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

[Stefan Berger]

On 07/14/2017 09:34 AM, Serge E. Hallyn wrote:
> Quoting Stefan Berger (stefanb@xxxxxxxxxxxxxxxxxx):
> > On 07/13/2017 08:38 PM, Eric W. Biederman wrote:
> > > Stefan Berger <stefanb@xxxxxxxxxxxxxxxxxx> writes:
> > >
> > > > On 07/13/2017 01:49 PM, Eric W. Biederman wrote:
> > > >
> > > > > My big question right now is can you implement Ted's suggested
> > > > > restriction.  Only one security.foo or secuirty.foo@... attribute ?
> > > > We need to raw-list the xattrs and do the check before writing them. I am fairly sure this can be done.
> > > >
> > > > So now you want to allow security.foo and one security.foo@uid=<> or just a single one security.foo(@[[:print:]]*)?
> > > The latter.
> > That case would prevent a container user from overriding the xattr
> > on the host. Is that what we want? For limiting the number of xattrs
> Not really.  If the file is owned by a uid mapped into the container,
> then the container root can chown the file which will clear the file
> capability, after which he can set a new one.  If the file is not
> owned by a uid mapped into the container, then container root could
> not set a filecap anyway.

Let's say I installed a container where all files are signed and thus 
have security.ima. Now for some reason I want to re-sign some or all 
files inside that container. How would I do that ? Would I need to get 
rid of security.ima first, possibly by copying each file, deleting the 
original file, and renaming the copied file to the original name, or 
should I just be able to write out a new signature, thus creating 
security.ima@uid=1000 besides the security.ima ?

   Stefan