netdev - Re: [PATCH net] net/sched: sch_fq: fix integer overflow of "credit"

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Message-ID: <CANn89iJy57p6rxguw_FFAb1KoQsaxzSCCGtdcA=ckeLe-bs4Fw@mail.gmail.com>
Date:   Mon, 17 Apr 2023 13:16:06 +0200
From:   Eric Dumazet <edumazet@...gle.com>
To:     Davide Caratti <dcaratti@...hat.com>
Cc:     Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Christoph Paasch <cpaasch@...le.com>, netdev@...r.kernel.org
Subject: Re: [PATCH net] net/sched: sch_fq: fix integer overflow of "credit"

On Mon, Apr 17, 2023 at 1:02 PM Davide Caratti <dcaratti@...hat.com> wrote:
>
> if sch_fq is configured with "initial quantum" having values greater than
> INT_MAX, the first assignment of "credit" does signed integer overflow to
> a very negative value.
> In this situation, the syzkaller script provided by Cristoph triggers the
> CPU soft-lockup warning even with few sockets. It's not an infinite loop,
> but "credit" wasn't probably meant to be minus 2Gb for each new flow.
> Capping "initial quantum" to INT_MAX proved to fix the issue.
>
> Reported-by: Christoph Paasch <cpaasch@...le.com>
> Link: https://github.com/multipath-tcp/mptcp_net-next/issues/377
> Fixes: afe4fd062416 ("pkt_sched: fq: Fair Queue packet scheduler")
> Signed-off-by: Davide Caratti <dcaratti@...hat.com>
> ---

Reviewed-by: Eric Dumazet <edumazet@...gle.com>
Thanks.