[PATCH net] ath9k_htc: fix possibly missing barrier in ath9k_htc_rxep()

[Thomas Fourier <fourier.thomas@gmail.com>]

ath9k_rx_init() initialises the rx buffer and its lock then calls a
memory barrier and then sets the priv->rx.initialized flag. However,
ath9k_htc_rxep() reads that flag and imidiatly takes the lock. This may
cause the lock to be taken while not fully initialized.

Add a barrier to prevent speculative read of the lock before checking
the initized flag.

Fixes: b0ec7e55fce6 ("ath9k_htc: fix NULL pointer dereference at ath9k_htc_rxep()")
Cc: <stable@vger.kernel.org>
Signed-off-by: Thomas Fourier <fourier.thomas@gmail.com>
---
 drivers/net/wireless/ath/ath9k/htc_drv_txrx.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/net/wireless/ath/ath9k/htc_drv_txrx.c b/drivers/net/wireless/ath/ath9k/htc_drv_txrx.c
index bed7ea2425a0..97d61f3f0aad 100644
--- a/drivers/net/wireless/ath/ath9k/htc_drv_txrx.c
+++ b/drivers/net/wireless/ath/ath9k/htc_drv_txrx.c
@@ -1145,6 +1145,12 @@ void ath9k_htc_rxep(void *drv_priv, struct sk_buff *skb,
 	if (!data_race(priv->rx.initialized))
 		goto err;
 
+	/*
+	 * Make sure all the ath9k_rx_init() memory writes are visible before
+	 * proceeding.
+	 */
+	smp_rmb();
+
 	spin_lock_irqsave(&priv->rx.rxbuflock, flags);
 	list_for_each_entry(tmp_buf, &priv->rx.rxbuf, list) {
 		if (!tmp_buf->in_process) {
-- 
2.43.0