gh-153539: Fix use-after-free in TextIOWrapper.tell() with a reentrant decoder - #153540
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serhiy-storchaka merged 2 commits intoAug 17, 2026
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…entrant decoder TextIOWrapper.tell() used a borrowed next_input from the snapshot across the decoder's getstate/decode/setstate calls, so a decoder that reenters seek() from getstate could free it and leave tell() reading freed memory. Own the reference across those calls, matching the sibling textiowrapper_read_chunk.
serhiy-storchaka
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needs backport to 3.13
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LGTM. 👍
But the main problem is concurrency -- if two threads call seek() concurrently they can reproduce this bug. Please reflect this in NEWS and comments.
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Done in e011fa3: noted the concurrent |
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Thanks @tonghuaroot for the PR, and @serhiy-storchaka for merging it 🌮🎉.. I'm working now to backport this PR to: 3.13, 3.14, 3.15. |
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…entrant decoder (pythonGH-153540) TextIOWrapper.tell() used a borrowed next_input from the snapshot across the decoder's getstate/decode/setstate calls, so a decoder that reenters seek() from getstate could free it and leave tell() reading freed memory. Own the reference across those calls, matching the sibling textiowrapper_read_chunk.
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TextIOWrapper.tell()used a borrowednext_inputfrom the snapshot across the decoder'sgetstate/decode/setstatecalls, so a decoder that re-entersseek()fromgetstatecould free it and leavetell()reading freed memory. Own the reference across those calls, matchingtextiowrapper_read_chunk.