Bug Report

Setup

CometBFT version

v0.38 and main

What happened?

Invalid vote extensions are included in the ExtendedCommitInfo offered to the ABCI application via PrepareProposal.

What did you expect to happen?

ExtendedCommitInfo only includes valid vote extensions.

Moreover, the LastCommit field of a block should only contain Precommits whose extensions were accepted by the application.

How to reproduce it

A validator receives a Precommit from the previous height with an invalid vote extension during the NewHeightRoundStep.

How to fix it

There are a few options:

• do not fix
  • instead, inform applications that PrepareProposal may receive non-validated extensions
  • the downsides are
    • 2/3N extensions may be verified twice by the proposer, once in VerifyVoteExtension and once in PrepareProposal.
    • the LastCommit field of a block may contain information of Precommits whose vote extensions are invalid.
• verify the extensions of Precommits received while waiting for timeout_commit
  • the downsides are
    • the application has already moved on to the next height and will now be required to validate extensions from the previous height.
    • makes the spec more complex.
  • a simple and correct option here is to reject extensions for the previous height, however this would impact in the reward distribution (undo what timeout_commit is supposed to enable).