cfg80211: fix for duplicate userspace replies

This fixes an incorrect assumption (BUG_ON) made in
cfg80211 when handling country IE regulatory requests.
The assumption was that we won't try to call_crda()
twice for the same event and therefore we will not
recieve two replies through nl80211 for the regulatory
request. As it turns out it is true we don't call_crda()
twice for the same event, however, kobject_uevent_env()
*might* send the udev event twice and/or userspace can
simply process the udev event twice. We remove the BUG_ON()
and simply ignore the duplicate request.

For details refer to this thread:

http://marc.info/?l=linux-wireless&m=124149987921337&w=2

Cc: stable@kernel.org
Reported-by: NMaxim Levitsky <maximlevitsky@gmail.com>
Signed-off-by: NLuis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

net/wireless/reg.c

@@ -2171,7 +2171,13 @@ static int __set_regdom(const struct ieee80211_regdomain *rd)
 	 * the country IE rd with what CRDA believes that country should have
 	 */
 
-	BUG_ON(!country_ie_regdomain);
+	/*
+	 * Userspace could have sent two replies with only
+	 * one kernel request. By the second reply we would have
+	 * already processed and consumed the country_ie_regdomain.
+	 */
+	if (!country_ie_regdomain)
+		return -EALREADY;
 	BUG_ON(rd == country_ie_regdomain);
 
 	/*