davido@gordon.UUCP (David Ornstein) (07/10/87)
Recently, gordon (my site) had a problem. This problem was the result of
a bug in a news<-->mail gateway that I built for the VMS machines here.
Following is a description of how the system is supposed to work and what
the symptoms of the looping problem were (if you haven't seen them!)
Once I get the system running in a bug-free kind-o-way I'll post the
whole thing for everyone.
Any help in determining the exact problem with the gateway would be
appreciated as well as any general or specific suggestions about the
mechanism.
Here is the man page for the system that I have put together...
=========================================================================
newsmail(5)
<PRELIMINARY - KNOWN BUGS - DON'T INSTALL THIS>
NAME
newsmail - VMS Mail interface to USEnet
INTRODUCTION
USENET (Users' Network) is a bulletin board shared among
many computer systems around the world. USENET is a logical
network, sitting on top of several physical netwroks,
including UUCP, BLICN, BERKNET, X.25 and the ARPANET. Sites
on USENET include many universities, private companies and
research organizations. Currently, there are over 75,000
participants at over 2500 USENET sites in the USA, Canada,
Europe, Japan and Korea with more joining literally every
day. Most are running the UNIX operating system.
USENET is organized into a heirarchy of newsgroups each of
which contains discussions about a various subject. There
are currently over 300 newsgroups that are generally distri-
buted to every site on the net. In addition, each site may
have its own groups for discussions that should be held only
within the company. The subjects in the network-wide news-
groups carry a great range of discussions centering around
everything from the details of the latest security bug found
in VMS to discussions about skiing to what happened last
week on General Hospital.
Because no single person is going to be interested in read-
ing all of the articles in all of the newsgroups, it is pos-
sible to limit your receipt of articles from USENET to only
those articles that exist in specific groups in which you
are interested.
DESCRIPTION
There are many different ways to read news and the appropri-
ate one really depends on your reading habits and personal
preferences. If you read a high volume of news each day, a
dedicated news reading program (such as rn) probably makes
sense. rn is a sophisticated program that allows you to
quickly and easily sift through a large number of articles
with mechanisms like subject kill and others. To use rn,
you must log into the machine that is running the news
software (GORDON) and use the program there.
If, however, you read a reasonably small number of news-
groups, a second option is now available to you: newsmail.
newsmail is a set of capabilities that allow various users
on a local network to have news articles from various groups
be sent to them using standard mail facilities. Each user
declares which newsgroups they are interested in receiving
and all new messages in those groups are automatically for-
warded to them (via whatever mailing machinations are
needed).
Each message that is forwarded is received by the user on
his or her home machine in the following format:
From: <newsgroup_name>
Subject: <Article subject>
<blank line>
<Article header lines>
<Article body>
This forging of the sender of the article allows the user to
use the REPLY capability of his/her mail program to post
reply articles. For example, if an article is received in a
group called comp.os.vms, the user would receive a message
from a user named comp.os.vms (on the machine running the
newsmail software - GORDON at Access). If the user replys to
this message, the reply is caught by the machine in the net-
work that runs the news software and the article is posted.
As a natural side effect of this, you can post an article by
simply sending mail to GORDON::groupname.
NEWSGROUPS
At the end of this document is a listing of what newsgroups
we are currently receiving. There are a couple hundred more
that we could be getting, but don't because of space on on
GORDON's disk. If you are interested in the list, let me
(David Ornstein) know and I'll send you a copy. Individual
groups are pretty easy to turn on.
As mentioned in the introduction, it is very easy to create
company-wide newsgroups that will not be distributed outside
of Access. If you have ideas for these groups, let me know
and we can try setting some of them up.
If you are interested in trying out the news system via
newsmail, let me know which groups you are interested in and
I will turn them on for you.
IMPLEMENTATION
The news forwarding system is built using fake system
entries for users in the sys file for news. Each user has a
line of the form:
Musername:newsgroups::/usr/local/bin/forgemail %s user-
name
This causes the news software to send the article off (using
the article's file location as the %s replacement operator)
to the forgemail command. This program (see source in
/usr/src/local/forgemail) sets the uid to that of a trusted
user and calls a script called mailart in /usr/local/bin.
This script figures out what the subject and newsgroup of
the article are and sends the message off to the given user,
forging the from line to be the newsgroup name.
Articles being sent to USEnet via mail (in reply to a mailed
article or directly mailed) get sent to a script called
rcvart in /usr/local/bin. This forwarding is done in the
aliases file in /usr/lib. There must be a line in this file
for each newsgroup that is active for posting-via-mail to
work correctly. The rcvart script takes the incoming article
and figures out who it came from, what newsgroup it is to
and posts the article using inews.
NEWSGROUP LIST
[big list removed]
------------------------------------------------------------------
That's the man pages.
Now the problem. As I best understand the problem, here's what happened:
Somebody on one of the VMS machines mailed an article to soc.singles
on gordon.
The article was sent out to the net.
I know that the From line was incorrectly: ...gordon!soc.singles.
Somebody out there (bob@acornrc?) replied, via mail, to the
posting. This mail was sent to gordon!soc.singles.
The newsmail system caught the article (via the mail aliases in the
/usr/lib/aliases file).
[some stuff]
This mailed reply was posted.
This posting was sent back in to the newsmail system and it sat
reposting the article, tacking a news header on each time.
Now, my problem is: I don't understand what [some stuff] is. I would have
expected that the trapped article would have been sent to the rcvart script
and that the article would be posted. I just don't understand how it got out
of news again.
Thanks for any help you can give...
==========================================================================
Here are the scripts and the source to forgemail.c:
#! /bin/sh
# This is a shell archive, meaning:
# 1. Remove everything above the #! /bin/sh line.
# 2. Save the resulting text in a file.
# 3. Execute the file with /bin/sh.
# The following files will be created:
export PATH; PATH=/bin:$PATH
if test -f 'rcvart'
then
echo shar: over-writing existing file "'rcvart'"
fi
echo extracting "'rcvart'"
cat << \SHAR_EOF > 'rcvart'
cat > /tmp/rcvart.$$
logfile=/usr/lib/news/newsmail/log
from=`grep "From " /tmp/rcvart.$$ | cut -d" " -f2`
grp=`grep "To:" /tmp/rcvart.$$ |/usr/local/bin/validgrp -d`
group=$grp
title=`grep "Subject:" /tmp/rcvart.$$ | cut -c10-`
cat /tmp/rcvart.$$ | awk -f /usr/local/bin/trimhdr.awk > /tmp/artbody.$$
/usr/lib/news/inews -n $group -f $from -t "$title" < /tmp/artbody.$$
rm /tmp/*.$$
echo -n "Article posted to $group by $from on " >> $logfile
date >> $logfile
SHAR_EOF
if test -f 'trimhdr.awk'
then
echo shar: over-writing existing file "'trimhdr.awk'"
fi
echo extracting "'trimhdr.awk'"
cat << \SHAR_EOF > 'trimhdr.awk'
BEGIN {inhdrs = 1}
{
if ($0 == "")
inhdrs = 0;
if (inhdrs != 1)
print $0
}
SHAR_EOF
if test -f 'validgrp.c'
then
echo shar: over-writing existing file "'validgrp.c'"
fi
echo extracting "'validgrp.c'"
cat << \SHAR_EOF > 'validgrp.c'
/* VALIDGRP.C */
/* This program operates as a filter on all of its arguments to determine
what the first valid newsgroup listed is. This is echoed to stdout.
*/
#include <stdio.h>
#include <ctype.h>
int groups;
char *glist[600];
char grpbuf[30000];
char *validName();
main(argc, argv)
int argc;
char *argv[];
{
FILE *actfile;
FILE *reject;
char *grpptr;
char linebuf[200];
char *testgrp[20];
char testbuf[1000];
char *testptr;
char *src;
int gcount;
int i;
int c;
char *newname;
actfile = fopen("/usr/lib/news/active", "r");
if (actfile == NULL)
exit(1);
if (strcmp(argv[1], "-d") == 0) {
reject = fopen("/usr/lib/news/newsmail/rejectgrps", "a");
if (reject == NULL)
exit(1);
} else
reject = NULL;
groups = 0;
grpptr = grpbuf;
while (fgets(linebuf, sizeof(linebuf) - 1, actfile) != NULL) {
glist[groups++] = grpptr;
src = linebuf;
while (*src != ' ' && *src != '\0')
*grpptr++ = *src++;
*grpptr++ = '\0';
}
gcount = 0;
testptr = testbuf;
testgrp[gcount++] = testbuf;
while((c = getchar()) != EOF) {
if (c == ' ' || c == ',') {
*testptr++ = '\0';
testgrp[gcount++] = testptr;
} else
*testptr++ = (char)c;
}
*testptr++ = '\0';
for (i = 0; i < gcount; i++)
if ((newname = validName(testgrp[i])) != NULL) {
printf("%s", newname);
break;
} else {
if (reject != NULL)
fprintf(reject, "%s\n", testgrp[i]);
}
fclose(actfile);
if (reject != NULL)
fclose(reject);
if (i == argc)
exit(1);
else
exit(0);
}
char *validName(str)
char *str;
{
int i;
static char ngname[200];
char wrkbuf[200];
char *s, *d;
if (strlen(str) == 0)
return NULL;
strcpy(ngname, str);
/* Trim anything to the right of an '@' */
s = ngname;
d = wrkbuf;
while (*s != '\0')
if (*s == '@')
break;
else
*d++ = *s++;
*d++ = '\0';
strcpy(ngname, wrkbuf);
/* Get rid of punctuation except periods that aren't on the edge */
s = ngname;
d = wrkbuf;
while (*s != '\0') {
if (*s == '.' && s > ngname) {
*d++ = *s++;
continue;
}
if ((*s >= 'a' && *s <= 'z') || (*s >= 'A' && *s <= 'Z') ||
(*s >= '0' && *s <= '9'))
*d++ = *s++;
else
s++;
}
*d++ = '\0';
strcpy(ngname, wrkbuf);
/* Search the group list */
for (i = 0; i < groups; i++) {
if (strlen(glist[i]) != 0) {
if (icmp(ngname, glist[i]))
return ngname;
}
}
return NULL;
}
icmp(str1, str2)
char *str1, *str2;
{
int len1 = strlen(str1);
int len2 = strlen(str2);
int i;
if (len1 != len2)
return 0;
for (i = 0; i < len1; i++)
if (str1[i] != str2[i])
return 0;
return 1;
}
SHAR_EOF
if test -f 'mailart'
then
echo shar: over-writing existing file "'mailart'"
fi
echo extracting "'mailart'"
cat << \SHAR_EOF > 'mailart'
grep Subject: $1 > /tmp/mailart.$$
echo "" >> /tmp/mailart.$$
grep -v Subject: $1 >> /tmp/mailart.$$
from=`grep Newsgroups: $1|cut -c13-|cut -d, -f1`
/usr/lib/sendmail -f $from $2 < /tmp/mailart.$$
rm /tmp/mailart.$$
SHAR_EOF
if test -f 'forgemail.c'
then
echo shar: over-writing existing file "'forgemail.c'"
fi
echo extracting "'forgemail.c'"
cat << \SHAR_EOF > 'forgemail.c'
/* FORGEMAIL.C */
/* This program takes a file and mails it to a specific user, forging
the from entry based on the Newsgroups: line inthe file.
Usage: forgemail article to
*/
#include <stdio.h>
main(argc, argv)
int argc;
char **argv;
{
char cmdbuf[200];
int x;
/* Do a setuid to uucp's user id */
x = setreuid(4,4);
/* Build the command buffer */
sprintf(cmdbuf, "/usr/local/bin/mailart %s %s",
argv[1], argv[2]);
system(cmdbuf);
}
SHAR_EOF
# End of shell archive
exit 0
--
-----------------------------------------------------------------------------
David Ornstein "Never join a religion that has a water slide."
Internet: davido@gordon.uucp
UUCP: {mit-eddie|seismo}!mirror!gordon!davido
or {harvard|ames|decvax|husc6}!necntc!davido
US Snail: Access Technology, 6 Pleasant St, Natck MA 01760
-----------------------------------------------------------------------------