1 /* Copyright (C) 2000, 2002 Free Software Foundation, Inc.
2 This file is part of the GNU C Library.
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.
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.
14 You should have received a copy of the GNU Lesser General Public
15 License along with the GNU C Library; if not, write to the Free
16 Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
24 #include <sys/sysmacros.h>
26 /* Try to get a machine dependent instruction which will make the
27 program crash. This is used in case everything else fails. */
28 #include <abort-instr.h>
29 #ifndef ABORT_INSTRUCTION
30 /* No such instruction is available. */
31 # define ABORT_INSTRUCTION
34 #include <device-nrs.h>
37 /* Should other OSes (e.g., Hurd) have different versions which can
38 be written in a better way? */
40 check_one_fd (int fd
, int mode
)
42 if (__builtin_expect (__libc_fcntl (fd
, F_GETFD
), 0) == -1
47 /* Something is wrong with this descriptor, it's probably not
48 opened. Open /dev/null so that the SUID program we are
49 about to start does not accidently use this descriptor. */
50 int nullfd
= __libc_open (_PATH_DEVNULL
, mode
);
51 /* We are very paranoid here. With all means we try to ensure
52 that we are actually opening the /dev/null device and nothing
55 Note that the following code assumes that STDIN_FILENO,
56 STDOUT_FILENO, STDERR_FILENO are the three lowest file
57 decsriptor numbers, in this order. */
58 if (__builtin_expect (nullfd
!= fd
, 0)
59 || __builtin_expect (__fxstat64 (_STAT_VER
, fd
, &st
), 0) != 0
60 || __builtin_expect (S_ISCHR (st
.st_mode
), 1) == 0
61 #if defined DEV_NULL_MAJOR && defined DEV_NULL_MINOR
62 || st
.st_rdev
!= makedev (DEV_NULL_MAJOR
, DEV_NULL_MINOR
)
65 /* We cannot even give an error message here since it would
66 run into the same problems. */
68 /* Try for ever and ever. */
75 __libc_check_standard_fds (void)
77 /* This is really paranoid but some people actually are. If /dev/null
78 should happen to be a symlink to somewhere else and not the device
79 commonly known as "/dev/null" we bail out. We can detect this with
80 the O_NOFOLLOW flag for open() but only on some system. */
84 /* Check all three standard file descriptors. */
85 check_one_fd (STDIN_FILENO
, O_RDONLY
| O_NOFOLLOW
);
86 check_one_fd (STDOUT_FILENO
, O_RDWR
| O_NOFOLLOW
);
87 check_one_fd (STDERR_FILENO
, O_RDWR
| O_NOFOLLOW
);