The l2tp_ip6_getname function in net/l2tp/l2tp_ip6.c in the Linux kernel before 3.6 does not initialize a certain structure member, which allows local users to obtain sensitive information from kernel stack memory via a crafted application.
https://www.kernel.org/pub/linux/kernel/v3.x/patch-3.6.bz2
https://github.com/torvalds/linux/commit/04d4fbca1017c11381e7d82acea21dd741e748bc