The Linux kernel before 3.4.5 on the x86 platform, when Physical Address Extension (PAE) is enabled, does not properly use the Page Middle Directory (PMD), which allows local users to cause a denial of service (panic) via a crafted application that triggers a race condition.
http://marc.info/?l=bugtraq&m=139447903326211&w=2
http://rhn.redhat.com/errata/RHSA-2012-0743.html
https://bugzilla.redhat.com/show_bug.cgi?id=822821
https://github.com/torvalds/linux/commit/26c191788f18129af0eb32a358cdaea0c7479626
http://ubuntu.com/usn/usn-1529-1