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

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Date:   Tue, 22 Oct 2019 14:46:21 +0200
From:   walter harms <wharms@....de>
To:     Colin King <colin.king@...onical.com>
CC:     Amit Kucheria <amit.kucheria@...aro.org>,
        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-pm@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, kernel-janitors@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH][next] drivers: thermal: tsens: fix potential integer
 overflow on multiply



Am 22.10.2019 13:49, schrieb Colin King:
> 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;
>  
looks ok
just to offer an alternative to avoid the cast;
	u64 code = degc;

	code = code * s->slope + s->offset;
	code/=SLOPE_FACTOR;

ym2c
re,
wh


>  	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);