linux-kernel - Re: [RFC] cgroups: implement device whitelist lsm (v2)

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Date:	Fri, 14 Mar 2008 09:35:34 -0500
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	Paul Menage <menage@...gle.com>
Cc:	"Serge E. Hallyn" <serue@...ibm.com>,
	lkml <linux-kernel@...r.kernel.org>,
	linux-security-module@...r.kernel.org, Greg KH <greg@...ah.com>,
	Stephen Smalley <sds@...ch.ncsc.mil>,
	Casey Schaufler <casey@...aufler-ca.com>,
	Pavel Emelianov <xemul@...nvz.org>
Subject: Re: [RFC] cgroups: implement device whitelist lsm (v2)

Quoting Paul Menage (menage@...gle.com):
> On Fri, Mar 14, 2008 at 7:05 AM, Serge E. Hallyn <serue@...ibm.com> wrote:
> >  > >  A task may only be moved to another devcgroup if it is moving to
> >  > >  a direct descendent of its current devcgroup.
> >  >
> >  > What's the rationale for that?
> >
> >  To prevent it escaping to laxer device permissions, which of course only
> >  makes sense if we do what you recommend above :)
> >
> 
> That makes it impossible for a root process to enter a child cgroup,
> do something, and then go back to its own cgroup.

Yes, but it can fire off a child in the child cgroup to do something,
and go on on its own cgroup when the child finishes.

> Why aren't the
> existing cgroup security semantics sufficient?

Because the point of this is to provide some restrictions to otherwise
privileged users, and cgroups only provides dac-based permissions.

But that doesn't mean that I'm not doing too much.  I could just add a
CAP_SYS_ADMIN or CAP_CONT_OVERRIDE+CAP_SYS_ADMIN check, and not restrict
which cgroups a task can move to.  Does that sound good?

-serge
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