linux-kernel - Re: [PATCH][RFC] security: revalidate rw permissions for sys_splice and sys

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Date:	Wed, 30 May 2007 14:29:09 -0400 (EDT)
From:	James Morris <jmorris@...ei.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Jens Axboe <jens.axboe@...cle.com>, Ingo Molnar <mingo@...e.hu>,
	linux-kernel@...r.kernel.org, Stephen Smalley <sds@...ho.nsa.gov>
Subject: Re: [PATCH][RFC] security: revalidate rw permissions for sys_splice
 and  sys_vmsplice

On Wed, 30 May 2007, Andrew Morton wrote:

> On Wed, 30 May 2007 09:15:01 +0200
> Jens Axboe <jens.axboe@...cle.com> wrote:
> 
> > On Tue, May 29 2007, James Morris wrote:
> > > Revalidate read/write permissions for splice(2) and vmslice(2), in case 
> > > security policy has changed since the files were opened.
> > 
> > I guess it was inevitably going to happen :-)
> > 
> > Signed-off-by: Jens Axboe <jens.axboe@...cle.com>
> > 
> 
> Probably acked-by was more appropriate.
> 
> James, is this considered needed-for-2.6.22?

No, it's tightening things up.  We don't have full revocation in any case, 
and the primary security check is performed on open.

> > +	ret = security_file_permission(out, MAY_WRITE);
> > +	if (unlikely(ret < 0))
> > +		return ret;
> 
> 
> ot: all the unlikely()s are irksome.  I wonder if there was some way of
> doing this in security_file_permission() instead.  eg:

This is the only place where we do this -- it's to remain consistent with 
the surrounding splice code, which does this for other checks.  Given that 
it's calling out to a typically non-trivial security module, it may be 
better to remove the unlikelys here.



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