netdev - Re: [RFC] net: ipv4: drop unicast encapsulated in L2 multicast

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Date:	Wed, 27 Aug 2014 13:23:17 +0300 (EEST)
From:	Julian Anastasov <ja@....bg>
To:	Johannes Berg <johannes@...solutions.net>
cc:	David Miller <davem@...emloft.net>, linux-wireless@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: [RFC] net: ipv4: drop unicast encapsulated in L2 multicast


	Hello,

On Wed, 27 Aug 2014, Johannes Berg wrote:

> On Fri, 2014-08-22 at 10:54 -0700, David Miller wrote:
> 
> > > 	Is this place better, after checking for RTN_BROADCAST?
> > > 
> > > 	/* ARP link-layer broadcasts are acceptable here */
> > > 	if ((skb->pkt_type == PACKET_BROADCAST ||
> > > 	     skb->pkt_type == PACKET_MULTICAST) &&
> > > 	    skb->protocol == htons(ETH_P_IP))
> > > 		goto e_inval;
> > 
> > Indeed, this would make ARP happier, but that still leaves open the
> > issue of CLUSTERIP.
> 
> Unfortunately, I have no idea how to determine that CLUSTERIP is active
> here? Do we need to tag frames, or would a sysctl work?
> 
> Or should we go back to the drawing board and not make this change in
> the IP stack at all? But parsing all the IP layer in the wireless stack
> is really quite ugly as well.

	CLUSTERIP works in LOCAL_IN. My preference is to
add checks in every protocol where it is missing but if
you prefer a global check, ip_local_deliver_finish() is
a good place: CLUSTERIP already changed pkt_type to
PACKET_HOST. For example:

	if (!(skb_rtable(skb)->rt_flags &
	      (RTCF_BROADCAST | RTCF_MULTICAST)) &&
	    (skb->pkt_type == PACKET_BROADCAST ||
	     skb->pkt_type == PACKET_MULTICAST)) {
		kfree_skb(skb);
		return;
	}

	By this way we protect the local stack globally.
BTW, what kind of packets (protocol) we want to drop? UDP?

	As for ip_forward(), there is already check for
PACKET_HOST.

	Not sure, may be a MIB counter for such drops
would be useful.

Regards

--
Julian Anastasov <ja@....bg>
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