Using the “World’s Worst Fuzzer” To Find A Kernel Bug In The FiiO M6

This post was originally published on my personal blog.

Overview:

A few months ago, I was cleaning off my hardware workbench when I came across my FiiO M6, an Android-based “portable high-resolution lossless music player”. I originally purchased the device to aid in my language learning studies and dabble in the world of “hi-fi” audio. With both those phases of my life well in the past, the device seemed to make a perfect vulnerability research target. Coincidentally, I had also just watched through all of gamozolabs’s Android exploitation livestream, so I was feeling even more inspired to target an Android-based device.

Prior to this project, I had never looked for Android vulns and had no kernel VR/exploit dev experience. As such, quite a bit of reading, watching, and asking was involved to find even the trivial bug presented in this write-up. Should anyone more knowledgeable in these topics notice any inconsistencies or misunderstandings, please do not hesitate to reach out. While this post is primarily focused on the bug itself, I do plan to make a corresponding video to go more in-depth on the…