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: 0e27921816ad ("net: dsa: Use PHYLINK for the CPU/DSA ports")
Signed-off-by: Russell King <[e-mail]>
Reviewed-by: Andrew Lunn <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/dsa/dsa_priv.h

···
 /* 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

···
 		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;
···
 	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);
 
 	if (ds->ops->port_disable)
 		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)
···
 		pr_err("could not attach to PHY: %d\n", err);
 		goto err_phy_connect;
 	}
-
-	rtnl_lock();
-	phylink_start(dp->pl);
-	rtnl_unlock();
 
 	return 0;
 

net/dsa/slave.c

···
 			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;
 
···
 	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);