How to block internet access to certain programs on Linux

Question

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?

Solution 1

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.

Solution 2

A more straightforward possibility: use firejail. It runs the application inside sandbox. At the sandbox, you can control the access of the application to any network or folder in your computer.

To execute a certain application without network access do following:

firejail --net=none <application>

In that case, "The sandbox looks like a computer without any network interfaces." (See Network Section in documentation)

For example, firejail --net=none firefox will start firefox without any network connection.

Installation

See the Installation documentation. You should install from the package system in your distribution, or better get the latest version LTS. (For example, this latest LTS version, 9.56.2, works also in Ubuntu 16.04.)

Solution 3

From answer for How to disable Internet connection for a single process and Block network access of a process

Then, starting a process without network access is as simple as:

unshare -n program ...

This creates an empty network namespace for the process. That is, it is run with no network interfaces, including no loopback. In below example we add -r to run the program only after the current effective user and group IDs have been mapped to the superuser ones (avoid sudo):

unshare -r -n ping google.com

Comments

[Admin]

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.

[onse]

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}"

[Admin]

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).

[SarK0Y]

unshare -n YourAppToBlock > use "nointernet" instead of "no-internet". perhaps, 'no\\-internet'?

[Viatorus]

I tried it like described but for me, after adding me to "no-internet" and set the ip-tables I cannot connect to the internet anymore (with and without the bash script no-internet).

[kasperd]

I would change the second line of the script to be exec sg no-internet "$@".

[Ilia]

@kasperd yeah, thanks. Having expansion is a good idea.

[Ruslan]

It would be useful to note that for this manual to work one has to have xt_owner module loaded (or built-in), so that /proc/net/ip_tables_matches contains a line owner. Otherwise you'll get "no chain/target/match by that name" error from iptables command. Also, after adding a group one has to gpasswd it to some valid password, otherwise sg will give you a cryptic Invalid argument error after you enter "some" password.

[multithr3at3d]

Not to revive an old thread, but to avoid the password issues, just use sudo -g no-internet. Also it's a little simpler to throw this into a shell alias. Also, I wouldn't recommend using unshare, since it probably requires root, and you will be running the untrusted program as root.

[Maciej Krawczyk]

I couldn't get this to work when I wanted to use it as a user added to the no-internet group. If you find it more convenient to create a user account with limited network access (e.g. this way you can more easily share file access), use iptables -A OUTPUT -m owner --uid-owner $USERNAME -j DROP

[alper]

Can I use firejail for slurm as well?

[alper]

Why do we need item 2?

[loved.by.Jesus]

I could not run libreoffice6.0 with firejail, but your method worked. :)

[xeruf]

any hint on adjusting these to also allow ipv6?