3 .\" $Id: fw.1,v 1.18 2003/11/29 23:03:19 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 1.18 2003/11/29 23:03:19 mdw
32 .\" Little formatting fixes.
34 .\" Revision 1.17 2003/11/29 20:36:07 mdw
35 .\" Privileged outgoing connections.
37 .\" Revision 1.16 2003/11/25 14:46:50 mdw
38 .\" Update docco for new options.
40 .\" Revision 1.15 2003/01/24 20:13:04 mdw
41 .\" Fix bogus examples. Explain quoting rules for `exec' endpoints.
43 .\" Revision 1.14 2002/02/23 00:05:12 mdw
44 .\" Fix spacing around full stops (at last!).
46 .\" Revision 1.13 2002/02/22 23:45:01 mdw
47 .\" Add option to change the listen(2) parameter.
49 .\" Revision 1.12 2001/02/23 09:11:29 mdw
50 .\" Update manual style.
52 .\" Revision 1.11 2001/02/05 19:47:11 mdw
53 .\" Minor fixings to wording.
55 .\" Revision 1.10 2001/02/03 20:30:03 mdw
56 .\" Support re-reading config files on SIGHUP.
58 .\" Revision 1.9 2000/03/23 00:37:33 mdw
59 .\" Add option to change user and group after initialization. Naughtily
60 .\" reassign short equivalents of --grammar and --options.
62 .\" Revision 1.8 1999/12/22 15:44:43 mdw
63 .\" Fix some errors, and document new option.
65 .\" Revision 1.7 1999/10/22 22:45:15 mdw
66 .\" Describe new socket connection options.
68 .\" Revision 1.6 1999/10/10 16:46:29 mdw
69 .\" Include grammar and options references at the end of the manual.
71 .\" Revision 1.5 1999/09/26 18:18:05 mdw
72 .\" Remove a fixed bug from the list. Fix some nasty formatting
75 .\" Revision 1.4 1999/08/19 18:32:48 mdw
76 .\" Improve lexical analysis. In particular, `chmod' patterns don't have to
77 .\" be quoted any more.
79 .\" Revision 1.3 1999/07/30 06:49:00 mdw
80 .\" Minor tidying and typo correction.
82 .\" Revision 1.2 1999/07/26 23:31:04 mdw
83 .\" Document lots of new features and syntax.
86 .\"----- Various bits of fancy styling --------------------------------------
88 .\" --- Indented paragraphs with right-aligned tags ---
92 \h'-\w'\fB\\$1\ \fP'u'\fB\\$1\ \fP\c
95 .\" --- Verbatim-oid typesetting ---
109 .\" --- Grammar markup ---
111 .\" This is mainly for the benefit of the automatic scripts which
112 .\" generate the grammar summary.
131 .\" --- Other bits of styling ---
147 .\"--------------------------------------------------------------------------
149 .TH fw 1 "1 July 1999" "Straylight/Edgeware" "fw port forwarder"
151 .\"--------------------------------------------------------------------------
156 .\"--------------------------------------------------------------------------
169 .\"--------------------------------------------------------------------------
174 program is a simple port forwarder. It supports a number of features
175 the author hasn't found in similar programs:
177 .I "Connection logging"
178 Each connection attempt to the forwarder is logged, giving the time of
179 the connection, the DNS-resolved hostname (if available), and the user
180 name resulting from an RFC931 lookup. These lookups are done
181 asynchronously to the main forwarder's operation.
184 Each forwarded port may have an access control list attached to it.
185 Only authorized hosts are allowed to connect. Access control checks are
186 performed by quick checks on the client's IP address.
188 .I "Nonblocking single-process design"
189 The internal structure of the server is completely nonblocking. The
190 connections don't block; the reading and writing don't block; the name
191 lookups don't block. This is all done in a single process, with the
192 single exception of the DNS resolver.
194 .I "Support for Unix-domain sockets"
195 Connections from and to Unix-domain sockets can be handled just as
196 easily as more normal Internet sockets. Access control doesn't work on
197 Unix domain sockets, though. (Yet.)
198 .SS "Command line options"
201 program understands a few simple command line options:
204 Displays a screen of help text on standard output and exits
207 .B "\-v, \-\-version"
208 Writes the version number to standard output and exits successfully.
211 Writes a terse usage summary to standard output and exits successfully.
213 .B "\-G, \-\-grammar"
214 Writes a summary of the configuration file grammar to standard output
215 and exits successfully.
217 .B "\-O, \-\-options"
218 Writes a summary of the source and target options to standard output and
221 .BI "\-f, \-\-file=" file
222 Read configuration information from
227 configuration file statement.
229 .B "\-d, \-\-daemon, \-\-fork"
230 Forks into the background after reading the configuration and
231 initializing properly.
233 .B "\-l, \-\-syslog, \-\-log"
234 Emit logging information to the system log, rather than standard error.
237 Don't output any logging information. This option is not recommended
238 for normal use, although it can make system call traces clearer so I use
241 .BI "\-s, \-\-setuid=" user
242 Change uid to that of
244 which may be either a user name or uid number, after initializing all
245 the sources. This will usually require elevated privileges.
247 .BI "\-g, \-\-setgid=" group
248 Change gid to that of
250 which may be either a group name or gid number, after initializing all
251 the sources. If the operating system understands supplementary groups
252 then the supplementary groups list is altered to include only
255 Any further command line arguments are interpreted as configuration
256 lines to be read. Configuration supplied in command line arguments has
257 precisely the same syntax as configuration in files. If there are no
258 configuration statements on the command line, and no
260 options were supplied, configuration is read from standard input, if
261 stdin is not a terminal.
263 .\"--------------------------------------------------------------------------
264 .SH "CONFIGURATION LANGUAGE"
268 program has a fairly sophisticated configuration language to let you
269 describe which things should be forwarded where and what special
270 features there should be.
271 .SS "Lexical structure"
272 There are four types of characters.
274 .I "word constituent characters"
275 Word constituent characters are gathered together into words.
276 Depending on its surrounding context, a word might act as a keyword or a
277 string. All alphanumerics are word constituents, as is the hyphen
279 Other characters may change their status in future versions.
281 .I "self-delimiting characters"
282 Self-delimiting characters always stand alone. They act as punctuation,
283 shaping the sequence of words into more complex grammatical forms. The
296 are self-delimiting. Note that while some characters, e.g.,
300 require escaping by the shell, they are mostly optional in the grammar
301 and can tend to be omitted in quick hacks at the shell prompt.
303 .I "whitespace characters"
304 Whitespace characters separate words but are otherwise ignored. All
305 `normal' whitespace characters (e.g., space, tab and newline) are
306 considered to be whitespace for these purposes.
308 .I "special characters"
309 There are three special characters. The
311 character, if it appears at the start of a word, introduces a
313 which extends to the end of the current line or command-line argument.
314 Within a word, it behaves like a normal word-constituent character. The
317 escapes the following character causing it to be interpreted as a word
318 constituent regardless of its normal type. The double-quote
320 escapes all characters other than backslashes up to the next
321 double-quote and causes them to be regarded as word constituents. Note
322 that you don't have to quote a whole word. The backslash can escape a
323 quote character allowing you to insert it into a word if really
327 The overall syntax looks a bit like this:
366 If you prefer, the keyword
374 .SS "Sources and targets"
375 Forwarding is set up by attaching
379 Sources are things which are capable of
381 one end of a data flow on their own, while targets are things which are
382 capable of setting up the other end on demand. In the case of a TCP
383 port forwarder, the part which listens for incoming client connections
384 is the source, while the part which sets up outgoing connections to the
385 destination server is the target.
389 does is set up a collection of sources and targets based on your
390 configuration file so that when a source decides to initiate a data
391 flow, it tells its target to set its end up, and then squirts data back
392 and forth between the two until there's no more.
396 they stay around indefinitely setting up multiple attachments to
399 they set up one connection and then disappear. If all the sources
400 defined are transient, then
402 will quit when no more active sources remain and all connections have
407 program is fairly versatile. It allows you to attach any supported type
408 of source to any supported type of target. This will, I hope, be the
409 case in all future versions.
415 depend on the source or target type, and are therefore described in the
416 sections specific to the various types.
418 .SS "Options structure"
419 Most of the objects that
421 knows about (including sources and targets, but also other more specific
422 things such as socket address types) can have their behaviour modified
425 The options available at a particular point in the configuration depend
428 A global option, outside of a
430 has no context unless it is explicitly qualified, and affects global
431 behaviour. A local option, applied to a source or target in a
433 has the context of the type of source or target to which it is applied,
434 and affects only that source or target.
436 Note that it's important to distinguish between an option's context
437 (which is affected by its qualification) and its local or global
438 status. No matter how qualified, a global option will always control
439 default options for objects, and a local option will only affect a
440 specific source or target.
442 The syntax for qualifying options is like this:
467 Thus, you may qualify either an individual option or a sequence of
468 options. The two are equivalent; for example,
477 exec.rlimit.core = 0;
480 For each option, there is a sequence of prefixes which maximally qualify
481 that option. An option prefixed with this sequence is
482 .IR "fully qualified" .
483 In actual use, some or all of those prefixes may be omitted. However,
484 it's possible for the option to become
486 if you do this. For example, the option
491 .BR socket.unix.fattr.owner .
492 In this case, the ambiguity is benign: a local option will have as its
493 context an appropriate source or target, and both global options
494 actually control the same default. However, the option
500 which have separate defaults, and which one you actually get depends on
501 the exact implementation of
503 option parser. (Currently this would resolve to
505 although this may change in a later version.)
507 In this manual, options are usually shown in their fully-qualified form.
509 .SS "File attributes for created files: `fattr'"
514 sources and targets can create new filesystem objects. The
516 options allow control over the attributes of the newly-created objects.
521 use the same set of defaults, so a prefix of
523 is good enough for setting global options, and the implicit context
524 disambiguates local options.
526 The following file attribute options are supported:
527 .OS "File attribute options (`fattr')"
528 .IB prefix .fattr.mode
532 Sets the permissions mode for a new file. The
534 argument may be either an octal number or a
536 string which acts on the default permissions established by the
539 setting. The characters
543 do not have to be quoted within the mode string.
545 .OS "File attribute options (`fattr')"
546 .IB prefix .fattr.owner
550 Sets the owner for newly created files. On non-broken systems you will
551 need to be the superuser to set the owner on a file. The
553 may either be a numeric uid or a username. The default is not to change
554 the owner of the file once it's created. The synonyms
558 are accepted in place of
561 .OS "File attribute options (`fattr')"
562 .IB prefix .fattr.group
566 Sets the group for newly created files. You will usually need to be a
567 member of the group in question order to set the group of a file. The
569 may either be a numeric gid or a group name. The default is not to
570 change the group of the file once it's created. The synonym
572 is accepted in place of
576 .SS "The `file' source and target types"
579 source and target allow data to move to and from objects other
580 than sockets within the Unix filesystem. (Unix-domain sockets are
587 is used as a source, it is set up immediately.
591 sources and targets is like this:
592 .GS "File sources and targets"
625 .RB [[ : ] file [ : ]]
655 specification describes two files, the first to be used as input, the
656 second to be used as output, each described by an
659 If none of the keywords
664 are given, the type of an
666 is deduced from its nature: if it matches one of the strings
670 or begins with a digit, it's considered to be a file descriptor;
671 otherwise it's interpreted as a filename.
675 spec describes a file by its name within the filesystem. It is opened
676 when needed and closed again after use. For output files, the precise
677 behaviour is controlled by options described below.
681 spec attaches the input or output of the source or target to
686 spec uses an existing open file descriptor, given either by number or a
687 symbolic name. The name
689 refers to standard input (file descriptor 0 on normal systems) and
691 refers to standard output (file descriptor 1). The names work in
692 exactly the same way as the equivalent file descriptor numbers.
696 is omitted, the input
698 is used for both input and output. Exception: if the input refers to
699 standard input then the output will refer to standard output instead.
703 options apply equally to sources and targets. The options are as
710 Whether to create the output file if it doesn't exist. If
712 (the default), an error is reported if the file doesn't exist. If
714 the file is created if it doesn't exist.
719 .BR no | truncate | append
721 Controls the behaviour if the output file already exists. If
723 an error is reported. If
725 (the default), the existing file is replaced by the new data. If
727 the new data is appended to the file.
734 source and target also accept
736 options for controlling the attributes of the created file.
739 Under no circumstances will
741 create a file through a `dangling' symbolic link.
743 .SS "The `exec' source and target types"
746 source and target execute programs and allow access to their standard
747 input and output streams. Both source and target have the same syntax,
749 .GS "Exec source and target"
789 If a single word is given, it is a
791 and will be passed to the Bourne shell for execution. If a
792 bracket-enclosed sequence of words is given, it is considered to be a
793 list of arguments to pass to the program: if a
795 is also supplied, it names the file containing the program to execute;
796 otherwise the file named by the first argument
800 Note that the shell command or program name string must, if present,
801 have any delimiter characters (including
805 quoted; this is not required in the
809 The standard input and output of the program are forwarded to the other
810 end of the connection. The standard error stream is caught by
816 source and target both understand the same set of options. The list of
817 options supported is as follows:
823 Whether to log the start and end of executed programs. If
825 (the default), a log message is emitted when the program is started
826 listing its process id, and another is emitted when the program finishes
827 giving its process id and exit status. If
829 these messages are not emitted. However the standard error stream is
832 abbreviation is accepted as a synonym for
840 Sets the current directory from which the the program should be run.
841 The default is not to change directory. The synonyms
846 are accepted in place of
854 Sets the root directory for the program, using the
856 system call. You must be the superuser for this option to work. The
857 default is not to set a root directory. The synonym
859 is accepted in place of
867 Sets the user (real and effective uid) to run the program as. This will
868 usually require superuser privileges to work. The default is not to
869 change uid. The synonym
871 is accepted in place of
879 Sets the group (real and effective gid) to run the program as. If
880 running with superuser privileges, the supplementary groups list is
881 cleared at the same time. The default is not to change gid (or clear
882 the supplementary groups list). The synonym
884 is accepted in place of
888 .BI exec.rlimit. limit \c
889 .RB [ .hard | .soft ]
893 Set resource limits for the program. The
895 may be one of the resource limit names described in
897 in lower-case and without the
905 is a number, followed optionally by
907 to multiply by 1024 (2\*(ss10\*(se),
909 to multiply by 1048576 (2\*(ss20\*(se), or
911 to multiply by 1073741824 (2\*(ss30\*(se); purists can use upper-case
912 versions of these if they want. If
916 was specified, only the hard or soft limit is set; otherwise both are
917 set to the same value. Only the superuser can raise the hard limit.
918 The soft limit cannot be set above the hard limit.
923 Clears the program's environment.
931 from the program's environment. It is not an error if no variable named
936 .BR exec.env. [ set ]
945 in the program's environment, possibly replacing the existing value.
948 may be omitted if the
950 qualifier is present.
953 Note that environment variable modifications are performed in order,
954 global modifications before local ones.
956 .SS "The `socket' source and target types"
959 source and target provide access to network services. Support is
960 currently provided for TCP/IP and Unix-domain sockets, although other
961 address types can be added with reasonable ease.
963 The syntax for socket sources and targets is:
964 .GS "Socket source and target"
976 .RB [ socket [ .\& ]]
984 .RB [ socket [ .\& ]]
991 The syntax of the source and target addresses depend on the address
992 types, which are described below. The default address type, if no
997 Socket sources support options; socket targets do not. The source
998 options provided are:
1003 .BR unlimited | one-shot
1005 Controls the behaviour of the source when it receives connections. A
1007 limits the number of simultaneous connections. The value
1011 removes any limit on the number of connections possible. The value
1013 will remove the socket source after a single successful connection.
1014 (Connections refused by access control systems don't count here.)
1015 The default is to apply a limit of 256 concurrent connections. Use of
1018 option is not recommended.
1020 .OS "Socket options"
1025 Sets the maximum of the kernel incoming connection queue for this socket
1026 source. This is the number given to the
1028 system call. The default is 5.
1030 .OS "Socket options"
1035 Whether to log incoming connections. If
1037 (the default) incoming connections are logged, together with information
1038 about the client (where available) and whether the connection was
1039 accepted or refused. If
1041 log messages are not generated.
1044 Address types also provide their own options.
1046 .SS "The `inet' socket address type"
1049 address type provides access to TCP ports. The
1051 source and target addresses have the following syntax:
1052 .GS "Socket source and target"
1079 may be given as a port number or a service name from the
1081 file (or YP map if you do that sort of thing). A
1083 may be a textual hostname or a numerical IP address.
1087 source address accepts the following options:
1088 .OS "Socket options"
1089 .B socket.inet.source.addr
1094 Specify the IP address on which to listen for incoming connections. The
1097 which means to listen on all addresses, though it may be useful to
1098 specify this explicitly, if the global setting is different.
1100 .OS "Socket options"
1101 .BR socket.inet.source. [ allow | deny ]
1107 Adds an entry to the source's access control list. If only one
1109 is given, the entry applies only to that address; if two are given, the
1110 first is a network address and the second is a netmask either in
1111 dotted-quad format or a simple number of bits (e.g.,
1115 mean the same), and the entry applies to any address which, when masked
1116 by the netmask, is equal to the masked network address.
1118 .OS "Socket options"
1119 .BR socket.inet.source. [ allow | deny ]
1122 Accept or reject connections from low-numbered `privileged' ports, in
1125 .OS "Socket options"
1126 .B socket.inet.dest.addr
1131 Specify the IP address to bind the local socket to when making an
1132 outbound connection. The default is
1134 which means to use whichever address the kernel thinks is most
1135 convenient. This option is useful if the destination is doing
1136 host-based access control and your server is multi-homed.
1138 .OS "Socket options"
1139 .B socket.inet.dest.priv-port
1143 Make a privileged connection (i.e., from a low-numbered port) to the
1144 target. This only works if
1146 was started with root privileges. However, it still works if
1150 privileges after initialization (the
1152 option). Before dropping privileges,
1154 forks off a separate process which continues to run with root
1155 privileges, and on demand passes sockets bound to privileged ports and
1156 connected to the appropriate peer back to the main program. The
1157 privileged child only passes back sockets connected to peer addresses
1158 named in the configuration; even if the
1160 process is compromised, it can't make privileged connections to other
1161 addresses. Note that because of this privilege separation, it's also
1162 not possible to reconfigure
1164 to make privileged connections to different peer addresses later by
1165 changing configuration files and sending the daemon a
1169 The access control rules are examined in the order: local entries first,
1170 then global ones, each in the order given in the configuration file.
1171 The first matching entry is used. If no entries match, the behaviour is
1174 of the last entry tried. If there are no entries defined, the default
1175 is to allow all clients.
1177 .SS "The `unix' socket address type"
1180 address type allows access to Unix-domain sockets. The syntax for
1182 source and target addresses is like this:
1183 .GS "Socket source and target"
1192 The following options are supported by the
1194 source address type:
1195 .OS "Socket options"
1196 .BR socket.unix.fattr. *
1200 source address accepts
1202 options to control the attributes of the socket file created.
1205 Sockets are removed if
1207 exits normally (which it will do if it runs out of sources or
1210 shuts down in a clean way).
1212 To forward the local port 25 to a main mail server:
1214 from 25 to mailserv:25
1216 To attach a fortune server to a Unix-domain socket:
1218 from unix:/tmp/fortunes
1219 to exec [/usr/games/fortune] { user nobody }
1221 To fetch a fortune from the server:
1223 from file stdin, stdout to unix:/tmp/fortunes
1228 from file stdin, null to file null, stdout
1230 .sp -1 \" undo final space
1232 .\"--------------------------------------------------------------------------
1233 .SH "SIGNAL HANDLING"
1237 program responds to various signals when it's running. If it receives
1244 shutdown: it removes all of its sources, and will exit when no more
1245 connections are running. (Note that if the disposition
1249 does not re-enable the signal. You'll have to send
1257 shutdown: it removes all sources and extant connections and closes down
1258 more-or-less immediately.
1260 Finally, if any configuration files (other than standard input) were
1263 on its command line using the
1267 signal may be sent to instruct
1269 to reload its configuration. Any existing connections are allowed to
1270 run their course. If no such configuration files are available,
1272 just logs a message about the signal and continues.
1274 .\"--------------------------------------------------------------------------
1275 .SH "GRAMMAR SUMMARY"
1339 .SS "File source and target"
1366 .RB [[ : ] fd [ : ]]
1368 .RB | stdin | stdout
1372 .RB [[ : ] file [ : ]]
1398 .RB [ : ] null [ : ]
1400 .SS "Exec source and target"
1440 .SS "Socket source and target"
1452 .RB [ socket [ .\& ]]
1460 .RB [ socket [ .\& ]]
1499 .\"--------------------------------------------------------------------------
1500 .SH "OPTION SUMMARY"
1502 .SS "File attributes (`fattr')"
1503 .IB prefix .fattr.mode
1507 .IB prefix .fattr.owner
1511 .IB prefix .fattr.group
1522 .BR no | truncate | append
1547 .BI exec.rlimit. limit \c
1548 .RB [ .hard | .soft ]
1557 .BR exec.env. [ set ]
1562 .SS "Socket options"
1566 .BR unlimited | one-shot
1576 .BR socket.inet.source. [ allow | deny ]
1582 .BR socket.inet.source. [ allow | deny ]
1585 .B socket.inet.source.addr
1590 .B socket.inet.dest.addr
1595 .B socket.inet.dest.priv-port
1599 .BR socket.unix.fattr. *
1601 .\"--------------------------------------------------------------------------
1604 The syntax for IP addresses and filenames is nasty.
1606 IPv6 is not supported yet. Because of
1608 socket address architecture, it's probably not a major piece of work to
1611 Please inform me of any security problems you think you've identified in
1612 this program. I take security very seriously, and I will fix security
1613 holes as a matter of priority when I find out about them. I will be
1614 annoyed if I have to read about problems on Bugtraq because they weren't
1617 The program is too complicated, and this manual page is too long.
1619 .\"--------------------------------------------------------------------------
1622 Mark Wooding, <mdw@nsict.org>
1624 .\"----- That's all, folks --------------------------------------------------
~mdw / fwd / blob