Dansguardian
Dansguardian web content filtering
Description
Dansguardian is a web content filter, which analyses the actual content of web pages based on many criteria including phrase matching, PICS filtering, URL filtering and lists of banned sites. Each content type is given a score, and when the threshold score is exceeded, access to the web site is blocked. For additional information see http://dansguardian.org
This HOWTO requires command line control to edit configuration files & restart the dansguardian service after configuration changes.
There is a commercial implementation of Dansguardian for sme server which adds a server manager panel to allow GUI control of all Dansguardian functionality & settings, see http://dungog.net/wiki/Dungog-dansguardian
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 and other websites referred to, 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
Install dansguardian and it's dependencies from the smecontribs repository
yum --enablerepo=smecontribs install smeserver-dansguardian
Optional, download and install a set of blacklists from http://urlblacklist.com/ alternatively you can choose ftp://ftp.ut-capitole.fr/pub/reseau/cache/squidguard_contrib/blacklists.tar.gz from http://dsi.ut-capitole.fr/blacklists/
Upgrading
There are substantial changes between dansguardian v2.9 over previous v2.8 (or earlier) installations. The recommendation from dansguardian.org is to edit the new configuration files/lists rather than try to edit your old ones.
Upgrading from 2.9 versions creates .rpmnew config files under /etc/dansguardian. This preserves your existing config files, but there is a chance that dansguardian won't start if parameters in the config file have changed.
Clamav libraries can cause problems when updating. If while updating you see something like
Error: Missing Dependency: libclamav.so.3 is needed by package dansguardian
Update with
yum update --enablerepo=smecontribs dansguardian clamav
then
yum update
Modifying Firewall and Proxy
Configuring your system to force Dansguardian usage & prevent bypassing
These instructions assume that the sme server is running in server gateway mode and acting as the gateway for your network, and the squid proxy is running on the same machine that Dansguardian is running on.
If your server is configured in server only mode, then you will need to point your browser at that machine to find the squid proxy rather than the default gateway.
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 ALL 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 the required custom firewall rules using iptables is built in to the smeserver-dansguardian and is configured with the following commands. The Transparent proxy must also be enabled (which is the sme default) to prevent users bypassing Dansguardian filtering.
config setprop squid TransparentPort 8080 config setprop squid Transparent yes config setprop dansguardian portblocking yes signal-event post-upgrade; signal-event reboot
To return Transparent Proxy port to default value and to disable portblocking and to enable the Transparent proxy (which is the sme default)
config setprop squid TransparentPort 3128 config setprop squid Transparent yes 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
Bypass Proxy
Allow individual PC's or selected sites to bypass the proxy (and dansguardian) entirely see Firewall#Bypass_Proxy.
Workstation IP allocation
Control of workstation access to the web (when using dansguardian), is implemented by nominating the workstation IP in the various dansguardian configuration files (ie the local LAN IP address). To apply consistent filtering rules or allow proxy bypass (see section above), the workstation IP must remain the same throughout restarts & DHCP IP refreshes or allocations. Configuring your workstations to have a consistent IP is a fundamental & important step when configuring your whole computer system.
This can be achieved by manually specifying a fixed IP address when each workstation is configured, but requires every workstation to be setup individually. Alternatively the workstation can be configured for auto allocation of an IP, and the Hostnames and Addresses panel in server manager can then be used to force the allocation of a specified IP by the SME DHCP server, based on the workstation NIC mac address. See the SME Manual for further details at http://wiki.contribs.org/SME_Server:Documentation:Administration_Manual:Chapter13#Reserving_IP_Addresses_Through_DHCP The basic steps are to determine the mac address of your workstation NIC and then create a hostname eg station5 and enter the mac address and the required "forced or fixed" IP eg 192.168.1.5
Any reference to the filtering of station5 then uses the IP 192.168.1.5, which will always stay the same, unless the NIC is changed. Remember to re-enter the mac address details into server manager, in the event the workstation NIC or motherboard is changed.
Configuring Proxy to use Auth login
Dansguardian supports different types of auth login ie ncsa, pam & ident, and allows control of web site access based on user name. For more details regarding the various auth login methods & other configuration requirements, see http://dansguardian.org or Google.
Enable this functionality using the appropriate command, depending on your requirements. Most users of sme will probably use pam auth as that will authorise access against sme users and passwords.
Choose one of the following
config setprop squid RequireAuth pam config setprop squid RequireAuth ncsa 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
Using NCSA Auth login
If you are using ncsa auth, create the user & password authentication list (you don't require users to be valid sme users)
touch /etc/proxyusers
Enter user names & password combinations one by one using this command
htpasswd -b /etc/proxyusers username password
You can test the authentication list using the following command
/usr/lib/squid/ncsa_auth /etc/proxyusers
Then enter the username & password when asked
You will see a ERR or OK response
Using Ident login
If you are using ident auth, you will require a ident client on your workstation. One windows ident client is available from:
https://sourceforge.net/projects/retinascan
In some cases, the Windows firewall blocks access to the ident client and you will have to add an exception in your firewall rules as follows:
Control Panel >> Windows Firewall >> Exceptions >> Add Port
- Name: auth
- Port number: 113
- TCP
Modifying Dansguardian Configuration Files
Modifying Dansguardian dansguardian.conf & dansguardianf1.conf files
You need to manually modify various configuration files. As a minimum the following basic changes need to be made:
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
To save & exit
Ctrl o Ctrl x
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
Save & exit
Ctrl o Ctrl x
Additional Options can be found here, http://wiki.contribs.org/Dansguardian/ConfigFiles under the topic dansguardian.conf & dansguardianf1.conf
If you have additional filter groups, then additional configuration files will need to be created and modified. See section on "Filter Groups and Auth login" below.
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/f2/...
& so on and subfolders
eg
pico -w /etc/dansguardian/lists/f2/bannedextensionlist
make the required changes
Ctrl o 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.
For many more details and descriptions on the configuration files see Dansguardian/ConfigFiles page 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
After you make any changes to the template.html you will need to run the command,
/etc/init.d/dansguardian restart
for the changes to take effect.
Filter Groups and Auth login
Dansguardian supports filter groups, which allow web access control of users based on filter group membership. Different users can have different access rights, and to achieve this each filter groups configuration files are configured with different access rights. Users are made members of the required filter group by editing /etc/dansguardian/lists/filtergroupslist
When you open a web browser you get asked to login with a username & password. Depending on the users group membership they get filtered or unfiltered access.
For additional information on filtering users access rights based on group membership (in conjunction with Auth login), see http:/dansguardian.org
In order to use filter groups, you must be using one of the Auth login methods.
If you wish to authenticate users when opening a browser using pam auth method, then you will need to disable Transparent Proxy as it is not compatible with this method.
Issue the following command
config setprop squid Transparent no expand-template /etc/squid/squid.conf sv t /service/squid
Doing the above will also require you to manually specify the proxy settings in your browser, so you will need to add the server IP eg 192.168.1.1 and port 8080 for the proxy setting
You cannot have pam auth enabled and Transparent Proxy set to yes.
Issue one of the following commands to enable the type of Auth login required, which will then permit the configuration & use of Filter Groups
config setprop squid RequireAuth pam config setprop squid RequireAuth ncsa config setprop squid RequireAuth ident
To enable any of the above settings do
expand-template /etc/squid/squid.conf sv t /service/squid
When using Filter Groups, a typical situation may have:
Filter Group 1 - blocked users (no access) - See [1] Filter Group 2 - standard users (standard access rights) Filter Group 3 - guest users (limited access rights) Filter Group 4 - power users (more generous access & file download rights) Filter Group 5 - admin users (unlimited access)
To create the additional filter group configuration files and folders do
cp /etc/dansguardian/dansguardianf1.conf /etc/dansguardian/dansguardianf2.conf cp /etc/dansguardian/dansguardianf1.conf /etc/dansguardian/dansguardianf3.conf cp /etc/dansguardian/dansguardianf1.conf /etc/dansguardian/dansguardianf4.conf cp /etc/dansguardian/dansguardianf1.conf /etc/dansguardian/dansguardianf5.conf
Because the Filter Group 1 (default) uses the configuration files located at the root of "/lists" directory, it is only necessary to create the rest of the directories f2, f3, f4 and f5 to host the configuration files for each Filter Group.
Each filter directory (f2, f3, etc.) will house all the configuration files located at the root of "/lists" directory unless filtergroupslist, bannediplist and exceptioniplist, because they are not used for filtering because only they are called (logically) from the general configuration file dansguardian.conf.
Because the configuration files are modified, is a smart idea to create a "virgin" copy of the files and then use it to create new filters directory. This directory will named "virgin" or something similar.
mkdir -p /etc/dansguardian/lists/virgin cp /etc/dansguardian/lists/* /etc/dansguardian/lists/virgin rm -f /etc/dansguardian/lists/virgin/filtergroupslist rm -f /etc/dansguardian/lists/virgin/bannediplist rm -f /etc/dansguardian/lists/virgin/exceptioniplist cp -R /etc/dansguardian/lists/virgin /etc/dansguardian/lists/f2 cp -R /etc/dansguardian/lists/virgin /etc/dansguardian/lists/f3 cp -R /etc/dansguardian/lists/virgin /etc/dansguardian/lists/f4 cp -R /etc/dansguardian/lists/virgin /etc/dansguardian/lists/f5
(which will include all subfolders and files)
Then edit & save the various main configuration files
pico -w /etc/dansguardian/dansguardianf2.conf
and change all instances of /lists/ to /lists/f2/ in filename locations
pico -w /etc/dansguardian/dansguardianf3.conf
and change all instances of /lists/ to /lists/f3/ in filename locations
pico -w /etc/dansguardian/dansguardianf4.conf
and change all instances of /lists/ to /lists/f4/ in filename locations
pico -w /etc/dansguardian/dansguardianf5.conf
and change all instances of /lists/ to /lists/f5/ in filename locations
Edit & save the main dansguardian configuration file to setup filter groups
pico -w /etc/dansguardian/dansguardian.conf
Configure the following settings as shown
#Filter group options filtergroups = 5
(or however many filter groups you want to have)
#Auth plugins authplugin = '/etc/dansguardian/authplugins/proxy-basic.conf'
(leave other possibilities with # at start of line)
Edit Filter Group 1 main configuration file
pico -w /etc/dansguardian/dansguardianf1.conf
Configure the following settings as shown
#Filter group mode groupmode = 0
#Filter group name groupname = 'Blocked Users'
Edit & save Filter Group 2 main configuration file
pico -w /etc/dansguardian/dansguardianf2.conf
Configure the following settings as shown
#Filter group mode groupmode = 1
#Filter group name groupname = 'Standard Users'
Edit & save Filter Group 3 main configuration file
pico -w /etc/dansguardian/dansguardianf3.conf
Configure the following settings as shown
#Filter group mode groupmode = 1
#Filter group name groupname = 'Guest Users'
Edit & save Filter Group 4 main configuration file
pico -w /etc/dansguardian/dansguardianf4.conf
Configure the following settings as shown
#Filter group mode groupmode = 1
#Filter group name groupname = 'Power Users'
Edit & save Filter Group 5 main configuration file
pico -w /etc/dansguardian/dansguardianf5.conf
Configure the following settings as shown
#Filter group mode groupmode = 2
#Filter group name groupname = 'Admin Users'
Edit & save the Filter Groups List file to add details of users and their group membership
All users are automatically members of Filter Group 1, so you only need to add details of users who are in other groups.
pico -w /etc/dansguardian/lists/filtergroupslist
add entries for users who are members of other filter groups, use this format
username=filtergroupnumber
for example
ray=filter2 george=filter3 mary=filter4 peter=filter5
and so on.
Filter group 2,3,4 & 5 settings override filter group 1 settings.
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.
edit the exception and banned lists in
pico -w /etc/dansguardian/lists/f2/exceptionsitelist
etc etc
and in each other group list structure eg f3, f4 & f5
Where f2 is a blocked group then setting changes to exception & other lists for that group will have no effect. Where f5 is a unfiltered group then setting changes to exception & other lists for that group will have no effect.
ClamAV support
If you want to use DansGuardian with SME antivirus, edit /etc/dansguardian/dansguardian.conf and uncomment following line:
contentscanner = '/etc/dansguardian/contentscanners/clamdscan.conf'
Now at the end of the file, add following lines:
# OPTION: virusscanexceptions # If off, antivirus scanner will ignore exception sites and urls. virusscanexceptions = on
also edit /etc/dansguardian/contentscanners/clamdscan.conf and uncomment
+ clamdudsfile = '/var/clamav/clamd.socket' - #clamdudsfile = '/var/run/clamav/clamd.socket'
If you also want to be warned each time a bad page is blocked, edit /etc/dansguardian/dansguardianf1.conf and modify default settings:
usesmtp = on mailfrom = 'dansguardian' avadmin = 'admin' contentadmin = 'admin' notifyav = on <= virus mail alert notifycontent = on <= content mail alert
Restart dansguardian and try to download eicar test virus
DansGuardian should block the download!
Other Dansguardian Config Files
There are many other config files, including but not limited to the ones in this appendix
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
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.
Using Group Policy Editor to force proxy port setting on workstations
If you are using Windows & Internet Explorer you can use Group Policy Editor (gpedit.msc) to configure your workstation settings, to force all users of the workstation to use preset proxy port settings.
Refer to this forum thread for additional details
http://forums.contribs.org/index.php?topic=38284.0
Some users report that this method does not seem to work for them.
An alternative approach (which is known to work OK), is to use gpedit.msc to remove the IE menu option for changing connection settings. Do this using the following brief steps.
Run gpedit.msc
Select Local Computer Policy
Select User Configuration
Select Administrative Templates
Select Windows Components
Select Internet Explorer
Select Disable changing connection settings
Select Enabled then click OK
This will disable the Internet Explorer menu Tools/Internet Options/Connections, so ensure you have made the correct desired settings first.
Note that if TransparentPort = 8080 and portblocking = yes and you are not using Group Filtering, workstations can be set to "Auto detect proxy port" and will be forced to use Dansguardian.
Note that if Transparent = no and you are using Group Filtering with user login authentication, then your browsers proxy port will need to be set to port 8080 (for all users). If you are using Windows & Internet Explorer, then using gpedit.msc can simplify configuration for all users of workstations.
Bugs
Please raise bugs under the SME-Contribs section in bugzilla and select the smeserver-dansguardian component or use this link .