netdev - Re: [PATCH net] netfilter: nf_qeueue: Drop queue entries on nf_unregister

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Message-ID: <20150620190040.GB3567@salvia>
Date:	Sat, 20 Jun 2015 21:00:40 +0200
From:	Pablo Neira Ayuso <pablo@...filter.org>
To:	Patrick McHardy <kaber@...sh.net>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	netfilter-devel@...r.kernel.org
Subject: Re: [PATCH net] netfilter: nf_qeueue: Drop queue entries on
 nf_unregister_hook

On Sat, Jun 20, 2015 at 01:32:48PM +0200, Patrick McHardy wrote:
> On 20.06, Pablo Neira Ayuso wrote:
> > On Fri, Jun 19, 2015 at 02:03:39PM -0500, Eric W. Biederman wrote:
> > > 
> > > Add code to nf_unregister_hook to flush the nf_queue when a hook is
> > > unregistered.  This guarantees that the pointer that the nf_queue code
> > > retains into the nf_hook list will remain valid while a packet is
> > > queued.
> > 
> > I think the real problem is that struct nf_queue_entry holds a pointer
> > to struct nf_hook_ops, which will be gone after removal. So you
> > uncovered a long standing problem that will amplify by when pernet
> > hooks are in place.
> > 
> > Regarding the pointer to nf_hook_list, now that new netdevice variant
> > doesn't support nf_queue yet, so that nf_hook_list will be always
> > valid since it will point to the global nf_hooks in the core.
> 
> I think Eric's patch is the right thing to do. I'm not sure I get
> your netdev comment, but we certainly do want to drop packets once
> a hook is gone.

I agree this patch is fine, of course.

> > > +{
> > > +	const struct nf_queue_handler *qh;
> > > +	struct net *net;
> > > +
> > > +	rtnl_lock();
> > 
> > Why rtnl_lock() here?
> 
> for_each_net(). Would actually be nice to have a variant that doesn't
> need the rtnl since it makes locking order analysis a lot harder.

OK, thanks for explaining.
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