Module: Rex::Post::Meterpreter::PacketDispatcher

Included in:
Client
Defined in:
lib/rex/post/meterpreter/packet_dispatcher.rb

Overview

Handles packet transmission, reception, and correlation, and processing

Constant Summary collapse

PACKET_TIMEOUT =

Defualt time, in seconds, to wait for a response after sending a packet

600
PING_TIME =

Number of seconds to wait without getting any packets before we try to send a liveness check. A minute should be generous even on the highest latency networks

See Also:

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Instance Attribute Summary collapse

Instance Method Summary collapse

Instance Attribute Details

#comm_mutexObject

This mutex is used to lock out new commands during an active migration. Unused if this is a passive dispatcher


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# File 'lib/rex/post/meterpreter/packet_dispatcher.rb', line 58

def comm_mutex
  @comm_mutex
end

#dispatcher_threadObject (protected)

:nodoc:


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# File 'lib/rex/post/meterpreter/packet_dispatcher.rb', line 623

def dispatcher_thread
  @dispatcher_thread
end

#passive_serviceRex::ServiceManager?

Passive Dispatching

Returns:


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# File 'lib/rex/post/meterpreter/packet_dispatcher.rb', line 70

def passive_service
  @passive_service
end

#receiver_threadObject (protected)

:nodoc:


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# File 'lib/rex/post/meterpreter/packet_dispatcher.rb', line 622

def receiver_thread
  @receiver_thread
end

#recv_queueArray

Returns:

  • (Array)

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# File 'lib/rex/post/meterpreter/packet_dispatcher.rb', line 76

def recv_queue
  @recv_queue
end

#send_queueArray

Returns:

  • (Array)

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# File 'lib/rex/post/meterpreter/packet_dispatcher.rb', line 73

def send_queue
  @send_queue
end

#session_guidObject

The guid that identifies an active Meterpreter session


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# File 'lib/rex/post/meterpreter/packet_dispatcher.rb', line 61

def session_guid
  @session_guid
end

#tlv_enc_keyObject

This contains the key material used for TLV encryption


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# File 'lib/rex/post/meterpreter/packet_dispatcher.rb', line 64

def tlv_enc_key
  @tlv_enc_key
end

#waitersObject (protected)

:nodoc:


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# File 'lib/rex/post/meterpreter/packet_dispatcher.rb', line 624

def waiters
  @waiters
end

Instance Method Details

#add_response_waiter(request, completion_routine = nil, completion_param = nil) ⇒ Object

Adds a waiter association with the supplied request packet.


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# File 'lib/rex/post/meterpreter/packet_dispatcher.rb', line 487

def add_response_waiter(request, completion_routine = nil, completion_param = nil)
  if self.pivot_session
    return self.pivot_session.add_response_waiter(request, completion_routine, completion_param)
  end

  waiter = PacketResponseWaiter.new(request.rid, completion_routine, completion_param)

  self.waiters << waiter

  return waiter
end

#decrypt_inbound_packet(packet) ⇒ Object

Decrypt the given packet with the appropriate key depending on if this session is a pivot session or not.


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# File 'lib/rex/post/meterpreter/packet_dispatcher.rb', line 548

def decrypt_inbound_packet(packet)
  pivot_session = self.find_pivot_session(packet.session_guid)
  tlv_enc_key = self.tlv_enc_key
  tlv_enc_key = pivot_session.pivoted_session.tlv_enc_key if pivot_session
  packet.from_r(tlv_enc_key)
  packet
end

#deregister_inbound_handler(handler) ⇒ Object

Deregisters a previously registered inbound packet handler.


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# File 'lib/rex/post/meterpreter/packet_dispatcher.rb', line 616

def deregister_inbound_handler(handler)
  @inbound_handlers.delete(handler)
end

#dispatch_inbound_packet(packet) ⇒ Object

Dispatches and processes an inbound packet. If the packet is a response that has an associated waiter, the waiter is notified. Otherwise, the packet is passed onto any registered dispatch handlers until one returns success.


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# File 'lib/rex/post/meterpreter/packet_dispatcher.rb', line 562

def dispatch_inbound_packet(packet)
  handled = false

  # Uncomment this line if you want to see inbound packets in the console
  #STDERR.puts("RECV: #{packet.inspect}\n")

  # Update our last reply time
  self.last_checkin = Time.now

  pivot_session = self.find_pivot_session(packet.session_guid)
  pivot_session.pivoted_session.last_checkin = self.last_checkin if pivot_session

  # If the packet is a response, try to notify any potential
  # waiters
  if packet.response? && notify_response_waiter(packet)
    return true
  end

  # Enumerate all of the inbound packet handlers until one handles
  # the packet
  @inbound_handlers.each { |handler|

    handled = nil
    begin

      if packet.response?
        handled = handler.response_handler(self, packet)
      else
        handled = handler.request_handler(self, packet)
      end

    rescue ::Exception => e
      dlog("Exception caught in dispatch_inbound_packet: handler=#{handler} #{e.class} #{e} #{e.backtrace}", 'meterpreter', LEV_1)
      return true
    end

    if (handled)
      break
    end
  }
  return handled
end

#initialize_inbound_handlersObject

Initializes the inbound handlers.


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# File 'lib/rex/post/meterpreter/packet_dispatcher.rb', line 540

def initialize_inbound_handlers
  @inbound_handlers = []
end

#initialize_passive_dispatcherObject


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# File 'lib/rex/post/meterpreter/packet_dispatcher.rb', line 78

def initialize_passive_dispatcher
  self.send_queue   = []
  self.recv_queue   = []
  self.waiters      = []
  self.alive        = true
end

#keepalivevoid

This method returns an undefined value.

Send a ping to the server.

Our 'ping' is a check for eof on channel id 0. This method has no side effects and always returns an answer (regardless of the existence of chan 0), which is all that's needed for a liveness check. The answer itself is unimportant and is ignored.


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# File 'lib/rex/post/meterpreter/packet_dispatcher.rb', line 242

def keepalive
  if @ping_sent
    if Time.now.to_i - last_checkin.to_i > PING_TIME*2
      dlog("No response to ping, session #{self.sid} is dead", LEV_3)
      self.alive = false
    end
  else
    pkt = Packet.create_request(COMMAND_ID_CORE_CHANNEL_EOF)
    pkt.add_tlv(TLV_TYPE_CHANNEL_ID, 0)
    add_response_waiter(pkt, Proc.new { @ping_sent = false })
    send_packet(pkt)
    @ping_sent = true
  end
end

#monitor_socketObject

Monitors the PacketDispatcher's sock for data in its own thread context and parsers all inbound packets.


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# File 'lib/rex/post/meterpreter/packet_dispatcher.rb', line 284

def monitor_socket

  # Skip if we are using a passive dispatcher
  return if self.passive_service

  # redirect to pivot keepalive if we're a pivot session
  return pivot_keepalive_start if self.pivot_session

  self.comm_mutex = ::Mutex.new

  self.waiters = []

  # This queue is where the new incoming packets end up
  @new_packet_queue = ::Queue.new
  # This is where we put packets that aren't new, but haven't
  # yet been handled.
  @incomplete_queue = ::Queue.new
  @ping_sent = false

  # Spawn a thread for receiving packets
  self.receiver_thread = Rex::ThreadFactory.spawn("MeterpreterReceiver", false) do
    while (self.alive)
      begin
        rv = Rex::ThreadSafe.select([ self.sock.fd ], nil, nil, PING_TIME)
        if rv
          packet = receive_packet
          # Always enqueue the new packets onto the new packet queue
          @new_packet_queue << decrypt_inbound_packet(packet) if packet
        elsif self.send_keepalives && @new_packet_queue.empty?
          keepalive
        end
      rescue ::Exception => e
        dlog("Exception caught in monitor_socket: #{e.class}: #{e}", 'meterpreter', LEV_1)
        dlog("Call stack: #{e.backtrace.join("\n")}", 'meterpreter', LEV_2)
        self.alive = false
        break
      end
    end
  end

  # Spawn a new thread that monitors the socket
  self.dispatcher_thread = Rex::ThreadFactory.spawn("MeterpreterDispatcher", false) do
    begin
    while (self.alive)
      # This is where we'll store incomplete packets on
      # THIS iteration
      incomplete = []
      # The backlog is the full list of packets that aims
      # to be handled this iteration
      backlog    = []

      # If we have any left over packets from the previous
      # iteration, we need to prioritise them over the new
      # packets. If we don't do this, then we end up in
      # situations where data on channels can be processed
      # out of order. We don't do a blocking wait here via
      # the .pop method because we don't want to block, we
      # just want to dump the queue.
      while @incomplete_queue.length > 0
        backlog << @incomplete_queue.pop
      end

      # If the backlog is empty, we don't have old/stale
      # packets hanging around, so perform a blocking wait
      # for the next packet
      backlog << @new_packet_queue.pop if backlog.length == 0
      # At this point we either received a packet off the wire
      # or we had a backlog to process. In either case, we
      # perform a non-blocking queue dump to fill the backlog
      # with every packet we have.
      while @new_packet_queue.length > 0
        backlog << @new_packet_queue.pop
      end

      #
      # Prioritize message processing here
      # 1. Close should always be processed at the end
      # 2. Command responses always before channel data
      #

      tmp_command = []
      tmp_channel = []
      tmp_close   = []
      backlog.each do |pkt|
        if(pkt.response?)
          tmp_command << pkt
          next
        end
        if(pkt.method == COMMAND_ID_CORE_CHANNEL_CLOSE)
          tmp_close << pkt
          next
        end
        tmp_channel << pkt
      end

      backlog = []
      backlog.push(*tmp_command)
      backlog.push(*tmp_channel)
      backlog.push(*tmp_close)

      #
      # Process the message queue
      #
      backlog.each do |pkt|

        begin
        unless dispatch_inbound_packet(pkt)
          # Keep Packets in the receive queue until a handler is registered
          # for them. Packets will live in the receive queue for up to
          # PACKET_TIMEOUT seconds, after which they will be dropped.
          #
          # A common reason why there would not immediately be a handler for
          # a received Packet is in channels, where a connection may
          # open and receive data before anything has asked to read.
          if (::Time.now.to_i - pkt.created_at.to_i < PACKET_TIMEOUT)
            incomplete << pkt
          end
        end

        rescue ::Exception => e
          dlog("Dispatching exception with packet #{pkt}: #{e} #{e.backtrace}", 'meterpreter', LEV_1)
        end
      end

      # If the backlog and incomplete arrays are the same, it means
      # dispatch_inbound_packet wasn't able to handle any of the
      # packets. When that's the case, we can get into a situation
      # where @new_packet_queue is not empty and, since nothing else bounds this
      # loop, we spin CPU trying to handle packets that can't be
      # handled. Sleep here to treat that situation as though the
      # queue is empty.
      if (backlog.length > 0 && backlog.length == incomplete.length)
        ::IO.select(nil, nil, nil, 0.10)
      end

      # If we have any packets that weren't handled, they go back
      # on the incomplete queue so that they're prioritised over
      # new packets that are coming in off the wire.
      dlog("Requeuing #{incomplete.length} packet(s)", 'meterpreter', LEV_1) if incomplete.length > 0
      while incomplete.length > 0
        @incomplete_queue << incomplete.shift
      end

      # If the old queue of packets gets too big...
      if(@incomplete_queue.length > 100)
        removed = []
        # Drop a bunch of them.
        (1..25).each {
          removed << @incomplete_queue.pop
        }
        dlog("Backlog has grown to over 100 in monitor_socket, dropping older packets: #{removed.map{|x| x.inspect}.join(" - ")}", 'meterpreter', LEV_1)
      end
    end
    rescue ::Exception => e
      dlog("Exception caught in monitor_socket dispatcher: #{e.class} #{e} #{e.backtrace}", 'meterpreter', LEV_1)
    ensure
      self.receiver_thread.kill if self.receiver_thread
    end
  end
end

#monitor_stopObject

Stop the monitor


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# File 'lib/rex/post/meterpreter/packet_dispatcher.rb', line 464

def monitor_stop
  if self.receiver_thread
    self.receiver_thread.kill
    self.receiver_thread.join
    self.receiver_thread = nil
  end

  if self.dispatcher_thread
    self.dispatcher_thread.kill
    self.dispatcher_thread.join
    self.dispatcher_thread = nil
  end
end

#notify_response_waiter(response) ⇒ Object

Notifies a whomever is waiting for a the supplied response, if anyone.


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# File 'lib/rex/post/meterpreter/packet_dispatcher.rb', line 503

def notify_response_waiter(response)
  if self.pivot_session
    return self.pivot_session.notify_response_waiter(response)
  end

  handled = false
  self.waiters.each() { |waiter|
    if (waiter.waiting_for?(response))
      waiter.notify(response)
      remove_response_waiter(waiter)
      handled = true
      break
    end
  }
  return handled
end

#on_passive_request(cli, req) ⇒ Object


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# File 'lib/rex/post/meterpreter/packet_dispatcher.rb', line 92

def on_passive_request(cli, req)
  begin
    self.last_checkin = Time.now
    resp = send_queue.shift
    cli.send_response(resp)
  rescue => e
    send_queue.unshift(resp) if resp
    elog("Exception sending a reply to the reader request #{cli.inspect}", error: e)
  end
end

#pivot_keepalive_startObject

Reception


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# File 'lib/rex/post/meterpreter/packet_dispatcher.rb', line 263

def pivot_keepalive_start
  return unless self.send_keepalives
  self.receiver_thread = Rex::ThreadFactory.spawn("PivotKeepalive", false) do
    while self.alive
      begin
        Rex::sleep(PING_TIME)
        keepalive
      rescue ::Exception => e
        dlog("Exception caught in pivot keepalive: #{e.class}: #{e}", 'meterpreter', LEV_1)
        dlog("Call stack: #{e.backtrace.join("\n")}", 'meterpreter', LEV_2)
        self.alive = false
        break
      end
    end
  end
end

#receive_packetObject

Parses data from the dispatcher's sock and returns a Packet context once a full packet has been received.


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# File 'lib/rex/post/meterpreter/packet_dispatcher.rb', line 450

def receive_packet
  packet = parser.recv(self.sock)
  if packet
    packet.parse_header!
    if self.session_guid == NULL_GUID
      self.session_guid = packet.session_guid.dup
    end
  end
  packet
end

#register_inbound_handler(handler) ⇒ Object

Registers an inbound packet handler that implements the InboundPacketHandler interface.


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# File 'lib/rex/post/meterpreter/packet_dispatcher.rb', line 609

def register_inbound_handler(handler)
  @inbound_handlers << handler
end

#remove_response_waiter(waiter) ⇒ Object

Removes a waiter from the list of waiters.


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# File 'lib/rex/post/meterpreter/packet_dispatcher.rb', line 523

def remove_response_waiter(waiter)
  if self.pivot_session
    self.pivot_session.remove_response_waiter(waiter)
  else
    self.waiters.delete(waiter)
  end
end

#send_packet(packet, opts = {}) ⇒ Object

Sends a packet without waiting for a response.


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# File 'lib/rex/post/meterpreter/packet_dispatcher.rb', line 112

def send_packet(packet, opts={})
  if self.pivot_session
    opts[:session_guid] = self.session_guid
    opts[:tlv_enc_key] = self.tlv_enc_key
    return self.pivot_session.send_packet(packet, opts)
  end

  if opts[:completion_routine]
    add_response_waiter(packet, opts[:completion_routine], opts[:completion_param])
  end

  session_guid = self.session_guid
  tlv_enc_key = self.tlv_enc_key

  # if a session guid is provided, use all the details provided
  if opts[:session_guid]
    session_guid = opts[:session_guid]
    tlv_enc_key = opts[:tlv_enc_key]
  end

  # Uncomment this line if you want to see outbound packets in the console.
  #STDERR.puts("SEND: #{packet.inspect}\n")

  bytes = 0
  raw   = packet.to_r(session_guid, tlv_enc_key)
  err   = nil

  # Short-circuit send when using a passive dispatcher
  if self.passive_service
    send_queue.push(raw)
    return raw.size # Lie!
  end

  if raw
    self.comm_mutex.synchronize do
      begin
        bytes = self.sock.write(raw)
      rescue ::Exception => e
        err = e
      end
    end


    if bytes.to_i == 0
      # Mark the session itself as dead
      self.alive = false

      # Reraise the error to the top-level caller
      raise err if err
    end
  end

  return bytes
end

#send_packet_wait_response(packet, timeout) ⇒ Object

Transmits a packet and waits for a response.

Parameters:

  • packet (Packet)

    the request packet to send

  • timeout (Integer, nil)

    number of seconds to wait, or nil to wait forever


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# File 'lib/rex/post/meterpreter/packet_dispatcher.rb', line 199

def send_packet_wait_response(packet, timeout)
  # First, add the waiter association for the supplied packet
  waiter = add_response_waiter(packet)

  bytes_written = send_packet(packet)

  # Transmit the packet
  if (bytes_written.to_i <= 0)
    # Remove the waiter if we failed to send the packet.
    remove_response_waiter(waiter)
    return nil
  end

  if not timeout
    return nil
  end

  # Wait for the supplied time interval
  response = waiter.wait(timeout)

  # Remove the waiter from the list of waiters in case it wasn't
  # removed. This happens if the waiter timed out above.
  remove_response_waiter(waiter)

  # wire in the UUID for this, as it should be part of every response
  # packet
  if response && !self.payload_uuid
    uuid = response.get_tlv_value(TLV_TYPE_UUID)
    self.payload_uuid = Msf::Payload::UUID.new({:raw => uuid}) if uuid
  end

  # Return the response packet, if any
  return response
end

#send_request(packet, timeout = self.response_timeout) ⇒ Object

Sends a packet and waits for a timeout for the given time interval.

Parameters:

  • packet (Packet)

    request to send

  • timeout (Integer, nil) (defaults to: self.response_timeout)

    seconds to wait for response, or nil to ignore the response and return immediately


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# File 'lib/rex/post/meterpreter/packet_dispatcher.rb', line 174

def send_request(packet, timeout = self.response_timeout)
  response = send_packet_wait_response(packet, timeout)

  if timeout.nil?
    return nil
  elsif response.nil?
    raise TimeoutError.new("Send timed out")
  elsif (response.result != 0)
    einfo = lookup_error(response.result)
    e = RequestError.new(packet.method, einfo, response.result)

    e.set_backtrace(caller)

    raise e
  end

  return response
end

#shutdown_passive_dispatcherObject


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# File 'lib/rex/post/meterpreter/packet_dispatcher.rb', line 85

def shutdown_passive_dispatcher
  self.alive      = false
  self.send_queue = []
  self.recv_queue = []
  self.waiters    = []
end