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

[Olivier MOYSAN]

Hi,

On 10/3/21 5:47 PM, Jonathan Cameron wrote:
> On Sun, 8 Aug 2021 18:32:43 +0100
> Jonathan Cameron <jic23@xxxxxxxxxx> wrote:
>
> > On Sat, 24 Jul 2021 16:48:40 +0100
> > Jonathan Cameron <jic23@xxxxxxxxxx> wrote:
> >
> > > On Mon, 19 Jul 2021 19:53:11 +0000
> > > Yizhuo <yzhai003@xxxxxxx> 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@xxxxxxx>
> > >
> > > 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.
> >
> > To stm32 people, can someone take a look at this?
>
> This one is still outstanding.  If anyone from stm32 side of things could take a look
> that would be great,
>
> Jonathan

I cannot see side effects with reordering itself.
However, if we get an error with the read access, just leaving with
irq_handled status is probably not enough.
In such case we are facing a serious issue and it would make sense to 
return irq_none instead, as the interrupt will probably never be 
acknowledged.

BRs

> > Thanks,
> >
> > Jonathan
> >
> > >    
> > > > ---
> > > >   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),
> > >