[refer #393] Support periodic random connection eviction

src/main/resources/reference.conf

@@ -183,6 +183,8 @@ scorex {
     # Max penalty score peer can accumulate before being banned
     penaltyScoreThreshold = 100
 
+    # interval of evicting random peer to avoid eclipsing
+    peerEvictInterval = 1h
   }
 
   ntp {

src/main/scala/scorex/core/network/NetworkController.scala

@@ -1,7 +1,6 @@
 package scorex.core.network
 
 import java.net._
-
 import akka.actor._
 import akka.io.Tcp._
 import akka.io.{IO, Tcp}
@@ -21,7 +20,7 @@ import scorex.util.ScorexLogging
 import scala.concurrent.ExecutionContext
 import scala.concurrent.duration._
 import scala.language.{existentials, postfixOps}
-import scala.util.Try
+import scala.util.{Random, Try}
 
 /**
   * Control all network interaction
@@ -89,6 +88,7 @@ class NetworkController(settings: NetworkSettings,
       log.info("Successfully bound to the port " + settings.bindAddress.getPort)
       scheduleConnectionToPeer()
       scheduleDroppingDeadConnections()
+      scheduleEvictRandomConnections()
 
     case CommandFailed(_: Bind) =>
       log.error("Network port " + settings.bindAddress.getPort + " already in use!")
@@ -231,6 +231,23 @@ class NetworkController(settings: NetworkSettings,
   }
 
   /**
+    * Schedule a periodic eviction of random connection.
+    * It is needed to prevent eclipsing (https://www.usenix.org/system/files/conference/usenixsecurity15/sec15-paper-heilman.pdf)
+    */
+  private def scheduleEvictRandomConnections(): Unit = {
+   context.system.scheduler.scheduleWithFixedDelay(settings.peerEvictInterval, settings.peerEvictInterval) {
+     () =>
+       val connectedPeers = connections.values.filter(_.peerInfo.nonEmpty).toSeq
+       if (!connectedPeers.isEmpty) {
+         val victim = Random.nextInt(connectedPeers.size)
+         val cp = connectedPeers(victim)
+         log.info(s"Evict connection to ${cp.peerInfo}")
+         cp.handlerRef ! CloseConnection
+       }
+    }
+  }
+
+    /**
     * Schedule a periodic dropping of connections which seem to be inactive
     */
   private def scheduleDroppingDeadConnections(): Unit = {

src/main/scala/scorex/core/network/peer/PeerManager.scala

@@ -149,15 +149,28 @@ object PeerManager {
                           sc: ScorexContext): Map[InetSocketAddress, PeerInfo] = knownPeers
     }
 
+    // Extract /16 IPv4 prefix (IP group)
+    private  def getIpGroup(addr : InetSocketAddress) : Int = {
+      val ip = addr.getAddress.getAddress
+      val group = ((ip(0) & 0xFF) << 8) | (ip(1) & 0xFF)
+      group
+    }
+
     case class RandomPeerExcluding(excludedPeers: Seq[PeerInfo]) extends GetPeers[Option[PeerInfo]] {
 
       override def choose(knownPeers: Map[InetSocketAddress, PeerInfo],
                           blacklistedPeers: Seq[InetAddress],
                           sc: ScorexContext): Option[PeerInfo] = {
-        val candidates = knownPeers.values.filterNot { p =>
-          excludedPeers.exists(_.peerSpec.address == p.peerSpec.address) &&
-            blacklistedPeers.exists(addr => p.peerSpec.address.map(_.getAddress).contains(addr))
+        // First of all try to establish connections to the hosts from different IP group
+		// It will complicate eclipse attacks
+        val excludedGroups = excludedPeers.flatMap(_.peerSpec.address).map(getIpGroup(_)).toSet
+        val allCandidates = knownPeers.values.filterNot { p =>
+          excludedPeers.exists(_.peerSpec.address == p.peerSpec.address) ||
+          blacklistedPeers.exists(addr => p.peerSpec.address.map(_.getAddress).contains(addr))
         }.toSeq
+        val preferredCandidates = allCandidates.filterNot(_.peerSpec.address.fold(true)(addr => excludedGroups.contains(getIpGroup(addr))))
+		// If it is not possible to connect to the node from different IP group, then try to connect somewhere
+        val candidates = if (preferredCandidates.nonEmpty) preferredCandidates else allCandidates
         if (candidates.nonEmpty) Some(candidates(Random.nextInt(candidates.size)))
         else None
       }

src/main/scala/scorex/core/settings/Settings.scala

@@ -50,7 +50,8 @@ case class NetworkSettings(nodeName: String,
                            maxPeerSpecObjects: Int,
                            temporalBanDuration: FiniteDuration,
                            penaltySafeInterval: FiniteDuration,
-                           penaltyScoreThreshold: Int)
+                           penaltyScoreThreshold: Int,
+                           peerEvictInterval: FiniteDuration)
 
 case class ScorexSettings(dataDir: File,
                           logDir: File,