mac80211: flush keys for AP mode on ieee80211_do_stop

Userspace can add keys to an AP mode interface before start_ap has been
called. If there have been no calls to start_ap/stop_ap in the mean
time, the keys will still be around when the interface is brought down.
Signed-off-by: NFelix Fietkau <nbd@openwrt.org>
[adjust comments, fix AP_VLAN case]
Signed-off-by: NJohannes Berg <johannes.berg@intel.com>

net/mac80211/iface.c

@@ -898,6 +898,8 @@ static void ieee80211_do_stop(struct ieee80211_sub_if_data *sdata,
 		list_del(&sdata->u.vlan.list);
 		mutex_unlock(&local->mtx);
 		RCU_INIT_POINTER(sdata->vif.chanctx_conf, NULL);
+		/* see comment in the default case below */
+		ieee80211_free_keys(sdata, true);
 		/* no need to tell driver */
 		break;
 	case NL80211_IFTYPE_MONITOR:
@@ -923,17 +925,16 @@ static void ieee80211_do_stop(struct ieee80211_sub_if_data *sdata,
 		/*
 		 * When we get here, the interface is marked down.
 		 * Free the remaining keys, if there are any
-		 * (shouldn't be, except maybe in WDS mode?)
+		 * (which can happen in AP mode if userspace sets
+		 * keys before the interface is operating, and maybe
+		 * also in WDS mode)
 		 *
 		 * Force the key freeing to always synchronize_net()
 		 * to wait for the RX path in case it is using this
-		 * interface enqueuing frames * at this very time on
+		 * interface enqueuing frames at this very time on
 		 * another CPU.
 		 */
 		ieee80211_free_keys(sdata, true);
-
-		/* fall through */
-	case NL80211_IFTYPE_AP:
 		skb_queue_purge(&sdata->skb_queue);
 	}