[PATCH 4.15 24/53] ath9k: Protect queue draining by rcu_read_lock()

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

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

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

From: Toke Høiland-Jørgensen <toke@toke.dk>

commit 182b1917109892ab9f26d66bfdcbc4ba6f0a0a65 upstream.

When ath9k was switched over to use the mac80211 intermediate queues,
node cleanup now drains the mac80211 queues. However, this call path is
not protected by rcu_read_lock() as it was previously entirely internal
to the driver which uses its own locking.

This leads to a possible rcu_dereference() without holding
rcu_read_lock(); but only if a station is cleaned up while having
packets queued on the TXQ. Fix this by adding the rcu_read_lock() to the
caller in ath9k.

Fixes: 50f08edf9809 ("ath9k: Switch to using mac80211 intermediate software queues.")
Cc: stable@vger.kernel.org
Reported-by: Ben Greear <greearb@candelatech.com>
Signed-off-by: Toke Høiland-Jørgensen <toke@toke.dk>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/net/wireless/ath/ath9k/xmit.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/drivers/net/wireless/ath/ath9k/xmit.c
+++ b/drivers/net/wireless/ath/ath9k/xmit.c
@@ -2892,6 +2892,8 @@ void ath_tx_node_cleanup(struct ath_soft
 	struct ath_txq *txq;
 	int tidno;
 
+	rcu_read_lock();
+
 	for (tidno = 0; tidno < IEEE80211_NUM_TIDS; tidno++) {
 		tid = ath_node_to_tid(an, tidno);
 		txq = tid->txq;
@@ -2909,6 +2911,8 @@ void ath_tx_node_cleanup(struct ath_soft
 		if (!an->sta)
 			break; /* just one multicast ath_atx_tid */
 	}
+
+	rcu_read_unlock();
 }
 
 #ifdef CONFIG_ATH9K_TX99