Dbus daemon arch linux

tcp sockets can accept IPv4 addresses, IPv6 addresses or hostnames. If a hostname resolves to multiple addresses, the server will bind to all of them. The family=ipv4 or family=ipv6 options can be used to force it to bind to a subset of addresses

A special case is using a port number of zero (or omitting the port), which means to choose an available port selected by the operating system. The port number chosen can be obtained with the —print-address command line parameter and will be present in other cases where the server reports its own address, such as when DBUS_SESSION_BUS_ADDRESS is set.

tcp/nonce-tcp addresses also allow a bind=hostname option, used in a listenable address to configure the interface on which the server will listen: either the hostname is the IP address of one of the local machine’s interfaces (most commonly 127.0.0.1), a DNS name that resolves to one of those IP addresses, ‘0.0.0.0’ to listen on all IPv4 interfaces simultaneously, or ‘::’ to listen on all IPv4 and IPv6 interfaces simultaneously (if supported by the OS). If not specified, the default is the same value as «host».

Lists permitted authorization mechanisms. If this element doesn’t exist, then all known mechanisms are allowed. If there are multiple elements, all the listed mechanisms are allowed. The order in which mechanisms are listed is not meaningful.

On non-Windows operating systems, allowing only the EXTERNAL authentication mechanism is strongly recommended. This is the default for the well-known system bus and for the well-known session bus.

Adds a directory to search for .service files, which tell the dbus-daemon how to start a program to provide a particular well-known bus name. See the D-Bus Specification for more details about the contents of .service files.

If a particular service is found in more than one , the first directory listed in the configuration file takes precedence. If two service files providing the same well-known bus name are found in the same directory, it is arbitrary which one will be chosen (this can only happen if at least one of the service files does not have the recommended name, which is its well-known bus name followed by «.service»).

requests a standard set of session service directories. Its effect is similar to specifying a series of elements for each of the data directories, in the order given here. It is not exactly equivalent, because there is currently no way to disable directory monitoring or enforce strict service file naming for a .

As with elements, if a particular service is found in more than one service directory, the first directory takes precedence. If two service files providing the same well-known bus name are found in the same directory, it is arbitrary which one will be chosen (this can only happen if at least one of the service files does not have the recommended name, which is its well-known bus name followed by «.service»).

On Unix, the standard session service directories are:

Unlike the other standard session service directories, this directory enforces strict naming for the service files: the filename must be exactly the well-known bus name of the service, followed by «.service».

Also unlike the other standard session service directories, this directory is never monitored with inotify(7) or similar APIs. Programs that create service files in this directory while a dbus-daemon is running are expected to call the dbus-daemon’s ReloadConfig() method after they have made changes.

/.local/share (see the XDG Base Directory Specification): this location is specified by the D-Bus Specification, and is suitable for per-user, locally-installed software.

/.local/share/flatpak/exports/share/ and /var/lib/flatpak/exports/share/ when flatpak(1) is used.

The «XDG Base Directory Specification» can be found at http://freedesktop.org/wiki/Standards/basedir-spec if it hasn’t moved, otherwise try your favorite search engine.

On Windows, the standard session service directories are:

The option is only relevant to the per-user-session bus daemon defined in /etc/dbus-1/session.conf. Putting it in any other configuration file would probably be nonsense.

specifies the standard system-wide activation directories that should be searched for service files. As with session services, the first directory listed has highest precedence.

On Unix, the standard session service directories are:

On Windows, there is no standard system bus, so there are no standard system bus directories either.

The option is only relevant to the per-system bus daemon defined in /usr/share/dbus-1/system.conf. Putting it in any other configuration file would probably be nonsense.

specifies the setuid helper that is used to launch system daemons with an alternate user. Typically this should be the dbus-daemon-launch-helper executable in located in libexec.

The option is only relevant to the per-system bus daemon defined in /usr/share/dbus-1/system.conf. Putting it in any other configuration file would probably be nonsense.

establishes a resource limit. For example:

The name attribute is mandatory. Available limit names are:

The max incoming/outgoing queue sizes allow a new message to be queued if one byte remains below the max. So you can in fact exceed the max by max_message_size.

max_completed_connections divided by max_connections_per_user is the number of users that can work together to denial-of-service all other users by using up all connections on the systemwide bus.

Limits are normally only of interest on the systemwide bus, not the user session buses.

Currently, the system bus has a default-deny policy for sending method calls and owning bus names, and a default-allow policy for receiving messages, sending signals, and sending a single success or error reply for each method call that does not have the NO_REPLY flag. Sending more than the expected number of replies is not allowed.

In general, it is best to keep system services as small, targeted programs which run in their own process and provide a single bus name. Then, all that is needed is an rule for the «own» permission to let the process claim the bus name, and a «send_destination» rule to allow traffic from some or all uids to your service.

element has one of four attributes:

Policies are applied to a connection as follows:

Policies applied later will override those applied earlier, when the policies overlap. Multiple policies with the same user/group/context are applied in the order they appear in the config file.

A element appears below a

The possible attributes of these elements are:

The element’s attributes determine whether the deny «matches» a particular action. If it matches, the action is denied (unless later rules in the config file allow it).

Rules with one or more of the send_* family of attributes are checked in order when a connection attempts to send a message. The last rule that matches the message determines whether it may be sent. The well-known session bus normally allows sending any message. The well-known system bus normally allows sending any signal, selected method calls to the dbus-daemon, and exactly one reply to each previously-sent method call (either success or an error). Either of these can be overridden by configuration; on the system bus, services that will receive method calls must install configuration that allows them to do so, usually via rules of the form

Rules with one or more of the receive_* family of attributes, or with the eavesdrop attribute and no others, are checked for each recipient of a message (there might be more than one recipient if the message is a broadcast or a connection is eavesdropping). The last rule that matches the message determines whether it may be received. The well-known session bus normally allows receiving any message, including eavesdropping. The well-known system bus normally allows receiving any message that was not eavesdropped (any unicast message addressed to the recipient, and any broadcast message).

The eavesdrop, min_fds and max_fds attributes are modifiers that can be applied to either send_* or receive_* rules, and are documented below.

send_destination and receive_sender rules mean that messages may not be sent to or received from the *owner* of the given name, not that they may not be sent *to that name*. That is, if a connection owns services A, B, C, and sending to A is denied, sending to B or C will not work either. As a special case, send_destination=»*» matches any message (whether it has a destination specified or not), and receive_sender=»*» similarly matches any message.

Rules with send_broadcast=»true» match signal messages with no destination (broadcasts). Rules with send_broadcast=»false» are the inverse: they match any unicast destination (unicast signals, together with all method calls, replies and errors) but do not match messages with no destination (broadcasts). This is not the same as send_destination=»*», which matches any sent message, regardless of whether it has a destination or not.

The other send_* and receive_* attributes are purely textual/by-value matches against the given field in the message header, except that for the attributes where it is allowed, * matches any message (whether it has the relevant header field or not). For example, send_interface=»*» matches any sent message, even if it does not contain an interface header field. More complex glob matching such as foo.bar.* is not allowed.

«Eavesdropping» occurs when an application receives a message that was explicitly addressed to a name the application does not own, or is a reply to such a message. Eavesdropping thus only applies to messages that are addressed to services and replies to such messages (i.e. it does not apply to signals).

For , [send|receive]_requested_reply=»false» is the default but indicates that the rule matches only when the reply was not requested. [send|receive]_requested_reply=»true» indicates that the rule applies always, regardless of pending reply state.

The min_fds and max_fds attributes modify either send_* or receive_* rules. A rule with the min_fds attribute only matches messages if they have at least that many Unix file descriptors attached. Conversely, a rule with the max_fds attribute only matches messages if they have no more than that many file descriptors attached. In practice, rules with these attributes will most commonly take the form , or .

Rules with the user or group attribute are checked when a new connection to the message bus is established, and control whether the connection can continue. Each of these attributes cannot be combined with any other attribute. As a special case, both user=»*» and group=»*» match any connection. If there are no rules of this form, the default is to allow connections from the same user ID that owns the dbus-daemon process. The well-known session bus normally uses that default behaviour, while the well-known system bus normally allows any connection.

Rules with the own or own_prefix attribute are checked when a connection attempts to own a well-known bus names. As a special case, own=»*» matches any well-known bus name. The well-known session bus normally allows any connection to own any name, while the well-known system bus normally does not allow any connection to own any name, except where allowed by further configuration. System services that will own a name must install configuration that allows them to do so, usually via rules of the form

It does not make sense to deny a user or group inside a

for a user or group; user/group denials can only be inside context=»default» or context=»mandatory» policies.

A single rule may specify combinations of attributes such as send_destination and send_interface and send_type. In this case, the denial applies only if both attributes match the message being denied. e.g. would deny messages with the given interface AND the given bus name. To get an OR effect you specify multiple rules.

You can’t include both send_ and receive_ attributes on the same rule, since «whether the message can be sent» and «whether it can be received» are evaluated separately.

Be careful with send_interface/receive_interface, because the interface field in messages is optional. In particular, do NOT specify ! This will cause no-interface messages to be blocked for all services, which is almost certainly not what you intended. Always use rules of the form:

The element contains settings related to Security Enhanced Linux. More details below.

This means that if a connection asks to own the name «org.freedesktop.Foobar» then the source context will be the context of the connection and the target context will be «foo_t» — see the short discussion of SELinux below.

Note, the context here is the target context when requesting a name, NOT the context of the connection owning the name.

There’s currently no way to set a default for owning any name, if we add this syntax it will look like:

If you find a reason this is useful, let the developers know. Right now the default will be the security context of the bus itself.

The default mode is «enabled». In «enabled» mode, AppArmor mediation will be performed if AppArmor support is available in the kernel. If it is not available, dbus-daemon will start but AppArmor mediation will not occur. In «disabled» mode, AppArmor mediation is disabled. In «required» mode, AppArmor mediation will be enabled if AppArmor support is available, otherwise dbus-daemon will refuse to start.

The AppArmor mediation mode of the bus cannot be changed after the bus starts. Modifying the mode in the configuration file and sending a SIGHUP signal to the daemon has no effect on the mediation mode.

SELINUX

Every subject (process) and object (e.g. file, socket, IPC object, etc) in the system is assigned a collection of security attributes, known as a security context. A security context contains all of the security attributes associated with a particular subject or object that are relevant to the security policy.

In order to better encapsulate security contexts and to provide greater efficiency, the policy enforcement code of SELinux typically handles security identifiers (SIDs) rather than security contexts. A SID is an integer that is mapped by the security server to a security context at runtime.

When a security decision is required, the policy enforcement code passes a pair of SIDs (typically the SID of a subject and the SID of an object, but sometimes a pair of subject SIDs or a pair of object SIDs), and an object security class to the security server. The object security class indicates the kind of object, e.g. a process, a regular file, a directory, a TCP socket, etc.

Access decisions specify whether or not a permission is granted for a given pair of SIDs and class. Each object class has a set of associated permissions defined to control operations on objects with that class.

D-Bus performs SELinux security checks in two places.

First, any time a message is routed from one connection to another connection, the bus daemon will check permissions with the security context of the first connection as source, security context of the second connection as target, object class «dbus» and requested permission «send_msg».

If a security context is not available for a connection (impossible when using UNIX domain sockets), then the target context used is the context of the bus daemon itself. There is currently no way to change this default, because we’re assuming that only UNIX domain sockets will be used to connect to the systemwide bus. If this changes, we’ll probably add a way to set the default connection context.

Second, any time a connection asks to own a name, the bus daemon will check permissions with the security context of the connection as source, the security context specified for the name in the config file as target, object class «dbus» and requested permission «acquire_svc».

APPARMOR

The daemon performs AppArmor security checks in three places.

First, any time a message is routed from one connection to another connection, the bus daemon will check permissions with the label of the first connection as source, label and/or connection name of the second connection as target, along with the bus name, the path name, the interface name, and the member name. Reply messages, such as method_return and error messages, are implicitly allowed if they are in response to a message that has already been allowed.

Second, any time a connection asks to own a name, the bus daemon will check permissions with the label of the connection as source, the requested name as target, along with the bus name.

Third, any time a connection attempts to eavesdrop, the bus daemon will check permissions with the label of the connection as the source, along with the bus name.

AppArmor rules for bus mediation are not stored in the bus configuration files. They are stored in the application’s AppArmor profile. Please see apparmor.d(5) for more details.

DEBUGGING

Remember that the system bus is heavily locked down and if you haven’t installed a security policy file to allow your message through, it won’t work. For the session bus, this is not a concern.

The simplest way to figure out what’s happening on the bus is to run the dbus-monitor program, which comes with the D-Bus package. You can also send test messages with dbus-send. These programs have their own man pages.

If you want to know what the daemon itself is doing, you might consider running a separate copy of the daemon to test against. This will allow you to put the daemon under a debugger, or run it with verbose output, without messing up your real session and system daemons.

To run a separate test copy of the daemon, for example you might open a terminal and type:

The test daemon address will be printed when the daemon starts. You will need to copy-and-paste this address and use it as the value of the DBUS_SESSION_BUS_ADDRESS environment variable when you launch the applications you want to test. This will cause those applications to connect to your test bus instead of the DBUS_SESSION_BUS_ADDRESS of your real session bus.

DBUS_VERBOSE=1 will have NO EFFECT unless your copy of D-Bus was compiled with verbose mode enabled. This is not recommended in production builds due to performance impact. You may need to rebuild D-Bus if your copy was not built with debugging in mind. (DBUS_VERBOSE also affects the D-Bus library and thus applications using D-Bus; it may be useful to see verbose output on both the client side and from the daemon.)

If you want to get fancy, you can create a custom bus configuration for your test bus (see the session.conf and system.conf files that define the two default configurations for example). This would allow you to specify a different directory for .service files, for example.

AUTHOR

NOTES

Package name: core/dbus Version: 1.12.20-1 Upstream: https://wiki.freedesktop.org/www/Software/dbus/ Licenses: GPL, custom Manuals: /listing/core/dbus/ Table of contents

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