cfg80211: fix in nl80211_set_reg()

There is a race on access to last_request and its alpha2
through reg_is_valid_request() and us possibly processing
first another regulatory request on another CPU. We avoid
this improbably race by locking with the cfg80211_mutex as
we should have done in the first place. While at it add
the assert on locking on reg_is_valid_request().

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

net/wireless/nl80211.c

@@ -2570,6 +2570,8 @@ static int nl80211_set_reg(struct sk_buff *skb, struct genl_info *info)
 			return -EINVAL;
 	}
 
+	mutex_lock(&cfg80211_mutex);
+
 	if (!reg_is_valid_request(alpha2)) {
 		r = -EINVAL;
 		goto bad_reg;
@@ -2607,13 +2609,14 @@ static int nl80211_set_reg(struct sk_buff *skb, struct genl_info *info)
 
 	BUG_ON(rule_idx != num_rules);
 
-	mutex_lock(&cfg80211_mutex);
 	r = set_regdom(rd);
+
 	mutex_unlock(&cfg80211_mutex);
 
 	return r;
 
  bad_reg:
+	mutex_unlock(&cfg80211_mutex);
 	kfree(rd);
 	return r;
 }

net/wireless/reg.c

@@ -382,6 +382,8 @@ static int call_crda(const char *alpha2)
 /* Used by nl80211 before kmalloc'ing our regulatory domain */
 bool reg_is_valid_request(const char *alpha2)
 {
+	assert_cfg80211_lock();
+
 	if (!last_request)
 		return false;