------------[ cut here ]------------
refcount_t: addition on 0; use-after-free.
WARNING: lib/refcount.c:25 at refcount_warn_saturate+0x111/0x130 lib/refcount.c:25, CPU#1: kworker/u8:4/58
Modules linked in:
CPU: 1 UID: 0 PID: 58 Comm: kworker/u8:4 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
Workqueue: netns cleanup_net
RIP: 0010:refcount_warn_saturate+0x111/0x130 lib/refcount.c:25
Code: cc e8 a3 a5 0f fd 48 8d 3d 0c cf ec 0b 67 48 0f b9 3a e8 92 a5 0f fd 5b 5d e9 8b 25 a4 06 e8 86 a5 0f fd 48 8d 3d ff ce ec 0b <67> 48 0f b9 3a e8 75 a5 0f fd 5b 5d c3 cc cc cc cc 48 89 df e8 46
RSP: 0018:ffffc900015f7478 EFLAGS: 00010293
RAX: 0000000000000000 RBX: ffff88803677503c RCX: ffffffff84f9d4ab
RDX: ffff88801dbca500 RSI: ffffffff84f9d55a RDI: ffffffff90e6a460
RBP: 0000000000000002 R08: 0000000000000005 R09: 0000000000000004
R10: 0000000000000002 R11: 000000000000765b R12: ffff888021345000
R13: 0000000000000000 R14: ffff888057894c00 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff8881243db000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000110c2f2716 CR3: 0000000086567000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 __refcount_add include/linux/refcount.h:289 [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+0xc39/0xe40 drivers/net/netdevsim/fib.c:1043
 call_fib_notifier+0x3c/0x80 net/core/fib_notifier.c:25
 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+0x360/0x5a0 net/ipv4/fib_trie.c:2217
 fib4_dump+0x48/0x60 net/ipv4/fib_notifier.c:45
 fib_net_dump net/core/fib_notifier.c:70 [inline]
 register_fib_notifier+0x123/0x470 net/core/fib_notifier.c:108
 nsim_fib_create+0x8f5/0xc10 drivers/net/netdevsim/fib.c:1596
 nsim_dev_reload_create drivers/net/netdevsim/dev.c:1604 [inline]
 nsim_dev_reload_up+0x3ea/0x830 drivers/net/netdevsim/dev.c:1058
 devlink_reload+0x2f2/0x7a0 net/devlink/dev.c:475
 devlink_pernet_pre_exit+0x247/0x370 net/devlink/core.c:558
 ops_pre_exit_list net/core/net_namespace.c:161 [inline]
 ops_undo_list+0x187/0xab0 net/core/net_namespace.c:234
 cleanup_net+0x499/0x920 net/core/net_namespace.c:702
 process_one_work+0xa0e/0x1980 kernel/workqueue.c:3302
 process_scheduled_works kernel/workqueue.c:3385 [inline]
 worker_thread+0x5ef/0xe50 kernel/workqueue.c:3466
 kthread+0x370/0x450 kernel/kthread.c:436
 ret_from_fork+0x72b/0xd50 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:	cc                   	int3
   1:	e8 a3 a5 0f fd       	call   0xfd0fa5a9
   6:	48 8d 3d 0c cf ec 0b 	lea    0xbeccf0c(%rip),%rdi        # 0xbeccf19
   d:	67 48 0f b9 3a       	ud1    (%edx),%rdi
  12:	e8 92 a5 0f fd       	call   0xfd0fa5a9
  17:	5b                   	pop    %rbx
  18:	5d                   	pop    %rbp
  19:	e9 8b 25 a4 06       	jmp    0x6a425a9
  1e:	e8 86 a5 0f fd       	call   0xfd0fa5a9
  23:	48 8d 3d ff ce ec 0b 	lea    0xbecceff(%rip),%rdi        # 0xbeccf29
* 2a:	67 48 0f b9 3a       	ud1    (%edx),%rdi <-- trapping instruction
  2f:	e8 75 a5 0f fd       	call   0xfd0fa5a9
  34:	5b                   	pop    %rbx
  35:	5d                   	pop    %rbp
  36:	c3                   	ret
  37:	cc                   	int3
  38:	cc                   	int3
  39:	cc                   	int3
  3a:	cc                   	int3
  3b:	48 89 df             	mov    %rbx,%rdi
  3e:	e8                   	.byte 0xe8
  3f:	46                   	rex.RX