Add convenient exploit for _IO_wide_data

[RocketMaDev]

After glibc 2.35, one of exploitable paths is FSOP, utilizing unchecked vtable for _IO_wide_data. This PR brings related structures in Python and convenient methods to create out-of-box payload.

WIP.

[peace-maker]

We should keep a proxy pwnlib/filepointer.py which just reexports the new pwnlib/file/filepointer.py for backwards compatibility.

[RocketMaDev]

Oh I see. In case someone use pwntools in library mode right? Should I just write from pwnlib.file.filepointer import * in the proxy file?

[RocketMaDev]

Since I work on an old branch, should I update my branch with rebase when I'm done and write down the changelog?

[RocketMaDev]

How to meet the doctest requirement both in Python 2 and Python 3? bytes's repr behavior is different between 2 versions...

[Arusekk]

I believe the latest failure is not about bytes' repr, but rather about bytes constructor from array. You can use bytearray, which works the same across both, and cast that to bytes later, like: bytes(bytarray(L)). You can also stick with the bytearray, as it is more convenient to work with anyway.

The documentation should be py3-native (or even py3-only). Back when porting to py3, I implemented a custom doctest comparator for py2 that should accept enough py3 to pass the tests successfully.

[RocketMaDev]

So do you mean that I should replace [0] * maxlen with bytearray(maxlen)?