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BUG: KASAN: use-after-free in disk_unblock_events+0x55/0x60 block/genhd.c:1644
Read of size 8 at addr ffff8880954bb848 by task blkid/7402

CPU: 1 PID: 7402 Comm: blkid Not tainted 4.14.170-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x142/0x197 lib/dump_stack.c:58
 print_address_description.cold+0x7c/0x1dc mm/kasan/report.c:252
 kasan_report_error mm/kasan/report.c:351 [inline]
 kasan_report mm/kasan/report.c:409 [inline]
 kasan_report.cold+0xa9/0x2af mm/kasan/report.c:393
 __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:430
 disk_unblock_events+0x55/0x60 block/genhd.c:1644
 __blkdev_get+0x7d6/0x1120 fs/block_dev.c:1556
 blkdev_get+0xa8/0x8e0 fs/block_dev.c:1612
 blkdev_open+0x1d1/0x260 fs/block_dev.c:1770
 do_dentry_open+0x73b/0xeb0 fs/open.c:777
 vfs_open+0x105/0x220 fs/open.c:891
 do_last fs/namei.c:3428 [inline]
 path_openat+0x917/0x3e50 fs/namei.c:3569
 do_filp_open+0x18e/0x250 fs/namei.c:3603
 do_sys_open+0x2c5/0x430 fs/open.c:1084
 SYSC_open fs/open.c:1102 [inline]
 SyS_open+0x2d/0x40 fs/open.c:1097
 do_syscall_64+0x1e8/0x640 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x7f5f56b9f120
RSP: 002b:00007ffd6391d7e8 EFLAGS: 00000246 ORIG_RAX: 0000000000000002
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f5f56b9f120
RDX: 00007ffd6391ff35 RSI: 0000000000000000 RDI: 00007ffd6391ff35
RBP: 0000000000000000 R08: 0000000000000078 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000147b030
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000005

Allocated by task 7368:
 save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
 save_stack+0x45/0xd0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_kmalloc mm/kasan/kasan.c:551 [inline]
 kasan_kmalloc+0xce/0xf0 mm/kasan/kasan.c:529
 kmem_cache_alloc_node_trace+0x153/0x770 mm/slab.c:3661
 kmalloc_node include/linux/slab.h:526 [inline]
 kzalloc_node include/linux/slab.h:672 [inline]
 alloc_disk_node+0x64/0x3e0 block/genhd.c:1387
 alloc_disk+0x1b/0x20 block/genhd.c:1371
 loop_add+0x3e7/0x850 drivers/block/loop.c:1869
 loop_control_ioctl+0x1f4/0x2f0 drivers/block/loop.c:2027
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:500 [inline]
 do_vfs_ioctl+0x7ae/0x1060 fs/ioctl.c:684
 SYSC_ioctl fs/ioctl.c:701 [inline]
 SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
 do_syscall_64+0x1e8/0x640 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x42/0xb7

Freed by task 7402:
 save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
 save_stack+0x45/0xd0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_slab_free+0x75/0xc0 mm/kasan/kasan.c:524
 __cache_free mm/slab.c:3496 [inline]
 kfree+0xcc/0x270 mm/slab.c:3815
 disk_release+0x24b/0x2d0 block/genhd.c:1230
 device_release+0xf6/0x1a0 drivers/base/core.c:831
 kobject_cleanup lib/kobject.c:646 [inline]
 kobject_release lib/kobject.c:675 [inline]
 kref_put include/linux/kref.h:70 [inline]
 kobject_put+0x14e/0x210 lib/kobject.c:692
 put_disk+0x23/0x30 block/genhd.c:1452
 __blkdev_get+0x73c/0x1120 fs/block_dev.c:1549
 blkdev_get+0xa8/0x8e0 fs/block_dev.c:1612
 blkdev_open+0x1d1/0x260 fs/block_dev.c:1770
 do_dentry_open+0x73b/0xeb0 fs/open.c:777
 vfs_open+0x105/0x220 fs/open.c:891
 do_last fs/namei.c:3428 [inline]
 path_openat+0x917/0x3e50 fs/namei.c:3569
 do_filp_open+0x18e/0x250 fs/namei.c:3603
 do_sys_open+0x2c5/0x430 fs/open.c:1084
 SYSC_open fs/open.c:1102 [inline]
 SyS_open+0x2d/0x40 fs/open.c:1097
 do_syscall_64+0x1e8/0x640 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x42/0xb7

The buggy address belongs to the object at ffff8880954bb2c0
 which belongs to the cache kmalloc-2048 of size 2048
The buggy address is located 1416 bytes inside of
 2048-byte region [ffff8880954bb2c0, ffff8880954bbac0)
The buggy address belongs to the page:
page:ffffea0002552e80 count:1 mapcount:0 mapping:ffff8880954ba1c0 index:0x0 compound_mapcount: 0
flags: 0xfffe0000008100(slab|head)
raw: 00fffe0000008100 ffff8880954ba1c0 0000000000000000 0000000100000003
raw: ffffea0002254c20 ffffea00020714a0 ffff8880aa800c40 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8880954bb700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8880954bb780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8880954bb800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                              ^
 ffff8880954bb880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8880954bb900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
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