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65341f7bbe
Linux 6.6 (09da082b07bbae1c) added support for fchmodat2, which has
similar semantics as fchmodat with an extra flag argument. This
allows fchmodat to implement AT_SYMLINK_NOFOLLOW and AT_EMPTY_PATH
without the need for procfs.
The syscall is registered on all architectures (with value of 452
except on alpha which is 562, commit 78252deb023cf087).
The tst-lchmod.c requires a small fix where fchmodat checks two
contradictory assertions ('(st.st_mode & 0777) == 2' and
'(st.st_mode & 0777) == 3').
Checked on x86_64-linux-gnu on a 6.6 kernel.
Reviewed-by: Florian Weimer <fweimer@redhat.com>
105 lines
3.5 KiB
C
105 lines
3.5 KiB
C
/* Change the protections of file relative to open directory. Linux version.
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Copyright (C) 2006-2023 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 <fd_to_filename.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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#if !__ASSUME_FCHMODAT2
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static int
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fchmodat_fallback (int fd, const char *file, mode_t mode, int flag)
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{
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if (flag != AT_SYMLINK_NOFOLLOW)
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return INLINE_SYSCALL_ERROR_RETURN_VALUE (EINVAL);
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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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/* Use fstatat because fstat does not work on O_PATH descriptors
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before Linux 3.6. */
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struct __stat64_t64 st;
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if (__fstatat64_time64 (pathfd, "", &st, AT_EMPTY_PATH) != 0)
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{
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__close_nocancel (pathfd);
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return -1;
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}
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/* Some Linux versions with some file systems can actually
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change symbolic link permissions via /proc, but this is not
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intentional, and it gives inconsistent results (e.g., error
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return despite mode change). The expected behavior is that
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symbolic link modes cannot be changed at all, and this check
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enforces that. */
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if (S_ISLNK (st.st_mode))
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{
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__close_nocancel (pathfd);
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__set_errno (EOPNOTSUPP);
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return -1;
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}
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/* For most file systems, fchmod does not operate on O_PATH
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descriptors, so go through /proc. */
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struct fd_to_filename filename;
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int ret = __chmod (__fd_to_filename (pathfd, &filename), 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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#endif
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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 __ASSUME_FCHMODAT2
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return INLINE_SYSCALL_CALL (fchmodat2, fd, file, mode, flag);
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#else
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if (flag == 0)
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return INLINE_SYSCALL_CALL (fchmodat, fd, file, mode);
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int r = INLINE_SYSCALL_CALL (fchmodat2, fd, file, mode, flag);
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if (r != 0 && errno == ENOSYS)
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return fchmodat_fallback (fd, file, mode, flag);
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return r;
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#endif
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}
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libc_hidden_def (fchmodat)
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