netdev - Re: [PATCH 19/19] netfilter: gre: fix resource leak when unregister gre proto

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Message-ID: <20130107023808.GA14431@1984>
Date:	Mon, 7 Jan 2013 03:38:08 +0100
From:	Pablo Neira Ayuso <pablo@...filter.org>
To:	Gao feng <gaofeng@...fujitsu.com>
Cc:	netfilter-devel@...r.kernel.org, netdev@...r.kernel.org,
	canqunzhang@...il.com, kaber@...sh.net, ebiederm@...ssion.com
Subject: Re: [PATCH 19/19] netfilter: gre: fix resource leak when
 unregister gre proto

On Mon, Jan 07, 2013 at 03:15:17AM +0100, Pablo Neira Ayuso wrote:
> Hi Gao,
> 
> On Mon, Jan 07, 2013 at 09:27:37AM +0800, Gao feng wrote:
> > Hi Pablo,
> > 
> > On 01/05/13 11:50, Pablo Neira Ayuso wrote:
> > > Hi Gao,
> > > 
> > > On Fri, Dec 28, 2012 at 10:36:46AM +0800, Gao feng wrote:
> > >> Currectly we unregister proto before all conntrack entries of
> > >> this proto being destroyed. so in function destroy_conntrack
> > >> we can't find proper l4proto to call l4proto->destroy.
> > >> this will cause resource leak.
> > > 
> > > Good catch.
> > > 
> > > But better to remove the entries before unregistering the protocol
> > > tracker, so l4proto->destroy is always called.
> > > 
> > 
> > I think the reason we unregister proto before remove all entries
> > is to avoid new entry for this protocol being created.
> > 
> > If we remove all contrack entries before unregistration, there maybe
> > some new entries being created between nf_ct_iterate_cleanup and
> > nf_conntrack_l4proto_unregister_net.this will cause some terrible things.
> 
> Leaks are less likely to happen, but may well still happen while
> racing with protocol removal, agreed.
> 
> > SO I think we should make proto unavailable first,remove all entries next,
> > and remove proto from nf_ct_protos arrays finally.
> 
> Your proposal adds a branch in the packet path to fix an issue that is
> specific of the GRE protocol tracker. In the current code, this fixes
> the memory leak while removing the nf_conntrack_proto_gre module,
> which is a rare operation.
> 
> We have to come with a less intrusive solution.

Wait. The existing code is calling nf_ct_gre_keymap_flush in
proto_gre_net_exit path, so those keymap objects are not leaked.
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