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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 ffff8880af33b988 by task syz-executor.0/8014

CPU: 1 PID: 8014 Comm: syz-executor.0 Not tainted 4.14.212-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+0x54/0x1d3 mm/kasan/report.c:252
 kasan_report_error.cold+0x8a/0x194 mm/kasan/report.c:351
 kasan_report mm/kasan/report.c:409 [inline]
 __asan_report_load8_noabort+0x68/0x70 mm/kasan/report.c:430
 disk_unblock_events+0x4b/0x50 block/genhd.c:1644
 __blkdev_get+0x83b/0x1090 fs/block_dev.c:1556
 blkdev_get+0x88/0x890 fs/block_dev.c:1611
 blkdev_open+0x1cc/0x250 fs/block_dev.c:1772
 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+0x628/0x2970 fs/namei.c:3569
 do_filp_open+0x179/0x3c0 fs/namei.c:3603
 do_sys_open+0x296/0x410 fs/open.c:1081
 do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x46/0xbb
RIP: 0033:0x417c51
RSP: 002b:00007ffcc4b86610 EFLAGS: 00000293 ORIG_RAX: 0000000000000002
RAX: ffffffffffffffda RBX: 000000000000e777 RCX: 0000000000417c51
RDX: 00007ffcc4b866aa RSI: 0000000000000002 RDI: 00007ffcc4b866a0
RBP: 000000000000001a R08: 0000000000000000 R09: 000000000000000a
R10: 0000000000000075 R11: 0000000000000293 R12: 0000000000000000
R13: 00007ffcc4b86650 R14: 00007ffcc4b86660 R15: 000000000000e745

Allocated by task 1:
 save_stack mm/kasan/kasan.c:447 [inline]
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_kmalloc+0xeb/0x160 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_init+0x19a/0x1e0 drivers/block/loop.c:2115
 do_one_initcall+0x88/0x202 init/main.c:826
 do_initcall_level init/main.c:892 [inline]
 do_initcalls init/main.c:900 [inline]
 do_basic_setup init/main.c:918 [inline]
 kernel_init_freeable+0x553/0x614 init/main.c:1075
 kernel_init+0xd/0x165 init/main.c:1000
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:404

Freed by task 8014:
 save_stack mm/kasan/kasan.c:447 [inline]
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_slab_free+0xc3/0x1a0 mm/kasan/kasan.c:524
 __cache_free mm/slab.c:3496 [inline]
 kfree+0xc9/0x250 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+0x251/0x550 lib/kobject.c:692
 put_disk+0x1f/0x30 block/genhd.c:1452
 __blkdev_get+0x7a6/0x1090 fs/block_dev.c:1549
 blkdev_get+0x88/0x890 fs/block_dev.c:1611
 blkdev_open+0x1cc/0x250 fs/block_dev.c:1772
 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+0x628/0x2970 fs/namei.c:3569
 do_filp_open+0x179/0x3c0 fs/namei.c:3603
 do_sys_open+0x296/0x410 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 ffff8880af33b400
 which belongs to the cache kmalloc-2048 of size 2048
The buggy address is located 1416 bytes inside of
 2048-byte region [ffff8880af33b400, ffff8880af33bc00)
The buggy address belongs to the page:
page:ffffea0002bcce80 count:1 mapcount:0 mapping:ffff8880af33a300 index:0x0 compound_mapcount: 0
flags: 0xfff00000008100(slab|head)
raw: 00fff00000008100 ffff8880af33a300 0000000000000000 0000000100000003
raw: ffffea0002bccda0 ffffea0002bce420 ffff88813fe80c40 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8880af33b880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8880af33b900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8880af33b980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                      ^
 ffff8880af33ba00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8880af33ba80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
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