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

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Date:	Wed, 24 Oct 2007 21:04:44 +0200 (CEST)
From:	Jan Engelhardt <jengelh@...putergmbh.de>
To:	Simon Arlott <simon@...e.lp0.eu>
cc:	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 Oct 24 2007 19:59, Simon Arlott wrote:
>On 24/10/07 19:51, Jan Engelhardt wrote:
>> On Oct 24 2007 19:11, Simon Arlott wrote:
>>>
>>>* (I've got a list of access rules which are scanned in order until one of 
>>>them matches, and an array of one bit for every port for per-port default 
>>>allow/deny - although the latter could be removed.
>>>http://svn.lp0.eu/simon/portac/trunk/)
>> 
>> Besides the 'feature' of inhibiting port binding,
>> is not this task of blocking connections something for a firewall?
>
>The firewall blocks incoming connections where appropriate, yes, but it 
>doesn't stop one user binding to a port that another user expected to be able 
>to use. "Ownership" of ports (1-1023) shouldn't be something only root (via 
>CAP_NET_BIND_SERVICE) has. Lots of services also don't have standard ports 
>below 1024 and it's useful to be able to prevent users from binding to them 
>too.

Indeed.


There has been a feature in the security framework that probably did
not get much attention. It looks like YAGNI first, but on a closer look,
it becomes useful pretty quick - secondary_register.

As more and more simple LSM plugins pop up, stacking/chaining by means
of secondary_register becomes attractive again, especially if these LSMs
target different actions. This is probably the most useful thing why
the LSM interface should remain modular:

# Secure my files
modprobe apparmor
# -*- assuming apparmor implemented secondaries -*-
# Secure my ports
modprobe portac
# More rights to users
modprobe multiadm
# -*- whatever else comes along -*-
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