gh-115649: Copy the filename into main interpreter before intern in import.c (#120315)

Co-authored-by: Kumar Aditya <[email protected]>

Author: aisk

Lib/test/test_import/__init__.py

@@ -2138,6 +2138,8 @@ def test_single_init_extension_compat(self):
             self.check_incompatible_here(module)
         with self.subTest(f'{module}: strict, fresh'):
             self.check_incompatible_fresh(module)
+        with self.subTest(f'{module}: isolated, fresh'):
+            self.check_incompatible_fresh(module, isolated=True)
 
     @unittest.skipIf(_testmultiphase is None, "test requires _testmultiphase module")
     def test_multi_init_extension_compat(self):

Python/import.c

@@ -1969,7 +1969,17 @@ import_run_extension(PyThreadState *tstate, PyModInitFunction p0,
             if (info->filename != NULL) {
                 // XXX There's a refleak somewhere with the filename.
                 // Until we can track it down, we intern it.
-                PyObject *filename = Py_NewRef(info->filename);
+                PyObject *filename = NULL;
+                if (switched) {
+                    // The original filename may be allocated by subinterpreter's
+                    // obmalloc, so we create a copy here.
+                    filename = _PyUnicode_Copy(info->filename);
+                    if (filename == NULL) {
+                        return NULL;
+                    }
+                } else {
+                    filename = Py_NewRef(info->filename);
+                }
                 PyUnicode_InternInPlace(&filename);
                 if (PyModule_AddObjectRef(mod, "__file__", filename) < 0) {
                     PyErr_Clear(); /* Not important enough to report */