netdev - Re: [PATCH] tcp: assign the sock correctly to an outgoing SYNACK packet

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Date:	Mon, 8 Apr 2013 22:34:36 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Paul Moore <pmoore@...hat.com>
CC:	David Miller <davem@...emloft.net>, <eric.dumazet@...il.com>,
	<netdev@...r.kernel.org>, <mvadkert@...hat.com>,
	<selinux@...ho.nsa.gov>, <linux-security-module@...r.kernel.org>
Subject: Re: [PATCH] tcp: assign the sock correctly to an outgoing SYNACK
 packet

On Mon, 2013-04-08 at 17:24 -0400, Paul Moore wrote:
> On Monday, April 08, 2013 05:15:12 PM David Miller wrote:
> > From: Paul Moore <pmoore@...hat.com>
> > Date: Mon, 08 Apr 2013 17:10:43 -0400
> > 
> > > On Monday, April 08, 2013 02:32:00 PM Paul Moore wrote:
> > >> On Monday, April 08, 2013 02:12:01 PM Paul Moore wrote:
> > >> > On Monday, April 08, 2013 10:47:47 AM Eric Dumazet wrote:
> > >> > > On Mon, 2013-04-08 at 13:40 -0400, Paul Moore wrote:
> > >> > > > Sort of a similar problem, but not really the same.  Also,
> > >> > > > arguably,
> > >> > > > there is no real associated sock/socket for a RST so orphaning the
> > >> > > > packet makes sense. In the case of a SYNACK we can, and should,
> > >> > > > associate the packet with a sock/socket.
> > >> > > 
> > >> > > What is the intent ?
> > >> > 
> > >> > We have to do a number of painful things in SELinux because we aren't
> > >> > allowed a proper security blob (void *security) in a sk_buff.  One of
> > >> > those things ...
> > >> 
> > >> Actually, I wonder if this problem means it is a good time to revisit the
> > >> no- security-blob-in-sk_buff decision?  The management of the blob would
> > >> be hidden behind the LSM hooks like everything else and it would have a
> > >> number of advantages including making problems like we are seeing here
> > >> easier to fix or avoid entirely.  It would also make life much easier for
> > >> those of working on LSM stuff and it would pave the way for including
> > >> network access controls in the stacked-LSM stuff Casey is kicking around.
> > > 
> > > No comment, or am I just too anxious?
> > 
> > There is no way I'm putting LSM overhead into sk_buff, it's already
> > too big.
> 
> If the void pointer is wrapped by a #ifdef (plenty of precedence for that) and 
> the management of that pointer is handled by LSM hooks why is it a concern?  I 
> apologize for pushing on the issue, but I'm having a hard time reconciling the 
> reason for the "no" with the comments/decisions about the regression fix; at 
> present there seems to be a level of contradiction between the two.

Most Linux users are running distribution kernels with one or more LSMs
built-in.  Anything you make dependent on CONFIG_SECURITY or similar
generic symbol will have a cost for all those users, whether or not they
actually use the LSM.

Ben.

> > I didn't comment because it wasn't worth a comment, but since you're
> > pushing me on the issue, I'll make the no explicit.
> 

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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