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* [PATCH v2] iio: addac: Do not reference negative array offsets
@ 2022-01-05 18:02 Kees Cook
  2022-01-06  6:31 ` Tanislav, Cosmin
  0 siblings, 1 reply; 4+ messages in thread
From: Kees Cook @ 2022-01-05 18:02 UTC (permalink / raw)
  To: Lars-Peter Clausen
  Cc: Kees Cook, Michael Hennerich, Cosmin Tanislav, Jonathan Cameron,
	linux-iio, Linus Walleij, linux-kernel, linux-hardening

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://lore.kernel.org/lkml/20211215232321.2069314-1-keescook@chromium.org/
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


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Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
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2022-01-05 18:02 [PATCH v2] iio: addac: Do not reference negative array offsets Kees Cook
2022-01-06  6:31 ` Tanislav, Cosmin
2022-01-15 18:12   ` Jonathan Cameron
2022-01-15 18:37     ` Jonathan Cameron

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