drivers: net: cpsw: fix segfault in case of bad phy-handle

If an emac node has a phy-handle property that points to something
which is not a phy, then a segmentation fault will occur when the
interface is brought up. This is because while phy_connect() will
return ERR_PTR() on failure, of_phy_connect() will return NULL.
The common error check uses IS_ERR(), and so missed when
of_phy_connect() fails. The NULL pointer is then dereferenced.

Also, the common error message referenced slave->data->phy_id,
which would be empty in the case of phy-handle. Instead, use the
name of the device_node as a useful identifier. And in the phy_id
case add the error code for completeness.

Fixes: 9e42f715 ("drivers: net: cpsw: add phy-handle parsing")
Signed-off-by: David Rivshin <drivshin@allworx.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/ti/cpsw.c

@@ -1147,25 +1147,34 @@ static void cpsw_slave_open(struct cpsw_slave *slave, struct cpsw_priv *priv)
 		cpsw_ale_add_mcast(priv->ale, priv->ndev->broadcast,
 				   1 << slave_port, 0, 0, ALE_MCAST_FWD_2);
 
-	if (slave->data->phy_node)
+	if (slave->data->phy_node) {
 		slave->phy = of_phy_connect(priv->ndev, slave->data->phy_node,
 				 &cpsw_adjust_link, 0, slave->data->phy_if);
-	else
+		if (!slave->phy) {
+			dev_err(priv->dev, "phy \"%s\" not found on slave %d\n",
+				slave->data->phy_node->full_name,
+				slave->slave_num);
+			return;
+		}
+	} else {
 		slave->phy = phy_connect(priv->ndev, slave->data->phy_id,
 				 &cpsw_adjust_link, slave->data->phy_if);
 		if (IS_ERR(slave->phy)) {
-		dev_err(priv->dev, "phy %s not found on slave %d\n",
-			slave->data->phy_id, slave->slave_num);
+			dev_err(priv->dev,
+				"phy \"%s\" not found on slave %d, err %ld\n",
+				slave->data->phy_id, slave->slave_num,
+				PTR_ERR(slave->phy));
 			slave->phy = NULL;
-	} else {
+			return;
+		}
+	}
+
 	phy_attached_info(slave->phy);
 
 	phy_start(slave->phy);
 
 	/* Configure GMII_SEL register */
-		cpsw_phy_sel(&priv->pdev->dev, slave->phy->interface,
-			     slave->slave_num);
-	}
+	cpsw_phy_sel(&priv->pdev->dev, slave->phy->interface, slave->slave_num);
 }
 
 static inline void cpsw_add_default_vlan(struct cpsw_priv *priv)