linux-kernel - Re: [PATCH] Add PR_{GET,SET}_NO_NEW_PRIVS to prevent execve from granting privs

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Date:	Fri, 13 Jan 2012 13:54:51 -0500
From:	Eric Paris <eparis@...hat.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Oleg Nesterov <oleg@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	Will Drewry <wad@...omium.org>, torvalds@...ux-foundation.org,
	linux-kernel@...r.kernel.org, keescook@...omium.org,
	john.johansen@...onical.com, serge.hallyn@...onical.com,
	coreyb@...ux.vnet.ibm.com, pmoore@...hat.com, djm@...drot.org,
	segoon@...nwall.com, rostedt@...dmis.org, jmorris@...ei.org,
	scarybeasts@...il.com, avi@...hat.com, penberg@...helsinki.fi,
	viro@...iv.linux.org.uk, luto@....EDU, mingo@...e.hu,
	akpm@...ux-foundation.org, khilman@...com, borislav.petkov@....com,
	amwang@...hat.com, ak@...ux.intel.com, eric.dumazet@...il.com,
	gregkh@...e.de, dhowells@...hat.com, daniel.lezcano@...e.fr,
	linux-fsdevel@...r.kernel.org,
	linux-security-module@...r.kernel.org, olofj@...omium.org,
	mhalcrow@...gle.com, dlaor@...hat.com, corbet@....net
Subject: Re: [PATCH] Add PR_{GET,SET}_NO_NEW_PRIVS to prevent execve from
 granting privs

On Fri, 2012-01-13 at 18:24 +0000, Alan Cox wrote:
> This still appears to be a bit broken
> 
> There are three problems here
> 
> 1. I can stop an app changing privs which in some SELinux or APParmour
> cases might mean I prevent it being dropped into a less privileged
> position. That's something only the security policy knows.
> 
> So for SELinux and Apparmour and the like in some situations you are
> potentially adding a security hole. That one seems hard to fix unless you
> fail the exec if it causes a security transition, as opposed to just
> keeping the old one. For non change cases we can however still pass the
> filter on, which is the usual sane case.

I can't speak about AppArmour at all, but not transitioning in SELinux
(the same as MNT_NOSUID) is safe since policy will still make a security
decision if you are allowed to launch the binary without transitioning.
I have thoughts on how to make the SELinux approach more flexible and
policy controlled, but I'd be fine with this flag just applying no
transition for now and adding that as a new feature down the road.

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