netdev - Re: [Patch net] net_sched: refetch skb protocol for each filter

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Date:   Mon, 14 Jan 2019 18:13:11 -0500
From:   Lucas Bates <lucasb@...atatu.com>
To:     Jamal Hadi Salim <jhs@...atatu.com>
Cc:     Cong Wang <xiyou.wangcong@...il.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Martin Olsson <martin.olsson+netdev@...torsecurity.com>,
        Jiri Pirko <jiri@...nulli.us>
Subject: Re: [Patch net] net_sched: refetch skb protocol for each filter

On Sat, Jan 12, 2019 at 7:23 AM Jamal Hadi Salim <jhs@...atatu.com> wrote:
>
> On 2019-01-11 9:55 p.m., Cong Wang wrote:
> > Martin reported a set of filters don't work after changing
> > from reclassify to continue. Looking into the code, it
> > looks like skb protocol is not always fetched for each
> > iteration of the filters. But, as demonstrated by Martin,
> > TC actions could modify skb->protocol, for example act_vlan,
> > this means we have to refetch skb protocol in each iteration,
> > rather than using the one we fetch in the beginning of the loop.
> >
> > This bug is _not_ introduced by commit 3b3ae880266d
> > ("net: sched: consolidate tc_classify{,_compat}"), technically,
> > if act_vlan is the only action that modifies skb protocol, then
> > it is commit c7e2b9689ef8 ("sched: introduce vlan action") which
> > introduced this bug.
> >
>
> +Cc Lucas
> Do we have a test case for a setup like this in tdc?
> i.e incoming tagged and then vlan popped by action?
> Otherwise a test with IFE which resets the ethertype
> would be sufficient i.e just something that will messup
> with skb->protocol.

Sorry, I've been a little caught up in things around here.

There isn't currently a test case like this, but I can look at the
example Cong provided and see if I can make it tdc-friendly.

- Lucas