netdev - Re: [PATCH net] sch_cake: Return __NET_XMIT_STOLEN when consuming enqueued skb

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Message-ID: <875yi83xs5.fsf@toke.dk>
Date:   Wed, 31 Aug 2022 23:31:38 +0200
From:   Toke Høiland-Jørgensen <toke@...e.dk>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, cake@...ts.bufferbloat.net,
        netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net] sch_cake: Return __NET_XMIT_STOLEN when consuming
 enqueued skb

Eric Dumazet <edumazet@...gle.com> writes:

> On Wed, Aug 31, 2022 at 2:25 AM Toke Høiland-Jørgensen <toke@...e.dk> wrote:
>>
>> When the GSO splitting feature of sch_cake is enabled, GSO superpackets
>> will be broken up and the resulting segments enqueued in place of the
>> original skb. In this case, CAKE calls consume_skb() on the original skb,
>> but still returns NET_XMIT_SUCCESS. This can confuse parent qdiscs into
>> assuming the original skb still exists, when it really has been freed. Fix
>> this by adding the __NET_XMIT_STOLEN flag to the return value in this case.
>>
>
> I think you forgot to give credits to the team who discovered this issue.
>
> Something like this
>
> Reported-by: zdi-disclosures@...ndmicro.com # ZDI-CAN-18231

Ah, right; apologies, will respin!

It also looks like fixing it this way will actually break other things
(most notably sch_cake as a child of sch_htb), so will send a different
patch as v2...

-Toke