Merge patch series "can: j1939: avoid possible use-after-free when j1939_can_rx_register fails"

Fedor Pchelkin <pchelkin@ispras.ru> says:

The patch series fixes a possible racy use-after-free scenario
described in 2/2: if j1939_can_rx_register() fails then the concurrent
thread may have already read the invalid priv structure.

The 1/2 makes j1939_netdev_lock a mutex so that access to
j1939_can_rx_register() can be serialized without changing GFP_KERNEL
to GFP_ATOMIC inside can_rx_register(). This seems to be safe.

Note that the patch series has been tested only via Syzkaller and not
with a real device.

Link: https://lore.kernel.org/r/20230526171910.227615-1-pchelkin@ispras.ruSigned-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

net/can/j1939/main.c

@@ -126,7 +126,7 @@ static void j1939_can_recv(struct sk_buff *iskb, void *data)
 #define J1939_CAN_ID CAN_EFF_FLAG
 #define J1939_CAN_MASK (CAN_EFF_FLAG | CAN_RTR_FLAG)
 
-static DEFINE_SPINLOCK(j1939_netdev_lock);
+static DEFINE_MUTEX(j1939_netdev_lock);
 
 static struct j1939_priv *j1939_priv_create(struct net_device *ndev)
 {
@@ -220,7 +220,7 @@ static void __j1939_rx_release(struct kref *kref)
 	j1939_can_rx_unregister(priv);
 	j1939_ecu_unmap_all(priv);
 	j1939_priv_set(priv->ndev, NULL);
-	spin_unlock(&j1939_netdev_lock);
+	mutex_unlock(&j1939_netdev_lock);
 }
 
 /* get pointer to priv without increasing ref counter */
@@ -248,9 +248,9 @@ static struct j1939_priv *j1939_priv_get_by_ndev(struct net_device *ndev)
 {
 	struct j1939_priv *priv;
 
-	spin_lock(&j1939_netdev_lock);
+	mutex_lock(&j1939_netdev_lock);
 	priv = j1939_priv_get_by_ndev_locked(ndev);
-	spin_unlock(&j1939_netdev_lock);
+	mutex_unlock(&j1939_netdev_lock);
 
 	return priv;
 }
@@ -260,14 +260,14 @@ struct j1939_priv *j1939_netdev_start(struct net_device *ndev)
 	struct j1939_priv *priv, *priv_new;
 	int ret;
 
-	spin_lock(&j1939_netdev_lock);
+	mutex_lock(&j1939_netdev_lock);
 	priv = j1939_priv_get_by_ndev_locked(ndev);
 	if (priv) {
 		kref_get(&priv->rx_kref);
-		spin_unlock(&j1939_netdev_lock);
+		mutex_unlock(&j1939_netdev_lock);
 		return priv;
 	}
-	spin_unlock(&j1939_netdev_lock);
+	mutex_unlock(&j1939_netdev_lock);
 
 	priv = j1939_priv_create(ndev);
 	if (!priv)
@@ -277,29 +277,31 @@ struct j1939_priv *j1939_netdev_start(struct net_device *ndev)
 	spin_lock_init(&priv->j1939_socks_lock);
 	INIT_LIST_HEAD(&priv->j1939_socks);
 
-	spin_lock(&j1939_netdev_lock);
+	mutex_lock(&j1939_netdev_lock);
 	priv_new = j1939_priv_get_by_ndev_locked(ndev);
 	if (priv_new) {
 		/* Someone was faster than us, use their priv and roll
 		 * back our's.
 		 */
 		kref_get(&priv_new->rx_kref);
-		spin_unlock(&j1939_netdev_lock);
+		mutex_unlock(&j1939_netdev_lock);
 		dev_put(ndev);
 		kfree(priv);
 		return priv_new;
 	}
 	j1939_priv_set(ndev, priv);
-	spin_unlock(&j1939_netdev_lock);
 
 	ret = j1939_can_rx_register(priv);
 	if (ret < 0)
 		goto out_priv_put;
 
+	mutex_unlock(&j1939_netdev_lock);
 	return priv;
 
  out_priv_put:
 	j1939_priv_set(ndev, NULL);
+	mutex_unlock(&j1939_netdev_lock);
+
 	dev_put(ndev);
 	kfree(priv);
 
@@ -308,7 +310,7 @@ struct j1939_priv *j1939_netdev_start(struct net_device *ndev)
 
 void j1939_netdev_stop(struct j1939_priv *priv)
 {
-	kref_put_lock(&priv->rx_kref, __j1939_rx_release, &j1939_netdev_lock);
+	kref_put_mutex(&priv->rx_kref, __j1939_rx_release, &j1939_netdev_lock);
 	j1939_priv_put(priv);
 }