reimplement HD's session interrupt handler

reimplement HD's work on a session interrupt handler
so that if an exploit fails the handler does not continue
waiting for a session that will never come

MS-385

Author: David Maloney

lib/msf/core/exploit.rb

@@ -1197,9 +1197,15 @@ def handler_enabled?
   # value can be one of the Handler::constants.
   #
   def handler(*args)
-    return if not payload_instance
-    return if not handler_enabled?
-    return payload_instance.handler(*args)
+    unless payload_instance && handler_enabled?
+      payload_instance.handler(*args)
+    end
+  end
+
+  def interrupt_handler
+    if payload_instance && handler_enabled? && payload_instance.respond_to?(:interrupt_wait_for_session)
+      payload_instance.interrupt_wait_for_session()
+    end
   end
 
   ##
@@ -1351,6 +1357,9 @@ def handle_exception e
 
     # Report the failure (and attempt) in the database
     self.report_failure
+
+    # Interrupt any session waiters in the handler
+    self.interrupt_handler
   end
 
   def report_failure

lib/msf/core/handler.rb

@@ -163,6 +163,14 @@ def wait_for_session(t = wfs_delay)
     return session
   end
 
+  #
+  # Interrupts a wait_for_session call by notifying with a nil event
+  #
+  def interrupt_wait_for_session
+    return unless session_waiter_event
+    session_waiter_event.notify(nil)
+  end
+
   #
   # Set by the exploit module to configure handler
   #