mac80211: match only assigned bss in sta_info_get_bss

sta_info_get_bss() is used to match STA pointers
for VLAN/AP interfaces, but if the same station
is also added to multiple other interfaces it
will erroneously match because both pointers are
NULL, fix this by ignoring NULL pointers here.

Reported-by: Ben Greear <greearb@candelatech.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/mac80211/sta_info.c

@@ -125,7 +125,7 @@ struct sta_info *sta_info_get_bss(struct ieee80211_sub_if_data *sdata,
 				    lockdep_is_held(&local->sta_mtx));
 	while (sta) {
 		if ((sta->sdata == sdata ||
-		     sta->sdata->bss == sdata->bss) &&
+		     (sta->sdata->bss && sta->sdata->bss == sdata->bss)) &&
 		    memcmp(sta->sta.addr, addr, ETH_ALEN) == 0)
 			break;
 		sta = rcu_dereference_check(sta->hnext,