ath9k: fix a buffer leak in A-MPDU completion

When ath_tx_complete_aggr() is called, it's responsible for returning
all buffers in the linked list. This was not done when the STA lookup
failed, leading to a race condition that could leak a few buffers when
a STA just disconnected.
Fix this by immediately returning all buffers to the free list in this case.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Cc: stable@kernel.org
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/ath9k/xmit.c

@@ -329,6 +329,7 @@ static void ath_tx_complete_aggr(struct ath_softc *sc, struct ath_txq *txq,
 	int isaggr, txfail, txpending, sendbar = 0, needreset = 0, nbad = 0;
 	bool rc_update = true;
 	struct ieee80211_tx_rate rates[4];
+	unsigned long flags;
 
 	skb = bf->bf_mpdu;
 	hdr = (struct ieee80211_hdr *)skb->data;
@@ -344,6 +345,10 @@ static void ath_tx_complete_aggr(struct ath_softc *sc, struct ath_txq *txq,
 	sta = ieee80211_find_sta_by_hw(hw, hdr->addr1);
 	if (!sta) {
 		rcu_read_unlock();
+
+		spin_lock_irqsave(&sc->tx.txbuflock, flags);
+		list_splice_tail_init(bf_q, &sc->tx.txbuf);
+		spin_unlock_irqrestore(&sc->tx.txbuflock, flags);
 		return;
 	}