Merge pull request #5947

36cba8f Alert if it is very likely we are getting a bad chain (Gavin Andresen)

4 files changed, 133 insertions, 0 deletions

diff --git a/src/init.cpp b/src/init.cpp
index b44233d90f..dc9080fec3 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -39,7 +39,9 @@
 
 #include <boost/algorithm/string/predicate.hpp>
 #include <boost/algorithm/string/replace.hpp>
+#include <boost/bind.hpp>
 #include <boost/filesystem.hpp>
+#include <boost/function.hpp>
 #include <boost/interprocess/sync/file_lock.hpp>
 #include <boost/thread.hpp>
 #include <openssl/crypto.h>
@@ -1392,6 +1394,12 @@ bool AppInit2(boost::thread_group& threadGroup, CScheduler& scheduler)
 
     StartNode(threadGroup, scheduler);
 
+    // Monitor the chain, and alert if we get blocks much quicker or slower than expected
+    int64_t nPowTargetSpacing = Params().GetConsensus().nPowTargetSpacing;
+    CScheduler::Function f = boost::bind(&PartitionCheck, &IsInitialBlockDownload,
+                                         boost::ref(cs_main), boost::cref(chainActive), nPowTargetSpacing);
+    scheduler.scheduleEvery(f, nPowTargetSpacing);
+
 #ifdef ENABLE_WALLET
     // Generate coins in the background
     if (pwalletMain)
diff --git a/src/main.cpp b/src/main.cpp
index d3956fafda..ac7d50ce65 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -28,6 +28,7 @@
 #include <boost/algorithm/string/replace.hpp>
 #include <boost/filesystem.hpp>
 #include <boost/filesystem/fstream.hpp>
+#include <boost/math/distributions/poisson.hpp>
 #include <boost/thread.hpp>
 
 using namespace std;
@@ -1685,6 +1686,64 @@ void ThreadScriptCheck() {
     scriptcheckqueue.Thread();
 }
 
+//
+// Called periodically asynchronously; alerts if it smells like
+// we're being fed a bad chain (blocks being generated much
+// too slowly or too quickly).
+//
+void PartitionCheck(bool (*initialDownloadCheck)(), CCriticalSection& cs, const CChain& chain, int64_t nPowTargetSpacing)
+{
+    if (initialDownloadCheck()) return;
+
+    static int64_t lastAlertTime = 0;
+    int64_t now = GetAdjustedTime();
+    if (lastAlertTime > now-60*60*24) return; // Alert at most once per day
+
+    const int SPAN_HOURS=4;
+    const int SPAN_SECONDS=SPAN_HOURS*60*60;
+    int BLOCKS_EXPECTED = SPAN_SECONDS / nPowTargetSpacing;
+
+    boost::math::poisson_distribution<double> poisson(BLOCKS_EXPECTED);
+
+    std::string strWarning;
+    int64_t startTime = GetAdjustedTime()-SPAN_SECONDS;
+
+    LOCK(cs);
+    int h = chain.Height();
+    while (h > 0 && chain[h]->GetBlockTime() >= startTime)
+        --h;
+    int nBlocks = chain.Height()-h;
+
+    // How likely is it to find that many by chance?
+    double p = boost::math::pdf(poisson, nBlocks);
+
+    LogPrint("partitioncheck", "%s : Found %d blocks in the last %d hours\n", __func__, nBlocks, SPAN_HOURS);
+    LogPrint("partitioncheck", "%s : likelihood: %g\n", __func__, p);
+
+    // Aim for one false-positive about every fifty years of normal running:
+    const int FIFTY_YEARS = 50*365*24*60*60;
+    double alertThreshold = 1.0 / (FIFTY_YEARS / SPAN_SECONDS);
+
+    if (p <= alertThreshold && nBlocks < BLOCKS_EXPECTED)
+    {
+        // Many fewer blocks than expected: alert!
+        strWarning = strprintf(_("WARNING: check your network connection, %d blocks received in the last %d hours (%d expected)"),
+                               nBlocks, SPAN_HOURS, BLOCKS_EXPECTED);
+    }
+    else if (p <= alertThreshold && nBlocks > BLOCKS_EXPECTED)
+    {
+        // Many more blocks than expected: alert!
+        strWarning = strprintf(_("WARNING: abnormally high number of blocks generated, %d blocks received in the last %d hours (%d expected)"),
+                               nBlocks, SPAN_HOURS, BLOCKS_EXPECTED);
+    }
+    if (!strWarning.empty())
+    {
+        strMiscWarning = strWarning;
+        CAlert::Notify(strWarning, true);
+        lastAlertTime = now;
+    }
+}
+
 static int64_t nTimeVerify = 0;
 static int64_t nTimeConnect = 0;
 static int64_t nTimeIndex = 0;
diff --git a/src/main.h b/src/main.h
index 07a709b75c..6c380b104d 100644
--- a/src/main.h
+++ b/src/main.h
@@ -194,6 +194,8 @@ bool ProcessMessages(CNode* pfrom);
 bool SendMessages(CNode* pto, bool fSendTrickle);
 /** Run an instance of the script checking thread */
 void ThreadScriptCheck();
+/** Try to detect Partition (network isolation) attacks against us */
+void PartitionCheck(bool (*initialDownloadCheck)(), CCriticalSection& cs, const CChain& chain, int64_t nPowTargetSpacing);
 /** Check whether we are doing an initial block download (synchronizing from disk or network) */
 bool IsInitialBlockDownload();
 /** Format a string that describes several potential problems detected by the core */
diff --git a/src/test/alert_tests.cpp b/src/test/alert_tests.cpp
index 6b6df5199a..cd5b416bd0 100644
--- a/src/test/alert_tests.cpp
+++ b/src/test/alert_tests.cpp
@@ -7,10 +7,13 @@
 //
 
 #include "alert.h"
+#include "chain.h"
+#include "chainparams.h"
 #include "clientversion.h"
 #include "data/alertTests.raw.h"
 
 #include "chainparams.h"
+#include "main.h"
 #include "serialize.h"
 #include "streams.h"
 #include "util.h"
@@ -193,4 +196,65 @@ BOOST_AUTO_TEST_CASE(AlertNotify)
     SetMockTime(0);
 }
 
+static bool falseFunc() { return false; }
+
+BOOST_AUTO_TEST_CASE(PartitionAlert)
+{
+    // Test PartitionCheck
+    CCriticalSection csDummy;
+    CChain chainDummy;
+    CBlockIndex indexDummy[100];
+    CChainParams& params = Params(CBaseChainParams::MAIN);
+    int64_t nPowTargetSpacing = params.GetConsensus().nPowTargetSpacing;
+
+    // Generate fake blockchain timestamps relative to
+    // an arbitrary time:
+    int64_t now = 1427379054;
+    SetMockTime(now);
+    for (int i = 0; i < 100; i++)
+    {
+        indexDummy[i].phashBlock = NULL;
+        if (i == 0) indexDummy[i].pprev = NULL;
+        else indexDummy[i].pprev = &indexDummy[i-1];
+        indexDummy[i].nHeight = i;
+        indexDummy[i].nTime = now - (100-i)*nPowTargetSpacing;
+        // Other members don't matter, the partition check code doesn't
+        // use them
+    }
+    chainDummy.SetTip(&indexDummy[99]);
+
+    // Test 1: chain with blocks every nPowTargetSpacing seconds,
+    // as normal, no worries:
+    PartitionCheck(falseFunc, csDummy, chainDummy, nPowTargetSpacing);
+    BOOST_CHECK(strMiscWarning.empty());
+
+    // Test 2: go 3.5 hours without a block, expect a warning:
+    now += 3*60*60+30*60;
+    SetMockTime(now);
+    PartitionCheck(falseFunc, csDummy, chainDummy, nPowTargetSpacing);
+    BOOST_CHECK(!strMiscWarning.empty());
+    BOOST_TEST_MESSAGE(std::string("Got alert text: ")+strMiscWarning);
+    strMiscWarning = "";
+
+    // Test 3: test the "partition alerts only go off once per day"
+    // code:
+    now += 60*10;
+    SetMockTime(now);
+    PartitionCheck(falseFunc, csDummy, chainDummy, nPowTargetSpacing);
+    BOOST_CHECK(strMiscWarning.empty());
+
+    // Test 4: get 2.5 times as many blocks as expected:
+    now += 60*60*24; // Pretend it is a day later
+    SetMockTime(now);
+    int64_t quickSpacing = nPowTargetSpacing*2/5;
+    for (int i = 0; i < 100; i++) // Tweak chain timestamps:
+        indexDummy[i].nTime = now - (100-i)*quickSpacing;
+    PartitionCheck(falseFunc, csDummy, chainDummy, nPowTargetSpacing);
+    BOOST_CHECK(!strMiscWarning.empty());
+    BOOST_TEST_MESSAGE(std::string("Got alert text: ")+strMiscWarning);
+    strMiscWarning = "";
+
+    SetMockTime(0);
+}
+
 BOOST_AUTO_TEST_SUITE_END()