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

   1 /* Copyright (C) 2004-2024 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    <https://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           /* Process has reached the maximum number of open files.  */
  47           || errno == EMFILE)
  48         return 1;
  49       return -1;
  50     }
  51
  52   /* We need no locking.  */
  53   __fsetlocking (fp, FSETLOCKING_BYCALLER);
  54
  55   char *line = NULL;
  56   size_t linelen = 0;
  57
  58   while (! __feof_unlocked (fp))
  59     {
  60       if (__getdelim (&line, &linelen, '\n', fp) <= 0)
  61         break;
  62
  63       char *p;
  64       uintptr_t from = strtoul (line, &p, 16);
  65
  66       if (p == line || *p++ != '-')
  67         break;
  68
  69       char *q;
  70       uintptr_t to = strtoul (p, &q, 16);
  71
  72       if (q == p || *q++ != ' ')
  73         break;
  74
  75       if (from < (uintptr_t) ptr_end && to > (uintptr_t) ptr)
  76         {
  77           /* Found an entry that at least partially covers the area.  */
  78           if (*q++ != 'r' || *q++ != '-')
  79             break;
  80
  81           if (from <= (uintptr_t) ptr && to >= (uintptr_t) ptr_end)
  82             {
  83               size = 0;
  84               break;
  85             }
  86           else if (from <= (uintptr_t) ptr)
  87             size -= to - (uintptr_t) ptr;
  88           else if (to >= (uintptr_t) ptr_end)
  89             size -= (uintptr_t) ptr_end - from;
  90           else
  91             size -= to - from;
  92
  93           if (!size)
  94             break;
  95         }
  96     }
  97
  98   fclose (fp);
  99   free (line);
 100
 101   /* If the whole area between ptr and ptr_end is covered by read-only
 102      VMAs, return 1.  Otherwise return -1.  */
 103   return size == 0 ? 1 : -1;
 104 }