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Date: Fri, 28 Sep 2018 09:43:23 +1000 (AEST)
From: James Morris <jmorris@...ei.org>
To: "Schaufler, Casey" <casey.schaufler@...el.com>
cc: Casey Schaufler <casey@...aufler-ca.com>,
"kristen@...ux.intel.com" <kristen@...ux.intel.com>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>,
"Dock, Deneen T" <deneen.t.dock@...el.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"Hansen, Dave" <dave.hansen@...el.com>,
"linux-security-module@...r.kernel.org" <linux-security-module@...r.kernel.org>,
"selinux@...ho.nsa.gov" <selinux@...ho.nsa.gov>,
"arjan@...ux.intel.com" <arjan@...ux.intel.com>
Subject: RE: [PATCH v5 5/5] sidechannel: Linux Security Module for
sidechannel
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@...ei.org>
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