regulatory: use RCU to protect global and wiphy regdomains

To simplify the locking and not require cfg80211_mutex
(which nl80211 uses to access the global regdomain) and
also to make it possible for drivers to access their
wiphy->regd safely, use RCU to protect these pointers.

Acked-by: Luis R. Rodriguez <mcgrof@do-not-panic.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

include/net/cfg80211.h

@@ -2369,7 +2369,7 @@ struct wiphy {
 
 	/* fields below are read-only, assigned by cfg80211 */
 
-	const struct ieee80211_regdomain *regd;
+	const struct ieee80211_regdomain __rcu *regd;
 
 	/* the item in /sys/class/ieee80211/ points to this,
 	 * you need use set_wiphy_dev() (see below) */

include/net/regulatory.h

@@ -18,6 +18,7 @@
  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
 
+#include <linux/rcupdate.h>
 
 /**
  * enum environment_cap - Environment parsed from country IE
@@ -101,6 +102,7 @@ struct ieee80211_reg_rule {
 };
 
 struct ieee80211_regdomain {
+	struct rcu_head rcu_head;
 	u32 n_reg_rules;
 	char alpha2[2];
 	u8 dfs_region;

net/wireless/nl80211.c

@@ -3787,12 +3787,8 @@ static int nl80211_req_set_reg(struct sk_buff *skb, struct genl_info *info)
 	 * window between nl80211_init() and regulatory_init(), if that is
 	 * even possible.
 	 */
-	mutex_lock(&cfg80211_mutex);
-	if (unlikely(!cfg80211_regdomain)) {
-		mutex_unlock(&cfg80211_mutex);
+	if (unlikely(!rcu_access_pointer(cfg80211_regdomain)))
 		return -EINPROGRESS;
-	}
-	mutex_unlock(&cfg80211_mutex);
 
 	if (!info->attrs[NL80211_ATTR_REG_ALPHA2])
 		return -EINVAL;
@@ -4152,6 +4148,7 @@ static int nl80211_update_mesh_config(struct sk_buff *skb,
 
 static int nl80211_get_reg(struct sk_buff *skb, struct genl_info *info)
 {
+	const struct ieee80211_regdomain *regdom;
 	struct sk_buff *msg;
 	void *hdr = NULL;
 	struct nlattr *nl_reg_rules;
@@ -4174,35 +4171,36 @@ static int nl80211_get_reg(struct sk_buff *skb, struct genl_info *info)
 	if (!hdr)
 		goto put_failure;
 
-	if (nla_put_string(msg, NL80211_ATTR_REG_ALPHA2,
-			   cfg80211_regdomain->alpha2) ||
-	    (cfg80211_regdomain->dfs_region &&
-	     nla_put_u8(msg, NL80211_ATTR_DFS_REGION,
-			cfg80211_regdomain->dfs_region)))
-		goto nla_put_failure;
-
 	if (reg_last_request_cell_base() &&
 	    nla_put_u32(msg, NL80211_ATTR_USER_REG_HINT_TYPE,
 			NL80211_USER_REG_HINT_CELL_BASE))
 		goto nla_put_failure;
 
+	rcu_read_lock();
+	regdom = rcu_dereference(cfg80211_regdomain);
+
+	if (nla_put_string(msg, NL80211_ATTR_REG_ALPHA2, regdom->alpha2) ||
+	    (regdom->dfs_region &&
+	     nla_put_u8(msg, NL80211_ATTR_DFS_REGION, regdom->dfs_region)))
+		goto nla_put_failure_rcu;
+
 	nl_reg_rules = nla_nest_start(msg, NL80211_ATTR_REG_RULES);
 	if (!nl_reg_rules)
-		goto nla_put_failure;
+		goto nla_put_failure_rcu;
 
-	for (i = 0; i < cfg80211_regdomain->n_reg_rules; i++) {
+	for (i = 0; i < regdom->n_reg_rules; i++) {
 		struct nlattr *nl_reg_rule;
 		const struct ieee80211_reg_rule *reg_rule;
 		const struct ieee80211_freq_range *freq_range;
 		const struct ieee80211_power_rule *power_rule;
 
-		reg_rule = &cfg80211_regdomain->reg_rules[i];
+		reg_rule = &regdom->reg_rules[i];
 		freq_range = &reg_rule->freq_range;
 		power_rule = &reg_rule->power_rule;
 
 		nl_reg_rule = nla_nest_start(msg, i);
 		if (!nl_reg_rule)
-			goto nla_put_failure;
+			goto nla_put_failure_rcu;
 
 		if (nla_put_u32(msg, NL80211_ATTR_REG_RULE_FLAGS,
 				reg_rule->flags) ||
@@ -4216,17 +4214,20 @@ static int nl80211_get_reg(struct sk_buff *skb, struct genl_info *info)
 				power_rule->max_antenna_gain) ||
 		    nla_put_u32(msg, NL80211_ATTR_POWER_RULE_MAX_EIRP,
 				power_rule->max_eirp))
-			goto nla_put_failure;
+			goto nla_put_failure_rcu;
 
 		nla_nest_end(msg, nl_reg_rule);
 	}
+	rcu_read_unlock();
 
 	nla_nest_end(msg, nl_reg_rules);
 
 	genlmsg_end(msg, hdr);
 	err = genlmsg_reply(msg, info);
 	goto out;
 
+nla_put_failure_rcu:
+	rcu_read_unlock();
 nla_put_failure:
 	genlmsg_cancel(msg, hdr);
 put_failure: