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Adventures in SELinux

Security Enhanced Linux (SELinux) is a pretty powerful technology that adds another layer of access control to a Linux system. It helps significantly limit the ability for an attacker who has partly compromised a system to use their access to jump deeper into the system.

It has been standard in Red Hat Enterprise Linux and its derivatives for quite some time, and is often the cause of many a headache when something doesn’t work because it is being (apparently) silently blocked by SELinux’s security enhancements!

Its potential to cause breakage, especially when third-party bits and pieces are brought into the mix, means the advice from well-meaning individuals is often a cry of “just turn off SELinux!”, rendering a system without that extra layer of protection.

I will not pretend that my recent dealings with SELinux in CentOS 7 have been free of frustration, but a few simple tools have made it a surprisingly simple affair to get something up and running again if a particular behaviour (always of something a bit third-party in my experience!) is being erroneously blocked.

I think a big part of what makes SELinux get switched off in frustration is the perception that it is breaking things silently, and the psychological impact of its verbose ‘scariness’ when you do find those logs!

audit2why

As long as you remember that SELinux can be the cause of potential unexplained weirdness, your first port of call can be audit2why:

audit2why -a

What is particularly nice about this tool is how quickly you get (semi-)human readable output, detailing which rules an application is breaking. If you do hit one of these ‘weird problems’, a quick trip to this tool usually makes it clear that SELinux is the cause of the failure!

audit2allow

I was surprised by how relatively quick it was to identify an issue with audit2why and make a custom module with audit2allow to get an application working again.

There are a good set of instructions in the Red Hat manual.

It sounds like a big deal, but the tools have made it almost completely automated — it really isn’t necessary to have a deep understanding of SELinux’s internal workings.

setsebool

Finally, there are some flags that are disabled by default for SELinux protected applications that you might need. Again, audit2why will often make it clear what you need to toggle using this tool!

For example, a web server process that does legitimately send out emails might need the appropriate flag switched on. Without it, the web server doesn’t get the right to talk to sendmail.

Give SELinux Another Chance!

I suppose my point in this rambling is this: give SELinux a chance if you have given up on it in the past. If you have the time to set up your system properly (and you should!), taking a little extra to figure out how to grant only the permissions really needed does make a material difference to your security should one application be compromised. An attacker being able to get their foot in the door needs to be assumed to be possible, so making their life a lot harder at that point is worth making your life slightly harder on the odd occasion.

With a little patience and the use of the tools I have talked about, I think it is a lot easier to work with than it might seem at first glance, or when it first arrived in RHEL many moons ago!

Notes on Creating an Encrypted Bootable SuperDuper Backup

SuperDuper icon

SuperDuper is one of my favourite backup applications for the Mac, and I use it as part of my backup and recovery strategy.

One of its benefits is creating a bootable clone, so in the case of any trouble, you can connect the backup drive, hold Option/Alt and boot your alternative system.

The world has changed since I first used this tool, and full-disk encryption is now essential for maintaining privacy and “not-having-your-life-turned-upside-down” in the event of a loss of control of the drive with your life on it. FileVault on OS X since Lion works beautifully for your boot drive, but unfortunately I had to sacrifice the bootability of my SuperDuper backup in order to ensure it was encrypted.

Recently, a drive failure on my SuperDuper backup drive (yep, they do happen, and that’s why we back up!) required me to replace the drive. That gives a good excuse to play, and try and make a bootable and encrypted backup — FileVault-style, but on an external disk that we manage ourselves.

» Read the rest of this post…

Total Slider 2.0

Total Slider Banner

I am very excited to be able to announce that Total Slider 2.0 has been released!

Version 2.0 is a significant milestone in the plugin’s history, and brings a very important behind-the-scenes change to the way your slide information is stored. In addition to that, and a lot of cleanup work in the code itself, there is now the capability of having draft slides as well as auto-saving of those drafts, making it much more difficult to lose data!

Total Slider 2.0 draft functionality

Being a side project that has to fit in around my day job and other work, this has taken much longer to get out there than I would have liked, but I am very happy with the result. The particular challenge of making sure the data format upgrade goes without a hitch involved some extensive testing, but I’m pretty confident (about as confident as you can be!) that the upgrade process will be very smooth. In the unlikely event there is an issue, you can roll back the plugin to v1.1.5 without any loss of data. Obviously, taking a database backup is a good idea, though! :)

With this big infrastructure change out of the way, I’m looking forward to the future of this plugin. I hope we can deliver more graphical goodness (a slider template previewer would be nice!) and a greater variety of templates that ship with the plugin to support the different preferences people have for their sliders.

It’s really exciting to finally get this released to the 1,000+ active users (according to its WordPress plugin page) this software has, and I’m looking forward to making it even better as and when I can!

You can download Total Slider from the WordPress Plugins Directory.

Piwik for Web Analytics

Google Analytics is almost ubiquitous as the solution for collecting useful information about how your website is being used by visitors. It is a good product, and has evolved over the years to be very flexible indeed.

But since it first launched, my opinions of Google have certainly changed, as have many others. Without wishing to get into a debate on the subject, there definitely is a market for a competitor to this very useful tool that might free us of that reliance on Google infrastructure, and be more respecting of our visitors, by means of initatives like Do Not Track.

Piwik screenshot

Piwik’s desktop and mobile views

I recently deployed Piwik, an open source PHP-based application intended to replace Google Analytics. A full disclosure — it will not be as full-featured as Google Analytics for those people using the full power of that solution, but it puts the power and control back in your hands. Moreover, it uses a very similar-looking (perhaps even largely compatible) JavaScript API, meaning I had to do little work to figure out how to track the events that I wanted.

With built-in support for avoiding the use of cookies altogether, you can sidestep the well-meaning, but ridiculously ill-conceived EU Cookie law and its onerous “we use cookies!” notifications entirely, while still delivering enough tracking capability for many simpler analytics applications where detailed insights into repeat visits aren’t so important.

I haven’t made the time to replace Google Analytics on this site with it yet, but that is on my list of things to do! Right now, I have some custom code server-side that detects your Do Not Track status and suppresses the Google Analytics JavaScript entirely, but Piwik would do away with that need for complexity.

It might not do enough for your application — but as a way to put your money where your mouth is and genuinely support the user’s right to give and withdraw consent for tracking, it is most definitely worth a look.

Pushing System Center Operations Manager Alerts to iOS and Android

I’m a huge fan of the Pushover Simple Notification Service for receiving critical alerts about the servers for which I am responsible. It’s beautifully simple — in short, it takes the ‘walled garden’ of Google or Apple’s push notification system and extends it, so that you can push any text notification you want through their API, and it’ll get to your phone.

In this post, I will share how I get critical alerts from a Microsoft System Center Operations Manager instance to Pushover.

» Read the rest of this post…

5.0

As I move closer to the significant milestone of one decade of having this personal blog, I felt that it was time for a significant overhaul of the look and feel of this site, as well as some of its non-blog post content.

Enter the 5.0 release! :)

Responsive and Refined…

pwdb50_fullsize

Rather than evolving the existing stylesheet and making changes, I actually started over, using a new SASS-based CSS workflow. If you look really hard, you will see bits and pieces of the old CSS hanging around that I have migrated forward for the moment. In the fullness of time, though, any of the old code should be gone!

The result is a site that is truly responsive — it is designed for small screens first, then it scales up to larger displays, rather than having a full-size only layout, but removing content for display on smaller screens. I did have a retro-fitted responsive system before, but this approach is much cleaner and delivers a more consistent result.

PWDB 5.0 Mobile display

A Font First!

Adding to the use of Colaborate for headings from my last design refresh, this design actually débuts my first experiment with editing fonts.

Thanks to the GPLv3 licensing terms of Colaborate, I was able to take it into TypeTool, and tone down its rather characterful lowercase ‘t’ for use as body text. The result is a custom font that, while it has its imperfections with kerning and missing ligatures, is an exciting first experiment for me — putting my interest type design to some practical use. I hope I will look back upon this first experiment with embarrassment later on when I have learned so much more, but for the moment it is very gratifying to have something to say “I did this” about!

You can download my source files for this font. This font, as it is based on Colaborate, is also licensed under the GPLv3 with font exception.

A More Modern Portfolio

The content on my Portfolio page had definitely aged, and was long overdue an overhaul. It now focuses on four main areas — Devops and Automation, Systems Administration, Web Development and Software Development.

More to Come!

As mentioned, this is a big change, but that doesn’t mean I am done! There are various other places where older content and design still might be evident, and I hope to get to more in the coming weeks.

My Alternative Christmas Wish

Conflict minerals 5 by Sasha Lezhnev of the Enough Project - http://www.enoughproject.org/

Conflict minerals 5 by Sasha Lezhnev of the Enough Project

Licensed under CC-BY-ND 2.0

I am always interested to know where the products I buy come from, and at this particularly consumer-focused time of the year, it highlights the issue further. It is interesting to me just how complex the chains of dependencies involved in making any non-trivial ‘thing’ really are.

The computer I am writing this on was assembled in the UK, but I would suggest that most, or all, of its components were not. What about the suppliers who provided sub-components for those components? What about the raw materials, including the traces of rare earth minerals needed to do its electronic magic?

Unfortunately, the result of this enormous complexity, and the fact that the retailers from which we buy care about little but the price they pay, means it is very difficult to verify really important aspects of how the goods we consume were made. It seems that nobody, not even the retailers at this end of the chain, has the depth of insight into their supply chain needed to affirmatively say “this is how our product was made”.

So, when cost is the primary concern, and nobody really digs deep to understand what is happening at each stage of a product’s life, how can consumers at this side of the transaction be empowered to make more ethical choices?

If I go to my local big-name supermarket to buy a kettle, for example, I cannot look at all the options and make an assessment about which product was made in a way that best aligns with my values. Did the manufacture of the cheapest £5 kettle involve the exploitation of somebody? Probably. Is the £30 ‘luxury’ choice any better? We just don’t know.

There are pockets of hope in this area — initiatives like Fairtrade have, for some product categories, encouraged supermakets to go ‘all Fairtrade’ for particular items, and for other companies (tea and coffee businesses being a good example) to take steps to at least appear to be sourcing more ethically.

I just wish there were a big push from somewhere to gather accurate intelligence about how our stuff is made, and begin labelling more products in a way that empowers consumers to make better choices. I think there is a good portion of the population who want to make better choices that support human rights, environmental protection and social progress, but without high quality, verifiable information about what goes into what we consume, we are in the dark. While we remain uninformed, we cannot exert pressure on the market to do better as a whole.

Serving Pi

I recently completed a physical migration of my server, the one that hosts this very page! It all went successfully, and without any noticeable downtime for this site, which I am pleased to be able to do.

There was, however, a period of time during which this server needed to be physically switched off and moved to the new location. To enable zero downtime, something would need to be able to host the server during that period.

Enter my Raspberry Pi!

Raspberry Pi in box

This amazing little thing is capable of running Raspbian, a modified version of Debian, which means I get access to the rich library of Debian packages that are available. I have a private Git repository containing a modular set of Puppet manifests. These describe the exact configuration of this server, so by applying the Puppet manifests, I can spin up a new instance of this particular server’s configuration on a whim.

So, I dusted off an SD card that was lying around, dropped Raspbian on it, and installed Puppet and Git and applied the manifests.

If I’m honest, there were a few components that weren’t quite so happy to run, despite packages being available. Varnish didn’t seem to like my VCL file, so I had to run the site here directly with Nginx pointing to PHP-FPM instead.

To cut a long story short, it worked! I was successfully serving up this site, from the Pi, using (almost) my existing configuration. Performance was not stellar, even compared to the modest hardware that normally serves this page, with page load times about 10 times slower than uncached page loads normally would be. The main blog page did take 1.5 seconds to render! For the short time I needed it though, I was very happy to have a very inexpensive and easy solution.

Working on Total Slider 2.0

Total Slider Banner

I’ve been fortunate this week to have a little time to work on Total Slider, my (and Van Patten Media’s) open source WordPress plugin for making those neat little slideshow things, like so:

Example Total Slider slider

I have been meaning to get to this project again for a while, so it is great to get a moment or two to give it the love and attention it deserves.

My focus thus far has been on a complete overhaul of Total Slider’s data storage format — away from using wp_option records and using a custom post type.

This change is not only the right thing to do to clean things up and follow best practices, but it opens doors to other neat features that will make Total Slider feel like it fits into the WordPress Way even more. Without making undeliverable promises, I’d love to see automatic saving of slide drafts make it into 2.0! 😉

One of the things I have found that is pleasing is that much of the code I have already written is sufficiently abstracted that ripping out the fundamentals of the data format has been a lot less painful than it could have been!

It is nice as well to use this blog for one of its original purposes, to give updates on the projects I am working on. :)

You can follow progress in the unstable branch on the project’s GitHub page.

The Changing Face of Vulnerability News

Heartbleed logo  Shellshock Logo

The recent news about the bash vulnerability being called “ShellShock”, and the degree to which it is getting mainstream press has got me thinking about how software vulnerabilities are now being reported in the mainstream media.

Apparently, no vulnerability these days is complete without a catchy name and logo — see Heartbleed and Shellshock! Joking aside, though, the very fact that these vulnerabilities are making non-tech news headlines puts pressure on everyone running potentially vulnerable systems to do their duty — usually as straightforward as running a pre-packaged security update.

The Heartbleed and Shellshock stories are taking the place of what we used to see reserved for particularly influental computer worms, like Sasser and Mydoom. It’s most definitely positive that some vulnerabilities are getting attention — unfortunately it is still the case that for some companies and system administrators, only outside pressure will convince them to promptly, diligently and consistently apply security updates.

What I’d like to see, is some way for people interested in improving computer security, the “good guys” for lack of a better term, to leverage this media interest to send a message to system administrators that it’s always necessary to apply software updates promptly, even when they don’t get on the TV news!

The Curse of The Black Box

The other key issue that Shellshock highlights, as did Heartbleed, is the issue of embedded ‘black box’ systems that might be vulnerable. This kind of system is everywhere — and because in many cases they are ‘set it and forget it’ machines, they represent a particular risk. It’s often very difficult to convince vendors of these systems of the importance of pushing upstream software updates down to end users, particularly when there is a lack of understanding and a lack of financial incentive.

Something big and mainstream, like Shellshock and Heartbleed, might convince system administrators to badger vendors to release patches for this kind of product, but we need to extend this further, and make it a social (or even a legal) expectation on vendors to supply security updates for any product they ship, for a reasonable lifetime period for that product.

The security landscape is too complex, and everything too interconnected, for anyone to have the opinion that “I don’t need to patch that, because there’s nothing important on it”.

Leaving Yourself in the Loop

I want to part with a few bullet points, with some actions I try to take to stay up-to-date. Automatic updates are increasingly common, but not universal, and these simple things can help you not miss a known vulnerability.

  • Document and understand the whole software footprint of the systems for which you are responsible. (This means embedded systems, software libraries, and more!)
  • Subscribe to announce mailing lists, follow Twitter accounts of the software projects and systems you use. (It pays to be in the know about available updates, and not hear about them after it is too late!)
  • Look for useful vulnerability resources for particular projects you use. (For example, for WordPress, the recently launched WPScan Vulnerability Database.)