wireshark/epan/dissectors/packet-skype.c

/* packet-skype.c
 * Routines for the disassembly of Skype
 *
 * Copyright 2009 Joerg Mayer (see AUTHORS file)
 *
 * Wireshark - Network traffic analyzer
 * By Gerald Combs <gerald@wireshark.org>
 * Copyright 1998 Gerald Combs
 *
 * SPDX-License-Identifier: GPL-2.0-or-later
 */

/*
 * Documentation that formed the basis of the packet decoding:
 * https://github.com/matthiasbock/OpenSkype/wiki/Skype's-UDP-Format
 * For additional information see:
 *     https://gitlab.com/wireshark/wireshark/-/wikis/Skype
 *
 *  TODO:
 *  - Authentication
 *  - TCP
 *  - Conversation stuff (to obtain external IPs for decryption)
 *  - Decryption (with given keys)
 *  - Test CRC check (requires working decryption)
 *  - Heuristics to reliably detect Skype traffic - most likely impossible
 *    to implement in Wireshark (see
 *    https://gitlab.com/wireshark/wireshark/-/wikis/Skype)
 *  - Improve tests
 */

#include "config.h"

#include <epan/packet.h>
#include <epan/conversation.h>

void proto_register_skype(void);
void proto_reg_handoff_skype(void);

/* Things we may want to remember for a whole conversation */
typedef struct _skype_udp_conv_info_t {
	guint32 global_src_ip;
	guint32 global_dst_ip;
} skype_udp_conv_info_t;

/* protocol handles */
static int proto_skype = -1;

/* ett handles */
static int ett_skype = -1;

#define SKYPE_SOM_UNK_MASK	0xF0
#define SKYPE_SOM_TYPE_MASK	0x0F

/* hf elements */
/* Start of Message */
static int hf_skype_som_id = -1;
static int hf_skype_som_unk = -1;
static int hf_skype_som_type = -1;
/* Message body */
/* Unknown_0 */
static int hf_skype_unknown_0_unk1 = -1;
/* Payload */
static int hf_skype_payload_iv = -1;
static int hf_skype_payload_crc = -1;
static int hf_skype_payload_enc_data = -1;
/* Resend */
static int hf_skype_ffr_num = -1;
static int hf_skype_ffr_unk1 = -1;
static int hf_skype_ffr_iv = -1;
static int hf_skype_ffr_crc = -1;
static int hf_skype_ffr_enc_data = -1;
/* Nat info */
static int hf_skype_natinfo_srcip = -1;
static int hf_skype_natinfo_dstip = -1;
/* Nat request */
static int hf_skype_natrequest_srcip = -1;
static int hf_skype_natrequest_dstip = -1;
/* Audio */
static int hf_skype_audio_unk1 = -1;
/* Unknown_f */
static int hf_skype_unknown_f_unk1 = -1;
/* Unknown packet type */
static int hf_skype_unknown_packet = -1;


#define PROTO_SHORT_NAME "SKYPE"
#define PROTO_LONG_NAME "SKYPE"

typedef enum {
	SKYPE_TYPE_UNKNOWN_0 = 0,
	SKYPE_TYPE_PAYLOAD = 2,
	SKYPE_TYPE_FFR = 3,
	SKYPE_TYPE_NAT_INFO = 5,
	SKYPE_TYPE_NAT_REPEAT = 7,
	SKYPE_TYPE_AUDIO = 0xd,
	SKYPE_TYPE_UNKNOWN_F = 0xf
} skype_type_t;


static const value_string skype_type_vals[] = {
	{ SKYPE_TYPE_UNKNOWN_0,	"Unknown_0" },
	{ SKYPE_TYPE_PAYLOAD,	"Payload" },
	{ SKYPE_TYPE_FFR,	"Fragment/Forward/Resend" },
	{ SKYPE_TYPE_NAT_INFO ,	"NAT info" },
	{ SKYPE_TYPE_NAT_REPEAT,"NAT repeat" },
	{ SKYPE_TYPE_AUDIO,	"Audio" },
	{ SKYPE_TYPE_UNKNOWN_F,	"Unknown_F" },

	{ 0,	NULL }
};


static int
dissect_skype_tcp(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
{
	proto_item *ti;
	proto_tree *skype_tree = NULL;
	guint32 offset = 0;
	guint32 packet_length;
	guint8 packet_type;

	/* XXX: Just until we know how to decode skype over tcp */
	packet_type = 255;

	packet_length = tvb_captured_length(tvb);

	col_set_str(pinfo->cinfo, COL_PROTOCOL, PROTO_SHORT_NAME);
	col_add_str(pinfo->cinfo, COL_INFO, val_to_str(packet_type,
		skype_type_vals, "Type 0x%1x"));

	if (tree) {
		/* Start of message dissection */
		ti = proto_tree_add_item(tree, proto_skype, tvb, offset, -1,
		    ENC_NA);
		skype_tree = proto_item_add_subtree(ti, ett_skype);

		/* Body dissection */
		switch (packet_type) {

		default:
			proto_tree_add_item(skype_tree, hf_skype_unknown_packet, tvb, offset, -1,
				ENC_NA);
			offset = packet_length;
			break;
		}
	}
	return offset;
}

static int
dissect_skype_udp(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
{
	proto_item *ti;
	proto_tree *skype_tree = NULL;
	guint32 offset = 0;
	guint32 packet_length;
	guint8 packet_type, packet_unk;

	conversation_t   *conversation = NULL;
	skype_udp_conv_info_t *skype_udp_info;

	/* look up the conversation */
	conversation = find_or_create_conversation(pinfo);

	/* if conversation found get the data pointer that you stored */
	skype_udp_info = (skype_udp_conv_info_t *)conversation_get_proto_data(conversation, proto_skype);
	if (!skype_udp_info) {
		/* new conversation create local data structure */
		skype_udp_info = wmem_new(wmem_file_scope(), skype_udp_conv_info_t);
		skype_udp_info->global_src_ip = 0;
		skype_udp_info->global_dst_ip = 0;
		conversation_add_proto_data(conversation, proto_skype,
			skype_udp_info);
	}
	/* at this point the conversation data is ready */

	packet_type = tvb_get_guint8(tvb, 2) & SKYPE_SOM_TYPE_MASK;
	packet_unk = (tvb_get_guint8(tvb, 2) & SKYPE_SOM_UNK_MASK) >> 4;

	packet_length = tvb_captured_length(tvb);

	col_set_str(pinfo->cinfo, COL_PROTOCOL, PROTO_SHORT_NAME);
	col_add_str(pinfo->cinfo, COL_INFO, val_to_str(packet_type,
		skype_type_vals, "Type 0x%1x"));
	if (packet_unk) {
		col_append_fstr(pinfo->cinfo, COL_INFO, " Unk: %1x", packet_unk);
	}

	if (tree) {
		/* Start of message dissection */
		ti = proto_tree_add_item(tree, proto_skype, tvb, offset, -1,
		    ENC_NA);
		skype_tree = proto_item_add_subtree(ti, ett_skype);

		proto_tree_add_item(skype_tree, hf_skype_som_id, tvb, offset, 2,
			ENC_BIG_ENDIAN);
		offset += 2;
		proto_tree_add_item(skype_tree, hf_skype_som_unk, tvb, offset, 1,
			ENC_BIG_ENDIAN);
		proto_tree_add_item(skype_tree, hf_skype_som_type, tvb, offset, 1,
			ENC_BIG_ENDIAN);
		offset += 1;

		/* Body dissection */
		switch (packet_type) {

		case SKYPE_TYPE_UNKNOWN_0:
			proto_tree_add_item(skype_tree, hf_skype_unknown_0_unk1, tvb, offset, -1,
				ENC_NA);
			offset = packet_length;
			break;
		case SKYPE_TYPE_PAYLOAD:
			proto_tree_add_item(skype_tree, hf_skype_payload_iv, tvb, offset, 4,
				ENC_BIG_ENDIAN);
			offset += 4;
			proto_tree_add_item(skype_tree, hf_skype_payload_crc, tvb, offset, 4,
				ENC_BIG_ENDIAN);
			offset += 4;
			proto_tree_add_item(skype_tree, hf_skype_payload_enc_data, tvb, offset, -1,
				ENC_NA);
			offset = packet_length;
			break;
		case SKYPE_TYPE_FFR:
			proto_tree_add_item(skype_tree, hf_skype_ffr_num, tvb, offset, 1,
				ENC_BIG_ENDIAN);
			offset += 1;
			proto_tree_add_item(skype_tree, hf_skype_ffr_unk1, tvb, offset, 4,
				ENC_BIG_ENDIAN);
			offset += 4;
			proto_tree_add_item(skype_tree, hf_skype_ffr_iv, tvb, offset, 4,
				ENC_BIG_ENDIAN);
			offset += 4;
			proto_tree_add_item(skype_tree, hf_skype_ffr_crc, tvb, offset, 4,
				ENC_BIG_ENDIAN);
			offset += 4;
			proto_tree_add_item(skype_tree, hf_skype_ffr_enc_data, tvb, offset, -1,
				ENC_NA);
			offset = packet_length;
			break;
		case SKYPE_TYPE_NAT_INFO:
			proto_tree_add_item(skype_tree, hf_skype_natinfo_srcip, tvb, offset, 4,
				ENC_BIG_ENDIAN);
			skype_udp_info->global_src_ip = tvb_get_ipv4(tvb, offset);
			offset += 4;
			proto_tree_add_item(skype_tree, hf_skype_natinfo_dstip, tvb, offset, 4,
				ENC_BIG_ENDIAN);
			skype_udp_info->global_dst_ip = tvb_get_ipv4(tvb, offset);
			offset += 4;
			break;
		case SKYPE_TYPE_NAT_REPEAT:
			proto_tree_add_item(skype_tree, hf_skype_natrequest_srcip, tvb, offset, 4,
				ENC_BIG_ENDIAN);
			skype_udp_info->global_src_ip = tvb_get_ipv4(tvb, offset);
			offset += 4;
			proto_tree_add_item(skype_tree, hf_skype_natrequest_dstip, tvb, offset, 4,
				ENC_BIG_ENDIAN);
			skype_udp_info->global_dst_ip = tvb_get_ipv4(tvb, offset);
			offset += 4;
			break;
		case SKYPE_TYPE_AUDIO:
			proto_tree_add_item(skype_tree, hf_skype_audio_unk1, tvb, offset, -1,
				ENC_NA);
			offset = packet_length;
			break;
		case SKYPE_TYPE_UNKNOWN_F:
			proto_tree_add_item(skype_tree, hf_skype_unknown_f_unk1, tvb, offset, -1,
				ENC_NA);
			offset = packet_length;
			break;
		default:
			proto_tree_add_item(skype_tree, hf_skype_unknown_packet, tvb, offset, -1,
				ENC_NA);
			offset = packet_length;
			break;
		}
	}
	return offset;
}

static gboolean
test_skype_udp(tvbuff_t *tvb)
{
	/* Minimum of 3 bytes, check for valid message type */
	if (tvb_captured_length(tvb) > 3)
	{
		guint8 type = tvb_get_guint8(tvb, 2) & 0xF;
		if ( type == 0   ||
			/* FIXME: Extend this by minimum or exact length per message type */
			type == 2   ||
			type == 3   ||
			type == 5   ||
			type == 7   ||
			type == 0xd ||
			type == 0xf
			)
		{
			return TRUE;
		}
	}
	return FALSE;
}

static gboolean
dissect_skype_heur(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void *data _U_)
{
	if ( !test_skype_udp(tvb) ) {
		return FALSE;
	}

	dissect_skype_udp(tvb, pinfo, tree);
	return TRUE;
}

static int
dissect_skype_static(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void *data _U_)
{
	/*
	 * Don't test for valid packet - we only end here when
	 * the user did a decode-as.
	 */
	if (pinfo->ptype == PT_UDP) {
		return dissect_skype_udp(tvb, pinfo, tree);
	} else if (pinfo->ptype == PT_TCP) {
		return dissect_skype_tcp(tvb, pinfo, tree);
	}
	return 0;
}

void
proto_register_skype(void)
{
	static hf_register_info hf[] = {

	/* Start of message fields */
		{ &hf_skype_som_id,
		{ "ID",	"skype.som.id", FT_UINT16, BASE_HEX, NULL,
			0x0, "Message ID", HFILL }},

		{ &hf_skype_som_unk,
		{ "Unknown",	"skype.som.unk", FT_UINT8, BASE_HEX, NULL,
			SKYPE_SOM_UNK_MASK, NULL, HFILL }},

		{ &hf_skype_som_type,
		{ "Type",	"skype.som.type", FT_UINT8, BASE_HEX, VALS(skype_type_vals),
			SKYPE_SOM_TYPE_MASK, "Message type", HFILL }},

	/* Message body */

	/* Unknown_0 */
		{ &hf_skype_unknown_0_unk1,
		{ "Unknown1",   "skype.unknown_0.unk1", FT_BYTES, BASE_NONE, NULL,
			0x0, NULL, HFILL }},

	/* Payload */
		{ &hf_skype_payload_iv,
		{ "IV",   "skype.payload.iv", FT_UINT32, BASE_HEX, NULL,
			0x0, NULL, HFILL }},

		{ &hf_skype_payload_crc,
		{ "CRC",   "skype.payload.crc", FT_UINT32, BASE_HEX, NULL,
			0x0, NULL, HFILL }},

		{ &hf_skype_payload_enc_data,
		{ "Enc Data",   "skype.payload.encdata", FT_BYTES, BASE_NONE, NULL,
			0x0, NULL, HFILL }},

	/* Resend */
		{ &hf_skype_ffr_num,
		{ "Num",   "skype.ffr.num", FT_UINT8, BASE_HEX, NULL,
			0x0, NULL, HFILL }},

		{ &hf_skype_ffr_unk1,
		{ "Unk1",   "skype.ffr.unk1", FT_UINT32, BASE_HEX, NULL,
			0x0, NULL, HFILL }},

		{ &hf_skype_ffr_iv,
		{ "IV",   "skype.ffr.iv", FT_UINT32, BASE_HEX, NULL,
			0x0, NULL, HFILL }},

		{ &hf_skype_ffr_crc,
		{ "CRC",   "skype.ffr.crc", FT_UINT32, BASE_HEX, NULL,
			0x0, NULL, HFILL }},

		{ &hf_skype_ffr_enc_data,
		{ "Enc Data",   "skype.ffr.encdata", FT_BYTES, BASE_NONE, NULL,
			0x0, NULL, HFILL }},

	/* Nat info */
		{ &hf_skype_natinfo_srcip,
		{ "Src IP",   "skype.natinfo.srcip", FT_IPv4, BASE_NONE, NULL,
			0x0, "Global source IP", HFILL }},

		{ &hf_skype_natinfo_dstip,
		{ "Dst IP",   "skype.natinfo.dstip", FT_UINT32, BASE_HEX, NULL,
			0x0, "Global destination IP", HFILL }},

	/* Nat request */
		{ &hf_skype_natrequest_srcip,
		{ "Src IP",   "skype.natrequest.srcip", FT_IPv4, BASE_NONE, NULL,
			0x0, "Global source IP", HFILL }},

		{ &hf_skype_natrequest_dstip,
		{ "Dst IP",   "skype.natrequest.dstip", FT_UINT32, BASE_HEX, NULL,
			0x0, NULL, HFILL }},

	/* Audio */
		{ &hf_skype_audio_unk1,
		{ "Unknown1",   "skype.audio.unk1", FT_BYTES, BASE_NONE, NULL,
			0x0, NULL, HFILL }},

	/* Unknown_F */
		{ &hf_skype_unknown_f_unk1,
		{ "Unknown1",   "skype.unknown_f.unk1", FT_BYTES, BASE_NONE, NULL,
			0x0, NULL, HFILL }},

	/* Unknown packet */
		{ &hf_skype_unknown_packet,
		{ "Unknown Packet",   "skype.unknown_packet", FT_BYTES, BASE_NONE, NULL,
			0x0, NULL, HFILL }},

	};
	static gint *ett[] = {
		&ett_skype,
	};

	proto_skype = proto_register_protocol(PROTO_LONG_NAME, PROTO_SHORT_NAME, "skype");
	proto_register_field_array(proto_skype, hf, array_length(hf));
	proto_register_subtree_array(ett, array_length(ett));
}

void
proto_reg_handoff_skype(void)
{
	dissector_handle_t skype_handle;

	skype_handle = create_dissector_handle(dissect_skype_static, proto_skype);
	dissector_add_for_decode_as_with_preference("tcp.port", skype_handle);
	dissector_add_for_decode_as_with_preference("udp.port", skype_handle);

	heur_dissector_add("udp", dissect_skype_heur, "Skype over UDP", "skype_udp", proto_skype, HEURISTIC_DISABLE);
}

/*
 * Editor modelines  -  https://www.wireshark.org/tools/modelines.html
 *
 * Local variables:
 * c-basic-offset: 8
 * tab-width: 8
 * indent-tabs-mode: t
 * End:
 *
 * vi: set shiftwidth=8 tabstop=8 noexpandtab:
 * :indentSize=8:tabSize=8:noTabs=false:
 */