[LSM Stacking] SELinux policy inside container affects a processon Host

[Paul Moore]

On Sun, Aug 6, 2023 at 1:16 PM Dr. Greg <greg at enjellic.com> wrote:
> On Fri, Jul 28, 2023 at 10:54:23AM +0900, Leesoo Ahn wrote:
> > 2023-07-07 ?????? 11:20??? Paul Moore ???(???) ??? ???:
> > >On Fri, Jul 7, 2023 at 4:29???AM Leesoo Ahn <lsahn at wewakecorp.com> wrote:
> >
> > [...]
> >
> > >
> > >What you are looking for is a combination of LSM stacking and
> > >individual LSM namespacing. Sadly, I think the communications around
> > >LSM stacking have not been very clear on this and I worry that many
> > >people are going to be disappointed with LSM stacking for this very
> > >reason.
> > >
> > >While stacking of LSMs is largely done at the LSM layer, namespacing
> > >LSMs such that they can be customized for individual containers
> > >requires work to be done at the per-LSM level as each LSM is
> > >different. AppArmor already has a namespacing concept, but SELinux
> > >does not. Due to differences in the approach taken by the two LSMs,
> > >namespacing is much more of a challenge for SELinux, largely due to
> > >issues around filesystem labeling. We have not given up on the idea,
> > >but we have yet to arrive at a viable solution for namespacing
> > >SELinux.
> > >
> > >If you are interested in stacking SELinux and AppArmor, I believe the
> > >only practical solution is to run SELinux on the host system (initial
> > >namespace) and run AppArmor in the containers.
>
> > Paul, I don't get that SELinux on the host system and run AppArmor
> > in the containers is the only practical solution. Could you please
> > explain that in more details?
>
> It appears that Paul is extremely busy, so I thought the 'Quixote
> Group' would try and offer some reflections that may help with your
> efforts.

My apologies, yes I am rather busy at the moment, but I also stopped
following this thread a while ago as it didn't seem to be going
anywhere meaningful.  I happen to read this last email while I'm
waiting in an airport, so let me try and provide a quick explanation
about why running SELinux only in a container is a bad idea.

As you probably know, the Linux kernel has no concept of a container,
it only supports subsystem specific namespaces, e.g. mount namespace,
network namespace, etc.  SELinux does not provide a subsystem
namespace, and it does not generally concern itself with other
subsystem names.  From a SELinux perspective there is no difference
between a process running in the host namespace or a
container/namespace; both are treated the same with access control
decisions made based on the processes' SELinux domain, the type of the
target resource, and the access requested.

If one were to load a SELinux policy inside a container, even if it
were allowed, the system would likely behave in unexpected ways as the
container-loaded policy will take effect across the entire system, not
just inside the container.

-- 
paul-moore.com