SetupSquidTransparentProxy

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Squid Transparent Proxy on Palm Pre

Ok, someone asked for it, so I figured it out, how to do it for fun and profit:

Preparation

First, you need to have root access to your device. How to get root, is described here. It would be a good idea to know a little about linux and networking too. Be warned: this can make your networking unfunctional!

Next thing you need to do is to install the package Optware Advanced Linux Command Line Installer from Preware, which installs ipkg-opt!

Installing Squid

Login to the pre console and make your root disk writable:

root@palm-webos-device: # cd / && mount -v -o remount,rw /

Type this command to install the squid optware package

root@palm-webos-device: # ipkg-opt update
...
root@palm-webos-device: # ipkg-opt install squid
Installing squid (2.6.21-2) to root...
Downloading http://ipkg.nslu2-linux.org/feeds/optware/cs08q1armel/cross/unstable/squid_2.6.21-2_arm.ipk
Configuring squid
create default cache and logs dir
chown: unknown user/group nobody:nobody
chown: unknown user/group nobody:nobody
FATAL: Could not determine fully qualified hostname.Please set 'visible_hostname'
 
Squid Cache (Version 2.6.STABLE21): Terminated abnormally.
CPU Usage: 0.020 seconds = 0.010 user + 0.010 sys
Maximum Resident Size: 0 KB
Page faults with physical i/o: 0
Segmentation fault
 
You should review the configuration file /opt/etc/squid/squid.conf,
make any necessary change, and complete the install by running -
/opt/etc/init.d/S80squid start
 
Successfully terminated.

Ignore the errors for the moment, we'll get to it soon.

Create a basic proxy config

Change to the directory /opt/etc/squid and move the file squid.conf which is already there to somewhere else. Now create a new squid.conf, which should have the following contents:

visible_hostname localhost
http_port 3128 transparent                 
hierarchy_stoplist cgi-bin ?               
access_log /var/cache/squid/squid.log squid          
acl QUERY urlpath_regex cgi-bin \?                   
cache deny QUERY 
 
# replace the ip address with the address of your proxy
# replace the port 3128 with the port of your proxy
cache_peer 192.168.2.205 parent 3128 3130 default 
 
# if your proxy requires authentication, use this:
# cache_peer 192.168.2.205 parent 3128 3130 default login USERNAME PASSWORD
 
refresh_pattern ^ftp:           1440    20%     10080
refresh_pattern ^gopher:        1440    0%      1440
refresh_pattern .               0       20%     4320
acl apache rep_header Server ^Apache                
broken_vary_encoding allow apache    
coredump_dir /var/cache/squid        
cache_dir ufs /var/cache/squid 20 5 5
access_log /var/cache/squid/squid.log
cache_log /var/cache/squid/cache.log
cache_store_log /dev/null
 
acl all src 0.0.0.0/0.0.0.0
acl manager proto cache_object
acl localhost src 127.0.0.1/255.255.255.255
acl to_localhost dst 127.0.0.0/8
acl SSL_ports port 443
acl Safe_ports port 80          # http
acl Safe_ports port 21          # ftp
acl Safe_ports port 443         # https
acl Safe_ports port 70          # gopher
acl Safe_ports port 210         # wais
acl Safe_ports port 1025-65535  # unregistered ports
acl Safe_ports port 280         # http-mgmt
acl Safe_ports port 488         # gss-http
acl Safe_ports port 591         # filemaker
acl Safe_ports port 777         # multiling http
acl CONNECT method CONNECT
http_access allow manager localhost
http_access deny manager
http_access deny !Safe_ports
http_access deny CONNECT !SSL_ports
# example for an ACL, uncomment and modify
#acl enemy dstdomain www.apple.com
#http_access deny enemy
 
http_access allow all
icp_access allow all

Basically this is a config for a transparent proxy, thus a browser will be redirected to it without knowing that it is actually connected to a proxy. We must configure it this way because the WebOS browser cannot be configured to use a proxy.

Note that we have added a single ACL here, which denies access to some random site *g*. Any other requests will be allowed. SSL (HTTPS) will not be passed through the proxy because this requires the browser to connect to it using a proxy request.

You WILL need to modify the squid.conf variable cache_peer, it points to your upstream proxy, e.g. your companys proxy. Refer to the comments for the syntax.

Prepare the directories for squid

Squid needs a directory where to store it's files, as content it caches and logfiles. You may consider to disable caching and logging. But caching may be a good idea if your traffic is limited, so you'll save some. Logging is always usefull for debugging. If you want to turn it off, use /dev/null as target for the logfiles.

mkdir /var/cache/squid
chown nobody /var/cache/squid

Next you need let squid to prepare the directory structure using the -z option:

root@palm-webos-device: # squid -z -f squid.conf
2009/11/26 23:19:29| Creating Swap Directories

You should not see any errors here!

Starting squid

The installer already added it to the startup daemons, now we will start it manually:

/opt/etc/init.d/S80squid start

Look in /var/cache/squid/cache.log for any errors. Use ps to see if it really runs. You may consider to install lynx and test the proxy:

ipkg-opt install lynx
export http_proxy=http://localhost:3128
lynx www.google.com

If you see a google textmode site, it works.

Turn it off if everything is ok:

/opt/etc/init.d/S80squid stop

Add the rules to the squid startup file

Now comes the ugly part. I'll not explain it in detail: we install some iptable Rules. We tell iptables to forward any traffic destined to tcp port 80 to localhost port 3128 (this is where squid listens for incoming connections). To avoid that the requests of the proxy itself are forwarded to localhost (which would create a loop), we add a rule telling iptables to not forward web traffic if it were generated by user nobody (the user squid runs as).

To do that, edit /opt/etc/init.d/S80squid so that it looks like this:

#! /bin/sh
 
case "$1" in
    start)
        echo -n "Starting proxy server: "
        if [ -n "`pidof quotacheck`" ]; then
           #you don't need it if you don't have quota check enable.
           echo "Starting squid-cache server after delay for few mins:"
           /opt/etc/squid/squid.delay-start.sh&
        else
           /opt/sbin/squid -f /opt/etc/squid/squid.conf
           iptables -t nat -A OUTPUT -p tcp --dport 80 -m owner --gid-owner 65534 -j ACCEPT
           iptables -t nat -A OUTPUT -p tcp --dport 80 -j DNAT --to-destination 127.0.0.1:3128
           echo "done."
        fi
        echo "done."
        ;;
    stop)
        echo -n "Stopping proxy server: "
        /opt/sbin/squid -f /opt/etc/squid/squid.conf -k shutdown
        iptables -t nat -D OUTPUT -p tcp --dport 80 -m owner --gid-owner 65534 -j ACCEPT
        iptables -t nat -D OUTPUT -p tcp --dport 80 -j DNAT --to-destination 127.0.0.1:3128
        echo "done."
        ;;
    reload|force-reload)
        echo -n "Reloading proxy server configuration files: "
        /opt/sbin/squid -f /opt/etc/squid/squid.conf -k reconfigure
        echo "done."
        ;;
    restart)
        echo -n "Restarting proxy server: "
        /opt/sbin/squid -f /opt/etc/squid/squid.conf -k shutdown
        sleep 2
        /opt/sbin/squid -f /opt/etc/squid/squid.conf
        echo "done."
        ;;
    *)
        echo "Usage: /opt/etc/init.d/S80squid {start|stop|reload|force-reload|restart}"
        exit 1
        ;;
esac

Configure network to startup squid if WIFI comes up

Now we need to alter the behavior of the palm network manager so that it starts squid if WIFI comes up and stops it when WIFI goes down.

Change to directory /etc/pmnetconfig/.

In the file if-up modify this part:

 if [ "$ISPPP" -ne 4 ] && [ "$ISRMNET" -ne 6 ] && [ "$ISTUN" -ne 4 ] && [ "$ISCSCOTUNVPN" -ne 8 ]; then
    NetCfgSetAddr
    CMSERVICES=$((${CMSERVICES} | ${CMSVCINTERNET}))
 fi

to

 if [ "$ISPPP" -ne 4 ] && [ "$ISRMNET" -ne 6 ] && [ "$ISTUN" -ne 4 ] && [ "$ISCSCOTUNVPN" -ne 8 ]; then
    NetCfgSetAddr
    CMSERVICES=$((${CMSERVICES} | ${CMSVCINTERNET}))
    /usr/bin/logger "wifi up: execute /opt/etc/init.d/S80squid start" 
    /opt/etc/init.d/S80squid start
 fi

In the file if-down modify this part:

 if [ ${CMINTERFACE} = ${CMBTINTERFACENAME} ] || [ ${CMINTERFACE} = ${CMBRINTERFACENAME} ]; then
    ${LOG} "${IPTABLES} -t nat -D POSTROUTING -s  $CMNETADDR/$CMPREFIXLEN -j MASQUERADE"
    ${IPTABLES} -t nat -D POSTROUTING -s $CMNETADDR/$CMPREFIXLEN -j MASQUERADE
    ${LOG} "${ECHO} 0 >/proc/sys/net/ipv4/ip_forward"
    ${ECHO} 0 >/proc/sys/net/ipv4/ip_forward
 fi

to:

 if [ ${CMINTERFACE} = ${CMBTINTERFACENAME} ] || [ ${CMINTERFACE} = ${CMBRINTERFACENAME} ]; then
    ${LOG} "${IPTABLES} -t nat -D POSTROUTING -s  $CMNETADDR/$CMPREFIXLEN -j MASQUERADE"
    ${IPTABLES} -t nat -D POSTROUTING -s $CMNETADDR/$CMPREFIXLEN -j MASQUERADE
    ${LOG} "${ECHO} 0 >/proc/sys/net/ipv4/ip_forward"
    ${ECHO} 0 >/proc/sys/net/ipv4/ip_forward
    /usr/bin/logger "wifi up: execute /opt/etc/init.d/S80squid stop"     
    /opt/etc/init.d/S80squid stop         
 fi

Make your root disk read-only again

root@palm-webos-device: # cd / && mount -v -o remount,ro /

See it working

So, let's see how it works. Enable WIFI and fire up the browser and see if it works. You should see your requests on the remote proxy.

If you added an ACL as mentioned earlier, a message like the following should appear if you enter the url of your favourite enemy vendor (the one we configured above):

Squid-access-denied-palm-pre.png

Blocking Adverts

Now squid is set up, we can use it for ad blocking. There are two steps to this:

Obtain a block list

An excellent ad block list is maintained at http://pgl.yoyo.org/as/. We need to download it in a suitable format for squid, which can be done by running the following command:

wget -q -O/opt/etc/squid/blocklist 'http://pgl.yoyo.org/as/serverlist.php?hostformat=squid-dstdom-regex;showintro=0&nohtml=true&mimetype=plaintext > /opt/etc/squid/blocklist

(Technical details: the wget command downloads the URL given in single quotes, then we strip the HTML mark-up and blank lines using grep. The filename at the end is where the black list will be stored.)

Configure squid to use the block list

Now we need to tell squid to block the list of URLs in the file we've just created. Open the /opt/etc/squid/squid.conf file we created above, and scroll down to where it reads:

acl enemy dstdomain www.apple.com

Replace this line with:

acl enemy dstdom_regex "/opt/etc/squid/blocklist"

Finally, restart squid:

/opt/etc/init.d/S80squid restart

To test it's working, open a browser and try to visit ads.msn.com (one of the blocked URLs). The error given should be similar to the screenshot given above.

If in the future you need to update the ad blocking list, run the commands:

cd / && mount -v -o remount,rw /
wget -q -O - 'http://pgl.yoyo.org/as/serverlist.php?hostformat=squid-dstdom-regex;showintro=0'  | grep -v ">" | grep "." > /opt/etc/squid/blocklist
/opt/etc/init.d/S80squid restart

For further details of filtering URLs using squid, please refer to the excelent documentation of the squid cache project.

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