recvfrom_nonblock need flag = 0, not nil

lib/rex/post/meterpreter/channels/datagram.rb

@@ -33,8 +33,10 @@ class Datagram < Rex::Post::Meterpreter::Channel
       'udp'
     end
 
-    def recvfrom_nonblock(length,flags = nil)
-      return [super(length, flags)[0], super(length, flags)[0]]
+    def recvfrom_nonblock(length, flags = 0)
+      data = super(length, flags)[0]
+      sockaddr = super(length, flags)[0]
+      [data, sockaddr]
     end
 
     def send(buf, flags, saddr)
@@ -53,17 +55,12 @@ class Datagram < Rex::Post::Meterpreter::Channel
     )
 
     if peerhost && peerport
-      # Maxlen here is 65507, to ensure we dont overflow, we need to write twice
-      # If the other side has a full 64k, handle by splitting up the datagram and
-      # writing multiple times along with the sockaddr. Consumers calling recvfrom
-      # repeatedly will buffer up all the pieces.
-      while data.length > 65507
-        rsock.syswrite(data[0..65506])
-        rsock.syswrite(Rex::Socket.to_sockaddr(peerhost,peerport))
-        data = data - data[0..65506]
-      end
-      rsock.syswrite(data)
-      rsock.syswrite(Rex::Socket.to_sockaddr(peerhost,peerport))
+      # A datagram can be maximum 65507 bytes, truncate longer messages
+      rsock.syswrite(data[0..65506])
+
+      # We write the data and sockaddr data to the local socket, the pop it
+      # back in recvfrom_nonblock.
+      rsock.syswrite(Rex::Socket.to_sockaddr(peerhost, peerport))
       return true
     else
       return false