nl80211: check channel switch validity better

Before allowing userspace to initiate a channel switch, check
that it's actually connected in some sense. Also use a more
appropriate error code for the not connected case.
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/wireless/nl80211.c

@@ -5771,10 +5771,15 @@ static int nl80211_channel_switch(struct sk_buff *skb, struct genl_info *info)
 
 		/* useless if AP is not running */
 		if (!wdev->beacon_interval)
-			return -EINVAL;
+			return -ENOTCONN;
 		break;
 	case NL80211_IFTYPE_ADHOC:
+		if (!wdev->ssid_len)
+			return -ENOTCONN;
+		break;
 	case NL80211_IFTYPE_MESH_POINT:
+		if (!wdev->mesh_id_len)
+			return -ENOTCONN;
 		break;
 	default:
 		return -EOPNOTSUPP;