netdev - Re: [PATCH] netfilter: per netns nf_conntrack

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Message-ID: <4B6AD30C.8050107@trash.net>
Date:	Thu, 04 Feb 2010 15:00:44 +0100
From:	Patrick McHardy <kaber@...sh.net>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	Alexey Dobriyan <adobriyan@...il.com>,
	Jon Masters <jonathan@...masters.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	netdev <netdev@...r.kernel.org>,
	netfilter-devel <netfilter-devel@...r.kernel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH] netfilter: per netns nf_conntrack_cachep

Eric Dumazet wrote:
> [PATCH] netfilter: per netns nf_conntrack_cachep
> 
> nf_conntrack_cachep is currently shared by all netns instances, but
> because of SLAB_DESTROY_BY_RCU special semantics, this is wrong.
> 
> If we use a shared slab cache, one object can instantly flight between
> one hash table (netns ONE) to another one (netns TWO), and concurrent
> reader (doing a lookup in netns ONE, 'finding' an object of netns TWO)
> can be fooled without notice, because no RCU grace period has to be
> observed between object freeing and its reuse.
> 
> We dont have this problem with UDP/TCP slab caches because TCP/UDP
> hashtables are global to the machine (and each object has a pointer to
> its netns).
> 
> If we use per netns conntrack hash tables, we also *must* use per netns
> conntrack slab caches, to guarantee an object can not escape from one
> namespace to another one.

Applied with the discussed change to allocate a unique name (attached
again for reference), thanks Eric.


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