linux-kernel - Re: [PATCH] audit: speedup for syscalls when auditing is disabled

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Date:	Mon, 23 Aug 2010 23:51:12 -0400
From:	Eric Paris <eparis@...hat.com>
To:	Anton Blanchard <anton@...ba.org>
Cc:	Michael Neuling <mikey@...ling.org>, linux-audit@...hat.com,
	linux-kernel@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH] audit: speedup for syscalls when auditing is disabled

On Tue, 2010-08-24 at 12:16 +1000, Anton Blanchard wrote:
> Hi Eric,
> 
> > 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.
> 
> That's a good point. What if we went through and created an audit context
> for each thread at the point where we add a rule to the audit subsystem?
> 
> That would make the common case where no one touches audit go fast. It's
> only once you add a rule that you get the syscall entry/exit overhead of
> audit.
> 
> Anton

It might be viable but I certainly couldn't say.  I'm a bit scared of
allocating and attaching a struct audit_context to a running task as we
have no idea if that task is about to exit a syscall with an unfilled
out audit_context struct nor do I personally off the top of my head know
the task flag setting rules (especially when you want to set other
people's flags)

Maybe another approach would be to move audit_alloc() into the syscall
entry path rather than only at fork().

I think the best solution is going to be some better way of
setting/clearing TIF_SYSCALL_AUDIT. (notice the thing is never cleared,
ever, today)

-Eric

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