epan/dissectors/packet-mtp2.c

   1 /* packet-mtp2.c
   2  * Routines for MTP2 dissection
   3  * It is hopefully (needs testing) compliant to
   4  * ITU-T Q.703 and Q.703 Annex A.
   5  *
   6  * Copyright 2001, 2004 Michael Tuexen <tuexen [AT] fh-muenster.de>
   7  *
   8  * $Id$
   9  *
  10  * Wireshark - Network traffic analyzer
  11  * By Gerald Combs <gerald@wireshark.org>
  12  * Copyright 1998 Gerald Combs
  13  *
  14  * Copied from packet-m2pa.c
  15  *
  16  * This program is free software; you can redistribute it and/or
  17  * modify it under the terms of the GNU General Public License
  18  * as published by the Free Software Foundation; either version 2
  19  * of the License, or (at your option) any later version.
  20  *
  21  * This program is distributed in the hope that it will be useful,
  22  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  23  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  24  * GNU General Public License for more details.
  25  *
  26  * You should have received a copy of the GNU General Public License
  27  * along with this program; if not, write to the Free Software
  28  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  29  */
  30
  31 #include "config.h"
  32
  33 #include <glib.h>
  34 #include <epan/packet.h>
  35 #include <epan/prefs.h>
  36 #include <epan/crc16-tvb.h>
  37 #include <epan/expert.h>
  38
  39 /* Initialize the protocol and registered fields */
  40 static int proto_mtp2        = -1;
  41 static int hf_mtp2_bsn       = -1;
  42 static int hf_mtp2_ext_bsn   = -1;
  43 static int hf_mtp2_ext_res   = -1;
  44 static int hf_mtp2_bib       = -1;
  45 static int hf_mtp2_ext_bib   = -1;
  46 static int hf_mtp2_fsn       = -1;
  47 static int hf_mtp2_ext_fsn   = -1;
  48 static int hf_mtp2_fib       = -1;
  49 static int hf_mtp2_ext_fib   = -1;
  50 static int hf_mtp2_li        = -1;
  51 static int hf_mtp2_ext_li    = -1;
  52 static int hf_mtp2_spare     = -1;
  53 static int hf_mtp2_ext_spare = -1;
  54 static int hf_mtp2_sf        = -1;
  55 static int hf_mtp2_sf_extra  = -1;
  56
  57 static expert_field ei_mtp2_checksum_error = EI_INIT;
  58
  59 /* Initialize the subtree pointers */
  60 static gint ett_mtp2       = -1;
  61
  62 static dissector_handle_t mtp3_handle;
  63 static gboolean use_extended_sequence_numbers_default = FALSE;
  64 static gboolean use_extended_sequence_numbers         = FALSE;
  65
  66 #define BSN_BIB_LENGTH          1
  67 #define FSN_FIB_LENGTH          1
  68 #define LI_LENGTH               1
  69 #define HEADER_LENGTH           (BSN_BIB_LENGTH + FSN_FIB_LENGTH + LI_LENGTH)
  70
  71 #define EXTENDED_BSN_BIB_LENGTH 2
  72 #define EXTENDED_FSN_FIB_LENGTH 2
  73 #define EXTENDED_LI_LENGTH      2
  74 #define EXTENDED_HEADER_LENGTH  (EXTENDED_BSN_BIB_LENGTH + EXTENDED_FSN_FIB_LENGTH + EXTENDED_LI_LENGTH)
  75
  76 #define BSN_BIB_OFFSET          0
  77 #define FSN_FIB_OFFSET          (BSN_BIB_OFFSET + BSN_BIB_LENGTH)
  78 #define LI_OFFSET               (FSN_FIB_OFFSET + FSN_FIB_LENGTH)
  79 #define SIO_OFFSET              (LI_OFFSET + LI_LENGTH)
  80
  81 #define EXTENDED_BSN_BIB_OFFSET 0
  82 #define EXTENDED_FSN_FIB_OFFSET (EXTENDED_BSN_BIB_OFFSET + EXTENDED_BSN_BIB_LENGTH)
  83 #define EXTENDED_LI_OFFSET      (EXTENDED_FSN_FIB_OFFSET + EXTENDED_FSN_FIB_LENGTH)
  84 #define EXTENDED_SIO_OFFSET     (EXTENDED_LI_OFFSET + EXTENDED_LI_LENGTH)
  85
  86 #define BSN_MASK                0x7f
  87 #define BIB_MASK                0x80
  88 #define FSN_MASK                0x7f
  89 #define FIB_MASK                0x80
  90 #define LI_MASK                 0x3f
  91 #define SPARE_MASK              0xc0
  92
  93 #define EXTENDED_BSN_MASK       0x0fff
  94 #define EXTENDED_RES_MASK       0x7000
  95 #define EXTENDED_BIB_MASK       0x8000
  96 #define EXTENDED_FSN_MASK       0x0fff
  97 #define EXTENDED_FIB_MASK       0x8000
  98 #define EXTENDED_LI_MASK        0x01ff
  99 #define EXTENDED_SPARE_MASK     0xfe00
 100
 101 static void
 102 dissect_mtp2_header(tvbuff_t *su_tvb, proto_item *mtp2_tree)
 103 {
 104   if (mtp2_tree) {
 105     if (use_extended_sequence_numbers) {
 106       proto_tree_add_item(mtp2_tree, hf_mtp2_ext_bsn,   su_tvb, EXTENDED_BSN_BIB_OFFSET, EXTENDED_BSN_BIB_LENGTH, ENC_LITTLE_ENDIAN);
 107       proto_tree_add_item(mtp2_tree, hf_mtp2_ext_res,   su_tvb, EXTENDED_BSN_BIB_OFFSET, EXTENDED_BSN_BIB_LENGTH, ENC_LITTLE_ENDIAN);
 108       proto_tree_add_item(mtp2_tree, hf_mtp2_ext_bib,   su_tvb, EXTENDED_BSN_BIB_OFFSET, EXTENDED_BSN_BIB_LENGTH, ENC_LITTLE_ENDIAN);
 109       proto_tree_add_item(mtp2_tree, hf_mtp2_ext_fsn,   su_tvb, EXTENDED_FSN_FIB_OFFSET, EXTENDED_FSN_FIB_LENGTH, ENC_LITTLE_ENDIAN);
 110       proto_tree_add_item(mtp2_tree, hf_mtp2_ext_res,   su_tvb, EXTENDED_BSN_BIB_OFFSET, EXTENDED_BSN_BIB_LENGTH, ENC_LITTLE_ENDIAN);
 111       proto_tree_add_item(mtp2_tree, hf_mtp2_ext_fib,   su_tvb, EXTENDED_FSN_FIB_OFFSET, EXTENDED_FSN_FIB_LENGTH, ENC_LITTLE_ENDIAN);
 112       proto_tree_add_item(mtp2_tree, hf_mtp2_ext_li,    su_tvb, EXTENDED_LI_OFFSET,      EXTENDED_LI_LENGTH,      ENC_LITTLE_ENDIAN);
 113       proto_tree_add_item(mtp2_tree, hf_mtp2_ext_spare, su_tvb, EXTENDED_LI_OFFSET,      EXTENDED_LI_LENGTH,      ENC_LITTLE_ENDIAN);
 114     } else {
 115       proto_tree_add_item(mtp2_tree, hf_mtp2_bsn,   su_tvb, BSN_BIB_OFFSET, BSN_BIB_LENGTH, ENC_LITTLE_ENDIAN);
 116       proto_tree_add_item(mtp2_tree, hf_mtp2_bib,   su_tvb, BSN_BIB_OFFSET, BSN_BIB_LENGTH, ENC_LITTLE_ENDIAN);
 117       proto_tree_add_item(mtp2_tree, hf_mtp2_fsn,   su_tvb, FSN_FIB_OFFSET, FSN_FIB_LENGTH, ENC_LITTLE_ENDIAN);
 118       proto_tree_add_item(mtp2_tree, hf_mtp2_fib,   su_tvb, FSN_FIB_OFFSET, FSN_FIB_LENGTH, ENC_LITTLE_ENDIAN);
 119       proto_tree_add_item(mtp2_tree, hf_mtp2_li,    su_tvb, LI_OFFSET,      LI_LENGTH,      ENC_LITTLE_ENDIAN);
 120       proto_tree_add_item(mtp2_tree, hf_mtp2_spare, su_tvb, LI_OFFSET,      LI_LENGTH,      ENC_LITTLE_ENDIAN);
 121     }
 122   }
 123 }
 124 /*
 125 *******************************************************************************
 126 * DETAILS : Calculate a new FCS-16 given the current FCS-16 and the new data.
 127 *******************************************************************************
 128 */
 129 static guint16
 130 mtp2_fcs16(tvbuff_t * tvbuff)
 131 {
 132     guint len = tvb_length(tvbuff)-2;
 133
 134     /* Check for Invalid Length */
 135     if (len == 0)
 136         return (0x0000);
 137     return crc16_ccitt_tvb(tvbuff, len);
 138 }
 139
 140 /*
 141  * This function for CRC16 only is based on the decode_fcs of packet_ppp.c
 142  */
 143 static tvbuff_t *
 144 mtp2_decode_crc16(tvbuff_t *tvb, proto_tree *fh_tree, packet_info *pinfo)
 145 {
 146   tvbuff_t   *next_tvb;
 147   gint       len, reported_len;
 148   int        rx_fcs_offset;
 149   guint32    rx_fcs_exp;
 150   guint32    rx_fcs_got;
 151   int proto_offset=0;
 152   proto_item *cause;
 153
 154   /*
 155    * Do we have the entire packet, and does it include a 2-byte FCS?
 156    */
 157   len = tvb_length_remaining(tvb, proto_offset);
 158   reported_len = tvb_reported_length_remaining(tvb, proto_offset);
 159   if (reported_len < 2 || len < 0) {
 160     /*
 161      * The packet is claimed not to even have enough data for a 2-byte FCS,
 162      * or we're already past the end of the captured data.
 163      * Don't slice anything off.
 164      */
 165     next_tvb = tvb_new_subset_remaining(tvb, proto_offset);
 166   } else if (len < reported_len) {
 167     /*
 168      * The packet is claimed to have enough data for a 2-byte FCS, but
 169      * we didn't capture all of the packet.
 170      * Slice off the 2-byte FCS from the reported length, and trim the
 171      * captured length so it's no more than the reported length; that
 172      * will slice off what of the FCS, if any, is in the captured
 173      * length.
 174      */
 175     reported_len -= 2;
 176     if (len > reported_len)
 177       len = reported_len;
 178     next_tvb = tvb_new_subset(tvb, proto_offset, len, reported_len);
 179   } else {
 180     /*
 181      * We have the entire packet, and it includes a 2-byte FCS.
 182      * Slice it off.
 183      */
 184     len -= 2;
 185     reported_len -= 2;
 186     next_tvb = tvb_new_subset(tvb, proto_offset, len, reported_len);
 187
 188     /*
 189      * Compute the FCS and put it into the tree.
 190      */
 191     rx_fcs_offset = proto_offset + len;
 192     rx_fcs_exp = mtp2_fcs16(tvb);
 193     rx_fcs_got = tvb_get_letohs(tvb, rx_fcs_offset);
 194     if (rx_fcs_got != rx_fcs_exp) {
 195       cause=proto_tree_add_text(fh_tree, tvb, rx_fcs_offset, 2,
 196                                 "FCS 16: 0x%04x [incorrect, should be 0x%04x]",
 197                                 rx_fcs_got, rx_fcs_exp);
 198       expert_add_info(pinfo, cause, &ei_mtp2_checksum_error);
 199     } else {
 200       proto_tree_add_text(fh_tree, tvb, rx_fcs_offset, 2,
 201                           "FCS 16: 0x%04x [correct]",
 202                           rx_fcs_got);
 203     }
 204   }
 205   return next_tvb;
 206 }
 207
 208
 209 static void
 210 dissect_mtp2_fisu(packet_info *pinfo)
 211 {
 212   col_set_str(pinfo->cinfo, COL_INFO, "FISU ");
 213 }
 214
 215 static const value_string status_field_vals[] = {
 216   { 0x0, "Status Indication O" },
 217   { 0x1, "Status Indication N" },
 218   { 0x2, "Status Indication E" },
 219   { 0x3, "Status Indication OS" },
 220   { 0x4, "Status Indication PO" },
 221   { 0x5, "Status Indication B" },
 222   { 0,   NULL}
 223 };
 224
 225 /* Same as above but in acronym form (for the Info column) */
 226 static const value_string status_field_acro_vals[] = {
 227   { 0x0, "SIO" },
 228   { 0x1, "SIN" },
 229   { 0x2, "SIE" },
 230   { 0x3, "SIOS" },
 231   { 0x4, "SIPO" },
 232   { 0x5, "SIB" },
 233   { 0,   NULL}
 234 };
 235
 236 #define SF_OFFSET          (LI_OFFSET + LI_LENGTH)
 237 #define EXTENDED_SF_OFFSET (EXTENDED_LI_OFFSET + EXTENDED_LI_LENGTH)
 238
 239 #define SF_LENGTH                       1
 240 #define SF_EXTRA_OFFSET                 (SF_OFFSET + SF_LENGTH)
 241 #define EXTENDED_SF_EXTRA_OFFSET        (EXTENDED_SF_OFFSET + SF_LENGTH)
 242 #define SF_EXTRA_LENGTH                 1
 243
 244 static void
 245 dissect_mtp2_lssu(tvbuff_t *su_tvb, packet_info *pinfo, proto_item *mtp2_tree)
 246 {
 247   guint8 sf = 0xFF;
 248   guint8 sf_offset, sf_extra_offset;
 249
 250   if (use_extended_sequence_numbers) {
 251     sf_offset = EXTENDED_SF_OFFSET;
 252     sf_extra_offset = EXTENDED_SF_EXTRA_OFFSET;
 253   } else {
 254     sf_offset = SF_OFFSET;
 255     sf_extra_offset = SF_EXTRA_OFFSET;
 256   }
 257
 258   proto_tree_add_item(mtp2_tree, hf_mtp2_sf, su_tvb, sf_offset, SF_LENGTH, ENC_LITTLE_ENDIAN);
 259   sf = tvb_get_guint8(su_tvb, SF_OFFSET);
 260
 261   /*  If the LI is 2 then there is an extra octet following the standard SF
 262    *  field but it is not defined what this octet is.
 263    *  (In any case the first byte of the SF always has the same meaning.)
 264    */
 265   if ((tvb_get_guint8(su_tvb, LI_OFFSET) & LI_MASK) == 2)
 266     proto_tree_add_item(mtp2_tree, hf_mtp2_sf_extra, su_tvb, sf_extra_offset, SF_EXTRA_LENGTH, ENC_LITTLE_ENDIAN);
 267
 268   col_set_str(pinfo->cinfo, COL_INFO, val_to_str_const(sf, status_field_acro_vals, "Unknown"));
 269 }
 270
 271 static void
 272 dissect_mtp2_msu(tvbuff_t *su_tvb, packet_info *pinfo, proto_item *mtp2_item, proto_item *tree)
 273 {
 274   gint sif_sio_length;
 275   tvbuff_t *sif_sio_tvb;
 276
 277   col_set_str(pinfo->cinfo, COL_INFO, "MSU ");
 278
 279   if (use_extended_sequence_numbers) {
 280     sif_sio_length = tvb_length(su_tvb) - EXTENDED_HEADER_LENGTH;
 281     sif_sio_tvb = tvb_new_subset(su_tvb, EXTENDED_SIO_OFFSET, sif_sio_length, sif_sio_length);
 282   } else {
 283     sif_sio_length = tvb_length(su_tvb) - HEADER_LENGTH;
 284     sif_sio_tvb = tvb_new_subset(su_tvb, SIO_OFFSET, sif_sio_length, sif_sio_length);
 285   }
 286   call_dissector(mtp3_handle, sif_sio_tvb, pinfo, tree);
 287
 288   if (tree) {
 289     if (use_extended_sequence_numbers)
 290       proto_item_set_len(mtp2_item, EXTENDED_HEADER_LENGTH);
 291     else
 292       proto_item_set_len(mtp2_item, HEADER_LENGTH);
 293   }
 294 }
 295
 296 static void
 297 dissect_mtp2_su(tvbuff_t *su_tvb, packet_info *pinfo, proto_item *mtp2_item, proto_item *mtp2_tree, proto_tree *tree,gboolean validate_crc)
 298 {
 299   guint16 li;
 300   tvbuff_t  *next_tvb = NULL;
 301
 302   dissect_mtp2_header(su_tvb, mtp2_tree);
 303   if (validate_crc)
 304     next_tvb = mtp2_decode_crc16(su_tvb, mtp2_tree, pinfo);
 305
 306   if (use_extended_sequence_numbers)
 307     li = tvb_get_letohs(su_tvb, EXTENDED_LI_OFFSET) & EXTENDED_LI_MASK;
 308   else
 309     li = tvb_get_guint8(su_tvb, LI_OFFSET) & LI_MASK;
 310   switch(li) {
 311   case 0:
 312     dissect_mtp2_fisu(pinfo);
 313     break;
 314   case 1:
 315   case 2:
 316     if (validate_crc)
 317       dissect_mtp2_lssu(next_tvb, pinfo, mtp2_tree);
 318     else
 319       dissect_mtp2_lssu(su_tvb, pinfo, mtp2_tree);
 320     break;
 321   default:
 322     /* In some capture files (like .rf5), CRC are not present */
 323     /* So, to avoid trouble, give the complete buffer if CRC validation is disabled */
 324     if (validate_crc)
 325       dissect_mtp2_msu(next_tvb, pinfo, mtp2_item, tree);
 326     else
 327       dissect_mtp2_msu(su_tvb, pinfo, mtp2_item, tree);
 328     break;
 329   }
 330 }
 331
 332 static void
 333 dissect_mtp2_common(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, gboolean validate_crc)
 334 {
 335   proto_item *mtp2_item = NULL;
 336   proto_tree *mtp2_tree = NULL;
 337
 338   if (pinfo->annex_a_used == MTP2_ANNEX_A_USED_UNKNOWN)
 339     use_extended_sequence_numbers = use_extended_sequence_numbers_default;
 340   else
 341     use_extended_sequence_numbers = (pinfo->annex_a_used == MTP2_ANNEX_A_USED);
 342
 343   col_set_str(pinfo->cinfo, COL_PROTOCOL, "MTP2");
 344
 345   if (tree) {
 346     mtp2_item = proto_tree_add_item(tree, proto_mtp2, tvb, 0, -1, ENC_NA);
 347     mtp2_tree = proto_item_add_subtree(mtp2_item, ett_mtp2);
 348   };
 349
 350   dissect_mtp2_su(tvb, pinfo, mtp2_item, mtp2_tree, tree, validate_crc);
 351 }
 352
 353 /* Dissect MTP2 frame with/without CRC16 included at end of payload */
 354 static void
 355 dissect_mtp2(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
 356 {
 357   /* If the link extension indicates the FCS presence, then the Checkbits
 358    * have to be proceeded in the MTP2 dissector */
 359   if ( pinfo->fd->lnk_t == WTAP_ENCAP_ERF ) {
 360     dissect_mtp2_common(tvb, pinfo, tree, TRUE);
 361   } else {
 362     dissect_mtp2_common(tvb, pinfo, tree, FALSE);
 363   }
 364 }
 365
 366 void
 367 proto_register_mtp2(void)
 368 {
 369
 370   static hf_register_info hf[] = {
 371     { &hf_mtp2_bsn,       { "Backward sequence number", "mtp2.bsn",      FT_UINT8,  BASE_DEC, NULL,                    BSN_MASK,            NULL, HFILL } },
 372     { &hf_mtp2_ext_bsn,   { "Backward sequence number", "mtp2.bsn",      FT_UINT16, BASE_DEC, NULL,                    EXTENDED_BSN_MASK,   NULL, HFILL } },
 373     { &hf_mtp2_ext_res,   { "Reserved",                 "mtp2.res",      FT_UINT16, BASE_DEC, NULL,                    EXTENDED_RES_MASK,   NULL, HFILL } },
 374     { &hf_mtp2_bib,       { "Backward indicator bit",   "mtp2.bib",      FT_UINT8,  BASE_DEC, NULL,                    BIB_MASK,            NULL, HFILL } },
 375     { &hf_mtp2_ext_bib,   { "Backward indicator bit",   "mtp2.bib",      FT_UINT16, BASE_DEC, NULL,                    EXTENDED_BIB_MASK,   NULL, HFILL } },
 376     { &hf_mtp2_fsn,       { "Forward sequence number",  "mtp2.fsn",      FT_UINT8,  BASE_DEC, NULL,                    FSN_MASK,            NULL, HFILL } },
 377     { &hf_mtp2_ext_fsn,   { "Forward sequence number",  "mtp2.fsn",      FT_UINT16, BASE_DEC, NULL,                    EXTENDED_FSN_MASK,   NULL, HFILL } },
 378     { &hf_mtp2_fib,       { "Forward indicator bit",    "mtp2.fib",      FT_UINT8,  BASE_DEC, NULL,                    FIB_MASK,            NULL, HFILL } },
 379     { &hf_mtp2_ext_fib,   { "Forward indicator bit",    "mtp2.fib",      FT_UINT16, BASE_DEC, NULL,                    EXTENDED_FIB_MASK,   NULL, HFILL } },
 380     { &hf_mtp2_li,        { "Length Indicator",         "mtp2.li",       FT_UINT8,  BASE_DEC, NULL,                    LI_MASK,             NULL, HFILL } },
 381     { &hf_mtp2_ext_li,    { "Length Indicator",         "mtp2.li",       FT_UINT16, BASE_DEC, NULL,                    EXTENDED_LI_MASK,    NULL, HFILL } },
 382     { &hf_mtp2_spare,     { "Spare",                    "mtp2.spare",    FT_UINT8,  BASE_DEC, NULL,                    SPARE_MASK,          NULL, HFILL } },
 383     { &hf_mtp2_ext_spare, { "Spare",                    "mtp2.spare",    FT_UINT16, BASE_DEC, NULL,                    EXTENDED_SPARE_MASK, NULL, HFILL } },
 384     { &hf_mtp2_sf,        { "Status field",             "mtp2.sf",       FT_UINT8,  BASE_DEC, VALS(status_field_vals), 0x0,                 NULL, HFILL } },
 385     { &hf_mtp2_sf_extra,  { "Status field extra octet", "mtp2.sf_extra", FT_UINT8,  BASE_HEX, NULL,                    0x0,                 NULL, HFILL } }
 386   };
 387
 388   static gint *ett[] = {
 389     &ett_mtp2
 390   };
 391
 392   static ei_register_info ei[] = {
 393      { &ei_mtp2_checksum_error, { "mtp2.checksum.error", PI_CHECKSUM, PI_WARN, "MTP2 Frame CheckFCS 16 Error", EXPFILL }},
 394   };
 395
 396   module_t *mtp2_module;
 397   expert_module_t* expert_mtp2;
 398
 399   proto_mtp2 = proto_register_protocol("Message Transfer Part Level 2", "MTP2", "mtp2");
 400   register_dissector("mtp2", dissect_mtp2, proto_mtp2);
 401
 402   proto_register_field_array(proto_mtp2, hf, array_length(hf));
 403   proto_register_subtree_array(ett, array_length(ett));
 404   expert_mtp2 = expert_register_protocol(proto_mtp2);
 405   expert_register_field_array(expert_mtp2, ei, array_length(ei));
 406
 407   mtp2_module = prefs_register_protocol(proto_mtp2, NULL);
 408   prefs_register_bool_preference(mtp2_module,
 409                                  "use_extended_sequence_numbers",
 410                                  "Use extended sequence numbers",
 411                                  "Whether the MTP2 dissector should use extended sequence numbers as described in Q.703, Annex A as a default.",
 412                                  &use_extended_sequence_numbers_default);
 413
 414
 415 }
 416
 417 void
 418 proto_reg_handoff_mtp2(void)
 419 {
 420   dissector_handle_t mtp2_handle;
 421
 422   mtp2_handle = find_dissector("mtp2");
 423   dissector_add_uint("wtap_encap", WTAP_ENCAP_MTP2, mtp2_handle);
 424   dissector_add_uint("wtap_encap", WTAP_ENCAP_MTP2_WITH_PHDR, mtp2_handle);
 425
 426   mtp3_handle   = find_dissector("mtp3");
 427 }