cfg80211: always notify userspace of new wireless netdevs

This change alters the semantics of NL80211_CMD_NEW_INTERFACE events
by always sending this event whenever a new net_device object
associated with a wdev is registered.  Prior to this change, this event
was only sent as a result of NL80211_CMD_NEW_INTERFACE command sent
from userspace.  This allows userspace to reliably detect new wireless
interfaces (e.g. due to hardware hot-plug events, etc).

For wdevs created without an associated net_device object (e.g.
NL80211_IFTYPE_P2P_DEVICE), the NL80211_CMD_NEW_INTERFACE event is
still generated inside the relevant nl80211 command handler.
Signed-off-by: Denis Kenzior <denkenz@gmail.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/wireless/core.c

@@ -1079,6 +1079,8 @@ static int cfg80211_netdev_notifier_call(struct notifier_block *nb,
 		     wdev->iftype == NL80211_IFTYPE_P2P_CLIENT ||
 		     wdev->iftype == NL80211_IFTYPE_ADHOC) && !wdev->use_4addr)
 			dev->priv_flags |= IFF_DONT_BRIDGE;
+
+		nl80211_notify_iface(rdev, wdev, NL80211_CMD_NEW_INTERFACE);
 		break;
 	case NETDEV_GOING_DOWN:
 		cfg80211_leave(rdev, wdev);

net/wireless/nl80211.c

@@ -2751,7 +2751,7 @@ static int nl80211_new_interface(struct sk_buff *skb, struct genl_info *info)
 	struct cfg80211_registered_device *rdev = info->user_ptr[0];
 	struct vif_params params;
 	struct wireless_dev *wdev;
-	struct sk_buff *msg, *event;
+	struct sk_buff *msg;
 	int err;
 	enum nl80211_iftype type = NL80211_IFTYPE_UNSPECIFIED;
 	u32 flags;
@@ -2855,20 +2855,15 @@ static int nl80211_new_interface(struct sk_buff *skb, struct genl_info *info)
 		return -ENOBUFS;
 	}
 
-	event = nlmsg_new(NLMSG_DEFAULT_SIZE, GFP_KERNEL);
-	if (event) {
-		if (nl80211_send_iface(event, 0, 0, 0,
-				       rdev, wdev, false) < 0) {
-			nlmsg_free(event);
-			goto out;
-		}
-
-		genlmsg_multicast_netns(&nl80211_fam, wiphy_net(&rdev->wiphy),
-					event, 0, NL80211_MCGRP_CONFIG,
-					GFP_KERNEL);
-	}
+	/*
+	 * For wdevs which have no associated netdev object (e.g. of type
+	 * NL80211_IFTYPE_P2P_DEVICE), emit the NEW_INTERFACE event here.
+	 * For all other types, the event will be generated from the
+	 * netdev notifier
+	 */
+	if (!wdev->netdev)
+		nl80211_notify_iface(rdev, wdev, NL80211_CMD_NEW_INTERFACE);
 
-out:
 	return genlmsg_reply(msg, info);
 }
 
@@ -11847,6 +11842,29 @@ void nl80211_notify_wiphy(struct cfg80211_registered_device *rdev,
 				NL80211_MCGRP_CONFIG, GFP_KERNEL);
 }
 
+void nl80211_notify_iface(struct cfg80211_registered_device *rdev,
+				struct wireless_dev *wdev,
+				enum nl80211_commands cmd)
+{
+	struct sk_buff *msg;
+
+	WARN_ON(cmd != NL80211_CMD_NEW_INTERFACE &&
+		cmd != NL80211_CMD_DEL_INTERFACE);
+
+	msg = nlmsg_new(NLMSG_DEFAULT_SIZE, GFP_KERNEL);
+	if (!msg)
+		return;
+
+	if (nl80211_send_iface(msg, 0, 0, 0, rdev, wdev,
+			       cmd == NL80211_CMD_DEL_INTERFACE) < 0) {
+		nlmsg_free(msg);
+		return;
+	}
+
+	genlmsg_multicast_netns(&nl80211_fam, wiphy_net(&rdev->wiphy), msg, 0,
+				NL80211_MCGRP_CONFIG, GFP_KERNEL);
+}
+
 static int nl80211_add_scan_req(struct sk_buff *msg,
 				struct cfg80211_registered_device *rdev)
 {

net/wireless/nl80211.h

@@ -7,6 +7,9 @@ int nl80211_init(void);
 void nl80211_exit(void);
 void nl80211_notify_wiphy(struct cfg80211_registered_device *rdev,
 			  enum nl80211_commands cmd);
+void nl80211_notify_iface(struct cfg80211_registered_device *rdev,
+			  struct wireless_dev *wdev,
+			  enum nl80211_commands cmd);
 void nl80211_send_scan_start(struct cfg80211_registered_device *rdev,
 			     struct wireless_dev *wdev);
 struct sk_buff *nl80211_build_scan_msg(struct cfg80211_registered_device *rdev,