consesus/mekle: don't perform the ignored malleation check for witnesses

The result of the malleation check is ignored, since it's not possible
to exploit it for the witness tree without exploiting it for the
transaction tree (where we do check it).

The check involves going through all the leaves and nodes of the tree
and comparing them. Since the result is ignored, we better not perform
the check at all.

Since the ignored `malleated` boolean was the only call site, remove the
argument altogether.

src/consensus/merkle.cpp

@@ -72,14 +72,14 @@ uint256 BlockMerkleRoot(const CBlock& block, bool* mutated)
     return ComputeMerkleRoot(std::move(leaves), mutated);
 }
 
-uint256 BlockWitnessMerkleRoot(const CBlock& block, bool* mutated)
+uint256 BlockWitnessMerkleRoot(const CBlock& block)
 {
     std::vector<uint256> leaves;
     leaves.resize(block.vtx.size());
     leaves[0].SetNull(); // The witness hash of the coinbase is 0.
     for (size_t s = 1; s < block.vtx.size(); s++) {
         leaves[s] = block.vtx[s]->GetWitnessHash();
     }
-    return ComputeMerkleRoot(std::move(leaves), mutated);
+    return ComputeMerkleRoot(std::move(leaves));
 }
 

src/consensus/merkle.h

@@ -22,6 +22,6 @@ uint256 BlockMerkleRoot(const CBlock& block, bool* mutated = nullptr);
  * Compute the Merkle root of the witness transactions in a block.
  * *mutated is set to true if a duplicated subtree was found.
  */
-uint256 BlockWitnessMerkleRoot(const CBlock& block, bool* mutated = nullptr);
+uint256 BlockWitnessMerkleRoot(const CBlock& block);
 
 #endif // BITCOIN_CONSENSUS_MERKLE_H

src/validation.cpp

@@ -3754,7 +3754,7 @@ std::vector<unsigned char> ChainstateManager::GenerateCoinbaseCommitment(CBlock&
     int commitpos = GetWitnessCommitmentIndex(block);
     std::vector<unsigned char> ret(32, 0x00);
     if (commitpos == NO_WITNESS_COMMITMENT) {
-        uint256 witnessroot = BlockWitnessMerkleRoot(block, nullptr);
+        uint256 witnessroot = BlockWitnessMerkleRoot(block);
         CHash256().Write(witnessroot).Write(ret).Finalize(witnessroot);
         CTxOut out;
         out.nValue = 0;
@@ -3893,8 +3893,7 @@ static bool ContextualCheckBlock(const CBlock& block, BlockValidationState& stat
     if (DeploymentActiveAfter(pindexPrev, chainman, Consensus::DEPLOYMENT_SEGWIT)) {
         int commitpos = GetWitnessCommitmentIndex(block);
         if (commitpos != NO_WITNESS_COMMITMENT) {
-            bool malleated = false;
-            uint256 hashWitness = BlockWitnessMerkleRoot(block, &malleated);
+            uint256 hashWitness = BlockWitnessMerkleRoot(block);
             // The malleation check is ignored; as the transaction tree itself
             // already does not permit it, it is impossible to trigger in the
             // witness tree.