linux-kernel - Re: Suspect loop in dmi_scan

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Message-ID: <1373358947.4391.3.camel@chaos.site>
Date:	Tue, 09 Jul 2013 10:35:47 +0200
From:	Jean Delvare <jdelvare@...e.de>
To:	Ben Hutchings <ben@...adent.org.uk>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: Suspect loop in dmi_scan_machine()

Hi Ben,

Le Monday 08 July 2013 à 17:33 +0100, Ben Hutchings a écrit :
> On Mon, Jul 08, 2013 at 05:49:14PM +0200, Jean Delvare wrote:
> > I am looking at this commit of yours:
> > 
> > https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/drivers/firmware/dmi_scan.c?id=79bae42d51a5d498500c890c19ef76df41d2bf59
> > 
> > and am a little worried about the for loop in dmi_scan_machine()
> > (non-EFI case):
> [...]
> 
> I don't see any of the bugs you describe.  Let me explain what
> I probably should have put in a comment:
> 
> We want to find a DMI header at [0xf0000, 0xffff0] and possibly an
> SMBIOS header 16 bytes before that.  buf contains a copy of the 32
> bytes centred at p.  On the first iteration p - 16 is out of range, so
> the first 16 bytes of the buffer are filled with zeroes.
> 
> Does that address your concerns?  If not then please explain precisely
> how this loop can go wrong.

Wow. I'm not sure what I was up to yesterday evening but I definitely
should have waited a bit before posting. I read your code again this
morning and it is completely correct, and the concerns I raised
yesterday were plain crap. I suppose your code was too smart for my
tired brain...

Sorry for the noise,
-- 
Jean Delvare
Suse L3

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