==================================================================
BUG: KASAN: use-after-free in locks_remove_flock+0x33c/0x350 fs/locks.c:2567
Read of size 8 at addr ffff8801c78a6458 by task syz-executor3/14865

CPU: 1 PID: 14865 Comm: syz-executor3 Not tainted 4.20.0-rc1-next-20181107+ #107
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x244/0x39d lib/dump_stack.c:113
 print_address_description.cold.7+0x9/0x1ff mm/kasan/report.c:256
 kasan_report_error mm/kasan/report.c:354 [inline]
 kasan_report.cold.8+0x242/0x309 mm/kasan/report.c:412
 __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433
 locks_remove_flock+0x33c/0x350 fs/locks.c:2567
 locks_remove_file+0x148/0x5c0 fs/locks.c:2607
 __fput+0x2f0/0xa70 fs/file_table.c:271
 ____fput+0x15/0x20 fs/file_table.c:312
 task_work_run+0x1e8/0x2a0 kernel/task_work.c:113
 tracehook_notify_resume include/linux/tracehook.h:188 [inline]
 exit_to_usermode_loop+0x318/0x380 arch/x86/entry/common.c:166
 prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline]
 syscall_return_slowpath arch/x86/entry/common.c:268 [inline]
 do_syscall_64+0x6be/0x820 arch/x86/entry/common.c:293
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x457569
Code: fd b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 cb b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f56f6486c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000049
RAX: 0000000000000000 RBX: 0000000000000002 RCX: 0000000000457569
RDX: 0000000000000000 RSI: 0000000000000002 RDI: 0000000000000005
RBP: 000000000072bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f56f64876d4
R13: 00000000004bdd9e R14: 00000000004ccdb8 R15: 00000000ffffffff

Allocated by task 14865:
 save_stack+0x43/0xd0 mm/kasan/kasan.c:448
 set_track mm/kasan/kasan.c:460 [inline]
 kasan_kmalloc+0xc7/0xe0 mm/kasan/kasan.c:553
 kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:490
 kmem_cache_alloc+0x12e/0x730 mm/slab.c:3554
 kmem_cache_zalloc include/linux/slab.h:731 [inline]
 locks_alloc_lock+0x9e/0x300 fs/locks.c:304
 flock_make_lock+0x22c/0x2a0 fs/locks.c:438
 __do_sys_flock fs/locks.c:2057 [inline]
 __se_sys_flock fs/locks.c:2038 [inline]
 __x64_sys_flock+0x12b/0x350 fs/locks.c:2038
 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 14865:
 save_stack+0x43/0xd0 mm/kasan/kasan.c:448
 set_track mm/kasan/kasan.c:460 [inline]
 __kasan_slab_free+0x102/0x150 mm/kasan/kasan.c:521
 kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528
 __cache_free mm/slab.c:3498 [inline]
 kmem_cache_free+0x83/0x290 mm/slab.c:3760
 locks_free_lock+0x295/0x420 fs/locks.c:341
 __do_sys_flock fs/locks.c:2078 [inline]
 __se_sys_flock fs/locks.c:2038 [inline]
 __x64_sys_flock+0x289/0x350 fs/locks.c:2038
 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff8801c78a6418
 which belongs to the cache file_lock_cache of size 264
The buggy address is located 64 bytes inside of
 264-byte region [ffff8801c78a6418, ffff8801c78a6520)
The buggy address belongs to the page:
page:ffffea00071e2980 count:1 mapcount:0 mapping:ffff8801d9a1c3c0 index:0xffff8801c78a6d10
flags: 0x2fffc0000000200(slab)
raw: 02fffc0000000200 ffff8801d9a82f38 ffffea0006f1d108 ffff8801d9a1c3c0
raw: ffff8801c78a6d10 ffff8801c78a6040 0000000100000009 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801c78a6300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801c78a6380: fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc fc
>ffff8801c78a6400: fc fc fc fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                    ^
 ffff8801c78a6480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801c78a6500: fb fb fb fb fc fc fc fc fc fc fc fc 00 00 00 00
==================================================================