linux-kernel - Re: [PATCH v3] audit: Turn off TIF_SYSCALL

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Message-ID: <CALCETrXReQ_AT9W4At4VZnyqnaYgTBB3X8-_V=-qJnucGjV2rg@mail.gmail.com>
Date:	Mon, 10 Feb 2014 12:04:07 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Steve Grubb <sgrubb@...hat.com>
Cc:	Oleg Nesterov <oleg@...hat.com>, linux-audit@...hat.com,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andi Kleen <andi@...stfloor.org>,
	Eric Paris <eparis@...hat.com>
Subject: Re: [PATCH v3] audit: Turn off TIF_SYSCALL_AUDIT when there are no rules

On Mon, Feb 10, 2014 at 11:12 AM, Steve Grubb <sgrubb@...hat.com> wrote:
> On Monday, February 10, 2014 11:01:36 AM Andy Lutomirski wrote:
>> >> And I still think this needs more changes. Once again, I do not think
>> >> that, say, __audit_log_bprm_fcaps() should populate context->aux if
>> >> !TIF_SYSCALL_AUDIT, this list can grow indefinitely. Or
>> >> __audit_signal_info()...
>> >>
>> >> Perhaps __audit_syscall_exit() should also set context->dummy?
>> >
>> > That would work.
>> >
>> > I'm still torn between trying to make it possible for things like
>> > __audit_log_bprm_fcaps to start a syscall audit record in the middle
>> > of a syscall or to just try to tighten up the current approach to the
>> > point where it will work correctly.
>>
>> This is worse than I thought.  Things like signal auditing can enter
>> the audit system from outside of a syscall.  I don't think there's
>> currently any way to tell whether you're in a syscall (when
>> TIF_SYSCALL_AUDIT is clear) so getting this to work right would
>> require arch help.
>>
>> I'll ask what people on the Fedora list think about just changing the
>> default to -t task,never.
>
> I can't recall ever seeing the task filter used in real life. But assuming you
> wanted to audit no tasks, what is the difference between using that filter and
> never setting audit_enable in the first place?

Two possible differences:

1. You can toggle it both ways at runtime.  Setting audit_enabled is a
one-way street (at least as far TIF_SYSCALL_AUDIT is concerned).

2. Do AVC denial messages still get logged if audit_enable == 0?  If
not, then audit_enable is a non-starter.

--Andy
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