------------[ cut here ]------------
refcount_t: addition on 0; use-after-free.
WARNING: lib/refcount.c:25 at refcount_warn_saturate+0x9f/0x110 lib/refcount.c:25, CPU#1: syz.0.656/6713
Modules linked in:
CPU: 1 UID: 0 PID: 6713 Comm: syz.0.656 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
RIP: 0010:refcount_warn_saturate+0x9f/0x110 lib/refcount.c:25
Code: eb 66 85 db 74 3e 83 fb 01 75 4c e8 cb b2 16 fd 48 8d 3d f4 18 6d 0b 67 48 0f b9 3a eb 4a e8 b8 b2 16 fd 48 8d 3d f1 18 6d 0b <67> 48 0f b9 3a eb 37 e8 a5 b2 16 fd 48 8d 3d ee 18 6d 0b 67 48 0f
RSP: 0018:ffffc900037a7d48 EFLAGS: 00010293
RAX: ffffffff84aeee48 RBX: 0000000000000002 RCX: ffff8880293b9e80
RDX: 0000000000000000 RSI: ffffffff8ef017a0 RDI: ffffffff901c0740
RBP: ffffc900037a7e48 R08: ffff8880293b9e80 R09: 0000000000000005
R10: 0000000000000004 R11: 0000000000000000 R12: 1ffff920006f4fb4
R13: 1ffff110042f1105 R14: ffff88807b5f76c8 R15: dffffc0000000000
FS:  0000555579fcf500(0000) GS:ffff888125561000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f9ab31456b8 CR3: 000000006cfa0000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 ax25_dev_hold include/net/ax25.h:283 [inline]
 ax25_setsockopt+0xab5/0xc30 net/ax25/af_ax25.c:705
 do_sock_setsockopt+0x17c/0x1b0 net/socket.c:2315
 __sys_setsockopt net/socket.c:2340 [inline]
 __do_sys_setsockopt net/socket.c:2346 [inline]
 __se_sys_setsockopt net/socket.c:2343 [inline]
 __x64_sys_setsockopt+0x13d/0x1b0 net/socket.c:2343
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f0c3d59c799
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:00007ffce50cd688 EFLAGS: 00000246 ORIG_RAX: 0000000000000036
RAX: ffffffffffffffda RBX: 00007f0c3d815fa0 RCX: 00007f0c3d59c799
RDX: 0000000000000019 RSI: 0000000000000101 RDI: 000000000000000a
RBP: 00007f0c3d632c99 R08: 0000000000000010 R09: 0000000000000000
R10: 00002000000001c0 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f0c3d815fac R14: 00007f0c3d815fa0 R15: 00007f0c3d815fa0
 </TASK>
----------------
Code disassembly (best guess):
   0:	eb 66                	jmp    0x68
   2:	85 db                	test   %ebx,%ebx
   4:	74 3e                	je     0x44
   6:	83 fb 01             	cmp    $0x1,%ebx
   9:	75 4c                	jne    0x57
   b:	e8 cb b2 16 fd       	call   0xfd16b2db
  10:	48 8d 3d f4 18 6d 0b 	lea    0xb6d18f4(%rip),%rdi        # 0xb6d190b
  17:	67 48 0f b9 3a       	ud1    (%edx),%rdi
  1c:	eb 4a                	jmp    0x68
  1e:	e8 b8 b2 16 fd       	call   0xfd16b2db
  23:	48 8d 3d f1 18 6d 0b 	lea    0xb6d18f1(%rip),%rdi        # 0xb6d191b
* 2a:	67 48 0f b9 3a       	ud1    (%edx),%rdi <-- trapping instruction
  2f:	eb 37                	jmp    0x68
  31:	e8 a5 b2 16 fd       	call   0xfd16b2db
  36:	48 8d 3d ee 18 6d 0b 	lea    0xb6d18ee(%rip),%rdi        # 0xb6d192b
  3d:	67                   	addr32
  3e:	48                   	rex.W
  3f:	0f                   	.byte 0xf