Videos and slides from the 2023 Linux Security summits may be found here:
Linux Security Summit North America (LSS-NA), May 10-12 2023, Vancouver, Canada.
Linux Security Summit Europe (LSS-EU), September 20-21 2023, Bilbao, Spain.
Note: if you wish to follow Linux Security Summit announcements and event updates via Mastodon, see https://social.kernel.org/LinuxSecSummit. You can follow this via the Fediverse or the RSS reader of your choice.
I’ve uploaded the slides from essentially all of the talks I’ve given to Slideshare. This is likely more useful than my previous strategy of dumping them in a directory and leaving the rest up to search engine bots.
Click here for the full list of slides. They are all published under the Creative Commons attribution share-alike license.
One interesting slide title, which I’d forgotten about, is Kernel Security for 2.8, from the 2004 Kernel Summit. This was from when we were still expecting a 2.7 development kernel leading to a 2.8 stable kernel — I think Linus announced the change in development model at that summit.
Included in this set of slides are several introductory and deeper technical overviews of SELinux; I hope they are useful for people who are looking for information for themselves, or if making their own slides. As the license suggests, please feel free to copy and extend them (but note that the older ones are going to be more out of date).
I mean, SLUGs…
Paul Wayper gave a couple of talks on SELinux at this weeks’ SLUG meeting, and includes links to a couple of very useful slide decks:
The sysadmin slides look particularly useful, as they focus on solving common issues such as running FTP/SAMBA/Apache servers, and provide some very useful general tips, such as looking in the audit log and using policy booleans for high-level policy tweaking.
These slides may be the best, short introduction for sysadmins on the topic that I’ve seen. It’s a difficult thing to get right.
Here’s an update on the major changes to the kernel security subsystem for the 2.6.30 kernel.
init->httpd->perl may not be permitted for init->httpd->bash. Sample policy may be found here.compat_net option for the likely few people who were using them. The old code has now been removed entirely, and users should transition to Secmark: Paul Moore has written a detailed guide for this.The remaining changes were primarily bugfixes and enhancements across most parts of the security subsystem, including SELinux, SMACK, and keys.
Paul and I are finalizing the schedule for the security microconf at the upcoming Linux Plumbers Conference. It’s looking like a great line-up at this stage—stay tuned for more details soon.
Just a reminder for SELinux developers and anyone interested in the internals of SELinux that the SELinux Developer Summit CfP closes on July 1st, which is about a week away.
Details of the CfP are here. Don’t forget to join the event mailing list if you’re attending.
Proposals for presentations, lightning talks, and development sessions should be submitted via email per the instructions in the CfP. Proposals do not need to be especially detailed: if you have a good idea, simply send it in.
For reading this, you are rewarded with a mystery object (pictured above). See if you can figure out what it is before clicking on it and reading the comments @ flickr.
In the process of preparing my talk for KCA, I re-read the classic paper: The UNIX Time-Sharing System by Ritchie & Thompson. This paper was revised several times between 1973 and 1978, and the authors’ observations are well worth remembering:
First: because we are programmers, we naturally designed the system to make it easy to write, test, and run programs. The most important expression of our desire for programming convenience was that the system was arranged for interactive use, even though the original version only supported one user. We believe that a properly designed interactive system is much more productive and satisfying to use than a “batch” system. Moreover, such a system is rather easily adaptable to noninteractive use, while the converse is not true.
Second: there have always been fairly severe size constraints on the system and its software. Given the partially antagonistic desires for reasonable efficiency and expressive power, the size constraint has encouraged not only economy, but also a certain elegance of design. This may be a thinly disguised version of the “salvation through suffering” philosophy, but in our case it worked.
Third: nearly from the start, the system was able to, and did, maintain itself. This fact is more important than it might seem. If designers of a system are forced to use that system, they quickly become aware of its functional and superficial deficiencies and are strongly motivated to correct them before it is too late. Because all source programs were always available and easily modified on-line, we were willing to revise and rewrite the system and its software when new ideas were invented, discovered, or suggested by others.
It’s clear that the success of Linux (and FOSS more generally), is underpinned by these principles. These principles are not merely about technology; they’re a way of thinking about technology and the people who create and use it.
sVirt (MAC security for Linux Virtualization), which I’ve previously discussed here, and formally presented at LCA in January, was released today as an integral part of virtualization in Fedora 11.
If you’d like to give it a spin, simply download and install Fedora and use the GUI admin tools to create a new virtual machine.
Thanks again to Dan Walsh, Dan Berrange and all the developers who helped with input and the heavy lifting work of completing the userland code. It still amazes me how fast things move in FOSS.
As mentioned in my last+1 post, Dan W will be talking on this topic at the upcoming LinuxCon.
Further developments in this area are already underway, and you can expect to hear about them in the coming months—see the talk slides for possible hints.
Dan Walsh recently introduced SELinux sandbox. This is a mechanism for launching untrusted applications from the command line, which uses a strict MAC policy to isolate the executed application from the rest of the system. There’s been a good discussion of the topic LWN, and I thought it might be worth highlighting a few points.
Firstly, this sandboxing scheme is not a separate package. It’s an addition to the standard SELinux security policy to define the sandboxed domain (sandbox_t) coupled with a script to set up the environment and launch applications in the sandboxed domain.
The idea for this came out of a few emails following a recent discussion about extending seccomp for more generalized sandboxing. Essentially, the question was asked "what can we do with SELinux and simple sandboxing?", and the result is now available in Fedora development. If you update to the latest policycoreutils and selinux-policy packages, it should simply be there ready to go.
The security policy for the sandbox_t domain is designed to provide the sandboxed application with only the absolute minimum set of permissions required to run. It can load shared libraries, for example, although a future refinement could provide an option to run only static binaries. It cannot interact in an ad-hoc manner with the rest of the system. A scratch tmpfs filesystem may be optionally mounted for the application if required, and unique MCS labels are used to separate sandboxes from each other. Another future refinement will likely include launching sandboxes in private namespaces.
# sandbox id -Z
unconfined_u:unconfined_r:sandbox_t:s0:c226,c674
The above shows how the id command launched via the new sandbox utility is running in the sandbox_t domain, with MCS categories c226 and c674. The values of these don’t matter, as long as they’re unique on the system.
As root (and note that this is not designed to be run as root, but for demonstration purposes it helps to show the confinement of privileges if they exist), you can’t do anything special via sandbox:
# sandbox cat /etc/shadow
/bin/cat: /etc/shadow: Permission denied
# sandbox touch /tmp/moo.txt
/bin/touch: cannot touch `/tmp/moo.txt': Permission denied
In fact, you can’t open any files on the global system.
Ambient authority describes the form of authority commonly seen in general purpose operating systems. This form of authority is what allows, for example, a user on a Linux system to open any file for which she has read access, whether she needs to open the file or not. It is seen as problematic in establishing strong security, due to problems such as The Confused Deputy, where authority (i.e. the ability to perform an action) is arbitrarily escalated throughout the system.
(For a particularly clear explanation of these concepts, they are covered in the first ten minutes of this talk by David Wagner).
When an application is launched via sandbox, with no inessential permissions, as much ambient authority as is possible has been removed by SELinux MAC. Instead, authority is explicitly provided to the sandboxed application via a pipe file descriptor handed to it via the launching process (i.e. the standard Unix scheme of constructing pipelines).
Note carefully the difference between these two commands:
# wc -l /etc/shadow
43 /etc/shadow
and
# cat /etc/shadow | wc -l
43
In the first example, the wc application directly opened the file /etc/shadow for reading. It used ambient authority to do this.
In the second example, wc was handed a file descriptor which was already opened by the calling process, and did not require any ambient authority to read the data in the file: the authority was explicitly tied to the file by the caller, and wc was entirely unaware of which file it was reading. wc in this case does not need any permissions except to access the file descriptor passed by the caller. (It still has ambient authority, however, it just didn’t need to use it here).
Running the above with SELinux sandboxing in effect:
# sandbox wc -l /etc/shadow
/usr/bin/wc: /etc/shadow: Permission denied
and
# cat /etc/shadow | sandbox wc -l
43
Note that wc now has no authority now except as invoked by the calling process and passed via the sandbox. In other words, it does not have ambient authority when invoked via the sandbox.
This is a very simple and powerful concept for security purposes, as it is possible to define strict information flows between applications in a dynamic and controlled manner, without the need for additional global security policy. It’s inherently Unix-y, too.
There are many potential applications of this form of sandboxing, particularly where you need to process information between different security realms (e.g. incoming mail which needs to be passed through a chain of scanning and filtering applications), and for dealing with large and complicated applications processing arbitrary untrusted data.
Keep an eye on Dan’s blog for upcoming work on desktop security with SELinux sandboxing.
Several Linux security events are planned in association with LinuxCon this year in Portland, Oregon.
I’ll be giving a LinuxCon talk on adding extended attributes support to NFSv3, presenting a prototype implementation (based on the GPL IRIX code) for discussion. xattrs are a very common feature in Unix and Linux filesystems, but there is no standard for them, nor for conveying them over NFS. NFSv4 supports “named attributes”, although this is based on the Solaris extended attribute scheme (subfiles), and somewhat incompatible the simple name/value string-based xattrs supported by Linux, BSD, IRIX etc. It would be nice to have Linux-style xattrs supported in NFSv3, with the current work then potentially forming the basis for a future NFSv4 protocol extension. If you’re interested in this stuff, please consider attending and helping with the discussion.
The date for the 2009 SELinux Developer Summit has been set for Sunday 20th September, and it will be held as an ancillary event of LinuxCon in Portland.
This is a pre-announcement so that people who are thinking of attending LinuxCon and/or Plumbers Conference can take advantage of the first level of early registration for LinuxCon, which ends June 1st (this Monday).
A full announcement for the SELinux developer summit with a CfP will follow shortly.
p.s. I maintain an Identica (an open Twitter-like service) account for more regular and briefer notes: http://identi.ca/jamesm . You can subscribe via RSS or simply get an account like all the cool kids.