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BUG: KASAN: use-after-free in disk_unblock_events+0x51/0x60 block/genhd.c:1657
Read of size 8 at addr ffff8801bb30c600 by task syzkaller181568/4025

CPU: 0 PID: 4025 Comm: syzkaller181568 Not tainted 4.15.0-rc6-mm1+ #50
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+0x137/0x198 lib/dump_stack.c:53
 print_address_description+0x73/0x250 mm/kasan/report.c:256
 kasan_report_error mm/kasan/report.c:354 [inline]
 kasan_report+0x23b/0x360 mm/kasan/report.c:412
 __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433
 disk_unblock_events+0x51/0x60 block/genhd.c:1657
 __blkdev_get+0x6e9/0x1140 fs/block_dev.c:1534
 blkdev_get+0x32d/0x920 fs/block_dev.c:1590
 blkdev_open+0x1c9/0x250 fs/block_dev.c:1748
 do_dentry_open+0x667/0xd40 fs/open.c:752
 vfs_open+0x107/0x220 fs/open.c:866
 do_last fs/namei.c:3397 [inline]
 path_openat+0x5a5/0x26e0 fs/namei.c:3537
 do_filp_open+0x19d/0x290 fs/namei.c:3572
 do_sys_open+0x336/0x4b0 fs/open.c:1059
 SYSC_open fs/open.c:1077 [inline]
 SyS_open+0x2d/0x40 fs/open.c:1072
 entry_SYSCALL_64_fastpath+0x23/0x9a
RIP: 0033:0x401770
RSP: 002b:00007ffe0dd66288 EFLAGS: 00000246 ORIG_RAX: 0000000000000002
RAX: ffffffffffffffda RBX: 000000000000000a RCX: 0000000000401770
RDX: 0000000000000000 RSI: 0000000000044042 RDI: 00007ffe0dd66330
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000000079bf
R13: 0000000000402950 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 4029:
 save_stack+0x43/0xd0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:552
 kmem_cache_alloc_node_trace+0x150/0x750 mm/slab.c:3650
 kmalloc_node include/linux/slab.h:554 [inline]
 kzalloc_node include/linux/slab.h:716 [inline]
 __alloc_disk_node+0x69/0x3e0 block/genhd.c:1400
 loop_add+0x3e3/0x990 drivers/block/loop.c:1808
 loop_probe+0x146/0x170 drivers/block/loop.c:1915
 kobj_lookup+0x2ac/0x410 drivers/base/map.c:124
 get_gendisk+0x37/0x2c0 block/genhd.c:789
 __blkdev_get+0x3ce/0x1140 fs/block_dev.c:1432
 blkdev_get+0x32d/0x920 fs/block_dev.c:1590
 blkdev_open+0x1c9/0x250 fs/block_dev.c:1748
 do_dentry_open+0x667/0xd40 fs/open.c:752
 vfs_open+0x107/0x220 fs/open.c:866
 do_last fs/namei.c:3397 [inline]
 path_openat+0x5a5/0x26e0 fs/namei.c:3537
 do_filp_open+0x19d/0x290 fs/namei.c:3572
 do_sys_open+0x336/0x4b0 fs/open.c:1059
 SYSC_open fs/open.c:1077 [inline]
 SyS_open+0x2d/0x40 fs/open.c:1072
 entry_SYSCALL_64_fastpath+0x23/0x9a

Freed by task 4025:
 save_stack+0x43/0xd0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 __kasan_slab_free+0x11a/0x170 mm/kasan/kasan.c:520
 kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:527
 __cache_free mm/slab.c:3485 [inline]
 kfree+0xd9/0x260 mm/slab.c:3800
 disk_release+0x251/0x2d0 block/genhd.c:1249
 device_release+0x7c/0x210 drivers/base/core.c:812
 kobject_cleanup lib/kobject.c:646 [inline]
 kobject_release lib/kobject.c:675 [inline]
 kref_put include/linux/kref.h:70 [inline]
 kobject_put+0x14c/0x250 lib/kobject.c:692
 put_disk+0x23/0x30 block/genhd.c:1465
 __blkdev_get+0x649/0x1140 fs/block_dev.c:1527
 blkdev_get+0x32d/0x920 fs/block_dev.c:1590
 blkdev_open+0x1c9/0x250 fs/block_dev.c:1748
 do_dentry_open+0x667/0xd40 fs/open.c:752
 vfs_open+0x107/0x220 fs/open.c:866
 do_last fs/namei.c:3397 [inline]
 path_openat+0x5a5/0x26e0 fs/namei.c:3537
 do_filp_open+0x19d/0x290 fs/namei.c:3572
 do_sys_open+0x336/0x4b0 fs/open.c:1059
 SYSC_open fs/open.c:1077 [inline]
 SyS_open+0x2d/0x40 fs/open.c:1072
 entry_SYSCALL_64_fastpath+0x23/0x9a

The buggy address belongs to the object at ffff8801bb30c080
 which belongs to the cache kmalloc-2048 of size 2048
The buggy address is located 1408 bytes inside of
 2048-byte region [ffff8801bb30c080, ffff8801bb30c880)
The buggy address belongs to the page:
page:ffffea0006ecc300 count:1 mapcount:0 mapping:ffff8801bb30c080 index:0x0 compound_mapcount: 0
flags: 0x2fffc0000008100(slab|head)
raw: 02fffc0000008100 ffff8801bb30c080 0000000000000000 0000000100000003
raw: ffffea0007396ba0 ffffea0006ecc3a0 ffff8801db000c40 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801bb30c500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801bb30c580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8801bb30c600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                   ^
 ffff8801bb30c680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801bb30c700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
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