Add an optional parameter to specify the ip address for reverse connections

For security reasons, it can be important to limit which IP addresses a
LibVNCClient-based client should listen for reverse connections. This
commit adds that option.

To preserve binary backwards-compatibility, the field was added to the end
of the rfbclient struct, and the function ListenAtTcpPort retains its
signature (but calls the new ListenAtTcpPortAndAddress).

[jes: shortened the commit subject, added a longer explanation in the
commit body and adjusted style]
Signed-off-by: Luca Stauble <gnekoz@gmail.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

libvncclient/listen.c

@@ -55,7 +55,7 @@ listenForIncomingConnections(rfbClient* client)
 
   client->listenSpecified = TRUE;
 
-  listenSocket = ListenAtTcpPort(client->listenPort);
+  listenSocket = ListenAtTcpPortAndAddress(client->listenPort, client->listenAddress);
 
   if ((listenSocket < 0))
     return;
@@ -133,7 +133,7 @@ listenForIncomingConnectionsNoFork(rfbClient* client, int timeout)
 
   if (client->listenSock < 0)
     {
-      client->listenSock = ListenAtTcpPort(client->listenPort);
+      client->listenSock = ListenAtTcpPortAndAddress(client->listenPort, client->listenAddress);
 
       if (client->listenSock < 0)
 	return -1;

libvncclient/sockets.c

@@ -479,6 +479,19 @@ FindFreeTcpPort(void)
 
 int
 ListenAtTcpPort(int port)
+{
+  return ListenAtTcpPortAndAddress(port, NULL);
+}
+
+
+
+/*
+ * ListenAtTcpPortAndAddress starts listening at the given TCP port on
+ * the given IP address
+ */
+
+int
+ListenAtTcpPortAndAddress(int port, const char *address)
 {
   int sock;
   struct sockaddr_in addr;
@@ -486,7 +499,11 @@ ListenAtTcpPort(int port)
 
   addr.sin_family = AF_INET;
   addr.sin_port = htons(port);
+  if (address) {
+    addr.sin_addr.s_addr = inet_addr(address);
+  } else {
     addr.sin_addr.s_addr = htonl(INADDR_ANY);
+  }
 
   if (!initSockets())
     return -1;

libvncclient/vncviewer.c

@@ -196,6 +196,7 @@ rfbClient* rfbGetClient(int bitsPerSample,int samplesPerPixel,
 #endif
   client->sock = -1;
   client->listenSock = -1;
+  client->listenAddress = NULL;
   client->clientAuthSchemes = NULL;
   return client;
 }

rfb/rfbclient.h

@@ -345,6 +345,9 @@ typedef struct _rfbClient {
         int listenSock;
 
 	FinishedFrameBufferUpdateProc FinishedFrameBufferUpdate;
+
+	char *listenAddress;
+
 } rfbClient;
 
 /* cursor.c */
@@ -541,6 +544,7 @@ extern rfbBool ReadFromRFBServer(rfbClient* client, char *out, unsigned int n);
 extern rfbBool WriteToRFBServer(rfbClient* client, char *buf, int n);
 extern int FindFreeTcpPort(void);
 extern int ListenAtTcpPort(int port);
+extern int ListenAtTcpPortAndAddress(int port, const char *address);
 extern int ConnectClientToTcpAddr(unsigned int host, int port);
 extern int ConnectClientToTcpAddr6(const char *hostname, int port);
 extern int ConnectClientToUnixSock(const char *sockFile);