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

[Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>]

On Thu, 2010-08-26 at 09:34 +0100, Eric Dumazet wrote:
> Le jeudi 26 aoÃt 2010 Ã 09:14 +0100, Ian Campbell a Ãcrit :
> > 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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