Re: [PATCH v4] iio: adc: mt6359: fix unchecked return value in mt6358_read_imp

[Jonathan Cameron <jic23@kernel.org>]

On Mon, 27 Apr 2026 21:12:38 +0100
Salah Triki <salah.triki@gmail.com> wrote:

> In mt6358_read_imp(), the variable val_v is passed to regmap_read()
> but the return value is not checked. If the read fails, val_v remains
> uninitialized and its random stack content is subsequently reported
> as a measurement result.
> 
> Initialize val_v to zero to ensure a predictable value is reported
> in case of bus failure and to prevent potential stack data leakage.
> This also satisfies static analyzers that might otherwise flag the
> variable as used uninitialized.
> 
> Fixes: 3587914bf61 ("iio: adc: Add support for MediaTek MT6357/8/9 Auxiliary ADC")
> Signed-off-by: Salah Triki <salah.triki@gmail.com>

Applied and marked for stable. Risk of this occurring is very low, but
the risk of the patch causing trouble is effectively zero so I'm fine
with this being backported.

Thanks

Jonathan


> ---
> Changes in v4:
> - Move val_v initialization just before regmap_read() call as suggested 
>   by Andy Shevchenko to improve maintainability.
> 
> Changes in v3:
> - Initialize val_v to zero at declaration instead of checking regmap_read()
>   return value, as suggested by Jonathan Cameron and Andy Shevchenko.
> - Update commit message to reflect this new approach
> 
> Changes in v2:
> - Added Fixes tag.
> - Re-examined the entire driver for unchecked regmap operations.
>   While several regmap_write() and regmap_set_bits() calls also ignore
>   return values, I focused on this specific regmap_read() in
>   mt6358_read_imp() because it leads to an uninitialized variable usage
>   (val_v). This makes this fix critical for reporting correct data
>   to userspace
> 
>  drivers/iio/adc/mt6359-auxadc.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/iio/adc/mt6359-auxadc.c b/drivers/iio/adc/mt6359-auxadc.c
> index 6b9ed9b1fde2..1d9724ef0983 100644
> --- a/drivers/iio/adc/mt6359-auxadc.c
> +++ b/drivers/iio/adc/mt6359-auxadc.c
> @@ -497,6 +497,7 @@ static int mt6358_read_imp(struct mt6359_auxadc *adc_dev,
>  		return ret;
>  
>  	/* Read the params before stopping */
> +	val_v = 0;
>  	regmap_read(regmap, reg_adc0 + (cinfo->imp_adc_num << 1), &val_v);
>  
>  	mt6358_stop_imp_conv(adc_dev);