SystemError buffer overflow in `fcntl.fcntl`

[YuanchengJiang]

Bug report

Bug description:

import tempfile
import os
import fcntl

nbytes = 2024
tf = tempfile.NamedTemporaryFile(delete=2**15 - 1)
tf_name = tf.name

with open(tf_name, 'wb') as f:
    get_result = fcntl.fcntl(f, fcntl.F_GETOWN_EX, b'' * nbytes)

SystemError: buffer overflow
cpython/Lib/tempfile.py:484: ResourceWarning: Implicitly cleaning up <_TemporaryFileWrapper file=<_io.BufferedRandom name='/tmp/tmp_o0z83c9'>>

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

[typenoob]

working on it👀

[serhiy-storchaka]

This is expected behavior. You call fcntl.fcntl() with a buffer of unsuitable for F_GETOWN_EX (zero) size.