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

   1 /* Copyright (C) 2004, 2005 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 <errno.h>
  20 #include <stdint.h>
  21 #include <stdio.h>
  22 #include <stdio_ext.h>
  23 #include <stdlib.h>
  24 #include <string.h>
  25 #include "libio/libioP.h"
  26
  27 /* Return 1 if the whole area PTR .. PTR+SIZE is not writable.
  28    Return -1 if it is writable.  */
  29
  30 int
  31 __readonly_area (const char *ptr, size_t size)
  32 {
  33   const void *ptr_end = ptr + size;
  34
  35   FILE *fp = fopen ("/proc/self/maps", "rc");
  36   if (fp == NULL)
  37     {
  38       /* It is the system administrator's choice to not have /proc
  39          available to this process (e.g., because it runs in a chroot
  40          environment.  Don't fail in this case.  */
  41       if (errno == ENOENT
  42           /* The kernel has a bug in that a process is denied access
  43              to the /proc filesystem if it is set[ug]id.  There has
  44              been no willingness to change this in the kernel so
  45              far.  */
  46           || errno == EACCES)
  47         return 1;
  48       return -1;
  49     }
  50
  51   /* We need no locking.  */
  52   __fsetlocking (fp, FSETLOCKING_BYCALLER);
  53
  54   char *line = NULL;
  55   size_t linelen = 0;
  56
  57   while (! feof_unlocked (fp))
  58     {
  59       if (_IO_getdelim (&line, &linelen, '\n', fp) <= 0)
  60         break;
  61
  62       char *p;
  63       uintptr_t from = strtoul (line, &p, 16);
  64
  65       if (p == line || *p++ != '-')
  66         break;
  67
  68       char *q;
  69       uintptr_t to = strtoul (p, &q, 16);
  70
  71       if (q == p || *q++ != ' ')
  72         break;
  73
  74       if (from < (uintptr_t) ptr_end && to > (uintptr_t) ptr)
  75         {
  76           /* Found an entry that at least partially covers the area.  */
  77           if (*q++ != 'r' || *q++ != '-')
  78             break;
  79
  80           if (from <= (uintptr_t) ptr && to >= (uintptr_t) ptr_end)
  81             {
  82               size = 0;
  83               break;
  84             }
  85           else if (from <= (uintptr_t) ptr)
  86             size -= to - (uintptr_t) ptr;
  87           else if (to >= (uintptr_t) ptr_end)
  88             size -= (uintptr_t) ptr_end - from;
  89           else
  90             size -= to - from;
  91
  92           if (!size)
  93             break;
  94         }
  95     }
  96
  97   fclose (fp);
  98   free (line);
  99
 100   /* If the whole area between ptr and ptr_end is covered by read-only
 101      VMAs, return 1.  Otherwise return -1.  */
 102   return size == 0 ? 1 : -1;
 103 }