gh-156204: Guard recursion in PyErr_GivenExceptionMatches

Lib/test/test_exceptions.py

@@ -2778,6 +2778,30 @@ def test_except_star_invalid_exception_type(self):
             except (ValueError, 42):
                 pass
 
+    @cpython_only
+    @unittest.skipIf(_testcapi is None, "requires _testcapi")
+    def test_given_exception_matches_nested_tuple(self):
+        # Nested tuples are searched recursively.
+        self.assertTrue(
+            _testcapi.err_givenexceptionmatches(ValueError(), ((ValueError,),)))
+        self.assertFalse(
+            _testcapi.err_givenexceptionmatches(TypeError(), ((ValueError,),)))
+
+    @cpython_only
+    @unittest.skipIf(_testcapi is None, "requires _testcapi")
+    @support.skip_emscripten_stack_overflow()
+    @support.skip_wasi_stack_overflow()
+    @support.run_with_limited_c_stack(depth=500_000)
+    def test_given_exception_matches_deeply_nested_tuple(self):
+        # gh-156204: PyErr_GivenExceptionMatches() used to exhaust the C stack
+        # and crash the interpreter on deeply nested tuples of exception types.
+        tup = (ValueError,)
+        for _ in range(500_000):
+            tup = (tup,)
+
+        with self.assertRaises(RecursionError):
+            _testcapi.err_givenexceptionmatches(TypeError(), tup)
+
 
 class PEP626Tests(unittest.TestCase):
 

Misc/NEWS.d/next/Core_and_Builtins/2026-08-21-18-49-12.gh-issue-156204.ZusA7e.rst

@@ -0,0 +1,3 @@
+Fix unhandled recursion error in :c:func:`PyErr_GivenExceptionMatches` when
+evaluating deeply nested exception tuples, preventing crashes caused by
+stack exhaustion.

Modules/_testcapi/exceptions.c

@@ -54,6 +54,24 @@ err_restore(PyObject *self, PyObject *args) {
     return NULL;
 }
 
+static PyObject *
+err_givenexceptionmatches(PyObject *Py_UNUSED(module), PyObject *args)
+{
+    PyObject *err, *exc;
+    if (!PyArg_ParseTuple(args, "OO", &err, &exc)) {
+        return NULL;
+    }
+    assert(!PyErr_Occurred());
+    int res = PyErr_GivenExceptionMatches(err, exc);
+    /* PyErr_GivenExceptionMatches() has no failure return value, but it can
+     * set RecursionError on a deeply nested tuple; report that to the caller.
+     */
+    if (res == 0 && PyErr_Occurred()) {
+        return NULL;
+    }
+    return PyBool_FromLong(res);
+}
+
 /*[clinic input]
 _testcapi.exception_print
     exception as exc: object
@@ -544,6 +562,7 @@ static PyTypeObject PyRecursingInfinitelyError_Type = {
 
 static PyMethodDef test_methods[] = {
     {"err_restore",             err_restore,                     METH_VARARGS},
+    {"err_givenexceptionmatches", err_givenexceptionmatches,     METH_VARARGS},
     {"err_writeunraisable",     err_writeunraisable,             METH_VARARGS},
     {"err_formatunraisable",    err_formatunraisable,            METH_VARARGS},
     _TESTCAPI_ERR_SET_RAISED_METHODDEF

Python/errors.c

@@ -335,17 +335,20 @@ PyErr_GivenExceptionMatches(PyObject *err, PyObject *exc)
         return 0;
     }
     if (PyTuple_Check(exc)) {
-        Py_ssize_t i, n;
-        n = PyTuple_Size(exc);
-        for (i = 0; i < n; i++) {
+        if (Py_EnterRecursiveCall(" in PyErr_GivenExceptionMatches")) {
+            return 0;
+        }
+        int res = 0;
+        Py_ssize_t n = PyTuple_GET_SIZE(exc);
+        for (Py_ssize_t i = 0; i < n; i++) {
             /* Test recursively */
-             if (PyErr_GivenExceptionMatches(
-                 err, PyTuple_GET_ITEM(exc, i)))
-             {
-                 return 1;
-             }
+            if (PyErr_GivenExceptionMatches(err, PyTuple_GET_ITEM(exc, i))) {
+                res = 1;
+                break;
+            }
         }
-        return 0;
+        Py_LeaveRecursiveCall();
+        return res;
     }
     /* err might be an instance, so check its class. */
     if (PyExceptionInstance_Check(err))