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

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Date:	Tue, 21 Apr 2015 19:03:30 +0300
From:	"Ivan.khoronzhuk" <ivan.khoronzhuk@...ballogic.com>
To:	Jean Delvare <jdelvare@...e.de>
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

Jean,

On 21.04.15 18:36, Jean Delvare wrote:
> Hi again Ivan,
>
> On Mon, 20 Apr 2015 13:19:46 +0300, Ivan Khoronzhuk wrote:
>> +	bin_attr_DMI.size = dmi_len;
>> +	bin_attr_DMI.private = dmi_table;
>> +	ret = sysfs_create_bin_file(tables_kobj, &bin_attr_DMI);
>> +	if (!ret)
>> +		return 0;
> 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.
Let me know when your fix will be ready and I will re-base the
series if it has conflicts.

-- 
Regards,
Ivan Khoronzhuk

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