLUDE_PROTO(ndpi_struct, flow);
}
void init_openvpn_dissector(struct ndpi_detection_module_struct *ndpi_struct,
u_int32_t *id, NDPI_PROTOCOL_BITMASK *detection_bitmask) {
ndpi_set_bitmask_protocol_detection("OpenVPN", ndpi_struct, detection_bitmask, *id,
NDPI_PROTOCOL_OPENVPN,
ndpi_search_openvpn,
NDPI_SELECTION_BITMASK_PROTOCOL_TCP_OR_UDP_WITH_PAYLOAD,
SAVE_DETECTION_BITMASK_AS_UNKNOWN,
ADD_TO_DETECTION_BITMASK);
*id += 1;
}