Re: [PATCH] can: j1939: implement NETDEV_UNREGISTER notification handler
From: Marc Kleine-Budde <mkl@pengutronix.de>
Date: 2025-09-09 11:48:32
Also in:
linux-can, lkml
On 25.08.2025 23:07:24, Tetsuo Handa wrote:
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() to continue.
Reported-by: syzbot <redacted>
Closes: https://syzkaller.appspot.com/bug?extid=881d65229ca4f9ae8c84
Tested-by: syzbot <redacted>
Fixes: 9d71dd0c7009 ("can: add support of SAE J1939 protocol")
Fixes: 25fe97cb7620 ("can: j1939: move j1939_priv_put() into sk_destruct callback")
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>Applied to linux-can.
quoted hunk ↗ jump to hunk
--- a/net/can/j1939/socket.c +++ b/net/can/j1939/socket.c@@ -1303,6 +1303,55 @@ 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(). */
^^ I've removed the space while applying the patch. regards, Marc -- Pengutronix e.K. | Marc Kleine-Budde | Embedded Linux | https://www.pengutronix.de | Vertretung Nürnberg | Phone: +49-5121-206917-129 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-9 |
Attachments
- signature.asc [application/pgp-signature] 488 bytes