85 lines
2.9 KiB
C
85 lines
2.9 KiB
C
/* Copyright (C) 2000 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Library General Public License as
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published by the Free Software Foundation; either version 2 of the
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License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Library General Public License for more details.
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You should have received a copy of the GNU Library General Public
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License along with the GNU C Library; see the file COPYING.LIB. If not,
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write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
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Boston, MA 02111-1307, USA. */
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#include <errno.h>
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#include <fcntl.h>
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#include <paths.h>
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#include <unistd.h>
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#include <sys/stat.h>
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#include <sys/sysmacros.h>
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/* Try to get a machine dependent instruction which will make the
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program crash. This is used in case everything else fails. */
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#include <abort-instr.h>
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#ifndef ABORT_INSTRUCTION
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/* No such instruction is available. */
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# define ABORT_INSTRUCTION
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#endif
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#include <device-nrs.h>
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/* Should other OSes (e.g., Hurd) have different versions which can
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be written in a better way? */
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static void
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check_one_fd (int fd, int mode)
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{
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if (__builtin_expect (__libc_fcntl (fd, F_GETFD), 0) == -1
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&& errno == EBADF)
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{
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struct stat64 st;
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/* Something is wrong with this descriptor, it's probably not
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opened. Open /dev/null so that the SUID program we are
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about to start does not accidently use this descriptor. */
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int nullfd = __libc_open (_PATH_DEVNULL, mode);
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/* We are very paranoid here. With all means we try to ensure
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that we are actually opening the /dev/null device and nothing
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else. */
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if (__builtin_expect (nullfd, 0) == -1
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|| __builtin_expect (__fxstat64 (_STAT_VER, nullfd, &st), 0) != 0
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|| __builtin_expect (S_ISCHR (st.st_mode), 1) == 0
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#if defined DEV_NULL_MAJOR && defined DEV_NULL_MINOR
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|| st.st_rdev != makedev (DEV_NULL_MAJOR, DEV_NULL_MINOR)
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#endif
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)
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/* We cannot even give an error message here since it would
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run into the same problems. */
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while (1)
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/* Try for ever and ever. */
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ABORT_INSTRUCTION;
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}
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}
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void
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__libc_check_standard_fds (void)
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{
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/* This is really paranoid but some people actually are. If /dev/null
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should happen to be a symlink to somewhere else and not the device
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commonly known as "/dev/null" be bail out. We can detect this with
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the O_NOFOLLOW flag for open() but only on some system. */
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#ifndef O_NOFOLLOW
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# define O_NOFOLLOW 0
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#endif
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/* Check all three standard file descriptors. */
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check_one_fd (STDIN_FILENO, O_RDONLY | O_NOFOLLOW);
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check_one_fd (STDOUT_FILENO, O_RDWR | O_NOFOLLOW);
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check_one_fd (STDERR_FILENO, O_RDWR | O_NOFOLLOW);
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}
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