> [*] Leak in process[-] add_key: Disk quota exceeded

I'm taking an educated guess, try:

    sysctl user.max_user_namespaces

I'm guessing it's "0", which means user namespaces are disabled on your system. This would be an effective mitigation against most of these namespace exploits. If you type "unshare -rT" you'll likely get a "No space left on device" or something instead of a faux-root namespace shell.