cfg80211: fix race in giwrate

cfg80211_wext_giwrate doesn't lock the wdev, so it
cannot access current_bss race-free. Also, there's
little point in trying to ask the driver for an AP
that it never told us about, so avoid that case.
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/wireless/wext-compat.c

@@ -1127,7 +1127,7 @@ int cfg80211_wext_giwrate(struct net_device *dev,
 	struct cfg80211_registered_device *rdev = wiphy_to_dev(wdev->wiphy);
 	/* we are under RTNL - globally locked - so can use a static struct */
 	static struct station_info sinfo;
-	u8 *addr;
+	u8 addr[ETH_ALEN];
 	int err;
 
 	if (wdev->iftype != NL80211_IFTYPE_STATION)
@@ -1136,12 +1136,15 @@ int cfg80211_wext_giwrate(struct net_device *dev,
 	if (!rdev->ops->get_station)
 		return -EOPNOTSUPP;
 
+	err = 0;
+	wdev_lock(wdev);
 	if (wdev->current_bss)
-		addr = wdev->current_bss->pub.bssid;
-	else if (wdev->wext.connect.bssid)
-		addr = wdev->wext.connect.bssid;
+		memcpy(addr, wdev->current_bss->pub.bssid, ETH_ALEN);
 	else
-		return -EOPNOTSUPP;
+		err = -EOPNOTSUPP;
+	wdev_unlock(wdev);
+	if (err)
+		return err;
 
 	err = rdev->ops->get_station(&rdev->wiphy, dev, addr, &sinfo);
 	if (err)