[syzbot] [kernel?] WARNING: refcount bug in bnep_session (2)

[syzbot <syzbot+98baa83c342e86a836d7@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    5d6919055dec Linux 7.1-rc3
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=165f7bce580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=59da38148f3a3d24
dashboard link: https://syzkaller.appspot.com/bug?extid=98baa83c342e86a836d7
compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/dd917153d1cc/disk-5d691905.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/f40450ccdad7/vmlinux-5d691905.xz
kernel image: https://storage.googleapis.com/syzbot-assets/91d021f99576/bzImage-5d691905.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+98baa83c342e86a836d7@syzkaller.appspotmail.com

------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: lib/refcount.c:28 at refcount_warn_saturate+0xf4/0x130 lib/refcount.c:28, CPU#1: kbnepd bnep0/6521
Modules linked in:
CPU: 1 UID: 0 PID: 6521 Comm: kbnepd bnep0 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
RIP: 0010:refcount_warn_saturate+0xf4/0x130 lib/refcount.c:28
Code: cc e8 30 3b 0f fd 48 8d 3d 89 d1 e8 0b 67 48 0f b9 3a e8 1f 3b 0f fd 5b 5d e9 58 4f 94 06 e8 13 3b 0f fd 48 8d 3d 7c d1 e8 0b <67> 48 0f b9 3a e8 02 3b 0f fd 5b 5d c3 cc cc cc cc e8 f6 3a 0f fd
RSP: 0018:ffffc900059ff958 EFLAGS: 00010293
RAX: 0000000000000000 RBX: ffff888052bcdc78 RCX: ffffffff84f96b3b
RDX: ffff888020be8000 RSI: ffffffff84f96bcd RDI: ffffffff90e23d50
RBP: 0000000000000003 R08: 0000000000000005 R09: 0000000000000004
R10: 0000000000000003 R11: 0000000000000000 R12: ffff88802b509000
R13: ffff888052bcdc78 R14: ffffffff86352db0 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff888124472000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fea969ea4c0 CR3: 000000005c73e000 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 lib/klist.c:206 [inline]
 klist_put+0x18a/0x1d0 lib/klist.c:217
 device_del+0x1b8/0x9b0 drivers/base/core.c:3872
 unregister_netdevice_many_notify+0x179e/0x24f0 net/core/dev.c:12453
 unregister_netdevice_many net/core/dev.c:12481 [inline]
 unregister_netdevice_queue net/core/dev.c:12291 [inline]
 unregister_netdevice_queue+0x30b/0x3c0 net/core/dev.c:12281
 unregister_netdevice include/linux/netdevice.h:3444 [inline]
 unregister_netdev+0x1f/0x60 net/core/dev.c:12499
 bnep_session+0x223f/0x2d90 net/bluetooth/bnep/core.c:532
 kthread+0x370/0x450 kernel/kthread.c:436
 ret_from_fork+0x72b/0xd50 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
----------------
Code disassembly (best guess):
   0:	cc                   	int3
   1:	e8 30 3b 0f fd       	call   0xfd0f3b36
   6:	48 8d 3d 89 d1 e8 0b 	lea    0xbe8d189(%rip),%rdi        # 0xbe8d196
   d:	67 48 0f b9 3a       	ud1    (%edx),%rdi
  12:	e8 1f 3b 0f fd       	call   0xfd0f3b36
  17:	5b                   	pop    %rbx
  18:	5d                   	pop    %rbp
  19:	e9 58 4f 94 06       	jmp    0x6944f76
  1e:	e8 13 3b 0f fd       	call   0xfd0f3b36
  23:	48 8d 3d 7c d1 e8 0b 	lea    0xbe8d17c(%rip),%rdi        # 0xbe8d1a6
* 2a:	67 48 0f b9 3a       	ud1    (%edx),%rdi <-- trapping instruction
  2f:	e8 02 3b 0f fd       	call   0xfd0f3b36
  34:	5b                   	pop    %rbx
  35:	5d                   	pop    %rbp
  36:	c3                   	ret
  37:	cc                   	int3
  38:	cc                   	int3
  39:	cc                   	int3
  3a:	cc                   	int3
  3b:	e8 f6 3a 0f fd       	call   0xfd0f3b36


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup