`_io.BytesIO.getbuffer()`: unshare_buffer: Assertion `self->exports == 0' failed

[chgnrdv]

Crash report

What happened?

import io
f = io.BytesIO()
a = f.getbuffer()
b = f.getbuffer()

Output:

python: ./Modules/_io/bytesio.c:112: unshare_buffer: Assertion `self->exports == 0' failed.
Aborted (core dumped)

Reproduced on 3.8 and 3.11-3.13.

CPython versions tested on:

3.8, 3.11, 3.12, CPython main branch

Operating systems tested on:

Linux

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

Python 3.13.0a1+ (heads/main:11312eae6e, Oct 22 2023, 02:44:38) [GCC 10.2.1 20210110]

Linked PRs

• gh-111174: Fix crash in getbuffer() called repeatedly for empty BytesIO #111210
• [3.12] gh-111174: Fix crash in getbuffer() called repeatedly for empty BytesIO (GH-111210) #111314
• [3.11] gh-111174: Fix crash in getbuffer() called repeatedly for empty BytesIO (GH-111210) #111315

[Eclips4]

cc @serhiy-storchaka as author of unshare_buffer function

[chgnrdv]

Docs for BytesIO.getbuffer say that it returns readable and writable view over the buffer of corresponding BytesIO object without copying the contents of this buffer, and that mutating the view updates the buffer it wraps. Should bytesiobuf_getbuffer call unshare_buffer at all in this case, or I am missing something?

[serhiy-storchaka]

The cause is that empty bytes objects are shared across the interpreter. So Py_REFCNT(self->buf) > 1 even for just created self->buf if it is empty.