On 7/12/2021 5:49 AM, Greg Kurz wrote: > On Fri, 9 Jul 2021 08:34:41 -0700 > Casey Schaufler <casey@xxxxxxxxxxxxxxxx> wrote: > >> On 7/9/2021 8:27 AM, Vivek Goyal wrote: >>> On Fri, Jul 09, 2021 at 11:19:15AM +0200, Christian Brauner wrote: >>>> On Thu, Jul 08, 2021 at 01:57:38PM -0400, Vivek Goyal wrote: >>>>> Currently user.* xattr are not allowed on symlink and special files. >>>>> >>>>> man xattr and recent discussion suggested that primary reason for this >>>>> restriction is how file permissions for symlinks and special files >>>>> are little different from regular files and directories. >>>>> >>>>> For symlinks, they are world readable/writable and if user xattr were >>>>> to be permitted, it will allow unpriviliged users to dump a huge amount >>>>> of user.* xattrs on symlinks without any control. >>>>> >>>>> For special files, permissions typically control capability to read/write >>>>> from devices (and not necessarily from filesystem). So if a user can >>>>> write to device (/dev/null), does not necessarily mean it should be allowed >>>>> to write large number of user.* xattrs on the filesystem device node is >>>>> residing in. >>>>> >>>>> This patch proposes to relax the restrictions a bit and allow file owner >>>>> or priviliged user (CAP_FOWNER), to be able to read/write user.* xattrs >>>>> on symlink and special files. >>>>> >>>>> virtiofs daemon has a need to store user.* xatrrs on all the files >>>>> (including symlinks and special files), and currently that fails. This >>>>> patch should help. >>>>> >>>>> Link: https://lore.kernel.org/linux-fsdevel/20210625191229.1752531-1-vgoyal@xxxxxxxxxx/ >>>>> Signed-off-by: Vivek Goyal <vgoyal@xxxxxxxxxx> >>>>> --- >>>> Seems reasonable and useful. >>>> Acked-by: Christian Brauner <christian.brauner@xxxxxxxxxx> >>>> >>>> One question, do all filesystem supporting xattrs deal with setting them >>>> on symlinks/device files correctly? >>> Wrote a simple bash script to do setfattr/getfattr user.foo xattr on >>> symlink and device node on ext4, xfs and btrfs and it works fine. >> How about nfs, tmpfs, overlayfs and/or some of the other less conventional >> filesystems? >> > How about virtiofs then ? :-) One of the "less conventional filesystems", surely. �
