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

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Date:   Mon, 14 Jan 2019 10:15:40 +0100 (CET)
From:   Martin Olsson <martin.olsson+netdev@...torsecurity.com>
To:     Jamal Hadi Salim <jhs@...atatu.com>
cc:     Cong Wang <xiyou.wangcong@...il.com>, netdev@...r.kernel.org,
        Jiri Pirko <jiri@...nulli.us>,
        Lucas Bates <lucasb@...atatu.com>
Subject: Re: [Patch net] net_sched: refetch skb protocol for each filter


> "did this setup use to work before? If yes, rough idea of which 
> kernels?"

Unknown. I haven't tried it before.

/Martin


On Sat, 12 Jan 2019, Jamal Hadi Salim 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.
> Cong,
> I am a little worried about the impact of this change. Smells
> more like it has to do with Vlan action or related issues
> than with reclassifying.
> Martin,
> did this setup use to work before? If yes, rough idea of
> which kernels?
>
> cheers,
> jamal
>
>