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I have a webserver with several applications of several users. Since I'm not sure what the applications are doing and which outbound http/https traffic they produce, I want to get more control about it. So my thought is to use an internal Squid which is only listening to 127.0.0.1:3128. At first I just want to have a look into the access log, the second step would be a black/whitelist for securityrelevant urls and domains. These lists should filter the outbound traffic of the apache and all the child processes (for example: one of the applications is running a curl as system call).

I already added http_proxy to /etc/sysconfig/proxy, to /etc/environment and to .bashrc of the apache system user. Everything is worling fine when I'm using the shell, the apache doesn't use the proxy at all. I've already restarted the apche after the changes, but without success.

By the way I have OpenSuse 11 running on the web server.

The solution: (thanks to ALex_hha, sorry I guess I was reading your answer too fast) I entered the following iptables - rules:

iptables -t nat -I OUTPUT -p tcp --dport 80 -m owner --uid-owner apache -j DNAT --to-destination 127.0.0.1:3128

and set the Squid to transparent mode:

http_port 127.0.0.1:3128 transparent

and now it's running very fine.

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1 Answer 1

You can redirect all outgoing http traffic to the squid. The squid should be running in transparent mode

# iptables -t nat -I OUTPUT -p tcp --dport 80 -j DNAT --to-destination 127.0.0.1:3128

But you can't identify from which user was the traffic. But you could try to run squid on a few ports, each one for specific user

http_port 127.0.0.1:3128 transparent
http_port 127.0.0.1:3129 transparent
http_port 127.0.0.1:3130 transparent

And then redirect outgoing traffic to specific port

# iptables -t nat -I OUTPUT -p tcp --dport 80 -m owner --uid-owner apache -j DNAT --to-destination 127.0.0.1:3128

# iptables -t nat -I OUTPUT -p tcp --dport 80 -m owner --uid-owner joe -j DNAT --to-destination 127.0.0.1:3129

# iptables -t nat -I OUTPUT -p tcp --dport 80 -m owner --uid-owner jack -j DNAT --to-destination 127.0.0.1:3130

And use lp in the squid log format

logformat uniq_user %lp %>a %ui %un [%tl] "%rm %ru HTTP/%rv" %>Hs %<st %Ss:%Sh

I'm getting a lot of 403 errors in the log file. I added the IP-address of the server to the cal but that didn't work. I think the request would end up in an endless loop anyways

you need to bypass all requests from squid himself

# iptables -t nat -I OUTPUT -p tcp --dport 80 -m owner --uid-owner squid -j ACCEPT

I assumed, that your instance of the squid is running under squid:squid, which is by default

Working config of the squid

acl manager proto cache_object
acl localhost src 127.0.0.1/32 ::1
acl to_localhost dst 127.0.0.0/8 0.0.0.0/32 ::1
acl localnet src 10.0.0.0/8     # RFC1918 possible internal network
acl localnet src 172.16.0.0/12  # RFC1918 possible internal network
acl localnet src 192.168.0.0/16 # RFC1918 possible internal network
acl localnet src fc00::/7       # RFC 4193 local private network range
acl localnet src fe80::/10      # RFC 4291 link-local (directly plugged) machines
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
http_access allow all
http_access allow localnet
http_access allow localhost
http_access deny all

http_port localhost:3128 transparent
http_port localhost:3129 transparent
http_port localhost:3130 transparent


hierarchy_stoplist cgi-bin ?
coredump_dir /var/spool/squid

refresh_pattern ^ftp:           1440    20%     10080
refresh_pattern ^gopher:        1440    0%      1440
refresh_pattern -i (/cgi-bin/|\?) 0     0%      0
refresh_pattern .               0       20%     4320

logformat uniq_user %lp %>a %ui %un [%tl] "%rm %ru HTTP/%rv" %>Hs %<st %Ss:%Sh
access_log /var/log/squid/squid-users.log uniq_user

Squid version and system details

# squid -v | head -1
Squid Cache: Version 3.1.10

# uname -r
2.6.32-358.14.1.el6.x86_64

# cat /etc/redhat-release
CentOS release 6.4 (Final)

Make sure that first rule in the OUTPUT chain is - "-p tcp --dport 80 -m owner --uid-owner squid -j ACCEPT"

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I added this rule to my iptables but the squid couldn't handle the request. The requested URL could not be retrieved. Unfortunately now even the Nagios isn't running anymore (the nagios requests are running through the squid as well now). –  Burt Wonderstone Aug 14 '13 at 14:20
    
I guess I have to switch the squid into some kind of a transparent mode before I can use the iptables rule. –  Burt Wonderstone Aug 14 '13 at 14:39
    
What's to prevent the requests proxied by squid from being redirected back to squid? –  symcbean Aug 14 '13 at 15:17
    
yes, that could be the reason why this config didn't work. Perhaps my requests ended up in an endless loop. Isn't there a way to solve this without iptables? –  Burt Wonderstone Aug 14 '13 at 19:23
    
So now I switched the squid into transparent mode but it doesn't work either. I'm getting a lot of 403 errors in the log file. I added the IP-address of the server to the cal but that didn't work. I think the request would end up in an endless loop anyways. –  Burt Wonderstone Aug 15 '13 at 9:11

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