Re: [PATCH v2] xattr: Enable security.capability in user namespaces

[Stefan Berger]

On 07/18/2017 03:01 AM, James Morris wrote:
> On Thu, 13 Jul 2017, Stefan Berger wrote:
>
> > A file shared by 2 containers, one mapping root to uid=1000, the other mapping
> > root to uid=2000, will show these two xattrs on the host (init_user_ns) once
> > these containers set xattrs on that file.
> I may be missing something here, but what happens when say the uid=2000
> container and associated user is deleted from the system, then another is
> created with the same uid?
>
> Won't this mean that you have unexpected capabilities turning up in the
> new container?

Yes, that's right. I don't know any solution for that. We would have to 
walk the filesystems and find all 'stale' xattrs with such a uid. This 
is independent of whether the uid is encoded on the name side, as in 
this patch, or on the value side, as in Serge's original proposal. And 
uids of a mapped container root user don't necessarily have to have an 
account on the host so that an account deletion could trigger that.

    Stefan