[v6.6] WARNING: refcount bug in ax25_release

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 3f5b4c104b7d Linux 6.6.95
git tree: linux-6.6.y
console output: https://syzkaller.appspot.com/x/log.txt?x=12cff08c580000
kernel config: https://syzkaller.appspot.com/x/.config?x=b80883c3ded77c16
dashboard link: https://syzkaller.appspot.com/bug?extid=c4481f358c239cae7335
compiler: Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/0efd4e01816e/disk-3f5b4c10.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/f7c9d20858cc/vmlinux-3f5b4c10.xz
kernel image: https://storage.googleapis.com/syzbot-assets/18f8dc74ef68/bzImage-3f5b4c10.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+c4481f...@syzkaller.appspotmail.com

ax25_connect(): syz.6.4719 uses autobind, please contact jre...@yaina.de
------------[ cut here ]------------
refcount_t: decrement hit 0; leaking memory.
WARNING: CPU: 0 PID: 30299 at lib/refcount.c:31 refcount_warn_saturate+0x147/0x1b0 lib/refcount.c:31
Modules linked in:
CPU: 0 PID: 30299 Comm: syz.6.4719 Not tainted 6.6.95-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
RIP: 0010:refcount_warn_saturate+0x147/0x1b0 lib/refcount.c:31
Code: 0a 01 48 c7 c7 20 12 fc 8a e8 75 95 30 fd 0f 0b eb a8 e8 fc 30 66 fd c6 05 6a f6 14 0a 01 48 c7 c7 40 13 fc 8a e8 59 95 30 fd <0f> 0b eb 8c e8 e0 30 66 fd c6 05 4b f6 14 0a 01 48 c7 c7 20 12 fc
RSP: 0018:ffffc9000531f928 EFLAGS: 00010246
RAX: 1d6dbdf28cca1000 RBX: 0000000000000004 RCX: 0000000000080000
RDX: ffffc9000cbe9000 RSI: 0000000000013c39 RDI: 0000000000013c3a
RBP: ffffc9000531fa80 R08: ffffc9000531f527 R09: 1ffff92000a63ea4
R10: dffffc0000000000 R11: fffff52000a63ea5 R12: ffff88807da925b8
R13: dffffc0000000000 R14: ffff88807da925fc R15: 0000000000000001
FS: 00007f1b6756d6c0(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b2e11eff8 CR3: 000000002e2c6000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
__refcount_dec include/linux/refcount.h:344 [inline]
refcount_dec include/linux/refcount.h:359 [inline]
ref_tracker_free+0x698/0x7d0 lib/ref_tracker.c:236
netdev_tracker_free include/linux/netdevice.h:4130 [inline]
netdev_put include/linux/netdevice.h:4147 [inline]
ax25_release+0x356/0x930 net/ax25/af_ax25.c:1080
__sock_release net/socket.c:659 [inline]
sock_close+0xbd/0x230 net/socket.c:1421
__fput+0x234/0x970 fs/file_table.c:384
task_work_run+0x1ce/0x250 kernel/task_work.c:239
get_signal+0x1235/0x1400 kernel/signal.c:2678
arch_do_signal_or_restart+0x96/0x780 arch/x86/kernel/signal.c:310
exit_to_user_mode_loop+0x70/0x110 kernel/entry/common.c:174
exit_to_user_mode_prepare+0xb1/0x140 kernel/entry/common.c:210
__syscall_exit_to_user_mode_work kernel/entry/common.c:291 [inline]
syscall_exit_to_user_mode+0x1a/0x50 kernel/entry/common.c:302
do_syscall_64+0x61/0xb0 arch/x86/entry/common.c:87
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f1b6678e929
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f1b6756d038 EFLAGS: 00000246 ORIG_RAX: 000000000000002a
RAX: fffffffffffffe00 RBX: 00007f1b669b5fa0 RCX: 00007f1b6678e929
RDX: 0000000000000048 RSI: 00002000000001c0 RDI: 000000000000000b
RBP: 00007f1b66810b39 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f1b669b5fa0 R15: 00007ffc05be9948
</TASK>


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