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Date: Thu, 28 Apr 2011 11:20:15 -0500
From: "Serge E. Hallyn" <serge@hallyn.com>
To: Will Drewry <wad@chromium.org>
Cc: Steven Rostedt <rostedt@goodmis.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>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>, Jiri Slaby <jslaby@suse.cz>,
        David Howells <dhowells@redhat.com>
Subject: Re: [PATCH 3/7] seccomp_filter: Enable ftrace-based system call
 filtering
Message-ID: <20110428162015.GA1927@hallyn.com>
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Quoting Will Drewry (wad@chromium.org):
> >> ?void __secure_computing(int this_syscall)
> >> ?{
> >> - ? ? int mode = current->seccomp.mode;
> >> + ? ? int mode = -1;
> >> ? ? ? int * syscall;
> >> -
> >> + ? ? /* Do we need an RCU read lock to access current's state? */
> >
> > I'm actually confused to why you are using RCU. What are you protecting.
> > Currently, I see the state is always accessed from current->seccomp. But
> > current should not be fighting with itself.
> >
> > Maybe I'm missing something.
> 
> I'm sure it's me that's missing something.  I believe the seccomp
> pointer can be accessed from:
> - current
> - via /proc/<pid>/seccomp_filter (read-only)
> 
> Given those cases, would it make sense to ditch the RCU interface for it?

ISTM you need them to protect the reader.

-serge
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