> In message <1282586177.2681.43.camel@localhost.localdomain> you wrote:
> > On Fri, 2010-08-20 at 12:13 +1000, Michael Neuling wrote:
> > > We found that when auditing is disabled using "auditctl -D", that
> > > there's still a significant overhead when doing syscalls. This overhead
> > > is not present when a single never rule is inserted using "auditctl -a
> > > task,never".
> > >
> > > Using Anton's null syscall microbenchmark from
> > >
http://ozlabs.org/~anton/junkcode/null_syscall.c we currently have on a
> > > powerpc machine:
> > >
> > > # auditctl -D
> > > No rules
> > > # ./null_syscall
> > > null_syscall: 739.03 cycles 100.00%
> > > # auditctl -a task,never
> > > # ./null_syscall
> > > null_syscall: 204.63 cycles 100.00%
> > >
> > > This doesn't seem right, as we'd hope that auditing would have the same
> > > minimal impact when disabled via -D as when we have a single never rule.
> > >
> > > The patch below creates a fast path when initialising a task. If the
> > > rules list for tasks is empty (the disabled -D option), we mark auditing
> > > as disabled for this task.
> > >
> > > When this is applied, our null syscall benchmark improves in the
> > > disabled case to match the single never rule case.
> > >
> > > # auditctl -D
> > > No rules
> > > # ./null_syscall
> > > null_syscall: 204.62 cycles 100.00%
> > > # auditctl -a task,never
> > > # ./null_syscall
> > > null_syscall: 204.63 cycles 100.00%
> > >
> > > Reported-by: Anton Blanchard <anton@samba.org>
> > > Signed-off-by: Michael Neuling <mikey@neuling.org>
> > > ---
> > > I'm not familiar with the auditing code/infrastructure so I may have
> > > misunderstood something here
> > >
> > > diff --git a/kernel/auditsc.c b/kernel/auditsc.c
> > > index 1b31c13..1cd6ec7 100644
> > > --- a/kernel/auditsc.c
> > > +++ b/kernel/auditsc.c
> > > @@ -666,6 +666,11 @@ static enum audit_state audit_filter_task(struct task_
> struct *tsk, char **key)
> > > enum audit_state state;
> > >
> > > rcu_read_lock();
> > > + /* Fast path. If the list is empty, disable auditing */
> > > + if (list_empty(&audit_filter_list[AUDIT_FILTER_TASK])) {
> > > + rcu_read_unlock();
> > > + return AUDIT_DISABLED;
> > > + }
> > > list_for_each_entry_rcu(e, &audit_filter_list[AUDIT_FILTER_TASK], list)
> {
> > > if (audit_filter_rules(tsk, &e->rule, NULL, NULL, &state)) {
> > > if (state == AUDIT_RECORD_CONTEXT)
> >
> > I don't think this works at all. I don't see how syscall audit'ing can
> > work. What if I have nothing in the AUDIT_FILTER_TASK list but I want
> > to audit all 'open(2)' syscalls? This patch is going to leave the task
> > in the DISABLED state and we won't ever be able to match on the syscall
> > rules.
>
> Sorry my bad. I'm not too familiar with the audit infrastructure.
>
> On reflection, we might have a bug in audit_alloc though. Currently we
> have this:
>
> int audit_alloc(struct task_struct *tsk)
> {
> <snip>
> state = audit_filter_task(tsk, &key);
> if (likely(state == AUDIT_DISABLED))
> return 0;
>
> <snip>
> set_tsk_thread_flag(tsk, TIF_SYSCALL_AUDIT);
> return 0;
> }
>
> This gets called on fork. If we have "task,never" rule, we hit this
> state == AUDIT_DISABLED path, return immediately and the tasks
> TIF_SYSCALL_AUDIT flags doesn't get set. On powerpc, we check
> TIF_SYSCALL_AUDIT in asm on syscall entry to fast path not calling the
> syscall audit code.
