add firejail post

diff --git a/personal/_posts/2019-03-09-firejail.md b/personal/_posts/2019-03-09-firejail.md
new file mode 100644 (file)
index 0000000..6f16557
--- /dev/null
+++ b/personal/_posts/2019-03-09-firejail.md
@@ -0,0 +1,91 @@
+---
+title: "Sandboxing All The Things with Firejail"
+categories: sysadmin
+---
+
+Sometimes, I run software that I trust less.
+All software I use on a daily basis is open-source, but there is still closed-source software I run occasionally, like video games.
+Unfortunately, the usual Unix security model does not protect against such software misbehaving, as illustrated by [this XKCD](https://www.xkcd.com/1200/).
+There is no good reason that these applications should have access to all my personal information and secret keys that I have stored on my system, but without proper application isolation (like we are used to on mobile devices nowadays) nothing stops them from leaking all this data.
+I didn't want to wait until such technology becomes the default on Linux desktops, so I did some research for ways to sandbox existing applications and ended up with [Firejail](https://github.com/netblue30/firejail).
+
+<!-- MORE -->
+
+Firejail is packaged for Debian and other distributions, so you should be able to install it with your distribution's package manager.
+It runs an application in a sandbox, the details of which are configured in a *profile*.
+Firejail comes with profiles for many applications.
+For example, `firejail firefox` will start Firefox inside the sandbox.
+This adds an extra layer of security around Firefox' security mechanisms.
+
+However, I have found that my setup is sufficiently non-standard that I often have to customize the profiles.
+The most complex piece of the profile is to configure which parts of the file system the application will be able to access.
+Unfortunately, the configuration language can be quite hard to use---it is often difficult to find out why access to a particular file does not work.
+Also, the whitelisting mechanism is fairly inflexible: you cannot control which directory gets whitelisted; instead, when you whitelist something in `/home/user/foo`, whitelisting gets turned on for all of `/home` (and similar for a bunch of other hard-coded "whitelisting roots").
+But with some experimentation, you'll get things to work eventually.
+
+For example, if there are extra directories that no sandboxed application should be able to access, you can add them in `/etc/firejail/disable-common.local`.
+I am blacklisting all my personal files:
+```
+# Personal files
+blacklist ${HOME}/Documents
+```
+This will affect all sandboxes, because `disable-common.inc` is included pretty much everywhere, and that includes `disable-common.local`.
+
+## Custom Profiles
+
+Firejail cannot come with profiles for all applications, so sometimes you have to write your own.
+For example, I use one profile for all video games as well as TeamSpeak, which is based on the profile for Steam and looks like this (I store it in `/etc/firejail/gaming.profile`):
+```
+# Steam profile (applies to games/apps launched from Steam as well)
+noblacklist ${HOME}/.steam
+noblacklist ${HOME}/.steampath
+noblacklist ${HOME}/.steampid
+noblacklist ${HOME}/.local/share/steam
+noblacklist ${HOME}/.wine
+noblacklist ${HOME}/.ts3client
+include /etc/firejail/disable-common.inc
+include /etc/firejail/disable-programs.inc
+include /etc/firejail/disable-passwdmgr.inc
+
+caps.drop all
+netfilter
+nonewprivs
+noroot
+protocol unix,inet,inet6,netlink
+# wine/games don't work properly with seccomp
+#seccomp
+
+# give access to some directories
+read-write ${HOME}/.cache/winetricks
+read-write ${HOME}/.ts3client
+read-write ${HOME}/.steam
+read-write ${HOME}/bin/teamspeak3
+whitelist /mnt/store/r/games
+# -> implicitly, the rest of /mnt is blocked
+```
+Obviously, you will have to adjust the paths.
+If one particular application needs something that got globally blacklisted, you can use `noblacklist`.
+However, you might also have to `whitelist` it if something else sets up a whitelist for this directory.
+Also, there seems to be no way to have something on the `blacklist` globally but then make it `read-only` for a particular sandbox only.
+(This is what I mean by the configuration language being hard to use.)
+
+Next, it is a good idea to test the profile.
+You can start a shell inside the sandbox with:
+```
+firejail --profile=/etc/firejail/gaming.profile bash
+```
+Now you can do things like `ls ~/.ssh` to make sure your secret keys are not accessible in the sandbox.
+Also test accessing the directories where the games are stored.
+Use `exit` to leave the sandbox.
+
+I have created a file `~/bin/gamejail` to conveniently start an application inside the sandbox:
+```
+#!/bin/bash
+exec firejail --profile=/etc/firejail/gaming.profile "$@"
+```
+Now you just have to wrap the call to run the application inside `gamejail`, for example `gamejail steam`.
+
+That's all I got.
+I hope this little tutorial helps you to make your system a bit more secure by restricting application privileges.
+Firejail is far from perfect, but it works quite well and it is extremely customizable.
+In case you have trouble configuring the sandbox properly, I have found it very helpful to look at all the examples that are shipped in `/etc/firejail`.