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.
https://github.com/torvalds/linux/commit/11f3710417d026ea2f4fcf362d866342c5274185
https://bugzilla.redhat.com/show_bug.cgi?id=1355650
http://www.ubuntu.com/usn/USN-3070-4
http://www.ubuntu.com/usn/USN-3070-3
http://www.ubuntu.com/usn/USN-3070-2
http://www.ubuntu.com/usn/USN-3070-1
http://www.securitytracker.com/id/1036273
http://www.securityfocus.com/bid/91709
http://www.oracle.com/technetwork/topics/security/ovmbulletinjul2016-3090546.html
http://www.oracle.com/technetwork/topics/security/linuxbulletinjul2016-3090544.html
http://www.openwall.com/lists/oss-security/2016/07/11/8
http://rhn.redhat.com/errata/RHSA-2016-1875.html