1 files changed, 46 insertions, 3 deletions
diff --git a/actionpack/test/controller/parameters/parameters_permit_test.rb b/actionpack/test/controller/parameters/parameters_permit_test.rb
index 84e007b5d0..aa894ffa17 100644
--- a/actionpack/test/controller/parameters/parameters_permit_test.rb
+++ b/actionpack/test/controller/parameters/parameters_permit_test.rb
@@ -8,9 +8,16 @@ class ParametersPermitTest < ActiveSupport::TestCase
   end
 
   setup do
-    @params = ActionController::Parameters.new({ person: {
-      age: "32", name: { first: "David", last: "Heinemeier Hansson" }
-    }})
+    @params = ActionController::Parameters.new(
+      person: {
+        age: '32',
+        name: {
+          first: 'David',
+          last: 'Heinemeier Hansson'
+        },
+        addresses: [{city: 'Chicago', state: 'Illinois'}]
+      }
+    )
 
     @struct_fields = []
     %w(0 1 12).each do |number|
@@ -147,6 +154,41 @@ class ParametersPermitTest < ActiveSupport::TestCase
     assert_equal :foo, e.param
   end
 
+  test "fetch with a default value of a hash does not mutate the object" do
+    params = ActionController::Parameters.new({})
+    params.fetch :foo, {}
+    assert_equal nil, params[:foo]
+  end
+
+  test 'hashes in array values get wrapped' do
+    params = ActionController::Parameters.new(foo: [{}, {}])
+    params[:foo].each do |hash|
+      assert !hash.permitted?
+    end
+  end
+
+  # Strong params has an optimization to avoid looping every time you read
+  # a key whose value is an array and building a new object. We check that
+  # optimization here.
+  test 'arrays are converted at most once' do
+    params = ActionController::Parameters.new(foo: [{}])
+    assert_same params[:foo], params[:foo]
+  end
+
+  # Strong params has an internal cache to avoid duplicated loops in the most
+  # common usage pattern. See the docs of the method `converted_arrays`.
+  #
+  # This test checks that if we push a hash to an array (in-place modification)
+  # the cache does not get fooled, the hash is still wrapped as strong params,
+  # and not permitted.
+  test 'mutated arrays are detected' do
+    params = ActionController::Parameters.new(users: [{id: 1}])
+
+    permitted = params.permit(users: [:id])
+    permitted[:users] << {injected: 1}
+    assert_not permitted[:users].last.permitted?
+  end
+
   test "fetch doesnt raise ParameterMissing exception if there is a default" do
     assert_equal "monkey", @params.fetch(:foo, "monkey")
     assert_equal "monkey", @params.fetch(:foo) { "monkey" }
@@ -215,6 +257,7 @@ class ParametersPermitTest < ActiveSupport::TestCase
     assert @params.permitted?
     assert @params[:person].permitted?
     assert @params[:person][:name].permitted?
+    assert @params[:person][:addresses][0].permitted?
   end
 
   test "permitted takes a default value when Parameters.permit_all_parameters is set" do