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* sysdeps/unix/sysv/linux/check_fds.c: New file.
	* sysdeps/generic/check_fds.c: Check that file opened is really
	/dev/null.
This commit is contained in:
Ulrich Drepper
2000-09-26 06:42:06 +00:00
parent 5f2de3379c
commit 3ee561ad46
3 changed files with 51 additions and 5 deletions
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30
sysdeps/generic/check_fds.c
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@ -20,6 +20,8 @@
#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. */
@ -38,11 +40,22 @@ 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);
if (__builtin_expect (nullfd, 0) == -1)
/* 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)
@ -55,8 +68,15 @@ check_one_fd (int fd, int mode)
void
__libc_check_standard_fds (void)
{
/* Check all three standard file descriptors. */
check_one_fd (STDIN_FILENO, O_RDONLY);
check_one_fd (STDOUT_FILENO, O_RDWR);
check_one_fd (STDERR_FILENO, O_RDWR);
/* 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);
}