NAME¶

unlang - FreeRADIUS Processing un-language

DESCRIPTION¶

FreeRADIUS supports a simple processing language in its configuration files. We call it an "un-language" because the intention is NOT to create yet another programming language. If you need something more complicated than what is described here, we suggest using the Perl or Python modules rlm_perl, or rlm_python. The goal of the language is to allow simple policies to be written with minimal effort. Those policies are then applied when a request is being processed. Requests are processed through virtual servers (including the default one), in the sections titled "authorize", "authenticate", "post-auth", "preacct", "accounting", "pre-proxy", "post-proxy", and "session". These policies cannot be used in any other part of the configuration files, such as module or client configuration.

KEYWORDS¶

The keywords for the language are a combination of pre-defined keywords, and references to loadable module names. We document only the pre-defined keywords here. Subject to a few limitations described below, any keyword can appear in any context. The language consists of a series of entries, each one one line. Each entry begins with a keyword. Entries are organized into lists. Processing of the language is line by line, from the start of the list to the end. Actions are executed per-keyword.

module-name

A reference to the named module. When processing reaches this point, the pre-compiled module is called. The module may succeed or fail, and will return a status to "unlang" if so. This status can be tested in a condition. See the "Simple Conditions" text in the CONDITIONS section, and MODULE RETURN CODES, below.

 

if

 

Checks for a particular condition. If true, the block after the condition is processed. Otherwise, the block is ignored. See CONDITIONS, below, for documentation on the format of the conditions.

 

else

 

Define a block to be executed only if the previous "if" condition returned false.

 

elsif

 

Define a block to be executed only if the previous "if" condition returned false, and if the specified condition evaluates to true.

 

switch

 

Evaluate the given string, and choose the first matching "case" statement inside of the current block. If the string is surrounded by double quotes, it is expanded as described in the DATA TYPES section, below.

 

No statement other than "case" can appear in a "switch" block.

 

case

 

Define a static string to match a parent "switch" statement. The strings given here are not expanded as is done with the parent "switch" statement.

 

A "case" statement cannot appear outside of a "switch" block.

 

A default entry can be defined by omitting the static string. This entry will be used if no other "case" entry matches. Only one default entry can exist in a "switch" section.

update

 

Update a particular attribute list, based on the attributes given in the current block.

 

The <list> can be one of "request", "reply", "proxy-request", "proxy-reply", "coa", "disconnect", or "control". The "control" list is the list of attributes maintainted internally by the server that controls how the server processes the request. Any attribute that does not go in a packet on the network will generally be placed in the "control" list. For backwards compatibility with older versions, "check" is accepted as a synonym for "control". The use of "check" is deprecated, and will be removed in a future release. For EAP methods with tunneled authentication sessions (i.e. PEAP and EAP-TTLS), the inner tunnel session can also reference "outer.request", "outer.reply", and "outer.control". Those references allow you to address the relevant list in the outer tunnel session. The "coa" and "disconnect" sections can only be used when the server receives an Access-Request or Accounting-Request. Use "request" and "reply" instead of "coa" when the server receives a CoA-Request or Disconnect-Request packet. Adding one or more attributes to either of the "coa" or "disconnect" list causes server to originate a CoA-Request or Disconnect-Request packet. That packet is sent when the current Access-Request or Accounting-Request has been finished, and a reply sent to the NAS. See raddb/sites-available/originate-coa for additional information. The only contents permitted in an "update" section are attributes and values. The contents of the "update" section are described in the ATTRIBUTES section below.

redundant

This section contains a simple list of modules. The first module is called when the section is being processed. If the first module succeeds in its operation, then the server stops processing the section, and returns to the parent section.

 

If, however, the module fails, then the next module in the list is tried, as described above. The processing continues until one module succeeds, or until the list has been exhausted.

 

Redundant sections can contain only a list of modules, and cannot contain keywords that perform conditional operations (if, else, etc) or update an attribute list.

 

load-balance

This section contains a simple list of modules. When the section is entered, one module is chosen at random to process the request. All of the modules in the list should be the same type (e.g. ldap or sql). All of the modules in the list should behave identically, otherwise the load-balance section will return different results for the same request.

 

Load-balance sections can contain only a list of modules, and cannot contain keywords that perform conditional operations (if, else, etc) or update an attribute list.

 

In general, we recommend using "redundant-load-balance" instead of "load-balance".

redundant-load-balance

This section contains a simple list of modules. When the section is entered, one module is chosen at random to process the request. If that module succeeds, then the server stops processing the section. If, however, the module fails, then one of the remaining modules is chosen at random to process the request. This process repeats until one module succeeds, or until the list has been exhausted.

 

All of the modules in the list should be the same type (e.g. ldap or sql). All of the modules in the list should behave identically, otherwise the load-balance section will return different results for the same request.

 

Load-balance sections can contain only a list of modules, and cannot contain keywords that perform conditional operations (if, else, etc) or update an attribute list.

 

CONDITIONS¶

The conditions are similar to C conditions in syntax, though quoted strings are supported, as with the Unix shell.

Simple

conditions

 

Evalutes to true if 'foo' is a non-empty string (single quotes, double quotes, or back-quoted). Also evaluates to true if 'foo' is a non-zero number. Note that the language is poorly typed, so the string "0000" can be interpreted as a numerical zero. This issue can be avoided by comparings strings to an empty string, rather than by evaluating the string by itself. If the word 'foo' is not a quoted string, then it can be taken as a reference to a named attribute. See "Referencing attribute lists", below, for examples of attribute references. The condition evaluates to true if the named attribute exists. Otherwise, if the word 'foo' is not a quoted string, and is not an attribute reference, then it is interpreted as a reference to a module return code. The condition evaluates to true if the most recent module return code matches the name given here. Valid module return codes are given in MODULE RETURN CODES, below.

Negation

Evalutes to true if 'foo' evaluates to false, and vice-versa. Short-circuit operators

Comparisons

Compares 'foo' to 'bar', and evaluates to true if the comparison holds true. Valid comparison operators are "==", "!=", "<", "<=", ">", ">=", "=~", and "!~", all with their usual meanings. Invalid comparison operators are ":=" and "=". Conditions may be nested to any depth, subject only to line length limitations (8192 bytes).

DATA TYPES¶

There are only a few data types supported in the language. Reference to attributes, numbers, and strings. Any data type can appear in stand-alone condition, in which case they are evaluated as described in "Simple conditions", above. They can also appear (with some exceptions noted below) on the left-hand or on the right-hand side of a comparison.

numbers

Numbers are composed of decimal digits. Floating point, hex, and octal numbers are not supported. The maximum value for a number is machine-dependent, but is usually 32-bits, including one bit for a sign value.

word

"strings"

'strings'

Single-quoted strings are evaluated as-is. Their values are not expanded as with double-quoted strings above, and they are not interpreted as attribute references.

`strings`

Back-quoted strings are evaluated by expanding the contents of the string, as described above for double-quoted strings. The resulting command given inside of the string in a sub-shell, and taking the output as a string. This behavior is much the same as that of Unix shells.

 

Note that for security reasons, the input string is split into command and arguments before variable expansion is done.

 

For performance reasons, we suggest that the use of back-quoted strings be kept to a minimum. Executing external programs is relatively expensive, and executing a large number of programs for every request can quickly use all of the CPU time in a server. If you believe that you need to execute many programs, we suggest finding alternative ways to achieve the same result. In some cases, using a real language may be sufficient.

/regex/i

These strings are valid only on the right-hand side of a comparison, and then only when the comparison operator is "=~" or "!~". They are regular expressions, as implemented by the local regular expression library on the system. This is usually Posix regular expressions.

 

The trailing 'i' is optional, and indicates that the regular expression match should be done in a case-insensitive fashion.

 

If the comparison operator is "=~", then parantheses in the regular expression will define variables containing the matching text, as described below in the VARIABLES section.

VARIABLES¶

Run-time variables are referenced using the following syntax Note that unlike C, there is no way to declare variables, or to refer to them outside of a string context. All references to variables MUST be contained inside of a double-quoted or back-quoted string. Many potential variables are defined in the dictionaries that accompany the server. These definitions define only the name and type, and do not define the value of the variable. When the server receives a packet, it uses the packet contents to look up entries in the dictionary, and instantiates variables with a name taken from the dictionaries, and a value taken from the packet contents. This process means that if a variable does not exist, it is usually because it was not mentioned in a packet that the server received. Once the variable is instantiated, it is added to an appropriate attribute list, as described below. In many cases, attributes and variables are inter-changeble, and are often talked about that way. However, variables can also refer to run-time calls to modules, which may perform operations like SQL SELECTs, and which may return the result as the value of the variable. Referencing attribute lists Results of regular expression matches Obtaining results from databases Conditional Syntax String lengths and arrays

ATTRIBUTES¶

The attribute lists described above may be edited by listing one or more attributes in an "update" section. Once the attributes have been defined, they may be referenced as described above in the VARIABLES section. The following syntax defines attributes in an "update" section. Each attribute and value has to be all on one line in the configuration file. There is no need for commas or semi-colons after the value. Attribute names

Operators

The operator used to assign the value of the attribute may be one of the following, with the given meaning.

Enforcement and Filtering Operators

Values

 

The format of the value is attribute-specific, and is usually a string, integer, IP address, etc. Prior to the attribute being instantiated, the value may be expanded as described above in the DATA TYPES section, above. This flexibility means that, for example, you can assign an IP address value to an attribute by specifying the IP address directly, or by having the address returned from a database query, or by having the address returned as the output of a program that is executed.

 

When string values are finally assigned to a variable, they can have a maximum length of 253 characters. This limit is due in part to both protocol and internal server requirements. That is, the strings in the language can be nearly 8k in length, say for a long SQL query. However, the output of that SQL query should be no more than 253 characters in length.

OTHER KEYWORDS¶

Other keywords in the language are taken from the names of modules loaded by the server. These keywords are dependent on both the modules, and the local configuration. Some use keywords that are defined in the default configuration file are:

fail

Cause the request to be treated as if a database failure had occurred.

noop

Do nothing. This also serves as an instruction to the configurable failover tracking that nothing was done in the current section.

ok

Instructs the server that the request was processed properly. This keyword can be used to over-ride earlier failures, if the local administrator determines that the faiures are not catastrophic.

reject

Causes the request to be immediately rejected

MODULE RETURN CODES¶

When a module is called, it returns one of the following codes to "unlang", with the following meaning. These return codes can be tested for in a condition, as described above in the CONDITIONS section. See also the file doc/configurable_failover for additional methods of trapping and modifying module return codes.

FILES¶

/etc/raddb/radiusd.conf

SEE ALSO¶

radiusd.conf(5), dictionary(5)

AUTHOR¶

Alan DeKok <aland@deployingradius.com>