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SubjectKASAN: use-after-free Read in io_wq_flush
From
Hello,

syzbot found the following crash on:

HEAD commit: 7ddd09fc Add linux-next specific files for 20191220
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=11a074c1e00000
kernel config: https://syzkaller.appspot.com/x/.config?x=f183b01c3088afc6
dashboard link: https://syzkaller.appspot.com/bug?extid=a2cf8365eb32fc6dbb5e
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1190743ee00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=12b97f1ee00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+a2cf8365eb32fc6dbb5e@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in io_wq_flush+0x1f7/0x210 fs/io-wq.c:1009
Read of size 8 at addr ffff88809ea14b00 by task kworker/1:2/2797

CPU: 1 PID: 2797 Comm: kworker/1:2 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 9381:
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 9381:
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 ffff88809ea14b00
which belongs to the cache kmalloc-192 of size 192
The buggy address is located 0 bytes inside of
192-byte region [ffff88809ea14b00, ffff88809ea14bc0)
The buggy address belongs to the page:
page:ffffea00027a8500 refcount:1 mapcount:0 mapping:ffff8880aa400000
index:0x0
raw: 00fffe0000000200 ffffea00027a8148 ffffea00027a8f08 ffff8880aa400000
raw: 0000000000000000 ffff88809ea14000 0000000100000010 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff88809ea14a00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff88809ea14a80: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
> ffff88809ea14b00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff88809ea14b80: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
ffff88809ea14c00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
==================================================================


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
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syzbot can test patches for this bug, for details see:
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