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Subject: Re: [syzbot] KASAN: use-after-free Read in
 check_all_holdout_tasks_trace
To:     paulmck@kernel.org, Dmitry Vyukov <dvyukov@google.com>
Cc:     syzbot <syzbot+7b2b13f4943374609532@syzkaller.appspotmail.com>,
        rcu@vger.kernel.org, Andrew Morton <akpm@linux-foundation.org>,
        Andrii Nakryiko <andrii@kernel.org>,
        Alexei Starovoitov <ast@kernel.org>,
        Jens Axboe <axboe@kernel.dk>, bpf <bpf@vger.kernel.org>,
        Christian Brauner <christian@brauner.io>,
        Daniel Borkmann <daniel@iogearbox.net>,
        John Fastabend <john.fastabend@gmail.com>,
        Martin KaFai Lau <kafai@fb.com>,
        KP Singh <kpsingh@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        netdev <netdev@vger.kernel.org>,
        Shakeel Butt <shakeelb@google.com>,
        Song Liu <songliubraving@fb.com>,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
        Yonghong Song <yhs@fb.com>
References: <000000000000f034fc05c2da6617@google.com>
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 <20210524041350.GJ4441@paulmck-ThinkPad-P17-Gen-1>
 <20210524224602.GA1963972@paulmck-ThinkPad-P17-Gen-1>
From:   "Xu, Yanfei" <yanfei.xu@windriver.com>
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On 5/25/21 6:46 AM, Paul E. McKenney wrote:
> [Please note: This e-mail is from an EXTERNAL e-mail address]
> 
> On Sun, May 23, 2021 at 09:13:50PM -0700, Paul E. McKenney wrote:
>> On Sun, May 23, 2021 at 08:51:56AM +0200, Dmitry Vyukov wrote:
>>> On Fri, May 21, 2021 at 7:29 PM syzbot
>>> <syzbot+7b2b13f4943374609532@syzkaller.appspotmail.com> wrote:
>>>>
>>>> Hello,
>>>>
>>>> syzbot found the following issue on:
>>>>
>>>> HEAD commit:    f18ba26d libbpf: Add selftests for TC-BPF management API
>>>> git tree:       bpf-next
>>>> console output: https://syzkaller.appspot.com/x/log.txt?x=17f50d1ed00000
>>>> kernel config:  https://syzkaller.appspot.com/x/.config?x=8ff54addde0afb5d
>>>> dashboard link: https://syzkaller.appspot.com/bug?extid=7b2b13f4943374609532
>>>>
>>>> Unfortunately, I don't have any reproducer for this issue yet.
>>>>
>>>> IMPORTANT: if you fix the issue, please add the following tag to the commit:
>>>> Reported-by: syzbot+7b2b13f4943374609532@syzkaller.appspotmail.com
>>>
>>> This looks rcu-related. +rcu mailing list
>>
>> I think I see a possible cause for this, and will say more after some
>> testing and after becoming more awake Monday morning, Pacific time.
> 
> No joy.  From what I can see, within RCU Tasks Trace, the calls to
> get_task_struct() are properly protected (either by RCU or by an earlier
> get_task_struct()), and the calls to put_task_struct() are balanced by
> those to get_task_struct().
> 
> I could of course have missed something, but at this point I am suspecting
> an unbalanced put_task_struct() has been added elsewhere.
> 
> As always, extra eyes on this code would be a good thing.
> 
> If it were reproducible, I would of course suggest bisection.  :-/
> 
>                                                          Thanx, Paul
> 
Hi Paul,

Could it be?

        CPU1                                        CPU2
trc_add_holdout(t, bhp)
//t->usage==2
                                       release_task
                                         put_task_struct_rcu_user
                                           delayed_put_task_struct
                                             ......
                                             put_task_struct(t)
                                             //t->usage==1 

check_all_holdout_tasks_trace
   ->trc_wait_for_one_reader
     ->trc_del_holdout
       ->put_task_struct(t)
       //t->usage==0 and task_struct freed
   READ_ONCE(t->trc_reader_checked)
   //ops， t had been freed.

So, after excuting trc_wait_for_one_reader（）, task might had been 
removed from holdout list and the corresponding task_struct was freed.
And we shouldn't do READ_ONCE(t->trc_reader_checked).

I investigate the trc_wait_for_one_reader（） and found before we excute 
trc_del_holdout, there is always set t->trc_reader_checked=true. How 
about we just set the checked flag and unified excute trc_del_holdout()
in check_all_holdout_tasks_trace with checking the flag?


Thanks,
Yanfei


>>>> ==================================================================
>>>> BUG: KASAN: use-after-free in check_all_holdout_tasks_trace+0x302/0x420 kernel/rcu/tasks.h:1084
>>>> Read of size 1 at addr ffff88802767a05c by task rcu_tasks_trace/12
>>>>
>>>> CPU: 0 PID: 12 Comm: rcu_tasks_trace Not tainted 5.12.0-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+0x141/0x1d7 lib/dump_stack.c:120
>>>>   print_address_description.constprop.0.cold+0x5b/0x2f8 mm/kasan/report.c:233
>>>>   __kasan_report mm/kasan/report.c:419 [inline]
>>>>   kasan_report.cold+0x7c/0xd8 mm/kasan/report.c:436
>>>>   check_all_holdout_tasks_trace+0x302/0x420 kernel/rcu/tasks.h:1084
>>>>   rcu_tasks_wait_gp+0x594/0xa60 kernel/rcu/tasks.h:358
>>>>   rcu_tasks_kthread+0x31c/0x6a0 kernel/rcu/tasks.h:224
>>>>   kthread+0x3b1/0x4a0 kernel/kthread.c:313
>>>>   ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294
>>>>
>>>> Allocated by task 8477:
>>>>   kasan_save_stack+0x1b/0x40 mm/kasan/common.c:38
>>>>   kasan_set_track mm/kasan/common.c:46 [inline]
>>>>   set_alloc_info mm/kasan/common.c:428 [inline]
>>>>   __kasan_slab_alloc+0x84/0xa0 mm/kasan/common.c:461
>>>>   kasan_slab_alloc include/linux/kasan.h:236 [inline]
>>>>   slab_post_alloc_hook mm/slab.h:524 [inline]
>>>>   slab_alloc_node mm/slub.c:2912 [inline]
>>>>   kmem_cache_alloc_node+0x269/0x3e0 mm/slub.c:2948
>>>>   alloc_task_struct_node kernel/fork.c:171 [inline]
>>>>   dup_task_struct kernel/fork.c:865 [inline]
>>>>   copy_process+0x5c8/0x7120 kernel/fork.c:1947
>>>>   kernel_clone+0xe7/0xab0 kernel/fork.c:2503
>>>>   __do_sys_clone+0xc8/0x110 kernel/fork.c:2620
>>>>   do_syscall_64+0x3a/0xb0 arch/x86/entry/common.c:47
>>>>   entry_SYSCALL_64_after_hwframe+0x44/0xae
>>>>
>>>> Freed by task 12:
>>>>   kasan_save_stack+0x1b/0x40 mm/kasan/common.c:38
>>>>   kasan_set_track+0x1c/0x30 mm/kasan/common.c:46
>>>>   kasan_set_free_info+0x20/0x30 mm/kasan/generic.c:357
>>>>   ____kasan_slab_free mm/kasan/common.c:360 [inline]
>>>>   ____kasan_slab_free mm/kasan/common.c:325 [inline]
>>>>   __kasan_slab_free+0xfb/0x130 mm/kasan/common.c:368
>>>>   kasan_slab_free include/linux/kasan.h:212 [inline]
>>>>   slab_free_hook mm/slub.c:1581 [inline]
>>>>   slab_free_freelist_hook+0xdf/0x240 mm/slub.c:1606
>>>>   slab_free mm/slub.c:3166 [inline]
>>>>   kmem_cache_free+0x8a/0x740 mm/slub.c:3182
>>>>   __put_task_struct+0x26f/0x400 kernel/fork.c:747
>>>>   trc_wait_for_one_reader kernel/rcu/tasks.h:935 [inline]
>>>>   check_all_holdout_tasks_trace+0x179/0x420 kernel/rcu/tasks.h:1081
>>>>   rcu_tasks_wait_gp+0x594/0xa60 kernel/rcu/tasks.h:358
>>>>   rcu_tasks_kthread+0x31c/0x6a0 kernel/rcu/tasks.h:224
>>>>   kthread+0x3b1/0x4a0 kernel/kthread.c:313
>>>>   ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294
>>>>
>>>> Last potentially related work creation:
>>>>   kasan_save_stack+0x1b/0x40 mm/kasan/common.c:38
>>>>   kasan_record_aux_stack+0xe5/0x110 mm/kasan/generic.c:345
>>>>   __call_rcu kernel/rcu/tree.c:3038 [inline]
>>>>   call_rcu+0xb1/0x750 kernel/rcu/tree.c:3113
>>>>   put_task_struct_rcu_user+0x7f/0xb0 kernel/exit.c:180
>>>>   release_task+0xca1/0x1690 kernel/exit.c:226
>>>>   wait_task_zombie kernel/exit.c:1108 [inline]
>>>>   wait_consider_task+0x2fb5/0x3b40 kernel/exit.c:1335
>>>>   do_wait_thread kernel/exit.c:1398 [inline]
>>>>   do_wait+0x724/0xd40 kernel/exit.c:1515
>>>>   kernel_wait4+0x14c/0x260 kernel/exit.c:1678
>>>>   __do_sys_wait4+0x13f/0x150 kernel/exit.c:1706
>>>>   do_syscall_64+0x3a/0xb0 arch/x86/entry/common.c:47
>>>>   entry_SYSCALL_64_after_hwframe+0x44/0xae
>>>>
>>>> Second to last potentially related work creation:
>>>>   kasan_save_stack+0x1b/0x40 mm/kasan/common.c:38
>>>>   kasan_record_aux_stack+0xe5/0x110 mm/kasan/generic.c:345
>>>>   __call_rcu kernel/rcu/tree.c:3038 [inline]
>>>>   call_rcu+0xb1/0x750 kernel/rcu/tree.c:3113
>>>>   put_task_struct_rcu_user+0x7f/0xb0 kernel/exit.c:180
>>>>   context_switch kernel/sched/core.c:4342 [inline]
>>>>   __schedule+0x91e/0x23e0 kernel/sched/core.c:5147
>>>>   preempt_schedule_common+0x45/0xc0 kernel/sched/core.c:5307
>>>>   preempt_schedule_thunk+0x16/0x18 arch/x86/entry/thunk_64.S:35
>>>>   try_to_wake_up+0xa12/0x14b0 kernel/sched/core.c:3489
>>>>   wake_up_process kernel/sched/core.c:3552 [inline]
>>>>   wake_up_q+0x96/0x100 kernel/sched/core.c:597
>>>>   futex_wake+0x3e9/0x490 kernel/futex.c:1634
>>>>   do_futex+0x326/0x1780 kernel/futex.c:3738
>>>>   __do_sys_futex+0x2a2/0x470 kernel/futex.c:3796
>>>>   do_syscall_64+0x3a/0xb0 arch/x86/entry/common.c:47
>>>>   entry_SYSCALL_64_after_hwframe+0x44/0xae
>>>>
>>>> The buggy address belongs to the object at ffff888027679c40
>>>>   which belongs to the cache task_struct of size 6976
>>>> The buggy address is located 1052 bytes inside of
>>>>   6976-byte region [ffff888027679c40, ffff88802767b780)
>>>> The buggy address belongs to the page:
>>>> page:ffffea00009d9e00 refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff88802767b880 pfn:0x27678
>>>> head:ffffea00009d9e00 order:3 compound_mapcount:0 compound_pincount:0
>>>> flags: 0xfff00000010200(slab|head|node=0|zone=1|lastcpupid=0x7ff)
>>>> raw: 00fff00000010200 ffffea000071e208 ffffea0000950808 ffff888140005140
>>>> raw: ffff88802767b880 0000000000040003 00000001ffffffff 0000000000000000
>>>> page dumped because: kasan: bad access detected
>>>> page_owner tracks the page as allocated
>>>> page last allocated via order 3, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 243, ts 14372676818, free_ts 0
>>>>   prep_new_page mm/page_alloc.c:2358 [inline]
>>>>   get_page_from_freelist+0x1033/0x2b60 mm/page_alloc.c:3994
>>>>   __alloc_pages+0x1b2/0x500 mm/page_alloc.c:5200
>>>>   alloc_pages+0x18c/0x2a0 mm/mempolicy.c:2272
>>>>   alloc_slab_page mm/slub.c:1644 [inline]
>>>>   allocate_slab+0x2c5/0x4c0 mm/slub.c:1784
>>>>   new_slab mm/slub.c:1847 [inline]
>>>>   new_slab_objects mm/slub.c:2593 [inline]
>>>>   ___slab_alloc+0x44c/0x7a0 mm/slub.c:2756
>>>>   __slab_alloc.constprop.0+0xa7/0xf0 mm/slub.c:2796
>>>>   slab_alloc_node mm/slub.c:2878 [inline]
>>>>   kmem_cache_alloc_node+0x12f/0x3e0 mm/slub.c:2948
>>>>   alloc_task_struct_node kernel/fork.c:171 [inline]
>>>>   dup_task_struct kernel/fork.c:865 [inline]
>>>>   copy_process+0x5c8/0x7120 kernel/fork.c:1947
>>>>   kernel_clone+0xe7/0xab0 kernel/fork.c:2503
>>>>   kernel_thread+0xb5/0xf0 kernel/fork.c:2555
>>>>   call_usermodehelper_exec_work kernel/umh.c:174 [inline]
>>>>   call_usermodehelper_exec_work+0xcc/0x180 kernel/umh.c:160
>>>>   process_one_work+0x98d/0x1600 kernel/workqueue.c:2275
>>>>   worker_thread+0x64c/0x1120 kernel/workqueue.c:2421
>>>>   kthread+0x3b1/0x4a0 kernel/kthread.c:313
>>>>   ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294
>>>> page_owner free stack trace missing
>>>>
>>>> Memory state around the buggy address:
>>>>   ffff888027679f00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>>>>   ffff888027679f80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>>>>> ffff88802767a000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>>>>                                                      ^
>>>>   ffff88802767a080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>>>>   ffff88802767a100: 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@googlegroups.com.
>>>>
>>>> syzbot will keep track of this issue. See:
>>>> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
>>>>
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