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>

diff --git a/drivers/iio/common/cros_ec_sensors/cros_ec_sensors_core.c b/drivers/iio/common/cros_ec_sensors/cros_ec_sensors_core.c
index b72d39fc2434e44071cae83ae9b33e027c40eae1..6bfe5d6847e75469ccc69a2940548e9c90b77b17 100644 (file)
--- a/drivers/iio/common/cros_ec_sensors/cros_ec_sensors_core.c
+++ b/drivers/iio/common/cros_ec_sensors/cros_ec_sensors_core.c
@@ -190,8 +190,11 @@ int cros_ec_sensors_push_data(struct iio_dev *indio_dev,
        /*
         * Ignore samples if the buffer is not set: it is needed if the ODR is
         * set but the buffer is not enabled yet.
+        *
+        * Note: iio_device_claim_buffer_mode() returns -EBUSY if the buffer
+        * is not enabled.
         */
-       if (!iio_buffer_enabled(indio_dev))
+       if (iio_device_claim_buffer_mode(indio_dev) < 0)
                return 0;
 
        out = (s16 *)st->samples;
@@ -210,6 +213,7 @@ int cros_ec_sensors_push_data(struct iio_dev *indio_dev,
        iio_push_to_buffers_with_timestamp(indio_dev, st->samples,
                                           timestamp + delta);
 
+       iio_device_release_buffer_mode(indio_dev);
        return 0;
 }
 EXPORT_SYMBOL_GPL(cros_ec_sensors_push_data);