Closes issue 11133. Fixes two cases where inspect.getattr_static could trigger code execution

2 files changed, 68 insertions, 6 deletions

diff --git a/Lib/inspect.py b/Lib/inspect.py
index ed10ac5..aa951d8 100644
--- a/Lib/inspect.py
+++ b/Lib/inspect.py
@@ -1069,15 +1069,16 @@ def _check_instance(obj, attr):
         instance_dict = object.__getattribute__(obj, "__dict__")
     except AttributeError:
         pass
-    return instance_dict.get(attr, _sentinel)
+    return dict.get(instance_dict, attr, _sentinel)
 
 
 def _check_class(klass, attr):
     for entry in _static_getmro(klass):
-        try:
-            return entry.__dict__[attr]
-        except KeyError:
-            pass
+        if not _shadowed_dict(type(entry)):
+            try:
+                return entry.__dict__[attr]
+            except KeyError:
+                pass
     return _sentinel
 
 def _is_type(obj):
@@ -1087,6 +1088,19 @@ def _is_type(obj):
         return False
     return True
 
+def _shadowed_dict(klass):
+    dict_attr = type.__dict__["__dict__"]
+    for entry in _static_getmro(klass):
+        try:
+            class_dict = dict_attr.__get__(entry)["__dict__"]
+        except KeyError:
+            pass
+        else:
+            if not (type(class_dict) is types.GetSetDescriptorType and
+                    class_dict.__name__ == "__dict__" and
+                    class_dict.__objclass__ is entry):
+                return True
+    return False
 
 def getattr_static(obj, attr, default=_sentinel):
     """Retrieve attributes without triggering dynamic lookup via the
@@ -1101,8 +1115,9 @@ def getattr_static(obj, attr, default=_sentinel):
     """
     instance_result = _sentinel
     if not _is_type(obj):
-        instance_result = _check_instance(obj, attr)
         klass = type(obj)
+        if not _shadowed_dict(klass):
+            instance_result = _check_instance(obj, attr)
     else:
         klass = obj
 
diff --git a/Lib/test/test_inspect.py b/Lib/test/test_inspect.py
index ccfcaba..331d247 100644
--- a/Lib/test/test_inspect.py
+++ b/Lib/test/test_inspect.py
@@ -906,6 +906,53 @@ class TestGetattrStatic(unittest.TestCase):
         self.assertEqual(inspect.getattr_static(Something(), 'foo'), 3)
         self.assertEqual(inspect.getattr_static(Something, 'foo'), 3)
 
+    def test_dict_as_property(self):
+        test = self
+        test.called = False
+
+        class Foo(dict):
+            a = 3
+            @property
+            def __dict__(self):
+                test.called = True
+                return {}
+
+        foo = Foo()
+        foo.a = 4
+        self.assertEqual(inspect.getattr_static(foo, 'a'), 3)
+        self.assertFalse(test.called)
+
+    def test_custom_object_dict(self):
+        test = self
+        test.called = False
+
+        class Custom(dict):
+            def get(self, key, default=None):
+                test.called = True
+                super().get(key, default)
+
+        class Foo(object):
+            a = 3
+        foo = Foo()
+        foo.__dict__ = Custom()
+        self.assertEqual(inspect.getattr_static(foo, 'a'), 3)
+        self.assertFalse(test.called)
+
+    def test_metaclass_dict_as_property(self):
+        class Meta(type):
+            @property
+            def __dict__(self):
+                self.executed = True
+
+        class Thing(metaclass=Meta):
+            executed = False
+
+            def __init__(self):
+                self.spam = 42
+
+        instance = Thing()
+        self.assertEqual(inspect.getattr_static(instance, "spam"), 42)
+        self.assertFalse(Thing.executed)
 
 class TestGetGeneratorState(unittest.TestCase):