wifi: mac80211: fix NULL pointer deref with non-MLD STA

If we have a non-MLD STA on an AP MLD, we crash while
adding the station. Fix that, in this case we need to
use the STA's address also on the link data structure.

Fixes: f36fe0a2 ("wifi: mac80211: fix up link station creation/insertion")
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/cfg.c

@@ -1854,10 +1854,15 @@ static int ieee80211_add_station(struct wiphy *wiphy, struct net_device *dev,
 	    !sdata->u.mgd.associated)
 		return -EINVAL;
 
+	/*
+	 * If we have a link ID, it can be a non-MLO station on an AP MLD,
+	 * but we need to have a link_mac in that case as well, so use the
+	 * STA's MAC address in that case.
+	 */
 	if (params->link_sta_params.link_id >= 0)
 		sta = sta_info_alloc_with_link(sdata, mac,
 					       params->link_sta_params.link_id,
-					       params->link_sta_params.link_mac,
+					       params->link_sta_params.link_mac ?: mac,
 					       GFP_KERNEL);
 	else
 		sta = sta_info_alloc(sdata, mac, GFP_KERNEL);