------------[ cut here ]------------
refcount_t: increment on 0; use-after-free.
WARNING: CPU: 0 PID: 20669 at lib/refcount.c:153 refcount_inc_checked+0x5d/0x70 lib/refcount.c:153
Kernel panic - not syncing: panic_on_warn set ...

CPU: 0 PID: 20669 Comm: syz-executor3 Not tainted 4.19.0-rc5+ #38
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x1c4/0x2b4 lib/dump_stack.c:113
 panic+0x238/0x4e7 kernel/panic.c:184
kobject: 'loop0' (00000000b71d7528): kobject_uevent_env
 __warn.cold.8+0x163/0x1ba kernel/panic.c:536
 report_bug+0x254/0x2d0 lib/bug.c:186
 fixup_bug arch/x86/kernel/traps.c:178 [inline]
 do_error_trap+0x1fc/0x4d0 arch/x86/kernel/traps.c:296
kobject: 'loop0' (00000000b71d7528): fill_kobj_path: path = '/devices/virtual/block/loop0'
 do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:316
 invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:993
RIP: 0010:refcount_inc_checked+0x5d/0x70 lib/refcount.c:153
Code: 1d 1a a0 62 06 31 ff 89 de e8 df be f2 fd 84 db 75 df e8 06 be f2 fd 48 c7 c7 00 74 40 88 c6 05 fa 9f 62 06 01 e8 f3 b0 bc fd <0f> 0b eb c3 0f 1f 44 00 00 66 2e 0f 1f 84 00 00 00 00 00 55 48 89
RSP: 0018:ffff8801ce716ca0 EFLAGS: 00010282
RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffc90007f20000
RDX: 000000000000f8e4 RSI: ffffffff8164e3f5 RDI: 0000000000000005
RBP: ffff8801ce716ca8 R08: ffff8801b7650440 R09: ffffed003b5c3ee2
R10: ffffed003b5c3ee2 R11: ffff8801dae1f717 R12: 0000000000000000
R13: 0000000000000008 R14: ffff8801b3e46480 R15: dffffc0000000000
 igmp_start_timer+0xaf/0xe0 net/ipv4/igmp.c:217
kobject: 'loop4' (000000006978022c): kobject_uevent_env
 igmp_mod_timer net/ipv4/igmp.c:255 [inline]
 igmp_heard_query net/ipv4/igmp.c:1026 [inline]
 igmp_rcv+0x190e/0x3020 net/ipv4/igmp.c:1061
kobject: 'loop4' (000000006978022c): fill_kobj_path: path = '/devices/virtual/block/loop4'
 ip_local_deliver_finish+0x2e9/0xda0 net/ipv4/ip_input.c:215
 NF_HOOK include/linux/netfilter.h:287 [inline]
 ip_local_deliver+0x1e9/0x750 net/ipv4/ip_input.c:256
 dst_input include/net/dst.h:450 [inline]
 ip_rcv_finish+0x1f9/0x300 net/ipv4/ip_input.c:415
 NF_HOOK include/linux/netfilter.h:287 [inline]
 ip_rcv+0xed/0x610 net/ipv4/ip_input.c:524
 __netif_receive_skb_one_core+0x14d/0x200 net/core/dev.c:4891
 __netif_receive_skb+0x2c/0x1e0 net/core/dev.c:5001
 netif_receive_skb_internal+0x12c/0x620 net/core/dev.c:5104
 napi_frags_finish net/core/dev.c:5642 [inline]
 napi_gro_frags+0x75a/0xc90 net/core/dev.c:5715
 tun_get_user+0x31d5/0x42a0 drivers/net/tun.c:1922
 tun_chr_write_iter+0xb9/0x154 drivers/net/tun.c:1967
 call_write_iter include/linux/fs.h:1808 [inline]
 do_iter_readv_writev+0x8b0/0xa80 fs/read_write.c:680
 do_iter_write+0x185/0x5f0 fs/read_write.c:959
 vfs_writev+0x1f1/0x360 fs/read_write.c:1004
 do_writev+0x11a/0x310 fs/read_write.c:1039
 __do_sys_writev fs/read_write.c:1112 [inline]
 __se_sys_writev fs/read_write.c:1109 [inline]
 __x64_sys_writev+0x75/0xb0 fs/read_write.c:1109
 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x457431
Code: 75 14 b8 14 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 54 b5 fb ff c3 48 83 ec 08 e8 1a 2d 00 00 48 89 04 24 b8 14 00 00 00 0f 05 <48> 8b 3c 24 48 89 c2 e8 63 2d 00 00 48 89 d0 48 83 c4 08 48 3d 01
RSP: 002b:00007f13f578cba0 EFLAGS: 00000293 ORIG_RAX: 0000000000000014
kobject: 'loop5' (00000000766ce980): kobject_uevent_env
RAX: ffffffffffffffda RBX: 000000000000002a RCX: 0000000000457431
RDX: 0000000000000001 RSI: 00007f13f578cbf0 RDI: 00000000000000f0
RBP: 0000000020000240 R08: 00000000000000f0 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000293 R12: 00007f13f578d6d4
R13: 00000000004c48a4 R14: 00000000004d7b90 R15: 00000000ffffffff
kobject: 'loop5' (00000000766ce980): fill_kobj_path: path = '/devices/virtual/block/loop5'
Kernel Offset: disabled
Rebooting in 86400 seconds..