[PATCH 4.9 068/117] iio:gyro:itg3200: Fix timestamp alignment and prevent data leak.

[Greg Kroah-Hartman]

From: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>

commit 10ab7cfd5522f0041028556dac864a003e158556 upstream.

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 array of smaller elements on the stack.
This is fixed by using an explicit c structure. As there are no
holes in the structure, there is no possiblity of data leakage
in this case.

The explicit alignment of ts is not strictly necessary but potentially
makes the code slightly less fragile.  It also removes the possibility
of this being cut and paste into another driver where the alignment
isn't already true.

Fixes: 36e0371e7764 ("iio:itg3200: Use iio_push_to_buffers_with_timestamp()")
Reported-by: Lars-Peter Clausen <lars@xxxxxxxxxx>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
Reviewed-by: Andy Shevchenko <andy.shevchenko@xxxxxxxxx>
Cc: <Stable@xxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20200722155103.979802-6-jic23@xxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/iio/gyro/itg3200_buffer.c |   13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

--- a/drivers/iio/gyro/itg3200_buffer.c
+++ b/drivers/iio/gyro/itg3200_buffer.c
@@ -49,13 +49,20 @@ static irqreturn_t itg3200_trigger_handl
 	struct iio_poll_func *pf = p;
 	struct iio_dev *indio_dev = pf->indio_dev;
 	struct itg3200 *st = iio_priv(indio_dev);
-	__be16 buf[ITG3200_SCAN_ELEMENTS + sizeof(s64)/sizeof(u16)];
+	/*
+	 * Ensure correct alignment and padding including for the
+	 * timestamp that may be inserted.
+	 */
+	struct {
+		__be16 buf[ITG3200_SCAN_ELEMENTS];
+		s64 ts __aligned(8);
+	} scan;
 
-	int ret = itg3200_read_all_channels(st->i2c, buf);
+	int ret = itg3200_read_all_channels(st->i2c, scan.buf);
 	if (ret < 0)
 		goto error_ret;
 
-	iio_push_to_buffers_with_timestamp(indio_dev, buf, pf->timestamp);
+	iio_push_to_buffers_with_timestamp(indio_dev, &scan, pf->timestamp);
 
 	iio_trigger_notify_done(indio_dev->trig);