linux

701 Articles

Linux Fu: Heads Or Tails For VPN

August 10, 2026 by 4 Comments

If you’ve done much networking, you surely know the frustration of trying to connect to something, say a Raspberry Pi, that lives behind your consumer router. There are a number of solutions for this, ranging from opening ports on your router along with dynamic DNS. Or, you can operate a VPN server on your network. Modern Linux has a facility called Wireguard that lets you create secure network tunnels very easily, but it is a little difficult to set up. But there are tools like Tailscale that can do most of the work for you. There’s only one problem: Tailscale is sorta-kinda free, but not really. But it turns out, you can build your own Tailscale network, and it is easier than you might imagine.

In all fairness, Tailscale’s free tier is good and recently got even more generous, allowing unlimited nodes and up to six users. That’s plenty for most hackers. However, as we’ve seen before, what they can give they can also take away. Besides, there are some extra services you still have to pay for if you want them, but overall, the free tier is more than enough for most people.

On the other hand, no matter how great the free tier may be, some people don’t want to run things on other people’s hardware. Or you need that 7th user. Or you need paywalled features. No worries. Headscale is a self-hosted service that can do nearly everything the cloud portion of Tailscale does, and if you have a place to host it, you can be your own Tailscale server.

For the client side? That’s the best part. Headscale works seamlessly with the existing Tailscale clients. You simply have to point them to your server instead of the defaults.

Continue reading “Linux Fu: Heads Or Tails For VPN” →

This Filesystem Is Born To Fail

August 7, 2026 by 38 Comments

Sandboxing a Linux process usually means spending a lot of effort deciding what it isn’t allowed to see. You might put it in a mount namespace, bind-mount a few directories into place, hide some others, add a chroot, and generally construct a carefully restricted version of the filesystem. But a new Linux kernel feature is about to change all of that. Instead of carefully hiding most of the filesystem, why not just take the filesystem away?

That’s essentially the idea behind FailFS, a tiny pseudo-filesystem expected to land in Linux 7.3. As the name suggests, it doesn’t do very much. In fact, that’s the point: every operation that reaches FailFS returns EOPNOTSUPP, meaning “operation not supported.”

The interesting bit is what happens when a process uses FailFS as its root or current working directory. At that point, normal pathname lookup essentially ceases to work. Absolute paths fail. Absolute symbolic links fail. Relative paths using the normal current-directory mechanism fail. If the application tries to open /etc/passwd, there simply isn’t a useful /etc to find.

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This Week In Security: What’s In A Name, The AI Bugpocalypse Hits Everyone, OpenWRT Flaws, And Duress Passwords

July 31, 2026 by 22 Comments

The great thing about standards is there’s so many to pick from, right?. (Insert obligatory XKCD #927 here.) Several companies have developed naming schemes to refer to groups of attacks, and now Google has too.

Sometimes, malware, ransomware, or exploit groups name themselves: “Shinyhunters”, “LapSus$”, “Cl0p”, “Lockbit”, and so on. For the groups that don’t advertise their presence, identification and naming can be more difficult. Mostly state-run affairs that didn’t want to draw attention to themselves, these Advanced Persistent Threats (APT) groups were originally simply given numbers. APT28 refers to the Russian GRU Intelligence Directorate suspected of hacking the Democratic Party email servers, APT38 is a North Korean governmental agency involved in financial and crypto currency theft.

Multiple companies and agencies have developed naming schemes to make referring to threat groups easier, typically including a regional identifier as well. CrowdStrike naming uses name groups like “Bear” group for suspected Russian actors, “Panda” for China, “Spider” for unattributed crime groups, while Microsoft uses “Blizzard”, “Typhoon”, and “Tempest”.

Google, deciding there weren’t enough classifications already, now introduces “RELIC”, “CASTLE”, and “COMET”. Of course, each naming organization has dozens of other classification groups as well, but now the next time you hear about an attack being attributed to “Scattered Spider” you know it’s the CrowdStrike name for a crime group.

Critical OpenWRT DHCP Flaw Fixed

The Hacker News reports on a major release of OpenWRT which includes fixes to the odhcpd server, the embedded DHCPv4 and DHCPv6 server written by OpenWRT.

The bug is a straight-forward stack style attack where a buffer is allocated, but not length-checked against the data required to reply to a malformed request. OpenWRT runs on a wide range of devices, but one of the most popular legacy platforms still in use, the MIPS processor architecture, lacks most modern security protections against stack-based attacks, making this attack sting more than it might on other architectures.

The latest OpenWRT releases also fix issues in the uhttpd embedded web server, multiple issues in the LUCI web configuration interface that allowed attackers to inject cross-site scripting content and Linux kernel security fixes. If you run a direct OpenWRT build on your equipment, update! These bugs will have an extremely long tail however, with tens of thousands, or likely more, OpenWRT-based devices that will never see updates.

The company behind several of the findings, Hacker House, say they used multiple AI tools and both open and frontier models to discover the bugs, then manual review and testing to confirm before reporting.

Cisco to Stop Assigning (some) CVEs

Cisco has announced it is moving to a twice-monthly patch cycle. Additionally, Cisco will no longer assign CVEs to each bug in the release.

Cisco says this is in reaction to the rapid increase in bugs found by AI tools, and that “Assessing security risk CVE-by-CVE and applying point mitigations is no longer fit for purpose.” Cisco will still assign a CVE to a bug that “requires compensating controls” or is known to be exploited.

It seems like it will be business as usual for the most severe bugs, but it will be interesting to see what happens when exploits are found for bugs which did not get a CVE in a prior release.

Microsoft Suggests Three-Day Patch Race

Microsoft is now recommending a 3 day patch window for new patches. This is, to say the least, an “aggressive” schedule for applying new patches, given the recent track record of issues introduced by patches.

A update that crashes is inconvenient on a home computer — even more so if it’s your parent’s computer — but could be catastrophic when it brings down an entire corporate fleet. Most large organizations have their own internal patch schedules and internal testing requirements before patches are deployed, delaying the patch process further.

Systems like the CISA KEV database, a list of vulnerabilities known to be actively exploited, are in place to help identify the most important issues. With repeated record-breaking numbers of vulnerabilities pushed in Patch Tuesday and the decreasing support of the KEV and related vulnerability indexing systems, the load on IT departments and administrators is becoming impossible.

The AI “bugpocalypse” is finding record numbers of vulnerabilities, while also closing the timeline between bug to exploit to hours in some cases. The time between bug and exploit then drives the patch cycle, which means less testing. With less testing, the patches are less stable, leading to less trust in rapidly installing them.

Oracle Patches Almost 1500 CVEs

Moving directly from the impacts of the flood of Microsoft security issues, the July 2026 patch set from Oracle included fixes for 1499 security issues and 1434 CVEs over 334 Oracle products.

Oracle is also pressuring administrators to move to a monthly patch cycle, but acknowledges “transitioning to a monthly security patching cadence may require updates to existing operational processes”. Not to worry – there is a Oracle consulting service you can hire to help you patch your Oracle problems.

Linux Patches 323 CVEs in Two Days

After announcing over 400 CVEs in the Linux kernel last week, Linux mainters have announced an additional 323 in the last three days alone. The vulnerabilities cover Bluetooth, Ethernet, USB gadget mode, WiFi drivers, virtualization systems, SMB file sharing, and of course more.

One benefit to the architecture of the Linux kernel is that typically all the fixes will arrive in a single kernel update, but when almost every week brings critical updates and a new kernel, patch fatigue is a real thing. Either users stop applying every update, or the uptime and testing requirements of a company prohibits constantly updating and changing servers.

Duress Passwords Aren’t Necessarily a Good Thing

The security-hardened Android variant Graphene, is in the news this week for the use of duress passwords.

A duress password is a mechanism where a second PIN or password can be used to initiate a device wipe. The hope is that in a situation where you are compelled to unlock a device, providing a password which then wipes the device is a preferable option.

The legality of a duress password depends on the environment it is used in. The United States Customs and Border Patrol claims that by wiping a device during an inspection at the US border, Samuel Tunick destroyed evidence and property in violation of federal laws. The issue is compounded because the stop happened at a border, where many US laws against search, seizure, and the availability of a lawyer are suspended, even for US citizens.

The inclusion of duress passwords, and their cousin hidden encrypted volumes, can sound like a good idea, but can place users in serious danger when in situations with less strict rules of law. Having the ability to wipe data sounds great in isolation, but protestors, human rights workers, and other targeted groups have faced direct and physical threats under some regimes. Facing retaliation for wiping a device, or facing physical violence before providing an unlock code out of fear that it might wipe a device, can be a real risk for some.

FreeBSD Fixes a WireGuard Bug

FreeBSD has issued a security update pertaining to the WireGuard VPN implementation.

WireGuard is a modern VPN with excellent performance even on low-end systems, and which has implementations on basically every platform. The FreeBSD implementation, however, didn’t fully validate VPN packets, accepting packets without checking one of the cryptographic validation measures.

Attackers are able to inject data to a FreeBSD WireGuard implementation if they are able to guess some attributes of the connection, and able to fully modify the data in the VPN if they are able to intercept the packets.

The bug impacts any FreeBSD user of WireGuard. FreeBSD has released updated kernels.

The Need For Speed: Internet Speed Measurement (or DIY?)

July 22, 2026 by 14 Comments

Car enthusiasts want to know how quickly they can make a quarter mile. Weightlifters are forever trying to add one more plate to the bar. Internet denizens have their own favorite number to brag about: the result from a speed test.

The ritual is familiar. Close a few browser tabs, click the big “Go” button, and watch the needle climb. Perhaps you pay for gigabit service and see 940 megabits per second, which produces a satisfied nod. Perhaps you see 299 megabits and begin obsessing over network hardware. But before you get too excited either way, try another test. There is a fair chance it will give you a different answer.

That does not necessarily mean one test is lying. “Internet speed” is not a single physical quantity waiting to be measured. A speed test measures the performance of a particular device, over a particular local connection, through a particular ISP route, to a particular server, at a particular time using a particular test method. Change any of those things and the answer can change too. Continue reading “The Need For Speed: Internet Speed Measurement (or DIY?)” →

Compile Here, Run Everywhere: Crosstool-Ng

July 22, 2026 by 10 Comments

In a recent post, I mentioned that I wanted to build some tools for a stripped-down Linux running on a 3D printer with a MIPS CPU. I had two options: build a toolchain to cross-compile, or use Zig, which, in theory, has built-in toolchains for MIPS. I had to jump through hoops to get Zig to work, and I did mention Crosstool-Ng, so you might wonder why I didn’t start there. Turns out, it had its own set of hoops to work through.

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Putting Some Zig In A Linux-Based 3D Printer

July 15, 2026 by 17 Comments

Having Linux on so many devices is both a blessing and a curse. Sure, it is great that you can hack on things and modify them or even totally repurpose them. But it also means you have a fleet of Linux devices you have to manage and keep track of.

My current “main” 3D printer is a Flashforge AD5X: a nice, cheap machine that does four colors with the purge/exchange method. It sort of runs Klipper. I say sort of because Flashforge has Klipper running on a Linux host in the box, but it is massively crippled and modified. I’m sure it works for most folks. I’m also sure that if you know nothing about Linux, Klipper, or 3D printing, the experience is probably better thanks to all the cloud point-and-click interfaces. But, of course, I check none of those boxes.

I’ve had the printer for probably a year or more. Almost immediately, I put a “mod” on the printer to give it a more true Klipper interface and gave me things like shell access. There are several that I think will do this, but I used Zmod, which doesn’t totally replace the printer’s firmware; it just sort of patches it and extends it. You can easily bypass or even remove it and go back to the stock printer, although I would not want to.

In my case, the issue was a printer, but the same idea might apply to any embedded Linux system, from a router to a thermostat. Sure, it runs Linux, but is it Linux you can change?

The Problem

The AD5X runs Linux… sort of.

The Flashforge firmware and Zmod both will run on the AD5X’s little sister, the AD5M. However, the AD5M has a significantly less capable processor board than the AD5X. That means that Linux on the boxes is very stripped down. From Flashforge’s point of view, no one should be in the Linux OS anyway, and the author of Zmod probably figures every byte used is a byte taken away from the user or other advanced Zmod features.

It may seem like a first-world problem, but there were two things that irked me about the printer’s Linux. There was no less or more command for poking around files. There was also only vi as an editor. I did a few hacks to make myself happy. I wrote a pager in shell script, for example. I would try to remember to use my desktop emacs and tramp to edit files on the box. But it was a shame that there were some very basic tools lacking. Besides that, even the tools that were there like ls lacked help commands in case you want some strange option you can’t remember.

No Install

To save space, the printer doesn’t really have programs like ls, cat, and grep. Instead, it has a single busybox executable. This is common on small systems. You get one copy of the libraries and a single executable that will do all the work you need. You can invoke, for example, grep by running “busybox grep” or, if you make a symlink to busybox named grep, the user may never realize that you don’t really have grep installed.

However, busybox has to be built. You can’t easily install packages to it. So I couldn’t just run some package manager and install less or anything else. My plan was to produce a new busybox package myself to supply at least the missing commands and maybe some of the more basic ones, too. How hard could it be?

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Linux Fu: The Local Phonebook

July 8, 2026 by 31 Comments

I’ll admit it: I miss the simplicity of /etc/hosts. There was something elegant about it. You wanted laserprinter to mean 192.168.1.40, so you opened a text file and wrote:

192.168.1.40 laserprinter

Done. No cloud account, no discovery daemon, no dashboard with material-themed icons. Just a name and an address. The trouble, of course, is that /etc/hosts is only simple when you have one machine. The moment you have a desktop, a laptop, a Raspberry Pi, a NAS, a test box, and a phone or two, every little network change becomes a tiny distributed-database problem. Which copy of /etc/hosts is authoritative? Did you update the laptop? What about the machine you only boot once a month?

One Solution

Modern LANs solved this with mDNS, using Avahi on Linux. It resolves addresses that end in .local. Instead of asking a central DNS server “who is thing.local?”, a machine sends a multicast query on the local network: “who has thing.local?” The device that owns the name answers. This is why your Linux box named spock and usually be reached as spock.local on your LAN.

There are limits. mDNS is link-local; it is meant for the local LAN, not the whole Internet and shouldn’t route across subnets. Each device is supposed to publish its own name. That works fine when the device cooperates. But what about devices that do not publish mDNS? Or little embedded things that barely even have an IP address?

That is where I wanted the best of both worlds: keep a small authoritative /etc/hosts file on one Linux box, but publish selected entries onto the LAN using mDNS.

Continue reading “Linux Fu: The Local Phonebook” →