[PATCH 4.9 27/70] iio:accel:mma8452: Fix timestamp alignment and prevent data leak.

From: Greg Kroah-Hartman
Date: Mon Sep 21 2020 - 12:36:21 EST

From: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>

commit 89226a296d816727405d3fea684ef69e7d388bd8 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 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.

The additional forcing of the 8 byte alignment of the timestamp
is not strictly necessary but makes the code less fragile by
making this explicit.

Fixes: c7eeea93ac60 ("iio: Add Freescale MMA8452Q 3-axis accelerometer driver")
Reported-by: Lars-Peter Clausen <lars@xxxxxxxxxx>
Cc: Peter Meerwald <pmeerw@xxxxxxxxxx>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
Reviewed-by: Andy Shevchenko <andy.shevchenko@xxxxxxxxx>
Cc: <Stable@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

drivers/iio/accel/mma8452.c | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)

--- a/drivers/iio/accel/mma8452.c
+++ b/drivers/iio/accel/mma8452.c
@@ -105,6 +105,12 @@ struct mma8452_data {
u8 ctrl_reg1;
u8 data_cfg;
const struct mma_chip_info *chip_info;
+ /* Ensure correct alignment of time stamp when present */
+ struct {
+ __be16 channels[3];
+ s64 ts __aligned(8);
+ } buffer;

@@ -985,14 +991,13 @@ static irqreturn_t mma8452_trigger_handl
struct iio_poll_func *pf = p;
struct iio_dev *indio_dev = pf->indio_dev;
struct mma8452_data *data = iio_priv(indio_dev);
- u8 buffer[16]; /* 3 16-bit channels + padding + ts */
int ret;

- ret = mma8452_read(data, (__be16 *)buffer);
+ ret = mma8452_read(data, data->buffer.channels);
if (ret < 0)
goto done;

- iio_push_to_buffers_with_timestamp(indio_dev, buffer,
+ iio_push_to_buffers_with_timestamp(indio_dev, &data->buffer,