[1.7.x] Fixed DoS possibility in ModelMultipleChoiceField.

This is a security fix. Disclosure following shortly.

Thanks Keryn Knight for the report and initial patch.

1 files changed, 21 insertions, 0 deletions

diff --git a/tests/model_forms/tests.py b/tests/model_forms/tests.py
index 78c3bca416..a1871bf2bf 100644
--- a/tests/model_forms/tests.py
+++ b/tests/model_forms/tests.py
@@ -1573,6 +1573,27 @@ class ModelMultipleChoiceFieldTests(TestCase):
         self.assertTrue(form.is_valid())
         self.assertTrue(form.has_changed())
 
+    def test_show_hidden_initial_changed_queries_efficiently(self):
+        class WriterForm(forms.Form):
+            persons = forms.ModelMultipleChoiceField(
+                show_hidden_initial=True, queryset=Writer.objects.all())
+
+        writers = (Writer.objects.create(name=str(x)) for x in range(0, 50))
+        writer_pks = tuple(x.pk for x in writers)
+        form = WriterForm(data={'initial-persons': writer_pks})
+        with self.assertNumQueries(1):
+            self.assertTrue(form.has_changed())
+
+    def test_clean_does_deduplicate_values(self):
+        class WriterForm(forms.Form):
+            persons = forms.ModelMultipleChoiceField(queryset=Writer.objects.all())
+
+        person1 = Writer.objects.create(name="Person 1")
+        form = WriterForm(data={})
+        queryset = form.fields['persons'].clean([str(person1.pk)] * 50)
+        sql, params = queryset.query.sql_with_params()
+        self.assertEqual(len(params), 1)
+
 
 class ModelOneToOneFieldTests(TestCase):
     def test_modelform_onetoonefield(self):