gh-96821: Fix undefined behaviour in _testcapimodule.c (GH-96915)

matthiasgoergens · CAM-Gerlach · web-flow · commit cbdeda8ce7a3 · 2022-09-19T15:59:13.000+08:00
* gh-96821: Assert for demonstrating undefined behaviour * Fix UB Co-authored-by: C.A.M. Gerlach <CAM.Gerlach@Gerlach.CAM>
diff --git a/Misc/NEWS.d/next/Core and Builtins/2022-09-18-08-47-40.gh-issue-96821.Co2iOq.rst b/Misc/NEWS.d/next/Core and Builtins/2022-09-18-08-47-40.gh-issue-96821.Co2iOq.rst
@@ -0,0 +1 @@
+Fix undefined behaviour in ``_testcapimodule.c``.
diff --git a/Modules/_testcapimodule.c b/Modules/_testcapimodule.c
@@ -4918,8 +4918,10 @@ meth_fastcall_keywords(PyObject* self, PyObject* const* args,
     if (pyargs == NULL) {
         return NULL;
     }
+    assert(args != NULL || nargs == 0);
+    PyObject* const* args_offset = args == NULL ? NULL : args + nargs;
     PyObject *pykwargs = PyObject_Vectorcall((PyObject*)&PyDict_Type,
-                                              args + nargs, 0, kwargs);
+                                              args_offset, 0, kwargs);
     return Py_BuildValue("NNN", _null_to_none(self), pyargs, pykwargs);
 }
 

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1 @@`
	`1`	+Fix undefined behaviour in ``_testcapimodule.c``.
Original file line number	Diff line number	Diff line change
`@@ -4918,8 +4918,10 @@ meth_fastcall_keywords(PyObject* self, PyObject* const* args,`
`4918`	`4918`	`if (pyargs == NULL) {`
`4919`	`4919`	`return NULL;`
`4920`	`4920`	`}`
	`4921`	`+ assert(args != NULL \|\| nargs == 0);`
	`4922`	`+ PyObject* const* args_offset = args == NULL ? NULL : args + nargs;`
`4921`	`4923`	`PyObject pykwargs = PyObject_Vectorcall((PyObject)&PyDict_Type,`
`4922`		`- args + nargs, 0, kwargs);`
	`4924`	`+ args_offset, 0, kwargs);`
`4923`	`4925`	`return Py_BuildValue("NNN", _null_to_none(self), pyargs, pykwargs);`
`4924`	`4926`	`}`
`4925`	`4927`