The mbcache feature in the ext2 and ext4 filesystem implementations in the Linux kernel before 4.6 mishandles xattr block caching, which allows local users to cause a denial of service (soft lockup) via filesystem operations in environments that use many attributes, as demonstrated by Ceph and Samba.
git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=82939d7999dfc1f1998c4b1c12e2f19edbdff272
git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=be0726d33cb8f411945884664924bed3cb8c70ee
git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=f9a61eb4e2471c56a63cd804c7474128138c38ac
www.openwall.com/lists/oss-security/2016/08/22/2
www.openwall.com/lists/oss-security/2016/08/25/4
bugzilla.kernel.org/show_bug.cgi?id=107301
bugzilla.redhat.com/show_bug.cgi?id=1360968
github.com/torvalds/linux/commit/82939d7999dfc1f1998c4b1c12e2f19edbdff272
github.com/torvalds/linux/commit/be0726d33cb8f411945884664924bed3cb8c70ee
github.com/torvalds/linux/commit/f9a61eb4e2471c56a63cd804c7474128138c38ac
lwn.net/Articles/668718/
usn.ubuntu.com/3582-1/
usn.ubuntu.com/3582-2/