[PATCH] audit: shorten PATH cap values when zero

[Steve Grubb]

On Friday, November 16, 2018 12:10:01 PM EST Richard Guy Briggs 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>

Ack. 

Thanks for doing this. It helps to alleviate my concern about wasted disk 
space for normal files.

-Steve

> ---
>  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) {
> +		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);
>  	}
>  }