Wrap Msf::Framework#threads in Metasploit::Framework::ThreadFactoryProvider

MSP-11605

`Rex::ThreadFactory.provider` needs to be set in
`Msf::Framework#initialize`, but setting it directly to
`Msf::Framework#threads` eliminates the laziness of
`Msf::Framework#threads`.  In order keep `framework.threads` lazy,
`framework` is wrapped in a
`Metasploit::Framework::ThreadFactoryProvider`, which responds to
`spawn`, which is needed by `Rex::ThreadFactory`, by calling
`framework.threads.spawn`, which lazily initialized `framework.threads`
when the first thread needs to be spawned.

lib/metasploit/framework.rb

@@ -35,6 +35,7 @@ module Metasploit
     extend ActiveSupport::Autoload
 
     autoload :Spec
+    autoload :ThreadFactoryProvider
 
     # Returns the root of the metasploit-framework project.  Use in place of
     # `Rails.root`.

lib/metasploit/framework/thread_factory_provider.rb

@@ -0,0 +1,26 @@
+# Wraps {Msf::Framework} so that {Msf::Framework#threads} is only created on the first call to {#spawn} by
+# {Rex::ThreadFactory#spawn}, which allows the threads used by {Msf::ThreadManager} to be created lazily.
+#
+# @example Setting Rex::ThreadFactory.provider and spawning threads
+#   Rex::ThreadFactory.provider = Metasploit::Framework::ThreadFactoryProvider.new(framework: framework)
+#   # framework.threads created here
+#   Rex::ThreadFactory.spawn("name", false) { ... }
+#
+class Metasploit::Framework::ThreadFactoryProvider < Metasploit::Model::Base
+  #
+  # Attributes
+  #
+
+  # @!attribute framework
+  #   The framework managing the spawned threads.
+  #
+  #   @return [Msf::Framework]
+  attr_accessor :framework
+
+  # Spawns a thread monitored by {Msf::ThreadManager} in {Msf::Framework#threads}.
+  #
+  # (see Msf::ThreadManager#spawn)
+  def spawn(name, critical, *args, &block)
+    framework.threads.spawn(name, critical, *args, &block)
+  end
+end

lib/msf/core/framework.rb

@@ -93,7 +93,7 @@ class Framework
     self.plugins   = PluginManager.new(self)
 
     # Configure the thread factory
-    Rex::ThreadFactory.provider = self.threads
+    Rex::ThreadFactory.provider = Metasploit::Framework::ThreadFactoryProvider.new(framework: self)
 
     subscriber = FrameworkEventSubscriber.new(self)
     events.add_exploit_subscriber(subscriber)