Fix(modexp): do not return an error when length cannot be cast to usize #737
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birchmd
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aleksuss
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Mar 31, 2023
joshuajbouw
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Mar 31, 2023
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## [2.9.0] 2023-04-05 ### Added - Enabled XCC for mainnet release by [@birchmd]. ([#694]) - Added `set_owner` contract method which sets the owner of the contract by [@hskang9]. ([#690]) - New variant of submit function `submit_with_args` which accepts additional arguments along with the transaction such as the max gas price a user is ready to pay by [@aleksuss]. ([#696]) - Added the ability to create and fund XCC sub-accounts from external NEAR accounts by [@birchmd]. ([#735]) ### Changes - Replaced `rjson` with `serde_json` by [@aleksuss]. ([#677]) - Changed owner intended contract methods to now require owner or the contract itself by [@hskang9]. ([#676]) ### Fixes - Fixed nonce incorrectly being incremented on an out of fund failure by [@joshuajbouw]. ([#671]) - Fixed a check in promise results before executing cross contract calls (XCC) callbacks by [@birchmd]. ([#693]) - Fixed a reachable panic in `receive_erc20_tokens` by [@0x3bfc]. ([#709]) - Fixed a lack of minimum size checks when instantiating a new `EthGas` object by [@lempire123]. ([#722]) - Fixed a lack of division by 0 checks in `EthGas::Div()` by [@lempire123]. ([#718]) - Fixed the validation of the return of `exports:storage_remove` by [@0x3bfc]. ([#712]) - Fixed missing account validations of NEAR account IDs by [@0x3bfc]. ([#703]) - Fixed a reachable panic in the `exitToNear` and `exitToEthereum` precompiles if the input amount is greater than 1^128 when cast from a `U256` to `u128` by [@0x3bfc]. ([#681]) - Fixed a reachable panic in `modExp` due to arithmetic overflow by [@0x3bfc]. ([#688]) - Fixed the ability attaching values to Aurora specific precompiles, this no longer is possible, by [@0x3bfc]. ([#714]) - Fixed a return error if an ecrecover signature length is not exactly 65 by [@0x3bfc]. ([#717]) - Fixed size checks on input array passed to `exitToNear` and `exitToEthereum` precompiles by [@0x3bfc]. ([#684]) - Fixed missing gas costs in `exitToNear` and `exitToEthereum` precompiles by [@lempire123]. ([#687]) - Fixed a reachable panic due to out of memory in the `modExp` precompile by [@0x3bfc]. ([#689]) - Fixed an assurance that the `sender_id` has a balance greater than the amount in `ft_transfer_call` by [@0x3bfc]. ([#708]) - Fixed returning `0x` when a length cannot be cast as `usize` instead of returning an error in the `modExp` precompile by [@birchmd]. ([#737]) - Miscellaneous minor fixes by [@0x3bfc]. ([#738]) --------- Signed-off-by: dependabot[bot] <[email protected]> Co-authored-by: Leandro Casuso Montero <[email protected]> Co-authored-by: Michael Birch <[email protected]> Co-authored-by: Alexey Lapitsky <[email protected]> Co-authored-by: Oleksandr Anyshchenko <[email protected]> Co-authored-by: Alexey Lapitsky <[email protected]> Co-authored-by: Hyungsuk Kang <[email protected]> Co-authored-by: Ahmed Ali <[email protected]> Co-authored-by: lempire123 <[email protected]> Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
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Description
EVM precompiles generally do not return errors; they take whatever input users give and do their best to return a sensible output. For example
We see this input calls
modexpwith the size of both base and modulus both equal to zero, and the size of the exponent equal tou64::MAX. Since themodexpprecompile output is bounded by the size of the modulus, we know the output is empty because the size of the modulus is zero, even though an exponent of the requested size could not actually exist in most hardware.In our implementation we return an error from the
modexpprecompile if the lengths do not fit in ausizevalue, which in the case of Wasm is 32 bits. Therefore our implementation returns an error on the above input instead of retuning the empty value that geth returns. This PR fixes the issue by using a saturating cast intousizefrom the given input. This should be fine because non-trivial inputs (i.e. inputs where the modulus is non-zero) will have lengths that fit intousizeno problem, or else the computation will run out of gas.This problem of returning an error for the
usizecast is actually a little worse than just incompatibility with Ethereum. It also creates an inconsistency with the standalone engine because Wasm has 32-bitusizewhile the standalone tends to run on 64-bit platforms. This means that the above input (with exponent length equal tou64::MAX) returns an error in the Wasm contract, but passed in the standalone engine. After the change in this PR it passes on both compilation targets (as verified by the new integration test case).Testing
Additional test case in
modexpintegration tests.