------------[ 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#0: kworker/u8:2/36 Modules linked in: CPU: 0 UID: 0 PID: 36 Comm: kworker/u8:2 Not tainted syzkaller #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026 Workqueue: netns cleanup_net RIP: 0010:refcount_warn_saturate+0x111/0x130 lib/refcount.c:25 Code: fc e8 03 00 14 fd 48 8d 3d cc c7 ef 0b 67 48 0f b9 3a e8 f2 ff 13 fd 5b 5d e9 56 ae 1b fc e8 e6 ff 13 fd 48 8d 3d bf c7 ef 0b <67> 48 0f b9 3a e8 d5 ff 13 fd 5b 5d e9 39 ae 1b fc 48 89 df e8 06 RSP: 0018:ffffc90000ac7478 EFLAGS: 00010293 RAX: 0000000000000000 RBX: ffff888028210e3c RCX: ffffffff84f4920b RDX: ffff888020eb1e80 RSI: ffffffff84f492ba RDI: ffffffff90e45a80 RBP: 0000000000000002 R08: 0000000000000005 R09: 0000000000000004 R10: 0000000000000002 R11: 00000000000075eb R12: ffff8880574c6000 R13: 0000000000000000 R14: ffff888032be8900 R15: 0000000000000000 FS: 0000000000000000(0000) GS:ffff888124346000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000000 CR3: 00000000345b6000 CR4: 0000000000350ef0 Call Trace: __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: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+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:69 [inline] register_fib_notifier+0x123/0x470 net/core/fib_notifier.c:107 nsim_fib_create+0x8f5/0xc10 drivers/net/netdevsim/fib.c:1596 nsim_dev_reload_create drivers/net/netdevsim/dev.c:1583 [inline] nsim_dev_reload_up+0x3ea/0x830 drivers/net/netdevsim/dev.c:1058 devlink_reload+0x2b7/0x790 net/devlink/dev.c:474 devlink_pernet_pre_exit+0x222/0x330 net/devlink/core.c:507 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:704 process_one_work+0x9d7/0x1920 kernel/workqueue.c:3275 process_scheduled_works kernel/workqueue.c:3358 [inline] worker_thread+0x5da/0xe40 kernel/workqueue.c:3439 kthread+0x370/0x450 kernel/kthread.c:436 ret_from_fork+0x754/0xd80 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 ---------------- Code disassembly (best guess): 0: fc cld 1: e8 03 00 14 fd call 0xfd140009 6: 48 8d 3d cc c7 ef 0b lea 0xbefc7cc(%rip),%rdi # 0xbefc7d9 d: 67 48 0f b9 3a ud1 (%edx),%rdi 12: e8 f2 ff 13 fd call 0xfd140009 17: 5b pop %rbx 18: 5d pop %rbp 19: e9 56 ae 1b fc jmp 0xfc1bae74 1e: e8 e6 ff 13 fd call 0xfd140009 23: 48 8d 3d bf c7 ef 0b lea 0xbefc7bf(%rip),%rdi # 0xbefc7e9 * 2a: 67 48 0f b9 3a ud1 (%edx),%rdi <-- trapping instruction 2f: e8 d5 ff 13 fd call 0xfd140009 34: 5b pop %rbx 35: 5d pop %rbp 36: e9 39 ae 1b fc jmp 0xfc1bae74 3b: 48 89 df mov %rbx,%rdi 3e: e8 .byte 0xe8 3f: 06 (bad)