netdev - Re: [PATCH] net: sched: drr: dont intepret cls results when asked to drop

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Date: Fri, 15 Sep 2023 19:58:18 -0300
From: Victor Nogueira <victor@...atatu.com>
To: Jamal Hadi Salim <jhs@...atatu.com>, Eric Dumazet <edumazet@...gle.com>
Cc: Pedro Tammela <pctammela@...atatu.com>, Ma Ke <make_ruc2021@....com>,
 xiyou.wangcong@...il.com, jiri@...nulli.us, davem@...emloft.net,
 kuba@...nel.org, pabeni@...hat.com, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: sched: drr: dont intepret cls results when asked to
 drop



On 15/09/2023 19:55, Jamal Hadi Salim wrote:
> On Fri, Sep 15, 2023 at 11:06 AM Eric Dumazet <edumazet@...gle.com> wrote:
>>
>> On Fri, Sep 15, 2023 at 5:03 PM Pedro Tammela <pctammela@...atatu.com> wrote:
>>>
>>> On 15/09/2023 09:55, Eric Dumazet wrote:
>>>> On Fri, Sep 15, 2023 at 12:42 PM Ma Ke <make_ruc2021@....com> wrote:
>>>>>
>>>>> If asked to drop a packet via TC_ACT_SHOT it is unsafe to
>>>>> assume res.class contains a valid pointer.
>>>>>
>>>>> Signed-off-by: Ma Ke <make_ruc2021@....com>
>>>>> ---
>>>>>    net/sched/sch_drr.c | 2 ++
>>>>>    1 file changed, 2 insertions(+)
>>>>>
>>>>> diff --git a/net/sched/sch_drr.c b/net/sched/sch_drr.c
>>>>> index 19901e77cd3b..2b854cb6edf9 100644
>>>>> --- a/net/sched/sch_drr.c
>>>>> +++ b/net/sched/sch_drr.c
>>>>> @@ -309,6 +309,8 @@ static struct drr_class *drr_classify(struct sk_buff *skb, struct Qdisc *sch,
>>>>>           *qerr = NET_XMIT_SUCCESS | __NET_XMIT_BYPASS;
>>>>>           fl = rcu_dereference_bh(q->filter_list);
>>>>>           result = tcf_classify(skb, NULL, fl, &res, false);
>>>>> +       if (result == TC_ACT_SHOT)
>>>>> +               return NULL;
>>>>>           if (result >= 0) {
>>>>>    #ifdef CONFIG_NET_CLS_ACT
>>>>>                   switch (result) {
>>>>> --
>>>>> 2.37.2
>>>>>
>>>>
>>>>    I do not see a bug, TC_ACT_SHOT is handled in the switch (result) just fine
>>>> at line 320 ?
>>>
>>> Following the code path (with CONFIG_NET_CLS_ACT=n in mind), it looks
>>> like there are a couple of places which return TC_ACT_SHOT before
>>> calling any classifiers, which then would cause some qdiscs to look into
>>> a uninitialized 'struct tcf_result res'.
>>> I could be misreading it... But if it's the problem the author is trying
>>> to fix, the obvious way to do it would be:
>>>          struct tcf_result res = {};
>>
>> CONFIG_NET_CLS_ACT=n, how come TC_ACT_SHOT could be used ?
>>
>> Can we get rid of CONFIG_NET_CLS_ACT, this seems obfuscation to me at
>> this point.
> 
> The problem is the verdict vs return code are intermixed - not saying
> this was fixing anything useful.
> We discussed this in the past after/during commit
> caa4b35b4317d5147b3ab0fbdc9c075c7d2e9c12
> Victor worked on a patch to resolve that. Victor, maybe revive that
> patch and post as RFC?

Okk, will review, rebase on top of net-next and post.

cheers,
Victor