linux-kernel - Re: [PATCH][next][V2] drivers: thermal: tsens: fix potential integer overflow on multiply

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Message-ID: <CAHLCerPX5WPvVRxfgAQyAguomBaEsCyncJUuOafkY2cMjQmsaQ@mail.gmail.com>
Date:   Mon, 4 Nov 2019 11:45:22 +0530
From:   Amit Kucheria <amit.kucheria@...aro.org>
To:     Colin King <colin.king@...onical.com>
Cc:     Andy Gross <agross@...nel.org>, Zhang Rui <rui.zhang@...el.com>,
        Eduardo Valentin <edubezval@...il.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Stephen Boyd <swboyd@...omium.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Linux PM list <linux-pm@...r.kernel.org>,
        kernel-janitors@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH][next][V2] drivers: thermal: tsens: fix potential integer
 overflow on multiply

On Fri, Nov 1, 2019 at 3:30 PM Colin King <colin.king@...onical.com> 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.
>
> Also use div_u64 for the divide as suggested by Daniel Lezcano.
>
> Addresses-Coverity: ("Unintentional integer overflow")
> Fixes: fbfe1a042cfd ("drivers: thermal: tsens: Add interrupt support")
> Signed-off-by: Colin Ian King <colin.king@...onical.com>

Reviewed-by: Amit Kucheria <amit.kucheria@...aro.org>

> ---
>
> V2: use div_u64 for the divide as suggested by Daniel Lezcano.
>
> ---
>  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..c6b551ec7323 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 = div_u64(((u64)degc * s->slope + s->offset), SLOPE_FACTOR);
>
>         pr_debug("%s: raw_code: 0x%llx, degc:%d\n", __func__, code, degc);
>         return clamp_val(code, THRESHOLD_MIN_ADC_CODE, THRESHOLD_MAX_ADC_CODE);
> --
> 2.20.1
>