linux

613 Articles

Gaming Mouse Becomes Digital Camera

May 16, 2022 by 15 Comments

Ever since the world decided to transition from mechanical ball mice to optical mice, we have been blessed with computer pointing devices that don’t need regular cleaning and have much better performance than their ancestors. They do this by using what is essentially a tiny digital camera to monitor changes in motion. As we’ve seen before, it is possible to convert this mechanism into an actual camera, but until now we haven’t seen something like this on a high-performance mouse designed for FPS gaming.

For this project [Ankit] is disassembling the Logitech G402, a popular gaming mouse with up to 4000 dpi. Normally this is processed internally in the mouse to translate movement into cursor motion, but this mouse conveniently has a familiar STM32 processor with an SPI interface already broken out on the PCB that could be quickly connected to in order to gather image data. [Ankit] created a custom USB vendor-specific endpoint and wrote a Linux kernel module to parse the data into a custom GUI program that can display the image captured by the mouse sensor on-screen.

It’s probably best to not attempt this project if you plan to re-use the mouse, as the custom firmware appears to render the mouse useless as an actual mouse. But as a proof-of-concept project this high-performance mouse does work fairly well as a camera, albeit with a very low resolution by modern digital camera standards. It is much improved on older mouse-camera builds we’ve seen, though, thanks to the high performance sensors in gaming mice.

Linux Fu: The Infinite Serial Port

May 3, 2022 by 23 Comments

Ok, the title is a bit misleading. Like most things in life, it really isn’t infinite. But I’m going to show you how you can use a very interesting Linux feature to turn one serial port from a microcontroller into a bunch of virtual ports. In theory, you could create over 200 ports, but the reality is you will probably want to stick with fewer.

The feature in question is what’s known as pseudoterminal or sometimes a pty or pts. These special files were made to feed data to programs that expect to accept data from a terminal. The files provide two faces. To the client, it looks like any other terminal device. To the creator, though, it is just another file. What you write to that file goes to the fake terminal and you can read anything that is sent from the program connected to the terminal. You use these all the time, probably, without realizing it since running a shell under X Windows, for example, doesn’t attach to a real terminal, after all.

You could, of course, do the same trick with a composite USB device, assuming you have one. Also assuming you can find a working driver and get it working. However, many microcontrollers have a serial port — even one with a USB converter built-in — but fewer have full-blown USB hardware. Even the ones that do are often at odds with strange drivers on the PC side. Serial ports work and work well even on the simplest microcontrollers.

The Plan

The plan is simple enough. A Linux program listens to a real serial port and watches for special character sequences in the data stream. Those sequences will allow you to switch data so that the data stream will go to a particular terminal. Data coming back from the terminals will go to the real serial port after sending a sequence that identifies its source.

Continue reading “Linux Fu: The Infinite Serial Port” →

This Week In Security: Android And Linux, VirusTotal, More Psychic Signatures

April 29, 2022 by 10 Comments

To start our week of vulnerabilities in everything, there’s a potentially big vulnerability in Android handsets, but it’s Apple’s fault. OK, maybe that’s a little harsh — Apple released the code to their Apple Lossless Audio Codec (ALAC) back in 2011 under the Apache License. This code was picked up and shipped as part of the driver stack for multiple devices by various vendors, including Qualcomm and MediaTek. The problem is that the Apple code was terrible, one researcher calling it a “walking colander” of security problems.

Apple has fixed their code internally over the years, but never pushed those updates to the public code-base. It’s a fire-and-forget source release, and that can cause problems like this. The fact that ALAC was released under a permissive license may contribute to the problem. Someone (in addition to Apple) likely found and fixed the security problems, but the permissive license doesn’t require sharing those fixes with a broader community. It’s worth pondering whether a Copyleft license like the GPL would have gotten a fix distributed years ago.

Regardless, CVE-2021-0674 and CVE-2021-0675 were fixed in both Qualcomm and MediaTek’s December 2021 security updates. These vulnerabilities are triggered by malicious audio files, and can result in RCE. An app could use this trick to escape the sandbox and escalate privileges. This sort of flaw has been used by actors like the NSO group to compromise devices via messaging apps. Continue reading “This Week In Security: Android And Linux, VirusTotal, More Psychic Signatures” →

A Real GPU On The Raspberry Pi — Barely.

April 28, 2022 by 36 Comments

[Jeff Geerling] saw the Raspberry Pi Compute Module 4 and its exposed PCI-Express 1x connection, and just naturally wondered whether he could plug a GPU into that slot and get it to work. It didn’t. There were a few reasons why, such as the limited Base Address Register space, and drivers that just weren’t written for ARM hardware. A bit of help from the Raspberry Pi software engineers and other Linux kernel hackers and those issues were fixed, albeit with a big hurdle in the CPU. The Broadcom chip in the Pi 4, the BCM2711, has a broken PCIe implementation.

There has finally been a breakthrough — Thanks to the dedicated community that has sprung up around this topic, a set of kernel patches manage to work around the hardware issues. It’s now possible to run a Radeon HD 5000/6000/7000 card on the Raspberry Pi 4 Compute Module. There are still glitches, and the Kernel patches to make this work will likely never land upstream. That said, It’s possible to run a desktop environment on the Radeon GPU on a Pi, and even a few simple benchmarks. The results… aren’t particularly inspiring, but that wasn’t really ever the point. You may be asking what real-world use is for a full-size GPU on the Pi. Sure, maybe crypto-mining or emulation, or being able to run more monitors for digital signage. More than that, it might help ensure the next Pi has a working PCIe implementation. But like many things we cover here, the real reason is that it’s a challenge that a group of enthusiasts couldn’t leave alone.

Continue reading “A Real GPU On The Raspberry Pi — Barely.” →

SSH Is Magic, But Tunnels Are Even Better

April 24, 2022 by 17 Comments

Once upon a time, I was doing on-site support for a hardware install at a hotel a few years ago. The remote tech’s remote desktop software didn’t want to play with my Linux laptop, so he couldn’t get into the switch he needed to configure, to make the install work. I asked if it had an SSH port he could use, were he were in the room with me. Of course it did, but that didn’t do him much good. I ran a reverse SSH tunnel out to my public server, and pointed it at the switch on the local side. I convinced him to SSH to my server on the given port, and he was magically connected to his switch. He was literally in awe of that trick, and demanded to know how it could be done. SSH is magical, but tunneling traffic over SSH is straight-up wizardry. [Shawn Powers] agrees, and decided to help the rest of us understand the process.
Continue reading “SSH Is Magic, But Tunnels Are Even Better” →

Meet The RouterPi, A Compute Module 4 Based GbE Router

April 22, 2022 by 26 Comments

[Zak Kemble] likes to build things, and for several years has been pining over various Raspberry Pi products with an eye on putting them into service as a router. Sadly, none of them so far provided what he was looking for with regard to the raw throughput of the Gigabit Ethernet ports. His hopes were renewed when the Compute Module 4 came on scene, and [Zak] set out to turn the CM4 module into a full Gigabit Ethernet router. The project is documented on his excellent website, and sources are provided via a link to GitHub.

A view underneath shows off the RTC, power supply, and more.

Of course the Compute Module 4 is just a module- it’s designed to be built into another product, and this is one of the many things differentiating it from a traditional Raspberry Pi. [Zak] designed a simple two layer PCB that breaks out the CM4’s main features. But a router with just one Ethernet port, even if it’s GbE, isn’t really a router. [Zak] added a Realtek RTL8111HS GbE controller to the PCIe bus, ensuring that he’d be able to get the full bandwidth of the device.

The list of fancy addons is fairly long, but it includes such neat hacks as the ability to power other network devices by passing through the 12 V power supply, having a poweroff button and a hard reset button, and even including an environmental sensor (although he doesn’t go into why… but why not, right?).

Testing the RouterPi uncovered some performance bottlenecks that were solved with some clever tweaks to the software that assigned different ports an tasks to different CPU cores. Overall, it’s a great looking device and has been successfully server [Zak] as a router, a DNS resolver, and more- what more can you ask for from an experimental project?

This CM4 based project is a wonderful contrast to Cisco’s first network product, which in itself was innovative at the the time, but definitely didn’t have Gigabit Ethernet. Thanks to [Adrian] for the tip!

Linux Fu: An Odd Use For Fork()

April 21, 2022 by 46 Comments

If you are a Star Trek fan, you’ll probably remember the phrase “You have to learn why things work on a starship.” The truth is, in most episodes, knowing how to override another ship’s console or make gunpowder didn’t come in very handy, but boy when it did, it really saved the day. Linux is a lot like that. There are a few things you probably don’t need to know very often, but when you do need to know, it makes a huge difference. In this particular post, I want to look at an odd use of the fork system call. For many purposes, you’ll never need to know this particular irregular use. But when you need it, you are really going to need it.

This is actually based on an old client of mine who used Unix to run a massive and very critical report every day.  The report had a lot of math since they were trying to optimize something and then generate a lot of reports. In those days, the output of the report was on old green-bar paper on a line printer. The problem was that the report took something like 14 hours to run including the printouts. If someone discovered something wrong, there was no time to run the report again because the next day’s report would have to start before the second run would finish.

The client had a bunch of Windows programmers and — at that time — there wasn’t anything really analogous to a real fork call in Windows. I looked at the code and realized that probably most of the code was spending time waiting to print the output. The computer had multiple CPUs and there were multiple printers, but that one program was hanging on the one printer. There was a lot of data, so writing it to a database and then running different reports against it wasn’t a great option. The answer was to use the power of fork. With a change in the code that took less than 30 minutes, the report ran in five hours. They were very pleased.

So how did I do it? The answer lies in how fork works. Just about every time you see a fork, you see some sort of exec call to start a new program. So if you think about fork at all, you probably think it is part of how you start a new program and, most of the time, that’s true. Continue reading “Linux Fu: An Odd Use For Fork()” →