linux-kernel - Re: [BUG]memblock: fix overflow of array index

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Message-ID: <20120426150159.GA27486@google.com>
Date:	Thu, 26 Apr 2012 08:01:59 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Peter Teoh <htmldeveloper@...il.com>
Cc:	linux-kernel@...r.kernel.org,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, linux-mm@...ck.org
Subject: Re: [BUG]memblock: fix overflow of array index

Hello,

On Thu, Apr 26, 2012 at 08:50:58AM +0800, Peter Teoh wrote:
> Thanks for the reply.   Just an educational question:  is it possible
> to set one-byte per memblock?    And what is the minimum memblock
> size?

1 byte.

> Even if 2G memblock is a huge number, it still seemed like a bug to me
> that there is no check on the maximum number (which is 2G) of this
> variable (assuming signed int).   Software can always purposely push
> that number up and the system can panic?

Yeah, if somebody messes the BIOS / firmware to oblivion.  I don't
really care at that point tho.  memblock is a boot time memory
allocator and it assumes BIOS / firmware isn't completely crazy.  It
uses contiguous tables to describe all the blocks, walks them
one-by-one for allocation and even compacts them.

Well before memblock fails from any of the above, the machine would be
failing miserably in firmware / BIOS.

Thanks.

-- 
tejun
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