3 .\" $Id: fw.1,v 1.9 2000/03/23 00:37:33 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 1.9 2000/03/23 00:37:33 mdw
32 .\" Add option to change user and group after initialization. Naughtily
33 .\" reassign short equivalents of --grammar and --options.
35 .\" Revision 1.8 1999/12/22 15:44:43 mdw
36 .\" Fix some errors, and document new option.
38 .\" Revision 1.7 1999/10/22 22:45:15 mdw
39 .\" Describe new socket connection options.
41 .\" Revision 1.6 1999/10/10 16:46:29 mdw
42 .\" Include grammar and options references at the end of the manual.
44 .\" Revision 1.5 1999/09/26 18:18:05 mdw
45 .\" Remove a fixed bug from the list. Fix some nasty formatting
48 .\" Revision 1.4 1999/08/19 18:32:48 mdw
49 .\" Improve lexical analysis. In particular, `chmod' patterns don't have to
50 .\" be quoted any more.
52 .\" Revision 1.3 1999/07/30 06:49:00 mdw
53 .\" Minor tidying and typo correction.
55 .\" Revision 1.2 1999/07/26 23:31:04 mdw
56 .\" Document lots of new features and syntax.
59 .\"----- Various bits of fancy styling --------------------------------------
61 .\" --- Indented paragraphs with right-aligned tags ---
65 \h'-\w'\fB\\$1\ \fP'u'\fB\\$1\ \fP\c
68 .\" --- Verbatim-oid typesetting ---
82 .\" --- Grammar markup ---
84 .\" This is mainly for the benefit of the automatic scripts which
85 .\" generate the grammar summary.
104 .\" --- Other bits of styling ---
120 .\"--------------------------------------------------------------------------
122 .TH fw 1 "1 July 1999" fw
124 .\"--------------------------------------------------------------------------
129 .\"--------------------------------------------------------------------------
142 .\"--------------------------------------------------------------------------
147 program is a simple port forwarder. It supports a number of features
148 the author hasn't found in similar programs:
150 .I "Connection logging"
151 Each connection attempt to the forwarder is logged, giving the time of
152 the connection, the DNS-resolved hostname (if available), and the user
153 name resulting from an RFC931 lookup. These lookups are done
154 asynchronously to the main forwarder's operation.
157 Each forwarded port may have an access control list attached to it.
158 Only authorized hosts are allowed to connect. Access control checks are
159 performed by quick checks on the client's IP address.
161 .I "Nonblocking single-process design"
162 The internal structure of the server is completely nonblocking. The
163 connections don't block; the reading and writing don't block; the name
164 lookups don't block. This is all done in a single process, with the
165 single exception of the DNS resolver.
167 .I "Support for Unix-domain sockets"
168 Connections from and to Unix-domain sockets can be handled just as
169 easily as more normal Internet sockets. Access control doesn't work on
170 Unix domain sockets, though. (Yet.)
171 .SS "Command line options"
174 program understands a few simple command line options:
177 Displays a screen of help text on standard output and exits
180 .B "\-v, \-\-version"
181 Writes the version number to standard output and exits successfully.
184 Writes a terse usage summary to standard output and exits successfully.
186 .B "\-G, \-\-grammar"
187 Writes a summary of the configuration file grammar to standard output
188 and exits successfully.
190 .B "\-O, \-\-options"
191 Writes a summary of the source and target options to standard output and
194 .BI "\-f, \-\-file=" file
195 Read configuration information from
200 configuration file statement.
202 .B "\-d, \-\-daemon, \-\-fork"
203 Forks into the background after reading the configuration and
204 initializing properly.
206 .B "\-l, \-\-syslog, \-\-log"
207 Emit logging information to the system log, rather than standard error.
210 Don't output any logging information. This option is not recommended
211 for normal use, although it can make system call traces clearer so I use
214 .BI "\-s, \-\-setuid=" user
215 Change uid to that of
217 which may be either a user name or uid number, after initializing all
218 the sources. This will usually require elevated privileges.
220 .BI "\-g, \-\-setgid=" group
221 Change gid to that of
223 which may be either a group name or gid number, after initializing all
224 the sources. If the operating system understands supplementary groups
225 then the supplementary groups list is altered to include only
228 Any further command line arguments are interpreted as configuration
229 lines to be read. Configuration supplied in command line arguments has
230 precisely the same syntax as configuration in files. If there are no
231 configuration statements on the command line, and no
233 options were supplied, configuration is read from standard input, if
234 stdin is not a terminal.
236 .\"--------------------------------------------------------------------------
237 .SH "CONFIGURATION LANGUAGE"
241 program has a fairly sophisticated configuration language to let you
242 describe which things should be forwarded where and what special
243 features there should be.
244 .SS "Lexical structure"
245 There are four types of characters.
247 .I "word constituent characters"
248 Word constituent characters are gathered together into words.
249 Depending on its surrounding context, a word might act as a keyword or a
250 string. All alphanumerics are word constituents, as is the hyphen
252 Other characters may change their status in future versions.
254 .I "self-delimiting characters"
255 Self-delimiting characters always stand alone. They act as punctuation,
256 shaping the sequence of words into more complex grammatical forms. The
269 are self-delimiting. Note that while some characters, e.g.,
273 require escaping by the shell, they are strictly optional in the grammar
274 and can be omitted in quick hacks at the shell prompt.
276 .I "whitespace characters"
277 Whitespace characters separate words but are otherwise ignored. All
278 `normal' whitespace characters (e.g., space, tab and newline) are
279 considered to be whitespace for these purposes.
281 .I "special characters"
282 There are three special characters. The
284 character, if it appears at the start of a word, introduces a
286 which extends to the end of the current line or command-line argument.
287 Within a word, it behaves like a normal word-constituent character. The
290 escapes the following character causing it to be interpreted as a word
291 constituent regardless of its normal type. The double-quote
293 escapes all characters other than backslashes up to the next
294 double-quote and causes them to be regarded as word constituents. Note
295 that you don't have to quote a whole word. The backslash can escape a
296 quote character allowing you to insert it into a word if really
300 The overall syntax looks a bit like this:
339 If you prefer, the keyword
347 .SS "Sources and targets"
348 Forwarding is set up by attaching
352 Sources are things which are capable of
354 one end of a data flow on their own, while targets are things which are
355 capable of setting up the other end on demand. In the case of a TCP
356 port forwarder, the part which listens for incoming client connections
357 is the source, while the part which sets up outgoing connections to the
358 destination server is the target.
362 does is set up a collection of sources and targets based on your
363 configuration file so that when a source decides to initiate a data
364 flow, it tells its target to set its end up, and then squirts data back
365 and forth between the two until there's no more.
369 they stay around indefinitely setting up multiple attachments to
372 they set up one connection and then disappear. If all the sources
373 defined are transient, then
375 will quit when no more active sources remain and all connections have
380 program is fairly versatile. It allows you to attach any supported type
381 of source to any supported type of target. This will, I hope, be the
382 case in all future versions.
388 depend on the source or target type, and are therefore described in the
389 sections specific to the various types.
391 .SS "Options structure"
392 Most of the objects that
394 knows about (including sources and targets, but also other more specific
395 things such as socket address types) can have their behaviour modified
398 The options available at a particular point in the configuration depend
401 A global option, outside of a
403 has no context unless it is explicitly qualified, and affects global
404 behaviour. Local options, applied to a source or target in a
406 has the context of the type of source or target to which it is applied,
407 and affects only that source or target.
409 Note that it's important to distinguish between an option's context
410 (which is affected by its qualification) and its local or global
411 status. No matter how qualified, a global option will always control
412 default options for objects, and a local option will only affect a
413 specific source or target.
415 The syntax for qualifying options is like this:
440 Thus, you may qualify either an individual option or a sequence of
441 options. The two are equivalent; for example,
450 exec.rlimit.core = 0;
453 For each option, there is a sequence of prefixes which maximally qualify
454 that option. An option prefixed with this sequence is
455 .IR "fully qualified" .
456 In actual use, some or all of those prefixes may be omitted. However,
457 it's possible for the option to become
459 if you do this. For example, the option
464 .BR socket.unix.fattr.owner .
465 In this case, the ambiguity is benign: a local option will have as its
466 context an appropriate source or target, and both global options
467 actually control the same default. However, the option
473 which have separate defaults, and which one you actually get depends on
474 the exact implementation of
476 option parser. (Currently this would resolve to
478 although this may change in a later version.)
480 In this manual, options are usually shown in their fully-qualified form.
482 .SS "File attributes for created files: `fattr'"
487 sources and targets can create new filesystem objects. The
489 options allow control over the attributes of the newly-created objects.
494 use the same set of defaults, so a prefix of
496 is good enough for setting global options, and the implicit context
497 disambiguates local options.
499 The following file attribute options are supported:
500 .OS "File attribute options (`fattr')"
501 .IB prefix .fattr.mode
505 Sets the permissions mode for a new file. The
507 argument may be either an octal number or a
509 string which acts on the default permissions established by the
512 setting. The characters
516 do not have to be quoted within the mode string.
518 .OS "File attribute options (`fattr')"
519 .IB prefix .fattr.owner
523 Sets the owner for newly created files. On non-broken systems you will
524 need to be the superuser to set the owner on a file. The
526 may either be a numeric uid or a username. The default is not to change
527 the owner of the file once it's created. The synonyms
531 are accepted in place of
534 .OS "File attribute options (`fattr')"
535 .IB prefix .fattr.group
539 Sets the group for newly created files. You will usually need to be a
540 member of the group in question order to set the group of a file. The
542 may either be a numeric gid or a group name. The default is not to
543 change the group of the file once it's created. The synonym
545 is accepted in place of
549 .SS "The `file' source and target types"
552 source and target allow data to move to and from objects other
553 than sockets within the Unix filesystem. (Unix-domain sockets are
560 is used as a source, it is set up immediately.
564 sources and targets is like this:
565 .GS "File sources and targets"
598 .RB [[ : ] file [ : ]]
628 specification describes two files, the first to be used as input, the
629 second to be used as output, each described by an
632 If none of the keywords
637 are given, the type of an
639 is deduced from its nature: if it matches one of the strings
643 or begins with a digit, it's considered to be a file descriptor;
644 otherwise it's interpreted as a filename.
648 spec describes a file by its name within the filesystem. It is opened
649 when needed and closed again after use. For output files, the precise
650 behaviour is controlled by options described below.
654 spec attaches the input or output of the source or target to
659 spec uses an existing open file descriptor, given either by number or a
660 symbolic name. The name
662 refers to standard input (file descriptor 0 on normal systems) and
664 refers to standard output (file descriptor 1). The names work in
665 exactly the same way as the equivalent file descriptor numbers.
669 is omitted, the input
671 is used for both input and output. Exception: if the input refers to
672 standard input then the output will refer to standard output instead.
676 options apply equally to sources and targets. The options are as
683 Whether to create the output file if it doesn't exist. If
685 (the default), an error is reported if the file doesn't exist. If
687 the file is created if it doesn't exist.
692 .BR no | truncate | append
694 Controls the behaviour if the output file already exists. If
696 an error is reported. If
698 (the default), the existing file is replaced by the new data. If
700 the new data is appended to the file.
707 source and target also accept
709 options for controlling the attributes of the created file.
712 Under no circumstances will
714 create a file through a `dangling' symbolic link.
716 .SS "The `exec' source and target types"
719 source and target execute programs and allow access to their standard
720 input and output streams. Both source and target have the same syntax,
722 .GS "Exec source and target"
762 If a single word is given, it is a
764 and will be passed to the Bourne shell for execution. If a
765 bracket-enclosed sequence of words is given, it is considered to be a
766 list of arguments to pass to the program: if a
768 is also supplied, it names the file containing the program to execute;
769 otherwise the file named by the first argument
773 The standard input and output of the program are forwarded to the other
774 end of the connection. The standard error stream is caught by
780 source and target both understand the same set of options. The list of
781 options supported is as follows:
787 Whether to log the start and end of executed programs. If
789 (the default), a log message is emitted when the program is started
790 listing its process id, and another is emitted when the program finishes
791 giving its process id and exit status. If
793 these messages are not emitted. However the standard error stream is
796 abbreviation is accepted as a synonym for
804 Sets the current directory from which the the program should be run.
805 The default is not to change directory. The synonyms
810 are accepted in place of
818 Sets the root directory for the program, using the
820 system call. You must be the superuser for this option to work. The
821 default is not to set a root directory. The synonyms
826 are accepted in place of
834 Sets the user (real and effective uid) to run the program as. This will
835 usually require superuser privileges to work. The default is not to
836 change uid. The synonym
838 is accepted in place of
846 Sets the group (real and effective gid) to run the program as. If
847 running with superuser privileges, the supplementary groups list is
848 cleared at the same time. The default is not to change gid (or clear
849 the supplementary groups list). The synonym
851 is accepted in place of
855 .BI exec.rlimit. limit \c
856 .RB [ .hard | .soft ]
860 Set resource limits for the program. The
862 may be one of the resource limit names described in
864 in lower-case and without the
872 is a number, followed optionally by
874 to multiply by 1024 (2\*(ss10\*(se),
876 to multiply by 1048576 (2\*(ss20\*(se), or
878 to multiply by 1073741824 (2\*(ss30\*(se); purists can use upper-case
879 versions of these if they want. If
883 was specified, only the hard or soft limit is set; otherwise both are
884 set to the same value. Only the superuser can raise the hard limit.
885 The soft limit cannot be set above the hard limit.
890 Clears the program's environment.
898 from the program's environment. It is not an error if no variable named
903 .BR exec.env. [ set ]
912 in the program's environment, possibly replacing the existing value.
915 may be omitted if the
917 qualifier is present.
920 Note that environment variable modifications are performed in order,
921 global modifications before local ones.
923 .SS "The `socket' source and target types"
926 source and target provide access to network services. Support is
927 currently provided for TCP/IP and Unix-domain sockets, although other
928 address types can be added with reasonable ease.
930 The syntax for socket sources and targets is:
931 .GS "Socket source and target"
958 The syntax of the source and target addresses depend on the address
959 types, which are described below. The default address type, if no
964 Socket sources support options; socket targets do not. The source
965 options provided are:
970 .BR unlimited | one-shot
972 Controls the behaviour of the source when it receives connections. A
974 limits the number of simultaneous connections. The value
978 removes any limit on the number of connections possible. The value
980 will remove the socket source after a single successful connection.
981 (Connections refused by access control systems don't count here.)
982 The default is to apply a limit of 256 concurrent connections. Use of
985 option is not recommended.
992 Whether to log incoming connections. If
994 (the default) incoming connections are logged, together with information
995 about the client (where available) and whether the connection was
996 accepted or refused. If
998 log messages are not generated.
1001 Address types also provide their own options.
1003 .SS "The `inet' socket address type"
1006 address type provides access to TCP ports. The
1008 source and target addresses have the following syntax:
1009 .GS "Socket source and target"
1036 may be given as a port number or a service name from the
1038 file (or YP map if you do that sort of thing). A
1040 may be a textual hostname or a numerical IP address.
1044 source address accepts the following options:
1045 .OS "Socket options"
1046 .BR socket.inet. [ allow | deny ]
1052 Adds an entry to the source's access control list. If only one
1054 is given, the entry applies only to that address; if two are given, the
1055 first is a network address and the second is a netmask either in
1056 dotted-quad format or a simple number of bits (e.g.,
1060 mean the same), and the entry applies to any address which, when masked
1061 by the netmask, is equal to the masked network address.
1064 The access control rules are examined in the order: local entries first,
1065 then global ones, each in the order given in the configuration file.
1066 The first matching entry is used. If no entries match, the behaviour is
1069 of the last entry tried. If there are no entries defined, the default
1070 is to allow all clients.
1072 .SS "The `unix' socket address type"
1075 address type allows access to Unix-domain sockets. The syntax for
1077 source and target addresses is like this:
1078 .GS "Socket source and target"
1087 The following options are supported by the
1089 source address type:
1090 .OS "Socket options"
1091 .BR socket.unix.fattr. *
1095 source address accepts
1097 options to control the attributes of the socket file created.
1100 Sockets are removed if
1102 exits normally (which it will do if it runs out of sources or
1103 connections, or if killed by SIGINT or SIGTERM).
1105 To forward the local port 25 to a main mail server:
1107 from 25 to mailserv:25
1109 To attach a fortune server to a Unix-domain socket:
1111 from unix:/tmp/fortunes
1112 to exec [/usr/games/fortune] { user nobody }
1114 To fetch a fortune from the server:
1116 from file stdin, stdout to unix:/tmp/fortunes
1121 from stdin, null to null, stdout
1124 .\"--------------------------------------------------------------------------
1125 .SH "GRAMMAR SUMMARY"
1189 .SS "File source and target"
1216 .RB [[ : ] fd [ : ]]
1218 .RB | stdin | stdout
1222 .RB [[ : ] file [ : ]]
1248 .RB [ : ] null [ : ]
1250 .SS "Exec source and target"
1290 .SS "Socket source and target"
1349 .\"--------------------------------------------------------------------------
1350 .SH "OPTION SUMMARY"
1352 .SS "File attributes (`fattr')"
1353 .IB prefix .fattr.mode
1357 .IB prefix .fattr.owner
1361 .IB prefix .fattr.group
1372 .BR no | truncate | append
1397 .BI exec.rlimit. limit \c
1398 .RB [ .hard | .soft ]
1407 .BR exec.env. [ set ]
1412 .SS "Socket options"
1416 .BR unlimited | one-shot
1422 .BR socket.inet. [ allow | deny ]
1428 .BR socket.unix.fattr. *
1430 .\"--------------------------------------------------------------------------
1433 The syntax for IP addresses and filenames is nasty.
1435 IPv6 is not supported yet. Because of
1437 socket address architecture, it's probably not a major piece of work to
1440 Please inform me of any security problems you think you've identified in
1441 this program. I take security very seriously, and I will fix security
1442 holes as a matter of priority when I find out about them. I will be
1443 annoyed if I have to read about problems on Bugtraq because they weren't
1446 .\"--------------------------------------------------------------------------
1449 Mark Wooding, <mdw@nsict.org>
1451 .\"----- That's all, folks --------------------------------------------------
~mdw / fwd / blob