[Python-Dev] Deprecate invalid ctypes call protection on Windows
steve.dower at python.org
Mon May 22 14:17:18 EDT 2017
One of the main reasons we are stuck with an old libffi fork in CPython
is because the newer versions do not support protection from calling
functions with too few/many arguments:
There are a number of caveats here, including "this only works on
Windows", but since it is documented we cannot just remove the behaviour
without a deprecation period.
I'd like to propose a highly-accelerated deprecation period for this
specific feature, starting in CPython 3.6.2 and being "completed" in
3.7.0, when we will hopefully move onto a newer libffi.
In general, the "feature" is a misfeature anyway, since calling a native
function with incorrect arguments is unsupported and a very easy way to
cause information leakage or code execution vulnerabilities. There may
be an argument for removing the functionality immediately, but honestly
I think changing libffi in a point release is higher risk.
Once the special protection is removed, most of these cases will become
OSError due to the general protection against segmentation faults. Some
will undoubtedly fall through the cracks and crash the entire
interpreter, but these are unavoidable (and really ought to crash to
avoid potential exploits).
Does anyone have any reasons to oppose this? It already has votes from
another Windows expert and the 3.6/3.7 Release Manager, but we wanted to
see if anyone has a concern we haven't thought of.
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