wifi: mt76: add wcid publish check in mt76_sta_add

commit 20b1269 upstream.

Since mt7925_mac_sta_add publishes wcid, add publish check in mt76_sta_add
to avoid reinitializing the wcid->poll_list.

Found dev->sta_poll_list corruption when using mt7925 and 7.1-rc4.
According to the corruption information, prev->next was changed to itself.

wlan0: disconnect from AP 90:fb:5d:94:8b:e3 for new auth to 90:fb:5d:94:8b:e2
wlan0: authenticate with 90:fb:5d:94:8b:e2 (local address=84:9e:56:9c:7e:6b)
wlan0: send auth to 90:fb:5d:94:8b:e2 (try 1/3)
 slab kmalloc-8k start ffff8c80958a6000 pointer offset 4160 size 8192
list_add corruption. prev->next should be next (ffff8c808a7488f8), but was ffff8c80958a7040. (prev=ffff8c80958a7040).

 mt76_wcid_add_poll+0x95/0xd0 [mt76]
 mt7925_mac_add_txs.part.0+0xa5/0xe0 [mt7925_common]
 mt7925_rx_check+0xa7/0xc0 [mt7925_common]
 mt76_dma_rx_poll+0x50d/0x790 [mt76]
 mt792x_poll_rx+0x52/0xe0 [mt792x_lib]

Signed-off-by: Jiajia Liu <liujiajia@kylinos.cn>
Link: https://patch.msgid.link/20260528033814.46418-1-liujiajia@kylinos.cn
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Jiajia Liu

drivers/net/wireless/mediatek/mt76/mac80211.c

@@ -1568,6 +1568,7 @@ mt76_sta_add(struct mt76_phy *phy, struct ieee80211_vif *vif,
 {
 	struct mt76_wcid *wcid = (struct mt76_wcid *)sta->drv_priv;
 	struct mt76_dev *dev = phy->dev;
+	struct mt76_wcid *published;
 	int ret;
 	int i;
 
@@ -1587,11 +1588,19 @@ mt76_sta_add(struct mt76_phy *phy, struct ieee80211_vif *vif,
 		mtxq->wcid = wcid->idx;
 	}
 
-	ewma_signal_init(&wcid->rssi);
-	rcu_assign_pointer(dev->wcid[wcid->idx], wcid);
+	published = rcu_dereference_protected(dev->wcid[wcid->idx],
+					      lockdep_is_held(&dev->mutex));
+	if (published != wcid) {
+		WARN_ON_ONCE(published);
+		ewma_signal_init(&wcid->rssi);
+		rcu_assign_pointer(dev->wcid[wcid->idx], wcid);
+		mt76_wcid_init(wcid, phy->band_idx);
+	} else {
+		wcid->phy_idx = phy->band_idx;
+	}
+
 	phy->num_sta++;
 
-	mt76_wcid_init(wcid, phy->band_idx);
 out:
 	mutex_unlock(&dev->mutex);