nl80211: Convert sched_scan_req pointer to RCU pointer

Because of possible races when accessing sched_scan_req pointer in
rdev, the sched_scan_req is converted to RCU pointer.
Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

include/net/cfg80211.h

@@ -1516,6 +1516,7 @@ struct cfg80211_match_set {
  * @mac_addr_mask: MAC address mask used with randomisation, bits that
  *	are 0 in the mask should be randomised, bits that are 1 should
  *	be taken from the @mac_addr
+ * @rcu_head: RCU callback used to free the struct
  */
 struct cfg80211_sched_scan_request {
 	struct cfg80211_ssid *ssids;
@@ -1537,6 +1538,7 @@ struct cfg80211_sched_scan_request {
 	struct wiphy *wiphy;
 	struct net_device *dev;
 	unsigned long scan_start;
+	struct rcu_head rcu_head;
 
 	/* keep last */
 	struct ieee80211_channel *channels[0];

net/wireless/core.c

@@ -867,6 +867,7 @@ void __cfg80211_leave(struct cfg80211_registered_device *rdev,
 		      struct wireless_dev *wdev)
 {
 	struct net_device *dev = wdev->netdev;
+	struct cfg80211_sched_scan_request *sched_scan_req;
 
 	ASSERT_RTNL();
 	ASSERT_WDEV_LOCK(wdev);
@@ -877,7 +878,8 @@ void __cfg80211_leave(struct cfg80211_registered_device *rdev,
 		break;
 	case NL80211_IFTYPE_P2P_CLIENT:
 	case NL80211_IFTYPE_STATION:
-		if (rdev->sched_scan_req && dev == rdev->sched_scan_req->dev)
+		sched_scan_req = rtnl_dereference(rdev->sched_scan_req);
+		if (sched_scan_req && dev == sched_scan_req->dev)
 			__cfg80211_stop_sched_scan(rdev, false);
 
 #ifdef CONFIG_CFG80211_WEXT
@@ -956,6 +958,7 @@ static int cfg80211_netdev_notifier_call(struct notifier_block *nb,
 	struct net_device *dev = netdev_notifier_info_to_dev(ptr);
 	struct wireless_dev *wdev = dev->ieee80211_ptr;
 	struct cfg80211_registered_device *rdev;
+	struct cfg80211_sched_scan_request *sched_scan_req;
 
 	if (!wdev)
 		return NOTIFY_DONE;
@@ -1021,8 +1024,9 @@ static int cfg80211_netdev_notifier_call(struct notifier_block *nb,
 			___cfg80211_scan_done(rdev, false);
 		}
 
-		if (WARN_ON(rdev->sched_scan_req &&
-			    rdev->sched_scan_req->dev == wdev->netdev)) {
+		sched_scan_req = rtnl_dereference(rdev->sched_scan_req);
+		if (WARN_ON(sched_scan_req &&
+			    sched_scan_req->dev == wdev->netdev)) {
 			__cfg80211_stop_sched_scan(rdev, false);
 		}
 

net/wireless/core.h

@@ -70,7 +70,7 @@ struct cfg80211_registered_device {
 	u32 bss_generation;
 	struct cfg80211_scan_request *scan_req; /* protected by RTNL */
 	struct sk_buff *scan_msg;
-	struct cfg80211_sched_scan_request *sched_scan_req;
+	struct cfg80211_sched_scan_request __rcu *sched_scan_req;
 	unsigned long suspend_at;
 	struct work_struct scan_done_wk;
 	struct work_struct sched_scan_results_wk;

net/wireless/nl80211.c

@@ -6190,6 +6190,7 @@ static int nl80211_start_sched_scan(struct sk_buff *skb,
 	struct cfg80211_registered_device *rdev = info->user_ptr[0];
 	struct net_device *dev = info->user_ptr[1];
 	struct wireless_dev *wdev = dev->ieee80211_ptr;
+	struct cfg80211_sched_scan_request *sched_scan_req;
 	int err;
 
 	if (!(rdev->wiphy.flags & WIPHY_FLAG_SUPPORTS_SCHED_SCAN) ||
@@ -6199,27 +6200,29 @@ static int nl80211_start_sched_scan(struct sk_buff *skb,
 	if (rdev->sched_scan_req)
 		return -EINPROGRESS;
 
-	rdev->sched_scan_req = nl80211_parse_sched_scan(&rdev->wiphy, wdev,
+	sched_scan_req = nl80211_parse_sched_scan(&rdev->wiphy, wdev,
 						  info->attrs);
-	err = PTR_ERR_OR_ZERO(rdev->sched_scan_req);
+
+	err = PTR_ERR_OR_ZERO(sched_scan_req);
 	if (err)
 		goto out_err;
 
-	err = rdev_sched_scan_start(rdev, dev, rdev->sched_scan_req);
+	err = rdev_sched_scan_start(rdev, dev, sched_scan_req);
 	if (err)
 		goto out_free;
 
-	rdev->sched_scan_req->dev = dev;
-	rdev->sched_scan_req->wiphy = &rdev->wiphy;
+	sched_scan_req->dev = dev;
+	sched_scan_req->wiphy = &rdev->wiphy;
+
+	rcu_assign_pointer(rdev->sched_scan_req, sched_scan_req);
 
 	nl80211_send_sched_scan(rdev, dev,
 				NL80211_CMD_START_SCHED_SCAN);
 	return 0;
 
 out_free:
-	kfree(rdev->sched_scan_req);
+	kfree(sched_scan_req);
 out_err:
-	rdev->sched_scan_req = NULL;
 	return err;
 }
 

net/wireless/scan.c

@@ -257,7 +257,7 @@ void __cfg80211_sched_scan_results(struct work_struct *wk)
 
 	rtnl_lock();
 
-	request = rdev->sched_scan_req;
+	request = rtnl_dereference(rdev->sched_scan_req);
 
 	/* we don't have sched_scan_req anymore if the scan is stopping */
 	if (request) {
@@ -279,7 +279,8 @@ void cfg80211_sched_scan_results(struct wiphy *wiphy)
 {
 	trace_cfg80211_sched_scan_results(wiphy);
 	/* ignore if we're not scanning */
-	if (wiphy_to_rdev(wiphy)->sched_scan_req)
+
+	if (rcu_access_pointer(wiphy_to_rdev(wiphy)->sched_scan_req))
 		queue_work(cfg80211_wq,
 			   &wiphy_to_rdev(wiphy)->sched_scan_results_wk);
 }
@@ -308,6 +309,7 @@ EXPORT_SYMBOL(cfg80211_sched_scan_stopped);
 int __cfg80211_stop_sched_scan(struct cfg80211_registered_device *rdev,
 			       bool driver_initiated)
 {
+	struct cfg80211_sched_scan_request *sched_scan_req;
 	struct net_device *dev;
 
 	ASSERT_RTNL();
@@ -315,7 +317,8 @@ int __cfg80211_stop_sched_scan(struct cfg80211_registered_device *rdev,
 	if (!rdev->sched_scan_req)
 		return -ENOENT;
 
-	dev = rdev->sched_scan_req->dev;
+	sched_scan_req = rtnl_dereference(rdev->sched_scan_req);
+	dev = sched_scan_req->dev;
 
 	if (!driver_initiated) {
 		int err = rdev_sched_scan_stop(rdev, dev);
@@ -325,8 +328,8 @@ int __cfg80211_stop_sched_scan(struct cfg80211_registered_device *rdev,
 
 	nl80211_send_sched_scan(rdev, dev, NL80211_CMD_SCHED_SCAN_STOPPED);
 
-	kfree(rdev->sched_scan_req);
-	rdev->sched_scan_req = NULL;
+	RCU_INIT_POINTER(rdev->sched_scan_req, NULL);
+	kfree_rcu(sched_scan_req, rcu_head);
 
 	return 0;
 }