Issue #4176: Pickle would crash the interpreter when a __reduce__ function

does not return an iterator for the 4th and 5th items.
(sequence-like and mapping-like state)

A list is not an iterator...

Will backport to 2.6 and 2.5.

Lib/test/pickletester.py

@@ -849,6 +849,29 @@ class AbstractPickleTests(unittest.TestCase):
             y = self.loads(s)
             self.assertEqual(y._reduce_called, 1)
 
+    def test_reduce_bad_iterator(self):
+        # Issue4176: crash when 4th and 5th items of __reduce__()
+        # are not iterators
+        class C(object):
+            def __reduce__(self):
+                # 4th item is not an iterator
+                return list, (), None, [], None
+        class D(object):
+            def __reduce__(self):
+                # 5th item is not an iterator
+                return dict, (), None, None, []
+
+        # Protocol 0 is less strict and also accept iterables.
+        for proto in 0, 1, 2:
+            try:
+                self.dumps(C(), proto)
+            except (AttributeError, pickle.PickleError, cPickle.PickleError):
+                pass
+            try:
+                self.dumps(D(), proto)
+            except (AttributeError, pickle.PickleError, cPickle.PickleError):
+                pass
+
 # Test classes for reduce_ex
 
 class REX_one(object):

Misc/NEWS

@@ -12,6 +12,9 @@ What's New in Python 2.7 alpha 1
 Core and Builtins
 -----------------
 
+- Issue #4176: Fixed a crash when pickling an object which ``__reduce__``
+  method does not return iterators for the 4th and 5th items.
+
 - Issue #4209: Enabling unicode_literals and the print_function in the same
   __future__ import didn't work.
 

Modules/cPickle.c

@@ -2206,13 +2206,14 @@ save_pers(Picklerobject *self, PyObject *args, PyObject *f)
  * appropriate __reduce__ method for ob.
  */
 static int
-save_reduce(Picklerobject *self, PyObject *args, PyObject *ob)
+save_reduce(Picklerobject *self, PyObject *args, PyObject *fn, PyObject *ob)
 {
 	PyObject *callable;
 	PyObject *argtup;
-        PyObject *state = NULL;
-        PyObject *listitems = NULL;
-        PyObject *dictitems = NULL;
+	PyObject *state = NULL;
+	PyObject *listitems = Py_None;
+	PyObject *dictitems = Py_None;
+	Py_ssize_t size;
 
 	int use_newobj = self->proto >= 2;
 
@@ -2220,6 +2221,14 @@ save_reduce(Picklerobject *self, PyObject *args, PyObject *ob)
 	static char build = BUILD;
 	static char newobj = NEWOBJ;
 
+	size = PyTuple_Size(args);
+	if (size < 2 || size > 5) {
+		cPickle_ErrFormat(PicklingError, "tuple returned by "
+			"%s must contain 2 through 5 elements",
+			"O", fn);
+		return -1;
+	}
+
 	if (! PyArg_UnpackTuple(args, "save_reduce", 2, 5,
 				&callable,
 				&argtup,
@@ -2229,17 +2238,32 @@ save_reduce(Picklerobject *self, PyObject *args, PyObject *ob)
 		return -1;
 
 	if (!PyTuple_Check(argtup)) {
-		PyErr_SetString(PicklingError,
-				"args from reduce() should be a tuple");
+		cPickle_ErrFormat(PicklingError, "Second element of "
+			"tuple returned by %s must be a tuple",
+			"O", fn);
 		return -1;
 	}
 
 	if (state == Py_None)
 		state = NULL;
+
 	if (listitems == Py_None)
 		listitems = NULL;
+	else if (!PyIter_Check(listitems)) {
+		cPickle_ErrFormat(PicklingError, "Fourth element of "
+			"tuple returned by %s must be an iterator, not %s",
+			"Os", fn, Py_TYPE(listitems)->tp_name);
+		return -1;
+	}
+
 	if (dictitems == Py_None)
 		dictitems = NULL;
+	else if (!PyIter_Check(dictitems)) {
+		cPickle_ErrFormat(PicklingError, "Fifth element of "
+			"tuple returned by %s must be an iterator, not %s",
+			"Os", fn, Py_TYPE(dictitems)->tp_name);
+		return -1;
+	}
 
         /* Protocol 2 special case: if callable's name is __newobj__, use
          * NEWOBJ.  This consumes a lot of code.
@@ -2363,9 +2387,8 @@ save(Picklerobject *self, PyObject *args, int pers_save)
 {
 	PyTypeObject *type;
 	PyObject *py_ob_id = 0, *__reduce__ = 0, *t = 0;
-	PyObject *arg_tup;
 	int res = -1;
-	int tmp, size;
+	int tmp;
 
 	if (Py_EnterRecursiveCall(" while pickling an object"))
 		return -1;
@@ -2591,30 +2614,14 @@ save(Picklerobject *self, PyObject *args, int pers_save)
 		goto finally;
 	}
 
-	if (! PyTuple_Check(t)) {
+	if (!PyTuple_Check(t)) {
 		cPickle_ErrFormat(PicklingError, "Value returned by "
 				"%s must be string or tuple",
 				"O", __reduce__);
 		goto finally;
 	}
 
-	size = PyTuple_Size(t);
-	if (size < 2 || size > 5) {
-		cPickle_ErrFormat(PicklingError, "tuple returned by "
-			"%s must contain 2 through 5 elements",
-			"O", __reduce__);
-		goto finally;
-	}
-
-	arg_tup = PyTuple_GET_ITEM(t, 1);
-	if (!(PyTuple_Check(arg_tup) || arg_tup == Py_None))  {
-		cPickle_ErrFormat(PicklingError, "Second element of "
-			"tuple returned by %s must be a tuple",
-			"O", __reduce__);
-		goto finally;
-	}
-
-	res = save_reduce(self, t, args);
+	res = save_reduce(self, t, __reduce__, args);
 
   finally:
 	Py_LeaveRecursiveCall();