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>

1 files changed, 66 insertions, 47 deletions

diff --git a/net/wireless/reg.c b/net/wireless/reg.c
index 35541d6d4145..9b64b201cdf1 100644
--- a/net/wireless/reg.c
+++ b/net/wireless/reg.c
@@ -95,15 +95,15 @@ static struct device_type reg_device_type = {
  * Central wireless core regulatory domains, we only need two,
  * the current one and a world regulatory domain in case we have no
  * information to give us an alpha2.
- * Protected by the cfg80211_mutex.
  */
-const struct ieee80211_regdomain *cfg80211_regdomain;
+const struct ieee80211_regdomain __rcu *cfg80211_regdomain;
 
 /*
  * Protects static reg.c components:
- *     - cfg80211_world_regdom
- *     - last_request
- *     - reg_num_devs_support_basehint
+ *      - cfg80211_regdomain (if not used with RCU)
+ *      - cfg80211_world_regdom
+ *      - last_request
+ *      - reg_num_devs_support_basehint
  */
 static DEFINE_MUTEX(reg_mutex);
 
@@ -118,6 +118,25 @@ static inline void assert_reg_lock(void)
         lockdep_assert_held(&reg_mutex);
 }
 
+static const struct ieee80211_regdomain *get_cfg80211_regdom(void)
+{
+        return rcu_dereference_protected(cfg80211_regdomain,
+                                         lockdep_is_held(&reg_mutex));
+}
+
+static const struct ieee80211_regdomain *get_wiphy_regdom(struct wiphy *wiphy)
+{
+        return rcu_dereference_protected(wiphy->regd,
+                                         lockdep_is_held(&reg_mutex));
+}
+
+static void rcu_free_regdom(const struct ieee80211_regdomain *r)
+{
+        if (!r)
+                return;
+        kfree_rcu((struct ieee80211_regdomain *)r, rcu_head);
+}
+
 /* Used to queue up regulatory hints */
 static LIST_HEAD(reg_requests_list);
 static spinlock_t reg_requests_lock;
@@ -186,22 +205,25 @@ MODULE_PARM_DESC(ieee80211_regdom, "IEEE 802.11 regulatory domain code");
 static void reset_regdomains(bool full_reset,
                              const struct ieee80211_regdomain *new_regdom)
 {
-        assert_cfg80211_lock();
+        const struct ieee80211_regdomain *r;
+
         assert_reg_lock();
 
+        r = get_cfg80211_regdom();
+
         /* avoid freeing static information or freeing something twice */
-        if (cfg80211_regdomain == cfg80211_world_regdom)
-                cfg80211_regdomain = NULL;
+        if (r == cfg80211_world_regdom)
+                r = NULL;
         if (cfg80211_world_regdom == &world_regdom)
                 cfg80211_world_regdom = NULL;
-        if (cfg80211_regdomain == &world_regdom)
-                cfg80211_regdomain = NULL;
+        if (r == &world_regdom)
+                r = NULL;
 
-        kfree(cfg80211_regdomain);
-        kfree(cfg80211_world_regdom);
+        rcu_free_regdom(r);
+        rcu_free_regdom(cfg80211_world_regdom);
 
         cfg80211_world_regdom = &world_regdom;
-        cfg80211_regdomain = new_regdom;
+        rcu_assign_pointer(cfg80211_regdomain, new_regdom);
 
         if (!full_reset)
                 return;
@@ -219,7 +241,6 @@ static void update_world_regdomain(const struct ieee80211_regdomain *rd)
 {
         WARN_ON(!last_request);
 
-        assert_cfg80211_lock();
         assert_reg_lock();
 
         reset_regdomains(false, rd);
@@ -280,11 +301,11 @@ static bool alpha2_equal(const char *alpha2_x, const char *alpha2_y)
 
 static bool regdom_changes(const char *alpha2)
 {
-        assert_cfg80211_lock();
+        const struct ieee80211_regdomain *r = get_cfg80211_regdom();
 
-        if (!cfg80211_regdomain)
+        if (!r)
                 return true;
-        return !alpha2_equal(cfg80211_regdomain->alpha2, alpha2);
+        return !alpha2_equal(r->alpha2, alpha2);
 }
 
 /*
@@ -727,7 +748,6 @@ int freq_reg_info(struct wiphy *wiphy, u32 center_freq,
         const struct ieee80211_regdomain *regd;
 
         assert_reg_lock();
-        assert_cfg80211_lock();
 
         /*
          * Follow the driver's regulatory domain, if present, unless a country
@@ -736,9 +756,9 @@ int freq_reg_info(struct wiphy *wiphy, u32 center_freq,
         if (last_request->initiator != NL80211_REGDOM_SET_BY_COUNTRY_IE &&
             last_request->initiator != NL80211_REGDOM_SET_BY_USER &&
             wiphy->regd)
-                regd = wiphy->regd;
+                regd = get_wiphy_regdom(wiphy);
         else
-                regd = cfg80211_regdomain;
+                regd = get_cfg80211_regdom();
 
         return freq_reg_info_regd(wiphy, center_freq, reg_rule, regd);
 }
@@ -809,8 +829,6 @@ static void handle_channel(struct wiphy *wiphy,
         const struct ieee80211_freq_range *freq_range = NULL;
         struct wiphy *request_wiphy = NULL;
 
-        assert_cfg80211_lock();
-
         request_wiphy = wiphy_idx_to_wiphy(last_request->wiphy_idx);
 
         flags = chan->orig_flags;
@@ -1060,15 +1078,17 @@ static void wiphy_update_beacon_reg(struct wiphy *wiphy)
 
 static bool reg_is_world_roaming(struct wiphy *wiphy)
 {
-        assert_cfg80211_lock();
+        const struct ieee80211_regdomain *cr = get_cfg80211_regdom();
+        const struct ieee80211_regdomain *wr = get_wiphy_regdom(wiphy);
 
-        if (is_world_regdom(cfg80211_regdomain->alpha2) ||
-            (wiphy->regd && is_world_regdom(wiphy->regd->alpha2)))
+        if (is_world_regdom(cr->alpha2) || (wr && is_world_regdom(wr->alpha2)))
                 return true;
+
         if (last_request &&
             last_request->initiator != NL80211_REGDOM_SET_BY_COUNTRY_IE &&
             wiphy->flags & WIPHY_FLAG_CUSTOM_REGULATORY)
                 return true;
+
         return false;
 }
 
@@ -1165,13 +1185,12 @@ static void wiphy_update_regulatory(struct wiphy *wiphy,
 {
         enum ieee80211_band band;
 
-        assert_cfg80211_lock();
         assert_reg_lock();
 
         if (ignore_reg_update(wiphy, initiator))
                 return;
 
-        last_request->dfs_region = cfg80211_regdomain->dfs_region;
+        last_request->dfs_region = get_cfg80211_regdom()->dfs_region;
 
         for (band = 0; band < IEEE80211_NUM_BANDS; band++)
                 handle_band(wiphy, initiator, wiphy->bands[band]);
@@ -1188,6 +1207,8 @@ static void update_all_wiphy_regulatory(enum nl80211_reg_initiator initiator)
         struct cfg80211_registered_device *rdev;
         struct wiphy *wiphy;
 
+        assert_cfg80211_lock();
+
         list_for_each_entry(rdev, &cfg80211_rdev_list, list) {
                 wiphy = &rdev->wiphy;
                 wiphy_update_regulatory(wiphy, initiator);
@@ -1402,7 +1423,7 @@ static void reg_set_request_processed(void)
  *
  * Returns one of the different reg request treatment values.
  *
- * Caller must hold &cfg80211_mutex and &reg_mutex
+ * Caller must hold &reg_mutex
  */
 static enum reg_request_treatment
 __regulatory_hint(struct wiphy *wiphy,
@@ -1412,20 +1433,18 @@ __regulatory_hint(struct wiphy *wiphy,
         bool intersect = false;
         enum reg_request_treatment treatment;
 
-        assert_cfg80211_lock();
-
         treatment = get_reg_request_treatment(wiphy, pending_request);
 
         switch (treatment) {
         case REG_REQ_INTERSECT:
                 if (pending_request->initiator ==
                     NL80211_REGDOM_SET_BY_DRIVER) {
-                        regd = reg_copy_regd(cfg80211_regdomain);
+                        regd = reg_copy_regd(get_cfg80211_regdom());
                         if (IS_ERR(regd)) {
                                 kfree(pending_request);
                                 return PTR_ERR(regd);
                         }
-                        wiphy->regd = regd;
+                        rcu_assign_pointer(wiphy->regd, regd);
                 }
                 intersect = true;
                 break;
@@ -1439,13 +1458,13 @@ __regulatory_hint(struct wiphy *wiphy,
                  */
                 if (treatment == REG_REQ_ALREADY_SET &&
                     pending_request->initiator == NL80211_REGDOM_SET_BY_DRIVER) {
-                        regd = reg_copy_regd(cfg80211_regdomain);
+                        regd = reg_copy_regd(get_cfg80211_regdom());
                         if (IS_ERR(regd)) {
                                 kfree(pending_request);
                                 return REG_REQ_IGNORE;
                         }
                         treatment = REG_REQ_ALREADY_SET;
-                        wiphy->regd = regd;
+                        rcu_assign_pointer(wiphy->regd, regd);
                         goto new_request;
                 }
                 kfree(pending_request);
@@ -2051,6 +2070,8 @@ static int __set_regdom(const struct ieee80211_regdomain *rd)
 
         /* Some basic sanity checks first */
 
+        assert_reg_lock();
+
         if (!reg_is_valid_request(rd->alpha2))
                 return -EINVAL;
 
@@ -2120,7 +2141,7 @@ static int __set_regdom(const struct ieee80211_regdomain *rd)
                 if (IS_ERR(regd))
                         return PTR_ERR(regd);
 
-                request_wiphy->regd = regd;
+                rcu_assign_pointer(request_wiphy->regd, regd);
                 reset_regdomains(false, rd);
                 return 0;
         }
@@ -2128,7 +2149,7 @@ static int __set_regdom(const struct ieee80211_regdomain *rd)
         /* Intersection requires a bit more work */
 
         if (last_request->initiator != NL80211_REGDOM_SET_BY_COUNTRY_IE) {
-                intersected_rd = regdom_intersect(rd, cfg80211_regdomain);
+                intersected_rd = regdom_intersect(rd, get_cfg80211_regdom());
                 if (!intersected_rd)
                         return -EINVAL;
 
@@ -2138,7 +2159,7 @@ static int __set_regdom(const struct ieee80211_regdomain *rd)
                  * domain we keep it for its private use
                  */
                 if (last_request->initiator == NL80211_REGDOM_SET_BY_DRIVER)
-                        request_wiphy->regd = rd;
+                        rcu_assign_pointer(request_wiphy->regd, rd);
                 else
                         kfree(rd);
 
@@ -2156,14 +2177,12 @@ static int __set_regdom(const struct ieee80211_regdomain *rd)
 /*
  * Use this call to set the current regulatory domain. Conflicts with
  * multiple drivers can be ironed out later. Caller must've already
- * kmalloc'd the rd structure. Caller must hold cfg80211_mutex
+ * kmalloc'd the rd structure.
  */
 int set_regdom(const struct ieee80211_regdomain *rd)
 {
         int r;
 
-        assert_cfg80211_lock();
-
         mutex_lock(&reg_mutex);
 
         /* Note that this doesn't update the wiphys, this is done below */
@@ -2177,7 +2196,8 @@ int set_regdom(const struct ieee80211_regdomain *rd)
         }
 
         /* This would make this whole thing pointless */
-        if (WARN_ON(!last_request->intersect && rd != cfg80211_regdomain)) {
+        if (WARN_ON(!last_request->intersect &&
+                    rd != get_cfg80211_regdom())) {
                 r = -EINVAL;
                 goto out;
         }
@@ -2185,7 +2205,7 @@ int set_regdom(const struct ieee80211_regdomain *rd)
         /* update all wiphys now with the new established regulatory domain */
         update_all_wiphy_regulatory(last_request->initiator);
 
-        print_regdomain(cfg80211_regdomain);
+        print_regdomain(get_cfg80211_regdom());
 
         nl80211_send_reg_change_event(last_request);
 
@@ -2238,7 +2258,8 @@ void wiphy_regulatory_deregister(struct wiphy *wiphy)
         if (!reg_dev_ignore_cell_hint(wiphy))
                 reg_num_devs_support_basehint--;
 
-        kfree(wiphy->regd);
+        rcu_free_regdom(get_wiphy_regdom(wiphy));
+        rcu_assign_pointer(wiphy->regd, NULL);
 
         if (last_request)
                 request_wiphy = wiphy_idx_to_wiphy(last_request->wiphy_idx);
@@ -2273,13 +2294,13 @@ int __init regulatory_init(void)
 
         reg_regdb_size_check();
 
-        cfg80211_regdomain = cfg80211_world_regdom;
+        rcu_assign_pointer(cfg80211_regdomain, cfg80211_world_regdom);
 
         user_alpha2[0] = '9';
         user_alpha2[1] = '7';
 
         /* We always try to get an update for the static regdomain */
-        err = regulatory_hint_core(cfg80211_regdomain->alpha2);
+        err = regulatory_hint_core(cfg80211_world_regdom->alpha2);
         if (err) {
                 if (err == -ENOMEM)
                         return err;
@@ -2313,10 +2334,8 @@ void regulatory_exit(void)
         cancel_delayed_work_sync(&reg_timeout);
 
         /* Lock to suppress warnings */
-        mutex_lock(&cfg80211_mutex);
         mutex_lock(&reg_mutex);
         reset_regdomains(true, NULL);
-        mutex_unlock(&cfg80211_mutex);
         mutex_unlock(&reg_mutex);
 
         dev_set_uevent_suppress(&reg_pdev->dev, true);