From e0bd0cd43e4105dcb4e7f1849879170ae3d9da78 Mon Sep 17 00:00:00 2001 From: Daniel P. Berrangé Date: Tue, 11 May 2021 10:23:52 +0100 Subject: docs: add table of contents to QAPI references The QAPI reference docs for the guest agent, storage daemon and QMP are all rather long and hard to navigate unless you already know the name of the command and can do full text search for it. A table of contents in each doc will help people locate stuff much more easily. Reviewed-by: Connor Kuehl Signed-off-by: Daniel P. Berrangé --- docs/interop/qemu-ga-ref.rst | 3 +++ docs/interop/qemu-qmp-ref.rst | 3 +++ docs/interop/qemu-storage-daemon-qmp-ref.rst | 3 +++ 3 files changed, 9 insertions(+) (limited to 'docs') diff --git a/docs/interop/qemu-ga-ref.rst b/docs/interop/qemu-ga-ref.rst index 3f1c4f908f..db1e946124 100644 --- a/docs/interop/qemu-ga-ref.rst +++ b/docs/interop/qemu-ga-ref.rst @@ -10,4 +10,7 @@ QEMU Guest Agent Protocol Reference TODO: display the QEMU version, both here and in our Sphinx manuals more generally. +.. contents:: + :depth: 3 + .. qapi-doc:: qga/qapi-schema.json diff --git a/docs/interop/qemu-qmp-ref.rst b/docs/interop/qemu-qmp-ref.rst index c8abaaf8e3..b5bebf6b9a 100644 --- a/docs/interop/qemu-qmp-ref.rst +++ b/docs/interop/qemu-qmp-ref.rst @@ -10,4 +10,7 @@ QEMU QMP Reference Manual TODO: display the QEMU version, both here and in our Sphinx manuals more generally. +.. contents:: + :depth: 3 + .. qapi-doc:: qapi/qapi-schema.json diff --git a/docs/interop/qemu-storage-daemon-qmp-ref.rst b/docs/interop/qemu-storage-daemon-qmp-ref.rst index caf9dad23a..d0ebb42ebd 100644 --- a/docs/interop/qemu-storage-daemon-qmp-ref.rst +++ b/docs/interop/qemu-storage-daemon-qmp-ref.rst @@ -10,4 +10,7 @@ QEMU Storage Daemon QMP Reference Manual TODO: display the QEMU version, both here and in our Sphinx manuals more generally. +.. contents:: + :depth: 3 + .. qapi-doc:: storage-daemon/qapi/qapi-schema.json -- cgit v1.2.3-55-g7522 From 491024a5b4efcf79ef46ddfd5c02957102d60175 Mon Sep 17 00:00:00 2001 From: Daniel P. Berrangé Date: Tue, 23 Feb 2021 15:35:45 +0000 Subject: docs: document how to pass secret data to QEMU Reviewed-by: Marc-André Lureau Signed-off-by: Daniel P. Berrangé --- docs/system/index.rst | 1 + docs/system/secrets.rst | 162 ++++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 163 insertions(+) create mode 100644 docs/system/secrets.rst (limited to 'docs') diff --git a/docs/system/index.rst b/docs/system/index.rst index b05af716a9..6aa2f8c05c 100644 --- a/docs/system/index.rst +++ b/docs/system/index.rst @@ -30,6 +30,7 @@ Contents: guest-loader vnc-security tls + secrets gdb managed-startup cpu-hotplug diff --git a/docs/system/secrets.rst b/docs/system/secrets.rst new file mode 100644 index 0000000000..4a177369b6 --- /dev/null +++ b/docs/system/secrets.rst @@ -0,0 +1,162 @@ +.. _secret data: + +Providing secret data to QEMU +----------------------------- + +There are a variety of objects in QEMU which require secret data to be provided +by the administrator or management application. For example, network block +devices often require a password, LUKS block devices require a passphrase to +unlock key material, remote desktop services require an access password. +QEMU has a general purpose mechanism for providing secret data to QEMU in a +secure manner, using the ``secret`` object type. + +At startup this can be done using the ``-object secret,...`` command line +argument. At runtime this can be done using the ``object_add`` QMP / HMP +monitor commands. The examples that follow will illustrate use of ``-object`` +command lines, but they all apply equivalentely in QMP / HMP. When creating +a ``secret`` object it must be given a unique ID string. This ID is then +used to identify the object when configuring the thing which need the data. + + +INSECURE: Passing secrets as clear text inline +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +**The following should never be done in a production environment or on a +multi-user host. Command line arguments are usually visible in the process +listings and are often collected in log files by system monitoring agents +or bug reporting tools. QMP/HMP commands and their arguments are also often +logged and attached to bug reports. This all risks compromising secrets that +are passed inline.** + +For the convenience of people debugging / developing with QEMU, it is possible +to pass secret data inline on the command line. + +:: + + -object secret,id=secvnc0,data=87539319 + + +Again it is possible to provide the data in base64 encoded format, which is +particularly useful if the data contains binary characters that would clash +with argument parsing. + +:: + + -object secret,id=secvnc0,data=ODc1MzkzMTk=,format=base64 + + +**Note: base64 encoding does not provide any security benefit.** + +Passing secrets as clear text via a file +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +The simplest approach to providing data securely is to use a file to store +the secret: + +:: + + -object secret,id=secvnc0,file=vnc-password.txt + + +In this example the file ``vnc-password.txt`` contains the plain text secret +data. It is important to note that the contents of the file are treated as an +opaque blob. The entire raw file contents is used as the value, thus it is +important not to mistakenly add any trailing newline character in the file if +this newline is not intended to be part of the secret data. + +In some cases it might be more convenient to pass the secret data in base64 +format and have QEMU decode to get the raw bytes before use: + +:: + + -object secret,id=sec0,file=vnc-password.txt,format=base64 + + +The file should generally be given mode ``0600`` or ``0400`` permissions, and +have its user/group ownership set to the same account that the QEMU process +will be launched under. If using mandatory access control such as SELinux, then +the file should be labelled to only grant access to the specific QEMU process +that needs access. This will prevent other processes/users from compromising the +secret data. + + +Passing secrets as cipher text inline +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +To address the insecurity of passing secrets inline as clear text, it is +possible to configure a second secret as an AES key to use for decrypting +the data. + +The secret used as the AES key must always be configured using the file based +storage mechanism: + +:: + + -object secret,id=secmaster,file=masterkey.data,format=base64 + + +In this case the ``masterkey.data`` file would be initialized with 32 +cryptographically secure random bytes, which are then base64 encoded. +The contents of this file will by used as an AES-256 key to encrypt the +real secret that can now be safely passed to QEMU inline as cipher text + +:: + + -object secret,id=secvnc0,keyid=secmaster,data=BASE64-CIPHERTEXT,iv=BASE64-IV,format=base64 + + +In this example ``BASE64-CIPHERTEXT`` is the result of AES-256-CBC encrypting +the secret with ``masterkey.data`` and then base64 encoding the ciphertext. +The ``BASE64-IV`` data is 16 random bytes which have been base64 encrypted. +These bytes are used as the initialization vector for the AES-256-CBC value. + +A single master key can be used to encrypt all subsequent secrets, **but it is +critical that a different initialization vector is used for every secret**. + +Passing secrets via the Linux keyring +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +The earlier mechanisms described are platform agnostic. If using QEMU on a Linux +host, it is further possible to pass secrets to QEMU using the Linux keyring: + +:: + + -object secret_keyring,id=secvnc0,serial=1729 + + +This instructs QEMU to load data from the Linux keyring secret identified by +the serial number ``1729``. It is possible to combine use of the keyring with +other features mentioned earlier such as base64 encoding: + +:: + + -object secret_keyring,id=secvnc0,serial=1729,format=base64 + + +and also encryption with a master key: + +:: + + -object secret_keyring,id=secvnc0,keyid=secmaster,serial=1729,iv=BASE64-IV + + +Best practice +~~~~~~~~~~~~~ + +It is recommended for production deployments to use a master key secret, and +then pass all subsequent inline secrets encrypted with the master key. + +Each QEMU instance must have a distinct master key, and that must be generated +from a cryptographically secure random data source. The master key should be +deleted immediately upon QEMU shutdown. If passing the master key as a file, +the key file must have access control rules applied that restrict access to +just the one QEMU process that is intended to use it. Alternatively the Linux +keyring can be used to pass the master key to QEMU. + +The secrets for individual QEMU device backends must all then be encrypted +with this master key. + +This procedure helps ensure that the individual secrets for QEMU backends will +not be compromised, even if ``-object`` CLI args or ``object_add`` monitor +commands are collected in log files and attached to public bug support tickets. +The only item that needs strongly protecting is the master key file. -- cgit v1.2.3-55-g7522 From 1c45af36e77ca315b33f237786f8a9fda512a8d3 Mon Sep 17 00:00:00 2001 From: Daniel P. Berrangé Date: Fri, 14 May 2021 18:20:30 +0100 Subject: docs: document usage of the authorization framework The authorization framework provides a way to control access to network services after a client has been authenticated. This documents how to actually use it. Reviewed-by: Marc-André Lureau Signed-off-by: Daniel P. Berrangé --- docs/system/authz.rst | 263 ++++++++++++++++++++++++++++++++++++++++++++++++++ docs/system/index.rst | 1 + 2 files changed, 264 insertions(+) create mode 100644 docs/system/authz.rst (limited to 'docs') diff --git a/docs/system/authz.rst b/docs/system/authz.rst new file mode 100644 index 0000000000..942af39602 --- /dev/null +++ b/docs/system/authz.rst @@ -0,0 +1,263 @@ +.. _client authorization: + +Client authorization +-------------------- + +When configuring a QEMU network backend with either TLS certificates or SASL +authentication, access will be granted if the client successfully proves +their identity. If the authorization identity database is scoped to the QEMU +client this may be sufficient. It is common, however, for the identity database +to be much broader and thus authentication alone does not enable sufficient +access control. In this case QEMU provides a flexible system for enforcing +finer grained authorization on clients post-authentication. + +Identity providers +~~~~~~~~~~~~~~~~~~ + +At the time of writing there are two authentication frameworks used by QEMU +that emit an identity upon completion. + + * TLS x509 certificate distinguished name. + + When configuring the QEMU backend as a network server with TLS, there + are a choice of credentials to use. The most common scenario is to utilize + x509 certificates. The simplest configuration only involves issuing + certificates to the servers, allowing the client to avoid a MITM attack + against their intended server. + + It is possible, however, to enable mutual verification by requiring that + the client provide a certificate to the server to prove its own identity. + This is done by setting the property ``verify-peer=yes`` on the + ``tls-creds-x509`` object, which is in fact the default. + + When peer verification is enabled, client will need to be issued with a + certificate by the same certificate authority as the server. If this is + still not sufficiently strong access control the Distinguished Name of + the certificate can be used as an identity in the QEMU authorization + framework. + + * SASL username. + + When configuring the QEMU backend as a network server with SASL, upon + completion of the SASL authentication mechanism, a username will be + provided. The format of this username will vary depending on the choice + of mechanism configured for SASL. It might be a simple UNIX style user + ``joebloggs``, while if using Kerberos/GSSAPI it can have a realm + attached ``joebloggs@QEMU.ORG``. Whatever format the username is presented + in, it can be used with the QEMU authorization framework. + +Authorization drivers +~~~~~~~~~~~~~~~~~~~~~ + +The QEMU authorization framework is a general purpose design with choice of +user customizable drivers. These are provided as objects that can be +created at startup using the ``-object`` argument, or at runtime using the +``object_add`` monitor command. + +Simple +^^^^^^ + +This authorization driver provides a simple mechanism for granting access +based on an exact match against a single identity. This is useful when it is +known that only a single client is to be allowed access. + +A possible use case would be when configuring QEMU for an incoming live +migration. It is known exactly which source QEMU the migration is expected +to arrive from. The x509 certificate associated with this source QEMU would +thus be used as the identity to match against. Alternatively if the virtual +machine is dedicated to a specific tenant, then the VNC server would be +configured with SASL and the username of only that tenant listed. + +To create an instance of this driver via QMP: + +:: + + { + "execute": "object-add", + "arguments": { + "qom-type": "authz-simple", + "id": "authz0", + "props": { + "identity": "fred" + } + } + } + + +Or via the command line + +:: + + -object authz-simple,id=authz0,identity=fred + + +List +^^^^ + +In some network backends it will be desirable to grant access to a range of +clients. This authorization driver provides a list mechanism for granting +access by matching identities against a list of permitted one. Each match +rule has an associated policy and a catch all policy applies if no rule +matches. The match can either be done as an exact string comparison, or can +use the shell-like glob syntax, which allows for use of wildcards. + +To create an instance of this class via QMP: + +:: + + { + "execute": "object-add", + "arguments": { + "qom-type": "authz-list", + "id": "authz0", + "props": { + "rules": [ + { "match": "fred", "policy": "allow", "format": "exact" }, + { "match": "bob", "policy": "allow", "format": "exact" }, + { "match": "danb", "policy": "deny", "format": "exact" }, + { "match": "dan*", "policy": "allow", "format": "glob" } + ], + "policy": "deny" + } + } + } + + +Due to the way this driver requires setting nested properties, creating +it on the command line will require use of the JSON syntax for ``-object``. +In most cases, however, the next driver will be more suitable. + +List file +^^^^^^^^^ + +This is a variant on the previous driver that allows for a more dynamic +access control policy by storing the match rules in a standalone file +that can be reloaded automatically upon change. + +To create an instance of this class via QMP: + +:: + + { + "execute": "object-add", + "arguments": { + "qom-type": "authz-list-file", + "id": "authz0", + "props": { + "filename": "/etc/qemu/myvm-vnc.acl", + "refresh": true + } + } + } + + +If ``refresh`` is ``yes``, inotify is used to monitor for changes +to the file and auto-reload the rules. + +The ``myvm-vnc.acl`` file should contain the match rules in a format that +closely matches the previous driver: + +:: + + { + "rules": [ + { "match": "fred", "policy": "allow", "format": "exact" }, + { "match": "bob", "policy": "allow", "format": "exact" }, + { "match": "danb", "policy": "deny", "format": "exact" }, + { "match": "dan*", "policy": "allow", "format": "glob" } + ], + "policy": "deny" + } + + +The object can be created on the command line using + +:: + + -object authz-list-file,id=authz0,\ + filename=/etc/qemu/myvm-vnc.acl,refresh=on + + +PAM +^^^ + +In some scenarios it might be desirable to integrate with authorization +mechanisms that are implemented outside of QEMU. In order to allow maximum +flexibility, QEMU provides a driver that uses the ``PAM`` framework. + +To create an instance of this class via QMP: + +:: + + { + "execute": "object-add", + "arguments": { + "qom-type": "authz-pam", + "id": "authz0", + "parameters": { + "service": "qemu-vnc-tls" + } + } + } + + +The driver only uses the PAM "account" verification +subsystem. The above config would require a config +file /etc/pam.d/qemu-vnc-tls. For a simple file +lookup it would contain + +:: + + account requisite pam_listfile.so item=user sense=allow \ + file=/etc/qemu/vnc.allow + + +The external file would then contain a list of usernames. +If x509 cert was being used as the username, a suitable +entry would match the distinguished name: + +:: + + CN=laptop.berrange.com,O=Berrange Home,L=London,ST=London,C=GB + + +On the command line it can be created using + +:: + + -object authz-pam,id=authz0,service=qemu-vnc-tls + + +There are a variety of PAM plugins that can be used which are not illustrated +here, and it is possible to implement brand new plugins using the PAM API. + + +Connecting backends +~~~~~~~~~~~~~~~~~~~ + +The authorization driver is created using the ``-object`` argument and then +needs to be associated with a network service. The authorization driver object +will be given a unique ID that needs to be referenced. + +The property to set in the network service will vary depending on the type of +identity to verify. By convention, any network server backend that uses TLS +will provide ``tls-authz`` property, while any server using SASL will provide +a ``sasl-authz`` property. + +Thus an example using SASL and authorization for the VNC server would look +like: + +:: + + $QEMU --object authz-simple,id=authz0,identity=fred \ + --vnc 0.0.0.0:1,sasl,sasl-authz=authz0 + +While to validate both the x509 certificate and SASL username: + +:: + + echo "CN=laptop.qemu.org,O=QEMU Project,L=London,ST=London,C=GB" >> tls.acl + $QEMU --object authz-simple,id=authz0,identity=fred \ + --object authz-list-file,id=authz1,filename=tls.acl \ + --object tls-creds-x509,id=tls0,dir=/etc/qemu/tls,verify-peer=yes \ + --vnc 0.0.0.0:1,sasl,sasl-authz=auth0,tls-creds=tls0,tls-authz=authz1 diff --git a/docs/system/index.rst b/docs/system/index.rst index 6aa2f8c05c..6092eb2d91 100644 --- a/docs/system/index.rst +++ b/docs/system/index.rst @@ -31,6 +31,7 @@ Contents: vnc-security tls secrets + authz gdb managed-startup cpu-hotplug -- cgit v1.2.3-55-g7522 From e2bf32dfabbfe6aabde4a0400b25b768b4481785 Mon Sep 17 00:00:00 2001 From: Daniel P. Berrangé Date: Thu, 4 Mar 2021 18:14:26 +0000 Subject: docs: recommend SCRAM-SHA-256 SASL mech instead of SHA-1 variant The SHA-256 variant better meats modern security expectations. Also warn that the password file is storing entries in clear text. Reviewed-by: Marc-André Lureau Signed-off-by: Daniel P. Berrangé --- docs/system/vnc-security.rst | 7 ++++--- qemu.sasl | 11 ++++++----- 2 files changed, 10 insertions(+), 8 deletions(-) (limited to 'docs') diff --git a/docs/system/vnc-security.rst b/docs/system/vnc-security.rst index 830f6acc73..4c1769eeb8 100644 --- a/docs/system/vnc-security.rst +++ b/docs/system/vnc-security.rst @@ -168,7 +168,7 @@ 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 +never be used any more. The SCRAM-SHA-256 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. @@ -191,11 +191,12 @@ reasonable configuration is :: - mech_list: scram-sha-1 + mech_list: scram-sha-256 sasldb_path: /etc/qemu/passwd.db The ``saslpasswd2`` program can be used to populate the ``passwd.db`` -file with accounts. +file with accounts. Note that the ``passwd.db`` file stores passwords +in clear text. Other SASL configurations will be left as an exercise for the reader. Note that all mechanisms, except GSSAPI, should be combined with use of diff --git a/qemu.sasl b/qemu.sasl index fb8a92ba58..abdfc686be 100644 --- a/qemu.sasl +++ b/qemu.sasl @@ -19,15 +19,15 @@ 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 +# 'scram-sha-256' plugin allows plain username/password authentication # to be performed # -#mech_list: scram-sha-1 +#mech_list: scram-sha-256 # 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 +#mech_list: scram-sha-256 gssapi # Some older builds of MIT kerberos on Linux ignore this option & # instead need KRB5_KTNAME env var. @@ -38,7 +38,8 @@ mech_list: gssapi # mechanism this can be commented out. keytab: /etc/qemu/krb5.tab -# If using scram-sha-1 for username/passwds, then this is the file +# If using scram-sha-256 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 +# to add entries, and 'sasldblistusers2 -f [sasldb_path]' to browse it. +# Note that this file stores passwords in clear text. #sasldb_path: /etc/qemu/passwd.db -- cgit v1.2.3-55-g7522