Fedora » Squid

Crack: Google Authentication Services are Vulnerable

Kulbir Saini — Fri, 05 Dec 2008 18:41:58 +0000

There is a vulnerability in the way Google authentication service works. Whenever you login to any of the Google’s online services like GMail, Orkut, Groups, Docs, Youtube, Calendar etc., you are redirected to an authentication server which authenticates against the entered username and password and redirect back to the required service (GMail, Youtube etc.) setting the session variables.

Now, if you are able to grab the url used to set the session variables, you can login as the user to whom that url belongs from any machine on the Internet (need not be the machine belonging to the same subnet) without entering the username and password of the user.

The proxy servers in the organizations can be used to exploit this vulnerability. Squid is the most popular proxy server used. In the default configuration, squid strips the query terms of a url before logging. So, this vulnerability can’t be exploited. But if you turn off the stripping mechanism by adding the line shown below, then squid will log the complete url.

strip_query_terms off

So, after turning stripping mechanism off, the log will contain urls which will look like this

http://www.google.co.in/accounts/SetSID?ssdc=1&amp;sidt=Q5UrfB0BAAA%3D.oHVGErODzffQ%2Bms%2FOKfk53g5naReDKehRNHOBsmJlBu3VTNXjF03SbgX%2FVEEhmImhR4mlu5IAAjM%2BdbuXvMMSIb0oU8IGCYpnLcSNkbCIrG%2BQnm81YmX5%2Brcrq7U6Qx65%2F1yaQ2NzgmKD94jg0Iw13iXDen3qD5qn6L%2FhmmYWwTrcOeuTzGbO%2BAehpjEU3mrWapRafaq3b4kxyigJ68s8QrGQqZTINNE%2Bs%2BoIkZWmGt5kNzoT8fkVAsWJeu3CKFkxj4oVMngeDvpwb1nyFpsJCltOzmAr46fTxVJSpvQdx0%3D.BMLtjUdIDCcuszktZSvYzA%3D%3D&amp;continue=http%3A%2F%2Fwww.orkut.com%2FRedirLogin.aspx%3Fmsg%3D0%26ts%3D1226148773097%3A1226148773386%3A1226148774868%26auth%3DDQAAAIcAAAC1pPE1QT4chKgrU4B3oyKZrQRkEVPtYlclpESQoXV_d9x9gdoe75Z0hfJ_22Pn5tVMR7j-uV5YCps3NB48L0bFlDeX-4PGHVT6Loztp_ru3tAy_gxDa9_YAEbz4d9CO4wD2VTKtzax9zvpGgrnJVZQfoWPkkIomUmxDtVGoH7g3fA3UjS0vdBJ2PJtgFMElso

Replace .co.in with your tld specific to your country. If you paste this url in any browser, it’ll directly log you in and you can do whatever you want to that account. Remember that all such urls remains valid only for two minutes. So, if you use that url after two minutes, it’ll lead nowhere.

At the time of writing this post Orkut, Google Docs, Google Calendar, Google Books and Youtube are vulnerable.

So, make sure your squid has stripping mechanism turned on and your squid server is properly firewalled.

You can watch the Video proof for Orkut on Blip.tv, Youtube.

IntelligentMirror: RPM and DEB Caching Improved (0.5)

Kulbir Saini — Wed, 19 Nov 2008 04:15:28 +0000

After spending a lot of time with youtube cache, now I am trying to devote some time to update intelligentmirror with required features and enhancements that youtube cache already enjoys. In the same direction here is version 0.5 of intelligentmirror.

Improvements

Added max_parallel_downloads options to controll the maximum threading fetching from upstream to cache the packages.
Fine grained control on logging via max_logfile_size and max_logfile_backups option.
Added setup script to help you install intelligentmirror. No need to execute commands one by one for installation. Just run

 [root@localhost]# python setup.py install [ENTER]

Added update script (update-im). So in case you decide to change the locations for caching rpm/deb packages, just run

 [root@localhost]# update-im [ENTER]

 [root@localhost]# /usr/sbin/update-im [ENTER]

Download scheduler similar to youtube cache is added to facilitate the download queing in case of large number of requests.
More informative logging.
cache.log is not flooding anymore with XMLRPC logs and python tracebacks.
Added extensive exception handling thoughout the program.

Availability

Installation and Configuration

INSTALL and README files should help you throughout the installation and configuration process.

In case you have questions, ask them here in comments. Suggestions for improvement are welcome

Fedora Tutorials and Videocache by Kulbir Saini.

IntelligentMirror Gets Even More Intelligent (1.0.1)

Kulbir Saini — Tue, 23 Sep 2008 04:09:14 +0000

Warning : This version of IntelligentMirror is compatible with only squid-2.7 as of now. It is NOT compatible even with squid-3.0.

IntelligentMirror Version 1.0.1

I have been following squid development regularly (at least the part in which I am interested) and they have introduced a new directive in squid-2.7 known as StoreUrlRewrite (storeurl_rewrite_program). Using this directive you can instruct squid to cache url A (http://abc.com/foo/bar/version/crap.rpm) as url B (http://proxy.fedora.co.in/intelligentmirror/crap.rpm). In simple words you can direct squid to cache any url as any other url without any extra efforts.

So keeping the above directive in mind, I have worked out a different version of intelligentmirror especially for squid-2.7.

IntelligentMirror : Old method of operation

IntelligentMirror gets a client request for a URL.
Check: if URL is not in (RPM, metadata file)
- Then its none of our business.
- Let proxy handle it the normal way.
- Done and exit.
Check: if RPM/metadata is available in cache
- Stream the RPM/metadata from cache.
- Done and exit.
Check: if RPM/metadata is not available in cache
- Download in parallel for caching in some dir and stream.
- Done and exit.

IntelligentMirror : New method of operation

IntelligentMirror gets a client request for a URL.
Check: if request for rpm
1. Direct squid to cache the request as http:///intelligentmirror/.rpm
Check: if request for deb
1. Direct squid to cache the request as http:///intelligentmirror/.deb
Done and exit.

So your squid will see every request for an rpm package as a request http:///intelligentmirror/.rpm. So, if you happen to request the same rpm from a different mirror, it’ll still be served from cache

Improvements

No need to check if the url supplied by squid is for rpm or not because storeurl_rewrite_program has an acl controller attached which will invoke intelligentmirror for urls ending in .rpm .
No need to check if the url is already cached or not. No need to worry about the directory where you are going to store the packages. No human intervention is needed in maintaining the cache. Almighty squid is doing everything for us.
No need to worry if the target package has changed because of the resigning or whatever because squid will do that for you.
No need to actually download the package in parallel for caching because squid is already doing that.
No need to worry about the hashing algorithms and storage optimizations for the cached content.

Availability

Install and Configure

The install and configure files should be enough to guide you through the installation if you choose the tar ball way. Otherwise you can always install from rpm from the above link.

Note1: You have to configure your squid to use intelligentmirror as a plugin even if you install via rpm. Check the configure file at the above link.

Note2: StoreUrlRewrite will probably be available in squid-3.1.

Fedora Tutorials and Videocache by Kulbir Saini.

IntelligentMirror: RPM and DEB Caching Improved (0.4)

Kulbir Saini — Fri, 19 Sep 2008 04:06:47 +0000

IntelligentMirror version 0.4 is available now. There have been significant improvements in intelligent mirror since last release.

Improvements

Fixed defunct process problem. You will not see defunct python processes hanging around anymore. Previously every forked daemon used to got defucnt because parent never waited for the forked child to finish.
IntelligentMirror now supports caching of Debian packages just like rpms. So now IntelligentMirror is best suited shared environments where people have different tastes.
Intelligent Mirror now uses url_rewrite_program instead of redirect_program. This boosts the efficiency of IntelligentMirror by a significant factor as url_rewrite_program has an acl controller url_rewrite_access. And using url_rewrite_access only requests for rpm/deb packages will be passed to Intelligent Mirror. So, IM now need not process each and every incoming request. Also, it has redirector_bypass directive which will bypass IM in case all the instances of IM are busy serving requests. So, squid will not die with a fatal error in case of huge requests.
Options to enable/disable caching for rpm and Debian packages have been added.
Options to control the total size of caching directories and the size of individual package to be cached have also been introduced.
Proxy authentication is also supported now just the way it is supported in yum.
Packages are not checked for last-modified time anymore. Because in principle two rpms A and B can only have same name iff they have the same contents. So, the delay in response time in case of hits has reduced.

Availability

Installation and configuration is easy and the INSTALL and README files should serve the purpose.

In case you have any suggestions or problems, leave a comment here or file a ticket on project page.

Fedora Tutorials and Videocache by Kulbir Saini.

IntelligentMirror: Available for Testing

Kulbir Saini — Tue, 19 Aug 2008 04:12:52 +0000

Note : A newer version of intelligentmirror is available now. Please check this.

Intelligent Mirror is basically a tool or squid plugin (redirector) to cache rpm packages so that the subsequent requests for the same package can be served from the local cache which will eventually save a lot of bandwidth and downloading time.

Who needs Intelligent Mirror?

If you are on a shared network where a lot of people use linux distros with RPM as their package manager, then you need this. Universities should come under this category.
If you have a set of systems having red hat derivatives and almost identical OS versions, you need this. LAN setups at home should come under this category.
If you can’t afford to or don’t want to mirror entire fedora repo for local access due to bandwidth limitations, you need this.

What it does?

As described above, Intelligent Mirror, just caches rpms which are requested by the clients in a shared network. And subsequent requests for those rpms are served from the cache. For a detailed description, check the project page.

Why not use Squid in caching mode?

Squid caching is based on url hashing. Let me explain with an example how Intelligent Mirror is actually intelligent as compared to squid while caching rpms.

Let us say there is an rpm yum-3.2.0-1.fc7.i386.rpm . You executed “yum update yum“. And let us say the newer version of yum is yum-3.2.18-1.fc9.i386.rpm which was fetched from one of the fedora mirrors http://abc.com/ (say). Now someone on the same network launched “yum update yum” and he got the same rpm yum-3.2.18-1.fc9.i386.rpm. But this time rpm was fetched from another mirror http://xyz.com/ (say).

Case I : Squid caching

Squid will cache http://abc.com/linux/fc9/updates/i386/yum-3.2.18-1.fc9.i386.rpm . And when http://xyz.com/linux/fc9/updates/i386/yum-3.2.18-1.fc9.i386.rpm will be requested, it’ll result in a cache miss and squid will again download the same package and will cache this one as well. Now there are two problems

Squid is not able to serve from the cache, though the package was the same.
Additional storage space is being wasted in caching the same package. And this can really harm if unluckily a different mirror is picked in all the subsequent queries.

Case II : IntelligentMirror caching

Intelligent Mirror will cache the package yum-3.2.18-1.fc9.i386.rpm without bothering about its origin. And even if yum picks up a different mirror for the subsequent request, the package will be served from the cache and will not be fetched from upstream. So, the obvious advantage of saving the bandwidth and downloading time.

Download

Intelligent Mirror source tarball, rpm, source rpm are available for download from here.

Installing and Configuring Intelligent Mirror

Install Guide

Configuration Guide

Issues and Suggestions

If you see any issue or you have any suggestions for improving the functionality, either mail me at kulbirsaini25 AT GMAIL DoT COM or file a ticket on the project page.

Fedora Tutorials and Videocache by Kulbir Saini.

IntelligentMirror: GSOC Project Update

Kulbir Saini — Mon, 02 Jun 2008 04:03:24 +0000

Brief Introduction

IntelligentMirror can be used to create a mirror of static HTTP content on your local network. When you download something (say a software package) from Internet, it is stored/cached on a local machine on your network and subsequent downloads of that particular software package are supplied from the storage/cache of the local machine. This facilitate the efficient usage of bandwidth and also reduces the average download time. IntelligentMirror can also do pre-fetching of RPM packages from fedora repositories spread all over the world and can also pre-populate the local repo with popular packages like mplayer, vlc, gstreamer which are normally accessed immediately after a fresh install.

Definition for a lay man

Think of Internet as a hard disk, your proxy server as a cache and your Intranet as a CPU. Now, whenever your CPU needs to process something, it needs data from cache. If data is not there in cache, it’ll be fetched from RAM and/or hard disk. IntelligentMirror sits on your proxy server and keep caching packages in a browsable manner which can be served via http for subsequent requests.

For further details about IntelligentMirror, go here.

Update

After getting the hosting space on fedorahosted.org, I pushed the code I have written. You can check the source tree here.

We are buidling IntelligentMirror as a plugin to squid which taps requests from clients and checks them against a cache. Checkout how to write a custom redirector or how to tap requests to squid. And acts accordingly. We are working on live streaming the partially downloaded package to the end user while caching it.

If you have any suggestion, feel free to leave them as a comment here or edit the wiki page

Fedora Tutorials and Videocache by Kulbir Saini.

How To: Configure Squid Proxy Server

Kulbir Saini — Fri, 02 May 2008 08:31:31 +0000

Mission

To configure squid for simple proxying without caching anything.

Use Cases

When you want to have control on what people browse on your lan.
When number of machine is more than the number of IP addresses you can afford to buy.
When you want to help this holy world in saving some IPV4 addresses

Assumptions

You have a machine connected directly to internet that you are going to use as a proxy server for other machines on your network.
The machines on your network are using 192.168.0.0/16 as private address space. You can use anyone/multiple address spaces of the available but for this howto we assume 192.168.0.0/16 as the local network.
The local IP address of the machine which will run squid proxy server is 192.168.36.204. You can have any IP, but for this howto we assume this.

How to proceed

First of all ensure that you have squid installed. After installing squid, you need to set access control in squid configuration file which resides in /etc/squid by default. Open /etc/squid/squid.conf and add/edit following lines according to your preferences. Few lines already exist in the configuration file, you can add the rest.

# The port on which squid will listen for requests
http_port 8080
# If 'cgi-bin' or '?' is in query, squid should not check with neighbours'/parents' cache
# and should go to target web-server.
hierarchy_stoplist cgi-bin ?
# If url contains 'cgi-bin' or '?', then it must not be cached
acl QUERY urlpath_regex cgi-bin \?
cache deny QUERY
acl apache rep_header Server ^Apache
broken_vary_encoding allow apache
# Absolute path to squid access log.
access_log /var/log/squid/access.log squid
refresh_pattern ^ftp:           1440    20%     10080
refresh_pattern ^gopher:        1440    0%      1440
refresh_pattern .               0       20%     4320
# Access control list to control every IP address
acl all src 0.0.0.0/0.0.0.0
# Access control list for source machine in LAN
acl lan_src src 192.168.0.0/16
# Access control list for destination machine in LAN
acl lan_dst dst 192.168.0.0/16
# Access control list to manage squid cache
acl manager proto cache_object
# Access control list to define IP address allowed for source localhost
acl localhost src 127.0.0.1/255.255.255.255
# Access control list to define IP addresses allowed for localhost as destination
acl to_localhost dst 127.0.0.0/8
# Access control list to define Safe ports that should be allowed by default
acl SSL_ports port 443 563 1863 5190 5222 5050 6667
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
# Allow cache management only from localhost
http_access allow manager localhost
# Deny cache management from remote hosts
http_access deny manager
# Deny http access via all the ports which are not listed as safe
http_access deny !Safe_ports
# Deny all connections via all ports which are not listed as safe
http_access deny CONNECT !SSL_ports
# Allow http access from localhost
http_access allow localhost
# Allow http access from machines on LAN
http_access allow lan_src
http_access deny all
http_reply_access allow all
icp_access allow all
# Deny caching for everyone so that there is not caching at all
cache deny all
coredump_dir /var/spool/squid
# Never allow direct connection to machines on the internet
prefer_direct off
never_direct allow all
# Allow direct connetion if the destination machine is on LAN
always_direct allow lan_dst
# Delete this line if you don't have /etc/hosts file
hosts_file /etc/hosts
# Allow AIM connections
# Delete the following 9 lines if you don't want people to connect to AIM
acl AIM_ports port 5190 9898 6667
acl AIM_domains dstdomain .oscar.aol.com .blue.aol.com .freenode.net
acl AIM_domains dstdomain .messaging.aol.com .aim.com
acl AIM_hosts dstdomain login.oscar.aol.com login.glogin.messaging.aol.com toc.oscar.aol.com irc.freenode.net
acl AIM_nets dst 64.12.0.0/255.255.0.0
acl AIM_methods method CONNECT
http_access allow AIM_methods AIM_ports AIM_nets
http_access allow AIM_methods AIM_ports AIM_hosts
http_access allow AIM_methods AIM_ports AIM_domains
# Allow connections to Yahoo Messenger
# Delete the following 6 lines if you don't want people to connect to Yahoo Messenger
acl YIM_ports port 5050
acl YIM_domains dstdomain .yahoo.com .yahoo.co.jp
acl YIM_hosts dstdomain scs.msg.yahoo.com cs.yahoo.co.jp
acl YIM_methods method CONNECT
http_access allow YIM_methods YIM_ports YIM_hosts
http_access allow YIM_methods YIM_ports YIM_domains
# Allow connections to Google Talk
# Delete the following 6 lines if you don't want people to connect to Google Talk
acl GTALK_ports port 5222 5050
acl GTALK_domains dstdomain .google.com
acl GTALK_hosts dstdomain talk.google.com
acl GTALK_methods method CONNECT
http_access allow GTALK_methods GTALK_ports GTALK_hosts
http_access allow GTALK_methods GTALK_ports GTALK_domains
# Allow connections to MSN
# Delete the following 6 lines if you don't want people to connect to Google Talk
acl MSN_ports port 1863 443 1503
acl MSN_domains dstdomain .microsoft.com .hotmail.com .live.com .msft.net .msn.com .passport.com
acl MSN_hosts dstdomain messenger.hotmail.com
acl MSN_nets dst 207.46.111.0/255.255.255.0
acl MSN_methods method CONNECT
http_access allow MSN_methods MSN_ports MSN_hosts

Now, start the squid proxy server as

service squid start

Also, if you want squid to be started every time you boot the machine, execute the following command

chkconfig --level 345 squid on

You have a squid proxy server running now. You can ask clients to configure there browsers to use 192.168.36.204 as a proxy server with 8080 as proxy port. Command line utilities like elinks, lynx, yum, wget etc. can be asked to use proxy by exporting http_proxy variable as below. Users can also add these lines to ~/.bashrc file to avoid exporting every-time.

export http_proxy='http://192.168.36.204:8080'
export ftp_proxy='http://192.168.36.204:8080'

I highly recommend the book “Squid: The Definitive Guide (Paperback)” for further reading.

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Fedora Tutorials and Videocache by Kulbir Saini.

How To: Write Custom Redirector or Rewritor Plugin For Squid in Python

Kulbir Saini — Tue, 29 Apr 2008 19:31:26 +0000

Mission

To write a custom Python program which can act as a plugin for Squid to redirect a given URL to another URL. This is useful when already existing redirector plugins for Squid doesn’t suit your needs or you want everything of your own.

Use Cases

When you want to redirect URLs using a database like mysql or postgresql.
When you want to redirect based on mappings stored in simple text files.
When you want to build a redirector which can learn by itself using AI techniques

How to proceed

From Squid FAQ,

The redirector program must read URLs (one per line) on standard input, and write rewritten URLs or blank lines on standard output. Note that the redirector program can not use buffered I/O. Squid writes additional information after the URL which a redirector can use to make a decision.

The format of the line read from the standard input by the program is as follows.

1
2
3

URL ip-address/fqdn ident method
# for example
http://saini.co.in 172.17.8.175/saini.co.in - GET -

The implementation sounds very simple and it is indeed very simple to implement. The only thing that should be taken care of is the unbuffered I/O. You should immediately flush the output to standard output once decision is taken.

For this howto, we assume we have a method called ‘modify_url()‘ which returns either a blank line or a modified URL to which the client should be redirected.

#!/usr/bin/env python
 
import sys
def modify_url(line):
    list = line.split(' ')
    # first element of the list is the URL
    old_url = list[0]
    new_url = '\n'
    # take the decision and modify the url if needed
    # do remember that the new_url should contain a '\n' at the end.
    if old_url.endswith('.avi'):
        new_url = 'http://fedora.co.in/errors/accessDenied.html' + new_url
    return new_url
 
while True:
    # the format of the line read from stdin is
    # URL ip-address/fqdn ident method
    # for example
    # http://saini.co.in 172.17.8.175/saini.co.in - GET -
    line = sys.stdin.readline().strip()
    # new_url is a simple URL only
    # for example
    # http://fedora.co.in
    new_url = modify_url(line)
    sys.stdout.write(new_url)
    sys.stdout.flush()

Save the above file somewhere. We save this example file in /etc/squid/custom_redirect.py. Now, we have the function for redirecting clients. We need to configure squid to use custom_redirect.py . Below is the squid configuration for telling squid to use the above program as redirector.

# Add these lines to /etc/squid/squid.conf file.
# /usr/bin/python should be replaced by the path to python executable if you installed it somewhere else.
redirect_program /usr/bin/python /etc/squid/custom_redirect.py
# Number of instances of the above program that should run concurrently.
# 5 is good enough but you should go for 10 at least. Anything below 5 would not work properly.
redirect_children 5

Now, start/reload/restart squid. That’s all we need to write and use a custom redirector plugin for squid.

Fedora Tutorials and Videocache by Kulbir Saini.

How To: Write Custom Basic Authentication Plugin for Squid in Python

Kulbir Saini — Wed, 23 Apr 2008 19:37:19 +0000

Mission

To write a Python program which can be used to authenticate for Squid proxy server. This is useful when you don’t want to configure complex systems like LDAP, ntlm etc.

Use Cases

When you want to authenticate clients using mysql database.
When you want to authenticate clients using flat files or /etc/passwd file or some custom service on your network.

How to proceed

From auth_param section in squid.conf file:

Specify the command for the external authenticator. Such a program reads a line containing "username password" and replies "OK" or "ERR" in an endless loop. "ERR" responses may optionally be followed by a error description available as %m in the returned error page.

By default, the basic authentication scheme is not used unless a program is specified.

That clearly states that our python program should read a line from standard input (stdin) and write the appropriate response to the standard output (stdout). But there are some issues with I/O. The output should be unbuffered and should be flushed to standard output immediately after the response is known.

So, lets see a small program where we authenticate using a function ‘matchpassword()‘. This function returns True when username, password pair matches and returns False when they mismatch.

#!/usr/bin/python
 
import sys
import socket
"""USAGE:The function returns True if the user and passwd match False otherwise"""
def matchpasswd(login,passwd):
    # Write your own function definition. 
    # Use mysql, files, /etc/passwd or some service or whatever you want
    pass
 
while True:
    # read a line from stdin
    line = sys.stdin.readline()
    # remove '\n' from line
    line = line.strip()
    # extract username and password from line
    username = line[:line.find(' ')]
    password = line[line.find(' ')+1:]
 
    if matchpasswd(username, password):
        sys.stdout.write('OK\n')
    else:
        sys.stdout.write('ERR\n')
    # Flush the output to stdout.
    sys.stdout.flush()

Save the above file somewhere. We save this example file in /etc/squid/custom_auth.py .Now, we have the function for authenticating clients. We need to configure squid to use custom_auth.py . Below is the squid configuration for telling squid to use the above program as basic authenticator.

# you need to specify /usr/bin/python if your file is not executable and needs an interpreter to be invoked.
# Replace /usr/bin/python with /usr/bin/php , if you write auth program in php.
auth_param basic program /usr/bin/python /etc/squid/custom_auth.py
# how many instances of the above program should run concurrently
auth_param basic children 5
# display some message to clients when they are asked for username, password
auth_param basic realm Please enter your proxy server username and password
# for how much time the authentication should be valid
auth_param basic credentialsttl 2 hours
# whether username, password should be case sensitive or not
auth_param basic casesensitive on

Now, to force clients to authenticate, configure the acls as follow. Below we assume, you want to force all clients on your lan to authenticate for using proxy server.

# acl to force proxy authentication
acl authenticated proxy_auth REQUIRED
# acl to define IPs from your lan
acl lan src 192.168.0.0/16
# acl to force clients on your lan to authenticate
http_access allow lan authenticated

Now, reload/restart squid. That’s all we need to write and use a custom authentication plugin for squid.

Limitation

Username can’t contain spaces. Otherwise program will not be able to parse/extract username, password from standard input.

Fedora Tutorials and Videocache by Kulbir Saini.

How To: Configure Hierarchicy of Proxy Servers (Squid)

Kulbir Saini — Wed, 05 Mar 2008 10:51:13 +0000

Yesterday I came across this idea of caching all the data that I browse on my hard disk so that the average load time of a website decreases. Actually the idea is I’ll cache all the static data that I browse like images, static html pages, CSS files and similar things which does not change frequently and can be served from the cache. But while setting up the proxy server on my machine, I faced the problem that my machine which is going to act as a proxy server is behind my institute’s proxy. So, a simple caching proxy server can’t serve my needs and I have to really figure out how to setup a hierarchical proxy server. Below we’ll see how to setup a hierarchical proxy server.

Approach

When I thought of setting up a caching proxy server, squid immediately struck my mind. Actually I don’t know about any other proxy servers. I never setup proxy server before this ( I tried a lot of time, but in vain). So, I started googling about squid setup. There were a lot of tutorials, but either they were too small to get things going or they were too verbose that I couldn’t manage to read them. So, I directly jump into squid configuration file squid.conf . And with references from here and there, I managed to setup the proxy server successfully.

Note: The configurations below worked on Fedora 7 with squid 2.6STABLE16. The same configurations may work with other squid versions and on other operating systems as well, but try them at your own risk.

Part 1 : Setting up simple proxy server with squid

Setting up a very simple and usable proxy server is really easy. You need to add/edit only 2-3 lines /etc/squid/squid.conf to get started.

Add your ip to the access list.

1
2
3

acl myip src 172.17.8.175 # (e.g. )
http_access allow myip
http_port 8080 # (this is 3128 by default. you can set it to anything you like. e.g. 8080)

Save the squid.conf file. Then issue these commands.

1 2	[root@localhost squid]# squid -z [Enter] (as root) (This needs to be executed only once.) [root@localhost squid]# service squid start [Enter] (as root)

If you want to start the squid server on boot, issue this command.

[root@localhost squid]# chkconfig --level 345 squid on [Enter] (as root)

Now, your machine is a proxy server. You can setup your browser to use the machine as a proxy server.

Conditions

The proxy server will work only if your machine has a public IP and is directly connected to internet.

Part 2: Setting up a hierarchical caching proxy server with squid

The above setup works fine if a machine is directly connected to internet. But my machine itself is behind a proxy, so setting up a proxy on my machine is of no use unless the proxy on my machine uses the institute proxy for connecting to internet. So, here we jump into squid.conf again and this time we have to really do some brain storming. If you are a newbie to Linux and don’t know how to make a system work when nothing seems to help, you will probably be better off by using institute’s proxy.

Here is the scenario.

1. Your browser sends a content request to proxy on your machine.
2. Check: if a cache HIT from institute proxy cache (HIT means content was found in cache)
	2a. Check: if content is older than the original upstream content
		2aa. Fetch content from upstream and serve the client
	2b. else
		2ba. Serve the content from the cache
3. Check: if cache HIT from proxy on your machine
	3a. Check: if content is older than the original upstream content
		3aa. Fetch content from upstream and serve the client
	3b. else
		3ba. Serve the content from the cache
4. Cache MISS from both the proxies
	4a. Fetch the content from upstream and serve the client

The above method of operation is very basic and is my understanding of squid. It may not be the exact squid behavior.

Now, lets see the configurations needed for setting up the hierarchical caching proxy server with squid.

Assumptions

I assume that we already have squid setup at institute’s proxy whether in caching mode or not. The best way to add/edit the following lines in your squid.conf is to search for particular parameter and then edit the value to set as given.

I also assume that you have simple proxy server setup on your machine and now we want to make it act as child proxy of the institute’s proxy.

Configuration

# Your local machine will act as a sibling proxy
cache_peer 172.17.8.175 sibling 3128 3130 no-query weight=10
# The institute's proxy server will act as a parent proxy
# 'default' mean the last-resort
cache_peer 192.168.36.204 parent 8080 3130 no-query proxy-only no-digest default
# allow accessing peer cache for access list 'myip'
cache_peer_access 172.17.8.175 allow myip
# Don't cache dynamic content
hierarchy_stoplist cgi-bin ?
acl QUERY urlpath_regex cgi-bin \?
cache deny QUERY
# Size of main memory to be used for caching
cache_mem 200 MB
# max size of content to be stored in main memory
maximum_object_size_in_memory 7000 KB
# policy for cache replacement if memory is full
cache_replacement_policy heap LFUDA
# the directory to be used for storing cache on your hdd
cache_dir aufs /var/spool/squid 200 16 256
# max file descriptor open at a time .. 0(unlimited)
max_open_disk_fds 0
# min object size to cache on hdd
minimum_object_size 0 KB
# max object size to cache on hdd
maximum_object_size 16384 KB
# access log
access_log /var/log/squid/access.log squid
refresh_pattern ^ftp:           1440    20%     10080
refresh_pattern ^gopher:        1440    0%      1440
refresh_pattern .               0       20%     4320
store_avg_object_size 20 KB
acl apache rep_header Server ^Apache
broken_vary_encoding allow apache
refresh_stale_hit 5 seconds
acl SSL_ports port 443 563 1863 5190 5222 5050 6667
# Allow AIM protocols
acl AIM_ports port 5190 9898 6667
acl AIM_domains dstdomain .oscar.aol.com .blue.aol.com .freenode.net
acl AIM_domains dstdomain .messaging.aol.com .aim.com
acl AIM_hosts dstdomain login.oscar.aol.com login.glogin.messaging.aol.com toc.oscar.aol.com irc.freenode.net
acl AIM_nets dst 64.12.0.0/255.255.0.0
acl AIM_methods method CONNECT
http_access allow AIM_methods AIM_ports AIM_nets
http_access allow AIM_methods AIM_ports AIM_hosts
http_access allow AIM_methods AIM_ports AIM_domains
# Allow Yahoo Messenger
acl YIM_ports port 5050
acl YIM_domains dstdomain .yahoo.com .yahoo.co.jp
acl YIM_hosts dstdomain scs.msg.yahoo.com cs.yahoo.co.jp
acl YIM_methods method CONNECT
http_access allow YIM_methods YIM_ports YIM_hosts
http_access allow YIM_methods YIM_ports YIM_domains
# Allow GTalk
acl GTALK_ports port 5222 5050
acl GTALK_domains dstdomain .google.com
acl GTALK_hosts dstdomain talk.google.com
acl GTALK_methods method CONNECT
http_access allow GTALK_methods GTALK_ports GTALK_hosts
http_access allow GTALK_methods GTALK_ports GTALK_domains
# Allow MSN
acl MSN_ports port 1863 443 1503
acl MSN_domains dstdomain .microsoft.com .hotmail.com .live.com .msft.net .msn.com .passport.com
acl MSN_hosts dstdomain messenger.hotmail.com
acl MSN_nets dst 207.46.111.0/255.255.255.0
acl MSN_methods method CONNECT
http_access allow MSN_methods MSN_ports MSN_hosts
# Turn this off if hierarchical behavior is needed
nonhierarchical_direct off
never_direct deny myip
hosts_file /etc/hosts
coredump_dir /var/spool/squid

That’s the minimal configuration you need for running squid in hierarchical way. Save the squid.conf file and start/restart/reload the squid service. Setup your browser to use your machine as proxy and while using it’ll cache all the static content. You should experience some reduction in average page load time.

Advantages

I am currently using squid in above configuration. And its turning out to be nice for me. I am browsing websites faster and saving a chunk of bandwidth for my institute.

Disadvantages

Introduction of another proxy server increases the latency for dynamic content.

Notice

The above configurations and views are a result of my understanding of squid. If you feel this may break your system or it may have adverse effects, don’t use them. At least don’t use these on a production system.

Fedora Tutorials and Videocache by Kulbir Saini.

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