[PATCH AUTOSEL 4.18 025/100] mac80211_hwsim: fix locking when iterating radios during ns exit

[Sasha Levin]

From: Martin Willi <martin@xxxxxxxxxxxxxx>

[ Upstream commit 628980e5c8f038f730582c6ee50b7410741cd96e ]

The cleanup of radios during namespace exit has recently been reworked
to directly delete a radio while temporarily releasing the spinlock,
fixing a race condition between the work-queue execution and namespace
exits. However, the temporary unlock allows unsafe modifications on the
iterated list, resulting in a potential crash when continuing the
iteration of additional radios.

Move radios about to destroy to a temporary list, and clean that up
after releasing the spinlock once iteration is complete.

Fixes: 8cfd36a0b53a ("mac80211_hwsim: fix use-after-free bug in hwsim_exit_net")
Signed-off-by: Martin Willi <martin@xxxxxxxxxxxxxx>
Signed-off-by: Johannes Berg <johannes.berg@xxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 drivers/net/wireless/mac80211_hwsim.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/net/wireless/mac80211_hwsim.c b/drivers/net/wireless/mac80211_hwsim.c
index 80e2c8595c7c..6b90bef58293 100644
--- a/drivers/net/wireless/mac80211_hwsim.c
+++ b/drivers/net/wireless/mac80211_hwsim.c
@@ -3523,6 +3523,7 @@ static __net_init int hwsim_init_net(struct net *net)
 static void __net_exit hwsim_exit_net(struct net *net)
 {
 	struct mac80211_hwsim_data *data, *tmp;
+	LIST_HEAD(list);
 
 	spin_lock_bh(&hwsim_radio_lock);
 	list_for_each_entry_safe(data, tmp, &hwsim_radios, list) {
@@ -3533,17 +3534,19 @@ static void __net_exit hwsim_exit_net(struct net *net)
 		if (data->netgroup == hwsim_net_get_netgroup(&init_net))
 			continue;
 
-		list_del(&data->list);
+		list_move(&data->list, &list);
 		rhashtable_remove_fast(&hwsim_radios_rht, &data->rht,
 				       hwsim_rht_params);
 		hwsim_radios_generation++;
-		spin_unlock_bh(&hwsim_radio_lock);
+	}
+	spin_unlock_bh(&hwsim_radio_lock);
+
+	list_for_each_entry_safe(data, tmp, &list, list) {
+		list_del(&data->list);
 		mac80211_hwsim_del_radio(data,
 					 wiphy_name(data->hw->wiphy),
 					 NULL);
-		spin_lock_bh(&hwsim_radio_lock);
 	}
-	spin_unlock_bh(&hwsim_radio_lock);
 
 	ida_simple_remove(&hwsim_netgroup_ida, hwsim_net_get_netgroup(net));
 }
-- 
2.17.1