SIGBUS: writing to `mmap`ed device beyond file size

Crash report

What happened?

# DEV=/dev/foo
# blockdev --getsize64 $DEV
1048576
# tail $DEV
# python3.12 bug.py
Bus error (core dumped)
# tail $DEV
hell#

from mmap import mmap

with open('/dev/foo', 'r+b') as file:
    m = mmap(file.fileno(), 1024 ** 2 + 1)

m.seek(1024 ** 2 - 4)

for b in b'hello world!':
    m.write(bytes([b]))

I hope you don't mind my reference to Madagascar

CPython versions tested on:

3.12

Operating systems tested on:

Linux

Output from running 'python -VV' on the command line:

Python 3.12.3 (main, Apr 27 2024, 19:00:21) [GCC 11.4.0]

首先，在 Linux 上使用大小與報告相符的裝置執行提供的 bug.py 重現，然後檢查 mmap 的寫入行為與現有的 mmap 測試。確定 mapping 延伸超過裝置大小時的預期處理方式；當該重現由回歸測試涵蓋且不再意外崩潰時，即視為完成。