Stack overflow in repr of deeply nested dicts #76318
Comments
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repr() of deeply nested dicts and dictviews can cause a stack overflow. >>> x = {}
>>> for i in range(100000):
... x = {1: x}
...
>>> repr(x)
Segmentation fault
>>> x = {}
>>> for i in range(100000):
... x = {1: x}
...
>>> repr(x.values())
Segmentation faultrepr() of virtually all other deeply nested collections are guarded by using Py_EnterRecursiveCall(). >>> x = ()
>>> for i in range(100000):
... x = (x,)
...
>>> repr(x)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
RecursionError: maximum recursion depth exceeded while getting the repr of a tuple
>>> x = []
>>> for i in range(100000):
... x = [x]
...
>>> repr(x)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
RecursionError: maximum recursion depth exceeded while getting the repr of a list
>>> x = frozenset()
>>> for i in range(100000):
... x = frozenset({x})
...
>>> repr(x)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
RecursionError: maximum recursion depth exceeded while getting the repr of a list
>>> from collections import OrderedDict
>>> x = {}
>>> for i in range(100000):
... x = OrderedDict({1: x})
...
>>> repr(x)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
RecursionError: maximum recursion depth exceeded while getting the repr of a list
>>> from collections import deque
>>> x = deque()
>>> for i in range(100000):
... x = deque([x])
...
>>> repr(x)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
RecursionError: maximum recursion depth exceeded while getting the repr of a listBut the case of infinite recursion already is handled: >>> x = {}
>>> x[1] = x
>>> repr(x)
'{1: {...}}'Only finite but very deep recursion causes a crash. The one possible solution -- add Py_EnterRecursiveCall() in the implementation of dict.__repr__(), like it already is added in list.__repr__() and tuple.__repr__(). The more general solution -- add Py_EnterRecursiveCall() in PyObject_Repr(). In any case it is called before calling PyObject_Repr() for every item in the repr of most collections except dict. And it is already added in PyObject_Str(). Therefore adding it will not add much overhead, but can handle more corner cases. |
serhiy-storchaka
added
3.7 (EOL)
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PR 4812 is an alternate fix for 3.6. It doesn't touch reprs of other types. |
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The issue seems somewhat contrived but the fix looks fine to me. |
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