1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
|
/* Copyright (C) 2000 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Library General Public License as
published by the Free Software Foundation; either version 2 of the
License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Library General Public License for more details.
You should have received a copy of the GNU Library General Public
License along with the GNU C Library; see the file COPYING.LIB. If not,
write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA. */
#include <errno.h>
#include <fcntl.h>
#include <paths.h>
#include <unistd.h>
#include <sys/stat.h>
#include <sys/sysmacros.h>
/* Try to get a machine dependent instruction which will make the
program crash. This is used in case everything else fails. */
#include <abort-instr.h>
#ifndef ABORT_INSTRUCTION
/* No such instruction is available. */
# define ABORT_INSTRUCTION
#endif
/* Should other OSes (e.g., Hurd) have different versions which can
be written in a better way? */
static void
check_one_fd (int fd, int mode)
{
if (__builtin_expect (__libc_fcntl (fd, F_GETFD), 0) == -1
&& errno == EBADF)
{
struct stat64 st;
/* Something is wrong with this descriptor, it's probably not
opened. Open /dev/null so that the SUID program we are
about to start does not accidently use this descriptor. */
int nullfd = __libc_open (_PATH_DEVNULL, mode);
/* We are very paranoid here. With all means we try to ensure
that we are actually opening the /dev/null device and nothing
else. */
if (__builtin_expect (nullfd, 0) == -1
|| __builtin_expect (__fxstat64 (_STAT_VER, nullfd, &st), 0) != 0
|| __builtin_expect (S_ISCHR (st.st_mode), 1) == 0
#if defined DEV_NULL_MAJOR && defined DEV_NULL_MINOR
|| st.st_rdev != makedev (DEV_NULL_MAJOR, DEV_NULL_MINOR)
#endif
)
/* We cannot even give an error message here since it would
run into the same problems. */
while (1)
/* Try for ever and ever. */
ABORT_INSTRUCTION;
}
}
void
__libc_check_standard_fds (void)
{
/* This is really paranoid but some people actually are. If /dev/null
should happen to be a symlink to somewhere else and not the device
commonly known as "/dev/null" be bail out. We can detect this with
the O_NOFOLLOW flag for open() but only on some system. */
#ifndef O_NOFOLLOW
# define O_NOFOLLOW 0
#endif
/* Check all three standard file descriptors. */
check_one_fd (STDIN_FILENO, O_RDONLY | O_NOFOLLOW);
check_one_fd (STDOUT_FILENO, O_RDWR | O_NOFOLLOW);
check_one_fd (STDERR_FILENO, O_RDWR | O_NOFOLLOW);
}
|
