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

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Message-ID: <149ae818c30.2806.85c95baa4474aabc7814e68940a78392@paul-moore.com>
Date:	Fri, 14 Nov 2014 08:32:48 -0500
From:	Paul Moore <paul@...l-moore.com>
To:	Richard Guy Briggs <rgb@...hat.com>, 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

My apologies, yes I was concerned about LATEST. Try the test that Steve 
described and if that works I'm happy.
--
paul moore
www.paul-moore.com



On November 13, 2014 8:09:11 PM Richard Guy Briggs <rgb@...hat.com> wrote:

> 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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