kernel/ptrace.c in the Linux kernel through 4.4.1 mishandles uid and gid mappings, which allows local users to gain privileges by establishing a user namespace, waiting for a root process to enter that namespace with an unsafe uid or gid, and then using the ptrace system call. NOTE: the vendor states "there is no kernel bug here.
https://lkml.org/lkml/2015/12/25/71
https://bugzilla.redhat.com/show_bug.cgi?id=1295287
http://www.securitytracker.com/id/1034899
http://www.securityfocus.com/bid/79899
http://www.openwall.com/lists/oss-security/2015/12/31/5
http://www.openwall.com/lists/oss-security/2015/12/17/12
http://www.debian.org/security/2016/dsa-3434
http://marc.info/?l=linux-kernel&m=145204641422813&w=2
http://marc.info/?l=linux-kernel&m=145204362722256&w=2
http://lists.opensuse.org/opensuse-security-announce/2016-07/msg00005.html
http://lists.opensuse.org/opensuse-security-announce/2016-04/msg00037.html
http://lists.opensuse.org/opensuse-security-announce/2016-04/msg00036.html
http://lists.opensuse.org/opensuse-security-announce/2016-04/msg00034.html
http://lists.opensuse.org/opensuse-security-announce/2016-04/msg00033.html
http://lists.opensuse.org/opensuse-security-announce/2016-04/msg00032.html
http://lists.opensuse.org/opensuse-security-announce/2016-04/msg00031.html
http://lists.opensuse.org/opensuse-security-announce/2016-04/msg00030.html
http://lists.opensuse.org/opensuse-security-announce/2016-04/msg00029.html
http://lists.opensuse.org/opensuse-security-announce/2016-04/msg00028.html
http://lists.opensuse.org/opensuse-security-announce/2016-04/msg00027.html
http://lists.opensuse.org/opensuse-security-announce/2016-04/msg00026.html
http://lists.opensuse.org/opensuse-security-announce/2016-04/msg00025.html
http://lists.opensuse.org/opensuse-security-announce/2016-04/msg00019.html
http://lists.opensuse.org/opensuse-security-announce/2016-04/msg00015.html
http://lists.fedoraproject.org/pipermail/package-announce/2016-February/176484.html