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BUG: KASAN: use-after-free in disk_unblock_events+0x51/0x60 block/genhd.c:1550
Read of size 8 at addr ffff8801d6a09660 by task blkid/3700

CPU: 1 PID: 3700 Comm: blkid Not tainted 4.9.135+ #15
 ffff8801cef6f6f8 ffffffff81b36bf9 ffffea00075a8200 ffff8801d6a09660
 0000000000000000 ffff8801d6a09660 0000000000000000 ffff8801cef6f730
 ffffffff815009ad ffff8801d6a09660 0000000000000008 0000000000000000
Call Trace:
 [<ffffffff81b36bf9>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81b36bf9>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff815009ad>] print_address_description+0x6c/0x234 mm/kasan/report.c:256
 [<ffffffff81500db7>] kasan_report_error mm/kasan/report.c:355 [inline]
 [<ffffffff81500db7>] kasan_report.cold.6+0x242/0x2fe mm/kasan/report.c:412
 [<ffffffff814f2fc4>] __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433
 [<ffffffff81b08e41>] disk_unblock_events+0x51/0x60 block/genhd.c:1550
 [<ffffffff815c8ef6>] __blkdev_get+0x6b6/0xd60 fs/block_dev.c:1360
 [<ffffffff815cb77a>] blkdev_get+0x2da/0x920 fs/block_dev.c:1416
 [<ffffffff815cbfd5>] blkdev_open+0x1a5/0x250 fs/block_dev.c:1571
 [<ffffffff81501e2f>] do_dentry_open+0x3ef/0xc90 fs/open.c:766
 [<ffffffff8150575c>] vfs_open+0x11c/0x210 fs/open.c:879
 [<ffffffff8153c532>] do_last fs/namei.c:3410 [inline]
 [<ffffffff8153c532>] path_openat+0x542/0x2790 fs/namei.c:3534
 [<ffffffff81541607>] do_filp_open+0x197/0x270 fs/namei.c:3568
 [<ffffffff8150616d>] do_sys_open+0x30d/0x5c0 fs/open.c:1072
 [<ffffffff8150644d>] SYSC_open fs/open.c:1090 [inline]
 [<ffffffff8150644d>] SyS_open+0x2d/0x40 fs/open.c:1085
 [<ffffffff810056ef>] do_syscall_64+0x19f/0x550 arch/x86/entry/common.c:285
 [<ffffffff8280ac13>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb

Allocated by task 3691:
 save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:57
 save_stack mm/kasan/kasan.c:505 [inline]
 set_track mm/kasan/kasan.c:517 [inline]
 kasan_kmalloc.part.1+0x62/0xf0 mm/kasan/kasan.c:609
 kasan_kmalloc+0xaf/0xc0 mm/kasan/kasan.c:594
 kmem_cache_alloc_trace+0x117/0x2e0 mm/slub.c:2742
 kmem_cache_alloc_node_trace include/linux/slab.h:381 [inline]
 kmalloc_node include/linux/slab.h:528 [inline]
 kzalloc_node include/linux/slab.h:647 [inline]
 alloc_disk_node+0x54/0x3a0 block/genhd.c:1294
 alloc_disk+0x18/0x20 block/genhd.c:1286
 loop_add+0x368/0x7a0 drivers/block/loop.c:1817
 loop_control_ioctl+0x136/0x300 drivers/block/loop.c:1949
 C_SYSC_ioctl fs/compat_ioctl.c:1602 [inline]
 compat_SyS_ioctl+0x12d/0x1fd0 fs/compat_ioctl.c:1549
 do_syscall_32_irqs_on arch/x86/entry/common.c:328 [inline]
 do_fast_syscall_32+0x2f1/0xa10 arch/x86/entry/common.c:390
 entry_SYSENTER_compat+0x90/0xa2 arch/x86/entry/entry_64_compat.S:137

Freed by task 3700:
 save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:57
 save_stack mm/kasan/kasan.c:505 [inline]
 set_track mm/kasan/kasan.c:517 [inline]
 kasan_slab_free+0xac/0x190 mm/kasan/kasan.c:582
 slab_free_hook mm/slub.c:1355 [inline]
 slab_free_freelist_hook mm/slub.c:1377 [inline]
 slab_free mm/slub.c:2958 [inline]
 kfree+0xfb/0x310 mm/slub.c:3878
 disk_release+0x259/0x330 block/genhd.c:1147
 device_release+0x7e/0x220 drivers/base/core.c:247
 kobject_cleanup lib/kobject.c:643 [inline]
 kobject_release lib/kobject.c:672 [inline]
 kref_sub include/linux/kref.h:73 [inline]
 kref_put include/linux/kref.h:98 [inline]
 kobject_put+0x148/0x250 lib/kobject.c:689
 put_disk+0x23/0x30 block/genhd.c:1358
 __blkdev_get+0x616/0xd60 fs/block_dev.c:1353
 blkdev_get+0x2da/0x920 fs/block_dev.c:1416
 blkdev_open+0x1a5/0x250 fs/block_dev.c:1571
 do_dentry_open+0x3ef/0xc90 fs/open.c:766
 vfs_open+0x11c/0x210 fs/open.c:879
 do_last fs/namei.c:3410 [inline]
 path_openat+0x542/0x2790 fs/namei.c:3534
 do_filp_open+0x197/0x270 fs/namei.c:3568
 do_sys_open+0x30d/0x5c0 fs/open.c:1072
 SYSC_open fs/open.c:1090 [inline]
 SyS_open+0x2d/0x40 fs/open.c:1085
 do_syscall_64+0x19f/0x550 arch/x86/entry/common.c:285
 entry_SYSCALL_64_after_swapgs+0x5d/0xdb

The buggy address belongs to the object at ffff8801d6a09100
 which belongs to the cache kmalloc-2048 of size 2048
The buggy address is located 1376 bytes inside of
 2048-byte region [ffff8801d6a09100, ffff8801d6a09900)
The buggy address belongs to the page:
page:ffffea00075a8200 count:1 mapcount:0 mapping:          (null) index:0x0 compound_mapcount: 0
flags: 0x4000000000004080(slab|head)
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801d6a09500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801d6a09580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8801d6a09600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                       ^
 ffff8801d6a09680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801d6a09700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
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