From 1c832cbce7a521a9d110a613cb4aa3a1c28616a7 Mon Sep 17 00:00:00 2001
From: Oliver Gugger <gugger@gmail.com>
Date: Mon, 7 Sep 2020 18:02:44 +0200
Subject: [PATCH] chanfunding: verify inputs are signed in raw tx

---
 lnwallet/chanfunding/psbt_assembler.go      | 23 ++++++++++++
 lnwallet/chanfunding/psbt_assembler_test.go | 39 +++++++++++++++++++++
 2 files changed, 62 insertions(+)

diff --git a/lnwallet/chanfunding/psbt_assembler.go b/lnwallet/chanfunding/psbt_assembler.go
index 69c1c6946..8b53d0fa3 100644
--- a/lnwallet/chanfunding/psbt_assembler.go
+++ b/lnwallet/chanfunding/psbt_assembler.go
@@ -316,6 +316,14 @@ func (i *PsbtIntent) FinalizeRawTX(rawTx *wire.MsgTx) error {
 		return fmt.Errorf("inputs differ from verified PSBT: %v", err)
 	}
 
+	// We also check that we have a signed TX. This is only necessary if the
+	// FinalizeRawTX is called directly with a wire format TX instead of
+	// extracting the TX from a PSBT.
+	err = verifyInputsSigned(rawTx.TxIn)
+	if err != nil {
+		return fmt.Errorf("inputs not signed: %v", err)
+	}
+
 	// As far as we can tell, this TX is ok to be used as a funding
 	// transaction.
 	i.State = PsbtFinalized
@@ -539,3 +547,18 @@ func verifyInputPrevOutpointsEqual(ins1, ins2 []*wire.TxIn) error {
 	}
 	return nil
 }
+
+// verifyInputsSigned verifies that the given list of inputs is non-empty and
+// that all the inputs either contain a script signature or a witness stack.
+func verifyInputsSigned(ins []*wire.TxIn) error {
+	if len(ins) == 0 {
+		return fmt.Errorf("no inputs in transaction")
+	}
+	for idx, in := range ins {
+		if len(in.SignatureScript) == 0 && len(in.Witness) == 0 {
+			return fmt.Errorf("input %d has no signature data "+
+				"attached", idx)
+		}
+	}
+	return nil
+}
diff --git a/lnwallet/chanfunding/psbt_assembler_test.go b/lnwallet/chanfunding/psbt_assembler_test.go
index a58ea38bf..cc40887ad 100644
--- a/lnwallet/chanfunding/psbt_assembler_test.go
+++ b/lnwallet/chanfunding/psbt_assembler_test.go
@@ -18,6 +18,7 @@ import (
 	"github.com/davecgh/go-spew/spew"
 	"github.com/lightningnetwork/lnd/input"
 	"github.com/lightningnetwork/lnd/keychain"
+	"github.com/stretchr/testify/require"
 )
 
 var (
@@ -496,6 +497,44 @@ func TestPsbtFinalize(t *testing.T) {
 				return i.Finalize(p)
 			},
 		},
+		{
+			name:        "raw tx - nil transaction",
+			expectedErr: "raw transaction is nil",
+			doFinalize: func(amt int64, p *psbt.Packet,
+				i *PsbtIntent) error {
+
+				return i.FinalizeRawTX(nil)
+			},
+		},
+		{
+			name: "raw tx - no witness data in raw tx",
+			expectedErr: "inputs not signed: input 0 has no " +
+				"signature data attached",
+			doFinalize: func(amt int64, p *psbt.Packet,
+				i *PsbtIntent) error {
+
+				rawTx, err := psbt.Extract(p)
+				require.NoError(t, err)
+				rawTx.TxIn[0].Witness = nil
+
+				return i.FinalizeRawTX(rawTx)
+			},
+		},
+		{
+			name:        "happy path",
+			expectedErr: "",
+			doFinalize: func(amt int64, p *psbt.Packet,
+				i *PsbtIntent) error {
+
+				err := i.Finalize(p)
+				require.NoError(t, err)
+
+				require.Equal(t, PsbtFinalized, i.State)
+				require.NotNil(t, i.FinalTX)
+
+				return nil
+			},
+		},
 	}
 
 	// Create a simple assembler and ask it to provision a channel to get