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
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 /* 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 (stream: 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 (ptr: 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}
105

source code of glibc/sysdeps/unix/sysv/linux/readonly-area.c