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From: stuart@rennet.cs.wisc.edu (Stuart Friedberg)
Newsgroups: comp.protocols.tcp-ip
Subject: BSD and SunOS bug in UDP ICMP_UNREACH_PORT handling
Summary: Too many notifications, as well as too few
Message-ID: <7497@spool.cs.wisc.edu>
Date: 9 May 89 18:48:02 GMT
References: <8905032253.AA00554@lear.ultra.com> <363@lupine.UUCP>
Sender: news@spool.cs.wisc.edu
Reply-To: stuart@rennet.cs.wisc.edu (Stuart Friedberg)
Organization: U of Wisconsin CS Dept
Lines: 27

Once upon a time, someone wrote:
> Could some BSD guru  out there please tell me if the BSD UDP in fact
> DOES notify anyone > when it gets an ICMP_UNREACH_PORT, and how?

In article <363@lupine.UUCP> djm@lupine.UUCP (Dave Mackie) replied:
> IP receives the ICMP message and eventually calls udp_ctlinput().  [...]
> The routine in_pcbnotify() is called to find the correct pcb.      [...]
> If you're just using sendto(), the error message gets dropped.

And now I add:
It's even worse than that due to a bug in (or a misuse of) in_pcbnotify().
An error is delivered to all UDP sockets bound to the remote HOST
that generated the ICMP_PORT_UNREACHABLE, no matter which remote PORT
they are bound to.

I once spent 15 minutes setting up by hand a network demo using UDP.
Someone killed one process, and the whole thing unravelled in about 4
seconds due to this bug.   Extremely frustrating!

The bug was present in 4.2 and inherited by 4.3.  It has probably
survived so long because most people don't use UDP, those who use UDP
don't bind to a remote host/port, and those who bind don't test their
code. :-) Many Unix ports based on BSD networking have it; for example,
its present in SunOS's 2.0 through 4.0.1.  I think Mt.Xinu may have
fixed it at one point in their VAX support, but I'm no longer sure.

Stu Friedberg  (stuart@cs.wisc.edu)