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gh-148688: Fix _BlocksOutputBuffer_Finish() double free #148689

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gh-148688: Fix _BlocksOutputBuffer_Finish() double free #148689

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8637c67
gh-148688: Fix _BlocksOutputBuffer_Finish() double free
vstinner Apr 17, 2026
7b15279
lzma and zlib are also affected
vstinner Apr 17, 2026
2bf1d69
NEWS entry: mention alos compression.zstd
vstinner Apr 17, 2026
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7 changes: 5 additions & 2 deletions Include/internal/pycore_blocks_output_buffer.h
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Original file line number Diff line number Diff line change
Expand Up @@ -242,9 +242,12 @@ static inline PyObject *
_BlocksOutputBuffer_Finish(_BlocksOutputBuffer *buffer,
const Py_ssize_t avail_out)
{
PyObject *obj;
assert(buffer->writer != NULL);
return PyBytesWriter_FinishWithSize(buffer->writer,
buffer->allocated - avail_out);
obj = PyBytesWriter_FinishWithSize(buffer->writer,
buffer->allocated - avail_out);
buffer->writer = NULL;
return obj;
}

/* Clean up the buffer when an error occurred. */
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Library/2026-04-17-16-31-58.gh-issue-148688.vVugFn.rst
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@@ -0,0 +1,2 @@
:mod:`bz2`, :mod:`compression.zstd`, :mod:`lzma`, :mod:`zlib`: Fix a double
free in on memory allocation failure. Patch by Victor Stinner.
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