fs/eventpoll.c in the Linux kernel before 2.6.38 places epoll file descriptors within other epoll data structures without properly checking for (1) closed loops or (2) deep chains, which allows local users to cause a denial of service (deadlock or stack memory consumption) via a crafted application that makes epoll_create and epoll_ctl system calls.
https://lkml.org/lkml/2011/2/5/220
https://bugzilla.redhat.com/show_bug.cgi?id=681575
http://openwall.com/lists/oss-security/2011/03/02/2