------------[ cut here ]------------
refcount_t: addition on 0; use-after-free.
WARNING: lib/refcount.c:25 at refcount_warn_saturate+0x9f/0x110 lib/refcount.c:25, CPU#1: kworker/u8:5/68
Modules linked in:
CPU: 1 UID: 0 PID: 68 Comm: kworker/u8:5 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
Workqueue: netns cleanup_net
RIP: 0010:refcount_warn_saturate+0x9f/0x110 lib/refcount.c:25
Code: eb 66 85 db 74 3e 83 fb 01 75 4c e8 4b de 26 fd 48 8d 3d 64 73 d7 0a 67 48 0f b9 3a eb 4a e8 38 de 26 fd 48 8d 3d 61 73 d7 0a <67> 48 0f b9 3a eb 37 e8 25 de 26 fd 48 8d 3d 5e 73 d7 0a 67 48 0f
RSP: 0018:ffffc9000154f270 EFLAGS: 00010293
RAX: ffffffff849d5368 RBX: 0000000000000002 RCX: ffff88801db01ec0
RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffffff8f74c6d0
RBP: 0000000000000000 R08: ffff88801db01ec0 R09: 0000000000000005
R10: 0000000000000100 R11: 0000000000000004 R12: ffff88803fd1d000
R13: dffffc0000000000 R14: ffff88802768523c R15: ffff88803fd1d000
FS:  0000000000000000(0000) GS:ffff888126438000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f301836e000 CR3: 0000000038afe000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 __refcount_add include/linux/refcount.h:-1 [inline]
 __refcount_inc include/linux/refcount.h:366 [inline]
 refcount_inc include/linux/refcount.h:383 [inline]
 fib_info_hold include/net/ip_fib.h:629 [inline]
 nsim_fib4_prepare_event drivers/net/netdevsim/fib.c:930 [inline]
 nsim_fib_event_schedule_work drivers/net/netdevsim/fib.c:1000 [inline]
 nsim_fib_event_nb+0x1055/0x1240 drivers/net/netdevsim/fib.c:1043
 call_fib_notifier+0x45/0x80 net/core/fib_notifier.c:24
 call_fib_entry_notifier net/ipv4/fib_trie.c:90 [inline]
 fib_leaf_notify net/ipv4/fib_trie.c:2176 [inline]
 fib_table_notify net/ipv4/fib_trie.c:2194 [inline]
 fib_notify+0x36b/0x5e0 net/ipv4/fib_trie.c:2217
 fib_net_dump net/core/fib_notifier.c:69 [inline]
 register_fib_notifier+0x184/0x360 net/core/fib_notifier.c:107
 nsim_fib_create+0x85d/0x9f0 drivers/net/netdevsim/fib.c:1596
 nsim_dev_reload_create drivers/net/netdevsim/dev.c:1583 [inline]
 nsim_dev_reload_up+0x374/0x7c0 drivers/net/netdevsim/dev.c:1058
 devlink_reload+0x50e/0x8e0 net/devlink/dev.c:474
 devlink_pernet_pre_exit+0x1ea/0x3f0 net/devlink/core.c:507
 ops_pre_exit_list net/core/net_namespace.c:161 [inline]
 ops_undo_list+0x187/0x940 net/core/net_namespace.c:234
 cleanup_net+0x56e/0x800 net/core/net_namespace.c:702
 process_one_work kernel/workqueue.c:3288 [inline]
 process_scheduled_works+0xb5d/0x1860 kernel/workqueue.c:3371
 worker_thread+0xa53/0xfc0 kernel/workqueue.c:3452
 kthread+0x388/0x470 kernel/kthread.c:436
 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
----------------
Code disassembly (best guess):
   0:	eb 66                	jmp    0x68
   2:	85 db                	test   %ebx,%ebx
   4:	74 3e                	je     0x44
   6:	83 fb 01             	cmp    $0x1,%ebx
   9:	75 4c                	jne    0x57
   b:	e8 4b de 26 fd       	call   0xfd26de5b
  10:	48 8d 3d 64 73 d7 0a 	lea    0xad77364(%rip),%rdi        # 0xad7737b
  17:	67 48 0f b9 3a       	ud1    (%edx),%rdi
  1c:	eb 4a                	jmp    0x68
  1e:	e8 38 de 26 fd       	call   0xfd26de5b
  23:	48 8d 3d 61 73 d7 0a 	lea    0xad77361(%rip),%rdi        # 0xad7738b
* 2a:	67 48 0f b9 3a       	ud1    (%edx),%rdi <-- trapping instruction
  2f:	eb 37                	jmp    0x68
  31:	e8 25 de 26 fd       	call   0xfd26de5b
  36:	48 8d 3d 5e 73 d7 0a 	lea    0xad7735e(%rip),%rdi        # 0xad7739b
  3d:	67                   	addr32
  3e:	48                   	rex.W
  3f:	0f                   	.byte 0xf