linux-kernel - Re: [PATCH][next] drivers: thermal: tsens: fix potential integer overflow on multiply

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Date:   Wed, 30 Oct 2019 18:22:43 +0530
From:   Amit Kucheria <amit.kucheria@...aro.org>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:     Colin King <colin.king@...onical.com>,
        Andy Gross <agross@...nel.org>,
        Zhang Rui <rui.zhang@...el.com>,
        Eduardo Valentin <edubezval@...il.com>,
        Stephen Boyd <swboyd@...omium.org>,
        Linux PM list <linux-pm@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        kernel-janitors@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH][next] drivers: thermal: tsens: fix potential integer
 overflow on multiply

On Wed, Oct 30, 2019 at 1:10 AM Daniel Lezcano
<daniel.lezcano@...aro.org> wrote:
>
> On 22/10/2019 13:49, Colin King wrote:
> > From: Colin Ian King <colin.king@...onical.com>
> >
> > Currently a multiply operation is being performed on two int values
> > and the result is being assigned to a u64, presumably because the
> > end result is expected to be probably larger than an int. However,
> > because the multiply is an int multiply one can get overflow. Avoid
> > the overflow by casting degc to a u64 to force a u64 multiply.
> >
> > Addresses-Coverity: ("Unintentional integer overflow")
> > Fixes: fbfe1a042cfd ("drivers: thermal: tsens: Add interrupt support")
> > Signed-off-by: Colin Ian King <colin.king@...onical.com>
> > ---
> >  drivers/thermal/qcom/tsens-common.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/thermal/qcom/tsens-common.c b/drivers/thermal/qcom/tsens-common.c
> > index 03bf1b8133ea..3d7855106ecd 100644
> > --- a/drivers/thermal/qcom/tsens-common.c
> > +++ b/drivers/thermal/qcom/tsens-common.c
> > @@ -92,7 +92,7 @@ void compute_intercept_slope(struct tsens_priv *priv, u32 *p1,
> >
> >  static inline u32 degc_to_code(int degc, const struct tsens_sensor *s)
> >  {
> > -     u64 code = (degc * s->slope + s->offset) / SLOPE_FACTOR;
> > +     u64 code = ((u64)degc * s->slope + s->offset) / SLOPE_FACTOR;
>
>
> -       u64 code = ((u64)degc * s->slope + s->offset) / SLOPE_FACTOR;
> +       u64 code = div_u64(((u64)degc * s->slope + s->offset),
> SLOPE_FACTOR);

This implementation should handle 32-bit architectures too. Colin,
could you respin?

Regards,
Amit