iio: buffer: check if a buffer has been set up when poll is called

commit 4cd140b upstream.

If no iio buffer has been set up and poll is called return 0.
Without this check there will be a null pointer dereference when
calling poll on a iio driver without an iio buffer.

Cc: [email protected]
Signed-off-by: Stefan Windfeldt-Prytz <[email protected]>
Signed-off-by: Jonathan Cameron <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: Stefan Windfeldt-Prytz

drivers/iio/industrialio-buffer.c

@@ -175,7 +175,7 @@ unsigned int iio_buffer_poll(struct file *filp,
 	struct iio_dev *indio_dev = filp->private_data;
 	struct iio_buffer *rb = indio_dev->buffer;
 
-	if (!indio_dev->info)
+	if (!indio_dev->info || rb == NULL)
 		return 0;
 
 	poll_wait(filp, &rb->pollq, wait);