fs/proc/root.c in the procfs implementation in the Linux kernel before 3.2 does not properly interact with CLONE_NEWPID clone system calls, which allows remote attackers to cause a denial of service (reference leak and memory consumption) by making many connections to a daemon that uses PID namespaces to isolate clients, as demonstrated by vsftpd.
git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git%3Ba=commit%3Bh=905ad269c55fc62bee3da29f7b1d1efeba8aa1e1
ubuntu.com/usn/usn-1607-1
www.kernel.org/pub/linux/kernel/v3.x/
www.kernel.org/pub/linux/kernel/v3.x/patch-3.2.bz2
www.openwall.com/lists/oss-security/2012/04/20/25
www.openwall.com/lists/oss-security/2012/04/22/1
www.securityfocus.com/bid/55774
www.ubuntu.com/usn/USN-1594-1
bugzilla.novell.com/show_bug.cgi?id=757783
bugzilla.redhat.com/show_bug.cgi?id=815188
github.com/torvalds/linux/commit/905ad269c55fc62bee3da29f7b1d1efeba8aa1e1