/* packet-null.c

 * Routines for null packet disassembly

 *

 * Wireshark - Network traffic analyzer

 * By Gerald Combs <gerald@wireshark.org>

 *

 * This file created by Mike Hall <mlh@io.com>

 * Copyright 1998

 *

 * SPDX-License-Identifier: GPL-2.0-or-later

 */

#include "config.h"

#include <wsutil/pint.h>

#include <epan/packet.h>

#include <epan/capture_dissectors.h>

#include "packet-ip.h"

#include "packet-ppp.h"

#include <epan/etypes.h>

#include <epan/aftypes.h>

void proto_register_null(void);

void proto_reg_handoff_null(void);

static dissector_table_t null_dissector_table;

static dissector_table_t ethertype_dissector_table;

/* protocols and header fields */

static int proto_null;

static int hf_null_etype;

static int hf_null_family;

static int ett_null;

/* Null/loopback structs and definitions */

/* Family values. */

static const value_string family_vals[] = {

  {BSD_AF_INET,          "IP"             },

  {BSD_AF_ISO,           "OSI"            },

  {BSD_AF_APPLETALK,     "Appletalk"      },

  {BSD_AF_IPX,           "Netware IPX/SPX"},

  {BSD_AF_INET6_BSD,     "IPv6"           },

  {BSD_AF_INET6_FREEBSD, "IPv6"           },

  {BSD_AF_INET6_DARWIN,  "IPv6"           },

  {0,                    NULL             }

};

static dissector_handle_t null_handle, loop_handle;

static capture_dissector_handle_t null_cap_handle;

static dissector_handle_t ppp_hdlc_handle;

static capture_dissector_handle_t ppp_hdlc_cap_handle;

static bool

capture_null( const unsigned char *pd, int offset _U_, int len, capture_packet_info_t *cpinfo, const union wtap_pseudo_header *pseudo_header _U_ )

{

  uint32_t null_header;

  /*

   * BSD drivers that use DLT_NULL - including the FreeBSD 3.2 ISDN-for-BSD

   * drivers, as well as the 4.4-Lite and FreeBSD loopback drivers -

   * stuff the AF_ value for the protocol, in *host* byte order, in the

   * first four bytes.

   *

   * However, the IRIX and UNICOS/mp snoop socket mechanism supplies,

   * on loopback devices, a 4-byte header that has a 2 byte (big-endian)

   * AF_ value and 2 bytes of 0, so it's

   *

   *    0000AAAA

   *

   * when read on a little-endian machine and

   *

   *    AAAA0000

   *

   * when read on a big-endian machine.  The current CVS version of libpcap

   * compensates for this by converting it to standard 4-byte format before

   * processing the packet, but snoop captures from IRIX or UNICOS/mp

   * have the 2-byte+2-byte header, as might tcpdump or libpcap captures

   * with older versions of libpcap.

   *

   * AF_ values are small integers, and probably fit in 8 bits (current

   * values on the BSDs do), and have their upper 24 bits zero.

   * This means that, in practice, if you look at the header as a 32-bit

   * integer in host byte order:

   *

   *    on a little-endian machine:

   *

   *            a little-endian DLT_NULL header looks like

   *

   *                    000000AA

   *

   *            a big-endian DLT_NULL header, or a DLT_LOOP header, looks

   *            like

   *

   *                    AA000000

   *

   *            an IRIX or UNICOS/mp DLT_NULL header looks like

   *

   *                    0000AA00

   *

   *    on a big-endian machine:

   *

   *            a big-endian DLT_NULL header, or a DLT_LOOP header, looks

   *            like

   *

   *                    000000AA

   *

   *            a little-endian DLT_NULL header looks like

   *

   *                    AA000000

   *

   *            an IRIX or UNICOS/mp DLT_NULL header looks like

   *

   *                    00AA0000

   *

   * However, according to Gerald Combs, a FreeBSD ISDN PPP dump that

   * Andreas Klemm sent to wireshark-dev has a packet type of DLT_NULL,

   * and the family bits look like PPP's protocol field.  (Was this an

   * older, or different, ISDN driver?)  Looking at what appears to be

   * that capture file, it appears that it's using PPP in HDLC framing,

   * RFC 1549, wherein the first two octets of the frame are 0xFF

   * (address) and 0x03 (control), so the header bytes are, in order:

   *

   *    0xFF

   *    0x03

   *    high-order byte of a PPP protocol field

   *    low-order byte of a PPP protocol field

   *

   * If we treat that as a 32-bit host-byte-order value, it looks like

   *

   *    PPPP03FF

   *

   * where PPPP is a byte-swapped PPP protocol type if we read it on

   * a little-endian machine and

   *

   *    FF03PPPP

   *

   * where PPPP is a PPP protocol type if we read it on a big-endian

   * machine.  0x0000 does not appear to be a valid PPP protocol type

   * value, so at least one of those hex digits is guaranteed not to

   * be 0.

   *

   * Old versions of libpcap for Linux used DLT_NULL for loopback devices,

   * but not any other devices.  (Current versions use DLT_EN10MB for it.)

   * The Linux loopback driver puts an *Ethernet* header at the beginning

   * of loopback packets, with fake source and destination addresses and

   * the appropriate Ethernet type value; however, those older versions of

   * libpcap for Linux compensated for this by skipping the source and

   * destination MAC addresses, replacing them with 2 bytes of 0.

   * This means that if we're reading the capture on a little-endian

   * machine, the header, treated as a 32-bit integer, looks like

   *

   *    EEEE0000

   *

   * where EEEE is a byte-swapped Ethernet type, and if we're reading it

   * on a big-endian machine, it looks like

   *

   *    0000EEEE

   *

   * where EEEE is an Ethernet type.

   *

   * If the first 2 bytes of the header are FF 03:

   *

   *    it can't be a big-endian BSD DLT_NULL header, or a DLT_LOOP

   *    header, as AF_ values are small so the first 2 bytes of the

   *    header would be 0;

   *

   *    it can't be a little-endian BSD DLT_NULL header, as the

   *    resulting AF_ value would be >= 0x03FF, which is too big

   *    for an AF_ value;

   *

   *    it can't be an IRIX or UNICOS/mp DLT_NULL header, as the

   *    resulting AF_ value with be 0x03FF.

   *

   * So the first thing we do is check the first two bytes of the

   * header; if it's FF 03, we treat the packet as a PPP frame.

   *

   * Otherwise, if the upper 16 bits are non-zero, either:

   *

   *    it's a BSD DLT_NULL header whose AF_ value is not in our

   *    byte order;

   *

   *    it's an IRIX or UNICOS/mp DLT_NULL header being read on

   *    a big-endian machine;

   *

   *    it's a Linux DLT_NULL header being read on a little-endian

   *    machine.

   *

   * In all those cases except for the IRIX or UNICOS/mp DLT_NULL header,

   * we should byte-swap it (if it's a Linux DLT_NULL header, that'll

   * put the Ethernet type in the right byte order).  In the case

   * of the IRIX or UNICOS/mp DLT_NULL header, we should just get

   * the upper 16 bits as an AF_ value.

   *

   * If it's a BSD DLT_NULL header whose AF_ value is not in our byte

   * order, then the upper 2 hex digits would be non-zero and the next

   * 2 hex digits down would be zero, as AF_ values fit in 8 bits, and

   * the upper 2 hex digits are the *lower* 8 bits of the value.

   *

   * If it's an IRIX or UNICOS/mp DLT_NULL header, the upper 2 hex digits

   * would be zero and the next 2 hex digits down would be non-zero, as

   * the upper 16 bits are a big-endian AF_ value.  Furthermore, the

   * next 2 hex digits down are likely to be < 0x60, as 0x60 is 96,

   * and, so far, we're far from requiring AF_ values that high.

   *

   * If it's a Linux DLT_NULL header, the third hex digit from the top

   * will be >= 6, as Ethernet types are >= 1536, or 0x0600, and

   * it's byte-swapped, so the second 2 hex digits from the top are

   * >= 0x60.

   *

   * So, if the upper 16 bits are non-zero:

   *

   *    if the upper 2 hex digits are 0 and the next 2 hex digits are

   *    in the range 0x00-0x5F, we treat it as a big-endian IRIX or

   *    UNICOS/mp DLT_NULL header;

   *

   *    otherwise, we byte-swap it and do the next stage.

   *

   * If the upper 16 bits are zero, either:

   *

   *    it's a BSD DLT_NULL header whose AF_ value is in our byte

   *    order;

   *

   *    it's an IRIX or UNICOS/mp DLT_NULL header being read on

   *    a little-endian machine;

   *

   *    it's a Linux DLT_NULL header being read on a big-endian

   *    machine.

   *

   * In all of those cases except for the IRIX or UNICOS/mp DLT_NULL header,

   * we should *not* byte-swap it.  In the case of the IRIX or UNICOS/mp

   * DLT_NULL header, we should extract the AF_ value and byte-swap it.

   *

   * If it's a BSD DLT_NULL header whose AF_ value is in our byte order,

   * the upper 6 hex digits would all be zero.

   *

   * If it's an IRIX or UNICOS/mp DLT_NULL header, the upper 4 hex

   * digits would be zero and the next 2 hex digits would not be zero.

   * Furthermore, the third hex digit from the bottom would be <

   */

  if (!BYTES_ARE_IN_FRAME(0, len, 2))

    return false;

  if (pd[0] == 0xFF && pd[1] == 0x03) {

    /*

     * Hand it to PPP.

     */

    return call_capture_dissector(ppp_hdlc_cap_handle, pd, 0, len, cpinfo, pseudo_header);

  } else {

    /*

     * Treat it as a normal DLT_NULL header.

     */

    if (!BYTES_ARE_IN_FRAME(0, len, (int)sizeof(null_header)))

      return false;

    memcpy((char *)&null_header, (const char *)&pd[0], sizeof(null_header));

    if ((null_header & 0xFFFF0000) != 0) {

      /*

       * It is possible that the AF_ type was only a 16 bit value.

       * IRIX and UNICOS/mp loopback snoop use a 4 byte header with

       * AF_ type in the first 2 bytes!

       * BSD AF_ types will always have the upper 8 bits as 0.

       */

      if ((null_header & 0xFF000000) == 0 &&

          (null_header & 0x00FF0000) < 0x00060000) {

        /*

         * Looks like a IRIX or UNICOS/mp loopback header, in the

         * correct byte order.  Set the null header value to the

         * AF_ type, which is in the upper 16 bits of "null_header".

         */

        null_header >>= 16;

      } else {

        /* Byte-swap it. */

        null_header = GUINT32_SWAP_LE_BE(null_header);

      }

    } else {

      /*

       * Check for an IRIX or UNICOS/mp snoop header.

       */

      if ((null_header & 0x000000FF) == 0 &&

          (null_header & 0x0000FF00) < 0x00000600) {

        /*

         * Looks like a IRIX or UNICOS/mp loopback header, in the

         * wrong byte order.  Set the null header value to the AF_

         * type; that's in the lower 16 bits of "null_header", but

         * is byte-swapped.

         */

        null_header = GUINT16_SWAP_LE_BE(null_header & 0xFFFF);

      }

    }

    /*

     * The null header value must be greater than the IEEE 802.3 maximum

     * frame length to be a valid Ethernet type; if it is, hand it

     * to "capture_ethertype()", otherwise treat it as a BSD AF_type (we

     * wire in the values of the BSD AF_ types, because the values

     * in the file will be BSD values, and the OS on which

     * we're building this might not have the same values or

     * might not have them defined at all; XXX - what if different

     * BSD derivatives have different values?).

     */

    if (null_header > IEEE_802_3_MAX_LEN)

      return try_capture_dissector("ethertype", null_header, pd, 4, len, cpinfo, pseudo_header);

    else

      return try_capture_dissector("null.bsd", null_header, pd, 4, len, cpinfo, pseudo_header);

  }

  return false;

}

static int

dissect_null(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void* data _U_)

{

  uint32_t      null_header;

  proto_tree    *fh_tree;

  proto_item    *ti;

  tvbuff_t      *next_tvb;

  /*

   * See comment in "capture_null()" for an explanation of what we're

   * doing.

   */

  if (tvb_get_ntohs(tvb, 0) == 0xFF03) {

    /*

     * Hand it to PPP.

     */

    call_dissector(ppp_hdlc_handle, tvb, pinfo, tree);

  } else {

    /* load the top pane info. This should be overwritten by

       the next protocol in the stack */

    col_set_str(pinfo->cinfo, COL_RES_DL_SRC, "N/A");

    col_set_str(pinfo->cinfo, COL_RES_DL_DST, "N/A");

    col_set_str(pinfo->cinfo, COL_PROTOCOL, "N/A");

    col_set_str(pinfo->cinfo, COL_INFO, "Null/Loopback");

    /*

     * Treat it as a normal DLT_NULL header.  Fetch it in host

     * byte order.

     */

    null_header = tvb_get_h_uint32(tvb, 0);

    if ((null_header & 0xFFFF0000) != 0) {

      /*

       * It is possible that the AF_ type was only a 16 bit value.

       * IRIX and UNICOS/mp loopback snoop use a 4 byte header with

       * AF_ type in the first 2 bytes!

       * BSD AF_ types will always have the upper 8 bits as 0.

       */

      if ((null_header & 0xFF000000) == 0 &&

          (null_header & 0x00FF0000) < 0x00060000) {

        /*

         * Looks like a IRIX or UNICOS/mp loopback header, in the

         * correct byte order.  Set the null header value to the

         * AF_ type, which is in the upper 16 bits of "null_header".

         */

        null_header >>= 16;

      } else {

        /* Byte-swap it. */

        null_header = GUINT32_SWAP_LE_BE(null_header);

      }

    } else {

      /*

       * Check for an IRIX or UNICOS/mp snoop header.

       */

      if ((null_header & 0x000000FF) == 0 &&

          (null_header & 0x0000FF00) < 0x00000600) {

        /*

         * Looks like a IRIX or UNICOS/mp loopback header, in the

         * wrong byte order.  Set the null header value to the AF_

         * type; that's in the lower 16 bits of "null_header", but

         * is byte-swapped.

         */

        null_header = GUINT16_SWAP_LE_BE(null_header & 0xFFFF);

      }

    }

    /*

     * The null header value must be greater than the IEEE 802.3 maximum

     * frame length to be a valid Ethernet type; if it is, dissect it

     * as one, otherwise treat it as a BSD AF_type (we wire in the values

     * of the BSD AF_ types, because the values in the file will be BSD

     * values, and the OS on which we're building this might not have the

     * same values or might not have them defined at all; XXX - what if

     * different BSD derivatives have different values?).

     */

    if (null_header > IEEE_802_3_MAX_LEN) {

      if (tree) {

        ti = proto_tree_add_item(tree, proto_null, tvb, 0, 4, ENC_NA);

        fh_tree = proto_item_add_subtree(ti, ett_null);

        proto_tree_add_uint(fh_tree, hf_null_etype, tvb, 0, 4,

          (uint16_t) null_header);

      }

      next_tvb = tvb_new_subset_remaining(tvb, 4);

      if (!dissector_try_uint(ethertype_dissector_table,

            (uint16_t) null_header, next_tvb, pinfo, tree))

        call_data_dissector(next_tvb, pinfo, tree);

    } else {

      /* populate a tree in the second pane with the status of the link

         layer (ie none) */

      if (tree) {

        ti = proto_tree_add_item(tree, proto_null, tvb, 0, 4, ENC_NA);

        fh_tree = proto_item_add_subtree(ti, ett_null);

        proto_tree_add_uint(fh_tree, hf_null_family, tvb, 0, 4, null_header);

      }

      next_tvb = tvb_new_subset_remaining(tvb, 4);

      if (!dissector_try_uint(null_dissector_table, null_header,

            next_tvb, pinfo, tree)) {

        /* No sub-dissector found.  Label rest of packet as "Data" */

        call_data_dissector(next_tvb, pinfo, tree);

      }

    }

  }

  return tvb_captured_length(tvb);

}

/*

 * OpenBSD DLT_LOOP; like DLT_NULL, but with the first 4 byte *always*

 * being a *big-endian* type.

 */

static int

dissect_loop(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void* data _U_)

{

  uint32_t      loop_family;

  proto_tree    *fh_tree;

  proto_item    *ti;

  tvbuff_t      *next_tvb;

  /* load the top pane info. This should be overwritten by

     the next protocol in the stack */

  col_set_str(pinfo->cinfo, COL_RES_DL_SRC, "N/A");

  col_set_str(pinfo->cinfo, COL_RES_DL_DST, "N/A");

  col_set_str(pinfo->cinfo, COL_PROTOCOL, "N/A");

  col_set_str(pinfo->cinfo, COL_INFO, "Null/Loopback");

  /* populate a tree in the second pane with the status of the link

     layer (ie none) */

  loop_family = tvb_get_ntohl(tvb, 0);

  if (tree) {

    ti = proto_tree_add_item(tree, proto_null, tvb, 0, 4, ENC_NA);

    fh_tree = proto_item_add_subtree(ti, ett_null);

    proto_tree_add_uint(fh_tree, hf_null_family, tvb, 0, 4, loop_family);

  }

  next_tvb = tvb_new_subset_remaining(tvb, 4);

  if (!dissector_try_uint(null_dissector_table, loop_family,

        next_tvb, pinfo, tree)) {

    /* No sub-dissector found.  Label rest of packet as "Data" */

    call_data_dissector(next_tvb, pinfo, tree);

  }

  return tvb_captured_length(tvb);

}

void

proto_register_null(void)

{

  static hf_register_info hf[] = {

    /* registered here but handled in ethertype.c */

    { &hf_null_etype,

      { "Type",         "null.type", FT_UINT16, BASE_HEX, VALS(etype_vals), 0x0,

        NULL, HFILL }},

    { &hf_null_family,

      { "Family",       "null.family", FT_UINT32, BASE_DEC, VALS(family_vals), 0x0,

        NULL, HFILL }}

  };

  static int *ett[] = {

    &ett_null,

  };

  proto_null = proto_register_protocol("Null/Loopback", "Null", "null");

  proto_register_field_array(proto_null, hf, array_length(hf));

  proto_register_subtree_array(ett, array_length(ett));

  /* subdissector code */

  null_dissector_table = register_dissector_table("null.type",

                                                  "Null type", proto_null, FT_UINT32, BASE_DEC);

  register_capture_dissector_table("null.bsd", "Null/Loopback BSD AF");

  null_handle = register_dissector("null", dissect_null, proto_null);

  loop_handle = register_dissector("null.loop", dissect_loop, proto_null);

  null_cap_handle = register_capture_dissector("null", capture_null, proto_null);

}

void

proto_reg_handoff_null(void)

{

  /*

   * Get a handle for the PPP-in-HDLC-like-framing dissector and

   * the "I don't know what this is" dissector.

   */

  ppp_hdlc_handle = find_dissector_add_dependency("ppp_hdlc", proto_null);

  ethertype_dissector_table = find_dissector_table("ethertype");

  dissector_add_uint("wtap_encap", WTAP_ENCAP_NULL, null_handle);

  dissector_add_uint("wtap_encap", WTAP_ENCAP_LOOP, loop_handle);

  capture_dissector_add_uint("wtap_encap", WTAP_ENCAP_NULL, null_cap_handle);

  capture_dissector_add_uint("wtap_encap", WTAP_ENCAP_LOOP, null_cap_handle);

  ppp_hdlc_cap_handle = find_capture_dissector("ppp_hdlc");

}

/*

 * Editor modelines

 *

 * Local Variables:

 * c-basic-offset: 2

 * tab-width: 8

 * indent-tabs-mode: nil

 * End:

 *

 * ex: set shiftwidth=2 tabstop=8 expandtab:

 * :indentSize=2:tabSize=8:noTabs=true:

 */