netdev - [PATCH 1/3] mac80211_hwsim: fix locking when iterating radios during ns exit

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Date:   Tue, 25 Sep 2018 09:41:13 +0200
From:   Martin Willi <martin@...ongswan.org>
To:     Johannes Berg <johannes@...solutions.net>
Cc:     linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        Benjamin Beichler <benjamin.beichler@...-rostock.de>
Subject: [PATCH 1/3] mac80211_hwsim: fix locking when iterating radios during ns exit

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@...ongswan.org>
---
 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 f3863101af78..8c76e9a3499a 100644
--- a/drivers/net/wireless/mac80211_hwsim.c
+++ b/drivers/net/wireless/mac80211_hwsim.c
@@ -3642,6 +3642,7 @@ 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) {
@@ -3652,17 +3653,19 @@ 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