File: ftp-proxy.c

package info (click to toggle)
freebsd-utils 10.1~svn273304-1
  • links: PTS, VCS
  • area: main
  • in suites: jessie-kfreebsd
  • size: 14,620 kB
  • sloc: ansic: 155,497; yacc: 5,768; sh: 3,098; xml: 1,853; makefile: 1,231; cpp: 1,071; lex: 468; perl: 242
file content (1142 lines) | stat: -rw-r--r-- 28,723 bytes parent folder | download
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
/*	$OpenBSD: ftp-proxy.c,v 1.19 2008/06/13 07:25:26 claudio Exp $ */

/*
 * Copyright (c) 2004, 2005 Camiel Dobbelaar, <cd@sentia.nl>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");

#include <sys/queue.h>
#include <sys/types.h>
#include <sys/time.h>
#include <sys/resource.h>
#include <sys/socket.h>

#include <net/if.h>
#include <net/pfvar.h>
#include <netinet/in.h>
#include <arpa/inet.h>

#include <err.h>
#include <errno.h>
#include <event.h>
#include <fcntl.h>
#include <netdb.h>
#include <pwd.h>
#include <signal.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <syslog.h>
#include <unistd.h>
#include <vis.h>

#include "filter.h"

#define CONNECT_TIMEOUT	30
#define MIN_PORT	1024
#define MAX_LINE	500
#define MAX_LOGLINE	300
#define NTOP_BUFS	3
#define TCP_BACKLOG	10

#define CHROOT_DIR	"/var/empty"
#define NOPRIV_USER	"proxy"

/* pfctl standard NAT range. */
#define PF_NAT_PROXY_PORT_LOW	50001
#define PF_NAT_PROXY_PORT_HIGH	65535

#ifndef LIST_END
#define LIST_END(a)     NULL
#endif

#ifndef getrtable
#define getrtable(a)    0
#endif

#define	sstosa(ss)	((struct sockaddr *)(ss))

enum { CMD_NONE = 0, CMD_PORT, CMD_EPRT, CMD_PASV, CMD_EPSV };

struct session {
	u_int32_t		 id;
	struct sockaddr_storage  client_ss;
	struct sockaddr_storage  proxy_ss;
	struct sockaddr_storage  server_ss;
	struct sockaddr_storage  orig_server_ss;
	struct bufferevent	*client_bufev;
	struct bufferevent	*server_bufev;
	int			 client_fd;
	int			 server_fd;
	char			 cbuf[MAX_LINE];
	size_t			 cbuf_valid;
	char			 sbuf[MAX_LINE];
	size_t			 sbuf_valid;
	int			 cmd;
	u_int16_t		 port;
	u_int16_t		 proxy_port;
	LIST_ENTRY(session)	 entry;
};

LIST_HEAD(, session) sessions = LIST_HEAD_INITIALIZER(sessions);

void	client_error(struct bufferevent *, short, void *);
int	client_parse(struct session *s);
int	client_parse_anon(struct session *s);
int	client_parse_cmd(struct session *s);
void	client_read(struct bufferevent *, void *);
int	drop_privs(void);
void	end_session(struct session *);
void	exit_daemon(void);
int	bsd_getline(char *, size_t *);
void	handle_connection(const int, short, void *);
void	handle_signal(int, short, void *);
struct session * init_session(void);
void	logmsg(int, const char *, ...);
u_int16_t parse_port(int);
u_int16_t pick_proxy_port(void);
void	proxy_reply(int, struct sockaddr *, u_int16_t);
void	server_error(struct bufferevent *, short, void *);
int	server_parse(struct session *s);
int	allow_data_connection(struct session *s);
void	server_read(struct bufferevent *, void *);
const char *sock_ntop(struct sockaddr *);
void	usage(void);

char linebuf[MAX_LINE + 1];
size_t linelen;

char ntop_buf[NTOP_BUFS][INET6_ADDRSTRLEN];

struct sockaddr_storage fixed_server_ss, fixed_proxy_ss;
const char *fixed_server, *fixed_server_port, *fixed_proxy, *listen_ip, *listen_port,
    *qname, *tagname;
int anonymous_only, daemonize, id_count, ipv6_mode, loglevel, max_sessions,
    rfc_mode, session_count, timeout, verbose;
extern char *__progname;

void
client_error(struct bufferevent *bufev __unused, short what, void *arg)
{
	struct session *s = arg;

	if (what & EVBUFFER_EOF)
		logmsg(LOG_INFO, "#%d client close", s->id);
	else if (what == (EVBUFFER_ERROR | EVBUFFER_READ))
		logmsg(LOG_ERR, "#%d client reset connection", s->id);
	else if (what & EVBUFFER_TIMEOUT)
		logmsg(LOG_ERR, "#%d client timeout", s->id);
	else if (what & EVBUFFER_WRITE)
		logmsg(LOG_ERR, "#%d client write error: %d", s->id, what);
	else
		logmsg(LOG_ERR, "#%d abnormal client error: %d", s->id, what);

	end_session(s);
}

int
client_parse(struct session *s)
{
	/* Reset any previous command. */
	s->cmd = CMD_NONE;
	s->port = 0;

	/* Commands we are looking for are at least 4 chars long. */
	if (linelen < 4)
		return (1);

	if (linebuf[0] == 'P' || linebuf[0] == 'p' ||
	    linebuf[0] == 'E' || linebuf[0] == 'e') {
		if (!client_parse_cmd(s))
			return (0);

		/*
		 * Allow active mode connections immediately, instead of
		 * waiting for a positive reply from the server.  Some
		 * rare servers/proxies try to probe or setup the data
		 * connection before an actual transfer request.
		 */
		if (s->cmd == CMD_PORT || s->cmd == CMD_EPRT)
			return (allow_data_connection(s));
	}
	
	if (anonymous_only && (linebuf[0] == 'U' || linebuf[0] == 'u'))
		return (client_parse_anon(s));

	return (1);
}

int
client_parse_anon(struct session *s)
{
	if (strcasecmp("USER ftp\r\n", linebuf) != 0 &&
	    strcasecmp("USER anonymous\r\n", linebuf) != 0) {
		snprintf(linebuf, sizeof linebuf,
		    "500 Only anonymous FTP allowed\r\n");
		logmsg(LOG_DEBUG, "#%d proxy: %s", s->id, linebuf);

		/* Talk back to the client ourself. */
		linelen = strlen(linebuf);
		bufferevent_write(s->client_bufev, linebuf, linelen);

		/* Clear buffer so it's not sent to the server. */
		linebuf[0] = '\0';
		linelen = 0;
	}

	return (1);
}

int
client_parse_cmd(struct session *s)
{
	if (strncasecmp("PASV", linebuf, 4) == 0)
		s->cmd = CMD_PASV;
	else if (strncasecmp("PORT ", linebuf, 5) == 0)
		s->cmd = CMD_PORT;
	else if (strncasecmp("EPSV", linebuf, 4) == 0)
		s->cmd = CMD_EPSV;
	else if (strncasecmp("EPRT ", linebuf, 5) == 0)
		s->cmd = CMD_EPRT;
	else
		return (1);

	if (ipv6_mode && (s->cmd == CMD_PASV || s->cmd == CMD_PORT)) {
		logmsg(LOG_CRIT, "PASV and PORT not allowed with IPv6");
		return (0);
	}

	if (s->cmd == CMD_PORT || s->cmd == CMD_EPRT) {
		s->port = parse_port(s->cmd);
		if (s->port < MIN_PORT) {
			logmsg(LOG_CRIT, "#%d bad port in '%s'", s->id,
			    linebuf);
			return (0);
		}
		s->proxy_port = pick_proxy_port();
		proxy_reply(s->cmd, sstosa(&s->proxy_ss), s->proxy_port);
		logmsg(LOG_DEBUG, "#%d proxy: %s", s->id, linebuf);
	}

	return (1);
}

void
client_read(struct bufferevent *bufev, void *arg)
{
	struct session	*s = arg;
	size_t		 buf_avail, clientread;
	int		 n;

	do {
		buf_avail = sizeof s->cbuf - s->cbuf_valid;
		clientread = bufferevent_read(bufev, s->cbuf + s->cbuf_valid,
		    buf_avail);
		s->cbuf_valid += clientread;

		while ((n = bsd_getline(s->cbuf, &s->cbuf_valid)) > 0) {
			logmsg(LOG_DEBUG, "#%d client: %s", s->id, linebuf);
			if (!client_parse(s)) {
				end_session(s);
				return;
			}
			bufferevent_write(s->server_bufev, linebuf, linelen);
		}

		if (n == -1) {
			logmsg(LOG_ERR, "#%d client command too long or not"
			    " clean", s->id);
			end_session(s);
			return;
		}
	} while (clientread == buf_avail);
}

int
drop_privs(void)
{
	struct passwd *pw;

	pw = getpwnam(NOPRIV_USER);
	if (pw == NULL)
		return (0);

	tzset();
	if (chroot(CHROOT_DIR) != 0 || chdir("/") != 0 ||
	    setgroups(1, &pw->pw_gid) != 0 ||
	    setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) != 0 ||
	    setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) != 0)
		return (0);

	return (1);
}

void
end_session(struct session *s)
{
	int serr;

	logmsg(LOG_INFO, "#%d ending session", s->id);

	/* Flush output buffers. */
	if (s->client_bufev && s->client_fd != -1)
		evbuffer_write(s->client_bufev->output, s->client_fd);
	if (s->server_bufev && s->server_fd != -1)
		evbuffer_write(s->server_bufev->output, s->server_fd);

	if (s->client_fd != -1)
		close(s->client_fd);
	if (s->server_fd != -1)
		close(s->server_fd);

	if (s->client_bufev)
		bufferevent_free(s->client_bufev);
	if (s->server_bufev)
		bufferevent_free(s->server_bufev);

	/* Remove rulesets by commiting empty ones. */
	serr = 0;
	if (prepare_commit(s->id) == -1)
		serr = errno;
	else if (do_commit() == -1) {
		serr = errno;
		do_rollback();
	}
	if (serr)
		logmsg(LOG_ERR, "#%d pf rule removal failed: %s", s->id,
		    strerror(serr));

	LIST_REMOVE(s, entry);
	free(s);
	session_count--;
}

void
exit_daemon(void)
{
	struct session *s, *next;

	for (s = LIST_FIRST(&sessions); s != LIST_END(&sessions); s = next) {
		next = LIST_NEXT(s, entry);
		end_session(s);
	}

	if (daemonize)
		closelog();

	exit(0);
}

int
bsd_getline(char *buf, size_t *valid)
{
	size_t i;

	if (*valid > MAX_LINE)
		return (-1);

	/* Copy to linebuf while searching for a newline. */
	for (i = 0; i < *valid; i++) {
		linebuf[i] = buf[i];
		if (buf[i] == '\0')
			return (-1);
		if (buf[i] == '\n')
			break;
	}

	if (i == *valid) {
		/* No newline found. */
		linebuf[0] = '\0';
		linelen = 0;
		if (i < MAX_LINE)
			return (0);
		return (-1);
	}

	linelen = i + 1;
	linebuf[linelen] = '\0';
	*valid -= linelen;
	
	/* Move leftovers to the start. */
	if (*valid != 0)
		bcopy(buf + linelen, buf, *valid);

	return ((int)linelen);
}

void
handle_connection(const int listen_fd, short event __unused, void *ev __unused)
{
	struct sockaddr_storage tmp_ss;
	struct sockaddr *client_sa, *server_sa, *fixed_server_sa;
	struct sockaddr *client_to_proxy_sa, *proxy_to_server_sa;
	struct session *s;
	socklen_t len;
	int client_fd, fc, on;

	/*
	 * We _must_ accept the connection, otherwise libevent will keep
	 * coming back, and we will chew up all CPU.
	 */
	client_sa = sstosa(&tmp_ss);
	len = sizeof(struct sockaddr_storage);
	if ((client_fd = accept(listen_fd, client_sa, &len)) < 0) {
		logmsg(LOG_CRIT, "accept failed: %s", strerror(errno));
		return;
	}

	/* Refuse connection if the maximum is reached. */
	if (session_count >= max_sessions) {
		logmsg(LOG_ERR, "client limit (%d) reached, refusing "
		    "connection from %s", max_sessions, sock_ntop(client_sa));
		close(client_fd);
		return;
	}

	/* Allocate session and copy back the info from the accept(). */
	s = init_session();
	if (s == NULL) {
		logmsg(LOG_CRIT, "init_session failed");
		close(client_fd);
		return;
	}
	s->client_fd = client_fd;
	memcpy(sstosa(&s->client_ss), client_sa, client_sa->sa_len);

	/* Cast it once, and be done with it. */
	client_sa = sstosa(&s->client_ss);
	server_sa = sstosa(&s->server_ss);
	client_to_proxy_sa = sstosa(&tmp_ss);
	proxy_to_server_sa = sstosa(&s->proxy_ss);
	fixed_server_sa = sstosa(&fixed_server_ss);

	/* Log id/client early to ease debugging. */
	logmsg(LOG_DEBUG, "#%d accepted connection from %s", s->id,
	    sock_ntop(client_sa));

	/*
	 * Find out the real server and port that the client wanted.
	 */
	len = sizeof(struct sockaddr_storage);
	if ((getsockname(s->client_fd, client_to_proxy_sa, &len)) < 0) {
		logmsg(LOG_CRIT, "#%d getsockname failed: %s", s->id,
		    strerror(errno));
		goto fail;
	}
	if (server_lookup(client_sa, client_to_proxy_sa, server_sa) != 0) {
	    	logmsg(LOG_CRIT, "#%d server lookup failed (no rdr?)", s->id);
		goto fail;
	}
	if (fixed_server) {
		memcpy(sstosa(&s->orig_server_ss), server_sa,
		    server_sa->sa_len);
		memcpy(server_sa, fixed_server_sa, fixed_server_sa->sa_len);
	}

	/* XXX: check we are not connecting to ourself. */

	/*
	 * Setup socket and connect to server.
	 */
	if ((s->server_fd = socket(server_sa->sa_family, SOCK_STREAM,
	    IPPROTO_TCP)) < 0) {
		logmsg(LOG_CRIT, "#%d server socket failed: %s", s->id,
		    strerror(errno));
		goto fail;
	}
	if (fixed_proxy && bind(s->server_fd, sstosa(&fixed_proxy_ss),
	    fixed_proxy_ss.ss_len) != 0) {
		logmsg(LOG_CRIT, "#%d cannot bind fixed proxy address: %s",
		    s->id, strerror(errno));
		goto fail;
	}

	/* Use non-blocking connect(), see CONNECT_TIMEOUT below. */
	if ((fc = fcntl(s->server_fd, F_GETFL)) == -1 ||
	    fcntl(s->server_fd, F_SETFL, fc | O_NONBLOCK) == -1) {
		logmsg(LOG_CRIT, "#%d cannot mark socket non-blocking: %s",
		    s->id, strerror(errno));
		goto fail;
	}
	if (connect(s->server_fd, server_sa, server_sa->sa_len) < 0 &&
	    errno != EINPROGRESS) {
		logmsg(LOG_CRIT, "#%d proxy cannot connect to server %s: %s",
		    s->id, sock_ntop(server_sa), strerror(errno));
		goto fail;
	}

	len = sizeof(struct sockaddr_storage);
	if ((getsockname(s->server_fd, proxy_to_server_sa, &len)) < 0) {
		logmsg(LOG_CRIT, "#%d getsockname failed: %s", s->id,
		    strerror(errno));
		goto fail;
	}

	logmsg(LOG_INFO, "#%d FTP session %d/%d started: client %s to server "
	    "%s via proxy %s ", s->id, session_count, max_sessions,
	    sock_ntop(client_sa), sock_ntop(server_sa),
	    sock_ntop(proxy_to_server_sa));

	/* Keepalive is nice, but don't care if it fails. */
	on = 1;
	setsockopt(s->client_fd, SOL_SOCKET, SO_KEEPALIVE, (void *)&on,
	    sizeof on);
	setsockopt(s->server_fd, SOL_SOCKET, SO_KEEPALIVE, (void *)&on,
	    sizeof on);

	/*
	 * Setup buffered events.
	 */
	s->client_bufev = bufferevent_new(s->client_fd, &client_read, NULL,
	    &client_error, s);
	if (s->client_bufev == NULL) {
		logmsg(LOG_CRIT, "#%d bufferevent_new client failed", s->id);
		goto fail;
	}
	bufferevent_settimeout(s->client_bufev, timeout, 0);
	bufferevent_enable(s->client_bufev, EV_READ | EV_TIMEOUT);

	s->server_bufev = bufferevent_new(s->server_fd, &server_read, NULL,
	    &server_error, s);
	if (s->server_bufev == NULL) {
		logmsg(LOG_CRIT, "#%d bufferevent_new server failed", s->id);
		goto fail;
	}
	bufferevent_settimeout(s->server_bufev, CONNECT_TIMEOUT, 0);
	bufferevent_enable(s->server_bufev, EV_READ | EV_TIMEOUT);

	return;

 fail:
	end_session(s);
}

void
handle_signal(int sig, short event __unused, void *arg __unused)
{
	/*
	 * Signal handler rules don't apply, libevent decouples for us.
	 */

	logmsg(LOG_ERR, "exiting on signal %d", sig);

	exit_daemon();
}
	

struct session *
init_session(void)
{
	struct session *s;

	s = calloc(1, sizeof(struct session));
	if (s == NULL)
		return (NULL);

	s->id = id_count++;
	s->client_fd = -1;
	s->server_fd = -1;
	s->cbuf[0] = '\0';
	s->cbuf_valid = 0;
	s->sbuf[0] = '\0';
	s->sbuf_valid = 0;
	s->client_bufev = NULL;
	s->server_bufev = NULL;
	s->cmd = CMD_NONE;
	s->port = 0;

	LIST_INSERT_HEAD(&sessions, s, entry);
	session_count++;

	return (s);
}

void
logmsg(int pri, const char *message, ...)
{
	va_list	ap;

	if (pri > loglevel)
		return;

	va_start(ap, message);

	if (daemonize)
		/* syslog does its own vissing. */
		vsyslog(pri, message, ap);
	else {
		char buf[MAX_LOGLINE];
		char visbuf[2 * MAX_LOGLINE];

		/* We don't care about truncation. */
		vsnprintf(buf, sizeof buf, message, ap);
#if 1
		strvis(visbuf, buf, VIS_CSTYLE | VIS_NL);
#else
		strnvis(visbuf, buf, sizeof visbuf, VIS_CSTYLE | VIS_NL);
#endif
		fprintf(stderr, "%s\n", visbuf);
	}

	va_end(ap);
}

int
main(int argc, char *argv[])
{
	struct rlimit rlp;
	struct addrinfo hints, *res;
	struct event ev, ev_sighup, ev_sigint, ev_sigterm;
	int ch, error, listenfd, on;
	const char *errstr;

	/* Defaults. */
	anonymous_only	= 0;
	daemonize	= 1;
	fixed_proxy	= NULL;
	fixed_server	= NULL;
	fixed_server_port = "21";
	ipv6_mode	= 0;
	listen_ip	= NULL;
	listen_port	= "8021";
	loglevel	= LOG_NOTICE;
	max_sessions	= 100;
	qname		= NULL;
	rfc_mode	= 0;
	tagname		= NULL;
	timeout		= 24 * 3600;
	verbose		= 0;

	/* Other initialization. */
	id_count	= 1;
	session_count	= 0;

	while ((ch = getopt(argc, argv, "6Aa:b:D:dm:P:p:q:R:rT:t:v")) != -1) {
		switch (ch) {
		case '6':
			ipv6_mode = 1;
			break;
		case 'A':
			anonymous_only = 1;
			break;
		case 'a':
			fixed_proxy = optarg;
			break;
		case 'b':
			listen_ip = optarg;
			break;
		case 'D':
			loglevel = strtonum(optarg, LOG_EMERG, LOG_DEBUG,
			    &errstr);
			if (errstr)
				errx(1, "loglevel %s", errstr);
			break;
		case 'd':
			daemonize = 0;
			break;
		case 'm':
			max_sessions = strtonum(optarg, 1, 500, &errstr);
			if (errstr)
				errx(1, "max sessions %s", errstr);
			break;
		case 'P':
			fixed_server_port = optarg;
			break;
		case 'p':
			listen_port = optarg;
			break;
		case 'q':
			if (strlen(optarg) >= PF_QNAME_SIZE)
				errx(1, "queuename too long");
			qname = optarg;
			break;
		case 'R':
			fixed_server = optarg;
			break;
		case 'r':
			rfc_mode = 1;
			break;
		case 'T':
			if (strlen(optarg) >= PF_TAG_NAME_SIZE)
				errx(1, "tagname too long");
			tagname = optarg;
			break;
		case 't':
			timeout = strtonum(optarg, 0, 86400, &errstr);
			if (errstr)
				errx(1, "timeout %s", errstr);
			break;
		case 'v':
			verbose++;
			if (verbose > 2)
				usage();
			break;
		default:
			usage();
		}
	}

	if (listen_ip == NULL)
		listen_ip = ipv6_mode ? "::1" : "127.0.0.1";

	/* Check for root to save the user from cryptic failure messages. */
	if (getuid() != 0)
		errx(1, "needs to start as root");

	/* Raise max. open files limit to satisfy max. sessions. */
	rlp.rlim_cur = rlp.rlim_max = (2 * max_sessions) + 10;
	if (setrlimit(RLIMIT_NOFILE, &rlp) == -1)
		err(1, "setrlimit");

	if (fixed_proxy) {
		memset(&hints, 0, sizeof hints);
		hints.ai_flags = AI_NUMERICHOST;
		hints.ai_family = ipv6_mode ? AF_INET6 : AF_INET;
		hints.ai_socktype = SOCK_STREAM;
		error = getaddrinfo(fixed_proxy, NULL, &hints, &res);
		if (error)
			errx(1, "getaddrinfo fixed proxy address failed: %s",
			    gai_strerror(error));
		memcpy(&fixed_proxy_ss, res->ai_addr, res->ai_addrlen);
		logmsg(LOG_INFO, "using %s to connect to servers",
		    sock_ntop(sstosa(&fixed_proxy_ss)));
		freeaddrinfo(res);
	}

	if (fixed_server) {
		memset(&hints, 0, sizeof hints);
		hints.ai_family = ipv6_mode ? AF_INET6 : AF_INET;
		hints.ai_socktype = SOCK_STREAM;
		error = getaddrinfo(fixed_server, fixed_server_port, &hints,
		    &res);
		if (error)
			errx(1, "getaddrinfo fixed server address failed: %s",
			    gai_strerror(error));
		memcpy(&fixed_server_ss, res->ai_addr, res->ai_addrlen);
		logmsg(LOG_INFO, "using fixed server %s",
		    sock_ntop(sstosa(&fixed_server_ss)));
		freeaddrinfo(res);
	}

	/* Setup listener. */
	memset(&hints, 0, sizeof hints);
	hints.ai_flags = AI_NUMERICHOST | AI_PASSIVE;
	hints.ai_family = ipv6_mode ? AF_INET6 : AF_INET;
	hints.ai_socktype = SOCK_STREAM;
	error = getaddrinfo(listen_ip, listen_port, &hints, &res);
	if (error)
		errx(1, "getaddrinfo listen address failed: %s",
		    gai_strerror(error));
	if ((listenfd = socket(res->ai_family, SOCK_STREAM, IPPROTO_TCP)) == -1)
		errx(1, "socket failed");
	on = 1;
	if (setsockopt(listenfd, SOL_SOCKET, SO_REUSEADDR, (void *)&on,
	    sizeof on) != 0)
		err(1, "setsockopt failed");
	if (bind(listenfd, (struct sockaddr *)res->ai_addr,
	    (socklen_t)res->ai_addrlen) != 0)
	    	err(1, "bind failed");
	if (listen(listenfd, TCP_BACKLOG) != 0)
		err(1, "listen failed");
	freeaddrinfo(res);

	/* Initialize pf. */
	init_filter(qname, tagname, verbose);

	if (daemonize) {
		if (daemon(0, 0) == -1)
			err(1, "cannot daemonize");
		openlog(__progname, LOG_PID | LOG_NDELAY, LOG_DAEMON);
	}

	/* Use logmsg for output from here on. */

	if (!drop_privs()) {
		logmsg(LOG_ERR, "cannot drop privileges: %s", strerror(errno));
		exit(1);
	}
	
	event_init();

	/* Setup signal handler. */
	signal(SIGPIPE, SIG_IGN);
	signal_set(&ev_sighup, SIGHUP, handle_signal, NULL);
	signal_set(&ev_sigint, SIGINT, handle_signal, NULL);
	signal_set(&ev_sigterm, SIGTERM, handle_signal, NULL);
	signal_add(&ev_sighup, NULL);
	signal_add(&ev_sigint, NULL);
	signal_add(&ev_sigterm, NULL);

	event_set(&ev, listenfd, EV_READ | EV_PERSIST, handle_connection, &ev);
	event_add(&ev, NULL);

	logmsg(LOG_NOTICE, "listening on %s port %s", listen_ip, listen_port);

	/*  Vroom, vroom.  */
	event_dispatch();

	logmsg(LOG_ERR, "event_dispatch error: %s", strerror(errno));
	exit_daemon();

	/* NOTREACHED */
	return (1);
}

u_int16_t
parse_port(int mode)
{
	unsigned int	 port, v[6];
	int		 n;
	char		*p;

	/* Find the last space or left-parenthesis. */
	for (p = linebuf + linelen; p > linebuf; p--)
		if (*p == ' ' || *p == '(')
			break;
	if (p == linebuf)
		return (0);

	switch (mode) {
	case CMD_PORT:
		n = sscanf(p, " %u,%u,%u,%u,%u,%u", &v[0], &v[1], &v[2],
		    &v[3], &v[4], &v[5]);
		if (n == 6 && v[0] < 256 && v[1] < 256 && v[2] < 256 &&
		    v[3] < 256 && v[4] < 256 && v[5] < 256)
			return ((v[4] << 8) | v[5]);
		break;
	case CMD_PASV:
		n = sscanf(p, "(%u,%u,%u,%u,%u,%u)", &v[0], &v[1], &v[2],
		    &v[3], &v[4], &v[5]);
		if (n == 6 && v[0] < 256 && v[1] < 256 && v[2] < 256 &&
		    v[3] < 256 && v[4] < 256 && v[5] < 256)
			return ((v[4] << 8) | v[5]);
		break;
	case CMD_EPSV:
		n = sscanf(p, "(|||%u|)", &port);
		if (n == 1 && port < 65536)
			return (port);
		break;
	case CMD_EPRT:
		n = sscanf(p, " |1|%u.%u.%u.%u|%u|", &v[0], &v[1], &v[2],
		    &v[3], &port);
		if (n == 5 && v[0] < 256 && v[1] < 256 && v[2] < 256 &&
		    v[3] < 256 && port < 65536)
			return (port);
		n = sscanf(p, " |2|%*[a-fA-F0-9:]|%u|", &port);
		if (n == 1 && port < 65536)
			return (port);
		break;
	default:
		return (0);
	}

	return (0);
}

u_int16_t
pick_proxy_port(void)
{
	/* Random should be good enough for avoiding port collisions. */
	return (IPPORT_HIFIRSTAUTO +
	    arc4random_uniform(IPPORT_HILASTAUTO - IPPORT_HIFIRSTAUTO));
}

void
proxy_reply(int cmd, struct sockaddr *sa, u_int16_t port)
{
	u_int i;
	int r = 0;

	switch (cmd) {
	case CMD_PORT:
		r = snprintf(linebuf, sizeof linebuf,
		    "PORT %s,%u,%u\r\n", sock_ntop(sa), port / 256,
		    port % 256);
		break;
	case CMD_PASV:
		r = snprintf(linebuf, sizeof linebuf,
		    "227 Entering Passive Mode (%s,%u,%u)\r\n", sock_ntop(sa),
		        port / 256, port % 256);
		break;
	case CMD_EPRT:
		if (sa->sa_family == AF_INET)
			r = snprintf(linebuf, sizeof linebuf,
			    "EPRT |1|%s|%u|\r\n", sock_ntop(sa), port);
		else if (sa->sa_family == AF_INET6)
			r = snprintf(linebuf, sizeof linebuf,
			    "EPRT |2|%s|%u|\r\n", sock_ntop(sa), port);
		break;
	case CMD_EPSV:
		r = snprintf(linebuf, sizeof linebuf,
		    "229 Entering Extended Passive Mode (|||%u|)\r\n", port);
		break;
	}

	if (r < 0 || ((u_int)r) >= sizeof linebuf) {
		logmsg(LOG_ERR, "proxy_reply failed: %d", r);
		linebuf[0] = '\0';
		linelen = 0;
		return;
	}
	linelen = (size_t)r;

	if (cmd == CMD_PORT || cmd == CMD_PASV) {
		/* Replace dots in IP address with commas. */
		for (i = 0; i < linelen; i++)
			if (linebuf[i] == '.')
				linebuf[i] = ',';
	}
}

void
server_error(struct bufferevent *bufev __unused, short what, void *arg)
{
	struct session *s = arg;

	if (what & EVBUFFER_EOF)
		logmsg(LOG_INFO, "#%d server close", s->id);
	else if (what == (EVBUFFER_ERROR | EVBUFFER_READ))
		logmsg(LOG_ERR, "#%d server refused connection", s->id);
	else if (what & EVBUFFER_WRITE)
		logmsg(LOG_ERR, "#%d server write error: %d", s->id, what);
	else if (what & EVBUFFER_TIMEOUT)
		logmsg(LOG_NOTICE, "#%d server timeout", s->id);
	else
		logmsg(LOG_ERR, "#%d abnormal server error: %d", s->id, what);

	end_session(s);
}

int
server_parse(struct session *s)
{
	if (s->cmd == CMD_NONE || linelen < 4 || linebuf[0] != '2')
		goto out;

	if ((s->cmd == CMD_PASV && strncmp("227 ", linebuf, 4) == 0) ||
	    (s->cmd == CMD_EPSV && strncmp("229 ", linebuf, 4) == 0))
		return (allow_data_connection(s));

 out:
	s->cmd = CMD_NONE;
	s->port = 0;

	return (1);
}

int
allow_data_connection(struct session *s)
{
	struct sockaddr *client_sa, *orig_sa, *proxy_sa, *server_sa;
	int prepared = 0;

	/*
	 * The pf rules below do quite some NAT rewriting, to keep up
	 * appearances.  Points to keep in mind:
	 * 1)  The client must think it's talking to the real server,
	 *     for both control and data connections.  Transparently.
	 * 2)  The server must think that the proxy is the client.
	 * 3)  Source and destination ports are rewritten to minimize
	 *     port collisions, to aid security (some systems pick weak
	 *     ports) or to satisfy RFC requirements (source port 20).
	 */
	
	/* Cast this once, to make code below it more readable. */
	client_sa = sstosa(&s->client_ss);
	server_sa = sstosa(&s->server_ss);
	proxy_sa = sstosa(&s->proxy_ss);
	if (fixed_server)
		/* Fixed server: data connections must appear to come
		   from / go to the original server, not the fixed one. */
		orig_sa = sstosa(&s->orig_server_ss);
	else
		/* Server not fixed: orig_server == server. */
		orig_sa = sstosa(&s->server_ss);

	/* Passive modes. */
	if (s->cmd == CMD_PASV || s->cmd == CMD_EPSV) {
		s->port = parse_port(s->cmd);
		if (s->port < MIN_PORT) {
			logmsg(LOG_CRIT, "#%d bad port in '%s'", s->id,
			    linebuf);
			return (0);
		}
		s->proxy_port = pick_proxy_port();
		logmsg(LOG_INFO, "#%d passive: client to server port %d"
		    " via port %d", s->id, s->port, s->proxy_port);

		if (prepare_commit(s->id) == -1)
			goto fail;
		prepared = 1;

		proxy_reply(s->cmd, orig_sa, s->proxy_port);
		logmsg(LOG_DEBUG, "#%d proxy: %s", s->id, linebuf);

		/* rdr from $client to $orig_server port $proxy_port -> $server
		    port $port */
		if (add_rdr(s->id, client_sa, orig_sa, s->proxy_port,
		    server_sa, s->port) == -1)
			goto fail;

		/* nat from $client to $server port $port -> $proxy */
		if (add_nat(s->id, client_sa, server_sa, s->port, proxy_sa,
		    PF_NAT_PROXY_PORT_LOW, PF_NAT_PROXY_PORT_HIGH) == -1)
			goto fail;

		/* pass in from $client to $server port $port */
		if (add_filter(s->id, PF_IN, client_sa, server_sa,
		    s->port) == -1)
			goto fail;

		/* pass out from $proxy to $server port $port */
		if (add_filter(s->id, PF_OUT, proxy_sa, server_sa,
		    s->port) == -1)
			goto fail;
	}

	/* Active modes. */
	if (s->cmd == CMD_PORT || s->cmd == CMD_EPRT) {
		logmsg(LOG_INFO, "#%d active: server to client port %d"
		    " via port %d", s->id, s->port, s->proxy_port);

		if (prepare_commit(s->id) == -1)
			goto fail;
		prepared = 1;

		/* rdr from $server to $proxy port $proxy_port -> $client port
		    $port */
		if (add_rdr(s->id, server_sa, proxy_sa, s->proxy_port,
		    client_sa, s->port) == -1)
			goto fail;

		/* nat from $server to $client port $port -> $orig_server port
		    $natport */
		if (rfc_mode && s->cmd == CMD_PORT) {
			/* Rewrite sourceport to RFC mandated 20. */
			if (add_nat(s->id, server_sa, client_sa, s->port,
			    orig_sa, 20, 20) == -1)
				goto fail;
		} else {
			/* Let pf pick a source port from the standard range. */
			if (add_nat(s->id, server_sa, client_sa, s->port,
			    orig_sa, PF_NAT_PROXY_PORT_LOW,
			    PF_NAT_PROXY_PORT_HIGH) == -1)
			    	goto fail;
		}

		/* pass in from $server to $client port $port */
		if (add_filter(s->id, PF_IN, server_sa, client_sa, s->port) ==
		    -1)
			goto fail;

		/* pass out from $orig_server to $client port $port */
		if (add_filter(s->id, PF_OUT, orig_sa, client_sa, s->port) ==
		    -1)
			goto fail;
	}

	/* Commit rules if they were prepared. */
	if (prepared && (do_commit() == -1)) {
		if (errno != EBUSY)
			goto fail;
		/* One more try if busy. */
		usleep(5000);
		if (do_commit() == -1)
			goto fail;
	}

	s->cmd = CMD_NONE;
	s->port = 0;

	return (1);

 fail:
	logmsg(LOG_CRIT, "#%d pf operation failed: %s", s->id, strerror(errno));
	if (prepared)
		do_rollback();
	return (0);
}
	
void
server_read(struct bufferevent *bufev, void *arg)
{
	struct session	*s = arg;
	size_t		 buf_avail, srvread;
	int		 n;

	bufferevent_settimeout(bufev, timeout, 0);

	do {
		buf_avail = sizeof s->sbuf - s->sbuf_valid;
		srvread = bufferevent_read(bufev, s->sbuf + s->sbuf_valid,
		    buf_avail);
		s->sbuf_valid += srvread;

		while ((n = bsd_getline(s->sbuf, &s->sbuf_valid)) > 0) {
			logmsg(LOG_DEBUG, "#%d server: %s", s->id, linebuf);
			if (!server_parse(s)) {
				end_session(s);
				return;
			}
			bufferevent_write(s->client_bufev, linebuf, linelen);
		}

		if (n == -1) {
			logmsg(LOG_ERR, "#%d server reply too long or not"
			    " clean", s->id);
			end_session(s);
			return;
		}
	} while (srvread == buf_avail);
}

const char *
sock_ntop(struct sockaddr *sa)
{
	static int n = 0;

	/* Cycle to next buffer. */
	n = (n + 1) % NTOP_BUFS;
	ntop_buf[n][0] = '\0';

	if (sa->sa_family == AF_INET) {
		struct sockaddr_in *sin = (struct sockaddr_in *)sa;

		return (inet_ntop(AF_INET, &sin->sin_addr, ntop_buf[n],
		    sizeof ntop_buf[0]));
	}

	if (sa->sa_family == AF_INET6) {
		struct sockaddr_in6 *sin6 = (struct sockaddr_in6 *)sa;

		return (inet_ntop(AF_INET6, &sin6->sin6_addr, ntop_buf[n],
		    sizeof ntop_buf[0]));
	}

	return (NULL);
}

void
usage(void)
{
	fprintf(stderr, "usage: %s [-6Adrv] [-a address] [-b address]"
	    " [-D level] [-m maxsessions]\n                 [-P port]"
	    " [-p port] [-q queue] [-R address] [-T tag]\n"
            "                 [-t timeout]\n", __progname);
	exit(1);
}