Linux Nested User Namespace idmap Limit Local Privilege Escalation

This module exploits a vulnerability in Linux kernels 4.15.0 to 4.18.18,
and 4.19.0 to 4.19.1, where broken uid/gid mappings between nested user
namespaces and kernel uid/gid mappings allow elevation to root
(CVE-2018-18955).

The target system must have unprivileged user namespaces enabled and
the newuidmap and newgidmap helpers installed (from uidmap package).

This module has been tested successfully on:

Fedora Workstation 28 kernel 4.16.3-301.fc28.x86_64;
Kubuntu 18.04 LTS kernel 4.15.0-20-generic (x86_64);
Linux Mint 19 kernel 4.15.0-20-generic (x86_64);
Ubuntu Linux 18.04.1 LTS kernel 4.15.0-20-generic (x86_64).