Integer underflow in the ieee80211_rx function in net/ieee80211/ieee80211_rx.c in the Linux kernel 2.6.x before 2.6.23 allows remote attackers to cause a denial of service (crash) via a crafted SKB length value in a runt IEEE 802.11 frame when the IEEE80211_STYPE_QOS_DATA flag is set, aka an "off-by-two error."