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edhoedt wants to merge 15 commits into from
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Callback on include #58

edhoedt wants to merge 15 commits into from

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@edhoedt edhoedt commented Aug 28, 2017

Python interface for pull request VirusTotal/yara#727

Example usage:

import yara
import sys
if sys.version_info >= (3, 0):
    import urllib.request as urllib
else:
    import urllib as urllib

def mycallback(requested_filename, filename, namespace):
    if requested_filename == 'req.yara':
        uf = urllib.urlopen('https://pastebin.com/raw/siZ2sMTM')
        sources = uf.read()
        if sys.version_info >= (3, 0):
            sources = str(sources, 'utf-8')
        return sources
    else:
        raise Exception(filename+": Can't fetch "+requested_filename)

rules = yara.compile(source='include "req.yara" rule r{ condition: true }',
                     include_callback=mycallback)

plusvic
plusvic reviewed Aug 31, 2017
View reviewed changes
yara-python.c
py_calling_ns = Py_None;
}

PyObject* result = PyObject_CallFunctionObjArgs(callback,
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The string returned by the callback is never freed. When PyObject_CallFunctionObjArgs returns the reference count for result is >=1 and your code has the ownership for that string. In order to let the garbage collector free the string you must do a Py_DECREF at some point.

The problem here is that you can't do it in yara_include_callback, because then you are returning to YARA a string that could be freed by the garbage collector at any time. But if you can't do it here, then where?

yara-python.c

if (include_name != NULL)
{
py_incl_name = PY_STRING(include_name);
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You must do a Py_DECREF(py_incl_name) when you are done with the Python string in order to let the garbage collector free the memory. The same applies to py_calling_fn and py_calling_ns.

yara-python.c
py_calling_ns = Py_None;
}

PyObject* result = PyObject_CallFunctionObjArgs(callback,
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You must do Py_INCREF(callback) before PyObject_CallFunctionObjArgs and Py_DECREF(callback) after it.

yara-python.c
PyObject* py_calling_fn = NULL;
PyObject* py_calling_ns = NULL;

if (include_name != NULL)
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Before calling any Python function you must acquire the global interpreter lock (GIL) with PyGILState_Ensure and release it with PyGILState_Release.

@plusvic plusvic mentioned this pull request Aug 31, 2017
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plusvic added a commit that referenced this pull request Oct 31, 2017
@plusvic
Merge PR #58
97e3bce
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plusvic commented Oct 31, 2017

@edhoedt please check #67

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plusvic commented Oct 31, 2017

Closing this PR as #67 fix conflicts and some other issues.

@plusvic plusvic closed this Oct 31, 2017
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@edhoedt @plusvic