bpo-41288: Fix a crash in unpickling invalid NEWOBJ_EX. (GH-21458)

Automerge-Triggered-By: @tiran
(cherry picked from commit 4f309ab)

Co-authored-by: Serhiy Storchaka <[email protected]>

Author: miss-islington

Lib/test/pickletester.py

@@ -1170,6 +1170,24 @@ def test_compat_unpickle(self):
             self.assertIs(type(unpickled), collections.UserDict)
             self.assertEqual(unpickled, collections.UserDict({1: 2}))
 
+    def test_bad_reduce(self):
+        self.assertEqual(self.loads(b'cbuiltins\nint\n)R.'), 0)
+        self.check_unpickling_error(TypeError, b'N)R.')
+        self.check_unpickling_error(TypeError, b'cbuiltins\nint\nNR.')
+
+    def test_bad_newobj(self):
+        error = (pickle.UnpicklingError, TypeError)
+        self.assertEqual(self.loads(b'cbuiltins\nint\n)\x81.'), 0)
+        self.check_unpickling_error(error, b'cbuiltins\nlen\n)\x81.')
+        self.check_unpickling_error(error, b'cbuiltins\nint\nN\x81.')
+
+    def test_bad_newobj_ex(self):
+        error = (pickle.UnpicklingError, TypeError)
+        self.assertEqual(self.loads(b'cbuiltins\nint\n)}\x92.'), 0)
+        self.check_unpickling_error(error, b'cbuiltins\nlen\n)}\x92.')
+        self.check_unpickling_error(error, b'cbuiltins\nint\nN}\x92.')
+        self.check_unpickling_error(error, b'cbuiltins\nint\n)N\x92.')
+
     def test_bad_stack(self):
         badpickles = [
             b'.',                       # STOP

Misc/NEWS.d/next/Library/2020-07-13-15-06-35.bpo-41288.8mn5P-.rst

@@ -0,0 +1,2 @@
+Unpickling invalid NEWOBJ_EX opcode with the C implementation raises now
+UnpicklingError instead of crashing.

Modules/_pickle.c

@@ -5988,23 +5988,30 @@ load_newobj_ex(UnpicklerObject *self)
     }
 
     if (!PyType_Check(cls)) {
-        Py_DECREF(kwargs);
-        Py_DECREF(args);
         PyErr_Format(st->UnpicklingError,
                      "NEWOBJ_EX class argument must be a type, not %.200s",
                      Py_TYPE(cls)->tp_name);
-        Py_DECREF(cls);
-        return -1;
+        goto error;
     }
 
     if (((PyTypeObject *)cls)->tp_new == NULL) {
-        Py_DECREF(kwargs);
-        Py_DECREF(args);
-        Py_DECREF(cls);
         PyErr_SetString(st->UnpicklingError,
                         "NEWOBJ_EX class argument doesn't have __new__");
-        return -1;
+        goto error;
+    }
+    if (!PyTuple_Check(args)) {
+        PyErr_Format(st->UnpicklingError,
+                     "NEWOBJ_EX args argument must be a tuple, not %.200s",
+                     Py_TYPE(args)->tp_name);
+        goto error;
+    }
+    if (!PyDict_Check(kwargs)) {
+        PyErr_Format(st->UnpicklingError,
+                     "NEWOBJ_EX kwargs argument must be a dict, not %.200s",
+                     Py_TYPE(kwargs)->tp_name);
+        goto error;
     }
+
     obj = ((PyTypeObject *)cls)->tp_new((PyTypeObject *)cls, args, kwargs);
     Py_DECREF(kwargs);
     Py_DECREF(args);
@@ -6014,6 +6021,12 @@ load_newobj_ex(UnpicklerObject *self)
     }
     PDATA_PUSH(self->stack, obj, -1);
     return 0;
+
+error:
+    Py_DECREF(kwargs);
+    Py_DECREF(args);
+    Py_DECREF(cls);
+    return -1;
 }
 
 static int