[PATCH] wifi: ath9k: add a defensive NULL check to prevent null-pointer dereference in ath9k_beacon_remove_slot()

[Tuo Li <islituo@gmail.com>]

In this function, bf is guarded by an if statement, indicating that it may
be NULL:

  if (bf && bf->bf_mpdu) {...}

If bf is NULL, calling list_add_tail() may result in a null-pointer
dereference:

  list_add_tail(&bf->list, &sc->beacon.bbuf);

Therefore, add a defensive NULL check before invoking list_add_tail() to
prevent this issue.

Signed-off-by: Tuo Li <islituo@gmail.com>
---
 drivers/net/wireless/ath/ath9k/beacon.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/wireless/ath/ath9k/beacon.c b/drivers/net/wireless/ath/ath9k/beacon.c
index 4a27e3753c03..e39e2738ba1a 100644
--- a/drivers/net/wireless/ath/ath9k/beacon.c
+++ b/drivers/net/wireless/ath/ath9k/beacon.c
@@ -236,7 +236,8 @@ void ath9k_beacon_remove_slot(struct ath_softc *sc, struct ieee80211_vif *vif)
 
 	avp->av_bcbuf = NULL;
 	sc->beacon.bslot[avp->av_bslot] = NULL;
-	list_add_tail(&bf->list, &sc->beacon.bbuf);
+	if (bf)
+		list_add_tail(&bf->list, &sc->beacon.bbuf);
 
 	tasklet_enable(&sc->bcon_tasklet);
 }
-- 
2.43.0