net: socket: Implement SO_BINDTODEVICE socket option

Implement SO_BINDTODEVICE socket option which allows to bind an open
socket to a particular network interface. Once bound, the socket will
only send and receive packets through that interface.

For the TX path, simply avoid overwriting the interface pointer by
net_context_bind() in case it's already bound to an interface with an
option. For the RX path, drop the packet in case the connection handler
detects that the net_context associated with that connection is bound to
a different interface that the packet origin interface.

Signed-off-by: Robert Lubos <robert.lubos@nordicsemi.no>

include/net/net_context.h

@@ -65,6 +65,9 @@ enum net_context_state {
 /** Is the socket closing / closed */
 #define NET_CONTEXT_CLOSING_SOCK  BIT(10)
 
+/* Context is bound to a specific interface */
+#define NET_CONTEXT_BOUND_TO_IFACE BIT(11)
+
 struct net_context;
 
 /**
@@ -336,6 +339,13 @@ static inline bool net_context_is_used(struct net_context *context)
 	return context->flags & NET_CONTEXT_IN_USE;
 }
 
+static inline bool net_context_is_bound_to_iface(struct net_context *context)
+{
+	NET_ASSERT(context);
+
+	return context->flags & NET_CONTEXT_BOUND_TO_IFACE;
+}
+
 /**
  * @brief Is this context is accepting data now.
  *

include/net/socket.h

@@ -803,6 +803,13 @@ static inline char *inet_ntop(sa_family_t family, const void *src, char *dst,
 #define EAI_FAMILY DNS_EAI_FAMILY
 #endif /* defined(CONFIG_NET_SOCKETS_POSIX_NAMES) */
 
+#define IFNAMSIZ Z_DEVICE_MAX_NAME_LEN
+
+/** Interface description structure */
+struct ifreq {
+	char ifr_name[IFNAMSIZ]; /* Interface name */
+};
+
 /** sockopt: Socket-level option */
 #define SOL_SOCKET 1
 
@@ -822,6 +829,9 @@ static inline char *inet_ntop(sa_family_t family, const void *src, char *dst,
 /** sockopt: Send timeout */
 #define SO_SNDTIMEO 21
 
+/** sockopt: Bind a socket to an interface */
+#define SO_BINDTODEVICE	25
+
 /** sockopt: Timestamp TX packets */
 #define SO_TIMESTAMPING 37
 /** sockopt: Protocol used with the socket */

subsys/net/ip/connection.c

@@ -245,6 +245,7 @@ int net_conn_register(uint16_t proto, uint8_t family,
 		      const struct sockaddr *local_addr,
 		      uint16_t remote_port,
 		      uint16_t local_port,
+		      struct net_context *context,
 		      net_conn_cb_t cb,
 		      void *user_data,
 		      struct net_conn_handle **handle)
@@ -348,6 +349,7 @@ int net_conn_register(uint16_t proto, uint8_t family,
 	conn->flags = flags;
 	conn->proto = proto;
 	conn->family = family;
+	conn->context = context;
 
 	if (handle) {
 		*handle = (struct net_conn_handle *)conn;
@@ -622,6 +624,12 @@ enum net_verdict net_conn_input(struct net_pkt *pkt,
 	}
 
 	SYS_SLIST_FOR_EACH_CONTAINER(&conn_used, conn, node) {
+		if (conn->context != NULL &&
+		    net_context_is_bound_to_iface(conn->context) &&
+		    net_pkt_iface(pkt) != net_context_get_iface(conn->context)) {
+			continue;
+		}
+
 		/* For packet socket data, the proto is set to ETH_P_ALL or IPPROTO_RAW
 		 * but the listener might have a specific protocol set. This is ok
 		 * and let the packet pass this check in this case.

subsys/net/ip/connection.h

@@ -17,6 +17,7 @@
 
 #include <sys/util.h>
 
+#include <net/net_context.h>
 #include <net/net_core.h>
 #include <net/net_ip.h>
 #include <net/net_pkt.h>
@@ -59,6 +60,11 @@ struct net_conn {
 	/** Callback to be called when matching UDP packet is received */
 	net_conn_cb_t cb;
 
+	/** A pointer to the net_context corresponding to the connection.
+	 *  Can be NULL if no net_context is associated.
+	 */
+	struct net_context *context;
+
 	/** Possible user to pass to the callback */
 	void *user_data;
 
@@ -83,6 +89,7 @@ struct net_conn {
  * @param remote_port Remote port of the connection end point.
  * @param local_port Local port of the connection end point.
  * @param cb Callback to be called
+ * @param context net_context structure related to the connection.
  * @param user_data User data supplied by caller.
  * @param handle Connection handle that can be used when unregistering
  *
@@ -94,6 +101,7 @@ int net_conn_register(uint16_t proto, uint8_t family,
 		      const struct sockaddr *local_addr,
 		      uint16_t remote_port,
 		      uint16_t local_port,
+		      struct net_context *context,
 		      net_conn_cb_t cb,
 		      void *user_data,
 		      struct net_conn_handle **handle);
@@ -103,6 +111,7 @@ static inline int net_conn_register(uint16_t proto, uint8_t family,
 				    const struct sockaddr *local_addr,
 				    uint16_t remote_port,
 				    uint16_t local_port,
+				    struct net_context *context,
 				    net_conn_cb_t cb,
 				    void *user_data,
 				    struct net_conn_handle **handle)
@@ -114,6 +123,7 @@ static inline int net_conn_register(uint16_t proto, uint8_t family,
 	ARG_UNUSED(remote_port);
 	ARG_UNUSED(local_port);
 	ARG_UNUSED(cb);
+	ARG_UNUSED(context);
 	ARG_UNUSED(user_data);
 	ARG_UNUSED(handle);
 

subsys/net/ip/dhcpv4.c

@@ -1265,7 +1265,7 @@ int net_dhcpv4_init(void)
 	ret = net_udp_register(AF_INET, NULL, &local_addr,
 			       DHCPV4_SERVER_PORT,
 			       DHCPV4_CLIENT_PORT,
-			       net_dhcpv4_input, NULL, NULL);
+			       NULL, net_dhcpv4_input, NULL, NULL);
 	if (ret < 0) {
 		NET_DBG("UDP callback registration failed");
 		return ret;

subsys/net/ip/net_context.c

@@ -528,6 +528,10 @@ int net_context_bind(struct net_context *context, const struct sockaddr *addr,
 			return -EINVAL;
 		}
 
+		if (net_context_is_bound_to_iface(context)) {
+			iface = net_context_get_iface(context);
+		}
+
 		if (net_ipv6_is_addr_mcast(&addr6->sin6_addr)) {
 			struct net_if_mcast_addr *maddr;
 
@@ -540,15 +544,18 @@ int net_context_bind(struct net_context *context, const struct sockaddr *addr,
 			ptr = &maddr->address.in6_addr;
 
 		} else if (net_ipv6_is_addr_unspecified(&addr6->sin6_addr)) {
-			iface = net_if_ipv6_select_src_iface(
+			if (iface == NULL) {
-				&net_sin6(&context->remote)->sin6_addr);
+				iface = net_if_ipv6_select_src_iface(
+					&net_sin6(&context->remote)->sin6_addr);
+			}
 
 			ptr = (struct in6_addr *)net_ipv6_unspecified_address();
 		} else {
 			struct net_if_addr *ifaddr;
 
-			ifaddr = net_if_ipv6_addr_lookup(&addr6->sin6_addr,
+			ifaddr = net_if_ipv6_addr_lookup(
-							 &iface);
+					&addr6->sin6_addr,
+					iface == NULL ? &iface : NULL);
 			if (!ifaddr) {
 				return -ENOENT;
 			}
@@ -622,6 +629,10 @@ int net_context_bind(struct net_context *context, const struct sockaddr *addr,
 			return -EINVAL;
 		}
 
+		if (net_context_is_bound_to_iface(context)) {
+			iface = net_context_get_iface(context);
+		}
+
 		if (net_ipv4_is_addr_mcast(&addr4->sin_addr)) {
 			struct net_if_mcast_addr *maddr;
 
@@ -634,13 +645,16 @@ int net_context_bind(struct net_context *context, const struct sockaddr *addr,
 			ptr = &maddr->address.in_addr;
 
 		} else if (addr4->sin_addr.s_addr == INADDR_ANY) {
-			iface = net_if_ipv4_select_src_iface(
+			if (iface == NULL) {
-				&net_sin(&context->remote)->sin_addr);
+				iface = net_if_ipv4_select_src_iface(
+					&net_sin(&context->remote)->sin_addr);
+			}
 
 			ptr = (struct in_addr *)net_ipv4_unspecified_address();
 		} else {
-			ifaddr = net_if_ipv4_addr_lookup(&addr4->sin_addr,
+			ifaddr = net_if_ipv4_addr_lookup(
-							 &iface);
+					&addr4->sin_addr,
+					iface == NULL ? &iface : NULL);
 			if (!ifaddr) {
 				return -ENOENT;
 			}
@@ -1473,7 +1487,8 @@ static int context_sendto(struct net_context *context,
 		 * second or later network interface.
 		 */
 		if (net_ipv6_is_addr_unspecified(
-				&net_sin6(&context->remote)->sin6_addr)) {
+				&net_sin6(&context->remote)->sin6_addr) &&
+		    !net_context_is_bound_to_iface(context)) {
 			iface = net_if_ipv6_select_src_iface(&addr6->sin6_addr);
 			net_context_set_iface(context, iface);
 		}
@@ -1512,7 +1527,8 @@ static int context_sendto(struct net_context *context,
 		 * network interfaces and we are trying to send data to
 		 * second or later network interface.
 		 */
-		if (net_sin(&context->remote)->sin_addr.s_addr == 0U) {
+		if (net_sin(&context->remote)->sin_addr.s_addr == 0U &&
+		    !net_context_is_bound_to_iface(context)) {
 			iface = net_if_ipv4_select_src_iface(&addr4->sin_addr);
 			net_context_set_iface(context, iface);
 		}
@@ -1962,6 +1978,7 @@ static int recv_udp(struct net_context *context,
 				laddr,
 				ntohs(net_sin(&context->remote)->sin_port),
 				ntohs(lport),
+				context,
 				net_context_packet_received,
 				user_data,
 				&context->conn_handler);
@@ -2029,6 +2046,7 @@ static int recv_raw(struct net_context *context,
 	ret = net_conn_register(net_context_get_ip_proto(context),
 				net_context_get_family(context),
 				NULL, local_addr, 0, 0,
+				context,
 				net_context_raw_packet_received,
 				user_data,
 				&context->conn_handler);

subsys/net/ip/tcp2.c

@@ -1476,7 +1476,7 @@ static struct tcp *tcp_conn_new(struct net_pkt *pkt)
 				&context->remote, &local_addr,
 				ntohs(conn->dst.sin.sin_port),/* local port */
 				ntohs(conn->src.sin.sin_port),/* remote port */
-				tcp_recv, context,
+				context, tcp_recv, context,
 				&context->conn_handler);
 	if (ret < 0) {
 		NET_ERR("net_conn_register(): %d", ret);
@@ -2235,7 +2235,7 @@ int net_tcp_connect(struct net_context *context,
 				net_context_get_family(context),
 				remote_addr, local_addr,
 				ntohs(remote_port), ntohs(local_port),
-				tcp_recv, context,
+				context, tcp_recv, context,
 				&context->conn_handler);
 	if (ret < 0) {
 		goto out;
@@ -2335,7 +2335,7 @@ int net_tcp_accept(struct net_context *context, net_tcp_accept_cb_t cb,
 				 &context->remote : NULL,
 				 &local_addr,
 				 remote_port, local_port,
-				 tcp_recv, context,
+				 context, tcp_recv, context,
 				 &context->conn_handler);
 }
 
@@ -2636,6 +2636,7 @@ static void test_cb_register(sa_family_t family, uint8_t proto, uint16_t remote_
 				    &addr,	/* local address */
 				    local_port,
 				    remote_port,
+				    NULL,
 				    cb,
 				    NULL,	/* user_data */
 				    &conn_handle);

subsys/net/ip/udp.c

@@ -129,13 +129,14 @@ int net_udp_register(uint8_t family,
 		     const struct sockaddr *local_addr,
 		     uint16_t remote_port,
 		     uint16_t local_port,
+		     struct net_context *context,
 		     net_conn_cb_t cb,
 		     void *user_data,
 		     struct net_conn_handle **handle)
 {
 	return net_conn_register(IPPROTO_UDP, family, remote_addr, local_addr,
-				 remote_port, local_port, cb, user_data,
+				 remote_port, local_port, context, cb,
-				 handle);
+				 user_data, handle);
 }
 
 int net_udp_unregister(struct net_conn_handle *handle)

subsys/net/ip/udp_internal.h

@@ -105,6 +105,7 @@ struct net_udp_hdr *net_udp_input(struct net_pkt *pkt,
  * @param local_addr Local address of the connection end point.
  * @param remote_port Remote port of the connection end point.
  * @param local_port Local port of the connection end point.
+ * @param context net_context structure related to the connection.
  * @param cb Callback to be called
  * @param user_data User data supplied by caller.
  * @param handle UDP handle that can be used when unregistering
@@ -116,6 +117,7 @@ int net_udp_register(uint8_t family,
 		     const struct sockaddr *local_addr,
 		     uint16_t remote_port,
 		     uint16_t local_port,
+		     struct net_context *context,
 		     net_conn_cb_t cb,
 		     void *user_data,
 		     struct net_conn_handle **handle);

subsys/net/lib/sockets/sockets.c

@@ -1764,6 +1764,50 @@ int zsock_setsockopt_ctx(struct net_context *ctx, int level, int optname,
 			}
 
 			break;
+
+		case SO_BINDTODEVICE: {
+			struct net_if *iface;
+			const struct device *dev;
+			struct ifreq *ifreq = (struct ifreq *)optval;
+
+			if (net_context_get_family(ctx) != AF_INET &&
+			    net_context_get_family(ctx) != AF_INET6) {
+				errno = EAFNOSUPPORT;
+				return -1;
+			}
+
+			/* optlen equal to 0 or empty interface name should
+			 * remove the binding.
+			 */
+			if ((optlen == 0) || (ifreq != NULL &&
+					      strlen(ifreq->ifr_name) == 0)) {
+				ctx->flags &= ~NET_CONTEXT_BOUND_TO_IFACE;
+				return 0;
+			}
+
+			if ((ifreq == NULL) || (optlen != sizeof(*ifreq))) {
+				errno = EINVAL;
+				return -1;
+			}
+
+			dev = device_get_binding(ifreq->ifr_name);
+			if (dev == NULL) {
+				errno = ENODEV;
+				return -1;
+			}
+
+			iface = net_if_lookup_by_dev(dev);
+			if (iface == NULL) {
+				errno = ENODEV;
+				return -1;
+			}
+
+			net_context_set_iface(ctx, iface);
+			ctx->flags |= NET_CONTEXT_BOUND_TO_IFACE;
+
+			return 0;
+		}
+
 		}
 
 		break;

tests/net/ipv6_fragment/src/main.c

@@ -1429,7 +1429,7 @@ static void setup_udp_handler(const struct in6_addr *raddr,
 	remote_addr.sa_family = AF_INET6;
 
 	ret = net_udp_register(AF_INET6, &remote_addr, &local_addr,
-			       remote_port, local_port, udp_data_received,
+			       remote_port, local_port, NULL, udp_data_received,
 			       NULL, &handle);
 	zassert_equal(ret, 0, "Cannot register UDP handler");
 }

tests/net/udp/src/main.c

@@ -509,7 +509,7 @@ void test_udp(void)
 				       (struct sockaddr *)raddr,	\
 				       (struct sockaddr *)laddr,	\
 				       rport, lport,			\
-				       test_ok, &user_data,		\
+				       NULL, test_ok, &user_data,	\
 				       &handlers[i]);			\
 		if (ret) {						\
 			printk("UDP register %s failed (%d)\n",		\
@@ -525,7 +525,8 @@ void test_udp(void)
 			       (struct sockaddr *)raddr,		\
 			       (struct sockaddr *)laddr,		\
 			       rport, lport,				\
-			       test_fail, INT_TO_POINTER(0), NULL);	\
+			       NULL, test_fail, INT_TO_POINTER(0),	\
+			       NULL);					\
 	if (!ret) {							\
 		printk("UDP register invalid match %s failed\n",	\
 		       "DST="#raddr"-SRC="#laddr"-RP="#rport"-LP="#lport); \