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

[YuanchengJiang]

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

• gh-141311: Avoid assertion in BytesIO readinto #141333

[cmaloney]

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);