epan/dissectors/packet-null.c

   1 /* packet-null.c
   2  * Routines for null packet disassembly
   3  *
   4  * Wireshark - Network traffic analyzer
   5  * By Gerald Combs <gerald@wireshark.org>
   6  *
   7  * This file created by Mike Hall <mlh@io.com>
   8  * Copyright 1998
   9  *
  10  * SPDX-License-Identifier: GPL-2.0-or-later
  11  */
  12
  13 #include "config.h"
  14
  15 #include <wsutil/pint.h>
  16
  17 #include <epan/packet.h>
  18 #include <epan/capture_dissectors.h>
  19 #include "packet-ip.h"
  20 #include "packet-ppp.h"
  21 #include <epan/etypes.h>
  22 #include <epan/aftypes.h>
  23
  24 void proto_register_null(void);
  25 void proto_reg_handoff_null(void);
  26
  27 static dissector_table_t null_dissector_table;
  28 static dissector_table_t ethertype_dissector_table;
  29
  30 /* protocols and header fields */
  31 static int proto_null;
  32 static int hf_null_etype;
  33 static int hf_null_family;
  34
  35 static int ett_null;
  36
  37 /* Null/loopback structs and definitions */
  38
  39 /* Family values. */
  40 static const value_string family_vals[] = {
  41   {BSD_AF_INET,          "IP"             },
  42   {BSD_AF_ISO,           "OSI"            },
  43   {BSD_AF_APPLETALK,     "Appletalk"      },
  44   {BSD_AF_IPX,           "Netware IPX/SPX"},
  45   {BSD_AF_INET6_BSD,     "IPv6"           },
  46   {BSD_AF_INET6_FREEBSD, "IPv6"           },
  47   {BSD_AF_INET6_DARWIN,  "IPv6"           },
  48   {0,                    NULL             }
  49 };
  50
  51 static dissector_handle_t null_handle, loop_handle;
  52 static capture_dissector_handle_t null_cap_handle;
  53
  54 static dissector_handle_t ppp_hdlc_handle;
  55 static capture_dissector_handle_t ppp_hdlc_cap_handle;
  56
  57 static bool
  58 capture_null( const unsigned char *pd, int offset _U_, int len, capture_packet_info_t *cpinfo, const union wtap_pseudo_header *pseudo_header _U_ )
  59 {
  60   uint32_t null_header;
  61
  62   /*
  63    * BSD drivers that use DLT_NULL - including the FreeBSD 3.2 ISDN-for-BSD
  64    * drivers, as well as the 4.4-Lite and FreeBSD loopback drivers -
  65    * stuff the AF_ value for the protocol, in *host* byte order, in the
  66    * first four bytes.
  67    *
  68    * However, the IRIX and UNICOS/mp snoop socket mechanism supplies,
  69    * on loopback devices, a 4-byte header that has a 2 byte (big-endian)
  70    * AF_ value and 2 bytes of 0, so it's
  71    *
  72    *    0000AAAA
  73    *
  74    * when read on a little-endian machine and
  75    *
  76    *    AAAA0000
  77    *
  78    * when read on a big-endian machine.  The current CVS version of libpcap
  79    * compensates for this by converting it to standard 4-byte format before
  80    * processing the packet, but snoop captures from IRIX or UNICOS/mp
  81    * have the 2-byte+2-byte header, as might tcpdump or libpcap captures
  82    * with older versions of libpcap.
  83    *
  84    * AF_ values are small integers, and probably fit in 8 bits (current
  85    * values on the BSDs do), and have their upper 24 bits zero.
  86    * This means that, in practice, if you look at the header as a 32-bit
  87    * integer in host byte order:
  88    *
  89    *    on a little-endian machine:
  90    *
  91    *            a little-endian DLT_NULL header looks like
  92    *
  93    *                    000000AA
  94    *
  95    *            a big-endian DLT_NULL header, or a DLT_LOOP header, looks
  96    *            like
  97    *
  98    *                    AA000000
  99    *
 100    *            an IRIX or UNICOS/mp DLT_NULL header looks like
 101    *
 102    *                    0000AA00
 103    *
 104    *    on a big-endian machine:
 105    *
 106    *            a big-endian DLT_NULL header, or a DLT_LOOP header, looks
 107    *            like
 108    *
 109    *                    000000AA
 110    *
 111    *            a little-endian DLT_NULL header looks like
 112    *
 113    *                    AA000000
 114    *
 115    *            an IRIX or UNICOS/mp DLT_NULL header looks like
 116    *
 117    *                    00AA0000
 118    *
 119    * However, according to Gerald Combs, a FreeBSD ISDN PPP dump that
 120    * Andreas Klemm sent to wireshark-dev has a packet type of DLT_NULL,
 121    * and the family bits look like PPP's protocol field.  (Was this an
 122    * older, or different, ISDN driver?)  Looking at what appears to be
 123    * that capture file, it appears that it's using PPP in HDLC framing,
 124    * RFC 1549, wherein the first two octets of the frame are 0xFF
 125    * (address) and 0x03 (control), so the header bytes are, in order:
 126    *
 127    *    0xFF
 128    *    0x03
 129    *    high-order byte of a PPP protocol field
 130    *    low-order byte of a PPP protocol field
 131    *
 132    * If we treat that as a 32-bit host-byte-order value, it looks like
 133    *
 134    *    PPPP03FF
 135    *
 136    * where PPPP is a byte-swapped PPP protocol type if we read it on
 137    * a little-endian machine and
 138    *
 139    *    FF03PPPP
 140    *
 141    * where PPPP is a PPP protocol type if we read it on a big-endian
 142    * machine.  0x0000 does not appear to be a valid PPP protocol type
 143    * value, so at least one of those hex digits is guaranteed not to
 144    * be 0.
 145    *
 146    * Old versions of libpcap for Linux used DLT_NULL for loopback devices,
 147    * but not any other devices.  (Current versions use DLT_EN10MB for it.)
 148    * The Linux loopback driver puts an *Ethernet* header at the beginning
 149    * of loopback packets, with fake source and destination addresses and
 150    * the appropriate Ethernet type value; however, those older versions of
 151    * libpcap for Linux compensated for this by skipping the source and
 152    * destination MAC addresses, replacing them with 2 bytes of 0.
 153    * This means that if we're reading the capture on a little-endian
 154    * machine, the header, treated as a 32-bit integer, looks like
 155    *
 156    *    EEEE0000
 157    *
 158    * where EEEE is a byte-swapped Ethernet type, and if we're reading it
 159    * on a big-endian machine, it looks like
 160    *
 161    *    0000EEEE
 162    *
 163    * where EEEE is an Ethernet type.
 164    *
 165    * If the first 2 bytes of the header are FF 03:
 166    *
 167    *    it can't be a big-endian BSD DLT_NULL header, or a DLT_LOOP
 168    *    header, as AF_ values are small so the first 2 bytes of the
 169    *    header would be 0;
 170    *
 171    *    it can't be a little-endian BSD DLT_NULL header, as the
 172    *    resulting AF_ value would be >= 0x03FF, which is too big
 173    *    for an AF_ value;
 174    *
 175    *    it can't be an IRIX or UNICOS/mp DLT_NULL header, as the
 176    *    resulting AF_ value with be 0x03FF.
 177    *
 178    * So the first thing we do is check the first two bytes of the
 179    * header; if it's FF 03, we treat the packet as a PPP frame.
 180    *
 181    * Otherwise, if the upper 16 bits are non-zero, either:
 182    *
 183    *    it's a BSD DLT_NULL header whose AF_ value is not in our
 184    *    byte order;
 185    *
 186    *    it's an IRIX or UNICOS/mp DLT_NULL header being read on
 187    *    a big-endian machine;
 188    *
 189    *    it's a Linux DLT_NULL header being read on a little-endian
 190    *    machine.
 191    *
 192    * In all those cases except for the IRIX or UNICOS/mp DLT_NULL header,
 193    * we should byte-swap it (if it's a Linux DLT_NULL header, that'll
 194    * put the Ethernet type in the right byte order).  In the case
 195    * of the IRIX or UNICOS/mp DLT_NULL header, we should just get
 196    * the upper 16 bits as an AF_ value.
 197    *
 198    * If it's a BSD DLT_NULL header whose AF_ value is not in our byte
 199    * order, then the upper 2 hex digits would be non-zero and the next
 200    * 2 hex digits down would be zero, as AF_ values fit in 8 bits, and
 201    * the upper 2 hex digits are the *lower* 8 bits of the value.
 202    *
 203    * If it's an IRIX or UNICOS/mp DLT_NULL header, the upper 2 hex digits
 204    * would be zero and the next 2 hex digits down would be non-zero, as
 205    * the upper 16 bits are a big-endian AF_ value.  Furthermore, the
 206    * next 2 hex digits down are likely to be < 0x60, as 0x60 is 96,
 207    * and, so far, we're far from requiring AF_ values that high.
 208    *
 209    * If it's a Linux DLT_NULL header, the third hex digit from the top
 210    * will be >= 6, as Ethernet types are >= 1536, or 0x0600, and
 211    * it's byte-swapped, so the second 2 hex digits from the top are
 212    * >= 0x60.
 213    *
 214    * So, if the upper 16 bits are non-zero:
 215    *
 216    *    if the upper 2 hex digits are 0 and the next 2 hex digits are
 217    *    in the range 0x00-0x5F, we treat it as a big-endian IRIX or
 218    *    UNICOS/mp DLT_NULL header;
 219    *
 220    *    otherwise, we byte-swap it and do the next stage.
 221    *
 222    * If the upper 16 bits are zero, either:
 223    *
 224    *    it's a BSD DLT_NULL header whose AF_ value is in our byte
 225    *    order;
 226    *
 227    *    it's an IRIX or UNICOS/mp DLT_NULL header being read on
 228    *    a little-endian machine;
 229    *
 230    *    it's a Linux DLT_NULL header being read on a big-endian
 231    *    machine.
 232    *
 233    * In all of those cases except for the IRIX or UNICOS/mp DLT_NULL header,
 234    * we should *not* byte-swap it.  In the case of the IRIX or UNICOS/mp
 235    * DLT_NULL header, we should extract the AF_ value and byte-swap it.
 236    *
 237    * If it's a BSD DLT_NULL header whose AF_ value is in our byte order,
 238    * the upper 6 hex digits would all be zero.
 239    *
 240    * If it's an IRIX or UNICOS/mp DLT_NULL header, the upper 4 hex
 241    * digits would be zero and the next 2 hex digits would not be zero.
 242    * Furthermore, the third hex digit from the bottom would be <
 243    */
 244   if (!BYTES_ARE_IN_FRAME(0, len, 2))
 245     return false;
 246
 247   if (pd[0] == 0xFF && pd[1] == 0x03) {
 248     /*
 249      * Hand it to PPP.
 250      */
 251     return call_capture_dissector(ppp_hdlc_cap_handle, pd, 0, len, cpinfo, pseudo_header);
 252   } else {
 253     /*
 254      * Treat it as a normal DLT_NULL header.
 255      */
 256     if (!BYTES_ARE_IN_FRAME(0, len, (int)sizeof(null_header)))
 257       return false;
 258
 259     memcpy((char *)&null_header, (const char *)&pd[0], sizeof(null_header));
 260
 261     if ((null_header & 0xFFFF0000) != 0) {
 262       /*
 263        * It is possible that the AF_ type was only a 16 bit value.
 264        * IRIX and UNICOS/mp loopback snoop use a 4 byte header with
 265        * AF_ type in the first 2 bytes!
 266        * BSD AF_ types will always have the upper 8 bits as 0.
 267        */
 268       if ((null_header & 0xFF000000) == 0 &&
 269           (null_header & 0x00FF0000) < 0x00060000) {
 270         /*
 271          * Looks like a IRIX or UNICOS/mp loopback header, in the
 272          * correct byte order.  Set the null header value to the
 273          * AF_ type, which is in the upper 16 bits of "null_header".
 274          */
 275         null_header >>= 16;
 276       } else {
 277         /* Byte-swap it. */
 278         null_header = GUINT32_SWAP_LE_BE(null_header);
 279       }
 280     } else {
 281       /*
 282        * Check for an IRIX or UNICOS/mp snoop header.
 283        */
 284       if ((null_header & 0x000000FF) == 0 &&
 285           (null_header & 0x0000FF00) < 0x00000600) {
 286         /*
 287          * Looks like a IRIX or UNICOS/mp loopback header, in the
 288          * wrong byte order.  Set the null header value to the AF_
 289          * type; that's in the lower 16 bits of "null_header", but
 290          * is byte-swapped.
 291          */
 292         null_header = GUINT16_SWAP_LE_BE(null_header & 0xFFFF);
 293       }
 294     }
 295
 296     /*
 297      * The null header value must be greater than the IEEE 802.3 maximum
 298      * frame length to be a valid Ethernet type; if it is, hand it
 299      * to "capture_ethertype()", otherwise treat it as a BSD AF_type (we
 300      * wire in the values of the BSD AF_ types, because the values
 301      * in the file will be BSD values, and the OS on which
 302      * we're building this might not have the same values or
 303      * might not have them defined at all; XXX - what if different
 304      * BSD derivatives have different values?).
 305      */
 306     if (null_header > IEEE_802_3_MAX_LEN)
 307       return try_capture_dissector("ethertype", null_header, pd, 4, len, cpinfo, pseudo_header);
 308     else
 309       return try_capture_dissector("null.bsd", null_header, pd, 4, len, cpinfo, pseudo_header);
 310   }
 311
 312   return false;
 313 }
 314
 315 static int
 316 dissect_null(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void* data _U_)
 317 {
 318   uint32_t      null_header;
 319   proto_tree    *fh_tree;
 320   proto_item    *ti;
 321   tvbuff_t      *next_tvb;
 322
 323   /*
 324    * See comment in "capture_null()" for an explanation of what we're
 325    * doing.
 326    */
 327   if (tvb_get_ntohs(tvb, 0) == 0xFF03) {
 328     /*
 329      * Hand it to PPP.
 330      */
 331     call_dissector(ppp_hdlc_handle, tvb, pinfo, tree);
 332   } else {
 333
 334     /* load the top pane info. This should be overwritten by
 335        the next protocol in the stack */
 336     col_set_str(pinfo->cinfo, COL_RES_DL_SRC, "N/A");
 337     col_set_str(pinfo->cinfo, COL_RES_DL_DST, "N/A");
 338     col_set_str(pinfo->cinfo, COL_PROTOCOL, "N/A");
 339     col_set_str(pinfo->cinfo, COL_INFO, "Null/Loopback");
 340
 341     /*
 342      * Treat it as a normal DLT_NULL header.  Fetch it in host
 343      * byte order.
 344      */
 345     null_header = tvb_get_h_uint32(tvb, 0);
 346
 347     if ((null_header & 0xFFFF0000) != 0) {
 348       /*
 349        * It is possible that the AF_ type was only a 16 bit value.
 350        * IRIX and UNICOS/mp loopback snoop use a 4 byte header with
 351        * AF_ type in the first 2 bytes!
 352        * BSD AF_ types will always have the upper 8 bits as 0.
 353        */
 354       if ((null_header & 0xFF000000) == 0 &&
 355           (null_header & 0x00FF0000) < 0x00060000) {
 356         /*
 357          * Looks like a IRIX or UNICOS/mp loopback header, in the
 358          * correct byte order.  Set the null header value to the
 359          * AF_ type, which is in the upper 16 bits of "null_header".
 360          */
 361         null_header >>= 16;
 362       } else {
 363         /* Byte-swap it. */
 364         null_header = GUINT32_SWAP_LE_BE(null_header);
 365       }
 366     } else {
 367       /*
 368        * Check for an IRIX or UNICOS/mp snoop header.
 369        */
 370       if ((null_header & 0x000000FF) == 0 &&
 371           (null_header & 0x0000FF00) < 0x00000600) {
 372         /*
 373          * Looks like a IRIX or UNICOS/mp loopback header, in the
 374          * wrong byte order.  Set the null header value to the AF_
 375          * type; that's in the lower 16 bits of "null_header", but
 376          * is byte-swapped.
 377          */
 378         null_header = GUINT16_SWAP_LE_BE(null_header & 0xFFFF);
 379       }
 380     }
 381
 382     /*
 383      * The null header value must be greater than the IEEE 802.3 maximum
 384      * frame length to be a valid Ethernet type; if it is, dissect it
 385      * as one, otherwise treat it as a BSD AF_type (we wire in the values
 386      * of the BSD AF_ types, because the values in the file will be BSD
 387      * values, and the OS on which we're building this might not have the
 388      * same values or might not have them defined at all; XXX - what if
 389      * different BSD derivatives have different values?).
 390      */
 391     if (null_header > IEEE_802_3_MAX_LEN) {
 392       if (tree) {
 393         ti = proto_tree_add_item(tree, proto_null, tvb, 0, 4, ENC_NA);
 394         fh_tree = proto_item_add_subtree(ti, ett_null);
 395         proto_tree_add_uint(fh_tree, hf_null_etype, tvb, 0, 4,
 396           (uint16_t) null_header);
 397       }
 398
 399       next_tvb = tvb_new_subset_remaining(tvb, 4);
 400       if (!dissector_try_uint(ethertype_dissector_table,
 401             (uint16_t) null_header, next_tvb, pinfo, tree))
 402         call_data_dissector(next_tvb, pinfo, tree);
 403     } else {
 404       /* populate a tree in the second pane with the status of the link
 405          layer (ie none) */
 406       if (tree) {
 407         ti = proto_tree_add_item(tree, proto_null, tvb, 0, 4, ENC_NA);
 408         fh_tree = proto_item_add_subtree(ti, ett_null);
 409         proto_tree_add_uint(fh_tree, hf_null_family, tvb, 0, 4, null_header);
 410       }
 411
 412       next_tvb = tvb_new_subset_remaining(tvb, 4);
 413       if (!dissector_try_uint(null_dissector_table, null_header,
 414             next_tvb, pinfo, tree)) {
 415         /* No sub-dissector found.  Label rest of packet as "Data" */
 416         call_data_dissector(next_tvb, pinfo, tree);
 417       }
 418     }
 419   }
 420   return tvb_captured_length(tvb);
 421 }
 422
 423 /*
 424  * OpenBSD DLT_LOOP; like DLT_NULL, but with the first 4 byte *always*
 425  * being a *big-endian* type.
 426  */
 427 static int
 428 dissect_loop(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void* data _U_)
 429 {
 430   uint32_t      loop_family;
 431   proto_tree    *fh_tree;
 432   proto_item    *ti;
 433   tvbuff_t      *next_tvb;
 434
 435   /* load the top pane info. This should be overwritten by
 436      the next protocol in the stack */
 437   col_set_str(pinfo->cinfo, COL_RES_DL_SRC, "N/A");
 438   col_set_str(pinfo->cinfo, COL_RES_DL_DST, "N/A");
 439   col_set_str(pinfo->cinfo, COL_PROTOCOL, "N/A");
 440   col_set_str(pinfo->cinfo, COL_INFO, "Null/Loopback");
 441
 442   /* populate a tree in the second pane with the status of the link
 443      layer (ie none) */
 444   loop_family = tvb_get_ntohl(tvb, 0);
 445   if (tree) {
 446     ti = proto_tree_add_item(tree, proto_null, tvb, 0, 4, ENC_NA);
 447     fh_tree = proto_item_add_subtree(ti, ett_null);
 448     proto_tree_add_uint(fh_tree, hf_null_family, tvb, 0, 4, loop_family);
 449   }
 450
 451   next_tvb = tvb_new_subset_remaining(tvb, 4);
 452   if (!dissector_try_uint(null_dissector_table, loop_family,
 453         next_tvb, pinfo, tree)) {
 454     /* No sub-dissector found.  Label rest of packet as "Data" */
 455     call_data_dissector(next_tvb, pinfo, tree);
 456   }
 457   return tvb_captured_length(tvb);
 458 }
 459
 460 void
 461 proto_register_null(void)
 462 {
 463   static hf_register_info hf[] = {
 464
 465     /* registered here but handled in ethertype.c */
 466     { &hf_null_etype,
 467       { "Type",         "null.type", FT_UINT16, BASE_HEX, VALS(etype_vals), 0x0,
 468         NULL, HFILL }},
 469
 470     { &hf_null_family,
 471       { "Family",       "null.family", FT_UINT32, BASE_DEC, VALS(family_vals), 0x0,
 472         NULL, HFILL }}
 473   };
 474   static int *ett[] = {
 475     &ett_null,
 476   };
 477
 478   proto_null = proto_register_protocol("Null/Loopback", "Null", "null");
 479   proto_register_field_array(proto_null, hf, array_length(hf));
 480   proto_register_subtree_array(ett, array_length(ett));
 481
 482   /* subdissector code */
 483   null_dissector_table = register_dissector_table("null.type",
 484                                                   "Null type", proto_null, FT_UINT32, BASE_DEC);
 485
 486   register_capture_dissector_table("null.bsd", "Null/Loopback BSD AF");
 487
 488   null_handle = register_dissector("null", dissect_null, proto_null);
 489   loop_handle = register_dissector("null.loop", dissect_loop, proto_null);
 490   null_cap_handle = register_capture_dissector("null", capture_null, proto_null);
 491 }
 492
 493 void
 494 proto_reg_handoff_null(void)
 495 {
 496   /*
 497    * Get a handle for the PPP-in-HDLC-like-framing dissector and
 498    * the "I don't know what this is" dissector.
 499    */
 500   ppp_hdlc_handle = find_dissector_add_dependency("ppp_hdlc", proto_null);
 501
 502   ethertype_dissector_table = find_dissector_table("ethertype");
 503
 504   dissector_add_uint("wtap_encap", WTAP_ENCAP_NULL, null_handle);
 505
 506   dissector_add_uint("wtap_encap", WTAP_ENCAP_LOOP, loop_handle);
 507
 508   capture_dissector_add_uint("wtap_encap", WTAP_ENCAP_NULL, null_cap_handle);
 509   capture_dissector_add_uint("wtap_encap", WTAP_ENCAP_LOOP, null_cap_handle);
 510
 511   ppp_hdlc_cap_handle = find_capture_dissector("ppp_hdlc");
 512 }
 513
 514 /*
 515  * Editor modelines
 516  *
 517  * Local Variables:
 518  * c-basic-offset: 2
 519  * tab-width: 8
 520  * indent-tabs-mode: nil
 521  * End:
 522  *
 523  * ex: set shiftwidth=2 tabstop=8 expandtab:
 524  * :indentSize=2:tabSize=8:noTabs=true:
 525  */