netdev - Re: PROBLEM: BUG (NULL ptr dereference in ipv4_dst

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Message-ID: <1311954208.2843.31.camel@edumazet-HP-Compaq-6005-Pro-SFF-PC>
Date:	Fri, 29 Jul 2011 17:43:28 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	synapse@...py.csoma.elte.hu, netdev@...r.kernel.org
Subject: Re: PROBLEM: BUG (NULL ptr dereference in ipv4_dst_check)

Le vendredi 29 juillet 2011 à 08:19 -0700, David Miller a écrit :
> From: Eric Dumazet <eric.dumazet@...il.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.


Oh well, we already use RCU in neigh_destroy(), so adding rcu would need
to change all dst_get_neighbour() callers to be in one rcu_read_lock()
section.

I'll take a look, I suspect its mostly already done.



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