transparent ftp proxy, based on Obtuse Systems juniper stuff with much

modernizing and cleanup. still needs looking at.

Currently supports PORT PASV EPRT data connections with only a pf rdr to
capture the control connection. (I.E. you don't need ip forwarding
or other NAT stuff). Runs from inetd.

Supports all passive (EPSV PASV) when using -n flag, where the proxy
ignores passive mode data connections (and assumes nat will get them
through).

Todo yet:
	More audit
	IpV6
	Handle EPSV in proxy (with an rdr added then removed)
	Option to Daemonize and bind only to the loopback
	More Content/Login filtering, etc. etc. and more bloat

1 files changed, 1320 insertions, 0 deletions

diff --git a/libexec/ftp-proxy/ftp-proxy.c b/libexec/ftp-proxy/ftp-proxy.c
new file mode 100644
index 00000000000..54e12936614
--- /dev/null
+++ b/libexec/ftp-proxy/ftp-proxy.c
@@ -0,0 +1,1320 @@
+/* $OpenBSD: ftp-proxy.c,v 1.1 2001/08/19 04:11:12 beck Exp $ */
+/*
+ * Copyright (c) 1996-2001
+ *	Obtuse Systems Corporation.  All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of the Obtuse Systems nor the names of its contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY OBTUSE SYSTEMS AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL OBTUSE SYSTEMS CORPORATION OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, 
+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
+ * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+ * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
+ * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF 
+ * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *   
+ */
+
+/*
+ * ftp proxy, Originally based on juniper_ftp_proxy from the Obtuse
+ * Systems juniper firewall, written by Dan Boulet <danny@obtuse.com>
+ * and Bob Beck <beck@obtuse.com>
+ *
+ * This version basically passes everything through unchanged except
+ * for the PORT and the * "227 Entering Passive Mode" reply.
+ *
+ * A PORT command is handled by noting the IP address and port number
+ * specified and then configuring a listen port on some very high port
+ * number and telling the server about it using a PORT message.
+ * We then watch for an in-bound connection on the port from the server
+ * and connect to the client's port when it happens.
+ *
+ * A "227 Entering Passive Mode" reply is handled by noting the IP address
+ * and port number specified and then configuring a listen port on some
+ * very high port number and telling the client about it using a
+ * "227 Entering Passive Mode" reply.
+ * We then watch for an in-bound connection on the port from the client
+ * and connect to the server's port when it happens.
+ *
+ * supports tcp wrapper lookups/access control with the -w flag using
+ * the real destination address - the tcp wrapper stuff is done after
+ * the real destination address is retreived from pf
+ * 
+ */
+
+/* 
+ * TODO:
+ * Plenty, this is very basic, with the idea to get it in clean first.
+ * 
+ * - Ipv6 and EPASV support 
+ * - Content filter support
+ * - filename filter support
+ * - per-user rules perhaps.
+ */
+
+#include <sys/types.h>
+#include <sys/time.h>
+#include <sys/socket.h>
+
+#include <net/if.h>
+#include <netinet/in.h>
+
+#include <arpa/inet.h>
+
+#include <ctype.h>
+#include <errno.h>
+#include <netdb.h>
+#include <signal.h>
+#include <stdarg.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sysexits.h>
+#include <syslog.h>
+#include <tcpd.h>
+#include <unistd.h>
+
+#include "util.h"
+
+int allow_severity = LOG_INFO;
+int deny_severity = LOG_NOTICE;
+
+int min_port = IPPORT_HIFIRSTAUTO;
+int max_port = IPPORT_HILASTAUTO;
+
+#define STARTBUFSIZE  1024	/* Must be at least 3 */
+
+/*
+ * Variables used to support PORT mode connections.
+ *
+ * This gets a bit complicated.
+ *
+ * If PORT mode is on then client_listen_sa describes the socket that
+ * the real client is listening on and server_listen_sa describes the
+ * socket that we are listening on (waiting for the real server to connect
+ * with us).
+ *
+ * If PASV mode is on then client_listen_sa describes the socket that
+ * we are listening on (waiting for the real client to connect to us on)
+ * and server_listen_sa describes the socket that the real server is
+ * listening on.
+ *
+ * If the socket we are listening on gets a connection then we connect
+ * to the other side's socket.  Similarily, if a connected socket is
+ * shutdown then we shutdown the other side's socket.
+ */
+
+double xfer_start_time;
+
+struct sockaddr_in real_server_sa;
+struct sockaddr_in client_listen_sa;
+struct sockaddr_in server_listen_sa;
+
+int client_listen_socket = -1;	/* Only used in PASV mode */
+int client_data_socket = -1;	/* Connected socket to real client */
+int server_listen_socket = -1;	/* Only used in PORT mode */
+int server_data_socket = -1;	/* Connected socket to real server */
+int client_data_bytes, server_data_bytes;
+
+int AnonFtpOnly;
+int Verbose;
+int NatMode;
+
+
+char ClientName[NI_MAXHOST];
+char RealServerName[NI_MAXHOST];
+char OurName[NI_MAXHOST];
+
+char *argstr = "m:M:D:t:AnVwr";
+
+extern int Debug_Level;
+extern int Use_Rdns;
+extern char *__progname;
+
+typedef enum {
+	UNKNOWN_MODE,
+	PORT_MODE,
+	PASV_MODE,
+	EPRT_MODE,
+	EPSV_MODE
+} connection_mode_t;
+
+connection_mode_t connection_mode;
+
+extern void debuglog(int debug_level, const char *fmt, ...);
+
+static void
+usage()
+{
+	syslog(LOG_NOTICE,
+	    "usage: %s [-ArVw] [-t timeout] [-D debuglevel] %s",
+	    __progname, "[-m min_port] [-M max_port ]\n");
+	exit(EX_USAGE);
+}
+
+/* 
+ * Check a connection against the tcpwrapper, log if we're going to
+ * reject it, returns: 0 -> reject, 1 -> accept. We add in hostnames
+ * if we are set to do reverse DNS, otherwise no.
+ */
+
+static int
+check_host(struct sockaddr_in *client_sin, struct sockaddr_in *server_sin)
+{
+
+	char cname[NI_MAXHOST];
+	char sname[NI_MAXHOST];
+	struct request_info request;
+	int i;
+
+	request_init(&request, RQ_DAEMON, __progname, RQ_CLIENT_SIN, 
+	    client_sin, RQ_SERVER_SIN, server_sin, RQ_CLIENT_ADDR,
+	    inet_ntoa(client_sin->sin_addr), 0);
+
+	if (Use_Rdns) {
+
+		/*
+		 * We already looked these up, but we have to do it again
+		 * for tcp wrapper, to ensure that we get the DNS name, since
+		 * the tcp wrapper cares about these things, and we don't
+		 * want to pass in a printed address as a name.
+		 */
+		
+		if (Use_Rdns)  {
+			i = getnameinfo(
+			    (struct sockaddr *) &client_sin->sin_addr,
+			    sizeof(&client_sin->sin_addr), cname, 
+			    sizeof(cname), NULL, 0, NI_NAMEREQD);
+			if (i == -1)
+				strlcpy(cname, STRING_UNKNOWN, sizeof(cname));
+
+			i = getnameinfo(
+			    (struct sockaddr *)&server_sin->sin_addr, 
+			    sizeof(&server_sin->sin_addr), sname, 
+			    sizeof(sname), NULL, 0, NI_NAMEREQD);
+			if (i == -1)
+				strlcpy(sname, STRING_UNKNOWN, sizeof(sname));
+		} else {
+			/*
+			 * ensure the TCP wrapper doesn't start doing
+			 * reverse DNS lookups if we aren't supposed to.
+			 */
+			strlcpy(cname, STRING_UNKNOWN, sizeof(cname));
+			strlcpy(sname, STRING_UNKNOWN, sizeof(sname));
+		}
+	}
+	
+	request_set(&request, RQ_SERVER_ADDR, inet_ntoa(server_sin->sin_addr),
+	    0);
+	request_set(&request, RQ_CLIENT_NAME, cname, RQ_SERVER_NAME, sname, 0);
+
+	if (!hosts_access(&request)) {
+		syslog(LOG_NOTICE, "tcpwrappers rejected: %s -> %s",
+		    ClientName, RealServerName);
+		return(0);
+	}
+	return(1);
+}
+
+double
+wallclock_time()
+{
+	struct timeval tv;
+	
+	gettimeofday(&tv,NULL);
+	return(tv.tv_sec + tv.tv_usec / 1e6);
+}
+
+/*
+ * Show the stats for this data transfer
+ */
+
+void
+show_xfer_stats()
+{
+	char tbuf[1000];
+	double delta;
+	size_t len;
+	int i;
+	
+	if (!Verbose)
+		return;
+
+	delta = wallclock_time() - xfer_start_time;
+	
+	if (delta < 0.001) 
+		delta = 0.001;
+
+	if (client_data_bytes == 0 && server_data_bytes == 0) {
+		syslog(LOG_INFO,
+		  "data transfer completed (no bytes transferred)");
+		return;
+	}
+	
+	len = sizeof(tbuf);
+
+	if (delta >= 60) {
+		int idelta;
+		
+		idelta = delta + 0.5;
+		if (idelta >= 60*60) {
+			i = snprintf(tbuf, len,
+			    "data transfer completed (%dh %dm %ds",
+			    idelta / (60*60), (idelta % (60*60)) / 60, 
+			    idelta % 60);
+			if (i >= len)
+				goto logit;
+			len -= i;
+				
+		}
+		else {
+			i = snprintf(tbuf, len, 
+			    "data transfer completed (%dm %ds", idelta / 60,
+			    idelta % 60);
+			if (i >= len)
+				goto logit;
+			len -= i;
+		}
+	} else {
+		i = snprintf(tbuf, len, "data transfer completed (%.1fs",
+		    delta);
+		if (i >= len)
+			goto logit;
+		len -= i;
+	}
+
+	if (client_data_bytes > 0) {
+		i = snprintf(&tbuf[strlen(tbuf)], len, 
+		    ", %d (%.1fKB/s) to server", client_data_bytes,
+		    (client_data_bytes / delta) / (double)1024);
+		if (i >= len)
+			goto logit;
+		len -= i;
+	}
+	if (server_data_bytes > 0) {
+		i = snprintf(&tbuf[strlen(tbuf)], len,
+		    ", %d (%.1fKB/s) to client", server_data_bytes,
+		    (server_data_bytes / delta) / (double)1024);
+		if (i >= len)
+			goto logit;
+		len -= i;
+	}
+	strlcat(tbuf,")", len);
+ logit:	
+	syslog(LOG_INFO,"%s",tbuf);
+}
+
+/*
+ * Are we in PORT mode, PASV mode or unknown mode?
+ */
+
+void 
+log_control_command (char * cmd, int client)
+{
+	/* log an ftp control command or reply */
+	char * logstring;
+	int level = LOG_DEBUG;
+
+	if (!Verbose) 
+		return;
+
+	/* don't log passwords */
+	if (strncasecmp(cmd,"pass ",5) == 0)
+		logstring = "PASS XXXX";
+	else
+		logstring = cmd;
+	if (client) {
+		/* log interesting stuff at LOG_INFO, rest at LOG_DEBUG */
+		if ((strncasecmp(cmd,"user ",5) == 0) || 
+		    (strncasecmp(cmd,"retr ",5) == 0) ||
+		    (strncasecmp(cmd,"cwd ",4) == 0) ||
+		    (strncasecmp(cmd,"stor ",5) == 0))
+			level = LOG_INFO;
+	}
+	syslog(level, "%s %s", (client?"from client:":"server reply:"),
+	    logstring);
+}
+
+
+/*
+ * set ourselves up for a new data connection. Direction is toward client if
+ * "server" is 0, towards server otherwise.
+ */
+
+int
+new_dataconn(int server)
+{
+	
+	/*
+	 * Close existing data conn.
+	 */
+	
+	if (client_listen_socket != -1) {
+		close(client_listen_socket);
+		client_listen_socket = -1;
+	}
+	if (client_data_socket != -1) {
+		shutdown(client_data_socket,2);
+		close(client_data_socket);
+		client_data_socket = -1;
+	}
+	if (server_listen_socket != -1) {
+		close(server_listen_socket);
+		server_listen_socket = -1;
+	}
+	if (server_data_socket != -1) {
+		shutdown(server_data_socket,2);
+		close(server_data_socket);
+		server_data_socket = -1;
+	}
+	
+	if (server) {
+		bzero (&server_listen_sa, sizeof(server_listen_sa));
+		
+		server_listen_socket = get_backchannel_socket(
+			SOCK_STREAM,
+			min_port,
+			max_port,
+			-1,
+			1,
+		&server_listen_sa);
+		
+		if (server_listen_socket == -1) {
+			syslog(LOG_INFO,"bind of server socket failed (%m)");
+			exit(EX_OSERR);
+		}
+		if (listen(server_listen_socket, 5) != 0) {
+			syslog(LOG_INFO,"listen on server socket failed (%m)");
+			exit(EX_OSERR);
+		}
+		
+	} else {
+		bzero(&client_listen_sa, sizeof(client_listen_sa)); 
+		
+		client_listen_socket = get_backchannel_socket(SOCK_STREAM,
+		    min_port, max_port, -1, 1, &client_listen_sa);
+
+		if (client_listen_socket == -1) {
+			syslog(LOG_NOTICE,
+			    "can't get client listen socket (%m)");
+			exit(EX_OSERR);
+		}
+		if (listen(client_listen_socket, 5) != 0) {
+			syslog(LOG_NOTICE,
+			    "can't listen on client socket (%m)");
+			exit(EX_OSERR);
+		}
+	}
+	return(0);
+}
+
+void
+do_client_cmd(struct csiob *client, struct csiob *server)
+{
+	int i,j,rv;
+	char tbuf[100];
+	char *sendbuf = NULL; 
+
+	log_control_command((char *)client->line_buffer, 1);
+	
+	/* client->line_buffer is an ftp control command.
+	 * There is no reason for these to be very long.
+	 * In the interest of limiting buffer overrun attempts,
+	 * we catch them here. 
+	 */
+	
+	if (strlen((char *)client->line_buffer) > 512) {
+		syslog(LOG_NOTICE, "excessively long control command");
+		exit(EX_DATAERR);
+	}
+
+	/*
+	 * Check the client user provided if needed
+	 */
+
+	if (AnonFtpOnly && strncasecmp((char *)client->line_buffer,"user ",
+	    strlen("user ")) == 0) {
+		char * cp;
+		cp = client->line_buffer + strlen("user ");
+		if ((strcasecmp(cp,"ftp\r\n") != 0) 
+		    && (strcasecmp(cp, "anonymous\r\n") != 0)) {
+			/*
+			 * this isn't anonymous - give the client an 
+			 * error before they send a password
+			 */
+			snprintf(tbuf, sizeof(tbuf), 
+			    "500 Only anonymous ftp is allowed\r\n");
+			j = 0;
+			i = strlen(tbuf);
+			do {
+				rv = send(client->fd, tbuf + j, i - j, 0);
+				if (rv == -1 && errno != EAGAIN && 
+				    errno != EINTR)
+					break;
+				else if (rv != -1)
+					j += rv;
+			} while (j >= 0 && j < i);
+			sendbuf = NULL;
+		} else 
+			sendbuf = client->line_buffer;
+	}
+
+		
+	/*
+	 * Watch out for EPRT commands.
+	 */
+	
+	else if ((strncasecmp((char *)client->line_buffer,"eprt ", 
+ 	    strlen("eprt ")) == 0)) { 
+
+		char *line = NULL; 
+		char *q, *p;
+		char *result[3];
+		char delim;
+		struct addrinfo hints;
+		struct addrinfo *res = NULL;
+		unsigned long proto;
+		
+		j = 0;
+		line = strdup(client->line_buffer+strlen("eprt "));
+		if (line == NULL) {
+			syslog(LOG_ERR, "insufficient memory");
+			exit(EX_UNAVAILABLE);
+		}
+		p = line;
+		delim = p[0];
+		p++;
+
+		memset(result,0, sizeof(result));
+		for (i = 0; i < 3; i++) {
+			q = strchr(p, delim);
+			if (!q || *q != delim)
+				goto parsefail;
+			*q++ = '\0';
+			result[i] = p;
+			p = q;
+		}
+
+		proto = strtoul(result[0], &p, 10);
+		if (!*result[0] || *p)
+			goto protounsupp;
+
+		memset(&hints, 0, sizeof(hints));
+		if (proto != 1) /* 1 == AF_INET - all we support for now */
+			goto protounsupp;
+		hints.ai_family = AF_INET;
+		hints.ai_socktype = SOCK_STREAM;
+		hints.ai_flags = AI_NUMERICHOST;	/*no DNS*/
+		if (getaddrinfo(result[1], result[2], &hints, &res))
+			goto parsefail;
+		if (res->ai_next)
+			goto parsefail;
+		if (sizeof(client_listen_sa) < res->ai_addrlen)
+			goto parsefail;
+		memcpy(&client_listen_sa, res->ai_addr, res->ai_addrlen);
+		
+		debuglog(1,"client wants us to use %s:%u\n",
+		    inet_ntoa(client_listen_sa.sin_addr), 
+		    htons(client_listen_sa.sin_port));
+
+		/*
+		 * Configure our own listen socket and tell the server about it
+		 */
+
+		new_dataconn(1);
+		
+		connection_mode = EPRT_MODE;
+
+		debuglog(1,"we want server to use %s:%u\n",
+		    inet_ntoa(server->sa.sin_addr),
+		    ntohs(server_listen_sa.sin_port));	 
+
+		snprintf(tbuf, sizeof(tbuf), "EPRT |%d|%s|%u|\r\n", 1,
+		    inet_ntoa(server->sa.sin_addr), 
+		    ntohs(server_listen_sa.sin_port));		
+		debuglog(1,"to server(modified):  %s",tbuf);
+		sendbuf = tbuf;
+		goto out;
+parsefail:
+		snprintf(tbuf, sizeof(tbuf), 
+		    "500 Invalid argument, rejected\r\n");
+		sendbuf = NULL;
+		goto out;
+protounsupp: 
+		/* we only support AF_INET for now */
+		if (proto == 2)
+			snprintf(tbuf, sizeof(tbuf), 
+			    "522 Protocol not supported, use (1)\r\n");
+		else
+			snprintf(tbuf, sizeof(tbuf), 
+			    "501 Protocol not supported\r\n");
+		sendbuf = NULL;
+out:
+		if (line)
+			free(line);
+		if (res)
+			freeaddrinfo(res);
+		if (sendbuf == NULL) {
+			debuglog(1, "to client(modified):  %s\n",tbuf);
+			i = strlen(tbuf);
+			do {
+				rv = send(client->fd, tbuf + j, i - j, 0);
+				if (rv == -1 && errno != EAGAIN && 
+				    errno != EINTR)
+					break;
+				else if (rv != -1)
+					j += rv;
+			} while (j >= 0 && j < i);
+		}
+	} else if (!NatMode && (strncasecmp((char *)client->line_buffer,"epsv",
+	    strlen("epsv")) == 0)) { 
+
+		/*
+		 * If we aren't in NAT mode, deal with EPSV.
+		 * EPSV is a problem - Unliks PASV, the reply from the 
+		 * server contains *only* a port, we can't modify the reply
+		 * to the client and get the client to connect to us without
+		 * resorting to using a dynamic rdr rule we have to add in
+		 * for the reply to this connection, and take away afterwards.
+		 * so this will wait until we have the right solution for rule
+		 * addtions/deletions in pf. 
+		 *
+		 * in the meantime we just tell the client we don't do it, 
+		 * and most clients should fall back to using PASV.
+		 */
+		
+		snprintf(tbuf, sizeof(tbuf), 
+		    "500 EPSV command not understood\r\n");
+		debuglog(1, "to client(modified):  %s\n",tbuf);
+		j = 0;
+		i = strlen(tbuf);
+		do {
+			rv = send(client->fd, tbuf + j, i - j, 0);
+			if (rv == -1 && errno != EAGAIN && errno != EINTR)
+				break;
+			else if (rv != -1)
+				j += rv;
+		} while (j >= 0 && j < i);
+		sendbuf = NULL;
+	} else if (strncasecmp((char *)client->line_buffer,"port ", 
+	    strlen("port ")) == 0) { 
+		unsigned int values[6];
+		int byte_number;
+		u_char *tailptr, ch;
+
+		debuglog(1,"Got a PORT command\n");
+		
+		tailptr = &client->line_buffer[strlen("port ")];
+		byte_number = 0;
+		values[0] = 0;
+		while ((ch = *tailptr) == ',' || isdigit(ch)) {
+			if (isdigit(ch)) {
+				values[byte_number] = values[byte_number]
+				  * 10 + ch - '0';
+				if (values[byte_number] > 255) {
+					syslog(LOG_NOTICE, "%s %s %s",
+					    "ERROR - byte value greater",
+					    "than 255 in PORT command",
+					    "- terminating session");
+					exit(EX_DATAERR);
+				}
+			} else if (ch == ',') {
+				byte_number += 1;
+				if (byte_number < 6)
+					values[byte_number] = 0;
+				else {
+					syslog(LOG_NOTICE, "%s %s",
+					    "too many byte values in PORT",
+					    "command - terminating session");
+					exit(EX_DATAERR);
+				}
+			}
+			tailptr += 1;
+		}
+
+		if (byte_number != 5) {
+			syslog(LOG_NOTICE, "Too few byte values in %s",
+			    "PORT command - session terminated");
+			exit(EX_DATAERR);
+		}
+		
+		client_listen_sa.sin_family = AF_INET;
+		client_listen_sa.sin_addr.s_addr = htonl((values[0] << 24) 
+		    | (values[1] << 16) | (values[2] <<  8) 
+		    | (values[3] <<  0));
+
+		client_listen_sa.sin_port = htons((values[4] << 8) 
+		    | values[5]);
+		debuglog(1,"client wants us to use %u.%u.%u.%u:%u\n",
+		    values[0], values[1], values[2], values[3],
+		    (values[4] << 8) | values[5]);
+		
+		/*
+		 * Configure our own listen socket and tell the server about it
+		 */
+
+		new_dataconn(1);
+		
+		connection_mode = PORT_MODE;
+		
+		debuglog(1,"we want server to use %s:%u\n",
+		    inet_ntoa(server->sa.sin_addr),
+		    ntohs(server_listen_sa.sin_port));	 
+		
+		snprintf(tbuf, sizeof(tbuf), "PORT %u,%u,%u,%u,%u,%u\r\n",
+			 ((u_char *)&server->sa.sin_addr.s_addr)[0],
+			 ((u_char *)&server->sa.sin_addr.s_addr)[1],
+			 ((u_char *)&server->sa.sin_addr.s_addr)[2],
+			 ((u_char *)&server->sa.sin_addr.s_addr)[3],
+			 ((u_char *)&server_listen_sa.sin_port)[0],
+			 ((u_char *)&server_listen_sa.sin_port)[1]);
+		
+		debuglog(1,"to server(modified):  %s",tbuf);
+		
+		sendbuf = tbuf;
+	} else
+		sendbuf = client->line_buffer;
+	
+	/* 
+	 *send our (possibly modified) control command in sendbuf
+	 * on it's way to the server
+	 */
+	if (sendbuf != NULL) {
+		j = 0;
+		i = strlen(sendbuf);
+		do {
+			rv = send(server->fd, sendbuf + j, i - j, 0);
+			if (rv == -1 && errno != EAGAIN && errno != EINTR)
+				break;
+			else if (rv != -1)
+				j += rv;
+		} while (j >= 0 && j < i);
+	}
+}
+
+void
+do_server_reply(struct csiob *server, struct csiob *client)
+{
+	int code, i, j, rv;
+	struct in_addr *iap;
+	char tbuf[100];
+	char *sendbuf;
+	
+	log_control_command((char *)server->line_buffer, 0);
+	
+	if (strlen((char *)server->line_buffer) > 512) {
+		/*
+		 * someone's playing games. Have a cow in the syslogs and
+		 * exit - we don't pass this on for fear of hurting
+		 * our other end, which might be poorly implemented.
+		 */
+		syslog(LOG_NOTICE, "Long (> 512 bytes) ftp control reply");
+		exit(EX_DATAERR);
+	}
+	
+	/*
+	 * Watch out for "227 Entering Passive Mode ..." replies
+	 */
+	
+	code = atoi((char *)server->line_buffer);
+	if (code <= 0 || code > 999) {
+		syslog(LOG_INFO,"invalid server reply code %d", code);
+		exit(EX_DATAERR);
+	}
+	if (code == 227 && !NatMode) {
+		u_char ch;
+		u_char *tailptr;
+		int byte_number;
+		unsigned int values[6];
+		
+		debuglog(1, "Got a PASV reply\n");
+		debuglog(1, "{%s}\n",(char *)server->line_buffer);
+		
+		tailptr = strchr((char *)server->line_buffer,'(');
+		if (tailptr == NULL) {
+			syslog(LOG_NOTICE, "malformed 227 reply");
+			exit(EX_DATAERR);
+		}
+		
+		tailptr += 1;	/* Move past the open-parentheses */
+		byte_number = 0;
+		values[0] = 0;
+		while ((ch = *tailptr) == ',' || isdigit(ch)) {
+			if (isdigit(ch)) {
+				values[byte_number] = values[byte_number]
+				    * 10 + ch - '0';
+				if (values[byte_number] > 255) {
+					syslog(LOG_NOTICE,
+					    "malformed 227 reply");
+					exit(EX_DATAERR);
+				}
+			} else if (ch == ',') {
+				byte_number += 1;
+				if (byte_number < 6) {
+					values[byte_number] = 0;
+				} else {
+					syslog(LOG_NOTICE,
+					    "malformed 227 reply");
+					exit(EX_DATAERR);
+				}
+			}
+			tailptr += 1;
+		}
+		
+		/*
+		 * The PASV reply should be terminated by a closing
+		 * parentheses.
+		 */
+		
+		if (ch != ')') {
+			syslog(LOG_INFO,"malformed 227 reply, junk at end");
+			exit(EX_DATAERR);
+		}
+
+		/* we need the righr number of bytes for ipv4 and port here */
+		
+		if (byte_number != 5) {
+			syslog(LOG_NOTICE,
+			    "malformed 227 reply, missing bytes");
+			exit(EX_DATAERR);
+		}
+		
+		server_listen_sa.sin_family = AF_INET;
+		server_listen_sa.sin_addr.s_addr = htonl(
+			(values[0] << 24) |
+			(values[1] << 16) |
+			(values[2] <<  8) |
+			(values[3] <<  0)
+			);
+		server_listen_sa.sin_port = htons((values[4] << 8)
+						  | values[5]);
+
+		debuglog(1,"server wants us to use %s:%u\n",
+			inet_ntoa(server_listen_sa.sin_addr),
+			(values[4] << 8) | values[5]);
+		
+		new_dataconn(0);
+		
+		connection_mode = PASV_MODE;
+		
+		iap = &(server->sa.sin_addr);
+		
+		debuglog(1,"we want client to use %s:%u\n", inet_ntoa(*iap),
+		    (((u_char *)&client_listen_sa.sin_port)[0] << 8)
+			| ((u_char *)&client_listen_sa.sin_port)[1]);
+		
+		snprintf(tbuf, sizeof(tbuf),
+		    "227 Entering Passive Mode (%u,%u,%u,%u,%u,%u\r\n",
+		    ((u_char *)iap)[0], ((u_char *)iap)[1],
+		    ((u_char *)iap)[2], ((u_char *)iap)[3],
+		    ((u_char *)&client_listen_sa.sin_port)[0],
+		    ((u_char *)&client_listen_sa.sin_port)[1]);
+		
+		debuglog(1, "to client(modified):  %s\n",tbuf);
+		
+		sendbuf = tbuf;
+	} else 
+		sendbuf = server->line_buffer;
+
+	/* 
+	 *send our (possibly modified) control command in sendbuf
+	 * on it's way to the client
+	 */
+
+	j = 0;
+	i = strlen(sendbuf);
+	do {
+		rv = send(client->fd, sendbuf + j, i - j, 0);
+		if (rv == -1 && errno != EAGAIN && errno != EINTR)
+			break;
+		else if (rv != -1)
+			j += rv;
+	} while (j >= 0 && j < i);
+
+}
+
+int
+main(int argc, char **argv)
+{
+	struct csiob client_iob, server_iob;
+	struct timeval tv;
+	long timeout_seconds = 0;
+	struct sigaction new_sa, old_sa;
+	int sval, ch, salen, flags, i; 
+	int use_tcpwrapper = 0;
+	int one = 1;
+
+	while ((ch = getopt(argc, argv, argstr)) != -1) {
+		switch (ch) {
+		case 'A':
+			AnonFtpOnly = 1; /* restrict to anon usernames only */
+			break;
+		case 'w':
+			use_tcpwrapper = 1; /* do the libwrap thing */
+			break;
+		case 'V':
+			Verbose = 1;
+			break;
+		case 't':
+			timeout_seconds = atoi(optarg);
+			break;
+		case 'D':
+			Debug_Level = atoi(optarg);
+			break;
+		case 'r':
+			Use_Rdns = 1; /* look up hostnames */
+			break;
+		case 'n':
+			NatMode = 1; /* pass all passives, we're using NAT */
+			break;
+		case 'm':
+			min_port = atoi(optarg);
+			if (min_port < 0 || min_port > USHRT_MAX)
+				usage();
+			break;
+		case 'M':
+			max_port = atoi(optarg);
+			if (min_port < 0 || min_port > USHRT_MAX)
+				usage();
+			break;
+		default:
+			usage();
+			/* NOTREACHED */
+		}
+	}
+	argc -= optind;
+	argv += optind;
+	
+
+	if (max_port < min_port) 
+		usage();
+
+	openlog(__progname, LOG_NDELAY|LOG_PID, LOG_DAEMON);
+	
+	setlinebuf(stdout);
+	setlinebuf(stderr);
+	
+	memset(&client_iob, 0, sizeof(client_iob));
+	memset(&server_iob, 0, sizeof(server_iob));
+	
+	if (get_proxy_env(0, &real_server_sa, &client_iob.sa) == -1) 
+		exit(EX_PROTOCOL);
+	
+	/*
+	 * We check_host after get_proxy_env so that checks are done 
+	 * against the original destination endpoint, not the endpoint
+	 * of our side of the rdr. This allows the use of tcpwrapper
+	 * rules to restrict destinations as well as sources of connections
+	 * for ftp.
+	 */
+
+	if (Use_Rdns) 
+		flags = NI_NUMERICHOST | NI_NUMERICSERV;
+	else 
+		flags = 0;
+
+	i = getnameinfo((struct sockaddr *)&client_iob.sa,
+	    sizeof(client_iob.sa), ClientName, sizeof(ClientName), NULL, 0,
+	    flags);
+
+	if (i == -1) {
+		syslog (LOG_ERR, "getnameinfo failed (%m)");
+		exit(EX_OSERR);
+	}	
+
+	i = getnameinfo((struct sockaddr *)&real_server_sa, 
+	    sizeof(real_server_sa), RealServerName, sizeof(RealServerName),
+	    NULL, 0, flags);
+
+	if (i == -1) {
+		syslog (LOG_ERR, "getnameinfo failed (%m)");
+		exit(EX_OSERR);
+	}	
+
+	if (use_tcpwrapper && !check_host(&client_iob.sa, &real_server_sa))
+		exit(EX_NOPERM);
+
+	client_iob.fd = 0;
+	
+	
+	/*  Check to see if we have a timeout defined, if so, 
+	 * set a timeout for this select call to that value, so 
+	 * we may time out if don't see any data in timeout
+	 * seconds. 
+	 */
+	
+	tv.tv_sec = timeout_seconds;
+	tv.tv_usec = 0;	
+	
+	timeout_seconds=tv.tv_sec;
+	
+	
+	debuglog(1, "client is %s:%u\n", ClientName,
+	    ntohs(client_iob.sa.sin_port));
+	
+	debuglog(1, "target server is %s:%u\n", RealServerName,
+	    ntohs(real_server_sa.sin_port));
+	
+	server_iob.fd = get_backchannel_socket(SOCK_STREAM, min_port, max_port,
+	    -1,	1, &server_iob.sa);
+		
+	if (connect(server_iob.fd, (struct sockaddr *)&real_server_sa,
+	    sizeof(real_server_sa)) != 0) {
+		syslog(LOG_INFO, "Can't connect to %s:%u (%m)", RealServerName,
+		    ntohs(real_server_sa.sin_port));
+		exit(EX_NOHOST);
+	}
+	
+	/*
+	 * Now that we are connected to the real server, get the name
+	 * of our end of the server socket so we know our IP address
+	 * from the real server's perspective.  
+	 */
+
+	i = getnameinfo((struct sockaddr *)&client_iob.sa, 
+	    sizeof(client_iob.sa), OurName, sizeof(OurName), NULL, 0, flags);
+	
+	salen = sizeof(server_iob.sa);
+	getsockname(server_iob.fd, (struct sockaddr *)&server_iob.sa, &salen);
+	
+	debuglog(1, "our end of socket to server is %s:%u\n", OurName,
+	    ntohs(server_iob.sa.sin_port));
+	
+	/* ignore sigpipe */
+	
+	new_sa.sa_handler = SIG_IGN;
+	(void)sigemptyset(&new_sa.sa_mask);
+	new_sa.sa_flags = SA_RESTART;
+
+	if (sigaction(SIGPIPE, &new_sa, &old_sa) != 0) {
+		syslog(LOG_ERR,"sigaction failed (%m)");
+		exit(EX_OSERR);
+	}
+	
+	if (setsockopt(client_iob.fd, SOL_SOCKET, SO_OOBINLINE, (char *)&one,
+	    sizeof(one)) == -1) {
+		syslog(LOG_NOTICE,"Can't set SO_OOBINLINE (%m) - exiting");
+		exit(EX_OSERR);
+	}
+		    
+	client_iob.line_buffer_size = STARTBUFSIZE;
+	client_iob.line_buffer = malloc(client_iob.line_buffer_size);
+	client_iob.io_buffer_size = STARTBUFSIZE;
+	client_iob.io_buffer = malloc(client_iob.io_buffer_size);
+	client_iob.next_byte = 0;
+	client_iob.io_buffer_len = 0;
+	client_iob.alive = 1;
+	client_iob.who = "client";
+	client_iob.send_oob_flags = 0;
+	client_iob.real_sa = client_iob.sa;
+	
+	
+	server_iob.line_buffer_size = STARTBUFSIZE;
+	server_iob.line_buffer = malloc(server_iob.line_buffer_size);
+	server_iob.io_buffer_size = STARTBUFSIZE; 
+	server_iob.io_buffer = malloc(server_iob.io_buffer_size);
+	server_iob.next_byte = 0;
+	server_iob.io_buffer_len = 0;
+	server_iob.alive = 1;
+	server_iob.who = "server";
+	server_iob.send_oob_flags = MSG_OOB;
+	server_iob.real_sa = real_server_sa;
+
+	if (client_iob.line_buffer == NULL  ||  client_iob.io_buffer == NULL
+	     || server_iob.line_buffer == NULL || server_iob.io_buffer == NULL)
+	    {	
+		syslog (LOG_NOTICE,  "Insufficient memory (malloc failed)");
+		exit(EX_UNAVAILABLE);
+	    }
+	
+	
+	while (client_iob.alive || server_iob.alive) {
+		fd_set fds;
+
+		/*
+		 * we use a static fd_set here, any individual
+		 * instance of this program can't possibly have too
+		 * many open files for FD_SETSIZE - we deal here only
+		 * with one ftp connection
+		 */
+		
+		debuglog(3,"client is %s, server is %s\n",
+			client_iob.alive ? "alive" : "dead",
+			server_iob.alive ? "alive" : "dead");
+
+		FD_ZERO(&fds);
+		
+		if (client_iob.alive && telnet_getline(&client_iob, 
+		    &server_iob)) {
+			debuglog(3, "client line buffer is \"%s\"\n",
+			    (char *)client_iob.line_buffer);
+			if (client_iob.line_buffer[0] != '\0') 
+				do_client_cmd(&client_iob, &server_iob);
+		} else if (server_iob.alive && telnet_getline(&server_iob,
+		    &client_iob)) {
+			debuglog(3,"server line buffer is \"%s\"\n",
+			    (char *)server_iob.line_buffer);
+			if (server_iob.line_buffer[0] != '\0') 
+				do_server_reply(&server_iob, &client_iob);
+		} else {
+			if (client_iob.alive) {
+				FD_SET(client_iob.fd, &fds);
+				if (client_listen_socket >= 0) 
+					FD_SET(client_listen_socket, &fds);
+				if (client_data_socket >= 0)
+					FD_SET(client_data_socket, &fds);
+			}
+			if (server_iob.alive) {
+				FD_SET(server_iob.fd, &fds); 
+				if (server_listen_socket >= 0)
+					FD_SET(server_listen_socket, &fds);
+				if (server_data_socket >= 0) 
+					FD_SET(server_data_socket, &fds);
+			}
+			
+			tv.tv_sec = timeout_seconds;
+			tv.tv_usec = 0;	
+
+		doselect:
+			switch (sval = select(FD_SETSIZE, &fds, NULL, NULL,
+			    (tv.tv_sec == 0) ? NULL : &tv)) {
+			case 0:
+				/* 
+				 * This proxy has timed out. Expire it 
+				 * quietly with an obituary in the syslogs 
+				 * for any passing mourners.
+				 */
+				syslog(LOG_INFO, 
+				   "timeout, no data for %ld seconds",
+				   timeout_seconds);
+				exit(EX_OK); 
+				break;
+				
+			case -1:
+				if (errno == EINTR  || errno == EAGAIN)
+					goto doselect;
+				syslog(LOG_NOTICE,
+				    "select failed (%m) - exiting");
+				exit(EX_OSERR);
+				break;
+				
+			default:
+				if (client_data_socket >= 0 &&
+				    FD_ISSET(client_data_socket,&fds)) {
+					int rval;
+					debuglog(3,"xfer client to server\n");
+					rval = xfer_data("client to server",
+					    client_data_socket,
+					    server_data_socket,
+					    client_iob.sa.sin_addr,
+					    real_server_sa.sin_addr);
+					if (rval <= 0) {
+						shutdown(client_data_socket,2);
+						close(client_data_socket);
+						client_data_socket = -1;
+						shutdown(server_data_socket,2);
+						close(server_data_socket);
+						server_data_socket = -1;
+						show_xfer_stats();
+					} else 
+						client_data_bytes += rval;
+				}
+				if (server_data_socket >= 0 &&
+				    FD_ISSET(server_data_socket,&fds)) {
+					int rval;
+					
+					debuglog(3,"xfer server to client\n");
+					rval = xfer_data("server to client",
+					    server_data_socket,
+					    client_data_socket,
+					    real_server_sa.sin_addr,
+					    client_iob.sa.sin_addr);
+					if (rval <= 0) {
+						shutdown(client_data_socket,2);
+						close(client_data_socket);
+						client_data_socket = -1;
+						shutdown(server_data_socket,2);
+						close(server_data_socket);
+						server_data_socket = -1;
+						show_xfer_stats();
+					} else 
+						server_data_bytes += rval;
+				}
+				if (server_listen_socket >= 0 &&
+				    FD_ISSET(server_listen_socket,&fds)) {
+					struct sockaddr_in listen_sa;
+					
+					/*
+					 * We are about to accept a 
+					 * connection from the server.
+					 * This is a PORT or EPRT data
+					 * connection.
+					 */
+					
+					debuglog(2,
+					    "server listen socket ready\n");
+					
+					if (server_data_socket >= 0) {
+						shutdown(server_data_socket,2);
+						close(server_data_socket);
+						server_data_socket = -1;
+					}
+					if (client_data_socket >= 0) {
+						shutdown(client_data_socket,2);
+						close(client_data_socket);
+						client_data_socket = -1;
+					}
+					salen = sizeof(listen_sa);
+					server_data_socket =
+					    accept(server_listen_socket,
+					    (struct sockaddr *)&listen_sa,
+					    &salen);
+					if (server_data_socket < 0) {
+						syslog(LOG_NOTICE,
+						    "accept failed (%m)");
+						exit(EX_OSERR);
+					}
+					close(server_listen_socket);
+					server_listen_socket = -1;
+					client_data_socket = socket(AF_INET,
+				    	    SOCK_STREAM, 0);
+					salen = 1;
+
+					listen_sa.sin_family = AF_INET;
+					
+					bzero(&listen_sa.sin_addr,
+					    sizeof(struct in_addr));
+					
+					debuglog(2,"setting sin_addr to %s\n",
+					    inet_ntoa(client_iob.sa.sin_addr));
+					
+					listen_sa.sin_port = htons(20);
+					salen = 1;
+					setsockopt(client_data_socket,
+					    SOL_SOCKET, SO_REUSEADDR, &salen,
+					    sizeof(salen));
+					if (bind(client_data_socket, 
+					     (struct sockaddr *)&listen_sa,
+					     sizeof(listen_sa)) < 0) {
+						syslog(LOG_NOTICE,
+						    "bind to 20 failed (%m)");
+						exit(EX_OSERR);
+					}
+					
+					if (connect(client_data_socket,
+					    (struct sockaddr *)
+					    &client_listen_sa,
+					    sizeof(client_listen_sa)) != 0) {
+						syslog(LOG_INFO,
+						   "can't connect (%m)");
+						exit(EX_NOHOST);
+					}
+					client_data_bytes = 0;
+					server_data_bytes = 0;
+					xfer_start_time = wallclock_time();
+				}
+				if (client_listen_socket >= 0 &&
+				    FD_ISSET(client_listen_socket,&fds)) {
+					struct sockaddr_in listen_sa;
+					int salen;
+					
+					/*
+					 * We are about to accept a
+					 * connection from the client.
+					 * This is a PASV data
+					 * connection. 
+					 */
+					
+					debuglog(2,
+					    "client listen socket ready\n");
+					
+					if (server_data_socket >= 0) {
+						shutdown(server_data_socket,2);
+						close(server_data_socket);
+						server_data_socket = -1;
+					}
+					if (client_data_socket >= 0) {
+						shutdown(client_data_socket,2);
+						close(client_data_socket);
+						client_data_socket = -1;
+					}
+					salen = sizeof(listen_sa);
+					client_data_socket = 
+					    accept(client_listen_socket,
+					    (struct sockaddr *)&listen_sa,
+					    &salen);
+					if (client_data_socket < 0) {
+						syslog(LOG_NOTICE, 
+						   "accept failed (%m)");
+						exit(EX_OSERR);
+					}
+					
+					close(client_listen_socket);
+					client_listen_socket = -1;
+					memset(&listen_sa, 0,
+					    sizeof(listen_sa));
+					server_data_socket =
+					    get_backchannel_socket(SOCK_STREAM,
+					    min_port, max_port, -1, 1,
+					    &listen_sa);
+					if (server_data_socket < 0) {
+						syslog(LOG_NOTICE,
+						    "backchannel failed (%m)");
+						exit(EX_OSERR);
+					}
+					if (connect(server_data_socket,
+					    (struct sockaddr *)
+					    &server_listen_sa,
+					    sizeof(server_listen_sa)) != 0) {
+						syslog(LOG_NOTICE,
+						    "connect failed (%m)");
+						exit(EX_NOHOST);
+					}
+					client_data_bytes = 0;
+					server_data_bytes = 0;
+					xfer_start_time = wallclock_time();
+				}
+				if (client_iob.alive &&
+				    FD_ISSET(client_iob.fd,&fds)) {
+					client_iob.data_available = 1;
+				}
+				
+				if (server_iob.alive &&
+				    FD_ISSET(server_iob.fd,&fds)) {
+					server_iob.data_available = 1;
+				}
+				
+			}
+		}
+		
+		if (client_iob.got_eof) {
+			shutdown(server_iob.fd,1);
+			shutdown(client_iob.fd,0);
+			client_iob.got_eof = 0;
+			client_iob.alive = 0;
+		}
+		
+		if (server_iob.got_eof) {
+			shutdown(client_iob.fd,1);
+			shutdown(server_iob.fd,0);
+			server_iob.got_eof = 0;
+			server_iob.alive = 0;
+		}
+		
+	}
+	exit(EX_OK);
+}