[New-bugs-announce] [issue34912] Update overflow checks in resize_buffer

[Windson Yang]

New submission from Windson Yang <wiwindson at gmail.com>:

In [resize_buffer](https://github.com/python/cpython/blob/e42b705188271da108de42b55d9344642170aa2b/Modules/_io/stringio.c#L85)

    /* For simplicity, stay in the range of the signed type. Anyway, Python
       doesn't allow strings to be longer than this. */
    if (size > PY_SSIZE_T_MAX)
        goto overflow;
        ...

IMO, we should check the overflow with

    if (size > PY_SSIZE_T_MAX/sizeof(Py_UCS4))

Or we can just delete this code because we will check later at [alloc_check](https://github.com/python/cpython/blob/e42b705188271da108de42b55d9344642170aa2b/Modules/_io/stringio.c#L107）

BTW, I found we only use PY_SIZE_MAX here in CPython, I wonder why we do not use PY_SSIZE_T_MAX instead?

----------
components: IO
messages: 327223
nosy: Windson Yang
priority: normal
severity: normal
status: open
title: Update overflow checks in resize_buffer
versions: Python 3.4, Python 3.5, Python 3.6, Python 3.7, Python 3.8

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue34912>
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