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

[Lingzhu Xiang]

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@xxxxxxxxx>
> >
> > 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@xxxxxxxx>
> > Cc: Matthew Garrett <mjg59@xxxxxxxxxxxxx>
> > Cc: Josh Boyer <jwboyer@xxxxxxxxxx>
> > Cc: Michael Schroeder <mls@xxxxxxxx>
> > Cc: Lee, Chun-Yi <jlee@xxxxxxxx>
> > Cc: Lingzhu Xiang <lxiang@xxxxxxxxxx>
> > Cc: Seiji Aguchi <seiji.aguchi@xxxxxxx>
> > Signed-off-by: Matt Fleming <matt.fleming@xxxxxxxxx>
> > [ 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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