linux-kernel - [PATCH net 1/2] net: lapbether: ignore ops-locked netdevs

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Message-ID: <20250806213726.1383379-1-sdf@fomichev.me>
Date: Wed,  6 Aug 2025 14:37:25 -0700
From: Stanislav Fomichev <sdf@...ichev.me>
To: netdev@...r.kernel.org
Cc: davem@...emloft.net,
	edumazet@...gle.com,
	kuba@...nel.org,
	pabeni@...hat.com,
	andrew+netdev@...n.ch,
	ms@....tdt.de,
	ast@...nel.org,
	daniel@...earbox.net,
	hawk@...nel.org,
	john.fastabend@...il.com,
	sdf@...ichev.me,
	aleksander.lobakin@...el.com,
	linux-kernel@...r.kernel.org,
	linux-x25@...r.kernel.org,
	bpf@...r.kernel.org,
	syzbot+e67ea9c235b13b4f0020@...kaller.appspotmail.com
Subject: [PATCH net 1/2] net: lapbether: ignore ops-locked netdevs

Syzkaller managed to trigger lock dependency in xsk_notify via
register_netdevice. As discussed in [0], using register_netdevice
in the notifiers is problematic so skip adding lapbeth for ops-locked
devices.

       xsk_notifier+0xa4/0x280 net/xdp/xsk.c:1645
       notifier_call_chain+0xbc/0x410 kernel/notifier.c:85
       call_netdevice_notifiers_info+0xbe/0x140 net/core/dev.c:2230
       call_netdevice_notifiers_extack net/core/dev.c:2268 [inline]
       call_netdevice_notifiers net/core/dev.c:2282 [inline]
       unregister_netdevice_many_notify+0xf9d/0x2700 net/core/dev.c:12077
       unregister_netdevice_many net/core/dev.c:12140 [inline]
       unregister_netdevice_queue+0x305/0x3f0 net/core/dev.c:11984
       register_netdevice+0x18f1/0x2270 net/core/dev.c:11149
       lapbeth_new_device drivers/net/wan/lapbether.c:420 [inline]
       lapbeth_device_event+0x5b1/0xbe0 drivers/net/wan/lapbether.c:462
       notifier_call_chain+0xbc/0x410 kernel/notifier.c:85
       call_netdevice_notifiers_info+0xbe/0x140 net/core/dev.c:2230
       call_netdevice_notifiers_extack net/core/dev.c:2268 [inline]
       call_netdevice_notifiers net/core/dev.c:2282 [inline]
       __dev_notify_flags+0x12c/0x2e0 net/core/dev.c:9497
       netif_change_flags+0x108/0x160 net/core/dev.c:9526
       dev_change_flags+0xba/0x250 net/core/dev_api.c:68
       devinet_ioctl+0x11d5/0x1f50 net/ipv4/devinet.c:1200
       inet_ioctl+0x3a7/0x3f0 net/ipv4/af_inet.c:1001

0: https://lore.kernel.org/netdev/20250625140357.6203d0af@kernel.org/
Fixes: 4c975fd70002 ("net: hold instance lock during NETDEV_REGISTER/UP")
Suggested-by: Jakub Kicinski <kuba@...nel.org>
Reported-by: syzbot+e67ea9c235b13b4f0020@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=e67ea9c235b13b4f0020
Signed-off-by: Stanislav Fomichev <sdf@...ichev.me>
---
 drivers/net/wan/lapbether.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/wan/lapbether.c b/drivers/net/wan/lapbether.c
index 995a7207bdf8..f357a7ac70ac 100644
--- a/drivers/net/wan/lapbether.c
+++ b/drivers/net/wan/lapbether.c
@@ -81,7 +81,7 @@ static struct lapbethdev *lapbeth_get_x25_dev(struct net_device *dev)
 
 static __inline__ int dev_is_ethdev(struct net_device *dev)
 {
-	return dev->type == ARPHRD_ETHER && strncmp(dev->name, "dummy", 5);
+	return dev->type == ARPHRD_ETHER && !netdev_need_ops_lock(dev);
 }
 
 /* ------------------------------------------------------------------------ */
-- 
2.50.1