Problem: user can specify a excessive tx gas limit to occupy block space without paying the price

[yihuang]

System info: ethermint main

Steps to reproduce:

After a recent gas meter fix, tendermint will include tx to block according to the sum of tx gas limits, but we'll refund the unused gas for EVM transaction, which means one can occupy block space with low cost by specifying an excessive tx gas limit.

Expected behavior: shouldn't be vulnerable to dos attack

Actual behavior: [What actually happened]

Additional info: [Include gist of relevant config, logs, etc.]

[yihuang]

Compare solutions

Non-breaking

Change the gasWanted returned in check tx.

1. Execute the tx in check tx mode, and return the gasUsed.
   • Performance degradation
2. 0 this is what we have before the gas meter fix, can mitigate the issue by limiting the mempool size. (or using a smaller block size limit, need an upgrade).
3. Return some other constant value to limit the number of transaction in block to: block gas limit / constant gasWanted.

Breaking

Change the gas refund rules.

5. Don't refund unused gas at all, same as cosmos-sdk
   • hurt UX.
6. Refund a percentage of it, Refunding unused but allocated gas cosmos/cosmos-sdk#2150

Long term solution

PrepareProposal in abci++
We can run the tx in the PrepareProposal phase, and truncate the preliminary transaction list according to the gas used.