Secure with rootwrap¶

Rootwrap allows unprivileged users to safely run Compute actions as the root user. Compute previously used sudo for this purpose, but this was difficult to maintain, and did not allow advanced filters. The rootwrap command replaces sudo for Compute.

To use rootwrap, prefix the Compute command with nova-rootwrap. For example:

$ sudo nova-rootwrap /etc/nova/rootwrap.conf command

A generic sudoers entry lets the Compute user run nova-rootwrap as root. The nova-rootwrap code looks for filter definition directories in its configuration file, and loads command filters from them. It then checks if the command requested by Compute matches one of those filters and, if so, executes the command (as root). If no filter matches, it denies the request.

Rootwrap is fully controlled by the root user. The root user owns the sudoers entry which allows Compute to run a specific rootwrap executable as root, and only with a specific configuration file (which should also be owned by root). The nova-rootwrap command imports the Python modules it needs from a cleaned, system-default PYTHONPATH. The root-owned configuration file points to root-owned filter definition directories, which contain root-owned filters definition files. This chain ensures that the Compute user itself is not in control of the configuration or modules used by the nova-rootwrap executable.

Rootwrap is configured using the rootwrap.conf file. Because it’s in the trusted security path, it must be owned and writable by only the root user. The file’s location is specified in both the sudoers entry and in the nova.conf configuration file with the rootwrap_config=entry parameter.

The rootwrap.conf file uses an INI file format with these sections and parameters:

If the root wrapper is not performing correctly, you can add a workaround option into the nova.conf configuration file. This workaround re-configures the root wrapper configuration to fall back to running commands as sudo, and is a Kilo release feature.

Including this workaround in your configuration file safeguards your environment from issues that can impair root wrapper performance. Tool changes that have impacted Python Build Reasonableness (PBR) for example, are a known issue that affects root wrapper performance.

To set up this workaround, configure the disable_rootwrap option in the [workaround] section of the nova.conf configuration file.

The filters definition files contain lists of filters that rootwrap will use to allow or deny a specific command. They are generally suffixed by .filters . Since they are in the trusted security path, they need to be owned and writable only by the root user. Their location is specified in the rootwrap.conf file.

Filter definition files use an INI file format with a [Filters] section and several lines, each with a unique parameter name, which should be different for each filter you define: