look up descriptor by objclass in _getattr instead of eval

dill/_dill.py

@@ -1032,23 +1032,20 @@ def _create_capsule(pointer, name, context, destructor):
         return capsule
 
 def _getattr(objclass, name, repr_str):
-    # hack to grab the reference directly
-    try: #XXX: works only for __builtin__ ?
-        attr = repr_str.split("'")[3]
-        return eval(attr+'.__dict__["'+name+'"]')
-    except Exception:
-        try:
-            attr = objclass.__dict__
-            if type(attr) is DictProxyType:
-                if sys.hexversion > 0x30f00a0 and name in ('__weakref__','__dict__'):
-                    attr = _dictproxy_helper.__dict__[name]
-                else:
-                    attr = attr[name]
+    # grab the descriptor directly off its owning class; repr_str is kept
+    # for backward compatibility with existing pickles but is not evaluated
+    try:
+        attr = objclass.__dict__
+        if type(attr) is DictProxyType:
+            if sys.hexversion > 0x30f00a0 and name in ('__weakref__','__dict__'):
+                attr = _dictproxy_helper.__dict__[name]
             else:
-                attr = getattr(objclass,name)
-        except (AttributeError, KeyError):
+                attr = attr[name]
+        else:
             attr = getattr(objclass,name)
-        return attr
+    except (AttributeError, KeyError):
+        attr = getattr(objclass,name)
+    return attr
 
 def _get_attr(self, name):
     # stop recursive pickling

dill/tests/test_selected.py

@@ -62,6 +62,21 @@ def test_class_descriptors():
     assert ok
   if verbose: print ("")
 
+# descriptors are restored via dill._dill._getattr; the attribute name
+# carried in the pickle must be looked up, never evaluated as code
+def test_descriptor_getattr():
+  from dill._dill import _getattr
+  for i in (int.__dict__['real'], str.__dict__['__len__']):
+    assert dill.copy(i) is i
+  # a crafted name that would run code if passed to eval() must instead be
+  # treated as a plain (missing) lookup key
+  name = '__doc__"].count("zz") or setattr(__import__("dill"), "_pwned", True) or object.__dict__["__doc__'
+  try:
+    _getattr(object, name, "x'x'x'object'x")
+  except (AttributeError, KeyError):
+    pass
+  assert not getattr(dill, "_pwned", False)
+
 # (__main__) class instance for new-style classes
 def test_class():
   o = _d()
@@ -118,4 +133,5 @@ def test_typing():
   test_dict_contents()
   test_class()
   test_class_descriptors()
+  test_descriptor_getattr()
   test_typing()