3 .\" $Id: fw.1,v 1.7 1999/10/22 22:45:15 mdw Exp $
7 .\" (c) 1999 Straylight/Edgeware
10 .\"----- Licensing notice ---------------------------------------------------
12 .\" This file is part of the `fw' port forwarder.
14 .\" `fw' is free software; you can redistribute it and/or modify
15 .\" it under the terms of the GNU General Public License as published by
16 .\" the Free Software Foundation; either version 2 of the License, or
17 .\" (at your option) any later version.
19 .\" `fw' is distributed in the hope that it will be useful,
20 .\" but WITHOUT ANY WARRANTY; without even the implied warranty of
21 .\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
22 .\" GNU General Public License for more details.
24 .\" You should have received a copy of the GNU General Public License
25 .\" along with `fw'; if not, write to the Free Software Foundation,
26 .\" Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
28 .\" ---- Revision history ---------------------------------------------------
31 .\" Revision 1.7 1999/10/22 22:45:15 mdw
32 .\" Describe new socket connection options.
34 .\" Revision 1.6 1999/10/10 16:46:29 mdw
35 .\" Include grammar and options references at the end of the manual.
37 .\" Revision 1.5 1999/09/26 18:18:05 mdw
38 .\" Remove a fixed bug from the list. Fix some nasty formatting
41 .\" Revision 1.4 1999/08/19 18:32:48 mdw
42 .\" Improve lexical analysis. In particular, `chmod' patterns don't have to
43 .\" be quoted any more.
45 .\" Revision 1.3 1999/07/30 06:49:00 mdw
46 .\" Minor tidying and typo correction.
48 .\" Revision 1.2 1999/07/26 23:31:04 mdw
49 .\" Document lots of new features and syntax.
52 .\"----- Various bits of fancy styling --------------------------------------
54 .\" --- Indented paragraphs with right-aligned tags ---
58 \h'-\w'\fB\\$1\ \fP'u'\fB\\$1\ \fP\c
61 .\" --- Verbatim-oid typesetting ---
75 .\" --- Grammar markup ---
77 .\" This is mainly for the benefit of the automatic scripts which
78 .\" generate the grammar summary.
97 .\" --- Other bits of styling ---
113 .\"--------------------------------------------------------------------------
115 .TH fw 1 "1 July 1999" fw
117 .\"--------------------------------------------------------------------------
122 .\"--------------------------------------------------------------------------
131 .\"--------------------------------------------------------------------------
136 program is a simple port forwarder. It supports a number of features
137 the author hasn't found in similar programs:
139 .I "Connection logging"
140 Each connection attempt to the forwarder is logged, giving the time of
141 the connection, the DNS-resolved hostname (if available), and the user
142 name resulting from an RFC931 lookup. These lookups are done
143 asynchronously to the main forwarder's operation.
146 Each forwarded port may have an access control list attached to it.
147 Only authorized hosts are allowed to connect. Access control checks are
148 performed by quick checks on the client's IP address.
150 .I "Nonblocking single-process design"
151 The internal structure of the server is completely nonblocking. The
152 connections don't block; the reading and writing don't block; the name
153 lookups don't block. This is all done in a single process, with the
154 single exception of the DNS resolver.
156 .I "Support for Unix-domain sockets"
157 Connections from and to Unix-domain sockets can be handled just as
158 easily as more normal Internet sockets. Access control doesn't work on
159 Unix domain sockets, though. (Yet.)
160 .SS "Command line options"
163 program understands a few simple command line options:
166 Displays a screen of help text on standard output and exits
169 .B "\-v, \-\-version"
170 Writes the version number to standard output and exits successfully.
173 Writes a terse usage summary to standard output and exits successfully.
175 .BI "\-f, \-\-file=" file
176 Read configuration information from
181 configuration file statement.
183 .B "\-d, \-\-daemon, \-\-fork"
184 Forks into the background after reading the configuration and
185 initializing properly.
188 Don't output any logging information. This option is not recommended
189 for normal use, although it can make system call traces clearer so I use
192 Any further command line arguments are interpreted as configuration
193 lines to be read. Configuration supplied in command line arguments has
194 precisely the same syntax as configuration in files. If there are no
195 configuration statements on the command line, and no
197 options were supplied, configuration is read from standard input, if
198 stdin is not a terminal.
200 .\"--------------------------------------------------------------------------
201 .SH "CONFIGURATION LANGUAGE"
205 program has a fairly sophisticated configuration language to let you
206 describe which things should be forwarded where and what special
207 features there should be.
208 .SS "Lexical structure"
209 There are four types of characters.
211 .I "word constituent characters"
212 Word constituent characters are gathered together into words.
213 Depending on its surrounding context, a word might act as a keyword or a
214 string. All alphanumerics are word constituents, as is the hyphen
216 Other characters may change their status in future versions.
218 .I "self-delimiting characters"
219 Self-delimiting characters always stand alone. They act as punctuation,
220 shaping the sequence of words into more complex grammatical forms. The
233 are self-delimiting. Note that while some characters, e.g.,
237 require escaping by the shell, they are strictly optional in the grammar
238 and can be omitted in quick hacks at the shell prompt.
240 .I "whitespace characters"
241 Whitespace characters separate words but are otherwise ignored. All
242 `normal' whitespace characters (e.g., space, tab and newline) are
243 considered to be whitespace for these purposes.
245 .I "special characters"
246 There are three special characters. The
248 character, if it appears at the start of a word, introduces a
250 which extends to the end of the current line or command-line argument.
251 Within a word, it behaves like a normal word-constituent character. The
254 escapes the following character causing it to be interpreted as a word
255 constituent regardless of its normal type. The double-quote
257 escapes all characters other than backslashes up to the next
258 double-quote and causes them to be regarded as word constituents. Note
259 that you don't have to quote a whole word. The backslash can escape a
260 quote character allowing you to insert it into a word if really
264 The overall syntax looks a bit like this:
303 If you prefer, the keyword
311 .SS "Sources and targets"
312 Forwarding is set up by attaching
316 Sources are things which are capable of
318 one end of a data flow on their own, while targets are things which are
319 capable of setting up the other end on demand. In the case of a TCP
320 port forwarder, the part which listens for incoming client connections
321 is the source, while the part which sets up outgoing connections to the
322 destination server is the target.
326 does is set up a collection of sources and targets based on your
327 configuration file so that when a source decides to initiate a data
328 flow, it tells its target to set its end up, and then squirts data back
329 and forth between the two until there's no more.
333 they stay around indefinitely setting up multiple attachments to
336 they set up one connection and then disappear. If all the sources
337 defined are transient, then
339 will quit when no more active sources remain and all connections have
344 program is fairly versatile. It allows you to attach any supported type
345 of source to any supported type of target. This will, I hope, be the
346 case in all future versions.
352 depend on the source or target type, and are therefore described in the
353 sections specific to the various types.
355 .SS "Options structure"
356 Most of the objects that
358 knows about (including sources and targets, but also other more specific
359 things such as socket address types) can have their behaviour modified
362 The options available at a particular point in the configuration depend
365 A global option, outside of a
367 has no context unless it is explicitly qualified, and affects global
368 behaviour. Local options, applied to a source or target in a
370 has the context of the type of source or target to which it is applied,
371 and affects only that source or target.
373 Note that it's important to distinguish between an option's context
374 (which is affected by its qualification) and its local or global
375 status. No matter how qualified, a global option will always control
376 default options for objects, and a local option will only affect a
377 specific source or target.
379 The syntax for qualifying options is like this:
404 Thus, you may qualify either an individual option or a sequence of
405 options. The two are equivalent; for example,
414 exec.rlimit.core = 0;
417 For each option, there is a sequence of prefixes which maximally qualify
418 that option. An option prefixed with this sequence is
419 .IR "fully qualified" .
420 In actual use, some or all of those prefixes may be omitted. However,
421 it's possible for the option to become
423 if you do this. For example, the option
428 .BR socket.unix.fattr.owner .
429 In this case, the ambiguity is benign: a local option will have as its
430 context an appropriate source or target, and both global options
431 actually control the same default. However, the option
437 which have separate defaults, and which one you actually get depends on
438 the exact implementation of
440 option parser. (Currently this would resolve to
442 although this may change in a later version.)
444 In this manual, options are usually shown in their fully-qualified form.
446 .SS "File attributes for created files: `fattr'"
451 sources and targets can create new filesystem objects. The
453 options allow control over the attributes of the newly-created objects.
458 use the same set of defaults, so a prefix of
460 is good enough for setting global options, and the implicit context
461 disambiguates local options.
463 The following file attribute options are supported:
464 .OS "File attribute options (`fattr')"
465 .IB prefix .fattr.mode
469 Sets the permissions mode for a new file. The
471 argument may be either an octal number or a
473 string which acts on the default permissions established by the
476 setting. The characters
480 do not have to be quoted within the mode string.
482 .OS "File attribute options (`fattr')"
483 .IB prefix .fattr.owner
487 Sets the owner for newly created files. On non-broken systems you will
488 need to be the superuser to set the owner on a file. The
490 may either be a numeric uid or a username. The default is not to change
491 the owner of the file once it's created. The synonyms
495 are accepted in place of
498 .OS "File attribute options (`fattr')"
499 .IB prefix .fattr.group
503 Sets the group for newly created files. You will usually need to be a
504 member of the group in question order to set the group of a file. The
506 may either be a numeric gid or a group name. The default is not to
507 change the group of the file once it's created. The synonym
509 is accepted in place of
513 .SS "The `file' source and target types"
516 source and target allow data to move to and from objects other
517 than sockets within the Unix filesystem. (Unix-domain sockets are
524 is used as a source, it is set up immediately.
528 sources and targets is like this:
529 .GS "File sources and targets"
562 .RB [[ : ] file [ : ]]
592 specification describes two files, the first to be used as input, the
593 second to be used as output, each described by an
596 If none of the keywords
601 are given, the type of an
603 is deduced from its nature: if it matches one of the strings
607 or begins with a digit, it's considered to be a file descriptor;
608 otherwise it's interpreted as a filename.
612 spec describes a file by its name within the filesystem. It is opened
613 when needed and closed again after use. For output files, the precise
614 behaviour is controlled by options described below.
618 spec attaches the input or output of the source or target to
623 spec uses an existing open file descriptor, given either by number or a
624 symbolic name. The name
626 refers to standard input (file descriptor 0 on normal systems) and
628 refers to standard output (file descriptor 1). The names work in
629 exactly the same way as the equivalent file descriptor numbers.
633 is omitted, the input
635 is used for both input and output. Exception: if the input refers to
636 standard input then the output will refer to standard output instead.
640 options apply equally to sources and targets. The options are as
647 Whether to create the output file if it doesn't exist. If
649 (the default), an error is reported if the file doesn't exist. If
651 the file is created if it doesn't exist.
656 .BR no | truncate | append
658 Controls the behaviour if the output file already exists. If
660 an error is reported. If
662 (the default), the existing file is replaced by the new data. If
664 the new data is appended to the file.
671 source and target also accept
673 options for controlling the attributes of the created file.
676 Under no circumstances will
678 create a file through a `dangling' symbolic link.
680 .SS "The `exec' source and target types"
683 source and target execute programs and allow access to their standard
684 input and output streams. Both source and target have the same syntax,
686 .GS "Exec source and target"
726 If a single word is given, it is a
728 and will be passed to the Bourne shell for execution. If a
729 bracket-enclosed sequence of words is given, it is considered to be a
730 list of arguments to pass to the program: if a
732 is also supplied, it names the file containing the program to execute;
733 otherwise the file named by the first argument
737 The standard input and output of the program are forwarded to the other
738 end of the connection. The standard error stream is caught by
744 source and target both understand the same set of options. The list of
745 options supported is as follows:
751 Whether to log the start and end of executed programs. If
753 (the default), a log message is emitted when the program is started
754 listing its process id, and another is emitted when the program finishes
755 giving its process id and exit status. If
757 these messages are not emitted. However the standard error stream is
760 abbreviation is accepted as a synonym for
768 Sets the current directory from which the the program should be run.
769 The default is not to change directory. The synonyms
774 are accepted in place of
782 Sets the root directory for the program, using the
784 system call. You must be the superuser for this option to work. The
785 default is not to set a root directory. The synonyms
790 are accepted in place of
798 Sets the user (real and effective uid) to run the program as. This will
799 usually require superuser privileges to work. The default is not to
800 change uid. The synonym
802 is accepted in place of
810 Sets the group (real and effective gid) to run the program as. If
811 running with superuser privileges, the supplementary groups list is
812 cleared at the same time. The default is not to change gid (or clear
813 the supplementary groups list). The synonym
815 is accepted in place of
819 .BI exec.rlimit. limit \c
820 .RB [ .hard | .soft ]
824 Set resource limits for the program. The
826 may be one of the resource limit names described in
828 in lower-case and without the
836 is a number, followed optionally by
838 to multiply by 1024 (2\*(ss10\*(se),
840 to multiply by 1048576 (2\*(ss20\*(se), or
842 to multiply by 1073741824 (2\*(ss30\*(se); purists can use upper-case
843 versions of these if they want. If
847 was specified, only the hard or soft limit is set; otherwise both are
848 set to the same value. Only the superuser can raise the hard limit.
849 The soft limit cannot be set above the hard limit.
854 Clears the program's environment.
862 from the program's environment. It is not an error if no variable named
867 .BR exec.env. [ set ]
876 in the program's environment, possibly replacing the existing value.
879 may be omitted if the
881 qualifier is present.
884 Note that environment variable modifications are performed in order,
885 global modifications before local ones.
887 .SS "The `socket' source and target types"
890 source and target provide access to network services. Support is
891 currently provided for TCP/IP and Unix-domain sockets, although other
892 address types can be added with reasonable ease.
894 The syntax for socket sources and targets is:
895 .GS "Socket source and target"
922 The syntax of the source and target addresses depend on the address
923 types, which are described below. The default address type, if no
928 Socket sources support options; socket targets do not. The source
929 options provided are:
934 .BR unlimited | one-shot
936 Controls the behaviour of the source when it receives connections. A
938 limits the number of simultaneous connections. The value
942 removes any limit on the number of connections possible. The value
944 will remove the socket source after a single successful connection.
945 (Connections refused by access control systems don't count here.)
946 The default is to apply a limit of 256 concurrent connections. Use of
949 option is not recommended.
956 Whether to log incoming connections. If
958 (the default) incoming connections are logged, together with information
959 about the client (where available) and whether the connection was
960 accepted or refused. If
962 log messages are not generated.
965 Address types also provide their own options.
967 .SS "The `inet' socket address type"
970 address type provides access to TCP ports. The
972 source and target addresses have the following syntax:
973 .GS "Socket source and target"
1000 may be given as a port number or a service name from the
1002 file (or YP map if you do that sort of thing). A
1004 may be a textual hostname or a numerical IP address.
1008 source address accepts the following options:
1009 .OS "Socket options"
1010 .BR socket.inet. [ allow | deny ]
1016 Adds an entry to the source's access control list. If only one
1018 is given, the entry applies only to that address; if two are given, the
1019 first is a network address and the second is a netmask either in
1020 dotted-quad format or a simple number of bits (e.g.,
1024 mean the same), and the entry applies to any address which, when masked
1025 by the netmask, is equal to the masked network address.
1028 The access control rules are examined in the order: local entries first,
1029 then global ones, each in the order given in the configuration file.
1030 The first matching entry is used. If no entries match, the behaviour is
1033 of the last entry tried. If there are no entries defined, the default
1034 is to allow all clients.
1036 .SS "The `unix' socket address type"
1039 address type allows access to Unix-domain sockets. The syntax for
1041 source and target addresses is like this:
1042 .GS "Socket source and target"
1051 The following options are supported by the
1053 source address type:
1054 .OS "Socket options"
1055 .BR socket.unix.fattr. *
1059 source address accepts
1061 options to control the attributes of the socket file created.
1064 Sockets are removed if
1066 exits normally (which it will do if it runs out of sources or
1067 connections, or if killed by SIGINT or SIGTERM).
1069 To forward the local port 25 to a main mail server:
1071 from 25 to mailserv:25
1073 To attach a fortune server to a Unix-domain socket:
1075 from unix:/tmp/fortunes
1076 to exec [/usr/games/fortune] { user nobody }
1078 To fetch a fortune from the server:
1080 from file stdin, stdout to unix:/tmp/fortunes
1085 from stdin, null to null, stdout
1088 .\"--------------------------------------------------------------------------
1089 .SH "GRAMMAR SUMMARY"
1153 .SS "File source and target"
1180 .RB [[ : ] fd [ : ]]
1182 .RB | stdin | stdout
1186 .RB [[ : ] file [ : ]]
1212 .RB [ : ] null [ : ]
1214 .SS "Exec source and target"
1254 .SS "Socket source and target"
1313 .\"--------------------------------------------------------------------------
1314 .SH "OPTION SUMMARY"
1316 .SS "File attributes (`fattr')"
1317 .IB prefix .fattr.mode
1321 .IB prefix .fattr.owner
1325 .IB prefix .fattr.group
1336 .BR no | truncate | append
1361 .BI exec.rlimit. limit \c
1362 .RB [ .hard | .soft ]
1371 .BR exec.env. [ set ]
1376 .SS "Socket options"
1380 .BR unlimited | one-shot
1386 .BR socket.inet. [ allow | deny ]
1392 .BR socket.unix.fattr. *
1394 .\"--------------------------------------------------------------------------
1397 The syntax for IP addresses and filenames is nasty.
1399 IPv6 is not supported yet. Because of
1401 socket address architecture, it's probably not a major piece of work to
1404 Please inform me of any security problems you think you've identified in
1405 this program. I take security very seriously, and I will fix security
1406 holes as a matter of priority when I find out about them. I will be
1407 annoyed if I have to read about problems on Bugtraq because they weren't
1410 .\"--------------------------------------------------------------------------
1413 Mark Wooding, <mdw@nsict.org>
1415 .\"----- That's all, folks --------------------------------------------------
~mdw / fwd / blob