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

From: Jonathan Cameron <jic23@kernel.org>
To: Yizhuo <yzhai003@ucr.edu>
Cc: Lars-Peter Clausen <lars@metafoo.de>,
	Maxime Coquelin <mcoquelin.stm32@gmail.com>,
	Alexandre Torgue <alexandre.torgue@foss.st.com>,
	Andy Shevchenko <andy.shevchenko@gmail.com>,
	Mark Brown <broonie@kernel.org>,
	Mugilraj Dhavachelvan <dmugil2000@gmail.com>,
	Olivier Moysan <olivier.moysan@st.com>,
	Krzysztof Kozlowski <krzk@kernel.org>,
	Arnaud Pouliquen <arnaud.pouliquen@st.com>,
	linux-iio@vger.kernel.org,
	linux-stm32@st-md-mailman.stormreply.com,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] iio: adc: stm32-dfsdm: Fix the uninitialized use if regmap_read() fails
Date: Sat, 24 Jul 2021 16:48:40 +0100	[thread overview]
Message-ID: <20210724164840.7381053b@jic23-huawei> (raw)
In-Reply-To: <20210719195313.40341-1-yzhai003@ucr.edu>

On Mon, 19 Jul 2021 19:53:11 +0000
Yizhuo <yzhai003@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@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),