==================================================================
BUG: KASAN: use-after-free in disk_unblock_events+0x51/0x60 block/genhd.c:1543
Read of size 8 at addr ffff8800b21e0de8 by task blkid/2590

CPU: 1 PID: 2590 Comm: blkid Not tainted 4.4.166+ #17
 0000000000000000 957bae5ab9f252d1 ffff8801d569f6d0 ffffffff81aa62ad
 ffffea0002c87800 ffff8800b21e0de8 0000000000000000 ffff8800b21e0de8
 0000000000000000 ffff8801d569f708 ffffffff8148b12b ffff8800b21e0de8
Call Trace:
 [<ffffffff81aa62ad>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81aa62ad>] dump_stack+0xc1/0x124 lib/dump_stack.c:51
 [<ffffffff8148b12b>] print_address_description+0x6c/0x217 mm/kasan/report.c:252
 [<ffffffff8148b44b>] kasan_report_error mm/kasan/report.c:351 [inline]
 [<ffffffff8148b44b>] kasan_report.cold.6+0x175/0x2f7 mm/kasan/report.c:408
 [<ffffffff81480174>] __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:429
 [<ffffffff81a7b921>] disk_unblock_events+0x51/0x60 block/genhd.c:1543
 [<ffffffff8154911c>] __blkdev_get+0x70c/0xdf0 fs/block_dev.c:1297
 [<ffffffff8154ba8a>] blkdev_get+0x2da/0x920 fs/block_dev.c:1353
 [<ffffffff8154c2e5>] blkdev_open+0x1a5/0x250 fs/block_dev.c:1508
 [<ffffffff8148c4cd>] do_dentry_open+0x38d/0xbd0 fs/open.c:749
 [<ffffffff8148fc3a>] vfs_open+0x12a/0x210 fs/open.c:862
 [<ffffffff814bff20>] do_last fs/namei.c:3269 [inline]
 [<ffffffff814bff20>] path_openat+0xc10/0x3f10 fs/namei.c:3406
 [<ffffffff814c6eb7>] do_filp_open+0x197/0x270 fs/namei.c:3440
 [<ffffffff8149055c>] do_sys_open+0x31c/0x610 fs/open.c:1038
 [<ffffffff8149087d>] SYSC_open fs/open.c:1056 [inline]
 [<ffffffff8149087d>] SyS_open+0x2d/0x40 fs/open.c:1051
 [<ffffffff82715da1>] entry_SYSCALL_64_fastpath+0x1e/0x9a

Allocated by task 2584:
 [<ffffffff8102e3c6>] save_stack_trace+0x26/0x50 arch/x86/kernel/stacktrace.c:63
 [<ffffffff8147f1b2>] save_stack mm/kasan/kasan.c:512 [inline]
 [<ffffffff8147f1b2>] set_track mm/kasan/kasan.c:524 [inline]
 [<ffffffff8147f1b2>] kasan_kmalloc.part.1+0x62/0xf0 mm/kasan/kasan.c:616
 [<ffffffff8147f42f>] kasan_kmalloc+0xaf/0xc0 mm/kasan/kasan.c:601
 [<ffffffff8147b3e7>] kmem_cache_alloc_trace+0x117/0x2d0 mm/slub.c:2642
 [<ffffffff81a7ab44>] kmem_cache_alloc_node_trace include/linux/slab.h:367 [inline]
 [<ffffffff81a7ab44>] kmalloc_node include/linux/slab.h:514 [inline]
 [<ffffffff81a7ab44>] kzalloc_node include/linux/slab.h:631 [inline]
 [<ffffffff81a7ab44>] alloc_disk_node+0x54/0x3a0 block/genhd.c:1282
 [<ffffffff81a7aea8>] alloc_disk+0x18/0x20 block/genhd.c:1274
 [<ffffffff81d3c8db>] loop_add+0x36b/0x7c0 drivers/block/loop.c:1824
 [<ffffffff81d3d266>] loop_control_ioctl+0x136/0x300 drivers/block/loop.c:1956
 [<ffffffff8159463f>] C_SYSC_ioctl fs/compat_ioctl.c:1592 [inline]
 [<ffffffff8159463f>] compat_SyS_ioctl+0x4af/0x2220 fs/compat_ioctl.c:1544
 [<ffffffff810060fe>] do_syscall_32_irqs_on arch/x86/entry/common.c:330 [inline]
 [<ffffffff810060fe>] do_fast_syscall_32+0x31e/0xa80 arch/x86/entry/common.c:397
 [<ffffffff82717550>] sysenter_flags_fixed+0xd/0x1a

Freed by task 2590:
 [<ffffffff8102e3c6>] save_stack_trace+0x26/0x50 arch/x86/kernel/stacktrace.c:63
 [<ffffffff8147faac>] save_stack mm/kasan/kasan.c:512 [inline]
 [<ffffffff8147faac>] set_track mm/kasan/kasan.c:524 [inline]
 [<ffffffff8147faac>] kasan_slab_free+0xac/0x190 mm/kasan/kasan.c:589
 [<ffffffff8147ce84>] slab_free_hook mm/slub.c:1383 [inline]
 [<ffffffff8147ce84>] slab_free_freelist_hook mm/slub.c:1405 [inline]
 [<ffffffff8147ce84>] slab_free mm/slub.c:2859 [inline]
 [<ffffffff8147ce84>] kfree+0xf4/0x310 mm/slub.c:3749
 [<ffffffff81a793c9>] disk_release+0x259/0x330 block/genhd.c:1118
 [<ffffffff81cf130e>] device_release+0x7e/0x220 drivers/base/core.c:247
 [<ffffffff81aac0a4>] kobject_cleanup lib/kobject.c:643 [inline]
 [<ffffffff81aac0a4>] kobject_release lib/kobject.c:672 [inline]
 [<ffffffff81aac0a4>] kref_sub include/linux/kref.h:73 [inline]
 [<ffffffff81aac0a4>] kref_put include/linux/kref.h:98 [inline]
 [<ffffffff81aac0a4>] kobject_put+0x144/0x260 lib/kobject.c:689
 [<ffffffff81a770d3>] put_disk+0x23/0x30 block/genhd.c:1346
 [<ffffffff8154907c>] __blkdev_get+0x66c/0xdf0 fs/block_dev.c:1290
 [<ffffffff8154ba8a>] blkdev_get+0x2da/0x920 fs/block_dev.c:1353
 [<ffffffff8154c2e5>] blkdev_open+0x1a5/0x250 fs/block_dev.c:1508
 [<ffffffff8148c4cd>] do_dentry_open+0x38d/0xbd0 fs/open.c:749
 [<ffffffff8148fc3a>] vfs_open+0x12a/0x210 fs/open.c:862
 [<ffffffff814bff20>] do_last fs/namei.c:3269 [inline]
 [<ffffffff814bff20>] path_openat+0xc10/0x3f10 fs/namei.c:3406
 [<ffffffff814c6eb7>] do_filp_open+0x197/0x270 fs/namei.c:3440
 [<ffffffff8149055c>] do_sys_open+0x31c/0x610 fs/open.c:1038
 [<ffffffff8149087d>] SYSC_open fs/open.c:1056 [inline]
 [<ffffffff8149087d>] SyS_open+0x2d/0x40 fs/open.c:1051
 [<ffffffff82715da1>] entry_SYSCALL_64_fastpath+0x1e/0x9a

The buggy address belongs to the object at ffff8800b21e0880
 which belongs to the cache kmalloc-2048 of size 2048
The buggy address is located 1384 bytes inside of
 2048-byte region [ffff8800b21e0880, ffff8800b21e1080)
The buggy address belongs to the page:
audit: type=1400 audit(1543765010.594:5): avc:  denied  { sigchld } for  pid=2072 comm="syz-executor748" scontext=system_u:object_r:unlabeled_t:s0 tcontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tclass=process permissive=1
kasan: CONFIG_KASAN_INLINE enabled
kasan: GPF could be caused by NULL-ptr deref or user memory access[   38.256036] ------------[ cut here ]------------
WARNING: CPU: 0 PID: 2072 at kernel/sched/core.c:7946 __might_sleep+0x138/0x1a0 kernel/sched/core.c:7941()
do not call blocking ops when !TASK_RUNNING; state=1 set at [<ffffffff810df110>] do_wait+0x270/0xa30 kernel/exit.c:1503