sysdeps/unix/sysv/linux/readonly-area.c

   1 /* Copyright (C) 2004 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, write to the Free
  16    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  17    02111-1307 USA.  */
  18
  19 #include <stdint.h>
  20 #include <stdio.h>
  21 #include <stdio_ext.h>
  22 #include <stdlib.h>
  23 #include <string.h>
  24 #include "libio/libioP.h"
  25
  26 /* Return 1 if the whole area PTR .. PTR+SIZE is not writable.
  27    Return -1 if it is writable.  */
  28
  29 int
  30 __readonly_area (const char *ptr, size_t size)
  31 {
  32   const void *ptr_end = ptr + size;
  33
  34   FILE *fp = fopen ("/proc/self/maps", "rc");
  35   if (fp == NULL)
  36     /* We don't know.  Returning 1 here means that programs using %n
  37        and -D_FORTIFY_SOURCE=2 will work even when /proc is not mounted,
  38        but will allow %n even in writable areas.  */
  39     return 1;
  40
  41   /* We need no locking.  */
  42   __fsetlocking (fp, FSETLOCKING_BYCALLER);
  43
  44   char *line = NULL;
  45   size_t linelen = 0;
  46
  47   while (! feof_unlocked (fp))
  48     {
  49       if (_IO_getdelim (&line, &linelen, '\n', fp) <= 0)
  50         break;
  51
  52       char *p;
  53       uintptr_t from = strtoul (line, &p, 16);
  54
  55       if (p == line || *p++ != '-')
  56         break;
  57
  58       char *q;
  59       uintptr_t to = strtoul (p, &q, 16);
  60
  61       if (q == p || *q++ != ' ')
  62         break;
  63
  64       if (from < (uintptr_t) ptr_end && to > (uintptr_t) ptr)
  65         {
  66           /* Found an entry that at least partially covers the area.  */
  67           if (*q++ != 'r' || *q++ != '-')
  68             break;
  69
  70           if (from <= (uintptr_t) ptr && to >= (uintptr_t) ptr_end)
  71             {
  72               size = 0;
  73               break;
  74             }
  75           else if (from <= (uintptr_t) ptr)
  76             size -= to - (uintptr_t) ptr;
  77           else if (to >= (uintptr_t) ptr_end)
  78             size -= (uintptr_t) ptr_end - from;
  79           else
  80             size -= to - from;
  81
  82           if (!size)
  83             break;
  84         }
  85     }
  86
  87   fclose (fp);
  88   free (line);
  89
  90   /* If the whole area between ptr and ptr_end is covered by read-only
  91      VMAs, return 1.  Otherwise return -1.  */
  92   return size == 0 ? 1 : -1;
  93 }