mt76: mt7921: fix possible AOOB issue in mt7921_mcu_tx_rate_report

Fix possible array out of bound access in mt7921_mcu_tx_rate_report.
Remove unnecessary varibable in mt7921_mcu_tx_rate_report

Fixes: 1c099ab4 ("mt76: mt7921: add MCU support")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/91a1e8f6b6a3e6a929de560ed68132f6eb421720.1619187875.git.lorenzo@kernel.org

drivers/net/wireless/mediatek/mt76/mt7921/mcu.c

@@ -402,20 +402,22 @@ static void
 mt7921_mcu_tx_rate_report(struct mt7921_dev *dev, struct sk_buff *skb,
 			  u16 wlan_idx)
 {
-	struct mt7921_mcu_wlan_info_event *wtbl_info =
-		(struct mt7921_mcu_wlan_info_event *)(skb->data);
-	struct rate_info rate = {};
-	u8 curr_idx = wtbl_info->rate_info.rate_idx;
-	u16 curr = le16_to_cpu(wtbl_info->rate_info.rate[curr_idx]);
-	struct mt7921_mcu_peer_cap peer = wtbl_info->peer_cap;
+	struct mt7921_mcu_wlan_info_event *wtbl_info;
 	struct mt76_phy *mphy = &dev->mphy;
 	struct mt7921_sta_stats *stats;
+	struct rate_info rate = {};
 	struct mt7921_sta *msta;
 	struct mt76_wcid *wcid;
+	u8 idx;
 
 	if (wlan_idx >= MT76_N_WCIDS)
 		return;
 
+	wtbl_info = (struct mt7921_mcu_wlan_info_event *)skb->data;
+	idx = wtbl_info->rate_info.rate_idx;
+	if (idx >= ARRAY_SIZE(wtbl_info->rate_info.rate))
+		return;
+
 	rcu_read_lock();
 
 	wcid = rcu_dereference(dev->mt76.wcid[wlan_idx]);
@@ -426,7 +428,8 @@ mt7921_mcu_tx_rate_report(struct mt7921_dev *dev, struct sk_buff *skb,
 	stats = &msta->stats;
 
 	/* current rate */
-	mt7921_mcu_tx_rate_parse(mphy, &peer, &rate, curr);
+	mt7921_mcu_tx_rate_parse(mphy, &wtbl_info->peer_cap, &rate,
+				 le16_to_cpu(wtbl_info->rate_info.rate[idx]));
 	stats->tx_rate = rate;
 out:
 	rcu_read_unlock();