irqbypass: Disallow NULL token

A NULL token is meaningless and can only lead to unintended problems.
Error on registration with a NULL token, ignore de-registrations with
a NULL token.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/virt/lib/irqbypass.c b/virt/lib/irqbypass.c
index 09a03b5..52abac4 100644
--- a/virt/lib/irqbypass.c
+++ b/virt/lib/irqbypass.c
@@ -89,6 +89,9 @@
 	struct irq_bypass_producer *tmp;
 	struct irq_bypass_consumer *consumer;
 
+	if (!producer->token)
+		return -EINVAL;
+
 	might_sleep();
 
 	if (!try_module_get(THIS_MODULE))
@@ -136,6 +139,9 @@
 	struct irq_bypass_producer *tmp;
 	struct irq_bypass_consumer *consumer;
 
+	if (!producer->token)
+		return;
+
 	might_sleep();
 
 	if (!try_module_get(THIS_MODULE))
@@ -177,7 +183,8 @@
 	struct irq_bypass_consumer *tmp;
 	struct irq_bypass_producer *producer;
 
-	if (!consumer->add_producer || !consumer->del_producer)
+	if (!consumer->token ||
+	    !consumer->add_producer || !consumer->del_producer)
 		return -EINVAL;
 
 	might_sleep();
@@ -227,6 +234,9 @@
 	struct irq_bypass_consumer *tmp;
 	struct irq_bypass_producer *producer;
 
+	if (!consumer->token)
+		return;
+
 	might_sleep();
 
 	if (!try_module_get(THIS_MODULE))