net: phy: prevent stale pointer dereference in phy_init()

[ Upstream commit 1c613be ]

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: 55d8f05 ("net: phy: Register ethtool PHY operations")
Link: https://lore.kernel.org/netdev/[email protected]/
Suggested-by: Russell King (Oracle) <[email protected]>
Signed-off-by: Vladimir Oltean <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>

Author: vladimiroltean

drivers/net/phy/phy_device.c

@@ -3252,23 +3252,30 @@ 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;
 }