[PATCH v2 1/4] wifi: mt7601u: fix out-of-bounds access in rate index

[John Robin <johnrobin044@gmail.com>]

The rate->idx value can occasionally exceed the supported band's
bitrates array length, leading to a memory out-of-bounds access.
Add a bounds check to safely fall back to CCK rates if the index
is invalid.

Signed-off-by: John Robin <johnrobin044@gmail.com>
---
 drivers/net/wireless/mediatek/mt7601u/mac.c | 32 +++++++++++++--------
 1 file changed, 20 insertions(+), 12 deletions(-)

diff --git a/drivers/net/wireless/mediatek/mt7601u/mac.c b/drivers/net/wireless/mediatek/mt7601u/mac.c
index ca9cf628eb10d..bf485dabca745 100644
--- a/drivers/net/wireless/mediatek/mt7601u/mac.c
+++ b/drivers/net/wireless/mediatek/mt7601u/mac.c
@@ -118,19 +118,27 @@ u16 mt76_mac_tx_rate_val(struct mt7601u_dev *dev,
 		if (rate->flags & IEEE80211_TX_RC_40_MHZ_WIDTH)
 			bw = 1;
 	} else {
-		const struct ieee80211_rate *r;
-		int band = dev->chandef.chan->band;
-		u16 val;
-
-		r = &dev->hw->wiphy->bands[band]->bitrates[rate->idx];
-		if (rate->flags & IEEE80211_TX_RC_USE_SHORT_PREAMBLE)
-			val = r->hw_value_short;
-		else
-			val = r->hw_value;
 
-		phy = val >> 8;
-		rate_idx = val & 0xff;
-		bw = 0;
+		int band = dev->chandef.chan->band;
+		struct ieee80211_supported_band *sband =
+			dev->hw->wiphy->bands[band];
+
+		if (rate->idx < 0 || rate->idx >= sband->n_bitrates) {
+			phy = MT_PHY_TYPE_CCK;
+			rate_idx = 0;
+		} else {
+			const struct ieee80211_rate *r =
+				&sband->bitrates[rate->idx];
+			u16 val;
+
+			if (rate->flags & IEEE80211_TX_RC_USE_SHORT_PREAMBLE)
+				val = r->hw_value_short;
+			else
+				val = r->hw_value;
+
+			phy = val >> 8;
+			rate_idx = val & 0xff;
+		}
 	}
 
 	rateval = FIELD_PREP(MT_RXWI_RATE_MCS, rate_idx);
-- 
2.56.0