netdev - Re: [PATCH/RFC net-next 1/2] flow dissector: ND support

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Date:   Mon, 13 Mar 2017 14:50:08 +0100
From:   Simon Horman <simon.horman@...ronome.com>
To:     Jiri Pirko <jiri@...nulli.us>
Cc:     David Miller <davem@...emloft.net>,
        Dinan Gunawardena <dinan.gunawardena@...ronome.com>,
        netdev@...r.kernel.org, oss-drivers@...ronome.com
Subject: Re: [PATCH/RFC net-next 1/2] flow dissector: ND support

On Fri, Mar 10, 2017 at 03:27:32PM +0100, Jiri Pirko wrote:
> Fri, Mar 10, 2017 at 03:19:13PM CET, simon.horman@...ronome.com wrote:
> >On Tue, Feb 21, 2017 at 04:28:10PM +0100, Jiri Pirko wrote:
> >> Thu, Feb 02, 2017 at 11:37:34AM CET, simon.horman@...ronome.com wrote:
> >> >Allow dissection of Neighbour Discovery target IP, and source and
> >> >destination link-layer addresses for neighbour solicitation and
> >> >advertisement messages.
> >> >
> >> >Signed-off-by: Simon Horman <simon.horman@...ronome.com>
> >> >---
> >> 
> >> [...]
> >> 
> >> >@@ -633,6 +702,18 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
> >> > 						     FLOW_DISSECTOR_KEY_ICMP,
> >> > 						     target_container);
> >> > 		key_icmp->icmp = skb_flow_get_be16(skb, nhoff, data, hlen);
> >> >+
> >> >+		if (dissector_uses_key(flow_dissector, FLOW_DISSECTOR_KEY_ND) &&
> >> >+		    ip_proto == IPPROTO_IPV6 && key_icmp->code == 0 &&
> >> 
> >> IPPROTO_IPV6 say "IPv6-in-IPv4 tunnelling". Please use "NEXTHDR_IPV6"
> >> instead.
> >
> >Thanks, will do.
> >
> >> >+		    (key_icmp->type == NDISC_NEIGHBOUR_SOLICITATION ||
> >> >+		     key_icmp->type == NDISC_NEIGHBOUR_ADVERTISEMENT)) {
> >> >+			key_nd = skb_flow_dissector_target(flow_dissector,
> >> >+							   FLOW_DISSECTOR_KEY_ND,
> >> >+							   target_container);
> >> >+			if (!(skb_flow_dissect_nd(skb, key_nd, data, nhoff,
> >> >+						  hlen, ipv6_payload_len)))
> >> >+				goto out_bad;
> >> >+		}
> >> 
> >> You should put this under "switch (ip_proto) {"
> >
> >I see that makes sense in terms of the check against ip_proto.
> >But I added it here to allow checking against key_icmp->code
> >and key_icmp->type as well.
> 
> Sure. Just add under "switch (ip_proto) {" and call a wrapper nd
> function from there. In that function, you check dissector_uses_key and
> other needed things.

Hi Jiri,

I'm sorry but I'm having a bit of trouble understanding how best to
structure the extraction of ICMP and ND.

The way I see things is this:

* ICMP extraction may occur for IPv4 or IPv6 although currently neither
  IPv4 nor IPv6 is a condition of ICMP extraction.
* ND extraction may only occur for IPv6
* ND extraction may only occur for certain ICMP code/type values;
  thus ICMP extraction should occur before ND extraction.

I wonder if a good alternative to the approach I took above in my patch
would  be to provide:
* ICMP extraction conditional on IPv4 and;
* ICMP extraction conditional on IPv6 followed by
  ND extraction conditional on ICMP type and code