check for error conditions in _json #3623

Lib/json/tests/test_scanstring.py

@@ -2,6 +2,7 @@ import sys
 import decimal
 from unittest import TestCase
 
+import json
 import json.decoder
 
 class TestScanString(TestCase):
@@ -100,3 +101,9 @@ class TestScanString(TestCase):
         self.assertEquals(
             scanstring('["Bad value", truth]', 2, None, True),
             (u'Bad value', 12))
+
+    def test_issue3623(self):
+        self.assertRaises(ValueError, json.decoder.scanstring, b"xxx", 1,
+                          "xxx")
+        self.assertRaises(UnicodeDecodeError,
+                          json.encoder.encode_basestring_ascii, b"xx\xff")

Modules/_json.c

@@ -179,11 +179,13 @@ raise_errmsg(char *msg, PyObject *s, Py_ssize_t end)
         errmsg_fn = PyObject_GetAttrString(decoder, "errmsg");
         if (errmsg_fn == NULL)
             return;
-        Py_XDECREF(decoder);
+        Py_DECREF(decoder);
     }
     pymsg = PyObject_CallFunction(errmsg_fn, "(zOn)", msg, s, end);
-    PyErr_SetObject(PyExc_ValueError, pymsg);
-    Py_DECREF(pymsg);
+    if (pymsg) {
+        PyErr_SetObject(PyExc_ValueError, pymsg);
+        Py_DECREF(pymsg);
+    }
 /*
 
 def linecol(doc, pos):