[Bug]: Validation of ConsensusParams update doesn't follow CometBFT spec

[sergio-mena]

Is there an existing issue for this?

• I have searched the existing issues

What happened?

The ConsensusParams validator carried out by consensusParamsKeeper.UpdateParams is stateless. Therefore a malformed (or malicious) proposal may introduce ill-formed ConsensusParams in the module's store.

Cosmos SDK Version

0.50

How to reproduce?

• Set up an example chain with simapp, with just one validator
• Edit the genesis file to reduce gov's expedited_voting_period to 1 minute
• Start the node (the validator)
• Prepare a gov proposal with the following message:

{
  "@type": "/cosmos.consensus.v1.MsgUpdateParams",
  ...  
  "abci": {
    "vote_extensions_enable_height": 1
  }
}

• Make sure that the json has sensible values for all other fields of message cosmos.consensus.v1.MsgUpdateParams
• Submit the proposal and vote "yes"
• When the proposal passed, the chain will halt, as we are setting the Vote Extension enable height to a past heigh

These repro steps are the simplest, there are other cases when the ConsensusParams in the module's store are incorrect/incomplete.

[sergio-mena]

Take a look at the proposed fix in #20314

[sergio-mena]

And (extended) version for main: #20347