add -B bind device option (follows up on #29)

Makefile

@@ -5,7 +5,7 @@ prefix = /usr/local
 bindir = $(prefix)/bin
 
 PROG = microsocks
-SRCS =  sockssrv.c server.c sblist.c sblist_delete.c
+SRCS =  sockssrv.c server.c sblist.c sblist_delete.c bind2device.c
 OBJS = $(SRCS:.c=.o)
 
 LIBS = -lpthread

README.md

@@ -41,7 +41,7 @@ libc is not even 50 KB. that's easily usable even on the cheapest routers.
 command line options
 --------------------
 
-    microsocks -1 -q -i listenip -p port -u user -P passw -b bindaddr -w wl
+    microsocks -1 -q -i listenip -p port -u user -P passw -b bindaddr -B bind2device -w wl
 
 all arguments are optional.
 by default listenip is 0.0.0.0 and port 1080.

bind2device.c

@@ -0,0 +1,55 @@
+#undef _POSIX_C_SOURCE
+#define _POSIX_C_SOURCE 200809L
+
+#define _GNU_SOURCE
+#define _DARWIN_C_SOURCE
+
+#include <errno.h>
+#include <netinet/in.h>
+#include <net/if.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <string.h>
+
+#include "bind2device.h"
+
+#if (defined(IP_BOUND_IF) || defined(IPV6_BOUND_IF))
+
+int bind2device(int sockfd, int socket_family, const char *device)
+{
+	int ifindex = if_nametoindex(device);
+	if (ifindex == 0)
+		return -1;
+	switch (socket_family)
+	{
+#if defined(IPV6_BOUND_IF)
+	case AF_INET6:
+		return setsockopt(sockfd, IPPROTO_IPV6, IPV6_BOUND_IF, &ifindex, sizeof(ifindex));
+#endif
+#if defined(IP_BOUND_IF)
+	case AF_INET:
+		return setsockopt(sockfd, IPPROTO_IP, IP_BOUND_IF, &ifindex, sizeof(ifindex));
+#endif
+	default: // can't bind to interface for selected socket_family: operation not supported on socket
+		errno = EOPNOTSUPP;
+		return -1;
+	}
+}
+
+#elif defined(SO_BINDTODEVICE)
+
+int bind2device(int sockfd, int socket_family, const char *device)
+{
+	return setsockopt(sockfd, SOL_SOCKET, SO_BINDTODEVICE, device, strlen(device) + 1);
+}
+
+#else
+#pragma message "Platform does not support bind2device, generating stub."
+
+int bind2device(int sockfd, int socket_family, const char *device)
+{
+	errno = ENOSYS; // unsupported platform: not implemented
+	return -1;
+}
+
+#endif

bind2device.h

@@ -0,0 +1,6 @@
+#ifndef BIND2DEVICE_H
+#define BIND2DEVICE_H
+
+int bind2device(int sockfd, int socket_family, const char* device);
+
+#endif

sockssrv.c

@@ -35,6 +35,7 @@
 #include <limits.h>
 #include "server.h"
 #include "sblist.h"
+#include "bind2device.h"
 
 /* timeout in microseconds on resource exhaustion to prevent excessive
    cpu usage. */
@@ -68,6 +69,7 @@ static sblist* auth_ips;
 static pthread_rwlock_t auth_ips_lock = PTHREAD_RWLOCK_INITIALIZER;
 static const struct server* server;
 static union sockaddr_union bind_addr = {.v4.sin_family = AF_UNSPEC};
+static const char* bind_device;
 
 enum socksstate {
 	SS_1_CONNECTED,
@@ -159,6 +161,8 @@ static int connect_socks_target(unsigned char *buf, size_t n, struct client *cli
 	if(resolve(namebuf, port, &remote)) return -EC_GENERAL_FAILURE;
 	struct addrinfo* raddr = addr_choose(remote, &bind_addr);
 	int fd = socket(raddr->ai_family, SOCK_STREAM, 0);
+	if(bind_device && bind2device(fd, raddr->ai_family, bind_device) == -1)
+		goto eval_errno;
 	if(fd == -1) {
 		eval_errno:
 		if(fd != -1) close(fd);
@@ -383,7 +387,7 @@ static int usage(void) {
 	dprintf(2,
 		"MicroSocks SOCKS5 Server\n"
 		"------------------------\n"
-		"usage: microsocks -1 -q -i listenip -p port -u user -P pass -b bindaddr -w ips\n"
+		"usage: microsocks -1 -q -i listenip -p port -u user -P pass -b bindaddr -B bind2device -w ips\n"
 		"all arguments are optional.\n"
 		"by default listenip is 0.0.0.0 and port 1080.\n\n"
 		"option -q disables logging.\n"
@@ -413,7 +417,7 @@ int main(int argc, char** argv) {
 	const char *listenip = "0.0.0.0";
 	char *p, *q;
 	unsigned port = 1080;
-	while((ch = getopt(argc, argv, ":1qb:i:p:u:P:w:")) != -1) {
+	while((ch = getopt(argc, argv, ":1qb:B:i:p:u:P:w:")) != -1) {
 		switch(ch) {
 			case 'w': /* fall-through */
 			case '1':
@@ -439,6 +443,10 @@ int main(int argc, char** argv) {
 			case 'b':
 				resolve_sa(optarg, 0, &bind_addr);
 				break;
+			case 'B':
+				bind_device = strdup(optarg);
+				zero_arg(optarg);
+				break;
 			case 'u':
 				auth_user = strdup(optarg);
 				zero_arg(optarg);