From 83edae27299dfbfd4695205461ad354d0f4064fb Mon Sep 17 00:00:00 2001
From: "mergify[bot]" <37929162+mergify[bot]@users.noreply.github.com>
Date: Sat, 19 Feb 2022 09:18:26 -0800
Subject: [PATCH] fix app hash in state rollback (#7837) (#7882)

When testing rollback feature in the Cosmos SDK, we found that the app hash
in Tendermint after rollback was the value after the latest block, rather than
before it.

Co-authored-by: Callum Waters <cmwaters19@gmail.com>
(cherry picked from commit 8a238fdcb44461a4e029c8e7a4790c2d470d282b)

Co-authored-by: yihuang <huang@crypto.com>
---
 CHANGELOG_PENDING.md            |  1 +
 internal/state/rollback.go      |  9 +++++++--
 internal/state/rollback_test.go | 15 +++++++++++++--
 3 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/CHANGELOG_PENDING.md b/CHANGELOG_PENDING.md
index 0e8458078..e74746d2c 100644
--- a/CHANGELOG_PENDING.md
+++ b/CHANGELOG_PENDING.md
@@ -28,3 +28,4 @@ Special thanks to external contributors on this release:
 
 - [light] \#7640 Light Client: fix absence proof verification (@ashcherbakov)
 - [light] \#7641 Light Client: fix querying against the latest height (@ashcherbakov)
+- [cli] [#7837](https://github.com/tendermint/tendermint/pull/7837) fix app hash in state rollback. (@yihuang)
diff --git a/internal/state/rollback.go b/internal/state/rollback.go
index ea0eff4de..38f042559 100644
--- a/internal/state/rollback.go
+++ b/internal/state/rollback.go
@@ -41,6 +41,11 @@ func Rollback(bs BlockStore, ss Store) (int64, []byte, error) {
 	if rollbackBlock == nil {
 		return -1, nil, fmt.Errorf("block at height %d not found", rollbackHeight)
 	}
+	// we also need to retrieve the latest block because the app hash and last results hash is only agreed upon in the following block
+	latestBlock := bs.LoadBlockMeta(invalidState.LastBlockHeight)
+	if latestBlock == nil {
+		return -1, nil, fmt.Errorf("block at height %d not found", invalidState.LastBlockHeight)
+	}
 
 	previousLastValidatorSet, err := ss.LoadValidators(rollbackHeight)
 	if err != nil {
@@ -89,8 +94,8 @@ func Rollback(bs BlockStore, ss Store) (int64, []byte, error) {
 		ConsensusParams:                  previousParams,
 		LastHeightConsensusParamsChanged: paramsChangeHeight,
 
-		LastResultsHash: rollbackBlock.Header.LastResultsHash,
-		AppHash:         rollbackBlock.Header.AppHash,
+		LastResultsHash: latestBlock.Header.LastResultsHash,
+		AppHash:         latestBlock.Header.AppHash,
 	}
 
 	// persist the new state. This overrides the invalid one. NOTE: this will also
diff --git a/internal/state/rollback_test.go b/internal/state/rollback_test.go
index fb5ca9796..ad7f12afc 100644
--- a/internal/state/rollback_test.go
+++ b/internal/state/rollback_test.go
@@ -46,12 +46,22 @@ func TestRollback(t *testing.T) {
 		BlockID: initialState.LastBlockID,
 		Header: types.Header{
 			Height:          initialState.LastBlockHeight,
-			AppHash:         initialState.AppHash,
+			AppHash:         factory.RandomHash(),
 			LastBlockID:     factory.MakeBlockID(),
 			LastResultsHash: initialState.LastResultsHash,
 		},
 	}
-	blockStore.On("LoadBlockMeta", initialState.LastBlockHeight).Return(block)
+	nextBlock := &types.BlockMeta{
+		BlockID: initialState.LastBlockID,
+		Header: types.Header{
+			Height:          nextState.LastBlockHeight,
+			AppHash:         initialState.AppHash,
+			LastBlockID:     block.BlockID,
+			LastResultsHash: nextState.LastResultsHash,
+		},
+	}
+	blockStore.On("LoadBlockMeta", height).Return(block)
+	blockStore.On("LoadBlockMeta", nextHeight).Return(nextBlock)
 	blockStore.On("Height").Return(nextHeight)
 
 	// rollback the state
@@ -81,6 +91,7 @@ func TestRollbackNoBlocks(t *testing.T) {
 	stateStore := setupStateStore(t, height)
 	blockStore := &mocks.BlockStore{}
 	blockStore.On("Height").Return(height)
+	blockStore.On("LoadBlockMeta", height).Return(nil)
 	blockStore.On("LoadBlockMeta", height-1).Return(nil)
 
 	_, _, err := state.Rollback(blockStore, stateStore)