gh-135885: zstd: Use Py_XSETREF

Author: JelleZijlstra

Misc/NEWS.d/next/Library/2025-05-29-06-53-40.gh-issue-134885.-_L22o.rst

@@ -0,0 +1,2 @@
+Fix possible crash in the :mod:`compression.zstd` module related to setting
+parameter types. Patch by Jelle Zijlstra.

Modules/_zstd/_zstdmodule.c

@@ -514,13 +514,10 @@ _zstd_set_parameter_types_impl(PyObject *module, PyObject *c_parameter_type,
         return NULL;
     }
 
-    Py_XDECREF(mod_state->CParameter_type);
-    Py_INCREF(c_parameter_type);
-    mod_state->CParameter_type = (PyTypeObject*)c_parameter_type;
-
-    Py_XDECREF(mod_state->DParameter_type);
-    Py_INCREF(d_parameter_type);
-    mod_state->DParameter_type = (PyTypeObject*)d_parameter_type;
+    Py_XSETREF(
+        mod_state->CParameter_type, Py_NewRef((PyTypeObject*)c_parameter_type));
+    Py_XSETREF(
+        mod_state->DParameter_type, Py_NewRef((PyTypeObject*)d_parameter_type));
 
     Py_RETURN_NONE;
 }