==================================================================
BUG: KASAN: use-after-free in disk_unblock_events+0x55/0x60 block/genhd.c:1543
Read of size 8 at addr ffff8800b2f72fe8 by task blkid/5346

CPU: 1 PID: 5346 Comm: blkid Not tainted 4.4.174+ #17
 0000000000000000 98716ff70f64265d ffff8800b2ca7730 ffffffff81aad1a1
 0000000000000000 ffffea0002cbdc00 ffff8800b2f72fe8 0000000000000008
 0000000000000000 ffff8800b2ca7768 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 5339:
 [<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
 [<ffffffff81d43f44>] loop_probe+0x154/0x180 drivers/block/loop.c:1963
 [<ffffffff81d0efb1>] kobj_lookup+0x221/0x410 drivers/base/map.c:124
 [<ffffffff81a7fe3c>] get_gendisk+0x3c/0x2e0 block/genhd.c:689
 [<ffffffff81551744>] bd_start_claiming fs/block_dev.c:851 [inline]
 [<ffffffff81551744>] blkdev_get+0xf4/0x920 fs/block_dev.c:1346
 [<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
 [<ffffffff81599c4a>] C_SYSC_open fs/compat.c:1092 [inline]
 [<ffffffff81599c4a>] compat_SyS_open+0x2a/0x40 fs/compat.c:1090
 [<ffffffff8100603d>] do_syscall_32_irqs_on arch/x86/entry/common.c:330 [inline]
 [<ffffffff8100603d>] do_fast_syscall_32+0x32d/0xa90 arch/x86/entry/common.c:397
 [<ffffffff8271a350>] sysenter_flags_fixed+0xd/0x1a

Freed by task 5346:
 [<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 ffff8800b2f72a80
 which belongs to the cache kmalloc-2048 of size 2048
The buggy address is located 1384 bytes inside of
 2048-byte region [ffff8800b2f72a80, ffff8800b2f73280)
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: 5354 Comm: syz-executor.2 Not tainted 4.4.174+ #17
task: ffff8800bae3af80 task.stack: ffff8801d7448000
RIP: 0010:[<ffffffff810ba443>]  [<ffffffff810ba443>] write_cr3 arch/x86/include/asm/paravirt.h:86 [inline]
RIP: 0010:[<ffffffff810ba443>]  [<ffffffff810ba443>] load_new_mm_cr3+0x53/0xb0 arch/x86/mm/tlb.c:68
RSP: 0018:ffff8801d744fb40  EFLAGS: 00010046
RAX: 0000000000000000 RBX: 0000620002cbdc00 RCX: 1ffffffff0634a0a
RDX: 0000000000000000 RSI: ffffffff81b0abec RDI: 0000620002cbdc00
RBP: ffff8801d744fb48 R08: ffffffff82836880 R09: ffffffff831a5078
R10: ffff8801d8f2b1f4 R11: 0000000000000001 R12: 0000000000000000
R13: ffff8800b4caca80 R14: ffff8800b2c72f40 R15: 0000000000001815
FS:  0000000000000000(0000) GS:ffff8801db600000(0063) knlGS:0000000009552900
CS:  0010 DS: 002b ES: 002b CR0: 0000000080050033
CR2: 000000002ed23000 CR3: 00000001d0452000 CR4: 00000000001606b0
Stack:
 ffff8800b2c72f40 ffff8801d744fb90 ffffffff810bb182 ffff8801db61f1b0
 0000000000000003 ffff8800b4caca80 ffff8801db61e880 ffff8800b2c72f40
 ffff8800bae3b418 0000000000000003 ffff8801d744fc18 ffffffff82708159
Call Trace:
 [<ffffffff810bb182>] switch_mm_irqs_off+0x152/0xac0 arch/x86/mm/tlb.c:172
 [<ffffffff82708159>] context_switch kernel/sched/core.c:2788 [inline]
 [<ffffffff82708159>] __schedule+0x709/0x1ee0 kernel/sched/core.c:3326
 [<ffffffff82709b79>] schedule+0x99/0x1d0 kernel/sched/core.c:3355
 [<ffffffff8271631a>] freezable_schedule include/linux/freezer.h:171 [inline]
 [<ffffffff8271631a>] do_nanosleep+0x1da/0x4c0 kernel/time/hrtimer.c:1503
 [<ffffffff8126373e>] hrtimer_nanosleep+0x20e/0x540 kernel/time/hrtimer.c:1572
 [<ffffffff812b2ce3>] C_SYSC_nanosleep kernel/compat.c:254 [inline]
 [<ffffffff812b2ce3>] compat_SyS_nanosleep+0x173/0x2f0 kernel/compat.c:239
 [<ffffffff8100603d>] do_syscall_32_irqs_on arch/x86/entry/common.c:330 [inline]
 [<ffffffff8100603d>] do_fast_syscall_32+0x32d/0xa90 arch/x86/entry/common.c:397
 [<ffffffff8271a350>] sysenter_flags_fixed+0xd/0x1a
Code: 00 00 fc ff df 48 89 c1 83 e0 07 48 c1 e9 03 83 c0 03 0f b6 14 11 38 d0 7c 04 84 d2 75 1e 8b 05 14 ac 0e 02 85 c0 75 0d 48 89 df <0f> 22 df 0f 1f 40 00 5b 5d c3 e8 ae 24 00 00 eb ec 48 c7 c7 50 
RIP  [<ffffffff810ba443>] write_cr3 arch/x86/include/asm/paravirt.h:86 [inline]
RIP  [<ffffffff810ba443>] load_new_mm_cr3+0x53/0xb0 arch/x86/mm/tlb.c:68
 RSP <ffff8801d744fb40>
---[ end trace 25244f22eed50e2e ]---