ctypes: fix CThunkObject_new()

* Initialize restype and flags fields to fix a crash when Python runs on a
  read-only file system
* Use Py_ssize_t type rather than int for the "i" iterator variable
* Reorder assignements to be able to more easily check if all fields are
  initialized

Issue #11048. Initial patch written by Marcin Bachry.

diff --git a/Modules/_ctypes/callbacks.c b/Modules/_ctypes/callbacks.c
index 7cd61640f819ed32b976340f49564f5e11e3458a..91413d7dbf03f059bbd0ec14cf69dcdf01af4183 100644 (file)
--- a/Modules/_ctypes/callbacks.c
+++ b/Modules/_ctypes/callbacks.c
@@ -305,7 +305,7 @@ static void closure_fcn(ffi_cif *cif,
 static CThunkObject* CThunkObject_new(Py_ssize_t nArgs)
 {
     CThunkObject *p;
-    int i;
+    Py_ssize_t i;
 
     p = PyObject_GC_NewVar(CThunkObject, &PyCThunk_Type, nArgs);
     if (p == NULL) {
@@ -313,11 +313,13 @@ static CThunkObject* CThunkObject_new(Py_ssize_t nArgs)
         return NULL;
     }
 
-    p->pcl_exec = NULL;
     p->pcl_write = NULL;
+    p->pcl_exec = NULL;
     memset(&p->cif, 0, sizeof(p->cif));
+    p->flags = 0;
     p->converters = NULL;
     p->callable = NULL;
+    p->restype = NULL;
     p->setfunc = NULL;
     p->ffi_restype = NULL;