Add regression test for CVE-2017-16939

Based on the reproducing code from Mohammed Ghannam, published on
https://blogs.securiteam.com/index.php/archives/3535

Warning! If the kernel is vulnerable to this CVE, it will definitely die. So do not run this on a production machine!

---
Changes to v1:
v1 was copied from the original reproducer. This v2 now simplified things, like not using any fork() and only allocating memory in the setup(). In addition, the many small functions were merged into still rather short setup() and run().

---
 runtest/cve                    |  1 +
 testcases/cve/.gitignore       |  1 +
 testcases/cve/cve-2017-16939.c | 89 ++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 91 insertions(+)
 create mode 100644 testcases/cve/cve-2017-16939.c

index 0c385c670..78799e2ff 100644
@@ -30,3 +30,4 @@ cve-2017-17807 request_key04
 cve-2017-1000364 stack_clash
 cve-2017-5754 meltdown
 cve-2017-17052 cve-2017-17052
+cve-2017-16939 cve-2017-16939

index c878069f1..f813e56ed 100644
@@ -12,3 +12,4 @@ cve-2017-5669
 meltdown
 stack_clash
 cve-2017-17052
+cve-2017-16939

2.13.6

Hi!
Pushed, thanks.

Cyril Hrubis
[email protected]