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
29int
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