Merge: CVE-2025-39925: can: j1939: implement NETDEV_UNREGISTER notification handler

MR: https://gitlab.com/redhat/centos-stream/src/kernel/centos-stream-9/-/merge_requests/7521

JIRA: https://issues.redhat.com/browse/RHEL-124106
CVE: CVE-2025-39925

 * 7fcbe5b can: j1939: implement NETDEV_UNREGISTER notification handler
 * 93a27b5 can: j1939: add missing calls in NETDEV_UNREGISTER notification handler

Signed-off-by: CKI Backport Bot <cki-ci-bot+cki-gitlab-backport-bot@redhat.com>

---

<small>Created 2025-10-25 21:33 UTC by backporter - [KWF FAQ](https://red.ht/kernel_workflow_doc) - [Slack #team-kernel-workflow](https://redhat-internal.slack.com/archives/C04LRUPMJQ5) - [Source](https://gitlab.com/cki-project/kernel-workflow/-/blob/main/webhook/utils/backporter.py) - [Documentation](https://gitlab.com/cki-project/kernel-workflow/-/blob/main/docs/README.backporter.md) - [Report an issue](https://issues.redhat.com/secure/CreateIssueDetails!init.jspa?pid=12334433&issuetype=1&priority=4&summary=backporter+webhook+issue&components=kernel-workflow+/+backporter)</small>

Approved-by: Radu Rendec <rrendec@redhat.com>
Approved-by: Davide Caratti <dcaratti@redhat.com>
Approved-by: CKI KWF Bot <cki-ci-bot+kwf-gitlab-com@redhat.com>

Merged-by: CKI GitLab Kmaint Pipeline Bot <26919896-cki-kmaint-pipeline-bot@users.noreply.gitlab.com>

Author: CKI KWF Bot

net/can/j1939/j1939-priv.h

@@ -212,6 +212,7 @@ void j1939_priv_get(struct j1939_priv *priv);
 
 /* notify/alert all j1939 sockets bound to ifindex */
 void j1939_sk_netdev_event_netdown(struct j1939_priv *priv);
+void j1939_sk_netdev_event_unregister(struct j1939_priv *priv);
 int j1939_cancel_active_session(struct j1939_priv *priv, struct sock *sk);
 void j1939_tp_init(struct j1939_priv *priv);
 

net/can/j1939/main.c

@@ -381,6 +381,11 @@ static int j1939_netdev_notify(struct notifier_block *nb,
 		j1939_sk_netdev_event_netdown(priv);
 		j1939_ecu_unmap_all(priv);
 		break;
+	case NETDEV_UNREGISTER:
+		j1939_cancel_active_session(priv, NULL);
+		j1939_sk_netdev_event_netdown(priv);
+		j1939_sk_netdev_event_unregister(priv);
+		break;
 	}
 
 	j1939_priv_put(priv);

net/can/j1939/socket.c

@@ -1296,6 +1296,55 @@ void j1939_sk_netdev_event_netdown(struct j1939_priv *priv)
 	read_unlock_bh(&priv->j1939_socks_lock);
 }
 
+void j1939_sk_netdev_event_unregister(struct j1939_priv *priv)
+{
+	struct sock *sk;
+	struct j1939_sock *jsk;
+	bool wait_rcu = false;
+
+rescan: /* The caller is holding a ref on this "priv" via j1939_priv_get_by_ndev(). */
+	read_lock_bh(&priv->j1939_socks_lock);
+	list_for_each_entry(jsk, &priv->j1939_socks, list) {
+		/* Skip if j1939_jsk_add() is not called on this socket. */
+		if (!(jsk->state & J1939_SOCK_BOUND))
+			continue;
+		sk = &jsk->sk;
+		sock_hold(sk);
+		read_unlock_bh(&priv->j1939_socks_lock);
+		/* Check if j1939_jsk_del() is not yet called on this socket after holding
+		 * socket's lock, for both j1939_sk_bind() and j1939_sk_release() call
+		 * j1939_jsk_del() with socket's lock held.
+		 */
+		lock_sock(sk);
+		if (jsk->state & J1939_SOCK_BOUND) {
+			/* Neither j1939_sk_bind() nor j1939_sk_release() called j1939_jsk_del().
+			 * Make this socket no longer bound, by pretending as if j1939_sk_bind()
+			 * dropped old references but did not get new references.
+			 */
+			j1939_jsk_del(priv, jsk);
+			j1939_local_ecu_put(priv, jsk->addr.src_name, jsk->addr.sa);
+			j1939_netdev_stop(priv);
+			/* Call j1939_priv_put() now and prevent j1939_sk_sock_destruct() from
+			 * calling the corresponding j1939_priv_put().
+			 *
+			 * j1939_sk_sock_destruct() is supposed to call j1939_priv_put() after
+			 * an RCU grace period. But since the caller is holding a ref on this
+			 * "priv", we can defer synchronize_rcu() until immediately before
+			 * the caller calls j1939_priv_put().
+			 */
+			j1939_priv_put(priv);
+			jsk->priv = NULL;
+			wait_rcu = true;
+		}
+		release_sock(sk);
+		sock_put(sk);
+		goto rescan;
+	}
+	read_unlock_bh(&priv->j1939_socks_lock);
+	if (wait_rcu)
+		synchronize_rcu();
+}
+
 static int j1939_sk_no_ioctlcmd(struct socket *sock, unsigned int cmd,
 				unsigned long arg)
 {