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[3.11] gh-95778: CVE-2020-10735: Prevent DoS by very large int() (#96500)

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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.

This backports https://github.com/python/cpython/pull/96499 aka 511ca94520

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#).
This commit is contained in:
Gregory P. Smith 2022-09-02 09:48:57 -07:00 • committed by GitHub
parent 57116d5682
commit f8b71da9aa
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27 changed files with 775 additions and 23 deletions
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10
Lib/test/test_sys.py
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@ -550,11 +550,17 @@ class SysModuleTest(unittest.TestCase):
self.assertIsInstance(sys.executable, str)
self.assertEqual(len(sys.float_info), 11)
self.assertEqual(sys.float_info.radix, 2)
self.assertEqual(len(sys.int_info), 2)
self.assertEqual(len(sys.int_info), 4)
self.assertTrue(sys.int_info.bits_per_digit % 5 == 0)
self.assertTrue(sys.int_info.sizeof_digit >= 1)
self.assertGreaterEqual(sys.int_info.default_max_str_digits, 500)
self.assertGreaterEqual(sys.int_info.str_digits_check_threshold, 100)
self.assertGreater(sys.int_info.default_max_str_digits,
sys.int_info.str_digits_check_threshold)
self.assertEqual(type(sys.int_info.bits_per_digit), int)
self.assertEqual(type(sys.int_info.sizeof_digit), int)
self.assertIsInstance(sys.int_info.default_max_str_digits, int)
self.assertIsInstance(sys.int_info.str_digits_check_threshold, int)
self.assertIsInstance(sys.hexversion, int)
self.assertEqual(len(sys.hash_info), 9)
@ -677,7 +683,7 @@ class SysModuleTest(unittest.TestCase):
"dont_write_bytecode", "no_user_site", "no_site",
"ignore_environment", "verbose", "bytes_warning", "quiet",
"hash_randomization", "isolated", "dev_mode", "utf8_mode",
"warn_default_encoding", "safe_path")
"warn_default_encoding", "safe_path", "int_max_str_digits")
for attr in attrs:
self.assertTrue(hasattr(sys.flags, attr), attr)
attr_type = bool if attr in ("dev_mode", "safe_path") else int