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

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

[Stanislav Fomichev]

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@kernel.org>
Reported-by: syzbot+e67ea9c235b13b4f0020@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=e67ea9c235b13b4f0020
Signed-off-by: Stanislav Fomichev <sdf@fomichev.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

[PATCH net 2/2] hamradio: ignore ops-locked netdevs

[Stanislav Fomichev]

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 hamradio for ops-locked
devices.

       xsk_notifier+0x89/0x230 net/xdp/xsk.c:1664
       notifier_call_chain+0x1b6/0x3e0 kernel/notifier.c:85
       call_netdevice_notifiers_extack net/core/dev.c:2267 [inline]
       call_netdevice_notifiers net/core/dev.c:2281 [inline]
       unregister_netdevice_many_notify+0x14d7/0x1ff0 net/core/dev.c:12156
       unregister_netdevice_many net/core/dev.c:12219 [inline]
       unregister_netdevice_queue+0x33c/0x380 net/core/dev.c:12063
       register_netdevice+0x1689/0x1ae0 net/core/dev.c:11241
       bpq_new_device drivers/net/hamradio/bpqether.c:481 [inline]
       bpq_device_event+0x491/0x600 drivers/net/hamradio/bpqether.c:523
       notifier_call_chain+0x1b6/0x3e0 kernel/notifier.c:85
       call_netdevice_notifiers_extack net/core/dev.c:2267 [inline]
       call_netdevice_notifiers net/core/dev.c:2281 [inline]
       __dev_notify_flags+0x18d/0x2e0 net/core/dev.c:-1
       netif_change_flags+0xe8/0x1a0 net/core/dev.c:9608
       dev_change_flags+0x130/0x260 net/core/dev_api.c:68
       devinet_ioctl+0xbb4/0x1b50 net/ipv4/devinet.c:1200
       inet_ioctl+0x3c0/0x4c0 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@kernel.org>
Reported-by: syzbot+e6300f66a999a6612477@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=e6300f66a999a6612477
Signed-off-by: Stanislav Fomichev <sdf@fomichev.me>
---
 drivers/net/hamradio/bpqether.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/hamradio/bpqether.c b/drivers/net/hamradio/bpqether.c
index 0e0fe32d2da4..045c5177262e 100644
--- a/drivers/net/hamradio/bpqether.c
+++ b/drivers/net/hamradio/bpqether.c
@@ -138,7 +138,7 @@ static inline struct net_device *bpq_get_ax25_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

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

[patchwork-bot+netdevbpf]

Hello:

This series was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Wed,  6 Aug 2025 14:37:25 -0700 you wrote:
> 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
> 
> [...]

Here is the summary with links:
  - [net,1/2] net: lapbether: ignore ops-locked netdevs
    https://git.kernel.org/netdev/net/c/53898ebabe84
  - [net,2/2] hamradio: ignore ops-locked netdevs
    https://git.kernel.org/netdev/net/c/c64237960819

You are awesome, thank you!
-- 
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html