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From: Borislav Petkov <bp@alien8.de>
To: Seunghun Han <kkamagui@gmail.com>
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>
Subject: Re: [PATCH] x86: mce: fix kernel panic when check_interval is changed
Date: Wed, 28 Feb 2018 10:32:39 +0100	[thread overview]
Message-ID: <20180228093238.GA3769@pd.tnic> (raw)
In-Reply-To: <CAHjaAcTVUxm6LnD_3sp2BwGgR9ustuctoHUBFkMD1nZh4o6bTA@mail.gmail.com>

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.

Thx.

-- 
Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.

WARNING: multiple messages have this Message-ID (diff)
From: Borislav Petkov <bp@alien8.de>
To: Seunghun Han <kkamagui@gmail.com>
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>
Subject: x86: mce: fix kernel panic when check_interval is changed
Date: Wed, 28 Feb 2018 10:32:39 +0100	[thread overview]
Message-ID: <20180228093238.GA3769@pd.tnic> (raw)

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.

Thx.

  reply	other threads:[~2018-02-28  9:32 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-02-23 10:13 [PATCH] x86: mce: fix kernel panic when check_interval is changed Seunghun Han
2018-02-23 10:13 ` Seunghun Han
2018-02-23 10:42 ` [PATCH] " Borislav Petkov
2018-02-23 10:42   ` Borislav Petkov
2018-02-23 10:52 ` [PATCH] " Greg Kroah-Hartman
2018-02-23 10:52   ` Greg Kroah-Hartman
2018-02-25 20:05   ` [PATCH] " Seunghun Han
2018-02-25 20:05     ` Seunghun Han
2018-02-28  9:32     ` Borislav Petkov [this message]
2018-02-28  9:32       ` Borislav Petkov
2018-02-28  9:48       ` [PATCH] " Seunghun Han
2018-02-28  9:48         ` Seunghun Han

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