+  // Don't do anything if the process_path length is > PATH_LENGTH
    +  if (strlen(process_path) > PATH_LENGTH)
    +    return;

This page lists nothing under Packages but the author has actually made AUR packages for Archlinux:

https://github.com/Douane/Douane/wiki/Archlinux-Packaging

Here's a directly link to the installation instructions for anyone who'd want to try it out

https://github.com/Douane/Douane/wiki/Compilation

One trick I learned to negate that is to insert an iptables rule that blocks all out-of-LAN traffic except for specific secondary user-groups. Not primary groups, but ones which you have to manually grant to users.

Then, those applications which you do wish to access the Internet can be run using sg e.g.

  sg bobs_internet_access_group firefox

This is also very useful for stopping anything run by root from talking to the Internet, since that is a thing that should NEVER occur.

It does take a little configuration and it's probably best to create a new secondary group for each user ( and don't forget IPv6! ) but once it's set it just keeps working.

>The sg command works similar to newgrp but accepts a command. The command will be executed with the /bin/sh shell. With most shells you may run sg from, you need to enclose multi-word commands in quotes. Another difference between newgrp and sg is that some shells treat newgrp specially, replacing themselves with a new instance of a shell that newgrp creates. This doesn't happen with sg, so upon exit from a sg command you are returned to your previous group ID.

I could not find sg(1) for FreeBSD, neither in base nor in ports, but FreeBSD does have newgrp(1) mentioned above. The FreeBSD manpage for newgrp(1) notes:

>For security reasons, the newgrp utility is normally installed without the setuid bit. To enable it, run the following command:

> chmod u+s /usr/bin/newgrp

The main source file of newgrp(1), /usr/src/usr.bin/newgrp/newgrp.c is 310 lines long so I think creating an sg(1) based on that one and maybe also by looking at doas(1) -- which is in ports, not in base -- should not be too difficult.

However, I think using sg(1) to protect against random malicious binaries and shell scripts having internet access equates roughly to security by obscurity in that it only protects you as long as the malicious code is unaware of sg(1).

Consider the following (which I wrote without testing it with a group limiting firewall but it should work like this):

  nw_access_group=
  while IFS= read -r curr_group ; do
    nw_access_group="$curr_group"
    sg "$nw_access_group" 'curl -s http://www.example.com/' >/dev/null
    if [[ $? -eq 0 ]] ; then
      break
    fi
  done <<EOF
  $( getent group | grep "$USER" | cut -d':' -f1 )
  EOF

  echo "Would use group $nw_access_group for evil stuff."

- Signed packages from trusted repos should not need firewalling, at least not if you're using a serious distro rather than a hobby project. This isn't true in the general case, of course (hence things like OpenBSD's auditing of base packages), but this is a personal firewall, it's not exactly intended for server-grade equipment...

- If you install packages from dubious PPAs all over the Interwebs, a puny kernel module is unlikely to stop the two rootkits that you've probably already installed. Same for a system that has already been compromised.

- Untrusted applications (which you're running straight on your system, rather than nicely tucked in a VM with no network access because...?) -- as practical experience on Android and Windows shows -- will generally break as soon as they can't do their snooping because they'll segfault or block waiting for the answer that never came to the package that was never sent anyway.

I see a lot of talk in the Linux desktop field about building lines of defense against untrusted programs. I see why this is relevant to users who are routinely running closed-source programs (no, I don't personally audit every line of code running on my system, but a public source code repository is sort of a stupid place to hide malicious code when there's so much fully closed code being purchased from "app" stores and downloaded from all over the web and whatnot). I find it hard to understand why it would be relevant on an open source desktop.

Things like Wayland's sandboxing, I get to some degree -- it's only a matter of time before JavaScript code in a browser will get access to more stuff from your computer, which will eventually include stuff like keystrokes and mouse events and whatnot, so it'll have to be properly sandboxed. But why a personal firewall? What sort of applications do you find yourself wanting to block, and why for heaven's sake are you running them on your Linux computer, when it's really 2017 and there's plenty of choice in terms of applications.

Software has security vulnerabilities. So, even if the software is trusted, there could be a zero-day vulnerability that is exploited. I'd rather have software stopped in its tracks. (For this reason I think something like Little Snitch or Douane is not enough, you also need sandboxing.)

will generally break as soon as they can't do their snooping because they'll segfault or block waiting for the answer that never came to the package that was never sent anyway.

Maybe macOS apps are different, but I never had this experience during while using little snitch for almost 10 years. I recently started using Little Flocker (which is like Little Snitch/Douane, but for filesystem access) and so far no program has crashed as a result of denying access[1].

[1] Including the JDK installer, where I denied writing launch agents and Java itself trying to write to ~/.oracle_jre_usage.

How? When the zero day hits, the program has long been marked as trusted and the firewall will just happily let it go along. Besides, even if you're an experienced user and the firewall is smart enough to figure out that the application is talking to a server that it's never talked before (which isn't even sustainable for a lot of applications), it's very likely that you'll see the alert way before you read the news about the zero-day, and you'll just shrug and allow it to continue because you trust that program.

(Edit: maybe personal firewalls got smarter since I last used one and there's something else I'm missing here?)

> Maybe macOS apps are different, but I never had this experience during while using little snitch for almost 10 years.

The kind of applications that actively snoop on users as a business model -- the ones that you want to block in the first place -- sometimes even do this deliberately (which is something that I know from experience, not something that I suspect). Inexperienced users quickly figure out it's the firewall that gives them trouble, and they'll pick disabling the firewall over not playing with their toy any time. This works for pretty much any sort of permissions.

For example, last time I ran it on my tablet, Instagram's application was crippled to uselessness because I had disabled camera access (my girlfriend only needed to post a photo on an account that she managed): as soon as it opened, it spit out a big fat error message saying it can't access the camera and that you should allow camera access if you want to be able to take photos. As soon as you tapped ok, the same error popped up, and the application never loaded.

macOS apps aren't any different, you're just running the right ones :-).

This caused a lot of negativity in the open source community. It's a shame, because on a technical level, it's actually very good. Its developers have, more recently, attempted to address this problem and their plan looks like it should work. However, the proof of the pudding is in the eating, and we haven't had much time to eat it yet :-).

It's unfair to blame my frustration with Linux lately solely on GTK, too, I'm sorry if I gave that impression. A lot more factors are at work here. GTK has just been very representative of this mindframe lately.

No, the releases broke only themes and exactly that was communicated - that the CSS engine was work in progress and that themes were going to be broken.

Those, who didn't want to listen complained afterwards. Color me surprised.

The decision to include "work in progress" code in stable releases is also a little questionable.

The traditional way to filter a program's network traffic with netfilter is to give each software its own uid, which can then be filtered. You will need it anyway to set ulimits and file access rights.

Also avoid to decide policy by process name. Even using full path is problematic (where things like hard links can give nasty surprises). Better to do what SELinux does and tag executables with metadata instead. Any role based system will be much more expressive, but also complex, than a uid based one.

There is nothing bundled inside Netfilter for this anymore because this is racy: several unrelated processes can use the same socket. The processes may come and go whenever they want.

There is also some prior art (but it's a dead project): NuFirewall.

Edit: Looks like that only matches the process "task command name", so it probably won't work for full paths. I guess that's why they use their own kernel module?

Edit2: Never mind. That feature disappeared with 2.6.14, 10 years ago: https://lists.netfilter.org/pipermail/netfilter/2007-January...

I think a permission system like Douane’s would solve this divide.

Linux has been missing a personal firewall with good GUI for a looong time.

I'll probs give it a try on a VM and see how well it works.

well.

but TBH, I'd love to see some Little Snitch-like thingy on Linux.

https://github.com/subgraph/fw-daemon

it provides a very close experience to little snitch

*As always, a multi-faceted approach should be taken with security, and this isn't all you should be running if you're trying to defend yourself.