linux-kernel - Re: [PATCH 12/19] CacheFiles: Permit a process's create SID to be overridden

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Date:	Wed, 15 Nov 2006 11:19:00 -0500 (EST)
From:	James Morris <jmorris@...ei.org>
To:	David Howells <dhowells@...hat.com>
cc:	Linus Torvalds <torvalds@...l.org>, Andrew Morton <akpm@...l.org>,
	Stephen Smalley <sds@...ho.nsa.gov>,
	trond.myklebust@....uio.no, selinux@...ho.nsa.gov,
	linux-kernel@...r.kernel.org, aviro@...hat.com, steved@...hat.com
Subject: Re: [PATCH 12/19] CacheFiles: Permit a process's create SID to be
 overridden 

On Wed, 15 Nov 2006, David Howells wrote:

> James Morris <jmorris@...ei.org> wrote:
> 
> > > +static u32 selinux_set_fscreate_secid(u32 secid)
> > ...
> > The ability to set this needs to be mediated via MAC policy.
> 
> There could a problem with that...  Is it possible for there to be a race?

Well, the value can be changed at any time, so you could be using a 
temporary fscreate value, or your new value could be overwritten 
immediately by writing to /proc/$$/attr/fscreate

I think we need to add a separate field for this purpose, which can only 
be written to via the in-kernel API and overrides fscreate.

> I have to call the function twice per cache op: once to set the file 
> creation security ID and once to restore it back to what it was.
> 
> However, what happens if I can't restore the original security ID (perhaps the
> rules changed between the two invocations)?  I can't let the task continue as
> it's now running with the wrong security...

Kill the task?



- James
-- 
James Morris
<jmorris@...ei.org>
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