// checkInputsStandard performs a series of checks on a transaction's inputs
// to ensure they are "standard". A standard transaction input is one that
// that consumes the expected number of elements from the stack and that number
// is the same as the output script pushes. This help prevent resource
// exhaustion attacks by "creative" use of scripts that are super expensive to
// process like OP_DUP OP_CHECKSIG OP_DROP repeated a large number of times
// followed by a final OP_TRUE.
func checkInputsStandard(tx *btcutil.Tx, utxoView *blockchain.UtxoViewpoint) error {
// NOTE: The reference implementation also does a coinbase check here,
// but coinbases have already been rejected prior to calling this
// function so no need to recheck.
for i, txIn := range tx.MsgTx().TxIn {
// It is safe to elide existence and index checks here since
// they have already been checked prior to calling this
// function.
prevOut := txIn.PreviousOutPoint
entry := utxoView.LookupEntry(&prevOut.Hash)
originPkScript := entry.PkScriptByIndex(prevOut.Index)
// Calculate stats for the script pair.
scriptInfo, err := txscript.CalcScriptInfo(txIn.SignatureScript,
originPkScript, true)
if err != nil {
str := fmt.Sprintf("transaction input #%d script parse "+
"failure: %v", i, err)
return txRuleError(wire.RejectNonstandard, str)
}
// A negative value for expected inputs indicates the script is
// non-standard in some way.
if scriptInfo.ExpectedInputs < 0 {
str := fmt.Sprintf("transaction input #%d expects %d "+
"inputs", i, scriptInfo.ExpectedInputs)
return txRuleError(wire.RejectNonstandard, str)
}
// The script pair is non-standard if the number of available
// inputs does not match the number of expected inputs.
if scriptInfo.NumInputs != scriptInfo.ExpectedInputs {
str := fmt.Sprintf("transaction input #%d expects %d "+
"inputs, but referenced output script provides "+
"%d", i, scriptInfo.ExpectedInputs,
scriptInfo.NumInputs)
return txRuleError(wire.RejectNonstandard, str)
}
}
return nil
}
// TestCalcScriptInfo ensures the CalcScriptInfo provides the expected results
// for various valid and invalid script pairs.
func TestCalcScriptInfo(t *testing.T) {
t.Parallel()
tests := []struct {
name string
sigScript string
pkScript string
bip16 bool
scriptInfo txscript.ScriptInfo
scriptInfoErr error
}{
{
// Invented scripts, the hashes do not match
// Truncated version of test below:
name: "pkscript doesn't parse",
sigScript: "1 81 DATA_8 2DUP EQUAL NOT VERIFY ABS " +
"SWAP ABS EQUAL",
pkScript: "HASH160 DATA_20 0xfe441065b6532231de2fac56" +
"3152205ec4f59c",
bip16: true,
scriptInfoErr: txscript.ErrStackShortScript,
},
{
name: "sigScript doesn't parse",
// Truncated version of p2sh script below.
sigScript: "1 81 DATA_8 2DUP EQUAL NOT VERIFY ABS " +
"SWAP ABS",
pkScript: "HASH160 DATA_20 0xfe441065b6532231de2fac56" +
"3152205ec4f59c74 EQUAL",
bip16: true,
scriptInfoErr: txscript.ErrStackShortScript,
},
{
// Invented scripts, the hashes do not match
name: "p2sh standard script",
sigScript: "1 81 DATA_25 DUP HASH160 DATA_20 0x010203" +
"0405060708090a0b0c0d0e0f1011121314 EQUALVERIFY " +
"CHECKSIG",
pkScript: "HASH160 DATA_20 0xfe441065b6532231de2fac56" +
"3152205ec4f59c74 EQUAL",
bip16: true,
scriptInfo: txscript.ScriptInfo{
PkScriptClass: txscript.ScriptHashTy,
NumInputs: 3,
ExpectedInputs: 3, // nonstandard p2sh.
SigOps: 1,
},
},
{
// from 567a53d1ce19ce3d07711885168484439965501536d0d0294c5d46d46c10e53b
// from the blockchain.
name: "p2sh nonstandard script",
sigScript: "1 81 DATA_8 2DUP EQUAL NOT VERIFY ABS " +
"SWAP ABS EQUAL",
pkScript: "HASH160 DATA_20 0xfe441065b6532231de2fac56" +
"3152205ec4f59c74 EQUAL",
bip16: true,
scriptInfo: txscript.ScriptInfo{
PkScriptClass: txscript.ScriptHashTy,
NumInputs: 3,
ExpectedInputs: -1, // nonstandard p2sh.
SigOps: 0,
},
},
{
// Script is invented, numbers all fake.
name: "multisig script",
// Extra 0 arg on the end for OP_CHECKMULTISIG bug.
sigScript: "1 1 1 0",
pkScript: "3 " +
"DATA_33 0x0102030405060708090a0b0c0d0e0f1011" +
"12131415161718191a1b1c1d1e1f2021 DATA_33 " +
"0x0102030405060708090a0b0c0d0e0f101112131415" +
"161718191a1b1c1d1e1f2021 DATA_33 0x010203040" +
"5060708090a0b0c0d0e0f101112131415161718191a1" +
"b1c1d1e1f2021 3 CHECKMULTISIG",
bip16: true,
scriptInfo: txscript.ScriptInfo{
PkScriptClass: txscript.MultiSigTy,
NumInputs: 4,
ExpectedInputs: 4,
SigOps: 3,
},
},
}
for _, test := range tests {
sigScript := mustParseShortForm(test.sigScript)
pkScript := mustParseShortForm(test.pkScript)
si, err := txscript.CalcScriptInfo(sigScript, pkScript,
test.bip16)
if err != nil {
if err != test.scriptInfoErr {
t.Errorf("scriptinfo test \"%s\": got \"%v\""+
"expected \"%v\"", test.name, err,
test.scriptInfoErr)
}
continue
}
if test.scriptInfoErr != nil {
t.Errorf("%s: succeeded when expecting \"%v\"",
test.name, test.scriptInfoErr)
continue
}
if *si != test.scriptInfo {
t.Errorf("%s: scriptinfo doesn't match expected. "+
"got: \"%v\" expected \"%v\"", test.name,
*si, test.scriptInfo)
continue
}
}
}