[New-bugs-announce] [issue33279] Py_Build value is causing crashes with the "L" and "K" format characters when upcasting sub 64-bit integer types

[Dan Snider]

New submission from Dan Snider <mr.assume.away at gmail.com>:

New to both C and the CPython api so I'm not sure what compiler details matter but this is with VS14 and default compile parameters on windows 10 with 32bit Python.

The following function:

static PyObject *spam(PyObject *module) {
    digit w = 9;
    int x = 9;
    long y = 9;
    int32_t z = 9;
    return Py_BuildValue("(HIK)(lll)(LLL)", w,w,w,x,y,z,x,y,z);  
}

returns:

>>> spam()
((9, 9, 38654705673), (9, 9, 9), (38654705673, 438244858264171835, 6133859984))

Above was the most I could fit in a single Py_BuildValue call without causing a crash (it instantly crashes if "O" or "N" fields are present). I believe this happens because the ints are being upcasted as pointers, which is undefined behavior.

----------
components: Interpreter Core, Windows
messages: 315300
nosy: bup, paul.moore, steve.dower, tim.golden, zach.ware
priority: normal
severity: normal
status: open
title: Py_Build value is causing crashes with the "L" and "K" format characters when upcasting sub 64-bit integer types
type: crash
versions: Python 3.6

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue33279>
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