netdev - Re: [PATCH] Check net->nfnl for NULL in ctnetlink_conntrack_event to, avoid Oops on container destroy

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Date:	Mon, 12 Sep 2011 23:40:42 +0300 (EEST)
From:	Julian Anastasov <ja@....bg>
To:	Tim Gardner <tim.gardner@...onical.com>
cc:	kaber@...sh.net, linux-kernel@...r.kernel.org,
	David Miller <davem@...emloft.net>,
	netfilter-devel@...r.kernel.org, netfilter@...r.kernel.org,
	coreteam@...filter.org, netdev@...r.kernel.org
Subject: Re: [PATCH] Check net->nfnl for NULL in ctnetlink_conntrack_event
 to, avoid Oops on container destroy


	Hello,

On Mon, 12 Sep 2011, Tim Gardner wrote:

> Patrick,
> 
> I received this patch from a developer that uses lxc and network name spaces.
> I don't know the locking semantics well enough for CT to judge whether this
> fix is sufficient. Bug info can be found at
> http://bugs.launchpad.net/bugs/843892 . See comment #7 for his analysis.

	We found same problems triggered by IPVS during
subsys cleanup:

http://marc.info/?l=netfilter-devel&m=130765388528399&w=2

	It is a general problem for modules that register
callbacks to the netfilter core. nfnetlink is such example
with a mix of global (ctnl_notifier) and per-net (nfnetlink_net_ops) 
registrations. During net cleanup the module must be prepared
to be called by core because the core cleanup happens later.

	So, may be rcu_dereference under rcu lock is needed for
some functions (nfnetlink_has_listeners, nfnetlink_send) but
such changes should be audited by nfnetlink developers.
Using rcu_assign_pointer for net->nfnl without corresponding 
rcu_dereference looks like a problem.

Regards

--
Julian Anastasov <ja@....bg>
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