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752dd17443
/proc/self/fd files are special and chmod on O_PATH descriptors in that directory operates on the symbolic link itself (like lchmod).
79 lines
2.7 KiB
C
79 lines
2.7 KiB
C
/* Change the protections of file relative to open directory. Linux version.
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Copyright (C) 2006-2020 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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<https://www.gnu.org/licenses/>. */
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#include <errno.h>
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#include <fcntl.h>
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#include <not-cancel.h>
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#include <stdio.h>
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#include <sys/stat.h>
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#include <sys/types.h>
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#include <sysdep.h>
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#include <unistd.h>
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int
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fchmodat (int fd, const char *file, mode_t mode, int flag)
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{
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if (flag == 0)
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return INLINE_SYSCALL (fchmodat, 3, fd, file, mode);
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else if (flag != AT_SYMLINK_NOFOLLOW)
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return INLINE_SYSCALL_ERROR_RETURN_VALUE (EINVAL);
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else
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{
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/* The kernel system call does not have a mode argument.
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However, we can create an O_PATH descriptor and change that
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via /proc (which does not resolve symbolic links). */
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int pathfd = __openat_nocancel (fd, file,
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O_PATH | O_NOFOLLOW | O_CLOEXEC);
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if (pathfd < 0)
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/* This may report errors such as ENFILE and EMFILE. The
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caller can treat them as temporary if necessary. */
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return pathfd;
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char buf[32];
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if (__snprintf (buf, sizeof (buf), "/proc/self/fd/%d", pathfd) < 0)
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{
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/* This also may report strange error codes to the caller
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(although snprintf really should not fail). */
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__close_nocancel (pathfd);
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return -1;
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}
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/* This operates directly on the symbolic link if it is one.
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/proc/self/fd files look like symbolic links, but they are
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not. (fchmod and fchmodat do not work on O_PATH descriptors,
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similar to fstat before Linux 3.6.) */
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int ret = __chmod (buf, mode);
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if (ret != 0)
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{
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if (errno == ENOENT)
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/* /proc has not been mounted. Without /proc, there is no
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way to upgrade the O_PATH descriptor to a full
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descriptor. It is also not possible to re-open the
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file without O_PATH because the file name may refer to
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another file, and opening that without O_PATH may have
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side effects (such as blocking, device rewinding, or
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releasing POSIX locks). */
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__set_errno (EOPNOTSUPP);
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}
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__close_nocancel (pathfd);
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return ret;
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}
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}
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libc_hidden_def (fchmodat)
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