ath9k: fix a use-after-free-bug when ath_tx_setup_buffer() fails

ath_tx_setup_buffer() can fail if there is no ath_buf left, or if mapping DMA
failed. In this case it frees the skb passed to it.
If ath_tx_setup_buffer is called from ath_tx_form_aggr, the skb is still
linked into the tid buffer list and must be dequeued before being released.
Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Cc: stable@vger.kernel.org
Signed-off-by: John W. Linville <linville@tuxdriver.com>

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

@@ -64,7 +64,8 @@ static void ath_tx_update_baw(struct ath_softc *sc, struct ath_atx_tid *tid,
 static struct ath_buf *ath_tx_setup_buffer(struct ath_softc *sc,
 					   struct ath_txq *txq,
 					   struct ath_atx_tid *tid,
-					   struct sk_buff *skb);
+					   struct sk_buff *skb,
+					   bool dequeue);
 
 enum {
 	MCS_HT20,
@@ -811,7 +812,7 @@ static enum ATH_AGGR_STATUS ath_tx_form_aggr(struct ath_softc *sc,
 		fi = get_frame_info(skb);
 		bf = fi->bf;
 		if (!fi->bf)
-			bf = ath_tx_setup_buffer(sc, txq, tid, skb);
+			bf = ath_tx_setup_buffer(sc, txq, tid, skb, true);
 
 		if (!bf)
 			continue;
@@ -1726,7 +1727,7 @@ static void ath_tx_send_ampdu(struct ath_softc *sc, struct ath_atx_tid *tid,
 		return;
 	}
 
-	bf = ath_tx_setup_buffer(sc, txctl->txq, tid, skb);
+	bf = ath_tx_setup_buffer(sc, txctl->txq, tid, skb, false);
 	if (!bf)
 		return;
 
@@ -1753,7 +1754,7 @@ static void ath_tx_send_normal(struct ath_softc *sc, struct ath_txq *txq,
 
 	bf = fi->bf;
 	if (!bf)
-		bf = ath_tx_setup_buffer(sc, txq, tid, skb);
+		bf = ath_tx_setup_buffer(sc, txq, tid, skb, false);
 
 	if (!bf)
 		return;
@@ -1814,7 +1815,8 @@ u8 ath_txchainmask_reduction(struct ath_softc *sc, u8 chainmask, u32 rate)
 static struct ath_buf *ath_tx_setup_buffer(struct ath_softc *sc,
 					   struct ath_txq *txq,
 					   struct ath_atx_tid *tid,
-					   struct sk_buff *skb)
+					   struct sk_buff *skb,
+					   bool dequeue)
 {
 	struct ath_common *common = ath9k_hw_common(sc->sc_ah);
 	struct ath_frame_info *fi = get_frame_info(skb);
@@ -1863,6 +1865,8 @@ static struct ath_buf *ath_tx_setup_buffer(struct ath_softc *sc,
 	return bf;
 
 error:
+	if (dequeue)
+		__skb_unlink(skb, &tid->buf_q);
 	dev_kfree_skb_any(skb);
 	return NULL;
 }
@@ -1893,7 +1897,7 @@ static void ath_tx_start_dma(struct ath_softc *sc, struct sk_buff *skb,
 		 */
 		ath_tx_send_ampdu(sc, tid, skb, txctl);
 	} else {
-		bf = ath_tx_setup_buffer(sc, txctl->txq, tid, skb);
+		bf = ath_tx_setup_buffer(sc, txctl->txq, tid, skb, false);
 		if (!bf)
 			return;