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

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Date:   Wed, 25 Jul 2018 13:56:52 +0200
From:   Jiri Pirko <jiri@...nulli.us>
To:     Paolo Abeni <pabeni@...hat.com>
Cc:     netdev@...r.kernel.org, Jamal Hadi Salim <jhs@...atatu.com>,
        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

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....


>+		a->tcfa_action = TC_ACT_UNSPEC;
>+	}
>+
> 	return a;
> 
> err_mod:
>-- 
>2.17.1
>