From ee34b9c7b01c06332b6351f73acf7c637a96b2fa Mon Sep 17 00:00:00 2001
From: Conner Fromknecht <conner@lightning.engineering>
Date: Thu, 2 Aug 2018 16:45:03 -0700
Subject: [PATCH 1/3] channeldb/error: adds ErrDBReversion error

Adds an error for signaling that we detected
the case where a user is trying to revert
to prior version before a db migration.
---
 channeldb/error.go | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/channeldb/error.go b/channeldb/error.go
index 6ee24a87e..5c8e20982 100644
--- a/channeldb/error.go
+++ b/channeldb/error.go
@@ -7,6 +7,10 @@ var (
 	// created.
 	ErrNoChanDBExists = fmt.Errorf("channel db has not yet been created")
 
+	// ErrDBReversion is returned when detecting an attempt to revert to a
+	// prior database version.
+	ErrDBReversion = fmt.Errorf("channel db cannot revert to prior version")
+
 	// ErrLinkNodesNotFound is returned when node info bucket hasn't been
 	// created.
 	ErrLinkNodesNotFound = fmt.Errorf("no link nodes exist")

From e23fc40d638446557af8a9091cb0ed5354867817 Mon Sep 17 00:00:00 2001
From: Conner Fromknecht <conner@lightning.engineering>
Date: Thu, 2 Aug 2018 16:46:17 -0700
Subject: [PATCH 2/3] channeldb/db: check for db reversions on startup

---
 channeldb/db.go | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/channeldb/db.go b/channeldb/db.go
index f3b6ede1d..3f3ced0b9 100644
--- a/channeldb/db.go
+++ b/channeldb/db.go
@@ -663,12 +663,24 @@ func (d *DB) syncVersions(versions []version) error {
 		}
 	}
 
-	// If the current database version matches the latest version number,
-	// then we don't need to perform any migrations.
 	latestVersion := getLatestDBVersion(versions)
 	log.Infof("Checking for schema update: latest_version=%v, "+
 		"db_version=%v", latestVersion, meta.DbVersionNumber)
-	if meta.DbVersionNumber == latestVersion {
+
+	switch {
+
+	// If the database reports a higher version that we are aware of, the
+	// user is probably trying to revert to a prior version of lnd. We fail
+	// here to prevent reversions and unintended corruption.
+	case meta.DbVersionNumber > latestVersion:
+		log.Errorf("Refusing to revert from db_version=%d to "+
+			"lower version=%d", meta.DbVersionNumber,
+			latestVersion)
+		return ErrDBReversion
+
+	// If the current database version matches the latest version number,
+	// then we don't need to perform any migrations.
+	case meta.DbVersionNumber == latestVersion:
 		return nil
 	}
 

From dff7706d04161062338ccb143608101ccc84e277 Mon Sep 17 00:00:00 2001
From: Conner Fromknecht <conner@lightning.engineering>
Date: Thu, 2 Aug 2018 18:17:25 -0700
Subject: [PATCH 3/3] channeldb/meta_test: adds TestMigrationReversion

Adds a test asserting that we will fail to open
a channeldb with a version higher than the
highest known version to the current build of
lnd.
---
 channeldb/meta_test.go | 41 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)

diff --git a/channeldb/meta_test.go b/channeldb/meta_test.go
index 5890d6692..dbed0a2be 100644
--- a/channeldb/meta_test.go
+++ b/channeldb/meta_test.go
@@ -2,6 +2,7 @@ package channeldb
 
 import (
 	"bytes"
+	"io/ioutil"
 	"testing"
 
 	"github.com/coreos/bbolt"
@@ -380,3 +381,43 @@ func TestMigrationWithoutErrors(t *testing.T) {
 		migrationWithoutErrors,
 		false)
 }
+
+// TestMigrationReversion tests after performing a migration to a higher
+// database version, opening the database with a lower latest db version returns
+// ErrDBReversion.
+func TestMigrationReversion(t *testing.T) {
+	t.Parallel()
+
+	tempDirName, err := ioutil.TempDir("", "channeldb")
+	if err != nil {
+		t.Fatalf("unable to create temp dir: %v", err)
+	}
+
+	cdb, err := Open(tempDirName)
+	if err != nil {
+		t.Fatalf("unable to open channeldb: %v", err)
+	}
+
+	// Update the database metadata to point to one more than the highest
+	// known version.
+	err = cdb.Update(func(tx *bolt.Tx) error {
+		newMeta := &Meta{
+			DbVersionNumber: getLatestDBVersion(dbVersions) + 1,
+		}
+
+		return putMeta(newMeta, tx)
+	})
+
+	// Close the database. Even if we succeeded, our next step is to reopen.
+	cdb.Close()
+
+	if err != nil {
+		t.Fatalf("unable to increase db version: %v", err)
+	}
+
+	_, err = Open(tempDirName)
+	if err != ErrDBReversion {
+		t.Fatalf("unexpected error when opening channeldb, "+
+			"want: %v, got: %v", ErrDBReversion, err)
+	}
+}