Submission Details
Severity:
logic to calcute gas for sha256 is different for precompile and L1Messenger
Summary
Discrepency between logic for calculating sha gas cost lead to either to overchargin or underchaning users.
Vulnerability Details
Lets compare how two funcitons calculate number of rounds
// Copy calldata to memory for pad it
let bytesSize := calldatasize()
calldatacopy(0, 0, bytesSize)
// The sha256 padding includes additional 8 bytes of the total message's length in bits,
// so calculate the "full" message length with it.
let extendBytesLen := add(bytesSize, 8)
let padLen := sub(BLOCK_SIZE(), mod(extendBytesLen, BLOCK_SIZE())) // @ additional variable compare to l1messager
let paddedBytesSize := add(extendBytesLen, padLen)
let numRounds := div(paddedBytesSize, BLOCK_SIZE())
let precompileParams := unsafePackPrecompileParams(
0, // input offset in words
// Always divisible by 32, since `BLOCK_SIZE()` is 64 bytes
div(paddedBytesSize, 32), // input length in words (safe to pass, never exceed `type(uint32).max`)
0, // output offset in words
1, // output length in words
numRounds // number of rounds (safe to pass, never exceed `type(uint64).max`)
)
let gasToPay := mul(SHA256_ROUND_GAS_COST(), numRounds)
function sha256GasCost(uint256 _length) internal pure returns (uint256) {
return SHA256_ROUND_GAS_COST * ((_length + 8) / SHA256_ROUND_NUMBER_OF_BYTES + 1);
}
As we can see padLen := sub(BLOCK_SIZE(), mod(extendBytesLen, BLOCK_SIZE())) is not in a formula inside l1messagner.
Impact
Incorrect gas cost would be charged in l1messager
Tools Used
Recommendations
Align cost in l1messager with precompile formula
Updates
Lead Judging Commences
inallhonesty 5 months ago
Submission Judgement Published Assigned finding tags:
logic to calcute gas for sha256 is different for precompile and L1Messenger
Appeal created
inallhonesty
5 months ago
inallhonesty 5 months ago
Submission Judgement Published Assigned finding tags:
logic to calcute gas for sha256 is different for precompile and L1Messenger
Prize pool breakdown
Total prize
500,000 USDC
nSLOC
15,74132 USDC / LOC
475,000 USDC
25,000 USDC
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