Re: [PATCH v4] iio: vadc: Fix potential dereference of NULL pointer

Jonathan Cameron
2022-06-03T15:11:37Z

On Fri, 3 Jun 2022 16:02:22 +0100
Jonathan Cameron <jic23@kernel.org> wrote:

> On Sun, 22 May 2022 09:53:47 -0700
> Yongzhi Liu <lyz_cs@pku.edu.cn> wrote:
>
> > The return value of vadc_get_channel() needs to be checked to
> > avoid use of NULL pointer. vadc_do_conversion() already provides
> > error prints in at least some of it's error paths. Thus it is
> > reasonable to add the null pointer check on prop and drop the
> > extra reporting in vadc_measure_ref_points().
> >
> > Signed-off-by: Yongzhi Liu <lyz_cs@pku.edu.cn>
>
> Hi
>
> Biggest remaining thing is squashing
> ret = -ENODEV;
> return ret;
>
> into the shorter
> return -ENODEV;
>
One additional process thing I didn't mention before now as this is a
single patch.

Generally for IIO at least, don't send new versions in reply to old threads.
The threads can get very deep and confusing, so I'd much rather a new thread
for each version.

Thanks,

Jonathan

>
> > ---
> > drivers/iio/adc/qcom-spmi-vadc.c | 38 ++++++++++++++++++++++++++++----------
> > 1 file changed, 28 insertions(+), 10 deletions(-)
> >
> > diff --git a/drivers/iio/adc/qcom-spmi-vadc.c b/drivers/iio/adc/qcom-spmi-vadc.c
> > index 34202ba..43a52b1 100644
> > --- a/drivers/iio/adc/qcom-spmi-vadc.c
> > +++ b/drivers/iio/adc/qcom-spmi-vadc.c
> > @@ -358,22 +358,33 @@ static int vadc_measure_ref_points(struct vadc_priv *vadc)
> > vadc->graph[VADC_CALIB_ABSOLUTE].dx = VADC_ABSOLUTE_RANGE_UV;
> >
> > prop = vadc_get_channel(vadc, VADC_REF_1250MV);
> > + if (!prop) {
> > + dev_err(vadc->dev, "Please define 1.25V channel\n");
> Probably makes more sense to have the error as
> "No 1.25V channel found\n");
>
> It's not obvious to anyone getting this error what 'define' might mean
> without them looking at the code, so I'd rather we just said what had
> gone wrong rather offering incomplete advice.
>
> > + ret = -ENODEV;
>
> Don't bother assigning a variable just to return it in the next line.
>
> return -ENODEV;
>
> > + return ret;
> > + }
> > ret = vadc_do_conversion(vadc, prop, &read_1);
> > if (ret)
> > - goto err;
> > + return ret;
> >
> > /* Try with buffered 625mV channel first */
> > prop = vadc_get_channel(vadc, VADC_SPARE1);
> > - if (!prop)
> > + if (!prop) {
> > prop = vadc_get_channel(vadc, VADC_REF_625MV);
> > + if (!prop) {
> > + dev_err(vadc->dev, "Please define 0.625V channel\n");
> "No 0.625V channel found\n"
> > + ret = -ENODEV;
>
> return -ENODEV;
>
> > + return ret;
> > + }
> > + }
> >
> > ret = vadc_do_conversion(vadc, prop, &read_2);
> > if (ret)
> > - goto err;
> > + return ret;
> >
> > if (read_1 == read_2) {
> > ret = -EINVAL;
> > - goto err;
> > + return ret;
> > }
> >
> > vadc->graph[VADC_CALIB_ABSOLUTE].dy = read_1 - read_2;
> > @@ -381,25 +392,32 @@ static int vadc_measure_ref_points(struct vadc_priv *vadc)
> >
> > /* Ratiometric calibration */
> > prop = vadc_get_channel(vadc, VADC_VDD_VADC);
> > + if (!prop) {
> > + dev_err(vadc->dev, "Please define VDD channel\n");
>
> "No VDD channel found\n"
>
> > + ret = -ENODEV;
> > + return ret;
> > + }
> > ret = vadc_do_conversion(vadc, prop, &read_1);
> > if (ret)
> > - goto err;
> > + return ret;
> >
> > prop = vadc_get_channel(vadc, VADC_GND_REF);
> > + if (!prop) {
> > + dev_err(vadc->dev, "Please define GND channel\n");
>
> "No GND channel found\n"
>
> > + ret = -ENODEV;
> > + return ret;
>
> return -ENODEV;
>
> > + }
> > ret = vadc_do_conversion(vadc, prop, &read_2);
> > if (ret)
> > - goto err;
> > + return ret;
> >
> > if (read_1 == read_2) {
> > ret = -EINVAL;
> > - goto err;
> > + return ret;
>
> return -ENODEV;
>
> > }
> >
> > vadc->graph[VADC_CALIB_RATIOMETRIC].dy = read_1 - read_2;
> > vadc->graph[VADC_CALIB_RATIOMETRIC].gnd = read_2;
> > -err:
> > - if (ret)
> > - dev_err(vadc->dev, "measure reference points failed\n");
> >
> > return ret;
>
> Can't get here with anything other than ret == 0 so
> return 0;
> to make that explicit.
>
>
> > }
>