[issue20191] resource.prlimit(int, int, str) crashs

[STINNER Victor]

New submission from STINNER Victor:

$ ./python -c 'import resource; resource.prlimit(-3, 11, "\udbff\udfff")'
Erreur de segmentation (core dumped)

The problem is a generic problem with PyArg_Parse functions and "(O)" format. With this format, the caller does not hold a reference to the object nor the tuple. If arbitrary Python code is executed before the object is used, the object pointer becomes a dangling pointer.

resource.prlimit() uses:

    if (!PyArg_ParseTuple(args, _Py_PARSE_PID "i|(OO):prlimit",
                          &pid, &resource, &curobj, &maxobj))
        return NULL;

In this issue, it's worse: the string is casted to a sequence, and each string character becomes a temporary substring of 1 character. The problem is that PyArg_ParseTuple() nor resource_prlimit() hold the reference, and so the curobj and maxobj are dangling pointer.

Options:

- raise an error if the second parameter is not a tuple: implement the check in prlimit() or i PyArg_ParseTuple()?
- hold a reference to the sequence, to curobj and to maxobj instead of using borrowed references

----------
messages: 207686
nosy: haypo, serhiy.storchaka
priority: normal
severity: normal
status: open
title: resource.prlimit(int, int, str) crashs
type: crash
versions: Python 3.4

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue20191>
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