netdev - Re: [RFC PATCH v1 1/2] lsm: Add hooks to the TUN driver

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Message-ID: <20090806021558.GA17998@us.ibm.com>
Date:	Wed, 5 Aug 2009 21:15:58 -0500
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	Paul Moore <paul.moore@...com>
Cc:	eparis@...hat.com, netdev@...r.kernel.org,
	linux-security-module@...r.kernel.org, selinux@...ho.nsa.gov
Subject: Re: [RFC PATCH v1 1/2] lsm: Add hooks to the TUN driver

Quoting Paul Moore (paul.moore@...com):
> On Wednesday 05 August 2009 10:13:50 am Serge E. Hallyn wrote:
> > Quoting Paul Moore (paul.moore@...com):
> 
> [NOTE: my email has been out all day due to some mysterious FS issue so my 
> apologies for not replying sooner]
> 
> ...
> 
> > The checks before and after this patch are not equivalent.  Post-patch,
> > one must always have CAP_NET_ADMIN to do the attach, whereas pre-patch
> > you only needed those if current_cred() did not own the tun device.  Is
> > that intentional?
> 
> Nope, just a goof on my part; I misread the booleans and haven't fully tested 
> the patch yet so it slipped out, thanks for catching it.  This brings up a 
> good point, would we rather move the TUN owner/group checks into the cap_tun_* 
> functions or move the capable() call back into the TUN driver?  The answer 
> wasn't clear to me when I was looking at the code before and the uniqueness of 
> the TUN driver doesn't help much in this regard.

I see the question being asked as:  Does this device belong to
the caller and, if not, is the caller privileged to act
anyway?'  So I think the capable call should be moved back
into the tun driver, followed by a separate security_tun_dev_attach()
check, since that is a separate, restrictive question.

thanks,
-serge
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