Don't calculate tx fees for PSBTs with invalid money values

In decodepsbt if an invalid amount is seen, don't calculate the fee
but still show the invalid value in the decode.

In analyze psbt, if an invalid amount is seen, set the next step to
be the creator as the creator needs to remake the transaction so that
it is valid.

Author: achow101

src/node/psbt.cpp

@@ -2,6 +2,7 @@
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
+#include <amount.h>
 #include <coins.h>
 #include <consensus/tx_verify.h>
 #include <node/psbt.h>
@@ -31,6 +32,10 @@ PSBTAnalysis AnalyzePSBT(PartiallySignedTransaction psbtx)
         // Check for a UTXO
         CTxOut utxo;
         if (psbtx.GetInputUTXO(utxo, i)) {
+            if (!MoneyRange(utxo.nValue) || !MoneyRange(in_amt + utxo.nValue)) {
+                result.SetInvalid(strprintf("PSBT is not valid. Input %u has invalid value", i));
+                return result;
+            }
             in_amt += utxo.nValue;
             input_analysis.has_utxo = true;
         } else {
@@ -85,9 +90,16 @@ PSBTAnalysis AnalyzePSBT(PartiallySignedTransaction psbtx)
         // Get the output amount
         CAmount out_amt = std::accumulate(psbtx.tx->vout.begin(), psbtx.tx->vout.end(), CAmount(0),
             [](CAmount a, const CTxOut& b) {
+                if (!MoneyRange(a) || !MoneyRange(b.nValue) || !MoneyRange(a + b.nValue)) {
+                    return CAmount(-1);
+                }
                 return a += b.nValue;
             }
         );
+        if (!MoneyRange(out_amt)) {
+            result.SetInvalid(strprintf("PSBT is not valid. Output amount invalid"));
+            return result;
+        }
 
         // Get the fee
         CAmount fee = in_amt - out_amt;

src/rpc/rawtransaction.cpp

@@ -1077,7 +1077,12 @@ UniValue decodepsbt(const JSONRPCRequest& request)
             UniValue out(UniValue::VOBJ);
 
             out.pushKV("amount", ValueFromAmount(txout.nValue));
-            total_in += txout.nValue;
+            if (MoneyRange(txout.nValue) && MoneyRange(total_in + txout.nValue)) {
+                total_in += txout.nValue;
+            } else {
+                // Hack to just not show fee later
+                have_all_utxos = false;
+            }
 
             UniValue o(UniValue::VOBJ);
             ScriptToUniv(txout.scriptPubKey, o, true);
@@ -1087,7 +1092,13 @@ UniValue decodepsbt(const JSONRPCRequest& request)
             UniValue non_wit(UniValue::VOBJ);
             TxToUniv(*input.non_witness_utxo, uint256(), non_wit, false);
             in.pushKV("non_witness_utxo", non_wit);
-            total_in += input.non_witness_utxo->vout[psbtx.tx->vin[i].prevout.n].nValue;
+            CAmount utxo_val = input.non_witness_utxo->vout[psbtx.tx->vin[i].prevout.n].nValue;
+            if (MoneyRange(utxo_val) && MoneyRange(total_in + utxo_val)) {
+                total_in += utxo_val;
+            } else {
+                // Hack to just not show fee later
+                have_all_utxos = false;
+            }
         } else {
             have_all_utxos = false;
         }
@@ -1203,7 +1214,12 @@ UniValue decodepsbt(const JSONRPCRequest& request)
         outputs.push_back(out);
 
         // Fee calculation
-        output_value += psbtx.tx->vout[i].nValue;
+        if (MoneyRange(psbtx.tx->vout[i].nValue) && MoneyRange(output_value + psbtx.tx->vout[i].nValue)) {
+            output_value += psbtx.tx->vout[i].nValue;
+        } else {
+            // Hack to just not show fee later
+            have_all_utxos = false;
+        }
     }
     result.pushKV("outputs", outputs);
     if (have_all_utxos) {

test/functional/rpc_psbt.py

@@ -422,5 +422,14 @@ def test_psbt_input_keys(psbt_input, keys):
         assert_equal(analysis['next'], 'creator')
         assert_equal(analysis['error'], 'PSBT is not valid. Input 0 spends unspendable output')
 
+        self.log.info("PSBT with invalid values should have error message and Creator as next")
+        analysis = self.nodes[0].analyzepsbt('cHNidP8BAHECAAAAAfA00BFgAm6tp86RowwH6BMImQNL5zXUcTT97XoLGz0BAAAAAAD/////AgD5ApUAAAAAFgAUKNw0x8HRctAgmvoevm4u1SbN7XL87QKVAAAAABYAFPck4gF7iL4NL4wtfRAKgQbghiTUAAAAAAABAR8AgIFq49AHABYAFJUDtxf2PHo641HEOBOAIvFMNTr2AAAA')
+        assert_equal(analysis['next'], 'creator')
+        assert_equal(analysis['error'], 'PSBT is not valid. Input 0 has invalid value')
+
+        analysis = self.nodes[0].analyzepsbt('cHNidP8BAHECAAAAAfA00BFgAm6tp86RowwH6BMImQNL5zXUcTT97XoLGz0BAAAAAAD/////AgCAgWrj0AcAFgAUKNw0x8HRctAgmvoevm4u1SbN7XL87QKVAAAAABYAFPck4gF7iL4NL4wtfRAKgQbghiTUAAAAAAABAR8A8gUqAQAAABYAFJUDtxf2PHo641HEOBOAIvFMNTr2AAAA')
+        assert_equal(analysis['next'], 'creator')
+        assert_equal(analysis['error'], 'PSBT is not valid. Output amount invalid')
+
 if __name__ == '__main__':
     PSBTTest().main()