netdev - Re: debug: nt_conntrack and KVM crash

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Date:	Sat, 30 Jan 2010 09:33:35 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jon Masters <jonathan@...masters.org>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	netdev <netdev@...r.kernel.org>,
	netfilter-devel <netfilter-devel@...r.kernel.org>,
	Patrick McHardy <kaber@...sh.net>
Subject: Re: debug: nt_conntrack and KVM crash

Le samedi 30 janvier 2010 à 02:36 -0500, Jon Masters a écrit :

> I'll play later. Right now, I'm looking over every iptables/ip call
> libvirt makes - it explicitly plays with the netns for the loopback,
> which looks interesting. Supposing it does cause the hashtables to get
> unintentionally zereod or the sizing to get wiped out, we should also
> nonetheless catch the case that the hash function generates a whacko
> number or that the hash size is set to zero when we want to use it.
> 

I asked you if you had multiple namespaces, because I was not sure
conntracking hash was global (shared by all namespaces), or local.

If it is local, then we have a bug, because nf_conntrack_cachep 
is still shared.

Because of SLAB_DESTROY_BY_RCU constraint, we must use a distinct
cachep, or an object can be freed from a namespace and immediatly reused
into another namespace, without lookups being able to notice.



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