cfg80211: check regulatory request alpha2 early

Currently nl80211 allows userspace to send the kernel
a bogus regulatory domain with at most 32 rules set
and it won't reject it until after its allocated
memory. Let's be smart about it and take advantage
that the last_request is now available under RTNL
and check if the alpha2 matches an expected request
and reject any bogus userspace requests prior to
hitting the memory allocator.
Signed-off-by: Luis R. Rodriguez <mcgrof@do-not-panic.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/wireless/nl80211.c

@@ -5100,6 +5100,9 @@ static int nl80211_set_reg(struct sk_buff *skb, struct genl_info *info)
 			return -EINVAL;
 	}
 
+	if (!reg_is_valid_request(alpha2))
+		return -EINVAL;
+
 	size_of_regd = sizeof(struct ieee80211_regdomain) +
 		       num_rules * sizeof(struct ieee80211_reg_rule);
 

net/wireless/reg.c

@@ -450,7 +450,7 @@ static int call_crda(const char *alpha2)
 	return kobject_uevent(&reg_pdev->dev.kobj, KOBJ_CHANGE);
 }
 
-static bool reg_is_valid_request(const char *alpha2)
+bool reg_is_valid_request(const char *alpha2)
 {
 	struct regulatory_request *lr = get_last_request();
 

net/wireless/reg.h

@@ -18,6 +18,7 @@
 
 extern const struct ieee80211_regdomain __rcu *cfg80211_regdomain;
 
+bool reg_is_valid_request(const char *alpha2);
 bool is_world_regdom(const char *alpha2);
 bool reg_supported_dfs_region(u8 dfs_region);