gh-124513: Check args in framelocalsproxy_new() (#124515)

Fix a crash in FrameLocalsProxy constructor: check the number of
arguments.

1 files changed, 20 insertions, 3 deletions

diff --git a/Objects/frameobject.c b/Objects/frameobject.c
index 9f1c031..f3a66ff 100644
--- a/Objects/frameobject.c
+++ b/Objects/frameobject.c
@@ -310,14 +310,31 @@ framelocalsproxy_dealloc(PyObject *self)
 static PyObject *
 framelocalsproxy_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
 {
+    if (PyTuple_GET_SIZE(args) != 1) {
+        PyErr_Format(PyExc_TypeError,
+                     "FrameLocalsProxy expected 1 argument, got %zd",
+                     PyTuple_GET_SIZE(args));
+        return NULL;
+    }
+    PyObject *item = PyTuple_GET_ITEM(args, 0);
+
+    if (!PyFrame_Check(item)) {
+        PyErr_Format(PyExc_TypeError, "expect frame, not %T", item);
+        return NULL;
+    }
+    PyFrameObject *frame = (PyFrameObject*)item;
+
+    if (kwds != NULL && PyDict_Size(kwds) != 0) {
+        PyErr_SetString(PyExc_TypeError,
+                        "FrameLocalsProxy takes no keyword arguments");
+        return 0;
+    }
+
     PyFrameLocalsProxyObject *self = (PyFrameLocalsProxyObject *)type->tp_alloc(type, 0);
     if (self == NULL) {
         return NULL;
     }
 
-    PyFrameObject *frame = (PyFrameObject*)PyTuple_GET_ITEM(args, 0);
-    assert(PyFrame_Check(frame));
-
     ((PyFrameLocalsProxyObject*)self)->frame = (PyFrameObject*)Py_NewRef(frame);
 
     return (PyObject *)self;