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

[syzbot]

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=69778c8531605ad81b57
compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
CC: [da...@kernel.org drive...@lists.linux.dev gre...@linuxfoundation.org linux-...@vger.kernel.org raf...@kernel.org]

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+69778c...@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


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