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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 ffff8881d935f3e8 by task syz-executor.0/1857

CPU: 1 PID: 1857 Comm: syz-executor.0 Not tainted 4.14.155-syzkaller #0
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0xe5/0x154 lib/dump_stack.c:58
 print_address_description+0x60/0x226 mm/kasan/report.c:187
 __kasan_report.cold+0x1a/0x41 mm/kasan/report.c:316
 disk_unblock_events+0x4b/0x50 block/genhd.c:1644
 __blkdev_get+0x68f/0xf90 fs/block_dev.c:1556
 blkdev_get+0x97/0x8b0 fs/block_dev.c:1612
 blkdev_open+0x1cc/0x250 fs/block_dev.c:1770
 do_dentry_open+0x44e/0xe20 fs/open.c:789
 vfs_open+0x105/0x230 fs/open.c:903
 do_last fs/namei.c:3539 [inline]
 path_openat+0xb6c/0x2be0 fs/namei.c:3681
 do_filp_open+0x1a1/0x280 fs/namei.c:3715
 do_sys_open+0x2ca/0x590 fs/open.c:1096
 do_syscall_64+0x19b/0x520 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x4143b0
RSP: 002b:00007ffcc5d40478 EFLAGS: 00000246 ORIG_RAX: 0000000000000002
RAX: ffffffffffffffda RBX: 0000000000019329 RCX: 00000000004143b0
RDX: 00007ffcc5d4050a RSI: 0000000000000002 RDI: 00007ffcc5d40500
RBP: 0000000000000009 R08: 0000000000000000 R09: 000000000000000a
R10: 0000000000000075 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffcc5d404b0 R14: 0000000000018ff5 R15: 00007ffcc5d404c0

Allocated by task 1:
 save_stack mm/kasan/common.c:76 [inline]
 set_track mm/kasan/common.c:85 [inline]
 __kasan_kmalloc.part.0+0x53/0xc0 mm/kasan/common.c:501
 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+0x5b/0x3d0 block/genhd.c:1387
 loop_add+0x3ee/0x870 drivers/block/loop.c:1859
 loop_init+0x1aa/0x205 drivers/block/loop.c:2105
 do_one_initcall+0xa0/0x1ac init/main.c:849
 do_initcall_level init/main.c:915 [inline]
 do_initcalls init/main.c:923 [inline]
 do_basic_setup init/main.c:941 [inline]
 kernel_init_freeable+0x2ef/0x3b0 init/main.c:1098
 kernel_init+0xd/0x164 init/main.c:1023
 ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:404
 0xffffffffffffffff

Freed by task 1857:
 save_stack mm/kasan/common.c:76 [inline]
 set_track mm/kasan/common.c:85 [inline]
 __kasan_slab_free+0x164/0x210 mm/kasan/common.c:463
 slab_free_hook mm/slub.c:1407 [inline]
 slab_free_freelist_hook mm/slub.c:1458 [inline]
 slab_free mm/slub.c:3039 [inline]
 kfree+0x108/0x3a0 mm/slub.c:3976
 device_release+0xf4/0x1a0 drivers/base/core.c:823
 kobject_cleanup lib/kobject.c:646 [inline]
 kobject_release lib/kobject.c:675 [inline]
 kref_put include/linux/kref.h:70 [inline]
 kobject_put+0x142/0x200 lib/kobject.c:692
 put_disk+0x1f/0x30 block/genhd.c:1452
 __blkdev_get+0x5fa/0xf90 fs/block_dev.c:1549
 blkdev_get+0x97/0x8b0 fs/block_dev.c:1612
 blkdev_open+0x1cc/0x250 fs/block_dev.c:1770
 do_dentry_open+0x44e/0xe20 fs/open.c:789
 vfs_open+0x105/0x230 fs/open.c:903
 do_last fs/namei.c:3539 [inline]
 path_openat+0xb6c/0x2be0 fs/namei.c:3681
 do_filp_open+0x1a1/0x280 fs/namei.c:3715
 do_sys_open+0x2ca/0x590 fs/open.c:1096
 do_syscall_64+0x19b/0x520 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
 0xffffffffffffffff

The buggy address belongs to the object at ffff8881d935ee80
 which belongs to the cache kmalloc-2048 of size 2048
The buggy address is located 1384 bytes inside of
 2048-byte region [ffff8881d935ee80, ffff8881d935f680)
The buggy address belongs to the page:
page:ffffea000764d600 count:1 mapcount:0 mapping:          (null) index:0x0 compound_mapcount: 0
flags: 0x4000000000010200(slab|head)
raw: 4000000000010200 0000000000000000 0000000000000000 00000001000f000f
raw: dead000000000100 dead000000000200 ffff8881da802800 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8881d935f280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8881d935f300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8881d935f380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                          ^
 ffff8881d935f400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8881d935f480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
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