gh-142554: avoid `divmod` crashes due to bad `_pylong.int_divmod` (#142673)

diff --git a/Lib/test/test_int.py b/Lib/test/test_int.py
index 7a7cb73f67378782437535169dba015d215b7287..fa675f626cbe109d8f75741da6d0028f7cfaf3e6 100644 (file)
--- a/Lib/test/test_int.py
+++ b/Lib/test/test_int.py
@@ -778,6 +778,18 @@ class PyLongModuleTests(unittest.TestCase):
         a, b = divmod(n*3 + 1, n)
         assert a == 3 and b == 1
 
+    @support.cpython_only  # tests implementation details of CPython.
+    @unittest.skipUnless(_pylong, "_pylong module required")
+    def test_pylong_int_divmod_crash(self):
+        # Regression test for https://github.com/python/cpython/issues/142554.
+        bad_int_divmod = lambda a, b: (1,)
+        # 'k' chosen such that divmod(2**(2*k), 2**k) uses _pylong.int_divmod()
+        k = 10_000
+        a, b = (1 << (2 * k)), (1 << k)
+        with mock.patch.object(_pylong, "int_divmod", wraps=bad_int_divmod):
+            msg = r"tuple of length 2 is required from int_divmod\(\)"
+            self.assertRaisesRegex(ValueError, msg, divmod, a, b)
+
     def test_pylong_str_to_int(self):
         v1 = 1 << 100_000
         s = str(v1)

diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2025-12-13-17-20-38.gh-issue-142554.wNtEFF.rst b/Misc/NEWS.d/next/Core_and_Builtins/2025-12-13-17-20-38.gh-issue-142554.wNtEFF.rst
new file mode 100644 (file)
index 0000000..d0aafe2
--- /dev/null
+++ b/Misc/NEWS.d/next/Core_and_Builtins/2025-12-13-17-20-38.gh-issue-142554.wNtEFF.rst
@@ -0,0 +1,2 @@
+Fix a crash in :func:`divmod` when :func:`!_pylong.int_divmod` does not
+return a tuple of length two exactly. Patch by Bénédikt Tran.

diff --git a/Objects/longobject.c b/Objects/longobject.c
index 43c0db753a0fb9f6e0d74d1307c07d3e6744cbcf..8ba1fd65078f488518e8e6942bc7479428f13e1a 100644 (file)
--- a/Objects/longobject.c
+++ b/Objects/longobject.c
@@ -4434,10 +4434,10 @@ pylong_int_divmod(PyLongObject *v, PyLongObject *w,
     if (result == NULL) {
         return -1;
     }
-    if (!PyTuple_Check(result)) {
+    if (!PyTuple_Check(result) || PyTuple_GET_SIZE(result) != 2) {
         Py_DECREF(result);
         PyErr_SetString(PyExc_ValueError,
-                        "tuple is required from int_divmod()");
+                        "tuple of length 2 is required from int_divmod()");
         return -1;
     }
     PyObject *q = PyTuple_GET_ITEM(result, 0);