1 /* Copyright (C) 2004-2021 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
__readonly_area(const char * ptr,size_t size)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 (__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 }
103