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

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Date:	Thu, 13 Nov 2014 20:01:45 -0500
From:	Richard Guy Briggs <rgb@...hat.com>
To:	Joe Perches <joe@...ches.com>
Cc:	linux-audit@...hat.com, linux-kernel@...r.kernel.org,
	sgrubb@...hat.com, eparis@...isplace.org, pmoore@...hat.com
Subject: Re: [PATCH] audit: convert status version to a feature bitmap

On 14/11/13, Joe Perches wrote:
> On Thu, 2014-11-13 at 15:29 -0500, 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.
> 
> Maybe use DECLARE_BITMAP instead of u32 and test_bit/set_bit

I don't think so.  I'd like to code to be readable...  I certainly don't
need the overhead of test/set_bit.  That doesn't look appropriate for
anything in include/uapi/.

> > diff --git 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   )
> > +
> > +/* 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
> >  
> >  				/* Failure-to-log actions */
> >  #define AUDIT_FAIL_SILENT	0
> > @@ -403,7 +409,10 @@ struct audit_status {
> >  	__u32		backlog_limit;	/* waiting messages limit */
> >  	__u32		lost;		/* messages lost */
> >  	__u32		backlog;	/* messages waiting in queue */
> > -	__u32		version;	/* audit api version number */
> > +	union {
> > +		__u32	version;	/* deprecated: audit api version num */
> > +		__u32	feature_bitmap;	/* bitmap of kernel audit features */
> > +	};
> >  	__u32		backlog_wait_time;/* message queue wait timeout */
> >  };
> >  
> > diff --git a/kernel/audit.c b/kernel/audit.c
> > index 8ee4508..c9d0e30 100644
> > --- a/kernel/audit.c
> > +++ b/kernel/audit.c
> > @@ -842,7 +842,7 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
> >  		s.backlog_limit		= audit_backlog_limit;
> >  		s.lost			= atomic_read(&audit_lost);
> >  		s.backlog		= skb_queue_len(&audit_skb_queue);
> > -		s.version		= AUDIT_VERSION_LATEST;
> > +		s.feature_bitmap	= AUDIT_FEATURE_BITMAP;
> >  		s.backlog_wait_time	= audit_backlog_wait_time;
> >  		audit_send_reply(skb, seq, AUDIT_GET, 0, 0, &s, sizeof(s));
> >  		break;

- 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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