[GNUnet-SVN] [gnunet] 02/06: basics for UDP broadcast receiving

[gnunet]

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grothoff pushed a commit to branch master
in repository gnunet.

commit 4781fabceb3530e976c27ea37999c8eaa3165612
Author: Christian Grothoff <address@hidden>
AuthorDate: Wed Jan 30 04:51:22 2019 +0100

    basics for UDP broadcast receiving
---
 src/include/gnunet_signatures.h         |  7 ++-
 src/transport/gnunet-communicator-tcp.c |  3 +
 src/transport/gnunet-communicator-udp.c | 97 ++++++++++++++++++++++++++++++++-
 3 files changed, 103 insertions(+), 4 deletions(-)

diff --git a/src/include/gnunet_signatures.h b/src/include/gnunet_signatures.h
index 289ea9860..218dcbace 100644
--- a/src/include/gnunet_signatures.h
+++ b/src/include/gnunet_signatures.h
@@ -213,10 +213,15 @@ extern "C"
 #define GNUNET_SIGNATURE_COMMUNICATOR_TCP_REKEY 32
 
 /**
- * Signature used by UDP communicator handshake,
+ * Signature used by UDP communicator handshake
  */ 
 #define GNUNET_SIGNATURE_COMMUNICATOR_UDP_HANDSHAKE 33
 
+/**
+ * Signature used by UDP broadcasts.
+ */ 
+#define GNUNET_SIGNATURE_COMMUNICATOR_UDP_BROADCAST 34
+
 #if 0                           /* keep Emacsens' auto-indent happy */
 {
 #endif
diff --git a/src/transport/gnunet-communicator-tcp.c 
b/src/transport/gnunet-communicator-tcp.c
index d0ee326b1..d86fa03b6 100644
--- a/src/transport/gnunet-communicator-tcp.c
+++ b/src/transport/gnunet-communicator-tcp.c
@@ -24,6 +24,7 @@
  * @author Christian Grothoff
  *
  * TODO:
+ * - add and use util/ check for IPv6 availability (#V6)
  * - support DNS names in BINDTO option (#5528)
  * - support NAT connection reversal method (#5529)
  * - support other TCP-specific NAT traversal methods (#5531)
@@ -1166,6 +1167,8 @@ tcp_address_to_sockaddr (const char *bindto,
                  bindto);
       return NULL;
     }
+    /* FIXME: add test to util/ for IPv6 availability,
+       and depending on the result, go directly for v4-only */
     if (GNUNET_YES ==
        GNUNET_CONFIGURATION_get_value_yesno (cfg,
                                              COMMUNICATOR_CONFIG_SECTION,
diff --git a/src/transport/gnunet-communicator-udp.c 
b/src/transport/gnunet-communicator-udp.c
index 8e070d414..d464cd0d1 100644
--- a/src/transport/gnunet-communicator-udp.c
+++ b/src/transport/gnunet-communicator-udp.c
@@ -24,16 +24,22 @@
  * @author Christian Grothoff
  *
  * TODO:
- * - main BOXed sending logic
+ * - implement main BOXed sending logic
  * - figure out what to do with MTU: 1280 for IPv6 is obvious;
  *   what for IPv4? 1500? Also, consider differences in 
  *   headers for with/without box: need to give MIN of both
  *   to TNG (as TNG expects a fixed MTU!), or maybe
  *   we create a FRESH MQ while we have available BOXes SQNs?
  *   (otherwise padding will REALLY hurt)
+ * - add and use util/ check for IPv6 availability (#V6)
+ * - consider imposing transmission limits in the absence
+ *   of ACKs; or: maybe this should be done at TNG service level?
+ * - support broadcasting for neighbour discovery (#)
+ *   (think: what was the story again on address validation?
+ *    where is the API for that!?!)
  * - support DNS names in BINDTO option (#5528)
  * - support NAT connection reversal method (#5529)
- * - support other UDP-specific NAT traversal methods 
+ * - support other UDP-specific NAT traversal methods (#) 
  */
 #include "platform.h"
 #include "gnunet_util_lib.h"
@@ -241,6 +247,56 @@ struct UDPAck
 };
 
 
+/**
+ * Signature we use to verify that the broadcast was really made by
+ * the peer that claims to have made it.  Basically, affirms that the
+ * peer is really using this IP address (albeit possibly not in _our_
+ * LAN).  Makes it difficult for peers in the LAN to claim to 
+ * be just any global peer -- an attacker must have at least
+ * shared a LAN with the peer they're pretending to be here.
+ */
+struct UdpBroadcastSignature
+{
+  /**
+   * Purpose must be #GNUNET_SIGNATURE_COMMUNICATOR_UDP_BROADCAST
+   */
+  struct GNUNET_CRYPTO_EccSignaturePurpose purpose;
+
+  /**
+   * Identity of the inititor of the UDP broadcast.
+   */ 
+  struct GNUNET_PeerIdentity sender;
+
+  /**
+   * Hash of the sender's UDP address.
+   */ 
+  struct GNUNET_HashCode h_address;
+};
+
+
+/**
+ * Broadcast by peer in LAN announcing its presence.  Unusual in that
+ * we don't pad these to full MTU, as we cannot prevent being
+ * recognized in LAN as GNUnet peers if this feature is enabled
+ * anyway.  Also, the entire message is in cleartext.
+ */
+struct UDPBroadcast
+{
+
+  /**
+   * Sender's peer identity.
+   */
+  struct GNUNET_PeerIdentity sender;
+
+  /**
+   * Sender's signature of type
+   * #GNUNET_SIGNATURE_COMMUNICATOR_UDP_BROADCAST
+   */
+  struct GNUNET_CRYPTO_EddsaSignature sender_sig;  
+  
+};
+
+
 /**
  * UDP message box.  Always sent encrypted, only allowed after
  * the receiver sent a `struct UDPAck` for the base key!
@@ -1414,6 +1470,7 @@ sock_read (void *cls)
                         "recv");
     return;
   }
+
   /* first, see if it is a UDPBox */
   if (rcvd > sizeof (struct UDPBox))
   {
@@ -1431,7 +1488,39 @@ sock_read (void *cls)
       return;
     }
   }
-  /* next, test if it is a KX */
+
+  /* next, check if it is a broadcast */
+  if (sizeof (struct UDPBroadcast) == rcvd)
+  {
+    const struct UDPBroadcast *ub;
+    struct UdpBroadcastSignature uhs;
+
+    ub = (const struct UDPBroadcast *) buf;
+    uhs.purpose.purpose = htonl (GNUNET_SIGNATURE_COMMUNICATOR_UDP_BROADCAST);
+    uhs.purpose.size = htonl (sizeof (uhs));
+    uhs.sender = ub->sender;
+    GNUNET_CRYPTO_hash (&sa,
+                       salen,
+                       &uhs.h_address);
+    if (GNUNET_OK ==
+       GNUNET_CRYPTO_eddsa_verify (GNUNET_SIGNATURE_COMMUNICATOR_UDP_BROADCAST,
+                                   &uhs.purpose,
+                                   &ub->sender_sig,
+                                   &ub->sender.public_key))
+    {
+      GNUNET_STATISTICS_update (stats,
+                               "# broadcasts received",
+                               1,
+                               GNUNET_NO);
+      // FIXME: we effectively just got a HELLO!
+      // trigger verification NOW!
+      return;
+    }
+    /* continue with KX, mostly for statistics... */
+  }
+  
+
+  /* finally, test if it is a KX */
   if (rcvd < sizeof (struct UDPConfirmation) + sizeof (struct InitialKX))
   {
     GNUNET_STATISTICS_update (stats,
@@ -1535,6 +1624,8 @@ udp_address_to_sockaddr (const char *bindto,
                  bindto);
       return NULL;
     }
+    /* FIXME #V6: add test to util/ for IPv6 availability,
+       and depending on the result, go directly for v4-only */
     if (GNUNET_YES ==
        GNUNET_CONFIGURATION_get_value_yesno (cfg,
                                              COMMUNICATOR_CONFIG_SECTION,

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