[PATCH 2/2] cfg80211: fix dead lock for nl80211_del_interface()

[Aran Dalton]

Both nl80211_del_interface and cfg80211_netdev_notifier_call hold the
same wiphy_lock, then cause deadlock.

The main call stack as bellow:

nl80211_del_interface() takes wiphy_lock
 -> cfg80211_remove_virtual_intf
  -> rdev_del_virtual_intf
   -> rdev->ops->del_virtual_intf
    -> cfg80211_unregister_netdevice
     -> cfg80211_unregister_wdev
      -> _cfg80211_unregister_wdev
       -> unregister_netdevice
        -> unregister_netdevice_queue
         -> unregister_netdevice_many
          -> call_netdevice_notifiers(NETDEV_UNREGISTER, dev);
           -> call_netdevice_notifiers_extack
            -> call_netdevice_notifiers_info
             -> raw_notifier_call_chain
              -> cfg80211_netdev_notifier_call
               -> wiphy_lock(&rdev->wiphy), _cfg80211_unregister_wdev

Fixes: a05829a7222e ("cfg80211: avoid holding the RTNL when calling the driver")
Signed-off-by: Aran Dalton <arda@xxxxxxxxxxxxxxxxx>
---
 net/wireless/nl80211.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/net/wireless/nl80211.c b/net/wireless/nl80211.c
index bdacddc3ffa3..664bf977b7bc 100644
--- a/net/wireless/nl80211.c
+++ b/net/wireless/nl80211.c
@@ -4269,6 +4269,7 @@ static int nl80211_del_interface(struct sk_buff *skb, struct genl_info *info)
 {
 	struct cfg80211_registered_device *rdev = info->user_ptr[0];
 	struct wireless_dev *wdev = info->user_ptr[1];
+	int ret;
 
 	if (!rdev->ops->del_virtual_intf)
 		return -EOPNOTSUPP;
@@ -4296,9 +4297,11 @@ static int nl80211_del_interface(struct sk_buff *skb, struct genl_info *info)
 	else
 		dev_close(wdev->netdev);
 
+	ret = cfg80211_remove_virtual_intf(rdev, wdev);
+
 	mutex_lock(&rdev->wiphy.mtx);
 
-	return cfg80211_remove_virtual_intf(rdev, wdev);
+	return ret;
 }
 
 static int nl80211_set_noack_map(struct sk_buff *skb, struct genl_info *info)
-- 
2.29.0