mac80211: fix action frame length checks

The action frame length checks are one too small, there's not just
an action code as the comment makes you believe, there's a category
code too, and the category code is required in each action frame
(hence part of IEEE80211_MIN_ACTION_SIZE).

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/net/mac80211/mesh_hwmp.c b/net/mac80211/mesh_hwmp.c
index eeb0ce2..59fd7fe 100644
--- a/net/mac80211/mesh_hwmp.c
+++ b/net/mac80211/mesh_hwmp.c
@@ -581,6 +581,10 @@
 	size_t baselen;
 	u32 last_hop_metric;
 
+	/* need action_code */
+	if (len < IEEE80211_MIN_ACTION_SIZE + 1)
+		return;
+
 	baselen = (u8 *) mgmt->u.action.u.mesh_action.variable - (u8 *) mgmt;
 	ieee802_11_parse_elems(mgmt->u.action.u.mesh_action.variable,
 			len - baselen, &elems);