ChaCha20Poly1305 memory leak

[PaulWhitingS2]

Cryptography 39.0.0 introduced a memory leak in the ChaCha20Poly1305 class. It is still present in the most recent release (41.0.2).

1. python -m venv venv
2. source venv/bin/activate
3. pip install cryptography
4. Run the following script. Monitor memory usage using top.

from cryptography.hazmat.primitives.ciphers.aead import ChaCha20Poly1305
key = ChaCha20Poly1305.generate_key()
while True:
        chacha = ChaCha20Poly1305(key)

Cryptography 38.0.4 - Memory usage remains constant.
Cryptography >= 39.0.0 - Memory usage increases until the process is killed.

[reaperhulk]

Thanks for the report. While we chase this down, here is a reduced reproducer:

import gc

from cryptography.hazmat.bindings._rust import FixedPool


class Foo:
    def __init__(self):
        self._pool = FixedPool(self._method)

    def _method(self):
        pass


while True:
    Foo()
    gc.collect()

[reaperhulk]

It appears we need to implement __traverse__ and __clear__ so that the GC can properly collect everything (as there are circular references with the fixed pool). We'll get a fix up soon.