==================================================================
BUG: KASAN: use-after-free in disk_unblock_events+0x55/0x60 block/genhd.c:1543
Read of size 8 at addr ffff8800b6ac8568 by task blkid/3854

CPU: 1 PID: 3854 Comm: blkid Not tainted 4.4.174+ #4
 0000000000000000 7634df1abe7f4311 ffff8801cd6ef730 ffffffff81aad1a1
 0000000000000000 ffffea0002dab200 ffff8800b6ac8568 0000000000000008
 0000000000000000 ffff8801cd6ef768 ffffffff81490120 0000000000000000
Call Trace:
 [<ffffffff81aad1a1>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81aad1a1>] dump_stack+0xc1/0x120 lib/dump_stack.c:51
 [<ffffffff81490120>] print_address_description+0x6f/0x21b mm/kasan/report.c:252
 [<ffffffff81490358>] kasan_report_error mm/kasan/report.c:351 [inline]
 [<ffffffff81490358>] kasan_report mm/kasan/report.c:408 [inline]
 [<ffffffff81490358>] kasan_report.cold+0x8c/0x2be mm/kasan/report.c:393
 [<ffffffff81484ed4>] __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:429
 [<ffffffff81a82965>] disk_unblock_events+0x55/0x60 block/genhd.c:1543
 [<ffffffff8154efcc>] __blkdev_get+0x70c/0xdf0 fs/block_dev.c:1297
 [<ffffffff81551938>] blkdev_get+0x2e8/0x920 fs/block_dev.c:1353
 [<ffffffff8155219a>] blkdev_open+0x1aa/0x250 fs/block_dev.c:1508
 [<ffffffff8149154f>] do_dentry_open+0x38f/0xbd0 fs/open.c:749
 [<ffffffff81494d3b>] vfs_open+0x10b/0x210 fs/open.c:862
 [<ffffffff814c5ddf>] do_last fs/namei.c:3269 [inline]
 [<ffffffff814c5ddf>] path_openat+0x136f/0x4470 fs/namei.c:3406
 [<ffffffff814ccab1>] do_filp_open+0x1a1/0x270 fs/namei.c:3440
 [<ffffffff81495668>] do_sys_open+0x2f8/0x600 fs/open.c:1038
 [<ffffffff8149599d>] SYSC_open fs/open.c:1056 [inline]
 [<ffffffff8149599d>] SyS_open+0x2d/0x40 fs/open.c:1051
 [<ffffffff82718ba1>] entry_SYSCALL_64_fastpath+0x1e/0x9a

Allocated by task 3845:
 [<ffffffff8102e3c6>] save_stack_trace+0x26/0x50 arch/x86/kernel/stacktrace.c:63
 [<ffffffff81483f22>] save_stack mm/kasan/kasan.c:512 [inline]
 [<ffffffff81483f22>] set_track mm/kasan/kasan.c:524 [inline]
 [<ffffffff81483f22>] kasan_kmalloc.part.0+0x62/0xf0 mm/kasan/kasan.c:616
 [<ffffffff81484197>] kasan_kmalloc+0xb7/0xd0 mm/kasan/kasan.c:601
 [<ffffffff814801a3>] kmem_cache_alloc_trace+0x123/0x2d0 mm/slub.c:2642
 [<ffffffff81a81b50>] kmem_cache_alloc_node_trace include/linux/slab.h:367 [inline]
 [<ffffffff81a81b50>] kmalloc_node include/linux/slab.h:514 [inline]
 [<ffffffff81a81b50>] kzalloc_node include/linux/slab.h:631 [inline]
 [<ffffffff81a81b50>] alloc_disk_node+0x50/0x3c0 block/genhd.c:1282
 [<ffffffff81a81edb>] alloc_disk+0x1b/0x20 block/genhd.c:1274
 [<ffffffff81d436d0>] loop_add+0x380/0x830 drivers/block/loop.c:1857
 [<ffffffff81d440a8>] loop_control_ioctl+0x138/0x2f0 drivers/block/loop.c:1988
 [<ffffffff814d23f7>] vfs_ioctl fs/ioctl.c:43 [inline]
 [<ffffffff814d23f7>] file_ioctl fs/ioctl.c:470 [inline]
 [<ffffffff814d23f7>] do_vfs_ioctl+0x6e7/0xfa0 fs/ioctl.c:605
 [<ffffffff814d2d3f>] SYSC_ioctl fs/ioctl.c:622 [inline]
 [<ffffffff814d2d3f>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:613
 [<ffffffff82718ba1>] entry_SYSCALL_64_fastpath+0x1e/0x9a

Freed by task 3854:
 [<ffffffff8102e3c6>] save_stack_trace+0x26/0x50 arch/x86/kernel/stacktrace.c:63
 [<ffffffff81484820>] save_stack mm/kasan/kasan.c:512 [inline]
 [<ffffffff81484820>] set_track mm/kasan/kasan.c:524 [inline]
 [<ffffffff81484820>] kasan_slab_free+0xb0/0x190 mm/kasan/kasan.c:589
 [<ffffffff81481c44>] slab_free_hook mm/slub.c:1383 [inline]
 [<ffffffff81481c44>] slab_free_freelist_hook mm/slub.c:1405 [inline]
 [<ffffffff81481c44>] slab_free mm/slub.c:2859 [inline]
 [<ffffffff81481c44>] kfree+0xf4/0x310 mm/slub.c:3749
 [<ffffffff81a80375>] disk_release+0x255/0x330 block/genhd.c:1118
 [<ffffffff81cf785d>] device_release+0x7d/0x220 drivers/base/core.c:247
 [<ffffffff81ab309c>] kobject_cleanup lib/kobject.c:643 [inline]
 [<ffffffff81ab309c>] kobject_release lib/kobject.c:672 [inline]
 [<ffffffff81ab309c>] kref_sub include/linux/kref.h:73 [inline]
 [<ffffffff81ab309c>] kref_put include/linux/kref.h:98 [inline]
 [<ffffffff81ab309c>] kobject_put+0x14c/0x260 lib/kobject.c:689
 [<ffffffff81a7e013>] put_disk+0x23/0x30 block/genhd.c:1346
 [<ffffffff8154ef2c>] __blkdev_get+0x66c/0xdf0 fs/block_dev.c:1290
 [<ffffffff81551938>] blkdev_get+0x2e8/0x920 fs/block_dev.c:1353
 [<ffffffff8155219a>] blkdev_open+0x1aa/0x250 fs/block_dev.c:1508
 [<ffffffff8149154f>] do_dentry_open+0x38f/0xbd0 fs/open.c:749
 [<ffffffff81494d3b>] vfs_open+0x10b/0x210 fs/open.c:862
 [<ffffffff814c5ddf>] do_last fs/namei.c:3269 [inline]
 [<ffffffff814c5ddf>] path_openat+0x136f/0x4470 fs/namei.c:3406
 [<ffffffff814ccab1>] do_filp_open+0x1a1/0x270 fs/namei.c:3440
 [<ffffffff81495668>] do_sys_open+0x2f8/0x600 fs/open.c:1038
 [<ffffffff8149599d>] SYSC_open fs/open.c:1056 [inline]
 [<ffffffff8149599d>] SyS_open+0x2d/0x40 fs/open.c:1051
 [<ffffffff82718ba1>] entry_SYSCALL_64_fastpath+0x1e/0x9a

The buggy address belongs to the object at ffff8800b6ac8000
 which belongs to the cache kmalloc-2048 of size 2048
The buggy address is located 1384 bytes inside of
 2048-byte region [ffff8800b6ac8000, ffff8800b6ac8800)
The buggy address belongs to the page:
kasan: CONFIG_KASAN_INLINE enabled
kasan: GPF could be caused by NULL-ptr deref or user memory accessgeneral protection fault: 0000 [#1] PREEMPT SMP KASAN
Modules linked in:
CPU: 0 PID: 2181 Comm: syz-executor.2 Not tainted 4.4.174+ #4
task: ffff8801c4e24740 task.stack: ffff8800a9b30000
RIP: 0010:[<ffffffff81b0b904>]  [<ffffffff81b0b904>] lookup_object lib/debugobjects.c:120 [inline]
RIP: 0010:[<ffffffff81b0b904>]  [<ffffffff81b0b904>] __debug_object_init+0x134/0x880 lib/debugobjects.c:321
RSP: 0018:ffff8800a9b37cd8  EFLAGS: 00010002
RAX: 0000000000000004 RBX: 1ffff10015366fa2 RCX: 0000000000000813
RDX: dffffc0000000000 RSI: 0000000000000001 RDI: 0000000000004098
RBP: ffff8800a9b37d98 R08: 0000000000004080 R09: ffff8801c4e25028
R10: ffffffff83a4e480 R11: 0000000000000000 R12: ffff8800a9b37df8
R13: ffffffff8407b6c8 R14: 0000000000023800 R15: ffff8800a9b37d70
FS:  000000000221c940(0063) GS:ffff8801db600000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f40f44d9db8 CR3: 00000000a9aa5000 CR4: 00000000001606b0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffff8801c4e25000 ffff8801c4e25028 ffff880000000000 0000000100000001
 ffffffff8407b6c0 ffffffff82eafea0 0000000000000282 0000000041b58ab3
 ffffffff82c768fa ffffffff81b0b7d0 ffffffff82c4d560 ffffffff811ff5b0
Call Trace:
 <UNK> 
Code: 4c 89 c1 48 c1 e9 03 80 3c 11 00 0f 85 2d 05 00 00 4d 8b 00 4d 85 c0 0f 84 a4 00 00 00 49 8d 78 18 83 c0 01 48 89 f9 48 c1 e9 03 <80> 3c 11 00 0f 85 db 04 00 00 4d 3b 60 18 75 c5 4d 8d 78 10 48 
RIP  [<ffffffff81b0b904>] lookup_object lib/debugobjects.c:120 [inline]
RIP  [<ffffffff81b0b904>] __debug_object_init+0x134/0x880 lib/debugobjects.c:321
 RSP <ffff8800a9b37cd8>
---[ end trace d0c86d48911a0026 ]---