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Merge #9107: Safer modify new coins

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b50cd7a Fix dangerous condition in ModifyNewCoins. (Alex Morcos)
This commit is contained in:
Pieter Wuille
2017-01-04 11:56:05 -08:00
parent 0fc1c31a87 b50cd7a67e
commit 7dac1e5e9e
4 changed files with 181 additions and 62 deletions
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37
src/coins.cpp
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@@ -117,17 +117,37 @@ CCoinsModifier CCoinsViewCache::ModifyCoins(const uint256 &txid) {
return CCoinsModifier(*this, ret.first, cachedCoinUsage);
}
// ModifyNewCoins has to know whether the new outputs its creating are for a
// coinbase or not. If they are for a coinbase, it can not mark them as fresh.
// This is to ensure that the historical duplicate coinbases before BIP30 was
// in effect will still be properly overwritten when spent.
/* ModifyNewCoins allows for faster coin modification when creating the new
* outputs from a transaction. It assumes that BIP 30 (no duplicate txids)
* applies and has already been tested for (or the test is not required due to
* BIP 34, height in coinbase). If we can assume BIP 30 then we know that any
* non-coinbase transaction we are adding to the UTXO must not already exist in
* the utxo unless it is fully spent. Thus we can check only if it exists DIRTY
* at the current level of the cache, in which case it is not safe to mark it
* FRESH (b/c then its spentness still needs to flushed). If it's not dirty and
* doesn't exist or is pruned in the current cache, we know it either doesn't
* exist or is pruned in parent caches, which is the definition of FRESH. The
* exception to this is the two historical violations of BIP 30 in the chain,
* both of which were coinbases. We do not mark these fresh so we we can ensure
* that they will still be properly overwritten when spent.
*/
CCoinsModifier CCoinsViewCache::ModifyNewCoins(const uint256 &txid, bool coinbase) {
assert(!hasModifier);
std::pair<CCoinsMap::iterator, bool> ret = cacheCoins.insert(std::make_pair(txid, CCoinsCacheEntry()));
ret.first->second.coins.Clear();
if (!coinbase) {
ret.first->second.flags = CCoinsCacheEntry::FRESH;
// New coins must not already exist.
if (!ret.first->second.coins.IsPruned())
throw std::logic_error("ModifyNewCoins should not find pre-existing coins on a non-coinbase unless they are pruned!");
if (!(ret.first->second.flags & CCoinsCacheEntry::DIRTY)) {
// If the coin is known to be pruned (have no unspent outputs) in
// the current view and the cache entry is not dirty, we know the
// coin also must be pruned in the parent view as well, so it is safe
// to mark this fresh.
ret.first->second.flags |= CCoinsCacheEntry::FRESH;
}
}
ret.first->second.coins.Clear();
ret.first->second.flags |= CCoinsCacheEntry::DIRTY;
return CCoinsModifier(*this, ret.first, 0);
}
@@ -200,6 +220,11 @@ bool CCoinsViewCache::BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlockIn
itUs->second.coins.swap(it->second.coins);
cachedCoinsUsage += itUs->second.coins.DynamicMemoryUsage();
itUs->second.flags |= CCoinsCacheEntry::DIRTY;
// NOTE: It is possible the child has a FRESH flag here in
// the event the entry we found in the parent is pruned. But
// we must not copy that FRESH flag to the parent as that
// pruned state likely still needs to be communicated to the
// grandparent.
}
}
}