Re: [PATCH v5 0/7] fs: introduce file_getattr and file_setattr syscalls

[Andrey Albershteyn <aalbersh@redhat.com>]

On 2025-05-12 15:25:11, Andrey Albershteyn wrote:
> This patchset introduced two new syscalls file_getattr() and
> file_setattr(). These syscalls are similar to FS_IOC_FSSETXATTR ioctl()
> except they use *at() semantics. Therefore, there's no need to open the
> file to get a fd.
> 
> These syscalls allow userspace to set filesystem inode attributes on
> special files. One of the usage examples is XFS quota projects.
> 
> XFS has project quotas which could be attached to a directory. All
> new inodes in these directories inherit project ID set on parent
> directory.
> 
> The project is created from userspace by opening and calling
> FS_IOC_FSSETXATTR on each inode. This is not possible for special
> files such as FIFO, SOCK, BLK etc. Therefore, some inodes are left
> with empty project ID. Those inodes then are not shown in the quota
> accounting but still exist in the directory. This is not critical but in
> the case when special files are created in the directory with already
> existing project quota, these new inodes inherit extended attributes.
> This creates a mix of special files with and without attributes.
> Moreover, special files with attributes don't have a possibility to
> become clear or change the attributes. This, in turn, prevents userspace
> from re-creating quota project on these existing files.
> 
> NAME
> 
> 	file_getattr/file_setattr - get/set filesystem inode attributes
> 
> SYNOPSIS
> 
> 	#include <sys/syscall.h>    /* Definition of SYS_* constants */
> 	#include <unistd.h>
> 
> 	long syscall(SYS_file_getattr, int dirfd, const char *pathname,
> 		struct fsxattr *fsx, size_t size, unsigned int at_flags);
> 	long syscall(SYS_file_setattr, int dirfd, const char *pathname,
> 		struct fsxattr *fsx, size_t size, unsigned int at_flags);
> 
> 	Note: glibc doesn't provide for file_getattr()/file_setattr(),
> 	use syscall(2) instead.
> 
> DESCRIPTION
> 
> 	The syscalls take fd and path. If path is absolute, fd is not
> 	used. If path is empty, fd can be AT_FDCWD or any valid fd which
> 	will be used to get/set attributes on.
> 
> 	This is an alternative to FS_IOC_FSGETXATTR/FS_IOC_FSSETXATTR
> 	ioctl with a difference that file don't need to be open as we
> 	can reference it with a path instead of fd. By having this we
> 	can manipulated filesystem inode attributes not only on regular
> 	files but also on special ones. This is not possible with
> 	FS_IOC_FSSETXATTR ioctl as with special files we can not call
> 	ioctl() directly on the filesystem inode using file descriptor.
> 
> 	at_flags can be set to AT_SYMLINK_NOFOLLOW or AT_EMPTY_PATH.
> 
> RETURN VALUE
> 
> 	On success, 0 is returned.  On error, -1 is returned, and errno
> 	is set to indicate the error.
> 
> ERRORS
> 
> 	EINVAL		Invalid at_flag specified (only
> 			AT_SYMLINK_NOFOLLOW and AT_EMPTY_PATH is
> 			supported).
> 
> 	EINVAL		Size was smaller than any known version of
> 			struct fsxattr.
> 
> 	EINVAL		Invalid combination of parameters provided in
> 			fsxattr for this type of file.
> 
> 	E2BIG		Size of input argument **struct fsxattr** is too
> 			big.
> 
> 	EBADF		Invalid file descriptor was provided.
> 
> 	EPERM		No permission to change this file.
> 
> 	EOPNOTSUPP	Filesystem does not support setting attributes
> 			on this type of inode
> 
> HISTORY
> 
> 	Added in Linux 6.15.
> 
> EXAMPLE
> 
> Create directory and file "mkdir ./dir && touch ./dir/foo" and then
> execute the following program:
> 
> 	#include <fcntl.h>
> 	#include <errno.h>
> 	#include <string.h>
> 	#include <linux/fs.h>
> 	#include <stdio.h>
> 	#include <sys/syscall.h>
> 	#include <unistd.h>
> 
> 	int
> 	main(int argc, char **argv) {
> 		int dfd;
> 		int error;
> 		struct fsxattr fsx;
> 
> 		dfd = open("./dir", O_RDONLY);
> 		if (dfd == -1) {
> 			printf("can not open ./dir");
> 			return dfd;
> 		}
> 
> 		error = syscall(467, dfd, "./foo", &fsx, 0);
> 		if (error) {
> 			printf("can not call 467: %s", strerror(errno));
> 			return error;
> 		}
> 
> 		printf("dir/foo flags: %d\n", fsx.fsx_xflags);
> 
> 		fsx.fsx_xflags |= FS_XFLAG_NODUMP;
> 		error = syscall(468, dfd, "./foo", &fsx, 0);
> 		if (error) {
> 			printf("can not call 468: %s", strerror(errno));
> 			return error;
> 		}
> 
> 		printf("dir/foo flags: %d\n", fsx.fsx_xflags);
> 
> 		return error;
> 	}
> 
> SEE ALSO
> 
> 	ioctl(2), ioctl_iflags(2), ioctl_xfs_fsgetxattr(2)
> 
> ---
> Changes in v5:
> - Remove setting of LOOKUP_EMPTY flags which does not have any effect
> - Return -ENOSUPP from vfs_fileattr_set()
> - Add fsxattr masking (by Amir)
> - Fix UAF issue dentry
> - Fix getname_maybe_null() issue with NULL path
> - Implement file_getattr/file_setattr hooks
> - Return LSM return code from file_setattr
> - Rename from getfsxattrat/setfsxattrat to file_getattr/file_setattr
> - Link to v4: https://lore.kernel.org/r/20250321-xattrat-syscall-v4-0-3e82e6fb3264@kernel.org
> 
> Changes in v4:
> - Use getname_maybe_null() for correct handling of dfd + path semantic
> - Remove restriction for special files on which flags are allowed
> - Utilize copy_struct_from_user() for better future compatibility
> - Add draft man page to cover letter
> - Convert -ENOIOCTLCMD to -EOPNOSUPP as more appropriate for syscall
> - Add missing __user to header declaration of syscalls
> - Link to v3: https://lore.kernel.org/r/20250211-xattrat-syscall-v3-1-a07d15f898b2@kernel.org
> 
> Changes in v3:
> - Remove unnecessary "dfd is dir" check as it checked in user_path_at()
> - Remove unnecessary "same filesystem" check
> - Use CLASS() instead of directly calling fdget/fdput
> - Link to v2: https://lore.kernel.org/r/20250122-xattrat-syscall-v2-1-5b360d4fbcb2@kernel.org
> 
> v1:
> https://lore.kernel.org/linuxppc-dev/20250109174540.893098-1-aalbersh@kernel.org/
> 
> Previous discussion:
> https://lore.kernel.org/linux-xfs/20240520164624.665269-2-aalbersh@redhat.com/
> 
> ---
> Amir Goldstein (1):
>       fs: prepare for extending file_get/setattr()
> 
> Andrey Albershteyn (6):
>       fs: split fileattr related helpers into separate file
>       lsm: introduce new hooks for setting/getting inode fsxattr
>       selinux: implement inode_file_[g|s]etattr hooks
>       fs: split fileattr/fsxattr converters into helpers
>       fs: make vfs_fileattr_[get|set] return -EOPNOSUPP
>       fs: introduce file_getattr and file_setattr syscalls
> 
>  arch/alpha/kernel/syscalls/syscall.tbl      |   2 +
>  arch/arm/tools/syscall.tbl                  |   2 +
>  arch/arm64/tools/syscall_32.tbl             |   2 +
>  arch/m68k/kernel/syscalls/syscall.tbl       |   2 +
>  arch/microblaze/kernel/syscalls/syscall.tbl |   2 +
>  arch/mips/kernel/syscalls/syscall_n32.tbl   |   2 +
>  arch/mips/kernel/syscalls/syscall_n64.tbl   |   2 +
>  arch/mips/kernel/syscalls/syscall_o32.tbl   |   2 +
>  arch/parisc/kernel/syscalls/syscall.tbl     |   2 +
>  arch/powerpc/kernel/syscalls/syscall.tbl    |   2 +
>  arch/s390/kernel/syscalls/syscall.tbl       |   2 +
>  arch/sh/kernel/syscalls/syscall.tbl         |   2 +
>  arch/sparc/kernel/syscalls/syscall.tbl      |   2 +
>  arch/x86/entry/syscalls/syscall_32.tbl      |   2 +
>  arch/x86/entry/syscalls/syscall_64.tbl      |   2 +
>  arch/xtensa/kernel/syscalls/syscall.tbl     |   2 +
>  fs/Makefile                                 |   3 +-
>  fs/ecryptfs/inode.c                         |   8 +-
>  fs/file_attr.c                              | 475 ++++++++++++++++++++++++++++
>  fs/ioctl.c                                  | 309 ------------------
>  fs/overlayfs/inode.c                        |   2 +-
>  include/linux/fileattr.h                    |  26 ++
>  include/linux/lsm_hook_defs.h               |   2 +
>  include/linux/security.h                    |  16 +
>  include/linux/syscalls.h                    |   6 +
>  include/uapi/asm-generic/unistd.h           |   8 +-
>  include/uapi/linux/fs.h                     |   3 +
>  security/security.c                         |  30 ++
>  security/selinux/hooks.c                    |  14 +
>  29 files changed, 621 insertions(+), 313 deletions(-)
> ---
> base-commit: 0d8d44db295ccad20052d6301ef49ff01fb8ae2d
> change-id: 20250114-xattrat-syscall-6a1136d2db59
> 
> Best regards,
> -- 
> Andrey Albershteyn <aalbersh@kernel.org>
> 

Ignore please, somehow b4 crashed with timeout on gmail

-- 
- Andrey