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

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Message-ID: <20130411091256.GA11370@hercules>
Date:	Thu, 11 Apr 2013 10:12:56 +0100
From:	Luis Henriques <luis.henriques@...onical.com>
To:	Seiji Aguchi <seiji.aguchi@....com>
Cc:	Lingzhu Xiang <lxiang@...hat.com>,
	Ben Hutchings <ben@...adent.org.uk>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"stable@...r.kernel.org" <stable@...r.kernel.org>,
	"kernel-team@...ts.ubuntu.com" <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 Wed, Apr 10, 2013 at 03:57:12PM +0000, Seiji Aguchi wrote:
> 
> 
> > -----Original Message-----
> > From: Luis Henriques [mailto:luis.henriques@...onical.com]
> > Sent: Wednesday, April 10, 2013 8:18 AM
> > To: Lingzhu Xiang
> > Cc: Ben Hutchings; Seiji Aguchi; linux-kernel@...r.kernel.org; stable@...r.kernel.org; kernel-team@...ts.ubuntu.com; Matthew
> > Garrett; Josh Boyer; Michael Schroeder; Lee, Chun-Yi; Matt Fleming
> > Subject: Re: [PATCH 097/102] efivars: explicitly calculate length of VariableName
> > 
> > On Wed, Apr 10, 2013 at 06:27:13PM +0800, Lingzhu Xiang wrote:
> > > 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?
> > 
> > Ok, so just to clarify: you're suggesting me to pick the following commits:
> > 
> > 81fa4e581d9283f7992a0d8c534bb141eb840a14 efivars: Disable external interrupt while holding efivars->lock
> > a93bc0c6e07ed9bac44700280e65e2945d864fd4 efi_pstore: Introducing workqueue updating sysfs
> > ec50bd32f1672d38ddce10fb1841cbfda89cfe9a efivars: explicitly calculate length of VariableName
> > e971318bbed610e28bb3fde9d548e6aaf0a6b02e efivars: Handle duplicate names from get_next_variable()
> 
> I agree to add these commits to a stable tree.
> 
Thank you Seiji.  I'll queue these for the next 3.5 kernel.

Cheers,
--
Luis
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