regulatory: add NUL to alpha2

commit a5fe8e76 upstream.

alpha2 is defined as 2-chars array, but is used in multiple
places as string (e.g. with nla_put_string calls), which
might leak kernel data.

Solve it by simply adding an extra char for the NULL
terminator, making such operations safe.
Signed-off-by: Eliad Peller <eliadx.peller@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

include/net/regulatory.h

@@ -92,7 +92,7 @@ struct ieee80211_reg_rule {
 
 struct ieee80211_regdomain {
 	u32 n_reg_rules;
-	char alpha2[2];
+	char alpha2[3];
 	struct ieee80211_reg_rule reg_rules[];
 };