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

From: Stefan Berger
Date: Fri Jul 14 2017 - 11:22:40 EST

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 or 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 and one<> or just a single one[[: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 ?