CVE-2025-71182

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

can: j1939: make j1939sessionactivate() 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 NETDEVUNREGISTER notification handler") was added. A debug printk() patch found that j1939sessionactivate() can succeed even after j1939cancelactivesession() from j1939netdevnotify(NETDEV_UNREGISTER) has completed.

Since j1939cancelactivesession() is processed with the session list lock held, checking ndev->regstate in j1939sessionactivate() with the session list lock held can reliably close the race window.