resolv/ns_name_length_uncompressed.c

   1 /* Skip over an uncompressed name in wire format.
   2    Copyright (C) 2022-2023 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #include <arpa/nameser.h>
  20 #include <errno.h>
  21 #include <stdbool.h>
  22
  23 int
  24 __ns_name_length_uncompressed (const unsigned char *p,
  25                                 const unsigned char *eom)
  26 {
  27   const unsigned char *start = p;
  28
  29   while (true)
  30     {
  31       if (p == eom)
  32         {
  33           /* Truncated packet: no room for label length.  */
  34           __set_errno (EMSGSIZE);
  35           return -1;
  36         }
  37
  38       unsigned char b = *p;
  39       ++p;
  40       if (b == 0)
  41         {
  42           /* Root label.  */
  43           size_t length = p - start;
  44           if (length > NS_MAXCDNAME)
  45             {
  46               /* Domain name too long.  */
  47               __set_errno (EMSGSIZE);
  48               return -1;
  49             }
  50           return length;
  51         }
  52
  53       if (b <= 63)
  54         {
  55           /* Regular label.  */
  56           if (b <= eom - p)
  57             p += b;
  58           else
  59             {
  60               /* Truncated packet: label incomplete.  */
  61               __set_errno (EMSGSIZE);
  62               return -1;
  63             }
  64         }
  65       else
  66         {
  67           /* Compression reference or corrupted label length.  */
  68           __set_errno (EMSGSIZE);
  69           return -1;
  70         }
  71     }
  72 }