GH-140590: Fix setstate for functools.partial C-module (GH-140671)

Co-authored-by: Mikhail Efimov <efimov.mikhail@gmail.com>

Author: sergey-miryanov

Lib/test/test_functools.py

@@ -406,13 +406,16 @@ def test_setstate(self):
 
     def test_setstate_errors(self):
         f = self.partial(signature)
+
         self.assertRaises(TypeError, f.__setstate__, (capture, (), {}))
         self.assertRaises(TypeError, f.__setstate__, (capture, (), {}, {}, None))
         self.assertRaises(TypeError, f.__setstate__, [capture, (), {}, None])
         self.assertRaises(TypeError, f.__setstate__, (None, (), {}, None))
         self.assertRaises(TypeError, f.__setstate__, (capture, None, {}, None))
         self.assertRaises(TypeError, f.__setstate__, (capture, [], {}, None))
         self.assertRaises(TypeError, f.__setstate__, (capture, (), [], None))
+        self.assertRaises(TypeError, f.__setstate__, (capture, (), {}, ()))
+        self.assertRaises(TypeError, f.__setstate__, (capture, (), {}, 'test'))
 
     def test_setstate_subclasses(self):
         f = self.partial(signature)

Misc/NEWS.d/next/Library/2025-10-27-18-29-42.gh-issue-140590.LT9HHn.rst

@@ -0,0 +1,2 @@
+Fix arguments checking for the :meth:`!functools.partial.__setstate__` that
+may lead to internal state corruption and crash. Patch by Sergey Miryanov.

Modules/_functoolsmodule.c

@@ -778,7 +778,8 @@ partial_setstate(PyObject *self, PyObject *state)
     if (!PyArg_ParseTuple(state, "OOOO", &fn, &fnargs, &kw, &dict) ||
         !PyCallable_Check(fn) ||
         !PyTuple_Check(fnargs) ||
-        (kw != Py_None && !PyDict_Check(kw)))
+        (kw != Py_None && !PyDict_Check(kw)) ||
+        (dict != Py_None && !PyDict_Check(dict)))
     {
         PyErr_SetString(PyExc_TypeError, "invalid partial state");
         return NULL;