linux-kernel - Re: [PATCH] iio: tsl2583: Fix division by a zero lux

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Date:   Sat, 8 May 2021 17:12:58 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Colin King <colin.king@...onical.com>
Cc:     Lars-Peter Clausen <lars@...afoo.de>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Jon Brenner <jbrenner@...sinc.com>, linux-iio@...r.kernel.org,
        clang-built-linux@...glegroups.com,
        kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iio: tsl2583: Fix division by a zero lux_val

On Fri,  7 May 2021 19:30:41 +0100
Colin King <colin.king@...onical.com> wrote:

> From: Colin Ian King <colin.king@...onical.com>
> 
> The lux_val returned from tsl2583_get_lux can potentially be zero,
> so check for this to avoid a division by zero and an overflowed
> gain_trim_val.
> 
> Fixes clang scan-build warning:
> 
> drivers/iio/light/tsl2583.c:345:40: warning: Either the
> condition 'lux_val<0' is redundant or there is division
> by zero at line 345. [zerodivcond]
> 
> Fixes: ac4f6eee8fe8 ("staging: iio: TAOS tsl258x: Device driver")
> Signed-off-by: Colin Ian King <colin.king@...onical.com>
Definitely looks like it could happen so applied to the fixes-togreg branch of
iio.git and marked for stable.

Thanks,

Jonathan
> ---
>  drivers/iio/light/tsl2583.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/iio/light/tsl2583.c b/drivers/iio/light/tsl2583.c
> index 0f787bfc88fc..c9d8f07a6fcd 100644
> --- a/drivers/iio/light/tsl2583.c
> +++ b/drivers/iio/light/tsl2583.c
> @@ -341,6 +341,14 @@ static int tsl2583_als_calibrate(struct iio_dev *indio_dev)
>  		return lux_val;
>  	}
>  
> +	/* Avoid division by zero of lux_value later on */
> +	if (lux_val == 0) {
> +		dev_err(&chip->client->dev,
> +			"%s: lux_val of 0 will produce out of range trim_value\n",
> +			__func__);
> +		return -ENODATA;
> +	}
> +
>  	gain_trim_val = (unsigned int)(((chip->als_settings.als_cal_target)
>  			* chip->als_settings.als_gain_trim) / lux_val);
>  	if ((gain_trim_val < 250) || (gain_trim_val > 4000)) {