netdev - Re: [RFC Patch] net: reserve ports for applications using fixed port numbers

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Message-Id: <201002050305.22227.opurdila@ixiacom.com>
Date:	Fri, 5 Feb 2010 03:05:22 +0200
From:	Octavian Purdila <opurdila@...acom.com>
To:	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:	davem@...emloft.net, amwang@...hat.com,
	linux-kernel@...r.kernel.org, eric.dumazet@...il.com,
	linux-rdma@...r.kernel.org, netdev@...r.kernel.org,
	nhorman@...driver.com, linux-sctp@...r.kernel.org
Subject: Re: [RFC Patch] net: reserve ports for applications using fixed port numbers

On Friday 05 February 2010 02:41:12 you wrote:
> David Miller wrote:
> > > Octavian Purdila wrote:
> > >> int inet_is_reserved_local_port(int port)
> > >> {
> > >> 	if (test_bit(port, reserved_ports))
> > >> 		return 1;
> > >> 	return 0;
> > >> }
> > >
> > > Above check is exactly what I'm doing in the LSM hook.
> >
> > But his version can be done inline in 2 or 3 instructions.
> >
> > An LSM hook will result in an indirect function call,
> > all live registers spilled to the stack, then all of
> > those reloaded when the function returns.
> >
> > It will be much more expensive.
> 
> If you can accept his version, I want to use his version (with an interface
>  for updating above "reserved_ports" by not only root user's sysctl() but
>  also MAC's policy configuration).
> 

I think that simply using an interface to update the reserved_ports from MAC 
policy configuration module wouldn't work, as root will be able to modify the 
policy via sysctl.

I think that we might need to:

a) have a reserved_port updater

b) put a LSM hook into that

c) use the reserved_port updater from sysctl



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