arch/x86/kernel/tls.c in the Thread Local Storage (TLS) implementation in the Linux kernel through 3.18.1 allows local users to bypass the espfix protection mechanism, and consequently makes it easier for local users to bypass the ASLR protection mechanism, via a crafted application that makes a set_thread_area system call and later reads a 16-bit value.
git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git%3Ba=commit%3Bh=41bdc78544b8a93a9c6814b8bbbfef966272abbe
lists.opensuse.org/opensuse-security-announce/2015-03/msg00025.html
lists.opensuse.org/opensuse-security-announce/2015-04/msg00015.html
rhn.redhat.com/errata/RHSA-2015-1272.html
secunia.com/advisories/62801
www.debian.org/security/2015/dsa-3128
www.mandriva.com/security/advisories?name=MDVSA-2015:058
www.openwall.com/lists/oss-security/2014/12/15/6
www.securityfocus.com/bid/71684
www.ubuntu.com/usn/USN-2490-1
www.ubuntu.com/usn/USN-2491-1
www.ubuntu.com/usn/USN-2492-1
www.ubuntu.com/usn/USN-2493-1
www.ubuntu.com/usn/USN-2515-1
www.ubuntu.com/usn/USN-2516-1
www.ubuntu.com/usn/USN-2517-1
www.ubuntu.com/usn/USN-2518-1
bugzilla.redhat.com/show_bug.cgi?id=1172797
github.com/torvalds/linux/commit/41bdc78544b8a93a9c6814b8bbbfef966272abbe