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Now that Steam is officially available on Linux, I am very interested in it!

However, I wonder what is the security system in Steam?

When I download a game through Steam, will the game run as native application that has complete access to user data or in a sandboxed environment with declared permissions (similar to Android)?

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1  
I find it highly unlikely that it would be sandboxed, but I suppose it's possible. –  SevenSidedDie Feb 16 '13 at 18:45
    
@SevenSidedDie Since it is a cross-platform system, the games are probably running in a virtualised enviroment, in which case it is easy to sandbox it. –  HRJ Feb 17 '13 at 5:53
4  
The games are ported, not run in a virtualised environment. There is no emulation or compatibility layers in the Steam for Linux design. (That's why there is a limited selection available right now, rather than the whole library.) Given that, the only sandboxing that makes sense is if Steam launched each game in a chroot jail, and I'd be surprised if doing that even occurred to the Valve devs. –  SevenSidedDie Feb 17 '13 at 6:37
    
@SevenSidedDie Thanks for confirming it is not virtualised. So Steam is just a store + perhaps some networking API? Steam downloads about 175MB of stuff upon first installation; I wonder what exactly it provides. –  HRJ Feb 17 '13 at 10:00
    
Most of this stuff is graphical assets for the skin and Big Picture Mode which is a lot of eye candy. The client itself and the necessary binaries are rather small. –  NoneOfYourBusiness Sep 26 at 2:53

3 Answers 3

up vote 6 down vote accepted

Steam doesn't use sandboxes. For example, in Windows, Steam games usually save their data in My Documents, Appdata, their own installation folder or Steam's Steam Cloud folder (which syncs back to the online storage service for your saves, configurations and other user data). Some even install other programs, like a multiplayer component's library (e.g.: Games for Windows - LIVE).

Valve, however, put some restrictions in place to prevent unwanted behaviour, like a game installing a publisher's games marketplace without asking. The only thing closest to doing that is Ubisoft's uPlay, which Ubisoft wanted to use for updating their games, so instead of shipping the full client each game comes with a mini version that lacks the marketplace and can only be started when you start its associated game.

Games on Steam are mostly the same as their retail counterparts, only slightly modified to use Steam's authentication DRM and made downloadable through Steam's servers.

Steam offers additional services in return, like automatic updates, cloud synchronisation of game user data, achievements, leaderboards and other personalised data (look at a user's Team Fortress 2 stats for an example) and more.

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Would you do a DLL dependency check via ldd, if you have installed Steam under Linux? It would be highly interesting to see whether they modified the game binaries to require Steam to run, and, if so, how. –  DrFish Feb 20 '13 at 9:09
    
``` ldd which steam not a dynamic executable ``` –  HRJ Feb 20 '13 at 13:28

Steam doesn't protect your system from untrusted games, or from itself.

You might be interested in Stéphane Graber's article on using LXC to do this, and the steam-lxc project he created for that purpose.

September 2014 Update:

I finally got around to setting this up myself. The links above are a little out of date, but Stéphane posted a more recent set of articles on LXC 1.0 that were very helpful. Between those and a bit of experimenting, I got Steam working in an unprivileged container, and it works pretty well.

My command line for creating the container:

lxc-create -n steambox -t download -- -d ubuntu -r trusty -a amd64

I edited my container config file to look something like this:

# Distribution configuration
lxc.include = /usr/share/lxc/config/ubuntu.common.conf
lxc.include = /usr/share/lxc/config/ubuntu.userns.conf
lxc.arch = x86_64

# Container specific configuration
lxc.id_map = u 0 100000 1000
lxc.id_map = g 0 100000 1000
lxc.id_map = u 1000 1000 1
lxc.id_map = g 1000 1000 1
lxc.id_map = u 1001 101001 64535
lxc.id_map = g 1001 101001 64535
lxc.rootfs = /home/myusername/.local/share/lxc/steambox/rootfs
lxc.utsname = steambox

# Network
lxc.network.type = veth
lxc.network.flags = up
lxc.network.link = lxcbr0
lxc.network.hwaddr = 00:16:3e:77:48:b8

# Video
lxc.mount.entry = /tmp/.X11-unix tmp/.X11-unix none bind,optional,create=dir
lxc.mount.entry = /dev/dri dev/dri none bind,optional,create=dir
lxc.mount.entry = /dev/nvidia0 dev/nvidia0 none bind,optional,create=file
lxc.mount.entry = /dev/nvidiactl dev/nvidiactl none bind,optional,create=file
#lxc.cgroup.devices.allow = c 195:* rwm
# video0 doesn't exist on my system.
#lxc.mount.entry = /dev/video0 dev/video0 none bind,optional,create=file

# Sound
lxc.mount.entry = /dev/snd dev/snd none bind,optional,create=dir

# Game Controllers
# Steam uses SDL for controller support; SDL uses udev and /dev/input/*
lxc.mount.entry = /dev/input dev/input none bind,optional,create=dir
#lxc.cgroup.devices.allow = c 13:* r
# uinput might be needed for gamepad support with streaming
#lxc.mount.entry = /dev/uinput dev/uinput none bind,optional,create=file
#lxc.cgroup.devices.allow = c 10:223 rwm

# for debugging
#lxc.aa_profile = unconfined

# EOF

This is only meant to get you started. You'll still have to set up your host system as described in the articles, and probably reboot it, before it will work. Please don't ask me to troubleshoot your system.

I'm running Ubuntu with an nVidia card. Different distributions and video cards will probably require a few different paths, device file names, and device numbers.

Note that I haven't set lxc.cgroup.devices.deny = a yet, so the container isn't quite as locked down as it could be. (I'll change that once I finish experimenting.)

I deliberately used the amd64 architecture and the Ubuntu Trusty release for my container, despite the fact that Valve supports only i386 and Precise. I did this because I want Valve's spyware to count me among those using a modern OS, in hopes that they'll start supporting it sooner.

Once I had steam working in the container, I set up a launcher script on my host system. It's named steam and lives in my PATH, so steam command lines work pretty much just like they would if Steam was installed normally. Here's the script:

#!/bin/bash

CONTAINER=steambox
COMMAND=/usr/games/steam

# Finds joystick devices so we can tell Steam's old SDL library to use them
# https://github.com/ValveSoftware/steam-for-linux/issues/1894#issuecomment-25295972
function enum_joysticks {
  local joyprop=ID_INPUT_JOYSTICK=1
  for f in /dev/input/*; do
    if [ ! -c $f ]; then
      continue
    elif udevadm info --query=property --name=$f | grep --quiet $joyprop; then
      echo $f
    fi
  done
}

# Uses the first arg as a separator to join the remaining args
function join {
  local IFS="$1"
  shift
  echo "$*"
}

COMMAND="SDL_JOYSTICK_DEVICE=$(join : $(enum_joysticks)) $COMMAND"


STARTED=false
if ! lxc-wait -n $CONTAINER -s RUNNING -t 0; then
    lxc-start -n $CONTAINER -d
    lxc-wait -n $CONTAINER -s RUNNING
    STARTED=true
fi

lxc-attach --clear-env -n $CONTAINER -- sudo -u ubuntu -i \
    env DISPLAY=$DISPLAY $COMMAND "$@"

if [ "$STARTED" = "true" ]; then
    lxc-stop -n $CONTAINER -t 10
fi

The enum_joysticks, join, and COMMAND="SDL_JOYSTICK_DEVICE... parts are only there to work around a Steam bug that prevents Big Picture Mode from detecting game controllers on an Ubuntu Trusty system. You could probably remove those parts from the script if your container is running Ubuntu Precise or you don't use Big Picture Mode.

With that script installed in my PATH, I can copy the each game's .desktop file from my container to my host system to make the game appear in my applications menu. (I usually copy the icon as well, or edit the .desktop file to name an icon that's installed on my host.)

cp /home/myusername/.local/share/lxc/steambox/rootfs/home/ubuntu/.local/share/applications/thegame.dekstop /home/myusername/.local/share/applications/

Good luck!

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Indeed, I had started looking at lxc too, for this and other such uses. The links you posted are a great head start. –  HRJ Oct 20 '13 at 4:56
    
September update: thanks for the original and the recipe for unprivileged containers. I have been using LXCs quite a bit and I suspect this thread started my first foray into using them! –  HRJ Sep 26 at 6:40

You can use a partition with Steam Os to run all Steam games in a safe place separated from your files. All the files the games will access are those within the partition, and the worst virus could do is to wipe or alter user files in that sandbox.

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