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

[Luis Henriques]

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@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?

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()

Is this correct?

Cheers,
--
Luis
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