From 67cf948f261d392546f813290cad94479c97fcd2 Mon Sep 17 00:00:00 2001
From: Ethan Buchman <ethan@coinculture.info>
Date: Tue, 14 Feb 2017 01:34:24 -0500
Subject: [PATCH] ibc: check commit against blockID

---
 plugins/ibc/ibc.go | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/plugins/ibc/ibc.go b/plugins/ibc/ibc.go
index d1bd8d53b..53913b438 100644
--- a/plugins/ibc/ibc.go
+++ b/plugins/ibc/ibc.go
@@ -431,23 +431,22 @@ func verifyCommit(chainState BlockchainState, header *tm.Header, commit *tm.Comm
 		return errors.New(cmn.Fmt("Commit has no signatures"))
 	}
 	chainID := chainState.ChainID
-	vote0 := commit.Precommits[0]
 	vals := chainState.Validators
 	valSet := tm.NewValidatorSet(vals)
 
-	// Ensure the commit is for the header
-	if !bytes.Equal(header.Hash(), vote0.BlockID.Hash) {
-		return errors.New(cmn.Fmt("Commit.BlockID.Hash (%X) does not match header.Hash (%X)", vote0.BlockID.Hash, header.Hash()))
-	}
-
 	// NOTE: Currently this only works with the exact same validator set.
 	// Not this, but perhaps "ValidatorSet.VerifyCommitAny" should expose
 	// the functionality to verify commits even after validator changes.
-	err := valSet.VerifyCommit(chainID, vote0.BlockID, vote0.Height, commit)
+	blockID, err := valSet.VerifyCommitReturnBlockID(chainID, header.Height, commit)
 	if err != nil {
 		return err
 	}
 
+	// Ensure the committed blockID matches the header
+	if !bytes.Equal(header.Hash(), blockID.Hash) {
+		return errors.New(cmn.Fmt("blockID.Hash (%X) does not match header.Hash (%X)", blockID.Hash, header.Hash()))
+	}
+
 	// All ok!
 	return nil
 }