CVE-2025-71182

In the Linux kernel, the following vulnerability has been resolved:

can: j1939: make j1939_session_activate() fail if device is no longer registered

syzbot is still reporting

unregister_netdevice: waiting for vcan0 to become free. Usage count = 2

even after commit 93a27b5891b8 ("can: j1939: add missing calls in NETDEV_UNREGISTER notification handler") was added. A debug printk() patch found that j1939_session_activate() can succeed even after j1939_cancel_active_session() from j1939_netdev_notify(NETDEV_UNREGISTER) has completed.

Since j1939_cancel_active_session() is processed with the session list lock held, checking ndev->reg_state in j1939_session_activate() with the session list lock held can reliably close the race window.

A race in can j1939 j1939_session_activate could succeed after NETDEV_UNREGISTER, keeping references and causing unregister_netdevice to wait indefinitely. PR is typically L for local users able to create j1939 sessions, and the issue is not inherently network reachable. Impact is denial of service due to hang during device unregister.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.