==================================================================
BUG: KASAN: use-after-free in disk_unblock_events+0x55/0x60 block/genhd.c:1543
Read of size 8 at addr ffff8800b9c673e8 by task syz-executor.3/6520

CPU: 0 PID: 6520 Comm: syz-executor.3 Not tainted 4.4.174+ #17
 0000000000000000 ecf0677f3c34fb68 ffff8800a35676c0 ffffffff81aad1a1
 0000000000000000 ffffea0002e71800 ffff8800b9c673e8 0000000000000008
 0000000000000000 ffff8800a35676f8 ffffffff81490120 0000000000000000
Call Trace:
 [<ffffffff81aad1a1>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81aad1a1>] dump_stack+0xc1/0x120 lib/dump_stack.c:51
 [<ffffffff81490120>] print_address_description+0x6f/0x21b mm/kasan/report.c:252
 [<ffffffff81490358>] kasan_report_error mm/kasan/report.c:351 [inline]
 [<ffffffff81490358>] kasan_report mm/kasan/report.c:408 [inline]
 [<ffffffff81490358>] kasan_report.cold+0x8c/0x2be mm/kasan/report.c:393
 [<ffffffff81484ed4>] __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:429
 [<ffffffff81a82965>] disk_unblock_events+0x55/0x60 block/genhd.c:1543
 [<ffffffff8154efcc>] __blkdev_get+0x70c/0xdf0 fs/block_dev.c:1297
 [<ffffffff81551938>] blkdev_get+0x2e8/0x920 fs/block_dev.c:1353
 [<ffffffff8155219a>] blkdev_open+0x1aa/0x250 fs/block_dev.c:1508
 [<ffffffff8149154f>] do_dentry_open+0x38f/0xbd0 fs/open.c:749
 [<ffffffff81494d3b>] vfs_open+0x10b/0x210 fs/open.c:862
 [<ffffffff814c5ddf>] do_last fs/namei.c:3269 [inline]
 [<ffffffff814c5ddf>] path_openat+0x136f/0x4470 fs/namei.c:3406
 [<ffffffff814ccab1>] do_filp_open+0x1a1/0x270 fs/namei.c:3440
 [<ffffffff81495668>] do_sys_open+0x2f8/0x600 fs/open.c:1038
 [<ffffffff81599c4a>] C_SYSC_open fs/compat.c:1092 [inline]
 [<ffffffff81599c4a>] compat_SyS_open+0x2a/0x40 fs/compat.c:1090
 [<ffffffff8100603d>] do_syscall_32_irqs_on arch/x86/entry/common.c:330 [inline]
 [<ffffffff8100603d>] do_fast_syscall_32+0x32d/0xa90 arch/x86/entry/common.c:397
 [<ffffffff8271a350>] sysenter_flags_fixed+0xd/0x1a

Allocated by task 2144:
 [<ffffffff8102e3c6>] save_stack_trace+0x26/0x50 arch/x86/kernel/stacktrace.c:63
 [<ffffffff81483f22>] save_stack mm/kasan/kasan.c:512 [inline]
 [<ffffffff81483f22>] set_track mm/kasan/kasan.c:524 [inline]
 [<ffffffff81483f22>] kasan_kmalloc.part.0+0x62/0xf0 mm/kasan/kasan.c:616
 [<ffffffff81484197>] kasan_kmalloc+0xb7/0xd0 mm/kasan/kasan.c:601
 [<ffffffff814801a3>] kmem_cache_alloc_trace+0x123/0x2d0 mm/slub.c:2642
 [<ffffffff81a81b50>] kmem_cache_alloc_node_trace include/linux/slab.h:367 [inline]
 [<ffffffff81a81b50>] kmalloc_node include/linux/slab.h:514 [inline]
 [<ffffffff81a81b50>] kzalloc_node include/linux/slab.h:631 [inline]
 [<ffffffff81a81b50>] alloc_disk_node+0x50/0x3c0 block/genhd.c:1282
 [<ffffffff81a81edb>] alloc_disk+0x1b/0x20 block/genhd.c:1274
 [<ffffffff81d436d0>] loop_add+0x380/0x830 drivers/block/loop.c:1857
 [<ffffffff81d43f44>] loop_probe+0x154/0x180 drivers/block/loop.c:1963
 [<ffffffff81d0efb1>] kobj_lookup+0x221/0x410 drivers/base/map.c:124
 [<ffffffff81a7fe3c>] get_gendisk+0x3c/0x2e0 block/genhd.c:689
 [<ffffffff8154ec5c>] __blkdev_get+0x39c/0xdf0 fs/block_dev.c:1193
 [<ffffffff81551938>] blkdev_get+0x2e8/0x920 fs/block_dev.c:1353
 [<ffffffff8155219a>] blkdev_open+0x1aa/0x250 fs/block_dev.c:1508
 [<ffffffff8149154f>] do_dentry_open+0x38f/0xbd0 fs/open.c:749
 [<ffffffff81494d3b>] vfs_open+0x10b/0x210 fs/open.c:862
 [<ffffffff814c5ddf>] do_last fs/namei.c:3269 [inline]
 [<ffffffff814c5ddf>] path_openat+0x136f/0x4470 fs/namei.c:3406
 [<ffffffff814ccab1>] do_filp_open+0x1a1/0x270 fs/namei.c:3440
 [<ffffffff81495668>] do_sys_open+0x2f8/0x600 fs/open.c:1038
 [<ffffffff81599c4a>] C_SYSC_open fs/compat.c:1092 [inline]
 [<ffffffff81599c4a>] compat_SyS_open+0x2a/0x40 fs/compat.c:1090
 [<ffffffff8100603d>] do_syscall_32_irqs_on arch/x86/entry/common.c:330 [inline]
 [<ffffffff8100603d>] do_fast_syscall_32+0x32d/0xa90 arch/x86/entry/common.c:397
 [<ffffffff8271a350>] sysenter_flags_fixed+0xd/0x1a

Freed by task 6520:
 [<ffffffff8102e3c6>] save_stack_trace+0x26/0x50 arch/x86/kernel/stacktrace.c:63
 [<ffffffff81484820>] save_stack mm/kasan/kasan.c:512 [inline]
 [<ffffffff81484820>] set_track mm/kasan/kasan.c:524 [inline]
 [<ffffffff81484820>] kasan_slab_free+0xb0/0x190 mm/kasan/kasan.c:589
 [<ffffffff81481c44>] slab_free_hook mm/slub.c:1383 [inline]
 [<ffffffff81481c44>] slab_free_freelist_hook mm/slub.c:1405 [inline]
 [<ffffffff81481c44>] slab_free mm/slub.c:2859 [inline]
 [<ffffffff81481c44>] kfree+0xf4/0x310 mm/slub.c:3749
 [<ffffffff81a80375>] disk_release+0x255/0x330 block/genhd.c:1118
 [<ffffffff81cf785d>] device_release+0x7d/0x220 drivers/base/core.c:247
 [<ffffffff81ab309c>] kobject_cleanup lib/kobject.c:643 [inline]
 [<ffffffff81ab309c>] kobject_release lib/kobject.c:672 [inline]
 [<ffffffff81ab309c>] kref_sub include/linux/kref.h:73 [inline]
 [<ffffffff81ab309c>] kref_put include/linux/kref.h:98 [inline]
 [<ffffffff81ab309c>] kobject_put+0x14c/0x260 lib/kobject.c:689
 [<ffffffff81a7e013>] put_disk+0x23/0x30 block/genhd.c:1346
 [<ffffffff8154ef2c>] __blkdev_get+0x66c/0xdf0 fs/block_dev.c:1290
 [<ffffffff81551938>] blkdev_get+0x2e8/0x920 fs/block_dev.c:1353
 [<ffffffff8155219a>] blkdev_open+0x1aa/0x250 fs/block_dev.c:1508
 [<ffffffff8149154f>] do_dentry_open+0x38f/0xbd0 fs/open.c:749
 [<ffffffff81494d3b>] vfs_open+0x10b/0x210 fs/open.c:862
 [<ffffffff814c5ddf>] do_last fs/namei.c:3269 [inline]
 [<ffffffff814c5ddf>] path_openat+0x136f/0x4470 fs/namei.c:3406
 [<ffffffff814ccab1>] do_filp_open+0x1a1/0x270 fs/namei.c:3440
 [<ffffffff81495668>] do_sys_open+0x2f8/0x600 fs/open.c:1038
 [<ffffffff81599c4a>] C_SYSC_open fs/compat.c:1092 [inline]
 [<ffffffff81599c4a>] compat_SyS_open+0x2a/0x40 fs/compat.c:1090
 [<ffffffff8100603d>] do_syscall_32_irqs_on arch/x86/entry/common.c:330 [inline]
 [<ffffffff8100603d>] do_fast_syscall_32+0x32d/0xa90 arch/x86/entry/common.c:397
 [<ffffffff8271a350>] sysenter_flags_fixed+0xd/0x1a

The buggy address belongs to the object at ffff8800b9c66e80
 which belongs to the cache kmalloc-2048 of size 2048
The buggy address is located 1384 bytes inside of
 2048-byte region [ffff8800b9c66e80, ffff8800b9c67680)
The buggy address belongs to the page:
Initializing cgroup subsys cpu
Initializing cgroup subsys cpuacct
Linux version 4.4.174+ (syzkaller@ci) (gcc version 9.0.0 20181231 (experimental) (GCC) ) #17 SMP PREEMPT Fri Feb 8 11:11:08 UTC 2019
Command line: BOOT_IMAGE=/vmlinuz root=/dev/sda1 console=ttyS0 earlyprintk=serial vsyscall=native rodata=n oops=panic panic_on_warn=1 nmi_watchdog=panic panic=86400 workqueue.watchdog_thresh=140 nopti
KERNEL supported cpus:
  Intel GenuineIntel
  AMD AuthenticAMD
x86/fpu: xstate_offset[2]:  576, xstate_sizes[2]:  256
x86/fpu: Supporting XSAVE feature 0x01: 'x87 floating point registers'
x86/fpu: Supporting XSAVE feature 0x02: 'SSE registers'
x86/fpu: Supporting XSAVE feature 0x04: 'AVX registers'
x86/fpu: Enabled xstate features 0x7, context size is 832 bytes, using 'standard' format.
e820: BIOS-provided physical RAM map:
BIOS-e820: [mem 0x0000000000000000-0x000000000009fbff] usable
BIOS-e820: [mem 0x000000000009fc00-0x000000000009ffff] reserved
BIOS-e820: [mem 0x00000000000f0000-0x00000000000fffff] reserved
BIOS-e820: [mem 0x0000000000100000-0x00000000bfffcfff] usable
BIOS-e820: [mem 0x00000000bfffd000-0x00000000bfffffff] reserved
BIOS-e820: [mem 0x00000000fffbc000-0x00000000ffffffff] reserved
BIOS-e820: [mem 0x0000000100000000-0x000000021fffffff] usable
bootconsole [earlyser0] enabled
NX (Execute Disable) protection: active
Hypervisor detected: KVM
Kernel/User page tables isolation: disabled
e820: last_pfn = 0x220000 max_arch_pfn = 0x400000000
x86/PAT: Configuration [0-7]: WB  WC  UC- UC  UC  UC  UC  UC  
e820: last_pfn = 0xbfffd max_arch_pfn = 0x400000000
found SMP MP-table at [mem 0x000f2c80-0x000f2c8f] mapped at [ffff8800000f2c80]
Using GB pages for direct mapping
ACPI: Early table checksum verification disabled
ACPI: RSDP 0x00000000000F2A10 000014 (v00 Google)
ACPI: RSDT 0x00000000BFFFDA50 000038 (v01 Google GOOGRSDT 00000001 GOOG 00000001)
ACPI: FACP 0x00000000BFFFFF00 0000F4 (v02 Google GOOGFACP 00000001 GOOG 00000001)
ACPI: DSDT 0x00000000BFFFDA90 0018BA (v01 Google GOOGDSDT 00000001 GOOG 00000001)
ACPI: FACS 0x00000000BFFFFEC0 000040
ACPI: FACS 0x00000000BFFFFEC0 000040
ACPI: SSDT 0x00000000BFFFF540 000980 (v01 Google GOOGSSDT 00000001 GOOG 00000001)
ACPI: APIC 0x00000000BFFFF450 000076 (v01 Google GOOGAPIC 00000001 GOOG 00000001)
ACPI: WAET 0x00000000BFFFF420 000028 (v01 Google GOOGWAET 00000001 GOOG 00000001)
ACPI: SRAT 0x00000000BFFFF350 0000C8 (v01 Google GOOGSRAT 00000001 GOOG 00000001)
kvm-clock: Using msrs 4b564d01 and 4b564d00
kvm-clock: cpu 0, msr 2:1fffd001, primary cpu clock
kvm-clock: using sched offset of 1815178060 cycles
clocksource: kvm-clock: mask: 0xffffffffffffffff max_cycles: 0x1cd42e4dffb, max_idle_ns: 881590591483 ns
Zone ranges:
  DMA32    [mem 0x0000000000001000-0x00000000ffffffff]
  Normal   [mem 0x0000000100000000-0x000000021fffffff]
Movable zone start for each node
Early memory node ranges
  node   0: [mem 0x0000000000001000-0x000000000009efff]
  node   0: [mem 0x0000000000100000-0x00000000bfffcfff]
  node   0: [mem 0x0000000100000000-0x000000021fffffff]
Initmem setup node 0 [mem 0x0000000000001000-0x000000021fffffff]
kasan: KernelAddressSanitizer initialized
ACPI: PM-Timer IO Port: 0xb008
ACPI: LAPIC_NMI (acpi_id[0xff] dfl dfl lint[0x1])
IOAPIC[0]: apic_id 0, version 17, address 0xfec00000, GSI 0-23
ACPI: INT_SRC_OVR (bus 0 bus_irq 5 global_irq 5 high level)
ACPI: INT_SRC_OVR (bus 0 bus_irq 9 global_irq 9 high level)
ACPI: INT_SRC_OVR (bus 0 bus_irq 10 global_irq 10 high level)
ACPI: INT_SRC_OVR (bus 0 bus_irq 11 global_irq 11 high level)
Using ACPI (MADT) for SMP configuration information
smpboot: Allowing 2 CPUs, 0 hotplug CPUs
e820: [mem 0xc0000000-0xfffbbfff] available for PCI devices
Booting paravirtualized kernel on KVM
clocksource: refined-jiffies: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 19112604462750000 ns
setup_percpu: NR_CPUS:8 nr_cpumask_bits:8 nr_cpu_ids:2 nr_node_ids:1
PERCPU: Embedded 41 pages/cpu @ffff8801db600000 s130696 r8192 d29048 u1048576
Built 1 zonelists in Zone order, mobility grouping on.  Total pages: 1935238
Kernel command line: BOOT_IMAGE=/vmlinuz root=/dev/sda1 console=ttyS0 earlyprintk=serial vsyscall=native rodata=n oops=panic panic_on_warn=1 nmi_watchdog=panic panic=86400 workqueue.watchdog_thresh=140 nopti
PID hash table entries: 4096 (order: 3, 32768 bytes)
Dentry cache hash table entries: 1048576 (order: 11, 8388608 bytes)
Inode-cache hash table entries: 524288 (order: 10, 4194304 bytes)