The Free and Open source Software Developers’ European Meeting, or FOSDEM, is an institution that happens every year in Brussels. A busy, free and open event that gets a lot of developers together for two days of presentations and cross-pollination. There are typically the FOSDEM main tracks (a set of presentations chosen by the FOSDEM organization) and a set of devrooms, which are topic-oriented or project-oriented and can organize their own schedule freely.
This year, FOSDEM will host an unusual devroom, the Virtualization and Cloud devroom. It will happen in the Chavanne room, a 550-seat auditorium that was traditionally used for main tracks. And it will last for two whole days, while other devrooms typically last for a day or a half-day.
The Virtualization and Cloud devroom is the result of the merging of three separate devroom requests: Virtualization, Xen and OpenStack devrooms. It gives us a larger space and a lot of potential for cross-pollination across projects ! We had a lot of talks proposed, and here is an overview of what you’ll be able to see there.
Saturday, February 4
Saturday will be the “cloud” day. We will start with a set of talks about OpenStack, past, present and future. I will do an introduction and retrospective of what happened last year in the project, Soren Hansen will guide new developers to Nova, and Debo Dutta will look into future work on application scheduling and Donabe. Next we’ll have a session on various cloud-related technologies: libguestfs, pacemaker-cloud and OpenNebula. The afternoon will start with a nice session on cloud interoperability, including presentations on the Aeolus, CompatibleOne and Deltacloud efforts. We’ll continue with a session on cloud deployment, with a strong OpenStack focus: Ryan Lane will talk about how Wikimedia maintains infrastructure like an open source project, Mike McClurg will look into Ubuntu+XCP+OpenStack deployments, and Dave Walker will introduce the Orchestra project. The day will end with a town hall meeting for all OpenStack developers, including a panel of distribution packagers: I will blog more about that one in the next weeks.
Sunday, February 5
Sunday is more “virtualization” day ! The day will start early with two presentations by Hans de Goede about Spice and USB redirection over the network. Then we’ll have a session on virtualization management, with Guido Trotter giving more Ganeti news and three talks about oVirt. In the afternoon we’ll have a more technical session around virtualization in development: Antti Kantee will introduce ultralightweight kernel service virtualization with rump kernels, Renzo Davoli will lead a workshop on tracing and virtualization, and Dan Berrange will show how to build application sandboxes on top of LXC and KVM with libvirt. The day will end with another developers meeting, this time the Xen developers will meet around Ian Campbell and his Xen deployment troubleshooting workshop.
All in all, that’s two days packed with very interesting presentations, in a devroom large enough to accomodate a good crowd, so we hope to see you there !
2011 is almost finished, and what a year it has been. We started it with two core projects and one release behind us. During 2011, we got three releases out of the door, grew from 60 code contributors to about 200, added three new core projects, and met for two design summits.
The Essex-2 milestone was released last week. Here is our now-regular overview of the work that made it to OpenStack core projects since the previous milestone.
Nova was the busiest project. Apart from my work on a new secure root wrapper (detailed on previous articles of this blog), we added a pair of OpenStack API extensions to support the creation of snapshots and backups of volumes, the metadata service can now run separately from the API node, network limits can now be set using a per-network base and a per-flavor multiplier, and a small usability feature lets you retrieve the last error that occurred using nova-manage. But Essex is not about new features, it’s more about consistency and stability. On the consistency front, the HA network mode was extended to support XenServer, KVM compute nodes now report capabilities to zones like Xen ones, and the Quantum network manager now supports NAT. Under the hood, VM state transitions have been strengthened, the network data model has been overhauled, internal interfaces now support UUID instance references, and unused callbacks have been removed from the virt driver.
The other projects were all busy starting larger transitions (Keystone’s RBAC, Horizon new user experience, and Glance 2.0 API), leaving less room for essex-2 features. Glance still saw the addition of a custom directory for data buffering. Keystone introduced global endpoints templates and swauth-like ACL enforcement. Horizon added UI support for downloading RC files, while migrating under the hood from jquery-ui to bootstrap, and adding a versioning scheme for environment/dependencies.
The next milestone is in a bit more than a month: January 26th, 2012. Happy new year and holidays to all !
In the previous two posts of this series, we explored the deficiencies of the current model and the features of an alternative implementation. In this last post, we’ll discuss the advantages of a Python implementation and open discussion on how to secure it properly.
It’s quite easy to implement the features that were mentioned in the previous post in Python. The main advantage of doing so is that the code can happily live inside Nova code, in particular the filters definition files can be implemented as Python modules that are loaded if present. That solves the issue of shipping definitions within Nova and also the separation of allowed commands based on locally-deployed nodes. The code is simple and easy to review. The trick is to make sure that no malicious code can be injected in the elevated rights process. This is why I’d like to present a model and open it for comments in the community.
Proposed security model
The idea would be to have Nova code optionally use “sudo nova-rootwrap” instead of “sudo” as the root_helper. A generic sudoers file would allow the nova user to run /usr/bin/nova-rootwrap as root, while stripping environment variables like PYTHONPATH. To load its filters definitions, nova-rootwrap would try to import a set of predefined modules (like nova.rootwrap.compute), but if those aren’t present, it should ignore them. Can this model be abused ?
The obvious issue is to make sure sys.path (the set of directories from which Python imports its modules) is secure, so that nobody can insert their own modules in the process. I’ve given some thoughts to various checks, but actually there is no way around trusting the default sys.path you’re given when you start python as root from a cleaned env. If that’s compromised, you’re toasted the moment you “import sys” anyway. So using sudo to only allow /usr/bin/nova-rootwrap and cleaning the environment should be enough. Or am I missing something ?
Insecure mode ?
One thing we could do is check that sys.path all belongs to root and refuse to run in the case it’s not. That would tell the user that his setup is insecure (potentially allowing him to bypass that by running “sudo nova-rootwrap –insecure” as the root_helper). But that’s a convenience to detect insecure setups, not a security addition (the fact that it doesn’t complain doesn’t mean you’re safe, it could mean you’re already compromised).
Test mode ?
For tests, it’s convenient to allow to run code from branches. To allow this (unsafe) mode, you would tweak sudoers to allow it to run $BRANCH/bin/nova-rootwrap as root, and prepend “..” to sys.path in order to allow modules to be loaded from $BRANCH (maybe requiring –insecure mode for good measure). It sounds harmless, since if you run from /usr/bin/nova-rootwrap you can assume that /usr is safe… Or should that idea be abandoned altogether ?
Nothing beats peer review when it comes to secure design. I call all Python module-loading experts and security white-hats out there: would this work ? Are those safe assumptions ? How much do you like insecure and test modes ? Would you suggest something else ? If you’re one of those that can’t think in words but require code, you can get a glimpse of work in progress here. It will all be optional (and not used by default), so it can be added to Nova without much damage, but I’d rather do it right from the beginning :) Please comment !
In the previous post in this series we explored the current privilege escalation model used in OpenStack Compute (Nova), and discussed its limitations. Now that we are able to plug an alternative model (thanks to the root_helper option), we’ll discuss in this post what features this one should have. If you think we need more, please comment !
The most significant issue with the current model is that sudoers filters the executable used, but not the arguments. To fix that, our alternative model should allow precise argument filtering so that only very specific commands are allowed. It should use lists of filters: if one matches, the command is executed.
The basic CommandFilter would just check that the executable name matches (which is what sudoers does). A more advanced RegexpFilter would check that the number of arguments is right and that they all match provided regular expressions.
Taking that concept a step further, you should be able to plug any type of advanced filter. You may want to check that the argument to the command is an existing directory. Or one that is owned by a specific user. The framework should allow developers to define their own CommandFilter subclasses, to be as precise as they want when filtering the most destructive commands.
In some cases, Nova runs, as root, commands that it should just run as a different user. For example, it runs kill with root rights to interact with dnsmasq processes (owned by the nobody user). It doesn’t really need to run kill with root rights at all. Filters should therefore also allow to specify a lower-privileged user a specific matching command should run under.
Shipping filters in Nova code
Filter lists should live within Nova code and be deployed by packaging, rather than live in packaging. That allows people adding a new escalated command to add the corresponding filter in the same commit.
Limiting commands based on deployed nodes
As mentioned in the previous post, nova-api nodes don’t actually need to run any command as root, but in the current model their nova user is still allowed to run plenty of them. The solution for that is to separate the command filters based on the type of node that is allowed to run them, in different files. Then deploy the nova-compute filters file only on nova-compute nodes, the nova-volume filters file only on nova-volume nodes… A pure nova-api node will end up with no filters being deployed at all, effectively not being allowed any command as root. So this can be solved by smart packaging of filter files.
Missing features ?
Those are the features that I found useful for our alternative privilege escalation model. If you see others, please comment here ! I’d like to make sure all the useful features are included. In the next post, we’ll discuss a proposed Python implementation of this framework, and the challenges around securing it.
In this series, I’ll discuss how to strengthen the privilege escalation model for OpenStack Compute (Nova). Due to the way networking, virtualization and volume management work, some Nova nodes need to be able to run some commands as root. To reduce the effects of a potential compromise (attacker being able to run arbitrary code as the Nova user), we want to limit the commands that Nova can run as root on a given node to the strict necessary. Today we’ll explain how the current model works, its limitations, and the groundwork already implemented during the Diablo cycle to improve that.
Current model: sudo and sudoers
Currently, in a typical Nova deployment, the nodes run under an account with limited rights (usually called “nova”). When Nova needs to run a command as root, it prepends “sudo” to the command. The nova packages of your distribution of choice are supposed to ship a sudoers file that contains all the commands that nova is allowed to run as root without providing a password. This is a privilege escalation security model which is pretty well-known and easy to audit.
Limitations of the current model
That said, in the context of Nova, this model is very limited. The sudoers file does not allow to efficiently filter arguments, so you can basically pass any argument to the allowed command… and some of the commands that nova wants to use are rather open-ended. As an example, the current nova_sudoers file contains commands like chown, kill, dd or tee, which are more than enough to compromise a target system completely.
There are a couple other limitations. The sudoers file belongs to the distributions packaging, so it’s difficult to keep it in sync with the rest of Nova code when someone wants to add a privileged command. Last but not least, the same nova_sudoers file is used for any type of Nova node. A Nova API server, which does not need to run any command as root, is still allowed to run all the commands that a compute node requires, for example. Those other limitations could be fixed while still using sudo and sudoers files, but the first limitation would remain. Can we do better ?
Substitute a wrapper to sudo
To be able to propose alternative privilege escalation security models, we first needed to be able to change all the “sudo” calls in the code and make them potentially use something else. That’s what I worked on late during the Diablo timeframe: creating a run_as_root option in nova.utils.execute that would use a configurable root_helper command (by default, “sudo”), and force all the existing calls to go through that (rather than blindly calling “sudo” themselves).
Thanks to the default root_helper, everything still behaves the same, but now we have the possibility to use something else, if we can be smarter than sudoers files. Like call a wrapper that will do advanced filtering of the command that nova wants to use. In part 2 of this series, we’ll look into a proposed, alternative Python-based root_helper and open discussion on its security model.
Last week saw the delivery of the first milestone of the Essex development cycle for Keystone, Glance, Horizon and Nova. This early milestone collected about two months of post-Diablo work… but it’s not as busy in new features as most would think, since a big part of those last two months was spent releasing OpenStack 2011.3 and brainstorming Essex features.
Keystone delivered their first milestone as a core project, with a few new features like support for additional credentials, service registration and using certificate-based SSL client authentication to authenticate services. It should be easier to upgrade from now on, with support for database migrations.
Glance developers were busy preparing significant changes that will land in the next milestone. Several bugfixes and a few features made it to essex-1 though, including the long-awaited SSL client connections. It also moved to UUID image identifiers.
The Nova essex-1 effort was mostly spent on bugfixing, with 129 bugs fixed. New features include a new XenAPI SM volume driver, DHCP support in the Quantum network manager, and optional deferred deletion of instances. Under the hood, the volume code was significantly cleaned up and XML templates were added to simplify serialization in extensions.
Essex-1 was also the first official OpenStack milestone for Horizon, also known as the Dashboard. New features include a instance details page, support for managing Nova volumes and a new extensible modular architecture. The rest of the effort was spent on catching up with the best of core projects in internationalization, developer documentation, and QA (frontend testing and JS unit tests).
Now, keep your seatbelt fastened, as we are one month away from essex-2, where lots of new development work is expected to land !
The 200 open seats for the Essex Design Summit were all registered in less than 9 days ! If you missed the boat, you can still register on the waiting list at http://summit.openstack.org.
For the last seats we need to give priority to existing OpenStack developers and upstream/downstream community members, so the waiting list will be reviewed manually. You will receive an email if you get cleared and get one of the very last seats for the summit.
Sometime next week, the website should allow registered attendees (as well as attendees on the waiting list) to propose sessions for the summit, so stay tuned !