Merge #525: [0.17] Disallow extended encoding for non-witness transactions

e11c6f5 Disallow extended encoding for non-witness transactions (Pieter Wuille)

Pull request description:

  backport of #402 which is a backport of upstream

Tree-SHA512: 01cccbc0d54a9f039ed16c88f1d9ec7ebac3a936fb4a77e664c9103e06bb142741a743ac980887ec16570429ccc0f9614e5b3076084b1c949190b3169844ed7d

Author: instagibbs

src/primitives/transaction.h

@@ -351,6 +351,10 @@ inline void UnserializeTransaction(TxType& tx, Stream& s) {
             const_cast<CTxWitness*>(&tx.witness)->vtxinwit.resize(tx.vin.size());
             const_cast<CTxWitness*>(&tx.witness)->vtxoutwit.resize(tx.vout.size());
             s >> tx.witness;
+            if (!tx.HasWitness()) {
+                /* It's illegal to encode witnesses when all witness stacks are empty. */
+                throw std::ios_base::failure("Superfluous witness record");
+            }
         }
     } else {
         const bool fAllowWitness = !(s.GetVersion() & SERIALIZE_TRANSACTION_NO_WITNESS);
@@ -381,6 +385,10 @@ inline void UnserializeTransaction(TxType& tx, Stream& s) {
                     s >> tx.witness.vtxinwit[i].m_pegin_witness.stack;
                 }
             }
+            if (!tx.HasWitness()) {
+                /* It's illegal to encode witnesses when all witness stacks are empty. */
+                throw std::ios_base::failure("Superfluous witness record");
+            }
         }
         s >> tx.nLockTime;
     }