From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Borkmann Subject: Re: [PATCH net-next v3 1/5] tc/act: user space can't use TC_ACT_REDIRECT directly Date: Fri, 27 Jul 2018 04:48:51 +0200 Message-ID: <20049525-4903-ddf4-233e-a660f3a2fd28@iogearbox.net> References: <82c5852909788fef3c7b5c29d6ad8c90b60c7170.1532437050.git.pabeni@redhat.com> <20180725115652.GD2164@nanopsycho> <5d38822b635a18b102810a14883e65479f3841ab.camel@redhat.com> <20180725130330.GJ2164@nanopsycho> <15b57fa8-670a-a7a3-a5f5-0685207d054f@iogearbox.net> <20180726074300.GE2222@nanopsycho> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Cc: Paolo Abeni , Jamal Hadi Salim , netdev@vger.kernel.org, Cong Wang , Marcelo Ricardo Leitner , Eyal Birger , "David S. Miller" , alexei.starovoitov@gmail.com To: Jiri Pirko Return-path: Received: from www62.your-server.de ([213.133.104.62]:48136 "EHLO www62.your-server.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726212AbeG0EIn (ORCPT ); Fri, 27 Jul 2018 00:08:43 -0400 In-Reply-To: <20180726074300.GE2222@nanopsycho> Content-Language: en-US Sender: netdev-owner@vger.kernel.org List-ID: On 07/26/2018 09:43 AM, Jiri Pirko wrote: > Wed, Jul 25, 2018 at 06:29:54PM CEST, daniel@iogearbox.net wrote: >> On 07/25/2018 05:48 PM, Paolo Abeni wrote: >>> On Wed, 2018-07-25 at 15:03 +0200, Jiri Pirko wrote: >>>> Wed, Jul 25, 2018 at 02:54:04PM CEST, pabeni@redhat.com wrote: >>>>> On Wed, 2018-07-25 at 13:56 +0200, Jiri Pirko wrote: >>>>>> Tue, Jul 24, 2018 at 10:06:39PM CEST, pabeni@redhat.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 >>>>>>> --- >>>>>>> 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. >>>> >>>> Well it was obviously wrong to expose TC_ACT_REDIRECT to uapi and it >>>> really has no meaning for anyone to use it throughout its whole history. >> >> That claim is completely wrong. > > Why? Does addition of TC_ACT_REDIRECT to uapi have any meaning? BPF programs return TC_ACT_* as a verdict which is then further processed, including TC_ACT_REDIRECT. Hence, it's a contract for them similarly as e.g. helper enums (BPF_FUNC_*) and other things they make use of. Cheers, Daniel