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Recently, I have encountered a problem of limiting Internet Access to specific programs. Could anybody recommend a good way of doing that, without using any particular software?

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The solution for me happened to be straight forward.

  1. Create, validate new group; add required users to this group:
    • Create: groupadd no-internet
    • Validate: grep no-internet /etc/group
    • Add user: useradd -g no-internet username

      Note: If you're modifying already existing user you should run: usermod -a -G no-internet userName check with : sudo groups userName

  2. Create a script in your path and make it executable:
    • Create: nano /home/username/.local/bin/no-internet
    • Executable: chmod 755 /home/username/.local/bin/no-internet
    • Content: #!/bin/bash
                    sg no-internet "$@"

  3. Add iptables rule for dropping network activity for group no-internet:
    • iptables -I OUTPUT 1 -m owner --gid-owner no-internet -j DROP

      Note: Don't forget to make the changes permanent, so it would be applied automatically after reboot. Doing it, depends on your Linux distribution.


   4. Check it, for example on Firefox by running:

  • no-internet "firefox"

In case you would want to make an exception and allow a program to access local network:

  • iptables -A OUTPUT -m owner --gid-owner no-internet -d 192.168.1.0/24 -j ACCEPT
  • iptables -A OUTPUT -m owner --gid-owner no-internet -d 127.0.0.0/8 -j ACCEPT
  • iptables -A OUTPUT -m owner --gid-owner no-internet -j DROP

NOTE: In case of spawning the rules will be maintained. For example, if you run a program with no-internet rule and that program will open browser window, still the rules will be applied.

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2  
A few notes Ilia: Ad 1: - to modify existing user: usermod -a -G groupName userName - check with : sudo groups userName Ad 3: - I already have a lot of rules in iptables, The position of the new rule is crucial. should be the first rule in chain OUTPUT. Therefore I use insert : iptables -I OUTPUT 1 -m owner --gid-owner no-internet -j DROP To allow access to LAN: make sure the ACCEPT rules are above the DENY rule. Works like a charm. Use it for example on Wifiguard. Prog checks wlan for unknown devices, but "phones home" on every start. – user205602 Jan 15 '14 at 14:01
    
@rob thanks, pal! – Ilia Rostovtsev Jul 30 '14 at 13:55
    
The script will only pass the command. If you try launching a programm with parameters, you should use "$@" instead of "$1". For some reason, I had to temporarily store it in a variable for bash to process it correctly: cmd="$@"; sg no-internet "${cmd}" – onse Oct 20 '15 at 12:49
    
use "nointernet" instead of "no-internet". For whatever reason Ubuntu 14.04 can't handle the dash when you try to use sg or chgrp (it prompts for a password, then fails). – user318195 Oct 22 '15 at 20:38
    
unshare -n YourAppToBlock > use "nointernet" instead of "no-internet". perhaps, 'no\\-internet'? – SarK0Y Apr 15 '16 at 22:33

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