Monthly Archives: May 2008


I’ve set up a tumbleblog here:

essentially as a kind of public bookmarking of things which I find interesting, without much in the way of commentary (if any).

If you want to follow it, grab the rss feed. The topics will likely vary beyond the typically work-related stuff I post here, although still somewhat geeky & security-ish. I’d suggest not adding the feed to public blog aggregation sites.

Schneier on How to Sell Security

An insightful essay from Bruce Schneier: How to Sell Security.

He discusses the tendency for people to subjectively evaluate risk and tend toward taking greater chances with losses:

When faced with a gain, about 85 percent of people chose the sure smaller gain over the risky larger gain. But when faced with a loss, about 70 percent chose the risky larger loss over the sure smaller loss.

This is from an experiment demonstrating Prospect Theory, which interestingly predicts that people will tend to take greater risks for higher-probability losses.

Bruce talks about how this leads to a problem in the selling of security features, where people are inclined—according to prospect theory—to be increasingly risk-taking as the security threat increases. One option, which is favored in certain areas of the industry, is to fuel fear, although this approach has obvious ethical issues, and I think ultimately, damages credibility and becomes effectively counterproductive. Rather:

The better solution is not to sell security directly, but to include it as part of a more general product or service. Your car comes with safety and security features built in; they’re not sold separately. Same with your house. And it should be the same with computers and networks. Vendors need to build security into the products and services that customers actually want.


SELinux on Wall Street

SELinux was a factor in the recently announced NYSE Euronext adoption of Linux:

NYSE Euronext also relies on Red Hat Enterprise Linux and its included Security-Enhanced Linux (SELinux) functionality to preserve the security of its platform. With trillions of dollars flowing through the exchange each month, security is a large and very important organizational focus. “We are very security conscious because we have to be. The operating system is a key part of every server that we operate and each server must be secure at all times. We maintain the security of our systems by relying on the SELinux features within Red Hat Enterprise Linux,” said Rubinow.

Their system handles US$141 billion per day in trades.

Sliding into SELinux Policy Development with Fedora 9

In case you hadn’t noticed, Fedora 9 has been released. One of the many goodies to be included is SLIDE: the SELinux policy development IDE. This should be great news for application developers who want their projects to work well with SELinux.

It’s been possible for some time now to quickly develop a loadable policy module when an application clashes with the shipped SELinux policy. The technique is quite simple: parse the audit log and generate rules which allow the previously denied accesses. This is a form of “learning mode”, which risks encapsulating badness and being incomplete. It’s often handy for resolving local issues, but not necessarily the kind of thing that a developer would want to use for creating shippable and maintainable policy.

This is where SLIDE comes in. It’s an eclipse-based environment with deep knowledge of the SELinux policy infrastructure, facilitating policy development for everything from the simplest application through to the general system policy. It’s not “SELinux policy for Dummies”, but it does provide some useful high-level abstractions such as wizards. Developers who are interested in learning more about how to develop policy for their applications can now easily get started with SLIDE in Fedora 9. If not installed already, do so:

$ sudo yum install eclipse-slide selinux-policy-devel

SLIDE should then be available via Applications -> Programming -> Eclipse. Start a new project and follow the prompts to create a policy module for an application. The application doesn’t even need to exist—this is simply a good way to learn about the policy framework. Note that the location of reference policy is /usr/share/selinux/devel/include.

Here are some screenshots (click for larger images):


Creating a new policy module via the wizard.


Guided interface. These fields are automatically populated, while elements may be expanded out for greater control.


Automatically generated initial policy ready for building or further development.

It would be immensely useful now to have a simple worked tutorial to help people get started in a practical manner. I’m not sure if anyone is planning to do this currently, so if you’re looking for a way to dive in and contribute to the project, please get in touch via the mailing list. Otherwise, please wait until it falls from the sky.

Have fun!

Linux on Mumbai City Buses

Via a the Chennai ILUG mailing list, here’s an interesting story: Linux rides pillion on Mumbai city buses. I like how this system uses GPS to figure the cost of each trip, rather than alternatives such as a single fare or complicated fare schemes.

Deployed in January 2007, the system is so stable that it will this month be officially extended to part of Mumbai’s suburban railways as well. It is also secure, and has had no hacks and cracks, according to Kaizen.

Thanks to the system’s use of Linux, BEST saved about inr 1.2 million on the point of sale infrastructure alone, as compared with a Microsoft Windows setup, Goriani says.

It’s also slightly reassuring to see they’re moved from telnet to SSH for remote management.

Sydney recently canned a smartcard-based bus ticketing system after spending AUD$95 million. Given that the same company was developing both systems (as well as the system for Singapore), and that such systems are fairly commonplace in modern cities, I think you could reasonably surmise that the problems in the Sydney system were not technical.

Labeled NFS Requirements Draft Submitted

Dave Quigley has just submitted an Internet Draft to the IETF outlining the requirements for Labeled NFS:

MAC Security Label Requirements for NFSv4 (link)


This Internet-Draft outlines high-level requirements for the
integration of flexible Mandatory Access Control (MAC) functionality
into NFSv4.1 . It describes the level of protections that should be
provided over protocol components and the basic structure of the
proposed system. It also gives a brief explanation of what kinds of
protections MAC systems offer and why existing NFSv4 protection
mechanisms are not sufficient.

This draft is a generalization the original Security Enhanced NFS document posted last year, addressing the general need for mandatory access control support in NFS.

NFSv4 currently supports two access control schemes: standard DAC and ACLs. MAC labeling support is required for technologies such as SELinux and OpenSolaris FMAC.

Essentially what’s needed is a way to convey MAC labels over the wire (for both setting and retrieving their values), and to be able to enforce security policy using those labels. The server needs to be able to determine the security label of the remote client process when enforcing policy, and all systems need to be able to ensure they understand each other’s labels, or be able to translate them. A “Domain of Interpretation” (DOI) attribute is used to determine the meaning of labels, a term which may be familiar to those who’ve braved the IPsec specifications. The confidentiality and integrity of these security attributes must be protected in transit, while all parties need to be authenticated. We also need to be able to handle the case where either the client or server does not have MAC enabled, and to ensure non-breakage with existing implementations. There’s a lot more in the details, but that’s the gist of it.

It may seem at first glance that NFSv4 named attributes (NAs) would provide the required labeling functionality, but they’re not a good fit. NAs are specifed as opaque to the system and user-managed, while MAC security labels are managed by the system. NAs also do not provide necessary semantics such as conveying client security attributes or negotiation of DOI. There are also issues with attribute namespaces (which are user-managed and unspecified) and labeling atomicity. Another possible approach is to implement Linux/BSD-style extended attributes (EAs), which are simple text string attributes associated with files, in contrast with the NA “subfile” scheme. This would potentially only solve the attribute namespace issue, and is also not a good general solution. EAs are also not currently part of the NFSv4 specification, and it seems like a contentious area in any case.

The current Labeled NFS prototype code utilizes NFSv4 recommended attributes (RAs), which are fully extensible, already exist, and are already used for similar management of metadata (e.g. ACLs). This seems to be the simplest and most straightforward approach.

Once there’s consensus on the requirements, the next step will be to develop a protocol specification and hopefully have it incorporated into NFSv4. v4.1 is currently in “last call”, so the next candidate would be v4.2, it seems. The prototype code for Linux/SELinux will continue to be developed alongside the standards process.

For those interested in following or contributing to the project, there are several relevant mailing lists:

Dave is hoping to have further discussion IETF 72 in July, and will be presenting on the state of the project at the SELinux Developer Summit ahead of that.