Add support for multicast communication with UML/QEMU/KVM.

DeviceType = multicast allows one to specify a multicast address and port with
a Device statement. Tinc will then read/send packets to that multicast group
instead of to a tun/tap device. This allows interaction with UML, QEMU and KVM
instances that are listening on the same group.

src/Makefile.am

@@ -7,7 +7,7 @@ EXTRA_DIST = linux/device.c bsd/device.c solaris/device.c cygwin/device.c mingw/
 tincd_SOURCES = conf.c connection.c edge.c event.c graph.c logger.c meta.c net.c net_packet.c net_setup.c	\
 	net_socket.c netutl.c node.c process.c protocol.c protocol_auth.c protocol_edge.c protocol_misc.c	\
 	protocol_key.c protocol_subnet.c route.c subnet.c tincd.c \
-	dummy_device.c raw_socket_device.c
+	dummy_device.c raw_socket_device.c multicast_device.c
 	
 if UML
 tincd_SOURCES += uml_device.c

src/device.h

@@ -39,6 +39,7 @@ typedef struct devops_t {
 extern const devops_t os_devops;
 extern const devops_t dummy_devops;
 extern const devops_t raw_socket_devops;
+extern const devops_t multicast_devops;
 extern const devops_t uml_devops;
 extern const devops_t vde_devops;
 extern devops_t devops;

src/multicast_device.c

@@ -0,0 +1,216 @@
+/*
+    device.c -- multicast socket
+    Copyright (C) 2002-2005 Ivo Timmermans,
+                  2002-2012 Guus Sliepen <guus@tinc-vpn.org>
+
+    This program is free software; you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation; either version 2 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License along
+    with this program; if not, write to the Free Software Foundation, Inc.,
+    51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+*/
+
+#include "system.h"
+
+#include "conf.h"
+#include "device.h"
+#include "net.h"
+#include "logger.h"
+#include "netutl.h"
+#include "utils.h"
+#include "route.h"
+#include "xalloc.h"
+
+static char *device_info;
+
+static uint64_t device_total_in = 0;
+static uint64_t device_total_out = 0;
+
+static struct addrinfo *ai = NULL;
+static mac_t ignore_src = {0};
+
+static bool setup_device(void) {
+	char *host;
+	char *port;
+	char *space;
+	int ttl = 1;
+
+	device_info = "multicast socket";
+
+	get_config_string(lookup_config(config_tree, "Interface"), &iface);
+
+	if(!get_config_string(lookup_config(config_tree, "Device"), &device)) {
+		logger(LOG_ERR, "Device variable required for %s", device_info);
+		return false;
+	}
+
+	host = xstrdup(device);
+	space = strchr(host, ' ');
+	if(!space) {
+		logger(LOG_ERR, "Port number required for %s", device_info);
+		return false;
+	}
+
+	*space++ = 0;
+	port = space;
+	space = strchr(port, ' ');
+
+	if(space) {
+		*space++ = 0;
+		ttl = atoi(space);
+	}
+
+	ai = str2addrinfo(host, port, SOCK_DGRAM);
+	if(!ai)
+		return false;
+
+	device_fd = socket(ai->ai_family, SOCK_DGRAM, IPPROTO_UDP);
+	if(device_fd < 0) {
+		logger(LOG_ERR, "Creating socket failed: %s", sockstrerror(sockerrno));
+		return false;
+	}
+
+#ifdef FD_CLOEXEC
+	fcntl(device_fd, F_SETFD, FD_CLOEXEC);
+#endif
+
+	static const int one = 1;
+	setsockopt(device_fd, SOL_SOCKET, SO_REUSEADDR, (void *)&one, sizeof one);
+
+	if(bind(device_fd, ai->ai_addr, ai->ai_addrlen)) {
+		closesocket(device_fd);
+		logger(LOG_ERR, "Can't bind to %s %s: %s", host, port, sockstrerror(sockerrno));
+		return false;
+	}
+
+	switch(ai->ai_family) {
+		case AF_INET: {
+			struct ip_mreq mreq;
+			struct sockaddr_in in;
+			memcpy(&in, ai->ai_addr, sizeof in);
+			mreq.imr_multiaddr.s_addr = in.sin_addr.s_addr;
+			mreq.imr_interface.s_addr = htonl(INADDR_ANY);
+			if(setsockopt(device_fd, IPPROTO_IP, IP_ADD_MEMBERSHIP, &mreq, sizeof mreq)) {
+				logger(LOG_ERR, "Cannot join multicast group %s %s: %s", host, port, sockstrerror(sockerrno));
+				closesocket(device_fd);
+				return false;
+			}
+			setsockopt(device_fd, IPPROTO_IP, IP_MULTICAST_LOOP, &one, sizeof one);
+			setsockopt(device_fd, IPPROTO_IP, IP_MULTICAST_TTL, &ttl, sizeof ttl);
+		} break;
+
+		case AF_INET6: {
+			struct ipv6_mreq mreq;
+			struct sockaddr_in6 in6;
+			memcpy(&in6, ai->ai_addr, sizeof in6);
+			memcpy(&mreq.ipv6mr_multiaddr, &in6.sin6_addr, sizeof mreq.ipv6mr_multiaddr);
+			mreq.ipv6mr_interface = 0;
+			if(setsockopt(device_fd, IPPROTO_IPV6, IPV6_JOIN_GROUP, &mreq, sizeof mreq)) {
+				logger(LOG_ERR, "Cannot join multicast group %s %s: %s", host, port, sockstrerror(sockerrno));
+				closesocket(device_fd);
+				return false;
+			}
+			setsockopt(device_fd, IPPROTO_IPV6, IPV6_MULTICAST_LOOP, &one, sizeof one);
+			setsockopt(device_fd, IPPROTO_IPV6, IPV6_MULTICAST_HOPS, &ttl, sizeof ttl);
+		} break;
+	
+		default:
+			logger(LOG_ERR, "Multicast for address family %hx unsupported", ai->ai_family);
+			closesocket(device_fd);
+			return false;
+	}
+
+	logger(LOG_INFO, "%s is a %s", device, device_info);
+
+	return true;
+}
+
+static void close_device(void) {
+	close(device_fd);
+
+	free(device);
+	free(iface);
+
+	if(ai)
+		freeaddrinfo(ai);
+}
+
+static bool read_packet(vpn_packet_t *packet) {
+	int lenin;
+
+	if((lenin = recv(device_fd, packet->data, MTU, 0)) <= 0) {
+		logger(LOG_ERR, "Error while reading from %s %s: %s", device_info,
+			   device, strerror(errno));
+		return false;
+	}
+
+	if(!memcmp(&ignore_src, packet->data + 6, sizeof ignore_src)) {
+		ifdebug(SCARY_THINGS) logger(LOG_DEBUG, "Ignoring loopback packet of %d bytes from %s", lenin, device_info);
+		packet->len = 0;
+		return true;
+	}
+
+	packet->len = lenin;
+
+	device_total_in += packet->len;
+
+	ifdebug(TRAFFIC) logger(LOG_DEBUG, "Read packet of %d bytes from %s", packet->len,
+			   device_info);
+
+	return true;
+}
+
+static bool write_packet(vpn_packet_t *packet) {
+	ifdebug(TRAFFIC) logger(LOG_DEBUG, "Writing packet of %d bytes to %s",
+			   packet->len, device_info);
+
+	if(sendto(device_fd, packet->data, packet->len, 0, ai->ai_addr, ai->ai_addrlen) < 0) {
+		logger(LOG_ERR, "Can't write to %s %s: %s", device_info, device,
+			   strerror(errno));
+		return false;
+	}
+
+	device_total_out += packet->len;
+
+	memcpy(&ignore_src, packet->data + 6, sizeof ignore_src);
+
+	return true;
+}
+
+static void dump_device_stats(void) {
+	logger(LOG_DEBUG, "Statistics for %s %s:", device_info, device);
+	logger(LOG_DEBUG, " total bytes in:  %10"PRIu64, device_total_in);
+	logger(LOG_DEBUG, " total bytes out: %10"PRIu64, device_total_out);
+}
+
+const devops_t multicast_devops = {
+	.setup = setup_device,
+	.close = close_device,
+	.read = read_packet,
+	.write = write_packet,
+	.dump_stats = dump_device_stats,
+};
+
+#if 0
+
+static bool not_supported(void) {
+	logger(LOG_ERR, "Raw socket device not supported on this platform");
+	return false;
+}
+
+const devops_t multicast_devops = {
+	.setup = not_supported,
+	.close = NULL,
+	.read = NULL,
+	.write = NULL,
+	.dump_stats = NULL,
+};
+#endif

src/net.c

@@ -286,9 +286,11 @@ static void check_network_activity(fd_set * readset, fd_set * writeset) {
 	/* check input from kernel */
 	if(device_fd >= 0 && FD_ISSET(device_fd, readset)) {
 		if(devops.read(&packet)) {
-			errors = 0;
-			packet.priority = 0;
-			route(myself, &packet);
+			if(packet.len) {
+				errors = 0;
+				packet.priority = 0;
+				route(myself, &packet);
+			}
 		} else {
 			usleep(errors * 50000);
 			errors++;

src/net_setup.c

@@ -548,6 +548,8 @@ static bool setup_myself(void) {
 			devops = dummy_devops;
 		else if(!strcasecmp(type, "raw_socket"))
 			devops = raw_socket_devops;
+		else if(!strcasecmp(type, "multicast"))
+			devops = multicast_devops;
 #ifdef ENABLE_UML
 		else if(!strcasecmp(type, "uml"))
 			devops = uml_devops;