macOS < 10.14.3 / iOS < 12.1.3 - Arbitrary mach Port Name Deallocation in XPC Services due to Invalid mach Message Parsing in _xpc_serializer_unpack

/ xpcserializerunpack in libxpc parses mach messages which contain xpc messages. There are two reasons for an xpc mach message to contain descriptors: if the message body is large, then it's sent as a MACHMSGOOLDESCRIPTOR. Also if the message contains other port resources eg memory entry ports th...