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D-BUS message bus daemon configuration
===
The message bus daemon has a configuration file that specializes it
for a particular application. For example, one configuration
file might set up the message bus to be a systemwide message bus,
while another might set it up to be a per-user login session bus.
The configuration file also establishes resource limits, security
parameters, and so forth.
The configuration file is not part of any interoperability
specification and its backward compatibility is not guaranteed; this
document is documentation, not specification.
A DTD should be written here eventually, but for now I suck.
Doctype declaration:
<!DOCTYPE busconfig PUBLIC "-//freedesktop//DTD D-BUS Bus Configuration 1.0//EN"
"http://www.freedesktop.org/standards/dbus/1.0/busconfig.dtd">
Elements:
<busconfig>
Root element.
<include>
ignore_missing="(yes|no)" optional attribute, defaults to no
Include a file <include>filename.conf</include> at this point.
<user>
The user account the daemon should run as, as either a username or
a UID. If the daemon doesn't have and cannot change to this UID on
startup, it will exit. If this element is not present, the daemon
will not change or care about its UID.
The last <user> entry in the file "wins", the others are ignored.
<listen>
address="name" mandatory attribute
Add an address that the bus should listen on. The
address is in the standard D-BUS format that contains
a transport name plus possible parameters/options.
Example: <listen address="unix:path=/tmp/foo"/>
If there are multiple <listen> elements, then the bus listens
on multiple addresses.
<auth>
Lists permitted authorization mechanisms. If this element doesn't
exist, then all known mechanisms are allowed. If there are
multiple <auth> elements, the last one wins (they are not merged).
<policy>
context="(default|required)" one of the context/user/group
attributes is mandatory
user="username or userid"
group="group name or gid"
Encloses a policy to be applied to a particular set of
connections to the bus. A policy is made up of <limit>,
<allow>, <deny> elements.
Policies are applied to a connection as follows:
- all context="default" policies are applied
- all group="connection's user's group" policies are applied
- all user="connection's auth user" policies are applied
- all context="required" policies are applied
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.
<limit>
name="resource name" mandatory
Appears below a <policy> element and establishes a resource
limit. For example:
<limit name="max_message_size">64</limit>
<limit name="max_connections">512</limit>
<deny>
send="messagename"
receive="messagename"
own="servicename"
send_to="servicename"
receive_from="servicename"
Examples:
<deny send="org.freedesktop.System.Reboot"/>
<deny receive="org.freedesktop.System.Reboot"/>
<deny own="org.freedesktop.System"/>
<deny send_to="org.freedesktop.System"/>
<deny receive_from="org.freedesktop.System"/>
send_to and receive_from mean that messages may not be sent to
or received from the *owner* of the given service, not that
they may not be sent *to that service 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.
For "servicename" or "messagename" the character "*" can be
substituted, meaning "any." Complex globs like "foo.bar.*" aren't
allowed for now because they'd be work to implement and maybe
encourage sloppy security anyway.
FIXME should we allow send/send_to and receive/receive_from
to both be specified, in which case they would be ANDed together?
e.g. <deny send="foo.bar" send_to="foo.blah"/> would deny
messages of the given name AND to the given service.
Probably need to see how hard/slow all this will be to implement.
<allow>
send="messagename"
receive="messagename"
own="servicename"
send_to="servicename"
receive_from="servicename"
Makes an exception to previous <deny> statements. Works
just like <deny> but with the inverse meaning.
An <allow> only punches holes in the equivalent <deny>, it does
not unconditionally allow the message. For example:
<deny send="*"/>
<deny send_to="*"/>
<allow send="org.foo.Bar"/>
Here the policy still doesn't allow sending any messages, because
no recipients have been allowed. You have to add
<allow send_to="something"/> to make the policy useful.
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