bpo-38383: Fix possible integer overflow in startswith() of bytes and bytearray. (GH-16603)

miss-islington · shihai1991 · web-flow · commit b40442ba88fe · 2019-10-06T05:36:44.000-07:00
(cherry picked from commit 24ddd9c) Co-authored-by: Hai Shi <shihai1992@gmail.com>
diff --git a/Objects/bytes_methods.c b/Objects/bytes_methods.c
@@ -757,7 +757,7 @@ tailmatch(const char *str, Py_ssize_t len, PyObject *substr,
 
     if (direction < 0) {
         /* startswith */
-        if (start + slen > len)
+        if (start > len - slen)
             goto notfound;
     } else {
         /* endswith */
