Ubuntu Security Notice 4917-1 - It was discovered that the overlayfs implementation in the Linux kernel did not properly validate the application of file system capabilities with respect to user namespaces. A local attacker could use this to gain elevated privileges. Vincent Dehors discovered that the shiftfs file system in the Ubuntu Linux kernel did not properly handle faults in copy_from_user when passing through ioctls to an underlying file system. A local attacker could use this to cause a denial of service or execute arbitrary code. Various other issues were also addressed.