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414 lines
13 KiB
HTML
414 lines
13 KiB
HTML
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<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE html>
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<html xmlns="http://www.w3.org/1999/xhtml">
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<body>
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<h1>TLS x509 certificate setup</h1>
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<ul id="toc"></ul>
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<h2>
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<a id="Remote_PKI">Public Key Infrastructure set up</a>
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</h2>
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<p>
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If you are unsure how to create TLS certificates, skip to the
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next section.
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</p>
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<table class="top_table">
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<tr>
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<th> Location </th>
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<th> Machine </th>
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<th> Description </th>
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<th> Required fields </th>
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</tr>
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<tr>
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<td>
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<code>/etc/pki/CA/cacert.pem</code>
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</td>
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<td> Installed on the client and server </td>
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<td> CA's certificate (<a href="#Remote_TLS_CA">more info</a>)</td>
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<td> n/a </td>
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</tr>
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<tr>
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<td>
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<code>$HOME/.pki/cacert.pem</code>
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</td>
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<td> Installed on the client </td>
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<td> CA's certificate (<a href="#Remote_TLS_CA">more info</a>)</td>
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<td> n/a </td>
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</tr>
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<tr>
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<td>
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<code>/etc/pki/libvirt/private/serverkey.pem</code>
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</td>
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<td> Installed on the server </td>
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<td> Server's private key (<a href="#Remote_TLS_server_certificates">more info</a>)</td>
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<td> n/a </td>
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</tr>
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<tr>
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<td>
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<code>/etc/pki/libvirt/servercert.pem</code>
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</td>
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<td> Installed on the server </td>
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<td> Server's certificate signed by the CA.
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(<a href="#Remote_TLS_server_certificates">more info</a>) </td>
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<td> CommonName (CN) must be the hostname of the server as it
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is seen by clients. All hostname and IP address variants that might
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be used to reach the server should be listed in Subject Alt Name
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fields.</td>
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</tr>
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<tr>
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<td>
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<code>/etc/pki/libvirt/private/clientkey.pem</code>
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</td>
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<td> Installed on the client </td>
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<td> Client's private key. (<a href="#Remote_TLS_client_certificates">more info</a>) </td>
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<td> n/a </td>
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</tr>
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<tr>
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<td>
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<code>/etc/pki/libvirt/clientcert.pem</code>
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</td>
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<td> Installed on the client </td>
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<td> Client's certificate signed by the CA
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(<a href="#Remote_TLS_client_certificates">more info</a>) </td>
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<td> Distinguished Name (DN) can be checked against an access
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control list (<code>tls_allowed_dn_list</code>).
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</td>
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</tr>
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<tr>
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<td>
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<code>$HOME/.pki/libvirt/clientkey.pem</code>
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</td>
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<td> Installed on the client </td>
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<td> Client's private key. (<a href="#Remote_TLS_client_certificates">more info</a>) </td>
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<td> n/a </td>
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</tr>
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<tr>
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<td>
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<code>$HOME/.pki/libvirt/clientcert.pem</code>
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</td>
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<td> Installed on the client </td>
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<td> Client's certificate signed by the CA
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(<a href="#Remote_TLS_client_certificates">more info</a>) </td>
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<td> Distinguished Name (DN) can be checked against an access
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control list (<code>tls_allowed_dn_list</code>).
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</td>
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</tr>
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</table>
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<p>
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If 'pkipath' is specified in URI, then all the client
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certificates must be found in the path specified, otherwise the
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connection will fail with a fatal error. If 'pkipath' is not
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specified:
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</p>
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<ul>
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<li> For a non-root user, libvirt tries to find the certificates
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in $HOME/.pki/libvirt first. If the required CA certificate cannot
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be found, then the global default location
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(/etc/pki/CA/cacert.pem) will be used.
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Likewise, if either the client certificate
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or the client key cannot be found, then the global default
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locations (/etc/pki/libvirt/clientcert.pem,
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/etc/pki/libvirt/private/clientkey.pem) will be used.
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</li>
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<li> For the root user, the global default locations will always be used.</li>
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</ul>
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<h2>
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<a id="Remote_TLS_background">Background to TLS certificates</a>
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</h2>
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<p>
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Libvirt supports TLS certificates for verifying the identity
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of the server and clients. There are two distinct checks involved:
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</p>
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<ul>
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<li> The client should know that it is connecting to the right
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server. Checking done by client by matching the certificate that
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the server sends to the server's hostname. May be disabled by adding
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<code>?no_verify=1</code> to the
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<a href="#Remote_URI_parameters">remote URI</a>.
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</li>
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<li> The server should know that only permitted clients are
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connecting. This can be done based on client's IP address, or on
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client's IP address and client's certificate. Checking done by the
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server. May be enabled and disabled in the <a href="#Remote_libvirtd_configuration">libvirtd.conf file</a>.
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</li>
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</ul>
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<p>
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For full certificate checking you will need to have certificates
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issued by a recognised <a href="http://en.wikipedia.org/wiki/Certificate_authority">Certificate
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Authority (CA)</a> for your server(s) and all clients. To avoid the
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expense of getting certificates from a commercial CA, you can set up
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your own CA and tell your server(s) and clients to trust certificates
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issues by your own CA. Follow the instructions in the next section.
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</p>
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<p>
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Be aware that the <a href="#Remote_libvirtd_configuration">default
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configuration for libvirtd</a> allows any client to connect provided
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they have a valid certificate issued by the CA for their own IP
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address. You may want to change this to make it less (or more)
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permissive, depending on your needs.
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</p>
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<h2>
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<a id="Remote_TLS_CA">Setting up a Certificate Authority (CA)</a>
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</h2>
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<p>
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You will need the <a href="http://www.gnu.org/software/gnutls/manual/html_node/Invoking-certtool.html">GnuTLS
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certtool program documented here</a>. In Fedora, it is in the
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<code>gnutls-utils</code> package.
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</p>
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<p>
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Create a private key for your CA:
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</p>
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<pre>
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certtool --generate-privkey > cakey.pem
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</pre>
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<p>
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and self-sign it by creating a file with the
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signature details called
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<code>ca.info</code> containing:
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</p>
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<pre>
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cn = <i>Name of your organization</i>
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ca
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cert_signing_key
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</pre>
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<pre>
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certtool --generate-self-signed --load-privkey cakey.pem \
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--template ca.info --outfile cacert.pem
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</pre>
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<p>
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(You can delete <code>ca.info</code> file now if you
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want).
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</p>
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<p>
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Now you have two files which matter:
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</p>
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<ul>
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<li><code>cakey.pem</code> - Your CA's private key (keep this very secret!)
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</li>
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<li><code>cacert.pem</code> - Your CA's certificate (this is public).
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</li>
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</ul>
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<p><code>cacert.pem</code> has to be installed on clients and
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server(s) to let them know that they can trust certificates issued by
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your CA.
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</p>
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<p>
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The normal installation directory for <code>cacert.pem</code>
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is <code>/etc/pki/CA/cacert.pem</code> on all clients and servers.
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</p>
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<p>
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To see the contents of this file, do:
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</p>
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<pre><b>certtool -i --infile cacert.pem</b>
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X.509 certificate info:
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Version: 3
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Serial Number (hex): 00
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Subject: CN=Libvirt Project
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Issuer: CN=Libvirt Project
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Signature Algorithm: RSA-SHA
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Validity:
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Not Before: Mon Jun 18 16:22:18 2007
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Not After: Tue Jun 17 16:22:18 2008
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<i>[etc]</i>
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</pre>
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<p>
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This is all that is required to set up your CA. Keep the CA's private
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key carefully as you will need it when you come to issue certificates
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for your clients and servers.
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</p>
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<h2>
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<a id="Remote_TLS_server_certificates">Issuing server certificates</a>
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</h2>
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<p>
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For each server (libvirtd) you need to issue a certificate
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containing one or more hostnames and/or IP addresses.
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Historically the CommonName (CN) field would contain the
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hostname of the server and would match the hostname used
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in the URI that clients pass to libvirt. In most TLS implementations
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the CN field is considered legacy data. The preferential mechanism
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is to use Subject Alt Name (SAN) extension fields to validate
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against. In the future use of the CN field for validation may be
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discontinued entirely, so it is strongly recommended to
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include the SAN fields.
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</p>
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<p>
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In the example below, clients will be connecting to the
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server using a <a href="#Remote_URI_reference">URI</a> of
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<code>qemu://compute1.libvirt.org/system</code>, so the CN
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must be "<code>compute1.libvirt.org</code>".
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</p>
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<p>
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Make a private key for the server:
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</p>
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<pre>
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certtool --generate-privkey > serverkey.pem
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</pre>
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<p>
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and sign that key with the CA's private key by first
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creating a template file called <code>server.info</code>.
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The template file will contain a number of fields to define
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the server as follows:
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</p>
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<pre>
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organization = <i>Name of your organization</i>
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cn = compute1.libvirt.org
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dns_name = compute1
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dns_name = compute1.libvirt.org
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ip_address = 10.0.0.74
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ip_address = 192.168.1.24
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ip_address = 2001:cafe::74
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ip_address = fe20::24
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tls_www_server
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encryption_key
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signing_key
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</pre>
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<p>
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The 'cn' field should refer to the fully qualified public
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hostname of the server. For the SAN extension data, there
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must also be one or more 'dns_name' fields that contain all
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possible hostnames that can be reasonably used by clients
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to reach the server, both with and without domain name
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qualifiers. If clients are likely to connect to the server
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by IP address, then one or more 'ip_address' fields should
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also be added.
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</p>
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<p>
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Use the template file as input to a <code>certtool</code>
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command to sign the server certificate:
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</p>
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<pre>
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certtool --generate-certificate --load-privkey serverkey.pem \
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--load-ca-certificate cacert.pem --load-ca-privkey cakey.pem \
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--template server.info --outfile servercert.pem
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</pre>
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<p>
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This gives two files:
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</p>
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<ul>
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<li><code>serverkey.pem</code> - The server's private key.
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</li>
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<li><code>servercert.pem</code> - The server's public key.
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</li>
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</ul>
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<p>
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We can examine this certificate and its signature:
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</p>
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<pre><b>certtool -i --infile servercert.pem</b>
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X.509 certificate info:
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Version: 3
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Serial Number (hex): 00
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Subject: O=Libvirt Project,CN=compute1.libvirt.org
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Issuer: CN=Libvirt Project
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Signature Algorithm: RSA-SHA
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Validity:
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Not Before: Wed Oct 04 09:09:44 UTC 2017
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Not After: Thu Oct 04 09:09:44 UTC 2018
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Extensions:
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Basic Constraints (critical):
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Certificate Authority (CA): FALSE
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Subject Alternative Name (not critical):
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DNSname: compute1
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DNSname: compute1.libvirt.org
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IPAddress: 10.0.0.74
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IPAddress: 192.168.1.24
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IPAddress: 2001:cafe::74
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IPAddress: fe20::24
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</pre>
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<p>
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Note the "Issuer" CN is "Libvirt Project" (the CA) and
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the "Subject" CN is "compute1.libvirt.org" (the server).
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Notice that the hostname listed in the CN must also
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be duplicated as a DNSname entry
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</p>
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<p>
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Finally we have two files to install:
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</p>
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<ul>
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<li><code>serverkey.pem</code> is
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the server's private key which should be copied to the
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server <i>only</i> as
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<code>/etc/pki/libvirt/private/serverkey.pem</code>.
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</li>
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<li><code>servercert.pem</code> is the server's certificate
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which can be installed on the server as
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<code>/etc/pki/libvirt/servercert.pem</code>.
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</li>
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</ul>
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<h2>
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<a id="Remote_TLS_client_certificates">Issuing client certificates</a>
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</h2>
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<p>
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For each client (ie. any program linked with libvirt, such as
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<a href="http://virt-manager.org/">virt-manager</a>)
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you need to issue a certificate with the X.509 Distinguished Name (DN)
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set to a suitable name. You can decide this on a company / organisation
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policy. For example:
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</p>
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<pre>
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C=GB,ST=London,L=London,O=Libvirt Project,CN=<i>name_of_client</i>
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||
|
|
</pre>
|
||
|
|
<p>
|
||
|
|
The process is the same as for
|
||
|
|
<a href="#Remote_TLS_server_certificates">setting up the
|
||
|
|
server certificate</a> so here we just briefly cover the
|
||
|
|
steps.
|
||
|
|
</p>
|
||
|
|
<ol>
|
||
|
|
<li>
|
||
|
|
Make a private key:
|
||
|
|
<pre>
|
||
|
|
certtool --generate-privkey > clientkey.pem
|
||
|
|
</pre>
|
||
|
|
</li>
|
||
|
|
<li>
|
||
|
|
Act as CA and sign the certificate. Create client.info containing:
|
||
|
|
<pre>
|
||
|
|
country = GB
|
||
|
|
state = London
|
||
|
|
locality = London
|
||
|
|
organization = Libvirt Project
|
||
|
|
cn = client1
|
||
|
|
tls_www_client
|
||
|
|
encryption_key
|
||
|
|
signing_key
|
||
|
|
</pre>
|
||
|
|
and sign by doing:
|
||
|
|
<pre>
|
||
|
|
certtool --generate-certificate --load-privkey clientkey.pem \
|
||
|
|
--load-ca-certificate cacert.pem --load-ca-privkey cakey.pem \
|
||
|
|
--template client.info --outfile clientcert.pem
|
||
|
|
</pre>
|
||
|
|
</li>
|
||
|
|
<li>
|
||
|
|
Install the certificates on the client machine:
|
||
|
|
<pre>
|
||
|
|
cp clientkey.pem /etc/pki/libvirt/private/clientkey.pem
|
||
|
|
cp clientcert.pem /etc/pki/libvirt/clientcert.pem
|
||
|
|
</pre>
|
||
|
|
</li>
|
||
|
|
</ol>
|
||
|
|
<h2>
|
||
|
|
<a id="Remote_TLS_troubleshooting">Troubleshooting TLS certificate problems</a>
|
||
|
|
</h2>
|
||
|
|
<dl>
|
||
|
|
<dt> failed to verify client's certificate </dt>
|
||
|
|
<dd>
|
||
|
|
<p>
|
||
|
|
On the server side, run the libvirtd server with
|
||
|
|
the '--listen' and '--verbose' options while the
|
||
|
|
client is connecting. The verbose log messages should
|
||
|
|
tell you enough to diagnose the problem.
|
||
|
|
</p>
|
||
|
|
</dd>
|
||
|
|
</dl>
|
||
|
|
<p> You can use the virt-pki-validate shell script
|
||
|
|
to analyze the setup on the client or server machines, preferably as root.
|
||
|
|
It will try to point out the possible problems and provide solutions to
|
||
|
|
fix the set up up to a point where you have secure remote access.</p>
|
||
|
|
</body>
|
||
|
|
</html>
|