linux-kernel - Re: [PATCH] audit: convert status version to a feature bitmap

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Date:	Thu, 13 Nov 2014 20:08:52 -0500
From:	Richard Guy Briggs <rgb@...hat.com>
To:	Paul Moore <pmoore@...hat.com>
Cc:	linux-audit@...hat.com, linux-kernel@...r.kernel.org,
	sgrubb@...hat.com, eparis@...isplace.org
Subject: Re: [PATCH] audit: convert status version to a feature bitmap

On 14/11/13, Paul Moore wrote:
> On Thursday, November 13, 2014 03:29:10 PM Richard Guy Briggs wrote:
> > The version field defined in the audit status structure was found to have
> > limitations in terms of its expressibility of features supported.  This is
> > distict from the get/set features call to be able to command those features
> > that are present.
> > 
> > Converting this field from a version number to a feature bitmap will allow
> > distributions to selectively backport and support certain features and will
> > allow upstream to be able to deprecate features in the future.  It will
> > allow userspace clients to first query the kernel for which features are
> > actually present and supported.  Currently, EINVAL is returned rather than
> > EOPNOTSUP, which isn't helpful in determining if there was an error in the
> > command, or if it simply isn't supported yet.  Past features are not
> > represented by this bitmap, but their use may be converted to EOPNOTSUP if
> > needed in the future.
> > 
> > Since "version" is too generic to convert with a #define, use a union in the
> > struct status, introducing the member "feature_bitmap" unionized with
> > "version".
> > 
> > Convert existing AUDIT_VERSION_* macros over to AUDIT_FEATURE_BITMAP*
> > counterparts, leaving the former for backwards compatibility.
> > 
> > Signed-off-by: Richard Guy Briggs <rgb@...hat.com>
> > ---
> >  include/uapi/linux/audit.h |   17 +++++++++++++----
> >  kernel/audit.c             |    2 +-
> >  2 files changed, 14 insertions(+), 5 deletions(-)
> 
> Looks good for the most part, just a naming nit pick and a question about the 
> deprecated AUDIT_VERSION_* defines; see below ...
> 
> > diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
> > index 4d100c8..74aa584 100644
> > --- a/include/uapi/linux/audit.h
> > +++ b/include/uapi/linux/audit.h
> > @@ -322,9 +322,15 @@ enum {
> >  #define AUDIT_STATUS_BACKLOG_LIMIT	0x0010
> >  #define AUDIT_STATUS_BACKLOG_WAIT_TIME	0x0020
> > 
> > -#define AUDIT_VERSION_BACKLOG_LIMIT	1
> > -#define AUDIT_VERSION_BACKLOG_WAIT_TIME	2
> > -#define AUDIT_VERSION_LATEST AUDIT_VERSION_BACKLOG_WAIT_TIME
> > +#define AUDIT_FEATURE_BITMAP_BACKLOG_LIMIT	0x00000001
> > +#define AUDIT_FEATURE_BITMAP_BACKLOG_WAIT_TIME	0x00000002
> > +#define AUDIT_FEATURE_BITMAP ( AUDIT_FEATURE_BITMAP_BACKLOG_LIMIT | \
> > +				                AUDIT_FEATURE_BITMAP_BACKLOG_WAIT_TIME )
> 
> How about AUDIT_FEATURE_BIMAP_ALL instead of just AUDIT_FEATURE_BITMAP?

Sure, I'm fine with that.

> > +/* deprecated: AUDIT_VERSION_* */
> > +#define AUDIT_VERSION_LATEST 		AUDIT_FEATURE_BITMAP
> > +#define AUDIT_VERSION_BACKLOG_LIMIT	AUDIT_FEATURE_BITMAP_BACKLOG_LIMIT
> > +#define AUDIT_VERSION_BACKLOG_WAIT_TIME
> > ...                                AUDIT_FEATURE_BITMAP_BACKLOG_WAIT_TIME
> 
> So what terrible things happen to userspace if AUDIT_VERSION_BACKLOG_WAIT_TIME 
> becomes 0x03 instead of 0x02?

But it won't.  It gets the value of
AUDIT_FEATURE_BITMAP_BACKLOG_WAIT_TIME, which is 0x00000002.

I think you meant to ask about AUDIT_VERSION_LATEST, which would become 3.

You *did* already ask that question in a previous thread, and there
didn't seem to be a concern.  Steve Grubb could likely answer this
question better than me.

> paul moore

- RGB

--
Richard Guy Briggs <rbriggs@...hat.com>
Senior Software Engineer, Kernel Security, AMER ENG Base Operating Systems, Red Hat
Remote, Ottawa, Canada
Voice: +1.647.777.2635, Internal: (81) 32635, Alt: +1.613.693.0684x3545
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