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Most of the links were broken by moving the article into kbase, but in this case we need to also fix the anchor names. Signed-off-by: Peter Krempa <pkrempa@redhat.com> Reviewed-by: Ján Tomko <jtomko@redhat.com>
331 lines
11 KiB
ReStructuredText
331 lines
11 KiB
ReStructuredText
==========================
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TLS x509 certificate setup
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==========================
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.. contents::
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Public Key Infrastructure set up
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--------------------------------
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If you are unsure how to create TLS certificates, skip to the next section.
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.. list-table::
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:header-rows: 1
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* - Location
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- Machine
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- Description
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- Required fields
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* - ``/etc/pki/CA/cacert.pem``
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- Installed on the client and server
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- CA's certificate
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- n/a
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* - ``$HOME/.pki/cacert.pem``
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- Installed on the client
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- CA's certificate
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- n/a
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* - ``/etc/pki/libvirt/private/serverkey.pem``
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- Installed on the server
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- Server's private key
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- n/a
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* - ``/etc/pki/libvirt/servercert.pem``
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- Installed on the server
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- Server's certificate signed by the CA
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- CommonName (CN) must be the hostname of the server as it is seen by
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clients. All hostname and IP address variants that might be used to
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reach the server should be listed in Subject Alt Name fields.
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* - ``/etc/pki/libvirt/private/clientkey.pem``
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- Installed on the client
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- Client's private key
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- n/a
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* - ``/etc/pki/libvirt/clientcert.pem``
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- Installed on the client
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- Client's certificate signed by the CA
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- Distinguished Name (DN) can be checked against an access control list
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(``tls_allowed_dn_list``).
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* - ``$HOME/.pki/libvirt/clientkey.pem``
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- Installed on the client
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- Client's private key
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- n/a
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* - ``$HOME/.pki/libvirt/clientcert.pem``
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- Installed on the client
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- Client's certificate signed by the CA
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(see `Issuing client certificates`_)
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- Distinguished Name (DN) can be checked against an access control list
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(``tls_allowed_dn_list``).
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If 'pkipath' is specified in URI, then all the client certificates must be found
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in the path specified, otherwise the connection will fail with a fatal error. If
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'pkipath' is not specified:
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- For a non-root user, libvirt tries to find the certificates in
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$HOME/.pki/libvirt first. If the required CA certificate cannot be found,
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then the global default location (/etc/pki/CA/cacert.pem) will be used.
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Likewise, if either the client certificate or the client key cannot be found,
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then the global default locations (/etc/pki/libvirt/clientcert.pem,
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/etc/pki/libvirt/private/clientkey.pem) will be used.
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- For the root user, the global default locations will always be used.
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Background to TLS certificates
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------------------------------
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Libvirt supports TLS certificates for verifying the identity of the server and
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clients. There are two distinct checks involved:
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- The client should know that it is connecting to the right server. Checking
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done by client by matching the certificate that the server sends to the
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server's hostname. May be disabled by adding ``?no_verify=1`` to the `remote
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URI <../uri.html#tls-transport>`__.
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- The server should know that only permitted clients are connecting. This can
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be done based on client's IP address, or on client's IP address and client's
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certificate. Checking done by the server. May be enabled and disabled in the
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`libvirtd.conf file <../remote.html#libvirtd-configuration-file>`__.
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For full certificate checking you will need to have certificates issued by a
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recognised `Certificate Authority
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(CA) <https://en.wikipedia.org/wiki/Certificate_authority>`__ for your server(s)
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and all clients. To avoid the expense of getting certificates from a commercial
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CA, you can set up your own CA and tell your server(s) and clients to trust
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certificates issues by your own CA. Follow the instructions in the next section.
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Be aware that the `default configuration for
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libvirtd <../remote.html#libvirtd-configuration-file>`__ allows any client to
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connect provided 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) permissive,
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depending on your needs.
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Setting up a Certificate Authority (CA)
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---------------------------------------
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You will need the `GnuTLS certtool program documented
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here <https://www.gnutls.org/manual/html_node/certtool-Invocation.html>`__. In
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Fedora, it is in the ``gnutls-utils`` package.
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Create a private key for your CA:
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::
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certtool --generate-privkey > cakey.pem
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and self-sign it by creating a file with the signature details called
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``ca.info`` containing:
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::
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cn = Name of your organization
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ca
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cert_signing_key
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::
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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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(You can delete ``ca.info`` file now if you want).
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Now you have two files which matter:
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- ``cakey.pem`` - Your CA's private key (keep this very secret!)
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- ``cacert.pem`` - Your CA's certificate (this is public).
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``cacert.pem`` has to be installed on clients and server(s) to let them know
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that they can trust certificates issued by your CA.
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The normal installation directory for ``cacert.pem`` is
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``/etc/pki/CA/cacert.pem`` on all clients and servers.
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To see the contents of this file, do:
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::
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certtool -i --infile cacert.pem
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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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[etc]
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This is all that is required to set up your CA. Keep the CA's private key
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carefully as you will need it when you come to issue certificates for your
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clients and servers.
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Issuing server certificates
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---------------------------
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For each server (libvirtd) you need to issue a certificate containing one or
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more hostnames and/or IP addresses. Historically the CommonName (CN) field would
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contain the hostname of the server and would match the hostname used in the URI
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that clients pass to libvirt. In most TLS implementations the CN field is
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considered legacy data. The preferential mechanism is to use Subject Alt Name
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(SAN) extension fields to validate against. In the future use of the CN field
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for validation may be discontinued entirely, so it is strongly recommended to
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include the SAN fields.
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In the example below, clients will be connecting to the server using a
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`URI <../uri.html#remote-uris>`__ of ``qemu://compute1.libvirt.org/system``, so the
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CN must be "``compute1.libvirt.org``".
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Make a private key for the server:
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::
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certtool --generate-privkey > serverkey.pem
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and sign that key with the CA's private key by first creating a template file
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called ``server.info``. The template file will contain a number of fields to
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define the server as follows:
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::
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organization = Name of your organization
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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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The 'cn' field should refer to the fully qualified public hostname of the
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server. For the SAN extension data, there must also be one or more 'dns_name'
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fields that contain all possible hostnames that can be reasonably used by
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clients to reach the server, both with and without domain name qualifiers. If
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clients are likely to connect to the server by IP address, then one or more
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'ip_address' fields should also be added.
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Use the template file as input to a ``certtool`` command to sign the server
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certificate:
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::
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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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This gives two files:
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- ``serverkey.pem`` - The server's private key.
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- ``servercert.pem`` - The server's public key.
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We can examine this certificate and its signature:
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::
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certtool -i --infile servercert.pem
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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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Note the "Issuer" CN is "Libvirt Project" (the CA) and the "Subject" CN is
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"compute1.libvirt.org" (the server). Notice that the hostname listed in the CN
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must also be duplicated as a DNSname entry
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Finally we have two files to install:
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- ``serverkey.pem`` is the server's private key which should be copied to the
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server *only* as ``/etc/pki/libvirt/private/serverkey.pem``.
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- ``servercert.pem`` is the server's certificate which can be installed on the
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server as ``/etc/pki/libvirt/servercert.pem``.
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Issuing client certificates
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---------------------------
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For each client (ie. any program linked with libvirt, such as
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`virt-manager <https://virt-manager.org/>`__) you need to issue a certificate
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with the X.509 Distinguished Name (DN) set to a suitable name. You can decide
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this on a company / organisation policy. For example:
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::
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C=GB,ST=London,L=London,O=Libvirt Project,CN=name_of_client
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The process is the same as for `Issuing server certificates`_ so here we just
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briefly cover the steps.
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#. Make a private key:
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::
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certtool --generate-privkey > clientkey.pem
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#. Act as CA and sign the certificate. Create client.info containing:
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::
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country = GB
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state = London
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locality = London
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organization = Libvirt Project
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cn = client1
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tls_www_client
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encryption_key
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signing_key
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and sign by doing:
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::
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certtool --generate-certificate --load-privkey clientkey.pem \
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--load-ca-certificate cacert.pem --load-ca-privkey cakey.pem \
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--template client.info --outfile clientcert.pem
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#. Install the certificates on the client machine:
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::
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cp clientkey.pem /etc/pki/libvirt/private/clientkey.pem
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cp clientcert.pem /etc/pki/libvirt/clientcert.pem
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Troubleshooting TLS certificate problems
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----------------------------------------
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failed to verify client's certificate
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On the server side, run the libvirtd server with the '--listen' and
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'--verbose' options while the client is connecting. The verbose log messages
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should tell you enough to diagnose the problem.
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You can use the virt-pki-validate shell script to analyze the setup on the
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client or server machines, preferably as root. It will try to point out the
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possible problems and provide solutions to fix the set up up to a point where
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you have secure remote access.
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