Infinity recursion with a malicious finalizer

[sergey-miryanov]

Bug report

Bug description:

For the following example CPython runs infinitely (at least on my Windows build)

def test():
    class Wrong:
        def __del__(self):
            Wrong()

    Wrong()

test()

It works infinitely because of the trashcan mechanism. Should we address this, or should we consider it as another example of CPython VM abuse?

CPython versions tested on:

CPython main branch

Operating systems tested on:

Windows

[StanFromIreland]

For the following example CPython runs infinitely (at least on my Windows build)

I cannot reproduce on Linux.

[sergey-miryanov]

@StanFromIreland does it stop or crash?

[StanFromIreland]

After a few milliseconds:

$ cpython t.py
Exception ignored while calling deallocator <function test.<locals>.Wrong.__del__ at 0x7f61889ed910>:
Traceback (most recent call last):
  File "/tmp/t.py", line 4, in __del__
RecursionError: maximum recursion depth exceeded

[sergey-miryanov]

@StanFromIreland Thanks!
On Windows it looks like:

[efimov-mikhail]

On my Linux machine this code snippet works infinitely:

a = None
class Wrong:
    def __del__(self):
        a = Wrong()

Wrong()

[serhiy-storchaka]

This does not principally differ from

while True:
    pass

or

def f():
    f()
f()

Python is a programming language, and it allows you to write infinite loops or recursion, limited only by an artificial limit.

[sergey-miryanov]

But f() fails with

Running Release|x64 interpreter...
Traceback (most recent call last):
  File "X:\Work\cpython\issues\b140798.py", line 49, in <module>
    rec()
    ~~~^^
  File "X:\Work\cpython\issues\b140798.py", line 46, in rec
    rec()
    ~~~^^
  File "X:\Work\cpython\issues\b140798.py", line 46, in rec
    rec()
    ~~~^^
  File "X:\Work\cpython\issues\b140798.py", line 46, in rec
    rec()
    ~~~^^
  [Previous line repeated 996 more times]
RecursionError: maximum recursion depth exceeded