Subject: Re: sunrpc port allocation and IANA reserved list

From: "Chris Friesen" <[email-masked]>
Date: Tue, 10 Nov 2009 12:37:03 -0600

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.

Chris