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From:   Seunghun Han <kkamagui@gmail.com>
Date:   Wed, 28 Feb 2018 18:48:45 +0900
Message-ID: <CAHjaAcT2s0v8cZ4dvGZMVOZHzk=2-LpthC2umw7-FfjfsJczjQ@mail.gmail.com>
Subject: Re: [PATCH] x86: mce: fix kernel panic when check_interval is changed
To:     Borislav Petkov <bp@alien8.de>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Tony Luck <tony.luck@intel.com>, linux-edac@vger.kernel.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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Hello, Borislav.

2018-02-28 18:32 GMT+09:00 Borislav Petkov <bp@alien8.de>:
> On Mon, Feb 26, 2018 at 05:05:04AM +0900, Seunghun Han wrote:
>> >> It is a critical security problem because the attacker can make kernel panic
>> >> by writing a value to the check_interval file in userspace, and it can be
>> >> used for Denial-of-Service (DoS) attack.
>> >
>> > As only root can write to that file, it's not that critical of an issue,
>> > but yes, this is a problem.  Nice find and fix.
>
> This is still the wrong fix. You need to:
>
> 1. check the old value of check_interval in store_int_with_restart() and
> exit early if it is the same.
>
> 2. have mce_restart() grab a newly defined mutex, say, mce_sysfs_mutex
> or so, which synchronizes all CPUs so that their timers get deleted and
> reinitialized in the proper order.

Thank you for your advice.
I will change my patch like that and send it again.

Best regard.

Seunghun.

>
> Thx.
>
> --
> Regards/Gruss,
>     Boris.
>
> Good mailing practices for 400: avoid top-posting and trim the reply.