------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: lib/refcount.c:28 at 0x0, CPU#0: syz.1.3849/18902
Modules linked in:
CPU: 0 UID: 0 PID: 18902 Comm: syz.1.3849 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
RIP: 0010:refcount_warn_saturate+0xc9/0x120 lib/refcount.c:28
Code: 5d e9 0b e2 12 fd e8 06 e2 12 fd 48 8d 3d 7f 78 e5 0b 67 48 0f b9 3a 5b 5d e9 f3 e1 12 fd e8 ee e1 12 fd 48 8d 3d 77 78 e5 0b <67> 48 0f b9 3a 5b 5d e9 db e1 12 fd e8 d6 e1 12 fd 48 8d 3d 6f 78
RSP: 0018:ffffc90004e876f8 EFLAGS: 00010293
RAX: 0000000000000000 RBX: 0000000000000003 RCX: ffffffff84ac021c
RDX: ffff888053610000 RSI: ffffffff84ac0282 RDI: ffffffff90917b00
RBP: ffff888040109078 R08: 0000000000000005 R09: 0000000000000004
R10: 0000000000000003 R11: 0000000000000001 R12: ffff888035232800
R13: ffff888040109078 R14: ffffffff85e5c140 R15: ffffffff906b56a0
FS:  0000000000000000(0000) GS:ffff8880d6907000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffdc489dba8 CR3: 000000003b538000 CR4: 0000000000352ef0
DR0: ffffffffffffffff DR1: 00000000000001f8 DR2: 0000000000000083
DR3: ffffffffefffff15 DR6: 00000000ffff0ff0 DR7: 0000000000000400
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 lib/klist.c:206 [inline]
 klist_put+0x11b/0x1b0 lib/klist.c:217
 klist_del lib/klist.c:230 [inline]
 klist_remove+0x13f/0x2e0 lib/klist.c:249
 device_move+0x12d/0x1160 drivers/base/core.c:4615
 hci_conn_del_sysfs+0xaa/0x1a0 net/bluetooth/hci_sysfs.c:75
 hci_conn_cleanup net/bluetooth/hci_conn.c:173 [inline]
 hci_conn_del+0x680/0x11d0 net/bluetooth/hci_conn.c:1234
 hci_conn_hash_flush+0x186/0x290 net/bluetooth/hci_conn.c:2638
 hci_dev_close_sync+0x601/0x1260 net/bluetooth/hci_sync.c:5326
 hci_dev_do_close+0x2e/0xc0 net/bluetooth/hci_core.c:501
 hci_unregister_dev+0x227/0x680 net/bluetooth/hci_core.c:2715
 vhci_release+0x17d/0x230 drivers/bluetooth/hci_vhci.c:690
 __fput+0x402/0xb70 fs/file_table.c:468
 task_work_run+0x150/0x240 kernel/task_work.c:233
 exit_task_work include/linux/task_work.h:40 [inline]
 do_exit+0x87f/0x2bd0 kernel/exit.c:971
 do_group_exit+0xd3/0x2a0 kernel/exit.c:1112
 get_signal+0x2671/0x26d0 kernel/signal.c:3034
 arch_do_signal_or_restart+0x8f/0x7e0 arch/x86/kernel/signal.c:337
 __exit_to_user_mode_loop kernel/entry/common.c:41 [inline]
 exit_to_user_mode_loop+0x8c/0x540 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+0x4ee/0xf80 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fa5699c2085
Code: Unable to access opcode bytes at 0x7fa5699c205b.
RSP: 002b:00007fa56a78cf80 EFLAGS: 00000293 ORIG_RAX: 00000000000000e6
RAX: fffffffffffffdfc RBX: 00007fa569be5fa0 RCX: 00007fa5699c2085
RDX: 00007fa56a78cfc0 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 00007fa569a13f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000293 R12: 0000000000000000
R13: 00007fa569be6038 R14: 00007fa569be5fa0 R15: 00007ffdc48a10a8
 </TASK>
----------------
Code disassembly (best guess):
   0:	5d                   	pop    %rbp
   1:	e9 0b e2 12 fd       	jmp    0xfd12e211
   6:	e8 06 e2 12 fd       	call   0xfd12e211
   b:	48 8d 3d 7f 78 e5 0b 	lea    0xbe5787f(%rip),%rdi        # 0xbe57891
  12:	67 48 0f b9 3a       	ud1    (%edx),%rdi
  17:	5b                   	pop    %rbx
  18:	5d                   	pop    %rbp
  19:	e9 f3 e1 12 fd       	jmp    0xfd12e211
  1e:	e8 ee e1 12 fd       	call   0xfd12e211
  23:	48 8d 3d 77 78 e5 0b 	lea    0xbe57877(%rip),%rdi        # 0xbe578a1
* 2a:	67 48 0f b9 3a       	ud1    (%edx),%rdi <-- trapping instruction
  2f:	5b                   	pop    %rbx
  30:	5d                   	pop    %rbp
  31:	e9 db e1 12 fd       	jmp    0xfd12e211
  36:	e8 d6 e1 12 fd       	call   0xfd12e211
  3b:	48                   	rex.W
  3c:	8d                   	.byte 0x8d
  3d:	3d                   	.byte 0x3d
  3e:	6f                   	outsl  %ds:(%rsi),(%dx)
  3f:	78                   	.byte 0x78