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 #include "config.h"
  17
  18 #ifdef DEBUG
  19 #include <stdio.h>
  20 #endif
  21
  22 #include <epan/packet.h>
  23 #include "packet-wap.h"
  24
  25 /*
  26  * Accessor to retrieve variable length int as used in WAP protocol.
  27  * The value is encoded in the lower 7 bits. If the top bit is set, then the
  28  * value continues into the next byte.
  29  * The octetCount parameter holds the number of bytes read in order to return
  30  * the final value. Can be pre-initialised to start at offset+count.
  31  *
  32  * XXX This seems to be used exclusively for fetching size values. We should
  33  * probably rename this to wap_get_checked_size or something along those lines.
  34  */
  35 #define MAX_WAP_UINTVAR (100 * 1000 * 1000) // Arbitrary. We need a large number that won't overflow a unsigned.
  36 unsigned
  37 tvb_get_uintvar (tvbuff_t *tvb, unsigned offset,
  38         unsigned *octetCount, packet_info *pinfo, expert_field *ei)
  39 {
  40     unsigned value   = 0, previous_value;
  41     unsigned octet;
  42     unsigned counter = 0;
  43
  44 #ifdef DEBUG
  45     fprintf (stderr,
  46             "dissect_wap: Starting tvb_get_uintvar at offset %d\n", offset);
  47 #endif
  48
  49     do {
  50         octet = tvb_get_uint8 (tvb, offset+counter);
  51
  52         counter++;
  53
  54         previous_value = value;
  55         value <<= 7;  /* Value only exists in 7 of the 8 bits */
  56         value += (octet & 0x7F);
  57         if (value < previous_value || value > MAX_WAP_UINTVAR) {
  58             /* overflow; clamp the value at UINT_MAX */
  59             proto_tree_add_expert(NULL, pinfo, ei, tvb, offset, counter);
  60             value = MAX_WAP_UINTVAR;
  61             break;
  62         }
  63
  64 #ifdef DEBUG
  65         fprintf(stderr,
  66             "dissect_wap: computing: octet is %d (0x%02x), count=%d, value=%d\n",
  67                  octet, octet, counter, value);
  68 #endif
  69     } while (octet & 0x80);
  70
  71 #ifdef DEBUG
  72     fprintf (stderr,
  73             "dissect_wap: Leaving tvb_get_uintvar count=%d, value=%u\n",
  74             counter, value);
  75 #endif
  76
  77     if (octetCount)
  78         *octetCount = counter;
  79
  80     return value;
  81 }
  82
  83 /*
  84  * Editor modelines  -  https://www.wireshark.org/tools/modelines.html
  85  *
  86  * Local variables:
  87  * c-basic-offset: 4
  88  * tab-width: 8
  89  * indent-tabs-mode: nil
  90  * End:
  91  *
  92  * vi: set shiftwidth=4 tabstop=8 expandtab:
  93  * :indentSize=4:tabSize=8:noTabs=true:
  94  */