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

[Luis Henriques]

On Tue, Apr 09, 2013 at 11:45:06PM +0100, 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.

Ok, makes sense to me too.  So here's what I'll do: for this release
I'll just drop this commit and e971318bbed610e28bb3fde9d548e6aaf0a6b02e
('efivars: Handle duplicate names from get_next_variable()').

I'll queue them again for next release along with commit
a93bc0c6e07ed9bac44700280e65e2945d864fd4 ('efi_pstore: Introducing
workqueue updating sysfs').

Thanks for your review Ben.

Cheers,
--
Luis
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