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Revert "Add rules--presently disabled--for using GetMedianTimePast as endpoint for lock-time calculations"

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This reverts commit 9d55050773.

As noted by Luke-Jr, under some conditions this will accept transactions which are invalid by the network
 rules.  This happens when the current block time is head of the median time past and a transaction's
 locktime is in the middle.

This could be addressed by changing the rule to MAX(this_block_time, MTP+offset) but this solution and
 the particular offset used deserve some consideration.
This commit is contained in:
Gregory Maxwell
2015-11-01 20:05:18 +00:00
parent 8537ecdfc4
commit 40cd32e835
5 changed files with 7 additions and 54 deletions
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40
src/main.cpp
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@@ -650,35 +650,10 @@ bool IsFinalTx(const CTransaction &tx, int nBlockHeight, int64_t nBlockTime)
return true;
}
bool CheckFinalTx(const CTransaction &tx, int flags)
bool CheckFinalTx(const CTransaction &tx)
{
AssertLockHeld(cs_main);
// By convention a negative value for flags indicates that the
// current network-enforced consensus rules should be used. In
// a future soft-fork scenario that would mean checking which
// rules would be enforced for the next block and setting the
// appropriate flags. At the present time no soft-forks are
// scheduled, so no flags are set.
flags = std::max(flags, 0);
// CheckFinalTx() uses chainActive.Height()+1 to evaluate
// nLockTime because when IsFinalTx() is called within
// CBlock::AcceptBlock(), the height of the block *being*
// evaluated is what is used. Thus if we want to know if a
// transaction can be part of the *next* block, we need to call
// IsFinalTx() with one more than chainActive.Height().
const int nBlockHeight = chainActive.Height() + 1;
// Timestamps on the other hand don't get any special treatment,
// because we can't know what timestamp the next block will have,
// and there aren't timestamp applications where it matters.
// However this changes once median past time-locks are enforced:
const int64_t nBlockTime = (flags & LOCKTIME_MEDIAN_TIME_PAST)
? chainActive.Tip()->GetMedianTimePast()
: GetAdjustedTime();
return IsFinalTx(tx, nBlockHeight, nBlockTime);
return IsFinalTx(tx, chainActive.Height() + 1, GetAdjustedTime());
}
unsigned int GetLegacySigOpCount(const CTransaction& tx)
@@ -822,7 +797,7 @@ bool AcceptToMemoryPool(CTxMemPool& pool, CValidationState &state, const CTransa
// Only accept nLockTime-using transactions that can be mined in the next
// block; we don't want our mempool filled up with transactions that can't
// be mined yet.
if (!CheckFinalTx(tx, STANDARD_LOCKTIME_VERIFY_FLAGS))
if (!CheckFinalTx(tx))
return state.DoS(0, false, REJECT_NONSTANDARD, "non-final");
// is it already in the memory pool?
@@ -2748,15 +2723,10 @@ bool ContextualCheckBlock(const CBlock& block, CValidationState& state, CBlockIn
const Consensus::Params& consensusParams = Params().GetConsensus();
// Check that all transactions are finalized
BOOST_FOREACH(const CTransaction& tx, block.vtx) {
int nLockTimeFlags = 0;
int64_t nLockTimeCutoff = (nLockTimeFlags & LOCKTIME_MEDIAN_TIME_PAST)
? pindexPrev->GetMedianTimePast()
: block.GetBlockTime();
if (!IsFinalTx(tx, nHeight, nLockTimeCutoff)) {
BOOST_FOREACH(const CTransaction& tx, block.vtx)
if (!IsFinalTx(tx, nHeight, block.GetBlockTime())) {
return state.DoS(10, error("%s: contains a non-final transaction", __func__), REJECT_INVALID, "bad-txns-nonfinal");
}
}
// Enforce block.nVersion=2 rule that the coinbase starts with serialized block height
// if 750 of the last 1,000 blocks are version 2 or greater (51/100 if testnet):