[ 33/82] ath9k: fix stale pointers potentially causing access to freed skbs

[Ben Hutchings]

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

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

From: Felix Fietkau <nbd@xxxxxxxxxxx>

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@xxxxxxxxxxx>
Signed-off-by: John W. Linville <linville@xxxxxxxxxxxxx>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 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
@@ -288,6 +288,7 @@ 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);
@@ -1710,6 +1711,7 @@ 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;
 	ath_tx_fill_desc(sc, bf, txq, fi->framelen);
 	ath_tx_txqaddbuf(sc, txq, &bf_head, false);


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