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

   1 /* Copyright (C) 2004-2016 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, see
  16    <http://www.gnu.org/licenses/>.  */
  17
  18 #include <errno.h>
  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", "rce");
  35   if (fp == NULL)
  36     {
  37       /* It is the system administrator's choice to not have /proc
  38          available to this process (e.g., because it runs in a chroot
  39          environment.  Don't fail in this case.  */
  40       if (errno == ENOENT
  41           /* The kernel has a bug in that a process is denied access
  42              to the /proc filesystem if it is set[ug]id.  There has
  43              been no willingness to change this in the kernel so
  44              far.  */
  45           || errno == EACCES)
  46         return 1;
  47       return -1;
  48     }
  49
  50   /* We need no locking.  */
  51   __fsetlocking (fp, FSETLOCKING_BYCALLER);
  52
  53   char *line = NULL;
  54   size_t linelen = 0;
  55
  56   while (! feof_unlocked (fp))
  57     {
  58       if (_IO_getdelim (&line, &linelen, '\n', fp) <= 0)
  59         break;
  60
  61       char *p;
  62       uintptr_t from = strtoul (line, &p, 16);
  63
  64       if (p == line || *p++ != '-')
  65         break;
  66
  67       char *q;
  68       uintptr_t to = strtoul (p, &q, 16);
  69
  70       if (q == p || *q++ != ' ')
  71         break;
  72
  73       if (from < (uintptr_t) ptr_end && to > (uintptr_t) ptr)
  74         {
  75           /* Found an entry that at least partially covers the area.  */
  76           if (*q++ != 'r' || *q++ != '-')
  77             break;
  78
  79           if (from <= (uintptr_t) ptr && to >= (uintptr_t) ptr_end)
  80             {
  81               size = 0;
  82               break;
  83             }
  84           else if (from <= (uintptr_t) ptr)
  85             size -= to - (uintptr_t) ptr;
  86           else if (to >= (uintptr_t) ptr_end)
  87             size -= (uintptr_t) ptr_end - from;
  88           else
  89             size -= to - from;
  90
  91           if (!size)
  92             break;
  93         }
  94     }
  95
  96   fclose (fp);
  97   free (line);
  98
  99   /* If the whole area between ptr and ptr_end is covered by read-only
 100      VMAs, return 1.  Otherwise return -1.  */
 101   return size == 0 ? 1 : -1;
 102 }