[3.13] gh-154275: Do not crash on deeply nested `__parameters__` in `GenericAlias` (GH-154277) (#154340)

https://github.com/python/cpython/commit/09424550211089b059ff9ca255ee2e7e9aacc866
commit: 09424550211089b059ff9ca255ee2e7e9aacc866
branch: 3.13
author: sobolevn <[email protected]>
committer: sobolevn <[email protected]>
date: 2026-07-21T10:29:57Z
summary:

[3.13] gh-154275: Do not crash on deeply nested `__parameters__` in `GenericAlias` (GH-154277) (#154340)

* [3.13] gh-154275: Do not crash on deeply nested `__parameters__` in `GenericAlias` (GH-154277)
(cherry picked from commit 1034e07b7d55642c3a46252e6b0a631c2df588d2)

Co-authored-by: sobolevn <[email protected]>

files:
A Misc/NEWS.d/next/Core_and_Builtins/2026-07-20-20-16-08.gh-issue-154275.l961cA.rst
M Objects/genericaliasobject.c

diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2026-07-20-20-16-08.gh-issue-154275.l961cA.rst b/Misc/NEWS.d/next/Core_and_Builtins/2026-07-20-20-16-08.gh-issue-154275.l961cA.rst
new file mode 100644
index 000000000000000..998e91c77098e75
--- /dev/null
+++ b/Misc/NEWS.d/next/Core_and_Builtins/2026-07-20-20-16-08.gh-issue-154275.l961cA.rst
@@ -0,0 +1,2 @@
+Fix a crash when getting deeply nested ``__parameters__`` from a
+:class:`types.GenericAlias` objects.
diff --git a/Objects/genericaliasobject.c b/Objects/genericaliasobject.c
index 157facd16a7e64f..fb959dcefd8ad09 100644
--- a/Objects/genericaliasobject.c
+++ b/Objects/genericaliasobject.c
@@ -244,11 +244,16 @@ tuple_extend(PyObject **dst, Py_ssize_t dstindex,
 PyObject *
 _Py_make_parameters(PyObject *args)
 {
+    if (Py_EnterRecursiveCall(" in __parameter__ calculation")) {
+        return NULL;
+    }
+
     Py_ssize_t nargs = PyTuple_GET_SIZE(args);
     Py_ssize_t len = nargs;
     PyObject *parameters = PyTuple_New(len);
-    if (parameters == NULL)
-        return NULL;
+    if (parameters == NULL) {
+        goto cleanup;
+    }
     Py_ssize_t iparam = 0;
     for (Py_ssize_t iarg = 0; iarg < nargs; iarg++) {
         PyObject *t = PyTuple_GET_ITEM(args, iarg);
@@ -258,8 +263,7 @@ _Py_make_parameters(PyObject *args)
         }
         int rc = PyObject_HasAttrWithError(t, &_Py_ID(__typing_subst__));
         if (rc < 0) {
-            Py_DECREF(parameters);
-            return NULL;
+            goto error;
         }
         if (rc) {
             iparam += tuple_add(parameters, iparam, t);
@@ -268,8 +272,7 @@ _Py_make_parameters(PyObject *args)
             PyObject *subparams;
             if (PyObject_GetOptionalAttr(t, &_Py_ID(__parameters__),
                                      &subparams) < 0) {
-                Py_DECREF(parameters);
-                return NULL;
+                goto error;
             }
             if (subparams && PyTuple_Check(subparams)) {
                 Py_ssize_t len2 = PyTuple_GET_SIZE(subparams);
@@ -278,7 +281,7 @@ _Py_make_parameters(PyObject *args)
                     len += needed;
                     if (_PyTuple_Resize(&parameters, len) < 0) {
                         Py_DECREF(subparams);
-                        return NULL;
+                        goto cleanup;
                     }
                 }
                 for (Py_ssize_t j = 0; j < len2; j++) {
@@ -291,11 +294,17 @@ _Py_make_parameters(PyObject *args)
     }
     if (iparam < len) {
         if (_PyTuple_Resize(&parameters, iparam) < 0) {
-            Py_XDECREF(parameters);
-            return NULL;
+            goto error;
         }
     }
+    Py_LeaveRecursiveCall();
     return parameters;
+
+error:
+    Py_XDECREF(parameters);
+cleanup:
+    Py_LeaveRecursiveCall();
+    return NULL;
 }
 
 /* If obj is a generic alias, substitute type variables params

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