net: dsa: fix phylink_start()/phylink_stop() calls

Place phylink_start()/phylink_stop() inside dsa_port_enable() and
dsa_port_disable(), which ensures that we call phylink_stop() before
tearing down phylink - which is a documented requirement.  Failure
to do so can cause use-after-free bugs.

Fixes: 0e279218 ("net: dsa: Use PHYLINK for the CPU/DSA ports")
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/dsa/dsa_priv.h

@@ -117,7 +117,9 @@ static inline struct net_device *dsa_master_find_slave(struct net_device *dev,
 /* port.c */
 int dsa_port_set_state(struct dsa_port *dp, u8 state,
 		       struct switchdev_trans *trans);
+int dsa_port_enable_rt(struct dsa_port *dp, struct phy_device *phy);
 int dsa_port_enable(struct dsa_port *dp, struct phy_device *phy);
+void dsa_port_disable_rt(struct dsa_port *dp);
 void dsa_port_disable(struct dsa_port *dp);
 int dsa_port_bridge_join(struct dsa_port *dp, struct net_device *br);
 void dsa_port_bridge_leave(struct dsa_port *dp, struct net_device *br);

net/dsa/port.c

@@ -63,7 +63,7 @@ static void dsa_port_set_state_now(struct dsa_port *dp, u8 state)
 		pr_err("DSA: failed to set STP state %u (%d)\n", state, err);
 }
 
-int dsa_port_enable(struct dsa_port *dp, struct phy_device *phy)
+int dsa_port_enable_rt(struct dsa_port *dp, struct phy_device *phy)
 {
 	struct dsa_switch *ds = dp->ds;
 	int port = dp->index;
@@ -78,14 +78,31 @@ int dsa_port_enable(struct dsa_port *dp, struct phy_device *phy)
 	if (!dp->bridge_dev)
 		dsa_port_set_state_now(dp, BR_STATE_FORWARDING);
 
+	if (dp->pl)
+		phylink_start(dp->pl);
+
 	return 0;
 }
 
-void dsa_port_disable(struct dsa_port *dp)
+int dsa_port_enable(struct dsa_port *dp, struct phy_device *phy)
+{
+	int err;
+
+	rtnl_lock();
+	err = dsa_port_enable_rt(dp, phy);
+	rtnl_unlock();
+
+	return err;
+}
+
+void dsa_port_disable_rt(struct dsa_port *dp)
 {
 	struct dsa_switch *ds = dp->ds;
 	int port = dp->index;
 
+	if (dp->pl)
+		phylink_stop(dp->pl);
+
 	if (!dp->bridge_dev)
 		dsa_port_set_state_now(dp, BR_STATE_DISABLED);
 
@@ -93,6 +110,13 @@ void dsa_port_disable(struct dsa_port *dp)
 		ds->ops->port_disable(ds, port);
 }
 
+void dsa_port_disable(struct dsa_port *dp)
+{
+	rtnl_lock();
+	dsa_port_disable_rt(dp);
+	rtnl_unlock();
+}
+
 int dsa_port_bridge_join(struct dsa_port *dp, struct net_device *br)
 {
 	struct dsa_notifier_bridge_info info = {
@@ -614,10 +638,6 @@ static int dsa_port_phylink_register(struct dsa_port *dp)
 		goto err_phy_connect;
 	}
 
-	rtnl_lock();
-	phylink_start(dp->pl);
-	rtnl_unlock();
-
 	return 0;
 
 err_phy_connect:

net/dsa/slave.c

@@ -88,12 +88,10 @@ static int dsa_slave_open(struct net_device *dev)
 			goto clear_allmulti;
 	}
 
-	err = dsa_port_enable(dp, dev->phydev);
+	err = dsa_port_enable_rt(dp, dev->phydev);
 	if (err)
 		goto clear_promisc;
 
-	phylink_start(dp->pl);
-
 	return 0;
 
 clear_promisc:
@@ -114,9 +112,7 @@ static int dsa_slave_close(struct net_device *dev)
 	struct net_device *master = dsa_slave_to_master(dev);
 	struct dsa_port *dp = dsa_slave_to_port(dev);
 
-	phylink_stop(dp->pl);
-
-	dsa_port_disable(dp);
+	dsa_port_disable_rt(dp);
 
 	dev_mc_unsync(master, dev);
 	dev_uc_unsync(master, dev);