186 lines
5.7 KiB
Groff
186 lines
5.7 KiB
Groff
.\" $OpenBSD: ftp-proxy.8,v 1.7 2006/12/30 13:01:54 camield Exp $
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.\"
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.\" Copyright (c) 2004, 2005 Camiel Dobbelaar, <cd@sentia.nl>
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.\"
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.\" Permission to use, copy, modify, and distribute this software for any
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.\" purpose with or without fee is hereby granted, provided that the above
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.\" copyright notice and this permission notice appear in all copies.
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.\"
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.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
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.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
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.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
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.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd November 28, 2004
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.Dt FTP-PROXY 8
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.Os
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.Sh NAME
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.Nm ftp-proxy
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.Nd Internet File Transfer Protocol proxy daemon
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.Sh SYNOPSIS
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.Nm ftp-proxy
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.Op Fl 6Adrv
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.Op Fl a Ar address
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.Op Fl b Ar address
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.Op Fl D Ar level
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.Op Fl m Ar maxsessions
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.Op Fl P Ar port
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.Op Fl p Ar port
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.Op Fl q Ar queue
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.Op Fl R Ar address
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.Op Fl t Ar timeout
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.Sh DESCRIPTION
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.Nm
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is a proxy for the Internet File Transfer Protocol.
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FTP control connections should be redirected into the proxy using the
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.Xr pf 4
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.Ar rdr
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command, after which the proxy connects to the server on behalf of
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the client.
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.Pp
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The proxy allows data connections to pass, rewriting and redirecting
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them so that the right addresses are used.
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All connections from the client to the server have their source
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address rewritten so they appear to come from the proxy.
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Consequently, all connections from the server to the proxy have
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their destination address rewritten, so they are redirected to the
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client.
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The proxy uses the
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.Xr pf 4
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.Ar anchor
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facility for this.
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.Pp
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Assuming the FTP control connection is from $client to $server, the
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proxy connected to the server using the $proxy source address, and
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$port is negotiated, then
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.Nm ftp-proxy
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adds the following rules to the various anchors.
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(These example rules use inet, but the proxy also supports inet6.)
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.Pp
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In case of active mode (PORT or EPRT):
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.Bd -literal -offset 2n
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rdr from $server to $proxy port $port -> $client
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pass quick inet proto tcp \e
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from $server to $client port $port
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.Ed
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.Pp
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In case of passive mode (PASV or EPSV):
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.Bd -literal -offset 2n
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nat from $client to $server port $port -> $proxy
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pass in quick inet proto tcp \e
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from $client to $server port $port
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pass out quick inet proto tcp \e
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from $proxy to $server port $port
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.Ed
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.Pp
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The options are as follows:
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.Bl -tag -width Ds
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.It Fl 6
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IPv6 mode.
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The proxy will expect and use IPv6 addresses for all communication.
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Only the extended FTP modes EPSV and EPRT are allowed with IPv6.
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The proxy is in IPv4 mode by default.
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.It Fl A
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Only permit anonymous FTP connections.
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Either user "ftp" or user "anonymous" is allowed.
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.It Fl a Ar address
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The proxy will use this as the source address for the control
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connection to a server.
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.It Fl b Ar address
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Address where the proxy will listen for redirected control connections.
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The default is 127.0.0.1, or ::1 in IPv6 mode.
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.It Fl D Ar level
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Debug level, ranging from 0 to 7.
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Higher is more verbose.
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The default is 5.
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(These levels correspond to the
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.Xr syslog 3
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levels.)
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.It Fl d
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Do not daemonize.
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The process will stay in the foreground, logging to standard error.
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.It Fl m Ar maxsessions
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Maximum number of concurrent FTP sessions.
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When the proxy reaches this limit, new connections are denied.
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The default is 100 sessions.
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The limit can be lowered to a minimum of 1, or raised to a maximum of 500.
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.It Fl P Ar port
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Fixed server port.
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Only used in combination with
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.Fl R .
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The default is port 21.
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.It Fl p Ar port
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Port where the proxy will listen for redirected connections.
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The default is port 8021.
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.It Fl q Ar queue
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Create rules with queue
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.Ar queue
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appended, so that data connections can be queued.
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.It Fl R Ar address
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Fixed server address, also known as reverse mode.
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The proxy will always connect to the same server, regardless of
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where the client wanted to connect to (before it was redirected).
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Use this option to proxy for a server behind NAT, or to forward all
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connections to another proxy.
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.It Fl r
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Rewrite sourceport to 20 in active mode to suit ancient clients that insist
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on this RFC property.
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.It Fl t Ar timeout
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Number of seconds that the control connection can be idle, before the
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proxy will disconnect.
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The maximum is 86400 seconds, which is also the default.
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Do not set this too low, because the control connection is usually
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idle when large data transfers are taking place.
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.It Fl v
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Set the 'log' flag on pf rules committed by
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.Nm .
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Use twice to set the 'log-all' flag.
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The pf rules do not log by default.
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.El
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.Sh CONFIGURATION
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To make use of the proxy,
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.Xr pf.conf 5
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needs the following rules.
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All anchors are mandatory.
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Adjust the rules as needed.
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.Pp
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In the NAT section:
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.Bd -literal -offset 2n
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nat-anchor "ftp-proxy/*"
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rdr-anchor "ftp-proxy/*"
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rdr pass on $int_if proto tcp from $lan to any port 21 -> \e
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127.0.0.1 port 8021
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.Ed
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.Pp
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In the rule section:
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.Bd -literal -offset 2n
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anchor "ftp-proxy/*"
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pass out proto tcp from $proxy to any port 21
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.Ed
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.Sh SEE ALSO
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.Xr ftp 1 ,
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.Xr pf 4 ,
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.Xr pf.conf 5
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.Sh CAVEATS
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.Xr pf 4
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does not allow the ruleset to be modified if the system is running at a
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.Xr securelevel 7
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higher than 1.
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At that level
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.Nm ftp-proxy
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cannot add rules to the anchors and FTP data connections may get blocked.
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.Pp
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Negotiated data connection ports below 1024 are not allowed.
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.Pp
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The negotiated IP address for active modes is ignored for security
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reasons.
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This makes third party file transfers impossible.
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.Pp
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.Nm ftp-proxy
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chroots to "/var/empty" and changes to user "proxy" to drop privileges.
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