diff options
| -rw-r--r-- | qemu-doc.texi | 50 | ||||
| -rw-r--r-- | qemu.sasl | 54 |
2 files changed, 60 insertions, 44 deletions
diff --git a/qemu-doc.texi b/qemu-doc.texi index 794ab4a080..a4be7143b9 100644 --- a/qemu-doc.texi +++ b/qemu-doc.texi @@ -1732,37 +1732,45 @@ SASL service config /etc/sasl2/qemu.conf. If running QEMU as an unprivileged user, an environment variable SASL_CONF_PATH can be used to make it search alternate locations for the service config. -The default configuration might contain +If the TLS option is enabled for VNC, then it will provide session encryption, +otherwise the SASL mechanism will have to provide encryption. In the latter +case the list of possible plugins that can be used is drastically reduced. In +fact only the GSSAPI SASL mechanism provides an acceptable level of security +by modern standards. Previous versions of QEMU referred to the DIGEST-MD5 +mechanism, however, it has multiple serious flaws described in detail in +RFC 6331 and thus should never be used any more. The SCRAM-SHA-1 mechanism +provides a simple username/password auth facility similar to DIGEST-MD5, but +does not support session encryption, so can only be used in combination with +TLS. + +When not using TLS the recommended configuration is @example -mech_list: digest-md5 -sasldb_path: /etc/qemu/passwd.db +mech_list: gssapi +keytab: /etc/qemu/krb5.tab @end example -This says to use the 'Digest MD5' mechanism, which is similar to the HTTP -Digest-MD5 mechanism. The list of valid usernames & passwords is maintained -in the /etc/qemu/passwd.db file, and can be updated using the saslpasswd2 -command. While this mechanism is easy to configure and use, it is not -considered secure by modern standards, so only suitable for developers / -ad-hoc testing. +This says to use the 'GSSAPI' mechanism with the Kerberos v5 protocol, with +the server principal stored in /etc/qemu/krb5.tab. For this to work the +administrator of your KDC must generate a Kerberos principal for the server, +with a name of 'qemu/somehost.example.com@@EXAMPLE.COM' replacing +'somehost.example.com' with the fully qualified host name of the machine +running QEMU, and 'EXAMPLE.COM' with the Kerberos Realm. -A more serious deployment might use Kerberos, which is done with the 'gssapi' -mechanism +When using TLS, if username+password authentication is desired, then a +reasonable configuration is @example -mech_list: gssapi -keytab: /etc/qemu/krb5.tab +mech_list: scram-sha-1 +sasldb_path: /etc/qemu/passwd.db @end example -For this to work the administrator of your KDC must generate a Kerberos -principal for the server, with a name of 'qemu/somehost.example.com@@EXAMPLE.COM' -replacing 'somehost.example.com' with the fully qualified host name of the -machine running QEMU, and 'EXAMPLE.COM' with the Kerberos Realm. +The saslpasswd2 program can be used to populate the passwd.db file with +accounts. -Other configurations will be left as an exercise for the reader. It should -be noted that only Digest-MD5 and GSSAPI provides a SSF layer for data -encryption. For all other mechanisms, VNC should always be configured to -use TLS and x509 certificates to protect security credentials from snooping. +Other SASL configurations will be left as an exercise for the reader. Note that +all mechanisms except GSSAPI, should be combined with use of TLS to ensure a +secure data channel. @node gdb_usage @section GDB usage @@ -1,36 +1,44 @@ -# If you want to use the non-TLS socket, then you *must* include -# the GSSAPI or DIGEST-MD5 mechanisms, because they are the only -# ones that can offer session encryption as well as authentication. +# If you want to use VNC remotely without TLS, then you *must* +# pick a mechanism which provides session encryption as well +# as authentication. # -# If you're only using TLS, then you can turn on any mechanisms +# If you are only using TLS, then you can turn on any mechanisms # you like for authentication, because TLS provides the encryption # -# Default to a simple username+password mechanism -# NB digest-md5 is no longer considered secure by current standards -mech_list: digest-md5 +# If you are only using UNIX sockets then encryption is not +# required at all. +# +# NB, previously DIGEST-MD5 was set as the default mechanism for +# QEMU VNC. Per RFC 6331 this is vulnerable to many serious security +# flaws as should no longer be used. Thus GSSAPI is now the default. +# +# To use GSSAPI requires that a QEMU service principal is +# added to the Kerberos server for each host running QEMU. +# This principal needs to be exported to the keytab file listed below +mech_list: gssapi -# Before you can use GSSAPI, you need a service principle on the -# KDC server for libvirt, and that to be exported to the keytab -# file listed below -#mech_list: gssapi +# If using TLS with VNC, or a UNIX socket only, it is possible to +# enable plugins which don't provide session encryption. The +# 'scram-sha-1' plugin allows plain username/password authentication +# to be performed # -# You can also list many mechanisms at once, then the user can choose -# by adding '?auth=sasl.gssapi' to their libvirt URI, eg -# qemu+tcp://hostname/system?auth=sasl.gssapi -#mech_list: digest-md5 gssapi +#mech_list: scram-sha-1 + +# You can also list many mechanisms at once, and the VNC server will +# negotiate which to use by considering the list enabled on the VNC +# client. +#mech_list: scram-sha-1 gssapi # Some older builds of MIT kerberos on Linux ignore this option & # instead need KRB5_KTNAME env var. # For modern Linux, and other OS, this should be sufficient # -# There is no default value here, uncomment if you need this -#keytab: /etc/qemu/krb5.tab +# This file needs to be populated with the service principal that +# was created on the Kerberos v5 server. If switching to a non-gssapi +# mechanism this can be commented out. +keytab: /etc/qemu/krb5.tab -# If using digest-md5 for username/passwds, then this is the file +# If using scram-sha-1 for username/passwds, then this is the file # containing the passwds. Use 'saslpasswd2 -a qemu [username]' # to add entries, and 'sasldblistusers2 -f [sasldb_path]' to browse it -sasldb_path: /etc/qemu/passwd.db - - -auxprop_plugin: sasldb - +#sasldb_path: /etc/qemu/passwd.db |