epan/dissectors/packet-null.c

   1 /* packet-null.c
   2  * Routines for null packet disassembly
   3  *
   4  * $Id$
   5  *
   6  * Wireshark - Network traffic analyzer
   7  * By Gerald Combs <gerald@wireshark.org>
   8  *
   9  * This file created by Mike Hall <mlh@io.com>
  10  * Copyright 1998
  11  *
  12  * This program is free software; you can redistribute it and/or
  13  * modify it under the terms of the GNU General Public License
  14  * as published by the Free Software Foundation; either version 2
  15  * of the License, or (at your option) any later version.
  16  *
  17  * This program is distributed in the hope that it will be useful,
  18  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  19  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  20  * GNU General Public License for more details.
  21  *
  22  * You should have received a copy of the GNU General Public License
  23  * along with this program; if not, write to the Free Software
  24  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  25  */
  26
  27 #include "config.h"
  28
  29 #include <glib.h>
  30 #include <string.h>
  31
  32 #include <wsutil/pint.h>
  33
  34 #include <epan/packet.h>
  35 #include "packet-null.h"
  36 #include <epan/atalk-utils.h>
  37 #include <epan/prefs.h>
  38 #include "packet-ip.h"
  39 #include "packet-ipv6.h"
  40 #include "packet-ipx.h"
  41 #include "packet-osi.h"
  42 #include "packet-ppp.h"
  43 #include <epan/etypes.h>
  44 #include <epan/aftypes.h>
  45
  46 static dissector_table_t null_dissector_table;
  47 static dissector_table_t ethertype_dissector_table;
  48
  49 /* protocols and header fields */
  50 static int proto_null = -1;
  51 static int hf_null_etype = -1;
  52 static int hf_null_family = -1;
  53
  54 static gint ett_null = -1;
  55
  56 /* Null/loopback structs and definitions */
  57
  58 /* Family values. */
  59 static const value_string family_vals[] = {
  60     {BSD_AF_INET,          "IP"             },
  61     {BSD_AF_ISO,           "OSI"            },
  62     {BSD_AF_APPLETALK,     "Appletalk"      },
  63     {BSD_AF_IPX,           "Netware IPX/SPX"},
  64     {BSD_AF_INET6_BSD,     "IPv6"           },
  65     {BSD_AF_INET6_FREEBSD, "IPv6"           },
  66     {BSD_AF_INET6_DARWIN,  "IPv6"           },
  67     {0,                    NULL             }
  68 };
  69
  70 static dissector_handle_t ppp_hdlc_handle;
  71 static dissector_handle_t data_handle;
  72 void
  73 capture_null( const guchar *pd, int len, packet_counts *ld )
  74 {
  75   guint32 null_header;
  76
  77   /*
  78    * BSD drivers that use DLT_NULL - including the FreeBSD 3.2 ISDN-for-BSD
  79    * drivers, as well as the 4.4-Lite and FreeBSD loopback drivers -
  80    * stuff the AF_ value for the protocol, in *host* byte order, in the
  81    * first four bytes.  (BSD drivers that use DLT_LOOP, such as recent
  82    * OpenBSD loopback drivers, stuff it in *network* byte order in the
  83    * first four bytes.)
  84    *
  85    * However, the IRIX and UNICOS/mp snoop socket mechanism supplies,
  86    * on loopback devices, a 4-byte header that has a 2 byte (big-endian)
  87    * AF_ value and 2 bytes of 0, so it's
  88    *
  89    *    0000AAAA
  90    *
  91    * when read on a little-endian machine and
  92    *
  93    *    AAAA0000
  94    *
  95    * when read on a big-endian machine.  The current CVS version of libpcap
  96    * compensates for this by converting it to standard 4-byte format before
  97    * processing the packet, but snoop captures from IRIX or UNICOS/mp
  98    * have the 2-byte+2-byte header, as might tcpdump or libpcap captures
  99    * with older versions of libpcap.
 100    *
 101    * AF_ values are small integers, and probably fit in 8 bits (current
 102    * values on the BSDs do), and have their upper 24 bits zero.
 103    * This means that, in practice, if you look at the header as a 32-bit
 104    * integer in host byte order:
 105    *
 106    *    on a little-endian machine:
 107    *
 108    *            a little-endian DLT_NULL header looks like
 109    *
 110    *                    000000AA
 111    *
 112    *            a big-endian DLT_NULL header, or a DLT_LOOP header, looks
 113    *            like
 114    *
 115    *                    AA000000
 116    *
 117    *            an IRIX or UNICOS/mp DLT_NULL header looks like
 118    *
 119    *                    0000AA00
 120    *
 121    *    on a big-endian machine:
 122    *
 123    *            a big-endian DLT_NULL header, or a DLT_LOOP header, looks
 124    *            like
 125    *
 126    *                    000000AA
 127    *
 128    *            a little-endian DLT_NULL header looks like
 129    *
 130    *                    AA000000
 131    *
 132    *            an IRIX or UNICOS/mp DLT_NULL header looks like
 133    *
 134    *                    00AA0000
 135    *
 136    * However, according to Gerald Combs, a FreeBSD ISDN PPP dump that
 137    * Andreas Klemm sent to wireshark-dev has a packet type of DLT_NULL,
 138    * and the family bits look like PPP's protocol field.  (Was this an
 139    * older, or different, ISDN driver?)  Looking at what appears to be
 140    * that capture file, it appears that it's using PPP in HDLC framing,
 141    * RFC 1549, wherein the first two octets of the frame are 0xFF
 142    * (address) and 0x03 (control), so the header bytes are, in order:
 143    *
 144    *    0xFF
 145    *    0x03
 146    *    high-order byte of a PPP protocol field
 147    *    low-order byte of a PPP protocol field
 148    *
 149    * If we treat that as a 32-bit host-byte-order value, it looks like
 150    *
 151    *    PPPP03FF
 152    *
 153    * where PPPP is a byte-swapped PPP protocol type if we read it on
 154    * a little-endian machine and
 155    *
 156    *    FF03PPPP
 157    *
 158    * where PPPP is a PPP protocol type if we read it on a big-endian
 159    * machine.  0x0000 does not appear to be a valid PPP protocol type
 160    * value, so at least one of those hex digits is guaranteed not to
 161    * be 0.
 162    *
 163    * Old versions of libpcap for Linux used DLT_NULL for loopback devices,
 164    * but not any other devices.  (Current versions use DLT_EN10MB for it.)
 165    * The Linux loopback driver puts an *Ethernet* header at the beginning
 166    * of loopback packets, with fake source and destination addresses and
 167    * the appropriate Ethernet type value; however, those older versions of
 168    * libpcap for Linux compensated for this by skipping the source and
 169    * destination MAC addresses, replacing them with 2 bytes of 0.
 170    * This means that if we're reading the capture on a little-endian
 171    * machine, the header, treated as a 32-bit integer, looks like
 172    *
 173    *    EEEE0000
 174    *
 175    * where EEEE is a byte-swapped Ethernet type, and if we're reading it
 176    * on a big-endian machine, it looks like
 177    *
 178    *    0000EEEE
 179    *
 180    * where EEEE is an Ethernet type.
 181    *
 182    * If the first 2 bytes of the header are FF 03:
 183    *
 184    *    it can't be a big-endian BSD DLT_NULL header, or a DLT_LOOP
 185    *    header, as AF_ values are small so the first 2 bytes of the
 186    *    header would be 0;
 187    *
 188    *    it can't be a little-endian BSD DLT_NULL header, as the
 189    *    resulting AF_ value would be >= 0x03FF, which is too big
 190    *    for an AF_ value;
 191    *
 192    *    it can't be an IRIX or UNICOS/mp DLT_NULL header, as the
 193    *    resulting AF_ value with be 0x03FF.
 194    *
 195    * So the first thing we do is check the first two bytes of the
 196    * header; if it's FF 03, we treat the packet as a PPP frame.
 197    *
 198    * Otherwise, if the upper 16 bits are non-zero, either:
 199    *
 200    *    it's a BSD DLT_NULL or DLT_LOOP header whose AF_ value
 201    *    is not in our byte order;
 202    *
 203    *    it's an IRIX or UNICOS/mp DLT_NULL header being read on
 204    *    a big-endian machine;
 205    *
 206    *    it's a Linux DLT_NULL header being read on a little-endian
 207    *    machine.
 208    *
 209    * In all those cases except for the IRIX or UNICOS/mp DLT_NULL header,
 210    * we should byte-swap it (if it's a Linux DLT_NULL header, that'll
 211    * put the Ethernet type in the right byte order).  In the case
 212    * of the IRIX or UNICOS/mp DLT_NULL header, we should just get
 213    * the upper 16 bits as an AF_ value.
 214    *
 215    * If it's a BSD DLT_NULL or DLT_LOOP header whose AF_ value is not
 216    * in our byte order, then the upper 2 hex digits would be non-zero
 217    * and the next 2 hex digits down would be zero, as AF_ values fit in
 218    * 8 bits, and the upper 2 hex digits are the *lower* 8 bits of the value.
 219    *
 220    * If it's an IRIX or UNICOS/mp DLT_NULL header, the upper 2 hex digits
 221    * would be zero and the next 2 hex digits down would be non-zero, as
 222    * the upper 16 bits are a big-endian AF_ value.  Furthermore, the
 223    * next 2 hex digits down are likely to be < 0x60, as 0x60 is 96,
 224    * and, so far, we're far from requiring AF_ values that high.
 225    *
 226    * If it's a Linux DLT_NULL header, the third hex digit from the top
 227    * will be >= 6, as Ethernet types are >= 1536, or 0x0600, and
 228    * it's byte-swapped, so the second 2 hex digits from the top are
 229    * >= 0x60.
 230    *
 231    * So, if the upper 16 bits are non-zero:
 232    *
 233    *    if the upper 2 hex digits are 0 and the next 2 hex digits are
 234    *    in the range 0x00-0x5F, we treat it as a big-endian IRIX or
 235    *    UNICOS/mp DLT_NULL header;
 236    *
 237    *    otherwise, we byte-swap it and do the next stage.
 238    *
 239    * If the upper 16 bits are zero, either:
 240    *
 241    *    it's a BSD DLT_NULLor DLT_LOOP header whose AF_ value is in
 242    *    our byte order;
 243    *
 244    *    it's an IRIX or UNICOS/mp DLT_NULL header being read on
 245    *    a little-endian machine;
 246    *
 247    *    it's a Linux DLT_NULL header being read on a big-endian
 248    *    machine.
 249    *
 250    * In all of those cases except for the IRIX or UNICOS/mp DLT_NULL header,
 251    * we should *not* byte-swap it.  In the case of the IRIX or UNICOS/mp
 252    * DLT_NULL header, we should extract the AF_ value and byte-swap it.
 253    *
 254    * If it's a BSD DLT_NULL or DLT_LOOP header whose AF_ value is
 255    * in our byte order, the upper 6 hex digits would all be zero.
 256    *
 257    * If it's an IRIX or UNICOS/mp DLT_NULL header, the upper 4 hex
 258    * digits would be zero and the next 2 hex digits would not be zero.
 259    * Furthermore, the third hex digit from the bottom would be <
 260    */
 261   if (!BYTES_ARE_IN_FRAME(0, len, 2)) {
 262     ld->other++;
 263     return;
 264   }
 265   if (pd[0] == 0xFF && pd[1] == 0x03) {
 266     /*
 267      * Hand it to PPP.
 268      */
 269     capture_ppp_hdlc(pd, 0, len, ld);
 270   } else {
 271     /*
 272      * Treat it as a normal DLT_NULL header.
 273      */
 274     if (!BYTES_ARE_IN_FRAME(0, len, (int)sizeof(null_header))) {
 275       ld->other++;
 276       return;
 277     }
 278     memcpy((char *)&null_header, (const char *)&pd[0], sizeof(null_header));
 279
 280     if ((null_header & 0xFFFF0000) != 0) {
 281       /*
 282        * It is possible that the AF_ type was only a 16 bit value.
 283        * IRIX and UNICOS/mp loopback snoop use a 4 byte header with
 284        * AF_ type in the first 2 bytes!
 285        * BSD AF_ types will always have the upper 8 bits as 0.
 286        */
 287       if ((null_header & 0xFF000000) == 0 &&
 288           (null_header & 0x00FF0000) < 0x00060000) {
 289         /*
 290          * Looks like a IRIX or UNICOS/mp loopback header, in the
 291          * correct byte order.  Set the null header value to the
 292          * AF_ type, which is in the upper 16 bits of "null_header".
 293          */
 294         null_header >>= 16;
 295       } else {
 296         /* Byte-swap it. */
 297         null_header = BSWAP32(null_header);
 298       }
 299     } else {
 300       /*
 301        * Check for an IRIX or UNICOS/mp snoop header.
 302        */
 303       if ((null_header & 0x000000FF) == 0 &&
 304           (null_header & 0x0000FF00) < 0x00000600) {
 305         /*
 306          * Looks like a IRIX or UNICOS/mp loopback header, in the
 307          * wrong byte order.  Set the null header value to the AF_
 308          * type; that's in the lower 16 bits of "null_header", but
 309          * is byte-swapped.
 310          */
 311         null_header = BSWAP16(null_header & 0xFFFF);
 312       }
 313     }
 314
 315     /*
 316      * The null header value must be greater than the IEEE 802.3 maximum
 317      * frame length to be a valid Ethernet type; if it is, hand it
 318      * to "capture_ethertype()", otherwise treat it as a BSD AF_type (we
 319      * wire in the values of the BSD AF_ types, because the values
 320      * in the file will be BSD values, and the OS on which
 321      * we're building this might not have the same values or
 322      * might not have them defined at all; XXX - what if different
 323      * BSD derivatives have different values?).
 324      */
 325     if (null_header > IEEE_802_3_MAX_LEN)
 326       capture_ethertype((guint16) null_header, pd, 4, len, ld);
 327     else {
 328
 329       switch (null_header) {
 330
 331       case BSD_AF_INET:
 332         capture_ip(pd, 4, len, ld);
 333         break;
 334
 335       case BSD_AF_INET6_BSD:
 336       case BSD_AF_INET6_FREEBSD:
 337       case BSD_AF_INET6_DARWIN:
 338         capture_ipv6(pd, 4, len, ld);
 339         break;
 340
 341       default:
 342         ld->other++;
 343         break;
 344       }
 345     }
 346   }
 347 }
 348
 349 static void
 350 dissect_null(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
 351 {
 352   guint32       null_header;
 353   proto_tree    *fh_tree;
 354   proto_item    *ti;
 355   tvbuff_t      *next_tvb;
 356
 357   /*
 358    * See comment in "capture_null()" for an explanation of what we're
 359    * doing.
 360    */
 361   if (tvb_get_ntohs(tvb, 0) == 0xFF03) {
 362     /*
 363      * Hand it to PPP.
 364      */
 365     call_dissector(ppp_hdlc_handle, tvb, pinfo, tree);
 366   } else {
 367
 368     /* load the top pane info. This should be overwritten by
 369        the next protocol in the stack */
 370     col_set_str(pinfo->cinfo, COL_RES_DL_SRC, "N/A");
 371     col_set_str(pinfo->cinfo, COL_RES_DL_DST, "N/A");
 372     col_set_str(pinfo->cinfo, COL_PROTOCOL, "N/A");
 373     col_set_str(pinfo->cinfo, COL_INFO, "Null/Loopback");
 374
 375     /*
 376      * Treat it as a normal DLT_NULL header.
 377      */
 378     tvb_memcpy(tvb, (guint8 *)&null_header, 0, sizeof(null_header));
 379
 380     if ((null_header & 0xFFFF0000) != 0) {
 381       /*
 382        * It is possible that the AF_ type was only a 16 bit value.
 383        * IRIX and UNICOS/mp loopback snoop use a 4 byte header with
 384        * AF_ type in the first 2 bytes!
 385        * BSD AF_ types will always have the upper 8 bits as 0.
 386        */
 387       if ((null_header & 0xFF000000) == 0 &&
 388           (null_header & 0x00FF0000) < 0x00060000) {
 389         /*
 390          * Looks like a IRIX or UNICOS/mp loopback header, in the
 391          * correct byte order.  Set the null header value to the
 392          * AF_ type, which is in the upper 16 bits of "null_header".
 393          */
 394         null_header >>= 16;
 395       } else {
 396         /* Byte-swap it. */
 397         null_header = BSWAP32(null_header);
 398       }
 399     } else {
 400       /*
 401        * Check for an IRIX or UNICOS/mp snoop header.
 402        */
 403       if ((null_header & 0x000000FF) == 0 &&
 404           (null_header & 0x0000FF00) < 0x00000600) {
 405         /*
 406          * Looks like a IRIX or UNICOS/mp loopback header, in the
 407          * wrong byte order.  Set the null header value to the AF_
 408          * type; that's in the lower 16 bits of "null_header", but
 409          * is byte-swapped.
 410          */
 411         null_header = BSWAP16(null_header & 0xFFFF);
 412       }
 413     }
 414
 415     /*
 416      * The null header value must be greater than the IEEE 802.3 maximum
 417      * frame length to be a valid Ethernet type; if it is, dissect it
 418      * as one, otherwise treat it as a BSD AF_type (we wire in the values
 419      * of the BSD AF_ types, because the values in the file will be BSD
 420      * values, and the OS on which we're building this might not have the
 421      * same values or might not have them defined at all; XXX - what if
 422      * different BSD derivatives have different values?).
 423      */
 424     if (null_header > IEEE_802_3_MAX_LEN) {
 425       if (tree) {
 426         ti = proto_tree_add_item(tree, proto_null, tvb, 0, 4, ENC_NA);
 427         fh_tree = proto_item_add_subtree(ti, ett_null);
 428         proto_tree_add_uint(fh_tree, hf_null_etype, tvb, 0, 4,
 429           (guint16) null_header);
 430       }
 431
 432       next_tvb = tvb_new_subset_remaining(tvb, 4);
 433       if (!dissector_try_uint(ethertype_dissector_table,
 434             (guint16) null_header, next_tvb, pinfo, tree))
 435         call_dissector(data_handle, next_tvb, pinfo, tree);
 436     } else {
 437       /* populate a tree in the second pane with the status of the link
 438          layer (ie none) */
 439       if (tree) {
 440         ti = proto_tree_add_item(tree, proto_null, tvb, 0, 4, ENC_NA);
 441         fh_tree = proto_item_add_subtree(ti, ett_null);
 442         proto_tree_add_uint(fh_tree, hf_null_family, tvb, 0, 4, null_header);
 443       }
 444
 445       next_tvb = tvb_new_subset_remaining(tvb, 4);
 446       if (!dissector_try_uint(null_dissector_table, null_header,
 447             next_tvb, pinfo, tree)) {
 448         /* No sub-dissector found.  Label rest of packet as "Data" */
 449         call_dissector(data_handle,next_tvb, pinfo, tree);
 450       }
 451     }
 452   }
 453 }
 454
 455 void
 456 proto_register_null(void)
 457 {
 458         static hf_register_info hf[] = {
 459
 460                 /* registered here but handled in ethertype.c */
 461                 { &hf_null_etype,
 462                 { "Type",               "null.type", FT_UINT16, BASE_HEX, VALS(etype_vals), 0x0,
 463                         NULL, HFILL }},
 464
 465                 { &hf_null_family,
 466                 { "Family",             "null.family",  FT_UINT32, BASE_DEC, VALS(family_vals), 0x0,
 467                         NULL, HFILL }}
 468         };
 469         static gint *ett[] = {
 470                 &ett_null,
 471         };
 472
 473         proto_null = proto_register_protocol("Null/Loopback", "Null", "null");
 474         proto_register_field_array(proto_null, hf, array_length(hf));
 475         proto_register_subtree_array(ett, array_length(ett));
 476
 477         /* subdissector code */
 478         null_dissector_table = register_dissector_table("null.type",
 479            "Null type", FT_UINT32, BASE_DEC);
 480 }
 481
 482 void
 483 proto_reg_handoff_null(void)
 484 {
 485         dissector_handle_t null_handle;
 486
 487         /*
 488          * Get a handle for the PPP-in-HDLC-like-framing dissector and
 489          * the "I don't know what this is" dissector.
 490          */
 491         ppp_hdlc_handle = find_dissector("ppp_hdlc");
 492         data_handle = find_dissector("data");
 493
 494         ethertype_dissector_table = find_dissector_table("ethertype");
 495
 496         null_handle = create_dissector_handle(dissect_null, proto_null);
 497         dissector_add_uint("wtap_encap", WTAP_ENCAP_NULL, null_handle);
 498 }