This program demonstrates how to escalate privileges using an overlayfs mount within a user namespace.
You can download this exploit from the following link: https://packetstormsecurity.com/files/download/135219/UserNamespaceOverlayfsSetuidWriteExec.c
Source: https://packetstormsecurity.com/files/135219/Linux-Kernel-overlayfs-Local-Privilege-Escalation.html