WARNING: refcount bug in nr_insert_socket

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    4608a726 Add linux-next specific files for 20190709
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=1387b608600000
kernel config:  https://syzkaller.appspot.com/x/.config?x=7a02e36d356a9a17
dashboard link: https://syzkaller.appspot.com/bug?extid=ec1fd464d849d91c3665
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=16b47be8600000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15172e7ba00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+ec1fd464d849d91c3665@xxxxxxxxxxxxxxxxxxxxxxxxx

------------[ cut here ]------------
refcount_t: increment on 0; use-after-free.
WARNING: CPU: 0 PID: 14391 at lib/refcount.c:156 refcount_inc_checked  
lib/refcount.c:156 [inline]
WARNING: CPU: 0 PID: 14391 at lib/refcount.c:156  
refcount_inc_checked+0x61/0x70 lib/refcount.c:154
Kernel panic - not syncing: panic_on_warn set ...
CPU: 0 PID: 14391 Comm: syz-executor638 Not tainted 5.2.0-next-20190709 #34
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:
 <IRQ>
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x172/0x1f0 lib/dump_stack.c:113
 panic+0x2dc/0x755 kernel/panic.c:219
 __warn.cold+0x20/0x4c kernel/panic.c:576
 report_bug+0x263/0x2b0 lib/bug.c:186
 fixup_bug arch/x86/kernel/traps.c:179 [inline]
 fixup_bug arch/x86/kernel/traps.c:174 [inline]
 do_error_trap+0x11b/0x200 arch/x86/kernel/traps.c:272
 do_invalid_op+0x37/0x50 arch/x86/kernel/traps.c:291
 invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:1008
RIP: 0010:refcount_inc_checked lib/refcount.c:156 [inline]
RIP: 0010:refcount_inc_checked+0x61/0x70 lib/refcount.c:154
Code: 1d 83 26 64 06 31 ff 89 de e8 5b 44 35 fe 84 db 75 dd e8 12 43 35 fe  
48 c7 c7 60 04 c6 87 c6 05 63 26 64 06 01 e8 77 ab 06 fe <0f> 0b eb c1 90  
90 90 90 90 90 90 90 90 90 90 55 48 89 e5 41 57 41
RSP: 0018:ffff8880ae809bf0 EFLAGS: 00010282
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000000000000100 RSI: ffffffff815bfa86 RDI: ffffed1015d01370
RBP: ffff8880ae809c00 R08: ffff8880988924c0 R09: fffffbfff14a7757
R10: fffffbfff14a7756 R11: ffffffff8a53bab7 R12: ffff888097414c80
R13: ffff888097414c68 R14: ffff888096051348 R15: ffff888096051320
 sock_hold include/net/sock.h:649 [inline]
 sk_add_node include/net/sock.h:701 [inline]
 nr_insert_socket+0x2d/0xe0 net/netrom/af_netrom.c:137
 nr_rx_frame+0x1605/0x1e73 net/netrom/af_netrom.c:1023
 nr_loopback_timer+0x7b/0x170 net/netrom/nr_loopback.c:59
 call_timer_fn+0x1ac/0x780 kernel/time/timer.c:1322
 expire_timers kernel/time/timer.c:1366 [inline]
 __run_timers kernel/time/timer.c:1685 [inline]
 __run_timers kernel/time/timer.c:1653 [inline]
 run_timer_softirq+0x697/0x17a0 kernel/time/timer.c:1698
 __do_softirq+0x262/0x98c kernel/softirq.c:292
 invoke_softirq kernel/softirq.c:373 [inline]
 irq_exit+0x19b/0x1e0 kernel/softirq.c:413
 exiting_irq arch/x86/include/asm/apic.h:537 [inline]
 smp_apic_timer_interrupt+0x1a3/0x610 arch/x86/kernel/apic/apic.c:1095
 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:828
 </IRQ>
RIP: 0010:arch_local_irq_restore arch/x86/include/asm/paravirt.h:767  
[inline]
RIP: 0010:__raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:160  
[inline]
RIP: 0010:_raw_spin_unlock_irqrestore+0x95/0xe0  
kernel/locking/spinlock.c:191
Code: 48 c7 c0 d0 e3 d2 88 48 ba 00 00 00 00 00 fc ff df 48 c1 e8 03 80 3c  
10 00 75 39 48 83 3d d2 3e 99 01 00 74 24 48 89 df 57 9d <0f> 1f 44 00 00  
bf 01 00 00 00 e8 fc c8 14 fa 65 8b 05 6d 58 c8 78
RSP: 0018:ffff88808720fd10 EFLAGS: 00000286 ORIG_RAX: ffffffffffffff13
RAX: 1ffffffff11a5c7a RBX: 0000000000000286 RCX: 0000000000000000
RDX: dffffc0000000000 RSI: 0000000000000006 RDI: 0000000000000286
RBP: ffff88808720fd20 R08: ffff8880988924c0 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffffffff8aa79aa8
R13: ffffffff8aa79aa0 R14: ffff88809683add0 R15: ffff88808720fdc0
 debug_object_free lib/debugobjects.c:823 [inline]
 debug_object_free+0x1f1/0x390 lib/debugobjects.c:796
 destroy_hrtimer_on_stack kernel/time/hrtimer.c:432 [inline]
 hrtimer_nanosleep+0x2d8/0x570 kernel/time/hrtimer.c:1748
 __do_sys_nanosleep kernel/time/hrtimer.c:1767 [inline]
 __se_sys_nanosleep kernel/time/hrtimer.c:1754 [inline]
 __x64_sys_nanosleep+0x1a6/0x220 kernel/time/hrtimer.c:1754
 do_syscall_64+0xfd/0x6a0 arch/x86/entry/common.c:296
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x447811
Code: 75 14 b8 23 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 b4 1e fc ff c3 48  
83 ec 08 e8 6a 44 00 00 48 89 04 24 b8 23 00 00 00 0f 05 <48> 8b 3c 24 48  
89 c2 e8 b3 44 00 00 48 89 d0 48 83 c4 08 48 3d 01
RSP: 002b:00007ffcca488140 EFLAGS: 00000293 ORIG_RAX: 0000000000000023
RAX: ffffffffffffffda RBX: 0000000000000048 RCX: 0000000000447811
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00007ffcca488150
RBP: 00000000006dfc6c R08: 00000000004b1a31 R09: 00000000004b1a31
R10: 00007ffcca488180 R11: 0000000000000293 R12: 00000000006dfc60
R13: 0000000000000002 R14: 000000000000002d R15: 20c49ba5e353f7cf
Kernel Offset: disabled
Rebooting in 86400 seconds..


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