Just use YAML.safe_load and assume the format

lib/gitlab/serialize/yaml_variables.rb

@@ -10,36 +10,16 @@ module Gitlab
       def load(string)
         return unless string
 
-        object = YAML.load(string)
+        object = YAML.safe_load(string, [Symbol])
 
-        # We don't need to verify the object once we're using SafeYAML
-        if YamlVariables.verify_object(object)
-          YamlVariables.convert_object(object)
-        else
-          []
-        end
+        object.map(&YamlVariables.method(:convert_key_value_to_string))
       end
 
       def dump(object)
         YAML.dump(object)
       end
 
-      def verify_object(object)
-        YamlVariables.verify_type(object, Array) &&
-          object.all? { |obj| YamlVariables.verify_type(obj, Hash) }
-      end
-
-      # We use three ways to check if the class is exactly the one we want,
-      # rather than some subclass or duck typing class.
-      def verify_type(object, klass)
-        object.kind_of?(klass) &&
-          object.class == klass &&
-          klass === object
-      end
-
-      def convert_object(object)
-        object.map(&YamlVariables.method(:convert_key_value_to_string))
-      end
+      private
 
       def convert_key_value_to_string(variable)
         variable[:key] = variable[:key].to_s

spec/lib/gitlab/serialize/yaml_variables_spec.rb

@@ -16,25 +16,4 @@ describe Gitlab::Serialize::YamlVariables do
       { key: 'key', value: 'value', public: true },
       { key: 'wee', value: '1', public: false }])
   end
-
-  context 'with a subclass of Array' do
-    let(:object) do
-      Kaminari::PaginatableArray.new << 'I am evil'
-    end
-
-    it 'ignores it' do
-      is_expected.to eq([])
-    end
-  end
-
-  context 'with the array containing subclasses of Hash' do
-    let(:object) do
-      [ActiveSupport::OrderedOptions.new(
-        key: 'key', value: 'value', public: true)]
-    end
-
-    it 'ignores it' do
-      is_expected.to eq([])
-    end
-  end
 end