iio:light:st_uvis25: Fix timestamp alignment and prevent data leak.

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.
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()

This data is allocated with kzalloc() so no data can leak apart
from previous readings.

A local unsigned int variable is used for the regmap call so it
is clear there is no potential issue with writing into the padding
of the structure.

Fixes: 3025c8688c1e ("iio: light: add support for UVIS25 sensor")
Reported-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Acked-by: Lorenzo Bianconi <lorenzo@kernel.org>
Cc: <Stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20200920112742.170751-3-jic23@kernel.org

1 files changed, 5 insertions, 0 deletions

diff --git a/drivers/iio/light/st_uvis25.h b/drivers/iio/light/st_uvis25.h
index 78bc56aad129..283086887caf 100644
--- a/drivers/iio/light/st_uvis25.h
+++ b/drivers/iio/light/st_uvis25.h
@@ -27,6 +27,11 @@ struct st_uvis25_hw {
 	struct iio_trigger *trig;
 	bool enabled;
 	int irq;
+	/* Ensure timestamp is naturally aligned */
+	struct {
+		u8 chan;
+		s64 ts __aligned(8);
+	} scan;
 };
 
 extern const struct dev_pm_ops st_uvis25_pm_ops;