linux-kernel - Re: sunrpc port allocation and IANA reserved list

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Date:	Wed, 11 Nov 2009 05:26:39 +0900
From:	Trond Myklebust <trond.myklebust@....uio.no>
To:	Chris Friesen <cfriesen@...tel.com>
Cc:	Ben Hutchings <bhutchings@...arflare.com>, netdev@...r.kernel.org,
	Linux kernel <linux-kernel@...r.kernel.org>
Subject: Re: sunrpc port allocation and IANA reserved list

On Tue, 2009-11-10 at 12:37 -0600, Chris Friesen wrote:
> On 11/10/2009 11:53 AM, Ben Hutchings wrote:
> > On Tue, 2009-11-10 at 11:43 -0600, Chris Friesen wrote:
> 
> >> Given that a userspace application can be stopped and restarted at any
> >> time, and a sunrpc registration can happen at any time, what is the
> >> expected mechanism to prevent the kernel from allocating a port for use
> >> by sunrpc that reserved or well-known?
> >>
> >> Apparently Redhat and Debian have distro-specific ways of dealing with
> >> this, but is there a standard solution?  Should there be?
> >>
> >> The current setup seems suboptimal.
> > 
> > I believe both RH and Debian are using the same implementation:
> > <http://cyberelk.net/tim/software/portreserve/>.
> 
> That helps with the startup case, but still leaves a possible hole if an
> app using a fixed port number is restarted at runtime.  During the
> window where nobody is bound to the port, the kernel could randomly
> assign it to someone else.

Just use /proc/sys/sunrpc/{max,min}_resvport interface to restrict the
range used to a safer one. That's what it is for...

Trond

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