[evm] Use dynamic gas computation for the FunToken.sol precompile

[Unique-Divine]

Abstract / Summary

Scope: x/evm/precompile/funtoken.go

RequiredGas() (here in funtoken.go as well as in the other precompiles) charges a fixed amount of gas. This is problematic as the bankSend function accepts a dynamic type parameter, string memory to, as the transfer recipient.

If the bankSend precompile is called with the to string set to a very large string value, the DecomposeInput() call will consume a lot of computational resources to unpack the large to value, which the user is not charged for. The bank send will ultimately fail, but before it will have consumed a lot of gas. So this opens up a DoS/griefing vector.

If dynamic types are used as function parameters, it's very important to be accurate with gas accounting, as the value can potentially be very large. For example, consider parsing the input also in RequiredGas() and charge additional gas for dynamic size parameters (e.g. string, bytes, etc.)

Originally posted by @berndartmueller in https://github.com/code-423n4/2024-10-nibiru-zenith/pull/28#discussion_r1801090069

• Commit (2024-10-17): - 3348e14
• From: @berndartmueller

---