[3.13] gh-130851: Only intern constants of types generated by the compiler (GH-130901) (#130953)

colesbury · web-flow · commit 14230cd96cd9 · 2025-03-08T13:07:39.000-05:00
The free-threading build interns and immortalizes most constants generated by the bytecode compiler. However, users can construct their own code objects with arbitrary constants. We should not intern or immortalize these objects if they are not of a type that we know how to handle. This change fixes a reference leak failure in the recently added `test_code.test_unusual_constants` test. It also addresses a potential crash that could occur when attempting to destroy an immortalized object during interpreter shutdown. (cherry picked from commit 12db452)
diff --git a/Objects/codeobject.c b/Objects/codeobject.c
@@ -132,6 +132,38 @@ should_intern_string(PyObject *o)
 
 #ifdef Py_GIL_DISABLED
 static PyObject *intern_one_constant(PyObject *op);
+
+// gh-130851: In the free threading build, we intern and immortalize most
+// constants, except code objects. However, users can generate code objects
+// with arbitrary co_consts. We don't want to immortalize or intern unexpected
+// constants or tuples/sets containing unexpected constants.
+static int
+should_immortalize_constant(PyObject *v)
+{
+    // Only immortalize containers if we've already immortalized all their
+    // elements.
+    if (PyTuple_CheckExact(v)) {
+        for (Py_ssize_t i = PyTuple_GET_SIZE(v); --i >= 0; ) {
+            if (!_Py_IsImmortal(PyTuple_GET_ITEM(v, i))) {
+                return 0;
+            }
+        }
+        return 1;
+    }
+    else if (PyFrozenSet_CheckExact(v)) {
+        PyObject *item;
+        Py_hash_t hash;
+        Py_ssize_t pos = 0;
+        while (_PySet_NextEntry(v, &pos, &item, &hash)) {
+            if (!_Py_IsImmortal(item)) {
+                return 0;
+            }
+        }
+        return 1;
+    }
+    return (PyLong_CheckExact(v) || PyFloat_CheckExact(v) ||
+            PyComplex_Check(v) || PyBytes_CheckExact(v));
+}
 #endif
 
 static int
@@ -240,8 +272,8 @@ intern_constants(PyObject *tuple, int *modified)
         // we are also immortalizing objects that use deferred reference
         // counting.
         PyThreadState *tstate = PyThreadState_GET();
-        if (!_Py_IsImmortal(v) && !PyCode_Check(v) &&
-            !PyUnicode_CheckExact(v) &&
+        if (!_Py_IsImmortal(v) && !PyUnicode_CheckExact(v) &&
+            should_immortalize_constant(v) &&
             _Py_atomic_load_int(&tstate->interp->gc.immortalize) >= 0)
         {
             PyObject *interned = intern_one_constant(v);
