mdio_bus_init() and phy_driver_register() both have error paths, and if
those are ever hit, ethtool will have a stale pointer to the
phy_ethtool_phy_ops stub structure, which references memory from a
module that failed to load (phylib).

It is probably hard to force an error in this code path even manually,
but the error teardown path of phy_init() should be the same as
phy_exit(), which is now simply not the case.

Fixes: 55d8f053ce1b ("net: phy: Register ethtool PHY operations")
Link: https://lore.kernel.org/netdev/ZLaiJ4G6TaJYGJyU@shell.armlinux.org.uk/
Suggested-by: Russell King (Oracle) <linux@armlinux.org.uk>
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
---
 drivers/net/phy/phy_device.c | 21 ++++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
index 0c2014accba7..61921d4dbb13 100644
--- a/drivers/net/phy/phy_device.c
+++ b/drivers/net/phy/phy_device.c
@@ -3451,23 +3451,30 @@ static int __init phy_init(void)
 {
 	int rc;
 
+	ethtool_set_ethtool_phy_ops(&phy_ethtool_phy_ops);
+
 	rc = mdio_bus_init();
 	if (rc)
-		return rc;
+		goto err_ethtool_phy_ops;
 
-	ethtool_set_ethtool_phy_ops(&phy_ethtool_phy_ops);
 	features_init();
 
 	rc = phy_driver_register(&genphy_c45_driver, THIS_MODULE);
 	if (rc)
-		goto err_c45;
+		goto err_mdio_bus;
 
 	rc = phy_driver_register(&genphy_driver, THIS_MODULE);
-	if (rc) {
-		phy_driver_unregister(&genphy_c45_driver);
+	if (rc)
+		goto err_c45;
+
+	return 0;
+
 err_c45:
-		mdio_bus_exit();
-	}
+	phy_driver_unregister(&genphy_c45_driver);
+err_mdio_bus:
+	mdio_bus_exit();
+err_ethtool_phy_ops:
+	ethtool_set_ethtool_phy_ops(NULL);
 
 	return rc;
 }
-- 
2.34.1

Hello:

This patch was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Thu, 20 Jul 2023 03:02:31 +0300 you wrote:
> mdio_bus_init() and phy_driver_register() both have error paths, and if
> those are ever hit, ethtool will have a stale pointer to the
> phy_ethtool_phy_ops stub structure, which references memory from a
> module that failed to load (phylib).
> 
> It is probably hard to force an error in this code path even manually,
> but the error teardown path of phy_init() should be the same as
> phy_exit(), which is now simply not the case.
> 
> [...]

Here is the summary with links:
  - [net] net: phy: prevent stale pointer dereference in phy_init()
    https://git.kernel.org/netdev/net/c/1c613beaf877

You are awesome, thank you!
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