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

From: Aran Dalton
Date: Wed Sep 21 2022 - 05:20:46 EST


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