The security implications are that anything that can change the label
could also hide itself and its doings from the audit system and thus
would be used as a means to evade detection. I actually think this
means the label should be write once (once you've set it, you can't
change it) ...
Richard and I have talked about a write once approach, but the
thinking was that you may want to allow a nested container
orchestrator (Why? I don't know, but people always want to do the
craziest things.) and a write-once policy makes that impossible. If
we punt on the nested orchestrator, I believe we can seriously think
about a write-once policy to simplify things.
Nested containers are a very widely used use-case (see LXC system
containers, inside of which people run other container runtimes). So I
would definitely consider it something that "needs to be supported in
some way". While the LXC guys might be a *tad* crazy, the use-case isn't. :P
... and orchestration systems should begin as unlabelled
processes allowing them to do arbitrary forks.
My current thinking is that the default state is to start unlabeled (I
just vomited a little into my SELinux hat); in other words
init/systemd/PID-1 in the host system starts with an "unset" audit
container ID. This not only helps define the host system (anything
that has an unset audit container ID) but provides a blank slate for
the orchestrator(s).
For nested containers, I actually think the label should be
hierarchical, so you can add a label for the new nested container but
it still also contains its parents label as well.
I haven't made up my mind on this completely just yet, but I'm
currently of the mindset that supporting multiple audit container IDs
on a given process is not a good idea.
As long as creating a new "container" (that is, changing a process's
"audit container ID") is an audit event then I think that having a
hierarchy be explicit is not necessary (userspace audit can figure out
the hierarchy quite easily -- but also there are cases where thinking of
it as being hierarchical isn't necessarily correct).
--
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
https://www.cyphar.com/
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