The cookie feature in the packet action API implementation in net/sched/act_api.c in the Linux kernel 4.11.x through 4.11-rc7 mishandles the tb nlattr array which allows local users to cause a denial of service (uninitialized memory access and refcount underflow and system hang or crash) or possibly have unspecified other impact via \tc filter add\ commands in certain contexts. NOTE: this does not affect stable kernels such as 4.10.x from kernel.org.