Upstream implemented obfuscation for function pointers stored in stdio streams created with fopencookie:
Author: Florian Weimer <firstname.lastname@example.org>
Date: Sat Jun 11 12:07:14 2016 +0200
fopencookie: Mangle function pointers stored on the heap [BZ #20222]
This does not have ABI impact and is necessary to block libio-based code execution exploits (after vtable verification has been enabled).
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.
For information on the advisory, and where to find the updated
files, follow the link below.
If the solution does not work for you, open a new bug report.