diff options
Diffstat (limited to 'sysdeps/generic/check_fds.c')
| -rw-r--r-- | sysdeps/generic/check_fds.c | 30 |
1 files changed, 25 insertions, 5 deletions
diff --git a/sysdeps/generic/check_fds.c b/sysdeps/generic/check_fds.c index 4eea168794..9891b9c865 100644 --- a/sysdeps/generic/check_fds.c +++ b/sysdeps/generic/check_fds.c @@ -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); } |