DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 704AA2084A
From:   Felix Fietkau <nbd@nbd.name>
To:     linux-wireless@vger.kernel.org
Subject: [PATCH v2 3/7] mt76: fix race condition in station removal
Date:   Fri, 16 Nov 2018 12:12:31 +0100
Message-Id: <20181116111235.86347-3-nbd@nbd.name>
In-Reply-To: <20181116111235.86347-1-nbd@nbd.name>
References: <20181116111235.86347-1-nbd@nbd.name>
Sender: linux-wireless-owner@vger.kernel.org
Precedence: bulk

If there are still pending packets in the tx queue when removing a station,
it could possibly lead to a call to further attempts to pull packets from
the mac80211 tx queue after it has already been removed from the scheduling
list.
Prevent this from happening by calling synchronize_rcu after deleting the
wcid pointer before further cleaning up the tx queues.
To be extra careful, ensure that mtxq->list is always initialized properly.

Signed-off-by: Felix Fietkau <nbd@nbd.name>
---
v2: keep the call to mt76x02_mac_wcid_setup in place

 drivers/net/wireless/mediatek/mt76/mt76x02_util.c | 4 +++-
 drivers/net/wireless/mediatek/mt76/tx.c           | 2 +-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/net/wireless/mediatek/mt76/mt76x02_util.c b/drivers/net/wireless/mediatek/mt76/mt76x02_util.c
index d2ac1a84668c..1a51193d5d59 100644
--- a/drivers/net/wireless/mediatek/mt76/mt76x02_util.c
+++ b/drivers/net/wireless/mediatek/mt76/mt76x02_util.c
@@ -216,9 +216,11 @@ int mt76x02_sta_remove(struct ieee80211_hw *hw, struct ieee80211_vif *vif,
 	int idx = msta->wcid.idx;
 	int i;
 
+	rcu_assign_pointer(dev->mt76.wcid[idx], NULL);
+	synchronize_rcu();
+
 	mutex_lock(&dev->mt76.mutex);
 	mt76_tx_status_check(&dev->mt76, &msta->wcid, true);
-	rcu_assign_pointer(dev->mt76.wcid[idx], NULL);
 	for (i = 0; i < ARRAY_SIZE(sta->txq); i++)
 		mt76_txq_remove(&dev->mt76, sta->txq[i]);
 	mt76x02_mac_wcid_set_drop(dev, idx, true);
diff --git a/drivers/net/wireless/mediatek/mt76/tx.c b/drivers/net/wireless/mediatek/mt76/tx.c
index e42a24628e4f..f4093dc0e174 100644
--- a/drivers/net/wireless/mediatek/mt76/tx.c
+++ b/drivers/net/wireless/mediatek/mt76/tx.c
@@ -590,7 +590,7 @@ void mt76_txq_remove(struct mt76_dev *dev, struct ieee80211_txq *txq)
 
 	spin_lock_bh(&hwq->lock);
 	if (!list_empty(&mtxq->list))
-		list_del(&mtxq->list);
+		list_del_init(&mtxq->list);
 	spin_unlock_bh(&hwq->lock);
 
 	while ((skb = skb_dequeue(&mtxq->retry_q)) != NULL)
-- 
2.17.0