Why is syscall auditing on with no rules?

[Andy Lutomirski]

On Sat, Feb 1, 2014 at 6:32 PM, Andy Lutomirski <luto at amacapital.net> wrote:
> On a stock Fedora installation:
>
> $ sudo auditctl -l
> No rules
>
> Nonetheless TIF_SYSCALL_AUDIT is set and the __audit_syscall_entry and
> __audit_syscall_exit account for >20% of syscall overhead according to
> perf.
>
> This sucks.  Unless I'm missing something, syscall auditing is *off*.
>
> How hard would it be to arrange for TIF_SYSCALL_AUDIT to be cleared
> when there are no syscall rules?
>
> (This is extra bad in kernels before 3.13, where the clear call for
> TIF_SYSCALL_AUDIT was completely missing.)

The current code seems to have really odd effects.  For example,
processes that are created before the very first auditctl -e 1 (or
auditd) invocation will never be subject to syscall auditing.  But
auditctl -e 1; auditctl -e 0 will cause all subsequently started
processes to have audit contexts allocated and therefore to be subject
to syscall auditing.

I doubt that this behavior is considered desirable.

--Andy

>
> --Andy



-- 
Andy Lutomirski
AMA Capital Management, LLC