------------[ cut here ]------------
refcount_t: addition on 0; use-after-free.
WARNING: CPU: 0 PID: 13712 at lib/refcount.c:25 refcount_warn_saturate+0x1ca/0x210 lib/refcount.c:25
Modules linked in:
CPU: 0 UID: 0 PID: 13712 Comm: syz.2.909 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
RIP: 0010:refcount_warn_saturate+0x1ca/0x210 lib/refcount.c:25
Code: ff 89 de e8 88 dc d9 fc 84 db 0f 85 e6 fe ff ff e8 9b e1 d9 fc c6 05 a2 e4 b2 0b 01 90 48 c7 c7 20 a6 15 8c e8 77 db 98 fc 90 <0f> 0b 90 90 e9 c3 fe ff ff e8 78 e1 d9 fc c6 05 7d e4 b2 0b 01 90
RSP: 0018:ffffc9000670fd40 EFLAGS: 00010282
RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffc9000d061000
RDX: 0000000000080000 RSI: ffffffff817a0305 RDI: 0000000000000001
RBP: ffff88805f14acc8 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000000 R12: 1ffff92000ce1fb0
R13: 0000000000000000 R14: ffff88805f14ac00 R15: ffff888013a0c000
FS:  0000000000000000(0000) GS:ffff8880974b9000(0063) knlGS:00000000f548db40
CS:  0010 DS: 002b ES: 002b CR0: 0000000080050033
CR2: 00000000f742a374 CR3: 000000007560f000 CR4: 0000000000352ef0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
Call Trace:
 <TASK>
 __refcount_add include/linux/refcount.h:289 [inline]
 __refcount_inc include/linux/refcount.h:366 [inline]
 refcount_inc include/linux/refcount.h:383 [inline]
 ax25_dev_hold include/net/ax25.h:289 [inline]
 ax25_setsockopt+0xfed/0x1170 net/ax25/af_ax25.c:705
 do_sock_setsockopt+0xf3/0x1d0 net/socket.c:2344
 __sys_setsockopt+0x120/0x1a0 net/socket.c:2369
 __do_sys_setsockopt net/socket.c:2375 [inline]
 __se_sys_setsockopt net/socket.c:2372 [inline]
 __ia32_sys_setsockopt+0xbc/0x160 net/socket.c:2372
 do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:83 [inline]
 __do_fast_syscall_32+0x7c/0x300 arch/x86/entry/syscall_32.c:306
 do_fast_syscall_32+0x32/0x80 arch/x86/entry/syscall_32.c:331
 entry_SYSENTER_compat_after_hwframe+0x84/0x8e
RIP: 0023:0xf70be579
Code: b8 01 10 06 03 74 b4 01 10 07 03 74 b0 01 10 08 03 74 d8 01 00 00 00 00 00 00 00 00 00 00 00 00 00 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90 90 90 90 8d b4 26 00 00 00 00 8d b4 26 00 00 00 00
RSP: 002b:00000000f548d55c EFLAGS: 00000296 ORIG_RAX: 000000000000016e
RAX: ffffffffffffffda RBX: 0000000000000009 RCX: 0000000000000101
RDX: 0000000000000019 RSI: 00000000800001c0 RDI: 0000000000000010
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000296 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
 </TASK>
----------------
Code disassembly (best guess), 2 bytes skipped:
   0:	10 06                	adc    %al,(%rsi)
   2:	03 74 b4 01          	add    0x1(%rsp,%rsi,4),%esi
   6:	10 07                	adc    %al,(%rdi)
   8:	03 74 b0 01          	add    0x1(%rax,%rsi,4),%esi
   c:	10 08                	adc    %cl,(%rax)
   e:	03 74 d8 01          	add    0x1(%rax,%rbx,8),%esi
  1e:	00 51 52             	add    %dl,0x52(%rcx)
  21:	55                   	push   %rbp
  22:	89 e5                	mov    %esp,%ebp
  24:	0f 34                	sysenter
  26:	cd 80                	int    $0x80
* 28:	5d                   	pop    %rbp <-- trapping instruction
  29:	5a                   	pop    %rdx
  2a:	59                   	pop    %rcx
  2b:	c3                   	ret
  2c:	90                   	nop
  2d:	90                   	nop
  2e:	90                   	nop
  2f:	90                   	nop
  30:	8d b4 26 00 00 00 00 	lea    0x0(%rsi,%riz,1),%esi
  37:	8d b4 26 00 00 00 00 	lea    0x0(%rsi,%riz,1),%esi