1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
|
"""
There is a way to put keys of any type in a type's dictionary.
I think this allows various kinds of crashes, but so far I have only
found a convoluted attack of _PyType_Lookup(), which uses the mro of the
type without holding a strong reference to it. Probably works with
super.__getattribute__() too, which uses the same kind of code.
"""
class MyKey(object):
def __hash__(self):
return hash('mykey')
def __cmp__(self, other):
# the following line decrefs the previous X.__mro__
X.__bases__ = (Base2,)
# trash all tuples of length 3, to make sure that the items of
# the previous X.__mro__ are really garbage
z = []
for i in range(1000):
z.append((i, None, None))
return -1
class Base(object):
mykey = 'from Base'
class Base2(object):
mykey = 'from Base2'
# you can't add a non-string key to X.__dict__, but it can be
# there from the beginning :-)
X = type('X', (Base,), {MyKey(): 5})
print X.mykey
# I get a segfault, or a slightly wrong assertion error in a debug build.
|
