linux-kernel - Re: [syzbot] [net?] unregister_netdevice: waiting for DEV to become free (8)

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Message-ID: <20250826015036.5513-1-hdanton@sina.com>
Date: Tue, 26 Aug 2025 09:50:35 +0800
From: Hillf Danton <hdanton@...a.com>
To: syzbot <syzbot+881d65229ca4f9ae8c84@...kaller.appspotmail.com>
Cc: linux-kernel@...r.kernel.org,
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [net?] unregister_netdevice: waiting for DEV to become free (8)

> Date: Fri, 09 Jun 2023 18:34:58 -0700	[thread overview]
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    67faabbde36b selftests/bpf: Add missing prototypes for sev..
> git tree:       bpf-next
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=1381363b280000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=5335204dcdecfda
> dashboard link: https://syzkaller.appspot.com/bug?extid=881d65229ca4f9ae8c84
> compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=132faf93280000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=10532add280000

#syz test upstream master

--- a/net/can/j1939/j1939-priv.h
+++ b/net/can/j1939/j1939-priv.h
@@ -59,6 +59,7 @@ struct j1939_priv {
 	/* segments need a lock to protect the above list */
 	rwlock_t lock;
 
+	int unregistered;
 	struct net_device *ndev;
 
 	/* list of 256 ecu ptrs, that cache the claimed addresses.
--- a/net/can/j1939/main.c
+++ b/net/can/j1939/main.c
@@ -157,13 +157,15 @@ static void __j1939_priv_release(struct
 	struct j1939_priv *priv = container_of(kref, struct j1939_priv, kref);
 	struct net_device *ndev = priv->ndev;
 
-	netdev_dbg(priv->ndev, "%s: 0x%p\n", __func__, priv);
+	if (!priv->unregistered)
+		netdev_dbg(priv->ndev, "%s: 0x%p\n", __func__, priv);
 
 	WARN_ON_ONCE(!list_empty(&priv->active_session_list));
 	WARN_ON_ONCE(!list_empty(&priv->ecus));
 	WARN_ON_ONCE(!list_empty(&priv->j1939_socks));
 
-	dev_put(ndev);
+	if (!priv->unregistered)
+		dev_put(ndev);
 	kfree(priv);
 }
 
@@ -197,7 +199,8 @@ static void j1939_can_rx_unregister(stru
 {
 	struct net_device *ndev = priv->ndev;
 
-	can_rx_unregister(dev_net(ndev), ndev, J1939_CAN_ID, J1939_CAN_MASK,
+	if (!priv->unregistered)
+		can_rx_unregister(dev_net(ndev), ndev, J1939_CAN_ID, J1939_CAN_MASK,
 			  j1939_can_recv, priv);
 
 	/* The last reference of priv is dropped by the RCU deferred
@@ -377,6 +380,10 @@ static int j1939_netdev_notify(struct no
 		j1939_sk_netdev_event_netdown(priv);
 		j1939_ecu_unmap_all(priv);
 		break;
+	case NETDEV_UNREGISTER:
+		priv->unregistered++;
+		dev_put(priv->ndev);
+		break;
 	}
 
 	j1939_priv_put(priv);
--