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gh-95778: CVE-2020-10735: Prevent DoS by very large int() (#96499)

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Integer to and from text conversions via CPython's bignum `int` type is not safe against denial of service attacks due to malicious input. Very large input strings with hundred thousands of digits can consume several CPU seconds.

This PR comes fresh from a pile of work done in our private PSRT security response team repo.

Signed-off-by: Christian Heimes [Red Hat] <christian@python.org>
Tons-of-polishing-up-by: Gregory P. Smith [Google] <greg@krypto.org>
Reviews via the private PSRT repo via many others (see the NEWS entry in the PR).

<!-- gh-issue-number: gh-95778 -->
* Issue: gh-95778
<!-- /gh-issue-number -->

I wrote up [a one pager for the release managers](https://docs.google.com/document/d/1KjuF_aXlzPUxTK4BMgezGJ2Pn7uevfX7g0_mvgHlL7Y/edit#). Much of that text wound up in the Issue. Backports PRs already exist. See the issue for links.
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Gregory P. Smith 2022-09-02 09:35:08 -07:00 • committed by GitHub
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7
Doc/library/functions.rst
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@ -910,6 +910,13 @@ are always available. They are listed here in alphabetical order.
.. versionchanged:: 3.11
The delegation to :meth:`__trunc__` is deprecated.
.. versionchanged:: 3.12
:class:`int` string inputs and string representations can be limited to
help avoid denial of service attacks. A :exc:`ValueError` is raised when
the limit is exceeded while converting a string *x* to an :class:`int` or
when converting an :class:`int` into a string would exceed the limit.
See the :ref:`integer string conversion length limitation
<int_max_str_digits>` documentation.
.. function:: isinstance(object, classinfo)