bpo-42990: Functions inherit current builtins (GH-24564)

The types.FunctionType constructor now inherits the current builtins
if the globals dictionary has no "__builtins__" key, rather than
using {"None": None} as builtins: same behavior as eval() and exec()
functions.

Defining a function with "def function(...): ..." in Python is not
affected, globals cannot be overriden with this syntax: it also
inherits the current builtins.

PyFrame_New(), PyEval_EvalCode(), PyEval_EvalCodeEx(),
PyFunction_New() and PyFunction_NewWithQualName() now inherits the
current builtins namespace if the globals dictionary has no
"__builtins__" key.

* Add _PyEval_GetBuiltins() function.
* _PyEval_BuiltinsFromGlobals() now uses _PyEval_GetBuiltins() if
  builtins cannot be found in globals.
* Add tstate parameter to _PyEval_BuiltinsFromGlobals().

1 files changed, 4 insertions, 15 deletions

diff --git a/Objects/frameobject.c b/Objects/frameobject.c
index 0571bfe..056d42a 100644
--- a/Objects/frameobject.c
+++ b/Objects/frameobject.c
@@ -847,7 +847,7 @@ PyFrameObject*
 PyFrame_New(PyThreadState *tstate, PyCodeObject *code,
             PyObject *globals, PyObject *locals)
 {
-    PyObject *builtins = _PyEval_BuiltinsFromGlobals(globals);
+    PyObject *builtins = _PyEval_BuiltinsFromGlobals(tstate, globals);
     if (builtins == NULL) {
         return NULL;
     }
@@ -862,7 +862,6 @@ PyFrame_New(PyThreadState *tstate, PyCodeObject *code,
         .fc_closure = NULL
     };
     PyFrameObject *f = _PyFrame_New_NoTrack(tstate, &desc, locals);
-    Py_DECREF(builtins);
     if (f) {
         _PyObject_GC_TRACK(f);
     }
@@ -1163,7 +1162,7 @@ PyFrame_GetBack(PyFrameObject *frame)
 }
 
 PyObject*
-_PyEval_BuiltinsFromGlobals(PyObject *globals)
+_PyEval_BuiltinsFromGlobals(PyThreadState *tstate, PyObject *globals)
 {
     PyObject *builtins = _PyDict_GetItemIdWithError(globals, &PyId___builtins__);
     if (builtins) {
@@ -1171,21 +1170,11 @@ _PyEval_BuiltinsFromGlobals(PyObject *globals)
             builtins = PyModule_GetDict(builtins);
             assert(builtins != NULL);
         }
-        return Py_NewRef(builtins);
+        return builtins;
     }
-
     if (PyErr_Occurred()) {
         return NULL;
     }
 
-    /* No builtins! Make up a minimal one. Give them 'None', at least. */
-    builtins = PyDict_New();
-    if (builtins == NULL) {
-        return NULL;
-    }
-    if (PyDict_SetItemString(builtins, "None", Py_None) < 0) {
-        Py_DECREF(builtins);
-        return NULL;
-    }
-    return builtins;
+    return _PyEval_GetBuiltins(tstate);
 }