From 9cec5480ce103b3abca1b59da5af36c145830f56 Mon Sep 17 00:00:00 2001
From: Christian Grothoff <christian@grothoff.org>
Date: Mon, 19 Sep 2011 08:55:11 +0000
Subject: [PATCH] generate valid disconnect message -- Mantis #1789

---
 src/include/gnunet_signatures.h               |  6 +--
 src/transport/gnunet-service-transport.c      |  4 +-
 .../gnunet-service-transport_neighbours.c     | 48 +++++++++++++++++--
 3 files changed, 49 insertions(+), 9 deletions(-)

diff --git a/src/include/gnunet_signatures.h b/src/include/gnunet_signatures.h
index c54df3e85..580282d82 100644
--- a/src/include/gnunet_signatures.h
+++ b/src/include/gnunet_signatures.h
@@ -48,11 +48,9 @@ extern "C"
 #define GNUNET_SIGNATURE_PURPOSE_TRANSPORT_PONG_OWN 1
 
 /**
- * Signature for confirming that this peer connected to another peer
- * using a particular address (LEGACY)
+ * Signature for confirming that this peer intends to disconnect.
  */
-#define GNUNET_SIGNATURE_PURPOSE_TRANSPORT_PONG_USING 2
-
+#define GNUNET_SIGNATURE_PURPOSE_TRANSPORT_DISCONNECT 2
 
 /**
  * Purpose is to set a session key.
diff --git a/src/transport/gnunet-service-transport.c b/src/transport/gnunet-service-transport.c
index d1ef887fd..4687a0907 100644
--- a/src/transport/gnunet-service-transport.c
+++ b/src/transport/gnunet-service-transport.c
@@ -205,8 +205,8 @@ plugin_env_receive_callback (void *cls, const struct GNUNET_PeerIdentity *peer,
        * * way to communicate with this peer (other peer switched transport) */
       break;
     case GNUNET_MESSAGE_TYPE_TRANSPORT_SESSION_DISCONNECT:
-      /* TODO: do some validation to prevent an attacker from sending
-       * a fake disconnect message... */
+      /* FIXME: do some validation to prevent an attacker from sending
+       * a fake disconnect message... */     	  
       GST_neighbours_force_disconnect (peer);
       break;
     case GNUNET_MESSAGE_TYPE_TRANSPORT_SESSION_KEEPALIVE:
diff --git a/src/transport/gnunet-service-transport_neighbours.c b/src/transport/gnunet-service-transport_neighbours.c
index 6c7e135ce..89feffbd8 100644
--- a/src/transport/gnunet-service-transport_neighbours.c
+++ b/src/transport/gnunet-service-transport_neighbours.c
@@ -78,6 +78,39 @@ struct SessionConnectMessage
 };
 
 
+struct SessionDisconnectMessage
+{
+  /**
+   * Header of type 'GNUNET_MESSAGE_TYPE_TRANSPORT_SESSION_DISCONNECT'
+   */
+  struct GNUNET_MessageHeader header;
+
+  /**
+   * Always zero.
+   */
+  uint32_t reserved GNUNET_PACKED;
+
+  /**
+   * Purpose of the signature.  Extends over the timestamp.
+   * Purpose should be GNUNET_SIGNATURE_PURPOSE_TRANSPORT_DISCONNECT.
+   */
+  struct GNUNET_CRYPTO_RsaSignaturePurpose purpose;
+
+  /**
+   * Absolute time at the sender.  Only the most recent connect
+   * message implies which session is preferred by the sender.
+   */
+  struct GNUNET_TIME_AbsoluteNBO timestamp;
+
+  /**
+   * Signature of the peer that sends us the disconnect.  Only
+   * valid if the timestamp is AFTER the timestamp from the
+   * corresponding 'CONNECT' message.
+   */
+  struct GNUNET_CRYPTO_RsaSignature signature;
+};
+
+
 /**
  * For each neighbour we keep a list of messages
  * that we still want to transmit to the neighbour.
@@ -1023,7 +1056,7 @@ GST_neighbours_force_disconnect (const struct GNUNET_PeerIdentity *target)
 {
   struct NeighbourMapEntry *n;
   struct GNUNET_TRANSPORT_PluginFunctions *papi;
-  struct GNUNET_MessageHeader disconnect_msg;
+  struct SessionDisconnectMessage disconnect_msg;
 
   GNUNET_assert (neighbours != NULL);
 
@@ -1033,8 +1066,17 @@ GST_neighbours_force_disconnect (const struct GNUNET_PeerIdentity *target)
   if (GNUNET_YES == n->is_connected)
   {
     /* we're actually connected, send DISCONNECT message */
-    disconnect_msg.size = htons (sizeof (struct GNUNET_MessageHeader));
-    disconnect_msg.type = htons (GNUNET_MESSAGE_TYPE_TRANSPORT_CONNECT);
+    disconnect_msg.header.size = htons (sizeof (struct SessionDisconnectMessage));
+    disconnect_msg.header.type = htons (GNUNET_MESSAGE_TYPE_TRANSPORT_DISCONNECT);
+    disconnect_msg.reserved = htonl (0);
+    disconnect_msg.purpose.size = htonl (sizeof (struct GNUNET_CRYPTO_RsaSignaturePurpose) +
+					 sizeof (struct GNUNET_TIME_AbsoluteNBO));
+    disconnect_msg.purpose.purpose = htonl (GNUNET_MESSAGE_TYPE_TRANSPORT_SESSION_DISCONNECT);
+    disconnect_msg.timestamp = GNUNET_TIME_absolute_hton (GNUNET_TIME_absolute_get ());
+    GNUNET_assert (GNUNET_OK ==
+		   GNUNET_CRYPTO_rsa_sign (GST_my_private_key,
+					   &disconnect_msg.purpose,
+					   &disconnect_msg.signature));
     papi = GST_plugins_find (n->plugin_name);
     if (papi != NULL)
       papi->send (papi->cls, target, (const void *) &disconnect_msg,
-- 
2.25.1