[ 01/38] ath9k: fix stale pointers potentially causing access to freed skbs

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

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

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

From: Felix Fietkau <nbd@openwrt.org>

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 <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
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
@@ -272,6 +272,7 @@ 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);
@@ -1488,6 +1489,7 @@ static void ath_tx_send_normal(struct at
 	if (tid)
 		INCR(tid->seq_start, IEEE80211_SEQ_MAX);
 
+	bf->bf_next = NULL;
 	bf->bf_lastbf = bf;
 	fi = get_frame_info(bf->bf_mpdu);
 	ath_buf_set_rate(sc, bf, fi->framelen);