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From:   Vladimir Oltean <olteanv@gmail.com>
Date:   Tue, 3 Sep 2019 04:20:08 +0300
Message-ID: <CA+h21ho16BiOn=kRm-LkDwQR=myff+tJhM5cBR=tW3nzWJZceQ@mail.gmail.com>
Subject: Re: [PATCH] net: sched: taprio: Fix potential integer overflow in taprio_set_picos_per_byte
To:     "Gustavo A. R. Silva" <gustavo@embeddedor.com>
Cc:     Jamal Hadi Salim <jhs@mojatatu.com>,
        Cong Wang <xiyou.wangcong@gmail.com>,
        Jiri Pirko <jiri@resnulli.us>,
        "David S. Miller" <davem@davemloft.net>,
        netdev <netdev@vger.kernel.org>,
        lkml <linux-kernel@vger.kernel.org>,
        Vinicius Costa Gomes <vinicius.gomes@intel.com>
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On Tue, 3 Sep 2019 at 04:08, Gustavo A. R. Silva <gustavo@embeddedor.com> wrote:
>
> Add suffix LL to constant 1000 in order to avoid a potential integer
> overflow and give the compiler complete information about the proper
> arithmetic to use. Notice that this constant is being used in a context
> that expects an expression of type s64, but it's currently evaluated
> using 32-bit arithmetic.
>
> Addresses-Coverity-ID: 1453459 ("Unintentional integer overflow")
> Fixes: f04b514c0ce2 ("taprio: Set default link speed to 10 Mbps in taprio_set_picos_per_byte")
> Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
> ---

Acked-by: Vladimir Oltean <olteanv@gmail.com>

>  net/sched/sch_taprio.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c
> index 8d8bc2ec5cd6..956f837436ea 100644
> --- a/net/sched/sch_taprio.c
> +++ b/net/sched/sch_taprio.c
> @@ -966,7 +966,7 @@ static void taprio_set_picos_per_byte(struct net_device *dev,
>
>  skip:
>         picos_per_byte = div64_s64(NSEC_PER_SEC * 1000LL * 8,
> -                                  speed * 1000 * 1000);
> +                                  speed * 1000LL * 1000);
>
>         atomic64_set(&q->picos_per_byte, picos_per_byte);
>         netdev_dbg(dev, "taprio: set %s's picos_per_byte to: %lld, linkspeed: %d\n",
> --
> 2.23.0
>