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

From: Pablo Neira Ayuso <[email-masked]>
Date: Mon, 7 Jan 2013 03:15:17 +0100

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.

Regards.