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BUG: KASAN: use-after-free in disk_unblock_events+0x51/0x60 block/genhd.c:1654
Read of size 8 at addr ffff8801b893b028 by task syz-executor4/24238

CPU: 1 PID: 24238 Comm: syz-executor4 Not tainted 4.15.0-rc1+ #197
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+0x194/0x257 lib/dump_stack.c:53
 print_address_description+0x73/0x250 mm/kasan/report.c:252
 kasan_report_error mm/kasan/report.c:351 [inline]
 kasan_report+0x25b/0x340 mm/kasan/report.c:409
 __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:430
 disk_unblock_events+0x51/0x60 block/genhd.c:1654
 __blkdev_get+0x869/0x10e0 fs/block_dev.c:1535
 blkdev_get+0x3a1/0xad0 fs/block_dev.c:1591
 blkdev_open+0x1e4/0x270 fs/block_dev.c:1749
 do_dentry_open+0x682/0xd70 fs/open.c:752
 vfs_open+0x107/0x230 fs/open.c:866
 do_last fs/namei.c:3388 [inline]
 path_openat+0x1157/0x3530 fs/namei.c:3528
 do_filp_open+0x25b/0x3b0 fs/namei.c:3563
 do_sys_open+0x502/0x6d0 fs/open.c:1059
 SYSC_open fs/open.c:1077 [inline]
 SyS_open+0x2d/0x40 fs/open.c:1072
 entry_SYSCALL_64_fastpath+0x1f/0x96
RIP: 0033:0x40cd11
RSP: 002b:00007f0a79891780 EFLAGS: 00000293 ORIG_RAX: 0000000000000002
RAX: ffffffffffffffda RBX: cccccccccccccccd RCX: 000000000040cd11
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00007f0a79891830
RBP: 0000000000000597 R08: 0000000000000000 R09: 0000000000000000
R10: 000000000000000c R11: 0000000000000293 R12: 00000000006f56c8
R13: 00000000ffffffff R14: 00007f0a798926d4 R15: 0000000000000000

Allocated by task 24238:
 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:551
 kmem_cache_alloc_node_trace+0x150/0x760 mm/slab.c:3656
 kmalloc_node include/linux/slab.h:537 [inline]
 kzalloc_node include/linux/slab.h:699 [inline]
 __alloc_disk_node+0xb4/0x4e0 block/genhd.c:1397
 loop_add+0x44c/0xa70 drivers/block/loop.c:1808
 loop_probe+0x16d/0x1a0 drivers/block/loop.c:1915
 kobj_lookup+0x2ac/0x410 drivers/base/map.c:124
 get_gendisk+0x37/0x2c0 block/genhd.c:786
 __blkdev_get+0x3ea/0x10e0 fs/block_dev.c:1433
 blkdev_get+0x3a1/0xad0 fs/block_dev.c:1591
 blkdev_open+0x1e4/0x270 fs/block_dev.c:1749
 do_dentry_open+0x682/0xd70 fs/open.c:752
 vfs_open+0x107/0x230 fs/open.c:866
 do_last fs/namei.c:3388 [inline]
 path_openat+0x1157/0x3530 fs/namei.c:3528
 do_filp_open+0x25b/0x3b0 fs/namei.c:3563
 do_sys_open+0x502/0x6d0 fs/open.c:1059
 SYSC_open fs/open.c:1077 [inline]
 SyS_open+0x2d/0x40 fs/open.c:1072
 entry_SYSCALL_64_fastpath+0x1f/0x96

Freed by task 24238:
 save_stack+0x43/0xd0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_slab_free+0x71/0xc0 mm/kasan/kasan.c:524
 __cache_free mm/slab.c:3491 [inline]
 kfree+0xca/0x250 mm/slab.c:3806
 disk_release+0x327/0x410 block/genhd.c:1246
 device_release+0x7c/0x210 drivers/base/core.c:814
 kobject_cleanup lib/kobject.c:648 [inline]
 kobject_release lib/kobject.c:677 [inline]
 kref_put include/linux/kref.h:70 [inline]
 kobject_put+0x14c/0x250 lib/kobject.c:694
 put_disk+0x23/0x30 block/genhd.c:1462
 __blkdev_get+0x7c9/0x10e0 fs/block_dev.c:1528
 blkdev_get+0x3a1/0xad0 fs/block_dev.c:1591
 blkdev_open+0x1e4/0x270 fs/block_dev.c:1749
 do_dentry_open+0x682/0xd70 fs/open.c:752
 vfs_open+0x107/0x230 fs/open.c:866
 do_last fs/namei.c:3388 [inline]
 path_openat+0x1157/0x3530 fs/namei.c:3528
 do_filp_open+0x25b/0x3b0 fs/namei.c:3563
 do_sys_open+0x502/0x6d0 fs/open.c:1059
 SYSC_open fs/open.c:1077 [inline]
 SyS_open+0x2d/0x40 fs/open.c:1072
 entry_SYSCALL_64_fastpath+0x1f/0x96

The buggy address belongs to the object at ffff8801b893aa00
 which belongs to the cache kmalloc-2048 of size 2048
The buggy address is located 1576 bytes inside of
 2048-byte region [ffff8801b893aa00, ffff8801b893b200)
The buggy address belongs to the page:
page:ffffea0006e24e80 count:1 mapcount:0 mapping:ffff8801b893a180 index:0x0 compound_mapcount: 0
flags: 0x2fffc0000008100(slab|head)
raw: 02fffc0000008100 ffff8801b893a180 0000000000000000 0000000100000003
raw: ffffea00074b1c20 ffffea00072b1220 ffff8801db000c40 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801b893af00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801b893af80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8801b893b000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                  ^
 ffff8801b893b080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801b893b100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
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