linux-kernel - Re: [patch 0/4] MAP_NOZERO v2 - VM_NOZERO/MAP

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Date:	Mon, 02 Jul 2007 15:03:02 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Andy Isaacson <adi@...apodia.org>
CC:	Kyle Moffett <mrmacman_g4@....com>,
	Davide Libenzi <davidel@...ilserver.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [patch 0/4] MAP_NOZERO v2 - VM_NOZERO/MAP_NOZERO early summer
 madness

Andy Isaacson wrote:
> On Sat, Jun 30, 2007 at 08:21:52PM -0400, Kyle Moffett wrote:
>> That's why you'd need to call an LSM hook to get a unique identifier,  
>> as the LSM would actually need to allocate identifiers for  
>> equivalence classes.  Secondly, processes may change labels as they  
>> run, so you couldn't just call it once and cache the result, you  
>> would need to call it for every freed page (or every re-use of a page).
> 
> Davide's patch adds a owner_uid field to mm_struct.  Assuming that turns
> into a "mm security equivalence class identifier", the LSM can simply
> update it when a label-change-event occurs.  No need to call out to
> (potentially heavyweight!) LSM code in page allocation critical paths.
> 
> I'm a bit concerned that tracking the equivalence classes will get
> expensive.  I think you can end up with quadratic explosion in the worst
> case (every user using every permutation of LSM bits).

That should not happen.  The default SELinux configuration
in Fedora (and Debian?) runs a few daemons in their own
restricted modes and has most of the system running in
unconfined_t, including the majority of user programs.

-- 
Politics is the struggle between those who want to make their country
the best in the world, and those who believe it already is.  Each group
calls the other unpatriotic.
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