From 008138c04a3242b72dc5128ac3585b50ac44e84e Mon Sep 17 00:00:00 2001
From: Pieter Wuille <pieter.wuille@gmail.com>
Date: Sun, 4 Jan 2015 17:15:02 +0100
Subject: [PATCH] Bugfix: only track UTXO modification after lookup

Otherwise, if CCoinsViewCache::ModifyCoins throws an exception in between
setting hasModifier and constructing the CCoinsModifier, the cache ends up
in an inconsistent state, resulting in an assert failure in the next
modification.

Bug discovered by Wladimir J. van der Laan.

Rebased-From: 1c52aad540ec1370db60fd68fc3485413e3cb8e1
Github-Pull: #5597
---
 src/coins.cpp | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/src/coins.cpp b/src/coins.cpp
index c2e802c95..66919da11 100644
--- a/src/coins.cpp
+++ b/src/coins.cpp
@@ -106,7 +106,6 @@ bool CCoinsViewCache::GetCoins(const uint256 &txid, CCoins &coins) const {
 
 CCoinsModifier CCoinsViewCache::ModifyCoins(const uint256 &txid) {
     assert(!hasModifier);
-    hasModifier = true;
     std::pair<CCoinsMap::iterator, bool> ret = cacheCoins.insert(std::make_pair(txid, CCoinsCacheEntry()));
     if (ret.second) {
         if (!base->GetCoins(txid, ret.first->second.coins)) {
@@ -247,7 +246,10 @@ double CCoinsViewCache::GetPriority(const CTransaction &tx, int nHeight) const
     return tx.ComputePriority(dResult);
 }
 
-CCoinsModifier::CCoinsModifier(CCoinsViewCache& cache_, CCoinsMap::iterator it_) : cache(cache_), it(it_) {}
+CCoinsModifier::CCoinsModifier(CCoinsViewCache& cache_, CCoinsMap::iterator it_) : cache(cache_), it(it_) {
+    assert(!cache.hasModifier);
+    cache.hasModifier = true;
+}
 
 CCoinsModifier::~CCoinsModifier()
 {