<!-- Module User's Guide -->

<chapter>
    <chapterinfo>
	<revhistory>
	    <revision>
		<revnumber>$Revision: 1.3.2.1 $</revnumber>
		<date>$Date: 2005/06/22 23:12:07 $</date>
	    </revision>
	</revhistory>
    </chapterinfo>
    <title>User's Guide</title>
    
    <section>
	<title>Overview</title>
	<section id="sec-call-routing">
	    <title>Call Routing</title>
	    <para>
		The module can be used to determine if a call has appropriate permission to be
		established. Permission rules are stored in plaintext configuration files similar to
		<filename moreinfo="none">hosts.allow</filename> and <filename
		moreinfo="none">hosts.deny</filename> files used by tcpd.
	    </para>
	    <para>
		When <function moreinfo="none">allow_routing</function> function is called it tries
		to find a rule that matches selected fields of the message.
	    </para>
	    <para>
		SER is a forking proxy and therefore a single message can be sent to different
		destinations simultaneously. When checking permissions all the destinations must be
		checked and if one of them fails, the forwarding will fail.
	    </para>
	    <para>
		The matching algorithm is as follows, first match wins:
	    </para>
	    <itemizedlist>
		<listitem>
		    <para>
			Create a set of pairs of form (From, R-URI of branch 1), (From, R-URI of
			branch 2), etc.
		    </para>
		</listitem>
		<listitem>
		    <para>
			Routing will be allowed when all pairs match an entry in the allow file.
		    </para>
		</listitem>
		<listitem>
		    <para>
			Otherwise routing will be denied when one of pairs matches an entry in the
			deny file.
		    </para>
		</listitem>
		<listitem>
		    <para>
			Otherwise, routing will be allowed.
		    </para>
	    </listitem>
	    </itemizedlist>
	    <para>
		A non-existing permission control file is treated as if it were an empty file. Thus,
		permission control can be turned off by providing no permission control files.
	    </para>
	    <para>
		From header field and Request-URIs are always compared with regular expressions! For
		the syntax see the sample file: <filename moreinfo="none">config/permissions.allow</filename>.
	    </para>
	</section>
	<section id="sec-registration-permissions">
	    <title>Registration Permissions</title>
	    <para>
		In addition to call routing it is also possible to check REGISTER messages and
		decide--based on the configuration files--whether the message should be allowed and
		the registration accepted or not.
	    </para>
	    <para>
		Main purpose of the function is to prevent registration of "prohibited" IP
		addresses. One example, when a malicious user registers a contact containing IP
		address of a PSTN gateway, he might be able to bypass authorization checks performed
		by the SIP proxy. That is undesirable and therefore attempts to register IP address
		of a PSTN gateway should be rejected. Files <filename
		moreinfo="none">config/register.allow</filename> and <filename
		moreinfo="none">config/register.deny</filename> contain an example configuration.
	    </para>
	    <para>
		Function for registration checking is called <function
		moreinfo="none">allow_register</function> and the algorithm is very similar to the
		algorithm described in <xref linkend="sec-call-routing">. The only difference is in
		the way how pairs are created.
	    </para>
	    <para>
		Instead of From header field the function uses To header field because To header
		field in REGISTER messages contains the URI of the person being registered. Instead
		of the Request-URI of branches the function uses Contact header field.
	    </para>
	    <para>
		Thus, pairs used in matching will look like this: (To, Contact 1), (To, Contact
		2), (To, Contact 3), and so on..
	    </para>
	    <para>
		The algorithm of matching is same as described in <xref linkend="sec-call-routing">.
	    </para>
	</section>
    </section>
    <section>
	<title>Dependencies</title>
	<section>
	    <title>&ser; Modules</title>
	    <para>
		The following modules must be loaded before this module:
	    	<itemizedlist>
		    <listitem>
			<para>
			    <emphasis>No dependencies on other &ser; modules</emphasis>.
			</para>
		    </listitem>
	    	</itemizedlist>
	    </para>
	</section>
	<section>
	    <title>External Libraries or Applications</title>
	    <para>
		The following libraries or applications must be installed before running
		&ser; with this module loaded:
	    	<itemizedlist>
		    <listitem>
			<para>
			    <emphasis>None</emphasis>.
			</para>
		    </listitem>
	    	</itemizedlist>
	    </para>
	</section>
    </section>
    <section>
	<title>Exported Parameters</title>
	<section>
	    <title><varname>default_allow_file</varname> (string)</title>
	    <para>
		Default allow file used by functions without parameters. If you don't specify full
		pathname then the directory in which is the main config file is located will be used.
	    </para>
	    <para>
		<emphasis>
		    Default value is <quote>permissions.allow</quote>.
		</emphasis>
	    </para>
	    <example>
		<title>Set <varname>default_allow_file</varname> parameter</title>
		<programlisting format="linespecific">
...
modparam("permissions", "default_allow_file", "/etc/permissions.allow")
...
</programlisting>
	    </example>
	</section>
	<section>
	    <title><varname>default_deny_file</varname> (string)</title>
	    <para>
		Default file containing deny rules. The file is used by functions without
		parameters. If you don't specify full pathname then the directory in which the
		main config file is located will be used.
	    </para>
	    <para>
		<emphasis>
		    Default value is <quote>permissions.deny</quote>.
		</emphasis>
	    </para>
	    <example>
		<title>Set <varname>default_deny_file</varname> parameter</title>
		<programlisting format="linespecific">
...
modparam("permissions", "default_deny_file", "/etc/permissions.deny")
...
</programlisting>
	    </example>
	</section>
	<section>
	    <title><varname>check_all_branches</varname> (integer)</title>
	    <para>
		If set then allow_routing functions will check Request-URI of all branches
		(default). If disabled then only Request-URI of the first branch will be checked.
	    </para>
	    <warning>
		<para>
		    Do not disable this parameter unless you really know what you are doing.
		</para>
	    </warning>
	    <para>
		<emphasis>
		    Default value is 1.
		</emphasis>
	    </para>
	    <example>
		<title>Set <varname>check_all_branches</varname> parameter</title>
		<programlisting format="linespecific">
...
modparam("permissions", "check_all_branches", 0)
...
</programlisting>
	    </example>
	</section>
	<section>
	    <title><varname>allow_suffix</varname> (string)</title>
	    <para>
		Suffix to be appended to basename to create filename of the allow file when version
		with one parameter of either <function moreinfo="none">allow_routing</function> or
		<function moreinfo="none">allow_register</function> is used.
	    </para>
	    <note>
		<para>
		    Including leading dot.
		</para>
	    </note>
	    <para>
		<emphasis>
		    Default value is <quote>.allow</quote>.
		</emphasis>
	    </para>
	    <example>
		<title>Set <varname>allow_suffix</varname> parameter</title>
		<programlisting format="linespecific">
...
modparam("permissions", "allow_suffix", ".allow")
...
</programlisting>
	    </example>
	</section>
	<section>
	    <title><varname>deny_suffix</varname> (string)</title>
	    <para>
		Suffix to be appended to basename to create filename of the deny file when version
		with one parameter of either <function moreinfo="none">allow_routing</function> or
		<function moreinfo="none">allow_register</function> is used.
	    </para>
	    <note>
		<para>
		    Including leading dot.
		</para>
	    </note>
	    <para>
		<emphasis>
		    Default value is <quote>.deny</quote>.
		</emphasis>
	    </para>
	    <example>
		<title>Set <varname>deny_suffix</varname> parameter</title>
		<programlisting format="linespecific">
...
modparam("permissions", "deny_suffix", ".deny")
...
</programlisting>
	    </example>
	</section>

	<section>
	    <title><varname>db_url</varname> (string)</title>
	    <para>
		The URL of database to be used to obtain the list of trusted hosts.
	    </para>
	    <para>
		<emphasis>
		    Default value is "mysql://ser:heslo@localhost/ser".
		</emphasis>
	    </para>
	</section>

	<section>
	    <title><varname>db_mode</varname> (integer)</title>
	    <para>
		This parameter controls the cache that speeds up lookups of
		trusted hosts. The value 1 enables cache, 0 disables it (each
		query would result in a database lookup).
	    </para>
	    <para>
		<emphasis>
		    Default value is 0 (disable cache).
		</emphasis>
	    </para>
	</section>

	<section>
	    <title><varname>trusted_table</varname> (string)</title>
	    <para>
		The name of the table in database containing the list of
		trusted hosts.
	    </para>
	    <para>
		<emphasis>
		    Default value is "trusted".
		</emphasis>
	    </para>
	</section>

	<section>
	    <title><varname>source_col</varname> (string)</title>
	    <para>
		The name of the column in trusted table which contains source
		IP address.
	    </para>
	    <para>
		<emphasis>
		    Default value is "src_ip".
		</emphasis>
	    </para>
	</section>

	<section>
	    <title><varname>proto_col</varname> (string)</title>
	    <para>
		The name of the column in trusted table which contains the
		protocol identifier (UDP, TCP, TLS).
	    </para>
	    <para>
		<emphasis>
		    Default value is "proto".
		</emphasis>
	    </para>
	</section>

	<section>
	    <title><varname>from_col</varname> (string)</title>
	    <para>
		The name of the column in trusted table which contains regular
		expressions that will be matched agains From header field.
	    </para>
	    <para>
		<emphasis>
		    Default value is "from_pattern".
		</emphasis>
	    </para>
	</section>	
    </section>

    <section>
	<title>Exported Functions</title>
	<section>
	    <title>
		<function moreinfo="none">allow_routing()</function>
	    </title>
	    <para>
		Returns true if all pairs constructed as described in <xref
		linkend="sec-call-routing"> have appropriate permissions according to the
		configuration files. This function uses default configuration files specified in
		<varname>default_allow_file</varname> and <varname>default_deny_file</varname>.
	    </para>
	    <example>
		<title><function>allow_routing</function> usage</title>
		<programlisting format="linespecific">
...
if (allow_routing()) {
    t_relay();
};
...
</programlisting>
	    </example>
	</section>
	<section>
	    <title>
		<function moreinfo="none">allow_routing(basename)</function>
	    </title>
	    <para>
		Returns true if all pairs constructed as described in <xref
		linkend="sec-call-routing"> have appropriate permissions according to the
		configuration files given as parameters.
	    </para>
	    <para>Meaning of the parameters is as follows:</para>
	    <itemizedlist>
		<listitem>
		    <para><emphasis>basename</emphasis> - Basename from which allow and deny
			filenames will be created by appending contents of
			<varname>allow_suffix</varname> and <varname>deny_suffix</varname>
			parameters.
		    </para>
		    <para>
			If the parameter doesn't contain full pathname then the function expects the
			file to be located in the same directory as the main configuration file of
			the server.
		    </para>
		</listitem>
	    </itemizedlist>
	    <example>
		<title><function>allow_routing(basename)</function> usage</title>
		<programlisting format="linespecific">
...
if (allow_routing("basename")) {
    t_relay();
};
...
</programlisting>
	    </example>
	</section>
	<section>
	    <title>
		<function moreinfo="none">allow_routing(allow_file, deny_file)</function>
	    </title>
	    <para>
		Returns true if all pairs constructed as described in <xref
		linkend="sec-call-routing"> have appropriate permissions according to the
		configuration files given as parameters.
	    </para>
	    <para>Meaning of the parameters is as follows:</para>
	    <itemizedlist>
		<listitem>
		    <para><emphasis>allow_file</emphasis> - File containing allow rules.</para>
		    <para>
			If the parameter doesn't contain full pathname then the function expects the
			file to be located in the same directory as the main configuration file of
			the server.
		    </para>
		</listitem>
		<listitem>
		    <para><emphasis>deny_file</emphasis> - File containing deny rules.</para>
		    <para>
			If the parameter doesn't contain full pathname then the function expects the
			file to be located in the same directory as the main configuration file of
			the server.
		    </para>
		</listitem>
	    </itemizedlist>
	    <example>
		<title><function>allow_routing(allow_file, deny_file)</function> usage</title>
		<programlisting format="linespecific">
...
if (allow_routing("rules.allow", "rules.deny")) {
    t_relay();
};
...
</programlisting>
	    </example>
	</section>
	<section>
	    <title>
		<function moreinfo="none">allow_register(basename)</function>
	    </title>
	    <para>
		The function returns true if all pairs constructed as described in <xref
		linkend="sec-registration-permissions"> have appropriate permissions according to
		the configuration files given as parameters.
	    </para>
	    <para>Meaning of the parameters is as follows:</para>
	    <itemizedlist>
		<listitem>
		    <para><emphasis>basename</emphasis> - Basename from which allow and deny
			filenames will be created by appending contents of
			<varname>allow_suffix</varname> and <varname>deny_suffix</varname>
			parameters.
		    </para>
		    <para>
			If the parameter doesn't contain full pathname then the function expects the
			file to be located in the same directory as the main configuration file of
			the server.
		    </para>
		</listitem>
	    </itemizedlist>
	    <example>
		<title><function>allow_register(basename)</function> usage</title>
		<programlisting format="linespecific">
...
if (method=="REGISTER") {
    if (allow_register("register")) {
        save("location");
        break;
    } else {
        sl_send_reply("403", "Forbidden");
    };
};
...
</programlisting>
	    </example>
	</section>
	<section>
	    <title>
		<function moreinfo="none">allow_register(allow_file, deny_file)</function>
	    </title>
	    <para>
		The function returns true if all pairs constructed as described in <xref
		linkend="sec-registration-permissions"> have appropriate permissions according to
		the configuration files given as parameters.
	    </para>
	    <para>Meaning of the parameters is as follows:</para>
	    <itemizedlist>
		<listitem>
		    <para><emphasis>allow_file</emphasis> - File containing allow rules.</para>
		    <para>
			If the parameter doesn't contain full pathname then the function expects the
			file to be located in the same directory as the main configuration file of
			the server.
		    </para>
		</listitem>
		<listitem>
		    <para><emphasis>deny_file</emphasis> - File containing deny rules.</para>
		    <para>
			If the parameter doesn't contain full pathname then the function expects the
			file to be located in the same directory as the main configuration file of
			the server.
		    </para>
		</listitem>
	    </itemizedlist>
	    <example>
		<title><function>allow_register(allow_file, deny_file)</function> usage</title>
		<programlisting format="linespecific">
...
if (method=="REGISTER") {
    if (allow_register("register.allow", "register.deny")) {
        save("location");
        break;
    } else {
        sl_send_reply("403", "Forbidden");
    };
};
...
</programlisting>
	    </example>
	</section>

	<section>
	    <title>
		<function moreinfo="none">allow_trusted()</function>
	    </title>
	    <para>
		The function check the source IP, protocol, and the contents of
		From header field against entries in trusted table and returns
		true if there is a match. This means that the end-device is trusted.
	    </para>
	</section>
    </section>
</chapter>

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