[PATCH] iio: adc: stm32-dfsdm: Fix the uninitialized use if regmap_read() fails

[Jonathan Cameron]

On Mon, 19 Jul 2021 19:53:11 +0000
Yizhuo <yzhai003 at ucr.edu> wrote:

> Inside function stm32_dfsdm_irq(), the variable "status", "int_en"
> could be uninitialized if the regmap_read() fails and returns an error
> code.  However, they are directly used in the later context to decide
> the control flow, which is potentially unsafe.
> 
> Fixes: e2e6771c64625 ("IIO: ADC: add STM32 DFSDM sigma delta ADC support")
> 
> Signed-off-by: Yizhuo <yzhai003 at ucr.edu>

Hi Yizhou

I want to get some review of this from people familiar with the
hardware as there is a small possibility your reordering might have
introduced a problem.

> ---
>  drivers/iio/adc/stm32-dfsdm-adc.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iio/adc/stm32-dfsdm-adc.c b/drivers/iio/adc/stm32-dfsdm-adc.c
> index 1cfefb3b5e56..d8b78aead942 100644
> --- a/drivers/iio/adc/stm32-dfsdm-adc.c
> +++ b/drivers/iio/adc/stm32-dfsdm-adc.c
> @@ -1292,9 +1292,11 @@ static irqreturn_t stm32_dfsdm_irq(int irq, void *arg)
>  	struct stm32_dfsdm_adc *adc = iio_priv(indio_dev);
>  	struct regmap *regmap = adc->dfsdm->regmap;
>  	unsigned int status, int_en;
> +	int ret;
>  
> -	regmap_read(regmap, DFSDM_ISR(adc->fl_id), &status);
> -	regmap_read(regmap, DFSDM_CR2(adc->fl_id), &int_en);

Moving this later is only valid if there aren't any side effects.
The current ordering is strange enough it makes me wonder if there might be!

Jonathan

> +	ret = regmap_read(regmap, DFSDM_ISR(adc->fl_id), &status);
> +	if (ret)
> +		return IRQ_HANDLED;
>  
>  	if (status & DFSDM_ISR_REOCF_MASK) {
>  		/* Read the data register clean the IRQ status */
> @@ -1303,6 +1305,9 @@ static irqreturn_t stm32_dfsdm_irq(int irq, void *arg)
>  	}
>  
>  	if (status & DFSDM_ISR_ROVRF_MASK) {
> +		ret = regmap_read(regmap, DFSDM_CR2(adc->fl_id), &int_en);
> +		if (ret)
> +			return IRQ_HANDLED;
>  		if (int_en & DFSDM_CR2_ROVRIE_MASK)
>  			dev_warn(&indio_dev->dev, "Overrun detected\n");
>  		regmap_update_bits(regmap, DFSDM_ICR(adc->fl_id),