fix: return error if amount is greater than 2^128 (#681)

* fix: return error if amount is greater than `2^128`

* Update engine-precompiles/src/native.rs

Co-authored-by: Joshua J. Bouw <joshua@aurora.dev>

* Update engine-precompiles/src/native.rs

* chore: remove unused constant

* chore: should panic with error msg if amount > 2^128

* fix: remove `validate_amount` from tests

---------

Co-authored-by: Joshua J. Bouw <joshua@aurora.dev>

engine-precompiles/src/native.rs

@@ -229,6 +229,13 @@ fn get_nep141_from_erc20<I: IO>(erc20_token: &[u8], io: &I) -> Result<AccountId,
     .map_err(|_| ExitError::Other(Cow::Borrowed("ERR_INVALID_NEP141_ACCOUNT")))
 }
 
+fn validate_amount(amount: U256) -> Result<(), ExitError> {
+    if amount > U256::from(u128::MAX) {
+        return Err(ExitError::Other(Cow::from("ERR_INVALID_AMOUNT")));
+    }
+    Ok(())
+}
+
 impl<I: IO> Precompile for ExitToNear<I> {
     fn required_gas(_input: &[u8]) -> Result<EthGas, ExitError> {
         Ok(costs::EXIT_TO_NEAR_GAS)
@@ -331,6 +338,8 @@ impl<I: IO> Precompile for ExitToNear<I> {
                 let amount = U256::from_big_endian(&input[..32]);
                 input = &input[32..];
 
+                validate_amount(amount)?;
+
                 if let Ok(receiver_account_id) = AccountId::try_from(input) {
                     (
                         nep141_address,
@@ -519,6 +528,8 @@ impl<I: IO> Precompile for ExitToEthereum<I> {
                 let amount = U256::from_big_endian(&input[..32]);
                 input = &input[32..];
 
+                validate_amount(amount)?;
+
                 if input.len() == 20 {
                     // Parse ethereum address in hex
                     let eth_recipient: String = hex::encode(input);
@@ -585,8 +596,9 @@ impl<I: IO> Precompile for ExitToEthereum<I> {
 
 #[cfg(test)]
 mod tests {
-    use super::{exit_to_ethereum, exit_to_near};
+    use super::{exit_to_ethereum, exit_to_near, validate_amount};
     use crate::prelude::sdk::types::near_account_to_evm_address;
+    use aurora_engine_types::U256;
 
     #[test]
     fn test_precompile_id() {
@@ -614,4 +626,15 @@ mod tests {
             super::events::EXIT_TO_ETH_SIGNATURE
         );
     }
+
+    #[test]
+    #[should_panic(expected = "ERR_INVALID_AMOUNT")]
+    fn test_exit_with_invalid_amount() {
+        validate_amount(U256::MAX).unwrap();
+    }
+
+    #[test]
+    fn test_exit_with_valid_amount() {
+        validate_amount(U256::from(u128::MAX)).unwrap();
+    }
 }