------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: lib/refcount.c:28 at refcount_warn_saturate+0xb2/0x110 lib/refcount.c:28, CPU#1: syz.3.13206/19820
Modules linked in:
CPU: 1 UID: 0 PID: 19820 Comm: syz.3.13206 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: 04 8d fe 0a 67 48 0f b9 3a eb 4a e8 a8 fd 32 fd 48 8d 3d 01 8d fe 0a 67 48 0f b9 3a eb 37 e8 95 fd 32 fd 48 8d 3d fe 8c fe 0a <67> 48 0f b9 3a eb 24 e8 82 fd 32 fd 48 8d 3d fb 8c fe 0a 67 48 0f
RSP: 0018:ffffc9000cc47538 EFLAGS: 00010293
RAX: ffffffff848dfa2b RBX: 0000000000000003 RCX: ffff88802db05b80
RDX: 0000000000000000 RSI: ffffffff8e68e140 RDI: ffffffff8f8c8730
RBP: 0000000000000000 R08: ffff88802db05b80 R09: 0000000000000005
R10: 0000000000000004 R11: 0000000000000000 R12: ffff88807a416c00
R13: ffff888051eb2860 R14: ffff888051eb2878 R15: dffffc0000000000
FS:  0000000000000000(0000) GS:ffff888125f1f000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055555c225588 CR3: 0000000027c04000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 __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+0x193/0x730 drivers/base/core.c:4615
 hci_conn_del_sysfs+0xb8/0x1a0 net/bluetooth/hci_sysfs.c:75
 hci_conn_cleanup net/bluetooth/hci_conn.c:173 [inline]
 hci_conn_del+0xc36/0x1240 net/bluetooth/hci_conn.c:1234
 hci_conn_hash_flush+0x191/0x260 net/bluetooth/hci_conn.c:2638
 hci_dev_close_sync+0x821/0x1100 net/bluetooth/hci_sync.c:5326
 hci_dev_do_close net/bluetooth/hci_core.c:501 [inline]
 hci_unregister_dev+0x21a/0x5b0 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+0x694/0x22f0 kernel/exit.c:971
 do_group_exit+0x21c/0x2d0 kernel/exit.c:1112
 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+0x87/0x4e0 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]
 ret_from_fork+0x583/0xa50 arch/x86/kernel/process.c:167
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246
 </TASK>
----------------
Code disassembly (best guess):
   0:	04 8d                	add    $0x8d,%al
   2:	fe 0a                	decb   (%rdx)
   4:	67 48 0f b9 3a       	ud1    (%edx),%rdi
   9:	eb 4a                	jmp    0x55
   b:	e8 a8 fd 32 fd       	call   0xfd32fdb8
  10:	48 8d 3d 01 8d fe 0a 	lea    0xafe8d01(%rip),%rdi        # 0xafe8d18
  17:	67 48 0f b9 3a       	ud1    (%edx),%rdi
  1c:	eb 37                	jmp    0x55
  1e:	e8 95 fd 32 fd       	call   0xfd32fdb8
  23:	48 8d 3d fe 8c fe 0a 	lea    0xafe8cfe(%rip),%rdi        # 0xafe8d28
* 2a:	67 48 0f b9 3a       	ud1    (%edx),%rdi <-- trapping instruction
  2f:	eb 24                	jmp    0x55
  31:	e8 82 fd 32 fd       	call   0xfd32fdb8
  36:	48 8d 3d fb 8c fe 0a 	lea    0xafe8cfb(%rip),%rdi        # 0xafe8d38
  3d:	67                   	addr32
  3e:	48                   	rex.W
  3f:	0f                   	.byte 0xf