[3.8] bpo-39453: Fix contains method of list to hold strong references (GH-18204)

diff --git a/Lib/test/test_list.py b/Lib/test/test_list.py
index f4dcced9c167f858d780d834f378bba8d46f5a53..105ef650eee99e9d2686b4372298963b8fdb59c3 100644 (file)
--- a/Lib/test/test_list.py
+++ b/Lib/test/test_list.py
@@ -216,6 +216,13 @@ class ListTest(list_tests.CommonTest):
         with self.assertRaises(ValueError):
             lst.remove(lst)
 
+        # bpo-39453: list.__contains__ was not holding strong references
+        # to list elements while calling PyObject_RichCompareBool().
+        lst = [X(), X()]
+        3 in lst
+        lst = [X(), X()]
+        X() in lst
+
 
 if __name__ == "__main__":
     unittest.main()

diff --git a/Misc/NEWS.d/next/Core and Builtins/2020-01-25-23-51-17.bpo-39453.xCOkYk.rst b/Misc/NEWS.d/next/Core and Builtins/2020-01-25-23-51-17.bpo-39453.xCOkYk.rst
new file mode 100644 (file)
index 0000000..8c2e49f
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2020-01-25-23-51-17.bpo-39453.xCOkYk.rst
@@ -0,0 +1,2 @@
+Fixed a possible crash in :meth:`list.__contains__` when a list is changed
+during comparing items. Patch by Dong-hee Na.

diff --git a/Objects/listobject.c b/Objects/listobject.c
index 73afc44c39e36ea2b6e73a74e925d8aec0d68514..30444089ffaf96122b581dff08caf8a25f5d8311 100644 (file)
--- a/Objects/listobject.c
+++ b/Objects/listobject.c
@@ -445,12 +445,16 @@ list_length(PyListObject *a)
 static int
 list_contains(PyListObject *a, PyObject *el)
 {
+    PyObject *item;
     Py_ssize_t i;
     int cmp;
 
-    for (i = 0, cmp = 0 ; cmp == 0 && i < Py_SIZE(a); ++i)
-        cmp = PyObject_RichCompareBool(el, PyList_GET_ITEM(a, i),
-                                           Py_EQ);
+    for (i = 0, cmp = 0 ; cmp == 0 && i < Py_SIZE(a); ++i) {
+        item = PyList_GET_ITEM(a, i);
+        Py_INCREF(item);
+        cmp = PyObject_RichCompareBool(el, item, Py_EQ);
+        Py_DECREF(item);
+    }
     return cmp;
 }