Re: [PATCH v2] net: dsa: bcm_sf2: Fix possible memory leak in bcm_sf2_mdio_register()

[Simon Horman <horms@kernel.org>]

On Mon, Oct 09, 2023 at 04:39:06PM +0800, Jinjie Ruan wrote:
> In bcm_sf2_mdio_register(), the class_find_device() will call get_device()
> to increment reference count for priv->master_mii_bus->dev if
> of_mdio_find_bus() succeeds. If mdiobus_alloc() or mdiobus_register()
> fails, it will call get_device() twice without decrement reference count
> for the device. And it is the same if bcm_sf2_mdio_register() succeeds but
> fails in bcm_sf2_sw_probe(), or if bcm_sf2_sw_probe() succeeds. If the
> reference count has not decremented to zero, the dev related resource will
> not be freed.
> 
> So remove the get_device() in bcm_sf2_mdio_register(), and call
> put_device() if mdiobus_alloc() or mdiobus_register() fails and in
> bcm_sf2_mdio_unregister() to solve the issue.
> 
> Fixes: 461cd1b03e32 ("net: dsa: bcm_sf2: Register our slave MDIO bus")
> Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>

Hi Jinjie Ruan,

I agree with your analysis here, but I wonder if it would be nicer
to move bcm_sf2_mdio_register() to a more idiomatic way of unwinding
from errors.

Something like this (compile tested only!)

diff --git a/drivers/net/dsa/bcm_sf2.c b/drivers/net/dsa/bcm_sf2.c
index 0b62bd78ac50..037ce118ee00 100644
--- a/drivers/net/dsa/bcm_sf2.c
+++ b/drivers/net/dsa/bcm_sf2.c
@@ -617,8 +617,8 @@ static int bcm_sf2_mdio_register(struct dsa_switch *ds)
 	dn = of_find_compatible_node(NULL, NULL, "brcm,unimac-mdio");
 	priv->master_mii_bus = of_mdio_find_bus(dn);
 	if (!priv->master_mii_bus) {
-		of_node_put(dn);
-		return -EPROBE_DEFER;
+		err = -EPROBE_DEFER;
+		goto err_of_node_put;
 	}
 
 	get_device(&priv->master_mii_bus->dev);
@@ -626,8 +626,8 @@ static int bcm_sf2_mdio_register(struct dsa_switch *ds)
 
 	priv->slave_mii_bus = mdiobus_alloc();
 	if (!priv->slave_mii_bus) {
-		of_node_put(dn);
-		return -ENOMEM;
+		err = -ENOMEM;
+		goto err_put_master_mii_bus_device;
 	}
 
 	priv->slave_mii_bus->priv = priv;
@@ -684,12 +684,18 @@ static int bcm_sf2_mdio_register(struct dsa_switch *ds)
 	}
 
 	err = mdiobus_register(priv->slave_mii_bus);
-	if (err && dn) {
-		mdiobus_free(priv->slave_mii_bus);
-		of_node_put(dn);
-	}
+	if (err && dn)
+		goto err_free_slave_mii_bus;
 
 	return err;
+
+err_free_slave_mii_bus:
+	mdiobus_free(priv->slave_mii_bus);
+err_put_master_mii_bus_device:
+	put_device(&priv->master_mii_bus->dev);
+err_of_node_put:
+	of_node_put(dn);
+	return err;
 }
 
 static void bcm_sf2_mdio_unregister(struct bcm_sf2_priv *priv)