------------[ cut here ]------------
refcount_t: addition on 0; use-after-free.
WARNING: CPU: 0 PID: 19166 at lib/refcount.c:25 refcount_warn_saturate+0xfa/0x1d0
Modules linked in:
CPU: 0 UID: 0 PID: 19166 Comm: syz.0.2579 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
RIP: 0010:refcount_warn_saturate+0xfa/0x1d0
Code: 00 00 e8 c9 28 f7 fc 5b 41 5e e9 51 47 ad 06 cc e8 bb 28 f7 fc c6 05 f0 5f c4 0a 01 90 48 c7 c7 40 ba e2 8b e8 77 c5 ba fc 90 <0f> 0b 90 90 eb d7 e8 9b 28 f7 fc c6 05 d1 5f c4 0a 01 90 48 c7 c7
RSP: 0018:ffffc9000292fd48 EFLAGS: 00010246
RAX: 33b236b100f69e00 RBX: 0000000000000002 RCX: 0000000000080000
RDX: ffffc90022854000 RSI: 0000000000000715 RDI: 0000000000000716
RBP: ffffc9000292fe48 R08: ffff88804b024253 R09: 1ffff1100960484a
R10: dffffc0000000000 R11: ffffed100960484b R12: 1ffff1102245e605
R13: 1ffff92000525fb4 R14: ffff88810ca35ec8 R15: dffffc0000000000
FS:  00007fe43a1bd6c0(0000) GS:ffff8880b863d000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f31aec32fc8 CR3: 0000000121cdc000 CR4: 00000000000006f0
Call Trace:
 <TASK>
 ax25_setsockopt+0xabb/0xc20
 do_sock_setsockopt+0x17c/0x1b0
 __x64_sys_setsockopt+0x13f/0x1b0
 do_syscall_64+0xfa/0x3b0
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fe43938ec29
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:00007fe43a1bd038 EFLAGS: 00000246 ORIG_RAX: 0000000000000036
RAX: ffffffffffffffda RBX: 00007fe4395d6270 RCX: 00007fe43938ec29
RDX: 0000000000000019 RSI: 0000000000000101 RDI: 0000000000000008
RBP: 00007fe439411e41 R08: 0000000000000010 R09: 0000000000000000
R10: 00002000000001c0 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fe4395d6308 R14: 00007fe4395d6270 R15: 00007ffcff825528
 </TASK>
