The Linux kernel before 2.6.39 does not properly create transparent huge pages in response to a MAP_PRIVATE mmap system call on /dev/zero, which allows local users to cause a denial of service (system crash) via a crafted application.
https://bugzilla.redhat.com/show_bug.cgi?id=714761
http://www.openwall.com/lists/oss-security/2011/06/20/14
http://ftp.osuosl.org/pub/linux/kernel/v2.6/ChangeLog-2.6.39