------------[ cut here ]------------
refcount_t: addition on 0; use-after-free.
WARNING: lib/refcount.c:25 at refcount_warn_saturate+0x9f/0x110, CPU#1: syz.2.881/9463
Modules linked in:
CPU: 1 UID: 0 PID: 9463 Comm: syz.2.881 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+0x9f/0x110
Code: eb 66 85 db 74 3e 83 fb 01 75 4c e8 fb 38 2a fd 48 8d 3d a4 86 34 0b 67 48 0f b9 3a eb 4a e8 e8 38 2a fd 48 8d 3d a1 86 34 0b <67> 48 0f b9 3a eb 37 e8 d5 38 2a fd 48 8d 3d 9e 86 34 0b 67 48 0f
RSP: 0018:ffffc9000441fd48 EFLAGS: 00010293
RAX: ffffffff84983ae8 RBX: 0000000000000002 RCX: ffff88816d030000
RDX: 0000000000000000 RSI: ffffffff8ea8eb80 RDI: ffffffff8fccc190
RBP: ffffc9000441fe48 R08: ffff88816d030000 R09: 0000000000000005
R10: 0000000000000004 R11: 0000000000000000 R12: 1ffff92000883fb4
R13: 1ffff1102ea17d05 R14: ffff888173f16ac8 R15: dffffc0000000000
FS:  00007fe4bca346c0(0000) GS:ffff8882a9a08000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fe4b4000020 CR3: 0000000169e86000 CR4: 00000000000006f0
Call Trace:
 <TASK>
 ax25_setsockopt+0xab0/0xc30
 do_sock_setsockopt+0x17c/0x1b0
 __x64_sys_setsockopt+0x13d/0x1b0
 do_syscall_64+0xe2/0xf80
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fe4bbb9acb9
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fe4bca34028 EFLAGS: 00000246 ORIG_RAX: 0000000000000036
RAX: ffffffffffffffda RBX: 00007fe4bbe15fa0 RCX: 00007fe4bbb9acb9
RDX: 0000000000000019 RSI: 0000000000000101 RDI: 0000000000000007
RBP: 00007fe4bbc08bf7 R08: 0000000000000010 R09: 0000000000000000
R10: 0000200000000240 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fe4bbe16038 R14: 00007fe4bbe15fa0 R15: 00007ffc982bfde8
 </TASK>
