On 2025-02-24 11:54:34, Jan Kara wrote:
On Tue 11-02-25 18:22:47, 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.
Also, as vfs_fileattr_set() is now will be called on special files
too, let's forbid any other attributes except projid and nextents
(symlink can have an extent).
CC: linux-api@xxxxxxxxxxxxxxx
CC: linux-fsdevel@xxxxxxxxxxxxxxx
CC: linux-xfs@xxxxxxxxxxxxxxx
Signed-off-by: Andrey Albershteyn <aalbersh@xxxxxxxxxx>
Some comments below:
+SYSCALL_DEFINE4(getfsxattrat, int, dfd, const char __user *, filename,
+ struct fsxattr __user *, fsx, unsigned int, at_flags)
+{
+ CLASS(fd, dir)(dfd);
+ struct fileattr fa;
+ struct path filepath;
+ int error;
+ unsigned int lookup_flags = 0;
+
+ if ((at_flags & ~(AT_SYMLINK_NOFOLLOW | AT_EMPTY_PATH)) != 0)
+ return -EINVAL;
+
+ if (at_flags & AT_SYMLINK_FOLLOW)
^^ This should be !(at_flags & AT_SYMLINK_NOFOLLOW)?
In the check above you verify for AT_SYMLINK_NOFOLLOW and that also matches
what setxattrat() does...
Right, didn't notice that this is actually opposite to setxattrat(),
will change that.
+ lookup_flags |= LOOKUP_FOLLOW;
+
+ if (at_flags & AT_EMPTY_PATH)
+ lookup_flags |= LOOKUP_EMPTY;
+
+ if (fd_empty(dir))
+ return -EBADF;
This check is wrong and in fact the whole dfd handling looks buggy.
openat(2) manpage describes the expected behavior:
The dirfd argument is used in conjunction with the pathname argument as
follows:
• If the pathname given in pathname is absolute, then dirfd is ig-
nored.
^^^^ This is what you break. If the pathname is absolute, you're
not expected to touch dirfd.
• If the pathname given in pathname is relative and dirfd is the spe-
cial value AT_FDCWD, then pathname is interpreted relative to the
current working directory of the calling process (like open()).
^^^ Also AT_FDCWD handling would be broken by the above check.
• If the pathname given in pathname is relative, then it is inter-
preted relative to the directory referred to by the file descriptor
dirfd (rather than relative to the current working directory of the
calling process, as is done by open() for a relative pathname). In
this case, dirfd must be a directory that was opened for reading
(O_RDONLY) or using the O_PATH flag.
If the pathname given in pathname is relative, and dirfd is not a valid
file descriptor, an error (EBADF) results. (Specifying an invalid file
descriptor number in dirfd can be used as a means to ensure that path-
name is absolute.)
+
+ error = user_path_at(dfd, filename, lookup_flags, &filepath);
^^^ And user_path_at() isn't quite what you need either
because with AT_EMPTY_PATH we also want to allow for filename to be NULL
(not just empty string) and user_path_at() does not support that. That's
why I in my previous replies suggested you should follow what setxattrat()
does and that sadly it is more painful than it should be. You need
something like:
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, filename, lookup_flags, &filepath,
NULL);
if (error)
goto out;
error = vfs_fileattr_get(filepath.dentry, &fa);
path_put(&filepath);
}
if (!error)
error = copy_fsxattr_to_user(&fa, fsx);
out:
putname(name);
return error;
Longer term, we need to provide user_path_maybe_null_at() for this but I
don't want to drag you into this cleanup :)
Oh, I missed that, thanks for pointing this out, I will change it as
suggested.
--
- Andrey
