linux-kernel - Re: [PATCH] ip_tunnel: fix ip_tunnel

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Date:	Wed, 9 Jul 2014 04:47:59 +0400
From:	Dmitry Popov <ixaphire@...tor.net>
To:	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ip_tunnel: fix ip_tunnel_lookup

On Tue, 08 Jul 2014 15:12:10 -0700 (PDT)
David Miller <davem@...emloft.net> wrote:

> From: Dmitry Popov <ixaphire@...tor.net>
> Date: Sat, 5 Jul 2014 02:26:37 +0400
> 
> > @@ -205,6 +207,8 @@ struct ip_tunnel *ip_tunnel_lookup(struct ip_tunnel_net *itn,
> >  
> >  	hlist_for_each_entry_rcu(t, head, hash_node) {
> >  		if (t->parms.i_key != key ||
> > +		    t->parms.iph.saddr != 0 ||
> > +		    t->parms.iph.daddr != 0 ||
> >  		    !(t->dev->flags & IFF_UP))
> >  			continue;
> >  
> 
> I don't really understand the logic of these tests.
> 
> Usually the canonical way to test these kinds of things is:
> 
> 	if (parms->saddr && parms->saddr != saddr)
> 		goto no_match;
> 
> But you are signalling a non-match any time the address is not a
> wildcard.
> 
> Why?

Because that's exactly what I want: to skip any non-wildcard tunnels.

How I see ip_tunnel_lookup logic:
1) try to find exact match (and if found return this tunnel):
tunnel.saddr == iph.daddr && tunnel.daddr == iph.saddr && key_matched()
2) try to find matched (local) wildcard tunnel:
tunnel.saddr == any && tunnel.daddr == iph.saddr && key_matched()
3) try to find matched (remote) wildcard tunnel:
tunnel.saddr == iph.daddr && tunnel.daddr == any && key_matched()
(there is also a test for multicast tunnel, but let's skip it for simplicity)
4) try to find matched (full) wildcard tunnel:
tunnel.saddr == any && tunnel.daddr == any && key_matched()
5) if nothing found return default tunnel.

According to this logic, in 4th loop (the one you quoted) we have to test that
tunnel.daddr == any && tunnel.saddr == any. In my opinion those two new lines
are the best way to achieve it.
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