Add error handling around double-bind of ports

lib/msf/windows_error.rb

@@ -236,6 +236,9 @@ class WindowsError
   PROCESS_MODE_NOT_BACKGROUND = 403
   INVALID_ADDRESS = 487
 
+  # Socket stuff
+  ADDRESS_IN_USE = 10048
+
   #
   # Return a string representation of the constant for a number
   #
@@ -687,6 +690,8 @@ class WindowsError
       "The process is not in background processing mode."
     when INVALID_ADDRESS
       "Attempt to access invalid address."
+    when ADDRESS_IN_USE
+      "The address/port is already in use."
     else
       "#{code}"
     end

lib/rex/post/meterpreter/channel.rb

@@ -113,7 +113,9 @@ class Channel
 
     # Transmit the request and wait for the response
     response = client.send_request(request)
-    cid      = response.get_tlv(TLV_TYPE_CHANNEL_ID).value
+    cid      = response.get_tlv_value(TLV_TYPE_CHANNEL_ID)
+
+    return nil unless cid
 
     # Create the channel instance
     channel  = klass.new(client, cid, type, flags)

lib/rex/post/meterpreter/extensions/stdapi/net/socket_subsystem/tcp_server_channel.rb

@@ -79,14 +79,8 @@ class TcpServerChannel < Rex::Post::Meterpreter::Channel
   def self.open(client, params)
     c = Channel.create(client, 'stdapi_net_tcp_server', self, CHANNEL_FLAG_SYNCHRONOUS,
       [
-        {
-        'type'  => TLV_TYPE_LOCAL_HOST,
-        'value' => params.localhost
-        },
-        {
-        'type'  => TLV_TYPE_LOCAL_PORT,
-        'value' => params.localport
-        }
+        {'type'  => TLV_TYPE_LOCAL_HOST, 'value' => params.localhost},
+        {'type'  => TLV_TYPE_LOCAL_PORT, 'value' => params.localport}
       ] )
     c.params = params
     c

lib/rex/post/meterpreter/ui/console/command_dispatcher/stdapi/net.rb

@@ -454,20 +454,26 @@ class Console::CommandDispatcher::Stdapi::Net
             return
           end
 
-          channel = client.net.socket.create(
-            Rex::Socket::Parameters.new(
-              'LocalPort' => rport,
-              'Proto'     => 'tcp',
-              'Server'    => true
+          begin
+            channel = client.net.socket.create(
+              Rex::Socket::Parameters.new(
+                'LocalPort' => rport,
+                'Proto'     => 'tcp',
+                'Server'    => true
+              )
             )
-          )
 
-          # Start the local TCP reverse relay in association with this stream
-          service.start_reverse_tcp_relay(channel,
-            'LocalPort'         => rport,
-            'PeerHost'          => lhost,
-            'PeerPort'          => lport,
-            'MeterpreterRelay'  => true)
+            # Start the local TCP reverse relay in association with this stream
+            service.start_reverse_tcp_relay(channel,
+              'LocalPort'         => rport,
+              'PeerHost'          => lhost,
+              'PeerPort'          => lport,
+              'MeterpreterRelay'  => true)
+          rescue Exception => e
+            print_error("Failed to create relay: #{e.to_s}")
+            return false
+          end
+
         else
           # Validate parameters
           unless lport && rhost && rport