Introduction level presentation about how the pickle protocol actually works, and how one can exploit it in software development and security aspects.

1. Pickle - How it works

2. Intro
● (0) original, (1) old and (2) new protocols &
new style objects
● pickle, cPickle

3. What can be pickled?
Literals
Instances
Top-level classes & functions
No files
Code?

4. (0) Original - Basics
>>> print pickle.dumps(1)
I1
.
>>> print pickle.dumps([])
(lp0
.
>>> print pickle.dumps([1,2,3])
(lp0
I1
aI2
aI3
a.
Notion Opcode
I<arg1> Push Int
l List
a Append (Pop Value)
p<arg1> Put In Memo
( Marker Object
(va_args)
. Stop

5. MemoStack

6. (0) Original - Classes
>>> class A():
... def __init__(self, x):
... self.x = x
…
>>> print pickle.dumps(A(1))
(i__main__
A
p0
(dp1
S'x'
p2
I1
sb.
Notion Opcode
i<arg1>n<arg2> Build & Push
Instance
d Build Dict & Push
s Set Item
b call __setstate__
S<arg1> Push String

7. (0) Original - Classes
__getstate__ - hook for pickling
__setstate__ - hook for unpickling
class Foo(object):
def __init__(self):
self.log = “”
def __getstate__(self):
self.log += “pickling… ”
return self.__dict__
def __setstate__(self, d):
self.__dict__ = d
self.log += “unpickling… “
f = Foo(2)
f_string = pickle.dumps(f)
f_new = pickle.loads(f_string)
{'val': “pickling... unpickling... ”}

9. (0) Original - Imports & Calls
>>> print pickle.dumps({1, 2, 3})
c__builtin__
set
p0
((lp1
I1
aI2
aI3
atp2
Rp3
Notion Opcode
c<arg1>n<arg2> Find Class & Push
t Build Tuple & Push
R Reduce (Call<c,
args>)

10. (0) Original - Imports & Calls
>>> print pickle.dumps({1, 2, 3})
c__builtin__
set
p0
((lp1
I1
aI2
aI3
atp2
Rp3
Notion Opcode
c<arg1>n<arg2> Find Class & Push
t Build Tuple & Push
R Reduce (Call<c,
args>)
__builtin__.set
(1,2,3)
0 -> __builtin__.set
1 -> [1,2,3]
2 -> (1,2,3)

11. (0) Original - Imports & Calls
>>> print pickle.dumps({1, 2, 3})
c__builtin__
set
p0
((lp1
I1
aI2
aI3
atp2
Rp3
Notion Opcode
c<arg1>n<arg2> Find Class & Push
t Build Tuple & Push
R Reduce (Call<c,
args>)
__builtin__.set(1,2,3) 0 -> __builtin__.set
1 -> [1,2,3]
2 -> (1,2,3)
3 ->
__builtin__.set(1,2,3)

12. Demo - Code Execution
print “something” >>> pickle.loads("""c__builtin__
print
(lS"something"
aR.””")
something

13. References
https://github.com/python/cpython/blob/master/Lib/pickle.py
https://svn.python.org/projects/python/trunk/Lib/pickletools.py