[PATCH 26/32] iio:adc:ti-ads1015 Fix buffer element alignment

[Jonathan Cameron <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 an array of smaller elements on the stack.

Here we use an explicit structure and rely on that to enforce
alignment on the stack.  Note there was never a data leak here
due to the explicit memset.

Explicit alignment of ts is needed to avoid incorrect padding on
architectures which only enforce 4 byte alignment for s64 such
as x86_32

Fixes: ecc24e72f437 ("iio: adc: Add TI ADS1015 ADC driver support")
Reported-by: Lars-Peter Clausen <lars@metafoo.de>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
---
 drivers/iio/adc/ti-ads1015.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/drivers/iio/adc/ti-ads1015.c b/drivers/iio/adc/ti-ads1015.c
index 629c631e8f5c..6f4b54b97c5c 100644
--- a/drivers/iio/adc/ti-ads1015.c
+++ b/drivers/iio/adc/ti-ads1015.c
@@ -385,10 +385,14 @@ static irqreturn_t ads1015_trigger_handler(int irq, void *p)
 	struct iio_poll_func *pf = p;
 	struct iio_dev *indio_dev = pf->indio_dev;
 	struct ads1015_data *data = iio_priv(indio_dev);
-	s16 buf[8]; /* 1x s16 ADC val + 3x s16 padding +  4x s16 timestamp */
+	/* Ensure natural alignment for buffer elements */
+	struct {
+		s16 channel;
+		s64 ts __aligned(8);
+	} scan;
 	int chan, ret, res;
 
-	memset(buf, 0, sizeof(buf));
+	memset(&scan, 0, sizeof(scan));
 
 	mutex_lock(&data->lock);
 	chan = find_first_bit(indio_dev->active_scan_mask,
@@ -399,10 +403,10 @@ static irqreturn_t ads1015_trigger_handler(int irq, void *p)
 		goto err;
 	}
 
-	buf[0] = res;
+	scan.channel = res;
 	mutex_unlock(&data->lock);
 
-	iio_push_to_buffers_with_timestamp(indio_dev, buf,
+	iio_push_to_buffers_with_timestamp(indio_dev, &scan,
 					   iio_get_time_ns(indio_dev));
 
 err:
-- 
2.26.2