ProFTPD module mod

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_redis for Redis-based access lists/sets
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.

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 directive.

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 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.

WrapOptions

Syntax: WrapOptions opt1 ...
Default: None
Context: server config, <VirtualHost>, <Global>
Module: mod_wrap2
Compatibility: 1.3.4rc1 and later

The WrapOptions directive is used to configure various optional behavior of mod_wrap2. Note: all of the configured WrapOptions parameters must appear on the same line in the configuration; only the first WrapOptions directive that appears in the configuration is used.

Example:

  WrapOptions CheckOnConnect

The currently implemented options are:

CheckAllNames

This causes mod_wrap2 to check all of the known DNS names for the client IP address against the DNS names/patterns in the access rules, rather than just checking the first DNS name returned for the client IP address.
CheckOnConnect

This causes mod_wrap2 to check the allow/deny tables when the client first connects, rather than waiting until the client has authenticated before checking the access rules. This means that per-user/group allow/deny tables, and the use of the tilde (~) notation in table paths, is not supported when this option is used.
In addition, if mod_wrap2_sql is used, the order in which that module is loaded is very important. The mod_sql module must appear after the mod_wrap2 module in the --with-modules configure option, e.g.:
```
    --with-modules=mod_wrap2:mod_wrap2_sql:mod_sql:mod_sql_mysql
```
Or, if you are using shared/DSO modules, then you must ensure that the modules are loaded in the correct order via LoadModule:
```
  ...
  LoadModule mod_wrap2.c
  LoadModule mod_wrap2_sql.c
  ...
  LoadModule mod_sql.c
  LoadModule mod_sql_mysql.c
  ...
```
You will also need to ensure that mod_sql creates a database connection at connect time, using the PERCONNECTION connection policy; see SQLConnectInfo for more details:
```
  SQLConnectInfo database user password PERCONNECTION
```
Without this, the database connection will not be created at connect time, and the mod_wrap2 module will be unable to check any allow/deny rules stored in SQL tables when the client connects.

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.

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.

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 multiple 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 explicitly 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 an IPv4 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.
An expression of the form [address]/number is interpreted as an IPv6 net/mask pair. An IPv6 address is matched if the first number bits match the rule address. For example, [3ffe:505:2:1::]/64 matches every address in the range 3ffe:505:2:1:: through 3ffe:505:2:1:ffff:ffff:ffff:ffff:.
A string that begins with a `/' character is treated as a file name. A host name or address is matched if it matches any host name or address pattern listed in the named file. The file format is zero or more lines with zero or more host name or address patterns separated by whitespace. A file name pattern can be used anywhere a host name or address pattern can be used.
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

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.