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BUG: KASAN: use-after-free in disk_unblock_events+0x4b/0x50 block/genhd.c:1644
Read of size 8 at addr ffff8801c3644968 by task blkid/8271

CPU: 1 PID: 8271 Comm: blkid Not tainted 4.14.76+ #20
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0xb9/0x11b lib/dump_stack.c:53
 print_address_description+0x60/0x22b mm/kasan/report.c:252
 kasan_report_error mm/kasan/report.c:351 [inline]
 kasan_report.cold.6+0x11b/0x2dd mm/kasan/report.c:409
 disk_unblock_events+0x4b/0x50 block/genhd.c:1644
 __blkdev_get+0x68f/0xe50 fs/block_dev.c:1548
 blkdev_get+0x97/0x8c0 fs/block_dev.c:1604
 blkdev_open+0x1bd/0x240 fs/block_dev.c:1762
 do_dentry_open+0x426/0xda0 fs/open.c:764
 vfs_open+0x11c/0x210 fs/open.c:878
 do_last fs/namei.c:3408 [inline]
 path_openat+0x4eb/0x23a0 fs/namei.c:3550
 do_filp_open+0x197/0x270 fs/namei.c:3584
 do_sys_open+0x2ef/0x580 fs/open.c:1071
 do_syscall_64+0x19b/0x4b0 arch/x86/entry/common.c:289
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x7fec63078120
RSP: 002b:00007ffe99ea9f98 EFLAGS: 00000246 ORIG_RAX: 0000000000000002
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fec63078120
RDX: 00007ffe99eaaf45 RSI: 0000000000000000 RDI: 00007ffe99eaaf45
RBP: 0000000000000000 R08: 0000000000000078 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000142e030
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000005

Allocated by task 8252:
 save_stack mm/kasan/kasan.c:447 [inline]
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_kmalloc.part.1+0x4f/0xd0 mm/kasan/kasan.c:551
 kmem_cache_alloc_trace+0x138/0x300 mm/slub.c:2750
 kmem_cache_alloc_node_trace include/linux/slab.h:378 [inline]
 kmalloc_node include/linux/slab.h:526 [inline]
 kzalloc_node include/linux/slab.h:672 [inline]
 alloc_disk_node+0x5f/0x3b0 block/genhd.c:1387
 loop_add+0x3e9/0x840 drivers/block/loop.c:1827
 loop_control_ioctl+0x12e/0x310 drivers/block/loop.c:1959
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:500 [inline]
 do_vfs_ioctl+0x1a0/0x1030 fs/ioctl.c:684
 SYSC_ioctl fs/ioctl.c:701 [inline]
 SyS_ioctl+0x7e/0xb0 fs/ioctl.c:692
 do_syscall_64+0x19b/0x4b0 arch/x86/entry/common.c:289
 entry_SYSCALL_64_after_hwframe+0x42/0xb7

Freed by task 8271:
 save_stack mm/kasan/kasan.c:447 [inline]
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_slab_free+0xac/0x190 mm/kasan/kasan.c:524
 slab_free_hook mm/slub.c:1389 [inline]
 slab_free_freelist_hook mm/slub.c:1410 [inline]
 slab_free mm/slub.c:2966 [inline]
 kfree+0xf5/0x310 mm/slub.c:3897
 device_release+0xf4/0x1a0 drivers/base/core.c:822
 kobject_cleanup lib/kobject.c:646 [inline]
 kobject_release lib/kobject.c:675 [inline]
 kref_put include/linux/kref.h:70 [inline]
 kobject_put+0x146/0x200 lib/kobject.c:692
 put_disk+0x1f/0x30 block/genhd.c:1452
 __blkdev_get+0x5fa/0xe50 fs/block_dev.c:1541
 blkdev_get+0x97/0x8c0 fs/block_dev.c:1604
 blkdev_open+0x1bd/0x240 fs/block_dev.c:1762
 do_dentry_open+0x426/0xda0 fs/open.c:764
 vfs_open+0x11c/0x210 fs/open.c:878
 do_last fs/namei.c:3408 [inline]
 path_openat+0x4eb/0x23a0 fs/namei.c:3550
 do_filp_open+0x197/0x270 fs/namei.c:3584
 do_sys_open+0x2ef/0x580 fs/open.c:1071
 do_syscall_64+0x19b/0x4b0 arch/x86/entry/common.c:289
 entry_SYSCALL_64_after_hwframe+0x42/0xb7

The buggy address belongs to the object at ffff8801c3644400
 which belongs to the cache kmalloc-2048 of size 2048
The buggy address is located 1384 bytes inside of
 2048-byte region [ffff8801c3644400, ffff8801c3644c00)
The buggy address belongs to the page:
page:ffffea00070d9000 count:1 mapcount:0 mapping:          (null) index:0xffff8801c3647700 compound_mapcount: 0
flags: 0x4000000000008100(slab|head)
raw: 4000000000008100 0000000000000000 ffff8801c3647700 00000001800f000d
raw: 0000000000000000 0000000100000001 ffff8801da802800 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801c3644800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801c3644880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8801c3644900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                          ^
 ffff8801c3644980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801c3644a00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
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