------------[ cut here ]------------
refcount_t: addition on 0; use-after-free.
WARNING: lib/refcount.c:25 at 0x0, CPU#0: syz.2.1055/10646
Modules linked in:
CPU: 0 UID: 0 PID: 10646 Comm: syz.2.1055 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
RIP: 0010:refcount_warn_saturate+0x9f/0x110 lib/refcount.c:25
Code: eb 66 85 db 74 3e 83 fb 01 75 4c e8 2b 3f 2a fd 48 8d 3d 74 4c 36 0b 67 48 0f b9 3a eb 4a e8 18 3f 2a fd 48 8d 3d 71 4c 36 0b <67> 48 0f b9 3a eb 37 e8 05 3f 2a fd 48 8d 3d 6e 4c 36 0b 67 48 0f
RSP: 0018:ffffc900032e7d28 EFLAGS: 00010293
RAX: ffffffff8497b6c8 RBX: 0000000000000002 RCX: ffff88802de90000
RDX: 0000000000000000 RSI: ffffffff8eaa4940 RDI: ffffffff8fce0340
RBP: ffffc900032e7e38 R08: ffff88802de90000 R09: 0000000000000005
R10: 0000000000000004 R11: 0000000000000000 R12: 1ffff11006102605
R13: 1ffff9200065cfb0 R14: ffff88802a9576c8 R15: dffffc0000000000
FS:  00007efd5fddd6c0(0000) GS:ffff8881259eb000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007efd5fdbcd58 CR3: 0000000078d58000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 ax25_setsockopt+0xabb/0xc20 net/ax25/af_ax25.c:705
 do_sock_setsockopt+0x17c/0x1b0 net/socket.c:2337
 __sys_setsockopt net/socket.c:2362 [inline]
 __do_sys_setsockopt net/socket.c:2368 [inline]
 __se_sys_setsockopt net/socket.c:2365 [inline]
 __x64_sys_setsockopt+0x13f/0x1b0 net/socket.c:2365
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7efd6078f749
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:00007efd5fddd038 EFLAGS: 00000246 ORIG_RAX: 0000000000000036
RAX: ffffffffffffffda RBX: 00007efd609e6090 RCX: 00007efd6078f749
RDX: 0000000000000019 RSI: 0000000000000101 RDI: 0000000000000007
RBP: 00007efd60813f91 R08: 0000000000000010 R09: 0000000000000000
R10: 00002000000001c0 R11: 0000000000000246 R12: 0000000000000000
R13: 00007efd609e6128 R14: 00007efd609e6090 R15: 00007ffd46568508
 </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 2b 3f 2a fd       	call   0xfd2a3f3b
  10:	48 8d 3d 74 4c 36 0b 	lea    0xb364c74(%rip),%rdi        # 0xb364c8b
  17:	67 48 0f b9 3a       	ud1    (%edx),%rdi
  1c:	eb 4a                	jmp    0x68
  1e:	e8 18 3f 2a fd       	call   0xfd2a3f3b
  23:	48 8d 3d 71 4c 36 0b 	lea    0xb364c71(%rip),%rdi        # 0xb364c9b
* 2a:	67 48 0f b9 3a       	ud1    (%edx),%rdi <-- trapping instruction
  2f:	eb 37                	jmp    0x68
  31:	e8 05 3f 2a fd       	call   0xfd2a3f3b
  36:	48 8d 3d 6e 4c 36 0b 	lea    0xb364c6e(%rip),%rdi        # 0xb364cab
  3d:	67                   	addr32
  3e:	48                   	rex.W
  3f:	0f                   	.byte 0xf