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

[Yizhuo Zhai]

Hi Jonathan:
Thanks for your effort, and yes please take a look just in case.
FYI, I made the modifications align with Alexandru's help, this is the
original reply:

On Mon, Jul 19, 2021 at 12:47 AM Alexandru Ardelean
<ardeleanalex at gmail.com> wrote:
>
> On Mon, Jul 19, 2021 at 2:39 AM Yizhuo Zhai <yzhai003 at ucr.edu> wrote:
> >
> > Hi All:
> > 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. However,
> > stm32_dfsdm_irq() returns the type irqreturn_t and I could not return
>
> Just curious: are you seeing any issues with these variables being
> uninitialized?
>
> > the error code directly. Could you please advise me here?
>
> The correct way to do it, would be:
>
> ret = regmap_read(regmap, DFSDM_ISR(adc->fl_id), &status);
> if (ret)
>     return IRQ_HANDLED;
>
> IRQ handlers should return one of
> enum irqreturn {
>     IRQ_NONE        = (0 << 0),
>     IRQ_HANDLED     = (1 << 0),
>     IRQ_WAKE_THREAD     = (1 << 1),
> };
>
> If you want to fully optimize/correct this, then it may be something like:
>
>         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 */
>                 regmap_read(regmap, DFSDM_RDATAR(adc->fl_id), adc->buffer);
>
> // in this point, we could check for regmap_read(), but it won't make
> sense; we should call the complete() handler, either way
>
>                 complete(&adc->completion);
>         }
>
>         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),
>                                    DFSDM_ICR_CLRROVRF_MASK,
>                                    DFSDM_ICR_CLRROVRF_MASK);
>
> // in this point, we could also check the ret code; but we still need
> to call IRQ_HANDLED anyway;
>         }
>
>
> Quite often, when regmap_read() returns errors, then something is
> seriously wrong in the system.
> Something else would usually fail or crash worse than this interrupt handler.
> That being said, properly handling regmap_read() here is a good idea.
>
> >
> > The related code:
> >
> > static irqreturn_t stm32_dfsdm_irq(int irq, void *arg) {
> >     unsigned int status, int_en;
> >
> >     regmap_read(regmap, DFSDM_ISR(adc->fl_id), &status);
> >     regmap_read(regmap, DFSDM_CR2(adc->fl_id), &int_en);
> >
> >     if (status & DFSDM_ISR_REOCF_MASK) {}
> >     if (status & DFSDM_ISR_ROVRF_MASK) {}
> > }
> >
> >
> > --
> > Kind Regards,
> >
> > Yizhuo Zhai
> >
> > Computer Science, Graduate Student
> > University of California, Riverside


On Sun, Aug 8, 2021 at 10:29 AM Jonathan Cameron <jic23 at kernel.org> wrote:
>
> On Sat, 24 Jul 2021 16:48:40 +0100
> Jonathan Cameron <jic23 at kernel.org> wrote:
>
> > 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.
>
> To stm32 people, can someone take a look at this?
>
> 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),
> >
>


--
Kind Regards,

Yizhuo Zhai

Computer Science, Graduate Student
University of California, Riverside