ieee80211_find_sta_by_ifaddr() must be called under the RCU lock and
the resulting pointer is only valid under RCU lock as well.

Fix ath_tx_process_buffer() to hold RCU read lock before it calls
ieee80211_find_sta_by_ifaddr() and release it when the resulting
pointer is no longer needed.

This problem was found while reviewing code to debug RCU warn from
ath10k_wmi_tlv_parse_peer_stats_info() and a subsequent manual audit
of other callers of ieee80211_find_sta_by_ifaddr() that don't hold
RCU read lock.

Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
---
- Note: This patch is compile tested. I don't have access to
  hardware.

 drivers/net/wireless/ath/ath9k/xmit.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/net/wireless/ath/ath9k/xmit.c b/drivers/net/wireless/ath/ath9k/xmit.c
index e60d4737fc6e..1d36aae3f7b6 100644
--- a/drivers/net/wireless/ath/ath9k/xmit.c
+++ b/drivers/net/wireless/ath/ath9k/xmit.c

@@ -701,6 +701,9 @@ static void ath_tx_process_buffer(struct ath_softc *sc, struct ath_txq *txq,
 					     ts->ts_rateindex);
 
 	hdr = (struct ieee80211_hdr *) bf->bf_mpdu->data;
+
+	rcu_read_lock();
+
 	sta = ieee80211_find_sta_by_ifaddr(hw, hdr->addr1, hdr->addr2);
 	if (sta) {
 		struct ath_node *an = (struct ath_node *)sta->drv_priv;

@@ -725,6 +728,8 @@ static void ath_tx_process_buffer(struct ath_softc *sc, struct ath_txq *txq,
 
 	if (!flush)
 		ath_txq_schedule(sc, txq);
+
+	rcu_read_unlock();
 }
 
 static bool ath_lookup_legacy(struct ath_buf *bf)

-- 
2.27.0