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

Ben Hutchings ben at decadent.org.uk
Tue Apr 9 22:45:06 UTC 2013

On Mon, 2013-04-08 at 10:50 +0100, Luis Henriques wrote:
> -stable review patch.  If anyone has any objections, please let me know.
> ------------------
> From: Matt Fleming <matt.fleming at intel.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 at suse.com>
> Cc: Matthew Garrett <mjg59 at srcf.ucam.org>
> Cc: Josh Boyer <jwboyer at redhat.com>
> Cc: Michael Schroeder <mls at suse.com>
> Cc: Lee, Chun-Yi <jlee at suse.com>
> Cc: Lingzhu Xiang <lxiang at redhat.com>
> Cc: Seiji Aguchi <seiji.aguchi at hds.com>
> Signed-off-by: Matt Fleming <matt.fleming at intel.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.


Ben Hutchings
Life would be so much easier if we could look at the source code.
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