Harden against null pointer derefs

protocol.c

@@ -61,7 +61,9 @@ int protocol_events_set(struct mbox_context *context, uint8_t bmc_event)
 	 */
 	context->bmc_events |= bmc_event;
 
-	return context->transport->ops->set_events(context->transport, bmc_event, mask);
+	return (context->transport) ?
+	context->transport->set_events(context, bmc_event, mask) :
+        (mbox_log(LOG_ERR, "Called %s, but transport not assigned", __func__), -1);
 }
 
 /*
@@ -78,7 +80,9 @@ int protocol_events_clear(struct mbox_context *context, uint8_t bmc_event)
 
 	context->bmc_events &= ~bmc_event;
 
-	return context->transport->ops->clear_events(context->transport, bmc_event, mask);
+	return (context->transport) ?
+	    context->transport->ops->clear_events(context->transport, bmc_event, mask) :
+        (mbox_log(LOG_ERR, "Called %s, but transport not assigned", __func__), -1);
 }
 
 static int protocol_negotiate_version(struct mbox_context *context,