/* packet-pw-fr.c

 * Routines for Frame Relay MPLS PW dissection as per RFC4619.

 * Copyright 2009, Dmitry Trebich, Artem Tamazov <artem.tamazov@tellabs.com>

 *

 * Wireshark - Network traffic analyzer

 * By Gerald Combs <gerald@wireshark.org>

 * Copyright 1998 Gerald Combs

 *

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

 *

 * History:

 * ---------------------------------

 * 18.03.2009 initial implementation

 * - FR DLCI mode

 * Not supported yet:

 * - Correct FR decode for encapsulations which contain fragmented FR frames.

 * - FR DLCI Martini (legacy) mode (i.e. legacy CW).

 */

#include "config.h"

#include <epan/packet.h>

#include <epan/expert.h>

#include "packet-mpls.h"

void proto_register_pw_fr(void);

void proto_reg_handoff_pw_fr(void);

static int proto_encaps;

static int ett_encaps;

/* static int hf_pw_fr; */

static int hf_cw_bits03;

static int hf_cw_fecn;

static int hf_cw_becn;

static int hf_cw_de;

static int hf_cw_cr;

static int hf_cw_frg;

static int hf_cw_len;

static int hf_cw_seq;

static int hf_cw_padding;

static expert_field ei_payload_size_invalid;

static expert_field ei_cw_bits03;

static expert_field ei_cw_packet_size_too_small;

static const value_string vals_frg[] = {

  { 0x0,  "Unfragmented" },

  { 0x1,  "First fragment" },

  { 0x2,  "Last fragment" },

  { 0x3,  "Intermediate fragment" },

  { 0,  NULL }

};

static dissector_handle_t fr_stripped_address_handle;

static dissector_handle_t pw_fr_mpls_handle;

static int

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

{

  int packet_size;

  int payload_size;

  int payload_padding;

  const int encaps_size = 4; /*encapsulation consists of mandatory CW only*/

  enum {

    PQ_CW_BAD          = 0x001

    ,PQ_CW_BAD_BITS03        = 0x002

    ,PQ_CW_BAD_LEN_GT_PACKET       = 0x004

    ,PQ_CW_BAD_LEN_MUST_BE_ZERO    = 0x008

    ,PQ_CW_BAD_LEN_MUST_BE_NONZERO = 0x010

    ,PQ_PAYLOAD_SIZE_ZERO        = 0x020

  };

  int packet_quality;

  packet_size = tvb_reported_length_remaining(tvb, 0);

  if (packet_size < encaps_size)

  {

    {

      proto_item  *item;

      item = proto_tree_add_item(tree, proto_encaps, tvb, 0, -1, ENC_NA);

      expert_add_info_format(pinfo, item, &ei_cw_packet_size_too_small,

        "PW packet (%d) is smaller than PW encapsulation header (%d)",

        (int)packet_size,(int)encaps_size);

    }

    col_set_str(pinfo->cinfo, COL_PROTOCOL, "FR PW");

    col_set_str(pinfo->cinfo, COL_INFO, "Malformed: PW packet < PW encapsulation header");

    return 1;

  }

  if (dissect_try_cw_first_nibble(tvb,pinfo,tree))

  {

    return tvb_captured_length(tvb);

  }

  /* check how "good" is this packet */

  /* also decide payload length from packet size and CW */

  packet_quality = 0;

  if (0 != (tvb_get_uint8(tvb, 0) & 0xf0 /*bits03*/))

  {

    packet_quality |= PQ_CW_BAD + PQ_CW_BAD_BITS03;

  }

  {

    /* RFC4619:

     * [ If the frame's length (defined as the

     * length of the layer 2 payload plus the length of the control word)

     * is less than 64 octets, the length field MUST be set to the PW

     * payload length.  Otherwise, the length field MUST be set to zero. ]

     *

     * Note difference from RFC4385 which states that:

     * [..the length field MUST be set to the length of the PW payload

     * *plus* the length of the *PWMCW*. ]

     */

    int cw_len;

    int payload_size_packet; /*derived from packet size*/

    cw_len = tvb_get_uint8(tvb, 1) & 0x3f;

    payload_size_packet = packet_size - encaps_size;

    /*

     * Initial assumptions.

     */

    payload_size = payload_size_packet;

    payload_padding = 0;

    if (payload_size_packet < 64)

    {

      int payload_size_cw; /*derived from cw*/

      payload_size_cw = cw_len; /*RFC4619-specific*/

      if (payload_size_cw == 0)

      {

        packet_quality |= PQ_CW_BAD + PQ_CW_BAD_LEN_MUST_BE_NONZERO;

      }

      else if (payload_size_cw > payload_size_packet)

      {

        packet_quality |= PQ_CW_BAD + PQ_CW_BAD_LEN_GT_PACKET;

      }

      else /* ok */

      {

        payload_size = payload_size_cw;

        payload_padding = payload_size_packet - payload_size_cw; /* >=0 */

      }

    }

    else /* payload_size_packet >= 64 */

    {

      if (cw_len != 0)

      {

        packet_quality |= PQ_CW_BAD + PQ_CW_BAD_LEN_MUST_BE_ZERO;

      }

    }

  }

  if (payload_size == 0)

  {

    packet_quality |= PQ_PAYLOAD_SIZE_ZERO;

  }

  col_set_str(pinfo->cinfo, COL_PROTOCOL, "FR PW");

  col_clear(pinfo->cinfo, COL_INFO);

  if (packet_quality & PQ_CW_BAD)

  {

    col_set_str(pinfo->cinfo, COL_INFO, "CW:Malformed, ");

  }

  col_append_fstr(pinfo->cinfo, COL_INFO, "%d payload octets", (int)payload_size);

  if (payload_padding != 0)

  {

    col_append_fstr(pinfo->cinfo, COL_INFO, ", %d padding", (int)payload_padding);

  }

  {

    proto_tree* subtree;

    proto_item* item_headline;

    proto_item* item;

    item_headline = proto_tree_add_item(tree, proto_encaps, tvb, 0, 4, ENC_NA);

    proto_item_append_text(item_headline, ": 0x%.8" PRIx32, tvb_get_ntohl(tvb, 0));

    subtree = proto_item_add_subtree(item_headline, ett_encaps);

    if (packet_quality & PQ_CW_BAD_BITS03) /*display only if value is wrong*/

    {

      item = proto_tree_add_item(subtree, hf_cw_bits03, tvb, 0, 1, ENC_BIG_ENDIAN);

      expert_add_info(pinfo, item, &ei_cw_bits03);

    }

    proto_tree_add_item( subtree, hf_cw_fecn, tvb, 0, 1, ENC_BIG_ENDIAN );

    proto_tree_add_item( subtree, hf_cw_becn, tvb, 0, 1, ENC_BIG_ENDIAN );

    proto_tree_add_item( subtree, hf_cw_de,   tvb, 0, 1, ENC_BIG_ENDIAN );

    proto_tree_add_item( subtree, hf_cw_cr,   tvb, 0, 1, ENC_BIG_ENDIAN );

    proto_tree_add_item( subtree, hf_cw_frg,  tvb, 1, 1, ENC_BIG_ENDIAN );

    item = proto_tree_add_item( subtree, hf_cw_len, tvb, 1, 1, ENC_BIG_ENDIAN );

    if (packet_quality & PQ_CW_BAD_LEN_GT_PACKET)

    {

      expert_add_info_format(pinfo, item, &ei_payload_size_invalid,

        "Bad Length: greater than FR payload size (%d)",

        (int)payload_size);

    }

    if (packet_quality & PQ_CW_BAD_LEN_MUST_BE_NONZERO)

    {

      expert_add_info_format(pinfo, item, &ei_payload_size_invalid,

        "Bad Length: must be non-zero if FR PW packet size (%d) is < 64",

        (int)(payload_size+encaps_size));

    }

    if (packet_quality & PQ_CW_BAD_LEN_MUST_BE_ZERO)

    {

      expert_add_info_format(pinfo, item, &ei_payload_size_invalid,

        "Bad Length: must be 0 if FR PW packet size (%d) is >= 64",

        (int)(payload_size+encaps_size));

    }

    proto_tree_add_item( subtree, hf_cw_seq, tvb, 2, 2, ENC_BIG_ENDIAN );

    if (payload_padding > 0)

    {

      proto_tree_add_item(subtree, hf_cw_padding, tvb,

        encaps_size+payload_size, payload_padding, ENC_NA);

    }

    if (packet_quality & PQ_PAYLOAD_SIZE_ZERO)

    {

      expert_add_info_format(pinfo, item_headline, &ei_payload_size_invalid,

        "FR payload size must be non-zero");

    }

  }

  if (payload_size > 0)

  {

    tvbuff_t *tvb_payload;

    tvb_payload = tvb_new_subset_length(tvb, encaps_size, payload_size);

    call_dissector( fr_stripped_address_handle, tvb_payload, pinfo, tree );

  }

  return tvb_captured_length(tvb);

}

void

proto_register_pw_fr(void)

{

static hf_register_info hf[] = {

  {&hf_cw_bits03  ,{"Bits 0 to 3"   ,"pwfr.bits03"  ,FT_UINT8 ,BASE_HEX

        ,NULL      ,0xf0   ,NULL

        ,HFILL }},

  {&hf_cw_fecn  ,{"FR FECN"   ,"pwfr.fecn"  ,FT_UINT8 ,BASE_DEC

        ,NULL      ,0x08   ,"FR Forward Explicit Congestion Notification bit"

        ,HFILL}},

  {&hf_cw_becn  ,{"FR BECN"   ,"pwfr.becn"  ,FT_UINT8 ,BASE_DEC

        ,NULL      ,0x04   ,"FR Backward Explicit Congestion Notification bit"

        ,HFILL}},

  {&hf_cw_de  ,{"FR DE bit"   ,"pwfr.de"  ,FT_UINT8 ,BASE_DEC

        ,NULL      ,0x02   ,"FR Discard Eligibility bit"

        ,HFILL}},

  {&hf_cw_cr  ,{"FR Frame C/R"  ,"pwfr.cr"  ,FT_UINT8 ,BASE_DEC

        ,NULL      ,0x01   ,"FR frame Command/Response bit"

        ,HFILL}},

  {&hf_cw_frg ,{"Fragmentation" ,"pwfr.frag"  ,FT_UINT8 ,BASE_DEC

        ,VALS(vals_frg)  ,0xc0   ,NULL

        ,HFILL}},

  {&hf_cw_len ,{"Length"    ,"pwfr.length"  ,FT_UINT8 ,BASE_DEC

        ,NULL      ,0x3f   ,NULL

        ,HFILL}},

  {&hf_cw_seq ,{"Sequence number" ,"pwfr.seqno" ,FT_UINT16  ,BASE_DEC

        ,NULL      ,0    ,NULL

        ,HFILL}},

  {&hf_cw_padding,{"Padding"  ,"pwfr.padding" ,FT_BYTES, BASE_NONE

        ,NULL      ,0    ,NULL

        ,HFILL}}

};

  static int *ett[] = {

    &ett_encaps

  };

  static ei_register_info ei[] = {

    { &ei_cw_packet_size_too_small, { "pwfr.packet_size_too_small", PI_MALFORMED, PI_ERROR, "PW packet is smaller than PW encapsulation header", EXPFILL }},

    { &ei_cw_bits03, { "pwfr.cw.bits03.not_zero", PI_MALFORMED, PI_ERROR, "Bits 0..3 of Control Word must be 0", EXPFILL }},

    { &ei_payload_size_invalid, { "pwfr.payload.size_invalid", PI_MALFORMED, PI_ERROR, "Bad Length: greater than FR payload size", EXPFILL }},

  };

  expert_module_t* expert_pwfr;

  proto_encaps = proto_register_protocol( "PW Frame Relay DLCI Control Word",

            "Frame Relay DLCI PW",

            "pwfr");

  proto_register_field_array(proto_encaps, hf, array_length(hf));

  proto_register_subtree_array(ett, array_length(ett));

  expert_pwfr = expert_register_protocol(proto_encaps);

  expert_register_field_array(expert_pwfr, ei, array_length(ei));

  pw_fr_mpls_handle = register_dissector("pw_fr", dissect_pw_fr, proto_encaps );

}

void

proto_reg_handoff_pw_fr(void)

{

  dissector_add_for_decode_as("mpls.label", pw_fr_mpls_handle);

  dissector_add_for_decode_as("mpls.pfn", pw_fr_mpls_handle);

  fr_stripped_address_handle = find_dissector_add_dependency("fr_stripped_address", proto_encaps);

}

/*

 * Editor modelines  -  https://www.wireshark.org/tools/modelines.html

 *

 * Local variables:

 * c-basic-offset: 8

 * tab-width: 8

 * indent-tabs-mode: t

 * End:

 *

 * vi: set shiftwidth=8 tabstop=8 noexpandtab:

 * :indentSize=8:tabSize=8:noTabs=false:

 */