net: ftgmac100: fix potential NULL pointer access in ftgmac100_phy_disconnect

After the call to phy_disconnect() netdev->phydev is reset to NULL.
So fixed_phy_unregister() would be called with a NULL pointer as argument.
Therefore cache the phy_device before this call.

Fixes: e24a6c8 ("net: ftgmac100: Get link speed and duplex for NC-SI")
Cc: [email protected]
Signed-off-by: Heiner Kallweit <[email protected]>
Reviewed-by: Dawid Osuchowski <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: hkallweit

drivers/net/ethernet/faraday/ftgmac100.c

@@ -1750,16 +1750,17 @@ static int ftgmac100_setup_mdio(struct net_device *netdev)
 static void ftgmac100_phy_disconnect(struct net_device *netdev)
 {
 	struct ftgmac100 *priv = netdev_priv(netdev);
+	struct phy_device *phydev = netdev->phydev;
 
-	if (!netdev->phydev)
+	if (!phydev)
 		return;
 
-	phy_disconnect(netdev->phydev);
+	phy_disconnect(phydev);
 	if (of_phy_is_fixed_link(priv->dev->of_node))
 		of_phy_deregister_fixed_link(priv->dev->of_node);
 
 	if (priv->use_ncsi)
-		fixed_phy_unregister(netdev->phydev);
+		fixed_phy_unregister(phydev);
 }
 
 static void ftgmac100_destroy_mdio(struct net_device *netdev)