linux-kernel - Re: LSM conversion to static interface

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Date:	Tue, 23 Oct 2007 17:28:25 +0200 (CEST)
From:	Jan Engelhardt <jengelh@...putergmbh.de>
To:	"Serge E. Hallyn" <serge@...lyn.com>
cc:	Giacomo Catenazzi <cate@...ian.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andreas Gruenbacher <agruen@...e.de>,
	Thomas Fricaccia <thomas_fricacci@...oo.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	James Morris <jmorris@...ei.org>
Subject: Re: LSM conversion to static interface

On Oct 23 2007 10:20, Serge E. Hallyn wrote:
>
>Once the per-process capability bounding set is accepted
>(http://lkml.org/lkml/2007/10/3/315) you will be able to do something
>like:
>
>	1. Create user 'jdoe' with uid 0

UID 0 is _not_ acceptable for me.

>	2. write a pam module which, when jdoe logs in, takes
>	   CAP_NET_ADMIN out of his capability bounding set
>	3. Now jdoe can log in with the kind of capabilities subset
>	   you describe.

It is not that easy.
CAP_DAC_OVERRIDE is given to the subadmin to bypass the pre-security
checks in kernel code, and then the detailed implementation of
limitation is done inside multiadm.
This is not just raising or lowering capabilities.

>It's not a perfect solution, since it doesn't allow jdoe any way at all
>to directly execute a file with more caps (setuid and file capabilities
>are subject to the capbound).  So there is certainly still a place for
>multiadm.

A normal user can execute suid binaries today, and so can s/he with mtadm.
I do not see where that will change - it does not need any caps atm.
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