def _inject_key_into_fs(key, fs, execute=None):
    """Add the given public ssh key to root's authorized_keys.

    key is an ssh key string.
    fs is the path to the base of the filesystem into which to inject the key.
    """
    sshdir = os.path.join(fs, 'root', '.ssh')
    utils.execute('mkdir', '-p', sshdir, run_as_root=True)
    utils.execute('chown', 'root', sshdir, run_as_root=True)
    utils.execute('chmod', '700', sshdir, run_as_root=True)
    keyfile = os.path.join(sshdir, 'authorized_keys')
    key_data = [
        '\n',
        '# The following ssh key was injected by Nova',
        '\n',
        key.strip(),
        '\n',
    ]
    utils.execute('tee', '-a', keyfile,
                  process_input=''.join(key_data), run_as_root=True)
The software uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the software does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.