[3.14] gh-142831: Fix use-after-free in json encoder during re-entrant mutation (gh-142851)#150078
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… mutation (pythongh-142851) User callbacks invoked during JSON encoding (e.g. the `default` callback or a custom string encoder) can mutate or clear the dict or sequence being encoded, invalidating borrowed references to items, keys, and values. Hold strong references unconditionally while iterating. Co-authored-by: Kumar Aditya <kumaraditya@python.org> Co-authored-by: Gregory P. Smith <greg@krypto.org> (cherry picked from commit 235fa72)
This was referenced May 19, 2026
gpshead
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May 20, 2026
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Manual backport of #142851 to 3.14 (the bot couldn't cleanly cherry-pick due to refactors in
main).The fix had to be adapted because in 3.14 the dict/list iteration loops were not yet extracted into the
_encoder_iterate_*_lock_heldhelpers introduced later inmain. Added thePy_INCREF/Py_DECREFaround each borrowed item/key/value inline inencoder_listencode_dict(both thePyMapping_ItemsandPyDict_Nextpaths) andencoder_listencode_list.The two regression tests from the original PR were cherry-picked as-is.
Built
--with-pydebugand ran./python -m test test_json -vlocally — all 218 tests pass.json.encodermapping iteration via re-entrant key encoder #142831