3.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Felix Fietkau <redacted>

commit 8c6e30936a7893a85f6222084f0f26aceb81137a upstream.

bf->bf_next is only while buffers are chained as part of an A-MPDU
in the tx queue. When a tid queue is flushed (e.g. on tearing down
an aggregation session), frames can be enqueued again as normal
transmission, without bf_next being cleared. This can lead to the
old pointer being dereferenced again later.

This patch might fix crashes and "Failed to stop TX DMA!" messages.

Signed-off-by: Felix Fietkau <redacted>
Signed-off-by: John W. Linville <redacted>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/net/wireless/ath/ath9k/xmit.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/drivers/net/wireless/ath/ath9k/xmit.c
+++ b/drivers/net/wireless/ath/ath9k/xmit.c

@@ -337,6 +337,7 @@ static struct ath_buf *ath_tx_get_buffer
 	}
 
 	bf = list_first_entry(&sc->tx.txbuf, struct ath_buf, list);
+	bf->bf_next = NULL;
 	list_del(&bf->list);
 
 	spin_unlock_bh(&sc->tx.txbuflock);

@@ -1760,6 +1761,7 @@ static void ath_tx_send_normal(struct at
 	list_add_tail(&bf->list, &bf_head);
 	bf->bf_state.bf_type = 0;
 
+	bf->bf_next = NULL;
 	bf->bf_lastbf = bf;
 	ath_tx_fill_desc(sc, bf, txq, fi->framelen);
 	ath_tx_txqaddbuf(sc, txq, &bf_head, false);