fix BACnet/IP on OS to bind broadcast to specific port (#489)

* Fixes #346 by binding the broadcast socket to the port specific broadcast address rather than INADDR_ANY or INADDR_BROADCAST. Added additional compile and environment options for those who might need them. 

* Changed the define USE_CLASSADDR to BACNET_IP_BROADCAST_USE_CLASSADDR to help manage namespaces.

* Added BACNET_IP_BROADCAST_BIND_ADDR environment variable to override the default broadcast binding address.

---------

Co-authored-by: Steve Karg <skarg@users.sourceforge.net>

ports/linux/bip-init.c

@@ -73,6 +73,9 @@ static uint16_t BIP_Port;
 static struct in_addr BIP_Address;
 /* IP broadcast address - stored here in network byte order */
 static struct in_addr BIP_Broadcast_Addr;
+/* broadcast binding mechanism */
+static bool BIP_Broadcast_Binding_Address_Override;
+static struct in_addr BIP_Broadcast_Binding_Address;
 /* enable debugging */
 static bool BIP_Debug = false;
 /* interface name */
@@ -409,9 +412,11 @@ uint16_t bip_receive(
     debug_print_ipv4(
         "Received MPDU->", &sin.sin_addr, sin.sin_port, received_bytes);
     /* pass the packet into the BBMD handler */
-    offset = socket == BIP_Socket ?
-        bvlc_handler(&addr, src, npdu, received_bytes) :
-        bvlc_broadcast_handler(&addr, src, npdu, received_bytes);
+    if (socket == BIP_Socket) {
+        offset = bvlc_handler(&addr, src, npdu, received_bytes);
+    } else {
+        offset = bvlc_broadcast_handler(&addr, src, npdu, received_bytes);
+    }
     if (offset > 0) {
         npdu_len = received_bytes - offset;
         debug_print_ipv4(
@@ -749,6 +754,20 @@ int bip_get_local_netmask(struct in_addr *netmask)
     return rv;
 }
 
+/**
+ * @brief Set the broadcast socket binding address
+ * @param baddr The broadcast socket binding address, in host order.
+ * @return 0 on success
+ */
+int bip_set_broadcast_binding(
+    const char *ip4_broadcast)
+{
+    BIP_Broadcast_Binding_Address.s_addr = inet_addr(ip4_broadcast);
+    BIP_Broadcast_Binding_Address_Override = true;
+
+    return 0;
+}
+
 /** Gets the local IP address and local broadcast address from the system,
  *  and saves it into the BACnet/IP data structures.
  *
@@ -773,6 +792,29 @@ void bip_set_interface(char *ifname)
         fflush(stderr);
     }
     /* setup local broadcast address */
+#ifdef BACNET_IP_BROADCAST_USE_CLASSADDR
+    long broadcast_address;
+    long net_address;
+
+    broadcast_address = 0;
+    net_address = local_address.s_addr;
+    if (IN_CLASSA(ntohl(net_address))) {
+        broadcast_address =
+            (ntohl(net_address) & ~IN_CLASSA_HOST) | IN_CLASSA_HOST;
+    } else if (IN_CLASSB(ntohl(net_address))) {
+        broadcast_address =
+            (ntohl(net_address) & ~IN_CLASSB_HOST) | IN_CLASSB_HOST;
+    } else if (IN_CLASSC(ntohl(net_address))) {
+        broadcast_address =
+            (ntohl(net_address) & ~IN_CLASSC_HOST) | IN_CLASSC_HOST;
+    } else if (IN_CLASSD(ntohl(net_address))) {
+        broadcast_address =
+            (ntohl(net_address) & ~IN_CLASSD_HOST) | IN_CLASSD_HOST;
+    } else {
+        broadcast_address = INADDR_BROADCAST;
+    }
+    BIP_Broadcast_Addr.s_addr = htonl(broadcast_address);
+#else
     rv = bip_get_local_address_ioctl(ifname, &netmask, SIOCGIFNETMASK);
     if (rv < 0) {
         BIP_Broadcast_Addr.s_addr = ~0;
@@ -780,6 +822,7 @@ void bip_set_interface(char *ifname)
         BIP_Broadcast_Addr = local_address;
         BIP_Broadcast_Addr.s_addr |= (~netmask.s_addr);
     }
+#endif
     if (BIP_Debug) {
         fprintf(stderr, "BIP: Broadcast Address: %s\n",
             inet_ntoa(BIP_Broadcast_Addr));
@@ -817,9 +860,11 @@ static int createSocket(struct sockaddr_in *sin)
         return status;
     }
     /* Bind to the proper interface to send without default gateway */
-    setsockopt(sock_fd, SOL_SOCKET, SO_BINDTODEVICE, BIP_Interface_Name,
-        strlen(BIP_Interface_Name));
-
+    status = setsockopt(sock_fd, SOL_SOCKET, SO_BINDTODEVICE,
+        BIP_Interface_Name, strlen(BIP_Interface_Name));
+    if (status < 0) {
+        perror("SO_BINDTODEVICE: ");
+    }
     /* bind the socket to the local port number and IP address */
     status =
         bind(sock_fd, (const struct sockaddr *)sin, sizeof(struct sockaddr));
@@ -876,8 +921,17 @@ bool bip_init(char *ifname)
     if (sock_fd < 0) {
         return false;
     }
-
-    sin.sin_addr.s_addr = htonl(INADDR_ANY);
+    if (BIP_Broadcast_Binding_Address_Override) {
+        sin.sin_addr.s_addr = BIP_Broadcast_Binding_Address.s_addr;
+    } else {
+#if defined(BACNET_IP_BROADCAST_USE_INADDR_ANY)
+        sin.sin_addr.s_addr = htonl(INADDR_ANY);
+#elif defined(BACNET_IP_BROADCAST_USE_INADDR_BROADCAST)
+        sin.sin_addr.s_addr = htonl(INADDR_BROADCAST);
+#else
+        sin.sin_addr.s_addr = BIP_Broadcast_Addr.s_addr;
+#endif
+    }
     sock_fd = createSocket(&sin);
     BIP_Broadcast_Socket = sock_fd;
     if (sock_fd < 0) {