Add a check() for mssql_payload

modules/exploits/windows/mssql/mssql_payload.rb

@@ -68,6 +68,23 @@ class Metasploit3 < Msf::Exploit::Remote
       ])
   end
 
+  def check
+    if (not mssql_login_datastore)
+      print_status("Invalid SQL Server credentials")
+      return Exploit::CheckCode::Detected
+    end
+
+    mssql_query("select @@version", true)
+    if mssql_is_sysadmin
+      print_good "User #{datastore['USERNAME']} is a sysadmin"
+      Exploit::CheckCode::Vulnerable
+    else
+      Exploit::CheckCode::Safe
+    end
+  ensure
+    disconnect
+  end
+
   # This is method required for the CmdStager to work...
   def execute_command(cmd, opts)
     mssql_xpcmdshell(cmd, datastore['VERBOSE'])