gh-134144: Fix use-after-free in zapthreads() (#134145)

Lib/test/test_interpreters/test_api.py

@@ -1452,6 +1452,14 @@ class LowLevelTests(TestBase):
             self.assertFalse(
                 self.interp_exists(interpid))
 
+        with self.subTest('basic C-API'):
+            interpid = _testinternalcapi.create_interpreter()
+            self.assertTrue(
+                self.interp_exists(interpid))
+            _testinternalcapi.destroy_interpreter(interpid, basic=True)
+            self.assertFalse(
+                self.interp_exists(interpid))
+
     def test_get_config(self):
         # This test overlaps with
         # test.test_capi.test_misc.InterpreterConfigTests.

Misc/NEWS.d/next/C_API/2025-05-17-14-41-21.gh-issue-134144.xVpZik.rst

@@ -0,0 +1 @@
+Fix crash when calling :c:func:`Py_EndInterpreter` with a :term:`thread state` that isn't the initial thread for the interpreter.

Modules/_testinternalcapi.c

@@ -1690,11 +1690,12 @@ create_interpreter(PyObject *self, PyObject *args, PyObject *kwargs)
 static PyObject *
 destroy_interpreter(PyObject *self, PyObject *args, PyObject *kwargs)
 {
-    static char *kwlist[] = {"id", NULL};
+    static char *kwlist[] = {"id", "basic", NULL};
     PyObject *idobj = NULL;
+    int basic = 0;
     if (!PyArg_ParseTupleAndKeywords(args, kwargs,
-                                     "O:destroy_interpreter", kwlist,
+                                     "O|p:destroy_interpreter", kwlist,
-                                     &idobj))
+                                     &idobj, &basic))
     {
         return NULL;
     }
@@ -1704,7 +1705,27 @@ destroy_interpreter(PyObject *self, PyObject *args, PyObject *kwargs)
         return NULL;
     }
 
+    if (basic)
+    {
+        // Test the basic Py_EndInterpreter with weird out of order thread states
+        PyThreadState *t1, *t2;
+        PyThreadState *prev;
+        t1 = interp->threads.head;
+        if (t1 == NULL) {
+            t1 = PyThreadState_New(interp);
+        }
+        t2 = PyThreadState_New(interp);
+        prev = PyThreadState_Swap(t2);
+        PyThreadState_Clear(t1);
+        PyThreadState_Delete(t1);
+        Py_EndInterpreter(t2);
+        PyThreadState_Swap(prev);
+    }
+    else
+    {
+        // use the cross interpreter _PyXI_EndInterpreter normally
         _PyXI_EndInterpreter(interp, NULL, NULL);
+    }
     Py_RETURN_NONE;
 }
 

Python/pystate.c

@@ -1908,9 +1908,14 @@ tstate_delete_common(PyThreadState *tstate, int release_gil)
 static void
 zapthreads(PyInterpreterState *interp)
 {
+    PyThreadState *tstate;
     /* No need to lock the mutex here because this should only happen
-       when the threads are all really dead (XXX famous last words). */
+       when the threads are all really dead (XXX famous last words).
-    _Py_FOR_EACH_TSTATE_UNLOCKED(interp, tstate) {
+
+       Cannot use _Py_FOR_EACH_TSTATE_UNLOCKED because we are freeing
+       the thread states here.
+    */
+    while ((tstate = interp->threads.head) != NULL) {
         tstate_verify_not_active(tstate);
         tstate_delete_common(tstate, 0);
         free_threadstate((_PyThreadStateImpl *)tstate);