1. DBus, PolicyKit and YaSTIng. Ladislav Slezk YaST Developer

2. DBus 3. Novell, Inc. All rights reserved.3DBus What is DBus? Local interprocess communication (IPC) Message based (sends messages, not streams) Messages are transferred in binary form Supports 1:1 and 1:N communication 4. Novell, Inc. All rights reserved.4DBus Why? Unified communication for desktop replacing DCOP (KDE)and CORBA (GNOME) For communication between desktop applications or betweendesktop applications and system daemons, for handlingsystem events... 5. Novell, Inc. All rights reserved.5DBus Concepts Object oriented view DBus services provides objects But OOP is not required, service can be written in C Data types Basic data types: integer, string, boolean... Containers: array, hash, structure, variant> Containers can be recursive 6. Novell, Inc. All rights reserved.6DBus parts DBus daemon Runs a bus, processes and routes the messages DBus library (libdbus) Low-level C API Language bindings High-level API for Python, Ruby, Qt, Glib Wrappers for low-level C calls Conversion between native and DBus data types May provide object proxy for mapping native objects(GObject, QObject,...) and signals to DBus objects and signals 7. Novell, Inc. All rights reserved.7DBus Terminology Bus The place for transferring the messages Multiple buses can run in parallel> System wide bus single bus for system wide events and services, runsunder a system user (non-root)> Session bus one per user session, for desktop applications, created atlogin, runs with user privileges> Private bus special separate bus can be started by applications 8. Novell, Inc. All rights reserved.8DBus Terminology Connection/Service name Unique ID (:1.42, assigned by DBus) or well-known(org.freedesktop.PowerManagement, defined by service) Object path in object tree /org/freedesktop/PowerManagement Interface name Named group of methods and signals,org.freedesktop.PowerManagement Method name Suspend 9. Novell, Inc. All rights reserved.9DBus TerminologyService org.freedesktop.PowerManagementObject /org/freedesktop/PowerManagementBusInterface org.freedesktop.PowerManagementMethod Suspend() 10. Novell, Inc. All rights reserved.10DBus Message Message types Method call Method reply Error Signal (1:N publish/subscribe communication) Header Type, destination service, target object, method, sender,serial number, data type signature... Data Arguments in binary form 11. Novell, Inc. All rights reserved.11Object Introspection Query available objects in a service Runtime object browsing Needed by language proxies and DBus browsers 12. Novell, Inc. All rights reserved.12Service Activation DBus service can be provided by a running application can start be started on demand> Started service can continue running, it can exit immediately or exit after atimeout 13. Novell, Inc. All rights reserved.13Access Control Its possible to allow or deny access to a specificobject, interface, method, signal... 14. Novell, Inc. All rights reserved.14Python Example Method call exampleimport dbusbus = dbus.SessionBus()obj = bus.get_object(org.freedesktop.PowerManagement,/org/freedesktop/PowerManagement)iface = dbus.Interface(obj,org.freedesktop.PowerManagement)result = iface.CanHibernate()print result 15. Novell, Inc. All rights reserved.15GUI Tools qdbusviewer 16. Novell, Inc. All rights reserved.16GUI Tools kdbus 17. Novell, Inc. All rights reserved.17Command line tools dbus-send Sends a message dbus-monitor Monitors activity on a bus qdbus DBus browsing, sending messages 18. Novell, Inc. All rights reserved.18DBus Documentation Introduction to DBus http://www.freedesktop.org/wiki/IntroductionToDBus DBus tutorial http://dbus.freedesktop.org/doc/dbus-tutorial.html DBus FAQ http://dbus.freedesktop.org/doc/dbus-faq.html Low-level C API http://dbus.freedesktop.org/doc/dbus/api/html/group__DBus.html C example http://dbus.freedesktop.org/doc/dbus/libdbus-tutorial.html 19. PolicyKit 20. Novell, Inc. All rights reserved.20PolicyKit Framework for central policy management ofprivileged operations In contrast to /etc/sudoers, user group management... Extends DBus security model more fine grainedprivileges User can mount removable media, but cannot mount fixedmedia User can shutdown the machine from a local session 21. Novell, Inc. All rights reserved.21PolicyKit Model Application is split to privileged and unprivileged part,each part runs in a different process For security reasons the privileged part should be as small aspossible The privileged part is called Mechanism These parts communicate via IPC (DBus, pipes, ...) 22. Novell, Inc. All rights reserved.22PolicyKit Modelhttp://hal.freedesktop.org/docs/PolicyKit/diagram-bus-model.png 23. Novell, Inc. All rights reserved.23Mechanism Runs as a privileged user Parts of mechanism Decider part checkswhether the requester isallowed to call the actionpart Action part carries out theprivileged action The action is performedonly when the deciderpart says YesRequestMechanismAllowed?Do ActionError 24. Novell, Inc. All rights reserved.24Input for Decision Subject Attributes of the requester UID, application, local or remotesession, active session... Object Removable device, Package, Power management... Action What to do with the object Mount the device, install the package, reboot the system... PolicyKit encodes object and action to single Action ID e.g. org.freedesktop.hal.storage.mount-removable 25. Novell, Inc. All rights reserved.25Authorization Check Also the unprivileged part may check whether it can dothe privileged operation Disabled or locked options in UI 26. Novell, Inc. All rights reserved.26How to Obtain an Authorization User is allowed to do action By default (defined in configuration file) Under a special condition (e.g. active session) Administrator grants the authorization to the user Obtains the authorization via authentication 27. Novell, Inc. All rights reserved.27Authentication Authentication agent is a DBus service(org.freedesktop.PolicyKit.AuthenticationAgent) 28. Novell, Inc. All rights reserved.28Workflow HAL example Mount request senthttp://hal.freedesktop.org/docs/PolicyKit/diagram-interaction.png Check the authorization 29. Novell, Inc. All rights reserved.29Workflow An exception is returned The user authenticates 30. Novell, Inc. All rights reserved.30Workflow A token is written to DB The second attept is OK 31. Novell, Inc. All rights reserved.31Command Line Tools polkit-auth Manage authorizations display, obtain, revoke... polkit-action List actions, modify defaults polkit-policy-file-validate A validation tool for .policy files, should be called frommake check polkit-policy-file-validate Validates /etc/PolicyKit/PolicyKit.conf file 32. Novell, Inc. All rights reserved.32PolicyKit Documentation Design, API reference manual, tools... http://hal.freedesktop.org/docs/PolicyKit/index.html Package PolicyKit-doc 33. YaST DBus Service 34. Novell, Inc. All rights reserved.34YaST DBus Service Access the YaST functionality from other applications Needed for WebYaSTWhy DBus? Auto start (no running daemon) Starts YaST as root user (no SUID flag)Why PolicyKit? Admin tools available 35. Novell, Inc. All rights reserved.35YaST DBus Service Package yast2-dbus-server Service org.opensuse.YaST.modulesrunning on the system bus Object /org/opensuse/YaST/modules/ Interface org.opensuse.YaST.Values The service is started automatically Shuts down after 2 minutes 36. Novell, Inc. All rights reserved.36Solved Problems PolicyKit action ID Created from function name Checked before function call Stateful YaST modules Stateless wrappers (YaPI) Lock(), Unlock() methods YaST module autoloading No need to load all YaST modules YCP data types and special values Additional interface Bugfixes in Ruby DBus bindings 37. Questions? 38. Thank you!