linux-kernel - Re: [PATCH 097/102] efivars: explicitly calculate length of VariableName

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Date:	Wed, 10 Apr 2013 18:27:13 +0800
From:	Lingzhu Xiang <lxiang@...hat.com>
To:	Ben Hutchings <ben@...adent.org.uk>,
	Luis Henriques <luis.henriques@...onical.com>,
	Seiji Aguchi <seiji.aguchi@....com>
CC:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Josh Boyer <jwboyer@...hat.com>,
	Michael Schroeder <mls@...e.com>,
	"Lee, Chun-Yi" <jlee@...e.com>,
	Matt Fleming <matt.fleming@...el.com>
Subject: Re: [PATCH 097/102] efivars: explicitly calculate length of VariableName

On 04/10/2013 06:45 AM, Ben Hutchings wrote:
> On Mon, 2013-04-08 at 10:50 +0100, Luis Henriques wrote:
>> 3.5.7.10 -stable review patch.  If anyone has any objections, please let me know.
>>
>> ------------------
>>
>> From: Matt Fleming <matt.fleming@...el.com>
>>
>> commit ec50bd32f1672d38ddce10fb1841cbfda89cfe9a upstream.
>>
>> It's not wise to assume VariableNameSize represents the length of
>> VariableName, as not all firmware updates VariableNameSize in the same
>> way (some don't update it at all if EFI_SUCCESS is returned). There
>> are even implementations out there that update VariableNameSize with
>> values that are both larger than the string returned in VariableName
>> and smaller than the buffer passed to GetNextVariableName(), which
>> resulted in the following bug report from Michael Schroeder,
>>
>>    > On HP z220 system (firmware version 1.54), some EFI variables are
>>    > incorrectly named :
>>    >
>>    > ls -d /sys/firmware/efi/vars/*8be4d* | grep -v -- -8be returns
>>    > /sys/firmware/efi/vars/dbxDefault-pport8be4df61-93ca-11d2-aa0d-00e098032b8c
>>    > /sys/firmware/efi/vars/KEKDefault-pport8be4df61-93ca-11d2-aa0d-00e098032b8c
>>    > /sys/firmware/efi/vars/SecureBoot-pport8be4df61-93ca-11d2-aa0d-00e098032b8c
>>    > /sys/firmware/efi/vars/SetupMode-Information8be4df61-93ca-11d2-aa0d-00e098032b8c
>>
>> The issue here is that because we blindly use VariableNameSize without
>> verifying its value, we can potentially read garbage values from the
>> buffer containing VariableName if VariableNameSize is larger than the
>> length of VariableName.
>>
>> Since VariableName is a string, we can calculate its size by searching
>> for the terminating NULL character.
>>
>> Reported-by: Frederic Crozat <fcrozat@...e.com>
>> Cc: Matthew Garrett <mjg59@...f.ucam.org>
>> Cc: Josh Boyer <jwboyer@...hat.com>
>> Cc: Michael Schroeder <mls@...e.com>
>> Cc: Lee, Chun-Yi <jlee@...e.com>
>> Cc: Lingzhu Xiang <lxiang@...hat.com>
>> Cc: Seiji Aguchi <seiji.aguchi@....com>
>> Signed-off-by: Matt Fleming <matt.fleming@...el.com>
>> [ Backported for 3.4-stable. Removed workqueue code added in a93bc0c 3.9-rc1. ]
> [...]
>
> I thought the workqueue addition was a worthwhile fix in its own right,
> so for 3.2.y I cherry-picked that as well.

FWIW, the workqueue patch is 1/2 of this patchset[1] fixing closely 
related problems. The other one is 81fa4e58.

[1]: http://article.gmane.org/gmane.linux.kernel/1439570

I tried to avoid pulling too much for stable because the patchset is 
quite large and I suspect the problem it fixes is only theoretical. I 
reported the original bug but was unable to break anything except 
getting call traces with various CONFIG_DEBUG_*.

What's your opinion, Seiji?


Lingzhu Xiang
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