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Date:   Thu, 19 Sep 2019 08:36:15 +0200
From:   Greg KH <gregkh@linuxfoundation.org>
To:     Xiaoming Ni <nixiaoming@huawei.com>
Cc:     akpm@linux-foundation.org, vvs@virtuozzo.com,
        torvalds@linux-foundation.org, adobriyan@gmail.com,
        anna.schumaker@netapp.com, arjan@linux.intel.com,
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        viresh.kumar@linaro.org, stable@kernel.org,
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        linux-kernel@vger.kernel.org, linux-nfs@vger.kernel.org,
        netdev@vger.kernel.org
Subject: Re: [PATCH v4 1/3] kernel/notifier.c: intercepting duplicate
 registrations to avoid infinite loops
Message-ID: <20190919063615.GA2069346@kroah.com>
References: <1568861888-34045-1-git-send-email-nixiaoming@huawei.com>
 <1568861888-34045-2-git-send-email-nixiaoming@huawei.com>
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On Thu, Sep 19, 2019 at 10:58:06AM +0800, Xiaoming Ni wrote:
> Registering the same notifier to a hook repeatedly can cause the hook
> list to form a ring or lose other members of the list.
> 
> case1: An infinite loop in notifier_chain_register() can cause soft lockup
>         atomic_notifier_chain_register(&test_notifier_list, &test1);
>         atomic_notifier_chain_register(&test_notifier_list, &test1);
>         atomic_notifier_chain_register(&test_notifier_list, &test2);
> 
> case2: An infinite loop in notifier_chain_register() can cause soft lockup
>         atomic_notifier_chain_register(&test_notifier_list, &test1);
>         atomic_notifier_chain_register(&test_notifier_list, &test1);
>         atomic_notifier_call_chain(&test_notifier_list, 0, NULL);
> 
> case3: lose other hook test2
>         atomic_notifier_chain_register(&test_notifier_list, &test1);
>         atomic_notifier_chain_register(&test_notifier_list, &test2);
>         atomic_notifier_chain_register(&test_notifier_list, &test1);
> 
> case4: Unregister returns 0, but the hook is still in the linked list,
>         and it is not really registered. If you call notifier_call_chain
>         after ko is unloaded, it will trigger oops.
> 
> If the system is configured with softlockup_panic and the same
> hook is repeatedly registered on the panic_notifier_list, it
> will cause a loop panic.
> 
> Add a check in notifier_chain_register(),
> Intercepting duplicate registrations to avoid infinite loops
> 
> Signed-off-by: Xiaoming Ni <nixiaoming@huawei.com>
> Reviewed-by: Vasily Averin <vvs@virtuozzo.com>
> ---
>  kernel/notifier.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)

<formletter>

This is not the correct way to submit patches for inclusion in the
stable kernel tree.  Please read:
    https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for how to do this properly.

</formletter>

Same thing goes for all of the patches in this series.

thanks,

greg k-h