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WARNING: refcount bug in kvm_vm_ioctl


syzbot found the following crash on:

HEAD commit:    64c5e530ac2c Merge tag 'arc-4.19-rc8' of git://git.kernel...
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16343ea1400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=88e9a8a39dc0be2d
dashboard link: https://syzkaller.appspot.com/bug?extid=6df4d24a0a50fd5d1a08
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=133eb685400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+6df4d24a0a50fd5d1a08@xxxxxxxxxxxxxxxxxxxxxxxxx

8021q: adding VLAN 0 to HW filter on device team0
L1TF CPU bug present and SMT on, data leak possible. See CVE-2018-3646 and https://www.kernel.org/doc/html/latest/admin-guide/l1tf.html for details.
hrtimer: interrupt took 30857 ns
------------[ cut here ]------------
refcount_t: increment on 0; use-after-free.
WARNING: CPU: 1 PID: 8299 at lib/refcount.c:153 refcount_inc_checked+0x5d/0x70 lib/refcount.c:153
Kernel panic - not syncing: panic_on_warn set ...

CPU: 1 PID: 8299 Comm: syz-executor2 Not tainted 4.19.0-rc7+ #275
kobject: 'kvm' (00000000705acfae): kobject_uevent_env
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: 'kvm' (00000000705acfae): fill_kobj_path: path = '/devices/virtual/misc/kvm'
 __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: 'kvm' (00000000705acfae): kobject_uevent_env
kobject: 'kvm' (00000000705acfae): fill_kobj_path: path = '/devices/virtual/misc/kvm'
kobject: 'kvm' (00000000705acfae): kobject_uevent_env
 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
kobject: 'kvm' (00000000705acfae): fill_kobj_path: path = '/devices/virtual/misc/kvm' Code: 1d 2b 7d 62 06 31 ff 89 de e8 1f bc f2 fd 84 db 75 df e8 46 bb f2 fd 48 c7 c7 80 72 40 88 c6 05 0b 7d 62 06 01 e8 23 8e 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:ffff8801c1647708 EFLAGS: 00010286
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff81650405 RDI: 0000000000000005
RBP: ffff8801c1647710 R08: ffff8801c2b98300 R09: ffffed003b5e4fe8
R10: ffffed003b5e4fe8 R11: ffff8801daf27f47 R12: ffff8801c16477c0
R13: ffff8801c4225800 R14: ffffffff892b6ec0 R15: ffffc9000497b000
 kvm_get_kvm arch/x86/kvm/../../../virt/kvm/kvm_main.c:766 [inline]
kvm_ioctl_create_device arch/x86/kvm/../../../virt/kvm/kvm_main.c:2924 [inline]
 kvm_vm_ioctl+0xed7/0x1d40 arch/x86/kvm/../../../virt/kvm/kvm_main.c:3114
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:501 [inline]
 do_vfs_ioctl+0x1de/0x1720 fs/ioctl.c:685
 ksys_ioctl+0xa9/0xd0 fs/ioctl.c:702
 __do_sys_ioctl fs/ioctl.c:709 [inline]
 __se_sys_ioctl fs/ioctl.c:707 [inline]
 __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:707
 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
RIP: 0033:0x457579
Code: 1d b4 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 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 0f 83 eb b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f5511e6bc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000457579
RDX: 00000000200002c0 RSI: 00000000c00caee0 RDI: 0000000000000009
RBP: 000000000072bfa0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f5511e6c6d4
R13: 00000000004bfbd1 R14: 00000000004cfc58 R15: 00000000ffffffff
Kernel Offset: disabled
Rebooting in 86400 seconds..

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