Implement roll-back limit for reorganisation

Closes #713.

qa/pull-tester/rpc-tests.sh

@@ -44,6 +44,7 @@ testScripts=(
     'zcjoinsplit.py'
     'zcjoinsplitdoublespend.py'
     'zkey_import_export.py'
+    'reorg_limit.py'
     'getblocktemplate.py'
     'bip65-cltv-p2p.py'
     'bipdersig-p2p.py'

qa/rpc-tests/reorg_limit.py

@@ -0,0 +1,86 @@
+#!/usr/bin/env python2
+# Copyright (c) 2017 The Zcash developers
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#
+# Test reorg limit
+#
+
+from test_framework.test_framework import BitcoinTestFramework
+from test_framework.util import (
+    check_node,
+    connect_nodes_bi,
+    initialize_chain_clean,
+    start_node,
+    sync_blocks,
+)
+from time import sleep
+
+def check_stopped(i, timeout=10):
+    stopped = False
+    for x in xrange(1, timeout):
+        ret = check_node(i)
+        if ret is None:
+            sleep(1)
+        else:
+            stopped = True
+            break
+    return stopped
+
+class ReorgLimitTest(BitcoinTestFramework):
+
+    def run_test(self):
+        assert(self.nodes[0].getblockcount() == 200)
+        assert(self.nodes[2].getblockcount() == 200)
+
+        self.split_network()
+
+        print "Test the maximum-allowed reorg:"
+        print "Mine 99 blocks on Node 0"
+        self.nodes[0].generate(99)
+        assert(self.nodes[0].getblockcount() == 299)
+        assert(self.nodes[2].getblockcount() == 200)
+
+        print "Mine competing 100 blocks on Node 2"
+        self.nodes[2].generate(100)
+        assert(self.nodes[0].getblockcount() == 299)
+        assert(self.nodes[2].getblockcount() == 300)
+
+        print "Connect nodes to force a reorg"
+        connect_nodes_bi(self.nodes, 0, 2)
+        self.is_network_split = False
+        sync_blocks(self.nodes)
+
+        print "Check Node 0 is still running and on the correct chain"
+        assert(self.nodes[0].getblockcount() == 300)
+
+        self.split_network()
+
+        print "Test the minimum-rejected reorg:"
+        print "Mine 100 blocks on Node 0"
+        self.nodes[0].generate(100)
+        assert(self.nodes[0].getblockcount() == 400)
+        assert(self.nodes[2].getblockcount() == 300)
+
+        print "Mine competing 101 blocks on Node 2"
+        self.nodes[2].generate(101)
+        assert(self.nodes[0].getblockcount() == 400)
+        assert(self.nodes[2].getblockcount() == 401)
+
+        print "Sync nodes to force a reorg"
+        connect_nodes_bi(self.nodes, 0, 2)
+        self.is_network_split = False
+        # sync_blocks uses RPC calls to wait for nodes to be synced, so don't
+        # call it here, because it will have a non-specific connection error
+        # when Node 0 stops. Instead, we explicitly check for the process itself
+        # to stop.
+
+        print "Check Node 0 is no longer running"
+        assert(check_stopped(0))
+
+        # Dummy stop to enable the test to tear down
+        self.nodes[0].stop = lambda: True
+
+if __name__ == '__main__':
+    ReorgLimitTest().main()

qa/rpc-tests/test_framework/util.py

@@ -213,6 +213,10 @@ def start_nodes(num_nodes, dirname, extra_args=None, rpchost=None, binary=None):
 def log_filename(dirname, n_node, logname):
     return os.path.join(dirname, "node"+str(n_node), "regtest", logname)
 
+def check_node(i):
+    bitcoind_processes[i].poll()
+    return bitcoind_processes[i].returncode
+
 def stop_node(node, i):
     node.stop()
     bitcoind_processes[i].wait()

src/main.cpp

@@ -2631,6 +2631,31 @@ static bool ActivateBestChainStep(CValidationState &state, CBlockIndex *pindexMo
     const CBlockIndex *pindexOldTip = chainActive.Tip();
     const CBlockIndex *pindexFork = chainActive.FindFork(pindexMostWork);
 
+    // - On ChainDB initialization, pindexOldTip will be null, so there are no removable blocks.
+    // - If pindexMostWork is in a chain that doesn't have the same genesis block as our chain,
+    //   then pindexFork will be null, and we would need to remove the entire chain including
+    //   our genesis block. In practice this (probably) won't happen because of checks elsewhere.
+    auto reorgLength = pindexOldTip ? pindexOldTip->nHeight - (pindexFork ? pindexFork->nHeight : -1) : 0;
+    static_assert(MAX_REORG_LENGTH > 0, "We must be able to reorg some distance");
+    if (reorgLength > MAX_REORG_LENGTH) {
+        auto msg = strprintf(_(
+            "A block chain reorganization has been detected that would roll back %d blocks! "
+            "This is larger than the maximum of %d blocks, and so the node is shutting down for your safety."
+            ), reorgLength, MAX_REORG_LENGTH) + "\n\n" +
+            _("Reorganization details") + ":\n" +
+            "- " + strprintf(_("Current tip: %s, height %d, work %s"),
+                pindexOldTip->phashBlock->GetHex(), pindexOldTip->nHeight, pindexOldTip->nChainWork.GetHex()) + "\n" +
+            "- " + strprintf(_("New tip:     %s, height %d, work %s"),
+                pindexMostWork->phashBlock->GetHex(), pindexMostWork->nHeight, pindexMostWork->nChainWork.GetHex()) + "\n" +
+            "- " + strprintf(_("Fork point:  %s, height %d"),
+                pindexFork->phashBlock->GetHex(), pindexFork->nHeight) + "\n\n" +
+            _("Please help, human!");
+        LogPrintf("*** %s\n", msg);
+        uiInterface.ThreadSafeMessageBox(msg, "", CClientUIInterface::MSG_ERROR);
+        StartShutdown();
+        return false;
+    }
+
     // Disconnect active blocks which are no longer in the best chain.
     while (chainActive.Tip() && chainActive.Tip() != pindexFork) {
         if (!DisconnectTip(state))

src/main.h

@@ -56,6 +56,8 @@ static const unsigned int DEFAULT_BLOCK_PRIORITY_SIZE = DEFAULT_BLOCK_MAX_SIZE /
 static const bool DEFAULT_ALERTS = true;
 /** Minimum alert priority for enabling safe mode. */
 static const int ALERT_PRIORITY_SAFE_MODE = 4000;
+/** Maximum reorg length we will accept before we shut down and alert the user. */
+static const unsigned int MAX_REORG_LENGTH = COINBASE_MATURITY - 1;
 /** Maximum number of signature check operations in an IsStandard() P2SH script */
 static const unsigned int MAX_P2SH_SIGOPS = 15;
 /** The maximum number of sigops we're willing to relay/mine in a single tx */

src/wallet/wallet.h

@@ -8,9 +8,9 @@
 
 #include "amount.h"
 #include "coins.h"
-#include "consensus/consensus.h"
 #include "key.h"
 #include "keystore.h"
+#include "main.h"
 #include "primitives/block.h"
 #include "primitives/transaction.h"
 #include "tinyformat.h"
@@ -58,7 +58,7 @@ static const unsigned int MAX_FREE_TRANSACTION_CREATE_SIZE = 1000;
 //! Size of witness cache
 //  Should be large enough that we can expect not to reorg beyond our cache
 //  unless there is some exceptional network disruption.
-static const unsigned int WITNESS_CACHE_SIZE = COINBASE_MATURITY;
+static const unsigned int WITNESS_CACHE_SIZE = MAX_REORG_LENGTH + 1;
 
 class CBlockIndex;
 class CCoinControl;