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98 lines
3.2 KiB
C
98 lines
3.2 KiB
C
/* Copyright (C) 2000-2017 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 Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the 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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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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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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#include <not-cancel.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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/* Note that fcntl() with this parameter is not a cancellation point. */
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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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const char *name;
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dev_t dev;
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/* For writable descriptors we use /dev/full. */
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if ((mode & O_ACCMODE) == O_WRONLY)
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{
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name = _PATH_DEV "full";
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dev = makedev (DEV_FULL_MAJOR, DEV_FULL_MINOR);
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}
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else
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{
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name = _PATH_DEVNULL;
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dev = makedev (DEV_NULL_MAJOR, DEV_NULL_MINOR);
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}
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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 accidentally use this descriptor. */
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int nullfd = open_not_cancel (name, mode, 0);
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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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Note that the following code assumes that STDIN_FILENO,
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STDOUT_FILENO, STDERR_FILENO are the three lowest file
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decsriptor numbers, in this order. */
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struct stat64 st;
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if (__builtin_expect (nullfd != fd, 0)
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|| __builtin_expect (__fxstat64 (_STAT_VER, fd, &st), 0) != 0
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|| __builtin_expect (S_ISCHR (st.st_mode), 1) == 0
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|| st.st_rdev != dev)
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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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/* Check all three standard file descriptors. The O_NOFOLLOW flag
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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
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device commonly known as "/dev/null" we bail out. */
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check_one_fd (STDIN_FILENO, O_WRONLY | O_NOFOLLOW);
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check_one_fd (STDOUT_FILENO, O_RDONLY | O_NOFOLLOW);
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check_one_fd (STDERR_FILENO, O_RDONLY | O_NOFOLLOW);
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}
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