netdev - Re: [PATCH net-next v3 1/5] tc/act: user space can't use TC_ACT

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Message-ID: <5d38822b635a18b102810a14883e65479f3841ab.camel@redhat.com>
Date:   Wed, 25 Jul 2018 14:54:04 +0200
From:   Paolo Abeni <pabeni@...hat.com>
To:     Jiri Pirko <jiri@...nulli.us>, Jamal Hadi Salim <jhs@...atatu.com>
Cc:     netdev@...r.kernel.org, Cong Wang <xiyou.wangcong@...il.com>,
        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 v3 1/5] tc/act: user space can't use
 TC_ACT_REDIRECT directly

Hi,

On Wed, 2018-07-25 at 13:56 +0200, Jiri Pirko wrote:
> Tue, Jul 24, 2018 at 10:06:39PM CEST, pabeni@...hat.com wrote:
> > Only cls_bpf and act_bpf can safely use such value. If a generic
> > action is configured by user space to return TC_ACT_REDIRECT,
> > the usually visible behavior is passing the skb up the stack - as
> > for unknown action, but, with complex configuration, more random
> > results can be obtained.
> > 
> > This patch forcefully converts TC_ACT_REDIRECT to TC_ACT_UNSPEC
> > at action init time, making the kernel behavior more consistent.
> > 
> > v1 -> v3: use TC_ACT_UNSPEC instead of a newly definied act value
> > 
> > Signed-off-by: Paolo Abeni <pabeni@...hat.com>
> > ---
> > net/sched/act_api.c | 5 +++++
> > 1 file changed, 5 insertions(+)
> > 
> > diff --git a/net/sched/act_api.c b/net/sched/act_api.c
> > index 148a89ab789b..24b5534967fe 100644
> > --- a/net/sched/act_api.c
> > +++ b/net/sched/act_api.c
> > @@ -895,6 +895,11 @@ struct tc_action *tcf_action_init_1(struct net *net, struct tcf_proto *tp,
> > 		}
> > 	}
> > 
> > +	if (a->tcfa_action == TC_ACT_REDIRECT) {
> > +		net_warn_ratelimited("TC_ACT_REDIRECT can't be used directly");
> 
> Can't you push this warning through extack?
> 
> But, wouldn't it be more appropriate to fail here? User is passing
> invalid configuration....

Jiri, Jamal, thank you for the feedback.

Please allow me to answer both of you here, since you raised similar
concers.

I thought about rejecting the action, but that change of behavior could
break some users, as currently most kind of invalid tcfa_action values
are simply accepted.

If there is consensus about it, I can simply fail.

Thanks,

Paolo