From: Steve Grubb <sgrubb@redhat.com>
To: Oleg Nesterov <oleg@redhat.com>
Cc: linux-audit@redhat.com, Richard Guy Briggs <rgb@redhat.com>,
        linux-kernel@vger.kernel.org, Kees Cook <keescook@chromium.org>,
        Eric Paris <eparis@redhat.com>
Subject: Re: audit looks unmaintained? [was: Re: [PATCH 11/12] pid: rewrite task helper functions avoiding task->pid and task->tgid]
Date: Fri, 13 Sep 2013 14:42:56 -0400
Message-ID: <1759139.jak6GOp6Pt@x2>
Organization: Red Hat
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On Tuesday, September 10, 2013 07:20:33 PM Oleg Nesterov wrote:
> On 09/08, Oleg Nesterov wrote:
> > First of all, I do not pretend I understand this code. This was mostly
> > the question, and in fact I mostly asked about audit_bprm() in 0/1.
> > 
> > However,
> > 
> > On 08/30, Steve Grubb wrote:
> > > On Friday, August 30, 2013 03:06:46 PM Richard Guy Briggs wrote:
> > > > On Tue, Aug 27, 2013 at 07:11:34PM +0200, Oleg Nesterov wrote:
> > > > > Btw. audit looks unmaintained... if you are going to take care of
> > > > > this code, perhaps you can look at
> > > > > 
> > > > > 	http://marc.info/?l=linux-kernel&m=137589907108485
> > > > > 	http://marc.info/?l=linux-kernel&m=137590271809664
> > > 
> > > You don't want to clear the TIF audit flag when context == NULL. What
> > > that will do is make a bunch of inauditable processes. There are times
> > > when audit is disabled and then re-enabled later. If the flag gets
> > > cleared, then a task's syscall will never enter the auditing framework
> > > from kernel/entry_64.S.
> > > 
> > > That flag is 0 when auditing has never ever been enabled. If auditing is
> > > enabled, it should always be a 1 unless the task filter has determined
> > > that
> > > this process should not be audited ever. In practice, this is almost
> > > never
> > > used. But ensuring the TIF_SYSCALL_AUDIT set to 1 on all processes is
> > > why we have the boot argument. Not setting audit=1 on the boot
> > > arguments means that any process running before the audit daemon
> > > enables auditing can never ever be audited because the only place its
> > > set is when processes are cloned.> 
> > Then why audit_alloc() doesn't set TIF_SYSCALL_AUDIT unconditionally?
> > 
> > And I do not understand "when context == NULL" above. Say,
> > audit_syscall_entry() does nothing if !audit_context, and nobody except
> > copy_process() does audit_alloc(). So why do we need to trigger the
> > audit's paths if it is NULL?> 
> > > Hope this clears up the use. NAK to the patch, it'll break auditing.
> > 
> > Not really, but thanks for your reply anyway.
> 
> So, Steve, do you still think that patch was wrong? Attached below
> just in case.

I think this looks OK. If the task filter NACK's auditing the process, then 
clearing the flag is probably correct. I have design notes from back around the 
2.6.7 kernel saying this was the intention.

ACK.

-Steve


> [PATCH 1/1] audit_alloc: clear TIF_SYSCALL_AUDIT if !audit_context
> 
> If audit_filter_task() nacks the new thread it makes sense
> to clear TIF_SYSCALL_AUDIT which can be copied from parent
> by dup_task_struct().
> 
> A wrong TIF_SYSCALL_AUDIT is not really bad, but it triggers
> the "slow" audit paths in entry.S.
> 
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>
> ---
>  kernel/auditsc.c |    4 +++-
>  1 files changed, 3 insertions(+), 1 deletions(-)
> 
> diff --git a/kernel/auditsc.c b/kernel/auditsc.c
> index 9845cb3..95293ab 100644
> --- a/kernel/auditsc.c
> +++ b/kernel/auditsc.c
> @@ -943,8 +943,10 @@ int audit_alloc(struct task_struct *tsk)
>  		return 0; /* Return if not auditing. */
> 
>  	state = audit_filter_task(tsk, &key);
> -	if (state == AUDIT_DISABLED)
> +	if (state == AUDIT_DISABLED) {
> +		clear_tsk_thread_flag(tsk, TIF_SYSCALL_AUDIT);
>  		return 0;
> +	}
> 
>  	if (!(context = audit_alloc_context(state))) {
>  		kfree(key);
--
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