The key_user_lookup function in security/keys/key.c in Linux kernel 2.6.10 to 2.6.11.8 may allow attackers to cause a denial of service (oops) via SMP.
http://www.securityfocus.com/archive/1/427980/100/0/threaded
http://linux.bkbits.net:8080/linux-2.6/cset%40423078fafVa6mAyny23YZ87hDipmTw