epan/dissectors/packet-wap.c

   1 /* packet-wap.c
   2  *
   3  * Utility routines for WAP dissectors
   4  *
   5  * Wireshark - Network traffic analyzer
   6  * By Gerald Combs <gerald@wireshark.org>
   7  * Copyright 1998 Gerald Combs
   8  *
   9  * WAP dissector based on original work by Ben Fowler
  10  * Updated by Neil Hunter <neil.hunter@energis-squared.com>
  11  * WTLS support by Alexandre P. Ferreira (Splice IP)
  12  *
  13  * SPDX-License-Identifier: GPL-2.0-or-later
  14  */
  15
  16 #define WS_LOG_DOMAIN "packet-wap"
  17
  18 #include "config.h"
  19 #include <wireshark.h>
  20
  21 #include <epan/packet.h>
  22 #include "packet-wap.h"
  23
  24 /*
  25  * Accessor to retrieve variable length int as used in WAP protocol.
  26  * The value is encoded in the lower 7 bits. If the top bit is set, then the
  27  * value continues into the next byte.
  28  * The octetCount parameter holds the number of bytes read in order to return
  29  * the final value. Can be pre-initialised to start at offset+count.
  30  *
  31  * XXX This seems to be used exclusively for fetching size values. We should
  32  * probably rename this to wap_get_checked_size or something along those lines.
  33  */
  34 #define MAX_WAP_UINTVAR (100 * 1000 * 1000) // Arbitrary. We need a large number that won't overflow a unsigned.
  35 unsigned
  36 tvb_get_uintvar (tvbuff_t *tvb, unsigned offset,
  37         unsigned *octetCount, packet_info *pinfo, expert_field *ei)
  38 {
  39     unsigned value   = 0, previous_value;
  40     unsigned octet;
  41     unsigned counter = 0;
  42
  43     ws_debug("Starting tvb_get_uintvar at offset %d", offset);
  44
  45     do {
  46         octet = tvb_get_uint8 (tvb, offset+counter);
  47
  48         counter++;
  49
  50         previous_value = value;
  51         value <<= 7;  /* Value only exists in 7 of the 8 bits */
  52         value += (octet & 0x7F);
  53         if (value < previous_value || value > MAX_WAP_UINTVAR) {
  54             /* overflow; clamp the value at UINT_MAX */
  55             proto_tree_add_expert(NULL, pinfo, ei, tvb, offset, counter);
  56             value = MAX_WAP_UINTVAR;
  57             break;
  58         }
  59
  60         ws_debug("computing: octet is %d (0x%02x), count=%d, value=%d",
  61                  octet, octet, counter, value);
  62     } while (octet & 0x80);
  63
  64     ws_debug(" Leaving tvb_get_uintvar count=%d, value=%u",
  65             counter, value);
  66
  67     if (octetCount)
  68         *octetCount = counter;
  69
  70     return value;
  71 }
  72
  73 /*
  74  * Editor modelines  -  https://www.wireshark.org/tools/modelines.html
  75  *
  76  * Local variables:
  77  * c-basic-offset: 4
  78  * tab-width: 8
  79  * indent-tabs-mode: nil
  80  * End:
  81  *
  82  * vi: set shiftwidth=4 tabstop=8 expandtab:
  83  * :indentSize=4:tabSize=8:noTabs=true:
  84  */