greybus: operation: fix another cancellation use-after-free

An incoming operation could already be scheduled even if
gb_operation_result_set succeeds as its initial status is -EINPROGRESS.

Avoid potential use-after-free by never dropping the reference count for
incoming operations as part of cancellation.
Signed-off-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

drivers/staging/greybus/operation.c

@@ -853,12 +853,17 @@ void gb_connection_recv(struct gb_connection *connection,
  */
 void gb_operation_cancel(struct gb_operation *operation, int errno)
 {
-	if (gb_operation_result_set(operation, errno)) {
-		gb_message_cancel(operation->request);
-		gb_operation_put(operation);
-	} else if (gb_operation_is_incoming(operation)) {
-		if (!gb_operation_is_unidirectional(operation))
+	if (gb_operation_is_incoming(operation)) {
+		/* Cancel response if it has been allocated */
+		if (!gb_operation_result_set(operation, errno) &&
+				!gb_operation_is_unidirectional(operation)) {
 			gb_message_cancel(operation->response);
+		}
+	} else {
+		if (gb_operation_result_set(operation, errno)) {
+			gb_message_cancel(operation->request);
+			gb_operation_put(operation);
+		}
 	}
 }
 EXPORT_SYMBOL_GPL(gb_operation_cancel);