netdev - Re: [PATCH] net_sched: blackhole: tell upper qdisc about dropped packets

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAM_iQpX_oegtXj5z2Abun_OHz6afsjrwOZtKHrx-Pasp86qCZQ@mail.gmail.com>
Date:   Fri, 15 Jun 2018 21:03:10 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jiri Pirko <jiri@...nulli.us>,
        Jamal Hadi Salim <jhs@...atatu.com>
Subject: Re: [PATCH] net_sched: blackhole: tell upper qdisc about dropped packets

On Fri, Jun 15, 2018 at 9:00 PM, Cong Wang <xiyou.wangcong@...il.com> wrote:
> On Fri, Jun 15, 2018 at 6:21 AM, Konstantin Khlebnikov
> <khlebnikov@...dex-team.ru> wrote:
>> On 15.06.2018 16:13, Eric Dumazet wrote:
>>>
>>>
>>>
>>> On 06/15/2018 03:27 AM, Konstantin Khlebnikov wrote:
>>>>
>>>> When blackhole is used on top of classful qdisc like hfsc it breaks
>>>> qlen and backlog counters because packets are disappear without notice.
>>>>
>>>> In HFSC non-zero qlen while all classes are inactive triggers warning:
>>>> WARNING: ... at net/sched/sch_hfsc.c:1393 hfsc_dequeue+0xba4/0xe90
>>>> [sch_hfsc]
>>>> and schedules watchdog work endlessly.
>>>>
>>>> This patch return __NET_XMIT_BYPASS in addition to NET_XMIT_SUCCESS,
>>>> this flag tells upper layer: this packet is gone and isn't queued.
>>>>
>>>> Signed-off-by: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
>>>> ---
>>>>   net/sched/sch_blackhole.c |    2 +-
>>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/net/sched/sch_blackhole.c b/net/sched/sch_blackhole.c
>>>> index c98a61e980ba..9c4c2bb547d7 100644
>>>> --- a/net/sched/sch_blackhole.c
>>>> +++ b/net/sched/sch_blackhole.c
>>>> @@ -21,7 +21,7 @@ static int blackhole_enqueue(struct sk_buff *skb,
>>>> struct Qdisc *sch,
>>>>                              struct sk_buff **to_free)
>>>>   {
>>>>         qdisc_drop(skb, sch, to_free);
>>>> -       return NET_XMIT_SUCCESS;
>>>> +       return NET_XMIT_SUCCESS | __NET_XMIT_BYPASS;
>>>
>>>
>>> Why do not we use instead :
>>>
>>>         return qdisc_drop(skb, sch, to_free);
>>>
>>> Although noop_enqueue() seems to use :
>>>
>>>         return NET_XMIT_CN;
>>>
>>> Oh well.
>>>
>>>
>>
>> I suppose "blackhole" should work like "successful" xmit, but counted as
>> drop.
>
> But anything !NET_XMIT_SUCCESS is basically same for upper
> layer:
>
>         err = qdisc_enqueue(skb, cl->qdisc, to_free);
>         if (unlikely(err != NET_XMIT_SUCCESS)) {
>                 if (net_xmit_drop_count(err)) {
>                         cl->qstats.drops++;
>                         qdisc_qstats_drop(sch);
>                 }
>                 return err;
>         }
>
> So using NET_XMIT_DROP is same in this case?

Not same for __dev_xmit_skb()... Yeah, we should keep
the NET_XMIT_SUCCESS bit.