Official Go implementation of the Ethereum protocol
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go-ethereum/tests/fuzzers/modexp/modexp-fuzzer.go

90 lines
3.0 KiB

// Copyright 2022 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
package modexp
import (
"fmt"
"math/big"
"github.com/ethereum/go-ethereum/common"
"github.com/ethereum/go-ethereum/core/vm"
big2 "github.com/holiman/big"
)
// Fuzz is the fuzzing entry-point.
// The function must return
//
// - 1 if the fuzzer should increase priority of the
// given input during subsequent fuzzing (for example, the input is lexically
// correct and was parsed successfully);
// - -1 if the input must not be added to corpus even if gives new coverage; and
// - 0 otherwise
//
// other values are reserved for future use.
func Fuzz(input []byte) int {
if len(input) <= 96 {
return -1
}
// Abort on too expensive inputs
precomp := vm.PrecompiledContractsBerlin[common.BytesToAddress([]byte{5})]
if gas := precomp.RequiredGas(input); gas > 40_000_000 {
return 0
}
var (
baseLen = new(big.Int).SetBytes(getData(input, 0, 32)).Uint64()
expLen = new(big.Int).SetBytes(getData(input, 32, 32)).Uint64()
modLen = new(big.Int).SetBytes(getData(input, 64, 32)).Uint64()
)
// Handle a special case when both the base and mod length is zero
if baseLen == 0 && modLen == 0 {
return -1
}
input = input[96:]
// Retrieve the operands and execute the exponentiation
var (
base = new(big.Int).SetBytes(getData(input, 0, baseLen))
exp = new(big.Int).SetBytes(getData(input, baseLen, expLen))
mod = new(big.Int).SetBytes(getData(input, baseLen+expLen, modLen))
base2 = new(big2.Int).SetBytes(getData(input, 0, baseLen))
exp2 = new(big2.Int).SetBytes(getData(input, baseLen, expLen))
mod2 = new(big2.Int).SetBytes(getData(input, baseLen+expLen, modLen))
)
if mod.BitLen() == 0 {
// Modulo 0 is undefined, return zero
return -1
}
var a = new(big2.Int).Exp(base2, exp2, mod2).String()
var b = new(big.Int).Exp(base, exp, mod).String()
if a != b {
panic(fmt.Sprintf("Inequality %#x ^ %#x mod %#x \n have %s\n want %s", base, exp, mod, a, b))
}
return 1
}
// getData returns a slice from the data based on the start and size and pads
// up to size with zero's. This function is overflow safe.
func getData(data []byte, start uint64, size uint64) []byte {
length := uint64(len(data))
if start > length {
start = length
}
end := start + size
if end > length {
end = length
}
return common.RightPadBytes(data[start:end], int(size))
}