in scan_once, prevent the reading of arbitrary memory when passed a negative index
Bug reported by Guido Vranken.
diff --git a/Lib/json/tests/test_decode.py b/Lib/json/tests/test_decode.py
index ffd1aa4..78d7fbb 100644
--- a/Lib/json/tests/test_decode.py
+++ b/Lib/json/tests/test_decode.py
@@ -60,5 +60,10 @@
msg = 'escape'
self.assertRaisesRegexp(ValueError, msg, self.loads, s)
+ def test_negative_index(self):
+ d = self.json.JSONDecoder()
+ self.assertRaises(ValueError, d.raw_decode, 'a'*42, -50000)
+ self.assertRaises(ValueError, d.raw_decode, u'a'*42, -50000)
+
class TestPyDecode(TestDecode, PyTest): pass
class TestCDecode(TestDecode, CTest): pass
diff --git a/Misc/ACKS b/Misc/ACKS
index 2fd7e33..a618002 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -1369,6 +1369,7 @@
Frank Visser
Johannes Vogel
Alex Volkov
+Guido Vranken
Martijn Vries
Sjoerd de Vries
Niki W. Waibel
diff --git a/Misc/NEWS b/Misc/NEWS
index 7fef5b5..79eaada 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -43,6 +43,9 @@
Library
-------
+- Fix arbitrary memory access in JSONDecoder.raw_decode with a negative second
+ parameter. Bug reported by Guido Vranken.
+
- Issue #21172: isinstance check relaxed from dict to collections.Mapping.
- Issue #21191: In os.fdopen, alwyas close the file descriptor when an exception
diff --git a/Modules/_json.c b/Modules/_json.c
index eb4368a..56d9ee4 100644
--- a/Modules/_json.c
+++ b/Modules/_json.c
@@ -1468,7 +1468,10 @@
PyObject *res;
char *str = PyString_AS_STRING(pystr);
Py_ssize_t length = PyString_GET_SIZE(pystr);
- if (idx >= length) {
+ if (idx < 0)
+ /* Compatibility with the Python version. */
+ idx += length;
+ if (idx < 0 || idx >= length) {
PyErr_SetNone(PyExc_StopIteration);
return NULL;
}
@@ -1555,7 +1558,10 @@
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;
}