netdev - Re: [PATCH net] macvtap: make sure neighbour code can push ethernet header

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Message-Id: <20150301.003000.2087464960859465969.davem@davemloft.net>
Date:	Sun, 01 Mar 2015 00:30:00 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	brak@...tr.com, netdev@...r.kernel.org
Subject: Re: [PATCH net] macvtap: make sure neighbour code can push
 ethernet header

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Fri, 27 Feb 2015 18:35:35 -0800

> From: Eric Dumazet <edumazet@...gle.com>
> 
> Brian reported crashes using IPv6 traffic with macvtap/veth combo.
> 
> I tracked the crashes in neigh_hh_output()
> 
> -> memcpy(skb->data - HH_DATA_MOD, hh->hh_data, HH_DATA_MOD);
> 
> Neighbour code assumes headroom to push Ethernet header is
> at least 16 bytes.
> 
> It appears macvtap has only 14 bytes available on arches
> where NET_IP_ALIGN is 0 (like x86)
> 
> Effect is a corruption of 2 bytes right before skb->head,
> and possible crashes if accessing non existing memory.
> 
> This fix should also increase IPv4 performance, as paranoid code
> in ip_finish_output2() wont have to call skb_realloc_headroom()
> 
> Reported-by: Brian Rak <brak@...tr.com>
> Tested-by: Brian Rak <brak@...tr.com>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Applied and queued up for -stable, thanks.
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