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.

OpenSER 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. 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.

1.1.3. Referral Permissions

The module can be used to determine if referral is allowed to the destination specified by Refer-To header of REFER request. Permission rules are stored in plaintext configuration files similar to hosts.allow and hosts.deny used by tcpd.

When allow_refer_to function is called, it tries to find a rule that matches selected fields of the message. The matching algorithm is as follows, first match wins:

• Create a pair <From URI, Refer-To URI>.

• Referral will be allowed when the pair matches an entry in the allow file.

• Otherwise referral will be denied when the pair matches an entry in the deny file.

• Otherwise, referral 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 URI and Refer-To URI are always compared with regular expressions! For the syntax see the sample file: config/permissions.allow.

1.1.4. Trusted Requests

The module can be used to determine if an incoming request can be trusted without authentication.

When allow_trusted function is called, it tries to find a rule that matches the request. Rules contain the following fields: <source address, transport protocol, regular expression>.

A requests is accepted if there exists a rule, where

• source address is equal to source address of request,

• transport protocol is either "any" or equal to transport protocol of request, and

• regular expression matches From URI of request.

Otherwise the request is rejected.

Rules are stored in a database table specified by module parameters. There also exists a module parameter that determines if rules are cached into memory for faster matching or if database is consulted for each invocation of allow_trusted function call.

1.2.1. OpenSER Modules

The following modules must be loaded before this module:

• No dependencies on other OpenSER modules.

1.2.2. External Libraries or Applications

The following libraries or applications must be installed before running OpenSER with this module loaded:

• None.

1.3.1. 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".

...
modparam("permissions", "default_allow_file", "/etc/permissions.allow")
...

1.3.2. 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".

...
modparam("permissions", "default_deny_file", "/etc/permissions.deny")
...

1.3.3. 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.

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

Default value is 1.

...
modparam("permissions", "check_all_branches", 0)
...

1.3.4. 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.

Including leading dot.

Default value is ".allow".

...
modparam("permissions", "allow_suffix", ".allow")
...

1.3.5. 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.

Including leading dot.

Default value is ".deny".

...
modparam("permissions", "deny_suffix", ".deny")
...

1.3.6. db_url (string)

This is URL of the database to be used to store rules used by allow_trusted function.

Default value is "NULL".

...
modparam("permissions", "db_url", "mysql://openser:pass@db_host/openser")
...

1.3.7. db_mode (integer)

Database mode. 0 means non-caching, 1 means caching.

Default value is 0 (non-caching).

...
modparam("permissions", "db_mode", 1)
...

1.3.8. trusted_table (string)

Name of database table containing matching rules used by allow_register function.

Default value is "trusted".

...
modparam("permissions", "trusted_table", "pbx")
...

1.3.9. source_col (string)

Name of trusted table column containing source IP address that is matched against source IP address of received request.

Default value is "src_ip".

...
modparam("permissions", "source_col", "source_ip_address")
...

1.3.10. proto_col (string)

Name of trusted table column containing transport protocol that is matched against transport protocol of received request. Possible values that can be stored in proto_col are "any", "udp", "tcp", "tls", and "sctp".

Default value is "proto".

...
modparam("permissions", "proto_col", "transport")
...

1.3.11. from_col (string)

Name of trusted table column containing regular expression that is matched against From URI.

Default value is "from_pattern".

...
modparam("permissions", "from_col", "regexp")
...

1.4.1. allow_routing()

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

This function can be used from REQUEST_ROUTE, FAILURE_ROUTE.

...
if (allow_routing()) {
	t_relay();
};
...

1.4.2. allow_routing(basename)

Returns true if all pairs constructed as described in Section 1.1.1 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.

This function can be used from REQUEST_ROUTE, FAILURE_ROUTE.

...
if (allow_routing("basename")) {
	t_relay();
};
...

1.4.3. allow_routing(allow_file,deny_file)

Returns true if all pairs constructed as described in Section 1.1.1 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.

This function can be used from REQUEST_ROUTE, FAILURE_ROUTE.

...
if (allow_routing("rules.allow", "rules.deny")) {
	t_relay();
};
...

1.4.4. allow_register(basename)

The function returns true if all pairs constructed as described in Section 1.1.2 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.

This function can be used from REQUEST_ROUTE, FAILURE_ROUTE.

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

1.4.5. allow_register(allow_file, deny_file)

The function returns true if all pairs constructed as described in Section 1.1.2 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.

This function can be used from REQUEST_ROUTE, FAILURE_ROUTE.

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

1.4.6. allow_refer_to(basename)

Returns true if the pair constructed as described in Section 1.1.3 have appropriate permissions according to the configuration files specified by the parameter.

Meaning of the parameter 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.

This function can be used from REQUEST_ROUTE, FAILURE_ROUTE.

...
if (allow_refer_to("basename")) {
	t_relay();
};
...

1.4.7. allow_refer_to(allow_file, deny_file)

Returns true if the pair constructed as described in Section 1.1.3 have appropriate permissions according to the configuration files specified by 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.

This function can be used from REQUEST_ROUTE, FAILURE_ROUTE.

...
if (allow_refer_to("rules.allow", "rules.deny")) {
	t_relay();
};
...

1.4.8. allow_trusted()

Checks based on request's source address, transport protocol, and From URI if request can be trusted without authentication. Returns 1 if a match is found as described in Section 1.1.4 and -1 otherwise.

This function can be used from REQUEST_ROUTE, FAILURE_ROUTE.

...
if (allow_trusted()) {
	t_relay();
};
...

1.5.1. trusted_reload

Causes permissions module to re-read the contents of trusted table into cache memory.

1.5.2. trusted_dump

Causes permissions module to dump contents of trusted table from cache memory.