commit 99b5afab74428e5ddfd877bdf3aa8a8c479696b1
author Benjamin Peterson <benjamin@python.org> Sun Apr 13 22:10:38 2014 -0400
committer Benjamin Peterson <benjamin@python.org> Sun Apr 13 22:10:38 2014 -0400
tree 44293ac5d0a038577e6d671f2488126ef3cab7eb
parent 80e6af1f61f2d63ff45ada00be841db9ad5e6c9f

in scan_once, prevent the reading of arbitrary memory when passed a negative index

Bug reported by Guido Vranken.

Modules/_json.c

diff --git a/Modules/_json.c b/Modules/_json.c
index 01436b6..5bd52cb 100644
--- a/Modules/_json.c
+++ b/Modules/_json.c
@@ -930,7 +930,10 @@
     PyObject *res;
     Py_UNICODE *str = PyUnicode_AS_UNICODE(pystr);
     Py_ssize_t length = PyUnicode_GET_SIZE(pystr);
-    if (idx >= length) {
+    if (idx < 0)
+        /* Compatibility with Python version. */
+        idx += length;
+    if (idx < 0 || idx >= length) {
         PyErr_SetNone(PyExc_StopIteration);
         return NULL;
     }