iio:accel:mma8452: Fix timestamp alignment and prevent data leak.

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@metafoo.de>
Cc: Peter Meerwald <pmeerw@pmeerw.net>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/iio/accel/mma8452.c b/drivers/iio/accel/mma8452.c
index 08cb814..90d4179 100644 (file)
--- 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_handler(int irq, void *p)
        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,
                                           iio_get_time_ns(indio_dev));
 
 done: