1<?xml version="1.0" encoding="ISO-8859-1"?>
2<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
3                   "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd">
4<!-- lifted from troff+man by doclifter -->
5<refentry id='dbus-daemon'>
6<!--   -->
7<!--  dbus\-daemon manual page. -->
8<!--  Copyright (C) 2003 Red Hat, Inc. -->
9
10<refmeta>
11<refentrytitle>dbus-daemon</refentrytitle>
12<manvolnum>1</manvolnum>
13</refmeta>
14<refnamediv id='name'>
15<refname>dbus-daemon</refname>
16<refpurpose>Message bus daemon</refpurpose>
17</refnamediv>
18<!-- body begins here -->
19<refsynopsisdiv id='synopsis'>
20<cmdsynopsis>
21  <command>dbus-daemon</command></cmdsynopsis>
22<cmdsynopsis>
23  <command>dbus-daemon</command>    <arg choice='opt'>--version </arg>
24    <arg choice='opt'>--session </arg>
25    <arg choice='opt'>--system </arg>
26    <arg choice='opt'>--config-file=<replaceable>FILE</replaceable></arg>
27    <arg choice='opt'><arg choice='plain'>--print-address </arg><arg choice='opt'><replaceable>=DESCRIPTOR</replaceable></arg></arg>
28    <arg choice='opt'><arg choice='plain'>--print-pid </arg><arg choice='opt'><replaceable>=DESCRIPTOR</replaceable></arg></arg>
29    <arg choice='opt'>--fork </arg>
30    <sbr/>
31</cmdsynopsis>
32</refsynopsisdiv>
33
34
35<refsect1 id='description'><title>DESCRIPTION</title>
36<para><command>dbus-daemon</command> is the D-Bus message bus daemon. See
37<ulink url='http://www.freedesktop.org/software/dbus/'>http://www.freedesktop.org/software/dbus/</ulink> for more information about
38the big picture. D-Bus is first a library that provides one-to-one
39communication between any two applications; <command>dbus-daemon</command> is an
40application that uses this library to implement a message bus
41daemon. Multiple programs connect to the message bus daemon and can
42exchange messages with one another.</para>
43
44
45<para>There are two standard message bus instances: the systemwide message bus 
46(installed on many systems as the "messagebus" init service) and the 
47per-user-login-session message bus (started each time a user logs in).
48<command>dbus-daemon</command> is used for both of these instances, but with 
49a different configuration file.</para>
50
51
52<para>The --session option is equivalent to
53"--config-file=/etc/dbus-1/session.conf" and the --system
54option is equivalent to
55"--config-file=/etc/dbus-1/system.conf". By creating 
56additional configuration files and using the --config-file option,
57additional special-purpose message bus daemons could be created.</para>
58
59
60<para>The systemwide daemon is normally launched by an init script, 
61standardly called simply "messagebus".</para> 
62
63
64<para>The systemwide daemon is largely used for broadcasting system events, 
65such as changes to the printer queue, or adding/removing devices.</para>
66
67
68<para>The per-session daemon is used for various interprocess communication 
69among desktop applications (however, it is not tied to X or the GUI 
70in any way).</para>
71
72
73<para>SIGHUP will cause the D-Bus daemon to PARTIALLY reload its
74configuration file and to flush its user/group information caches. Some
75configuration changes would require kicking all apps off the bus; so they will
76only take effect if you restart the daemon. Policy changes should take effect
77with SIGHUP.</para>
78
79</refsect1>
80
81<refsect1 id='options'><title>OPTIONS</title>
82<para>The following options are supported:</para>
83<variablelist remap='TP'>
84  <varlistentry>
85  <term><option>--config-file=FILE</option></term>
86  <listitem>
87<para>Use the given configuration file.</para>
88  </listitem>
89  </varlistentry>
90  <varlistentry>
91  <term><option>--fork</option></term>
92  <listitem>
93<para>Force the message bus to fork and become a daemon, even if 
94the configuration file does not specify that it should.
95In most contexts the configuration file already gets this
96right, though.</para>
97  </listitem>
98  </varlistentry>
99  <varlistentry>
100  <term><option>--print-address[=DESCRIPTOR]</option></term>
101  <listitem>
102<para>Print the address of the message bus to standard output, or 
103to the given file descriptor. This is used by programs that 
104launch the message bus.</para>
105  </listitem>
106  </varlistentry>
107  <varlistentry>
108  <term><option>--print-pid[=DESCRIPTOR]</option></term>
109  <listitem>
110<para>Print the process ID of the message bus to standard output, or 
111to the given file descriptor. This is used by programs that 
112launch the message bus.</para>
113  </listitem>
114  </varlistentry>
115  <varlistentry>
116  <term><option>--session</option></term>
117  <listitem>
118<para>Use the standard configuration file for the per-login-session message
119bus.</para>
120  </listitem>
121  </varlistentry>
122  <varlistentry>
123  <term><option>--system</option></term>
124  <listitem>
125<para>Use the standard configuration file for the systemwide message bus.</para>
126  </listitem>
127  </varlistentry>
128  <varlistentry>
129  <term><option>--version</option></term>
130  <listitem>
131<para>Print the version of the daemon.</para>
132
133  </listitem>
134  </varlistentry>
135</variablelist>
136</refsect1>
137
138<refsect1 id='configuration_file'><title>CONFIGURATION FILE</title>
139<para>A message bus daemon has a configuration file that specializes it
140for a particular application. For example, one configuration 
141file might set up the message bus to be a systemwide message bus, 
142while another might set it up to be a per-user-login-session bus.</para>
143
144
145<para>The configuration file also establishes resource limits, security
146parameters, and so forth.</para>
147
148
149<para>The configuration file is not part of any interoperability
150specification and its backward compatibility is not guaranteed; this
151document is documentation, not specification.</para>
152
153
154<para>The standard systemwide and per-session message bus setups are
155configured in the files "/etc/dbus-1/system.conf" and
156"/etc/dbus-1/session.conf".  These files normally
157&lt;include&gt; a system-local.conf or session-local.conf; you can put local
158overrides in those files to avoid modifying the primary configuration
159files.</para>
160
161
162<para>The configuration file is an XML document. It must have the following
163doctype declaration:</para>
164<literallayout remap='.nf'>
165
166   &lt;!DOCTYPE busconfig PUBLIC "-//freedesktop//DTD D-Bus Bus Configuration 1.0//EN"
167    "<ulink url='http://www.freedesktop.org/standards/dbus/1.0/busconfig.dtd'>http://www.freedesktop.org/standards/dbus/1.0/busconfig.dtd</ulink>"&gt;
168
169</literallayout> <!-- .fi -->
170
171
172<para>The following elements may be present in the configuration file.</para>
173
174<variablelist remap='TP'>
175  <varlistentry>
176  <term><emphasis remap='I'>&lt;busconfig&gt;</emphasis></term>
177  <listitem>
178<para></para> 
179  </listitem>
180  </varlistentry>
181</variablelist>
182
183<para>Root element.</para>
184
185<variablelist remap='TP'>
186  <varlistentry>
187  <term><emphasis remap='I'>&lt;type&gt;</emphasis></term>
188  <listitem>
189
190<para></para> <!-- FIXME: blank list item -->
191  </listitem>
192  </varlistentry>
193</variablelist>
194
195<para>The well-known type of the message bus. Currently known values are
196"system" and "session"; if other values are set, they should be
197either added to the D-Bus specification, or namespaced.  The last
198&lt;type&gt; element "wins" (previous values are ignored).</para>
199
200
201<para>Example: &lt;type&gt;session&lt;/type&gt;</para>
202
203<variablelist remap='TP'>
204  <varlistentry>
205  <term><emphasis remap='I'>&lt;include&gt;</emphasis></term>
206  <listitem>
207<para></para> 
208  </listitem>
209  </varlistentry>
210</variablelist>
211
212<para>Include a file &lt;include&gt;filename.conf&lt;/include&gt; at this point.  If the
213filename is relative, it is located relative to the configuration file
214doing the including.</para>
215
216
217<para>&lt;include&gt; has an optional attribute "ignore_missing=(yes|no)"
218which defaults to "no" if not provided. This attribute 
219controls whether it's a fatal error for the included file 
220to be absent.</para>
221
222<variablelist remap='TP'>
223  <varlistentry>
224  <term><emphasis remap='I'>&lt;includedir&gt;</emphasis></term>
225  <listitem>
226
227<para></para> <!-- FIXME: blank list item -->
228  </listitem>
229  </varlistentry>
230</variablelist>
231
232<para>Include all files in &lt;includedir&gt;foo.d&lt;/includedir&gt; at this
233point. Files in the directory are included in undefined order.
234Only files ending in ".conf" are included.</para>
235
236
237<para>This is intended to allow extension of the system bus by particular
238packages. For example, if CUPS wants to be able to send out
239notification of printer queue changes, it could install a file to
240/etc/dbus-1/system.d that allowed all apps to receive
241this message and allowed the printer daemon user to send it.</para>
242
243<variablelist remap='TP'>
244  <varlistentry>
245  <term><emphasis remap='I'>&lt;user&gt;</emphasis></term>
246  <listitem>
247
248<para></para> <!-- FIXME: blank list item -->
249  </listitem>
250  </varlistentry>
251</variablelist>
252
253<para>The user account the daemon should run as, as either a username or a
254UID. If the daemon cannot change to this UID on startup, it will exit.
255If this element is not present, the daemon will not change or care
256about its UID.</para>
257
258
259<para>The last &lt;user&gt; entry in the file "wins", the others are ignored.</para>
260
261
262<para>The user is changed after the bus has completed initialization.  So
263sockets etc. will be created before changing user, but no data will be
264read from clients before changing user. This means that sockets 
265and PID files can be created in a location that requires root 
266privileges for writing.</para>
267
268<variablelist remap='TP'>
269  <varlistentry>
270  <term><emphasis remap='I'>&lt;fork&gt;</emphasis></term>
271  <listitem>
272<para></para>    
273  </listitem>
274  </varlistentry>
275</variablelist>
276
277<para>If present, the bus daemon becomes a real daemon (forks 
278into the background, etc.). This is generally used 
279rather than the --fork command line option.</para>
280
281<variablelist remap='TP'>
282  <varlistentry>
283  <term><emphasis remap='I'>&lt;listen&gt;</emphasis></term>
284  <listitem>
285
286<para></para> <!-- FIXME: blank list item -->
287  </listitem>
288  </varlistentry>
289</variablelist>
290
291<para>Add an address that the bus should listen on. The 
292address is in the standard D-Bus format that contains 
293a transport name plus possible parameters/options.</para>
294
295
296<para>Example: &lt;listen&gt;unix:path=/tmp/foo&lt;/listen&gt;</para>
297
298
299<para>If there are multiple &lt;listen&gt; elements, then the bus listens 
300on multiple addresses. The bus will pass its address to 
301started services or other interested parties with 
302the last address given in &lt;listen&gt; first. That is, 
303apps will try to connect to the last &lt;listen&gt; address first.</para>
304
305<variablelist remap='TP'>
306  <varlistentry>
307  <term><emphasis remap='I'>&lt;auth&gt;</emphasis></term>
308  <listitem>
309
310<para></para> <!-- FIXME: blank list item -->
311  </listitem>
312  </varlistentry>
313</variablelist>
314
315<para>Lists permitted authorization mechanisms. If this element doesn't
316exist, then all known mechanisms are allowed.  If there are multiple
317&lt;auth&gt; elements, all the listed mechanisms are allowed.  The order in
318which mechanisms are listed is not meaningful.</para>
319    
320
321<para>Example: &lt;auth&gt;EXTERNAL&lt;/auth&gt;</para>
322
323
324<para>Example: &lt;auth&gt;DBUS_COOKIE_SHA1&lt;/auth&gt;</para>
325
326<variablelist remap='TP'>
327  <varlistentry>
328  <term><emphasis remap='I'>&lt;servicedir&gt;</emphasis></term>
329  <listitem>
330
331<para></para> <!-- FIXME: blank list item -->
332  </listitem>
333  </varlistentry>
334</variablelist>
335
336<para>Adds a directory to scan for .service files. Directories are
337scanned starting with the last to appear in the config file 
338(the first .service file found that provides a particular 
339service will be used).</para>
340
341
342<para>Service files tell the bus how to automatically start a program.
343They are primarily used with the per-user-session bus, 
344not the systemwide bus.</para>
345
346<variablelist remap='TP'>
347  <varlistentry>
348  <term><emphasis remap='I'>&lt;standard_session_servicedirs/&gt;</emphasis></term>
349  <listitem>
350
351<para></para> <!-- FIXME: blank list item -->
352  </listitem>
353  </varlistentry>
354</variablelist>
355
356<para>&lt;standard_session_servicedirs/&gt; is equivalent to specifying a series
357of &lt;servicedir/&gt; elements for each of the data directories in the "XDG
358Base Directory Specification" with the subdirectory "dbus-1/services",
359so for example "/usr/share/dbus-1/services" would be among the
360directories searched.</para>
361
362
363<para>The "XDG Base Directory Specification" can be found at
364<ulink url='http://freedesktop.org/wiki/Standards/basedir-spec'>http://freedesktop.org/wiki/Standards/basedir-spec</ulink> if it hasn't moved,
365otherwise try your favorite search engine.</para>
366
367
368<para>The &lt;standard_session_servicedirs/&gt; option is only relevant to the
369per-user-session bus daemon defined in
370/etc/dbus-1/session.conf. Putting it in any other
371configuration file would probably be nonsense.</para>
372
373<variablelist remap='TP'>
374  <varlistentry>
375  <term><emphasis remap='I'>&lt;limit&gt;</emphasis></term>
376  <listitem>
377
378<para></para> <!-- FIXME: blank list item -->
379  </listitem>
380  </varlistentry>
381</variablelist>
382
383<para>&lt;limit&gt; establishes a resource limit. For example:</para>
384<literallayout remap='.nf'>
385  &lt;limit name="max_message_size"&gt;64&lt;/limit&gt;
386  &lt;limit name="max_completed_connections"&gt;512&lt;/limit&gt;
387</literallayout> <!-- .fi -->
388
389
390<para>The name attribute is mandatory.
391Available limit names are:</para>
392<literallayout remap='.nf'>
393      "max_incoming_bytes"         : total size in bytes of messages
394                                     incoming from a single connection
395      "max_outgoing_bytes"         : total size in bytes of messages
396                                     queued up for a single connection
397      "max_message_size"           : max size of a single message in
398                                     bytes
399      "service_start_timeout"      : milliseconds (thousandths) until 
400                                     a started service has to connect
401      "auth_timeout"               : milliseconds (thousandths) a
402                                     connection is given to
403                                     authenticate
404      "max_completed_connections"  : max number of authenticated connections  
405      "max_incomplete_connections" : max number of unauthenticated
406                                     connections
407      "max_connections_per_user"   : max number of completed connections from
408                                     the same user
409      "max_pending_service_starts" : max number of service launches in
410                                     progress at the same time
411      "max_names_per_connection"   : max number of names a single 
412                                     connection can own
413      "max_match_rules_per_connection": max number of match rules for a single 
414                                        connection
415      "max_replies_per_connection" : max number of pending method 
416                                     replies per connection
417                                     (number of calls-in-progress)
418      "reply_timeout"              : milliseconds (thousandths) 
419                                     until a method call times out   
420</literallayout> <!-- .fi -->
421
422
423<para>The max incoming/outgoing queue sizes allow a new message to be queued
424if one byte remains below the max. So you can in fact exceed the max
425by max_message_size.</para>
426
427
428<para>max_completed_connections divided by max_connections_per_user is the
429number of users that can work together to denial-of-service all other users by using
430up all connections on the systemwide bus.</para>
431
432
433<para>Limits are normally only of interest on the systemwide bus, not the user session 
434buses.</para>
435
436<variablelist remap='TP'>
437  <varlistentry>
438  <term><emphasis remap='I'>&lt;policy&gt;</emphasis></term>
439  <listitem>
440
441<para></para> <!-- FIXME: blank list item -->
442  </listitem>
443  </varlistentry>
444</variablelist>
445
446<para>The &lt;policy&gt; element defines a security policy to be applied to a particular
447set of connections to the bus. A policy is made up of
448&lt;allow&gt; and &lt;deny&gt; elements. Policies are normally used with the systemwide bus;
449they are analogous to a firewall in that they allow expected traffic 
450and prevent unexpected traffic.</para>
451
452
453<para>The &lt;policy&gt; element has one of three attributes:</para>
454<literallayout remap='.nf'>
455  context="(default|mandatory)"
456  user="username or userid"
457  group="group name or gid"
458</literallayout> <!-- .fi -->
459
460
461<para> 
462Policies are applied to a connection as follows:</para>
463<literallayout remap='.nf'>
464   - all context="default" policies are applied
465   - all group="connection's user's group" policies are applied
466     in undefined order
467   - all user="connection's auth user" policies are applied
468     in undefined order
469   - all context="mandatory" policies are applied
470</literallayout> <!-- .fi -->
471
472
473<para>Policies applied later will override those applied earlier, 
474when the policies overlap. Multiple policies with the same 
475user/group/context are applied in the order they appear 
476in the config file.</para>
477
478<variablelist remap='TP'>
479  <varlistentry>
480  <term><emphasis remap='I'>&lt;deny&gt;</emphasis></term>
481  <listitem>
482<para><emphasis remap='I'>&lt;allow&gt;</emphasis></para>
483
484  </listitem>
485  </varlistentry>
486</variablelist>
487
488<para>A &lt;deny&gt; element appears below a &lt;policy&gt; element and prohibits some
489action. The &lt;allow&gt; element makes an exception to previous &lt;deny&gt;
490statements, and works just like &lt;deny&gt; but with the inverse meaning.</para>
491
492
493<para>The possible attributes of these elements are:</para>
494<literallayout remap='.nf'>
495   send_interface="interface_name"
496   send_member="method_or_signal_name" 
497   send_error="error_name" 
498   send_destination="name" 
499   send_type="method_call" | "method_return" | "signal" | "error" 
500   send_path="/path/name"
501
502   receive_interface="interface_name"
503   receive_member="method_or_signal_name" 
504   receive_error="error_name" 
505   receive_sender="name" 
506   receive_type="method_call" | "method_return" | "signal" | "error"
507   receive_path="/path/name"
508
509   send_requested_reply="true" | "false"
510   receive_requested_reply="true" | "false"
511
512   eavesdrop="true" | "false"
513
514   own="name"
515   own_prefix="name"
516   user="username"
517   group="groupname"
518</literallayout> <!-- .fi -->
519
520
521<para>Examples:</para>
522<literallayout remap='.nf'>
523   &lt;deny send_interface="org.freedesktop.System" send_member="Reboot"/&gt; 
524   &lt;deny receive_interface="org.freedesktop.System" receive_member="Reboot"/&gt;
525   &lt;deny own="org.freedesktop.System"/&gt;
526   &lt;deny send_destination="org.freedesktop.System"/&gt;
527   &lt;deny receive_sender="org.freedesktop.System"/&gt;
528   &lt;deny user="john"/&gt;
529   &lt;deny group="enemies"/&gt;
530</literallayout> <!-- .fi -->
531
532
533<para>The &lt;deny&gt; element's attributes determine whether the deny "matches" a
534particular action. If it matches, the action is denied (unless later
535rules in the config file allow it).</para>
536
537
538<para>send_destination and receive_sender rules mean that messages may not be
539sent to or received from the *owner* of the given name, not that
540they may not be sent *to that name*. That is, if a connection
541owns services A, B, C, and sending to A is denied, sending to B or C
542will not work either.</para>
543
544
545<para>The other send_* and receive_* attributes are purely textual/by-value
546matches against the given field in the message header.</para>
547
548
549<para>"Eavesdropping" occurs when an application receives a message that
550was explicitly addressed to a name the application does not own.
551Eavesdropping thus only applies to messages that are addressed to
552services (i.e. it does not apply to signals).</para>
553
554
555<para>For &lt;allow&gt;, eavesdrop="true" indicates that the rule matches even 
556when eavesdropping. eavesdrop="false" is the default and means that 
557the rule only allows messages to go to their specified recipient.
558For &lt;deny&gt;, eavesdrop="true" indicates that the rule matches 
559only when eavesdropping. eavesdrop="false" is the default for &lt;deny&gt;
560also, but here it means that the rule applies always, even when 
561not eavesdropping. The eavesdrop attribute can only be combined with
562receive rules (with receive_* attributes).</para>
563
564
565
566<para>The [send|receive]_requested_reply attribute works similarly to the eavesdrop
567attribute. It controls whether the &lt;deny&gt; or &lt;allow&gt; matches a reply
568that is expected (corresponds to a previous method call message).
569This attribute only makes sense for reply messages (errors and method
570returns), and is ignored for other message types.</para>
571
572
573<para>For &lt;allow&gt;, [send|receive]_requested_reply="true" is the default and indicates that
574only requested replies are allowed by the
575rule. [send|receive]_requested_reply="false" means that the rule allows any reply
576even if unexpected.</para>
577
578
579<para>For &lt;deny&gt;, [send|receive]_requested_reply="false" is the default but indicates that
580the rule matches only when the reply was not
581requested. [send|receive]_requested_reply="true" indicates that the rule applies
582always, regardless of pending reply state.</para>
583
584
585<para>user and group denials mean that the given user or group may 
586not connect to the message bus.</para>
587
588
589<para>For "name", "username", "groupname", etc.
590the character "*" can be substituted, meaning "any." Complex globs
591like "foo.bar.*" aren't allowed for now because they'd be work to
592implement and maybe encourage sloppy security anyway.</para>
593
594<para>&lt;allow own_prefix="a.b"/&gt; allows you to own the name "a.b" or any
595name whose first dot-separated elements are "a.b": in particular,
596you can own "a.b.c" or "a.b.c.d", but not "a.bc" or "a.c".
597This is useful when services like Telepathy and ReserveDevice
598define a meaning for subtrees of well-known names, such as
599org.freedesktop.Telepathy.ConnectionManager.(anything)
600and org.freedesktop.ReserveDevice1.(anything).</para>
601
602<para>It does not make sense to deny a user or group inside a &lt;policy&gt;
603for a user or group; user/group denials can only be inside
604context="default" or context="mandatory" policies.</para>
605
606
607<para>A single &lt;deny&gt; rule may specify combinations of attributes such as
608send_destination and send_interface and send_type. In this case, the
609denial applies only if both attributes match the message being denied.
610e.g. &lt;deny send_interface="foo.bar" send_destination="foo.blah"/&gt; would
611deny messages with the given interface AND the given bus name.
612To get an OR effect you specify multiple &lt;deny&gt; rules.</para>
613
614
615<para>You can't include both send_ and receive_ attributes on the same
616rule, since "whether the message can be sent" and "whether it can be
617received" are evaluated separately.</para>
618
619
620<para>Be careful with send_interface/receive_interface, because the 
621interface field in messages is optional.</para>
622
623<variablelist remap='TP'>
624  <varlistentry>
625  <term><emphasis remap='I'>&lt;selinux&gt;</emphasis></term>
626  <listitem>
627
628<para></para> <!-- FIXME: blank list item -->
629  </listitem>
630  </varlistentry>
631</variablelist>
632
633<para>The &lt;selinux&gt; element contains settings related to Security Enhanced Linux.
634More details below.</para>
635
636<variablelist remap='TP'>
637  <varlistentry>
638  <term><emphasis remap='I'>&lt;associate&gt;</emphasis></term>
639  <listitem>
640
641<para></para> <!-- FIXME: blank list item -->
642  </listitem>
643  </varlistentry>
644</variablelist>
645
646<para>An &lt;associate&gt; element appears below an &lt;selinux&gt; element and
647creates a mapping. Right now only one kind of association is possible:</para>
648<literallayout remap='.nf'>
649   &lt;associate own="org.freedesktop.Foobar" context="foo_t"/&gt; 
650</literallayout> <!-- .fi -->
651
652
653<para>This means that if a connection asks to own the name
654"org.freedesktop.Foobar" then the source context will be the context
655of the connection and the target context will be "foo_t" - see the 
656short discussion of SELinux below.</para>
657
658
659<para>Note, the context here is the target context when requesting a name,
660NOT the context of the connection owning the name.</para>
661
662
663<para>There's currently no way to set a default for owning any name, if
664we add this syntax it will look like:</para>
665<literallayout remap='.nf'>
666   &lt;associate own="*" context="foo_t"/&gt; 
667</literallayout> <!-- .fi -->
668<para>If you find a reason this is useful, let the developers know.
669Right now the default will be the security context of the bus itself.</para>
670
671
672<para>If two &lt;associate&gt; elements specify the same name, the element
673appearing later in the configuration file will be used.</para>
674
675</refsect1>
676
677<refsect1 id='selinux'><title>SELinux</title>
678<para>See <ulink url='http://www.nsa.gov/selinux/'>http://www.nsa.gov/selinux/</ulink> for full details on SELinux. Some useful excerpts:</para>
679
680
681<para>Every subject (process) and object (e.g. file, socket, IPC object,
682etc) in the system is assigned a collection of security attributes,
683known as a security context. A security context contains all of the
684security attributes associated with a particular subject or object
685that are relevant to the security policy.</para>
686
687
688<para>In order to better encapsulate security contexts and to provide
689greater efficiency, the policy enforcement code of SELinux typically
690handles security identifiers (SIDs) rather than security contexts. A
691SID is an integer that is mapped by the security server to a security
692context at runtime.</para>
693
694
695<para>When a security decision is required, the policy enforcement code
696passes a pair of SIDs (typically the SID of a subject and the SID of
697an object, but sometimes a pair of subject SIDs or a pair of object
698SIDs), and an object security class to the security server. The object
699security class indicates the kind of object, e.g. a process, a regular
700file, a directory, a TCP socket, etc.</para>
701
702
703<para>Access decisions specify whether or not a permission is granted for a
704given pair of SIDs and class. Each object class has a set of
705associated permissions defined to control operations on objects with
706that class.</para>
707
708
709<para>D-Bus performs SELinux security checks in two places.</para>
710
711
712<para>First, any time a message is routed from one connection to another
713connection, the bus daemon will check permissions with the security context of
714the first connection as source, security context of the second connection
715as target, object class "dbus" and requested permission "send_msg".</para>
716
717
718<para>If a security context is not available for a connection 
719(impossible when using UNIX domain sockets), then the target 
720context used is the context of the bus daemon itself.
721There is currently no way to change this default, because we're 
722assuming that only UNIX domain sockets will be used to 
723connect to the systemwide bus. If this changes, we'll 
724probably add a way to set the default connection context.</para>
725
726
727<para>Second, any time a connection asks to own a name, 
728the bus daemon will check permissions with the security 
729context of the connection as source, the security context specified
730for the name in the config file as target, object 
731class "dbus" and requested permission "acquire_svc".</para>
732
733
734<para>The security context for a bus name is specified with the 
735&lt;associate&gt; element described earlier in this document.
736If a name has no security context associated in the 
737configuration file, the security context of the bus daemon 
738itself will be used.</para>
739
740</refsect1>
741
742<refsect1 id='author'><title>AUTHOR</title>
743<para>See <ulink url='http://www.freedesktop.org/software/dbus/doc/AUTHORS'>http://www.freedesktop.org/software/dbus/doc/AUTHORS</ulink></para>
744
745</refsect1>
746
747<refsect1 id='bugs'><title>BUGS</title>
748<para>Please send bug reports to the D-Bus mailing list or bug tracker,
749see <ulink url='http://www.freedesktop.org/software/dbus/'>http://www.freedesktop.org/software/dbus/</ulink></para>
750</refsect1>
751</refentry>
752
753