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Title: gh-143543: Fix re-entrant use-after-free in itertools.groupby by VanshAgarwal24036 · Pull Request #143738 · python/cpython · GitHub

Open Graph Title: gh-143543: Fix re-entrant use-after-free in itertools.groupby by VanshAgarwal24036 · Pull Request #143738 · python/cpython

X Title: gh-143543: Fix re-entrant use-after-free in itertools.groupby by VanshAgarwal24036 · Pull Request #143738 · python/cpython

Description: Fix a use-after-free in itertools.groupby when a user-defined eq re-enters next(groupby) during key comparison. groupby_next() compared borrowed references to currkey and tgtkey using PyObject_RichCompareBool(). A re-entrant eq could advance the iterator, replace and decref those keys, leaving the outer comparison accessing freed memory. The fix temporarily INCREFs both keys for the duration of the comparison, preventing re-entrancy from invalidating them. A regression test is added. Issue: gh-143543

Open Graph Description: Fix a use-after-free in itertools.groupby when a user-defined eq re-enters next(groupby) during key comparison. groupby_next() compared borrowed references to currkey and tgtkey using PyObject_Rich...

X Description: Fix a use-after-free in itertools.groupby when a user-defined eq re-enters next(groupby) during key comparison. groupby_next() compared borrowed references to currkey and tgtkey using PyObject_Rich...

Opengraph URL: https://github.com/python/cpython/pull/143738

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Show all changes 22 commits https://github.com/python/cpython/pull/143738/files
e898626 gh-143543: Fix re-entrant use-after-free in itertools.groupby VanshAgarwal24036 Jan 12, 2026 https://github.com/python/cpython/pull/143738/commits/e898626432a811fb000251efc12927cbd7c57836
ba974bc Fix whitespace per prek VanshAgarwal24036 Jan 12, 2026 https://github.com/python/cpython/pull/143738/commits/ba974bca279ae55feadbd099733cb61f82027d1e
0debc2a Add NEWS entry for itertools.groupby crash fix VanshAgarwal24036 Jan 13, 2026 https://github.com/python/cpython/pull/143738/commits/0debc2a0bd1fd2e3a7f7036e9215289733a37e34
8d83176 Fix NEWS filename for gh-143543 VanshAgarwal24036 Jan 13, 2026 https://github.com/python/cpython/pull/143738/commits/8d831767d3ee54448b3c8d0e038a0fc0258a8ff6
ca932bf Fix NEWS entry type for gh-143543 VanshAgarwal24036 Jan 13, 2026 https://github.com/python/cpython/pull/143738/commits/ca932bf3433216f30b038fc47ced40082129d50a
0e86303 Remove incorrect NEWS files for gh-143543 VanshAgarwal24036 Jan 13, 2026 https://github.com/python/cpython/pull/143738/commits/0e86303246ba709a7ecfbd871214899171ef8642
740218c Avoid borrowed references during groupby key comparison VanshAgarwal24036 Jan 13, 2026 https://github.com/python/cpython/pull/143738/commits/740218ccfe96ab468263a0f5c09a8c54628e7e44
e3a54be Clarify NEWS entry wording VanshAgarwal24036 Jan 13, 2026 https://github.com/python/cpython/pull/143738/commits/e3a54be56f0739c46983285a7825c35e80a1367c
9983345 Fix refcounting during groupby key comparison VanshAgarwal24036 Jan 13, 2026 https://github.com/python/cpython/pull/143738/commits/998334526afc8d636572e30a831697aaf6c2e70b
1ea51c0 Add NEWS entry via blurb for itertools.groupby crash VanshAgarwal24036 Jan 13, 2026 https://github.com/python/cpython/pull/143738/commits/1ea51c06d7afcdbded3acf9d50e4a90736c615a9
336c367 Fix duplicate variable declarations in groupby_next VanshAgarwal24036 Jan 13, 2026 https://github.com/python/cpython/pull/143738/commits/336c36748ab272ce0f980b19121084338d72772a
9cbe1a6 itertools: hold strong references during groupby key comparison VanshAgarwal24036 Jan 13, 2026 https://github.com/python/cpython/pull/143738/commits/9cbe1a6c3651ddde58eb9b388ff861a39205a058
8c61450 Clarify re-entrant groupby key comparison comment VanshAgarwal24036 Jan 14, 2026 https://github.com/python/cpython/pull/143738/commits/8c61450233d9cea60df098e63e9de4aead7d224c
90e995b Update Modules/itertoolsmodule.c VanshAgarwal24036 Jan 14, 2026 https://github.com/python/cpython/pull/143738/commits/90e995b1b817ca47ee17dc90d7e68bfa888811c2
4f2338f Update Lib/test/test_itertools.py VanshAgarwal24036 Jan 14, 2026 https://github.com/python/cpython/pull/143738/commits/4f2338f1c50fc29ffeed0da2d8491ad6f500a569
2cac26b Simplify groupby re-entrancy test VanshAgarwal24036 Jan 14, 2026 https://github.com/python/cpython/pull/143738/commits/2cac26be898e86976f2211387fd82e2a1cfa7236
fed7db7 Move rcmp declaration and clarify re-entrancy comment VanshAgarwal24036 Jan 14, 2026 https://github.com/python/cpython/pull/143738/commits/fed7db70b1fccd0e9d67fa3631c21ec0de3556c7
4939083 Move comment before declarations and inline rcmp VanshAgarwal24036 Jan 14, 2026 https://github.com/python/cpython/pull/143738/commits/4939083e12339646ff3dea681760e282b4fb0c74
e42b9b4 Remove Extra lines VanshAgarwal24036 Jan 14, 2026 https://github.com/python/cpython/pull/143738/commits/e42b9b419c30f47177b62188fbc9c6d287f4f801
e29c818 Remove extra Lines VanshAgarwal24036 Jan 15, 2026 https://github.com/python/cpython/pull/143738/commits/e29c8184917ff9936d8ff58f3858e9de73f9ecea
4be9d4f Update Lib/test/test_itertools.py VanshAgarwal24036 Feb 3, 2026 https://github.com/python/cpython/pull/143738/commits/4be9d4f3962a95354ce2d247cafd92bd8a5ae4af
b48d388 Merge branch 'main' into gh-143543-groupby-uaf encukou Feb 4, 2026 https://github.com/python/cpython/pull/143738/commits/b48d388d3e00a96505f828134734c52d2fadc848
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