------------[ 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/u8:8/28806 Modules linked in: CPU: 1 UID: 0 PID: 28806 Comm: kworker/u8:8 Not tainted syzkaller #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026 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 6b 5d 14 fd 48 8d 3d a4 2c 89 0b 67 48 0f b9 3a eb 4a e8 58 5d 14 fd 48 8d 3d a1 2c 89 0b <67> 48 0f b9 3a eb 37 e8 45 5d 14 fd 48 8d 3d 9e 2c 89 0b 67 48 0f RSP: 0018:ffffc90003b172f8 EFLAGS: 00010293 RAX: ffffffff84b1a8c8 RBX: 0000000000000002 RCX: ffff888032565d00 RDX: 0000000000000000 RSI: ffffffff8f1126a0 RDI: ffffffff903ad570 RBP: 0000000000000000 R08: ffff888032565d00 R09: 0000000000000005 R10: 0000000000000004 R11: 0000000000000000 R12: dffffc0000000000 R13: ffff888068826000 R14: ffff88802650143c R15: ffff88802650143c FS: 0000000000000000(0000) GS:ffff8881253a4000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 000000008017d018 CR3: 0000000056d1e000 CR4: 00000000003526f0 Call Trace: __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+0xfed/0x11d0 drivers/net/netdevsim/fib.c:1043 call_fib_notifier+0x45/0x80 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+0x341/0x5b0 net/ipv4/fib_trie.c:2217 fib_net_dump net/core/fib_notifier.c:70 [inline] register_fib_notifier+0x184/0x360 net/core/fib_notifier.c:108 nsim_fib_create+0x878/0xa00 drivers/net/netdevsim/fib.c:1596 nsim_dev_reload_create drivers/net/netdevsim/dev.c:1604 [inline] nsim_dev_reload_up+0x3a5/0x780 drivers/net/netdevsim/dev.c:1058 devlink_reload+0x4b2/0x890 net/devlink/dev.c:475 devlink_pernet_pre_exit+0x1ff/0x420 net/devlink/core.c:560 ops_pre_exit_list net/core/net_namespace.c:161 [inline] ops_undo_list+0x17d/0x8d0 net/core/net_namespace.c:234 cleanup_net+0x572/0x810 net/core/net_namespace.c:702 process_one_work kernel/workqueue.c:3314 [inline] process_scheduled_works+0xa8e/0x14e0 kernel/workqueue.c:3397 worker_thread+0xa47/0xfb0 kernel/workqueue.c:3478 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 ---------------- 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 6b 5d 14 fd call 0xfd145d7b 10: 48 8d 3d a4 2c 89 0b lea 0xb892ca4(%rip),%rdi # 0xb892cbb 17: 67 48 0f b9 3a ud1 (%edx),%rdi 1c: eb 4a jmp 0x68 1e: e8 58 5d 14 fd call 0xfd145d7b 23: 48 8d 3d a1 2c 89 0b lea 0xb892ca1(%rip),%rdi # 0xb892ccb * 2a: 67 48 0f b9 3a ud1 (%edx),%rdi <-- trapping instruction 2f: eb 37 jmp 0x68 31: e8 45 5d 14 fd call 0xfd145d7b 36: 48 8d 3d 9e 2c 89 0b lea 0xb892c9e(%rip),%rdi # 0xb892cdb 3d: 67 addr32 3e: 48 rex.W 3f: 0f .byte 0xf