Re: [PATCH 3/7] seccomp_filter: Enable ftrace-based system call filtering

[Steven Rostedt <rostedt@goodmis.org>]

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