cfg80211: Save the regulatory domain with a lock

Saving the regulatory domain while setting custom regulatory domain
was done while accessing a RCU protected pointer but without any
protection.

Fix this by using RTNL while accessing the pointer.
Signed-off-by: Ilan Peer <ilan.peer@intel.com>
Reported-by: syzbot+27771d4abcd9b7a1f5d3@syzkaller.appspotmail.com
Reported-by: syzbot+db4035751c56c0079282@syzkaller.appspotmail.com
Reported-by: Hans de Goede <hdegoede@redhat.com>
Fixes: beee2469 ("cfg80211: Save the regulatory domain when setting custom regulatory")
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20210105165657.613e9a876829.Ia38d27dbebea28bf9c56d70691d243186ede70e7@changeidSigned-off-by: Johannes Berg <johannes.berg@intel.com>

net/wireless/reg.c

@@ -5,7 +5,7 @@
  * Copyright 2008-2011	Luis R. Rodriguez <mcgrof@qca.qualcomm.com>
  * Copyright 2013-2014  Intel Mobile Communications GmbH
  * Copyright      2017  Intel Deutschland GmbH
- * Copyright (C) 2018 - 2019 Intel Corporation
+ * Copyright (C) 2018 - 2021 Intel Corporation
  *
  * Permission to use, copy, modify, and/or distribute this software for any
  * purpose with or without fee is hereby granted, provided that the above
@@ -139,6 +139,11 @@ static const struct ieee80211_regdomain *get_cfg80211_regdom(void)
 	return rcu_dereference_rtnl(cfg80211_regdomain);
 }
 
+/*
+ * Returns the regulatory domain associated with the wiphy.
+ *
+ * Requires either RTNL or RCU protection
+ */
 const struct ieee80211_regdomain *get_wiphy_regdom(struct wiphy *wiphy)
 {
 	return rcu_dereference_rtnl(wiphy->regd);
@@ -2571,9 +2576,13 @@ void wiphy_apply_custom_regulatory(struct wiphy *wiphy,
 	if (IS_ERR(new_regd))
 		return;
 
+	rtnl_lock();
+
 	tmp = get_wiphy_regdom(wiphy);
 	rcu_assign_pointer(wiphy->regd, new_regd);
 	rcu_free_regdom(tmp);
+
+	rtnl_unlock();
 }
 EXPORT_SYMBOL(wiphy_apply_custom_regulatory);