_sre: getstring() releases the buffer before using it

[vstinner]

BPO	13083
Nosy	@pitrou, @vstinner, @ezio-melotti, @serhiy-storchaka
Superseder	bpo-14212: Segfault when using re.finditer over mmap

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2013-08-05.13:08:04.716>
created_at = <Date 2011-10-01.01:50:50.848>
labels = ['expert-regex', 'library']
title = '_sre: getstring() releases the buffer before using it'
updated_at = <Date 2013-08-05.13:08:38.538>
user = 'https://github.com/vstinner'

bugs.python.org fields:

activity = <Date 2013-08-05.13:08:38.538>
actor = 'serhiy.storchaka'
assignee = 'none'
closed = True
closed_date = <Date 2013-08-05.13:08:04.716>
closer = 'serhiy.storchaka'
components = ['Library (Lib)', 'Regular Expressions']
creation = <Date 2011-10-01.01:50:50.848>
creator = 'vstinner'
dependencies = []
files = []
hgrepos = []
issue_num = 13083
keywords = []
message_count = 3.0
messages = ['144714', '193237', '194475']
nosy_count = 5.0
nosy_names = ['pitrou', 'vstinner', 'ezio.melotti', 'mrabarnett', 'serhiy.storchaka']
pr_nums = []
priority = 'normal'
resolution = 'duplicate'
stage = 'resolved'
status = 'closed'
superseder = '14212'
type = None
url = 'https://bugs.python.org/issue13083'
versions = ['Python 3.3', 'Python 3.4']

[vstinner]

getstring() of the _sre module contains the following code:
-------------

    ...
    buffer = Py_TYPE(string)->tp_as_buffer;
    if (!buffer || !buffer->bf_getbuffer ||
        (*buffer->bf_getbuffer)(string, &view, PyBUF_SIMPLE) < 0) {
            PyErr_SetString(PyExc_TypeError, "expected string or buffer");
            return NULL;
    }

/* determine buffer size */
bytes = view.len;
ptr = view.buf;

    /* Release the buffer immediately --- possibly dangerous
       but doing something else would require some re-factoring
    */
    PyBuffer_Release(&view);
    ...

---

getstring() is used to initialize a state or a pattern. State and pattern have destructors (pattern_dealloc() and state_fini()), so it should be possible to keep the view active and call PyBuffer_Release() in the destructor.

[mrabarnett]

It looks like this was fixed for issue bpo-14212.

[serhiy-storchaka]

Agree.