linux-kernel - Re: [Patch v2 2/3] firmware: dmi_scan: add SBMIOS entry and DMI tables

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Message-ID: <1429788839.4370.1.camel@chaos.site>
Date:	Thu, 23 Apr 2015 13:33:59 +0200
From:	Jean Delvare <jdelvare@...e.de>
To:	"Ivan.khoronzhuk" <ivan.khoronzhuk@...ballogic.com>
Cc:	linux-kernel@...r.kernel.org, matt.fleming@...el.com,
	ard.biesheuvel@...aro.org, grant.likely@...aro.org,
	linux-api@...r.kernel.org, linux-doc@...r.kernel.org,
	mikew@...gle.com, dmidecode-devel@...gnu.org,
	leif.lindholm@...aro.org, msalter@...hat.com, roy.franz@...aro.org
Subject: Re: [Patch v2 2/3] firmware: dmi_scan: add SBMIOS entry and DMI
 tables

Le Tuesday 21 April 2015 à 19:03 +0300, Ivan.khoronzhuk a écrit :
> On 21.04.15 18:36, Jean Delvare wrote:
> > I just found that more work is needed here for the SMBIOS v3 entry
> > point case. These entry points do not specify the exact length of the
> > table, but only its maximum. The real world sample I have access to
> > indeed specifies a maximum length of 6419 bytes, but the actual table
> > only spans over 2373 bytes. It is properly terminated with a type 127
> > DMI structure, so the kernel table parser ignores the garbage after it.
> > The garbage is however exported to user-space above.
> >
> > I taught dmidecode to ignore the garbage, but there are two problem
> > left here. First problem is a waste of memory. Minor issue I suppose,
> > who cares about a few kilobytes these days.
> >
> > Second problem is a security problem. We are leaking the contents of
> > physical memory to user-space. In my case it's filled with 0xffs so no
> > big deal. But what if actual data happens to be stored there? It
> > definitely shouldn't go to user-space.
> >
> > So dmi_len needs to be trimmed to the actual table size before the
> > attribute above is created. I have an idea how this could be
> > implemented easily, let me give it a try.
> >
> > Maybe we should trim the length for previous implementations, too.
> > There is no reason to walk past a type 127 structure anyway, ever.
> >
> 
> It can happen of-cause, I've also thought about that sometime ago,
> but forget...).
> I've sent the updated series already.

Got it, reviewed and ready to push upstream. I'll do so as soon as I'm
done with other duties.

> Let me know when your fix will be ready and I will re-base the
> series if it has conflicts.

Don't worry, I'm quite good at manual conflict resolution :)

Thanks,
-- 
Jean Delvare
SUSE L3 Support

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