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

[Schaufler, Casey]

> -----Original Message-----
> From: James Morris [mailto:jmorris@xxxxxxxxx]
> Sent: Thursday, September 27, 2018 3:47 PM
> To: Casey Schaufler <casey@xxxxxxxxxxxxxxxx>
> Cc: Schaufler, Casey <casey.schaufler@xxxxxxxxx>; kristen@xxxxxxxxxxxxxxx;
> kernel-hardening@xxxxxxxxxxxxxxxxxx; Dock, Deneen T
> <deneen.t.dock@xxxxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx; Hansen, Dave
> <dave.hansen@xxxxxxxxx>; linux-security-module@xxxxxxxxxxxxxxx;
> selinux@xxxxxxxxxxxxx; arjan@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH v5 5/5] sidechannel: Linux Security Module for sidechannel
> 
> On Thu, 27 Sep 2018, Casey Schaufler 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.