Cleanfeed - spam filter for Usenet news servers
SYNOPSIS
INN: Installed as filter_innd.pl, location is configured
into INN at compile time.
Highwind servers: <command line> -program cleanfeed -body
NNTPRelay: ExternalFilter=c:/perl/bin/perl.exe
c:/news/cleanfeed.pl
DESCRIPTION
A spam filter for Usenet servers. Cleanfeed blocks spam
on the way into your server, before it is written to disk
or propagated to outbound feeds. It can also block
binaries in non-binary newsgroups and includes several
other features to keep your newsfeed clean.
Cleanfeed currently works with INN, Cyclone, Typhoon,
Breeze, and NNTPRelay servers. See my webpage (listed at
the end of this document) for pointers to information
about using Cleanfeed with CNews, Diablo, Collabra, or INN
versions earlier than 1.5.1.
USAGE
For all versions, place the cleanfeed.conf configuration
file somewhere, then edit the Cleanfeed source file and
change the $config_dir option at the top to point to the
directory where the config file lives.
INN Install the filter file (called cleanfeed) as
filter_innd.pl, and cleanfeed.conf, in the location
you specified in config.data (INN 1.7.2 and earlier)
or when configuring INN 2.x (usually the bin/filter
directory under the installation root). Make sure
both files are readable by the news user. Once in
place, the filter is loaded with the command ctlinnd
reload filter.perl meow. Filtering can be turned on
with ctlinnd perl y and turned off with ctlinnd perl
n.
Cyclone/Typhoon/Breeze
Add the -program <file> and -body options to the
bin/start script, where <file> is the location and
name of the Cleanfeed program. Restart the server.
Cleanfeed will run as an external process (standalone
mode). IMPORTANT: make sure both cleanfeed and
cleanfeed.conf are readable by the news user! Double-
check the permissions as this is a fairly common
mistake!
NNTPRelay
Find the ExternalFilter directive in config.txt and
ExternalFilter=c:/perl/bin/perl.exe
c:/news/cleanfeed.pl
Cleanfeed will run as an external process (standalone
mode).
More detailed installation instructions are provided later
in this document.
CONFIGURATION OPTIONS
Configuration is accomplished by setting the various
options in the cleanfeed.conf configuration file. This
file is evaluated as Perl code, so comments can be
included in the usual Perl # syntax. A sample default
file is included with the distribution.
If you would rather not use cleanfeed.conf, you can set
its location to "undef" in the source and edit the
configuration variables directly in the source file.
cleanfeed.conf has two sections (which define perl
hashes): %config_local and %config_append. Entries in
%config_local will override the default settings of the
same name in the Cleanfeed source. Entries in
%config_append can be used to add to most of the default
regular expressions, for items such as badguys,
bin_allowed, poison_groups, etc. Settings in
%config_append for these items will be appended to the
default regexps, seperated by "|" (or).
If you want to completely override the default regexps for
these options, rather than just add to the defaults, you
can add an entry for them into the %config_local section
of cleanfeed.conf.
All of this is done quite blindly, so if you do anything
odd, be careful. (Cleanfeed will remove the common
mistake of including two "|" (or) signs in a row.) All
config options are exposed to %config_local, including any
that may not be present in the sample file. Only the
defined list of options are exposed to %config_append.
Options that are on/off or yes/no should be set to 1 for
on/yes, or 0 for off/no.
First, you need to tell Cleanfeed which news server
software you are using. At the top of the file, set the
appropriate variable to 1. For INN, set $inn; for
Cyclone, Typhoon, or Breeze, set $highwind; and for
NNTPRelay, set $nntprelay. Ensure the other two (the ones
you're not using) are set to 0.
aggressive
Set this to 0 to disable all content-based filters.
Helpful to please paranoid lawyers, or paranoid
customers.
active_file
Set this to the full path to an active file, to
allow Cleanfeed to know what groups are moderated.
This is normally your server's active file, but it
doesn't have to be; it is possible, for example,
to run Cyclone with no active file, but give one
to Cleanfeed anyway.
MD5 Body Filter Settings
do_md5 When turned on, the MD5 EMP checks will be done.
This should be left on unless you have a really
good reason to turn it off. If you're running
Hippo along with Cleanfeed, you might feel
Cleanfeed's MD5 checks are redundant and want to
turn them off, for example. It would probably be
better to leave it on with the history turned
down, instead.
md5maxmultiposts
Start rejecting articles after we have seen this
many copies, according to the MD5 checksum filter.
MD5History
How many articles to remember for MD5-based EMP
comparison. Since the MD5 filter is not prone to
false positives, setting this higher is a good
idea to catch more spam, if you have the RAM to
spare.
MD5maxlife
When a spam is identified by the MD5 EMP filter,
it is saved for continual rejection. MD5maxlife
specifies how long, in hours, to keep a saved MD5
id which is no longer getting any hits. (A spam
id which is still getting matches will be saved
regardless of age.) 24 hours works well.
fuzzy_md5
When turned on, the message bodies will be munged
up a bit before MD5 checksums are generated.
Whitespace and other non-alphanumeric characters
are stripped and letters are forced to lowercase,
as well as a couple other bits of treachery to try
to defeat the "hashbuster" spam-bots. This adds a
in a performance hit as well.
Since the smarter spammers have discovered
hashbusting, I recommend that this be turned on.
fuzzy_max_length
Sets the maximum amount of lines for an article
body to be subject to the fuzzy_md5 munging
(above). This keeps extremely large articles out
of those nasty regular expressions.
md5_skips_followups
Determines whether the MD5 filter checks articles
with References headers. The default is to skip
them. Setting this option to 0 will result in all
articles passing through the MD5 filter, which can
result in a major performance hit, but does close
another hole in the filter. If you turn this off,
you should increase MD5history as well to avoid
shortening your "window".
MD5HistSize
The maximum allowed size of the EMP memory for the
MD5-checksum EMP filter. Use this as a "sanity
check" to prevent a sudden burst of spam from
eating up all of your memory. It should be set
high enough so that you normally never hit this
number; use the MD5MaxLife to expire the hash
instead.
Header-Based EMP Filter Settings
do_phl Turns on the NNTP-Posting-Host/Lines EMP filter.
This filter identifies spam by identical posting-
host headers and article sizes in a short period
of time. You really don't want to turn this off.
do_fsl Turns on the From/Subject/Lines EMP filter. This
filter identifies spam by identical From and
Subject headers and article sizes in a short
period of time. This is the one that gets the
least number of hits these days, so you won't lose
much by shutting it off.
maxmultiposts
Start rejecting articles after we have seen this
many copies, according to the header-based EMP
filter. Since false positives are somewhat more
likely with this filter than with MD5, this should
be set appropriately higher to reduce the odds.
How many ids to remember for header-based EMP
comparison. Setting this higher will catch more
spam because there will be a larger "window" to
look at. Larger settings will also consume more
memory and have a (small) impact on performance,
as well as slightly increase the chance of a false
positive (since the sample size will be larger).
Most articles will actually take up two entries in
this history because there are two different
header-based filters.
EMPmaxlife
Same as MD5maxlife but for the header-based EMP
filter.
EMPHistSize
Same as MD5HistSize but for the header-based EMP
filter. If you are running the header-based
filter but not the MD5 filter for whatever reason,
set this high.
Excessive Crosspost Settings
maxgroups
Reject articles crossposted so that followups will
be to more than this many newsgroups.
low_xpost_maxgroups
Specify a special, lower crosspost limit for
certain groups, specifed by regular expression in
low_xpost_groups (below). Useful for being more
strict in groups plagued by crossposting, such as
sex, binaries, and jobs groups. (Replaces the old
tfjmaxgroups option.)
Misplaced Binaries Filter
block_binaries
Enables blocking of binary posts in non-binary
newsgroups. Which newsgroups allow binaries is
configured with bin_allowed (below).
max_encoded_lines
Sets the number of uuencoded or base64-encoded
lines to allow before considering a post to be a
binary. This should be set high enough to pass
regular PGP signatures. (Those satanic Netscape
crypto-sigs can die along with the other
binaries.) Default is 15 lines, which may be a
little low if you are lenient, which you're not.
If set, binaries are allowed in spite of
block_binaries if they are posted only to
moderated groups (requires active_file).
HTML
block_mime_html
Enables blocking of MIME-encapsulated HTML posts.
This does NOT affect straight text/html or
multipart/alternative posts of the type created by
misconfigured Netscape and Microsoft
"newsreaders", but ONLY posts which are
MIME-encapsulated HTML, a favorite format of sex
spammers which often sneaks in under the EMP
radar.
block_html
Enables blocking of HTML and multipart/alternative
posts. You can specify group patterns where HTML
is allowed by setting html_allowed (below).
Cancel Message Filtering
block_late_cancels
If turned on, cancels for recently rejected
articles will be rejected. Set the window with
MIDmaxlife (below). This will result in a huge
number of rejections if you have multiple full
feeds and you aren't backlogging. If you are
concerned about your downstream sites receiving
the cancels, leave this off. If you need a
performance boost, turn it on.
MIDmaxlife
How long to remember rejected message-ids so
cancels for these posts can later be rejected.
Specified in hours. This only has an effect if
block_late_cancels is enabled (above).
Disabling Other Filters
do_scoring_filter
Enables the (new) "scoring" filter. You probably
want to leave this on, even if you need to turn of
aggressive mode (turning off aggressive mode will
disable the content-based parts of the scoring
filter).
do_mid_filter (INN only)
Enables the message-id filter. This requires an
with Cleanfeed (but optional). The patch adds a
new Perl hook to check message-id's during the
NNTP CHECK transaction, and decide whether to
refuse the article. There is a patch for this for
INN 2.0 which may get incorporated into the INN
distribution at some point. The default is off.
do_bot_checks
Enables the filters that check for spam bot
signatures. The only reason you would ever want
to turn this off is if you've written your own
version, or something. Otherwise, leave it on.
do_supersedes_filter
Enables the Excessive Supersedes filter, to catch
rogue Supersedes attacks. This filter begins
dropping articles with Supersedes headers if too
many appear from the same posting-host in a short
time. Moderated groups are given a higher limit
(if active_file is set), as is news.answers.
Default is on.
check_supersedes_path
If set, bad_cancel_paths will also be applied to
Supersedes articles. Articles with Supersedes
headers, where a path element matches the regexp
in bad_cancel_paths, will be dropped. Default is
on.
drop_useless_controls
If set, all control messages of types sendsys,
senduuname, and version will be dropped. These
are no longer useful and are a hole for denial-of-
service attacks due to the way INN and some other
servers handle them. On by default.
drop_ihave_sendme
If set, control messages of types ihave and sendme
will be dropped. See drop_useless_controls. If
you use these types of control messages, turn this
off. If you're not sure, then you're not using
them.
drop_control_with_supersedes
Drops any and all control messages which contain a
Supersedes header. Since control messages are not
passed through the same filters as regular
messages, a rogue Supersedes attack can use
control messages to avoid filtering; this option
closes this hole. Legitimate control messages
don't have Supersedes headers. On by default.
trimcycles
The EMP memories are trimmed every trimcycles
times through the filter.
EMPstarttrimming
Tells the filter not to waste time trimming the
EMP memories until they have this many entries.
Just a minor performance enhancement during the
first hours the filter is running or when you
first start innd.
Logging
verbose When turned on, verbose logging to news.notice
will happen; spam domains will be listed, etc.
When off, only general messages will be logged,
making the news.daily summaries less interesting
but much shorter and more to the point. (There
is, alas, no way to shut off news.notice logging
entirely.) (news.notice only applies to INN.)
Note that this will not reduce the number of log
entries, but only their verbosity.
logfile (Standalone Mode)
If set to the path to a file, this will enable
logging of message-ids of all articles processed
by the filter. Rejections will be logged with the
reason for rejection. Note that this will create
a very large logfile which you will need to rotate
or delete (see max_log_size, below).
reportfile (Standalone Mode)
If set to the path to a file, this will enable
generation of a simple report of articles accepted
and rejected. The report file will contain one
entry per line with the start time, end time,
number of articles accepted, and number of
articles rejected, tab-separated.
log_accepts (Standalone Mode)
When using the above logfiles, this setting
determines whether articles accepted should be
logged. When disabled, only rejections will be
logged.
max_log_size (Standalone Mode)
The size at which to rotate the logfile. This
will be replaced by time-based rotation at some
point.
If this is set to the full path of a file, a crude
stats file will be written each time the filter is
reloaded with ctlinnd reload filter.perl meow (for
INN) or whenever the Cleanfeed process receives a
SIGUSR1 (for standalone mode). The file shows how
many entries are present in each of the EMP
histories, MID history and excessive supersedes
history; timer information if enabled (see
timer_info); and the contents of all configuration
settings. Posting-hosts in for each supersedes
entry will be listed, along with their counts;
these are not being rejected unless they are over
the threshold. The default for this is undef,
which disables creation of the stat file.
More comprehensive stats are planned for the
future.
Timing Info
timer_info
When enabled, Cleanfeed will generate timing
statistics telling you how many articles per
second are being examined by the filter and being
accepted by the filter. This information will
appear in the statfile if this is enabled, and in
the output of INN's ctlinnd mode if the mode.patch
is applied to INN. Note that the accepted/second
rate is not necessarily the rate at which your
server is accepting articles; articles can be
rejected by the server after Cleanfeed passes
them, for example if they are posted to groups not
in your active file.
timer_interval
The period over which to average timing
information, in seconds. The default is 600
seconds, or 5 minutes.
Debugging
debug_batch_directory
Specifies a directory where debugging "batchfiles"
can be written. See the Hacker's Guide in this
document for more information.
debug_batch_size
The maximum size of a debugging batchfile before
it gets rotated. Rotation is done by renaming the
file to file.1, file.2, etc., using the lowest
number that doesn't already exist.
You can add to most of these regular expressions in the
%config_append section of cleanfeed.conf; settings you add
there will be added to the defaults, rather than
overriding them. If you want to completely override the
default settings you can add entries for these to the
%config_local section instead.
bin_allowed
This is a regular expression telling the anti-
binary filter in which newsgroups binaries are
allowed. If all groups in the Newsgroups header
match this pattern, binaries are allowed through
the filter. (This obviously has no effect when
the binary filter is disabled.) If the binary
filter is enabled and this is set to a null string
(by overriding the default in the local config)
the result will be blocking all binaries
regardless of where they are posted.
poison_groups
If any groups in the Newsgroups header match this
regexp, the article will be rejected. Thus you
can reject crossposts to certain groups even if
they are also posted to groups you carry.
html_allowed
This is a regular expression telling the anti-HTML
filter in which newsgroups HTML and
multipart/alternative posts are allowed. This
only has an effect if block_html is turned on
(above). The default (to allow HTML in
microsoft.* groups) can be added to in
cleanfeed.conf.
If you don't want to allow HTML anywhere, not even
the microsoft.* groups, override this setting in
the local configuration and set it to a null
string or undef.
md5exclude
If an article is posted only to groups matching
this regexp, the MD5 EMP filter will not be
applied. Useful for "test" groups where it's okay
for lots of the posts to be the same.
allexclude
If an article is posted only to groups matching
this regexp, NO checks are applied at all.
low_xpost_groups
If a group matches this regular expression, it
gets a special crosspost limit, set in
crosspost limit set in maxgroups. This is useful
for groups plagued by excessive crossposting, such
as sex, binaries, and jobs groups. The default is
to limit crossposts to 6 groups in test, forsale,
and jobs groups. Setting this to a null string,
or undef, will disable this feature.
badguys This is a monster regular expression containing
domains of known spammers. Only the "middle" part
of the domains are listed; these are checked as
email addresses in From headers by appending a
list of top-level domains to the end, and as URLs
by prepending http:// and an optional "www.". If
you modify this list, be very careful not to end
up with "||" in there (two "or" signs in a row);
this will match every single post that comes
through, which is Bad.
baddomainpat
If a post contains a URL for a site whose domain
name matches this pattern (in .com, .net, and .nu
TLDs only) the post will be rejected. For
example, there are hundreds of spamming porn sites
whose domain names begin or end with "xxx". This
prevents us from having to keep up with their
nonsense. Yes, it's a little aggressive, but it
works.
exempt Regular expression of NNTP-Posting-Hosts that are
exempt from the posting-host-based EMP filter.
This is for high-output systems where all posts
contain the same NNTP-Posting-Host header, such as
AOL, which if not exempted would end up hitting
the posting-host EMP filter with all of their
posts. There aren't many of these out there; a
"regular" multi-user system does not present a
problem because the filter doesn't kick in until
it sees a large number of posts from the same
posting-host and also of the same length, in a
short period of time.
supersedes_exempt
Regular expression of NNTP-Posting-Hosts that are
exempt from the excessive supersedes filter.
Generally this will be systems which post a lot of
FAQs.
bad_cancel_paths
Cancel messages will be rejected if the Path
header contains elements matching this regular
expression. Also applied to the NNTP-Posting-
Host. If check_supersedes_path is set, this will
also be checked against the Path header of
contains sites which are or have recently been the
source of rogue cancel attacks.
refuse_messageids (INN only)
If you have do_mid_filter (above) enabled, and you
have the optional message-id patch applied to INN
(or otherwise have obtained the hook for
filter_messageid in INN 2.0), this regular
expression will be applied to message-ids as they
are offered to your server, and they will be
refused if it matches.
net_abuse_groups
spam_report_groups
These regular expressions are used to exempt
certain groups from certain filters; for example,
groups expected to contain spam reports, example
spams, NoCeM notices, etc. These are not in
cleanfeed.conf; if you need to add to them please
let me know.
After modifying the filter file, always check for mistakes
by typing:
perl -cw filter_innd.pl (or cleanfeed or whatever you called it)
There should be no errors and no warnings.
You can check cleanfeed.conf with:
perl -cw cleanfeed.conf
You will get several warnings about variables being used
only once; these can be ignored.
If you are running INN, you can modify the file and reload
it with ctlinnd reload filter.perl meow while the server
is running. The configuration in f<cleanfeed.conf> will
be reloaded at this time as well.
With the Highwind servers, modifying the program will
require a server restart (use the bin/restart script).
Note that this will result in all connections (including
newsreader clients) being dropped. This is not my fault.
:)
When in standalone mode, configuration from cleanfeed.conf
can be reloaded by sending Cleanfeed a SIGHUP.
I have no idea what NNTPRelay does, but I'm guessing it
needs a restart as well.
permissions on cleanfeed/filter_innd.pl, cleanfeed.conf,
and cleanfeed.local so that they are readable by the news
user. Please double-check your permissions! If Cleanfeed
is running, and fails to successfully load cleanfeed.conf,
it will use the default settings instead of those you
specified in the config file.
INSTALLATION - INN
These instructions assume you have the Perl hooks compiled
into INN. If you don't, you will need to add them and
rebuild the INN distribution before proceeding.
With INN, Perl is embedded into the innd program. The
filter file defines subroutines that are called by innd at
the appropriate times.
SYSTEM REQUIREMENTS
In order to run Cleanfeed with INN, you will need:
· INN 1.5.1 or later (1.7.2+insync1.1d or 2.1
recommended)
· Perl 5.004 or later
· Perl hooks compiled into INN
· The MD5 Perl module
INN is available from:
http://www.isc.org/inn.html
The Insync distribution of INN (highly recommended if you
aren't running INN 2.1) is available from:
http://www.insync.net/~aos/inn.html
The MD5 Perl module is available from:
http://www.perl.com/CPAN-local/modules/by-module/MD5/
Perl itself is available from the Perl home page:
http://www.perl.com/
PATCHES AND STUFF
INN 2.0 includes everything you need to run Cleanfeed,
except the MD5 Perl module.
With earlier versions, Cleanfeed requires some patches to
INN in order to function properly.
If you are running INN 1.7.2+insync1.1d, you already have
the original filter.patch and the dynamic-load.patch; You
need only apply the upgrade.patch.
feature" ones like mode.patch may not apply to 2.1. Ports
are always welcome.
filter.patch
This patch provides the basic functionality for
Cleanfeed by making some extra headers available to
the Perl filter, as well as message bodies. This
patch was changed in version 0.95.3. It is against
INN 1.7.2 and should be applied in the innd directory.
This patch is included in the insync "megapatch" for
INN as of version 1.1c, so if you are running this
version of INN you need not apply this patch. Not
necessary for INN 2.x.
dynamic-load.patch
This patch enables INN's Perl interpreter to load
dynamic modules. It is necessary for MD5 support.
The patch is against INN 1.7+insync and should be
applied in the lib directory (NOT the innd directory).
It applies cleanly to other versions of INN including
1.5.1 and 1.7.2. This patch is included in the insync
"megapatch" for INN as of version 1.1d, so if you are
running this version of INN you need not apply this
patch. Not necessary for INN 2.x.
If you are still using INN 1.5.1, you can use
dynamic-1.5.1.patch instead.
In order to compile INN with the new patch, you need
to edit the PERL_LIB entry in config.data. Type this
command at the shell, and paste its output into
config.data as PERL_LIB:
perl -MExtUtils::Embed -e ldopts
Most systems also allow you to simply enter that line
in backquotes as PERL_LIB.
This patch requires Perl 5.004 or later! INN will not
compile linked with Perl 5.003 after following these
instructions!
AIX: There is a problem with Perl dynamic loading from
INN under the AIX operating system. In simple terms,
it doesn't work. This seems to be a problem with the
gcc compiler. Success has been reported by rebuilding
both Perl and INN with IBM's commercial compiler CSet
(a.k.a. xlC).
Solaris: There have been multiple reports of Cleanfeed
not working under Solaris if any part of the system --
INN, Perl, or the MD5 module -- are compiled using
egcs. Success has been reported by recompiling
newest egcs.
upgrade.patch
For current users of Cleanfeed, this is a patch for an
already-patched INN, or for 1.7.2+insync1.1d, to bring
you up to the new version of the Cleanfeed patch. Not
applying this patch right now will only lose you a
couple of filters, and nothing will break if you don't
apply it (no changes to the filter source or
configuration will be required).
messageid.patch
This is a patch which adds a new Perl hook to innd,
filter_messageid. This allows you to run a Perl
subroutine against each message-id as it is offered to
your server, and decide whether to refuse the article
before it is even sent to your server. Cleanfeed
includes a small filter_messageid. This patch is
entirely optional.
mode.patch
This patch adds a line to INN's ctlinnd mode output
for Perl filter status. The output line is generated
by the filter_stats subroutine. The default output
contains the number of articles accepted, rejected and
refused since the filter started, and the sizes of the
EMP, Message-ID, and Excessive Supersedes hashes. If
timer_info is enabled, this will also include the rate
in articles per second (rounded to the nearest tenth)
at which articles were examined (total sent through
the filter) and accepted by the filter, averaged over
the timer_interval number of seconds.
After applying the patches, rebuild all of INN and do a
"make update". The first patch (filter.patch) only
requires innd to be rebuilt, but the dynamic-load.patch
requires you to rebuild the whole distribution. Current
users upgrading with upgrade.patch need only rebuild innd
and reinstall that executable.
Thus:
make clean
cd innd
cp wherever/filter.patch . [from the Cleanfeed distribution]
patch <filter.patch
cd ../lib
cp wherever/dynamic-load.patch [from the Cleanfeed distribution]
patch <dynamic-load.patch
cd ../config
emacs config.data [edit the PERL_LIB entry as above]
make all
make update
Finally, you need to install the MD5 Perl module, no
matter what version of INN you are running.
INSTALLING CLEANFEED - INN
In INN 1.7.2 and earlier, the location where INN looks for
the Perl filter is set in config.data, as
_PATH_PERL_FILTER_INND. By default, the filename is
filter_innd.pl. The Cleanfeed filter program file should
be installed in this location. INN comes with an example
filter_innd.pl file; move this file (or whatever other
filter is in place) out of the way first.
Before putting the filter in place, edit the file,
changing $config_dir to the location of your
cleanfeed.conf file.
After editing the file, always check for errors with the
command:
perl -cw filter_innd.pl
Once the file is in place, tell innd to reload it:
ctlinnd reload filter.perl meow
And, if Perl filtering is currently disabled, enable it:
ctlinnd perl y
Now, you can watch it working by looking at your
news.notice log:
tail -f /var/log/news/news.notice
If your server is running a full feed, you should start
seeing a constant stream of rejections almost immediately.
INSTALLATION - HIGHWIND SERVERS
The various Highwind server packages (Cyclone, Typhoon,
and Breeze) all have the same external filter interface.
input and writing to standard output.
SYSTEM REQUIREMENTS
In order to run Cleanfeed with a Highwind server, you will
need:
· Cyclone, Typhoon or Breeze
· Perl 5.003 or later
· The MD5 Perl module
The Highwind servers are commercial products. For more
information:
http://www.highwind.com/
The MD5 Perl module is available from:
http://www.perl.com/CPAN-local/modules/by-module/MD5/
Perl itself is available from the Perl home page:
http://www.perl.com/
INSTALLING CLEANFEED - HIGHWIND
The Cleanfeed program file should be installed as
"cleanfeed" in your news server's bin directory
(cyclone/bin, etc). Make it owned by news:news and make
it executable.
Before putting the filter in place, edit the file,
changing $config_dir to the location of your
cleanfeed.conf file. Also ensure that the shebang line
(the first line of the file, starting with #!) points to
the correct location of your perl executable.
After editing the file, always check for errors with the
command:
perl -cw cleanfeed
There should be no warnings.
Now, edit your bin/start script. You need to add two
options to the command line that starts up the server
process, the -program option to tell it what program to
use as a filter, and the -body option to tell it to send
the bodies as well as the headers.
typhoond -program /typhoon/bin/cleanfeed -body
...along with whatever else you have cluttering up the
command line.
file option in a future release.)
Now you can restart the server with the bin/restart
script. Check to make sure Cleanfeed is running, with "ps
-ef" or "top". If Cyclone/Typhoon is unable to start the
filter for some reason, it will log an error via syslog.
The error will not be terribly helpful.
You can make Cleanfeed reload its configuration from
cleanfeed.conf and local code from cleanfeed.local by
sending it a SIGHUP.
INSTALLATION - NNTPRELAY
Please note that I do not have an NNTPRelay server, nor
access to one, nor much interest in mucking around with
Windows NT, and thus I have not tested the NNTPRelay
filtering support myself. The necessary changes and notes
were contributed by someone else. Additions and
improvements to this documentation would be most welcome.
The filter interface in NNTPRelay is pretty much the same
as in the Highwind servers.
SYSTEM REQUIREMENTS
In order to run Cleanfeed with NNTPRelay, you will need:
· NNTPRelay version 1.1b4 or later
· Perl 5.003 or later
· The MD5 Perl module
NNTPRelay is available from:
http://nntprelay.maxwell.syr.edu/
An NT binary release of Perl 5.004, which apparently
includes the MD5 module, can be found at:
http://www.perl.com/CPAN/ports/win32/Standard/x86
The MD5 module (in source code) can be found at:
http://www.perl.com/CPAN-local/modules/by-module/MD5/
INSTALLING CLEANFEED - NNTPRELAY
Before putting the filter in place, edit the file,
changing $config_dir to the location of your
cleanfeed.conf file.
Install the Cleanfeed program file wherever is appropriate
on your system, as "cleanfeed.pl". Edit NNTPRelay's
config.txt file, adding an entry like this:
Of course, use the correct path to your Perl executable
and to the Cleanfeed program file. Now restart NNTPRelay.
If you defined a logfile in Cleanfeed, it should appear.
THE HACKER'S GUIDE
Cleanfeed will look for a file called cleanfeed.local, in
the same directory as cleanfeed.conf. If this file
exists, it will be loaded and evaluated as Perl code right
after the config file. This enables you to provide your
own local filter code which will survive an upgrade of the
main Cleanfeed source.
It will be reloaded when the filter is reloaded with
ctlinnd reload filter.perl meow (for INN), or when
configuration is reloaded with a SIGHUP (in standalone
mode). This means that you can modify the running code
without restarting Cleanfeed.
cleanfeed.local can define a number of different
subroutines, which, if defined, will be called at various
points in the filter process. Other subroutines can, of
course, be defined as required by your code.
The file is simply re-evaluated each time. So, if you
remove a subroutine from the file completely, that
subroutine will remain defined after the reload, because
nothing replaced it. You will need instead to define it
as an empty subroutine, or explicitely undef it, to make
it go away.
STUFF YOU CAN DEFINE
Cleanfeed will call the following subroutines, if they are
defined. See the section on return values for
instructions on what your code should return.
local_config
This is called after configuration is loaded, each
time. It will be called when the filter is reloaded
(with INN) or when configuration is reloaded with
SIGHUP (running standalone), as well as when the
filter is first run. No return value is expected.
local_filter_before_emp
Called for each (non-control) article, before any
other filters. General-purpose spam filters shouldn't
go here, because you really want to populate the EMP
hashes first.
local_filter_after_emp
Called for each (non-control) article, after the EMP
filters but before any other filters.
Called for each (non-control) article, after the
"simple" filters but before the "expensive" body
checks.
local_filter_scoring
Called during the scoring filter. Return the value,
positive or negative, by which to adjust the article's
score.
Warning: Here there be dragons! If you're going to
play with this please examine the existing source, and
use the debugging routines to watch what you're doing.
local_filter_last
Called for each (non-control) article, after all other
filters are done.
local_filter_cancel
Called for all cancel control messages.
local_filter_newrmgroup
Called for all newgroup and rmgroup control messages.
RETURN VALUES
The general filtering subroutines you can define
(local_filter_before_emp, local_filter_after_emp,
local_filter_middle, local_filter_last,
local_filter_cancel, and local_filter_newrmgroup) are
expected to return a value indicating whether you want to
accept the article being examined. If the article is
okay, you should return "" (empty string), in which case
filtering will proceed as usual. If you want to reject
the article, you return any other string, which will be
used as the reason.
The rejection code actually expects two return values --
the first string is the "verbose" rejection message, and
the second is the "non-verbose" message (see the verbose
configuration option). If only one is supplied, it will
be used for both purposes.
The scoring filter calls local_filter_scoring, which is
expected to return the value, postive or negative, by
which the article's score should be adjusted.
WHAT YOU GET
Your subroutines get information about the article in
several variables.
%hdr
A hash containing the article headers. The key is the
the value is the content of the header. When running
under INN, only headers known to INN will be included
in the hash (which includes any header used anywhere
in Cleanfeed). In standalone mode, all headers will
be present, but only the known headers will be sent in
canonical case; others will have the header name (and
thus hash key) in whatever case they are in the
article itself, making them difficult to find and use
consistently.
The message body is in this hash under the key
__BODY__. If running INN 2.x with storageapi, it will
be provided in wireformat, with lines terminated in
\r\n rather than just \n. With the traditional spool
format (and in all cases with INN prior to 2.x) lines
will be terminated only with \n.
Examples:
To get the Subject header as a scalar:
$hdr{'Subject'}
To get the entire message body as a scalar:
$hdr{'__BODY__'}
%lch
A hash containing lowercased versions of some of the
article headers. The hash keys are the header names
in all lowercase; the values are the contents of the
headers, with all letters forced to lowercase.
Currently, the only headers added to this hash are
From, Organization, Subject, Content-Type,
X-Newsreader, X-Newsposter, Message-ID, and Sender.
This hash is not availabe to local_filter_before_emp.
@groups
An array containing the newsgroups the article is
posted to (from the Newsgroups header). You can find
out how many groups the article is crossposted to with
"scalar @groups".
@followups
An array containing the newsgroups to which followups
are set (from the Followup-To header). If the article
has no Followup-To header, this array will be
identical to @groups. You can find out how many
groups followups are set to with "scalar @followups".
This is the preferred way to limit crossposting,
because limiting only by the Newsgroups header will
catch FAQs and such.
The number of lines in the message body. This is not
taken from the Lines header as that can be client-
supplied to fool filtering; this is determined by
counting the lines in the message body.
%gr A hash containing information about the groups the
article is posted to. This isn't very straightforward
and may not be useful to you, but I'm including it in
this documentation for completeness. The following
entries may be present in this hash:
$gr{'net'} - the number of net.* (Usenet II)
newsgroups the article is posted to, if any.
$gr{'other'} - the number of non-net.* groups the
article is posted to.
$gr{'md5skip'} - true if the article should be
exempted from the MD5 body checks (if all newsgroups
match the regexp in md5exclude).
$gr{'binary'} - true if the article is posted only to
groups where binaries are allowed (if all newsgroups
match bin_allowed).
$gr{'html'} - true if the article is posted only to
groups where html is allowed (if all newsgroups match
html_allowed).
$gr{'poison'} - number of 'poison' newsgroups this
article is posted to (matching poison_groups). If
this is present, you'll only see this entry in
local_filter_before_emp and local_filter_after_emp
because it will be rejected after that.
$gr{'abuse'} - number of 'net abuse' newsgroups this
article is posted to (matching net_abuse_groups).
$gr{'reports'} - number of 'spam reports' newsgroups
this article is posted to (matching
spam_report_groups).
$gr{'low_xpost'} - number of 'low crosspost limit'
groups this article is posted to (matching
low_xpost_groups).
$gr{'mod'} - number of moderated groups this article
is posted to (requires that Cleanfeed have an active
file).
$gr{'allmod'} - true if this article is posted only to
moderated groups.
news.answers.
%config
A hash containing all configuration options.
DEBUGGING
When you make filtering changes, you should always check
the results for false positives. I've provided two
subroutines to help you do this: writeheaders() and
writefull().
First, make sure debug_batch_directory is set in your
configuration. Set this to a directory that is writable
by the news user.
Call either of these subroutines with one argument, the
basename of the batch file you want to write the current
article to. writeheaders will dump the article's headers
out to the file (with INN this will only give you the
known headers). writefull will dump the full article,
headers (again, known headers with INN) and body. The
file will be rotated if it becomes larger than
debug_batch_size, set in your configuration. The rotation
is simple, a number is appended to the end of the file,
and incremented until the filename does not exist. You'll
have to delete the old files yourself.
When testing a new filter, simply call writeheaders
("batchfile") or writefull ("batchfile") when you're going
to reject an article. Then you can look at the file to
make sure you're doing what you think you're doing.
SIGNALS
When running under Cyclone, Typhoon, Breeze, or NNTPRelay
(standalone mode), Cleanfeed will catch SIGHUP, and reload
its configuration from cleanfeed.conf. It will also
reload and reevaluate cleanfeed.local if you're using it.
Note that, unlike INN, there is no way to reload the
filter code itself without restarting the server.
Cleanfeed in standalone mode will also catch SIGUSR1 and
write its crude current-status file (see statfile in the
config section) on the next cycle through the filter.
(I honestly don't know if SIGUSR1 and SIGHUP are things
which exist on NT for NNTPRelay.)
CREDITS
Written by Jeremy Nixon <jeremy@exit109.com>.
Originally based on Jeff Garzik's EMP filter.
or fixes for the filter, but I'd like to acknowledge the
substantial contributions of several people: Danhiel
Baker, Frank Copeland, Brian Moore, John Payne, Russ
Allbery, David Riley, and SeokChan LEE. Thanks, guys.
dynamic-load.patch is from Piers Cawley. The body-
filtering portion of the INN filter.patch is from Jeff
Garzik. messageid.patch is from Ed Mooring. mode.patch
is from John Payne.
COPYRIGHT
Copyright 1997-1998 by Jeremy Nixon, All Rights Reserved.
LICENSE
This software may be distributed freely, provided it is
intact (including all the files from the original
archive). You may modify it, and you may distribute your
modified version, provided the original work is credited
to the appropriate authors, and your work is credited to
you (don't make changes and pass them off as my work), and
that you aren't charging for it.
AVAILABILITY
This filter is available at:
http://www.exit109.com/~jeremy/news/antispam.html
ftp://ftp.exit109.com/users/jeremy/
Man(1) output converted with
man2html