netdev - Re: [Patch net v2 00/11] net_sched: make ->qlen

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Message-ID: <CAM0EoMnFXZWhn-c_pLak1FqB=EEBi1-MwsZ_4ka1sPS1C-kFwQ@mail.gmail.com>
Date: Mon, 7 Apr 2025 16:35:29 -0400
From: Jamal Hadi Salim <jhs@...atatu.com>
To: Cong Wang <xiyou.wangcong@...il.com>
Cc: netdev@...r.kernel.org, jiri@...nulli.us, victor@...atatu.com
Subject: Re: [Patch net v2 00/11] net_sched: make ->qlen_notify() idempotent

On Thu, Apr 3, 2025 at 5:10 PM Cong Wang <xiyou.wangcong@...il.com> wrote:
>
> Gerrard reported a vulnerability exists in fq_codel where manipulating
> the MTU can cause codel_dequeue() to drop all packets. The parent qdisc's
> sch->q.qlen is only updated via ->qlen_notify() if the fq_codel queue
> remains non-empty after the drops. This discrepancy in qlen between
> fq_codel and its parent can lead to a use-after-free condition.
>
> Let's fix this by making all existing ->qlen_notify() idempotent so that
> the sch->q.qlen check will be no longer necessary.
>
> Patch 1~5 make all existing ->qlen_notify() idempotent to prepare for
> patch 6 which removes the sch->q.qlen check. They are followed by 5
> selftests for each type of Qdisc's we touch here.
>
> All existing and new Qdisc selftests pass after this patchset.
>
> Fixes: 4b549a2ef4be ("fq_codel: Fair Queue Codel AQM")
> Fixes: 76e3cc126bb2 ("codel: Controlled Delay AQM")
>

For the patches:
Acked-by: Jamal Hadi Salim <jhs@...atatu.com>

cheers,
jamal