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Title: gh-143378: Fix UAF when `BytesIO` is concurrently mutated during `write` operations by superboy-zjc · Pull Request #143408 · python/cpython · GitHub

Open Graph Title: gh-143378: Fix UAF when `BytesIO` is concurrently mutated during `write` operations by superboy-zjc · Pull Request #143408 · python/cpython

X Title: gh-143378: Fix UAF when `BytesIO` is concurrently mutated during `write` operations by superboy-zjc · Pull Request #143408 · python/cpython

Description: PyObject_GetBuffer() can execute user code (e.g. via buffer), which may close or otherwise mutate a BytesIO object while write() or writelines() is in progress. This could invalidate the internal buffer and lead to a use-after-free. Temporarily bump the exports counter while acquiring the input buffer to block re-entrant mutation, and add regression tests to ensure such cases raise BufferError instead of crashing. Issue: gh-143378

Open Graph Description: PyObject_GetBuffer() can execute user code (e.g. via buffer), which may close or otherwise mutate a BytesIO object while write() or writelines() is in progress. This could invalidate the internal b...

X Description: PyObject_GetBuffer() can execute user code (e.g. via buffer), which may close or otherwise mutate a BytesIO object while write() or writelines() is in progress. This could invalidate the internal b...

Opengraph URL: https://github.com/python/cpython/pull/143408

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gh-143378: Fix UAF when BytesIO is concurrently mutated during write operations https://github.com/python/cpython/pull/143408/files#top
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2409319 gh-143378: Fix use-after-free BytesIO write via re-entrant buffer access superboy-zjc Jan 4, 2026 https://github.com/python/cpython/pull/143408/commits/240931999cd24ef56e087b77d127c697e4d81120
2c3035c gh-143378: Fix Sphinx references in NEWS entry superboy-zjc Jan 4, 2026 https://github.com/python/cpython/pull/143408/commits/2c3035cd564ba0e95e6aa91fe22f99278a9ff0e1
1a667a4 Update Lib/test/test_io/test_memoryio.py superboy-zjc Jan 4, 2026 https://github.com/python/cpython/pull/143408/commits/1a667a42dc911b10d0c5dfa30b28511338d85107
35f9856 Update Modules/_io/bytesio.c superboy-zjc Jan 4, 2026 https://github.com/python/cpython/pull/143408/commits/35f98563265618ab5dfe3ce9e0e99374bb6ac22f
5997e90 Update Lib/test/test_io/test_memoryio.py superboy-zjc Jan 4, 2026 https://github.com/python/cpython/pull/143408/commits/5997e9007a3eef30c772d2dcf13a09a4073d6249
27c99da gh-143378: reduce duplication in unit tests per review superboy-zjc Jan 4, 2026 https://github.com/python/cpython/pull/143408/commits/27c99dabc535b0585e7946401ba5c09314b1c642
586fbdc gh-143378: address review comments in NEWS entry superboy-zjc Jan 4, 2026 https://github.com/python/cpython/pull/143408/commits/586fbdc1c773d78a23f4897e3cec7d90ce11ed50
89b2cb7 gh-143378: clean up unit tests superboy-zjc Jan 4, 2026 https://github.com/python/cpython/pull/143408/commits/89b2cb76c700e1ceb2871e450456aa995a82a339
7805fa1 gh-143378: refactor the buffer check and unit tests for C and Python … superboy-zjc Jan 5, 2026 https://github.com/python/cpython/pull/143408/commits/7805fa1411f27a1d7915130bcf83eb1fb3b35b62
6ac90be gh-143378: clean up test comments superboy-zjc Jan 6, 2026 https://github.com/python/cpython/pull/143408/commits/6ac90be01f9ce9e8bcac4485f686ef71c32770a6
9956cef Merge branch 'main' into issue-143378 superboy-zjc Jan 6, 2026 https://github.com/python/cpython/pull/143408/commits/9956cef2ac6297a03b6bbdbe016bb5166bb6142a
2155e48 gh-143378: clean up duplicated shape check superboy-zjc Jan 6, 2026 https://github.com/python/cpython/pull/143408/commits/2155e48e2eb346be72b1b94960f7be3a6530c8fa
4f0b8b6 gh-143378: clean up duplicated shape check in Python implementation superboy-zjc Jan 8, 2026 https://github.com/python/cpython/pull/143408/commits/4f0b8b619001e7248f0f391195474a1eb7a1b797
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