The pppol2tp_xmit function in drivers/net/pppol2tp.c in the L2TP implementation in the Linux kernel before 2.6.34 does not properly validate certain values associated with an interface, which allows attackers to cause a denial of service (NULL pointer dereference and OOPS) or possibly have unspecified other impact via vectors related to a routing change.
git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git%3Ba=commit%3Bh=3feec9095d12e311b7d4eb7fe7e5dfa75d4a72a5
lists.opensuse.org/opensuse-security-announce/2010-08/msg00000.html
www.kernel.org/pub/linux/kernel/v2.6/ChangeLog-2.6.34
www.openwall.com/lists/oss-security/2010/06/23/3
www.openwall.com/lists/oss-security/2010/07/04/2
www.openwall.com/lists/oss-security/2010/07/04/3
www.openwall.com/lists/oss-security/2010/07/06/11
www.ubuntu.com/usn/USN-1000-1
bugzilla.redhat.com/show_bug.cgi?id=607054