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 上使用大小与报告相符的设备运行提供的 bug.py 复现，然后检查 mmap 的写入行为和现有的 mmap 测试。确定映射扩展到超出设备大小时的预期处理方式；当该复现由回归测试覆盖且不再意外崩溃时，即视为完成。