netdev - Re: [Bugme-new] [Bug 16529] New: xennet driver crashes when using with pseudowire aka l2tpv3

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Message-ID: <1282812941.12544.3246.camel@zakaz.uk.xensource.com>
Date:	Thu, 26 Aug 2010 09:55:41 +0100
From:	Ian Campbell <Ian.Campbell@...citrix.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	David Miller <davem@...emloft.net>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Chris Wright <chrisw@...s-sol.org>,
	"bugzilla-daemon@...zilla.kernel.org" 
	<bugzilla-daemon@...zilla.kernel.org>,
	"bugme-daemon@...zilla.kernel.org" <bugme-daemon@...zilla.kernel.org>,
	James Chapman <jchapman@...alix.com>,
	"heil@...minal-consulting.de" <heil@...minal-consulting.de>,
	"Xen-devel@...ts.xensource.com" <Xen-devel@...ts.xensource.com>
Subject: Re: [Bugme-new] [Bug 16529] New: xennet driver crashes when using
 with pseudowire aka l2tpv3

On Thu, 2010-08-26 at 09:34 +0100, Eric Dumazet wrote:
> Le jeudi 26 août 2010 à 09:14 +0100, Ian Campbell a écrit :
> > On Thu, 2010-08-26 at 09:03 +0100, Eric Dumazet wrote:
> > > Here is the patch, could you test it please ?
> > > 
> > > Thanks !
> > > 
> > > [PATCH] l2tp: test for malicious frames in l2tp_eth_dev_recv()
> > > 
> > > close https://bugzilla.kernel.org/show_bug.cgi?id=16529
> > > 
> > > Before calling dev_forward_skb(), we should make sure skb contains at
> > > least an ethernet header, even if length included in upper layer said
> > > so.
> > 
> > Does this imply that there is some problem with xen-netfront setting
> > skb->len or skb->data_len or something incorrectly? It's not clear where
> > data_len has come from in this context.
> 
> data_len is a 16bit field provided in a prior encapsulation header,
> provided by user (untrusted source)
> 
> Some buggy or malicious software sent an invalid frame,
> 
> 
> < encapsulation [len=1000] >  < 'runt' eth frame (len<14) > 
> 
> Another fix would be to change l2tp_recv_dequeue_skb(), and check
> 
> L2TP_SKB_CB(skb)->length against skb->len, before calling 
> 
> (*session->recv_skb)(session, skb, length);
> 
> 
> I prefer the one liner patch I sent you, as a minimum fix.

Thanks, I just wanted to be sure we weren't papering over a potential
issue in xen-netfront.

Ian.


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