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 1.8 2002/01/21 07:36:37 guy 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 #ifdef HAVE_SYS_TYPES_H
  50 # include <sys/types.h>
  51 #endif
  52
  53 #ifdef HAVE_NETINET_IN_H
  54 # include <netinet/in.h>
  55 #endif
  56
  57 #include <glib.h>
  58
  59 #ifdef NEED_SNPRINTF_H
  60 # include "snprintf.h"
  61 #endif
  62
  63 #include <epan/packet.h>
  64
  65 #define DEBUG
  66
  67 #define TCP_PORT_MBTCP          502     /* Modbus/TCP located on TCP port 502 */
  68
  69 /* Modbus protocol function codes */
  70 #define read_coils                              1
  71 #define read_input_discretes    2
  72 #define read_mult_regs                  3
  73 #define read_input_regs                 4
  74 #define write_coil                              5
  75 #define write_single_reg                6
  76 #define read_except_stat                7
  77 #define diagnostics                             8
  78 #define program_484                             9
  79 #define poll_484                                        10
  80 #define get_comm_event_ctrs     11
  81 #define get_comm_event_log              12
  82 #define program_584_984                 13
  83 #define poll_584_984                            14
  84 #define force_mult_coils                15
  85 #define write_mult_regs                 16
  86 #define report_slave_id                 17
  87 #define program_884_u84                 18
  88 #define reset_comm_link                 19
  89 #define read_genl_ref                   20
  90 #define write_genl_ref                  21
  91 #define mask_write_reg                  22
  92 #define read_write_reg                  23
  93 #define read_fifo_queue                 24
  94 #define program_ConCept                 40
  95 #define firmware_replace                125
  96 #define program_584_984_2               126
  97 #define report_local_addr_mb    127
  98
  99 /* Modbus protocol exception codes */
 100 #define illegal_function                0x01
 101 #define illegal_address                 0x02
 102 #define illegal_value                   0x03
 103 #define illegal_response                0x04
 104 #define acknowledge                             0x05
 105 #define slave_busy                              0x06
 106 #define negative_ack                            0x07
 107 #define memory_err                              0x08
 108 #define gateway_unavailable     0x0a
 109 #define gateway_trgt_fail               0x0b
 110
 111 /* return codes of function classifying packets as query/response */
 112 #define query_packet                            0
 113 #define response_packet                 1
 114 #define cannot_classify                 2
 115
 116 /* Modbus header */
 117 typedef struct _modbus_hdr {
 118         gchar           unit_id;                        /* unit identifier (previously slave addr) */
 119         gchar           function_code; /* Modbus function code */
 120 } modbus_hdr;
 121
 122 /* Modbus/TCP header, containing the Modbus header */
 123 typedef struct _mbtcp_hdr {
 124         guint16         transaction_id; /* copied by svr, usually 0 */
 125         guint16                 protocol_id;            /* always 0 */
 126         guint16         len;                                    /* len of data that follows */
 127         modbus_hdr      mdbs_hdr;                       /* mdbus hdr directly after mdbs/tcp hdr *
 128                                                                                          * in packet */
 129 } mbtcp_hdr;
 130
 131 /* Initialize the protocol and registered fields */
 132 static int proto_mbtcp = -1;
 133 static int hf_mbtcp_transid = -1;
 134 static int hf_mbtcp_protid = -1;
 135 static int hf_mbtcp_len = -1;
 136 static int hf_mbtcp_unitid = -1;
 137 static int hf_mbtcp_functioncode = -1;
 138
 139 /* Initialize the subtree pointers */
 140 static gint ett_mbtcp = -1;
 141 static gint ett_modbus_hdr = -1;
 142
 143 static int
 144 classify_packet(packet_info *pinfo)
 145 {
 146         /* see if nature of packets can be derived from src/dst ports */
 147         /* if so, return as found */
 148         if ( ( 502 == pinfo->srcport && 502 != pinfo->destport ) ||
 149                   ( 502 != pinfo->srcport && 502 == pinfo->destport ) ) {
 150                 /* the slave is receiving queries on port 502 */
 151                 if ( 502 == pinfo->srcport )
 152                         return response_packet;
 153                 else if ( 502 == pinfo->destport )
 154                         return query_packet;
 155         }
 156         /* else, cannot classify */
 157         return cannot_classify;
 158 }
 159
 160 /* returns string describing function, as given on p6 of
 161  * "Open Modbus/TCP Specification", release 1 by Andy Swales. */
 162 static char *
 163 function_string(guint16 func_code)
 164 {
 165         switch ( func_code ) {
 166                 case read_coils:                                return "Read coils";                                                            break;
 167                 case read_input_discretes:      return "Read input discretes";                          break;
 168                 case read_mult_regs:                    return "Read multiple registers";                       break;
 169                 case read_input_regs:           return "Read input registers";                          break;
 170                 case write_coil:                                return "Write coil";                                                            break;
 171                 case write_single_reg:          return "Write single register";                         break;
 172                 case read_except_stat:          return "Read exception status";                         break;
 173                 case diagnostics:                               return "Diagnostics";                                                   break;
 174                 case program_484:                               return "Program (484)";                                                 break;
 175                 case poll_484:                                  return "Poll (484)";                                                            break;
 176                 case get_comm_event_ctrs:       return "Get Comm. Event Counters";                      break;
 177                 case get_comm_event_log:        return "Get Comm. Event Log";                                   break;
 178                 case program_584_984:           return "Program (584/984)";                                     break;
 179                 case poll_584_984:                      return "Poll (584/984)";                                                break;
 180                 case force_mult_coils:          return "Force Multiple Coils";                          break;
 181                 case write_mult_regs:           return "Write Multiple Registers";                      break;
 182                 case report_slave_id:           return "Report Slave ID";                                               break;
 183                 case program_884_u84:           return "Program 884/u84";                                               break;
 184                 case reset_comm_link:           return "Reset Comm. Link (884/u84)";            break;
 185                 case read_genl_ref:                     return "Read General Reference";                                break;
 186                 case write_genl_ref:                    return "Write General Reference";                       break;
 187                 case mask_write_reg:                    return "Mask Write Register";                                   break;
 188                 case read_write_reg:                    return "Read Write Register";                                   break;
 189                 case read_fifo_queue:           return "Read FIFO Queue";                                               break;
 190                 case program_ConCept:           return "Program (ConCept)";                                     break;
 191                 case firmware_replace:          return "Firmware replacement";                          break;
 192                 case program_584_984_2:         return "Program (584/984)";                                     break;
 193                 case report_local_addr_mb:      return "Report local address (Modbus)"; break;
 194                 default:                                                        return "Unknown function";                                              break;
 195         }
 196 }
 197 static char *
 198 exception_string(guint8 exception_code)
 199 {
 200         switch( exception_code ) {
 201                 case illegal_function:          return "Illegal function";                              break;
 202                 case illegal_address:           return "Illegal data address";          break;
 203                 case illegal_value:                     return "Illegal data value";                    break;
 204                 case illegal_response:          return "Illegal response length";       break;
 205                 case acknowledge:                               return "Acknowledge";                                   break;
 206                 case slave_busy:                                return "Slave device busy";                     break;
 207                 case negative_ack:                      return "Negative acknowledge";          break;
 208                 case memory_err:                                return "Memory parity error";                   break;
 209                 case gateway_unavailable:       return "Gateway path unavailable";      break;
 210                 case gateway_trgt_fail:         return "Gateway target device failed to respond";       break;
 211                 default:                                                        return "Unknown exception code";                break;
 212         }
 213 }
 214
 215 /* Code to actually dissect the packets */
 216 static void
 217 dissect_mbtcp(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
 218 {
 219 /* Set up structures needed to add the protocol subtree and manage it */
 220         mbtcp_hdr       mh;
 221         proto_item      *mi, *mf;
 222         proto_tree      *mbtcp_tree, *modbus_tree;
 223         int                     offset = 0;
 224         gint                    packet_end, packet_len;
 225         char                    *func_string = "", pkt_type_str[9] = "";
 226         char                    err_str[100] = "";
 227         int                     packet_type;
 228         guint32         packet_num = 0; /* num to uniquely identify different mbtcp
 229                                                                                                  * packets in one TCP packet */
 230         guint8          exception_code = 0, exception_returned = 0;
 231
 232 /* Make entries in Protocol column on summary display */
 233         if (check_col(pinfo->cinfo, COL_PROTOCOL))
 234                 col_set_str(pinfo->cinfo, COL_PROTOCOL, "Modbus/TCP");
 235
 236         if (check_col(pinfo->cinfo, COL_INFO))
 237                 col_clear(pinfo->cinfo, COL_INFO);
 238
 239 /* Make entries in Info column on summary display (updated after building proto tree) */
 240         tvb_memcpy(tvb, (guint8 *)&mh, offset, sizeof(mbtcp_hdr));
 241         mh.transaction_id                               =       ntohs(mh.transaction_id);
 242         mh.protocol_id                                  =       ntohs(mh.protocol_id);
 243         mh.len                                                  =       ntohs(mh.len);
 244         if ( mh.mdbs_hdr.function_code & 0x80 ) {
 245                 mh.mdbs_hdr.function_code ^= 0x80;
 246                 exception_returned = 1;
 247         }
 248         func_string = function_string(mh.mdbs_hdr.function_code);
 249         if (check_col(pinfo->cinfo, COL_INFO))
 250         {
 251                 packet_type = classify_packet(pinfo);
 252                 switch ( packet_type ) {
 253                         case query_packet :                     strcpy(pkt_type_str, "query");
 254                                                                                                 break;
 255                         case response_packet :          strcpy(pkt_type_str, "response");
 256                                                                                                 break;
 257                         case cannot_classify :          strcpy(err_str, "Unable to classify as query or response.");
 258                                                                                                 strcpy(pkt_type_str, "unknown");
 259                                                                                                 break;
 260                         default :
 261                                                                                                 break;
 262                 }
 263                 if ( exception_returned )
 264                         strcpy(err_str, "Exception returned ");
 265                 col_add_fstr(pinfo->cinfo, COL_INFO,
 266                                 "%8s [%2u pkt(s)]: trans: %5u; unit: %3u, func: %3u: %s. %s",
 267                                 pkt_type_str, 1, mh.transaction_id, (unsigned char) mh.mdbs_hdr.unit_id,
 268                                 (unsigned char) mh.mdbs_hdr.function_code, func_string, err_str);
 269         }
 270
 271         /* build up protocol tree */
 272         do {
 273         /* Avoids alignment problems on many architectures. */
 274                 tvb_memcpy(tvb, (guint8 *)&mh, offset, sizeof(mbtcp_hdr));
 275                 mh.transaction_id                               =       ntohs(mh.transaction_id);
 276                 mh.protocol_id                                  =       ntohs(mh.protocol_id);
 277                 mh.len                                                  =       ntohs(mh.len);
 278
 279                 if ( mh.mdbs_hdr.function_code & 0x80 ) {
 280                         tvb_memcpy(tvb, (guint8 *)&exception_code, offset + sizeof(mbtcp_hdr), 1);
 281                         mh.mdbs_hdr.function_code ^= 0x80;
 282                         exception_returned = 1;
 283                 } else
 284                         exception_code = 0;
 285
 286                 packet_type = classify_packet(pinfo);
 287
 288                 /* if a tree exists, perform operations to add fields to it */
 289                 if (tree) {
 290                         packet_len = sizeof(mbtcp_hdr) - sizeof(modbus_hdr) + mh.len;
 291                         mi = proto_tree_add_protocol_format(tree, proto_mbtcp, tvb, offset,
 292                                         packet_len, "Modbus/TCP");
 293                         mbtcp_tree = proto_item_add_subtree(mi, ett_mbtcp);
 294
 295                         /* Add items to protocol tree */
 296                         /* Modbus/TCP */
 297                         proto_tree_add_uint(mbtcp_tree, hf_mbtcp_transid, tvb, offset, 2,
 298                                         mh.transaction_id);
 299                         proto_tree_add_uint(mbtcp_tree, hf_mbtcp_protid, tvb, offset + 2, 2,
 300                                         mh.protocol_id);
 301                         proto_tree_add_uint(mbtcp_tree, hf_mbtcp_len, tvb, offset + 4, 2,
 302                                         mh.len);
 303                         /* Modbus */
 304                         packet_end = mh.len;
 305                         mf = proto_tree_add_text(mbtcp_tree, tvb, offset + 6, packet_end,
 306                                         "Modbus");
 307                         modbus_tree = proto_item_add_subtree(mf, ett_modbus_hdr);
 308                         proto_tree_add_item(modbus_tree, hf_mbtcp_unitid, tvb, offset + 6, 1,
 309                                         mh.mdbs_hdr.unit_id);
 310                         mi = proto_tree_add_item(modbus_tree, hf_mbtcp_functioncode, tvb, offset + 7, 1,
 311                                         mh.mdbs_hdr.function_code);
 312                         func_string = function_string(mh.mdbs_hdr.function_code);
 313                         if ( 0 == exception_code )
 314                                 proto_item_set_text(mi, "function %u:  %s", mh.mdbs_hdr.function_code,
 315                                                 func_string);
 316                         else
 317                                 proto_item_set_text(mi, "function %u:  %s.  Exception: %s",
 318                                                 mh.mdbs_hdr.function_code, func_string, exception_string(exception_code));
 319
 320                         packet_end = mh.len - 2;
 321                         proto_tree_add_text(modbus_tree, tvb, offset + 8, packet_end,
 322                                         "Modbus data");
 323                 }
 324                 offset = offset + sizeof(mbtcp_hdr) + (mh.len - sizeof(modbus_hdr));
 325                 packet_num++;
 326         } while ( tvb_reported_length_remaining(tvb, offset) > 0 );
 327
 328
 329 /* Update entries in Info column on summary display */
 330         if (check_col(pinfo->cinfo, COL_INFO))
 331         {
 332                 switch ( packet_type ) {
 333                         case query_packet :                     strcpy(pkt_type_str, "query");
 334                                                                                                 break;
 335                         case response_packet :          strcpy(pkt_type_str, "response");
 336                                                                                                 break;
 337                         case cannot_classify :          strcpy(err_str, "Unable to classify as query or response.");
 338                                                                                                 strcpy(pkt_type_str, "unknown");
 339                                                                                                 break;
 340                         default :
 341                                                                                                 break;
 342                 }
 343                 if ( exception_returned )
 344                         strcpy(err_str, "Exception returned ");
 345                 col_add_fstr(pinfo->cinfo, COL_INFO,
 346                                 "%8s [%2u pkt(s)]: trans: %5u; unit: %3u, func: %3u: %s. %s",
 347                                 pkt_type_str, packet_num, mh.transaction_id, (unsigned char) mh.mdbs_hdr.unit_id,
 348                                 (unsigned char) mh.mdbs_hdr.function_code, func_string, err_str);
 349         }
 350
 351 /* If this protocol has a sub-dissector call it here, see section 1.8 */
 352 }
 353
 354
 355 /* Register the protocol with Ethereal */
 356
 357 /* this format is require because a script is used to build the C function
 358    that calls all the protocol registration.
 359 */
 360
 361 void
 362 proto_register_modbus(void)
 363 {
 364
 365 /* Setup list of header fields  See Section 1.6.1 for details*/
 366         static hf_register_info hf[] = {
 367                 /* Modbus/TCP header fields */
 368                 { &hf_mbtcp_transid,
 369                         { "transaction identifier",           "modbus_tcp.trans_id",
 370                         FT_UINT16, BASE_DEC, NULL, 0x0,
 371                         "", HFILL }
 372                 },
 373                 { &hf_mbtcp_protid,
 374                         { "protocol identifier",           "modbus_tcp.prot_id",
 375                         FT_UINT16, BASE_DEC, NULL, 0x0,
 376                         "", HFILL }
 377                 },
 378                 { &hf_mbtcp_len,
 379                         { "length",           "modbus_tcp.len",
 380                         FT_UINT16, BASE_DEC, NULL, 0x0,
 381                         "", HFILL }
 382                 },
 383                 /* Modbus header fields */
 384                 { &hf_mbtcp_unitid,
 385                         { "unit identifier",           "modbus_tcp.unit_id",
 386                         FT_UINT8, BASE_DEC, NULL, 0x0,
 387                         "", HFILL }
 388                 },
 389                 { &hf_mbtcp_functioncode,
 390                         { "function code ",           "modbus_tcp.func_code",
 391                         FT_UINT8, BASE_DEC, NULL, 0x0,
 392                         "", HFILL }
 393                 }
 394         };
 395
 396 /* Setup protocol subtree array */
 397         static gint *ett[] = {
 398                 &ett_mbtcp,
 399                 &ett_modbus_hdr
 400         };
 401
 402 /* Register the protocol name and description */
 403         proto_mbtcp = proto_register_protocol("Modbus/TCP",
 404             "Modbus/TCP", "mbtcp");
 405
 406 /* Required function calls to register the header fields and subtrees used */
 407         proto_register_field_array(proto_mbtcp, hf, array_length(hf));
 408         proto_register_subtree_array(ett, array_length(ett));
 409 }
 410
 411
 412 /* If this dissector uses sub-dissector registration add a registration routine.
 413    This format is required because a script is used to find these routines and
 414    create the code that calls these routines.
 415  */
 416 void
 417 proto_reg_handoff_mbtcp(void)
 418 {
 419         dissector_handle_t mbtcp_handle;
 420
 421         mbtcp_handle = create_dissector_handle(dissect_mbtcp, proto_mbtcp);
 422         dissector_add("tcp.port", TCP_PORT_MBTCP, mbtcp_handle);
 423 }