[PATCH] mt76: mt7915: potential array overflow in mt7915_mcu_tx_rate_report()

[Dan Carpenter]

Smatch complains that this comes from the "wcidx" value comes from the
network and thus cannot be trusted.  In this case, it actually seems to
come from the firmware.  If your wireless firmware is malicious then
probably no amount of carefulness can protect you.

On the other hand, these days we still try to check the firmware as much
as possible.  Verifying that the index is within bounds will silence a
static checker warning.  And it's harmless and a good exercise in kernel
hardening.  So I suggest that we do add a bounds check.

Fixes: e57b7901469f ("mt76: add mac80211 driver for MT7915 PCIe-based chipsets")
Signed-off-by: Dan Carpenter <dan.carpenter at oracle.com>
---
Normally for networking patches, when we change the declaration block,
we must update the order to make sure it's in reverse Christmas tree
format.  This code wasn't strictly in reverse Christmas tree order
originally because we needed to initialize "wcidx" before we could
initialize "wcid" etc.  Re-ordering the initializers makes the diff
slightly larger than people might expect but it's a required part of
networking patches.

 .../net/wireless/mediatek/mt76/mt7915/mcu.c   | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/drivers/net/wireless/mediatek/mt76/mt7915/mcu.c b/drivers/net/wireless/mediatek/mt76/mt7915/mcu.c
index c8c12c740c1a..8fb8255650a7 100644
--- a/drivers/net/wireless/mediatek/mt76/mt7915/mcu.c
+++ b/drivers/net/wireless/mediatek/mt76/mt7915/mcu.c
@@ -505,15 +505,22 @@ static void
 mt7915_mcu_tx_rate_report(struct mt7915_dev *dev, struct sk_buff *skb)
 {
 	struct mt7915_mcu_ra_info *ra = (struct mt7915_mcu_ra_info *)skb->data;
-	u16 wcidx = le16_to_cpu(ra->wlan_idx);
-	struct mt76_wcid *wcid = rcu_dereference(dev->mt76.wcid[wcidx]);
-	struct mt7915_sta *msta = container_of(wcid, struct mt7915_sta, wcid);
-	struct mt7915_sta_stats *stats = &msta->stats;
-	struct mt76_phy *mphy = &dev->mphy;
 	struct rate_info rate = {}, prob_rate = {};
+	u16 probe = le16_to_cpu(ra->prob_up_rate);
 	u16 attempts = le16_to_cpu(ra->attempts);
 	u16 curr = le16_to_cpu(ra->curr_rate);
-	u16 probe = le16_to_cpu(ra->prob_up_rate);
+	u16 wcidx = le16_to_cpu(ra->wlan_idx);
+	struct mt76_phy *mphy = &dev->mphy;
+	struct mt7915_sta_stats *stats;
+	struct mt7915_sta *msta;
+	struct mt76_wcid *wcid;
+
+	if (wcidx >= MT76_N_WCIDS)
+		return;
+
+	wcid = rcu_dereference(dev->mt76.wcid[wcidx]);
+	msta = container_of(wcid, struct mt7915_sta, wcid);
+	stats = &msta->stats;
 
 	if (msta->wcid.ext_phy && dev->mt76.phy2)
 		mphy = dev->mt76.phy2;
-- 
2.27.0