netdev - Re: [PATCH net] net/sched: sch_taprio: fix possible use-after-free

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Message-ID: <CAG_fn=X8iLhtHfoUXwRD2LDj=qnB6WXKZHWRaiB3Ri61PH6SiQ@mail.gmail.com>
Date:   Mon, 16 Jan 2023 10:03:16 +0100
From:   Alexander Potapenko <glider@...gle.com>
To:     shaozhengchao <shaozhengchao@...wei.com>
Cc:     Cong Wang <xiyou.wangcong@...il.com>,
        Eric Dumazet <edumazet@...gle.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
        eric.dumazet@...il.com, syzbot <syzkaller@...glegroups.com>,
        Vinicius Costa Gomes <vinicius.gomes@...el.com>
Subject: Re: [PATCH net] net/sched: sch_taprio: fix possible use-after-free

On Mon, Jan 16, 2023 at 3:07 AM shaozhengchao <shaozhengchao@...wei.com> wrote:
>
>
>
> On 2023/1/16 8:35, Cong Wang wrote:
> > On Fri, Jan 13, 2023 at 04:48:49PM +0000, Eric Dumazet wrote:
> >> syzbot reported a nasty crash [1] in net_tx_action() which
> >> made little sense until we got a repro.
> >>
> >> This repro installs a taprio qdisc, but providing an
> >> invalid TCA_RATE attribute.
> >>
> >> qdisc_create() has to destroy the just initialized
> >> taprio qdisc, and taprio_destroy() is called.
> >>
> >> However, the hrtimer used by taprio had already fired,
> >> therefore advance_sched() called __netif_schedule().
> >>
> >> Then net_tx_action was trying to use a destroyed qdisc.
> >>
> >> We can not undo the __netif_schedule(), so we must wait
> >> until one cpu serviced the qdisc before we can proceed.
> >>
> >
> > This workaround looks a bit ugly. I think we _may_ be able to make
> > hrtimer_start() as the last step of the initialization, IOW, move other
> > validations and allocations before it.
> >
> > Can you share your reproducer?
> >
> > Thanks,
> Maybe the issue is the same as
> https://syzkaller.appspot.com/bug?id=1ccb246eecb5114c440218336e4c7205aed5f2c8

Most certainly, yes.
I also think there were stall reports with the same stack trace where
qdisc_run was unable to take a freed lock because its value was set to
1 by another task.

-- 
Alexander Potapenko
Software Engineer

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