epan/dissectors/packet-lapb.c

   1 /* packet-lapb.c
   2  * Routines for lapb frame disassembly
   3  * Olivier Abad <oabad@noos.fr>
   4  *
   5  * Wireshark - Network traffic analyzer
   6  * By Gerald Combs <gerald@wireshark.org>
   7  * Copyright 1998
   8  *
   9  * SPDX-License-Identifier: GPL-2.0-or-later
  10  */
  11
  12 #include "config.h"
  13
  14 #include <epan/packet.h>
  15 #include <wiretap/wtap.h>
  16 #include <epan/xdlc.h>
  17 #include <epan/tfs.h>
  18 #include <wsutil/array.h>
  19
  20 void proto_register_lapb(void);
  21 void proto_reg_handoff_lapb(void);
  22
  23 static int proto_lapb;
  24 static int hf_lapb_address;
  25 static int hf_lapb_control;
  26 static int hf_lapb_n_r;
  27 static int hf_lapb_n_s;
  28 static int hf_lapb_p;
  29 static int hf_lapb_f;
  30 static int hf_lapb_s_ftype;
  31 static int hf_lapb_u_modifier_cmd;
  32 static int hf_lapb_u_modifier_resp;
  33 static int hf_lapb_ftype_i;
  34 static int hf_lapb_ftype_s_u;
  35
  36 static int ett_lapb;
  37 static int ett_lapb_control;
  38
  39 static dissector_handle_t x25_dir_handle;
  40 static dissector_handle_t x25_handle;
  41 static dissector_handle_t lapb_handle;
  42
  43 static const xdlc_cf_items lapb_cf_items = {
  44     &hf_lapb_n_r,
  45     &hf_lapb_n_s,
  46     &hf_lapb_p,
  47     &hf_lapb_f,
  48     &hf_lapb_s_ftype,
  49     &hf_lapb_u_modifier_cmd,
  50     &hf_lapb_u_modifier_resp,
  51     &hf_lapb_ftype_i,
  52     &hf_lapb_ftype_s_u
  53 };
  54
  55 static int
  56 dissect_lapb(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void* data _U_)
  57 {
  58     proto_tree          *lapb_tree, *ti;
  59     uint16_t            control;
  60     int                 is_response;
  61     uint8_t             byte0;
  62     tvbuff_t            *next_tvb;
  63
  64     col_set_str(pinfo->cinfo, COL_PROTOCOL, "LAPB");
  65     col_clear(pinfo->cinfo, COL_INFO);
  66
  67     switch (pinfo->p2p_dir) {
  68
  69     case P2P_DIR_SENT:
  70         col_set_str(pinfo->cinfo, COL_RES_DL_SRC, "DTE");
  71         col_set_str(pinfo->cinfo, COL_RES_DL_DST, "DCE");
  72         break;
  73
  74     case P2P_DIR_RECV:
  75         col_set_str(pinfo->cinfo, COL_RES_DL_SRC, "DCE");
  76         col_set_str(pinfo->cinfo, COL_RES_DL_DST, "DTE");
  77         break;
  78
  79     default:
  80         col_set_str(pinfo->cinfo, COL_RES_DL_SRC, "N/A");
  81         col_set_str(pinfo->cinfo, COL_RES_DL_DST, "N/A");
  82         break;
  83     }
  84
  85     byte0 = tvb_get_uint8(tvb, 0);
  86
  87     if (byte0 != 0x01 && byte0 != 0x03 && byte0 != 0x07 && byte0 != 0x0f) /* invalid LAPB frame */
  88     {
  89         col_set_str(pinfo->cinfo, COL_INFO, "Invalid LAPB frame");
  90         if (tree)
  91             proto_tree_add_protocol_format(tree, proto_lapb, tvb, 0, -1,
  92                             "Invalid LAPB frame");
  93         return 1;
  94     }
  95
  96     switch (pinfo->p2p_dir) {
  97
  98     case P2P_DIR_SENT:
  99         if (byte0 == 0x03)
 100             is_response = true;
 101         else
 102             is_response = false;
 103         break;
 104
 105     case P2P_DIR_RECV:
 106         if (byte0 == 0x01)
 107             is_response = true;
 108         else
 109             is_response = false;
 110         break;
 111
 112     default:
 113         /*
 114          * XXX - should we base this on the source and destination
 115          * addresses?  The problem is that we can tell one direction
 116          * from another with that, but we can't say which is DTE->DCE
 117          * and which is DCE->DTE.
 118          */
 119         is_response = false;
 120         break;
 121     }
 122
 123     ti = proto_tree_add_protocol_format(tree, proto_lapb, tvb, 0, 2,
 124                                         "LAPB");
 125     lapb_tree = proto_item_add_subtree(ti, ett_lapb);
 126     proto_tree_add_uint(lapb_tree, hf_lapb_address, tvb, 0, 1, byte0);
 127
 128     control = dissect_xdlc_control(tvb, 1, pinfo, lapb_tree, hf_lapb_control,
 129             ett_lapb_control, &lapb_cf_items, NULL, NULL, NULL,
 130             is_response, false, false);
 131
 132     /* information frame ==> X.25 */
 133     if (XDLC_IS_INFORMATION(control)) {
 134         next_tvb = tvb_new_subset_remaining(tvb, 2);
 135         switch (pinfo->p2p_dir) {
 136
 137         case P2P_DIR_SENT:
 138         case P2P_DIR_RECV:
 139             call_dissector(x25_dir_handle, next_tvb, pinfo, tree);
 140             break;
 141
 142         default:
 143             call_dissector(x25_handle, next_tvb, pinfo, tree);
 144             break;
 145         }
 146     }
 147     return tvb_captured_length(tvb);
 148 }
 149
 150 void
 151 proto_register_lapb(void)
 152 {
 153     static hf_register_info hf[] = {
 154         { &hf_lapb_address,
 155           { "Address", "lapb.address", FT_UINT8, BASE_HEX, NULL, 0x0,
 156             NULL, HFILL }},
 157
 158         { &hf_lapb_control,
 159           { "Control Field", "lapb.control", FT_UINT8, BASE_HEX, NULL, 0x0,
 160             NULL, HFILL }},
 161
 162         { &hf_lapb_n_r,
 163           { "N(R)", "lapb.control.n_r", FT_UINT8, BASE_DEC,
 164             NULL, XDLC_N_R_MASK, NULL, HFILL }},
 165
 166         { &hf_lapb_n_s,
 167           { "N(S)", "lapb.control.n_s", FT_UINT8, BASE_DEC,
 168             NULL, XDLC_N_S_MASK, NULL, HFILL }},
 169
 170         { &hf_lapb_p,
 171           { "Poll", "lapb.control.p", FT_BOOLEAN, 8,
 172             TFS(&tfs_set_notset), XDLC_P_F, NULL, HFILL }},
 173
 174         { &hf_lapb_f,
 175           { "Final", "lapb.control.f", FT_BOOLEAN, 8,
 176             TFS(&tfs_set_notset), XDLC_P_F, NULL, HFILL }},
 177
 178         { &hf_lapb_s_ftype,
 179           { "Supervisory frame type", "lapb.control.s_ftype", FT_UINT8, BASE_HEX,
 180             VALS(stype_vals), XDLC_S_FTYPE_MASK, NULL, HFILL }},
 181
 182         { &hf_lapb_u_modifier_cmd,
 183           { "Command", "lapb.control.u_modifier_cmd", FT_UINT8, BASE_HEX,
 184             VALS(modifier_vals_cmd), XDLC_U_MODIFIER_MASK, NULL, HFILL }},
 185
 186         { &hf_lapb_u_modifier_resp,
 187           { "Response", "lapb.control.u_modifier_resp", FT_UINT8, BASE_HEX,
 188             VALS(modifier_vals_resp), XDLC_U_MODIFIER_MASK, NULL, HFILL }},
 189
 190         { &hf_lapb_ftype_i,
 191           { "Frame type", "lapb.control.ftype", FT_UINT8, BASE_HEX,
 192             VALS(ftype_vals), XDLC_I_MASK, NULL, HFILL }},
 193
 194         { &hf_lapb_ftype_s_u,
 195           { "Frame type", "lapb.control.ftype", FT_UINT8, BASE_HEX,
 196             VALS(ftype_vals), XDLC_S_U_MASK, NULL, HFILL }},
 197     };
 198     static int *ett[] = {
 199         &ett_lapb,
 200         &ett_lapb_control,
 201     };
 202
 203     proto_lapb = proto_register_protocol("Link Access Procedure Balanced (LAPB)",
 204                                          "LAPB", "lapb");
 205     proto_register_field_array (proto_lapb, hf, array_length(hf));
 206     proto_register_subtree_array(ett, array_length(ett));
 207
 208     lapb_handle = register_dissector("lapb", dissect_lapb, proto_lapb);
 209 }
 210
 211 void
 212 proto_reg_handoff_lapb(void)
 213 {
 214     /*
 215      * Get handles for the X.25 dissectors; we don't get an X.25
 216      * pseudo-header for LAPB-over-Ethernet, but we do get it
 217      * for raw LAPB.
 218      */
 219     x25_dir_handle = find_dissector_add_dependency("x.25_dir", proto_lapb);
 220     x25_handle = find_dissector_add_dependency("x.25", proto_lapb);
 221
 222     dissector_add_uint("wtap_encap", WTAP_ENCAP_LAPB, lapb_handle);
 223 }
 224
 225 /*
 226  * Editor modelines  -  https://www.wireshark.org/tools/modelines.html
 227  *
 228  * Local variables:
 229  * c-basic-offset: 4
 230  * tab-width: 8
 231  * indent-tabs-mode: nil
 232  * End:
 233  *
 234  * vi: set shiftwidth=4 tabstop=8 expandtab:
 235  * :indentSize=4:tabSize=8:noTabs=true:
 236  */