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Moblin Will Run X Server As Logged-In User, Not Root
nerdyH writes "An architect of the Moblin Project has announced that Moblin 2.0 for netbooks and nettops is the first Linux distribution to run the X server as the logged-in user, rather than SUID'd to root. The fix to this decades-old security liability comes thanks to 'NRX' (No-root X) technology reportedly developed by Intel, Red Hat, and others in the X community, and the Moblin-sponsored 'Secure X' project. Besides making Linux netbooks a lot more snoop-proof, it seems like this could lead to an X-hosting renaissance of sorts, since you wouldn't be risking the whole system just to open up a specific user's account to remote X servers."
I'm not sure I grasp the concept of X Hosting, and how this non-SUID server would help that.
X is not required to be running on the remote system for X11 forwarding over SSH. Even running an Xvnc server doesn't require it to be SUID. This seems to be entirely a local security gain for users who will be interacting with local graphics hardware.
I don't know how they've done it, but I know this is a good thing.
They've done it by removing the responsibility of X talking directly to the graphics hardware by implementing Kernel Mode Switching for graphics drivers (among other much needed overhauls to the Linux graphics stack). Thus X can now access what it needs at the logged-in users' level and doesn't need root.
The article repeats the common misunderstanding: "in the backwards terminology of X"
What exactly is backwards about this? X is the server, and the apps are clients.
Think about it: The client initiates the conversation with the server. The client tells the server what to do.
How is this backwards?
Just got fixed by this. To be honest, I don't know how they've done it, but I know this is a good thing. This will make X and linux more secure and I can only applaud that.
I think what is basically boils down to, is that instead of X talking to the hardware directly it now talks to a file under /dev/ just like everything else.
> it seems like this could lead to an X-hosting renaissance of sorts,
> since you wouldn't be risking the whole system just to open up a
> specific user's account to remote X servers.
What a clueless statement. Somebody doesn't understand how X works. The server part that runs SUID root has never ran on the app server.
What this does do is stop a random remote app getting to root on your workstation but any local exploit of the X server gets them your user account and that can cause a lot of mischief and only needs a different local root exploit to get the rest of the way to 0wn1ng your local desktop machine.
Democrat delenda est
I am a bit confused by the submitter's comment about remote X servers. I understand the appeal of remote X clients: I can, e.g., log into a big fast machine and run MATLAB (the X client) there while interacting with the window on my less-powerful laptop (which runs the X server). But what's the point of a remote X server? Why would anyone want to run an X server (software sense of 'server') on a server (hardware sense of 'server')?
> Can someone spare me reading the article and let me know if DRI is still possible without root?
Yup, this whole thing rests on the new kernel modesetting. That was the last thing that required root to be able to directly frob bits on the video card. DRI also goes into the kernel as it should. The kernel is supposed to own all of the hardware and expose safe APIs for user apps to access it. For historical reasons video has been the exception to that rule. No longer.
Democrat delenda est
The X server is the program on the local machine that displays the pixels.
The program you run on some other system via the net is the client, even if the thing it's running on is called a server.
The X server traditionally runs as root. You are likely unaware of this because it's started automatically as part of the init process.
The X server running as root is independent of whether the X client is running as root.
GCHQ Quantum Insert installed. If only our tongues were made of glass, how much more careful we would be when we speak
I just loaded it on my Eee PC and it turns the machine into a kiosk. Very unappealing for anyone who actually wants to use their netbook. Its very flashy and friendly if all you do is check your email and browse the web though.
Mr. Green
Well, if the flaw is in an X *library*, it doesn't matter, as only the clients (running as the regular user) use those. The X server doesn't need or use libX11, libXrandr, libXext, etc. at all.
But yes, true -- any exploitable flaw in the X server itself (or any of the extensions compiled into or loaded dynamically by the server) could result in root access.
Xfce: Lighter than some, heavier than others. Just right.
> Sounds like Windows NT 3.5, wonder if it will get moved back into kernel
> space for performance reasons just like NT4 moved video back into kernel space.
Not the same thing. The video hardware belongs in the kernel in exactly the same way as sound, mass storage and the keyboard/mouse do. *NIX and Windows are now alike in that and it is good.
What Windows did was bring most of the next layer up the chain into kernel space. This would be more like putting the whole X server and bits of GTK and/or Qt into the kernel, not just running it as root. Yes it improved performance some, but the security implications are horrific.
Democrat delenda est
um, the end of the name of that picture (scrot.png) made it look really suspicious. for the rest who looked at the url of that link before clicking, its of a screenshot taken by the scrot cli screenshot program not a pict of some scrotum. FYI
It prevents any exploits for the xserver user from being able to effect the rest of the system outside of the confines of the user and whatever it can interface with graphically. Thus preventing it from gaining control to the rest of the system easily. Plus, selinux, apparmor can likely be enhanced to enforce the rules upon the xserver in other ways when it is running as a user process.
Change is certain; progress is not obligatory.
Windows in fact runs (almost) nothing at all as "Administrator". Please find a Windows machine and run Task Manager. There are multiple OS accounts used, like like SYSTEM, LOCAL SERVICE and NETWORK SERVICE, so unlike root on Unix these are shielded from each other and from parts of the system they have no business dealing in. And furthyermore, important parts of the windowing system are implemented as DLLs (shared libraries). Those are run in your process space, and thus under your user account.