packet-mbtcp.c

   1 /* packet-mbtcp.c
   2  * Routines for Modbus/TCP dissection
   3  * By Riaan Swart <rswart@cs.sun.ac.za>
   4  * Copyright 2001, Institute for Applied Computer Science
   5  *                                       University of Stellenbosch
   6  *
   7  * See
   8  *
   9  *      http://www.modicon.com/openmbus/
  10  *
  11  * for information on Modbus/TCP.
  12  *
  13  * $Id: packet-mbtcp.c,v 1.11 2002/08/28 21:00:20 jmayer Exp $
  14  *
  15  * Ethereal - Network traffic analyzer
  16  * By Gerald Combs <gerald@ethereal.com>
  17  * Copyright 1998 Gerald Combs
  18  *
  19  * This program is free software; you can redistribute it and/or
  20  * modify it under the terms of the GNU General Public License
  21  * as published by the Free Software Foundation; either version 2
  22  * of the License, or (at your option) any later version.
  23  *
  24  * This program is distributed in the hope that it will be useful,
  25  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  26  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  27  * GNU General Public License for more details.
  28  *
  29  * You should have received a copy of the GNU General Public License
  30  * along with this program; if not, write to the Free Software
  31  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  32  */
  33
  34 /*      TODO:
  35  *      Analysis of the payload of the Modbus packet.
  36  *              --      Based on the function code in the header, and the fact that the packet is
  37  *                      either a query or a response, the different fields in the payload can be
  38  *                      interpreted and displayed.
  39  */
  40
  41 #ifdef HAVE_CONFIG_H
  42 # include "config.h"
  43 #endif
  44
  45 #include <stdio.h>
  46 #include <stdlib.h>
  47 #include <string.h>
  48
  49 #include <glib.h>
  50
  51 #include <epan/packet.h>
  52
  53 #define DEBUG
  54
  55 #define TCP_PORT_MBTCP          502     /* Modbus/TCP located on TCP port 502 */
  56
  57 /* Modbus protocol function codes */
  58 #define read_coils                              1
  59 #define read_input_discretes    2
  60 #define read_mult_regs                  3
  61 #define read_input_regs                 4
  62 #define write_coil                              5
  63 #define write_single_reg                6
  64 #define read_except_stat                7
  65 #define diagnostics                             8
  66 #define program_484                             9
  67 #define poll_484                                        10
  68 #define get_comm_event_ctrs     11
  69 #define get_comm_event_log              12
  70 #define program_584_984                 13
  71 #define poll_584_984                            14
  72 #define force_mult_coils                15
  73 #define write_mult_regs                 16
  74 #define report_slave_id                 17
  75 #define program_884_u84                 18
  76 #define reset_comm_link                 19
  77 #define read_genl_ref                   20
  78 #define write_genl_ref                  21
  79 #define mask_write_reg                  22
  80 #define read_write_reg                  23
  81 #define read_fifo_queue                 24
  82 #define program_ConCept                 40
  83 #define firmware_replace                125
  84 #define program_584_984_2               126
  85 #define report_local_addr_mb    127
  86
  87 /* Modbus protocol exception codes */
  88 #define illegal_function                0x01
  89 #define illegal_address                 0x02
  90 #define illegal_value                   0x03
  91 #define illegal_response                0x04
  92 #define acknowledge                             0x05
  93 #define slave_busy                              0x06
  94 #define negative_ack                            0x07
  95 #define memory_err                              0x08
  96 #define gateway_unavailable     0x0a
  97 #define gateway_trgt_fail               0x0b
  98
  99 /* return codes of function classifying packets as query/response */
 100 #define query_packet                            0
 101 #define response_packet                 1
 102 #define cannot_classify                 2
 103
 104 /* Modbus header */
 105 typedef struct _modbus_hdr {
 106         gchar           unit_id;                        /* unit identifier (previously slave addr) */
 107         gchar           function_code; /* Modbus function code */
 108 } modbus_hdr;
 109
 110 /* Modbus/TCP header, containing the Modbus header */
 111 typedef struct _mbtcp_hdr {
 112         guint16         transaction_id; /* copied by svr, usually 0 */
 113         guint16                 protocol_id;            /* always 0 */
 114         guint16         len;                                    /* len of data that follows */
 115         modbus_hdr      mdbs_hdr;                       /* mdbus hdr directly after mdbs/tcp hdr *
 116                                                                                          * in packet */
 117 } mbtcp_hdr;
 118
 119 /* Initialize the protocol and registered fields */
 120 static int proto_mbtcp = -1;
 121 static int hf_mbtcp_transid = -1;
 122 static int hf_mbtcp_protid = -1;
 123 static int hf_mbtcp_len = -1;
 124 static int hf_mbtcp_unitid = -1;
 125 static int hf_mbtcp_functioncode = -1;
 126
 127 /* Initialize the subtree pointers */
 128 static gint ett_mbtcp = -1;
 129 static gint ett_modbus_hdr = -1;
 130
 131 static int
 132 classify_packet(packet_info *pinfo)
 133 {
 134         /* see if nature of packets can be derived from src/dst ports */
 135         /* if so, return as found */
 136         if ( ( 502 == pinfo->srcport && 502 != pinfo->destport ) ||
 137                   ( 502 != pinfo->srcport && 502 == pinfo->destport ) ) {
 138                 /* the slave is receiving queries on port 502 */
 139                 if ( 502 == pinfo->srcport )
 140                         return response_packet;
 141                 else if ( 502 == pinfo->destport )
 142                         return query_packet;
 143         }
 144         /* else, cannot classify */
 145         return cannot_classify;
 146 }
 147
 148 /* returns string describing function, as given on p6 of
 149  * "Open Modbus/TCP Specification", release 1 by Andy Swales. */
 150 static char *
 151 function_string(guint16 func_code)
 152 {
 153         switch ( func_code ) {
 154                 case read_coils:                                return "Read coils";                                                            break;
 155                 case read_input_discretes:      return "Read input discretes";                          break;
 156                 case read_mult_regs:                    return "Read multiple registers";                       break;
 157                 case read_input_regs:           return "Read input registers";                          break;
 158                 case write_coil:                                return "Write coil";                                                            break;
 159                 case write_single_reg:          return "Write single register";                         break;
 160                 case read_except_stat:          return "Read exception status";                         break;
 161                 case diagnostics:                               return "Diagnostics";                                                   break;
 162                 case program_484:                               return "Program (484)";                                                 break;
 163                 case poll_484:                                  return "Poll (484)";                                                            break;
 164                 case get_comm_event_ctrs:       return "Get Comm. Event Counters";                      break;
 165                 case get_comm_event_log:        return "Get Comm. Event Log";                                   break;
 166                 case program_584_984:           return "Program (584/984)";                                     break;
 167                 case poll_584_984:                      return "Poll (584/984)";                                                break;
 168                 case force_mult_coils:          return "Force Multiple Coils";                          break;
 169                 case write_mult_regs:           return "Write Multiple Registers";                      break;
 170                 case report_slave_id:           return "Report Slave ID";                                               break;
 171                 case program_884_u84:           return "Program 884/u84";                                               break;
 172                 case reset_comm_link:           return "Reset Comm. Link (884/u84)";            break;
 173                 case read_genl_ref:                     return "Read General Reference";                                break;
 174                 case write_genl_ref:                    return "Write General Reference";                       break;
 175                 case mask_write_reg:                    return "Mask Write Register";                                   break;
 176                 case read_write_reg:                    return "Read Write Register";                                   break;
 177                 case read_fifo_queue:           return "Read FIFO Queue";                                               break;
 178                 case program_ConCept:           return "Program (ConCept)";                                     break;
 179                 case firmware_replace:          return "Firmware replacement";                          break;
 180                 case program_584_984_2:         return "Program (584/984)";                                     break;
 181                 case report_local_addr_mb:      return "Report local address (Modbus)"; break;
 182                 default:                                                        return "Unknown function";                                              break;
 183         }
 184 }
 185 static char *
 186 exception_string(guint8 exception_code)
 187 {
 188         switch( exception_code ) {
 189                 case illegal_function:          return "Illegal function";                              break;
 190                 case illegal_address:           return "Illegal data address";          break;
 191                 case illegal_value:                     return "Illegal data value";                    break;
 192                 case illegal_response:          return "Illegal response length";       break;
 193                 case acknowledge:                               return "Acknowledge";                                   break;
 194                 case slave_busy:                                return "Slave device busy";                     break;
 195                 case negative_ack:                      return "Negative acknowledge";          break;
 196                 case memory_err:                                return "Memory parity error";                   break;
 197                 case gateway_unavailable:       return "Gateway path unavailable";      break;
 198                 case gateway_trgt_fail:         return "Gateway target device failed to respond";       break;
 199                 default:                                                        return "Unknown exception code";                break;
 200         }
 201 }
 202
 203 /* Code to actually dissect the packets */
 204 static void
 205 dissect_mbtcp(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
 206 {
 207 /* Set up structures needed to add the protocol subtree and manage it */
 208         mbtcp_hdr       mh;
 209         proto_item      *mi, *mf;
 210         proto_tree      *mbtcp_tree, *modbus_tree;
 211         int                     offset = 0;
 212         gint                    packet_end, packet_len;
 213         char                    *func_string = "", pkt_type_str[9] = "";
 214         char                    err_str[100] = "";
 215         int                     packet_type;
 216         guint32         packet_num = 0; /* num to uniquely identify different mbtcp
 217                                                                                                  * packets in one TCP packet */
 218         guint8          exception_code = 0, exception_returned = 0;
 219
 220 /* Make entries in Protocol column on summary display */
 221         if (check_col(pinfo->cinfo, COL_PROTOCOL))
 222                 col_set_str(pinfo->cinfo, COL_PROTOCOL, "Modbus/TCP");
 223
 224         if (check_col(pinfo->cinfo, COL_INFO))
 225                 col_clear(pinfo->cinfo, COL_INFO);
 226
 227 /* Make entries in Info column on summary display (updated after building proto tree) */
 228         tvb_memcpy(tvb, (guint8 *)&mh, offset, sizeof(mbtcp_hdr));
 229         mh.transaction_id                               =       g_ntohs(mh.transaction_id);
 230         mh.protocol_id                                  =       g_ntohs(mh.protocol_id);
 231         mh.len                                                  =       g_ntohs(mh.len);
 232         if ( mh.mdbs_hdr.function_code & 0x80 ) {
 233                 mh.mdbs_hdr.function_code ^= 0x80;
 234                 exception_returned = 1;
 235         }
 236         func_string = function_string(mh.mdbs_hdr.function_code);
 237         if (check_col(pinfo->cinfo, COL_INFO))
 238         {
 239                 packet_type = classify_packet(pinfo);
 240                 switch ( packet_type ) {
 241                         case query_packet :                     strcpy(pkt_type_str, "query");
 242                                                                                                 break;
 243                         case response_packet :          strcpy(pkt_type_str, "response");
 244                                                                                                 break;
 245                         case cannot_classify :          strcpy(err_str, "Unable to classify as query or response.");
 246                                                                                                 strcpy(pkt_type_str, "unknown");
 247                                                                                                 break;
 248                         default :
 249                                                                                                 break;
 250                 }
 251                 if ( exception_returned )
 252                         strcpy(err_str, "Exception returned ");
 253                 col_add_fstr(pinfo->cinfo, COL_INFO,
 254                                 "%8s [%2u pkt(s)]: trans: %5u; unit: %3u, func: %3u: %s. %s",
 255                                 pkt_type_str, 1, mh.transaction_id, (unsigned char) mh.mdbs_hdr.unit_id,
 256                                 (unsigned char) mh.mdbs_hdr.function_code, func_string, err_str);
 257         }
 258
 259         /* build up protocol tree */
 260         do {
 261         /* Avoids alignment problems on many architectures. */
 262                 tvb_memcpy(tvb, (guint8 *)&mh, offset, sizeof(mbtcp_hdr));
 263                 mh.transaction_id                               =       g_ntohs(mh.transaction_id);
 264                 mh.protocol_id                                  =       g_ntohs(mh.protocol_id);
 265                 mh.len                                                  =       g_ntohs(mh.len);
 266
 267                 if ( mh.mdbs_hdr.function_code & 0x80 ) {
 268                         tvb_memcpy(tvb, (guint8 *)&exception_code, offset + sizeof(mbtcp_hdr), 1);
 269                         mh.mdbs_hdr.function_code ^= 0x80;
 270                         exception_returned = 1;
 271                 } else
 272                         exception_code = 0;
 273
 274                 packet_type = classify_packet(pinfo);
 275
 276                 /* if a tree exists, perform operations to add fields to it */
 277                 if (tree) {
 278                         packet_len = sizeof(mbtcp_hdr) - sizeof(modbus_hdr) + mh.len;
 279                         mi = proto_tree_add_protocol_format(tree, proto_mbtcp, tvb, offset,
 280                                         packet_len, "Modbus/TCP");
 281                         mbtcp_tree = proto_item_add_subtree(mi, ett_mbtcp);
 282
 283                         /* Add items to protocol tree */
 284                         /* Modbus/TCP */
 285                         proto_tree_add_uint(mbtcp_tree, hf_mbtcp_transid, tvb, offset, 2,
 286                                         mh.transaction_id);
 287                         proto_tree_add_uint(mbtcp_tree, hf_mbtcp_protid, tvb, offset + 2, 2,
 288                                         mh.protocol_id);
 289                         proto_tree_add_uint(mbtcp_tree, hf_mbtcp_len, tvb, offset + 4, 2,
 290                                         mh.len);
 291                         /* Modbus */
 292                         packet_end = mh.len;
 293                         mf = proto_tree_add_text(mbtcp_tree, tvb, offset + 6, packet_end,
 294                                         "Modbus");
 295                         modbus_tree = proto_item_add_subtree(mf, ett_modbus_hdr);
 296                         proto_tree_add_item(modbus_tree, hf_mbtcp_unitid, tvb, offset + 6, 1,
 297                                         mh.mdbs_hdr.unit_id);
 298                         mi = proto_tree_add_item(modbus_tree, hf_mbtcp_functioncode, tvb, offset + 7, 1,
 299                                         mh.mdbs_hdr.function_code);
 300                         func_string = function_string(mh.mdbs_hdr.function_code);
 301                         if ( 0 == exception_code )
 302                                 proto_item_set_text(mi, "function %u:  %s", mh.mdbs_hdr.function_code,
 303                                                 func_string);
 304                         else
 305                                 proto_item_set_text(mi, "function %u:  %s.  Exception: %s",
 306                                                 mh.mdbs_hdr.function_code, func_string, exception_string(exception_code));
 307
 308                         packet_end = mh.len - 2;
 309                         proto_tree_add_text(modbus_tree, tvb, offset + 8, packet_end,
 310                                         "Modbus data");
 311                 }
 312                 offset = offset + sizeof(mbtcp_hdr) + (mh.len - sizeof(modbus_hdr));
 313                 packet_num++;
 314         } while ( tvb_reported_length_remaining(tvb, offset) > 0 );
 315
 316
 317 /* Update entries in Info column on summary display */
 318         if (check_col(pinfo->cinfo, COL_INFO))
 319         {
 320                 switch ( packet_type ) {
 321                         case query_packet :                     strcpy(pkt_type_str, "query");
 322                                                                                                 break;
 323                         case response_packet :          strcpy(pkt_type_str, "response");
 324                                                                                                 break;
 325                         case cannot_classify :          strcpy(err_str, "Unable to classify as query or response.");
 326                                                                                                 strcpy(pkt_type_str, "unknown");
 327                                                                                                 break;
 328                         default :
 329                                                                                                 break;
 330                 }
 331                 if ( exception_returned )
 332                         strcpy(err_str, "Exception returned ");
 333                 col_add_fstr(pinfo->cinfo, COL_INFO,
 334                                 "%8s [%2u pkt(s)]: trans: %5u; unit: %3u, func: %3u: %s. %s",
 335                                 pkt_type_str, packet_num, mh.transaction_id, (unsigned char) mh.mdbs_hdr.unit_id,
 336                                 (unsigned char) mh.mdbs_hdr.function_code, func_string, err_str);
 337         }
 338
 339 /* If this protocol has a sub-dissector call it here, see section 1.8 */
 340 }
 341
 342
 343 /* Register the protocol with Ethereal */
 344
 345 /* this format is require because a script is used to build the C function
 346    that calls all the protocol registration.
 347 */
 348
 349 void
 350 proto_register_modbus(void)
 351 {
 352
 353 /* Setup list of header fields  See Section 1.6.1 for details*/
 354         static hf_register_info hf[] = {
 355                 /* Modbus/TCP header fields */
 356                 { &hf_mbtcp_transid,
 357                         { "transaction identifier",           "modbus_tcp.trans_id",
 358                         FT_UINT16, BASE_DEC, NULL, 0x0,
 359                         "", HFILL }
 360                 },
 361                 { &hf_mbtcp_protid,
 362                         { "protocol identifier",           "modbus_tcp.prot_id",
 363                         FT_UINT16, BASE_DEC, NULL, 0x0,
 364                         "", HFILL }
 365                 },
 366                 { &hf_mbtcp_len,
 367                         { "length",           "modbus_tcp.len",
 368                         FT_UINT16, BASE_DEC, NULL, 0x0,
 369                         "", HFILL }
 370                 },
 371                 /* Modbus header fields */
 372                 { &hf_mbtcp_unitid,
 373                         { "unit identifier",           "modbus_tcp.unit_id",
 374                         FT_UINT8, BASE_DEC, NULL, 0x0,
 375                         "", HFILL }
 376                 },
 377                 { &hf_mbtcp_functioncode,
 378                         { "function code ",           "modbus_tcp.func_code",
 379                         FT_UINT8, BASE_DEC, NULL, 0x0,
 380                         "", HFILL }
 381                 }
 382         };
 383
 384 /* Setup protocol subtree array */
 385         static gint *ett[] = {
 386                 &ett_mbtcp,
 387                 &ett_modbus_hdr
 388         };
 389
 390 /* Register the protocol name and description */
 391         proto_mbtcp = proto_register_protocol("Modbus/TCP",
 392             "Modbus/TCP", "mbtcp");
 393
 394 /* Required function calls to register the header fields and subtrees used */
 395         proto_register_field_array(proto_mbtcp, hf, array_length(hf));
 396         proto_register_subtree_array(ett, array_length(ett));
 397 }
 398
 399
 400 /* If this dissector uses sub-dissector registration add a registration routine.
 401    This format is required because a script is used to find these routines and
 402    create the code that calls these routines.
 403  */
 404 void
 405 proto_reg_handoff_mbtcp(void)
 406 {
 407         dissector_handle_t mbtcp_handle;
 408
 409         mbtcp_handle = create_dissector_handle(dissect_mbtcp, proto_mbtcp);
 410         dissector_add("tcp.port", TCP_PORT_MBTCP, mbtcp_handle);
 411 }