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Comments: 205 +- Technology: Moblin Will Run X Server As Logged-In User, Not Root on Thursday July 09, @03:54PM
Posted
by
timothy
on Thursday July 09, @03:54PM
from the such-a-little-thing-makes-such-a-big-difference dept.
from the such-a-little-thing-makes-such-a-big-difference dept.
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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."
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IMHO (Score:2)
This is something that is long overdue.
Re: (Score:2)
Ya think? X is older than I am.
Can someone spare me reading the article and let me know if DRI is still possible without root?
Re:IMHO (Score:5, Informative)
> 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.
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Re: (Score:3, Interesting)
Re:IMHO (Score:5, Informative)
> 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.
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Re:IMHO (Score:4, Interesting)
Er, the same way USB was for years? Actually, DRI, too. The driver exposes a pseudo-device in /dev/, which actually is a socket-like, high-throughput mmap wrapper and the X server opens it. Given appropriate file permissions and group membership, this can be done from a user account.
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Re: (Score:3, Insightful)
Yes, DRI access is done through /dev/dri* and works correctly.
Confused article. (Score:5, Insightful)
Linux's SUID X server problem has been kind of a "dirty little secret" for many years. Most modern distributions include a few crude workarounds, such as dimming the display and then freezing X whenever the user is asked to type in a root password. Getting rid of the SUID bit altogether ought to make netbooks powered by Moblin technology much more difficult to snoop on over the network.
This does not make sense. Graphical sudo wrappers have nothing to do with X being suid, and neither does anything to do with network traffic.
It seems likely that with NRX technology, you could run X apps over a network with much less risk to the app server (the system that runs the "X client" component, in the backwards terminology of X).
This is actually backwards, the only place there's less risk is for the system that the X server is running on.
X Hosting? (Score:4, Informative)
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.
Re: (Score:3, Insightful)
> I'm not sure I grasp the concept of X Hosting, and how this non-SUID server would help
> that.
It wouldn't. The author of the article hasn't the foggiest notion of how X works (well, he does have a foggy notion, but it's wrong). The machine(s) running the client(s) run only the client code and run it as the user.
Re:X Hosting? (Score:4, Insightful)
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Re: (Score:3, Informative)
Ive used X over network connections and I know this to be incorrect, at least over a ethernet. THere are also solutions avialable for the problems you mention, or which can be addressed. There are various products that will compress the X data stream so that it uses less bandwidth and can perform quite acceptably. Such as NX. There was for a while a provide called xmove which was an X proxy to which your X clients would connect, you can send xmove command to redirect the display of the X client between diff
Correct me if im wrong (Score:2, Insightful)
But running apps remotely and having them display on a local X server _NEVER_ required root access of any kind on the remote server....
Re:Correct me if im wrong (Score:5, Informative)
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.
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Poor understanding of X (Score:5, Informative)
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?
Re:Poor understanding of X (Score:5, Informative)
How is this backwards?
It's only backwards in human thought, because people have the ingrained presupposition that the server is the Big Machine In Another Room, and the client is the Little Machine On Your Desk.
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Stupid (Score:4, Informative)
> 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.
Re: (Score:2)
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.
Yeah, the submitter is clearly clueless as is timothy since he couldn't notice such a glaring error.
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
Which is far less dangerous than them getting root access.
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.
Which basically makes it harder for someone to get root access since they have to find another exploit to gain it.
Re: (Score:3, Insightful)
> Yeah, the submitter is clearly clueless as is timothy since he couldn't notice such a glaring error.
Well the Slashdot editors went to the Grey Side (Mac) a decade ago so what the hell would they know about X. The /. servers are still *NIX so they know and care about that side a bit.
> Which basically makes it harder for someone to get root access since they have to find another exploit to gain it.
Sure, this move is a win for security because X was big complicated and running as root, but not cause f
Remote X servers? (Score:4, Informative)
Re: (Score:2)
You don't need X for Matlab. The interface isn't that good.
Re: (Score:2)
I doubt I know enough to answer your question, but your question itself confuses me. You understand why someone would want to run "remote X clients", but you don't understand why someone would want to run "remote X servers". If you don't have a server, then who is the client connecting to?
Re:Remote X servers? (Score:4, Informative)
The "X server" runs on the machine with the keyboard, mouse, and display. An "X client" is a program (e.g., xterm) that connects to an "X server" to which it sends drawing commands and from which it receives mouse and keyboard events. In the "writing network software sense," these names make sense, because it is the "X server" that sits and listens on a port, and the "X clients" that connect to it. What makes this confusing is that in practice an "X server" will usually run on a user's machine (which you would normally call a 'client') and an "X client" will run on a big machine elsewhere (which you would normally call a 'server'). The problem comes from using the words "client" and "server" to describe both programs and machines; basically, our jargon sucks.
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Re:Remote X servers? (Score:4, Informative)
It's not just the submitter. Apparently the writer of the blog post themselves don't even understand X all that well.
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Re:Remote X servers? (Score:5, Insightful)
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Graphics drivers (Score:5, Insightful)
If graphics drivers were implemented in the kernel instead of the X server, this problem wouldn't have existed in the first place.
Re:Graphics drivers (Score:4, Interesting)
Yes, it's interesting that KGI was rejected 10 years ago, but now we have KMS. What has changed?
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Re: (Score:3, Insightful)
What has changed?
The fanatics have become more reasonable?
Re:Graphics drivers (Score:5, Insightful)
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Re: (Score:3, Funny)
Linus isn't perfect
I met Linus in person a while back and asked him about this. He disagrees with you.
Since he's perfect, I kinda have to go with him on this one.
Re: (Score:3, Insightful)
If graphics drivers were implemented in the kernel instead of X, you would have to write new drivers for every kernel you want to run X on.
Re: (Score:3, Insightful)
We have that situation for all other drivers and somehow we survived. Also, it's common for vendors to write a single BSD-licensed driver and then port it to multiple OSes, sharing most of the code.
Is this right ? (Score:5, Interesting)
I am not sure that this is the right solution. Not running it as root is good, but running it as me - I don't know. I'd rather that the user that runneth the X server is some sort of 'xserver' user - to whose process I connect. That 'xserver' user then has the right to push my screen into VGA mode and all that. Also, this doesn't fix all those other services (that gnome has, for example) that allow my X programs to mount stuff etc. Which is, again, a security risk by itself.
Re: (Score:2)
Not running it as root is good, but running it as me - I don't know. I'd rather that the user that runneth the X server is some sort of 'xserver' user - to whose process I connect.
So if you have multiple users on the same machine running X, they can stomp on each other (by virtue of all interacting with the same "xserver user") ?
Re: (Score:3, Insightful)
I am not sure that this is the right solution. Not running it as root is good, but running it as me - I don't know. I'd rather that the user that runneth the X server is some sort of 'xserver' user - to whose process I connect. That 'xserver' user then has the right to push my screen into VGA mode and all that.
As another poster mentioned, this makes multi-user X a bit more difficult. What's the issue of having your user ID doing all this? If you're allowed to log into the console, then you're presumably allowed to run X (or not; you can still lock down the machine so particular users can't run X or access the graphics hardware). If you can run X, you can talk to the graphics hardware. Note that this doesn't give you carte-blanche to fiddle with the graphics card's registers to try to make the machine crash: y
I don't know... (Score:3, Insightful)
Certainly this isn't worse than the current situation. But if my data is still at risk I have a hard time caring much about any "security" advantage.
Without my data the machine is worse than worthless.
Re: (Score:3, Insightful)
What's the issue of having your user ID doing all this?
A remote hole in a process run as 'nobody' allows some log files to be trashed, maybe.
A remote hole in a process run as me allows all of my data to be destroyed.
Re: (Score:3, Informative)
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.
Been waiting for this (Score:2)
X is a large, clutterd and complex system that has no business running as root. It is good to see they finally managed to get away from that implementation, even if it adds a bit more complexity.
Have you used Moblin? (Score:5, Informative)
Re:Have you used Moblin? (Score:5, Insightful)
Its very flashy and friendly if all you do is check your email and browse the web though.
Almost like that was the entire point of the distro in the first place!
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Why not take it one step further? (Score:3, Insightful)
Does graphics mode switching inside the kernel mean that we can soon expect switching between VTs to work even if the X server is locked up? Or is the keyboard handling still going to prevent that? (Doing the switching from a remote login would work around the keyboard issue).
Re:One of the shortcommings in security (Score:5, Informative)
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.
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Re:One of the shortcommings in security (Score:5, Informative)
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.
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Re: (Score:3, Insightful)
How big of a security problem was this? I haven't seen a linux system with open ports for X in 10 years. Anyone who wants to use remote X just uses ssh -X, it's easier to set up than xhost anyway.
Re: (Score:3, Informative)
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.
Re:One of the shortcommings in security (Score:4, Interesting)
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Re:frost nixon (Score:5, Insightful)
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Re:frost nixon (Score:5, Insightful)
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Re:Two questions: (Score:4, Insightful)
1. Does this mean you can't login at a graphical interface? I.e. will you have to login at a terminal and then wait for X server to come up?
No. There should be a login X server (running as root or nobody or whatever) to display GDM, then during login this server will exit and launch a new server under your uid. Or something like that.
2. If multiple users login, will each user get their own instance of X server? This seems like overkill...
I think fast user switching already works that way. We don't consider it overkill that each user gets their own instance of Firefox; why is X any different?
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