From 7511047125c543841f0b776de9ac39e27b52c10a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Tomasz=20Mi=C4=85sko?= <>
Date: Wed, 25 Oct 2017 00:00:00 +0000
Subject: [PATCH] Fix null pointer dereference in dbm.ndbm get.

Change the default value in ndbm get method to None from b''.
Previous default used to be represented with C value of NULL,
and lead to a null pointer dereference when it was actually returned.
This also makes the default values consistent with other implementations
of dbm module.
---
 Lib/test/test_dbm_ndbm.py     | 4 ++++
 Modules/_dbmmodule.c          | 4 ++--
 Modules/clinic/_dbmmodule.c.h | 6 +++---
 3 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/Lib/test/test_dbm_ndbm.py b/Lib/test/test_dbm_ndbm.py
index 49f4426e4c..bc45b8b6b4 100644
--- a/Lib/test/test_dbm_ndbm.py
+++ b/Lib/test/test_dbm_ndbm.py
@@ -25,6 +25,10 @@ class DbmTestCase(unittest.TestCase):
         self.assertIn('a', self.d)
         self.assertIn(b'a', self.d)
         self.assertEqual(self.d[b'bytes'], b'data')
+        self.assertIsNone(self.d.get(b'xxx'))
+        self.assertEqual(self.d.get(b'xxx', b'foo'), b'foo')
+        self.assertEqual(self.d.setdefault(b'xxx', b'foo'), b'foo')
+        self.assertEqual(self.d[b'xxx'], b'foo')
         self.d.close()
 
     def test_modes(self):
diff --git a/Modules/_dbmmodule.c b/Modules/_dbmmodule.c
index 7e1344177b..f6c7846822 100644
--- a/Modules/_dbmmodule.c
+++ b/Modules/_dbmmodule.c
@@ -274,7 +274,7 @@ static PySequenceMethods dbm_as_sequence = {
 _dbm.dbm.get
 
     key: str(accept={str, robuffer}, zeroes=True)
-    default: object(c_default="NULL") = b''
+    default: object = None
     /
 
 Return the value for key if present, otherwise default.
@@ -283,7 +283,7 @@ Return the value for key if present, otherwise default.
 static PyObject *
 _dbm_dbm_get_impl(dbmobject *self, const char *key,
                   Py_ssize_clean_t key_length, PyObject *default_value)
-/*[clinic end generated code: output=b44f95eba8203d93 input=a3a279957f85eb6d]*/
+/*[clinic end generated code: output=b44f95eba8203d93 input=b788eba0ffad2e91]*/
 /*[clinic end generated code: output=4f5c0e523eaf1251 input=9402c0af8582dc69]*/
 {
     datum dbm_key, val;
diff --git a/Modules/clinic/_dbmmodule.c.h b/Modules/clinic/_dbmmodule.c.h
index c0e0b0b189..4bc16aefb7 100644
--- a/Modules/clinic/_dbmmodule.c.h
+++ b/Modules/clinic/_dbmmodule.c.h
@@ -39,7 +39,7 @@ _dbm_dbm_keys(dbmobject *self, PyObject *Py_UNUSED(ignored))
 }
 
 PyDoc_STRVAR(_dbm_dbm_get__doc__,
-"get($self, key, default=b\'\', /)\n"
+"get($self, key, default=None, /)\n"
 "--\n"
 "\n"
 "Return the value for key if present, otherwise default.");
@@ -57,7 +57,7 @@ _dbm_dbm_get(dbmobject *self, PyObject **args, Py_ssize_t nargs)
     PyObject *return_value = NULL;
     const char *key;
     Py_ssize_clean_t key_length;
-    PyObject *default_value = NULL;
+    PyObject *default_value = Py_None;
 
     if (!_PyArg_ParseStack(args, nargs, "s#|O:get",
         &key, &key_length, &default_value)) {
@@ -141,4 +141,4 @@ dbmopen(PyObject *module, PyObject **args, Py_ssize_t nargs)
 exit:
     return return_value;
 }
-/*[clinic end generated code: output=627d28ce1f3188dc input=a9049054013a1b77]*/
+/*[clinic end generated code: output=828255b052933a00 input=a9049054013a1b77]*/
-- 
2.15.0.rc2