CVE-2016-5195 test case

[Andy Lutomirski <luto () kernel org>]

I sat on this longer than makes any sense given how easy to reproduce
CVE-2016-5195 is, but here's a reasonably portable reproducer.  It's
intended to have no side effects, but your mileage may vary.

https://github.com/amluto/vulnerabilities/blob/master/others/CVE-2016-5195/test_CVE-2016-5195.c

This will use /proc/self/mem or ptrace automatically, and it's
intended to be portable to a wide range of kernels.  It's an improved
version of the test case I originally sent out to distros (oops!).

--Andy