netdev - Re: [PATCH] e1000: enhance frame fragment detection

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Date:	Tue, 12 Jan 2010 18:47:41 -0800 (Pacific Standard Time)
From:	"Brandeburg, Jesse" <jesse.brandeburg@...el.com>
To:	Neil Horman <nhorman@...driver.com>
cc:	"davem@...emloft.net" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>,
	"Allan, Bruce W" <bruce.w.allan@...el.com>,
	"Waskiewicz Jr, Peter P" <peter.p.waskiewicz.jr@...el.com>,
	"Ronciak, John" <john.ronciak@...el.com>,
	"e1000-devel@...ts.sourceforge.net" 
	<e1000-devel@...ts.sourceforge.net>
Subject: Re: [PATCH] e1000: enhance frame fragment detection

On Tue, 12 Jan 2010, Neil Horman wrote:
> I'm sorry, it doesn't clear much up, at least not for me.  The patch you're
> referencing above deals only with the jumbo receive path, not the non-jumbo
> case, which is not written to handle skb chains.  The vulnerability targets the
> latter case specifically.  We've seen cases in which an extra data is
> transferred into a subsequent buffer in the ring in that path.  Normally in our
> reproducing cases, I only saw a 4 byte overrun.  Theres a check specifically in
> the e1000(e) drivers for that case.  Unfortunately I never tested other cases,
> but if someone sets a low mtu (say 1000 bytes), I don't see why the same issue
> can't manifest as a buffer chain consisting of a 1000 byte skb followed by up to
> an extra 522 byte skb.  such a condition would bypass that check and result in
> admitting a garbage frame to the network stack.

Hm, you're right. /me smacks head.  Thanks for your comments Neil, they 
are very useful.

Wish we had thought to test the 1000 mtu case before I replied.  In any 
case, we now have verified that the fix in this thread is good in the case 
of 1000 mtu. 

So I now withdraw my withdrawal.  

We have a couple more things to test/fix before we post the final 
version(s), I know this is priority but I also don't want to rush out an 
incomplete fix.

Current plan is Jeff K will post the official version in the next couple 
of days, for e1000 and e1000e, which isn't necessary for >=1500 mtu, but 
is apparently necessary for smaller MTU.
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