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wireshark/packet-mbtcp.c

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/* packet-mbtcp.c
* Routines for Modbus/TCP dissection
* By Riaan Swart <rswart@cs.sun.ac.za>
* Copyright 2001, Institute for Applied Computer Science
* University of Stellenbosch
*
* See
*
* http://www.modicon.com/openmbus/
*
* for information on Modbus/TCP.
*
* $Id: packet-mbtcp.c,v 1.11 2002/08/28 21:00:20 jmayer Exp $
*
* Ethereal - Network traffic analyzer
* By Gerald Combs <gerald@ethereal.com>
* Copyright 1998 Gerald Combs
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version 2
* of the License, or (at your option) any later version.
*
* This program 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
*/
/* TODO:
* Analysis of the payload of the Modbus packet.
* -- Based on the function code in the header, and the fact that the packet is
* either a query or a response, the different fields in the payload can be
* interpreted and displayed.
*/
#ifdef HAVE_CONFIG_H
# include "config.h"
#endif
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <glib.h>
#include <epan/packet.h>
#define DEBUG
#define TCP_PORT_MBTCP 502 /* Modbus/TCP located on TCP port 502 */
/* Modbus protocol function codes */
#define read_coils 1
#define read_input_discretes 2
#define read_mult_regs 3
#define read_input_regs 4
#define write_coil 5
#define write_single_reg 6
#define read_except_stat 7
#define diagnostics 8
#define program_484 9
#define poll_484 10
#define get_comm_event_ctrs 11
#define get_comm_event_log 12
#define program_584_984 13
#define poll_584_984 14
#define force_mult_coils 15
#define write_mult_regs 16
#define report_slave_id 17
#define program_884_u84 18
#define reset_comm_link 19
#define read_genl_ref 20
#define write_genl_ref 21
#define mask_write_reg 22
#define read_write_reg 23
#define read_fifo_queue 24
#define program_ConCept 40
#define firmware_replace 125
#define program_584_984_2 126
#define report_local_addr_mb 127
/* Modbus protocol exception codes */
#define illegal_function 0x01
#define illegal_address 0x02
#define illegal_value 0x03
#define illegal_response 0x04
#define acknowledge 0x05
#define slave_busy 0x06
#define negative_ack 0x07
#define memory_err 0x08
#define gateway_unavailable 0x0a
#define gateway_trgt_fail 0x0b
/* return codes of function classifying packets as query/response */
#define query_packet 0
#define response_packet 1
#define cannot_classify 2
/* Modbus header */
typedef struct _modbus_hdr {
gchar unit_id; /* unit identifier (previously slave addr) */
gchar function_code; /* Modbus function code */
} modbus_hdr;
/* Modbus/TCP header, containing the Modbus header */
typedef struct _mbtcp_hdr {
guint16 transaction_id; /* copied by svr, usually 0 */
guint16 protocol_id; /* always 0 */
guint16 len; /* len of data that follows */
modbus_hdr mdbs_hdr; /* mdbus hdr directly after mdbs/tcp hdr *
* in packet */
} mbtcp_hdr;
/* Initialize the protocol and registered fields */
static int proto_mbtcp = -1;
static int hf_mbtcp_transid = -1;
static int hf_mbtcp_protid = -1;
static int hf_mbtcp_len = -1;
static int hf_mbtcp_unitid = -1;
static int hf_mbtcp_functioncode = -1;
/* Initialize the subtree pointers */
static gint ett_mbtcp = -1;
static gint ett_modbus_hdr = -1;
static int
classify_packet(packet_info *pinfo)
{
/* see if nature of packets can be derived from src/dst ports */
/* if so, return as found */
if ( ( 502 == pinfo->srcport && 502 != pinfo->destport ) ||
( 502 != pinfo->srcport && 502 == pinfo->destport ) ) {
/* the slave is receiving queries on port 502 */
if ( 502 == pinfo->srcport )
return response_packet;
else if ( 502 == pinfo->destport )
return query_packet;
}
/* else, cannot classify */
return cannot_classify;
}
/* returns string describing function, as given on p6 of
* "Open Modbus/TCP Specification", release 1 by Andy Swales. */
static char *
function_string(guint16 func_code)
{
switch ( func_code ) {
case read_coils: return "Read coils"; break;
case read_input_discretes: return "Read input discretes"; break;
case read_mult_regs: return "Read multiple registers"; break;
case read_input_regs: return "Read input registers"; break;
case write_coil: return "Write coil"; break;
case write_single_reg: return "Write single register"; break;
case read_except_stat: return "Read exception status"; break;
case diagnostics: return "Diagnostics"; break;
case program_484: return "Program (484)"; break;
case poll_484: return "Poll (484)"; break;
case get_comm_event_ctrs: return "Get Comm. Event Counters"; break;
case get_comm_event_log: return "Get Comm. Event Log"; break;
case program_584_984: return "Program (584/984)"; break;
case poll_584_984: return "Poll (584/984)"; break;
case force_mult_coils: return "Force Multiple Coils"; break;
case write_mult_regs: return "Write Multiple Registers"; break;
case report_slave_id: return "Report Slave ID"; break;
case program_884_u84: return "Program 884/u84"; break;
case reset_comm_link: return "Reset Comm. Link (884/u84)"; break;
case read_genl_ref: return "Read General Reference"; break;
case write_genl_ref: return "Write General Reference"; break;
case mask_write_reg: return "Mask Write Register"; break;
case read_write_reg: return "Read Write Register"; break;
case read_fifo_queue: return "Read FIFO Queue"; break;
case program_ConCept: return "Program (ConCept)"; break;
case firmware_replace: return "Firmware replacement"; break;
case program_584_984_2: return "Program (584/984)"; break;
case report_local_addr_mb: return "Report local address (Modbus)"; break;
default: return "Unknown function"; break;
}
}
static char *
exception_string(guint8 exception_code)
{
switch( exception_code ) {
case illegal_function: return "Illegal function"; break;
case illegal_address: return "Illegal data address"; break;
case illegal_value: return "Illegal data value"; break;
case illegal_response: return "Illegal response length"; break;
case acknowledge: return "Acknowledge"; break;
case slave_busy: return "Slave device busy"; break;
case negative_ack: return "Negative acknowledge"; break;
case memory_err: return "Memory parity error"; break;
case gateway_unavailable: return "Gateway path unavailable"; break;
case gateway_trgt_fail: return "Gateway target device failed to respond"; break;
default: return "Unknown exception code"; break;
}
}
/* Code to actually dissect the packets */
static void
dissect_mbtcp(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
{
/* Set up structures needed to add the protocol subtree and manage it */
mbtcp_hdr mh;
proto_item *mi, *mf;
proto_tree *mbtcp_tree, *modbus_tree;
int offset = 0;
gint packet_end, packet_len;
char *func_string = "", pkt_type_str[9] = "";
char err_str[100] = "";
int packet_type;
guint32 packet_num = 0; /* num to uniquely identify different mbtcp
* packets in one TCP packet */
guint8 exception_code = 0, exception_returned = 0;
/* Make entries in Protocol column on summary display */
if (check_col(pinfo->cinfo, COL_PROTOCOL))
col_set_str(pinfo->cinfo, COL_PROTOCOL, "Modbus/TCP");
if (check_col(pinfo->cinfo, COL_INFO))
col_clear(pinfo->cinfo, COL_INFO);
/* Make entries in Info column on summary display (updated after building proto tree) */
tvb_memcpy(tvb, (guint8 *)&mh, offset, sizeof(mbtcp_hdr));
mh.transaction_id = g_ntohs(mh.transaction_id);
mh.protocol_id = g_ntohs(mh.protocol_id);
mh.len = g_ntohs(mh.len);
if ( mh.mdbs_hdr.function_code & 0x80 ) {
mh.mdbs_hdr.function_code ^= 0x80;
exception_returned = 1;
}
func_string = function_string(mh.mdbs_hdr.function_code);
if (check_col(pinfo->cinfo, COL_INFO))
{
packet_type = classify_packet(pinfo);
switch ( packet_type ) {
case query_packet : strcpy(pkt_type_str, "query");
break;
case response_packet : strcpy(pkt_type_str, "response");
break;
case cannot_classify : strcpy(err_str, "Unable to classify as query or response.");
strcpy(pkt_type_str, "unknown");
break;
default :
break;
}
if ( exception_returned )
strcpy(err_str, "Exception returned ");
col_add_fstr(pinfo->cinfo, COL_INFO,
"%8s [%2u pkt(s)]: trans: %5u; unit: %3u, func: %3u: %s. %s",
pkt_type_str, 1, mh.transaction_id, (unsigned char) mh.mdbs_hdr.unit_id,
(unsigned char) mh.mdbs_hdr.function_code, func_string, err_str);
}
/* build up protocol tree */
do {
/* Avoids alignment problems on many architectures. */
tvb_memcpy(tvb, (guint8 *)&mh, offset, sizeof(mbtcp_hdr));
mh.transaction_id = g_ntohs(mh.transaction_id);
mh.protocol_id = g_ntohs(mh.protocol_id);
mh.len = g_ntohs(mh.len);
if ( mh.mdbs_hdr.function_code & 0x80 ) {
tvb_memcpy(tvb, (guint8 *)&exception_code, offset + sizeof(mbtcp_hdr), 1);
mh.mdbs_hdr.function_code ^= 0x80;
exception_returned = 1;
} else
exception_code = 0;
packet_type = classify_packet(pinfo);
/* if a tree exists, perform operations to add fields to it */
if (tree) {
packet_len = sizeof(mbtcp_hdr) - sizeof(modbus_hdr) + mh.len;
mi = proto_tree_add_protocol_format(tree, proto_mbtcp, tvb, offset,
packet_len, "Modbus/TCP");
mbtcp_tree = proto_item_add_subtree(mi, ett_mbtcp);
/* Add items to protocol tree */
/* Modbus/TCP */
proto_tree_add_uint(mbtcp_tree, hf_mbtcp_transid, tvb, offset, 2,
mh.transaction_id);
proto_tree_add_uint(mbtcp_tree, hf_mbtcp_protid, tvb, offset + 2, 2,
mh.protocol_id);
proto_tree_add_uint(mbtcp_tree, hf_mbtcp_len, tvb, offset + 4, 2,
mh.len);
/* Modbus */
packet_end = mh.len;
mf = proto_tree_add_text(mbtcp_tree, tvb, offset + 6, packet_end,
"Modbus");
modbus_tree = proto_item_add_subtree(mf, ett_modbus_hdr);
proto_tree_add_item(modbus_tree, hf_mbtcp_unitid, tvb, offset + 6, 1,
mh.mdbs_hdr.unit_id);
mi = proto_tree_add_item(modbus_tree, hf_mbtcp_functioncode, tvb, offset + 7, 1,
mh.mdbs_hdr.function_code);
func_string = function_string(mh.mdbs_hdr.function_code);
if ( 0 == exception_code )
proto_item_set_text(mi, "function %u: %s", mh.mdbs_hdr.function_code,
func_string);
else
proto_item_set_text(mi, "function %u: %s. Exception: %s",
mh.mdbs_hdr.function_code, func_string, exception_string(exception_code));
packet_end = mh.len - 2;
proto_tree_add_text(modbus_tree, tvb, offset + 8, packet_end,
"Modbus data");
}
offset = offset + sizeof(mbtcp_hdr) + (mh.len - sizeof(modbus_hdr));
packet_num++;
} while ( tvb_reported_length_remaining(tvb, offset) > 0 );
/* Update entries in Info column on summary display */
if (check_col(pinfo->cinfo, COL_INFO))
{
switch ( packet_type ) {
case query_packet : strcpy(pkt_type_str, "query");
break;
case response_packet : strcpy(pkt_type_str, "response");
break;
case cannot_classify : strcpy(err_str, "Unable to classify as query or response.");
strcpy(pkt_type_str, "unknown");
break;
default :
break;
}
if ( exception_returned )
strcpy(err_str, "Exception returned ");
col_add_fstr(pinfo->cinfo, COL_INFO,
"%8s [%2u pkt(s)]: trans: %5u; unit: %3u, func: %3u: %s. %s",
pkt_type_str, packet_num, mh.transaction_id, (unsigned char) mh.mdbs_hdr.unit_id,
(unsigned char) mh.mdbs_hdr.function_code, func_string, err_str);
}
/* If this protocol has a sub-dissector call it here, see section 1.8 */
}
/* Register the protocol with Ethereal */
/* this format is require because a script is used to build the C function
that calls all the protocol registration.
*/
void
proto_register_modbus(void)
{
/* Setup list of header fields See Section 1.6.1 for details*/
static hf_register_info hf[] = {
/* Modbus/TCP header fields */
{ &hf_mbtcp_transid,
{ "transaction identifier", "modbus_tcp.trans_id",
FT_UINT16, BASE_DEC, NULL, 0x0,
"", HFILL }
},
{ &hf_mbtcp_protid,
{ "protocol identifier", "modbus_tcp.prot_id",
FT_UINT16, BASE_DEC, NULL, 0x0,
"", HFILL }
},
{ &hf_mbtcp_len,
{ "length", "modbus_tcp.len",
FT_UINT16, BASE_DEC, NULL, 0x0,
"", HFILL }
},
/* Modbus header fields */
{ &hf_mbtcp_unitid,
{ "unit identifier", "modbus_tcp.unit_id",
FT_UINT8, BASE_DEC, NULL, 0x0,
"", HFILL }
},
{ &hf_mbtcp_functioncode,
{ "function code ", "modbus_tcp.func_code",
FT_UINT8, BASE_DEC, NULL, 0x0,
"", HFILL }
}
};
/* Setup protocol subtree array */
static gint *ett[] = {
&ett_mbtcp,
&ett_modbus_hdr
};
/* Register the protocol name and description */
proto_mbtcp = proto_register_protocol("Modbus/TCP",
"Modbus/TCP", "mbtcp");
/* Required function calls to register the header fields and subtrees used */
proto_register_field_array(proto_mbtcp, hf, array_length(hf));
proto_register_subtree_array(ett, array_length(ett));
}
/* If this dissector uses sub-dissector registration add a registration routine.
This format is required because a script is used to find these routines and
create the code that calls these routines.
*/
void
proto_reg_handoff_mbtcp(void)
{
dissector_handle_t mbtcp_handle;
mbtcp_handle = create_dissector_handle(dissect_mbtcp, proto_mbtcp);
dissector_add("tcp.port", TCP_PORT_MBTCP, mbtcp_handle);
}
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