Re: [PATCH v2] iio: addac: Do not reference negative array offsets

[Jonathan Cameron <jic23@kernel.org>]

On Sat, 15 Jan 2022 18:12:02 +0000
Jonathan Cameron <jic23@kernel.org> wrote:

> On Thu, 6 Jan 2022 06:31:55 +0000
> "Tanislav, Cosmin" <Cosmin.Tanislav@analog.com> wrote:
> 
> > Reviewed-by: Cosmin Tanislav <cosmin.tanislav@analog.com>
> > 
> > Put "iio: addac: ad74413r:" in patch title, maybe?  
> I can fix that up whilst applying.
Ah. I see you already sent it again.  Thanks as that's
even easier.

Jonathan

> 
> I'll pick this up after rc1 is out.
> 
> Thanks,
> 
> Jonathan
> 
> >   
> > > -----Original Message-----
> > > From: Kees Cook <keescook@chromium.org>
> > > Sent: Wednesday, January 5, 2022 8:02 PM
> > > To: Lars-Peter Clausen <lars@metafoo.de>
> > > Cc: Kees Cook <keescook@chromium.org>; Hennerich, Michael
> > > <Michael.Hennerich@analog.com>; Tanislav, Cosmin
> > > <Cosmin.Tanislav@analog.com>; Jonathan Cameron <jic23@kernel.org>;
> > > linux-iio@vger.kernel.org; Linus Walleij <linus.walleij@linaro.org>; linux-
> > > kernel@vger.kernel.org; linux-hardening@vger.kernel.org
> > > Subject: [PATCH v2] iio: addac: Do not reference negative array offsets
> > > 
> > > [External]
> > > 
> > > Instead of aiming rx_buf at an invalid array-boundary-crossing location,
> > > just skip the first increment. Fixes this warning seen when building
> > > with -Warray-bounds:
> > > 
> > > drivers/iio/addac/ad74413r.c: In function 'ad74413r_update_scan_mode':
> > > drivers/iio/addac/ad74413r.c:843:22: warning: array subscript -4 is below
> > > array bounds of 'u8[16]' { aka 'unsigned char[16]'} [-Warray-bounds]
> > >   843 |         u8 *rx_buf = &st->adc_samples_buf.rx_buf[-1 *
> > > AD74413R_FRAME_SIZE];
> > >       |
> > > ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > > drivers/iio/addac/ad74413r.c:84:20: note: while referencing 'rx_buf'
> > >    84 |                 u8 rx_buf[AD74413R_FRAME_SIZE *
> > > AD74413R_CHANNEL_MAX];
> > >       |                    ^~~~~~
> > > 
> > > Cc: Lars-Peter Clausen <lars@metafoo.de>
> > > Cc: Michael Hennerich <Michael.Hennerich@analog.com>
> > > Cc: Cosmin Tanislav <cosmin.tanislav@analog.com>
> > > Cc: Jonathan Cameron <jic23@kernel.org>
> > > Cc: linux-iio@vger.kernel.org
> > > Fixes: fea251b6a5db ("iio: addac: add AD74413R driver")
> > > Signed-off-by: Kees Cook <keescook@chromium.org>
> > > ---
> > > v1:
> > > https://urldefense.com/v3/__https://lore.kernel.org/lkml/20211215232321.
> > > 2069314-1-
> > > keescook@chromium.org/__;!!A3Ni8CS0y2Y!vadcwdERjyNVz3vFIp5m5S2ms
> > > oFHro8aKzH9ulwPevCKHpev6D53gibZrv5U9mPHGcoB$
> > > v2:
> > >  - use "xfer" for checking "first through the loop"
> > > ---
> > >  drivers/iio/addac/ad74413r.c | 7 ++++---
> > >  1 file changed, 4 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/drivers/iio/addac/ad74413r.c b/drivers/iio/addac/ad74413r.c
> > > index 5271073bb74e..aba9a643a4ca 100644
> > > --- a/drivers/iio/addac/ad74413r.c
> > > +++ b/drivers/iio/addac/ad74413r.c
> > > @@ -840,7 +840,7 @@ static int ad74413r_update_scan_mode(struct iio_dev
> > > *indio_dev,
> > >  {
> > >  	struct ad74413r_state *st = iio_priv(indio_dev);
> > >  	struct spi_transfer *xfer = st->adc_samples_xfer;
> > > -	u8 *rx_buf = &st->adc_samples_buf.rx_buf[-1 *
> > > AD74413R_FRAME_SIZE];
> > > +	u8 *rx_buf = st->adc_samples_buf.rx_buf;
> > >  	u8 *tx_buf = st->adc_samples_tx_buf;
> > >  	unsigned int channel;
> > >  	int ret = -EINVAL;
> > > @@ -894,9 +894,10 @@ static int ad74413r_update_scan_mode(struct
> > > iio_dev *indio_dev,
> > > 
> > >  		spi_message_add_tail(xfer, &st->adc_samples_msg);
> > > 
> > > -		xfer++;
> > >  		tx_buf += AD74413R_FRAME_SIZE;
> > > -		rx_buf += AD74413R_FRAME_SIZE;
> > > +		if (xfer != st->adc_samples_xfer)
> > > +			rx_buf += AD74413R_FRAME_SIZE;
> > > +		xfer++;
> > >  	}
> > > 
> > >  	xfer->rx_buf = rx_buf;
> > > --
> > > 2.30.2    
> >   
>