Sanity check transaction scripts in DecodeHexTx

Make sure that the scripts of decoded transactions are valid scripts.

Author: achow101

src/core_read.cpp

@@ -88,18 +88,40 @@ CScript ParseScript(const std::string& s)
     return result;
 }
 
+// Check that all of the input and output scripts of a transaction contains valid opcodes
+bool CheckTxScriptsSanity(const CMutableTransaction& tx)
+{
+    // Check input scripts for non-coinbase txs
+    if (!CTransaction(tx).IsCoinBase()) {
+        for (unsigned int i = 0; i < tx.vin.size(); i++) {
+            if (!tx.vin[i].scriptSig.HasValidOps() || tx.vin[i].scriptSig.size() > MAX_SCRIPT_SIZE) {
+                return false;
+            }
+        }
+    }
+    // Check output scripts
+    for (unsigned int i = 0; i < tx.vout.size(); i++) {
+        if (!tx.vout[i].scriptPubKey.HasValidOps() || tx.vout[i].scriptPubKey.size() > MAX_SCRIPT_SIZE) {
+            return false;
+        }
+    }
+    
+    return true;
+}
+
 bool DecodeHexTx(CMutableTransaction& tx, const std::string& strHexTx, bool fTryNoWitness)
 {
-    if (!IsHex(strHexTx))
+    if (!IsHex(strHexTx)) {
         return false;
+    }
 
     std::vector<unsigned char> txData(ParseHex(strHexTx));
 
     if (fTryNoWitness) {
         CDataStream ssData(txData, SER_NETWORK, PROTOCOL_VERSION | SERIALIZE_TRANSACTION_NO_WITNESS);
         try {
             ssData >> tx;
-            if (ssData.eof()) {
+            if (ssData.eof() && CheckTxScriptsSanity(tx)) {
                 return true;
             }
         }
@@ -111,8 +133,9 @@ bool DecodeHexTx(CMutableTransaction& tx, const std::string& strHexTx, bool fTry
     CDataStream ssData(txData, SER_NETWORK, PROTOCOL_VERSION);
     try {
         ssData >> tx;
-        if (!ssData.empty())
+        if (!ssData.empty()) {
             return false;
+        }
     }
     catch (const std::exception&) {
         return false;

src/script/script.cpp

@@ -273,7 +273,8 @@ bool CScript::HasValidOps() const
     CScript::const_iterator it = begin();
     while (it < end()) {
         opcodetype opcode;
-        if (!GetOp(it, opcode) || opcode > 0xb9) {
+        std::vector<unsigned char> item;
+        if (!GetOp(it, opcode, item) || opcode > MAX_OPCODE || item.size() > MAX_SCRIPT_ELEMENT_SIZE) {
             return false;
         }
     }

src/script/script.h

@@ -190,6 +190,9 @@ enum opcodetype
     OP_INVALIDOPCODE = 0xff,
 };
 
+// Maximum value that an opcode can be
+static const unsigned int MAX_OPCODE = OP_NOP10;
+
 const char* GetOpName(opcodetype opcode);
 
 class scriptnum_error : public std::runtime_error