1.\" $OpenBSD: ftp-proxy.8,v 1.10 2007/08/01 15:45:41 jmc Exp $ 2.\" 3.\" Copyright (c) 2004, 2005 Camiel Dobbelaar, <cd@sentia.nl> 4.\" 5.\" Permission to use, copy, modify, and distribute this software for any 6.\" purpose with or without fee is hereby granted, provided that the above 7.\" copyright notice and this permission notice appear in all copies. 8.\" 9.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES 10.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF 11.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR 12.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES 13.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN 14.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF 15.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. 16.\" 17.Dd September 9, 2010 18.Dt FTP-PROXY 8 19.Os 20.Sh NAME 21.Nm ftp-proxy 22.Nd Internet File Transfer Protocol proxy daemon 23.Sh SYNOPSIS 24.Nm 25.Bk -words 26.Op Fl 6Adrv 27.Op Fl a Ar address 28.Op Fl b Ar address 29.Op Fl D Ar level 30.Op Fl m Ar maxsessions 31.Op Fl P Ar port 32.Op Fl p Ar port 33.Op Fl q Ar queue 34.Op Fl R Ar address 35.Op Fl T Ar tag 36.Op Fl t Ar timeout 37.Ek 38.Sh DESCRIPTION 39.Nm 40is a proxy for the Internet File Transfer Protocol. 41FTP control connections should be redirected into the proxy using the 42.Xr pf 4 43.Ar rdr 44command, after which the proxy connects to the server on behalf of 45the client. 46.Pp 47The proxy allows data connections to pass, rewriting and redirecting 48them so that the right addresses are used. 49All connections from the client to the server have their source 50address rewritten so they appear to come from the proxy. 51Consequently, all connections from the server to the proxy have 52their destination address rewritten, so they are redirected to the 53client. 54The proxy uses the 55.Xr pf 4 56.Ar anchor 57facility for this. 58.Pp 59Assuming the FTP control connection is from $client to $server, the 60proxy connected to the server using the $proxy source address, and 61$port is negotiated, then 62.Nm 63adds the following rules to the various anchors. 64(These example rules use inet, but the proxy also supports inet6.) 65.Pp 66In case of active mode (PORT or EPRT): 67.Bd -literal -offset 2n 68rdr from $server to $proxy port $port -> $client 69pass quick inet proto tcp \e 70 from $server to $client port $port 71.Ed 72.Pp 73In case of passive mode (PASV or EPSV): 74.Bd -literal -offset 2n 75nat from $client to $server port $port -> $proxy 76pass in quick inet proto tcp \e 77 from $client to $server port $port 78pass out quick inet proto tcp \e 79 from $proxy to $server port $port 80.Ed 81.Pp 82The options are as follows: 83.Bl -tag -width Ds 84.It Fl 6 85IPv6 mode. 86The proxy will expect and use IPv6 addresses for all communication. 87Only the extended FTP modes EPSV and EPRT are allowed with IPv6. 88The proxy is in IPv4 mode by default. 89.It Fl A 90Only permit anonymous FTP connections. 91Either user "ftp" or user "anonymous" is allowed. 92.It Fl a Ar address 93The proxy will use this as the source address for the control 94connection to a server. 95.It Fl b Ar address 96Address where the proxy will listen for redirected control connections. 97The default is 127.0.0.1, or ::1 in IPv6 mode. 98.It Fl D Ar level 99Debug level, ranging from 0 to 7. 100Higher is more verbose. 101The default is 5. 102(These levels correspond to the 103.Xr syslog 3 104levels.) 105.It Fl d 106Do not daemonize. 107The process will stay in the foreground, logging to standard error. 108.It Fl m Ar maxsessions 109Maximum number of concurrent FTP sessions. 110When the proxy reaches this limit, new connections are denied. 111The default is 100 sessions. 112The limit can be lowered to a minimum of 1, or raised to a maximum of 500. 113.It Fl P Ar port 114Fixed server port. 115Only used in combination with 116.Fl R . 117The default is port 21. 118.It Fl p Ar port 119Port where the proxy will listen for redirected connections. 120The default is port 8021. 121.It Fl q Ar queue 122Create rules with queue 123.Ar queue 124appended, so that data connections can be queued. 125.It Fl R Ar address 126Fixed server address, also known as reverse mode. 127The proxy will always connect to the same server, regardless of 128where the client wanted to connect to (before it was redirected). 129Use this option to proxy for a server behind NAT, or to forward all 130connections to another proxy. 131.It Fl r 132Rewrite sourceport to 20 in active mode to suit ancient clients that insist 133on this RFC property. 134.It Fl T Ar tag 135Automatically tag packets passing through the 136.Xr pf 4 137rule with the name supplied. 138.It Fl t Ar timeout 139Number of seconds that the control connection can be idle, before the 140proxy will disconnect. 141The maximum is 86400 seconds, which is also the default. 142Do not set this too low, because the control connection is usually 143idle when large data transfers are taking place. 144.It Fl v 145Set the 'log' flag on pf rules committed by 146.Nm . 147Use twice to set the 'log-all' flag. 148The pf rules do not log by default. 149.El 150.Sh CONFIGURATION 151To make use of the proxy, 152.Xr pf.conf 5 153needs the following rules. 154All anchors are mandatory. 155Adjust the rules as needed. 156.Pp 157In the NAT section: 158.Bd -literal -offset 2n 159nat-anchor "ftp-proxy/*" 160rdr-anchor "ftp-proxy/*" 161rdr pass on $int_if proto tcp from $lan to any port 21 -> \e 162 127.0.0.1 port 8021 163.Ed 164.Pp 165In the rule section: 166.Bd -literal -offset 2n 167anchor "ftp-proxy/*" 168pass out proto tcp from $proxy to any port 21 169.Ed 170.Sh SEE ALSO 171.Xr ftp 1 , 172.Xr pf 4 , 173.Xr pf.conf 5 174.Sh CAVEATS 175.Xr pf 4 176does not allow the ruleset to be modified if the system is running at a 177securelevel 178.\".Xr securelevel 7 179higher than 1. 180At that level 181.Nm 182cannot add rules to the anchors and FTP data connections may get blocked. 183.Pp 184Negotiated data connection ports below 1024 are not allowed. 185.Pp 186The negotiated IP address for active modes is ignored for security 187reasons. 188This makes third party file transfers impossible. 189.Pp 190.Nm 191chroots to "/var/empty" and changes to user "proxy" to drop privileges. 192