WARNING: refcount bug in kobject_get

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    9a5682765a2e Merge branch 'x86-urgent-for-linus' of git://..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15ebecda400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=8f59875069d721b6
dashboard link: https://syzkaller.appspot.com/bug?extid=b74b8b6e712f33454561
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
userspace arch: i386
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10d982da400000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=10433266400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+b74b8b6e712f33454561@xxxxxxxxxxxxxxxxxxxxxxxxx

------------[ cut here ]------------
refcount_t: increment on 0; use-after-free.
WARNING: CPU: 1 PID: 5475 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: 5475 Comm: syz-executor799 Not tainted 4.19.0-rc2+ #133
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
 __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
 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 43 80 91 06 31 ff 89 de e8 8f 8b ef fd 84 db 75 df e8 b6 8a ef fd  
48 c7 c7 a0 81 44 88 c6 05 23 80 91 06 01 e8 03 75 b9 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:ffff8801b9c07640 EFLAGS: 00010282
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff8164f955 RDI: 0000000000000005
RBP: ffff8801b9c07648 R08: ffff8801c1e70680 R09: ffffed003b5e4fe8
R10: ffffed003b5e4fe8 R11: ffff8801daf27f47 R12: 0000000000000001
R13: ffff8801d8d9df20 R14: ffff8801d70bf940 R15: 0000000000000001
 kref_get include/linux/kref.h:47 [inline]
 kobject_get+0x66/0xc0 lib/kobject.c:613
 kset_get include/linux/kobject.h:213 [inline]
 kobj_kset_join lib/kobject.c:186 [inline]
 kobject_add_internal+0x178/0xb60 lib/kobject.c:238
 kobject_add_varg lib/kobject.c:382 [inline]
 kobject_add+0x13f/0x1b0 lib/kobject.c:426
 class_dir_create_and_add drivers/base/core.c:1554 [inline]
 get_device_parent.isra.27+0x367/0x5a0 drivers/base/core.c:1609
 device_add+0x30d/0x17f0 drivers/base/core.c:1865
 hci_register_dev+0x3e6/0xb80 net/bluetooth/hci_core.c:3196
 __vhci_create_device+0x2c1/0x580 drivers/bluetooth/hci_vhci.c:139
 vhci_create_device drivers/bluetooth/hci_vhci.c:163 [inline]
 vhci_get_user drivers/bluetooth/hci_vhci.c:219 [inline]
 vhci_write+0x2de/0x470 drivers/bluetooth/hci_vhci.c:299
 call_write_iter include/linux/fs.h:1807 [inline]
 new_sync_write fs/read_write.c:474 [inline]
 __vfs_write+0x6b8/0x9f0 fs/read_write.c:487
 vfs_write+0x1fc/0x560 fs/read_write.c:549
 ksys_write+0x101/0x260 fs/read_write.c:598
 __do_sys_write fs/read_write.c:610 [inline]
 __se_sys_write fs/read_write.c:607 [inline]
 __ia32_sys_write+0x71/0xb0 fs/read_write.c:607
 do_syscall_32_irqs_on arch/x86/entry/common.c:326 [inline]
 do_fast_syscall_32+0x34d/0xfb2 arch/x86/entry/common.c:397
 entry_SYSENTER_compat+0x70/0x7f arch/x86/entry/entry_64_compat.S:139
RIP: 0023:0xf7f3aca9
Code: 85 d2 74 02 89 0a 5b 5d c3 8b 04 24 c3 8b 0c 24 c3 8b 1c 24 c3 90 90  
90 90 90 90 90 90 90 90 90 90 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90  
90 90 90 eb 0d 90 90 90 90 90 90 90 90 90 90 90 90
RSP: 002b:00000000ff80ae8c EFLAGS: 00000246 ORIG_RAX: 0000000000000004
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00000000200000c0
RDX: 0000000000000002 RSI: 00000000ff80afd4 RDI: 00000000ff80afdc
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
Dumping ftrace buffer:
   (ftrace buffer empty)
Kernel Offset: disabled
Rebooting in 86400 seconds..


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