In recent months I have spent more of my time working on projects immediately above/related to the core libvirt library, such as libvirt-glib, libosinfo and virt-sandbox. To that list I have now added OpenStack, where my goal is to ensure that the libvirt driver is following all the best practices and start to take advantage of libosinfo for optimizing virtual hardware configuration. I’m familiar with hacking on python so that’s no big issue, but what is new about OpenStack is dealing with Gerrit. For the sake of reference, here were the steps I went through on Fedora 16 for my first patch (a tweak to the tools/install_venv.sh file)
- Get the initial Nova GIT checkout
$ mkdir $HOME/src/cloud
$ cd $HOME/src/cloud
$ git clone git://github.com/openstack/nova.git
$ cd nova
- Install some basic pre-reqs, and ensure python-distutils-extra is not present since that conflicts with part of the openstack build system
$ sudo yum install gcc python-pep8 python-virtualenv m2crypto libvirt libvirt-python libxslt-devel libxml2-devel
$ sudo yum remove python-distutils-extra
- Visit the OpenStack Gerrit Website, and follow ‘Sign In’ link which redirects to LaunchPad for authentication
- Back on Gerrit site, now signed in, follow ‘Settings’ link, select ‘SSH Public Keys’ page, and paste your SSH public key (eg contents of
$HOME/.ssh/id_rsa.pub)
- Test SSH connectivity from the CLI
$ ssh -p 29418 berrange@review.openstack.org
The authenticity of host '[review.openstack.org]:29418 ([173.203.103.119]:29418)' can't be established.
RSA key fingerprint is ee:2f:ac:1b:f8:25:d0:39:be:55:02:c7:76:5e:39:53.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added '[review.openstack.org]:29418,[173.203.103.119]:29418' (RSA) to the list of known hosts.
**** Welcome to Gerrit Code Review ****
Hi Daniel Berrange, you have successfully connected over SSH.
Unfortunately, interactive shells are disabled.
To clone a hosted Git repository, use:
git clone ssh://berrange@review.openstack.org:29418/REPOSITORY_NAME.git
Connection to review.openstack.org closed.
- Install commit hook to ensure ‘ChangeId’ fields get added to your commits
$ scp -p -P 29418 berrange@review.openstack.org:hooks/commit-msg .git/hooks/
- Add the gerrit remote to GIT config
$ git remote add gerrit ssh://berrange@review.openstack.org:29418/openstack/nova.git
- Start a new branch for your work
$ git checkout -b venv-install-fixes
- Make whatever code changes you need todo
$ vi tools/virtual_venv.py
$ git add -u
(Don't forget to add yourself to Authors if this is your first change)
- Commit the changes, checking the commit message gets a ‘Change-Id’ line added just prior to the signed-off-by line
$ git commit -s
$ git show
commit fd682a28fb4591c65f20129d4bfb4eccf1232cb8
Author: Daniel P. Berrange <berrange@redhat.com>
Date: Thu Jan 5 13:15:15 2012 +0000
Tell users what is about to be installed via sudo
Rather than just giving users the sudo password prompt immediately,
actually tell them what is about to be installed, so they know what
privileged action is being attempted.
Change-Id: Ic0c1de812be119384753895531a008075b13494e
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
If the commit is fixing a OpenStack bug, then the commit message should include a line “BugXXXX” where XXXX is the bug number. Gerrit uses this to link to the bug tracker
- Run the unit test suite, and the python pep8 syntax test suite; Be prepared to wait a long time
$ ./run_tests.sh
$ ./run_tests.sh --pep8
- Send the changes to Gerrit for review
$ git push gerrit HEAD:refs/for/master
- Wait for email notifications of review, or watch the OpenStack Gerrit Website.
- If problems are found by reviewers, or the automated smoke stack tests. Repeat steps 9->l;12, but use ‘git commit –amend’ to ensure you preserve the original “Change-Id” line in the commit message. This lets gerrit track followup patches.
- If everything passes review & testing, it will be automatically merged into master.
There is also a GIT plugin “git review” available in the git-review RPM, which can provide syntactic sugar for step 12, but personally I don’t find it adds significant value to be worth my while using.
I can see the attraction of Gerrit, but I personally still prefer the practice of using git send-email for reviewing on mailing lists. My problems with Gerrit are
- The email notifications sent out for new patches are almost worse than useless as an information source
- While very pretty, the web UI for browsing the diffs is really quite cumbersome to use
- Poor support for reviewing large patch series
- Use of merge commits makes navigating GIT history cumbersome, forcing the use of the graphical gitk viewer tool
A few months back the Red Hat KVM team held a mass keysigning party to setup a web of trust between each others keys. IIRC, there were approximately 20 people participating in this, which potentially meant alot of tedious typing of GPG commands, with the potential for error such tedium implies. Fortunately we had Jim Meyering on hand to give us some tips for facilitating/optimizing the process, the most important of which was to introduce us to the ‘Pius‘ tool. To quote from its website
pius (PGP Individual UID Signer) helps attendees of PGP keysigning parties. It is the main utility and allows you to quickly and easily sign each UID on a set of PGP keys. It is designed to take the pain out of the sign-all-the-keys part of PGP Keysigning Party while adding security to the process.
…
That can already be time consuming, but preferrably, you want to verify the identity in each UID, which means verifying the email addresses. There are a few ways to do this, but one of them is to sign each UID on the key individually (which requires import-sign-export-delete for each UID), encrypt-emailing that key to the email address in the UID. This can be incredibly time consuming.
That’s where pius comes in. Pius will do all the work for you – all you have to do is confirm the fingerprint for each key. It will then take care of signing each UID cleanly, minimizing the key, and using PGP/Mime email to send it, encrypted, to the email address in the UID.
The steps Jim defined for us to follow using Pius were as follows
- Collate a list of everyone’s key IDs. Our list looked like this (cut down to save space)
# cat > keyids.txt <<EOF
4096R/000BEEEE 2010-06-14 Jim Meyering
4096R/E1B768A0 2011-10-11 Richard W.M. Jones
4096R/15104FDF 2011-10-11 Daniel P. Berrange
...
EOF
- Download all the keys from a key server (it is assumed everyone has already uploaded their own key to a server)
# id_list=$(perl -nle 'm!^\d{4}R/(\S{8}) ! and print $1' keyids.txt)
# gpg --recv-keys $(echo $id_list)
- Generate a list of fingerprints for all keys that are to be signed
# gpg --fingerprint $(echo $id_list)
- Verify all the fingerprints and their owners’ identities.
This is the security critical part. You generally want to meet the person face-to-face, verify their identity via some trusted means (passport, driving license, etc). They should read their key fingerprint out to you, and you should verify that it matches the fingerprint of that downloaded from the key server.
- Use Pius to sign all the keys whose fingerprints were verified.
MAIL_HOST=smtp.your.mail.server.com
me=your@email.address.com (eg dan@berrange.com)
my_id=XXXXXXXXXXX (Your GPG Key ID eg 15104FDF)
# pius --mail-host=MAIL_HOST --no-pgp-mime --mail=$me --signer=$my_id $(echo $id_list)
What Pius does here is that for each key ID it is given, it will sign each individual identity (email address). The signature will be ascii-armoured and then sent to the email address associated with that identity. If a user has multiple email addresses on their key, they will receive one signature email per address. The email contains instructions for what the receipient should do. The email will look something like this
From: eblake@redhat.com
To: berrange@redhat.com
Subject: Your signed PGP key
[-- Attachment #1 --]
[-- Type: text/plain, Encoding: 7bit, Size: 0.7K --]
Hello,
Attached is a copy of your PGP key (0x15104fdf) signed by my key
(0xa7a16b4a2527436a).
If your key has more than one UID, than this key only has the UID associated
with this email address (berrange@redhat.com) signed and you will receive
additional emails containing signatures of the other UIDs at the respective
email addresses.
Please take the attached message and decrypt it and then import it.
Something like this should work:
gpg -d | gpg --import
Then, don't forget to send it to a keyserver:
gpg --keyserver pool.sks-keyservers.net --send-key 15104fdf
If you have any questions, let me know.
Generated by PIUS (http://www.phildev.net/pius/).
[-- Attachment #2: 15104fdf__berrange_at_redhat.com_ENCRYPTED.asc --]
[-- Type: application/octet-stream, Encoding: 7bit, Size: 4.6K --]
The final thing, once everyone has dealt with the emails they received, is to refresh your local key database to pull down all the new signatures
# gpg --recv-keys $(echo $id_list)
I should point out that Pius isn’t just for mass key signing parties. Even if you only have 1 single key you want to sign, it is still a very convenient tool to use. The simplified set of steps to go through would be
# gpg --recv-key XXXXXXXX
# gpg --fingerprint XXXXXXXX
# ...verify person's identity & fingerprint
# pius --mail-host=MAIL_HOST --no-pgp-mime --mail=$me --signer=$my_id XXXXXXX
# ....some time later...
# gpg --recv-key XXXXXXXX
Thanks again to Jim Meyering for pointing out Pius and doing the organization for our key signing party & defining the steps I describe above. BTW, Pius is available in Fedora from F16 onwards.
As many readers are no doubt aware, the FOSDEM 2012 conference is taking place this weekend in Brussels. This year I was organized enough to submit a proposal for a talk and was very happy to be accepted. My talk is titled “Building app sandboxes on top of LXC and KVM with libvirt” and is part of the Virtualization & Cloud Dev Room. As you can guess from the title, I will be talking in some detail about the libvirt-sandbox project I recently announced. Richard Jones is also attending to provide a talk on libguestfs and how it is used in cloud projects like OpenStack. There will be three talks covering different aspects of the oVirt project, a general project overview, technical look at the management engine and a technical look at the node agent VDSM. Finally the GNOME Boxes project I mentioned a few weeks ago will also be represented in the CrossDesktop devroom.
Besides these virtualization related speakers, there are a great many other Red Hat people attending FOSDEM this year, so we put together a small flyer highlighting all their talks. In keeping with the spirit of FOSDEM, these talks will of course be community / technically focused, not corporate marketing ware :-) I look forward to meeting many people at FOSDEM this year, and if all goes well, make it a regular conference to attend.
I have mentioned in passing every now & then over the past few months, that I have been working on a tool for creating application sandboxes using libvirt, LXC and KVM. Last Thursday, I finally got around to creating a first public release of a package that is now called libvirt-sandbox. Before continuing it is probably worth defining what I consider the term “application sandbox” to mean. My working definition is that an “application sandbox” is simply a way to confine the execution environment of an application, limiting the access it has to OS resources. To me one notable point is that there is no need for a separate / special installation of the application to be confined. An application sandbox ought to be able to run any existing application installed in the OS.
Background motivation & prototype
For a few Fedora releases, users have had the SELinux sandbox command which will execute a command with a strictly confined SELinux context applied. It is also able to make limited use of the kernel filesystem namespace feature, to allow changes to the mount table inside the sandbox. For example, the common case is to put in place a different $HOME. The SELinux sandbox has been quite effective, but there is a limit to what can be done with SELinux policy alone, as evidenced by the need to create a setuid helper to enable use of the kernel namespace feature. Architecturally this gets even more problematic as new feature requests need to be dealt with.
As most readers are no doubt aware, libvirt provides a virtualization management API, with support for a wide variety of virtualization technologies. The KVM driver is easily the most advanced and actively developed driver for libvirt with a very wide array of features for machine based virtualization. In terms of container based virtualization, the LXC driver is the most advanced driver in libvirt, often getting new features “for free” since it shares alot of code with the KVM driver, in particular anything cgroup based. The LXC driver has always had the ability to pass arbitrary host filesystems through to the container, and the KVM driver gained similar capabilities last year with the inclusion of support for virtio 9p filesystems. One of the well known security features in libvirt is sVirt, which leverages MAC technology like SELinux to strictly confine the execution environment of QEMU. This has also now been adapted to work for the LXC driver.
Looking at the architecture of the SELinux sandbox command last year, it occurred to me that the core concepts mapped very well to the host filesystem passthrough & sVirt features in libvirt’s KVM & LXC drivers. In other words, it ought to be possible to create application sandboxes using the libvirt API and suitably advanced drivers like KVM or LXC. A few weeks hacking resulted in a proof of concept tool virt-sandbox which can run simple commands in sandboxes built on LXC or KVM.
The libvirt-sandbox API
A command line tool for running applications inside a sandbox is great, but even more useful would be an API for creating application sandboxes that programmers can use directly. While libvirt provides an API that is portable across different virtualization technologies, it cannot magically hide the differences in feature set or architecture between the technologies. Thus the decision was taken to create a new library called libvirt-sandbox that provides a higher level API for managing application sandboxes, built on top of libvirt. The virt-sandbox command from the proof of concept would then be re-implemented using this library API.
The libvirt-sandbox library is built using GObject to enable it to be accessible to any programming language via GObject Introspection. The basic idea is that programmer simply defines the desired characteristics of the sandbox, such as the command to be executed, any arguments, filesystems to be exposed from host, any bind mounts, private networking configuration, etc. From this configuration description, libvirt-sandbox will decide upon & construct a libvirt guest XML configuration that can actually provided the requested characteristics. In other words, the libvirt-sandbox API is providing a layer of policy avoid libvirt, to isolate the application developer from the implementation details of the underlying hypervisor.
Building sandboxes using LXC is quite straightforward, since application confinement is a core competency of LXC. Thus I will move straight to the KVM implementation, which is where the real fun is. Booting up an entire virtual machine probably sounds like quite a slow process, but it really need not be particularly if you have a well constrained hardware definition which avoids any need for probing. People also generally assume that running a KVM guest, means having a guest operating system install. This is absolutely something that is not acceptable for application sandboxing, and indeed not actually necessary. In a nutshell, libvirt-sandbox creates a new initrd image containing a custom init binary. This init binary simply loads the virtio-9p kernel module and then mounts the host OS’ root filesystem as the guest’s root filesystem, readonly of course. It then hands off to a second boot strap process which runs the desired application binary and forwards I/O back to the host OS, until the sandboxed application exits. Finally the init process powers off the virtual machine. To get an idea of the overhead, the /bin/false binary can be executed inside a KVM sandbox with an overall execution time of 4 seconds. That is the total time for libvirt to start QEMU, QEMU to run its BIOS, the BIOS to load the kernel + initrd, the kenrel to boot up, /bin/false to run, and the kernel to shutdown & QEMU to exit. I think 3 seconds is pretty impressive todo all that. This is a constant overhead, so for a long running command like an MP3 encoder, it disappears into the background noise. With sufficient optimization, I’m fairly sure we could get the overhead down to approx 2 seconds.
Using the virt-sandbox command
The Fedora review of the libvirt-sandbox package was nice & straightforward, so the package is already available in rawhide for ready to test the VirtSandbox F17 feature. The virt-sandbox command is provided by the libvirt-sandbox RPM package
# yum install libvirt-sandbox
Assuming libvirt is already installed & able to run either LXC or KVM guests, everything is ready to use immediately.
A first example is to run the ‘/bin/date’ command inside a KVM sandbox:
$ virt-sandbox -c qemu:///session /bin/date
Thu Jan 12 22:30:03 GMT 2012
You want proof that this really is running an entire KVM guest ? How about looking at the /proc/cpuinfo contents:
$ virt-sandbox -c qemu:///session /bin/cat /proc/cpuinfo
processor : 0
vendor_id : GenuineIntel
cpu family : 6
model : 2
model name : QEMU Virtual CPU version 1.0
stepping : 3
cpu MHz : 2793.084
cache size : 4096 KB
fpu : yes
fpu_exception : yes
cpuid level : 4
wp : yes
flags : fpu de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pse36 clflush mmx fxsr sse sse2 syscall nx lm up rep_good nopl pni cx16 hypervisor lahf_lm
bogomips : 5586.16
clflush size : 64
cache_alignment : 64
address sizes : 40 bits physical, 48 bits virtual
power management:
How about using LXC instead of KVM, and providing an interactive console instead of just a one-shot command ? Yes, we can do that too:
$ virt-sandbox -c lxc:/// /bin/sh
sh-4.2$ ps -axuwf
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
root 1 0.0 0.0 165436 3756 pts/0 Ss+ 22:31 0:00 libvirt-sandbox-init-lxc
berrange 24 0.0 0.1 167680 4688 pts/0 S+ 22:31 0:00 libvirt-sandbox-init-common
berrange 47 0.0 0.0 13852 1608 pts/1 Ss 22:31 0:00 \_ /bin/sh
berrange 48 0.0 0.0 13124 996 pts/1 R+ 22:31 0:00 \_ ps -axuwf
Notice how we only see the processes from our sandbox, none from the host OS. There are many more examples I’d like to illustrate, but this post is already far too long.
Future development
This blog post might give the impression that every is complete & operational, but that is far from the truth. This is only the bare minimum functionality to enable some real world usage. Things that are yet to be dealt with include
- Write suitable SELinux policy extensions to allow KVM to access host OS filesystems in readonly mode. Currently you need to run in permissive mode which is obviously something that needs solving before F17
- Turn the virt-viewer command code for SPICE/VNC into a formal API and use that to provide a graphical sandbox running Xorg.
- Integrate a tool that is able to automatically create sandbox instances for system services like apache to facilitate confined vhosting deployments
- Correctly propagate exit status from the sandboxed command to the host OS
- Unentangle stderr and stdout from the sandboxed command
- Figure out how to make dhclient work nicely when / is readonly and resolv.conf must be updated in-place
- Expose all the libvirt performance tuning controls to allow disk / net I/O controls, CPU scheduling, NUMA affinity, etc
- Wire up libvirt’s firewall capability to allow detailed filtering of network traffic to/from sandboxes
- Much more…
For those attending FOSDEM this year, I will be giving a presentation about libvirt-sandbox in the virt/cloud track.
Oh and as well as the released tar.gz mentioned in the first paragraph, or the Fedora RPM, the code is all available in GIT