Freshmeat page: http://freshmeat.net/projects/kchuid/
kchuid is an experimental Linux kernel module that allows you to change the UID/GID/CAPS of a running process (by PID). Think of it as providing a setuid() system call that also has a pid_t argument. But it can do more now: It can alter the working directory and "root" of another process, so it's just about ready for replacing /bin/login. This is the first step in a full authentication system, and further, a full Unixish system devoid of setuid binaries/scripts.
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