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

Paul Moore
2014-11-13T22:12:06Z

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@redhat.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?

> +/* 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?

--
paul moore
security and virtualization @ redhat