[PATCH 06/11] iio:proximity:mb1232: Fix timestamp alignment and prevent data leak.

[jic23@kernel.org]

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 a 16 byte s16 array 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() data with alignment
ensured by use of an explicit c structure.  This data is allocated
with kzalloc so no data can leak appart from previous readings.

Fixes: 16b05261537e ("mb1232.c: add distance iio sensor with i2c")
Reported-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Andreas Klinger <ak@it-klinger.de>
---
 drivers/iio/proximity/mb1232.c | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/drivers/iio/proximity/mb1232.c b/drivers/iio/proximity/mb1232.c
index 166b3e6d7db8..5ec2d306f1c1 100644
--- a/drivers/iio/proximity/mb1232.c
+++ b/drivers/iio/proximity/mb1232.c
@@ -40,6 +40,11 @@ struct mb1232_data {
 	 */
 	struct completion	ranging;
 	int			irqnr;
+	/* Ensure correct alignment of data to push to IIO buffer */
+	struct {
+		s16 distance;
+		s64 ts;
+	} scan;
 };
 
 static irqreturn_t mb1232_handle_irq(int irq, void *dev_id)
@@ -113,17 +118,13 @@ static irqreturn_t mb1232_trigger_handler(int irq, void *p)
 	struct iio_poll_func *pf = p;
 	struct iio_dev *indio_dev = pf->indio_dev;
 	struct mb1232_data *data = iio_priv(indio_dev);
-	/*
-	 * triggered buffer
-	 * 16-bit channel + 48-bit padding + 64-bit timestamp
-	 */
-	s16 buffer[8] = { 0 };
 
-	buffer[0] = mb1232_read_distance(data);
-	if (buffer[0] < 0)
+	data->scan.distance = mb1232_read_distance(data);
+	if (data->scan.distance < 0)
 		goto err;
 
-	iio_push_to_buffers_with_timestamp(indio_dev, buffer, pf->timestamp);
+	iio_push_to_buffers_with_timestamp(indio_dev, &data->scan,
+					   pf->timestamp);
 
 err:
 	iio_trigger_notify_done(indio_dev->trig);
-- 
2.26.2