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| author | Wei-Ning Huang <w@dexon.org> | 2019-01-24 17:30:03 +0800 |
|---|---|---|
| committer | Wei-Ning Huang <w@dexon.org> | 2019-04-09 21:32:56 +0800 |
| commit | 72224d6ebc1763ee3787164fca00fe6d3ae501d6 (patch) | |
| tree | cf536e3a7602bad487f980260871ceabf163e8f7 /core | |
| parent | 87db7f44d06ff4610b7a7a0b3bc845b8d8e342d0 (diff) | |
| download | dexon-72224d6ebc1763ee3787164fca00fe6d3ae501d6.tar.gz dexon-72224d6ebc1763ee3787164fca00fe6d3ae501d6.tar.zst dexon-72224d6ebc1763ee3787164fca00fe6d3ae501d6.zip | |
core: vm: modify randomness calculation algorithm (#173)
The original algorithm used for calculating algorithm is vulnerable to
cross context re-entry attack. Example as follows:
contract B {
event Value(uint256 value);
uint256 public value;
function call() public {
value = rand;
emit Value(value);
}
}
contract A {
function randTwice(address bAddr) public {
B b = B(bAddr);
b.call.gas(100000)();
b.call.gas(100000)();
}
}
The two `b.call` will result in the same randomness value. This commit
fix the issue by recording a called index used to store how many times
opRand is called, and use it as argument to the Keccak call.
Diffstat (limited to 'core')
| -rw-r--r-- | core/vm/evm.go | 2 | ||||
| -rw-r--r-- | core/vm/instructions.go | 8 |
2 files changed, 7 insertions, 3 deletions
diff --git a/core/vm/evm.go b/core/vm/evm.go index 64f71e530..2eba9c2cb 100644 --- a/core/vm/evm.go +++ b/core/vm/evm.go @@ -101,6 +101,8 @@ type Context struct { Time *big.Int // Provides information for TIME Randomness []byte // Provides information for RAND Difficulty *big.Int // Provides information for DIFFICULTY + + RandCallIndex uint64 // Number of times opRand is called } // EVM is the Ethereum Virtual Machine base object and provides diff --git a/core/vm/instructions.go b/core/vm/instructions.go index 3a82190da..3d17287ed 100644 --- a/core/vm/instructions.go +++ b/core/vm/instructions.go @@ -417,14 +417,16 @@ func opRand(pc *uint64, interpreter *EVMInterpreter, contract *Contract, memory binaryNonce := make([]byte, binary.MaxVarintLen64) binary.PutUvarint(binaryNonce, nonce) - binaryGas := make([]byte, binary.MaxVarintLen64) - binary.PutUvarint(binaryGas, contract.Gas) + binaryUsedIndex := make([]byte, binary.MaxVarintLen64) + binary.PutUvarint(binaryUsedIndex, evm.RandCallIndex) + + evm.RandCallIndex += 1 hash := crypto.Keccak256( evm.Randomness, contract.Caller().Bytes(), binaryNonce, - binaryGas) + binaryUsedIndex) stack.push(interpreter.intPool.get().SetBytes(hash)) return nil, nil |