masternode: fix dseep DoS

When a dseep message with an invalid signature is received, the
lastDseep timestamp is updated to sigTime, but the message rejected.
Further messages with a sigTime before lastDseep will not be
processed, meaning the LastSeen timestamp will not get updated.

By disabling dseep processing for more than 65 minutes an attacker
can cause a master node to time out.

Only update the lastDseep stamp if the message is signed with the
correct key.

Signed-off-by: Patrick McHardy <[email protected]>

Author: Evan Duffield

src/clientversion.h

@@ -9,7 +9,7 @@
 #define CLIENT_VERSION_MAJOR       0
 #define CLIENT_VERSION_MINOR       10
 #define CLIENT_VERSION_REVISION    17
-#define CLIENT_VERSION_BUILD       22
+#define CLIENT_VERSION_BUILD       23
 
 // Set to true for release, false for prerelease or test build
 #define CLIENT_VERSION_IS_RELEASE  true

src/masternode.cpp

@@ -210,8 +210,6 @@ void ProcessMessageMasternode(CNode* pfrom, std::string& strCommand, CDataStream
             if(mn.vin.prevout == vin.prevout) {
                 // take this only if it's newer
                 if(mn.lastDseep < sigTime){ 
-                    mn.lastDseep = sigTime;
-
                     std::string strMessage = mn.addr.ToString() + boost::lexical_cast<std::string>(sigTime) + boost::lexical_cast<std::string>(stop);
 
                     std::string errorMessage = "";
@@ -221,6 +219,8 @@ void ProcessMessageMasternode(CNode* pfrom, std::string& strCommand, CDataStream
                         return;
                     }
 
+                    mn.lastDseep = sigTime;
+
                     if(!mn.UpdatedWithin(MASTERNODE_MIN_DSEEP_SECONDS)){
                         mn.UpdateLastSeen();
                         if(stop) {