Subject: Re: [(RFC) PATCH ] NULL pointer dereference on rmmod iptable_mangle.

From: Florian Westphal <[email-masked]>
Date: Mon, 15 Jun 2020 13:44:12 +0200

Florian Westphal <[email-masked]> wrote:
> dwilder <[email-masked]> wrote:
> > > Since the netns core already does an unconditional synchronize_rcu after
> > > the pre_exit hooks this would avoid the problem as well.
> > 
> > Something like this?  (un-tested)
> 
> Yes.
> 
> > diff --git a/net/ipv4/netfilter/iptable_mangle.c
> > b/net/ipv4/netfilter/iptable_mangle.c
> > index bb9266ea3785..0d448e4d5213 100644
> > --- a/net/ipv4/netfilter/iptable_mangle.c
> > +++ b/net/ipv4/netfilter/iptable_mangle.c
> > @@ -100,15 +100,26 @@ static int __net_init iptable_mangle_table_init(struct
> > net *net)
> >         return ret;
> >  }
> > 
> > +static void __net_exit iptable_mangle_net_pre_exit(struct net *net)
> > +{
> > +       struct xt_table *table = net->ipv4.iptable_mangle;
> > +
> > +       if (mangle_ops)
> > +               nf_unregister_net_hooks(net, mangle_ops,
> > +                       hweight32(table->valid_hooks));
> > +}
> 
> You probably need if (table) here, not mangle_ops.
> I'm not sure if it makes sense to add a new
> 
> xt_unregister_table_hook() helper, I guess one would have to try
> and see if that reduces copy&paste programming or not.
> 
> >  static void __net_exit iptable_mangle_net_exit(struct net *net)
> >  {
> >         if (!net->ipv4.iptable_mangle)
> >                 return;
> > -       ipt_unregister_table(net, net->ipv4.iptable_mangle, mangle_ops);
> > +       ipt_unregister_table(net, net->ipv4.iptable_mangle, NULL);
> 
> I guess the 3rd arg could be removed from the helper.
> 
> But yes, this looks like what I had in mind.

Will there be a followup?  Otherwise I will place this on my todo-list.

Thanks.