[PATCH] audit: shorten PATH cap values when zero

[Paul Moore]

On Fri, Nov 16, 2018 at 12:10 PM Richard Guy Briggs <rgb at redhat.com> wrote:
>
> Since the vast majority of files (99.993% on a typical system) have no
> fcaps, display "0" instead of the full zero-padded 16 hex digits in the
> two PATH record cap_f* fields to save netlink bandwidth and disk space.
>
> Simply changing the format to %x won't work since the value is two (or
> possibly more in the future) 32-bit hexadecimal values concatenated and
> bits in higher order values will be misrepresented.
>
> Passes audit-testsuite and userspace tools already work fine.
> Please see the github issue tracker for more details
> https://github.com/linux-audit/audit-kernel/issues/101
>
> Signed-off-by: Richard Guy Briggs <rgb at redhat.com>
> ---
>  kernel/audit.c | 15 ++++++++++-----
>  1 file changed, 10 insertions(+), 5 deletions(-)
>
> diff --git a/kernel/audit.c b/kernel/audit.c
> index 2a8058764aa6..90cbc89fd6d2 100644
> --- a/kernel/audit.c
> +++ b/kernel/audit.c
> @@ -2057,11 +2057,16 @@ void audit_log_key(struct audit_buffer *ab, char *key)
>  void audit_log_cap(struct audit_buffer *ab, char *prefix, kernel_cap_t *cap)
>  {
>         int i;
> -
> -       audit_log_format(ab, " %s=", prefix);
> -       CAP_FOR_EACH_U32(i) {
> -               audit_log_format(ab, "%08x",
> -                                cap->cap[CAP_LAST_U32 - i]);
> +       u32 nonzero = 0;
> +
> +       CAP_FOR_EACH_U32(i)
> +               nonzero |= cap->cap[CAP_LAST_U32 - i];
> +       if (nonzero) {

Let's use the existing cap_isclear() instead.  I'll admit it is pretty
trivial, but somebody is surely going to complain about the
open-coding at some point so let's fix it now.

> +               audit_log_format(ab, " %s=", prefix);
> +               CAP_FOR_EACH_U32(i)
> +                       audit_log_format(ab, "%08x", cap->cap[CAP_LAST_U32 - i]);
> +       } else {
> +               audit_log_format(ab, " %s=0", prefix);

Since you're doing a re-spin, you might as well drop the curly braces
here, they aren't needed.

>         }
>  }

-- 
paul moore
www.paul-moore.com