/* packet-mbtcp.c * Routines for Modbus/TCP dissection * By Riaan Swart * 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 * 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 #include #include #include #include #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); }