Subject: Re: [PATCH 3/7] seccomp_filter: Enable ftrace-based system call
 filtering
From: Steven Rostedt <rostedt@goodmis.org>
To: "Serge E. Hallyn" <serge@hallyn.com>
Cc: Will Drewry <wad@chromium.org>, linux-kernel@vger.kernel.org,
        kees.cook@canonical.com, eparis@redhat.com, agl@chromium.org,
        mingo@elte.hu, jmorris@namei.org,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Ingo Molnar <mingo@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>, Tejun Heo <tj@kernel.org>,
        Michal Marek <mmarek@suse.cz>, Oleg Nesterov <oleg@redhat.com>,
        Roland McGrath <roland@redhat.com>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>, Jiri Slaby <jslaby@suse.cz>,
        David Howells <dhowells@redhat.com>
In-Reply-To: <20110428185416.GB13071@hallyn.com>
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Date: Thu, 28 Apr 2011 15:07:18 -0400
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On Thu, 2011-04-28 at 13:54 -0500, Serge E. Hallyn wrote:
> Quoting Will Drewry (wad@chromium.org):
> > My intent was to make them available for use by seccomp.c during state
> > teardown/dup.  I don't think there's benefit to exposing them outside
> > of that.  Would dropping the export, and adding an local seccomp.h
> > with the shared functions in them resolve that more cleanly?
> 
> And add a clear comment explaining :)

Yes that always helps.

> 
> > > Your code would have been correct if you could call kzalloc under
> > > rcu_read_lock() (which you can on some kernel configurations but not
> > > all). The issue is that you need to pull out that allocation from the
> > > rcu_read_lock() because rcu_read_lock assumes you can't preempt, and
> > > that allocation can schedule out. The access to the filters must be done
> > > under rcu_read_lock(), other than that, you're fine.
> > 
> > That makes sense.  I think I'd prefer to not share those functions
> > rather than guard the list just in case a future consumer of the
> > interface comes along.  Would that make sense to you?  Since I don't
> > see any other users right now other than seccomp.c, it might make
> > sense to tackle the impact when an actual need arises.
> > 
> > I'll go whichever way pointed on this, though.
> 
> Complicating the locking for nonexistent users doesn't seem like the
> right way.

I agree.

-- Steve


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