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

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Date:	Tue, 10 Nov 2009 21:42:01 +0000
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Chuck Lever <chuck.lever@...cle.com>
Cc:	Chris Friesen <cfriesen@...tel.com>,
	Trond Myklebust <trond.myklebust@....uio.no>,
	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 16:34 -0500, Chuck Lever wrote:
> On Nov 10, 2009, at 4:32 PM, Ben Hutchings wrote:
> 
> > On Tue, 2009-11-10 at 15:06 -0600, Chris Friesen wrote:
> >> On 11/10/2009 02:26 PM, Trond Myklebust wrote:
[...]
> >>> Just use /proc/sys/sunrpc/{max,min}_resvport interface to restrict  
> >>> the
> >>> range used to a safer one. That's what it is for...
> >
> > Unless I'm much mistaken, that only affects in-kernel SunRPC users.
> >
> >> What constitutes a "safer range"?  IANA has ports assigned
> >> intermittently all the way through the default RPC range.  The  
> >> largest
> >> unassigned range is 922-988 (since 921 is used by lwresd).  If  
> >> someone
> >> needs more than 66 ports, how are they supposed to handle it?
> >
> > I'm sure we could afford 128 bytes for a blacklist of privileged  
> > ports.
> > However, the problem is that there is no API for userland to request
> > 'any free privileged port' - it has to just try binding to different
> > ports until it finds one available.
> 
> bindresvport(3) and bindresvport_sa(3t) ?

These are library calls; they are not an API between userland the
kernel.

> > This means that the kernel can't
> > tell whether a process is trying to allocate a specifically assigned
> > port or whether the blacklist should be applied.
> 
> Such a blacklist would have to be managed by glibc or libtirpc.

Right.

Ben.

-- 
Ben Hutchings, Senior Software Engineer, Solarflare Communications
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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