staging: vchiq_core: handle NULL result of find_service_by_handle

In case of an invalid handle the function find_servive_by_handle
returns NULL. So take care of this and avoid a NULL pointer dereference.

Reviewed-by: Nicolas Saenz Julienne <nsaenz@kernel.org>
Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Link: https://lore.kernel.org/r/1642968143-19281-18-git-send-email-stefan.wahren@i2se.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/vc04_services/interface/vchiq_arm/vchiq_core.c

@@ -2292,6 +2292,9 @@ void vchiq_msg_queue_push(unsigned int handle, struct vchiq_header *header)
 	struct vchiq_service *service = find_service_by_handle(handle);
 	int pos;
 
+	if (!service)
+		return;
+
 	while (service->msg_queue_write == service->msg_queue_read +
 		VCHIQ_MAX_SLOTS) {
 		if (wait_for_completion_interruptible(&service->msg_queue_pop))
@@ -2312,6 +2315,9 @@ struct vchiq_header *vchiq_msg_hold(unsigned int handle)
 	struct vchiq_header *header;
 	int pos;
 
+	if (!service)
+		return NULL;
+
 	if (service->msg_queue_write == service->msg_queue_read)
 		return NULL;