Issue #18426: Fix NULL pointer dereference in C extension import when

PyModule_GetDef() returns an error.

Misc/NEWS

@@ -10,6 +10,9 @@ What's New in Python 3.4.0 Alpha 1?
 Core and Builtins
 -----------------
 
+- Issue #18426: Fix NULL pointer dereference in C extension import when
+  PyModule_GetDef() returns an error.
+
 - Issue #17206: On Windows, increase the stack size from 2 MB to 4.2 MB to fix
   a stack overflow in the marshal module (fix a crash in test_marshal).
   Patch written by Jeremy Kloth.

Python/importdl.c

@@ -97,6 +97,8 @@ _PyImport_LoadDynamicModule(PyObject *name, PyObject *path, FILE *fp)
 
     /* Remember pointer to module init function. */
     def = PyModule_GetDef(m);
+    if (def == NULL)
+        goto error;
     def->m_base.m_init = p;
 
     /* Remember the filename as the __file__ attribute */