Monthly Archives: July 2009

2009 SELinux Developer Summit schedule published

We’ve just published the schedule for this year’s SELinux Developer Summit.

From the announcement:

This year's event will be divided into two main sessions.

The first will be for traditional conference presentations which
were accepted via the CfP:

  * Labeled NFS Community Involvement - Dave Quigley (NSA)
  * Update on Flask/TE Support for X - Eamon Walsh (NSA)
  * Work on a Higher-Level Policy Language - James Carter (NSA)
  * Video Streaming in Policy Confined Environments - Philip Tricca (USAF)
  * A New Policy Infrastructure for SELinux Joshua Brindle (Tresys)
  * Policy Distribution Joshua Brindle (Tresys)
  * Refpolicy and Userspace Joshua Brindle (Tresys)
  * Analysis of Flask Policies in VM Systems Trent Jaeger (PSU) 

Aside from Josh's talks (which are combined into one 60-minute slot),
these are 30-minute slots.  For speakers, the recommended format is
20-minutes of presenting and 10-minutes of Q&A.

The second main session, after lunch, is intended to be fully
collaborative in that everyone in attendance may (and should) participate.
This is divided into three sections:

  * Lightning talks, 5 minutes each.  Any attendee may propose a lightning
    talk via the wiki or on the day.

  * Development sessions.  This is a flexible format where developers can
    work in small self-organized groups on specific tasks, taking
    advantage of the fact that we're all in the same place for the day.
    We'll discuss this further on the event mailing list -- it's important
    to identify tasks, teams and goals beforehand, and also to make sure
    everyone is set up to get straight to work on the day.

  * General project discussion.  We'll spend about an hour discussing
    project and development issues.  Candidate agenda items should
    first be posted to the event mailing list, and the agenda will be
    finalized immediately prior to the event.

For attendees who are yet to do so, ensure you are registered for
LinuxCon, which is co-hosting the event for us:

LinuxCon registration is a requirement for attending the SELinux Developer
Summit.  The current discounted registration rate ends on August 15th.

The development sessions idea comes from last year’s development-oriented FOSS.IN, which I wrote about here.

If you’re still considering whether to attend the SELinux Developer Summit, keep in mind that in addition to being part of LinuxCon, there’s also Linux Plumbers directly following that at the same venue, which includes a general Linux security microconf.  Travel budgets are tight for everyone this year, so hopefully the co-location of these events will help make a business case for people who are still working on travel approval.

For those who can’t make it, we’ll try and ensure that all available materials and minutes from the event are published in a timely manner.   I’d encourage those who are able to attend to blog/dent/tweet anything related to the event that they feel might be useful to others.

KCA slides, photos and videos

I was in Brisbane last week to talk about Linux Kernel Security at Kernel Conference Australia (KCA).

The aims of the talk were to provide a general overview of security features in the Linux kernel, and to examine historical context around Unix security and how Linux is evolving to address modern security requirements.

People may be interested in my slides. They’re available as a PDF download and via Slideshare. Note that full speaker notes are included in the slides, in the second half of the deck.

The conference was streamed live online, and the video from my talk may be viewed here. I’m watching to see how the talk, and my speaking in general, might be improved. As painful as this may be, it seems very effective in understanding what worked and what didn’t. I think I can tighten this talk up for possible future use, and focus more on how our development process—not merely the technology—helps address evolving security requirements.

I later participated in an OS security panel with Cristina Cifuentes and Fernando Gont, the video of which is also online.

I’ve also uploaded a flickr photo set. Brisbane is a great location for a conference, especially in the southern hemisphere winter.

It was unusual being the only Linux speaker at a conference. I hope the talk was useful, if at least to encourage more thinking about security in operating systems.

The primary organizer of KCA, James MacPherson, has posted an initial wrap-up of the conference. If the conference continues—I hope it does; it has a lot of potential for the Australian kernel R&D community—I think it would be highly advantageous to more actively seek speakers (and even organizers), from the broader community. One major local Linux kernel developer had a Linux kernel video talk rejected, which seemed odd given that similar talks were accepted (e.g. the new OpenSolaris sound system), and that an additional OpenSolaris talk was added to the program after the CfP closed.

I understand that organizing conferences is difficult, so I hope this is taken as constructive feedback. I’d certainly be interested in helping review papers or otherwise help out in the future if the conference is held again, and if it is aimed at the broader community.

A brief note on the 2.6.30 kernel null pointer vulnerability

This is just to note that the Red Hat Security Response team have issued a preliminary comment on the 2.6.30 kernel null pointer vulnerability, as a comment in the associated bugzilla entry:

From Eugene Teo (Security Response Team)  2009-07-17 07:23:57 EDT

The Red Hat Security Response Team is aware of the Linux kernel local privilege
escalation exploit that is published in a number of security mailing lists and
websites. The flaw identified by CVE-2009-1897 is a null pointer dereference
vulnerability in the tun_chr_poll() function of the Linux kernel, introduced
via the upstream git commit 33dccbb0. This flaw affects kernel versions between
2.6.30-rc1 and 2.6.30-rc3 2.6.31-rc3 , and was addressed via the upstream
git commit 3c8a9c63.

The flaw affects only the Red Hat Enterprise Linux 5.4 beta kernel as the
upstream git commit 33dccbb0 was backported to the kernel as a normal bug fix.
We will be addressing this flaw in a future update to the beta kernel. It is
also possible to mitigate this flaw by ensuring that the permissions for
/dev/net/tun is restricted to root only.

The default SELinux policy, in Red Hat Enterprise Linux 5, allows processes in
the unconfined domains to map low memory in the kernel. The exploit did not
bypass the null pointer dereference protection in the Linux kernel. However, we
are updating the selinux-policy package to change this default configuration,
so that it prevents the unconfined processes from being able to map the low
memory. See bug 511143 for more information.

This issue does not affect any other released kernel in any Red Hat product.

In addition, future updates to Red Hat Enterprise Linux kernels may include the
'-fno-delete-null-pointer-checks' gcc CFLAGS. See:

We would like to thank Brad Spengler for bringing these issues to our

Note that I’m not a member of the security response team: I’m cc’d on the bug and noticed the statement when it was posted.

It is also worth highlighting that you should ensure that the permissions on


are correct.  It should look like this:

# ls -l /dev/net/tun
crw------- 1 root root 10, 200 2009-07-07 09:52 /dev/net/tun

It’s possible that some VPN package may change the permissions on this.

In terms of the SELinux aspect of the exploit, I’ve posted a brief comment in the LWN thread here.

Yes, there was a mistake in the SELinux policy, which allowed the unconfined user to bypass the mmap_min_addr check, which otherwise would have been enforced if the check was enabled (many disable it to get wine etc. working, btw, google disable mmap_min_addr).

This is being fixed in the policy.

The lesson learned here is that more careful review of policy changes needs to happen, and to ask the question as to whether the policy is capable of weakening default security.

The LSM interface is theoretically designed to only allow further restriction of access, but this is a special case, where we are applying policy to a kernel compilation option which can also have its value set via a sysctl. It’s not a typical “access this resource or not?” decision.

The policy bug is now fixed in the selinux-policy-2.4.6-252.el5 package.

The challenge now is to try and ensure that we don’t see this class of problem crop up again, for unusual cases such as this where the normally “restrictive” mode of LSM (i.e. where permissions can only be further restricted) does not apply.  We may need to rethink how this is managed in the kernel to reduce the possibility of such issues in LSM module policy, as the LSM API here appears to be violating the Hard to Misuse design principle.

FOSS.MY 2009 CFP Open

Kuala Lumpur

Kuala Lumpur

I just noticed that the Call for Participation for 2009 is now open, until August 15th.  I spoke at the inaugural event last year, and had a great time.  Held in Malaysia, this is a true grass-roots conference.  It’s modelled somewhat on other community events such as LCA and FOSS.IN, and probably the leading such event for Southeast Asia.

The conference will be held on the weekend of the 24th and 25th of October, immediately following the Japan Linux Symposium and the Kernel Summit.  If you’re visiting the region for either of the Tokyo events, Malaysia is relatively close-by, and there are several good budget airlines in the region.  I’d highly recommend submitting a proposal or simply attending.

Kuala Lumpur is certainly a great city to visit, too.

All my talk slides are now on Slideshare

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).