------------[ 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.0.2789/8864
Modules linked in:
CPU: 0 UID: 0 PID: 8864 Comm: syz.0.2789 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 7b a0 32 fd 48 8d 3d 94 68 fd 0a 67 48 0f b9 3a eb 4a e8 68 a0 32 fd 48 8d 3d 91 68 fd 0a <67> 48 0f b9 3a eb 37 e8 55 a0 32 fd 48 8d 3d 8e 68 fd 0a 67 48 0f
RSP: 0018:ffffc90002f57d28 EFLAGS: 00010293
RAX: ffffffff848f11e8 RBX: 0000000000000002 RCX: ffff8880305c9e80
RDX: 0000000000000000 RSI: ffffffff8e68e140 RDI: ffffffff8f8c7a80
RBP: ffffc90002f57e38 R08: ffff8880305c9e80 R09: 0000000000000005
R10: 0000000000000004 R11: 0000000000000000 R12: 1ffff1100f9aaf05
R13: 1ffff920005eafb0 R14: ffff8880319040c8 R15: dffffc0000000000
FS:  0000555557f0a500(0000) GS:ffff888125e35000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fed3eb19000 CR3: 0000000033d16000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 ax25_setsockopt+0xabb/0xc20 net/ax25/af_ax25.c:705
 do_sock_setsockopt+0x17c/0x1b0 net/socket.c:2322
 __sys_setsockopt net/socket.c:2347 [inline]
 __do_sys_setsockopt net/socket.c:2353 [inline]
 __se_sys_setsockopt net/socket.c:2350 [inline]
 __x64_sys_setsockopt+0x13f/0x1b0 net/socket.c:2350
 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: 0033:0x7f9bc578f749
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:00007ffebc6cd418 EFLAGS: 00000246 ORIG_RAX: 0000000000000036
RAX: ffffffffffffffda RBX: 00007f9bc59e5fa0 RCX: 00007f9bc578f749
RDX: 0000000000000019 RSI: 0000000000000101 RDI: 0000000000000004
RBP: 00007f9bc5813f91 R08: 0000000000000010 R09: 0000000000000000
R10: 0000200000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f9bc59e5fa0 R14: 00007f9bc59e5fa0 R15: 0000000000000005
 </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 7b a0 32 fd       	call   0xfd32a08b
  10:	48 8d 3d 94 68 fd 0a 	lea    0xafd6894(%rip),%rdi        # 0xafd68ab
  17:	67 48 0f b9 3a       	ud1    (%edx),%rdi
  1c:	eb 4a                	jmp    0x68
  1e:	e8 68 a0 32 fd       	call   0xfd32a08b
  23:	48 8d 3d 91 68 fd 0a 	lea    0xafd6891(%rip),%rdi        # 0xafd68bb
* 2a:	67 48 0f b9 3a       	ud1    (%edx),%rdi <-- trapping instruction
  2f:	eb 37                	jmp    0x68
  31:	e8 55 a0 32 fd       	call   0xfd32a08b
  36:	48 8d 3d 8e 68 fd 0a 	lea    0xafd688e(%rip),%rdi        # 0xafd68cb
  3d:	67                   	addr32
  3e:	48                   	rex.W
  3f:	0f                   	.byte 0xf