aboutgitcodebugslistschat
path: root/merd.c
blob: df2e511c4a6be9bb9cbabf6bb89cfe8407116834 (plain) (blame)
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
/* MERD - MacVTap Egress and Routing Daemon
 *
 * Author: Stefano Brivio <sbrivio@redhat.com>
 * License: GPLv2
 *
 * Grab packets from Ethernet interface via AF_PACKET, build AF_INET sockets for
 * each 5-tuple from ICMP, TCP, UDP packets, perform connection tracking and
 * forward them with destination address NAT. Forward packets received on
 * sockets back to the AF_PACKET interface (typically, a macvtap, tap or veth
 * interface towards a network namespace or a VM).
 *
 * TODO:
 * - steal packets from AF_INET sockets (using eBPF/XDP, or a new socket
 *   option): currently, incoming packets are also handled by in-kernel protocol
 *   handlers, so every incoming untracked TCP packet gets a RST. Workaround:
 *	iptables -A OUTPUT -m state --state INVALID,NEW,ESTABLISHED \
 *				-p tcp --tcp-flags RST RST -j DROP
 * - and use XDP sockmap on top of that to improve performance
 * - add IPv6 support. Current workaround on the namespace or machine on the
 *   tap side:
 *	echo 1 > /proc/sys/net/ipv6/conf/all/disable_ipv6
 * - reserve and translate ports
 * - aging and timeout/RST bookkeeping for connection tracking entries
 */

#include <stdio.h>
#include <sys/epoll.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <ifaddrs.h>
#include <linux/if_ether.h>
#include <linux/if_packet.h>
#include <linux/ipv6.h>
#include <linux/tcp.h>
#include <linux/udp.h>
#include <linux/if_link.h>
#include <net/ethernet.h>
#include <stdlib.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <net/if.h>
#include <netdb.h>
#include <string.h>
#include <errno.h>
#include <linux/ip.h>

#define EPOLL_EVENTS	10
#define CT_SIZE		4096

/**
 * struct ct4 - IPv4 connection tracking entry
 * @p:		IANA protocol number
 * @sa:		Source address (as seen from tap interface)
 * @da:		Destination address
 * @sp:		Source port, network order
 * @dp:		Destination port, network order
 * @hd:		Destination MAC address
 * @hs:		Source MAC address
 * @fd:		File descriptor for corresponding AF_INET socket
 */
struct ct4 {
	uint8_t p;
	uint32_t sa;
	uint32_t da;
	uint16_t sp;
	uint16_t dp;
	unsigned char hd[ETH_ALEN];
	unsigned char hs[ETH_ALEN];
	int fd;
};

/**
 * struct ctx - Execution context
 * @epollfd:	file descriptor for epoll instance
 * @ext_addr4:	IPv4 address for external, routable interface
 * @tap_idx:	Interface index for tap interface
 * @fd_tap4:	IPv4 AF_PACKET socket for tap interface
 * @map4:	Connection tracking table
 */
struct ctx {
	int epollfd;
	unsigned long ext_addr4;
	int tap_idx;
	int fd_tap4;
	struct ct4 map4[CT_SIZE];
};

/**
 * sock4_l3() - Create and bind AF_PACKET socket for IPv4, add to epoll list
 * @c:		Execution context
 * @ifn:	Name of tap interface
 * @type:	AF_PACKET protocol type
 *
 * Return: newly created socket, doesn't return on error
 */
static int sock4_l3(struct ctx *c, const char *ifn, int type)
{
	struct sockaddr_ll addr = {
		.sll_family = AF_PACKET,
		.sll_protocol = htons(ETH_P_IP),
		.sll_ifindex = if_nametoindex(ifn),
	};
	struct epoll_event ev = { 0 };
	int fd;

	fd = socket(AF_PACKET, type, htons(ETH_P_IP));
	if (fd < 0) {
		perror("L3 socket");
		exit(EXIT_FAILURE);
	}

	if (bind(fd, (const struct sockaddr *)&addr, sizeof(addr)) < 0) {
		perror("L3 bind");
		exit(EXIT_FAILURE);
	}

	ev.events = EPOLLIN;
	ev.data.fd = fd;
	if (epoll_ctl(c->epollfd, EPOLL_CTL_ADD, fd, &ev) == -1) {
		perror("epoll_ctl");
		exit(EXIT_FAILURE);
	}

	return fd;
}

/**
 * getaddrs_ext() - Fetch IP addresses of external routable interface
 * @c:		Execution context
 * @ifn:	Name of external interface
 */
static void getaddrs_ext(struct ctx *c, const char *ifn)
{
	struct ifaddrs *ifaddr, *ifa;

	if (getifaddrs(&ifaddr) == -1) {
		perror("getifaddrs");
		exit(EXIT_FAILURE);
	}

	for (ifa = ifaddr; ifa; ifa = ifa->ifa_next) {
		struct sockaddr_in *in_addr;

		if (strcmp(ifa->ifa_name, ifn))
			continue;

		if (!ifa->ifa_addr)
			continue;

		if (ifa->ifa_addr->sa_family != AF_INET)
			continue;

		in_addr = (struct sockaddr_in *)ifa->ifa_addr;
		c->ext_addr4 = in_addr->sin_addr.s_addr;
		freeifaddrs(ifaddr);
		return;
	}

	fprintf(stderr, "Couldn't get IPv4 address for external interface\n");
	freeifaddrs(ifaddr);
	exit(EXIT_FAILURE);
}

/**
 * sock4_l4() - Create and bind AF_INET socket for given L4, add to epoll list
 * @c:		Execution context
 * @proto:	Protocol number, network order
 * @port:	L4 port, network order
 *
 * Return: newly created socket, -1 on error
 */
static int sock4_l4(struct ctx *c, uint16_t proto, uint16_t port)
{
	struct sockaddr_in addr = {
		.sin_family = AF_INET,
		.sin_port = port,
		.sin_addr = { .s_addr = c->ext_addr4 },
	};
	struct epoll_event ev = { 0 };
	int fd;

	fd = socket(AF_INET, SOCK_RAW, proto);
	if (fd < 0) {
		perror("L4 socket");
		return -1;
	}

	if (bind(fd, (const struct sockaddr *)&addr, sizeof(addr)) < 0) {
		perror("bind");
		close(fd);
		return -1;
	}

	ev.events = EPOLLIN;
	ev.data.fd = fd;
	if (epoll_ctl(c->epollfd, EPOLL_CTL_ADD, fd, &ev) == -1) {
		perror("epoll_ctl");
		return -1;
	}

	return fd;
}

/**
 * usage() - Print usage and exit
 * @name:	Executable name
 */
void usage(const char *name)
{
	fprintf(stderr, "Usage: %s IF_TAP IF_EXT\n", name);

	exit(EXIT_FAILURE);
}

/**
 * lookup4() - Look up socket entry from tap-sourced packet, create if missing
 * @c:		Execution context
 * @in:		Packet buffer, L2 headers
 *
 * Return: -1 for unsupported or too many sockets, matching socket otherwise
 */
static int lookup4(struct ctx *c, const char *in)
{
	char buf_s[BUFSIZ], buf_d[BUFSIZ];
	struct ct4 *ct = c->map4;
	struct tcphdr *th;
	struct iphdr *iph;
	struct ethhdr *eh;
	int i;

	eh = (struct ethhdr *)in;
	iph = (struct iphdr *)(in + ETH_HLEN);
	th = (struct tcphdr *)(iph + 1);

	switch (iph->protocol) {
	case IPPROTO_ICMP:
	case IPPROTO_TCP:
	case IPPROTO_UDP:
		break;
	default:
		return -1;
	}

	for (i = 0; i < CT_SIZE; i++) {
		if (ct[i].p == iph->protocol &&
		    ct[i].sa == iph->saddr && ct[i].da == iph->daddr &&
		    (ct[i].p == IPPROTO_ICMP ||
		     (ct[i].sp == th->source && ct[i].dp == th->dest)) &&
		    !memcmp(ct[i].hd, eh->h_dest, ETH_ALEN) &&
		    !memcmp(ct[i].hs, eh->h_source, ETH_ALEN))
			return ct[i].fd;
	}

	for (i = 0; i < CT_SIZE && ct[i].p; i++);

	if (i == CT_SIZE) {
		fprintf(stderr, "\nToo many sockets, aborting ");
	} else {
		ct[i].fd = sock4_l4(c, iph->protocol, th->source);

		fprintf(stderr, "\n(socket %i) New ", ct[i].fd);
		ct[i].p = iph->protocol;
		ct[i].sa = iph->saddr;
		ct[i].da = iph->daddr;
		if (iph->protocol != IPPROTO_ICMP) {
			ct[i].sp = th->source;
			ct[i].dp = th->dest;
		}
		memcpy(&ct[i].hd, eh->h_dest, ETH_ALEN);
		memcpy(&ct[i].hs, eh->h_source, ETH_ALEN);
	}

	if (iph->protocol == IPPROTO_ICMP) {
		fprintf(stderr, "icmp connection\n\tfrom %s to %s\n\n",
			inet_ntop(AF_INET, &iph->saddr, buf_s, sizeof(buf_s)),
			inet_ntop(AF_INET, &iph->daddr, buf_d, sizeof(buf_d)));
	} else {
		fprintf(stderr, "%s connection\n\tfrom %s:%i to %s:%i\n\n",
			getprotobynumber(iph->protocol)->p_name,
			inet_ntop(AF_INET, &iph->saddr, buf_s, sizeof(buf_s)),
			ntohs(th->source),
			inet_ntop(AF_INET, &iph->daddr, buf_d, sizeof(buf_d)),
			ntohs(th->dest));
	}

	return (i == CT_SIZE) ? -1 : ct[i].fd;
}

/**
 * lookup4_r4() - Reverse look up connection tracking entry from incoming packet
 * @ct:		Connection tracking table
 * @in:		Packet buffer, L3 headers
 *
 * Return: matching entry if any, NULL otherwise
 */
struct ct4 *lookup_r4(struct ct4 *ct, const char *in)
{
	struct tcphdr *th;
	struct iphdr *iph;
	int i;

	iph = (struct iphdr *)in;
	th = (struct tcphdr *)(iph + 1);

	for (i = 0; i < CT_SIZE; i++) {
		if (iph->protocol == ct[i].p &&
		    iph->saddr == ct[i].da &&
		    (iph->protocol == IPPROTO_ICMP ||
		     (th->source == ct[i].dp && th->dest == ct[i].sp)))
			return &ct[i];
	}

	return NULL;
}

/**
 * nat4_out() - Perform outgoing IPv4 address translation
 * @addr:	Source address to be used
 * @in:		Packet buffer, L3 headers
 */
static void nat4_out(unsigned long addr, const char *in)
{
	struct iphdr *iph = (struct iphdr *)in;

	iph->saddr = addr;
}

/**
 * nat4_in() - Perform incoming IPv4 address translation
 * @addr:	Original destination address to be used
 * @in:		Packet buffer, L3 headers
 */
static void nat_in(unsigned long addr, const char *in)
{
	struct iphdr *iph = (struct iphdr *)in;

	iph->daddr = addr;
}

/**
 * csum_fold() - Fold long sum for IP and TCP checksum
 * @sum:	Original long sum
 *
 * Return: 16-bit folded sum
 */
static uint16_t csum_fold(uint32_t sum)
{
	while (sum >> 16)
		sum = (sum & 0xffff) + (sum >> 16);

	return sum;
}

/**
 * csum_ipv4() - Calculate IPv4 checksum
 * @buf:	Packet buffer, L3 headers
 * @len:	Total L3 packet length
 *
 * Return: 16-bit IPv4-style checksum
 */
static uint16_t csum_ip4(void *buf, size_t len)
{
	uint32_t sum = 0;
	uint16_t *p = buf;
	size_t len1 = len / 2;
	size_t off;

	for (off = 0; off < len1; off++, p++)
		sum += *p;

	if (len % 2)
		sum += *p & 0xff;

	return ~csum_fold(sum);
}

/**
 * csum_ipv4() - Calculate TCP checksum for IPv4 and set in place
 * @in:		Packet buffer, L3 headers
 */
static void csum_tcp4(uint16_t *in)
{
	struct iphdr *iph = (struct iphdr *)in;
	struct tcphdr *th;
	uint16_t tcp_len;
	uint32_t sum = 0;

	tcp_len = ntohs(iph->tot_len) - (iph->ihl << 2);
	th = (struct tcphdr *)(iph + 1);
	in = (uint16_t *)th;

	sum += (iph->saddr >> 16) & 0xffff;
	sum += iph->saddr & 0xffff;
	sum += (iph->daddr >> 16) & 0xffff;
	sum += iph->daddr & 0xffff;

	sum += htons(IPPROTO_TCP);
	sum += htons(tcp_len);

	th->check = 0;
	while (tcp_len > 1) {
		sum += *in++;
		tcp_len -= 2;
	}

	if (tcp_len > 0) {
		sum += *in & htons(0xff00);
	}

	th->check = (uint16_t)~csum_fold(sum);
}

/**
 * tap4_handler() - Packet handler for tap interface
 * @c:		Execution context
 * @len:	Total L2 packet length
 * @in:		Packet buffer, L2 headers
 */
static void tap4_handler(struct ctx *c, int len, char *in)
{
	struct iphdr *iph = (struct iphdr *)(in + ETH_HLEN);
	struct tcphdr *th = (struct tcphdr *)(iph + 1);
	struct udphdr *uh = (struct udphdr *)(iph + 1);
	struct sockaddr_in addr = {
		.sin_family = AF_INET,
		.sin_port = th->dest,
		.sin_addr = { .s_addr = iph->daddr },
	};
	char buf_s[BUFSIZ], buf_d[BUFSIZ];
	int fd;

	fd = lookup4(c, in);
	if (fd == -1)
		return;

	nat4_out(c->ext_addr4, in + ETH_HLEN);

	switch (iph->protocol) {
	case IPPROTO_TCP:
		csum_tcp4((uint16_t *)(in + ETH_HLEN));
		break;
	case IPPROTO_UDP:
		uh->check = 0;
		break;
	case IPPROTO_ICMP:
		break;
	default:
		return;
	}

	if (iph->protocol == IPPROTO_ICMP) {
		fprintf(stderr, "icmp from tap: %s -> %s (socket %i)\n",
			inet_ntop(AF_INET, &iph->saddr, buf_s, sizeof(buf_s)),
			inet_ntop(AF_INET, &iph->daddr, buf_d, sizeof(buf_d)),
			fd);
	} else {
		fprintf(stderr, "%s from tap: %s:%i -> %s:%i (socket %i)\n",
			getprotobynumber(iph->protocol)->p_name,
			inet_ntop(AF_INET, &iph->saddr, buf_s, sizeof(buf_s)),
			ntohs(th->source),
			inet_ntop(AF_INET, &iph->daddr, buf_d, sizeof(buf_d)),
			ntohs(th->dest),
			fd);
	}

	if (sendto(fd, in + sizeof(struct ethhdr) + sizeof(struct iphdr),
		   len - sizeof(struct ethhdr) - 4 * iph->ihl, 0,
		   (struct sockaddr *)&addr, sizeof(addr)) < 0)
		perror("sendto");

}

/**
 * tap4_handler() - Packet handler for external routable interface
 * @c:		Execution context
 * @len:	Total L3 packet length
 * @in:		Packet buffer, L3 headers
 */
static void ext4_handler(struct ctx *c, int len, char *in)
{
	struct sockaddr_ll addr = {
		.sll_family = AF_PACKET,
		.sll_protocol = ntohs(ETH_P_IP),
		.sll_ifindex = c->tap_idx,
		.sll_halen = ETHER_ADDR_LEN,
	};
	struct iphdr *iph = (struct iphdr *)in;
	struct tcphdr *th = (struct tcphdr *)(iph + 1);
	char buf_s[BUFSIZ], buf_d[BUFSIZ];
	struct ethhdr *eh;
	struct ct4 *entry;
	char buf[1 << 16];

	entry = lookup_r4(c->map4, in);
	if (!entry)
		return;

	nat_in(entry->sa, in);

	iph->check = 0;
	iph->check = csum_ip4(iph, 4 * iph->ihl);

	if (iph->protocol == IPPROTO_TCP)
		csum_tcp4((uint16_t *)in);
	else if (iph->protocol == IPPROTO_UDP) {
		struct udphdr *uh = (struct udphdr *)(iph + 1);
		uh->check = 0;
	}

	memcpy(&addr.sll_addr, entry->hs, ETH_ALEN);

	eh = (struct ethhdr *)buf;
	memcpy(eh->h_dest, entry->hs, ETH_ALEN);
	memcpy(eh->h_source, entry->hd, ETH_ALEN);
	eh->h_proto = ntohs(ETH_P_IP);

	memcpy(buf + sizeof(struct ethhdr), in, len);

	if (iph->protocol == IPPROTO_ICMP) {
		fprintf(stderr, "icmp (socket %i) to tap: %s -> %s\n",
			entry->fd,
			inet_ntop(AF_INET, &iph->saddr, buf_s, sizeof(buf_s)),
			inet_ntop(AF_INET, &iph->daddr, buf_d, sizeof(buf_d)));
	} else {
		fprintf(stderr, "%s (socket %i) to tap: %s:%i -> %s:%i\n",
			getprotobynumber(iph->protocol)->p_name,
			entry->fd,
			inet_ntop(AF_INET, &iph->saddr, buf_s, sizeof(buf_s)),
			ntohs(th->source),
			inet_ntop(AF_INET, &iph->daddr, buf_d, sizeof(buf_d)),
			ntohs(th->dest));
	}

	if (sendto(c->fd_tap4, buf, len + sizeof(struct ethhdr), 0,
		   (struct sockaddr *)&addr, sizeof(addr)) < 0)
		perror("sendto");
}

/**
 * main() - Entry point and main loop
 * @argc:	Argument count
 * @argv:	Interface names
 *
 * Return: 0 once interrupted, non-zero on failure
 */
int main(int argc, char **argv)
{
	struct epoll_event events[EPOLL_EVENTS];
	const char *if_tap, *if_ext;
	struct ctx c = { 0 };
	char buf[1 << 16];
	int nfds, i, len;

	if (argc != 3)
		usage(argv[0]);
	if_tap = argv[1];
	if_ext = argv[2];

	getaddrs_ext(&c, if_ext);
	c.tap_idx = if_nametoindex(if_tap);

	c.epollfd = epoll_create1(0);
	if (c.epollfd == -1) {
		perror("epoll_create1");
		exit(EXIT_FAILURE);
	}

	c.fd_tap4 = sock4_l3(&c, if_tap, SOCK_RAW);

loop:
	nfds = epoll_wait(c.epollfd, events, EPOLL_EVENTS, -1);
	if (nfds == -1) {
		perror("epoll_wait");
		exit(EXIT_FAILURE);
	}

	for (i = 0; i < nfds; i++) {
		len = recv(events[i].data.fd, buf, sizeof(buf), MSG_DONTWAIT);
		if (len == 0)
			continue;
		if (len < 0) {
			if (errno == EAGAIN || errno == EWOULDBLOCK)
				break;
			goto out;
		}

		if (events[i].data.fd == c.fd_tap4)
			tap4_handler(&c, len, buf);
		else
			ext4_handler(&c, len, buf);
	}

	goto loop;

out:
	return 0;
}