Integer signedness error in the genkbd_commonioctl function in sys/dev/kbd/kbd.c in FreeBSD 9.3 before p42, 10.1 before p34, 10.2 before p17, and 10.3 before p3 allows local users to obtain sensitive information from kernel memory, cause a denial of service (memory overwrite and kernel crash), or gain privileges via a negative value in the flen structure member in the arg argument in a SETFKEY ioctl call, which triggers a "two way heap and stack overflow."