On 9/27/2018 2:45 PM, James Morris wrote:

On Wed, 26 Sep 2018, Casey Schaufler wrote:

quoted

+	/*
+	 * 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. I think
these are the most sensible, but I'm willing to be educated.
I was also requested to check on potential issues between containers,
but as there is no kernel concept of containers this is the
best I see we can do.

It least make it user configurable.

Would you have a suggested granularity? I could have a
configuration option for each of cgroups, user and pid
namespaces but that's getting to be a lot of knobs to
twist.