Linux Kernel OverlayFS Logic Upper Attributes Local Privilege Escalation Exploit

On Ubuntu kernels carrying both c914c0e27eb0 and "UBUNTU: SAUCE: overlayfs: Skip permission checking for trusted.overlayfs.* xattrs", an unprivileged user may set privileged extended attributes on the mounted files, leading them to be set on the upper files without the appropriate security checks. This module exploits this in order to achieve LPE.