[PATCH v2] wifi: rtl8xxxu: fix potential use of uninitialized value

[Yi Cong <cong.yi@linux.dev>]

From: Yi Cong <yicong@kylinos.cn>

The local variables 'mcs' and 'nss' in rtl8xxxu_update_ra_report() are
passed to rtl8xxxu_desc_to_mcsrate() as output parameters. If the helper
function encounters an unhandled rate index, it may return without setting
these values, leading to the use of uninitialized stack data.

Remove the helper rtl8xxxu_desc_to_mcsrate() and inline the logic into
rtl8xxxu_update_ra_report(). This fixes the use of uninitialized 'mcs'
and 'nss' variables for legacy rates.

The new implementation explicitly handles:
- Legacy rates: Set bitrate only.
- HT rates (MCS0-15): Set MCS flags, index, and NSS (1 or 2) directly.
- Invalid rates: Return early.

Fixes: 7de16123d9e2 ("wifi: rtl8xxxu: Introduce rtl8xxxu_update_ra_report")
Cc: stable@vger.kernel.org
Suggested-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Yi Cong <yicong@kylinos.cn>
Link: https://lore.kernel.org/all/96e31963da0c42dcb52ce44f818963d7@realtek.com/

---
v2: Explicitly handle invalid rates by returning early instead of falling through.
---
 drivers/net/wireless/realtek/rtl8xxxu/core.c | 28 ++++++--------------
 1 file changed, 8 insertions(+), 20 deletions(-)

diff --git a/drivers/net/wireless/realtek/rtl8xxxu/core.c b/drivers/net/wireless/realtek/rtl8xxxu/core.c
index 794187d28caa..2f872c4f2eee 100644
--- a/drivers/net/wireless/realtek/rtl8xxxu/core.c
+++ b/drivers/net/wireless/realtek/rtl8xxxu/core.c
@@ -4697,20 +4697,6 @@ static const struct ieee80211_rate rtl8xxxu_legacy_ratetable[] = {
 	{.bitrate = 540, .hw_value = 0x0b,},
 };
 
-static void rtl8xxxu_desc_to_mcsrate(u16 rate, u8 *mcs, u8 *nss)
-{
-	if (rate <= DESC_RATE_54M)
-		return;
-
-	if (rate >= DESC_RATE_MCS0 && rate <= DESC_RATE_MCS15) {
-		if (rate < DESC_RATE_MCS8)
-			*nss = 1;
-		else
-			*nss = 2;
-		*mcs = rate - DESC_RATE_MCS0;
-	}
-}
-
 static void rtl8xxxu_set_basic_rates(struct rtl8xxxu_priv *priv, u32 rate_cfg)
 {
 	struct ieee80211_hw *hw = priv->hw;
@@ -4820,23 +4806,25 @@ static void rtl8xxxu_set_aifs(struct rtl8xxxu_priv *priv, u8 slot_time)
 void rtl8xxxu_update_ra_report(struct rtl8xxxu_ra_report *rarpt,
 			       u8 rate, u8 sgi, u8 bw)
 {
-	u8 mcs, nss;
-
 	rarpt->txrate.flags = 0;
 
 	if (rate <= DESC_RATE_54M) {
 		rarpt->txrate.legacy = rtl8xxxu_legacy_ratetable[rate].bitrate;
-	} else {
-		rtl8xxxu_desc_to_mcsrate(rate, &mcs, &nss);
+	} else if (rate >= DESC_RATE_MCS0 && rate <= DESC_RATE_MCS15) {
 		rarpt->txrate.flags |= RATE_INFO_FLAGS_MCS;
+		if (rate < DESC_RATE_MCS8)
+			rarpt->txrate.nss = 1;
+		else
+			rarpt->txrate.nss = 2;
 
-		rarpt->txrate.mcs = mcs;
-		rarpt->txrate.nss = nss;
+		rarpt->txrate.mcs = rate - DESC_RATE_MCS0;
 
 		if (sgi)
 			rarpt->txrate.flags |= RATE_INFO_FLAGS_SHORT_GI;
 
 		rarpt->txrate.bw = bw;
+	} else {
+		return;
 	}
 
 	rarpt->bit_rate = cfg80211_calculate_bitrate(&rarpt->txrate);
-- 
2.25.1