Issue #15738: Fix a missing NULL check in subprocess_fork_exec().

Lib/test/test_capi.py

@@ -68,6 +68,16 @@ class CAPITest(unittest.TestCase):
         self.assertRaises(TypeError, _posixsubprocess.fork_exec,
                           1,Z(),3,[1, 2],5,6,7,8,9,10,11,12,13,14,15,16,17)
 
+    @unittest.skipUnless(_posixsubprocess, '_posixsubprocess required for this test.')
+    def test_subprocess_fork_exec(self):
+        class Z(object):
+            def __len__(self):
+                return 1
+
+        # Issue #15738: crash in subprocess_fork_exec()
+        self.assertRaises(TypeError, _posixsubprocess.fork_exec,
+                          Z(),[b'1'],3,[1, 2],5,6,7,8,9,10,11,12,13,14,15,16,17)
+
 @unittest.skipUnless(threading, 'Threading required for this test.')
 class TestPendingCalls(unittest.TestCase):
 

Modules/_posixsubprocess.c

@@ -577,6 +577,8 @@ subprocess_fork_exec(PyObject* self, PyObject *args)
         /* Equivalent to:  */
         /*  tuple(PyUnicode_FSConverter(arg) for arg in process_args)  */
         fast_args = PySequence_Fast(process_args, "argv must be a tuple");
+        if (fast_args == NULL)
+            goto cleanup;
         num_args = PySequence_Fast_GET_SIZE(fast_args);
         converted_args = PyTuple_New(num_args);
         if (converted_args == NULL)