llmnrd: Allow to bind to a specific network interface

Add a command line option -i/--interface which allows to bind the llmnrd
sockets to a specific interface. If used, requests are only answered on
the specified interface.

Example: llmnrd -i eth0

Closes #9
Signed-off-by: Tobias Klauser <tklauser@distanz.ch>

1 files changed, 25 insertions, 2 deletions

diff --git a/socket.c b/socket.c
index 21e715a..1103779 100644
--- a/socket.c
+++ b/socket.c
@@ -36,7 +36,24 @@
 static const int YES = 1;
 static const int TTL = 255;
 
-int socket_open_ipv4(uint16_t port)
+static int socket_bind_to_device(int sock, const char *iface) {
+#ifdef SO_BINDTODEVICE
+	/* bind socket to specific interface */
+	if (iface) {
+		struct ifreq ifr;
+
+		memset(&ifr, 0, sizeof(ifr));
+		strncpy(ifr.ifr_name, iface, sizeof(ifr.ifr_name) - 1);
+		if (setsockopt(sock, SOL_SOCKET, SO_BINDTODEVICE, &ifr, sizeof(ifr)) < 0) {
+			log_err("Failed to bind socket to device %s: %s\n", iface, strerror(errno));
+			return -1;
+		}
+	}
+#endif
+	return 0;
+}
+
+int socket_open_ipv4(uint16_t port, const char *iface)
 {
 	int sock;
 	struct sockaddr_in sa;
@@ -64,6 +81,9 @@ int socket_open_ipv4(uint16_t port)
 		goto err;
 	}
 
+	if (socket_bind_to_device(sock, iface) < 0)
+		goto err;
+
 	/* bind the socket */
 	memset(&sa, 0, sizeof(sa));
 	sa.sin_family = AF_INET;
@@ -81,7 +101,7 @@ err:
 	return -1;
 }
 
-int socket_open_ipv6(uint16_t port)
+int socket_open_ipv6(uint16_t port, const char *iface)
 {
 	int sock, opt_pktinfo;
 	struct sockaddr_in6 sa;
@@ -120,6 +140,9 @@ int socket_open_ipv6(uint16_t port)
 		goto err;
 	}
 
+	if (socket_bind_to_device(sock, iface) < 0)
+		goto err;
+
 	/* bind the socket */
 	memset(&sa, 0, sizeof(sa));
 	sa.sin6_family = AF_INET6;