[bug report] net: mediatek: mtk_eth_sock: allocate dummy net_device dynamically

[Breno Leitao]

Hello Dan,

On Fri, Jul 19, 2024 at 06:52:50PM -0500, Dan Carpenter wrote:
> But it's free here.  (NULL dereference).  I really would suggest moving the
> free_netdev() to the release function.  The probe and release function are
> easier to read if they're in mirrored order where every allocation has a
> matching free.

Thanks for reporting it. It seems a real problem at the error path,
indeed.

I've hacked a patch with your suggestion. how does it look like?


Author: Breno Leitao <leitao at debian.org>
Date:   Mon Jul 22 02:14:19 2024 -0700

    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].
    
    Link: https://lore.kernel.org/all/4160f4e0-cbef-4a22-8b5d-42c4d399e1f7@stanley.mountain/ [1]
    Fixes: b209bd6d0bff ("net: mediatek: mtk_eth_sock: allocate dummy net_device dynamically")
    Reported-by: Dan Carpenter <dan.carpenter at linaro.org>
    Suggested-by: Dan Carpenter <dan.carpenter at linaro.org>
    Signed-off-by: Breno Leitao <leitao at debian.org>

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);
 }