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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 ffff88808da87808 by task systemd-udevd/10132

CPU: 1 PID: 10132 Comm: systemd-udevd Not tainted 4.14.184-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+0x1b2/0x283 lib/dump_stack.c:58
 print_address_description.cold+0x54/0x1dc 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+0xa9/0x2b9 mm/kasan/report.c:393
 disk_unblock_events+0x4b/0x50 block/genhd.c:1644
 __blkdev_get+0x79c/0x10c0 fs/block_dev.c:1556
 blkdev_get+0x84/0x8a0 fs/block_dev.c:1612
 blkdev_open+0x1cc/0x250 fs/block_dev.c:1770
 do_dentry_open+0x44b/0xec0 fs/open.c:777
 vfs_open+0x105/0x220 fs/open.c:888
 do_last fs/namei.c:3428 [inline]
 path_openat+0xb68/0x2aa0 fs/namei.c:3569
 do_filp_open+0x18e/0x250 fs/namei.c:3603
 do_sys_open+0x292/0x3e0 fs/open.c:1081
 do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x46/0xbb
RIP: 0033:0x7f306489a840
RSP: 002b:00007ffd9eaf2958 EFLAGS: 00000246 ORIG_RAX: 0000000000000002
RAX: ffffffffffffffda RBX: 0000555a614d02f0 RCX: 00007f306489a840
RDX: 0000555a612a7fe3 RSI: 00000000000a0800 RDI: 0000555a614ca600
RBP: 00007ffd9eaf2ad0 R08: 0000555a612a7670 R09: 0000000000000010
R10: 0000555a612a7d0c R11: 0000000000000246 R12: 00007ffd9eaf2a20
R13: 0000555a614c9800 R14: 0000000000000003 R15: 000000000000000e

Allocated by task 10112:
 save_stack mm/kasan/kasan.c:447 [inline]
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_kmalloc.part.0+0x4f/0xd0 mm/kasan/kasan.c:551
 kmem_cache_alloc_node_trace+0x153/0x400 mm/slab.c:3661
 kmalloc_node include/linux/slab.h:526 [inline]
 kzalloc_node include/linux/slab.h:672 [inline]
 alloc_disk_node+0x5d/0x3d0 block/genhd.c:1387
 loop_add+0x3cb/0x830 drivers/block/loop.c:1869
 loop_control_ioctl+0x13b/0x2d0 drivers/block/loop.c:2027
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:500 [inline]
 do_vfs_ioctl+0x75a/0xfe0 fs/ioctl.c:684
 SYSC_ioctl fs/ioctl.c:701 [inline]
 SyS_ioctl+0x7f/0xb0 fs/ioctl.c:692
 do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x46/0xbb

Freed by task 10132:
 save_stack mm/kasan/kasan.c:447 [inline]
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_slab_free+0xaf/0x190 mm/kasan/kasan.c:524
 __cache_free mm/slab.c:3496 [inline]
 kfree+0xcb/0x260 mm/slab.c:3815
 device_release+0xf0/0x1a0 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+0x13e/0x1f0 lib/kobject.c:692
 put_disk+0x1f/0x30 block/genhd.c:1452
 __blkdev_get+0x707/0x10c0 fs/block_dev.c:1549
 blkdev_get+0x84/0x8a0 fs/block_dev.c:1612
 blkdev_open+0x1cc/0x250 fs/block_dev.c:1770
 do_dentry_open+0x44b/0xec0 fs/open.c:777
 vfs_open+0x105/0x220 fs/open.c:888
 do_last fs/namei.c:3428 [inline]
 path_openat+0xb68/0x2aa0 fs/namei.c:3569
 do_filp_open+0x18e/0x250 fs/namei.c:3603
 do_sys_open+0x292/0x3e0 fs/open.c:1081
 do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x46/0xbb

The buggy address belongs to the object at ffff88808da87280
 which belongs to the cache kmalloc-2048 of size 2048
The buggy address is located 1416 bytes inside of
 2048-byte region [ffff88808da87280, ffff88808da87a80)
The buggy address belongs to the page:
page:ffffea000236a180 count:1 mapcount:0 mapping:ffff88808da86180 index:0x0 compound_mapcount: 0
flags: 0xfffe0000008100(slab|head)
raw: 00fffe0000008100 ffff88808da86180 0000000000000000 0000000100000003
raw: ffffea000237ffa0 ffffea0002416920 ffff8880aa800c40 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff88808da87700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88808da87780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88808da87800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                      ^
 ffff88808da87880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88808da87900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
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