Fast reject invalid consensus params (#331)

## Describe your changes and provide context
Previously, a proposal to change Tendermint consensus params to an
invalid value could be made, but could potentially halt the chain b/c at
the block in which the proposal passes, Tendermint will verify that the
params are valid and panic if the change is not valid (see
https://github.com/sei-protocol/sei-tendermint/blob/d426f1fe475eb0c406296770ff5e9f8869b3887e/internal/state/execution.go#L320),
thus halting the change. This PR early rejects the proposal so that the
chain will no longer halt.
## Testing performed to validate your change
- Added unit tests
- Verified on a internal chain:
```
root@ip-172-31-34-209:/home/ubuntu/sei-chain# seid tx gov submit-proposal param-change prop.json --from admin -b block --fees 20000usei
Enter keyring passphrase:
Error: block.MaxGas must be greater or equal to -1. Got -2
...
root@ip-172-31-34-209:/home/ubuntu/sei-chain# seid tx gov submit-proposal param-change prop.json --from admin -b block --fees 2000usei
Enter keyring passphrase:
Error: block.MaxBytes is too big. 2202009600000 > 104857600
```

x/params/types/proposal/proposal.go

@@ -1,7 +1,9 @@
 package proposal
 
 import (
+	"encoding/json"
 	"fmt"
+	"github.com/tendermint/tendermint/types"
 	"strings"
 
 	yaml "gopkg.in/yaml.v2"
@@ -96,7 +98,37 @@ func ValidateChanges(changes []ParamChange) error {
 		if len(pc.Value) == 0 {
 			return ErrEmptyValue
 		}
+		// We need to verify ConsensusParams since they are only validated once the proposal passes.
+		// If any of them are invalid at time of passing, this will cause a chain halt since validation is done during
+		// ApplyBlock: https://github.com/sei-protocol/sei-tendermint/blob/d426f1fe475eb0c406296770ff5e9f8869b3887e/internal/state/execution.go#L320
+		// Therefore, we validate when we get a param-change msg for ConsensusParams
+		if pc.Subspace == "baseapp" {
+			if err := verifyConsensusParamsUsingDefault(changes); err != nil {
+				return err
+			}
+		}
 	}
 
 	return nil
 }
+
+func verifyConsensusParamsUsingDefault(changes []ParamChange) error {
+	// Start with a default (valid) set of parameters, and update based on proposal then check
+	defaultCP := types.DefaultConsensusParams()
+	for _, change := range changes {
+		// Note: BlockParams seems to be the only support ConsensusParams available for modifying with proposal
+		switch change.Key {
+		case "BlockParams":
+			blockParams := types.DefaultBlockParams()
+			err := json.Unmarshal([]byte(change.Value), &blockParams)
+			if err != nil {
+				return err
+			}
+			defaultCP.Block = blockParams
+		}
+	}
+	if err := defaultCP.ValidateConsensusParams(); err != nil {
+		return err
+	}
+	return nil
+}

x/params/types/proposal/proposal_test.go

@@ -1,6 +1,8 @@
 package proposal
 
 import (
+	"fmt"
+	"github.com/tendermint/tendermint/types"
 	"testing"
 
 	"github.com/stretchr/testify/require"
@@ -25,3 +27,14 @@ func TestParameterChangeProposal(t *testing.T) {
 	pcp = NewParameterChangeProposal("test title", "test description", []ParamChange{pc4}, true)
 	require.Error(t, pcp.ValidateBasic())
 }
+
+func TestConsensusParameterChangeProposal(t *testing.T) {
+	// Valid block max_bytes (
+	pc1 := NewParamChange("baseapp", "BlockParams", fmt.Sprintf("{\"max_bytes\":\"%d\"}", types.MaxBlockSizeBytes))
+	pcp := NewParameterChangeProposal("test title", "test description", []ParamChange{pc1}, true)
+	require.Nil(t, pcp.ValidateBasic())
+
+	pc1 = NewParamChange("baseapp", "BlockParams", fmt.Sprintf("{\"max_bytes\":\"%d\"}", types.MaxBlockSizeBytes+1))
+	pcp = NewParameterChangeProposal("test title", "test description", []ParamChange{pc1}, true)
+	require.Error(t, pcp.ValidateBasic())
+}