I had been ignoring low memory on my android phone (Nexus 6P running copperhead OS) for some time.
OS suddenly crashed out of no where and started booting up infinitely. After forcing it to restart and entering the password for decryption, phone never finishes the boot procedure. Seems that due to zero or very less space, some error must be occurring, which doesn't let the OS finish the boot procedure.
It's my assumption that low memory could have been the issue, so trying to find a way to delete files and let OS have some space to boot up.
(1) Bootloader is locked. I can see "Device is LOCKED." at bootloader screen. So, unable to boot latest TWRP via
fastboot boot twrp.img. Receiving error
FAILED (remote: unlock device to use this command)
(2) ADB sideload option available in copperhead OS recovery doesn't allow any random update.zip. Tried to run an updater script but it fails. It seems that recovery is validating the package. Errors are
E: footer is wrong,
E: Signature verification failed,
E:error: 21 Installation aborted
(3) Tried to find some vulnerabilities which let bypass security features, but didn't find any except this which has been fixed in bootloader angler-03.79 being used.
(4) Phone is running an old android OS : 8.1.0 June 2018 AOSP build, and since then there could be security vulnerabilities being introduced. So are there any vulnerabilities or exploits which can be helpful here?