[syzbot] [net?] possible deadlock in __ethtool_get_link_ksettings

[syzbot <syzbot+9bb8bd77f3966641f298@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    2319688890d9 geneve: Fix off-by-one comparing with GRO_LEG..
git tree:       net-next
console output: https://syzkaller.appspot.com/x/log.txt?x=169064ae580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=a0842261b62cdea8
dashboard link: https://syzkaller.appspot.com/bug?extid=9bb8bd77f3966641f298
compiler:       Debian clang version 22.1.6 (++20260514074242+fc4aad7b5db3-1~exp1~20260514074407.73), Debian LLD 22.1.6

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/51d0476acca3/disk-23196888.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/7b1b6c54f1f5/vmlinux-23196888.xz
kernel image: https://storage.googleapis.com/syzbot-assets/c69ec4023055/bzImage-23196888.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+9bb8bd77f3966641f298@syzkaller.appspotmail.com

netlink: 'syz.1.3070': attribute type 10 has an invalid length.
netlink: 40 bytes leftover after parsing attributes in process `syz.1.3070'.
============================================
WARNING: possible recursive locking detected
syzkaller #0 Not tainted
--------------------------------------------
syz.1.3070/18201 is trying to acquire lock:
ffff888079ea6e18 (&dev_instance_lock_key#3){+.+.}-{4:4}, at: netdev_lock include/linux/netdevice.h:2837 [inline]
ffff888079ea6e18 (&dev_instance_lock_key#3){+.+.}-{4:4}, at: netdev_lock_ops include/net/netdev_lock.h:42 [inline]
ffff888079ea6e18 (&dev_instance_lock_key#3){+.+.}-{4:4}, at: __ethtool_get_link_ksettings+0x109/0x250 net/ethtool/ioctl.c:463

but task is already holding lock:
ffff888079ea6e18 (&dev_instance_lock_key#3){+.+.}-{4:4}, at: netdev_lock include/linux/netdevice.h:2837 [inline]
ffff888079ea6e18 (&dev_instance_lock_key#3){+.+.}-{4:4}, at: netdev_lock_ops include/net/netdev_lock.h:42 [inline]
ffff888079ea6e18 (&dev_instance_lock_key#3){+.+.}-{4:4}, at: do_setlink+0x3d4/0x4670 net/core/rtnetlink.c:3117
and the lock comparison function returns 0:

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(&dev_instance_lock_key#3);
  lock(&dev_instance_lock_key#3);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

2 locks held by syz.1.3070/18201:
 #0: ffffffff8fdc1540 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_lock net/core/rtnetlink.c:80 [inline]
 #0: ffffffff8fdc1540 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_nets_lock net/core/rtnetlink.c:341 [inline]
 #0: ffffffff8fdc1540 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_setlink+0x6a7/0xb20 net/core/rtnetlink.c:3527
 #1: ffff888079ea6e18 (&dev_instance_lock_key#3){+.+.}-{4:4}, at: netdev_lock include/linux/netdevice.h:2837 [inline]
 #1: ffff888079ea6e18 (&dev_instance_lock_key#3){+.+.}-{4:4}, at: netdev_lock_ops include/net/netdev_lock.h:42 [inline]
 #1: ffff888079ea6e18 (&dev_instance_lock_key#3){+.+.}-{4:4}, at: do_setlink+0x3d4/0x4670 net/core/rtnetlink.c:3117

stack backtrace:
CPU: 0 UID: 0 PID: 18201 Comm: syz.1.3070 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_deadlock_bug+0x279/0x290 kernel/locking/lockdep.c:3041
 check_deadlock kernel/locking/lockdep.c:3093 [inline]
 validate_chain kernel/locking/lockdep.c:3895 [inline]
 __lock_acquire+0x24bf/0x2cd0 kernel/locking/lockdep.c:5237
 lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5868
 __mutex_lock_common kernel/locking/mutex.c:646 [inline]
 __mutex_lock+0x19d/0x1590 kernel/locking/mutex.c:820
 netdev_lock include/linux/netdevice.h:2837 [inline]
 netdev_lock_ops include/net/netdev_lock.h:42 [inline]
 __ethtool_get_link_ksettings+0x109/0x250 net/ethtool/ioctl.c:463
 __team_port_change_send+0x245/0x560 drivers/net/team/team_core.c:3095
 __team_port_change_check drivers/net/team/team_core.c:3139 [inline]
 team_port_change_check+0x82/0x1d0 drivers/net/team/team_core.c:3160
 team_device_event+0x487/0x570 drivers/net/team/team_core.c:3181
 notifier_call_chain+0x1a5/0x3d0 kernel/notifier.c:85
 call_netdevice_notifiers_extack net/core/dev.c:2288 [inline]
 call_netdevice_notifiers net/core/dev.c:2302 [inline]
 __dev_notify_flags+0x1aa/0x310 net/core/dev.c:9791
 netif_change_flags+0xde/0x1b0 net/core/dev.c:9820
 dev_change_flags+0x128/0x260 net/core/dev_api.c:68
 vlan_device_event+0x1b4e/0x1f00 net/8021q/vlan.c:494
 notifier_call_chain+0x1a5/0x3d0 kernel/notifier.c:85
 call_netdevice_notifiers_extack net/core/dev.c:2288 [inline]
 call_netdevice_notifiers net/core/dev.c:2302 [inline]
 __dev_notify_flags+0x1aa/0x310 net/core/dev.c:9791
 netif_change_flags+0xde/0x1b0 net/core/dev.c:9820
 do_setlink+0xdd6/0x4670 net/core/rtnetlink.c:3207
 rtnl_setlink+0x77d/0xb20 net/core/rtnetlink.c:3537
 rtnetlink_rcv_msg+0x802/0xc00 net/core/rtnetlink.c:7068
 netlink_rcv_skb+0x226/0x4a0 net/netlink/af_netlink.c:2556
 netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
 netlink_unicast+0x7bb/0x940 net/netlink/af_netlink.c:1345
 netlink_sendmsg+0x813/0xb40 net/netlink/af_netlink.c:1900
 sock_sendmsg_nosec net/socket.c:787 [inline]
 __sock_sendmsg net/socket.c:802 [inline]
 ____sys_sendmsg+0x9b9/0xa20 net/socket.c:2699
 ___sys_sendmsg+0x2a5/0x360 net/socket.c:2753
 __sys_sendmsg net/socket.c:2785 [inline]
 __do_sys_sendmsg net/socket.c:2790 [inline]
 __se_sys_sendmsg net/socket.c:2788 [inline]
 __x64_sys_sendmsg+0x1bd/0x2a0 net/socket.c:2788
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f50af59ce59
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f50b0467028 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007f50af815fa0 RCX: 00007f50af59ce59
RDX: 0000000000000000 RSI: 0000200000000080 RDI: 0000000000000003
RBP: 00007f50af632d6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f50af816038 R14: 00007f50af815fa0 R15: 00007ffee67f33e8
 </TASK>


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