A couple of examples about how to attack the fact that _PyType_Lookup()
returns a borrowed ref. Many of the calls are open to attack.
diff --git a/Lib/test/crashers/borrowed_ref_1.py b/Lib/test/crashers/borrowed_ref_1.py
new file mode 100644
index 0000000..d16ede2
--- /dev/null
+++ b/Lib/test/crashers/borrowed_ref_1.py
@@ -0,0 +1,29 @@
+"""
+_PyType_Lookup() returns a borrowed reference.
+This attacks the call in dictobject.c.
+"""
+
+class A(object):
+ pass
+
+class B(object):
+ def __del__(self):
+ print 'hi'
+ del D.__missing__
+
+class D(dict):
+ class __missing__:
+ def __init__(self, *args):
+ pass
+
+
+d = D()
+a = A()
+a.cycle = a
+a.other = B()
+del a
+
+prev = None
+while 1:
+ d[5]
+ prev = (prev,)
diff --git a/Lib/test/crashers/borrowed_ref_2.py b/Lib/test/crashers/borrowed_ref_2.py
new file mode 100644
index 0000000..1a7b3ff
--- /dev/null
+++ b/Lib/test/crashers/borrowed_ref_2.py
@@ -0,0 +1,38 @@
+"""
+_PyType_Lookup() returns a borrowed reference.
+This attacks PyObject_GenericSetAttr().
+
+NB. on my machine this crashes in 2.5 debug but not release.
+"""
+
+class A(object):
+ pass
+
+class B(object):
+ def __del__(self):
+ print "hi"
+ del C.d
+
+class D(object):
+ def __set__(self, obj, value):
+ self.hello = 42
+
+class C(object):
+ d = D()
+
+ def g():
+ pass
+
+
+c = C()
+a = A()
+a.cycle = a
+a.other = B()
+
+lst = [None] * 1000000
+i = 0
+del a
+while 1:
+ c.d = 42 # segfaults in PyMethod_New(im_func=D.__set__, im_self=d)
+ lst[i] = c.g # consume the free list of instancemethod objects
+ i += 1