linux-kernel - Re: [PATCH 3/3] security: allow capable check to permit mmap or low vm space

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Date:	Sat, 17 Nov 2007 08:58:01 +1100 (EST)
From:	James Morris <jmorris@...ei.org>
To:	Eric Paris <eparis@...hat.com>
cc:	linux-kernel@...r.kernel.org, sds@...ho.nsa.gov,
	selinux@...ho.nsa.gov, alan@...hat.com, chrisw@...hat.com,
	hpa@...or.com, akpm@...ux-foundation.org
Subject: Re: [PATCH 3/3] security: allow capable check to permit mmap or low
 vm space

On Fri, 16 Nov 2007, Eric Paris wrote:

> On Sat, 2007-11-17 at 08:47 +1100, James Morris wrote:
> > On Fri, 16 Nov 2007, Eric Paris wrote:
> > 
> > > On a kernel with CONFIG_SECURITY but without an LSM which implements
> > > security_file_mmap it is impossible for an application to mmap addresses
> > > lower than mmap_min_addr.
> > 
> > Actually, should we be doing any checking in the dummy module, given that 
> > it is not done with !CONFIG_SECURITY ?
> 
> I'm not sure I understand the question.  We already do a number of
> capable type security checks in dummy functions. See dummy_settime() as
> just one example.

I mean just in this case.  If no mmap_min_addr check is done without 
CONFIG_SECURITY, then perhaps none should be done in the dummy module, 
i.e. preserving existing behavior.  LSM is theoretically supposed to be 
unnoticable from a behavioral pov unless a non-dummy module is loaded.

> 
> If we have !CONFIG_SECURITY we don't have any security protections (how
> could we?  we turned them off) so we don't get into dummy hooks.  If we
> do checks or not in uncompiled code doesn't seem to me to matter.
> 
> Maybe I'm just confused...
> 
> -Eric
> 

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