diff options
Diffstat (limited to 'csu/check_fds.c')
| -rw-r--r-- | csu/check_fds.c | 102 |
1 files changed, 102 insertions, 0 deletions
diff --git a/csu/check_fds.c b/csu/check_fds.c new file mode 100644 index 0000000..10ba3da --- /dev/null +++ b/csu/check_fds.c @@ -0,0 +1,102 @@ +/* Copyright (C) 2000, 2002, 2003, 2005 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 Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 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 + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; 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 + +#include <device-nrs.h> +#include <not-cancel.h> + + +/* 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) +{ + /* Note that fcntl() with this parameter is not a cancellation point. */ + if (__builtin_expect (__libc_fcntl (fd, F_GETFD), 0) == -1 + && errno == EBADF) + { + const char *name; + dev_t dev; + + /* For writable descriptors we use /dev/full. */ + if ((mode & O_ACCMODE) == O_WRONLY) + { + name = _PATH_DEV "full"; + dev = makedev (DEV_FULL_MAJOR, DEV_FULL_MINOR); + } + else + { + name = _PATH_DEVNULL; + dev = makedev (DEV_NULL_MAJOR, DEV_NULL_MINOR); + } + + /* 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 = open_not_cancel (name, mode, 0); + + /* We are very paranoid here. With all means we try to ensure + that we are actually opening the /dev/null device and nothing + else. + + Note that the following code assumes that STDIN_FILENO, + STDOUT_FILENO, STDERR_FILENO are the three lowest file + decsriptor numbers, in this order. */ + struct stat64 st; + if (__builtin_expect (nullfd != fd, 0) + || __builtin_expect (__fxstat64 (_STAT_VER, fd, &st), 0) != 0 + || __builtin_expect (S_ISCHR (st.st_mode), 1) == 0 + || st.st_rdev != dev) + /* 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" we 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_WRONLY | O_NOFOLLOW); + check_one_fd (STDOUT_FILENO, O_RDONLY | O_NOFOLLOW); + check_one_fd (STDERR_FILENO, O_RDONLY | O_NOFOLLOW); +} |