epan/dissectors/packet-loop.c

   1 /* packet-loop.c
   2  * Routines for Ethernet loopback/Configuration Test Protocol dissection,
   3  * as documented in section 8 "Ethernet Configuration Testing Protocol" of
   4  * the v2.0 DIX Ethernet specification.
   5  *
   6  * See
   7  *
   8  *    http://decnet.ipv7.net/docs/dundas/aa-k759b-tk.pdf
   9  *
  10  * for a copy of the DIX spec and
  11  *
  12  *    http://stuff.mit.edu/people/jhawk/ctp.html
  13  *
  14  * for section 8.
  15  *
  16  * Wireshark - Network traffic analyzer
  17  * By Gerald Combs <gerald@wireshark.org>
  18  * Copyright 1998 Gerald Combs
  19  *
  20  * SPDX-License-Identifier: GPL-2.0-or-later
  21  */
  22
  23 #include "config.h"
  24
  25 #include <epan/packet.h>
  26 #include <epan/etypes.h>
  27
  28 void proto_register_loop(void);
  29 void proto_reg_handoff_loop(void);
  30
  31 static dissector_handle_t loop_handle;
  32
  33 static int proto_loop;
  34 static int hf_loop_skipcount;
  35 static int hf_loop_function;
  36 static int hf_loop_relevant_function;
  37 static int hf_loop_receipt_number;
  38 static int hf_loop_forwarding_address;
  39
  40 static int ett_loop;
  41
  42 #define FUNC_REPLY              1
  43 #define FUNC_FORWARD_DATA       2
  44
  45 static const value_string function_vals[] = {
  46   { FUNC_REPLY, "Reply" },
  47   { FUNC_FORWARD_DATA, "Forward Data" },
  48   { 0, NULL }
  49 };
  50
  51 static int
  52 dissect_loop(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void* data _U_)
  53 {
  54   proto_tree  *loop_tree = NULL;
  55   proto_item  *ti;
  56   uint16_t    function;
  57   int         offset = 0;
  58   int         skip_offset;
  59   bool        set_info = true;
  60   bool        more_function;
  61   tvbuff_t    *next_tvb;
  62
  63   col_set_str(pinfo->cinfo, COL_PROTOCOL, "LOOP");
  64   col_clear(pinfo->cinfo, COL_INFO);
  65
  66   if (tree) {
  67     ti = proto_tree_add_item(tree, proto_loop, tvb, offset, -1, ENC_NA);
  68     loop_tree = proto_item_add_subtree(ti, ett_loop);
  69
  70     proto_tree_add_item(loop_tree, hf_loop_skipcount, tvb, offset, 2, ENC_LITTLE_ENDIAN);
  71   }
  72   skip_offset = 2 + tvb_get_letohs(tvb, offset);
  73   offset += 2;
  74
  75   do {
  76     function = tvb_get_letohs(tvb, offset);
  77     if (offset == skip_offset) {
  78       col_add_str(pinfo->cinfo, COL_INFO,
  79                     val_to_str(function, function_vals, "Unknown function (%u)"));
  80
  81       proto_tree_add_uint(loop_tree, hf_loop_relevant_function, tvb, offset, 2, function);
  82       set_info = false;
  83     }
  84     proto_tree_add_uint(loop_tree, hf_loop_function, tvb, offset, 2, function);
  85     offset += 2;
  86     switch (function) {
  87
  88     case FUNC_REPLY:
  89       proto_tree_add_item(loop_tree, hf_loop_receipt_number, tvb, offset, 2,
  90                             ENC_LITTLE_ENDIAN);
  91       offset += 2;
  92       more_function = false;
  93       break;
  94
  95     case FUNC_FORWARD_DATA:
  96       proto_tree_add_item(loop_tree, hf_loop_forwarding_address, tvb, offset,
  97                             6, ENC_NA);
  98       offset += 6;
  99       more_function = true;
 100       break;
 101
 102     default:
 103       more_function = false;
 104       break;
 105     }
 106   } while (more_function);
 107
 108   if (set_info) {
 109     col_set_str(pinfo->cinfo, COL_INFO, "No valid function found");
 110   }
 111
 112   if (tvb_reported_length_remaining(tvb, offset) > 0)
 113   {
 114     next_tvb = tvb_new_subset_remaining(tvb, offset);
 115     call_data_dissector(next_tvb, pinfo, tree);
 116   }
 117   return tvb_captured_length(tvb);
 118 }
 119
 120 void
 121 proto_register_loop(void)
 122 {
 123   static hf_register_info hf[] = {
 124     { &hf_loop_skipcount,
 125       { "skipCount",            "loop.skipcount",
 126     FT_UINT16,  BASE_DEC,       NULL,   0x0,
 127       NULL, HFILL }},
 128
 129     { &hf_loop_function,
 130       { "Function",             "loop.function",
 131     FT_UINT16,  BASE_DEC,       VALS(function_vals),    0x0,
 132       NULL, HFILL }},
 133
 134     { &hf_loop_relevant_function,
 135       { "Relevant function",            "loop.relevant_function",
 136     FT_UINT16,  BASE_DEC,       VALS(function_vals),    0x0,
 137       NULL, HFILL }},
 138
 139     { &hf_loop_receipt_number,
 140       { "Receipt number",       "loop.receipt_number",
 141     FT_UINT16,  BASE_DEC,       NULL,   0x0,
 142       NULL, HFILL }},
 143
 144     { &hf_loop_forwarding_address,
 145       { "Forwarding address",   "loop.forwarding_address",
 146     FT_ETHER,   BASE_NONE,      NULL,   0x0,
 147       NULL, HFILL }},
 148   };
 149   static int *ett[] = {
 150     &ett_loop,
 151   };
 152
 153   proto_loop = proto_register_protocol("Configuration Test Protocol (loopback)",
 154                                        "LOOP", "loop");
 155   proto_register_field_array(proto_loop, hf, array_length(hf));
 156   proto_register_subtree_array(ett, array_length(ett));
 157
 158   loop_handle = register_dissector("loop", dissect_loop, proto_loop);
 159 }
 160
 161 void
 162 proto_reg_handoff_loop(void)
 163 {
 164   dissector_add_uint("ethertype", ETHERTYPE_LOOP, loop_handle);
 165 }
 166
 167 /*
 168  * Editor modelines  -  https://www.wireshark.org/tools/modelines.html
 169  *
 170  * Local Variables:
 171  * c-basic-offset: 2
 172  * tab-width: 8
 173  * indent-tabs-mode: nil
 174  * End:
 175  *
 176  * ex: set shiftwidth=2 tabstop=8 expandtab:
 177  * :indentSize=2:tabSize=8:noTabs=true:
 178  */