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Ask Slashdot: Safe Learning Environment For VMs? 212

Posted by timothy
from the first-do-no-harm dept.
First time accepted submitter rarkian writes "I am the teacher in this story. I teach Python and C++ to high school students: grades 9-12. I use CentOS 6 with DRBL to run my computer lab. Some of my students have become Linux experts. Next year I'm planning on allowing students to create and run their own VMs in a segregated LAN. Any advice on which virtualization technology to use and security concerns with allowing students to be root in a VM?"
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Ask Slashdot: Safe Learning Environment For VMs?

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  • Set up VLANs (Score:4, Insightful)

    by Anonymous Coward on Tuesday May 28, 2013 @11:16AM (#43841605)

    for each of the students and don't allow any interface between them...and certainly no main network/internet access.

    • Re: (Score:2, Insightful)

      by ttucker (2884057)

      for each of the students and don't allow any interface between them...and certainly no main network/internet access.

      VLANs are not for security! Any two things plugged into the same switch, whether virtual or real, can talk to each other if sufficiently motivated.

      • Only if the switch lets them.
      • Re:Set up VLANs (Score:5, Informative)

        by LordLimecat (1103839) on Tuesday May 28, 2013 @12:56PM (#43842817)

        Not if they are on private VLANs (still not clear if it is a standard or not). VMWare supports this; the idea is roughly analogous to AP isolation on a wifi AP-- "isolated" nodes can all talk to the gateway (the community / public node), but cannot talk to each other.

        And VLANs actually are for security, and can provide far superior security than ACLs, since unless you have a trunk port or layer 3 switches, it is impossible for two devices on different VLANs to communicate, short of a switch misconfiguration. Its probably second to air-gapping in terms of security-- its sort of a logical implementation of "air gapped switches", except that they CAN be joined together if someone gets onto the switch.

        • by evilviper (135110)

          it is impossible for two devices on different VLANs to communicate, short of a switch misconfiguration. Its probably second to air-gapping in terms of security

          You're seriously over-stating the security of VLANs. While you should be safe if you follow the best practices, there are potential security issues to be aware of, and VLANs are certainly NOT more secure than layer-3 routing/firewalling.

      • Re:Set up VLANs (Score:4, Interesting)

        by MattW (97290) <matt@ender.com> on Tuesday May 28, 2013 @02:18PM (#43843527) Homepage

        VLANs are not for security! Any two things plugged into the same switch, whether virtual or real, can talk to each other if sufficiently motivated.

        As you pointed out below, VLANs in general are trustworthy when properly configured with a proper switch. I did nothing but netsec work in the late 90s, and everything was airgapped; we'd never have frames from two networks on the same wire. If you wanted to cross security zones, it was at L3 on a firewall and to different wires and switches.

        On the other hand, it seemed like back then a new practical way to defeat VLANs was coming out every other week, so this was a wise precaution.

        That said, keep in mind that VMware also affords some additional security in terms of VLANs. Physical switches have to connect to virtual switches to interact with the VMware layers (either the hypervisor for control traffic, or with the VMs for VM traffic), and the hypervisor itself will enforce a lot of things. On a VMware vSwitch properly configured:

        - VMs can't enter promiscuous mode, change their MAC address, or forge transmits with the wrong L2 address
        - QinQ frames are discarded
        - The hypervisor itself will determine which virtual nics on a vswitch should receive copies of a frame, depending on which VLAN tag is on a portgroup
        - Guests can't send tagged frames if their portgroup is set with a VLAN; you have to specifically configure a trunk on a portgroup to pass VLAN tags in and out of the guest environment

        If the network was homogeneously ESX nodes and administratively controlled network equipment, you could likely enforce security between VMs with VLANs even with a dumb hub.

        Obviously, airgapping and single-role wires will create better security than VLANs, because there always remains a chance that an undiscovered bug will allow breaching that L2 barrier, but that's true for everything.

      • That's not true at all. Yes there exists a VLAN hopping exploit, but it is easily prevented by modern switches. While VLANs weren't intended for security in the beginning, that has become one of their new purposes. Otherwise, layer 3 switches would probably never be used in any environment where security was major a concern, but that's simply not the case.

        Another extension of the VLAN concept is PVLANs, whose purpose is for nothing else other than security, primarily used in hotels to prevent hacking, but h

        • by ttucker (2884057)

          That's not true at all. Yes there exists a VLAN hopping exploit, but it is easily prevented by modern switches. While VLANs weren't intended for security in the beginning, that has become one of their new purposes. Otherwise, layer 3 switches would probably never be used in any environment where security was major a concern, but that's simply not the case.

          Another extension of the VLAN concept is PVLANs, whose purpose is for nothing else other than security, primarily used in hotels to prevent hacking, but has other uses as well, nearly all of them security related.

          Some further research indicates that my initial reaction to VLAN and security is somewhat dated, and VLAN tech has improved drastically since. Still, there does seem to be a few places where poor configuration could lead to a spectacular breach, simply because any exploit of the switch allows an attacker to access any VLAN segment.

      • Re:Set up VLANs (Score:4, Interesting)

        by evilviper (135110) on Tuesday May 28, 2013 @03:53PM (#43844425) Journal

        VLANs are not for security! Any two things plugged into the same switch, whether virtual or real, can talk to each other if sufficiently motivated.

        Umm, no. Not unless your switch is defective, or massively misconfigured. VLANs are very secure, when done properly. And the same security measures needed to protect VLANs are the same ones you need to protect switching in general (see CAM overflows, arp spoofing, and such).

        http://www.cisco.com/en/US/products/hw/switches/ps708/products_white_paper09186a008013159f.shtml [cisco.com]

        If you leave your trunk/native VLAN at 1, you're in trouble. If you configure user-facing ports as auto-negotiate, or trunk without explicitly specifying allowed VLANs, you're in trouble.

    • by raymorris (2726007) on Tuesday May 28, 2013 @11:53AM (#43842095)
      Thanks for going the extra mile with your students.

      As AC said, a separate LAN or VLAN, or multiple separate LANs/VLANs handles most of what's posted below. For example, a rogue DHCP server would only be visible on that VLAN.

      Red Hat has a Virtualization Security section in their manual:
      https://access.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Virtualization_Administration_Guide/chap-Virtualization-Security_for_virtualization.html

      CentOS/RHEL includes comprehensive support for KVM with virt-manager. While VirtualBox et al are fine for running one or two virtual machines on your desktop, for many VMs, with new ones created and removed each semester, the enterprise level support of KVM built into the distro is more appropriate. That support includes creating VLANs within the same management interface, for example, and integrates with the built in storage stack administration tools. Again, VirtualBox may be simpler to set up for one or to two machines, so I'm not saying it's not good - it's just not the best tool in this particular scenario. In this type of scenario, the KVM / virt-manager / virsh stack that RH baked in is probably a better match to the needs.
      • Another thing to add to this - my enterprise VM knowledge is pretty much limited to VMware, and I do know that if you use VMware, you can use the VMware Distributed Switch (VDS) which supports PVLANs. Place each individual set of VM's that belong to a given student into a community PVLAN, and make your default gateway a promiscuous PVLAN.

    • by Vrtigo1 (1303147)
      That, to me, defeats the entire point. Why even give the machines network adapters if there's nothing for them to talk to? It'd be much better in terms of experience, learning, practicality and fun if you just setup an isolated network for all of the student machines and create your own little Internet. That gives them the ability to setup client/server apps with other students and deal with security issues, just like they'd have to do in real life.

      Setting everyone up by themself might let them do som
  • The whole point of a VM is that being root isn't a safety concern.

    • Re: (Score:2, Interesting)

      by Anonymous Coward

      Unless they take down the network, e.g. running a rogue DHCP server. Or they use it to hack other systems on the network, e.g. password-sniffing the other student's credentials when they log in from their VMs.

      • Re:Safety? (Score:4, Interesting)

        by Joce640k (829181) on Tuesday May 28, 2013 @12:21PM (#43842435) Homepage

        Unless they take down the network, e.g. running a rogue DHCP server. Or they use it to hack other systems on the network, e.g. password-sniffing the other student's credentials when they log in from their VMs.

        So... nothing they couldn't do much easier/more safely by just pulling the network cable out of the physical machine and connecting it to their netbook?

      • I am not familiar with KVM or other Linux VM solutions.

        I do know that during my VCP cert course, all students were provided with a VMWare ESXi infrastructure that was entirely virtual, contained in a vApp on a parent vSphere infrastructure. We all had our own connection on our own vSwitch, but no uplinks to everyone else, so there really wasnt much anyone could do to interfere with other students.

        I suppose one of the students could try to defeat the vSwitch segregation via an exploit, but I think if they p

    • by fwice (841569)

      if the VM has a full root account, with a network address on the global network at large, then it has the ability to, for example, run a priviledged NMAP scan on the entire network. Which can expose open ports or vulnerabilities on another machine that can then be used to leverage access.

      • and run their own VMs in a segregated LAN

        Sounds like they'll be on their own little LAN

      • by Nerdfest (867930)

        They can always plug in their own laptop and do that anyway.

      • Re:Safety? (Score:4, Informative)

        by Archangel Michael (180766) on Tuesday May 28, 2013 @11:46AM (#43842009) Journal

        Which is why they need to setup their own VLAN to isolate the VMs to the classroom. VM traffic is isolated to non-routing VLANS. They call this setup a "sandbox", and it is generally a good practice for classroom work.

        As for which VM technology to use ... VMWare, or ZEN or even Microsoft's version are usable. VMWare is sort of free, Xen definitely is. I'm not familiar with pricing on Microsoft's versions but schools tend to get steep discounts for server licenses. Look at OpenStack for management, I hear it is decent when it works.

      • by Joce640k (829181)

        if the VM has a full root account, with a network address on the global network at large, then it has the ability to, for example, run a priviledged NMAP scan on the entire network. Which can expose open ports or vulnerabilities on another machine that can then be used to leverage access.

        Try reading the third line of the summary again. The bit where is says "segregated LAN" might interest you...

        • by fwice (841569)

          Try reading the third line of the summary again. The bit where is says "segregated LAN" might interest you...

          You made an incorrect blanket statement and I was pointing out a potential case to show this incorrectness.

          You claim that having root on a VM is not a security concern -- and I am showing a case where that is incorrect -- even if that does not conform the submitter's problem at large.

    • by h4rr4r (612664)

      Only if you think your VM software is perfect.

      I think all the popular products have at one time had exploits that allowed a guest root user to muck with the virt kernel or other guests.

      Heck, if you are not smart enough to limit how much resources one VM can take a nice fork bomb is a good way to slow down the whole shebang.

      • by Joce640k (829181)

        All of that applies to non-virtual machines, too.

        • by h4rr4r (612664)

          Indeed. I am not suggesting otherwise.
          I am only pointing out that VM software is not magic. It does the best it can, but cannot be relied upon to be infallible.

      • by NemosomeN (670035)
        Considering these are probably VMs that have their own machine to play on, you'll need one hell of an exploit to have a fork bomb impact the performance of another VM.
    • by bobbied (2522392)

      VM's are great for letting folks have "root" on a box safely for learning purposes. But I think one should consider what these boxes would be able to do on your standard corporate or school network. I assume that there is some kind of network security applied to the machines the students are allowed to touch. Having root access to a Linux box attached to the network will effectively bypass any existing security policies. I would be more worried about what the users can do to the local VM (Specifically to

  • Vagrant (Score:5, Informative)

    by Pinhedd (1661735) on Tuesday May 28, 2013 @11:18AM (#43841639)

    Vagrant is a wrapper for Virtualbox and VMWare Workstation that accelerates the deployment of development environments.

    http://www.vagrantup.com/ [vagrantup.com]

    • by rvw (755107)

      Vagrant is a wrapper for Virtualbox and VMWare Workstation that accelerates the deployment of development environments.

      http://www.vagrantup.com/ [vagrantup.com]

      Please tell a bit more about when and in what situations you would want to use this instead of a plain Virtualbox VM.

      • by Pinhedd (1661735)

        It automates the setup of the isolated development environment. A company can put a Vagrantfile into a development repository along with any associated setup scripts. As long as the developer has VirtualBox/VMWare Workstation and Vagrant installed, they can type `Vagrant up` from within the repository and it will automatically setup the development environment within the development VM. This is a really easy way to ensure that everyone is working on the same page.

      • Re: (Score:2, Insightful)

        by Anonymous Coward

        You can check in a Vagrantfile and Chef/Puppet scripts that create a working development, test, or production environment from a base OS install and Vagrant can spin them up with a single command. It simplifies creating a new development, build, or test environment, makes everything repeatable, and gives you assurance your stuff will run again when installed on a fresh box instead of a hand-crafted VM image. The Chef/Puppet stuff is applicable to production too, so through the course of dev/test you build

    • by FlipperPA (456193)

      +1 to Vagrant for local development. If there are any problems, you can easily just blow away the VM and start again. Vagrant scripts all of this with the same Chef repos you use for production. I modified and updated a Django Vagrant run-through I found on the net. It is free to the public on Github:

      https://github.com/FlipperPA/djangovagrant

      Naturally, this includes Python as well. I hope this helps gets you started, and thanks for going above and beyond with your students!

    • by styrotech (136124)

      I was going to suggest that too.

      Turn the problem on its head. Instead of supplying them with an actual virtual sandbox to play in (lots of work) - give them the ability to spin up a bunch of different virtual network/server configurations on their own machines.

      Vagrant configs can specify multiple servers and networks etc.

      They can easily be blown away and rebuilt, they can start sharing their own custom environments.

      BTW: checkout salty vagrant [github.com]. Salt is a Python based configuration management tool like Chef a

  • Virtual Box is lightweight and it won't matter if they are root. A VM eliminates all that trouble.
    "Oh you crashed the hell out of that machine, didn't you? oh well, reinstall."
    Since you are segregating the network they will have no outside access and no re...WTF am I saying?...VLANs
    • Re: (Score:2, Insightful)

      by h4rr4r (612664)

      Incorrect.

      A nice forkbomb in a single VM can cause headaches for the rest of the environment. There have also been exploits to allow one to interfere with either the host kernel or other guests, we have no reason to suspect all those bugs are crushed. VirtualBox is a fine desktop VM software, it is not however suited to this task.

      • Re:VirtualBOX (Score:4, Informative)

        by Archangel Michael (180766) on Tuesday May 28, 2013 @11:55AM (#43842123) Journal

        Forkbomb is only successful if you don't have limits on your VM environment. You have put limits on your environment, right?

      • A nice forkbomb in a single VM can cause headaches for the rest of the environment.

        Then it's a very poor environment.

        We're talking about one or many classes of students. If it's not built out to handle several VMs using their max CPU concurrently, then it's a very poor environment.

        Heck, everyone compiling at the same time would shut things down if the environment is built poorly.

        • by h4rr4r (612664)

          It has nothing to do with handling several servers or not. It has to do with the fact that if one VM can access all the CPUs it can keep them all busy.

          The disk is the same thing, if you do not limit a VM to a fixed amount of IO it can simply tie up all access to the disk for another easy DOS attack. This goes for any and all shared resources. Not very hard to soak a 1Gb network link just to be a jerk.

          • If one VM can access ALL of the CPU or disk, then it's a very poor environment.

            No sane sysadmin would set it up like that. And a good VM mgmt tool wouldn't let you easily.

            • by h4rr4r (612664)

              I agree with your first point. All the current VM management tools do not prevent this behavior. I honestly am not in favor of that level of handholding, but I can see where some might be.

  • virtual box is great. its free/open-source well supported on windows mac and linux. itis easy to set up. has the ability to take snapshots on the vm to roll back at a moments notice. good documentation don't know what else you could need here.

    • Re:Virtualbox (Score:4, Informative)

      by h4rr4r (612664) on Tuesday May 28, 2013 @11:33AM (#43841841)

      And is utter trash for anything that needs to be scalable.

      It is fine for a desktop VM system, but it simply does not offer the management interfaces that other solutions have. Basically the options here are VMware and KVM. The first if you want a shiny GUI the latter if you are ok without one. Both will let you script everything they do, which will be very handy when you need to reset 100 VMs for the next batch of students.

      • by greg1104 (461138)

        VirtualBox provides the VBoxManage [virtualbox.org] tool for automating operations. It works perfectly fine for this sort of thing. One of my small servers at home is running 28 VMs with all management happening through the command line, and that hasn't even gotten close to whatever the upper limit is. You certainly can run a classroom worth of VMs on a modestly sized box.

        The only major management feature that's much easier on VMWare than VirtualBox is moving VMs to new systems. That is very useful for large production

        • by h4rr4r (612664)

          Which is why I also suggested KVM.

          Virtualbox is neat, but it is very limited. It might be better to show them something that is actually used in industry.

    • Can we stop promoting the use of Oracle owned software already? I really would like to see the evil beast die.

      • Can we stop promoting the use of Oracle owned software already? I really would like to see the evil beast die.

        then use virtual box ose (open source eddition)

        i wonder if we will ever see a "librabox" fork akin to the libre/openoffice(.org) split?

  • VM is irrelevant (Score:5, Interesting)

    by onyxruby (118189) <.onyxruby. .at. .comcast.net.> on Tuesday May 28, 2013 @11:26AM (#43841747)

    The fact that your using VM's is largely moot and goes back to the line of thought that VM's are somehow not 'real' computers. VM's run the same operating systems, software, have the same bugs, vulnerabilities and everything else as a physical computer. You need to patch them just like any other computer and you need to license them just like a regular computer. The fact that they are VM's really only makes two differences practical differences that matter, fist is that is easy to roll them back and second is that your aren't running on bare metal.

    In other words you have a core issue that needs addressed of giving students root access to a computer. In an isolated environment this isn't necessarily a bad thing. Understand that they exploit root and see what they can do with it, however they are there to learn and if you can do so safely and without disruption of what your trying to teach then let them. Your focus needs to be on making it safe for those around them and that means making sure your VLAN and any related Internet access are properly setup. The lab is a lab and as long as you can make sure they aren't getting access to anyone persons computer than let them have at it.

    A good rule of thumb is to roll your sessions back prior to the start of every single class. This always gives a fresh machine and the students will quickly learn how to set their VM just the way they want it.

    • Re:VM is irrelevant (Score:5, Informative)

      by Archangel Michael (180766) on Tuesday May 28, 2013 @12:01PM (#43842193) Journal

      VMs have one advantage that non-virtualized systems don't have. The ability to put several machines in their own sandboxed network, all managed by a single student who needs to demonstrate cooperating systems. Give every student a template of needed machines and a VM server and you have a small lab on every computer. One that is easily setup, cleared and re-setup for every class, and as needed.

      VMs are a perfect solution for advanced computer systems management training.

      • VMs are a perfect solution for advanced computer systems management training.

        Which is not what is being taught.

        I teach Python and C++ to high school students

        • by bobbied (2522392)

          VMs are a perfect solution for advanced computer systems management training.

          Which is not what is being taught.

          I teach Python and C++ to high school students

          How about your own personal Rasberry Pi? Best of both worlds....

    • APT-Cacher, Squid (Score:4, Interesting)

      by SgtChaireBourne (457691) on Tuesday May 28, 2013 @12:07PM (#43842277) Homepage

      A good rule of thumb is to roll your sessions back prior to the start of every single class. This always gives a fresh machine and the students will quickly learn how to set their VM just the way they want it.

      They can start each class with a fresh snapshot. In effect they would be restoring from backups. The configuration files from some other networked storage or their thumb drives and the applications themselves from the repositories. I've done something similar, but on bare metal, and after about half a dozen times they don't notice -- it had become such second nature to install and restore applications. Heck you might even have them practice installing the whole system from scratch. If you go that route, they can become quite proficient with installation and resource allocation. PXE booting a netinstall image helps there.

      However, once you start to load packages from the net things can really slow down unless you prepare. The best way is to have a cache like APT-Cacher or Squid on your LAN or host system and have them configure their systems to use it for APT. For the cache to be most effective, you have to pre-load it before each class. That's easy and can be done while doing other things. It only takes time not attention. But once you have the cache loaded, installation will fly and can be done in 15 - 20 minutes. After that they weren't shy about installing on their own computers at home or helping their friends.

      • by tibit (1762298)

        Better yet, use squid and iptables to set up a transparent proxy. Then there's no need to configure any end-user systems at all.

    • The fact that they are VM's really only makes two differences practical differences that matter, fist is that is easy to roll them back and second is that your aren't running on bare metal.

      The third is that the VM soloution is essentially an operating system in it's own right. Like any other operating system it can suffer from privilage escalation exploits.

      • by onyxruby (118189)

        Agreed, that contributes to the need for a properly set up VLAN. You can't rely on the fact that the machines are virtual to handle your security.

  • SELinux on the host (Score:4, Interesting)

    by hpa (7948) on Tuesday May 28, 2013 @11:28AM (#43841769) Homepage
    Make sure you have SELinux enabled (and enforcing!) on the VM host, and keep the VMM software updated... there sometimes are security holes in VMM software which can be exploited. SELinux can help contain a breached VMM.
    • This is true...
      ...if you have a valid policy set up for SELinux to enforce. This can be very difficult to construct, especially when you're trying to control the behavior of something like a VM.

      For a student lab environment, this is likely to be overkill; if you have students in grades 9 thru 12 finding and exploiting holes in a VMM, you've got much bigger problems.
  • by StoneyMahoney (1488261) on Tuesday May 28, 2013 @11:29AM (#43841789)

    Just in case anyone gets a bit... shall we say "Adventurous" and tries to use their root access boxen to attack something they shouldn't, it might be worth isolating the VMs on their own VLAN away from the rest of the network, if you haven't already.

  • by bill_mcgonigle (4333) * on Tuesday May 28, 2013 @11:33AM (#43841837) Homepage Journal

    Next year I'm planning on allowing students to create and run their own VMs

    Running their own VM's is straightforward. Allowing the students to create their own VM's implies that they'll be root on the hypervisor.

    Do you intend to run the hypervisor on the client machines of the DRBL system, or run a single hypervisor on the server and deploy the VM's there as DRBL clients?

    To satisfy your requirements you probably want to run the hypervisor on the clients so they students can each have their own root on the hypervisor. This would require a hypervisor compatible with DRBL. I don't know how it works, but just from reading the description on the webpage, it sounds like it's geared to PXE booting a host OS.

    If you go with Xen, you'll have to probably separately PXE boot Xen and then DRBL boot the Dom0. Which would probably work fine and get you decent performance, but it will expose the students to DRBL (is this what you want?)

    If you go with KVM, the performance is a bit slower, but for a student shop that's probably OK, and you'll be able to DRBL-deploy the hypervisor and then let the students create their own non-DRBL (or DRBL) guests. This probably fits your model the best unless you have old hardware that KVM does not support - then you might need to go with the Xen-PXE-Boot model (because it can paravirtualize without hardware assistance).

    You could also use VirtualBox, and while it offers a nice GUI, it's probably too simple for teaching your students about virtualization (it just feels like an app).

    BTW, it sounds like you're doing great work based on that article. Kudos on your accomplishments and being an inspiration for others in your field.

    • Allowing the students to create their own VM's implies that they'll be root on the hypervisor.

      No, it doesn't. Virsh only requires to be told to let you manage VMs, done via group membership. There are also several web-based VM management tools so they don't even have to have shell access.

      Also, you have heard of sudo, right? And limited command shells?

      There's a lot of underwear-ringing here by people who have no fucking clue what they're talking about.

    • by Solandri (704621)

      Allowing the students to create their own VM's implies that they'll be root on the hypervisor.

      For most purposes (especially for teaching software), you can install a VM within a VM. You won't get the nifty virtualization features like direct hardware access (which means no 64-bit OSes). But several if not most virtualization software packages can do pure software emulation. Just for fun, I once used a Windows host to run a Linux guest, which ran an OS X guest, which ran a Windows guest.

      Since submitte

  • You can NAT the network off and and don't do port forwarding to the out side also have a quick kill where you just need to pull a cable to cut the VM's off from the rest of the network.

    • by h4rr4r (612664)

      No, stop!

      NAT is not the correct solution to this nor would it help. NAT does not stop anyone scanning outward, the NAT router will setup the address translation just as it should. VLANS are the correct answer. Pulling physical cables is too much work, and cannot be done remotely.

      • Pulling physical cables is a quick and fast way to know they are not on the network and that is more of a way to backup to remote control. What about a firewall box on the link from the switch the VM's are on to the rest of the network?

        • by h4rr4r (612664)

          It is not fast nor quick at 2am. Which is when one bored kid is going to try to find out how much fun he can have with an arp black hole or other such silliness.

          What about it? Should there be one? Of course it should probably even limit traffic to just http and other services they absolutely must have, there should also be an IDS on their network segment. That does not change the fact that VLANing off these folks is the best practice and that NAT offers nothing extra for this. You would not be trying to pr

          • by bobbied (2522392)

            It's not really VLAN's that are the issue here.. It's "Broadcast domain" isolation. Separate sub-net and broadcast domain is required (usually accomplished using a VLAN on a managed switch, but not always). NAT is also somewhat useful depending on where you put the WAN connection in your network. But, you are correct, you *really* need a firewall/Router that manages the external network access to the *MINIMUM* necessary in *BOTH* directions and a NAT only works in one direction.

      • by arth1 (260657)

        Even VLANs allow for DoS attacks - the VLAN runs on the host, not the guest, and bypass the limits you set on the guest. A malicious user controlling one or more VMs can flood the VLAN(s) and cause the host to slow down (or worse).

        Other ways to attack a host or other guests from a VM apart from networking include (but are not limited to) shared resources like USB, CD/DVD, serial, disk (sync flood!) and perhaps most of all, hardware accelerated graphics.
        If you really have to protect the host and other VMs f

        • by h4rr4r (612664)

          Actually I was suggesting not sharing NICs and using VLANs on a managed switch, if at all possible. So each VM has its own NIC and VLAN. They would not be allowed to talk to each other.

          I should have made my proposal more clear.

  • Don't let the higher-ups know you're running a rebel operating system, you might just get canned. What use is running Linux in school anyway, when the students should be learning REAL job skills (I.E. Microsoft Office)? /sarcasm

    (Sorry, I have been tainted by the education "industry" when it comes to anything Linux in school).

    • by iggymanz (596061)

      good little corporate droid trainees should also have a cisco phone on their desk which is surrounded by fabric covered foamboard or cardboard.

  • by i_want_you_to_throw_ (559379) on Tuesday May 28, 2013 @11:37AM (#43841887) Journal
    I see this as being similar to when we needed to have all of our developers in my company working in an environment that absolutely matched the production environment. Just use VMWare on each individual machine, run an Ubuntu image in that and best of all use a Puppet script to customize it and give 'em the goodies they need. The beauty of this is once the kids screw it up (and let's hope they do, they're learning after all) then you can rebuild this back to a pristine machine in no time. Good luck!
  • First, you're going to want to set a segregated network that cannot talk to the main network (A DMZ), your router accomplishes this in most cases.

    Second, there's 2 big options for you to look at: VMWare ESXi & Xen both are hypervisors that run on server hardware and can host as many VMs as the hardware can handle. Hyper-V may also be an option if you're part of the MSDN alliance. Install and configured chosen host software.

    Third, set up individual VMs, you're on a DMZ, so giving root is fine, the main

  • You could also look at it like this. If your students can crack their VM environment and run wild, hacking away, changing grades, and setting up Paypal fraud websites, then you have taught them very well and they will go on to a long and prosperous career, hopefully working for the good guys.

  • SmartOS is pretty amazing. You can create virtual environments that share a kernel space, meaning that YOUR os is running directly on the hardware, making it _extremely_ fast with almost no overhead. The file system (ZFS) is also 'shared' using zones and pools so there's almost no cost there either. Migration a vm between SmartOS hosts is also a pretty amazing thing. You can also create virtual NICs and route/bond/segment/tapdance. SmartOS has it's roots in Solaris, so it's a little different than Linux, b
  • by knarfling (735361) on Tuesday May 28, 2013 @11:44AM (#43841981) Journal

    Depending on your equipment and the time you want to spend, oVirt might be an answer.

    Although it is still fairly new and is in development, it runs on CentOS6, is free, can handle multiple guest OSes, can create VM's from a template, and has a power users portal page where trusted students/employees can create their own VM from supplied templates. This way, no student would have access to the host OS, but could create a VM as needed. The downside is that it can get quite complicated to set up the system, and could take a bit of time to learn and set it up properly. Since it is free, you are also dependent upon community support.

    You can access more info here. [ovirt.org]

  • ESXi. Its free, powerful, and offers a lot of pre-built appliances. I don't see any safety concerns if the network is segregated. If you have specific VM's that you want the students to learn within, keep screenshots of those so that you may roll anything back that gets damaged. This is great because it allows them do pretty much anything they want without creating a maintenance headache for you.

    If you want to teach them about specific technologies using VMs that go hand and hand with programming (like s
  • Oracle Virtualbox and VmWare. I use VirtualBox, which is free.
  • by dankney (631226) on Tuesday May 28, 2013 @12:09PM (#43842297) Homepage

    So far, I see lots of advice about VM breakouts and network isolation. If this were a production datacenter where uptime was a criteria, this is all well and good. I suspect that this isn't what you need to hear, however.

    I see three things you could be attempting to protect:

    1) The larger school network.
    2) The VM host infrastructure.
    3) The VMs themselves.

    1) A student on a VM is no more dangerous to the network than one who can connect to the school wireless with a laptop or smartphone. If the lab uplinks to the same network as the broader access, your risk profile is unchanged.

    2) Make sure the VMs can't route to the host and keep it patched. If a student managed to break out of a VM in a patched hosting environment, do some forensics and find the bug then sell it. It's probably worth more than you make in a year. Seriously, if they can do this, they deserve to win. You might as well worry about protecting against nation-state sponsored attacks.

    3) Make sure that the class work is backed up (a git server, perhaps) and then don't worry about it. Seriously, just throw the VMs away after each class (or every night, etc) and start with a clean one the next time they log in. Don't spend time trying to outsmart a classroom full of bored highschoolers. Instead, make it so it doesn't matter when they break something.

  • by jon3k (691256)
    I would have killed for this in high school. Kudos to you, what a great job.
  • by MattW (97290) <matt@ender.com> on Tuesday May 28, 2013 @02:56PM (#43843897) Homepage

    So, I co-wrote this book [amazon.com] on virtual security and am a former VMware Cloud Solutions Architect. And I'll preface this advice by saying that, if you want to talk more in depth, feel free to ping me. First initial, last name at gmail will work. (The email I have attached to slashdot I glance at occasionally, but it gets almost purely spam and so I'd likely miss anything.)

    From my perspective, the first question is which hypervisor to use:
    - VMware is mature, you can get a free license for the base hypervisor (which is quite feature rich; this is no trial product) for up to 32GB per physical box, is widely used. If VMware remains as relevant in the future as it is now, it's actually a very solid skillset to have.
    - If you have physical hosts over 32GB, VMware ceases to be free
    - Some features require more advanced VMware stuff, including vCenter server, which isn't free - for example, VMware's live vm migration feature (vMotion)
    - VMware is almost entirely closed on the internals; hypervisor is closed source (other than a not-useful-for-your-purposes "open source" bundle that contains their modified GPL code only); they have a bunch of APIs for internal functions (ie, tracking changed blocks on the virtual iscsi devices, for example), but those are generally restricted to partners; so if your students want to actually hack the virtualization layer, they can't. Then again, letting them do so wouldn't really be safe.
    - On the other hand, VMware layers do have nice APIs that are reasonably accessible for doing non-internals stuff; things like powering VMs on and off, changing their allocated RAM and cpus, etc
    - VMware has a nice set of tools, including CLI tools, which work well even with the free versions, that can allow you to move virtual machines in and out of specific hypervisors (not while the VMs are powered on), and into and out of VMware's desktop products (Workstation for Windows and Linux, Fusion for Mac). (google ovftool for the cross-platform CLI tool, for example; it can import/export to/from ESX, vCenter Server, Workstation, Fusion, and vCloud instances)
    - VMware has a nice set of tools for snapshots and backups, even on the base hypervisor; for example, I have a personal ESX box at a provider and I use this tool [vmware.com] to back up the VMs back and forth, which can be done from outside the OS without powering the VM down, and it's free.
    - I found using some things I'd think of as mandatory for a lab environment (ie, thin provisioning) were just built-in on the VMware side and required a fair bit of extra work and added extra wrinkles

    The virtual networking on VMware is dramatically more mature from my experience; my experience with Xen & KVM is now dated (it's been 2 years since I was in the thick of writing that book, which was the last time I was really in the thick of exploring the open-source hypervisor networking bits). I found that depending on the version of the hypervisor OS, which hypervisor, which kernel, which guest, etc, you could fall into all sorts of traps. I had some examples in the book where I showed, for example, generating and applying ebtables configurations to the host OS (the Xen Linux hypervisor OS) to block forged frames from coming across the bridge from one of the guest Linuxes, for example.

    Compare that to the VMware side, you could in theory wire up everything to dumb hubs, even, and enforce network separation at the hypervisor layer with VLAN tags applied to the portgroups where you attach VMs. (Warning: not suggesting you blindly do that; but VLAN enforcement on the VMware side is fairly rigid if configured in a good way.)

    My own book is a fun read for some of these concerns, although Haletky's book [amazon.com] is probably the canonical work on the subject. (Although it is -slightly- dated from bein

  • by loufoque (1400831)

    KVM is the virtualization technology that works the best with Linux.

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