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BUG: KASAN: use-after-free in io_wq_flush+0x1f7/0x210 fs/io-wq.c:1009
Read of size 8 at addr ffff8880a949fc00 by task kworker/0:2/2739

CPU: 0 PID: 2739 Comm: kworker/0:2 Not tainted 5.5.0-rc2-next-20191220-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: events io_ring_file_ref_switch
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x197/0x210 lib/dump_stack.c:118
 print_address_description.constprop.0.cold+0xd4/0x30b mm/kasan/report.c:374
 __kasan_report.cold+0x1b/0x41 mm/kasan/report.c:506
 kasan_report+0x12/0x20 mm/kasan/common.c:639
 __asan_report_load8_noabort+0x14/0x20 mm/kasan/generic_report.c:135
 io_wq_flush+0x1f7/0x210 fs/io-wq.c:1009
 io_destruct_skb+0x8e/0xc0 fs/io_uring.c:4668
 skb_release_head_state+0xeb/0x260 net/core/skbuff.c:652
 skb_release_all+0x16/0x60 net/core/skbuff.c:663
 __kfree_skb net/core/skbuff.c:679 [inline]
 kfree_skb net/core/skbuff.c:697 [inline]
 kfree_skb+0x101/0x420 net/core/skbuff.c:691
 io_ring_file_put fs/io_uring.c:4836 [inline]
 io_ring_file_ref_switch+0x68a/0xac0 fs/io_uring.c:4881
 process_one_work+0x9af/0x1740 kernel/workqueue.c:2264
 worker_thread+0x98/0xe40 kernel/workqueue.c:2410
 kthread+0x361/0x430 kernel/kthread.c:255
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352

Allocated by task 9522:
 save_stack+0x23/0x90 mm/kasan/common.c:72
 set_track mm/kasan/common.c:80 [inline]
 __kasan_kmalloc mm/kasan/common.c:513 [inline]
 __kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:486
 kasan_kmalloc+0x9/0x10 mm/kasan/common.c:527
 kmem_cache_alloc_trace+0x158/0x790 mm/slab.c:3551
 kmalloc include/linux/slab.h:555 [inline]
 kzalloc include/linux/slab.h:669 [inline]
 io_wq_create+0x52/0xa40 fs/io-wq.c:1024
 io_sq_offload_start fs/io_uring.c:5244 [inline]
 io_uring_create fs/io_uring.c:6002 [inline]
 io_uring_setup+0xf4a/0x2080 fs/io_uring.c:6062
 __do_sys_io_uring_setup fs/io_uring.c:6075 [inline]
 __se_sys_io_uring_setup fs/io_uring.c:6072 [inline]
 __x64_sys_io_uring_setup+0x54/0x80 fs/io_uring.c:6072
 do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 9520:
 save_stack+0x23/0x90 mm/kasan/common.c:72
 set_track mm/kasan/common.c:80 [inline]
 kasan_set_free_info mm/kasan/common.c:335 [inline]
 __kasan_slab_free+0x102/0x150 mm/kasan/common.c:474
 kasan_slab_free+0xe/0x10 mm/kasan/common.c:483
 __cache_free mm/slab.c:3426 [inline]
 kfree+0x10a/0x2c0 mm/slab.c:3757
 io_wq_destroy+0x2ce/0x3c0 fs/io-wq.c:1116
 io_finish_async+0x128/0x1b0 fs/io_uring.c:4657
 io_ring_ctx_free fs/io_uring.c:5569 [inline]
 io_ring_ctx_wait_and_kill+0x330/0x9a0 fs/io_uring.c:5644
 io_uring_release+0x42/0x50 fs/io_uring.c:5652
 __fput+0x2ff/0x890 fs/file_table.c:280
 ____fput+0x16/0x20 fs/file_table.c:313
 task_work_run+0x145/0x1c0 kernel/task_work.c:113
 tracehook_notify_resume include/linux/tracehook.h:188 [inline]
 exit_to_usermode_loop+0x316/0x380 arch/x86/entry/common.c:164
 prepare_exit_to_usermode arch/x86/entry/common.c:195 [inline]
 syscall_return_slowpath arch/x86/entry/common.c:278 [inline]
 do_syscall_64+0x676/0x790 arch/x86/entry/common.c:304
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff8880a949fc00
 which belongs to the cache kmalloc-192 of size 192
The buggy address is located 0 bytes inside of
 192-byte region [ffff8880a949fc00, ffff8880a949fcc0)
The buggy address belongs to the page:
page:ffffea0002a527c0 refcount:1 mapcount:0 mapping:ffff8880aa400000 index:0x0
raw: 00fffe0000000200 ffffea0002a535c8 ffffea0002a36788 ffff8880aa400000
raw: 0000000000000000 ffff8880a949f000 0000000100000010 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8880a949fb00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff8880a949fb80: 00 00 fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff8880a949fc00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                   ^
 ffff8880a949fc80: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
 ffff8880a949fd00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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