mac80211: fix HT information element parsing

There's no checking that the HT IEs are of the right length
which can be used by an attacker to cause an out-of-bounds
access by sending a too short HT information/capability IE.
Fix it by simply pretending those IEs didn't exist when too
short.
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/mac80211/ieee80211_i.h

@@ -816,8 +816,8 @@ struct ieee802_11_elems {
 	u8 *ext_supp_rates;
 	u8 *wmm_info;
 	u8 *wmm_param;
-	u8 *ht_cap_elem;
-	u8 *ht_info_elem;
+	struct ieee80211_ht_cap *ht_cap_elem;
+	struct ieee80211_ht_addt_info *ht_info_elem;
 	u8 *mesh_config;
 	u8 *mesh_id;
 	u8 *peer_link;
@@ -844,8 +844,6 @@ struct ieee802_11_elems {
 	u8 ext_supp_rates_len;
 	u8 wmm_info_len;
 	u8 wmm_param_len;
-	u8 ht_cap_elem_len;
-	u8 ht_info_elem_len;
 	u8 mesh_config_len;
 	u8 mesh_id_len;
 	u8 peer_link_len;

net/mac80211/mlme.c

@@ -1348,10 +1348,8 @@ static void ieee80211_rx_mgmt_assoc_resp(struct ieee80211_sub_if_data *sdata,
 	    (ifsta->flags & IEEE80211_STA_WMM_ENABLED)) {
 		struct ieee80211_ht_bss_info bss_info;
 		ieee80211_ht_cap_ie_to_ht_info(
-				(struct ieee80211_ht_cap *)
 				elems.ht_cap_elem, &sta->sta.ht_info);
 		ieee80211_ht_addt_info_ie_to_ht_bss_info(
-				(struct ieee80211_ht_addt_info *)
 				elems.ht_info_elem, &bss_info);
 		ieee80211_handle_ht(local, 1, &sta->sta.ht_info, &bss_info);
 	}
@@ -1709,7 +1707,6 @@ static void ieee80211_rx_mgmt_beacon(struct ieee80211_sub_if_data *sdata,
 		struct ieee80211_ht_bss_info bss_info;
 
 		ieee80211_ht_addt_info_ie_to_ht_bss_info(
-				(struct ieee80211_ht_addt_info *)
 				elems.ht_info_elem, &bss_info);
 		changed |= ieee80211_handle_ht(local, 1, &conf->ht_conf,
 					       &bss_info);

net/mac80211/util.c

@@ -529,12 +529,12 @@ void ieee802_11_parse_elems(u8 *start, size_t len,
 			elems->ext_supp_rates_len = elen;
 			break;
 		case WLAN_EID_HT_CAPABILITY:
-			elems->ht_cap_elem = pos;
-			elems->ht_cap_elem_len = elen;
+			if (elen >= sizeof(struct ieee80211_ht_cap))
+				elems->ht_cap_elem = (void *)pos;
 			break;
 		case WLAN_EID_HT_EXTRA_INFO:
-			elems->ht_info_elem = pos;
-			elems->ht_info_elem_len = elen;
+			if (elen >= sizeof(struct ieee80211_ht_addt_info))
+				elems->ht_info_elem = (void *)pos;
 			break;
 		case WLAN_EID_MESH_ID:
 			elems->mesh_id = pos;