Enable support for SO_MARK on Linux via compile-time flag

README.md

@@ -63,3 +63,17 @@ Supported SOCKS5 Features
 - IPv4, IPv6, DNS
 - TCP (no UDP at this time)
 
+compile time options
+--------------------
+
+    make CFLAGS=-DSOMARK 
+
+microsocks can be compiled with SO_MARK support on linux 2.6.25+. This
+enables 'marking' of outgoing packets for use with policy-based routing
+which allows to route packets through a non-default interface. E.g.:
+
+    ip rule add fwmark 1000 table 200
+    ip route add default dev tun1 table 200
+    microsocks -m 1000
+
+will route all connections through device `tun1`

sockssrv.c

@@ -54,6 +54,10 @@
 #define THREAD_STACK_SIZE 32*1024
 #endif
 
+#if defined(SOMARK)
+int somark;  /* mark outgoing connections' packets for adv. routing */
+#endif
+
 static const char* auth_user;
 static const char* auth_pass;
 static sblist* auth_ips;
@@ -167,6 +171,11 @@ static int connect_socks_target(unsigned char *buf, size_t n, struct client *cli
 	}
 	if(SOCKADDR_UNION_AF(&bind_addr) != AF_UNSPEC && bindtoip(fd, &bind_addr) == -1)
 		goto eval_errno;
+#if defined(SOMARK)
+	if(somark != 0) {
+		setsockopt(fd, SOL_SOCKET, SO_MARK, &somark, sizeof(somark));
+	}
+#endif
 	if(connect(fd, remote->ai_addr, remote->ai_addrlen) == -1)
 		goto eval_errno;
 
@@ -364,10 +373,16 @@ static int usage(void) {
 		"MicroSocks SOCKS5 Server\n"
 		"------------------------\n"
 		"usage: microsocks -1 -i listenip -p port -u user -P password -b bindaddr\n"
+#if defined(SOMARK)
+		"                  -m mark\n"
+#endif
 		"all arguments are optional.\n"
 		"by default listenip is 0.0.0.0 and port 1080.\n\n"
 		"option -b specifies which ip outgoing connections are bound to\n"
 		"option -1 activates auth_once mode: once a specific ip address\n"
+#if defined(SOMARK)
+		"option -m marks outgoing connections' packets with specified SO_MARK id\n"
+#endif
 		"authed successfully with user/pass, it is added to a whitelist\n"
 		"and may use the proxy without auth.\n"
 		"this is handy for programs like firefox that don't support\n"
@@ -387,7 +402,12 @@ int main(int argc, char** argv) {
 	int ch;
 	const char *listenip = "0.0.0.0";
 	unsigned port = 1080;
+#if defined(SOMARK)
+	somark = 0;
+	while((ch = getopt(argc, argv, ":1b:i:m:p:u:P:")) != -1) {
+#else
 	while((ch = getopt(argc, argv, ":1b:i:p:u:P:")) != -1) {
+#endif
 		switch(ch) {
 			case '1':
 				auth_ips = sblist_new(sizeof(union sockaddr_union), 8);
@@ -409,6 +429,11 @@ int main(int argc, char** argv) {
 			case 'p':
 				port = atoi(optarg);
 				break;
+#if defined(SOMARK)
+			case 'm':
+			    somark = atoi(optarg);
+				break;
+#endif
 			case ':':
 				dprintf(2, "error: option -%c requires an operand\n", optopt);
 				/* fall through */