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I have a Linux machine kernel 3.7.0 with Squid proxy server and a direct Internet connection. Browsers and Squid reside on the same machine. Is it possible to allow access to web only through Squid? Maybe use SELinux?

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migrated from security.stackexchange.com Mar 16 '13 at 22:35

This question came from our site for information security professionals.

up vote 7 down vote accepted

You can use the owner module in iptables (-m owner --uid-owner $SQUID_UID) to setup allow rules for Squid and then deny other traffic.

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Maybe something like this?

# Your debian machine (gateway)
LAN_IP="192.168.0.1"

# Your network
LAN_IP_RANGE="192.168.0.0/24"                                                               

# Your squid machine
PROXY_IP="192.168.0.254"                                                                   
PROXY_PORT="3128"

iptables -t mangle -A PREROUTING -s $LAN_IP_RANGE ! -d $LAN_IP_RANGE -p TCP --destination-port 80 -j MARK --set-mark 11                                     
iptables -t nat -A PREROUTING -m mark --mark 11 -p TCP -j DNAT --to-destination ${PROXY_IP}:${PROXY_PORT}                                                          
iptables -t nat -A POSTROUTING -m mark --mark 11 -p TCP -j SNAT --to-source $LAN_IP

Source

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Here is the code:

iptables -P INPUT DROP
iptables -P FORWARD DROP
#loopback interface
iptables -A INPUT -i lo -j ACCEPT
iptables -A OUTPUT -o lo -j ACCEPT
#DNS
iptables -A OUTPUT -p udp --dport 53 -j ACCEPT
iptables -A INPUT -p udp --sport 53 -j ACCEPT
#http,https traffic only through Squid - nobody user
iptables -A OUTPUT -p tcp -m multiport --dports 80,443 -m state -m owner --uid-owner nobody --state NEW,ESTABLISHED -j ACCEPT
iptables -A INPUT -p tcp -m multiport --sports 80,443 -m state  --state ESTABLISHED -j ACCEPT
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