==================================================================
BUG: KASAN: use-after-free in disk_unblock_events+0x55/0x60 block/genhd.c:1550
Read of size 8 at addr ffff8801c7de8560 by task syz-executor.0/19531

CPU: 0 PID: 19531 Comm: syz-executor.0 Not tainted 4.9.203-syzkaller #0
 ffff8801cbdc7730 ffffffff81b55f6b 0000000000000000 ffffea00071f7a00
 ffff8801c7de8560 0000000000000008 ffffffff81b2a415 ffff8801cbdc7768
 ffffffff8150c461 0000000000000000 ffff8801c7de8560 ffff8801c7de8560
Call Trace:
 [<00000000e81952d3>] __dump_stack lib/dump_stack.c:15 [inline]
 [<00000000e81952d3>] dump_stack+0xcb/0x130 lib/dump_stack.c:56
 [<00000000de94cfcd>] print_address_description+0x6f/0x23a mm/kasan/report.c:256
 [<00000000791cd44a>] kasan_report_error mm/kasan/report.c:355 [inline]
 [<00000000791cd44a>] kasan_report mm/kasan/report.c:413 [inline]
 [<00000000791cd44a>] kasan_report.cold+0x8c/0x2ba mm/kasan/report.c:397
 [<00000000691b224e>] __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:434
 [<00000000735c75a1>] disk_unblock_events+0x55/0x60 block/genhd.c:1550
 [<00000000c06cde2d>] __blkdev_get+0x6ba/0xeb0 fs/block_dev.c:1368
 [<000000008758f2d3>] blkdev_get+0x2e8/0x920 fs/block_dev.c:1424
 [<00000000727b44ac>] blkdev_open+0x1aa/0x250 fs/block_dev.c:1579
 [<00000000e62be47b>] do_dentry_open+0x422/0xd20 fs/open.c:791
 [<00000000a6343990>] vfs_open+0x105/0x230 fs/open.c:904
 [<00000000b14cf2cd>] do_last fs/namei.c:3457 [inline]
 [<00000000b14cf2cd>] path_openat+0xbf5/0x2f60 fs/namei.c:3581
 [<00000000ca9903df>] do_filp_open+0x1a1/0x280 fs/namei.c:3615
 [<00000000d2526bde>] do_sys_open+0x2f0/0x610 fs/open.c:1097
 [<0000000038504af3>] SYSC_open fs/open.c:1115 [inline]
 [<0000000038504af3>] SyS_open+0x2d/0x40 fs/open.c:1110
 [<00000000b4ae8af9>] do_syscall_64+0x1ad/0x5c0 arch/x86/entry/common.c:288
 [<0000000087cca8c7>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb

Allocated by task 20125:
 save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:57
 save_stack mm/kasan/kasan.c:512 [inline]
 set_track mm/kasan/kasan.c:524 [inline]
 kasan_kmalloc.part.0+0x62/0xf0 mm/kasan/kasan.c:616
 kasan_kmalloc+0xb7/0xd0 mm/kasan/kasan.c:601
 kmem_cache_alloc_trace+0x115/0x2d0 mm/slub.c:2742
 kmem_cache_alloc_node_trace include/linux/slab.h:381 [inline]
 kmalloc_node include/linux/slab.h:528 [inline]
 kzalloc_node include/linux/slab.h:647 [inline]
 alloc_disk_node+0x50/0x3c0 block/genhd.c:1294
 alloc_disk+0x1b/0x20 block/genhd.c:1286
 loop_add+0x37e/0x7d0 drivers/block/loop.c:1850
 loop_control_ioctl+0x138/0x320 drivers/block/loop.c:1982
 vfs_ioctl fs/ioctl.c:43 [inline]
 file_ioctl fs/ioctl.c:493 [inline]
 do_vfs_ioctl+0xb87/0x11d0 fs/ioctl.c:677
 SYSC_ioctl fs/ioctl.c:694 [inline]
 SyS_ioctl+0x8f/0xc0 fs/ioctl.c:685
 do_syscall_64+0x1ad/0x5c0 arch/x86/entry/common.c:288
 entry_SYSCALL_64_after_swapgs+0x5d/0xdb

Freed by task 19531:
 save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:57
 save_stack mm/kasan/kasan.c:512 [inline]
 set_track mm/kasan/kasan.c:524 [inline]
 kasan_slab_free+0xb0/0x190 mm/kasan/kasan.c:589
 slab_free_hook mm/slub.c:1355 [inline]
 slab_free_freelist_hook mm/slub.c:1377 [inline]
 slab_free mm/slub.c:2958 [inline]
 kfree+0xfc/0x310 mm/slub.c:3878
 disk_release+0x255/0x330 block/genhd.c:1147
 device_release+0x7d/0x220 drivers/base/core.c:248
 kobject_cleanup lib/kobject.c:643 [inline]
 kobject_release lib/kobject.c:672 [inline]
 kref_sub include/linux/kref.h:73 [inline]
 kref_put include/linux/kref.h:98 [inline]
 kobject_put+0x150/0x260 lib/kobject.c:689
 put_disk+0x23/0x30 block/genhd.c:1358
 __blkdev_get+0x61a/0xeb0 fs/block_dev.c:1361
 blkdev_get+0x2e8/0x920 fs/block_dev.c:1424
 blkdev_open+0x1aa/0x250 fs/block_dev.c:1579
 do_dentry_open+0x422/0xd20 fs/open.c:791
 vfs_open+0x105/0x230 fs/open.c:904
 do_last fs/namei.c:3457 [inline]
 path_openat+0xbf5/0x2f60 fs/namei.c:3581
 do_filp_open+0x1a1/0x280 fs/namei.c:3615
 do_sys_open+0x2f0/0x610 fs/open.c:1097
 SYSC_open fs/open.c:1115 [inline]
 SyS_open+0x2d/0x40 fs/open.c:1110
 do_syscall_64+0x1ad/0x5c0 arch/x86/entry/common.c:288
 entry_SYSCALL_64_after_swapgs+0x5d/0xdb

The buggy address belongs to the object at ffff8801c7de8000
 which belongs to the cache kmalloc-2048 of size 2048
The buggy address is located 1376 bytes inside of
 2048-byte region [ffff8801c7de8000, ffff8801c7de8800)
The buggy address belongs to the page:
page:ffffea00071f7a00 count:1 mapcount:0 mapping:          (null) index:0x0 compound_mapcount: 0
flags: 0x4000000000010200(slab|head)
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801c7de8400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801c7de8480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8801c7de8500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                       ^
 ffff8801c7de8580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801c7de8600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================