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bpo-25532: Protect against infinite loops in inspect.unwrap() #1717

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Merged
ncoghlan merged 5 commits into from
May 23, 2017
Merged

bpo-25532: Protect against infinite loops in inspect.unwrap() #1717

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e0d4789
Protect against infinite loops in inspect.unwrap()
takluyver May 22, 2017
87c0c0e
Add note about bpo-25532 in NEWS
takluyver May 22, 2017
2cb0a18
Add test for infinite loop protection in inspect.unwrap()
takluyver May 22, 2017
b12a0ac
Change memo set to a dict
takluyver May 22, 2017
553df25
Use len(memo) instead of a separate unwrap_count
takluyver May 22, 2017
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9 changes: 6 additions & 3 deletions Lib/inspect.py
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Original file line number Diff line number Diff line change
Expand Up @@ -505,13 +505,16 @@ def _is_wrapper(f):
def _is_wrapper(f):
return hasattr(f, '__wrapped__') and not stop(f)
f = func # remember the original func for error reporting
memo = {id(f)} # Memoise by id to tolerate non-hashable objects
# Memoise by id to tolerate non-hashable objects, but store objects to
# ensure they aren't destroyed, which would allow their IDs to be reused.
memo = {id(f): f}
recursion_limit = sys.getrecursionlimit()
while _is_wrapper(func):
func = func.__wrapped__
id_func = id(func)
if id_func in memo:
if (id_func in memo) or (len(memo) >= recursion_limit):
raise ValueError('wrapper loop when unwrapping {!r}'.format(f))
memo.add(id_func)
memo[id_func] = func
return func

# -------------------------------------------------- source code extraction
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18 changes: 18 additions & 0 deletions Lib/test/test_inspect.py
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Expand Up @@ -3554,6 +3554,19 @@ def test_builtins_have_signatures(self):
self.assertIsNone(obj.__text_signature__)


class NTimesUnwrappable:
def __init__(self, n):
self.n = n
self._next = None

@property
def __wrapped__(self):
if self.n <= 0:
raise Exception("Unwrapped too many times")
if self._next is None:
self._next = NTimesUnwrappable(self.n - 1)
return self._next

class TestUnwrap(unittest.TestCase):

def test_unwrap_one(self):
Expand Down Expand Up @@ -3609,6 +3622,11 @@ class C:
__wrapped__ = func
self.assertIsNone(inspect.unwrap(C()))

def test_recursion_limit(self):
obj = NTimesUnwrappable(sys.getrecursionlimit() + 1)
with self.assertRaisesRegex(ValueError, 'wrapper loop'):
inspect.unwrap(obj)

class TestMain(unittest.TestCase):
def test_only_source(self):
module = importlib.import_module('unittest')
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4 changes: 4 additions & 0 deletions Misc/NEWS
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Expand Up @@ -989,6 +989,10 @@ Library
- Issue #29581: ABCMeta.__new__ now accepts ``**kwargs``, allowing abstract base
classes to use keyword parameters in __init_subclass__. Patch by Nate Soares.

- Issue #25532: inspect.unwrap() will now only try to unwrap an object
sys.getrecursionlimit() times, to protect against objects which create a new
object on every attribute access.

Windows
-------

Expand Down