Issue #24913: Fix overrun error in deque.index().

Lib/test/test_deque.py

@@ -289,6 +289,11 @@ class TestBasic(unittest.TestCase):
                     else:
                         self.assertEqual(d.index(element, start, stop), target)
 
+    def test_insert_bug_24913(self):
+        d = deque('A' * 3)
+        with self.assertRaises(ValueError):
+            i = d.index("Hello world", 0, 4)
+
     def test_insert(self):
         # Test to make sure insert behaves like lists
         elements = 'ABCDEFGHI'

Misc/NEWS

@@ -18,6 +18,9 @@ Library
   header in part headers. Patch written by Peter Landry and reviewed by Pierre
   Quentel.
 
+- Issue #24913: Fix overrun error in deque.index().
+  Found by John Leitch and Bryce Darling.
+
 - Issue #24774: Fix docstring in http.server.test. Patch from Chiu-Hsiang Hsu.
 
 - Issue #21159: Improve message in configparser.InterpolationMissingOptionError.

Modules/_collectionsmodule.c

@@ -924,6 +924,8 @@ deque_index(dequeobject *deque, PyObject *args)
         if (stop < 0)
             stop = 0;
     }
+    if (stop > Py_SIZE(deque))
+        stop = Py_SIZE(deque);
 
     for (i=0 ; i<stop ; i++) {
         if (i >= start) {