arch/x86/kernel/entry_64.S in the Linux kernel before 3.17.5 does not properly handle faults associated with the Stack Segment (SS) segment register, which allows local users to gain privileges by triggering an IRET instruction that leads to access to a GS Base address from the wrong space.
http://lists.opensuse.org/opensuse-security-announce/2015-03/msg00025.html
http://lists.opensuse.org/opensuse-security-announce/2015-04/msg00015.html
http://lists.opensuse.org/opensuse-security-announce/2015-04/msg00020.html
http://marc.info/?l=bugtraq&m=142722450701342&w=2
http://marc.info/?l=bugtraq&m=142722544401658&w=2
http://rhn.redhat.com/errata/RHSA-2014-1998.html
http://rhn.redhat.com/errata/RHSA-2014-2008.html
http://rhn.redhat.com/errata/RHSA-2014-2028.html
http://rhn.redhat.com/errata/RHSA-2014-2031.html
http://rhn.redhat.com/errata/RHSA-2015-0009.html
https://bugzilla.redhat.com/show_bug.cgi?id=1172806
http://secunia.com/advisories/62336
https://github.com/torvalds/linux/commit/6f442be2fb22be02cafa606f1769fa1e6f894441
https://www.kernel.org/pub/linux/kernel/v3.x/ChangeLog-3.17.5
http://www.exploit-db.com/exploits/36266
http://www.openwall.com/lists/oss-security/2014/12/15/6