[3.13] gh-144100: Fix crash for POINTER(str) used in ctypes argtypes (#144108) (#144245)

gh-144100: Fix crash for POINTER(str) used in ctypes argtypes (#144108)


(cherry picked from commit 8f45925)

Co-authored-by: VanshAgarwal24036 <148854295+VanshAgarwal24036@users.noreply.github.com>

Author: vstinner

Lib/test/test_ctypes/test_pointers.py

@@ -235,6 +235,17 @@ class C(Structure):
         ptr.set_type(c_int)
         self.assertIs(ptr._type_, c_int)
 
+    def test_pointer_proto_missing_argtypes_error(self):
+        class BadType(ctypes._Pointer):
+            # _type_ is intentionally missing
+            pass
+
+        func = ctypes.pythonapi.Py_GetVersion
+        func.argtypes = (BadType,)
+
+        with self.assertRaises(ctypes.ArgumentError):
+            func(object())
+
 
 if __name__ == '__main__':
     unittest.main()

Misc/NEWS.d/next/Library/2026-01-21-19-39-07.gh-issue-144100.hLMZ8Y.rst

@@ -0,0 +1,3 @@
+Fixed a crash in ctypes when using a deprecated ``POINTER(str)`` type in
+``argtypes``. Instead of aborting, ctypes now raises a proper Python
+exception when the pointer target type is unresolved.

Modules/_ctypes/_ctypes.c

@@ -1338,7 +1338,13 @@ PyCPointerType_from_param_impl(PyObject *type, PyTypeObject *cls,
     /* If we expect POINTER(<type>), but receive a <type> instance, accept
        it by calling byref(<type>).
     */
-    assert(typeinfo->proto);
+    if (typeinfo->proto == NULL) {
+        PyErr_SetString(
+            PyExc_TypeError,
+            "cannot convert argument: POINTER _type_ type is not set"
+        );
+        return NULL;
+    }
     switch (PyObject_IsInstance(value, typeinfo->proto)) {
     case 1:
         Py_INCREF(value); /* _byref steals a refcount */