Re: Router dumping core

[mss1@cornell.edu (Michael S. Shappe)]

At 8:49 AM 6/28/94, Marco Hernandez wrote:
>Greetings all:
>
>        I'm just wondering if anyone has been experiencing their router
>process dumping core.  I am running version 2.90-940626 on a Sparc LX,
>sunos 4.1.3_U1 ...  Zmailer was compiled with gcc 2.5.8  ..
>
>        Outside of a few warning, compilation went fine ...  I am running
>six routerd, ... before I start lurking into the dumps, I'd like to
>know if anyone has had this problem ...

Marco -- there are a couple of problems that will occasionally cause a
stock Zmailer (that is, the Toronot 2.2 version) to dump core and die. Both
are rare enough that it takes a while to track down:

1] A header line that starts with just a colon, no keyword, e.g:
: Foobar.

This has a fairly easy fix (it's just an off-by-one error), which I believe
Matti has incorporated into the most recent versions.

2] A name-server CNAME loop -- that is, host A has a DNS entry that
contains a CNAME record pointing to host B, and host B points back to host
A.

This Shouldn't Happen(tm), but it does, and because ZM-router does it's own
recursion over DNS entries, rather than having the resolver library do it,
the result is an infinite recursion until the stack explodes. I've solved
this problem by adding a bit of idiot-proofing in the form of a counter
that gets set to zero just before a name lookup loop starts, gets bumped by
one every time it recurses, and will return a tempfail and put the message
on hold if the counter bumps over 25 (based on the theory that no
legitimate host entry will ever require one to go 25 hops deep to find an
address).

The core dumps from this turned out to not be directly useful for
debugging, since they were dumped after the stack was mangled, and thus,
all of the calling chain was lost.

Look for old files in postoffice/router (nothing in there should be older
than an hour or so, so anything that is is probably what caused your core
dump). Try using gdb over router and run router with '-i' to process them.

I should probably contribute back my fix for #2, shouldn't I...:-)

Mikey

--
Michael Scott Shappe
CIT Collaboration Systems
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