RE: [PATCH v5 5/5] sidechannel: Linux Security Module for sidechannel

[James Morris]

On Thu, 27 Sep 2018, Schaufler, Casey wrote:

> > > On 9/27/2018 2:45 PM, James Morris wrote:
> > > > On Wed, 26 Sep 2018, Casey Schaufler wrote:
> > > >
> > > >> +	/*
> > > >> +	 * Namespace checks. Considered safe if:
> > > >> +	 *	cgroup namespace is the same
> > > >> +	 *	User namespace is the same
> > > >> +	 *	PID namespace is the same
> > > >> +	 */
> > > >> +	if (current->nsproxy)
> > > >> +		ccgn = current->nsproxy->cgroup_ns;
> > > >> +	if (p->nsproxy)
> > > >> +		pcgn = p->nsproxy->cgroup_ns;
> > > >> +	if (ccgn != pcgn)
> > > >> +		return -EACCES;
> > > >> +	if (current->cred->user_ns != p->cred->user_ns)
> > > >> +		return -EACCES;
> > > >> +	if (task_active_pid_ns(current) != task_active_pid_ns(p))
> > > >> +		return -EACCES;
> > > >> +	return 0;
> > > > I really don't like the idea of hard-coding namespace security semantics
> > > > in an LSM.  Also, I'm not sure if these semantics make any sense.
> > >
> > > Checks on namespaces where explicitly requested.
> > 
> > By whom and what is the rationale?
> 
> The rationale is to protect containers. Since those closest thing
> there is to a definition of containers is "uses namespaces" that
> becomes the focus. Separating them out does not make too much
> sense as I would expect someone concerned with one to be concerned
> with all.

A lot of people will not be using user namespaces due to security 
concerns, so with this hard-coded logic, you are saying this case is 
'safe' in a sidechannel context.

Which hints at the deeper issue that containers are a userland 
abstraction.  Protection of containers needs to be defined by userland 
policy.



-- 
James Morris
<jmorris@xxxxxxxxx>