Dansguardian
Dansguardian web content filtering HOWTO install & configure on sme 7.x
Author: Ray Mitchell - mitchellcpa_AT_yahoo_dot_com_dot_au
Howto Release Date & Version: 11 July 2007 - v7.3
sme server version supported: 7.1.3
Contributors
Thanks to Stephen Noble at dungog.net for providing rpms & information generally. This HOWTO requires command line control to edit configuration files & restart the dansguardian service after configuration changes.
Dungog.net sells a commercial implementation of Dansguardian for sme server which adds a server manager panel to allow GUI control of all Dansguardian functionality & settings.
Information
To have a proper understanding of how Dansguardian works and the importance of certain configuration settings you should read the detailed installation notes and Manual at the Dansguardian web site http://dansguardian.org
An old version 2.4 installation notes are here: http://dansguardian.org/downloads/detailedinstallation2.4.html#further
The FAQ is here: http://sourceforge.net/docman/display_doc.php?docid=27215&group_id=131757
Information about group configuration is here: http://contentfilter.futuragts.com/wiki/index.php?title=Group_Configuration
Mailing list is here: http://tech.groups.yahoo.com/group/dansguardian/
The information on the Dansguardian website is of a generic nature and some of it is NOT applicable to sme server installations, refer to the instructions in this HOWTO in preference.
Installation instructions
Download the required rpms into an empty folder on your sme server using the Linux wget command
wget http://mirror.contribs.org/smeserver/contribs/rmitchell/smeserver/contribs/dansguardian/rpms/2.9.8-2/dansguardian-2.9.8-2.noarch.rpm
wget http://mirror.contribs.org/smeserver/contribs/rmitchell/smeserver/contribs/dansguardian/rpms/2.9.8-2/smeserver-dansguardian-2.9-3.el4.sme.noarch.rpm
wget http://mirror.contribs.org/smeserver/contribs/rmitchell/smeserver/contribs/dansguardian/rpms/2.8.0.6/dungog-blacklists-1.0-20061002.noarch.rpm
Install the rpms
yum localinstall *.rpm
Alternatively you can add the dungog repository
The following command will configure the Dungog repository on SME Server. The dungog repository will no longer be updated. All the contribs from this repository have been moved to the smecontribs repository.
DungogMember contribs are still at http://www.dungog.net After adding it to the database we have to update the changes to the configuration file:
signal-event yum-modify
yum --enablerepo=dungog install dansguardian smeserver-dansguardian dungog-blacklists pcre
To view available updates
yum --enablerepo=dungog list updates
Modifying Dansguardian configuration
You need to manually modify configuration files /etc/dansguardian/dansguardian.conf and /etc/dansguardian/dansguardianf1.conf and /etc/dansguardian/dansguardianf2.conf and /etc/dansguardian/dansguardianf3.conf and so on depending on the number of filter groups you wish to have.
pico -w /etc/dansguardian/dansguardian.conf
You will initially need to change:
accessdeniedaddress = 'http://YOURSERVER.YOURDOMAIN/cgi-bin/dansguardian.pl'
for example to
accessdeniedaddress = 'http://www.mydomain.com/cgi-bin/dansguardian.pl'
Make any other required changes to suit your situation by carefully reviewing the other setting possibilities
Ctrl o (to save)
Ctrl x (to exit)
pico -w /etc/dansguardian/dansguardianf1.conf
You may initially need to change (to suit adult level of protection)
naughtynesslimit = 50
to
naughtynesslimit = 160 (or even 250 or 300 depending on your sensitivity/tolerance requirements)
Make any other required changes to suit your situation by carefully reviewing the other setting possibilities
Ctrl o and Ctrl x
If you wish to use additional filter groups then edit further configuration files.
pico -w /etc/dansguardian/dansguardianf2.conf
Make any required changes to suit your situation by carefully reviewing all the setting possibilities
Ctrl o and Ctrl x
pico -w /etc/dansguardian/dansguardianf3.conf
Make any required changes to suit your situation by carefully reviewing all the setting possibilities
Ctrl o and Ctrl x
Modifying other Dansguardian configuration files
You will need to change other config files to suit your site requirements:
You can read information in the beginning of each config file that explains usage & syntax
These are located in /etc/dansguardian/lists... /etc/dansguardian/lists/f1/... /etc/dansguardian/lists/f2/... & so on and subfolders
eg
pico -w /etc/dansguardian/lists/f1/bannedextensionlist
make the required changes
Ctrl o and Ctrl x
Most users will need to change these 4 files as a minimum
bannedextensionlist
bannedsitelist
bannedurllist
exceptionsitelist
You should review ALL the dansguardian config files in /etc/dansguardian/lists and subfolders as part of your initial Dansguardian setup.
Some of the default settings in these files will prevent access to certain web sites and file types, which may conflict with your site requirements. See details in the "Further customisation" section at the end of this Howto or at http://dansguardian.org
Modifying the default html error message page
You may also want to tailor the html template for the error message displayed when Dansguardian blocks a site, see
/etc/dansguardian/languages/(languagename)/template.html
eg
pico -w /etc/dansguardian/languages/ukenglish/template.html
Starting Dansguardian
After install & initial configuration you must manually start Dansguardian to enable web content filtering
(Note that suitable links to start Dansguardian at startup/reboot are setup when the rpm is installed)
/etc/init.d/dansguardian start
Stopping Dansguardian
If you need to stop Dansguardian (ie to disable filtering or test your system without Dansguardian running)
/etc/init.d/dansguardian stop
Restarting Dansguardian
You will need to restart Dansguardian after making any configuration changes (so they can take effect)
/etc/init.d/dansguardian restart
Status check of Dansguardian
If you need to check that Dansguardian is running
/etc/init.d/dansguardian status
Configuring your system to force Dansguardian usage & prevent bypassing
Dansguardian uses port 8080 for web proxy requests. If your browser does not use port 8080 then Dansguardian filtering will be bypassed. To force this usage & prevent users bypassing filtering you should do the following steps:
1) Configure your sme server to use Transparent Proxy port 8080 and to block direct access to the squid proxy port 3128 & redirect port 80 to port 8080
Note the functionality to create custom firewall rules using iptables is built in to the rpms provided by http://www.dungog.net
config setprop squid TransparentPort 8080 config setprop dansguardian portblocking yes signal-event post-upgrade; signal-event-reboot
To return Transparent Proxy port to default value and to disable portblocking
config delprop squid TransparentPort 3128 config delprop dansguardian portblocking signal-event post-upgrade; signal-event-reboot
2) Configure your workstation web browser to auto detect proxy port
Go to your workstation and open your browser eg Internet Explorer or Firefox or your preferred browser
Change the settings for Connections to LAN
Select Auto detect proxy
Or alternatively use the server IP 192.168.1.1 (or whatever yours is) and use a port of 8080
Configuring Dansguardian to use Auth login
This functionality is built in to the rpms provided by http://www.dungog.net & requires enabling with a db command
Dansguardian supports different types of auth login ie nsca, pam & ident
Depending on your requirements, enable using the appropriate command. Most users of sme will probably use pam auth as that will authorise access against sme users and passwords.
For details regarding the various auth login methods & other configuration requirements, see http://dansguardian.org or Google, select one
config setprop squid RequireAuth pam config setprop squid RequireAuth nsca config setprop squid RequireAuth ident
To disable Auth login
config delprop squid RequireAuth
To enable any of the above setting changes you must follow the command with:
expand-template /etc/squid/squid.conf sv t /service/squid
If you are using nsca auth, create the user & password authentication list (you don't require users to be valid sme users)
touch /home/e-smith/db/proxyusers
Enter user names & password combinations one by one using this command
htpasswd -b /home/e-smith/db/proxyusers username password
You can test the authentication list using the following command
/usr/lib/squid/ncsa_auth /home/e-smith/db/proxyusers
Then enter the username & password when asked
You will see a ERR or OK response
If you are using ident auth, you will require a ident client/server on your workstation. One windows ident client is available from:
https://sourceforge.net/projects/retinascan
Groups and Auth login
See http:/dansguardian.org re Group configuration functionality in relation to Auth login (ie filtering users access rights based on group membership)
The Group filter files are located in:
/etc/dansguardian/lists/f1/...
/etc/dansguardian/lists/f2/...
/etc/dansguardian/lists/f3/...
and so on depending on the number of groups you set up
Edit these to suit your site requirements
*********************************************************************************************
The following are rough notes re creating additional files & configuration steps needed for multiple filter groups.
This section is a work in progress & will be tidied up later.
Do not literally use/copy these steps as if they are sme commands as they are not, they are procedural steps to give a brief indication of what is involved.
configure pam auth using the db command from howto
copy /etc/dansguardian/dansguardianf1.conf to /etc/dansguardian/dansguardianf2.conf
and to a f3 version if required also
Copy /etc/dansguardian/list/f1 to /etc/dansguardian/list/f2 including all subfolders and files
edit /etc/dansguardian/dansguardianf2.conf and change all instances of f1 to f2 in filename locations
edit /etc/dansguardian/dansguardian.conf
Filter group options
filtergroups = 2
or however many filter groups you want to have
Auth plugins
remove # from in front of
authplugin = '/etc/dansguardian/authplugins/proxy-basic.conf'
leave other possibilities with # at start of line
edit /etc/dansguardian/dansguardianf1.conf
change Filter group mode
leave this unchanged as this group will be the filtered standard users group
groupmode = 1
Filter group name
remove # from front of groupname =
change to
groupname = 'Standard Users'
edit /etc/dansguardian/dansguardianf2.conf
change Filter group mode
change this as this group will be the unfiltered Admin Users group
groupmode = 2
Filter group name
remove # from front of groupname =
change to
groupname = 'Admin Users'
Content filtering files location
change all these to show f2 in the location path
change all other occurrences of f1 to f2 in file paths
edit /etc/dansguardian/lists/filtergroupslist
add entries for users who are members of filter group2
use this format
username=filtergroupnumber
eg
ray=filter2
It's not necessary to add all users who are in filter group 1 as everyone is automatically a member of group 1 by default.
Filter group 2 settings override filter group 1
restart dansguardian for changes to take effect
/etc/init.d/dansguardian restart
You can create as many groups as you want, using similar steps as above.
Each group can have different levels of filtering eg different exceptionlists and naughtyness limits etc etc etc.
edit the exception and banned lists in
/etc/dansguardian/lists/f3/exceptionsitelist etc etc etc
and in each other group list structure eg f1 & f2
obviously if f2 is a unfiltered group then setting changes to exception & other lists will have no effect
In practice you get asked for a login user & password when you access a web site.
Depending on your group membership you get filtered or unfiltered access.
Testing access
From a workstation web browser go to the site of www.sex.com or www.sex.com.au
You should receive a message advising the site is blocked. Try browsing to other sites with inappropriate content or a site on your banned site list and you should receive a site blocked message.
Remember that access to sites is controlled by settings in the config files.
General information re Blacklists
You can install blacklists from mesd.k12.or.us or alternatively use the commercial blacklist from URLBlacklist.com
If you choose to use or trial the lists from blacklist .com, download the tgz file, uncompress and move to the
/etc/dansguardian/blacklists directory. There is also a blacklist from dungog.net that was installed at the beginning of this HOWTO.
Further customisation - configuration options
DansGuardian is highly configurable. The source code is available so you have the ultimate in configurability, although most people will be content with modifying the configuration files.
After you have modified any configuration file, to apply the changes you will need to restart DansGuardian.
There are two main configuration files, several banned lists and exception lists. These are all explained below:
exceptionsitelist
This contains a list of domain endings that if found in the requested URL, DansGuardian will not filter the page. Note that you should not put the http:// or the www. at the beginning of the entries.
exceptioniplist
This contains a list of client IPs who you want to bypass the filtering. For example, the network administrator's computer's IP.
exceptionuserlist
Usernames who will not be filtered (basic authentication or ident must be enabled).
exceptionphraselist
If any of the phrases listed here appear in a web page then the filtering is bypassed. Care should be taken adding phrases to this file as they can easily stop many pages from being blocked. It would be better to put a negative value in the weightedphraselist.
exceptionurllist
URLs in here are for parts of sites that filtering should be switched off for.
bannediplist
IP addresses of client machines to disallow web access to. Only put IP addresses here, not host names.
bannedphraselist
This contains a list of banned phrases. The phrases must be enclosed between < and >. DansGuardian is supplied with an example list. You can not use phrases such as <sex> as this will block sites such as Middlesex University. The phrases can contain spaces. Use them to your advantage. This is the most useful part of DansGuardian and will catch more pages than PICS and URL filtering put together.
Combinations of phrases can also be used, which if they are all found in a page, it is blocked. Exception phrases are no longer listed in this file - see exceptionphraselist.
banneduserlist
Users names, who, if basic proxy authentication is enabled, will automatically be denied web access.
bannedmimetypelist
This contains a list of banned MIME-types. If a URL request returns a MIME-type that is in this list, DansGuardian will block it. DansGuardian comes with some example MIME-types to deny. This is a good way of blocking inappropriate movies for example. It is obviously unwise to ban the MIME-types text/html or image/*.
bannedextensionlist
This contains a list of banned file extensions. If a URL ends in an extension that is in this list, DansGuardian will block it. DansGuardian comes with some example file extensions to deny. This is a good way of blocking kiddies from downloading those lovely screen savers and hacking tools. You are a fool if you ban the file extension .html, or .jpg etc.
bannedregexpurllist
This contains a list of banned regular expression URLs. For more information on regular expressions, see http://www.opengroup.org/onlinepubs/7908799/xbd/re.html
Regular expressions are a very powerful pattern matching system. This file allows you to match URLs using this method.
bannedsitelist
This file contains a list of banned sites. Entering a domain name here bans the entire site. For banning specific parts of a site, see bannedurllist. Also, you can have a blanket ban all sites except those specifically excluded in exceptionsitelist. You can also block sites specified only as an IP address, and include a stock squidGuard blacklists collection. To enable these blacklists, download them from the extras section http://dansguardian.org/?page=extras
Simply put them somewhere appropriate, un-comment the squidGuard blacklists collection lines at the bottom of the bannedsitelist file, and check the paths are correct. For URL blacklists, edit the bannedurllist in a similar way.
bannedurllist
This allows you to block specific parts of a site rather than the whole site. To block an entire site, see bannedsitelist. To enable squidGuard blacklists for URLs, you will need to download the blacklists and edit the squidGuard blacklists collection section at the bottom (as for bannedsitelist above).
weightedphraselist
Each phrase is given a value either positive or negative and the values are added up. Phrases to do with good subjects will have negative values, and bad subjects will have positive values. Once the naughtyness limit is reached (within dansguardian.conf), the page is blocked. See the Naughtyness Limit description within the dansguardian.conf section below.
pics
This file allows you to finely tune the PICS filtering. Each PICS section comes with a description of the allowed settings and what they represent. The default settings with DansGuardian are set for youngish children, for example mild profanities and artistic nudity are allowed. PICS filtering can also be totally disabled / enabled using the enablePICS = on | off option.
For more detailed information on PICS ratings, see http://www.w3.org/PICS/
contentregexplist
ICRA
The ICRA section is fairly self-explanatory. A value of 0 means nothing of that category is allowed, whereas a value of 1 allows it. For example,
ICRAnudityartistic = 1
allows nude art. For more in-depth information see http://www.rsac.org/
RSAC
RSAC is an older version of ICRA. The values here range from 0 meaning none allowed, through 2 (the default value), to 4, which allows wanton and gratuitous amounts of the given category. For more in-depth information see http://www.rsac.org/
evaluWEB
evaluWEB rating uses a system similar to the British Film classification system:
0 = U (Universal, ie. suitable for even the youngest viewer)
1 = PG (Parental Guidance recommended)
2 = 18 (Only suitable for viewers aged 18 and over)
SafeSurf
Similar to RSAC, but containing a larger range of categories with the range from 0 = full filtering to 9 = wanton and gratuitous. For more in-depth information, see http://www.safesurf.com
Weburbia
See evaluWEB. For more in-depth information, see http://www.weburbia.com/safe/index.shtml
Vancouver Webpages
This is yet another ratings scheme. See http://vancouver-webpages.com/VWP1.0/
for more information.
dansguardian.conf & dansguardianf1.conf
The only setting that is vital for you to configure in the dansguardian.conf file is the accessdeniedaddress setting. You should set this to the address (not the file path) of your Apache server with the perl access denied reporting script. For most people this will be the same server as squid and DansGuardian. If you really want you can change this address to a normal html static page on any server.
Reporting Level
You can change the reporting level for when a page gets denied. It can say just 'Access Denied', or report why, or report why and what the denied phrase is. The latter may be more useful for testing, but the middler would be more useful in a school environment. Stealth mode logs what would be denied but doesn't do any blocking.
Logging Settings
This setting lets you configure the logging level. You can log nothing, just denied pages, text based and all requests. HTTPS requests only get logged when the logging is set to 3 - all requests.
Log Exception Hits
Log if an exception (user, ip, URL, or phrase) is matched and so the page gets let through. This can be useful for diagnosing why a site gets through the filter.
Log File Format
This setting alters the format of the DansGuardian log file. Please note option 3 (standard log format) is not yet unimplemented.
Network Settings
These allow you to modify the IP address that DansGuardian is listening on, the port DansGuardian listens on, the IP address of the server running squid as well as the squid port. It is possible to configure the Access Denied reporting page here also.
Content Filtering Settings
Here you can modify the location of the list files. Adjusting these locations is not recommended.
Naughtyness limit
This setting refers to the weighted phrase limit over which the page will be blocked. Each weighted phrase is given a value either positive or negative and the values added up. Phrases to do with good subjects will have negative values, and bad subjects will have positive values. See the weightedphraselist file for examples. As a rough guide, a value of 50 is for young children, 100 for older children, 160 for young adults.
Show weighted phrases found
If enabled then the phrases found that made up the total which exceeds the naughtyness limit will be logged and, if the reporting level is high enough, reported.
Reverse Lookups for Banned Sites and URLs
If set to on, DansGuardian will look up the forward DNS for an IP URL address and search for both in the banned site and URL lists. This would prevent a user from simply entering the IP for a banned address. It will reduce searching speed somewhat so unless you have a local caching DNS server, leave it off and use the Blanket IP Block option in the bannedsitelist file instead.
Build bannedsitelist and bannedurllist Cache Files
This will compare the date stamp of the list file with the date stamp of the cache file and will recreate as needed. If a bsl or bul .processed file exists, then that will be used instead. It will increase process start speed by 300%. On slow computers this will be significant. Fast computers do not need this option.
POST protection (web upload and forms)
This is for blocking or limiting uploads, not for blocking forms without any file upload. The value is given in kilobytes after MIME encoding and header information.
Username identification methods (used in logging)
The proxyauth option is for when basic proxy authentication is used (obviously no good for transparent proxying). The ntlm option is for when the proxy supports the MS NTLM authentication. This only works with IE5.5 sp1 and later, and has not been implemented yet. The ident option causes DansGuardian to try to connect to an identd server on the computer originating the request.
Forwarded For
This option adds an X-Forwarded-For: <clientIP> to the HTTP request header. This may help solve some problem sites that need to know the source IP.
Max Children
This sets the maximum number of processes to spawn to handle the incoming connections. This will prevent DoS attacks killing the server with too many spawned processes. On large sites you might want to double or triple this number.
Log Connection Handling Errors
This option logs some debug info regarding fork()ing and accept()ing which can usually be ignored. These are logged by syslog. It is safe to leave this setting on or off.
