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

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Date:   Sat, 15 Jan 2022 18:12:02 +0000
From:   Jonathan Cameron <jic23@...nel.org>
To:     "Tanislav, Cosmin" <Cosmin.Tanislav@...log.com>,
        Lars-Peter Clausen <lars@...afoo.de>
Cc:     Kees Cook <keescook@...omium.org>,
        "Hennerich, Michael" <Michael.Hennerich@...log.com>,
        "linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-hardening@...r.kernel.org" <linux-hardening@...r.kernel.org>
Subject: Re: [PATCH v2] iio: addac: Do not reference negative array offsets

On Thu, 6 Jan 2022 06:31:55 +0000
"Tanislav, Cosmin" <Cosmin.Tanislav@...log.com> wrote:

> Reviewed-by: Cosmin Tanislav <cosmin.tanislav@...log.com>
> 
> Put "iio: addac: ad74413r:" in patch title, maybe?
I can fix that up whilst applying.

I'll pick this up after rc1 is out.

Thanks,

Jonathan

> 
> > -----Original Message-----
> > From: Kees Cook <keescook@...omium.org>
> > Sent: Wednesday, January 5, 2022 8:02 PM
> > To: Lars-Peter Clausen <lars@...afoo.de>
> > Cc: Kees Cook <keescook@...omium.org>; Hennerich, Michael
> > <Michael.Hennerich@...log.com>; Tanislav, Cosmin
> > <Cosmin.Tanislav@...log.com>; Jonathan Cameron <jic23@...nel.org>;
> > linux-iio@...r.kernel.org; Linus Walleij <linus.walleij@...aro.org>; linux-
> > kernel@...r.kernel.org; linux-hardening@...r.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@...afoo.de>
> > Cc: Michael Hennerich <Michael.Hennerich@...log.com>
> > Cc: Cosmin Tanislav <cosmin.tanislav@...log.com>
> > Cc: Jonathan Cameron <jic23@...nel.org>
> > Cc: linux-iio@...r.kernel.org
> > Fixes: fea251b6a5db ("iio: addac: add AD74413R driver")
> > Signed-off-by: Kees Cook <keescook@...omium.org>
> > ---
> > v1:
> > https://urldefense.com/v3/__https://lore.kernel.org/lkml/20211215232321.
> > 2069314-1-
> > keescook@...omium.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  
>