#3720: Interpreter crashes when an evil iterator removes its own next function.

amaury.forgeotdarc · amaury.forgeotdarc · commit b76ae2ade5ac · 2009-01-12T23:36:55.000Z
Now the slot is filled with a function that always raises. Will not backport: extensions compiled with 2.6.x would not run on 2.6.0. git-svn-id: http://svn.python.org/projects/python/trunk@68560 6015fed2-1504-0410-9fe1-9d1591cc4771
diff --git a/Include/abstract.h b/Include/abstract.h
@@ -636,7 +636,8 @@ xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx*/
 
 #define PyIter_Check(obj) \
     (PyType_HasFeature((obj)->ob_type, Py_TPFLAGS_HAVE_ITER) && \
-     (obj)->ob_type->tp_iternext != NULL)
+     (obj)->ob_type->tp_iternext != NULL && \
+     (obj)->ob_type->tp_iternext != &_PyObject_NextNotImplemented)
 
      PyAPI_FUNC(PyObject *) PyIter_Next(PyObject *);
      /* Takes an iterator object and calls its tp_iternext slot,
diff --git a/Include/object.h b/Include/object.h
@@ -473,6 +473,7 @@ PyAPI_FUNC(int) PyObject_SetAttr(PyObject *, PyObject *, PyObject *);
 PyAPI_FUNC(int) PyObject_HasAttr(PyObject *, PyObject *);
 PyAPI_FUNC(PyObject **) _PyObject_GetDictPtr(PyObject *);
 PyAPI_FUNC(PyObject *) PyObject_SelfIter(PyObject *);
+PyAPI_FUNC(PyObject *) _PyObject_NextNotImplemented(PyObject *);
 PyAPI_FUNC(PyObject *) PyObject_GenericGetAttr(PyObject *, PyObject *);
 PyAPI_FUNC(int) PyObject_GenericSetAttr(PyObject *,
 					      PyObject *, PyObject *);
diff --git a/Lib/test/crashers/iter.py b/Lib/test/crashers/iter.py
diff --git a/Lib/test/test_iter.py b/Lib/test/test_iter.py
@@ -120,6 +120,13 @@ def test_seq_class_for(self):
     def test_seq_class_iter(self):
         self.check_iterator(iter(SequenceClass(10)), range(10))
 
+    # Test a new_style class with __iter__ but no next() method
+    def test_new_style_iter_class(self):
+        class IterClass(object):
+            def __iter__(self):
+                return self
+        self.assertRaises(TypeError, iter, IterClass())
+
     # Test two-argument iter() with callable instance
     def test_iter_callable(self):
         class C:
@@ -877,6 +884,21 @@ def test_sinkstate_enumerate(self):
         self.assertEqual(list(b), zip(range(5), range(5)))
         self.assertEqual(list(b), [])
 
+    def test_3720(self):
+        # Avoid a crash, when an iterator deletes its next() method.
+        class BadIterator(object):
+            def __iter__(self):
+                return self
+            def next(self):
+                del BadIterator.next
+                return 1
+
+        try:
+            for i in BadIterator() :
+                pass
+        except TypeError:
+            pass
+
 
 def test_main():
     run_unittest(TestCase)
diff --git a/Misc/NEWS b/Misc/NEWS
@@ -12,6 +12,9 @@ What's New in Python 2.7 alpha 1
 Core and Builtins
 -----------------
 
+- Issue #3720: Fix a crash when an iterator modifies its class and removes its
+  __next__ method.
+
 - Issue #4893: Use NT threading on CE.
 
 - Issue #4915: Port sysmodule to Windows CE.
diff --git a/Modules/itertoolsmodule.c b/Modules/itertoolsmodule.c
@@ -886,7 +886,6 @@ dropwhile_next(dropwhileobject *lz)
 	long ok;
 	PyObject *(*iternext)(PyObject *);
 
-	assert(PyIter_Check(it));
 	iternext = *Py_TYPE(it)->tp_iternext;
 	for (;;) {
 		item = iternext(it);
@@ -1031,7 +1030,6 @@ takewhile_next(takewhileobject *lz)
 	if (lz->stop == 1)
 		return NULL;
 
-	assert(PyIter_Check(it));
 	item = (*Py_TYPE(it)->tp_iternext)(it);
 	if (item == NULL)
 		return NULL;
@@ -1218,7 +1216,6 @@ islice_next(isliceobject *lz)
 	Py_ssize_t oldnext;
 	PyObject *(*iternext)(PyObject *);
 
-	assert(PyIter_Check(it));
 	iternext = *Py_TYPE(it)->tp_iternext;
 	while (lz->cnt < lz->next) {
 		item = iternext(it);
@@ -1229,7 +1226,6 @@ islice_next(isliceobject *lz)
 	}
 	if (lz->stop != -1 && lz->cnt >= lz->stop)
 		return NULL;
-	assert(PyIter_Check(it));
 	item = iternext(it);
 	if (item == NULL)
 		return NULL;
@@ -1361,7 +1357,6 @@ starmap_next(starmapobject *lz)
 	PyObject *result;
 	PyObject *it = lz->it;
 
-	assert(PyIter_Check(it));
 	args = (*Py_TYPE(it)->tp_iternext)(it);
 	if (args == NULL)
 		return NULL;
@@ -2577,7 +2572,6 @@ ifilter_next(ifilterobject *lz)
 	long ok;
 	PyObject *(*iternext)(PyObject *);
 
-	assert(PyIter_Check(it));
 	iternext = *Py_TYPE(it)->tp_iternext;
 	for (;;) {
 		item = iternext(it);
@@ -2721,7 +2715,6 @@ ifilterfalse_next(ifilterfalseobject *lz)
 	long ok;
 	PyObject *(*iternext)(PyObject *);
 
-	assert(PyIter_Check(it));
 	iternext = *Py_TYPE(it)->tp_iternext;
 	for (;;) {
 		item = iternext(it);
@@ -3059,7 +3052,6 @@ izip_next(izipobject *lz)
 		Py_INCREF(result);
 		for (i=0 ; i < tuplesize ; i++) {
 			it = PyTuple_GET_ITEM(lz->ittuple, i);
-			assert(PyIter_Check(it));
 			item = (*Py_TYPE(it)->tp_iternext)(it);
 			if (item == NULL) {
 				Py_DECREF(result);
@@ -3075,7 +3067,6 @@ izip_next(izipobject *lz)
 			return NULL;
 		for (i=0 ; i < tuplesize ; i++) {
 			it = PyTuple_GET_ITEM(lz->ittuple, i);
-			assert(PyIter_Check(it));
 			item = (*Py_TYPE(it)->tp_iternext)(it);
 			if (item == NULL) {
 				Py_DECREF(result);
@@ -3411,7 +3402,6 @@ izip_longest_next(iziplongestobject *lz)
                                 Py_INCREF(lz->fillvalue);
                                 item = lz->fillvalue;
                         } else {
-                                assert(PyIter_Check(it));
                                 item = (*Py_TYPE(it)->tp_iternext)(it);
                                 if (item == NULL) {
                                         lz->numactive -= 1;      
@@ -3440,7 +3430,6 @@ izip_longest_next(iziplongestobject *lz)
                                 Py_INCREF(lz->fillvalue);
                                 item = lz->fillvalue;
                         } else {
-                                assert(PyIter_Check(it));
                                 item = (*Py_TYPE(it)->tp_iternext)(it);
                                 if (item == NULL) {
                                         lz->numactive -= 1;      
diff --git a/Objects/abstract.c b/Objects/abstract.c
@@ -3067,7 +3067,6 @@ PyObject *
 PyIter_Next(PyObject *iter)
 {
 	PyObject *result;
-	assert(PyIter_Check(iter));
 	result = (*iter->ob_type->tp_iternext)(iter);
 	if (result == NULL &&
 	    PyErr_Occurred() &&
diff --git a/Objects/object.c b/Objects/object.c
@@ -1305,6 +1305,20 @@ PyObject_SelfIter(PyObject *obj)
 	return obj;
 }
 
+/* Helper used when the __next__ method is removed from a type:
+   tp_iternext is never NULL and can be safely called without checking
+   on every iteration.
+ */
+
+PyObject *
+_PyObject_NextNotImplemented(PyObject *self)
+{
+	PyErr_Format(PyExc_TypeError,
+		     "'%.200s' object is not iterable",
+		     Py_TYPE(self)->tp_name);
+	return NULL;
+}
+
 /* Generic GetAttr functions - put these in your tp_[gs]etattro slot */
 
 PyObject *
diff --git a/Objects/typeobject.c b/Objects/typeobject.c
@@ -6090,8 +6090,12 @@ update_one_slot(PyTypeObject *type, slotdef *p)
 	}
 	do {
 		descr = _PyType_Lookup(type, p->name_strobj);
-		if (descr == NULL)
+		if (descr == NULL) {
+			if (ptr == (void**)&type->tp_iternext) {
+				specific = _PyObject_NextNotImplemented;
+			}
 			continue;
+		}
 		if (Py_TYPE(descr) == &PyWrapperDescr_Type) {
 			void **tptr = resolve_slotdups(type, p->name_strobj);
 			if (tptr == NULL || tptr == ptr)

Original file line number	Diff line number	Diff line change
`@@ -3067,7 +3067,6 @@ PyObject *`
`3067`	`3067`	`PyIter_Next(PyObject *iter)`
`3068`	`3068`	`{`
`3069`	`3069`	`PyObject *result;`
`3070`		`- assert(PyIter_Check(iter));`
`3071`	`3070`	`result = (*iter->ob_type->tp_iternext)(iter);`
`3072`	`3071`	`if (result == NULL &&`
`3073`	`3072`	`PyErr_Occurred() &&`