in scan_once, prevent the reading of arbitrary memory when passed a negative index
Bug reported by Guido Vranken.
diff --git a/Lib/test/json_tests/test_decode.py b/Lib/test/json_tests/test_decode.py
index 15a427f..a3d7b08 100644
--- a/Lib/test/json_tests/test_decode.py
+++ b/Lib/test/json_tests/test_decode.py
@@ -70,5 +70,9 @@
msg = 'escape'
self.assertRaisesRegex(ValueError, msg, self.loads, s)
+ def test_negative_index(self):
+ d = self.json.JSONDecoder()
+ self.assertRaises(ValueError, d.raw_decode, 'a'*42, -50000)
+
class TestPyDecode(TestDecode, PyTest): pass
class TestCDecode(TestDecode, CTest): pass
diff --git a/Misc/ACKS b/Misc/ACKS
index b950474..a932074 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -1139,6 +1139,7 @@
Johannes Vogel
Martijn Vries
Sjoerd de Vries
+Guido Vranken
Niki W. Waibel
Wojtek Walczak
Charles Waldman
diff --git a/Misc/NEWS b/Misc/NEWS
index 3913f94..e44219a 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -10,6 +10,9 @@
Library
-------
+- Fix arbitrary memory access in JSONDecoder.raw_decode with a negative second
+ parameter. Bug reported by Guido Vranken.
+
- Issue #21082: In os.makedirs, do not set the process-wide umask. Note this
changes behavior of makedirs when exist_ok=True.
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;
}