netdev - Re: [PATCH net-next v5 1/4] net/sched: user-space can't set unknown tcfa

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Date:   Tue, 31 Jul 2018 16:40:58 +0200
From:   Paolo Abeni <pabeni@...hat.com>
To:     Jamal Hadi Salim <jhs@...atatu.com>, netdev@...r.kernel.org
Cc:     Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Daniel Borkmann <daniel@...earbox.net>,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        Eyal Birger <eyal.birger@...il.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH net-next v5 1/4] net/sched: user-space can't set unknown
 tcfa_action values

On Tue, 2018-07-31 at 09:53 -0400, Jamal Hadi Salim wrote:
> BTW, I asked this earlier and Jiri said it was addressed in patch 2.
> I just looked again and i may be missing something basic:
> Lets say tomorrow in a new kernel we add new TC_ACT_XXX that then gets 
> exposed to uapi - so user space tc is updated.
> You then use the new tc specifying TC_ACT_XXX policy on kernel with your
> changes.
> If i read correctly because TC_ACT_XXX is out of bounds for current
> kernel(which has your changes) you will fix it to be UNSPEC, no?

You are right.

If we choose to reject unknown opcodes, such user-space configuration
will fail.

What would happen before this patch is that configurations using such
TC_ACT_XXXX value would be successful. This is why I proposed to keep
the fixup.

I initially thought the kernel behavior in the above scenario would
match exactly TC_ACT_UNSPEC processing, but as you noted with the
example in your previous email, TC_ACT_UNSPEC processing is actually a
bit different.

Cheers,

Paolo