Ready ThreadCanary_Type

Author: emontnemery

src/c/misc_thread_common.h

@@ -265,6 +265,13 @@ static PyTypeObject ThreadCanary_Type = {
 
 static void init_cffi_tls_zombie(void)
 {
+    /* thread_canary objects are created with PyObject_New(&ThreadCanary_Type);
+       the type must be readied so it has a valid metatype (ob_type). Otherwise
+       introspection of a canary from another module dereferences a NULL metatype
+       and crashes. */
+    if (PyType_Ready(&ThreadCanary_Type) < 0)
+        return;  /* error set; PyInit__cffi_backend checks PyErr_Occurred() */
+
     cffi_zombie_head.zombie_next = &cffi_zombie_head;
     cffi_zombie_head.zombie_prev = &cffi_zombie_head;
     cffi_zombie_lock = PyThread_allocate_lock();