If an XDMCP client provides more than one address to connect back with prefer to use the address the Request message came from.

This fixes faulty XDMCP clients that provide local addresses that can't be routed to.

1 files changed, 76 insertions, 43 deletions

diff --git a/src/xdmcp-server.c b/src/xdmcp-server.c
index 8d171b8d..aa337b75 100644
--- a/src/xdmcp-server.c
+++ b/src/xdmcp-server.c
@@ -258,10 +258,76 @@ decode_key (const gchar *key, guint8 *data)
     }
 }
 
+static GInetAddress *
+connection_to_address (XDMCPConnection *connection)
+{
+    switch (connection->type)
+    {
+    case XAUTH_FAMILY_INTERNET:
+        if (connection->address.length == 4)
+            return g_inet_address_new_from_bytes (connection->address.data, G_SOCKET_FAMILY_IPV4);
+        else
+            return NULL;
+    case XAUTH_FAMILY_INTERNET6:
+        if (connection->address.length == 16)
+            return g_inet_address_new_from_bytes (connection->address.data, G_SOCKET_FAMILY_IPV6);
+        else
+            return NULL;
+    default:
+        return NULL;
+    }
+}
+
+static gssize
+find_address (GInetAddress **addresses, gsize length, GSocketFamily family)
+{
+    int i;
+
+    for (i = 0; i < length; i++)
+    {
+        GInetAddress *address = addresses[i];
+        if (address && g_inet_address_get_family (address) == family)
+            return i;
+    }
+
+    return -1;
+}
+
+static XDMCPConnection *
+choose_connection (XDMCPPacket *packet, GInetAddress *source_address)
+{
+    GInetAddress **addresses;
+    gsize addresses_length, i;
+    gssize index = -1;
+
+    addresses_length = packet->Request.n_connections;
+    addresses = malloc (sizeof (GInetAddress *) * addresses_length);
+    for (i = 0; i < addresses_length; i++)
+        addresses[i] = connection_to_address (&packet->Request.connections[i]);
+
+    /* Use the address the request came in on as this is the least likely to have firewall / routing issues */
+    for (i = 0; i < addresses_length && index < 0; i++)
+        if (g_inet_address_equal (source_address, addresses[i]))
+            index = i;
+
+    /* Otherwise try and find an address that matches the incoming type */
+    if (index < 0)
+        index = find_address (addresses, addresses_length, g_inet_address_get_family (source_address));
+
+    /* Otherwise use the first available */
+    if (index < 0 && addresses_length > 0)
+        index = 0;
+
+    for (i = 0; i < addresses_length; i++)
+        g_object_unref (addresses[i]);
+    g_free (addresses);
+
+    return &packet->Request.connections[index];
+}
+
 static void
 handle_request (XDMCPServer *server, GSocket *socket, GSocketAddress *address, XDMCPPacket *packet)
 {
-    int i;
     XDMCPPacket *response;
     XDMCPSession *session;
     guint8 *authentication_data = NULL;
@@ -273,48 +339,15 @@ handle_request (XDMCPServer *server, GSocket *socket, GSocketAddress *address, X
     guint8 *session_authorization_data = NULL;
     gsize session_authorization_data_length = 0;
     gchar **j;
-    guint16 family;
-    GInetAddress *x_server_address = NULL;
+    XDMCPConnection *connection;
     gchar *display_number;
     XdmAuthKeyRec rho;
 
-    /* Try and find an IPv6 address */
-    for (i = 0; i < packet->Request.n_connections; i++)
-    {
-        XDMCPConnection *connection = &packet->Request.connections[i];
-        if (connection->type == XAUTH_FAMILY_INTERNET6 && connection->address.length == 16)
-        {
-            family = connection->type;
-            x_server_address = g_inet_address_new_from_bytes (connection->address.data, G_SOCKET_FAMILY_IPV6);
-
-            /* We can't use link-local addresses, as we need to know what interface it is on */
-            if (g_inet_address_get_is_link_local (x_server_address))
-            {
-                g_object_unref (x_server_address);
-                x_server_address = NULL;
-            }
-            else
-                break;
-        }
-    }
-
-    /* If no IPv6 address, then try and find an IPv4 one */
-    if (!x_server_address)
-    {
-        for (i = 0; i < packet->Request.n_connections; i++)
-        {
-            XDMCPConnection *connection = &packet->Request.connections[i];
-            if (connection->type == XAUTH_FAMILY_INTERNET && connection->address.length == 4)
-            {
-                family = connection->type;
-                x_server_address = g_inet_address_new_from_bytes (connection->address.data, G_SOCKET_FAMILY_IPV4);
-                break;
-            }
-        }
-    }
+    /* Choose an address to connect back on */
+    connection = choose_connection (packet, g_inet_socket_address_get_address (G_INET_SOCKET_ADDRESS (address)));
 
     /* Decline if haven't got an address we can connect on */
-    if (!x_server_address)
+    if (!connection)
     {
         response = xdmcp_packet_alloc (XDMCP_Decline);
         response->Decline.status = g_strdup ("No valid address found");
@@ -430,14 +463,14 @@ handle_request (XDMCPServer *server, GSocket *socket, GSocketAddress *address, X
     }
 
     session = add_session (server);
-    session->priv->address = x_server_address;
+    session->priv->address = connection_to_address (connection);
     session->priv->display_number = packet->Request.display_number;
     display_number = g_strdup_printf ("%d", packet->Request.display_number);
 
     /* We need to check if this is the loopback address and set the authority
      * for a local connection if this is so as XCB treats "127.0.0.1" as local
      * always */
-    if (g_inet_address_get_is_loopback (x_server_address))
+    if (g_inet_address_get_is_loopback (session->priv->address))
     {
         gchar hostname[1024];
         gethostname (hostname, 1024);
@@ -451,9 +484,9 @@ handle_request (XDMCPServer *server, GSocket *socket, GSocketAddress *address, X
                                                     session_authorization_data_length);
     }
     else
-        session->priv->authority = x_authority_new (family,
-                                                    g_inet_address_to_bytes (G_INET_ADDRESS (x_server_address)),
-                                                    g_inet_address_get_native_size (G_INET_ADDRESS (x_server_address)),
+        session->priv->authority = x_authority_new (connection->type,
+                                                    connection->address.data,
+                                                    connection->address.length,
                                                     display_number,
                                                     authorization_name,
                                                     session_authorization_data,