fs/overlayfs/dir.c in the OverlayFS filesystem implementation in the Linux kernel before 4.6 does not properly verify the upper dentry before proceeding with unlink and rename system-call processing, which allows local users to cause a denial of service (system crash) via a rename system call that specifies a self-hardlink. It was discovered that the OverlayFS implementation in the Linux kernel did not properly verify dentry state before proceeding with unlink and rename operations. A local attacker could use this to cause a denial of service (system crash).