[PATCH 04/11] iio:accel:mma7455: 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 u8 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: a84ef0d181d9 ("iio: accel: add Freescale MMA7455L/MMA7456L 3-axis accelerometer driver")
Reported-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
---
 drivers/iio/accel/mma7455_core.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/drivers/iio/accel/mma7455_core.c b/drivers/iio/accel/mma7455_core.c
index 8b5a6aff9bf4..b48caece170e 100644
--- a/drivers/iio/accel/mma7455_core.c
+++ b/drivers/iio/accel/mma7455_core.c
@@ -52,6 +52,14 @@
 
 struct mma7455_data {
 	struct regmap *regmap;
+	/*
+	 * Used to reorganize data.  Will ensure correct alignment of
+	 * the timestamp if present
+	 */
+	struct {
+		__le16 channels[3];
+		s64 ts;
+	} scan;
 };
 
 static int mma7455_drdy(struct mma7455_data *mma7455)
@@ -82,19 +90,19 @@ static irqreturn_t mma7455_trigger_handler(int irq, void *p)
 	struct iio_poll_func *pf = p;
 	struct iio_dev *indio_dev = pf->indio_dev;
 	struct mma7455_data *mma7455 = iio_priv(indio_dev);
-	u8 buf[16]; /* 3 x 16-bit channels + padding + ts */
 	int ret;
 
 	ret = mma7455_drdy(mma7455);
 	if (ret)
 		goto done;
 
-	ret = regmap_bulk_read(mma7455->regmap, MMA7455_REG_XOUTL, buf,
-			       sizeof(__le16) * 3);
+	ret = regmap_bulk_read(mma7455->regmap, MMA7455_REG_XOUTL,
+			       mma7455->scan.channels,
+			       sizeof(mma7455->scan.channels));
 	if (ret)
 		goto done;
 
-	iio_push_to_buffers_with_timestamp(indio_dev, buf,
+	iio_push_to_buffers_with_timestamp(indio_dev, &mma7455->scan,
 					   iio_get_time_ns(indio_dev));
 
 done:
-- 
2.26.2