------------[ cut here ]------------ refcount_t: underflow; use-after-free. WARNING: lib/refcount.c:28 at 0x0, CPU#0: syz.2.1672/12713 Modules linked in: CPU: 0 UID: 0 PID: 12713 Comm: syz.2.1672 Not tainted syzkaller #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025 RIP: 0010:refcount_warn_saturate+0xb2/0x110 lib/refcount.c:28 Code: 74 26 00 0b 67 48 0f b9 3a eb 4a e8 d8 d2 36 fd 48 8d 3d 71 26 00 0b 67 48 0f b9 3a eb 37 e8 c5 d2 36 fd 48 8d 3d 6e 26 00 0b <67> 48 0f b9 3a eb 24 e8 b2 d2 36 fd 48 8d 3d 6b 26 00 0b 67 48 0f RSP: 0018:ffffc900038cf578 EFLAGS: 00010293 RAX: ffffffff848a779b RBX: 0000000000000003 RCX: ffff888026f90000 RDX: 0000000000000000 RSI: ffffffff8e67b660 RDI: ffffffff8f8a9e10 RBP: 0000000000000000 R08: ffff888026f90000 R09: 0000000000000005 R10: 0000000000000004 R11: 0000000000000000 R12: ffff88802f72bc00 R13: ffff888058b83060 R14: ffff888058b83078 R15: dffffc0000000000 FS: 0000000000000000(0000) GS:ffff8881260b1000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f7651a4098b CR3: 0000000030b14000 CR4: 00000000003526f0 Call Trace: __refcount_sub_and_test include/linux/refcount.h:400 [inline] __refcount_dec_and_test include/linux/refcount.h:432 [inline] refcount_dec_and_test include/linux/refcount.h:450 [inline] kref_put include/linux/kref.h:64 [inline] klist_dec_and_del+0x3c7/0x3d0 lib/klist.c:206 klist_put lib/klist.c:217 [inline] klist_del lib/klist.c:230 [inline] klist_remove+0x1bd/0x340 lib/klist.c:249 device_move+0x193/0x700 drivers/base/core.c:4615 hci_conn_del_sysfs+0xb8/0x170 net/bluetooth/hci_sysfs.c:75 hci_conn_cleanup net/bluetooth/hci_conn.c:173 [inline] hci_conn_del+0xc36/0x11b0 net/bluetooth/hci_conn.c:1234 hci_conn_hash_flush+0x191/0x230 net/bluetooth/hci_conn.c:2638 hci_dev_close_sync+0x821/0xff0 net/bluetooth/hci_sync.c:5326 hci_dev_do_close net/bluetooth/hci_core.c:501 [inline] hci_unregister_dev+0x21a/0x510 net/bluetooth/hci_core.c:2715 vhci_release+0x152/0x1a0 drivers/bluetooth/hci_vhci.c:690 __fput+0x44c/0xa70 fs/file_table.c:468 task_work_run+0x1d4/0x260 kernel/task_work.c:233 exit_task_work include/linux/task_work.h:40 [inline] do_exit+0x6c5/0x2310 kernel/exit.c:973 do_group_exit+0x21c/0x2d0 kernel/exit.c:1114 get_signal+0x1285/0x1340 kernel/signal.c:3034 arch_do_signal_or_restart+0x9a/0x7a0 arch/x86/kernel/signal.c:337 __exit_to_user_mode_loop kernel/entry/common.c:41 [inline] exit_to_user_mode_loop+0x87/0x4f0 kernel/entry/common.c:75 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:226 [inline] syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:256 [inline] syscall_exit_to_user_mode_work include/linux/entry-common.h:159 [inline] syscall_exit_to_user_mode include/linux/entry-common.h:194 [inline] do_syscall_64+0x2e3/0xf80 arch/x86/entry/syscall_64.c:100 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7f538718f749 Code: Unable to access opcode bytes at 0x7f538718f71f. RSP: 002b:00007f5387f6b038 EFLAGS: 00000246 ORIG_RAX: 000000000000002e RAX: 000000000000003c RBX: 00007f53873e5fa0 RCX: 00007f538718f749 RDX: 0000000000000030 RSI: 0000200000000100 RDI: 0000000000000005 RBP: 00007f5387213f91 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 00007f53873e6038 R14: 00007f53873e5fa0 R15: 00007fff563e6928 ---------------- Code disassembly (best guess): 0: 74 26 je 0x28 2: 00 0b add %cl,(%rbx) 4: 67 48 0f b9 3a ud1 (%edx),%rdi 9: eb 4a jmp 0x55 b: e8 d8 d2 36 fd call 0xfd36d2e8 10: 48 8d 3d 71 26 00 0b lea 0xb002671(%rip),%rdi # 0xb002688 17: 67 48 0f b9 3a ud1 (%edx),%rdi 1c: eb 37 jmp 0x55 1e: e8 c5 d2 36 fd call 0xfd36d2e8 23: 48 8d 3d 6e 26 00 0b lea 0xb00266e(%rip),%rdi # 0xb002698 * 2a: 67 48 0f b9 3a ud1 (%edx),%rdi <-- trapping instruction 2f: eb 24 jmp 0x55 31: e8 b2 d2 36 fd call 0xfd36d2e8 36: 48 8d 3d 6b 26 00 0b lea 0xb00266b(%rip),%rdi # 0xb0026a8 3d: 67 addr32 3e: 48 rex.W 3f: 0f .byte 0xf