ProFTPD module mod_wrap2

## ProFTPD module `mod_wrap2`

The `mod_wrap2` package allows the `proftpd` daemon to provide `tcpwrapper`-like access control rules while running in standalone mode. It also allows for those access rules to be stored in various formats, such as files (e.g. `/etc/hosts.allow` and `/etc/hosts.deny`) or in SQL tables. Note that the `mod_wrap2` module does not require or use the standard tcpwrappers `libwrap` library, and instead implements the same functionality internally (in order to support SQL-based access rules). Please read the usage documentation for more details.

This module is contained in `mod_wrap2.c`, `mod_wrap2.h`, and in the submodules source files, for ProFTPD 1.3.x. These modules are not enabled by default. Installation notes follow the directive documentation.

The most current version of `mod_wrap2`'s submodules supports storage of access table information in various formats:

- `mod_wrap2_file` for file-based access tables
- `mod_wrap2_sql` for SQL-based access tables

The most current version of `mod_wrap2` is distributed with the ProFTPD source code.

## Author

Please contact TJ Saunders <tj at castaglia.org> with any questions, concerns, or suggestions regarding this module.

## Thanks

Many, many thanks to Wietse Venema for writing the `tcpwrappers` package and its `libwrap` library, from which this module drew much of its code.

2002-12-12: Thanks to Steve Grubb for pointing out a few cases where interrupted functions were not being properly handled, and for reviewing the module code.

## Directives

- WrapAllowMsg
- WrapDenyMsg
- WrapEngine
- WrapGroupTables
- WrapLog
- WrapServiceName
- WrapTables
- WrapUserTables

## WrapAllowMsg

Syntax: WrapAllowMsg mesg
Default: None
Context: server config, `<VirtualHost`, `<Global>`, `<Anonymous>`
Module: mod_wrap2
Compatibility: 1.3.1rc1 and later

The `WrapAllowMsg` directive configures a message that will be added to `proftpd`'s response to the connecting client when that client is allowed by `mod_wrap2`'s access check. In the mesg parameter, the magic cookie '%u' is replaced with the username specified by the client during login.

Example:

      WrapAllowMsg "User '%u' allowed by access rules"

## WrapDenyMsg

Syntax: WrapDenyMsg mesg
Default: None
Context: server config, `<VirtualHost`, `<Global>`, `<Anonymous>`
Module: mod_wrap2
Compatibility: 1.3.1rc1 and later

The `WrapDenyMsg` directive configures a message that will be sent to the connecting client when that client is denied by `mod_wrap2`'s access check, and disconnected. In the mesg parameter, the magic cookie '%u' is replaced with the username specified by the client during login.

Example:

      WrapDenyMsg "User '%u' denied by access rules"

## WrapEngine

Syntax: WrapEngine on|off
Default: None
Context: server config, `<VirtualHost>`, `<Global>`
Module: mod_wrap2
Compatibility: 1.3.1rc1 and later

The `WrapEngine` directive enables or disables the module's runtime access control engine. If it is set to off this module does no runtime processing at all. Use this directive to disable the module instead of commenting out all `mod_wrap2` directives.

## WrapGroupTables

Syntax: WrapGroupTables group-AND-expression source-type:allow-source-info source-type:deny-source-info [source-type:options-source-info]
Default: None
Context: server config, `<VirtualHost`, `<Global>`, `<Anonymous>`
Module: mod_wrap2
Compatibility: 1.3.1rc1 and later

The `WrapGroupTables` directive configures the information necessary for `mod_wrap2` to locate and use the tables containing the access rules for specific groups.

The group-AND-expression parameter is a logical AND expression, which means that the connecting user must be a member of all the groups listed for this directive to apply. Group names may be negated with a `!` prefix.

The next two parameters specify two tables, an allow and a deny table, each of which contain the IP addresses, networks or host/network masks to be allowed or denied.

Please consult the relevant submodule documentation for details on that module's syntax for specifying tables. The service name for which `mod_wrap2` will look in the indicated access tables is "proftpd" by default; this can be configured via the WrapServiceName, WrapTables, WrapUserTables

## WrapLog

Syntax: WrapLog file|"none"
Default: None
Context: server config, `<VirtualHost>`, `<Global>`
Module: mod_wrap2
Compatibility: 1.3.1rc1 and later

The `WrapLog` directive is used to a specify a log file for `mod_wrap2` reporting, and can be done a per-server basis. The file parameter must be the full path to the file to use for logging. Note that this path must not be to a world-writeable directory and, unless `AllowLogSymlinks` is explicitly set to on (generally a bad idea), the path must not be a symbolic link.

If file is "none", no logging will be done at all; this setting can be used to override a `WrapLog` setting inherited from a `<Global>` context.

## WrapServiceName

Syntax: WrapServiceName name
Default: `WrapServiceName proftpd`
Context: server config, `<VirtualHost>`, `<Global>`
Module: mod_wrap2
Compatibility: 1.3.1rc1 and later

`WrapServiceName` is used to configure the name of the service under which `mod_wrap2` will check the allow/deny tables. By default, this is the name of the program started, i.e. "proftpd". However, some administrators may want to use a different, more generic service name, such as "ftpd"; use this directive for such needs. The lookup using the configured name is case-sensitive.

## WrapTables

Syntax: WrapTables source-type:allow-source-info source-info:deny-source-info
Default: None
Context: server config, `<VirtualHost`, `<Global>`, `<Anonymous>`
Module: mod_wrap2
Compatibility: 1.3.1rc1 and later

The `WrapTables` directive configures the information necessary for `mod_wrap2` to locate and use the tables containing the access rules for all clients.

The two parameters specify two tables, an allow and a deny table, each of which contain the IP addresses, networks or host/network masks to be allowed or denied.

Please consult the relevant submodule documentation for details on that module's syntax for specifying tables. The service name for which `mod_wrap2` will look in the indicated access tables is "proftpd" by default; this can be configured via the WrapGroupTables, WrapServiceName, WrapUserTables

## WrapUserTables

Syntax: WrapUserTables user-OR-expression source-type:allow-source-info source-type:deny-source-info [source-type:option-source-info]
Default: None
Context: server config, `<VirtualHost`, `<Global>`, `<Anonymous>`
Module: mod_wrap2
Compatibility: 1.3.1rc1 and later

The `WrapUserTables` directive configures the information necessary for `mod_wrap2` to locate and use the tables containing the access rules for specific users.

The user-OR-expression parameter is a logical OR expression, which means that the connecting user can be any the users listed for this directive to apply. User names may be negated with a `!` prefix.

The next two parameters specify two tables, an allow and a deny table, each of which contain the IP addresses, networks or host/network masks to be allowed or denied.

Please consult the relevant submodule documentation for details on that module's syntax for specifying tables. The service name for which `mod_wrap2` will look in the indicated access tables is "proftpd" by default; this can be configured via the WrapGroupTables, WrapServiceName, WrapTables

## Usage

To use `mod_wrap2`'s functionality, you must first define the tables that together contain the access rules. Access rules are composed of daemon lists, client lists, and optional options lists. daemon lists are used so that the access rules can be configured for mulitple daemons; `mod_wrap2` ignores all daemons except that configured for `proftpd`. client lists are the heart of the access rules, specifying the host names, IP addresses, etc to be allowed or denied. The handling of options lists is done only if `mod_wrap2` is configured with the `--enable-wrapper-options option.

There is a built-in precedence to the `WrapUserTables`, `WrapGroupTables`, and `WrapTables` directives, if all are used. `mod_wrap2` will look for applicable `WrapUserTables` for the connecting user first. If no applicable `WrapUserTables` are found, `mod_wrap2` will search for `WrapGroupTables` which pertain to the connecting user. If not found, `mod_wrap2` will then look for the server-wide `WrapTables` directive. This allows for access control to be set on a per-server basis, and allow for per-user or per-group access control to be handled without interfering with the overall server access rules.

When checking the tables, `mod_wrap2` always checks the allow table first. If the client has been explicitly allowed by the rules in that table, processing stops and `mod_wrap2` allows the client to continue the session. If not explicitly allowed, `mod_wrap2` will then check the deny table's access rules. If the client has been explicity denied by rules in that table, `mod_wrap2` will disconnect the client. By default, if neither explicitly allowed or explicitly denied, `mod_wrap2` will allow the client to continue.

In addition to the various formats supported by the submodules, there is a special source type: "builtin". This is used in the situations where the administrator wishes to configure "mostly closed" access rules, the most common situation. For example, if all clients are to be denied by `mod_wrap2` by default, unless that client is granted access via an allow table entry, then the administrator can use:

      builtin:all

as the deny table parameter (e.g. in a `WrapUserTables`, `WrapGroupTables`, or `WrapTables` directive), rather than configuring a static deny table that always says ALL.

### Access Rules

When checking access rules, the check terminates when the first match is found. A client list is a list of one or more host names, host addresses, patterns or wildcards (see below) that will be matched against the client host name or address. The more complex daemon@host and user@host forms are explained in the sections on server endpoint patterns and on client username lookups, respectively. With the exception of NIS/YP netgroup lookups, all access control checks are case insensitive.

Patterns
The access control language implements the following patterns:

- A string that begins with a `.' character. A host name is matched if the last components of its name match the specified pattern. For example, the pattern `.castaglia.org` matches the host name `golem.devlan.castaglia.org`.

- A string that ends with a `.' character. A host address is matched if its first numeric fields match the given string. For example, the pattern `131.155.` matches the address of (almost) every host on the Eindhoven University network (`131.155.x.x`).

- A string that begins with an `@' character is treated as an NIS (formerly YP) netgroup name. A host name is matched if it is a host member of the specified netgroup. Netgroup matches are not supported for client user names. Note that `mod_wrap2` must be configured for NIS support for netgroup lookups to occur.

- An expression of the form n.n.n.n/m.m.m.m is interpreted as a `net/mask` pair. An IPv4 address is matched if the `net` portion is equal to the bitwise AND of the address and the `mask` portion. For example, the `net/mask` pattern `131.155.72.0/255.255.254.0` matches every address in the range `131.155.72.0` through `131.155.73.255`.

- Wildcards `*' and `?' can be used to match hostnames or IP addresses. This method of matching cannot be used in conjunction with `net/mask` matching, hostname matching beginning with `.' or IP address matching ending with `.'.

Wildcards
The access control language supports explicit wildcards:

- ALL
  The universal wildcard, always matches.

- LOCAL
  Matches any host whose name does not contain a dot character.

- UNKNOWN
  Matches any user whose name is unknown, and matches any host whose name or address are unknown. This pattern should be used with care: host names may be unavailable due to temporary name server problems.

- KNOWN
  Matches any user whose name is known, and matches any host whose name and address are known. This pattern should be used with care: host names may be unavailable due to temporary name server problems.

- PARANOID
  Matches any host whose name does not match its address, before looking at the access control tables.

Operators

- EXCEPT
  Intended use is of the form:

        list1 EXCEPT list2

  This construct matches anything that matches list1 unless it matches list2. The EXCEPT operator can be used in daemon lists and client lists. The EXCEPT operator can be nested: if the control language would permit the use of parentheses:

        a EXCEPT b EXCEPT c

  would parse as

        (a EXCEPT (b EXCEPT c))

Server Endpoint Patterns
In order to distinguish clients by the network address that they connect to, use patterns of the form:

      process-name@host-pattern : client-list ...

Patterns like these can be used when the machine has different Internet addresses with different Internet hostnames. Service providers can use this facility to offer FTP, GOPHER or WWW archives with Internet names that may even belong to different organizations. Some systems can have more than one Internet address on one physical interface.

The host-pattern obeys the same syntax rules as host names and addresses in client lists.

Client Username Lookup
When the client host supports the RFC 931 protocol, the `proftpd` daemon can retrieve additional information about the owner of a connection. Client username information, when available (i.e. when `IdentLookups` are not disabled), is logged together with the client host name, and can be used to match patterns like:

      daemon-list : ... user-pattern@host-pattern ...

A user-pattern has the same syntax as a daemon pattern, so the same wildcards apply (netgroup membership is not supported). One should not get carried away with username lookups, though:

- The client username information cannot be trusted when it is needed most, i.e. when the client system has been compromised. In general, ALL and (UN)KNOWN are the only user name patterns that make sense.

- Username lookups are possible only when the client host runs a suitable daemon; in all other cases the result is "unknown".

### Access Options

This section describes optional options list portion the access control language described above. The options list syntax uses the following format:

      opt1 : opt2 ...

Any `:' characters within options should be protected with a backslash.

An option is of the form `"keyword"` or `"keyword value"`. Options are processed in the specified order. For the sake of backwards compatibility with earlier versions, a `=' is permitted between keyword and value.

- ALLOW
  Grant service. This option must appear at the end of a rule.

- DENY
  Deny service. This option must appear at the end of a rule.

The allow and deny keywords make it possible to keep all access control rules within a single file, for example in the `hosts.allow` file. To permit access from specific hosts only:

        ALL: .friendly.domain: ALLOW
        ALL: ALL: DENY

To permit access from all hosts except a few trouble makers:

        ALL: .bad.domain: DENY
        ALL: ALL: ALLOW

Notice the leading dot on the domain name patterns.

- nice [number]
  Change the nice value of the process (default 10). Specify a positive value to spend more CPU resources on other processes.

- setenv name=value
  Place a `name=value` pair into the process environment. The value may contain whitespace (but leading and trailing blanks are stripped off).

Diagnostics
When a syntax error is found in an options list, the error is reported in the `WrapLog` and the access option will be ignored.

## Installation

After unpacking the latest proftpd-1.3.x source code, follow the usual steps for using third-party modules in `proftpd`:

      ./configure --with-modules=wrap-modules
      make
      make install

where wrap-modules will depend on the types of access tables you wish to support.

For file-based access tables, include the `mod_wrap2_file` submodule, e.g.:

      mod_wrap2:mod_wrap2_file

For SQL-based access tables, include the `mod_wrap2_sql` submodule, e.g.:

      mod_wrap2:mod_wrap2_sql

And, if you wish to support both file- and SQL-based access tables, use:

      mod_wrap2:mod_wrap2_file:mod_wrap2_sql

Note that SQL tables require that a correct installation of `mod_sql` (and any of its backend modules) also be used. Consult the `mod_sql` documentation for installation instructions for that module.

Author: $Author: castaglia $
Last Updated: $Date: 2006/09/06 23:09:58 $

© Copyright 2000-2006 TJ Saunders
All Rights Reserved

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