Date:   Wed, 23 Dec 2020 23:14:24 +0000
From:   Pavel Begunkov <asml.silence@...il.com>
To:     syzbot <syzbot+fef004c4db2d363bacd3@...kaller.appspotmail.com>,
        axboe@...nel.dk, io-uring@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        syzkaller-bugs@...glegroups.com, viro@...iv.linux.org.uk
Subject: Re: KASAN: use-after-free Read in io_ring_ctx_wait_and_kill

On 20/12/2020 01:24, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    a409ed15 Merge tag 'gpio-v5.11-1' of git://git.kernel.org/..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=1425527b500000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=f7c39e7211134bc0
> dashboard link: https://syzkaller.appspot.com/bug?extid=fef004c4db2d363bacd3
> compiler:       gcc (GCC) 10.1.0-syz 20200507
> 
> Unfortunately, I don't have any reproducer for this issue yet.

#syz dup: WARNING in percpu_ref_kill_and_confirm (2)

> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+fef004c4db2d363bacd3@...kaller.appspotmail.com
> 
> ==================================================================
> BUG: KASAN: use-after-free in __mutex_lock_common kernel/locking/mutex.c:938 [inline]
> BUG: KASAN: use-after-free in __mutex_lock+0x102f/0x1110 kernel/locking/mutex.c:1103
> Read of size 8 at addr ffff888073de33e0 by task syz-executor.1/13101
> 
> CPU: 1 PID: 13101 Comm: syz-executor.1 Not tainted 5.10.0-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:79 [inline]
>  dump_stack+0x107/0x163 lib/dump_stack.c:120
>  print_address_description.constprop.0.cold+0xae/0x4c8 mm/kasan/report.c:385
>  __kasan_report mm/kasan/report.c:545 [inline]
>  kasan_report.cold+0x1f/0x37 mm/kasan/report.c:562
>  __mutex_lock_common kernel/locking/mutex.c:938 [inline]
>  __mutex_lock+0x102f/0x1110 kernel/locking/mutex.c:1103
>  io_ring_ctx_wait_and_kill+0x21/0x450 fs/io_uring.c:8648
>  io_uring_release+0x3e/0x50 fs/io_uring.c:8687
>  __fput+0x283/0x920 fs/file_table.c:280
>  task_work_run+0xdd/0x190 kernel/task_work.c:140
>  exit_task_work include/linux/task_work.h:30 [inline]
>  do_exit+0xb89/0x2a00 kernel/exit.c:823
>  do_group_exit+0x125/0x310 kernel/exit.c:920
>  get_signal+0x3e9/0x2160 kernel/signal.c:2770
>  arch_do_signal_or_restart+0x2a8/0x1eb0 arch/x86/kernel/signal.c:811
>  handle_signal_work kernel/entry/common.c:147 [inline]
>  exit_to_user_mode_loop kernel/entry/common.c:171 [inline]
>  exit_to_user_mode_prepare+0x124/0x200 kernel/entry/common.c:201
>  __syscall_exit_to_user_mode_work kernel/entry/common.c:291 [inline]
>  syscall_exit_to_user_mode+0x19/0x50 kernel/entry/common.c:302
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> RIP: 0033:0x45e149
> Code: Unable to access opcode bytes at RIP 0x45e11f.
> RSP: 002b:00007f2290236be8 EFLAGS: 00000206 ORIG_RAX: 00000000000001a9
> RAX: fffffffffffffff4 RBX: 0000000020000080 RCX: 000000000045e149
> RDX: 00000000200b0000 RSI: 0000000020000080 RDI: 0000000000000001
> RBP: 000000000119c080 R08: 0000000020000000 R09: 0000000020000000
> R10: 0000000020000100 R11: 0000000000000206 R12: 00000000200b0000
> R13: 00000000200a0000 R14: 0000000020000000 R15: 0000000020000100
> 
> Allocated by task 13101:
>  kasan_save_stack+0x1b/0x40 mm/kasan/common.c:48
>  kasan_set_track mm/kasan/common.c:56 [inline]
>  __kasan_kmalloc.constprop.0+0xc2/0xd0 mm/kasan/common.c:461
>  kmalloc include/linux/slab.h:552 [inline]
>  kzalloc include/linux/slab.h:682 [inline]
>  io_ring_ctx_alloc fs/io_uring.c:1268 [inline]
>  io_uring_create fs/io_uring.c:9480 [inline]
>  io_uring_setup+0x1d5b/0x38b0 fs/io_uring.c:9613
>  do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> Freed by task 37:
>  kasan_save_stack+0x1b/0x40 mm/kasan/common.c:48
>  kasan_set_track+0x1c/0x30 mm/kasan/common.c:56
>  kasan_set_free_info+0x1b/0x30 mm/kasan/generic.c:352
>  __kasan_slab_free+0x102/0x140 mm/kasan/common.c:422
>  slab_free_hook mm/slub.c:1544 [inline]
>  slab_free_freelist_hook+0x5d/0x150 mm/slub.c:1577
>  slab_free mm/slub.c:3140 [inline]
>  kfree+0xdb/0x3c0 mm/slub.c:4122
>  process_one_work+0x98d/0x1630 kernel/workqueue.c:2275
>  worker_thread+0x64c/0x1120 kernel/workqueue.c:2421
>  kthread+0x3b1/0x4a0 kernel/kthread.c:292
>  ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296
> 
> Last potentially related work creation:
>  kasan_save_stack+0x1b/0x40 mm/kasan/common.c:48
>  kasan_record_aux_stack+0xc0/0xf0 mm/kasan/generic.c:343
>  insert_work+0x48/0x370 kernel/workqueue.c:1331
>  __queue_work+0x5c1/0xfb0 kernel/workqueue.c:1497
>  queue_work_on+0xc7/0xd0 kernel/workqueue.c:1524
>  io_uring_create fs/io_uring.c:9586 [inline]
>  io_uring_setup+0x1358/0x38b0 fs/io_uring.c:9613
>  do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> The buggy address belongs to the object at ffff888073de3000
>  which belongs to the cache kmalloc-2k of size 2048
> The buggy address is located 992 bytes inside of
>  2048-byte region [ffff888073de3000, ffff888073de3800)
> The buggy address belongs to the page:
> page:000000002686ff6f refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x73de0
> head:000000002686ff6f order:3 compound_mapcount:0 compound_pincount:0
> flags: 0xfff00000010200(slab|head)
> raw: 00fff00000010200 dead000000000100 dead000000000122 ffff888010842000
> raw: 0000000000000000 0000000000080008 00000001ffffffff 0000000000000000
> page dumped because: kasan: bad access detected
> 
> Memory state around the buggy address:
>  ffff888073de3280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff888073de3300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>> ffff888073de3380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>                                                        ^
>  ffff888073de3400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff888073de3480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ==================================================================
> 
> 
> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@...glegroups.com.
> 
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> 

-- 
Pavel Begunkov

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