Subject: Re: [discuss] portmapping sucks
From: Trond Myklebust <trond.myklebust@fys.uio.no>
To: Jan Engelhardt <jengelh@linux01.gwdg.de>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
In-Reply-To: <Pine.LNX.4.61.0701250030530.32656@yvahk01.tjqt.qr>
References: <Pine.LNX.4.61.0701250030530.32656@yvahk01.tjqt.qr>
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Date: Wed, 24 Jan 2007 19:10:19 -0800
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On Thu, 2007-01-25 at 00:50 +0100, Jan Engelhardt wrote:
> Hello list,
> 
> 
> I just don't know where else I could send this, it's sooo generic to 
> Linux and UNIX (perhaps blame SUN for inventing portmap?)
> Well, here goes...
> 
> As we all know, mountd and other SUNRPC (I question this invention too) 
> services are at a fixed RPC port number (/etc/rpc) which are mapped 
> to a random TCP/UDP port, and the application doing the mappings is
> portmap. This random TCP/UDP port selection is what makes it suck.
> 
> Already twice in 6 months, it has occurred to me that mountd was 
> assigned to vital TCP ports, among which there was:
> 
> 631/tcp causing
>   - cups could not start up properly
>   - samba went into an infinite loop upon startup trying
>     to access port 631 with IPP
> 
> There are a number of common ports in the 512-1023 range. All 
> obsolescence and meaninglessness aside, there _are_ rather "important" 
> services in that range, ldaps, rtsp, kerberos, rsync, ftps, imaps, just 
> to name a few from /etc/services. This map-to-random-port behavior is a 
> total DoS thing.
> 
> Not starting portmap until boot has finished does not work. Think 
> of importing NFS beforehand (/usr, anyone?). Even if, your admin would 
> be very puzzled if he finds that normally-disabled daemons cannot be 
> started at any later time.
> 
> At best I'd obsolete the whole SUNRPC stuff, do away with portmap (and 
> just use TCP/UDP port numbers already) and have a LOT of code simplified 
> (portmap registration for knfsd, to name a prime example).
> Or at least give it fixed TCP/UDP/etc. port numbers too.

1) What the hell does this have to do with the kernel mailing list?

2) Then assign a bloody port number to mountd, and stick to it. Why do
you think there is a '-p' command line option in the first place?

Trond

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