netlink: 4 bytes leftover after parsing attributes in process `syz.6.859'. ====================================================== WARNING: possible circular locking dependency detected 6.16.0-syzkaller-11952-g6e64f4580381 #0 Not tainted ------------------------------------------------------ syz.6.859/9074 is trying to acquire lock: ffff8880752c06b8 (&xs->mutex){+.+.}-{4:4}, at: xsk_notifier+0xd5/0x230 net/xdp/xsk.c:1668 but task is already holding lock: ffff888067689c98 (&net->xdp.lock){+.+.}-{4:4}, at: xsk_notifier+0x89/0x230 net/xdp/xsk.c:1664 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #2 (&net->xdp.lock){+.+.}-{4:4}: lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868 __mutex_lock_common kernel/locking/mutex.c:598 [inline] __mutex_lock+0x187/0x1360 kernel/locking/mutex.c:760 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 lapbeth_new_device drivers/net/wan/lapbether.c:420 [inline] lapbeth_device_event+0x78a/0xa30 drivers/net/wan/lapbether.c:462 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 sock_do_ioctl+0xdc/0x300 net/socket.c:1238 sock_ioctl+0x576/0x790 net/socket.c:1359 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:598 [inline] __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:584 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f -> #1 (&dev_instance_lock_key#20){+.+.}-{4:4}: lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868 __mutex_lock_common kernel/locking/mutex.c:598 [inline] __mutex_lock+0x187/0x1360 kernel/locking/mutex.c:760 netdev_lock include/linux/netdevice.h:2758 [inline] netdev_lock_ops include/net/netdev_lock.h:42 [inline] xsk_bind+0x2f7/0xf90 net/xdp/xsk.c:1193 __sys_bind_socket net/socket.c:1858 [inline] __sys_bind+0x2c6/0x3e0 net/socket.c:1889 __do_sys_bind net/socket.c:1894 [inline] __se_sys_bind net/socket.c:1892 [inline] __x64_sys_bind+0x7a/0x90 net/socket.c:1892 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f -> #0 (&xs->mutex){+.+.}-{4:4}: check_prev_add kernel/locking/lockdep.c:3165 [inline] check_prevs_add kernel/locking/lockdep.c:3284 [inline] validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3908 __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237 lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868 __mutex_lock_common kernel/locking/mutex.c:598 [inline] __mutex_lock+0x187/0x1360 kernel/locking/mutex.c:760 xsk_notifier+0xd5/0x230 net/xdp/xsk.c:1668 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 rtnl_delete_link net/core/rtnetlink.c:3513 [inline] rtnl_dellink+0x488/0x710 net/core/rtnetlink.c:3555 rtnetlink_rcv_msg+0x7cf/0xb70 net/core/rtnetlink.c:6946 netlink_rcv_skb+0x208/0x470 net/netlink/af_netlink.c:2552 netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline] netlink_unicast+0x82f/0x9e0 net/netlink/af_netlink.c:1346 netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1896 sock_sendmsg_nosec net/socket.c:714 [inline] __sock_sendmsg+0x21c/0x270 net/socket.c:729 ____sys_sendmsg+0x505/0x830 net/socket.c:2614 ___sys_sendmsg+0x21f/0x2a0 net/socket.c:2668 __sys_sendmsg net/socket.c:2700 [inline] __do_sys_sendmsg net/socket.c:2705 [inline] __se_sys_sendmsg net/socket.c:2703 [inline] __x64_sys_sendmsg+0x19b/0x260 net/socket.c:2703 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f other info that might help us debug this: Chain exists of: &xs->mutex --> &dev_instance_lock_key#20 --> &net->xdp.lock Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&net->xdp.lock); lock(&dev_instance_lock_key#20); lock(&net->xdp.lock); lock(&xs->mutex); *** DEADLOCK *** 2 locks held by syz.6.859/9074: #0: ffffffff8f534948 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_lock net/core/rtnetlink.c:80 [inline] #0: ffffffff8f534948 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_net_lock include/linux/rtnetlink.h:130 [inline] #0: ffffffff8f534948 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_dellink+0x331/0x710 net/core/rtnetlink.c:3547 #1: ffff888067689c98 (&net->xdp.lock){+.+.}-{4:4}, at: xsk_notifier+0x89/0x230 net/xdp/xsk.c:1664 stack backtrace: CPU: 1 UID: 0 PID: 9074 Comm: syz.6.859 Not tainted 6.16.0-syzkaller-11952-g6e64f4580381 #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025 Call Trace: dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120 print_circular_bug+0x2ee/0x310 kernel/locking/lockdep.c:2043 check_noncircular+0x134/0x160 kernel/locking/lockdep.c:2175 check_prev_add kernel/locking/lockdep.c:3165 [inline] check_prevs_add kernel/locking/lockdep.c:3284 [inline] validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3908 __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237 lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868 __mutex_lock_common kernel/locking/mutex.c:598 [inline] __mutex_lock+0x187/0x1360 kernel/locking/mutex.c:760 xsk_notifier+0xd5/0x230 net/xdp/xsk.c:1668 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 rtnl_delete_link net/core/rtnetlink.c:3513 [inline] rtnl_dellink+0x488/0x710 net/core/rtnetlink.c:3555 rtnetlink_rcv_msg+0x7cf/0xb70 net/core/rtnetlink.c:6946 netlink_rcv_skb+0x208/0x470 net/netlink/af_netlink.c:2552 netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline] netlink_unicast+0x82f/0x9e0 net/netlink/af_netlink.c:1346 netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1896 sock_sendmsg_nosec net/socket.c:714 [inline] __sock_sendmsg+0x21c/0x270 net/socket.c:729 ____sys_sendmsg+0x505/0x830 net/socket.c:2614 ___sys_sendmsg+0x21f/0x2a0 net/socket.c:2668 __sys_sendmsg net/socket.c:2700 [inline] __do_sys_sendmsg net/socket.c:2705 [inline] __se_sys_sendmsg net/socket.c:2703 [inline] __x64_sys_sendmsg+0x19b/0x260 net/socket.c:2703 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7fe3db78ebe9 Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007fe3dc670038 EFLAGS: 00000246 ORIG_RAX: 000000000000002e RAX: ffffffffffffffda RBX: 00007fe3db9b6090 RCX: 00007fe3db78ebe9 RDX: 0000000000000000 RSI: 00002000000003c0 RDI: 0000000000000006 RBP: 00007fe3db811e19 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 00007fe3db9b6128 R14: 00007fe3db9b6090 R15: 00007ffdf2a05b68