cfg80211: fix BSS struct IE access races

When a BSS struct is updated, the IEs are currently
overwritten or freed. This can lead to races if some
other CPU is accessing the BSS struct and using the
IEs concurrently.

Fix this by always allocating the IEs in a new struct
that holds the data and length and protecting access
to this new struct with RCU.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/wireless/reg.c

@@ -1797,7 +1797,7 @@ EXPORT_SYMBOL(regulatory_hint);
  */
 void regulatory_hint_11d(struct wiphy *wiphy,
 			 enum ieee80211_band band,
-			 u8 *country_ie,
+			 const u8 *country_ie,
 			 u8 country_ie_len)
 {
 	char alpha2[2];