Getting Root On Linux Amplifier Adds New Inputs

We remember when getting Linux on your average desktop computer was a tricky enough endeavor that only those with the most luxurious of graybeards would even attempt it. A “Linux box” in those heady days was more than likely an outdated machine salvaged from the dumpster, side panel forever removed, cranking away in a basement or garage. Fast forward today, and Linux is literally everywhere: from smartphones and luxury cars, to TVs and refrigerators. Ironically it’s still not on most desktop computers, but that’s a discussion for another time.

So when [Michael Nothhard] sent in the fascinating account of how he hacked his Linux-powered Bluesound Powernode N150 amplifier to unlock more inputs, the least surprising element was that there was a “smart amplifier” out there running the free and open source operating system. What piqued our interest was that he was able to bust his way in with relative ease and enable some impressive new capabilities that the manufacturer would probably have rather been kept under wraps.

Configuring the CM6206’s audio settings.

[Michael] explains that the N150 has a USB port on the back side of it, and that officially, it only works with mass storage devices and a handful of approved peripherals such as a Bluetooth dongle. But as he was hoping to connect some more devices to the input-limited amplifier, he wondered if he could get a USB audio adapter recognized by the OS. After using a known exploit to get root access, he started poking around at the underlying Linux system to see what kind of trickery the developers had done.

Based on a fairly common C-Media CM6206 chipset, the StarTech 7.1 USB audio adapter was picked up by the kernel without an issue. But to actually get it working with the amplifier’s stock software, he then needed to add a new <capture> entry to the system’s sovi_info.xml configuration file and make some changes to its default ALSA settings. With the appropriate files modified, the new USB audio input device popped up under the official Bluesound smartphone application.

At the end of the write-up [Michael] notes that you’ll need to jump through a few additional hoops to make sure that an upstream firmware update doesn’t wipe all your hard work. Luckily it sounds like backing up the configuration and returning it to the newly flashed Powernode is easy enough. We’ve certainly seen more elaborate methods of gaining control of one’s sound system over the years.

26 thoughts on “Getting Root On Linux Amplifier Adds New Inputs

    1. The GPLv2 does not prevent tivoization. The company is free to lock down their device as much as they want, as long as they release the source for any modifications they make to GPL software.

      Unfortunate, but this is probably part of the reason why Linux is so common in commercial products to begin with. I suspect that we’d need actual legislation to force companies to open up their devices to custom firmware.

      1. Yes criminals should be free to replace the firmware in their ankle brackets. And people should feel free to modify their vehicles for maximum smoke output. And get rid of the safety interlocks, because you are perfect and never make mistakes. And hey let’s sell these modified devices to unwitting people. Oh sorry about your severed thumb.

        1. Criminals don’t own their ankle bracelets, so of course they shouldn’t be able to replace it – cryptography can easily make it sure that the legitimate owner can replace the firmware with a provided key. People who modify their vehicles for maximum smoke output should be cited by the police and fail their road safety inspection.

        2. FFS, you can detune a *purely analog* automobile for “maximum smoke output”, and most safety interlock defeats happen at a hardware level at the sensors. That severed thumb happened because some guy on the shop floor zip-tied the machine cage closure detection switch in the “closed” position; there was no firmware tinkering involved.

          If there’s a behavior you don’t want to see happening, ban *the behavior itself*, not the freedoms that get abused in the process.

          1. The Brits have actual, honest-to-God knife control, I shit you not:


            “In Britain, it is currently illegal to carry a knife longer than three inches in public ‘without good reason’ and illegally carrying a knife can be punished with up to four years in prison and an ‘unlimited fine.’ Self-defense is not listed among the examples of ‘good reasons to carry a knife.’”

            They did this because gun control was such a smashing success, of course.

  1. Getting Linux installed – today – has become somewhat easier (I do have a grey beard though, partially thanks to Linux).

    USING Linux however … now … that’s a different beard … er …

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