XFS reports lchmod failure, but changes file system contents

[Christoph Hellwig]

On Wed, Feb 12, 2020 at 08:16:04AM -0800, Darrick J. Wong wrote:
> xfs_setattr_nonsize calls posix_acl_chmod which returns EOPNOTSUPP
> because the xfs symlink inode_operations do not include a ->set_acl
> pointer.
> 
> I /think/ that posix_acl_chmod code exists to enforce that the file mode
> reflects any acl that might be set on the inode, but in this case the
> inode is a symbolic link.
> 
> I don't remember off the top of my head if ACLs are supposed to apply to
> symlinks, but what do you think about adding get_acl/set_acl pointers to
> xfs_symlink_inode_operations and xfs_inline_symlink_inode_operations ?

Symlinks don't have permissions or ACLs, so adding them makes no
sense.

xfs doesn't seem all that different from the other file systems,
so I suspect you'll also see it with other on-disk file systems.
We probably need a check high up in the chmod and co code to reject
the operation early for O_PATH file descriptors pointing to symlinks.