From 68874a8502da440a1dc4746cf73262648b870aee Mon Sep 17 00:00:00 2001
From: Batuhan Taskaya <isidentical@gmail.com>
Date: Sat, 6 Jun 2020 15:44:16 +0300
Subject: bpo-40870: Invalidate usage of some constants with ast.Name
 (GH-20649)

---
 Python/ast.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

(limited to 'Python/ast.c')

diff --git a/Python/ast.c b/Python/ast.c
index c524b8e34e8..408591f3253 100644
--- a/Python/ast.c
+++ b/Python/ast.c
@@ -21,6 +21,25 @@ static int validate_nonempty_seq(asdl_seq *, const char *, const char *);
 static int validate_stmt(stmt_ty);
 static int validate_expr(expr_ty, expr_context_ty);
 
+static int
+validate_name(PyObject *name)
+{
+    assert(PyUnicode_Check(name));
+    static const char * const forbidden[] = {
+        "None",
+        "True",
+        "False",
+        NULL
+    };
+    for (int i = 0; forbidden[i] != NULL; i++) {
+        if (_PyUnicode_EqualToASCIIString(name, forbidden[i])) {
+            PyErr_Format(PyExc_ValueError, "Name node can't be used with '%s' constant", forbidden[i]);
+            return 0;
+        }
+    }
+    return 1;
+}
+
 static int
 validate_comprehension(asdl_seq *gens)
 {
@@ -173,6 +192,9 @@ validate_expr(expr_ty exp, expr_context_ty ctx)
         actual_ctx = exp->v.Starred.ctx;
         break;
     case Name_kind:
+        if (!validate_name(exp->v.Name.id)) {
+            return 0;
+        }
         actual_ctx = exp->v.Name.ctx;
         break;
     case List_kind:
-- 
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