The qdisc_notify function in net/sched/sch_api.c in the Linux kernel before 2.6.35 does not prevent tc_fill_qdisc function calls referencing builtin (aka CQ_F_BUILTIN) Qdisc structures, which allows local users to cause a denial of service (NULL pointer dereference and OOPS) or possibly have unspecified other impact via a crafted call.