Don't segfault on uninitialized cursor

It can happen with bad cursor subclasses not calling super's init. Raise
an exception instead of segfaulting.

Closes #195

NEWS

@@ -8,6 +8,8 @@ What's new in psycopg 2.5.3
   Chris Withers (:ticket:`#193`).
 - Avoid blocking async connections on connect (:ticket:`#194`). Thanks to
   Adam Petrovich for the bug report and diagnosis.
+- Don't segfault using poorly defined cursor subclasses which forgot to call
+  the superclass init (:ticket:`#195`).
 - Fixed debug build on Windows, thanks to James Emerton.
 
 

psycopg/cursor.h

@@ -97,11 +97,14 @@ HIDDEN int psyco_curs_scrollable_set(cursorObject *self, PyObject *pyvalue);
 
 /* exception-raising macros */
 #define EXC_IF_CURS_CLOSED(self) \
-do \
-    if ((self)->closed || ((self)->conn && (self)->conn->closed)) { \
+do { \
+    if (!(self)->conn) { \
+        PyErr_SetString(InterfaceError, "the cursor has no connection"); \
+        return NULL; } \
+    if ((self)->closed || (self)->conn->closed) { \
         PyErr_SetString(InterfaceError, "cursor already closed"); \
         return NULL; } \
-while (0)
+} while (0)
 
 #define EXC_IF_NO_TUPLES(self) \
 do \

tests/test_cursor.py

@@ -413,6 +413,20 @@ class CursorTests(ConnectingTestCase):
         cur.scroll(9, mode='absolute')
         self.assertEqual(cur.fetchone(), (9,))
 
+    def test_bad_subclass(self):
+        # check that we get an error message instead of a segfault
+        # for badly written subclasses.
+        # see http://stackoverflow.com/questions/22019341/
+        class StupidCursor(psycopg2.extensions.cursor):
+            def __init__(self, *args, **kwargs):
+                # I am stupid so not calling superclass init
+                pass
+
+        cur = StupidCursor()
+        self.assertRaises(psycopg2.InterfaceError, cur.execute, 'select 1')
+        self.assertRaises(psycopg2.InterfaceError, cur.executemany,
+            'select 1', [])
+
 
 def test_suite():
     return unittest.TestLoader().loadTestsFromName(__name__)