The device in question is a Samsung J4, the model was released in May 2018, and the device was purchased and activated in early 2019.
The device comes with Android 8.0, consists of a standard ARM processor with 4 cores, its short-term memory is 2 GB wide and its buffer memory is 16 GB high, its long-term memory is cloud-based and is compatible with Google and Facebook and is used for its most important functions. services, slow communication with Gmail, fast communication with Whatsapp and Google Drive, and long-term storage of the camera with Google Photos.
The patient started coming to consultations in November last year, the symptoms described were insufficient space errors and the constant deletion of files assisted by the operating system, a MicroSD card was prescribed. But two months later, the patient returned again, the problems persisted. On inspection, the SD card remains unused, apparently the operating system lacked automatic support. Furthermore, it was impossible to manually configure additional storage for any application, so the patient received training on how to clean up their most important sources of disk space consumption, WhatsApp videos.
The patient arrived in critical condition today, the phone was still working, a WhatsApp call was active in the background, but the screen was locked and the usual pattern password was not working. After some attempts made by the owner, the screen was unlocked again. It was also observed that the battery was running low.
A few minutes after the incident, the phone locked again, this time the user was unable to unlock it, they tried unsuccessfully to remove the battery, tried to generate a "Forgot your password" alert, but there seemed to be no protection against the brutal forces, at User was allowed to try as many combinations as he wanted. Google Device Finder was used to lock the phone, but there was no option to remove the pattern. Ultimately, the best course of action was considered to be to erase persistent phone storage and reinstall its operating system.
The patient is now receiving therapy to reinstall all their old applications and settings. A phone backup was offered but declined to avoid reinstalling old problems and prioritizing disk space.
My prevailing theory is that low disk space and low battery conditions triggered a chain reaction of failures, at some point an error was triggered by a non-atomic write that was interrupted by a kernel initiated crash due to low memory or reduced processing power initiated by low battery, most likely a combination of these two.
The mechanism of action of such error possibly consisted of:
- An overwrite of the pattern password.
- An overwrite of any of the binaries involved in decrypting and unlocking the device. In this case, the error chain would have degraded the error message by restricting it to a narrow, state-based error reporting API presented by the pattern unlock screen.
Some researchers show that this is a common occurrence, however, it is not known if the cause of death is common, or if there is a singular manifestation of various causes of death.
The question here is, how did the system crash so fatally as to allow the operating system to be unrecoverable even after rebooting?