[moderation] [bluetooth?] WARNING: refcount bug in hci_conn_del_sysfs

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 4c05c7ed880f selftests: tls: test skb copy under mem press..
git tree: net
console output: https://syzkaller.appspot.com/x/log.txt?x=1180ee42580000
kernel config: https://syzkaller.appspot.com/x/.config?x=4d8792ecb6308d0f
dashboard link: https://syzkaller.appspot.com/bug?extid=b079a2f2f8dc81927180
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
CC: [johan....@gmail.com linux-b...@vger.kernel.org linux-...@vger.kernel.org luiz....@gmail.com mar...@holtmann.org net...@vger.kernel.org]

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/6fac738c9e9e/disk-4c05c7ed.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/7cf38f833cd3/vmlinux-4c05c7ed.xz
kernel image: https://storage.googleapis.com/syzbot-assets/4746d958c4ac/bzImage-4c05c7ed.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b079a2...@syzkaller.appspotmail.com

------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: CPU: 1 PID: 17609 at lib/refcount.c:28 refcount_warn_saturate+0x11a/0x1d0 lib/refcount.c:28
Modules linked in:
CPU: 1 UID: 0 PID: 17609 Comm: syz-executor Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
RIP: 0010:refcount_warn_saturate+0x11a/0x1d0 lib/refcount.c:28
Code: 40 b7 e2 8b e8 47 f0 ba fc 90 0f 0b 90 90 eb d7 e8 db 54 f7 fc c6 05 e4 2d c5 0a 01 90 48 c7 c7 a0 b7 e2 8b e8 27 f0 ba fc 90 <0f> 0b 90 90 eb b7 e8 bb 54 f7 fc c6 05 c1 2d c5 0a 01 90 48 c7 c7
RAX: a59a10e567ef9000 RBX: 0000000000000003 RCX: ffff88802fe38000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000002
RBP: 0000000000000000 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffffbfff1bfa22c R12: ffff888057244c00
R13: ffff88804bd97460 R14: ffff88804bd97478 R15: dffffc0000000000
FS: 0000000000000000(0000) GS:ffff888125d15000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000641030 CR3: 000000000df36000 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
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+0xc33/0x11b0 net/bluetooth/hci_conn.c:1211
hci_conn_hash_flush+0x191/0x230 net/bluetooth/hci_conn.c:2600
hci_dev_close_sync+0xaef/0x1330 net/bluetooth/hci_sync.c:5294
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+0x449/0xa70 fs/file_table.c:468
task_work_run+0x1d1/0x260 kernel/task_work.c:227
exit_task_work include/linux/task_work.h:40 [inline]
do_exit+0x6b5/0x2300 kernel/exit.c:961
do_group_exit+0x21c/0x2d0 kernel/exit.c:1102
get_signal+0x1286/0x1340 kernel/signal.c:3034
arch_do_signal_or_restart+0x9a/0x750 arch/x86/kernel/signal.c:337
exit_to_user_mode_loop+0x75/0x110 kernel/entry/common.c:40
exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline]
syscall_exit_to_user_mode_work include/linux/entry-common.h:175 [inline]
syscall_exit_to_user_mode include/linux/entry-common.h:210 [inline]
do_syscall_64+0x2bd/0x3b0 arch/x86/entry/syscall_64.c:100
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f23025c1465
Code: Unable to access opcode bytes at 0x7f23025c143b.
RSP: 002b:00007ffc08e607a0 EFLAGS: 00000293 ORIG_RAX: 00000000000000e6
RAX: 0000000000000000 RBX: 00000000000000f9 RCX: 00007f23025c1465
RDX: 00007ffc08e607e0 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 00007ffc08e6084c R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000293 R12: 0000000000001388
R13: 00000000000927c0 R14: 000000000006328d R15: 00007ffc08e608a0
</TASK>


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