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chanfunding: extend PSBT witness input check

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Fixes #5287.

The PSBT spec is a bit vague when it comes to the WitnessUtxo field of
an input as it's not strictly required for witness inputs. Therefore
Electrum for example does not include the field.
We need to make the SegWit input check a bit more elaborate by looking
at the output script of the UTXO and also the redeem script in case it's
a nested SegWit spend.
This commit is contained in:
Oliver Gugger 2021-05-12 13:40:13 +02:00
parent 6a2fb316ca
commit 2d70b46269
No known key found for this signature in database
GPG Key ID: 8E4256593F177720
2 changed files with 158 additions and 9 deletions
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67
lnwallet/chanfunding/psbt_assembler.go
View File

@ -8,6 +8,7 @@ import (
"github.com/btcsuite/btcd/btcec"
"github.com/btcsuite/btcd/chaincfg"
"github.com/btcsuite/btcd/txscript"
"github.com/btcsuite/btcd/wire"
"github.com/btcsuite/btcutil"
"github.com/btcsuite/btcutil/psbt"
@ -249,13 +250,13 @@ func (i *PsbtIntent) Verify(packet *psbt.Packet) error {
"output amount sum")
}
// SumUtxoInputValues checks that packet.Inputs is non-empty. Here we
// check that each Input has a WitnessUtxo field, to avoid possible
// malleability.
for _, in := range packet.Inputs {
if in.WitnessUtxo == nil {
return fmt.Errorf("not all inputs are segwit spends")
}
// To avoid possible malleability, all inputs to a funding transaction
// must be SegWit spends.
err = verifyAllInputsSegWit(packet.UnsignedTx.TxIn, packet.Inputs)
if err != nil {
return fmt.Errorf("cannot use TX for channel funding, "+
"not all inputs are SegWit spends, risk of "+
"malleability: %v", err)
}
i.PendingPsbt = packet
@ -543,3 +544,55 @@ func verifyInputsSigned(ins []*wire.TxIn) error {
}
return nil
}
// verifyAllInputsSegWit makes sure all inputs to a transaction are SegWit
// spends. This is a bit tricky because the PSBT spec doesn't require the
// WitnessUtxo field to be set. Therefore if only a NonWitnessUtxo is given, we
// need to look at it and make sure it's either a witness pkScript or a nested
// SegWit spend.
func verifyAllInputsSegWit(txIns []*wire.TxIn, ins []psbt.PInput) error {
for idx, in := range ins {
switch {
// The optimal case is that the witness UTXO is set explicitly.
case in.WitnessUtxo != nil:
// Only the non witness UTXO field is set, we need to inspect it
// to make sure it's not P2PKH or bare P2SH.
case in.NonWitnessUtxo != nil:
utxo := in.NonWitnessUtxo
txIn := txIns[idx]
txOut := utxo.TxOut[txIn.PreviousOutPoint.Index]
if !isSegWitScript(txOut.PkScript) &&
!isSegWitScript(in.RedeemScript) {
return fmt.Errorf("input %d is non-SegWit "+
"spend or missing redeem script", idx)
}
// This should've already been caught by a previous check but we
// keep it in for completeness' sake.
default:
return fmt.Errorf("input %d has no UTXO information",
idx)
}
}
return nil
}
// isSegWitScript returns true if the given pkScript can be parsed successfully
// as a SegWit v0 spend.
func isSegWitScript(pkScript []byte) bool {
if len(pkScript) == 0 {
return false
}
parsed, err := txscript.ParsePkScript(pkScript)
if err != nil {
return false
}
return parsed.Class() == txscript.WitnessV0PubKeyHashTy ||
parsed.Class() == txscript.WitnessV0ScriptHashTy
}

100
lnwallet/chanfunding/psbt_assembler_test.go
View File

@ -5,6 +5,7 @@ import (
"crypto/sha256"
"fmt"
"reflect"
"strings"
"sync"
"testing"
"time"
@ -340,8 +341,11 @@ func TestPsbtVerify(t *testing.T) {
},
},
{
name: "missing witness-utxo field",
expectedErr: "not all inputs are segwit spends",
name: "missing witness-utxo field",
expectedErr: "cannot use TX for channel funding, not " +
"all inputs are SegWit spends, risk of " +
"malleability: input 1 is non-SegWit spend " +
"or missing redeem script",
doVerify: func(amt int64, p *psbt.Packet,
i *PsbtIntent) error {
@ -629,6 +633,98 @@ func TestPsbtFinalize(t *testing.T) {
}
}
func TestVerifyAllInputsSegWit(t *testing.T) {
testCases := []struct {
name string
packet string
shouldFail bool
}{{
// Electrum takes the spec literally and does not include the
// WitnessUtxo field in the PSBT.
name: "Electrum np2wkh spend",
packet: "cHNidP8BAFMCAAAAAcptbRo6Ez2R8WclfL4IAW+XEWIl8sNOHnw" +
"eXfeU3dTwAQAAAAD9////Ab26GQAAAAAAF6kUf+wXsa7Z4ejieW" +
"CSdKaGFwJmfbyHQyMeAAABAOACAAAAAAEBiS1A2NE4KW00wLQ1B" +
"9R05jFMINs6egYFNL/5vLseeXMBAAAAAP7///8CNl1m1AEAAAAX" +
"qRR/7Bexrtnh6OJ5YJJ0poYXAmZ9vIdDuxkAAAAAABepFMD8Ngx" +
"k/Z7M5nJM2ltpszQZ4KGahwJHMEQCIAD4EIg16hjWEnEf2pilRF" +
"UmWSk5UsMD7tTrR2FbFCurAiAiNvqpFQSr/FCCXknOV1HzeDVxe" +
"B9gXeDZ62tmZv04/AEhAxGTJ9E/ImiOp2Ti3w/l/JFHa95RvXCB" +
"UXFKifC/7f9dQyMeAAEEFgAU9pqV6WX0D/HEMfdw9yzU30MmkV4" +
"iBgP4kZAAjhAKuixOLJczugvMmlS0xxPc2eD+4IJPHVOeRgxGbt" +
"z0AAAAAAAAAAAAAA==",
}, {
name: "Electrum p2wkh spend",
packet: "cHNidP8BAFMCAAAAASaMwGRzF7QWjHMX9WaGyUp7f3jznuNigHF" +
"4l57hW0CgAAAAAAD9////AU+6GQAAAAAAF6kUf+wXsa7Z4ejieW" +
"CSdKaGFwJmfbyHRSMeAAABANYCAAAAAAEBym1tGjoTPZHxZyV8v" +
"ggBb5cRYiXyw04efB5d95Td1PABAAAAFxYAFPaalell9A/xxDH3" +
"cPcs1N9DJpFe/f///wG+uhkAAAAAABYAFPaalell9A/xxDH3cPc" +
"s1N9DJpFeAkcwRAIgRwfN0qpcM5DHR+YrgXFxhEi6F0qTf4dmQc" +
"c1cu3TnnICIH5wc0kkMbHZ2mqZUFEITRUXExR7US3wohctQK1lf" +
"q/oASED+JGQAI4QCrosTiyXM7oLzJpUtMcT3Nng/uCCTx1TnkZF" +
"Ix4AIgYD+JGQAI4QCrosTiyXM7oLzJpUtMcT3Nng/uCCTx1TnkY" +
"MRm7c9AAAAAAAAAAAAAA=",
}, {
name: "Bitcoind p2wkh spend",
packet: "cHNidP8BAHICAAAAAeEw64k3k+YEk5EgNTytvkGlpiF6iMSsm0o" +
"dCSm03dt7AAAAAAD+////AsSvp8oAAAAAFgAUzWRW/Ccwf/Cosy" +
"dy0uYe5fa/Gb0A4fUFAAAAABepFMD8Ngxk/Z7M5nJM2ltpszQZ4" +
"KGahwAAAAAAAQBxAgAAAAEtMrUZuqjRoaSEMU9sc7pS2zKlS8X3" +
"/CUaENX1IHOICgEAAAAA/v///wLcm53QAAAAABYAFB1zJOaGOpk" +
"NHVkIguiZ2Zh46dlmAGXNHQAAAAAWABTbjTIbrBMD+sWxE6mahK" +
"tKGa//O1wAAAABAR/cm53QAAAAABYAFB1zJOaGOpkNHVkIguiZ2" +
"Zh46dlmIgYDjVRSrQ7d5Rld1nDBTY/uA7Xp+SKUfaFpB0SQiM8O" +
"3usQBp+HNQAAAIABAACADwAAgAAiAgJ9LOXb4MwHRoq31B9fQ2U" +
"0K+Uj8BBJzy+MWc0OOOVuQxAGn4c1AAAAgAEAAIARAACAAAA=",
}, {
name: "Bitcoind p2pkh spend",
packet: "cHNidP8BAHICAAAAAdp3QE/zv3Q7RhkAR0JyzBWLttUqRHJ" +
"pAYmHLIqJzGXOAQAAAAD/////AoDw+gIAAAAAF6kUwPw2DGT9ns" +
"zmckzaW2mzNBngoZqHUN/6AgAAAAAWABRLzlCRi8BozkTClLcIN" +
"tnz8zYTtAAAAAAAAQB0AgAAAAHhMOuJN5PmBJORIDU8rb5BpaYh" +
"eojErJtKHQkptN3bewAAAAAA/v///wKcr6fKAAAAABYAFOvePfh" +
"lztKeDuQRgcGsHLS5BPhTAOH1BQAAAAAZdqkUt9QziR33rxhwcg" +
"ipzwrDti93vTWIrAAAAAAiBgNKzHC4j7KaSKeH9RYx3Ur3dHL5w" +
"YRjXpOAi3SI12WNFxAGn4c1AAAAgAAAAIAGAACAAAAiAgK8Fq3O" +
"5nnASvhn9LJMIJOkGBMYQFd5DcbvOCbBCX/VBRAGn4c1AAAAgAE" +
"AAIAVAACAAA==",
shouldFail: true,
}, {
name: "Bitcoind p2sh multisig spend",
packet: "cHNidP8BAHICAAAAAQvO6z5f4wghsQ2c5+Zcw2qdZ4FOYkyWBFe" +
"U/jiIKcwdAAAAAAD/////AkTc+gIAAAAAFgAU2kWEYfMLfgwVQ0" +
"2wJwFNsOmorBWA8PoCAAAAABepFMD8Ngxk/Z7M5nJM2ltpszQZ4" +
"KGahwAAAAAAAQByAgAAAAHad0BP8790O0YZAEdCcswVi7bVKkRy" +
"aQGJhyyKicxlzgAAAAAA/v///wIA4fUFAAAAABepFJdSg2Xdeo3" +
"mYbTqbcZnZIH8oWbPh4TDscQAAAAAFgAUs5d3GhxrF5Zdi8fQHy" +
"A05BSZr4t3AAAAAQRHUSEDdy41G190ATg/VnhXHE4dufESLLl53" +
"RewoYB2ZYRJ/4AhA6MR4qMgHUkIyqhXW0jEECV8cHg/DCiuLgUk" +
"YvQeub1zUq4AAAA=",
shouldFail: true,
}}
for _, tc := range testCases {
tc := tc
t.Run(tc.name, func(t *testing.T) {
r := strings.NewReader(tc.packet)
packet, err := psbt.NewFromRawBytes(r, true)
require.NoError(t, err)
txIns := packet.UnsignedTx.TxIn
ins := packet.Inputs
err = verifyAllInputsSegWit(txIns, ins)
if tc.shouldFail {
require.Error(t, err)
} else {
require.NoError(t, err)
}
})
}
}
// clonePsbt creates a clone of a PSBT packet by serializing then de-serializing
// it.
func clonePsbt(t *testing.T, p *psbt.Packet) *psbt.Packet {