------------[ 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#0: syz.9.4399/23447
Modules linked in:
CPU: 0 UID: 0 PID: 23447 Comm: syz.9.4399 Tainted: G             L      syzkaller #0 PREEMPT_{RT,(full)} 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
RIP: 0010:refcount_warn_saturate+0x9f/0x110 lib/refcount.c:25
Code: eb 66 85 db 74 3e 83 fb 01 75 4c e8 4b de 26 fd 48 8d 3d 64 73 d7 0a 67 48 0f b9 3a eb 4a e8 38 de 26 fd 48 8d 3d 61 73 d7 0a <67> 48 0f b9 3a eb 37 e8 25 de 26 fd 48 8d 3d 5e 73 d7 0a 67 48 0f
RSP: 0018:ffffc90005dc7d48 EFLAGS: 00010287
RAX: ffffffff849d5368 RBX: 0000000000000002 RCX: 0000000000080000
RDX: ffffc90015412000 RSI: 000000000000013e RDI: ffffffff8f74c6d0
RBP: ffffc90005dc7e48 R08: ffff888038350000 R09: 0000000000000005
R10: 0000000000000100 R11: 0000000000000004 R12: 1ffff92000bb8fb4
R13: 1ffff1100c17ac05 R14: ffff88805e1984c8 R15: dffffc0000000000
FS:  00007ff5d6a056c0(0000) GS:ffff888126338000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000224000 CR3: 0000000086d2c000 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:2387
 __sys_setsockopt net/socket.c:2412 [inline]
 __do_sys_setsockopt net/socket.c:2418 [inline]
 __se_sys_setsockopt net/socket.c:2415 [inline]
 __x64_sys_setsockopt+0x143/0x1b0 net/socket.c:2415
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7ff5d87cc819
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:00007ff5d6a05028 EFLAGS: 00000246 ORIG_RAX: 0000000000000036
RAX: ffffffffffffffda RBX: 00007ff5d8a46090 RCX: 00007ff5d87cc819
RDX: 0000000000000019 RSI: 0000000000000101 RDI: 000000000000000a
RBP: 00007ff5d8862c91 R08: 0000000000000010 R09: 0000000000000000
R10: 0000200000000240 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ff5d8a46128 R14: 00007ff5d8a46090 R15: 00007ffc9b046828
 </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 4b de 26 fd       	call   0xfd26de5b
  10:	48 8d 3d 64 73 d7 0a 	lea    0xad77364(%rip),%rdi        # 0xad7737b
  17:	67 48 0f b9 3a       	ud1    (%edx),%rdi
  1c:	eb 4a                	jmp    0x68
  1e:	e8 38 de 26 fd       	call   0xfd26de5b
  23:	48 8d 3d 61 73 d7 0a 	lea    0xad77361(%rip),%rdi        # 0xad7738b
* 2a:	67 48 0f b9 3a       	ud1    (%edx),%rdi <-- trapping instruction
  2f:	eb 37                	jmp    0x68
  31:	e8 25 de 26 fd       	call   0xfd26de5b
  36:	48 8d 3d 5e 73 d7 0a 	lea    0xad7735e(%rip),%rdi        # 0xad7739b
  3d:	67                   	addr32
  3e:	48                   	rex.W
  3f:	0f                   	.byte 0xf