Date: Fri, 15 Aug 2008 13:38:42 +0200
From: Ingo Molnar <mingo@elte.hu>
To: "Darrick J. Wong" <djwong@us.ibm.com>
Cc: Jonathan Corbet <corbet@lwn.net>,
       linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] msr: Fix NULL pointer deref due to msr_open on
	nonexistent CPUs
Message-ID: <20080815113842.GB31348@elte.hu>
References: <20080814224333.GG28450@tree.beaverton.ibm.com>
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* Darrick J. Wong <djwong@us.ibm.com> wrote:

> msr_open tests for someone trying to open a device for a nonexistent CPU.
> However, the function always returns 0, not ret like it should, hence userspace
> can BUG the kernel trivially.  This bug was introduced by the cdev lock_kernel
> pushdown patch last May.
> 
> The BUG can be reproduced with these commands:
> 
> # mknod fubar c 202 8 <-- pick a number less than NR_CPUS that is not
>                           the number of an online CPU
> # cat fubar

applied to tip/x86/urgent - thanks Darrick.

	Ingo
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