Making Root Unprivileged
This article demonstrates taking a stock Fedora 10 system and changing the privilege system from one where one userid (root's) automatically imparts privilege, to one where only file capabilities determine the privilege available to a caller. The root user turns from a privileged user to simply the userid that happens to own most system resources.
You can remove the privileged root user for a whole system. In this experiment, quite a bit of work still needs to be done to make that practical, say, for a whole distribution. Most important, legacy code makes assumptions based on userids. Setting up partially privileged users make system administration convenient, while making the privilege separation useful will be an interesting project.
In the meantime, you can exploit the per-process nature of the unprivileged-root mode. This article shows how to remove the privileged root user from any legacy software that always is intended to be unprivileged. You also should design new services to be capability-aware so that they too can run without a privileged root. Doing so can greatly reduce the impact of any bugs or exploits.
opensshd_caps.patch and upstart.patch are available at ftp.linuxjournal.com/pub/lj/listings/issue184/10249.tgz.
Serge Hallyn does Linux kernel and security coding with the IBM Linux Technology Center, mostly working with containers, application migration, POSIX capabilities and SELinux.
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