netdev - Re: [PATCH/RFC net-next v2 4/4] net/sched: cls_flower: allow control of tree traversal on packet parse errors

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Date:   Mon, 8 May 2017 13:54:37 +0200
From:   Simon Horman <simon.horman@...ronome.com>
To:     Jamal Hadi Salim <jhs@...atatu.com>
Cc:     Jiri Pirko <jiri@...lanox.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Dinan Gunawardena <dinan.gunawardena@...ronome.com>,
        netdev@...r.kernel.org, oss-drivers@...ronome.com,
        Benjamin LaHaise <benjamin.lahaise@...ronome.com>
Subject: Re: [PATCH/RFC net-next v2 4/4] net/sched: cls_flower: allow control
 of tree traversal on packet parse errors

On Mon, May 08, 2017 at 07:32:02AM -0400, Jamal Hadi Salim wrote:
> On 17-05-05 08:47 AM, Simon Horman wrote:
> >Allow control how the tree of qdisc, classes and filters is further
> >traversed if an error is encountered when parsing the packet in order to
> >match the cls_flower filters at a particular prio.
> >
> >By default continue to the next filter, the behaviour without this patch.
> >
> >A use-case for this is to allow configuration of dropping of packets with
> >truncated headers.
> >
> >For example, the following drops IPv4 packets that cannot be parsed by the
> >flow dissector up to the end of the UDP ports - e.g. because they are
> >truncated, and instantiates a continue action based on the port for packets
> >that can be parsed.
> >
> > # tc qdisc del dev eth0 ingress; tc qdisc add dev eth0 ingress
> > # tc filter add dev eth0 protocol ip parent ffff: flower \
> >       indev eth0 ip_proto udp dst_port 80 truncated drop action continue
> >
> >Signed-off-by: Simon Horman <simon.horman@...ronome.com>
> >Reviewed-by: Benjamin LaHaise <benjamin.lahaise@...ronome.com>
> 
> I agree with Cong on this. The default should be "didnt match" (which
> is accomplished by returning -1).

The default value for err_action is TC_ACT_UNSPEC (-1).
So I think we are in agreement there.

> The user could enter an explicit
> rule to override this behavior. i.e something like:
> 
> tc filter add dev eth0 protocol ip parent ffff: flower \
>         indev eth0 ip_proto udp dst_port 80 truncated action continue

This part I am struggling with but I will see what I can do
by making truncated part of the flow key .