linux-kernel - Re: [PATCH v2.1] audit: Only use the syscall slowpath when syscall audit rules exist

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Date:	Tue, 4 Feb 2014 20:11:29 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	linux-audit@...hat.com,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andi Kleen <andi@...stfloor.org>,
	Steve Grubb <sgrubb@...hat.com>, Eric Paris <eparis@...hat.com>
Subject: Re: [PATCH v2.1] audit: Only use the syscall slowpath when syscall
	audit rules exist

On 02/04, Andy Lutomirski wrote:
>
> On Tue, Feb 4, 2014 at 8:50 AM, Oleg Nesterov <oleg@...hat.com> wrote:
> > On 02/03, Andy Lutomirski wrote:
> >>
> >> +void audit_inc_n_rules()
> >> +{
> >> +     struct task_struct *p, *g;
> >> +     unsigned long flags;
> >> +
> >> +     read_lock_irqsave(&tasklist_lock, flags);
> >
> > Confused... read_lock(tasklist) doesn't need to disable irqs.
> >
> > (ftrace does this for no reason too, perhaps I should resend the patch)
>
> Is this because there are no interrupt handlers that write_lock(tasklist)?

Yes.

> >
> >> +     if (audit_n_rules++ == 0) {
> >
> > probably this can be done outside of read_lock?
>
> I don't think so.  I'm cheating and using the tasklist_lock to prevent
> audit_sync_flags

Ah, yes, you are right.

> >> +             do_each_thread(g, p) {
> >
> > for_each_process_thread ;) do_each_thread will die, I hope.
> >
>
> Sorry, forgot to mention: where is this mythical
> for_each_process_thread?

In Linus's tree, please see 0c740d0afc3bff.

> or you
> just hate do_each_thread so much that you imagined up an alternative
> :)

sort of ;)

> I think I'll wait for Eric to chime in.  I suspect that the real
> solution is to simplify all this stuff by relying on the fact that the
> syscall nr and args are saved by the (fast path and slow path) entry
> code, so the audit entry hook may be entirely unnecessary.

Perhaps... but even in this case we need to do something with, say,
__audit_log_bprm_fcaps().

At least this list should not grow indefinitely if the task skips
__audit_syscall_exit(). Although at first glance this can be probably
cleanuped too.

Oleg.

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