netdev - Re: [PATCH net v2] net/sched: pfifo_fast: fix wrong dereference when qdisc is reset

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Date:   Wed, 28 Aug 2019 14:46:40 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     dcaratti@...hat.com
Cc:     xiyou.wangcong@...il.com, jhs@...atatu.com, jiri@...nulli.us,
        netdev@...r.kernel.org, pabeni@...hat.com, sbrivio@...hat.com,
        shuali@...hat.com
Subject: Re: [PATCH net v2] net/sched: pfifo_fast: fix wrong dereference
 when qdisc is reset

From: Davide Caratti <dcaratti@...hat.com>
Date: Tue, 27 Aug 2019 12:29:09 +0200

> Now that 'TCQ_F_CPUSTATS' bit can be cleared, depending on the value of
> 'TCQ_F_NOLOCK' bit in the parent qdisc, we need to be sure that per-cpu
> counters are present when 'reset()' is called for pfifo_fast qdiscs.
> Otherwise, the following script:
 ...
> can generate the following splat:
 ...
> Fix this by testing the value of 'TCQ_F_CPUSTATS' bit in 'qdisc->flags',
> before dereferencing 'qdisc->cpu_qstats'.
> 
> Changes since v1:
>  - coding style improvements, thanks to Stefano Brivio
> 
> Fixes: 8a53e616de29 ("net: sched: when clearing NOLOCK, clear TCQ_F_CPUSTATS, too")
> CC: Paolo Abeni <pabeni@...hat.com>
> Reported-by: Li Shuang <shuali@...hat.com>
> Signed-off-by: Davide Caratti <dcaratti@...hat.com>

Applied and queued up for v5.2 -stable.