iio: cros_ec: fix an use-after-free in cros_ec_sensors_push_data()

iio: cros_ec: fix an use-after-free in cros_ec_sensors_push_data()

cros_ec_sensors_push_data() reads `indio_dev->active_scan_mask` and
calls iio_push_to_buffers_with_timestamp() without making sure the
`indio_dev` stays in buffer mode.  There is a race if `indio_dev` exits
buffer mode right before cros_ec_sensors_push_data() accesses them.

An use-after-free on `indio_dev->active_scan_mask` was observed.  The
call trace:
[...]
 _find_next_bit
 cros_ec_sensors_push_data
 cros_ec_sensorhub_event
 blocking_notifier_call_chain
 cros_ec_irq_thread

It was caused by a race condition: one thread just freed
`active_scan_mask` at [1]; while another thread tried to access the
memory at [2].

Fix it by calling iio_device_claim_buffer_mode() to ensure the
`indio_dev` can't exit buffer mode during cros_ec_sensors_push_data().

[1]: https://elixir.bootlin.com/linux/v6.5/source/drivers/iio/industrialio-buffer.c#L1189
[2]: https://elixir.bootlin.com/linux/v6.5/source/drivers/iio/common/cros_ec_sensors/cros_ec_sensors_core.c#L198

Cc: stable@vger.kernel.org
Fixes: aa984f1ba4a4 ("iio: cros_ec: Register to cros_ec_sensorhub when EC supports FIFO")
Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>
Reviewed-by: Guenter Roeck <groeck@chromium.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Link: https://lore.kernel.org/r/20230829030622.1571852-1-tzungbi@kernel.org
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>