Re: [PATCH 04/25] iio:light:st_uvis25 Fix timestamp alignment and prevent data leak.

[Jonathan Cameron <Jonathan.Cameron@Huawei.com>]

On Tue, 26 May 2020 09:55:05 +0200
Lorenzo Bianconi <lorenzo@kernel.org> wrote:

> > From: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> > 
> > One of a class of bugs pointed out by Lars in a recent review.
> > iio_push_to_buffers_with_timestamp assumes the buffer used is aligned
> > to the size of the timestamp (8 bytes).  This is not guaranteed in
> > this driver which uses an array of smaller elements on the stack.
> > As Lars also noted this anti pattern can involve a leak of data to
> > userspace and that indeed can happen here.  We close both issues by
> > moving to a suitable structure in the iio_priv()
> > 
> > This data is allocated with kzalloc so no data can leak apart
> > from previous readings.
> > 
> > Fixes: 3025c8688c1e ("iio: light: add support for UVIS25 sensor")
> > Reported-by: Lars-Peter Clausen <lars@metafoo.de>
> > Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> > Cc: Lorenzo Bianconi <lorenzo.bianconi83@gmail.com>  
> 
> Acked-by: Lorenzo Bianconi <lorenzo@kernel.org>

Unfortunately this is wrong (as Andy Schevchenko pointed out in one
of the other patches).  On x86_32 s64 is only aligned to 4 bytes
so the size of the structure will end up too small for the IIO alignment
rules.

There will be a v2 once we've figure out the best, consistent solution.

Sorry about that!

Jonathan

> 
> > ---
> >  drivers/iio/light/st_uvis25.h      | 5 +++++
> >  drivers/iio/light/st_uvis25_core.c | 6 +++---
> >  2 files changed, 8 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/iio/light/st_uvis25.h b/drivers/iio/light/st_uvis25.h
> > index 78bc56aad129..f7027e4c4493 100644
> > --- a/drivers/iio/light/st_uvis25.h
> > +++ b/drivers/iio/light/st_uvis25.h
> > @@ -27,6 +27,11 @@ struct st_uvis25_hw {
> >  	struct iio_trigger *trig;
> >  	bool enabled;
> >  	int irq;
> > +	/* Ensure timestamp is naturally aligned */
> > +	struct {
> > +		u8 chan;
> > +		s64 ts;
> > +	} scan;
> >  };
> >  
> >  extern const struct dev_pm_ops st_uvis25_pm_ops;
> > diff --git a/drivers/iio/light/st_uvis25_core.c b/drivers/iio/light/st_uvis25_core.c
> > index d262c254b895..fe1f2dc970c7 100644
> > --- a/drivers/iio/light/st_uvis25_core.c
> > +++ b/drivers/iio/light/st_uvis25_core.c
> > @@ -234,17 +234,17 @@ static const struct iio_buffer_setup_ops st_uvis25_buffer_ops = {
> >  
> >  static irqreturn_t st_uvis25_buffer_handler_thread(int irq, void *p)
> >  {
> > -	u8 buffer[ALIGN(sizeof(u8), sizeof(s64)) + sizeof(s64)];
> >  	struct iio_poll_func *pf = p;
> >  	struct iio_dev *iio_dev = pf->indio_dev;
> >  	struct st_uvis25_hw *hw = iio_priv(iio_dev);
> >  	int err;
> >  
> > -	err = regmap_read(hw->regmap, ST_UVIS25_REG_OUT_ADDR, (int *)buffer);
> > +	err = regmap_read(hw->regmap, ST_UVIS25_REG_OUT_ADDR,
> > +			  (unsigned int *)&hw->scan.chan);
> >  	if (err < 0)
> >  		goto out;
> >  
> > -	iio_push_to_buffers_with_timestamp(iio_dev, buffer,
> > +	iio_push_to_buffers_with_timestamp(iio_dev, &hw->scan,
> >  					   iio_get_time_ns(iio_dev));
> >  
> >  out:
> > -- 
> > 2.26.2
> >   
>