1. Permissions Module

Miklos Tirpak

Juha Heinanen

   Copyright © 2003, 2006 Miklos Tirpak, Juha Heinanen, iptelorg GmbH
   Revision History
   Revision $Revision: 1.6.2.1 $ $Date: 2008/06/11 13:12:01 $
     __________________________________________________________________

   1.1. Overview

        1.1.1. Call Routing
        1.1.2. Registration Permissions
        1.1.3. Refer-To Permissions
        1.1.4. Refer-To Permissions

   1.2. Parameters

        1.2.1. default_allow_file (string)
        1.2.2. default_deny_file (string)
        1.2.3. check_all_branches (integer)
        1.2.4. allow_suffix (string)
        1.2.5. deny_suffix (string)
        1.2.6. max_rule_files (int)
        1.2.7. safe_file_load (int)
        1.2.8. db_url (string)
        1.2.9. db_mode (int)
        1.2.10. ipmatch_table (string)

   1.3. Functions

        1.3.1. allow_routing()
        1.3.2. allow_routing(basename)
        1.3.3. allow_routing(allow_file, deny_file)
        1.3.4. allow_register(basename)
        1.3.5. allow_register(allow_file, deny_file)
        1.3.6. allow_refer_to(basename)

1.1. Overview

1.1.1. Call Routing

   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 hosts.allow and hosts.deny files used by
   tcpd.

   When allow_routing function is called it tries to find a rule that
   matches selected fields of the message.

   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.

   The matching algorithm is as follows, first match wins:
     * Create a set of pairs of form (From, R-URI of branch 1), (From,
       R-URI of branch 2), etc.
     * Routing will be allowed when all pairs match an entry in the allow
       file.
     * Otherwise routing will be denied when one of pairs matches an entry
       in the deny file.
     * Otherwise, routing will be allowed.

   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.

   From header field and Request-URIs are always compared with regular
   expressions! For the syntax see the sample file:
   config/permissions.allow.

1.1.2. Registration Permissions

   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.

   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 config/register.allow and config/register.deny
   contain an example configuration.

   Function for registration checking is called allow_register and the
   algorithm is very similar to the algorithm described in Section 1.1.1,
   "Call Routing". The only difference is in the way how pairs are
   created.

   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.

   Thus, pairs used in matching will look like this: (To, Contact 1), (To,
   Contact 2), (To, Contact 3), and so on..

   The algorithm of matching is same as described in Section 1.1.1, "Call
   Routing".

1.1.3. Refer-To Permissions

   In addition to call routing and REGISTER it is also possible to check
   REFER messages and decide--based on the configuration files-- whether
   or not the message should be accepted for forwarding.

   Main purpose of the function is to prevent referring a SIP UA to
   "prohibited" IP addresses. One example is user sending a REFER request
   to PSTN gateway trying to refer it to an expensive phone number.

   Function for Refer-To checking is called allow_refer_to and the
   algorithm is very similar to the algorithm described in Section 1.1.1.
   The only difference is in the way how pairs are created.

   Instead of Request-URI the function uses Refer-To header field because
   Refer-To header field in REFER messages contains the URI to which the
   UA is being referred to. The algorithm of matching is same as described
   in Section 1.1.1.

1.1.4. Refer-To Permissions

   The module can be also used for catching messages coming from or going
   to specific network elements, for example gateways or peering partners.

   Users can register or forward the calls to the address of a gateway
   resulting unauthorized access to them. Such calls must be catched and
   dropped, see ipmatch functions for details.

1.2. Parameters

   Revision History
   Revision $Revision: 1.6.2.1 $ $Date: 2008/06/11 13:12:01 $

1.2.1. default_allow_file (string)

   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.

   Default value is "permissions.allow".

   Example 1. Set default_allow_file parameter
...
modparam("permissions", "default_allow_file", "/etc/permissions.allow")
...

1.2.2. default_deny_file (string)

   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.

   Default value is "permissions.deny".

   Example 2. Set default_deny_file parameter
...
modparam("permissions", "default_deny_file", "/etc/permissions.deny")
...

   If both of the default file parameters are set to "" the module does
   not try to load them.

1.2.3. check_all_branches (integer)

   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.

Warning

   Do not disable this parameter unless you really know what you are
   doing.

   Default value is 1.

   Example 3. Set check_all_branches parameter
...
modparam("permissions", "check_all_branches", 0)
...

1.2.4. allow_suffix (string)

   Suffix to be appended to basename to create filename of the allow file
   when version with one parameter of either allow_routing or
   allow_register is used.

Note

   Including leading dot.

   Default value is ".allow".

   Example 4. Set allow_suffix parameter
...
modparam("permissions", "allow_suffix", ".allow")
...

1.2.5. deny_suffix (string)

   Suffix to be appended to basename to create filename of the deny file
   when version with one parameter of either allow_routing or
   allow_register is used.

Note

   Including leading dot.

   Default value is ".deny".

   Example 5. Set deny_suffix parameter
...
modparam("permissions", "deny_suffix", ".deny")
...

1.2.6. max_rule_files (int)

   Maximum number of allow/deny file pairs.

   Default value is 64.

1.2.7. safe_file_load (int)

   Module initialization fails in case of a missing config file if
   safe_file_load is true.

   Default value is 0 (false).

1.2.8. db_url (string)

   URL of the database to be used.

1.2.9. db_mode (int)

   Disables/enables database cache.

   Default value is 0 (cache is disabled)

   NOTE: ipmatch functions can operate only in cache mode, set db_mode to
   1 if you want to use them.

1.2.10. ipmatch_table (string)

   Name of the table containing ipmatch entries.

   Default value is "ipmatch".

1.3. Functions

   Revision History
   Revision $Revision: 1.6.2.1 $ $Date: 2008/06/11 13:12:01 $

1.3.1.  allow_routing()

   Returns true if all pairs constructed as described in Section 1.1.1,
   "Call Routing" have appropriate permissions according to the
   configuration files. This function uses default configuration files
   specified in default_allow_file and default_deny_file.

   Example 6. allow_routing usage
...
if (allow_routing()) {
    t_relay();
};
...

1.3.2.  allow_routing(basename)

   Returns true if all pairs constructed as described in Section 1.1.1,
   "Call Routing" have appropriate permissions according to the
   configuration files given as parameters.

   Meaning of the parameters is as follows:
     * basename - Basename from which allow and deny filenames will be
       created by appending contents of allow_suffix and deny_suffix
       parameters.
       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.

   Example 7. allow_routing(basename) usage
...
if (allow_routing("basename")) {
    t_relay();
};
...

1.3.3.  allow_routing(allow_file, deny_file)

   Returns true if all pairs constructed as described in Section 1.1.1,
   "Call Routing" have appropriate permissions according to the
   configuration files given as parameters.

   Meaning of the parameters is as follows:
     * allow_file - File containing allow rules.
       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.
     * deny_file - File containing deny rules.
       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.

   Example 8. allow_routing(allow_file, deny_file) usage
...
if (allow_routing("rules.allow", "rules.deny")) {
    t_relay();
};
...

1.3.4.  allow_register(basename)

   The function returns true if all pairs constructed as described in
   Section 1.1.2, "Registration Permissions" have appropriate permissions
   according to the configuration files given as parameters.

   Meaning of the parameters is as follows:
     * basename - Basename from which allow and deny filenames will be
       created by appending contents of allow_suffix and deny_suffix
       parameters.
       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.

   Example 9. allow_register(basename) usage
...
if (method=="REGISTER") {
    if (allow_register("register")) {
        save("location");
        break;
    } else {
        sl_send_reply("403", "Forbidden");
    };
};
...

1.3.5.  allow_register(allow_file, deny_file)

   The function returns true if all pairs constructed as described in
   Section 1.1.2, "Registration Permissions" have appropriate permissions
   according to the configuration files given as parameters.

   Meaning of the parameters is as follows:
     * allow_file - File containing allow rules.
       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.
     * deny_file - File containing deny rules.
       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.

   Example 10. allow_register(allow_file, deny_file) usage
...
if (method=="REGISTER") {
    if (allow_register("register.allow", "register.deny")) {
        save("location");
        break;
    } else {
        sl_send_reply("403", "Forbidden");
    };
};
...

1.3.6.  allow_refer_to(basename)

   The function returns true if all pairs constructed as described in
   Section 1.1.2, "Registration Permissions" have appropriate permissions
   according to the configuration files given as parameters.

   Meaning of the parameters is as follows:
     * basename - Basename from which allow and deny filenames will be
       created by appending contents of allow_suffix and deny_suffix
       parameters.
       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.

   Example 11. allow_register(basename) usage
...
if (method=="REGISTER") {
    if (allow_register("register")) {
        save("location");
        break;
    } else {
        sl_send_reply("403", "Forbidden");
    };
};
...
