Re: [PATCH v4 3/3] fs: introduce getfsxattrat and setfsxattrat syscalls

[Jan Kara]

On Fri 21-03-25 20:48:42, Andrey Albershteyn wrote:
> From: Andrey Albershteyn <aalbersh@xxxxxxxxxx>
> 
> Introduce getfsxattrat and setfsxattrat syscalls to manipulate inode
> extended attributes/flags. The syscalls take parent directory fd and
> path to the child together with struct fsxattr.
> 
> This is an alternative to 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 inode extended
> 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 fd.
> 
> This patch adds two new syscalls which allows userspace to get/set
> extended inode attributes on special files by using parent directory
> and a path - *at() like syscall.
> 
> CC: linux-api@xxxxxxxxxxxxxxx
> CC: linux-fsdevel@xxxxxxxxxxxxxxx
> CC: linux-xfs@xxxxxxxxxxxxxxx
> Signed-off-by: Andrey Albershteyn <aalbersh@xxxxxxxxxx>
> Acked-by: Arnd Bergmann <arnd@xxxxxxxx>

Looks good. Just two nits below:

> +SYSCALL_DEFINE5(getfsxattrat, int, dfd, const char __user *, filename,
> +		struct fsxattr __user *, ufsx, size_t, usize,
> +		unsigned int, at_flags)
> +{
> +	struct fileattr fa = {};
> +	struct path filepath;
> +	int error;
> +	unsigned int lookup_flags = 0;
> +	struct filename *name;
> +	struct fsxattr fsx = {};
> +
> +	BUILD_BUG_ON(sizeof(struct fsxattr) < FSXATTR_SIZE_VER0);
> +	BUILD_BUG_ON(sizeof(struct fsxattr) != FSXATTR_SIZE_LATEST);
> +
> +	if ((at_flags & ~(AT_SYMLINK_NOFOLLOW | AT_EMPTY_PATH)) != 0)
> +		return -EINVAL;
> +
> +	if (!(at_flags & AT_SYMLINK_NOFOLLOW))
> +		lookup_flags |= LOOKUP_FOLLOW;
> +
> +	if (at_flags & AT_EMPTY_PATH)
> +		lookup_flags |= LOOKUP_EMPTY;

Strictly speaking setting LOOKUP_EMPTY does not have any effect because
empty names are already handled by getname_maybe_null(). But it does not
hurt either so I don't really care...

> +
> +	if (usize > PAGE_SIZE)
> +		return -E2BIG;
> +
> +	if (usize < FSXATTR_SIZE_VER0)
> +		return -EINVAL;
> +
> +	name = getname_maybe_null(filename, at_flags);
> +	if (!name) {
> +		CLASS(fd, f)(dfd);
> +
> +		if (fd_empty(f))
> +			return -EBADF;
> +		error = vfs_fileattr_get(file_dentry(fd_file(f)), &fa);
> +	} else {
> +		error = filename_lookup(dfd, name, lookup_flags, &filepath,
> +					NULL);
> +		if (error)
> +			goto out;
> +		error = vfs_fileattr_get(filepath.dentry, &fa);
> +		path_put(&filepath);
> +	}
> +	if (error == -ENOIOCTLCMD)
> +		error = -EOPNOTSUPP;
> +	if (!error) {
> +		fileattr_to_fsxattr(&fa, &fsx);
> +		error = copy_struct_to_user(ufsx, usize, &fsx,
> +					    sizeof(struct fsxattr), NULL);
> +	}
> +out:
> +	putname(name);
> +	return error;
> +}
> +
> +SYSCALL_DEFINE5(setfsxattrat, int, dfd, const char __user *, filename,
> +		struct fsxattr __user *, ufsx, size_t, usize,
> +		unsigned int, at_flags)
> +{
> +	struct fileattr fa;
> +	struct path filepath;
> +	int error;
> +	unsigned int lookup_flags = 0;
> +	struct filename *name;
> +	struct mnt_idmap *idmap;
> +	struct dentry *dentry;
> +	struct vfsmount *mnt;
> +	struct fsxattr fsx = {};
> +
> +	BUILD_BUG_ON(sizeof(struct fsxattr) < FSXATTR_SIZE_VER0);
> +	BUILD_BUG_ON(sizeof(struct fsxattr) != FSXATTR_SIZE_LATEST);
> +
> +	if ((at_flags & ~(AT_SYMLINK_NOFOLLOW | AT_EMPTY_PATH)) != 0)
> +		return -EINVAL;
> +
> +	if (!(at_flags & AT_SYMLINK_NOFOLLOW))
> +		lookup_flags |= LOOKUP_FOLLOW;
> +
> +	if (at_flags & AT_EMPTY_PATH)
> +		lookup_flags |= LOOKUP_EMPTY;

Same comment regarding LOOKUP_EMPTY here.

> +
> +	if (usize > PAGE_SIZE)
> +		return -E2BIG;
> +
> +	if (usize < FSXATTR_SIZE_VER0)
> +		return -EINVAL;
> +
> +	error = copy_struct_from_user(&fsx, sizeof(struct fsxattr), ufsx, usize);
> +	if (error)
> +		return error;
> +
> +	fsxattr_to_fileattr(&fsx, &fa);
> +
> +	name = getname_maybe_null(filename, at_flags);
> +	if (!name) {
> +		CLASS(fd, f)(dfd);
> +
> +		if (fd_empty(f))
> +			return -EBADF;
> +
> +		idmap = file_mnt_idmap(fd_file(f));
> +		dentry = file_dentry(fd_file(f));
> +		mnt = fd_file(f)->f_path.mnt;
> +	} else {
> +		error = filename_lookup(dfd, name, lookup_flags, &filepath,
> +					NULL);
> +		if (error)
> +			return error;
> +
> +		idmap = mnt_idmap(filepath.mnt);
> +		dentry = filepath.dentry;
> +		mnt = filepath.mnt;
> +	}
> +
> +	error = mnt_want_write(mnt);
> +	if (!error) {
> +		error = vfs_fileattr_set(idmap, dentry, &fa);
> +		if (error == -ENOIOCTLCMD)
> +			error = -EOPNOTSUPP;
> +		mnt_drop_write(mnt);
> +	}
> +
> +	path_put(&filepath);

filepath will not be initialized here in case of name == NULL. 

> +	return error;
> +}

With this fixed feel free to add:

Reviewed-by: Jan Kara <jack@xxxxxxx>

								Honza

-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR