linux-kernel - Re: [PATCH 1/2] VM/SELinux: require CAP_SYS_RAWIO for all mmap

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Message-ID: <20090721160437.5bda68b4@lxorguk.ukuu.org.uk>
Date:	Tue, 21 Jul 2009 16:04:37 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Eric Paris <eparis@...hat.com>
Cc:	linux-kernel@...r.kernel.org, selinux@...ho.nsa.gov,
	linux-security-module@...r.kernel.org, sds@...ho.nsa.gov,
	jmorris@...ei.org, spender@...ecurity.net, dwalsh@...hat.com,
	cl@...ux-foundation.org, arjan@...radead.org, kyle@...artin.ca,
	cpardy@...hat.com, arnd@...db.de
Subject: Re: [PATCH 1/2] VM/SELinux: require CAP_SYS_RAWIO for all mmap_zero
 operations

On Tue, 21 Jul 2009 10:41:58 -0400
Eric Paris <eparis@...hat.com> wrote:

> Currently non-SELinux systems need CAP_SYS_RAWIO for an application to mmap
> the 0 page.  On SELinux systems they need a specific SELinux permission,
> but do not need CAP_SYS_RAWIO.  This has proved to be a poor decision by
> the SELinux team as, by default, SELinux users are logged in unconfined and
> thus a malicious non-root has nothing stopping them from mapping the 0 page
> of virtual memory.

So the poor decision is in fact that the SELinux users start as
unconfined rather than taking away a few things like the the min map
stuff which can then be given back to specific apps.

> On a non-SELinux system, a malicious non-root user is unable to do this, as
> they need CAP_SYS_RAWIO.
> 
> This patch checks CAP_SYS_RAWIO for all operations which attemt to map a
> page below mmap_min_addr.

So "wine" now needs to run with CAP_SYS_RAWIO or you turn all the
security off.

Am I missing something here, this "solution" sounds completely brain
dead ?

Alan
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