kernel: dell_rbu local oops

drivers/firmware/dellrbu.c in the Linux kernel before 2.6.27.13, and 2.6.28.x before 2.6.28.2, allows local users to cause a denial of service system crash via a read system call that specifies zero bytes from the 1 imagetype or 2 packetsize file in /sys/devices/platform/dellrbu/...