add a AST validator (closes #12575)

Include/ast.h

@@ -4,6 +4,7 @@
 extern "C" {
 #endif
 
+PyAPI_FUNC(int) PyAST_Validate(mod_ty);
 PyAPI_FUNC(mod_ty) PyAST_FromNode(
     const node *n,
     PyCompilerFlags *flags,

Misc/NEWS

@@ -10,6 +10,8 @@ What's New in Python 3.3 Alpha 1?
 Core and Builtins
 -----------------
 
+- Issue #12575: Validate user-generated AST before it is compiled.
+
 - Make type(None), type(Ellipsis), and type(NotImplemented) callable. They
   return the respective singleton instances.
 

Python/bltinmodule.c

@@ -604,6 +604,10 @@ builtin_compile(PyObject *self, PyObject *args, PyObject *kwds)
                 PyArena_Free(arena);
                 goto error;
             }
+            if (!PyAST_Validate(mod)) {
+                PyArena_Free(arena);
+                goto error;
+            }
             result = (PyObject*)PyAST_CompileEx(mod, filename,
                                                 &cf, optimize, arena);
             PyArena_Free(arena);