add exectuable validator

like the filepath validator but also checks
to see if the file is exectuable by the current
users.

app/validators/metasploit/framework/executable_path_validator.rb

@@ -0,0 +1,16 @@
+module Metasploit
+  module Framework
+    # This is a ActiveModel custom validator that assumes the attribute
+    # is supposed to be the path to a regular file. It checks whether the
+    # file exists and whether or not it is a regular file.
+    class ExecutablePathValidator < ActiveModel::EachValidator
+
+      def validate_each(record, attribute, value)
+        unless ::File.executable? value
+          record.errors[attribute] << (options[:message] || "is not a valid path to an executable file")
+        end
+      end
+    end
+  end
+end
+

lib/metasploit/framework/jtr/cracker.rb

@@ -48,6 +48,8 @@ module Metasploit
 
         validates :hash_path, :'Metasploit::Framework::File_path' => true, if: 'hash_path.present?'
 
+        validates :john_path, :'Metasploit::Framework::Executable_path' => true, if: 'john_path.present?'
+
         validates :pot, :'Metasploit::Framework::File_path' => true, if: 'pot.present?'
 
         validates :max_runtime,