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Assertion failure in Modules/_io/bytesio.c `_io_BytesIO_readinto_impl: Assertion 'self->pos + len < PY_SSIZE_T_MAX' failed.` · Issue #141311 · python/cpython · GitHub

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Assertion failure in Modules/_io/bytesio.c _io_BytesIO_readinto_impl: Assertion 'self->pos + len < PY_SSIZE_T_MAX' failed. #141311

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Assertion failure in Modules/_io/bytesio.c _io_BytesIO_readinto_impl: Assertion 'self->pos + len < PY_SSIZE_T_MAX' failed.#141311
Labels
3.13only security fixesextension-modulesC modules in the Modules dirtopic-IOtype-crashA hard crash of the interpreter, possibly with a core dump

Description

YuanchengJiang
opened on Nov 9, 2025

Bug report

Bug description:

import io

input_lines = ['windows\r\n']
joined = ''.join(input_lines)

encoding = 'utf-8'
newline = None
bufsize = 1

raw = io.BytesIO(joined.encode(encoding))
buf = io.BufferedReader(raw, buffer_size=bufsize)
textio = io.TextIOWrapper(buf, encoding=encoding, newline=newline)

textio.seek(2**63 - 1)
_ = textio.read(2)
python: ../Modules/_io/bytesio.c:616: _io_BytesIO_readinto_impl: Assertion `self->pos + len < PY_SSIZE_T_MAX' failed.
Aborted (core dumped)

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Linked PRs

Activity

  1. YuanchengJiang
    added
    type-bugAn unexpected behavior, bug, or error
    on Nov 9, 2025
  2. picnixz
    added
    extension-modulesC modules in the Modules dir
    topic-IO
    type-crashA hard crash of the interpreter, possibly with a core dump
    and removed
    type-bugAn unexpected behavior, bug, or error
    on Nov 9, 2025

  3. cmaloney commented on Nov 9, 2025

    cmaloney
    on Nov 9, 2025
    Contributor

    More minimal reproducer:

    import io

res = bytearray(2)
raw = io.BytesIO()
raw.seek(2**63 - 1)
_ = raw.readinto(res)

    There's an assert that self->pos (2**63-1) + len (2) should not overflow, but there should probably be an error emitted (or update to handle larger sizes):

    cpython/Modules/_io/bytesio.c

    Lines 616 to 617 in 807db68

    assert(self->pos + len < PY_SSIZE_T_MAX);
    assert(len >= 0);

  4. cmaloney
    added a commit that references this issue on Nov 10, 2025

    pythongh-141311: Avoid assertion in BytesIO readinto

    db81df6
  5. serhiy-storchaka
    added a commit that references this issue on Nov 12, 2025

    gh-141311: Avoid assertion in BytesIO.readinto() (GH-141333)

    7d54374
  6. miss-islington
    added a commit that references this issue on Nov 12, 2025

    pythongh-141311: Avoid assertion in BytesIO.readinto() (pythonGH-141333)

    7151cfb
  7. serhiy-storchaka
    added a commit that references this issue on Nov 12, 2025

    [3.14] gh-141311: Avoid assertion in BytesIO.readinto() (GH-141333) (G…

    75b5157
  8. StanFromIreland
    added
    3.13only security fixes
    on Nov 12, 2025
  9. serhiy-storchaka
    added a commit that references this issue on Nov 12, 2025

    [3.13] gh-141311: Avoid assertion in BytesIO.readinto() (GH-141333) (G…

    7c62bd5
  10. serhiy-storchaka
    closed this as completedon Nov 12, 2025
  11. StanFromIreland
    added a commit that references this issue on Dec 6, 2025

    pythongh-141311: Avoid assertion in BytesIO.readinto() (pythonGH-141333)

    7592d29
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