netdev - [PATCH][next] mt76: mt7615: Fix a dereference of pointer sta before it is null checked

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Date:   Mon, 19 Apr 2021 14:20:32 +0100
From:   Colin King <colin.king@...onical.com>
To:     Felix Fietkau <nbd@....name>,
        Lorenzo Bianconi <lorenzo.bianconi83@...il.com>,
        Ryder Lee <ryder.lee@...iatek.com>,
        Kalle Valo <kvalo@...eaurora.org>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH][next] mt76: mt7615: Fix a dereference of pointer sta before it is null checked

From: Colin Ian King <colin.king@...onical.com>

Currently the assignment of idx dereferences pointer sta before
sta is null checked, leading to a potential null pointer dereference.
Fix this by assigning idx when it is required after the null check on
pointer sta.

Addresses-Coverity: ("Dereference before null check")
Fixes: a4a5a430b076 ("mt76: mt7615: fix TSF configuration")
Signed-off-by: Colin Ian King <colin.king@...onical.com>
---
 drivers/net/wireless/mediatek/mt76/mt7615/usb_sdio.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/wireless/mediatek/mt76/mt7615/usb_sdio.c b/drivers/net/wireless/mediatek/mt76/mt7615/usb_sdio.c
index 4a370b9f7a17..f8d3673c2cae 100644
--- a/drivers/net/wireless/mediatek/mt76/mt7615/usb_sdio.c
+++ b/drivers/net/wireless/mediatek/mt76/mt7615/usb_sdio.c
@@ -67,7 +67,7 @@ static int mt7663_usb_sdio_set_rates(struct mt7615_dev *dev,
 	struct mt7615_rate_desc *rate = &wrd->rate;
 	struct mt7615_sta *sta = wrd->sta;
 	u32 w5, w27, addr, val;
-	u16 idx = sta->vif->mt76.omac_idx;
+	u16 idx;
 
 	lockdep_assert_held(&dev->mt76.mutex);
 
@@ -119,6 +119,7 @@ static int mt7663_usb_sdio_set_rates(struct mt7615_dev *dev,
 
 	sta->rate_probe = sta->rateset[rate->rateset].probe_rate.idx != -1;
 
+	idx = sta->vif->mt76.omac_idx;
 	idx = idx > HW_BSSID_MAX ? HW_BSSID_0 : idx;
 	addr = idx > 1 ? MT_LPON_TCR2(idx): MT_LPON_TCR0(idx);
 
-- 
2.30.2