remove timestamp check from solomachine misbehaviour (#7915)

* remove timestamp check from solomachine misbehaviour

* add more documentation

x/ibc/light-clients/06-solomachine/spec/01_concepts.md

@@ -154,6 +154,9 @@ If the misbehaviour is successfully processed:
 
 - the client is frozen by setting the frozen sequence to the misbehaviour sequence
 
+NOTE: Misbehaviour processing is data processing order dependent. A misbehaving solo machine
+could update to a new public key to prevent being frozen before misbehaviour is submitted. 
+
 ## Upgrades
 
 Upgrades to solo machine light clients are not supported since an entirely different type of 

x/ibc/light-clients/06-solomachine/types/misbehaviour_handle.go

@@ -11,6 +11,9 @@ import (
 // CheckMisbehaviourAndUpdateState determines whether or not the currently registered
 // public key signed over two different messages with the same sequence. If this is true
 // the client state is updated to a frozen status.
+// NOTE: Misbehaviour is not tracked for previous public keys, a solo machine may update to
+// a new public key before the misbehaviour is processed. Therefore, misbehaviour is data
+// order processing dependent.
 func (cs ClientState) CheckMisbehaviourAndUpdateState(
 	ctx sdk.Context,
 	cdc codec.BinaryMarshaler,
@@ -49,14 +52,10 @@ func (cs ClientState) CheckMisbehaviourAndUpdateState(
 
 // verifySignatureAndData verifies that the currently registered public key has signed
 // over the provided data and that the data is valid. The data is valid if it can be
-// unmarshaled into the specified data type or the timestamp of the signature is less
-// than the consensus state timestamp.
+// unmarshaled into the specified data type.
 func verifySignatureAndData(cdc codec.BinaryMarshaler, clientState ClientState, misbehaviour *Misbehaviour, sigAndData *SignatureAndData) error {
-	// timestamp less than consensus state would always fail and not succeed in fooling the
-	// light client
-	if sigAndData.Timestamp < clientState.ConsensusState.Timestamp {
-		return sdkerrors.Wrapf(clienttypes.ErrInvalidMisbehaviour, "timestamp is less than consensus state timestamp (%d < %d)", sigAndData.Timestamp, clientState.ConsensusState.Timestamp)
-	}
+
+	// do not check misbehaviour timestamp since we want to allow processing of past misbehaviour
 
 	// ensure data can be unmarshaled to the specified data type
 	if _, err := UnmarshalDataByType(cdc, sigAndData.DataType, sigAndData.Data); err != nil {

x/ibc/light-clients/06-solomachine/types/misbehaviour_handle_test.go

@@ -29,6 +29,14 @@ func (suite *SoloMachineTestSuite) TestCheckMisbehaviourAndUpdateState() {
 				},
 				true,
 			},
+			{
+				"old misbehaviour is successful (timestamp is less than current consensus state)",
+				func() {
+					clientState = solomachine.ClientState()
+					solomachine.Time = solomachine.Time - 5
+					misbehaviour = solomachine.CreateMisbehaviour()
+				}, true,
+			},
 			{
 				"client is frozen",
 				func() {
@@ -95,14 +103,6 @@ func (suite *SoloMachineTestSuite) TestCheckMisbehaviourAndUpdateState() {
 					misbehaviour = m
 				}, false,
 			},
-			{
-				"timestamp is less than consensus state timestamp",
-				func() {
-					clientState = solomachine.ClientState()
-					solomachine.Time = solomachine.Time - 5
-					misbehaviour = solomachine.CreateMisbehaviour()
-				}, false,
-			},
 			{
 				"invalid first signature data",
 				func() {