netdev - [PATCH net] net: mediatek: Fix potential NULL pointer dereference in dummy net

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Message-ID: <20240724080524.2734499-1-leitao@debian.org>
Date: Wed, 24 Jul 2024 01:05:23 -0700
From: Breno Leitao <leitao@...ian.org>
To: Felix Fietkau <nbd@....name>,
	Sean Wang <sean.wang@...iatek.com>,
	Mark Lee <Mark-MC.Lee@...iatek.com>,
	Lorenzo Bianconi <lorenzo@...nel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	Matthias Brugger <matthias.bgg@...il.com>,
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
Cc: leit@...a.com,
	Dan Carpenter <dan.carpenter@...aro.org>,
	netdev@...r.kernel.org (open list:MEDIATEK ETHERNET DRIVER),
	linux-kernel@...r.kernel.org (open list:ARM/Mediatek SoC support),
	linux-arm-kernel@...ts.infradead.org (moderated list:ARM/Mediatek SoC support),
	linux-mediatek@...ts.infradead.org (moderated list:ARM/Mediatek SoC support)
Subject: [PATCH net] net: mediatek: Fix potential NULL pointer dereference in dummy net_device handling

Move the freeing of the dummy net_device from mtk_free_dev() to
mtk_remove().

Previously, if alloc_netdev_dummy() failed in mtk_probe(),
eth->dummy_dev would be NULL. The error path would then call
mtk_free_dev(), which in turn called free_netdev() assuming dummy_dev
was allocated (but it was not), potentially causing a NULL pointer
dereference.

By moving free_netdev() to mtk_remove(), we ensure it's only called when
mtk_probe() has succeeded and dummy_dev is fully allocated. This
addresses a potential NULL pointer dereference detected by Smatch[1].

Fixes: b209bd6d0bff ("net: mediatek: mtk_eth_sock: allocate dummy net_device dynamically")
Reported-by: Dan Carpenter <dan.carpenter@...aro.org>
Closes: https://lore.kernel.org/all/4160f4e0-cbef-4a22-8b5d-42c4d399e1f7@stanley.mountain/ [1]
Suggested-by: Dan Carpenter <dan.carpenter@...aro.org>
Reviewed-by: Dan Carpenter <dan.carpenter@...aro.org>
Signed-off-by: Breno Leitao <leitao@...ian.org>
---
 drivers/net/ethernet/mediatek/mtk_eth_soc.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.c b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
index 0cc2dd85652f..16ca427cf4c3 100644
--- a/drivers/net/ethernet/mediatek/mtk_eth_soc.c
+++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
@@ -4223,8 +4223,6 @@ static int mtk_free_dev(struct mtk_eth *eth)
 		metadata_dst_free(eth->dsa_meta[i]);
 	}
 
-	free_netdev(eth->dummy_dev);
-
 	return 0;
 }
 
@@ -5090,6 +5088,7 @@ static void mtk_remove(struct platform_device *pdev)
 	netif_napi_del(&eth->tx_napi);
 	netif_napi_del(&eth->rx_napi);
 	mtk_cleanup(eth);
+	free_netdev(eth->dummy_dev);
 	mtk_mdio_cleanup(eth);
 }
 
-- 
2.43.0