linux-kernel - Re: Linux Security *Module* Framework (Was: LSM conversion to static interface)

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Date:	Wed, 24 Oct 2007 18:02:15 -0400
From:	"David P. Quigley" <dpquigl@...ho.nsa.gov>
To:	Jan Engelhardt <jengelh@...putergmbh.de>
Cc:	"Serge E. Hallyn" <serue@...ibm.com>,
	Simon Arlott <simon@...e.lp0.eu>,
	Adrian Bunk <bunk@...nel.org>,
	Chris Wright <chrisw@...s-sol.org>,
	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andreas Gruenbacher <agruen@...e.de>,
	Thomas Fricaccia <thomas_fricacci@...oo.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	James Morris <jmorris@...ei.org>,
	Crispin Cowan <crispin@...spincowan.com>,
	Giacomo Catenazzi <cate@...ian.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: Linux Security *Module* Framework (Was: LSM conversion to
	static interface)

On Wed, 2007-10-24 at 23:51 +0200, Jan Engelhardt wrote:
> On Oct 24 2007 16:37, Serge E. Hallyn wrote:
> >
> >Or, a better example, a privileged program reads some sensitive data -
> >as allowed by multiadm, writes it to a file, but apparmor prevented it
> >from chowning the file to the right user before writing,
> 
> Interesting find, I should pay attention to that :-)
> 
> But - note to dquigley - AFAICS, an LSM needs to _explicitly_ call
> the next LSM's function. No one (just a minimal grep in
> linux-2.6/security/) besides SELinux does that today. So
> while you could load AppArmor ontop of MultiAdm, it would never
> be invoked. This is what is known as "sufficient" in PAM parlance.
> SELinux OTOH is in "required" mode [again PAM-speak].

True but if we are talking about a true stackable architecture calling
down to your lower component shouldn't be an option it should be a
requirement of the semantics. I would hate to think some module which is
a subset of the restrictiveness of another could override it because its
"sufficient". If that was the case I could load in a module which just
returns 0 for everything and make it "sufficient" bypassing every other
module. This also introduces ordering dependencies. If you install
MultiAdm before AppArmor or SELinux and make it "sufficient" then you
defeated the point of having AppArmor or SELinux installed in the first
place. 

Dave

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