[PATCH] ath9k_htc: fix NULL pointer dereference at ath9k_htc_tx_get_packet()

syzbot is reporting NULL pointer dereference at get_htc_epid_queue() from
ath9k_htc_tx_get_packet() from ath9k_htc_txstatus() [1], for
ath9k_wmi_event_tasklet(WMI_TXSTATUS_EVENTID) depends on spin_lock_init()
 from ath9k_init_priv() being already completed.

Since ath9k_wmi_event_tasklet() is set by ath9k_init_wmi() from
ath9k_htc_probe_device(), it is possible that ath9k_wmi_event_tasklet() is
called via tasklet interrupt before spin_lock_init() from ath9k_init_priv()
 from ath9k_init_device() from ath9k_htc_probe_device() is called.

Let's hold ath9k_wmi_event_tasklet(WMI_TXSTATUS_EVENTID) no-op until
ath9k_tx_init() completes.

Link: https://syzkaller.appspot.com/bug?extid=31d54c60c5b254d6f75b [1]
Reported-by: syzbot <redacted>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Tested-by: syzbot+31d54c60c5b254d6f75b@syzkaller.appspotmail.com
---
 drivers/net/wireless/ath/ath9k/htc.h          | 1 +
 drivers/net/wireless/ath/ath9k/htc_drv_txrx.c | 3 +++
 drivers/net/wireless/ath/ath9k/wmi.c          | 3 +++
 3 files changed, 7 insertions(+)

diff --git a/drivers/net/wireless/ath/ath9k/htc.h b/drivers/net/wireless/ath/ath9k/htc.h
index 4f71e962279a..6b45e63fae4b 100644
--- a/drivers/net/wireless/ath/ath9k/htc.h
+++ b/drivers/net/wireless/ath/ath9k/htc.h

@@ -306,6 +306,7 @@ struct ath9k_htc_tx {
 	DECLARE_BITMAP(tx_slot, MAX_TX_BUF_NUM);
 	struct timer_list cleanup_timer;
 	spinlock_t tx_lock;
+	bool initialized;
 };
 
 struct ath9k_htc_tx_ctl {

diff --git a/drivers/net/wireless/ath/ath9k/htc_drv_txrx.c b/drivers/net/wireless/ath/ath9k/htc_drv_txrx.c
index 0d4595ee51ba..a5240a7f8c00 100644
--- a/drivers/net/wireless/ath/ath9k/htc_drv_txrx.c
+++ b/drivers/net/wireless/ath/ath9k/htc_drv_txrx.c

@@ -813,6 +813,9 @@ int ath9k_tx_init(struct ath9k_htc_priv *priv)
 	skb_queue_head_init(&priv->tx.data_vi_queue);
 	skb_queue_head_init(&priv->tx.data_vo_queue);
 	skb_queue_head_init(&priv->tx.tx_failed);
+	/* Allow ath9k_wmi_event_tasklet(WMI_TXSTATUS_EVENTID) to operate. */
+	smp_wmb();
+	priv->tx.initialized = true;
 	return 0;
 }
 

diff --git a/drivers/net/wireless/ath/ath9k/wmi.c b/drivers/net/wireless/ath/ath9k/wmi.c
index fe29ad4b9023..7e17d86bf5d3 100644
--- a/drivers/net/wireless/ath/ath9k/wmi.c
+++ b/drivers/net/wireless/ath/ath9k/wmi.c

@@ -169,6 +169,9 @@ void ath9k_wmi_event_tasklet(struct tasklet_struct *t)
 					     &wmi->drv_priv->fatal_work);
 			break;
 		case WMI_TXSTATUS_EVENTID:
+			/* Check if ath9k_tx_init() completed. */
+			if (!data_race(priv->tx.initialized))
+				break;
 			spin_lock_bh(&priv->tx.tx_lock);
 			if (priv->tx.flags & ATH9K_HTC_OP_TX_DRAIN) {
 				spin_unlock_bh(&priv->tx.tx_lock);

-- 
2.30.2