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

From: Paolo Abeni <pabeni@redhat.com>
To: Jamal Hadi Salim <jhs@mojatatu.com>, netdev@vger.kernel.org
Cc: Cong Wang <xiyou.wangcong@gmail.com>,
	Jiri Pirko <jiri@resnulli.us>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>,
	Eyal Birger <eyal.birger@gmail.com>,
	"David S. Miller" <davem@davemloft.net>
Subject: Re: [PATCH net-next v5 1/4] net/sched: user-space can't set unknown tcfa_action values
Date: Tue, 31 Jul 2018 16:40:58 +0200	[thread overview]
Message-ID: <e2a29da9514e38ab2caef2f2a592780e60ceda4c.camel@redhat.com> (raw)
In-Reply-To: <79b9d1a7-64ea-e385-1dcb-1f38955a01dd@mojatatu.com>

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