CVE-2025-39925

/// Technical description

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

can: j1939: implement NETDEV_UNREGISTER notification handler

syzbot is reporting

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

problem, for j1939 protocol did not have NETDEV_UNREGISTER notification

handler for undoing changes made by j1939_sk_bind().

Commit 25fe97cb7620 ("can: j1939: move j1939_priv_put() into sk_destruct

callback") expects that a call to j1939_priv_put() can be unconditionally

delayed until j1939_sk_sock_destruct() is called. But we need to call

j1939_priv_put() against an extra ref held by j1939_sk_bind() call

(as a part of undoing changes made by j1939_sk_bind()) as soon as

NETDEV_UNREGISTER notification fires (i.e. before j1939_sk_sock_destruct()

is called via j1939_sk_release()). Otherwise, the extra ref on "struct

j1939_priv" held by j1939_sk_bind() call prevents "struct net_device" from

dropping the usage count to 1; making it impossible for

unregister_netdevice

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References