GH-51044: [Python] Reject read-only readinto destinations - #51126
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raulcd merged 2 commits intoSep 9, 2026
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Immutable destinations expose a null mutable pointer and can crash the native read path. Validate destination mutability and cover bytes and read-only memoryviews with regression tests. Assisted-by: OpenAI Codex
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September 1, 2026 18:33
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I've reproduced this locally with 25.0.1, the fix seems reasonable to me:
$ python
Python 3.14.6 (main, Jun 10 2026, 18:54:31) [GCC 15.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import pyarrow as pa
>>> dst_buf=memoryview(b"a")
>>> with pa.BufferReader(b"x") as f:
... f.readinto(dst_buf)
...
Segmentation fault python
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Just a minor nit: can we move the test after test_nativefile_write_memoryview under the Buffers section in the same file?
Otherwise LGTM, thanks!
Move the existing decorated test immediately after test_nativefile_write_memoryview, as requested in review. AI-assisted mechanical relocation only; test logic and decorators are unchanged. Checked Python syntax, statement and byte equivalence, and whitespace. Runtime tests were not rerun for this ordering change.
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Only did a quick look, but LGTM |
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Rationale for this change
BufferReader.readinto()currently segfaults when passed a read-only destination such asbytesor a read-onlymemoryview.py_buffer()creates an immutable Arrow buffer,mutable_data()returns a null pointer, and the C++ read path attempts to copy into that pointer. A Python API misuse should raise a Python exception rather than terminate the interpreter.What changes are included in this PR?
NativeFile.readinto()destination is mutable before obtaining its writable pointer.TypeErrorfor immutable destinations.bytesand read-onlymemoryviewdestinations.Are these changes tested?
Yes. The focused
readintotests pass against a locally compiled patchedpyarrow.lib. The stock 25.0.1 wheel exits with status 139 for the issue reproducer, while the patched build raises the expectedTypeError; the writablebytearraycontrol continues to read successfully.Are there any user-facing changes?
Yes. Passing a read-only destination to
NativeFile.readinto()now raisesTypeErrorinstead of terminating the interpreter. Writable-buffer behavior is unchanged.Fixes #51044.
This contribution was developed with assistance from OpenAI Codex. I reviewed, tested, and take responsibility for the patch and this description.
BufferReader.readinto()segfaults on a read-only destination #51044