Fix UUID code so that it always deals with 16 bytes

Also re-add the payload ID to session validation now that the UUID stuff
is reliable.

lib/msf/base/sessions/meterpreter.rb

@@ -307,9 +307,7 @@ class Meterpreter < Rex::Post::Meterpreter::Client
 
     begin
       self.machine_id = self.core.machine_id(timeout)
-      # This is causing breakages thanks to Meterpeter not doing what it should
-      # be doing with the uuid.
-      #self.payload_uuid ||= self.core.uuid(timeout)
+      self.payload_uuid ||= self.core.uuid(timeout)
 
       return true
     rescue ::Rex::Post::Meterpreter::RequestError

lib/rex/payloads/meterpreter/config.rb

@@ -8,7 +8,6 @@ class Rex::Payloads::Meterpreter::Config
 
   include Msf::ReflectiveDLLLoader
 
-  UUID_SIZE = 64
   URL_SIZE = 512
   UA_SIZE = 256
   PROXY_HOST_SIZE = 128
@@ -48,7 +47,7 @@ private
   end
 
   def session_block(opts)
-    uuid = to_str(opts[:uuid].to_raw, UUID_SIZE)
+    uuid = opts[:uuid].to_raw
     exit_func = Msf::Payload::Windows.exit_types[opts[:exitfunk]]
 
     session_data = [

lib/rex/post/meterpreter/packet.rb

@@ -102,7 +102,7 @@ TLV_TYPE_TRANS_RETRY_WAIT    = TLV_META_TYPE_UINT   | 440
 TLV_TYPE_TRANS_GROUP         = TLV_META_TYPE_GROUP  | 441
 
 TLV_TYPE_MACHINE_ID          = TLV_META_TYPE_STRING | 460
-TLV_TYPE_UUID                = TLV_META_TYPE_STRING | 461
+TLV_TYPE_UUID                = TLV_META_TYPE_RAW    | 461
 
 TLV_TYPE_CIPHER_NAME         = TLV_META_TYPE_STRING | 500
 TLV_TYPE_CIPHER_PARAMETERS   = TLV_META_TYPE_GROUP  | 501