From f1ef7f0aa46338f4cd8de79696027a1bf868f359 Mon Sep 17 00:00:00 2001
From: Andrew Chow <achow101-github@achow101.com>
Date: Tue, 15 Oct 2019 17:15:22 -0400
Subject: [PATCH] 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.
---
 src/node/psbt.cpp           | 12 ++++++++++++
 src/rpc/rawtransaction.cpp  | 22 +++++++++++++++++++---
 test/functional/rpc_psbt.py |  9 +++++++++
 3 files changed, 40 insertions(+), 3 deletions(-)

diff --git a/src/node/psbt.cpp b/src/node/psbt.cpp
index 9a30c3f0830..69fb1a28a93 100644
--- a/src/node/psbt.cpp
+++ b/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;
diff --git a/src/rpc/rawtransaction.cpp b/src/rpc/rawtransaction.cpp
index 6a02984a0e0..67235a69428 100644
--- a/src/rpc/rawtransaction.cpp
+++ b/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) {
diff --git a/test/functional/rpc_psbt.py b/test/functional/rpc_psbt.py
index 2cc9650cb22..5986f197e11 100755
--- a/test/functional/rpc_psbt.py
+++ b/test/functional/rpc_psbt.py
@@ -422,5 +422,14 @@ class PSBTTest(BitcoinTestFramework):
         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()