From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Miller <davem@davemloft.net>
Subject: Re: PROBLEM: BUG (NULL ptr dereference in ipv4_dst_check)
Date: Fri, 29 Jul 2011 08:19:02 -0700 (PDT)
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From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Fri, 29 Jul 2011 17:11:46 +0200

> Thats tricky, because I am not sure we dont need RCU protection since we
> can now exchange dst neighbour on the fly.
> 
> Following patch would only reduce the window of bug, not a complete
> fix...
> 
> David, any opinion on this ?

Indeed, old code worked because we invalidated entire route cache
entry, and we never before ran arp_bind_neighbour() except on new
route cache entires before they become globally visible.

I think when we change an existing neigh we will need to release old
neigh via RCU, at a minimum.