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 07:32:02 -0400
From:   Jamal Hadi Salim <jhs@...atatu.com>
To:     Simon Horman <simon.horman@...ronome.com>,
        Jiri Pirko <jiri@...lanox.com>,
        Cong Wang <xiyou.wangcong@...il.com>
Cc:     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 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 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

cheers,
jamal